Synergistic activation of glucose-6-phosphate dehydrogenase and NAD(P)H oxidase by Src kinase elevates superoxide in type 2 diabetic, Zucker fa/fa, rat liver.
Glucose metabolism through the glycolysis and hexosamine pathway has been shown to be altered in type 2 diabetes. However, the fate of glucose through the pentose phosphate pathway (PPP) is currently unclear. In this study, we determined whether the activity of glucose-6-phosphate dehydrogenase (G6PD), the rate-limiting enzyme in the PPP, is modulated in the liver of Zucker obese fa/fa rats (9-11 weeks of age). We found that G6PD expression and activity, NADPH levels, and 6-phosphogluconate generation were significantly increased in the liver of fa/fa rats. Inhibition of PI3 kinase and Src kinases decreased (p < 0.05) G6PD activity in the fa/fa but not in the lean rat liver, suggesting that G6PD activity is regulated by PI3/Src kinase signaling pathways. G6PD-derived NADPH increased (p < 0.05) superoxide anion levels by 70-90% in fa/fa vs lean rat liver, which was inhibited by the NADPH oxidase inhibitor gp91(ds-tat) (50 microM) and G6PD inhibitors 6-aminonicotinamide (1 mM) and dehydroepiandrosterone (100 microM), therefore indicating that elevated G6PD activity may be responsible for mediating superoxide generation. Interestingly, we also found a positive correlation between liver hypertrophy/increased G6PD activity (r2 = 0.77; p = 0.0009) and liver hypertrophy/superoxide production (r2 = 0.51; p = 0.0091) in fa/fa rats. Increased G6PD and NADPH oxidase expression and activity, in young hyperglycemic and hyperinsulinemic rats before the development of diabetes, seems to be a contributing factor in the induction of oxidative stress. Because inhibition of G6PD activity decreases oxidative stress, we conclude that G6PD behaves as a pro-oxidant in the fa/fa rat liver in type 2 diabetes.
Gupte
Rakhee S
RS
Department of Biochemistry and Molecular Biology, University of South Alabama, Mobile, AL 36688, USA.
Floyd
Beverly C
BC
Kozicky
Mark
M
George
Shimran
S
Ungvari
Zoltan I
ZI
Neito
Vanessa
V
Wolin
Michael S
MS
Gupte
Sachin A
SA
D015120:6-Aminonicotinamide / Q000494:pharmacology; D000818:Animals; D002457:Cell Extracts; D002478:Cells, Cultured; D003687:Dehydroepiandrosterone / Q000494:pharmacology; D003924:Diabetes Mellitus, Type 2 / Q000201:enzymology* / Q000235:genetics / Q000473:pathology / Q000503:physiopathology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D015971:Gene Expression Regulation, Enzymologic / Q000187:drug effects; D005942:Gluconates / Q000494:pharmacology; D005954:Glucosephosphate Dehydrogenase / Q000235:genetics / Q000378:metabolism*; D006023:Glycoproteins / Q000494:pharmacology; D008099:Liver / Q000187:drug effects / Q000201:enzymology* / Q000473:pathology; D008297:Male; D019255:NADPH Oxidases / Q000235:genetics / Q000378:metabolism*; D009765:Obesity; D010427:Pentose Phosphate Pathway / Q000187:drug effects; D010477:Perfusion; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D051381:Rats; D011924:Rats, Zucker; D015398:Signal Transduction; D013481:Superoxides / Q000378:metabolism; D015854:Up-Regulation / Q000187:drug effects; D019061:src-Family Kinases / Q000378:metabolism*
D002457:Cell Extracts; D004791:Enzyme Inhibitors; D005942:Gluconates; D006023:Glycoproteins; C473031:gp91ds-tat protein, chimeric; D013481:Superoxides; D015120:6-Aminonicotinamide; D003687:Dehydroepiandrosterone; D005954:Glucosephosphate Dehydrogenase; D019255:NADPH Oxidases; D019869:Phosphatidylinositol 3-Kinases; D019061:src-Family Kinases; C008884:6-phosphogluconic acid