Homocysteine-induced endothelial cell injury in vitro: A model for the study of vascular injury

Direct chemical injury to vascular endothelium was determined in vitro by measuring independently cell detachment and release of ⁵¹Cr from labeled human endothelial cell monolayers. Homocysteine, a sulfhydryl amino acid, induced specific ⁵¹Cr release from endothelial cells in direct proportion to its concentration between 0.1 and 10 mM. The proportion of detached cells during exposure to homocysteine was also directly related to the concentration of homocysteine. In vitro preincubation of homocysteine resulted in a progressive loss of cytotoxicity with no activity persisting after 24 hours. Mercaptoethanol, a sulfhydryl agent similar to homocysteine, also induced endothelial injury in a concentration dependent manner. Penicillamine prevented the homocysteine mediated ⁵¹Cr-release at equimolar concentrations (p< 0.001). Catalase also inhibited the sulfydryl injury (90% reduction in ⁵¹Cr release at 0.1 mM homocysteine), but superoxide dismutase had no effect, thereby suggesting a role for hydrogen peroxide in mediating injury. Neither homocystine nor methionine, produced cell injury. Human arterial smooth muscle cells were insensitive to homocysteine levels less than 25 mM. These data demonstrate homocysteine-induced endothelial injury in vitro, and suggest that this process may in part be sulphydryl-mediated.