LXR modulation blocks prostaglandin E2 production and matrix degradation in cartilage and alleviates pain in a rat osteoarthritis model

Effect of 10.6-μm CO2 laser moxibustion on the fastest 15-m walking time in patients with knee osteoarthritis: a double-blind, sham-controlled, multi-site randomized trial

BACKGROUND

In this study, we investigated the impact of 10.6-μm CO2 laser moxibustion (LM) on the fastest 15-m walking time in individuals suffering from knee osteoarthritis (KOA).

METHODS

A total of 392 individuals diagnosed with KOA and meeting the specified eligibility criteria were assigned randomly into two groups: the LM treatment group and the sham LM control group (ratio 1:1). Both groups received either LM therapy or simulated LM therapy to address the affected area of the knee joint. This treatment was administered three times a week for a duration of 4 weeks.

RESULTS

In the LM group, the fastest 15-m walking times at both Week 4 and Week 12 were significantly reduced compared to the times before treatment (all P < 0.05). However, in the sham LM group, there were no notable differences in the fastest 15-m walking times after treatment (all P > 0.05). Moreover, the LM group exhibited shorter 15-m walking times than the sham LM group at both Week 4 and Week 12 (all P < 0.05).

CONCLUSION

The use of CO2 LM can lead to a substantial enhancement in the fastest 15-m walking time of individuals suffering from KOA, and its therapeutic impact can last for a minimum of 8 weeks post-treatment. The fastest 15-m walking time serves as an indicator of alterations in the walking capacity of patients with KOA.

Epigenetic Up-Regulation of ADAMTS4 in Sympathetic Ganglia is Involved in the Maintenance of Neuropathic Pain Following Nerve Injury

Sympathetic axonal sprouting into dorsal root ganglia is a major phenomenon implicated in neuropathic pain, and sympathetic ganglia blockage may relieve some intractable chronic pain in animal pain models and clinical conditions. These suggest that sympathetic ganglia participated in the maintenance of chronic pain. However, the molecular mechanism underlying sympathetic ganglia-mediated chronic pain is not clear. Here, we found that spared nerve injury treatment upregulated the expression of ADAMTS4 and AP-2α protein and mRNA in the noradrenergic neurons of sympathetic ganglia during neuropathic pain maintenance. Knockdown the ADAMTS4 or AP-2α by injecting specific retro scAAV-TH (Tyrosine Hydroxylase)-shRNA ameliorated the mechanical allodynia induced by spared nerve injury on day 21 and 28. Furthermore, chromatin immunoprecipitation and coimmunoprecipitation assays found that spared nerve injury increased the recruitment of AP-2α to the ADAMTS4 gene promoter, the interaction between AP-2α and histone acetyltransferase p300 and the histone H4 acetylation on day 28. Finally, knockdown the AP-2α reduced the acetylation of H4 on the promoter region of ADAMTS4 gene and suppressed the increase of ADAMTS4 expression induced by spared nerve injury. Together, these results suggested that the enhanced interaction between AP-2α and p300 mediated the epigenetic upregulation of ADAMTS4 in sympathetic ganglia noradrenergic neurons, which contributed to the maintenance of spared nerve injury induced neuropathic pain.

Wool keratin as a novel alternative protein: A comprehensive review of extraction, purification, nutrition, safety, and food applications

The growing global population and lifestyle changes have increased the demand for specialized diets that require protein and other essential nutrients for humans. Recent technological advances have enabled the use of food bioresources treated as waste as additional sources of alternative proteins. Sheep wool is an inexpensive and readily available bioresource containing 95%-98% protein, making it an outstanding potential source of protein for food and biotechnological applications. The strong structure of wool and its indigestibility are the main hurdles to achieving its potential as an edible protein. Although various methods have been investigated for the hydrolysis of wool into keratin, only a few of these, such as sulfitolysis, oxidation, and enzymatic processes, have the potential to generate edible keratin. In vitro and in vivo cytotoxicity studies reported no cytotoxicity effects of extracted keratin, suggesting its potential for use as a high-value protein ingredient that supports normal body functions. Keratin has a high cysteine content that can support healthy epithelia, glutathione synthesis, antioxidant functions, and skeletal muscle functions. With the recent spike in new keratin extraction methods, extensive long-term investigations that examine prolonged exposure of keratin generated from these techniques in animal and human subjects are required to ascertain its safety. Food applications of wool could improve the ecological footprint of sheep farming and unlock the potential of a sustainable protein source that meets demands for ethical production of animal protein.

Neuronal-microglial liver X receptor β activating decrease neuroinflammation and chronic stress-induced depression-related behavior in mice

Depression is accompanied by excessive neuroinflammation. Liver X receptor β (LXRβ) has been reported as a newly emerging target that exerts systemic and organic inflammation modulation. However, the modulatory mechanism in alleviating neuroinflammation are far from being revealed. In the current study, depression-related behaviors in mice were induced by chronic unpredictable mild stress (CUMS) and corticosterone (CORT) drinking. Mice received either TO901317, PLX-5622 and intra- bilateral basolateral amygdale (BLA) injection of rAAV9-hSyn-hM3D(Gq)-eGFP to activate LXRβ, eliminate microglia and pharmacogenetic activate neurons in BLA, respectively, followed by behavioral tests. Microglial pro-inflammatory and pro-phagocytic activation, as well as nuclear factor-κB (NF-κB) signaling pathway, NLRP3 inflammasome activation and interleukin-1β (IL-1β) release in BLA were investigated. Moreover, pro-inflammatory activation of BV2 cells-induced by CORT with or without TO901317 was detected. Neuroinflammation indicated by IL-1β release was measured in a co-culture system of HT22-primary microglia with or without TO901317. Our results indicated that chronic stress induced depression-related behaviors, which were accompanied with microglial pro-inflammatory and pro-phagocytic activation, as well as NF-κB signaling pathway and NLRP3 inflammasome activation in BLA. Accordingly, pharmacological activation of LXRβ inhibited microglial pro-inflammatory and pro-phagocytic activation, as well as NF-κB signaling pathway and NLRP3 inflammasome activation, and IL-1β release both in vivo and in vitro. Finally, both elimination of microglia and pharmacogenetic activation of neurons in BLA protected mice from chronic stress-induced depression-related behavior. Collectively, pharmacological activation of neuronal-microglial LXRβ alleviates depression-related behavior by modulating excessive neuroinflammation via inhibiting NF-κB signaling pathway and NLRP3 inflammasome activation.

LXR agonist modifies neuronal lipid homeostasis and decreases PGD2 in the dorsal root ganglia in western diet-fed mice

The prevalence of peripheral neuropathy is high in diabetic and overweight populations. Chronic neuropathic pain, a symptom of peripheral neuropathy, is a major disabling symptom that leads to a poor quality of life. Glucose management for diabetic and prediabetic individuals often fail to reduce or improve pain symptoms, therefore, exploring other mechanisms is necessary to identify effective treatments. A large body of evidence suggest that lipid signaling may be a viable target for management of peripheral neuropathy in obese individuals. The nuclear transcription factors, Liver X Receptors (LXR), are known regulators of lipid homeostasis, phospholipid remodeling, and inflammation. Notably, the activation of LXR using the synthetic agonist GW3965, delayed western diet (WD)-induced allodynia in rodents. To further understand the neurobiology underlying the effect of LXR, we used translating ribosome affinity purification and evaluated translatomic changes in the sensory neurons of WD-fed mice treated with the LXR agonist GW3965. We also observed that GW3965 decreased prostaglandin levels and decreased free fatty acid content, while increasing lysophosphatidylcholine, phosphatidylcholine, and cholesterol ester species in the sensory neurons of the dorsal root ganglia (DRG). These data suggest novel downstream interplaying mechanisms that modifies DRG neuronal lipid following GW3965 treatment.

L-Glutamine alleviates osteoarthritis by regulating lncRNA-NKILA expression through the TGF-β1/SMAD2/3 signalling pathway

Osteoarthritis (OA) is a heterogeneous condition characterized by cartilage degradation, subchondral sclerosis, and osteophyte formation, and accompanied by the generation of pro-inflammatory mediators and degradation of extracellular matrix. The current treatment for early OA is focused on the relief of symptoms, such as pain, but this treatment cannot delay the pathological process. L-Glutamine (L-Gln), which has anti-inflammatory and anti-apoptotic effects, is the most abundant amino acid in human blood. However, its role in OA has not been systematically studied. Therefore, the objective of this work was to explore the therapeutic effect and molecular mechanism of L-Gln on OA. In vitro, we found that L-Gln could up-regulate the expression of the long non-coding RNA NKILA, which is regulated by the transforming growth factor-β1/SMAD2/3 pathway, and inhibit the activity of nuclear factor-κB, thereby decreasing the expression of nitric oxide synthase, cyclooxygenase-2, and matrix metalloproteinase-13 (MMP-13). This led to a reduction in the generation of nitrous oxide, prostaglandin E-2, tumour necrosis factor-α, and degradation of the extracellular matrix (i.e. aggrecan and collagen II) in rat OA chondrocytes. Moreover, intragastric administration of L-Gln reduced the degradation of cartilage tissue and expression of MMP-13 in a rat OA model. L-Gln also relieved the clinical symptoms in some patients with early knee joint OA. These findings highlight that L-Gln is a potential therapeutic drug to delay the occurrence and development of OA.

Interleukin-1 Induces the Release of Lubricating Phospholipids from Human Osteoarthritic Fibroblast-like Synoviocytes

(1) Background: Synovial fluid (SF) from knee joints with osteoarthritis (OA) has increased levels of phospholipids (PL). We have reported earlier that TGF-ß and IGF-1 stimulate fibroblast-like synoviocytes (FLS) to synthesize increased amounts of PLs. The current study examined whether IL-1ß induces the release of PLs in FLS and the underlying mechanism. (2) Methods: Cultured human OA FLS were treated with IL-1ß alone and with pathway inhibitors or with synthetic liver X receptor (LXR) agonists. Cholesterol hydroxylases, ABC transporters, apolipoproteins (APO), LXR, sterol regulatory binding proteins (SREBPs), and 3-hydroxy-3-methylglutaryl-coenzyme A reductase (HMGCR) were analyzed by RT-PCR, Western blot, and ELISA. The release of radiolabeled PLs from FLS was determined, and statistical analysis was performed using R (N = 5–9). (3) Results: Like synthetic LXR agonists, IL-1ß induced a 1.4-fold greater release of PLs from FLS. Simultaneously, IL-1ß upregulated the level of the PL transporter ABCA1 and of cholesterol hydroxylases CH25H and CYP7B1. IL-1ß and T0901317 stimulated the expression of SREBP1c, whereas only T0901317 enhanced SREBP2, HMGCR, APOE, LXRα, and ABCG1 additionally. (4) Conclusions: IL-1ß partially controls PL levels in OA-SF by affecting the release of PLs from FLS. Our data show that IL-1ß upregulates cholesterol hydroxylases and thus the formation of oxysterols, which, as natural agonists of LXR, increase the level of active ABCA1, in turn enhancing the release of PLs.

Inhibitory Effects of IL-6-Mediated Matrix Metalloproteinase-3 and -13 by Achyranthes japonica Nakai Root in Osteoarthritis and Rheumatoid Arthritis Mice Models

Achyranthes japonica Nakai root (AJNR) is used to treat osteoarthritis (OA) and rheumatoid arthritis (RA) owing to its anti-inflammatory and antioxidant effects. This study investigated the inhibitory effects of AJNR on arthritis. AJNR was extracted using supercritical carbon dioxide (CO₂), and its main compounds, pimaric and kaurenoic acid, were identified. ANJR’s inhibitory effects against arthritis were evaluated using primary cultures of articular chondrocytes and two in vivo arthritis models: destabilization of the medial meniscus (DMM) as an OA model, and collagenase-induced arthritis (CIA) as an RA model. AJNR did not affect pro-inflammatory cytokine (IL-1β, TNF-α, IL-6)-mediated cytotoxicity, but attenuated pro-inflammatory cytokine-mediated increases in catabolic factors, and recovered pro-inflammatory cytokine-mediated decreases in related anabolic factors related to in vitro. The effect of AJNR is particularly specific to IL-6-mediated catabolic or anabolic alteration. In a DMM model, AJNR decreased cartilage erosion, subchondral plate thickness, osteophyte size, and osteophyte maturity. In a CIA model, AJNR effectively inhibited cartilage degeneration and synovium inflammation in either the ankle or knee and reduced pannus formation in both the knee and ankle. Immunohistochemistry analysis revealed that AJNR mainly acted via the inhibitory effects of IL-6-mediated matrix metalloproteinase-3 and -13 in both arthritis models. Therefore, AJNR is a potential therapeutic agent for relieving arthritis symptoms.

25-Hydroxycholesterol metabolism is altered by lung inflammation, and its local administration modulates lung inflammation in mice

Inflammation is a critical component of many lung diseases including asthma and acute lung injury (ALI). Using high-performance liquid chromatography-mass spectrometry, we quantified the levels of oxysterols in two different murine models of lung diseases. These are lipid mediators derived from cholesterol and known to modulate immunity and inflammation. Interestingly, 25-hydroxycholesterol (25-OHC) was the only oxysterol with altered levels during lung inflammation, and its levels were differently affected according to the model. Therefore, we sought to assess how this oxysterol would affect lung inflammatory responses. In a model of lipopolysaccharide (LPS)-induced acute lung inflammation, 25-OHC levels were increased, and most of the hallmarks of the model (eg, leukocyte recruitment, mRNA expression, and secretion of inflammatory cytokines) were decreased following its intratracheal administration. We also found that, when administered in the lung, 25-OHC is metabolized locally into 25-hydroxycholesterol-3-sulfate and 7α,25-dihydroxycholesterol. Their administration in the lungs did not recapitulate all the effects of 25-OHC. Conversely, in a model of allergic asthma induced by intranasal administration of house dust mites (HDM), 25-OHC levels were decreased, and when intranasally administered, this oxysterol worsened the hallmarks of the model (eg, leukocyte recruitment, tissue remodeling [epithelium thickening and peribranchial fibrosis], and cytokine expression) and induced changes in leukotriene levels. Ex vivo, we found that 25-OHC decreases LPS-induced primary alveolar macrophage activation while having no effect on neutrophil activation. Its sulfated metabolite, 25-hydroxycholesterol-3-sulfate, decreased neutrophil, but not macrophage activation. Taken together, our data support a differential role of 25-OHC in ALI and allergic inflammation models.

Recombinant platelet-derived growth factor-BB alleviates osteoarthritis in a rat model by decreasing chondrocyte apoptosis in vitro and in vivo

Osteoarthritis (OA) is a common joint disease that mainly affects the diarthrodial joints. Treatments for OA include non‐pharmacological interventions, topical and oral therapies, intra‐articular therapies and joint surgery. However, all the treatments mentioned above mainly aim to control the symptoms instead of improving or reversing the joint condition. In this research, we observed the effect of recombinant platelet‐derived growth factor (PDGF)‐BB on OA in a monosodium iodoacetate (MIA)–induced rat model and revealed the possible mechanisms. In vitro, the level of inflammation in the chondrocytes was gradually alleviated, and the apoptosis rate was gradually decreased by PDGF‐BB at increasing concentrations. The levels of p‐p38, Bax and caspase‐3 decreased, and the level of p‐Erk increased with increasing PDGF‐BB concentration. In vivo, PDGF‐BB could significantly reverse chondrocyte and matrix loss. Furthermore, high concentrations of PDGF‐BB could alleviate cartilage hyperplasia to remodel the tissue. The level of collagen II was up‐regulated, and the levels of collagen X and apoptosis were down‐regulated by increasing concentrations of PDGF‐BB. In conclusion, recombinant PDGF‐BB alleviated OA by down‐regulating caspase‐3‐dependent apoptosis. The effects of PDGF‐BB on OA mainly include inhibiting chondrocyte loss, reducing cartilage hyperplasia and osteophyte formation, and regulating collagen anabolism.

Liver X receptors conserve the therapeutic target potential for the treatment of rheumatoid arthritis

Rheumatoid arthritis (RA) is a chronic multi-system autoimmune disease with extremely complex pathogenesis. Significantly altered lipid paradox related to the inflammatory burden is reported in RA patients, inducing 50% higher cardiovascular risks. Recent studies have also demonstrated that lipid metabolism can regulate many functions of immune cells in which metabolic pathways have altered. The nuclear liver X receptors (LXRs), including LXRα and LXRβ, play a central role in regulating lipid homeostasis and inflammatory responses. Undoubtedly, LXRs have been considered as an attractive therapeutic target for the treatment of RA. However, there are some contradictory effects of LXRs agonists observed in previous animal studies where both pro-inflammatory role and anti-inflammatory role were revealed for LXRs activation in RA. Therefore, in addition to updating the knowledge of LXRs as the prominent regulators of lipid homeostasis, the purpose of this review is to summarize the effects of LXRs agonists in RA-associated immune cells, to explore the underlying reasons for the contradictory therapeutic effects of LXRs agonists observed in RA animal models, and to discuss future strategy for the treatment of RA with LXRs modulators.

Curcumin exerts a protective effect on murine knee chondrocytes treated with IL-1β through blocking the NF-κB/HIF-2α signaling pathway

Background

Osteoarthritis (OA) is characterized by erosion and degradation of articular cartilage. This study assessed the effects of curcumin on mouse knee cartilage chondrocytes.

Methods

Chondrocytes were treated for 24 hours with interleukin IL-1β (10 ng/mL) alone, or the combination of curcumin (10, 20, and 50 µM) and IL-1β. The proliferation, viability, and cytotoxicity of the chondrocytes were evaluated by the MTS assay. Expression of SOX9, AGG, Col2α, MMP9, ADAMTS5, COX2, iNOS, pIκB-α, pNF-κB, and hypoxia-inducible factor-2α (HIF-2α) were detected by western blotting or quantitative polymerase chain reaction (q-PCR). Nuclear translocation of NF-κB and HIF-2α were investigated by immunofluorescence and immunohistochemistry. In in vivo experiments, mice were subjected to destabilization of the medial meniscus (DMM) and given curcumin orally for 6 weeks. Cartilage integrity was evaluated by OARSI (Osteoarthritic Research Society International) scores.

Results

Curcumin significantly inhibited the IL-1β-induced reduction of cell viability, degradation of ECM, and the expression of SOX9, Col2α, and AGG (P<0.01). Western blotting, immunofluorescence and immunohistochemistry experiments demonstrated that curcumin dramatically inhibited the activation of NF-κB/HIF-2α in chondrocytes treated with IL-1β (P<0.01). The articular scores were significantly lower in the DMM-induced OA mice compared to OA mice treated with curcumin (P<0.01).

Conclusions

Curcumin may have the potential to inhibit OA development, partly through suppressing the activation of the NF-κB/HIF-2α pathway.

Arrabidaea chica Verlot fractions reduce MIA-induced osteoarthritis progression in rat knees

This study aims to investigate the activity of n-hexane, ethyl acetate and butanol fractions obtained from Arrabidaea chica Verlot against MIA-induced osteoarthritis (OA). The antinociceptive potentials of each fraction were evaluated through a cyclooxygenase (COX) 1 and 2 inhibition test and an in vivo OA-model. In addition, toxicity assessments in the liver, spleen and kidney, as well as radiographic and histopathological knee analyses, were performed. The chemical composition of the n-hexane fraction was elucidated, and a molecular docking protocol was carried out to identify which compounds are associated with the detected bioactivity. The n-hexane A. chica fraction preferentially inhibits COX-2, with 90% inhibition observed at 10 µg/mL. The fractions also produced significant improvements in OA incapacity, motor activity and hyperalgesia parameters and in radiological knee conditions. However, concerning the histopathological evaluations, these improvements were only significant in the hexane and ethyl acetate fraction treatments, which resulted in better average scores, suggesting that these fractions slow OA-promoted joint injury progression. Histopathological organ analyses indicate that the fractions are not toxic to animals. Twenty compounds were identified in the n-hexane fraction, comprising fatty acids, terpenes and phytosterols. In silico analyses indicate the presence of favourable interactions between some of the identified compounds and the COX-2 enzyme, mainly concerning alpha-tocopherol (Vitamin E), squalene and beta-sitosterol. The findings indicate that A. chica fractions display analgesic, anti-inflammatory properties, are non-toxic and are able to slow OA progression, and may, therefore, be prioritized as natural products in OA human clinical trials.

Liver X receptors and skeleton: Current state-of-knowledge

The liver X receptors (LXR) is a nuclear receptor that acts as a prominent regulator of lipid homeostasis and inflammatory response. Its therapeutic effectiveness against various diseases like Alzheimer's disease and atherosclerosis has been investigated in detail. Emerging pieces of evidence now reveal that LXR is also a crucial modulator of bone remodeling. However, the molecular mechanisms underlying the pharmacological actions of LXR on the skeleton and its role in osteoporosis are poorly understood. Therefore, in the current review, we highlight LXR and its actions through different molecular pathways modulating skeletal homeostasis. The studies described in this review propound that LXR in association with estrogen, PTH, PPARγ, RXR hedgehog, and canonical Wnt signaling regulates osteoclastogenesis and bone resorption. It regulates RANKL-induced expression of c-Fos, NFATc1, and NF-κB involved in osteoclast differentiation. Additionally, several studies suggest suppression of RANKL-induced osteoclast differentiation by synthetic LXR ligands. Given the significance of modulation of LXR in various physiological and pathological settings, our findings indicate that therapeutic targeting of LXR might potentially prevent or treat osteoporosis and improve bone quality.

Liver X Receptors: Regulators of Cholesterol Metabolism, Inflammation, Autoimmunity, and Cancer

The interplay between cellular stress and immune response can be variable and sometimes contradictory. The mechanisms by which stress-activated pathways regulate the inflammatory response to a pathogen, in autoimmunity or during cancer progression remain unclear in many aspects, despite our recent knowledge of the signalling and transcriptional pathways involved in these diseases. In this context, over the last decade many studies demonstrated that cholesterol metabolism is an important checkpoint for immune homeostasis and cancer progression. Indeed, cholesterol is actively metabolized and can regulate, through its mobilization and/or production of active derivatives, many aspects of immunity and inflammation. Moreover, accumulation of cholesterol has been described in cancer cells, indicating metabolic addiction. The nuclear receptors liver-X-receptors (LXRs) are important regulators of intracellular cholesterol and lipids homeostasis. They have also key regulatory roles in immune response, as they can regulate inflammation, innate and adaptive immunity. Moreover, activation of LXRs has been reported to affect the proliferation and survival of different cancer cell types that show altered metabolic pathways and accumulation of cholesterol. In this minireview we will give an overview of the recent understandings about the mechanisms through which LXRs regulate inflammation, autoimmunity, and cancer, and the therapeutic potential for future treatment of these diseases through modulation of cholesterol metabolism.

Dioscin exhibits anti-inflammatory effects in IL-1β-stimulated human osteoarthritis chondrocytes by activating LXRα

OBJECTIVE

Osteoarthritis (OA) is the most common joint disease that characterized by the degradation of articular cartilage. In this study, we aimed to investigate the anti-inflammatory activity of dioscin on IL-1β-stimulated human osteoarthritis chondrocytes.

METHODS

The production of PGE2 and NO was measured in this study. MMP1 and MMP3 were detected by ELISA. The expression of LXRα and NF-κB were tested by western blot analysis.

RESULTS

Treatment of dioscin suppressed the production of PGE2 and NO, as well as the expression of COX-2 and iNOS (their key regulatory genes). Dioscin also attenuated the secretion of MMP1 and MMP3. Furthermore, dioscin inhibited the phosphorylation of NF-κB p65 and IκBα induced by IL-1β. The degradation of IκBα induced by IL-1β was also suppressed by dioscin. Dioscin increased the expression of LXRα and pretreatment of GGPP, the LXRα inhibitor, blocked the anti-inflammatory effects of dioscin.

CONCLUSIONS

In conclusion, this study indicated that dioscin-mediated anti-inflammatory effect may be involved in the activation of LXRα.

LXR Suppresses Inflammatory Gene Expression and Neutrophil Migration through cis-Repression and Cholesterol Efflux

The activation of liver X receptor (LXR) promotes cholesterol efflux and repression of inflammatory genes with anti-atherogenic consequences. The mechanisms underlying the repressive activity of LXR are controversial and have been attributed to cholesterol efflux or to transrepression of activator protein-1 (AP-1) activity. Here, we find that cholesterol efflux contributes to LXR repression, while the direct repressive functions of LXR also play a key role but are independent of AP-1. We use assay for transposase-accessible chromatin using sequencing (ATAC-seq) to show that LXR reduces chromatin accessibility in cis at inflammatory gene enhancers containing LXR binding sites. Targets of this repressive activity are associated with leukocyte adhesion and neutrophil migration, and LXR agonist treatment suppresses neutrophil recruitment in a mouse model of sterile peritonitis. These studies suggest a model of repression in which liganded LXR binds in cis to canonical nuclear receptor binding sites and represses pro-atherogenic leukocyte functions in tandem with the induction of LXR targets mediating cholesterol efflux.

Thomas et al. show the roles of cholesterol efflux and direct repression in anti-inflammatory effects of LXR and establish the mechanism of LXR cis-repression using ATAC-seq. LXR agonists suppress neutrophil migration genes and neutrophil recruitment during inflammation, highlighting a potential role for these compounds in the control of neutrophil-predominant inflammatory conditions.

Inhibiting the PI3K/AKT/NF-κB signal pathway with nobiletin for attenuating the development of osteoarthritis: in vitro and in vivo studies

Osteoarthritis (OA), an age-related degenerative disease, is characterized by progressive degradation of the articular cartilage. There is increasing evidence that nobiletin (NOB) exerts special biological functions in a variety of diseases. However, whether it protects against OA remains unknown. In this study, we investigated the anti-inflammatory and chondroprotective effects of NOB on IL-1β-induced human OA chondrocytes and in the surgical DMM mice OA models. In vitro, NOB treatment completely suppressed the overproduction of pro-inflammatory mediators, including PGE2, NO, COX-2, iNOS, TNF-α and IL-6 in IL-1β-induced human OA chondrocytes. Moreover, NOB exerted a potent inhibitory effect on the expression of MMP-13 and ADAMTS-5 as well as the degradation of aggrecan and collagen-II, which leads to the degradation of the extracellular matrix. Furthermore, NOB dramatically suppressed the IL-1β-stimulated phosphorylation of PI3K/Akt and activation of NF-κB in human OA chondrocytes. In addition, treatment with NOB not only prevented the destruction of cartilage and the thickening of subchondral bone but also relieved synovitis in mice OA models. In conclusion, our study suggests that NOB holds novel therapeutic potential for the treatment of OA.

Epigenetic suppression of liver X receptor β in anterior cingulate cortex by HDAC5 drives CFA-induced chronic inflammatory pain

Background

Liver X receptors (LXRs), including LXRα and LXRβ, are key regulators of transcriptional programs for both cholesterol homeostasis and inflammation in the brain. Here, the modes of action of LXRs and the epigenetic mechanisms regulating LXRβ expression in anterior cingulate cortex (ACC) of chronic inflammatory pain (CIP) are investigated.

Methods

The deficit of LXR isoform and analgesic effect of LXR activation by GW3965 were evaluated using the mouse model of CIP induced by hindpaw injection of complete Freund’s adjuvant (CFA). The mechanisms involved in GW-mediated analgesic effects were analyzed with immunohistochemical methods, ELISA, co-immunoprecipitation (Co-IP), Western blot, and electrophysiological recording. The epigenetic regulation of LXRβ expression was investigated by chromatin immunoprecipitation, quantitative real-time PCR, and sequencing.

Results

We revealed that CFA insult led to LXRβ reduction in ACC, which was associated with upregulated expression of histone deacetylase 5 (HDAC5), and knockdown of LXRβ by shRNA led to thermal hyperalgesia. Co-IP showed that LXRβ interacted with NF-κB p65 physically. LXRβ activation by GW3965 exerted analgesic effects by inhibiting the nuclear translocation of NF-κB, reducing the phosphorylation of mitogen-activated protein kinases (MAPKs) in ACC, and decreasing the promoted input-output and enhanced mEPSC frequency in ACC neurons after CFA exposure. In vitro experiments confirmed that HDAC5 triggered histone deacetylation on the promoter region of Lxrβ, resulting in downregulation of Lxrβ transcription.

Conclusion

These findings highlight an epigenetic mechanism underlying LXRβ deficits linked to CIP, and LXRβ activation may represent a potential novel target for the treatment of CIP with an alteration in inflammation responses and synaptic transmission in ACC.

Electronic supplementary material

The online version of this article (10.1186/s12974-019-1507-3) contains supplementary material, which is available to authorized users.

Nobiletin Inhibits IL-1β-Induced Inflammation in Chondrocytes via Suppression of NF-κB Signaling and Attenuates Osteoarthritis in Mice

Osteoarthritis (OA), a common degenerative joint disease, is principally characterized by inflammation and destruction of cartilage. Nobiletin, an extract of the peel of citrus fruits, is known to have anti-inflammatory properties. However, the mechanisms by which nobiletin plays a protective role in osteoarthritis (OA) are not completely understood. In the present study, we investigated the anti-inflammatory effects of nobiletin in the progression of OA in both in vitro and in vivo experiments. Mouse chondrocytes were pretreated with nobiletin (0, 10, 20, 40 μM) for 24 h and then incubated with IL-1β (10 ng/ml, 24 h) in vitro. The generation of PGE2 and NO was evaluated by the Griess reaction and ELISAs. The protein expression of inducible nitric oxide synthase, matrix metalloproteinase-3, matrix metalloproteinase-13, A disintegrin and metalloproteinase with thrombospondin motifs-5 (ADAMTS5), cyclooxygenase-2, collagen II, and aggrecan was analyzed by Western blotting. Immunofluorescence and Western blot analysis were used to detect nuclear factor-κB (NF-κB) signaling molecules. Induction of proinflammatory and catabolic mediators by IL-1β stimulation of mouse chondrocytes could be partially blocked by treatment with nobiletin or ammonium pyrrolidine dithiocarbamate (an NF-κB inhibitor). Furthermore, our results indicated that nobiletin exhibited a therapeutic effect through active inhibition of the NF-κB signaling pathway. In a mouse model of OA, injection of nobiletin (20 mg/kg) every 2 days for 8 weeks after surgery inhibited cartilage destruction and synovitis. Taken together, our findings suggest that nobiletin may be a potential therapeutic agent for the treatment of OA.

Leonurine inhibits IL-1β induced inflammation in murine chondrocytes and ameliorates murine osteoarthritis

Osteoarthritis (OA) is a chronic degenerative joint disease characterized by cartilage degradation, subchondral bone sclerosis and synovitis. Leonurine, an active component extracted from the leaves of Herba leonuri, has been reported to possess various potent biological effects such as anti-oxidant, anti-apoptosis, and anti-inflammatory. However, the therapeutic benefits of leonurine on OA have not been reported. This study aimed to evaluate the therapeutic effect of leonurine on chondrocytes and in murine OA models. Murine chondrocytes were pre-treated with leonurine (5, 10, and 20 μM) for 2 h and then stimulated with IL-1β for 24 h. Production of NO, PGE2, IL-6, TNF-α, MMP-3, MMP-13, and ADAMTS-5 was assessed with the Griess reagent and ELISAs. The mRNA expression of COX-2, iNOS, MMP-3, MMP-13, ADAMTS-5, aggrecan, and collagen-II was tested with real-time polymerase chain reaction. The protein expression of iNOS, COX-2 and NF-κB-related signaling molecules was measured with western blotting. In this study, leonurine visibly inhibited the IL-1β-induced production of NO, PGE2, IL-6 and TNF-α; and decreased the expression of iNOS, COX-2, MMP-3, MMP-13 and ADAMTS-5 in chondrocytes. Furthermore, leonurine significantly suppressed IL-1β-stimulated NF-κB activation. In addition, treatment with leonurine not only prevented cartilage destruction and subchondral bone thickening, but also alleviated synovitis in a murine OA model. Taken together, these results suggest that leonurine may be a potential therapeutic agent in OA treatment.

Isofraxidin inhibits interleukin-1β induced inflammatory response in human osteoarthritis chondrocytes

Osteoarthritis (OA) is the most prevalent disease of knee especially in the aged people. Isofraxidin (IF) is a coumarin compound refined from traditional Chinese medicines with potential anti-inflammatory ability. This study aimed to evaluate protective anti-inflammatory effects of IF in human OA chondrocytes. The chondrocytes were isolated from OA patients and pretreated with IF before treatment with IL-1β. The results showed that IF blocked IL-1β-stimulated production of NO and PGE2. In addition, IF inhibited the expression of COX-2, iNOs, MMP-1, MMP-3, MMP-13, ADAMTS-4 and ADAMTS-5, and increased the levels of aggrecan and collagen-II. Mechanistically, IF suppressed IL-1β-induced IκB-α degradation and NF-κB activation. In conclusion, our results demonstrate that IF inhibits inflammation in OA via the regulation of NF-κB signaling, and suggest that IF may be a potential therapeutic agent for OA.

Radial extracorporeal shock wave therapy promotes osteochondral regeneration of knee joints in rabbits

Radial extracorporeal shock wave therapy (rESWT) has been proven to be effective for nonunion fractures. It was, thus, hypothesized that it may be used as a supplement therapy to promote osteochondral regeneration when combined with a scaffold previously prepared by our research group. In the present study, to verify this hypothesis, New Zealand white adult rabbits were anaesthetized and divided into three groups, as follows: Untreated control group, in which full-thickness cylindrical osteochondral defects were created without repairing; scaffold group, in which rabbits were implanted with the scaffolds; scaffold plus rESWT group, in which rabbits were implanted with scaffolds and then treated with rESWT at 2 weeks post-surgery. At 6 and 12 weeks after surgery, the animals were sacrificed. Nitric oxide (NO) levels in the synovial cavity of the knee joints were measured by the Griess method. In addition, macroscopic observation and the gross score according to the International Cartilage Repair Society (ICRS) histological scoring system were determined. Histological evaluation was also performed by hematoxylin-eosin and Safranin O/fast green staining. The results demonstrated that both the scaffold and scaffold plus rESWT treatments significantly reduced NO levels in the synovial cavity at 6 weeks after surgery (P<0.05), whereas no significant difference was observed at 12 weeks after surgery. The ICRS scores of the scaffold and scaffold plus rESWT groups were significantly higher in comparison with those in the control group (P<0.05), and rESWT further increased these scores at 12 weeks after surgery (P<0.05). Histological results revealed that osteochondral regeneration was improved after treatment with scaffold or scaffold plus rESWT, with the latter displaying better results. These data suggested that rESWT improved the osteochondral regeneration when applied in combination with the scaffold, and that one of the underlying mechanisms may involve the reduction of NO in the synovial fluid. Therefore, rESWT may be a useful treatment for knee osteochondral regeneration.

Nuclear receptors as potential drug targets in osteoarthritis

Osteoarthritis is amongst the major causes of disability worldwide, but no medications that can slow or stop progression of this disorder have been identified. Recent evidence suggests roles for a variety of members of the nuclear receptor family of ligand-activated transcription factors in various forms of osteoarthritis. Since nuclear receptors are amongst the major classes of drug targets, these studies suggest that modulators of nuclear receptor activity might provide novel strategies to treat osteoarthritis. This review focuses on recent advances in our understanding of the role of nuclear receptors in osteoarthritis onset and progression, as well as their therapeutic implications. Future studies should continue to examine the possible roles of additional nuclear receptors in the pathophysiology of different types of osteoarthritis.

Chrysin Attenuates IL-1β-Induced Expression of Inflammatory Mediators by Suppressing NF-κB in Human Osteoarthritis Chondrocytes

Osteoarthritis (OA) is a degenerative joint disease characterized by cartilage degradation and inflammation. Chrysin, a natural flavonoid extracted from honey and propolis, has been reported to have anti-inflammatory effects. However, the anti-inflammatory effects of chrysin on OA have not been reported. This study aimed to assess the effects of chrysin on human OA chondrocytes. Human OA chondrocytes were pretreated with chrysin (1, 5, 10 μM) for 2 h and subsequently stimulated with IL-1β for 24 h. Production of NO, PGE2, MMP-1, MMP-3, MMP-13, ADAMTS-4, and ADAMTS-5 was evaluated by the Griess reaction and ELISAs. The messenger RNA (mRNA) expression of COX-2, iNOS, MMP-1, MMP-3, MMP-13, ADAMTS-4, ADAMTS-5, aggrecan, and collagen-II was measured by real-time PCR. The protein expression of COX-2, iNOS, p65, p-p65, IκB-α, and p-IκB-α was detected by Western blot. The protein expression of collagen-II and p65 nuclear translocation was evaluated by immunofluorescence. We found that chrysin significantly inhibited the IL-1β-induced production of NO and PGE2; expression of COX-2, iNOS, MMP-1, MMP-3, MMP-13, ADAMTS-4, and ADAMTS-5; and degradation of aggrecan and collagen-II. Furthermore, chrysin dramatically blocked IL-1β-stimulated IκB-α degradation and NF-κB activation. Taken together, these results suggest that chrysin may be a potential agent in the treatment of OA.

Plumbagin Prevents IL-1β-Induced Inflammatory Response in Human Osteoarthritis Chondrocytes and Prevents the Progression of Osteoarthritis in Mice

Inflammation and inflammatory cytokines have been reported to play vital roles in the development of osteoarthritis (OA). Plumbagin, a quinonoid compound extracted from the roots of medicinal herbs of the Plumbago genus, has been reported to have anti-inflammatory effects. However, the anti-inflammatory effects of plumbagin on OA have not been reported. This study aimed to assess the effects of plumbagin on human OA chondrocytes and in a mouse model of OA induced by destabilization of the medial meniscus (DMM). In vitro, human OA chondrocytes were pretreated with plumbagin (2, 5, 10 μM) for 2 h and subsequently stimulated with IL-1β for 24 h. Production of NO, PGE2, MMP-1, MMP-3, and MMP-13 was evaluated by the Griess reagent and ELISAs. The messenger RNA (mRNA) expression of COX-2, iNOS, MMP-1, MMP-3, MMP-13, aggrecan, and collagen-II was measured by real-time PCR. The protein expression of COX-2, iNOS, p65, p-p65, IκBα, and p-IκBα was detected by Western blot. The protein expression of collagen-II was evaluated by immunofluorescence. In vivo, the severity of OA was determined by histological analysis. We found that plumbagin significantly inhibited the IL-1β-induced production of NO and PGE2; expression of COX-2, iNOS, MMP-1, MMP-3, and MMP-13; and degradation of aggrecan and collagen-II. Furthermore, plumbagin dramatically suppressed IL-1β-stimulated NF-κB activation. In vivo, treatment of plumbagin not only prevented the destruction of cartilage and the thickening of subchondral bone but also relieved synovitis in mice OA models. Taken together, these results suggest that plumbagin may be a potential agent in the treatment of OA.

Oleuropein inhibits the IL-1β-induced expression of inflammatory mediators by suppressing the activation of NF-κB and MAPKs in human osteoarthritis chondrocytes

Osteoarthritis (OA) is the most common form of joint disease and is widespread in the elderly population and is characterized by erosion of articular cartilage, subchondral bone sclerosis and synovitis. Oleuropein (OL), a secoiridoid, is considered as the most prevalent phenolic component in olive leaves and seeds, pulp and peel of unripe olives and has been shown to have potent anti-inflammatory effects. However, its effects on OA have not been clearly elucidated. This study aimed to assess the effect of OL on human OA chondrocytes. Human OA chondrocytes were pretreated with OL (10, 50 and 100 μM) for 2 h and subsequently stimulated with IL-1β for 24 h. The production of NO, PGE2, MMP-1, MMP-13, and ADAMTS-5 was evaluated by the Griess reaction and ELISA assays. The messenger RNA (mRNA) expression of COX-2, iNOS, MMP-1, MMP13, ADAMTS-5, aggrecan, and collagen-II was measured by using real-time PCR. The protein expressions of COX-2, iNOS, p65, IκB-α, JNK, p-JNK, ERK, p-ERK, p38, and p-p38 were tested by using western blot. We found that OL significantly inhibited the IL-1β-induced production of NO and PGE2; expression of COX-2, iNOS, MMP-1, MMP-13, and ADAMTS-5; and degradation of aggrecan and collagen-II. Furthermore, OL dramatically suppressed IL-1β-stimulated NF-κB and MAPK activation. Immunofluorescence staining demonstrated that OL could suppress IL-1β-induced phosphorylation of p65 nuclear translocation. These results indicate that the therapeutic effect of OL on OA is accomplished through the inhibition of both NF-κB and MAPK signaling pathways. Altogether, our findings provide the evidence to develop OL as a potential therapeutic agent for patients with OA.

Rosmarinic acid down-regulates NO and PGE2 expression via MAPK pathway in rat chondrocytes

Rosmarinic acid (RosA) is a water-soluble polyphenol, which can be isolated from many herbs such as orthosiphon diffuses and rosmarinus officinalis. Previous studies have shown that RosA possesses various biological properties. In this study, we investigate the anti-osteoarthritic effects of RosA in rat articular chondrocytes. Chondrocytes were pre-treated with RosA, followed by the stimulation of IL-1β. Real-time PCR and Western blot were performed to detect the expression of matrix metalloproteinase (MMP)-1, MMP-3 and MMP-13. Nitric oxide and PGE2 production were measured by Griess reagent and enzyme-linked immunosorbent assay (ELISA). The expression of mitogen-activated protein kinase (MAPK) and nuclear factor-κB (NF-κB) was also investigated by Western blot analysis. We found that RosA down-regulated the MMPs expression as well as nitric oxide and PGE2 production in IL-1β-induced chondrocytes. In addition, RosA inhibited p38 and JNK phosphorylation as well as p65 translocation. The results suggest that RosA may be considered a possible agent in the treatment of OA.

Saikosaponin A inhibits IL-1β-induced inflammatory mediators in human osteoarthritis chondrocytes by activating LXRα

Saikosaponin a (SSa), one of the main active components of Bupleurum falcatum, has been reported to have anti-inflammatory effect. In the present study, we investigated the anti-inflammatory effect of SSa on IL-1β-stimulated human osteoarthritis chondrocytes. The cells were pretreated with SSa 12 h before IL-1β treatment. The production of PGE2 and NO were detected by ELISA and Griess method. The levels of MMP1, MMP3, and MMP13 were measured by ELISA and qRT-PCR. The expression of NF-κB and LXRα were tested by western blot analysis. The results showed that SSa inhibited IL-1β-induced PGE2 and NO production in a concentration-dependent manner. SSa also suppressed IL-1β-induced MMP1, MMP3, and MMP13 production. Furthermore, SSa significantly attenuated IL-1β-induced phosphorylation levels of NF-κB p65 and IκBα. SSa also up-regulated the expression of LXRα. The inhibition of SSa on PGE2, NO, MMP1, MMP3, and MMP13 production were reversed by LXRα siRNA or GGPP, the inhibitor of LXRα. In conclusion, our results demonstrated that SSa inhibited inflammatory responses in human chondrocytes in vitro. SSa might be a potential therapeutic drug for osteoarthritis.

Baicalin suppresses IL-1β-induced expression of inflammatory cytokines via blocking NF-κB in human osteoarthritis chondrocytes and shows protective effect in mice osteoarthritis models

Osteoarthritis (OA) is a degenerative joint disease with an inflammatory component that drives the degradation of cartilage extracellular matrix. Baicalin, a predominant flavonoid isolated from the dry root of Scutellaria baicalensis Georgi, has been reported to have anti-inflammatory effects. However, the anti-inflammatory effects of baicalin on OA have not been reported. Our study aimed to investigate the effect of baicalin on OA both in vitro and in vivo. In vitro, human OA chondrocytes were pretreated with baicalin (10, 50, 100μM) for 2h and subsequently stimulated with IL-1β for 24h. Production of NO and PGE2 were evaluated by the Griess reaction and ELISAs. The mRNA expression of COX-2, iNOS, MMP-3, MMP-13, ADAMTS-5, aggrecan and collagen-II were measured by real-time PCR. The protein expression of COX-2, iNOS, MMP-3, MMP-13, ADAMTS-5, p65, p-p65, IκBα and p-IκBα was detected by Western blot. The protein expression of collagen-II was evaluated by immunofluorescence. Luciferase activity assay was used to assess the relative activity of NF-kB. In vivo, the severity of OA was determined by histological analysis. We found that baicalin significantly inhibited the IL-1β-induced production of NO and PGE2, expression of COX-2, iNOS, MMP-3, MMP-13 and ADAMTS-5 and degradation of aggrecan and collagen-II. Furthermore, baicalin dramatically suppressed IL-1β-stimulated NF-κB activation. In vivo, treatment of baicalin not only prevented the destruction of cartilage but also relieved synovitis in mice OA models. Taken together, these results suggest that baicalin may be a potential agent in the treatment of OA.

Silibinin protects against osteoarthritis through inhibiting the inflammatory response and cartilage matrix degradation in vitro and in vivo

Osteoarthritis (OA) is a degenerative joint disease characterized by cartilage degradation and inflammation. Silibinin, a polyphenolic flavonoid derived from fruits and seeds of Silybum marianum, has been reported to possess various potent beneficial biological effects, such as antioxidant, anti-cancer, hepatoprotective and anti-inflammatory activities. However, the anti-inflammatory effects of silibinin on OA have not been reported. This study aimed to assess the effects of silibinin on OA both in vitro and in vivo. In this study, we found that silibinin significantly inhibited the nterleukin-1β (IL-1β)-induced production of nitric oxide (NO), prostaglandin E2 (PGE2), tumor necrosis factor-α (TNF-α) and IL-6, expression of cyclooxygenase2 (COX-2), inducible nitric oxide synthase (iNOS), matrix metalloproteinase-1 (MMP-1), MMP-3, MMP-13, a disintegrin and metalloproteinase with thrombospondin motifs-4 (ADAMTS-4) and ADAMTS-5, degradation of aggrecan and collagen-II in human OA chondrocytes. Furthermore, silibinin dramatically suppressed IL-1β-stimulated phosphatidylinositol 3 kinase/ protein kinase B (PI3K/Akt) phosphorylation and nuclear factor-kappa B (NF-kB) activation in human OA chondrocytes. In addition, treatment of silibinin not only prevented the destruction of cartilage and the thickening of subchondral bone but also relieved synovitis in mice OA models. Also, the immunohistochemistry results showed that silibinin significantly decreased the expression of MMP-13 and ADAMTS-5 and increased the expression of collagen-II and aggrecan in mice OA. Taken together, these results suggest that silibinin may be a potential agent in the treatment of OA.

Knockdown of PRMT1 suppresses IL-1β-induced cartilage degradation and inflammatory responses in human chondrocytes through Gli1-mediated Hedgehog signaling pathway

Osteoarthritis (OA) is characterized by articular cartilage degradation and joint inflammation. The purpose of the present study is to elucidate the role of the specific function of PRMT1 in chondrocytes and its association with the pathophysiology of OA. We observed that the expression of PRMT1 was apparently upregulated in OA cartilage, as well as in chondrocytes stimulated with IL-1β. Additionally, knockdown of PRMT1 suppressed interleukin 1 beta (IL-1β)-induced extracellular matrix (ECM) metabolic imbalance by regulating the expression of MMP-13, ADAMTS-5, COL2A1, and ACAN. Furthermore, silencing of PRMT1 dramatically declined the production of prostaglandin E2 (PGE2) and nitric oxide as well as the level of pro-inflammatory cytokine IL-6 and TNF-α. Mechanistic analyses further revealed that IL-1β-induced activation of the Hedgehog/Gli-1 signaling is suppressed upon PRMT1 knockdown. However, the effects of inhibition of PRMT1-mediated IL-1β-induced cartilage matrix degradation and inflammatory response in OA chondrocytes were obviously abolished by Hedgehog agonist Purmorphamine (Pur). Our data collectively suggest that silencing of PRMT1 exerts anti-catabolic and anti-inflammatory effects on IL-1β-induced chondrocytes via suppressing the Gli-1 mediated Hedgehog signaling pathway, indicating that PRMT1 plays a critical role in OA development and serves as a promising therapeutic target for OA.

Melatonin inhibits Sirt1-dependent NAMPT and NFAT5 signaling in chondrocytes to attenuate osteoarthritis

Osteoarthritis (OA) is a degenerative joint disease mainly characterized by cartilage degradation. Interleukin-1β (IL-1β) contributes to OA pathogenesis by enhancing oxidative stress and inflammation. Melatonin reportedly elicits potent protection against OA. However, the role of melatonin and underlying mechanism in IL-1β-stimulated chondrocytes remain largely unclear. In this study, we found that melatonin inhibited IL-1β-induced toxicity and sirtuin 1 (Sirt1) enhancement in human chondrocytes. Melatonin reduced the IL-1β-increased nicotinamide phosphoribosyltransferase (NAMPT) expression and the NAD⁺ level in chondrocytes in a Sirt1-dependent manner. In turn, the inhibitory effect of melatonin on Sirt1 was mediated by NAMPT. Moreover, melatonin suppressed IL-1β-induced Sirt1-mediated matrix metalloproteinase (MMP)-3 and MMP-13 production. Melatonin also decreased the Sirt1-steered nuclear factor of activated T cells 5 (NFAT5) expression in IL-1β-challenged chondrocytes. NFAT5 depletion mimicked the suppressive effects of melatonin on IL-1β-elevated production of inflammatory mediators, including tumor necrosis factor-α (TNF-α), IL-1β, prostaglandin E2 (PGE₂), and nitric oxide (NO) in chondrocytes. TNF-α, IL-1β, PGE₂, or NO decrease caused the similar reduction of MMP-3 and MMP-13 by melatonin in IL-1β-insulted chondrocytes. Highly consistent with in vitro findings, in vivo results demonstrated that melatonin repressed the expression of relevant genes in rat OA pathogenesis in anterior cruciate ligament transection model. Overall, these results indicate that melatonin effectively reduced IL-1β-induced MMP production by inhibiting Sirt1-dependent NAMPT and NFAT5 signaling in chondrocytes, suggesting melatonin as a potential therapeutic alternative for chondroprotection of OA patients.

Tormentic Acid Inhibits IL-1β-Induced Inflammatory Response in Human Osteoarthritic Chondrocytes

The pro-inflammatory cytokine interleukin-1beta (IL-1β) plays critical roles in pathogenesis of osteoarthritis (OA). Tormentic acid (TA), a triterpene isolated from Rosa rugosa, has anti-inflammatory activity. However, the anti-inflammatory effect of TA on OA is still unclear. So, in the present study, we examined the effect of TA on IL-1β-induced inflammatory response in primary human OA chondrocytes. Our results demonstrated that TA significantly decreased the IL-1β-stimulated expression of matrix metalloproteinase-3 (MMP-3) and MMP-13. It also inhibited the IL-1β-induced expression of inducible nitric oxide (NO) synthase (iNOS) and cyclooxygenase-2 (COX-2), as well as the production of NO and prostaglandin E2 (PGE2) in human OA chondrocytes. Furthermore, TA greatly inhibited the IL-1β-induced NF-κB activation. In conclusion, this study is the first to demonstrate the anti-inflammatory activity of TA in human OA chondrocytes. TA significantly inhibits the IL-1β-induced inflammatory response by suppressing the NF-κB signaling pathway. Thus, TA may be a potential agent in the treatment of OA.

Nuclear receptors regulate lipid metabolism and oxidative stress markers in chondrocytes

Abstract

Joint homeostasis failure can result in osteoarthritis (OA). Currently, there are no treatments to alter disease progression in OA, but targeting early changes in cellular behavior has great potential. Recent data show that nuclear receptors contribute to the pathogenesis of OA and could be viable therapeutic targets, but their molecular mechanisms in cartilage are incompletely understood. This study examines global changes in gene expression after treatment with agonists for four nuclear receptor implicated in OA (LXR, PPARδ, PPARγ, and RXR). Murine articular chondrocytes were treated with agonists for LXR, PPARδ, PPARγ, or RXR and underwent microarray, qPCR, and cellular lipid analyses to evaluate changes in gene expression and lipid profile. Immunohistochemistry was conducted to compare two differentially expressed targets (Txnip, Gsta4) in control and cartilage-specific PPARδ knockout mice subjected to surgical destabilization of the medial meniscus (DMM). Nuclear receptor agonists induced different gene expression profiles with many responses affecting lipid metabolism. LXR activation downregulated gene expression of proteases involved in OA, whereas RXR agonism decreased expression of ECM components and increased expression of Mmp13. Functional assays indicate increases in cell triglyceride accumulation after PPARγ, LXR, and RXR agonism but a decrease after PPARδ agonism. PPARδ and RXR downregulate the antioxidant Gsta4, and PPARδ upregulates Txnip. Wild-type, but not PPARδ-deficient mice, display increased staining for Txnip after DMM. Collectively, these data demonstrate that nuclear receptor activation in chondrocytes primarily affects lipid metabolism. In the case of PPARδ, this change might lead to increased oxidative stress, possibly contributing to OA-associated changes.

Key message

Nuclear receptors regulate metabolic genes in chondrocytes.

Nuclear receptors affect triglyceride levels.

PPARδ mediates regulation of oxidative stress markers.

Nuclear receptors are promising therapeutic targets for osteoarthritis.

Electronic supplementary material

The online version of this article (doi:10.1007/s00109-016-1501-5) contains supplementary material, which is available to authorized users.

Echinocystic Acid Inhibits IL-1β-Induced COX-2 and iNOS Expression in Human Osteoarthritis Chondrocytes

Echinocystic acid (EA), a pentacyclic triterpene isolated from the fruits of Gleditsia sinensis Lam, displays a range of pharmacological activities including anti-inflammatory and antioxidant effects. However, the effect of EA on IL-1β-stimulated osteoarthritis chondrocyte has not been reported. The purpose of this study was to assess the effects of EA on IL-1β-stimulated human osteoarthritis chondrocyte. Chondrocytes were stimulated with IL-1β in the absence or presence of EA. NO and PGE2 production were measured by Griess reagent and ELISA. The expression of COX-2, iNOS, nuclear factor-κB (NF-κB), inhibitory kappa B (IκBα), c-Jun N-terminal kinase (JNK), p38, and extracellular signal-regulated kinase (ERK) were detected by Western blot analysis. The results showed that EA suppressed IL-1β-induced collagenase-3 (MMP-13), NO, and PGE2 production in a dose-dependent manner. IL-1β up-regulated the expression of COX-2 and iNOS, and the increase was inhibited by EA. Furthermore, IL-1β-induced NF-κB and mitogen-activated protein kinase (MAPK) activation were inhibited by EA. In conclusion, EA effectively attenuated IL-1β-induced inflammatory response in osteoarthritis chondrocyte which suggesting that EA may be a potential agent in the treatment of osteoarthritis.

Butein inhibits IL-1β-induced inflammatory response in human osteoarthritis chondrocytes and slows the progression of osteoarthritis in mice

Osteoarthritis (OA) is a progressive degenerative disease characterized by irreversible articular cartilage destruction. Butein, a polyphenolic compound isolated from the stem bark of cashews and Rhus verniciflua Stokes, has been reported to have anti-inflammatory effects. This study aimed to assess the effect of butein on human OA chondrocytes and mice OA models induced by destabilization of the medial meniscus (DMM). In vitro, human OA chondrocytes were pretreated with butein at 10, 50μM and subsequently stimulated with IL-1β (10ng/ml) for 24h. Production of NO, PGE2, TNF-α and IL-6 was evaluated by the Griess reaction and ELISAs. The mRNA expression of COX-2, iNOS, TNF-α, IL-6, MMP-1, MMP-3, MMP-13, ADAMTS-4, ADAMTS-5, COL-2 and SOX-9 were measured by real-time PCR. The protein expression of COX-2, iNOS, MMP-13, COL-2, SOX-9, p65 and IκB-α were detected by Western blot. P65 nuclear translocation was detected by immunofluorescence. In vivo, the severity of OA was determined by histological analysis. We found that butein significantly inhibited the IL-1β-induced production of NO and PGE2, expression of COX-2, iNOS, TNF-α, IL-6 and MMP-13, degradation of COL-2 and SOX-9 at mRNA and protein levels as well as MMP-1, MMP-3, ADAMTS-4 and ADAMTS-5 gene expression. Furthermore, butein dramatically suppressed IL-1β-stimulated IκB-α degradation and NF-kB p65 activation. In vivo, the cartilage in butein-treated mice exhibited less Safranin O loss, cartilage erosion and lower OARSI scores. Butein also reduced subchondral bone plate thickness and alleviated synovitis. Taken together, these findings indicate that butein may be a potential agent in the treatment of OA.

Resveratrol, a natural antioxidant, protects monosodium iodoacetate-induced osteoarthritic pain in rats

BACKGROUND

Osteoarthritis (OA) is a chronic progressive joint disease characterized by advanced joint pain, subchondral bone sclerosis and articular cartilage degeneration. Resveratrol has been shown to have anti-inflammatory, cardioprotective and antioxidant properties and to inhibit platelet aggregation and coagulation. However, the effects of resveratrol on OA have not been examined. In this study, we investigate the protective effects of resveratrol on monosodium iodoacetate (MIA)-induced OA through inhibition of cyclooxygenase (COX-2) and inducible nitric oxide synthase (iNOS) signaling pathway in a rat model.

METHODS

A single intra-articular injection of MIA was injected into rats for the induction of OA. The mechanical, heat and cold hyperalgesia were measured at days 0, 7 and 14. The serum and synovial fluid levels of IL-1β, IL-10 and TNF-α and osteocalcin were measured by enzyme-linked immunosorbent assay. The mRNA and protein expressions of IL-1β, IL-10, TNF-α, Il-6, MMP-13 and COX-2 and iNOS were determined by RT-PCR and western blot, respectively. Osteoarthritic lesion in the knee joint was evaluated by histological analysis.

RESULTS

MIA-injected rats treated with resveratrol at a dose of either 5 or 10mg/kg body weight were significantly reduced hyperalgesia of mechanical, heat and cold and increased the vertical and horizontal movements. Subsequently, MIA-injected rats increased serum and synovial fluid levels of IL-1β, IL-10, IL-6, TNF-α, MMP-13 and osteoclastic activity marker, osteocalcin and its articular cartilage mRNA and protein expressions. Further, MIA-injected rats increased COX-2 and iNOS mRNA and protein expressions were decreased by resveratrol. The protective effect of resveratrol was comparable to a reference drug, etoricoxib. The cartilage damage induced by MIA were attenuated by resveratrol.

CONCLUSIONS

Taken together, resveratrol has the potential to improve MIA-induced cartilage damage by inhibiting the levels and expressions of inflammatory mediators suggesting that resveratrol may be a potential therapeutic agent for OA.

Biochanin-A antagonizes the interleukin-1β-induced catabolic inflammation through the modulation of NFκB cellular signaling in primary rat chondrocytes

Biochanin-A, a phytoestrogen derived from herbal plants, protected from the IL-1β-induced loss of proteoglycans through the suppression of matrix degrading enzymes such as matrix metalloproteinase (MMP)-13, MMP-3, MMP-1, and ADAMTS-5 in primary rat chondrocytes and the knee articular cartilage. It also suppressed the expression of IL-1β-induced catabolic factors such as nitric oxide synthase 2, cyclooxygenase-2, prostaglandin E2, and inflammatory cytokines. Furthermore, biochanin-A suppressed the IL-1β-induced phosphorylation of NFκB, and inhibited its nuclear translocation in primary rat chondrocytes. These results indicate that biochanin-A antagonizes the IL-1β-induced catabolic effects through its anti-inflammatory activity that involves the modulation of NFκB signaling.

Liver X Receptor β Is Involved in Formalin-Induced Spontaneous Pain

Increasing evidence indicates that the liver X receptor(LXR) β modulates inflammatory pain. However, the molecular mechanisms through which LXRβ modulates pain are unclear. Here, we found that LXRβ-null mice responded more strongly to acute noxious stimuli than wild-type (WT) littermates (in the hot plate and Hargreaves tests) and had augmented tonic inflammatory pain (in the formalin test). This increased reactivity to inflammatory pain was accompanied by enhanced formalin-evoked Fos and pERK staining of second-order nociceptive neurons. Immunohistochemistry showed that the expression of CGRP, SP, and IB4 was increased in the lamina I-II of the lumbar dorsal horns in formalin-injected LXRβ knockout (KO) mice compared with the WT controls. In addition, LXRβ deletion in the mice enhanced the formalin-induced inflammation with more activated microglia and astrocytes in the spinal cord. Furthermore, the levels of pro-inflammatory cytokines (IL-1β ,TNF-α) as well as NFκB in the formalin-injected paw were elevated by the loss of LXRβ. Taken together, these data indicate that LXRβ is involved in acute as well as inflammatory pain, and thus, it may be considered as a new target for the development of analgesics.

The emerging roles of liver X receptors and their ligands in cancer

INTRODUCTION

Liver X receptors (LXRs) are nuclear receptors with well-known functions in cholesterol transport, fatty acid and glucose metabolism, and modulation of immune responses. Natural and synthetic ligands have been identified and are under development for the treatment of metabolic and inflammatory conditions and diseases. There is mounting evidence pointing to functional roles for LXRs in a variety of malignancies and the potential therapeutic efficacy of their ligands.

AREAS COVERED

This review summarizes the discovery and characterization of LXRs and their ligands, surveys their effects and mechanisms of action in cell-based and animal models of cancer, and proposes the future direction of basic and translational studies of LXRs and their ligands in cancer research and therapeutics.

EXPERT OPINION

Targeting LXRs is a promising strategy for cancer treatment, particularly for those cancers which do not have effective treatment options. Key questions remain, however, regarding the specific mechanisms of action, effects on other target cells within the tumor microenvironment, and receptor status in patient populations. Moreover, LXR ligands optimized for disease-specific functions and cancer-related endpoints are currently not available. These issues represent both challenges and significant opportunities for future research and development efforts.

Pharmacogenetics of cutaneous flushing response to niacin/laropiprant combination in Hong Kong Chinese patients with dyslipidemia

AIM

Cutaneous flushing with niacin varies between individuals and is substantially reduced by concomitant laropiprant. We investigated associations between baseline phenotypes and selected genotypes and flushing symptoms with niacin/laropiprant combination.

PATIENTS & METHODS

Flushing symptoms were quantified in 196 Chinese dyslipidaemic patients treated with niacin/laropiprant, and associations with phenotypes and selected polymorphisms were analyzed.

RESULTS

Moderate or severe flushing was associated with lower body mass index and the rs2279238 polymorphism in the LXRα on multivariate regression analysis and these factors accounted for 18.9% of the total variance.

CONCLUSION

Lower body mass index and the LXRα polymorphism appear to be associated with flushing symptoms with niacin/laropiprant. Whether these findings can be applicable to other niacin formulations without laropiprant needs to be verified.

Targeting liver X receptors in cancer therapeutics

Members of the nuclear receptor superfamily of ligand-dependent transcription factors carry out vital cellular functions and are highly druggable therapeutic targets. Liver X receptors (LXRs) are nuclear receptor family members that function in cholesterol transport, glucose metabolism and the modulation of inflammatory responses. There is now accumulating evidence to support the involvement of LXRs in a variety of malignancies and the potential efficacy of their ligands in these diseases. This Review summarizes the discovery and characterization of LXRs and their ligands, their effects and mechanisms in preclinical cancer models, and the future directions of basic and translational LXR research in cancer therapeutics.

Liver X Receptor activation delays chondrocyte hypertrophy during endochondral bone growth

OBJECTIVE

Activation of the Liver X Receptor (LXR) has recently been identified as a therapeutic strategy for osteoarthritis (OA). Human OA articular cartilage explants show decreased LXR expression, and LXRβ-null mice display OA-like symptoms. LXR agonist administration to OA articular cartilage explants suppresses proteoglycan degradation and restores LXR-activated transcription. We aimed to investigate the effect of LXR activation on chondrocyte differentiation to elucidate the molecular mechanisms behind its protection against OA.

METHOD

The specific LXR agonist, GW3965, was used to examine the effect of LXR activation on chondrocyte differentiation. Tibia organ cultures were used to examine the effect of LXR activation on bone growth and growth plate morphology, followed by immunohistochemical analysis. In ATDC5 and micromass cultures, chondrocyte differentiation was examined through cellular staining and proliferation assays. Various chondrogenic markers were analyzed by real-time reverse-transcription polymerase chain reaction (qRT-PCR) in micromass RNA.

RESULTS

Chondrocyte hypertrophy was suppressed by GW3965 treatment, as shown by decreased hypertrophic zone length in the tibial growth plate, decreased alkaline phosphatase staining in ATDC5 and micromass cultures, and down regulation of Col10a1, Mmp13 and Runx2 expression. Increased proliferation in treated ATDC5 cells and up-regulation of Col2a1 expression in treated micromass cultures suggest hypertrophy is suppressed secondary to prolonged proliferation. Decreased p57 levels in treated growth plates suggest this to be due to cell-cycle exit delay.

CONCLUSION

Our findings regarding LXR's role in cartilage development provide insight into how LXR activation prevents cartilage breakdown, further solidifying its potential as a therapeutic target of OA.

The role of prostaglandin E2 in human vascular inflammation

Prostaglandins (PG) are the product of a cascade of enzymes such as cyclooxygenases and PG synthases. Among PG, PGE2 is produced by 3 isoforms of PGE synthase (PGES) and through activation of its cognate receptors (EP1-4), this PG is involved in the pathophysiology of vascular diseases. Some anti-inflammatory drugs (e.g. glucocorticoids, nonsteroidal anti-inflammatory drugs) interfere with its metabolism or effects. Vascular cells can initiate many of the responses associated with inflammation. In human vascular tissue, PGE2 is involved in many physiological processes, such as increasing vascular permeability, cell proliferation, cell migration and control of vascular smooth muscle tone. PGE2 has been shown to contribute to the pathogenesis of atherosclerosis, abdominal aortic aneurysm but also in physiologic/adaptive processes such as angiogenesis. Understanding the roles of PGE2 and its cognate receptors in vascular diseases could help to identify diagnostic and prognostic biomarkers. In addition, from these recent studies new promising therapeutic approaches like mPGES-1 inhibition and/or EP4-antagonism should be investigated.

Connective tissue growth factor promotes interleukin-1β-mediated synovial inflammation in knee osteoarthritis

Connective tissue growth factor (CTGF), also known as CCN2, is a key proinflammatory mediator. In the present study, the involvement of the CTGF signaling pathway in human knee osteoarthritis (OA) fibroblast-like synoviocytes (FLSs) was investigated. FLSs were isolated from human OA synovium and incubated with CTGF in the absence or presence of interleukin‑1β (IL‑1β). The expression of relevant genes and proteins was analyzed by qPCR, western blotting and enzyme-linked immunosorbent assay (ELISA). Matrix metalloproteinase (MMP) activity and nuclear factor (NF)-κB activation were also evaluated. CTGF stimulation resulted in the significant production of IL-6, IL-8, C-C motif ligand 2 (CCL2), CCL20, MMP-1 and MMP-3 in FLSs in the presence, but not in the absence, of IL-1β. CTGF also enhanced the levels of phosphorylated extracellular signal-related kinase 1/2 (ERK1/2) and p38. In addition, CTGF at 25 ng/ml, in the presence of IL‑1β, significantly potentiated NF-κB activation. The results indicated that CTGF interacted with IL‑1β in FLSs to promote the inflammatory response in the synovium, leading to the initiation of the inflammatory cascade. These results support the proinflammatory role of CTGF in synovitis and joint destruction in OA.