An amperometric opiate assay

How new nanotechnologies are changing the opioid analysis scenery? A comparison with classical analytical methods

Opioids such as heroin, fentanyl, raw opium, and morphine have become a serious threat to the world population in the recent past, due to their increasing use and abuse. The detection of these drugs in biological samples is usually carried out by spectroscopic and/or chromatographic techniques, but the need for quick, sensitive, selective, and low-cost new analytical tools has pushed the development of new methods based on selective nanosensors, able to meet these requirements. Modern sensors, which utilize "next-generation" technologies like nanotechnology, have revolutionized drug detection methods, due to easiness of use, their low cost, and their high sensitivity and reliability, allowing the detection of opioids at trace levels in raw, pharmaceutical, and biological samples (e.g. blood, urine, saliva, and other biological fluids). The peculiar characteristics of these sensors not only have allowed on-site analyses (in the field, at the crime scene, etc.) but also they are nowadays replacing the gold standard analytical methods in the laboratory, even if a proper method validation is still required. This paper reviews advances in the field of nanotechnology and nanosensors for the detection of commonly abused opioids both prescribed (i.e. codeine and morphine) and illegal narcotics (i.e. heroin and fentanyl analogues).

Nanoarchitectonics for Abused-Drug Biosensors

Rapid, accessible, and highly accurate biosensors for the detection of addictive and abused drugs are needed to reduce the adverse personal and societal impacts of addiction. Modern sensors that utilize next-generation technologies, e.g., nanobiotechnology and nanoarchitectonics, have triggered revolutionary progress in the field as they allow accurate detection and tracking of trace levels of major classes of drugs. This paper reviews advances in the field of biosensors for the detection of commonly abused drugs, both prescribed such as codeine and morphine, and illegal narcotics like cocaine.

Chemiluminescence based immunoassay for the detection of heroin and its metabolites

Introduction: Continuous use of opiates causes drug-related illnesses, which poses an alarming situation to develop sensitive detection platform. In this study, a highly sensitive and reliable chemiluminescence immunoassay (CI) has been developed for the detection of heroin and its major metabolites in spiked urine samples. Methods: To develop robust immunoassay, monoacetyl morphine-bovine serum albumin (MAM-BSA) conjugate was synthesized and characterized thoroughly by physicochemical techniques. The anti-MAM antibodies were developed, labeled with horseradish peroxidase (HRP) and immunoassay was developed to detect the presence of target drug in spiked urine samples. Results: A competitive CI was developed, where heroin, MAM, morphine, and codeine concentration were ranged from 0-1000 ng/ mL in spiked urine samples and limit of detection were 80, 95, 90, 75 pg/ mL. Conclusion: The developed CI is highly sensitive, specific, point of care, cost-effective and can be used as a routine technique for quantitative analysis for screening of narcotic drugs.

Recent advances in immunosensor for narcotic drug detection

INTRODUCTION

Immunosensor for illicit drugs have gained immense interest and have found several applications for drug abuse monitoring. This technology has offered a low cost detection of narcotics; thereby, providing a confirmatory platform to compliment the existing analytical methods.

METHODS

In this minireview, we define the basic concept of transducer for immunosensor development that utilizes antibodies and low molecular mass hapten (opiate) molecules.

RESULTS

This article emphasizes on recent advances in immunoanalytical techniques for monitoring of opiate drugs. Our results demonstrate that high quality antibodies can be used for immunosensor development against target analyte with greater sensitivity, specificity and precision than other available analytical methods.

CONCLUSION

In this review we highlight the fundamentals of different transducer technologies and its applications for immunosensor development currently being developed in our laboratory using rapid screening via immunochromatographic kit, label free optical detection via enzyme, fluorescence, gold nanoparticles and carbon nanotubes based immunosensing for sensitive and specific monitoring of opiates.

Cytochrome P450 2D6 based electrochemical sensor for the determination of codeine

Considering the enzymatic activity of the cytochrome P450 2D6 on substrates such as codeine, the current paper includes the development of an enzymatic biosensor for detection of this drug. Home-made screen-printed electrodes were used as electrochemical transducers of the biosensor, in which the enzyme was covalently attached to the carbon surface of the working electrode, this type of modification being the most suitable for the immobilization of the biological element. Chronoamperometric measurements were carried out under optimum conditions of pH and working potential, pH 7 and +200 mV vs. screen-printed Ag/AgCl electrode, giving a reduction signal related to the concentration of codeine in solution. Consecutive additions of a solution of codeine were performed to obtain calibration curves in order to validate the electrochemical method in terms of precision and calculate its capability of detection. These biosensors were used for the determination of codeine in urine and commercial pharmaceutical samples.

Screen-printed biosensor based on the inhibition of the acetylcholinesterase activity for the determination of codeine

The current paper presents the chronoamperometric determination of codeine using screen-printed carbon electrodes that incorporate tetrathiafulvalene in the matrix of the working electrode, as mediator, and cross-linked acetylcholinesterase. Applying a potential of +250 mV, a 1mM solution of acetylthiocholine in electrolyte solution pH 7 gives an oxidation signal due to the dimerization of its metabolite after the reaction with the enzyme. This electrochemical signal is decreased by consecutive additions of a solution of codeine, which allows the performance of curves of calibration for the validation of this electrochemical method, giving a reproducibility of 3.31% (n=6) and a capability of detection of 20 µM. This type of inhibition has been studied by means of a Lineweaver-Burk plot. Additionally, the developed biosensor was used for the determination of the quantity of codeine in pharmaceutical commercial tablets and urine samples.

Calculating chemically accurate redox potentials for engineered flavoproteins from classical molecular dynamics free energy simulations

The tricyclic isoalloxazine nucleus of the redox cofactors flavin mononucleotide (FMN) and flavin adenine dinucleotide (FAD) acts as an electron sink in life-sustaining biological electron transfer (eT). The functional diversity of flavin-containing proteins (flavoproteins) transcends that of free flavins. A large body of experimental evidence attributes natural control of flavoprotein-mediated eT to tuning of the thermodynamic driving force by the protein environment. Understanding and engineering such modulation by the protein environment of the flavin redox potential (DeltaE(o)) is valuable in biotechnology and device design. In this study we employed classical molecular dynamics free energy simulations (MDFES), within a thermodynamic integration (TI) formalism, to calculate the change in FMN first reduction potential (DeltaDeltaE(o)(ox/sq)) imparted by 6 flavoprotein active site mutations. The combined performance of the AMBER ff03 (protein) and GAFF (cofactor) force fields was benchmarked against experimental data for mutations close to the isoalloxazine re- and si-faces that perturb the wild-type DeltaE(o)(ox/sq) value in Anabaena flavodoxin. The classical alchemical approach used in this study overestimates the magnitude of DeltaE(o) values, in common with other studies. Nevertheless, chemically accurate DeltaDeltaE(o) values--calculated to within 1 kcal mol(-1) of the experimental value--were obtained for five of the six mutations studied. We have shown that this approach is practical for quantitative in silico screening of the effect of mutations on the first reduction potential where experimental values and structural data are available for the wild-type flavoprotein. This approach promises to be useful as an integral part of future interdisciplinary strategies to engineer desired thermodynamic properties in flavoproteins of biotechnological interest.

Biotransformation of alkaloids

Biotransformations of alkaloids over the last decade have continued to encompass a wide variety of substrates and enzymes. The elucidation of novel alkaloid biosynthetic and catabolic pathways will continue to furnish new biocatalysts for the synthetic organic chemist. Furthermore, an improved understanding of the genetic and biochemical basis of metabolic pathways will also permit the engineering of pathways in plants and other heterologous hosts for the production of therapeutically important alkaloids. The combination of increasing commercial interest and advances in molecular biology will facilitate the availability of robust biocatalysts which are a prerequsite to achieve economically feasible processes for the production of alkaloid-based therapeutics.

Immunoassay for the determination of morphine-3-glucuronide using a surface plasmon resonance-based biosensor

Polyclonal antibodies were produced for the development of competitive ELISA's and surface plasmon resonance (SPR)-based BIAcore inhibition assays for the detection of morphine-3-glucuronide (M3G, the main metabolite of heroin and morphine). A conjugate consisting of M3G and ovalbumin was produced and used for the generation of antibodies, for the coating of immunoplates and for immobilisation onto BIAcore chips. Competition ELISA's were developed in PBS and urine to characterise the antibodies ability to recognise free M3G. SPR-based inhibition immunoassays on BIAcore were developed. The regeneration of the surface of a chip immobilised with conjugate following antibody binding, essential for the development of inhibition assays was investigated. Regeneration of the conjugate-coated surface was optimised for both polyclonal antibodies resulting in binding-regeneration capacities of approximately 60 cycles for one antibody and 50 cycles for the second antibody. The inhibition assays developed in urine had ranges of detection of 762-24,400 (antibody 1) and 976-62,500 pg ml(-1) (antibody 2). The inter-day coefficients of variation for the assays ranged from 1.48 to 11.24%.

Biotransformation of alkaloids

Biotransformations of alkaloids over the last decade have continued to encompass a wide variety of substrates and enzymes. The elucidation of novel alkaloid biosynthetic and catabolic pathways will continue to furnish new biocatalysts for the synthetic organic chemist. Furthermore, an improved understanding of the genetic and biochemical basis of metabolic pathways will also permit the engineering of pathways in plants and other heterologous hosts for the production of therapeutically important alkaloids. The combination of increasing commercial interest and advances in molecular biology will facilitate the availability of robust biocatalysts which are a prerequsite to achieve economically feasible processes for the production of alkaloid-based therapeutics.

Engineering novel biocatalytic routes for production of semisynthetic opiate drugs

The morphine alkaloids and their semisynthetic derivatives provide a diverse range of important pharmaceutical drugs. Current production of semisynthetic opiate drugs is by chemical means from naturally occurring morphine, codeine and thebaine. Although various microbial transformations of morphine alkaloids have been identified since the 1960s, more recently there has been considerable effort devoted to engineering biocatalytic routes for producing these important compounds. Such biocatalytic routes are attractive, as they would provide an alternative to the chemical production processes which suffer from limited supply of precursors, often low yields and toxic wastes. The biotransformation of morphine and codeine to the potent analgesic hydromorphone and the mild analgesic/antitussive hydrocodone, respectively, by recombinant Escherichia coli has been demonstrated and the problems encountered when engineering such a system will be discussed.

A membrane-based displacement flow immunoassay

The use of a membrane-based continuous flow displacement immunoassay for detection of nanomolar quantities of explosives is demonstrated, and the kinetics of this system are characterized through experimentation. Antibodies of 2,4,6-trinitrotoluene (TNT) are immobilized onto a porous membrane with surface reactive sites designed to facilitate the covalent binding of the antibody. After saturating the immobilized antibody binding sites with labeled antigen, target analyte is introduced in flow, and the displacement reactions are monitored using a fluorometer. The displaced labeled antigen detected is proportional to the concentration of the analyte introduced to the antibody-labeled antigen complex. Multiple assays were performed at flow rates of 2.0, 1.0, 0.50, and 0.25 mL/min using membranes saturated with varying TNT antibody concentrations. The signal intensity (i.e. the concentration of displaced labeled antigen) was independent of antibody concentration at 1.0 mL/min, but proportional to antibody concentration at 0.25 mL/min. Our data suggests that the lower flow rate created a longer interaction time between the injected analyte and the antibody-labeled antigen complex, resulting in greater displacement of the labeled antigen and higher signal intensities than seen at higher flow rates.

Molecular analysis of the Rhodococcus sp. strain H1 her gene and characterization of its product, a heroin esterase, expressed in Escherichia coli

The structural gene for heroin esterase was cloned from Rhodococcus sp. strain H1 and expressed in Escherichia coli BL21(DE3). The purified enzyme was found to be a tetramer with an M(r) of 137,000 and an apparent K(m) of 0.88 mM for 6-acetylmorphine. The G-x-S-x-G motif was observed in the deduced amino acid sequence, suggesting that the enzyme is a serin esterase.

Bacterial morphinone reductase is related to Old Yellow Enzyme

Morphinone reductase, produced by Pseudomonas putida M10, catalyses the NADH-dependent saturation of the carbon-carbon double bond of morphinone and codeinone, and is believed to be involved in the metabolism of morphine and codeine. The structural gene encoding morphinone reductase, designated morB, was cloned from Ps. putida M10 genomic DNA by the use of degenerate oligonucleotide probes based on elements of the amino acid sequence of the purified enzyme. Sequence analysis and structural characteristics indicated that morphinone reductase is related to the flavoprotein alpha/beta-barrel oxidoreductases, and is particularly similar to Old Yellow Enzyme of Saccharomyces spp. and the related oestrogen-binding protein of Candida albicans. Expressed sequence tags from several plant species show high homology to these enzymes, suggesting the presence of a family of enzymes conserved in plants and fungi. Although related bacterial proteins are known, morphinone reductase appears to be more similar to the eukaryotic proteins. Morphinone reductase was overexpressed in Escherichia coli, and has potential applications for the industrial preparation of semisynthetic opiates.

Biological production of semisynthetic opiates using genetically engineered bacteria

Semisynthetic derivatives of morphine and related alkaloids are in widespread clinical use. Due to the complexity of these molecules, however, chemical transformations are difficult to achieve in high yields. We recently identified the powerful analgesic hydromorphone as an intermediate in the metabolism of morphine by Pseudomonas putida M10. Here we describe the construction of recombinant strains of Escherichia coli that express morphine dehydrogenase and morphinone reductase. These strains are capable of efficiently transforming the naturally occurring alkaloids morphine and codeine to hydromorphone and the antitussive hydrocodone, respectively. Our results demonstrate the potential for recombinant DNA technology to provide biological routes for the synthesis of known and novel semisynthetic opiate drugs.