Methylglyoxal (MG) is a reactive dicarbonyl compound that is formed as a metabolic byproduct of glycolysis. 1,2) MG is found at high levels in the blood of diabetic patients. 3) MG causes nonenzymatic glycation of proteins to yield irreversible advanced glycation end products (AGEs), leading to cross-linking or degradation of proteins. 4) MG has been linked to the development of diabetic complications related to vascular injury. [3][4][5] MG might contribute to not only the development of diabetes but also the pathogenesis of hypertension. 6) MG induces the apoptosis of Schwann cells, 7,8) human monocytic leukemia U937 cells, 9) and human umbilical vein endothelial cells. 10) It is suggested that oxidative stress is involved in MG-induced apoptosis. Oxidative stress resulting from the accumulation of reactive oxygen species (ROS) has been well characterized in diabetic complications. 11,12) MG inactivates antioxidant enzymes, such as glutathione peroxidase and Cu,Zn-superoxide dismutase. 13,14) The dysfunction of antioxidant defense systems may lead to the progression of oxidative stress and finally cell death, such as apoptosis.Reduced glutathione (GSH), the most abundant non-protein thiol antioxidant in cells, is important for protection against oxidative injury. Chronic intake of MG by mice caused the depletion of blood GSH. 15) Intracellular GSH was depleted in Schwann cells incubated with MG. 8) It was also revealed that N-acetyl-L-cysteine, an antioxidant, restored the MG-induced GSH depletion in Schwann cells and prevented apoptosis. In human monocytic leukemia U937 cells, MG-induced apoptosis and oxidative stress were enhanced by DLbuthionine-(S,R)-sulfoximine (BSO), an inhibitor of GSH biosynthesis, and partially blocked by N-acetyl-L-cysteine. 9) However, it remains unknown whether BSO or N-acetyl-Lcysteine affects MG-induced apoptosis and oxidative stress in endothelial cells. Recently, we reported that MG induces apoptosis and oxidative stress in bovine aortic endothelial cells (BAECs). 16,17) MG affected GSH levels in BAECs. 17) In this study, we examined the effect of BSO on MG-induced apoptosis and oxidative stress by using BAECs.
MATERIALS AND METHODSMaterials MG (40% aqueous solution), BSO, and p-nitrophenyl phosphate were purchased from Sigma Chemical Co. (St. Louis, MO, U.S.A.). Fetal bovine serum (FBS) was from Lonza (Walkersville, MD, U.S.A.). Dulbecco's modified Eagle's medium (DMEM), Dulbecco's phosphate-buffered saline (DPBS), phosphate-buffered saline (PBS) at pH 7.4, Lglutamine, penicillin, and streptomycin were from Gibco BRL (Grand Island, NY, U.S.A.). All other chemicals used were of reagent grade.Endothelial Cell Culture BAECs were purchased from Lonza. Cells were obtained at the third passage, transferred to 75 cm 2 filter vent flasks, and grown to 80-90% confluence in DMEM containing 10% FBS, 4 nM L-glutamine, 100 U/ml penicillin, and 100 mg/ml streptomycin, with incubation at 37°C in a humidified atmosphere of 5% CO 2 and 95% air. Cells were passaged by trypsinization and those b...