Stinging Nettle: Background. Actions

2010

Common Name

Stinging Nettle

Other Names

Common nettle, brenessel, brennesselkraut, brennesselwurzel, urtica ortie, great stinging nettle, haarnesselkraut, haarnesselwurzel

Botanical Name / Family

Urtica dioica and Urtica urens (family Urticaceae)

Plant Parts Used

Leaf and root

Chemical Components

Constituents found within the leaf include vitamins A and C, beta-carotene, calcium and potassium, phosphorus, chlorophyll, magnesium and tannins, flavonoids, sterols and amines (US Department of Agriculture 2003).

Constituents found chiefly in the root include polysaccharides, lectins, lignans, fatty acids, terpenes and coumarin.

Historical Note

Stinging nettle has been used since ancient times, with Dioscorides and Galen in ancient Greece reporting diuretic and laxative effects for nettle leaf. It is also widely used for gynaecological complaints by North American Indians and in Ayurvedic medicine in India. The Latin root of urtica is uro, meaning ‘I burn’, indicative of the small stings caused by the hairs on the leaves of nettle when contact is made with the skin.

Stinging Nettle: Main Actions

ANTI-INFLAMMATORY AND ANALGESIC

In vitro studies have identified anti-inflammatory activity for Urtica extract . The mechanism of action has not been fully elucidated, but test tube studies have demonstrated inhibitory effects on NF-kappa B activation and partial inhibitory effects on cyclo-oxygenase and 5-lipoxygenase derived reactions. Additionally, isolated phenolic acid from nettle has been shown to inhibit leukotriene B4 synthesis in a concentration-dependent manner in vitro.

Although extensive investigation has not been conducted in humans to confirm anti-inflammatory mechanisms, one study of 20 volunteers showed that oral ingestion of 1.34 g nettle extract for 3 weeks significantly decreased lipopolysaccharide stimulated TNF-alpha and IL-1-beta when tested ex vivo but had no effects on cytokine levels.

In vitro data has shown that nettle leaf extract (IDS 30) reduces the induction of primary T-cell responses and TNF-alpha in T-cell mediated diseases such as RA. Faecal IL-1 -beta and TNF-alpha concentrations were significantly reduced in mice with induced Crohn’s disease treated with IDS 30. Mice treated with nettle extract displayed fewer histological changes and general disease symptoms. The authors conclude that the effect may be due to a decrease in Th1 response and may constitute a new treatment option for prolonging remission in inflammatory bowel disease.

HYPOTENSIVE AND DIURETIC

When administered intravenously to test animals, Urtica extract exerts an acute hypotensive action accompanied by diuretic and natriuretic effects. It is uncertain whether the same effects are seen with oral administration.

A review of in vitro and in vivo studies concluded that the hypotensive action of U. dioica is due in part to negative inotropic activity and a vasodilatory effect.

HYPOGLYCAEMIC

A 33% reduction in blood glucose was noted in rats administered 250 mg/kg of nettle leaf extract orally, 30 minutes before glucose loading. Nettle was shown to decrease glucose absorption in the small intestine of rats under anaesthesia; however, 500 mg/kg failed to modify blood glucose levels in alloxan-induced diabetic rats.

A six-fold increase in blood insulin levels occurred after intravenous administration of a nettle leaf fraction in streptozotocin diabetic rats, with a corresponding drop in blood sugar levels as compared to control. Details of the isolated fraction were not given.

ANTIPROUFERATIVE EFFECTS ON PROSTATE CELLS

The exact mechanism of action of the antiproliferative effects of nettle extract on prostate cells has not been fully elucidated. Results from several in vitro studies suggest that several mechanisms are responsible.

Reduced prostate cell metabolism and growth may result from inhibition of membrane ATPase activity and decreased binding capacity of sex hormone binding globulin to its receptor on human prostatic membranes. Additionally, reduced 5-alpha dihydrotestosterone binding to proteins in humans has been demonstrated.

Prostate cancer

One study found that a methanolic extract of stinging nettle roots slows the progression of prostate cancer in both an in vivo model and an in vitro system. One study involving 20 males with prostatic adenoma found that treatment for 7 days with nettle produced a significant drop in zinc level, thought to be a result of altering zinc-testosterone metabolism and diminishing zinc secretion in adenomatous tissue.

ANTIVIRAL

A lectin extracted from nettle had inhibitory effects against HIV-1, HIV-2, human cytomegalovirus, respiratory syncytial virus and influenza A virus in vitro.

ANTIOXIDANT

Nettle has shown potent antioxidant activity in a range of in-vitro tests: 50, 100 and 250 µg inhibited peroxidation of linoleic acid by 39%, 66% and 98%, respectively, as compared to 30% inhibition demonstrated by 60 µg/mL of alpha-tocopherol.

In the same study, nettle was shown to scavenge free radicals, hydrogen peroxide and superoxide anion radicals and to chelate heavy metals. Ozen and Korkmaz (2003) reported that constituents from nettle can regulate glutathione reductase, glutathione peroxidase, superoxide dismutase and catalase in vivo.

The fixed oil of nettle has demonstrated strong antioxidant activity in mice treated with carbon tetrachloride, by decreasing lipid peroxidation and increasing antioxidant status. Nettle extract is significantly effective in preventing fibrosis in liver tissue from carbon tetrachloride damage in vivo. Dried nettle added to the diet of rats decreased cerebral free radicals after forced-swim tests.

Stinging Nettle: Other Actions

Nettle has a mild diuretic action (ESCOP 2003).