Combination treatment with growth hormone and zoledronic acid in a mouse model of Osteogenesis imperfecta

Introduction: Osteogenesis imperfecta (01) or brittle bone disease is a genetic disorder that results in bone fragility. Bisphosphonates such as zoledronic acid (ZA) are used clinically to increase bone mass and reduce fracture risk. Human growth hormone (hGH) has been used to promote long bone growth and forestall short stature in children with CH. The potential for hGH to improve bone quality, particularly in combination with ZA has not been robustly studied. Methods: A preclinical study was performed using n = 80 mice split evenly by genotype (WT, Col1a2(+G610C)) Groups of n = 10 were treated with +/-ZA and +/-hGH in a factorial design for each genotype. Outcome measures included bone length, isolated muscle mass, bone parameters assessed by microCT analysis, dynamic histomorphometry, and biomechanical testing. Results: Treatment with hGH alone led to an increase in femur length in WT but not OI mice, however bone length was increased in both genotypes with the combination of hGH/ZA. MicroCT showed that hGH/ZA treatment increased cortical BV in both WT (+15%) and OI mice (+14.3%); hGH/ZA were also found to be synergistic in promoting cortical thickness in OI bone. ZA was found to have a considerably greater positive impact on trabecular bone than hGH. ZA was found to suppress bone turnover, and this was rescued by hGH treatment in terms of cortical periosteal perimeter, but not by dynamic bone remodeling. Statistically significant improvements in long bone by microCT did not translate into improvements in mechanical strength in a 4-point bending test, nor did vertebral strength improve in L4 compression testing in WT/OI bone. Discussion/Conclusion: These data support hGH/ZA combination as a treatment for short stature, however the improvements granted by hGH alone and in combination with ZA on bone quality are modest. Increased periosteal perimeter does show promise in improving bone strength in OI, however a longer treatment time may be required to see effects on bone strength through mechanical testing.

Automated summary

This preclinical study investigated the effects of human growth hormone (hGH) and zoledronic acid (ZA) on bone quality in mice with osteogenesis imperfecta (OI). The results showed that hGH alone increased bone length in wild-type mice, while the combination of hGH/ZA increased bone length in both wild-type and OI mice. MicroCT analysis revealed that hGH/ZA treatment increased cortical bone density and thickness. ZA had a greater impact on trabecular bone, but hGH rescued bone turnover. However, these improvements in bone quality did not translate into improvements in mechanical strength.