Acute-serum amyloid A and A-SAA-derived peptides as formyl peptide receptor (FPR) 2 ligands.

Originally, it was thought that a single serum amyloid A (SAA) protein was involved in amyloid A amyloidosis, but in fact, SAA represents a four-membered family wherein SAA1 and SAA2 are acute phase proteins (A-SAA). SAA is highly conserved throughout evolution within a wide range of animal species suggestive of an important biological function. In fact, A-SAA has been linked to a number of divergent biological activities wherein a number of these functions are mediated via the G protein-coupled receptor (GPCR), formyl peptide receptor (FPR) 2. For instance, through the activation of FPR2, A-SAA has been described to regulate leukocyte activation, atherosclerosis, pathogen recognition, bone formation and cell survival. Moreover, A-SAA is subject to post-translational modification, primarily through proteolytic processing, generating a range of A-SAA-derived peptides. Although very little is known regarding the biological effect of A-SAA-derived peptides, they have been shown to promote neutrophil and monocyte migration through FPR2 activation via synergy with other GPCR ligands namely, the chemokines CXCL8 and CCL3, respectively. Within this review, we provide a detailed analysis of the FPR2-mediated functions of A-SAA. Moreover, we discuss the potential role of A-SAA-derived peptides as allosteric modulators of FPR2.

Nanofiber Wound Dressing Materials-A Comparative Study of Wound Healing on a Porcine Model.

BACKGROUND: Nanofiber wound dressings remain the domain of in vitro studies. The purpose of our study was to verify the benefits of chitosan (CTS) and polylactide (PLA)-based nanofiber wound dressings on a porcine model of a naturally contaminated standardized wound and compare them with the conventional dressings, i.e., gauze and Inadine. MATERIAL AND METHODS: The study group included 32 pigs randomized into four homogeneous groups according to the wound dressing type. Standardized wounds were created on their backs, and wound dressings were regularly changed. We evaluated difficulty of handling individual dressing materials and macroscopic appearance of the wounds. Wound swabs were taken for bacteriological examination. Blood samples were obtained to determine blood count values and serum levels of acute phase proteins (serum amyloid A, C-reactive protein, and haptoglobin). The crucial point of the study was histological analysis. Microscopic evaluation was focused on the defect depth and tissue reactions, including formation of the fibrin exudate with neutrophil granulocytes, the layer of granulation and cellular connective tissue, and the reepithelialization. Statistical analysis was performed by using SPSS software. The analysis was based on the Kruskal-Wallis H test and Mann-Whitney U test followed by Bonferroni correction. Significance was set at P < .05. RESULTS: Macroscopic examination did not show any difference in wound healing among the groups. However, evaluation of histological findings demonstrated that PLA-based nanofiber dressing accelerated the proliferative (P = .025) and reepithelialization (P < .001) healing phases, while chitosan-based nanofiber dressing potentiated and accelerated the inflammatory phase (P = .006). No statistically significant changes were observed in the blood count or acute inflammatory phase proteins during the trial. Different dynamics were noted in serum amyloid A values in the group treated with PLA-based nanofiber dressing (P = .006). CONCLUSION: Based on the microscopic examination, we have documented a positive effect of nanofiber wound dressings on acceleration of individual phases of the healing process. Nanofiber wound dressings have a potential to become in future part of the common wound care practice.

Elevated SAA1 promotes the development of insulin resistance in ovarian granulosa cells in polycystic ovary syndrome.

BACKGROUND: Insulin resistance (IR) contributes to ovarian dysfunctions in polycystic ovarian syndrome (PCOS) patients. Serum amyloid A1 (SAA1) is an acute phase protein produced primarily by the liver in response to inflammation. In addition to its role in inflammation, SAA1 may participate in IR development in peripheral tissues. Yet, expressional regulation of SAA1 in the ovary and its role in the pathogenesis of ovarian IR in PCOS remain elusive. METHODS: Follicular fluid, granulosa cells and peripheral venous blood were collected from PCOS and non-PCOS patients with and without IR to measure SAA1 abundance for analysis of its correlation with IR status. The effects of SAA1 on its own expression and insulin signaling pathway were investigated in cultured primary granulosa cells. RESULTS: Ovarian granulosa cells were capable of producing SAA1, which could be induced by SAA1 per se. Moreover, the abundance of SAA1 significantly increased in granulosa cells and follicular fluid in PCOS patients with IR. SAA1 treatment significantly attenuated insulin-stimulated membrane translocation of glucose transporter 4 and glucose uptake in granulosa cells through induction of phosphatase and tensin homolog deleted on chromosome 10 (PTEN) expression with subsequent inhibition of Akt phosphorylation. These effects of SAA1 could be blocked by inhibitors for toll-like receptors 2/4 (TLR 2/4) and nuclear factor kappa light chain enhancer of activated B (NF-κB). CONCLUSIONS: Human granulosa cells are capable of feedforward production of SAA1, which significantly increased in PCOS patients with IR. Excessive SAA1 reduces insulin sensitivity in granulosa cells via induction of PTEN and subsequent inhibition of Akt phosphorylation upon activation of TLR2/4 and NF-κB pathway. These findings highlight that elevation of SAA1 in the ovary promotes the development of IR in granulosa cells of PCOS patients.

Serum Amyloid A1 Induces Classically Activated Macrophages: A Role for Enhanced Fibril Formation.

AA amyloidosis belongs to the group of amyloid diseases which can follow chronic inflammatory conditions of various origin. The disease is characterized by the deposition of insoluble amyloid fibrils formed by serum amyloid A1 (SAA1) leading eventually to organ failure. Macrophages are intimately involved in the fibrillogenesis as well as in the clearance of amyloid fibrils. In vivo, macrophages may occur as classically (M1) or alternatively activated (M2) macrophages. We investigate here how SAA1 might affect the macrophage phenotype and function. Gene microarray analysis revealed upregulation of 64 M1-associated genes by SAA1. M1-like polarization was further confirmed by the expression of the M1-marker MARCO, activation of the NF-κB transcription factor, and secretion of the M1-cytokines TNF-α, IL-6, and MCP-1. Additionally, we demonstrate here that M1-polarized macrophages exhibit enhanced fibrillogenic activity towards SAA1. Based on our data, we propose reconsideration of the currently used cellular amyloidosis models towards an in vitro model employing M1-polarized macrophages. Furthermore, the data suggest macrophage repolarization as potential intervention strategy in AA amyloidosis.

Hepatocytes derived increased SAA1 promotes intrahepatic platelet aggregation and aggravates liver inflammation in NAFLD.

Non-alcoholic fatty liver disease (NAFLD) is the pathological manifestation of metabolic syndrome in liver. Its pathological changes may evolve from the initial simple steatosis to non-alcoholic steatohepatitis, liver fibrosis and even liver cancer. Numerous studies have proved that platelets play a vital role in liver disease and homeostasis. Particularly, anti-platelet therapy can reduce intrahepatic platelet aggregation and improve the inflammation of fatty liver. Previous study has also confirmed that SAA is a gene closely related to high-fat diet (HFD) induced obesity, and SAA1 can promote liver insulin resistance induced by Palmitate or HFD. Here, we found that SAA1 treated platelets presented increased sensitivity of platelet aggregation, enhanced activation and increased adhesion ability, and such function was partly dependent on Toll-Like Receptor (TLR) 2 signaling. In addition, blocking SAA1 expression in vivo not only inhibited platelet aggregation in the liver tissues of NAFLD mice, but also alleviated the inflammation of fatty liver. In conclusion, our findings identify that HFD-induced hepatic overexpressed SAA1 aggravates fatty liver inflammation by promoting intrahepatic platelet aggregation, these results also imply that SAA1 may serve as a potential target for ameliorating NAFLD.

Serum amyloid A-induced blood-brain barrier dysfunction associated with decreased claudin-5 expression in rat brain endothelial cells and its inhibition by high-density lipoprotein in vitro.

The blood-brain barrier (BBB) is the multicellular interface located between the peripheral circulation and the brain parenchyma. BBB dysfunction is reported in many CNS diseases, such cognitive impairment, depression, Alzheimer's disease (AD), and multiple sclerosis (MS). Emerging evidence indicates that liver-derived inflammatory mediators are upregulated in neurological diseases with BBB dysfunction. Serum amyloid A (SAA), an acute phase protein secreted by hepatocytes, could be a candidate inflammatory signaling molecule transmitted from the liver to the brain; however, its contribution to BBB dysfunction is poorly understood. The present study aimed to elucidate the involvement of SAA in BBB impairment in an in vitro BBB model using rat brain microvascular endothelial cells (RBECs). We demonstrated that Apo-SAA significantly decreased transendothelial electrical resistance (TEER) and increased sodium fluorescein (Na-F) permeability in RBEC monolayers. Apo-SAA also decreased claudin-5 expression levels in RBECs. Furthermore, the Apo-SAA-mediated impairment of the BBB with decreased claudin-5 expression was inhibited by the addition of a high-density lipoprotein (HDL) related to SAA in plasma. These findings suggest that HDL counteracts the effects of SAA on BBB function. Therefore, the functional imbalance between SAA and HDL may induce BBB impairment, thereby triggering development of neuroinflammation. SAA could be a significant endogenous mediator in the liver-to-brain inflammation axis.

Serum amyloid A inhibits astrocyte migration via activating p38 MAPK.

BACKGROUND: The accumulation of astrocytes around senile plaques is one of the pathological characteristics in Alzheimer's disease (AD). Serum amyloid A (SAA), known as a major acute-phase protein, colocalizes with senile plaques in AD patients. Here, we demonstrate the role of SAA in astrocyte migration. METHODS: The effects of SAA on astrocyte activation and accumulation around amyloid ß (Aß) deposits were detected in APP/PS1 transgenic mice mated with Saa3-/- mice. SAA expression, astrocyte activation, and colocalization with Aß deposits were evaluated in mice using immunofluorescence staining and/or Western blotting. The migration of primary cultures of mouse astrocytes and human glioma U251 cells was examined using Boyden chamber assay and scratch-would assay. The actin and microtubule networks, protrusion formation, and Golgi apparatus location in astrocytes were determined using scratch-would assay and immunofluorescence staining. RESULTS: Saa3 expression was significantly induced in aged APP/PS1 transgenic mouse brain. Saa3 deficiency exacerbated astrocyte activation and increased the number of astrocytes around Aß deposits in APP/PS1 mice. In vitro studies demonstrated that SAA inhibited the migration of primary cultures of astrocytes and U251 cells. Mechanistic studies showed that SAA inhibited astrocyte polarization and protrusion formation via disrupting actin and microtubule reorganization and Golgi reorientation. Inhibition of the p38 MAPK pathway abolished the suppression of SAA on astrocyte migration and polarization. CONCLUSIONS: These results suggest that increased SAA in the brain of APP/PS1 mice inhibits the migration of astrocytes to amyloid plaques by activating the p38 MAPK pathway.

Low-Density Lipoproteins, High-Density Lipoproteins (HDL), and HDL-Associated Proteins Differentially Modulate Chronic Myelogenous Leukemia Cell Viability.

Cellular lipid metabolism, lipoprotein interactions, and liver X receptor (LXR) activation have been implicated in the pathophysiology and treatment of cancer, although findings vary across cancer models and by lipoprotein profiles. In this study, we investigated the effects of human-derived low-density lipoproteins (LDL), high-density lipoproteins (HDL), and HDL-associated proteins apolipoprotein A1 (apoA1) and serum amyloid A (SAA) on markers of viability, cholesterol flux, and differentiation in K562 cells-a bone marrow-derived, stem-like erythroleukemia cell model of chronic myelogenous leukemia (CML). We further evaluated whether lipoprotein-mediated effects were altered by concomitant LXR activation. We observed that LDL promoted higher K562 cell viability in a dose- and time-dependent manner and increased cellular cholesterol concentrations, while LXR activation by the agonist TO901317 ablated these effects. LXR activation in the presence of HDL, apoA1 and SAA-rich HDL suppressed K562 cell viability, while robustly inducing mRNA expression of ATP-binding cassette transporter A1 (ABCA1). HDL and its associated proteins additionally suppressed mRNA expression of anti-apoptotic B-cell lymphoma-extra large (BCL-xL), and the erythroid lineage marker 5'-aminolevulinate synthase 2 (ALAS2), while SAA-rich HDL induced mRNA expression of the megakaryocytic lineage marker integrin subunit alpha 2b (ITGA2B). Together, these findings suggest that lipoproteins and LXR may impact the viability and characteristics of CML cells.

Serum Amyloid A1 (SAA1) Revisited: Restricted Leukocyte-Activating Properties of Homogeneous SAA1.

Infection, sterile injury, and chronic inflammation trigger the acute phase response in order to re-establish homeostasis. This response includes production of positive acute phase proteins in the liver, such as members of the serum amyloid A (SAA) family. In humans the major acute phase SAAs comprise a group of closely related variants of SAA1 and SAA2. SAA1 was proven to be chemotactic for several leukocyte subtypes through activation of the G protein-coupled receptor FPRL1/FPR2. Several other biological activities of SAA1, such as cytokine induction, reported to be mediated via TLRs, have been debated recently. Especially commercial SAA1, recombinantly produced in Escherichia coli, was found to be contaminated with bacterial products confounding biological assays performed with this rSAA1. We purified rSAA1 by RP-HPLC to homogeneity, removing contaminants such as lipopolysaccharides, lipoproteins and formylated peptides, and re-assessed several biological activities attributed to SAA1 (chemotaxis, cytokine induction, MMP-9 release, ROS generation, and macrophage differentiation). The homogeneous rSAA1 (hrSAA1) lacked most cell-activating properties, but its leukocyte-recruiting capacity in vivo and it's in vitro synergy with other leukocyte attractants remained preserved. Furthermore, hrSAA1 maintained the ability to promote monocyte survival. This indicates that pure hrSAA1 retains its potential to activate FPR2, whereas TLR-mediated effects seem to be related to traces of bacterial TLR ligands in the E. coli-produced human rSAA1.

Serum amyloid A exhibits pH dependent antibacterial action and contributes to host defense against Staphylococcus aureus cutaneous infection.

Serum amyloid A (SAA), one of the major highly conserved acute-phase proteins in most mammals, is predominantly produced by hepatocytes and also by a variety of cells in extrahepatic tissues. It is well-known that the expression of SAA is sharply increased in bacterial infections. However, the exact physiological function of SAA during bacterial infection remains unclear. Herein, we showed that SAA expression significantly increased in abscesses of Staphylococcus aureus cutaneous infected mice, which exert direct antibacterial effects by binding to the bacterial cell surface and disrupting the cell membrane in acidic conditions. Mechanically, SAA disrupts anionic liposomes by spontaneously forming small vesicles or micelles under acidic conditions. Especially, the N-terminal region of SAA is necessary for membrane disruption and bactericidal activity. Furthermore, we found that mice deficient in SAA1/2 were more susceptible to infection by S. aureus In addition, the expression of SAA in infected skin was regulated by interleukin-6. Taken together, these findings support a key role of the SAA in host defense and may provide a novel therapeutic strategy for cutaneous bacterial infection.

Hydroxychloroquine inhibits IL-1ß production from amyloid-stimulated human neutrophils.

BACKGROUND: Hydroxychloroquine (HCQ) is used for the treatment of patients with rheumatic diseases. We tested the hypothesis that HCQ affects the NLRP3 inflammasome, which is involved in autoinflammation. METHODS: Human neutrophils were stimulated with serum amyloid A (SAA) in vitro and measured for IL-1ß and caspase-1 (p20) secretion by ELISA. Pro-IL-1ß mRNA expression in human neutrophils was quantified by real-time RT-PCR. RESULTS: SAA stimulation induced significant production of IL-1ß in human neutrophils. SAA stimulation also induced NF-κB activation, pro-IL-1ß mRNA expression, and NLRP3 protein expression in human neutrophils. HCQ pretreatment significantly inhibited the SAA-induced IL-1ß production in human neutrophils, but did not affect the SAA-induced NF-κB activation, pro-IL-1ß mRNA expression, and NLRP3 protein expression. Furthermore, SAA stimulation induced cleaved caspase-1 (p20) secretion from human neutrophils, and this release was suppressed by HCQ pretreatment. CONCLUSIONS: Treatment with HCQ was associated with impaired production of IL-1ß in SAA-stimulated human neutrophils without affecting the priming process of the NLRP3 inflammasome such as pro-IL-1ß or NLRP3 induction. These findings suggest that HCQ affects the NLRP3 activation process, resulting in the impaired IL-1ß production in human neutrophils, as representative innate immune cells.

Neutralizing effects of anti-infliximab antibodies on synergistically-stimulated human coronary artery endothelial cells.

BACKGROUND AND AIMS: Patients with rheumatic diseases have an increased risk of atherosclerosis with up-regulated serum amyloid A (SAA), tumor necrosis factor-α (TNF-α) and interleukin-1ß (IL-1ß), which were reported to activate human coronary artery endothelial cells (HCAEC). We aimed to investigate the effects of TNF-α inhibitor infliximab and anti-infliximab antibodies on the TNF-α/IL-1ß/SAA activated HCAEC. METHODS: HCAEC were incubated with TNF-α, IL-1ß, SAA, infliximab, anti-infliximab antibodies and their combinations. The protein levels of pro- and anti-atherogenic analytes were measured in supernatants using ELISA and multiplex assays, while mRNA expression was determined by RT-PCR. Anti-infliximab antibodies were purified from sera samples by affinity chromatography. RESULTS: IL-6, IL-8, GM-CSF and GRO-α were synergistically up-regulated in triple stimulation with TNF-α, IL-1ß and SAA, while their levels in solely SAA- or TNF-α-stimulated HCAEC did not increase. IL-1Ra, IL-1α, VCAM-1, MCP-1, IL-10 and IL-17A were increased, but no synergistic responses were observed in triple stimulation. Infliximab was effective in lowering the synergistic effect of IL-6, IL-8, GM-CSF and GRO-α in triple stimulation, while anti-infliximab antibodies restored the levels. The changes were confirmed at the mRNA expression level for IL-6, IL-8 and GM-CSF. CONCLUSIONS: Triple stimulation with TNF-α, IL-1ß and SAA synergistically elevated IL-6, IL-8, GM-CSF and GRO-α release in supernatants of HCAEC, with infliximab substantially inhibiting their levels. An isolated, enriched fraction of polyclonal anti-infliximab antibodies was capable of neutralizing infliximab, in the presence of TNF-α/IL-1ß/SAA. The long-term presence of anti-infliximab antibodies in the circulation of patients with chronic rheumatic diseases is potentially important for promoting the atherosclerotic process.

SAA1 increases NOX4/ROS production to promote LPS-induced inflammation in vascular smooth muscle cells through activating p38MAPK/NF-κB pathway.

BACKGROUND: To investigate the effects of serum amyloid A1 (SAA1) on lipopolysaccharide (LPS) -induced inflammation in vascular smooth muscle cells (VSMCs). SAA1 expression was detected in LPS induced VSMCs at different concentrations for different time by using Western blotting. After pre-incubation with recombinant SAA1 protein, VSMCs were treated with 1 µg/ml LPS for 24 h. The VSMCs were then divided into Control, SAA1 siRNA, Nox4 siRNA, LPS, LPS + SAA1 siRNA, LPS + Nox4 siRNA and LPS + SAA1 siRNA + Nox4 groups. MTT was performed to observe the toxicity of VSMCs. Lucigenin-enhanced chemiluminescence method was used to detect superoxide anion (O2-) production and NADPH oxidase activity. Quantitative real-time polymerase chain reaction (qRT-PCR) was used to determine expressions of inflammatory factors. Western blotting was used to determine expressions of NOX-4 and p38MAPK/NF-κB pathway related proteins. RESULTS: LPS promoted SAA1 protein expression in a concentration-/time-dependent manner. Recombinant SAA1 protein could increase NOX4/ROS production and promote the release of inflammatory factors (IL-1ß, IL-6, IL-8, IL-17, TNF-α and MCP-1) in LPS (1 µg/ml) - induced VSMCs. Besides, both SAA1 siRNA and NOX-4 siRNA could not only enhance the O2- production and NADPH oxidase activity, but also up-regulate the protein expression of NOX4, the release of inflammatory factors, and the levels of p-p38 and p-NF-κB p65 in LPS-induced VSMCs. However, no significant differences in each index were observed between LPS group and LPS + SAA1 siRNA + Nox4 group. CONCLUSION: SAA1-mediated NOX4/ROS pathway could activate p38MAPK/NF-κB pathway, thereby contributing to the release of inflammatory factors in LPS-induced VSMCs.

Involvement of STAT3 in the synergistic induction of 11ß-HSD1 by SAA1 and cortisol in human amnion fibroblasts.

PROBLEM: Cortisol, which is regenerated from biologically inactive cortisone by 11ß-hydroxysteroid dehydrogenase type 1 (11ß-HSD1) in human fetal membranes, may play an important role in human parturition. Recently, we have demonstrated that human fetal membranes are capable of de novo synthesis of serum amyloid A1 (SAA1), an acute-phase protein of inflammation, and SAA1 may be engaged in multiple actions associated with human parturition. It remains to be determined whether SAA1 can interact with cortisol in the regulation of 11ß-HSD1 in the fetal membranes. METHOD OF STUDY: In the current study, we examined the regulation of 11ß-HSD1 expression by SAA1, and the interaction between SAA1 and cortisol in the regulation of 11ß-HSD1 expression in primary human amnion fibroblasts and amnion tissue. RESULTS: Either SAA1 or cortisol induced 11ß-HSD1 expression in a concentration-dependent manner. Combination of SAA1 and cortisol synergistically enhanced 11ß-HSD1 expression. Mechanism studies revealed that SAA1 and cortisol induced the phosphorylation of the transcription factor STAT3 in a sequential order with the induction by SAA1 preceding the induction by cortisol. Furthermore, the induction of 11ß-HSD1 expression by either SAA1 or cortisol or combination of SAA1 and cortisol was blocked by STAT3 inhibition with its antagonist S3I-201 or siRNA-mediated knockdown. CONCLUSION: This study has demonstrated that SAA1 and cortisol can reinforce each other in the induction of 11ß-HSD1 expression through sequential phosphorylation of STAT3. The synergistic enhancement of 11ß-HSD1 expression by SAA1 and cortisol may lead to excessive cortisol accumulation in the fetal membranes at parturition.

Serum amyloid A primes microglia for ATP-dependent interleukin-1ß release.

BACKGROUND: Acute-phase response is a systemic reaction to environmental/inflammatory insults and involves production of acute-phase proteins, including serum amyloid A (SAA). Interleukin-1ß (IL-1ß), a master regulator of neuroinflammation produced by activated inflammatory cells of the myeloid lineage, in particular microglia, plays a key role in the pathogenesis of acute and chronic diseases of the peripheral nervous system and CNS. IL-1ß release is promoted by ATP acting at the purinergic P2X7 receptor (P2X7R) in cells primed with toll-like receptor (TLR) ligands. METHODS: Purified (> 99%) microglia cultured from neonatal rat cortex and cerebellum were first primed with the putative TLR4/TLR2 agonist SAA (recombinant human Apo-SAA) or the established TLR4 agonist lipopolysaccharide (LPS) followed by addition of ATP. Expression of genes for the NLRP3 inflammasome, IL-1ß, tumor necrosis factor-α (TNF-α), and SAA1 was measured by quantitative real-time polymerase chain reaction (q-PCR). Intracellular and extracellular amounts of IL-1ß were determined by ELISA. RESULTS: Apo-SAA stimulated, in a time-dependent manner, the expression of NLRP3, IL-1ß, and TNF-α in cortical microglia, and produced a concentration-dependent increase in the intracellular content of IL-1ß in these cells. A 2-h 'priming' of the microglia with Apo-SAA followed by addition of ATP for 1 h, resulting in a robust release of IL-1ß into the culture medium, with a concomitant reduction in its intracellular content. The selective P2X7R antagonist A740003 blocked ATP-dependent release of IL-1ß. Microglia prepared from rat cerebellum displayed similar behaviors. As with LPS, Apo-SAA upregulated SAA1 and TLR2 mRNA, and downregulated that of TLR4. LPS was less efficacious than Apo-SAA, perhaps reflecting an action of the latter at TLR4 and TLR2. The TLR4 antagonist CLI-095 fully blocked the action of LPS, but only partially that of Apo-SAA. Although the TLR2 antagonist CU-CPT22 was inactive against Apo-SAA, it also failed to block the TLR2 agonist Pam3CSK4. CONCLUSIONS: Microglia are central to the inflammatory process and a major source of IL-1ß when activated. P2X7R-triggered IL-1ß maturation and export is thus likely to represent an important contributor to this cytokine pool. Given that SAA is detected in Alzheimer disease and multiple sclerosis brain, together with IL-1ß-immunopositive microglia, these findings propose a link between P2X7R, SAA, and IL-1ß in CNS pathophysiology.

Analysis of Drug Effects on Primary Human Coronary Artery Endothelial Cells Activated by Serum Amyloid A.

BACKGROUND: RA patients have a higher incidence of cardiovascular diseases compared to the general population. Serum amyloid A (SAA) is an acute-phase protein, upregulated in sera of RA patients. AIM: To determine the effects of medications on SAA-stimulated human coronary artery endothelial cells (HCAEC). METHODS: HCAEC were preincubated for 2 h with medications from sterile ampules (dexamethasone, methotrexate, certolizumab pegol, and etanercept), dissolved in medium (captopril) or DMSO (etoricoxib, rosiglitazone, meloxicam, fluvastatin, and diclofenac). Human recombinant apo-SAA was used to stimulate HCAEC at a final 1000 nM concentration for 24 hours. IL-6, IL-8, sVCAM-1, and PAI-1 were measured by ELISA. The number of viable cells was determined colorimetrically. RESULTS: SAA-stimulated levels of released IL-6, IL-8, and sVCAM-1 from HCAEC were significantly attenuated by methotrexate, fluvastatin, and etoricoxib. Both certolizumab pegol and etanercept significantly decreased PAI-1 by an average of 43%. Rosiglitazone significantly inhibited sVCAM-1 by 58%. CONCLUSION: We observed marked influence of fluvastatin on lowering cytokine production in SAA-activated HCAEC. Methotrexate showed strong beneficial effects for lowering released Il-6, IL-8, and sVCAM-1. Interesting duality was observed for NSAIDs, with meloxicam exhibiting opposite-trend effects from diclofenac and etoricoxib. This represents unique insight into specific responsiveness of inflammatory-driven HCAEC relevant to atherosclerosis.

COOH-terminal SAA1 peptides fail to induce chemokines but synergize with CXCL8 and CCL3 to recruit leukocytes via FPR2.

A natural leukocyte chemoattractant was isolated from bovine serum by an established 4-step purification procedure. Based on its relative molecular mass of 7287 and NH2-terminal sequence, the protein was identified as a carboxy-terminal peptide of the acute phase protein serum amyloid A1 (SAA1). This SAA1(46-112) fragment and its human equivalent SAA1(47-104) were chemically synthesized. Unlike intact SAA1α, these SAA fragments failed to directly chemoattract neutrophils and monocytes, to induce chemokines, and to stimulate downstream extracellular signal-regulated kinase signaling in monocytes. However, the SAA fragments potently synergized with CCL3 to induce monocyte migration and with CXCL8 to stimulate neutrophil shape changes and chemotaxis. Unlike intact SAA1α, SAA1(46-112) did not induce CXCL6 ex vivo but provoked a cooperative intraperitoneal neutrophil recruitment in mice when coinjected with CXCL6 into the peritoneal cavity. Moreover, SAA1(47-104) desensitized the synergy between intact SAA1α and CXCL8 in neutrophil chemotaxis, suggesting that this peptide binds formyl peptide receptor 2 (FPR2). This was evidenced by a complete blockade of synergy between the COOH-terminal SAA1 fragments and CXCL8 or CCL3 in neutrophil and monocyte chemotaxis, respectively, by the FPR2 antagonist WRW4 Thus, SAA1 is degraded into fragments lacking chemokine-inducing capacity, while keeping synergy with cytokine-induced chemokines to sustain limited inflammation.

Suppression of Lipopolysaccharide-Induced Inflammatory Response by Fragments from Serum Amyloid A.

Serum amyloid A (SAA) is known as an acute-phase protein and a biomarker for inflammatory diseases. Published studies have shown that SAA possesses proinflammatory cytokine-like activity and is chemotactic for phagocytes, but the structural basis for these activities remains unidentified. In this article, we report that truncated SAA1 proteins lacking N- and C-terminal sequences exhibit reduced proinflammatory activity and strongly suppress LPS-induced expression of IL-1ß, IL-6, and TNF-α in macrophages. A truncated SAA1 containing aa 11-58 was examined further and found to facilitate p38 MAPK phosphorylation while reducing LPS-stimulated phosphorylation of ERK and JNK. In LPS-challenged mice, aa 11-58 reduced the severity of acute lung injury, with significantly less neutrophil infiltration in the lungs and attenuated pulmonary expression of IL-1ß, IL-6, and TNF-α. Coadministration of aa 11-58 markedly improved mouse survival in response to a lethal dose of LPS. A potent induction of IL-10 was observed in a TLR2-dependent, but TLR4-independent, manner in macrophages stimulated with aa 11-58. However, the aa 11-58 fragment of SAA1 was unable to induce chemotaxis or calcium flux through formyl peptide receptor 2. These results indicate that the N- and C-terminal sequences contain structural determinants for the proinflammatory and chemotactic activities of SAA1, and their removal switches SAA1 to an anti-inflammatory role. Given that proteolytic processing of SAA is associated with the pathological changes in several diseases, including secondary amyloidosis, our findings may shed light on the structure-function relationship of SAA1 with respect to its role in inflammation.

Human SR-BII mediates SAA uptake and contributes to SAA pro-inflammatory signaling in vitro and in vivo.

Serum amyloid A (SAA) is an acute phase protein with cytokine-like and chemotactic properties, that is markedly up-regulated during various inflammatory conditions. Several receptors, including FPRL-1, TLR2, TLR4, RAGE, class B scavenger receptors, SR-BI and CD36, have been identified as SAA receptors. This study provides new evidence that SR-BII, splice variant of SR-BI, could function as an SAA receptor mediating its uptake and pro-inflammatory signaling. The uptake of Alexa Fluor488 SAA was markedly (~3 fold) increased in hSR-BII-expressing HeLa cells when compared with mock-transfected cells. The levels of SAA-induced interleukin-8 secretion by hSR-BII-expressing HEK293 cells were also significantly (~3-3.5 fold) higher than those detected in control cells. Moderately enhanced levels of phosphorylation of all three mitogen-activated protein kinases, ERK1/2, and p38 and JNK, were observed in hSR-BII-expressing cells following SAA stimulation when compared with control wild type cells. Transgenic mice with pLiv-11-directed liver/kidney overexpression of hSR-BI or hSR-BII were used to assess the in vivo role of each receptor in SAA-induced pro-inflammatory response in these organs. Six hours after intraperitoneal SAA injection both groups of transgenic mice demonstrated markedly higher (~2-5-fold) expression levels of inflammatory mediators in the liver and kidney compared to wild type mice. Histological examinations of hepatic and renal tissue from SAA-treated mice revealed moderate level of damage in the liver of both transgenic but not in the wild type mice. Activities of plasma transaminases, biomarkers of liver injury, were also moderately higher in hSR-B transgenic mice when compared to wild type mice. Our findings identify hSR-BII as a functional SAA receptor that mediates SAA uptake and contributes to its pro-inflammatory signaling via the MAPKs-mediated signaling pathways.

Cloning, expression analysis, and antibacterial propertiesof three serum amyloid A in common carp (Cyprinus carpio).

Three serum amyloid A (SAA) genes were identified from the common carp (Cyprinus carpio) by PCR and RT-PCR. Considering both direction and sequence similarity with mammal's orthologs, they were named CcSAA3a, CcSAA3b and CcSAA1. CcSAA3b and CcSAA1 are adjacent on contig LHQP01017858, suggesting that the prototype of or the simplest SAA multigene family have occurred in common carp. A phylogenetic analysis of the SAAs indicated that the fish SAAs were closer to those of invertebrates and Ornithorhynchus anatinus, a primitive mammal, than to mammalian SAAs. Quantitative real-time RT-PCR results displayed different expression profiles of three CcSAAs. The CcSAA3a was detected in all tested tissues, and was most abundant in the muscle; CcSAA3b was predominately expressed in the intestine and liver, and CcSAA1 in the skin. The expression level of CcSAA3a was higher than that of CcSAA3b and CcSAA1 in most tissues. Stimulation with Aeromonas hydrophila dramatically induced the expression of the three CcSAAs in all examined tissues, especially in the liver. Like Epinephelus coioides SAA, all of three rCcSAA fusion proteins could bind to both Gram-negative bacteria (A. hydrophila and E. coli) and Gram-positive bacterium (S. aureus), playing a role in the identification of bacteria. However, only rCcSAA3a showed significantly anti-A. hydrophila and anti-E. coli in vitro antibacterial activity assays. These results suggested that the three CcSAAs were in functional differentiation and play significant roles in the innate immunity of common carp.