The Potential Effect of Insulin on AChE and Its Interactions with Rivastigmine In Vitro

There is no definite cure for Alzheimer’s disease (AD) due to its multifactorial origin. Drugs that inhibit acetylcholinesterase (AChE), such as rivastigmine, are promising symptomatic treatments for AD. Emerging evidence suggests that insulin therapy can hinder several aspects of AD pathology. Insulin has been shown to modify the activity of AChE, but it is still unknown how insulin and AChE interact. Combination therapy, which targets several features of the disease based on existing medications, can provide a worthy therapy option for AD management. However, to date, no studies have examined the potential interaction of insulin with AChE and/or rivastigmine in vitro. In the present study, we employed the Response Surface Methodology (RSM) as an in vitro assessment to investigate the effect of insulin on both AChE activity and rivastigmine inhibitory action using a common spectrophotometric assay for cholinesterase activity, Ellman’s method. Our results showed that insulin, even at high concentrations, has an insignificant effect on both the activity of AChE and rivastigmine’s inhibitory action. The variance of our data is near zero, which means that the dispersion is negligible. However, to improve our understanding of the possible interaction of insulin and rivastigmine, or its target AChE, more in silico modelling and in vivo studies are needed.

Acetylcholinesterase Enzyme Inhibitor Molecules with Therapeutic Potential for Alzheimer's Disease

: Acetylcholinesterase (AchE), hydrolase enzyme, regulates the hydrolysis of acetylcholine neurotransmitter in the neurons. AchE is found majorly in the central nervous system at the site of cholinergic neurotransmission. It is involved in the pathophysiology of Alzheimer’s disease-causing dementia, cognitive impairment, behavioral and psychological symptoms. Recent findings involved the inhibition of AchE that could aid in the treatment of Alzheimer's. Many drugs of different classes being analyzed in the clinical trials and examined for their potency. Drugs that are used in the treatment of Alzheimer’s disease are donepezil, galantamine, tacrine, rivastigmine shows major adverse effects. To overcome this, researchers work on novel drugs to elicit inhibition. This review comprises the many hybrids and non-hybrid forms of heteroaromatic and non-heteroaromatic compounds that were designed and evaluated for AchE inhibition by Ellman’s method of assay. These novel compounds may assist the future perspectives in the discovery of novel moieties against Alzheimer’s disease by the inhibition of AchE.

Multilevel Approach for the Treatment of Giardiasis by Targeting Arginine Deiminase

Giardiasis represents a latent problem in public health due to the exceptionally pathogenic strategies of the parasite Giardia lamblia for evading the human immune system. Strains resistant to first-line drugs are also a challenge. Therefore, new antigiardial therapies are urgently needed. Here, we tested giardial arginine deiminase (GlADI) as a target against giardiasis. GlADI belongs to an essential pathway in Giardia for the synthesis of ATP, which is absent in humans. In silico docking with six thiol-reactive compounds was performed; four of which are approved drugs for humans. Recombinant GlADI was used in enzyme inhibition assays, and computational in silico predictions and spectroscopic studies were applied to follow the enzyme’s structural disturbance and identify possible effective drugs. Inhibition by modification of cysteines was corroborated using Ellman’s method. The efficacy of these drugs on parasite viability was assayed on Giardia trophozoites, along with the inhibition of the endogenous GlADI. The most potent drug against GlADI was assayed on Giardia encystment. The tested drugs inhibited the recombinant GlADI by modifying its cysteines and, potentially, by altering its 3D structure. Only rabeprazole and omeprazole decreased trophozoite survival by inhibiting endogenous GlADI, while rabeprazole also decreased the Giardia encystment rate. These findings demonstrate the potential of GlADI as a target against giardiasis.

Hybrids of Thiazolidin-4-Ones and 1,3,4-Thiadiazole: Synthesis and Biological Screening of A Potential New Class of Acetylcholinesterae Inhibitors

Using propanoic acid and thiosemicarbazide as starting materials, a new sequence of thiazolidin-4-one analogs with thiadiazole derivative was synthesized in appreciable yield. Spectral techniques such as IR, 1H NMR, 13C NMR, and MS were used to validate the structures of the synthesized compounds (4a-t). In vitro acetylcholinesterase inhibitory activity of these synthesized compounds was assessed using an Ellman's method spectrophotometer and donepezil as a standard drug. Compounds 2-((5-ethyl-1,3,4-thiadiazol-2-yl)imino)-5-(4-methylbenzylidene)thiazolidin-4-one(4o) and 5-(4-(benzyloxy)benzylidene)-2-((5-ethyl-1,3,4-thiadiazol-2-yl)imino)thiazolidin-4-one(4i) were found to be potent AChE enzyme inhibitors, with pIC50 (mM) values of 1.30±0.007 and 1.22±0.002, respectively. Finally, these significant results could pave the way for the development of new AChE inhibitors and will serve as the basis for future research.

Cholinesterase Inhibition Activity and Molecular Docking Study of Eugenol Derivatives

The study was conducted to explore the anticholinesterase inhibition property of eugenol derived molecules. Ten eugenol derivatives were synthesized and evaluated for the inhibitory activities against acetylcholinesterase (AChE) and butyrylcholinesterase (BChE) by Ellman’s method. Most of the tested derivatives showed higher inhibition on BChE than AChE, however, their overall inhibitory activity was weak. In contrast, three derivatives (compounds 3,6,9) showed higher and good AChE inhibitory activity of more than 50% inhibition at 10 μg/mL. Among them, compound 9bearing a ethyl substituent at para position of the benzoyl ring showed the most potent AChE inhibition, with IC50 of 5.64 μg/mL. Ligand-protein docking simulation was also performed for the most active derived molecules (compounds 3,6,9).

Phenolic Compounds of Reynoutria sp. as Modulators of Oral Cavity Lactoperoxidase System

Lactoperoxidase (LPO) together with its (pseudo)halogenation cycle substrates, H2O2 and thiocyanate ions oxidized to hypothiocyanite ions, form one of the main systems involved in antimicrobial defense within the oral cavity. In bacterial diseases such as dental caries, lactoperoxidase is oxidized to a form known as Compound II, which is characterized by its inability to oxidize SCN–, resulting in a decreased generation of antimicrobial products. Reynoutria sp. rizome extracts, due to their high polyphenol content, have been tested as a source of compounds able to regenerate the antimicrobial activity of lactoperoxidase through converting the Compound II to the native LPO state. In the presented study, acetone extracts of R. japonica, R. sachalinensis, and R. x bohemica, together with their five fractions and four selected polyphenols dominating in the studied in extracts, were tested toward lactoperoxidase reactivating potential. For this purpose, IC50, EC50, and activation percentage were determined by Ellman’s method. Furthermore, the rate constants for the conversion of Compound I–Compound II and Compound II–native-LPO in the presence of extracts, extracts fractions, and selected polyphenols were determined. Finally, the ability to enhance the antimicrobial properties of the lactoperoxidase system was tested against Streptococcus mutans. We proved that Reynoutria sp. rhizome is the source of lactoperoxidase peroxidation cycle substrates, which can act as activators and inhibitors of the antimicrobial properties of that system. The presented study shows that the reactivation of lactoperoxidase could become a potential therapeutic target in prevention and treatment support in some infectious oral diseases.

In-vitro Evaluation of Acetylcholinesterase and Butyrylcholinesterase Inhibitory Activities of Antlion Larvae Extracts

Antlion is used in traditional medicine by natives of the southern part of Nigeria particularly the Yorubas for memory enhancement. The progress made so far in the use of this organism as a memory booster lead to investigating the acetylcholinesterase (AChE) and butyrylcholinesterase (BuChE) (the key enzymes in the pathogenesis of Alzheimer's disease) inhibitory activities of methanolic and phosphate buffered saline (PBS) extracts. The activities of these enzymes were investigated using Ellman’s method. The kinetics of the inhibition patterns was also studied using eserine as the standard inhibitor. The concentration of the extract required for 50% inhibition (IC50) of the AChE was 49.00 ± 1.20 and 271.40 ± 0.10 µg/mL, for the PBS and methanolic extracts respectively, compared to Eserine with IC50 of 2.25 x 10-2 ± 0.15 x 10-2 µg/mL. Similarly, the IC50 for the BuChE was 66.30 ± 0.40 and 216.70 ± 1.10 µg/mL respectively, for the methanol and PBS extracts, compared to Eserine with IC50 of 1.10 ± 0.30 µg/mL. The pattern of inhibition of the BuChE in the presence of the extracts was non-competitive, while AChE exhibited non-competitive and competitive inhibitions for the methanolic and PBS extracts respectively. It is therefore evident that extracts of the antlion larvae contained cholinesterase inhibitors which might be binding to AChE and BuChE; with the PBS extract inhibitory activity towards AChE being more potent than the methanolic extract. Suggesting a beneficial effect in cognitive deficit and related dementia associated with Alzheimer’s disease.

Synthesis and anti-acetylcholinesterase activities of novel glycosyl coumarylthiazole derivatives

Eleven glycosyl coumarylthiazole derivatives are synthesized by cyclization and condensation of glycosyl thiourea with 3-bromoacetyl coumarins in ethanol. The reaction conditions are optimized and good yields of products (80%–95%) are obtained. The structures of all new products were confirmed by IR, 1H and 13C NMR, and by HRMS (electrospray ionization). The in vitro acetylcholinesterase (AChE) inhibitory activities of these new compounds are tested by Ellman’s method. Among them, N-(2-acetamido-3,4,6-tri- O-acetyl-2-deoxy-β-D-glucopyranosyl)-4-(6-nitrocoumarinyl)-1,3-thiazole-2-amine showed the best activity with an in vitro AChE inhibitory rate of 58% and an IC50 value of 12 ± 0.38 μg/mL.

Synthesis, characterization, crystal structures, and the biological evaluation of 2-phenylthiazole derivatives as cholinesterase inhibitors

Four 2-phenylthiazole derivatives are synthesized, characterized, and evaluated as cholinesterase inhibitors. The structures of the 2-phenylthiazole derivatives are confirmed by 1H and 13C nuclear magnetic resonance spectroscopy, single-crystal X-ray diffraction studies, and Hirshfeld surfaces analysis. Hirshfeld surface analysis of the prepared compounds showed C–H···O intermolecular interactions. The cholinesterase inhibition activities of the synthesized compounds are tested by Ellman’s method. [2-(4-Benzyloxyphenyl)-thiazol-4-yl]-(3,5-dimethylpiperidin-1-yl)-methanone showed the best acetylcholinesterase inhibition activity with an IC50 value of 8.86 µM and the best butyrylcholinesterase inhibition activity with an IC50 value of 1.03 µM. A docking study demonstrates that the same compound interacts with the catalytic anionic site and peripheral anionic site of acetylcholinesterase and the catalytic anionic site of butyrylcholinesterase.

Comparative Study on the Inhibition of Acetylcholinesterase Activity by Hyptis marrubioides, Hyptis pectinata, and Hyptis suaveolens Methanolic Extracts

The inhibition of acetylcholinesterase (AChE), the key enzyme in the breakdown of acetylcholine, may be considered as one of the treatment approaches against several neurological disorders including Alzheimer’s. The purpose of this study is to evaluate, compare, and discuss the anti-acetylcholinesterase activity of three methanolics extracts from Hyptis leaves: Hyptis marrubioides (Hm), Hyptis pectinate (Hp), and Hyptis suaveolens (Hs). AChE activity was measured using a modified 96-well microplate assay based on Ellman’s method. IC50 (half maximal inhibitory concentration) values were calculated for Hm, Hp, and Hs methanolic extracts using physostigmine as a positive control. All the extracts exhibited a dose-dependent AChE percent inhibition with IC50 values lower for Hm, followed by Hp and Hs. Several polyphenols (such as flavonoids and phenolic acids) have been considered a prominent source of anti-Alzheimer disease compounds because of their potential AChE inhibitory activity allied to their well-known antioxidant activity and low toxicity. The results obtained are discussed under the light of the available literature regarding the phytochemical composition and antioxidant activity of Hyptis spp. extracts. Further studies are warranted regarding the role of these Hyptis extracts in the progression of neurological disorders.