A collection method and high-sensitivity enzyme immunoassay for sweat pyridinoline and deoxypyridinoline cross-links

Background Collagen cross-link molecules such as pyridinoline (PYD), deoxyp yridinoline (DPD), and N-terminal cross-linked peptides (NTX) have been mea sured in urine as indices of bone resorption. However, very little is known regarding the excretion of pyridinolines into other biological fluids. We report a collection device, normalizing analyte, and high-sensitivity immun oassay for quantitative analysis of free pyridinoline cross-links in sweat. Methods: Flame atomic emission and ion-selective electrode techniques were used to measure potassium as a sweat volume marker. The Pyrilinks immunoass ay for urine free pyridinolines was optimized to increase sensitivity for m easurements in sweat. The precision, accuracy, and detection limit of this assay were characterized. To assess values and variability of sweat pyridin olines in human subjects, a nonocclusive skin patch was used to collect swe at samples from a reference group and from a mixed group experiencing accel erated bone resorption, postmenopausal women and men receiving gonadotropin -releasing hormone for prostate cancer. Results: The immunoassay intra- and interassay variations were less than or equal to 10% and <1.6%, respectively, with a detection limit of 309 pmol/L . Linearity upon dilution and analytical recovery ranged from 93% to 109% a nd 85% to 122%, respectively. Sweat PYD values normalized to potassium outp ut yielded a weekly intraindividual biological variability of 14.7%. The me an increase in the population experiencing increased bone resorption vs the reference group was 36% (P <0.05) for sweat PYD/K vs 23-40% (P <0.05) for urinary PYD/Cr, DPD/Cr, and NTX/Cr. Conclusion: We conclude that this new platform sweat collection technology and PYD immunoassay show potential as an indicator of bone resorption. (C) 1999 American Association for Clinical Chemistry.