Abstract. Gabexate mesilate (GM), a serine protease inhibitor, often causes severe vascular injury, when injected in high concentration. In the present study, we investigated the mechanisms for the cytotoxicity of GM on porcine aorta endothelial cells (PAECs). GM (0.5 -5.0 mM) decreased cell viability in a dose-dependent manner and caused cell injury, whilst nafamostat mesilate (NM), another serine protease inhibitor, or mesilate itself had no effect on cell viability. zVAD-fmk, a pancaspase inhibitor, or zDEVD-fmk, a caspase-3 inhibitor, did not affect the GM (1.5 mM)-induced decrease of cell viability. Apoptotic cells or DNA fragmentation were also not observed after GM treatment. Moreover, Ca 2+ chelators, a nitric oxide (NO) synthase inhibitor, antioxidants, and radical scavengers had no effect on the GM-induced cell injury. On the other hand, cellular ATP content was decreased in the GM (2.0 mM)-treated cells. Surprisingly, GM (2.0 mM) immediately increased cellular uptake of propidium iodine. These findings suggest that GM induces necrotic cell death via injury of the cell membrane.

Abstract. Gabexate mesilate (GM), a serine protease inhibitor, often causes severe vascular injury. We previously reported that GM induced necrotic cell death via injury of the cell membrane in porcine aorta endothelial cells (PAECs). In the present study, we investigated the protective effects of amino acids against this GM-induced cell injury in PAECs.-threonine, and L-isoleucine significantly inhibited the GM-induced decrease of cell viability. Gly showed the most potent effect among these amino acids. Gly, L-Cys, L-Glu, and L-Gln also inhibited the GM-induced increase in the number of necrotic cells stained by propidium iodide (PI). However, these amino acids had no effect on the GM-induced inhibition of trypsin activity. Strychnine, MK-801, or dichlorokynurenic acid did not affect the protective effect of Gly. Gly completely suppressed the GM-induced increase in PI uptake, which occurred immediately after exposure to GM. These findings suggest that Gly exerts protection against GM-induced cellular membrane injury, and several amino acids such as Gly may be useful for prophylaxis of the GM-induced severe vascular injury.