Tetrandrine enhances the ubiquitination and degradation of Syk through an AhR-c-src-c-Cbl pathway and consequently inhibits osteoclastogenesis and bone destruction in arthritis

Therapeutic effects of tetrandrine in inflammatory diseases: a comprehensive review

Inflammation can be triggered by any factor. The primary pathological manifestations can be summarized as the deterioration, exudation, and proliferation of local tissues, which can cause systemic damage in severe cases. Inflammatory lesions are primarily localized but may interact with body systems to cause provocative storms, parenchymal organ lesions, vascular and central nervous system necrosis, and other pathologic responses. Tetrandrine (TET) is a bisbenzylquinoline alkaloid extracted from the traditional Chinese herbal medicine Stephania tetrandra, which has been shown to have significant efficacy in inflammatory conditions such as rheumatoid arthritis, hepatitis, nephritis, etc., through NF-κB, MAPK, ERK, and STAT3 signaling pathways. TET can regulate the body's imbalanced metabolic pathways, reverse the inflammatory process, reduce other pathological damage caused by inflammation, and prevent the vicious cycle. More importantly, TET does not disrupt body's normal immune function while clearing the body's inflammatory state. Therefore, it is necessary to pay attention to its dosage and duration during treatment to avoid unexpected side effects caused by a long half-life. In summary, TET has a promising future in treating inflammatory diseases. The author reviews current therapeutic studies of TET in inflammatory conditions to provide some ideas for subsequent anti-inflammatory studies of TET.

StemRegenin 1 attenuates the RANKL-induced osteoclastogenesis via inhibiting AhR-c-src-NF-κB/p-ERK MAPK-NFATc1 signaling pathway

The aryl hydrocarbon receptor (AhR) pathway may play an important role in the regulation of osteoclasts, but there are still conflicting studies on this aspect, and the specific mechanism of action has not been fully elucidated. Therefore, we conducted this study to find a drug to treat osteoporosis that targets AhR. We found that StemRegenin 1 inhibited RANKL-induced osteoclastogenesis in a concentration-dependent and time-dependent manner. Through further experiments, we found that SR1 can inhibit nuclear transcription of AhR and inhibit c-src phosphorylation, and ultimately regulates the activation of the NF-κB and p-ERK/mitogen-activated protein kinase pathways. Therefore, for the first time, we discovered the way in which the AhR-c-src-NF-κB/p-ERK MAPK-NFATc1 signaling pathway regulates the expression of osteoclast differentiation-associated proteins. Finally, SR1 was shown to successfully reverse bone loss in OVX mice. These studies provide us with ideas for finding new way to treat osteoporosis.

The Role of Aryl Hydrocarbon Receptor in Bone Biology

Aryl hydrocarbon receptor (AhR), a ligand-activated transcription factor, is crucial in maintaining the skeletal system. Our study focuses on encapsulating the role of AhR in bone biology and identifying novel signaling pathways in musculoskeletal pathologies using the GEO dataset. The GEO2R analysis identified 8 genes (CYP1C1, SULT6B1, CYB5A, EDN1, CXCR4B, CTGFA, TIPARP, and CXXC5A) involved in the AhR pathway, which play a pivotal role in bone remodeling. The AhR knockout in hematopoietic stem cells showed alteration in several novel bone-related transcriptomes (eg, Defb14, ZNF 51, and Chrm5). Gene Ontology Enrichment Analysis demonstrated 54 different biological processes associated with bone homeostasis. Mainly, these processes include bone morphogenesis, bone development, bone trabeculae formation, bone resorption, bone maturation, bone mineralization, and bone marrow development. Employing Functional Annotation and Clustering through DAVID, we further uncovered the involvement of the xenobiotic metabolic process, p450 pathway, oxidation-reduction, and nitric oxide biosynthesis process in the AhR signaling pathway. The conflicting evidence of current research of AhR signaling on bone (positive and negative effects) homeostasis may be due to variations in ligand binding affinity, binding sites, half-life, chemical structure, and other unknown factors. In summary, our study provides a comprehensive understanding of the underlying mechanisms of the AhR pathway in bone biology.

Developing Chinese herbal-based functional biomaterials for tissue engineering

The role of traditional Chinese medicine (TCM) in treating diseases is receiving increasing attention. Chinese herbal medicine is an important part of TCM with various applications and the active ingredients extracted from Chinese herbal medicines have physiological and pathological effects. Tissue engineering combines cell biology and materials science to construct tissues or organs in vitro or in vivo. TCM has been proposed by the World Health Organization as an effective treatment modality. In recent years, the potential use of TCM in tissue engineering has been demonstrated. In this review, the classification and efficacy of TCM active ingredients and delivery systems are discussed based on the TCM theory. We also summarized the current application status and broad prospects of Chinese herbal active ingredients in different specialized biomaterials in the field of tissue engineering. This review provides novel insights into the integration of TCM and modern Western medicine through the application of Chinese medicine in tissue engineering and regenerative medicine.

Association between combined exposure to dioxins and arthritis among US adults: a cross-sectional study

Dioxins and dioxin-like compounds (DLCs) are common pollutants hazardous to human health. We applied 12 dioxins and DLCs data of 1851 participants (including 484 arthritis patients) from National Health Examination Survey (NHANES) 2001-2004 and quadrupled them into rank variables. Multivariate logistic regression, weighted quantile sum (WQS) regression, and Bayesian kernel machine regression (BKMR) models were used to explore the relationship between individual or mixed exposure to the pollutants and arthritis after adjusting for multiple covariates. In multivariable logistic regression with an individual dioxin or DLC, almost every chemical was significantly positively associated with arthritis, except PCB66 (polychlorinated biphenyl 66) and 1,2,3,4,6,7,8-heptachlorodibenzofuran (hpcdf). The WQS model indicated that the combined exposure to the 12 dioxins and DLCs was positively linked to arthritis (OR: 1.884, 95% CI: 1.514-2.346), with PCB156 (weighted 0.281) making the greatest contribution. A positive trend between combined exposure and arthritis was observed in the BKMR model, with a posterior inclusion probability (PIP) of 0.987 for PCB156, which was also higher than the other contaminants.

Orchiectomy sensitizes cortical bone in male mice to the harmful effects of kynurenine

Kynurenine (Kyn) is a tryptophan metabolite that increases with age and promotes musculoskeletal dysfunction. We previously found a sexually dimorphic pattern in how Kyn affects bone, with harmful effects more prevalent in females than males. This raises the possibility that male sex steroids might exert a protective effect that blunts the effects of Kyn in males. To test this, orchiectomy (ORX) or sham surgeries were performed on 6-month-old C57BL/6 mice, after which mice received Kyn (10 mg/kg) or vehicle via intraperitoneal injection, once daily, 5×/week, for four weeks. Bone histomorphometry, DXA, microCT, and serum marker analyses were performed after sacrifice. In vitro studies were performed to specifically test the effect of testosterone on activation of aryl hydrocarbon receptor (AhR)-mediated signaling by Kyn in mesenchymal-lineage cells. Kyn treatment reduced cortical bone mass in ORX- but not sham-operated mice. Trabecular bone was unaffected. Kyn's effects on cortical bone in ORX mice were attributed primarily to enhanced endosteal bone resorption activity. Bone marrow adipose tissue was increased in Kyn-treated ORX animals but was unchanged by Kyn in sham-operated mice. ORX surgery increased mRNA expression of the aryl hydrocarbon receptor (AhR) and its target gene Cyp1a1 in the bone, suggesting a priming and/or amplification of AhR signaling pathways. Mechanistic in vitro studies revealed that testosterone blunted Kyn-stimulated AhR transcriptional activity and Cyp1a1 expression in mesenchymal-linage cells. These data suggest a protective role for male sex steroids in blunting the harmful effects of Kyn in cortical bone. Therefore, testosterone may play an important role in regulating Kyn/AhR signaling in musculoskeletal tissues, suggesting crosstalk between male sex steroids and Kyn signaling may influence age-associated musculoskeletal frailty.

Tetrandrine Represses Inflammation and Attenuates Osteoarthritis by Selective Inhibition of COX-2

OBJECTIVE

There is a lack of effective and long-term safe drugs for the treatment of osteoarthritis (OA). Tetrandrine (Tet) has been approved and used to treat rheumatoid arthritis for several decades, but its effect on OA has not been investigated. Herein, we explored the effect of Tet on OA and its underlying mechanism.

METHODS

OA was induced using destabilization of the medial meniscus (DMM) in C57BL/6J mice. The animals were randomly divided into sham, DMM, Tet, celecoxib (CXB), and indomethacin (INDO) groups. Each group was given solvent or corresponding drugs by gavage for 7 weeks after convalescence. Pathological staining, OARSI scores, micro-computed tomography and behavior tests were performed to evaluate the effects of Tet.

RESULTS

Tet remarkably alleviated cartilage injury in the knee joint, limited bone remodeling in the subchondral bone, and delayed progression of OA. Tet also significantly relieved joint pain and maintained function. Further mechanistic studies revealed that Tet lowered inflammatory cytokine levels and selectively suppressed gene and protein expression of cyclooxygenase (COX)-2 but not COX-1 (P<0.01). Tet also reduced the production of prostaglandin E2 without damaging the gastric mucosa.

CONCLUSION

We found that Tet could selectively inhibit COX-2 gene expression and decrease cytokine levels in mice, thus reducing inflammation and improving OA without obvious gastric adverse events. These results provide a scientific basis for the clinical application of Tet in the treatment of OA.

Functions of the aryl hydrocarbon receptor (AHR) beyond the canonical AHR/ARNT signaling pathway

The aryl hydrocarbon receptor (AHR) is a ligand-dependent transcription factor regulating adaptive and maladaptive responses toward exogenous and endogenous signals. Research from various biomedical disciplines has provided compelling evidence that the AHR is critically involved in the pathogenesis of a variety of diseases and disorders, including autoimmunity, inflammatory diseases, endocrine disruption, premature aging and cancer. Accordingly, AHR is considered an attractive target for the development of novel preventive and therapeutic measures. However, the ligand-based targeting of AHR is considerably complicated by the fact that the receptor does not always follow the beaten track, i.e. the canonical AHR/ARNT signaling pathway. Instead, AHR might team up with other transcription factors and signaling molecules to shape gene expression patterns and associated physiological or pathophysiological functions in a ligand-, cell- and micromilieu-dependent manner. Herein, we provide an overview about some of the most important non-canonical functions of AHR, including crosstalk with major signaling pathways involved in controlling cell fate and function, immune responses, adaptation to low oxygen levels and oxidative stress, ubiquitination and proteasomal degradation. Further research on these diverse and exciting yet often ambivalent facets of AHR biology is urgently needed in order to exploit the full potential of AHR modulation for disease prevention and treatment.

Cholinergic dysfunction-induced insufficient activation of alpha7 nicotinic acetylcholine receptor drives the development of rheumatoid arthritis through promoting protein citrullination via the SP3/PAD4 pathway

Both cholinergic dysfunction and protein citrullination are the hallmarks of rheumatoid arthritis (RA), but the relationship between the two phenomena remains unclear. We explored whether and how cholinergic dysfunction accelerates protein citrullination and consequently drives the development of RA. Cholinergic function and protein citrullination levels in patients with RA and collagen-induced arthritis (CIA) mice were collected. In both neuron-macrophage coculture system and CIA mice, the effect of cholinergic dysfunction on protein citrullination and expression of peptidylarginine deiminases (PADs) was assessed by immunofluorescence. The key transcription factors for PAD4 expression were predicted and validated. Cholinergic dysfunction in the patients with RA and CIA mice negatively correlated with the degree of protein citrullination in synovial tissues. The cholinergic or alpha7 nicotinic acetylcholine receptor (α7nAChR) deactivation and activation resulted in the promotion and reduction of protein citrullination in vitro and in vivo, respectively. Especially, the activation deficiency of α7nAChR induced the earlier onset and aggravation of CIA. Furthermore, deactivation of α7nAChR increased the expression of PAD4 and specificity protein-3 (SP3) in vitro and in vivo. Our results suggest that cholinergic dysfunction-induced deficient α7nAChR activation, which induces the expression of SP3 and its downstream molecule PAD4, accelerating protein citrullination and the development of RA.

Tetrandrine-induced downregulation of lncRNA NEAT1 inhibits rheumatoid arthritis progression through the STAT3/miR-17-5p pathway

BACKGROUND

The inhibitory effect of Tetrandrine (Tet) on rheumatoid arthritis (RA) is well established. However, its exact molecular mechanism remains unknown.

METHODS

RT-qPCR coupled with western blotting was employed to analyze the expression of NEAT1, miR-17-5p, and STAT3 in RA tissues and/or RA-fibroblast-like synoviocytes (RA-FLS) treated with 3 μmol/L of Tet for 48 h. Cell Counting Kit-8 assay and flow cytometry were performed to assess RA-FLS proliferation and apoptosis. Luciferase reporter assays were used to validate the interactions between miR-17-5p and STAT3 or NEAT1.

RESULTS

The expression of NEAT1 decreased in a time-dependent manner upon Tet treatment. Tet significantly inhibited RA-FLS proliferation and triggered apoptosis by downregulating NEAT1 expression. Additionally, NEAT1 directly targeted miR-17-5p to upregulate STAT3 expression. Tet-induced low NEAT1 expression impaired RA-FLS growth by targeting miR-17-5p and inhibiting STAT3.

CONCLUSION

Tet exerts its inhibitory role in RA progression by regulating the NEAT1/miR-17-5p/STAT3 pathway.

The bone-protective mechanisms of active components from TCM drugs in rheumatoid arthritis treatment

Rheumatoid arthritis (RA) is an autoimmune disease whose hallmarks are synovial inflammation and irreversible bone destruction. Bone resorption resulting from osteoclasts involves the whole immune and bone systems. Breakdown of bone remodeling is attributed to overactive immune cells that produce large quantities of cytokines, upregulated differentiation of osteoclasts with enhanced resorptive activities, suppressed differentiation of osteoblasts, invading fibroblasts and microbiota dysbiosis. Despite the mitigation of inflammation, the existing treatment in Western medicine fails to prevent bone loss during disease progression. Traditional Chinese medicine (TCM) has been used for thousands of years in RA treatment, showing great efficacy in bone preservation. The complex components from the decoctions and prescriptions exhibit various pharmacological activities. This review summarizes the research progress that has been made in terms of the bone-protective effect of some representative compounds from TCM drugs and proposes the substantial mechanisms involved in bone metabolism to provide some clues for future studies. These active components systemically suppress bone destruction via inhibiting joint inflammation, osteoclast differentiation, and fibroblast proliferation. Neutrophil, gut microenvironment and microRNA has been proposed as future focus.

Natural medicines of targeted rheumatoid arthritis and its action mechanism

Rheumatoid arthritis (RA) is an autoimmune disease involving joints, with clinical manifestations of joint inflammation, bone damage and cartilage destruction, joint dysfunction and deformity, and extra-articular organ damage. As an important source of new drug molecules, natural medicines have many advantages, such as a wide range of biological effects and small toxic and side effects. They have become a hot spot for the vast number of researchers to study various diseases and develop therapeutic drugs. In recent years, the research of natural medicines in the treatment of RA has made remarkable achievements. These natural medicines mainly include flavonoids, polyphenols, alkaloids, glycosides and terpenes. Among them, resveratrol, icariin, epigallocatechin-3-gallate, ginsenoside, sinomenine, paeoniflorin, triptolide and paeoniflorin are star natural medicines for the treatment of RA. Its mechanism of treating RA mainly involves these aspects: anti-inflammation, anti-oxidation, immune regulation, pro-apoptosis, inhibition of angiogenesis, inhibition of osteoclastogenesis, inhibition of fibroblast-like synovial cell proliferation, migration and invasion. This review summarizes natural medicines with potential therapeutic effects on RA and briefly discusses their mechanisms of action against RA.

Tetrandrine Ameliorates Rheumatoid Arthritis in Mice by Alleviating Neutrophil Activities

Rheumatoid arthritis (RA) is a common autoimmune disease worldwide. Neutrophils play critical roles in the onset and development of RA and are the promising target for RA treatment. Tetrandrine is a bis-benzyl isoquinoline alkaloid derived from the traditional Chinese herbal Stephania tetrandra S. Moore. Tetrandrine is effective in alleviating RA by inhibiting macrophage inflammatory response, fibroblast overproliferation, and pannus formation. However, whether tetrandrine regulates the activities of neutrophils in RA is largely unknown. In this study, we adopted adjuvant-induced arthritis (AA) murine model to explore the effect of tetrandrine on RA and neutrophils. Twenty-eight mice were divided into four groups. The control group was injected with PBS in the limbs and treated with PBS by intraperitoneal injection (i.p.) from Day 10 to Day 37. The arthritis murine model was induced by injecting FCA into the ankle joints of hind limbs. The AA group, the AA + TET group, and the AA + DEX group mice were treated with PBS, tetrandrine (6 mg/kg), or dexamethasone (1 mg/kg) i.p. daily, respectively. Arthritic scores were evaluated, and the joint diameter was measured every three days. A cytometric bead assay was performed to measure the concentrations of IFN-γ, TNF-α, and IL-6 in the serum. H&E staining and Safranin O-fast staining were adopted to monitor the tissue changes in the joint. Immunohistochemistry assays were applied to detect the MPO, NE, CitH3, and PAD4 expression levels. To assess the effect of tetrandrine on neutrophil activities in vitro, CCK8 tests were applied to determine cell viability. The qPCR and ELISA were performed to determine IL-1β and IL-6 expression levels. Immunofluorescence assays were performed to measure the formation of NETs. The results indicated that tetrandrine significantly alleviated the symptoms of RA in terms of the ankle diameter (from 4.629 ± 2.729 to 3.957 ± 0.257; P < 0.01) and ankle score (from 4.000 ± 0.000 to 3.286 ± 0.756; P < 0.05). Tetrandrine treatment significantly increased the cartilage areas and decreased serum IL-6 significantly (from 5.954 ± 2.127 to 2.882 ± 2.013; P < 0.01). The immunohistochemistry assays also showed decreased expression levels of NE, MPO, PAD4, and CitH3 induced by tetrandrine in comparison with the AA group (P < 0.01). The qPCR assays and ELISAs showed that tetrandrine had an anti-inflammatory effect in vitro by significantly inhibiting IL-6 (P < 0.01). The immunofluorescence assays showed that NET formation induced by PMA could be reduced by tetrandrine (P < 0.01). In conclusion, tetrandrine has good efficacy in treating RA by regulating neutrophil-involved inflammation and NET formation.

Polycyclic aromatic hydrocarbons in bone homeostasis

Prolonged exposure to polycyclic aromatic hydrocarbons (PAHs) may result in autoimmune diseases, such as rheumatoid arthritis (RA) and osteoporosis (OP), which are based on an imbalance in bone homeostasis. These diseases are characterized by bone erosion and even a disruption in homeostasis, including in osteoblasts and osteoclasts. Current evidence indicates that multiple factors affect the progression of bone homeostasis, such as genetic susceptibility and epigenetic modifications. However, environmental factors, especially PAHs from various sources, have been shown to play an increasingly prominent role in the progression of bone homeostasis. Hence, it is essential to investigate the effects and pathogenesis of PAHs in bone homeostasis. In this review, recent progress is summarized concerning the effects and mechanisms of PAHs and their ligands and receptors in bone homeostasis. Moreover, strategies based on the effects and mechanisms of PAHs in the regulation of the bone balance and alleviation of bone destruction are also reviewed. We further discuss the future challenges and perspectives regarding the roles of PAHs in autoimmune diseases based on bone homeostasis.

Inhibition of Human Osteoclast Differentiation by Kynurenine through the Aryl-Hydrocarbon Receptor Pathway

Aryl-hydrocarbon receptor (AhR) is a ligand-activated transcription factor and regulates differentiation and function of various immune cells such as dendritic cells, Th17, and regulatory T cells. In recent studies, it was reported that AhR is involved in bone remodeling through regulating both osteoblasts and osteoclasts. However, the roles and mechanisms of AhR activation in human osteoclasts remain unknown. Here we show that AhR is involved in human osteoclast differentiation. We found that AhR expressed highly in the early stage of osteoclastogenesis and decreased in mature osteoclasts. Kynurenine (Kyn), formylindolo[3,4-b] carbazole (FICZ), and benzopyrene (BaP), which are AhR agonists, inhibited osteoclast formation and Kyn suppressed osteoclast differentiation at an early stage. Furthermore, blockade of AhR signaling through CH223191, an AhR antagonist, and knockdown of AhR expression reversed Kyn-induced inhibition of osteoclast differentiation. Overall, our study is the first report that AhR negatively regulates human osteoclast differentiation and suggests that AhR could be good therapeutic molecule to prevent bone destruction in chronic inflammatory diseases such as rheumatoid arthritis (RA).

Pharmacological blockage of the AHR-CYP1A1 axis: a call for in vivo evidence

The aryl hydrocarbon receptor (AHR) is a ligand-activated transcription factor that can be activated by structurally diverse compounds arising from the environment and the microbiota and host metabolism. Expanding evidence has been shown that the modulation of the canonical pathway of AHR occurs during several chronic diseases and that its abrogation might be of clinical interest for metabolic and inflammatory pathological processes. However, most of the evidence on the pharmacological abrogation of the AHR-CYP1A1 axis has been reported in vitro, and therefore, guidance for in vivo studies is needed. In this review, we cover the state-of-the-art of the pharmacodynamic and pharmacokinetic properties of AHR antagonists and CYP1A1 inhibitors in different in vivo rodent (mouse or rat) models of disease. This review will serve as a road map for those researchers embracing this emerging therapeutic area targeting the AHR. Moreover, it is a timely opportunity as the first AHR antagonists have recently entered the clinical stage of drug development.

Glycogen Synthase Kinase 3 Beta Regulates the Human Aryl Hydrocarbon Receptor Cellular Content and Activity

The aryl hydrocarbon receptor (AHR) is a cytosolic receptor which is involved in diverse cellular events in humans. The most well-characterized function of AHR is its ability to upregulate gene transcription after exposure to its ligands, such as environmental toxicants, dietary antioxidants, drugs, and endogenous ligands. The cellular content of AHR is partly controlled by its degradation via the ubiquitin–proteasome system and the lysosome-dependent autophagy. We used human cervical cancer (HeLa) cells to investigate how AHR undergoes protein degradation and how its activity is modulated. Since the glycogen synthase kinase 3 beta (GSK3β)-mediated phosphorylation can trigger protein degradation and substrates of GSK3β contain stretches of serine/threonine residues which can be found in AHR, we examined whether degradation and activity of AHR can be controlled by GSK3β. We observed that AHR undergoes the GSK3β-dependent, LC3-mediated lysosomal degradation without ligand treatment. The AHR can be phosphorylated in a GSK3β-dependent manner at three putative sites (S436/S440/S444, S689/S693/T697, and S723/S727/T731), which leads to lysosomal degradation of the AHR protein. Inhibition of the GSK3β activity suppresses the ligand-activated transcription of an AHR target gene in HeLa, human liver cancer (Hep3B), and human breast cancer (MCF-7) cells. Collectively, our findings support that phosphorylation of AHR by GSK3β is essential for the optimal activation of its target gene transcription and this phosphorylation may partake as an “off” switch by subjecting the receptor to lysosomal degradation.

Biological Effects of β-Glucans on Osteoclastogenesis

Although the anti-tumor and anti-infective properties of β-glucans have been well-discussed, their role in bone metabolism has not been reviewed so far. This review discusses the biological effects of β-glucans on bone metabolisms, especially on bone-resorbing osteoclasts, which are differentiated from hematopoietic precursors. Multiple immunoreceptors that can recognize β-glucans were reported to be expressed in osteoclast precursors. Coordinated co-stimulatory signals mediated by these immunoreceptors are important for the regulation of osteoclastogenesis and bone remodeling. Curdlan from the bacterium Alcaligenes faecalis negatively regulates osteoclast differentiation in vitro by affecting both the osteoclast precursors and osteoclast-supporting cells. We also showed that laminarin, lichenan, and glucan from baker’s yeast, as well as β-1,3-glucan from Euglema gracilisas, inhibit the osteoclast formation in bone marrow cells. Consistent with these findings, systemic and local administration of β-glucan derived from Aureobasidium pullulans and Saccharomyces cerevisiae suppressed bone resorption in vivo. However, zymosan derived from S. cerevisiae stimulated the bone resorption activity and is widely used to induce arthritis in animal models. Additional research concerning the relationship between the molecular structure of β-glucan and its effect on osteoclastic bone resorption will be beneficial for the development of novel treatment strategies for bone-related diseases.

Non-Genomic AhR-Signaling Modulates the Immune Response in Endotoxin-Activated Macrophages After Activation by the Environmental Stressor BaP

Emerging studies revealed that the Aryl hydrocarbon receptor (AhR), a receptor sensing environmental contaminants, is executing an immunomodulatory function. However, it is an open question to which extent this is achieved by its role as a transcription factor or via non-genomic signaling. We utilized a multi-post-translational modification-omics approach to examine non-genomic AhR-signaling after activation with endogenous (FICZ) or exogenous (BaP) ligand in endotoxin-activated (LPS) monocyte-derived macrophages. While AhR activation affected abundances of few proteins, regulation of ubiquitination and phosphorylation were highly pronounced. Although the number and strength of effects depended on the applied AhR-ligand, both ligands increased ubiquitination of Rac1, which participates in PI3K/AKT-pathway-dependent macrophage activation, resulting in a pro-inflammatory phenotype. In contrast, co-treatment with ligand and LPS revealed a decreased AKT activity mediating an anti-inflammatory effect. Thus, our data show an immunomodulatory effect of AhR activation through a Rac1ubiquitination-dependent mechanism that attenuated AKT-signaling, resulting in a mitigated inflammatory response.

Microbiota-Derived Metabolites, Indole-3-aldehyde and Indole-3-acetic Acid, Differentially Modulate Innate Cytokines and Stromal Remodeling Processes Associated with Autoimmune Arthritis

Rheumatoid arthritis (RA) is an autoimmune disease characterized by chronic inflammation of the synovial joints. Inflammation, new blood vessel formation (angiogenesis) and bone resorption (osteoclastogenesis) are three key processes involved in the joint damage and deformities of arthritis. Various gut microbiota-derived metabolites are implicated in RA pathogenesis. However, there is barely any information about the impact of two such metabolites, indole-3-aldehyde (IAld) and indole-3-acetic acid (I3AA), on arthritis-related processes. We conducted a comparative analysis of IAld and I3AA using established cell-based models to understand how they might influence RA pathogenesis. Although structurally similar, the bioactivities of these two metabolites were profoundly different. IAld but not I3AA, inhibited the expression of pro-inflammatory cytokines (IL-1β and IL-6) in RAW 264.7 (RAW) cells stimulated with heat-killed M. tuberculosis sonicate (Mtb) and lipopolysaccharide (LPS). IAld also exhibited pro-angiogenic activity and pro-osteoclastogenic activity. In contrast, I3AA exhibited anti-angiogenic activity on endothelial cell tube formation but had no effect on osteoclastogenesis. Both IAld and I3AA have been proposed as aryl hydrocarbon receptor (AhR) agonists. Use of CH-223191, an inhibitor of the AhR, suppressed the anti-angiogenic activity of I3AA but failed to mitigate the effects of IAld. Further investigation of the anti-inflammatory activities of IAld and I3AA in LPS-treated RAW cells indicated that inhibition of MyD88-dependent activation of NF-κB and MAPK pathways was not likely involved. Our results suggest that the relative bioavailability of these indole derivatives may differentially impact RA progression and possibly other diseases that share similar cellular processes.

Traditional Chinese Medicine and orthopedic biomaterials: Host of opportunities from herbal extracts

The role of Traditional Chinese Medicine (TCM), especially herbs or herbal extracts, in treating diseases has received increasing attention. This review focuses on the use of herbal extracts as signaling molecules and functional materials in the field of orthopedics, biomaterial science and bone tissue engineering strategies. A literature review using both Chinese and English references on herbs and herbal extracts based on TCM theory used in orthopedics and biomaterial science was performed. We discuss the efficacy of herbs, the active extracts from these herbs, the combination of herbal extracts and biomaterials and, finally, the application of herbal extracts to the biomaterials specific to orthopedics. Only a few studies have confirmed the feasibility of applying herbal extracts to biomaterials to improve the role of biomaterials and/or optimize drug delivery and release in orthopedics. In this context, this review reveals a new and promising direction for herbal extracts, where the use of herbal extracts based on TCM systemic treatment, can change the limited modern medicine view of biomaterials as "only for local treatment" when considering its efficacy.

Novel Pentapeptide Derived from Chicken by-Product Ameliorates DSS-Induced Colitis by Enhancing Intestinal Barrier Function via AhR-Induced Src Inactivation

Managing patients with refractory inflammatory bowel diseases (IBD) is a common clinical challenge. Galli Gigeriae Endothelium Corneum (GGEC), a chicken by-product, has been used for centuries in Asian countries as a functional food and supplement for the treatment of gastrointestinal disorders. In this study, a novel peptide (LNLYP, LP-5) with gastrointestinal stability that can enhance the intestinal barrier function that was first identified in GGEC. Our work demonstrated that aryl hydrocarbon receptor (AhR) activation by LP-5 could inhibit the Src kinase to increase tight junction protein levels and down-regulate the expression of inflammatory cytokines to protect the intestinal barrier and finally alleviate dextran sulfate sodium (DSS)-induced colitis. This study revealed that LP-5 had the potential to develop into a therapeutic agent for the treatment of colitis and provided new high-valued utilization of GGEC.

Kynurenine Promotes RANKL-Induced Osteoclastogenesis In Vitro by Activating the Aryl Hydrocarbon Receptor Pathway

There is increasing evidence of the involvement of the tryptophan metabolite kynurenine (KYN) in disrupting osteogenesis and contributing to aging-related bone loss. Here, we show that KYN has an effect on bone resorption by increasing osteoclastogenesis. We have previously reported that in vivo treatment with KYN significantly increased osteoclast number lining bone surfaces. Here, we report the direct effect of KYN on receptor activator of nuclear factor kappa-B ligand (RANKL)-induced osteoclastogenesis in Raw 264.7 macrophage cells, and we propose a potential mechanism for these KYN-mediated effects. We show that KYN/RANKL treatment results in enhancement of RANKL-induced osteoclast differentiation. KYN drives upregulation and activation of the key osteoclast transcription factors, c-fos and NFATc1 resulting in an increase in the number of multinucleated TRAP+ osteoclasts, and in hydroxyapatite bone resorptive activity. Mechanistically, the KYN receptor, aryl hydrocarbon receptor (AhR), plays an important role in the induction of osteoclastogenesis. We show that blocking AhR signaling using an AhR antagonist, or AhR siRNA, downregulates the KYN/RANKL-mediated increase in c-fos and NFATc1 and inhibits the formation of multinucleated TRAP + osteoclasts. Altogether, this work highlights that the novelty of the KYN and AhR pathways might have a potential role in helping to regulate osteoclast function with age and supports pursuing additional research to determine if they are potential therapeutic targets for the prevention or treatment of osteoporosis.

The Role of Aryl-Hydrocarbon Receptor (AhR) in Osteoclast Differentiation and Function

Aryl hydrocarbon receptor (AhR) is a ligand-activated transcription factor that plays a crucial role in bone remodeling through altering the interplay between bone-forming osteoblasts and bone-resorbing osteoclasts. While effects of AhR signaling in osteoblasts are well understood, the role and mechanism of AhR signaling in regulating osteoclastogenesis is not widely understood. AhR, when binding with exogenous ligands (environmental pollutants such as polycylic aryl hydrocarbon (PAH), dioxins) or endogenous ligand indoxyl-sulfate (IS), has dual functions that are mediated by the nature of the binding ligand, binding time, and specific pathways of distinct ligands. In this review, AhR is discussed with a focus on (i) the role of AhR in osteoclast differentiation and function and (ii) the mechanisms of AhR signaling in inhibiting or promoting osteoclastogenesis. These findings facilitate an understanding of the role of AhR in the functional regulation of osteoclasts and in osteoclast-induced bone destructive conditions such as rheumatoid arthritis and cancer.

Potential Advantages of Bioactive Compounds Extracted From Traditional Chinese Medicine to Inhibit Bone Destructions in Rheumatoid Arthritis

Bone destruction is an important pathological feature of rheumatoid arthritis (RA), which finally leads to the serious decline of life quality in RA patients. Bone metabolism imbalance is the principal factor of bone destruction in RA, which is manifested by excessive osteoclast-mediated bone resorption and inadequate osteoblast-mediated bone formation. Although current drugs alleviate the process of bone destruction to a certain extent, there are still many deficiencies. Recent studies have shown that traditional Chinese medicine (TCM) could effectively suppress bone destruction of RA. Some bioactive compounds from TCM have shown good effect on inhibiting osteoclast differentiation and promoting osteoblast proliferation. This article reviews the research progress of bioactive compounds exacted from TCM in inhibiting bone destruction of RA, so as to provide references for further clinical and scientific research.

Tetrandrine Prevents Bone Loss in Ovariectomized Mice by Inhibiting RANKL-Induced Osteoclastogenesis

Postmenopausal osteoporosis (PMOP) is a metabolic bone disease characterized by decreased bone density and strength due to the imbalance between osteogenesis and osteoclastogenesis. Postmenopausal estrogen withdrawal increases proinflammatory cytokines and increases the serum level of Receptor activator of NF-kB ligand (RANKL)/Osteoprotegerin (OPG), which then leads to the overactivation of osteoclastogenesis. Tetrandrine, a bis-benzylisoquinoline alkaloid, has been widely used in the treatment of rheumatoid arthritis clinically in China. Here, we demonstrate that tetrandrine significantly prevented ovariectomy-induced bone loss and inhibited RANKL-induced osteoclastogenesis. In vivo, we found that intraperitoneal injection of tetrandrine (30 mg/kg) every other day markedly reduced bone loss in ovariectomized mice and the serum levels of TRAcp5b, TNF-a, IL-6, CTX-I, and RANKL/OPG were significantly decreased. In vitro, we found that tetrandrine significantly inhibited osteoclast differentiation in bone marrow monocytes (BMMs) and RAW264.7 cells according to the results of osteoclastogenesis-related gene expression, tartrate-resistant acid phosphatase (TRAP) staining and actin-ring formation as well as bone resorption assay. Mechanistically, tetrandrine inhibited RANKL-induced osteoclastogenesis by suppressing NF-kB, Ca2⁺, PI3K/AKT, and MAPKs signaling pathways. Taken together, our findings suggest that tetrandrine suppresses osteoclastogenesis through modulation of multiple pathways and has potential value as a therapeutic agent for PMOP, especially for those suffering from RA and PMOP at the same time.

Tetrandrine inhibits proliferation of colon cancer cells by BMP9/ PTEN/ PI3K/AKT signaling

Despite advances in screening and treatment, colon cancer remains one of the leading causes of cancer-related death. Finding novel and useful drug treatment targets is also an urgent need for clinical applications. Tetrandrine (Tet) is extracted from the Chinese medicinal herbal medicine, which is a well-known calcium blocker with a variety of pharmacological activities, including anti-cancer. In this study, we recruited cell viability assay, flow cytometry analysis, cloning formation to confirm that Tet can inhibit the proliferation of SW620 cells, and induce apoptosis. Mechanically, we confirmed that Tet up-regulates the mRNA and protein level of BMP9 in SW620 cells. Over-expression BMP9 enhances the anti-cancer effects of Tet in SW620 cells, but these effects can be partly reversed by silencing BMP9. Also, Tet reduces phosphorylation of Aktl/2/3 in SW620 cells, which could be elevated by overexpressed BMP9 and impaired by silencing BMP9. Furthermore, we demonstrated that Tet reduces phosphorylated PTEN, which can be promoted by overexpressed BMP9, analogously also be attenuated through silencing BMP9. Finally, we introduced a xenograft tumor model to investigate the anti-proliferative effect of Tet, further to explore the effects of BMP9 and PTEN in SW620 cells. Our findings suggested that the anti-cancer activity of Tet in SW620 cells may be mediated partly by up-regulating BMP9, followed by inactivation PI3K/Akt through up-regulating PTEN at least.

Antagonizing Effects of Clematis apiifolia DC. Extract against Benzo[a]pyrene-Induced Damage to Human Keratinocytes

Background. Benzo[a]pyrene (B[a]P), a polycyclic aromatic hydrocarbon present in the atmosphere, has cytotoxic and carcinogenic effects. There have been no reports to demonstrate involvement of Clematis apiifolia DC. extract (CAE) in B[a]P-induced effects. This study was conducted to investigate the effect of CAE on B[a]P-induced effects and to elucidate its mechanism of action in HaCaT human keratinocytes. CAE inhibited aryl hydrocarbon receptor (AhR) signaling by decreasing both XRE reporter activity and expression of cytochrome P450 1A1 (CYP1A1) induced by B[a]P treatment in HaCaT cells. We also found that B[a]P-induced nuclear translocation of AhR and production of reactive oxygen species (ROS) and proinflammatory cytokines were attenuated by CAE treatment. CAE treatment suppressed B[a]P-induced phosphorylation of Src (Tyr416). In addition, dasatinib, a Src inhibitor, also inhibited B[a]P-induced nuclear translocation of AhR, similar to CAE treatment. In addition, CAE activated antioxidant response element (ARE) signaling by increasing ARE luciferase reporter activity and expression of ARE-dependent genes such as nuclear factor (erythroid-derived 2)-like 2 (Nrf2), NAD(P)H dehydrogenase [quinone] 1 (NQO1), and heme oxygenase-1 (HO-1). Nuclear translocation of Nrf2 by CAE was demonstrated by Western blot analysis and immunocytochemistry. The effects of CAE on ARE signaling were attenuated by knockdown of the Nrf2 gene. Inhibition of AhR signaling and activation of antioxidant activity by CAE operated in a reciprocally independent manner as evidenced by AhR and Nrf2 siRNA experiments. These findings indicate that CAE exerts protective effects against B[a]P by inhibiting AhR signaling and activating Nrf2-mediated signaling, suggesting its potential in protection from harmful B[a]P-containing pollutants.