EC Pharmacology and Toxicology

β-sitosterol (SIT) improves symptoms and urinary flow parameters in treating benign prostatic hyperplasia. Normal and abnormal prostate growth is driven by the androgen dihydrotestosterone (DHT) formed from testosterone (T) by the catalytic action of the steroid 5α-reductase type 1/2 (SRD5A1/2). The effect of SIT as an inhibitor of the SRD5A activity in the human prostate has scarcely been studied.

This study aimed to determine the effect of SIT as an inhibitor of the activity of SRD5A2. So, the concentration of SIT was assessed, which blocks 50% of its activity (IC₅₀). The IC₅₀ value was 130 nM for 5RD5A2.

Additionally, the kinetic parameters of 5RD5A2 activity were calculated from the plots of T concentration versus DHT formed in the presence or absence of SIT. Kinetic parameters indicated a DHT formation rate of 27.54 ± 2.72 ng/mg protein/h both in the absence and the existence of SIT. At the same time, Km values were 8.03 ± 0.67 µM in the absence of the inhibitor, 20.8 ± 5.6 µM in the presence of SIT, 0.7 µM and 46.94 ± 8.8 µM in the presence of SIT, 1.4 µM.

The pharmacological effect of SIT was compared with that of finasteride on the hamster prostate. Results indicated that T-treatment increased the prostate weight of castrated hamsters compared to the vehicle-treated neutered control. The SIT plus T treatment decreased this gland's weight similarly to the T plus finasteride.

Keywords: β-Sitosterol; Type 2 5α-Reductase; Human Prostate; Finasteride; Competitive Inhibitor

1. Babu S and Jayaraman S. “An update on β-sitosterol: A potential herbal nutraceutical for diabetic management”. Biomedicine and Pharmacotherapy 131 (2020): 110702.
2. Weihrauch JL and Gardner JM. “Sterol content of foods of plant origin”. Journal of the American Dietetic Association 1 (1978): 39-47.
3. Awad AB., et al. “In vitro and in vivo (SCID mice) effects of phytosterols on the growth and dissemination of human prostate cancer PC-3 cells”. European Journal of Cancer Prevention 6 (2001).
4. Berges RR., et al. “A randomized, placebo-controlled, double-blind clinical trial of β-sitosterol in patients with benign prostatic hyperplasia”. The Lancet 8964 (1995): 1529-1532.
5. Senge T., et al. “The effectiveness of β-sitosterol in the treatment of benign prostatic hyperplasia”. Urologe A 2 (1995): 130-131.
6. Cabeza M., et al. “Effect of β-sitosterol as inhibitor of 5α-reductase in hamster prostate”. Proceedings of the Western Pharmacology Society 46 (2003): 153-155.
7. Andersson S., et al. “Expression cloning and regulation of steroid 5α-reductase, an enzyme essential for male sexual differentiation”. Journal of Biological Chemistry 27 (1989): 16249-16255.
8. Russell DW and Wilson JD. “Steroid 5α-Reductase: Two Genes/Two Enzymes”. Annual Review of Biochemistry 1 (1994): 25-61.
9. Bruchovsky N and Wilson JD. “The Conversion of Testosterone to 5α-Androstan-17β-ol-3-one by Rat Prostate in Vivo and in Vitro”. Journal of Biological Chemistry 8 (1968): 2012-2021.
10. Wu Y., et al. “Prostate cancer cells differ in testosterone accumulation, dihydrotestosterone conversion, and androgen receptor signaling response to steroid 5α-reductase inhibitors”. The Prostate 13 (2013): 1470-1482.
11. Uemura M., et al. “Novel 5α-steroid reductase (SRD5A3, type-3) is overexpressed in hormone-refractory prostate cancer”. Cancer Science 1 (2008): 81-86.
12. Normington K and Russell DW. “Tissue distribution and kinetic characteristics of rat steroid 5α-reductase isozymes. Evidence for distinct physiological functions”. Journal of Biological Chemistry 27 (1992): 19548-19554.
13. Arai S., et al. “Development of prostate cancer in a patient with primary hypogonadism: intratumoral steroidogenesis in prostate cancer tissues”. Andrology1 (2013): 169-174.
14. McEwan IJ and Brinkmann AO. “Androgen Physiology: Receptor and Metabolic Disorders”. In: Feingold KR, Anawalt B, Boyce A, Chrousos G, de Herder WW, Dhatariya K, et al., editors. Endotext. South Dartmouth (MA): MDText.com, Inc. Copyright © 2000-2022, MDText.com, Inc (2000).
15. Montgomery RB., et al. “Maintenance of intratumoral androgens in metastatic prostate cancer: a mechanism for castration-resistant tumor growth”. Cancer Research 68 (2008): 4447-4454.
16. Thigpen AE., et al. “Tissue distribution and ontogeny of steroid 5 alpha-reductase isozyme expression”. Journal of Clinical Investigation 2 (1993): 903-910.
17. Madersbacher S., et al. “Pathophysiology of Benign Prostatic Hyperplasia and Benign Prostatic Enlargement: A Mini-Review”. Gerontology5 (2019): 458-464.
18. Ding Y., et al. “Discovery and development of natural product oridonin-inspired anticancer agents”. European Journal of Medicinal Chemistry 122 (2016): 102-117.
19. Trapani G., et al. “A rapid method for obtaining finasteride, a 5α-reductase inhibitor, from commercial tablets”. Brain Research Protocols 2 (2002): 130-134.
20. Pérez-Ornelas V., et al. “New 5α-reductase inhibitors: In vitro and in vivo effects”. Steroids 3 (2005): 217-224.
21. Bratoeff E., et al. “Synthesis and biological activity of progesterone derivatives as 5α-reductase inhibitors, and their effect on hamster prostate weight”. Journal of Enzyme Inhibition and Medicinal Chemistry 3 (2010): 306-311.
22. Bratoeff E., et al. “17β-N-arylcarbamoylandrost-4-en-3-one Derivatives as Inhibitors of the Enzymes 3α-Hydroxysteroid Dehydrogenase and 5α-Reductase”. Current Enzyme Inhibition 1 (2018): 36-50.
23. Cabeza M., et al. “Effect of Pregnenolone Derivatives on the Selective Inhibition of 5α-Reductase 2 Activity”. Current Enzyme Inhibition 3 (2019): 179-189.
24. Cabeza M., et al. “New progesterone derivatives as inhibitors of 5α-reductase enzyme and prostate cancer cell growth”. Journal of Enzyme Inhibition and Medicinal Chemistry 4 (2006): 371-378.
25. Cabeza M., et al. “Recent Advances in Drug Design and Drug Discovery for Androgen-Dependent Diseases”. Current Medicinal Chemistry 8 (2016): 792-815.
26. Segel I. “Enzyme kinetics. Behavior and analysis of rapid equilibrium and steady-state enzyme systems”. John Wiley and Sons, INC. New York (1993).
27. Lineweaver H and Burk D. “The Determination of Enzyme Dissociation Constants”. Journal of the American Chemical Society 3 (1934): 658-666.
28. Faller B., et al. “Finasteride: A slow-binding 5α-reductase inhibitor”. Biochemistry21 (1993): 5705-5710.
29. Sanders DJ., et al. “The safety evaluation of phytosterol esters. Part 6. The comparative absorption and tissue distribution of phytosterols in the rat”. Food and Chemical Toxicology 6 (2000): 485-491.
30. Ritschel WA., et al. “Pharmacokinetics and bioavailability of β-sitosterol in the beagle dog”. Arzneimittelforschung 4 (1990): 463-468.
31. Guengerich FP and Yoshimoto FK. “Formation and Cleavage of C-C Bonds by Enzymatic Oxidation-Reduction Reactions”. Chemical Reviews 14 (2018): 6573-6655.
32. Arellano Y., et al. “New ester derivatives of dehydroepiandrosterone as 5α-reductase inhibitors”. Steroids 12 (2011): 1241-1246.
33. merck.com/product/patent/home.html