Objective: Although the protective effects of Momordica charantia L. (MC) extract on chemical-induced testicular damage have been studied, the preventive effects of MC extract on functional proteins in the epididymis under chronic stress have never been reported. This study investigated the protective effects of MC fruit extract on protein secretion, especially tyrosine-phosphorylated proteins, in the epididymis of rats exposed to chronic unpredictable stress (CUS).
Methods: Total phenolic compounds (TPC), total flavonoid compounds (TFC) and antioxidant capacities of MC extract were measured. Adult male rats were divided into 4 groups: control group, CUS group, and 2 groups of CUS that received different doses of MC extract (40 or 80 mg/kg). In treated groups, rats were given MC daily, followed by induction of CUS (1 stressor was randomly applied from a battery of 9 potential stressors) for 60 consecutive days. Plasma corticosterone and testosterone levels were analyzed after the end of experiment. Expressions of heat-shock protein 70 (HSP-70) and tyrosine-phosphorylated proteins present in the fluid of the head and tail of the epididymis were quantified using Western blot.
Results: MC extract contained TPC of (19.005 ± 0.270) mg gallic acid equivalents and TFC of (0.306 ± 0.012) mg catechin equivalents per gram, and had 2,2-diphenyl-1-picrylhydrazyl antioxidant capacity of (4.985 ± 0.086) mg trolox equivalents per gram, radical half-maximal inhibitory concentration of (2.011 ± 0.008) mg/mL and ferric reducing antioxidant power of (23.697 ± 0.819) μmol Fe(II) per gram. Testosterone level in the epididymis was significantly increased, while the corticosterone level was significantly improved in groups treated with MC extract, compared to the CUS animals. Particularly, an 80 mg/kg dose of MC extract prevented the impairments of HSP-70 and tyrosine-phosphorylated protein expressions in the luminal fluid of the epididymis of CUS rats.
Conclusion: MC fruit extract had antioxidant activities and improved the functional proteins secreted from the head and tail of the epididymis. It is possible to develop the MC fruit extract as a male fertility supplement for enhancing functional sperm maturation in stressed men.

Key words: Momordica charantia L., antioxidant activity, epididymis, tyrosine-phosphorylated proteins, chronic unpredictable stress