Abstract 473: Aldose Reductase Expression In Foam Cells As Possible Link Between Diabetes, Hyperlipidemia And Atherosclerosis

Abstract

Aldose reductase (AR) is the rate-limiting enzyme of the polyol pathway, which under normoglycemic conditions detoxifies aldehydes. With increased glucose levels, however, AR uses glucose as substrate, resulting in increased osmotic and oxidative stress as shown in diabetic microvascular complications like polyneuropathy or nephropathy. Recently, overex-pression of human AR has been shown to increase atherosclerotic lesions in LDL receptor knock out mice. We hypothesized that AR is expressed in foam cells and contributes to atherosclerosis in humans. To evaluate the relevance of AR expression in human foam cells, monocytes were isolated from peripheral blood by gradient centrifugation and negative isolation. Macrophages were generated by treating monocytes with either macrophage colony-stimulating factor (M-CSF) or CXCL4 (platelet factor-4) for 6 days. To induce foam cell formation, macrophages were treated with oxidized low density lipoprotein (oxLDL, 100 μg/ml) or medium for 0, 2, 4, 6, 8, 12, 24, or 48 hours. AR expression was assessed by real-time RT-PCR. AR activity was determined photometrically by measurement of NADPH consumption. At 4 hours, AR gene expression was found increased about 1.4- (M-CSF) and 1.8-fold (CXCL4), respectively. In accordance with these findings, AR activity was significantly increased in macrophages stimulated with oxLDL and could be inhibited by treatment with the AR inhibitor epalrestat. oxLDL-dependent upregulation of AR was further elevated under hyperglycemic conditions (30 mM glucose) supporting a synergistic effect of hyperlipidemia and diabetes mellitus. Inhibition of AR by epalrestat resulted in reduction of oxLDL-dependent IL-6 upregulation suggesting that pro-inflammatory effects of oxLDL are at least partly mediated by AR. The in-vivo relevance of AR expression was demonstrated by immunohistochemistry showing expression AR in human atherosclerotic plaque. In summary, we demonstrate oxLDL-dependent upregulation of AR in human macrophages as a novel pro-inflammatory mechanism in foam cells. AR might represent a potential link between hyperlipidemia, diabetes mellitus and atherosclerosis and might be a relevant therapeutic target.