Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:1.1.1.1 (alcohol dehydrogenase)
 9,284 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

4-Hydroxy-2,3-nonenal is a major aldehydic end-product of lipid peroxidation known to exert several biological and cytotoxic effects and to be produced during conditions of chronic cholestasis. Here we report that viable hepatocytes isolated from cholestatic livers of bile duct-ligated rats (BDL hepatocytes) show a significantly lower rate of HNE metabolism than control cells. This feature is likely to be the consequence of a significant inhibition in the activity of HNE-metabolizing cytosolic glutathione-S-transferase and alcohol dehydrogenase in BDL hepatocytes. Particulate NADP-dependent aldehyde dehydrogenase was also inhibited. No significant change was found for aldehyde reductase activity. A decreased hepatocellular metabolism of HNE can expose liver parenchymal and non-parenchymal cells to cytotoxic as well as pro-inflammatory and pro-fibrogenic effects of HNE, contributing to the development of chronic cholestatic liver damage.
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PMID:Hepatocellular metabolism of 4-hydroxy-2,3-nonenal is impaired in conditions of chronic cholestasis. 767 80

It has previously been reported that isolated rat hepatocytes rapidly and completely metabolize high concentrations of 4-hydroxy-2,3-(E)-nonenal (4-HNE). However, until this report, the degree to which oxidative-reductive and nonoxidative metabolic pathways function in the depletion of 4-HNE by isolated rat hepatocytes has been speculative. The objective of the present study was to quantitate the extent to which cellular aldehyde dehydrogenases (ALDH; EC 1.2.1.3.), alcohol dehydrogenase (ADH; EC 1.1.1.1.), and glutathione S-transferases (GST; EC 2.5.1.18) function simultaneously during hepatocellular metabolism of 4-HNE. Hepatocytes were incubated with varying concentrations of 4-HNE (50, 100, 250 microM) and reversed-phase HPLC was used to quantitate 4-HNE and the oxidative and reductive metabolites, 4-hydroxy-2-nonenoic acid and 1,4-dihydroxy-2-nonene, respectively. Conjugative metabolism of 4-HNE was determined from the depletion of cellular reduced glutathione (GSH) and concomitant formation of a GSH-4-HNE adduct detected as 2,4-dinitrofluorobenzene derivatives measured by reversed-phase HPLC. Hepatocellular elimination of 4-HNE was estimated at rates of 1.666, 0.902, and 0.219 nmol min-1 10(6) hepatocytes-1 for 50, 100, and 250 microM aldehyde, respectively. At aldehyde concentrations of 50, 100, and 250 microM the maximal concentrations of oxidative (acid) metabolites formed were 5.9, 12.7, and 28.9 nmoles 10(6) hepatocytes-1, whereas the concentrations of the reductive (diol) metabolite were 0.4, 12.6, and 42.3 nmoles 10(6) hepatocytes-1, respectively. The presence of 4-methylpyrazole or cyanamide abolished formation of the reductive metabolite 1,4-dihydroxy-2-nonene or the oxidative metabolite 4-hydroxy-2-nonenoic acid in hepatocyte suspensions. At all 4-HNE concentrations evaluated, hepatocellular glutathione was not completely depleted by the aldehyde and the depletion of cellular reduced GSH corresponded to the production of the GSH-4-HNE conjugate. Metabolism by the alcohol/aldehyde dehydrogenase pathways accounted for approximately 10% of the 4-HNE elimination, while bioconversion by GST represent 50-60% of the total 4-HNE removal by hepatocytes. The enzymatic pathways responsible for the remaining 40% of 4-HNE metabolism remain to be identified. Taken together these results describe the quantitative and dynamic importance of oxidative, reductive, and nonoxidative routes in the metabolism and detoxification of 4-HNE.
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PMID:The hepatocellular metabolism of 4-hydroxynonenal by alcohol dehydrogenase, aldehyde dehydrogenase, and glutathione S-transferase. 784 Jun 16

It is well established that many types of tumor cells have reduced lipid peroxidation capacity compared to their normal counterparts. Changes in the activity of enzymes metabolizing aldehydes produced by lipid peroxidation have also been reported in a variety of tumor cells. We have investigated the relationship between changes in lipid peroxidation and changes in aldehyde-metabolizing enzymes in normal hepatocytes and two representative rat hepatoma cell lines, McA-RH-7777 and JM2. Compared to hepatocytes, both 7777 and JM2 cells have significantly lower basal and prooxidant-induced levels of lipid peroxidation than normal hepatocytes. Using 4-hydroxynonenal (4-HNE) as substrate, both cell lines also have significantly reduced activities of alcohol dehydrogenase (ADH) and glutathione S-transferase (GST) compared to hepatocytes. JM2 cells have significantly increased aldehyde dehydrogenase (ALDH) and aldehyde reductase (ALRD) activities with 4-HNE. In 7777 cells the ALDH and ALRD activities are not different from hepatocytes. The changes in enzyme activity are inversely correlated with the sensitivity of cells to 4-HNE. JM2 cells, with increased ALDH and ALRD and decreased ADH and GST, are much more resistant to the toxic effects of 4-HNE than 7777 cells. Normal hepatocytes and JM2 cells are approximately equally resistant to 4-HNE even though hepatocytes rely primarily on GST-mediated aldehyde conjugation to metabolize 4-HNE. Coupled with previous results from our laboratories, the overall increased sensitivity of certain hepatoma cells to lipid aldehydes appears due to decreased ability of these hepatoma cells to remove toxic products of lipid peroxidation. Moreover, hepatoma cells with increased levels of aldehyde dehydrogenase and aldehyde reductase appear most like hepatocytes in their ability to metabolize lipid aldehydes.
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PMID:Role of aldehyde metabolizing enzymes in mediating effects of aldehyde products of lipid peroxidation in liver cells. 803 12

4-Hydroxynonenal (4-HNE), produced during the oxidative lipid breakdown of biological membranes, modulates various biochemical processes in normal liver and in hepatoma cells. It is very probable that the effects of 4-HNE are related to the quantity formed in the cells and to the cells' ability to metabolize it. Aldehyde catabolism takes place within the cells through oxidative and reductive enzymes, and through conjugation with intracellular glutathione. In this paper, the various enzymatic pathways involved in the metabolism of 4-HNE were studied in normal hepatocytes and in hepatoma cells. The hepatocyte pathway undergoes a complex variety of change during neoplastic transformation. In hepatoma cells, generally, 4-HNE metabolism was due mainly to aldehyde dehydrogenases, whereas in normal hepatocytes 4-HNE metabolism was mainly due to alcohol dehydrogenase and glutathione-S-transferase. The increase in oxidative enzymes compared to normal tissue was not the same in all types of hepatoma: in HTC hepatoma cells, the enzyme levels were considerably higher; in AH-130 hepatoma cells of Yoshida, they were lower in subcellular particles and similar in the cytosol. Indeed, consumption of externally-added 4-HNE in hepatoma cells was proportional to their content of 4-HNE metabolizing enzymes.
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PMID:Ability of different hepatoma cells to metabolize 4-hydroxynonenal. 832 85

Our laboratory has previously reported on the ability of 4-hydroxynonenal (4-HNE), a primary product of lipid peroxidation, to inhibit acetaldehyde metabolism in isolated mouse liver mitochondria. The purpose of the present study is to determine whether the co-metabolism of ethanol and 4-HNE compromises the elimination of either substrate in isolated rat hepatocytes. Hepatocytes were isolated and incubated with ethanol and 4-HNE. Ethanol elimination and acetaldehyde accumulation were monitored by gas chromatography, whereas 4-HNE elimination and metabolite accumulation were measured by UV detection and reversed-phase HPLC at 202 nm. In the absence of 4-HNE, hepatocytes metabolized ethanol at an initial rate of 9.4 nmol/min/million cells. Ethanol elimination was moderately inhibited by the presence of 4-HNE. Accumulation of ethanol-derived acetaldehyde was not apparent in incubations with only ethanol. In contrast, in incubations containing both substrates, ethanol-derived acetaldehyde accumulation exceeded that observed in hepatocytes exposed only to ethanol and was proportional to the 4-HNE concentration in the incubations. In all instances, the rate of 4-HNE elimination was not compromised by the presence of ethanol. Accordingly, ethanol metabolism did not alter the oxidative or conjugative metabolism of 4-HNE. However, the reductive metabolism of 4-HNE was affected by the presence of ethanol, wherein accumulation of 1,4-dihydroxy-2-nonene increased > 2-fold of that observed in incubations with only 4-HNE. To determine further if 4-HNE and ethanol are metabolized through the same metabolic pathways, cells were preincubated with either 4-methylpyrazole or cyanamide to inhibit alcohol dehydrogenase (E.C. 1.1.1.1.) and aldehyde dehydrogenase (E.C. 1.2.1.2.), respectively. Expectantly, 4-methylpyrazole blocked the formation of 1,4-dihydroxy-2-nonene, but had no effect on the rate of 4-HNE elimination. In contrast, cyanamide substantially inhibited the formation of 4-hydroxy-2-nonenoic acid, decreased the rate of 1,4-dihydroxy-2-nonene formation, but did not decrease the elimination rate of 4-HNE. Overall, these results support our previous observation that 4-HNE inhibits acetaldehyde metabolism and establish that ethanol and 4-HNE are metabolized through the same alcohol dehydrogenase- and aldehyde dehydrogenase-mediated pathways. These data continue to suggest that, as a consequence of enhanced lipid peroxidation resulting from chronic ethanol consumption, increased 4-HNE levels could compromise cellular elimination of ethanol-derived acetaldehyde and thus function in the potentiation of alcoholic liver fibrosis.
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PMID:Co-metabolism of ethanol, ethanol-derived acetaldehyde, and 4-hydroxynonenal in isolated rat hepatocytes. 911 67

The cellular metabolism of 4-hydroxy-2-nonenal (4-HNE), a cytotoxic and genotoxic product of oxidative stress-induced lipid peroxidation, was investigated in rat H35 hepatoma cells. Previous studies from our laboratory (1) have characterized the degree to which oxidative, reductive, and conjugative metabolic pathways function simultaneously during hepatocellular metabolism of 4-HNE to rapidly eliminate the compound from suspensions of freshly isolated rat hepatocytes. In the current studies, we have extended the investigation of 4-HNE metabolism to examine the pharmacokinetic parameters of 4-HNE elimination and export in a hepatoma cell line and determined that the ensuing oxidative and conjugative metabolites of 4-HNE are rapidly and efficiently transported out the cell. Low concentrations of 4-HNE (25 microM) were used in an attempt to simulate physiologically relevant conditions. The H35 hepatoma cell line studied was first evaluated for enzymes known to play important roles in the metabolism of 4-HNE and were found to possess activities for glutathione S-transferase, aldehyde dehydrogenase (ALDH), and alcohol dehydrogenase of 24.00 +/- 1.12, 3. 45 +/- 0.17, and 6.44 +/- 0.29 nmol min-1 mg-1 protein, respectively. Hepatoma cells were incubated with 25 microM 4-HNE and metabolites in intra- and extracellular fractions were quantitated by reversed-phase HPLC over the time course of treatment. Reduced glutathione (GSH) and the GSH metabolites of 4-HNE were quantitated by reversed-phase HPLC as the dinitrobenzene derivatives. Uptake of 4-HNE from the extracellular medium occurred with an estimated rate of 0.398 +/- 0.181 min-1 10(6) hepatoma cells-1. The oxidative metabolite of 4-HNE, 4-hydroxy-2-nonenoic acid (HNA), produced by ALDH, appeared rapidly in the intracellular fraction achieving concentrations of 0.28 HNA nmol 10(6) hepatoma cells-1 and was efficiently eliminated with a first-order rate constant of 0.988 min-1. The GST-mediated conjugative metabolite, 3-glutathionyl-4-hydroxy-2-nonanal (4-HNE-SG), rapidly reached maximal intracellular concentrations of 1.88 +/- 0.44 nmol 10(6) hepatoma cells-1 and was eliminated at a rate of 0.101 +/- 0.033 min-1. Extracellular rates of formation, representing export, for HNA and 4-HNE-SG were 0.247 +/- 0.045 and 0.044 +/- 0.009 min-1 10(6) hepatoma cells-1, resulting in maximal extracellular concentrations for HNA and 4-HNE-SG of 0.70 +/- 0.10 and 3.03 +/- 0. 84 nmol 10(6) hepatoma cells-1. Approximately 75% of the administered concentration of 4-HNE was converted to measurable metabolites, with the 4-HNE-GSH conjugate accounting for 61% of total administered 4-HNE and HNA accounting for 14%. Collectively, these results demonstrate that oxidative and conjugative pathways are primarily responsible for elimination of 4-HNE at low concentrations in the hepatoma cell line evaluated and that the 4-HNE metabolites resulting from these pathways are rapidly and efficiently exported out of the cell.
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PMID:Formation and export of the glutathione conjugate of 4-hydroxy-2, 3-E-nonenal (4-HNE) in hepatoma cells. 988 35

The glycolytic enzyme glyceraldehyde-3-phosphate dehydrogenase was irreversibly and (S)-selectively inactivated by the enantiomers of racemic 4-hydroxy-2(E)-nonenal (HNE), a reactive product released from biomembranes by lipid peroxidation in cells. Rates of the enzyme inactivations were 1.7, 3.0, and 6.0 M(-1).s(-1) for (R)-, racemic and (S)-HNEs respectively. In rat liver cytosol the HNE was detoxified 2.5-fold more (S)-selectively by GSH conjugation and 2. 4-fold more (R)-selectively by NADH-dependent reduction mediated by alcohol dehydrogenase (ADH) than the opposite enantiomers. However, in the cytosol the GSH conjugation of (R)-HNE proceeded at a much higher rate than did its ADH-mediated reduction. The minor glutathione S-transferase (GST) isoform, A4-4, in the rat (r) liver had a major role in the cytosolic (S)-selective GSH conjugation. The catalytic efficiency, k(cat)/K(m), of purified rGSTA4-4 was 4-fold higher for (S)-HNE than for (R)-HNE; the K(m) was 3-fold higher for (R)-HNE than for (S)-HNE. (S)-HNE was preferentially detoxified to (R)-HNE by rGSTA4-4 when racemic HNE was used as a substrate.
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PMID:4-Hydroxy-2(E)-nonenal enantiomers: (S)-selective inactivation of glyceraldehyde-3-phosphate dehydrogenase and detoxification by rat glutathione S-transferase A4-4. 1090 33

During oxidative stress, reactive aldehydes, including trans-4-hydroxy-2-nonenal (4-HNE), are generated by peroxidation of membrane lipids and purportedly stimulate hepatic stellate cells to produce excessive extracellular matrix, including type I collagen. An important question concerning the ability of 4-HNE to modulate collagen production by stellate cells is the potential of these specialized cells to detoxify 4-HNE. The objective of the present study was to characterize the ability of stellate cell lines, derived from normal (NFSC) and cirrhotic (CFSC) rat livers, to metabolize 4-HNE by oxidative, reductive and conjugative pathways. These two stellate cell lines were noted to have differing susceptibilities to the cytotoxic effect of 4-HNE. Treatment of both stellate cell lines with a range of 4-HNE doses demonstrated that the concentration which was cytotoxic to 50% of CFSC (TD(50)) was 25% greater than that for NFSC (967.57+/-9.26 nmol/10(6) cells vs. 769.90+/-5.32 nmol/10(6) cells respectively). The capacity of these cell lines to metabolizes 4-HNE was determined by incubating them in suspension with 50 microM 4-HNE (10 nmol/10(6) cell); 4-HNE elimination and metabolite formation were quantified over a 20 min time course. Both stellate cell lines rapidly metabolized 4-HNE, with the CFSC line eliminating 4-HNE at a rate that was approx. 2-fold greater than the NFSC line. The rate of 4-HNE metabolism attributable to glutathione S-transferase (GST) was similar in both cell lines, though differential cell specific expressions of GST isoforms GSTP1-1 and GSTA4-4 were observed. The greater rate of 4-HNE elimination by CFSC was attributable to its aldehyde dehydrogenase (ALDH) activity which accounted for approx. 50% of 4-HNE metabolism in CFSC but was insignificant in NFSC. Neither cell line had detectable alcohol dehydrogenase activity or protein levels. Measurement of cellular GSH concentrations revealed that NFSC contain approx. 2-fold greater concentrations of GSH when compared to CFSC and that following 4-HNE treatment, GSH levels were rapidly depleted from both cell lines. Concomitant with 4-HNE mediated GSH depletion, a corresponding increase in the 4-HNE-glutathione adduct formation was observed with the NFSC line forming greater amounts of the glutathione adduct than did the CFSC line. Taken together, these data demonstrate that both stellate cell lines have the capacity to metabolize 4-HNE but that CFSC have a greater rate of metabolism which is attributable to their greater ALDH activity, suggesting that the stellate cells isolated from cirrhotic liver may be differentially responsive to the biologic effects of 4-HNE.
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PMID:Characterization of 4-hydroxy-2-nonenal metabolism in stellate cell lines derived from normal and cirrhotic rat liver. 1101 74

Kupffer cells are known to participate in the early events of liver injury involving lipid peroxidation. 4-Hydroxy-2,3-(E)-nonenal (4-HNE), a major aldehydic product of lipid peroxidation, has been shown to modulate numerous cellular systems and is implicated in the pathogenesis of chemically induced liver damage. The purpose of this study was to characterize the metabolic ability of Kupffer cells to detoxify 4-HNE through oxidative (aldehyde dehydrogenase; ALDH), reductive (alcohol dehydrogenase; ADH), and conjugative (glutathione S-transferase; GST) pathways. Aldehyde dehydrogenase and GST activity was observed, while ADH activity was not detectable in isolated Kupffer cells. Additionally, immunoblots demonstrated that Kupffer cells contain ALDH 1 and ALDH 2 isoforms as well as GST A4-4, P1-1, Ya, and Yb. The cytotoxicity of 4-HNE on Kupffer cells was assessed and the TD50 value of 32.5+/-2.2 microM for 4-HNE was determined. HPLC measurement of 4-HNE metabolism using suspensions of Kupffer cells incubated with 25 microLM 4-HNE indicated a loss of 4-HNE over the 30-min time period. Subsequent production of 4-hydroxy-2-nonenoic acid (HNA) suggested the involvement of the ALDH enzyme system and formation of the 4-HNE-glutathione conjugate implicated GST-mediated catalysis. The basal level of glutathione in Kupffer cells (1.33+/-0.3 nmol of glutathione per 10(6) cells) decreased significantly during incubation with 4-HNE concurrent with formation of the 4-HNE-glutathione conjugate. These data demonstrate that oxidative and conjugative pathways are primarily responsible for the metabolism of 4-HNE in Kupffer cells. However, this cell type is characterized by a relatively low capacity to metabolize 4-HNE in comparison to other liver cell types. Collectively, these data suggest that Kupffer cells are potentially vulnerable to the increased concentrations of 4-HNE occurring during oxidative stress.
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PMID:Metabolism of 4-hydroxynonenal by rat Kupffer cells. 1137 Jun 75

This study assesses whether the HNE accumulation we formerly observed in liver microsomes and mitochondria of BB/Wor diabetic rats depends on an increased rate of lipoperoxidation or on impairment of enzymatic removal. There are three main HNE metabolizing enzymes: glutathione-S-transferase (GST), aldehyde dehydrogenase (ALDH), and alcohol dehydrogenase (ADH). In this study we show that GST and ALDH activities are reduced in liver microsomes and mitochondria of diabetic rats; in contrast, ADH activity remains unchanged. The role of each enzyme in HNE removal was evaluated by using enzymatic inhibitors. The roles of both GST and ALDH were markedly reduced in diabetic rats, while ADH-mediated consumption was significantly increased. However, the higher level of lipohydroperoxides in diabetic liver indicated more marked lipoperoxidation. We therefore think that HNE accumulation in diabetic liver may depend on both mechanisms: increased lipoperoxidation and decreased enzymatic removal. We suggest that glycoxidation and/or hyperglycemic pseudohypoxia may be involved in the enzymatic impairment observed. Moreover, since HNE exerts toxic effects on enzymes, HNE accumulation, deficiency of HNE removal, and production of reactive oxygen species can generate vicious circles able to amplify the damage.
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PMID:Diabetes impairs the enzymatic disposal of 4-hydroxynonenal in rat liver. 1184 25


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