Enzymatic synthesis of dioxygen-18 labeled 8-epi-prostanglandin F-2 alpha and its use in quantitative GC-tandem MS

8-epi-Prostaglandin F-2 alpha (8-epi-PGF(2 alpha)) is an endogenous potent vasoconstrictor, noncyclooxygenase -derived prostanoid which may be suitable as an index of oxidative stress in living organisms. For quantitative determination of 8-epi-PGF(2 alpha) in biological fluids we describe here the one-step enzymatic synthesis of [1,1-O-18(2)]-8-epi-PGF(2 alpha) starting from commercially available unlabeled 8-epi-PGF2 alpha, (H2O)-O-18 and an unspecific porcine liver esterase. The isolated and purified reaction product was found to contain 80.3% of [1,1-O-18(2)]-8-epi-PGF(2 alpha), 17.7% of [1,1-(OO)-O-18-O-16]-8-epi-PGF(2 alpha) and only 2.0% of unlabeled 8-epi-PGF(2 alpha). [1,1-O-18(2)]-g-epi-PGF(2 alpha) is demonstrated to be a suited internal standard for quantitative determination of 8-epi-PGF(2 alpha) in human urine by GC-MS/MS. In 5-ml aliquots of human urine samples from spontaneous micturation on different days, 8-epi-PGF(2 alpha) was found to be present at concentrations of 300 and 490 pg/mg creatinine, respectively.