P2. Use of semaphorin 3A for improving osseointegration of titanium implants in type 2 diabetes mellitus rats

BACKGROUND CONTEXT Type 2 diabetes mellitus (T2DM) is a systemic disease that can compromise osseointegration of metal implants; thus, technologies that can improve osteogenesis in T2DM patients are needed. Semaphorin 3A (3A) is a novel osteoprotective protein that has been reported to improve bone formation. Our goal was to assess 3A for potential clinical use. However, current T2DM rat models lack translatability to human conditions. It is important to clarify osseointegration in a more translational T2DM. For this study, we used the Zucker diabetic Sprague Dawley rat (ZDSD) as a more clinically relevant T2DM model. It is a polygenic model with an intact leptin pathway as in humans, and exhibits human-like type 2 diabetes progression. PURPOSE This study used grit blasted/acid etched (SLA) Ti implants (microrough/hydrophobic) in ZDSD rat femurs to determine if 3A can improve their osseointegration in T2DM. METHODS Thirty male, 15-week-old ZDSD rats (D, Charles River) and 24 aged-matched male Sprague Dawley rats (N, Charles River) were used (IACUC approved). Rats were paired fed with a high-fat diet (Purina 5SCA) until 70% of D rats turned diabetic (blood glucose >250mg/dL for a week) and switched to a normal diet (Purina 5008) for the rest of the study. Three weeks after turning diabetic, D rats were randomized to three groups: click hydrogel delivery vehicle (D GEL), hydrogel containing 3A (D 3A+GEL), hydrogel implanted and 3A injected separately (D i3A+GEL) with n=7. N rats were randomized to N GEL, N 3A+GEL, N i3A+GEL with n=8. Holes were created bilaterally in the metaphysis of distal femurs, and hydrogels were inserted in the hole by mixing PEG-N3 and PEG-DBCO crosslinker with either 0.9% sterile saline in GEL and i3A+GEL or with 6ug 3A in 3A+GEL. SLA implants (Institut Straumann AG) were inserted immediately into the holes after GEL. i3A+GEL had bilateral subperiosteal 3A injections (6ug/leg) at implant sites on day 3 and day 10 post-surgery. Rats were euthanized at 4 weeks postop. Bone phenotype and osseointegration of isolated fixed femurs were assessed by micro-computed tomography (microCT). Total bone to implant contact (BIC) was defined as the percentage of the implant surface in contact with newly formed bone. Evaluations of BIC were also performed separately for two subregions, the medullary (bone marrow BIC) and the cortical compartment (cortical BIC). Removal torque testing was performed with fresh, non-fixed femurs. RESULTS D GEL had less trabecular bone formation than N GEL. Cortical bones at metaphysis and mid-diaphysis were not affected by T2DM. D GEL had less total BIC and less bone marrow BIC but no difference in cortical BIC than N GEL. D 3A+GEL had less total BIC and cortical BIC than N 3A+GEL but bone marrow BIC in D 3A+GEL was the same as in N 3A+GEL. Similar results were observed between D i3A+GEL and N i3A+GEL. Maximum torque and torsional stiffness were less in D GEL than N GEL but not different between D 3A+GEL and N 3A+GEL or D i3A+GEL and N i3A+GEL. There was no significant difference in torsional energy among all groups. CONCLUSIONS T2DM reduced trabecular bone formation but did not affect cortical bone. Osseointegration was impaired in T2DM indicated by having less total BIC. Sema3A improved osseointegration in T2DM indicated by increased bone marrow BIC and increased mechanical properties of integrated bone tissues after sema3A delivered by hydrogel or local injection. FDA DEVICE/DRUG STATUS This abstract does not discuss or include any applicable devices or drugs.