The −174G/C polymorphism of IL-6 is useful to screen old subjects at risk for atherosclerosis or to reach successful ageing

Abstract

High levels of IL-6 are coupled with impaired immune efficiency, morbidity and mortality in ageing. Elderly men with GG (C−) genotype in −174 locus of IL-6 promoter are disadvantaged for longevity due to higher IL-6 than CG or CC (C+) carriers. As IL-6 increases in atherosclerosis, the study of the polymorphism of IL-6 may be a useful tool in identifying old subjects at risk for atherosclerosis. Thus, we divided old men into C+ and C− genotypes. Natural killer (NK) cell cytotoxicity, IL-6, IL-10, TNF-α, MTmRNA and zinc ion bioavailability were also evaluated and compared with nonagenarians and old patients affected by carotid stenosis. Old C− patients display, other than elevated IL-6, higher IL-10, TNF-α and MTmRNA coupled with impaired NK cell cytotoxicity and lower zinc ion bioavailability than C+ patients. The same trend is observed in old subjects with C− phenotype. Nonagenarians with C+ genotype show less inflammation, low MTmRNA, satisfactory NK cell cytotoxicity and good zinc bioavailability than long-living individuals with C− genotype. A higher degree of bilateral carotid stenosis is observed in C− patients than in C+ patients (88 vs 52%). Therefore, C− genotype is coupled with chronic inflammation, impaired immune efficiency, low zinc ion bioavailability and high MTmRNA. As such, C− genotype is a risk factor for the appearance of severe atherosclerosis. Thus, the polymorphism of IL-6, together with the analysis of zinc turnover and immune parameters, is of a great clinical relevance in order to genetically identify old subjects at risk in developing severe atherosclerosis and, at the same time, to predict subjects predestined to successful ageing. As a consequence, more convenient therapies may be prepared for a complete recovery.

Introduction

High serum levels of IL-6 are coupled with diseases, disability and mortality in the elderly population (Harris et al., 1999). IL-6 affects the gene expression of metallothioneins (MTs) that are abnormally increased in aging (Mocchegiani et al., 2000). MTs are zinc-binding proteins, which play a key role in zinc metabolism and in intracellular zinc homeostasis. Zinc is a crucial trace element for the immune efficiency. A lack in zinc ion bioavailability impairs immune response (Mocchegiani et al., 1998). In old mice and humans, increased zinc-bound MTs are strictly related to low free zinc ion bioavailability with subsequent impaired peripheral immune functions, such as Natural killer (NK) cell activity (Mocchegiani et al., 2002). By contrast, low zinc-bound MTs are coupled with good zinc ion bioavailability, low IL-6 and satisfactory NK cell activity in very old mice and in centenarians (Mocchegiani et al., 2002, Mocchegiani et al., 2003). Therefore, the homeostasis of zinc-bound MTs, via IL-6, is crucial in conferring immune performances and, at the same time, to reach successful ageing.

IL-6 plays a major role in acute phase response and in pro/anti-inflammatory cytokine polarisation. (Xing et al., 1998). A dysregulation of IL-6 is involved in the pathogenesis of some age-related diseases, including chronic heart failure (Sharma et al., 2001) and atherosclerosis; the latter has a substantial inflammatory background (Ross, 1999; Jones et al., 2001) also due to an altered TNF-α and IL-10 production (Bruunsgaard et al., 2001a). These last cytokines have complex and opposite roles during inflammation. IL-10 limits inflammatory responses, whereas TNF-α determines the strength and the length of local and systemic inflammatory reactions (Lio et al., 2003). Therefore, an altered production of pro/anti inflammatory cytokines promote an atherogenic profile leading to the appearance of atherosclerosis (Bruunsgaard et al., 2001a), which is also a pathology characterized by impaired peripheral immune efficiency (Bruunsgaard et al., 2001b) and by zinc deficiency that impairs the integrity of the endothelial cells during inflammatory conditions (Hennig et al., 1999).

−174 G/C polymorphism of IL-6 is strictly linked with the appearance of cardiovascular diseases. The GG genotype of IL-6 was associated with a history of ischaemic stroke (Pola et al., 2003) and with a major thickness of intima-media wall (IMT). This occurs either in subjects affected by stenosis of carotid arteries (Rundek et al., 2002) or in atherosclerotic patients affected by coronary artery disease (Rauramaa et al., 2000) or by peripheral artery occlusive disease (Flex et al., 2002).

Recently, it has been shown that aged males with GG genotype (called C−) at −174 C/G locus display higher serum levels of IL-6 than old subjects and centenarians with CC or CG genotypes (called C+) (Bonafe et al., 2001). Moreover, the frequency of C− genotype decreases in centenarians, especially in males (Bonafe et al., 2001). This intriguing finding suggests that old men with C− genotype have less probability to reach successful ageing with the appearance of age-related diseases, including atherosclerosis, due to chronic inflammation by high persistent levels of IL-6 (Franceschi et al., 1995).

On this basis, the aim of the present paper is to screen atherosclerotic male patients for the two IL-6 genotypes (C+ and C−) in relation to zinc ion bioavailability, MTs homeostasis and peripheral immune response (NK cell activity) in comparison with elderly and nonagenarian subjects, who will be in turn screened for the same IL-6 genotypes. Moreover, the degree of carotid stenosis in C+ and C− patients will be evaluated. This genetic screening may be useful in characterizing old subjects at risk for the appearance and progression of atherosclerosis. This implies a better knowledge of the atherosclerotic patients at the clinical level. As a consequence, a more convenient or improved therapy may be suggested for a complete recovery.