TYPE-I COLLAGEN C-TELOPEPTIDE DEGRADATION PRODUCTS AS BONE-RESORPTIONMARKERS

Degradation products of the C-telopeptides from type I collagen (CTC) can be measured with commercially available immunoassays (e.g., CrossL aps(TM) assays). It is well established that the urinary excretion of CTC fragments is closely correlated with the rate of bone degradation (resorption). Data obtained with a recently developed assay for CTC fr agments in serum also suggest that serum CTC is a sensitive and specif ic index of bone resorption. Several structures of the CTC fragments h ave been elucidated. It has become clear that the peptide sequence mea sured in the CrossLaps assays can spontaneously beta-isomerize to prod uce unusual isoaspartyl peptides. This sign of protein aging is believ ed to ensure that the urinary CrossLaps ELISA and the Serum CrossLaps One Step ELISA, both specific for beta-isomerized fragments, measure d egradation of relatively old bone. Conversely, the alpha-CrossLaps RIA , specific for non-isomerized CTC fragments, measures degradation of r elatively young bone. Currently, the assays are being evaluated to cla rify their potential clinical applications. They have also been shown to be efficient tools for monitoring antiresorptive therapy. Assessmen t of future risk of bone loss and fracture is being investigated with promising results. It is expected that the routine use of the CrossLap s assays will become established within the next few years.