Abstract: In the current study, we aimed to investigate the protective effects of astaxanthin (AX) against non-alcoholic fatty liver disease (NAFLD) via a circadian rhythm-related mechanism. A high-fat and high-cholesterol diet was adopted to build an NAFLD mouse model. Male SPF C57BL/6 mice were divided into three groups: normal chow (control), HFD model, and HFD + AX groups. After 12 weeks of feeding, blood biochemical indexes such as triglyceride, total cholesterol (TC), high density lipoprotein cholesterol (HDL-C) and low density lipoprotein cholesterol (LDL-C), as well as liver injury indexes such as alanine aminotransferase (ALT) and aspartate transaminase (AST) were determined. Morphological variations of liver tissue were observed by hematoxylin-eosin staining. Real-time quantitative polymerase chain reaction (qPCR) was used to examine the expression levels of genes related to liver lipid metabolism, cholesterol metabolism and circadian rhythm. The results showed that body mass, liver/body mass ratio and obesity index of mice in the HFD group were significantly higher when compared with the control group (P < 0.001). Both liver/body mass ratio and obesity index dropped dramatically after dietary supplementation of AX (P < 0.01). High-fat fed mice showed higher blood lipid levels (except HDL-C); in particular, a significant increase was observed in LDL-C. Dietary supplementation of AX effectively reduced TC and LDL-C, increased HDL-C, and improved lipid metabolism when compared with the HFD group. HFD significantly increased the levels of serum ALT and AST and caused liver injury (P < 0.001). These effects could be significantly rescued by AX (P < 0.01). Moreover, AX could remarkably improve the expression of key enzyme genes related to liver lipid metabolism including fatty acid synthase and hydroxymethylglutaryl-CoA reductase. In addition, AX also increased the expression of cholesterol 7α- hydroxy-lase, promoted cholesterol oxidation in liver. AX regulated the expression of these genes in a circadian rhythm-dependent way. AX could alleviate or correct the disorders of clock circadian regulator gene expression and circadian expression of brain and muscle ARNT-like 1 and key genes involved in lipid metabolism in the liver of HFD fed rats, which suggested that AX played a regulatory role in improving the rhythmicity of hepatic metabolism disorder caused by high-fat diet.

Key words: astaxanthin, non-alcoholic fatty liver disease, circadian rhythm