Michael F. Sorrell

National Institutes of Health consensus development conference statement: management of hepatitis B.

National Institutes of Health (NIH) consensus and stateof-the-science statements are prepared by independent panels of health professionals and public representatives on the basis of 1) the results of a systematic literature review prepared under contract with the Agency for Healthcare Research and Quality (AHRQ); 2) presentations by investigators working in areas relevant to the conference questions during a 2-day public session; 3) questions and statements from conference attendees during open discussion periods that are part of the public session; and 4) closed deliberations by the panel during the remainder of the second day and morning of the third. This statement is an independent report of the panel and is not a policy statement of the National Institutes of Health or the U.S. government. The statement reflects the panel’s assessment of medical knowledge available at the time the statement was written. Thus, it provides a “snapshot in time” of the state of knowledge on the conference topic. When reading the statement, keep in mind that new knowledge is inevitably accumulating through medical research. Hepatitis B is a major cause of liver disease worldwide, ranking as a substantial cause of cirrhosis and hepatocellular carcinoma. The development and use of a vaccine for hepatitis B virus (HBV) has resulted in a substantial decline in the number of new cases of acute hepatitis B among children, adolescents, and adults in the United States. However, this success has not yet been duplicated worldwide, and both acute and chronic HBV infection continue to represent important global health problems. Seven treatments are currently approved for adult patients with chronic HBV infection in the United States: interferon-, pegylated interferon-, lamivudine, adefovir dipivoxil, entecavir, telbivudine, and tenofovir disoproxil fumarate. Interferon- and lamivudine have been approved for children with HBV infection. Although available randomized, controlled trials (RCTs) show encouraging short-term results— demonstrating the favorable effect of these agents on such intermediate markers of disease as HBV DNA level, liver enzyme tests, and liver histology— limited rigorous evidence exists demonstrating the effect of these therapies on important long-term clinical outcomes, such as the development of hepatocellular carcinoma or a reduction in deaths. Questions therefore remain about which groups of patients benefit from therapy and at which point in the course of disease this therapy should be initiated.

Acetaldehyde adducts with proteins: Binding of [14C]acetaldehyde to serum albumin

Acetaldehyde, the immediate oxidation product of ethanol metabolism, was assessed for its ability to bind covalently to a purified protein in solution. Bovine serum albumin (BSA) was used as the model protein incubated in the presence of 0.2 mM [14C]acetaldehyde at pH 7.4 and at 37 degrees C. Acetaldehyde formed both stable and unstable adducts with serum albumin. Unstable adducts were identified following stabilization with the reducing agent sodium borohydride. We examined both types of binding using trichloroacetic acid precipitation, gel filtration, and dialysis as means to separate bound from free acetaldehyde. All three methods of analysis gave comparable results except that the number of stable acetaldehyde adducts with albumin were significantly lower following separation by dialysis. The effects of L-cysteine, L-lysine, and reduced glutathione were assessed for their abilities as competitive reagents to decrease binding of [14C]acetaldehyde to BSA. Addition of cysteine caused a rather dramatic concentration-dependent reduction in [14C]acetaldehyde binding to BSA when compared to that caused by lysine which displayed a relatively mild effect on covalent binding. The presence of glutathione caused a concentration-dependent decrease in protein-bound radioactivity that was stronger than that by lysine but not as effective as cysteine. The ability of each reagent to reverse the formation of preformed acetaldehyde adducts with BSA was also examined. Only L-cysteine effectively decreased the number of unstable acetaldehyde adducts with BSA while stable binding of acetaldehyde remained essentially unaffected by any of the three reagents. These results indicate that acetaldehyde can covalently bind to protein and form unstable as well as stable adducts.

Cerebral oedema and increased intracranial pressure in chronic liver disease.

BACKGROUND Cerebral oedema is a cause of morbidity and mortality in fulminant hepatic failure but has not been well documented as a complication of chronic liver diseases. We report here the development of cerebral oedema and increased intracranial pressure in 12 patients with chronic liver disease. METHODS Between July 1, 1987, and Dec 31, 1993, we studied 12 patients aged 29-67 years with end-stage chronic liver disease. All the patients had cirrhosis, portal hypertension, hypoprothrombinaemia, hepatic encephalopathy, and decreased serum concentrations of albumin (<25 g/L). During the study, the patients developed signs of increased intracranial pressure and had documented intracranial hypertension, cerebral oedema, or both. Intracranial hypertension was suspected on physical examination and confirmed by epidural catheters. We detected cerebral oedema by computed axial tomography of the head and necropsy of the brain when possible. FINDINGS All the patients had intracranial hypertension and cerebral oedema. Two patients had successful treatment of cerebral hypertension with improvement of intracranial pressure such that orthotopic liver transplantation was undertaken. Both patients became neurologically normal after transplantation. Eight patients had only a transient response to treatment and died of cerebral oedema before a transplant could be done. INTERPRETATION Cerebral oedema and increased intracranial pressure can occur in chronic liver disease and presents as neurological deterioration. Treatment guided by monitoring of intracranial pressure can lead to the reversal of intracranial hypertension, but in most patients cerebral oedema contributes to death or places them at too high a risk for liver transplantation.

REACTION OF ACETALDEHYDE WITH HUMAN ERYTHROCYTE MEMBRANE PROTEINS

Proposed mechanisms for these abnormalities include an altered membrane choles- terol to phospholipid ratio, folate deficiency and direct bone-marrow toxicity by ethanol. We suggest that acetaldehyde, the first product of ethanol oxida- tion, may account for some of the erythrocytic altera- tions by reacting with erythrocyte spectrin and actin. It is known that free blood acetaldehyde accumulates to about 0.05 mM in chronic alcoholics [ 51. Further- more, spectrin and actin are thought to be involved in the maintenance of erythrocyte shape and flexibility [6-131. Although there is no direct evidence that acetal- dehyde binds to proteins of the human erythrocyte, it has been known that this compound can cross-link proteins [ 141 and can alter certain physical properties of erythrocytes [ 15-171. Unfortunately, these studies were performed mainly at unusually high acetaldehyde concentrations (2% or greater) and at temperatures at or beyond the boiling point of acetaldehyde (20°C) making interpretation difficult. Steck [ 181 has pre-

The Functional Implications of Acetaldehyde Binding to Cell Constituents

Chronic ethanol consumption is a major cause of liver disease. Although the underlying pathogenic mechanisms are unclear, present evidence indicates that ethanol and/or its metabolites are directly injurious to the liver. However, genetic, environmental. and nutritional factors may also modulate the hepatotoxicity of ethanol.’-’ Since ethanol is primarily metabolized in the liver, which is a major target organ of ethanol-induced toxicity, many of the functional and structural alterations in the liver produced by ethanol consumption have been attributed to the products of ethanol 0xidati0n.l~~ I n this regard, formation of acetaldehyde, the first metabolite of ethanol, and the altered redox state (increased NADH/NAD ratios in the cytosolic and mitochondria1 compartments) have been implicated in many of the ethanol-induced alterations of hepatic structure and function.’-5 Recently, we have formulated a hypothesis, postulating that acetaldehyde via its covalent binding to hepatic proteins may be a critical event leading to liver inj~ry.~*’Such a ypothesis is consistent with the evidence implicating ethanol as a direct hepatotoxin and, in addition, takes into account the possible role of metabolic, nutritional, and environmental factors in the pathogenesis of alcoholic liver injury. In this report, we will briefly describe some of the characteristics of acetaldehyde binding to proteins, but will mostly focus on potential consequences of such binding.

Detection of circulating antibodies to malondialdehyde-acetaldehyde adducts in ethanol-fed rats

BACKGROUND & AIMS Malondialdehyde and acetaldehyde react together with proteins and form hybrid protein conjugates designated as MAA adducts, which have been detected in livers of ethanol-fed rats. The aim of this study was to examine the immune response to MAA adducts and other aldehyde adducts during long-term ethanol exposure. METHODS Rats were pair-fed for 7 months with a liquid diet containing either ethanol or isocaloric carbohydrate. Circulating antibody titers against MAA adducts and acetaldehyde adducts were measured and characterized in these animals. RESULTS A significant increase in antibody titers against MAA-adducted proteins was observed in the ethanol-fed animals. Competitive inhibitions of antibody binding indicated that the circulating antibodies against MAA-modified proteins in the ethanol-fed rats recognized mainly a specific, chemically defined MAA epitope. Antibody titers to reduced and nonreduced acetaldehyde adducts were very low, and no significant differences were observed between ethanol-fed and control animals. Significant plasma immunoreactivity to not only MAA-adducted but also unmodified rat liver proteins (cytosol, microsomes, and especially plasma membrane) were also observed in the ethanol-fed rats. CONCLUSIONS Long-term ethanol feeding generates circulating antibodies not only against MAA epitopes but possibly also against unmodified, native (self) protein epitopes, suggesting that MAA adducts could trigger harmful autoimmune responses.

Fulminant Liver Failure Associated with the Use of Black Cohosh

After the article was published, it was brought to the authors’ attention through legal documentation and testimony that the patient admitted to consuming alcohol and had been taking other medications at the time of her initial presentation of liver failure. From these records, she reported drinking no more than six glasses of wine per week. In addition, up until presentation, she was taking valacyclovir 500 mg daily for herpes prophylaxis for 2 years, an occasional pseudoephedrine tablet, calcium carbonate 500 mg three times daily, iron sulfate 325 mg daily and ibuprofen up to three times weekly. She had been taking erythromycin tablets but discontinued those 3 months prior to presentation. The authors regret the omission of this information from the original case report. While this new information is important to include as a correction to the history, it does not change the authors’ clinical opinion as to the association between the patient’s consumption of black cohosh and the development of liver failure. She was not consuming enough alcohol, pseudoephedrine, or ibuprofen to lead to the clinical presentation or pathologic appearance described in their report. Valacyclovir, a drug often given to liver transplant recipients for herpes and cytomegalovirus prophylaxis, has only been shown in one case report to be associated with hepatitis [1] and had been given at low doses without modification for 2 years prior to presentation. Finally, while there are clear reports of erythromycininduced hepatotoxicity, the patient had stopped this medication 3 months prior to presentation.

The interaction of acetaldehyde with tubulin.

Acetaldehyde covalently binds to purified tubulin in vitro to form both stable and unstable adducts. The formation of stable adducts can be greatly facilitated by the inclusion of the relatively gentle and Schiff base specific reducing agent, sodium cyanoborohydride. Although the tubulin molecule has multiple lysine resides available to react with acetaldehyde, certain key lysine residues on the alpha-chain appear to be selective targets for adduct formation. The formation of alpha-chain specific stable acetaldehyde-tubulin adducts results in functional impairment of the ability of tubulin to polymerize. Under relatively physiologic conditions where acetaldehyde-to-protein ratios are low, alpha-chain specific binding is prominent. These results, coupled with the studies presented in another report in this volume, raise the possibility that low levels of adduct formation may be detrimental to the structure or function of certain proteins (e.g. tubulin) in the liver. The alteration of this or other biologically important proteins by sustained low levels of adduct formation may contribute to the pathogenesis of alcoholic liver injury.

National Institutes of Health Consensus Development Conference Statement: Management of Hepatitis B

Hepatitis B is a major cause of liver disease worldwide, ranking as a substantial cause of cirrhosis and hepatocellular carcinoma. The development and use of a vaccine for hepatitis B virus (HBV) has resulted in a substantial decline in the number of new cases of acute hepatitis B among children, adolescents, and adults in the United States. However, this success has not yet been duplicated worldwide, and both acute and chronic HBV infection continue to represent important global health problems. Seven treatments are currently approved for adult patients with chronic HBV infection in the United States: interferon, pegylated interferon, lamivudine, adefovir dipivoxil, entecavir, telbivudine, and tenofovir disoproxil fumarate. Interferonand lamivudine have been approved for children with HBV infection. Although available randomized, controlled trials (RCTs) show encouraging short-term results—demonstrating the favorable effect of these agents on such intermediate markers of disease as HBV DNA level, liver enzyme tests, and liver histology—limited rigorous evidence exists demonstrating the effect of these therapies on important long-term clinical outcomes, such as the development of hepatocellular carcinoma or a reduction in deaths. Questions therefore remain about which groups of patients benefit from therapy and at which point in the course of disease this therapy should be initiated.

Acetaldehyde and Microtubules

Acetaldehyde covalently binds to tubulin to form stable and unstable adducts. Although tubulin has numerous lysine residues available to react with acetaldehyde, a key highly reactive lysine (HRL) on the alpha chain appears to be a preferential target for stable binding. The HRL residue is available for selective binding when tubulin is in the free (dimer) state but not when it is in the polymerized (microtubule) state. Stable binding of acetaldehyde to the HRL residue markedly inhibits tubulin assembly into microtubules, whereas stable binding to other residues (bulk adducts) has little influence on assembly. Substoichiometric stable binding of acetaldehyde to the HRL is sufficient to inhibit polymerization, via direct interference of tubulin dimer-dimer interactions, and an HRL adduct on only one out of 20 tubulin molecules can totally inhibit polymerization. These findings, along with our previous studies demonstrating impaired microtubule-dependent protein trafficking pathways in livers of ethanol-fed animals, indicate that low acetaldehyde concentrations, formed during ethanol oxidation in vivo, could generate sufficient amounts of HRL adducts on the alpha chain of tubulin in cellular systems to alter microtubule formation and function. In addition to alpha-tubulin, calmodulin and actin have also been found to have enhanced reactivity toward acetaldehyde. Thus, a general hypothesis to describe cellular injury induced by acetaldehyde adducts can be formulated: during ethanol oxidation, acetaldehyde forms stable adducts via binding to reactive lysine residues of preferential target proteins, resulting in selective functional impairment of these proteins and ultimately leading to cellular injury.