Whole-Hoodia powder contains variable amounts of fibre, organic material, antioxidants and biologically active substances including steroidal glycosides. One substance in particular is common to at least five species of Hoodia. This is the steroidal trisaccharide called 3-0-[beta-D-thevetopyranosyl-(1 ^ 4)-beta-D-cymaropyranosyl-(1 ^ 4)-beta-D-cymaropyranosyl]-12beta-0-tigloyloxy-14-hydroxy-14beta-pregn-5-en-20-one. It has been termed 'P57' because it was the 57th plant-derived compound investigated for commercial development by the British pharmaceutical company Phytopharm. An excellent review of the history of the development of Hoodia appears on the Internet (BioMolecular Sciences, Inc). P57 has been patented by Phytopharm and developed in collaboration with the CSIR (South African Council of Scientific and Industrial Research). The P57 originating from H. gordonii, as supplied by Phytopharm, is named P57AS3. It is this compound that is said to be responsible for the anorectic quality of the plant. Of three scientific reports on animal studies involving P57, only one has been published in a peer-reviewed journal (MacLean & Luo, 2004). The other two have only appeared in abstract form in conference presentations (Tulp et al., 2001, 2002). Tulp et al. (2001, 2002) showed a 50% reduction in ad libitum food intake in rats fed Hoodia compared with control. The mean effective dose for appetite suppression in rats during a 4-h feeding test ranged from 1.8 to 2.7 g per kg body weight for the various Hoodia species. The values were similar in both lean and obese rats. Over a 2-3 week period, marked reduction in body weight was seen in the obese rats and a moderate reduction in the Hoodia-fed lean rats. Control rats gained weight normally during the same period. The decrease in spontaneous food intake was not due to unpalatability of the Hoodia diet (Phytopharm and Pfizer, unpublished observation).
MacLean and Luo (2004) recently studied the effects in rats of the steroidal glycoside P57AS3 purified from H. gordonii, supplied by Phytopharm and Pfizer. Intracerebroventricular injection of the purified P57AS3 resulted in an increased ATP content in the hypothalamic neurons. P57AS3 injections into the third ventricle (at doses of 0.4-40 nmol) reduced 24 hour food intake by rats by up to 60%. Subsequent experiments showed that in rats fed a low-calorie diet for 4 days, the content of ATP in the hypothalami fell by 30-50%. This effect was blocked by intracerebroventricular injections of P57AS3 (MacLean and Luo, 2004). Based on these findings, the authors hypothesize that ATP level may be a signal for the energy-sensing of satiety. More research is required to fully understand the mechanism of action of P57AS3 in weight control.
A double-blind placebo-controlled study testing P57 (reported to be from H. Gordonii) was carried out by Phytopharm in healthy overweight subjects. The results of this study have not yet been published and only a little information is available from the article by Habeck (2002) and from press releases on the Phytopharm website (http://www.phytopharm.co.uk). The first two stages of the study were aimed at assessing the safety, tolerabil-ity and pharmacokinetics of P57 whilst the third stage studied 19 overweight males fed either the P57 compound (at an unknown dose) or placebo twice daily for 15 days. The treatment group achieved a 30% reduction in calorie intake and a significant reduction in body fat content of 1 kg (Habeck, 2002).
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