α-tocopherol decreases superoxide anion release in human monocytes under hyperglycemic conditions via inhibition of protein kinase C-α

Diabetes is a major risk factor for premature atherosclerosis, and oxidative stress appears to be an important mechanism. Previously, we showed that diabetic monocytes produce increased superoxide anion (O-2(-)), and alpha-tocopherol (AT) supplementation decreases this. The aim of this study was to elucidate the mechanism(s) of O-2(-) release and inhibition by AT under hyperglycemic (HG) conditions in monocytes. O-2(-) release, protein kinase C (PKC) activity, and translocation of PKC-alpha and -betaII and p47phox were increased in THP-1 cells (human monocytic cell line) under HG (15 mmol/l glucose) conditions, whereas AT supplementation inhibited these changes. AT, NADPH oxidase inhibitors (apocynin and diphenyleneiodonium chloride [DPI]), and an inhibitor to PKC-alpha and other isoforms (2,2',3,3',4,4'-hexahydroxy-1,1'-biphenyl-6,6'-dimethanol dimethyl ether [HBDDE]) but not PKC-beta II (LY379196) decreased O-2(-) release and p47phox translocation. Antisense oligodeoxynucleotides to PKC-alpha and p47phox but not to PKC-betaII inhibited HG-induced O-2(-) release and p47phox translocation in THP-1 cells. Under HG conditions, reactive oxygen species release from monocytes was not inhibited by agents affecting mitochondrial metabolism but was inhibited in human endothelial cells. We conclude that under HG conditions, monocytic O-2(-) release is dependent on NADPH oxidase activity but not the mitochondrial respiratory chain; HG-induced O-2(-) release is triggered by PKC-alpha, and AT inhibits O-2(-) release via inhibition of PKC-alpha.