Anti-arthritic effects of combined treatment with histone deacetylase inhibitor and low-intensity ultrasound in the presence of microbubbles in human rheumatoid synovial cells

Epi-revolution in rheumatology: the potential of histone deacetylase inhibitors for targeted rheumatoid arthritis intervention

Autoimmune diseases hold significant importance in the realm of medical research, prompting a thorough exploration of potential therapeutic interventions. One crucial aspect of this exploration involves understanding the intricate processes of histone acetylation and deacetylation. Histone acetylation, facilitated by histone acetyl transferases (HATs), is instrumental in rendering DNA transcriptionally active. Conversely, histone deacetylases (HDACs) are responsible for the removal of acetyl groups, influencing gene expression regulation. The upregulation of HDACs, observed in various cancers, has steered attention towards histone deacetylase inhibitors (HDACi) as promising anti-cancer agents. Beyond cancer, HDACi has demonstrated anti-inflammatory properties, prompting interest in their potential therapeutic applications for inflammatory diseases such as rheumatoid arthritis (RA). RA, characterized by the immune system erroneously attacking healthy cells, leads to joint inflammation. Recent studies suggest that HDACi could offer a viable therapeutic strategy for RA, with potential mechanisms including the inhibition of synovial tissue growth and suppression of pro-inflammatory cytokines. Furthermore, HDACi may exert protective effects on bone and cartilage, common targets in RA pathology. In-depth investigations through in vivo and histopathology studies contribute to the ongoing discourse on the therapeutic benefits of HDACis in the context of RA treatment.

Histone deacetylase inhibitors attenuated interleukin-1β-induced chondrogenesis inhibition in synovium-derived mesenchymal stem cells of the temporomandibular joint

Aims

In the repair of condylar cartilage injury, synovium-derived mesenchymal stem cells (SMSCs) migrate to an injured site and differentiate into cartilage. This study aimed to confirm that histone deacetylase (HDAC) inhibitors, which alleviate arthritis, can improve chondrogenesis inhibited by IL-1β, and to explore its mechanism.

Methods

SMSCs were isolated from synovium specimens of patients undergoing temporomandibular joint (TMJ) surgery. Chondrogenic differentiation potential of SMSCs was evaluated in vitro in the control, IL-1β stimulation, and IL-1β stimulation with HDAC inhibitors groups. The effect of HDAC inhibitors on the synovium and condylar cartilage in a rat TMJ arthritis model was evaluated.

Results

Interleukin (IL)-1β inhibited the chondrogenic differentiation potential of SMSCs, while the HDAC inhibitors, suberoylanilide hydroxamic acid (SAHA) and panobinostat (LBH589), attenuated inhibition of IL-1β-induced SMSC chondrogenesis. Additionally, SAHA attenuated the destruction of condylar cartilage in rat TMJ arthritis model. IL-6 (p < 0.001) and matrix metalloproteinase 13 (MMP13) (p = 0.006) were significantly upregulated after IL-1β stimulation, while SAHA and LBH589 attenuated IL-6 and MMP13 expression, which was upregulated by IL-1β in vitro. Silencing of IL-6 significantly downregulated MMP13 expression and attenuated IL-1β-induced chondrogenesis inhibition of SMSCs.

Conclusion

HDAC inhibitors SAHA and LBH589 attenuated chondrogenesis inhibition of SMSC induced by IL-1β in TMJ, and inhibition of IL-6/MMP13 pathway activation contributes to this biological progress. This study provides a theoretical basis for the application of HDAC inhibitors in the treatment of TMJ arthritis.

Cite this article: Bone Joint Res 2022;11(1):40–48.

Transformation of fibroblast-like synoviocytes in rheumatoid arthritis; from a friend to foe

Swelling and the progressive destruction of articular cartilage are major characteristics of rheumatoid arthritis (RA), a systemic autoimmune disease that directly affects the synovial joints and often causes severe disability in the affected positions. Recent studies have shown that type B synoviocytes, which are also called fibroblast-like synoviocytes (FLSs), as the most commonly and chiefly resident cells, play a crucial role in early-onset and disease progression by producing various mediators. During the pathogenesis of RA, the FLSs' phenotype is altered, and represent invasive behavior similar to that observed in tumor conditions. Modified and stressful microenvironment by FLSs leads to the recruitment of other immune cells and, eventually, pannus formation. The origins of this cancerous phenotype stem fundamentally from the significant metabolic changes in glucose, lipids, and oxygen metabolism pathways. Moreover, the genetic abnormalities and epigenetic alterations have recently been implicated in cancer-like behaviors of RA FLSs. In this review, we will focus on the mechanisms underlying the transformation of FLSs to a cancer-like phenotype during RA. A comprehensive understanding of these mechanisms may lead to devising more effective and targeted treatment strategies.

Epigenetics in rheumatoid arthritis; fibroblast-like synoviocytes as an emerging paradigm in the pathogenesis of the disease

Rheumatoid arthritis (RA) is characterized by immune dysfunctions and chronic inflammation that mainly affects diarthrodial joints. Genetics has long been surveyed in searching for the etiopathogenesis of the disease and partially clarified the conundrums within this context. Epigenetic alterations, such as DNA methylation, histone modifications, and noncoding RNAs, which have been considered to be involved in RA pathogenesis, likely explain the nongenetic risk factors. Epigenetic modifications may influence RA through fibroblast-like synoviocytes (FLSs). It has been shown that FLSs play an essential role in the onset and exacerbation of RA, and therefore, they may illustrate some aspects of RA pathogenesis. These cells exhibit a unique DNA methylation profile in the early stage of the disease that changes with disease progression. Histone acetylation profile in RA FLSs is disrupted through the imbalance of histone acetyltransferases and histone deacetylase activity. Furthermore, dysregulation of microRNAs (miRNAs) is immense. Most of these miRNAs have shown an aberrant expression in FLSs that are involved in proliferation and cytokine production. Besides, dysregulation of long noncoding RNAs in FLSs has been revealed and attributed to RA pathogenesis. Further investigations are needed to get a better view of epigenetic alterations and their interactions. We also discuss the role of these epigenetic alterations in RA pathogenesis and their therapeutic potential.

DNA Methylation as a Future Therapeutic and Diagnostic Target in Rheumatoid Arthritis

Rheumatoid arthritis (RA) is a long-term autoimmune disease of unknown etiology that leads to progressive joint destruction and ultimately to disability. RA affects as much as 1% of the population worldwide. To date, RA is not a curable disease, and the mechanisms responsible for RA development have not yet been well understood. The development of more effective treatments and improvements in the early diagnosis of RA is direly needed to increase patients' functional capacity and their quality of life. As opposed to genetic mutation, epigenetic changes, such as DNA methylation, are reversible, making them good therapeutic candidates, modulating the immune response or aggressive synovial fibroblasts (FLS-fibroblast-like synoviocytes) activity when it is necessary. It has been suggested that DNA methylation might contribute to RA development, however, with insufficient and conflicting results. Besides, recent studies have shown that circulating cell-free methylated DNA (ccfDNA) in blood offers a very convenient, non-invasive, and repeatable "liquid biopsy", thus providing a reliable template for assessing molecular markers of various diseases, including RA. Thus, epigenetic therapies controlling autoimmunity and systemic inflammation may find wider implications for the diagnosis and management of RA. In this review, we highlight current challenges associated with the treatment of RA and other autoimmune diseases and discuss how targeting DNA methylation may improve diagnostic, prognostic, and therapeutic approaches.

Epigenetic alterations in rheumatoid arthritis fibroblast-like synoviocytes

Rheumatoid arthritis is an immune-mediated disease that primarily affects diarthrodial joints. Susceptibility and severity of this disease are influenced by nongenetic factors, such as environmental stress, suggesting an important role of epigenetic changes. In this review, we summarize the epigenetic changes (DNA methylation, histone modification and miRNA expression) in fibroblast-like synoviocytes, which are the joint-lining mesenchymal cells that play an important role in joint inflammation and damage. We also review the effects of these epigenetic changes on rheumatoid arthritis pathogenesis and discuss their therapeutic potential.

The Effects of Histone Deacetylase Inhibition on the Levels of Cerebral Cytokines in an Animal Model of Mania Induced by Dextroamphetamine

Studies have suggested the involvement of inflammatory processes in the physiopathology of bipolar disorder. Preclinical evidences have shown that histone deacetylase inhibitors may act as mood-stabilizing agents and protect the brain in models of mania and depression. The aim of the present study was to evaluate the effects of sodium butyrate (SB) and valproate (VPA) on behavioral changes, histone deacetylase activity, and the levels of cytokines in an animal model of mania induced by dextroamphetamine (d-AMPH). Wistar rats were first given d-AMPH or saline (Sal) for a period of 14 days, and then, between the 8th and 14th days, the rats were treated with SB, VPA, or Sal. The activity of histone deacetylase and the levels of cytokines (interleukin (IL) IL-4, IL-6, and IL-10 and tumor necrosis factor-alpha (TNF-α)) were evaluated in the frontal cortex and striatum of the rats. The administration of d-AMPH increased the activity of histone deacetylase in the frontal cortex. Administration of SB or VPA decreased the levels of histone deacetylase activity in the frontal cortex and striatum of rats. SB per se increased the levels of cytokines in both of the brain structures evaluated. AMPH increased the levels of cytokines in both of the brain structures evaluated, and VPA reversed this alteration. The effects of SB on d-AMPH-induced cytokine alterations were dependent on the brain structure and the cytokine evaluated. Despite VPA and SB having a similar mechanism of action, both being histone deacetylase inhibitors, they showed different effects on the levels of cytokines. The present study reinforces the need for more research into histone deacetylase inhibitors being used as a possible target for new medications in the treatment of bipolar disorder.

Low intensity ultrasound promotes the sensitivity of rat brain glioma to Doxorubicin by down-regulating the expressions of p-glucoprotein and multidrug resistance protein 1 in vitro and in vivo

The overall prognosis for malignant glioma is extremely poor, and treatment options are limited in part because of multidrug resistant proteins. Our previous findings suggest low intensity ultrasound (LIUS) can induce apoptosis of glioma cells. Given this finding, we were interested in determining if LIUS could help treat glioma by inhibiting multidrug resistant proteins, and if so, which pathways are involved. In this study, the toxicity sensitivity and multidrug resistance proteins of glioma induced by LIUS were investigated using CCK-8, immunohistochemistry, immunofluorency, and RT-PCR in tissue samples and cultured cells. LIUS inhibited increase of C6 cells in an intensity- and time-dependent manner. The toxicity sensitivity of C6 cells increased significantly after LIUS sonication (intensity of 142.0 mW/cm²) or Doxorubicin (DOX) at different concentration, particularly by the combination of LIUS sonication and DOX. The expressions of P-gp and MRP1 decreased significantly post-sonication at intensity of 142.0 mW/cm² both in vitro and in vivo. The expressions of p110 delta (PI3K), NF-κB-p65, Akt/PKB, and p-Akt/PKB were downregulated by LIUS sonication and DOX treatment separately or in combination at the same parameters in rat glioma. These results indicate that LIUS could increase the toxicity sensitivity of glioma by down-regulating the expressions of P-gp and MRP1, which might be mediated by the PI3K/Akt/NF-κB pathway.

Comparison between pulsed ultrasound and low level laser therapy on experimental haemarthrosis

The use of pulsed ultrasound (PUS) and low level laser therapy (LLLT) in patients with haemophilia has been recommended for supportive treatment of acute and chronic phases of haemarthrosis but its role has not been supported by experimental evidence. The purpose of the present study was to evaluate the effect of these modalities on joint swelling, friction and biomechanical parameters of articular cartilage. An experimental rabbit knee haemarthrosis model was used to test the hypothesis that LLLT and PUS favourably impacted on the biotribological and biomechanical properties of cartilage after joint bleeding. To test this, 35 male albino rabbits weighing 1.5-2 kg were used. The left knee of 30 rabbits was injected with 1 mL of fresh autologous blood two times per week for four consecutive weeks to simulate recurrent haemarthrosis; five rabbits served as non-bleeding controls. Ten rabbits were treated with PUS and 10 with LLLT and the remaining 10 were not treated. The treatments were started after 2 days and the treatment duration was planned for 5 days (sessions) in ultrasound and laser groups. A low level Ga-Al-As laser was applied with an 810 nm wavelength, 25 mW power, and 1 J cm(-2) dosage for 200 s duration. The PUS treatment was applied with a duty cycle of 1/9, frequency of 1 MHz, and power of 0.4 W cm(-2) for 150 s. Joint perimeter was measured before the procedure at the beginning of therapies and after cessation of the procedure. Friction and biomechanical parameters were measured immediately after the killing of the animals. The results demonstrate that PUS was more effective in reducing knee joint swelling than LLLT. Moreover, PUS had the unique ability of reducing the joint friction below normal values. However, it was not successful in returning the articular cartilage force and stiffness to normal state. LLLT was more effective in increasing equilibrium force of the articular cartilage than PUS, however, neither therapy normalized this parameter. From these data, we conclude that PUS is more effective than LLLT in reducing joint swelling and articular joint friction after experimental haemarthrosis.

Hypomethylation of proximal CpG motif of interleukin-10 promoter regulates its expression in human rheumatoid arthritis

AIM

The promoter of human interleukin-10 (IL10), a cytokine crucial for suppressing inflammation and regulating immune responses, contains an interspecies-conserved sequence with CpG motifs. The aim of this study was to investigate whether methylation of CpG motifs could regulate the expression of IL10 in rheumatoid arthritis (RA).

METHODS

Bioinformatic analysis was conducted to identify the interspecies-conserved sequence in human, macaque and mouse IL10 genes. Peripheral blood mononuclear cells (PBMCs) from 20 RA patients and 20 health controls were collected. The PBMCs from 6 patients were cultured in the presence or absence of 5-azacytidine (5 μmol/L). The mRNA and protein levels of IL10 were examined using RT-PCR and ELISA, respectively. The methylation of CpGs in the IL10 promoter was determined by pyrosequencing. Chromatin immunoprecipitation (ChIP) assays were performed to detect the cyclic AMP response element-binding protein (CREB)-DNA interactions.

RESULTS

One interspecies-conserved sequence was found within the IL10 promoter. The upstream CpGs at -408, -387, -385, and -355 bp were hypermethylated in PBMCs from both the RA patients and healthy controls. In contrast, the proximal CpG at -145 was hypomethylated to much more extent in the RA patients than in the healthy controls (P=0.016), which was correlated with higher IL10 mRNA and serum levels. In the 5-azacytidine-treated PBMCs, the CpG motifs were demethylated, and the expression levels of IL10 mRNA and protein was significantly increased. CHIP assays revealed increased phospho-CREB binding to the IL10 promoter.

CONCLUSION

The methylation of the proximal CpGs in the IL10 promoter may regulate gene transcription in RA.

Prospects for epigenetic compounds in the treatment of autoimmune disease

There is growing evidence for a role for epigenetic mechanisms in the development of autoimmune diseases. In most cases ofautoimmune disease the precise epigenetic mechanism involved remains to be resolved, however DNA hypomethylation accompanied by hypoacetylation ofhistone H3/H4 is commonly observed. Due to the reversible nature of epigenetic marks their maintenance enzymes such as DNA methyltransferases (DNMTs), histone deacetylases (HDACs) and histone lysine methyltransferases (HKMT) are attractive drug targets. Small molecule inhibitors of histone modification and DNA methylation maintenance are increasingly becoming available and will be useful chemical biological tools to dissect epigenetic mechanisms in these diseases. However, although epigenetic therapies used in cancer treatment are a promising starting point for the exploration of autoimmune disease treatment, there is a requirement for more specific and less toxic agents for these chronic diseases or for use as chemopreventative agents.

Histone deacetylase inhibitors MS-275 and SAHA induced growth arrest and suppressed lipopolysaccharide-stimulated NF-kappaB p65 nuclear accumulation in human rheumatoid arthritis synovial fibroblastic E11 cells

OBJECTIVES

MS-275 and suberoylanilide hydroxamic acid (SAHA) are histone deacetylase (HDAC) inhibitors currently tested in oncology trials. They have also been found to display potent anti-rheumatic activities in rodent models for RA. However, the anti-rheumatic mechanisms of action remain unknown. The study was carried out with the intent of determining the anti-inflammatory and anti-rheumatic mechanisms of the HDAC inhibitors.

METHODS

In this study, the anti-rheumatic mechanisms of MS-275 and SAHA were investigated in several cell culture models.

RESULTS

MS-275 and SAHA inhibited human RA synovial fibroblastic E11 cell proliferation in a non-cytotoxic manner. The anti-proliferative activities were associated with G(0)/G(1) phase arrest and induction of cyclin-dependent kinase inhibitor p21. In addition, MS-275 and SAHA suppressed lipopolysaccharide (LPS)-induced NF-kappaB p65 nuclear accumulation, IL-6, IL-18 and nitric oxide (NO) secretion as well as down-regulated pro-angiogenic VEGF and MMP-2 and MMP-9 production in E11 cells at sub-micromolar levels. At similar concentrations, MS-275 and SAHA suppressed LPS-induced NF-kappaB p65 nuclear accumulation and IL-1beta, IL-6, IL-18 and TNF-alpha secretion in THP-1 monocytic cells. Moreover, NO secretion in RAW264.7 macrophage cells was also inhibited.

CONCLUSIONS

In summary, MS-275 and SAHA exhibited their anti-rheumatic activities by growth arrest in RA synovial fibroblasts, inhibition of pro-inflammatory cytokines and NO, as well as down-regulation in angiogenesis and MMPs. Their anti-rheumatic activities may be mediated through induction of p21 and suppression of NF-kappaB nuclear accumulation.

A comprehensive molecular interaction map for rheumatoid arthritis

Background

Computational biology contributes to a variety of areas related to life sciences and, due to the growing impact of translational medicine - the scientific approach to medicine in tight relation with basic science -, it is becoming an important player in clinical-related areas. In this study, we use computation methods in order to improve our understanding of the complex interactions that occur between molecules related to Rheumatoid Arthritis (RA).

Methodology

Due to the complexity of the disease and the numerous molecular players involved, we devised a method to construct a systemic network of interactions of the processes ongoing in patients affected by RA. The network is based on high-throughput data, refined semi-automatically with carefully curated literature-based information. This global network has then been topologically analysed, as a whole and tissue-specifically, in order to translate the experimental molecular connections into topological motifs meaningful in the identification of tissue-specific markers and targets in the diagnosis, and possibly in the therapy, of RA.

Significance

We find that some nodes in the network that prove to be topologically important, in particular AKT2, IL6, MAPK1 and TP53, are also known to be associated with drugs used for the treatment of RA. Importantly, based on topological consideration, we are also able to suggest CRKL as a novel potentially relevant molecule for the diagnosis or treatment of RA. This type of finding proves the potential of in silico analyses able to produce highly refined hypotheses, based on vast experimental data, to be tested further and more efficiently. As research on RA is ongoing, the present map is in fieri, despite being -at the moment- a reflection of the state of the art. For this reason we make the network freely available in the standardised and easily exportable .xml CellDesigner format at ‘www.picb.ac.cn/ClinicalGenomicNTW/temp.html’ and ‘www.celldesigner.org’.

Deacetylase inhibition increases regulatory T cell function and decreases incidence and severity of collagen-induced arthritis

Collagen-induced arthritis (CIA) is an established mouse model of disease with hallmarks of clinical rheumatoid arthritis. Histone/protein deacetylase inhibitors (HDACi) are known to inhibit the pathogenesis of CIA and other models of autoimmune disease, although the mechanisms responsible are unclear. Regulatory T cell (Treg) function is defective in rheumatoid arthritis. FOXP3 proteins in Tregs are present in a dynamic protein complex containing histone acetyltransferase and HDAC enzymes, and FOXP3 itself is acetylated on lysine residues. We therefore investigated the effects of HDACi therapy on regulatory T cell function in the CIA model. Administration of an HDACi, valproic acid (VPA), significantly decreased disease incidence (p<0.005) and severity (p<0.03) in CIA. In addition, VPA treatment increased both the suppressive function of CD4(+)CD25(+) Tregs (p<0.04) and the numbers of CD25(+)FOXP3(+) Tregs in vivo. Hence, clinically approved HDACi such as VPA may limit autoimmune disease in vivo through effects on the production and function of FOXP3(+) Treg cells.

Melatonin inhibits human fibroblast-like synoviocyte proliferation via extracellular signal-regulated protein kinase/P21(CIP1)/P27(KIP1) pathways

The excessive proliferation and migration of synoviocytes are well-characterized phenomena that play key roles in the pathophysiology of rheumatoid arthritis (RA). Melatonin has been shown to have potent anti-proliferative effect in various cancer cells such as breast and prostate cancer cells. In this study, we examined the role of melatonin on synoviocyte proliferation in primary cultured human fibroblast-like synoviocytes (FLSs) by analyzing protein expression of P21(CIP1) (P21) and P27(KIP1) (P27), the cyclin-dependent kinase inhibitors that are important in cell cycle control, and the phosphorylation of mitogen-activated protein kinases (MAPKs). RA-FLS proliferation was determined by a [(3)H]-thymidine incorporation assay. Western blot analysis was applied to examine the underlying mechanisms of melatonin's effect. Melatonin inhibited RA-FLS proliferation in a dose-dependent manner. It reduced proliferation of passage 2 FLSs by 25% at 10 microm and by nearly 40% at 100 microm concentrations. The inhibitory effect of melatonin on RA-FLS proliferation was also observed in passages 4 and 6. Melatonin upregulated the expression levels of P21 and P27 dose-dependently (24 hr), induced the phosphorylation of extracellular signal-regulated protein kinase (ERK) time-dependently (10 microm), but did not affect phosphorylation of P38 in RA-FLSs. In addition, the expression of P21 and P27 triggered by melatonin was inhibited by the pretreatment of the ERK inhibitor, PD98059 (10 microm). The anti-proliferative action of melatonin in RA-FLSs was also blocked by PD98059. Taken together, these results suggest that melatonin exerts the inhibitory effect of the proliferation of RA-FLSs through the activation of P21 and P27 mediated by ERK. Hence we suggest that melatonin could be used as a therapeutic agent for the treatment of RA.

Evaluation and comparison of three novel microbubbles: enhancement of ultrasound-induced cell death and free radicals production

Three novel lipid-shell-type microbubbles (MBs), AS-0100, BG6356A and BG6356B, have been evaluated for their impact on ultrasound (US)-induced cell death and free radicals production. Previously studied and well-characterized US exposure conditions were employed in which human myelomonocytic lymphoma U937 cells were exposed to 1MHz pulsed US beam (0.3W/cm(2), 10% duty factor) for 1min with or without MBs. Three different concentrations of each MB were used. Apoptosis and cell lysis were assessed by examining phosphatidylserine externalization and by counting viable cells, respectively, 6h post-exposure. Free radicals production and scavenging activities were evaluated using electron paramagnetic resonance (EPR)-spin trapping. The results showed that only AS-0100 and BG6356A were able to enhance the US-induced apoptosis, mainly by increasing the secondary necrosis. Apoptosis and cell lysis seemed to depend more on mechanical forces exerted by oscillating MBs while free radicals played a trivial role. BG series MBs exhibited pronounced scavenging activities. Generally, despite the need for further optimization, AS-0100 and BG6356A appear to be promising as adjuncts in cases where US-induced cell death is required.

Epigenetic modifications in rheumatoid arthritis

Over the last decades, genetic factors for rheumatoid diseases like the HLA haplotypes have been studied extensively. However, during the past years of research, it has become more and more evident that the influence of epigenetic processes on the development of rheumatic diseases is probably as strong as the genetic background of a patient. Epigenetic processes are heritable changes in gene expression without alteration of the nucleotide sequence. Such modifications include chromatin methylation and post-translational modification of histones or other chromatin-associated proteins. The latter comprise the addition of methyl, acetyl, and phosphoryl groups or even larger moieties such as binding of ubiquitin or small ubiquitin-like modifier. The combinatory nature of these processes forms a complex network of epigenetic modifications that regulate gene expression through activation or silencing of genes. This review provides insight into the role of epigenetic alterations in the pathogenesis of rheumatoid arthritis and points out how a better understanding of such mechanisms may lead to novel therapeutic strategies.

Inflammatory signalling as mediator of epigenetic modulation in tissue-specific chronic inflammation

Recent successes of therapeutic intervention in chronic inflammatory diseases using epigenetic modifiers such as histone deacetylase inhibitors and inhibitors of DNA methylation suggest that epigenetic reprogramming plays a role in the aetiology of these diseases. The epigenetic signature of a given immune cell is reflected in the history of modifications from different signals the cell has been subjected to during differentiation. Like other cells, differentiating immune cells are dependent on a complex combination of inter- and intracell signalling as well as transcription machineries to modulate their epigenomes in order to mediate differentiation. Despite extensive research into these processes, the link between cellular signalling and epigenetic modulation remains poorly understood. Here, we review recent progress and discuss key factors driving epigenetic modulation in chronic inflammation.