Fresh leaves of stinging nettle contain acetyl choline, serotonin and histamine and have anti-inflammatory and analgesic properties. Caffeoyl acid inhibits leukotriene synthesis related to 5-lipoxigenase in vitro. In animals, anesthetic and local analgesic effect, and in various studies, an anti-rheumatoid and joint anti-inflammatory effect has been demonstrated.(1) The flowering aerial parts and fresh or dried leaves of various species of nettle (Urtica dioica, Urtica urens), their hybrids or combinations have been recommended for symptomatic treatment of rheumatoid arthritis or osteoarthritis and for induction of diuresis, for instance in infections of the urinary system.
In an in vitro study, the ability of the extract of stinging nettle leaves and it main phenolic compound, caffeic malic acid, in inhibition of biosynthesis of metabolites of arachidonic acid was studied and the extract of stinging nettle leaves dose-dependently inhibited the reactions derived from cyclooxygenase, and the phenolic acid isolated from the extract dose-dependently inhibited the synthesis of B4 leukotriene. This study demonstrated that the anti-inflammatory properties of stinging nettle are due to its enzymatic effects on more than one path. In an open study on 40 patients with acute knee pain due to osteoarthritis, rheumatoid arthritis or gout, stinging nettle leaf extract had synergistic effect with diclofenac.
In another 3-week open study on 1528 patients with arthritis (most patients) or rheumatoid arthritis, administration of stinging nettle leaf extract resulted in significant improvement in the symptoms of patients with one drug regimens and multi-drug regimens with other Non-Steroidal Anti-inflammatory Drugs (NSAIDS). The studied parameters for the evaluation of the efficacy of the treatment included: pain at rest, pain in movement and limitation of movement. After 3 weeks of taking 770 mg stinging nettle leaf extract twice per day, 50% reduction in use of NSAIDS was reported in the multi-drug regimen. 29% of the patients in this group did not manage to reduce the concomitant dose of NSAID. The average reduction in the score for symptoms in the one-drug regimen group was 45% and 42% in the multi-drug regimen group. In terms of efficacy, no significant difference was observed between the two groups. Generally, pain at rest decreased 52%, pain in movement decreased 44% and limitation in movement in 37% of the patients. 75% of physicians and patients reported the outcomes of treatment with stinging nettle as very good and/or good. 5 patients in the one-drug regimen group and 5 patients in the multi-regimen group reported gastrointestinal discomfort. Also, 6 patients reported allergic reactions (mostly of dermatological nature) and 3 patients an increase in diuresis.
Due to existence of high concentrations of flavonoids and caffeic acid derivatives, which are found in abundance in the lipophilic fraction of stinging nettle, in in vitro pharmacological studies, animal studies and in comparison with diclofenac, anti-inflammatory, antioxidant and analgesic properties of this plant have been demonstrated. Presence of high proportions of potassium-sodium in the extract of stinging nettle might explain the diuretic effects of this plant.