Suppression of T cell-induced osteoclast formation

The immune cells in modulating osteoclast formation and bone metabolism

Osteoclasts are pivotal in regulating bone metabolism, with immune cells significantly influencing both physiological and pathological processes by modulating osteoclast functions. This is particularly evident in conditions of inflammatory bone resorption, such as rheumatoid arthritis and periodontitis. This review summarizes and comprehensively analyzes the research progress on the regulation of osteoclast formation by immune cells, aiming to unveil the underlying mechanisms and pathways through which diseases, such as rheumatoid arthritis and periodontitis, impact bone metabolism.

Rheumatoid arthritis molecular targets and their importance to flavonoid-based therapy

Rheumatoid arthritis (RA) is a progressive, chronic, autoimmune, inflammatory, and systemic condition that primarily affects the synovial joints and adjacent tissues, including bone, muscle, and tendons. The World Health Organization recognizes RA as one of the most prevalent chronic inflammatory diseases. In the last decade, there was an expansion on the available RA therapeutic options which aimed to improve patient's quality of life. Despite the extensive research and the emergence of new therapeutic approaches and drugs, there are still significant unwanted side effects associated to these drugs and still a vast number of patients that do not respond positively to the existing therapeutic strategies. Over the years, several references to the use of flavonoids in the quest for new treatments for RA have emerged. This review aimed to summarize the existing literature about the flavonoids' effects on the major pathogenic/molecular targets of RA and their potential use as lead compounds for the development of new effective molecules for RA treatment. It is demonstrated that flavonoids can modulate various players in synovial inflammation, regulate immune cell function, decrease synoviocytes proliferation and balance the apoptotic process, decrease angiogenesis, and stop/prevent bone and cartilage degradation, which are all dominant features of RA. Although further investigation is necessary to determine the effectiveness of flavonoids in humans, the available data from in vitro and in vivo models suggest their potential as new disease-modifying anti-rheumatic drugs. This review highlights the use of flavonoids as a promising avenue for future research in the treatment of RA.

Flavonoids as potential phytotherapeutics to combat cytokine storm in SARS-CoV-2

Emergence of severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) infection, COVID-19, has become the global panic since December 2019, which urges the global healthcare professionals to identify novel therapeutics to counteract this pandemic. So far, there is no approved treatment available to control this public health issue; however, a few antiviral agents and repurposed drugs support the patients under medical supervision by compromising their adverse effects, especially in emergency conditions. Only a few vaccines have been approved to date. In this context, several plant natural products-based research studies are evidenced to play a crucial role in immunomodulation that can prevent the chances of infection as well as combat the cytokine release storm (CRS) generated during COVID-19 infection. In this present review, we have focused on flavonoids, especially epicatechin, epigallocatechin gallate, hesperidin, naringenin, quercetin, rutin, luteolin, baicalin, diosmin, ge nistein, biochanin A, and silymarin, which can counteract the virus-mediated elevated levels of inflammatory cytokines leading to multiple organ failure. In addition, a comprehensive discussion on available in silico, in vitro, and in vivo findings with critical analysis has also been evaluated, which might pave the way for further development of phytotherapeutics to identify the potential lead candidatetoward effective and safe management of the SARS-CoV-2 disease.

A mechanistic insight of phytoestrogens used for Rheumatoid arthritis: An evidence-based review

Assessment of the potential therapeutic benefits offered by naturally occurring phytoestrogens necessitate inspection of their potency and sites of action in impeding the chronic, systemic, autoimmune, joint destructing disorder Rheumatoid arthritis (RA). Possessing structural and functional similarity with human estrogen, phytoestrogen promisingly replaces the use of hormone therapy in eradicating RA symptoms with their anti-inflammatory, anti-oxidative, anti-proliferative, anti-angiogenesis, immunomodulatory, joint protection properties abolishing the harmful side effects of synthetic drugs. Scientific evidences revealed that use of phytoestrogens from different chemical categories including flavonoids, alkaloids, stilbenoids derived from different plant species manifest beneficial effects on RA through various cellular mechanisms including suppression of pro-inflammatory cytokines in particular tumor necrosis factor (TNF-α), interleukin(IL-6) and nuclear factor kappa B (NF-κB) and destructive metalloproteinases, inhibition of oxidative stress, suppressing inflammatory signalling pathways, attenuating osteoclastogenesis ameliorating cartilage degradation and bone erosion. This review summarizes the evidences of different phytoestrogen treatment and their pharmacological mechanisms in both in vitro and in vivo studies along with discussing clinical evaluations in RA patients showing phytoestrogen as a promising agent for RA therapy. Further investigations and more clinical trials are mandatory to clarify the utility of these plant derived compounds in RA prevention and in managing oestrogen deficient diseases in patients.

The role of microbiota in tissue repair and regeneration

A comprehensive understanding of the human body endogenous microbiota is essential for acquiring an insight into the involvement of microbiota in tissue healing and regeneration process in order to enable development of biomaterials with a better integration with human body environment. Biomaterials used for biomedical applications are normally germ-free, and the human body as the host of the biomaterials is not germ-free. The complexity and role of the body microbiota in tissue healing/regeneration have been underestimated historically. Traditionally, studies aiming at the development of novel biomaterials had focused on the effects of environment within the target tissue, neglecting the signals generated from the microbiota and their impact on tissue regeneration. The significance of the human body microbiota in relation to metabolism, immune system, and consequently tissue regeneration has been recently realised and is a growing research field. This review summarises recent findings on the role of microbiota and mechanisms involved in tissue healing and regeneration, in particular skin, liver, bone, and nervous system regrowth and regeneration highlighting the potential new roles of microbiota for development of a new generation of biomaterials.

Improved RANKL expression and osteoclastogenesis induction of CD27+CD38- memory B cells: A link between B cells and alveolar bone damage in periodontitis

BACKGROUND AND OBJECTIVE

Periodontitis is a bacteria-induced disease that often leads to alveolar bone damage. Its mechanisms were considered to be complicated, involving an imbalance of the formation and resorption of bone. We sought to disclose the antibody-independent function of B cells during periodontitis.

MATERIAL AND METHODS

Production of receptor activator for nuclear factor-κB ligand (RANKL) by total lymphocytes or sorted B-cell subsets in gingiva from healthy or experimental periodontitis animals was examined by flow cytometry, real-time polymerase chain reaction, and enzyme-linked immunosorbent assay. To define the effects of lymphocytes or B-cell subsets on osteoclastogenesis induction, bone marrow mononuclear cells were culture in culture medium of lymphocytes or cocultured with B-cell subsets. Osteoclasts were enumerated by tartrate-resistant acid phosphatase staining. Constituent ratio of B-cell subsets in healthy or experimental periodontitis was also detected by flow cytometry.

RESULT

Gingiva B cells produce more RANKL and support more osteoclastogenesis than T and other lymphocytes, and this potential improved in periodontitis. Memory B cells (CD27+CD38-) decreased their percentage in periodontitis. Memory B cells have the highest propensity for RANKL production. Remarkably, memory B cells from periodontitis animals expressed significantly more RANKL compared to healthy controls. Memory B cells supported osteoclast differentiation in vitro in a RANKL-dependent manner, and the number of osteoclasts was higher in cultures with memory B cells from periodontitis animals than in those derived from healthy ones. Other B-cell subsets have limited impact on osteoclast formation.

CONCLUSION

Findings of this study further disclose the roles of B cells engaged in periodontal immunomodulation and reveal the considerable importance of memory B cells in alveolar bone homeostasis and their likely contribution to alveolar bone destruction in periodontitis.

Vγ9Vδ2 T cells inhibit immature dendritic cell transdifferentiation into osteoclasts through downregulation of RANK, c‑Fos and ATP6V0D2

Osteoimmunological studies have revealed that T cells exert a powerful impact on the formation and activity of osteoclasts and bone remodeling. Evidence demonstrates that immature dendritic cells (iDCs) are more efficient transdifferentiating into osteoclasts (OCs) than monocytes. However, whether Vγ9Vδ2 T (γδ T) cells stimulate or inhibit iDC transdifferentiation into OCs has never been reported. The aim of the present study was to investigate the effects of γδ T cells on this transdifferentiation process. γδ T cells and iDCs were isolated from the peripheral blood of healthy volunteers separately and were co-cultured with Transwelll inserts, with γδ T cells in the upper chamber and iDCs in the lower chamber. IDCs were treated with macrophage-colony stimulating factor and receptor activator of nuclear factor-κB (RANK) ligand. Tartrate resistant acid phosphatase (TRAP) assay and dentine resorption assay were performed to detect OC formation and their resorption capacity, respectively. The mRNA expression of OCs was examined using a micro-array and real time-quantitative polymerase chain reaction to trace the changes during iDC transdifferentiation into OCs. The results demonstrated that γδ T cells significantly inhibited the generation of the TRAP-positive OCs from iDCs and their resorption capacity. The microarray analysis identified decreased expression level of Fos proto-oncogene AP-1 transcription factor subunit (c-Fos), ATPase H⁺ transporting V0 subunit d (ATP6V0D2) and cathepsin K when iDCs were co-cultured with γδ T cells. These genes are associated with OC differentiation, indicating that γδ T cells suppressed iDCs osteoclastogenesis by downregulation of the RANK/c-Fos/ATP6V0D2 signaling pathway. The present findings provide novel insights into the interactions between human γδ T cells and iDCs, and demonstrate that γδ T cells are capable of inhibiting OC formation and their activity via downregulation of genes associated with OC differentiation.

Gut Microbiota and Bone Health

The past decade has seen an explosion of research in the area of how the bacteria that inhabit the human body impact health and disease. One of the more surprising concepts to emerge from this work is the ability of the intestinal microbiota to impact virtually all systems in the body. Recently, the role of gut bacteria in bone health and disease has received more significant attention. In this chapter, we review what has been learned about how the gut microbiome impacts bone health and discuss possible mechanisms of how the gut-bone axis may be connected. We also discuss the use of therapeutic microbes in the modulation of bone health. Finally, we propose an emerging field of the gut-brain-bone axis, in which the gut drives bone physiology via regulation of key hormones that are originally synthesized in the brain.

Coumestrol inhibits autoantibody production through modulating Th1 response in experimental autoimmune thyroiditis

Coumestrol is a common phytoestrogen found in plants and Chinese medicinal herbs. Its influences on experimental autoimmune thyroiditis (EAT) were investigated in this study. Female adult CBA/J mice were fed with drinking water containing 1% Tween80 only (Control group), 0.8 mg/l (L group) and 8 mg/l coumestrol (H group) from 6 to 15 weeks of age, respectively. Their serum coumestrol concentrations were determined by high performance liquid chromatography, which were undetectable, 43.70 ± 21.74 ng/ml and 135.07 ± 70.40 ng/ml, respectively. In addition, the mice (n = 14–16/group) were immunized twice with thyroglobulin (Tg) and Freund's adjuvant to induce EAT during the meantime. Although no overt changes in the extent of intrathyroidal mononuclear cell infiltration were shown in the two coumestrol-treated groups as compared with the controls, serum anti-Tg IgG2a, IgG3 and IgG1 titers, ratio of IgG2a to IgG1 and the percentage of T helper (Th)1 cells in the splenocytes were significantly reduced in the L group. Another consistent change was the significantly decreased expression of splenic IFN-γ mRNA after low dose of coumestrol exposure. Uterine weight was also markedly reduced in the mice of L group. These findings suggest that coumestrol treatment may have some beneficial actions against thyroid-specific autoantibody production in the development of autoimmune thyroiditis through suppression of Th1 response due to its anti-estrogenic activity.

Microbiota Reconstitution Does Not Cause Bone Loss in Germ-Free Mice

The microbiota has been shown to be an important regulator of health and development. With regard to its effect on bone health, a previous study has suggested that gut microbes negatively impact bone density. However, we show here that this is not generalizable to all microbial communities and mouse strain backgrounds. Our results demonstrate that colonization of mice, both outbred and inbred strains, did not have a major impact on bone health. The identification of microbial communities that do not negatively impact bone health may provide a foundation for future investigations that seek to identify microbes that are either beneficial or detrimental to bone metabolism.

Annually, an estimated 2 million osteoporotic fractures occur in the United States alone. Osteoporosis imparts a great burden on the health care system. The identification of novel regulators of bone health is critical for developing more effective therapeutics. A previous study on the colonization of germ-free (GF) mice with a microbial community has demonstrated that bacterial colonization dramatically increases bone loss. We therefore investigated the impact of multiple microbial communities in different mice to understand how generalizable the impact of bacterial colonization is on bone health. To investigate the impact of different microbial communities on bone health in outbred and inbred mouse strains, gavage was performed on GF Swiss Webster and GF C57BL/6 mice to introduce distinct microbiotas that originated from either humans or mice. GF mice displayed a high degree of colonization, as indicated by more than 90% of the operational taxonomic units present in the starting inoculum being successfully colonized in the mice when they were examined at the end of the experiment. In spite of the successful colonization of GF mice with gut microbiota of either mouse or human origin, bone mass did not change significantly in any of the groups tested. Furthermore, static and dynamic bone parameters and osteoclast precursor and T cell populations, as well as the expression of several inflammatory markers, were mostly unchanged following microbial colonization of GF mice.

IMPORTANCE The microbiota has been shown to be an important regulator of health and development. With regard to its effect on bone health, a previous study has suggested that gut microbes negatively impact bone density. However, we show here that this is not generalizable to all microbial communities and mouse strain backgrounds. Our results demonstrate that colonization of mice, both outbred and inbred strains, did not have a major impact on bone health. The identification of microbial communities that do not negatively impact bone health may provide a foundation for future investigations that seek to identify microbes that are either beneficial or detrimental to bone metabolism.