Pre-enrichment of modified low density lipoproteins with alpha-tocopherol mitigates adverse effects on cultured retinal capillary cells

Purpose. We determined whether pre-enrichment of low density lipoproteins ( LDL) with alpha-tocopherol mitigates their adverse effects, following in vi tro glycation, oxidation or glycoxidation, towards cultured bovine retinal capillary endothelial cells (RCEC) and pericytes. Methods. LDL, while still in plasma obtained and pooled from non-diabetic h umans, was supplemented in vitro with alpha-tocopherol. It was then isolate d and modified in vitro by glycation, minimal oxidation, and glycoxidation. Bovine RCEC and pericytes were exposed to LDL (100mg protein/ml) for three days. Cell count was determined by cell counting, supernatant levels of pl asminogen activator inhibitor-1 (PAI-1) and endothelin-1 (ET-1) by ELISA, a nd nitrite levels by spectroscopic colorimetric assay. Results. While pre-enrichment of LDL with alpha-tocopherol did not reduce t he measured extent of lipoprotein modification, it abolished the reduction in cell count observed with glycated, oxidized and glycoxidized LDL v. norm al LDL. Pre-enrichment of LDL with alpha-tocopherol also reduced RCEC super natant PAI-1 and ET-1 (corrected for cell counts) and increased RCEC and pe ricyte-associated supernatant nitrite levels: such effects of a-tocopherol may inhibit clot formation and favor vasodilatation. Conclusions. Enrichment of LDL with alpha-tocopherol abolishes adverse effe cts of glycated, mildly oxidized, and glycoxidized LDL on cultured retinal cell count, and mitigates adverse effects on modulators of fibrinolysis and vascular tone. Direct evidence is required before Vitamin E supplementatio n is recommended for people with diabetes.