Article

Acute and chronic studies with the anticholinesterase huperzine A: Effect on central nervous system cholinergic parameters

Authors:
To read the full-text of this research, you can request a copy directly from the authors.

Abstract

High affinity choline transport, choline acetyltransferase (ChAT) and acetylcholinesterase (AChE) were assessed in rats after acute and chronic administration of the AChE inhibitor Huperzine A. Acute treatment: Forty-five min after a single injection of Huperzine A (0.5 mg/kg i.p.) the activity of AChE was significantly decreased by 15-30% in hippocampus, striatum and septum. The activity of ChAT was not altered. In the hippocampus high affinity choline transport was attenuated by 25%, whereas no effect in the striatum was observed. After 90 min, both inhibition of AChE and attenuation of high affinity choline transport had returned to control values. A dose of 0.1 mg/kg (i.p.) did not produce significant effects. Similar results were obtained with physostigmine (0.25 mg/kg), although the duration of inhibition of AChE was shorter than that with Huperzine A. Chronic treatment: After 5 days (twice a day), at 0.5 mg/kg, the activity of AChE was significantly reduced by 20-30% in every region of the brain studied. High affinity choline transport in the hippocampus was reduced by 28%, 45 min after the last injection, but in the striatum there was no effect. The activity of ChAT was not affected in any region of the brain studied. Thus, acute or chronic treatment with Huperzine A: did not alter ChAT; reduced high affinity choline transport in the hippocampus in a transient manner; and had a longer duration of action as an AChE inhibitor than physostigmine. Moreover, tolerance to low-toxicity doses of Huperzine A was minimal, contrary to what has been observed with other inhibitors of AChE.

No full-text available

Request Full-text Paper PDF

To read the full-text of this research,
you can request a copy directly from the authors.

... The advantage of Huperzine A is reflected in its ability to pass through a blood-brain barrier, which means that AChE in central nerve system can be reached and protected during nerve agent poisoning. [7] Protective effects of FDA-approved drugs for the treatment of Alzheimer's disease, donepezil and galantamine, were also investigated [8][9][10][11][12]. [8]- [12] In this work we present the design, synthesis, NMR characterization, and anticholinesterase activity of four novel nanomolar dual-binding reversible inhibitors of cholinesterases. ...
Conference Paper
Organophosphorous chemical warfare agents (i.e., nerve agents) exhibit toxic effects mainly through covalent, irreversible inhibition of acetylcholinesterase (EC 3.1.1.7), an enzyme that terminates cholinergic neurotransmission, by hydrolyzing acetylcholine at nerve and nerve-muscle junctions. Use of nerve agents is strictly limited to research purposes only and it is under control of Organisation for the Prohibition of Chemical Weapons, OPCW. Despite all efforts to limit the use of nerve agents, unfortunately the danger of nerve agents being used in war aggression and terrorist attacks is still present. The reversible inhibition of AChE was suggested as the pre-treatment option against nerve agents' intoxications. Aiming to investigate novel pre-treatment options, we designed and synthesized the four novel compounds of tacrine and aroylacrylic acid phenylamide moieties, connected via a long methylene chain to target two distinct topologically separated anionic areas on the AChE. The inhibitory activity of the compounds toward the Electric eel AChE's as well as the horse serum BChE was determined by Ellman assay. The designed compounds may represent a new class of promising leads for developing more effective pre-treatment options.
... It was subsequently synthesized by Kozikowski (Kozikowski et al., 1991), and kinetic studies showed that it is a slow reversible and highly potent inhibitor of AChE, with a rate constant of k on 5 10 6 M 21 min 21 (Ashani et al., 1992). Huperzine A is a more potent inhibitor of AChE than physostigmine and also has a longer biological half-life in rats and humans, and penetrates the BBB (Laganiére et al., 1991;Tang et al., 1989). Natural huperzine A is stereochemically pure, designated with (-) while the synthetic one represents the mixture of the two isomers. ...
Chapter
Nerve agents rapidly inactivate acetylcholinesterase (AChE), leading to the accumulation of acetylcholine in the synaptic cleft, ultimately causing death by respiratory failure. Due to the inefficiency of the standard antidotal therapy consisting of atropine, oxime, and diazepam, the pretreatment option is introduced, given to healthy individuals when a chemical attack is expected. The pyridostigmine bromide is currently the only approved drug for the pretreatment against nerve agent exposure, but in the past few decades, several other AChE inhibitors have been proposed including carbamates (physostigmine and rivastigmine) and the reversible inhibitors AChE used for the treatment of Alzheimer’s disease (huperzine A, donepezil, and galanthamine). In this chapter, we present a comprehensive review of the newest in vitro and in vivo studies of these drugs as pretreatment options, along with the recently designed AChE reversible inhibitors, also tested in vitro for protection of the enzyme against irreversible inhibition by nerve agents. Special attention is paid to the results of the in vitro studies and kinetic behavior of AChE inhibitors and their relation to the protective effects exerted in the in vivo animal models.
... These findings indicated that Hup A has higher bioavailability and penetrates the blood brain barrier more easily. Moreover, repeated doses of Hup A showed no significant difference on the AChE inhibition compared with that of single dose, indicating no tolerance to Hup A (Wang et al. 1998;Laganiere et al. 1991). ...
Article
Full-text available
Lycopodium is a genus of the family Pteridophytes, which is widely distributed in temperate and tropical climates and tropical mountains. Plants of genus Lycopodium are ancient medicinal plants which have been used in different traditional medicinal system to treat many diseases, mainly focus on central nervous system and inflammation-related diseases. Rigorous pharmacological and clinical studies conducted in recent decades have demonstrated their special efficacy in the treatment of Alzheimer's disease (AD). Furthermore, secondary metabolites and extracts from these plants have been proven to possess neuroprotective, anti-tumor, anti-inflammatory, anti-microbial, and antiviral effects, which supports most of traditional medicinal uses of Lycopodium plants. To date, a total of 508 secondary metabolites have been reported from the 46 species belonging to genus Lycopodium. Among those metabolites, Lycopodium alkaloids and serratene triterpenoids represent two major classes of bioactive ingredients. Notably, huperzine A, a Lycopodium alkaloid originally isolated from L. serratum, was licensed in China as a drug for the treatment of AD and in the United States as a dietary supplement. Besides, serratane-type triterpenoids may be potential candidates for the development of anticancer drugs. This review covers the literatures available from 1947 to 2020 and mainly discusses knowledge on ethnopharmacology, secondary metabolites, pharmacological activities, clinical trials, toxicology, and quality control of Lycopodium species. In addition, the present review also draws attention to the gaps that still exist in the scientific studies on Lycopodium plants, which would accelerate the contemporary development of this traditional medicinal plant. Graphic abstract
... Tang et al. (1989) found that Hup A (0.5-1 mg/kg) provided the greatest inhibition of AChE throughout the entire brain (up to 42%), with the fewest side effects. Laganiere et al. (1991) found that 0.5 mg/kg Hup A significantly reduced AChE activity in the hippocampus, striatum, and septum (20-45%), whereas 0.1 mg/kg Hup A only slightly reduced AChE activity in these brain regions. In Rhesus monkeys, Myers et al. (2010) also found that Hup A (5-40 µg/kg) resulted in a dose-dependent inhibition of AChE activity (31-74%) without adverse cognitive effects. ...
Article
Full-text available
De novo loss-of-function mutations in the voltage-gated sodium channel (VGSC) SCN1A (encoding Nav1.1) are the main cause of Dravet syndrome (DS), a catastrophic early-life encephalopathy associated with prolonged and recurrent early-life febrile seizures (FSs), refractory afebrile epilepsy, cognitive and behavioral deficits, and a 15–20% mortality rate. SCN1A mutations also lead to genetic epilepsy with febrile seizures plus (GEFS+), which is an inherited disorder characterized by early-life FSs and the development of a range of adult epilepsy subtypes. Current antiepileptic drugs often fail to protect against the severe seizures and behavioral and cognitive deficits found in patients with SCN1A mutations. To address the need for more efficacious treatments for SCN1A-derived epilepsies, we evaluated the therapeutic potential of Huperzine A, a naturally occurring reversible acetylcholinesterase inhibitor. In CF1 mice, Hup A (0.56 or 1 mg/kg) was found to confer protection against 6 Hz-, pentylenetetrazole (PTZ)-, and maximal electroshock (MES)-induced seizures. Robust protection against 6 Hz-, MES-, and hyperthermia-induced seizures was also achieved following Hup A administration in mouse models of DS (Scn1a+/−) and GEFS+ (Scn1aRH/+). Furthermore, Hup A-mediated seizure protection was sustained during 3 weeks of daily injections in Scn1aRH/+ mutants. Finally, we determined that muscarinic and GABAA receptors play a role in Hup A-mediated seizure protection. These findings indicate that Hup A might provide a novel therapeutic strategy for increasing seizure resistance in DS and GEFS+, and more broadly, in other forms of refractory epilepsy.
... Compared to physostigmine, HupA was found to exhibit a threefold higher inhibitory effect against AChE (Zhu 1991), and it displayed, in rodents, a relative potency in inhibiting brain AChE activity 64-times higher than that of tacrine and eightfold superior to that shown by donepezil (Cheng et al. 1996;Wang and Tang 1998b;Cheng and Tang 1998). Additionally, in opposition to other AChE inhibitors (Hallak and Giacobini 1989), repeated doses of HupA do not increase the tolerance for AChE inhibition (Laganière et al. 1991), and the AChE inhibition seems to preferentially occur in the cortex and hippocampus areas, which are the cerebral regions where the presynaptic cholinergic markers are significantly reduced in AD Pepping 2000). In fact, when compared with donepezil and rivastigmine, (-)-HupA showed the longest effects in the elevation of cortical ACh levels (Liang and Tang 2004). ...
Article
The use and popularity of herbal medicines has been increasing worldwide. In fact, today, the traditional Chinese medicine offers a vast repertory for pharmaceutical research, as is the case of Huperzia serrata, a member of Huperziaceae family. This review reports the Lycopodium alkaloids that have been isolated from this plant. However, it was mainly focused on the huperzine A (HupA), a promising therapeutic option in several acute and chronic disorders. The major therapeutic interest described for HupA has been directed to the treatment of acetylcholine-deficit dementia, including Alzheimer's disease. However, HupA was also shown to be effective on cerebrovascular dementia and other neurodegenerative disorders with an ischemic component, as well as on other kind of cognitive impairments; the value of HupA on myasthenia gravis, organophosphate poisoning and schizophrenia has also been described. In addition, many other pharmacological properties have been ascribed to HupA, namely its anti-inflammatory, antinociceptive and anticonvulsant properties, which was recently identified, promoting a growing interest on HupA research. Furthermore, its particular chemical structure and the fact that HupA is well tolerated in humans, even at doses well above those clinically required, along with its favorable pharmacokinetics, also boosted an intense research in the pharmaceutical industry. Therefore, several HupA-related features are addressed in this review, including not only its therapeutic properties, but also its chemistry, biological and chemical sources, structure-activity relationship, pharmacokinetics and toxicology, which are discussed in detail covering the literature published from 1962 to 2014.
... In fact, neural activity can vary during different cognitive processes, becoming rhythmic during such a brain activity; in particular, hippocampal theta-frequency rhythmicity could contribute to learning and memory in brain [53][54][55]. In rat, spatial memory is supported by interaction between hippocampus and cortical areas, mainly frontal cortex, which is critically involved in attention and learning [52][53][54][55][56][57][58]. ...
Article
Full-text available
Huperzine A (Hup-A), an alkaloid isolated from Huperzia serrata (Thunb.) Trevis. (Lycopodiaceae), acts as a selective inhibitor of acetylcholinesterase and shows memory-enhancing properties. Although Hup-A has shown promising expectation for Alzheimer's disease (AD) patients, controlled clinical trials supporting its use are limited. The aim of this work was to study in vivo, in an animal model of AD, the pharmacological activity of systemic administration of Hup-A on cortex- and hippocampus-dependent memory. With this purpose, a set of experiments was planned to evaluate attention, learning, working and spatial memory with respect to cortical and hippocampal electroencephalogram (EEG) theta rhythm during the object recognition test and Morris water maze in animals with lesion of the nucleus basalis of Meynert (NBM). In NBM-lesioned animals, compared with control, an increased theta power in the cortex and a reduced theta rhythm oscillation in the hippocampus were found. These EEG changes were correlated with worse performance in learning and memory tasks. In rats with damaged NBM, Hup-A (0.5 mg/kg i.p.) was able to restore EEG architecture, producing cortical desynchronization and reduction in theta power, while in the hippocampus the drug increased theta oscillation and reduced the impairment in attention/working memory as well as spatial navigation performance in the behavioral tasks. Taken together, the present data suggest that Hup-A is able to restore cholinergic cortico-hippocampal functional connectivity. In conclusion, the present results are in agreement with other experimental evidence that promote the clinical use of this natural drug.
... Repeated doses of HA showed no significant decline in AChE inhibition as compared with that of a single dose, which demonstrates that no tolerance to HA occurred. 43 ...
Article
Huperzine A (HA), a Lycopodium alkaloid isolated from traditional Chinese herbs, was a potent, selective, and reversible acetylcholinesterase inhibitor (AChEI), and which crosses the blood-brain barrier smoothly, and shows high specificity for AChE with a prolonged biological half-life. It has been approved as a drug for the treatment of Alzheimer disease (AD) in China. This paper represents a comprehensive documentation of the overview of studies on HA up to Feb, 2004, covering the fields of plant resource, chemistry, pharmacology, structural biology, and clinical trials. Furthermore, the development of ZT-1, a Schiff base derivative of HA as an improved agent against AD, was also described.
... Huperzia serrata (Lycopodiaceae) is used in TCM to prepare "Qian Ceng Ta" which is prescribed to alleviate memory loss [103]. Huperzine A (27, Fig. 6), a lycopodium alkaloid related to the quinolizidines isolated from H. serrata, is a reversible inhibitor of AChE in vitro and in vivo [2,3,[104][105][106][107], capable of improving memory retention processes in cognitively impaired rats [108], attenuating cognitive deficits in chronically hyperfused rats [109], and in gerbils following cerebral ischemia [110]. Clinical evaluation of 27 revealed a significant improvement of memory and behavior in AD patients, selectively inhibiting AChE with less toxic effects than the commercially available drugs donepezil and tacrine [111,112]. ...
Article
Full-text available
The present review is part II in a series (part I focuses on Parkinson's Disease) that addresses the value of natural product chemistry in the discovery of medicines for the treatment of neurodegenerative disorders. Data reviewed document that a host of products from plant species and derivatives have neuroprotectant effects in vitro and in vivo. In addition, besides neuroprotection, natural products also demonstrate biological effects that target biochemical pathways underlying associated symptoms of neurdegnerative disorders that include cognitive impairments, energy/fatigue, mood, and anxiety. This part of the review series focuses specifically upon Alzheimer's Disease (AD). AD is postulated to result from extracellular formation of amyloid plaques and intracellular deposits of neurofibrilary tangles in the hippocampus, cerebral cortex and other areas of the brain essential for cognitive function. Plaques are formed mostly from the deposition β-amyloid (Aβ), a peptide derived from the amyloid precursor protein (APP). Filamentous tangles are formed from paired helical filaments composed of neurofilament and hyperphosphorilated tau protein, a microtubule-associated protein. In addition, environmental factors can engender the production of cytokines that are closely related to the installation of an inflammatory process that contributes to neuronal death and the development and the progression of AD. In this review we focus on the recent main contribuitions of natural products chemistry to the discovery of new chemical entities usefull to the control and prevention of AD installation and progression. More than sixteen plant species, including Ginseng, Celastrus paniculatus, Centella asiatica, Curcuma longa, Ginkgo biloba, Huperzia serrata, Lycoris radiate, Galanthus nivalis, Magnolia officinalis, Polygala tenuifolia, Salvia lavandulaefolia, Salvia miltiorrhiza, Coptis chinensis, Crocus sativus, Evodia rutaecarpa, Sanguisorba officinalis, Veratrum grandiflorum and Picrorhiza kurvoa, are discussed as potential sources of active extracts. In addition, more than sixty secondary metabolites are under evaluation for their efficacy on controlling symptoms and to impede the development and progression of AD.
... Otra ventaja de la huperzina A con respecto a los carbamatos es su inhibición prácticamente selectiva de la AChE eritrocítica, mientras que la piridostigmina y la fisostigmina inhiben tanto la AChE eritrocítica como la butirilcolinestarasa plasmática [58]. Por otra parte, estudios in vivo con animales han demostrado que es capaz de atravesar la barrera hematoencefálica sin que se hayan observado efectos secundarios a este nivel [54,55,59]. En un estudio prospectivo a doble ciego en 103 pacientes que padecían la enfermedad de Alzheimer, el 58% de los pacientes mostró una mejora de la función cognitiva, memoria y comportamiento [60]. ...
Article
El bromuro de piridostigmina (bromuro de 3-dimetilaminocarboniloxi- N-metilpiridinio) se utiliza como pretratamiento en escenarios en los que existe riesgo de utilización de agentes neurotóxicos de guerra. De hecho, este pretratamiento fue utilizado por las tropas Aliadas durante la Guerra del Golfo Pérsico. Desde su vuelta a casa muchos veteranos de esta guerra se han quejado de padecer síntomas debidos a lesiones que afectan al sistema nervioso. Las causas de estos síntomas son aún desconocidas, pero el pretratamiento con piridostigmina se está estudiando como posible factor causal. Aunque a la dosis empleada en el pretratamiento los efectos secundarios son mínimos y no se han observado efectos a largo plazo, se ha planteado la posibilidad de que en situaciones de estrés los efectos de la piridostigmina a nivel del sistema nervioso central se vean incrementados, si bien los distintos estudios in vivo arrojan resultados contradictorios. Otros estudios in vivo, sin embargo, sí han observado un incremento de la actividad central de la piridostigmina al coadministrarse con DEET (N,N-dietil-m-toluamida), utilizado como repelente de insectos por algunas tropas durante la Guerra del Golfo Pérsico. Este hecho recomendaría la necesidad de controlar la utilización de repelentes de insectos en caso de que sea necesario llevar a cabo un pretratamiento con piridostigmina. Recientemente se han empezado a estudiar nuevas alternativas en el pretratamiento de las intoxicaciones por agentes neurotóxicos de guerra de las cuales destaca la huperzina A (9-amino-13-etilidén-11-metil-4-azatriciclo[7.3.1.0(3,8)]trideca- 3(8),6,11-trien-5-ona) por sus propiedades farmacocinéticas y mayor eficacia
... Huperzine A (HupA) is an inhibitor of AChE that is found naturally in the club moss Huperzia serrata and has relatively low toxicity. 6 These characteristics render HupA as a promising candidate for the treatment of Alzheimer's disease. ...
Article
Two molecular dynamics simulations were performed for a modeled complex of mouse acetylcholinesterase liganded with huperzine A (HupA). Analysis of these simulations shows that HupA shifts in the active site toward Tyr 337 and Phe 338, and that several residues in the active site area reach out to make hydrogen bonds with the inhibitor. Rapid fluctuations of the gorge width are observed, ranging from widths that allow substrate access to the active site, to pinched structures that do not allow access of molecules as small as water. Additional openings or channels to the active site are found. One opening is formed in the side wall of the active site gorge by residues Val 73, Asp 74, Thr 83, Glu 84, and Asn 87. Another opening is formed at the base of the gorge by residues Trp 86, Val 132, Glu 202, Gly 448, and Ile 451. Both of these openings have been observed separately in the Torpedo californica form of the enzyme. These channels could allow transport of waters and ions to and from the bulk solution.
... It is an alkaloid isolated from the club moss, Huperzia serrata, which has gained popularity in Chinese herbal medicine. The compound's unique pharmacological features and relative lack of toxicity [45] makes it a potent compound for AD treatment. The structure of racemic Huperzine A shows some similarity to other known AChE inhibitors [46]. ...
Article
Full-text available
A wide range of evidence shows that acetylcholinesterase (AChE) inhibitors can interfere with the progression of Alzheimer's disease (AD). The successful development of these compounds was based on a well-accepted theory that the decline in cognitive and mental functions associated with AD is related to the loss of cortical cholinergic neurotransmission. The earliest known AChE inhibitors, namely, physostigmine and tacrine, showed modest improvement in the cognitive function of Alzheimer's patients. However, clinical studies show that physostigmine has poor oral activity, brain penetration and pharmacokinetic parameters while tacrine has hepatotoxic liability. Studies were then focused on finding a new type of acetylcholinesterase inhibitor that would overcome the disadvantages of these two compounds. Donepezil hydrochloride inaugurates a new class of AChE inhibitors with longer and more selective action with manageable adverse effects. Currently, there are about 19 new Alzheimer's drugs in various phases of clinical development.
... 1,2 Huperzine A has no significant affinity for muscarinic or nicotinic receptors, is devoid of presynaptic and postsynaptic activity, and does not influence the synthesis or release of acetylcholine. 1,3,4 The relative potency of huperzine A in inhibiting brain acetylcholinesterase activity in rodents was found to be 8 times that of E2020 and 64 times that of tacrine. 1 In addition, huperzine A had a higher bioavailability and more readily crossed the blood-brain barrier than did either E2020 or tacrine. 1 The cholinergic adverse-effect profile of huperzine A in rats was considerably lower than that of tacrine or E2020, most probably because of its selectivity for brain acetylcholinesterase (in comparison with peripheral butyrylcholinesterase effects seen with tacrine). 5 Intraperitoneal huperzine A doses of 0.1, 0.3, and 0.5 mg/kg in rats increased brain levels of acetylcholine by 54%, 129%, and 220%, respectively. ...
Chapter
For centuries, the rare Chinese club moss Huperzia serrata has been used in the preparation of the traditional Chinese medicine Qian Ceng Ta, a treatment for fever and inflammation (Skolnick, 1997). In 1986, an alkaloid, huperzine A was isolated from this herbal medicine and shown to be a potent inhibitor of the enzyme acetylcholinesterase (Bai et al., 2000). Acetylcholinesterase breaks down acetylcholine, an important neurotransmitter involved in thought, reasoning, and judgment. Scientists have long recognized that compounds with the ability to inhibit acetylcholinesterase can help improve memory and thus be used to treat the symptoms of Alzheimer’ s disease and other dementias.
Article
Ethnopharmacological relevance: Epilepsy is one of the most prevalent neurological human diseases, affecting 1% of the population in all age groups. Despite the availability of over 25 anti-seizure medications (ASMs), which are approved in most industrialized countries, approximately 30% of epilepsy patients still experience seizures that are resistant to these drugs. Since ASMs target only limited number of neurochemical mechanisms, drug-resistant epilepsy (DRE) is not only an unmet medical need, but also a formidable challenge in drug discovery. Aim: In this review, we examine recently approved epilepsy drugs based on natural product (NP) such as cannabidiol (CBD) and rapamycin, as well as NP-based epilepsy drug candidates still in clinical development, such as huperzine A. We also critically evaluate the therapeutic potential of botanical drugs as polytherapy or adjunct therapy specifically for DRE. Methods: Articles related to ethnopharmacological anti-epileptic medicines and NPs in treating all forms of epilepsy were collected from PubMed and Scopus using keywords related to epilepsy, DRE, herbal medicines, and NPs. The database clinicaltrials.gov was used to find ongoing, terminated and planned clinical trials using herbal medicines or NPs in epilepsy treatment. Results: A comprehensive review on antiepileptic herbal drugs and natural products from the ethnomedical literature is provided. We discuss the ethnomedical context of recently approved drugs and drug candidates derived from NPs, including CBD, rapamycin, and huperzine A. Recently published studies on natural products with preclinical efficacy in animal models of DRE are summarized. Moreover, we highlight that natural products capable of pharmacologically activating the vagus nerve (VN), such as CBD, may be therapeutically useful to treat DRE. Conclusions: The review highlights that herbal drugs utilized in traditional medicine offer a valuable source of potential anti-epileptic drug candidates with novel mechanisms of action, and with clinical promise for the treatment of drug-resistant epilepsy (DRE). Moreover, recently developed NP-based anti-seizure medications (ASMs) indicate the translational potential of metabolites of plant, microbial, fungal and animal origin.
Article
Full-text available
Huperzine A (Hup A) is an important drug for treating Alzheimer’s disease (AD) and mainly extracted from the Huperzia serrata (Thunb.) Trevis. (Lycopodiaceae) (HS). Nevertheless, the content of Hup A in HS is very low of 0.007% with growing circle of 8 to 10 years, and the chemical synthesis of Hup A still has some insurmountable limitations in the industrialized production. So, the available resources of Hup A for clinical treatment of AD are scarce. The purpose of this work was to construct a biosynthesis platform based on the endophytic fungi from HS. In this work, five endophytic fungi Mucor racemosus NSH-D, Mucor fragilis NSY-1, Fusarium verticillioides NSH-5, Fusarium oxysporum NSG-1, and Trichoderma harzianum NSW-V were firstly found and isolated from the Chinese folk medicine HS, which were identified according to their morphological characteristics and nuclear ribosomal DNA ITS sequences. The highest efficient fungus could effectively biosynthesize Hup A in a liquid culture of 319.8 ± 0.17 mg/L which were 112 times higher than that of other reported conventional endophytic fungi. Moreover, these fungi with higher hereditary stability could possess the initial expressing ability of Hup A after 40 generations, and the expressed Hup A from these biosynthesis systems has prior physicochemical properties, a better inhibition activity of acetylcholinesterase and a lower cytotoxicity compared with the listed active pharmaceutical ingredients (APIs) of Hup A. These results provide promising alternative resources for producing Hup A at an industrial scale by biosynthesis, and it may also shed light on millions of AD patients. Key points • Five novel endophytic fungi with high stability could highly express prior Hup A Graphical abstract
Article
The dissociation of huperzine A (hupA) from Torpedo californica acetylcholinesterase (TcAChE) was investigated by 4-microsecond unbiased and biased all-atom molecular dynamics (MD) simulations in explicit solvent. We performed our study using memetic sampling (MS) for the determination of reaction pathways (RPs), metadynamics to calculate free energy, and maximum-likelihood estimation (MLE) to recover kinetic rates from unbiased MD simulations. Our simulations suggest that the dissociation of hupA occurs mainly via two RPs: a front-door along the axis of the active-site gorge (pwf) and through a new transient side-door (pws), i.e., formed by the Omega-loop (residues 67--94 of TcAChE). Analysis of the inhibitor unbinding along the RPs suggests that pws is opened transiently after hupA and the Omega-loop reach a low free-energy transition state characterized by the orientation of the pyridone group of the inhibitor directed toward the Omega-loop plane. Unlike pws, pwf does not require large structural changes of TcAChE to be accessible. The estimated free energies and rates agree well with available experimental data. The dissociation rates along the unbinding pathways are similar, suggesting that the dissociation of hupA along pws is likely to be relevant. This indicates that perturbations to hupA-TcAChE interactions could potentially induce pathway hopping. In summary, out results characterize the slow-onset inhibition of TcAChE by hupA, which may provide the structural and energetic basis for the rational design of the next-generation slow-onset inhibitors with optimized pharmacokinetic properties for the treatment of Alzheimer's disease.
Chapter
Around 600 diseases have been characterized in the nervous system, including Parkinson's disease (PD) and Alzheimer's disease (AD). Natural products represent one of the most important sources of currently available medicines to treat neurological disorders. Studies showed that practically about half new drugs permitted since 1994 are based on natural products. In this chapter, we present an overview of those natural products that have been found useful for AD and PD therapy and highlight some of the recent drug developments against both these diseases.
Article
Resumen Introducción La enfermedad de Alzheimer constituye la principal causa de demencia en el mundo. No se ha determinado completamente el rol de la nutrición en la prevención de este o de otros tipos de demencia. Objetivos Se realiza esta revisión sistemática con el fin de analizar la evidencia y formular recomendaciones prácticas sobre nutrición y demencia. Resultados Se recomienda: 1) minimizar la ingesta de grasas saturadas y grasas trans; 2) considerar a los vegetales, legumbres, frutas y granos como principales fuentes de la dieta y 3) considerar la ingesta de vitamina B a dosis estipuladas a través de alimentos fortificados o suplementos. Se discuten el papel del aluminio, la utilidad de las vitaminas antioxidantes, huperzina A, resveratrol, Ginkgo biloba y los nutracéuticos disponibles. Conclusión La evidencia disponible no es suficiente para determinar el poder de recomendación de una guía de prevención del deterioro cognitivo o de la enfermedad de Alzheimer, no obstante, se proponen recomendaciones para tal fin.
Chapter
Alzheimer's disease (AD), one of the most common neurodegenerative disorders, is characterized by progressive loss of memory. Various strategies have been developed to prevent or slow the progression of the disease. Despite several advancements in the field of medical therapeutics, an effective treatment for AD is the need of the hour. Since ages past, plants have played a role in catering to the therapeutic needs of humans and in the process of drug discovery. Based on the traditional literature, various new therapeutically active compounds or their leads have been isolated from plants, including for use in cognitive disorders. We are blessed with plethora of such literature from different traditional systems of medicines. This chapter discusses plants and their active constituents found effective in treatment of memory disorders, including their preclinical and clinical efficacy and their mechanism of action.
Chapter
Acetylcholinesterase (AChE) terminates synaptic transmission at cholinergic synapses by rapid hydrolysis of acetylcholine (ACh) (Quinn, 1987). Anticholinesterase agents are used in the treatment of various disorders (Taylor, 1990), and have been proposed as therapeutic agents for the management of Alzheimer’s disease (Giacobini & Becker, 1991, 1994). Two such anti- cholinesterase agents, both of which act as reversible inhibitors of AChE, have been licensed by the FDA: tacrine (Gauthier & Gauthier, 1991), under the trade name Cognex, and, more recently, E2020 (Sugimoto et al., 1992), under the trade name Aricept. Several other anticholinesterase agents are at advanced stages of clinical evaluation. The acive site of AChE contains a catalytic subsite, and a so-called ‘anionic’subsite, which binds the quaternary group of ACh (Quinn, 1987). A second, ‘peripheral’anionic site is so named since it is distant from the active site (Taylor & Lappi, 1975). Bisquaternary inhibitors of AChE derive their enhanced potency, relative to homologous monoquaternary ligands (Main, 1976), from their ability to span these two ‘anionic’sites, which are ca. 14 Å apart.
Chapter
Natural products have a widespread public appeal that appears only to be growing. The fastest growth is in the western world although in lesser economically developed countries the demand remains as strong as ever. This appeal is aided by the almost universal, though completely irrational assumption, that if a product is natural it must be safe. This chapter will consider those naturally-occurring substances that are believed to beneficially affect cognitive function.
Article
Pyridostigmine bromide (3-dimethylaminocarbonyloxy-N-methylpyridinium bromide) is used as a pretreatment drug in scenarios where there is a risk of exposure to nerve agents. Pyridostigmine bromide was actually used by many Allied troops in the Persian Gulf War. Since their return, many veterans of this war are complaining of neurological symptoms. The causes of the symptoms are still unknown, but pretreatment with pyridostigmine is being studied as a possible causal factor. Although the currently recommended pretreatment dose has minimal adverse effects and long term effects have not been reported, the possibility of an increased central effect of pyridostigmine in stress situations has been raised, although in vivo studies reviewed report contradictory results. Nevertheless, other in vivo studies have reported an increased central activity of pyridostigmine when administered with DEET (N,N-diethyl-m-toluamide), an insect repellent used by some troops in the Persian Gulf War. This fact recommends the control of insect repellent use if pretreatment with pyridostigmine has to be established because of nerve agent exposure risk. New alternatives to the pyridostigmine pretreatment have been proposed and huperzine A (9-amino-13-ethylidene-11-methyl-4-azatricyclo[7.3.1.0(3,8)]trideca- 3(8),6,11-trien-5-one) stands out because of its pharmacokinetical properties and effectiveness.
Article
Huperzine A has been shown to be a powerful selective inhibitor of acetylcholinesterase and has attracted widespread attention because of its unique pharmacological profile and low toxicity. The total synthesis, structural modification and structure-activity relationship of huperzine A have been systematically reviewed.
Article
Huperzine A, an alkaloid used as acetylcholinesterase inhibitor isolated from traditional Chinese herb, was studied using semiempirical method AM1, ab initio Hartree–Fock (HF), and density-functional theory (DFT) B3LYP method at different basis set levels. The calculated results showed that the three-ring structure of HupA is rigid and the pyridone ring is planar. However, the hydrogen atom positions of its amide and amino groups will shift when the molecular environment changes, especially for the amino group. HF/4-31G calculated results revealed that the amino group can rotate at room temperature. The investigation also indicated that the B3LYP/6-31G* method is better than AM1 and HF/6-31G* for studying infra-red (IR) spectrum of HupA and its analogues. The predicted vibrational bands at B3LYP/6-31G* level are in good agreement with the observed spectrum except the vibrational modes which relate to the atoms of amide and amino groups. The reason for the differences of structure and vibrational bands is probably that these groups can form intermolecular hydrogen bonds in the crystal structure, which will affect the force properties and the vibrational frequency.
Article
Chemical warfare nerve agents such as soman exert their toxic effects through an irreversible inhibition of acetylcholinesterase (AChE) and subsequently glutamatergic function, leading to uncontrolled seizures. The natural alkaloid (-)-huperzine A is a potent inhibitor of AChE and has been demonstrated to exert neuroprotection at an appropriate dose. It is hypothesized that analogs of both (+)- and (-)-huperzine A with an improved ability to interact with NMDA receptors together with reduced AChE inhibition will exhibit more effective neuroprotection against nerve agents. In this manuscript, the tested huperzine A analogs 2 and 3 were demonstrated to improve survival of guinea pigs exposed to soman at either 1.2 or 2×LD(50).
Article
An abstract is unavailable. This article is available as HTML full text and PDF.
Article
Full-text available
Quantum chemical DFT-B3LYP/6-31G * method and IR spectrometry have been used to investigate the natural and binding structures of Huperzine B (HupB) in order to better understand the interaction nature between acetylcholinesterase (AChE) and its inhibitor, with the view of designing new AChE inhibitors. The predicted and experimental results reveal that both the natural state and binding form of HupB adopt the chair conformation. Furthermore, the B3LYP/6-31G * results suggest that structure S1 should be the dominant form of the two possible chair structures (S1 and S2, Fig. 2). The calculated results also show that the condensed ring structure composing of rings A, B and C is very rigid. Therefore, its flexibility does not need to be considered when we try to dock this structure to its target. Indeed, this supposition is confirmed by the excellent alignment of the binding structure produced from our recent X-ray crystallographic structure of the HupB-AChE complex with the B3LYP/6-31G * predicted geome-try. Among all the 111 predicted vibrational bands, the mode 110, which is resulted from the stretching of the bond N2–H and having the second highest frequency, is essential for the geometrical identification. The difference between our predicted strongest absorption band and experimental IR spectrum suggests Corresponding authors. 81 82 X. Luo et al. that a strong intermolecular interaction, which could be a hydrogen bond, exists in HupB crystal. The electrostatic potential surface of HupB derived from our B3LYP/6-31G * CHelpG atomic charge suggests a mechanism of how HupB would interact with its target. In addition, the good agreement between predicted vibrational bands (scaled by a factor of 0.96) and experimental result shows that B3LYP/6-31G * is a good tool for studying such kind of natural compound.
Article
HupA, a novel alkaloid isolated from the Chinese medicinal herb Huperzia serrata, is a reversible, potent, and selective inhibitor of AChE. Compared with other well-known AChEIs, such as physostigmine, galanthamine, tacrine, and even donepezil, HupA has better penetration through the blood-brain barrier, higher oral bioavailability, and longer duration of AChE inhibitory action. HupA exhibited memory-enhancing efficacy in a broad range of animal models of cognitive impairment. Double-blind and placebo-controlled clinical trials have demonstrated that HupA produced significant improvements in memory deficiencies in aged patients and patients with AD. Furthermore, both animal and clinical safety testings showed that HupA was devoid of unexpected toxicity, particularly the dose-limiting hepatotoxicity induced by tacrine. These encouraging preclinical and clinical findings suggest that HupA is a highly promising candidate for clinical development as a symptomatic treatment for AD and other memory disorders related to a central cholinergic deficiency.
Article
Qinghao (Artemisia annua L. composites) as a medicinal herb has been used in China for over four millenniums. Its antimalarial application was described as early as about AC 300, and thousands years later, its antimalarial principle qinghaosu, a unique peroxide sisquiterpene, was isolated and identified in 1970s'. Qinghaosu has rapid action and excellent antimalarial activity, especially for chloroquine-resistant parasite Plasmodium falciparum. This chapter reviews the discovery and the further studies on qinghaosu and its derivatives or analogues over the last decades in the fields of medicinal chemistry and some pharmacology research, with an emphasis on the progress achieved in China.
Article
The chemical warfare nerve agent (CWNA) soman irreversibly inhibits acetylcholinesterase (AChE) causing seizure, neuropathology and neurobehavioral deficits. Pyridostigmine bromide (PB), the currently approved pretreatment for soman, is a reversible AChE inhibitor that does not cross the blood-brain barrier (BBB) to protect against central nervous system damage. [-]-Huperzine A, a natural reversible AChE inhibitor, rapidly passes through the BBB and has numerous neuroprotective properties that are beneficial for protection against soman. However, [-]-Huperzine A is toxic at higher doses due to potent AChE inhibition which limits the utilization of its neuroprotective properties. [+]-Huperzine A, a synthetic stereoisomer of [-]-Huperzine A and a weak inhibitor of AChE, is non-toxic. In this study, we evaluated the efficacy of [+]-Huperzine A for protection against soman toxicity in guinea pigs. Pretreatments with [+]-Huperzine A, i.m., significantly increased the survival rate in a dose-dependent manner against 1.2× LD(50) soman exposures. Behavioral signs of soman toxicity were significantly reduced in 20 and 40 mg/kg [+]-Huperzine A treated animals at 4 and 24 h compared to vehicle and PB controls. Electroencephalogram (EEG) power spectral analysis showed that [+]-Huperzine A significantly reduces soman-induced seizure compared to PB. [+]-Huperzine A (40 mg/kg) preserved higher blood and brain AChE activity compared to PB in soman exposed animals. These data suggest that [+]-Huperzine A protects against soman toxicity stronger than PB and warrant further development as a potent medical countermeasure against CWNA poisoning.
Article
Huperzine A is a natural cholinesterase inhibitor derived from the Chinese herb Huperzia serrata that may compare favorably in symptomatic efficacy to cholinesterase inhibitors currently in use for Alzheimer disease (AD). We assessed the safety, tolerability, and efficacy of huperzine A in mild to moderate AD in a multicenter trial in which 210 individuals were randomized to receive placebo (n = 70) or huperzine A (200 μg BID [n = 70] or 400 μg BID [n = 70]), for at least 16 weeks, with 177 subjects completing the treatment phase. The primary analysis assessed the cognitive effects of huperzine A 200 μg BID (change in Alzheimer's Disease Assessment Scale-cognitive subscale [ADAS-Cog] at week 16 at 200 μg BID compared to placebo). Secondary analyses assessed the effect of huperzine A 400 μg BID, as well as effect on other outcomes including Mini-Mental State Examination, Alzheimer's Disease Cooperative Study-Clinical Global Impression of Change scale, Alzheimer's Disease Cooperative Study Activities of Daily Living scale, and Neuropsychiatric Inventory (NPI). Huperzine A 200 μg BID did not influence change in ADAS-Cog at 16 weeks. In secondary analyses, huperzine A 400 μg BID showed a 2.27-point improvement in ADAS-Cog at 11 weeks vs 0.29-point decline in the placebo group (p = 0.001), and a 1.92-point improvement vs 0.34-point improvement in the placebo arm (p = 0.07) at week 16. Changes in clinical global impression of change, NPI, and activities of daily living were not significant at either dose. The primary efficacy analysis did not show cognitive benefit with huperzine A 200 μg BID. Classification of evidence: This study provides Class III evidence that huperzine A 200 μg BID has no demonstrable cognitive effect in patients with mild to moderate AD.
Article
La intoxicación por vía parenteral debida a insecticidas organoclorados e hidrocarburos aromáticos, es muy poco frecuente. La toxicidad comporta efectos locales y sistémicos que pueden llegar a comprometer la vida del paciente. Se presenta el caso clínico de un varón que desarrolló una importante reacción local necrótico-inflamatoria, con leve afectación sistémica hepática y renal, tras administrarse los mencionados productos por vía parenteral en una tentativa de suicidio
Article
Full-text available
El botulismo es una toxi-infección producida por la bacteria anaerobia Clostridium botulinum por medio de una potentísima toxina, la toxina botulínica, de la cual existen ocho serotipos diferentes. Ésta es capaz de provocar en humanos al menos cuatro cuadros clínicos diferentes por bloqueo de la transmisión neuromuscular, y que pueden variar en gravedad desde la casi ausencia de síntomas hasta la muerte por parálisis respiratoria. Paradójicamente, la toxina botulínica se presenta también como un arma terapéutica eficaz y segura en decenas de enfermedades, si bien gran parte de estas potenciales aplicaciones está aún en fase de investigación
Article
Rats were trained to run in a spatial, radial arm maze using a procedure to determine two memory functions, working and reference memory. The muscarinic antagonist, not the nicotinic antagonist, impaired both working and reference memory of rats. Scopolamine (0.125, 0.15, and 0.2 mg/kg, IP, 30 min before a session) significantly impaired choice accuracy in the eight-arm maze. In contrast, mecamylamine (5, 10, and 15 mg/kg) did not affect the performance. Huperzine A (0.1, 0.2, and 0.3 mg/kg, IP, 30 min before testing) and physostigmine (0.3 mg/kg, IP, 20 min before testing) could reverse scopolamine-induced deficits in the task. Chronic treatment with huperzine A (0.25 mg/kg, PO, once a day) for 8 consecutive days was as potent as acute treatment on attenuating the scopolamine-induced amnesia.
Article
Huperzine A (HUP) is a naturally-occurring, potent, reversible inhibitor of acetylcholinesterase (AChE) that crosses the blood-brain barrier. To examine its ability to protect against nerve agent poisoning, HUP was administered i.p. to mice, and the s.c. LD50 of soman was determined at various time intervals after pretreatment. Results were compared to those obtained for animals treated with physostigmine. A protective ratio of approximately 2 was maintained for at least 6 hr after a single injection of HUP, without the need for any post-challenge drug therapy. By contrast, pretreatment with physostigmine increased the LD50 of soman by 1.4- to 1.5-fold for only up to 90 min. The long-lasting antidotal efficacy displayed by HUP correlated with the time course of the blood-AChE inhibition. The results suggest that the protection of animals by HUP from soman poisoning was achieved by temporarily sequestering the active site region of the physiologically important AChE.
Article
Huperzine A, a novel, potent, reversible, and selective acetylcholinesterase (AChE) inhibitor has been expected to be superior to other AChE inhibitors now for the treatment of memory deficits in patients with Alzheimer's disease. We have assessed the effects of huperzine A on performance of AF64A-treated rats in the radial maze. AF64A (2 nmol per side, i.c.v.) caused significant impairment in rats' ability to perform the spatial working memory task. This behavioural impairment was associated with a significant decrease in the activity of choline acetyltransferase (ChAT) in the hippocampus. Huperzine A (0.4-0.5 mg kg-1, i.p.) significantly ameliorated the AF64A-induced memory deficit. These results suggest that AF64A is a useful agent for disrupting working memory processes by altering hippocampal cholinergic function, and such impairment can be effectively ameliorated by huperzine A.
Article
Full-text available
(-)-Huperzine A (HupA) is found in an extract from a club moss that has been used for centuries in Chinese folk medicine. Its action has been attributed to its ability to strongly inhibit acetylcholinesterase (AChE). The crystal structure of the complex of AChE with optically pure HupA at 2.5 A resolution shows an unexpected orientation for the inhibitor with surprisingly few strong direct interactions with protein residues to explain its high affinity. This structure is compared to the native structure of AChE devoid of any inhibitor as determined to the same resolution. An analysis of the affinities of structural analogues of HupA, correlated with their interactions with the protein, shows the importance of individual hydrophobic interactions between HupA and aromatic residues in the active-site gorge of AChE.
Article
Huperzine A (HUP) is a potent reversible inhibitor of acetylcholinesterase (AChE) that crosses the blood-brain barrier. Its ability to prevent seizures and subsequent hippocampal neuropathological changes induced by the organophosphate soman was studied in guinea pigs. Results were compared to guinea pigs treated with pyridostigmine (PYR, 0.2 mg/kg, subcutaneously). HUP pretreatment at 0.5 mg/kg, intraperitoneally, totally prevented seizures and ensured the survival of all animals for 24 h after intoxication. Hippocampal tissue was then free of any neuronal damage. Comparatively, all animals pretreated with PYR exhibited epileptic activity after soman poisoning and five of six animals died. Examination of the hippocampus of the only surviving guinea pig pretreated with PYR showed extensive neuropathological changes. Although HUP or PYR induced similar inhibitions of blood AChE activity, only HUP pretreatment led to a decrease in central AChE activity. In binding studies on guinea-pig brain homogenates, HUP had no affinity for muscarinic, alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid (AMPA) and gamma-aminobutyric acid (GABA)A receptors and only a very low one for N-methyl-D-aspartate (NMDA) receptors. In conclusion, HUP, unlike PYR, protects against soman-induced convulsions and neuropathological changes in the hippocampus. This efficacy seems to be related to a protection by HUP of both peripheral and central stores of AChE.
Article
Comparative effects of cholinesterase inhibitors (ChEI) huperzine A with E2020 and tacrine on the radial maze performance in ethylcholine mustard aziridinium ion (AF64A)-treated rat and inhibition of cholinesterase activity were studied. The intracerebroventricular (i.c.v.) injection of AF64A (3 nmol/side) caused significant impairment in the rat's ability to fulfill the partially baited maze paradigm. Oral huperzine A (0.5-0.8 mg/kg), E2020 (1.0-2.0 mg/kg), and tacrine (8.0 mg/kg) effectively reversed AF64A-induced working memory deficit. The doses that improved AF64A-induced memory deficit were correlated to about 25-30% (huperzine A) and less than 10% (E2020, tacrine) inhibition of acetylcholinesterase (AChE) activity in the cortex and hippocampus. Huperzine A, E2020 and tacrine all produced dose-dependent inhibition of brain AChE following i.c.v. and oral administration. Oral huperzine A exhibited higher efficacy on the inhibition of AChE in the cortex and hippocampus than those of E2020 and tacrine. Tacrine was more effective in inhibiting plasma butyrylcholinesterase (BuChE) than it was brain AChE. Conversely, the BuChE activity was less affected by huperzine A and E2020. The results showed that huperzine A had high bioavailability and more selective inhibition on AChE activity in cortex and hippocampus. Huperzine A fits more closely with the established criteria for an ideal AChE inhibitor to be used in clinical studies.
Article
Full-text available
Huperzine A, alkaloid from the Chinese herbal medicine Qian Ceng Ta, which is prepared from the moss Huperzia serrata, has been used in China for centuries to treat fever and inflammation. Huperzine A is a strong inhibitor of cholinesterases with high selectivity to acetylcholinesterase and in China is developed as therapeutic against Alzheimer's disease. May be that huperzine A will be better than other centrally active anticholinesterases in treating this neurodegenerative disorder. Huperzine A appears to have additional pharmacological properties that make it an attractive candidate therapy for clinical trials.
Article
Recent data indicate that the neurotoxic effects of organophosphate compounds, including those of the nerve agents VX and sarin, are not solely due to irreversible cholinesterase inhibition. In this study we applied the patch clamp technique to hippocampal neurons in culture and slices to investigate the effects of VX, sarin and huperzine A on transmitter release and the mechanisms related with such effects. The nerve agents VX and sarin at very low concentrations significantly reduced the evoked release of GABA and glutamate. This effect was dependent of the activation of muscarinic receptors. In the presence or absence of the Na(+)-channel blocker tetrodotoxin (TTX), VX increased the frequency of spontaneous glutamate and GABA-induced postsynaptic currents. The effect of VX on TTX-insensitive spontaneous currents appears to be unrelated to cholinesterase inhibition, because it could be detected even after cholinesterase was blocked by high concentrations of the nerve agent soman. The ability of the nerve gases to decrease evoked release of GABA and increase spontaneous transmitter release may underlie some of the neurotoxic effects of the compounds. Huperzine A did not affect spontaneous or evoked release of GABA and glutamate, suggesting that this compound may be a pure cholinesterase inhibitor and had no effect on postsynaptic GABAA or AMPA receptors.
Article
To compare the anticholinesterase effects of huperzine A (Hup A), E2020, and tacrine in rats. Spectrophotometry was used to determine AChE activity in brain and BuChE activity in serum. Following intragastric gavage, Hup A, E2020, and tacrine all produced dose-dependent inhibitions of brain AChE. Oral Hup A exhibited a higher inhibition than E2020 and tacrine. Tacrine was more effective in inhibiting serum BuChE correlated with severe peripheral adverse effects. The BuChE activity was less affected by Hup A and E2020. After a single oral dose of Hup A, a relatively steady state of AChE inhibition produced, which was longer than that after E2020 and tacrine. No change in the cholinesterase inhibition was seen for the 3 drugs following repeated i.g. medications. Hup A i.g. exhibited a higher efficacy, a longer duration of action, and a more selective inhibition on AChE than E2020 and tacrine.
Article
Choline (Ch) supplementation during embryonic days (ED) 12-17 enhances spatial and temporal memory in adult and aged rats, whereas prenatal Ch deficiency impairs attention performance and accelerates age-related declines in temporal processing. To characterize the neurochemical and neuroanatomical mechanisms that may mediate these behavioral effects in rats, we studied the development [postnatal days (PD) 1, 3, 7, 17, 27, 35, 90, and 26 months postnatally] of acetylcholinesterase (AChE) activity in hippocampus, neocortex and striatum as a function of prenatal Ch availability. We further measured the density of AChE-positive laminae (PD27 and PD90) and interneurons (PD20) in the hippocampus as a function of prenatal Ch availability. During ED11-ED17 pregnant Sprague-Dawley rats received a Ch-deficient, control or Ch-supplemented diet (average Ch intake 0, 1.3 and 4.6 mmol/kg/day, respectively). Prenatal Ch deficiency increased hippocampal AChE activity as compared to control animals in both males and females from the 2nd to 5th week postnatally. Moreover, prenatal Ch supplementation reduced hippocampal AChE activity as compared to control animals over the same developmental period. There was no effect of prenatal Ch status on either cortical or striatal AChE activity at any age measured, and by PD90 the effect of Ch on hippocampal AChE was no longer observed. In order to localize the early changes in hippocampal AChE activity anatomically, frozen coronal brain sections (PD20, PD27, PD90) were stained histochemically for AChE. Consistent with biochemical results, the AChE staining intensity was reduced in PD27 hippocampal laminae in the Ch-supplemented group and increased in the Ch-deficient group compared to control animals. There was no effect of the diet on hippocampal AChE staining intensity on PD90. In addition, the prenatal Ch availability was found to alter the size and density of AChE-positive PD20 interneurons. These results show that prenatal Ch availability has long-term consequences on the development of the hippocampal cholinergic system.
Article
HupA is a potent, reversible and selective inhibitor of AChE with a rapid absorption and penetration into the brain in animal tests. It exhibits memory-enhancing activities in animal and clinical trials. Compared to tacrine and donepezil, HupA possesses a longer duration of action and higher therapeutic index, and the peripheral cholinergic side effects are minimal at therapeutic doses. This review article deals with a comprehensive survey of the progress in chemical and pharmacological studies of HupA including the isolation and structure elucidation, pharmacological actions, total synthesis, SAR studies and the future development of HupA. Recently, it has been reported that HupA could reduce neuronal cell death caused by glutamate. The dual bio-activities of HupA would further enhance its value and potentiality as the therapeutic agent for Alzheimer s disease.
Article
If a woman does not want to use, or cannot use, hormone replacement therapy, then she must consider other ways to address two issues related to menopause: reducing her risk of developing cardiovascular disease, osteoporosis, and other health problems that increase as women age, and symptomatology. Risk reduction of an array of health problems can be achieved through diet, exercise, and stress management. The nutraceuticals of specific vitamins, minerals, phytoestrogens, and essential fatty acid supplementations are a vital component of the risk reduction health program. Risk reduction of osteoporosis can be enhanced specifically through the use of ipriflavone and a comprehensive "bone building" vitamin and mineral program. Control of homocysteine levels for prevention of CAD, osteoporosis, and other health problems can be accomplished through B vitamin supplementation. The same interventions for risk reduction also may prove to be effective in prevention and treatment of menopausal-related symptoms, particularly when the B vitamins, magnesium, isoflavones, and essential fatty acids are used. If lifestyle interventions and nutraceuticals do not adequately address symptomatology, however, a woman has several alternative therapies from which to choose. There are numerous excellent multiherbal and homeopathic therapies that can be purchased over the counter. A woman also can choose to be evaluated by an alternative therapy practitioner and have a program designed specifically for her health needs. Although there has been limited clinical research of herbal and homeopathic alternative therapies for the menopause, when taken according to directions and if no contraindications exist, they have the potential for being extremely effective and safe options.
Article
Herbs from Lycopodium are generally reputed to be nontoxic and are occasionally used for preparing a salubrious tea. In Europe, the common Lycopodium clavatum can be easily confused with Lycopodium selago, the fir club moss. We report 2 patients who drank a tea, erroneously prepared from dried herbs of Lycopodium selago, which resulted in sweating, vomiting, diarrhea, dizziness, cramps, and slurred speech. These symptoms were suggestive of a cholinergic mechanism. To elucidate the active principle, aqueous extracts of Lycopodium selago were checked for their suspected anticholinesterase activity using human erythrocytes as an enzyme source in a modified Ellman assay. The extracts did exhibit significant anticholinesterase activity. The anticholinesterase(s) were most effectively extracted with dichloromethane and isolated by high-performance liquid chromatography. The major compound with anticholinesterase activity co-chromatographed with authentic huperzine A, but had a 2-3-fold higher inhibitory potency than the racemic standard. The amount of huperzine A found in the Lycopodium selago sample used for the tea preparation was calculated to be sufficient for a relevant acetylcholinesterase inhibition. The signs and symptoms of Lycopodium selago poisoning are consistent with the anticholinesterase activity of huperzine A and should favorably respond to atropine therapy. This report demonstrates once more that laymen should not be encouraged to gather their remedies from "Mother Nature" without advanced botanical knowledge.
Article
PYR, a reversible AChE inhibitor, is the current pretreatment against OP intoxication. However, PHY in the presence or absence of SCO on one side, and HUP on the other side, could be considered as potential substitutes for PYR. In the present study, the effects of the subchronic administration of these different current or potential pretreatments on the BBB permeability for blood-borne albumin and on the activity of the blood and central cholinesterases are comparatively evaluated in guinea-pigs. Altogether, although some marginal disruptions of BBB are detected, the different current or potential pretreatments studied seem to have a total innocuousness on the permeability of the BBB for proteins. Finally, at the light of its particular inhibitory effects on blood and central cholinesterases, HUP, compared to the other drugs, seems to be the optimal candidate to be used as pretreatment against OP poisoning.
Article
Effects of subchronic administration of huperzine A, a cholinesterase inhibitor, on spatial memory were studied in guinea pig. Spatial memory was appreciated by the Morris water maze test. At a dose of 0.25 microgram/h, inhibiting 36% of blood AChE and 14-20% of central AChE, no effect on spatial learning was found. At a dose of 1 microgram/h, inhibiting 20% of blood AChE and 14-20% of central AChE, no memory impairment was found, on the other hand, a memory enhancing effect, limited to the first day was shown. It thus appears that subchronic administration of huperzine A did not induce deleterious effects on spatial memory.
Article
Full-text available
In vivo K(+), Na(+), Ca(2+) and Cl(-) activities in the cytosol and the contractile vacuole fluid of Paramecium multimicronucleatum were determined in cells adapted to a number of external osmolarities and ionic conditions by using ion-selective microelectrodes. It was found that: (1) under standardized saline conditions K(+) and Cl(-) were the major osmolytes in both the cytosol and the contractile vacuole fluid; and (2) the osmolarity of the contractile vacuole fluid, determined from K(+) and Cl(-) activities only, was always more than 1.5 times higher than that of the cytosol. These findings indicate that excess cytosolic water crosses the contractile vacuole complex membrane osmotically. Substitution of choline or Ca(2+) for K(+) in the external solution or the external application of furosemide caused concomitant decreases in the cytosolic K(+) and Cl(-) activities that were accompanied by a decrease in the water segregation activity of the contractile vacuole complex. This implies that the cytosolic K(+) and Cl(-) are actively coimported across the plasma membrane. Thus, the osmotic gradients across both the plasma membrane and the membrane of the contractile vacuole complex ensure a controlled cascade of water flow through the cell that can provide for osmoregulation as well as the possible extrusion of metabolic waste by the contractile vacuole complex.
Article
—The accumulation of [3H]choline into synaptosome-enriched homogenates of rat corpus striatum, cerebral cortex and cerebellum was studied at [3H]choline concentrations varying from 0.5 to 100 μm. The accumulation of [3H]choline in these brain regions was saturable. Kinetic analysis of the accumulation of the radiolabel was performed by double-reciprocal plots and by least squares iterative fitting of a substrate-velocity curve to the data. With both of these techniques, the data were best satisfied by two transport components, a high affinity uptake system with Km. values of 1.4 μM (corpus striatum), and 3.1 μM (ceμ(cerebral cortex) and a low affinity uptake system with respective Km. values of 93 and 33 μM for these two brain regions. In the cerebellum choline was accumulated only by the low affinity system. When striatal homogenates were fractionated further into synaptosomes and mitochondria and incubated with varying concentrations of [3H]choline, the high affinity component of choline uptake was localized to the synaptosomal fraction. The high affinity uptake system required sodium, was sensitive to various metabolic inhibitors and was associated with considerable formation of [3H]acetylcholine. The low affinity uptake system was much less dependent on sodium, and was not associated with a marked degree of [3H]acetylcholine formation. Hemicholinium-3 and acetylcholine were potent inhibitors of the high affinity uptake system. A variety of evidence suggests that the high affinity transport represents a selective accumulation of choline by cholinergic neurons, while the low affinity uptake system has some less specific function.
Article
This review describes recent advances made in the understanding of the regulation of acetylcholine synthesis in brain with regard to the availability of its two precursors, choline and acetylCoA. Choline availability appears to be regulated by the high affinity choline transport system. Investigations of the localization and inhibition of this system are reviewed. Procedures for measuring high affinity choline transport and their shortcomings are described. The kinetics and effects of previous in vivo and in vitro treatments on high affinity choline transport are reviewed. Kinetic and direct coupling of the transport and acetylation of choline are discussed. Recent investigations of the source of acetylCoA used for the synthesis of acetylcholine are reviewed. Three sources of acetylCoA have recently received support: citrate conversion catalyzed by citrate lyase, direct release of acetylCoA from mitochondria following its synthesis from pyruvate catalyzed by pyruvate dehydrogenase, and production of acetylCoA by cytoplasmic pyruvate dehydrogenase. Investigations indicating that acetylCoA availability may limit acetylcholine synthesis are reviewed. A model for the regulation of acetylcholine synthesis which incorporates most of the reviewed material is presented.
Article
— The relationship between choline availability and the synthesis of acetylcholine in discrete brain regions was studied in animals treated with the organophosphorus cholinesterase inhibitor paraoxon. Administration of paraoxon (0.23 mg/kg) inhibited acetylcholinesterase activity by approx 90% in the striatum, hippocampus and cerebral cortex and increased acetylcholine levels to 149%, 124% and 152% of control values, respectively. Free choline levels were unaltered by paraoxon in the hippocampus and cerebral cortex, but were significantly decreased in the striatum to 74% of control. When animals were injected with choline chloride (60 mg/kg), 60 min prior to the administration of paraoxon, the paraoxon-induced choline depletion in the striatum was prevented and the paraoxon-induced acetylcholine increase was potentiated from 149% to 177% of control values. Choline pretreatment had no significant effect in either the hippocampus or cerebral cortex, brain regions that did not exhibit a decrease in free choline levels after paraoxon administration. Results indicate that choline administration, which had no significant effect on acetylcholine levels by itself, increased acetylcholine synthesis in the striatum in the presence of acetylcholinesterase inhibition. However, this effect was not apparent in either the hippocampus or the cerebral cortex at similar levels of enzyme inhibition. It appears that choline generated from the hydrolysis of acetylcholine may play a significant role in the regulation of neurotransmitter synthesis in the striatum, but not in the other brain areas studied. The evidence supports the concept that the regulatory mechanisms controlling the synthesis of acetylcholine in striatal interneurons may differ from those in other brain regions.
Article
We have compared the effect of treatments known to release acetylcholine (ACh) on high affinity choline (Ch) uptake in rat striatum and hippocampus. First, Ch uptake into synaptosome-rich P2 fractions was measured after the systemic administration of drugs which increase ACh release. Pentylenetetrazol (75 mg/kg, i.p.) increased the uptake of Ch into hippocampal P2 fractions by 45%. However, this treatment had no effect on striatal Ch uptake. Fluphenazine (0.5 or 5 mg/kg, s.c.), a drug which selectively increases ACh release in striatum, also failed to alter Ch uptake by tissue fractions prepared from that region. Second, P2 fractions were incubated in a depolarizing, high potassium (62 mM) Krebs-Ringer phosphate buffer, after which Ch uptake was measured. This treatment increased hippocampal Ch uptake by 150%, while uptake into striatal tissue was increased by only 31%. The results of these studies suggest that Ch uptake is considerably less responsive in striatum than in hippocampus to the effects of prior alterations in ACh release. This is true whether alterations are induced or . These findings indicate that ACh synthesis may be regulated differently in the two brain regions.
Article
We have measured the turnover rate of acetylcholine (ACh) in the brains of mice injected with doses of oxotremorine and physostigmine that cause a prolonged increase of ACh concentration in brain. The method used to measure turnover rate of ACh is an application of principles of steady-state kinetics to the change with time of brain choline (Ch) and ACh specific radioactivities after an intravenous pulse injection of phosphorylcholine. We have found that when the concentration of brain ACh and Ch is increased to a new steady state as a result of oxotremorine and physostigmine injections the turnover rate of brain ACh decreases from 0.34 mumol/g/hr (in saline-treated mice) to 0.12 and 0.061 mumol/g/hr, respectively. The possibility that an increase of brain Ch or ACh concentrations plays a role in the control of brain ACh turnover rate is discussed.
Article
Previous reports indicate that alterations of activity of cholinergic neurons are followed by parallel changes in sodium-dependent high affinity choline uptake . These results are consistent with the proposal that this portion of choline uptake is regulatory in the synthesis of ACh. These results also suggest the possibility of utilizing sodium-dependent high affinity choline uptake as a measure of the relative state of cholinergic activity . In this study, we administer a number of drugs reported to alter turnover and release of ACh (both are measures of cholinergic activity , and subsequently examine sodium-dependent high affinity choline uptake . Administration of pentobarbital, chloral hydrate, morphine, physostigmine, Δ9 THC, hemicholinium-3 and oxotremorine, drugs which decrease ACh turnover and release, caused a reduction in choline uptake. Conversely, administration of pentylenetetrazol, atropine, scopolamine, and haloperidol, drugs which increase ACh turnover and release, caused an increase in choline uptake . These findings support the proposal that sodium-dependent high affinity choline uptake can be used as a relative measure of the activity of cholinergic neurons .
Article
High affinity uptake of choline, the rate-limiting, regulatory step for the synthesis of acetylcholine (ACh), was found to be regulated via presynaptic auto- and heteroreceptors. The transport rate was reduced by a muscarinic agonist and neuropeptides, but was significantly enhanced by octopamine. Intracellular messengers, including cyclic nucleotides, appear to modulate the transport activity, apparently by activating specific protein kinases.
Article
The present study represents the first comprehensive investigation of the effect of huperzine A (HUP-A), a new cholinesterase inhibitor (ChEI) isolated from a Lycopodium species, upon acetylcholinesterase (AChE) activity, acetylcholine (ACh) levels and release, and cholinergic receptors in rat brain following acute i.m. or i.p. administration. The study shows that HUP-A can produce a long-term inhibition of AChE activity in brain (up to 360 min) and an increase in the ACh levels up to 40% at 60 min. There is considerable regional variation in the degree of ACh elevation after HUP-A with maximal values seen in frontal (125%) and parietal (105%) cortex and smaller increases (22-65%) in other brain regions. HUP-A at concentrations of 10(-6) to 10(-4) M does not significantly alter the electrically evoked release of 3H-ACh from cortical slices. With the exception of the highest concentrations (6 X 10(-4) M) the displacement effect of HUP-A for cholinergic ligands is stronger for 3H-(-)nicotine than for 3H-QNB. A parallel autoradiographic study in the mouse shows that 60 min after i.v. injection (183 micrograms/kg) the drug is present in all brain regions, but it is particularly concentrated in certain areas such as frontoparietal cortex, nucleus accumbens, hippocampal, and striatal cortex. Radio-activity is practically absent in the whole body at 12 hr. Our study suggests that this new ChEI has interesting cholinomimetic properties, and its effects satisfy more closely established criteria for an ideal ChEI for therapeutic use than previously tested compounds.
Article
Heptyl-physostigmine (Heptyl-Phy; MF-201) is a new carbamate derivative of physostigmine (Phy) with greater lipophilicity and longer inhibitory action on cholinesterase (ChE) activity than the parent compound. Following single dose administration of 5 mg/kg heptyl-Phy i.m., maximal whole brain acetylcholinesterase (AChE) inhibition (82%) if reached at 60 min. Inhibition of plasma BuChE butyrylcholinesterase (BuChE) remains close to the steady state level (60%) between 120 and 360 min. At 360 min, whole brain AChE activity is still 67% inhibited compared to controls. Inhibition of AChE activity displays brain regional differences which are more significant at 360 min. At this time point, AChe activity in cerebellum is only 40% inhibited while frontal cortex and medial septum are still 80% inhibited. Increases in acetylcholine (ACh) levels also show regional differences, however, there is no direct relationship between AChE inhibition and ACh increase. The electrically evoked [3H]ACh release in cortical slices was inhibited only by the highest concentration of heptyl-Phy tested (10(-4) M). At this concentration ChE activity was 97% inhibited in vitro. In conclusion, our results demonstrate that heptyl-Phy compares favorably to other reversible cholinesterase inhibitors (ChEI), particularly to Phy as far as producing a more long-lasting inhibition of AChE and a more prolonged increase of ACh in brain with less severe side effects. Therefore, it represents an interesting candidate for cholinomimetic therapy of Alzheimer disease (AD).
Article
The effects of two consecutive intramuscular doses of three cholinesterase inhibitors (physostigmine, tetrahydroaminoacridine and metrifonate) were compared in rats. The results revealed major differences in biochemical effects on the brain of the rat including the extent and duration of inhibition of cholinesterase, inhibition of release of acetylcholine and increase in levels of acetylcholine. Side effects were also markedly different in the time of appearance, duration and severity. These results suggest that there are significant differences in the mechanisms of action of various cholinesterase inhibitors. Since all three cholinesterase inhibitors are currently used in the experimental treatment of Alzheimer's disease, these findings have potential implications for the symptomatic therapy of these patients.
Article
Over 80 substances were studied for their inhibition of high-affinity uptake of [3H]choline into a mouse brain synaptosomal fraction. Kinetic experiments tested a number of them for competitive behavior. A minimal provisional model for the choline uptake process is envisioned that is consistent with current data and with relevant observations in the literature. There are two hydrophilic anionic sites on the choline transporter that are separated from each other by a cationic hydrophobic domain. Association of choline in a Na+-dependent manner with one or both of the sites is necessary for the transport of choline to take place. The choline binding anionic sites are sufficiently large and/or flexible to allow attachment of cationic moieties larger than choline. The cationic hydrophobic domain of the transporter is flexible, probably tending to planarity. The length of the hydrophobic region between the anionic sites is approximately that of 10 extended methylene groups, and the minimal width is approximated by the distance across the condensed ring system of chlorpromazine. The probability of attachment of the highly hydrophilic choline to its binding sites is increased both by hydrogen-bonding to a proton-acceptor within the anionic sites and by repulsion from the cationic hydrophobic region. A number of substances that potently and competitively inhibit high affinity choline uptake possess quaternary ammonium groups and neutral or negatively charged lipophilic groups. In general, substances in which two quaternary ammonium groups are separated by an appropriately configured hydrophobic group and which can combine with both anionic sites and the hydrophobic region between them are more potent inhibitors than monoquaternary substance with the same or similar groups. However, substances with a single high-affinity quaternary group and an appropriately structured hydrophobic group, e.g. the trimethoxy-3-butynyl quaternary ammonium compounds, possess inhibitory efficacies similar to those shown by the most potent bisquaternaries. The above suggests that further delineation of the characteristics of the structures of the above sites of the transporter could lead to devisal of more potent reversible inhibitors of choline uptake than now are available.
Article
Tolerance to the effects of physostigmine and oxotremorine in rats was evaluated using a multiple fixed-ratio 10, extinction schedule of food presentation. Physostigmine was administered either once daily or three times daily for 18 consecutive days. Tolerance to physostigmine's response decreasing effects was observed under both administration regimens. Cumulative dose-effect functions for oxotremorine (0.0056-0.562 mg/kg) were determined before and after chronic physostigmine administration. Oxotremorine's potency to produce response rate suppression decreased in rats receiving physostigmine three times daily but did not substantially change in rats receiving single daily injections. These results demonstrate that the dose or duration of action of physostigmine can determine whether tolerance to physostigmine's effects is accompanied by cross-tolerance to oxotremorine's effects.
Article
In the present paper various routes of administration (i.m., i.v. and i.c.v.) of physostigmine are compared and the effect of two drugs producing inhibition of cholinesterase, physostigmine and metrifonate, on the activity of cholinesterase in the brain of the rat and on levels of acetylcholine (ACh) and choline (Ch). After intramuscular administration of physostigmine (500 μg/kg), the activity of cholinesterase in brain was maximally inhibited (76%) at 5 min and recovered to 50% at 40 min. At 5 min, areas of the brain such as the striatum and medulla oblongata showed 49 and 67% inhibition, respectively. Levels of physostigmine in brain peaked at 5 min (1.28 nmol/g). With the exception of the cerebellum, there was a direct correlation between the concentration of physostigmine and inhibition of cholinesterase in a given area.
Article
By using an intravenous single pulse injection of choline [C14] into the tail vein of mice and measuring the endogenous levels of choline and acetylcholine, the effects of agents which influence acetylcholine metabolism in mouse brain were studied. The results were consistent with a feedback activation of cholinergic neurons with scopolamine, choline O acetyltransferase inhibition with naphthylvinylpyridine, inhibition of acetylcholine release by morphine and cholinesterase inhibition with physostigmine. The interactions of these agents with the cholinergic system further suggest certain characteristics of cholinergic neurons, e.g. that choline O acetyltransferase activity is accelerated by a decrease in intracellular acetylcholine levels and retarded by an increase in intracellular acetylcholine levels, that the choline transport mechanism is functioning at maximum capacity under normal physiological conditions and that the synaptic levels of endogenous choline play a role in tracer choline capture.
Article
The regional distribution of choline and acetylcholine was examined in rat brain. Choline was found to have a distribution similar to that of acetylcholine. With the exception of the cerebellum the ratio of choline to acetylcholine in different brain regions ranged between 2.5 and 3.6. When the majority of the cholinergic nerve endings in the hippocampus were destroyed by placement of a lesion in the medial septal area the concentrations of acetylcholine and choline in the hippocampus were reduced by 70–74 and 20–32 %, respectively. These results suggest that a significant portion of the free choline in brain is associated with cholinergic neurones.
Article
The accumulation of [3H] choline into synaptosome enriched homogenates of rat corpus striatum, cerebral cortex and cerebellum was studied at [3H] choline concentrations varying from 0.5 to 100 μM. The accumulation of [3H] choline in these brain regions was saturable. Kinetic analysis of the accumulation of the radiolabel was performed by double reciprocal plots and by least squares iterative fitting of a substrate velocity curve to the data. With both of these techniques, the data were best satisfied by two transport components, a high affinity uptake system with Km values of 1.4 μM (corpus striatum), and 3.1 μM (cerebral cortex) and a low affinity uptake system with respective Km values of 93 and 33 μM for these two brain regions. In the cerebellum, choline was accumulated only by the low affinity system. When striatal homogenates were fractionated further into synaptosomes and mitochondria and incubated with varying concentrations of [3H] choline, the high affinity component of choline uptake was localized to the synaptosomal fraction. The high affinity uptake system required sodium was sensitive to various metabolic inhibitors, and was associated with considerable formation of [3H]acetylcholine. The low affinity uptake system was much less dependent on sodium, and was not associated with a marked degree of [3H]acetylcholine formation. Hemicholinium 3 and acetylcholine were potent inhibitors of the high affinity uptake system. A variety of evidence suggests that the high affinity transport represents a selective accumulation of choline by cholinergic neurons, while the low affinity uptake system has a less specific function.
Article
Overt neurological impairment is the endpoint currently used to document a case of methylmercury poisoning. No consideration is given to possible subtle consequences. Offspring from mice exposed to methylmercury on day 7 or 9 of pregnancy were apparently unaffected during postnatal development. However, subtle behavioral differences between treated and control offspring were found when the overtly normal animals were tested in an open field and evaluated in a swimming apparatus at 1 month of age. Brain weight, protein, choline acetyltransferase, and cholinesterase were not significantly altered.
Article
—Choline acetyltransferase (ChAc) was localized in discrete layers in hippocampus regio superior and in area dentata. The highest activity in hippocampus was found in a narrow infrapyramidal zone, but high activities were also observed in the rest of stratum oriens and in stratum pyramidale. In area dentata the highest activities were found in a narrow supragranular zone and in hilus fasciae dentatae. The localization corresponded very closely to that of acetylcholinesterase. The main part of ChAc activity was confined to the synaptosome fraction. The results are compatible with the view that pyramidal and granular cells are excited by cholinergic boutons, mainly located on the basal or apical dendrites near the somata.
Article
Administration of multiple, sublethal doses of organophosphorus insecticides induces the development of tolerance to their toxicity. Among the different hypotheses investigated to explain the mechanism of this phenomenon, the one which has received the greatest experimental support is a downregulation of the muscarinic cholinergic receptors. Subsensitivity to cholinergic agonist has been demonstrated in vivo and in vitro in isolated organ preparations. Receptor binding experiments using muscarinic antagonists and agonists revealed a decrease of cholinergic receptors in central and peripheral tissues. Tolerance to another class of acetylcholinesterase inhibitors, carbamates has also been demonstrated. Differences from and similarities to organophosphate tolerance are discussed.
Article
Since 1922 when Wu proposed the use of the Folin phenol reagent for the measurement of proteins (l), a number of modified analytical pro- cedures ut.ilizing this reagent have been reported for the determination of proteins in serum (2-G), in antigen-antibody precipitates (7-9), and in insulin (10). Although the reagent would seem to be recommended by its great sen- sitivity and the simplicity of procedure possible with its use, it has not found great favor for general biochemical purposes. In the belief that this reagent, nevertheless, has considerable merit for certain application, but that its peculiarities and limitations need to be understood for its fullest exploitation, it has been studied with regard t.o effects of variations in pH, time of reaction, and concentration of react- ants, permissible levels of reagents commonly used in handling proteins, and interfering subst.ances. Procedures are described for measuring pro- tein in solution or after precipitation wit,h acids or other agents, and for the determination of as little as 0.2 y of protein.
Methyl mercury exposure in utero: subtle effects on postnatal behavior in mice
  • Spyker