Anabolic effect of intermittent PTH(1-34) on the local microenvironment during the late phase of periodontal repair in a rat model of tooth root resorption

LITTIP/Lgr6/HnRNPK complex regulates cementogenesis via Wnt signaling

Orthodontically induced tooth root resorption (OIRR) is a serious complication during orthodontic treatment. Stimulating cementum repair is the fundamental approach for the treatment of OIRR. Parathyroid hormone (PTH) might be a potential therapeutic agent for OIRR, but its effects still lack direct evidence, and the underlying mechanisms remain unclear. This study aims to explore the potential involvement of long noncoding RNAs (lncRNAs) in mediating the anabolic effects of intermittent PTH and contributing to cementum repair, as identifying lncRNA-disease associations can provide valuable insights for disease diagnosis and treatment. Here, we showed that intermittent PTH regulates cell proliferation and mineralization in immortalized murine cementoblast OCCM-30 via the regulation of the Wnt pathway. In vivo, daily administration of PTH is sufficient to accelerate root regeneration by locally inhibiting Wnt/β-catenin signaling. Through RNA microarray analysis, lncRNA LITTIP (LGR6 intergenic transcript under intermittent PTH) is identified as a key regulator of cementogenesis under intermittent PTH. Chromatin isolation by RNA purification (ChIRP) and RNA immunoprecipitation (RIP) assays revealed that LITTIP binds to mRNA of leucine-rich repeat-containing G-protein coupled receptor 6 (LGR6) and heterogeneous nuclear ribonucleoprotein K (HnRNPK) protein. Further co-transfection experiments confirmed that LITTIP plays a structural role in the formation of the LITTIP/Lgr6/HnRNPK complex. Moreover, LITTIP is able to promote the expression of LGR6 via the RNA-binding protein HnRNPK. Collectively, our results indicate that the intermittent PTH administration accelerates root regeneration via inhibiting Wnt pathway. The lncRNA LITTIP is identified to negatively regulate cementogenesis, which activates Wnt/β-catenin signaling via high expression of LGR6 promoted by HnRNPK.

Impact of Orthodontic Forces on Plasma Levels of Markers of Bone Turnover and Inflammation in a Rat Model of Buccal Expansion

Plasma levels of protein analytes might be markers to predict and monitor the kinetics of bone and tissue remodeling, including maximization of orthodontic treatment stability. They could help predict/prevent and/or diagnose possible adverse effects such as bone dehiscences, gingival recession, or root resorption. The objective of this study was to measure plasma levels of markers of bone turnover and inflammation during orthodontic force application in a rat model of orthodontic expansion. Two different orthodontic forces for bilateral buccal expansion of the maxillary arches around second and third molars were applied in 10 rats equally distributed in low-force (LF) or conventional force (CF) groups. Four rats served as the control group. Blood samples were collected at days 0, 1, 2, 3, 6, 13, 21, and 58. Longitudinal concentrations of osteoprotegerin (OPG), soluble receptor activator of nuclear factor kappaB ligand (sRANKL), interleukin-4 (IL-4), interleukin-6 (IL-6), interleukin-10 (IL-10), tumor necrosis factor α (TNF), and parathyroid hormone (PTH) were determined in blood samples by a multiplex immunoassay. CF and LF resulted in a significantly maxillary skeletal expansion while the CF group demonstrated significantly higher expansion than the LF group in the long term. Bone turnover demonstrated a two-phase response. During the “early phase” (up to 6 days of force application), LF resulted in more sRANKL expression and increased sRANKL/OPG ratio than the CF and control animals. There was a parallel increase in PTH levels in the early phase in response to LF. During the “late phase” (6–58 days), the markers of bone turnover were stable in both groups. IL-4, IL-6, and IL-10 levels did not significantly change the test groups throughout the study. These results suggest that maxillary expansion in response to different orthodontic forces follows different phases of bone turnover that may be force specific.

Intermittent parathyroid hormone promotes cementogenesis via ephrinB2-EPHB4 forward signaling

Intermittent parathyroid hormone (PTH) promotes periodontal repair, but the underlying mechanisms remained unclear. Recent studies found that ephrinB2-EPHB4 forward signaling mediated the anabolic effect of PTH in bone homeostasis. Considering the similarities between cementum and bone, we aimed to examine the therapeutic effect of PTH on resorbed roots and explore the role of forward signaling in this process. In vivo experiments showed that intermittent PTH significantly accelerated the regeneration of root resorption and promoted expression of EPHB4 and ephrinB2. When the signaling was blocked, the resorption repair was also delayed. In vitro studies showed that intermittent PTH promoted the expression of EPHB4 and ephrinB2 in OCCM-30 cells. The effects of PTH on the mineralization capacity of OCCM-30 cells was mediated through the ephrinB2-EPHB4 forward signaling. These results support the premise that the anabolic effects of intermittent PTH on the regeneration of root resorption is via the ephrinB2-EPHB4 forward signaling pathway.

Long noncoding RNA expression profiles in intermittent parathyroid hormone induced cementogenesis

The aim of this study was to explore the involvement of long noncoding RNAs (lncRNAs) during intermittent parathyroid hormone (PTH) induced cementogenesis. Expression profiles of lncRNAs and mRNAs were obtained using high-throughput microarray. Gene Ontology enrichment analysis, Kyoto Encyclopedia of Genes and Genomes pathway analysis, and coding-noncoding gene coexpression networks construction were performed. We identified 190 lncRNAs and 135 mRNAs that were differentially expressed during intermittent PTH-induced cementogenesis. In this process, the Wnt signaling pathway was negatively regulated, and eight lncRNAs were identified as possible core regulators of Wnt signaling. Based on the results of microarrray analysis, we further verified the repressed expression of Wnt signaling crucial components β-catenin, APC and Axin2. Above all, we speculated that lncRNAs may play important roles in PTH-induced cementogenesis via the negative regulation of Wnt pathway.

Influence of parathyroid hormone on periodontal healing in animal models: A systematic review

OBJECTIVES

The purpose of this systematic review was to determine the potential interest of parathyroid hormone (PTH) as an adjunct to periodontal treatment based on studies performed in rodents.

MATERIALS & METHODS

Electronic databases (MEDLINE, Web of Science) were searched up to December 2019. Studies assessing the impact of PTH administration in experimental periodontitis in rodents have been identified.

RESULTS

Amongst the 247 identified articles, 10 met the inclusion criteria and were included in this systematic review. Experimental periodontitis was mainly induced by ligature placement or surgically with a dental bur. All studies considered bone healing after PTH administration at different frequencies as primary outcome. Results showed that an intermittent administration of PTH promoted bone healing and neovascularization. Nevertheless, a decrease of soft tissue inflammation was also observed.

CONCLUSION

Intermittent administration of PTH appears to enhance significantly periodontal healing and to promote alveolar bone regeneration. However, due to the risk of side effects, the development of scaffolds allowing its local and time-controlled delivery is of importance.

Inhibitory Effects of 4-Hexylresorcinol on Root Resorption Induced by Orthodontic Tooth Movement

Root resorption during orthodontic tooth movement (OTM) is caused by an imbalance between the bone turnover rate and applied mechanical stress. The administration of 4-hexylresorcinol (4HR) increases the bone turnover rate and factors associated with bone formation. Thus, 4HR may show protective activity against root resorption during orthodontic tooth movement (OTM). A total of 40 rats (male: 20; female: 20) were included in this study, and the mandibular first molar was subjected to excessive orthodontic force. The experimental group (n = 20) received 12.8 mg/kg of 4HR every 2 weeks. The controls (n = 20) received a solvent without 4HR. Both groups had the same sex distribution. On Day 28 after the initiation of OTM, all the animals were sacrificed for micro-computed tomography analysis, Western blot analysis, and immunohistochemistry. The ratios of the root length and root volume to the total volume were significantly higher in the experimental group compared to those in the control group (p < 0.05). The expression levels of OPG, RANKL, alkaline phosphatase, and Runx2 in the experimental group according to Western blotting were significantly higher in the experimental group compared to those in the control group (p < 0.05). Their expression was mainly found in the periodontal ligament area. In conclusion, the administration of 4HR decreased the root resorption caused by OTM and increased the expression levels of OPG, RANKL, alkaline phosphatase, and Runx2.

Intermittent parathyroid hormone improves orthodontic retention via insulin-like growth factor-1

OBJECTIVES

This study aimed to investigate the effects of intermittent parathyroid hormone (iPTH) on the stability of orthodontic retention and to explore the possible regulatory role of insulin-like growth factor-1 (IGF-1) in this process.

METHODS

Forty-eight 6-week-old male Wistar rats were adopted in this study. An orthodontic relapsing model was established to investigate the effects of iPTH on orthodontic retention. In vitro, an immortalized mouse cementoblast cell line OCCM-30 was detected by flow cytometry to study the effects of iPTH on cell proliferation and apoptosis. By application of a specific IGF-1 receptor inhibitor, the role of IGF-1 was also explored.

RESULTS

In vivo study found that daily injection of PTH significantly reduced the relapsing distance. Histological staining and ELISA assay showed faster periodontal regeneration during retention period in PTH group with increased RANKL/OPG ratio and greater amount of OCN, ALP, and IGF-1 in gingival cervical fluid (GCF). Cell experiment revealed that iPTH promoted proliferation and suppressed apoptosis of cementoblast. IGF-1 receptor inhibitor significantly restrained the anabolic effect of iPTH on OCCM-30 cells.

CONCLUSIONS

These findings suggest that iPTH could improve the stability of tooth movement by promoting periodontal regeneration. IGF-1 is essential in mediating the anabolic effects of iPTH.

Effects of estrogen on root repair after orthodontically induced root resorption in ovariectomized rats

INTRODUCTION

This study aimed to investigate the effects of estrogen on root repair after orthodontically induced root resorption.

METHODS

Seventy-two 6-week-old female Wistar rats were randomly divided into 3 groups: ovariectomy only (OVX), ovariectomy plus estradiol injection (OVX + E2), and sham operation (control). E2 was administrated to all the experimental animals after the establishment of the root repair model. One-way analysis of variance with the Tukey post-hoc test was used to analyze the experimental results.

RESULTS

Micro-computed tomography and hematoxylin and eosin staining showed that the total volumes of resorption lacunae were significantly smaller in the control and OVX + E2 groups than those in the OVX group. Alkaline phosphatase and tartrate-resistant acid phosphatase stainings suggested that the cementoblastic activities and the amount of new cementum formation were inhibited while the activities of osteoclasts were obvious in the OVX group. The immunohistochemistry stainings revealed that the osteoprotegerin to receptor activator of nuclear factor-кB ligand ratio and the phosphorylated extracellular signal-regulated kinases to extracellular signal-regulated kinases ratio of the control and OVX + E2 groups were significantly greater than those of the OVX group.

CONCLUSIONS

These findings demonstrated that estrogen administration might be a solution to reduce orthodontically induced root resorption through the activation of extracellular signal-regulated kinase-1/2 pathway and enhancement of cementogenesis.

Intermittent parathyroid hormone promotes cementogenesis in a PKA- and ERK1/2-dependent manner

BACKGROUND

Intermittent parathyroid hormone (PTH) promotes cementogenesis and provides a promising biotherapeutic to rehabilitate resorbed roots. However, the underlying mechanisms remain inconclusive. Cyclic aenosine monophosphate (AMP)-dependent protein kinases A (PKA) and extracellular signal-regulated MAP kinases 1/2 (ERK1/2) are key regulators of bone remodeling. The present study aims to investigate whether PKA and ERK1/2 are involved in the process of intermittent PTH-promoted cementogenesis.

METHODS

Sprague-Dawley rats in experimental group (n = 30) received a daily subcutaneous injection of PTH and the control (n = 30) received placebo vehicle for 1, 2, 3, 4, and 5 weeks. Results were evaluated by hematoxylin and eosin and immunohistochemistry staining. In vitro, OCCM-30 cells were incubated with intermittent PTH. H89 and U0126 were used to determine the role of PKA and ERK1/2, respectively. The cementogenic results were analyzed by reverse transcription-polymerase chain reaction (RT-PCR), western blotting, alkaline phosphatase activity assay and Alizarin Red S staining. The interaction of PKA and p-ERK1/2 was determined by co-immunoprecipitation (Co-IP).

RESULTS

Intermittent PTH exerted anabolic effect on cellular cementum in developing teeth with elevated expression of osteocalcin, osteopontin, and PKA (catalytic subunit) in PTH injection group. The promoting effects of intermittent PTH on cementogenesis and osteogenic differentiation were abrogated by H89 and U0126 in vitro, respectively. Blocking of PKA pathway downregulated intermittent PTH-induced ERK1/2 phosphorylation.

CONCLUSIONS

Intermittent PTH promotes cementogenesis in a PKA- and ERK1/2-dependent manner. In this process, PKA and p-ERK1/2 interact with each other. These results support the future biotherapeutic applications of PTH in cementum resorption.

Reduced Orthodontic Tooth Movement in Enpp1 Mutant Mice with Hypercementosis

Previous studies revealed that cementum formation is tightly regulated by inorganic pyrophosphate (PP_i), a mineralization inhibitor. Local PP_i concentrations are determined by regulators, including ectonucleotide pyrophosphatase/phosphodiesterase 1 (ENPP1), which increases PP_i concentrations by adenosine triphosphate hydrolysis. Orthodontic forces stimulate alveolar bone remodelling, leading to orthodontic tooth movement (OTM). To better understand how disturbed mineral metabolism and the resulting altered periodontal structures affect OTM, we employed Enpp1 mutant mice that feature reduced PP_i and increased cervical cementum in a model of OTM induced by a stretched closed-coil spring ligated between the maxillary left first molar and maxillary incisors. We analyzed tooth movement, osteoclast/odontoclast response, and tooth root resorption by micro-computed tomography, histology, histomorphometry, and immunohistochemistry. Preoperatively, we noted an altered periodontium in Enpp1 mutant mice, with significantly increased periodontal ligament (PDL) volume and thickness, as well as increased PDL-bone/tooth root surface area, compared to wild-type (WT) controls. After 11 d of orthodontic treatment, Enpp1 mutant mice displayed 38% reduced tooth movement versus WT mice. Molar roots in Enpp1 mutant mice exhibited less change in PDL width in compression and tension zones compared to WT mice. Root resorption was noted in both groups with no difference in average depths, but resorption lacunae in Enpp1 mutant mice were almost entirely limited to cementum, with 150% increased cementum resorption and 92% decreased dentin resorption. Osteoclast/odontoclast cells were reduced by 64% in Enpp1 mutant mice, with a predominance of tartrate-resistant acid phosphatase (TRAP)-positive cells on root surfaces, compared to WT mice. Increased numbers of TRAP-positive cells on root surfaces were associated with robust immunolocalization of osteopontin (OPN) and receptor-activator of NF-κB ligand (RANKL). Collectively, reduced response to orthodontic forces, decreased tooth movement, and altered osteoclast/odontoclast distribution suggests Enpp1 loss of function has direct effects on clastic function/recruitment and/or indirect effects on periodontal remodeling via altered periodontal structure or tissue mineralization.

CD8+ T cells mediate the regenerative PTH effect in hPDL cells via Wnt10b signaling

It was the aim of the present investigation to examine whether the stimulating effect of parathyroid hormone (PTH) on human periodontal ligament (hPDL) cell proliferation and differentiation would be enhanced by hPDL/T-cell interaction involving Wnt10b signaling as a mediating pathway. hPDL cells were cultured from healthy premolar tissues of three adolescent orthodontic patients and exposed to PTH(1-34) in monocultures or co-cultures with CD8⁺ T cells. At harvest, proliferation, alkaline phosphatase-specific activity (ALP), and osteocalcin production were determined by immunofluorescence cytochemistry, real-time PCR, biochemical assay, and ELISA. Wnt10b signaling was analyzed by the use of a specific WNT10b neutralizing antibody. PTH(1-34) stimulation of T cells significantly increased Wnt10b expression and production. Wnt10b exposure of hPDL cells enhanced proliferation and differentiation. PDL cells co-cultured with T cells showed a Wnt10b-dependent regulation of proliferation and differentiation parameters. The addition of a Wnt10b-neutralizing Ab to the co-culture medium resulted in a significant inhibition of the PTH(1-34) effect on proliferation, ALP-specific activity, and osteocalcin protein expression. Our findings provide novel insight into the mechanism of action of PTH on hPDL cells and establish the interplay of T cells and hPDL cells via the Wnt10b pathway as a modulating factor for the anabolic properties of the hormone in periodontal regeneration.

Mechanical loading influences the effects of bisphosphonates on human periodontal ligament fibroblasts

OBJECTIVES

There is increasing evidence that bisphosphonates affect orthodontic tooth movement. The object of the study was to investigate the changes produced by tensile strain on human periodontal ligament fibroblasts (HPdLFs) treated with clodronate or zoledronate.

MATERIALS AND METHODS

HPdLF were cultured with 5 and 50 μM clodronate or zoledronate for 48 h and applied to tensile strain (TS) (5 and 10 %) for 12 h in vitro. Viability was verified by MTT assay and apoptosis rate via caspase 3/7 assay. Gene expression of receptor activator of nuclear factor kappa-B ligand (RANKL) and osteoprotegerin (OPG) was investigated using real-time PCR. OPG was also analyzed by ELISA and RANKL by immunocytochemical staining.

RESULTS

Zoledronate (50 μM) reduced the viability of HPdLF (76 vs 100 %) and combined with 5 % TS to 53 %. TS of 10 % and clodronate reduced viability to 79 % with increased caspase 3/7 activity. Clodronate (5 μM) led to a slight increase of OPG gene expression, zoledronate (5 μM) to a slight decrease. Combined with 5 % TS, both increased OPG gene expression (2-3-fold) and OPG synthesis. Zoledronate increased gene expression of RANKL (4-fold). Combined with 5 % of TS, this increase was abolished. TS of 10 % in combination amplified increase of RANKL ending up with a 9-fold gene expression by clodronate and high RANKL protein synthesis.

CONCLUSIONS

This study shows for the first time that mechanical loading alters the effects of bisphosphonates on viability, apoptosis rate, and OPG/RANKL system of HPdLF dependent on the applied strength. Low forces and bisphosphonates increase factors for bone apposition, whereas high forces combined with bisphosphonates stimulate osteoclastogenesis.

CLINICAL RELEVANCE

Mechanical loading of periodontal ligament with high strengths should be avoided during bisphosphonate therapy.

Orthodontic and surgical management of cleidocranial dysplasia

Cleidocranial dysplasia (CCD), an autosomal dominant disorder with a prevalence of 1 in 1,000,000 individuals, is mainly caused by mutations in Runx2, a gene required for osteoblastic differentiation. It is generally characterized by hypoplastic clavicles, narrow thorax, and delayed or absent fontanel closure. Importantly, its orofacial manifestations, including midfacial hypoplasia, retained primary teeth, and impacted permanent and supernumerary teeth, severely impede the well-being of affected individuals. Successful treatment of the orofacial problems requires the combined efforts of dental specialists. However, only a few successfully treated cases have been reported because of the rarity of CCD and complexity of the treatment. This article presents the University of California, San Francisco (UCSF) treatment protocol for the dentofacial manifestations of CCD based on two treated and 17 diagnosed cases. The records of two patients with CCD who had been treated at the UCSF School of Dentistry and the treatment options reported in the literature were reviewed. The UCSF treatment protocol produced a successful case and a partially successful one (inadequate oral hygiene in the retention stage resulted in decay and loss of teeth). It provides general guidelines for successfully treating the orofacial manifestations of CCD.

Regulation of macrophage migration and activity by high-mobility group box 1 protein released from periodontal ligament cells during orthodontically induced periodontal repair: an in vitro and in vivo experimental study

OBJECTIVE

Recent studies have shown that periodontal ligament (PDL) cells interact with macrophages from the immune system during orthodontically induced repair of periodontal tissue. Hypothesizing that high-mobility group box 1 (HMGB1) protein is released by mechanically stressed PDL cells into the extracellular space and has a role in mediating the local immune response by acting as an "alarmin", this study was performed to further elucidate these cellular interactions, with a special focus on the impact of proinflammatory mediators secreted by PDL cells on macrophage physiology.

MATERIALS AND METHODS

The study included an in vivo part in which orthodontic stress was induced in rats and their PDL analyzed for expression of HMGB1 by immunohistochemistry after 5 days of tooth movement. In the in vitro part, human PDL cells were subjected to compressive loading, followed by stimulating human macrophages with conditioned supernatants of these stressed PDL cells and analyzing how mediators that had been released by these cells into the medium would impact macrophage physiology. Assays for macrophage migration and osteoclast differentiation were used in addition to immunohistochemistry, enzyme-linked immunosorbent assays, and western blotting.

RESULTS

Induction of mechanical stress was found to upregulate HMGB1 expression both in vivo and in vitro. At the same time, translocation HMGB1 from nuclei into cytoplasm was observed. Culturing macrophages in conditioned PDL cell medium was associated with enhanced chemotactic migration and osteoclast differentiation. Addition of anti-HMGB1 antibodies to inhibit HMGB1 in the conditioned medium was found to significantly attenuate these effects. A less marked increase of migration and osteoclast differentiation by macrophages was observed after isolated addition of HMGB1, at its observed pathological concentration, to nonconditioned medium.

CONCLUSION

This study clearly indicates an immunomodulatory potential of human PDL cells via release of mediators, including HMGB1 protein. Our finding that these mediators modify the migration and differentiation of macrophages as a function of periodontal repair during orthodontic treatment broadens the theoretical basis toward developing interventional strategies to avoid orthodontically induced root resorption.

Intermittent parathyroid hormone administration improves periodontal healing in rats

BACKGROUND

Intermittent administration of parathyroid hormone (PTH) promotes new bone formation in patients with osteoporosis and bone fractures. It was shown previously that PTH also reduces periodontitis-related bone loss. The aim of this study is to evaluate the effect of treatment with PTH on periodontal healing in rats.

METHODS

Fenestration defects were created at the buccal surface of the distal root of the mandibular first molars, and both periodontal ligament (PDL) and cementum were removed. Animals were then assigned to two groups (eight animals per group): group 1: control, placebo administration; and group 2: test, human PTH (hPTH) 1-34 administration at a concentration of 40 μg/kg. For both groups, the animals were injected every 2 days, and the animals were sacrificed at 14 and 21 days after surgery. Specimens were harvested and processed for routine decalcified histologic sections. The following parameters were assessed: 1) remaining bone defect extension (RBDE); 2) newly formed bone density (NFBD); 3) total callus area (TCA); 4) osteoclast number (ON) in the callus region; and 5) newly formed dental cementum-like tissue (NFC). Birefringence of root PDL reattachment was also evaluated.

RESULTS

Birefringence analysis showed root PDL reattachment for both groups 21 days after treatment. Intermittent hPTH 1-34 administration decreased RBDE (P <0.01) and increased NFBD (P <0.01), TCA (P <0.01), area of NFC (P <0.01), and ON in the callus region (P <0.01).

CONCLUSION

Within the limits of the present study, intermittent administration of hPTH 1-34 led to an enhanced periodontal healing process compared with non-treated animals.

Potential role of high mobility group box protein 1 and intermittent PTH (1-34) in periodontal tissue repair following orthodontic tooth movement in rats

OBJECTIVES

Recent studies indicate that high mobility group box protein 1 (HMGB1) can be released by necrotic and damaged cells and functions as an alarmin that is recognized by the innate immune system. Little is known about the role of HMGB1 within the periodontal ligament (PDL). Therefore, we examined HMGB1 expression by PDL cells in vitro and compared the findings to an in vivo model of orthodontically induced tooth root resorption. In addition, we addressed the question of whether a potentially anabolic intermittent administration of parathyroid hormone (iPTH) would modulate the expression of HMGB1.

MATERIALS AND METHODS

In confluent PDL cell cultures, HMGB1 messenger RNA (mRNA) expression was quantified by real-time polymerase chain reaction. In a rat model comprising 25 animals, mechanical loading for 5 days was followed by administration of either iPTH (1-34) systemically or sham injections for up to 56 days. HMGB1 expression was determined by means of immunohistochemistry and histomorphometry.

RESULTS

The in vitro experiments revealed an inhibitory effect of iPTH on basal HMGB1 mRNA expression in confluent PDL cells. In vivo, the mechanical force-induced enhanced HMGB1 protein expression declined time dependently. Intermittent PTH further inhibited HMGB1 expression. The significantly higher basal HMGB1 protein expression in the former compression side was followed by a more pronounced time- and iPTH-dependent decline in the same area.

CONCLUSIONS

These data indicate a major role for HMGB1 in the regulation of PDL wound healing following mechanical load-induced tissue injury.

CLINICAL RELEVANCE

The findings point to the potential benefit of iPTH in the attempt to support these immune-associated reparative processes.

Parathyroid hormone and its effects on dental tissues

In the current era, various pharmacological agents exist for osteoporosis management, and synthetic parathyroid hormone (PTH) (Teriparatide, Forteo) is one of the treatment options. Depending on the timing of administration, PTH has a unique ability to cause both bone apposition and bone resorption. This review focuses on the effects of PTH on the bone, specifically the jaw bones mandible and maxilla. The article briefly describes the fundamental mechanism of PTH action at the molecular level, as well as in experimental animals and in humans. It differentiates intermittent administration of PTH, especially at doses tolerated by humans that increase bone strength and prevent bone fractures, from continuous use that may lead to bone loss. In particular, it shows how intermittent administration of PTH can play a significant role in periodontal repair and implant success via stimulation of bone mineral content especially in the pre-alveolar region.

A review on endogenous regenerative technology in periodontal regenerative medicine

Periodontitis is a globally prevalent inflammatory disease that causes the destruction of the tooth-supporting apparatus and potentially leads to tooth loss. Currently, the methods to reconstitute lost periodontal structures (i.e. alveolar bone, periodontal ligament, and root cementum) have relied on conventional mechanical, anti-infective modalities followed by a range of regenerative procedures such as guided tissue regeneration, the use of bone replacement grafts and exogenous growth factors (GFs), and recently developed tissue engineering technologies. However, all current or emerging paradigms have either been shown to have limited and variable outcomes or have yet to be developed for clinical use. To accelerate clinical translation, there is an ongoing need to develop therapeutics based on endogenous regenerative technology (ERT), which can stimulate latent self-repair mechanisms in patients and harness the host's innate capacity for regeneration. ERT in periodontics applies the patient's own regenerative 'tools', i.e. patient-derived GFs and fibrin scaffolds, sometimes in association with commercialized products (e.g. Emdogain and Bio-Oss), to create a material niche in an injured site where the progenitor/stem cells from neighboring tissues can be recruited for in situ periodontal regeneration. The choice of materials and the design of implantable devices influence therapeutic potential and the number and invasiveness of the associated clinical procedures. The interplay and optimization of each niche component involved in ERT are particularly important to comprehend how to make the desired cell response safe and effective for therapeutics. In this review, the emerging opportunities and challenges of ERT that avoid the ex vivo culture of autologous cells are addressed in the context of new approaches for engineering or regeneration of functional periodontal tissues by exploiting the use of platelet-rich products and its associated formulations as key endogenous resources for future clinical management of periodontal tissue defects.

Parathyroid hormone (PTH) peptides through the regulation of hyaluronan metabolism affect osteosarcoma cell migration

Parathyroid hormone (PTH) strongly stimulates hyaluronan (HA) synthesis and secretion of both normal and carcinogenic cells of the osteoblastic lineage and improves skeletal microarchitecture. HA, a glycosaminoglycan component of the extracellular matrix (ECM), is capable of transmitting ECM-derived signals to regulate cellular function. In this study, we investigated whether the changes of HA metabolism induced by PTH (1-34) and PTH (7-84) peptides in moderately MG-63 and well-differentiated Saos 2 osteosarcoma cell lines, are correlated to their migration capabilities. Our results demonstrate that intermittent PTH (1-34) treatment significantly (P < or = 0.01) supported the migration of MG-63 cells, increased their HA-synthase-2 (HAS2) expression (P < or = 0.001), and enhanced their high-molecular size HA deposition in the pericellular matrix. Both increased endogenous HA production (P < or = 0.01) and treatment with exogenous high-molecular weight HA (P < or = 0.05) correlated to a significant increase of MG-63 cell migration capacity. Transfection with siHAS2 showed that PTH (1-34), mainly through HAS2, enhanced HA and regulated MG-63 cell motility. Interestingly, continuous PTH (1-34) treatment stimulated both Saos 2 cell HAS2 (P < or = 0.001) and HAS1 (P < or = 0.001) isoform expression inhibited their HYAL2 expression (P < or = 0.001) and modestly (P < or = 0.05) enhanced their migration. Therefore, the PTH (1-34) administration mode appears to distinctly modulate the migratory responses of the MG-63 moderately and Saos 2 well-differentiated osteosarcoma cell lines. Conclusively, the obtained data suggest that there is a regulatory effect of PTH (1-34), in an administration mode-dependent manner, on HA metabolism that is essential for osteosarcoma cell migration.