Devil’s claw: Background. Actions

2010

Historical Note

The botanical name Harpagophytum means ‘hook plant’ in Greek, after the hook-covered fruits of the plant. Devil’s claw is native to southern Africa and has been used traditionally as a bitter tonic for digestive disturbances, febrile illnesses, allergic reactions and to relieve pain. It has been used in Europe for the treatment of rheumatic conditions for over 50 years, and was first cited in the literature by Zorn at the University of Jena, Germany, who described his observations on the antiphlogistic and anti-arthritic effects after administration of oral aqueous extracts prepared from the secondary roots of Harpagophytum procumbens in patients suffering from arthritides.

Common Names

Devil’s claw root, grapple plant, harpagophytum, wood spider

Botanical Name / Family

Harpagophytum procumbens (family Pedaliaceae)

Plant Part Used

Dried tuber/root

Chemical Components

The major active constituent is considered to be the bitter iridoid glucoside, harpagoside, which should constitute not less than 1.2% of the dried herb. Other iridoid glycosides include harpagide and procumbide. About 50% of the herb consists of sugars. There are also triterpenes, phytosterols, plant phenolic acids, flavonol glycosides and phenolic glycosides. Harpagophytum zeyheri, which has a lower level of active compounds, may be partially substituted for Harpagophytum procumbens in some commercial preparations. The extraction solvent (e.g. water, ethanol) has a major impact on the active principle of the products.

Main Actions

ANTI-INFLAMMATORY/ANALGESIC

There is good in vitro and in vivo pharmacological evidence of the anti-inflammatory and analgesic properties of devil’s claw, although some negative findings have also been reported. Overall, greatest activity appears to be in semi-chronic rather than acute conditions.

Devil’s claw exerted significant analgesic effects against thermally and chemically induced nociceptive pain stimuli in mice and significant dose-related reduction of experimentally induced acute inflammation in rats, as well as reducing pain and inflammation in Freund’s adjuvant-induced arthritis in rats.

The iridoids, particularly harpagoside, are thought to be the main active constituents responsible for the anti-inflammatory activity, although the mechanism of action is unknown and devil’s claw is also rich in water-soluble antioxidants.

It has been suggested that the suppression of matrix metalloproteinases in chondrocytesvia the inhibition of inflammatory cytokine synthesis, demonstrated in vitro, could explain its therapeutic effect in arthritic inflammation. In vitro evidence also suggests that the anti-inflammatory effect may be due to effects on TNF-alpha or antioxidant activity. Additionally, inhibition of leukotriene synthesis has been observed in vitro, which appears to relate to the amount of harpagoside present.

Contradictory evidence exists as to whether devil’s claw affects prostaglandin (PG) synthesis. Early in vitro and in vivo studies suggest that it does not inhibit PG synthesis and this is supported by studies of PG production in humans. However, more recent investigations have suggested that its anti-inflammatory and analgesic activities are due to suppression of PGE2 synthesis and nitric oxide production and that the herb may suppress expressions of COX-2 and iNOS. More recently, methanoloic extracts of devil’s claw have been shown to inhibit COX-2 in vivo.

In vivo experiments have determined that the method of administration of devil’s claw affects its anti-inflammatory properties. Intraperitoneal and intraduodenal administration was shown to reduce carrageenan-induced oedema, whereas oral administration had no effect, suggesting that exposure to stomach acid may reduce its anti-inflammatory activity. This is supported by a study that found a loss of anti-inflammatory activity after acid treatment.

In vitro studies on rat mesangial cells suggest that devil’s claw may be used as an anti-inflammatory agent in the treatment of glomerular inflammatory diseases. Devils claw extract produced a concentration-dependent suppression of nitrite formation in rat mesangial cells in vitro due to an inhibition of iNOS expression through interference with the transcriptional activation of iNOS. It was found that this activity was due to harpagoside, together with other constituents that possibly have strong anti-oxidant activity.

CHONDROPROTECTIVE

In-vitro data suggests that the active principles of Harpagophytum procumbens inhibit not only inflammatory mediators but also mediators of cartilage destruction, such as TNF-alpha, IL-1 -beta, matrix metalloproteinases, NO and elastase. A study using an animal model confirmed a chondroprotective effect in which the tissue inhibitor of metalloproteinase-2 is involved.

HYPOGLYCAEMIC

Devil’s claw extract produced a dose-dependent, significant reduction in the blood glucose concentrations of both fasted normal and fasted diabetic rats.

Other Actions

In vitro and in vivo evidence suggests that harpagoside may exhibit cardiac affects and lower blood pressure, heart rate and reduce arrhythmias. As an extremely bitter herb, devil’s claw is thought to increase appetite and bile production.. Diterpenes extracted from the roots and seeds of devil’s claw exhibited selective antiplasmodial activity in vitro, which may have future relevance in view of the increasing resistance to conventional antimalarials.