Circulating retinol-binding protein-4, insulin sensitivity, insulin secretion, and insulin disposition index in obese and nonobese subjects.
OBJECTIVE
Recent investigations disclosed an upregulation of retinol-binding protein-4 (RBP4) in the adipose tissue of several insulin-resistant mouse models and increased serum RBP4 concentration in subjects with obesity and type 2 diabetes in association with insulin resistance. There is some experimental evidence that RBP4 also could been linked to insulin secretion.


METHODS
We aimed to evaluate insulin secretion, insulin sensitivity, insulin disposition index (minimal model analysis), and circulating RBP4 (enzyme-linked immunosorbent assay) in nondiabetic men with a wide range of obesity (n = 107).


RESULTS
Serum RBP4 concentration was nonsignificantly different among lean, overweight, and obese subjects. Circulating RBP4 was not associated with age, BMI, waist-to-hip ratio, or metabolic parameters, including insulin sensitivity (r = -0.03, P = 0.6). On the contrary, circulating RBP4 was negatively associated with insulin secretion, especially in obese subjects (r = -0.48, P = 0.007), in whom RBP4 also was linked to insulin disposition index (r = -0.44, P = 0.01). On multiple regression analyses to predict insulin secretion (acute insulin response [AIR(g)]), insulin sensitivity was the only factor that contributed to 17% of AIR(g) variance in nonobese subjects. In obese subjects, however, RBP4 emerged as an independent factor that contributed independently to AIR(g) variance (23%).


CONCLUSIONS
Our results suggest that oversecretion of RBP4 may negatively affect beta-cell function directly or by preventing the binding of transthyretin to its receptor. These mechanisms could be behind the association between increased circulating RBP4 and type 2 diabetes. RBP4 could be one signal from insulin-resistant tissues that impacts on beta-cell secretion.
Broch
Montserrat
M
Reseach Unit, Pere Virgili Institute for Biomedical Research, Tarragona, Spain.
Vendrell
Joan
J
Ricart
Wifredo
W
Richart
Cristóbal
C
Fernández-Real
José-Manuel
JM
D000328:Adult; D006801:Humans; D007328:Insulin / Q000096:biosynthesis; D007333:Insulin Resistance / Q000502:physiology; D008297:Male; D008875:Middle Aged; D009765:Obesity / Q000097:blood / Q000503:physiopathology*; D050177:Overweight / Q000502:physiology; D011446:Prospective Studies; D012177:Retinol-Binding Proteins / Q000032:analysis / Q000502:physiology*; D054839:Retinol-Binding Proteins, Plasma; D013851:Thinness
D007328:Insulin; C101326:RBP4 protein, human; D012177:Retinol-Binding Proteins; D054839:Retinol-Binding Proteins, Plasma