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Dietary L-arginine supplementation reduces fat mass in diet-induced obese rats

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Abstract

This study was conducted to test the hypothesis that dietary arginine supplementation reduces fat mass in diet-induced obese rats. Male Sprague-Dawley rats were fed either low- or high-fat diets for 15 wks (16 rats/diet). Thereafter, lean or obese rats continued to be fed their same respective diets and received drinking water containing either 1.51% L-arginine-HCl or 2.55% alanine (isonitrogenous control) (n=8/treatment group). Twelve weeks after the initiation of the arginine treatment, rats were euthanized to obtain tissues for biochemical analyses. Results were statistically analyzed as a 2x2 factorial experimental design using ANOVA. High-fat diet increased the mass of white adipose tissues at different anatomical locations by 49-96% compared to the low-fat diet. Concentrations of serum cholesterol as well as lipids in skeletal muscle and liver were higher in obese rats than in lean rats. L-Arginine supplementation reduced white adipose tissue mass by 20-40% while increasing brown adipose tissue mass by 15-20%. In addition, arginine treatment decreased adipocyte size, serum concentrations of glucose, triglycerides and leptin, improved glucose tolerance, and enhanced glucose and oleic acid oxidation in skeletal muscles. The mRNA levels for hepatic fatty acid synthase and stearoyl-CoA desaturase were reduced, but mRNA levels for hepatic AMP-activated protein kinase (AMPK), PPAR coactivator-1 and carnitine palmitoyltransferase I (CPT-I) as well as muscle CPT-I were increased in response to the arginine treatment. Subsequent experiments were conducted with cell models to define the direct effects of arginine on energy-substrate metabolism in insulin-sensitive cells. In BNL CL.2 mouse hepatocytes, C2C12 mouse myotubes and 3T3-L1 mouse adipocytes, increasing extracellular concentrations of arginine from 0 to 400 µM increased AMPK expression as well as glucose and oleic acid oxidation. Inhibition of nitric oxide synthesis moderately attenuated the arginine-stimulated increases of substrate oxidation as well as AMPK and ACC phosphorylation in BNL CL.2 cells, but had no effect in C2C12 and 3T3-L1 cells. Collectively, these results suggest that arginine increases AMPK expression and energy-substrate oxidation in a cell-specific manner, thereby reducing fat mass in diet-induced obese rats. The findings have important implications for treating obesity in humans and companion animals as well as decreasing fat deposition in livestock species.

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... Extensive studies in vitro have revealed that arginine stimulates lipolysis in adipocytes and promotes oxidation of long-chain fatty acids in insulin-sensitive tissues (1,8,(16)(17). For example, Jobgen (18) treated 3T3-L1 preadipocytes with different extracellular concentrations of L-arginine (50 -400 μM) and found that the rates of glucose and oleic acid oxidation were 45% and 40% greater, respectively, in the presence of arginine than in its absence. Similarly, in cultured human adipocytes, increasing extracellular concentrations of arginine from 0.4 to 2 mM increased the oxidation of 1 mM palmitate and 5 mM glucose by 32% and 51%, respectively (9). ...
... Interestingly, the reported effects of arginine on lipogenesis in white adipocytes have not been consistent. For example, in differentiated 3T3-L1 preadipocytes, the incorporation of oleic acid into lipids was increased by 190% in the presence of 400 μM arginine than in its absence (18), and high levels of arginine enhanced the expression of peroxisome proliferator-activated receptor (PPAR) gamma (a key regulator of adipogenesis) in preadipocytes and their differentiation (19). In contrast, arginine decreased the incorporation of palmitate and glucose into triglycerides in human adipocytes by 35% and 39%, respectively (9). ...
... Consistent with the reduction of white-fat mass, arginine treatment decreased circulating levels of glucose and nonesterified fatty acids and increased the oxidation of glucose and octanoate in abdominal and epididymal adipose tissues of obese rats (20). Moreover, arginine increased the expression of carnitine palmitoyltransferase 1 (CPT1), PCG-1alpha, and malonyl-CoA decarboxylase (MCD) in liver and depressed the expression of fatty acid synthase (FAS) and stearoyl coenzyme-A desaturase-1 (SCD1) (18). These results indicate a potent effect of arginine on inhibiting hepatic fatty acid synthesis from glucose. ...
Article
As the nitrogenous precursor of nitric oxide, L-arginine regulates multiple metabolic pathways involved in the metabolism of fatty acids, glucose, amino acids, and proteins through cell signaling and gene expression. Specifically, arginine stimulates lipolysis and the expression of key genes responsible for activation of fatty acid oxidation to CO2 and water. The underlying mechanisms involve increases in the expression of peroxisome proliferator-activated receptor-gamma coactivator-1 alpha (PGC-1 alpha), mitochondrial biogenesis, and the growth of brown adipose tissue growth. Furthermore, arginine regulates adipocyte-muscle crosstalk and energy partitioning via the secretion of cytokines and hormones. In addition, arginine enhances AMP-activated protein kinase (AMPK) expression and activity, thereby modulating lipid metabolism and energy balance toward the loss of triacylglycerols. Growing evidence shows that dietary supplementation with arginine effectively reduces white adipose tissue in Zucker diabetic fatty rats, diet-induced obese rats, growing-finishing pigs, and obese patients with type II diabetes. Thus, arginine can be used to prevent and treat adiposity and the associated metabolic syndrome.
... Our previous studies using Zucker diabetic fatty rats (Fu et al. 2005) and diet-induced obese rats (Jobgen 2007;Jobgen et al. 2009) demonstrated that dietary supplementation with Arg increased glucose and fatty acid oxidation in skeletal muscle and white adipose tissue, therefore reducing body white-fat mass. Beneficial effects of Arg supplementation on reducing white fat, increasing lean tissue mass, and improving metabolic profiles have also been reported by many research groups for rodents and other members of the animal kingdom, including diet-induced obese rats (Alam et al. 2013;Miczke et al. 2015), mice (Sellmann et al. 2017), and sheep (Satterfield et al. 2012); growingfinishing pigs (Tan et al. 2011), poultry (Fouad et al. 2013), and fish (Li et al. 2020); individuals with diabetes mellitus (Mariotti 2020;Szlas et al. 2022); and obese persons (Boon et al. 2019;Khosroshahi et al. 2020;McNeal et al. 2018). ...
... Beneficial effects of Arg supplementation on reducing white fat, increasing lean tissue mass, and improving metabolic profiles have also been reported by many research groups for rodents and other members of the animal kingdom, including diet-induced obese rats (Alam et al. 2013;Miczke et al. 2015), mice (Sellmann et al. 2017), and sheep (Satterfield et al. 2012); growingfinishing pigs (Tan et al. 2011), poultry (Fouad et al. 2013), and fish (Li et al. 2020); individuals with diabetes mellitus (Mariotti 2020;Szlas et al. 2022); and obese persons (Boon et al. 2019;Khosroshahi et al. 2020;McNeal et al. 2018). Further, we found that the beneficial effect of Arg on metabolic health was mediated partially through the activation of hepatic AMP-activated protein kinase (AMPK) (Jobgen 2007;Jobgen and Wu 2022). However, the underlying biochemical mechanisms remain largely unknown (McKnight et al. 2010;Mariotti 2020;Szlas et al. 2022). ...
... 6.40 ± 1.12 b 6.88 ± 1.98 b 10.9 ± 1.38 b 25.7 ± 3.64 a 31.6 ± 3.05 a 0.0005 in the skeletal muscle and adipose tissue of obese rats (Fu et al. 2005;Jobgen 2007), as well whole-body glucose oxidation and insulin sensitivity in obese men (Boon et al. 2019). Because the BNL CL.2, C2C12, and 3T3-L1 cells were derived from the fetal mouse liver, the dystrophic adult mouse skeletal muscle, and the mouse embryonic fibroblast (Kuppusamy et al. 2021;Muller and Danner 2004), these cell lines may differ from the hepatocytes, skeletal muscle, Table 4 The effect of l-arginine on nitrite production in BNL CL.2, C2C12 and 3T3-L1 cells Cells were incubated for 48 h in customized DMEM containing 0, 15, 50, 100 or 400 µM of L-arginine. ...
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Previous work has shown that dietary l-arginine (Arg) supplementation reduced white fat mass in obese rats. The present study was conducted with cell models to define direct effects of Arg on energy-substrate oxidation in hepatocytes, skeletal muscle cells, and adipocytes. BNL CL.2 mouse hepatocytes, C2C12 mouse myotubes, and 3T3-L1 mouse adipocytes were treated with different extracellular concentrations of Arg (0, 15, 50, 100 and 400 µM) or 400 µM Arg + 0.5 mM NG-nitro-l-arginine methyl ester (L-NAME; an NOS inhibitor) for 48 h. Increasing Arg concentrations in culture medium dose-dependently enhanced (P < 0.05) the oxidation of glucose and oleic acid to CO2 in all three cell types, lactate release from C2C12 cells, and the incorporation of oleic acid into esterified lipids in BNL CL.2 and 3T3-L1 cells. Arg at 400 µM also stimulated (P < 0.05) the phosphorylation of AMP-activated protein kinase (AMPK) in all three cell types and increased (P < 0.05) NO production in C2C12 and BNL CL.2 cells. The inhibition of NOS by L-NAME moderately reduced (P < 0.05) glucose and oleic acid oxidation, lactate release, and the phosphorylation of AMPK and acetyl-CoA carboxylase (ACC) in BNL CL.2 cells, but had no effect (P > 0.05) on these variables in C2C12 or 3T3-L1 cells. Collectively, these results indicate that Arg increased AMPK activity and energy-substrate oxidation in BNL CL.2, C2C12, and 3T3-L1 cells through both NO-dependent and NO-independent mechanisms.
... We found that dietary L-arginine (Arg) supplementation increased the oxidation of glucose and fatty acids in skeletal muscle, reduced body fat and serum concentrations of triglycerides, enhanced the mass of skeletal muscle, and improved insulin sensitivity in diet-induced obese (DIO) rats (Jobgen 2007;Jobgen et al. 2009). Consistent with our findings, dietary supplementation with 5% Arg for 8 weeks decreased abdominal fat and improved whole-body insulin sensitivity in adult rats fed a HF diet (Alam et al. 2013). ...
... Skeletal muscle also plays a crucial role in the homeostasis of glucose and fatty acids (Jobgen et al. 2006). Results from our research indicate that the rates of oxidation of these substrates in extensor digitorum longus muscle and soleus muscle, as measured with [U-14 C]glucose and [1-14 C]oleic acid, were decreased by high-fat feeding but increased in response to dietary Arg supplementation (Jobgen 2007). Arg treatment did not affect glucose or oleic acid oxidation in RP adipose tissue when expressed per 10 6 adipocytes (Jobgen 2007). ...
Article
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The goal of this study was to elucidate the molecular mechanisms responsible for the anti-obesity effect of L-arginine supplementation in diet-induced obese rats. Male Sprague–Dawley rats were fed either a low-fat or high-fat diet for 15 weeks. Thereafter, lean or obese rats were pair-fed their same respective diets and received drinking water containing either 1.51% L-arginine-HCl or 2.55% L-alanine (isonitrogenous control) for 12 weeks. Gene and protein expression of key enzymes in the metabolism of energy substrates were determined using real-time polymerase-chain reaction and western blotting techniques. The mRNA levels of hepatic fatty acid synthase and stearoyl-CoA desaturase were reduced (P < 0.05) but those of hepatic AMP-activated protein kinase-α (AMPKα), peroxisome proliferator activator receptor γ coactivator-1α, and carnitine palmitoyltransferase I (CPT-I), as well as skeletal muscle CPT-I were increased (P < 0.05) by L-arginine treatment. The protein expression and activity of hepatic AMPKα markedly increased (P < 0.05) but the activity of hepatic acetyl-CoA carboxylase (ACC) decreased (P < 0.05) in response to dietary L-arginine supplementation. Collectively, our results indicate that liver is the major target for the action of dietary L-arginine supplementation on reducing white-fat mass in diet-induced obese rats by inhibiting fatty acid synthesis and increasing fatty acid oxidation via the AMPK-ACC signaling pathway. Additionally, increased CPT-I expression in skeletal muscle may also contribute to the enhanced oxidation of long-chain fatty acids in L-arginine-supplemented rats.
... Insulin also promotes hepatic lipogenesis through several mechanisms and research has shown that arginine can affect lipid metabolism 10,13,45 . In our previous study, arginine supplementation (1.62% and 1.96%) increased whole body fat accretion in juvenile blunt snout bream 2 . ...
... In another study, arginine supplementation (7.20% of dietary protein) resulted in the highest fat gain in Atlantic salmon (Salmo salar) 45 , which supports our current experi- mental results. Our study and Andersen's study differ from studies carried out with mammals, which demonstrate a loss in fat mass after arginine supplementation [10][11][12][13] . To the best of our knowledge, most of the reports concern- ing the effect of arginine on fat gain in mammals have been based on observations of adult animals. ...
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This study evaluated the mechanisms governing insulin resistance, glucose metabolism and lipogenesis in juvenile fish fed with graded levels of dietary arginine. The results showed that, compared with the control group (0.87%), 2.31% dietary arginine level resulted in the upregulation of the relative gene expression of IRS-1, PI3K and Akt in the insulin signaling pathway, while 2.70% dietary arginine level led to inhibition of these genes. 1.62% dietary arginine level upregulated glycolysis by increasing GK mRNA level; 2.70% dietary arginine level upregulated gluconeogenesis and resulted in high plasma glucose content by increasing PEPCK and G6P mRNA level. Furthermore, 2.70% dietary arginine level significantly lowered GLUT2 and increased PK mRNA levels. 1.62% dietary arginine level significantly upregulated ACC, FAS and G6PDH mRNA levels in the fat synthesis pathway and resulted in high plasma TG content. These results indicate that 1.62% dietary arginine level improves glycolysis and fatty acid synthesis in juvenile blunt snout bream. However, 2.70% dietary arginine level results in high plasma glucose, which could lead to negative feedback of insulin resistance, including inhibition of IRS-1 mRNA levels and activation of gluconeogenesis-related gene expression. This mechanism seems to be different from mammals at the molecular level.
... These pathways also involve activation of various proteins in the cytoplasm and the nucleus and have important implications for animal nutrition. For example, dietary supplementation with arginine increases expression of the AMPK gene in white adipose tissue of Zucker diabetic fatty rats (18) and diet-induced obese rats (39), as well as phosphorylation of the AMPK protein in skeletal muscle and liver of diet-induced obese rats (54). Furthermore, G-protein-coupled receptors participate in monosodium glutamate (MSG)-induced chemical sensing in the gastrointestinal tract, leading to increases in its motility, secretions, and absorptive ability (53). ...
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Amino acids (AA) have enormous physiological importance, serving as building blocks for proteins and substrates for synthesis of low-molecular-weight substances. Based on growth or nitrogen balance, AA were traditionally classified as nutritionally essential or nonessential for animals. Although those AA that are not synthesized in eukaryotes (nutritionally essential AA, EAA) must be present in animal diets, nutritionally nonessential AA (NEAA) have long been ignored for all species. Emerging evidence shows that nonruminants cannot adequately synthesize NEAA or conditionally essential AA (CEAA) to realize their growth or anti-infection potential. Likewise, all preformed AA are needed for high-producing cows and rapidly growing ruminants. Many NEAA and CEAA (e.g., arginine, glutamine, glutamate, glycine, and proline) and certain EAA (e.g., leucine and tryptophan) participate in cell signaling, gene expression, and metabolic regulation. Thus, functions of AA beyond protein synthesis must be considered in dietary formulations to improve efficiency of nutrient use, growth, development, reproduction, lactation, and well-being in animals.
... It has been suggested that nitric oxide (NO), a signaling molecule produced from L-arginine by various isoforms of NO synthase (NOS), is involved in the regulation of hepatic gluconeogenesis. It was shown that physiological levels of NO stimulate glucose uptake and oxidation in insulin-sensitive tissues and inhibit the synthesis of glucose in target tissues (Jobgen, 2007). In this study increment of dietary arginine level enhanced T-NOS activity and this can be at least partially responsible for reduction of plasma glucose concentration at increased arginine levels. ...
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A 9-week feeding trial was carried out to evaluate dietary arginine requirement of juvenile red sea bream. Six isonitrogenous and isocaloric diets (50% crude protein and 17.7 kJ g−1 gross energy) were formulated to contain graded levels of arginine including 1.42, 1.88, 2.22, 2.54, 3.08 and 3.43% of diet (2.84–6.86% of dietary protein), and fed triplicate groups of fish (13.3 ± 0.2 g) to apparent satiation twice daily. At the end of the feeding trial, fish fed ≥2.22% arginine showed significantly (P b 0.05) higher growth than those fed 1.42% arginine. Significant improvement in protein productive value was found at dietary arginine level of 2.54% compared to the fish fed 1.42% arginine. Significant reductions in whole-body and muscle lipid contents were found by increment of arginine level and whole-body protein increased significantly in fish fed 2.22–2.54% arginine compared to those fed 1.42% arginine. Plasma total protein level significantly was increased in fish fed 2.54–3.08% arginine, and alanine aminotransferase activity and glucose level were significantly decreased in fish fed 2.22–2.54% and ≥1.88% arginine, respectively, compared to the group fed 1.42% arginine. Significant improvements in lysozyme and myeloperoxidase activities and total immunoglobulin level were obtained by dietary arginine increment. Also, significantly higher total nitric oxide synthase activity was recorded at 3.08% arginine level in comparison to 1.42% arginine. A broken-line regression analysis on weight gain showed that the optimum dietary arginine level is 2.37% of diet (4.74% of dietary protein).
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Dietary L-arginine (Arg) supplementation reduces white-fat gain in diet-induced obese rats but the underlying mechanisms are unknown. This study tested the hypothesis that Arg treatment affects expression of genes related to lipid metabolism in adipose tissue. Four-week-old male Sprague-Dawley rats were fed a low-fat (LF) or high-fat (HF) diet for 15 weeks. Thereafter, lean or obese rats continued to be fed their same respective diets and received drinking water containing 1.51% Arg-HCl or 2.55% L: -alanine (isonitrogenous control). After 12 weeks of Arg supplementation, rats were euthanized to obtain retroperitoneal adipose tissue for analyzing global changes in gene expression by microarray. The results were confirmed by RT-PCR analysis. HF feeding decreased mRNA levels for lipogenic enzymes, AMP-activated protein kinase, glucose transporters, heme oxygenase 3, glutathione synthetase, superoxide dismutase 3, peroxiredoxin 5, glutathione peroxidase 3, and stress-induced protein, while increasing expression of carboxypeptidase-A, peroxisome proliferator activated receptor (PPAR)-alpha, caspase 2, caveolin 3, and diacylglycerol kinase. In contrast, Arg supplementation reduced mRNA levels for fatty acid binding protein 1, glycogenin, protein phosphates 1B, caspases 1 and 2, and hepatic lipase, but increased expression of PPARgamma, heme oxygenase 3, glutathione synthetase, insulin-like growth factor II, sphingosine-1-phosphate receptor, and stress-induced protein. Biochemical analysis revealed oxidative stress in white adipose tissue of HF-fed rats, which was prevented by Arg supplementation. Collectively, these results indicate that HF diet and Arg supplementation differentially regulate gene expression to affect energy-substrate oxidation, redox state, fat accretion, and adipocyte differentiation in adipose tissue. Our findings provide a molecular mechanism to explain a beneficial effect of Arg on ameliorating diet-induced obesity in mammals.
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Obesity is a multifactorial, chronic disorder that has reached epidemic proportions in most industrialized countries and is threatening to become a global epidemic. Obese patients are at higher risk from coronary artery disease, hypertension, hyperlipidemia, diabetes mellitus, cancers, cerebrovascular accidents, osteoarthritis, restrictive pulmonary disease, and sleep apnoea. In particular, visceral fat accumulation is usually accompanied by insulin resistance or type 2 diabetes mellitus, hypertension, hypertriglyceridemia, high uremic acid levels, low high density lipoprotein (HDL) cholesterol to define a variously named syndrome or metabolic syndrome. Metabolic syndrome is now considered a major cardiovascular risk factor in a large percentage of population in worldwide. Both obesity and metabolic syndrome are particularly challenging clinical conditions to treat because of their complex pathophysiological basis. Indeed, body weight represents the integration of many biological and environmental components and relationships among fat and glucose tolerance or blood pressure are not completely understood. Efforts to develop innovative anti-obesity drugs, with benefits for metabolic syndrome, have been recently intensified. In general two distinct strategies can be adopted: first, to reduce energy intake; second, to increase energy expenditure. Here we review some among the most promising avenues in these two fields of drug therapy of obesity and, consequently, of metabolic syndrome.
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The First Law of Thermodynamics provides a framework for understanding the imbalance between energy intake and expenditure that produces obesity, but it does not help understand the role of genetics, the regulation of food intake, the distribution of body fat, the mechanisms by which diets work or the mechanism by which portion control has gotten out of control. In animals, increasing dietary fat increases body fat, and it is unlikely that humans escape this important biological rule. In epidemiological studies, increasing dietary fat is associated with increased prevalence of obesity probably by increasing the intake of energy dense foods. In the National Weight Loss Registry, three things were associated with weight loss: continued monitoring of food intake, lowering dietary fat intake, and increased exercise. The relation of dietary fat is most evident when physical activity is low. The speed of adaptation to dietary fat is increased by exercise. When dietary fat is reduced, weight is lost, but weight loss eventually plateaus. The rate of weight loss during the initial phase is about 1.6 g/day for each 1% decrease in fat intake. When dietary fat is replaced with olestra to reduce fat intake from 33% to 25% in obese men, weight loss continues for about 9 months reaching a maximum of nearly 6% of body weight and a loss of 18% of initial body fat. In the control group with a 25% reduced-fat diet, weight loss stopped after 3 months and was regained over the next 6 months, indicating the difficulty of adhering to a conventional low-fat diet. Thus, dietary fat is an important contributor to obesity in some people.
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We investigated whether a dietary intake of arginine is associated with risk for cardiovascular disease as determined by levels of C-reactive protein (CRP). We analyzed the Third National Health Nutrition and Examination Survey, a national public-use dataset collected between 1988 and 1994. Arginine intake was calculated from the 24-h dietary recall using the nutrient composition database of the University of Minnesota Nutrition Coordinating Center. A logistic regression model was used to evaluate the relation between arginine intake and serum levels of CRP while controlling for age, sex, race, exercise, total caloric intake, body mass index, smoking status, diabetes, hypertension, and fiber intake. In the unadjusted model, the likelihoods of having a high level of CRP (>3.0 mg/L), from the lowest to the highest level of arginine intake, were 34.8%, 31.0%, 27.7%, and 18.4% respectively. Arginine intake below the median range was associated with higher levels of CRP (P < 0.05), and arginine intake above the median range was associated with lower levels of CRP (P < 0.05). In the adjusted regression, subjects in the highest level (90th percentile) of arginine intake were 30% less likely to have a CRP above 3.0 mg/L than were subjects with a median arginine intake (odds ratio= 0.70, 95% confidence interval = 0.56 to 0.88). The results of this study show a relation between arginine intake and CRP level that persisted after controlling for factors associated with CRP. Individuals may be able to lower their risk for cardiovascular disease by consuming more arginine-rich foods such as nuts and fish.