Cat's claw (Uncaria spp)

By the CAM-Cancer Collaboration | 07. Sep 2020

Abstract and key points
What is it?
Does it work?
Is it safe?
References
Photos: Mostphotos.com

                    Photo: Mostphotos.com

Description

Cat's claw or ‘Uña de Gato’ is a thick woody vine classified in the Rubiaceae family. For medicinal purposes, the stem bark or root from the species Uncaria tomentosa and U. guianensis are most commonly used. These have traditionally been used for allergies, asthma, wound healing, viral infections, fevers, arthritis, gastric ulcers, rheumatism, inflammation, contraception and menstrual irregularities. Uncaria tomentosa and U. guianensis contain over 60 different biologically active compounds that could be complementary and/or synergic in their actions.

Efficacy

Despite some positive preclinical data, there are no clinical trials investigating cat’s claw as a direct anticancer agent. There is not enough evidence for other outcomes. Only two clinical trials investigated the role of cat’s claw in alleviating the adverse effects of chemotherapy. While in the first trial cat’s claw was not effective in reducing the most prevalent adverse effects, the second trial reported reduce neutropenia caused by chemotherapy. One small uncontrolled trial suggests improvement of quality of life and fatigue but no effects on biochemical and inflammatory markers or tumour response. 

Safety

Cat’s claw seems well tolerated at normal clinical doses but larger doses have been reported to cause some abdominal pain or gastrointestinal problems, including diarrhoea. Historically cat's claw has been used as an immunostimulant as well as for its antifertility effects. It can also reduce platelet aggregation and could theoretically be an anticoagulant.

Citation

Wider B, CAM Cancer Collaboration. Cat's claw (Uncaria spp) [online document], Aug 31, 2020.

Document history

Assessed as up to date in August 2020 by Barbara Wider.

Assessed as up to date in January 2019 by Barbara Wider.
Revised in March 2017 by Barbara Wider.
Assessed as up to date in September 2014 by Barbara Wider.
Summary first published in February 2013, authored by Klara Rombauts and Italo M Cesari.

Description

Cat's claw or “Uña de Gato” is a thick woody vine (liana) belonging to the Rubiaceae family1,2.

Names

The plant, described by its Spanish common name “Uña de Gato”, derives its name from hook-like thorns that grow along the vine1. There are several species of cat’s claw but the two most common species used as a medicinal herb are U. tomentosa(Willd. DC.) and U. guianensis (Aubl, Gmel.). These species are indigenous to the Amazon rainforest and other tropical areas of South and Central America. Other common names include saventero, samento , vilcacora, etc.1,2.

Ingredients/components

Fifty-six compounds have been isolated from U. tomentosa and an additional eight from U. guianensis based on a search in Reaxys (an online search and retrieval system for chemical compounds, bibliographic data, and chemical reactions) in December 2012. Among the 56 compounds isolated from U. tomentosa, pharmacological activity has been demonstrated for 27. Among the eight compounds isolated from U. guianensis pharmacological activity has been demonstrated for six3-11. Characteristic phytochemicals belong to indole alkaloids (for instance, pentacyclic oxindoles such as pteropodine, isopteropodine, mytraphylline and tetracyclic oxindoles like rhyncophlline), triterpenes including quinovic acid and derivatives thereof, stigmasterol, sterols, flavonoids (procyanidins, catechins and flavonols, tannins), and low molecular weight carboxyl alkyl esters (CAEs).

Cat's claw is included in the United States Pharmacopeial Convention (USP) as a dietary supplement. In the pharmacopeia cat's claw consists of the inner bark of the stems of U. tomentosa (Willd.) DC. (Rubiaceae). It contains not less than 0.3% of pentacyclic oxindole alkaloids as isopteropodine, calculated on the dried basis, as the sum of speciophylline, uncarine F, mitraphylline, isomitraphylline, pteropodine and isopteropodine.

Application and dosage

In South America, about 20-30 g of the root or bark is prepared as a decoction in 1 litre of water for 20-30 minutes and the extract is consumed as tea. The dosage of a standard decoction for general health and maintenance is 0.5-1 cup of decoction once daily, up to three cups daily if necessary. Alcoholic extracts from the bark are also traditionally used12,13.

Nowadays cat's claw is available in many different forms: dried cut-and-sifted root and stem, powdered root and stem, encapsulated powdered material or lyophilized aqueous extracts, tinctures, tablets and other types extracts. Cat’s claw is also available in preparations for external uses (ointments, gels).

History and providers

Cat’s claw has been used as a sacred plant of healing for over 2,000 years. The priests of the Asháninka Indian tribe in Central Peru considered cat's claw to have great powers and health-improving properties and used the herb to ward off disease. This tribe has the longest recorded history of use of this plant. They are also the largest commercial source of cat's claw from Peru today13,14.

Alleged indications/claims of efficacy

Cat’s claw has been used traditionally as an anti-inflammatory, contraceptive, immunostimulant, cancer remedy and anti-viral5.

Mechanism of action

The wide range of biological/pharmacological effects of Uncaria spp preparations are due to the concomitant presence of numerous and differently bioactive chemical structures that could be complementary and/or synergic in their actions16. The pentacyclic oxindole alkaloids are immunostimulants and can be selectively cytostatic/cytotoxic to some cancer cells; they are considered biomarkers in alcoholic extracts of U. tomentosa; the tetracyclic oxindole alkaloids have effects on the cardiovascular system and DNA protection. Pentacyclic triterpenes are anti-microbial, anti-viral, and anti-inflammatory. Sterols appear to be anti-inflammatory only. Uncaria polyphenols (flavonoids) have strong antioxidant as well as antiviral, anti-allergic, anti-platelet, anti-inflammatory, and anti-tumour activities13,16,17.

The suppressive effects of some aqueous U. tomentosa extracts on tumour cell growth would appear to be mediated by the induction of apoptosis18,19. Moreover, U. tomentosa extracts are able to reduce the serum response of the proinflammatory cytokines TNF-α and IL-6, and to inhibit the nitric oxide production as well as the NF-κB activity20-24. Dreifuss et al.24, using an U. tomentosa hydroalcoholic extract in vivo, demonstrated that the anti-tumour activity could, at least partially, result from the ability of U. tomentosa to restore redox and metabolism homeostasis through downregulation of the NF-κB transcription factor and superoxide dismutase (SOD) activities.

Effects of cat’s claw have been shown in vitro in several cell lines of different tumour origins: breast29,33, lung28 and medullary thyroid carcinoma38 as well as in glioma32, neuroblastoma32, melanoma20,21, lymphoma and leukaemia cell lines30. Although some results were confirmed in vivo in mice (metastatic melanoma20,21 and Lewis lung carcinoma28), more research is still needed in animal models and humans before any conclusions can be drawn22,27,28,31.

Prevalence of use

There is no information available about the prevalence of use of cat’s claw worldwide but review papers describe it as one of the most popular herbs in the USA13-15. In a survey on the use of herbal supplements amongst 998 black breast cancer survivors 0.9% reported using cat’s claw37.

Legal issues

Cat's claw is not listed on the Food and Drug Administration’s Generally Regarded as Safe (GRAS) list15. It is widely available on the internet and in pharmacies.

Clinical trials

No controlled clinical trials investigating cat’s claw as an anticancer agent are available.

Two randomized clinical trials focusing on the reduction of side effects caused by chemotherapy are available25,26. Both trials using an ethanolic extract of cat’s claw were published by the same group. The treatment consisted of oral tablets containing 300 mg of U. tomentosa dried ethanolic extract on top of chemotherapy. The control group received chemotherapy only. In the first trial (n=43), in this population and at the dose used, cat’s claw dry extract was not effective in reducing the most prevalent adverse events caused by treatment with 5-fluorouracil and oxaliplatin in colorectal cancer patients25. In the second trial, cat’s claw was able to reduce neutropenia caused by a regimen consisting of fluorouracil, doxorubicin and cyclophosphamide and was also able to restore cellular DNA damage in the treatment of breast cancer. Cat’s claw showed no effect on antioxidant activity and on immune response. The dose of extract used in both trials was not tested in a dose-finding study but was based on the dose used in other (not cancer-related) clinical trials (discussed in the ‘Is it safe?’ section below (34-36)). Since these trials used an aqueous extract, different phytochemicals were extracted so there is no rationale to use this dose. It is unknown if the optimal dose was used in these trials.

One uncontrolled trial of 51 patients with advanced solid tumours assessed the effects of a 100mg dose of a dry extract of cat’s claw three times daily39. Some improvements in overall quality of life, social functioning and fatigue were reported. None of the biochemical or inflammatory parameters assessed changed significantly and no tumour response was detected.

Case series/studies

Although a large number of case reports are available on the internet, none have been published in peer-reviewed journals.

Adverse events

Three clinical trials with human volunteers showed no toxicity. The treatment of two trials consisted of a commercially available water extract of U. tomentosa called C-Med-100. In one trial the dose was 250 mg in one group and 350 mg in the other group, taken for 8 weeks; volunteers in the second trial used 2 x 350 mg daily for 2 months. In the third trial, patients with osteoarthritis of the knee were treated with freeze-dried U. guianensis34-36. The two trials in cancer patients discussed in the ‘Does it work?’ section above also showed no toxicity measured as liver enzyme and kidney function, or any adverse events25-26. Here an alcoholic extract was used instead of the aqueous extract in C-Med-100. It must be noted that both products contain different phytochemicals and can therefore not be compared.

Cat’s claw can cause diarrhoea or loose stools but symptoms tend to be mild and improve with continued use13-15.

Contraindications

Cat's claw has been traditionally used for its immunostimulant and antifertility effects14 and is contraindicated before or following any organ or bone-marrow transplant or skin graft, and also for women seeking to become pregnant. Theoretically, cat's claw can reduce platelet aggregation and have a anticoagulant effect so caution is warranted when taking anticoagulant drugs13-15.

Interactions

Owing to its purported immunostimulant effects, there might be interactions between cat’s claw and medications intended to suppress the immune system, such as cyclosporin or other medications prescribed following an organ transplant. These possible interactions still need to be proven scientifically however. Based on in vivo rat studies, cat's claw may protect against gastrointestinal damage associated with nonsteroidal anti-inflammatory drugs (NSAIDs) such as ibuprofen. Cat's claw may increase the effect of anticoagulants13-15.

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