Methylglyoxal (MGO) is a reactive metabolite of glucose. Since plasma concentration of MGO is increased in diabetic patients, MGO is implicated in diabetes-associated vascular endothelial cells (ECs) injury, which might be responsible for atherosclerosis. In the present study, we examined effects of treatment of human umbilical vein ECs with MGO on ECs morphology and inflammatory responses. MGO (24 h) induced cytotoxic morphological changes in a concentration-dependent manner (0-420 µM). MGO induced mRNA and protein expression of cyclooxygenase (COX)-2 in a concentration (0-420 µM)- and time (6-24 h)-dependent manners. COX-2 induction was associated with increased prostaglandin (PG) E₂ release. Acute treatment with MGO (20 min) induced concentration-dependent (0-420 µM) activation of JNK and p38 MAP kinase but not ERK or NF-B. Both a JNK inhibitor SP600125 and a p38 inhibitor SB203580 prevented the MGO induction of COX-2. However, inhibiting JNK and p38 or COX-2 was ineffective to the morphological damage by MGO (420 µM, 24 h). EUK134, a synthetic combined superoxide dismutase/catalase mimetic, had no effect on MGO-induced COX-2. Present results indicated that MGO mediates JNK- and p38-dependnt ECs inflammatory responses, which might be independent of oxidative stress. On the other hand, MGO-induced morphological cell damage seems unlikely to be associated with COX-2-PGE₂.