New perspectives on parathyroid hormone therapy

Comparison of the effects of once-weekly and once-daily rhPTH (1-34) injections on promoting fracture healing in rodents

To compare the efficacy of once-weekly and once-daily subcutaneous injections of teriparatide (recombinant human parathyroid hormone 1-34) on fracture healing, 50 adult male Sprague-Dawley rats were subjected to a unilateral tibia fracture and received internal fixation with a Kirschner needle. Based on the injection dose and frequency, the rats were randomly divided into five groups (n = 10 each): subcutaneous injections of saline or 10 µg/kg/w, 20 µg/kg/w, 10 µg/kg/d, and 20 µg/kg/d teriparatide. Four weeks later, the rats were euthanatized, and the fractured tibiae were assessed using X-rays, dual-energy X-ray absorptiometry, micro-computed tomography, the three-point bending biomechanics test, and histology. Compared to the saline control group, either daily or weekly subcutaneous injections of teriparatide significantly increased bone mass, improved the bone microarchitecture, and promoted fracture healing (p < 0.05). There were no significant differences in bone mineral density (BMD), bone microstructure or bone strength between the 20 µg/kg/w and 10 µg/kg/d groups (p > 0.05). Teriparatide 20 µg weekly injections promoted bone fracture healing to the same extent as teriparatide 10 µg daily injections, which can dramatically decrease the cumulative dosage of teriparatide injections. © 2017 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 36:1145-1152, 2018.

Osteoporosis drug therapy strategies in the setting of disease-modifying agents for autoimmune disease

The purpose of this systematic review is to evaluate the effects of methotrexate (MTX) and tumor necrosis factor-alpha (TNF-α) inhibitors on bone mineral properties in the clinical literature. A systematic review of the literature identifying relevant case reports, population-based studies, cohort studies, case control studies, and randomized controlled trials in Pubmed and Web of Science databases from inception to December 31, 2011 was conducted. The following keywords were used: "bone turnover," "bone mineral density," "TNF-α inhibitors," "infliximab," "adalimumab," "etanercept," and "MTX." The bibliographies of all retrieved studies were also reviewed to identify additional articles. Based on these results, a rational drug therapy strategy was suggested for treating osteoporosis in patients with inflammatory disease. MTX and TNF-α inhibitors do not appear to have an adverse effect on BMD in patients with inflammatory disease. Their negative effects on BMD and bone turnover in pre-clinical models appear to be outweighed by their anti-disease effects in clinical studies. Treatment with MTX or TNF-α inhibitors has no adverse effect on BMD in patients with inflammatory disease. Future studies will focus on developing optimal drug strategies when combining DMARDs with anti-osteoporotic agents in this patient population.

Risedronate did not block the maximal anabolic effect of PTH in aged rats

The study was designed to investigate if pre-treating rats with a therapeutic equivalent dose of risedronate blunted the anabolic effects of PTH, and whether a withdrawal period prior to PTH treatment would alter any effect of risedronate on PTH treatment. Skeletally mature rats were treated for 18 weeks with vehicle, risedronate, or risedronate for 8 weeks followed by vehicle for 10 weeks (withdrawal period). At the end of this period, animals were treated for a further 12 weeks with PTH or PTH vehicle. Trabecular and cortical bone mass were monitored by serial pQCT, or by DXA and microCT. Bone histomorphometry was performed on the proximal tibiae and tibial shafts for bone turnover parameters at week 40. Risedronate alone moderately increased while PTH alone markedly increased trabecular bone mass at the proximal tibial (35% and 200%, respectively) and lumbar vertebral body (14% and 36%, respectively). The maximum bone gains were similar with and without pretreatment with risedronate as compared to the PTH alone. Continuous administration of risedronate for 18 weeks prior to PTH treatment had lower percentage increases in proximal tibial BMD during the first 8 weeks of PTH treatments, and had lower active bone forming surface and bone formation rates after being treated with PTH 12 weeks as compared to the PTH alone group. However, with the 10-week withdrawal period, risedronate did not blunt the stimulatory effect of PTH on osteoblast activity as shown by similar bone formation rates as with PTH alone. Our findings suggest that while risedronate pretreatment may slow the bone anabolic response to PTH, a withdrawal period prior to PTH treatment allows osteoblastic activity to respond normally to PTH stimulation.