Effects of alcohol on hepatic mitochondrial function and DNA

Nobiletin protects against alcohol-induced mitochondrial dysfunction and liver injury by regulating the hepatic NRF1-TFAM signaling pathway

OBJECTIVES

Alcohol and its metabolites, such as acetaldehyde, induced hepatic mitochondrial dysfunction play a pathological role in the development of alcohol-related liver disease (ALD).

METHODS

In this study, we investigated the potential of nobiletin (NOB), a polymethoxylated flavone, to counter alcohol-induced mitochondrial dysfunction and liver injury.

RESULTS

Our findings demonstrate that NOB administration markedly attenuated alcohol-induced hepatic steatosis, endoplasmic reticulum stress, inflammation, and tissue damage in mice. NOB reversed hepatic mitochondrial dysfunction and oxidative stress in both alcohol-fed mice and acetaldehyde-treated hepatocytes. Mechanistically, NOB restored the reduction of hepatic mitochondrial transcription factor A (TFAM) at both mRNA and protein levels. Notably, the protective effects of NOB against acetaldehyde-induced mitochondrial dysfunction and cell death were abolished in hepatocytes lacking Tfam. Furthermore, NOB administration reinstated the levels of hepatocellular NRF1, a key transcriptional regulator of TFAM, which were decreased by alcohol and acetaldehyde exposure. Consistent with these findings, hepatocyte-specific overexpression of Nrf1 protected against alcohol-induced hepatic Tfam reduction, mitochondrial dysfunction, oxidative stress, and liver injury.

CONCLUSIONS

Our study elucidates the involvement of the NRF1-TFAM signaling pathway in the protective mechanism of NOB against chronic-plus-binge alcohol consumption-induced mitochondrial dysfunction and liver injury, suggesting NOB supplementation as a potential therapeutic strategy for ALD.

cGAS/STING signaling pathway-mediated microglial activation in the PFC underlies chronic ethanol exposure-induced anxiety-like behaviors in mice

Chronic ethanol consumption is a prevalent condition in contemporary society and exacerbates anxiety symptoms in healthy individuals. The activation of microglia, leading to neuroinflammatory responses, may serve as a significant precipitating factor; however, the precise molecular mechanisms underlying this phenomenon remain elusive. In this study, we initially confirmed that chronic ethanol exposure (CEE) induces anxiety-like behaviors in mice through open field test and elevated plus maze test. The cGAS/STING signaling pathway has been confirmed to exhibits a significant association with inflammatory signaling responses in both peripheral and central systems. Western blot analysis confirmed alterations in the cGAS/STING signaling pathway during CEE, including the upregulation of p-TBK1 and p-IRF3 proteins. Moreover, we observed microglial activation in the prefrontal cortex (PFC) of CEE mice, characterized by significant alterations in branching morphology and an increase in cell body size. Additionally, we observed that administration of CEE resulted in mitochondrial dysfunction within the PFC of mice, accompanied by a significant elevation in cytosolic mitochondrial DNA (mtDNA) levels. Furthermore, our findings revealed that the inhibition of STING by H-151 effectively alleviated anxiety-like behavior and suppressed microglial activation induced by CEE. Our study unveiled a significant association between anxiety-like behavior, microglial activation, inflammation, and mitochondria dysfunction during CEE.

The behavioral and physiological effects of high-fat diet and alcohol consumption: Sex differences in C57BL6/J mice

BACKGROUND AND OBJECTIVE

Animal studies can be a great tool to investigate sex differences in a variety of different ways, including behavioral and physiological responses to drug treatments and different "lifestyle variables" such as diets. Consumption of both high-fat diets and alcohol is known to affect anxiety behaviors and overall health. This project investigated how high-fat diet and alcohol access and its combination affected the behavior and physiology of male and female C57BL/6J mice.

METHOD

Mice were separated into three food groups: high-fat diet, 10% fat diet, and regular chow, and each group was paired with either water or 10% alcohol. Behavioral assays included diet and alcohol preference, light-dark box, open field, and feeding and drinking measurements. Physiological measures included glucose tolerance tests and measurement of brain-derived neurotrophic factor, insulin, and leptin levels.

RESULTS

Females and males differed in the open field, as male mice decreased activity, while females increased activity when consuming high-fat diet. While females consumed more ethanol than males, alcohol consumption was able to improve glucose tolerance and increase anxiety in both sexes. Lastly, females were more resistant to the physiological changes caused by high-fat diet than males, as females consuming high-fat diet exhibited decreased insulin secretion, less change to brain-derived neurotrophic factor levels, and better glucose tolerance than males consuming high-fat diet.

CONCLUSION

These results suggest that the response to high-fat diet and alcohol consumption is sex dependent and that males are more affected both behaviorally and physiologically by high-fat diet compared to females.

Circulating mitochondrial DNA content associated with the risk of liver cirrhosis: a nested case-control study

BACKGROUND AND AIMS

Accumulating evidence has indicated that variations of mitochondrial DNA (mtDNA) content may affect the susceptibility to hepatocellular carcinoma (HCC). However, no study has been conducted to evaluate the association of circulating mtDNA content and the risk of liver cirrhosis, a leading cause of HCC.

METHODS

We conducted a nested case-control study including 136 cirrhotic hepatitis B virus (HBV) cases and 136 frequency-matched non-cirrhotic HBV controls. We determined mtDNA content in serum DNA using quantitative real-time PCR and analyzed its association with cirrhosis risk.

RESULTS

We found that cirrhotic HBV patients had significantly lower levels of mtDNA content than non-cirrhotic HBV controls (P = 0.0184). Compared to patients with high mtDNA content, those with low mtDNA content had a 2.25-fold increased risk of cirrhosis [odds ratio (OR) 2.25, 95 % confidence interval (CI) 1.26-4.02]. This association exhibited a significant dose relationship as evidenced in both tertile and quartile analyses (P for trend = 0.0018 and 0.0008, respectively). Stratified analyses showed that the association was prominent in younger patients (P = 0.0122), males (P = 0.0069), never smokers (P = 0.0063), never drinkers (P = 0.0078), patients with a family history of HBV infection (P = 0.0062), and patients with low values of aspartate aminotransferase to platelet ratio index (APRI), a commonly used noninvasive marker for cirrhosis (P = 0.0109). Moreover, a joint effect was observed between low mtDNA content and high APRI values on cirrhosis risk (OR 24.07, 95 % CI 6.72-86.24).

CONCLUSIONS

Low circulating mtDNA content may confer an increased cirrhosis risk in HBV patients. Further prospective studies are warranted to validate these findings and explore the clinical significance.

Risk marker associations with venous thrombotic events: a cross-sectional analysis

OBJECTIVE

To examine the interrelations among, and risk marker associations for, superficial and deep venous events-superficial venous thrombosis (SVT), deep venous thrombosis (DVT) and pulmonary embolism (PE).

DESIGN

Cross-sectional analysis.

SETTING

San Diego, California, USA.

PARTICIPANTS

2404 men and women aged 40-79 years from four ethnic groups: non-Hispanic White, Hispanic, African-American and Asian. The study sample was drawn from current and former staff and employees of the University of California, San Diego and their spouses/significant others.

OUTCOME MEASURES

Superficial and deep venous events, specifically SVT, DVT, PE and combined deep venous events (DVE) comprising DVT and PE.

RESULTS

Significant correlates on multivariable analysis were, for SVT: female sex, ethnicity (African-American=protective), lower educational attainment, immobility and family history of varicose veins. For DVT and DVE, significant correlates included: heavy smoking, immobility and family history of DVEs (borderline for DVE). For PE, significant predictors included immobility and, in contrast to DVT, blood pressure (BP, systolic or diastolic). In women, oestrogen use duration for hormone replacement therapy, in all and among oestrogen users, predicted PE and DVE, respectively.

CONCLUSIONS

These findings fortify evidence for known risk correlates/predictors for venous disease, such as family history, hormone use and immobility. New risk associations are shown. Striking among these is an association of PE, but not DVT, to elevated BP: we conjecture PE may serve as cause rather than consequence. Future studies should evaluate the temporal direction of this association. Oxidative stress and cell energy compromise are proposed to explain and predict many risk factors, operating through cell-death mediated triggering of coagulation activation.

Alteration of the copy number and deletion of mitochondrial DNA in human hepatocellular carcinoma

Somatic mutations in mitochondrial DNA (mtDNA) have been detected in hepatocellular carcinoma (HCC). However, it remains unclear whether mtDNA copy number and mitochondrial biogenesis are altered in HCC. In this study, we found that mtDNA copy number and the content of mitochondrial respiratory proteins were reduced in HCCs as compared with the corresponding non-tumorous livers. MtDNA copy number was significantly reduced in female HCC but not in male HCC. Expression of the peroxisome proliferator-activated receptor γ coactivator-1 was significantly repressed in HCCs (P<0.005), while the expression of the mitochondrial single-strand DNA-binding protein was upregulated, indicating that the regulation of mitochondria biogenesis is disturbed in HCC. Moreover, 22% of HCCs carried a somatic mutation in the mtDNA D-loop region. The non-tumorous liver of the HCC patients with a long-term alcohol-drinking history contained reduced mtDNA copy number (P<0.05) and higher level of the 4977 bp-deleted mtDNA (P<0.05) as compared with non-alcohol patients. Our results suggest that reduced mtDNA copy number, impaired mitochondrial biogenesis and somatic mutations in mtDNA are important events during carcinogenesis of HCC, and the differential alterations in mtDNA of male and female HCC may contribute to the differences in the clinical manifestation between female and male HCC patients.

Pathogenesis and management of alcoholic hepatitis

Alcoholic hepatitis is a potentially life-threatening complication of alcoholic abuse, typically presenting with symptoms and signs of hepatitis in the presence of an alcohol use disorder. The definitive diagnosis requires liver biopsy, but this is not generally required. The pathogenesis is uncertain, but relevant factors include metabolism of alcohol to toxic products, oxidant stress, acetaldehyde adducts, the action of endotoxin on Kupffer cells, and impaired hepatic regeneration. Mild alcoholic hepatitis recovers with abstinence and the long-term prognosis is determined by the underlying disorder of alcohol use. Severe alcoholic hepatitis is recognized by a Maddrey discriminant function >32 and is associated with a short-term mortality rate of almost 50%. Primary therapy is abstinence from alcohol and supportive care. Corticosteroids have been shown to be beneficial in a subset of severely ill patients with concomitant hepatic encephalopathy, but their use remains controversial. Pentoxifylline has been shown in one study to improve short-term survival rates. Other pharmacological interventions, including colchicine, propylthiouracil, calcium channel antagonists, and insulin with glucagon infusions, have not been proven to be beneficial. Nutritional supplementation with available high-calorie, high-protein diets is beneficial, but does not improve mortality. Orthotopic liver transplantation is not indicated for patients presenting with alcoholic hepatitis who have been drinking until the time of admission, but may be considered in those who achieve stable abstinence if liver function fails to recover.

Impaired adaptive resynthesis and prolonged depletion of hepatic mitochondrial DNA after repeated alcohol binges in mice

BACKGROUND & AIMS

A single dose of alcohol causes transient hepatic mitochondrial DNA (mtDNA) depletion in mice followed by increased mtDNA synthesis and an overshoot of mtDNA levels. We determined the effect of repeated alcohol binges on hepatic mtDNA in mice.

METHODS

Ethanol (5 g/kg) was administered by gastric intubation daily for 4 days, and mtDNA levels, synthesis, and integrity were assessed by slot blot hybridization, in organello [3H]deoxythymidine triphosphate incorporation, and long polymerase chain reaction analysis, respectively.

RESULTS

mtDNA levels were decreased for 48 hours after the last dose, with no overshoot phenomenon later on. Two and 24 hours after the fourth dose, long polymerase chain reaction experiments showed DNA lesions that blocked the progress of the polymerases and in organello mtDNA synthesis was decreased, although DNA polymerase gamma activity was unchanged with synthetic templates. Mitochondria exhibited ultrastructural abnormalities, and respiration was impaired 2 and 24 hours after the fourth binge. Cytochrome P450 2E1, mitochondrial generation of peroxides, thiobarbituric acid reactants, and ethane exhalation were increased.

CONCLUSIONS

After repeated doses of ethanol, the accumulation of unrepaired mtDNA lesions (possibly involving lipid peroxidation-induced adducts) blocks the progress of polymerase gamma on mtDNA and prevents adaptive mtDNA resynthesis, causing prolonged hepatic mtDNA depletion.

A soluble NH(2)-terminally truncated catalytically active form of rat cytochrome P450 2E1 targeted to liver mitochondria(1)

The role of the NH(2)-terminus of cytochrome P450 2E1 (CYP2E1) in intracellular targeting was investigated. Two NH(2)-terminal CYP2E1 mutants, Delta(2-29)2E1, lacking the transmembrane domain, and N(++)2E1, having Ala2Lys and Val3Arg substitutions, were generated and expressed in the H2.35 mouse hepatoma cell line. In cells transfected with both constructs, a 40 kDa fragment of CYP2E1 (Delta2E1) was found to be localized to mitochondria as evidenced from immunofluorescence microscopy and subcellular fractionation studies. Delta2E1 was shown to be a soluble protein localized inside the mitochondria, displayed catalytic activity when reconstituted with adrenodoxin and adrenodoxin reductase, and was also present in mitochondria isolated from rat liver. It is concluded that in the absence of the hydrophobic NH(2)-terminal sequence, a putative mitochondrial import signal is exposed which targets CYP2E1 to this organelle where it is further processed.