Monotropein improves late-onset hypogonadism in TM3 Leydig cells and aged rats

BACKGROUND AND AIM: Late-onset hypogonadism (LOH) is an age-related condition characterized by declining testosterone levels and impaired reproductive and metabolic functions. Fermented Morinda citrifolia extract (FME) has demonstrated therapeutic potential against LOH; however, its active constituents and underlying mechanisms remain unclear. The aim of this study was to identify the key bioactive compounds in FME and evaluate their efficacies and mechanisms of action in alleviating LOH. METHODS: High-performance liquid chromatography (HPLC) was used to quantify the iridoids and coumarins in FME. Among these four candidates, monotropein (MON) was selected for functional evaluation. In vitro assays using TM3 Leydig cells were used to assess the effects of MON on steroidogenic gene and protein expression under oxidative stress. In vivo studies involved oral administration of MON (40 mg/kg/day) to aged Sprague-Dawley rats for 4 weeks. Hormonal, histological, reproductive, metabolic, and safety parameters were measured. RESULTS: MON significantly restored testosterone production and upregulated key steroidogenic enzymes (StAR, 3β-HSD2, 17,20-desmolase, and 17β-HSD3) in vitro and in vivo. It improved serum testosterone levels, spermatogenesis, and sperm motility in aged rats. MON also reduced age-associated increases in total cholesterol and triglyceride levels without altering luteinizing hormone, follicle-stimulating hormone, or estradiol, and without inducing hepatic, renal, or prostate toxicity. CONCLUSION: MON was identified as the principal active compound of FME responsible for its LOH-alleviating effects. MON enhanced testicular steroidogenesis and improved reproductive and metabolic outcomes without causing systemic toxicity, supporting its potential as a targeted phytotherapeutic agent against age-related androgen deficiency.