Protein-acetaldehyde adducts in serum of alcoholic patients

Synergistic and Detrimental Effects of Alcohol Intake on Progression of Liver Steatosis

Nonalcoholic fatty liver disease (NAFLD) and alcoholic liver disease (ALD) are the most common liver disorders worldwide and the major causes of non-viral liver cirrhosis in the general population. In NAFLD, metabolic abnormalities, obesity, and metabolic syndrome are the driving factors for liver damage with no or minimal alcohol consumption. ALD refers to liver damage caused by excess alcohol intake in individuals drinking more than 5 to 10 daily units for years. Although NAFLD and ALD are nosologically considered two distinct entities, they show a continuum and exert synergistic effects on the progression toward liver cirrhosis. The current view is that low alcohol use might also increase the risk of advanced clinical liver disease in NAFLD, whereas metabolic factors increase the risk of cirrhosis among alcohol risk drinkers. Therefore, special interest is now addressed to individuals with metabolic abnormalities who consume small amounts of alcohol or who binge drink, for the role of light-to-moderate alcohol use in fibrosis progression and clinical severity of the liver disease. Evidence shows that in the presence of NAFLD, there is no liver-safe limit of alcohol intake. We discuss the epidemiological and clinical features of NAFLD/ALD, aspects of alcohol metabolism, and mechanisms of damage concerning steatosis, fibrosis, cumulative effects, and deleterious consequences which include hepatocellular carcinoma.

Autoimmune hepatitis induced by syngeneic liver cytosolic proteins biotransformed by alcohol metabolites

BACKGROUND AND AIMS

Aldehydes that are produced following the breakdown of ethanol (acetaldehyde) and lipid peroxidation of membranes (malondialdehyde) have been shown to bind (adduct) proteins. Additionally, these two aldehydes can combine (MAA) on nonsyngeneic and syngeneic proteins to initiate numerous immune responses to the unmodified part of the protein in the absence of an adjuvant. Therefore, these studies provide a potential mechanism for the development of antigen-specific immune responses resulting in liver damage should syngeneic liver proteins be adducted with MAA.

METHODS

This study sought to test whether MAA-modified syngeneic liver cytosolic proteins administered daily in the absence of adjuvant into C57BL/6 mice abrogates tolerance to initiate a MAA-induced autoimmune-like hepatitis.

RESULTS

In mice immunized with MAA-modified cytosols, there was an increase in liver damage as assessed by aspartate aminotransferase/alanine aminotransferase levels that correlated with liver pathology scores and the presence of the pro-fibrotic factors, smooth muscle actin, TGF-β, and collagen. IgG antibodies and T-cell proliferative responses specific for cytosolic proteins were also detected. Pro-inflammatory cytokines were produced in the livers of animals exposed to MAA-modified cytosols. Finally, transfer of immunized T cells to naïve animals caused biochemical and histological evidence of liver damage.

CONCLUSIONS

These data demonstrate that a disease with an autoimmune-like pathophysiology can be generated in this animal model using soluble MAA-modified syngeneic liver cytosols as the immunogen. These studies provide insight into potential mechanism(s) that the metabolites of alcohol may play in contributing to the onset of an autoimmune-like disease in patients with alcoholic liver disease.

A new CE-ESI-MS method for the detection of stable hemoglobin acetaldehyde adducts, potential biomarkers of alcohol abuse

A new CE-ESI-MS method was developed to provide a simple way to study changes to hemoglobin (HbA) induced by acetaldehyde (Ach) in vitro. Instrumental parameters were univariately optimized in order to maximize the sensitivity of the CE-ESI-MS method. The electrophoretic separations were carried out in poly-E323-coated capillaries using 60 mM formic acid raised to pH 3.0 with ammonia and containing 5% 2-propanol while the sheath liquid, 2-propanol/water (30:70) with 0.1% formic acid, was delivered at 1.0 microL/min through a coaxial sheath flow electrospray interface. The HbA was incubated with Ach for intervals up to 24 h at concentration varying in the window 0.2-20 mM. Four stable Ach-hemoglobin adducts in the hemoglobin tryptic digest were observed at the submillimolar Ach concentration and characterized by MS/MS experiments: although the alpha and beta N-amino terminal modifications were expected, the two internal ones arising, respectively, from the condensation of Ach molecules on the histidine residue in position 4 in alpha4 (i.e. the fourth peptide after tryptic digestion of alpha chain starting from amino terminal) and on the asparagine residue in position 2 in beta3, were identified for the first time. During the in vitro experiments higher concentrations of Ach were also used; however, it was not possible to identify any other stable modification of hemoglobin. Interestingly, those stable modifications are the only ones in vivo identified in the hemoglobin of moderate alcohol drinkers.

The effect of acetaldehyde on human plasma factor XIII function

The effect of acetaldehyde on the transglutaminase activity in pooled normal human plasma has been investigated. In this study, 0.05, 0.2, and 0.7 ml of pooled human plasma were preincubated for 30 min. at room temperature with buffer or acetaldehyde at final concentrations of 40.6, 22.4, and 11.2 mM before being utilized for Factor XIIIa assay with fibrinogen and thrombin which had been preheated at 40 degrees C to destroy endogenous Factor XIII/XIIIa activity. At all concentrations of acetaldehyde and all concentrations of plasma-containing Factor XIII which were employed, prolongation of both clotting time and stabilization time was observed. The 11.2 mM acetaldehyde is within the range of daily acetaldehyde production to be predicted in severe alcoholics as a consequence of imbibing alcohol. The stabilization times measured for Factor XIIIa activity appear to be the most sensitive to acetaldehyde compared to acetaldehyde effects on thrombin, Factor Xa, and fibrinogen studied earlier in this laboratory, as well as Factors II, VII, and X.

Immunological response in alcoholic liver disease

The development of alcoholic liver disease (ALD) can be attributed to many factors that cause damage to the liver and alter its functions. Data collected over the last 30 years strongly suggests that an immune component may be involved in the onset of this disease. This is best evidenced by the detection of circulating autoantibodies, infiltration of immune cells in the liver, and the detection of hepatic aldehyde modified proteins in patients with ALD. Experimentally, there are numerous immune responses that occur when proteins are modified with the metabolites of ethanol. These products are formed in response to the high oxidative state of the liver during ethanol metabolism, causing the release of many inflammatory processes and potential of necrosis or apoptosis of liver cells. Should cellular proteins become modified with these reactive alcohol metabolites and be recognized by the immune system, then immune responses may be initiated. Therefore, it was the purpose of this article to shed some insight into how the immune system is involved in the development and/or progression of ALD.

Alcoholic macrocytosis--is there a role for acetaldehyde and adducts?

Although alcohol abuse is known to cause a wide array of adverse effects on blood cell formation, the molecular mechanisms by which alcohol exerts its toxic actions have remained poorly defined. Elevated mean corpuscular volume (MCV), macrocytosis, is the most typical morphological abnormality induced by excessive ethanol consumption. This paper reviews recent data indicating that acetaldehyde, the first metabolite of ethanol, may play a role in the haematological derangements in peripheral blood cells and in bone marrow of alcoholic patients. Studies in experimental animals and in human alcoholics have shown that acetaldehyde can bind to proteins and cellular constituents forming stable adducts. Elevated adduct levels have been found from the erythrocytes of alcohol abusers, which may also be associated with ethanol-induced effects in haematopoiesis and adverse consequences in cellular functions.

Chromatographic methods for the determination of markers of chronic and acute alcohol consumption

The development in chromatographic methods for the determination of markers of alcohol consumption is summarized in this review. The markers included in this article are ethanol in body fluids, ethanol congeners, fatty acid ethyl esters (FAEEs), ethyl glucuronide (EtG), cocaethylene (CE), carbohydrate-deficient transferrin (CDT), phosphatidylethanol (PEth), 5-hydroxytryptophol (5-HTOL), dolichol, ketone bodies, acetaldehyde-protein adducts, and salsolinol (SAL). Some of these markers for alcohol consumption do not only indicate previous ethanol ingestion, but also approximate the amount of intake and the time when ethanol ingestion last occurred. Basic information about the procedures, work-up, and chromatographic conditions are summarized in tables. Also the main metabolic pathways and reaction schemes are demonstrated in figures. Some examples of typical applications are presented. The author points out that in many of the reviewed papers validation data of the procedures as well as specificities and sensitivities were not clearly presented and consequently were not comparable.

Short- and long-term effects of acetaldehyde on plasma

The effect of low concentrations of acetaldehyde on activated partial thromboplastin time (APTT) and prothrombin time (PT) of Accuclot coagulation plasmas was monitored over a prolonged time to mimic effects observed in alcoholism. A prolongation of the APTT from 31.9 +/- 0.7 s to 32.6 +/- 0.9 s (n = 8; P =.007) was observed after a 30-min preincubation time with 140 microM acetaldehyde. However, a minimum of 3.6 mM acetaldehyde was required to extend the APTT from 36.6 +/- 1.0 s to 41.2 +/- 0.8 s (P =.001) over an 18-h exposure time. Plasma acetaldehyde levels as low as 2.24 mM caused elevation of PTs from 12.5 +/- 0.5 s to 14.4 +/- 0.2 s (P =.005) after a 24-h preincubation time. These findings seem to indicate that short-term contact of acetaldehyde with plasma, probably yielding reversible interactions, may interfere with APTTs to a greater extent than long-term contact, which would presumably yield stable, irreversible interactions. In comparing the effects of 8.94, 17.9, 89.4, and 447 mM acetaldehyde on the PTs of Level I, II, and III plasma, the PTs were most increasingly prolonged in Level III plasma and least prolonged in Level I plasma at each acetaldehyde concentration, although the plasmas have comparable protein concentrations. These findings seem to indicate that coagulation factors are sensitive to inactivation by acetaldehyde.

Relationship between serum levels of anti-low-density lipoprotein-acetaldehyde-adduct antibody and aldehyde dehydrogenase 2 heterozygotes in patients with alcoholic liver injury

We prepared low-density lipoprotein (LDL)-acetaldehyde-adduct (hereafter abbreviated as LDL-adduct) and anti-LDL-adduct antibody by using Watanabe hyperlipidemic rabbits, and determined values of serum anti-LDL-adduct antibody levels by the ELISA method in healthy adults and patients with alcoholic liver injury. In the nondrinking group in healthy adults, values of anti-LDL-adduct antibody levels were 25 +/- 13 microg/ml, and there was no significant difference between moderate drinkers without diseases and the nondrinking group in healthy adults. Values of anti-LDL-adduct antibody in alcoholic disease groups, 17 +/- 9 microg/ml for the patients with the fatty liver group, 21 +/- 14 microg/ml for the hepatic fibrosis group, 70 +/- 21 microg/ml for the alcoholic hepatitis group, 41 +/- 50 microg/ml for the alcoholic cirrhosis group, and 19 +/- 18 microg/ml for the alcoholic pancreatitis group. Examinations of aldehyde dehydrogenase 2 (ALDH2) genetic variations by the polymerase chain reaction-single-strand conformation polymorphism (PCR-SSCP) method in the healthy group and the liver injury group revealed a tendency for patients with ALDH2(1)/2(2) in the liver injury group to have relatively mild liver lesions. When comparing anti-LDL-adduct antibody levels between ALDH2 genetic variations, those for the patients with ALDH2(1)/2(2) (36 +/- 40 microg/ml) were significantly higher than those for patients with ALDH2(1)/2(2) (11 +/- 5 microg/ml). Results of the present study suggest that genetic variation may influence the progression of liver injury.

Soluble proteins modified with acetaldehyde and malondialdehyde are immunogenic in the absence of adjuvant

Recent studies have shown that the alcohol metabolites malondialdehyde and acetaldehyde can combine to form a stable adduct (MAA) on proteins. This adduct has been detected in the livers of rats chronically consuming ethanol, and serum antibodies to MAA have been observed at significantly higher concentrations in ethanol-fed when compared with pair-fed or chow-fed control rats. More recently, preliminary studies have strongly suggested that the MAA adduct is capable of stimulating antibody responses to soluble proteins in the absence of adjuvants. The antibodies produced recognize either the MAA epitope or the carrier protein itself. Therefore, it was the purpose of this study to examine the potential immunogenicity of MAA-modified exogenous proteins in the absence of adjuvants. Balb/c mice were immunized in the presence or absence of adjuvant with different concentrations of unmodified or MAA-modified proteins. The antibody response to both the MAA epitope and unmodified protein epitopes were determined by ELISA. In the absence of adjuvant, significant antibody responses were induced to both the MAA epitope and nonmodified protein epitopes. Smaller immunizing doses of MAA-protein conjugate favored the production of antibodies to nonmodified proteins, whereas larger doses induced a strong anti-MAA response. In studies to begin determining a mechanism for the specificity of the response in the absence of adjuvants, peritoneal macrophages were found to bind and degrade MAA-adducted proteins through the use of a scavenger receptor. This indicated that MAA-adducted proteins may be specifically taken up and epitopes presented to the humoral immune system in the absence of adjuvants. Importantly, these are the first data showing that an alcohol-related metabolite can induce an antibody response in the absence of adjuvant and suggesting a mechanism by which antibody to the MAA adduct or its carrier (exogenous or endogenous) proteins may be generated in vivo.

Early alcoholic liver injury: formation of protein adducts with acetaldehyde and lipid peroxidation products, and expression of CYP2E1 and CYP3A

The formation of protein adducts with reactive aldehydes resulting from ethanol metabolism and lipid peroxidation has been suggested to play a role in the pathogenesis of alcoholic liver injury. To gain further insight on the contribution of such aldehydes in alcoholic liver disease, we have compared the appearance of acetaldehyde, malondialdehyde, and 4-hydroxynonenal adducts with the expression of cytochrome P-450IIE1, and cytochrome P-4503A enzymes in the liver of rats fed alcohol with a high-fat diet for 2 to 4 weeks according to the Tsukamoto-French procedure and in control rats (high-fat liquid diet or no treatment). Urine alcohol and serum aminotransferase levels were recorded, and the liver pathology was scored from 0 to 10 according to the presence of steatosis, inflammation, necrosis, and fibrosis. The ethanol treatment resulted in the accumulation of fat, mild necrosis and inflammation, and a mean liver pathology score of 3 (range: 1 to 5). Liver specimens from the ethanol-fed animals with early alcohol-induced liver injury were found to contain perivenular, hepatocellular acetaldehyde adducts. Malondialdehyde and 4-hydroxynonenal adducts were also present showing a more diffuse staining pattern with occasional sinusoidal reactions. In the control animals, a faint positive reaction for the hydroxynonenal adduct occurred in some of the animals fed the high fat diet, whereas no specific staining was observed in the livers from the animals receiving no treatment. Expression of both CYP2E1 and CYP3A correlated with the amount of protein adducts in the liver of alcohol-treated rats. Distinct CYP2E1-positive immunohistochemistry was seen in 3 of 7 of the ethanol-fed animals. In 5 of 7 of the ethanol-fed animals, the staining intensities for CYP3A markedly exceeded those obtained from the controls. The present findings indicate that acetaldehyde and lipid peroxidation-derived adducts are generated in the early phase of alcohol-induced liver disease. The formation of protein adducts appears to be accompanied by induction of both CYP2E1 and CYP3A.

Determination of biological markers for alcohol abuse

Alcoholism is one of the most frequent addictions and an important subject in forensic medicine and clinical toxicology. Several laboratory abnormalities are associated with excessive alcohol consumption. They are useful in the diagnosis of alcoholism especially during the follow-up of various treatment programs. The biological markers mostly used for diagnosis of alcoholism are presented. Especially, methods for the determination of the following diagnostic tools are reviewed: congener alcohols, gamma-glutamyltransferase, aspartate and alanine aminotransferase, beta-hexosaminidase, erythrocyte aldehyde dehydrogenase, alpha-amino-n-butyric acid to leucine ratio, macrocytosis, carbohydrate-deficient transferrin, (apo)lipoproteins, fatty acid ethyl esters, blood acetate, acetaldehyde adducts, 5-hydroxytryptophol, dolichol and condensation products. No laboratory test exists that is reliable enough for the exact diagnosis of alcoholism. The combination of physician interview, questionnaire and laboratory markers is necessary for the diagnosis of alcoholism.

An enzyme immune assay for serum anti-acetaldehyde adduct antibody using low-density lipoprotein adduct and its significance in alcoholic liver injury

An acetaldehyde (AcH) adduct was prepared using rabbit low-density lipoprotein as carrier proteins. An antibody against this adduct was raised in Watanabe heritable hyperlipidemic rabbits and cross-reacted with human low-density lipoprotein and bovine serum albumin adducts. Using this antibody, serum anti-AcH-adduct antibody levels were measured by a direct ELISA method in 56 Japanese adults (healthy adults and patients with nonalcoholic gastrointestinal diseases, alcoholic liver injury, or alcoholic pancreatitis). The antibody level (mean +/- SD) was 22 +/- 10 microg/ml in healthy adults, 22 +/- 11 microg/ml in nonalcoholic gastrointestinal diseases, and 16 +/- 13 microg/ml in alcoholic pancreatitis. These antibody levels tended to increase with the progression of alcoholic liver injury, starting from fatty liver via hepatitis to cirrhosis, 29 +/- 24 microg/ml in fatty liver, 35 +/- 29 microg/ml in alcoholic hepatitis, and 46 +/- 54 microg/ml in alcoholic cirrhosis. The antibody level in patients taking 100 g or more of ethanol per day tended to be higher, compared with those in people taking less ethanol. A follow-up observation revealed that alcohol abstinence after hospitalization raised serum anti-AcH-adduct antibody level in some patients and kept it constantly low in other patients. The immunohistochemical study using the anti-AcH-adduct antibody revealed the presence of adduct-like substance in hepatocytes of liver biopsy specimens obtained from patients with alcoholic liver disease. The results indicate that the anti-AcH-adduct antibody may be associated with the progress of alcoholic liver diseases.

Binding of acetaldehyde to rat gastric mucosa during ethanol oxidation

Acetaldehyde, the first product of ethanol metabolism, has previously been shown to form potentially harmful adducts with various proteins. The aim of this study was to investigate whether acetaldehyde--either exogenous or metabolically derived--binds to gastric mucosal proteins. Homogenized rat gastric mucosa was incubated with various concentrations of radiolabeled acetaldehyde or ethanol for different time periods. Acetaldehyde-protein adducts were determined by a liquid scintillation counter. In addition, mucosa was incubated with nonlabeled ethanol, and the acetaldehyde formed was measured by using headspace gas chromatography. Incubation of gastric mucosa with (14C)-acetaldehyde led to a concentration- and time-dependent radiolabeling of mucosal proteins. Formation of acetaldehyde adducts occurred relatively rapidly within 30 minutes and even at low acetaldehyde levels (5 micromol/L). Stable adducts represented 77% +/- 5% (mean +/- SEM) of the total adducts formed. In the presence of ethanol, acetaldehyde production and adduct formation took place in a concentration- and time-dependent manner. 4-Methylpyrazole and sodium azide inhibited acetaldehyde production to 7% +/- 1% of control and decreased the amount of acetaldehyde adducts to 55% +/- 8%. Enhanced acetaldehyde formation (to 420% +/- 50%) was clearly reflected in increased adduct formation (550% +/- 110%). In conclusion, both exogenous and endogenous acetaldehyde binds to gastric mucosal proteins in vitro. Gastric mucosal acetaldehyde production and the consequent adduct formation could be a pathogenetic factor behind ethanol-associated gastric injury.

Protein targets of xenobiotic reactive intermediates

Many xenobiotics are metabolically activated to electrophilic intermediates that form covalent adducts with proteins; the mechanism of toxicity is either intrinsic or idiosyncratic in nature. Many intrinsic toxins covalently modify cellular proteins and somehow initiate a sequence of events that leads to toxicity. Major protein adducts of several intrinsic toxins have been identified and demonstrate significant decreases in enzymatic activity. The reactivity of intermediates and subcellular localization of major targets may be important in the toxicity. Idiosyncratic toxicities are mediated through either a metabolic or immune-mediated mechanism. Xenobiotics that cause hypersensitivity/autoimmunity appear to have a limited number of protein targets, which are localized within the subcellular fraction where the electrophile is produced, are highly substituted, and are accessible to the immune system. Metabolic idiosyncratic toxins appear to have limited targets and are localized within a specific subcellular fraction. Identification of protein targets has given us insights into mechanisms of xenobiotic toxicity.

The formation and stability of imidazolidinone adducts from acetaldehyde and model peptides. A kinetic study with implications for protein modification in alcohol abuse

The kinetics of the reaction of acetaldehyde (AcH) with the alpha-amino group of several di- and tripeptides to form 2-methylimidazolidin-4-one adducts were determined at pH 7, 4, 37 degrees C, using reverse phase HPLC to separate peptides from adducts. The imidazolidin-4-one structure of the adducts was confirmed by 13C NMR spectroscopy. The reaction of val-gly-gly with AcH was shown to follow second-order kinetics over a wide range of concentrations of both reactants, with k2 = 0.734 +/- 0.032 M(-1) min(-1). Under conditions similar to those in the liver of an alcoholic during chronic ethanol oxidation ([Ach]o = 50-910 microm; [free peptide alpha-amino groups]o = 1.5 mM), the reaction proceeded until effectively all of the AcH had been consumed. The side chain of the N-terminal amino acid was shown not to have a marked effect on the rate of imidazolidinone formation. The decomposition of the imidazolidinone adduct of val-gly-gly and AcH was observed at 60-100 degrees C. Extrapolation of an Arrhenius plot to 37 degrees C provided an estimate of K(obs) of 0.002 h-1 (t1/2 approximately 14 days). Based on these kinetic studies, it is concluded that imidazolidinone adducts of AcH with proteins may be present in the liver and, possibly, in the blood of alcoholics.

Interaction of acetaldehyde with plasma proteins of the renin-angiotensin system

Chronic alcohol abuse may lead to hypertension by stimulating the activity of the renin angiotensin system (RAS). While there are reports on the alcohol associated increase of angiotensin II in rats and increases of plasma renin activity in rats and human alcoholics, the exact mechanisms of stimulation of the RAS activity is not clear. This study provides evidence for a biochemical interaction of acetaldehyde, the primary oxidative metabolite of ethanol, upon bilaterally nephrectomized (NEPEX) rat plasma that contains significant quantities of angiotensinogen and lacks active renin. Rat plasma served as the source of renin in this study. Preincubation of NEPEX plasma with 0.2 M acetaldehyde at 4 degrees C for 2 h resulted in a 21% increase in the angiotensin I (A I) formation by the rat plasma renin and 27% increase in the A I formation by the trypsinized rat plasma renin. When the rat plasma which contains modest quantities of endogenous angiotensinogen in addition to renin was preincubated with 0.2 M acetaldehyde at 4 degrees C for 2 h, the rate of A I formation was increased by 10%. Equivalent amounts of ethanol did not modify the rate of A I generation when added to NEPEX plasma or rat plasma. These results suggest the possibility of a biochemical interaction of acetaldehyde with the renin substrate which may enhance the activity of the RAS cascade, thereby contributing to hypertension in chronic alcoholics.

Acetaldehyde exposure causes growth inhibition in a Chinese hamster ovary cell line that expresses alcohol dehydrogenase

Chronic ethanol exposure causes many pathophysiological changes in cellular function due to ethanol itself and/or the effects of its metabolism (i.e., generation of acetaldehyde and redox equivalents). However, the role of each of these effects remains controversial. To address these questions, we have developed a cell line that expresses alcohol dehydrogenase. This cell line permits separate examination of the effects of ethanol and its metabolite acetaldehyde on cell function. An expression vector for the mouse liver alcohol dehydrogenase was constructed and transfected into Chinese hamster ovary cells. Cells expressing alcohol dehydrogenase were identified by screening with allyl alcohol, which is metabolized by alcohol dehydrogenase to the toxic aldehyde acrolein. A number of cell lines were identified that expressed alcohol dehydrogenase. A-10 cells were selected for further study because of their high sensitivity to allyl alcohol, suggesting a high level of alcohol dehydrogenase expression. These cells expressed a mRNA that hybridizes with the alcohol dehydrogenase cDNA and had an alcohol dehydrogenase activity comparable to murine liver. When cultures of these cells were exposed to ethanol, acetaldehyde was detected in both the medium and cells. The acetaldehyde concentration in the medium remained constant for at least 1 week in culture and was a function of the added ethanol concentration. Chronic exposure of A-10 cells to ethanol resulted in a dose-dependent reduction in the number of cells that accumulated over 7 days. Ethanol-treated cells remained viable, and growth inhibition was reversible. Growth inhibition was blocked by the alcohol dehydrogenase inhibitor 4-methylpyrazole, suggesting that acetaldehyde and not ethanol was responsible for growth inhibition in these cells.

Improved separation of acetaldehyde-induced hemoglobin

A fast-eluting minor variant of hemoglobin A, designated as HbA1-AcH, appears elevated after the incubation of red blood cell hemolysates with acetaldehyde (AcH) and has been proposed as a diagnostic marker for alcoholism or as an indicator for heavy drinking. We have developed an improved HPLC separation of this peak and others elevated by AcH using a polyaspartic acid column (PolyCAT A, PolyLC, Inc.) and a nonlinear buffer gradient with pH changes from 6.6 to 6.8. Saline-washed red blood cells were treated with sodium acetate buffer (pH 5.5) to remove unstable Schiff bases, and then hemolyzed by addition of an equal volume of H2O and 0.4 volumes of CCI4. HbA1-AcH and several others, including two peaks in the HbA1a+b cluster, Hb Pre-A1c, and HbA1d3 were significantly increased by AcH incubation, and the changes were only partially reversible with time. Improved resolution of these peaks allows more accurate quantitation of AcH adducts of hemoglobin.

Characteristics of Helicobacter pylori alcohol dehydrogenase

BACKGROUND

Helicobacter pylori shows alcohol dehydrogenase activity, which in the presence of ethanol leads to in vitro production of acetaldehyde, a toxic and highly reactive substance. The present study was undertaken to further define H. pylori-related ethanol and acetaldehyde metabolism by characterizing H. pylori alcohol dehydrogenase and by determining whether the organism possesses aldehyde dehydrogenase.

METHODS

Cytosolic alcohol and aldehyde dehydrogenase activities were determined spectrophotometrically. Acetaldehyde produced by cytosol during incubation with ethanol was measured by head space gas chromatography. Isoenzyme pattern was studied using isoelectric focusing.

RESULTS

Significant alcohol dehydrogenase activity was observed at a neutral pH known to occur in gastric mucus. The Km for ethanol oxidation was approximately 100 mmol/L for the two strains tested. Acetaldehyde was formed already from a low ethanol concentration known to prevail in the stomach endogenously. Isoelectric focusing of the enzyme showed activity bands with pI at 7.1-7.3, a pattern different from that of gastric mucosal alcohol dehydrogenase. 4-methylpyrazole inhibited enzyme activity in a competitive manner and suppressed the growth of the organism during culture. Neither Helicobacter strain studied showed aldehyde dehydrogenase activity and can thus not remove acetaldehyde by that pathway.

CONCLUSIONS

Acetaldehyde production by H. pylori from exogenous or endogenous ethanol may be a pathogenetic mechanism behind mucosal injury associated with the organism.

Production of antibodies that recognize the heterogeneity of immunoreactive sites in human hemoglobin chemically modified by acetaldehyde

Human hemoglobin (Hgb) was incubated with acetaldehyde under two different conditions: (a) in the presence of 250 mM acetaldehyde for 1 hr then reduced with 100 mM NaCNBH3 for an additional 4 hr at room temperature; and (b) in the presence of 500 mM acetaldehyde for 10 days at room temperature and then reduced with 1 mM NaBH4 for 1 hr. It was found that 44% and 27% of free amino groups in Hgb-acetaldehyde adduct (AA) remained unmodified when Hgb was treated under conditions (a) and (b), respectively. SDS-PAGE analysis revealed that the molecular weight of Hgb-AA(a) [Hgb modified under condition (a)] was slightly greater than that of unmodified Hgb and extensive protein cross-linking had occurred in Hgb-AA(b) [Hgb modified under condition (b)]. Electrophoresis on agarose gel showed the order of negative charge was Hgb-AA(b) > Hgb-AA(a) > unmodified Hgb. Polyclonal antibody raised in rabbits using keyhole limpet hemocyanin as the carrier protein modified by acetaldehyde under condition (a) [i.e., KLH-AA(a)] preferentially recognized Hgb-AA(a), whereas antibody raised using KLH-AA(b) as the immunogen recognized only Hgb-AA(b). In conclusion, antibodies raised with protein-AA antigens produced under different conditions recognize different epitopes.

Measurement of hemoglobin-acetaldehyde adduct in alcoholic patients

A sensitive and specific test for chronic alcohol abuse is useful in the diagnosis and management of alcoholic patients. Herein, we report the measurement of hemoglobin-acetaldehyde adducts (Hb-AA) in alcoholic patients by a sandwich ELISA using different antibodies. Keyhole limpet hemocyanin (KLH), a peptide consists of eight amino acid residues (8-pep, V1 to K8) at the N-terminus of beta-chain of human sickle-cell Hb and a segment of HbA beta-chain consists of 11 amino acids rich in lysine or K (11-pep, G56-K66) were incubated with acetaldehyde and NaCNBH3 to form protein-AAs. 8-Pep-AA and 11-pep-AA were individually conjugated to unmodified KLH as the carrier. Anti-protein-AA IgGs were raised in rabbits using these three protein-AA immunogens. When anti-KLH-AA IgG was used in ELISA, optical densities for alcoholic patients and controls were 0.311 +/- 0.124 and 0.147 +/- 0.042 (means +/- SD, n = 40/group, p < 0.001), respectively. Using mean value +/- 2 SD of controls as the cut-off, sensitivities to detect alcoholic patients were 78, 75, and 43%, respectively, when anti-KLH-AA, anti-11-pep-AA, and anti-8-pep-AA were used. Correlation among optical densities obtained from the first two IgGs was excellent (R2 = 0.905). We conclude that: (1) Hb-AA has the potential of being a good marker for alcohol abuse, and (2) the site of Hb that is modified by acetaldehyde in vivo is primarily located in a surface-accessible domain near the center of the beta-chain of HbA where several lysine residues are clustered.

Localization of protein-acetaldehyde adducts on cell surface of hepatocytes by flow cytometry

Acetaldehyde, a highly reactive intermediate of ethanol metabolism, has been shown to form adducts with liver proteins (e.g., a cytosolic 37 kDa protein and the microsomal cytP450IIE1) in rats fed alcohol chronically. In this study, flow cytometry was utilized to test for the presence of protein-acetaldehyde adducts (-AAs) on the surface of hepatocytes and immunotransblot was used to detect for the 37 kDa protein-AA in cytosol as was previously described. For flow cytometric analysis, rabbit anti-hemocyanin-AA IgG and fluorescein isothiocyanate-conjugated goat anti-rabbit serum IgG were used as the primary and secondary antibodies to label surface protein-AAs on hepatocytes at 0 degrees to 4 degrees C. After labeling and washing, hepatocytes were fixed with paraformaldehyde-cacodylate and analyzed with a flow cytometer. In an experiment wherein hepatocytes isolated from rats pair-fed liquid diets with and without ethanol were treated by adding both the primary and secondary IgGs, some hepatocytes from both alcohol-fed and control rats exhibited positive fluorescence but no significant difference in fluorescence intensity was noted. In another experiment, hepatocytes were isolated from rats pair-fed cyanamide (a selective aldehyde dehydrogenase inhibitor) with and without ethanol. The number of hepatocytes showing positive fluorescence in the presence of both primary and secondary IgGs was significantly higher in rats fed cyanamide plus ethanol than in rats fed cyanamide only. Of note, the 37 kDa protein-AA could be detected by immunotransblot in liver cytosol of alcohol-fed rats but not in the controls of both experiments with and without cyanamide supplementation.(ABSTRACT TRUNCATED AT 250 WORDS)

Modification of proteins and other biological molecules by acetaldehyde: adduct structure and functional significance

1. Chronic ethanol consumption is a major cause of liver disease. The modification of hepatic proteins by acetaldehyde (AcH), the primary metabolite of ethanol, has for some time been suggested as one of the major events initiating alcoholic liver disease. 2. These alterations in protein structure are believed to affect liver cell function, and may serve to activate the immune system. 3. This review considers the interaction between AcH and macromolecules and its functional implications.

Biochemistry of alcoholic liver disease

The biochemistry of alcohol liver disease as it relates to clinical medicine and experimental alcohol liver disease is presented. Clinical features are emphasized in the diagnosis of alcohol liver disease, particularly as it relates to staging the disease and predictors of prognosis. Currently, it is true that the biochemical diagnosis of alcohol liver disease is at best very limited in terms of the sensitivity tests and specificity of the test. It is particularly difficult to detect alcohol liver disease biochemically in the early stages when steatohepatitis is not severe. Consequently, 50% of the patients have already developed cirrhosis at the time they are diagnosed clinically. In this review indicators of malnutrition are emphasized because they have the strongest implications regarding survival during the acute hospitalization stage of the disease. They are also the best indicators of response to therapy during the recovery phase. With respect to experimental work on the pathogenesis of alcohol liver disease, it appears that necrosis is due to the inability to increase blood flow to compensate for increased oxygen utilization. The hypothesis that mitochondrial damage is the cause of liver cell damage is regarded as less important in the pathogenesis of necrosis. The shift in the redox state during alcohol metabolism accounts for the fatty change noted in the central lobular area of the liver in animals fed alcohol. Apparently, there is strong experimental evidence that highly reactive intermediates are important in the pathogenesis of liver damage due to the induction of the isozyme cytochrome P450 IIE1 by alcohol ingestion. This mechanism is enhanced by a diet high in polyunsaturated fatty acids.

Modern approach to alcoholic liver disease

The pathogenesis of alcoholic liver disease is unclear. The recent literature on pathogenic factors, including direct effects of ethanol and its proximate metabolite acetaldehyde, associated nutritional factors, the formation of acetaldehyde-protein adducts, associated immune alterations, and the potential for liver injury due to coexisting hepatitis virus infection, is highlighted. The therapy of patients with advanced alcoholic liver injury, especially alcoholic hepatitis, is also controversial. It seems reasonable that all patients should receive adequate nutrition even if parenteral or enteral supplementation is required. Corticosteroid administration may benefit those patients with alcoholic hepatitis who have coexisting spontaneous hepatic encephalopathy and no gastrointestinal bleeding. For patients with complications from end-stage alcoholic cirrhosis, liver transplantation should be considered, as the patient with alcoholic cirrhosis does as well after liver transplantation as those patients with other forms of end-stage liver disease.

Hemoglobin-acetaldehyde adducts are elevated in women carrying alcohol-damaged fetuses

Alcohol use exceeding 3 to 5 daily drinks is associated with a 30% to 50% risk of delivering a child with fetal alcohol effects (FAE). FAE could be prevented if women were counseled and if they decreased their drinking. Therefore, we need sensitive and specific markers to detect alcohol abuse during pregnancy. We investigated whether acetaldehyde-hemoglobin adducts (Hb-Ach) could be such a marker. Using an antiserum specific for acetaldehyde-generated epitopes in proteins, we measured the levels of Hb-Ach from the red cells of 19 women visiting the outpatient department of pregnant alcohol abusers and from 14 nonpregnant controls. The pregnant women were carefully followed to receive personal antenatal care and intensive counseling on alcohol. Nevertheless, eight of the women delivered infants with FAE. The remaining 11 women had healthy infants, although only four of them stopped drinking totally. The highest concentrations of Hb-Ach were found from women who subsequently delivered children with FAE. When compared with the pregnant women abstaining from ethanol the Hb-Ach values were found to be elevated in five of eight (63%) of the women who gave birth to children with FAE, whereas only in two/seven (28%) of the mothers who despite drinking delivered healthy children. Hb-Ach measurements during pregnancy may prove to be useful to monitor the compliance of women withdrawing from alcohol and to distinguish the mothers at risk of affected offspring. The studies also support a pathophysiological role of acetaldehyde in producing ethanol-associated fetal injury.

Formation of a 37 kilodalton liver protein-acetaldehyde adduct in vivo and in liver cell culture during chronic alcohol exposure

With the use of antibodies that can recognize acetaldehyde adducts and the application of various immunological techniques, several protein-AAs have now been shown to form in vivo during chronic alcohol ingestion. These protein-AAs include the 37-kDa liver protein-AA, the CytP450IIE1-AA, hemoglobin-AA, two serum protein-AAs with molecular weights of 50 kDa and 103 kDa, and collagen type I protein-AA in liver. If acetaldehyde is the agent responsible for alcoholic liver injury, acetaldehyde toxicity in chronic alcohol ingestion must be linked to the ability of acetaldehyde to form adducts with proteins and perhaps other macromolecules. This is at least one mechanism of acetaldehyde-mediated liver injury. For proteins that serve critical functions, acetaldehyde adduct formation may alter their functions and thereby produce organ damage. Acetaldehyde adduct formation can also elicit humoral or cytotoxic immune responses and these responses may also lead to organ injury.

Immunohistochemical demonstration of acetaldehyde-modified epitopes in human liver after alcohol consumption

Acetaldehyde, the toxic product of ethanol metabolism in the liver, covalently binds to a variety of proteins. Recent studies indicate that such binding can stimulate the production of antibodies against the acetaldehyde adducts. We raised rabbit antibodies which recognized various protein-acetaldehyde conjugates but not the corresponding control proteins. Such antibodies were used in immunohistochemical studies to find out whether acetaldehyde-generated epitopes can be detected from liver specimens of 13 human subjects with different degrees of alcohol consumption. While the specimens obtained from alcohol abusers (n = 4) and alcoholics (n = 3) exhibited marked positive staining for acetaldehyde adducts inside the hepatocytes in a granular uneven pattern, the control samples (n = 6) were almost devoid of immunoreactivity. In the alcohol abusers with an early stage of alcohol-induced liver damage, staining was detected exclusively around the central veins. The data indicate that intracellular acetaldehyde adducts occur in the centrilobular region of the liver of individuals consuming excessive amounts of alcohol. Immunohistochemical detection of such adducts may prove to be of value in the early identification of alcohol abuse and in elucidating the mechanisms of alcohol-induced organ damage.

Biological markers of alcoholism

Biological markers are biochemical or physiological characteristics which may help to classify a person according to the presence or absence of some disease or risk of disease, either with respect to their current status or future susceptibility. Many biological markers related to alcoholism have been described; this review suggests a classification of them and indicates areas where they are well-established and other areas where further investigation may be useful.