Valine-alanine manganese superoxide dismutase polymorphism is not associated with alcohol-induced oxidative stress or liver fibrosis

Genetic and Epigenetic Modifiers of Alcoholic Liver Disease

Alcoholic liver disease (ALD), a disorder caused by excessive alcohol consumption is a global health issue. More than two billion people consume alcohol in the world and about 75 million are classified as having alcohol disorders. ALD embraces a wide spectrum of hepatic lesions including steatosis, alcoholic steatohepatitis (ASH), fibrosis, cirrhosis, and hepatocellular carcinoma (HCC). ALD is a complex disease where environmental, genetic, and epigenetic factors contribute to its pathogenesis and progression. The severity of alcohol-induced liver disease depends on the amount, method of usage and duration of alcohol consumption as well as on age, gender, presence of obesity, and genetic susceptibility. Genome-wide association studies and candidate gene studies have identified genetic modifiers of ALD that can be exploited as non-invasive biomarkers, but which do not completely explain the phenotypic variability. Indeed, ALD development and progression is also modulated by epigenetic factors. The premise of this review is to discuss the role of genetic variants and epigenetic modifications, with particular attention being paid to microRNAs, as pathogenic markers, risk predictors, and therapeutic targets in ALD.

Superoxide Dismutase 2 Genetic Variation as a Susceptibility Risk Factor for Alcoholic Cirrhosis

AIMS

Superoxide dismutase 2 (SOD2) is an important antioxidant phase 2 enzyme. The associations of SOD2 genetic variation and the risk of advanced alcoholic liver diseases are still debatable. We aimed to investigate the association of the main SOD2 genetic variant (47T>C) and the susceptibility to alcoholic cirrhosis.

METHODS

A total of 80 patients with alcoholic cirrhosis (AC), 80 patients with alcoholic non-cirrhosis (ANC), 80 with viral hepatitis B-related cirrhosis (VC), and 165 healthy controls (HC) were enrolled into this study. A polymerase chain reaction was used to genotype their SOD2 47T>C (rs4880).

RESULTS

There was no statistical difference in the frequency distribution of the three SOD2 47T>C genotypes among groups. However, if individuals with C variant were grouped together, the AC group had higher frequency of SOD2 C/C or C/T genotype than ANC, VC and HC groups had (38.7% vs. 21.3%, 26.3% and 21.8%, respectively, P = 0.010). After adjustment for confounders, the SOD2 C/C and C/T genotypes remained associated with the risk of AC (adjusted OR: 2.79 and 3.50, respectively, P < 0.03, compared with ANC and HC groups). In contrast, there was no significant difference of SOD2 genetic variation between VC and HC groups.

CONCLUSIONS

Anti-oxidative enzyme SOD2 47T>C genetic variant may increase the susceptibility to AC. This suggests that oxidative stress plays a role in the development of AC.

Genetic background in nonalcoholic fatty liver disease: A comprehensive review

In the Western world, nonalcoholic fatty liver disease (NAFLD) is considered as one of the most significant liver diseases of the twenty-first century. Its development is certainly driven by environmental factors, but it is also regulated by genetic background. The role of heritability has been widely demonstrated by several epidemiological, familial, and twin studies and case series, and likely reflects the wide inter-individual and inter-ethnic genetic variability in systemic metabolism and wound healing response processes. Consistent with this idea, genome-wide association studies have clearly identified Patatin-like phosholipase domain-containing 3 gene variant I148M as a major player in the development and progression of NAFLD. More recently, the transmembrane 6 superfamily member 2 E167K variant emerged as a relevant contributor in both NAFLD pathogenesis and cardiovascular outcomes. Furthermore, numerous case-control studies have been performed to elucidate the potential role of candidate genes in the pathogenesis and progression of fatty liver, although findings are sometimes contradictory. Accordingly, we performed a comprehensive literature search and review on the role of genetics in NAFLD. We emphasize the strengths and weaknesses of the available literature and outline the putative role of each genetic variant in influencing susceptibility and/or progression of the disease.

Alcoholic and non-alcoholic steatohepatitis

This paper is based upon the "Charles Lieber Satellite Symposia" organized by Manuela G. Neuman at the Research Society on Alcoholism (RSA) Annual Meetings, 2013 and 2014. The present review includes pre-clinical, translational and clinical research that characterize alcoholic liver disease (ALD) and non-alcoholic steatohepatitis (NASH). In addition, a literature search in the discussed area was performed. Strong clinical and experimental evidence lead to recognition of the key toxic role of alcohol in the pathogenesis of ALD. The liver biopsy can confirm the etiology of NASH or alcoholic steatohepatitis (ASH) and assess structural alterations of cells, their organelles, as well as inflammatory activity. Three histological stages of ALD are simple steatosis, ASH, and chronic hepatitis with hepatic fibrosis or cirrhosis. These latter stages may also be associated with a number of cellular and histological changes, including the presence of Mallory's hyaline, megamitochondria, or perivenular and perisinusoidal fibrosis. Genetic polymorphisms of ethanol metabolizing enzymes such as cytochrome p450 (CYP) 2E1 activation may change the severity of ASH and NASH. Alcohol mediated hepatocarcinogenesis, immune response to alcohol in ASH, as well as the role of other risk factors such as its co-morbidities with chronic viral hepatitis in the presence or absence of human immunodeficiency virus are discussed. Dysregulation of hepatic methylation, as result of ethanol exposure, in hepatocytes transfected with hepatitis C virus (HCV), illustrates an impaired interferon signaling. The hepatotoxic effects of ethanol undermine the contribution of malnutrition to the liver injury. Dietary interventions such as micro and macronutrients, as well as changes to the microbiota are suggested. The clinical aspects of NASH, as part of metabolic syndrome in the aging population, are offered. The integrative symposia investigate different aspects of alcohol-induced liver damage and possible repair. We aim to (1) determine the immuno-pathology of alcohol-induced liver damage, (2) examine the role of genetics in the development of ASH, (3) propose diagnostic markers of ASH and NASH, (4) examine age differences, (5) develop common research tools to study alcohol-induced effects in clinical and pre-clinical studies, and (6) focus on factors that aggravate severity of organ-damage. The intention of these symposia is to advance the international profile of the biological research on alcoholism. We also wish to further our mission of leading the forum to progress the science and practice of translational research in alcoholism.

Non-alcoholic fatty liver disease: what the clinician needs to know

Non-alcoholic fatty liver disease (NAFLD) is the most frequent cause of liver disease in the Western world. Furthermore, it is increasing worldwide, paralleling the obesity pandemic. Though highly frequent, only about one fifth of affected subjects are at risk of developing the progressive form of the disease, non-alcoholic steatohepatitis with fibrosis. Even in the latter, liver disease is slowly progressive, though, since it is so prevalent, it is already the third cause of liver transplantation in the United States, and it is predicted to get to the top of the ranking in few years. Of relevance, fatty liver is also associated with increased overall mortality and particularly increased cardiovascular mortality. The literature and amount of published papers on NAFLD is increasing as fast as its prevalence, which makes it difficult to keep updated in this topic. This review aims to summarize the latest knowledge on NAFLD, in order to help clinicians understanding its pathogenesis and advances on diagnosis and treatment.

Effect of alcohol exposure on hepatic superoxide generation and hepcidin expression

AIM: To understand the role of mitochondrial-produced superoxide (O₂^•-) in the regulation of iron-regulatory hormone, hepcidin by alcohol in the liver.

METHODS: For alcohol experiments, manganese superoxide dismutase knockout mice heterozygous for Sod2 gene expression (Sod2^+/-) and age-matched littermate control mice (LMC), expressing Sod2 gene on both alleles, were exposed to either 10% (w/v) ethanol in the drinking water or plain water (control) for 7 d. Total cellular O₂^•- levels in hepatocytes isolated from the livers of mice were measured by electron paramagnetic resonance spectroscopy. The mitochondrial-targeted, O₂^•--sensitive fluorogenic probe, MitoSOX Red and flow cytometry were utilized to measure O₂^•- in mitochondria. Gene and protein expression were determined by Taqman Real-time quantitative PCR and Western blotting, respectively.

RESULTS: Sod2^+/- mice expressed 40% less MnSOD protein (SOD2) in hepatocytes compared to LMC mice. The deletion of Sod2 allele did not alter the basal expression level of hepcidin in the liver. 10% ethanol exposure for 1 wk inhibited hepatic hepcidin mRNA expression three-fold both in Sod2^+/- and LMC mice. O₂^•- levels in hepatocytes of untreated Sod2^+/- mice were three-fold higher than in untreated LMC mice, as observed by electron paramagnetic resonance spectroscopy. O₂^•- levels in mitochondria of Sod2^+/ mice were four-fold higher than in mitochondria of untreated LMC mice, as measured by MitoSOX Red fluorescence and flow cytometry. Alcohol induced a two-fold higher increase in O₂^•- levels in hepatocytes of LMC mice than in Sod2^+/- mice compared to respective untreated counterparts. In contrast, 1 wk alcohol exposure did not alter mitochondrial O₂^•- levels in both Sod2^+/- and control mice.

CONCLUSION: Mitochondrial O₂^•- is not involved in the inhibition of liver hepcidin transcription and thereby regulation of iron metabolism by alcohol. These findings also suggest that short-term alcohol consumption significantly elevates O₂^•- levels in hepatocytes, which appears not to originate from mitochondria.

Genetic determinants of hepatic steatosis in man

Hepatic steatosis is one of the most common liver disorders in the general population. The main cause of hepatic steatosis is nonalcoholic fatty liver disease (NAFLD), representing the hepatic component of the metabolic syndrome, which is characterized by type 2 diabetes, obesity, and dyslipidemia. Insulin resistance and excess adiposity are considered to play key roles in the pathogenesis of NAFLD. Although the risk factors for NAFLD are well established, the genetic basis of hepatic steatosis is largely unknown. Here we review recent progress on genomic variants and their association with hepatic steatosis and discuss the potential impact of these genetic studies on clinical practice. Identifying the genetic determinants of hepatic steatosis will lead to a better understanding of the pathogenesis and progression of NAFLD.

Genetic polymorphisms in non-alcoholic fatty liver disease in obese Egyptian children

BACKGROUND/AIM

Polymorphisms in the promoter of microsomal triglyceride transfer protein (MTP) lead to decreased MTP transcription, less export of triglyceride from hepatocytes, and greater intracellular triglyceride accumulation. Therefore, functional polymorphisms in MTP may be involved in determining susceptibility to nonalcoholic steatohepatitis (NASH). The aim of this study is to examine the effect of some genetic influences among a group of obese Egyptian children.

PATIENTS AND METHODS

A cross-sectional study was conducted on 76 overweight and obese children presenting to the Pediatric Endocrinology Unit, Cairo University Children's Hospital, Egypt, as well as on 20 healthy controls. Anthropometric measurements were taken for all the patients and they underwent clinical examination, ultrasonographic examination of the liver, and liver biopsy when appropriate. Liver functions, blood glucose, serum insulin, C-peptide, and lipid profile were assessed and HOMA-IR calculated. Blood samples from biopsy-proven NASH patients and controls were analyzed by polymerase chain reaction (PCR) and restriction fragment length polymorphism for the -493 G/T polymorphism in the promoter of MTP and the 1183 T/C polymorphism in the mitochondrial targeting sequence of manganese superoxide dismutase (MnSOD).

RESULTS

Eight had biopsy-proven simple steatosis and 7 had NASH. NASH patients had a much higher incidence of the MTP G/G genotype (P = 0.002, CI: 2.9-392) compared with the controls. NASH patients also had a 100% prevalence of the MnSOD T/T genotype.

CONCLUSION

Certain genotypes in MTP and MnSOD are significantly more prevalent among obese children with NASH and may be responsible for such a phenotype.

Mitochondrial dysfunction and oxidative stress in the pathogenesis of alcohol- and obesity-induced fatty liver diseases

Fatty liver disease associated with chronic alcohol consumption or obesity/type 2 diabetes has emerged as a serious public health problem. Steatosis, accumulation of triglyceride in hepatocytes, is now recognized as a critical "first-hit" in the pathogenesis of liver disease. It is proposed that steatosis "primes" the liver to progress to more severe liver pathologies when individuals are exposed to subsequent metabolic and/or environmental stressors or "second-hits." Genetic risk factors can also influence the susceptibility to and severity of fatty liver disease. Furthermore, oxidative stress, disrupted nitric oxide (NO) signaling, and mitochondrial dysfunction are proposed to be key molecular events that accelerate or worsen steatosis and initiate progression to steatohepatitis and fibrosis. This review article will discuss the following topics regarding the pathobiology and molecular mechanisms responsible for fatty liver disease: (1) the "two-hit" or "multi-hit" hypothesis, (2) the role of mitochondrial bioenergetic defects and oxidant stress, (3) the interplay between NO and mitochondria in fatty liver disease, (4) genetic risk factors and oxidative stress-responsive genes, and (5) the feasibility of antioxidants for treatment.

Genes or environment to determine alcoholic liver disease and non-alcoholic fatty liver disease

While the vast majority of heavy drinkers and individuals with obesity, insulin resistance, and the metabolic syndrome will have steatosis, only a minority will ever develop steatohepatitis, fibrosis, and cirrhosis. Genetic and environmental risk factors for advanced alcoholic liver disease (ALD) and non-alcoholic fatty liver disease (NAFLD) seem likely to include factors that influence the severity of steatosis and oxidative stress, the cytokine milieu, the magnitude of the immune response, and/or the severity of fibrosis. For ALD, the dose and pattern of alcohol intake, along with obesity are the most important environmental factors determining disease risk. For NAFLD, dietary saturated fat and antioxidant intake and small bowel bacterial overgrowth may play a role. Family studies and interethnic variations in susceptibility suggest that genetic factors are important in determining disease risk. For ALD, functional polymorphisms in the alcohol dehydrogenases and aldehyde dehydrogenase alcohol metabolising genes play a role in determining susceptibility in Oriental populations. No genetic associations with advanced NAFLD have been replicated in large studies. Preliminary data suggest that polymorphisms in the genes encoding microsomal triglyceride transfer protein, superoxide dismutase 2, the CD14 endotoxin receptor, TNF-alpha, transforming growth factor-beta, and angiotensinogen may be associated with steatohepatitis and/or fibrosis.