β2-Adrenoceptor Polymorphisms Relate to Insulin Resistance and Sympathetic Overactivity as Early Markers of Metabolic Disease in Nonobese, Normotensive Individuals

Background The genes responsible for insulin resistance are also candidate genes for insulin resistance-related diseases, such as obesity and hypertension. Functional polymorphisms in the β2- and β3-adrenergic receptors have been reported to be associated with diabetes, hypertension, and obesity. To clarify the relevance of the β-adrenergic receptor polymorphisms to insulin resistance, we studied their association with polymorphisms of β2 (Arg16Gly, Gln27Glu) and β3 (Trp64Arg) adrenoceptor genes. Methods We studied 155 young, nonobese Japanese men using the homeostasis model assessment of insulin resistance (HOMA-IR) to divide individuals into insulin-sensitive and insulin-resistant groups. Insulin resistance in the participants was defined as HOMA-IR equal to or greater than the average plus 1 SD of 3.1. There were 69 men who were insulin resistant and 86 men who were insulin sensitive. Body mass index (BMI), blood pressure (BP), plasma glucose, insulin, leptin, norepinephrine (NE) levels, and the polymorphisms of Arg16Gly and Gln27Glu of the β2- and Trp64Arg of the β3-adrenoceptor polymorphisms were measured in all participants. Results The insulin-resistant group had higher frequency of the Gly16 allele of Arg16Gly compared with the insulin-sensitive group, whereas the frequencies of genotypes or alleles of Gln27Glu and Trp64Arg were similar. The insulin-resistant group had a higher mean HOMA-IR, fasting insulin, NE, and total fat mass compared with levels in the insulin-sensitive group, but the BMI and leptin levels were similar. The subjects carrying the Gly16 allele of the β2-adrenoceptor gene had a higher mean HOMA-IR, fasting insulin, NE, body fat mass, and BP than those without the Gly16 allele. Conclusions The Gly16 mutation of the β2-adrenoceptor gene is associated with increased insulin resistance, adiposity, and BP accompanied by higher plasma NE levels early in the metabolic disease in developing obesity. These findings show an important role of β2-adrenoceptor gene polymorphisms in the association of insulin resistance in hypertension and obesity.