TO DETERMINE THE EFFECTS OF ULTRAVIOLET-LIGHT, NATURAL LIGHT AND IONIZING-RADIATION ON PYRIDINIUM CROSS-LINKS IN BONE AND URINE USING HIGH-PERFORMANCE LIQUID-CHROMATOGRAPHY

The aims of the study were to characterize the denaturation of urinary free and conjugated pyridinoline (Pyr) and deoxypyridinoline (Dpyr) o n exposure to ultraviolet (UV) and natural light at different pH level s and to study the effects of X- and gamma-irradiation on Pyr and Dpyr in urine and in the mineralized and non-mineralized compartments of h uman bone. Urine samples from six normal subjects, adjusted to pH 3.0, 7.0 and 9.0, were exposed to UV light for up to 3 days. Urine collect ions (2 mL, and 24 h) from three subjects, pH adjusted to 1.0, 2.0, 3. 0, 4.0 and 5.0, were exposed to natural light for up to 1 day. Urine s amples and bone slices from seven human cadaveric femurs were irradiat ed with increasing doses of X-rays (0-100 Gy) and high-dose gamma-radi ation (28 kGy). Mineralized and non-mineralized bone were separated us ing a modification of a published method employing heat denaturation f ollowed by trypsin hydrolysis and analysed for Pyr, Dpyr and hydroxypr oline (Hypro). The rate of UV photolysis of urinary Pyr and Dpyr incre ased with pH and was faster in the free fraction (after 3 days' exposu re: free Pyr and Dpyr at pH 7.0 vs. 9.0, P < 0.05, conjugated pH 3.0 v s. 9.0, P < 0.05). Exposure to natural light for 3 h did not significa ntly decrease urinary Pyr and Dpyr in either sample collections, but l evels were reduced in the 2-mL aliquots after exposure for 1 day (P < 0.05). X-irradiation of urine and bone did not affect Pyr and Dpyr. Py r content was similar in both bone compartments (Pyr/ Hypro = 0.12 +/- 0.004), but Dpyr was higher in the nonmineralized compartment (Dpyr/H ypro = 0.047 +/- 0.002 vs. 0.038 +/- 0.002, P < 0.001). UV light and g amma-irradiation result in denaturation of pyridinium cross-links in u rine. These cross-links are present in both the mineralized and non-mi neralized bone compartments but are not affected by the doses of gamma -irradiation that denature these cross-links in urine.