Combination of Local and Systemic Parathyroid Hormone Enhances Bone Regeneration

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Abstract
Parathyroid hormone is one of the most promising therapeutic agents for osteopororosis, but its use to facilitate bone regeneration in osseous defects is less clear. The purpose of the current study was to determine the effects of combining systematic parathyroid hormone and a local parathyroid hormone gene theraphy in a critical-sized osteotomy model. Rats received bilateral femoral osteotomies followed by implantation of a gene-activated matrix encoding parathyroid hormone (1–34) on one side and a control gene-activated matrix on te opposite side. Systematic parthyroid hormone (1–34) or vehicle was injected daily and rats were sacrificed 6 weeks later. Systematic parathyroid hormone increased bone mineral density and bone mineral content measured by dual-energy xray absorptiometry analysis of tibias and vertebrae, and increased serum osteocalcin levels during healing of osteotomies. Furthermore, comparing osteotomy sites that received the same gene-activated matrices as vehicle-injected rats, parathyroid hormone-injected rats showed trends of greater bone areas via histomorphometric and microdiographic analyses and higher osteocalcin mesenger ribonucleic acid expression via Northern blot analyses. The combination of systemic and local parathyroid hormone led to higher bone mineral density, bone mineral content, and bone area, a trend for greater radiographic-detected bone area and higher expression of osteocalcin in osteotomy sites when compared with the individual treatment or control groups. Local parathyroid hormone gene theraphy enhanced the anabolic effect of systemic parathyroid hormone during osteomy healing. This study supports the concept of a combined local and systemic approach for enhancing the repair of a fracture at risk for nonunion.

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