Short-end injection procedure in capillary electrophoresis for determination of enzymatic reaction kinetics

Integrated analysis and separation of 5-lipoxygenase inhibitors from triterpenes of Poria cocos using bioaffinity ultrafiltration UPLC-Q-Exactive, molecular docking and target-based multiple complex networks

Poria cocos (Schw.) Wolf (P. cocos) has been widely used as medical plant in East Asia with remarkable anti-Alzheimer's disease (anti-AD) activity. However, the underlying mechanisms are still confused. In this study, based on the β-Amyloid deposition hypothesis of AD, an integrated analysis was conducted to screen and separation 5-lipoxygenase (5-LOX) inhibitors from triterpenoids of P. cocos and investigate the anti-AD mechanisms, containing bioaffinity ultrafiltration UPLC-Q-Exactive, molecular docking, and multiple complex networks. Five triterpenoids were identified as potential 5-LOX inhibitors, including Tumulosic acid, Polyporenic acid C, 3-Epi-dehydrotumulosic acid, Pachymic acid and Dehydrotrametenolic acid. Five potential 5-LOX inhibitors were screened by ultrafiltration affinity assay in P. cocos. The molecular docking simulation results are consistent with the ultrafiltration experimental results, which further verifies the accuracy of the experiment. The commercial 5-LOX inhibitor that Zileuton was used as a positive control to evaluate the inhibitory effect of active ingredients on 5-LOX. Subsequently, the established separation method allowed the five active ingredients (Pachymic acid, 3-Epi-dehydrotumulosic acid, Dehydrotrametenolic acid, Tumulosic acid and Polyporenic acid C) with high purity to be isolated. Targeting network pharmacology analysis showed that five active ingredients correspond to a total of 286 targets. Kyoto encyclopedia of genes and genomes (KEGG) enrichment analysis found that target cells were mainly enriched in Pathways in cancer, Lipid and atherosclerosis. Our results indicate that P. cocos extract has the potential to be used in the prevention and treatment of neurodegenerative diseases. This will help elucidate the mechanisms of action of various medicinal plants at the molecular level and provide more opportunities for the discovery and development of new potential treatments from health food resources.

Efficient Combination of Complex Chromatography, Molecular Docking and Enzyme Kinetics for Exploration of Acetylcholinesterase Inhibitors from Poria cocos

Poria cocos (P. cocos) is a traditional Chinese medicinal product with the same origin as medicine and food. It has diuretic, anti-inflammatory and liver protection properties, and has been widely used in a Chinese medicine in the treatment of Alzheimer's disease (AD). This study was conducted to explore the activity screening, isolation of acetylcholinesterase inhibitors (AChEIs), and in vitro inhibiting effect of P. cocos. The aim was to develop a new extraction process optimization method based on the Matlab genetic algorithm combined with a traditional orthogonal experiment. Moreover, bio-affinity ultrafiltration combined with molecular docking was used to screen and evaluate the activity of the AChEIs, which were subsequently isolated and purified using high-speed counter-current chromatography (HSCCC) and semi-preparative high-performance liquid chromatography (semi-preparative HPLC). The change in acetylcholinesterase (AChE) activity was tested using an enzymatic reaction kinetics experiment to reflect the inhibitory effect of active compounds on AChE and explore its mechanism of action. Five potential AChEIs were screened via bio-affinity ultrafiltration. Molecular docking results showed that they had good binding affinity for the active site of AChE. Meanwhile, the five active compounds had reversible inhibitory effects on AChE: Polyporenic acid C and Tumulosic acid were non-competitive inhibitors; 3-Epidehydrotumulosic acid was a mixed inhibitor; and Pachymic acid and Dehydrotrametenolic acid were competitive inhibitors. This study provided a basis for the comprehensive utilization of P. cocos and drug development for the treatment of AD.

Capillary electrophoretic screening for the inhibition of homocysteine thiolactone-induced protein oligomerization

We report the first demonstration of rapid electrophoretic monitoring of homocysteine thiolactone-induced protein oligomerization (HTPO), a unique type of post-translational protein modification that may have clinical significance as an indicator of cardiovascular and neurovascular diseases. HTPO of the model protein bovine cytochrome c was initiated in vitro. The relative monomer and aggregate levels of the resultant protein mixtures were determined following separation using capillaries coated with the cationic polymer, poly(diallyldimethylammonium chloride). UV detection provided adequate sensitivity for the monitoring of higher order species, which exist at relatively low concentrations in the protein reaction mixture as compared to the monomeric species. Separations performed under standard injection conditions were optimized on the basis of applied voltage and sample denaturation conditions. Separations performed using short-end injection allowed for more rapid analyses, typically in less than 70 s. Relative errors for run-to-run migration times were less than 0.5%. This novel oligomeric system provides a rapid and straightforward in vitro method to screen therapeutic agents for their ability to inhibit HTPO. Changes in peak area for monomer and aggregate species were used to assess HTPO inhibition as a function of pyridoxal 5-phosphate (PLP) concentration. PLP was shown to effectively inhibit HTPO in vitro. Rapid analysis times of approximately 1.5 min were achieved for inhibition screening.

Integration of short-end injection mode into electrophoretically mediated microanalysis

The possibility of integration of the short-end injection mode in the EMMA methodology is demonstrated in this work on the kinetic studies of haloalkane dehalogenase and rhodanese enzymatic reactions. The essential validations of the EMMA methods combined with the short-end and long-end injection modes were performed first to confirm their accuracy. The qualitative and quantitative parameters of both approaches such as repeatabilities of migration times and peak areas, limits of detection and correlation coefficients were in acceptable ranges. In addition, estimated Michaelis constants for the corresponding substrate(s) were comparable being in accordance with previous literature data. Moreover, the ping-pong reaction mechanism of rhodanese reaction was confirmed by means of both injection modes. This combination thus preserves the benefits of these instrumental approaches. Whereas the short-end injection procedure brought 5-6.5 times reduction of the analysis time and 2.5-4 times increase of the sensitivity, the EMMA methodology allowed full automatization of the assays while the whole kinetic studies needed only 20 microl of corresponding enzyme preparation.

Determination of enzymatic activity by capillary electrophoresis

Enzymes are biological catalysts that play an important role in biochemical reactions necessary for normal growth, maturation and reproduction through whole live world. Their accurate quantitation in biological samples is important in many fields of biochemistry, not only in routine biochemistry and in fundamental research, but also in clinical and pharmacological research and diagnosis. Since the direct measurement of enzymes by masses is impossible, they must be quantified by their catalytic activities. Many different methods have been applied for this purpose so far. Although photometric methods are undoubtedly the most frequently used, separation methods will further gain their position in this field. The article reviews different possibilities for the assay of enzymatic activity by means of capillary electrophoresis (CE). Both the off-line and on-line enzyme assays based on CE are discussed.

On-line monitoring of enzymatic conversion of adenosine triphosphate to adenosine diphosphate by micellar electrokinetic chromatography

Capillary electrophoresis can be a valuable tool for the on-line monitoring of bioprocesses. The enzymatic conversion of nucleotide adenosine triphosphate (ATP) to adenosine diphosphate (ADP) by hexokinase (HK) was monitored in the bioreactor interfaced by a laboratory-built microsampler to a capillary electrophoresis unit. The use of this specially designed sampling device enabled rapid consecutive injections to be performed without high-voltage (HV) interruptions. No additional sample preparation was required. The method of micellar electrokinetic chromatography, employing reversed electroosmotic flow (EOF) by cationic surfactant and reversed polarity mode provided a good resolution and short analysis time of less than 5 min. The samples were injected electrokinetically, using -25 kV voltage for 3 s and detected by their UV absorbance at 254 nm. The analytes were detected at a microg/ml level with a reproducibility of about 7%. To demonstrate the potential of CE in understanding the processes of biological interest, such as nucleotide degradation and metabolism, the investigation of the efficiency and the time course of the enzymatic transformation was carried out.