Effects of ultraviolet light on free and peptide-bound pyridinoline and deoxypyridinoline cross-links. Protective effect of acid pH against photolytic degradation.
Little is known about the photodegradation of pyridinoline (Pyd) and deoxypyridinoline (Dpd), which are two mature cross-links stabilizing collagen within extracellular matrix. In this study, highly purified free Pyd and Dpd cross-links have been degraded by irradiation with ultraviolet light and we have shown that photolysis varies with the pH value. Assessment of photolysis in basic (pH 9) and neutral (pH 7) solutions by high-performance liquid chromatography as well as by UV absorbance measurement indicates that both cross-links are degraded after a 24 h UV exposure, while in acidic solution (pH 3) only Dpd is photolysed, suggesting that acid pH provides major protection against Pyd photolysis. Photodegradation products have been studied by amino-acid and mass spectral analysis. Both methods confirm the lack of Pyd degradation in acid pH. Furthermore, amino-acid analysis allows us to identify hydroxylysine and lysine as a result of Pyd and Dpd photolysis, respectively, indicating that the mechanism of photodegradation involves the cleavage of the pyridinium ring on each side of the quaternary nitrogen. Finally, we have also studied the photolysis of different molecular species of type I collagen peptides, obtained by digestion with collagenase of demineralized turkey bone. Our results indicate that even when they are part of the structure of collagen peptide, Pyd and Dpd can be photolysed. However, we have shown that the larger the peptide is, the smaller are the effects of UV irradiation.
Meddah
B
B
Laboratory of Clinical Pharmacy, Faculty of Pharmacy, Amiens, France.
Kamel
S
S
Giroud
C
C
Brazier
M
M
D000596:Amino Acids / Q000528:radiation effects*; D000818:Animals; D002851:Chromatography, High Pressure Liquid / Q000379:methods; D003432:Cross-Linking Reagents; D006863:Hydrogen-Ion Concentration; D008239:Lysine / Q000032:analysis; D009555:Ninhydrin / Q000032:analysis; D010455:Peptides / Q000528:radiation effects*; D010782:Photolysis / Q000528:radiation effects*; D014422:Turkeys; D014466:Ultraviolet Rays
D000596:Amino Acids; D003432:Cross-Linking Reagents; D010455:Peptides; C015484:pyridinoline; C036020:deoxypyridinoline; D009555:Ninhydrin; D008239:Lysine