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Query: UMLS:C1260386 (GSH)
 38,102 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

We previously described the establishment of a transfected cell line (V79HGGT) that stably produces the highest recombinant human gamma-glutamyltransferase (GGT) activity. We now report the utilization of V79HGGT as a model system for studying human GGT. The papain-solubilized recombinant enzyme has been highly purified from cultured cells by a new procedure. Studies on the purified enzyme, either by N-terminal sequencing or by characterization of its enzymic activities, confirmed that recombinant GGT shares structural and catalytic identity with native human enzymes. The circular dichroism analysis indicated an alpha-helical content of 19%. Based on these data, we have undertaken a study on the functional consequences of elevated GGT activity on the reduced glutathione (GSH) content. GSH status was followed in V79 and V79HGGT cells throughout growth. A particular pattern was observed for each cell line, depending on, but differentially affected by, alteration of the culture medium. Elevated GGT activity was associated with a 2.5-fold reduced GSH content, clearly suggesting a negative influence of the highly expressed enzyme on the GSH level under normal growth conditions. Possible mechanisms involved are proposed. Our findings pointed out that, among the GSH-related enzymes, GGT could constitute an important factor determining the steady-state content of GSH.
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PMID:Molecular and functional characterization of recombinant human gamma-glutamyltransferase. Coupling of its activity to glutathione levels in V79 cells. 791 33

Using a vascularly perfused rat intestinal preparation, we found that large quantities (i.e., 100-200 microM) of acid-soluble thiols accumulated in the jejunal lumen in 10-30 min and that the accumulation was largely unaffected by dietary food restriction for 24 or 48 h. Depending on the length of perfusion, cysteine comprised 20-40% of total luminal thiols, whereas glutathione (GSH) made up only 0-3%. To determine whether luminal cysteine accumulation resulted from mucosal secretion of GSH and subsequent degradation by brush-border gamma-glutamyltransferase (gamma-GT) and dipeptidases, acivicin or serine-borate was used to inhibit gamma-GT. Both agents inhibited gamma-GT activity by > 95%, reduced luminal cysteine by approximately 40-50%, and caused a modest elevation of luminal GSH to approximately 10-13 microM, indicating that GSH secretion does occur but cannot account for all of the luminal cysteine accumulation. Luminal thiol trapping experiments with Ellman's reagent supported this conclusion. Given that cysteine made up 15-20% of the mucosal thiol pool in jejunum, secretion of cysteine from mucosa to lumen likely accounted for the majority of luminal cysteine. Given the mucolytic nature of thiols and the role of cysteine in iron absorption, intestinal thiol secretion may be important in intestinal function.
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PMID:Secretion of cysteine and glutathione from mucosa to lumen in rat small intestine. 791 97

Organs of the digestive tract, including pancreas, small intestine, and colon, have mechanisms to modulate plasma thiol-disulfide balance. Because plasma glutathione disulfide (GSSG) concentration may be elevated from < 1 microM in control rats to over 25 microM during oxidative stress, we examined whether GSSG was cleared from rat mesenteric vasculature. When 100 microM GSSG was perfused through the gut via the superior mesenteric artery, an average of 45% was lost in a single pass. Results showed that gamma-glutamyltransferase (gamma-GT)-dependent and -independent mechanisms were involved in GSSG loss. Acivicin (AT125) treatment inhibited gamma-GT activity in the mesenteric vasculature by 94% and attenuated the loss of GSSG equivalents by 44%. These results supported a role for gamma-GT in GSSG loss from the mesenteric vasculature but indicated that still other mechanisms were involved in GSSG clearance. Elevations of portal levels of glutathione (GSH) and the mixed disulfide of cysteine and GSH (CySSG) also occurred with vascular GSSG perfusion and could account for about 40% of GSSG equivalents lost. Because portal elevations of GSH and CySSG were not inhibited by AT125, they were formed by a gamma-GT-independent mechanism(s). Given that cysteine was present in the mesenteric vasculature, the most likely mechanism to explain GSH and CySSG formation was via nonenzymatic thiol-disulfide exchange between GSSG and cysteine. Uptake of vascular GSSG by pancreas, small intestine (jejunum and ileum), or colon apparently did not occur as tissue contents of GSSG or GSH were not elevated, except for a small elevation of GSH in pancreas when mesenteric gamma-GT was inhibited with AT125. Additionally, GSSG was not transported from mesenteric vasculature into the small intestinal lumen because luminal levels of GSSG or GSH were not elevated. Further, total cysteine equivalents in lumen were unchanged indicating that GSSG was not transported to lumen and degraded to cystine by gamma-GT and dipeptidases localized to the intestinal brush-border. These results indicate that GSSG present in mesenteric vasculature is metabolized in the vascular compartment by gamma-GT-dependent and -independent reactions; together, these account for over 80% of lost GSSG equivalents. They also suggest that organs of the mesentery may play a quantitatively important role in plasma GSSG clearance and modulation of vascular thiol-disulfide balance.
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PMID:Clearance of glutathione disulfide from rat mesenteric vasculature. 799 17

The mechanism for the choleresis induced by CCK-receptor antagonists, proglumide, loxiglumide, and CR 1409, was examined in anesthetized rats and compared to the effects of CCK itself. These agents were infused intravenously over a 2-hr period, and bile flow, and biliary excretion of bicarbonate, total bile acids, and glutathione were measured in 30-min intervals. All three antagonists produced a dose-dependent choleresis, but a significant decrease in bile acid excretion, indicating that they stimulate bile flow via a bile acid-independent mechanism. The increase in bile flow was associated with a parallel increase in biliary glutathione and bicarbonate output in rats treated with proglumide and loxiglumide. In animals pretreated with acivicin to inhibit gamma-glutamyltransferase activity, proglumide was shown to stimulate biliary excretion of reduced glutathione (GSH), but not glutathione disulfide (GSSG), indicating the absence of oxidative stress in the liver. GSH output was increased by only 0.5-0.9 mumol/30 min after infusion of proglumide at a dose of 75 mg/kg/hr, whereas bile volume was increased 0.2-0.4 ml/30 min, indicating that this increased biliary GSH excretion can account for only a small fraction of the increased bile volume, given an osmotic efficiency for GSH of 34 microliters/mumol. In contrast to CCK receptor antagonists, CCK itself had no effect on bile flow and outputs of bicarbonate, GSH, and bile acids, suggesting that the effects of the antagonists are not related to their interaction with CCK receptors. These findings demonstrate that proglumide and loxiglumide stimulate a bile acid-independent bile flow that is only partially explained by an increase in GSH excretion.
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PMID:CCK-receptor antagonists proglumide and loxiglumide stimulate bile flow and biliary glutathione excretion. 808 6

The effect of thyroid hormone administration on liver glutathione (GSH) content and gamma-glutamyltransferase activity in the isolated perfused liver was studied for a period of 1-7 days in fed rats following a single dose of 0.1 mg 3,5,3'-L-triiodothyronine (T3)/kg. T3 elicited an early and transient calorigenic response, together with GSH depletion at 1 day after treatment. Recovery of hepatic GSH content and enhancement in total basolateral gamma-glutamyltransferase activity occurred in parallel 2-3 days after T3 treatment, parameters that were normalized in the 4- to 7-day time interval studied. The increase in total basolateral gamma-glutamyltransferase activity by T3 at early times after treatment was due mainly to increments in its transpeptidation mechanism, and was characterized by increments in the apparent maximum velocities without changes in the apparent Michaelis constant (Km) for the substrate gamma-glutamyl-p-nitroanilide. Data presented suggest that the elevation in sinusoidal gamma-glutamyltransferase activity could be related to the recovery of hepatic GSH content after depletion by T3 treatment, by supplying the precursors for intracellular GSH synthesis, an effect that seems to be mediated by enhanced synthesis of the enzyme.
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PMID:Influence of thyroid hormone administration on hepatic glutathione content and basolateral gamma-glutamyltransferase ectoactivity in the isolated perfused rat liver. 810 Oct 79

To identify potential mechanisms for hepatic removal of circulating glutathione (GSH) conjugates, uptake and metabolism of S-2,4-dinitrophenylglutathione (DNP-SG) were examined in isolated perfused livers from rat and guinea pig. Guinea pig livers perfused with 5 mumol of DNP-SG in a recirculating system (50 microM initial concn) rapidly cleared the conjugate from the perfusate (half time 3.7 min), whereas clearance was considerably slower in rat liver (half time 35 min). Disappearance of DNP-SG from the perfusate was accompanied by a simultaneous appearance of DNP-SG and its metabolites in bile. Addition of acivicin, an inhibitor of gamma-glutamyltransferase (gamma-GT), to the perfusate resulted in a marked decrease in DNP-SG clearance by guinea pig liver but had no effect in rat liver, suggesting that in the guinea pig this process is largely dependent on sinusoidal gamma-GT activity. However, even in the presence of acivicin, rat and guinea pig livers removed nearly one-half of the administered DNP-SG from the recirculating perfusate over 30 min. High concentrations of DNP-SG were found in bile (up to 3.7 mM), indicating that the liver is capable of transporting the intact conjugate from the circulation. When rat livers were perfused with higher concentrations of DNP-SG (100 and 250 microM), biliary excretion of DNP-SG increased dose dependently, with concentrations in bile reaching 10 mM at the higher dose. This was accompanied by a dose-dependent choleresis.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Hepatic uptake of intact glutathione S-conjugate, inhibition by organic anions, and sinusoidal catabolism. 810 95

Various doses of dibromobenzene isomers (1,2-dBB, 1,3-dBB, 1,4-dBB) were administered (i.p.) to BALB mice. The levels of reduced glutathione (GSH) and malondialdehyde (MDA) in the liver, and glutamate-pyruvate transaminase (GPT) (EC.2.6.1.2) gamma-glutamyltransferase (gamma-GT) (EC.2.3.2.2) and triglycerides (TG) in the serum were estimated. A considerable decrease of GSH was observed between 2 and 12 h after administration of the compounds. Increases in serum GPT activity (up to 100-fold) and gamma-GT (three-to fivefold) were observed after treatment using 1,2- and 1,3-dibromobenzenes; TG decreased in concentration initially and then slightly increased. Histopathological examination confirmed the strong necrotic effect of 1,2- and 1,3-dBB isomers. No such changes (elevation of serum GPT activity and necrosis) were noticed after 1,4-dBB.
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PMID:Comparison of hepatotoxicity of 1,2-, 1,3- and 1,4-dibromobenzenes: the dynamics of changes of selected parameters of liver necrosis in acute poisoning in mice. 882 73

The purpose of our study was to investigate the effect of oxidative stress or intracellular glutathione (GSH) depletion on gamma-glutamyltransferase (gamma-GT) activity in cultured type II pneumocytes. Twenty-four hours after isolation, primary cultures of rat type II pneumocytes were preincubated with one of four compounds: 15, 30, 60, 125, 250 microM L-buthionine-[SR]-sulfoximine (BSO) for 3 h; 100, 200, 400, 800 microM tertiary-butylhydroperoxide (t-BOOH) for 45 min; 10, 25, 50, 100 microM menadione for 15 min; 100, 1000 microM paraquat for 1 h. GSH levels, H2O2 and O2.- generation were measured immediately after the incubation, gamma-GT activity and GSH levels also up to 24 h or 48 h later. Exposure to BSO led to a persistent GSH depletion without increase in H2O2 or O2.- production, together with a dose and time-dependent increase (doubling) of gamma-GT activity with a nonsignificant increase in gamma-GT mRNA expression 24 h after exposure to BSO. Exposure to 100 microM menadione, which increased H2O2 production, decreased gamma-GT activity. t-BOOH or paraquat did not give rise to a measurable increase in H2O2 or O2.-. Paraquat did not affect initial GSH levels, but increased GSH and decreased gamma-GT activity 24 h later. t-BOOH (400 and 800 microM) initially decreased GSH, and tended to increase GSH 24 h later, 100 and 200 microM increased gamma-GT activity 24 h later, but 800 microM decreased it. Restoration of intracellular GSH levels by addition of GSH to the culture medium completely prevented the increase in gamma-GT activity by BSO, while the addition of catalase or DMTU had no effect. We conclude that at least two effects are operating upon gamma-GT activity: GSH depletion seems to increase gamma-GT activity, while exposure to compounds generating oxidative stress correlates with a decrease in gamma-GT activity.
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PMID:Increase in gamma-glutamyltransferase by glutathione depletion in rat type II pneumocytes. 898 Oct 45

Rats were used to study acute and subacute hepatotoxicity of 1,3-dibromobenzene (1,3-dBB). In the single-exposure experiment, maximum hepatic 1,3-dBB concentrations were found to occur 1 to 12 h after the exposure, depending on the dose. Maximum concentrations of covalently bound adducts were reached after 12 h. Depletion of hepatic glutathione (GSH) content occurred during the first 24 h following the exposure, but was not accompanied by changes in alanine aminotransferase (ALT) activity. The increased number of doses also did not result in necrotic lesions of the liver. In the subacute (28-day) experiment, higher hepatic GSH levels and increased blood serum gamma-glutamyltransferase (gamma-GT) activity were observed. Exposure to 1,3-dBB resulted in increased porphyrin excretion in urine, without accompanying increase in the removal of delta-aminolevulinic acid (AlA-U). The results indicate that subacute exposure to 1,3-dBB produces porphyrinuria in the rat.
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PMID:Biochemical alterations as measures of acute and subacute hepatotoxicity of 1,3-dibromobenzene in rat. 901 May 91

Although apoptosis has been believed to play important roles in ontogenic development of animals, the molecular mechanism that triggers the regression of liver hemopoiesis during perinatal period is not known. Apoptosis is induced by many factors, such as decrease in growth factors and increased oxygen stress. Because hepatic gamma-glutamyltransferase (GGT) changes markedly during the perinatal period of a rodent, metabolism of glutathione (GSH), a naturally occurring major antioxidant, might change significantly in and around liver cells. To know the possible involvement of apoptosis and GSH metabolism in the regression of hemopoiesis, hepatocytes and hemopoietic cells were isolated from fetal rat liver. Biochemical analysis revealed that, during the perinatal period, hepatic GGT levels transiently increased predominantly with hepatocytes, suggesting a marked change in thiol status in and around these cells. Cell culture analysis revealed that hemopoietic cells but not hepatocytes exhibited a marked apoptosis in a thiol-free medium, as judged from DNA fragmentation. The apoptosis of hemopoietic cells was inhibited by various thiols, such as L-cysteine, N-acetyl-L-cysteine (NAC), and GSH. These observations suggested that a marked change in GSH status in and around liver cells might play critical roles in triggering apoptosis of hemopoietic cells, thereby enhancing the regression of liver hemopoiesis.
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PMID:Role of glutathione metabolism and apoptosis in the regression of liver hemopoiesis. 916 2


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