Chemiluminescent high-throughput microassay for evaluation of acetylcholinesterase inhibitors

Optical Detection of Enzymatic Activity and Inhibitors on Non-Covalently Functionalized Fluorescent Graphene Oxide

It has been of great interest to measure the activity of acetylcholinesterase (AChE) and its inhibitor, as AChE is known to accelerate the aggregation of the amyloid beta peptides that underlie Alzheimer's disease. Herein, we report the development of graphene oxide (GO) fluorescence-based biosensors for the detection of AChE activity and AChE inhibitors. To this end, GO was non-covalently functionalized with phenoxy-modified dextran (PhO-dex-GO) through hydrophobic interaction; the resulting GO showed excellent colloidal stability and intense fluorescence in various aqueous solutions as compared to pristine GO and the GO covalently functionalized with dextran. The fluorescence of PhO-dex-GO remarkably increased as AChE catalyzed the hydrolysis of acetylthiocholine (ATCh) to give thiocholine and acetic acid. It was found that the turn-on fluorescence response of PhO-dex-GO to AChE activity was induced by protonation of carboxyl groups on it from the product of the enzymatic hydrolysis reaction, acetic acid. On the basis of its turn-on fluorescence response, PhO-dex-GO was able to report kinetic and thermodynamic parameters involving a maximum velocity, a Michaelis constant, and an inhibition dissociation constant for AChE activity and inhibition. These parameters enable us to determine the activity of AChE and the efficiency of the inhibitor.

Black soybean extract protects against TMT-induced cognitive defects in mice

To find a neuroactive compound with a potent inhibitory effect on acetylcholinesterase (AChE) and in vivo anti-amnesic activity from natural resources, we evaluated anthocyanins and nonanthocyanins from black soybean extract. Nonanthocyanins from black soybean extract were the most potent and dose-dependent AChE inhibitors. Intracellular reactive oxygen species accumulation resulting from H₂O₂ treatment was significantly decreased compared with cells treated with H₂O₂ only. Nonanthocyanins were also neuroprotective against H₂O₂ treated neurotoxicity by 3-[4,5-dimethythiazol-2-yl]-2,5-diphenyl tetrazolium bromide (MTT) and lactate dehydrogenase (LDH) assay. Finally, nonanthocyanins from black soybean in the preadministration group attenuated trimethyltin (TMT)-induced memory injury in both in vivo tests. AChE, prepared from mice brain tissues, was inhibited by nonanthocyanins from black soybean in a dose-dependent manner. Malondialdehyde generation in the brain homogenates of mice treated with nonanthocyanins from black soybean was decreased. We concluded that nonanthocyanins from black soybean had an efficacious in vitro AChE inhibitory activity, and protected against H₂O₂-induced neurotoxicity. In addition, our findings suggest that nonanthocyanins from black soybean may improve the TMT-induced learning and memory deficit because of AChE inhibition of mice brain tissue. Consequently, these results demonstrate that the nonanthocyanins from black soybean could possess a wide range of beneficial activities for neurodegenerative disorders.

Colorimetric and fluorometric assays for acetylcholinesterase and its inhibitors screening based on a fluorescein derivate

A fluorescein-based sensor was developed for the AChE activity assay and the inhibitor screening. The sensor provided the dual assay methods for the screening of AChE activity in the presence or absence of inhibitor. The colorimetric and fluorometric assays were based on the following processes: (1) owing to the hydrolysis of acetylthiocholine in the presence of AChE, the fluorescein-based probe can rapidly induce 1,4-addition of the hydrolysis product thiocholine to α,β-unsaturated ketone in the compound 1, resulting in strong fluorescence and absorption changes; (2) in the presence of the corresponding inhibitor, the fluorescence enhancement or the absorption change would be inhibited in that the formation of thiocholine was hindered.

Rapid and label-free screening of enzyme inhibitors using segmented flow electrospray ionization mass spectrometry

Electrospray ionization mass spectrometry (ESI-MS) is an attractive analytical tool for high-throughput screening because of its rapid scan time and ability to detect compounds without need for labels. Impediments to the use of ESI-MS for screening have been the relatively large sample consumed and slow sample introduction rates associated with commonly used flow injection analysis. We have previously shown that by segmenting nanoliter plugs of sample with air, an array of discrete samples can be delivered to a platinum-coated emitter tip for ESI-MS analysis with throughput as high as 0.8 Hz and carry-over between samples less than 0.1%. This method was applied to screening for inhibitors of acetylcholinesterase as a demonstration of the potential of segmented flow ESI-MS for such applications. Each enzyme assay consumed 10 nL of sample. At 1 microL/min infusion rate, 102 samples were analyzed, corresponding to a 0.65 Hz sample analysis rate. Linear quantification of choline was achieved from 200 microM to 10 mM using this method and Z' values were over 0.8 for the assay. Detailed pharmacologic dose-response curves of selected inhibitors were also measured in high-throughput fashion to validate the method.

Screening of acetylcholinesterase inhibitors in natural extracts by CE with electrophoretically mediated microanalysis technique

An electrophoretically mediated microanalysis (EMMA) method for screening acetylcholinesterase (AChE) inhibitors in natural extracts is described. In this method, solutions of AChE and the mixture of the substrate and the natural extract were successively injected into the capillary, and mixed electrophoretically by applying a voltage for a short time. Afterwards the voltage was reapplied to separate the product from the unreacted substrate and the natural extract. The measured peak area of the product at UV 230 nm represents the enzyme activity. Since the extract is mixed with the substrate, there is no need to separate the components before testing the inhibition. The inhibitory activity of the natural extract as a whole can be easily found if the peak area of the product is reduced. This makes the present method suitable for screening inhibitors in complex mixtures, such as natural extracts. Compared to the commonly used spectrometric method for screening of AChE inhibitors, the major advantage of the present method is the elimination of Ellman reagent, which is essential for the spectrometric method. This not only simplifies the experimental procedure but also minimizes false-positive results. Moreover, it is an obvious advantage of combining the separation power with the on-column enzyme assay for further investigating which compound(s) is/are responsible for the inhibition. The method was validated using a commercially available AChE inhibitor tacrine and a small chemical library containing four AChE inhibitors and 32 natural extracts. Inhibitors in natural extracts were identified with the present method.

Homogeneous chemiluminescent assays for free choline in human plasma and whole blood

Choline was oxidized in the presence of choline oxidase and the hydrogen peroxide generated was detected using a chemiluminescent acridinium-9-carboxamide. The dose response for choline (0-150 microM) was established in buffer and was validated for the quantification of choline in human plasma and whole blood. This homogeneous assay was performed in a 96-well microplate format and required minimal sample volume (4 microL) and short analysis time (<5s per well). The new assay(s) correlated well (R>0.98, plasma; R>0.97, whole blood) with LC-MS/MS.

Synthesis and chemiluminescent high throughput screening for inhibition of acetylcholinesterase activity by imidazo[2,1-b]thiazole derivatives

The synthesis of a new series of imidazo[2,1-b]thiazole derivatives is described. They were tested as acetylcholinesterase inhibitors by means of a chemiluminescent method suitable for high throughput screening. The compounds without quaternization had no appreciable inhibitory potency probably because they are poorly soluble in water. The corresponding quaternized compounds were good inhibitors with activity related to the spacer employed.