Quantification of desmosine and isodesmosine using MALDI-ion trap tandem mass spectrometry.

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 analyses 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 irradiation (254 nm) 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. Graphical abstract ᅟ.

Ultraviolet radiation reduces desmosine cross-links in elastin.

Elastic fibers, a major component of the extracellular matrix of the skin, are often exposed to ultraviolet (UV) radiation throughout mammalian life. We report on an in vitro study of the alterations in bovine nuchal ligament elastic fibers resulting from continuous UV-A exposure by the use of transmission electron microscopy (TEM), histology, mass spectrometry, and solid state 13C NMR methodologies. TEM images reveal distinct cracks in elastic fibers as a result of UV-A irradiation and histological measurements show a disruption in the regular array of elastic fibers present in unirradiated samples; elastic fibers appear shorter, highly fragmented, and thinner after UV-A treatment. Magic angle spinning 13C NMR was applied to investigate possible secondary structural changes or dynamics in the irradiated samples; our spectra reveal no differences between UV-A irradiated and non-irradiated samples. Lastly, MALDI mass spectrometry indicates that the concentration of desmosine, which forms cross-links in elastin, is observed to decrease by 11 [Formula: see text] following 9 days of continuous UV-A irradiation, in comparison to unirradiated samples. These alterations presumably play a significant role in the loss of elasticity observed in UV exposed skin.