We recently developed a new therapy using effective-mononuclear cells (E-MNCs) and demonstrated its efficacy in treating radiation-damaged salivary glands (SGs). The activity of E-MNCs in part involves constituent immunoregulatory -CD11b/macrophage scavenger receptor 1(Msr1)-positive-M2 macrophages, which exert anti-inflammatory and tissue-regenerating effects via phagocytic clearance of extracellular high mobility group box 1 (HMGB1). Focusing on the phenomena, this study investigated significance of regulating the HMGB1/toll-like receptor 4 (TLR4)/receptor for advanced glycation end products (RAGE) signaling pathway in the treatment of SG dysfunction caused by radiation damage. E-MNCs were transplanted into radiation-damaged mice SGs, and changes of TLR4/RAGE expression were observed. Furthermore, the activation of downstream signals was investigated in both intact SGs and cultured SG epithelial cells after irradiation. Subsequently, TLR4-knock-out (KO) mice were employed to examine how HMGB1/TLR4/RAGE signaling affected damage progression. Expression of both TLR4 and RAGE was diminished in ductal cells and macrophages/vascular endothelial cells of damaged SGs with E-MNC transplantation, respectively. Meanwhile, expression of TLR2/4 and RAGE in damaged SGs markedly increased in association with extracellular HMGB1 accumulation. Downstream signals were activated, and intranuclear localization of phospho-nuclear factor-kappa B (p–NF–KB) in ductal cells and production of IL-6, tumor necrosis factor-α (TNF-α), and interferon-γ (IFN-γ) were observed. Additionally, culture supernatant of irradiated cultured SG epithelial cells contained damaged associated molecular pattern (DAMP)/senescence-associated secretory phenotype (SASP) factors. Treatment of cultured SG epithelial cells with this supernatant activated TLR4 signaling pathway and induced cellular senescence. In TLR4-KO mice, onset of radiogenic SG dysfunction was markedly delayed. However, TLR2/RAGE signalings were alternatively activated, and SG function was impaired. Clearance of DAMPs such as HMGB1 may attenuate sterile inflammation in damaged SGs via suppression of the TLR4/RAGE signaling pathway. This cellular mechanism may have significant implications for the development of future cell-based regenerative therapies.

Background: To explore the effects of topographical modification of titanium substrates at submicron level by oxalic acid treatment on bone quality and quantity around dental implants in rabbit tibiae.Methods: A total of 60 blasted CP-grade IV titanium dental implants were used. Twenty-eight control implant surfaces were treated with a mixture of HCl/H₂SO₄, whereas 28 other test implant surfaces were treated with oxalic acid following HCl/H₂SO₄treatment. Two randomly selected sets of control or test implants were placed in randomly selected proximal tibiae of 14 female Japanese white rabbits. Euthanasia was performed 4 and 8 weeks post-implant placement. Bone to implant contact (BIC), bone area fraction (BAF), ratios of mature and immature bone to total bone, and the amount and types of collagen fibers were evaluated quantitatively. Two control and two test implants were used to analyze surface characteristics.Results: Treatment by oxalic acid significantly decreased Sa and increased Ra of test implant surfaces. BIC in test implants was increased without alteration of BAF and collagen contents at 4 and 8 weeks after implant placement when compared with control implants. The ratios of immature and mature bone to total bone differed significantly between groups at 4 weeks post-implantation. Treatment by oxalic acid increased type I collagen and decreased type III collagen in bone matrices around test implants when compared with control implants at 8 weeks after implant placement. The effects of topographical changes of implant surfaces induced by oxalic acid on BAF, mature bone, collagen contents, and type I collagen were significantly promoted with decreased immature bone formation and type III collagen in the later 4 weeks post-implantation.Conclusions: Treatment of implant surfaces with oxalic acid rapidly increases osseointegration from the early stages after implantation. Moreover, submicron topographical changes of dental implants induced by oxalic acid improve bone quality based on bone maturation and increased production of type I collagen surrounding dental implants in the late stage after implant placement.