Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: UMLS:C1332347 (ADH)
 2,230 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

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.
 ...
PMID:The hepatocellular metabolism of 4-hydroxynonenal by alcohol dehydrogenase, aldehyde dehydrogenase, and glutathione S-transferase. 784 Jun 16

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.
 ...
PMID:Metabolism of 4-hydroxynonenal by rat Kupffer cells. 1137 Jun 75

The lipid peroxidation product 4-hydroxynonenal (4-HNE) has been shown to interfere with protein function. The goal of this study was to determine the effects of substrate modification by 4-HNE on protein degradation. Equine liver alcohol dehydrogenase (ADH, EC 1.1.1.1) treated with 2-fold molar excess 4-HNE was degraded by a rabbit reticulocyte lysate (RRL) system approximately 1.5-fold faster than control, while treatment with concentrations up to 100-fold molar excess aldehyde were inhibitory to degradation. Involvement of the 26S proteasome (EC 3.4.99.46) was demonstrated through the use of specific proteasome and ATPase inhibitors, and confirmed by measuring the extent of ADH polyubiquitination. Tryptic digestion and LC/MS analysis of 4-HNE-treated ADH identified modification of two zinc chelating Cys residues. Through molecular modeling experiments a conformational shift in both zinc-containing regions was predicted, with an approximate doubling of the distance between the structural zinc and its respective chelating residues. Modification of residues in the active site zinc binding motif resulted in less pronounced alteration in protein structure. The data presented here demonstrate accelerated ubiquitination and proteasomal degradation of ADH modified with 4-HNE, and suggest a conformational change after 4-HNE docking as a mechanism behind these observations.
 ...
PMID:4-Hydroxynonenal regulates 26S proteasomal degradation of alcohol dehydrogenase. 1545 82