Effect-based detection of synthetic glucocorticoids in bovine urine

Challenges to testing for the illicit use of anabolic substances in meat-producing animals stem from the production of new synthetic compounds and the administration of low-dose cocktails to circumvent detection by the surveillance schemes of European Union member states. This work evaluated for the first time GR-CALUX, a highly sensitive reporter gene assay, as a screening tool for the detection of synthetic glucocorticoids in bovine urine. In order to verify the effect of natural corticosteroids on the method, the bioassay was tested first using blank urine samples collected at the farm and the slaughterhouse. Next, the dose-response curves were measured for the most commonly used synthetic glucocorticoids. The bioassay's ability to detect them in spiked and incurred samples of bovine urine was then evaluated. Finally, its performance was compared against a commercially available ELISA kit ordinarily used in screening activities. GR-CALUX performance did not appear to be influenced by physiological levels of endogenous corticosteroids in the farm samples, whereas an increase in these hormones might invalidate the analysis in samples obtained at the slaughterhouse. Using pure compounds, GR-CALUX showed a high sensitivity toward the synthetic glucocorticosteroids tested in order of relative potencies: flumethasone ≫ dexamethasone > betamethasone > methylprednisolone > prednisolone. As expected, the bioassay failed to detect the prohormone prednisone. The results obtained from analysis of the spiked and incurred specimens reproduced those of the blank samples and the pure compounds. GR-CALUX is a promising screening tool for the detection of illicit treatments in meat-producing bovines. Its ability to detect the most commonly used synthetic glucocorticoids was comparable with the ELISA test. Importantly, it appeared to be less susceptible to matrix effects than ELISA.