High fish oil diet promotes liver inflammation and activates the complement system.

Diets rich in n-3 polyunsaturated fatty acid (n-3 PUFA) fish oil (FO) have beneficial effects in obesity‑associated metabolic disease. However, contradictory roles in inflammatory disease intervention have been reported. Our previous work revealed that a high‑FO diet promoted myeloid cell differentiation by modifying the bone marrow microenvironment; however, its effects on liver inflammation and complement system activation remain unknown. By performing ELISA, reverse transcription‑quantitative polymerase chain reaction, flow cytometry and histology on mice fed with high‑FO and low‑fat diets, the present study demonstrated that a 4‑week high‑FO diet promoted liver inflammation in mice without affecting body or liver weight. The livers of high‑FO diet mice exhibited increased infiltration of T cells and CD11b+ Gr‑1+ myeloid cells. Additionally, a higher level of IL‑1β and MCP‑1 mRNA expression was detected, suggesting that the high‑FO diet promoted liver inflammation. Further experiments indicated that the high‑FO diet increased the total hemolytic complement activity (CH50), promoted the production of the membrane attack complex and increased the levels of various complement proteins in vivo, including complement components C3, C4b, C1qb and factor B. Furthermore, higher concentrations of triglyceride were detected in the peripheral blood of high‑FO diet mice, indicating the potential protective roles of n‑3 PUFAs in FO against lipotoxicity in hyperlipidemia. Collectively, the present study demonstrated that high FO intake induced inflammation and activated the complement system in the liver. However, further study is required to determine the exact mechanisms.