AKKERMANSIA MUCINIPHILA PROMOTING EQUOL PRODUCTION ALLEVIATES OVARIECTOMY-INDUCED ANXIETY-LIKE BEHAVIORS IN RAT

Background and Aims:
Anxiety is one of the common diseases of postmenopausal women. Our previous study showed that berberine, a natural alkaloid, could alleviate ovariectomized (OVX)-induced anxiety-like behaviors and enrich Akkermansia muciniphila (AKK) in rats. Whether Akkermansia muciniphila, as a potential psychobiotic, could alleviate OVX-induced anxiety-like behaviors deserves further exploration.
Methods:
Experimental anxiety was established in germ-free (GF) OVX rats. The GF rats were randomly divided into four groups, which were the OVX+vehicle (20% glycerin in phosphate buffered saline), OVX+AKK (Fig. 1A), OVX+vehicle (sterile water) and OVX+Equol (Fig. 2A). Before undergoing behavioral tests, OVX+AKK group were gavaged with 10⁹ CFU/ml AKK every other day for 4 weeks, and OVX+Equol group were gavaged with 2 mg/kg equol every day for 4 weeks. The other groups received the corresponding vehicle for the same duration. The open field test (OFT) and elevated plus maze test (EPM) were used to measure anxiety levels. Liquid chromatography/mass spectrometry analysis (LC/MS) was used to measure serum equol and daidzein levels. Enzyme linked immunosorbent assay was used to measure serum estradiol level. Metagenomic sequencing was used to detected Akkermansia muciniphila functional gene expression.
Results:
The OPT showed that, compared with OVX+vehicle rats, OVX+AKK rats exhibited decreased anxiety-like behaviors and increased travel distance and residence time into the center of the arena (Fig. 1B). The EPM showed that, compared with OVX+vehicle rats, OVX+AKK rats showed a tendency to recover their open-arm exploration ability (Fig. 1C). After AKK administration, the serum estradiol levels were not significantly affected (Fig. 1D). Compared with OVX+vehicle rats, the microbial metabolite equol appeared in the serum after intragastric administration of AKK, and the level of daidzein showed a relatively lower trend in the OVX+AKK group (Fig. 1E). After administration of equol to GF OVX rats, the OPT showed that, compared with OVX+vehicle rats, OVX+Equol rats exhibited decreased anxiety-like behaviors and increased residence time and entries into the center of the arena (Fig. 2B). The EPM showed that, compared with OVX+vehicle rats, OVX+Equol rats exhibited restored open arm exploration (Fig. 2C). Through metagenomic sequencing of AKK, the data showed that AKK expresses daidzein reductase, the key rate-limiting enzyme for converting daidzein into equol.
Conclusion:
Akkermansia muciniphila could alleviates ovariectomy-induced anxiety-like behaviors through converting daidzein into equol by expressing daidzein reductase.