Single local injection of 3S-HMGB1 enhances early bone healing and titanium implant osseointegration in type 2 diabetic mice

Introduction: Diabetes significantly impairs bone healing through several mechanisms, including sustained inflammation, oxidative stress, and poor osteogenic responses. The fully reduced isoform of High Mobility Group Box 1 with three serine substitutions (3S-HMGB1) has shown regenerative properties while being resistant to oxidative degradation. Therefore, this study aims to evaluate the therapeutic potential of a single local dose of 3S-HMGB1 in early osseointegration under diabetic conditions in mice. Methodology: Forty-eight male 129/Sv mice (24 non-diabetic [ND], 24 diabetic [D]) received titanium implants following maxillary first molar extraction. ND and D mice (n:12) were injected with either saline (control) or 3S-HMGB1 (0.75 mg/kg) into the fresh extraction socket. Osseointegration was evaluated at 7 and 21 days post-implantation using micro-CT, histology (bone-to-implant contact [BIC] and birefringence), and immunohistochemistry for Runx2 and CXCR4. Results: ND controls exhibited early osteogenic activity, with a predominance of Runx2-positive cells at 7 days and successful osseointegration by 21 days. In contrast, D controls showed reduced numbers of Runx2-positive cells and markedly lower BV/TV compared to ND controls, indicating compromised bone healing at 21 days. Treatment with 3S-HMGB1 resulted in significantly increased bone volume at the implant site in D animals (55.6 ± 7.20% vs. 44.6 ± 6.23%) and restored BIC from 44.9 ± 9.32% (D Controls) to 61.78 ± 11.31% (D 3S-HMGB1), near-ND levels (65.16 ± 7.64%). Both ND and D groups treated with 3S-HMGB1 showed enhanced collagen organization. No significant differences were found in CXCR4 among groups; however, in D animals, a distinct peri-implant staining pattern suggested impaired recruitment despite preserved stem cell niches in the bone marrow. Conclusions: Collectively, our findings indicate that a single administration of redox-stable 3S-HMGB1 may represent a promising regenerative strategy to mitigate early implant failure in diabetes. Future studies should explore sustained delivery approaches to enhance long-term outcomes.