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Abstract |
An Immunoassay for Measuring Fragments of Newly Synthesized Collagen Type I Produced During Metastatic Invasion of Bone |
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Degradation products of collagen type I can be measured by CrossLaps (CTX) immunoassays, providing an index of bone resorption. The CTX epitope EKAHDGGR comprises a DG-motif susceptible to post-translational modifications. In newly synthesized collagen this motif is in the native form denoted αCTX, but converts to an isomerized form (βCTX) during aging of bone. Furthermore, the lysine residue (K) within the CTX epitope participates in inter-molecular cross-links in mature bone. The present paper describes an assay, ALPHA CTX ELISA for measurement of cross-linked αCTX molecules (α-αCTX) in urine. The ALPHA CTX ELISA demonstrated a high specificity and technical precision for measuring such fragments. The assay was evaluated in a cross-sectional study, comparing the urinary excretion of the marker in 100 breast cancer patients with bone metastases (BC+) and 15 breast cancer patients without metastases to bone (BC-) as well as 31 age-matched healthy postmenopausal women (PM). For comparison α, β, and β-βCTX was also measured using commercially available immunoassays. In BC+ urinary α-αCTX increased significantly compared to BC- and PM with p-values of 0.005 and <0.0001, respectively. In contrast, the age-modified form β-βCTX, representing the degradation of old bone, was less increased. Z-score analysis was used to compare the ability of the CTX markers to discriminate between BC+ and PM. The α-αCTX marker was found to provide a far better discrimination (Z=7.5) than β-βCTX (Z=3.6). In conclusion, measurement of α-αCTX fragments may provide a clinically relevant assessment of bone resorption related
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