Chemical Constituents of Stinging Nettle

Numerous analyses of nettle have revealed the presence of more than fifty different chemical constituents. The roots of stinging nettle have been studied extensively and found to contain starch, gum, albumen, sugar, and two resins. Histamine, acetylcholine, choline, and serotonin are also present. In addition, oleanol acid, sterols and steryl glycosides (including 3-beta-sitosterin), scopoletin (a coumarin), secoisolariciresinol, and neo-olivil (both lignans), and homovanillyl alcohol have been found. An immunologically active polysaccharide fraction was isolated which yielded neutral sugar, protein, and uronic acid. Methalonic extract of the roots were investigated for their inhibitory effect in aromatase, a key enzyme in steroid hormone metabolism. Many active constituents such as phytosterols, pentacyclin triterpenes, coumarins, ceramides, and hydroxyl fatty acids have been isolated from the lipophilic fraction, the compounds having an affiliation for lipids. Six isolectins, collectively referred to as U. dioica agglutinin (UDA), and some polysaccharides were isolated from the hydrophilic fraction (compounds that dissolve or mix with water), and are considered to be very important pharmacological findings.

Fresh nettle leaves contain a similar range of constituents, with smaller amounts of plant sterols, but proportionally higher levels of flavonol glycosides such as quercitin, and carbonic and formic acid. Many carotenoids have been found such as beta-carotene, violaxanthin, xanthophylls, zeaxanthin, luteoxanthin, and lutein epoxide. In a study done by Kavalali and Akcasu in 1983, an anti-coagulant was isolated from nettle leaves. Terpene diols, terpene diol glucosides, and alpha-tocopherol were also detected. Five new monoterpenoid components were found, as well as 18 phenolic compounds and eight lignans, some of which were previously unknown. In relatively recent studies done by Weglarz and Roslon in 2000 and 2001, the content of polyphenolic acids both in the leaves and rhizomes was found to be higher in the male form of the plant than the female form, but the chemical composition of the female polyphenolic acids were much more complex. An acetylcholine synthesizing enzyme, choline acetyl-transferase, was found, and it appears that Urtica dioica is the only plant to have this enzyme.

Stinging nettle is a powerhouse of nutrients. It contains on average 22% protein, 4% fats, 37% non-nitrogen extracts, 9-21% fiber, and 19-29% ash. The leaves contain about 4.8 mg chlorophyll per gram of dry leaves, depending on whether the plant was grown in the sun or shade. Surprisingly, more chlorophyll and carotenoids are found in plants that have been grown in the shade. The dried leaf of nettle contains 40% protein. They are one of the highest known sources of protein in a leafy green, and of superior quality than many other green leafy vegetables, The fresh leaves contain vitamins A, C, D, E, F, K, P, and b-complexes as well as thiamin, riboflavin, niacin, and vitamin B-6, all of which were found in high levels, and act as antioxidants.    The leaves are also noted for their particularly high content of the metals selenium, zinc, iron, and magnesium. They contain boron, sodium, iodine, chromium, copper, and sulfur. They also contain tannic and gallic acids, gum, and wax. Sixteen free amino acids have been found in the leaves, as well as high silicon levels in the leaves, stems and roots. Amino acids in dehydrated nettle meal are nutritionally superior to those of alfalfa meal.

Samples of dried flowers have been analyzed for nutrient content. They were found to be rich in alpha-tocopherol, riboflavin, iron, zinc, calcium, phosphorous, and potassium. However, the analyses indicated that as a result of the drying and storage process, total loss of vitamin C and a substantial loss of beta-carotene had been incurred.

The hairs contain an acrid fluid. The active principles of this fluid are thought to be acetylcholine, histamine, and formic acid. Formic acid is the same acid that ants have in their saliva glands. Other chemicals found in the hairs are silica, serotonin, and 5-hydroxy tryptamine. Many of these chemicals are smooth muscle stimulants. U. dioica contains a high level of UDA acetylcholine in both the fresh hairs and leaves.

There are few studies of the seeds, but those that have been done have found linoleic acid and linolenic acid as well as vitamins C, E, and B6, thiamin, riboflavin, niacin, iron, zinc, copper, calcium, phosphorous, magnesium, manganese, sodium, potassium, and selenium.

UDA, the six isolectins previously mentioned, are found in the rhizomes, roots, and seeds, but not in the leaves and stems. These lectins differ from all the other plant lectins due to its molecular structure. It was shown to possess both antifungal and insecticidal activity and to act synergistically with chitinase in inhibiting fungal growth. It was also shown to directly inhibit cell proliferation and block the binding of epidermal growth factor to its receptor on a tumor cell line.   It is a potent and selective inhibitor of the HIV virus and shows anti-prostatic activity by interfering with sex-hormone binding globulin (SHBG). Nettle influences hormones through its wealth of lipids including triglycerides, fatty acids, tocopherols, sterols, and galactosyldiglycerides.