Glucose Toxicity for Human Endothelial Cells in Culture: Delayed Replication, Disturbed Cell Cycle, and Accelerated Death

Abstract

Functional and anatomical abnormalities of endothelium may represent a pathway to the increased vascular permeability and accelerated atherosclerosis characteristic of diabetes. To identify whether and how hyperglycemia may compromise the endothelial barrier, we have employed an in vitro system of human endothelial cells obtained from umbilical veins and cultured in elevated glucose concentrations (20 mM). Under these conditions, the achievement of saturation density was substantially delayed, with cell counts throughout most of the growth curve being 70–80% of control (P < 0.002). More profound suppression of cell number was present in cultures exposed to 40 mM glucose. Similar, albeit slightly lesser, effects were observed in cultures exposed to 20 mM mannitol, mimicking the hypertonicity of the high glucose media. The effect of elevated glucose and mannitol was primarily mediated by a decrease in overall rate of replication of the endothelium as documented by the lower mitotic index (P < 0.025). Analysis of the distribution of cells along phases of the cell cycle uncovered in the high glucose cultures a decreased proportion of cells in G0-G1 (70.5 ± 5% versus 73.2 ± 4% in controls, P < 0.05) and an increased proportion of cells in S phase (16.5 ± 2.7% versus 13.5 ± 2.2% in controls, P < 0.01), suggesting that the replicative delay is likely to occur between the phase of DNA synthesis and mitosis. Increased cellular death was specifically observed in the cultures exposed to elevated glucose concentrations (P < 0.05), but it could account for only a minor portion of the deficit in cell number. The mechanism(s) underlying the described ill effects of high glucose/hypertonicity on endothelium and the relevance of such abnormalities to diabetic angiopathy are currently under investigation.