Targeted Metabolomics for the Analysis of p-Cresol in Mouse Brain: Impact of Biological Sex and Strain.

p-Cresol, an environmental contaminant and endogenous metabolite derived primarily from the conversion of l-tyrosine by intestinal microflora, is gaining increasing attention, due to its potential impact on human health. Recent studies have highlighted elevated levels of p-cresol and its metabolites, including p-cresyl sulfate and p-cresyl glucuronide, in various populations, suggesting a correlation with neurodevelopmental and neurodegenerative conditions. While the role of this compound as a uremic toxin is well established, its presence and concentration within the central nervous system (CNS) remain largely unexplored. To address this gap, an high-performance liquid chromatography-electrospray ionization-tandem mass spectrometry (HPLC-ESI-MS/MS) method was optimized and validated for the first time in this work for the targeted metabolomics of p-cresol in brain tissues. This method enabled the quantification of this compound in different brain areas of adult male and female C57BL/6J mice and in the cortex of various mouse strains, including CD-1 and the idiopathic autism model BTBR T⁺Itpr3^tf/J. Additionally, preliminary analyses of human cortex samples confirmed the presence of p-cresol, suggesting its relevance in human brain health. Moreover, metabolomic analyses have further explored the correlations between p-cresol and neurotransmitters, with a particular focus on dopaminergic and noradrenergic pathways. These findings pave the way for understanding the potential impact of p-cresol on neurochemical networks and its implications for neurodevelopmental and neurodegenerative disorders.