Visfatin, retinol binding protein-4, and vaspin concentrations in plasma and different tissues and their relationship to insulin resistance in morbidly obese subjects

The purpose of this study was to measure visfatin, vaspin, and retinol binding protein-4 (RBP-4) gene expression levels and protein concentrations in subcutaneous, omental, and mesenteric adipose tissue, liver, muscle tissue, and plasma in severely obese patients and to investigate the relationship between these proteins and insulin resistance markers. Thirty eight morbidly obese (BMI ≥40) subjects had the subcutaneous, omental, and mesenteric adipose, liver, and muscle tissues and blood samples taken at the time of Roux-en-Y surgeries. Visfatin, vaspin and RBP-4 gene expressions were measured by Real Time PCR, and their protein concentrations were measured with ELISA kits (Adipogen, Korea). Subjects were divided into three groups as normal (n=13), pre-diabetic (n=12) and diabetic (n=13) according to blood HbA1c levels. Results were analyzed using ANOVA and Pearson correlation with p <0.05 being significant. Visfatin gene expression levels were significantly lower in subcutaneous adipose tissue in all three diabetic classification groups. Omental visfatin expression levels were positively correlated with blood HbA1c levels (r = 0.351) and Homeostasis Model of Assessment - Insulin Resistance (HOMA-IR) (r = 0.401). Livers (23.1 ± 8.53 ng/mg protein) and muscle tissues (9.9 ± 8.74 ng/mg protein) had the highest and lowest visfatin protein concentrations, respectively. Omental visfatin protein concentrations were positively correlated with HOMA-IR (r=0.456) and blood HbA1c (r=0.481). Livers had the highest RBP-4 expression levels. Omental RBP-4 expression levels were positively correlated with HOMA-IR (r=0.355 ) and blood glucose levels (r=0.454). Livers (11621 ± 1033.5 ng/mg protein) had the highest RBP-4 protein concentrations, and mesenteric (339.4 ± 47.78 ng/mg protein) had the lowest concentrations. RBP-4 protein concentrations in omental were positively correlated with blood glucose levels (r = 0.363). Omental vaspin expression levels were positively correlated with blood HbA1c levels. Livers (2.19 ± 0.34 ng/mg protein) and mesenteric adipose tissues (0.36 ± 0.16 ng/mg protein) had the highest and lowest vaspin protein concentrations, respectively. Mesenteric vaspin protein concentrations were positively correlated with HOMA-IR, blood glucose, and HbA1c levels. In conclusion, visfatin, vaspin, and RBP-4 might play important roles in insulin resistance. Higher concentrations of visfatin and RBP-4 in omental adipose tissues and vaspin in mesenteric adipose tissues were associated with higher levels of insulin resistance. The correlations of visfatin, vaspin, and RBP-4 with insulin resistance are tissue-dependent. Further studies are needed to investigate the underlying mechanisms of these inflammatory factors in insulin resistance.