Liver Aldehyde Dehydrogenase Research Articles

Modulation of nitrogen dioxide toxicity by lithium.

The effect of short-term intake of LiCl in drinking fluid on NO2 toxicity was studied in mice as a function of mortality and of specific activities of mouse liver alcohol dehydrogenase (L-ADH) and aldehyde dehydrogenases (L-ALDH). Pretreatment with LiCl for 10 days decreased mortality in mice exposed to 60 to 70 PPM NO2 for 6 hr compared to controls. Pretreatment with LiCl for 10 days under continued exposure to 5 PPM NO2 resulted in a decrease in liver weight compared to control. Lithium treated mice exposed to NO2 showed less gain in body weight than the controls treated with LiCl and exposed to air. The latter group showed an induction of mitochondrial but not cytoplasmic L-ALDH and the NO2 exposure did not alter endogenous L-ALDH from corresponding controls. This induction of mitochondrial ALDH was associated with an increase in both Vmax and the apparent Km. Exposure to NO2 for 10 consecutive days resulted in inhibition of cytoplasmic L-ALDH. The data suggest that Li+ antagonized NO2 toxicity. A possible mechanism for reduction of NO2 toxicity by LiCl may be due to Li+ action on stabilizing cell membranes and/or modifying intercellular pulmonary response to NO2 injury.

Expression of tumor-associated aldehyde dehydrogenase during rat hepatocarcinogenesis using the resistant hepatocyte model.

The resistant hepatocyte model was used to study expression of tumor-associated aldehyde dehydrogenase (ALDH) activity during the course of rat hepatocarcinogenesis. The hepatic ALDH phenotype was determined at intervals over 280 days by histochemical analysis, total ALDH activity assays and gel electrophoresis, using propionaldehyde and NAD (P/NAD) to characterize normal liver ALDH activity or benzaldehyde and NADP (B/NADP) to determine tumor-associated ALDH activity. By total activity assays and gel electrophoresis, no significant changes in ALDH activity occurred until day 70. However, histochemical analysis clearly demonstrated changes in ALDH activity early in neoplastic development. Intense focal hepatocyte staining with P/NAD and/or B/NADP was first detectable at day 28. The number of P/NAD-positive foci increased until day 35 then declined until day 70. The number of B/NADP-positive foci also increased until day 35, but then remained relatively constant for the remainder of the experiment. GGT activity of serial sections indicated that early ALDH-positive lesions represent a small subpopulation (9%) of all GGT-positive foci. However, by day 168 a significant portion (80%) of persistent GGT-positive neoplastic nodules were also B/NADP-positive histochemically. In addition, virtually all hepatocellular carcinomas (96%) generated by this protocol possessed significantly elevated levels of tumor-associated ALDH by histochemical analysis, total ALDH activity and gel electrophoresis. These results indicate that early appearing ALDH-positive lesions may define one early subpopulation of all initiated cells that have a high probability of progressing to the ultimate neoplasm.

Extrapyramidal disorders: A possible underlying mechanism

In vivo and in vitro studies have been presented to suggest an interrelationship between drugs used in the management of, or known for their induction of, extrapyramidal disorder and certain dehydrogenase enzymes involved in ths metabolic pathway of the biogenic amines. This relationship is discussed to advance a tentative hypothesis explaining a possible underlying mechanism and to provide an explanation for the implication of alcohol consumption in worsening of extrapyramidal symptoms during certain pharmacotherapy. The major neutral metabolites of the biogenic amines acted as substrate to or induced rat liver alcohol dehydrogenase (L-ADH) and drugs used in the management of tardive dyskinesia similarly induced L-ADH. This induction of L-ADH could enhance the metabolic biotransformation of the neutral metabolites of the monoamines. Conversely, drugs known to evoke extrapyramidal dyskinesias inhibited rat liver aldehyde dehydrogenase (L-ALDH). This inhibition of ALDH may give rise to toxic condensation products between biogenic amine aldehydes and their precursors which may be implicated in certain dyskinesias. It is proposed that one of the mechanisms underlying the biogenic amine involvement in the pathogenesis of certain extrapyramidal diseases may include a critical balance between their reductive and oxidative routes of metabolism.

Metabolism of malondialdehyde by rat liver aldehyde dehydrogenase

Mammalian liver contains a group of pyridine nucleotide linked aldehyde dehydrogenases [E.C. 1.2.1.3] which are present in high specific activity and possess wide substrate specificities. Malondialdehyde (MDA), a difunctional three-carbon aldehyde thought to be toxic, is generated during membrane lipid peroxidation in hepatocytes. The role of aldehyde dehydrogenase (ALDH) in the metabolism of MDA was tested in vitro with subcellular fractions and semipurified cytosolic preparations from rat livers. The cytosolic fraction accounted for virtually all of the MDA (50 μ m) metabolizing activity observed in the postnuclear supernatant fraction. The rate of MDA disappearance was relatively low in the mitochondrial fraction and was not detectable in reaction mixtures which contained microsomes. Rat liver cytosol contained two ALDHs with MDA metabolizing activity. These enzymes were separated by DEAE-cellulose ion exchange chromatography and had apparent K m values of 16 μ m and 128 μ m for malondialdehyde. Mitochondria contained an ALDH enzyme with lower affinity ( K m of 7.3 m m with NAD +) for malondialdehyde. These data show that rat liver contains at least three ALDH enzymes which oxidize malondialdehyde.

Chlorpromazine and lithium interaction: A biochemical and histological study

Biochemical and histological studies on the effect of separate and combined administration of LiCl and of chlorpromazine (CPZ) on female C 57BL 6J mice were performed. Mice were divided into 4 groups. One group was given an intraperitoneal injection daily of CPZ HCl, 5 mg/kg for 4 days followed by 4 more days of a daily dosage of 10 mg/kg. A second group was maintained on 0.4% ( w v ) LiCl solution as the sole drinking fluid for 8 consecutive days and a third group received the same LiCl solution but with daily CPZ injection as the initial group for 8 days. The fourth group served as saline-controls. Hepatic liver alcohol dehydrogenase was induced by combined drug treatment from respective controls. The Li-treatment inhibited mitochondrial liver aldehyde dehydrogenase, and coadministration of CPZ with LiCl antagonized this effect. Mice treated with CPZ showed corneal cellularity and mitotic figure appearance without inflammation. The LiCl treated mice displayed variations in base corneal cell size, shape and pigmentation with aggregation of the nuclei, and the presence of mitotic activity without inflammation. Mice receiving combined drug treatment showed similar corneal alterations, but mitotic figures were found above base cell layer suggesting an enhanced corneal toxicity. The results suggest a drug-drug interaction phenomenon which may explain some of their adverse reaction when given concurrently.

A chemical and enzymological account of the multiple forms of human liver aldehyde dehydrogenase Implications for ethnic differences in alcohol metabolism

The major low-p I zones of aldehyde dehydrogenase (aldehyde: NAD + oxidoreductase, EC 1.2.1.3) may be visualized with specific histochemical staining after starch gel electrophoresis at pH 7.4 of Caucasian human liver extracts, whereas about 50% of Chinese human liver extracts show only two such zones. The three zones of activity were purified to apparent homogeneity from Caucasian liver. The substrate specificity of each form was investigated by double reciprocal plots using 13 aldehydes of various chemistries. The acetaldehyde-preferring isozyme I lacking in 50% of Chinese livers had a slightly lower native and subunit molecular weight than the ‘universal’ isozymes IIa and IIb. All forms were highly sensitive to disulfiram inbibition. this inhibition could be protected against, or reversed, by dithiothreitol. 2,2′-Dithiodipyridine was a slower inhibitor of isoenzyme I. All three purified forms of the enzyme, as well as crude extracts of normal and isozyme I-deficient Chinese livers, showed positive immunoreactivity to antibodies prepared in rabbits against type I enzyme. Tryptic peptide maps of forms IIa and IIb were almost identical, whereas that of form I, although showing some similarities, was clearly different. These results provide a consistent explanation for the acetaldehyde-mediated extreme sensitivity to moderate alcohol ingestion shown normally by abut 50% of oriental subjects and during disulfiram (Antabuse) therapy by all subjects.

Disulfiram and erythrocyte aldehyde dehydrogenase inhibition.

During disulfiram therapy erythrocyte aldehyde dehydrogenase (ALDH) was fully inhibited. The time for total loss of erythrocyte ALDH activity ranged from 36 to 120 hr. In contrast to the 85% recovery of in vitro disulfiram-inhibited ALDH activity, this in vivo disulfiram-ALDH inhibition could not be reversed by mercaptoethanol. It is proposed that the in vivo and in vitro mechanisms of ALDH inhibition by disulfiram differ. Erythrocyte ALDH activity can be readily monitored to determine patient compliance and is an accessible model for investigations of in vivo mechanisms of drug inhibition. Because the disulfiram-inhibited erythrocyte ALDH is not regenerated until new erythrocytes are made (120 days), a significant portion of the extrahepatic acetaldehyde metabolic capacity remains inhibited for long periods after disulfiram is discontinued. Thus, the recidivistic patient who discontinues disulfiram and waits several days (to regenerate liver ALDH activity) before drinking will be exposed to even higher ethanol-derived blood acetaldehyde levels than usual, which may induce further alcohol-associated organ damage and alcohol dependence.

Determinants of Blood Acetaldehyde Level during Ethanol Oxidation in Chronic Alcoholics

We analyzed the blood alcohol and acetaldehyde concentrations in nine alcoholics and four healthy nonalcoholic controls during and after an intravenous infusion of a high and a low dose of alcohol. In the alcoholics, the mean rates of plasma ethanol disappearance were significantly higher than in nonalcoholic controls. In the control subjects, the blood acetaldehyde levels were, in general, below the detection limit (less than 0.5 microM), but in sharp contrast to this, an elevated blood acetaldehyde during ethanol infusion was found in 6/9 alcoholics. Peak blood acetaldehyde values were higher after the high than the low dose of alcohol. Fructose infusion significantly enhanced the rate of plasma ethanol disappearance both in controls and in alcoholics, and this was usually associated with a significant elevation of blood acetaldehyde level. The maximal specific activities (expressed as milliunits/mg og protein) of alcohol, lactate, and aldehyde dehydrogenases in liver were significantly lower in alcoholics than in controls. Even more importantly, the peak blood acetaldehyde correlated negatively with the activity of hepatic "low-Km" aldehyde dehydrogenase. Our results suggest that the main reason for blood acetaldehyde elevation seen in these chronic alcoholics is their impaired capacity to metabolize acetaldehyde. This may be further accentuated by the increased rate of ethanol oxidation.

Effects of magnesium and calcium on mitochondrial and cytosolic liver aldehyde dehydrogenases

The effects of Mg 2+ and Ca 2+ ions on the activities of mitochondrial and cytosolic aldehyde dehydrogenases isolated from horse, rat, and beef livers were investigated in 0.1 M sodium phosphate, pH 7.5, at 25°C. As with the Mg 2+-enhancement of the horse liver mitochondrial enzyme [17], Mg 2+-activation was observed for the mitochondrial enzymes from rat and beef. The cytosolic enzymes from horse, rat, and beef livers were inhibited in the presence of Mg 2+ ions. The effects of Ca 2+ ions on the activity were essentially the same as those observed in the presence of Mg 2+ ions; the mitochondrial isozymes were activated while the cytosolic isozymes were inhibited. The fact that only the activity of mitochondrial forms of mammalian liver aldehyde dehydrogenase was enhancd by Ca 2+ or Mg 2+ ions may be related to the in vivo regulation of aldehyde metabolism, a presumed mitochondrial event.

Remarkable positional (Regio)specificity of xanthine oxidase and some dehydrogenases in the reactions with substituted benzaldehydes

Upon an increase in the size of the substituent, the reactivity of xanthine oxidase to ortho-substituted benzaldehydes drastically decreases while that to para-substituted benzaldehydes does not change significantly. The enzyme exhibits this regiospecificity with respect to both electron-withdrawing substituents (e.g., halogens) and electron-donating ones (alkyls and alkoxyls). Xanthine oxidase-catalyzed oxidation of m- and p-nitrobenzaldehyde is more than 300-times faster than that of the o-isomer, whereas the rates of their non-enzymatic oxidation are comparable, as are the rates of the enzymatic oxidation of p- and o-nitrocinnamaldehyde. These and other findings of this work indicate that the discovered positional specificity of xanthine oxidase is due to steric hindrances in the reaction of the enzyme's active center with the aldehyde moiety having a bulky substituent in its close proximity. Such regiospecificity of the enzyme exists regardless of the nature of the electron acceptor used and can be employed for the separation of mixtures of positional isomers of substituted benzaldehydes. A marked positional specificity in the xanthine oxidase-catalyzed oxidation of substituted benzaldehydes appears to be a rather general phenomenon: three other enzymes tested, alcohol dehydrogenases from horse liver and yeast and aldehyde dehydrogenase from yeast, all follow a similar pattern in the reactions with para- and ortho-substituted halobenzaldehydes.

Subcellular distribution and kinetic parameters of HS mouse liver aldehyde dehydrogenase

1. Aldehyde dehydrogenase subcellular distribution studies were performed in a heterogeneous stock (HS) of male and female mice ( Mus musculus) with propionaldehyde (5 mM and 50 μM) and formaldehyde (1 mM) and NAD + or NADP +. 2. The relative percents of distribution were: cytosolic 55–68%, mitochondrial 12–20%, microsomal 9–18% and lysosomal 3–15% for both propionaldehyde concentrations and NAD +. 3. Kinetic experiments using propionaldehyde and acetaldehyde with NAD + revealed two separate enzymes, Enzyme I (low K m ) and Enzyme II (high K m ) in the cytosolic and mitochondrial fractions. 4. The kinetic data also indicated a spectrum of cytosolic low K m values that exhibited a bimodal distribution with one −40 μM and one −5 μM. 5. It was concluded that there was no significant difference in aldehyde-metabolizing capability between male and female HS mice, compared on a per gram of liver basis. The cytosolic low K m enzyme plays a major role in aldehyde oxidation at moderate to low aldehyde concentrations.

Effects of cephem antibiotics on rat liver aldehyde dehydrogenases.

Effects of cephem antibiotics, which have a tetrazolethiol side chain, on rat liver mitochondrial aldehyde dehydrogenases (ALDH) were investigated in vitro and in vivo. The antibiotics tested were cefmetazole (CMZ), cefamandole (CMD), cefotiam (CTM), cefoperazone (CPZ) and latamoxef (LMOX). The antibiotics inhibited low-Km ALDH activity by 17-30% at 5 mM in vitro. The degrees of inhibition were in the order: CMZ = CTM = CMD greater than LMOX greater than CPZ. Disulfiram inhibited the enzyme activity by 50% at approx. 40 microM. The antibiotics (except CTM) at a dose of 1,000 mg/kg i.v. inhibited the low-Km ALDH activity by 36-52% of the control 24 hr after pretreatment, but did not alter the high-Km ALDH activity. The degrees of inhibition were in the order: LMOX = CMD greater than CPZ greater than CMZ. Disulfiram at a dose of 300 mg/kg p.o. markedly inhibited the low-Km ALDH activity, but did not alter the high-Km ALDH activity. The blood acetaldehyde levels during ethanol metabolism were elevated 1.3-2.6 times in rats treated with the cephem antibiotics (except CTM) for 24 hr at a dose of 1,000 mg/kg i.v. The degrees of elevation at 1 hr after ethanol injection were in the order: LMOX greater than CMD greater than CPZ greater than CMZ. The present experiments demonstrated that the rise in blood acetaldehyde levels coincided with the inhibition rates of the low-Km ALDH activity by the cephem antibiotics.

A two-site model for the esterase and dehydrogenase activities of sheep liver aldehyde dehydrogenase

Although aldehyde dehydrogenase (ALDH) from sheep liver cytosol has a broad specificity, it will not oxidize the aldehyde group of glyoxylic acid which is in fact an inhibitor of the enzyme. The inhibition pattern is non-linear but competitive at high propionaldehyde concentrations (2–20 mM); however, a simple non-competitive pattern is observed at low (< 100 μM) propionaldehyde concentrations (K i = 1.6 mM). The esterase activity was unaffected by glyoxylic acid in the absence of NAD + but a simple competitive inhibition pattern (K i = 2.5 mM) was observed with respect to 4-nitrophenyl acetate in the presence of NAD +. The data require a two-site model in which ester and aldehyde binding sites are distinct but with a second propionaldehyde molecule, and glyoxylic acid, binding at or near the ester binding site. Consistent with this model is the fact that chloral hydrate was a non-competitive inhibitor of the esterase activity in the presence of NAD + but a competitive inhibitor in its absence. The enzyme exhibited hysteretic behavior governed by the protonated form of an ionizable group with an apparent pK a of 7.55.

Activity and electrophoretic profiles of liver aldehyde dehydrogenases from mice of inbred strains with different alcohol preference

1. 1. The activity of low K m-aldehyde dehydrogenase (ALDH) in the liver mitochondrial fraction (MT-fraction) from male C57BL/6J strain mice (alcohol preferring) was significantly higher than that from DBA/2 mice (alcohol avoiding). The F 1 hybrids (C57BL/6J × DBA, 2) did not exhibit the intermediate activity to these two strains. 2. 2. Strain differences in liver mitochondrial ALDH isozymcs were observed by isoelectric focusing. C57BL/6J strain had two isozymes at pH 7.1 while DBA/2 had no band at this pH. F 1 hybrid mice had similar two bands with lower density to those of C57BL/6J at pH 7.1. There was no difference in zymograms of the soluble fraction between C57BL/6J and DBA/2 strains. 3. 3. The present results suggest that the difference in alcohol preference of mice may depend on some restricted ALDH isozymes with different pI or electric mobility rather than the enzymatic activity in the liver MT-fraction.

Structural relationships among aldehyde dehydrogenases

Two functional regions of liver aldehyde dehydrogenase were characterized before; other structures of homologous parts from isoenzymes have now been determined to obtain further information on the isoenzyme relationships. In a 22-residue region from the horse cytoplasmic and mitochondrial isoenzymes, substitutions occur at 12 positions, including a continuous six-residue portion characterized by non-conservative changes. In contrast, the same structure from the cytoplasmic isoenzyme shows exchanges at only three positions when compared to its counterpart from human cytoplasm. A similar estimate of substitution frequency between species is obtained from a larger sampling at 236 positions. Thus, the isoenzyme difference between aldehyde dehydrogenase from the same species is about five-fold greater than the species difference between corresponding isoenzymes. Hence, the relationship between cytoplasmic and mitochondrial aldehyde dehydrogenases, while recognizable, is distant. This is compatible with the fact that a property such as high sensitivity to disulfiram is a characteristic of only the cytoplasmic isoenzyme.

Identification of a segment containing a reactive cysteine residue in human liver cytoplasmic aldehyde dehydrogenase (isoenzyme E1).

A single cysteine residue is selectively alkylated by iodoacetamide in cytoplasmic human liver aldehyde dehydrogenase (isoenzyme E1). The amino acid sequence of a 35-residue fragment containing this residue is determined, showing two additional cysteine residues and also three histidine residues. The alkylation is selective for Cys-30 of this fragment, with only little alkylation even at an adjacent residue, Cys-29. The region examined is likely to be of significance in the reaction of this isoenzyme with disulfiram since disulfiram blocks the selective alkylation.

Interaction of di-(2-ethylhexyl) phthalate with the pharmacological response and metabolic aspects of ethanol in mice

The interactions of di-(2-ethylhexyl) phthalate (DEHP) with the pharmacological response and metabolic aspects of ethanol in mice were investigated at oral doses of DEHP of 1.5, 3.0 and 7.5 g/kg or intraperitoneal doses of 3.7, 7.5 and 18.9 g/kg, administered once or daily for 7 days. A single oral or intraperitoneal administration of DEHP resulted in a significant increase in the ethanol-induced sleeping time, associated with an inhibition of alcohol dehydrogenase activity in liver; the effect of intraperitoneal administration was significant only at the highest dose. The activities of high and low K m aldehyde dehydrogenases in mouse liver were not affected by a single dose of DEHP by either route. Repeated oral doses of DEHP produced significant reductions in the ethanol-induced sleeping time and increases in the activities of alcohol and aldehyde dehydrogenases, whereas repeated intraperitoneal doses of DEHP significantly increased the sleeping time and decreased the activity of alcohol dehydrogenase, without any perceptible effect on the activities of aldehyde dehydrogenases. In vitro studies with mouse liver preparations revealed significant inhibition of alcohol dehydrogenase activity by mono-(2-ethylhexyl) phthalate and 2-ethylhexanol and of high and low K m aldehyde dehydrogenase activitieses by DEHP and mono-(2-ethylhexyl) phthalate at concentrations ranging from 0.03 to 1.00 mM. In all cases, in vitro enzyme inhibition by mono-(2-ethylhexyl) phthalate was most pronounced.

Effect of the central ?-adrenoblocker IEM-611 on alcohol and aldehyde dehydrogenases in rat liver

Effect of the central ?-adrenoblocker IEM-611 on alcohol and aldehyde dehydrogenases in rat liver

Inhibition of aldehyde dehydrogenases in rat brain and liver by disulfiram and coprine.

Rats were treated with either coprine or disulfiram and the inhibition of aldehyde dehydrogenase (ALDH) in liver and brain mitochondria was measured with acetaldehyde, 3,4-dihydroxyphenylacetaldehyde (DOPAL), and succinate semialdehyde at different concentrations. The inhibition pattern was similar for both inhibitors, but the degree of inhibition was lower with disulfiram. The ALDH activity both in the liver and the brain was inhibited at low concentrations of acetaldehyde and DOPAL, but not with succinate semialdehyde. The high-Km enzyme activities with acetaldehyde were not inhibited in liver and brain. The activity at high concentration of DOPAL was inhibited in the liver, but only slightly affected in the brain, suggesting the presence of a brain enzyme with an intermediate Km value for DOPAL. In contrast with the results observed in vivo, it was found that the high-Km activities with acetaldehyde and DOPAL in brain mitochondrial preparations were more sensitive to the inhibitors in vitro than the low-Km activities. Kinetic studies on ALDH preparations from brain and liver mitochondria suggested that acetaldehyde and DOPAL are metabolized by the same low-Km ALDH.

Oxidation of the 17-aldol (20β hydroxy-21-aldehyde) intermediate of corticosteroid metabolism to hydroxy acids by homogeneous human liver aldehyde dehydrogenases

In human liver, the oxidation of corticosteroids to 20-hydroxy-21-oic acids proceeds via the formation and oxidation of aldol (20-hydroxy-21-aldehyde) intermediates. Human liver aldehyde dehydrogenases E 1 and E 2, which we have previously purified to homogeneity, catalyzed the oxidation of steroid aldols by NAD + to 20-hydroxy-21-oic acids. The hydroxy acids formed after oxidation of the aldol isomer of cortisol (isocortisol) or of 11-deoxycorticosterone (isoDOC) by E 1 and E 2 respectively, were identified by the criteria of chromatographic mobility, derivatization, and reverse isotope dilution of 4- 14C labeled acid end products. Both enzymes showed broad substrate specificity and oxidized both 17-hydroxy and 17-deoxy steroids, though at widely varying rates. Kinetic analysis of the course of oxidation of isocortisol and isoDOC by NAD + gave intersecting initial velocity plots that conform with a sequential mechanism. The inhibition patterns for both enzymes with thionicotinamide adenine dinucleotide or chloral hydrate were consistent with random sequential behavior.