FAILURE OF VITAMIN-E TO PROTECT CULTURED HUMAN ARTERIAL SMOOTH-MUSCLECELLS AGAINST OXYSTEROL-INDUCED CYTOTOXICITY

Objective: The cytotoxicity of oxysterols including 7 alpha-hydroxycho lesterol (7 alpha OHC), 7 beta-hydroxycholesterol (7 beta OHC), choles terol 5 alpha,6 alpha-epoxide (alpha epoxyC), cholesterol 5 beta,6 bet a-epoxide (beta epoxyC), 7-ketocholesterol (7ketoC), 26-hydroxycholest erol (26OHC), cholesterol-3 beta,5 alpha,6 beta-triol (TriolC) and the possible protecting effect of vitamin E on 26OHC-induced cytotoxicity were investigated in smooth muscle cells isolated from the arteries o f human umbilical cords. Methods: To study the cytotoxicity of oxyster ols, the cells were incubated with each oxysterol at a level of 10 mu g/ml from 24 to 120 hours, then Ca-45(++) uptake, cytosolic free Ca+level, [H-3]thymidine incorporation, total DNA content and viable cell number were measured. Cholesterol was used as a control. For tracing the possible origin of cytotoxicity of 26OHC, cholesterol, phospholipi d and 26OHC content in the membrane were investigated from 24 to 72 ho urs. For determining whether antioxidants had a protective effect agai nst the cytotoxicity of 26OHC, vitamin E and butylated hydroxytoluene (BHT) were used. Results: The results indicated that the oxysterols el evated Ca-45(++) uptake and cytosolic free Ca++ level, but diminished [H-3]thymidine incorporation, total DNA content and viable cell number . 26OHC lowered the cholesterol content of the membrane and incorporat ed into the membrane after 24 hours of the incubation, but did not alt er the total phospholipid content of the membrane until 72 hours. Neit her vitamin E or BHT significantly protected the cells from the 26OHC- induced alterations. Conclusion: We suggest that the cytotoxicity of o xysterols, which might result in an alteration in Ca++ ion flow into t he cell by decreasing cholesterol content and incorporating oxysterol itself into the membranes, could not be protected by vitamin E.