Human gastric alcohol dehydrogenase: its inhibition by H2-receptor antagonists, and its effect on the bioavailability of ethanol

Alcohol-Associated Tissue Injury: Current Views on Pathophysiological Mechanisms

At-risk alcohol use is a major contributor to the global health care burden and leads to preventable deaths and diseases including alcohol addiction, alcoholic liver disease, cardiovascular disease, diabetes, traumatic injuries, gastrointestinal diseases, cancers, and fetal alcohol syndrome. Excessive and frequent alcohol consumption has increasingly been linked to alcohol-associated tissue injury and pathophysiology, which have significant adverse effects on multiple organ systems. Extensive research in animal and in vitro models has elucidated the salient mechanisms involved in alcohol-induced tissue and organ injury. In some cases, these pathophysiological mechanisms are shared across organ systems. The major alcohol- and alcohol metabolite-mediated mechanisms include oxidative stress, inflammation and immunometabolic dysregulation, gut leak and dysbiosis, cell death, extracellular matrix remodeling, endoplasmic reticulum stress, mitochondrial dysfunction, and epigenomic modifications. These mechanisms are complex and interrelated, and determining the interplay among them will make it possible to identify how they synergistically or additively interact to cause alcohol-mediated multiorgan injury. In this article, we review the current understanding of pathophysiological mechanisms involved in alcohol-induced tissue injury.

Molecular mechanisms of ethanol biotransformation: enzymes of oxidative and nonoxidative metabolic pathways in human

Ethanol, as a small-molecule organic compound exhibiting both hydrophilic and lipophilic properties, quickly pass through the biological barriers. Over 95% of absorbed ethanol undergoes biotransformation, the remaining amount is excreted unchanged, mainly with urine and exhaled air.The main route of ethyl alcohol metabolism is its oxidation to acetaldehyde, which is converted into acetic acid with the participation of cytosolic NAD⁺ - dependent alcohol (ADH) and aldehyde (ALDH) dehydrogenases. Oxidative biotransformation pathways of ethanol also include reactions catalyzed by the microsomal ethanol oxidizing system (MEOS), peroxisomal catalase and aldehyde (AOX) and xanthine (XOR) oxidases. The resulting acetic acid can be activated to acetyl-CoA by the acetyl-CoA synthetase (ACS).It is also possible, to a much smaller extent, non-oxidative routes of ethanol biotransformation including its esterification with fatty acids by ethyl fatty acid synthase (FAEES), re-esterification of phospholipids, especially phosphatidylcholines, with phospholipase D (PLD), coupling with sulfuric acid by alcohol sulfotransferase (SULT) and with glucuronic acid using UDP-glucuronyl transferase (UGT, syn. UDPGT).The intestinal microbiome plays a significant role in the ethanol biotransformation and in the initiation and progression of liver diseases stimulated by ethanol and its metabolite - acetaldehyde, or by lipopolysaccharide and ROS.

Drug Interactions with Antiulcer Agents: Considerations in the Treatment of Acid-Peptic Disease

All of the antiulcer agents have been implicated in drug interactions. These agents generally influence the absorption, metabolism, or elimination of other medications. However, these interactions can lead to alterations in pharmacodynamic response. The mechanisms by which antiulcer agents produce drug interactions differ among the agents. It is beyond the scope of this article to review all of the drug interactions that have been reported with antiulcer agents. However, it is the intent to provide the reader with a detailed understanding of the mechanisms by which antiulcer agents may interact with other medications and to provide insight into factors that may influence the potential magnitude or clinical consequences of these interactions. An understanding of antiulcer drug interactions will aid pharmacists in assisting clinicians with drug selection and/or monitoring of drug interactions. Specifically, pharmacists can assist with the identification of potential antiulcer drug interactions and develop strategies designed to minimize adverse consequences of these interactions.

Pharmacokinetic and pharmacodynamic drug interactions with ethanol (alcohol)

Ethanol (alcohol) is one of the most widely used legal drugs in the world. Ethanol is metabolized by alcohol dehydrogenase (ADH) and the cytochrome P450 (CYP) 2E1 drug-metabolizing enzyme that is also responsible for the biotransformation of xenobiotics and fatty acids. Drugs that inhibit ADH or CYP2E1 are the most likely theoretical compounds that would lead to a clinically significant pharmacokinetic interaction with ethanol, which include only a limited number of drugs. Acute ethanol primarily alters the pharmacokinetics of other drugs by changing the rate and extent of absorption, with more limited effects on clearance. Both acute and chronic ethanol use can cause transient changes to many physiologic responses in different organ systems such as hypotension and impairment of motor and cognitive functions, resulting in both pharmacokinetic and pharmacodynamic interactions. Evaluating drug interactions with long-term use of ethanol is uniquely challenging. Specifically, it is difficult to distinguish between the effects of long-term ethanol use on liver pathology and chronic malnutrition. Ethanol-induced liver disease results in decreased activity of hepatic metabolic enzymes and changes in protein binding. Clinical studies that include patients with chronic alcohol use may be evaluating the effects of mild cirrhosis on liver metabolism, and not just ethanol itself. The definition of chronic alcohol use is very inconsistent, which greatly affects the quality of the data and clinical application of the results. Our study of the literature has shown that a significantly higher volume of clinical studies have focused on the pharmacokinetic interactions of ethanol and other drugs. The data on pharmacodynamic interactions are more limited and future research addressing pharmacodynamic interactions with ethanol, especially regarding the non-central nervous system effects, is much needed.

Inhibition of human alcohol and aldehyde dehydrogenases by cimetidine and assessment of its effects on ethanol metabolism

Previous studies have reported that cimetidine, an H2-receptor antagonist used to treat gastric and duodenal ulcers, can inhibit alcohol dehydrogenases (ADHs) and ethanol metabolism. Human alcohol dehydrogenases and aldehyde dehydrogenases (ALDHs), the principal enzymes responsible for metabolism of ethanol, are complex enzyme families that exhibit functional polymorphisms among ethnic groups and distinct tissue distributions. We investigated the inhibition by cimetidine of alcohol oxidation by recombinant human ADH1A, ADH1B1, ADH1B2, ADH1B3, ADH1C1, ADH1C2, ADH2, and ADH4, and aldehyde oxidation by ALDH1A1 and ALDH2 at pH 7.5 and a cytosolic NAD(+) concentration. Cimetidine acted as competitive or noncompetitive inhibitors for the ADH and ALDH isozymes/allozymes with near mM inhibition constants. The metabolic interactions between cimetidine and ethanol/acetaldehyde were assessed by computer simulation using the inhibition equations and the determined kinetic constants. At therapeutic drug levels (0.015 mM) and physiologically relevant concentrations of ethanol (10 mM) and acetaldehyde (10 μM) in target tissues, cimetidine could weakly inhibit (<5%) the activities of ADH1B2 and ADH1B3 in liver, ADH2 in liver and small intestine, ADH4 in stomach, and ALDH1A1 in the three tissues, but not significantly affect ADH1A, ADH1B1, ADH1C1/2, or ALDH2. At higher drug levels, which may accumulate in cells (0.2 mM), the activities of the weakly-inhibited enzymes may be decreased more significantly. The quantitative effects of cimetidine on metabolism of ethanol and other physiological substrates of ADHs need further investigation.

Metabolism of ethanol and associated hepatotoxicity

Over the last three decades, direct hepatotoxic effects of ethanol were established, some of which were linked to redox changes produced by NADH generated via the alcohol dehydrogenase (ADH) pathway and shown to affect the metabolism of lipids, carbohydrates, proteins, and purines. It was also determined that ethanol can be oxidized by a microsomal ethanol oxidizing system (MEOS) involving a specific cytochrome P-450; this newly discovered ethanol-inducible cytochrome P-450 (P-450 IIEi) contributes to ethanol metabolism, tolerance, energy wastage (with associated weight loss), and the selective hepatic perivenular toxicity of various xenobiotics. Their activation by P-450IIEi now provides an understanding of the increased susceptibility of the heavy drinker to the toxicity of industrial solvents, anaesthetic agents, commonly prescribed drugs, over-the-counter analgesics, and chemical carcinogens. P-450 induction also explains depletion (and toxicity) of nutritional factors such as vitamin A. As a consequence, treatment with vitamin A and other nutritional factors is beneficial, but must take into account a narrowed therapeutic window in alcoholics who have increased needs for nutrients and also display an enhanced susceptibility to some of their adverse effects. Acetaldehyde (the metabolite produced from ethanol by either ADH or MEOS) impairs hepatic oxygen utilization and forms protein adducts, resulting in antibody production, enzyme inactivation, and decreased DNA repair. It also stimulates collagen production by the vitamin A storing cells (lipocytes) and myofibroblasts, and causes glutathione depletion. Supplementation with S-adenosyl-L-methionine partly corrects the depletion and associated mitochondrial injury, whereas administration of polyunsaturated lecithin opposes the fibrosis. Thus, at the cellular level, the classic dichotomy between the nutritional and toxic effects of ethanol has now been bridged. The understanding of how the ensuing injury eventually results in irreversible scarring or cirrhosis may provide us with improved modalities for treatment and prevention.

Lactic acid bacteria prevent alcohol-induced steatohepatitis in rats by acting on the pathways of alcohol metabolism

The objective is to study the possible mechanism by which lactic acid bacteria (LAB) prevent alcohol-induced steatohepatitis in rats. A total of 25 Wistar rats were divided into three groups: a LAB-fed group, an alcohol-treated group and a control group. Both the LAB-fed group and the alcohol-treated group received alcohol (10 g kg(-1) per day) orally for up to 5 days (125 h). Before exposure to alcohol, the LAB-fed group were first treated daily with 1.5 ml/100 g of a mixture comprising 4 x 10(10) ml(-1) of Lactobacillus acidophilus and 2.5 x 10(7) ml(-1) of Bifidobacterium longum, while the control group was treated with normal saline only. Biochemical data, alcohol dehydrogenase (ADH) activity and histology of the liver and stomach were evaluated. The ADH activity in the LAB mixture was 3.52 +/- 0.45 mumol mg(-1) protein (10(9) CFU ml(-1)), and was dose-dependent. By 30 min after taking alcohol, serum alcohol concentrations were 514.24 +/- 80.21 microg ml(-1) in the LAB-fed group and 795.15 +/- 203.45 microg ml(-1) in the alcohol-treated group (P < 0.005). Serum alcohol concentrations were reduced by 48% (P < 0.01) in the LAB-fed group, but by only 4% in the alcohol-treated group (P > 0.05) 120 min after oral intake of alcohol. The blood levels of endotoxin, AST and ALT were improved in the LAB-fed group compared to the alcohol-fed group (P < 0.01). All alcohol-treated rats showed moderate to severe steatohepatitis, but the LAB-fed rats showed almost normal histology or very slight lesions only. In conclusion, LAB decreased the alcohol concentration in the blood by increasing the first-pass metabolism in both the stomach and the liver, and effectively protected against alcohol-induced gastric and liver injury. It is interesting to note that the protection was more effective in the liver.

Drug interactions involving ethanol and alcoholic beverages

Ethanol is likely among the most widely and extensively used drugs in the world. It has also been demonstrated to alter the expression or activity of some drug-metabolizing enzymes. Thus, marked ethanol-provoked drug interactions could be of notable clinical importance. To date, relatively few clinically important interactions have been reported, involving cocaine, disulfiram and tacrolimus. Limited or modest interactions with ethanol have also been reported for drugs such as abacavir, cisapride, 'ecstasy' (3,4-methylenedioxymetamfetamine), gamma-hydroxybutyrate, methylyphenidate, metronidazole and verapamil. Most of these interactions do not seem to involve CYP2E1, the enzyme initially characterized and cloned based on its ability to metabolize and be induced by ethanol. Important work has elucidated the relationship between CYP2E1-mediated formation of the hepatotoxic metabolite of acetaminophen and alcohol consumption. Lastly, drug interactions involving other components of alcoholic beverages such as flavonoid and other polyphenolic components of red wine have been reported.

Alcohol dehydrogenase (ADH) isoenzyme activity in the sera of patients with Helicobacter pylori infection

Human gastric mucosa contains three classes of alcohol dehydrogenase (ADH) isoenzymes: I, III, and IV. Various factors have been found to influence gastric ADH activity. One of them is Helicobacter pylori infection, which is associated with gastric mucosal injury and leads to a decrease in gastric ADH activity. The aim of the study was to assess the effect of H. pylori infection on the serum activity of ADH isoenzymes. Serum samples were taken from 35 patients with H. pylori infection and from 35 healthy subjects. For measurement of class I isoenzyme activity we employed the fluorometric method, with class-specific fluorogenic substrate (4-methoxy-1-naphthaldehyde). The activities of class III and IV ADH isoenzymes were measured by the photometric method with formaldehyde and with m-nitrobenzaldehyde as substrate, respectively. Total activity of ADH was measured by a photometric method with p-nitrosodimethylaniline. The total activities of ADH and class IV isoenzyme were significantly higher in sera of patients with H. pylori infection compared to healthy subjects. The serum activity of other tested isoenzymes of ADH did not differ significantly between infected and noninfected groups. We conclude that H. pylori infection of gastric mucosa is reflected in the serum by a significant increase in class IV and total ADH activity.

Metabolism of alcohol

Most tissues of the body contain enzymes capable of ethanol oxidation or nonoxidative metabolism, but significant activity occurs only in the liver and, to a lesser extent, in the stomach. Hence, medical consequences are predominant in these organs. In the liver, ethanol oxidation generates an excess of reducing equivalents, primarily as NADH, causing hepatotoxicity. An additional system, containing cytochromes P-450 inducible by chronic alcohol feeding, was demonstrated in liver microsomes and found to be a major cause of hepatotoxicity.

Alcohol metabolism: role in toxicity and carcinogenesis

This article contains the proceedings of a symposium at the 2002 RSA Meeting in San Francisco, organized and co-chaired by Thomas M. Badger, Paul Shih-Jiun Yin, and Helmut Seitz. The presentations were (1) First-pass metabolism of ethanol: Basic and clinical aspects, by Charles Lieber; (2) Intracellular CYP2E1 transport, oxidative stress, cytokine release, and ALD, by Magnus Ingelman-Sundberg; (3) Pulsatile ethanol metabolism in intragastric infusion models: Potential role in toxic outcomes, by Thomas M. Badger and Martin J.J. Ronis; (4) Free radicals, adducts, and autoantibodies resulting from ethanol metabolism: Role in ethanol-associated toxicity, by Emanuele Albano; and (5) Gastrointestinal metabolism of ethanol and its possible role in carcinogenesis, by Helmut Seitz.

A sensitive, colorimetric, microtitre assay for alcohol dehydrogenase in standard endoscopic gastric biopsies

Traditional assays of alcohol dehydrogenase (ADH) activity in gastric mucosa use spectrophotometry of tissue homogenates, which are based on the reduction of nicotinamide adenine dinucleotide (NAD). We describe a colorimetric method using the coupled reduction of N,N-dimethyl-4-nitrosoaniline. This method has increased sensitivity, allowing activity to readily be determined in standard endoscopic biopsies. Tissue homogenisation has been replaced by an incubation stage, and the method has been optimised for a 96-well plate reader, allowing rapid processing of large numbers of samples. We found that Helicobacter pylori infection and age have a significant effect on gastric ADH activity.

Effect of common over-the-counter medications on blood alcohol levels

OBJECTIVE

To assess the clinical and legal significance of the potential pharmacokinetic interaction between common over-the-counter (OTC) medications and alcohol that may result in increased blood alcohol levels (BALs).

DATA SOURCES

A MEDLINE search (1966-February 2000) of English-language articles was performed using the terms aspirin, acetaminophen, histamine (H2)-receptor antagonist, ethanol, and blood alcohol level and then supplemented by a bibliographic review of relevant articles.

STUDY SELECTION AND DATA EXTRACTION

Two H2-receptor antagonist studies using methodologies representative of other published trials and a meta-analysis of 24 H2-receptor antagonist trials were chosen for detailed review. All identified studies examining aspirin and acetaminophen were addressed.

DATA SYNTHESIS

More than 30 studies have examined the potential interaction between OTC drugs and blood alcohol. Because this issue has important medical and legal implications for patients, prescribing physicians, and pharmaceutical manufacturers, a critical analysis of the literature addressing this potential interaction is presented.

CONCLUSIONS

Numerous factors arguing against a clinically significant interaction were identified. First, data from the relevant studies cannot be extrapolated to the general population because of the multitude of variables that determine an individual's BAL. Also, a publication bias for small studies (< or = 10 subjects) finding a statistically significant increase in peak BAL was observed. In addition, study results supporting an increase in BAL were often irreproducible when these trials were repeated under similar conditions. Finally, although some studies detected statistically significant increases in peak BAL, these changes were often clinically irrelevant.

Alcohol dehydrogenase activities in the human gastric mucosa: effects of Helicobacter pylori infection, sex, age, and the part of the stomach

BACKGROUND

Human gastric mucosa contains three alcohol dehydrogenase (ADH) isozymes (classes I, III, and IV). Various factors such as Helicobacter pylori infection, sex, age, and the part of the stomach involved have been suggested to affect alcohol dehydrogenase activities, although these views are controversial. In this study, these unsettled issues were reexamined.

METHODS

Activities of class I and IV ADHs were evaluated in the cytosolic fraction of human gastric mucosa samples by reduction of their preferred substrates, namely acetaldehyde and m-nitrobenzaldehyde, and activities of class III were evaluated by oxidation of its preferred substrate, formaldehyde. Then, effects of Helicobacter pylori infection, sex, age, and the part of the stomach involved were examined.

RESULTS

Class I, III, and IV ADH activities were 17.5 +/- 8.4, 4.2 +/- 2.5, and 8.9 +/- 3.9 nmol of nicotinamide adenine dinucleotide oxidation per minute per milligram of protein, respectively, for the entire population. Helicobacter pylori infection significantly reduced class I and IV ADH activities but did not affect activity of class III. In the samples without Helicobacter pylori infection and severe gastritis, sex did not affect class I, III, or IV ADH activities. In the same series, class IV ADH activity significantly decreased with age (p = 0.006), whereas no correlation was found between age and ADH activity of class I and III ADHs. The level of class IV ADH activity was significantly higher in the upper body than in the lower regions, whereas no such heterogeneity was observed in class I and III ADH.

CONCLUSIONS

Various factors affect human gastric ADH activities, such that careful interpretation of their significance is necessary.

Nicotinamide adenine dinucleotide-dependent retinoic acid formation from retinol in the human gastric mucosa: inhibition by ethanol, acetaldehyde, and H2 blockers

All-trans retinoic acid formation from all-trans retinol (vitamin A) in the human gastric mucosa was studied. When all-trans retinol and the human gastric mucosa were incubated together, all-trans retinoic acid was formed in the presence of nicotinamide adenine dinucleotide (NAD). When the NAD was not added, hardly any formation was observed. The formation of all-trans retinoic acid tended to be attenuated by 10 mM ethanol. Moreover, it was significantly attenuated in a concentration-dependent manner by ethanol at concentrations of 100 mM and above. Acetaldehyde at concentrations of 50 microM and above also significantly attenuated its formation in a concentration-dependent manner. Some H2 blockers, which include ranitidine hydrochloride and cimetidine, significantly attenuated the formation of all-trans retinoic acid, whereas famotidine failed to suppress it. There is an NAD-dependent pathway by which all-trans retinoic acid is produced from all-trans retinol in the human gastric mucosa. Inhibitors of alcohol dehydrogenase, which include ethanol and some H2 blockers, and of aldehyde dehydrogenase, which include acetaldehyde, inhibit its production.

No sex and age influence on the expression pattern and activities of human gastric alcohol and aldehyde dehydrogenases

BACKGROUND

Alcohol dehydrogenase (ADH) and aldehyde dehydrogenase (ALDH) are the principal enzymes responsible for ethanol metabolism in humans. The stomach is involved in the metabolism of alcohol during absorption. Conflicting reports exist with regard to the influence of sex and age on the activity of ADH in the human gastric mucosa. The purpose of the present study was to determine the effects of age and sex on the expression pattern and activities of stomach ADH and ALDH.

METHODS

A total of 115 endoscopic gastric biopsy specimens were investigated from Han Chinese men (n = 70) and women (n = 45) aged 20-79 years with approximately even distribution among 10-year age intervals. The expression patterns of ADH and ALDH were identified by isoelectric focusing, and the activities were assayed spectrophotometrically.

RESULTS

The expression patterns of gastric ADH and ALDH remained unchanged with respect to sex and age. At 33 mM or 500 mM ethanol, pH 7.5, the ADH activities did not differ significantly among the various age groups or between men and women. At 200 microM or 20 mM acetaldehyde, the ALDH activities did not differ significantly in relation to sex and age. No correlations were found between the ADH or ALDH activities at both the high and low substrate concentrations and the ages in men and women.

CONCLUSIONS

The results indicate that there is no significant effect of either sex or age on the expression pattern and activity of ADH and ALDH in the human gastric mucosa. The stomach ADH seems unlikely to account for possible variations in the first-pass metabolism of alcohol with regard to sex and age.

ALCOHOL: its metabolism and interaction with nutrients

In the past, alcoholic liver disease was attributed exclusively to dietary deficiencies, but experimental and judicious clinical studies have now established alcohol's hepatotoxicity. Despite an adequate diet, it can contribute to the entire spectrum of liver diseases, mainly by generating oxidative stress through its microsomal metabolism via cytochrome P4502E1 (CYP2E1). It also interferes with nutrient activation, resulting in changes in nutritional requirements. This is exemplified by methionine, one of the essential amino acids for humans, which needs to be activated to S-adenosylmethionine (SAMe), a process impaired by liver disease. Thus, SAMe rather than methionine is the compound that must be supplemented in the presence of significant liver disease. In baboons, SAMe attenuated mitochondrial lesions and replenished glutathione; it also significantly reduced mortality in patients with Child A or B cirrhosis. Similarly, decreased phosphatidylethanolamine methyltransferase activity is associated with alcoholic liver disease, resulting in phosphatidylcholine depletion and serious consequences for the integrity of membranes. This can be offset by polyenylphosphatidylcholine (PPC), a mixture of polyunsaturated phosphatidylcholines comprising dilinoleoylphosphatidylcholine (DLPC), which has high bioavailability. PPC (and DLPC) opposes major toxic effects of alcohol, with down-regulation of CYP2E1 and reduction of oxidative stress, deactivation of hepatic stellate cells, and increased collagenase activity, which in baboons, results in prevention of ethanol-induced septal fibrosis and cirrhosis. Corresponding clinical trials are ongoing.

Alcohol levels are increased in social drinkers receiving ranitidine

OBJECTIVE

Ranitidine increases blood alcohol concentrations by decreasing the first pass metabolism of ethanol. The effect of ranitidine on alcohol levels has been found to be variable when using large doses of alcohol or conditions in which its first pass metabolism is known to be minimal. Despite a consensus that the drug increases alcohol levels after small doses of ethanol, this effect has been considered inconsequential, because of the low alcohol levels. However, social drinking comprises repetitive consumption of small doses of alcohol and the ranitidine effect could thereby be potentiated.

METHODS

To study this factor, alcohol levels were determined by breath analysis in nine men (social drinkers), after four drinks of 0.15 g/kg ethanol given postprandially every 45 min, before and after ranitidine (150 mg b.i.d. for 7 days).

RESULTS

Their blood alcohol increased with repeated doses, reaching peak values of 24+/-3 mg/dl before ranitidine and 33+/-2 after ranitidine (p = 0.04). In seven of the nine subjects blood alcohol exceeded 25 mg/dl, a level at which impairment of judgment and of finely tuned skills occurs and which exceeds legal limits of driving in some European countries. Moreover, the high levels persisted for a longer time with than without the drug. These effects were associated with a 62% decrease in first pass metabolism.

CONCLUSION

Under conditions mimicking social drinking, ranitidine increases blood alcohol to levels known to impair psychomotor skills needed for driving.

Alcohol and the health of aging men

Alcohol drinking, alcohol abuse, and alcoholism are more common among men than women at all ages. This article reviews the epidemiology and clinical effects of alcohol use in aging men. Alcoholism demands aggressive intervention when encountered in cognitively impaired people.

Is there an interaction between H2-antagonists and alcohol?

H2-antagonists are commonly prescribed drugs and alcohol use is widespread in the community. Any possible interaction may be important because of the frequent co-administration of both drugs and the potential for unexpected impairment of pyschomotor function, in particular, driving skills. Hepatic ADH is the major site of alcohol metabolism. ADH is also found in the stomach, but it is uncertain whether gastric ADH is able to metabolise a significant amount of alcohol in vivo. Significant first-pass metabolism can be demonstrated at lower doses of alcohol, and if alcohol is given after meals. Varying degrees of extraction of alcohol from the portal circulation probably explains the data regarding first pass metabolism rather than gastric metabolism by gastric ADH. H2-receptor antagonists inhibit gastric ADH activity to a variable extent. If gastric metabolism of alcohol is negligible then this inhibition has no relevance. Given the uncertainty regarding a mechanism of interaction, only carefully conducted studies in controlled environments will answer the question. The large inter-subject variability of alcohol absorption means that any study which seeks to determine the effect of an H2-receptor antagonist on ethanol metabolism must have sufficient numbers. A cross-over design, with each subject acting as his own control, is preferable to avoid ascribing an effect to treatment rather than to chance. The alcohol dosing studies are reviewed and the results summarised according to dose of alcohol given. At a dose of 0.15 g/kg of alcohol, four commonly used H2-antagonists may cause a small increase in blood alcohol concentrations in certain conditions. This absolute increase is very small. The magnitude of effect is far less than the effect of taking a meal before alcohol. At doses of 0.3 g/kg and above the majority of evidence favours no interaction between H2-antagonists and alcohol. There is no interaction at doses that would be expected to impair psychomotor skills (above 25 mg/dl). There remains a question regarding the cumulative effect of repeated small doses of alcohol and further studies are required. The relationship between ethanol absorption and gastric emptying raises the possibility that the effects of H2-receptor antagonists observed at very low doses of alcohol may be due to the acceleration of gastric emptying by these drugs. This is an attractive hypothesis that explains many aspects of the debate, but studies of the effect of H2-antagonists on gastric emptying have been conflicting.

Alcohol, vitamin A, and beta-carotene: adverse interactions, including hepatotoxicity and carcinogenicity

Isozymes of alcohol and other dehydrogenases convert ethanol and retinol to their corresponding aldehydes in vitro. In addition, new pathways of retinol metabolism have been described in hepatic microsomes that involve, in part, cytochrome P450s, which can also metabolize various drugs. In view of these overlapping metabolic pathways, it is not surprising that multiple interactions between retinol, ethanol, and other drugs occur. Accordingly, prolonged use of alcohol, drugs, or both, results not only in decreased dietary intake of retinoids and carotenoids, but also accelerates the breakdown of retinol through cross-induction of degradative enzymes. There is also competition between ethanol and retinoic acid precursors. Depletion ensues, with associated hepatic and extrahepatic pathology, including carcinogenesis and contribution to fetal defects. Correction of deficiency through vitamin A supplementation has been advocated. It is, however, complicated by the intrinsic hepatotoxicity of retinol, which is potentiated by concomitant alcohol consumption. By contrast, beta-carotene, a precursor of vitamin A, was considered innocuous until recently, when it was found to also interact with ethanol, which interferes with its conversion to retinol. Furthermore, the combination of beta-carotene with ethanol results in hepatotoxicity. Moreover, in smokers who also consume alcohol, beta-carotene supplementation promotes pulmonary cancer and, possibly, cardiovascular complications. Experimentally, beta-carotene toxicity was exacerbated when administered as part of beadlets. Thus ethanol, while promoting a deficiency of vitamin A also enhances its toxicity as well as that of beta-carotene. This narrowing of the therapeutic window for retinol and beta-carotene must be taken into account when formulating treatments aimed at correcting vitamin A deficiency, especially in drinking populations.

Gastritis in the alcoholic: relationship to gastric alcohol metabolism and Helicobacter pylori

Chronic gastritis is common in the alcoholic. It is characterized by histological inflammation of the gastric mucosa and is associated with variable symptomatology. Its etiology is still the subject of debate. Recently, a new alcohol dehydrogenase isoenzyme, called sigma ADH, absent from the liver but predominant in the upper GI tract, has been fully characterized, its gene cloned, and it appears to play a major role in gastric ethanol metabolism. Indeed, it has now been established, both in vivo in experimental animals and in vitro in cultured human gastric cells, that alcohol is metabolized in the gastric mucosa, resulting in the production of acetaldehyde, a toxic metabolite. In addition, Helicobacter pylori infection is common in the alcoholic, resulting in the breakdown of urea to ammonia, another toxic product. A number of studies carried out over the last 40 years revealed that antibiotic treatment eradicates ammonia production and results in histological and symptomatic improvement in the majority of patients with alcoholic gastritis. Non-invasive tests for the detection of H. pylori are now available which will facilitate the large scale studies needed to confirm whether, in H. pylori -positive patients, antibiotics should become routine treatment for alcoholic gastritis.

Effect of histamine-2 receptor antagonists on blood alcohol levels: a meta-analysis

OBJECTIVE

To determine the effect, if any, of histamine type 2 receptor antagonists (H2RAs) on serum alcohol levels under various conditions including type of H2RA receptor antagonist, alcohol dose, and fed status of the subject.

STUDY DESIGN

Meta-analysis of the published literature.

DATA SOURCES

Studies were identified by MEDLINE (January 1982 through December 1997) using the key words H2 receptor antagonists and alcohol. Other studies were identified by reviewing bibliographies of retrieved articles and by discussion with colleagues.

STUDY SELECTION

Studies were selected if they involved the coadministration of H2RAs and alcohol in healthy, human volunteers. Studies that may have addressed this goal but were performed in another context, for instance the measurement of ulcer healing, were excluded.

DATA EXTRACTION

Data were extracted on the design, number of participants, participant characteristics, type and dose of H2RA administered, serum alcohol levels (measured as Cmax) along with standard deviations, dose of alcohol received, and fed or fasted status of participants. Alcohol dose was arbitrarily divided into low dose (< or = 0.5 g/kg body weight) versus high dose (> 0.5 g/kg body weight). In addition, studies involving ranitidine and cimetidine were stratified by sample size into small (n < or = 10) versus not small (n > 10).

MEASUREMENTS AND MAIN RESULTS

Twenty-four trials met selection criteria. Small elevations in Cmax were noted when cimetidine (2.71 mg/DL; 95% confidence internal [CI] 1.60, 3.83) or ranitidine (6.95 mg/DL; 95% CI 5.83, 8.08) were coadministered with alcohol. No such differences were noted for famotidine (0.28 mg/DL; 95% CI -1.24, 1.80) or nizatidine (2.33 mg/DL;, 95% CI -0.06, 4.72). The elevation detected with cimetidine and ranitidine was most pronounced in smaller studies (n < 10). Separate analyses investigating the effect of alcohol dose and fed or fasted status of participants revealed no clinically important differences.

CONCLUSIONS

Cimetidine and ranitidine, but not the other H2RAs, can cause small elevations of serum alcohol level when alcohol and drug are administered concurrently. Studies with larger numbers of participants were less likely to demonstrate this effect. Relative to accepted, legal definitions of intoxication, the effect of any H2RA on blood alcohol level is unlikely to be clinically relevant.

Alcohol and injuries in elderly people

Injuries are a common cause of morbidity and mortality among elderly people. Falls are the most common type of accident, accounting for around 40% of injuries. There is substantial evidence that heavy alcohol use is an important risk factor for injuries in younger people, but results of the few studies of alcohol and injuries among elderly people have been inconsistent. In this paper, we review the literature on the effects of alcohol on gait and balance and present reasons that a causal relationship between alcohol and injuries is biologically plausible. We review the epidemiological studies of the relationship between alcohol and falls, hip fractures and other injuries in the elderly population and discuss sources of error in these studies. Selection bias, small sample sizes, measurement error and potential confounders such as age, gender, health status and medications may have played a substantial role in negative results from several studies. Further research that will help clarify the relationship between alcohol and injuries in elderly people is sorely needed.

Gastrointestinal alcohol dehydrogenase

Alcohol dehydrogenase (ADH) consists of a family of isozymes that convert alcohols to their corresponding aldehydes using NAD+ as a cofactor. The metabolism of ethanol by gastrointestinal ADH isozymes results in the production of acetaldehyde, a highly toxic compound that binds to cellular protein and DNA if not further metabolized to acetate by acetaldehyde dehydrogenase isozymes. Acetaldehyde seems to be involved in ethanol-associated cocarcinogenesis. The metabolism of retinol and the generation of retinoic acid is a function of class I and class IV ADH, and its inhibition by alcohol may lead to an alteration of epithelial cell differentiation and cell growth and may also be involved in ethanol-associated gastrointestinal cocarcinogenesis.

Metabolism of ethanol and some associated adverse effects on the liver and the stomach

Current knowledge of alcohol oxidation and its effects on hepatic metabolism and its toxicity are summarized. This includes an evaluation of the relationship of the level of consumption to its interaction with nutrients (especially retinoids, carotenoids, and folate) and the development of various stages of liver disease. Ethanol metabolism in the stomach and its link to pathology and Helicobacter pylori is reviewed. Promising therapeutic approaches evolving from newly gained insight in the pathogenesis of medical complications of alcoholism are outlined. At present, the established approach for the prevention and treatment of alcoholism are outlined. At present, the established approach for the prevention and treatment of alcoholic liver injury is to control alcohol abuse, with the judicial application of selective antioxidant therapy, instituted at early stages, prior to the social or medical disintegration of the patient, and associated with antiinflammatory agents at the acute phase of alcoholic hepatitis. In addition, effective antifibrotic therapy may soon become available.

Gastric ethanol metabolism and gastritis: interactions with other drugs, Helicobacter pylori, and antibiotic therapy (1957-1997)--a review

The stomach provides some protection against the penetration of ethanol into the body by contributing to the metabolism of ethanol. The latter is attenuated by various drugs and, although the magnitude of this effect is still the subject of debate, patients should be warned of the corresponding possible increase in blood alcohol levels. Furthermore, oxidation of ethanol generates acetaldehyde, a toxic metabolite. In addition, chronic alcohol abuse seems to favor colonization by Helicobacter pylori, which produces ammonia that also contributes to the commonly associated chronic gastritis. Because antibiotics were shown over the last 4 decades to effectively eliminate gastric ammonia, they should be considered for the routine treatment of such chronic gastritis in the way they are now being used for ulcer therapy.

Factors predicting relapse during maintenance treatment with famotidine in patients with healed reflux esophagitis. Dutch Esophagitis Study Group

Little is known about possible predictive factors influencing the relapse rate in patients with healed reflux esophagitis during maintenance therapy with histamine2 (H2)-receptor antagonists. Therefore, the efficacy of famotidine 20 mg twice daily was evaluated in an open-label prospective study in 317 patients who had experienced healing of erosive reflux esophagitis after treatment with famotidine; 259 patients completed the study and were assessable according to study protocol. The cumulative endoscopic relapse rates at 4, 8, and 12 months were 20%, 30%, and 36%, respectively, according to the per-protocol analysis. The most predictive determinant of relapse was the duration of acute treatment required to achieve healing: Relapse occurred significantly less often in patients who experienced healing with 6 weeks of acute treatment than in those who experienced healing with 12 and 24 weeks of treatment. The second most important determinant was the initial endoscopic severity of the disease. Patients with initial grade I esophagitis had significantly fewer relapses. Relapse rate appeared to be unrelated to initial severity and duration of symptoms, smoking habits, or strength of acute treatment. The results showed that maintenance therapy with famotidine 20 mg twice daily is effective in a large proportion of patients with healed reflux esophagitis, with few adverse effects reported.

Pharmacokinetic interactions between alcohol and other drugs

The frequent use of alcohol (ethanol) together with prescription drugs gives any described pharmacokinetic interaction significant clinical implications. The issue is both the effect of alcohol on the pharmacokinetics of various drugs and also the effect of those drugs on the pharmacokinetics of alcohol. This review discusses these pharmacokinetic interactions but also briefly describes some other effects of alcohol that are clinically relevant to drug prescribing. The use of several different study designs may be required before we can confidently state the presence or absence of any alcohol-drug interaction. Short term administration of alcohol in volunteers is the most common study design but studies of social drinking and prolonged moderate alcohol intake can be important in some situations. Community-based studies may illustrate the clinical relevance of any interaction. Alcohol can affect the pharmacokinetics of drugs by altering gastric emptying or liver metabolism (by inducing cytochrome P450 2E1). Drugs may affect the pharmacokinetics of alcohol by altering gastric emptying and inhibiting gastric alcohol dehydrogenase. The role of gastric alcohol dehydrogenase in the first-pass metabolism of alcohol is reviewed in this article and the arguments for and against any potential interaction between alcohol and H2 receptor antagonists are also discussed. The inhibition of the metabolism of acetaldehyde may cause disulfiram-like reactions. Pharmacodynamic interactions between alcohol and prescription drugs are common, particularly the additive sedative effects with benzodiazepines and also with some of the antihistamine drugs; other interactions may occur with tricyclic antidepressants. Alcohol intake may be a contributing factor to the disease state which is being treated and may complicate treatment because of various pathophysiological effects (e.g. impairment of gluconeogenesis and the risk of hypoglycaemia with oral hypoglycaemic agents). The combination of nonsteroidal anti-inflammatory drugs and alcohol intake increases the risk of gastrointestinal haemorrhage.

The effect of cimetidine on ethanol concentrations in fasting women and men after two different doses of alcohol

BACKGROUND

Serum ethanol concentrations may become higher when alcohol is consumed during treatment with histamine receptor antagonists, especially if ethanol is ingested postprandially. Only a few studies have investigated fasting subjects, and women have only been investigated sporadically.

METHODS

The present study compared serum ethanol concentrations after a 4-h fast followed by a low (0.15 g/kg) and a high (0.45 g/kg) dose of ethanol, on two separate occasions in six women and six men. The study was carried out before and after treatment with 400 mg cimetidine twice daily.

RESULTS

Cimetidine administration did not change the area under the concentration-time curve or the maximal serum ethanol concentration in either women or men, irrespective of ethanol dose. Ethanol elimination rate was unchanged by cimetidine.

CONCLUSION

Cimetidine does not influence the ethanol concentration-time curve when ethanol is ingested on an empty stomach.

Ethanol metabolism, cirrhosis and alcoholism

Alcohol-induced tissue damage results from associated nutritional deficiencies as well as some direct toxic effects, which have now been linked to the metabolism of ethanol. The main pathway involves liver alcohol dehydrogenase which catalyzes the oxidation of ethanol to acetaldehyde, with a shift to a more reduced state, and results in metabolic disturbances, such as hyperlactacidemia, acidosis, hyperglycemia, hyperuricemia and fatty liver. More severe toxic manifestations are produced by an accessory pathway, the microsomal ethanol oxidizing system involving an ethanol-inducible cytochrome P450 (2E1). After chronic ethanol consumption, there is a 4- to 10-fold induction of 2E1, associated not only with increased acetaldehyde generation but also with production of oxygen radicals that promote lipid peroxidation. Most importantly, 2E1 activates many xenobiotics to toxic metabolites. These include solvents commonly used in industry, anaesthetic agents, medications such as isoniazid, over the counter analgesics (acetaminophen), illicit drugs (cocaine), chemical carcinogens, and even vitamin A and its precursor beta-carotene. Furthermore, enhanced microsomal degradation of retinoids (together with increased hepatic mobilization) promotes their depletion and associated pathology. Induction of 2E1 also yields increased acetaldehyde generation, with formation of protein adducts, resulting in antibody production, enzyme inactivation, decreased DNA repair, impaired utilization of oxygen, glutathione depletion, free radical-mediated toxicity, lipid peroxidation, and increased collagen synthesis. New therapies include adenosyl-L-methionine which, in baboons, replenishes glutathione, and attenuates mitochondrial lesions. In addition, polyenylphosphatidylcholine (PPC) fully prevents ethanol-induced septal fibrosis and cirrhosis, opposes ethanol-induced hepatic phospholipid depletion, decreased phosphatidylethanolamine methyltransferase activity and activation of hepatic lipocytes, whereas its dilinoleoyl species increases collagenase activity. Current clinical trials with PPC are targeted on susceptible populations, namely heavy drinkers at precirrhotic stages.

Ethnic differences in gastric sigma-alcohol dehydrogenase activity and ethanol first-pass metabolism

We assessed whether the low sigma-alcohol dehydrogenase (ADH) activity in Japanese (compared with Caucasians) affects the first-pass metabolism of ethanol. ADH isozyme activities were determined in endoscopic biopsies of the gastric corpus from 24 Japanese and 41 Caucasian men by starch gel electrophoresis and by comparing the reduction of m-nitrobenzaldehyde (a preferred substrate of sigma-ADH) with that of acetaldehyde (a preferred substrate of gamma-ADH) and the glutathione-dependent formaldehyde oxidation (a specific reaction of chi-ADH). Alcohol pharmacokinetics was compared in 10 Japanese and 10 Caucasians after administration of ethanol (300 mg/kg of body weight) intravenously or orally, using 5 and 40% oral solutions. Japanese exhibited lower sigma-ADH activity than Caucasians, with no difference in the other gastric isozymes. With 5% ethanol, first-pass metabolism was strikingly lower in Japanese than in Caucasians. Blood alcohol levels were similar because of the high elimination rate in Japanese due to the hepatic beta 2-ADH variant. With 40% ethanol, the first-pass metabolism increased in both groups to comparable levels, suggesting an additional contribution by chi-ADH at high ethanol concentrations. These results indicate that sigma-ADH activity contributes significantly to gastric ethanol oxidation and its lower activity in Japanese is associated with lesser first-pass metabolism.

Reversion by histamine H2-receptor antagonists of plasma membrane alterations in ethanol-induced gastritis

Ethanol administration rapidly damages surface epithelial cells of rat stomach, leading to altered cellular plasma membranes. Histamine H2-receptor antagonists (H2RA) have been shown to have preventive properties against ethanol-induced gastric mucosal injury. Therefore, the possible reverting properties of H2RA (cimetidine, ranitidine, and famotidine) were tested in ethanol-induced gastritis. Subchronic ethanol administration elicited a histological profile of gastritis and alterations at the plasma membrane level (diminution of some phospholipids, increased cholesterol, and decreased activity of 5'-nucleotidase). H2RA administration to rats with gastritis promptly corrected the ethanol-induced mucosal damage. In addition, cytosolic enzyme activities (alcohol and lactate dehydrogenases) were also modified by gastritis and treatment with H2RA. In conclusion, our data suggest that H2RA improved restitution of the gastric mucosa contributing to the healing process of the gastric damage. The latter indicates reverting properties of H2RA on gastric damage, as well as their cytoprotective effect already described.

Failure to find exon 7 polymorphism of the ADH7 gene in Chinese, Japanese, African-Americans, and Caucasians

Class IV alcohol dehydrogenase (sigma-ADH) activity has been found in high levels in the stomach and esophagus, but not in liver. Gastric ADH activity has been reported to influence blood alcohol levels after oral ethanol ingestion, suggesting that sigma-ADH activity plays a role in first-pass metabolism. It has also been reported that women have lower sigma-ADH activity than men and that Asians have lower sigma-ADH activity than Caucasians and African-Americans. A genetic basis for these gender and ethnic differences in sigma-ADH activity has been postulated. A recent study in a Japanese subject found a point mutation in the codon for amino acid 287 of the ADH7 gene (which encodes sigma-ADH), changing the amino acid from glycine to valine. A polymerase chain reaction-sequencing assay was established to determine the frequency of this polymorphism in the Asian, Caucasian, and African-American populations. The polymorphism was not present in the 21 Asians, 15 Caucasians, and 3 African-Americans we genotyped, suggesting that if this polymorphism exists, its frequency is low in these ethnic groups. It is therefore unlikely to be responsible for the absence of sigma-ADH activity in gastric specimens from Asians.