Isotope Dilution nanoLC-MS/MS Quantitation of Methylglyoxal DNA-Protein Crosslinks: Formation and Repair in Human Cells

DNA-protein crosslinks (DPCs) represent a prevalent form of DNA damage that form when cellular proteins become covalently trapped to DNA strands upon exposure to various endogenous and exogenous agents. Methylglyoxal, is an endogenous metabolite that reacts with guanine and adenine bases in DNA and RNA, as well as cysteine, arginine and lysine residues in proteins, generating advanced glycation end-products (AGEs) including DPCs. These modifications have been linked to human disease, including cancer, liver disease, diabetes, and neurodegenerative disorders. Herein, we present a mass spectrometry method for quantifying MGO-induced DNA-protein crosslinks (DPCs) in human cells. We prepared an isotope ¹⁵ N ₂ ¹³ C ₆ -dG-MGO-Lys internal standard to develop a quantitative LC-MS/MS method for detecting and quantifying the formation and repair of dG-MGO-Lys DPCs in cells. Genomic DNA was extracted, subjected to sequential protease and nuclease digestion, purified by offline HPLC, and analyzed by LC-MS/MS. The method’s standard curve showed a strong linear relationship across a concentration range of 10-1000 fmol (R ² = 0.9994). The method achieved limits of detection (LOD) and quantification (LOQ) of 10 and 20 fmol, respectively. Inhibition of proteasome and SPRTN activity revealed that SPRTN functions as a predominant proteolytic enzyme in MGO DPC repair. Overall, this analytical approach can offer valuable insights into the relevance of DPCs in diseases linked to elevated MGO levels.