Objective: Circulating levels of interleukin (IL)-18 are associated with the metabolic syndrome and risk for the development of cardiovascular disease (CVD). This study investigated the association between the circulating IL-18 levels and the -137 G/C polymorphism within the IL-18 gene with metabolic risk factors for CVD in normal-weight and obese black South African women.
Methods: Blood pressure (BP), body composition (dual-energy X-ray absorptiometer), visceral adiposity (computerized tomography), as well as fasting glucose, insulin, lipid profile, IL-18 levels, and IL-18 genotype were measured in 104 normal-weight (body mass index (BMI) < or = 25 kg/m2) and 124 obese (BMI > or = 30 kg/m2) black South African women.
Results: Subjects with a GC genotype (23%) had a greater mean arterial pressure (MAP, 90.6+/-11.1 vs 85.5+/-10.3 mmHg, P<0.001) than the subjects with the GG genotype. Serum IL-18 levels were not associated with IL-18 genotype (P=0.985); however, they significantly correlated with percentage of body fat (r=0.25, P<0.001), visceral adiposity (r=0.32, P<0.001), MAP (r=0.22, P=0.001), HOMA-IR (r=0.33, P<0.001), fasting insulin (r=0.25, P<0.001), triglyceride (r=0.16, P<0.05), and high-density lipoprotein-cholesterol (r=-0.14, P<0.05) levels, after adjusting for age and body fatness.
Conclusions: We show for the first time that the GC genotype of the IL-18 -137 G/C polymorphism and the circulating IL-18 levels are independently associated with raised BP. Moreover, fasting IL-18 levels are associated with the other metabolic risk factors for CVD in normal-weight and obese black South African women.