Acute-phase Protein Serum Amyloid A Research Articles

1 (Nano)Particle Exposure, Acute Phase Response and Cardiovascular Disease

Abstract Particle inhalation is linked to diseases including cancer, COPD, fibrosis and cardiovascular disease. We propose a biological mechanism-of-action for particle-induced cardiovascular disease causally linking particle exposure to induction of acute phase response, which in turn is a known risk factor for atherosclerosis and cardiovascular disease. Inhalation and pulmonary deposition of particles induce inflammation, which is proportional to the total surface area of the pulmonary-deposited particles. In mice, inflammation is accompanied by an acute phase response, which is long-lasting for insoluble particles. Acute phase protein Serum Amyloid A (SAA) is among the most differentially expressed genes in lung tissue following particle exposure. SAA is causally implicated in atherosclerosis and both overexpression and pulmonary dosing of SAA promote plaque formation in ApoE-/- mice. In mice, we show that both soluble and insoluble metal fume particles induce acute phase response but with different time-dependence. Neutrophil influx, pulmonary Saa expression and SAA blood levels are highly correlated in mice and may be used as biomarkers of each other. In humans, controlled exposure to metal oxides and combustion particles induces dose-dependent increases in blood levels of SAA and C-reactive protein. Blood levels of acute phase proteins SAA and C-reactive protein are risk factors for cardiovascular disease in prospective, epidemiological studies. Nanoparticles have a higher specific surface area than larger particles with similar chemical composition, and consequently, nanoparticles are more hazardous than larger particles of similar chemical composition in relation to cardiovascular disease. This underscores cardiovascular disease as a particle-induced occupational disease.

Association between a urinary biomarker for exposure to PAH and blood level of the acute phase protein serum amyloid A in coke oven workers

BackgroundCoke oven workers are exposed to both free and particle bound PAH. Through this exposure, the workers may be at increased risk of cardiovascular diseases. Systemic levels of acute phase response proteins have been linked to cardiovascular disease in epidemiological studies, suggesting it as a marker of these conditions. The aim of this study was to assess whether there was association between PAH exposure and the blood level of the acute phase inflammatory response marker serum amyloid A (SAA) in coke oven workers.MethodsA total of 87 male Polish coke oven workers from two different plants comprised the study population. Exposure was assessed by means of the individual post-shift urinary excretion of 1-hydroxypyrene, as internal dose of short-term PAH exposure, and by anti-benzo[a]pyrene diolepoxide (anti-B[a]PDE)-DNA), as a biomarker of long-term PAH exposure. Blood levels of acute phase proteins SAA and CRP were measured by immunoassay. C-reactive protein (CRP) levels were included to adjust for baseline levels of SAA.ResultsMultiple linear regression showed that the major determinants of increased SAA levels were urinary 1-hydroxypyrene (beta = 0.56, p = 0.030) and serum CRP levels (beta = 7.08; p < 0.0001) whereas anti-B[a]PDE-DNA, the GSTM1 detoxifying genotype, diet, and smoking were not associated with SAA levels.ConclusionsUrinary 1-hydroxypyrene as biomarker of short-term PAH exposure and serum levels of CRP were predictive of serum levels of SAA in coke oven workers. Our data suggest that exposure of coke oven workers to PAH can lead to increased systemic acute response and therefore potentially increased risk of cardiovascular disease.

Abstract 414: Local Artery Wall Inflammation Overrides Systemic Inflammation in Diabetes-Accelerated Atherosclerosis

Human genomic studies have highlighted the importance of arterial wall-specific inflammatory processes in cardiovascular disease (CVD) risk. Diabetes increases systemic inflammation, local arterial inflammation, and CVD risk. To clarify the relative contributions of systemic inflammation versus artery wall inflammatory processes in atherosclerosis, we studied LDL receptor-deficient mice with streptozotocin-induced diabetes. The damage-associated molecular pattern protein S100A9 and toll-like receptor 4 (TLR4) have both been implicated in diabetes-induced inflammation. S100A9-deficient bone marrow chimeras were used to inhibit systemic inflammation, 5-aminosalicylic acid (5-ASA) was used to inhibit intestinal inflammation, and TLR4-deficient bone marrow chimeras were used to inhibit artery wall inflammation. No model affected the severity of diabetes, plasma cholesterol or blood leukocyte numbers. Hematopoietic S100A9-deficiency, but not TLR4-deficiency, reduced diabetes-associated systemic inflammation to levels observed in non-diabetic mice. 5-ASA differentially altered measures of systemic inflammation. Thus, diabetes induced a 2-fold increase in circulating leukocyte Il1b mRNA, which was normalized by S100A9-deficiency (p&lt;0.01, n=7-10) and 5-ASA, but was not reduced by hematopoietic TLR4-deficiency (n=11-14). Similarly, diabetes increased plasma levels of the acute-phase protein serum amyloid-A (SAA), which were normalized by S100A9-deficiency (p&lt;0.01, n=5-12), but not by TLR4-deficiency (n=5-10) or 5-ASA. Conversely, hematopoietic TLR4-deficiency (p&lt;0.05), but not hematopoietic S100A9-deficiency or 5-ASA, reduced diabetes-accelerated myeloid cell accumulation in the artery wall determined by aortic en face Sudan IV staining (n=16-21). Finally, laser capture microdissection of CD68-positive lesional macrophages revealed that hematopoietic TLR4-deficiency prevents diabetes-induced inflammatory processes in the artery wall including expression of Il1b, Ccr2 , and S100a9 mRNA. Together, our data strongly suggest that although systemic inflammation is increased in diabetes, inhibition of inflammatory processes in the artery wall is required to prevent lesional macrophage accumulation.

Serum amyloid A: an ozone-induced circulating factor with potentially important functions in the lung-brain axis.

Accumulating evidence suggests that O3 exposure may contribute to CNS dysfunction. Here, we posit that inflammatory and acute-phase proteins in the circulation increase after O3 exposure and systemically convey signals of O3 exposure to the CNS. To model acute O3 exposure, female Balb/c mice were exposed to 3 ppm O3 or forced air for 2 h and were studied after 6 or 24 h. Of 23 cytokines and chemokines, only KC/CXCL1 was increased in blood 6 h after O3 exposure. The acute-phase protein serum amyloid A (A-SAA) was significantly increased by 24 h, whereas C-reactive protein was unchanged. A-SAA in blood correlated with total leukocytes, macrophages, and neutrophils in bronchoalveolar lavage from O3-exposed mice. A-SAA mRNA and protein were increased in the liver. We found that both isoforms of A-SAA completely crossed the intact blood-brain barrier, although the rate of SAA2.1 influx was approximately 5 times faster than that of SAA1.1. Finally, A-SAA protein, but not mRNA, was increased in the CNS 24 h post-O3 exposure. Our findings suggest that A-SAA is functionally linked to pulmonary inflammation in our O3 exposure model and that A-SAA could be an important systemic signal of O3 exposure to the CNS.-Erickson, M. A., Jude, J., Zhao, H., Rhea, E. M., Salameh, T. S., Jester, W., Pu, S., Harrowitz, J., Nguyen, N., Banks, W. A., Panettieri, R. A., Jr., Jordan-Sciutto, K. L. Serum amyloid A: an ozone-induced circulating factor with potentially important functions in the lung-brain axis.

Occupational exposure levels of bioaerosol components are associated with serum levels of the acute phase protein Serum Amyloid A in greenhouse workers.

BackgroundOccupational exposure to particles may be associated with increased inflammation of the airways. Animal experiments suggest that inhaled particles also induce a pulmonary acute phase response, leading to systemic circulation of acute phase proteins. Greenhouse workers are exposed to elevated levels of bioaerosols. The objective of this study is to assess whether greenhouse workers personal exposure to bioaerosol components was associated with serum levels of the acute phase proteins Serum Amyloid A (SAA) and C-reactive protein (CRP).MethodsSAA and CRP levels were determined in serum sampled repeatedly from 33 greenhouse workers. Blood was drawn repeatedly on Mondays and Thursdays during work weeks. Acute phase protein levels were compared to levels in a comparison group of 42 people and related to individual exposure levels to endotoxin, dust, bacteria, fungi and β-glucan.ResultsSerum levels of SAA and CRP were not significantly different in greenhouse workers and a reference group, or on the two work days. In a mixed model, SAA levels were positively associated with endotoxin exposure levels (p = 0.0007). Results for fungi were not clear. CRP levels were positively associated with endotoxin exposures (p = 0.022). Furthermore, when workers were categorized into three groups based on SAA and CRP serum levels endotoxin exposure was highest in the group with the highest SAA levels and in the group with middle and highest CRP levels. SAA and CRP levels were elevated in workers with asthma.ConclusionGreenhouse workers did not have elevated serum levels of SAA and CRP compared to a reference group. However, occupational exposure to endotoxin was positively associated with serum levels of the acute phase proteins SAA and CRP. Preventive measures to reduce endotoxin exposure may be beneficial.

Mechanism and Clinical Significance of IL-6 Combined with TNF-α or IL-1 for the Induction of Acute Phase Proteins SAA and CRP in Chronic Inflammatory Diseases

Serum amyloid A (SAA) and C-reactive protein (CRP) are two major acute phase proteins whose serum concentrations increase in response to inflammation, though the exact mechanism underlying this induction remains unknown. Dysregulated production of interleukin (IL)-6 plays a pathogenic role in various inflammatory diseases such as rheumatoid arthritis, Castleman’s disease and systemic juvenile idiopathic arthritis. IL-6 blocking therapy with an anti-IL-6 receptor antibody (tocilizumab) can ameliorate clinical symptoms and abnormal laboratory findings, and completely normalize CRP and SAA levels in rheumatoid arthritis patients. Conversely, therapy for blocking tumor necrosis factor (TNF)-α, another key pathogenic factor in rheumatoid arthritis, barely lowers CRP and SAA to within their normal range, suggesting that IL-6 and TNF-α play different roles in the induction of acute phase protein expression. To clarify the different pathogenic roles and mechanisms of IL-6 and TNF-α or IL-1 in the induction of CRP and SAA in chronic inflammatory diseases, we investigated the transcriptional regulation mechanisms of SAA and CRP using hepatoma-derived cell lines in vitro, and related these mechanisms to the different effects of IL-6 and TNF-α blocking therapies on serum SAA and CRP in rheumatoid arthritis patients in vivo. We propose transcriptional regulation models for inflammatory cytokine-induced SAA and CRP expression that explain why IL-6 plays an essential role in the induction of SAA and CRP in the presence of inflammation.

Serum amyloid A: high-density lipoproteins interaction and cardiovascular risk.

High-density lipoproteins (HDLs) are considered as anti-atherogenic. Recent experimental findings suggest that their biological properties can be modified in certain clinical conditions by accumulation of serum amyloid A (SAA). The effect of SAA on the association between HDL-cholesterol (HDL-C) and cardiovascular outcome remains unknown. We examined the association of SAA and HDL-C with mortality in the Ludwigshafen Risk and Cardiovascular Health (LURIC) study, which included 3310 patients undergoing coronary angiography. To validate our findings, we analysed 1255 participants of the German Diabetes and Dialysis study (4D) and 4027 participants of the Cooperative Health Research in the Region of Augsburg (KORA) S4 study. In LURIC, SAA concentrations predicted all-cause and cardiovascular mortality. In patients with low SAA, higher HDL-C was associated with lower all-cause and cardiovascular mortality. In contrast, in patients with high SAA, higher HDL-C was associated with increased all-cause and cardiovascular mortality, indicating that SAA indeed modifies the beneficial properties of HDL. We complemented these clinical observations by in vitro experiments, in which SAA impaired vascular functions of HDL. We further derived a formula for the simple calculation of the amount of biologically 'effective' HDL-C based on measured HDL-C and SAA from the LURIC study. In 4D and KORA S4 studies, we found that measured HDL-C was not associated with clinical outcomes, whereas calculated 'effective' HDL-C significantly predicted better outcome. The acute-phase protein SAA modifies the biological effects of HDL-C in several clinical conditions. The concomitant measurement of SAA is a simple, useful, and clinically applicable surrogate for the vascular functionality of HDL.

The role of serum amyloid A and sphingosine-1-phosphate on high-density lipoprotein functionality.

The high-density lipoprotein (HDL) is one of the most important endogenous cardiovascular protective markers. HDL is an attractive target in the search for new pharmaceutical therapies and in the prevention of cardiovascular events. Some of HDL's anti-atherogenic properties are related to the signaling molecule sphingosine-1-phosphate (S1P), which plays an important role in vascular homeostasis. However, for different patient populations it seems more complicated. Significant changes in HDL's protective potency are reduced under pathologic conditions and HDL might even serve as a proatherogenic particle. Under uremic conditions especially there is a change in the compounds associated with HDL. S1P is reduced and acute phase proteins such as serum amyloid A (SAA) are found to be elevated in HDL. The conversion of HDL in inflammation changes the functional properties of HDL. High amounts of SAA are associated with the occurrence of cardiovascular diseases such as atherosclerosis. SAA has potent pro-atherogenic properties, which may have impact on HDL's biological functions, including cholesterol efflux capacity, antioxidative and anti-inflammatory activities. This review focuses on two molecules that affect the functionality of HDL. The balance between functional and dysfunctional HDL is disturbed after the loss of the protective sphingolipid molecule S1P and the accumulation of the acute-phase protein SAA. This review also summarizes the biological activities of lipid-free and lipid-bound SAA and its impact on HDL function.

High density lipoproteins down-regulate transcriptional expression of pro-inflammatory factors and oxidative burst in head kidney leukocytes from rainbow trout, Oncorhynchus mykiss

Teleosts are the first group of vertebrates possessing an acquired immune system; however, it is less developed than in mammals and is highly influenced by environmental changes. Therefore, innate immunity effectors play a more critical role in survival of pathogen-challenged fish. In a previous study we showed that trout high density lipoprotein (HDL), and its major apolipoprotein (ApoA-I) are widely expressed in primary defense barriers and other immune-relevant tissues, displaying important antibacterial activity in vitro. Here we show that trout HDL inhibits both basal and LPS-induced transcript expression of pro-inflammatory cytokines such as TNF-α and IL-1β, and the acute phase protein serum amyloid A (A-SAA), in head kidney leukocytes (HLK) from rainbow trout. In addition, trout HDL was able to block the respiratory burst of PMA-stimulated HKL, at physiological concentrations and in a dose dependent manner. Moreover, this effect was only partially mimicked by supra-physiologic concentrations of the HDL-transported carotenoid, astaxanthin. These results constitute the first data suggesting that in addition to its antimicrobial activity, HDL would have a relevant immunomodulatory role in salmonid fish.

Serum Amyloid A (SAA) Is a Sensitive Surrogate Marker for IL-6R Blockage by Therapeutic IL6R Antibody: A Study in a Mouse Model of Allosensitization

Purpose Serum amyloid A (SAA) is one of the acute phase proteins generated by hepatocytes through IL-6 stimulation. This study evaluated the usefulness of measuring SAA as a surrogate marker to monitor IL-6R blockage using anti-IL6R antibody in a mouse model of allosensitization. Methods and Materials A mouse model of allosensitization involving a C57BL/6 mouse recipient of a skin graft (SG) from HLA.A2 transgenic mouse was employed. The SG recipients were divided into different treatment groups, receiving anti-IL6R, anti-CD20, IVIG and control antibodies, respectively. Serum samples were collected at designated time points post skin grafting and treatments. SAA2 titers were measured in an ELISA. Results Normal mice showed low titers of serum amyloid A2 in sera (0.54+0.04 μg/ml). SAA2 titers in sera of SG recipient mice increased by >100-fold at Day 1 Ptx (66.3+2.14 μg/ml, P=6.79E-09 vs. normal sera), and then gradually returning to normal levels at Day 7 after skin allograft rejection (39.02+5.9, 42.75+15.31 and 3.7+0.08 μg/ml at Days 2, 3, and 7, respectively). In contrast, SAA2 titers in sera from anti-IL6R treated mice remained at baseline levels (2.14+1.7, 0.8+0.1, 2.35+1.6 and 0.67+0.08 μg/ml at Days 1, 2, 3 and 7, respectively), indicating SAA suppression by IL-6 blockage. SG recipients treated with B-cell depleting anti-CD20 mAb exhibited high levels of SAA2 (20.96+7.91μg/ml) while those treated with IVIG had moderately increased SAA2 (6.75+0.45 μg/ml). The latter indicates IVIG also suppresses acute phase protein SAA. Conclusions We conclude that SAA titers globally reflect status of allograft rejection, inflammation and treatment responses to IL-6 receptor blockage and immune modulation by IVIG, but not B-cell depletion by anti-CD20. Measurement of SAA, in combination with other rejection/inflammation markers may have value in monitoring transplant patients.

Inflammatory Markers: Serum Amyloid A, Fibrinogen and C-Reactive Protein — A Revisited Study

The acute phase response is the part of the innate defence system of an animal against trauma, inflammation or infection. During this response, there is increased production and release of certain plasma proteins known as acute phase proteins, which include C-reactive protein (CRP), serum amyloid A (SAA) and fibrinogen (Fg). CRP consists of five identical subunits of 206 amino acids with a molecular weight of approximately 23 kDa. There is strong evidence from numerous studies that CRP is a predictor of inflammation. The acute-phase protein serum amyloid A (SAA) is a clinically useful marker of inflammation. SAA plays not only an important role in the development of AA amyloidosis (an important complication of rheumatoid arthritis) but also interacts with events closely involved in the metabolic syndrome as a high- and low-grade inflammatory modulator. Fibrinogen (Fg) is a high molecular weight plasma adhesion protein and is a biomarker of inflammation. It is synthesized and assembled in hepatocytes and fibroblasts and when secreted into the circulation, its plasma half-life ranges from 3 to 4 days. Several cytokines, are involved in the induction of acute phase protein synthesis, but the mutual importance of these cytokines seems to be cell-type specific and to vary in various experimental settings. Here we revisited the classic acute phase proteins SAA, C-Reactive protein and fibrinogen in their role in inflammation and their interrelationship with some cytokines.

Elevation of intact and proteolytic fragments of acute phase proteins constitutes the earliest systemic antiviral response in HIV-1 infection.

The earliest immune responses activated in acute human immunodeficiency virus type 1 infection (AHI) exert a critical influence on subsequent virus spread or containment. During this time frame, components of the innate immune system such as macrophages and DCs, NK cells, β-defensins, complement and other anti-microbial factors, which have all been implicated in modulating HIV infection, may play particularly important roles. A proteomics-based screen was performed on a cohort from whom samples were available at time points prior to the earliest positive HIV detection. The ability of selected factors found to be elevated in the plasma during AHI to inhibit HIV-1 replication was analyzed using in vitro PBMC and DC infection models. Analysis of unique plasma donor panels spanning the eclipse and viral expansion phases revealed very early alterations in plasma proteins in AHI. Induction of acute phase protein serum amyloid A (A-SAA) occurred as early as 5–7 days prior to the first detection of plasma viral RNA, considerably prior to any elevation in systemic cytokine levels. Furthermore, a proteolytic fragment of alpha–1-antitrypsin (AAT), termed virus inhibitory peptide (VIRIP), was observed in plasma coincident with viremia. Both A-SAA and VIRIP have anti-viral activity in vitro and quantitation of their plasma levels indicated that circulating concentrations are likely to be within the range of their inhibitory activity. Our results provide evidence for a first wave of host anti-viral defense occurring in the eclipse phase of AHI prior to systemic activation of other immune responses. Insights gained into the mechanism of action of acute-phase reactants and other innate molecules against HIV and how they are induced could be exploited for the future development of more efficient prophylactic vaccine strategies.

Alfalfa pellet-induced subacute ruminal acidosis in dairy cows increases bacterial endotoxin in the rumen without causing inflammation

A study was conducted to determine if subacute ruminal acidosis (SARA) induced by feeding alfalfa pellets results in increases in free bacterial lipopolysaccharide (LPS) in rumen fluid and peripheral blood, and acute phase proteins in plasma, and to determine the effect of alfalfa pellet-induced SARA on feed intake, rumen fermentation characteristics, milk production and composition, and blood metabolites. Eight lactating Holstein cows, 4 of which were ruminally cannulated, were used in a 6-wk experiment and were fed once daily at 0900h. During wk 1, cows received a diet containing 50% of DM as concentrate and 50% of DM chopped alfalfa hay. Between wk 2 and wk 6, alfalfa hay was gradually replaced with alfalfa pellets at the rate of 8% per week to reduce rumen pH. Rumen pH was monitored continuously in the ruminally cannulated cows using indwelling pH probes. Rumen fluid and peripheral blood were sampled 15min before feed delivery and at 6h after feed delivery. Based on adopted threshold of SARA of at least 180 min/d below pH 5.6, SARA was induced from wk 3 onwards. Replacing 40% of alfalfa hay with alfalfa pellets quadratically increased the DMI from 18.1kg/d in wk 1 to 23.4kg/d in wk 6. This replacement linearly decreased milk yield (32.7 vs. 35.9kg/d) and milk fat percentage and yield (2.32 vs. 3.22%, and 0.77 vs. 1.14kg/d, respectively), but increased milk protein percentage and yield (3.80 vs. 3.04%, and 1.23 vs. 1.07kg/d, respectively). This gradual replacement also linearly increased the daily averages of total volatile fatty acids (90 to 121.9mM), acetate (53.9 to 66.8mM), propionate (21.5 to 39.6mM), and osmolality (277.7 to 293.8 mmol/kg) in the rumen and decreased the acetate to propionate ratio from 2.62 to 1.73. Replacing alfalfa hay with alfalfa pellets linearly increased blood lactate from 1.00mM in wk 1 to a peak of 3.46mM in wk 5. Induction of SARA in this study increased free rumen LPS concentration from 42,122 endotoxin unit (EU)/mL in wk 1 to 145,593 EU/mL in wk 6. However, this increase was not accompanied by an increase in LPS (<0.05 EU/mL) and in acute phase proteins serum amyloid-A, haptoglobin, and LPS-binding protein in peripheral circulation. Results suggest that SARA induced by alfalfa pellets increased LPS in the rumen without causing translocation of LPS and an immune response.

Acute-phase protein synthesis in human hepatoma cells: differential regulation of serum amyloid A (SAA) and haptoglobin by interleukin-1 and interleukin-6

Interleukin-6 (IL-6, BSF-2 or IFN-beta 2) is thought to be the major regulator of the acute-phase protein response that follows tissue injury and inflammation, with interleukin-1 (IL-1), tumour necrosis factor and more recently, LIF or HSF III, slightly stimulatory on only certain acute phase proteins. The synthesis of the major acute-phase protein SAA, originally described as being synthesized in response to IL-1, has been claimed recently to be mainly under IL-6 regulation. Our results show that in the human hepatoma cell line HuH-7, IL-1 is the major stimulating cytokine increasing SAA synthesis by a factor in excess of 100-fold. We also show that under most conditions interleukin-6 and tumour necrosis factor stimulate additively in combination with IL-1. Isoelectric focusing has demonstrated that SAA1 and SAA2 alpha are expressed but not SAA2 beta. The HuH-7 cell line is IL-6 responsive since haptoglobin is stimulated mainly by IL-6.

Acute‐phase serum amyloid A stimulation of angiogenesis, leukocyte recruitment, and matrix degradation in rheumatoid arthritis through an NF‐κB–dependent signal transduction pathway

To examine the role of the acute-phase protein serum amyloid A (A-SAA) in regulating cell adhesion molecule expression, leukocyte recruitment, and angiogenesis in rheumatoid arthritis (RA). Intercellular adhesion molecule 1 (ICAM-1), vascular cell adhesion molecule 1 (VCAM-1), and matrix metalloproteinase 1 (MMP-1) expression was examined in RA fibroblast-like synoviocytes (FLS) and human microvascular endothelial cells (HMVECs) using flow cytometry and enzyme-linked immunosorbent assay techniques. Peripheral blood mononuclear cell (PBMC) adhesion to FLS/HMVECs was determined by flow cytometry. Angiogenesis was examined using a Boyden chemotaxis chamber and Matrigel tubule formation. NF-kappaB/IkappaBalpha mediation of the effects of A-SAA was investigated using a specific NF-kappaB inhibitor and Western blotting. A-SAA significantly enhanced the time- and dose-dependent expression of ICAM-1 and VCAM-1 as effectively as interleukin-1beta/tumor necrosis factor alpha. A-SAA promoted the adhesion of PBMCs to FLS and HMVECs. In addition, A-SAA at 10 mug/ml and 50 mug/ml significantly increased endothelial cell tube formation by 69% and 207%, respectively. At 50 mug/ml and 100 mug/ml, A-SAA increased HMVEC migration by 188 +/- 54% and 296 +/- 71%, respectively (mean +/- SEM). A-SAA-induced expression of VCAM-1, ICAM-1, and MMP-1 was down-regulated by NF-kappaB inhibition. Furthermore, A-SAA induced IkappaBalpha degradation and NF-kappaB translocation, suggesting that its proinflammatory effects are mediated in part by NF-kappaB signaling. Our findings demonstrate the ability of A-SAA to induce adhesion molecule expression, angiogenesis, and matrix degradation, mechanisms that are mediated by NF-kappaB. Targeting A-SAA and its signaling pathways may represent a new therapeutic approach in the treatment of RA.

Serum Amyloid A Promotes Cholesterol Efflux Mediated by Scavenger Receptor B-I

Serum amyloid A (SAA) is an acute phase protein whose expression is markedly up-regulated during inflammation and infection. The physiological function of SAA is unclear. In this study, we reported that SAA promotes cellular cholesterol efflux mediated by scavenger receptor B-I (SR-BI). In Chinese hamster ovary cells, SAA promoted cellular cholesterol efflux in an SR-BI-dependent manner, whereas apoA-I did not. Similarly, SAA, but not apoA-I, promoted cholesterol efflux from HepG2 cells in an SR-BI-dependent manner as shown by using the SR-BI inhibitor BLT-1. When SAA was overexpressed in HepG2 cells using adenovirus-mediated gene transfer, the endogenously expressed SAA promoted SR-BI-dependent efflux. To assess the effect of SAA on SR-BI-mediated efflux to high density lipoprotein (HDL), we compared normal HDL, acute phase HDL (AP-HDL, prepared from mice injected with lipopolysaccharide), and AdSAA-HDL (HDL prepared from mice overexpressing SAA). Both AP-HDL and AdSAA-HDL promoted 2-fold greater cholesterol efflux than normal HDL. Lipid-free SAA was shown to also stimulate ABCA1-dependent cholesterol efflux in fibroblasts, in line with an earlier report (Stonik, J. A., Remaley, A. T., Demosky, S. J., Neufeld, E. B., Bocharov, A., and Brewer, H. B. (2004) Biochem. Biophys. Res. Commun. 321, 936-941). When added to cells together, SAA and HDL exerted a synergistic effect in promoting ABCA1-dependent efflux, suggesting that SAA may remodel HDL in a manner that releases apoA-I or other efficient ABCA1 ligands from HDL. SAA also facilitated efflux by a process that was independent of SR-BI and ABCA1. We conclude that the acute phase protein SAA plays an important role in HDL cholesterol metabolism by promoting cellular cholesterol efflux through a number of different efflux pathways.

Tissue-specific regulation of the human acute-phase serum amyloid A genes, SAA1 and SAA2, by glucocorticoids in hepatic and epithelial cells.

The human acute-phase protein serum amyloid A (A-SAA), encoded by the SAA1 and SAA2 genes, is dramatically induced by pro-inflammatory mediators during the acute-phase response to infection or injury. Circulating A-SAA is predominantly synthesized by the liver. However, other tissues are the source of locally produced A-SAA. Here, we establish that the qualitative and kinetic aspects of SAA1 and SAA2 transcription following treatment of HepG2 hepatoma cells and KB epithelial cells with glucocorticoids and cytokines are quite distinct. Untreated HepG2 cells do not express A-SAA mRNA and glucocorticoids, when administered alone, fail to induce either SAA1 or SAA2. In contrast, untreated KB cells constitutively express SAA1 mRNA. Following cytokine stimulation, both A-SAA genes are rapidly up-regulated to similar extents. As in the hepatoma cell line, co-stimulation of KB cells with glucocorticoids places SAA1 at a transcriptional advantage over SAA2. Interestingly, SAA1 can be significantly induced by glucocorticoids alone in KB cells. The effects of glucocorticoids on SAA1 in both cell lines is glucocorticoid receptor-dependent. Differential regulation of A-SAA expression in these cell lines may reflect different temporal and spatial requirements for A-SAA synthesis in response to different inflammatory challenges.

Inhibition of cell adhesion to glycoproteins of the extracellular matrix by peptides corresponding to serum amyloid A

Synthetic peptides related to amino acid residues 29-42 of human serum amyloid A (SAA), Tyr-Ile-Gly-Ser-Asp-Lys-Tyr-Phe-His-Ala-Arg-Gly-Asn-Tyr, were found to inhibit the adhesion of human T-lymphocytes and of mouse M4 melanoma cells to surfaces coated with the major cell adhesive glycoproteins of the extracellular matrix, laminin or fibronectin. Correspondingly inhibitory activity was manifested by the entire 14-residue peptide, by its YIGSD laminin-related domain, and by RGN, the fibronectin-related domain. Intact recombinant SAA (rSAA) and its 1-76 fragment, an amyloid A (AA) protein, also inhibited cell adhesion. The peptides did not inhibit collagen and ADP-induced aggregation of human platelets. Proteolysis of SAA by lysosomal enzymes originating from human neutrophils led to generation of specific peptide segments some of which pertain to the 29-42 domain. It is suggested that the acute-phase protein SAA might be involved, either directly or via its peptide fragments, in inhibition of inflammatory reactions or metastatic processes which depend on integrin and possibly other extracellular-matrix-specific receptors mediated specific recognition and interactions with immobilized components of blood-vessel walls.

Inhibition of the oxidative burst response of N-formyl peptide-stimulated neutrophils by serum amyloid-A protein

Strong binding of the acute phase protein serum amyloid-A (SAA) to human neutrophils was found using flow cytometry. This binding was shown to be functionally relevant with respect to the oxidative burst reaction assayed on N-formyl peptide-stimulated neutrophils by the intracellular oxidation of nonfluorescent dihydrorhodamine to fluorescent rhodamine 123. The results show reduction of the oxidative burst reponse by isolated SAA (and recombinant SAA2). Inhibition was also demonstrated by acute phase as compared to normal human serum. This inhibitory effect was abolished by the purified monoclonal anti-amyloid A antibody mc29, strongly suggesting that SAA counteracts neutrophil responses to cytokines or bacterial products. This newly recognized function of SAA may help to prevent oxidative tissue destruction.