AssayPro—Human RBP4 ELISA Kit（

Introduction
Serum retinol-binding protein (RBP 4) is secreted by liver and adipocytes and is implicated in systemic insulin resistance. RBP 4 transports retinol and circulates in the plasma by binding to the larger transthyretin (TTR) homotetramer, forming a protein complex that reduces renal clearance of RBP 4. In insulin-resistant ob/ob mice, urinary fractional excretion of RBP 4 was reduced, consistent with increased retention; while TTR level is elevated (1). RBP 4 is encoded by the RBP 4 gene that maps to chromosome 10q23-q24 linked to increased risk for type 2 diabetes in different populations (2, 3). Transgenic overexpression of human RBP 4 or injection of recombinant RBP 4 in normal mice causes insulin resistance. Conversely, genetic deletion of RBP 4 enhances insulin sensitivity. Increasing serum RBP 4 induces hepatic expression of the gluconeogenic enzyme phosphoenolpyruvate carboxykinase and impairs insulin signaling in muscle (4). Expression of RBP 4 is induced in adipose tissue as a consequence of decreased glucose transporter GLUT4 expression. Increased human serum RBP 4 is associated with insulin resistance, Type II diabetes, and metabolic syndrome such as obesity, glucose intolerance, dyslipidemia, and hypertension (5, 6). Human plasma RBP 4 concentration might be a biomarker of nephropathy and cardiovascular disease in type 2 diabetic subjects (7).




Principal of the Assay
The AssayMax Human RBP 4 ELISA kit is designed for detection of human RBP 4 in urine, plasma, serum, milk, saliva, and cell culture supernatants. This assay employs a quantitative sandwich enzyme immunoassay that measures RBP 4 in less than 4 hours. A polyclonal antibody specific for RBP 4 has been pre-coated onto a microplate. RBP 4 in standards and samples is sandwiched by the immobilized antibody and biotinylated polyclonal antibody specific for RBP 4, which is recognized by a streptavidin-peroxidase conjugate. All unbound material is then washed away and a peroxidase enzyme substrate is added. The color development is stopped and the intensity of the color is measured.