The role of alcoholism and liver disease in the appearance of serum antibodies against acetaldehyde adducts

Quantitative immunohistochemical analysis of lymphocyte subsets in alcoholic liver disease

To investigate the role of lymphocytes frequently observed in the parenchyma of alcoholic liver disease (ALD), lymphocytes infiltrating into the liver were stained immunohistochemically with monoclonal antibodies (MoAb) and were quantitatively assessed by a morphometric analysis in 17 patients with ALD and, for comparison in five patients with chronic active hepatitis B (B-CAH). In patients with alcoholic hepatitis, the number of CD8+ lymphocytes in the hepatic lobule was similar to that in patients with B-CAH but was significantly greater than that in alcoholics with hepatic fibrosis (HF). The CD4/CD8 ratio in the hepatic lobule was low in both alcoholic hepatitis and B-CAH compared with that of alcoholic patients with HF. When Mallory bodies (MB) and lymphocytes were simultaneously stained with a specific antibody against MB and MoAb, respectively, only CD3+ and CD8+ lymphocytes were found to have a close contact with MB. These results suggest that in alcoholic hepatitis, hepatocyte necrosis may be partly mediated by immunological mechanisms involving cytotoxic T cells infiltrating into the hepatic lobule.

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)

Immunoglobulin A antibody to a 200-kilodalton cytosolic acetaldehyde adduct in alcoholic hepatitis

Considerable clinical and experimental evidence points to the importance of immune responses in the development of alcoholic liver disease. In the present study it was investigated whether circulating antibodies from patients with alcoholic liver disease recognize acetaldehyde-liver protein adducts. Cytosolic and microsomal fractions from livers of Wistar rats or from normal human liver were incubated with acetaldehyde (0.5-2.5 mmol/L) and/or cyanoborohydride (100 mmol/L) then analysed by immunoblotting. Cytosolic fractions that had been incubated with acetaldehyde and cyanoborohydride expressed a 200-kilodalton protein antigen not present in untreated fractions or fractions incubated with acetaldehyde or cyanoborohydride alone. The 200-kilodalton antigen was recognized by immunoglobulin (Ig)A antibodies in a large proportion of sera from patients with alcoholic hepatitis (70%, n = 23), but in significantly smaller proportions of sera from patients with alcoholic cirrhosis without hepatitis (30%, n = 10; P < 0.05), heavy drinkers without overt liver disease (20%, n = 10; P < 0.02), patients with nonalcoholic liver disease (35%, n = 17; P < 0.05), or normal control subjects consuming moderate quantities of alcohol (25%, n = 20%; P < 0.005). These results indicate that IgA antibodies to a 200-kilodalton acetaldehyde-protein adduct are present in a large proportion of patients with alcoholic liver disease and in a significantly smaller proportion of other individuals.

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.

The associations of alcohol drinking and drinking cessation to measures of the immune system in middle-aged men

To estimate the association between the immunologic responses of the cell-mediated and humoral systems and alcohol drinking, we used data from the Vietnam Experience Study conducted by the Centers for Disease Control. That study, conducted from 1985 to 1986, was based on a random sample of 4462 male, Vietnam-era, U.S. veterans. By using linear regression, we evaluated how (1) the number of alcoholic drinks the subjects consumed per month and (2) the drinking cessation of certain subjects were associated with their relative and absolute T, B, CD4, and CD8 lymphocyte counts and immunoglobulin A (IgA), IgM, and IgG levels. We used geometric means and percentage differences in geometric means of immune status to measure the associations and adjusted these values to account for the effect of covariates. The results indicated that measures of immune status differed among the drinking categories and that, generally, the differences changed after adjustment for covariates. These differences consisted, as alcohol consumption increased, of higher IgA and IgM levels, relative T and CD4 lymphocytes, and the ratio of CD4 to CD8 cells, and of lower IgG levels, relative B and CD8 lymphocytes, absolute lymphocyte, and lymphocyte subset counts after adjusting for other covariates. Among former drinkers, we found no clear-cut pattern in measures of immunity for a few years after cessation and then found that values of former drinkers tended to return toward values of nondrinkers as they continued to abstain.

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.

Alcohol, liver, and nutrition

Until two decades ago, dietary deficiencies were considered to be the major reason why alcoholics developed liver disease. As the overall nutrition of the population improved, more emphasis was placed on secondary malnutrition. Direct hepatotoxic effects of ethanol were also established, some of which were linked to redox changes produced by reduced nicotinamide adenine dinucleotide (NADH) generated via the alcohol dehydrogenase (ADH) pathway. It was also determined that ethanol can be oxidized by a microsomal ethanol oxidizing system (MEOS) involving cytochrome P-450: the newly discovered ethanol-inducible cytochrome P-450 (P-450IIE1) contributes to ethanol metabolism, tolerance, energy wastage (with associated weight loss), and the selective hepatic perivenular toxicity of various xenobiotics. P-450 induction also explains depletion (and enhanced toxicity) of nutritional factors such as vitamin A. Even at the early fatty-liver stage, alcoholics commonly have a very low hepatic concentration of vitamin A. Ethanol administration in animals was found to depress hepatic levels of vitamin A, even when administered with diets containing large amounts of the vitamin, reflecting, in part, accelerated microsomal degradation through newly discovered microsomal pathways of retinol metabolism, inducible by either ethanol or drug administration. The hepatic depletion of vitamin A was strikingly exacerbated when ethanol and other drugs were given together, mimicking a common clinical occurrence. Hepatic retinoid depletion was found to be associated with lysosomal lesions and decreased detoxification of chemical carcinogens. To alleviate these adverse effects, as well as to correct problems of night blindness and sexual inadequacies, the alcoholic patient should be provided with vitamin A supplementation. Such therapy, however, is complicated by the fact that in excessive amounts vitamin A is hepatotoxic, an effect exacerbated by long-term ethanol consumption. This results in striking morphologic and functional alterations of the mitochondria with leakage of mitochondrial enzymes, hepatic necrosis, and fibrosis. Thus, treatment with vitamin A and other nutritional factors (such as proteins) is beneficial but must take into account a narrowed therapeutic window in alcoholics who have increased needs for such nutrients, but also display an enhanced susceptibility to their adverse effects. Massive doses of choline also exerted some toxic effects and failed to prevent the development of alcoholic cirrhosis. 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 enhances pyridoxine and perhaps folate degradation and stimulates collagen production by the vitamin A storing cells (lipocytes) and myofibroblasts.(ABSTRACT TRUNCATED AT 400 WORDS)

Low density lipoprotein derivatization by acetaldehyde affects lysine residues and the B/E receptor binding affinity

Acetaldehyde (AcA), the first metabolite in ethanol oxidation, forms covalent adducts with the free amino groups of various proteins. In this study, we examined how acetaldehyde modification affects the chemical and biological properties of the atherogenic low density lipoprotein (LDL). AcA modification did not alter the protein and lipid composition of LDL, but the AcA concentration used in the incubation correlated strongly with the electrophoretic mobility of acetaldehyde-treated LDL (AcA-LDL) (r = 0.97, p less than 0.001) and the percentage of the free amino groups in AcA-LDL (r = -0.90, p less than 0.01). Amino acid analysis of AcA-LDL showed that lysine was the predominant residue in LDL modified by AcA. Assays with monoclonal antibodies (MB47, 2b, 4G3, and C1.1) directed against different epitopes of the LDL apoprotein B suggested that AcA modification reduced the immunological recognition of the LDL receptor binding region and its vicinity. Also, the binding affinity of AcA-LDL to B/E receptors correlated negatively with the percentage of modified lysine residues in AcA-LDL (r = -0.96, p less than 0.001). The results suggest that AcA derivatizes the lysine residues of LDL, and thus decreases the B/E receptor binding affinity of LDL. However, major changes in LDL receptor binding were produced only with non-physiologically high concentrations of AcA, and, therefore, the role of the present findings in vivo remains uncertain.

Hepatic, metabolic and toxic effects of ethanol: 1991 update

Until two decades ago, dietary deficiencies were considered to be the only reason for alcoholics to develop liver disease. As the overall nutrition of the population improved, more emphasis was placed on secondary malnutrition and direct hepatotoxic effects of ethanol were established. Ethanol is hepatotoxic through redox changes produced by the NADH generated in its oxidation via the alcohol dehydrogenase pathway, which in turn affects the metabolism of lipids, carbohydrates, proteins, and purines. Ethanol is also oxidized in liver microsomes by an ethanol-inducible cytochrome P-450 (P-450IIE1) that contributes to ethanol metabolism and tolerance, and activates xenobiotics to toxic radicals thereby explaining increased vulnerability of the heavy drinker to industrial solvents, anesthetic agents, commonly prescribed drugs, over-the-counter analgesics, chemical carcinogens, and even nutritional factors such as vitamin A. In addition, ethanol depresses hepatic levels of vitamin A, even when administered with diets containing large amounts of the vitamin, reflecting, in part, accelerated microsomal degradation through newly discovered microsomal pathways of retinol metabolism, inducible by either ethanol or drug administration. The hepatic depletion of vitamin A is strikingly exacerbated when ethanol and other drugs were given together, mimicking a common clinical occurrence. Microsomal induction also results in increased production of acetaldehyde. Acetaldehyde, in turn, causes injury through the formation of protein adducts, resulting in antibody production, enzyme inactivation, decreased DNA repair, and alterations in microtubules, plasma membranes and mitochondria with a striking impairment of oxygen utilization. Acetaldehyde also causes glutathione depletion and lipid peroxidation, and stimulates hepatic collagen production by the vitamin A storing cells (lipocytes) and myofibroblasts.(ABSTRACT TRUNCATED AT 250 WORDS)

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.

Antibodies against acetaldehyde-modified epitopes: an elevated IgA response in alcoholics

Several recent reports have shown that antibodies reactive with acetaldehyde (AcH)-modified epitopes are present in alcoholics. However, similar antibodies have also been found in patients with non-alcoholic liver disease and control subjects. In each of these studies total immunoglobulin binding to the AcH-modified proteins was measured, with no attempt being made to identify the classes of immunoglobulin involved. In the present study we employed an enzyme-linked immunosorbent assay (ELISA) to assess the classes of immunoglobulin involved in this response, using plasma samples from 97 alcoholics with varying degrees of liver disease, 35 patients with non-alcoholic liver disease and 33 control subjects. All three groups exhibited a large IgM response and a negligible IgG response. However, the alcoholics exhibited a significantly higher IgA response than either of the other groups. This suggests that the measurement of the IgA response to AcH-modified epitopes may be a specific marker of ethanol abuse.

The generation of cytotoxic T lymphocytes against acetaldehyde-modified syngeneic cells

The major metabolic product of ethanol is acetaldehyde. It is highly reactive with proteins. In situ this modification is significant enough to generate an antibody response. Whether an effector cellular immune response can be generated against these acetaldehyde modified adducts on syngeneic cells is not known. In this paper we have demonstrated in the murine system that acetaldehyde modified splenic cells can generate cytotoxic T lymphocytes (CTL). These CTL are specific for the acetaldehyde modified syngeneic cells, and not acetaldehyde modified allogeneic cells. The ability of the CTL to lyse-specific targets is dependent on the formation of stable acetaldehyde adducts. Cold target inhibition studies reveal that modified syngeneic cells can inhibit lysis as effectively as unmodified cells. Therefore, the present study lends support to the hypothesis that acetaldehyde modified cells can generate a cellular immune response and may do so in pathologic states.

Acetaldehyde-collagen adducts in CCl4-induced liver injury in rats

Circulating AC levels as well as antibodies against AC-protein adducts are increased in non-alcoholic liver injury. To identify the adducts, we used rats with CCl4-induced cirrhosis. Liver subcellular fractions were analyzed by immunochemical staining of protein slot blots and of electrophoretically separated proteins, transferred to nitrocellulose, using AC-protein adduct-specific antibodies. One reactive protein of about 200 kD was detected in the liver soluble fraction and in the cytosol of isolated hepatocytes and, to a lesser extent in the liver microsomes of CCl4-treated rats; in control animals, this reactivity was much weaker. The immunopositive AC adduct co-migrated with the beta 1,2 dimer of rat collagen type I; it was sensitive to digestion by a highly purified collagenase and also reacted with anti-rat collagen type I-specific IgG. In addition, comparison of peptides of the CNBr-digested, immunoprecipitated AC adduct with those of rat collagen type I revealed a high degree of similarity. Thus, AC adduct formation occurs in liver injury of non-alcoholic origin, and a target protein appears to be related to collagen type I, most likely the procollagen precursor.

Mechanism of ethanol induced hepatic injury

Ethanol is hepatotoxic through redox changes produced by the NADH generated in its oxidation via the alcohol dehydrogenase pathway, which in turn affects the metabolism of lipids, carbohydrates, proteins and purines. Ethanol is also oxidized in liver microsomes by an ethanol-inducible cytochrome P-450 (P-450IIE1) which contributes to ethanol metabolism and tolerance, and activates xenobiotics to toxic radicals thereby explaining increased vulnerability of the heavy drinker to industrial solvents, anesthetic agents, commonly prescribed drugs, over-the-counter analgesics, chemical carcinogens and even nutritional factors such as vitamin A. Induction also results in energy wastage and increased production of acetaldehyde. Acetaldehyde, in turn, causes injury through the formation of protein adducts, resulting in antibody production, enzyme inactivation, decreased DNA repair, and alterations in microtubules, plasma membranes and mitochondria with a striking impairment of oxygen utilization. Acetaldehyde also causes glutathione depletion and lipid peroxidation, and stimulates hepatic collagen synthesis, thereby promoting fibrosis.

High levels of acetaldehyde in nonalcoholic liver injury after threonine or ethanol administration

Acetaldehyde, a product of ethanol oxidation which forms adducts with proteins, has been incriminated in the pathogenesis of alcoholic liver injury. High serum antibody titers against acetaldehyde-protein adducts have been found not only in alcoholics but also in patients with nonalcoholic liver disease, suggesting a contribution of acetaldehyde derived from sources other than exogenous ethanol. To investigate the effect of liver injury on the removal and the production of acetaldehyde, we produced fibrosis and cirrhosis (by chronic administration of carbon tetrachloride) and fatty liver (with very small doses of dimethylnitrosamine) in rats. Endogenous blood acetaldehyde levels increased by 38% in rats with severe liver injury (p less than 0.005), but not significantly in rats with fatty liver. However, an i.v. load of threonine (a physiological source of acetaldehyde), in amounts equivalent to the daily intake of this amino acid, increased blood and hepatic acetaldehyde levels in the rats with both types of liver injury more than in controls. Threonine dehydrogenase and dehydratase activities, involved in the major pathways for threonine degradation in mitochondria and cytosol, respectively, were markedly decreased in rats with liver injury with a resulting increase in hepatic threonine concentration. Moreover, the threonine aldolase activity, which splits threonine into glycine and acetaldehyde, remained unaffected or even slightly increased. Liver injury was also associated with impaired mitochondrial functions, including a 10 to 23% decrease in acetaldehyde oxidation (depending upon the severity of the lesions). As a consequence, administration of ethanol (an exogenous source of acetaldehyde) resulted in striking elevations in the levels of acetaldehyde in carbon tetrachloride-treated rats.(ABSTRACT TRUNCATED AT 250 WORDS)

Formation of acetaldehyde adducts with ethanol-inducible P450IIE1 in vivo

Hepatic microsomes, obtained from rats pair-fed liquid diets supplemented with either ethanol or an isocaloric amount of carbohydrates (for 4 weeks), were subjected to crossed immunoelectrophoresis. Anti-acetaldehyde adduct-specific immunoglobulin reacted on the protein blots with a single major 52,000 dalton polypeptide. This same protein was recognized by antibodies specific for P450IIE1, an ethanol-inducible P450 isozyme. Furthermore, a single protein, also reactive with anti-P450IIE1 IgG, was isolated from liver microsomes of ethanol-fed rats by immunoaffinity chromatography on Sepharose-conjugated anti-acetaldehyde adduct IgG. These results indicate that P450IIE1 is a target protein for acetaldehyde binding in liver microsomes in vivo.