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The role of mitochondrial glutathione and cellular protein sulfhydryls in formaldehyde toxicity in glutathione-depleted rat hepatocytes.

Depletion of cellular GSH by diethyl maleate (DEM) potentiates CH2O toxicity in isolated rat hepatocytes and it was postulated that this increase in toxicity is due to the further decrease in GSH caused by CH2O in DEM-pretreated hepatocytes (1). The present investigation was conducted to investigate further the effects of CH2O, DEM, and acrolein (a compound which is structurally related to CH2O and DEM) on subcellular GSH pools and on protein sulfhydryl groups (PSH). CH2O caused a decrease in cytosolic GSH but had no effect on mitochondrial GSH either in previously untreated hepatocytes or in DEM-pretreated hepatocytes in which GSH was approximately 25% of control. DEM decreased both cytosolic and mitochondrial GSH but it did not produce toxicity. Neither CH2O (up to 7.5 mM) nor DEM (20 mM) decreased PSH. However, in cells pretreated with 1 mM DEM, CH2O (7.5 mM) decreased PSH and this effect preceded cell death. Acrolein decreased both cytosolic and mitochondrial GSH and it also decreased PSH significantly prior to causing cell death. CH2O and acrolein stimulated phosphorylase alpha activity, indicative of an increase in cytosolic free Ca2+, by a PSH-independent and PSH-dependent mechanism, respectively. These results suggest that the further depletion of cellular GSH by CH2O in DEM-pretreated cells is not due to the depletion of mitochondrial GSH. CH2O toxicity in DEM-pretreated cells is, however, correlated with depletion of PSH. The critical sulfhydryl protein(s) responsible for cell death remain to be more clearly defined.

Acrolein↗

Inhibition of mouse glutathione transferases and glutathione peroxidase II by dicumarol and other ligands.

Dicumarol, often used as a specific inhibitor of DT diaphorase (NAD(P)H:(quinone-acceptor) oxidoreductase; EC 1.6.99.2), was found to potently inhibit GSH transferases (EC 2.5.1.18). Dicumarol exhibited an IC50 of 11 microM in inhibiting the conjugation of 1-chloro-2,4-dinitrobenzene (50 microM) by GSH transferase GT-8.7, the major hepatic class mu isoenzyme of CD-1 mice. The activities of GT-8.7 and of the class pi isoenzyme, GT-9.0, toward a carcinogenic substrate, 4-nitroquinoline 1-oxide (100 microM), were inhibited by dicumarol with IC50 values of 14 and 9 microM, respectively. Dicumarol also affected GSH peroxidase II activity, inhibiting the reduction of cumene hydroperoxide by GT-10.6, the predominant class alpha GSH transferase of mouse liver, with an IC50 of 14 microM. GSH peroxidase I (EC 1.11.1.9) and GSH peroxidase II activities were resolved by chromatography of liver and testis cytosols. While inhibiting GSH peroxidase II with IC50 of 9-10 microM, dicumarol did not affect the activity of the selenoenzyme, GSH peroxidase I. Whereas several other non-substrate ligands were more potent inhibitors of 1-chloro-2,4-dinitrobenzene conjugation, dicumarol effectively inhibited GSH transferase and GSH peroxidase II activities in the range of dicumarol concentrations frequently used for detection of DT diaphorase action. These results indicate that physiological consequences resulting from the use of supramicromolar concentrations of dicumarol should not be interpreted in terms of DT diaphorase inhibition alone.

4-Nitroquinoline-1-oxide↗

Glutathione biosynthesis in the isolated perfused rat lung: utilization of extracellular glutathione.

The isolated perfused rat lung catalyzed the biosynthesis of GSH when the sulfur amino acids cysteine or N-acetylcysteine, but not methionine, were supplied in the perfusion medium. The lung also had the capacity to utilize extracellular GSH for this purpose. Replenishment of intracellular GSH in perfused lungs from diethylmaleate-treated rats was pronounced even at 25 microM GSH in the perfusion medium. The utilization of extracellular GSH is probably primarily through extracellular break-down and resynthesis rather than direct uptake as indicated by the inhibitory effect of the gamma-glutamylcysteine synthetase inhibitor, buthionine sulfoximine and the gamma-glutamyl transferase inhibitor, anthglutin. The results indicate that the lung in addition to the kidney may utilize circulating plasma GSH.

Acetylcysteine↗