Novel Receptor-Binding-Based Assay for the Detection of Opioids in Human Urine Samples

Consumption of opioids is a growing global health problem. The gold standard for drugs of abuse screening is immunochemical assays. However, this method comes with some disadvantages when screening for a wide variety of opioids. Detection of the binding of a compound at the human mu-opioid receptor (MOR) offers a promising alternative target. Here, we set up a urine assay to allow for detection of compounds that bind at the MOR, thus allowing the assay to be utilized as a screening tool for opioid intake. The assay is based on the incubation of MOR-containing cell membranes with the selective MOR-ligand DAMGO and urine. After filtration, the amount of DAMGO in the eluate is analyzed by liquid chromatography tandem mass spectroscopy (LC-MS/MS). The absence of DAMGO in the eluate corresponds to a competing MOR ligand in the urine sample, thus indicating opiate/opioid intake by the suspect. Sensitivity and specificity were determined by the analysis of 200 consecutive forensic routine casework urine samples. A pronounced displacement of DAMGO was observed in 29 of the 35 opiate/ opioid-positive samples. Detection of fentanyl intake proved to be the most challenging aspect. Applying a cut-off value of, e.g., 10% DAMGO binding would lead to a sensitivity of 83% and a specificity of 95%. Consequently, the novel assay proved to be a promising screening tool for opiate/opioid presence in urine samples. The nontargeted approach and possible automation of the assay make it a promising alternative to conventional methods.