Uncaria guianensis

Pentacyclic oxindole alkaloids (POAs) are considered the characteristic immunomodulatory principle of cat's claw, enhancing phagocytosis and modulating cytokine release. In U. guianensis they occur at lower concentrations than in U. tomentosa, and comparative studies found the anti-inflammatory activity of the plant to be largely independent of alkaloid content.

Tetracyclic oxindole alkaloids (TOAs) such as rhynchophylline have vasodilatory, antihypertensive and calcium-channel-blocking actions in experimental models. Their presence varies by chemotype and provenance.

Quinovic acid glycosides contribute to the anti-inflammatory and antiviral activity attributed to cat's claw and are among the compounds isolated from Uncaria bark.

Polyphenolic proanthocyanidins are potent antioxidants and scavengers of peroxynitrite and other reactive species. They are considered a principal driver of the antioxidant and anti-inflammatory effects of U. guianensis, which were shown to be more potent than U. tomentosa in some in vitro assays.

These glucoalkaloids are secondary constituents of the Uncaria genus with reported hypotensive and platelet-modulating activity in experimental studies.

Plant sterols and pentacyclic triterpenes contribute to anti-inflammatory and cytoprotective activity of the bark.

Traditionally, roughly 10-20 g of shredded inner bark is simmered in water for 30-60 minutes and taken as a bitter tea. Amazonian practitioners use the bark decoction for arthritis, gastrointestinal complaints and inflammation.

Freeze-dried aqueous extract capsules were used at 100 mg once daily in the osteoarthritis trial. Commercial 'cat's claw' products (often not distinguishing U. guianensis from U. tomentosa) are commonly standardized to oxindole alkaloid or polyphenol content.

Hydroalcoholic extracts are used in Western herbalism. Cat's claw is traditionally contraindicated in pregnancy and lactation (historical use as a contraceptive/abortifacient), and caution is advised in autoimmune disease, transplant recipients and before surgery.

Forty-five patients with knee osteoarthritis received freeze-dried U. guianensis extract (100 mg/day, 30 patients) or placebo (15 patients) for four weeks. Cat's claw reduced pain associated with activity, medical scores and patient assessment scores within the first week, while pain at rest and knee circumference were unchanged. The extract was well tolerated with no serious adverse events and no changes in serum ALT/AST. In vitro the species scavenged free radicals and inhibited TNF-alpha production.

Both cat's claw species scavenged DPPH radicals, inhibited lipopolysaccharide-induced TNF-alpha production and reduced nitrite/peroxynitrite formation. U. guianensis was in several assays more potent than U. tomentosa, and activity did not correlate with oxindole alkaloid content, implicating the polyphenolic fraction.

'Uña de gato' (cat's claw) has long been used by Amazonian peoples of Peru, Bolivia and neighbouring regions as a bark decoction for inflammation, joint pain, wounds and gastrointestinal and gynaecological complaints. U. guianensis is the species more commonly used in Brazilian and Guianan folk medicine, while U. tomentosa predominates in the Peruvian trade.

Cat's claw entered European and North American herbalism only in the 1970s-1990s, with Austrian and German researchers popularising Uncaria and distinguishing its oxindole-alkaloid chemotypes; it has no place in classical Old-World herbals.