Simona Baldi

It is now widely accepted that the microcirculation plays a role in the complications of atherosclerosis, but the microcirculation response to atherosclerosis risk factors like diabetes, hypercholesterolemia and hypertension, is still unclear. Alterations in the endothelial production of IL6, NO and ET-1 are known to be correlate with these diseases. Simulating the presence of hyperglycemia, hypercholesterolemia and hypertension, this in vitro study investigated the effect of glucose, angiotensin II, and nLDL treatments on IL-6, ET-1 and NO in HMEC-1. The medium concentrations of IL6 and ET-1 were measured by ELISA assay, whereas NO by a colorimetric assay. The mRNA and protein expressions of IL-6, Pre-po-ET-1 and eNOS by extracted cells were also investigated by RT-PCR. NO concentration in the medium of HMEC-1 increased in a dose-dependent manner by glucose after 24 hours and by nLDL both at 6 and 24 h, with higher values at 6 hours. The eNOS mRNA expression at 6h induced by nLDL, showed a parallel trend to the medium NO. No increment dose dependent NO concentration was observed by angiotensin II.nLDL induced a dose-dependent increase of ET-1 medium levels, more accentuated in 6h respect to 24h. The expression of prepro-ET-1 showed a parallel dose-dependent increased after 6 hours. Both glucose and nLDL increased IL-6 levels in a dose-dependent manner at 6 and 24 h. In conclusion, glucose treatment on HMEC-1 cells exerted a mild stimulus on NO and IL-6 production. nLDL treatment showed a similar glucose stimulus on NOx, but it induced an intense pro-inflammatory activity and showed the ability to stimulate ET-1 synthesis.

Cardiovascular diseases represent the major cause of mortality in hemodialysis (HD) patients. HD increases oxidative stress and oxidation of low-density lipoprotein (LDL) is a crucial step in the development of atherosclerosis. Vitamin E has been shown to reduce LDL oxidation. Our aim was to test the effect of a single HD session and chronic vitamin E supplementation on LDL oxidizability in HD patients. LDL susceptibility to copper-induced oxidation (lag-phase, LP) was measured in 19 HD patients, both immediately before and after hemodialysis; 18 age-matched healthy subjects served as controls. Both pre-HD and post-HD measurements were repeated after 12 weeks of vitamin E supplementation (800 IU/day) in a placebo-controlled, randomized design. At baseline, HD patients showed hypertriglyceridemia, a significant triglyceride enrichment in LDL and HDL and an enhanced LDL resistance to oxidation (186 ± 6 vs. 163 ± 4 min, p<0.003). A single HD session decreased (to 172 ± 6 min, or -8%, p<0.002), and chronic vitamin E administration increased, LDL resistance to oxidation (+19%, p = 0.002 vs. placebo) without changing the serum lipid profile or lipoprotein lipid composition. We conclude that in patients on chronic hemodialysis, hypertriglyceridemia and triglyceride enrichment of LDL and HDL particles are associated with increased resistance of LDL to in vitro oxidation despite the fact that each dialysis session acutely increases LDL oxidizability. Vitamin E supplementation improves LDL resistance to oxidation without modifying circulating lipid levels and partitioning.

Abstract —Increased free radical production and hyperinsulinemia are thought to play a role in experimental and human atherosclerosis, but the relation between the 2 abnormalities has not been studied. In 23 healthy volunteers, we measured the susceptibility of circulating low-density lipoprotein (LDL) cholesterol particles to in vitro copper sulfate oxidation (measured as the lag phase) and cell-mediated oxidative modification (measured as malondialdehyde generation in LDL during incubation with human umbilical vein endothelial cells), as well as the vitamin E content of LDL cholesterol at baseline and after 2 hours of physiological hyperinsulinemia (euglycemic insulin clamp). The lag time of LDL oxidation decreased from control values of 108±3 and 107±3 minutes (at baseline and after 2 hours of saline infusion) to 101±3 minutes after 2 hours of clamping ( P P =0.0006), whereas the LDL vitamin E content decreased from 6.78±0.06 and 6.77±0.06 to 6.64±0.06 μg/mg ( P <0.04). The insulin-induced shortening of the lag phase was directly related to the decrement of vitamin E in LDL; furthermore, in subjects with higher baseline serum triglyceride levels, insulin induced a greater shortening of the lag phase than in subjects with low baseline triglycerides. We conclude that in healthy humans acute physiological hyperinsulinemia enhances the oxidative susceptibility of LDL cholesterol particles. This effect may have pathogenic significance for atherogenesis in insulin resistant states.