Induction of glucose-6-phosphate dehydrogenase by lipopolysaccharide contributes to preventing nitric oxide-mediated glutathione depletion in cultured rat astrocytes.
Treatment of cultured rat astrocytes with lipopolysaccharide (LPS; 1 microg/ml) increased mRNA expression of glucose-6-phosphate dehydrogenase (G6PD), the rate-limiting step in the pentose phosphate pathway (PPP), in a time-dependent fashion (0-24 h). This effect was accompanied by an increase in G6PD activity (1.74-fold) and in the rate of glucose oxidation through the PPP (6.32-fold). Inhibition of inducible nitric oxide synthase (iNOS) activity by 2-amino-5,6-dihydro-6-methyl-4H-1,3-thiazine (AMT; 50 microM) did not alter the LPS-mediated enhancement of G6PD mRNA expression or PPP activity. Blockade of nuclear factor-kappaB (NF-kappaB) activation by N-benzyloxycarbonyl-Ile-Glu-(O-tert-butyl)-Ala-leucinal (1 microM) prevented the expression of both iNOS mRNA and G6PD mRNA, suggesting that iNOS and G6PD are co-induced by LPS through a common transcriptional pathway involving NF-kappaB activation. Incubation of cells with LPS for 24 h increased intracellular NADPH concentrations (1.63-fold) as compared with untreated cells, but GSH concentrations were not modified by LPS treatment up to 60 h of incubation. However, inhibition of G6PD activity by dehydroepiandrosterone (DHEA; 100 microM), which prevented LPS-mediated enhancements in PPP activity and NADPH concentrations, caused a 50% decrease in the GSH/GSSG ratio after 24-36 h and in GSH concentrations after 60 h of incubation. Furthermore, the changes in glutathione concentrations caused by DHEA were abolished by AMT, suggesting that nitric oxide and/or its reactive derivatives would be involved in this process. From these results, we conclude that LPS-mediated G6PD expression prevents GSH depletion due to nitric oxide and suggest that this phenomenon may be a contributing factor in the defense mechanisms that protect astrocytes against nitric oxide-mediated cell injury.
García-Nogales
P
P
Departamento de Bioquímica y Biología Molecular, Universidad de Salamanca, Spain.
Almeida
A
A
Fernández
E
E
Medina
J M
JM
Bolaños
J P
JP
D000276:Adjuvants, Immunologic / Q000494:pharmacology; D000818:Animals; D001253:Astrocytes / Q000166:cytology / Q000201:enzymology*; D015152:Blotting, Northern; D002478:Cells, Cultured; D003687:Dehydroepiandrosterone / Q000494:pharmacology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D015971:Gene Expression Regulation, Enzymologic / Q000187:drug effects; D005954:Glucosephosphate Dehydrogenase / Q000235:genetics* / Q000378:metabolism; D005978:Glutathione / Q000378:metabolism*; D008070:Lipopolysaccharides; D009249:NADP / Q000032:analysis; D016328:NF-kappa B / Q000378:metabolism; D009410:Nerve Degeneration / Q000378:metabolism; D009569:Nitric Oxide / Q000378:metabolism*; D019001:Nitric Oxide Synthase / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism; D052247:Nitric Oxide Synthase Type II; D010427:Pentose Phosphate Pathway / Q000502:physiology; D016548:Prosencephalon / Q000166:cytology; D012333:RNA, Messenger / Q000032:analysis; D051381:Rats; D017208:Rats, Wistar; D013843:Thiazines / Q000494:pharmacology
C093124:2-amino-5,6-dihydro-6-methyl-4H-1,3-thiazine; D000276:Adjuvants, Immunologic; D004791:Enzyme Inhibitors; D008070:Lipopolysaccharides; D016328:NF-kappa B; D012333:RNA, Messenger; D013843:Thiazines; D009569:Nitric Oxide; D003687:Dehydroepiandrosterone; D009249:NADP; D005954:Glucosephosphate Dehydrogenase; D019001:Nitric Oxide Synthase; D052247:Nitric Oxide Synthase Type II; C496318:Nos2 protein, rat; D005978:Glutathione