Interleukin 6 and the prognosis of abdominal aortic aneurysms

Abstract

Abstract Background Abdominal aortic aneurysm (AAA) is a familial disorder, inflammation being an important pathophysiological feature. Increased plasma concentrations of the inflammatory cytokine interleukin (IL) 6 have been associated with AAA and early aortic dilatation. This study was designed to test the hypothesis that high concentrations of plasma IL-6 and/or IL-6 genotype predict rapid AAA growth. Methods Genomic DNA from 466 patients, kept under ultrasonographic surveillance for small AAAs, was analysed for a G to C polymorphism at position −174 of the IL-6 promoter. Baseline plasma IL-6 concentration was measured by enzyme-linked immunosorbent assay and AAA growth rates were calculated by linear regression. Results The median concentration of plasma IL-6 was 4·9 (range 0–604) pg ml−1. IL-6 concentration was not associated with aneurysm growth rate. The frequency of the C allele was 0·40, similar to that in the healthy population. Patients of GG genotype had a lower plasma concentration of IL-6 than patients of either GC or CC genotype (median 1·9, 4·8 and 15·6 pg ml−1 respectively; P = 0·047, Kruskal–Wallis test). The AAA growth rate for patients of GG, GC and CC genotypes was 0·38, 0·36 and 0·36 cm per year respectively (P = 0·37). Mortality was lower for patients of GG genotype than for those with GC or CC genotype: hazard ratio 0·51 (95 per cent confidence interval (c.i.) 0·25–1·00), P = 0·05; and 0·32 (95 per cent c.i. 0·12–0·93), P = 0·036, for all-cause and cardiovascular mortality respectively. Conclusion Genetic polymorphism is associated with clinical events in patients with an AAA. The G to C IL-6 polymorphism at position −174 predicts future cardiovascular mortality. Neither plasma IL-6 concentration nor IL-6 genotype predicts AAA growth.