Nontargeted Identification of Plasma Proteins O‑, N‑, and S‑Transmethylated by O‑Methyl Organophosphates

Organophosphates (OPs) are used worldwide as pesticides. However, acute and chronic exposure to OPs can cause serious adverse health effects. The mechanism of delayed OP toxicity is thought to involve off-target inhibition of serine proteases, although the precise molecular details remain unclear ow...

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Bibliographic Details
Published in:Analytical chemistry (Washington) 2020-12, Vol.92 (23), p.15420-15428
Main Authors: Wang, Huixin, Leeming, Michael G, Cochran, Blake J, Hook, James M, Ho, Junming, Nguyen, Giang T. H, Zhong, Ling, Supuran, Claudiu T, Donald, William A
Format: Article
Language:English
Subjects:
Adducts
Amino acids
Analytical chemistry
Antioxidants
Blood plasma
Blood Proteins - chemistry
Chemical reactions
Chemistry
Chromatography, Liquid
Chronic exposure
Dichlorvos
Electronic structure
Glutathione
Health risks
Humans
Identification methods
Liquid chromatography
Mass spectrometry
Mass spectroscopy
Methylation
Nitrogen - chemistry
NMR
Nuclear magnetic resonance
Organophosphates
Organophosphates - chemistry
Organophosphates - toxicity
Oxidation
Oxygen - chemistry
Peptides
Pesticides
Plasma proteins
Protein adducts
Proteins
Residues
Scientific imaging
Serine
Spectroscopy
Sulfur - chemistry
Tandem Mass Spectrometry
Target detection
Toxicity
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Summary:Organophosphates (OPs) are used worldwide as pesticides. However, acute and chronic exposure to OPs can cause serious adverse health effects. The mechanism of delayed OP toxicity is thought to involve off-target inhibition of serine proteases, although the precise molecular details remain unclear owing to the lack of an analytical method for global detection of protein targets of OPs. Here, we report the development of a mass spectrometry method to identify OP-adducted proteins from complex mixtures in a nontargeted manner. Human plasma was incubated with the OP dichlorvos that was 50% isotopically labeled and 50% unlabeled. Proteins and protein adducts were extracted, digested, and analyzed by liquid chromatography–tandem mass spectrometry (LC-MS/MS) to detect “twin ions” of peptides that were covalently modified by a chemical reaction with dichlorvos. The LC-MS/MS data were processed by a blended data analytics software (Xenophile) to detect the amino acid residue sites of proteins that were covalently modified by exposure to OPs. We discovered that OPs can transmethylate the N, S, and O side chains of His, Cys, Glu, Asp, and Lys residues. For model systems, such transmethylation reactions were confirmed by LC-MS, nuclear magnetic resonance (NMR), and rationalized using electronic structure calculations. Methylation of the ubiquitous antioxidant glutathione by dichlorvos can decrease the reducing/oxidizing equilibrium of glutathione in liver extracts, which has been implicated in diseases and pathological conditions associated with delayed OP toxicity.
ISSN:0003-2700
1520-6882
DOI:10.1021/acs.analchem.0c03077