Liver Aldehyde Dehydrogenase Activity Research Articles

Enhanced 5-HT2A Receptors in Brain Stem and ALDH Activity in Brain Stem and Liver: 5-HT2A Regulation on ALDH in Primary Hepatocytes Cultures In Vitro

Brain serotonin (5-HT) modulates the neural effects of ethanol. In the present study, we investigated the changes in 5-HT level, 5-HT(2A) receptor binding and aldehyde dehydrogenase (ALDH) activity in brain stem and liver of ethanol treated rats and 5-HT(2A) regulation on ALDH in hepatocyte cultures in vitro. The 5-HT content in the brain stem and liver significantly decreased with an increased 5-HIAA/5-HT ratio in the ethanol treated rats compared to control. Scatchard analysis of [(3)H] (+/-)2,3-dimethoxyphenyl-1-[2-(-4-piperidine)-methanol] [(3)H] MDL 100907 against ketanserin in brain stem of ethanol treated rats showed a significant increase in B (max) without any change in K (d) compared to control. The competition curve for [(3)H] MDL 100907 against ketanserin fitted one-site model in both control and ethanol treated rats with unity as Hill slope value. A significant increase in V (max) of ALDH activity in liver and a significant decrease in K (m) in liver and brain stem of ethanol treated rats compared to control was observed. In 24 h culture studies, an increase in enzyme activity was observed in cells in medium with 10% ethanol. The elevated ALDH activity in ethanol treated cells was reversed to control level in presence of 10(-5) and 10(-7) M 5-HT. Ketanserin, an antagonist of 5-HT(2A), reversed the effect of 5HT on 10% ethanol induced ALDH activity in hepatocytes. Our results showed that there was a decreased 5-HT content with an enhanced 5-HT(2A) receptor and aldehyde dehydrogenase activity in the brain stem of alcohol treated rats and in vitro hepatocyte cultures. The enhanced ALDH activity in ethanol supplemented hepatocytes was reversed to control level in presence of 10(-5) and 10(-7) M 5-HT.

Enhanced dopamine D2 receptor function in hypothalamus and corpus striatum: their role in liver, plasma and in vitro hepatocyte ALDH regulation in ethahol treated rats

Dopamine D(2) receptors are involved in ethanol self- administration behavior and also suggested to mediate the onset and offset of ethanol drinking. In the present study, we investigated dopamine (DA) content and Dopamine D(2) (DA D(2)) receptors in the hypothalamus and corpus striatum of ethanol treated rats and aldehyde dehydrogenase (ALDH) activity in the liver and plasma of ethanol treated rats and in vitro hepatocyte cultures. Hypothalamic and corpus striatal DA content decreased significantly (P < 0.05, P < 0.001 respectively) and homovanillic acid/dopamine (HVA/DA) ratio increased significantly (P < 0.001) in ethanol treated rats when compared to control. Scatchard analysis of [(3)H] YM-09151-2 binding to DA D(2) receptors in hypothalamus showed a significant increase (P < 0.001) in B(max) without any change in K(d) in ethanol treated rats compared to control. The K(d) of DA D(2) receptors significantly decreased (P < 0.05) in the corpus striatum of ethanol treated rats when compared to control. DA D(2) receptor affinity in the hypothalamus and corpus striatum of control and ethanol treated rats fitted to a single site model with unity as Hill slope value. The in vitro studies on hepatocyte cultures showed that 10(-5) M and 10(-7) M DA can reverse the increased ALDH activity in 10% ethanol treated cells to near control level. Sulpiride, an antagonist of DA D(2), reversed the effect of dopamine on 10% ethanol induced ALDH activity in hepatocytes. Our results showed a decreased dopamine concentration with enhanced DA D(2) receptors in the hypothalamus and corpus striatum of ethanol treated rats. Also, increased ALDH was observed in the plasma and liver of ethanol treated rats and in vitro hepatocyte cultures with 10% ethanol as a compensatory mechanism for increased aldehyde production due to increased dopamine metabolism. A decrease in dopamine concentration in major brain regions is coupled with an increase in ALDH activity in liver and plasma, which contributes to the tendency for alcoholism. Since the administration of 10(-5) M and 10(-7) M DA can reverse the increased ALDH activity in ethanol treated cells to near control level, this has therapeutic application to correct ethanol addicts from addiction due to allergic reaction observed in aldehyde accumulation.

Decreased dopamine D2 receptor function in cerebral cortex and brain stem: their role in hepatic ALDH regulation in ethanol treated rats

Ethanol exerts numerous pharmacological effects through its interaction with various neurotransmitters. The dopaminergic pathway is associated with cognitive, endocrine, and motor functions, and reinforcement of addictive substances or behaviours. Aldehyde dehydrogenase (ALDH) is a vital enzyme involved with alcohol metabolism and detoxification. In the present study, we investigated the role of cerebral cortex and brain stem dopamine D(2) receptors in the functional regulation on ALDH enzyme activity, in ethanol administrated rats. Two groups of rats were selected viz. control and alcoholic. Cerebral cortex, brain stem and the liver dopamine content was decreased significantly (P < 0.05, 0.05, 0.001, respectively) and homovanillic acid/dopamine (HVA/DA) ratio has significantly increased (P < 0.05, 0.001 and 0.001), respectively in ethanol treated rats when compared to control. Scatchard analysis of [(3)H]YM-09151-2 binding to synaptic membrane preparations of cerebral cortex and brain stem showed a significant decrease (P < 0.001, 0.05, respectively) in B (max) in ethanol treated rats compared to control and the K (d) also decreased significantly (P < 0.05). The ALDH analysis showed a significant increase (P < 0.05) in V (max) in cerebral cortex, plasma and liver of experimental rats when compared with control without having significant change in brain stem but with decreased K (m) (P < 0.001). Our results suggest that decreased function of dopamine mediated through DA D(2) receptor in the cerebral cortex and brain stem enhanced the brain, plasma and liver ALDH activity in ethanol treated rats. This ALDH regulation has significance to correct alcoholics from addiction due to allergic reaction observed in aldehyde accumulation.

Aldehyde dehydrogenase of mice inhibited by thiocarbamate herbicides

The herbicide S -ethyl N,N -dipropylthiocarbamate (EPTC) and three of its candidate metabolites (the sulfoxide, N -depropyl and S -methyl derivatives) inhibit mitochondrial low-K m aldehyde dehydrogenase (ALDH) in liver by 56 to 82% 2 hr after these thiocarbamates are administered intraperitoneally (ip) to mice at 8 mg/kg. They also greatly elevate the acetaldehyde level (determined as the O -benzyloxime ether) in blood (up to 500 μM) and brain (up to 3 ppm) 30 min after two ip treatments, the first with the thiocarbamate at 40 mg/kg and 2 hr later with ethanol at 1000 mg/kg. EPTC at 4 mg/kg inhibits liver ALDH activity by 50% and at 8 and 18 mg/kg gives half of the maximum ethanol-dependent elevation of acetaldehyde levels in blood and brain, respectively. The in vivo effects of other thiocarbamate herbicides at 8 mg/kg on ALDH activity and 40 mg/kg on acetaldehyde levels decrease in the order of thiobencarb, pebulate, vernolate and molinate > butylate and triallate >> cycloate. The percentage inhibition of liver ALDH activity generally correlates with the elevation in blood and brain acetaldehyde under these treatment protocols. B.W. Hart and M.D. Faiman ( Biochem. Pharmacol. 43 403–406, 1992) have shown that the alcohol-aversion drug disulfiram is metabolized to S -methyl N,N -diethylthiocarbamate and its sulfoxide as the penultimate and ultimate metabolites inhibiting ALDH. Thus, the thiocarbamate herbicides and their metabolites are similar to the disulfiram metabolites not only in homologous structure but also in their potency range as ALDH inhibitors in vivo . On this basis some of the thiocarbamate herbicides may sensitize agricultural workers to ethanol intoxication.

Acceleration of ethanol metabolism by past thiamine deficiency.

Six months after severe thiamine deficiency, when their body and liver weights had normalized, male Sprague-Dawley rats were exposed to constant ethanol vapor concentrations for 6 days in an inhalation chamber and blood ethanol concentrations (BECs) were determined. Previously induced thiamine deficiency was associated with about a 50% reduction of BECs and a significant increase in liver alcohol dehydrogenase (ADH) activity suggesting a persistent acceleration of ethanol metabolism. No significant changes were found in liver aldehyde dehydrogenase activity, plasma levels of thyroxine, testosterone, or estradiol, or brain or liver histology. Plasma growth hormone concentrations were about 60% lower in the experimental group than in controls, but this effect of previous thiamine deprivation did not correlate with changes in ADH activity. Therefore, it remains to be elucidated how thiamine deficiency-induced central nervous system alterations may contribute to the development of metabolic tolerance to ethanol.

O-031 - Inhibition by disulfiram of aldehyde dehydrogenase activity in liver and intestine and the participation of intestinal enzyme in the in vivo metabolism of alcohol.

O-031 - Inhibition by disulfiram of aldehyde dehydrogenase activity in liver and intestine and the participation of intestinal enzyme in the in vivo metabolism of alcohol.

Effect of disulfiram on canine liver aldehyde dehydrogenase activity: in vivo inactivation in a nonrodent animal model.

Dogs were used as nonrodent animal models to study the in vivo effects of disulfiram on hepatic aldehyde dehydrogenase (ALDH) activity. Dogs were treated with disulfiram either intraperitoneally or orally (100 mg/kg/day for 2 days followed by 40 mg/kg/day for 3 days). Liver biopsies from control and treated animals were fractionated by differential centrifugation and the subcellular fractions were analyzed for ALDH activity. Significantly less activity was observed in cell homogenates from treated animals (20-50% of control activity per gram of liver). The majority of loss in activity was accounted for by a decrease in ALDH activity in the soluble fraction of the cell (12-30% of control activity) and in the mitochondrial fraction (23-30% of control activity). Activities at both high (5 mM) and low (50 microM) acetaldehyde concentrations were affected. The subcellular distribution of ALDH activity and in vivo inhibition by disulfiram in dogs is different from that reported for rats.

Changes in aldehyde dehydrogenase activity during diethylnitrosamine-initiated rat hepatocarcinogenesis.

Diethylnitrosamine following partial hepatectomy followed by phenobarbital promotion was used to study changes in aldehyde dehydrogenase (ALDH) activity during rat hepatocarcinogenesis. Over a period of 350 days, animals were killed at intervals and the ALDH phenotype of normal liver and any lesions was characterized by histochemical analysis, total activity assays and gel electrophoresis using propionaldehyde and NAD+ to detect normal liver ALDH activities, and benzaldehyde and NADP+ for tumor-associated ALDH. In contrast to previously tested protocols, no significant changes in ALDH activity were demonstrable by histochemistry or total activity assays in preneoplastic livers. However, nine of 16 (56%) of the hepatocellular carcinomas examined expressed the tumor-associated ALDH phenotype. The present results are integrated with previous observations as a hypothesis explaining the roles of initiation and promotion in expression of the tumor-associated aldehyde dehydrogenase phenotype.

Comparative subcellular distribution of aldehyde dehydrogenase in rat, mouse and rabbit liver

The subcellular distribution of hepatic aldehyde dehydrogenase (ALDH) activity was determined in Buffalo, Fischer 344, Long-Evans, Sprague-Dawley, Wistar and Purdue/Wistar rats. These subcellular distributions were compared to the distribution of mouse and rabbit liver ALDH. For the six rat strains, at millimolar propionaldehyde concentrations, NAD-dependent ALDH activity was associated primarily with mitochondria (51%) and microsomes (30%). At millimolar acetaldehyde concentrations, NAD-dependent ALDH was primarily mitochondrial (up to 80%). Less than 1% of total NAD-dependent aldehyde dehydrogenase was found in the cytosol. The highly inbred Purdue/ Wistar line possessed significantly less acetaldehyde-NAD ALDH activity as well as less total NADP-dependent ALDH activity than the other strains. In CD-1 mouse liver, millimolar K m NAD-dependent ALDH activity was found in mitochondria (60%), microsomes (23%) and cytosol (5%). In rabbit liver, millimolar K m NAD-dependent ALDH was also distributed among mitochondria (36%), microsomes (19%) and cytosol (28%). At micromolar substrate concentrations, mitochondria possessed the majority of rat, mouse and rabbit liver ALDH activity. In all three species, NADP-dependent ALDH activity was found predominantly in the microsomal fraction (up to 65%). The cytosol possessed little NADP-dependent ALDH in any species. We conclude that there are significant species differences in the subcellular distribution of aldehyde dehydrogenase between rat, mouse and rabbit liver. In all three species, mitochondria and microsomes possessed the majority of hepatic aldehyde dehydrogenase activity. However, the cytosol of mouse and rabbit liver also made a significant contribution to total ALDH activity. For the six rat strains examined, liver cytosol possessed little or no ALDH activity.

Enhancement of Aldehyde Dehydrogenase Activity in Rat Liver by Clofibrate Feeding

Treatment over a 3-week period of male rats with the hypolipidemic drug clofibrate results in a more than twofold increase of aldehyde dehydrogenase activity in liver homogenate and mitochondrial fraction. As a comparable rise is also found in the postmitochondrial fraction, it is suggested that not only the mitochondrial but also the microsomal moiety of aldehyde dehydrogenase is induced by clofibrate. Possibly the known enhancement of ethanol catabolism and some protective effect on the liver of clofibrate-treated animals is due, at least in part, to the increased acetaldehyde oxidation by liver aldehyde dehydrogenase.

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.

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.

The influence of age, sex and genotype on the subcellular distribution of hepatic aldehyde dehydrogenase activity in the mouse

1. 1. The influence of age on hepatic aldehyde dehydrogenase (AlDH) was studied in both sexes of two selectively bred lines of mice ( Mus musculus). 2. 2. Whole liver AlDH activity increased from the 60-day-old level linearly up to 200 days of age. The enzyme activity of the females remained at the 200-day-old level, but in males, AlDH continued to increase up to 400 days of age. Males had higher AlDH activity than females. 3. 3. The AlDH activities of 3 subcellular fractions: cytosol, mitochondria and microsomes also increased with age, but were more dependent on sex and genotype than was the whole liver activity. 4. 4. It was concluded that AlDH activity increases with age in mouse liver but it was influenced greatly by sex, genotype and subcellular fraction studied.

Aldehyde dehydrogenase inhibitors and voluntary ethanol drinking by rats.

Aldehyde dehydrogenase (ALDH) inhibitors, cyanamide (200 mg or 40 mg/kg food) and coprine (N5-(hydroxycyclopropyl)-L-glutamine, 500 mg/kg food), strongly suppressed, with similar time courses, the free-choice consumption of 10% v/v ethanol. The suppression occurred with both continual and alternate access to alcohol. The presence of the inhibitors (plus 4-methylpyrazole to prevent acetaldehyde accumulation) did not affect ethanol-induced (1.5 g/kg i.p.) motor impairment on the tilting plane, but the rats on alternate-day access, which consumed more alcohol on days of access, were significantly less impaired.

The aversive effect of acetaldehyde on alcohol drinking behavior in the rat.

There are a number of indications suggesting that acetaldehyde (AcH) is one factor affecting the alcohol drinking behavior in laboratory animals. In the present study, the voluntary alcohol consumption in a free-choice situation was recorded in 17 females Sprague-Dawley rats fed with two different diets. The first diet (commercial Astra-Ewos, Sweden) caused significantly (p less than 0.001) higher blood AcH concentrations after oral alcohol administration and lower alcohol preferences (alcohol intake as percentage of total fluid intake) than the other diet (prepared at the Alko laboratories). With the Alko diet, the individual preference values correlated negatively with the blood AcH concentrations (p less than 0.01) and positively with the liver aldehyde dehydrogenase activities (p less than 0.05). Hepatic alcohol oxidation rate was found to correlate positively with the AcH concentrations from perfused livers (p less than 0.05) and negatively with the alcohol preferences (p less than 0.05), Alko diet). The results are discussed considering a possible biphasic relation between the AcH metabolism and alcohol drinking behavior.

Elevated blood acetaldehyde in alcoholics with accelerated ethanol elimination

Alcoholics and controls given ethanol (1.2 g/kg body weight) were analyzed for blood and breath acetaldehyde using the more sensitive and reliable semicarbazide method. The acetaldehyde levels in controls were almost undetectable (less than 2 microM), but were found to be elevated (10--10 microM) in 6 of 8 alcoholics. Breath acetaldehyde and blood acetaldehyde co-fluctuated during the experiments. Fructose infusion transiently increased blood acetaldehyde, but only in 4 of the alcoholics. The apparent discrepancy between our finding and the simultaneously reported low acetaldehyde level in alcoholics (Eriksson and Peachy, this volume) may be explained by the different status of the alcoholics tested. Our alcoholics were tested on the day after hospital admission and eliminated ethanol 5% faster than controls. It is suggested that elevated blood acetaldehyde occurs regularly after interrupted drinking in heavy alcohol abusers with fast ethanol elimination, possibly combined with reduced liver aldehyde dehydrogenase activity, but that the phenomenon may rapidly disappear upon abstinence and hospital treatment, which reduces disturbances in hepatic functions and the ethanol elimination rate.

Liver alcohol and aldehyde dehydrogenase: inhibition and potentiation by histamine agonists and antagonists.

1. The in vitro effects of histamine, some other H1- and H2-receptor agonists and some antagonists were studied on the specific activities and kinetics of rat liver alcohol dehydrogenase (ADH), and cytoplasmic and mitochondrial liver aldehyde dehydrogenase (ALDH). 2. Histamine (H1- and H2-agonist) non-competitively inhibited ADH. There were no changes of cytoplasmic and mitochondrial liver ALDH activities in the presence of 2-(2-aminoethyl) pyridine. 3. Betazole (H2-receptor agonist) produced a competitive inhibition of mitochondrial ALDH but not of ADH or cytoplasmic ALDH. 4. Diphenhydramine (H1-receptor antagonist) non-competitively inhibited ADH at a lower concentration. It stimulated mitochondrial ALDH activity without changes in cytoplasmic ALDH from control values. 5. Burimamide (H2-receptor antagonist) produced a biphasic and dose-dependent stimulation and non-competitive inhibition of ADH and it non-competitively inhibited ALDH in both cytoplasmic and mitochondrial fractions. Metiamide (H2-receptor antagonist) non-competitively inhibited all ADH and ALDH of both liver fraction studied. 6. It is concluded that liver ADH and ALDH activity can be altered by compounds which affect both H1- and H2-histamine receptors and that these compounds may cause an in vivo potentiation and/or reduction of the toxic effect of ethanol.

Brain aldehyde dehydrogenase: Adaptive increase following prolonged ethanol administration in rats

Chronic ethanol ingestion (8–12 g/kg bodyweight per day) by rats led to a significant rise in the levels of total brain aldehyde dehydrogenase (ALDH) activity. This effect was noted after 60 days from the start of the ethanol regimen and was found to parallel reduction in levels of liver ALDH activity. Neither the normal levels of whole brain ALDH activity nor ALDH inducibility were significantly affected by age. Furthermore, while the normal level of brain ALDH was consistently higher in females, the magnitude of induction of the enzyme was larger in males. Finally, there were differences in normal levels of ALDH as well as in ALDH inducibility between the cortex, the midbraindiencephalon and the cerebellum. The data suggest that induction of brain ALDH activity may reflect a physiological mechanism that mediates the adaptation of neurones in the brain to some of the acetaldehyde-mediated effects of ethanol. The implications of these findings to the development of tolerance to ethanol are discussed.

Aldehyde dehydrogenase in 2-acetylaminofluorene-induced rat hepatomas. Characterization of antigens recognized by anti-hepatoma aldehyde dehydrogenase sera

The material in normal rat liver which cross-reacts with anti-hepatoma aldehyde dehydrogenase sera has been partially purified. The normal liver cross-reacting material is a series of proteins electrophoretically identical to the series of hepatoma-specific aldehyde dehydrogenases (aldehyde:NAD(P) + oxidoreductase, EC 1.2.1.5) induced by 2-acetylaminofluorene. The molecular weights (100 000) and the isoelectric points (6.8–7.2) of the cross-reacting material are identical to the molecular weights and pI values of the hepatoma-specific isozymes. Absorption of anti-hepatoma aldehyde dehydrogenase sera with the cross-reacting material removes an antibody population which recognizes a normal liver aldehyde dehydrogenase. This isozyme accounts for 35% of the total normal liver aldehyde dehydrogenase. A second antibody population recognizes an antigen which accounts for 10% of the total normal liver aldehyde dehydrogenase. Approx. 55% of the normal liver aldehyde dehydrogenase activity is not recognized by any antibody population. In hepatomas, 15% of the total aldehyde dehydrogenase activity is immunochemically identical to the normal liver cross-reacting material. The remaining 85% of the tumor aldehyde dehydrogenase is characterizable as hepatoma specific on the basis of these immunochemical studies.

Brain and liver aldehyde dehydrogenase activity and voluntary ethanol consumption by rats: relations to strain, sex, and age.

Voluntary ethanol consumption and brain and liver aldehyde dehydrogenase (ALDH) activity were measured in male and female rats of the Tryon Maze-Bright (S1), Tryon Maze-Dull (S3), and Wistar strains. The levels of brain ALDH measured in the different groups, corresponded well to the levels of ethanol consumption, while differences in liver ALDH corresponded well to only the strain differences in ethanol intake. Within individual groups, levels of ethanol consumption correlated better with levels of brain and liver aldehyde-oxidizing capacity. Age affected both voluntary ethanol intake and liver ALDH levels, but there were no systematic relations between the two effects. Age did not significantly affect the cerebral-aldehyde oxidizing capacity. It is argued that inherent variation in brain ALDH activity may be a principal biochemical counterpart of the differences in ethanol intake amoung different strains and sexes of laboratory rats.