Development of a robust LC-MS/MS method for determination of desmosine and isodesmosine in human urine

Desmosine (DES) and isodesmosine (IDES) are both pyridinium amino acid isomers that serve as cross-linking molecules binding the polymeric chains of amino acids into elastin. Found in urine, they are markers for the degradation of elastin which occurs in chronic obstructive pulmonary disease (COPD). In this study, a robust method using ultra-performance liquid chromatography coupled to tandem mass spectrometry (UPLC-MS/MS) with selected reaction monitoring (SRM) mode was developed for the analysis of DES and IDES in human urine. Pyridylethyl-cysteine (PE-Cys) as internal standard (I.S.) was employed for the quantification of DES and IDES. The analytes and I.S. were extracted by solid-phase extraction with Oasis MCX cartridges and separated on an AccQ-Tag Ultra column. The assay was accurate (-6.8% to 14.5%) and precise (2.8% to 13.8%) within the concentration range of 1 to 250 pmol/mL. Moreover, the recovery and stability (working/ I.S. solution, urine samples with added elastin, and pretreated sample) was investigated, and these parameters were found acceptable. The UPLC-MS/MS method was validated and had good reproducibility and stability for the quantification of DES and IDES, which requires only 100 mL of human urine. This assay will be a useful means for measuring DES and IDES levels in urine with robustness and characterizing patients with COPD.