Non-alcoholic steatohepatitis: clinical significance and pathogenesis

Oxidative Stress in Non-alcoholic Fatty Liver Disease. An Updated Mini Review

Non-alcoholic fatty liver disease (NAFLD) is a challenging disease caused by multiple factors, which may partly explain why it remains still orphan of an adequate therapeutic strategy. Herein we focus on the interplay between oxidative stress (OS) and the other causal pathogenetic factors. Different reactive oxygen species (ROS) generators contribute to NAFLD inflammatory and fibrotic progression, which is quite strictly linked to the lipotoxic liver injury from fatty acids and/or a wide variety of their biologically active metabolites in the context of either a two-hit or a (more recent) multiple parallel hits theory. An antioxidant defense system is usually able to protect hepatic cells from damaging effects caused by ROS, including those produced into the gastrointestinal tract, i.e., by-products generated by usual cellular metabolic processes, normal or dysbiotic microbiota, and/or diet through an enhanced gut–liver axis. Oxidative stress originating from the imbalance between ROS generation and antioxidant defenses is under the influence of individual genetic and epigenetic factors as well. Healthy diet and physical activity have been shown to be effective on NAFLD also with antioxidant mechanisms, but compliance to these lifestyles is very low. Among several considered antioxidants, vitamin E has been particularly studied; however, data are still contradictory. Some studies with natural polyphenols proposed for NAFLD prevention and treatment are encouraging. Probiotics, prebiotics, diet, or fecal microbiota transplantation represent new therapeutic approaches targeting the gut microbiota dysbiosis. In the near future, precision medicine taking into consideration genetic or environmental epigenetic risk factors will likely assist in further selecting the treatment that could work best for a specific patient.

Contribution of the HNE-immunohistochemistry to modern pathological concepts of major human diseases

Excessive production of reactive oxygen species can induce peroxidation of the polyunsaturated fatty acids thus generating reactive aldehydes like 4-hydroxy-2-nonenal (HNE), denoted as "the second messenger of free radicals". Because HNE has high binding affinity for cysteine, histidine and lysine it forms relatively stable and hardly metabolized protein adducts. By changing structure and function of diverse structural and regulatory proteins, HNE achieves not only cytotoxic, but also regulatory functions in various pathophysiological processes. Numerous animal model studies and clinical trials confirmed HNE as one of the crucial factors in development and progression of many disorders, in particular of cancer, (neuro)degenerative, metabolic and inflammatory diseases. Since HNE has multiple biological effects and is in the living system usually bound to proteins and peptides, many research groups work on development of specific immunochemical methods targeting the HNE-histidine adducts as major bioactive marker of lipid peroxidation, following the research pathway initiated by Hermann Esterbauer, who discovered HNE in 60's. Such immunohistochemical studies did not only prove the high biomedical importance of HNE, but have also given new insights into major diseases of the modern man. Immunohistochemical studies have shown reversibility of formation of the HNE-protein adducts, as well as differential onset of the HNE-mediated lipid peroxidation between age- associated atherosclerosis and photoaging, revealing eventually selective anti-cancer effects of HNE produced by non-malignant cells in vicinity of cancer. This review summarizes some of the HNE-histidine immunohistochemistry findings we believe are of broad biomedical interest and could inspire new studies in the field.

Attenuation of high cholesterol-induced oxidative stress in rabbit liver by thymoquinone

BACKGROUND/AIMS

This study examines the modifying effects of thymoquinone (TQ), an agent with antioxidant and hypolipidemic properties, on reactive oxygen species, antioxidant activity, and steatosis in livers of hyperlipidemic rabbit.

METHODS

Oxidative stress was induced in New Zealand White rabbit by a high-cholesterol diet for 8 weeks. Four groups of six animals each were divided into a control group; a high cholesterol group (received 1% cholesterol diet); a high cholesterol/low TQ group (received 1% cholesterol diet plus TQ 10 mg/kg/day), and a high cholesterol/high TQ (20 mg/kg/day) group. Blood samples were taken at the end of the study and examined for fasting serum glucose, insulin, and aminotransaminases. Hepatic tissue samples were examined for malondialdehyde, protein carbonyls, antioxidant enzymes, and steatosis.

RESULTS

There was severe hepatic steatosis and elevated serum alanine aminotransferase in the high cholesterol group (group II) but not in the high cholesterol and low or high TQ groups (groups III, IV). The hepatic reactive oxygen species activity in the high cholesterol group was significantly higher while the antioxidant enzymes were lower (P<0.05) when compared with the control (group I) or either of the high cholesterol and TQ groups.

CONCLUSION

TQ attenuates hepatic oxidative stress in fatty liver injury induced by high-cholesterol diet in rabbits.

N-acetylcysteine attenuates oxidative stress and liver pathology in rats with non-alcoholic steatohepatitis

AIM: To evaluate attenuating properties of N-acetylcysteine (NAC) on oxidative stress and liver pathology in rats with non-alcoholic steatohepatitis (NASH).

METHODS: Male Sprague-Dawley rats were randomly divided into three groups. Group 1 (control, n = 8) was free accessed to regular dry rat chow (RC) for 6 wk. Group 2 (NASH, n = 8) was fed with 100% fat diet for 6 wk. Group 3 (NASH + NAC₂₀, n = 9) was fed with 100% fat diet plus 20 mg/kg per day of NAC orally for 6 wk. All rats were sacrificed to collect blood and liver samples at the end of the study.

RESULTS: The levels of total glutathione (GSH) and hepatic malondialdehyde (MDA) were increased significantly in the NASH group as compared with the control group (GSH; 2066.7 ± 93.2 vs 1337.5 ± 31.5 μmol/L and MDA; 209.9± 43.9 vs 3.8 ±1.7 μmol/g protein, respectively, P < 0.05). Liver histopathology from group 2 showed moderate to severe macrovesicular steatosis, hepatocyte ballooning, and necroinflammation. NAC treatment improved the level of GSH (1394.8 ± 81.2 μmol/L, P < 0.05), it did not affect MDA (150.1 ± 27.0 μmol/g protein), but led to a decrease in fat deposition and necroinflammation.

CONCLUSION: NAC treatment could attenuate oxidative stress and improve liver histology in rats with NASH.

Doença hepática não-alcoólica: evolução após derivação gastrojejunal em Y-de-Roux pela técnica de fobi-capella

RACIONAL: A doença hepática não-alcoólica apresenta alta prevalência entre pacientes com obesidade mórbida, podendo evoluir de esteatose hepática até esteatohepatite e cirrose. OBJETIVO: Determinar o efeito da derivação gástrica na incidência de doença hepática não-alcoólica e co-morbidades relacionadas em pacientes com obesidade mórbida. MÉTODOS: Os pacientes foram prospectivamente avaliados no pré-operatório e, no mínimo, após 6 meses de pós-operatório. Foram analisados: dados antropométricos, co-morbidades, medicamentos em uso, colesterol, triglicerídeos, provas hepáticas e incidência de doença hepática não-alcoólica. Todos os pacientes com alteração de provas hepáticas foram submetidos a biopsia hepática no peroperatório. RESULTADO: Vinte e oito pacientes com doença hepática não-alcoólica foram incluídos no estudo com índice de massa corpórea médio de 42 ± 4 kg/m². Vinte e cinco pacientes apresentaram 59 co-morbidades, sendo as mais freqüentes: elevação de triglicerídeos (n = 23), elevação de colesterol total (n = 13) e hipertensão arterial (n = 11). Foram submetidos a biopsia 22 pacientes: 10 apresentaram esteatose macrogoticular moderada, 5 esteatose macrogoticular discreta e 7 esteatohepatite. Os doentes foram analisados em média após 230 dias de pós-operatório. Apresentaram perda de 64% do excesso de peso, redução do índice de massa corpórea médio para 29,6 ± 3 kg/m² e 21 co-morbidades em 13 pacientes. Houve diminuição estatisticamente significante do número dos acometidos de elevação de triglicerídeos, elevação de colesterol total, hipertensão arterial e na incidência de doença hepática não-alcoólica. CONCLUSÃO: A perda de peso proporcionada pela derivação gastrojejunal em Y-de-Roux pela técnica de Fobi-Capella em pacientes com doença hepática não-alcoólica está associada à diminuição de sua incidência e de outras co-morbidades.

Association of cardiorespiratory fitness, body mass index, and waist circumference to nonalcoholic fatty liver disease

BACKGROUND & AIMS

There is a need for more work examining the potential of physical activity and/or weight control as a preventive and/or therapeutic option in the treatment of fatty liver diseases. The purpose of this study was to examine the association between cardiorespiratory fitness, body mass index (BMI), and waist circumference with markers of nonalcoholic fatty liver disease (NAFLD).

METHODS

Participants consisted of 218 apparently healthy nonsmoking, nonalcoholic men aged 33-73 years. Cardiorespiratory fitness was assessed by a maximal treadmill test. Liver and spleen density were measured using a computed tomography scan. We defined the presence of NAFLD as the following 3 conditions being met: (1) liver to spleen density of 1.0 or less, (2) serum alanine transaminase level greater than 30 U/L, and (3) serum aspartate transaminase/alanine transaminase level less than 1.0.

RESULTS

Twenty-four (11%) of the participants met the NAFLD definition. There was an inverse association between fitness categories, and a positive association for BMI categories (and waist circumference categories) with the prevalence of NAFLD (P for trend <.001 for all). Fitness and BMI were independent of each other in their associations with the prevalence of NAFLD. The addition of waist circumference to the regression model attenuated the association with prevalence of NAFLD for both fitness (P value changed from <.0001 to .06) and BMI (P value changed from <.001 to .22).

CONCLUSIONS

Fitness (inversely) and BMI (directly) were associated with the prevalence of NAFLD. However, these associations were attenuated when abdominal obesity was included in the statistical model.

Nonalcoholic steatohepatitis: recent advances from experimental models to clinical management

A condition defined as nonalcoholic fatty liver disease (NAFLD) is frequently found in humans. Deemed as a benign condition until recently, more emphasis is now put on the potential harmful evolution of the inflammatory form, that is, nonalcoholic steatohepatitis (NASH), toward end-stage liver disease. This review highlights the major morphologic and pathophysiological features of NASH. The link between experimental biochemical findings in animal models and clinical and therapeutic approaches in humans is discussed. Once all the other causes of persistent elevation of serum transaminase levels have been excluded, the diagnosis of NASH can be only confirmed by liver histology. Other noninvasive diagnostic tools, however, are being investigated to assess specific subcellular functions and to allow the follow-up of patients at higher risk for major liver dysfunction. A better understanding of various pathogenic aspects of NASH will help in identifying potential therapeutic approaches in these patients.

Non-alcoholic steatohepatitis: review of a growing medical problem

Non-alcoholic steatohepatitis (NASH) is a metabolic liver disorder that is seen in 2-6% of the general population. It manifests itself by elevated liver enzymes, frequently without symptoms. The histological findings include steatosis, inflammation, fibrosis, and cirrhosis. Three case reports are presented to illustrate features of NASH. A two-hit model has been proposed in the pathogenesis of NASH. The first hit is hepatic steatosis. A hypercaloric diet with high levels of carbohydrates and saturated fatty acids results in elevated plasma free fatty acids (FFA) and expands the adipose tissue. Insulin resistance develops and augments steatosis. Oxidation of FFA yields toxic free radicals, resulting in lipid peroxidation. They cause the second hits: increased oxidative stress on hepatocytes and induction of pro-inflammatory cytokines. When the antioxidant capacities of the liver are insufficient, mitochondrial dysfunction and tumor necrosis factor alpha (TNF-alpha) cause inflammation and fibrosis. Treatment consists of life style modifications, particularly weight loss and exercise. Many drugs have been tried in the treatment of NASH. The insulin-sensitizing drugs metformin, rosiglitazone, and pioglitazone, and the antioxidant vitamin E show promising results. Further investigation of therapeutic options is needed to direct the choice of therapy in the future.

Nonalcoholic fatty liver disease (NAFLD) in children

Nonalcoholic fatty liver disease (NAFLD) is common in obese children and is a growing problem, given the increase in prevalence of obesity. NAFLD is also associated with diabetes, insulin resistance, hypercholesterolemia, and hypertriglyceridemia. Although mostly benign, some children with NAFLD develop fibrosis and cirrhosis, which necessitates close monitoring. Chronically elevated plasma liver enzyme levels is the most frequent finding. Ultrasound (US) examination allows confirmation of the diagnosis and it is useful for the follow-up. Gradual and sustained weight reduction is a management option that is worth trying initially. Other modalities of management, although interesting, await evidence as well as information on long-term benefits and effects. Sustained increase of transaminases despite weight reduction is a cause for concern and may require a liver biopsy both to assess severity of liver damage and for prognostic purposes.

Lyophilized apple counteracts the development of hypercholesterolemia, oxidative stress, and renal dysfunction in obese Zucker rats

Apples may have selective effects on abnormalities associated with the plurimetabolic syndrome. Therefore, the effects of 20% lyophilized apple supplementation on plasma and tissue lipids and on protection against susceptibility to oxidative stress and renal dysfunction were investigated in Zucker lean (Fa/-) or obese (fa/fa) rats. The experimental diets were equilibrated for sugar supply, contained 0.25 g/100 g cholesterol and provided only one third of the vitamin E requirement. Obese Zucker rats were hypercholesterolemic with cholesterol accumulation in LDL and HDL fractions. The apple diet lowered plasma and LDL cholesterol (-22 and -70%, respectively, P < 0.01) in obese Zucker rats and, in parallel, reduced triglyceride accumulation in heart and liver. Zucker rats fed the apple diet also had a larger intestinal pool and greater fecal excretion of bile acids. The heart concentration and urinary excretion of malondialdehyde were reduced by apple consumption in obese Zucker rats, suggesting better protection against peroxidation. Glucosuria and proteinuria in obese Zucker rats were also suppressed by the apple diet. In conclusion, despite their moderate fiber content, apples improve substantially the lipid status and peroxidative parameters in obese Zucker rats, suggesting that other plant constituents such as polyphenols are involved in these effects.