Pharmacological characterization of new β-agonists using Huβ1- and Huβ2-adrenergic receptor binding assay in transfected HEK-293 cells

The continuous turn over of beta-agonists molecules, may affect the reliability of screening tests. To overcome possible false negative results, a bioassay is under development to detect the presence of new beta-agonists in feeds and biological matrices and so to provide a valid tool for a multi-analyte screening method. Preliminary study were focused on the pharmacological characterisation of new beta-agonists, with the aim to combine both the screening results with a toxicological evaluation about the potential health risk for consumers. The interaction of G4, G5, G6, G8 adrenergic drugs with human beta(1) - and beta(2)-adrenergic receptors expressed separately in membranes of human embryonic kidney cells in culture (HEK-293-Hubeta(1) and HEK-293-Hubeta(2)), Were studied by a receptor binding assay and results compared with those from a well-known P-adrenergic agonist (clenbuterol). The specificity of the test was assured by the use of a specific radiolabel tracer ligand ([I-125]iodopindolol) as competitor. For compounds G4, G5 and G6 the affinity (IC50) for beta(1)-adrenergic binding sites was of the same magnitude of that from clenbuterol. By contrast, G8 showed a 100-fold higher affinity. On beta(2)-adrenergic receptors the binding affinity was similar for G4 and G6, but about 10-fold higher for G5 and G8 with respect to that from clenbuterol. (C) 2004 Elsevier B.V. All rights reserved.