DIRECT, ENZYME-LINKED IMMUNOASSAY FOR URINARY DEOXYPYRIDINOLINE AS A SPECIFIC MARKER FOR MEASURING BONE-RESORPTION

Several studies in recent years have shown that the pyridinium crossli nks of collagen provide good urinary markers of collagen degradation, primarily reflecting bone resorption. Most studies, however, were base d on time-consuming HPLC assays of the crosslinks. We now describe the development of an immunoassay (ELISA) based on a monoclonal antibody for free deoxypyridinoline (Dpd) and its use in healthy individuals an d patients with bone-related disorders to measure the urinary excretio n of Dpd as an improved assessment of bone resorption rate. The Dpd an tibody exhibited less than 1% cross-reaction with free pyridinoline an d was shown to react only with free Dpd in urine, having no significan t interaction with peptide forms of the crosslinks. The intra- and int erassay variations were less than 10 and 15%, respectively. A total of 402 urine samples from patients and healthy volunteers were analyzed by both the immunoassay and HPLC. The ELISA results were highly correl ated with those for total Dpd measured by HPLC over the full range of sample groups (r = 0.95). In normal adults, the excretion of Dpd (mean +/- SD) was 4.7 +/- 1.6 nmol/mmol creatinine, with about fivefold hig her excretion rates in children. For 31 osteoporotic patients, the ELI SA Dpd values (median 6.7; range 3.0-13.5 nmol/mmol Cr) were significa ntly higher (p < 0.0001) than the corresponding values for age- and se x-matched controls (median 4.0; range 1.8-7.4), The difference between the groups was similar for total Dpd by HPLC (osteoporotic: mean 12.8 , range 4.8-30.7; controls: 6.6, range 3.0-18.1; p < 0.0001). For othe r patient groups, comparisons of the Dpd excretion with healthy contro ls revealed similar differences for both the immunoassay and total Dpd analyses in primary HPT (n = 23: p < 0.0001), Paget's disease (n = 28 ,p < 0.0001), renal dysfunction (n = 26, no significant difference), a nd breast cancer (n = 17,p < 0.0001), We conclude that the immunoassay constitutes a simpler, more direct way of assessing bone resorption r ates that provides similar information to the more cumbersome HPLC met hods.