👤 Giusi Marrone

In non-alcoholic steatohepatitis (NASH), the function of urea cycle enzymes (UCEs) may be affected, resulting in hyperammonemia and the risk of disease progression. We aimed to determine whether the expression and function of UCEs are altered in an animal model of NASH and in patients with non-alcoholic fatty liver disease (NAFLD), and whether this process is reversible. Rats were first fed a high-fat, high-cholesterol diet for 10 months to induce NASH, before being switched onto a normal chow diet to recover. In humans, we obtained liver biopsies from 20 patients with steatosis and 15 with NASH. Primary rat hepatocytes were isolated and cultured with free fatty acids. We measured the gene and protein expression of ornithine transcarbamylase (OTC) and carbamoylphosphate synthetase (CPS1), as well as OTC activity, and ammonia concentrations. Moreover, we assessed the promoter methylation status of OTC and CPS1 in rats, humans and steatotic hepatocytes. In NASH animals, gene and protein expression of OTC and CPS1, and the activity of OTC, were reversibly reduced. Hypermethylation of Otc promoter genes was also observed. Additionally, in patients with NAFLD, OTC enzyme concentration and activity were reduced and ammonia concentrations were increased, which was further exacerbated in those with NASH. Furthermore, OTC and CPS1 promoter regions were hypermethylated. In primary hepatocytes, induction of steatosis was associated with Otc promoter hypermethylation, a reduction in the gene expression of Otc and Cps1, and an increase in ammonia concentration in the supernatant. NASH is associated with a reduction in the gene and protein expression, and activity, of UCEs. This results in hyperammonemia, possibly through hypermethylation of UCE genes and impairment of urea synthesis. Our investigations are the first to describe a link between NASH, the function of UCEs, and hyperammonemia, providing a novel therapeutic target. In patients with fatty liver disease, the enzymes that convert nitrogen waste into urea may be affected, leading to the accumulation of ammonia, which is toxic. This accumulation of ammonia can lead to scar tissue development, increasing the risk of disease progression. In this study, we show that fat accumulation in the liver produces a reversible reduction in the function of the enzymes that are involved in detoxification of ammonia. These data provide potential new targets for the treatment of fatty liver disease. Show less

The patatin-like phospholipase domain-containing 3 gene (PNPLA3) and the apolipoprotein C3 gene (APOC3) have been studied in relation to liver steatosis and liver disease outcome. The aim of this study was to evaluate the influence of PNPLA3 p.I148M and APOC3 rs2854116 and rs2854117 polymorphisms on the clinical and histological presentation of chronic hepatitis C in an Italian population and their relationship with viral and anthropometric parameters. Patients with hepatitis C (n = 166) entered the study receiving a clinical, histological, virological and biochemical evaluation. APOC3 (rs2854116 and rs2854117) and PNPLA3 (p.I148M) variants were genotyped. PNPLA3 polymorphisms were associated with liver steatosis, which was significantly higher in patients with p.148I/M (P = 0.034) and p.148M/M (P = 0.004) variants than those homozygous for the PNPLA3 wild type. Excluding patients with HCV genotype 3, the association with liver steatosis and PNPLA3 variants was more marked (p.148I/I genotype vs p.148I/M, P = 0.02, and vs p.148M/M, P = 0.005). The APOC3 polymorphism was not associated with any of the evaluated parameters. Among the interacting factors, BMI and waist circumference correlated with liver steatosis (P = 0.008 and 0.004, respectively). Relationship between waist circumference and liver steatosis was analysed for the different PNPLA3 genotypes. Homozygous 148M patients showed a stronger correlation between waist circumference and steatosis than those carrying the other genotypes (P = 0.0047). In our hepatitis C-infected population, the PNPLA3 polymorphism influenced the development of liver steatosis, but not fibrosis progression. APOC3 polymorphisms had no effect on the development of steatosis and no influence on the PNPLA3 polymorphism. The amount of abdominal fat can increase the association of PNPLA3 p.I148M with liver steatosis. Show less