Elucidating dietary fructose and alcohol interactions during liver cancer development

Project Summary/Abstract Hepatocellular carcinoma (HCC) has been alarmingly increased, in part due to rapid increases in fatty liver disease. Owing to the lack of early diagnostic markers, HCC's 5-year survival is only 10%. Alcoholism is a well-known HCC risk factor, but the mechanism of how alcohol induces HCC is still unclear. Another HCC risk factor is consumption of dietary fructose, especially in liquid form (soft drinks), which has increased 100-fold over the past two centuries. Based on our preliminary data, we hypothesize that fructose alters hepatic alcohol metabolism via induction of acetyl-CoA synthetase 2 (ACSS2), which enhances the hepatic usage of alcohol carbons to generate carcinogenic metabolites and thereby creates a pro-tumorigenic environment. When alcohol reaches the liver, it is converted to acetate and mostly released into circulation. However, when ACSS2 is activated, flux is shifted from acetate release to acetate catabolism, resulting in excessive production of acetyl-CoA, a high-energy- charged, reactive metabolite. This alteration can initiate and support HCC in many ways, including carcinogenic metabolite production. Indeed, ACSS overexpression and increased acetate usage are commonly observed in cancers including HCC. We recently found that mice exposed to fructose showed strongly induced hepatic ACSS2 activity and acetate usage. Thus, fructose drinking will shift the metabolic fate of alcohol from release as acetate to usage of acetate within the liver. Fructose drinking also induces gut leakiness and alters microbiota metabolism. The resulting toxic microbiota metabolites cause chronic hepatic inflammation, which is a pro-tumorigenic microenvironment. We will test these hypotheses by systematically defining the impact of fructose-elicited ACSS2 induction and microbiota changes on liver alcohol metabolic flux. In Aim 1, we will determine whether and how fructose and alcohol synergistically increase HCC risk. Using in vivo stable isotope tracing of 13C- ethanol and hepatic-portal comparative metabolomics in mice, we will quantitatively define progressive changes of hepatic alcohol metabolism during HCC initiation and progression. This will build a comprehensive catalog of HCC-associated, alcohol-derived metabolites. We will then choose the top candidate metabolites and test whether these metabolites can trigger HCC. In Aim 2, we will test our hypothesis that fructose-induced hepatic ACSS2 activity and/or colonic microbiota changes enhance carcinogenic metabolite production in the liver, thereby triggering HCC. To this end, we will use our newly generated liver-specific ACSS2 knockdown mice and antibiotics treatment. These studies will provide molecular evidence for a clinically relevant question about how the two best-known dietary risk factors, alcohol and fructose, synergistically initiate and advance HCC. Our study's success will have direct impacts on public dietary guidelines and provide mechanistic insights into alcohol-induced HCC.