Interleukin-10 and tumor necrosis factor gene polymorphisms and risk of coronary artery disease and myocardial infarction

Abstract

Inflammation plays an important role in the pathogenesis of atherosclerosis and acute coronary syndromes. Cytokines IL-10 and TNF-α exert opposite functions in inflammatory reactions, IL-10 acting predominantly as an antiinflammatory and TNF-α as a proinflammatory factor. Functional single nucleotide polymorphisms in the genes of IL-10, TNF-α, and TNF-β are associated with gene expression and plasma levels of IL-10 and TNF-α. The aim of the study was to assess whether these IL-10 and TNF gene polymorphisms are related to the risk of coronary artery disease (CAD) and myocardial infarction (MI). Consecutive, angiographically examined patients with significant coronary stenoses but without symptoms or signs of old or acute MI constituted the group with CAD (n=998) and patients with old or acute MI constituted the group with MI (n=793). Subjects with neither angiographic CAD nor symptoms or signs of MI (n=340) served as controls. They were matched with the patients for age and sex. Genotyping was performed with techniques based on the polymerase chain reaction. Allele frequencies, genotype distributions, and frequencies of allele combinations for three IL-10 promoter polymorphisms, −1082G/A, −819C/T and −592C/A, were similar between CAD patients, MI patients, and matched controls. Similarly, genetic analysis did not reveal group-specific differences for the TNF-α promoter polymorphisms −863C/A and −308G/A, as well as for the TNF-β intron 1 polymorphism 252G/A. In addition, no relationship was found between specific combinations of IL-10 and TNF alleles, indicative of low IL-10 and high TNF-α production, respectively, and CAD or MI. The lack of association persisted also after adjusting for other cardiovascular risk factors. Our findings suggest that six different and functionally relevant polymorphisms of the genes coding for IL-10, TNF-α, and TNF-β are neither separately nor in cooperation associated with the risk of CAD or MI in angiographically examined patients.

Introduction

The major contribution of inflammatory mechanisms to atherosclerosis has recently been emphasized [1], [2], [3], [4]. The pattern and magnitude of cytokine release at the site of tissue injury is considered to be a critical determinant of severity and duration of the response. Interleukin-10 (IL-10) and tumor necrosis factor alpha (TNF-α) have complex and predominantly opposing roles in inflammation [1], [2], [5], [6], [7], [8], [9]. An autoregulatory loop appears to exist in which TNF-α stimulates IL-10 production, which, in turn, reduces TNF-α synthesis [10].

Playing a major role in suppressing immune and inflammatory responses, several functions of IL-10 are centered on inhibition of macrophage function, including cytotoxic activity and cytokine synthesis. In experiments with cultured cells and mice, IL-10 was found to block atherosclerotic events and it was suggested that IL-10 may arrest and reverse the chronic inflammatory response in established atherosclerosis, as well as limit thrombotic complications [11], [12].

TNF-α is a potent immunomediator and proinflammatory cytokine that has been implicated in the pathogenesis of a large number of human diseases [13]. The presence of TNF-α in the majority of atherosclerotic lesions and absence from normal tissues suggests its involvement in atherogenesis [14], [15]. TNF-α may contribute to atherosclerosis by activation of growth factors, cytokines, and chemoattractants and by effecting the synthesis and stimulation of adhesion molecules [16], [17]. Secretion of TNF-α from mononuclear leukocytes of patients with stable and unstable angina pectoris is elevated when compared with control individuals [18]. In addition, TNF-α possibly increases the risk of thrombotic events by stimulation of procoagulant activity and suppression of antithrombotic pathways in endothelial cells [19].

The human IL-10 gene is located on chromosome 1 and has been mapped to the junction between 1q31 and 1q32 [20], [21]. The genes for TNF-α and TNF-β are situated close to each other within the human leukocyte antigen (HLA) class III gene cluster on the short arm of chromosome 6, approximately 220 kilo base pairs (kbp) centromeric of the HLA-B locus and about 850 kbp telomeric of the HLA class II region [22]. Stimulation of human blood samples with bacterial lipopolysaccharide showed large interindividual variations of IL-10 and TNF-α production, suggesting a genetic component of approximately 75 and 60%, respectively [23]. Interindividual differences in the regulation of IL-10 and TNF-α production may be critical in a variety of healthy and abnormal inflammatory responses.

Several polymorphisms located close to or within the IL-10, TNF-α, and TNF-β genes are potentially associated with transcription levels, however, the molecular mechanisms linking these polymorphisms to gene expression and posttranscriptional processing are only partially known [9], [13], [24], [25], [26], [27], [28], [29], [30], [31], [32]. The best documented of these polymorphisms are the IL-10 gene promoter polymorphisms −1082G/A, −819C/T, and −592C/A, the TNF-α promoter polymorphisms −863C/A and −308G/A, as well as the TNF-β intron 1 polymorphism 252G/A [28], [33], [34], [35], [36], [37].

This study was based on the assumption that the IL-10 and TNF gene polymorphisms have a measurable influence on atherosclerotic mechanisms and contribute to or reduce the occurrence of coronary artery disease (CAD) and myocardial infarction (MI).