Kostenuik, Paul J.

Objective: This post hoc analysis evaluated the efficacy of abaloparatide treatment in a subgroup of postmenopausal women from the Abaloparatide Comparator Trial In Vertebral Endpoints (ACTIVE; NCT01343004) study who met high fracture risk criteria (defined in several professional society guidelines). Methods: Women from ACTIVE meeting ≥1 of the following fracture risk criteria were included: fracture within the past 12 months or prevalent vertebral fracture, baseline T score of <−3.0 at any site, very high fracture risk probability by FRAX (ie, 10-yr major osteoporotic fracture >30% or hip fracture >4.5%), or multiple prior fractures at baseline since age ≥45 years. Results: A total of 2,026 participants met ≥1 fracture risk criteria defined in clinical guidelines (abaloparatide, n = 664; placebo, n = 677; teriparatide, n = 685). New vertebral fracture risk was reduced in participants receiving abaloparatide (4 [0.72%]) and teriparatide (6 [0.99%]) versus placebo (28 [4.77%]; both P < 0.0001). Estimated Kaplan-Meier cumulative incidence of nonvertebral fracture was 3.0%, 5.3%, and 3.0% in the abaloparatide, placebo, and teriparatide groups, respectively; 4.0%, 9.0%, 4.3% for clinical fracture; 1.6%, 6.8%, 3.0% for major osteoporotic fractures; and 1.1%, 2.1%, 2.1% for wrist fracture. Abaloparatide was associated with bone mineral density gains from baseline at the lumbar spine, total hip, and femoral neck at all time points (6, 12, and 18 mo; P < 0.0001 for all). Common adverse events reported in participants treated with abaloparatide were hypercalciuria (11.5%), dizziness (11.0%), and arthralgia (8.9%). Conclusions: Abaloparatide reduced fracture incidence and increased bone mineral density in participants at highest fracture risk, consistent with the overall ACTIVE study.

Context: Intermittent PTH treatment stimulates bone formation, but the mechanism(s) of this effect remain unclear. Sclerostin is an inhibitor of Wnt signaling, and animal studies have demonstrated that PTH suppresses sclerostin production. Objective: The objective of the study was to test whether intermittent PTH treatment of postmenopausal women alters circulating sclerostin levels. Design: Prospective study. Setting: The study was conducted at a clinical research unit. Participants and Interventions: Participants included 27 postmenopausal women treated with PTH (1-34) for 14 d and 28 control women. Main Outcome Measures: Serum sclerostin levels were measured. Results: Circulating sclerostin levels decreased significantly in the PTH-treated subjects, from (mean ± SEM) 551 ± 32 to 482 ± 31 pg/ml (−12.7%, P &lt; 0.0001) but did not change in the control women (baseline, 559 ± 34 pg/ml; end point, 537 ± 40 pg/ml, P = 0.207; P = 0.017 for difference in changes between groups). Bone marrow plasma was obtained in a subset of the control and PTH-treated subjects (n = 19 each) at the end of the treatment period, and marrow plasma and peripheral serum sclerostin levels were significantly correlated (R = 0.64, P &lt; 0.0001). Marrow plasma sclerostin levels were 24% lower in PTH-treated compared with control women, but perhaps due to the smaller sample size, this difference was not statistically significant (P = 0.173). Conclusions: Circulating sclerostin levels correlate with bone marrow plasma levels and are reduced by intermittent PTH therapy in postmenopausal women. Further studies are needed to assess the extent to which decreases in sclerostin production contribute to the anabolic skeletal response to PTH.

Abstract Skeletal unloading decreases bone formation and osteoblast number in vivo and decreases the number and proliferation of bone marrow osteoprogenitor (BMOp) cells in vitro. We tested the ability of parathyroid hormone (PTH) to stimulate BMOp cells in vivo by treating Sprague Dawley rats (n = 32) with intermittent PTH(1–34) (1 h/day at 8 μ g/100 g of body weight), or with vehicle via osmotic minipumps during 7 days of normal weight bearing or hind limb unloading. Marrow cells were flushed from the femur and cultured at the same initial density for up to 21 days. PTH treatment of normally loaded rats caused a 2.5-fold increase in the number of BMOp cells, with similar increases in alkaline phosphatase (ALP) activity and mineralization, compared with cultures from vehicle-treated rats. PTH treatment of hind limb unloaded rats failed to stimulate BMOp cell number, ALP activity, or mineralization. Hind limb unloading had no significant effect on PTH receptor mRNA or protein levels in the tibia. Direct in vitro PTH challenge of BMOp cells isolated from normally loaded bone failed to stimulate their proliferation and inhibited their differentiation, suggesting that the in vivo anabolic effect of intermittent PTH on BMOp cells was mediated indirectly by a PTH-induced factor. We hypothesize that this factor is insulin-like growth factor-I (IGF-I), which stimulated the in vitro proliferation and differentiation of BMOp cells isolated from normally loaded bone, but not from unloaded bone. These results suggest that IGF-I mediates the ability of PTH to stimulate BMOp cell proliferation in normally loaded bone, and that BMOp cells in unloaded bone are resistant to the anabolic effect of intermittent PTH therapy due to their resistance to IGF-I.