by Gregory Kelly



My first encounter with stinging nettle was on a hike in San Diego County in the summer of 1989. At that point in my beginning steps of self-education (I was a newcomer to herbs and herbal medicine in 1989), I was inclined to touch and examine every new plant I encountered. For those of you familiar with stinging nettles, I am sure you have already guessed that I was in for quite a shock that day. Yes, I discovered that stinging nettle's do sting!.

For those of you who have never seen a stinging nettle plant, the stem is covered with fine hair-like protrusions. When they are touched, watch out. They release a burning fluid made of histamine and formic acid. It is believed that the histamine is responsible for the immediate stinging sensation (very much like a bee sting for those of you lucky enough to have not been as silly as I was). The sting ultimately produces a temporary inflamed and irritated welt. Ironically, the juice from the stinging nettle acts as an antidote to the sting when applied topically (I wish I had known this in 1989).

Today both the root and leaves of stinging nettle are used in the supplement industry; however, many traditional cultures used nettles topically to stimulate paralyzed muscles or to provide temporary relief from rheumatic pains.

While the leaf and root overlap a bit in their activities (especially in the area of balancing immune messenger molecules), each of these parts of the plant have some unique actions.

Pharmacology

Stinging nettle contains formic acid, a high proportion of chlorophyll, flavonoids, plant sterols, plant enzymes, a wide range of minerals, and plant lignans. Stinging nettle also contains a small-molecular-weight lectin (Urtica dioica agglutinin (UDA)) purified from the rhizomes (roots), which exhibits antiviral activity and is capable favorably inducing a balanced immune response. This lectin is an example of a "good" lectin. It is probably a major reason for the plant's cytokine (immune messenger molecules) balancing activity. Choline acetyltransferase has been demonstrated in stinging nettle plants, as well as, choline, acetylcholine and serotonin.(1) Since these components of the plant are critical for nervous system health and neurotransmitter balance, this plant might have some usefulness as added nutrition in neurological disorders. However, to date this aspect of the plant has not been explored.

Actions

Anti-inflammatory

Stinging nettle demonstrates anti-inflammatory activity in experimental situations. The extract partially inhibits the activity of 5-lipoxygenase and shows a concentration dependent inhibition of the synthesis of cyclooxygenase derived reactions.(2) (Note: these are the same enzymes that aspirin inhibits). A new class of drugs (called Cox2 inhibitors) aimed specifically at modulating cyclooxygenase enzymes is one of the new darling in the pharmaceutical industry.

Stinging nettle (both the leaf and root) also appears to prevent the over stimulation of proinflammatory cytokines like tumor necrosis factor-alpha and interleukin-1 beta. Cytokines can be thought of in simple terms as immune system messengers. And while a discussion of these proinflammatory cytokines and immune system balance is beyond the scope of this column, cytokine balance is a growing area of interest in medicine. In fact, virtually all immune disorders (from HIV, to cancer, to autoimmune diseases), allergic conditions (like asthma and allergies) and even obesity/insulin resistance have characteristic imbalances in cytokine levels as part of the functional derangement occurring at a metabolic level.

Between the lipoxygenase, cyclooxygenase, and cytokine modulating activities of this plant, stinging nettle is literally a treasure chest of unexplored potential.

Anti-viral and Immune Balancing

UDA Superantigen Stinging nettle actually contains a "super lectin" called UDA superantigen (UDA for short). For those interested, UDA appears to be an N-acetylglucosamine specific lectin. Evidence indicates that this super lectin can inhibit a range of viruses including those responsible for HIV, colds, and influenza.(4)

UDA is also T-cell mitogen, distinguishable from classical T-cell lectin mitogens, by its ability to discriminate a particular population of CD4+ and CD8+ T-cells, as well as its capacity to induce an original pattern of T-cell activation and cytokine production.(5) Basically, what this means is that unlike most things that stimulate the immune system only toward greater activity, the super lectin in stinging nettles appears to stimulate the immune system to be in balance.(6)

While studies in humans are lacking (and would be extremely desirable), the UDA super lectin has been shown to prevent the progression of experimentally induced systemic lupus erythematosus-like pathology in mice. In the experiment, UDA-lectin treated animals did not develop overt clinical signs of lupus and nephritis (kidney disease). UDA was also shown to alter the production of autoantibodies in a sex-dependent manner.(14)

Allergic Rhinitis

The leaf of stinging nettle was investigated for allergies (the root is typically not used for this application). Sixty-nine individuals completed a double-blind randomized study comparing the effects of a freeze-dried preparation of stinging nettle with placebo on allergic rhinitis. Efficacy with stinging nettle was rated higher than placebo in global assessments and slightly higher than placebo when comparing diary data.(7) While the overall improvement in this study was not mind-boggling, I have had many patients who have felt benefits from taking this as a dietary supplement during allergy season.

Benign Prostatic Hypertrophy

Extracts of the root of stinging nettle are approved for the treatment of prostatic diseases in Germany. In the U.S., the roots are classified as a dietary supplement. Experimental evidence suggests that some constituent in the roots (maybe the UDA super lectin or the plant sterols or some combination of all the ingredients) inhibit the membrane sodium- and potassium-ATPase activity of the prostate, which may subsequently suppress prostate-cell metabolism and growth.(8) Since BPH is characterized by cells that have grown to large (the "H" in BPH stands for hyperplasia which translates in simple terms as enlarged cells), this ability to limit the growth and metabolism of prostate cells would seem to be of obvious importance.

Aqueous extracts from the root are also capable of inhibiting the binding of sex hormone binding globulin (SHBG) to its receptors on human prostatic membranes, in a dose-dependent manner.(9) It is believed that the lignans found in the root are responsible for inhibiting the binding of SHBG with receptors.(10) The net effect of this anti SHBG activity is a positive influence on testosterone metabolism. Testosterone is also metabolized by enzymes called aromatase and 5-alpha-reductase. Prostate enlargement is characterized by elevated testosterone levels (specifically elevated levels of the enzymes involved in testosterone metabolism), and stinging nettle is thought to lower the activity of one or both of these enzymes (probably aromatase).

In German research, the combined use of extracts of stinging nettle root and saw palmetto has shown efficacy in the treatment of benign prostatic hyperplasia. A before-and-after comparison revealed an improvement in the pathological findings and in the obstructive and irritative symptoms. For the most part, the efficacy and tolerability of the preparation was assessed as very good" or "good".(11) When an extract combining stinging nettle and saw palmetto was compared to Finasteride in patients suffering from benign prostatic hyperplasia, similar improvements in measured parameters were observed; however, in terms of safety, fewer reports of diminished ejaculation volume, erectile dysfunction and headache were reported in the patients utilizing the herbal combination.(12) A combination of stinging nettle and Pygeum (an African plant) has also demonstrated efficacy in benign prostatic hyperplasia. Urine flow, residual urine, and night time urination were significantly improved by treatment.(13)

Side Effects

Nettle root taken orally can occasionally result in mild GI complaints and a burning sensation of the skin. Occasionally swelling of the skin (fluid retention and diminished volume of urine as compared with the amount of fluid consumed are observed subsequent to the use of root preparations. Allergic reactions to the leaf (edema and skin reactions) have been reported in rare cases. In case of any of these side effects, it is recommended that the stinging nettle product be discontinued. In both cases, reports of side effects have been exceedingly rare.



North American Pharmacal produces 2 different Urtica dioica preparations:

UDA PLUS: The rhizome (root) preparation

URTICA DIOICA: The leaf portion of the plant



References

1. Smallman BN, Maneckjee A. The synthesis of acetylcholine by plants. Biochem J 1981;194:361-364.

2. Obertreis B, Giller K, Teucher T, et al. Anti-inflammatory effect of Urtica dioica folia extract in comparison to caffeic malic acid. Arzneimittelforschung 1996;46:52-56. [Article in German]

3. Obertreis B, Ruttkowski T, Teucher T, et al. Ex-vivo in-vitro inhibition of lipopolysaccharide stimulated tumor necrosis factor-alpha and interleukin-1 beta secretion in human whole blood by extractum urticae dioicae foliorum. Arzneimittelforschung 1996;46:389-394.

4. Balzarini J, Neyts J, Schols D, et al. The mannose-specific plant lectins from Cymbidium hybrid and Epipactis helleborine and the (N-acetylglucosamine)n-specific plant lectin from Urtica dioica are potent and selective inhibitors of human immunodeficiency virus and cytomegalovirus replication in vitro. Antiviral Res 1992;18:191-207.

5. Galelli A, Truffa-Bachi P. Urtica dioica agglutinin. A superantigenic lectin from stinging nettle rhizome. J Immunol 1993;151:1821-1831.

6. Galelli A, Delcourt M, Wagner MC, et al. Selective expansion followed by profound deletion of mature V beta 8.3+ T cells in vivo after exposure to the superantigenic lectin Urtica dioica agglutinin. J Immunol 1995;154:2600-2611.

7. Mittman P. Randomized, double-blind study of freeze-dried Urtica dioica in the treatment of allergic rhinitis. Planta Med 1990;56:44-47.

8. Hirano T, Homma M, Oka K. Effects of stinging nettle root extracts and their steroidal components on the Na+,K(+)-ATPase of the benign prostatic hyperplasia. Planta Med 1994;60:30-33.

9. Hryb DJ, Khan MS, Romas NA, Rosner W. The effect of extracts of the roots of the stinging nettle (Urtica dioica) on the interaction of SHBG with its receptor on human prostatic membranes. Planta Med 1995;61:31-32.

10. Schottner M, Gansser D, Spiteller G. Lignans from the roots of Urtica dioica and their metabolites bind to human sex hormone binding globulin. Planta Med 1997;63:529-532.

11. Schneider HJ, Honold E, Masuhr T. Treatment of benign prostatic hyperplasia. Results of a treatment study with the phytogenic combination of Sabal extract WS 1473 and Urtica extract WS 1031 in urologic specialty practices. Fortschr Med 1995;113:37-40. [Article in German]

12. Sokeland J, Albrecht J. Combination of Sabal and Urtica extract vs. finasteride in benign prostatic hyperplasia (Aiken stages I to II). Comparison of therapeutic effectiveness in a one year double-blind study. Urologe A 1997;36:327-333. [Article in German]

13. Krzeski T, Kazon M, Borkowski A, et al. Combined extracts of Urtica dioica and Pygeum africanum in the treatment of benign prostatic hyperplasia: double-blind comparison of two doses. Clin Ther 1993;15:1011-1020.

14. Musette P, Galelli A, Chabre H, Callard P, Peumans W, et al. Urtica dioica agglutinin, a V beta 8.3-specific superantigen, prevents the development of the systemic lupus erythematosus-like pathology of MRL lpr/lpr mice. Eur J Immunol 1996;26:1707-1711.