Analytical Biochemistry 292, 148-154 (2001) Available online at http://www.idealibrary.com Gas Chromatography/Mass Spectrometry Method to Quantify Blood Hydroxycitrate Concentration Yu-chi C. Loe, Nathalie Bergeron, Nestor Rodriquez, and Jean-Marc Schwarz Department of Nutritional Sciences, University of California at Berkeley, 119 Morgan Hall, Berkely, California 94720-3104 Hydroxycitrate (HCA), a popular dietary supplement for weight loss, is a competitive inhibitor of ATP-citrate lyase, an extramitochondrial enzyme involved in the initial steps of de novo lipogenesis (DNL). Although animal studies have shown that HCA effectively inhibits DNL and induces weight loss, these findings have not been consistent in humans. This raises the possibility that the bioavailability of HCA may differ among species. We developed a new GC/MS method to measure HCA levels in blood, using [U-13 C] citrate (CA*) as internal standard to account for losses associated with the isolation, derivatization, and measurement of HCA. HCA and CA* were derivatized with BSTFA + 10% TMCS and analyzed using PCI/GC/MS (CA*, m/z 471; and HCA, m/z 553). The plasma HCA concentration was measured over a 3.5-h period in four subjects having ingested 2 g of HCA. Their plasma HCA concentration ranged from 0.8 to 8.4 ug/ml 30 min and 2 h after ingestion, respectively. These results demonstrate that when taken acutely, HCA is absorbed, yet present in small quantities in human plasma. This simple method requiring minimal sample preparation is able to measure trace amounts of HCA with accuracy and precision. Aloe Vera Supplements Key words: hydroxycitrate; Garcinia cambogia; dietary supplement; GC/MS

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