Impact of Alginate Oligosaccharides on Ovarian Performance and the Gut Microbial Community in Mice with D-Galactose-Induced Premature Ovarian Insufficiency

Premature ovarian insufficiency (POI) is an important factor in female infertility and is often associated with oxidative stress. Alginate oligosaccharides (AOSs), derived from the degradation of alginate, have been demonstrated to have protective effects against various oxidative stress-related diseases. However, the impact of AOSs on POI has not been previously explored. The current study explored the effects of AOSs on ovarian dysfunction in a mouse model of POI induced by D-galactose (D-gal). Female C57BL/6 mice were randomly divided into five groups: the control (CON), POI model (D-gal), and low-, medium-, and high-dose AOS groups (AOS-L, 100 mg/kg/day; AOS-M, 150 mg/kg/day; AOS-H, 200 mg/kg/day). For 42 consecutive days, mice in the D-gal, AOS-L, AOS-M, and AOS-H groups received daily intraperitoneal injections of D-gal (200 mg/kg/day), whereas those in the CON group received equivalent volumes of sterile saline. Following D-gal injection, AOSs were administered via gavage at the specified doses; mice in the CON and D-gal groups received sterile saline instead. AOS treatment markedly improved estrous cycle irregularities, normalized serum hormone levels, reduced granulosa cell apoptosis, and increased follicle counts in POI mice. Moreover, AOSs significantly reduced ovarian oxidative stress and senescence in POI mice, as indicated by lower levels of malondialdehyde (MDA), higher activities of catalase (CAT) and superoxide dismutase (SOD), and decreased protein expression of 4-hydroxynonenal (4-HNE), nitrotyrosine (NTY), 8-hydroxydeoxyguanosine (8-OHdG), and p16 in ovarian tissue. Analysis of the gut microbiota through 16S rRNA gene sequencing and short-chain fatty acid (SCFA) analysis revealed significant differences in gut microbiota composition and SCFA levels (acetic acid and total SCFAs) between control and D-gal-induced POI mice. These differences were largely alleviated by AOS treatment. AOSs changed the gut microbiota by increasing the abundance of Ligilactobacillus and decreasing the abundance of Clostridiales, Clostridiaceae, Marinifilaceae, and ClostridiumT. Additionally, AOSs mitigated the decline in acetic acid and total SCFA levels observed in POI mice. Notably, the total SCFA level was significantly correlated with the abundance of Ligilactobacillus, Marinifilaceae, and ClostridiumT. In conclusion, AOS intervention effectively mitigates ovarian oxidative stress, restores gut microbiota homeostasis, and regulates the microbiota–SCFA axis, collectively improving D-gal-induced POI. Therefore, AOSs represent a promising therapeutic strategy for POI management.