cis-9,10-epoxystearic acid in human leukocytes: isolation and quantitative determination

Racemic cis-9,10-epoxystearic acid was isolated from total lipids of human leukocytes. Identification of the epoxy acid was based mainly on gas liquid chromatographic-mass spectrometric analysis and on its chemical conversion into threo-9,10-dihydroxystearic acid. A mass spectrometric method for quantitative determination of cis-9,10-epoxystearic acid using the tetradeuterated compound as internal standard was developed. Using this method, nonstimulated human leukocytes were found to contain 5.1 +/- 2.2 micrograms (SD) of cis-9,10-epoxystearic acid per 10(9) cells (n = 8). More than 90% of the epoxy acid occurred in its esterified form in leukocyte lipids.