Moderate consumption of fermented alcoholic beverages diminishes diet-induced non-alcoholic fatty liver disease through mechanisms involving hepatic adiponectin signaling in mice

Concomitant western diet and chronic-binge alcohol dysregulate hepatic metabolism

BACKGROUND AND AIMS

There is significant overlap between non-alcoholic fatty liver disease (NAFLD) and alcohol-associated liver disease (ALD) with regards to risk factors and disease progression. However, the mechanism by which fatty liver disease arises from concomitant obesity and overconsumption of alcohol (syndrome of metabolic and alcohol-associated fatty liver disease; SMAFLD), is not fully understood.

METHODS

Male C57BL6/J mice were fed chow diet (Chow) or high-fructose, high-fat, high-cholesterol diet (FFC) for 4 weeks, then administered either saline or ethanol (EtOH, 5% in drinking water) for another 12 weeks. The EtOH treatment also consisted of a weekly 2.5 g EtOH/kg body weight gavage. Markers for lipid regulation, oxidative stress, inflammation, and fibrosis were measured by RT-qPCR, RNA-seq, Western blot, and metabolomics.

RESULTS

Combined FFC-EtOH induced more body weight gain, glucose intolerance, steatosis, and hepatomegaly compared to Chow, EtOH, or FFC. Glucose intolerance by FFC-EtOH was associated with decreased hepatic protein kinase B (AKT) protein expression and increased gluconeogenic gene expression. FFC-EtOH increased hepatic triglyceride and ceramide levels, plasma leptin levels, hepatic Perilipin 2 protein expression, and decreased lipolytic gene expression. FFC and FFC-EtOH also increased AMP-activated protein kinase (AMPK) activation. Finally, FFC-EtOH enriched the hepatic transcriptome for genes involved in immune response and lipid metabolism.

CONCLUSIONS

In our model of early SMAFLD, we observed that the combination of an obesogenic diet and alcohol caused more weight gain, promoted glucose intolerance, and contributed to steatosis by dysregulating leptin/AMPK signaling. Our model demonstrates that the combination of an obesogenic diet with a chronic-binge pattern alcohol intake is worse than either insult alone.

Transcriptional and Epigenetic Regulation of Monocyte and Macrophage Dysfunction by Chronic Alcohol Consumption

Drinking alcohol, even in moderation, can affect the immune system. Studies have shown disproportionate effects of alcohol on circulating and tissue-resident myeloid cells (granulocytes, monocytes, macrophages, dendritic cells). These cells orchestrate the body's first line of defense against microbial challenges as well as maintain tissue homeostasis and repair. Alcohol's effects on these cells are dependent on exposure pattern, with acute drinking dampening but chronic drinking enhancing production of inflammatory mediators. Although chronic drinking is associated with heightened systemic inflammation, studies on tissue resident macrophage populations in several organs including the spleen, liver, brain, and lung have also shown compromised functional and metabolic capacities of these cells. Many of these effects are thought to be mediated by oxidative stress caused by alcohol and its metabolites which can directly impact the cellular epigenetic landscapes. In addition, since myeloid cells are relatively short-lived in circulation and are under constant repopulation from the bone marrow compartment, alcohol's effects on bone marrow progenitors and hematopoiesis are important for understanding the impact of alcohol systemically on these myeloid populations. Alcohol-induced disruption of progenitor, circulating, and tissue resident myeloid populations contribute to the increased susceptibility of patients with alcohol use disorders to viral and bacterial infections. In this review, we provide an overview of the impact of chronic alcohol consumption on the function of monocytes and macrophages in host defense, tissue repair and inflammation. We then summarize our current understanding of the mechanisms underlying alcohol-induced disruption and examine changes in transcriptome and epigenome of monocytes and mcrophages. Overall, chronic alcohol consumption leads to hyper-inflammation concomitant with decreased microbial and wound healing responses by monocytes/macrophages due to a rewiring of the epigentic and transcriptional landscape. However, in advanced alcoholic liver disease, myeloid cells become immunosuppressed as a response to the surrounding hyper-inflammatory milieu. Therefore, the effect of chronic alcohol on the inflammatory response depends on disease state and the immune cell population.

Distinctive gut microbial dysbiosis between chronic alcoholic fatty liver disease and metabolic-associated fatty liver disease in mice

The gut microbiota, which may affect normal physiological and biochemical functions, has an important role in the development of human liver diseases. The aim of the present study was to investigate differences in the gut microbiota between chronic alcoholic fatty liver disease (AFLD) and metabolic-associated fatty liver disease (MAFLD). AFLD was induced by chronic alcohol administration and MAFLD was induced by a Western-style diet in C57BL/6 mice. After 8 weeks, the levels of plasma alanine aminotransferase (ALT), aspartate aminotransferase (AST), triglyceride (TG), total cholesterol (TC), lipopolysaccharide (LPS), tumor necrosis factor (TNF)-α, interleukin (IL)-6, IL-1β and IL-10 were assessed and H&E staining of mouse liver tissue was performed. High-throughput sequencing of 16S ribosomal DNA from the intestinal contents was used to analyze the different effects of AFLD and MAFLD on the gut microbiota. Differences in the gut microbiota composition were assessed by the t-test. The results revealed increases in LPS, ALT, AST, TG, IL-1β and TNF-α in the AFLD group. Compared with those in the MAFLD control group, the MAFLD group exhibited increased plasma ALT, TG, TC, IL-6, IL-1β and TNF-α levels and decreased plasma IL-10 levels. In addition, the α- and β-diversities revealed that the AFLD and MAFLD groups exhibited obvious changes in the gut structure (with an increase in abundance in the AFLD group and a decrease in abundance in the MAFLD group). In comparison to the AFLD control group, Enterococcaceae were the most abundant bacteria at the family level and Enterococcus and Streptococcus were the most abundant bacteria at the genus level in the AFLD group. However, in the MAFLD group, Lachnospiraceae was the most abundant at the family level, with increases in Erysipelatoclostridium, Gordonibacter and Streptococcus at the genus level and a decrease in the genus Bifidobacterium. In conclusion, the present study confirmed that the AFLD and MAFLD groups harbored differences in the gut microbiota. The marked differences in the gut microbiota at the family and genus levels may contribute to the development process of FLD.

Experimental models of metabolic and alcoholic fatty liver disease

Non-alcoholic fatty liver disease (NAFLD) is a multi-systemic disease that is considered the hepatic manifestation of metabolic syndrome (MetS). Because alcohol consumption in NAFLD patients is common, there is a significant overlap in the pathogenesis of NAFLD and alcoholic liver disease (ALD). Indeed, MetS also significantly contributes to liver injury in ALD patients. This “syndrome of metabolic and alcoholic steatohepatitis” (SMASH) is thus expected to be a more prevalent presentation in liver patients, as the obesity epidemic continues. Several pre-clinical experimental models that couple alcohol consumption with NAFLD-inducing diet or genetic obesity have been developed to better understand the pathogenic mechanisms of SMASH. These models indicate that concomitant MetS and alcohol contribute to lipid dysregulation, oxidative stress, and the induction of innate immune response. There are significant limitations in the applicability of these models to human disease, such as the ability to induce advanced liver injury or replicate patterns in human food/alcohol consumption. Thus, there remains a need to develop models that accurately replicate patterns of obesogenic diet and alcohol consumption in SMASH patients.

Oxidative Stress Parameters in the Liver of Growing Male Rats Receiving Various Alcoholic Beverages

Typical alcohol consumption begins in the adolescence period, increasing the risk of alcoholic liver disease (ALD) in adolescents and young adults, and while the pathophysiology of ALD is still not completely understood, it is believed that oxidative stress may be the major contributor that initiates and promotes the progression of liver damage. The aim of the present study was to assess the influence of alcohol consumption on the markers of oxidative stress and liver inflammation in the animal model of prolonged alcohol consumption in adolescents using various alcoholic beverages. In a homogenic group of 24 male Wistar rats (4 groups—6 animals per group), since 30th day of life, in order to mimic the alcohol consumption since adolescence, animals received (1) no alcoholic beverage (control group), (2) ethanol solution, (3) red wine, or (4) beer (experimental groups) for 6 weeks. Afterwards, the activities of alcohol dehydrogenase (ADH), alanine aminotransferase (ALT), and aspartate aminotransferase (AST), as well as levels of cytochrome P450-2E1 (CYP2E1), thiobarbituric acid-reactive substances (TBARS), protein carbonyl groups, tumor necrosis factor-α (TNF-α), and interleukine-10 (IL-10) were measured in liver homogenates. The difference between studied groups was observed for CYP2E1 and protein carbonyl groups levels (increased levels for animals receiving beer compared with control group), as well as for ALT activity (decreased activity for animals receiving beer compared with other experimental groups) (p < 0.05). The results suggested that some components of beer, other than ethanol, are responsible for its influence on the markers of oxidative stress and liver inflammation observed in the animal model of prolonged alcohol consumption in adolescents. Taking this into account, beer consumption in adolescents, which is a serious public health issue, should be assessed in further studies to broaden the knowledge of the progression of liver damage caused by alcohol consumption in this group.