Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound   Target Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound

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Query: EC:3.1.1.7 (acetylcholinesterase)
28,390 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

A review of the reported foliar residue data has revealed a number of deficiencies in the reentry intervals currently regulated, in particular, by the EPA and some by California. Deficiencies were also identified in the available information necessary to recommend better reentry intervals. Information regarding the frequency of exposure for individual or groups of harvesters is the most fundamental deficiency. It is needed to define a more realistic chronic criterion of allowable daily cholinesterase inhibition without cumulative symptoms. The second criterion of preventing acute overexposure is more readily defined. For the purposes of this study, the criteria of 4% mean daily inhibition and 50% acute inhibition were chosen as acceptable. Based on these criteria, the available data, and by using the unified field model assessment as the basis for comparison (Table 9), EPA reentry intervals for nine insecticides in Table 4 appear inadequate (i.e., not within the range of the model recommendations); 10 are adequate; and only one appears excessive as summarized in Table 10. A similar comparison of California's reentry intervals indicates only two may be inadequate or marginal; 13 are adequate; and five may be excessive. Although these conclusions are based on a considerable amount of residue data, the data are not equally distributed among all pesticides nor has the model been confirmed in all the cropping and harvest conditions examined. However, the model has been developed under realistic field tests, most of its premises have been confirmed in a limited number of tests, and its simulated predictions appear to parallel experience in California where pesticide use and decay conditions may have been most severe but recently well scrutinized. The model's recommendations largely substantiate the regulations developed in California. However, its conclusions definitely suggest that improved levels of protection are needed in other regions. Future reentry intervals will require more comprehensive residue data. The toxicities of detectable metabolites for a few insecticides will need to be determined. More crop residue dosing coefficients are also needed for manually harvested crops. These data must be interpreted in terms of the potential both for acute poisoning from variable residues and for chronic poisoning from repeated exposure to more consistent residues. Surveys of the temporal exposure patterns of harvesters or crews of harvesters are vital to assess the cumulative effects and set the most appropriate chronic cholinesterase response limits. While we await further data, there is sufficient information now to justify longer reentry intervals to protect harvesters nationally.
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PMID:Reentry field data and conclusions. 141 Jun 90

The carcinogen potential of methidathion, a dimethoxyorganic phosphorus pesticide and cholinesterase inhibitor, was evaluated by the Health Effects Division of the Office of Pesticide Programs using a consensus peer review process and the EPA's guidelines for risk assessment. Methidathion was categorized as a Group C (possible human) carcinogen based upon evidence of an increased incidence of benign and malignant hepatocellular tumors, alone and in combination, in a single study involving male Chr-CD-1 mice. The compound was not carcinogenic in female Chr-CD-1 mice in the same study or in Sprague-Dawley rats of either sex in a second study. Methidathion was not genotoxic in a variety of in vitro or in vivo tests designed to detect DNA damage, chromosome aberrations, gene mutations, and sister chromatid exchange. Although methidathion was identified as being structurally similar to two other organophosphate insecticides, prothidathion and lythidathion, no toxicological data were available on either of these agents for comparative purposes. The biological information on methidathion was reviewed by the agency's FIFRA Scientific Advisory Panel who agreed with the category C designation for methidathion. The data were not found to be sufficient to quantify human risk to methidathion.
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PMID:Evaluation of the carcinogenic potential of pesticides. 2. Methidathion. 225 53

After 30 years of experience with human exposure to dichlorvos (DDVP) in the home, workplace, and sickroom, the U.S. EPA has published its intent to revoke the food additive registration of this cholinesterase-inhibiting insecticide. The basis for the Agency action is the result of the National Toxicology Program (NTP) toxicology and carcinogenesis study of DDVP in rats and mice (NTP Technical Report No. 342, September 1989). In those experiments the NTP considered the result in the female mouse portion of the study to afford unequivocal evidence of carcinogenicity. The NTP considered the interpretations of the male and female rat and the male mouse studies to be less than clear. Despite the NTP interpretation, the EPA considers the male rat data (increased incidence of mononuclear cell leukemia) to be sufficient to warrant the regulatory change. The purpose of this report is to summarize a review of the interpretation of the NTP data and to assess the predictive validity of the results relative to potential human health impact. Critical review of experimental data indicates that the evidence for a carcinogenic effect of DDVP in animals is equivocal. Further, DDVP possess no in vivo mutagenic activity in mammalian assay systems and it bears no significant structural similarity to known carcinogens. Therefore, a weight-of-the-evidence analysis leads to the conclusion that DDVP poses neither mutagenic nor carcinogenic risks to humans exposed under normal conditions of use of foreseeable conditions of misuse.
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PMID:Dichlorvos carcinogenicity: an assessment of the weight of experimental evidence. 772 38

Many publications, primarily of work performed in Japan, report findings in human populations of an increased incidence of myopia and of a more advanced visual disease syndrome (Saku disease), which reportedly correlated with increasing use of organophosphate pesticides in agriculture. Follow-up studies in animals performed in Japan using such agents as ethylthiometon, fenthion and fenitrothion demonstrate adverse effects of organophosphates on the visual system. The several ocular effects in question are dose dependent, ranging in severity from lenticular and electro-retinographic changes to the seemingly more serious histophysiological changes in such tissues as the ciliary body and retina. An important question arising from this work is that of the role of cholinesterase inhibition in the etiology of the effects. Studies currently in progress on particular organophosphates being conducted at EPA's research facility and by certain registrants of pesticides, which are in various stages of completion, appear to be substantiating much that has been reported in Japan. While animal studies clearly show that some organophosphates elicit ocular toxicity, there are many knowledge gaps with regard to effects in humans and the ocular toxicity in general, e.g. time and dose dependency, cholinesterase inhibition vs ocular effects and effects of routes of exposure. Consequently, the office is unable at this time to incorporate hazard assessment data with exposure assessment data or to perform risk assessments on organophosphates based on the ocular toxicity potential of this class of chemicals.
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PMID:Ocular effects of organophosphates: a historical perspective of Saku disease. 802 7

Sulprofos, disulfoton, azinphos-methyl, methamidophos, trichlorfon, and tebupirimphos were screened for neurotoxic potential, in accordance with U.S. EPA (FIFRA) requirements. Each organophosphate was administered through the diet for 13 weeks to separate groups of Fischer 344 rats at four dose levels, including a vehicle control. For each study, 12 rats/sex/dietary level were tested using a functional observational battery (FOB), automated measures of activity (figure-8 maze), and detailed clinical observations, with half of the animals perfused at term for microscopic examination of neural and muscle tissues. Separate groups of satellite animals (6/sex/dietary level) were used to measure the effect of each treatment on plasma, erythrocyte (RBC), and brain cholinesterase (ChE) activity. The results show that measures of ChE activity were consistently the most sensitive indices of exposure and assisted in the interpretation of findings. All treatment-related neurobehavioral findings were ascribed to cholinergic toxicity, occurring only at dietary levels that produced more than 20% inhibition of plasma, RBC, and brain ChE activity. Neurobehavioral tests provided no evidence of additional cumulative toxicity after 8 weeks of treatment. The FOB and motor activity findings did not alter the conclusions and generally did not reduce the neurobehavioral no-observed-effect level (NOEL) for any of the six compounds, relative to the results from detailed clinical observations as conducted in these studies. The one exception occurred with tebupirimphos, where the NOEL for motor activity was one dose level lower than the NOEL for the FOB and clinical observations. These results support the value of detailed clinical observations to screen for the neurotoxic potential of organophosphates and a general standard of more than 20% inhibition of brain ChE activity for cholinergic neurotoxicity.
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PMID:Subchronic neurotoxicity screening studies with six organophosphate insecticides: an assessment of behavior and morphology relative to cholinesterase inhibition. 902 78

Categorical regression is a mathematical tool that can be adapted to estimate potential health risk from chemical exposures. By regressing ordered categories of toxic severity or pathological staging on exposure dose, this method can estimate the likelihood of observing any of the categories of severity at any dose level. Depending on the nature of the available data, these estimates can take the form of incidence rates for any of the categories in an exposed population or the probability of a new study conducted at a specified dose level being classified as one of the categories. Categorical regression is illustrated using toxicity data on aldicarb. For aldicarb, the data fall into three different groups: human clinical studies, dietary exposures in experimental animals, and accidental human exposure by contaminated crops. The U.S. EPA has assessed this literature and developed a reference dose (RfD) of 0.001 mg/kg-day. The results of applying categorical regression to data from human clinical studies suggests a maximum likelihood risk estimate of adverse effects of 0.008% at a 10-fold higher dose than the RfD when blood cholinesterase inhibition is not considered as an adverse effect. When blood cholinesterase inhibition of 20% or more is considered as an adverse effect, a maximum likelihood risk estimate of adverse effects is 0.1% at a dose 10-fold higher than the RfD.
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PMID:Categorical regression of toxicity data: a case study using aldicarb. 918 88

The Food Quality Protection Act of 1996 (FQPA) requires the EPA to consider "available information concerning the cumulative effects of such residues and other substances that have a common mechanism of toxicity ... in establishing, modifying, leaving in effect, or revoking a tolerance for a pesticide chemical residue." This directive raises a number of scientific questions to be answered before the FQPA can be implemented. Among these questions is: What constitutes a common mechanism of toxicity? The ILSI Risk Science Institute (RSI) convened a group of experts to examine this and other scientific questions using the organophosphorus (OP) pesticides as the case study. OP pesticides share some characteristics attributed to compounds that act by a common mechanism, but produce a variety of clinical signs of toxicity not identical for all OP pesticides. The Working Group generated a testable hypothesis, anticholinesterase OP pesticides act by a common mechanism of toxicity, and generated alternative hypotheses that, if true, would cause rejection of the initial hypothesis and provide criteria for subgrouping OP compounds. Some of the alternative hypotheses were rejected outright and the rest were not supported by adequate data. The Working Group concluded that OP pesticides act by a common mechanism of toxicity if they inhibit acetylcholinesterase by phosphorylation and elicit any spectrum of cholinergic effects. An approach similar to that developed for OP pesticides could be used to determine if other classes or groups of pesticides that share structural and toxicological characteristics act by a common mechanism of toxicity or by distinct mechanisms.
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PMID:Common mechanism of toxicity: a case study of organophosphorus pesticides. 952 Mar 37

The toxicity, exposure, and risk from chlorpyrifos are briefly discussed in juxtaposition with two recent articles in Environmental Health Perspectives concerning potential exposures to children. In studies conducted according to EPA guidelines, chlorpyrifos has been shown not to be mutagenic, carcinogenic, or teratogenic, nor does it adversely affect reproduction. Chlorpyrifos toxicity does not occur in the absence of significant cholinesterase inhibition. If exposures are less than those that cause significant cholinesterase depression, then no signs or symptoms related to chlorpyrifos exposure occur. The weight of empirical evidence indicates that the risk of adults or children experiencing an adverse health effect from exposure to chlorpyrifos through both nondietary and dietary sources is negligible. Both the research supporting the registration of these products and their long history of widespread use suggest that unless these products are seriously misused, their margins of safety are wide enough to protect everyone with the potential to be exposed. A weight-of-evidence review of the entire scientific knowledge base relating to chlorpyrifos products supports these conclusions.
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PMID:Human exposure and risk from indoor use of chlorpyrifos. 1039 32

Donepezil HCI is a piperidine-based reversible acetylcholinesterase (AChE) inhibitor, chemically distinct from other cholinesterase (ChE) inhibitors and rationally designed to treat the symptoms of Alzheimer's disease (AD). It is highly selective for AChE in the central nervous system (CNS), with little or no affinity for butyrylcholinesterase (BuChE). In preclinical studies in animals, donepezil produced increased CNS acetylcholine. The resultant enhancement of cholinergic activity gave rise to improved performance by rats on tests of learning and memory, with no evidence of hepatic or renal toxicity. In subsequent phase I clinical evaluations in healthy volunteers, donepezil demonstrated favorable pharmacokinetic, pharmacodynamic and safety profiles. Its long terminal disposition half-life supported once-daily administration, with no requirement for dose modification in the elderly or in patients with renal or hepatic impairment. A 14-week, phase II dose-finding study in patients with mild to moderate AD (Clinical Dementia Rating [CDR], 1-2; Mini-Mental State Examination [MMSE], 10-26) showed that donepezil at a dose of 5 mg/day produced highly significant improvements in cognition (as measured by the Alzheimer's Disease Assessment Scale, cognitive subscale [ADAS-cog]). Subsequently, two pivotal parallel-group, placebo-controlled phase III trials (of 15 and 30 weeks' duration) showed highly statistically significant improvements in ADAS-cog, MMSE, Clinician's Interview-Based Impression of Change with caregiver input (CIBIC plus) and CDR-SB (Sum of the Boxes) scores, compared with placebo, in mild to moderate AD patients treated with either 5 or 10 mg/day donepezil. Adverse events in the phase II and III trials were mild and transient and resolved with continued donepezil administration. The donepezil clinical trials program has shown that this drug is a clinically effective and well-tolerated once-daily treatment for the symptoms of mild to moderate AD.
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PMID:Perspectives in the management of Alzheimer's disease: clinical profile of donepezil. 985

Alzheimer's disease (AD) is associated with a deficiency of acetylcholine (ACh) in the forebrain that correlates with brain pathology and cognitive dysfunction. The most promising approach to enhancing central ACh neurotransmission has been the utilization of agents that inhibit cholinesterases which block its catabolism. Initially, the success of this strategy was limited by subtherapeutic levels of acetylcholinesterase (AChE) inhibition, tolerability problems and toxicity of the first agents. Donepezil HCI represents a new chemical class of AChE inhibitors, the piperidines. In clinical trials, donepezil has been shown to improve significantly cognition and global function in patients with mild to moderately severe AD, and has demonstrated an excellent tolerability and safety profile. These benefits, as well as a simple, once-daily dosing regimen, make donepezil a viable therapeutic option for AD patients.
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PMID:Clinical benefits of a new piperidine-class AChE inhibitor. 1033 37


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