Myricetin Modulates Macrophage Polarization and Mitigates Liver Inflammation and Fibrosis in a Murine Model of Nonalcoholic Steatohepatitis

Abstract

This study aimed to investigate the beneficial effects of myricetin in a diet-induced nonalcoholic steatohepatitis (NASH) model and the underlying mechanism. C57BL/6J mice were fed a standard chow or the choline-deficient, L-amino acid-defined, high-fat diet (CDAHFD) for 8 weeks with the treatment of myricetin (100 mg/kg) or vehicle by daily gavage. Hepatic inflammation, steatosis, fibrosis, and hepatic stellate cells (HSC) activation were assessed. We also analyzed M1 and M2 macrophages and its related markers in livers from NASH mice and in RAW264.7 macrophages stimulated by lipopolysaccharide (LPS) or interleukin 4 (IL-4) in vitro. Furthermore, we determined the effect of myricetin on the triggering receptor expressed on myeloid cells-1 (TREM-1), toll like receptor (TLR) 2 and 4, and myeloid differentiation factor 88 (MyD88) signaling both in livers from mice and in RAW264.7 cells stimulated by LPS. Our results revealed that myricetin remarkably ameliorated hepatic steatosis, inflammation, and inhibited hepatic macrophage infiltration in CDAHFD-fed mice. Myricetin-treated to CDAHFD-fed mice also inhibited liver fibrosis and HSC activation when compared with vehicle-treated to those mice. Moreover, myricetin inhibited M1 macrophage polarization and its relative markers in livers of NASH mice while induced M2 polarization. Similarly, in vitro study, myricetin inhibited the LPS-induced mRNA expression of M1 macrophages marker genes and induced IL-4-induced M2 macrophage marker genes in RAW264.7 macrophages. Mechanically, myricetin inhibited the expression of TREM-1 and TLR2/4-MyD88 signaling molecules in livers from NASH mice and in RAW264.7 macrophages stimulated by LPS in vitro. Additionally, myricetin inhibited the activation of nuclear factor (NF)-κB signaling and the phosphorylation of the signal transducer and activation of transcription 3 (STAT3) in LPS-stimulated RAW264.7 macrophages. Taken together, our data indicated that myricetin modulated the polarization of macrophages via inhibiting the TREM-1-TLR2/4-MyD88 signaling molecules in macrophages and therefore mitigated NASH and hepatic fibrosis in the CDAHFD-diet-induced NASH model in mice.

Macrophage Polarization and Its Role in Liver Disease

“…In addition, Yao et al. ( 164 ) found that myricetin suppressed M1 and promoted M2 polarization by inhibiting the TREM-1-TLR2/4-MyD88 signaling pathway and the phosphorylation of STAT3, thus attenuating the NASH induced by choline-deficient, L-amino acid-defined, and high-fat diet. β-cryptoxanthin and astaxanthin, two carotenoids with anti-oxidant effects, could inhibit M1 macrophage polarization to improve insulin resistance and NASH induced by a high-cholesterol and high-fat diet in mice ( 165 , 166 ).…”

Function of TREM1 and TREM2 in Liver-Related Diseases

“…Then, these inflammatory factors will induce the activation of HSCs [58]. When TREM1 is inhibited, the TREM1-TLR2/4-MyD88-mediated inflammatory signaling pathway is inhibited, and the polarization of M1-type macrophages are also reduced [101]. TREM2 expressed on KCs and HSCs dampen TLR4-induced inflammation, and the combined action of liver resident and infiltrating cells is also necessary to dampen inflammation [20].…”

Wild Bitter Melon Extract Regulates LPS-Induced Hepatic Stellate Cell Activation, Inflammation, Endoplasmic Reticulum Stress, and Ferroptosis

“…Wang et al demonstrated that trans-cinnamic acid has antiobesity effects in oleic acid- (OA-) induced HepG2 cells and high-fat diet- (HFD-) fed mice [ 92 ]; however, the role played by trans-cinnamic acid in HSCs remains unclear. Myricetin modulated the polarization of macrophages via the inhibition of TREM-1-TLR2/4-MyD88 signaling molecules in macrophages and attenuated liver inflammation and fibrosis in a choline-deficient, L-amino acid-defined, high-fat diet-induced nonalcoholic steatohepatitis model [ 93 ]. Quercetin caused decreased oxidative stress and inflammation and prevented liver fibrosis via the induction of HSC apoptosis [ 94 ].…”