Exploring the Inhibitory Potential of Phytosterols β-Sitosterol, Stigmasterol, and Campesterol on 5-Alpha Reductase Activity in the Human Prostate: An In Vitro and In Silico Approach

Steroidal 5α-reductase type 2 (S5αR2) is a key enzyme involved in the conversion of testosterone (TST) to dihydrotestosterone (DHT), a crucial process in the development of benign prostatic hyperplasia (BPH). Phytosterols (PSs), natural plant-derived compounds, have been proposed as potential inhibitors of S5αR2, but studies on their efficacy are limited. This study evaluates the inhibitory effects of three PSs (β-sitosterol, stigmasterol, and campesterol) on S5αR2 activity using a combined in vitro and in silico approach. The inhibitory activity of the respective PSs was assessed in vitro, by measuring TST and DHT, while molecular docking and dynamics explored PS interactions with S5αR2's active site. The in vitro tests indicated significantly higher IC₅₀ values (β-sitosterol, 3.24 ± 0.32 µM; stigmasterol, 31.89 ± 4.26 µM; and campesterol, 15.75 ± 5.56 µM) for PSs compared to dutasteride (4.88 × 10^-3 ± 0.33 µM), suggesting a lower efficiency in inhibiting S5αR2. The in silico studies confirmed these observations, explained by the lower binding affinity identified for PSs to the enzyme's active site in the molecular docking studies and the reduced stability of the interactions with the active site of the enzyme during the molecular dynamics simulations compared to dutasteride. The results suggest that PSs exhibit low-to-negligible inhibitory activity against S5αR2 (µM range) compared to the synthetic inhibitor dutasteride (nM range). Among the three PSs studied, β-sitosterol showed the highest inhibitory activity and the best stability in its interaction with S5αR2, when compared with stigmasterol and campesterol.