Early increases in bone turnover markers (BTMs) in response to anabolic therapy correlate with 18-month bone mineral density (BMD) increases in postmenopausal women with osteoporosis; however, this relationship has not been assessed in men. In this analysis, the correlation between changes from baseline in fasting intact serum procollagen type I N propeptide (PINP) and serum carboxy-terminal cross-linking telopeptide of type I collagen (CTX) at 1, 3, 6, and 12 months and percent increase from baseline in BMD at 12 months in men from the randomized phase 3 ATOM study (NCT03512262) were evaluated using Pearson's correlation coefficients. The uncoupling index (UI), a measure of the balance between markers of bone formation (PINP) and bone resorption (CTX), with positive UI favoring bone formation, was calculated. Results in men were compared to 12-month results for women from the ACTIVE study using the z score test after Fisher's Z transformation. In abaloparatide-treated men, PINP increases at 1 month (r = 0.485), 3 months (r = 0.614), 6 months (r = 0.632), and 12 months (r = 0.521) were highly correlated (P<.0001) with 12-month lumbar spine BMD increases. The mean UI for abaloparatide-treated men was greater than placebo as early as 1 month (2.26 versus -0.25). At month 3, the mean UI for men was greater (1.32) than for women (0.88) (P<.001). There was a significant correlation between 3-month UI and lumbar spine BMD at 12 months in both men (r = 0.453; P<.001) and women (r = 0.252; P<.01); UI at months 6 and 12 were also significantly correlated with 12-month lumbar spine BMD in men and women, but the correlation was stronger in men than women. These data support that early changes in BTMs in men treated with abaloparatide are associated with subsequent changes in BMD similar to what has been reported in women. Trial registration: clinicaltrials.gov Identifier NCT03512262.
Keywords: Abaloparatide; Bone turnover markers; Ctx; Osteoporosis; Pinp; Uncoupling index.
Bone turnover markers are proteins measured in the blood to evaluate bone formation (PINP) and resorption (CTX). Early change in the balance between these proteins, called the uncoupling index, are related to subsequent changes in bone mineral density (BMD). This study in men treated with abaloparatide showed that increased bone turnover markers and uncoupling index at 1, 3, 6, and 12 months were associated with subsequent changes in BMD. These findings are similar to results in women treated with abaloparatide, supporting that early changes in bone turnover markers can indicate that BMD will increase in response to abaloparatide.
© The Author(s) 2025. Published by Oxford University Press on behalf of the American Society for Bone and Mineral Research.