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.

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.

Introduction : Activation of innate immune responses have been postulated to impair reverse cholesterol transport (RCT). In this proof of concept study we provide the first in vivo functional evidence to support this hypothesis by tracking macrophage 3 H-cholesterol into plasma, liver, bile and feces in C57BL/6 mice during endotoxemia. Methods: C57BL/6 mice were injected subcutaneously with lipopolysaccharide (LPS) (10mg/kg daily for 2 days) or saline prior to intraperitoneal (IP) administration of 3 H-cholesterol-loaded macrophages. 3 H-cholesterol levels in plasma, liver, spleen, bile and feces were measured over 48 h. Lipid profiles were analyzed, enzymatically, using a Cobas FARA analyzer. Plasma (5 %), isolated from control or LPS treated mice (without macrophage injection), was used as an acceptor in ex vivo cholesterol efflux studies from 3 H-cholesterol-loaded J774 macrophages. Results: In a pilot non-RCT study (n = 4), as previously reported, LPS significantly increased total and HDL cholesterol, phospholipid and triglyceride levels (2.05 ± 0.09, 2.41 ± 0.28, 1.98 ± 0.08 and 2.57 ± 0.33 fold increase respectively, p < 0.01). In RCT studies, despite increased HDL cholesterol, LPS significantly decreased 3 H-cholesterol plasma counts at 4 h (−20.4 ± 2.0 %, p < 0.001) and 24 h (−27.1 ± 3.4 %, p < 0.001), as well as 3 H-cholesterol in liver, bile and feces (22.9 ± 3.2, 41.9 ± 10.7, and 75.3 ± 4.1 % decrease, p < 0.05, p = 0.05 and p < 0.01 respectively) (n = 8 –12 per group). LPS decreased hepatic SRB1, ABCG1, ABCG5 and HL mRNA expression. Ex vivo efflux to plasma isolated from LPS treated mice was significantly impaired relative to control (77.5 ± 7.4 % of control, p < 0.05, n = 5). Conclusions: Sub-acute endotoxemia impaired RCT in mice, despite increased plasma HDL cholesterol levels. This coincided with reduced hepatic expression of the HDL receptor, SRB1, and the transporters responsible for cholesterol transport to bile, ABCG5/8. In addition, ex vivo studies suggest impaired HDL particle efflux function during endotoxemia. In summary, we demonstrate for the first time in vivo that inflammation impairs several components of the reverse cholesterol transport pathway.