Andrea Cerutti
Davide Carratta
Introduction
Stinging nettle or common nettle, Urtica dioica, is a herbaceous perennial flowering plant, native to Europe, Asia, northen Africa, and North America and is the best-known member of the nettle genus Urtica. The plant has many hollow stinging hairs called trichomes on its leaves and stems, which act like hypodermic needles, injecting histamine and other chemicals that produce a stinging sensation when contacted by humans and other animals. The plant has a long history of use as a medicine and as a food source.
Figura 1. Urtica dioica
Composition
The trichomes of stinging are made of fine hollow needles of silica, being the hairs that do the stinging. The trichomes are so sharp that just a gentle brush of the back of the hand is sufficient for the trichomes to penetrate skin and inject a cocktail of substances. It is commonly thought that the compound which caused the pain was formic acid, but that is now known to be untrue. A mixture of six other substances which irritate the skin and cause inflammation, the effects of which can last a considerable time, is now thought to be involved.
Amongst this concoction are three mammalian neuro-transmitters, serotonin, histamine, and acetylcholine, but although all three are super-irritants, experimental injection under the skin does still not unleash the full sting effect of nettles.
Figura 2. Moroidin
The bicyclic octapeptide moroidin is also found in nettle stings, and it is this compound that is responsible for most of the pain and redness of nettle rash. It was first discovered in the trichomes of Laportea Moroides (hence the name), with which contact is a far more terrifying than is stinging nettle, for the painful rash can last for months, or even forever, and there is no cure. Moroidin has anti-mitotic activity because it strongly inhibits the polymerization of tubulin, meaning it interferes with cell division.
Both Leukotriene C4 and Leukotriene B4 are also found in nettle stings; these are also are constituents of snake venoms. Both histamine and the leukotrienes are naturally produced by the human body as part of the inflammatory response. The cysteinyl leukotrienes (such as LTC4, but not LTB4) are responsible both for the symptoms of asthma (especially the bronchial constriction) and for anaphylactic shock, both life-threatening conditions.
Medicinal uses
Arthritis
Nettle leaf is a herb that has a long tradition of use as an adjuvant remedy in the treatment of arthritis in Germany. Nettle leaf extract contains active compounds that reduce TNF-α and other inflammatory cytokines
Cytokine secretion in whole blood of healthy subjects following oral administration of Urtica dioica L. Plant extract, 1996
It has also been demonstrated that nettle leaf lowers TNF-α levels by potently inhibiting the genetic transcription factor that activates TNF-α and IL-1B in the synovial tissue that lines the joint.
Plant extracts from stinging nettle (Urtica dioica), an antirheumatic remedy, inhibit the proinflammatory transcription factor NF-kappaB, 1999
Urtication, or flogging with nettles, is the process of deliberately applying stinging nettles to the skin in order to provoke inflammation. An agent thus used is known as a rubefacient (something that causes redness). This is done as a folk remedy for rheumatism, providing temporary relief from pain. The counter-irritant action to which this is often attributed can be preserved by the preparation of an alcoholic tincture which can be applied as part of a topical preparation, but not as an infusion, which drastically reduces the irritant action.
Evidence for antirheumatic effectiveness of Herba Urticae dioicae in acute arthritis, 1997
Benign prostatic hyperplasia
Nettle root extracts have been extensively studied in human clinical trials as a treatment for symptoms of benign prostatic hyperplasia (BPH). These extracts have been shown to help to relieve symptoms compared to placebo both by themselves
Urtica dioica for treatment of benign prostatic hyperplasia: A prospective, randomized, double-blind, placebo-controlled, crossover study, 2005
and when combined with other herbal medicines.
Long-term efficacy and safety of a combination of sabal and urtica extract for lower urinary tract symptoms—a placebo-controlled, double-blind, multicenter trial, 2005
Aromatase is a key enzyme in steroid hormone metabolism. It is responsible for the conversion of androgens into estrogens. Estrogens appear to be involved in the etiology of benign prostatic hyperplasia (BPH). Therefore, inhibition of aromatase could improve prostate disorder.
Aromatase inhibitors from Urtica dioica roots, 1995
Because it contains 3,4-divanillyltetrahydrofuran, certain extracts of the nettle are used by bodybuilders in an effort to increase free testosterone by occupying sex-hormone binding globulin a glycoprotein that binds to sex hormones (androgens and estrogens).
Lignans from the roots of Urtica dioica and their metabolites bind to human sex hormone binding globulin (SHBG), 1997
Interaction of lignans with human sex hormone binding globulin (SHBG), 1997
Lignans interfering with 5 alpha-dihydrotestosterone binding to human sex hormone-binding globulin, 1998
Nettle is believed to be a galactagogue, a substance that promotes lactation, but no scientific studies have already been performed until now.
Other uses
Food
Stinging nettle can also be used as a dietary supplement. Some examples are shown below.
Urtica dioica has a flavour similar to spinach and cucumber when cooked and is rich in vitamins A, C, iron, potassium, manganese, zinc and calcium.
Herbal infusions as a source of calcium, magnesium, iron, zinc and copper in human nutrition, 2012
Young plants were harvested by native americans and used as a cooked plant in spring when other food plants were scarce. Soaking nettles in water or cooking will remove the stinging chemicals from the plant, which allows them to be handled and eaten without incidence of stinging.
After stinging nettle enters its flowering and seed setting stages the leaves develop gritty particles called cystoliths, which can irritate the urinary tract. In its peak season, stinging nettle contains up to 25% protein, dry weight, which is high for a leafy green vegetable. The young leaves are edible and make a very good pot-herb. The leaves are also dried and may then be used to make a tisane, as can also be done with the nettle's flowers.
Drink
Nettle leaves are steeped in a concentrated sugar solution so the flavour is extracted into the sugar solution. The leaves are then removed and a source of citric acid (usually lemon juice) is added to help preserve the cordial and add a tart flavor.
Treatments
Anti-itch drugs, usually in the form of creams containing antihistaminich or hydrocortisone may provide relief from the symptoms of being stung by nettles.
But due to the combination of chemicals involved other remedies may be required. Calamine lotion may be helpful. Many folk remedies exist for treating the itching including dandelion, horsetail (Equisetopsida spp.), leaf of dock (Rumex spp.), saliva, or sodium bicarbonate, oil and onions, and topical use of milk of magnesia. Lemon juice also works for treatment. Alternatively, one can simply ignore the stinging sensation and let it run its (harmless) course. Simply washing with water (immediately after stinging) also helps.
Recent studies
Some findings showed that the hydro alcoholic extract of nettle has increasing effects on TAC (Total Antioxidant Capacity) and SOD (Superoxidant Dismutase) in patients with type 2 diabetes without no changes in Malondialdehyde (MDA) and Glutathione Peroxidase (GPX) after eight weeks intervention.
The effect of hydro alcoholic nettle (Urtica dioica) extract on oxidative stress in patients with type 2 diabetes: a randomized double-blind clinical trial, 2012
It is also demostrated that hydro alcoholic extract of nettle has decreasing effects on IL-6 and hs-CRP in patients with type 2 diabetes after eight weeks intervention.
The effect of hydro alcoholic Nettle (Urtica dioica) extracts on insulin sensitivity and some inflammatory indicators in patients with type 2 diabetes: a randomized double-blind control trial, 2011.
Urtica dioica has a protective effect on the liver in hepatic ischemia‐reperfusion‐injured rats.
Effects of Urtica dioica on hepatic ischemia‐reperfusion injury in rats, 2010
A study provides, for the first time, a mechanistic understanding of the role of nettle extracts in reducing allergic and other inflammatory responses in vitro.
Nettle extract (Urtica dioica) affects key receptors and enzymes associated with allergic rhinitis, 2009.
