5α-reductase inhibition and hair growth promotion of some Thai plants traditionally used for hair treatment

Many Thai traditional herbs have been used for hundreds of years for hair treatment and nourishment, including hair loss. However, scientific evidence about their mechanisms of action has not yet been elucidated. The purpose of this research is to define the possible mechanisms involved in hair loss treatment of the selected plants by determining the 5α-reductase enzyme inhibition and hair growth promoting activities, and the relationship between these two activities. Seventeen Thai plants traditionally used for hair treatment were selected. The plants were dried, ground and extracted by maceration with ethyl alcohol. These extracts were further tested for 5α-reductase inhibition using enzymes from rat livers. Hair growth promoting activity was tested in C57BL/6 mice. Carthamus tinctorius L. was the most potent 5α-reductase inhibitor, with a finasteride equivalent 5α-reductase inhibitory activity (FEA) value of 24.30 ± 1.64 mg finasteride equivalent per 1 g crude extract. Phyllanthus emblica L. was the second most potent inhibitor, with FEA of 18.99 ± 0.40. Rhinacanthus nasutus (L.) Kurz. was the least potent 5α-reductase inhibitor (FEA 10.69 ± 0.96). Carthamus tinctorius also was the most potent hair growth promoter in C57BL/6 mice. There were strong relationships between 5α-reductase inhibitory activity and hair growth promoting activity (r = 0.719), and between 5α-reductase inhibitory activity and hair follicle count (r = 0.766). Ethanolic extract of Carthamus tinctorius was the most potent 5α-reductase inhibitor and hair growth promoter. This discovery may lead to the development of new alternative medicines for hair loss prevention and treatment.