Acetylcholinesterase: old questions and new developments

Acetylcholine and Malpighian tubules of the kissing bug, Rhodnius prolixus: Evidence for expression of the non-neuronal cholinergic system and a diuretic action of acetylcholine

Acetylcholine (ACh) and its signaling pathways are expressed in peripheral tissues in mammals, leading to the concept of a non-neuronal cholinergic signaling system. This non-neuronal ACh is now known to participate as an autocrine/paracrine in many processes, including transport of ions and water, immunity, and reproduction. Non-neuronal cholinergic signaling in insects has only recently been explored, with transcriptome analyses disclosing the presence of transcripts for pivotal components of the cholinergic system in non-neuronal tissues, including Malpighian tubules (MTs), ovaries, hemocytes, and fat body. A recent transcriptome analysis of MTs of the Chagas disease vector Rhodnius prolixus revealed the presence of transcripts for muscarinic ACh receptors and for acetylcholinesterase, raising the possibility that non-neuronal ACh may play a role in the control of MTs. Here we provide evidence for a non-neuronal ACh signaling pathway in MTs of R. prolixus. Transcripts for ACh signaling are expressed, and ACh is capable of stimulating small increases in secretion by isolated MTs (small, relative to the true diuretic neurohormones in R. prolixus). The effects of ACh are mimicked by carbachol and pilocarpine, with atropine inhibiting ACh- and pilocarpine-stimulated secretion. Blood gorging alters expression of transcripts for ACh signaling. We discuss the physiological relevance for ACh since MTs are much more than diuresis; they play major roles in immunity, detoxification, and in tolerance to overall stress. Perhaps ACh is a signaling component of these essential functions that might require an increase in secretion rate by MTs that is separate from the well described rapid post-prandial diuresis.

Beyond the virus: ecotoxicological and reproductive impacts of SARS-CoV-2 lysate protein in C57Bl/6j female mice

Since the establishment of the COVID-19 pandemic, a range of studies have been developed to understand the pathogenesis of SARS-CoV-2 infection, vaccine development, and therapeutic testing. However, the possible impacts that these viruses can have on non-target organisms have been explored little, and our knowledge of the consequences of the COVID-19 pandemic for biota is still very limited. Thus, the current study aimed to address this knowledge gap by evaluating the possible impacts of oral exposure of C57Bl/6 J female mice to SARS-CoV-2 lysate protein (at 20 µg/L) for 30 days, using multiple methods, including behavioral assessments, biochemical analyses, and histopathological examinations. Although we did not have evidence of hematological, mutagenic, or genotoxic effects, we noted that the ingestion of SARS-CoV-2 lysate protein-induced behavioral disorders (hypoactivity, anxiety-like behavior, and short-term memory deficit), which were associated with oxidative stress and dopaminergic and cholinesterase imbalance in the animal brain. Furthermore, the elevation of bilirubin levels and lactate dehydrogenase levels in these animals suggests the occurrence of hepatic changes, and the redox imbalance, nitrosative stress, and elevated production of IFN-γ and inflammatory infiltration in the duodenum, disrupted follicular structure, and presence of vacuoles in granulosa cells, in ovarian, indicate that the SARS-CoV-2-exposed group showed significant toxicity. Principal component analysis (PCA) and cluster analysis confirmed that the groups were clearly separated and showed that the largest changes upon SARS-CoV-2 exposure were related to ROS, MDA, nitrite, IFN-γ/IL-10 levels and SOD and catalase activity in the ovary; IFN-γ/IL-10 production and SOD activity in the duodenum; BChE activity in the brain; bilirubin levels and lactate dehydrogenase activity in the serum; number of primary follicles in the ovary. In conclusion, our study provides new insights into the toxicity of SARS-CoV-2 lysate proteins in a non-target terrestrial organism of infection and, therefore, expands our understanding of the real extent of the ecological/environmental impact of the COVID-19 pandemic.

Advances in Cholinesterase Inhibitor Research-An Overview of Preclinical Studies of Selected Organoruthenium(II) Complexes

Cholinesterase (ChE) inhibitors are crucial therapeutic agents for the symptomatic treatment of certain chronic neurodegenerative diseases linked to functional disorders of the cholinergic system. Significant research efforts have been made to develop novel derivatives of classical ChE inhibitors and ChE inhibitors with novel scaffolds. Over the past decade, ruthenium complexes have emerged as promising novel therapeutic alternatives for the treatment of neurodegenerative diseases. Our research group has investigated a number of newly synthesized organoruthenium(II) complexes for their inhibitory activity against acetylcholinesterase (AChE) and butyrylcholinesterase (BChE). Three complexes (C1a, C1-C, and C1) inhibit ChE in a pharmacologically relevant range. C1a reversibly inhibits AChE and BChE without undesirable peripheral effects, making it a promising candidate for the treatment of Alzheimer's disease. C1-Cl complex reversibly and competitively inhibits ChEs, particularly AChE. It inhibits nerve-evoked skeletal muscle twitch and tetanic contraction in a concentration-dependent manner with no effect on directly elicited twitch and tetanic contraction and is promising for further preclinical studies as a competitive neuromuscular blocking agent. C1 is a selective, competitive, and reversible inhibitor of BChE that inhibits horse serum BChE (hsBChE) without significant effect on the peripheral neuromuscular system and is a highly species-specific inhibitor of hsBChE that could serve as a species-specific drug target. This research contributes to the expanding knowledge of ChE inhibitors based on ruthenium complexes and highlights their potential as promising therapeutic candidates for chronic neurodegenerative diseases.

Comparative transcriptome and methylome of polar bears, giant and red pandas reveal diet-driven adaptive evolution

Epigenetic regulation plays an important role in the evolution of species adaptations, yet little information is available on the epigenetic mechanisms underlying the adaptive evolution of bamboo-eating in both giant pandas (Ailuropoda melanoleuca) and red pandas (Ailurus fulgens). To investigate the potential contribution of epigenetic to the adaptive evolution of bamboo-eating in giant and red pandas, we performed hepatic comparative transcriptome and methylome analyses between bamboo-eating pandas and carnivorous polar bears (Ursus maritimus). We found that genes involved in carbohydrate, lipid, amino acid, and protein metabolism showed significant differences in methylation and expression levels between the two panda species and polar bears. Clustering analysis of gene expression revealed that giant pandas did not form a sister group with the more closely related polar bears, suggesting that the expression pattern of genes in livers of giant pandas and red pandas have evolved convergently driven by their similar diets. Compared to polar bears, some key genes involved in carbohydrate metabolism and biological oxidation and cholesterol synthesis showed hypomethylation and higher expression in giant and red pandas, while genes involved in fat digestion and absorption, fatty acid metabolism, lysine degradation, resistance to lipid peroxidation and detoxification showed hypermethylation and low expression. Our study elucidates the special nutrient utilization mechanism of giant pandas and red pandas and provides some insights into the molecular mechanism of their adaptive evolution of bamboo feeding. This has important implications for the breeding and conservation of giant pandas and red pandas.

Acetylcholinesterase is regulated by exposure of ultraviolet B in skin keratinocytes: A potential inducer of cholinergic urticaria

Cholinergic urticaria is a dermatological disease characterized by the presence of large patches of red skin and transient hives triggered by factors, such as exercise, sweating, and psychological tension. This skin problem is hypothesized to be attributed to a reduced expression of acetylcholinesterase (AChE), an enzyme responsible for hydrolyzing acetylcholine (ACh). Consequently, ACh is thought to the leak from sympathetic nerves to skin epidermis. The redundant ACh stimulates the mast cells to release histamine, triggering immune responses in skin. Here, the exposure of ultraviolet B in skin suppressed the expression of AChE in keratinocytes, both in in vivo and in vitro models. The decrease of the enzyme was resulted from a declined transcription of ACHE gene mediated by micro-RNAs, that is, miR-132 and miR-212. The levels of miR-132 and miR-212 were markedly induced by exposure to ultraviolet B, which subsequently suppressed the transcriptional rate of ACHE. In the presence of low level of AChE, the overflow ACh caused the pro-inflammatory responses in skin epidermis, including increased secretion of cytokines and COX-2. These findings suggest that ultraviolet B exposure is one of the factors contributing to cholinergic urticaria in skin.

Sunset Yellow induced biochemical and histopathological alterations in rat brain sub-regions

Sunset Yellow, a synthetic orange azo food dye was examined in this study for its impact on the Wistar rat brain sub-regions. The dye was administered orally to weanling rats at the Acceptable Daily Intake level (4 mg/kg/bw) for 40 days, and brain sub-regions viz., frontal cortex, cerebellum and hippocampus were examined for biochemical and histopathological changes. The results showed a significant decrease in tissue protein levels, superoxide dismutase, and catalase activity, as well as a significant increase in lipid peroxide levels in all brain sub-regions. Glutathione-S-transferase and Glutathione Reductase activities decreased, while Glutathione peroxidase activity increased. The biogenic amine levels and Acetylcholinesterase activity were also altered, with the frontal cortex and hippocampus being the most affected. Additionally, the dye caused histopathological damage in all brain sub-regions examined. This study indicates that the ADI level of Sunset Yellow may adversely affect brain tissue by causing oxidative damage.

Evaluation of Antidiabetic Effect of Combined Leaf and Seed Extracts of Moringa oleifera (Moringaceae) on Alloxan-Induced Diabetes in Mice: A Biochemical and Histological Study

Moringa oleifera (Moringaceae) is a medicinal plant rich in biologically active compounds. The aim of the present study was to screen M. oleifera methanolic leaf (L) extract, seed (S) extract, and a combined leaf/seed extract (2L : 1S ratio) for antidiabetic and antioxidant activities in mice following administration at a dose level of 500 mg/kg of body weight/day. Diabetes was induced by alloxan administration. Mice were treated with the extracts for 1 and 3 months and compared with the appropriate control. At the end of the study period, the mice were euthanized and pancreas, liver, kidney, and blood samples were collected for the analysis of biochemical parameters and histopathology. The oral administration of the combined L/S extract significantly reduced fasting blood glucose to normal levels compared with L or S extracts individually; moreover, a significant decrease in cholesterol, triglycerides, creatinine, liver enzymes, and oxidant markers was observed, with a concomitant increase in antioxidant biomarkers. Thus, the combined extract has stronger antihyperlipidemic and antioxidant properties than the individual extracts. The histopathological results also support the biochemical parameters, showing recovery of the pancreas, liver, and kidney tissue. The effects of the combined L/S extracts persisted throughout the study period tested. To the best of our knowledge, this is the first study to report on the antidiabetic, antioxidant, and antihyperlipidemic effects of a combined L/S extract of M. oleifera in an alloxan-induced diabetic model in mice. Our results suggest the potential for developing a natural potent antidiabetic drug from M. oleifera; however, clinical studies are required.

Novel Organoruthenium(II) Complex C1 Selectively Inhibits Butyrylcholinesterase without Side Effects on Neuromuscular Transmission

Enzyme butyrylcholinesterase (BChE) shows increased activity in some brain regions after progression of Alzheimer's disease and is therefore one of the therapeutic targets for symptomatic treatment of this neurodegenerative disorder. The organoruthenium(II) complex [(η⁶-p-cymene)Ru(II)(1-hydroxy-3-methoxypyridine-2(1H)-thionato)pta]PF₆ (C1) was designed based on the results of our previous structure-activity studies. Inhibitory activity toward cholinesterase enzymes shows that this complex selectively, competitively, and reversibly inhibits horse serum BChE (hsBChE) with an IC₅₀ value of 2.88 µM. When tested at supra-pharmacological concentrations (30, 60, 90, and 120 µM), C1 had no significant effect on the maximal amplitude of nerve-evoked and directly elicited single-twitch and tetanic contractions. At the highest tested concentration (120 µM), C1 had no effect on resting membrane potential, but significantly decreased the amplitude of miniature end-plate potentials (MEPP) without reducing their frequency. The same concentration of C1 had no effect on the amplitude of end-plate potentials (EPP), however it shortened the half-decay time of MEPPs and EPPs. The decrease in the amplitude of MEPPs and shortening of the half-decay time of MEPPs and EPPs suggest a possible weak inhibitory effect on muscle-type nicotinic acetylcholine receptors (nAChR). These combined results show that, when applied at supra-pharmacological concentrations up to 120 µM, C1 does not importantly affect the physiology of neuromuscular transmission and skeletal muscle contraction.

Impact of chronic sub-lethal methylparaben exposure on cardiac hypoxia and alterations in neuroendocrine factors in zebrafish model

BACKGROUND

Endocrine-disrupting chemicals have been shown to cause toxicity in different systems of the body including the endocrine, cardiovascular and nervous systems. This study aims to analyze the adverse effects of Methylparaben (MP) on cardiac functions, neurodevelopment, and behavior of zebrafish.

METHODS AND RESULTS

Adult male and female zebrafish were exposed to MP for 30 days to study the toxicity effects. Zebrafish were grouped into control, solvent control, 1/10th (110 ppb), 1/100th, and 1/1000th (1 ppb) lethal concentration 50 of MP. Neurobehavioral assays, acetylcholinesterase (AChE) activity, serotonin levels, and expression of genes-Hypoxia-inducible factor 1 alpha, Neurotrophic Receptor Tyrosine Kinase, Paired box protein Pax-6, and tnnt2 were investigated in zebrafish. Results of the study showed more anxiety-like behavior in MP-treated female zebrafish when compared to males on chronic exposure. There was a dose-dependent reduction of AChE activity in both male and female zebrafish. Female zebrafish showed a dose-dependent increase in serotonin level on MP exposure while male zebrafish showed a dose-independent decrease in serotonin level. On MP exposure, there was also a dose-dependent dysregulation in the expression of cardiac hypoxia and neuronal differentiation-related genes in female zebrafish while a dose-independent change was observed in male zebrafish.

CONCLUSION

Chronic MP exposure affects cardiac functions, neuronal functions, and behavior of zebrafish by exhibiting changes in AChE activity, serotonin levels, and altering the expression of genes related to cardiac hypoxia and neuronal differentiation even at sub-lethal doses.

Synergistic Inhibition of Acetylcholinesterase by Alkaloids Derived from Stephaniae Tetrandrae Radix, Coptidis Rhizoma and Phellodendri Chinensis Cortex

Alkaloids having acetylcholinesterase (AChE) inhibitory activity are commonly found in traditional Chinese medicine (TCM); for example, berberine from Coptis chinensis, galantamine from Lycoris radiata, and huperzine A from Huperzia serrata. In practice of TCM, Stephaniae Tetrandrae Radix (STR) is often combined with Coptidis Rhizoma (CR) or Phellodendri Chinensis Cortex (PCC) as paired herbs during clinical application. Fangchinoline from STR and coptisine and/or berberine from CR and/or PCC are active alkaloids in inhibiting AChE. The traditional usage of paired herbs suggests the synergistic effect of fangchinoline–coptisine or fangchinoline–berberine pairing in AChE inhibition. HPLC was applied to identify the main components in herbal extracts of STR, CR, and PCC, and the AChE inhibition of their main components was determined by Ellman assay. The synergism of herb combination and active component combination was calculated by median-effect principle. Molecular docking was applied to investigate the underlying binding mechanisms of the active components with the AChE protein. It was found that fangchinoline showed AChE inhibitory potency; furthermore, fangchinoline–coptisine/berberine pairs (at ratios of 1:5, 1:2, 1:1, and 2:1) synergistically inhibited AChE; the combination index (CI) at different ratios was less than one when Fa = 0.5, suggesting synergistic inhibition of AChE. Furthermore, the molecular docking simulation supported this enzymatic inhibition. Therefore, fangchinoline–coptisine/berberine pairs, or their parental herbal mixtures, may potentially be developed as a possible therapeutic strategy for Alzheimer’s patients.

Non-neuronal acetylcholine involved in reproduction in mammals and honeybees

Bacteria and archaea synthesize acetylcholine (ACh). Thus, it can be postulated that ACh was created by nature roughly three billion years ago. Therefore, the wide expression of ACh in nature (i.e., in bacteria, archaea, unicellular organisms, plants, fungi, non-vertebrates and vertebrates and in the abundance of non-neuronal cells of mammals) is not surprising. The term non-neuronal ACh and non-neuronal cholinergic system have been introduced to describe the auto- and paracrine, that is, local regulatory actions of ACh in cells not innervated by neuronal cholinergic fibers and to communicate among themselves. In this way non-neuronal ACh binds to the nicotinic or muscarinic receptors expressed on these local and migrating cells and modulates basic cells functions such as proliferation, differentiation, migration and the transport of ions and water. The present article is focused to the effects of non-neuronal ACh linked to reproduction; data on the expression and function of the non-neuronal cholinergic system in the following topics are summarized: (i) Sperm, granulosa cells, oocytes; (ii) Auxiliary systems (ovary, oviduct, placenta); (iii) Embryonic stem cells as first step for reproduction of a new individual after fertilization; (iv) Larval food as an example of reproduction in insects (honeybees) and adverse effects of the neonicotinoids, a class of world-wide applied insecticides. The review article will show that non-neuronal ACh is substantially involved in the regulation of reproduction in mammals and also non-mammals like insects (honeybees). There is a need to learn more about this biological role of ACh. In particular, we have to consider that insecticides like the neonicotinoids, but also carbamates and organophosphorus pesticides, interfere with the non-neuronal cholinergic system thus compromising for example the breeding of honeybees. But it is possible that other species may also be adversely affected as well, a mechanism which may contribute to the observed decline in biodiversity. This is an article for the special issue XVth International Symposium on Cholinergic Mechanisms.

Sunitinib, a Clinically Used Anticancer Drug, Is a Potent AChE Inhibitor and Attenuates Cognitive Impairments in Mice

Sunitinib, a tyrosine kinase inhibitor, is clinically used for the treatment of cancer. In this study, we found for the first time that sunitinib inhibits acetylcholinesterase (AChE) at submicromolar concentrations in vitro. In addition, sunitinib dramatically decreased the hippocampal and cortical activity of AChE in a time-dependent manner in mice. Molecular docking analysis further demonstrates that sunitinib might interact with both the catalytic anion and peripheral anionic sites within AChE, which is in accordance with enzymatic activity results showing that sunitinib inhibits AChE in a mixed pattern. Most importantly, we evaluated the effects of sunitinib on scopolamine-induced cognitive impairments in mice by using novel object recognition and Morris water maze tests. Surprisingly, sunitinib could attenuate cognitive impairments to a similar extent as donepezil, a marketed AChE inhibitor used for the treatment of Alzheimer's disease. In summary, our results have shown that sunitinib could potently inhibit AChE and attenuate cognitive impairments in mice.

Fucoxanthin, a Marine Carotenoid, Reverses Scopolamine-Induced Cognitive Impairments in Mice and Inhibits Acetylcholinesterase in Vitro

Fucoxanthin, a natural carotenoid abundant in edible brown seaweeds, has been shown to possess anti-cancer, anti-oxidant, anti-obesity and anti-diabetic effects. In this study, we report for the first time that fucoxanthin effectively protects against scopolamine-induced cognitive impairments in mice. In addition, fucoxanthin significantly reversed the scopolamine-induced increase of acetylcholinesterase (AChE) activity and decreased both choline acetyltransferase activity and brain-derived neurotrophic factor (BDNF) expression. Using an in vitro AChE activity assay, we discovered that fucoxanthin directly inhibits AChE with an IC₅₀ value of 81.2 μM. Molecular docking analysis suggests that fucoxanthin likely interacts with the peripheral anionic site within AChE, which is in accordance with enzymatic activity results showing that fucoxanthin inhibits AChE in a non-competitive manner. Based on our current findings, we anticipate that fucoxanthin might exhibit great therapeutic efficacy for the treatment of Alzheimer’s disease by acting on multiple targets, including inhibiting AChE and increasing BDNF expression.

Effect of Marine Collagen Peptides on Physiological and Neurobehavioral Development of Male Rats with Perinatal Asphyxia

Asphyxia during delivery produces long-term deficits in brain development. We investigated the neuroprotective effects of marine collagen peptides (MCPs), isolated from Chum Salmon skin by enzymatic hydrolysis, on male rats with perinatal asphyxia (PA). PA was performed by immersing rat fetuses with uterine horns removed from ready-to-deliver rats into a water bath for 15 min. Caesarean-delivered pups were used as controls. PA rats were intragastrically administered with 0.33 g/kg, 1.0 g/kg and 3.0 g/kg body weight MCPs from postnatal day 0 (PND 0) till the age of 90-days. Behavioral tests were carried out at PND21, PND 28 and PND 90. The results indicated that MCPs facilitated early body weight gain of the PA pups, however had little effects on early physiological development. Behavioral tests revealed that MCPs facilitated long-term learning and memory of the pups with PA through reducing oxidative damage and acetylcholinesterase (AChE) activity in the brain, and increasing hippocampus phosphorylated cAMP-response element binding protein (p-CREB) and brain derived neurotrophic factor (BDNF) expression.