Context: Plantain fruit pulp has been used as a natural remedy to manage erectile dysfunction (ED) in traditional medicine. However, the potency of the peel has not been examined with respect to ED management.
Objective: This study investigated and compared the inhibitory potential of unripe (UPP) and ripe (RPP) plantain peels on some enzymes associated with ED and Fe2+-induced oxidative stress in albino rat penile homogenate in vitro.
Materials and method: Aqueous extract of the peels was prepared and the effect on phosphodiesterase-5 (PDE-5), arginase, acetylcholinesterase (AChE), angiotensin-I converting enzyme (ACE) and Fe2+-induced malonyladehyde in isolated albino rat penile homogenate were investigated. Phenolic constituents of the peels powder were characterized using high-performance liquid chromatography coupled with diode array detector (HPLC-DAD).
Result: Extract from UPP had higher PDE-5 (IC50 = 3.10 μg/mL), arginase (IC50 = 0.96 μg/mL), AChE (IC50 = 6.30 μg/mL) and ACE (IC50 = 0.41 μg/mL) inhibitory ability compared with RPP (PDE-5, IC50 = 4.33 μg/mL; arginase, IC50 = 1.34 μg/mL; AChE, IC50 = 8.64 μg/mL; ACE, IC50 = 0.63 μg/mL). The extract from UPP also had higher inhibition of Fe2+-induced lipid peroxidation. HPLC-DAD analysis revealed that gallic and caffeic acids, rutin, quercitrin and quercetin were abundant in UPP, while catechin, kaempferol, chlorogenic and ellagic acids were the dominant phenolic compounds in RPP.
Discussion and conclusion: Inhibition of enzymes associated with ED and lipid peroxidation could be linked with the phenolic compounds. However, UPP appeared to be more potent.
Keywords: acetylcholinesterase; angiotensin-I converting enzyme; antioxidant; arginase; lipid peroxidation; phosphodiesterase-5; polyphenols.