Hyperbaric Oxygen Inhibits Growth But Not Differentiation of Normal and Irradiated Osteoblasts

Hyperbaric Oxygen Therapy Improves the Osteogenic and Vasculogenic Properties of Mesenchymal Stem Cells in the Presence of Inflammation In Vitro

Hyperbaric oxygen (HBO) therapy has been reported to be beneficial for treating many conditions of inflammation-associated bone loss. The aim of this work was to in vitro investigate the effect of HBO in the course of osteogenesis of human Mesenchymal Stem Cells (MSCs) grown in a simulated pro-inflammatory environment. Cells were cultured with osteogenic differentiation factors in the presence or not of the pro-inflammatory cytokine Tumor Necrosis Factor-α (TNF-α), and simultaneously exposed daily for 60 min, and up to 21 days, at 2,4 atmosphere absolute (ATA) and 100% O₂. To elucidate osteogenic differentiation-dependent effects, cells were additionally pre-committed prior to treatments. Cell metabolic activity was evaluated by means of the MTT assay and DNA content quantification, whereas osteogenic and vasculogenic differentiation was assessed by quantification of extracellular calcium deposition and gene expression analysis. Metabolic activity and osteogenic properties of cells did not differ between HBO, high pressure (HB) alone, or high oxygen (HO) alone and control if cells were pre-differentiated to the osteogenic lineage. In contrast, when treatments started contextually to the osteogenic differentiation of the cells, a significant reduction in cell metabolic activity first, and in mineral deposition at later time points, were observed in the HBO-treated group. Interestingly, TNF-α supplementation determined a significant improvement in the osteogenic capacity of cells subjected to HBO, which was not observed in TNF-α-treated cells exposed to HB or HO alone. This study suggests that exposure of osteogenic-differentiating MSCs to HBO under in vitro simulated inflammatory conditions enhances differentiation towards the osteogenic phenotype, providing evidence of the potential application of HBO in all those processes requiring bone regeneration.

Hypoxic Stress Forces Adaptive and Maladaptive Placental Stress Responses in Early Pregnancy

This review focuses on hypoxic stress and its effects on the placental lineage and the earliest differentiation events in mouse and human placental trophoblast stem cells (TSCs). Although the placenta is a decidual organ at the end of pregnancy, its earliest rapid growth and function at the start of pregnancy precedes and supports growth and function of the embryo. Earliest function requires that TSCs differentiate, however, "hypoxia" supports rapid growth, but not differentiation of TSCs. Most of the literature on earliest placental "hypoxia" studies used 2% oxygen which is normoxic for TSCs. Hypoxic stress happens when oxygen level drops below 2%. It decreases anabolism, proliferation, potency/stemness and increases differentiation, despite culture conditions that would sustain proliferation and potency. Thus, to study the pathogenesis due to TSC dysfunction, it is important to study hypoxic stress below 2%. Many studies have been performed using 0.5 to 1% oxygen in cultured mouse TSCs. From all these studies, a small number has examined human trophoblast lines and primary first trimester placental hypoxic stress responses in culture. Some other stress stimuli, aside from hypoxic stress, are used to elucidate common and unique aspects of hypoxic stress. The key outcomes produced by hypoxic stress are mitochondrial, anabolic, and proliferation arrest, and this is coupled with stemness loss and differentiation. Hypoxic stress can lead to depletion of stem cells and miscarriage, or can lead to later dysfunctions in placentation and fetal development. Birth Defects Research 109:1330-1344, 2017. © 2017 Wiley Periodicals, Inc.

Osteoradionecrosis of the Posterior Maxilla: A New Approach Combining Erbium: Yttrium Aluminium Garnet Laser and Bichat Bulla Flap

Osteoradionecrosis (ORN) of the jaw is a complication of radiation therapy for head and neck cancers. We report a case of ORN of the posterior maxilla treated with Er: YAG laser and a pedicled buccal fat pad (bichat bulla adipose) flap. A 69-year-old man presented complaining of pain on left maxilla. He had received high-dose radiotherapy (90 Gy) for squamous cell carcinoma of the left soft palate 2 years earlier. Clinical and radiographic examinations revealed ORN of the left maxillary molar region and maxillary sinusitis. Daily home care consisted of 0.9% saline irrigation and 0.8% H2O2 gel application. Sequestrectomy and tooth extraction were followed by debridement with Er: YAG laser and repair with a pedicled buccal fat pad flap. Complete resolution of ORN and maxillary sinusitis was established one year postsurgically. The excellent clinical outcome suggests that Er: YAG laser debridement and pedicled buccal fat pad flap are a viable option to treat ORN of the posterior maxilla.

Gene expression analysis reveals inhibition of radiation-induced TGFβ-signaling by hyperbaric oxygen therapy in mouse salivary glands

A side effect of radiation therapy in the head and neck region is injury to surrounding healthy tissues such as irreversible impaired function of the salivary glands. Hyperbaric oxygen therapy (HBOT) is clinically used to treat radiation-induced damage but its mechanism of action is largely unknown. In this study, we investigated the molecular pathways that are affected by HBOT in mouse salivary glands two weeks after radiation therapy by microarray analysis. Interestingly, HBOT led to significant attenuation of the radiation-induced expression of a set of genes and upstream regulators that are involved in processes such as fibrosis and tissue regeneration. Our data suggest that the TGFβ-pathway, which is involved in radiation-induced fibrosis and chronic loss of function after radiation therapy, is affected by HBOT. On the longer term, HBOT reduced the expression of the fibrosis-associated factor α-smooth muscle actin in irradiated salivary glands. This study highlights the potential of HBOT to inhibit the TGFβ-pathway in irradiated salivary glands and to restrain consequential radiation induced tissue injury.

Hyperbaric oxygen promotes osteogenic differentiation of bone marrow stromal cells by regulating Wnt3a/β-catenin signaling--an in vitro and in vivo study

We hypothesized that the effect of hyperbaric oxygen (HBO) on bone formation is increased via osteogenic differentiation of bone marrow stromal cells (BMSCs), which is regulated by Wnt3a/β-catenin signaling. Our in vitro data showed that HBO increased cell proliferation, Wnt3a production, LRP6 phosphorylation, and cyclin D1 expression in osteogenically differentiated BMSCs. The mRNA and protein levels of Wnt3a, β-catenin, and Runx2 were upregulated while those of GSK-3β were downregulated after HBO treatment. The relative density ratio (phospho-protein/protein) of Akt and GSK-3β was both up-regulated while that of β-catenin was down-regulated after HBO treatment. We next investigated whether HBO affects the accumulation of β-catenin. Our Western blot analysis showed increased levels of translocated β-catenin that stimulated the expression of target genes after HBO treatment. HBO increased TCF-dependent transcription, Runx2 promoter/Luc gene activity, and the expression of osteogenic markers of BMSCs, such as alkaline phosphatase activity, type I collagen, osteocalcin, calcium, and the intensity of Alizarin Red staining. HBO dose dependently increased the bone morphogenetic protein (BMP2) and osterix production. We further demonstrated that HBO increased the expression of vacuolar-ATPases, which stimulated Wnt3a secretion from BMSCs. Finally, we showed that the beneficial effects of HBO on bone formation were related to Wnt3a/β-catenin signaling in a rabbit model by histology, mechanical testing, and immunohistochemical assays. Accordingly, we concluded that HBO increased the osteogenic differentiation of BMSCs by regulating Wnt3a secretion and signaling.

Hyperbaric oxygen therapy suppresses osteoclast formation and bone resorption

The cellular and molecular mechanism through which hyperbaric oxygen therapy (HBO) improves osteonecrosis (ON) is unclear. The present study therefore examined the effect of HBO, pressure and hyperoxia on RANKL-induced osteoclast formation in RAW 264.7 cells and human peripheral blood monocytes (PBMC). Daily exposure to HBO (2.4 ATA, 97% O2 , 90 min), hyperbaric pressure (2.4 ATA, 8.8% O2 , 90 min) or normobaric hyperoxia (1 ATA, 95% O2 , 90 min) significantly decreased RANKL-induced osteoclast formation and bone resorption in normoxic conditions. HBO had a more pronounced anti-osteoclastic effect than hyperoxia or pressure alone and also directly inhibited osteoclast formation and resorption in hypoxic conditions a hallmark of many osteolytic skeletal disorders. The suppressive action of HBO was at least in part mediated through a reduction in RANK, NFATc1, and Dc-STAMP expression and inhibition of hypoxia-induced HIF-1α mRNA and protein expression. This data provides mechanistic evidence supporting the use of HBO as an adjunctive therapy to prevent osteoclast formation and bone loss associated with low oxygen partial pressure.

Hyperbaric oxygen-stimulated proliferation and growth of osteoblasts may be mediated through the FGF-2/MEK/ERK 1/2/NF-κB and PKC/JNK pathways

We investigated whether the hyperbaric oxygen (O₂) could promote the proliferation of growth-arrested osteoblasts in vitro and the mechanisms involved in this process. Osteoblasts were exposed to different combinations of saturation and pressure of O₂ and evaluated at 3 and 7 days. Control cells were cultured under ambient O₂ and normal pressure [1 atmosphere (ATA)]; high-pressure group cells were treated with high pressure (2.5 ATA) twice daily; high-O₂ group cells were treated with a high concentration O₂ (50% O₂) twice daily; and high pressure plus high-O₂ group cells were treated with high pressure (2.5 ATA) and a high concentration O₂ (50% O₂) twice daily. Hyperbaric O₂ significantly promoted osteoblast proliferation and cell cycle progression after 3 days of treatment. Hyperbaric O₂ treatment stimulated significantly increased mRNA expression of fibroblast growth factor (FGF)-2 as well as protein expression levels of Akt, p70(S6K), phosphorylated ERK, nuclear factor (NF)-κB, protein kinase C (PKC)α, and phosphorylated c-Jun N-terminal kinase (JNK). Our findings indicate that high pressure and high O₂ saturation stimulates growth-arrested osteoblasts to proliferate. These findings suggest that the proliferative effects of hyperbaric O₂ on osteoblasts may contribute to the recruitment of osteoblasts at the fracture site. The FGF-2/MEK/ERK 1/2/Akt/p70(S6K)/NF-κB and PKC/JNK pathways may be involved in mediating this process.

Molecular genetic studies of gene identification for osteoporosis: the 2009 update

Osteoporosis is a complex human disease that results in increased susceptibility to fragility fractures. It can be phenotypically characterized using several traits, including bone mineral density, bone size, bone strength, and bone turnover markers. The identification of gene variants that contribute to osteoporosis phenotypes, or responses to therapy, can eventually help individualize the prognosis, treatment, and prevention of fractures and their adverse outcomes. Our previously published reviews have comprehensively summarized the progress of molecular genetic studies of gene identification for osteoporosis and have covered the data available to the end of September 2007. This review represents our continuing efforts to summarize the important and representative findings published between October 2007 and November 2009. The topics covered include genetic association and linkage studies in humans, transgenic and knockout mouse models, as well as gene-expression microarray and proteomics studies. Major results are tabulated for comparison and ease of reference. Comments are made on the notable findings and representative studies for their potential influence and implications on our present understanding of the genetics of osteoporosis.

Hyperbaric oxygen: therapy for patients with maxillofacial implants?

Osseointegration was an innovative treatment in dentistry during the last 3 decades. The success of osseointegration is related to factors such as material biocompatibility, adequate quality of bone tissue that allows implantation, surgical technique, and macrostructure and microstructure of implant. The osseointegrated implants are successfully applied in dental clinic including oral and facial rehabilitations mainly for patients submitted to mutilating surgeries. However, patients submitted to radiation therapy present risks to treatment with implants owing to adverse effects on bone tissue. Nowadays, the literature suggests different therapies to improve the success of osseointegration such as hyperbaric oxygen therapy that aims to prepare bone and adjacent tissues to receive the implant. Therefore, the purpose of this study was to present a literature review concerning indications, contraindications, successes, and difficulties with hyperbaric oxygen therapy associated to maxillofacial implants.