Objectives: Leptin is a multifunctional polypeptide produced primarily by adipocytes and associated with the occurrence of obesity and insulin resistance. Tumor necrosis factor-alpha (TNF-alpha), a polypeptide cytokine produced primarily by mononuclear phagocytes, plays a key role in the initiation of the inflammatory response but has a multitude of effects in many tissues. The interactions between TNF-alpha and insulin on leptin expression are complicated and have not been completely described. The purpose of this study is to evaluate interactions between TNF-alpha and insulin on circulating leptin levels among normal and overweight children.
Design and methods: After multi-stage sampling, we randomly selected 1,500 school children in this survey. All children completed a questionnaire on their disease history and lifestyle characteristics. We measured body weight, height, waist and hip circumference of children and calculated BMI and Waist-to-hip ratio (WHR). We also measured plasma tumor necrosis factor-receptor 1 (TNF-R1) by ELISA, plasma insulin and circulating leptin levels by RIA using commercial kits. We divided the children into normal or overweight groups using BMI criteria (85th percentile) to evaluate the relationship of TNF-R1 and insulin on circulating leptin concentrations.
Results: In general, boys were taller, heavier and had higher TNF-R1 and lower leptin levels than girls. Plasma leptin levels were positively correlated with anthropometric variables and insulin levels among children in both genders. In multivariate regression analyses, plasma insulin levels were significantly positive associated with leptin levels in normal weight children. Plasma TNF-R1 levels were positively associated with leptin levels even after adjusting for BMI in girls only.
Conclusions: From this study, we found that plasma insulin plays certain role in leptin expression among normal weight children. However, TNF-R1 plays a more significant role in leptin expression among girls only.