Decreased levels of soluble receptor for advanced glycation end products in patients with primary Sjögren's syndrome

Role of Advanced Glycation End Products as New Biomarkers in Systemic Lupus Erythematosus

Advanced glycation end-products (AGEs) may play a relevant role as inducers in the chronic inflammatory pathway present in immune-mediated diseases, such as systemic lupus erythematosus (SLE). AGEs concentrations have been associated, with discrepant results to date, with some parameters such as disease activity or accrual damage, suggesting their potential usefulness as biomarkers of the disease. Our objectives are to confirm differences in AGEs levels measured by cutaneous autofluorescence between SLE patients and healthy controls (HC) and to study their correlation with various disease parameters. Cross-sectional study, where AGEs levels were measured by skin autofluorescence, and SLE patients' data were compared with those of sex- and age-matched HC in a 1:3 proportion through a multiple linear regression model. Associations of AGEs levels with demographic and clinical data were analyzed through ANOVA tests. Both analyses were adjusted for confounders. AGEs levels in SLE patients were significantly higher than in HC (p < 0.001). We found statistically significant positive associations with SLE disease activity index (SLEDAI) and damage index (SDI), physician and patient global assessment, C-reactive protein, leukocyturia, complement C4, IL-6 and oral ulcers. We also found a negative statistically significant association with current positivity of anti-nuclear and anti-Ro60 antibodies. AGEs seem to have a contribution in LES pathophysiology, being associated with activity and damage and having a role as a new management and prognosis biomarker in this disease. The association with specific antibodies and disease manifestations may indicate a specific clinical phenotype related to higher or lower AGEs levels.

The Potential Influence of Advanced Glycation End Products and (s)RAGE in Rheumatic Diseases

Advanced glycation end products (AGEs) are a class of compounds formed by nonenzymatic interactions between reducing sugars and proteins, lipids, or nucleic acids. AGEs can alter the protein structure and activate one of their receptors, specifically the receptor for advanced glycation end products (RAGE). These phenomena impair the functions of cells, extracellular matrix, and tissues. RAGE is expressed by a variety of cells and has been linked to chronic inflammatory autoimmune disorders such as rheumatoid arthritis, systemic lupus erythematosus, and Sjögren's syndrome. The soluble (s)RAGE cleavage product is a positively charged 48-kDa cleavage product that retains the ligand binding site but loses the transmembrane and signaling domains. By acting as a decoy, this soluble receptor inhibits the pro-inflammatory processes mediated by RAGE and its ligands. In the present review, we will give an overview of the role of AGEs, sRAGE, and RAGE polymorphisms in several rheumatic diseases. AGE overproduction may play a role in the pathogenesis and is linked to accelerated atherosclerosis. Low serum sRAGE concentrations are linked to an increased cardiovascular risk profile and a poor prognosis. Some RAGE polymorphisms may be associated with increased disease susceptibility. Finally, sRAGE levels can be used to track disease progression.

Sialylated Immunoglobulins for the Treatment of Immuno-Inflammatory Diseases

Immunoglobulins are the potent effector proteins of the humoral immune response. In the course of evolution, immunoglobulins have formed extremely diverse types of molecular structures with antigen-recognizing, antigen-binding, and effector functions embedded in a single molecule. Polysaccharide moiety of immunoglobulins plays the essential role in immunoglobulin functioning. There is growing evidence that the carbohydrate composition of immunoglobulin-linked glycans, and especially their terminal sialic acid residues, provide a key effect on the effector functions of immunoglobulins. Possibly, sialylation of Fc glycan is a common mechanism of IgG anti-inflammatory action in vivo. Thus, the post-translational modification (glycosylation) of immunoglobulins opens up significant possibilities in the diagnosis of both immunological and inflammatory disorders and in their therapies. This review is focused on the analysis of glycosylation of immunoglobulins, which can be a promising addition to improve existing strategies for the diagnosis and treatment of various immuno-inflammatory diseases.

Relationship between serum-soluble receptor for advanced glycation end products (sRAGE) and disease activity in rheumatoid arthritis patients

Objective: Considering the important role of serum soluble receptor for advanced glycation end product (sRAGE/RAGE)-ligand system in rheumatoid arthritis (RA), this study aimed to evaluate serum sRAGE levels in RA patients compared to healthy subjects and to assess whether there is an association between sRAGE levels and disease characteristics in RA.Methods: In this cross-sectional study, 60 RA patients according to the ACR/EULAR 2010 criteria and 30 age- and sex-matched healthy controls were included. In patients, clinical examination was performed and disease activity score 28 (DAS-28) measure of disease activity was assessed. Serum sRAGE level was measured using ELISA kit.Results: The mean ± SD age of patients and controls was 54.86 ± 11.65 and 50.71 ± 3.72 years, respectively). Serum sRAGE level was significantly higher in RA patients (median [25th and 75th percentiles], 1000.3 [792.00, 1486.8]) compared to healthy controls (median [25th and 75th percentiles], 293.25 [220.35, 364.24]) (p < .001). There was significant difference in serum sRAGE level according to the activity of disease (p < .001). There were significant positive correlations between serum sRAGE level with disease activity (r = 0.67, p < .001), ESR (r = 0.411, p = .001) and CRP (r = 0.273, p = .035). There were no significant correlations between serum sRAGE level with demographic characteristics as well as biochemical measurements including serum creatinine, BUN, RF, and Anti-CCP (p > .05).Conclusions: Our study revealed higher serum sRAGE levels in RA patients compared to healthy controls, which correlated positively with disease activity.

Association of High Mobility Group Box Chromosomal Protein 1 and Receptor for Advanced Glycation End Products Serum Concentrations With Extraglandular Involvement and Disease Activity in Sjögren's Syndrome

OBJECTIVE

To assess serum levels of high mobility group box chromosomal protein 1 (HMGB-1) and the soluble receptor for advanced glycation end products (sRAGE) in patients with Sjögren's syndrome (SS) and explore correlations with disease activity.

METHODS

Thirty-nine patients with SS and 21 healthy controls were included in this cross-sectional study. Clinical and laboratory values were obtained from all patients. Disease activity was assessed using the European League Against Rheumatism SS Disease Activity Index (ESSDAI). Serum samples were collected and HMGB-1 and sRAGE levels were measured using enzyme-linked immunosorbent assay (ELISA), and HMGB-1 concentrations were semiquantified by Western blotting.

RESULTS

In ELISA, HMGB-1 serum levels did not differ between healthy controls and patients with SS (P = 0.783). When measured by semiquantitative Western blotting, HMGB-1 levels were increased in patients with SS compared to healthy controls (P = 0.012). HMGB-1 serum levels detected by Western blotting were higher in patients with extraglandular manifestations (P = 0.003) and were correlated with ESSDAI disease activity (r = 0.544, P < 0.0001). Furthermore, sRAGE was elevated in the sera of patients with SS (P = 0.003) compared to healthy controls and was also correlated with the ESSDAI (r = 0.545, P = 0.002).

CONCLUSION

Serum levels of total HMGB-1 and sRAGE were elevated in patients with SS compared to healthy controls and correlated with disease activity as measured by the ESSDAI. Patients with extraglandular involvement had high serum levels of HMGB-1.

Alterations in the Salivary Proteome and N-Glycome of Sjögren's Syndrome Patients

We used isobaric mass tagging (iTRAQ) and lectin affinity capture mass spectrometry (MS)-based workflows for global analyses of parotid saliva (PS) and whole saliva (WS) samples obtained from patients diagnosed with primary Sjögren's Syndrome (pSS) who were enrolled in the Sjögren's International Collaborative Clinical Alliance (SICCA) as compared with two control groups. The iTRAQ analyses revealed up- and down-regulation of numerous proteins that could be involved in the disease process (e.g., histones) or attempts to mitigate the ensuing damage (e.g., bactericidal/permeability increasing fold containing family (BPIF) members). An immunoblot approach applied to independent sample sets confirmed the pSS associated up-regulation of β2-microglobulin (in PS) and down-regulation of carbonic anhydrase VI (in WS) and BPIFB2 (in PS). Beyond the proteome, we profiled the N-glycosites of pSS and control samples. They were enriched for glycopeptides using lectins Aleuria aurantia and wheat germ agglutinin, which recognize fucose and sialic acid/N-acetyl glucosamine, respectively. MS analyses showed that pSS is associated with increased N-glycosylation of numerous salivary glycoproteins in PS and WS. The observed alterations of the salivary proteome and N-glycome could be used as pSS biomarkers enabling easier and earlier detection of this syndrome while lending potential new insights into the disease process.

Follicular fluid soluble receptor for advanced glycation endproducts (sRAGE): a potential protective role in polycystic ovary syndrome

PURPOSE

To explore the relationships between the soluble receptor for advanced glycation endproducts (sRAGE) and the outcome parameters following in vitro fertilization-embryo transfer (IVF-ET) in patients with polycystic ovary syndrome (PCOS) and investigate the protective effect of sRAGE in PCOS development regarding inflammation.

METHODS

We conducted a prospective analysis of a subsample of 74 participants from the Reproductive Medical Center of the First Affiliated Hospital of Zhengzhou University. We quantified sRAGE, vascular endothelial growth factor (VEGF), tumor necrosis factor (TNF-α), interleukelin-6 (IL-6), and C-reactive protein (CPR) protein levels in the follicular fluid from 39 PCOS and 35 non-PCOS reproductive-age women. sRAGE and VEGF, TNF-α, IL-6, and CRP in follicular fluid aspirated without blood were measured by ELISA.

RESULTS

sRAGE concentrations in the follicular fluid were significantly lower in the PCOS group compared to those in the control group, while VEGF, TNF-α, IL-6, and CRP concentrations were significantly higher in the PCOS group than in the control group (P < 0.05). sRAGE was significantly, inversely correlated with the total dose of gonadotropin (Gn) in the PCOS group undergoing IVF treatment (r = -0.451, P = 0.004). After adjusting for age and Gn dose (in international units used per cycle), sRAGE protein levels in the follicular fluid were significantly, inversely related to VEGF (r = -0.378, P = 0.018), TNF-α (r = -0.450, P = 0.004), IL-6 (r = -0.455, P = 0.004), and CRP (r = -0.375, P = 0.019).

CONCLUSION

sRAGE in the follicular fluid might exert a protective effect against the inflammatory action of PCOS development.

The plasma level of soluble receptor for advanced glycation end products is decreased in patients with systemic lupus erythematosus

In recent years, the role of high mobility group box-1 (HMGB1) protein and its receptors in autoimmune diseases has received increasing attention. It has been documented that HMGB1 is associated with disease activity in patients with systemic lupus erythematosus (SLE). This study was undertaken to determine the potential role of receptor for advanced glycation end products (RAGE), one receptor for HMGB1, in the pathogenesis of SLE. Plasma levels of soluble RAGE (sRAGE) from 105 patients with clinical diagnosis of SLE and 43 healthy controls were determined by ELISA. Associations between sRAGE levels and clinical, laboratory characteristics were assessed. The data showed that plasma levels of sRAGE in patients with SLE were significantly lower than those in healthy controls (HC) (P = 0.003). Plasma sRAGE in patients receiving short-period treatment showed an immediate decrease compared with the untreated patients (P = 0.023). In contrast, plasma sRAGE in patients receiving long-period treatment were significantly increased compared to those with short-period treatment (P = 0.000) and comparable with those in HC (P = 0.305). The significant decreased levels of sRAGE in patients with SLE suggest the potential association of RAGE signalling and SLE clinical pathology, whereas, long-period antilupus treatment may counteract the decreased sRAGE levels in patients with SLE.

Modulation of RAGE isoforms expression in the brain and plasma of rats exposed to transient focal cerebral ischemia

Activation of RAGE (receptor for advanced glycation endproducts) and of its subtypes may play a role in neuronal damage and neuroinflammation associated with brain ischemia, though the underlying mechanisms remain unclear. In this study, we have examined by Western blotting the expression of RAGE isoforms in the cerebral cortex and striatum of Wistar rats subjected to transient (1 or 2 h) middle cerebral artery occlusion (tMCAo). The findings show that the full-length RAGE (~50 kDa) and its isoforms in the 26-43 kDa range are significantly decreased in the ischemic cortex, but not in the striatum, after 1 and 2 h tMCAo when compared to the sham group. By contrast, in the striatum, ischemia-reperfusion injury caused a significant increase of full-length RAGE and its isoforms in the 72-100 kDa range. We also investigated the soluble form of RAGE, which was significantly decreased in the plasma of rats subjected to transient or permanent MCAo. In conclusion, the present data demonstrate that regional brain expression of RAGE is differentially affected by tMCAo in rat. These modifications are accompanied by a decrease in the plasma levels of soluble RAGE, thereby suggesting a potential role for soluble RAGE as a peripheral biomarker of focal ischemia.

Soluble receptor for advanced glycation endproducts is decreased in patients with juvenile idiopathic arthritis (ERA category) and inversely correlates with disease activity and S100A12 levels

OBJECTIVE

Membrane-bound receptor for advanced glycation endproducts (mRAGE) is overexpressed in response to increasing concentrations of its ligand (e.g., S100A12) and triggers an inflammatory immune response. In contrast, soluble RAGE (sRAGE) acts as a decoy receptor and downmodulates inflammation. Decreased sRAGE levels are associated with autoimmune diseases; however, limited data are available in juvenile idiopathic arthritis (JIA). We studied sRAGE levels in patients with JIA [enthesitis-related arthritis (ERA) category].

METHODS

sRAGE levels were estimated in the serum of patients with ERA JIA (n = 101), systemic-onset JIA and polyarticular JIA (n = 10 each), and healthy controls (n = 45). Synovial fluid (SF) sRAGE was measured in patients with ERA, rheumatoid arthritis, reactive arthritis, and osteoarthritis (n = 10). Levels of S100A12 were also measured. Twenty-four patients with ERA were followed for 4 months. Disease activity was assessed by swollen joint count (SJC), tender joint count (TJC), and erythrocyte sedimentation rate (ESR). All levels are expressed as median (range).

RESULTS

The serum sRAGE (pg/ml) level was significantly lower in patients compared to healthy controls [515 (64-1887) vs 1542 (627-3159); p < 0.0001]. In paired samples, SF had lower levels compared to corresponding plasma level [102 (51-799) vs 481 (134-1006); p < 0.0001]. The level of S100A12 (ng/ml) was higher in SF (1042; 573-1415) than serum (638; 208-779). Serum sRAGE correlated negatively with S100A12 levels (r = -0.474; p < 0.01.), ESR (r = -0.306; p < 0.01), and SJC (r = -0.237; p < 0.05), but not with TJC (r = -0.134; p = NS). The levels of sRAGE remained stable over time in patients with stable disease.

CONCLUSION

Levels of sRAGE are reduced in patients with ERA and correlate negatively with disease activity and S100A12 levels. sRAGE may be a modulator of inflammation in these patients.

Concentrations of receptor for advanced glycation end products, VEGF and CML in plasma, follicular fluid, and peritoneal fluid in women with and without endometriosis

The etiology and pathogenesis of endometriosis is largely unknown. It has been reported that advanced glycation end products-receptor for advanced glycation end products regulation relates to oxidative stress, inflammatory reaction, apoptosis, and angiogenesis through vascular endothelial growth factor activation. The purpose of this study was to examine whether advanced glycation end products-receptor for advanced glycation end products regulation contributes to the pathogenesis of endometriosis. Plasma, follicular, and peritoneal fluid samples were collected from women with or without endometriosis, and soluble receptor for advanced glycation end products, vascular endothelial growth factor and carboxymethyl lysine levels were measured by enzyme-linked immunosorbent assay. Vascular endothelial growth factor and soluble receptor for advanced glycation end products concentrations were similar in plasma; however, their concentrations in follicular fluid were significantly increased in endometriosis patients (soluble receptor for advanced glycation end products was 132 + 31 pg/mg of protein vs. 105 + 27 pg/mg; vascular endothelial growth factor was 70 + 3 pg/mg vs. 49 + 18 pg/mg, expressed as the mean + standard deviation). Increased soluble receptor for advanced glycation end products and vascular endothelial growth factor levels in a local environment suggest that the advanced glycation end products-receptor for advanced glycation end products may contribute to the pathogenesis of endometriosis.

Soluble receptor for advanced glycation end products (sRAGE) in plasma and synovial fluid is inversely associated with disease severity of knee osteoarthritis

OBJECTIVES

The aim of this study was to measure soluble receptor for advanced glycation end products (sRAGE) in plasma and synovial fluid of knee osteoarthritis (OA) patients and to determine the correlation between sRAGE levels and disease severity.

DESIGN AND METHODS

Thirty-six OA patients and 15 healthy controls were enrolled in this study. OA grading was performed using the Kellgren-Lawrence classification. sRAGE levels in plasma and synovial fluid were analyzed by enzyme-linked immunosorbent assay.

RESULTS

Plasma sRAGE levels were significantly lower in OA patients than in healthy controls (P=0.01). sRAGE levels in plasma were remarkably higher with regard to paired synovial fluid (P=0.001). Additionally, sRAGE concentrations in plasma and synovial fluid showed significant inverse correlation with disease severity (r=-0.65, P<0.001 and r=-0.55, P=0.001, respectively). Further analysis showed that there was a strong positive correlation between plasma and synovial sRAGE concentration (r=0.81, P<0.001).

CONCLUSIONS

sRAGE levels were significantly lower in OA patients compared with controls, and sRAGE levels in plasma and synovial fluid also decreased significantly as the disease severity increased. Accordingly, sRAGE levels could be used as a biochemical marker for assessing the severity and progression of knee OA.

RAGE expression and NF-kappaB activation attenuated by extracellular domain of RAGE in human salivary gland cell line

The receptor for advanced-glycation-end-products (RAGE) has been implicated as a pro-inflammatory factor in chronic inflammatory conditions such as diabetes mellitus and rheumatoid arthritis. The aim of this study was to investigate the inhibitory effect of the soluble-RAGE (sRAGE), the extracellular domain of RAGE, on RAGE expression and NF-kappaB translocation in human-salivary gland-cell-lines (HSG). Cells were stimulated with agonist S100A4, fusion protein of RAGE encompassing the extracellular domain of RAGE (ex-RAGE), ex-RAGE followed by S100A4, or S100A4 followed by ex-RAGE. Our study indicates that RAGE expression was highest at 150 microg/microl of S100A4 and efficiently down-regulated by 1.8-fold (P < 0.05) when ex-RAGE was incubated prior to agonist S100A4. RAGE protein was also consistently down-regulated by 20-40% with pre-incubation of ex-RAGE. More importantly, nuclear translocation of p65 and p52 of NF-kappaB by S100A4 was inhibited in the presence of ex-RAGE, confirming anti-inflammatory function of ex-RAGE. In conclusion, ex-RAGE down-regulates RAGE expression and inhibits p65 and p52 activation in HSG, providing evidence that ex-RAGE functions as a "decoy" to RAGE-ligand interaction and thus potentially dampening inflammatory conditions.

Soluble receptor for advanced glycation end products: a new biomarker in diagnosis and prognosis of chronic inflammatory diseases

The formation of advanced glycation end products (AGEs) is a result of the non-enzymatic reaction between sugars and free amino groups of proteins. AGEs, through interacting with their specific receptor for AGEs (RAGE), result in activation of pro-inflammatory states and are involved in numerous pathologic situations. The soluble form of RAGE (sRAGE) is able to act as a decoy to avoid interaction of RAGE with its pro-inflammatory ligands (AGEs, HMGB1, S100 proteins). sRAGE levels have been found to be decreased in chronic inflammatory diseases including atherosclerosis, diabetes, renal failure and the aging process. The use of measuring circulating sRAGEs may prove to be a valuable vascular biomarker and in this review, we describe the implications of sRAGE in inflammation and propose that this molecule may represent a future therapeutic target in chronic inflammatory diseases.

RAGE: therapeutic target and biomarker of the inflammatory response--the evidence mounts

The RAGE binds multiple ligand families linked to hyperglycemia, aging, inflammation, neurodegeneration, and cancer. Activation of RAGE by its ligands stimulates diverse signaling cascades. The recent observation that the cytoplasmic domain of RAGE interacts with diaphanous or mDia-1 links RAGE signal transduction to cellular migration and activation of the Rho GTPases, cdc42 and rac-1. Pharmacological blockade of RAGE or genetic deletion of RAGE imparts significant protection in murine models of diabetes, inflammatory conditions, Alzheimer's disease, and tumors. Intriguingly, soluble forms of RAGE, including the splice variant-derived esRAGE, circulate in human plasma. Studies in human subjects suggest that sRAGE levels may be modulated by the diseases impacted by RAGE and its ligands. Thus, in addition to being a potential therapeutic target in chronic disease, monitoring of plasma sRAGE levels may provide a novel biomarker platform for tracking chronic inflammatory diseases, their severity, and response to therapeutic intervention.

The measurements of RAGE, VEGF, and AGEs in the plasma and follicular fluid of reproductive women: the influence of aging

OBJECTIVE

To examine the advanced glycation end products (AGEs), the soluble isoform of the receptor for AGEs (sRAGE), and vascular endothelial growth factor (VEGF) concentrations in plasma and follicular fluid (FF) from reproductive-age women.

DESIGN

Clinical preliminary study based on the regulations of the ethical committee at National Center for Child Health and Development (NCCHD).

SETTING

Women's health clinical office at NCCHD and Aska clinic.

PATIENT(S)

Reproductive-age women, young group (<35 yrs) and old group (>or=35 yrs), who agreed to let us use plasma or FF samples for the measurements of AGEs, sRAGE, and VEGF.

MAIN OUTCOME MEASURE(S)

Measurements of AGEs, sRAGE, and VEGF in plasma and FF by ELISA to examine the difference by aging and reproductive dysfunction.

RESULT(S)

The plasma concentration of sRAGE was significantly higher in the young group; VEGF in FF was significantly higher in the old group. sRAGE in FF showed a tendency of positive correlation with the number of oocytes. The plasma sRAGE concentration was significantly correlated positively with FF sRAGE and inversely with FF VEGF at the time of egg collection.

CONCLUSION(S)

The measurement results suggest a possibility that RAGE-VEGF regulation may be related to reproductive dysfunction in aging women, and that plasma sRAGE might be a biologic marker of reproductive condition.

Receptor for advanced glycation end products: its role in Alzheimer's disease and other neurological diseases

The receptor for advanced glycation end products (RAGE) has been demonstrated to play a central role in the pathogenic mechanisms of a growing number of important neurological diseases, including Alzheimer's disease (AD) and stroke. Two functional types of RAGE have been associated with neurological diseases: cell membrane-bound (full length) and soluble. In general, ligand binding to full-length RAGE initiates sustained cellular activation and receptor-dependent signaling resulting in inflammation and cellular stress, and is ultimately associated with increased RAGE expression. By comparison, soluble forms of RAGE, generated either by alternative splicing or by proteolysis, can reduce the severity of the consequence of ligand-membrane RAGE interactions by preventing ligands from binding to the full-length RAGE. This can inhibit the neurotoxic or proinflammatory responses involved in disease states. This article reviews the pathobiology of RAGE, with emphasis on soluble forms of RAGE, and discusses its relevance to AD and to other neurological diseases, as well as how manipulation of the different forms of RAGE is becoming a powerful therapeutic strategy.