Association of serum levels of retinol-binding protein 4 with male sex but not with insulin resistance in obese patients.
BACKGROUND
Retinol-binding protein 4 (RBP4) is secreted by adipocytes and by the liver and modulates insulin sensitivity in animal models. However, controversial data exist regarding the association of serum levels of RBP4 with insulin resistance in humans. Obesity confers a major risk to develop insulin resistance.


OBJECTIVE
Therefore, we investigated RBP4 levels in non-diabetic obese patients and analysed the association with insulin sensitivity and other metabolic markers.


METHODS
Glucose tolerance was assessed by oral glucose tolerance tests and 70 normal glucose tolerant patients (36 women, 34 men; body mass index >30 kg/m(2)) were included in our study. We compared the serum level of RBP4 (measured by ELISA) with clinical features (age, sex, BMI, waist-to-hip-ratio, blood pressure) and laboratory findings (total cholesterol, triglycerides, fasting glucose, 2-hour glucose, fasting insulin, HOMA-IR and HOMA-B). The associations between RBP4 and the above mentioned variables were assessed using multiple linear regression models.


RESULTS
The mean age (+/-SD) of the subjects included was 48.1 (+/- 12.3) years and the mean BMI 41.6 (+/- 7.4) kg/m(2). We found significantly higher RBP4 levels in men (53.0 +/- 20.8 microg/ml) than in women (39.7 +/- 12.3 microg/ml) (p = 0.0013). However, age and sex-adjusted multiple linear regression models showed no significant association of serum RBP4 levels with BMI, waist-to-hip-ratio, blood pressure, cholesterol, triglycerides, fasting glucose, 2-hour glucose, insulin resistance (as assessed by HOMA-IR), or insulin secretion (as assessed by HOMA-B).


CONCLUSIONS
Our data show higher RBP4 levels in obese men than in obese women. However, there was no association of RBP4 levels with insulin resistance or other components of the metabolic syndrome. We conclude that obesity might already be associated with elevated RBP4 levels which then show no additional correlation with metabolic markers.
Ulgen
Fatma
F
Department of Endocrinology, Diabetes and Rheumatology, University Hospital Düsseldorf, Moorenstrasse 5, Düsseldorf, Germany.
Herder
Christian
C
Kühn
Markus C
MC
Willenberg
Holger S
HS
Schott
Matthias
M
Scherbaum
Werner A
WA
Schinner
Sven
S
D017667:Adipocytes / Q000378:metabolism; D000328:Adult; D001794:Blood Pressure; D015992:Body Mass Index; D005260:Female; D005947:Glucose / Q000378:metabolism; D005951:Glucose Tolerance Test; D006801:Humans; D007328:Insulin / Q000097:blood / Q000378:metabolism; D007333:Insulin Resistance / Q000502:physiology*; D016014:Linear Models; D008099:Liver / Q000378:metabolism; D008297:Male; D024821:Metabolic Syndrome / Q000097:blood / Q000378:metabolism; D008875:Middle Aged; D009765:Obesity / Q000097:blood* / Q000378:metabolism; D054839:Retinol-Binding Proteins, Plasma / Q000378:metabolism*; D014280:Triglycerides / Q000378:metabolism; D049629:Waist-Hip Ratio
D007328:Insulin; D054839:Retinol-Binding Proteins, Plasma; D014280:Triglycerides; D005947:Glucose