Benign Prostatic Hyperplasia (BPH) is the most prevalent disorder affecting elderly men, which manifests itself as obstructive and irritative symptoms. 50-80% of men over 50 years suffer from symptoms of BPH. Use of medicinal plants is very common for treatment of these symptoms and stinging nettle is the most famous of these plants.
Root of stinging nettle contains a combination of substances soluble in water and in alcohol including lectins, phenols, sterols and lignins. Use of stinging nettle root for prostate and irritable bladder complaints has been approved by Comission E. Based on the views of this commission, stinging nettle root reduces residual urine and increases urine flow. Products made with stinging nettle root have been used to treat the voiding symptoms in stage I and II (Alken, 1973) or II and III (Anonymous, 2003; Vahlensieck & Fabricius, 1996) of BPH and result in alleviation of symptoms caused by hyperplasia of prostate.
Pharmacological Properties: in vitro studies
- Reaction with Sex Hormone Binding Globulin (SHBG): Aqueous extract of stinging nettle root dose-dependently blocks the binding of this substance to the membrane receptors of the prostate. Polar ligands, like secoisolariciresinol interfere with the binding of SHBG to steroids. Suggested mechanisms include: 1- alteration in the blood levels of free (active) steroidal hormones by their displacement from their binding spots to SHBG; 2- Prevention of interaction between prostate receptors with SHBG.
- Reaction with aromatase enzyme: Strong evidence exists with regard to the intervention of stinging nettle extract in the conversion of testosterone to estrogen. In vitro, ethanol extract of stinging nettle root inhibits the aromatization of androstenedione, in which the lipophilic fraction of the extract seem to be involved.
- Reaction with 5α-Reductase: only large sums of methanolic extract of stinging nettle root have resulted in inhibition of 5α-reductase.
- Anti-inflammatory properties: inhibition of elastase in human leucocytes signifies anti-inflammatory properties. Ethanolic extract of stinging nettle root has shown to inhibit leucocyte elastase in cows. Also, methanolic extract and polysaccharide substances of stinging nettle root inhibit the alternative pathway of the complement system.
- Impact on cell growth in prostate: stinging nettle root extract might suppress the growth and metabolism of prostate cells by reaction with steroidal membrane receptors in prostate. Steroidal compounds present in raw extract of stinging nettle root accelerate the movement of macrophages to their target and aid the anti-inflammatory effects of the drug. Furthermore, steroids inhibit the function of Na+K+ATPase enzyme and therefore inhibit the metabolism and growth of prostate cells.
Pharmacological Properties: in vivo studies
- Anti-inflammatory properties: the effect of the oral extract of the root of stinging nettle root and its constituents (especially polysaccharides) on rat paw edema induced by carrageenan has been studied and a potential anti-inflammatory effect has been demonstrated. However, it still needs to be demonstrated whether or not this effect is related to the effects of stinging nettle on the prostate or not.
- Impact on prostate cell growth: in dogs, treatment with stinging nettle root for 100 days has reduced the size of prostate and serum levels of testosterone.
Pharmacological Studies in Human
- Impact on sex hormones: in two placebo-controlled, double-blind studies, in the course of treatment with extract of stinging nettle root (1200 mg/day), a reduction in SHBG was observed. Nonetheless, Fischer and Wilbert (1992) observed a 10% increase in testosterone concentration, 5α-reductase and estradiol over a treatment course of 7 months. In a non-controlled open study, it has been demonstrated that estradiol and estrone are more involved in the mechanism of action of stinging nettle root than testosterone and DHT.
- Impact on prostate cell growth: After treatment with stinging nettle extract (600 mg per day), histological changes in prostate cells were observed. After 9 weeks, the changes presented themselves as death of glandular cells, and reactive inflammation (Streber, 1986). After 20 weeks of treatment with a dose of 1200 mg per day, changes were reported as reduction in cellular metabolism (Ziegler, 1982).
- The first case report regarding the positive effects of a tisane made with the root of stinging nettle goes back to Rückle (1950), in which the diuretic properties of the plant as an adverse effect attracted some attention. in 34 clinical trials, about 40,000 men suffering BPH have been treated with various products containing stinging nettle root.(2)
- In a placebo-controlled clinical trial including 79 patients suffering BHP, extract of stinging nettle root (600 mg per day, 5:1 extract for 6-8 weeks) was superior to the placebo in all measured parameters (urine flow, volume and residual urine). In another similar clinical trial, 50 patients with stage I and II BPH, who were administered extract of stinging nettle root (600 mg per day, 5:1 extract for 9 weeks), showed considerable reduction in SHBG (p<0.0005) and considerable correction of urine volume and maximum urinary flow rate.
To determine the therapeutic effect of stinging nettle for symptomatic improvement of secondary Lower Urinary Tract Symptoms (LUTS) to BPH, in a comparative, placebo-controlled, cross-sectional, randomized, double-blind clinical trial, 620 patients were studied for 6 months with regard to their International Prostate Symptom Score (IPSS), maximum urinary flow rate (Qmax), post-void residual (PVR) urine volume, Prostate-Specific Antigen (PSA), testosterone level and prostate mass. At the end of 6 months, the patients who had taken placebo began to take stinging nettle and both groups continued their treatment for another 18 months. 558 patients finished the study. At the end of the 6-month trial, using intention-to-treat analysis, in comparison to the 16% in the placebo group, 81% of the patients in the stinging nettle group showed improvement in LUTS (p<0.001). In the case of IPSS and Qmax, the improvement with the drug was greater than that of placebo. IPSS in the stinging nettle group shifted from 19.8 to 11.8 and in the placebo group from 19.2 to 17.7 (p=0.002). The maximum urinary flow rate improved 3.4 ml/s in the placebo group and 8.2 ml/s in the medication group (p<0.05). In the stinging nettle group, PVR dropped from the primary level of 73 ml to 36 ml (p<0.05), but no considerable change was observed in the placebo group. In both groups, PSA and testosterone levels remained unchanged. At the end of the study, using transrectal ultrasonography (TRUS), a mild reduction in prostate size was observed in the stinging nettle group (from the initial 40.1 cc to 36.3 cc, p<0.001), but in the placebo group no change in the size of the prostate was observed. In the 18th month follow-up, only those patients who had continued their treatment showed desirable levels of clinical parameters. In both groups no adverse reaction was observed. The researchers came to the conclusion that stinging nettle has positive effects in symptomatic treatment of BPH.