Plasma adrenomedullin in rheumatoid arthritis compared with other rheumatic diseases

Signalling and putative therapeutic molecules on the regulation of synoviocyte signalling in rheumatoid arthritis

Rheumatoid arthritis (RA) is an autoimmune disease characterized by symmetrical and chronic polyarthritis. Fibroblast-like synoviocytes are mainly involved in joint inflammation and cartilage and bone destruction by inflammatory cytokines and matrix-degrading enzymes in RA. Approaches that induce various cellular growth alterations of synoviocytes are considered as potential strategies for treating RA. However, since synoviocytes play a critical role in RA, the mechanism and hyperplastic modulation of synoviocytes and their motility need to be addressed. In this review, we focus on the alteration of synoviocyte signalling and cell fate provided by signalling proteins, various antioxidant molecules, enzymes, compounds, clinical candidates, to understand the pathology of the synoviocytes, and finally to achieve developed therapeutic strategies of RA.

Cite this article: Bone Joint Res 2021;10(4):285–297.

Adrenomedullin Regulates IL-1β Gene Expression in F4/80+ Macrophages during Synovial Inflammation

Adrenomedullin (AM) plays an important role in the regulation of inflammatory processes; however, the role and expression of AM in synovial inflammation have not been determined. To investigate the expression and role of AM in inflamed synovial tissue (ST), the gene expression profiles of AM in the ST, including synovial macrophages and fibroblasts, of a murine patellar surgical dislocation model were characterized. In addition, the effects of interleukin- (IL-) 1β and AM in cultured synovial cells were also examined. CD11c⁺ macrophages were found to be elevated in ST of the surgically dislocated patella. Higher gene expression of CD11c, IL-1β, AM, receptor activity-modifying proteins 2 (RAMP2), and 3 (RAMP3) was also observed in ST obtained from the dislocated side. AM expression was also significantly increased in synovial fibroblasts and macrophages in response to IL-1β treatment. Synovial macrophages also highly expressed RAMP3 compared to fibroblasts and this expression was further stimulated by exogenously added IL-1β. Further, the treatment of the F4/80-positive cell fraction obtained from ST with AM inhibited IL-1β expression. Taken together, these findings demonstrated that AM was produced by synovial fibroblasts and macrophages in inflamed ST and that increased levels of AM may exert anti-inflammatory effects on synovial macrophages.

Adrenomedullin protects from experimental autoimmune encephalomyelitis at multiple levels

Adrenomedullin is a neuropeptide known for its cardiovascular activities and anti-inflammatory effects. Here, we investigated the effect of adrenomedullin in a model of experimental autoimmune encephalomyelitis (EAE) that mirrors chronic progressive multiple sclerosis. A short-term systemic treatment with adrenomedullin reduced clinical severity and incidence of EAE, the appearance of inflammatory infiltrates in spinal cord and the subsequent demyelination and axonal damage. This effect was exerted at multiple levels affecting both early and late events of the disease. Adrenomedullin decreased the presence/activation of encephalitogenic Th1 and Th17 cells and down-regulated several inflammatory mediators in peripheral lymphoid organs and central nervous system. Noteworthy, adrenomedullin inhibited the production by encephalitogenic cells of osteopontin and of Granulocyte Macrophage Colony-Stimulating Factor (GM-CSF), two critical cytokines in the development of EAE. At the same time, adrenomedullin increased the number of IL-10-producing regulatory T cells with suppressive effects on the progression of EAE. Furthermore, adrenomedullin generated dendritic cells with a semi-mature phenotype that impaired encephalitogenic responses in vitro and in vivo. Finally, adrenomedullin regulated glial activity and favored an active program of neuroprotection/regeneration. Therefore, the use of adrenomedullin emerges as a novel multimodal therapeutic approach to treat chronic progressive multiple sclerosis.

Adrenomedullin increases fibroblast-like synoviocyte adhesion to extracellular matrix proteins by upregulating integrin activation

Introduction

Rheumatoid arthritis (RA) is characterized by bone and cartilage invasion by fibroblast-like synoviocytes (FLSs). Adrenomedullin, a peptide with anabolic and antiapoptotic properties, is secreted by rheumatoid FLSs. Adrenomedullin also increases the expression of adhesion molecules in endothelial cells and keratinocytes. Here, we investigated whether adrenomedullin mediated FLS adhesion to extracellular matrix (ECM) proteins.

Methods

FLSs were isolated from synovial tissues from RA and osteoarthritis (OA) patients. Plates were coated overnight with the ECM proteins vitronectin, fibronectin, and type I collagen (Coll.I). Adrenomedullin was used as a soluble FLS ligand before plating. We tested interactions with the adrenomedullin receptor antagonist (22-52)adrenomedullin and with the protein kinase A (PKA) inhibitor H-89, and inhibition of co-receptor RAMP-2 by siRNA. Cell adhesion was measured by using color densitometry. Activation of α₂ and β₁ integrins was evaluated by fluorescent microscopy; integrin inhibition, by RGD peptides; and the talin-integrin interaction, by immunoprecipitation (IP).

Results

Adrenomedullin specifically increased RA-FLS adhesion to vitronectin, fibronectin, and Coll.I; no such effect was found for OA-FLS adhesion. Basal or adrenomedullin-stimulated RA-FLS adhesion was inhibited by (22-52)adrenomedullin, H-89, and RAMP-2 siRNA. Adrenomedullin-stimulated adhesion was inhibited by RGD peptides, and associated with α₂ and β₁ integrin activation. This activation was shown with IP to be related to an integrin-talin interaction and was significantly decreased by (22-52)adrenomedullin.

Conclusions

Adrenomedullin-stimulated RA-FLS adhesion was specific for ECM proteins and mediated by α₂ and β₁ integrins. This effect of adrenomedullin was dependent on adrenomedullin receptors. These results support a new role for adrenomedullin in rheumatoid synovial fibroblast pathobiology.

Plasma adrenomedullin and proadrenomedullin N-terminal 20 peptide in patients diagnosed as having early rheumatoid arthritis

The aim of this study was to investigate plasma adrenomedullin (AM) and proadrenomedullin N-terminal 20 peptide (PAMP) level in patients diagnosed with early rheumatoid arthritis (RA). Furthermore, several inflammatory cytokines were measured in those patients to clarify the roles of AM and PAMP. Forty patients diagnosed with early RA (women 46 +/- 8.5 years old) and 10 healthy controls (women 57 +/- 5 years old) were studied. Plasma levels of AM, PAMP, matrix metalloprotease 3 (MMP-3), interleukin 6 (IL-6), tumor necrosis factor alpha (TNF-alpha), and C-reactive protein (CRP) were measured using an immunoradiometric assay and enzyme-linked immunosorbent asay (ELISA) methods. The plasma levels of AM (17.5 +/- 8.4 fmol/ml) and PAMP (2.01 +/- 0.57 fmol/ml) in patients exceeded those in healthy controls (AM 8.6 +/- 1.7, PAMP 1.17 +/- 0.34 fmol/ml). Moreover, plasma AM and PAMP levels demonstrated a significantly positive correlation with plasma MMP-3 and IL-6 levels. Nevertheless, CRP and TNF-alpha levels in these patients showed no significant correlation with plasma AM and PAMP levels. These data support the possible role for AM and PAMP in the pathophysiology of early RA.

Therapeutic efficacy of intra-articular adrenomedullin injection in antigen-induced arthritis in rabbits

Introduction

Adrenomedullin is a potent vasodilatory and hypotensive peptide as well as an endogenous immunomodulatory factor with predominantly anti-inflammatory effects. The purpose of the present study was to evaluate the therapeutic effects of adrenomedullin in rabbits with antigen-induced arthritis, an experimental model of rheumatoid arthritis.

Methods

Following the induction of arthritis in both knee joints by ovalbumin injection into the joint spaces of pre-immunized rabbits, increasing daily doses of adrenomedullin were injected into the knee joint spaces or saline was injected into the contralateral knee joint spaces as the control. For time-course experiments, adrenomedullin and saline were injected into the knee joint spaces daily for 7 days and 20 days. The degree of joint swelling and the histological change in the knee joints injected with adrenomedullin were compared with the control knee joints. Histological evaluation of the infrapatellar fat pads and synovial tissue was performed. TNFα, IL-6, vascular endothelial growth factor and transforming growth factor-beta mRNA levels in the synovial tissue were measured using real-time quantitative PCR.

Results

Daily injections of adrenomedullin into the knee joint spaces of rabbits with antigen-induced arthritis decreased joint swelling. Histological examination revealed that adrenomedullin reduced edematous changes and the infiltration of inflammatory cells in the synovial tissues. Analysis of mRNA levels showed that adrenomedullin significantly reduced TNFα mRNA expression by 21% to 49% in a dose-dependent manner, and dose-dependently increased IL-6 mRNA expression by 45% to 121%.

Conclusions

These results suggest that daily injections of adrenomedullin into the knee joint spaces of rabbits with antigen-induced arthritis ameliorated the inflammatory response in arthritic joints. Adrenomedullin may thus be useful as a treatment for rheumatoid arthritis; however, the effect of adrenomedullin on IL-6 production in the synovial tissue may be an undesirable adverse effect in rheumatoid arthritis therapy.

Endogenous anti-inflammatory neuropeptides and pro-resolving lipid mediators: a new therapeutic approach for immune disorders

Identification of the factors that regulate the immune tolerance and control the appearance of exacerbated inflammatory conditions is crucial for the development of new therapies of inflammatory and autoimmune diseases. Although much is known about the molecular basis of initiating signals and pro-inflammatory chemical mediators in inflammation, it has only recently become apparent that endogenous stop signals are critical at early checkpoints within the temporal events of inflammation. Some neuropeptides and lipid mediators that are produced during the ongoing inflammatory response have emerged as endogenous anti-inflammatory agents that participate in the regulation of the processes that ensure self-tolerance and/or inflammation resolution. Here we examine the latest research findings, which indicate that neuropeptides participate in maintaining immune tolerance in two distinct ways: by regulating the balance between pro-inflammatory and anti-inflammatory factors, and by inducing the emergence of regulatory T cells with suppressive activity against autoreactive T-cell effectors. On the other hand, we also focus on lipid mediators biosynthesized from omega-3 and omega-6 polyunsaturated fatty-acids in inflammatory exudates that promote the resolution phase of acute inflammation by regulating leucocyte influx to and efflux from local inflamed sites. Both anti-inflammatory neuropeptides and pro-resolving lipid mediators have shown therapeutic potential for a variety of inflammatory and autoimmune disorders and could be used as biotemplates for the development of novel pharmacologic agents.

Circulating adrenomedullin levels in ankylosing spondylitis and Familial Mediterranean Fever

INTRODUCTION

Adrenomedullin (AM) is a 52-amino acid peptide with vasorelaxant properties. Apart from its roles on vascular tonus, AM can also contribute to inflammatory events. Plasma AM levels were elevated in connective tissue diseases and vasculitic disorders. Ankylosing spondylitis (AS) is a chronic inflammatory disease of the spine initiating in the sacroiliac joints. Familial Mediterranean Fever (FMF) is a hereditary disorder characterized by self-limiting acute attacks of fever and the presence of sustained subclinical inflammation in the attack-free periods. In this study, we investigated plasma AM levels in patients with AS and patients with FMF.

METHODS

Twenty AS patients with active disease manifestations (mean age: 41.6+/-10.9 years, female/male: 7/13), 28 FMF patients with acute attack (mean age: 27.4+/-10.7 years, female/male: 17/11), and 26 healthy controls (mean age: 39.9+/-5.5 years, female/male: 16/10) were enrolled in this study. AM levels were also measured in 11 FMF patients 2 months after the cessation of their attacks. AM levels of those 11 patients during their FMF attacks and attack-free periods were also compared.

RESULTS

Median plasma AM levels were 23.86 (17.24-40.09) pmol/mL, 27.33 (17.24-38.52) pmol/mL, and 26.11 (17.05-37.42) pmol/mL in AS patients, FMF patients with acute attack, and healthy controls, respectively (p>0.05). AM levels were also similar in the attack-free periods of FMF patients [26.35 (24.35-34.14) pmol/mL]. There was no correlation between plasma AM levels and C-reactive protein, or between plasma AM levels and erythrocyte sedimentation rate.

CONCLUSIONS

AM does not seem to have any role in the pathogenesis of AS and FMF. Previous reports of elevated levels of AM in connective tissue disorders and vasculitic diseases are probably disease specific, and AM does not seem to be a common component of inflammatory rheumatic disorders.

Tuning inflammation with anti-inflammatory neuropeptides

The immune system is confronted with the daunting task of defending the organism against invading pathogens while at the same time remaining self-tolerant to the body's own constituents and preserving its integrity. The loss of immune tolerance stemming from an unbalance in pro-inflammatory factors versus anti-inflammatory cytokines, or of autoreactive/inflammatory T helper 1 cells versus regulatory/suppressive T cells, results in the breakdown of immune homeostasis and the subsidiary appearance of exacerbated inflammatory and autoimmune diseases. Some neuropeptides have been shown to have anti-inflammatory properties and to participate in maintaining immune tolerance. Here the authors examine the most recent developments in this field and highlight the effectiveness of using neuropeptides in treating several inflammatory and autoimmune disorders.

Adrenomedullin protects from experimental arthritis by down-regulating inflammation and Th1 response and inducing regulatory T cells

Rheumatoid arthritis is a chronic autoimmune disease of unknown etiology characterized by chronic inflammation in the joints and subsequent destruction of the cartilage and bone. The present study proposes a new strategy for the treatment of arthritis: the administration of the immunomodulatory neuropeptide adrenomedullin. Treatment with adrenomedullin significantly reduced incidence and severity of collagen-induced arthritis, an experimental model of rheumatoid arthritis, completely abrogating joint swelling and destruction of cartilage and bone. The therapeutic effect of adrenomedullin was associated with a striking reduction of the two deleterious components of the disease, ie, the Th1-driven autoimmune and inflammatory responses. Adrenomedullin also induced the generation and/or activation of efficient CD4+ CD25+ regulatory T cells in arthritis with capacity to suppress autoreactive response and restore immune tolerance, which could play a pivotal role in the therapeutic effect of adrenomedullin on experimental arthritis contributing to the restoration of immune tolerance.

A critical role for adrenomedullin-calcitonin receptor-like receptor in regulating rheumatoid fibroblast-like synoviocyte apoptosis

Rheumatoid arthritis (RA) is characterized by fibroblast-like synoviocyte (FLS) hyperplasia, which is partly ascribable to decreased apoptosis. In this study, we show that adrenomedullin (ADM), an antiapoptotic peptide, is constitutively secreted in larger amounts by FLS from joints with RA (RA-FLS) than with osteoarthritis (OA-FLS). ADM secretion was regulated by TNF-alpha. Peptidylglycine alpha-amidating monooxygenase, the ADM-processing enzyme, was expressed at the mRNA level by both RA-FLS and OA-FLS. Constituents of the ADM heterodimeric receptor calcitonin receptor-like receptor (CRLR)/receptor activity-modifying protein (RAMP)-2 were up-regulated at the mRNA and protein levels in cultured RA-FLS compared with OA-FLS. ADM induced rapid intracellular cAMP production in FLS and reduced caspase-3 activity, DNA fragmentation, and chromatin condensation in RA-FLS exposed to apoptotic conditions, indicating that CRLR/RAMP-2 was fully functional. ADM-induced cAMP production was less marked in OA-FLS than in RA-FLS, suggesting differences in receptor regulation and expression. ADM dose-dependently inhibited RA-FLS apoptosis, and this effect was reversed by the 22-52 ADM antagonist peptide. ADM inhibited RA-FLS apoptosis triggered by extrinsic and intrinsic pathways. Our data suggest that ADM may prevent or reduce RA-FLS apoptosis, via up-regulation of its functional receptor CRLR/RAMP-2. Regulation of ADM secretion and/or CRLR/RAMP-2 activation may constitute new treatment strategies for RA.

Production of adrenomedullin from synovial cells in rheumatoid arthritis patients

It was recently reported that plasma levels of adrenomedullin (AM), identified as a vasorelaxant peptide, are significantly higher in rheumatoid arthritis (RA) patients than in osteoarthritis (OA) patients. The objective of the present study was to elucidate AM production in synovial cells from patients with RA. Adrenomedullin mRNA was detected in cultured synovial cells from RA patients by reverse transcription polymerase chain reaction (RT-PCR). Immunohistochemical analysis demonstrated the presence of AM in synovial cells from RA patients. In addition, we investigated AM levels in knee joint fluids from RA and OA patients. Those from RA patients were elevated approximately threefold over those of OA patients. In this study, we demonstrated for the first time AM expression in synovial cells from RA patients and high levels of AM production in RA joint fluid.

A comparative study of the ability of calcitonin gene-related peptide and adrenomedullin(13 - 52) to modulate microvascular but not thermal hyperalgesia responses

Calcitonin gene-related peptide (CGRP), a neuropeptide, is a potent vasodilator. Adrenomedullin (ADM) is suggested to be produced by vascular cells in inflamed tissue. ADM shares some structural homology with CGRP. We have compared the ability of CGRP and ADM to modulate microvascular and thermal hyperalgesic responses in rat skin. Vasodilator activity was assessed by laser Doppler flowmetry, inflammatory oedema by the extravascular accumulation of intravenously-injected labelled albumin, and neutrophil accumulation by tissue myeloperoxidase, in dorsal skin. Hyperalgesia was assessed by a thermal hyperalgesimeter in paw skin. ADM (10-300 pmol) was 3 fold less potent than CGRP (3-100 pmol) as a direct vasodilator. CGRP (30 pmol) potentiated oedema formation induced by mediators of increased microvascular permeability, as expected (P<0.01). However, ADM (30-100 pmol) was without a potentiating effect, although ADM (300 pmol) was effective (P<0.01). By comparison ADM (100 pmol) potentiated neutrophil accumulation induced by interleukin-1beta (P<0.05), whereas CGRP (30 pmol) did not. No thermal hyperalgesia was observed to either CGRP or ADM, when given as single or repeated treatments. Thus despite a dilator activity neither CGRP nor ADM appears to mediate hyperalgesic activity in the periphery. However ADM, like CGRP, has the ability to potentiate inflammatory oedema formation and, in addition, ADM can potentiate neutrophil accumulation. ADM may, as suggested for CGRP, act as a modulator of the vascular phases of inflammation. The property of the two compounds of evoking differential microvascular responses and neutrophil accumulation may be due to differing mechanisms of action.