Abstract 1182: Inflammation Impairs Reverse Cholesterol Transport in vivo
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 3H-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 3H-cholesterol-loaded macrophages. 3H-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 3H-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 3H-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 3H-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.