Thymic peptide protects vascular endothelial cells from hydrogen peroxide-induced oxidant injury

Oxidant injury of the vascular endothelium is considered an early event in the pathogenesis of atherosclerosis. In this study, the antioxidant effect of a 6-kDa thymic peptide (TP), isolated from calf thymus, was investigated in vitro using vascular endothelial cells. Confluent monolayers of bovine pulmonary artery endothelial cells (PAEC) were preincubated with different concentrations of TP for 24 h, washed, and then exposed to hydrogen peroxide (H2O2) for 2 or 4 h. Cell injury was assessed by measuring cell viability with methylthiazol tetrazolium (MTT) assay, and by determining the release of intracellular lactate dehydrogenase (LDH). Lipid peroxidation products of PAEC were monitored as malondialdehyde (MDA) with a thiobarbituric acid fluorometric assay. H2O2 (120 or 240 microM) incubated with PAEC decreased cell viability, increased LDH release, and elevated MDA production. Preincubation of PAEC with TP (25-150 micrograms/ml) before H2O2 exposure significantly increased cell viability, decreased LDH release, and reduced MDA production. These results demonstrate that TP can protect vascular endothelial cells from oxidant injury. The data thus suggest that TP may be useful for the prevention and/or treatment of atherosclerosis, and further suggest that immune modulating agents may directly or indirectly influence the functions of vascular endothelium.