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      Lack of association between polymorphisms of the IL18R1 and IL18RAP genes and cardiovascular risk: the MORGAM Project

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          Abstract

          Background

          Interleukin-18 is a pro-inflammatory cytokine suspected to be associated with atherosclerosis and its complications. We had previously shown that one single nucleotide polymorphism (SNP) of the IL18 gene was associated with cardiovascular disease (CVD) through an interaction with smoking. As a further step for elucidating the contribution of the IL-18 pathway to the etiology of CVD, we here investigated the association between the genetic variability of two IL-18 receptor genes, IL18R1 and IL18RAP, with the risk of developing CVD.

          Methods

          Eleven tagging SNPs, 5 in IL18R1 and 6 in IL18RAP, characterizing the haplotypic variability of the corresponding genes; were genotyped in 5 European prospective CVD cohorts including 1416 cases and 1772 non-cases, as part of the MORGAM project. Both single-locus and haplotypes analyses were carried out to investigate the association of these SNPs with CVD.

          Results

          We did not find any significant differences in allele, genotype and haplotype frequencies between cases and non-cases for either of the two genes. Moreover, the search for interactions between SNPs located in different genes, including 5 IL18 SNPs previously studied in the MORGAM project, and between SNPs and environmental factors remained unfruitful.

          Conclusion

          Our analysis suggests that the variability of IL18R1 and IL18RAP genes are unlikely to contribute to modulate the risk of CVD.

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          Most cited references22

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          Expression of interleukin-18 in human atherosclerotic plaques and relation to plaque instability.

          Interleukin (IL)-18 is a potent proinflammatory cytokine with potential atherogenic properties. Its expression and role in atherosclerosis, however, are unknown. In the present study, we examined stable and unstable human carotid atherosclerotic plaques retrieved by endarterectomy for the presence of IL-18 using reverse transcription-polymerase chain reaction (PCR), Western blot, and immunohistochemical techniques. IL-18 was highly expressed in the atherosclerotic plaques compared with control normal arteries and was localized mainly in plaque macrophages. IL-18 receptor was also upregulated in plaque macrophages and endothelial cells, suggesting potential biological effects. To examine the role of IL-18 in atherosclerosis, we determined the relation between IL-18 mRNA expression and signs of plaque instability using real-time quantitative PCR. Interestingly, significantly higher levels of IL-18 mRNA were found in symptomatic (unstable) plaques than asymptomatic (stable) plaques (P<0.01). These results suggest, for the first time, a major role for IL-18 in atherosclerotic plaque destabilization leading to acute ischemic syndromes.
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            Interleukin-18 is a strong predictor of cardiovascular death in stable and unstable angina.

            Interleukin (IL)-18 plays a central role in orchestrating the cytokine cascade and accelerates atherosclerosis and plaque vulnerability in animal models. However, epidemiological data evaluating the role of IL-18 levels in atherosclerosis are lacking. In a prospective study of 1229 patients with documented coronary artery disease, we measured baseline serum concentrations of IL-18 and other markers of inflammation. During the follow-up period (median, 3.9 years), 95 patients died of cardiovascular causes. Median serum concentrations of IL-18 were significantly higher among patients who had a fatal cardiovascular event than among those who did not (68.4 versus 58.7 pg/mL; P<0.0001). The hazard risk ratio of future cardiovascular death increased with increasing quartiles of IL-18 (hazard risk ratio, 1.46; 95% CI 1.21 to 1.76; P for trend <0.0001). After adjustment for most potential confounders, including the strong predictor ejection fraction as well as the inflammatory variables IL-6, high-sensitive C-reactive protein, and fibrinogen, this relation remained almost unchanged, such that patients within the highest quartile of IL-18 had a 3.3-fold increase in hazard risk compared with those in the first quartile (95% CI, 1.3 to 8.4, P=0.01). This relation was observed in patients with stable angina and patients with unstable angina at baseline. Serum IL-18 level was identified as a strong independent predictor of death from cardiovascular causes in patients with coronary artery disease regardless of the clinical status at admission. This result strongly supports recent experimental evidence of IL-18-mediated inflammation leading to acceleration and vulnerability of atherosclerotic plaques.
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              Purification and characterization of the human interleukin-18 receptor.

              Interleukin (IL)-18 was identified as a molecule that induces IFN-gamma production and enhances NK cell cytotoxicity. In this paper, we report upon the purification and characterization of human IL-18 receptor (hIL-18R). We selected the Hodgkin's disease cell line, L428, as the most strongly hIL-18R-expressing cell line based on the results of binding assays. This binding was inhibited by IL-18 but not by IL-1beta. The dissociation constant (Kd) of 125I-IL-18 binding to L428 cells was about 18.5 nM, with 18,000 binding sites/cell. After immunizing mice with L428 cells and cloning, a single monoclonal antibody (mAb) against hIL-18R was obtained (mAb 117-10C). Sequentially, hIL-18R was purified from 3-[(3-cholamidopropyl)dimethylammonio]-1-propanesulfonic acid (CHAPS)-extracted L428 cells by wheat germ lectin-Sepharose 4B chromatography and mAb 117-10C-Sepharose chromatography. The internal amino acid sequences of hIL-18R all matched those of human IL-1 receptor-related protein (IL-1Rrp), the ligand of which was unknown to date. When expressed in COS-1 cells, the cDNA of IL-1Rrp conferred IL-18 binding properties on the cells and the capacity for signal transduction. From these results, we conclude that a functional IL-18 receptor component is IL-1Rrp.
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                Author and article information

                Journal
                BMC Med Genet
                BMC Medical Genetics
                BioMed Central
                1471-2350
                2009
                27 May 2009
                : 10
                : 44
                Affiliations
                [1 ]INSERM, UMR_S 937, F-75013, Paris, France
                [2 ]UPMC Univ Paris 06, UMR_S 937, F-75013, Paris, France
                [3 ]Department of Molecular Medicine, National Public Health Institute, Helsinki, Finland
                [4 ]Department of Health Promotion and Chronic Disease Prevention, National Public Health Institute, Helsinki, Finland
                [5 ]Department of Internal Medicine, University of Umeå, Umeå, Sweden
                [6 ]Centre Department of Epidemiology and Public Health, Queen's University of Belfast, Belfast, UK
                Article
                1471-2350-10-44
                10.1186/1471-2350-10-44
                2692850
                19473509
                dc5247ed-3b9c-408a-8082-0030cbfe712c
                Copyright © 2009 Grisoni et al; licensee BioMed Central Ltd.

                This is an Open Access article distributed under the terms of the Creative Commons Attribution License ( http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

                Categories
                Research Article

                Genetics
                Genetics

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