Hydroxytyrosol Enhances the Nrf2/HO-1 Signalling Pathway to Inhibit Oxidative Stress and Apoptosis and Improve Premature Ovarian Insufficiency In Vitro and In Vivo

Premature ovarian insufficiency (POI) poses a serious risk to the reproductive health and psychological well-being of women. Here, the protective effects of hydroxytyrosol (HT), the primary phenolic component of olive oil, on POI were investigated. In vitro, human ovarian granulosa-like tumour cell lines (KGN cells) were challenged by D-galactose (D-gal) with or without HT. HT administration effectively alleviated KGN cell damage, decreased the number of senescence-associated β-galactosidase (SA-β-gal)-positive cells, increased superoxide dismutase (SOD) activity, reduced reactive oxygen species (ROS) and malondialdehyde (MDA) levels, enhanced the expression level of Bcl-2, inhibited the expression level of Bax, and inhibited cell apoptosis in D-gal-treated KGN cells. In vivo, HT administration reversed the decreased ovarian index, oestrous cycle disruption, and abnormal sex hormone levels observed in D-gal-induced POI mice. HT administration increased glutathione (GSH) levels, reduced the MDA levels, and attenuated apoptosis in ovarian tissues, as evidenced by a decreased number of TUNEL-positive cells, upregulated Bcl-2 expression, and downregulated Bax expression. Mechanistically, HT downregulated the expression level of Kelch-like ECH-associated protein 1 (Keap1) and enhanced the expression levels of heme oxygenase-1 (HO-1) and nuclear factor erythroid 2-related factor 2 (Nrf2) in vitro and in vivo. In conclusion, HT ameliorates D-gal-induced POI in vitro and in vivo by activating the Nrf2/HO-1 signalling pathway.