[Comparative evaluation of the cytotoxic effect of hydrogen peroxide and tumor necrosis factor alpha on nonischemic and ischemic endothelial cells].

We studied cytotoxic effects (CTE) induced in confluent cultures of human umbilical vein endothelial cells (HUVEC) by initiators of free-radical reactions (FRR): H2O2 (10(-6)-10(-9) M), recombinant human tumor necrosis factor-[symbol; see text] (TNF-alpha, 0.05-100 ng/ml), and a combination of TNF-alpha with low-density lipoproteins (LDL, 100 microgram/ml). HUVEC were incubated with these substances for 6 or 24 h in parallel tests performed under aerobic (CO2-incubator) and ischemic conditions (a mixture of 95% N2 + 5% CO2 in RPMI-1640 medium containing no substrate additives, growth factor or protein). HUVEC viability was determined by counting cells adherent to the bottom of wells after 24 h of reincubation under aerobic conditions in the growth medium (Plating Efficiency Index). The data showed that: 1) CTE of these compounds were dose-dependent (H2O2 and TNF-alpha) and time-dependent (TNF-alpha); 2) CTE of FRR initiators and CTE of ischemia were synergistic, that is, their combination produced a greater decrease HUVEC viability than any substance examined or ischemia alone; 3) CTE of TNF-alpha observed in experiments in substrate-deficient, protein-free medium was considerably stronger than in the growth medium; 4) a combination of TNF-a and LDL caused a stronger CTE on HUVEC than either factor alone, and this synergism was more pronounced during incubation under ischemic conditions. Thus, the data indicate that FRR initiators and TNF-alpha + LDL particularly increase the severity of ischemic injuries of EC and therefore they can be factors which in hypercholesterolemic patiens predispose vascular wall to atherosclerosis.