Generation of protein adducts with malondialdehyde and acetaldehyde in muscles with predominantly type I or type II fibers in rats exposed to ethanol and the acetaldehyde dehydrogenase inhibitor cyanamide

Alcoholic Hepatitis: Lost in Translation

Alcoholic hepatitis is the most severe and acute form of alcoholic liver disease. The mortality rate associated with alcoholic hepatitis is high, largely due to the lack of suitable pharmacological interventions. While there has been substantial research in the area, generating pharmacological interventions has been plagued by the lack of a robust mouse model both for testing and for understanding the underlying pathology. A number of major notable advances have been made in this area recently, with the goal of generating a mouse model of alcoholic hepatitis. The purpose of this article is to review recent advances in modeling alcoholic liver disease both in vitro and in vivo in the mouse, and place them in the context of the greater spectrum of alcoholic liver disease, with a focus on how we can translate current advances into a high-fidelity model of alcoholic hepatitis. In addition, we will review the basic mechanisms of alcoholic hepatitis as it is currently understood, focusing on recent advancements in diagnosis, prognosis and current pathophysiology, especially as it relates to the profound immune dysfunction present during alcoholic hepatitis.

[Direct mechanism of action in toxic myopathies]

Toxic myopathies are a large group of disorders generated by surrounding agents and characterized by structural and/or functional disturbances of muscles. The most recurrent are those induced by commonly used medications. Illicit drugs, environmental toxins from animals, vegetables, or produced by micro-organisms as well as chemical products commonly used are significant causes of such disorders. The muscle toxicity results from multiple mechanisms at different biological levels. Many agents can induce myotoxicity through a direct mechanism in which statins, glucocorticoids and ethyl alcohol are the most representative. Diverse mechanisms were highlighted as interaction with macromolecules and induction of metabolic and cellular dysfunctions. Muscle damage can be related to amphiphilic properties of some drugs (chloroquine, hydroxychloroquine, etc.) leading to specific lysosomal disruptions and autophagic dysfunctions. Some agents affect the whole muscle fiber by inducing oxidative stress (ethyl alcohol and some statins) or triggering cell death pathways (apoptosis or necrosis) resulting in extensive alterations. More studies on these mechanisms are needed. They would allow a better knowledge of the intracellular mediators involved in these pathologies in order to develop targeted therapies of high efficiency.

Alcohol-induced autophagy contributes to loss in skeletal muscle mass

Patients with alcoholic cirrhosis and hepatitis have severe muscle loss. Since ethanol impairs skeletal muscle protein synthesis but does not increase ubiquitin proteasome-mediated proteolysis, we investigated whether alcohol-induced autophagy contributes to muscle loss. Autophagy induction was studied in: A) Human skeletal muscle biopsies from alcoholic cirrhotics and controls, B) Gastrocnemius muscle from ethanol and pair-fed mice, and C) Ethanol-exposed murine C2C12 myotubes, by examining the expression of autophagy markers assessed by immunoblotting and real-time PCR. Expression of autophagy genes and markers were increased in skeletal muscle from humans and ethanol-fed mice, and in myotubes following ethanol exposure. Importantly, pulse-chase experiments showed suppression of myotube proteolysis upon ethanol-treatment with the autophagy inhibitor, 3-methyladenine (3MA) and not by MG132, a proteasome inhibitor. Correspondingly, ethanol-treated C2C12 myotubes stably expressing GFP-LC3B showed increased autophagy flux as measured by accumulation of GFP-LC3B vesicles with confocal microscopy. The ethanol-induced increase in LC3B lipidation was reversed upon knockdown of Atg7, a critical autophagy gene and was associated with reversal of the ethanol-induced decrease in myotube diameter. Consistently, CT image analysis of muscle area in alcoholic cirrhotics was significantly reduced compared with control subjects. In order to determine whether ethanol per se or its metabolic product, acetaldehyde, stimulates autophagy, C2C12 myotubes were treated with ethanol in the presence of the alcohol dehydrogenase inhibitor (4-methylpyrazole) or the acetaldehyde dehydrogenase inhibitor (cyanamide). LC3B lipidation increased with acetaldehyde treatment and increased further with the addition of cyanamide. We conclude that muscle autophagy is increased by ethanol exposure and contributes to sarcopenia.

Modification of carbonic anhydrase II with acetaldehyde, the first metabolite of ethanol, leads to decreased enzyme activity

BACKGROUND

Acetaldehyde, the first metabolite of ethanol, can generate covalent modifications of proteins and cellular constituents. However, functional consequences of such modification remain poorly defined. In the present study, we examined acetaldehyde reaction with human carbonic anhydrase (CA) isozyme II, which has several features that make it a suitable target protein: It is widely expressed, its enzymatic activity can be monitored, its structural and catalytic properties are known, and it contains 24 lysine residues, which are accessible sites for aldehyde reaction.

RESULTS

Acetaldehyde treatment in the absence and presence of a reducing agent (NaBH3(CN)) caused shifts in the pI values of CA II. SDS-PAGE indicated a shift toward a slightly higher molecular mass. High-resolution mass spectra of CA II, measured with and without NaBH3(CN), indicated the presence of an unmodified protein, as expected. Mass spectra of CA II treated with acetaldehyde revealed a modified protein form (+26 Da), consistent with a "Schiff base" formation between acetaldehyde and one of the primary NH2 groups (e.g., in lysine side chain) in the protein structure. This reaction was highly specific, given the relative abundance of over 90% of the modified protein. In reducing conditions, each CA II molecule had reacted with 9-19 (14 on average) acetaldehyde molecules (+28 Da), consistent with further reduction of the "Schiff bases" to substituted amines (N-ethyllysine residues). The acetaldehyde-modified protein showed decreased CA enzymatic activity.

CONCLUSION

The acetaldehyde-derived modifications in CA II molecule may have physiological consequences in alcoholic patients.

Demonstration of ethanol-induced protein adducts in oral leukoplakia (pre-cancer) and cancer

BACKGROUND

Excessive alcohol consumption is a common cause for upper gastrointestinal tract cancers. However, the primary mechanisms of alcohol-induced carcinogenesis have remained poorly defined.

METHOD

We examined the generation and subcellular distribution of protein adducts with acetaldehyde (AA), the first metabolite of ethanol, and end products of lipid peroxidation, malondialdehyde (MDA) and 4-hydroxynonenal (HNE), from oral biopsy specimens obtained from 36 subjects (11 British, 25 Japanese) reporting alcohol misuse. All patients had been diagnosed with oral pre-cancer (leukoplakia, n = 7) or squamous cell carcinoma (SCC; n = 29). Automated immunostaining for AA, MDA and HNE adducts was performed using monospecific antibodies.

RESULTS

Positive staining for AA, MDA and HNE adducts was observed in the dysplastic or malignant epithelial cells, HNE being relatively the most abundant adduct species. The subgroup of Japanese patients had higher levels of AA and MDA, although not HNE, than the British sample. When the material was divided to those with SCC or leukoplakia, MDA adducts but not the other antigens were more prominent in the former group. Significant correlations were found between the different adducts (AA vs. MDA, r = 0.68, P < 0.001; AA vs. HNE, r = 0.47, P < 0.01 and MDA vs. HNE, r = 0.59, P < 0.001). In addition, cytochrome P450 2E1 staining was found in these samples, correlating with both AA and MDA adducts.

CONCLUSION

The data indicates that AA- and lipid peroxidation-derived adducts are formed in oral tissues of alcohol misusers with oral leukoplakia and cancer. The findings also support a pathogenic role of AA and excessive oxidative stress in carcinogenesis.

Skeletal muscle and liver oxysterols during fasting and alcohol exposure

Oxysterols are cytotoxic agents that have a range of cellular actions, including impairment of albumin synthesis, cell differentiation, and induction of apoptosis. Their regulations by nutritional factors are poorly described. Our objective was to test the hypothesis that the imposition of food withdrawal and alcohol exposure increases tissue oxysterol concentrations. We measured the concentrations of the oxysterols 7alpha-hydroxycholest-5-en-3beta-ol (7alpha-OH), 7beta-hydroxycholest-5-en-3beta-ol (7beta-OH), and 3beta-hydroxycholest-5-en-7-one (7-keto) in liver and skeletal muscle of fed and fasted (food withdrawal for 1 and 2 days) male Wistar rats. Both oxidative (type I; soleus) and glycolytic (type II; plantaris) muscles were analyzed. We also investigated the effects of a nutritional perturbant induced by a short-term bolus of ethanol (75 mmol/kg weight IP administered 2.5 hours before sacrifice). The results showed that in response to fasting there were significant increases in 7alpha-OH, 7beta-OH, and 7-keto in liver and both type I and II skeletal muscle (P < .001 in all instances). For skeletal muscle, the increases were blunted or ameliorated after 2 days when compared with data from rats starved for 1 day. In contrast, the increases in liver after 1 day's fasting were relatively sustained at 2 days. Short-term ethanol increased 7alpha-OH, 7beta-OH, and 7-keto in type I muscle of fed animals only (P < .001 in all instances) with a significant interaction between fasting and alcohol (P < .001 in all instances). For the first time, we have shown that oxysterols can increase in muscle and liver in response to food withdrawal and in response to an immediately imposed nutritional perturbant (ie, alcohol). Increased oxysterols represent elevated oxidative stress and/or disturbances in their formation or clearance. Because of the reported cytotoxic properties of oxysterols, these data are important in understanding cellular pathology because episodic anorexia and/or oxidative stress occur in a variety of disease conditions including sepsis, cancer cachexia, ischemia, and hormonal imbalance.

Alcoholic myopathy: lack of effect of zinc supplementation

A chronic form of myopathy has been described in alcoholics, characterized by atrophy of type II fibers, due both to reduced protein synthesis and increased protein breakdown. Increased production of reactive oxygen species could probably play a role in increased protein breakdown. In addition, treatment with zinc might be beneficial, since it acts as a cofactor of several enzymes involved in the synthesis of proteins and antioxidants as copper-zinc-superoxidedismutase (SOD) and selenium dependent glutathione peroxidase (GPX). Based on these facts, we analyze the relative and combined effects of ethanol, protein malnutrition and treatment with zinc, 227 mg/l in form of zinc sulphate, on muscle changes in 8 groups of adult Sprague-Dawley rats fed following the Lieber-de Carli model during 5 weeks. We also study the association between muscle histological changes and the activity of GPX, SOD and lipid peroxidation products (MDA), with hormones such as IGF-1, and with trace elements involved in antioxidant systems and/or in lipid peroxidation, such as selenium, copper, zinc, and iron. We found type IIa and IIb fiber atrophy in the alcoholic animals, especially in the low-protein fed ones. This effect was mainly due to protein deficiency. Zinc played no role at all. Muscle iron increased in ethanol, low protein fed rats, either with or without zinc, and was directly related with muscle MDA levels, which in turn were related with muscle atrophy, as was also found for serum IGF-1 levels. Ethanol was the main responsible for all these changes, although protein undernutrition also played an independent role in MDA levels. A positive interaction between ethanol and protein deficiency on serum IGF-1 was also detected. These results suggest that both protein deficiency and ethanol contribute to muscle atrophy observed in alcoholized rats; this atrophy is associated with increased lipid peroxidation and muscle iron overload. Treatment with zinc sulphate confers no benefit.

PROTEIN ADDUCT SPECIES IN MUSCLE AND LIVER OF RATS FOLLOWING ACUTE ETHANOL ADMINISTRATION

AIMS

Previous immunohistochemical studies have shown that the post-translational formation of aldehyde-protein adducts may be an important process in the aetiology of alcohol-induced muscle disease. However, other studies have shown that in a variety of tissues, alcohol induces the formation of various other adduct species, including hybrid acetaldehyde-malondialdehyde-protein adducts and adducts with free radicals themselves, e.g. hydroxyethyl radical (HER)-protein adducts. Furthermore, acetaldehyde-protein adducts may be formed in reducing or non-reducing environments resulting in distinct molecular entities, each with unique features of stability and immunogenicity. Some in vitro studies have also suggested that unreduced adducts may be converted to reduced adducts in situ. Our objective was to test the hypothesis that in muscle a variety of different adduct species are formed after acute alcohol exposure and that unreduced adducts predominate.

METHODS

Rabbit polyclonal antibodies were raised against unreduced and reduced aldehydes and the HER-protein adducts. These were used to assay different adduct species in soleus (type I fibre-predominant) and plantaris (type II fibre-predominant) muscles and liver in four groups of rats administered acutely with either [A] saline (control); [B] cyanamide (an aldehyde dehydrogenase inhibitor); [C] ethanol; [D] cyanamide+ethanol.

RESULTS

Amounts of unreduced acetaldehyde and malondialdehyde adducts were increased in both muscles of alcohol-dosed rats. However there was no increase in the amounts of reduced acetaldehyde adducts, as detected by both the rabbit polyclonal antibody and the RT1.1 mouse monoclonal antibody. Furthermore, there was no detectable increase in malondialdehyde-acetaldehyde and HER-protein adducts. Similar results were obtained in the liver.

CONCLUSIONS

Adducts formed in skeletal muscle and liver of rats exposed acutely to ethanol are mainly unreduced acetaldehyde and malondialdehyde species.

Protein deficiency and muscle damage in carbon tetrachloride induced liver cirrhosis

Protein undernutrition, alterations of hormones such as IGF-1, testosterone and cortisol, and increased lipid peroxidation-which may be related with deranged metabolism of some elements such as iron (Fe), zinc (Zn), manganese (Mn), selenium (Se) or copper (Cu)-may contribute to muscle damage in non alcoholic cirrhosis. Here, we analyse the effect of protein deficiency on muscle Cu, Fe, Zn, Mn and Se in carbon-tetrachloride (CCl(4)) induced liver cirrhosis. We also study the association between protein undernutrition and these trace elements with the activity of glutathione peroxidase (GPX), superoxide dismutase (SOD) and lipid peroxidation products, and how all these are related with muscle morphological changes in 40 male adult Sprague-Dawley rats. Liver cirrhosis was induced by intraperitoneal injection of CCl(4) to 10 rats fed a 2% protein diet, and to another 10 fed a 18% protein control diet. Two further groups included rats without cirrhosis fed the 2% protein and the 18% protein diets. After sacrifice (6 weeks later), we found type IIa fibre atrophy in the cirrhotic animals, especially in the low-protein fed ones and this was due to protein deficiency. Muscle Fe increased in low protein fed cirrhotic rats. No relationship was found between muscle changes and any of the hormones, enzymes and trace elements analysed, or with liver fibrosis. These results suggest that muscle atrophy observed in CCl(4)-induced cirrhosis is related with protein deficiency, but not with cirrhosis itself.

Ca2+-regulatory muscle proteins in the alcohol-fed rat

Alcoholic myopathy is characterized by muscle weakness and difficulties in gait and locomotion. It is one of the most prevalent skeletal muscle disorders in the Western hemisphere, affecting between 40% and 60% of all chronic alcohol misusers. However, the pathogenic mechanisms are unknown, although recent studies have suggested that membrane defects occur as a consequence of chronic alcohol exposure. It was our hypothesis that alcohol ingestion perturbs membrane-located proteins associated with intracellular signalling and contractility, in particular those relating to calcium homeostasis. To test this, we fed male Wistar rats nutritionally complete liquid diets containing ethanol as 35% of total dietary energy. Controls were pair-fed identical amounts of the same diet in which ethanol was replaced by isocaloric glucose. At the end of 6 weeks, rats were killed and skeletal muscles dissected. These were used to determine important ion-regulatory skeletal muscle proteins including sarcalumenin (SAR), sarcoplasmic-endoplasmic reticulum Ca(2+)-adenosine triphosphatase (ATPase) (SERCA1), the junctional face protein of 90 kd (90-JFP), alpha(1)- and alpha(2)-dihydropyridine receptor (alpha(1)-DHPR and alpha(2)-DHPR), and calsequestrin (CSQ) by immunoblotting. The relative abundance of microsomal proteins was determined by immunoblotting using the enhanced chemiluminescence (ECL) technique. The data showed that alcohol-feeding significantly reduced gastrocnemius and hind limb muscle weights (P <.05 in both instances). Concomitant changes included increases in the relative amounts of SERCA1 (P <.05) and Ca(2+)-ATPase activity (P <.025). However, there were no statistically significant changes in either SAR, 90-JFP, alpha(1)-DHPR or alpha(2)-DHPR (P >.2 in all instances). Reductions in CSQ were of marginal significance (P =.0950). We conclude that upregulation of SERCA1 protein and Ca(2+)-ATPase activity may be an adaptive mechanism and/or a contributory process in the pathology of alcohol-induced muscle disease.