Tetrahydroisoquinoline derivatives of enkephalins: synthesis and properties

Oxidative and nitrative modifications of enkephalins by reactive nitrogen species

The interaction of Leucine-enkephalin (Leu-enkephalin) with reactive nitrogen species has been investigated. Reactive nitrogen species are capable of nitrating and oxidizing Leu-enkephalin. HPLC analysis shows the formation of two major enkephalin derivatives by peroxynitrite. The tyrosine amino-terminal residue of Leu-enkephalin is converted either to 3-nitrotyrosine thus producing nitroenkephalin and to dityrosine by dimerization with the production of an enkephalin dimer. The evidence of the formation of the nitroenkephalin and of the enkephalin dimer--dienkephalin--was achieved by electrospray ionisation mass spectrometry. In addition to peroxynitrite, the methylene blue photosensitized oxidation of enkephalin in the presence of nitrite leads to the formation of the nitrated peptide. Moreover, the nitropeptide can be also obtained by peroxidase-generated nitrogen reactive species.

Identification of 4-methylspinaceamine, a pictet-spengler condensation reaction product of histamine with acetaldehyde, in fermented foods and its metabolite in human urine

Previous study demonstrated that 4-methylspinaceamine (4-methyl-4,5,6,7-tetrahydro-1H-imidazo[4,5-c]pyridine), a Pictet-Spengler condensation reaction product of histamine with acetaldehyde, is present in human urine. The current study sought to determine whether 4-methylspinaceamine is present in fermented foods; its presence might be expected since both histamine and acetaldehyde are often present in these foods. Soy sauce, fish sauce, cheese, and shao hsing wine (Chinese wine) were found to contain 4-methylspinaceamine. The concentration of 4-methylspinaceamine excreted in human urine was greatly elevated after ingestion of a meal containing soy sauce as a dietary source of 4-methylspinaceamine, demonstrating that the level of 4-methylspinaceamine in human urine was affected by dietary foods. In addition, a metabolite of 4-methylspinaceamine in human urine was investigated. An enhanced peak in the HPLC chromatogram of human urine samples after ingestion of 4-methylspinaceamine-containing foods was observed. A peak at the same retention time was also observed from a human urine sample after administration of 4-methylspinaceamine, suggesting that the peak was due to a metabolite. By comparison with the newly synthesized authentic compound, the metabolite was identified as 1,4-dimethylspinaceamine.

Identification of 4-methylspinaceamine - a Pictet – Spengler condensation reaction product of histamine with acetaldehyde - in human urine

This study reports the first identification of 4-methylspinaceamine (4-MSPA)-a Pictet Spengler condensation reaction product of histamine with acetaldehyde-in human urine. 4-MSPA was identified and quantified as follows: the target compound was partially purified by solvent extraction from a urine sample spiked with N-methylpiperazine (N-MP) as an internal standard, then derivatized to a naphthylthiourea derivative with 1-naphthylisothiocyanate (NITC) and finally analyzed by HPLC. For verification, 4-MSPA was also analyzed by ion spray-mass spectrometry (IS-MS), using 4-MSPA-d4 as an internal standard. The amount of 4-MSPA in human urine varied between individuals and from day-to-day, ranging from undetectable to 0.80 nmol/mL.