Variant screening of the serum amyloid A1 gene and functional study of the p.Gly90Asp variant for its role in atherosclerosis

Investigating the Correlation between Serum Amyloid A and Infarct-Related Artery Patency Prior to Percutaneous Coronary Intervention in ST-Segment Elevation Myocardial Infarction Patients

Serum amyloid A (SAA) is a cardiovascular risk factor and may serve as a predictor of infarct-related artery (IRA) patency in patients with ST-segment elevation myocardial infarction (STEMI). We measured SAA levels in STEMI patients who underwent percutaneous coronary intervention (PCI) and investigated their association with IRA patency. According to the Thrombolysis in Myocardial Infarction (TIMI) flow grade, 363 STEMI patients undergoing PCI in our hospital were divided into an occlusion group (TIMI 0-2) and a patency group (TIMI 3). The SAA level before PCI was significantly higher in STEMI patients with IRA occluded than in those with patent ones. At a cutoff value of 36.9 mg/L, SAA had a sensitivity of 63.0% and a specificity of 90.6% (area under the ROC curve [AUC] = .833, 95% CI: .793-.873, P < .001). Multivariate logistic regression analysis showed that SAA was an independent predictor of IRA patency in STEMI patients before PCI (odds ratio [OR] = 1.041, 95% CI: 1.020-1.062, P < .001). SAA can be used as a potential predictor of IRA patency in STEMI patients before PCI.

Fluorescent quenching probes based SAA 1 genotyping with a fully automated system

Objective

The aim of the present study is to develop and validate a reliable and simple application for genotyping serum amyloid A1 (SAA1).

Methods

The specific nested PCR was performed to amplify a product of SAA1 gene. Two quenching probes (QPs) were designed for detecting two single nucleotide polymorphism (SNP) sites, rs1136743(C/T) and rs1136747(C/T) respectively for SAA1 genotypes. The specific nested PCR and QPs of SAA1 genotying was introduced into a fully automated genotyping system (I-densy, ARKRAY, Inc.), which enables the genotyping of SAA1 from whole blood.

Results

Six genotypes of SAA1 (α^+/+, β^+/+, γ^+/+, αβ, αγ and βγ) could be determined by monitoring the fluorescence intensity of two QPs with melting temperature (TM) analysis. Total 121 clinical samples were SAA1 genotyped in the fluorescent quenching probes based method with a fully automated I-densy system and were further sequence confirmed with a PCR direct sequencing approach.

Conclusion

This fully automated system is a rapid and reliable strategy for the SAA1 genotyping and for its future clinical application.

Investigating the pernicious effects of heparan sulfate in serum amyloid A1 protein aggregation: a structural bioinformatics approach

Amyloid-A mediated (AA) amyloidosis is the pathogenic byproduct of body's prolonged exposure to inflammatory conditions. It is described by the aggregation of mutated/misfolded serum amyloid A1 (SAA1) protein in various tissues and organs. Genetic polymorphism G90D is suspected to cause AA amyloidosis, although the causal mechanism remains cryptic. Recent experimental findings insinuate that heparan sulphate (HS), a glycosaminoglycans, exhibits binding with SAA1 to promote its aggregation. To foster the enhanced binding of HS, we computationally determined the pernicious modifications in G90D mutant SAA1 protein. Also, we examined the influence of HS on the dynamic conformation of mutant SAA1 that could potentially succor amyloidosis. Accordingly, the protein-ligand binding studies indicate that upon SNP G90D, SAA1 protein exhibited an augmented association with HS. Further, the simulation of HS bound mutant SAA1 complex delineates an increase in RMSD, Rg, and RMSF. Also, both RMSD and Rg evinced a fluctuating trajectory. Further, the complex showed increase of beta turn in its secondary structural composition. Additionally, the free energy landscape of mutant SAA1-HS complex posits the occurrence of multiple global minima conformers as opposed to the presence of a single global energy minima conformation in native SAA1 protein. In conclusion, the aforementioned conformational ramifications induced by HS on SAA1 could potentially be the proteopathic incendiary behind AA amyloidosis; this incendiary will need to be considered in future studies for developing effective therapeutics against AA amyloidosis.Communicated by Ramaswamy H. Sarma.

Serum amyloid A1 can be a novel biomarker for evaluating the presence and severity of acute coronary syndrome

BACKGROUND

Serum amyloid A (SAA) is an acute phase protein and a novel inflammatory biomarker of cardiovascular diseases. Of the four subtypes, SAA1 is the most representative biomarker. In this study, we aimed to assess the value of SAA1 as a novel biomarker for evaluating the presence and severity of acute coronary syndrome (ACS) in Chinese patients.

METHODS AND RESULTS

A total of 140 ACS patients and 88 non-ACS patients (including 36 stable coronary artery disease (SCAD) patients and 52 healthy controls) who underwent coronary angiography were enrolled. The SAA1 level was significantly higher in ACS patients compared with the SCAD and healthy control subgroups (P < 0.001, respectively), and was significantly higher in the high SYNTAX Score II (SS II) group compared with the medium SS II group and low SS II group (P < 0.001, respectively) in ACS patients. The cutoff level of SAA1 for indicating the presence of ACS was 324.65 ng/mL (sensitivity of 77.9%, specificity of 60.2% and an area under the curve of 0.717). The increased SAA1 levels were positively associated with the presence (OR = 1.013, P < 0.001) and severity (OR = 1.023, P < 0.001) of ACS. Furthermore, there was a positive correlation between SAA1 levels and SS II (r = 0.467, P < 0.001).

CONCLUSIONS

Our results suggest that elevated SAA1 levels may be a novel biomarker for evaluating the presence of ACS and the severity of CAD in ACS patients. Measuring SAA1 levels makes it possible to evaluate the presence of ACS and severity of CAD in ACS patients.

Characterization of differentially expressed plasma proteins in patients with acute myocardial infarction

Acute myocardial infarction (AMI) remains a leading cause of morbidity and mortality worldwide. Novel biomarkers are needed to identify NSTEMI in AMI patients. The study objective was to use proteomics to identify novel plasma biomarkers for STEMI and NSTEMI patients. iTRAQ analysis was performed on pooled samples from 8 healthy controls and 12 STEMI and 12 NSTEMI patients. Bioinformatics analysis identified 95 differentially expressed proteins that were differentially expressed in the plasma of AMI patients and healthy controls; 28 of these proteins were found in STEMI/Con (22 upregulated and 6 downregulated), 48 in NSTEMI/Con (12 upregulated and 36 downregulated), and 44 in NSTEMI/STEMI (11 upregulated and 33 downregulated). Protein network analysis was then performed using STRING software. Functional analysis revealed that the identified plasma proteins were mainly involved with carbon metabolism, toll-like receptor signaling pathway, and hypertrophic cardiomyopathy. Nine of the proteins (SSA1, MDH1, FCN2, GPI, S100A8, LBP, vinculin, VDBP, and RBP4) that changed levels during AMI progression were further validated by ELISA. The constructed plasma proteome could reflect the AMI pathogenesis molecular mechanisms and provide a method for the early identification of NSTEMI in AMI patients. SIGNIFICANCE: The aim of this study was to use proteomics to identify novel predictive plasma biomarkers for patients with acute myocardial infarction (AMI), which would allow for either identification of individuals at risk of an infarction, and early identification of NSTEMI in patients with AMI. Using an approach that combined iTRAQ with LC-MS/MS, we found 95 proteins that showed significant differences in expression levels among the AMI patients and healthy controls. The proteins SSA1, MDH1, FCN2, GPI, S100A8, LBP, vinculin, VDBP, and RBP4 were found to play crucial roles in the pathogenesis of AMI. Using bioinformatics analysis, we found that dysregulation of carbon metabolism, toll-like receptor signaling pathway, and hypertrophic cardiomyopathy may be the major driving forces for cardiac damage during myocardial infarction. However, further investigations are needed to verify the mechanisms involved in the development of AMI especially NSTEMI. Taken together, our findings lay the foundation for understanding the molecular mechanisms underlying the pathogenic processes of AMI, and suggest potential applications for specific biomarkers in early diagnosis and determination of prognosis.

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-1β, 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.

Acute phase reactant serum amyloid A in inflammation and other diseases

Acute-phase reactant serum amyloid A (A-SAA) plays an important role in acute and chronic inflammation and is used in clinical laboratories as an indicator of inflammation. Although both A-SAA and C-reactive protein (CRP) are acute-phase proteins, the detection of A-SAA is more conclusive than the detection of CRP in patients with viral infections, severe acute pancreatitis, and rejection reactions to kidney transplants. A-SAA has greater clinical diagnostic value in patients who are immunosuppressed, patients with cystic fibrosis who are treated with corticoids, and preterm infants with late-onset sepsis. Nevertheless, for the assessment of the inflammation status and identification of viral infection in other pathologies, such as bacterial infections, the combinatorial use of A-SAA and other acute-phase proteins (APPs), such as CRP and procalcitonin (PCT), can provide more information and sensitivity than the use of any of these proteins alone, and the information generated is important in guiding antibiotic therapy. In addition, A-SAA-associated diseases and the diagnostic value of A-SAA are discussed. However, the relationship between different A-SAA isotypes and their human diseases are mostly derived from research laboratories with limited clinical samples. Thus, further clinical evaluations are necessary to confirm the clinical significance of each A-SAA isotype. Furthermore, the currently available A-SAA assays are based on polyclonal antibodies, which lack isotype specificity and are associated with many inflammatory diseases. Therefore, these assays are usually used in combination with other biomarkers in the clinic.

Serum amyloid A1: Structure, function and gene polymorphism

Inducible expression of serum amyloid A (SAA) is a hallmark of the acute-phase response, which is a conserved reaction of vertebrates to environmental challenges such as tissue injury, infection and surgery. Human SAA1 is encoded by one of the four SAA genes and is the best-characterized SAA protein. Initially known as a major precursor of amyloid A (AA), SAA1 has been found to play an important role in lipid metabolism and contributes to bacterial clearance, the regulation of inflammation and tumor pathogenesis. SAA1 has five polymorphic coding alleles (SAA1.1-SAA1.5) that encode distinct proteins with minor amino acid substitutions. Single nucleotide polymorphism (SNP) has been identified in both the coding and non-coding regions of human SAA1. Despite high levels of sequence homology among these variants, SAA1 polymorphisms have been reported as risk factors of cardiovascular diseases and several types of cancer. A recently solved crystal structure of SAA1.1 reveals a hexameric bundle with each of the SAA1 subunits assuming a 4-helix structure stabilized by the C-terminal tail. Analysis of the native SAA1.1 structure has led to the identification of a competing site for high-density lipoprotein (HDL) and heparin, thus providing the structural basis for a role of heparin and heparan sulfate in the conversion of SAA1 to AA. In this brief review, we compares human SAA1 with other forms of human and mouse SAAs, and discuss how structural and genetic studies of SAA1 have advanced our understanding of the physiological functions of the SAA proteins.

Genetic polymorphisms of serum amyloid A1 and coronary artery disease risk

Serum amyloid A (SAA) protein is not only an inflammatory factor but also an apolipoprotein that can replace apolipoprotein A1 (apoA1) as the major apolipoprotein of high-density lipoprotein cholesterol (HDL-C). However, the relationship between genetic polymorphisms of SAA and coronary artery disease (CAD) remains unclear. A total of four single nucleotide polymorphisms (rs12218, rs4638289, rs7131332, and rs11603089) of the SAA gene were genotyped using the polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) method in two independent case-control studies, one of the Han population (1416 CAD patients and 1373 control subjects) and the other of the Uygur population (588 CAD patients and 529 control subjects). We found that the rs12218 CC genotype was more frequent among the CAD patients than among the controls in both the Han (8.3% vs. 4.8%, P < 0.001) and Uygur populations (15.5% vs. 11.3%, P < 0.05). After adjustments for confounding factors, such as sex, age, smoking, drinking, hypertension, diabetes, and serum levels of triglycerides, total cholesterol, HDL, and plasma SAA, the differences remained significant in the Han (CC vs. CT+TT, P < 0.001, OR = 3.863, 95% CI: 1.755-12.477) and Uygur groups (CC vs. CT+TT, P = 0.031, OR = 3.022, 95% CI: 1.033-8.840). Genetic polymorphisms in SAA1 are associated with CAD in the Han and Uygur populations in western China.