Background: The conversion of testosterone to dihydrotestosterone; 5alpha-androstan-17beta-ol-3-one by 5alpha-reductase plays a crucial role in hair baldness and prostatomegaly. Recent approach showed specific inhibitors for 5alpha-reductase type 2 such as finasteride promoted hair growth in male pattern alopecia.
Objective: In order to search for effective medicinal plant extracts applied topically for androgenetic alopecia, we screened natural plant extracts having inhibitory activities of 5alpha-reductase type 2 and demonstrated its biological function in androgen-related animal models.
Methods: We evaluated the inhibition activities of numerous plant extracts by contact cell based metabolic method using a stable HEK 293 cell line expressing human 5alpha-reductase (type 2). To elucidate the biological activity in vivo, the Thujae occidentalis semen (TOS) extract was topically applied to fuzzy rat and androchronogenetic alopecia (AGA) mouse, respectively. The secreted sebum and the size of sebaceous glands of fuzzy rat were measured after 6 weeks. Also, after the topical treatment with TOS extract and androgen receptor antagonist (cyproterone acetate) simultaneously with subcutaneous injection of testosterone (1 mg/mice/day), hair loss patterns of female B6CBAF1/j hybrid mouse were observed.
Results: TOS extract showed higher inhibition activity of 5alpha-reductase type 2(IC(50) value=2.6 microg/ml) than that of gamma-linolenic acid, but lower than that of finasteride. When applied to fuzzy rat, the amount of sebum and sebaceous gland size decreased remarkably. In AGA model, alopecia degrees of two groups, treated with TOS extract (P<0.015) or cyproterone acetate (P<0.01), were lower than that of vehicle (propylene glycol:ethanol=7:3) and there was no difference between above two groups.
Conclusion: We have demonstrated the inhibitory activity of TOS extract for 5alpha-reductase type 2 and its biological action in two animal models, suggesting that TOS extract would be used as an effective agent for male pattern baldness by modifying androgen conversion.