Metabolomic Analyses of Body Fluids after Subchronic Manganese Inhalation in Rhesus Monkeys

Abstract

Neurotoxicity is linked with high-dose manganese inhalation. There are few biomarkers that correlate with manganese exposure. Blood manganese concentrations depend upon the magnitude and duration of the manganese exposure and inconsistently reflect manganese exposure concentrations. The objective of this study was to search for novel biomarkers of manganese exposure in the urine and blood obtained from rhesus monkeys following subchronic manganese sulfate (MnSO₄) inhalation. Liquid chromatography-mass spectrometry was used to identify putative biomarkers. Juvenile rhesus monkeys were exposed 5 days/week to airborne MnSO₄ at 0, 0.06, 0.3, or 1.5 mg Mn/m³ for 65 exposure days or 1.5 mg Mn/m³ for 15 or 33 days. Monkeys exposed to MnSO₄ at ≥ 0.06 mg Mn/m³ developed increased brain manganese concentrations. A total of 1097 parent peaks were identified in whole blood and 2462 peaks in urine. Principal component analysis was performed on a subset of 113 peaks that were found to be significantly changed following subchronic manganese exposure. Using the Nearest Centroid analysis, the subset of 113 significantly perturbed components predicted globus pallidus manganese concentrations with 72.9% accuracy for all subchronically exposed monkeys. Using the five confirmed components, the prediction rate for high brain manganese levels remained > 70%. Three of the five identified components, guanosine, disaccharides, and phenylpyruvate, were significantly correlated with brain manganese levels. In all, 27 metabolites with statistically significant expression differences were structurally confirmed by MS-MS methods. Biochemical changes identified in manganese-exposed monkeys included endpoints relate to oxidative stress (e.g., oxidized glutathione) and neurotransmission (aminobutyrate, glutamine, phenylalanine).