Retinol binding protein 4(RBP4), originally known as a specific transport of retinol in blood, is also a novel inflammatory and insulin resistance marker. Serum RBP4 levels are elevated in insulin-resistant mice and humans with obesity and type 2 diabetes. Animal experiments found that increased secretion of RBP4 might reduce insulin-dependent glucose uptake by muscle tissue by reducing the activity of PI(3)K (phosphoinositide 3-kinase), and increased hepatic glucose output by increasing the expression of the enzyme PEPCK2 . Studies suggested that elevated serum RBP4 was associated with components of the metabolic syndrome, including increased body-mass index, waist-to-hip ratio, serum triglyceride levels, and systolic blood pressure and decreased HDL cholesterol levels. Furthermore, circulating RBP4 concentrations were associated with subclinical cardiovascular disease, which imply that RBP4 could be involved in the development of atherosclerosis its serum levels decreased significantly under the condition of liver injury or malnutrition.

In the kidney, since RBP4 is mainly absorbed and degraded by the proximal renal tubular epithelial cells, urine RBP4 is currently the most sensitive functional biomarker of proximal tubule. Its serum and urine levels increase 50- to 100-fold in several renal disorders.

Each kit is sufficient for one 96-well plate and contains the following components:

  1. Microtiter Strips (96 wells) coated with a mouse monoclonal antibody against human RBP4
  2. 10×Wash Buffer, 40 mL
  3. 5×Assay Buffer, 30 mL
  4. 100×Detection Antibody, a mouse monoclonal antibody against human RBP4 conjugated with horseradish peroxidase, 0.12 mL
  5. Human RBP4 Standard, 200 ng of recombinant human RBP4, lyophilized
  6. Substrate solution, 12 mL, ready for use
  7. Stop Solution, 12 mL, ready for use

Sample type: serum, plasma, and adipocyte extracts or cell culture supernate samples

Sample volume:  100 uL, serum sample generally requires a 500-fold dilution in this assay.

Species:  human RBP4 and does not cross-react with mouse and rat RBP4

Detection Range:  3.12 – 200 ng/mL

Sensitivity:  3.12 ng/mL

Run time:  < 3 hours

Storage:  2-8°C upon receipt, and all reagents should be equilibrated to room temperature before use