A study on the metabolism of spermidine in mammals: purification and identification of a newly identified metabolite, 2-oxo-1-pyrrolidinepropionic acid, in rat urine.

In order to study the metabolism of spermidine in mammals, radioactive spermidine was injected intraperitoneally into a rat and urine was collected for analysis. Incorporation of radioactivity into putreanine, isoputreanine, spermidic acid, and N-aminopropylpyrrolidin-2-one was confirmed by ion-exchange chromatography, thin layer chromatography, and paper electrophoresis, the highest radioactivity being observed in the non-polar and acidic fraction of the collected urine. A radioactive compound was purified from the non-polar and acidic fraction, and identified as 2-oxo-1-pyrrolidinepropionic acid by comparison of its behavior on ion-exchange chromatography and thin layer chromatography with that of authentic 2-oxo-1-pyrrolidinepropionic acid, and recrystallization with the authentic compound. Acid hydrolysis of the radioactive compound produced radioactive spermidic acid, confirming the identification. To examine the interconversion between isoputreanine and N-aminopropylpyrrolidin-2-one, these compounds were deuterated and then intraperitoneally injected into a rat. Analysis of 24-h urine by gas-chromatography-mass-spectrometry indicated no interconversion between the two metabolites of spermidine under these conditions. An intracerebroventricular injection of radioactive spermidine into a rat showed that radioactivity was also incorporated into the metabolites of spermidine in the brain, and oxidative deamination of the aminopropyl moiety of spermidine was thought to be dominant in the central nervous system and vice versa in peripheral organs.