Circulating Retinol-Binding Protein-4, Insulin Sensitivity, Insulin Secretion, and Insulin Disposition Index in Obese and Nonobese Subjects
Response to Broch et al.
- Norbert Stefan, MD,
- Anita M. Hennige, MD,
- Harald Staiger, PHD,
- Erwin Schleicher, PHD,
- Andreas Fritsche, MD and
- Hans-Ulrich Häring, MD
- From the Department of Internal Medicine, Divisions of Endocrinology, Nephrology, Vascular Disease, and Clinical Chemistry, University of Tübingen, Tübingen, Germany
- Address correspondence to Norbert Stefan, MD, Department of Internal Medicine, University of Tübingen, Otfried-Müller-Str. 10, 72076 Tübingen, Germany. E-mail: norbert.stefan{at}med.uni-tuebingen.de
In the recent article by Broch et al. (1), circulating retinol-binding protein-4 (RBP4) (measured by nephelometry) was not correlated with adiposity or insulin sensitivity; however, negative correlations with indexes of insulin secretion were detected. The authors concluded that RBP4 may impair β-cell function in human subjects.
This is an interesting hypothesis, particularly because retinol seems to be required for adequate glucose-stimulated insulin secretion (2). However, retinoids in blood are not exclusively transported by RBP4 but also by albumin and lipoprotein particles (3). This suggests that the availability of retinoids in …
