Diabetesmellitus (DM) is a primary risk factor for cardiovascular disease. Althoughrecent studies have demonstrated an important role for extracellular matrixmetalloproteinases (MMPs) in atherosclerosis, little is known about theeffects of hyperglycemia on MMP regulation in vascular cells. Gelatinzymography and Western blot analysis revealed that the activity and expressionof 92-kDa (MMP-9) gelatinase, but not of 72 kDa (MMP-2) gelatinase, weresignificantly increased in vascular tissue and plasma of two distinct rodentmodels of DM. Bovine aortic endothelial cells (BAECs) grown in culture did notexpress MMP-9 constitutively; however, chronic (2-week) incubation with highglucose medium induced MMP-9 promoter activity, mRNA and protein expression,and gelatinase activity in BAECs. On the other hand, high glucose culture didnot change MMP-9 activity from vascular smooth muscle cells or macrophages.Electron paramagnetic resonance studies indicate that BAECs chronically grownin high glucose conditions produce 70% more ROS than do control cells.Enhanced MMP-9 activity was significantly reduced by treatment with theantioxidants polyethylene glycol-superoxide dismutase andN-acetyl- l -cysteinebut not by inhibitors of protein kinase C. In conclusion, vascular MMP-9activity is increased in DM, in part because of enhanced elaboration fromvascular endothelial cells, and oxidative stress plays an important role. Thisnovel mechanism of redox-sensitive MMP-9 expression by hyperglycemia mayprovide a rationale for antioxidant therapy to modulate diabetic vascularcomplications.