BMP-2/7 heterodimer strongly induces bone regeneration in the absence of increased soft tissue inflammation

Publication date: Available online 20 July 2017
Source:The Spine Journal
Author(s): Takashi Kaito, Tokimitsu Morimoto, Yuki Mori, Sadaaki Kanayama, Takahiro Makino, Shota Takenaka, Yusuke Sakai, Satoru Otsuru, Yoshichika Yoshioka, Hideki Yoshikawa
Background ContextBone morphogenetic protein (BMP)-2/7 heterodimer is a stronger inducer of bone regeneration than individual homodimers. However, clinical application of its potent bone induction ability may be hampered if its use is accompanied by excessive inflammatory reactions.PurposeWe sought to quantitatively evaluate bone induction and inflammatory reactions by BMP heterodimer and corresponding BMP homodimers using ultra-high resolution magnetic resonance imaging (MRI) and micro-computed tomography.Study DesignExperimental animal study.MethodsA total of 32 absorbable collagen sponge implantations into dorsal muscle were performed in rats of four different groups (control group, 0 µg BMP; recombinant human (rh)BMP-7 group, 3 µg rhBMP-7; rhBMP-2 group, 3 µg rhBMP-2; rhBMP-2/7 group, 3 µg rhBMP-2/7). Inflammatory reactions were evaluated by 11.7-T MRI (axial T2-weighted imaging using Rapid Acquisition with Relaxation Enhancement) at postoperative days 2 and 7. Bone volumes (BVs) of the induced ectopic bone were quantified at postoperative day 7. In addition, immunohistochemical staining for IL-1β, IL-6, and TNF-α was performed in samples obtained on postoperative day 2. Bone formation (BF)/inflammation (IM) ratios were calculated by dividing bone volumes by values of inflamed areas.ResultsAt postoperative day 2, the mean volume of T2 high area on MRI scans in BMP-2 group was significantly larger than that in control group. In contrast, the BMP-2/7 had no difference in the mean volume of T2 high area compared to the control group, however there was no difference between the BMP-2/7 compared to BMP-2 group. At postoperative day 7, the volumes of T2 high area were not different between the groups. Mean BV of the newly formed bone on postoperative day 7 was significantly greater in BMP-2/7 group than in BMP-7 groups. No new bone formation was observed in control group. BF/IM ratio in BMP-2/7 group was significantly higher than those in BMP-2 and BMP-7 homodimer groups. Immunohistochemistry experiments did not reveal differences in expression levels of IL-1β, IL-6, or TNF-α in samples from BMP-2, BMP-7, and BMP-2/7 groups.ConclusionsThis study demonstrated that BMP-2/7 heterodimer has stronger bone induction ability without accompanying increased inflammatory reactions (the increased bone formation to inflammation ratio) than those observed by BMP-2 or BMP-7 homodimers. These results suggest that BMP-2/7 heterodimer can be an alternative to BMP-2 and BMP-7 homodimers in clinical applications, although further translational studies including whether lower doses of BMP heterodimer may produce similar bone formation compared to the BMP homodimers but produce a reduced inflammatory response are required.



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