DETERMINATION OF PYRIDINOLINE AND DEOXYPYRIDINOLINE IN URINE, WITH SPECIAL ATTENTION TO RETAINING THEIR STABILITY

Urinary excretion of the pyridinium crosslinks pyridinoline (Pyr) and deoxypyridinoline (Dpyr) is used as a biochemical marker of bone resor ption. The present study was undertaken to determine the long-term sta bility of these compounds in stored urine, using the HPLC method. Syst ematic investigation of their chemical stability in urine demonstrated that both the free and conjugated forms of Pyr and Dpyr are extremely stable: No significant changes were observed after 6 weeks at -20 deg rees C storage (e.g., free Pyr 9.6 +/- 1.2 mu mol/mol creatinine (befo re) and 10.6 +/- 3.2 (after); free Dpyr 2.3 +/- 0.2 mu mol/mol creatin ine (before) and 2.5 +/- 1.2 (after)). These results predict stability of urines stored for 10-20 years at -20 degrees C in the dark. Also, freezing and thawing as many as 10 times had no effect on the concentr ations of the crosslinks. Study of the stability of the excretion patt ern in healthy women showed substantially higher variations in excreti ons of free and total Dpyr (18% and 13%, respectively) than of Pyr (10 % for both forms).