Gas chromatography/mass spectrometry method to quantify blood hydroxycitrate concentration

Hydroxycitrate (HCA), a popular dietary supplement for weight loss, is a co mpetitive inhibitor of ATP-citrate lyase, an extramitochondrial enzyme invo lved in the initial steps of de novo lipogenesis (DNL), Although animal stu dies have shown that HCA effectively inhibits DNL and induces weight loss, these findings have not been consistent in humans. This raises the possibil ity that the bioavailability of RCA may differ among species. We developed a new GC/MS method to measure HCA levels in blood, using [U-C-13]citrate (C A*) as internal standard to account for losses associated with the isolatio n, derivatization, and measurement of HCA. HCA and CA* were derivatized wit h 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 fou r subjects having ingested 2 g of HCA, Their plasma HCA concentration range d from 0.8 to 8.4 mug/ml 30 min and 2 h after ingestion, respectively. Thes e 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 an d precision. (C) 2001 Academic Press.