Long-term administration of royal jelly regulates age-related disorders and improves gut function in naturally aging mice

A natural aging mouse model can exhibit physiological characteristics that closely resemble those of human aging. Through long-term observation, it reflects the occurrence and development of the aging process more accurately. Although numerous beneficial effects of royal jelly (RJ) have been extensively demonstrated in multiple experimental models, the effects of RJ on naturally aging mice have not yet been investigated. In this study, middle-aged male C57BL/6J mice were given RJ for 9 consecutive months to investigate its impact on the intestinal barrier function, gut microbiota, short-chain fatty acids (SCFAs) content and possible mechanisms. The results confirmed that RJ modulated serum lipids by reducing the levels of total cholesterol (TC), triglycerides (TG), and low-density lipoprotein cholesterol (LDL-C). Additionally, it protected the liver by increasing antioxidant enzyme levels while decreasing inflammatory cytokines TNF-α (by 51.97%), IL-6 (by 29.73%), and IL-1β (by 43.89%). Furthermore, RJ inhibited the expression of cell cycle-dependent kinase inhibitors including p16, p21, and p53. Importantly, RJ ameliorated gut dysfunctions by inhibiting reduction of tight junction proteins and reducing inflammatory cytokines content in the colon. We also observed an alteration in gut microbiota characterized by an elevated ratio of Firmicutes to Bacteroides (F/B) along with increased abundance of beneficial bacteria, i.e., Lachnospiraceae NK4A136 and Akkermansia. Correlation analysis revealed positive associations between most bacterial genera and SCFAs production. Functional profiling of gut microbiota composition indicated that RJ intervention regulated amino acid metabolism, glycan biosynthesis, and cofactor/vitamin metabolism. Overall, our findings provide an effective dietary intervention strategy for modulating age-associated frailty through the modulation of the gut microbiota.