Interleukin-6 Gene −174G>C and −572G>C Promoter Polymorphisms Are Strong Predictors of Plasma Interleukin-6 Levels After Coronary Artery Bypass Surgery

Abstract

Interleukin-6 (IL-6) synthesized in response to diverse stimuli may play an important role in bridging the inflammatory and atherosclerotic processes. The acute-phase response after coronary artery bypass graft surgery (CABG) is associated with the induction and release of cytokines, such as IL-6. We have examined the effect of common polymorphisms in the IL-6 gene promoter (−174G>C, −572G>C, and −597G>A) on IL-6 levels after elective CABG. DNA extracted from the peripheral blood of 127 patients was amplified by polymerase chain reaction. IL-6 genotypes were resolved by gel electrophoresis after restriction enzyme digestion. Serum IL-6 was measured before surgery and in serial samples at 6, 24, 48, and 72 hours after CABG. Genotype distribution was as expected for a population in Hardy-Weinberg equilibrium for all polymorphisms. Rare allele frequencies (±95% CIs) were similar to those reported previously: −597A 0.36 (0.30 to 0.42), −572C 0.07 (0.04 to 0.10), and −174C 0.37 (0.31 to 0.43). The −174G>C and −597G>A genotypes were in strong allelic association (Δ=0.97, P <0.001). Baseline IL-6 levels did not significantly differ between patients with different genotypes for any polymorphism. However, 6 hours after CABG, peak IL-6 levels were significantly higher ( P =0.03) in carriers of the −572C allele than in those of the −572GG genotype (355±67 versus 216±13 pg/mL, respectively) and in those with genotype −174CC compared with −174G allele carriers (287±31 versus 227±15 pg/mL, respectively; P =0.04). These effects remained statistically significant after adjusting for possible confounders, including age, sex, smoking, duration of cardiopulmonary bypass, aortic cross-clamp time, and total duration of surgery. These data demonstrate that IL-6 promoter polymorphisms influence peak IL-6 production after CABG, suggesting that these polymorphisms, which are functional in vitro, are also functional in vivo, suggesting a genetic influence on IL-6 levels after acute severe injury.