TNF system activity and plasma RBP4 and apelin-36 levels in obese and normal weight women

Objective
Tumour necrosis factor α (TNF-α), retinol-binding protein 4 (RBP4), and apelin-36 are adipokines with increased circulating levels in obesity, which are involved in the development of insulin resistance. It was shown that TNF-α stimulates synthesis of apelin-36 and inhibits RBP4 expression in adipocytes. The aim of the study was the assessment of relationships between TNF system activity and plasma RBP4 and apelin-36 levels in obese and normal weight women.

Material and methods
A total of 116 women (72 obese and 44 normal weight) were enrolled into the study. In addition to the anthropometric measurements and routine biochemical parameters, plasma TNF-α, sTNFRs, RBP4, and apelin-36, insulin levels were assessed by ELISA.

Results
In obese group plasma TNF-α, sTNFR1, RBP-4, and apelin-36 levels were significantly higher, while sTNFR2 levels were lower than in the normal-weight group (Me 4.4 vs. 2.3 pg/mL, p < 0.05; 1908 vs. 1285 pg/mL, p < 0.001; 27.6 vs. 14.7 ng/mL, p < 0.001; 1.6 vs. 1.2 ng/mL, p < 0.05, and 2361 vs. 2574 pg/mL, p < 0.05, respectively). Multivariate regression analysis revealed that plasma RBP4 levels were proportional to age (β = 0.01), and plasma TNF-α (β = 0.26) and sTNFR1 (β = 0.39) levels, and inversely proportional to sTNFR2 levels (β = –0.55) independently of body mass index (BMI) and waist circumference, while apelin-36 was proportional to BMI (β = 0.01) and insulin levels (β = 0.19) and inversely proportional to age (β = –0.01), independently of waist circumference and TNF system activity.

Conclusions
Plasma RBP4, but not apelin-36 level, is associated with TNF system activity.