Osteoclastic resorptive capacity is suppressed in patients receiving hyperbaric oxygen therapy

PRMT6 Epigenetically Drives Metabolic Switch from Fatty Acid Oxidation toward Glycolysis and Promotes Osteoclast Differentiation During Osteoporosis

Epigenetic regulation of metabolism profoundly influences cell fate commitment. During osteoclast differentiation, the activation of RANK signaling is accompanied by metabolic reprogramming, but the epigenetic mechanisms by which RANK signaling induces this reprogramming remain elusive. By transcriptional sequence and ATAC analysis, this study identifies that activation of RANK signaling upregulates PRMT6 by epigenetic modification, triggering a metabolic switching from fatty acids oxidation toward glycolysis. Conversely, Prmt6 deficiency reverses this shift, markedly reducing HIF-1α-mediated glycolysis and enhancing fatty acid oxidation. Consequently, PRMT6 deficiency or inhibitor impedes osteoclast differentiation and alleviates bone loss in ovariectomized (OVX) mice. At the molecular level, Prmt6 deficiency reduces asymmetric dimethylation of H3R2 at the promoters of genes including Ppard, Acox3, and Cpt1a, enhancing genomic accessibility for fatty acid oxidation. PRMT6 thus emerges as a metabolic checkpoint, mediating metabolic switch from fatty acid oxidation to glycolysis, thereby supporting osteoclastogenesis. Unveiling PRMT6's critical role in epigenetically orchestrating metabolic shifts in osteoclastogenesis offers a promising target for anti-resorptive therapy.

Hyperbaric oxygen and treadmill exercise partially prevented bone loss and bone microarchitecture deterioration in ovariectomized rats

INTRODUCTION

Previous studies have demonstrated the beneficial effects of treadmill exercise (EX) on osteoporosis, and of hyperbaric oxygen (HBO) on osteoblast and osteoclast formation in vitro. We investigated the effects of HBO and the combination of HBO and EX on osteoporosis in ovariectomized rats.

METHODS

Forty 3-month-old female Sprague-Dawley rats were randomly divided into 5 groups (n = 8): a sham control group (Control); an ovariectomy group; an ovariectomy with treadmill exercise treatment group; an ovariectomy with HBO treatment group; and an ovariectomy with HBO treatment combined with treadmill exercise group. The HBO exposures were 203 kPa, 85-90% O₂, 90 min and the exercise regimen was 20 m·min⁻¹, 40 min·day¹, 5° slope. Both treatments were administered once daily, five days a week for 12 weeks until the rats were sacrificed.

RESULTS

All three treatments (HBO, exercise, and both combined) significantly promoted the expression of the osteoblast-related gene and oxidative metabolism-related gene (PGC-1α). They also exerted significant inhibitory effects on the osteoclast-related mRNA expression (RANKL) and bone resorption marker CTX-I. Additionally, exercise and the combination exercise-HBO treatment increased serum superoxide dysmutase (SOD) and sclerostin expression. No significant between-group difference was observed.

CONCLUSIONS

Hyperbaric oxygen, exercise, and the combination ameliorated bone microarchitecture deterioration and ovariectomy-induced bone loss in rats, and these inhibitory effects may be associated with the increased SOD and up-regulated PGC-1α.

The Effects of Hyperbaric Oxygen on Rheumatoid Arthritis: A Pilot Study

BACKGROUND/OBJECTIVE

This case series pilot study assessed the effects of hyperbaric oxygen therapy (HBO2) for treating rheumatoid arthritis (RA).

METHODS

Ten RA subjects received 30 HBO2 treatments over 6 to 10 weeks. Serial rheumatologic evaluations (ie, the Disease Activity Scale [DAS28], the Routine Assessment of Patient Index Data 3, and the Pain and Sleep Quality Questionnaire) were completed at baseline, throughout the course of the study, and at the 6-month follow-up.

RESULTS

There was a statistically significant effect of HBO2 therapy over time on the DAS28-Global Health (p = 0.01), the DAS28-C-reactive protein (p = 0.002), and the DAS28-erythrocyte sedimentation rate (p = 0.008) measures; these analyses excluded 2 patients who were in clinical remission at baseline. Selected post hoc comparisons showed significantly lower DAS28-Global Health, DAS28-C-reactive protein, and DAS28-erythrocyte sedimentation rate scores at 3 and 6 months relative to baseline. In addition, statistically significant decreases in pain as measured by the Routine Assessment of Patient Index Data 3 and Pain and Sleep Quality Questionnaire were observed at the end of HBO2 relative to baseline.

CONCLUSIONS

Hyperbaric oxygen therapy is effective for joint pain in patients with RA based on data from multiple, validated clinical measures. Further research with more subjects and the use of a control group is necessary.

Evidence-Supported HBO Therapy in Femoral Head Necrosis: A Systematic Review and Meta-Analysis

Although many studies have shown that hyperbaric oxygen (HBO) therapy can significantly improve symptoms and quality of life of patients affected by femoral head necrosis, this therapy is not worldwide approved yet. This meta-analysis was performed to evaluate its clinical effect. Relevant studies published before May 2020 were systematically searched using terms related to HBO and femoral head necrosis. Fixed and random-effects models were used to estimate the odds ratio (OR) with 95% confidence intervals (CI). Subgroup analyses and publication bias tests were carried out to explore potential study heterogeneity and bias. Ten studies involving 353 controls and 368 HBO-treated cases were included, most of which were conducted on Asian population. The clinical effect in the HBO therapy group was 3.84 times higher than in the control group (OR = 3.84, 95% CI (2.10, 7.02), p < 0.00001). Subgroup analyses showed that the clinical effect of HBO therapy was statistically significant in the Asian subpopulation which represented most of the subjects (OR = 3.53, 95% CI (1.87, 6.64), p < 0.00001), but not in the non-Asian subpopulation, probably because of insufficient numerosity (OR = 7.41, 95% CI (0.73, 75.71), p = 0.09). The results of this meta-analysis suggest that patients with femoral head necrosis treated with HBO therapy can achieve a significant clinical improvement.

HIF-1α regulates osteoclast activation and mediates osteogenesis during mandibular bone repair via CT-1

OBJECTIVES

Hypoxia is one of the characteristics of microenvironmental changes after orthognathic surgery for fractures. HIF-1α is a main regulator of the hypoxic response and plays a crucial role in bone formation, remodelling, and homeostasis. Osteoclasts participate in bone absorption and affect osteogenesis, and osteoclasts differentiate in a path from the oxygen-rich bone marrow to oxygen-deficient bone lesions. Thus, we aimed to study the key functions of HIF-1α in osteoclasts during mandibular healing after osteotomy.

MATERIALS AND METHODS

The function of HIF-1α in osteoclasts during fracture healing in osteoclast-specific HIF-1α-conditional-knockout mice was investigated in mandibular osteotomy. Primary osteoclasts were used to explore the expression of HIF-1α and cardiotrophin-1 (CT-1) at both the mRNA and protein levels. The ability of BMSCs co-cultured with conditioned media from osteoclast-specific HIF-1α-knockout primary osteoclasts was detected using osteoclast-mediated osteogenesis experiments.

RESULTS

Hypoxia-inducible factor-1α increased osteoclastogenesis and bone resorption, and a delay in bone healing was found in osteoclast-specific HIF-1α-conditional-knockout mice compared with normal mice. HIF-1α-knockout primary osteoclasts inhibited bone resorption and CT-1 expression, and HIF-1α enhanced the osteoclast-mediated stimulation of BMSC differentiation by secreting CT-1.

CONCLUSIONS

Hypoxia-inducible factor-1α can play a key role in the physiology and pathogenesis of bone resorption by promoting osteoclastogenesis during fracture and influencing osteogenesis through CT-1 during bone healing.

Metabolic properties of the osteoclast

Osteoclasts are defined as cells capable of excavating 3-dimensional resorption pits in bone and other mineralised tissues. They are derived from the differentiation/fusion of promonocytic precursors, and are usually large, multinucleated cells. In common with other cells from this myeloid lineage such as macrophages and dendritic cells, they are adapted to function in hypoxic, acidic environments. The process of bone resorption is rapid and is presumably highly energy-intensive, since osteoclasts must actively extrude protons to dissolve hydroxyapatite mineral, whilst secreting cathepsin K to degrade collagen, as well as maintaining a high degree of motility. Osteoclasts are well known to contain abundant mitochondria but they are also able to rely on glycolytic (anaerobic) metabolism to generate the ATP needed to power their activity. Their primary extracellular energy source appears to be glucose. Excessive accumulation of mitochondrial reactive oxygen species in osteoclasts during extended periods of high activity in oxygen-poor environments may promote apoptosis and help to limit bone resorption - a trajectory that could be termed "live fast, die young". In general, however, the metabolism of osteoclasts remains a poorly-investigated area, not least because of the technical challenges of studying actively resorbing cells in appropriate conditions.

Hyperbaric Oxygen Therapy is Ineffective as an Adjuvant to Daptomycin with Rifampicin Treatment in a Murine Model of Staphylococcus aureus in Implant-Associated Osteomyelitis

Implant-associated infections caused by bacterial biofilms are difficult to treat. Surgical intervention is often necessary to cure the patient, as the antibiotic recalcitrance of biofilms renders them untreatable with conventional antibiotics. Intermittent hyperbaric oxygen treatment (HBOT) has been proposed as an adjuvant to conventional antibiotic treatment and it has been speculated that combining HBOT with antibiotics could improve treatment outcomes for biofilm infections. In this study we addressed whether HBOT could improve treatment outcomes of daptomycin and rifampicin combination therapy. The effect of HBOT on the treatment outcomes of daptomycin and rifampicin against implant-associated osteomyelitis was quantified in a murine model. In total, 80 mice were randomized into two groups receiving antibiotics, either alone or in combination with daily intermittent HBOT (304 kPa for 60 min) following injection of antibiotics. Treatment was initiated 11 days after animals were infected with Staphylococcus aureus and treatment duration was 14 days. We found that HBOT did not improve the cure rate and did not reduce the bacterial load on the implant surface or in the surrounding tissue. Cure rates of daptomycin + rifampicin were 40% in infected tibias and 75% for implants while cure rates for HBOT-daptomycin + rifampicin were 50% and 85%, respectively, which were not significantly higher (Fisher’s exact test). While it is encouraging that the combination of daptomycin and rifampicin is very effective, our study demonstrates that this efficacy cannot be improved by adjuvant HBOT.

[Morphometric and molecular biological features of femoral head tissue in different nosological entities of coxarthrosis]

AIM

to comparatively analyze the morphometric and molecular biological characteristics of femoral head tissue in different nosological entities of coxarthrosis.

MATERIAL AND METHODS

A total of 95 samples of femoral head tissue extirpated during hip endoprosthesis in patients with coxarthrosis were investigated. Clinical findings were used to identify the following nosological entities of coxarthrosis: dysplastic, postischemic and posttraumatic. Histological, immunohistochemical and morphometric studies were used. Osteoclast resorptive activity was assessed by determining the cytoplasmic expression of TRAcP (9C5, «Cell Marque»). Vasculogenesis was evaluated by estimating the mean area of vessels with CD34 (QBEnd/10, «Ventana») from the positive stained endothelium and by determining the cytoplasmic expression level of VEGF (SP28, «Spring Bio») in osteoblasts and osteoclasts.

RESULTS

Specific histopathological signs were described for each nosological entity of coxarthrosis. Morphometric analysis could reveal a number of additional characteristics of the magnitude of fibrous changes and the thickness of the articular surface and bone rods. Immunohistochemical assessment of molecular biological parameters, such as the expression level of VEGF and TRAcP, also pointed to the characteristic features of bony tissue in the above-mentioned nosological entities of coxarthrosis. In dysplastic coxarthrosis, the maximal expression level of VEGF was recorded in osteoblasts and the expression of VEGF and TRAcP in osteoclasts remained at the minimum level. The lowest expression of VEGF in osteoblasts was found in posttraumatic coxarthrosis. In postischemic coxarthrosis, the highest expression of VEGF and TRAcP was recorded in osteoclasts.

CONCLUSION

The comparative analysis of the morphometric and molecular biological characteristics of femoral head tissue in different nosological entities of coxarthrosis indicated a number of peculiar features. The most specific manifestations of certain morphological and molecular biological signs were identified for each nosological entity of coxarthrosis.

Hypoxic regulation of osteoclast differentiation and bone resorption activity

Bone integrity is maintained throughout life via the homeostatic actions of bone cells, namely, osteoclasts, which resorb bone, and osteoblasts, which produce bone. Disruption of this balance in favor of osteoclast activation results in pathological bone loss, which occurs in conditions including osteoporosis, rheumatoid arthritis, primary bone cancer, and cancer metastasis to bone. Hypoxia also plays a major role in these conditions, where it is associated with disease progression and poor prognosis. In recent years, considerable interest has arisen in the mechanisms whereby hypoxia and the hypoxia-inducible transcription factors, HIF-1α and HIF-2α, affect bone remodeling and bone pathologies. This review summarizes the current evidence for hypoxia-mediated regulation of osteoclast differentiation and bone resorption activity. Role(s) of HIF and HIF target genes in the formation of multinucleated osteoclasts from cells of the monocyte-macrophage lineage and in the activation of bone resorption by mature osteoclasts will be discussed. Specific attention will be paid to hypoxic metabolism and generation of ATP by osteoclasts. Hypoxia-driven increases in both glycolytic flux and mitochondrial metabolic activity, along with consequent generation of mitochondrial reactive oxygen species, have been found to be essential for osteoclast formation and resorption activity. Finally, evidence for the use of HIF inhibitors as potential therapeutic agents targeting bone resorption in osteolytic disease will be discussed.