Constantly low HDL-cholesterol concentration relates to endothelial dysfunction and increased in vivo LDL-oxidation in healthy young men

To test the hypothesis that low HDL-C concentration interferes with vascula r endothelial function and lipoprotein oxidation, we measured endothelium-d ependent flow mediated dilatation FMD, % of the brachial artery in young me n (n = 20) classified prospectively into two groups on basis of having eith er low or high HDL-C concentration over the past 2 years. As an estimate of in vivo low-density lipoprotein oxidation (ox-LDL), we measured LDL diene conjugation. FMD was present in the group with high HDL-C concentration, bu t impaired in the group with low HDL-C (5.5 +/- 3.2 vs 0.2 +/- 1.2%, P < 0. 001). The group with high HDL-C level had significantly lower levels of ox- LDL compared to low HDL-C group (18.0 +/- 1.8 vs 22.9 +/- 4.4, P less than or equal to 0.01). In all subjects, FMD correlated with HDL-C (r = 0.59, P = 0.006), HDL-C (r = 0.62? P = 0.004) and ox-LDL (r = - 0.56, P = 0.013) bu t not with HDL-C (r = 0.16, P = 0.52). We conclude that constantly low HDL- C concentration is related with endothelial dysfunction and increased oxida tive stress in healthy young men, consistent with the idea that HDL particl es may protect endothelium and inhibit the oxidation of LDL. These findings may offer insight into increased atherosclerosis associated with low HDL-C levels. (C) 1999 Elsevier Science Ireland Ltd. All rights reserved.