Dietary fructose augments ethanol-induced liver pathology

The interplay of Western diet and binge drinking on the onset, progression, and outlook of liver disease

Non-alcoholic fatty liver disease and alcoholic liver disease, the two most prevalent liver diseases worldwide, share a common pathology but have largely been considered disparate diseases. Liver diseases are widely underestimated, but their prevalence is increasing worldwide. The Western diet (high-fat, high-sugar) and binge drinking (rapid consumption of alcohol in a short period of time) are two highly prevalent features of standard life in the United States, and both are linked to the development and progression of liver disease. Yet, few studies have been conducted to elucidate their potential interactions. Data shows binge drinking is on the rise in several age groups, and poor dietary trends continue to be prevalent. This review serves to summarize the sparse findings on the hepatic consequences of the combination of binge drinking and consuming a Western diet, while also drawing conclusions on potential future impacts. The data suggest the potential for a looming liver disease epidemic, indicating that more research on its progression as well as its prevention is needed on this critical topic.

Elevated Fructose and Uric Acid Through Aldose Reductase Contribute to Experimental and Human Alcoholic Liver Disease

BACKGROUND AND AIMS

Alcohol-associated liver disease (ALD) is a common chronic liver disease worldwide with high morbidity and mortality, and no Food and Drug Administration-approved therapies. Fructose (dietary or endogenous), its metabolite uric acid, and aldose reductase (AR, the only endogenous enzyme that produces fructose) are strongly associated with the development of nonalcoholic fatty liver disease. However, the role of AR or its metabolites in ALD remains understudied and was examined using human specimens, cultured cells, and mouse model systems.

APPROACH AND RESULTS

We demonstrated in liver specimens from patients with alcoholic hepatitis, the AR up-regulation and elevated AR metabolites (sorbitol, fructose, and uric acid), which correlated significantly with (1) increased lipid peroxidation byproducts and endoplasmic reticulum (ER) stress, (2) decreased protective ER chaperones, and (3) greater cell death and liver injury. Furthermore, we established a causal role for AR in ALD by showing that the genetic deficiency of AR (knockout mice) prevented alcohol-induced increase in harmful AR metabolites, toxic aldehydes, steatosis, ER stress, apoptosis, and liver injury. Finally, we demonstrated the therapeutic potential of pharmacological AR inhibition against alcohol-induced hepatic injury in experimental ALD.

CONCLUSIONS

Our data demonstrate that hepatic AR up-regulation, and consequent elevation in fructose, sorbitol and/or uric acid, are important factors contributing to alcohol-induced steatosis, ER stress, apoptosis, and liver injury in both experimental and human ALD. Our study provides a strong rationale to evaluate AR as a potential therapeutic target and to test AR inhibitors to ameliorate alcohol-induced liver injury.

Rosmarinic acid alleviates ethanol-induced lipid accumulation by repressing fatty acid biosynthesis

Recent studies have demonstrated that rosmarinic acid is a valuable natural product for treatment of alcoholic liver disease. However, the mechanisms whereby rosmarinic acid improves alcoholic liver disease remain unclear. Here we performed experiments using a non-transformed mouse hepatocyte cell line (AML12). Oil-red O staining demonstrated that rosmarinic acid reduced ethanol-induced lipid accumulation. It was shown that rosmarinic acid prevented ethanol-induced elevation of the malondialdehyde level. We also found that rosmarinic acid inhibited ethanol-induced mRNA expression of tumor necrosis factor-α and interleukin 6. Metabolomics analysis revealed that rosmarinic acid ameliorated ethanol-induced fatty acid biosynthesis in the cytoplasm. In addition, palmitic acid was a candidate biomarker in cells exposed to ethanol or ethanol plus rosmarinic acid. Rosmarinic acid prevented the ethanol-induced increase in sorbitol that is a component of the polyol pathway. Moreover, we confirmed that rosmarinic acid attenuated ethanol-induced mRNA expression of fatty acid synthase, probably by modulating the AMPK/SREBP-1c pathway. Furthermore, rosmarinic acid prevented the ethanol-induced decrease in eight metabolites that are involved in mitochondrial metabolism, including glycine and succinic acid which are the components of carnitine synthesis. These results provide a crucial insight into the molecular mechanism of rosmarinic acid in alleviating ethanol-induced injury.

The Role of Autophagy in Liver Epithelial Cells and Its Impact on Systemic Homeostasis

Autophagy plays a role in several physiological and pathological processes as it controls the turnover rate of cellular components and influences cellular homeostasis. The liver plays a central role in controlling organisms’ metabolism, regulating glucose storage, plasma proteins and bile synthesis and the removal of toxic substances. Liver functions are particularly sensitive to autophagy modulation. In this review we summarize studies investigating how autophagy influences the hepatic metabolism, focusing on fat accumulation and lipids turnover. We also describe how autophagy affects bile production and the scavenger function within the complex homeostasis of the liver. We underline the role of hepatic autophagy in counteracting the metabolic syndrome and the associated cardiovascular risk. Finally, we highlight recent reports demonstrating how the autophagy occurring within the liver may affect skeletal muscle homeostasis as well as different extrahepatic solid tumors, such as melanoma.

Aldose reductase inhibitor protects mice from alcoholic steatosis by repressing saturated fatty acid biosynthesis

Alcoholic liver injury results in morbidity and mortality worldwide, but there are currently no effective and safe therapeutics. Previously we demonstrated that aldose reductase (AR) inhibitor ameliorated alcoholic hepatic steatosis. To clarify the mechanism whereby AR inhibitor improves alcoholic hepatic steatosis, herein we investigated the effect of AR inhibitor on hepatic metabolism in mice fed a Lieber-DeCarli liquid diet with 5% ethanol. Nontargeted metabolomics showed carbohydrates and lipids were characteristic categories in ethanol diet-fed mice with or without AR inhibitor treatment, whereas AR inhibitor mainly affected carbohydrates and peptides. Ethanol-induced galactose metabolism and fatty acid biosynthesis are important for the induction of hepatic steatosis, while AR inhibitor impaired galactose metabolism without perturbing fatty acid biosynthesis. In parallel with successful treatment of steatosis, AR inhibitor suppressed ethanol-activated galactose metabolism and saturated fatty acid biosynthesis. Sorbitol in galactose metabolism and stearic acid in saturated fatty acid biosynthesis were potential biomarkers responsible for ethanol or ethanol plus AR inhibitor treatment. In vitro analysis confirmed that exogenous addition of sorbitol augmented ethanol-induced steatosis and stearic acid. These findings not only reveal metabolic patterns associated with disease and treatment, but also shed light on functional biomarkers contribute to AR inhibition therapy.