Estrogen/estrogen receptor activation protects against DEN-induced liver fibrosis in female rats via modulating TLR-4/NF-kβ signaling

Men are more susceptible to liver fibrosis (LF) than women. However, the underlying molecular mechanism, especially the role of estrogen/estrogen receptor (ER) activation in this sexual dimorphism is unclear. Therefore, the aim of the current study was to investigate the impact and the underlying molecular mechanisms of estrogen/ER activation on diethyl nitrosamine (DEN)-induced LF. Thirty ovariectomized (OVX) female rats were randomly allocated into five groups (n = 6), and received no treatment, diethyl nitrosamine (DEN), DEN/fulvestrant, DEN/silymarin or DEN/estradiol benzoate (EB). In addition, three sham groups received no treatment, DEN or DEN/fulvestrant, and one control group that neither ovariectomized nor treated. Directly after treatment, liver injury biomarkers were measured. In addition, hepatic tissue hydroxyproline, TNF- α, TGF- β, and IL-10 were evaluated. Expression of NF-kβ, CD68 (a marker for macrophage infiltration), ER-β and TLR-4 were measured. Finally, liver tissue histopathology was assessed. Ovariectomy aggravates DEN-induced LF, as it significantly elevated all liver tissue injury biomarkers. This effect has become even worse after blocking ER by fulvestrant, indicating a protective role of estrogen/ER activation against DEN-induced LF. Inhibition of TLR-4/NF-kβ signaling pathway contributed to this protective effect, as estrogen deprivation or blocking of ER significantly activates this pathway during the onset of LF. While administration of EB or silymarin (selective ER-β activator) improved LF indices and deactivated this pathway. These results provide new insight into the pivotal role of estrogen/ER activation via modulation of TLR-4/NF-kβ, in the alleviation of LF pathogenesis.