Effects of two polyphenol-rich food ingredients, obtained from apple and onion, in the prevention of hepatic steatosis in rats

Abstract

[Background]: Hepatic steatosis, whose prevalence is increasing worldwide, is considered a benign condition, asymptomatic and reversible. However, it can lead to more severe pathologies, such as steatohepatitis, cirrhosis or even cancer. Dietary treatment is critical in the management of steatosis, and polyphenols have been considered as preventive or therapeutic tools.

[Objectives]: To analyse the effect of two polyphenol-rich food ingredients (obtained from apple and onion) on hepatic steatosis in obese Zucker (fa/fa) rats, exploring their mechanism of action.

[Methods]: 24 Zucker fa/fa rats were fed a standard diet and divided into 3 groups (n=8): control (C), supplemented with 10% of an apple ingredient (AI) or an onion ingredient (OI) for 8 weeks. Hepatic triglyceride content, fatty acid synthase (FAS) and carnitine palmitoyl transferase-1a (CPT- 1a) activities were assessed by spectrophotometry. Acetyl-CoA carboxylase (ACC), fatty acid transport protein 5 (FATP5), aquaporin 9 (AQP9) and mitochondrial transcription factor A (mtTFA) protein expressions were determined by western blot.

[Results]: Hepatic triglyceride content was significantly reduced in OI group compared with C group (48.59±0.80; 36.57±1.87). Regarding de novo lipogenesis, in AI group but not in OI group, FAS activity (p<0.05) and AQP9 protein expression (p<0.05) were higher compared with control rats, whereas the expressions of the other lipogenic proteins remained unchanged. Regarding fatty acid oxidation, rats fed the polyphenol food ingredient enriched diets showed a tendency to increased) CPT-1a activity (p<0.1) when compared with C group. Finally, although no statistical differences were observed, the values of mtTFA roughly doubled control values. Conclusion: Onion ingredient, but not apple ingredient, could be useful in the prevention/treatment of hepatic steatosis likely due to the involvement of an increased fatty acid oxidation.