Nettle leaf extract (Urtica dioica)

Traditional Indications

Nettle is astringent, haemostatic, dermatological agent, mild diuretic, tonic; extracts are reported to have hypoglycaemic properties. Nettle is also a natural anti-histamine. It is indicated for rheumatic conditions, uterine haemorrhage, cutaneous eruptions, infantile and psychogenic eczema, epistaxis, melaena. Nettle is specifically indicated in nervous eczema.
Nettles are rich in vitamins A, C, D, iron, potassium, manganese, and calcium and chlorophyll making nettle an excellent blood tonic and remedy in anaemia and other debilitated states. They strengthen and support the whole body. Throughout Europe they are used as a spring tonic and general detoxifying remedy. They are specific for rheumatism, arthritis and eczema especially associated with blood deficiency. The herb has an important effect on the kidney and on fluid and uric acid excretion, so is of benefit in gout and other arthritic conditions, particularly if there is an element of anaemia. Urtica is also of benefit in chronic skin conditions such as eczema, helping to cleanse the body of accumulated toxins (1).

Pharmacognosy

Nettle leaf is a potent anti-inflammatory (2). A nettle leaf extract shows in vitro inhibition of several key inflammatory events that cause the symptoms of seasonal allergies including antagonist and negative agonist activity against the Histamine-1 (H(1)) receptor and the inhibition of mast cell tryptase preventing degranulation and release of a host of pro-inflammatory mediators that cause the symptoms of hay fevers. The nettle extract also inhibits prostaglandin formation through inhibition of Cyclooxygenase-1 (COX-1), Cyclooxygenase-2 (COX-2), and Hematopoietic Prostaglandin D(2) synthase (HPGDS), central enzymes in pro-inflammatory pathways (3).
Nettle root is a natural 5α-reductase inhibitor and acts like the drug Finasteride. 5α-reductase inhibitors, also known as dihydrotestosterone blockers, are a class of medications with antiandrogenic effects which are used primarily in the treatment of enlarged prostate and scalp hair loss (4). A study investigating the inhibitory effects on aromatase of stinging nettle root extract found that the compounds secoisolariciresinol, oleanolic and ursolic acid, (9Z,11E)-13-hydroxy-9,11-octadecadienoic acid, and 14-octacosanol displayed weak to moderate activity (5).

Animal and human studies conclude nettle root extract could prevent from some of prostatic hyperplasia effect in some benign prostatic hyperplasia (6). A prospective, randomised, double-blind, placebo-controlled, crossover study looking at Urtica dioica for treatment of benign prostatic hyperplasia concluded that Urtica dioica has beneficial effects in the treatment of symptomatic BPH (7).

Nettle is exceptionally high in quercetin 3-O-rhamnosylglucoside (rutin) and 3-O-glucoside (isoquercetin) (8). The flavonoid quercetin is a powerful antioxidant, anti-inflammatory, and antihistamine (antiallergic). Quercetin is found in many plants, including citrus, berries, leafy vegetables, herbs, spices, legumes, tea, and cocoa. Nettle leaf extract (Urtica dioica) has many phytochemicals however is particularly rich in the flavonoid quercetin (9).

The angiotensin-converting enzyme 2 (ACE2) is the host functional receptor for the new virus SARS-CoV-2 causing coronavirus Disease 2019 (COVID-19/C-19) (10). Additionally SARS-CoV-2 proteases, the Mpro/3CLpro and papain-like protease (PLpro) are promising targets for antiviral drug development (11). Quercetin has been shown to be a more a potent inhibitors of COVID-19 Mpro/3CLpro and ACE2 than hydroxychloroquine (12). A randomised double-blind study published in June 2021 on ClinicalTrials.gov seeks to explore the effectiveness of a quercetin supplement in the treatment of SARS-COV 2 (13).

1. PFAF. Urtica dioica. 2019.
2. Johnson TA, Sohn J, Inman WD, Bjeldanes LF, Rayburn K. Lipophilic stinging nettle extracts possess potent anti-inflammatory activity, are not cytotoxic and may be superior to traditional tinctures for treating inflammatory disorders. Phytomedicine : international journal of phytotherapy and phytopharmacology. 2013;20(2):143-7.
3. Roschek Jr B, Fink RC, McMichael M, Alberte RS. Nettle extract (Urtica dioica) affects key receptors and enzymes associated with allergic rhinitis. Phytotherapy Research. 2009;23(7):920-6.
4. Nahata A, Dixit VK. Ameliorative effects of stinging nettle (Urtica dioica) on testosterone-induced prostatic hyperplasia in rats. 2012;44(s1):396-409.
5. Gansser D, Spiteller G. Aromatase inhibitors from Urtica dioica roots. Planta Med. 1995;61(2):138-40.
6. Moradi HR, Erfani Majd N, Esmaeilzadeh S, Fatemi Tabatabaei SR. The histological and histometrical effects of Urtica dioica extract on rat's prostate hyperplasia. Veterinary research forum : an international quarterly journal. 2015;6(1):23-9.
7. Safarinejad MR. Urtica dioica for treatment of benign prostatic hyperplasia: a prospective, randomized, double-blind, placebo-controlled, crossover study. Journal of herbal pharmacotherapy. 2005;5(4):1-11.
8. Kregiel D, Pawlikowska E, Antolak H. Urtica spp.: Ordinary Plants with Extraordinary Properties. Molecules (Basel, Switzerland). 2018;23(7):1664.
9. Taheri Y, Quispe C, Herrera-Bravo J, Sharifi-Rad J, Ezzat SM, Merghany RM, et al. Urtica dioica-Derived Phytochemicals for Pharmacological and Therapeutic Applications. Evidence-based complementary and alternative medicine : eCAM. 2022;2022:4024331.
10. Medina-Enríquez MM, Lopez-León S, Carlos-Escalante JA, Aponte-Torres Z, Cuapio A, Wegman-Ostrosky T. ACE2: the molecular doorway to SARS-CoV-2. Cell & Bioscience. 2020;10(1):148.
11. Agrawal PK, Agrawal C, Blunden G. Naringenin as a Possible Candidate Against SARS-CoV-2 Infection and in the Pathogenesis of COVID-19. Natural product communications. 2021;16(12):1934578X211066723.
12. Sekiou O, Bouziane I, Bouslama Z, Djemel A. In-Silico Identification of Potent Inhibitors of COVID-19 Main Protease (Mpro) and Angiotensin Converting Enzyme 2 (ACE2) from Natural Products: Quercetin, Hispidulin, and Cirsimaritin Exhibited Better Potential Inhibition than Hydroxy-Chloroquine Against COVID-19 Main Protease Active Site and ACE22020.
13. ClinicalTrials.gov. Quercetin In The Treatment Of SARS-COV 2 (QUERCOV) Maryland, US: U.S. National Library of Medicine 2021 [Available from: https://clinicaltrials.gov/ct2/show/NCT04853199.