Background Inflammation is proposed to impair reverse cholesterol transport (RCT), a major atheroprotective function of HDL. This study presents the first integrated functional evidence that inflammation retards numerous components of RCT. Methods and Results We employed sub-acute endotoxemia in the rodent macrophage-to-feces RCT model to assess the effects of inflammation on RCT in vivo, and performed proof of concept experimental endotoxemia studies in humans. Endotoxemia (3mg/kg, SQ) reduced 3H-cholesterol movement from macrophage to plasma and 3H-cholesterol associated with HDL fractions. At 48h bile and fecal counts were markedly reduced consistent with downregulation of hepatic expression of ABCG5, ABCG8 and ABCB11 biliary transporters. Low dose LPS (0.3mg/kg, SQ) also reduced bile and fecal counts, as well as expression of biliary transporters, but in the absence of effects on plasma or liver counts. In vitro, LPS impaired 3H-cholesterol efflux from human macrophages to apoA-I and serum coincident with reduced expression of the cholesterol transporter, ABCA1. During human (3ng/kg; n=20) and murine endotoxemia (3mg/kg, SQ), ex vivo macrophage cholesterol efflux to acute phase HDL was attenuated. Conclusions We provide the first in vivo evidence that inflammation impairs RCT at multiple steps in the RCT pathway, particularly cholesterol flux through liver to bile and feces. Attenuation of RCT and HDL efflux function, independent of HDL-cholesterol levels, may contribute to atherosclerosis in chronic inflammatory states including obesity, metabolic syndrome and type-2 diabetes.

OBJECTIVEAn emerging model of metabolic syndrome and type 2 diabetes is of adipose dysfunction with leukocyte recruitment into adipose leading to chronic inflammation and insulin resistance (IR). This study sought to explore potential mechanisms of inflammatory-induced IR in humans with a focus on adipose tissue.RESEARCH DESIGN AND METHODSWe performed a 60-h endotoxemia protocol (3 ng/kg intravenous bolus) in healthy adults (n = 20, 50% male, 80% Caucasian, aged 27.3 ± 4.8 years). Before and after endotoxin, whole-blood sampling, subcutaneous adipose biopsies, and frequently sampled intravenous glucose tolerance (FSIGT) testing were performed. The primary outcome was the FSIGT insulin sensitivity index (Si). Secondary measures included inflammatory and metabolic markers and whole-blood and adipose mRNA and protein expression.RESULTSEndotoxemia induced systemic IR as demonstrated by a 35% decrease in Si (3.17 ± 1.66 to 2.06 ± 0.73 × 10−4 [μU · ml−1 · min−1], P < 0.005), while there was no effect on pancreatic β-cell function. In adipose, endotoxemia suppressed insulin receptor substrate-1 and markedly induced suppressor of cytokine signaling proteins (1 and 3) coincident with local activation of innate (interleukin-6, tumor necrosis factor) and adaptive (monocyte chemoattractant protein-1 and CXCL10 chemokines) inflammation. These changes are known to attenuate insulin receptor signaling in model systems.CONCLUSIONSWe demonstrate, for the first time in humans, that acute inflammation induces systemic IR following modulation of specific adipose inflammatory and insulin signaling pathways. It also provides a rationale for focused mechanistic studies and a model for human proof-of-concept trials of novel therapeutics targeting adipose inflammation in IR and related consequences in humans.

Saturated fatty acid (SFA) high-fat diets (HFDs) enhance interleukin (IL)-1β–mediated adipose inflammation and insulin resistance. However, the mechanisms by which different fatty acids regulate IL-1β and the subsequent effects on adipose tissue biology and insulin sensitivity in vivo remain elusive. We hypothesized that the replacement of SFA for monounsaturated fatty acid (MUFA) in HFDs would reduce pro-IL-1β priming in adipose tissue and attenuate insulin resistance via MUFA-driven AMPK activation. MUFA-HFD–fed mice displayed improved insulin sensitivity coincident with reduced pro-IL-1β priming, attenuated adipose IL-1β secretion, and sustained adipose AMPK activation compared with SFA-HFD–fed mice. Furthermore, MUFA-HFD–fed mice displayed hyperplastic adipose tissue, with enhanced adipogenic potential of the stromal vascular fraction and improved insulin sensitivity. In vitro, we demonstrated that the MUFA oleic acid can impede ATP-induced IL-1β secretion from lipopolysaccharide- and SFA-primed cells in an AMPK-dependent manner. Conversely, in a regression study, switching from SFA- to MUFA-HFD failed to reverse insulin resistance but improved fasting plasma insulin levels. In humans, high-SFA consumers, but not high-MUFA consumers, displayed reduced insulin sensitivity with elevated pycard-1 and caspase-1 expression in adipose tissue. These novel findings suggest that dietary MUFA can attenuate IL-1β–mediated insulin resistance and adipose dysfunction despite obesity via the preservation of AMPK activity.

High-fat diet-induced obesity is associated with a chronic state of low-grade inflammation, which pre-disposes to insulin resistance (IR), which can subsequently lead to type 2 diabetes mellitus. Macrophages represent a heterogeneous population of cells that are instrumental in initiating the innate immune response. Recent studies have shown that macrophages are key mediators of obesity-induced IR, with a progressive infiltration of macrophages into obese adipose tissue. These adipose tissue macrophages are referred to as classically activated (M1) macrophages. They release cytokines such as IL-1β, IL-6 and TNFα creating a pro-inflammatory environment that blocks adipocyte insulin action, contributing to the development of IR and type 2 diabetes mellitus. In lean individuals macrophages are in an alternatively activated (M2) state. M2 macrophages are involved in wound healing and immunoregulation. Wound-healing macrophages play a major role in tissue repair and homoeostasis, while immunoregulatory macrophages produce IL-10, an anti-inflammatory cytokine, which may protect against inflammation. The functional role of T-cell accumulation has recently been characterised in adipose tissue. Cytotoxic T-cells are effector T-cells and have been implicated in macrophage differentiation, activation and migration. Infiltration of cytotoxic T-cells into obese adipose tissue is thought to precede macrophage accumulation. T-cell-derived cytokines such as interferon γ promote the recruitment and activation of M1 macrophages augmenting adipose tissue inflammation and IR. Manipulating adipose tissue macrophages/T-cell activity and accumulation in vivo through dietary fat modification may attenuate adipose tissue inflammation, representing a therapeutic target for ameliorating obesity-induced IR.

Recent reports demonstrate T-cell infiltration of adipose tissue in early obesity. We hypothesized that interferon (IFN) ␥, a major T-cell inflammatory cytokine, would attenuate human adipocyte functions and sought to establish signaling mechanisms. Differentiated human adipocytes were treated with IFN␥ ؎ pharmacological inhibitors prior to insulin stimulation.

OBJECTIVEHigh-fat diet (HFD)-induced adipose tissue inflammation is a critical feature of diet-induced insulin resistance (IR); however, the contribution of interleukin-1 receptor I (IL-1RI)-mediated signals to this phenotype has not been defined. We hypothesized that lack of IL-1RI may ameliorate HFD-induced IR by attenuating adipose tissue inflammation.RESEARCH DESIGN AND METHODSGlucose homeostasis was monitored in chow- and HFD-fed wild-type (WT) and IL-1RI−/− mice by glucose tolerance and insulin tolerance tests. Macrophage recruitment and cytokine signature of adipose tissue macrophages was evaluated. Insulin sensitivity and cytokine secretion from adipose explants was quantified. Cytokine secretion and adipocyte insulin sensitivity was measured in cocultures of WT or IL-1RI−/− macrophages with 3T3L1 adipocytes. Synergistic effects of IL-1β with tumor necrosis factor (TNF)-α on inflammation was monitored in WT and IL-1RI−/− bone-marrow macrophages and adipose explants.RESULTSLean and obese IL-1RI−/− animals exhibited enhanced glucose homeostasis by glucose tolerance test and insulin tolerance test. M1/M2 macrophage number in adipose tissue was comparable between genotypes; however, TNF-α and IL-6 secretion was lower from IL-1RI−/− adipose tissue macrophages. IL-1RI−/− adipose exhibited enhanced insulin sensitivity, elevated pAKT, lower cytokine secretion, and attenuated induction of phosphorylated signal transducer and activator of transcription 3 and suppressor of cytokine signaling molecule 3 after HFD. Coculture of WT, but not IL-1RI−/− macrophages, with 3T3L1 adipocytes enhanced IL-6 and TNF-α secretion, reduced adiponectin secretion, and impaired adipocyte insulin sensitivity. TNF-α and IL-1β potently synergized to enhance inflammation in WT macrophages and adipose, an effect lost in the absence of IL-1RI.CONCLUSIONSLack of IL-1RI protects against HFD-induced IR coincident with reduced local adipose tissue inflammation, despite equivalent immune cell recruitment.

SFA represent metabolic triggers priming the inflammasome, promoting adipocyte inflammation/IR, suggesting direct effects of SFA on inflammasome activation via TLR4.

Background-Adipose harbors a large depot of free cholesterol. However, a role for adipose in cholesterol lipidation of high-density lipoprotein (HDL) in vivo is not established. We present the first evidence that adipocytes support transfer of cholesterol to HDL in vivo as well as in vitro and implicate ATP-binding cassette subfamily A member 1 (ABCA1) and scavenger receptor class B type I (SR-BI), but not ATP-binding cassette subfamily G member 1 (ABCG1), cholesterol transporters in this process. Methods and Results-Cholesterol efflux from wild-type, ABCA1Ϫ/Ϫ , SR-BI Ϫ/Ϫ, and ABCG1 Ϫ/Ϫ adipocytes to apolipoprotein A-I (apoA-I) and HDL3 were measured in vitro. 3T3L1 adipocytes, labeled with 3 H-cholesterol, were injected intraperitoneally into wild-type, apoA-I transgenic, and apoA-I Ϫ/Ϫ mice, and tracer movement onto plasma HDL was monitored. Identical studies were performed with labeled wild-type, ABCA1 Ϫ/Ϫ , or SR-BI Ϫ/Ϫ mouse embryonic fibroblast adipocytes. The effect of tumor necrosis factor-␣ on transporter expression and cholesterol efflux was monitored during adipocyte differentiation. Cholesterol efflux to apoA-I and HDL3 was impaired in ABCA1 Ϫ/Ϫ and SR-BI Ϫ/Ϫ adipocytes, respectively, with no effect observed in ABCG1 Ϫ/Ϫ adipocytes. Intraperitoneal injection of labeled 3T3L1 adipocytes resulted in increased HDL-associated 3 H-cholesterol in apoA-I transgenic mice but reduced levels in apoA-I Ϫ/Ϫ animals. Intraperitoneal injection of labeled ABCA1 Ϫ/Ϫ or SR-BI Ϫ/Ϫ adipocytes reduced plasma counts relative to their respective controls. Tumor necrosis factor-␣ reduced both ABCA1 and SR-BI expression and impaired cholesterol efflux from partially differentiated adipocytes. Conclusions-These data suggest a novel metabolic function of adipocytes in promoting cholesterol transfer to HDL in vivo and implicate adipocyte SR-BI and ABCA1, but not ABCG1, in this process. Furthermore, adipocyte modulation of HDL may be impaired in adipose inflammatory disease states such as type 2 diabetes mellitus. Clinical Perspective on p 1355Lipidation of HDL is determined via a number of cholesterol transporters in several cholesterol-rich tissues. Although macrophage cholesterol efflux to HDL plays a major role in attenuating atherosclerosis, macrophages play a minor role in regulation of HDL-C levels. 4 In contrast, hepatic ATPbinding cassette subfamily A member 1 (ABCA1), through lipidation of apolipoprotein A-I (apoA-I), is required for formation of nascent HDL particles. 5 Indeed, in cholesterolrich tissues, both hepatic and extrahepatic, ABCA1 has discrete and essential roles in the maintenance of plasma HDL-C. 6,7 ATP-binding cassette subfamily G member 1 (ABCG1) mediates cholesterol efflux from macrophages to mature HDL particles 8,9 and may play a role in regulating plasma HDL-C levels. 10 In contrast to ABC transporters, scavenger receptor class B type I (SR-BI) is a bidirectional transporter that plays a major role in hepatic uptake of HDL Received July 25, 2009; accepted January 15, 2010. 15,16 In fact, adip...