Circulating Soluble IL-6 Receptor Concentration and Visceral Adipocyte Size Are Related to Insulin Resistance in Taiwanese Adults with Morbid Obesity.

Abstract

Morbid obesity is related to chronic inflammation and many metabolic complications. Interleukin (IL)-6 plays a pivotal pathophysiological role in obesity, and IL-6 trans-signaling through the soluble IL-6 receptor (sIL-6R) has a major proinflammatory effect. The aim of this study was to investigate the association between sIL-6R, adipocyte size, and insulin resistance in morbidly obese individuals. We measured concentrations of sIL-6R, high-sensitivity C-reactive protein, and lipid parameters and estimated homeostasis model assessment of insulin resistance (HOMA-IR) before the patients underwent bariatric surgery. Mesenteric adipose tissue was collected during surgery, and adipocyte size and concentrations of membrane-bound IL-6 receptor (mIL-6R) were evaluated. In total, 35 adults (20 men and 15 women) were recruited. The subjects with high HOMA-IR (≥2.4) had higher fasting glucose/insulin, triglycerides, sIL-6R, and adipocyte size and lower high-density lipoprotein cholesterol and mIL-6R than those with low HOMA-IR (<2.4). Adipocyte size positively correlated with sIL-6R (r = 0.559, P = 0.001) and HOMA-IR (r = 0.773, P ≤ 0.001) independent of age, gender, body mass index (BMI), waist, and use of diabetic drugs. In addition, every 1 ng/mL increase in sIL-6R concentration corresponded to a 10.2% decrease in the likelihood of maintaining lower insulin resistance. Furthermore, an sIL-6R level of 77.45 ng/mL was a reasonable cutoff level to propose lower insulin resistance in morbidly obese subjects. Circulating sIL-6R is more closely associated with insulin resistance status than waist-to-hip ratio or BMI in morbidly obese Taiwanese adults. sIL-6R may be a useful biomarker to assess insulin resistance among morbidly obese subjects.