Validation of a New Recombinant Antibody Fragment (rFab)-Based Homogeneous Enzyme Immunoassay for the Highly Specific Detection of 6-Acetylmorphine in Urine.

The detection of 6-acetylmorphine (6-AM) in urine by immunoassay methods is challenging due to its short half-life and its similarity in structure to many commonly abused opiates that are often present at very high concentrations in urine. Current 6-AM homogeneous enzyme immunoassays use lyophilized reagents because of the instability of 6-AM in water or lack of the required specificity due to high cross-reactivity with morphine. A new 6-AM rFab-based homogeneous enzyme immunoassay (HEIA) has been developed with highly improved specificity. Using a cutoff concentration of 10 ng/mL, morphine or morphine glucuronides did not produce a positive signal up to 300,000 or 1,000,000 ng/mL, respectively. Assay imprecision (n = 80) was less than 1.5% using four replicates per day for 20 days over the range 0-20 ng/mL. Cross-reactivity with structurally related or non-related compounds was assessed at concentrations up to 1,000,000 ng/mL. Interferences from endogenous compounds at ±25% cutoff were also performed at the concentrations ranging from 100,000 to 500,000 ng/mL. The effect of varied pH values on assay performance at ±25% cutoff was investigated; no false-positive or false-negative results were observed between pH 4 and -11. Based on the analysis of 149 authentic urine samples, the accuracy of the 6-AM HEIA compared with LC-MS-MS was 100%. These results demonstrated that rFab can be suitable for traditional HEIA with desired detection sensitivity and stability.

Validation of a new homogeneous immunoassay for the detection of carisoprodol in urine.

The objective of this project was to validate a new high-throughput homogeneous enzyme immunoassay (HEIA) for the rapid detection of carisoprodol in human urine. Carisoprodol (Soma(®)) and meprobamate are widely prescribed as musculoskeletal pain relief drugs and are listed as one of the 10 most frequently identified drugs associated with DUI cases. Carisoprodol has a short elimination half-life of 1-3 h; however, its major active metabolite, meprobamate, has a longer elimination half-life of 6-17 h. As a result, it is important for an immunoassay to cross-react with both compounds. The advantage of this new assay is that cutoff concentrations can be adjusted between 100 and 500 ng/mL. The reportable range was 25 to 1000 ng/mL for carisoprodol and 50 to 10,000 ng/mL for meprobamate. The intraday coefficient of variation (% CV) for the semi-quantitative assay was less than 1%. The homogeneous assay was validated with a total of 86 urine samples previously analyzed by liquid chromatography-tandem mass spectrometry with carisoprodol concentrations ranging from 50 to 10,000 ng/mL. The accuracy was found to be 100% when immunoassay cutoff concentrations of carisoprodol and meprobamate were set at 100 and 1000 ng/mL, respectively.

Development of a homogeneous immunoassay for the detection of fentanyl in urine.

OBJECTIVE: Fentanyl is an extremely potent synthetic opioid that is widely used for chronic pain treatment; it is highly addictive and prone to abuse. The objective is to develop a high throughput homogeneous enzyme immunoassay (HEIA) for the rapid detection of fentanyl in human urine. METHODS: The HEIA is based on an immunoassay format in which both the antibody and enzyme-drug conjugate are in ready-to-use solution. In the absence of the target analyte in the specimen, enzyme-labeled drug conjugate binds to the antibody and results in a decrease of the enzyme (G6PDH) activity; hence there is lower absorbance at 340 nm. If the target analyte is present in the specimen, it competes with the enzyme-labeled drug to bind to limited amount of specific antibody that result in more enzyme activity and yields an increased absorbance at 340 nm. A polyclonal "in-house" antibody was selected that is capable of measuring fentanyl at low concentrations thus the assay detection limit was determined to be 1 ng/mL. The assay was validated with clinical urine specimens that previously confirmed positively or negatively for fentanyl/norfentanyl by LC-MS/MS. RESULTS: The intra-day (n = 20) and inter-day (n = 100) precision of the assay was less than 1% CV. No interferences from structurally unrelated and commonly ingested drugs were observed at a concentration of 10,000 ng/mL. A total of 209 LC-MS/MS confirmed urine specimens (149 positive and 57 negative samples) were analyzed by HEIA. The sensitivity, specificity, and accuracy values were 99%, 95%, and 98% respectively. CONCLUSION: This paper describes the development of a highly sensitive homogenous enzyme immunoassay for detecting fentanyl in urine at a cut-off concentration of 2 ng/mL.

A nonafluoro nucleoside as a sensitive 19f NMR probe of nucleic acid conformation.

A nucleoside carrying a perfluorinated tert-butyl group ( 4) was prepared by a Sonogashira coupling of 5-iodo-2'-deoxyuridine with 4,4,4-trifluoro-3,3-bis(trifluoromethyl)-1-butyne in nearly quantitative yield and subsequently incorporated into DNA oligomers. Thermal denaturation studies showed that 4 had a negligible effect on duplex stability when compared to thymidine. Transition from single strand to duplex was monitored by (19)F NMR spectroscopy at micromolar concentrations of oligomers, demonstrating the sensitivity of 4 as an NMR reporter nucleoside.

Development and GC-MS validation of a highly sensitive recombinant G6PDH-based homogeneous immunoassay for the detection of buprenorphine and norbuprenorphine in urine.

Buprenorphine is now increasingly prescribed as an alternative to methadone for the treatment of heroin addiction. Because of its potency (dosage usages from 0.2 mg to 8 mg), the drug concentrations in body fluids are normally very low. Here, we report the first recombinant glucose-6-phosphate dehydrogenase (G6PDH)-based homogeneous immunoassay (EMIT-type assay) for free buprenorphine and free norbuprenorphine in urine. The antibody used in this assay cross-reacts nearly identically with buprenorphine and norbuprenorphine and, at the same time, has less than 1% cross-reactivity with a wide range of commonly prescribed opiates, particularly those structurally related compounds such as morphine, codeine, and dihydrocodeine. More importantly, this assay has a low detection limit of 1 ng/mL for buprenorphine or norbuprenorphine. Further evaluation of this technique using gas chromatography-mass spectrometry (GC-MS) of authentic urine samples demonstrated that the accuracy of the assay is greater than 95%. Because this assay is designed to measure the free drugs in urine, it resulted in simplification for GC-MS or liquid chromatography-MS confirmation methods that did not require urine hydrolysis before solid-phase or liquid-liquid extraction.