Background: Human hair is one of the essential components that define appearance and is a useful source of samples for\r\nnon-invasive biomonitoring. We describe a novel application of imaging mass spectrometry (IMS) of hair biomolecules for\r\nadvanced molecular characterization and a better understanding of hair aging. As a cosmetic and biomedical application,\r\nmolecules whose levels in hair altered with aging were comprehensively investigated.\r\nMethods: Human hair was collected from 15 young (2065 years old) and 15 older (5065 years old) volunteers. Matrix-free\r\nlaser desorption/ionization IMS was used to visualize molecular distribution in the hair sections. Hair-specific ions displaying\r\na significant difference in the intensities between the 2 age groups were extracted as candidate markers for aging. Tissue\r\nlocalization of the molecules and alterations in their levels in the cortex and medulla in the young and old groups were\r\ndetermined.\r\nResults: Among the 31 molecules detected specifically in hair sections, 2ââ?¬â?one at m/z 153.00, tentatively assigned to be\r\ndihydrouracil, and the other at m/z 207.04, identified to be 3,4-dihydroxymandelic acid (DHMA)ââ?¬â?exhibited a higher signal\r\nintensity in the young group than in the old, and 1 molecule at m/z 164.00, presumed to be O-phosphoethanolamine,\r\ndisplayed a higher intensity in the old group. Among the 3, putative O-phosphoethanolamine showed a cortex-specific\r\ndistribution. The 3 molecules in cortex presented the same pattern of alteration in signal intensity with aging, whereas\r\nthose in medulla did not exhibit significant alteration.\r\nConclusion: Three molecules whose levels in hair altered with age were extracted. While they are all possible markers for\r\naging, putative dihydrouracil and DHMA, are also suspected to play a role in maintaining hair properties and could be\r\ntargets for cosmetic supplementation. Mapping of ion localization in hair by IMS is a powerful method to extract\r\nbiomolecules in specified regions and determine their tissue distribution.
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