Effects of the aerial parts of Orostachys japonicus and its bioactive component on hepatic alcohol-metabolizing enzyme system

In the course of screening medicinal plants that modulate hepatic alcohol-metabolizing enzymes and lipid peroxidation, effects of the methanol extract (ME) of Orostachys japonicus and its major bioactive compound, gallic acid (GA), were investigated in rats treated with 10% ethanol solution for 6 weeks. The ME and GA greatly enhanced the activities of hepatic alcohol dehydrogenase (ADH), the microsomal ethanol-oxidizing system (MEOS), and aldehyde dehydrogenase (ALDH) in a dose-dependent manner, but had no effect on catalase. The hepatic lipid peroxide level increased by ethanol administration was moderately reduced by treatment with ME or GA. The results suggest that the detoxification of hepatic alcohol by O. japonicus ME under our experimental conditions was due to the enhanced activities of the alcohol-oxidizing enzymes, ADH, MEOS, and ALDH. In addition, GA may be partly responsible for the effects.     

CHARACTERISTICS OF ALDEHYDE DEHYDROGENASES OF CERTAIN AEROBIC BACTERIA REPRESENTING HUMAN COLONIC FLORA

We have proposed the existence of a bacteriocolonic pathwayfor ethanol oxidation resulting in high intracolonic levelsof toxic and carcinogenic acetaldehyde. This study was aimedat determining the ability of the aldehyde dehydrogenases (ALDH)of aerobic bacteria representing human colonic flora to metabolizeintracolonically derived acetaldehyde. The apparent Michaelisconstant (K_m) values for acetaldehyde were determined in crudeextracts of five aerobic bacterial strains, alcohol dehydrogenase(ADH) and ALDH activities of these bacteria at conditions prevailingin the human large intestine after moderate drinking were thencompared. The effect of cyanamide, a potent inhibitor of mammalianALDH, on bacterial ALDH activity was also studied. The apparentK_m for acetaldehyde varied from 6.8 (NADP⁺ -linked ALDH of Escherichiacoli IH 13369) to 205 µM (NAD⁺ -linked ALDH of Pseudomonasaeruginosa IH 35342), and maximal velocity varied from 6 nmol/min/mg(NAD⁺ -linked ALDH of Klebsiella pneumoniae IH 35385) to 39nmol/min/mg (NAD⁺ -linked ALDH of Pseudomonas aeruginosa IH35342). At pH 7.4, and at ethanol and acetaldehyde concentrationsthat may be prevalent in the human colon after moderate drinking,ADH activity in four out of five bacterial strains were 10–50times higher than their ALDH activity. Cyanamide inhibited onlyNAD⁺ -linked ALDH activity of Pseudomonas aeruginosa IH 35342at concentrations starting from 0.1 mM. We conclude that ALDHsof the colonic aerobic bacteria are able to metabolize endogenicacetaldehyde. However, the ability of ALDHs to metabolize intracolonicacetaldehyde levels associated with alcohol drinking is ratherlow. Large differences between ADH and ALDH activities of thebacteria found in this study may contribute to the accumulationof acetaldehyde in the large intestine after moderate drinking.ALDH activities of colonic bacteria were poorly inhibited bycyanamide. This study supports the crucial role of intestinalbacteria in the accumulation of intracolonic acetaldehyde afterdrinking alcohol. Individual variations in human colonic floramay contribute to the risk of alcohol-related gastrointestinalmorbidity.     

Expression pattern, ethanol-metabolizing activities, and cellular localization of alcohol and aldehyde dehydrogenases in human large bowel: association of the functional polymorphisms of ADH and ALDH genes with hemorrhoids and colorectal cancer

Alcohol dehydrogenase (ADH) and aldehyde dehydrogenase (ALDH) are principal enzymes responsible for metabolism of ethanol. Functional polymorphisms of ADH1B, ADH1C, and ALDH2 genes occur among racial populations. The goal of this study was to systematically determine the functional expressions and cellular localization of ADHs and ALDHs in human rectal mucosa, the lesions of adenocarcinoma and hemorrhoid, and the genetic association of allelic variations of ADH and ALDH with large bowel disorders. Twenty-one surgical specimens of rectal adenocarcinoma and the adjacent normal mucosa, including 16 paired tissues of rectal tumor, normal mucosae of rectum and sigmoid colon from the same individuals, and 18 surgical mixed hemorrhoid specimens and leukocyte DNA samples from 103 colorectal cancer patients, 67 hemorrhoid patients, and 545 control subjects recruited in previous study, were investigated. The isozyme/allozyme expression patterns of ADH and ALDH were identified by isoelectric focusing and the activities were assayed spectrophotometrically. The protein contents of ADH/ALDH isozymes were determined by immunoblotting using the corresponding purified class-specific antibodies; the cellular activity and protein localizations were detected by immunohistochemistry and histochemistry, respectively. Genotypes of ADH1B, ADH1C, and ALDH2 were determined by polymerase chain reaction-restriction fragment length polymorphisms. At 33 mM ethanol, pH 7.5, the activity of ADH1C*1/1 phenotypes exhibited 87% higher than that of the ADH1C*1/*2 phenotypes in normal rectal mucosa. The activity of ALDH2-active phenotypes of rectal mucosa was 33% greater than ALDH2-inactive phenotypes at 200 μM acetaldehyde. The protein contents in normal rectal mucosa were in the following order: ADH1 > ALDH2 > ADH3 ≈ ALDH1A1, whereas those of ADH2, ADH4, and ALDH3A1 were fairly low. Both activity and content of ADH1 were significantly decreased in rectal tumors, whereas the ALDH activity remained unchanged. The ADH activity was also significantly reduced in hemorrhoids. ADH4 and ALDH3A1 were uniquely expressed in the squamous epithelium of anus at anorectal junctions. The allele frequencies of ADH1C*1 and ALDH2*2 were significantly higher in colorectal cancer and that of ALDH2*2 also significantly greater in hemorrhoids. In conclusion, ADH and ALDH isozymes are differentially expressed in mucosal cells of rectum and anus. The results suggest that acetaldehyde, an immediate metabolite of ethanol, may play an etiological role in pathogenesis of large bowel diseases.     

Microbes and mucosa in the regulation of intracolonic acetaldehyde concentration during ethanol challenge

— Aims: The bacteriocolonic pathway for ethanol oxidationleads to high intracolonic levels of carcinogenic acetaldehyde.The respective roles of colonic mucosal cells and gut florain the regulation of intracolonic acetaldehyde concentrationare not known. Disulfiram inhibits hepatic acetaldehyde oxidationand may have an effect on colonic mucosal cells. On the otherhand, metronidazole treatment leads to overgrowth of acetaldehyde-producingaerobic flora in the large intestine. The aim of this studywas to characterize by means of disulfiram and metronidazolethe contribution of colonic mucosal cells and intracolonic microbesto the regulation of intracolonic acetaldehyde concentrationduring ethanol oxidation in rats. Methods: Forty male Wistarrats were used. Three groups of 10 rats each received metronidazole,disulfiram, or both for 5 days, and a fourth group of 10 ratsserved as controls and did not receive any premedication. Faecalsamples were taken for the ALDH (aldehyde dehydrogenase) determinationbefore the injection of ethanol, after which all rats receivedethanol (1.5 g/kg) 2 h prior to taking samples from blood, liver,colonic mucosa and colonic contents. Results: Disulfiram decreasedsignificantly hepatic and colonic mucosal ALDH activities, andresulted in increased blood and intracolonic acetaldehyde levels.In disulfiram-treated rats, mean intracolonic acetaldehyde levelwas 8-fold higher than that in the blood. Metronidazole inhibitedonly colonic mucosal high K_M ALDH and increased intracolonic,but not blood, acetaldehyde levels. Faecal ALDH activity wasnot detectable in any of the groups. Conclusions: This studydemonstrates that during ethanol challenge, intracolonic acetaldehydelevel is regulated not only by intracolonic microbes, but alsoby colonic mucosal cells.     

Metabolism of ethyl alcohol in the human body

More than 90% of ingested ethanol is metabolized in the body to acetaldehyde and acetate. Ethanol is metabolized in the liver via three distinct enzymatic pathways: alcohol dehydrogenase (ADH), the microsomal ethanol oxidizing system (MEOS) and catalase. It is generally accepted that alcohol dehydrogenase is the predominant pathway for hepatic ethanol oxidation. Acetaldehyde is metabolized to acetate by a group of dehydrogenase enzymes called aldehyde dehydrogenase.     

Effect of acute ethanol drinking on alcohol metabolism in subjects with different ADH and ALDH genotypes

The effect of different amounts of orally ingested ethanol on plasma alcohol dehydrogenase (ADH) and erythrocyte aldehyde dehydrogenase (ALDH), as well as on the blood ethanol and acetaldehyde levels, was examined in healthy nonalcoholic subjects. The genotypes at ADH2 and ALDH2 locus were identified in enzymatically amplified blood DNA by hybridization with allele-specific oligonucleotides. While the Japanese subject was found to be genotypically heterozygous for both ADH2 and ALDH2, the Caucasian subjects were genotypically homozygous normal for these alleles. A faster ethanol elimination associated with a higher blood acetaldehyde level was observed in the Japanese subject as compared to Caucasian subjects. However, no significant change in ADH and ALDH enzyme activities was detected as the result of acute ethanol intake.     

Ciprofloxacin administration decreases enhanced ethanol elimination in ethanol-fed rats

Many colonic aerobic bacteria possess alcohol dehydrogenase (ADH) activity and are capable of oxidizing ethanol to acetaldehyde. Accordingly, some ingested ethanol can be metabolized in the colon in vivo via the bacteriocolonic pathway for ethanol oxidation. By diminishing the amount of aerobic colonic bacteria with ciprofloxacin treatment, we recently showed that the bacteriocolonic pathway may contribute up to 9% of total ethanol elimination in naive rats. In the current study we evaluated the role of the bacteriocolonic pathway in enhanced ethanol metabolism following chronic alcohol administration by diminishing the amount of gut aerobic flora by ciprofloxacin treatment. We found that ciprofloxacin treatment totally abolished the enhancement in ethanol elimination rate (EER) caused by chronic alcohol administration and significantly diminished the amount of colonic aerobic bacteria and faecal ADH activity. However, ciprofloxacin treatment had no significant effects on the hepatic microsomal ethanol-oxidizing system, hepatic ADH activity or plasma endotoxin level. Our data suggest that the decrease in the amount of the aerobic colonic bacteria and in faecal ADH activity by ciprofloxacin is primarily responsible for the decrease in the enhanced EER in rats fed alcohol chronically. Extrahepatic ethanol metabolism by gastrointestinal bacteria may therefore contribute significantly to enhanced EER.     

Overview of the role of alcohol dehydrogenase and aldehyde dehydrogenase and their variants in the genesis of alcohol-related pathology

Alcohol dehydrogenase (ADH) and mitochondrial aldehyde dehydrogenase (ALDH2) are responsible for metabolizing the bulk of ethanol consumed as part of the diet and their activities contribute to the rate of ethanol elimination from the blood. They are expressed at highest levels in liver, but at lower levels in many tissues. This pathway probably evolved as a detoxification mechanism for environmental alcohols. However, with the consumption of large amounts of ethanol, the oxidation of ethanol can become a major energy source and, particularly in the liver, interferes with the metabolism of other nutrients. Polymorphic variants of the genes for these enzymes encode enzymes with altered kinetic properties. The pathophysiological effects of these variants may be mediated by accumulation of acetaldehyde; high-activity ADH variants are predicted to increase the rate of acetaldehyde generation, while the low-activity ALDH2 variant is associated with an inability to metabolize this compound. The effects of acetaldehyde may be expressed either in the cells generating it, or by delivery of acetaldehyde to various tissues by the bloodstream or even saliva. Inheritance of the high-activity ADH beta2, encoded by the ADH2*2 gene, and the inactive ALDH2*2 gene product have been conclusively associated with reduced risk of alcoholism. This association is influenced by gene-environment interactions, such as religion and national origin. The variants have also been studied for association with alcoholic liver disease, cancer, fetal alcohol syndrome, CVD, gout, asthma and clearance of xenobiotics. The strongest correlations found to date have been those between the ALDH2*2 allele and cancers of the oro-pharynx and oesophagus. It will be important to replicate other interesting associations between these variants and other cancers and heart disease, and to determine the biochemical mechanisms underlying the associations.     

Hepatoprotective effects on alcoholic liver disease of fermented silkworms with Bacillus subtilis and Aspergillus kawachii

The purpose of this study was to investigate the protective effect of Bacillus subtilis fermented silkworm powder (BFSP) and Aspergillus kawachii fermented silkworms powder (AFSP) on alcohol-induced hepatotoxicity in Sprague-Dawley rats. Alcohol-feeding rats were fed with diets containing silkworm powder (SP) or both BFSP and AFSP at the 5% (w/w) levels for 4 weeks. Alcohol administration resulted in a significant increase in the activities of liver marker enzymes, aspartate aminotransferase (AST), γ-glutamyl transpeptidase (γ-GTP) and lactate dehydrogenase (LDH). Administration of BFSP markedly prevented alcohol-induced elevation of serum AST, γ-GTP and LDH activities, and the levels of blood alcohol and acetaldehyde. Interestingly, in comparison with both SP and AFSP, BFSP administration drastically increased both hepatic alcohol dehydrogenase (ADH) and acetaldehyde dehydrogenase (ALDH) activities, suggesting that BFSP was more effective in the reduction of blood alcohol and acetaldehyde. BFSP administration showed the highest induction of hepatic ADH expression in alcohol-feeding rats. Also, alcohol treatment resulted in increasing lipid peroxidative index (thiobarbituric acid-reactive substances) and decreasing antioxidant status (reduced glutathione) in the liver. Thus, these results suggest that BFSP treatment improved the antioxidant status of alcoholic rats by decreasing the levels of lipid peroxidative index and by increasing the levels of antioxidant status in the liver and serum. Specially, the concentrations of serum total cholesterol, free fatty acid and hepatic triglyceride were increased, but these parameters were significantly influenced by the BFSP in the alcohol treatment. Unlike the action of alcohol treatment on fatty liver, BFSP administration attenuated lipid droplet accumulation in hepatocytes. A high level of ADH was also observed in AFSP administered rats; on the other hand, a significant change in ALDH was not observed. Therefore, the SP can be a promising candidate in the prevention alcohol-induced hepatotoxicity and oxidative stress.     

Acetaldehyde production and metabolism by human indigenous and probiotic Lactobacillus and Bifidobacterium strains

Many human gastrointestinal facultative anaerobic and aerobic bacteria possess alcohol dehydrogenase (ADH) activity and are therefore capable of oxidizing ethanol to acetaldehyde. We examined whether human gastrointestinal lactobacilli (three strains), bifidobacteria (five strains) and probiotic Lactobacillus GG ATCC 53103 are also able to metabolize ethanol and acetaldehyde in vitro. Acetaldehyde production by bacterial suspensions was determined by gas chromatography after a 1-h incubation with 22 mM ethanol. To determine the acetaldehyde consumption, the suspensions were incubated with 50 microM or 500 microM acetaldehyde as well as with 500 microM acetaldehyde and 22 mM ethanol, i.e. under conditions resembling those in the human colon after alcohol intake. The influence of growth media and bacterial concentration on the ability of lactobacilli to metabolize acetaldehyde and to produce acetate from acetaldehyde were determined. ADH and aldehyde dehydrogenase (ALDH) activities were determined spectrophotometrically. Neither measurable ADH nor ALDH activities were found in aerobically grown Lactobacillus GG ATCC 53103 and Lactobacillus acidophilus ATCC 4356 strains. All the lactobacilli and bifidobacteria strains revealed a very limited capacity to oxidize ethanol to acetaldehyde in vitro. Lactobacillus GG ATCC 53103 had the highest acetaldehyde-metabolizing capacity, which increased significantly with increasing bacterial concentrations. This was associated with a marked production of acetate from acetaldehyde. The type of the growth media had no effect on acetaldehyde consumption. Addition of ethanol to the incubation media diminished the acetaldehyde-metabolizing capacity of all strains. However, in the presence of ethanol, Lactobacillus GG ATCC 53103 still demonstrated the highest capacity for acetaldehyde metabolism of all strains. These data suggest a beneficial impact of Lactobacillus GG ATCC 53103 on high gastrointestinal acetaldehyde levels following alcohol intake. The possible clinical implications of this finding remain to be established in in vitro studies.     

THE ROLE OF GASTROINTESTINAL FACTORS IN ALCOHOL METABOLISM

Although the liver is the major organ responsible for ethanolmetabolism, such metabolism also occurs in the gastrointestinal(GI) tract. However, compared to the liver, GI metabolism ofethanol is quantitatively much lower. Various enzyme systemshave been characterized in GI mucosal cells including variousisozymes of alcohol dehydrogenase (ADH), cytochrome P450 2E1(CYP 2E1) and catalase. Gastric ADH activity is one factor bywhich first pass metabolism (FPM) is influenced and its activityis modulated by genetics, gender, age, drugs and gastric morphologyAnother important factor in FPM of ethanol is the speed of gastricemptying. In addition to mucosal ethanol metabolism, ethanolcan also be oxidized by many bacterial species in the upperGI tract including oropharynx and stomach as well as in thelarge intestine. GI metabolism of ethanol may influence systemicbioavailability of ethanol and may lead to local toxicity mostlikely mediated by acetaldehyde. Such toxicity could be of importancein ethanol-associated carcinogenesis.     

Regulation of Alcohol and Acetaldehyde Metabolism by a Mixture of Lactobacillus and Bifidobacterium Species in Human

Excessive alcohol consumption is one of the most significant causes of morbidity and mortality worldwide. Alcohol is oxidized to toxic and carcinogenic acetaldehyde by alcohol dehydrogenase (ADH) and further oxidized to a non-toxic acetate by aldehyde dehydrogenase (ALDH). There are two major ALDH isoforms, cytosolic and mitochondrial, encoded by ALDH1 and ALDH2 genes, respectively. The ALDH2 polymorphism is associated with flushing response to alcohol use. Emerging evidence shows that Lactobacillus and Bifidobacterium species encode alcohol dehydrogenase (ADH) and acetaldehyde dehydrogenase (ALDH) mediate alcohol and acetaldehyde metabolism, respectively. A randomized, double-blind, placebo-controlled crossover clinical trial was designed to study the effects of Lactobacillus and Bifidobacterium probiotic mixture in humans and assessed their effects on alcohol and acetaldehyde metabolism. Here, twenty-seven wild types (ALDH2*1/*1) and the same number of heterozygotes (ALDH2*2/*1) were recruited for the study. The enrolled participants were randomly divided into either the probiotic (Duolac ProAP4) or the placebo group. Each group received a probiotic or placebo capsule for 15 days with subsequent crossover. Primary outcomes were measurement of alcohol and acetaldehyde in the blood after the alcohol intake. Blood levels of alcohol and acetaldehyde were significantly downregulated by probiotic supplementation in subjects with ALDH2*2/*1 genotype, but not in those with ALDH2*1/*1 genotype. However, there were no marked improvements in hangover score parameters between test and placebo groups. No clinically significant changes were observed in safety parameters. These results suggest that Duolac ProAP4 has a potential to downregulate the alcohol and acetaldehyde concentrations, and their effects depend on the presence or absence of polymorphism on the ALDH2 gene.     

Research on alcohol metabolism among Asians and its implications for understanding causes of alcoholism

Research into the causes of alcoholism is a relatively recent scientific endeavor. One area of study which could lead to better understanding of the disease is the possibility of a genetic predisposition to alcoholism. Recent work has demonstrated that people have varying complements of enzymes to metabolize alcohol. Current knowledge is examined about the influence of various ethanol metabolizing enzymes on alcohol consumption by Asians and members of other ethnic groups. The two principal enzymes involved in ethanol oxidative metabolism are alcohol dehydrogenase (ADH) and aldehyde dehydrogenase (ALDH). ADH is responsible for the metabolism of ethanol to acetaldehyde. ALDH catalyzes the conversion of acetaldehyde to acetate. The different isozymes account for the diversity of alcohol metabolism among individuals. An isozyme of ADH (beta 2 beta 2) is found more frequently in Asians than in whites, and an ALDH isozyme (ALDH2), although present in Asians, often is in an inactive form. The presence of an inactive form of ALDH2 is thought to be responsible for an increase in acetaldehyde levels in the body. Acetaldehyde is considered responsible for the facial flushing reaction often observed among Asians who have consumed alcohol. A dysphoric reaction to alcohol, producing uncomfortable sensations, is believed to be a response to deter further consumption. Although the presence of an inactive ALDH2 isozyme may serve as a deterrent to alcohol consumption, its presence does not fully explain the levels of alcohol consumption by those with the inactive isozyme. Other conditions, such as social pressure, and yet undetermined biological factors, may play a significant role in alcohol consumption.     

Ethanol and intestinal carcinogenesis in the rat

The effect of chronic ethanol administration on 1,2-dimethylhydrazine induced rectal carcinogenesis was investigated in 32 paired male Sprague-Dawley rats fed a nutritionally adequate liquid diet containing 36% of total calories either as ethanol or isocaloric carbohydrates. Chronic ethanol ingestion increased the total number of rectal tumors significantly (17 vs. 6, p less than 0.02), whereas no cocarcinogenic effect of ethanol was observed in other parts of the intestine. Alcohol did not influence tumor size or histopathology. A 47% increase in the activity of mucosal alcohol dehydrogenase in the distal colorectum was found between chronically ethanol fed and pair fed controls (0.241 +/- 0.019 vs. 0.164 +/- 0.020 mumol mg protein-1 hr-1, p less than 0.01). This could in part explain the cocarcinogenic effect of alcohol in this tissue. The data give experimental support to the epidemiologic findings of an increased incidence of rectal cancer in the alcoholic.     

Inhibition of human alcohol and aldehyde dehydrogenases by acetaminophen: Assessment of the effects on first-pass metabolism of ethanol

Acetaminophen is one of the most widely used over-the-counter analgesic, antipyretic medications. Use of acetaminophen and alcohol are commonly associated. Previous studies showed that acetaminophen might affect bioavailability of ethanol by inhibiting gastric alcohol dehydrogenase (ADH). However, potential inhibitions by acetaminophen of first-pass metabolism (FPM) of ethanol, catalyzed by the human ADH family and by relevant aldehyde dehydrogenase (ALDH) isozymes, remain undefined. ADH and ALDH both exhibit racially distinct allozymes and tissue-specific distribution of isozymes, and are principal enzymes responsible for ethanol metabolism in humans. In this study, we investigated acetaminophen inhibition of ethanol oxidation with recombinant human ADH1A, ADH1B1, ADH1B2, ADH1B3, ADH1C1, ADH1C2, ADH2, and ADH4, and inhibition of acetaldehyde oxidation with recombinant human ALDH1A1 and ALDH2. The investigations were done at near physiological pH 7.5 and with a cytoplasmic coenzyme concentration of 0.5 mm NAD⁺. Acetaminophen acted as a noncompetitive inhibitor for ADH enzymes, with the slope inhibition constants (K_is) ranging from 0.90 mm (ADH2) to 20 mm (ADH1A), and the intercept inhibition constants (K_ii) ranging from 1.4 mm (ADH1C allozymes) to 19 mm (ADH1A). Acetaminophen exhibited noncompetitive inhibition for ALDH2 (K_is = 3.0 mm and K_ii = 2.2 mm), but competitive inhibition for ALDH1A1 (K_is = 0.96 mm). The metabolic interactions between acetaminophen and ethanol/acetaldehyde were assessed by computer simulation using inhibition equations and the determined kinetic constants. At therapeutic to subtoxic plasma levels of acetaminophen (i.e., 0.2–0.5 mm) and physiologically relevant concentrations of ethanol (10 mm) and acetaldehyde (10 μm) in target tissues, acetaminophen could inhibit ADH1C allozymes (12–26%) and ADH2 (14–28%) in the liver and small intestine, ADH4 (15–31%) in the stomach, and ALDH1A1 (16–33%) and ALDH2 (8.3–19%) in all 3 tissues. The results suggest that inhibition by acetaminophen of hepatic and gastrointestinal FPM of ethanol through ADH and ALDH pathways might become significant at higher, subtoxic levels of acetaminophen.     

Comparative analysis of hepatic ethanol metabolism in Fawn-Hooded and Wistar-Kyoto rats.

Results of a number of studies have supported the suggestion that a correlation exists between voluntary ethanol consumption and enhanced ethanol metabolism in some (but not all) rodent strains. However, as yet, the capacity for alcohol-preferring Fawn-Hooded (FH) rats to metabolize ethanol has not been investigated. Hence, the aim of the current study was to compare the activities of the major hepatic enzymes involved in ethanol metabolism--cytosolic alcohol dehydrogenase (ADH) and mitochondrial aldehyde dehydrogenase (ALDH)--in the FH rat and its alcohol-nonpreferring counterpart, the Wistar-Kyoto (WKY) rat. In addition, the effect of chronic (5 weeks in vivo) ethanol pretreatment on the activity of these enzymes was investigated. Alcohol-naive FH rats were found to have significantly higher ADH activity (+61%) and no significant change in ALDH activity when compared with findings for WKY rats. In addition, chronic ethanol self-administration produced a small increase in ADH activity (+14%) in WKY rats only. Taken as a whole, these findings are the first to demonstrate an increased in vitro hepatic ethanol metabolism in alcohol-preferring FH rats and further demonstrate an association between hepatic ethanol metabolism and voluntary ethanol self-administration in rodents.     

Alcohol and aldehyde dehydrogenase

The enzymes mainly responsible for ethanol degradation in humans are liver alcohol dehydrogenases (ADH) and aldehyde dehydrogenases (ALDH). Polymorphisms occur in both enzymes, with marked differences in the steady-state kinetic constants. The Km-values for ethanol of ADH isoenzymes relevant for alcohol degradation range from 49 microM to 36 microM, and the Vmax-values from 0.6 to 10 U/mg. Expression of an inactive form of the ALDH2 isoenzyme, the so-called Oriental variant, results in impaired acetaldehyde metabolizing capacity. The differences in ethanol and acetaldehyde metabolizing activities of allelic enzyme forms may be responsible in part for the large variation in the alcohol metabolism rate in humans. Interindividual differences in the isoenzyme pattern may contribute to the genetically determined predisposition for excessive alcohol intake.     

海参岩藻聚糖硫酸酯对长期饮酒小鼠肝脏保护作用的研究

目的研究海参岩藻聚糖硫酸酯(SC-FUC)对长期饮酒导致的小鼠肝脏功能损伤的改善作用。方法从海地瓜(Acaudina molpadioides)中制备SC-FUC。将ICR小鼠随机分为4组:正常组、模型组以及SC-FUC低、高剂量组,每组12只。各组小鼠按0.08 ml/g bw灌胃受试物,1h后再灌胃白酒,每天一次,连续8w。实验结束后分别检测血清丙氨酸氨基转移酶(ALT)和天门冬氨酸氨基转移酶(AST)活性,肝脏乙醇脱氢酶(ADH)、乙醛脱氢酶(ALDH)、谷胱甘肽过氧化物酶(GSH-Px)、超氧化物歧化酶(SOD)活性、丙二醛(MDA)、谷胱甘肽(GSH)含量以及肝脏中CYP2e1mRNA的表达量。结果 SC-FUC能显著降低小鼠血清ALT和AST活力(P<0.05),提高肝脏ADH、ALDH、GSH-Px活力(P<0.05)和GSH含量(P<0.05),降低MDA含量(P<0.05);降低肝脏中CYP2e1mRNA的表达量(P<0.05)。结论 SC-FUC对长期饮酒小鼠肝脏具有显著的保护作用。     

The regulation of alcohol consumption in rats: The role of alcohol-metabolizing enzymes—Catalase and aldehyde dehydrogenase

Aldehyde dehydrogenase (ALDH) and catalase enzymatic activities in brain were assayed and compared to measures of alcohol consumption in two groups of animals screened and maintained on free-choice alcohol access under different conditions. In the first group of Long-Evans rats screened and maintained in home cages, mean alcohol intake was 3.49 g/kg/day with a range of 1.69–5.33 g/kg/day. When alcohol intake (g/kg), total ALDH, low K_m ALDH, and catalase activities were entered in a multiple regression, a significant correlation of r = 0.51 (p < 0.05) was obtained. In the second group of rats consisting of Long-Evans, P, and NP rats screened using a drinkometer procedure, a multiple correlation between ALDH and catalase enzyme activities and alcohol intake of r = 0.42 (p < 0.05) was obtained. There was a strong relationship between the frequency of alcohol drinking bouts and the activities of catalase and ALDH (r = 0.68, p < 0.0001). The P rats had significantly higher catalase activities than either the NP or Long-Evans rats. The results of the present study confirmed earlier reports on the role of alcohol-metabolizing enzymes in the regulation of alcohol intake. The results also highlighted the fact that the activity of these alcohol-metabolizing enzymes may play a mediating role in patterns of alcohol intake displayed by animals selected for high and low alcohol drinking and also unselected animals.     

Individual susceptibility and alcohol effects:biochemical and genetic aspects

The large interethnic and interindividual variability in alcohol-induced toxic effects comes from a combination of genetic and environmental factors, influencing ethanol toxicokinetics. The hepatic enzymatic systems involved in ethanol metabolism are alcohol dehydrogenase (ADH), aldehyde dehydrogenase (ALDH) and microsomal P4502E1 (CYP2E1). ADH oxidizes ethanol to acetaldehyde, which is very efficiently oxidized to acetate by ALDH. About 10% of moderate quantities of ethanol is metabolised by CYP2E1; the percentage increases when ADH is saturated. During ethanol metabolism reactive oxygen species and hydroxyethyl radicals are generated, causing oxidative stress, responsible for most ethanol-induced liver damage. For their critical role in detoxifying radicals, glutathione S-transferase are gaining attention in the etiology of alcoholism. All these enzymes have been shown to be polymorphic, giving rise to altered phenotypes. For this reason recent studies have looked for a correlation between metabolic variability and differences in alcohol abuse-related effects.