Biological Effect of Human Recombinant Parathyroid Hormone at Critical Size Defects

Abstract

Recombinant Human Parathyroid Hormone (rhPTH 1-34) is an effective treatment to improve bone mass in patients with osteoporosis, however its effects on bone lose other etiology are still unclear. The aim of this study was to evaluate rhPTH action on bone healing process at calvaria critical size defect (CZD). Methods: In 43 wistar female rat (body weight 150 ± 50 g), a CZD (5mm) was created on calvariae. The animals were divided in 2 groups: A) Control Group (CG) that no received any treatment and B) Experimental Group (EG): that received daily, a rhPTH (20ug/kg/day) subcutaneous injection. Blood and urine samples were taken to evaluate bone response from biochemical markers. Bone healing was evaluated at 1º, 3º and 6º weeks post surgery with soft X ray, histological and morphometrical studies. Soft X Ray Results: a rounded radiolucent image within radiopaque irregular areas were observed, at both groups; however were more important in EG. Histological Results: CG: at 1º, 3º weeks; new bone formation was observed on the CZD edges. There were some osteoblasts and linning cells, with few osteoclasts. At 6° weeks bone formation was observed on CZD edges and also in central area. EG: an increment in the number and activity of osteoblast and linning cells were observed at 1° week. At 3° weeks, reticular and lamellar bone, and a disrupted mineralization wkere obtained. And at 6° week bone formation periosteal and endocortical organized in looping or networking pattern. Calcemia, calciuria, alkaline phosphatase and Tartrate resistant acid phosphatise levels were similar at baseline as well as 1, 3 and 6 weeks after treatment. Morphometric Results: CG: 0.21%, 0.65 %, 1.06 % at 1°, 3° y 6° week respectively. EG: 0.84 %, 0.42 % y 2.81 % at same time periods. The data were submitted to statistically analysis by Kruskal Wallis Test. Statistical difference between CG and EG was observed at 6° weeks (p= 0.023). Conclusion: Under these experimental conditions, rhPTH on CZD at calvariae generate an increased activity of Bone Multicellular Units. Also, the new bone formed has a pattern like Hyperostosis (AFIP 1993).

La parathormona recombinate humana (rhPTH) es una terápéurica eficaz para el tratamiento de la Osteoporosis, sin embargo se desconoce su respuesta en pérdidas óseas de diferentes etiologías. OBJETIVO: evaluar el efecto biológico de la rhPTH intermitente durante la regeneración ósea de defectos óseos críticos (DOC) en calota. METODOS: en 43 ratas Wistar hembras (150± 50 g) se realizaron DOC de 5 mm de diámetro en hueso parietal. Se dividieron en dos grupos: control (GC), no recibió ningún tratamineto postquirúrgico; y grupo experiemntal (GE), una inyección diaria de 20 ug/kg/día (rhPTH) vía subcutánea. Se recogieron muestras de sangre y orina (pre y post tratamiento), para estudiar marcadores bioquímicos óseos. la regeneración ósea se evaluó a la 1°, 3° y 6° semana (s) post quirúrgica; utilizando rayos X blandos, estudios histológicos y morfométricos. RESULTADOS RADIOGRAFICOS: En ambos grupos se observó áreas radiolúcidas circulares correspondientes al DOC, áreas radiopacas internas e irregulares de mayor tamaño en GE. RESULTADOS HISTOLÓGICOS: GC: a la 1° y 3° s se observó neoformación ósea incipiente en extremos del DOC, con presencia de osteoblastos y células linning y escasos osteoclastos. A la 6° s se observó formación ósea incipiente en extremos y en el área central del DOC. En el GE: a la 1° s: aumento del número y actividad de osteoblastos, células linnig y osteoclastos; a la 3° s hueso reticular, laminar y mineralización ósea desordenada; a la 6° s el hueso parietal presentó formación ósea perióstica y endóstica, dispuesta en capas arremilnadas. RESULTADOS BIOQUIMICOS: calcemia, calciuria , fosfatasa alcalina y fosfatasa ácida tartrato resistente presentaron valores semejantes al nivel basal y a la 1°,3° y 6° semanas post tratamiento. RESULTADOS HISTOME TRICOS: GC: 0.21%, 0.65%, 1.06% a la 1°, 3°y 6° s repectivamente. Mientras que en GE: 0.84%, 0.42% y 2.81% en iguales períodos. Los datos obtenidos fueron analizados estadísticamente con el Test de Kruskal Wallis, observándose diferencias significativas entre el GC y GE a la 6° semana (p=0.023) CONCLUSION: la rh PTH activó e incrementó la actividad de la Unidad Multicelular Ósea, presentando un cuadro semejante a la Hiperostosis (AFIP 1993).