Effects of retinoic acid on simple hepatic steatosis and DGAT2 expression in nonalcoholic fatty liver disease (NAFLD) rats

Abstract

Non-alcoholic fatty liver disease (NAFLD) is an increasing public health problem worldwide, with limited effective treatment available. The main pathological feature of the disease is the accumulation of triglycerides in hepatocytes. Hepatic triglyceride synthesis is mediated by diacylglycerol acyltransferase-2 (DGAT2). Retinoic acid (RA), the active form of vitamin A, is metabolised and stored mainly in the liver. RA has been implicated in the pathogenesis of NAFLD. However, its effect on hepatic steatosis and its possible regulatory role on DGAT2 expression in NAFLD remain unclear. This study aimed to investigate the effectiveness of RA in a NAFLD animal model, and determine its role in hepatic DGAT2 expression. The study was conducted in two phases: a pilot study to determine the time required to induce liver steatosis using a 12% high cholesterol diet (HCD), followed by the main study using the same diet. Forty-five Sprague�Dawley rats were divided into five groups; control, control + RA, HCD, HCD + vehicle, and HCD+ RA. After hepatic steatosis induction, selected groups received RA or vehicle for four weeks.Body weight, liver weight, serum biochemical parameters, hepatic TG content and histopathological changes were assessed. Hepatic DGAT2 expression was determined using immunohistochemistry and ImageJ software, while scanning electron microscope (SEM) was used to assess hepatic sinusoidal endothelial cells fenestration and porosity. Data were analysed using one-way ANOVA. The pilot study demonstrated that animals fed with 12% high cholesterol diet exhibited histopathological progression of NAFLD, from a simple steatosis in the four weeks group to non-alcoholic steatohepatitis (NASH) in the five- and six-week groups. In the second phase, a significant decrease in body weight by 20% was observed in RA-treated animals compared with HCD-fed rats. Liver weight and TG content were also significantly reduced. However, serum TG was not significantly lower in the RA-treated HCD group compared with the untreated HCD group, and RA had no noticeable effect on serum total cholesterol.Histopathological results showed improvement in hepatic steatosis, ballooning, and inflammation in the RA-treated group compared with the HCD group. The NAFLD Activity Score (NAS) and hepatic DGAT2 expression were both significantly reduced in HCD animals receiving RA. SEM analysis revealed significantly diminished fenestration frequency and porosity in all HCD groups, with no significant improvement following RA treatment. In conclusion, the results demonstrate that RA mainly improved hepatic lipid accumulation and histological injury, potentially through reduced hepatic DGAT2 expression, but had limited effects on the serum lipid profile and LSEC ultrastructural changes.