How does your fat affect your liver when you drink?

Gowda SG, K. Shukla P, Gowda D, Nath LR, Chiba H, Rao R, Hui SP. Sex-Specific Effect of Ethanol on Colon Content Lipidome in a Mice Model Using Nontargeted LC/MS

Consumption of alcohol has widespread effects on the human body. The organs that are most significantly impacted are the liver and digestive system. When alcohol is consumed, it is absorbed in the intestines and processed by the liver. However, excessive alcohol use may affect gut epithelial integrity, microbiome composition, and lipid metabolism. Despite past studies investigating the effect of ethanol on hepatic lipid metabolism, the focus on colonic lipid metabolism has not been well explored. In this study, we investigated the sex-specific effect of ethanol on the colonic content lipidome in a mouse model using nontargeted liquid chromatography-mass spectrometry. Comprehensive lipidome analysis of colonic flush samples was performed using ethanol-fed (EF) and pair-fed (PF) mice of each sex. Partial least-squares discriminant analysis revealed that ethanol altered colonic lipid composition largely in male mice compared with female mice. A significant increase in free fatty acids, ceramides, and hexosylceramides and decreased phosphatidylglycerols (PG) was observed in the EF group compared to the PF group in male mice. Phosphatidylethanolamine (PE) levels were increased significantly in the EF group of both sexes compared to the PF group. The volcanic plot shows that PG (O-15:1/15:0) and PE (O-18:2/15:0) are common markers that are increased in both sexes of the EF group. In addition, decreased fatty acid esters of hydroxy fatty acids (FAHFA) were observed specifically in the EF group of female mice. Overall, a significant variation in the mice colonic content lipidome between the EF and PF groups was observed. Target pathways, such as sphingolipid metabolism in males, FAHFA in females, and PE metabolism in both sexes, were suggested. This study provides new insight into the sex-dependent lipid change associated with alcohol-induced gut-microbiota dysfunction and its potential health impacts.

Adipose lipolysis is important for ethanol to induce fatty liver in the National Institute on Alcohol Abuse and Alcoholism murine model of chronic and binge ethanol feeding

BACKGROUND AND AIMS

Alcohol-associated liver disease (ALD) pathologies include steatosis, inflammation, and injury, which may progress to fibrosis, cirrhosis, and cancer. The liver receives ~60% of fatty acids from adipose tissue triglyceride hydrolysis, but the role of this lipolytic pathway in ALD development has not been directly examined in any genetic animal models with selective inactivation of adipose lipolysis.

APPROACH AND RESULTS

Using adipose-specific comparative gene identification-58 (CGI-58) knockout (FAT-KO) mice, a model of impaired adipose lipolysis, we show that mice deficient in adipose lipolysis are almost completely protected against ethanol-induced hepatic steatosis and lipid peroxidation when subjected to the National Institute on Alcohol Abuse and Alcoholism chronic and binge ethanol feeding model. This is unlikely due to reduced lipid synthesis because this regimen of ethanol feeding down-regulated hepatic expression of lipogenic genes similarly in both genotypes. In the pair-fed group, FAT-KO relative to control mice displayed increased hepatocyte injury, neutrophil infiltration, and activation of the transcription factor signal transducer and activator of transcription 3 (STAT3) in the liver; and none of these were exacerbated by ethanol feeding. Activation of STAT3 is associated with a marked increase in hepatic leptin receptor mRNA expression and adipose inflammatory cell infiltration.

CONCLUSIONS

Our findings establish a critical role of adipose lipolysis in driving hepatic steatosis and oxidative stress during ALD development.

Enhanced Ca2+-channeling complex formation at the ER-mitochondria interface underlies the pathogenesis of alcohol-associated liver disease

Ca2+ overload-induced mitochondrial dysfunction is considered as a major contributing factor in the pathogenesis of alcohol-associated liver disease (ALD). However, the initiating factors that drive mitochondrial Ca2+ accumulation in ALD remain elusive. Here, we demonstrate that an aberrant increase in hepatic GRP75-mediated mitochondria-associated ER membrane (MAM) Ca2+-channeling (MCC) complex formation promotes mitochondrial dysfunction in vitro and in male mouse model of ALD. Unbiased transcriptomic analysis reveals PDK4 as a prominently inducible MAM kinase in ALD. Analysis of human ALD cohorts further corroborate these findings. Additional mass spectrometry analysis unveils GRP75 as a downstream phosphorylation target of PDK4. Conversely, non-phosphorylatable GRP75 mutation or genetic ablation of PDK4 prevents alcohol-induced MCC complex formation and subsequent mitochondrial Ca2+ accumulation and dysfunction. Finally, ectopic induction of MAM formation reverses the protective effect of PDK4 deficiency in alcohol-induced liver injury. Together, our study defines a mediatory role of PDK4 in promoting mitochondrial dysfunction in ALD.

Crosstalk between gut microbiota and host lipid metabolism in a mouse model of alcoholic liver injury by chronic baijiu or ethanol feeding

A growing body of evidence highlights the important role of gut microbiota and host metabolism, particularly for lipid metabolism, in the development and progression of alcoholic liver disease (ALD). However, the effects of fermented alcoholic beverages on gut microbiota and host lipid metabolism remain under-investigated. Moreover, the crosstalk between gut microbiota and host lipid metabolism is still unclear in experimental ALD. Baijiu is a traditional Chinese alcoholic beverage. It contains large amounts of small molecule bioactive compounds in addition to a significant amount of ethanol (EtOH). In this study, we showed that baijiu caused lower degrees of liver injury than pure EtOH as revealed by phenotypic, biochemical and histologic analyses. Furthermore, baijiu and EtOH gavage resulted in different gut microbiota structures. Specifically, the baijiu group had a significantly higher abundance of Ruminococcus, Oscillospira, Mucispirillum, Bilophila, Parabacteroides and Odoribacter and a lower abundance of Helicobacter and Prevotella than that of the EtOH group. Using a targeted metabolomics approach, we also observed a greater than 19% increase of total hepatic free fatty acids (FFAs) after baijiu feeding and a 33% increase of hepatic FFAs after EtOH feeding. Baijiu feeding significantly increased total hepatic mono-unsaturated FAs (MUFAs). In contrast, polyunsaturated fatty acids (PUFAs), MUFAs and saturated FAs were significantly increased by EtOH feeding. Finally, Spearman's rank correlation showed that the increased levels of FFAs (mainly C20 and C22 unsaturated FAs) significantly correlated with key different gut microbiota, including a positive correlation with Desulfovibrio, Maihella, Helicobacter, Acholeplasma, Parasutterella, Prevotella, AF12 and Alistipes, and a negative correlation with Dorea, Olsenella, Adlercreutzia and Akkermansia. Our results suggest that compounds in baijiu attenuated the development of ALD and thus provided supporting evidence that the host-gut microbiota metabolic interactions play an important role in the development of ALD.

Bile Acid-Mediated Activation of Brown Fat Protects From Alcohol-Induced Steatosis and Liver Injury in Mice

BACKGROUND & AIMS

Alcohol-associated liver disease (AALD) is one of the most common causes of liver injury and failure. Limited knowledge of the mechanisms underlying AALD impedes the development of efficacious therapies. Bile acid (BA) signaling was shown to participate in the progression of AALD. However, the mechanisms remain poorly understood.

METHODS

C57BL/6J wild-type (WT), Takeda G-protein-coupled bile acid receptor 5 (TGR5) knockout (KO) and brown adipose tissue (BAT)-specific TGR5 knockdown mice were subjected to ethanol feeding-induced AALD. Liver samples from alcoholic hepatitis patients were used to examine the BA circulation signaling. Human Embryonic Kidney Cells 293 were used for the TGR5 reporter assay. 23(S)-methyl-lithocholic acid was used as a molecular tool to confirm the regulatory functions of BAT in the AALD mouse model.

RESULTS

Ethanol feeding increased the expression of the thermogenesis genes downstream of TGR5 in BAT of WT, but not TGR5 KO, mice. TGR5 deficiency significantly blocked BAT activity and energy expenditure in mice after ethanol feeding. Alcohol increased serum BA levels in mice and human beings through altering BA transportation, and the altered BAs activated TGR5 signaling to regulate metabolism. Compared with ethanol-fed WT mice, ethanol-fed TGR5 KO mice showed less free fatty acid (FFA) β-oxidation in BAT, leading to higher levels of FFA in the circulation, increased liver uptake of FFAs, and exacerbated AALD. BAT-specific TGR5 knockdown mice showed similar results with TGR5 KO mice in AALD. Agonist treatment significantly activated TGR5 signaling in BAT, increased thermogenesis, reduced serum FFA level, and ameliorated hepatic steatosis and injury in AALD mice, while these effects were lost in TGR5 KO mice.

CONCLUSIONS

BA signaling plays a protective role in AALD by enhancing BAT thermogenesis. Targeting TGR5 in BAT may be a promising approach for the treatment of AALD.

Obesity and binge alcohol intake are deadly combination to induce steatohepatitis: A model of high-fat diet and binge ethanol intake

Obesity and binge drinking often coexist and work synergistically to promote steatohepatitis; however, the underlying mechanisms remain obscure. In this mini-review, we briefly summarize clinical evidence of the synergistical effect of obesity and heavy drinking on steatohepatitis and discuss the underlying mechanisms obtained from the study of several mouse models. High-fat diet (HFD) feeding and binge ethanol synergistically induced steatohepatitis and fibrosis in mice with significant intrahepatic neutrophil infiltration; such HFD-plus-ethanol treatment markedly up-regulated the hepatic expression of many chemokines with the highest fold (approximately 30-fold) induction of chemokine (C-X-C motif) ligand 1 (Cxcl1), which contributes to hepatic neutrophil infiltration and liver injury. Furthermore, HFD feeding activated peroxisome proliferator-activated receptor gamma that subsequently inhibited CXCL1 upregulation in hepatocytes, thereby forming a negative feedback loop to prevent neutrophil overaction; whereas binge ethanol blocked this loop and then exacerbated CXCL1 elevation, neutrophil infiltration, and liver injury. Interestingly, inflamed mouse hepatocytes attracted neutrophils less effectively than inflamed human hepatocytes due to the lower induction of CXCL1 and the lack of the interleukin (IL)-8 gene in the mouse genome, which may be one of the reasons for difficulty in development of mouse models of alcoholic steatohepatitis and nonalcoholic steatohepatitis (NASH). Hepatic overexpression of Cxcl1 and/or IL-8 promoted steatosis-to-NASH progression in HFD-fed mice by inducing neutrophil infiltration, oxidative stress, hepatocyte death, fibrosis, and p38 mitogen-activated protein kinase activation. Collectively, obesity and binge drinking synergistically promote steatohepatitis via the induction of CXCL1 and subsequent hepatic neutrophil infiltration.