Metabolism of tresperimus by rat aorta semicarbazide-sensitive amine oxidase (SSAO).

Tresperimus (Cellimis), a new immunosuppressive agent, is mainly eliminated in the rat through metabolism, in which the oxidative deamination of the primary amine of the drug plays a major role. We have previously demonstrated in vivo the significant involvement of semicarbazide-sensitive amine oxidase (SSAO) in this reaction. Rat aorta, a tissue with one of the highest specific SSAO activities, was tested as a new in vitro model to elucidate tresperimus metabolism, using a combination of liquid chromatography/mass spectrometry (LC/MS) and high-performance liquid chromatography (HPLC) analyses. The metabolites resulting from the main metabolic pathway of the drug were formed in rat aorta homogenates. The use of various SSAO, lysyl oxidase and monoamine oxidase inhibitors confirmed that SSAO is predominantly involved in the main site of tresperimus metabolism but also in every metabolic pathway of the drug, including deamination of tresperimus metabolites M3 (desaminopropyl derivative of tresperimus) and M6 (guanidinohexylamine). A microsomal fraction of the rat aorta was used to characterize tresperimus deamination. The moderate affinity of membrane-bound SSAO for tresperimus, with a Km value of 66 microM, was counterbalanced by a catalytic efficiency superior to that of certain physiological substrates of SSAO, such as methylamine. The rat aorta provided an interesting model with which to study tresperimus metabolism, highlighting the important role that SSAO could play as a phase I oxidative enzyme in the metabolism of certain exogenous amines at the vascular level.

Involvement of semicarbazide-sensitive amine oxidase in tresperimus metabolism in human and in rat.

The metabolism of tresperimus, a new immunosuppressive agent, was investigated in vivo and in vitro in rat and in human. Two metabolic pathways were identified at each side of the molecule with two deamination reactions on the spermidine moiety and hydrolysis of the amide bond leading to the liberation of guanidinohexylamine. As the major metabolic pathway of the drug seemed to be the oxidative deamination, the capacity of different amine oxidases to metabolize tresperimus was then tested using in vivo experiments in rat and in vitro studies in rat and human plasma. The increase of tresperimus plasma levels induced by the administration of hydralazine, an irreversible in vivo inhibitor of semicarbazide-sensitive amine oxidase (SSAO), reflected the major involvement of this enzyme in tresperimus metabolism. This result was confirmed in vitro in rat and human plasma by the use of semicarbazide, a specific SSAO inhibitor. As opposed to rat plasma, human plasma may be an interesting in vitro model to study the metabolism of a drug extensively metabolized by SSAO such as tresperimus. Indeed, SSAO activity was significantly higher in human plasma than in rat plasma. The second metabolic pathway of the drug, which only occurred in rat plasma, appeared thus as the major route of tresperimus metabolism in this biological matrix.