Oxysterols, Cholesterol Biosynthesis, and Vascular Endothelial Cell Monolayer Barrier Function

A spectrum of cholesterol oxidation derivatives (oxysterols) is generated in food products exposed to heat or radiation in the presence of oxygen. One of these derivatives (cholestan-3β,5α,6β-triol) was shown to compromise the selective barrier function of cultured vascular endothelial cell monolayers, an action that may initiate atherosclerotic lesion formation. This study sought to investigate the relationship of cholesterol synthesis inhibition by several naturally occurring oxysterols to depression of vascular endothelial cell monolayer barrier function, determined as an increase in albumin transfer across cultured endothelial monolayers. All oxysterols tested caused a variable time- and dose-dependent elevation in trans-endothelial albumin transfer, and they were also able to inhibit cholesterol biosynthesis to varying degrees. Pure cholesterol was without effect on both counts. The correlation between the increase in albumin transfer related to oxysterol exposure and the ability of oxysterols to suppress cholesterol biosynthesis was, however, poor. Moreover, mevinolin, a water-soluble competitive inhibitor of cholesterol synthesis, reduced the rate of cholesterol synthesis to 0.9% of control but did not significantly increase albumin transfer. Cholestan-3β,5α,6β-triol caused a 660% elevation in albumin transfer while cholesterol synthesis remained at 11% of control. We conclude that changes in endothelial barrier function caused by exposure to the oxysterols examined, but not pure cholesterol, are probably related to factors other than the well-known action of cholesterol biosynthesis inhibition. These findings may have implications in the development of atherosclerosis.