Identification of novel metabolites of prostaglandin E-2 formed by isolated rat hepatocytes

The metabolism of prostaglandin E-2 (PGE(2)) in isolated rat hepatocytes led to the formation of four major as well as several minor products which were structurally characterized using electrospray tandem mass spectrometry. The major metabolites identified included dinor-PGE(1), dinor-PGE(2), and tetranor-PGE(1) and the taurine conjugates of dinor-PGE(1) and dinor-PGE(2). Several minor metabolites including the taurine conjugates of PGE(2) and tetranor PGE(1) along with a glucuronide conjugate of PGE(2) were also identified. These taurine conjugates had not been previously identified in studies of PGE(2) metabolism, yet comprised nearly 50% of the mixture of metabolites after 40-min incubations. Experiments carried out with deuterium-labeled PGE(2) ([3,3,4,4-D-4]PGE(2)) resulted in the complete loss of all deuterium atoms in dinor-PGE(1), dinor-PGE(2), and tetranor metabolites during incubation with hepatocytes. Metabolism via classic beta-oxidation pathways would predict one deuterium atom retained by dinor-PGE(1) and two deuterium atoms retained by dinor-PGE(2). When PGE(2) was incubated with isolated rat hepatocytes in buffer containing 30% D2O, substantial incorporation (30%) of one deuterium atom could be observed in the diner metabolites along with 10% incorporation into the tetranor and residual PGE(2). Deuterium-labeled PGE(1) ([3,3,4,4-D-4]PGE(1)) was metabolized to D-2-dinor-PGE(1), tetranor-PGE(1), and the taurine conjugate of D-2-dinor-PGE(1) by isolated rat hepatocytes. The loss of deuterium during metabolism of the deuterated substrates of PGE(2), but not PGE(1), as well as the incorporation of deuterium atoms from the aqueous solvent into PGE(2) metabolites suggested that the Delta(5) double bond and sequential isomerization reactions lead to eventual exchange of the protons from carbon atom 4 of PGE(2) with water. (C) 1997 Academic Press.