Hormone-mediated down-regulation of hepatic glutathione synthesis in the rat.

Abstract

Our present work characterized the role of hormone-mediated signal transduction pathways in regulating hepatic reduced glutathione (GSH) synthesis. Cholera toxin, dibutyryl cAMP (DBcAMP), and glucagon inhibited GSH synthesis in cultured hepatocytes by 25-43%. Cellular cAMP levels exhibited a lower threshold for stimulation of the GSH efflux than inhibition of its synthesis. The effect of DBcAMP was independent of the type of sulfur amino acid precursor and cellular ATP levels and unassociated with increased GSH mixed disulfide formation or altered GSH/oxidized glutathione ratio. In liver cytosols, addition of DBcAMP and cAMP-dependent protein kinase (A-kinase) inhibited GSH synthesis from substrates (cysteine, ATP, glutamate, and glycine) by -20% which was prevented by the A-kinase inhibitor. However, if only substrates of the second step in GSH synthesis were used (y-glutamylcysteine, glycine, and ATP), DBcAMP and A-kinase exerted no inhibitory effect. Phenylephrine, vasopressin, and phorbol ester also inhibited GSH synthesis in cultured cells by -20%, and depleted cell GSH independent of the type of sulfur amino acid precursor. Cellular cysteine level was unchanged despite the significant fall in GSH after glucagon or phenylephrine treatment. Pretreatment with either staurosporine, C-kinase inhibitor, or calmidazolium, a calmodulin inhibitor, partially prevented but, together, completely prevented the inhibitory effect of phenylephrine. The same combination had no effect on the inhibitory effect of glucagon. The effects of hormones were confirmed in both the intact perfused liver and after in vivo administration. Thus, two classes of hormones acting through distinct signal transduction pathways may down-regulate hepatic GSH synthesis by phosphorylation of y-glutamylcysteine synthetase. (J. Clin. Invest. 1991. 88:260-269.) Key words:

Molecular Mechanism of the Regulation of Glutathione Synthesis by Tumor Necrosis Factor-α and Dexamethasone in Human Alveolar Epithelial Cells

“…However, the ratio of GSH/GSSG levels was decreased by dexamethasone, suggesting that dexamethasone may impose oxidative stress in A549 epithelial cells. Depletion of liver GSH in mice and inhibition of GSH synthesis by dexamethasone have been observed in a rat hepatic cell line (50,51). Similarly, depletion of antioxidant enzyme activities have been shown in various rat tissues by glucocorticoid supplementation, and this depletion was more pronounced when rats were challenged with oxidative stress (52).…”

Suppression of Cell-cycle Progression during the S Phase of Rat Fibroblasts by 3-Deoxyglucosone, a Maillard Reaction Intermediate

“…23,24) Glucagon and phenylephrine were found to depress the concentrations of GSH in hepatocytes by inhibition of an activity of gamma-glutamylcysteine synthetase, which is a key enzyme responsible for a rate-limiting step of the synthesis of GSH. 25 ) It has often been discussed how GSH metabolism may be associated with aging and diabetic complications. A negative correlation between GSH content and age was found in human bone marrow 26 ) and murine liver, kidney, and heart.…”

Oxidative stress and regulation of glutathione in lung inflammation

“…Various inflammatory agents such as cyclic adenosine monophosphate (cAMP) and intracellular calcium, which are released during inflammation, may inhibit GSH synthesis at the translational level (table 3) [107]. It has been shown that c-GCS activity is inhibited by agonists of various signal transduction pathways in rat hepatocytes [107], suggesting a role for signalling mechanisms in the TNF-a: tumour necrosis factor-a IL: interleukin.…”

“…LU et al [107] reported that hepatic GSH synthesis is downregulated in response to hormones known to mediate their effects through the activation of distinct signal transduction pathways. Using various specific inhibitors of signalling pathways, these investigators determined that hormone-specific inhibition of GSH synthesis was mediated by the activation of protein kinase A, protein kinase C and Ca 2+ /calmodulindependent kinase II.…”

“…GSH-related structural compounds, such as glutathione-S-conjugates and GSH ethyl ester, inhibit cellular GSH uptake or influx [137,138]. Furthermore, a more oxidized extracellular environment stimulates cells to retain GSH, whereas a more reduced extracellular state facilitates GSH efflux [137,140]. However, these effects are in direct contrast with the situation in lungs in vivo, since the increased oxidant burden imposed by smoking and endogenous oxidative stress during inflammation could cause lung cells to retain GSH, rather than release it into the ELF.…”