Serum amyloid A protein concentration in progressive systemic sclerosis (scleroderma)

Serum Amyloid A in Inflammatory Rheumatic Diseases: A Compendious Review of a Renowned Biomarker

Serum amyloid A (SAA) is an acute phase protein with a significant importance for patients with inflammatory rheumatic diseases (IRD). The central role of SAA in pathogenesis of IRD has been confirmed by recent discoveries, including its involvement in the activation of the inflammasome cascade and recruitment of interleukin 17 producing T helper cells. Clinical utility of SAA in IRD was originally evaluated nearly half a century ago. From the first findings, it was clear that SAA could be used for evaluating disease severity and monitoring disease activity in patients with rheumatoid arthritis and secondary amyloidosis. However, cost-effective and more easily applicable markers, such as C-reactive protein (CRP) and erythrocyte sedimentation rate (ESR), overwhelmed its use in clinical practice. In the light of emerging evidences, SAA has been discerned as a more sensitive biomarker in a wide spectrum of IRD, especially in case of subclinical inflammation. Furthermore, a growing number of studies are confirming the advantages of SAA over many other biomarkers in predicting and monitoring response to biological immunotherapy in IRD patients. Arising scientific discoveries regarding the role of SAA, as well as delineating SAA and its isoforms as the most sensitive biomarkers in various IRD by recently developing proteomic techniques are encouraging the revival of its clinical use. Finally, the most recent findings have shown that SAA is a biomarker of severe Coronavirus disease 2019 (COVID-19). The aim of this review is to discuss the SAA-involving immune system network with emphasis on mechanisms relevant for IRD, as well as usefulness of SAA as a biomarker in various IRD. Therefore, over a hundred original papers were collected through an extensive PubMed and Scopus databases search. These recently arising insights will hopefully lead to a better management of IRD patients and might even inspire the development of new therapeutic strategies with SAA as a target.

Toll-like receptors in mediating pathogenesis in systemic sclerosis

Toll-like receptors (TLRs) are evolutionarily conserved receptors essential for the host defence against pathogens. Both immune and non-immune cells can express TLRs, although at different levels. Systemic sclerosis (SSc) is a chronic disease in which autoimmunity, dysregulated profibrotic mediator release and activation of fibroblasts lead to dysregulated collagen deposition and fibrosis. There is now increasing knowledge that the innate immune system and, in particular, TLRs take a part in SSc pathogenesis. The list of endogenous ligands that can stimulate TLRs in SSc is growing: these ligands represent specific danger-associated molecular patterns (DAMPs), involved either in the initiation or the perpetuation of inflammation, and in the release of factors that sustain the fibrotic process or directly stimulate the cells that produce collagen and the endothelial cells. This review reports evidences concerning TLR signalling involvement in SSc. We report the new DAMPs, as well as the TLR-linked pathways involved in disease, with emphasis on type I interferon signature in SSc, the role of plasmacytoid dendritic cells (pDCs) and platelets. The dissection of the contribution of all these pathways to disease, and their correlation with the disease status, as well as their values as prognostic tools, can help to plan timely intervention and design new drugs for more appropriate therapeutic strategies.

Serum amyloid A: A potential biomarker of lung disorders

Serum amyloid A is an acute-phase protein with multiple immunological functions. Serum amyloid A is involved in lipid metabolism, inflammatory reactions, granuloma formation, and cancerogenesis. Additionally, serum amyloid A is involved in the pathogenesis of different autoimmune lung diseases. The levels of serum amyloid A has been evaluated in biological fluids of patients with different lung diseases, including autoimmune disorders, chronic obstructive pulmonary diseases, obstructive sleep apnea syndrome, sarcoidosis, asthma, lung cancer, and other lung disorders, such as idiopathic pulmonary fibrosis, tuberculosis, radiation pneumonitis, and cystic fibrosis. This review focuses on the cellular and molecular interactions of serum amyloid A in different lung diseases and suggests this acute-phase protein as a prognostic marker.

High acute phase protein levels correlate with pulmonary and skin involvement in patients with diffuse systemic sclerosis

Objective

This study was performed to evaluate the serum amyloid A (SAA) and C-reactive protein (CRP) levels in patients with diffuse systemic sclerosis (dSSc) in relation to a control group, disease duration, and skin and pulmonary involvement.

Methods

This case-control study included 18 patients with early dSSc, 15 patients with late dSSc, and 15 healthy controls. The SAA and CRP levels, modified Rodnan skin score (mRSS), and diffusing capacity of the lungs for carbon monoxide (DLCO) were determined in all patients.

Results

The SAA and CRP levels were significantly higher in patients with early and late dSSc than in healthy controls. The frequency of detection of elevated SAA and CRP levels was approximately 66% and 85%, respectively. A significant correlation was found between the SAA and CRP levels in patients with dSSc. The SAA and CRP levels were inversely correlated with DLCO. The CRP level was positively correlated with the mRSS.

Conclusions

High SAA and CRP levels could serve as biomarkers for pulmonary involvement. The serum CRP level accurately reflects the extension of skin thickening in patients with dSSc.

Serum amyloid A is a marker for pulmonary involvement in systemic sclerosis

Inflammation in systemic sclerosis (SSc) is a prominent, but incompletely characterized feature in early stages of the disease. The goal of these studies was to determine the circulating levels, clinical correlates and biological effects of the acute phase protein serum amyloid A (SAA), a marker of inflammation, in patients with SSc. Circulating levels of SAA were determined by multiplex assays in serum from 129 SSc patients and 98 healthy controls. Correlations between SAA levels and clinical and laboratory features of disease were analyzed. The effects of SAA on human pulmonary fibroblasts were studied ex vivo. Elevated levels of SAA were found in 25% of SSc patients, with the highest levels in those with early-stage disease and diffuse cutaneous involvement. Significant negative correlations of SAA were found with forced vital capacity and diffusion capacity for carbon monoxide. Patients with elevated SAA had greater dyspnea and more frequent interstitial lung disease, and had worse scores on patient-reported outcome measures. Incubation with recombinant SAA induced dose-dependent stimulation of IL-6 and IL-8 in normal lung fibroblasts in culture. Serum levels of the inflammatory marker SAA are elevated in patients with early diffuse cutaneous SSc, and correlate with pulmonary involvement. In lung fibroblasts, SAA acts as a direct stimulus for increased cytokine production. These findings suggest that systemic inflammation in SSc may be linked to lung involvement and SAA could serve as a potential biomarker for this complication.

Serum amyloid A induces interleukin-6 in dermal fibroblasts via Toll-like receptor 2, interleukin-1 receptor-associated kinase 4 and nuclear factor-κB

Systemic sclerosis is an autoimmune idiopathic connective tissue disease, characterized by vasculopathy, inflammation and fibrosis. There appears to be a link between inflammation and fibrosis, although the exact nature of the relationship is unknown. Serum amyloid A (SAA) is an acute-phase protein that is elevated up to 1000-fold in times of infection or inflammation. This acute-phase reactant, as well as being a marker of inflammation, may initiate signals in a cytokine-like manner, possibly through toll-like receptors (TLRs) promoting inflammation. This study addressed the role of SAA in initiating interleukin-6 (IL-6) production in dermal fibroblasts and the role of TLR2 in this system. We show that SAA induces IL-6 secretion in healthy dermal fibroblasts and that blockade of TLR2 with a neutralizing antibody to TLR2 or specific small interfering RNA attenuated the SAA-induced IL-6 secretion and that this was also mediated through the TLR adaptor protein IL-1 receptor-associated kinase 4. The effect is nuclear factor-κB-mediated because blockade of nuclear factor-κB reduced the induction. We also demonstrate that dermal fibroblasts express TLR2; this is functional and over-expressed in the fibroblasts of patients with systemic sclerosis. Taken together these data suggest that SAA is a danger signal that initiates IL-6 signalling in systemic sclerosis via enhanced TLR2 signalling.

Proteome analysis of biological fluids from autoimmune-rheumatological disorders

Autoimmune-rheumatological diseases are worldwide distributed disorders and represent a complex array of illnesses characterized by autoreactivity (reactivity against self-antigens) of T-B lymphocytes and by the synthesis of autoantibodies crucial for diagnosis (biomarkers). Yet, the effects of the autoimmune chronic inflammation on the infiltrated tissues and organs generally lead to profound tissue and organ damage with loss of function (i.e., lung, kidney, joints, exocrine glands). Although progresses have been made on the knowledge of these disorders, much still remains to be investigated on their pathogenesis and identification of new biomarkers useful in clinical practice. The rationale of using proteomics in autoimmune-rheumatological diseases has been the unmet need to collect, from biological fluids that are easily obtainable, a summary of the final biochemical events that represent the effects of the interplay between immune cells, mesenchymal cells and endothelial cells. Proteomic analysis of these fluids shows encouraging results and in this review, we addressed four major autoimmune-rheumatological diseases investigated through proteomic techniques and provide evidence-based data on the highlights obtained in systemic sclerosis, primary and secondary Sjogren's syndrome, systemic lupus erythematosus and rheumatoid arthritis.

Comparative proteomic analysis of serum from patients with systemic sclerosis and sclerodermatous GVHD. Evidence of defective function of factor H

Background

Systemic sclerosis (SSc) is an autoimmune disease characterized by immunological and vascular abnormalities. Until now, the cause of SSc remains unclear. Sclerodermatous graft-versus-host disease (ScGVHD) is one of the most severe complications following bone marrow transplantation (BMT) for haematological disorders. Since the first cases, the similarity of ScGVHD to SSc has been reported. However, both diseases could have different etiopathogeneses. The objective of this study was to identify new serum biomarkers involved in SSc and ScGVHD.

Methodology

Serum was obtained from patients with SSc and ScGVHD, patients without ScGVHD who received BMT for haematological disorders and healthy controls. Bi-dimensional electrophoresis (2D) was carried out to generate maps of serum proteins from patients and controls. The 2D maps underwent image analysis and differently expressed proteins were identified. Immuno-blot analysis and ELISA assay were used to validate the proteomic data. Hemolytic assay with sheep erythrocytes was performed to evaluate the capacity of Factor H (FH) to control complement activation on the cellular surface. FH binding to endothelial cells (ECs) was also analysed in order to assess possible dysfunctions of this protein.

Principal Findings

Fourteen differentially expressed proteins were identified. We detected pneumococcal antibody cross-reacting with double stranded DNA in serum of all bone marrow transplanted patients with ScGVHD. We documented higher levels of FH in serum of SSc and ScGVHD patients compared healthy controls and increased sheep erythrocytes lysis after incubation with serum of diffuse SSc patients. In addition, we observed that FH binding to ECs was reduced when we used serum from these patients.

Conclusions

The comparative proteomic analysis of serum from SSc and ScGVHD patients highlighted proteins involved in either promoting or maintaining an inflammatory state. We also found a defective function of Factor H, possibly associated with ECs damage.

Serum amyloid A (SAA): an acute phase protein and apolipoprotein

Serum amyloid A (SAA) proteins comprise a family of apolipoproteins coded for by at least three genes with allelic variation and a high degree of homology between species. The synthesis of certain members of the family is greatly increased in inflammation. However, SAA is not often used as an acute-phase marker despite being at least as sensitive as C-reactive protein. SAA proteins can be considered as apolipoproteins since they associate with plasma lipoproteins mainly within the high density range, perhaps through amphipathic alpha-helical structure. It is not known why certain subjects expressing SAA develop secondary systemic amyloidosis. There is still no specific function attributed to SAA; however, a popular hypothesis suggests that SAA may modulate metabolism of high density lipoproteins (HDL). This may impede the protective function of HDL against the development of atherosclerosis. The potential significance of the association between SAA and lipoproteins needs further evaluation.

Bronchioloalveolar carcinoma and generalized amyloidosis complicating progressive systemic sclerosis

We report a patient with progressive systemic sclerosis in whom an autopsy, performed 13 years after diagnosis, revealed the presence of bronchioloalveolar carcinoma and of generalized amyloidosis. Characterization of the amyloid fibril protein suggested an immunoglobulin light chain (AL) origin.

Acute phase reactants in predicting disease outcome

From the studies which are reviewed above, it is generally apparent that in terms of the acute phase response, the initial findings in early inflammatory arthritis (particularly rheumatoid arthritis, with which the majority of such studies are concerned) have little predictive value for either the functional outcome or mortality. The wide interindividual variability in these measurements is also likely to limit their clinical usefulness as predictors of disease outcome. The trend in certain acute phase reactants may be more useful in indicating disease activity, although the number of satisfactory studies in this area is very limited.