Photodynamic therapy in periodontitis: A narrative review

BACKGROUND

Periodontitis, a chronic infectious disease, is primarily caused by a dysbiotic microbiome, leading to the destruction of tooth-supporting tissues and tooth loss. Photodynamic therapy (PDT), which combines excitation light with photosensitizers (PS) and oxygen to produce antibacterial reactive oxygen species, is emerging as a promising adjuvant treatment for periodontitis.

METHODS

This review focuses on studies examining the antibacterial effects of PDT against periodontal pathogens. It also explores the impact of PDT on various aspects of periodontal health, including periodontal immune cells, human gingival fibroblasts, gingival collagen, inflammatory mediators, cytokines in the periodontium, vascular oxidative stress, vascular behavior, and alveolar bone health. Clinical trials assessing the types of PSs and light sources used in PDT, as well as its effects on clinical and immune factors in gingival sulcus fluid and the bacterial composition of dental plaque, are discussed.

RESULTS

The findings indicate that PDT is effective in reducing periodontal pathogens and improving markers of periodontal health. It has shown positive impacts on periodontal immune response, tissue integrity, and alveolar bone preservation. Clinical trials have demonstrated improvements in periodontal health and alterations in the microbial composition of dental plaque when PDT is used alongside conventional treatments.

CONCLUSIONS

PDT offers a promising adjunctive treatment for periodontitis, with benefits in bacterial reduction, tissue healing, and immune modulation. This article highlights the potential of PDT in periodontal therapy and emphasizes the need for further research to refine its clinical application and efficacy.

Modes and Mechanisms of Salivary Gland Epithelial Cell Death in Sjogren's Syndrome

Sjogren's syndrome is an autoimmune disease in middle and old-aged women with a dry mucosal surface, which is caused by the dysfunction of secretory glands, such as the oral cavity, eyeballs, and pharynx. Pathologically, Sjogren's syndrome are characterized by lymphocyte infiltration into the exocrine glands and epithelial cell destruction caused by autoantibodies Ro/SSA and La/SSB. At present, the exact pathogenesis of Sjogren's syndrome is unclear. Evidence suggests epithelial cell death and the subsequent dysfunction of salivary glands as the main causes of xerostomia. This review summarizes the modes of salivary gland epithelial cell death and their role in Sjogren's syndrome progression. The molecular mechanisms involved in salivary gland epithelial cell death during Sjogren's syndrome as potential leads to treating the disease are also discussed.

The Paracrine Effect of Hyaluronic Acid-Treated Endothelial Cells Promotes BMP-2-Mediated Osteogenesis

The combination of hyaluronic acid (HA) and BMP-2 has been reported to promote bone regeneration. However, the interaction of endothelial cells and bone marrow mesenchymal stem cells (BMSCs) during HA + BMP-2 treatment is not fully understood. This study aimed to analyze the direct effect of HA, as well as the paracrine effect of HA-treated endothelial cells, on the BMP-2-mediated osteogenic differentiation of BMSCs. The angiogenic differentiation potential of HA at different molecular weights and different concentrations was tested. The direct effect of HA, as well as the indirect effect of HA-treated human umbilical cord endothelial cells (HUVECs, i.e., conditioned medium (CM)-based co-culture) on the BMP-2-mediated osteogenic differentiation of BMSCs was analyzed using alkaline phosphatase (ALP) staining and activity, alizarin red S (ARS) staining, and RT-qPCR of osteogenic markers. Angiogenic differentiation markers were also analyzed in HUVECs after treatment with HA + BMP-2. The bone regeneration potential of BMP-2 and HA + BMP-2 was analyzed in a rat ectopic model. We found that 1600 kDa HA at 300 µg/mL promoted tube formation by HUVECs in vitro and upregulated the mRNA expression of the angiogenic markers CD31, VEGF, and bFGF. HA inhibited, but conditioned medium from HA-treated HUVECs promoted, the BMP-2-mediated osteogenic differentiation of BMSCs, as indicated by the results of ALP staining and activity, ARS staining, and the mRNA expression of the osteogenic markers RUNX-2, ALP, COLI, and OPN. HA + BMP-2 (50 ng/mL) upregulated the expression of the angiogenesis-related genes VEGF and bFGF in HUVECs and bone regeneration in vivo compared to BMP-2 treatment. In conclusion, the paracrine effect of hyaluronic acid-treated endothelial cells promotes BMP-2-mediated osteogenesis, suggesting the application potential of HA + BMP-2 in bone tissue engineering.

Glipizide Alleviates Periodontitis Pathogenicity via Inhibition of Angiogenesis, Osteoclastogenesis and M1/M2 Macrophage Ratio in Periodontal Tissue

New consensus indicates type 2 diabetes mellitus (T2DM) and periodontitis as comorbidity and may share common pathways of disease progression. Sulfonylureas have been reported to improve the periodontal status in periodontitis patients. Glipizide, a sulfonylurea widely used in the treatment of T2DM, has also been reported to inhibit inflammation and angiogenesis. The effect of glipizide on the pathogenicity of periodontitis, however, has not been studied. We developed ligature-induced periodontitis in mice and treated them with different concentrations of glipizide and then analyzed the level of periodontal tissue inflammation, alveolar bone resorption, and osteoclast differentiation. Inflammatory cell infiltration and angiogenesis were analyzed using immunohistochemistry, RT-qPCR, and ELISA. Transwell assay and Western bolt analyzed macrophage migration and polarization. 16S rRNA sequencing analyzed the effect of glipizide on the oral microbial flora. mRNA sequencing of bone marrow-derived macrophages (BMMs) stimulated by P. gingivalis lipopolysaccharide (Pg-LPS) after treatment with glipizide was analyzed. Glipizide decreases alveolar bone resorption, periodontal tissue degradation, and the number of osteoclasts in periodontal tissue affected by periodontitis (PAPT). Glipizide-treated periodontitis mice showed reduced micro-vessel density and leukocyte/macrophage infiltration in PAPT. Glipizide significantly inhibited osteoclast differentiation in vitro experiments. Glipizide treatment did not affect the oral microbiome of periodontitis mice. mRNA sequencing and KEGG analysis showed that glipizide activated PI3K/AKT signaling in LPS-stimulated BMMs. Glipizide inhibited the LPS-induced migration of BMMs but promoted M2/M1 macrophage ratio in LPS-induced BMMs via activation of PI3K/AKT signaling. In conclusion, glipizide inhibits angiogenesis, macrophage inflammatory phenotype, and osteoclastogenesis to alleviate periodontitis pathogenicity suggesting its' possible application in the treatment of periodontitis and diabetes comorbidity.

Resveratrol Alleviates Diabetic Periodontitis-Induced Alveolar Osteocyte Ferroptosis Possibly via Regulation of SLC7A11/GPX4

The mode and mechanism of diabetic periodontitis-induced alveolar-osteocyte death are still unclear. This study aimed to investigate the occurrence of ferroptosis in alveolar osteocytes during diabetic periodontitis and the therapeutic potential of resveratrol to alleviate osteocyte ferroptosis. Diabetic periodontitis was induced in C57/BL6-male mice and treated with or without resveratrol. Periodontitis pathogenicity was analyzed by micro-CT and histology, and alveolar-osteocyte ferroptosis was analyzed by immunohistochemistry. MLOY4 osteocytes were treated with P. gingivalis-derived lipopolysaccharide (LPS)+advanced glycosylated end products (AGEs) mimicking diabetic periodontitis condition in vitro, with or without resveratrol or ferrostatin-1 (ferroptosis inhibitor). Osteocyte ferroptosis and expression of inflammatory mediators were analyzed. Diabetic periodontitis aggravated periodontitis pathogenicity and inhibited the expression of GPX4 and SLC7A11 in alveolar osteocytes and resveratrol alleviated these effects. LPS+AGEs triggered osteocyte ferroptosis in vitro as indicated by the downregulated GPX4 and SLC7A11, upregulated malondialdehyde, disrupted mitochondrial morphology, and overexpressed pro-inflammatory mediators IL-1β, TNF-α, SOST, RANKL, and IL-6, and ferrostatin-1 or resveratrol treatment reversed these effects. LPS+AGEs upregulated pIKBα and pNF-κB p65 expression in osteocytes, and resveratrol or ferrostatin-1 reversed this effect. In conclusion, diabetic periodontitis triggers alveolar osteocyte ferroptosis possibly via disruption of the SLC7A11/GPX4 axis, and resveratrol has therapeutic potential to correct this biological event.

Human Salivary Histatin-1 Attenuates Osteoarthritis through Promoting M1/M2 Macrophage Transition

Osteoarthritis (OA) is an inflammation-driven degenerative joint disease. Human salivary peptide histatin-1 (Hst1) shows pro-healing and immunomodulatory properties. but its role in OA treatment is not fully understood. In this study, we investigated the efficacy of Hst1 in the inflammation modulation-mediated attenuation of bone and cartilage damage in OA. Hst1 was intra-articularly injected into a rat knee joint in a monosodium iodoacetate (MIA)-induced OA model. Micro-CT, histological, and immunohistochemical analyses showed that Hst1 significantly attenuates cartilage and bone deconstruction as well as macrophage infiltration. In the lipopolysaccharide-induced air pouch model, Hst1 significantly reduced inflammatory cell infiltration and inflammation. Enzyme-linked immunosorbent assay (ELISA), RT-qPCR, Western blot, immunofluorescence staining, flow cytometry (FCM), metabolic energy analysis, and high-throughput gene sequencing showed that Hst1 significantly triggers M1-to-M2 macrophage phenotype switching, during which it significantly downregulated nuclear factor kappa-B (NF-κB) and mitogen-activated protein kinases (MAPK) signaling pathways. Furthermore, cell migration assay, Alcian blue, Safranin O staining, RT-qPCR, Western blot, and FCM showed that Hst1 not only attenuates M1-macrophage-CM-induced apoptosis and matrix metalloproteinase expression in chondrogenic cells, but it also restores their metabolic activity, migration, and chondrogenic differentiation. These findings show the promising potential of Hst1 in treating OA.

Human serum-derived exosomes modulate macrophage inflammation to promote VCAM1-mediated angiogenesis and bone regeneration

During exogenous bone-graft-mediated bone defect repair, macrophage inflammation dictates angiogenesis and bone regeneration. Exosomes from different human cells have shown macrophage immunomodulation-mediated bone regeneration potential. However, the effect of human serum-derived exosomes (serum-Exo) on macrophage immunomodulation-mediated angiogenesis during bone defect repair has not been investigated yet. In this study, we explored the effects of serum-Exo on macrophage inflammation regulation-mediated angiogenesis during bone defect repair and preliminarily elucidated the mechanism. Healthy serum-Exo was isolated by ultracentrifugation. The effect of serum-Exo on LPS-induced M1 macrophage inflammation was analysed in vitro. The conditioned medium of serum-Exo-treated LPS-induced M1 macrophage (serum-Exo-treated M1 macrophage-CM) was used to culture human umbilical vein endothelial cells (HUVEC), and the effect on angiogenesis was analysed by western blot, qRT-PCR, etc. mRNA-sequencing of HUVECs was performed to identify deferentially expressed genes. Finally, the rat mandibular defect model was established and treated with Bio-Oss and Bio-Oss + Exo. The effect of the Bio-Oss + Exo combination on mandibular bone regeneration was observed by micro-computed tomography (micro-CT), haematoxylin and eosin (HE) staining, Masson staining, and immunohistochemical staining. Serum-Exo promoted the proliferation of RAW264.7 macrophages and reduced the expression of M1-related genes such as IL-6, IL-1β, iNOS, and CD86. Serum-Exo-treated M1 macrophage-CM induced the proliferation, migration, and angiogenic differentiation of HUVEC, as well as the expression of H-type blood vessel markers CD31 and endomucin (EMCN), compared with M1 macrophage-CM. Moreover, higher expression of vascular endothelial adhesion factor 1 (VCAM1) in HUVEC cultured with serum-Exo-treated M1 macrophage-CM compared with M1 macrophages-CM. Inhibition of VCAM1 signalling abrogated the pro-angiogenic effect of serum-Exo-treated M1 macrophage-CM on HUVEC. Local administration of serum-Exo during mandibular bone defect repair reduced the number of M1 macrophages and promoted angiogenesis and osteogenesis. Collectively, our results demonstrate the macrophage inflammation regulation-mediated pro-angiogenic potential of serum-Exo during bone defect repair possibly via upregulation of VCAM1 signalling in HUVEC.

Silica nanocarrier-mediated intracellular delivery of rapamycin promotes autophagy-mediated M2 macrophage polarization to regulate bone regeneration

Targeting macrophages to regulate the immune microenvironment is a new strategy for bone regeneration with nano-drugs. Nano-drugs have achieved surprising anti-inflammatory and bone-regenerative effects, however, their underlying mechanisms in macrophages remain to be clarified. Macrophage polarization, immunomodulation, and osteogenesis are governed by autophagy. Rapamycin, an autophagy inducer, has shown promising results in bone regeneration, but high dose-mediated cytotoxicity and low bioavailability hinder its clinical application. This study aimed to develop rapamycin-loaded virus-like hollow silica nanoparticles (R@HSNs) which are easily phagocytosed by macrophages and translocated to lysosomes. R@HSNs induced macrophage autophagy, promoted M2 polarization, and alleviated the degree of M1 polarization as indicated by the downregulation of inflammatory factors IL-6, IL-1β, TNF-α, and iNOS, and upregulation of anti-inflammatory factors CD163, CD206, IL-1ra, IL-10, and TGF-β. These effects were nullified by cytochalasin B-induced inhibition of R@HSNs uptake in macrophages. The conditioned medium (CM) collected from R@HSNs-treated macrophages promoted osteogenic differentiation of mouse bone marrow mesenchymal stromal cells (mBMSCs). In a mouse calvaria defect model, free rapamycin treatment was inhibited, but R@HSNs robustly promoted bone defect healing. In conclusion, silica nanocarrier-mediated intracellular rapamycin delivery to macrophages effectively triggers autophagy-mediated M2 macrophage polarization, further enhancing bone regeneration by triggering osteogenic differentiation of mBMSCs.

Cannabidiol Rescues TNF-α-Inhibited Proliferation, Migration, and Osteogenic/Odontogenic Differentiation of Dental Pulp Stem Cells

Strategies to promote dental pulp stem cells (DPSCs) functions including proliferation, migration, pro-angiogenic effects, and odontogenic/osteogenic differentiation are in urgent need to restore pulpitis-damaged dentin/pulp regeneration and DPSCs-based bone tissue engineering applications. Cannabidiol (CBD), an active component of Cannabis sativa has shown anti-inflammation, chemotactic, anti-microbial, and tissue regenerative potentials. Based on these facts, this study aimed to analyze the effect of CBD on DPSCs proliferation, migration, and osteogenic/odontogenic differentiation in basal and inflammatory conditions. Highly pure DPSCs with characteristics of mesenchymal stem cells (MSCs) were successfully isolated, as indicated by the results of flowcytometry and multi-lineage (osteogenic, adipogenic, and chondrogenic) differentiation potentials. Among the concentration tested (0.1-12.5 µM), CBD (2.5 μM) showed the highest anabolic effect on the proliferation and osteogenic/odontogenic differentiation of DPSCs. Pro-angiogenic growth factor VEGF mRNA expression was robustly higher in CBD-treated DPSCs. CBD also prompted the migration of DPSCs and CBD receptor CB1 and CB2 expression in DPSCs. TNF-α inhibited the viability, migration, and osteogenic/odontogenic differentiation of DPSCs and CBD reversed these effects. CBD alleviated the TNF-α-upregulated expression of pro-inflammatory cytokines TNF-α, interleukin (IL)-1β, and IL-6 in DPSCs. In conclusion, our results indicate the possible application of CBD on DPSCs-based dentin/pulp and bone regeneration.

Rare earth smart nanomaterials for bone tissue engineering and implantology: Advances, challenges, and prospects

Bone grafts or prosthetic implant designing for clinical application is challenging due to the complexity of integrated physiological processes. The revolutionary advances of nanotechnology in the biomaterial field expedite and endorse the current unresolved complexity in functional bone graft and implant design. Rare earth (RE) materials are emerging biomaterials in tissue engineering due to their unique biocompatibility, fluorescence upconversion, antimicrobial, antioxidants, and anti-inflammatory properties. Researchers have developed various RE smart nano-biomaterials for bone tissue engineering and implantology applications in the past two decades. Furthermore, researchers have explored the molecular mechanisms of RE material-mediated tissue regeneration. Recent advances in biomedical applications of micro or nano-scale RE materials have provided a foundation for developing novel, cost-effective bone tissue engineering strategies. This review attempted to provide an overview of RE nanomaterials' technological innovations in bone tissue engineering and implantology and summarized the osteogenic, angiogenic, immunomodulatory, antioxidant, in vivo bone tissue imaging, and antimicrobial properties of various RE nanomaterials, as well as the molecular mechanisms involved in these biological events. Further, we extend to discuss the challenges and prospects of RE smart nano-biomaterials in the field of bone tissue engineering and implantology.

Inflammatory factors in the circulation of patients with active rheumatoid arthritis stimulate osteoclastogenesis via endogenous cytokine production by osteoblasts

SUMMARY

The combination of cytokines present in the circulation of patients with active rheumatoid arthritis might contribute to the generalized bone loss that commonly occurs in these patients, by directly inhibiting osteoblast proliferation and differentiation, but especially by enhancing endogenous cytokine (i.e., receptor activator of nuclear factor-kappa B ligand (RANKL) and interleukin-6 (IL)-6) production by osteoblasts, thereby stimulating osteoclastogenesis.

INTRODUCTION

Generalized bone loss, as occurs in patients with rheumatoid arthritis (RA), is related to elevated levels of circulating cytokines. Individual cytokines have deleterious effects on proliferation and differentiation of osteoblast cell lines, but little is known about the effect of the interaction between inflammatory factors in the circulation of patients with active RA on human osteoblast function, including their communication towards other bone cells. We investigated whether serum from patients with active RA enhances cytokine production by osteoblasts, thereby effectively altering osteoblast-stimulated osteoclastogenesis.

METHODS

Serum was obtained from 20 patients with active RA (active RA sera) and from the same patients in clinical remission (remission RA sera). To determine osteoclastogenesis, RA serum-pretreated primary human osteoblast cultures were established in direct contact with human osteoclast precursors in the presence or absence of osteoprotegerin (OPG) or IL-6 inhibitor.

RESULTS

Compared to remission RA sera, active RA sera inhibited osteoblast proliferation and differentiation in vitro as demonstrated by a reduced DNA content and gene expression of KI-67, collagen type 1, osteopontin, and osteocalcin. Active RA sera inhibited OPG expression and enhanced RANKL and IL-6 expression but did not alter IL-8 expression in osteoblasts. IL-1β, IL-17, and tumor necrosis factor-α (TNF-α) expression were undetectable. In coculture, active RA sera treatment of osteoblasts stimulated while addition of OPG or IL-6 inhibitory antibodies significantly reduced the number of osteoclasts.

CONCLUSION

Active RA sera contain circulating factors, likely cytokines and chemokines, that might contribute to bone loss by directly inhibiting osteoblast proliferation and differentiation, but especially, these factors modulate endogenous cytokine production by osteoblasts, thereby affecting osteoclastogenesis.