Bone mineral density and serum levels of aminoterminal propeptides and cross-linked N-telopeptides of type I collagen in elderly men

Serum levels of aminoterminal extension propeptides (PINP), the carboxyterminal telopeptide (ICTP), and the cross-linked N-telopeptides (NTx) of type I collagen were determined in 78 healthy, elderly men aged 76 ± 5 years in 1993 and 1996 and compared with bone mineral density (BMD) measurements of their lumbar spine, femoral neck, and total body regions made using dual X-ray absorptiometry. Compared with 11 men who had normal lumbar spine (SBMD) and femoral neck BMD (NBMD), 13 of the subjects with SBMD and NBMD classified as osteopenic by t-score criterion had higher mean serum levels of PINP and alkaline phosphatase activity, but these increases were not statistically significant at the 95% confidence interval. In osteopenic men, a correlation between SBMD and NTx was detected (r = −0.66, p = 0.01). Within the entire population, the serum NTx level correlated with NBMD (r = −0.26, p< 0.05) and PINP (r = +0.63, p< 0.0001), and the change in the circulating concentration of PINP over the 3 year interval correlated with the magnitude of change in total body BMD (r = −0.28, p = 0.02), NBMD (r = −0.24, p = 0.05), and SBMD (r = −0.36, p = 0.03) as well as with the change in serum NTx levels (r = 0.43, p< 0.001). The change in the circulating ICTP level was also related to the change in NBMD (r = −0.24, p = 0.01). Together, weight and the serum PINP level accounted for 25% of total body BMD variance in elderly men. These results indicate that larger populations of men and women should be screened over longer time intervals to explore the value of serial measurement of serum collagen metabolites in predicting bone loss in the spine and hip.