Quantification of Desmosine and Isodesmosine Using MALDI-Ion Trap Tandem Mass Spectrometry

摘要

Desmosine (Des) and Isodesmosine (Isodes), cross-linking amino acids in the biomolecule elastin, may be used as biomarkers for various pathological conditions associated with elastin degradation. The current study presents a novel approach to quantify Des and Isodes using Matrix-Assisted Laser Desorption Ionization (MALDI)-tandem mass spectrometry (MS²) in a linear ion trap coupled to a vacuum MALDI source. MALDI-MS² analysis of Des and Isodes are performed using stable-isotope labeled desmosine d4 (Labeled-Des) as an internal standard in different biological fluids, such as urine and serum. The method demonstrated linearity over two orders of magnitude with a detection limit of 0.02 ng/μL in both urine and serum without enrichment prior to mass spectrometry, and relative standard deviation of <5%. The method is used to evaluate the time-dependent degradation of Des upon UV radiation (254nm) and found to be consistent with quantification by ¹H NMR. This is the first characterized MALDI-MS² method for quantification of Des and Isodes and illustrates the potential of MALDI-ion trap MS² for effective quantification of biomolecules. The reported method represents improvement over current liquid chromatography-based methods with respect to analysis time and solvent consumption, while maintaining similar analytical characteristics.