Aim of the study was to evaluate the effect of rhOPG-Fc on bone structure of growing pigs to gain basic data for the evaluation of the pig as a large animal model for this specific treatment option of osteoporosis.
Twelve 2 months old Large White pigs were assigned to two groups with 6 pigs each. The first group received 5 mg rhOPGFc/kg IV at day 0, the control group was given 0.9% NaCl solution. Venous blood samples were taken every 5 days to evaluate rhOPG-Fc serum levels. At day 20 pigs were euthanized. Femoral neck, tuber ischiadicum, L4, and two regions of the proximal tibia (proximal and distal of the epiphysis) were subjected to µCT analysis and femora to DXA scans. For statistical analysis a non-parametrical test (U-test) was employed. µCT analysis showed a significantly higher connectivity density (femur, tibia R1, L4) as well as BMD-tissue (femur, hip, tibia R1) in the OPG group. The degree of anisotropy was significantly lower in the tibiae of OPG-Fc pigs. Concerning trabecular parameters besides connectivity density, Tb.Th was significantly lower in OPG-Fc pigs (femur, hip, L4).
On the other hand, Tb.N was higher (femur) and a trend towards lower Tb.Sp (tibia R1) was evident, leading to a significantly higher BS/BV (femur, hip, L4) in OPG-Fc pigs. Peak OPG-Fc levels were seen at day 5 and continuously declined thereafter. At day 15, measureable levels could only be detected in 2/6 animals. DXA data and ash density did not differ significantly between the two groups. Treatment of growing pigs with rhOPG-Fc seemed to predominantly have an effect on trabecular architecture and bone mineralisation. Concerning bone microstructure, OPG-Fc treatment led to a more arborescent architecture and higher mineralisation in the weight-bearing skeleton.