Increased nitroxidative stress promotes mitochondrial dysfunction in alcoholic and nonalcoholic fatty liver disease

Alcohol-induced hormonal and metabolic alterations in plasma and erythrocytes-a gender-based study

PURPOSE

This study aimed to understand the gender-specific alcohol-induced biochemical changes and TBARS association with the endocrine system.

METHODS

Human male and female subjects ranging from 35 ± 10 years old with an 8-10-year drinking history were included in the study.

RESULTS

The results demonstrated that testosterone levels were lower in male alcoholics and higher in female alcoholics, as well as higher estrogen and cortisol levels in both genders. In addition, we found lower T3, T4, and thyroid-stimulating hormone (TSH) levels in alcoholics of both sexes. Furthermore, plasma TBARS, protein carbonyls, nitrite, and nitrate levels increased significantly with concomitant decrease in reduced glutathione (GSH), catalase (CAT), superoxide dismutase (SOD) and glutathione peroxidase (GPx) activities in both male and female alcoholics. Furthermore, erythrocyte lysate nitrite and nitrate levels membrane total cholesterol, phospholipid and cholesterol/phospholipid (C/P) ratio with lower total membrane proteins in both genders of alcoholics. SDS-PAGE analysis of erythrocyte membrane proteins revealed increased density of band 3, protein 4.1, 4.2, 4.9 and glycophorins, whereas decreases in spectrin (α and β) were observed in both genders of alcoholics. Besides, alcoholics of both sexes had a lower ability to resist osmotic hemolysis. Plasma TBARS was negatively correlated with testosterone, TSH, T3 and T4 in male alcoholics, moreover, estradiol and cortisol were positively correlated in males and females respectively.

CONCLUSION

Female alcoholics may be more susceptible to osmotic hemolysis due to increased erythrocyte membrane lipid peroxidation with decreased antioxidant status, which results in an altered membrane C/P ratio and membrane protein composition.

Contributing roles of mitochondrial dysfunction and hepatocyte apoptosis in liver diseases through oxidative stress, post-translational modifications, inflammation, and intestinal barrier dysfunction

This review provides an update on recent findings from basic, translational, and clinical studies on the molecular mechanisms of mitochondrial dysfunction and apoptosis of hepatocytes in multiple liver diseases, including but not limited to alcohol-associated liver disease (ALD), metabolic dysfunction-associated steatotic liver disease (MASLD), and drug-induced liver injury (DILI). While the ethanol-inducible cytochrome P450-2E1 (CYP2E1) is mainly responsible for oxidizing binge alcohol via the microsomal ethanol oxidizing system, it is also responsible for metabolizing many xenobiotics, including pollutants, chemicals, drugs, and specific diets abundant in n-6 fatty acids, into toxic metabolites in many organs, including the liver, causing pathological insults through organelles such as mitochondria and endoplasmic reticula. Oxidative imbalances (oxidative stress) in mitochondria promote the covalent modifications of lipids, proteins, and nucleic acids through enzymatic and non-enzymatic mechanisms. Excessive changes stimulate various post-translational modifications (PTMs) of mitochondrial proteins, transcription factors, and histones. Increased PTMs of mitochondrial proteins inactivate many enzymes involved in the reduction of oxidative species, fatty acid metabolism, and mitophagy pathways, leading to mitochondrial dysfunction, energy depletion, and apoptosis. Unique from other organelles, mitochondria control many signaling cascades involved in bioenergetics (fat metabolism), inflammation, and apoptosis/necrosis of hepatocytes. When mitochondrial homeostasis is shifted, these pathways become altered or shut down, likely contributing to the death of hepatocytes with activation of inflammation and hepatic stellate cells, causing liver fibrosis and cirrhosis. This review will encapsulate how mitochondrial dysfunction contributes to hepatocyte apoptosis in several types of liver diseases in order to provide recommendations for targeted therapeutics.

Melatonin Prevents Alcohol- and Metabolic Dysfunction- Associated Steatotic Liver Disease by Mitigating Gut Dysbiosis, Intestinal Barrier Dysfunction, and Endotoxemia

Melatonin (MT) has often been used to support good sleep quality, especially during the COVID-19 pandemic, as many have suffered from stress-related disrupted sleep patterns. It is less known that MT is an antioxidant, anti-inflammatory compound, and modulator of gut barrier dysfunction, which plays a significant role in many disease states. Furthermore, MT is produced at 400-500 times greater concentrations in intestinal enterochromaffin cells, supporting the role of MT in maintaining the functions of the intestines and gut-organ axes. Given this information, the focus of this article is to review the functions of MT and the molecular mechanisms by which it prevents alcohol-associated liver disease (ALD) and metabolic dysfunction-associated steatotic liver disease (MASLD), including its metabolism and interactions with mitochondria to exert its antioxidant and anti-inflammatory activities in the gut-liver axis. We detail various mechanisms by which MT acts as an antioxidant, anti-inflammatory compound, and modulator of intestinal barrier function to prevent the progression of ALD and MASLD via the gut-liver axis, with a focus on how these conditions are modeled in animal studies. Using the mechanisms of MT prevention and animal studies described, we suggest behavioral modifications and several exogenous sources of MT, including food and supplements. Further clinical research should be performed to develop the field of MT in preventing the progression of liver diseases via the gut-liver axis, so we mention a few considerations regarding MT supplementation in the context of clinical trials in order to advance this field of research.

Mitochondrial hydrogen peroxide production by pyruvate dehydrogenase and α-ketoglutarate dehydrogenase in oxidative eustress and oxidative distress

Pyruvate dehydrogenase (PDH) and α-ketoglutarate dehydrogenase (KGDH) are vital entry points for monosaccharides and amino acids into the Krebs cycle and thus integral for mitochondrial bioenergetics. Both complexes produce mitochondrial hydrogen peroxide (mH2O2) and are deactivated by electrophiles. Here, we provide an update on the role of PDH and KGDH in mitochondrial redox balance and their function in facilitating metabolic reprogramming for the propagation of oxidative eustress signals in hepatocytes and how defects in these pathways can cause liver diseases. PDH and KGDH are known to account for ∼45% of the total mH2O2 formed by mitochondria and display rates of production several-fold higher than the canonical source complex I. This mH2O2 can also be formed by reverse electron transfer (RET) in vivo, which has been linked to metabolic dysfunctions that occur in pathogenesis. However, the controlled emission of mH2O2 from PDH and KGDH has been proposed to be fundamental for oxidative eustress signal propagation in several cellular contexts. Modification of PDH and KGDH with protein S-glutathionylation (PSSG) and S-nitrosylation (PSNO) adducts serves as a feedback inhibitor for mH2O2 production in response to glutathione (GSH) pool oxidation. PSSG and PSNO adduct formation also reprogram the Krebs cycle to generate metabolites vital for interorganelle and intercellular signaling. Defects in the redox modification of PDH and KGDH cause the over generation of mH2O2, resulting in oxidative distress and metabolic dysfunction-associated fatty liver disease (MAFLD). In aggregate, PDH and KGDH are essential platforms for emitting and receiving oxidative eustress signals.

High glucose and high lipid induced mitochondrial dysfunction in JEG-3 cells through oxidative stress

Few studies focused on the roles of high glucose combined with high lipid in placental development or fetal growth. This study was designed to investigate the roles of high glucose combined with high lipid in mitochondrial dysfunction of JEG-3 cells. We determined the cellular proliferation and apoptosis, superoxide dismutase (SOD) activity, concentration of malondialdehyde (MDA), and lactic acid dehydrogenase in control group, high glucose group, high lipid group, and high glucose and high lipid group, together with the mitochondrial dysfunction, Nrf2, HO-1, SMAC, and cytochrome C (Cyt-C) expression. Significant decrease of SOD and significant elevation of MDA was seen in high glucose and high lipid group compared with the other three groups. There was significant decrease in mitochondrial SMAC and Cyt-C in high glucose group, high lipid group, and high glucose and high lipid group compared with those of control group. Nrf2 and HO-1 protein expression in high glucose combined with high lipid group showed significant decrease compared with that of high lipid group or high glucose group. We speculated that combination of high glucose and high lipid induced oxidative stress in JEG-3 cells, and Nrf2/ARE pathway may be related to this process.

Genistein Protects against Acetaldehyde-Induced Oxidative Stress and Hepatocyte Injury in Chronic Alcohol-Fed Mice

Alcohol-related liver disease (ALD) is one of the most prevalent forms of liver disease in the world. Acetaldehyde, an intermediate product of alcohol catabolism, is a cause of liver injury caused by alcohol. This study was designed to evaluate the protective role and mechanism(s) of genistein against acetaldehyde-induced liver injury in the pathological process of ALD. We found that genistein administration significantly ameliorated alcohol-induced hepatic steatosis, injury, and inflammation in mice. Genistein supplementation markedly reversed hepatic oxidative stress, endoplasmic reticulum stress, mitochondrial dysfunction, and hepatocellular apoptosis in both alcohol-fed mice liver and acetaldehyde-treated hepatocytes. The mechanistic experiments revealed that the restoration of genistein administration rescued heme oxygenase-1 (HO-1) reduction at both transcriptional and protein levels in either alcohol-fed mice liver or acetaldehyde-treated hepatocytes, and the beneficial aspects derived from genistein were abolished in antioxidase heme oxygenase-1 (HO-1)-deficient hepatocytes. Moreover, we confirmed that genistein administration-restored hepatic nuclear factor erythroid 2-related factor 2 (NRF2), a key transcriptional regulator of HO-1, was involved in the protective role of genistein in ALD. This study demonstrated that genistein ameliorated acetaldehyde-induced oxidative stress and liver injury by restoring the hepatic NRF2-HO-1 signaling pathway in response to chronic alcohol consumption. Therefore, genistein may serve as a potential therapeutic choice for the treatment of ALD.

6- shogaol suppresses AOM/DSS-mediated colorectal adenoma through its antioxidant and anti-inflammatory effects in mice

Colorectal adenoma appears as benign lesions and is a precursor of colorectal adenocarcinoma. The effect of 6-Shogaol (6-[S]), a bioactive agent from ginger, in early colonic adenoma growth is unknown. As a result, this study examines the effect of 6-[S] in a mouse colorectal adenoma model induced by Azoxymethane (AOM) and dextran sulfate sodium (DSS). Adult male mice served as control in Group 1. Group 2 was treated orally with 6-[S] extract (20 mg/kg BW). Group 3 was exposed to AOM (25 mg/kg BW, ip) and one cycle of DSS (2.5%) in drinking water alone while Group 4 was co-treated with 6-[S] for twenty-one (21) days. The body weight gain, organ weight and length, oxidative stress indices, inflammatory markers and histological examination were estimated. Our findings show that 6-[S] co-treatment reversed AOM/DSS-induced elevation in colon weight, colon length, nitric oxide (NO), myeloperoxidase (MPO), hydrogen peroxidase (H₂ O₂ ), and tumor necrosis factor-alpha (TNF-α). However, the antioxidant enzyme activities measured namely catalase (CAT), superoxide dismutase (SOD), reduced glutathione (GSH), and glutathione-S-transferase were significantly increased in 6-[S] treated mice. Taken together, the protective effect of 6-[S] on oxidative burden, inflammation, and histological aberration observed in the colon of the AOM/DSS model of adenoma growth in mice is mediated primarily owing to its anti-inflammatory and anti-oxidative properties. Thus, this study reveals 6-[S] as a useful agent in the possible clinical intervention of colorectal adenoma. PRACTICAL APPLICATIONS: Certain spices have been reported to have numerous phytochemicals with numerous medicinal purposes. However, no studies have been conducted to investigate the role of 6-[S], a phytochemical found in ginger, in the treatment of colorectal adenoma. The study's findings show that 6-[S] is protective in early colonic cancer development, as it manages colorectal adenoma cancer models of AOM/DSS. As a result, 6-[S]'s ability to reduce oxidative stress and inflammation in the colon may be a potential nutritional therapeutic adjuvant for colorectal adenoma.

Effects of Different Green Tea Extracts on Chronic Alcohol Induced-Fatty Liver Disease by Ameliorating Oxidative Stress and Inflammation in Mice

Alcoholic fatty liver disease (AFLD) is a common chronic liver disease and has become a critical global public health problem. Green tea is a popular drink worldwide and contains several bioactive compounds. Different green teas could contain diverse compounds and possess distinct bioactivities. In the present study, the effects of 10 green teas on chronic alcohol induced-fatty liver disease in mice were explored and compared. The results showed that several green teas significantly reduced triacylglycerol levels in serum and liver as well as the aminotransferase activities in mice at a dose of 200 mg/kg, suggesting that they possess hepatoprotective effects. Moreover, several green teas remarkably decreased the expression of cytochrome P450 2E1, the levels of malondialdehyde and 4-hydroxynonenoic acid, and the contents of proinflammatory cytokines, indicating that they could alleviate oxidation damage and inflammation induced by chronic alcohol exposure. In addition, Seven Star Matcha Tea and Selenium-Enriched Matcha Tea could increase glutathione level. Furthermore, the main phytochemical components in green teas were determined and quantified by high-performance liquid chromatography, and the correlation analysis showed that gallic acid, gallocatechin, catechin, chlorogenic acid, and epigallocatechin gallate might at least partially contribute to protective effects on AFLD. In conclusion, Selenium-Enriched Chaoqing Green Tea, Xihu Longjing Tea, Taiping Houkui Tea, and Selenium-Enriched Matcha Tea showed the strongest preventive effects on AFLD. This research also provides the public with new insights about the effects of different green teas on AFLD.

Protective effects of tea extracts against alcoholic fatty liver disease in mice via modulating cytochrome P450 2E1 expression and ameliorating oxidative damage

The alcoholic fatty liver disease (AFLD) has been a severe public health problem. Oxidative stress is involved in the initiation and progression of AFLD. Tea is a popular beverage worldwide with strong antioxidant activity. In this research, our purpose is to explore and compare the effects of 12 selected teas on AFLD. The ethanol liquid diet was used to feed the mice, and 12 tea extracts were administrated at 200 mg/kg body weight every day for 4 weeks. The results showed that the application of several tea extracts exhibited different inhibitory effects on lipid accumulation induced by sub-acute alcohol consumption based on the determination of triglyceride concentration and the histological alteration in the liver. In addition, several teas significantly decreased serum alanine aminotransferase and aspartate aminotransferase activities, inhibited the cytochrome P450 2E1 expression, and promoted alcohol metabolism (p < .05). Besides, compared with the model group, several teas obviously elevated superoxide dismutase and glutathione peroxidase activities as well as glutathione content, and remarkably decreased malondialdehyde level (p < .05). In general, Fried Green Tea, Fenghuang Narcissus Oolong Tea, and Pu-erh Dark Tea possessed potential preventive effects on AFLD. Moreover, the main phytochemicals in the three tea extracts were determined and quantified via high-performance liquid chromatography, and the most commonly detected ingredients were catechins and caffeine, which could exert the protective effects on AFLD.

Oxidative Stress-A Key Player in the Course of Alcohol-Related Liver Disease

Oxidative stress is known to be an inseparable factor involved in the presentation of liver disorders. Free radicals interfere with DNA, proteins, and lipids, which are crucial in liver metabolism, changing their expression and biological functions. Additionally, oxidative stress modifies the function of micro-RNAs, impairing the metabolism of hepatocytes. Free radicals have also been proven to influence the function of certain transcriptional factors and to alter the cell cycle. The pathological appearance of alcohol-related liver disease (ALD) constitutes an ideal example of harmful effects due to the redox state. Finally, ethanol-induced toxicity and overproduction of free radicals provoke irreversible changes within liver parenchyma. Understanding the underlying mechanisms associated with the redox state in the course of ALD creates new possibilities of treatment for patients. The future of hepatology may become directly dependent on the effective action against reactive oxygen species. This review summarizes current data on the redox state in the natural history of ALD, highlighting the newest reports on this topic.

Melatonin, Its Metabolites and Their Interference with Reactive Nitrogen Compounds

Melatonin and several of its metabolites are interfering with reactive nitrogen. With the notion of prevailing melatonin formation in tissues that exceeds by far the quantities in blood, metabolites come into focus that are poorly found in the circulation. Apart from their antioxidant actions, both melatonin and N¹-acetyl-5-methoxykynuramine (AMK) downregulate inducible and inhibit neuronal NO synthases, and additionally scavenge NO. However, the NO adduct of melatonin redonates NO, whereas AMK forms with NO a stable product. Many other melatonin metabolites formed in oxidative processes also contain nitrosylatable sites. Moreover, AMK readily scavenges products of the CO₂-adduct of peroxynitrite such as carbonate radicals and NO₂. Protein AMKylation seems to be involved in protective actions.

Cardioprotective effects of a new glutamic acid derivative in chronic alcohol intoxication

Alcohol abuse is a risk factor for heart damage and deterioration of its inotropic function. Currently, there is no pathogenetic pharmacological treatment for alcohol-induced myocardial injury. Therefore, the study of drugs with cardioprotective action is of current interest. Our earlier studies of stress-induced heart damage showed that a new derivative of glutamic acid - glufimet - protects the myocardium's inotropic function and limits lipid peroxidation. Additionally, we found that it increases the activity of antioxidant enzymes and improves mitochondrial respiration. The purpose of our study was to assess the effect of glufimet on the heart after chronic alcohol intoxication (CAI). The comparison drug was mildronate, which possesses cardioprotective properties and is used to treat alcohol withdrawal. We conducted our study using female Wistar rats (10 months old, 280-320 g). CAI was simulated by replacing drinking water with a 10% ethanol solution sweetened with sucrose (50 g/L) over a period of 24 weeks. The day after the animals stopped ethanol solution drinking, the control group was injected intraperitoneally (i.p.) with a saline solution once a day for 14 days, while the experimental groups received glufimet (28.7 mg/kg) and the drug of comparison mildronate (50 mg/kg), respectively. After that, we studied the heart contractility by measuring volume load, adrenergic reactivity, and maximum isometric load. Under CAI, the control group showed significantly lower growth in left ventricular pressure (LVP), myocardium contraction rate, and relaxation rate during functional tests. Higher concentrations of LPO products (malondialdehyde) and low activity of antioxidant enzymes (superoxide dismutase, glutathione peroxidase), indicating a disturbance in mitochondrial respiration compared to the control group, were registered. While being treated with glufimet and mildronate, the animals demonstrated higher growth rates of myocardial contraction, myocardial relaxation, and LVP, compared to the control group. Mitochondrial functioning and activity of the antioxidant enzymes increased in the same group as well.

Assessment of mitochondrial function in metabolic dysfunction-associated fatty liver disease using obese mouse models

Metabolic dysfunction-associated fatty liver disease (MAFLD) is characterized by deregulated hepatic lipid metabolism; however, the association between MAFLD development and mitochondrial dysfunction has yet to be confirmed. Herein, we employed high-resolution respirometry, blue native polyacrylamide gel electrophoresis-based in-gel activity measurement and immunoblot analysis to assess mitochondrial function in obesity-induced mouse models with varying degrees of MAFLD. Results showed a slight but significant decrease in hepatic mitochondrial respiration in some MAFLD mice compared to mice fed a standard diet. However, the activities and levels of mitochondrial oxidative phosphorylation complexes remained unchanged during obesity-induced MAFLD progression. These results suggest that mitochondrial function, particularly oxidative phosphorylation, was mildly affected during obesity-induced MAFLD development. Moreover, transcriptome profiling of mouse and human liver tissues with varying degrees of MAFLD revealed that the decreased activation of mitochondria-related pathways was only associated with MAFLD of a high histological grade, whereas the major regulators of mitochondrial biogenesis were not altered in mice or humans during MAFLD development. Collectively, our results suggest that impaired hepatic mitochondrial function is not closely associated with obesity-induced MAFLD. Therefore, therapeutic strategies targeting mitochondria for the treatment of MAFLD should be reconsidered.

The Effects of PK11195 and Protoporphyrin IX Can Modulate Chronic Alcohol Intoxication in Rat Liver Mitochondria under the Opening of the Mitochondrial Permeability Transition Pore

Decades of active research have shown that mitochondrial dysfunction, the associated oxidative stress, impaired anti-stress defense mechanisms, and the activation of the proapoptotic signaling pathways underlie pathological changes in organs and tissues. Pathologies caused by alcohol primarily affect the liver. Alcohol abuse is the cause of many liver diseases, such as steatosis, alcoholic steatohepatitis, fibrosis, cirrhosis, and, potentially, hepatocellular cancer. In this study, the effect of chronic alcohol exposure on rat liver mitochondria was investigated. We observed an ethanol-induced increase in sensitivity to calcium, changes in the level of protein kinase Akt and GSK-3β phosphorylation, an induction of the mitochondrial permeability transition pore (mPTP), and strong alterations in the expression of mPTP regulators. Moreover, we also showed an enhanced effect of PK11195 and PPIX, on the parameters of the mPTP opening in rat liver mitochondria (RLM) isolated from ethanol-treated rats compared to the RLM from control rats. We suggest that the results of this study could help elucidate the mechanisms of chronic ethanol action on the mitochondria and contribute to the development of new therapeutic strategies for treating the effects of ethanol-related diseases.

Nitrosative Stress and Its Association with Cardiometabolic Disorders

Reactive nitrogen species (RNS) are formed when there is an abnormal increase in the level of nitric oxide (NO) produced by the inducible nitric oxide synthase (iNOS) and/or by the uncoupled endothelial nitric oxide synthase (eNOS). The presence of high concentrations of superoxide anions (O₂⁻) is also necessary for their formation. RNS react three times faster than O₂⁻ with other molecules and have a longer mean half life. They cause irreversible damage to cell membranes, proteins, mitochondria, the endoplasmic reticulum, nucleic acids and enzymes, altering their activity and leading to necrosis and to cell death. Although nitrogen species are important in the redox imbalance, this review focuses on the alterations caused by the RNS in the cellular redox system that are associated with cardiometabolic diseases. Currently, nitrosative stress (NSS) is implied in the pathogenesis of many diseases. The mechanisms that produce damage remain poorly understood. In this paper, we summarize the current knowledge on the participation of NSS in the pathology of cardiometabolic diseases and their possible mechanisms of action. This information might be useful for the future proposal of anti-NSS therapies for cardiometabolic diseases.

Investigating the effect of Crocus sativus L. petal hydroalcoholic extract on inflammatory and enzymatic indices resulting from alcohol use in kidney and liver of male rats

Background

Studies have shown that consumption of high levels of alcohol causes many negative effects on the liver and kidneys where antioxidant ingredients can be a proper solution to reducing the resulting damages. So, the present study investigated the effect of hydroalcoholic extract of Crocus sativus L. (saffron) petal with antioxidant properties on the changes in inflammatory and enzymatic indices resulting from alcohol use in the male rats’ kidney and liver.

Materials and methods

After preparing the extract, LD₅₀ was determined and high-performance liquid chromatography (HPLC) was employed to specify the type and the rate of the active ingredients of the extract. Then, 36 male Wistar rats were randomly assigned into six groups (n=6). The first group was only administered with normal saline and the second group only received ethyl alcohol 6 mL/kg/day·BW. The third and the fourth groups received ethyl alcohol 6 mL/kg/day·BW plus 167.5 and 335 mg/kg/day·BW saffron petal extract for 8 weeks. The fifth and the sixth groups received ethyl alcohol 6 mL/kg/day·BW for the first 8 weeks and were subsequently gavage fed on saffron extract for 167.5 and 335 mg/kg/day·BW, respectively, during the next 8 weeks. In the beginning and after the termination of the treatment, blood samples were collected from all rats.

Results

The LD₅₀ of the extract was about 670 mg/kg. The HPLC results indicated that the extract contains important antioxidant ingredients. At the end of the study, the serum concentration of the inflammatory indices, renal enzymes, and hepatic enzymes experienced a significant reduction in all of the intervened groups compared to the negative control group (minimum significant difference: P<0.05) except for the treatment group 1.

Conclusion

Based on the current results, the extract has a protective effect in a dosage-dependent way and greater protective roles were documented for higher dosages.

Contributing Roles of CYP2E1 and Other Cytochrome P450 Isoforms in Alcohol-Related Tissue Injury and Carcinogenesis

The purpose of this review is to briefly summarize the roles of alcohol (ethanol) and related compounds in promoting cancer and inflammatory injury in many tissues. Long-term chronic heavy alcohol exposure is known to increase the chances of inflammation, oxidative DNA damage, and cancer development in many organs. The rates of alcohol-mediated organ damage and cancer risks are significantly elevated in the presence of co-morbidity factors such as poor nutrition, unhealthy diets, smoking, infection with bacteria or viruses, and exposure to pro-carcinogens. Chronic ingestion of alcohol and its metabolite acetaldehyde may initiate and/or promote the development of cancer in the liver, oral cavity, esophagus, stomach, gastrointestinal tract, pancreas, prostate, and female breast. In this chapter, we summarize the important roles of ethanol/acetaldehyde in promoting inflammatory injury and carcinogenesis in several tissues. We also review the updated roles of the ethanol-inducible cytochrome P450-2E1 (CYP2E1) and other cytochrome P450 isozymes in the metabolism of various potentially toxic substrates, and consequent toxicities, including carcinogenesis in different tissues. We also briefly describe the potential implications of endogenous ethanol produced by gut bacteria, as frequently observed in the experimental models and patients of nonalcoholic fatty liver disease, in promoting DNA mutation and cancer development in the liver and other tissues, including the gastrointestinal tract.

Antioxidant Versus Pro-Apoptotic Effects of Mushroom-Enriched Diets on Mitochondria in Liver Disease

Mitochondria play a central role in non-alcoholic fatty liver disease (NAFLD) progression and in the control of cell death signalling during the progression to hepatocellular carcinoma (HCC). Associated with the metabolic syndrome, NAFLD is mostly driven by insulin-resistant white adipose tissue lipolysis that results in an increased hepatic fatty acid influx and the ectopic accumulation of fat in the liver. Upregulation of beta-oxidation as one compensatory mechanism leads to an increase in mitochondrial tricarboxylic acid cycle flux and ATP generation. The progression of NAFLD is associated with alterations in the mitochondrial molecular composition and respiratory capacity, which increases their vulnerability to different stressors, including calcium and pro-inflammatory molecules, which result in an increased generation of reactive oxygen species (ROS) that, altogether, may ultimately lead to mitochondrial dysfunction. This may activate further pro-inflammatory pathways involved in the progression from steatosis to steatohepatitis (NASH). Mushroom-enriched diets, or the administration of their isolated bioactive compounds, have been shown to display beneficial effects on insulin resistance, hepatic steatosis, oxidative stress, and inflammation by regulating nutrient uptake and lipid metabolism as well as modulating the antioxidant activity of the cell. In addition, the gut microbiota has also been described to be modulated by mushroom bioactive molecules, with implications in reducing liver inflammation during NAFLD progression. Dietary mushroom extracts have been reported to have anti-tumorigenic properties and to induce cell-death via the mitochondrial apoptosis pathway. This calls for particular attention to the potential therapeutic properties of these natural compounds which may push the development of novel pharmacological options to treat NASH and HCC. We here review the diverse effects of mushroom-enriched diets in liver disease, emphasizing those effects that are dependent on mitochondria.

Orally administration of Neolentinus lepideus extracts attenuated ethanol induced accumulation of hepatic lipid in mice

In this study, we examined the effects of the water extract of Neolentinus lepideus (WENL), an edible mushroom, on ethanol-induced hepatic lipid accumulation. Ethanol-induced oil red O-positive spots on AML-12 hepatocytes were attenuated by WENL treatment. Furthermore, the oral administration of WENL in acute and chronic ethanol-fed mouse models resulted in the decrease in blood triglyceride and the accumulation of lipid droplets in the liver. Interestingly, the transcriptional expression related to lipid metabolisms, such as sterol regulatory element-binding protein 1, and cytochrome P450 2E1, was decreased by WENL treatment in both ethanol-induced AML-12 hepatocytes and our chronic ethanol-fed mouse models. In addition, WENL effectively attenuated the ethanol induced activation of MAP kinases and NF-κB in AML-12 hepatocytes. Taken together, our results suggested that WENL can be effective in alleviating alcohol-induced hepatic lipid accumulation and may be used as potential candidate for the prevention of alcoholic fatty liver disease.

Role of CYP2E1 in Mitochondrial Dysfunction and Hepatic Injury by Alcohol and Non-Alcoholic Substances

Alcoholic fatty liver disease (AFLD) and non-alcoholic fatty liver disease (NAFLD) are two pathological conditions that are spreading worldwide. Both conditions are remarkably similar with regard to the pathophysiological mechanism and progression despite different causes. Oxidative stressinduced mitochondrial dysfunction through post-translational protein modifications and/or mitochondrial DNA damage has been a major risk factor in both AFLD and NAFLD development and progression. Cytochrome P450-2E1 (CYP2E1), a known important inducer of oxidative radicals in the cells, has been reported to remarkably increase in both AFLD and NAFLD. Interestingly, CYP2E1 isoforms expressed in both endoplasmic reticulum (ER) and mitochondria, likely lead to the deleterious consequences in response to alcohol or in conditions of NAFLD after exposure to high fat diet (HFD) and in obesity and diabetes. Whether CYP2E1 in both ER and mitochondria work simultaneously or sequentially in various conditions and whether mitochondrial CYP2E1 may exert more pronounced effects on mitochondrial dysfunction in AFLD and NAFLD are unclear. The aims of this review are to briefly describe the role of CYP2E1 and resultant oxidative stress in promoting mitochondrial dysfunction and the development or progression of AFLD and NAFLD, to shed a light on the function of the mitochondrial CYP2E1 as compared with the ER-associated CYP2E1. We finally discuss translational research opportunities related to this field.

Cellular Abnormalities and Emerging Biomarkers in Alcohol-Associated Liver Disease

Alcohol-associated liver disease (AALD) is the third most common preventable cause for disease burden and mortality in the US. AALD, including alcoholic hepatitis (AH), contributes to half of admissions from decompensated liver disease and 20% of all liver transplants in the US. Peripheral blood cells contribute to systemic inflammation, oxidative stress, mitochondrial dysfunction, and fibrosis in AALD and AH. Alcohol dysregulates function of lymphocytes, neutrophils, monocytes, and tissue macrophages of the innate immune system. These alterations in turn can modulate adaptive immune responses. In this review, we describe these disruptive effects of alcohol on cells of the innate and adaptive immune system and focus on cellular-based emerging biomarkers on diagnosis and prognosis of patients with AALD and AH.

Modulatory effect of some citrus (Citrus limon, Citrus reticulata, Citrus maxima) peels on monoamine oxidase, phosphodiesterase-5 and angiotensin-1 converting enzyme activities in rat heart homogenate

Background

Citrus peels have been reported useful in folk medicine for the management of cardiovascular diseases, but there is dearth of information on the possible mechanisms for their therapeutic action. The aim of this study was to investigate the effect of methanolic extracts from some citrus [lime (Citrus limon), tangerine (Citrus reticulata), shaddock (Citrus maxima)] peels on some enzymes relevant to the management of cardiovascular diseases [monoamine oxidase (MAO), phosphodiesterase-5 (PDE-5) and angiotensin-1-converting enzyme (ACE)].

Methods

Effect of methanolic extracts of lime, tangerine and shaddock peels on MAO, PDE-5 and ACE were carried out using standard methods. In addition, the ability of the extracts to prevent oxidative damage in rat heart homogenates was also investigated. Finally, the total polyphenol content of extracts was determined.

Results

The results revealed that methanolic extracts of lime, tangerine and shaddock peels inhibited MAO, PDE-5, ACE and pro-oxidants induced lipid peroxidation in rat heart homogenate in a concentration-dependent manner.

Conclusions

Findings in this study revealed citrus peel methanolic extracts as natural inhibitor of enzymes (MAO, PDE-5 and ACE) implicated in cardiovascular diseases. Therefore, citrus peels could help in the management of cardiovascular diseases possibly through inhibition of these enzymes.

Selection of reference genes for expression analysis in mouse models of acute alcoholic liver injury

Investigations of hepatic gene expression are crucial for determining the molecular factors involved in acute alcoholic liver injury. The results of liver molecular investigations may reveal etiologically important genomic alterations. Therefore, it is necessary to normalize gene expression data to identify stable genes, which may be used as a reference under different experimental conditions. The aim of the present study was to apply reverse transcription‑quantitative polymerase chain reaction analysis and use analysis software to investigate the expression stability of candidate reference genes in hepatic tissues from mice with acute alcoholic liver injury. The acute alcoholic liver injury models were established by the intragastric administration of alcohol (5 mg/kg) in Imprinting Control Region mice. Total RNA was isolated from the mouse livers, following which the expression levels of seven reference genes, β-actin, glyceraldehyde 3-phosphate dehydrogenase (Gadph), glucuronidase β, hypoxanthine phosphoribosyltransferase 1 (Hprt1), 18S ribosomal RNA, TATA binding protein and β‑2 microglobulin, were examined, and gene expression stability was assessed using the geNorm, NormFinder and BestKeeper tools. The geNorm analysis revealed that the gene with the lowest variability was Hprt1. Hprt1 and Gapdh were validated as the optimal reference gene pair in all samples from all groups. The NormFinder and BestKeeper results showed that Hprt1 was the most stable gene in all samples. Alcohol induces endoplasmic reticulum (ER) stress, causing changes in the expression levels of ER stress‑associated genes. The stability of Hprt1 was verified by the expression analysis of ER stress‑associated genes, and gene expression levels in the ethanol groups were upregulated, with a significant difference in expression, compared with those in the control group. Therefore, Hprt1 was selected as the most stable gene, and Hprt1 and Gapdh were determined to be the optimum gene pair in mouse models of acute alcoholic liver injury. The reliability of the Hprt1 gene was confirmed by expression analysis of ER stress‑associated genes.

Mitochondria-targeted ubiquinone (MitoQ) enhances acetaldehyde clearance by reversing alcohol-induced posttranslational modification of aldehyde dehydrogenase 2: A molecular mechanism of protection against alcoholic liver disease

Alcohol metabolism in the liver generates highly toxic acetaldehyde. Breakdown of acetaldehyde by aldehyde dehydrogenase 2 (ALDH2) in the mitochondria consumes NAD⁺ and generates reactive oxygen/nitrogen species, which represents a fundamental mechanism in the pathogenesis of alcoholic liver disease (ALD). A mitochondria-targeted lipophilic ubiquinone (MitoQ) has been shown to confer greater protection against oxidative damage in the mitochondria compared to untargeted antioxidants. The present study aimed to investigate if MitoQ could preserve mitochondrial ALDH2 activity and speed up acetaldehyde clearance, thereby protects against ALD. Male C57BL/6 J mice were exposed to alcohol for 8 weeks with MitoQ supplementation (5 mg/kg/d) for the last 4 weeks. MitoQ ameliorated alcohol-induced oxidative/nitrosative stress and glutathione deficiency. It also reversed alcohol-reduced hepatic ALDH activity and accelerated acetaldehyde clearance through modulating ALDH2 cysteine S-nitrosylation, tyrosine nitration and 4-hydroxynonenol adducts formation. MitoQ ameliorated nitric oxide (NO) donor-mediated ADLH2 S-nitrosylation and nitration in Hepa-1c1c7 cells under glutathion depletion condition. In addition, alcohol-increased circulating acetaldehyde levels were accompanied by reduced intestinal ALDH activity and impaired intestinal barrier. In accordance, MitoQ reversed alcohol-increased plasma endotoxin levels and hepatic toll-like receptor 4 (TLR4)-NF-κB signaling along with subsequent inhibition of inflammatory cell infiltration. MitoQ also reversed alcohol-induced hepatic lipid accumulation through enhancing fatty acid β-oxidation. Alcohol-induced ER stress and apoptotic cell death signaling were reversed by MitoQ. This study demonstrated that speeding up acetaldehyde clearance by preserving ALDH2 activity critically mediates the beneficial effect of MitoQ on alcohol-induced pathogenesis at the gut-liver axis.

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PTMs of ALDH2 participated in the pathogenesis of alcoholic liver disease.

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MitoQ treatment accelerated acetaldehyde detoxification.

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MitoQ ameliorated acetaldehyde-related tight junction disruption.

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MitoQ reversed TLR4-mediated inflammatory response in alcoholic liver disease.

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MitoQ counteracts alcohol-induced ER stress and cell apoptosis.

Cytochrome P450-2E1 is involved in aging-related kidney damage in mice through increased nitroxidative stress

The aim of this study was to investigate the role of cytochrome P450-2E1 (CYP2E1) in aging-dependent kidney damage since it is poorly understood. Young (7 weeks) and aged female (16-17 months old) wild-type (WT) and Cyp2e1-null mice were used. Kidney histology showed that aged WT mice exhibited typical signs of kidney aging such as cell vacuolation, inflammatory cell infiltration, cellular apoptosis, glomerulonephropathy, and fibrosis, along with significantly elevated levels of renal TNF-α and serum creatinine than all other groups. Furthermore, the highest levels of renal hydrogen peroxide, protein carbonylation and nitration were observed in aged WT mice. These increases in the aged WT mice were accompanied by increased levels of iNOS and mitochondrial nitroxidative stress through altered amounts and activities of the mitochondrial complex proteins and significantly reduced levels of the antioxidant glutathione (GSH). In contrast, the aged Cyp2e1-null mice exhibited significantly higher antioxidant capacity with elevated heme oxygenase-1 and catalase activities compared to all other groups, while maintaining normal GSH levels with significantly less mitochondrial nitroxidative stress compared to the aged WT mice. Thus, CYP2E1 is important in causing aging-related kidney damage most likely through increasing nitroxidative stress and that CYP2E1 could be a potential target in preventing aging-related kidney diseases.

Glutamate contributes to alcohol hepatotoxicity by enhancing oxidative stress in mitochondria

Chronic alcohol intoxication is associated with increased oxidative stress. However, the mechanisms by which ethanol triggers an increase in the production of reactive oxygen species (ROS) and the role of mitochondria in the development of oxidative stress has been insufficiently studied. The biochemical and proteomic data obtained in the present work suggest that one of the main causes of an increase in ROS generation is enhanced oxidation of glutamate in response to long-term alcohol exposure. In the course of glutamate oxidation, liver mitochondria from alcoholic rats generated more superoxide anion and H₂O₂ than in the presence of other substrates and more than control organelles. In mitochondria from alcoholic rats, rates of H₂O₂ production and NAD reduction in the presence of glutamate were almost twice higher than in the control. The proteomic study revealed a higher content of glutamate dehydrogenase in liver mitochondria of rats subjected to chronic alcohol exposure. Simultaneously, the content of mitochondrial catalase decreased compared to control. Each of these factors stimulates the production of ROS in addition to ROS generated by the respiratory chain complex I. The results are consistent with the conclusion that glutamate contributes to alcohol hepatotoxicity by enhancing oxidative stress in mitochondria.

Polydatin alleviates alcohol-induced acute liver injury in mice: Relevance of matrix metalloproteinases (MMPs) and hepatic antioxidants

BACKGROUND

Alcohol, a most commonly consumed beverage, is the foremost cause of liver injury throughout the world. Polydatin, a stilbenoid glucoside, was known to possess antioxidant and anti-inflammatory properties and is being investigated for use in various disorders.

PURPOSE

The present study was intended at investigating the hepatoprotective efficacy of polydatin against acute-alcohol induced liver injury model in mice.

STUDY DESIGN

C57BL/6 mice were fed with five doses of 50% ethyl alcohol (10ml/kg body weight) to induce acute liver injury. Effect of polydatin against alcohol induced hepatic injury was investigated by giving 50 or 100mg/kg polydatin, orally, for 8 days.

METHODS

Serum markers of liver injury, morphology, histology and fibrosis of liver tissue, levels of enzymatic and non-enzymatic antioxidants and the mitochondrial respiratory enzyme activities in liver tissue were investigated. The activities and the protein expression of matrix metalloproteinases (MMP-2 and -9), the expression of NF-κB in the liver tissue were also studied.

RESULTS

Polydatin pre-treatment significantly alleviated the alcohol induced hepatic injury by reducing the serum liver injury markers, alanine aminotransferase (ALT) and aspartate aminotransferase (AST), attenuating oxidative stress and restoring antioxidant balance in the hepatic tissue. Simultaneously, polydatin pre-treatment also prevented alcohol induced mitochondrial damage and refurbished the matrix metalloproteinases levels of the hepatic tissue.

CONCLUSION

The findings of the present study suggest that polydatin may have a potential benefit in preventing alcohol-induced acute hepatic injury.

Diet high in fructose promotes liver steatosis and hepatocyte apoptosis in C57BL/6J female mice: Role of disturbed lipid homeostasis and increased oxidative stress

The effects of high (H)-fructose (FR) diet (D) (HFRD) on hepatic lipid homeostasis, oxidative stress, inflammation and hepatocyte apoptosis were investigated in 6-week old female C57BL/6J mice fed a regular chow (ContD) or HFRD (35% fructose-derived calories) for 3 weeks. HFRD-fed mice exhibited increased levels of hepatic steatosis with a significant elevation of serum levels of triglyceride, cholesterol and TNFα compared to ContD-fed mice (P<0.05). HFRD-fed mice exhibited ∼2.7- fold higher levels FAS along with significantly decreased protein levels of adiponection-R2 (∼30%), P-AMPK (∼60%), P-ACC (∼70%) and RXR-α (∼55%), suggesting decreased hepatic fat oxidation compared to controls. Interestingly, hepatic fatty acid uptake into hepatocytes and lipolysis were significantly increased in HFRD-fed mice, as shown by decreased CD36 and fatty acid transporter protein-2, and increased adipose triglyceride lipase, respectively (P<0.05). Increased hepatic levels of iNOS and GSSG/GSH suggest elevated oxidative stress with a higher number of macrophages in the adipose tissue in HFRD-fed mice (P<0.05). Significantly elevated rates of hepatocyte apoptosis (∼2.4-fold), as determined by TUNEL analysis with increased Bax/Bcl2 ratio and PARP-1 levels (∼2- and 1.5-fold, respectively), were observed in HFRD-fed mice. Thus, HFRD exposure increased hepatic steatosis accompanied by oxidative stress and inflammation, leading to hepatocyte apoptosis.

Prepregnancy maternal diabetes combined with obesity impairs placental mitochondrial function involving Nrf2/ARE pathway and detrimentally alters metabolism of offspring

Metabolic disorders usually increase the level of reactive oxygen species (ROS) and damage mitochondrial function. The placenta supplies nutrients and hormonal signals to the fetus for regulating fetal metabolism, and is also prone to injury by oxidants. The aim of this study was to determine the effect of pre-existing maternal type 2 diabetes mellitus (DM) combined with obesity on placental mitochondrial function and metabolism disorders of offspring. The study included 96 pregnant women. The women were put into the following groups: healthy women (control, n=24), women with DM (DM, n=24), women with obesity (OB, n=24) and women with both DM and obesity (DM+OB, n=24). The ROS level, mitochondrial content, and the mitochondrial respiratory complex activities of the placenta were measured in the four groups. The expression of nuclear factor erythroid 2-related factor 2 (Nrf2) and heme oxygenase-1 (HO-1) was detected by immunofluorescence staining and western blotting. In addition, serum levels of insulin, glucose, leptin, nonesterified fatty acid (NEFA), adiponectin and triglycerides of their offspring were also measured. Maternal DM combined with obesity markedly increased ROS level, reduced mitochondrial DNA (mtDNA) content and mitochondrial respiratory complex I, II-III activities in placenta compared to the placenta from the control group and the DM group. Maternal DM combined with obesity significantly decreased Nrf2 and HO-1 expression. Furthermore, maternal DM combined with obesity influenced the glucose and lipid metabolism in their offspring. In conclusion, women with both DM and obesity detrimentally alter placenta function in oxidative stress regulation, and the Nrf2/ARE (antioxidant responsive element) pathway is involved. This may increase metabolic disturbance susceptibility in their offspring.

Association between alcohol-induced erythrocyte membrane alterations and hemolysis in chronic alcoholics

The present study aimed to understand the association between erythrocyte membrane alterations and hemolysis in chronic alcoholics. Study was conducted on human male volunteers aged between 35-45 years with a drinking history of 8-10 years. Results showed that plasma marker enzymes AST, ALT, ALP and γGT were increased in alcoholic subjects. Plasma and erythrocyte membrane lipid peroxidation, erythrocyte lysate nitric oxide (NOx) levels were also increased significantly in alcoholics. Furthermore, erythrocyte membrane protein carbonyls, total cholesterol, phospholipid and cholesterol/phospholipid (C/P) ratio were increased in alcoholics. SDS-PAGE analysis of erythrocyte membrane proteins revealed that increased density of band 3, protein 4.2, 4.9, actin and glycophorins, whereas glyceraldehyde 3-phosphate dehydrogenase (GAPDH) and glycophorin A showed slight increase, however, decreased ankyrin with no change in spectrins (α and β) and protein 4.1 densities were observed in alcoholics. Moreover, alcoholics red blood cells showed altered morphology with decreased resistance to osmotic hemolysis. Increased hemolysis showed strong positive association with lipid peroxidation (r = 0.703, p<0.05), protein carbonyls (r = 0.754, p<0.05), lysate NOx (r = 0.654, p<0.05) and weak association with C/P ratio (r = 0.240, p<0.05). Bottom line, increased lipid and protein oxidation, altered membrane C/P ratio and membrane cytoskeletal protein profile might be responsible for the increased hemolysis in alcoholics.

Mitochondrial dysfunction and cell death in neurodegenerative diseases through nitroxidative stress

Mitochondria are important for providing cellular energy ATP through the oxidative phosphorylation pathway. They are also critical in regulating many cellular functions including the fatty acid oxidation, the metabolism of glutamate and urea, the anti-oxidant defense, and the apoptosis pathway. Mitochondria are an important source of reactive oxygen species leaked from the electron transport chain while they are susceptible to oxidative damage, leading to mitochondrial dysfunction and tissue injury. In fact, impaired mitochondrial function is commonly observed in many types of neurodegenerative diseases, including Alzheimer's disease, Parkinson's disease, Huntington's disease, alcoholic dementia, brain ischemia-reperfusion related injury, and others, although many of these neurological disorders have unique etiological factors. Mitochondrial dysfunction under many pathological conditions is likely to be promoted by increased nitroxidative stress, which can stimulate post-translational modifications (PTMs) of mitochondrial proteins and/or oxidative damage to mitochondrial DNA and lipids. Furthermore, recent studies have demonstrated that various antioxidants, including naturally occurring flavonoids and polyphenols as well as synthetic compounds, can block the formation of reactive oxygen and/or nitrogen species, and thus ultimately prevent the PTMs of many proteins with improved disease conditions. Therefore, the present review is aimed to describe the recent research developments in the molecular mechanisms for mitochondrial dysfunction and tissue injury in neurodegenerative diseases and discuss translational research opportunities.

Involvement of ATF3 in the negative regulation of iNOS expression and NO production in activated macrophages

Macrophage-associated nitric oxide (NO) production plays a crucial role in the pathogenesis of tissue damage. However, negative factors that regulate NO production remains poorly understood despite its significance of NO homeostasis. Here, we show that activating transcription factor 3 (ATF3), a transcriptional regulator of cellular stress responses, was strongly induced in activated macrophages and its depletion resulted in pronounced enhancement of inducible nitric oxide synthase (iNOS) gene expression and subsequently the induction of high levels of NO production. In response to lipopolysaccharide (LPS) and IFN-γ, ATF3 inhibited transcriptional activity of NF-κB by interacting with the N-terminal (1-200 amino acids) of p65 and was bound to the NF-κB promoter, leading to suppression of iNOS gene expression. In addition, inhibitory effects of ATF3 on iNOS and NO secretion were suppressed by inhibitor of casein kinase II (CK2) activity or its knockdown. Moreover, the levels of ATF3 were highly elevated in established cecal ligation and puncture or LPS-injected mice, a model of endotoxemia. ATF3 is also elevated in peritoneal macrophages. Collectively, our findings suggest that ATF3 regulates NO homeostasis by associating with NF-κB component, leading to the repression of its transcriptional activity upon inflammatory signals and points to its potential relevance for the control of cell injuries mediated by NO during macrophage activation.

Cytochrome P450-2E1 promotes aging-related hepatic steatosis, apoptosis and fibrosis through increased nitroxidative stress

The role of ethanol-inducible cytochrome P450-2E1 (CYP2E1) in promoting aging-dependent hepatic disease is unknown and thus was investigated in this study. Young (7 weeks) and aged female (16 months old) wild-type (WT) and Cyp2e1-null mice were used in this study to evaluate age-dependent changes in liver histology, steatosis, apoptosis, fibrosis and many nitroxidative stress parameters. Liver histology showed that aged WT mice exhibited markedly elevated hepatocyte vacuolation, ballooning degeneration, and inflammatory cell infiltration compared to all other groups. These changes were accompanied with significantly higher hepatic triglyceride and serum cholesterol in aged WT mice although serum ALT and insulin resistance were not significantly altered. Aged WT mice showed the highest rates of hepatocyte apoptosis and hepatic fibrosis. Further, the highest levels of hepatic hydrogen peroxide, lipid peroxidation, protein carbonylation, nitration, and oxidative DNA damage were observed in aged WT mice. These increases in the aged WT mice were accompanied by increased levels of mitochondrial nitroxidative stress and alteration of mitochondrial complex III and IV proteins in aged WT mice, although hepatic ATP levels seems to be unchanged. In contrast, the aging-related nitroxidative changes were very low in aged Cyp2e1-null mice. These results suggest that CYP2E1 is important in causing aging-dependent hepatic steatosis, apoptosis and fibrosis possibly through increasing nitroxidative stress and that CYP2E1 could be a potential target for translational research in preventing aging-related liver disease.

Mitochondrial dysfunction and tissue injury by alcohol, high fat, nonalcoholic substances and pathological conditions through post-translational protein modifications

Mitochondria are critically important in providing cellular energy ATP as well as their involvement in anti-oxidant defense, fat oxidation, intermediary metabolism and cell death processes. It is well-established that mitochondrial functions are suppressed when living cells or organisms are exposed to potentially toxic agents including alcohol, high fat diets, smoking and certain drugs or in many pathophysiological states through increased levels of oxidative/nitrative stress. Under elevated nitroxidative stress, cellular macromolecules proteins, DNA, and lipids can undergo different oxidative modifications, leading to disruption of their normal, sometimes critical, physiological functions. Recent reports also indicated that many mitochondrial proteins are modified via various post-translation modifications (PTMs) and primarily inactivated. Because of the recently-emerging information, in this review, we specifically focus on the mechanisms and roles of five major PTMs (namely oxidation, nitration, phosphorylation, acetylation, and adduct formation with lipid-peroxides, reactive metabolites, or advanced glycation end products) in experimental models of alcoholic and nonalcoholic fatty liver disease as well as acute hepatic injury caused by toxic compounds. We also highlight the role of the ethanol-inducible cytochrome P450-2E1 (CYP2E1) in some of these PTM changes. Finally, we discuss translational research opportunities with natural and/or synthetic anti-oxidants, which can prevent or delay the onset of mitochondrial dysfunction, fat accumulation and tissue injury.

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Hepatotoxic agents including alcohol and high fat elevate nitroxidative stress.

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Increased nitroxidative stress promotes post-translational protein modifications.

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Post-translational protein modifications of many proteins lead to their inactivation.

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Inactivation of mitochondrial proteins contributes to mitochondrial dysfunction.

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Mitochondrial dysfunction contributes to necrotic or apoptotic tissue injury.

Translational Implications of the Alcohol-Metabolizing Enzymes, Including Cytochrome P450-2E1, in Alcoholic and Nonalcoholic Liver Disease

Fat accumulation (hepatic steatosis) in alcoholic and nonalcoholic fatty liver disease is a potentially pathologic condition which can progress to steatohepatitis (inflammation), fibrosis, cirrhosis, and carcinogenesis. Many clinically used drugs or some alternative medicine compounds are also known to cause drug-induced liver injury, which can further lead to fulminant liver failure and acute deaths in extreme cases. During liver disease process, certain cytochromes P450 such as the ethanol-inducible cytochrome P450-2E1 (CYP2E1) and CYP4A isozymes can be induced and/or activated by alcohol and/or high-fat diets and pathophysiological conditions such as fasting, obesity, and diabetes. Activation of these P450 isozymes, involved in the metabolism of ethanol, fatty acids, and various drugs, can produce reactive oxygen/nitrogen species directly and/or indirectly, contributing to oxidative modifications of DNA/RNA, proteins and lipids. In addition, aldehyde dehydrogenases including the mitochondrial low Km aldehyde dehydrogenase-2 (ALDH2), responsible for the metabolism of acetaldehyde and lipid aldehydes, can be inactivated by various hepatotoxic agents. These highly reactive acetaldehyde and lipid peroxides, accumulated due to ALDH2 suppression, can interact with cellular macromolecules DNA/RNA, lipids, and proteins, leading to suppression of their normal function, contributing to DNA mutations, endoplasmic reticulum stress, mitochondrial dysfunction, steatosis, and cell death. In this chapter, we specifically review the roles of the alcohol-metabolizing enzymes including the alcohol dehydrogenase, ALDH2, CYP2E1, and other enzymes in promoting liver disease. We also discuss translational research opportunities with natural and/or synthetic antioxidants, which can prevent or delay the onset of inflammation and liver disease.

Dysfunctional mitochondrial bioenergetics and the pathogenesis of hepatic disorders

The liver is involved in a variety of critical biological functions including the homeostasis of glucose, fatty acids, amino acids, and the synthesis of proteins that are secreted in the blood. It is also at the forefront in the detoxification of noxious metabolites that would otherwise upset the functioning of the body. As such, this vital component of the mammalian system is exposed to a notable quantity of toxicants on a regular basis. It therefore comes as no surprise that there are over a hundred disparate hepatic disorders, encompassing such afflictions as fatty liver disease, hepatitis, and liver cancer. Most if not all of liver functions are dependent on energy, an ingredient that is primarily generated by the mitochondrion, the power house of all cells. This organelle is indispensable in providing adenosine triphosphate (ATP), a key effector of most biological processes. Dysfunctional mitochondria lead to a shortage in ATP, the leakage of deleterious reactive oxygen species (ROS), and the excessive storage of fats. Here we examine how incapacitated mitochondrial bioenergetics triggers the pathogenesis of various hepatic diseases. Exposure of liver cells to detrimental environmental hazards such as oxidative stress, metal toxicity, and various xenobiotics results in the inactivation of crucial mitochondrial enzymes and decreased ATP levels. The contribution of the latter to hepatic disorders and potential therapeutic cues to remedy these conditions are elaborated.

Nitric oxide and mitochondria in metabolic syndrome

Metabolic syndrome (MS) is a cluster of metabolic disorders that collectively increase the risk of cardiovascular disease. Nitric oxide (NO) plays a crucial role in the pathogeneses of MS components and is involved in different mitochondrial signaling pathways that control respiration and apoptosis. The present review summarizes the recent information regarding the interrelations of mitochondria and NO in MS. Changes in the activities of different NO synthase isoforms lead to the formation of metabolic disorders and therefore are highlighted here. Reduced endothelial NOS activity and NO bioavailability, as the main factors underlying the endothelial dysfunction that occurs in MS, are discussed in this review in relation to mitochondrial dysfunction. We also focus on potential therapeutic strategies involving NO signaling pathways that can be used to treat patients with metabolic disorders associated with mitochondrial dysfunction. The article may help researchers develop new approaches for the diagnosis, prevention and treatment of MS.

Functional roles of protein nitration in acute and chronic liver diseases

Nitric oxide, when combined with superoxide, produces peroxynitrite, which is known to be an important mediator for a number of diseases including various liver diseases. Peroxynitrite can modify tyrosine residue(s) of many proteins resulting in protein nitration, which may alter structure and function of each target protein. Various proteomics and immunological methods including mass spectrometry combined with both high pressure liquid chromatography and 2D PAGE have been employed to identify and characterize nitrated proteins from pathological tissue samples to determine their roles. However, these methods contain a few technical problems such as low efficiencies with the detection of a limited number of nitrated proteins and labor intensiveness. Therefore, a systematic approach to efficiently identify nitrated proteins and characterize their functional roles is likely to shed new insights into understanding of the mechanisms of hepatic disease pathophysiology and subsequent development of new therapeutics. The aims of this review are to briefly describe the mechanisms of hepatic diseases. In addition, we specifically describe a systematic approach to efficiently identify nitrated proteins to study their causal roles or functional consequences in promoting acute and chronic liver diseases including alcoholic and nonalcoholic fatty liver diseases. We finally discuss translational research applications by analyzing nitrated proteins in evaluating the efficacies of potentially beneficial agents to prevent or treat various diseases in the liver and other tissues.

Carbonyl stress in aging process: role of vitamins and phytochemicals as redox regulators

There is a growing scientific agreement that the cellular redox regulators such as antioxidants, particularly the natural polyphenolic forms, may help lower the incidence of some pathologies, including metabolic diseases like diabetes and diabesity, cardiovascular and neurodegenerative abnormalities, and certain cancers or even have anti-aging properties. The recent researches indicate that the degree of metabolic modulation and adaptation response of cells to reductants as well as oxidants establish their survival and homeostasis, which is linked with very critical balance in imbalances in cellular redox capacity and signaling, and that might be an answer the questions why some antioxidants or phytochemicals potentially could do more harm than good, or why some proteins lose their function by increase interactions with glyco- and lipo-oxidation mediates in the cells (carbonyl stress). Nonetheless, pursue of healthy aging has led the use of antioxidants as a means to disrupt age-associated physiological dysfunctions, dysregulated metabolic processes or prevention of many age-related diseases. Although it is still early to define their exact clinical benefits for treating age-related disease, a diet rich in polyphenolic or other forms of antioxidants does seem to offer hope in delaying the onset of age-related disorders. It is now clear that any deficiency in antioxidant vitamins, inadequate enzymatic antioxidant defenses can distinctive for many age-related disease, and protein carbonylation can used as an indicator of oxidative stress associated diseases and aging status. This review examines antioxidant compounds and plant polyphenols as redox regulators in health, disease and aging processes with hope that a better understanding of the many mechanisms involved with these distinct compounds, which may lead to better health and novel treatment approaches for age-related diseases.

Mitochondria-targeted heme oxygenase-1 induces oxidative stress and mitochondrial dysfunction in macrophages, kidney fibroblasts and in chronic alcohol hepatotoxicity

The inducible form of Heme Oxygenase-1 (HO-1), a major endoplasmic reticulum (ER) associated heme protein, is known to play important roles in protection against oxidative and chemical stress by degrading free heme released from degradation of heme proteins. In this study we show that induced expression of HO-1 by subjecting macrophage RAW-264.7 cells to chemical or physiological hypoxia resulted in significant translocation of HO-1 protein to mitochondria. Transient transfection of COS-7 cells with cloned cDNA also resulted in mitochondrial translocation of HO-1. Deletion of N-terminal ER targeting domain increased mitochondrial translocation under the transient transfection conditions. Mitochondrial localization of both intact HO-1 and N-terminal truncated HO-1 caused loss of heme aa-3 and cytochrome c oxidase (CcO) activity in COS-7 cells. The truncated protein, which localizes to mitochondria at higher levels, induced substantially steeper loss of CcO activity and reduced heme aa3 content. Furthermore, cells expressing mitochondria targeted HO-1 also induced higher ROS production. Consistent with dysfunctional state of mitochondria induced by HO-1, the mitochondrial recruitment of autophagy markers LC-3 and Drp-1 was also increased in these cells. Chronic ethanol feeding in rats also caused an increase in mitochondrial HO-1 and decrease in CcO activity. These results show that as opposed to the protective effect of the ER associated HO-1, mitochondria targeted HO-1 under normoxic conditions induces mitochondrial dysfunction.

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Under hypoxia, the inducible Heme Oxygenase-1 (HO-1) is localized in mitochondria.

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N-terminal truncated HO-1 is more efficiently translocated to mitochondria.

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Mitochondria targeted HO-1 induces oxidative stress and CcO dysfunction.

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Mitochondrial HO-1 content is increased in alcohol treated rat livers.