[Show abstract][Hide abstract] ABSTRACT: HDL from healthy humans and lean mice inhibits palmitate-induced adipocyte inflammation; however, the effect of the inflammatory state on the functional properties of HDL on adipocytes is unknown. Here, we found that HDL from mice injected with AgNO3 fails to inhibit palmitate-induced inflammation and reduces cholesterol efflux from 3T3-L1 adipocytes. Moreover, HDL isolated from obese mice with moderate inflammation and humans with systemic lupus erythematosus had similar effects. Since serum amyloid A (SAA) concentrations in HDL increase with inflammation, we investigated whether elevated SAA is a causal factor in HDL dysfunction. HDL from AgNO3-injected mice lacking Saa1.1 and Saa2.1 exhibited a partial restoration of antiinflammatory and cholesterol efflux properties in adipocytes. Conversely, incorporation of SAA into HDL preparations reduced antiinflammatory properties but not to the same extent as HDL from AgNO3-injected mice. SAA-enriched HDL colocalized with cell surface-associated extracellular matrix (ECM) of adipocytes, suggesting impaired access to the plasma membrane. Enzymatic digestion of proteoglycans in the ECM restored the ability of SAA-containing HDL to inhibit palmitate-induced inflammation and cholesterol efflux. Collectively, these findings indicate that inflammation results in a loss of the antiinflammatory properties of HDL on adipocytes, which appears to partially result from the SAA component of HDL binding to cell-surface proteoglycans, thereby preventing access of HDL to the plasma membrane.
Full-text · Article · Dec 2015 · Journal of Clinical Investigation
[Show abstract][Hide abstract] ABSTRACT: Conjugated linoleic acid (CLA) is a naturally occurring dietary trans fatty acid found in food from ruminant sources. One specific CLA isomer, 10E,12Z-CLA, has been associated with health benefits such as reduced adiposity, while simultaneously promoting deleterious effects such as systemic inflammation, insulin resistance, and dyslipidemia. The precise mechanisms by which 10E,12Z-CLA exerts these effects remain unknown. Despite such potential health consequences, CLA continues to be advertised as a natural weight loss supplement, warranting further studies on its effects on lipid metabolism. We hypothesized that 10E,12Z-CLA impairs lipid storage in adipose tissue by altering the lipid metabolism of white adipocytes. We demonstrate that 10E,12Z-CLA reduced triglyceride storage due to enhanced fatty acid oxidation and lipolysis, coupled with diminished glucose uptake and utilization in cultured adipocytes. This switch to lipid utilization was accompanied by a potent pro-inflammatory response, including the generation of cytokines, monocyte chemotactic factors and mitochondrial superoxide. Disrupting fatty acid oxidation restored glucose utilization and attenuated the inflammatory response to 10E,12Z-CLA, suggesting that fatty acid oxidation is critical in promoting this phenotype. With further investigation into the biochemical pathways involved in adipocyte responses to 10E,12Z-CLA, we can discern more information about its safety and efficacy in promoting weight loss.
No preview · Article · Aug 2013 · The Journal of Lipid Research
[Show abstract][Hide abstract] ABSTRACT: Rationale:
Macrophage accumulation in adipose tissue associates with insulin resistance and increased cardiovascular disease risk. We previously have shown that generation of reactive oxygen species and monocyte chemotactic factors after exposure of adipocytes to saturated fatty acids, such as palmitate, occurs via translocation of NADPH oxidase 4 into lipid rafts (LRs). The anti-inflammatory effects of apolipoprotein AI (apoAI) and high-density lipoprotein (HDL) on macrophages and endothelial cells seem to occur via cholesterol depletion of LRs. However, little is known concerning anti-inflammatory effects of HDL and apoAI on adipocytes.
To determine whether apoAI and HDL inhibit inflammation in adipocytes and adipose tissue, and whether this is dependent on LRs.
Methods and results:
In 3T3L-1 adipocytes, apoAI, HDL, and methyl-β-cyclodextrin inhibited chemotactic factor expression. ApoAI and HDL also disrupted LRs, reduced plasma membrane cholesterol content, inhibited NADPH oxidase 4 translocation into LRs, and reduced palmitate-induced reactive oxygen species generation and monocyte chemotactic factor expression. Silencing ATP-binding cassette A-1 abrogated the effect of apoAI, but not HDL, whereas silencing ATP-binding cassette G-1 or scavenger receptor B-1 abrogated the effect of HDL but not apoAI. In vivo, apoAI transgenic mice fed a high-fat, high-sucrose, cholesterol-containing diet showed reduced chemotactic factor and proinflammatory cytokine expression and reduced macrophage accumulation in adipose tissue.
ApoAI and HDL have anti-inflammatory effects in adipocytes and adipose tissue similar to their effects in other cell types. These effects are consistent with disruption and removal of cholesterol from LRs, which are regulated by cholesterol transporters, such as ATP-binding cassette A-1, ATP-binding cassette G-1, and scavenger receptor B-1.
Full-text · Article · Mar 2013 · Circulation Research
[Show abstract][Hide abstract] ABSTRACT: Adipose tissue inflammation is associated with insulin resistance and increased cardiovascular disease risk in obesity. We previously showed that addition of cholesterol to a diet rich in saturated fat and refined carbohydrate significantly worsens dyslipidemia, insulin resistance, adipose tissue macrophage accumulation, systemic inflammation, and atherosclerosis in LDL receptor-deficient (Ldlr(-/-)) mice. To test whether inhibition of intestinal cholesterol absorption would improve metabolic abnormalities and adipose tissue inflammation in obesity, we administered ezetimibe, a dietary and endogenous cholesterol absorption inhibitor, to Ldlr(-/-) mice fed chow or high-fat, high-sucrose (HFHS) diets without or with 0.15% cholesterol (HFHS+C). Ezetimibe blunted weight gain and markedly reduced plasma lipids in the HFHS+C group. Ezetimibe had no effect on glucose homeostasis or visceral adipose tissue macrophage gene expression in the HFHS+C fed mice, although circulating inflammatory markers serum amyloid A (SSA) and serum amyloid P (SSP) levels decreased. Nevertheless, ezetimibe treatment led to a striking (>85%) reduction in atherosclerotic lesion area with reduced lesion lipid and macrophage content in the HFHS+C group. Thus, in the presence of dietary cholesterol, ezetimibe did not improve adipose tissue inflammation in obese Ldlr(-/-) mice, but it led to a major reduction in atherosclerotic lesions associated with improved plasma lipids and lipoproteins.
No preview · Article · Sep 2012 · The Journal of Lipid Research
[Show abstract][Hide abstract] ABSTRACT: Excess glucose and free fatty acids delivered to adipose tissue causes local inflammation, which contributes to insulin resistance. Glucose and palmitate generate reactive oxygen species (ROS) in adipocytes, leading to monocyte chemotactic factor gene expression. Docosahexaenoate (DHA) has the opposite effect. In this study, we evaluated the potential sources of ROS in the presence of excess nutrients. Differentiated 3T3-L1 adipocytes were exposed to palmitate and DHA (250 μM) in either 5 or 25 mM glucose to evaluate the relative roles of mitochondrial electron transport and NADPH oxidases (NOX) as sources of ROS. Excess glucose and palmitate did not increase mitochondrial oxidative phosphorylation. However, glucose exposure increased glycolysis. Of the NOX family members, only NOX4 was expressed in adipocytes. Moreover, its activity was increased by excess glucose and palmitate and decreased by DHA. Silencing NOX4 inhibited palmitate- and glucose-stimulated ROS generation and monocyte chemotactic factor gene expression. NADPH, a substrate for NOX, and pentose phosphate pathway activity increased with glucose but not palmitate and decreased with DHA exposure. Inhibition of the pentose phosphate pathway by glucose-6-phosphate dehydrogenase inhibitors and siRNA suppressed ROS generation and monocyte chemotactic factor gene expression induced by both glucose and palmitate. Finally, both high glucose and palmitate induced NOX4 translocation into lipid rafts, effects that were blocked by DHA. Excess glucose and palmitate generate ROS via NOX4 rather than by mitochondrial oxidation in cultured adipocytes. NOX4 is regulated by both NADPH generated in the PPP and translocation of NOX4 into lipid rafts, leading to expression of monocyte chemotactic factors.
Full-text · Article · Jan 2012 · Journal of Biological Chemistry
[Show abstract][Hide abstract] ABSTRACT: Obesity is associated with monocyte-macrophage accumulation in adipose tissue. Previously, we showed that glucose-stimulated production by adipocytes of serum amyloid A (SAA), monocyte chemoattractant protein (MCP)-1, and hyaluronan (HA) facilitated monocyte accumulation. The current objective was to determine how the other major nutrient, free fatty acids (FFAs), affects these molecules and monocyte recruitment by adipocytes.
Differentiated 3T3-L1, Simpson-Golabi-Behmel syndrome adipocytes, and mouse embryonic fibroblasts were exposed to various FFAs (250 micromol/l) in either 5 or 25 mmol/l (high) glucose for evaluation of SAA, MCP-1, and HA regulation in vitro.
Saturated fatty acids (SFAs) such as laurate, myristate, and palmitate increased cellular triglyceride accumulation, SAA, and MCP-1 expression; generated reactive oxygen species (ROS); and increased nuclear factor (NF) kappaB translocation in both 5 and 25 mmol/l glucose. Conversely, polyunsaturated fatty acids (PUFAs) such as arachidonate, eicosapentaenate, and docosahexaenate (DHA) decreased these events. Gene expression could be dissociated from triglyceride accumulation. Although excess glucose increased HA content, SFAs, oleate, and linoleate did not. Antioxidant treatment repressed glucose- and palmitate-stimulated ROS generation and NFkappaB translocation and decreased SAA and MCP-1 expression and monocyte chemotaxis. Silencing toll-like receptor-4 (TLR4) markedly reduced SAA and MCP-1 expression in response to palmitate but not glucose. DHA suppressed NFkappaB translocation stimulated by both excess glucose and palmitate via a peroxisome prolifterator-activated receptor (PPAR) gamma-dependent pathway.
Excess glucose and SFAs regulate chemotactic factor expression by a mechanism that involves ROS generation, NFkappaB, and PPARgamma, and which is repressed by PUFAs. Certain SFAs, but not excess glucose, trigger chemotactic factor expression via a TLR4-dependent pathway.
[Show abstract][Hide abstract] ABSTRACT: Adipose tissue secretes proteins like serum amyloid A (SAA), which plays important roles in local and systemic inflammation. Circulating SAA levels increase in obese humans, but the roles of adipose-derived SAA and hyperlipidemia in this process are unclear. We took advantage of the difference in the inducible isoforms of SAA secreted by adipose tissue (SAA3) and liver (SAA1 and 2) of mice to evaluate whether adipose tissue contributes to the circulating pool of SAA in obesity and hyperlipidemia. Genetically obese (ob/ob) mice, but not hyperlipidemic mice deficient in apolipoprotein E (Apoe(-/-)), had significantly higher circulating levels of SAA than their littermate controls. SAA1/2 mRNA expression in the liver and SAA3 mRNA expression in intra-abdominal fat were significantly higher in obese than thin mice, but they were not affected by hyperlipidemia in Apoe(-/-) mice. However, only SAA1/2 and the constitutive form of SAA (SAA4) could be detected in the circulation by mass spectrometric analysis of HDL, the major carrier of circulating SAA. In contrast, SAA3 could be detected in medium from cultured adipocytes. Our findings indicate that the expression of SAA3 in adipose tissue is upregulated by obesity, but it does not contribute to the circulating pool of SAA in mice.
Full-text · Article · Apr 2009 · The Journal of Lipid Research
[Show abstract][Hide abstract] ABSTRACT: Chronic systemic inflammation accompanies obesity and predicts development of cardiovascular disease. Dietary cholesterol has been shown to increase inflammation and atherosclerosis in LDL receptor-deficient (LDLR(-/-)) mice. This study was undertaken to determine whether dietary cholesterol and obesity have additive effects on inflammation and atherosclerosis.
LDLR(-/-) mice were fed chow, high-fat, high-carbohydrate (diabetogenic) diets without (DD) or with added cholesterol (DDC) for 24 weeks. Effects on adipose tissue, inflammatory markers, and atherosclerosis were studied. Despite similar weight gain between DD and DDC groups, addition of dietary cholesterol increased insulin resistance relative to DD. Adipocyte hypertrophy, macrophage accumulation, and local inflammation were observed in intraabdominal adipose tissue in DD and DDC, but were significantly higher in the DDC group. Circulating levels of the inflammatory protein serum amyloid A (SAA) were 4.4-fold higher in DD animals and 15-fold higher in DDC animals than controls, suggesting chronic systemic inflammation. Hepatic SAA mRNA levels were similarly elevated. Atherosclerosis was increased in the DD-fed animals and further increased in the DDC group.
Obesity-induced macrophage accumulation in adipose tissue is exacerbated by dietary cholesterol. These local inflammatory changes in adipose tissue are associated with insulin resistance, systemic inflammation, and increased atherosclerosis in this mouse model.
Full-text · Article · May 2008 · Arteriosclerosis Thrombosis and Vascular Biology
[Show abstract][Hide abstract] ABSTRACT: Obesity is characterized by adipocyte hypertrophy and macrophage accumulation in adipose tissue. Monocyte chemoattractant protein-1 (MCP-1) plays a role in macrophage recruitment into adipose tissue. However, other adipocyte-derived factors, e.g., hyaluronan and serum amyloid A (SAA), can facilitate monocyte adhesion and chemotaxis, respectively. The objective was to test the potential involvement of these factors in macrophage recruitment. Differentiated 3T3-L1 adipocytes made hypertrophic by growth in high glucose conditions were used to study SAA and hyaluronan regulation in vitro. Two mouse models of obesity were used to study their expression in vivo. Nuclear factor-kappaB was upregulated and peroxisome proliferator-activated receptor (PPAR)gamma was downregulated in hypertrophic 3T3-L1 cells, with increased expression of SAA3 and increased hyaluronan production. Rosiglitazone, a PPARgamma agonist, reversed these changes. Hypertrophic adipocytes demonstrated overexpression of SAA3 and hyaluronan synthase 2 in vitro and in vivo in diet-induced and genetic obesity. SAA and hyaluronan existed as part of a complex matrix that increased the adhesion and retention of monocytes. This complex, purified by binding to a biotinylated hyaluronan binding protein affinity column, also showed monocyte chemotactic activity, which was dependent on the presence of SAA3 and hyaluronan but independent of MCP-1. We hypothesize that adipocyte hypertrophy leads to increased production of SAA and hyaluronan, which act in concert to recruit and retain monocytes, thereby leading to local inflammation in adipose tissue.
[Show abstract][Hide abstract] ABSTRACT: During inflammation, the serum amyloid A (SAA) content of HDL increases, whereas apolipoprotein A-I (apoA-I) and paraoxonase-1 (PON-1) decrease. It remains unclear whether SAA physically displaces apoA-I or if these changes derive from coordinated but inverse transcriptional regulation of the HDL apolipoprotein genes. Because cytokines stimulate the hepatic expression of inflammatory markers, we investigated their role in regulating SAA, apoA-I, and PON-1 expression.
A cytokine mixture (tumor necrosis factor [TNF]-alpha, interleukin [IL]-1beta, and IL-6) simultaneously induced SAA and repressed apoA-I and PON-1 expression levels. These effects were partially inhibited in cells pretreated with either nuclear factor kappaB (NF-kappaB) inhibitors (pyrrolidine dithiocarbamate, SN50, and overexpression of super-repressor inhibitor kappaB) or after exposure to the peroxisome proliferator-activated receptor-alpha (PPARalpha) ligands (WY-14643 and fenofibrate). Consistent with these findings, the basal level of SAA was increased, whereas apoA-I and PON-1 decreased in primary hepatocytes from PPARalpha-deficient mice as compared with wild-type mice. Moreover, neither WY-14643 nor fenofibrate had any effect on SAA, apoA-I, or PON-1 expression in the absence of PPARalpha.
These results suggest that cytokines increase the expression of SAA through NF-kappaB transactivation, while simultaneously decreasing the expression of apoA-I and PON-1 by inhibiting PPARalpha activation. Inflammation may convert HDL de novo into a more proatherogenic form by coordinate but inverse transcriptional regulation in the liver, rather than by physical displacement of apoA-I by SAA.
[Show abstract][Hide abstract] ABSTRACT: In humans, a chronically increased circulating level of C-reactive protein (CRP), a positive acute-phase reactant, is an independent risk factor for cardiovascular disease. This observation has led to considerable interest in the role of inflammatory proteins in atherosclerosis. In this review, after discussing CRP, we focus on the potential role in the pathogenesis of human vascular disease of inflammation-induced proteins that are carried by lipoproteins. Serum amyloid A (SAA) is transported predominantly on HDL, and levels of this protein increase markedly during acute and chronic inflammation in both animals and humans. Increased SAA levels predict the risk of cardiovascular disease in humans. Recent animal studies support the proposal that SAA plays a role in atherogenesis. Evidence is accruing that secretory phospholipase A(2), an HDL-associated protein, and platelet-activating factor acetylhydrolase, a protein associated predominantly with LDL in humans and HDL in mice, might also play roles both as markers and mediators of human atherosclerosis. In contrast to positive acute-phase proteins, which increase in abundance during inflammation, negative acute-phase proteins have received less attention. Apolipoprotein A-I (apoA-I), the major apolipoprotein of HDL, decreases during inflammation. Recent studies also indicate that HDL is oxidized by myeloperoxidase in patients with established atherosclerosis. These alterations may limit the ability of apoA-I to participate in reverse cholesterol transport. Paraoxonase-1 (PON1), another HDL-associated protein, also decreases during inflammation. PON1 is atheroprotective in animal models of hypercholesterolemia. Controversy over its utility as a marker of human atherosclerosis may reflect the fact that enzyme activity rather than blood level (or genotype) is the major determinant of cardiovascular risk. Thus, multiple lipoprotein-associated proteins that change in concentration during acute and chronic inflammation may serve as markers of cardiovascular disease. In future studies, it will be important to determine whether these proteins play a causal role in atherogenesis.
Preview · Article · Apr 2005 · The Journal of Lipid Research
[Show abstract][Hide abstract] ABSTRACT: Chronic inflammation in vascular disease affects the organization of the extracellular matrix (ECM) in such a way as to promote the events associated with atherosclerosis and restenosis. Versican and hyaluronan are two ECM components that are affected by inflammation and, in turn, affect the inflammatory response. Inflammatory growth factors such as TGF-β1 and PDGF stimulate the production of versican and hyaluronan by arterial smooth muscle cells (ASMCs). These ECM components accumulate in vascular disease and promote the proliferation and migration of ASMCs, contributing to intimal hyperplasia. Hyaluronan also serves as attachment ligand for inflammatory cells and may be partly responsible for leukocyte retention as part of the early inflammatory response. Inflammation also leads to destruction of the ECM and failure of the ECM to remodel. Elastic fibers are absent in atherosclerotic and restenotic lesions and controlled expression of a versican variant, V3, in ASMCs restores the ability of these cells to form elastic fibers. ECM assembly is critical to vascular healing and the prevention of vascular disease.
Full-text · Article · May 2004 · International Congress Series