Microsequential injection analysis/lab-on-valve system for the automatic evaluation of acetylcholinesterase inhibitors

A miniaturized microsequential injection/lab-on-valve (µSIA-LOV) system was developed and shown to be a useful alternative to perform inhibitory studies on acetylcholinesterase. These studies are essential for the evaluation of the potential therapeutic effect of drugs commonly used in the treatment of Alzheimer's disease. Donepezil, galantamine, and rivastigmine were tested, in addition to compounds based on the xanthone scaffold. Four of these xanthone derivatives were identified as having EC₅₀ values between 676 and 4466 µmol/l, showing a potential inhibitory effect higher than the clinical agent rivastigmine. The developed automatic system added advantages of reduction of reagents and sample consumption (around 55 µl per analysis), lower cost per analysis, and the generation of less waste (around 1.2 ml per analysis). The µSIA-LOV system is also a robust, rapid, reliable, and simple system to use. Docking studies suggested a possible mode of interaction with the target acetylcholinesterase protein.

Enzymatic Reactions in a Lab-on-Valve System: Cholesterol Evaluations

The micro sequential injection analysis / lab-on-valve (µSIA-LOV) system is a miniaturized SIA system resulting from the implementation of a lab-on-valve (LOV) atop of the selection valve. It integrates the detection cell and the sample processing channels into the same device, promoting the reduction of reagent consumption and waste generation, the improvement of the versatility, and the reduction of the time of analysis. All of these characteristics are really relevant to the implementation of enzymatic reactions. Additionally, the evaluation of cholesterol in serum samples is widely relevant in clinical diagnosis, since higher values of cholesterol in human blood are actually an important risk factor for cardiovascular problems. An automatic methodology was developed based on the µSIA-LOV system in order to evaluate its advantages in the implementation of enzymatic reactions performed by cholesterol esterase, cholesterol oxidase and peroxidase. Considering these reactions, the developed methodology was also used for the evaluation of cholesterol in human serum samples, showing reliable and accurate results. The developed methodology presented detection and quantification limits of 1.36 and 4.53 mg dL⁻¹ and a linear range up to 40 mg dL⁻¹. This work confirmed that this µSIA-LOV system is a simple, rapid, versatile, and robust analytical tool for the automatic implementation of enzymatic reactions performed by cholesterol esterase, cholesterol oxidase, and peroxidase. It is also a useful alternative methodology for the routine determinations of cholesterol in real samples, even when compared with other automatic methodologies.

Hypolipidemic effects of flavonoids extracted from Lomatogonium rotatum

Contained in the Mongolian volumes of Chinese Materia Medica, Lomatogonium rotatum Fries ex Nym. may reduce blood lipid levels and prevent obesity; however, its exact mechanism of action remains unclear. The present study investigated the hypolipidemic and obesity-inhibiting effects of four similarly structured flavonoids extracted from L. rotatum. According to a well-established method, flavonoids such as decussatin were extracted from the whole herb of L. rotatum, and male Wistar rats were subsequently fed a high-fructose diet supplemented with flavonoids (20 mg/kg) for 12 weeks. The levels of total cholesterol, triglyceride (TG), low-density lipoprotein-cholesterol and high-density lipoprotein-cholesterol (HDL-C) were detected. In addition, hepatic and epididymal adipose tissues were weighed, and levels of blood glucose, alanine aminotransferase, aspartate aminotransferase, non-esterified fatty acid, insulin and leptin were determined. The mRNA expression levels of fatty acid synthase (FAS) were analyzed using a reverse transcription polymerase chain reaction; whereas FAS, adenosine monophosphate-activated protein kinase (AMPK) and threonine-172 phosphorylated AMPK protein levels were detected by western blotting. The epididymal adipose tissues of rats fed with flavonoids were lighter, as compared with those fed with fructose in the model group. Following a 12-week administration of flavonoids, the serum levels of fasting blood glucose, feeding blood glucose and leptin were decreased. Furthermore, flavonoid treatment reduced TG and cholesterol levels in the blood and increased serum HDL-C levels, as compared with the model group. High-fructose diet administration significantly increased FAS mRNA and protein expression levels, whereas the FAS protein levels of flavonoid-treated rats were markedly reduced. The flavonoid compounds also enhanced threonine-172 phosphorylation of AMPK in the liver lysate, and all flavonoids successfully downregulated leptin levels and the majority decreased the relative weights of epididymal adipose tissue. Therefore, flavonoids may function in a similar way to epigallocatechin gallate, which has previously been shown to inhibit FAS activity by stimulating AMPK in hepatocyte cells via the liver kinase B1 pathway.

Automated evaluation of the effect of ionic liquids on catalase activity

An automated assay for the evaluation of the influence of ionic liquids on the activity of catalase was developed. The activity and inhibition assays were implemented in a sequential injection analysis (SIA) system and intended to contribute for the estimation of the toxicity of the tested compounds. The fast developed methodology was based on the oxidation of the non-fluorescent probe amplex red, in the presence of H₂O₂, to produce resorufin, a strong fluorescent compound. Catalase activity was monitored by the decreased of the fluorescence intensity due to the consumption of H₂O₂ by the enzyme. The activity assays were performed in strictly aqueous media and in the presence of increasing concentrations of seven commercially available ionic liquids and sodium azide, a strong inhibitor of catalase. IC₅₀ values between 0.15 and 2.77 M were obtained for the tested compounds, revealing distinct inhibitory effects. This allowed us to perform some considerations about the toxicity of the tested cations and anions. The developed SIA methodology showed to be robust and exhibited good repeatability in all the assay conditions. On the other hand, it proved to be in good agreement with the actual concerns of "Green Chemistry" since it involved the consumption of less than 200 μL of reagents and the production of only 1.7 mL of effluent (per cycle) and at the same time reduced the operator exposure resulting in increased environmental and human safety.