Steroidal 5-alpha-reductase

5alpha-reductase; 5alpha-reductase

Under the name Steroid-5alpha-Reductase (SRD5) or short 5-alpha-Reductases, there are 3 isoenzymes (the 5α-Reductase Type I, Type II and Type III), oxidoreductases that play an important role in vertebrates. These isozymes catalyze the conversion of the sex hormone testosterone into the biologically more effective dihydrotestosterone (DHT). The coding genes (SRD5A1, SRD5A2 and SRD5A3) are located on chromosomes 5 and 2.

Type I is mainly found in the CNS, epididymis and skin; type II in muscles, liver, kidneys, prostate and only to a very small extent in the skin; type III mainly in the brain, mammary glands, uterus, skin, ovaries, testes, prostate and various visceral organs (pancreas, spleen, kidneys, heart, stomach, liver).

A haplotype of SRD5A2 associated with increased 5α reductase activity has been shown in women at increased risk of polycystic ovarian syndrome.

A deficiency of type II - alpha-reductase can lead to hypospadias and intersexuality in the male fetus.

Inhibition of steroid_5α reductase (5α reductase inhibitors) leads to reduced production of dihydrotestosterone and allopregnanolone with beneficial effects in benign prostatic hyperplasia and androgenetic alopecia. Side effects include gynecomastia, depression, erectile dysfunction and loss of libido. The use of 5α reductase inhibitors in prostate cancer is controversial.

Indications for 5α reductase inhibitors are benign prostatic hyperplasia (BPH), pubertas praecox, hirsutism and androgenetic alopecia.

Various placebo-controlled therapy studies have shown that phytopharmaceuticals, especially the phytosterol-containing extracts from Hypoxis rooperi, or sabal and pumpkin seed extracts, also effectively inhibit 5α reductase.

1. Herman A et al (2016) Mechanism of action of herbs and their active constituents used in hair loss treatment. Fitoterapia 114:18-25.
2. Liu L et al. (2016) Effect of 5α-Reductase Inhibitors on Sexual Function: A Meta-Analysis and Systematic Review of Randomized Controlled Trials. J Sex Med 13:1297-310.
3. Shiota M et al (2016) Suppressed recurrent bladder cancer after androgen suppression with androgen-deprivation therapy or 5α-reductase inhibitor. J Urol doi: 10.1016/j.juro.2016.08.006.
4. Yin J et al(2016) Inhibitory Activities of Phenolic Compounds Isolated from Adina rubella Leaves Against 5α-Reductase Associated with Benign Prostatic Hypertrophy. Molecules doi:10.3390/molecules21070887.