Effect of Dyslipidemia on Pro-inflammatory Adhesion Molecule Expression in Human Retinal Vascular Endothelial Cells

Abstract

Abstract: : Purpose: Diabetic retinopathy is one of the most disabling diabetic complications and is a leading cause of blindness in adults. The initial determinants of retinal microvascular damage are not well understood. Hyperglycemia and dyslipidemia are two major metabolic disorders of diabetes mellitus. The effects of hyperglycemia have been extensively studied, however, the role of diabetic dyslipidemia in the development of diabetic retinopathy has received much less attention. The purpose of this study is to mimic the diabetic environment by exposing retinal microvascular cells to free fatty acids at levels expected in diabetic plasma. Methods: Human retinal vascular endothelial cells (hRVE) were treated with 10 to 100 microM of serum albumin bound free fatty acids (16:0; 18:1 (n9); 18:2 (n6); 20:4 (n6), 20:5 (n3)) for 6, 12 or 24 hrs. Fatty acids composition of hRVE cells before and after treatment was measured by RP-HPLC and GC-MS. The expression of adhesion molecules such as intercellular adhesion molecules-1 (ICAM-1) and vascular adhesion molecules (VCAM)-1 were assayed by Western Blotting. The mechanisms underlying the induction of adhesion molecules by certain fatty acids were further investigated by using general COX inhibitor flubiprofen and LOX inhibitor NDGA. Results: Exposure of hRVE cells to fatty acids caused corresponding changes in the intracellular fatty acid profile. Linoleic acid and arachidonic acid induced a dose-dependent increase in the VCAM-1 and ICAM-1 expression starting at 12 hr. The maximal response (10 fold increase in VCAM-1 expression and 6 fold increase in ICAM-1 expression) was observed after 24 hr exposure to 100 microM of linoleic or arachidonic acids. Palmitic, oleic, and EPA, did not effect adhesion molecules expression in hRVE cells. Flurbiprofen, a general COX inhibitor and NDGA, a general LOX inhibitor, at 100 microM completely abolished the fatty acid induced upregulation of adhesion molecules. Conclusions: The results of this study demonstrate that exposure of hRVE cells to linoleic and arachidonic acid leads to expression of pro-inflammatory adhesion molecules. This finding is consistent with the emerging hypothesis recognizing very early stage diabetic retinopathy as a low-grade chronic inflammatory disease. Dysregulation of fatty acid metabolism in diabetes resulting in excess circulating free fatty acids could represent a missing link between diabetes and retinal microvascular damage.

Keywords: diabetic retinopathy • inflammation • lipids