Locally delivered rhTGF-β 2 enhances bone ingrowth and bone regeneration at local and remote sites of skeletal injury

Abstract

The purposes of the present study were to determine if recombinant human transforming growth factor-beta-2 (rhTGF-β 2) enhances bone ingrowth into porous-coated implants and bone regeneration in gaps between the implant and surrounding host bone. The implants were placed bilaterally for four weeks in the proximal humeri of skeletally mature, adult male dogs in the presence of a 3-mm gap. In three treatment groups of animals, the test implant was treated with hydroxyapatite/tricalcium phosphate (HA/TCP) and rhTGF-β 2 in buffer at a dose per implant of 1.2 μg ( n=6), 12 μg ( n=7), or 120 μg ( n=7) and placed in the left humerus. In these same animals, an internal control implant treated only with HA/TCP and buffer was placed in the right humerus. In a non-TGF-β treated external control group of animals ( n=7), one implant was treated with HA/TCP while the contralateral implant was not treated with the ceramic. In vitro analyses showed that approximately 15% of the applied dose was released within 120 h with most of the release occurring in the first 24 h. The TGF-β treated implants had significantly more bone ingrowth than the controls with the greatest effect in the 12 μg/ implant group (a 2.2-fold increase over the paired internal control ( P=0.004) and a 4-fold increase over the external control ( P<0.001)). The TGF-β treated implants had significantly more bone formation in the gap than the controls with the greatest effect in the 12 and 120 μg groups (1.8-fold increases over the paired internal controls ( P=0.003 and P=0.012, respectively) and 2.8-fold increases over the external controls ( P<0.001 and P=0.001, respectively)). Compared to the external controls, the internal control implants tended to have more bone ingrowth (1.9-fold increase, P=0.066) and had significantly more bone formation in the gap (1.7-fold increase, P=0.008). Thus, application of rhTGF-β 2 to a porous-coated implant-stimulated local bone ingrowth and gap healing in a weakly dose-dependent manner and stimulated bone regeneration in the 3-mm gap surrounding the contralateral control implant, a site remote from the local treatment with the growth factor.