Detection of Nɛ-monomethyllysine using high-performance liquid chromatography and high-performance liquid chromatography–mass spectrometry

Nɛ-Monomethyllysine was identified in the serum, urine, brain, and liver samples of rats treated per os with l-deprenyl. The identification procedure included reaction with Fmoc chloride, clean-up, and analysis using HPLC–UV–MS. Oral administration of (−)-N-14C-methyl-N-propynyl(2-phenyl-1-methyl)ethylammonium hydrochloride l-deprenyl) to rats resulted in transfer of the radiolabelled methyl group to the Nɛ-amino group of the endogenous lysine. The radiolabelled Nɛ-monomethyllysine was urinary eliminated together with the other radiolabelled deprenyl metabolites, such as deprenyl-N-oxide and methamphetamine. The presence of Nɛ-monomethyllysine has also been traced, and its concentrations were compared in the serum, liver and brain of rats subjected to l-deprenyl treatment. Methyl group transfer from the l-deprenyl to endogenous compounds; and the urinary elimination of their products may offer a vital way to eliminate or to decrease the degree of drug transmethylation to the lysine constituents of blood vessels’ proteins.