Metabolomic profiling of brain tissues of mice chronically exposed to heroin.

The chronic neurotoxicity of heroin on the nervous system is poorly understood. To address this issue, we comprehensively assessed the alteration of brain metabolomics caused by chronic heroin exposure and the withdrawal of heroin. Male C57BL/6J mice (n = 10) were given heroin (15 μmol/kg, i.p., twice a day) for 12 days while the withdrawal group received saline-treatment instead of heroin for the last two days. The control group received saline. We developed an UPLC-TOF/MS-based metabolomic approach to analyze the metabolites and carry out a metabolic pathway analysis in the brain. The major metabolites contributing to the discrimination were identified as amino acids, tricarboxylic-acid cycle intermediates, neurotransmitters, nucleotides and other compounds. A marked reduction in histidine and a slight but significant increase in phenylalanine and tryptophan were observed after heroin was withdrawn while the increased level of catecholamines was restored to baseline. Interestingly, N-acetylserotonin - a precursor of melatonin - was increased with the withdrawal of heroin while melatonin was markedly reduced along with the sub-chronic exposure to heroin. This shows that heroin disrupts not only the energy metabolism but also the biosynthesis of both catecholamines and melatonin in the mouse brain. Therefore, these substances are candidate biomarkers for chronic heroin-abuse.