Antioxidant and acetylcholinesterase inhibitory activity of selected southern African medicinal plants

Alzheimer's disease (AD) is the most common type of dementia in the aging population. Enhancement of acetylcholine levels in the brain is one means of treating the disease. However, the drugs presently used in the management of the disease have various drawbacks. New treatments are required and in this study, extracts of Salvia tiliifolia Vahl. (whole plant), Chamaecrista mimosoides L. Greene (roots), Buddleja salviifolia (L.) Lam. (whole plant) and Schotia brachypetala Sond. (root and bark) were evaluated to determine their polyphenolic content, antioxidant and acetylcholinesterase inhibitory (AChEI) activity. The DPPH and ABTS assays were used to determine antioxidant activity and Ellman colorimetric method to quantify AChEI activity. Although all four plants showed activity in both assays, the organic extracts of C. mimosoides root was found to contain the highest AChEI activity (IC₅₀ = 0.03 ± 0.08 mg/ml) and B. salviifolia whole plant had the highest antioxidant activity (ABTS; IC₅₀ = 0.14 ± 0.08 mg/ml and DPPH; IC₅₀ = 0.23 ± 0.01 mg/ml). The results suggest that the tested plant species may provide a substantial source of secondary metabolites, which act as natural antioxidants and acetylcholinesterase inhibitors, and may be beneficial in the treatment of AD.     

Swimming impairment and acetylcholinesterase inhibition in zebrafish exposed to copper or chlorpyrifos separately,or as mixtures

Pesticides such as chlorpyrifos (CPF) and metals such as copper can impair swimming behavior in fish. However, the impact to swimming behavior from exposure to mixtures of neurotoxicants has received little attention. In the current study, we analyzed spontaneous swimming rates of adult zebrafish (Danio rerio) to investigate in vivo mixture interactions involving two chemical classes. Zebrafish were exposed to the neurotoxicants copper chloride (CuCl, 0.1 μM, 0.25 μM, 0.6 μM, or 6.3, 16, 40 ppb), chlorpyrifos (CPF, 0.1 μM, 0.25 μM, 0.6 μM, or 35, 88, 220 ppb) and binary mixtures for 24 h to better understand the effects of Cu on CPF neurotoxicity. Exposure to CPF increased the number of animals undergoing freeze responses (an anti-predator behavior) and, at the highest CPF dose (0.6 μM), elicited a decrease in zebrafish swimming rates. Interestingly, the addition of Cu caused a reduction in the number of zebrafish in the CPF exposure groups undergoing freeze responses. There was no evidence of additive or synergistic toxicity between Cu and CPF. Although muscle AChE activity was significantly reduced by CPF, there was a relatively poor relationship among muscle AChE concentrations and swimming behavior, suggesting non-muscle AChE mechanisms in the loss of swimming behavior. In summary, we have observed a modulating effect of Cu on CPF swimming impairment that appears to involve both AChE and non-AChE mechanisms. Our study supports the utility of zebrafish in understanding chemical mixture interactions and neurobehavioral injury.     

Selective acetylcholinesterase inhibitors derived from muscle relaxant dantrolene

Dantrolene, the only therapeutic agent for malignant hyperthermia, is known to have not only a muscle relaxant effect, but also a neuroprotective effect and Alzheimer's disease improving effect. Recently, it has been reported that dantrolene has a weak inhibitory effect on acetylcholinesterase (AChE), which is a therapeutic drug target for Alzheimer's disease. Thus, we focused on developing of AChE inhibitors with benzylpiperidine/piperazine moieties that are based on the dantrolene skeleton. Several derivatives showed an inhibitory activity. Among them, ortho-nitro derivative 8c showed the most potent inhibitory activity with the IC₅₀ value of 34.2 nM. Furthermore, Lineweaver-Burk plot analysis indicated that 8c is AChE-selective inhibitor, which shows only a weak inhibitory effect on butyrylcholinesterase (BuChE) and a non-competitive inhibition.     

Discovery of biphenyl pyrazole scaffold for neurodegenerative diseases: A novel class of acetylcholinesterase-centered multitargeted ligands

Multitargeted ligands have demonstrated remarkable efficiency as potential therapeutics for neurodegenerative diseases as they target multiple pathways involved in the progression of these diseases. Herein, we report first-in-class dual inhibitor of acetylcholinesterase (AChE) and tau aggregation as a novel class of multitargeted ligands for neurodegenerative diseases. The reported biphenyl pyrazole scaffold binds monomeric tau with submicromolar affinity and impedes the formation of tau oligomers at early stages. Additionally, the lead compound inhibited AChE activity with an IC₅₀ value of 0.35 ± 0.02 μM. Remarkably, the neuroprotective effect of this lead in induced cytotoxicity model of SH-SY5Y neuroblastoma cells is superior to single-targeted AChE and tau-aggregation inhibitors. This scaffold would enable development of new generation of multitargeted ligands for neurodegenerative diseases that function through dual targeting of AChE and monomeric tau.     

Amperometric biosensor based on enzymes immobilized in hybrid mesoporous membranes for the determination of acetylcholine

Acetylcholine sensor is successfully prepared by using immobilized enzymes, i.e., acetylcholinesterase and choline oxidase within separate hybrid mesoporous silica membranes with 12 nm pore diameter (F127M). The measurement was based on the detection of hydrogen peroxide produced by two sequential enzyme reactions. The determination range and the response time are 6.0–800 μM and within approximately 3 min, respectively. The sensor is very stable compared to free enzymes and 80% of the initial response was maintained even after storage for 80 days. These results show that two enzymes are successfully immobilized and well stabilized, and at the same time, two sequential enzyme reactions efficiently proceed within the separate hybrid mesoporous membranes. Further, we studied the possible detection of organophosphorus pesticides in terms of the inhibition of acetylcholinesterase activity, i.e., the decrease of current response, and demonstrated that the nanomolar concentrations of pesticide (DZN-oxon) can be detected with our sensor.     

3种植物乙醇提取物对南方根结线虫卵囊酯酶活力影响及其成分预分析

2000μg/ml合欢叶、黄花菊花和万寿菊叶乙醇提取物溶液处理根结线虫卵囊24h、48h和120h后,采用酶标仪分别对卵囊羧酸酯酶和乙酰胆碱酯酶活力进行了测定。结果表明各处理对根结线虫卵囊羧酸酯酶和乙酰胆碱酯酶的活性均有显著的抑制作用。与对照无菌水相比,合欢叶、黄花菊花和万寿菊叶乙醇提取物溶液处理卵囊120h后,卵囊羧酸酯酶活力抑制率分别为85.94%、86.16%和65.18%,乙酰胆碱酯酶活力抑制率分别为51.16%、46.51%和34.88%。并对3种植物乙醇提取物化学成分进行预分析。     

Acetylcholinesterase‐Inhibitory Activities of the Extracts from Sponges Collected in Mauritius Waters

Patients diagnosed with Alzheimer's disease (AD) show a characteristic neurochemical deficit of acetylcholine, especially in the basal forebrains. The use of acetylcholinesterase (AChE) inhibitors to retard the hydrolysis of acetylcholine has been suggested as a promising strategy for AD treatment. In this study, we evaluated the acetylcholinesterase inhibitory (AChEI) activities of 134 extracts obtained from 45 species of marine sponges. Thin‐layer chromatography (TLC) and microplate assays reveal potent acetylcholinsterase inhibitory activities of two AcOEt extracts from the sponges Pericharax heteroraphis and Amphimedon navalis Pulitzer‐Finali . We further investigated the inhibitory kinetics of the extracts and found them to display mixed competitive/noncompetitive inhibition and associated their inhibitory activity partly to terpenoids. Acetylcholinesterase inhibitors from marine organisms have been rarely studied, and this study demonstrated the potential of marine sponges as a source of pharmaceutical leads against neurodegenerative diseases.     

Quinones bearing non-steroidal anti-inflammatory fragments as multitarget ligands for Alzheimer’s disease

The anti-amyloid properties shared by several quinones inspired the design of a new series of hybrids derived from the multi-target drug candidate memoquin (1). The hybrids consist of a central benzoquinone core and a fragment taken from non-steroidal anti-inflammatory drugs, connected through polyamine linkers. The new hybrids retain the potent anti-aggregating activity of the parent 1, while exhibiting micromolar AChE inhibitory activities. Remarkably, 2, 4, (R)-6 and (S)-6 were Aβ aggregation inhibitors even more potent than 1. The balanced amyloid/cholinesterase inhibitory profile is an added value that makes the present series of compounds promising leads against Alzheimer’s disease.     

Novel racemic tetrahydrocurcuminoid dihydropyrimidinone analogues as potent acetylcholinesterase inhibitors

The synthesis of racemic tetrahydrocurcumin- (THC-), tetrahydrodemethoxycurcumin- (THDC-) and tetrahydrobisdemethoxycurcumin- (THBDC-) dihydropyrimidinone (DHPM) analogues was achieved by utilizing the multi-component Biginelli reaction in the presence of copper sulphate as a catalyst. The evaluation of acetylcholinesterase inhibitors for Alzheimer’s disease of these compounds showed that they exhibited higher inhibitory activity than their parent analogues. THBDC–DHPM demonstrated the most potent inhibitory activity with an IC₅₀ value of 1.34 ± 0.03 μM which was more active than the approved drug galanthamine (IC₅₀ = 1.45 ± 0.04 μM).     

Dual Substrate Model for Novel Approach Towards a Kinetic Study of Acetylcholinesterase Inhibition by Diazinon

Limited reports as compared to other insecticides appear in the literature for acetylcholinester-ase (AChE) inhibition by diazinon. In the current study, new kinetic parameters of AChE inhibition by diazinon have been investigated. The assay was done with bovine retinal AChE using two different substrate (ASCh) concentrations in the absence and presence of diazinon (0.08-1.28 mM). The optical density was monitored up to 25min (reaction time) for the assay. New kinetic parameters (k¹_oms, k¹_sms, k¹_oms, k¹_sms, k¹_asms and k¹_asms) were calculated from these experimental data.