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.

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.

Rationale An efficient and reproducible source of genotype-specific human macrophages is essential for study of human macrophage biology and related diseases. Objective To perform integrated functional and transcriptome analyses of human induced pluripotent stem cell-derived macrophages (IPSDM) and their isogenic PBMC-derived macrophages (HMDM) counterparts and assess the application of IPSDM in modeling macrophage polarization and Mendelian disease. Methods and Results We developed an efficient protocol for differentiation of IPSDM, which expressed macrophage-specific markers and took up modified lipoproteins in a similar manner to HMDM. Like HMDM, IPSDM revealed reduction in phagocytosis, increase in cholesterol efflux capacity and characteristic secretion of inflammatory cytokines in response to M1 (LPS+IFN-γ) activation. RNA-Seq revealed that non-polarized (M0) as well as M1 or M2 (IL-4) polarized IPSDM shared transcriptomic profiles with their isogenic HMDM counterparts while also revealing novel markers of macrophage polarization. Relative to IPSDM and HMDM of control individuals, patterns of defective cholesterol efflux to apoA-I and HDL3 were qualitatively and quantitatively similar in IPSDM and HMDM of patients with Tangier disease (TD), an autosomal recessive disorder due to mutations in ATP-binding cassette transporter A1. TD-IPSDM also revealed novel defects of enhanced pro-inflammatory response to LPS stimulus. Conclusions Our protocol-derived IPSDM are comparable to HMDM at phenotypic, functional and transcriptomic levels. TD-IPSDM recapitulated hallmark features observed in HMDM and reveal novel inflammatory phenotypes. IPSDM provide a powerful tool for study of macrophage-specific function in human genetic disorders as well as molecular studies of human macrophage activation and polarization.

Modulation of adipokine signaling may contribute to the insulin resistant, atherogenic state associated with human inflammatory syndromes. Targeting of individual adipokines or their upstream regulation may prove effective in preventing acute and chronic inflammation-related metabolic complications.

OBJECTIVELeukocyte infiltration of adipose is a critical determinant of obesity-related metabolic diseases. Fractalkine (CX3CL1) and its receptor (CX3CR1) comprise a chemokine system involved in leukocyte recruitment and adhesion in atherosclerosis, but its role in adipose inflammation and type 2 diabetes is unknown.RESEARCH DESIGN AND METHODSCX3CL1 mRNA and protein were quantified in subcutaneous adipose and blood during experimental human endotoxemia and in lean and obese human adipose. CX3CL1 cellular source was probed in human adipocytes, monocytes, and macrophages, and CX3CL1-blocking antibodies were used to assess its role in monocyte-adipocyte adhesion. The association of genetic variation in CX3CR1 with metabolic traits was determined in a community-based sample. Finally, plasma CX3CL1 levels were measured in a case-control study of type 2 diabetes.RESULTSEndotoxemia induced adipose CX3CL1 mRNA (32.7-fold, P < 1 × 10−5) and protein (43-fold, P = 0.006). Obese subjects had higher CX3CL1 levels in subcutaneous adipose compared with lean (0.420 ± 0.387 vs. 0.228 ± 0.187 ng/mL, P = 0.04). CX3CL1 was expressed and secreted by human adipocytes and stromal vascular cells. Inflammatory cytokine induction of CX3CL1 in human adipocytes (27.5-fold mRNA and threefold protein) was completely attenuated by pretreatment with a peroxisome proliferator–activated receptor-γ agonist. A putative functional nonsynonymous single nucleotide polymorphism (rs3732378) in CX3CR1 was associated with adipose and metabolic traits, and plasma CX3CL1 levels were increased in patients with type 2 diabetes vs. nondiabetics (0.506 ± 0.262 vs. 0.422 ± 0.210 ng/mL, P < 0.0001).CONCLUSIONSCX3CL1-CX3CR1 is a novel inflammatory adipose chemokine system that modulates monocyte adhesion to adipocytes and is associated with obesity, insulin resistance, and type 2 diabetes. These data provide support for CX3CL1 as a diagnostic and therapeutic target in cardiometabolic disease.

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...

Objectives Inflammation may directly impair HDL functions, in particular reverse cholesterol transport (RCT), but limited data support this concept in humans. Methods and Results We employed low-dose human endotoxemia to assess the effects of inflammation on HDL and RCT-related parameters in vivo. Endotoxemia induced remodelling of HDL with depletion of pre-β1a HDL particles determined by 2-D gel electrophoresis (-32.2 ± 9.3% at 24h, p<0.05) as well as small (-23.0 ± 5.1%, p<0.01, at 24h) and medium (-57.6 ± 8.0% at 16h, p<0.001) HDL estimated by nuclear magnetic resonance (NMR). This was associated with induction of class II secretory phospholipase A2 (~36 fold increase) and suppression of lecithin:cholesterol acyltransferase activity (-20.8 ± 3.4% at 24h, p<0.01) and cholesterol ester transfer protein mass (-22.2 ± 6.8% at 24h, p<0.001). The HDL fraction, isolated following endotoxemia, had reduced capacity to efflux cholesterol in vitro from SR-BI and ABCA1, but not ABCG1 transporter cell models. Conclusions These data support the concept that “atherogenic-HDL dysfunction” and impaired RCT occur in human inflammatory syndromes, largely independent of changes in plasma HDL-C and ApoA-I levels.