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Chromium Enhances Insulin Responsiveness via AMPK

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... Vanadium(IV) and chromium(III) (Cr(III)) have long been studied for their insulin-enhancing properties. While their essentiality in humans is debated, they exhibit tremendous therapeutic potential as anti-type 2 diabetic agents [85][86][87][88][89][90][91][92]. Both manifest their insulin-enhancing effect via related but distinct molecular mechanistic routes that are believed to be tied to the transport offered by sTf. ...
... In the holo form, chromodulin binds to the insulin-bound, activated insulin receptor and is believed to further enable the phosphorylation cascade of the insulin signaling process that leads to glucose uptake ( Figure 16) although there is some debate about the relevance of the chromodulin and insulin receptor interaction [64]. Cr(III) is also capable of protecting against physiological hyperinsulinemia-induced plasma membrane cholesterol accumulation and cortical filamentous actin (F-actin) loss as observed in L6 skeletal muscle myotubes [90]. The adenosine monophosphate-activated protein kinase (AMPK) is responsible for the inhibition of cholesterol synthesis via the phosphorylation of 3-hydroxyl-3-methyl-glutaryl coenzyme A reductase (HGMR). ...
... AMPK activation was found to be an important aspect of the mechanism of Cr(III) action in the insulin-resistant skeletal muscle cells. It resulted in a decrease of membrane cholesterol, which results in restoration of F-actin integrity, required for proper insulin-regulated GLUT4 translocation and glucose transport [90]. Despite the observation of the these therapeutic properties of Cr(III), there is skepticism regarding the drug potential of the metal ion because of evidence that suggests its accumulation in the body can be toxic [64]. ...
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Article
Serum transferrin (sTf) plays a pivotal role in regulating iron biodistribution and homeostasis within the body. The molecular details of sTf Fe(III) binding blood transport, and cellular delivery through transferrin receptor-mediated endocytosis are generally well-understood. Emerging interest exists in exploring sTf complexation of nonferric metals as it facilitates the therapeutic potential and toxicity of several of them. This review explores recent X-ray structural and physiologically relevant metal speciation studies to understand how sTf partakes in the bioactivity of key non-redox active hard Lewis acidic metals. It challenges preconceived notions of sTf structure function correlations that were based exclusively on the Fe(III) model by revealing distinct coordination modalities that nonferric metal ions can adopt and different modes of binding to metal-free and Fe(III)-bound sTf that can directly influence how they enter into cells and, ultimately, how they may impact human health. This knowledge informs on biomedical strategies to engineer sTf as a delivery vehicle for metal-based diagnostic and therapeutic agents in the cancer field. It is the intention of this work to open new avenues for characterizing the functionality and medical utility of nonferric-bound sTf and to expand the significance of this protein in the context of bioinorganic chemistry.
... Vanadium(IV) and chromium(III) (Cr(III)) have long been studied for their insulin-enhancing properties. While their essentiality in humans is debated, they exhibit tremendous therapeutic potential as anti-type 2 diabetic agents [85][86][87][88][89][90][91][92]. Both manifest their insulin-enhancing effect via related but distinct molecular mechanistic routes that are believed to be tied to the transport offered by sTf. ...
... In the holo form, chromodulin binds to the insulin-bound, activated insulin receptor and is believed to further enable the phosphorylation cascade of the insulin signaling process that leads to glucose uptake ( Figure 16) although there is some debate about the relevance of the chromodulin and insulin receptor interaction [64]. Cr(III) is also capable of protecting against physiological hyperinsulinemia-induced plasma membrane cholesterol accumulation and cortical filamentous actin (F-actin) loss as observed in L6 skeletal muscle myotubes [90]. The adenosine monophosphate-activated protein kinase (AMPK) is responsible for the inhibition of cholesterol synthesis via the phosphorylation of 3-hydroxyl-3-methyl-glutaryl coenzyme A reductase (HGMR). ...
... AMPK activation was found to be an important aspect of the mechanism of Cr(III) action in the insulin-resistant skeletal muscle cells. It resulted in a decrease of membrane cholesterol, which results in restoration of F-actin integrity, required for proper insulin-regulated GLUT4 translocation and glucose transport [90]. Despite the observation of the these therapeutic properties of Cr(III), there is skepticism regarding the drug potential of the metal ion because of evidence that suggests its accumulation in the body can be toxic [64]. ...
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Preprint
Serum transferrin (sTf) plays a pivotal role in regulating iron biodistribution and homeostasis within the body. The molecular details of sTf Fe(III) binding, blood transport, and cellular delivery through transferrin receptor-mediated endocytosis are generally well-understood. Emerging interest exists in exploring sTf complexation of nonferric metals as it facilitates the therapeutic potential and toxicity of several of them. This review explores recent X-ray structural and physiologically relevant metal speciation studies to understand how sTf partakes in the bioactivity of key non-redox active hard Lewis acidic metals. It challenges preconceived notions of sTf structure function correlations that were based exclusively on the Fe(III) model by revealing distinct coordination modalities that nonferric metal ions can adopt and different modes of binding to metal-free and Fe(III)-bound sTf that can directly influence how they enter into cells and, ultimately, how they may impact human health. This knowledge informs on biomedical strategies to engineer sTf as a delivery vehicle for metal-based diagnostic and therapeutic agents in the cancer field. It is the intention of this work to open new avenues for characterizing the functionality and medical utility of nonferric-bound sTf and to expand the significance of this protein in the context of bioinorganic chemistry.
... Chromium (Cr) has been shown to improve insulin signaling and subsequently induce glucose and amino acid uptake in insulin sensitive tissues such as skeletal muscle and adipose tissue [11]. Intake of Cr increased glucose uptake by enhancing insulin responsiveness through various signaling pathways [8,12]. ...
... The impact of Cr source on AMP-activated protein kinase (AMPK) activity has also been reported in vitro and in vivo [12]. Variation of phosphorylated-AMPKα in muscle and adipose tissue can trigger metabolic changes that switch the cell from metabolic processes geared toward energy storage to energy consuming pathways [13]. ...
... In the current study, the ratio of phosphorylated-AMPK to AMPK was decreased when CrAc was added to IM adipocytes; however, this did not occur in SC adipocytes. Conversely, chromium picolinate increased AMPK activity in L6 skeletal muscle cells [12]. ...
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Article
Objectives: We hypothesized that Cr source can alter adipogenic-related transcriptional regulations and cell signaling. Therefore, the objective of the study was to evaluate the biological effects of chromium acetate (CrAc) on bovine intramuscular and subcutaneous adipose cells. Methods: Bovine preadipocytes isolated from two different adipose tissue depots; IM and SC were used to evaluate the effect of CrAc treatment during differentiation on adipogenic gene expression. Adipocytes were incubated with various doses of CrAc: 0 (differentiation media only, Control), 0.1, 1, and 10µM. Cells were harvested and then analyzed by real-time quantitative PCR (RT-qPCR) in order to measure the quantity of adenosine monophosphate-activated protein kinase-α (AMPK-α), CCAAT enhancer binding protein-β (C/EBPβ), G protein-coupled receptor 41(GPR41),GPR43, Peroxisome proliferator-activated receptor-γ (PPARγ), and stearoyl CoA desaturase (SCD) mRNA relative to ribosomal protein subunit 9 (RPS9). The ratio of phosphorylated-AMPK (pAMPK) to AMPK was determined using a western blot technique in order to determine changing concentration. Results: The high dose (10µM) of CrAc increased C/EBPβ, in both IM (P = 0.02) and SC (P = 0.02). Expression of PPARγ was upregulated by 10µM of CrAc in IM but not in SC. Expression of SCD was also increased in both IM and SC with 10μM of CrAc treatment. Addition of CrAc did not alter gene expression of GLUT4, GPR41, or GPR43 in both IM and SC adipocytes. Addition of CrAc, resulted in a decreased pAMPKα to AMPKα ration (P < 0.01) in IM. Conclusion: These data may indicate that Cr source may influence lipid filling in IM adipocytes via inhibitory action of AMPK phosphorylation and upregulating expression of adipogenic genes.
... Chromium (Cr) has been recognized as an essential trace mineral [9][10][11][12], which is thought to be necessary for normal carbohydrate, appropriate protein, and lipid metabolism [12,13], though the assertion is disputable [14,15]. Numerous experiments have been conducted to study the effects of Cr from different chemical forms, such as chromium chloride (CrCl 3 ) [15], chromium picolinate (CrPic) [16][17][18], chromium nicotinate (CrNic) [19], chromium propionate (CrProp) [20], chromium (D-phenylalanine) 3 [21], chromium nanocomposites (CrNano) [22][23][24] and oligomannuronate-chromium [25]. Supplementation of the diet with Cr could decrease the blood glucose levels in growing and finishing pigs [16,24,26], broilers [27], and mice [3]. ...
... Supplementation of the diet with Cr could decrease the blood glucose levels in growing and finishing pigs [16,24,26], broilers [27], and mice [3]. Some studies have shown that Cr is able to promote glucose uptake and metabolism by activating AMPK which may explain the beneficial effects of Cr on GLUT4 and glucose transport regulation [18,21,28]. ...
... In muscle cells, there are two important signal pathways to regulate glucose transport and metabolism (i.e., the insulin signaling pathway [38] and AMPK pathway [39]). According to the previous investigations [18,21,28], Cr did not have significant effects on basal glucose uptake and metabolism in the absence of insulin. Thus, these results demonstrate that the mechanisms of rapid stimulating effects of Cr-CNP on GLUT4 translocation and glucose uptake in skeletal muscle cells are related to insulin. ...
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Article
The study was conducted to evaluate the effects of chromium-loaded chitosan nanoparticles (Cr-CNP) on glucose transporter 4 (GLUT4), relevant messenger RNA (mRNA), and proteins involved in phosphatidylinositol 3-kinase (PI3K), Akt2-kinase, and AMP-activated protein kinase (AMPK) of skeletal muscles in finishing pigs. A total of 120 crossbred barrows (BW 65.00 ± 1.26 kg) were randomly allotted to four dietary treatments, with three pens per treatment and 10 pigs per pen. Pigs were fed the basal diet supplemented with 0, 100, 200, or 400 μg/kg of Cr from Cr-CNP for 35 days. After the feeding trials, 24 pigs were slaughtered to collect longissimus muscle samples for analysis. Cr-CNP supplementation increased GLUT4 messenger RNA (mRNA) (quadratically, P < 0.01) and total and plasma membrane GLUT4 protein contents (linearly and quadratically, P < 0.001) in skeletal muscles. Glycogen synthase kinase 3β (GSK-3β) mRNA was decreased linearly (P < 0.001) and quadratically (P < 0.001). Supplemental Cr-CNP increased insulin receptor (InsR) mRNA quadratically (P < 0.01), Akt2 total protein level linearly (P < 0.01) and quadratically (P < 0.001), and PI3K total protein was increased significantly (P < 0.05) in 200 μg/kg treatment group. The mRNA of AMPK subunit gamma-3 (PRKAG3) and protein of AMPKα1 was significantly increased (P < 0.001) with the addition of Cr-CNP. The results indicate that dietary supplementation of Cr-CNP may promote glucose uptake by leading to recruitment of GLUT4 to the plasma membrane in skeletal muscles, and these actions may be associated with the insulin signal transduction and AMPK.
... Collectively, these studies appear to indicate that chromium availability favorably impacts carbohydrate and lipid metabolism as well as GLUT-4 translocation. Furthermore, chromium appears to increase insulin responsiveness via an AMPK mediated pathway [18] and can instigate favorable changes to the insulin receptor [14]. Evans reported that supplementation with chromium picolinate improved cholesterol and glucose levels in non-diabetic and diabetic adults and was also associated with significant losses of fat mass and increases in lean mass [16]. ...
... In this respect, investigating the post insulin receptor signal transduction pathways and phosphorylation cascades, including activation of IRS-1 (insulin receptor substrate-1) /PI3K (phosphatidylinositol-3 kinase)/Akt (protein kinase B)/mTORC /p70S6 kinase axis, are central to understanding the molecular mechanisms of muscle protein synthesis [28][29][30]. If WPACr acutely enhances these intracellular responses to insulin as indicated by previous work in culture [18], animal [13] and human studies [16], then it may potentially augment the anabolic response of skeletal muscle to an otherwise suboptimal dose of whey protein. This is an important consideration as the present study examined acute changes in fractional synthesis rates of mixed muscle proteins, but did not explore the impact of the chromium-containing compound on overall muscle protein balance, rates of muscle protein breakdown, or whole-body net protein balance. ...
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Article
Background Previous research has demonstrated the permissive effect of insulin on muscle protein kinetics, and the enhanced insulin sensitizing effect of chromium. In the presence of adequate whole protein and/or essential amino acids (EAA), insulin has a stimulatory effect on muscle protein synthesis, whereas in conditions of lower blood EAA concentrations, insulin has an inhibitory effect on protein breakdown. In this study, we determined the effect of an amylopectin/chromium (ACr) complex on changes in plasma concentrations of EAA, insulin, glucose, and the fractional rate of muscle protein synthesis (FSR). Methods Using a double-blind, cross-over design, ten subjects (six men, four women) consumed 6 g whey protein + 2 g of the amylopectin-chromium complex (WPACr) or 6 g whey protein (WP) after an overnight fast. FSR was measured using a primed, continuous infusion of ring-d5-phenylalanine with serial muscle biopsies performed at 2, 4, and 8 h. Plasma EAA and insulin were assayed by ion-exchange chromatography and ELISA, respectively. After the biopsy at 4 h, subjects ingested their respective supplement, completed eight sets of bilateral isotonic leg extensions at 80% of their estimated 1-RM, and a final biopsy was obtained 4 h later. ResultsBoth trials increased EAA similarly, with peak levels noted 30 min after ingestion. Insulin tended (p = 0.09) to be higher in the WPACr trial. Paired samples t-tests using baseline and 4-h post-ingestion FSR data separately for each group revealed significant increases in the WPACr group (+0.0197%/h, p = 0.0004) and no difference in the WP group (+0.01215%/hr, p = 0.23). Independent t-tests confirmed significant (p = 0.045) differences in post-treatment FSR between trials. Conclusions These data indicate that the addition of ACr to a 6 g dose of whey protein (WPACr) increases the FSR response beyond what is seen with a suboptimal dose of whey protein alone.
... Cr (III) appeared to have important roles in immunity and inflammation summarized in the following examples. When going through Cr (III) mechanisms of improving insulin sensitivity, it is noticed that Cr (III) affects some inflammatory cytokines and immune pathways (Moradi et al. 2019;Hua et al. 2012;Jain et al. 2010;Hoffman et al. 2014), some of these pathways are related to FOXP3 expression (Ruan et al. 2012;Huber et al. 2008), inhibition or activation of which is found to be useful for RA remission (Makarov 2001;McHugh 2019). Moreover, Cr (III) appeared to treat some inflammatory conditions associated with diabetes, such as respiratory system inflammation (Kolahian et al. 2015). ...
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Article
Background Rheumatoid arthritis (RA) is a known debilitating autoimmune disease. Immune-suppressants that are used for disease treatment have serious side effects, therefore, trivalent chromium (Cr (III)); which has shown evidence of its influences on some inflammatory pathways and cytokines; was used in this study for the first time to be assessed for its therapeutic effect in RA rat model and was compared to prednisolone in a trial to find a treatment with lesser side effects. Methods Adult male albino rats were randomly divided into four groups: normal, untreated RA, prednisolone treated RA (1.25 mg/kg/day) and Cr (III) treated RA groups (80 μg/kg/day), induction of RA was done by subcutaneous complete Freund adjuvant injection. Study duration was 4 weeks throughout which arthritis scoring and weight measurement were pursued. Histopathological examination and immunohistochemical FOXP3 assessment were done for joint biopsies. Serum inflammatory markers (interleukin 17, interleukin 10, CRP) and synovial erosive arthritis marker (Cathepsin G) were measured. HDL and non-HDL cholesterol were estimated as well. Results Cr (III) treatment showed marked clinical and histopathological improvement, also astonishing anti-inflammatory effects (increase in FOXP3 expression and interleukin 10, with decrease in interleukin 17, CRP and synovial Cathepsin G) to the extent that Cr (III) effects on inflammation abolishment were comparable to that of prednisolone and even better at some aspects. Moreover, Cr (III) was protective from side effects, i.e., weight gain and dyslipidemia that were seen with prednisolone treatment. Conclusions Cr (III) is promising in treating RA and it lacks some side effects of accustomed immune-modulatory agents including prednisolone. Further experimental studies and clinical trials should be held to see the efficacy of Cr (III) in different doses and to assess its long term side effects when used for rheumatoid arthritis and other autoimmune diseases treatment.
... In the previous study, the sulfated rhamnose polysaccharides after the introduction of Cr(III) enhanced glucose metabolism by regulating the insulinmediated PI3K/PKB/GSK-3β [45]. Cr(III) also could enhance insulin responsiveness by the AMPK signaling pathway [51]. These results suggested that Cr(III) in PPP-Cr(III) had a strong hypoglycemic activity. ...
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Article
The aim of our study was to synthesize a pumpkin peel polysaccharide (PPP)-Cr(III) complex and investigate its hypoglycemic activity. Firstly, a novel PPP-Cr(III) complex with a Cr content of 23.77 mg/g was synthesized and characterized. Physicochemical characterization indicated that PPP-Cr(III) had some changes in chemical composition, monosaccharide composition, and morphological structure compared with PPP. The molecular weights of PPP-Cr(III) and PPP were 1.398 × 106 g/mol and 3.386 × 106 g/mol, respectively, showing a lower molecular weight after the introduction of Cr(III). Fourier transform infrared spectroscopy showed that a new characteristic absorption peak of Cr-O appeared at 534 cm-1 in PPP-Cr(III), indicating that Cr(III) was successfully complexed with PPP. Secondly, the hypoglycemic activity of PPP-Cr(III) based on α-glucosidase inhibitory and insulin resistance (IR)-HepG2 cells was evaluated. Compared with PPP, PPP-Cr(III) exhibited a more significantly α-glucosidase inhibitory activity. The IR-HepG2 cells confirmed an obvious increase in glucose consumption. Western blot analysis demonstrated that the treated IR-HepG2 cells were able to increase the protein levels of p-AMPK and p-GSK-3β, indicating that IR-HepG2 cells exerted hypoglycemic activity via the AMPK/GSK-3β signaling pathway. These results suggested that PPP-Cr(III) had good hypoglycemic activity, which could provide theoretical support for the development of novel hypoglycemic products.
... **P < 0.01 relative to the model group. *P < 0.05 relative to the model group sensor 5' AMP-activated protein kinase (Hoffmana et al. 2014). Chromium can also reduce plasma membrane cholesterol by lowering the biological effect of tyrosine phosphatase 1B and irritating the transfer of the GLUT4 glucose transporter (Wang et al. 2006). ...
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Article
Sulfated rhamnose polysaccharide (SRP) derived from Enteromorpha prolifera is a metal-ion chelating agent that could potentially be used to treat diabetes. The aim of our study was to determine the effect of a variant of SRP on DIABETES. First, we synthesized and characterized SRPE-3 chromium(III) [SRPE-3-Cr(III)] complex using an enzymatic method. The maximum chelation rate was 18.2% under optimal chelating conditions of pH 6.0, time 4 h, and temperature 60 °C. Fourier transform infrared spectroscopy results showed important sites for Cr(III)-binding were O–H and C=O groups. We then studied the hypolipidemic effects of SRPE-3-Cr(III) on type 2 diabetes mellitus (T2DM) induced by a high-fat, high-sucrose diet (HFSD). Decreased blood glucose content, body fat ratio, serum TG, TC, LDL-C, and increased serum HDL-C were observed after treatment with SRPE-3-Cr(III). In addition, SRPE-3-Cr(III) significantly reduced leptin, resistin, and TNF-α levels, and increased adiponectin contents relative to T2DM. Histopathology results also showed that SRPE-3-Cr(III) could alleviate the HFSD-lesioned tissues. SRPE-3-Cr(III) also improved lipid metabolism via a reduction in aspartate aminotransferase, alanine aminotransferase, fatty acid synthase, and acetyl-CoA carboxylase activities in the liver. SRPE-3-Cr(III) at low doses exhibited better lipid-lowering activities, hence, could be considered to be a novel compound to treat hyperlipidemia and also act as an anti-diabetic agent.
... Many elements are involved in various physiological functions and energy metabolisms in mammals and play a corresponding role as well (Fiore et al. 2020). Part of animal experiments indicated that many elements can directly modulate glucose homeostasis and insulin activity, such as Se, Zn, As, and Cr (Hoffman et al. 2014;Norouzi et al. 2018;Yao et al. 2021;Zhang et al. 2020). Epidemiological studies have recently shown that transportation, distribution, excretion, and accumulation of various kinds of elements, including Zn, Cu, Se, and As, differ in prediabetes, and diabetes patients relative to healthy individuals (Menke et al. 2016;Sanjeevi et al. 2018;Wang et al. 2020a). ...
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Article
Epidemiological studies have demonstrated that various kinds of urinary element concentrations were different between healthy, prediabetes, and diabetes patients. Meanwhile, many studies have explored the relationship between element concentration and fasting blood glucose (FBG), but the association between joint exposure to co-existing elements and FBG level has not been well understood. The study explored the associations of joint exposure to co-existing urinary elements with FBG level in a cross-sectional design. 275 retired elderly people were recruited from Beijing, China. The questionnaire survey was conducted, and biological samples were collected. The generalized linear model (GLM) and two-phase Bayesian kernel machine regression (BKMR) model were used to perform in-depth association analysis between urinary elements and FBG. The GLM analysis showed that Zn, Sr, and Cd were significantly correlated with the FBG level, under control potential confounding factors. The BKMR analysis demonstrated 8 elements (Zn, Se, Fe, Cr, Ni, Cd, Mn, and Al) had a higher influence on FBG (posterior inclusion probabilities > 0.1). Further intensive analyses result of the BKMR model indicated that the overall estimated exposure of 8 elements was positively correlated with the FBG level and was statistically significant when all creatinine-adjusted element concentrations were at their 65th percentile. Meanwhile, the BKMR analysis showed that Cd and Zn had a statistically significant association with FBG levels when other co-existing elements were controlled at different levels (25th, 50th, or 75th percentile), respectively. The results of the GLM and BKMR model were inconsistent. The BKMR model could flexibly calculate the joint exposure to co-existing elements, evaluate the possible interaction effects and nonlinear correlations. The meaningful conclusions were found that it was difficult to get by traditional methods. This study will provide methodological reference and experimental evidence for the association between joint exposure to co-existing elements and FBG in elderly people.
... The role of Cr in insulin secretion is multi-faceted [50]. Most importantly, Cr increases the activity of 5′AMP-activated protein kinase, which plays a key role in the response to insulin, and insulin receptor kinase, thus enhancing insulin signalling [51,52]. Chromium also induces translocation of glucose transporter 4 (GluT4) to the cell membrane, thereby promoting glucose metabolism [53]. ...
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Article
Aims The aim of the study was to determine how the administration of a high-fat diet supplemented with various forms of chromium to rats affects accumulation of this element in the tissues and levels of leptin, ghrelin, insulin, glucagon, serotonin, noradrenaline and histamine, as well as selected mineral elements. Methods The experiment was conducted on 56 male Wistar rats, which were divided into 8 experimental groups. The rats received standard diet or high fat diet (HFD) with addition of 0.3 mg/kg body weight of chromium(III) picolinate (Cr-Pic), chromium(III)-methioninate (Cr-Met), or chromium nanoparticles (Cr-NP). Results Chromium in organic forms was found to be better retained in the body of rats than Cr in nanoparticles form. However, Cr-Pic was the only form that increased the insulin level, which indicates its beneficial effect on carbohydrate metabolism. In blood plasma of rats fed a high-fat diet noted an increased level of serotonin and a reduced level of noradrenaline. The addition of Cr to the diet, irrespective of its form, also increased the serotonin level, which should be considered a beneficial effect. Rats fed a high-fat diet had an unfavourable reduction in the plasma concentrations of Ca, P, Mg and Zn. The reduction of P in the plasma induced by supplementation with Cr in the form of Cr-Pic or Cr-NP may exacerbate the adverse effect of a high-fat diet on the level of this element. Conclusion A high-fat diet was shown to negatively affect the level of hormones regulating carbohydrate metabolism (increasing leptin levels and decreasing levels of ghrelin and insulin).
... It is also known that Tf can bind V(IV) and Cr(III) and therefore expediate the delivery of metal ions known to have an insulin-like effect as described for the latter metal ions [270,271]. Cannon and Chasteen firstly described the binding of VO 2+ to Tf in 1975 and it is known that oxovanadium ions can bind Tf to both metal-binding sites [272]. ...
Article
Transferrin (Tf) is an essential protein, probably ubiquitous to all metazoans. The main function of this family of proteins is to bind and transport ferric ions, increasing Fe(III) solubility under physiological conditions and preventing its deleterious pro-oxidant role in aerobic environments. In humans, Tf is responsible for the safe transport of this essential micronutrient through circulation and its delivery to requiring cells. Cellular uptake occurs through endocytosis mediated by the transferrin receptor (TfR). Although there is a good understanding of the general molecular mechanisms governing Tf iron binding and cellular iron delivery, several aspects of Tf biochemistry remain unclear. In this review, we provide an overview of the inorganic biochemistry of human Tf (hTf), exploring the available structural information on hTf and the hTf/TfR complex to discuss physiologically relevant aspects, such as iron binding site distribution, mechanism of iron loading and TfR priming of iron release in vivo. In addition, we consider the role of hTf microheterogeneity on its function. Post-translational modifications such as phosphorylation, glycation and oxidation may occur at relevant hTf sites, which will compromise iron binding, inter lobe cooperativity or interaction with the TfR. Furthermore, these modifications may contribute to the deregulation of systemic iron transport and distribution on a disease specific manner. Finally, a brief review of the role of hTf as one of the main blood serum ligands for toxic and therapeutic metal ions is presented. hTf is a long known and studied protein, but it is essential to understand the factors governing its expression and catabolism and how specific modifications modulate its function, in order to fully comprehend its role in human pathology or to explore its potential as a therapeutic agent.
... Due to their role as cofactors in metabolic pathways, some minerals have been suggested to enhance insulin action [2]. For example, chromium improves glucose homeostasis through increased insulin sensitivity [63]. Glucose is the primary metabolic fuel for fetal metabolism, and it is crucial for fetal development [59]. ...
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Article
Maternal nutrients are essential for proper fetal and placental development and function. However, the effects of vitamin and mineral supplementation under two rates of maternal weight gain on placental genome-wide gene expression have not been investigated so far. Furthermore, biological processes and pathways in the placenta that act in response to early maternal nutrition are yet to be elucidated. Herein, we examined the impact of maternal vitamin and mineral supplementation (from pre-breeding to day 83 post-breeding) and two rates of gain during the first 83 days of pregnancy on the gene expression of placental caruncles (CAR; maternal placenta) and cotyledons (COT; fetal placenta) of crossbred Angus beef heifers. We identified 267 unique differentially expressed genes (DEG). Among the DEGs from CAR, we identified ACAT2, SREBF2, and HMGCCS1 that underlie the cholesterol biosynthesis pathway. Furthermore, the transcription factors PAX2 and PAX8 were over-represented in biological processes related to kidney organogenesis. The DEGs from COT included SLC2A1, SLC2A3, SLC27A4, and INSIG1. Our over-representation analysis retrieved biological processes related to nutrient transport and ion homeostasis, whereas the pathways included insulin secretion, PPAR signaling, and biosynthesis of amino acids. Vitamin and mineral supplementation and rate of gain were associated with changes in gene expression, biological processes, and KEGG pathways in beef cattle placental tissues.
... It has been proposed the participation of an oligopeptide called chromodulin, which has the property of binding four chromium atoms; the linkage leads to translocation of Glucose transporter GLUT4 to the cell membrane resulting in biological activity. Some other studies show the increase of AMP-activated protein kinase (AMPK) as the mechanism involved [15][16][17]. Nutritional supplements with Cr, especially chromium picolinate (CrPic), have become popular to lose weight. According to preliminary studies, its use can have beneficial effects in certain diseases such as diabetes, metabolic syndrome, polycystic ovary syndrome and atypical depression, however few studies state a clear mechanistic basis for this assertion, so the research on the pharmacological effects of Cr supplementation must continue [18,19]. ...
Article
Despite the knowledge about heavy metals toxicity on humans, its use is widely spread mainly for industrial processes. Chromium is an element that belongs to this group and although it is present in our daily diet, it can also be harmful for humans, causing skin allergies and increasing the risk of lung cancer, among other health effects reported. In this review, we highlight its nutritional role, its toxicokinetic and toxicodynamic in humans, its regulation in the industry and the biomonitoring proposal of this element in blood and urine samples with the aim to control the level of exposure of the workers in military industry and also of the general population.
... As this carbohydrate is not stored, it is believed that the high glucose content found in the liver is that circulating in the blood in this organ. Considering that micronutrients, such as zinc, vanadium, and chromium, have participation in insulin action (decreasing its resistance or increasing its secretion) (Brautigan et al., 2006;Hoffman et al., 2014;Cruz et al., 2018), the chelating agents present in L. alba leaves impair the glucose transport and uptake. This effect causes a dysregulation in glucose homeostasis (hyperglycemia). ...
Article
The dietary addition of Lippia alba essential oil has been studied in fish, showing excellent results against lipid peroxidation. The objective of this study was to evaluate the compounds present in the plant and the growth, hematology, metabolism, and oxidative parameters of silver catfish fed diets containing L. alba leaf. The experimental design was completely randomized with 500 silver catfish distributed in 5 treatments and 4 replicates in a water recirculation system. The treatments tested were: control (without leaf inclusion); 0.5; 1; 1.5 and 2% inclusion of L. alba leaf powder. All diets tested had the same composition matrix, containing 37.49% crude protein and 10.04% lipids. Leaf compounds have been found that may have great antioxidant capacity such as caffeic acid, verbascoside, and calceolarioside E. However, some compounds present in the leaf may cause damage to fish performance such as malic acid and quinic acid. Fish fed diets containing L. alba leaf presented lower growth and changes in hematological parameters compared to control fish. At the higher levels of L. alba leaf inclusion, undesirable metabolic changes occurred as increased plasma alanine aminotransferase activity, indicating liver damage. The presence of L. alba leaf in diets resulted in decreased muscle lipid peroxidation and increased the amount of non-protein thiols in the gills and muscle. This indicates that the plant leaves have antioxidant potential in fish. Therefore, at the tested levels, the addition of L. alba leaf powder in diets for juveniles of silver catfish is not recommended. Summary statement This article is interesting because it assesses the inclusion of natural products in fish diets, resulting in improved health.
... Follow-up data collected by Hoffman et al., utilizing siRNA-targeted knockdown of AMPK catalytic activity, are consistent with AMPK mediating the protective effect of Cr 3+ against GLUT4 and glucose transport dysregulation (Hoffman et al., 2014). Unfortunately, due to the large amount of siRNA oligos and cellular starting material required for membrane cholesterol and F-actin analyses, these analyses were not performed. ...
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Chapter
More than 50 years of basic and clinical data demonstrate that trivalent chromium (Cr3 +) is important for the regulation of carbohydrate and lipid metabolism. Despite long-acclaimed glycemic and cardiovascular benefits, clinical trials using Cr3 + have provided conflicting data. Moreover, a dearth of mechanistic understanding of Cr3 + action has stalled the potential clinical application and significance of Cr3 + in health and disease. Novel insights into cholesterol metabolism, intracellular nutrient signaling systems, inflammatory responses, and oxidative stress now afford a fresh perspective on how Cr3 + benefits metabolic health. In this chapter, we will review new animal model and human subject data, and expand on recent cellular and molecular mechanisms that provide an integrated basis for the beneficial effects of Cr3 + in multiple pathologies characterized by metabolic dysregulation including diabetes, insulin resistance, and related macrovascular, microvascular, and cardiovascular complications.
... Chromium (Cr) functions to potentiate the action of insulin in insulin-sensitive tissues. Although the mode of action whereby Cr enhances insulin responsiveness has not been clearly defined, a number of different mechanisms have been proposed (Hua et al., 2012;Hoffman et al., 2014). Considerable research with Cr in human nutrition resulted in the Institute of Medicine establishing an adequate intake of Cr for humans in 2001 (National Academies, 2001). ...
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Forty-eight Quarter Horse geldings (3 - 8 yr of age) were used to determine the effects of dietary chromium (Cr), in the form of Cr propionate (Cr Prop) on insulin sensitivity. Horses were blocked by age, body condition score, and glucose response to concentrate feeding on d 0, and randomly assigned to treatments. Treatments consisted of 0, 2, 4, or 8 mg Cr/d from Cr Prop. Horses were fed daily a concentrate mix at a rate of 0.2 kg/100 kg BW and grass hay at 1.75 to 2.0 kg/100 kg BW. All horses were fed the control diet for 7 d prior to initiation of the study. After an overnight fast, blood samples from the jugular vein were obtained at 0, 2, and 4 h after concentrate feeding on d 0 and 28 for determination of glucose, NEFA, and insulin. A glucose tolerance test (GTT) was conducted on d 42. Glucose was infused via jugular vein catheters, and blood samples were collected at various times relative to dosing for glucose and insulin determination. Plasma glucose on d 28 was affected (P < 0.05) by treatment, time, and treatment x time. Horses fed 4 mg Cr/d had lesser (P < 0.05) plasma glucose concentrations than those in the other treatments at 0 h. At 2 h post feeding glucose concentrations were greater (P < 0.05) in horses fed 0 or 8 mg Cr/d than in those given 4 mg Cr. Horses fed 2 mg Cr/d had lesser ( P < 0.05) plasma glucose at 4 h post feeding compared to those fed 0 or 8 mg Cr. Plasma glucose did not differ among horses receiving 2 or 4 mg Cr/d at 2 or 4 h. Serum insulin was affected (P < 0.05) by treatment, time, and treatment x time. Insulin concentrations were greater (P < 0.05) in horses fed 0 or 2 mg Cr/d than in those given 4 or 8 mg Cr at 0 h. At 4 h post feeding insulin concentrations were greater (P < 0.05) in horses given 0 or 8 mg Cr than in those fed 2 or 4 mg Cr/d. Plasma glucose was affected (P < 0.05) by treatment and time, but not by treatment x time following the GTT. Mean plasma glucose (across sampling times) were greater (P < 0.05) in controls than in horses fed 2 or 4 mg Cr/d. Glucose concentrations following the GTT did not differ among controls and horses given 8 mg Cr/d. Following glucose infusion, serum insulin concentrations were greater (P < 0.05) in horses fed 2 or 4 mg Cr and tended to be greater in those fed 8 mg Cr/d compared to controls. Results of this study indicate that 2 or 4 mg Cr/d from Cr Prop increased insulin sensitivity in adult horses following oral carbohydrate consumption.
... The correlation with Cr 6+ (logK 2 Cr 2 O 7 ) was weaker (Fig. 3, Table 2). While Cr 6+ is a known human carcinogen, its reduction to Cr 3+ renders the metal less mutagenic and carcinogenic and even essential or beneficial in some situations like diabetes 43,44 . In basidiomycete yeasts, the strongest predictor of CIRgrowth was the maximum temperature that supported growth (T max ), rather than heavy metal tolerance (Fig. 3, Table 2). ...
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Exposure to chronic ionizing radiation (CIR) from nuclear power plant accidents, acts of terrorism, and space exploration poses serious threats to humans. Fungi are a group of highly radiation-resistant eukaryotes, and an understanding of fungal CIR resistance mechanisms holds the prospect of protecting humans. We compared the abilities of 95 wild-type yeast and dimorphic fungal isolates, representing diverse Ascomycota and Basidiomycota, to resist exposure to five environmentally-relevant stressors: CIR (long-duration growth under 36 Gy/h) and acute (10 kGy/h) ionizing radiation (IR), heavy metals (chromium, mercury), elevated temperature (up to 50 °C), and low pH (2.3). To quantify associations between resistances to CIR and these other stressors, we used correlation analysis, logistic regression with multi-model inference, and customized machine learning. The results suggest that resistance to acute IR in fungi is not strongly correlated with the ability of a given fungal isolate to grow under CIR. Instead, the strongest predictors of CIR resistance in fungi were resistance to chromium (III) and to elevated temperature. These results suggest fundamental differences between the mechanisms of resistance to chronic and acute radiation. Convergent evolution towards radioresistance among genetically distinct groups of organisms is considered here.
... Previous studies showed that CrPic is capable of increasing adenosine monophosphate activity (AMP) -activated protein kinase (AMPK) (Hoffman et al., 2014). AMPK acts as an energy regulator, which benefits carbohydrate metabolism (Ruderman, Saha, & Kraegen, 2013). ...
Article
The objective of this review was to understand the role of trace elements in the form of supplements in metabolic control of Type 2 Diabetes Mellitus (T2DM). A systematic research was performed following PRISMA recommendations. Although 3236 studies were identified, only 18 studies composed of nine animal studies and nine clinical studies were included in this review. The included trace elements were Chromium (Cr), Selenium (Se), Zinc (Zn) and Vanadium (V). The time, dose and type of supplement varied among the studies. Se, Cr, Zn and V improved glycemic profile and antioxidant status while Se, Cr and Zn affected lipid profile. Se and Zn supplementation improved endothelial function. Also, Se modified inflammatory profile. In general, cautious supplementation of trace elements promotes the metabolic control of T2DM.
... Hyperinsulinemia is another aspect that needs to be taken into account when describing factors affecting the CrPic action on cholesterol metabolism. Hoffman et al. [38] found that CrPic improved insulin action in hyperinsulinemia condition and prevented an increase in membrane cholesterol level. This mechanism compromised F-actin integrity, which is necessary for GLUT-4 translocation regulated by insulin. ...
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The aim of the study was to evaluate the hypoglycaemic potential of supplementary Cr in the form of chromium(III) glycinate (CrGly) in the diabetic model of rats. The experiment was conducted on 40 male Wistar rats, of which 30 were made diabetic by injection of a single dose of streptozotocin (55 mg/kg b.m.), while the remaining 10 rats served as the healthy control. After inducing hyperglycaemia, 2 groups of diabetic rats (10 rats each) were supplemented with Cr either as CrGly or chromium(III) picolinate (CrPic) given orally at a dose of 10 mg/kg diet (about 0.75 mg Cr/kg b.m.) with adequate AIN-93M diet for 7 weeks. At the termination of experiment, all animals were sacrificed to collect blood and internal organs for biochemical assays. Blood biochemical indices and tissular trace element contents (Fe, Zn, Cu, Cr) were measured and compared with the values of the untreated groups. It was found that CrGly significantly decreased blood glucose, total cholesterol, HDL cholesterol and triacylglycerol levels more efficiently than CrPic. Furthermore, both Cr compounds normalized disturbed the serum, renal and cardiac molar Cu/Zn ratio, as well as restored the kidney Zn and Cu levels in rats with hyperglycaemia. Supplementary Cr did not increase the tissular Cr levels in diabetic rats. The study confirmed the hypoglycaemic potential of CrGly in the diabetic model of rats.
... In the present study, post-exercise ingestion of SAC increased insulin, FSR, glycogen, and amino acid levels. The increase in insulin level after treatment with chromium corroborated some previous studies which demonstrated that chromium appears to increase insulin responsiveness via an AMPK-mediated pathway [34]. Evans and Bowman [35] reported that chromium ingestion can increase insulin level and markedly increase leucine uptake in cultured rat skeletal muscle cells. ...
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The present study was undertaken to investigate the effect of the combination of soy protein, amylopectin, and chromium (SAC) on muscle protein synthesis and signal transduction pathways involved in protein synthesis (mTOR pathways, IGF-1, and AktSer473) and proteolysis (FOXO1Ser256; MURF1, MAFbx) after exercise. Thirty-five Wistar rats were randomly divided into five groups: (1) control (C); (2) exercise (E); (3) exercise + soy protein (3.1 g/kg/day) (E + S); (4) exercise + soy protein + chromium (E + S + Cr); (5) exercise + soy protein + amylopectin + chromium (E + S + A + Cr). Post-exercise ingestion of SAC significantly increased the fractional rate of protein synthesis (FSR), insulin, glycogen, and amino acid levels with the highest effect observed in E + S + A + Cr group (P ˂ 0.05). However, SAC supplementation decreased the lactic acid concentration (P ˂ 0.05). A reduction in forkhead box protein O1 (FOXO1) and forkhead box protein O3 (FOXO3) (regulators of ubiquitin-related proteolysis) and muscle atrophy F-box (MAFbx) levels was noted after treatment with SAC (P < 0.05). Insulin-like growth factor 1(IGF-1) level was increased in the E + S, E + S + Cr, and E + S + A + Cr groups (P < 0.05). While the phosphorylation of 4E-BP1Thr37/46, AktSer473, mTORSer2448, and S6K1Thr389 levels increased after SAC supplementation, phosphorylated muscle ring finger 1 (MuRF-1, an E3-ubiquitin ligase gene) was found to be significantly lower compared with the E group (P ˂ 0.05). These results indicate that SAC supplementation improves FSR, insulin, and glycogen levels after exercise. SAC improves protein synthesis by inhibiting the ubiquitin–proteasome pathway and inducing anabolic metabolism.
... The physiological function of chromium in human is currently under debate. Though some cellular functions of chromium have been reported, in 2014, the European food safety authority officially removed it from their list of essential micronutrients [114,115]. The impact of chromium exposition on osteoblasts was investigated in several studies, whereby only toxic effects, causing reduced DNA, RNA and protein synthesis, were reported [116,117]. ...
Article
The regeneration of bone tissue is the main purpose of most therapies in dental medicine. For bone regeneration, calcium phosphate (CaP)-based substitute materials based on natural (allo-and xenografts) and synthetic origins (alloplastic materials) are applied for guiding the regeneration processes. The optimal bone substitute has to act as a substrate for bone ingrowth into a defect, as well as resorb in the time frame needed for complete regeneration up to the condition of restitution ad integrum. In this context, the modes of action of CaP-based substitute materials have been frequently investigated, where it has been shown that such materials strongly influence regenerative processes such as osteoblast growth or differentiation and also osteoclastic resorption due to different physicochemical properties of the materials. However, the material characteristics needed for the required ratio between new bone tissue formation and material degradation has not been found, until now. The addition of different substances such as collagen or growth factors and also of different cell types has already been tested but did not allow for sufficient or prompt application. Moreover, metals or metal ions are used differently as a basis or as supplement for different materials in the field of bone regeneration. Moreover, it has already been shown that different metal ions are integral components of bone tissue, playing functional roles in the physiological cellular environment as well as in the course of bone healing. The present review focuses on frequently used metals as integral parts of materials designed for bone regeneration, with the aim to provide an overview of currently existing knowledge about the effects of metals in the field of bone regeneration.
... For example, there is evidence that increased membrane cholesterol is key to impaired GLUT4 traffic in insulin-resistance and T2DM, though studies have focused on skeletal muscle given its contribution to systemic insulin sensitivity and glucose homeostasis: glucose-intolerant animal models and humans accumulate cholesterol in skeletal muscle membranes [331,335]; high-fat diets also increase skeletal muscle cholesterol [332]; DM also increases cardiac cholesterol levels [195]; cholesterol depletion with methyl-β-cyclodextrin reversibly and dose-dependently increases plasma membrane GLUT4 incorporation in myotubes [334]; and cholesterol depletion improves glucose homeostasis in high-fat fed animals, together with insulin-dependent GLUT4 translocation and glucose uptake in muscle fibers [335]. The cholesterol depleting agent chromium also improves glycemic control in T2DM patients [341], and activates GLUT4 trafficking and insulin-stimulated glucose transport in a cholesterol-and AMPK-dependent manner [342]. This is consistent with evidence AMPK improves insulin-stimulated GLUT4 control by lowering membrane cholesterol [335]. ...
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Cardiovascular disease, predominantly ischemic heart disease (IHD), is the leading cause of death in diabetes mellitus (DM). In addition to eliciting cardiomyopathy, DM induces a ‘wicked triumvirate’: (i) increasing the risk and incidence of IHD and myocardial ischemia; (ii) decreasing myocardial tolerance to ischemia–reperfusion (I–R) injury; and (iii) inhibiting or eliminating responses to cardioprotective stimuli. Changes in ischemic tolerance and cardioprotective signaling may contribute to substantially higher mortality and morbidity following ischemic insult in DM patients. Among the diverse mechanisms implicated in diabetic impairment of ischemic tolerance and cardioprotection, changes in sarcolemmal makeup may play an overarching role and are considered in detail in the current review. Observations predominantly in animal models reveal DM-dependent changes in membrane lipid composition (cholesterol and triglyceride accumulation, fatty acid saturation vs. reduced desaturation, phospholipid remodeling) that contribute to modulation of caveolar domains, gap junctions and T-tubules. These modifications influence sarcolemmal biophysical properties, receptor and phospholipid signaling, ion channel and transporter functions, contributing to contractile and electrophysiological dysfunction, cardiomyopathy, ischemic intolerance and suppression of protective signaling. A better understanding of these sarcolemmal abnormalities in types I and II DM (T1DM, T2DM) can inform approaches to limiting cardiomyopathy, associated IHD and their consequences. Key knowledge gaps include details of sarcolemmal changes in models of T2DM, temporal patterns of lipid, microdomain and T-tubule changes during disease development, and the precise impacts of these diverse sarcolemmal modifications. Importantly, exercise, dietary, pharmacological and gene approaches have potential for improving sarcolemmal makeup, and thus myocyte function and stress-resistance in this ubiquitous metabolic disorder.
... [91][92][93] We have found that AMPK stimulation improves GLUT4-mediated glucose transport and ABCA1/ ApoA1-mediated cholesterol efflux from insulin-resistant 3T3-L1 adipocytes via lowering membrane cholesterol levels. 2,29,94 ...
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Cholesterol is an essential component of cell membranes, and during the past several years, diabetes researchers have found that membrane cholesterol levels in adipocytes, skeletal muscle fibers and pancreatic beta cells influence insulin action and insulin secretion. Consequently, it is thought that dysregulated cell cholesterol homeostasis could represent a determinant of type 2 diabetes (T2D). Recent clinical findings compellingly add to this notion by finding increased T2D susceptibility in individuals with alterations in a variety of cholesterol metabolism genes. While it remains imperfectly understood how statins influence glucose metabolism, the fact that they display an influence on blood glucose levels and diabetes susceptibility seems to intensify the emerging importance of understanding cellular cholesterol in glucose metabolism. Taking this into account, this review first presents cell system and animal model findings that demonstrate the negative impact of cellular cholesterol accumulation or diminution on insulin action and insulin secretion. With this framework, a description of how changes in cholesterol metabolism genes are associated with T2D susceptibility will be presented. In addition, the connection between statins and T2D risk will be reviewed with expanded information on pitavastatin, a newer statin medication that displays actions favoring metabolic health.
... Treatment with chromium picolinate, a compound that removes membrane cholesterol, activates GLUT4 trafficking and enhances insulin-stimulated glucose transport via a cholesterol-dependent mechanism [79]. In addition, chromium supplementation significantly improves fasting glycemia in T2DM patients [80]. ...
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Membrane cholesterol is critical for signaling processes in a variety of tissues. We will address here current evidence supporting an emerging role of cholesterol on excitation-contraction coupling and glucose transport in skeletal muscle. We have centered our review on the transverse tubule system, a complex network of narrow plasma membrane invaginations that propagate membrane depolarization into the fiber interior and allow nutrient delivery into the fibers. We will discuss current evidence showing that transverse tubule membranes have remarkably high cholesterol levels and we will address how modifications of cholesterol content influence excitation-contraction coupling. In addition, we will discuss how membrane cholesterol levels affect glucose transport by modulating the insertion into the membrane of the main insulin-sensitive glucose transporter GLUT4. Finally, we will address how the increased membrane cholesterol levels displayed by obese animals, which also present insulin resistance, affect these two particular skeletal muscle functions.
... The potential mechanism of modulating glucose was reported to be the enhancement of intracellular signaling which increased insulin binding to the cells and activated insulin receptor kinase to improve the utilization of glucose (Anderson, 2000). The trivalent chromium could enhance the translocation of GLUT4 and insulin responsiveness via AMPK (Adenosine Monophosphate Activated Protein Kinase) signaling pathway (Pattar et al., 2006;Hoffman et al., 2014). However, it should be noted that chromium might cause harms when the intake dose is too high. ...
... In vitro and in vivo studies have demonstrated that under insulin resistance conditions, Cr(III) augments insulin-dependent Glut4 membrane translocation [10]. It seems that Cr(III) favorably affects membrane fluidity through decrease in membrane cholesterol [15] and protects against pathological increases that compromise F-actin integrity required for proper insulinregulated Glut4 translocation [16]. Emerging evidence also suggest that Cr(III) alleviates endoplasmic reticulum stress which plays crucial role in the development of insulin resistance [17], but the exact mechanism remains unclear [10]. ...
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PurposeChromium (Cr)-enriched yeast supplementation to whole wheat bread (WWCrB) has been shown to ameliorate postprandial glycemic response in healthy subjects. The present study investigates the long-term benefit of WWCrB consumption for patients with type-2 diabetes mellitus (T2DM). Methods Thirty patients with T2DM were randomly assigned to a group receiving WWCrB or the plain whole wheat bread (WWB) group. Plasma glucose, insulin, glycosylated hemoglobin (HbA1c) and insulin resistance were determined, and oral glucose tolerance test (OGTT) was performed at the beginning and the end of the dietary intervention, which lasted for 12 weeks. Biochemical parameters related to the disease, markers of inflammation as well as body weight and energy balance were examined. ResultsAt the end of the study, subjects of WWCrB group exerted lower levels of glucose, insulin and HbA1c and improved insulin resistance (P < 0.05 against before treatment). Area under the glucose curve attained during OGTT decreased after the intervention (28,117.5 ± 1266.4 vs. 31,588.5 ± 1187.5 mg min/dL before treatment, P < 0.05) with significantly lower values of glucose concentration at 0 and 60 min. A significant reduction in body weight and systolic blood pressure (SBP) was observed (P < 0.05 against before treatment). Markers of inflammation and lipid profiles were not affected by WWCrB consumption. Conclusions Inclusion of WWCrB in the daily dietary pattern of diabetic patients resulted in improvement of glucose tolerance and insulin resistance, significant reduction in HbA1c, weight loss and lower SBP. Patients with inadequate glycemic control may benefit from the consumption of WWCrB.
... The various outcomes may be resulted from differences in the feeding period or the forms of Cr. It is reported that Cr is able to promote glucose uptake and metabolism by increasing the activity of the cellular energy sensor 5′AMP-activated protein kinase that can mediate the beneficial effects of Cr on glucose transporter 4 and glucose transport regulation [27]. Blood glucose levels were decreased in CrMet-treated groups in the present research, which was in accordance with the results in finishing pigs [5,11] and in broilers [28]. ...
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The effects of dietary chromium methionine (CrMet) on growth performance, serum metabolites, endocrine parameters, antioxidant status, and immune traits in growing pigs were investigated. A total of 180 crossbred pigs (30.18 ± 0.28 kg initial body mass) were randomly divided into five groups, each group with six pens, six pigs per pen. Pigs were fed on the same basal diet supplemented with 0 (control), 100, 200, 400, and 800 μg/kg Cr from CrMet for 35 days. The results showed that supplemental CrMet did not affect growth performance. Cr at 200-800 μg/kg significantly decreased serum glucose levels (P < 0.05), while other serum metabolites were unaffected by Cr supplementation. Serum growth hormone (GH) levels were significantly decreased by Cr addition (P < 0.05). Furthermore, serum insulin-like growth factor I (IGF-I) levels were linearly decreased with increased Cr dose, and a significant reduction was observed in pigs fed 800 μg/kg Cr diets (P < 0.05). Serum immunoglobulin A, G, and M concentrations were increased linearly with increased Cr dosage, and pigs fed 400 μg/kg Cr had greater serum immunoglobulin M contents (P < 0.05). Cr at 400 μg/kg significantly increased serum superoxide dismutase and total antioxidant capacity activities (T-AOC) (P < 0.05). However, Cr at 800 μg/kg increased serum catalase activities, while decreasing serum T-AOC contents (P < 0.05). Additionally, there was a significant increase in serum malondialdehyde levels for pigs fed 800 μg/kg Cr diets (P < 0.05). These results indicated that dietary supplementation CrMet decreased serum glucose, GH, and IGF-I levels. Besides, supplemental 400 μg/kg Cr as CrMet improved serum antioxidant status and immune responses, but additional 800 μg/kg Cr resulted in lipid peroxidation in growing pigs.
... The role of chromium in glucose and insulin metabolism is mediated by numerous pathways [30]. Particularly, chromium enhances 5 AMP-activated protein kinase activity [31] that plays a critical role in insulin responsiveness [32]. Moreover, chromium compounds increase insulin receptor kinase activity potentiating insulin signaling [33]. ...
Article
Among the many heavy metals, chromium (Cr) is one of the fascinating ones. In its two most prevalent oxidation forms, trivalent (Cr³⁺) and hexavalent (Cr⁶⁺), Cr has completely different toxicity and essentiality in human health, as well as in the soil. In humans, Cr³⁺ is a necessary micronutrient for metabolism of glucose, lipid, and proteins. In contrast, Cr⁶⁺ has no recognized biological functions and is a potent carcinogen. In the search for new and effective ways to protect humans from heavy metals, “gut remediation” using probiotics has been found to be a promising and sustainable approach. Here, we have reviewed the most recent literature on how Cr causes cellular toxicity and DNA damage via cellular oxidation and epigenetic modifications, along with current biological, chemical, and herbal remediation methods, with a focus on sustainable strategies such as gut remediation.
Article
Background Researchers have reported that chromium (Cr) exposure may be associated with metabolism of glucose and lipids in residents living in a long-term Cr polluted area. Previous statistical analysis is mainly focused on individual chromium exposure. Furtherly, we aim to investigated the independent, combined, and interaction effects of the co-exposure of urine Cr (UCr) with cadmium (UCd), lead (UPb) and manganese (UMn) on body mass index (BMI), waist circumference, and the risk of overweight and abdominal obesity. Method We enrolled 1187 participants from annual surveys between 2017 and 2019. Heavy metal concentrations in urine were standardized using covariate-adjusted urine creatinine levels. Multiple linear/logistic regression models were applied to measure the single effect of urine heavy metal concentration on the outcomes. The quantile-based g-computation (g-comp) model was used to evaluate the combined effect of metal mixture on the outcomes and to compare the contribution of each metal. Both additive and multiplicative interactions were measured for UCr with UCd, UPb, UMn on the outcomes. Analysis was performed on the overall population and stratified by smoking habit. Results For the overall study population, UCr was positively associated with BMI (p trend = 0.023) and waist circumference (p trend = 0.018). For smoking participants, the g-comp model demonstrated that the metal mixture was negatively associated with BMI, with UCr and UCd contributing the most in the positive and negative direction. A negative additive interaction was observed between UCr and UCd on BMI and abdominal obesity. We did not observe a significant interaction effect of UCr with UPb or UMn. Conclusion Our study indicated that Cr and Cd exposure may be associated with BMI and waist circumference, with combined and interaction effects of the heavy metals noted. Further epidemiological and experimental researches could simultaneously consider single and complex mixed exposure to verify the findings and biological mechanisms.
Article
A 60‐day feeding trial was conducted to evaluate the effects of different chromium sources on the common carp. Four diets (32.2% crude protein and 6% lipids of dry matter) were formulated to add chromium oxide (Cr2O3), chromium picolinate (CrPic) and chromium methionine (CrMet) with 2 mg/kg Cr3+, respectively, and one basal diet. Each diet was randomly assigned to triplicate groups of 60 juvenile common carp (approximately 40.95 ± 4.80 g). The results indicated that fish fed CrMet diets had significantly higher weight gain, specific growth rate and feed efficiency than other groups (p < 0.05). No significant differences in the whole body compositions except the lipid content significantly increased in CrMet diets (p < 0.05). Fish that were fed chromium diets had significantly higher lactic dehydrogenase and creatine kinase in serum, succinic acid dehydrogenase and lactic acid in muscle, pyruvate kinase and glycogen synthase in hepatopancreas, lower glucose concentration and phosphoenolpyruvate carboxykinase activities in hepatopancreas than those given the basal diet (p < 0.05). Insulin receptor (IR) in serum, IR gene expression in hepatopancreas and sodium‐dependent glucose transporter 1 (SGLT1) in intestinal was increased (p < 0.05), while the cortisol decreased significantly in the dietary of CrMet or CrPic (p < 0.05). CrMet supplementation also increased HK activities, up‐regulated glucose transporter 2 (GLUT2) in hepatopancreas (p < 0.05). In conclusion, dietary addition of CrMet improved growth performance, adjusted glycometabolism enzyme activities, IR, GLUT2 and SGLT1 gene expression and had a significant impact on the carbohydrate utilization of juvenile common carp fed high corn diets compared with CrPic and Cr2O3.
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Increasing fat deposition and feed conversion ratio over the days in finishing phase directly influence pork quality and productive profitability. Nonetheless, the slaughter of heavier pigs can result in benefits for the slaughterhouse due to dilution of production and processing costs, as well as economic benefits for the pig producer resulting from the dilution of production costs. Therefore, dietary supplementation of chromium for finishing pigs of high lean-genotypes is a strategy to increase lean tissue accretion and minimize fat deposition, reflecting positively on growth performance. This review discussed recent studies results and mechanisms of action of this modifier of performance and carcass a traits in finishing pigs. Chromium increases the insulin action, facilitating insulin binding to the receptors on cell membrane. As a result, insulin-sensitive cells uptake more glucose, which will be later converted into energy. This additional energy is use to increase protein synthesis, thereby increasing the amount of lean tissue and reducing fat content in the carcass, without altering protein intake by pigs. Chromium also reduces lipid oxidation rate maintaining meat quality for longer period. In conclusion, dietary Cr supplementation for finishing pigs have shown that 0.2 mg/kg of organic Cr sources for pigs from ~60 kg until the slaughter can improve growth performance, lean gain and reduce fat content in carcass. However, the development of nanotechnology has allowed the use of inorganic Cr source at 0.2 mg/kg of inclusion, leading to improve the growth performance and carcass traits of finishing pigs.
Article
Implant wear and corrosion have been associated with adverse tissue reactions that can lead to implant failure. Wear and corrosion products are therefore of great clinical concern. For example, Co²⁺ and Cr³⁺ originating from CoCrMo‐based implants have been shown to induce a pro‐inflammatory response in macrophages in vitro . Previous studies have also shown that the activation of macrophages by some pro‐inflammatory stimuli is associated with a hypoxia‐inducible factor‐1α (HIF‐1α)‐dependent metabolic shift from oxidative phosphorylation (OXPHOS) towards glycolysis. However, the potential of Co²⁺ and Cr³⁺ to induce this metabolic shift, which plays a determining role in the pro‐inflammatory response of macrophages, remains largely unexplored. We recently demonstrated that Co²⁺, but not Cr³⁺, increased oxidative stress and decreased OXPHOS in RAW 264.7 murine macrophages. In the present study, we analyzed the effects of Co²⁺ and Cr³⁺ on glycolytic flux and HIF‐1α stabilization in the same experimental model. Cells were exposed to 6–24 ppm Co²⁺ or 50–250 ppm Cr³⁺. Glycolytic flux was measured by extracellular flux analysis and lactate determinations, while HIF‐1α stabilization was analyzed by immunoblotting. Results showed that Co²⁺, and to a lesser extent Cr³⁺, increased glycolytic flux; however only Co²⁺ did so through HIF‐1α stabilization. Overall, these results, together with our previous results (showing that Co²⁺ increases oxidative stress and decreases OXPHOS) suggest that Co²⁺ (but not Cr³⁺) can induce a HIF‐1α‐dependent metabolic shift from OXPHOS towards glycolysis in macrophages. This shift may play a pivotal role in the pro‐inflammatory response induced by Co²⁺ in the periprosthetic environment. This article is protected by copyright. All rights reserved.
Chapter
Global human population is going to increase day by day, and it is almost doubled every 20–30 years. With this increase, it has exerted huge pressure on the environment. Water, soil and air pollution has become a permanent problem not only for the human population but also for other fauna and flora of the Earth. Heavy metals are used in various industries, and the effluent containing these metals is thrown in the water channels everywhere, especially in developing countries. Various departments in different parts of the world are working to cope with such tragic situations. But a detailed effort is needed to assess their source, toxicity and remediation strategies. Here, some of these factors are discussed which can be helpful for the remediation of the polluted environment.
Article
Polysaccharide from Ganoderma lucidum is one of the best metal-ion chelating agents because of its structural characteristics and excellent functional activities. In this study, we synthesized and characterized a novel G. lucidum polysaccharide‑chromium (III) [GLP-Cr(III)] complex. Response surface methodology (RSM) was used to optimize the reaction conditions for the maximum chelation rate of GLP-Cr(III) complex. The optimal reaction conditions obtained from RSM were as follows: concentration of CrCl3 5.71 mg/mL, pH 6.36, temperature 66.4 °C and time 2.0 h, respectively. The pH was the most significant factor, followed by reaction temperature and CrCl3 concentration. Under the optimal conditions, the experimental chelation rate was 94.17 ± 1.0% for GLP-Cr(III) complex, which agreed closely with the predicted value (94.60%). Fourier transform infrared (FT-IR) spectroscopy revealed that the primary sites of chromium (III)-binding in G. lucidum polysaccharide were OH and CO groups, which induce the morphology change from flat sheet to rough surface. Meanwhile, according to the result of X-ray diffraction (XRD), the crystal degree of GLP was disappeared after chelation with Cr(III). The presence of a "blind zone" in the 1H NMR spectrum obviously indicated the binding of Cr(III) to GLP. Additionally, the effects of GLP-Cr(III) complex on hyperglycemia and hyperlipidemia in high fructose and fat diet-induced pre-diabetic mice were also investigated. Results showed that the serum total cholesterol (TC), triglyceride (TG), low density lipoprotein cholesterol (LDL-C), fasting blood glucose levels and glucose tolerance in mice supplemented with GLP-Cr(III) complex (50 mg/kg day) were significantly lower than the model group (P < 0.01). More importantly, the GLP-Cr(III) complex had no significant adverse effects on the physiological metabolism, organ index, and liver tissue morphology of mice fed a normal diet. These results suggest that GLP-Cr(III) complex could be used as potential functional food ingredients for the prevention or treatment of hyperglycemia and hyperlipidemia.
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Meat quality is a complex trait that is influenced by genetic and environmental factors, which includes mineral concentration. However, the association between mineral concentration and meat quality, and the specific molecular pathways underlying this association, are not well explored. We therefore analyzed gene expression as measured with RNA-seq in Longissimus thoracis muscle of 194 Nelore steers for association with three meat quality traits (intramuscular fat, meat pH, and tenderness) and the concentration of 13 minerals (Ca, Cr, Co, Cu, Fe, K, Mg, Mn, Na, P, S, Se, and Zn). We identified seven sets of co-expressed genes (modules) associated with at least two traits, which indicates that common pathways influence these traits. From pathway analysis of module hub genes, we further found an over-representation for energy and protein metabolism (AMPK and mTOR signaling pathways) in addition to muscle growth, and protein turnover pathways. Among the identified hub genes FASN, ELOV5, and PDE3B are involved with lipid metabolism and were affected by previously identified eQTLs associated to fat deposition. The reported hub genes and over-represented pathways provide evidence of interplay among gene expression, mineral concentration, and meat quality traits. Future studies investigating the effect of different levels of mineral supplementation in the gene expression and meat quality traits could help us to elucidate the regulatory mechanism by which the genes/pathways are affected.
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As an oral hypoglycemic agent, metformin (Met) has become a best-selling inexpensive drug worldwide. In this thesis, [Cr(metformin)3] (CrMet) complex was synthesized and characterized by elemental analysis (EA), electrospray ionization-mass spectrometry (ESI-MS), nuclear magnetic resonance (NMR), infrared (IR), UV-visible (UV-vis) and molar conductivity. Meanwhile, the molecule structure of CrMet complex was optimized using Gaussian 09. Considering the therapeutic effect of Met and Met/Cr(III) complex on type 2 diabetes mellitus (T2DM), the biological activities of CrMet in streptozocin (STZ)-induced diabetic mice were evaluated in detail from the aspects of fasting blood-glucose (FBG), fasting serum insulin (FINS), triglyceride (TG), total cholesterol (TC), low density lipoprotein cholesterol (LDL-c) and high density lipoprotein cholesterol (HDL-c) levels. These results indicated that CrMet had beneficial function on blood glucose (BG) and lipid metabolism for diabetes. Additionally, the results of cytotoxicity and toxicity experiments showed that CrMet had no damage to cells and relatively high safety in mice. It may be a potential candidate as a therapeutic agent in T2DM.
Article
Our previous study showed that chromium malate improved the regulation of blood glucose in mice with alloxan-induced diabetes. The present study was designed to evaluate the 90-day oral toxicity of chromium malate in Sprague-Dawley rats. The present study inspected the effect of chromium malate on glycometabolism, glycometabolism-related enzymes, lipid metabolism, and learning and memory ability in metabolically healthy Sprague-Dawley rats. The results showed that all rats survived and pathological, toxic, feces, and urine changes were not observed. Chromium malate did not cause measurable damage on liver, brain, and kidney. The fasting blood glucose, serum insulin, insulin resistance index, C-peptide, hepatic glycogen, glucose-6-phosphate dehydrogenase, glucokinase, total cholesterol, low-density lipoprotein cholesterol, high-density lipoprotein cholesterol, and triglyceride levels of normal rats in chromium malate groups had no significant change when compared with control group and chromium picolinate group under physiologically relevant conditions. The serum and organ content of Cr in chromium malate groups had no significant change compared with control group. No significant changes were found in morris water maze test and superoxide dismutase (SOD), glutathione peroxidase (GSH-Px), and true choline esterase (TChE) activity. The results indicated that supplementation with chromium malate did not cause measurable toxicity and has no obvious effect on glycometabolism and related enzymes, learning and memory ability, and related enzymes and lipid metabolism of female and male rats. The results of this study suggest that chromium malate is safe for human consumption.
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Obese sheep were used to assess the effects of palmitoleic (C16:1 cis-9) acid infusion on lipogenesis and circulating insulin levels. Infusion of 10 mg/kg body weight (BW)/day C16:1 intravenously in obese sheep reduced (P<0.01) weight gain by 77%. Serum palmitoleic levels increased (P<0.05) in a linear manner with increasing levels of C16:1 infusion. Cis-11 vaccenic (C18:1 cis-11) acid, a known elongation product of palmitoleic acid, was also elevated (P<0.05) in serum after 14 days and 21 days of infusion. Plasma insulin levels were lower (P<0.05) (10 mg/kg BW/day C16:1) than controls (0 mg/kg BW/day C16:1) at 14 days and 28 days of infusion. Infusion of C16:1 resulted in linear increases in tissue concentrations of palmitoleic, cis-11 vaccenic, eicosapentaenoic, and docosapentaenoic acids in a dose-dependent manner. Total lipid content of the semitendinosus (ST) muscle and mesenteric adipose tissue was reduced (P<0.01) in both 5 mg/kg and 10 mg/kg BW C16:1 dose levels. Total lipid content and mean adipocyte size in the longissimus muscle was reduced (P<0.05) in the 10 mg/kg BW C16:1 dose level only, whereas total lipid content and adipocyte size of the subcutaneous adipose tissue was not altered. Total lipid content of the liver was also unchanged with C16:1 infusion. Palmitoleic acid infusion upregulated (P<0.05) acetyl-CoA carboxylase (ACC), fatty acid elongase-6 (ELOVL6), and Protein kinase, AMP-activated, alpha 1 catalytic subunit, transcript variant 1 (AMPK) mRNA expressions in liver, subcutaneous adipose, and ST muscle compared to the controls. However, mRNA expression of glucose transporter type 4 (GLUT4) and carnitine palmitoyltransferase 1b (CPT1B) differed between tissues. In the subcutaneous adipose and liver, C16:1 infusion upregulated (P<0.05) GLUT4 and CPT1B, whereas these genes were downregulated (P<0.05) in ST muscle with C16:1 infusion. These results show that C16:1 infusion for 28 days reduced weight gain, intramuscular adipocyte size and total lipid content, and circulating insulin levels. These changes appear to be mediated through alterations in expression of genes regulating glucose uptake and fatty acid oxidation specifically in the muscles.
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The Rab-GTPase-activating protein TBC1D1 has emerged as a novel candidate involved in metabolic regulation. Our aim was to determine whether TBC1D1 is involved in insulin as well as energy-sensing signals controlling skeletal muscle metabolism. TBC1D1-deficient congenic B6.SJL-Nob1.10 (Nob1.10(SJL)) and wild-type littermates were studied. Glucose and insulin tolerance, glucose utilization, hepatic glucose production, and tissue-specific insulin-mediated glucose uptake were determined. The effect of insulin, AICAR, or contraction on glucose transport was studied in isolated skeletal muscle. Glucose and insulin tolerance tests were normal in TBC1D1-deficient Nob1.10(SJL) mice, yet the 4-h-fasted insulin concentration was increased. Insulin-stimulated peripheral glucose utilization during a euglycemic hyperinsulinemic clamp was similar between genotypes, whereas the suppression of hepatic glucose production was increased in TBC1D1-deficient mice. In isolated extensor digitorum longus (EDL) but not soleus muscle, glucose transport in response to insulin, AICAR, or contraction was impaired by TBC1D1 deficiency. The reduction in glucose transport in EDL muscle from TBC1D1-deficient Nob1.10(SJL) mice may be explained partly by a 50% reduction in GLUT4 protein, since proximal signaling at the level of Akt, AMPK, and acetyl-CoA carboxylase (ACC) was unaltered. Paradoxically, in vivo insulin-stimulated 2-deoxyglucose uptake was increased in EDL and tibialis anterior muscle from TBC1D1-deficient mice. In conclusion, TBC1D1 plays a role in regulation of glucose metabolism in skeletal muscle. Moreover, functional TBC1D1 is required for AICAR- or contraction-induced metabolic responses, implicating a role in energy-sensing signals.
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AMP-activated protein kinase (AMPK) enhances glucose transporter GLUT4 regulation. AMPK also suppresses energy-consuming pathways such as cholesterol synthesis. Interestingly, recent in vitro and in vivo data suggest that excess membrane cholesterol impairs GLUT4 regulation. Therefore, this study tested whether a beneficial, GLUT4-regulatory aspect of AMPK stimulation involved cholesterol lowering. Using L6 myotubes stably expressing an exofacial myc-epitope-tagged-GLUT4, AMPK stimulation by 5-aminoimidazole-4-carboxamide-1-β-d-ribonucleoside (AICAR; 45 min, 1 mm) or 2,4-dinitrophenol (DNP; 30 min, 200 μm) increased cell surface GLUT4myc labeling by approximately ≈ 25% (P < 0.05). Insulin (20 min, 100 nm) also increased GLUT4myc labeling by about 50% (P < 0.05), which was further enhanced (≈ 25%, P < 0.05) by AICAR or DNP. Consistent with AMPK-mediated suppression of cholesterol synthesis, AICAR and DNP decreased membrane cholesterol by 20-25% (P < 0.05). Whereas AMPK knockdown prevented the enhanced basal and insulin-stimulated GLUT4myc labeling by AICAR and DNP, cholesterol replenishment only blocked the AMPK-associated enhancement in insulin action. Cells cultured in a hyperinsulinemic milieu, resembling conditions in vivo that promote the progression/worsening of insulin resistance, displayed an increase in membrane cholesterol. This occurred concomitantly with a loss of cortical filamentous actin (F-actin) and defects in GLUT4 regulation by insulin. These derangements were prevented by AMPK stimulation. Examination of skeletal muscle from insulin-resistant Zucker rats revealed a similar elevation in membrane cholesterol and loss of F-actin. Lowering cholesterol to control levels restored F-actin structure and insulin sensitivity. In conclusion, these data suggest a novel aspect of GLUT4 regulation by AMPK involves membrane cholesterol lowering. Moreover, this AMPK-mediated process protected against hyperinsulinemia-induced insulin resistance.
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AS160 and its closely related protein TBC1D1 have emerged as key mediators for both insulin- and contraction-stimulated muscle glucose uptake through regulating GLUT4 trafficking. Insulin increases AS160 phosphorylation at multiple Akt/PKB consensus sites, including Thr(649), and promotes its binding to 14-3-3 proteins through phospho-Thr(649). We recently provided genetic evidence that AS160-Thr(649) phosphorylation/14-3-3 binding plays a key role in mediating insulin-stimulated glucose uptake in muscle. Contraction has also been proposed to increase phosphorylation of AS160 and TBC1D1 via AMPK, which could be detected by a generic phospho-Akt substrate (PAS) antibody. Here, analysis of AS160 immunoprecipitates from muscle extracts with site-specific phospho-antibodies revealed that contraction and AICAR caused no increase but rather a slight decrease in phosphorylation of the major PAS recognition site AS160-Thr(649). In line with this, contraction failed to enhance 14-3-3 binding to AS160. Consistent with previous reports, we also observed that in situ contraction stimulated the signal intensity of PAS antibody immunoreactive protein of ∼150-160 kDa in muscle extracts. Using a TBC1D1 deletion mutant mouse, we showed that TBC1D1 protein accounted for the majority of the PAS antibody immunoreactive signals of ∼150-160 kDa in extracts of contracted muscles. Consistent with the proposed role of AS160-Thr(649) phosphorylation/14-3-3 binding in mediating glucose uptake, AS160-Thr(649)Ala knock-in mice displayed normal glucose uptake upon contraction and AICAR in isolated muscles. We conclude that the previously reported PAS antibody immunoreactive band ∼150-160 kDa, which were increased upon contraction, does not represent AS160 but TBC1D1, and that AS160-Thr(649)Ala substitution impairs insulin- but neither contraction- nor AICAR-stimulated glucose uptake in mouse skeletal muscle.
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Diminished cortical filamentous actin (F-actin) has been implicated in skeletal muscle insulin resistance, yet the mechanism(s) is unknown. Here we tested the hypothesis that changes in membrane cholesterol could be a causative factor, as organised F-actin structure emanates from cholesterol-enriched raft microdomains at the plasma membrane. Skeletal muscle samples from high-fat-fed animals and insulin-sensitive and insulin-resistant human participants were evaluated. The study also used L6 myotubes to directly determine the impact of fatty acids (FAs) on membrane/cytoskeletal variables and insulin action. High-fat-fed insulin-resistant animals displayed elevated levels of membrane cholesterol and reduced F-actin structure compared with normal chow-fed animals. Moreover, human muscle biopsies revealed an inverse correlation between membrane cholesterol and whole-body glucose disposal. Palmitate-induced insulin-resistant myotubes displayed membrane cholesterol accrual and F-actin loss. Cholesterol lowering protected against the palmitate-induced defects, whereas characteristically measured defects in insulin signalling were not corrected. Conversely, cholesterol loading of L6 myotube membranes provoked a palmitate-like cytoskeletal/GLUT4 derangement. Mechanistically, we observed a palmitate-induced increase in O-linked glycosylation, an end-product of the hexosamine biosynthesis pathway (HBP). Consistent with HBP activity affecting the transcription of various genes, we observed an increase in Hmgcr, a gene that encodes 3-hydroxy-3-methyl-glutaryl coenzyme A reductase, the rate-limiting enzyme in cholesterol synthesis. In line with increased HBP activity transcriptionally provoking a membrane cholesterol-based insulin-resistant state, HBP inhibition attenuated Hmgcr expression and prevented membrane cholesterol accrual, F-actin loss and GLUT4/glucose transport dysfunction. Our results suggest a novel cholesterolgenic-based mechanism of FA-induced membrane/cytoskeletal disorder and insulin resistance.
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Chromium picolinate (CrPic) has been indicated to activate glucose transporter 4 (GLUT4) trafficking to the plasma membrane (PM) to enhance glucose uptake in 3T3-L1 adipocytes. In skeletal and heart muscle cells, insulin directs the intracellular trafficking of the fatty acid translocase/CD36 to induce the uptake of cellular long-chain fatty acid (LCFA). The current study describes the effects of CrPic and insulin on the translocation of CD36 from intracellular storage pools to the PM in 3T3-L1 adipocytes in comparison with that of GLUT4. Immunofluorescence microscopy and immunoblotting revealed that both CD36 and GLUT4 were expressed and primarily located intracellularly in 3T3-L1 adipocytes. Upon insulin or CrPic stimulation, PM expression of CD36 increased in a similar manner as that for GLUT4; the CrPic-stimulated PM expression was less strong than that of insulin. The increase in PM localization for these two proteins by insulin paralleled LCFA ([1-(14)C]palmitate) or [(3)H]deoxyglucose uptake in 3T3-L1 adipocytes. The induction of the PM expression of GLUT4, but not CD36, or substrate uptake by insulin and CrPic appears to be additive in adipocytes. Furthermore, wortmannin completely inhibited the insulin-stimulated translocation of GLUT4 or CD36 and prevented the increased uptake of glucose or LCFA in these cells. Taken together, for the first time, these findings suggest that both insulin and CrPic induce CD36 translocation to the PM in 3T3-L1 adipocytes and that their translocation-inducing effects are not additive. The signaling pathway inducing the translocations is different, apparently resulting in a differential activity of CD36.
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TBC1D4 (also known as AS160) regulates glucose transporter 4 (GLUT4) translocation and glucose uptake in adipocytes and skeletal muscle. Its mode of action involves phosphorylation of serine (S)/threonine (T) residues by upstream kinases resulting in inactivation of Rab-GTPase-activating protein (Rab-GAP) activity leading to GLUT4 mobilization. The majority of known phosphorylation sites on TBC1D4 lie within the Akt consensus motif and are phosphorylated by insulin stimulation. However, the 5'-AMP-activated protein kinase (AMPK) and other kinases may also phosphorylate TBC1D4, and therefore we hypothesized the presence of additional phosphorylation sites. Mouse skeletal muscles were contracted or stimulated with 5-aminoimidazole-4-carboxamide-1-beta-d-ribofuranoside (AICAR), and muscle lysates were subjected to mass spectrometry analyses resulting in identification of novel putative phosphorylation sites on TBC1D4. The surrounding amino acid sequence predicted that S711 would be recognized by AMPK. Using a phosphospecific antibody against S711, we found that AICAR and contraction increased S711 phosphorylation in mouse skeletal muscle, and this increase was abolished in muscle-specific AMPKalpha2 kinase-dead transgenic mice. Exercise in human vastus lateralis muscle also increased TBC1D4 S711 phosphorylation. Recombinant AMPK, but not Akt1, Akt2, or PKCzeta, phosphorylated purified muscle TBC1D4 on S711 in vitro. Interestingly, S711 was also phosphorylated in response to insulin in an Akt2- and rapamycin-independent, but a wortmannin-sensitive, manner, suggesting this site is regulated by one or more additional upstream kinases. Despite increased S711 phosphorylation with AICAR, contraction, and insulin, mutation of S711 to alanine did not alter glucose uptake in response to these stimuli. S711 is a novel TBC1D4 phosphorylation site regulated by AMPK in skeletal muscle.
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TBC1D1 is a Rab-GTPase-activating protein (GAP) known to be phosphorylated in response to insulin, growth factors, pharmacological agonists that activate 5'-AMP-activated protein kinase (AMPK), and muscle contraction. Silencing TBC1D1 in L6 muscle cells by siRNA increases insulin-stimulated GLUT4 translocation, and overexpression of TBC1D1 in 3T3-L1 adipocytes with low endogenous TBC1D1 expression inhibits insulin-stimulated GLUT4 translocation, suggesting a role of TBC1D1 in regulating GLUT4 translocation. Aiming to unravel the regulation of TBC1D1 during contraction and the potential role of AMPK in intact skeletal muscle, we used EDL muscles from wild-type (WT) and AMPK kinase dead (KD) mice. We explored the site-specific phosphorylation of TBC1D1 Ser(237) and Thr(596) and their relation to 14-3-3 binding, a proposed mechanism for regulation of GAP function of TBC1D1. We show that muscle contraction increases 14-3-3 binding to TBC1D1 as well as phosphorylation of Ser(237) and Thr(596) in an AMPK-dependent manner. AMPK activation by AICAR induced similar Ser(237) and Thr(596) phosphorylation of, and 14-3-3 binding to, TBC1D1 as muscle contraction. Insulin did not increase Ser(237) phosphorylation or 14-3-3 binding to TBC1D1. However, insulin increased Thr(596) phosphorylation, and intriguingly this response was fully abolished in the AMPK KD mice. Thus, TBC1D1 is differentially regulated in response to insulin and contraction. This study provides genetic evidence to support an important role for AMPK in regulating TBC1D1 in response to both of these physiological stimuli.
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Understanding the influence of insulin on glucose turnover is the key to interpreting a great number of metabolic situations. Little is known, however, about insulin's effect on the distribution and exchange of glucose in body pools. We developed a physiological compartmental model to describe the kinetics of plasma glucose in normal man in the basal state and under steady-state conditions of euglycemic hyperinsulinemia. A bolus of [3-3H]glucose was rapidly injected into a peripheral vein in six healthy volunteers, and the time-course of plasma radioactivity was monitored at very short time intervals for 150 min. A 1-mU/min kg insulin clamp was then started, thereby raising plasma insulin levels to a high physiological plateau (approximately 100 microU/ml). After 90 min of stable euglycemic hyperinsulinemia, a second bolus of [3-3H]glucose was given, and plasma radioactivity was again sampled frequently for 90 min more while the clamp was continued. Three exponential components were clearly identified in the plasma disappearance curves of tracer glucose of each subject studied, both before and after insulin. Based on stringent statistical criteria, the data in the basal state were fitted to a three-compartment model. The compartment of initial distribution was identical to the plasma pool (40 +/- 3 mg/kg); the other two compartments had similar size (91 +/- 12 and 96 +/- 9 mg/kg), but the former was in rapid exchange with plasma (at an average rate of 1.09 +/- 0.15 min-1), whereas the latter exchanged 10 times more slowly (0.12 +/- 0.01 min-1). The basal rate of glucose turnover averaged 2.15 +/- 0.12 mg/min kg, and the total distribution volume of glucose in the postabsorptive state was 26 +/- 1% of body weight. In view of current physiological information, it was assumed that the more rapidly exchanging pool represented the insulin-independent tissues of the body, while the slowly exchanging pool was assimilated to the insulin-dependent tissues. Insulin-independent glucose uptake was estimated (from published data) at 75% of basal glucose uptake, and was constrained not to change with euglycemic hyperinsulinemia. When the kinetic data obtained during insulin administration were fitted to this model, neither the size nor the exchange rates of the plasma or the rapid pool were appreciably changed. In contrast, the slow pool was markedly expanded (from 96 +/- 9 to 190 +/- 30 mg/kg, P less than 0.02) at the same time as total glucose disposal rose fourfold above basal (to 7.96 +/- 0.85 mg/min kg, P less than 0.001). Furthermore, a significant direct correlation was found to exist between the change in size of the slow pool and the insulin-stimulated rate of total glucose turnover (r=0.92, P<0.01). We conclude that hyperinsulinemia, independent of hyperglycemia, markedly increases the exchangeable mass of glucose in the body, presumably reflecting the accumulation of free, intracellular glucose in insulin-dependent tissues.
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The cis-monoenoic fatty acids vaccenate and oleate stimulate D-glucose transport when partitioned into isolated plasma membranes from rat adipocytes. The magnitude of hexose transport stimulation due to these agents is equal to that observed in plasma membranes derived from insulin-treated adipocytes. Addition of cis-unsaturated fatty acids to plasma membranes derived from insulin-treated cells results in no further stimulation of glucose transport over that due to the hormone alone. In contrast, treatment of membranes exhibiting insulin-activated D-glucose transport activity with saturated fatty acids reduces transport activity to control levels. No effect of the saturated fatty acids was observed on D-glucose transport in control membranes. Because cis-unsaturated fatty acids fluidize plasma membranes under the conditions used in these experiments, these data demonstrate a positive correlation between membrane fluidity and adipocyte D-glucose transport system activity. In addition, the results suggest that enhanced bilayer fluidity or increased affinity of the glucose transporter for fluid microenvironments of the membrane may play a key role in transport regulation by insulin.
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The effects of chromium compounds on 3-O-methylglucose (3-O-MG) transport were studied in isolated rat adipocytes. Sodium chromate significantly stimulated 3-O-MG uptake into adipocytes in a dose-dependent manner without altering the equilibrium space of 3-O-MG in adipocytes. The stimulatory effect reached the maximum at 300 microM, and the effect was 60-70% of the maximal insulin effect that was obtained with 20 nM insulin. The chromate concentration achieving a half-maximal effect was estimated at 50 microM. The effect of the combination of 1 mM chromate and 20 nM insulin was equipotent to that of 20 nM insulin alone, which showed that these two effects were not additive. The stimulatory effects of 1 mM chromate and 20 nM insulin were entirely abolished in adipocytes deprived of ATP, which indicated that these effects were completely ATP-dependent. Judging from experiments using various chromium compounds, CrO4(2-) was responsible for the insulinomimetic action. These results indicate that the action of CrO4(2-) is exerted through a mechanism analogous to that of insulin action, and that CrO4(2-) is a novel and useful tool for studying issues involved in insulin actions.
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We studied the expression of the glucose transporter GLUT 4 in the soleus and red gastrocnemius muscles from obese, diabetic (fa/fa) Zucker rats compared to their lean littermates (Fa/-), with and without treatment with the antidiabetic drug metformin. In the untreated groups of rats, the GLUT 4 content in a crude membrane fraction of both the soleus and the red gastrocnemius muscles were significantly lower in the obese (fa/fa) rats (3.46 +/- 0.28 vs. 6.04 +/- 0.41, p < 0.001 and 6.0 +/- 0.24 vs. 9.1 +/- 0.48, p < 0.0001, respectively). Differences in GLUT 4 expression in soleus muscle from the same rats were confirmed by quantitative immunofluorescence microscopy, and the results were significantly correlated with the results obtained from quantitative immunoblotting (rho = 0.70, p < 0.0005). The decreased expression of GLUT 4 in fa/fa rats could contribute to the well-established insulin resistance in skeletal muscle of these animals. After 4 weeks of treatment with metformin, weight gain was not affected in either the diabetic (fa/fa) rats or the lean (Fa/-) rats. Improvement of glucose homeostasis by metformin was not associated with normalization of the GLUT 4 expression in the skeletal muscles studied, indicating (1) that the decreased GLUT 4 expression is not directly related to hyperinsulinaemia and diabetes mellitus and (2) that metformin does not normalize the expression of GLUT 4 in skeletal muscle of the diabetic (fa/fa) Zucker rats.
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Human studies suggest that chromium picolinate (CrPic) decreases insulin levels and improves glucose disposal in obese and type 2 diabetic populations. To evaluate whether CrPic may aid in treatment of the insulin resistance syndrome, we assessed its effects in JCR:LA-corpulent rats, a model of this syndrome. Male lean and obese hyperinsulinemic rats were randomly assigned to receive oral CrPic [80 microg/(kg. d); n = 5 or 6, respectively) in water or to control conditions (water, n = 5). After 3 mo, a 120-min intraperitoneal glucose tolerance test (IPGTT) and a 30-min insulin tolerance test were performed. Obese rats administered CrPic had significantly lower fasting insulin levels (1848 +/- 102 vs. 2688 +/- 234 pmol/L; P < 0.001; mean +/- SEM) and significantly improved glucose disappearance (P < 0.001) compared with obese controls. Glucose and insulin areas under the curve for IPGTT were significantly less for obese CrPic-treated rats than in obese controls (P < 0.001). Obese CrPic-treated rats had lower plasma total cholesterol (3.57 +/- 0.28 vs. 4.11 +/- 0.47 mmol/L, P < 0.05) and higher HDL cholesterol levels (1.92 +/- 0.09 vs. 1.37 +/- 0.36 mmol/L, P < 0.01) than obese controls. CrPic did not alter plasma glucose or cholesterol levels in lean rats. Total skeletal muscle glucose transporter (Glut)-4 did not differ among groups; however, CrPic significantly enhanced membrane-associated Glut-4 in obese rats after insulin stimulation. Thus, CrPic supplementation enhances insulin sensitivity and glucose disappearance, and improves lipids in male obese hyperinsulinemic JCR:LA-corpulent rats.
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Cell culture work suggests that signaling to polymerize cortical filamentous actin (F-actin) represents a required pathway for the optimal redistribution of the insulin-responsive glucose transporter, GLUT4, to the plasma membrane. Recent in vitro study further suggests that the actin-regulatory neural Wiskott-Aldrich syndrome protein (N-WASP) mediates the effect of insulin on the actin filament network. Here we tested whether similar cytoskeletal mechanics are essential for insulin-regulated glucose transport in isolated rat epitrochlearis skeletal muscle. Microscopic analysis revealed that cortical F-actin is markedly diminished in muscle exposed to latrunculin B. Depolymerization of cortical F-actin with latrunculin B caused a time- and concentration-dependent decline in 2-deoxyglucose transport. The loss of cortical F-actin and glucose transport was paralleled by a decline in insulin-stimulated GLUT4 translocation, as assessed by photolabeling of cell surface GLUT4 with Bio-LC-ATB-BMPA. Although latrunculin B impaired insulin-stimulated GLUT4 translocation and glucose transport, activation of phosphatidylinositol 3-kinase and Akt by insulin was not rendered ineffective. In contrast, the ability of insulin to elicit the cortical F-actin localization of N-WASP was abrogated. These data provide the first evidence that actin cytoskeletal mechanics are an essential feature of the glucose transport process in intact skeletal muscle. Furthermore, these findings support a distal actin-based role for N-WASP in insulin action in vivo.
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Muscle and fat cells develop insulin resistance when cultured under hyperinsulinemic conditions for sustained periods. Recent data indicate that early insulin signaling defects do not fully account for the loss of insulin action. Given that cortical filamentous actin (F-actin) represents an essential aspect of insulin regulated glucose transport, we tested to see whether cortical F-actin structure was compromised during chronic insulin treatment. The acute effect of insulin on GLUT4 translocation and glucose uptake was diminished in 3T3-L1 adipocytes exposed to a physiological level of insulin (5 nm) for 12 h. This insulin-induced loss of insulin responsiveness was apparent under both low (5.5 mm) and high (25 mm) glucose concentrations. Microscopic and biochemical analyses revealed that the hyperinsulinemic state caused a marked loss of cortical F-actin. Since recent data link phosphatidylinositol 4,5-bisphosphate (PIP2) to actin cytoskeletal mechanics, we tested to see whether the insulin-resistant condition affected PIP2 and found a noticeable loss of this lipid from the plasma membrane. Using a PIP2 delivery system, we replenished plasma membrane PIP2 in cells following the sustained insulin treatment and observed a restoration in cortical F-actin and insulin responsiveness. These data reveal a novel molecular aspect of insulin-induced insulin resistance involving defects in PIP2/actin regulation.
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Study has demonstrated an essential role of cortical filamentous actin (F-actin) in insulin-regulated glucose uptake by skeletal muscle. Here, we tested whether perturbations in F-actin contributed to impaired insulin responsiveness provoked by hyperinsulinemia. In L6 myotubes stably expressing GLUT4 that carries an exofacial myc-epitope tag, acute insulin stimulation (20 min, 100 nM) increased GLUT4myc translocation and glucose uptake by approximately 2-fold. In contrast, a hyperinsulinemic state, induced by inclusion of 5 nM insulin in the medium for 12 h decreased the ability of insulin to stimulate these processes. Defects in insulin signaling did not readily account for the observed disruption. In contrast, hyperinsulinemia reduced cortical F-actin. This occurred concomitant with a loss of plasma membrane phosphatidylinositol 4,5-bisphosphate (PIP(2)), a lipid involved in cytoskeletal regulation. Restoration of plasma membrane PIP(2) in hyperinsulinemic cells restored F-actin and insulin responsiveness. Consistent with these in vitro observations suggesting that the hyperinsulinemic state negatively affects cortical F-actin structure, epitrochlearis skeletal muscle from insulin-resistant hyperinsulinemic Zucker fatty rats displayed a similar loss of F-actin structure compared with that in muscle from lean insulin-sensitive littermates. We propose that a component of insulin-induced insulin resistance in skeletal muscle involves defects in PIP(2)/F-actin structure essential for insulin-regulated glucose transport.
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A novel niacin-bound, chromium-based energy formula (EF; InterHealth Nutraceuticals, Benicia, CA) has been developed in conjunction with D-ribose, caffeine, ashwagandha extract (containing 5% withanolides), and selected amino acids. We have assessed the efficacy of oral administration of EF (40 mg x kg body wt(-1) x day(-1)) in male and female rats over a period of 90 consecutive days on the cardiovascular and pathophysiological functions in an isolated rat heart model. After 30, 60, and 90 days of treatment with EF, the hearts of male and female rats were subjected to 30 min of global ischemia followed by 2 h of reperfusion and were measured for myocardial ATP, creatine phosphate (CP), phosphorylated AMP kinase (p-AMPK), and heat shock proteins. Myocardial ATP and CP levels were increased in both male and female rats after EF treatment compared with the controls. Western blot analyses were performed to quantify the expression of stress-related proteins such as heat shock proteins (HSP-70, -32, and -25) and are found to be increased in both male and female rats after EF treatment. The p-AMPK level, which is a sensor for the energy state in various cell types, was also found to be increased after treatment with EF in both male and female rats. Aortic flow, maximum first derivative of developed pressure, left ventricular developed pressure, and infarct size were observed after ischemia-reperfusion and found to be significantly improved in EF-treated rats compared with control animals. Thus EF demonstrated long-term safety as well as exhibiting significant cardioprotective ability during ischemia and reperfusion injury by increased energy production, improved cardiac function, and reduced infarct size.
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Berberine has been shown to have antidiabetic properties, although its mode of action is not known. Here, we have investigated the metabolic effects of berberine in two animal models of insulin resistance and in insulin-responsive cell lines. Berberine reduced body weight and caused a significant improvement in glucose tolerance without altering food intake in db/db mice. Similarly, berberine reduced body weight and plasma triglycerides and improved insulin action in high-fat-fed Wistar rats. Berberine downregulated the expression of genes involved in lipogenesis and upregulated those involved in energy expenditure in adipose tissue and muscle. Berberine treatment resulted in increased AMP-activated protein kinase (AMPK) activity in 3T3-L1 adipocytes and L6 myotubes, increased GLUT4 translocation in L6 cells in a phosphatidylinositol 3' kinase-independent manner, and reduced lipid accumulation in 3T3-L1 adipocytes. These findings suggest that berberine displays beneficial effects in the treatment of diabetes and obesity at least in part via stimulation of AMPK activity.
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Plasma membrane cholesterol accumulation has been implicated in cellular insulin resistance. Given the role of the hexosamine biosynthesis pathway (HBP) as a sensor of nutrient excess, coupled to its involvement in the development of insulin resistance, we delineated whether excess glucose flux through this pathway provokes a cholesterolgenic response induced by hyperinsulinemia. Exposing 3T3-L1 adipocytes to physiologically relevant doses of hyperinsulinemia (250pM-5000pM) induced a dose-dependent gain in the mRNA/protein levels of 3-hydroxy-3-methyl-glutaryl-coenzyme A reductase (HMGR). These elevations were associated with elevated plasma membrane cholesterol. Mechanistically, hyperinsulinemia increased glucose flux through the HBP and O-linked β-N-acetylglucosamine modification of specificity protein 1 (Sp1), known to activate cholesterolgenic gene products such as the sterol response element-binding protein (SREBP1) and HMGR. Chromatin immunoprecipitation demonstrated that increased N-acetylglucosamine modification of Sp1 resulted in a higher binding affinity of Sp1 to the promoter regions of SREBP1 and HMGR. Luciferase assays confirmed that HMGR promoter activity was elevated under these conditions and that inhibition of the HBP with 6-diazo-5-oxo-l-norleucine prevented hyperinsulinemia-induced activation of the HMGR promoter. In addition, both 6-diazo-5-oxo-l-norleucine and the Sp1 DNA-binding inhibitor mithramycin prevented the hyperinsulinemia-induced increases in HMGR mRNA/protein and plasma membrane cholesterol. In these mithramycin-treated cells, both cortical filamentous actin structure and insulin-stimulated glucose transport were restored. Together, these data suggest a novel mechanism whereby increased HBP activity increases Sp1 transcriptional activation of a cholesterolgenic program, thereby elevating plasma membrane cholesterol and compromising cytoskeletal structure essential for insulin action.
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The lipid domains of the cell membrane are believed to be one of the sites where biguanides exert their antihyperglycemic effect. We have examined the effects of metformin on the membrane fluidity of intact erythrocytes in vivo and in vitro. Membrane fluidity was measured by monitoring changes in the anisotropy of the fluorescent probe 6-antroyloxystearic acid (6-AS). The erythrocyte membranes from patients with non-insulin dependent diabetes mellitus treated with metformin were more fluid than those from non-insulin dependent diabetes mellitus patients treated by diet or healthy controls. There was no correlation between membrane fluidity and the plasma lipids or the parameters of metabolic control, suggesting that the high fluidity is an effect of metformin itself. Incubation of erythrocytes from healthy controls and diabetic patients treated by diet or glibenclamide with metformin in vitro confirmed that metformin increases the fluidity of erythrocyte membranes. In vitro metformin did not alter the fluidity of membranes from diabetic patients treated with metformin, perhaps because the basal high fluidity due to their in vivo interaction with plasma metformin could be increased no further. Since insulin appears to be required for the antihyperglycemic effect of metformin, the effect of insulin on membrane fluidity was also evaluated. Insulin generally had a small fluidizing effect on erythrocytes in vitro. The fluidizing action of both insulin and metformin could represent a membrane event common to the hormone and drug leading to additive or synergistic effects in vivo.
Article
Hyperinsulinemia is known to promote the progression/worsening of insulin resistance. Evidence reveals a hidden cost of hyperinsulinemia on plasma membrane (PM) phosphatidylinositol 4,5-bisphosphate (PIP(2))-regulated filamentous actin (F-actin) structure, components critical to the normal operation of the insulin-regulated glucose transport system. Here we delineated whether increased glucose flux through the hexosamine biosynthesis pathway (HBP) causes PIP(2)/F-actin dysregulation and subsequent insulin resistance. Increased glycosylation events were detected in 3T3-L1 adipocytes cultured under conditions closely resembling physiological hyperinsulinemia (5 nm insulin; 12 h) and in cells in which HBP activity was amplified by 2 mm glucosamine (GlcN). Both the physiological hyperinsulinemia and experimental GlcN challenge induced comparable losses of PIP(2) and F-actin. In addition to protecting against the insulin-induced membrane/cytoskeletal abnormality and insulin-resistant state, exogenous PIP(2) corrected the GlcN-induced insult on these parameters. Moreover, in accordance with HBP flux directly weakening PIP(2)/F-actin structure, pharmacological inhibition of the rate-limiting HBP enzyme [glutamine-fructose-6-phosphate amidotransferase (GFAT)] restored PIP(2)-regulated F-actin structure and insulin responsiveness. Conversely, overexpression of GFAT was associated with a loss of detectable PM PIP(2) and insulin sensitivity. Even less invasive challenges with glucose, in the absence of insulin, also led to PIP(2)/F-actin dysregulation. Mechanistically we found that increased HBP activity increased PM cholesterol, the removal of which normalized PIP(2)/F-actin levels. Accordingly, these data suggest that glucose transporter-4 functionality, dependent on PIP(2) and/or F-actin status, can be critically compromised by inappropriate HBP activity. Furthermore, these data are consistent with the PM cholesterol accrual/toxicity as a mechanistic basis of the HBP-induced defects in PIP(2)/F-actin structure and impaired glucose transporter-4 regulation.
Article
Trivalent chromium (Cr3+) is an essential micronutrient. Findings since the 1950s suggest that Cr3+ might benefit cholesterol homeostasis. Here we present mechanistic evidence in support of this role of Cr3+. High-density lipoprotein cholesterol generation in 3T3-L1 adipocytes, which are rendered ineffective by the hyperinsulinemia that is known to accompany disorders of lipid metabolism, was corrected by Cr3+. Mechanistically, Cr3+ reversed hyperinsulinemia-induced cellular cholesterol accrual and associated defects in cholesterol transporter ATP-binding cassette transporter-A1 trafficking and apolipoprotein A1-mediated cholesterol efflux. Moreover, direct activation of AMP-activated protein kinase, which is known to be activated by Cr3+, or inhibition of hexosamine biosynthesis pathway activity, which is known to be elevated by hyperinsulinemia, mimics Cr3+ action. These findings suggest a mechanism of Cr3+ action that fits with long-standing claims of its role in cholesterol homeostasis. Furthermore, these data imply a mechanistic basis for the coexistence of dyslipidemia with hyperinsulinemia.
Article
Solving how insulin regulates glucose transport into skeletal muscle and adipose tissue remains a fundamental challenge in biology and a significant issue in medicine. A central feature of this process is the coordinated accumulation of the glucose transporter GLUT4 into the plasma membrane. New signaling and cytoskeletal mechanisms of insulin-stimulated GLUT4 exocytosis are of emerging interest, particularly those at or just beneath the plasma membrane. This review examines signals that functionally engage GLUT4 exocytosis, considers cytoskeletal regulation of the stimulated GLUT4 itinerary, and appraises the involvement of plasma membrane parameters in GLUT4 control. We also explore how these newly-defined signaling, cytoskeletal and membrane mechanisms could be of therapeutic interest in the treatment and/or prevention of GLUT4 dysregulation in disease.
Article
1. Chromium picolinate (CrPic) has been recommended as an alternative therapeutic regimen for Type 2 diabetes mellitus (T2DM). However, the molecular mechanism underlying the action of CrPic is poorly understood. 2. Using normal and insulin-resistant 3T3-L1 adipocytes, we examined the effects of CrPic on the gene transcription and secretion of adiponectin and resistin. In addition, using immunoblotting, ELISA and real-time reverse transcription-polymerase chain reaction (RT-PCR), we investigated the effects of 10 nmol/L CrPic for 24 h on AMP-activated protein kinase (AMPK) to determine whether this pathway contributed to the regulation of adiponectin and resistin expression and secretion. 3. Chromium picolinate did not modulate the expression of adiponectin and resistin; however, it did significantly inhibit the secretion of resistin, but not adiponectin, by normal and insulin-resistant 3T3-L1 adipocytes in vitro. Furthermore, although CrPic markedly elevated levels of phosphorylated AMPK and acetyl CoA carboxylase in 3T3-L1 adipocytes, it had no effect on the levels of AMPK alpha-1 and alpha-2 mRNA transcripts. Importantly, inhibition of AMPK by 2 h pretreatment of cells with 20 micromol/L compound C completely abolished the CrPic-induced suppression of resistin secretion. 4. In conclusion, the data suggest that CrPic inhibits resistin secretion via activation of AMPK in normal and insulin-resistant 3T3-L1 adipocytes.
Article
The aim of this study was to evaluate the impact of three different chromium forms as chromic chloride (CrCl), chromium picolinate (CrPic), and a newly synthesized complex of chromium chelated with small peptides (CrSP) on glucose uptake and metabolism in vitro. In cultured skeletal muscle cells, chromium augmented insulin-stimulated glucose uptake and metabolism as assessed by a reduced glucose concentration of culture medium. At the molecular level, insulin significantly increased the mRNA levels of insulin receptor (IR), glucose transporter 4 (GLUT4), glycogen synthase (GS), and uncoupling protein-3 (UCP3), and these impacts can be enhanced by the addition of chromium, especially in the form of CrSP. Collectively, results of this study demonstrate that chromium improves glucose uptake and metabolism through upregulating the mRNA levels of IR, GLUT4, GS, and UCP3 in skeletal muscle cells, and CrSP has higher efficacy on glucose uptake and metabolism compared to the forms of CrCl and CrPic.
Article
Chromium picolinate (CrPic) has been discovered as a supplemental or alternative medication for type 2 diabetes, but its mechanism of action is not well understood. The purpose of this study was to explore the possible anti-diabetic mechanisms of CrPic in insulin-resistant 3T3-L1 adipocytes; the insulin resistance was induced by treatment with high glucose and insulin for 24 h. The effects of CrPic on glucose metabolism and the glucose uptake-inducing activity of CrPic were investigated. Meanwhile, the effects of CrPic on glucose transporter 4 (GLUT4) translocation were visualized by immonofluorescence microscopy. In addition, its effects on insulin signaling pathways and mitogen-activated protein kinase (MAPK) signaling cascades were assessed by immunoblotting analysis and real-time PCR. The results showed that CrPic induced glucose metabolism and uptake, as well as GLUT4 translocation to plasma membrane (PM) in both control and insulin-resistant 3T3-L1 adipocytes without any changes in insulin receptor beta (IR-beta), protein kinase B (AKt), c-Cbl, extracellular signal-regulated kinase (ERK), c-Jun phosphorylation and c-Cbl-associated protein (CAP) mRNA levels. Interestingly, CrPic was able to increase the basal and insulin-stimulated levels of p38 MAPK activation in the control and insulin-resistant cells. Pretreatment with the specific p38 MAPK inhibitor SB203580 partially inhibited the CrPic-induced glucose transport, but CrPic-activated translocation of GLUT4 was not inhibited by SB203580. This study provides an experimental evidence of the effects of CrPic on glucose uptake through the activation of p38 MAPK and it is independent of the effect on GLUT4 translocation. The findings also suggest exciting new insights into the role of p38 MAPK in glucose uptake and GLUT4 translocation.
Article
We synthesized the chromium (phenylalanine)(3) [Cr(D-phe)(3)] by chelating chromium(III) with D-phenylalanine ligand in aqueous solution to improve the bioavailability of chromium, and reported that Cr(D-phe)(3) improved insulin sensitivity. AMP-activated protein kinase (AMPK) is a key mediator for glucose uptake and insulin sensitivity. To address the molecular mechanisms by which Cr(d-phe)(3) increases insulin sensitivity, we investigated whether Cr(D-phe)(3) stimulates glucose uptake via activation of AMPK signaling pathway. H9c2 myoblasts and isolated cardiomyocytes were treated with Cr(D-phe)(3) (25microM). Western blotting was used for signaling determination. The glucose uptake was determined by 2-deoxy-D-glucose-(3)H accumulation. HPLC measured concentrations of AMP. The mitochondrial membrane potential (Deltapsi) was detected by JC-1 fluorescence assay. Cr(D-phe)(3) stimulated the phosphorylation of alpha catalytic subunit of AMPK at Thr(172), as well the downstream targets of AMPK, acetyl-CoA carboxylase (ACC, Ser(212)) and eNOS (Ser(1177)). Moreover, Cr(D-phe)(3) significantly stimulated glucose uptake in both H9c2 cells and cardiomyocytes. AMPK inhibitor compound C (10microM) dramatically inhibited the glucose uptake stimulated by Cr(D-phe)(3), while it did not affect insulin stimulation of glucose uptake. Furthermore, in vivo studies showed that Cr(D-phe)(3) also activated cardiac AMPK signaling pathway. The increase of cardiac AMP concentration and the decrease of mitochondrial membrane potential (Deltapsi) may contribute to the activation of AMPK induced by Cr(D-phe)(3). Cr(D-phe)(3) is a novel compound that activates AMPK signaling pathway, which contributes to the regulation of glucose transport during stress conditions that may be associated the role of AMPK in increasing insulin sensitivity.
Article
Diabetes, one of the major risk factors of metabolic syndrome culminates in the development of Ischemic Heart Disease (IHD). Refined diets that lack micronutrients, mainly trivalent chromium (Cr(3+)) have been identified as the contributor in the rising incidence of diabetes. We investigated the effect of niacin-bound chromium (NBC) during ischemia/reperfusion (IR) injury in streptozotocin induced diabetic rats. Rats were randomized into: Control (Con); Diabetic (Dia) and Diabetic rats fed with NBC (Dia+NBC). After 30 days of treatment, the isolated hearts were subjected to 30 min of global ischemia followed by 2 h of reperfusion. NBC treatment demonstrated significant increase in left ventricular functions and significant reduction in infarct size and cardiomyocyte apoptosis in Dia+NBC compared with Dia. Increased Glut-4 translocation to the lipid raft fractions was also observed in Dia+NBC compared to Dia. Reduced Cav-1 and increased Cav-3 expression along with phosphorylation of Akt, eNOS and AMPK might have resulted in increased Glut-4 translocation in Dia+NBC. Our results indicate that the cardioprotective effect of NBC is mediated by increased activation of AMPK, Akt and eNOS resulting in increased translocation of Glut-4 to the caveolar raft fractions thereby alleviating the effects of IR injury in the diabetic myocardium.
Article
The effects of the oral hypoglycemic drug metformin on glucose and amino acid transporter activity and subcellular localization of GLUT1 and GLUT4 glucose transporters were tested in cultured L6 myotubes. In muscle cells preexposed to maximal doses of metformin (2 mM, for 16 h), 2-deoxyglucose uptake was stimulated by over 2-fold from 5.9 +/- 0.3 to 13.3 +/- 0.5 pmol/min.mg protein. Uptake of the nonmetabolizable amino acid analog methylaminoisobutyrate was unaffected by treatment with the drug under identical conditions. Extracellular calcium was required to preserve the full response to the biguanide. Exposure of muscle cells to insulin in the presence of metformin resulted in further activation of 2-deoxyglucose transport. The latter effect was additive to the maximum effect of metformin, suggesting that the biguanide stimulates hexose uptake into muscle cells by an insulin-independent mechanism. Glucose transporter number quantified by performing studies of D-glucose-protectable binding of cytochalasin-B in plasma membranes (PM) and internal membranes (IM) prepared from L6 myotubes revealed that a 16-h treatment with 800 microM metformin significantly elevated glucose transporter number in the PM (by 47%), with an equivalent decrement in glucose transporter number (47%) in the IM. Western blot analysis using antisera reactive with the GLUT1 and GLUT4 isoforms of glucose transporters showed that metformin caused a reduction in GLUT1 content in the IM fraction and a concomitant increase in the PM. Unlike insulin, metformin treatment had no effect on the subcellular distribution of GLUT4. We propose that the molecular basis of metformin action in skeletal muscle involves the subcellular redistribution of GLUT1 proteins from an intracellular compartment to the plasma membrane. Such a recruitment process may form an integral part of the mechanism by which the drug stimulates glucose uptake (and utilization) in skeletal muscle and facilitates lowering of blood glucose in the management of type II diabetes.
Article
L6 muscle cells grown in culture to the stage of fused myotubes were incubated with the oral hypoglycemic drug metformin to test the effects of this drug on glucose transport. Metformin increased the initial rate of uptake of 2-deoxyglucose and 3-O-methylglucose. The effect was time dependent, with half-maximal stimulation at 5-6 h and maximal stimulation by about 16 h. The stimulation of hexose uptake was not prevented by cycloheximide. In 15 mM glucose medium, the basal rate of transport was lower than in 5 mM glucose medium. The stimulation of hexose uptake by metformin was comparable in absolute units in both media; hence, relative to basal uptake, stimulation was greater in the high glucose medium than in the low glucose medium. In 5 mM glucose medium, half-maximal stimulation was obtained with 800 microM metformin when tested for 24 h. The stimulation of hexose transport by metformin was only detectable in fused myotubes and not in perfusion myoblasts. No significant changes were observed in glucose transporter levels in total cell membranes from L6 myotubes (measured as D-glucose-protectable binding sites for cytochalasin-B) or in the total levels of the immunoreactive glucose transporter isoforms GLUT4 or GLUT1. It is concluded that metformin stimulates hexose transport into differentiated muscle cells by acting at a posttranslational level. We speculate that this might also constitute the basis for the ability of the drug to lower glycemia in diabetic individuals.
Article
Glucose transport in the rat erythrocyte is subject to feedback regulation by sugar metabolism at high but not at low temperatures [Abumrad et al. (1988) Biochim. Biophys. Acta 938, 222-230]. This indicates that temperature, which is known to alter membrane fluidity, also alters sensitivity of transport to regulation. In the present work, we have investigated a possible correlation between the effects of temperature on rate-limiting steps of glucose transport and on membrane fluidity. The dependences of methylglucose efflux and influx on cis and trans methylglucose concentrations were studied at temperatures between 17 and 37 degrees C. Membrane fluidity was monitored over the same temperature range by using electron paramagnetic resonance spectroscopy. External sugar did not affect efflux, and the Km and Vmax of sugar exit were respectively the same as the Km and Vmax of equilibrium exchange. These Km's were relatively temperature independent, but the Vmax's increased sharply with temperature. The Km and Vmax of methylglucose entry were respectively much lower than the Km and Vmax of exit and exchange. Consistent with the above, intracellular sugar greatly enhanced sugar influx, and did so by increasing the influx Vmax without affecting the influx Km. Both lines of evidence indicated that the conformational change of the empty sugar-binding site from in-facing to out-facing orientation is the rate-limiting step of sugar entry into the rat erythrocyte. This was the case at all temperatures; however, the discrepancies of coefficients declined significantly with increasing temperature.2+ The temperature dependence of the slowest step (change from in- to out-facing empty carrier) was evaluated.(ABSTRACT TRUNCATED AT 250 WORDS)
Article
The mechanism(s) and site(s) of the insulin resistance were examined in nine normal-weight noninsulin-dependent diabetic (NIDD) subjects. The euglycemic insulin clamp technique (insulin concentration approximately 100 microU/ml) was employed in combination with hepatic and femoral venous catheterization and measurement of endogenous glucose production using infusion of tritiated glucose. Total body glucose metabolism in the NIDD subjects (4.37 +/- 0.45 mg/kg per min) was 38% (P less than 0.01) lower than in controls (7.04 +/- 0.63 mg/kg per min). Quantitatively, the most important site of the insulin resistance was found to be in peripheral tissues. Leg glucose uptake in the diabetic group was reduced by 45% as compared with that in controls (6.0 +/- 0.2 vs. 11.0 +/- 0.1 mg/kg leg wt per min; P less than 0.01). A strong positive correlation was observed between leg and total body glucose uptake (r = 0.70, P less than 0.001). Assuming that muscle is the primary leg tissue responsible for glucose uptake, it could be estimated that 90 and 87% of the infused glucose was disposed of by peripheral tissues in the control and NIDD subjects, respectively. Net splanchnic glucose balance during insulin stimulation was slightly more positive in the control than in the diabetic subjects (0.31 +/- 0.10 vs. 0.05 +/- 0.19 mg/kg per min; P less than 0.07). The difference (0.26 mg/kg per min) in net splanchnic glucose balance in NIDD represented only 10% of the reduction (2.67 mg/kg per min) in total body glucose uptake in the NIDD group and thus contributed very little to the insulin resistance. The results emphasize the importance of the peripheral tissues in the disposal of infused glucose and indicate that muscle is the most important site of the insulin resistance in NIDD.
Article
Current work in the area of insulin action relates directly to some of the most pressing unsolved questions in membrane biochemistry, including those related to receptor dynamics, transmembrane signaling, and the molecular mechanisms by which biologic transport systems operate. Thus, the well-recognized rapid action of insulin to modulate fluxes of both charged and neutral substances across cell surface membranes is of great interest. In the last few years experimental approaches have been developed which are now yielding structural information about cell surface membrane components involved in eliciting transport activation by insulin. These advances include affinity labeling of the insulin receptor as well as solubilization and reconstitution of the hexose transport system from an insulin-sensitive cell type. Of the known insulin-sensitive transport systems, which include transporters for cations as well as amino acids and anions the D-glucose transport systems have probably been the most actively studied. The classic target tissues in which hexose uptake is markedly enhanced by the hormone are muscle and fat. Hexose transport in these tissues is stereospecific and operates by facilitated diffusion such that the concentration gradient of D-glucose across the cell surface membrane provides the driving force for net influx. Thus, the insulin response in these systems may be viewed as a simple gating effect for an uncharged solute. This paper will focus attention on advances in our understanding of the molecular aspects of insulin action on hexose transport made over the past few years.
Article
1. The present study was designed to clarify the cellular mechanism through which the antihyperglycaemic drug, metformin, exerts its effects. For this purpose the contents of glucose transporter protein isoforms GLUT1 and GLUT4 were measured in plasma membrane and intracellular membrane fractions of skeletal muscle obtained from genetically obese, insulin-resistant Zucker rats. 2. Hindlimb muscles were dissected from metformin-treated (300 mg kg-1 day-1, p.o., for 12 days) and control rats in basal treatment state, and after acute stimulation with insulin (22 u kg-1, i.p.). Since metformin treatment reduces food intake, we also used a pair-fed control group to investigate the effects of altered insulinaemia per se. Glucose transporter levels were analysed by Western blot and slot blot-techniques. In addition, 2-deoxy-[14C]-glucose uptake in isolated muscle strips was evaluated. 3. No changes were noted in the contents of GLUT1 proteins in any of the subcellular fractions after metformin treatment. The contents of GLUT4 in subcellular fractions were not altered in the basal treatment state. After acute insulin exposure the content of GLUT4 in the intracellular membrane fraction declined significantly in the metformin-treated group, while no significant effect was seen in the plasma membrane fraction. In agreement with these results, metformin treatment did not alter 2-deoxyglucose uptake into isolated muscle strips. 4. In conclusion, the present study does not support the concept that metformin would enhance translocation of glucose transporter proteins from the intracellular compartment to the plasma membrane in skeletal muscle in vivo.
Article
The effects of the antidiabetic drug metformin on glucose transport were investigated in freshly isolated heart muscle cells from healthy and streptozotocin-diabetic rats. In vivo treatment of diabetic rats with metformin failed to affect the basal and insulin-stimulated rate of glucose transport measured in isolated cells. In vitro exposure to therapeutic concentrations (< or = 10(-4) M) of metformin did not influence glucose transport, even upon incubation times up to 5 h or in the presence of high glucose (20 nM). In contrast, higher metformin concentrations produced an 8- to 12-fold increase in glucose uptake (with a lag of 90 min, and a maximum at 180 min and approximately 5 mM). In the presence of submaximal insulin concentrations (< or = 3.10(-10) M), the effects of metformin (5 mM) and of insulin were more than additive, whereas, at saturating insulin concentrations (10(-8) M), partial additivity was observed. Like insulin, metformin caused an approximately 1.6-fold increase in the content of both glucose transporter isoforms GLUT1 and GLUT4 in the plasma membrane of cardiac myocytes, with a corresponding decrease in an intracellular membrane fraction. cAMP-elevating treatments depressed the metformin-, but not the insulin-dependent glucose uptake, by 20-30%. In myocytes from diabetic rats, the rate of metformin-activated glucose transport was similar to that of cells from control animals, whereas basal and insulin-stimulated transport were substantially diminished. Finally, metformin (5 mM) induced a slight depression of oxygen consumption and energy metabolism of myocytes (as determined by measuring their level of energy-rich phosphates) comparable to the effects of hypoxia in rat hearts. In conclusion, these data do not provide evidence in favor of the hypothesis that glucose uptake by muscle tissue represents the site of metformin's therapeutic action in vivo. On the other hand, the large, insulin-independent effect of metformin at high concentrations (approximately mM) in vitro may be related to the action of hypoxia and occurs through a redistribution of glucose carriers from an intracellular locus to the plasma membrane. The mechanism (or signal) involved in metformin's action is likely to differ from that triggered by insulin and is not impaired in the diabetic state.