Chemiluminescence imaging in bioanalysis

Recent advances in hydrogen peroxide imaging for biological applications

Mounting evidence supports the role of hydrogen peroxide (H2O2) in physiological signaling as well as pathological conditions. However, the subtleties of peroxide-mediated signaling are not well understood, in part because the generation, degradation, and diffusion of H2O2 are highly volatile within different cellular compartments. Therefore, the direct measurement of H2O2 in living specimens is critically important. Fluorescent probes that can detect small changes in H2O2 levels within relevant cellular compartments are important tools to study the spatial dynamics of H2O2. To achieve temporal resolution, the probes must also be photostable enough to allow multiple readings over time without loss of signal. Traditional fluorescent redox sensitive probes that have been commonly used for the detection of H2O2 tend to react with a wide variety of reactive oxygen species (ROS) and often suffer from photostablilty issues. Recently, new classes of H2O2 probes have been designed to detect H2O2 with high selectivity. Advances in H2O2 measurement have enabled biomedical scientists to study H2O2 biology at a level of precision previously unachievable. In addition, new imaging techniques such as two-photon microscopy (TPM) have been employed for H2O2 detection, which permit real-time measurements of H2O2 in vivo. This review focuses on recent advances in H2O2 probe development and optical imaging technologies that have been developed for biomedical applications.

Luminol-based chemiluminescent signals: clinical and non-clinical application and future uses

Chemiluminescence (CL) is an important method for quantification and analysis of various macromolecules. A wide range of CL agents such as luminol, hydrogen peroxide, fluorescein, dioxetanes and derivatives of oxalate, and acridinium dyes are used according to their biological specificity and utility. This review describes the application of luminol chemiluminescence (LCL) in forensic, biomedical, and clinical sciences. LCL is a very useful detection method due to its selectivity, simplicity, low cost, and high sensitivity. LCL has a dynamic range of applications, including quantification and detection of macro and micromolecules such as proteins, carbohydrates, DNA, and RNA. Luminol-based methods are used in environmental monitoring as biosensors, in the pharmaceutical industry for cellular localization and as biological tracers, and in reporter gene-based assays and several other immunoassays. Here, we also provide information about different compounds that may enhance or inhibit the LCL along with the effect of pH and concentration on LCL. This review covers most of the significant information related to the applications of luminol in different fields.

Isolation of the acetylcholinesterase inhibitor ungeremine from Nerine bowdenii by preparative HPLC coupled on-line to a flow assay system

In an attempt to isolate the active compound while detecting acetylcholinesterase inhibitory activity, we applied a fluorometric flow assay system to an on-line coupled preparative HPLC. The MeOH extract of Nerine bowdenii showed a strong inhibitory peak in the on-line assay, and the active compound was isolated by CPC and HPLC. It was identified as ungeremine by analysis of its (1)H-NMR, 2D-NMR, and NOESY spectra. The assignment of the active N. bowdenii constituent was also confirmed by co-TLC, co-HPLC, and co-(1)H-NMR experiments using an authentic sample of synthetic ungeremine. The IC(50) value of ungeremine was 0.35 microM, showing stronger activity than galanthamine (2.2 microM).

Determining acetylcholinesterase inhibitory activity in plant extracts using a fluorimetric flow assay

A fluorometric assay for acetylcholinesterase inhibitory activity was developed in a flow system using the fluorogenic substrate 7-acetoxy-1-methyl quinolinium iodide which is hydrolysed to the highly fluorescent 7-hydroxy-1-methyl quinolinium iodide. The detection limit of galanthamine is 0.5 microM, which is about 20 times more sensitive than in the colorimetric flow assay. In the presence of 30% methanol or of 5% acetonitrile, about 70% of the enzyme activity could still be detected. Various plant extracts have been screened using the described system including bulbs of Galanthus nivalis, Eucharis amazonica (E. x grandiflora), Crinum powelli and Nerine bowdenii (all members of the Amaryllidaceae), which showed strong AchE inhibitory activity.

Synthesis and screening for antiacetylcholinesterase activity of (1-benzyl-4-oxopiperidin-3-ylidene)methylindoles and -pyrroles related to donepezil

The design, synthesis, and rapid evaluation of a new class of acetylcholinesterase (AChE) inhibitors related to donepezil are reported. A molecular dynamics simulation of the complex between AChE and one representative compound of the series showed a possible inhibitor binding mode in which favorable interactions are formed between the benzylpiperidinone moiety and some active-site residues. The biochemical evaluation of this newly synthesized series was performed using a chemiluminescent method suitable for high-throughput screening.

Assessing gene expression in vivo: magnetic resonance imaging and spectroscopy

Recent developments in magnetic resonance imaging and spectroscopy afford the possibility of detecting and assessing transfer, expression and subsequent therapeutic changes of effector or marker transgenes noninvasively. In the field of MR imaging, 'smart' MR contrast agents are being developed, so called because they change their conformational structure and in so doing induce MR detectable changes in a given tissue. These agents become 'switched on' in response to physiological changes brought about by the enzymatic action of a given gene product (enzymes), and are being developed for use in intact cells, isolated organs and animal models. Ultimately, these agents hold the promise of bridging the gap between the laboratory and the patient with noninvasive detection of transgene expression in vivo in man. Similarly, magnetic resonance spectroscopy is being developed as a noninvasive method to assess transgene expression indirectly by means of MR visible intracellular markers. These markers take the form of intracellular endo/exogenous metabolites associated with exogenous enzyme expression and function. Again, this technique will be applicable to a variety of different situations, from cell suspensions through to clinical imaging of the whole body. In this article the unique opportunities for laboratory-based and clinical studies afforded by MR techniques are discussed.

High-throughput and ultra-high-throughput screening: solution- and cell-based approaches

The trend towards assay miniaturization for high-throughput and ultra-high-throughput screening continues to spur development of homogeneous, fluorescence-based assays in higher density, smaller volume microplate formats. Recently, first-generation microfluidic devices have been designed for performing continuous-flow biochemical and cell-based assays. These devices provide orders-of-magnitude reduction in reagent consumption, and offer the potential for implementing high-throughput screening in formats that integrate up-front compound handling with unique assay functionality.