An herb to forget - cat's claw - Uncaria tomentosa

Nutrition Forum, Sept-Oct, 1997 by Varro E. Tyler

There's a joke presently making the rounds about the woman who, not realizing that the herb cat's claw was so named for its long curving thorns, refused to take it because she was a vegetarian. Now science has come up with a far better reason for caution in consuming this ancient folkloric remedy derived from the tropical vine Uncaria tomentosa.

Commonly referred to by its Spanish name una de gato, the herb has been popularized in the United States in recent years by South American immigrants. Several books in the Spanish language recommend it for a wide variety of diseases and syndromes ranging from arthritis, cancer, and AIDS to hemorrhoids, acne, and PMS. The evidence of its utility is anecdotal. No substantial clinical studies of the efficacy of cat's claw for any condition have ever been published in peer-reviewed medical analysis, journals.

Trouble Signs

Recent studies have shown that there is a significant problem associated with the consumption of the plant that has been collected at random in the Peruvian jungle. It turns out that there are two kinds of Uncaria tomentosa that are distinguishable one from another only on the basis of their chemical constituents. Such plants which look alike but differ markedly in their composition are referred to as chemotypes (chemical types) or chemovars (chemical varieties).

The root of one chemotype of U. tomentosa contains quantities of several pentacyclic (5-ring) oxindole alkaloids, including pteropodine, speciophylline, and mitraphylline. Tests in small animals have shown that these compounds produced a number of effects which resulted in a general strengthening of the immune system. In other words, they helped the animals resist disease. Other animal tests showed acute toxicity to be low, and mutagenic activity was not detected.

The constituents of the other chemotype of U. tomentosa are quite different. It contains the tetracyclic (4-ring) oxindole alkaloids rhynchophylline and isorhynchophylline, which counteract the immunomodulating action of the pentacyclic alkaloids found in the other variety. They also exert negative chronotropic and inotropic activities, slowing and decreasing the force of the heartbeat. addition, they have a sedative effect which in chemical high doses depresses one respiration and produces ataxia (lack of muscular you. coordination).

Obviously, none of these activities is desirable, and the tetracyclic chemotype of cat's claw when mixed with the pentacyclic variety -- as is often the case in commercial samples -- will simply neutralize whatever beneficial effect the latter may have on the consumer's immune system. The admixture is apparently not detectable by either macroscopic or microscopic examination of the herb; it is readily observed by simple chromatographic techniques (HPLC or TLC). Yet these analytical procedures are not routinely carried out on cat's claw products in the American market.

Because the two varieties are not readily separated at the point of collection, it is difficult to prevent contamination of the potentially useful pentacyclic variety with at least some of the negative-acting tetracyclic one. Consequently, on practical grounds it is recommended that the content of the latter type oxindole alkaloids be limited to less than 0.02%.

Does it Work?

The jury is still out on the effectiveness of any type of cat's claw in stimulating the activity of the human immune system. We simply won't know its utility with any degree of accuracy until clinical trials have been conducted on a substantial number of subjects and the results published in peer-reviewed medical journals.

In the meantime, those wishing to use cat's claw are best advised to restrict consumption to products certified to be free (or at least not containing more than 0.02%) of tetracyclic oxindole alkaloids as determined by suitable analytical methods. Possibly at some future date, specific botanical characteristics will be found that will enable the two chemical varieties of Uncaria tomentosa to be distinguished in the field. That would greatly simplify collection of the proper variety. Until such time, the only assurance of possible immunomodulatory efficacy of cat's claw is to use products that have been identified unequivocally by suitable laboratory procedures.

Dr. Tyler is a Board Member of Nutrition Forum; a Distinguished Professor Emeritus of Pharmacognosy, Purdue University; and the author of The Honest Herbal, a classic in the field.