Genetic predisposition to adverse consequences of anti-cholinesterases in 'atypical' BCHE carriers

Low-level exposures to organophosphorus esters and peripheral nerve function

This review evaluates the epidemiological and clinical evidence linking low-level and prolonged exposures to organophosphorus esters, used as insecticides or nerve agents, to peripheral nerve dysfunction. The clinical effects of large doses of these chemicals-including the cholinergic syndrome, the intermediate syndrome, and the delayed polyneuropathy-are all well established and are summarized. Based on these clinical observations and experimental studies, dose-effect relationships indicate that peripheral neuropathy always develops after cholinergic toxicity. However, several studies have suggested that this relationship may be different after low-level prolonged exposures, as, for instance, those experienced by Gulf War veterans and British sheep farmers, thereby leading to the development of peripheral neuropathy without preceding cholinergic toxicity. A critical assessment of these studies, involving subjects with either current or past exposures, indicates that changes in peripheral nerve function were mild, inconsistent, and unexplained and that most studies lack exposure data. Suggestions made about individual hypersusceptibility to delayed polyneuropathy lack support. It is concluded that there is no evidence of peripheral nerve dysfunction caused by low-level prolonged exposures to organophosphate insecticides or nerve agents.

Runx1/AML1 in leukemia: disrupted association with diverse protein partners

Runx1/AML1, a chromosome 21q22 hematopoietic regulator, is frequently translocated in leukemia. Its protein product, a relatively weak transcriptional activator, becomes an effective transcriptional enhancer or repressor, when co-operating with transcriptional co-activators or co-repressors. Runx1/AML1 association with its partners is disrupted in leukemia. For example, Runx1/AML1 mutations and translocations (e.g. t(8;21), t(12;21) and t(3;21)) impair binding of Runx1/AML1-CBFbeta complexes to Runt motifs in myelopoietically active promoters, preventing normal hematopoiesis. However, Runx1/AML1-associated translocations are not leukemogenic in animal models, suggesting the involvement of yet unidentified regulatory proteins. New candidates are cholinesterases, inhibition of which increases leukemic risk in a manner potentially associated with Runx1/AML1.

Frequent blood-brain barrier disruption in the human cerebral cortex

1. The blood-brain barrier (BBB) protects the brain from circulating xenobiotic agents. The pathophysiology, time span, spatial pattern, and pathophysiological consequences of BBB disruptions are not known. 2. Here, we report the quantification of BBB disruption by measuring enhancement levels in computerized tomography brain images. 3. Pathological diffuse enhancement associated with elevated albumin levels in the cerebrospinal fluid (CSF) was observed in the cerebral cortex of 28 out of 43 patients, but not in controls. Four patients displayed weeks-long focal BBB impairment. In 19 other patients, BBB disruption was significantly associated with elevated blood pressure, body temperature, serum cortisol, and stress-associated CSF 'readthrough" acetylcholinesterase. Multielectrode electroencephalography revealed enhanced slow-wave activities in areas of focal BBB disruption. Thus, quantification of BBB disruption using minimally invasive procedures, demonstrated correlations with molecular, clinical, and physiological stress-associated indices. 4. These sequelae accompany a wide range of neurological disorders, suggesting that persistent, detrimental BBB disruption is considerably more frequent than previously assumed.

Reactive oxygen species mediate pyridostigmine-induced neuronal apoptosis: involvement of muscarinic and NMDA receptors

Pyridostigmine bromide (PB) is a reversible cholinesterase inhibitor used for treatment of myasthenia gravis and for prophylactic protection against organophosphate nerve agent. We previously showed PB can induce apoptotic death in rat brain following systemic treatment. To study mechanisms by which PB induces brain cell death, cultured rat cerebellar granule cells were used. Cytotoxicity was determined after exposure to PB (10-1000 microM) for 24 h; a high concentration of PB (>500 microM) significantly increased lactate dehydrogenase release, which was reduced by pretreatment with the antioxidant, N-t-butyl-alpha-phenyl-nitrone (PBN). Apoptosis, as determined by TUNEL staining, was concentration dependent (10-250 microM) after a 24-h exposure and cytotoxicity was confirmed by gel electrophoresis of DNA, release of cytochrome c from mitochondria, elevation of caspase activity, and electron microscopy. The oxidant-sensitive fluorescent dye 2',7'-dichlorofluorescin diacetate was used to detect reactive oxidative species (ROS) generation. Pretreatment with PBN, superoxide dismutase, catalase, or the nitric oxide synthase inhibitor N(G)-nitro-L-arginine methyl ester (L-NAME) blocked PB-induced ROS generation and apoptotic cell death. Pretreatment with atropine or MK-801 blocked ROS generation and the subsequent neurotoxicity, showing that both muscarinic and NMDA receptors mediate the response. DNA extracted from PB-treated cells revealed oligonucleosomal fragmentation on gel electrophoresis and antioxidants attenuated the DNA fragmentation, providing further evidence for a link of ROS generation and apoptosis. These results indicate that muscarinic receptor-mediated ROS generation is an initiating factor in PB-induced apoptotic cell death and activation of the NMDA glutamate receptor is directly linked to the response.

Biological consequences of multiple vaccine and pyridostigmine pretreatment in the guinea pig

An investigation of the possible interactions between combinations of vaccines and pyridostigmine bromide (PB) has been undertaken in the guinea pig. This study is part of a research programme funded by the UK Government to determine any effects of the pretreatment regimes given to UK Forces during the Persian Gulf conflict of 1990-1991. The study was designed to simulate PB administration and to model multiple vaccination protocols that were experienced by UK Forces, modelling a "worst case" situation in which all ten vaccines and PB were administered within a short period of time. Seven of the vaccines were health and hygiene (H+H) vaccines given to protect against endemic diseases and two vaccines to protect against the biological warfare agents anthrax and plague. In addition, pertussis vaccine was administered as an adjuvant to reduce the time to achieve immunity against anthrax. Four groups of eight animals were treated with 1/20th, 1/10th or 1/5th human doses of vaccines or vehicles, respectively. The PB or saline was delivered by implanted 28 day mini-osmotic pumps to achieve a mean red blood cell acetylcholinesterase (AChE) inhibition of around 30%. Body weight, temperature, immunological response, biochemical indices and spontaneous activity were monitored for 72 days. Although immunological responses to bacterial vaccines were observed, there were no remarkable findings in the parameters measured other than minor changes in body weight (4.9% decrease at the 1/5th human dose of vaccines) and temperature increases in response to vaccination. Animals in all groups remained generally healthy and active without visible adverse signs throughout the study. Reproduced with the permission of Her Majesty's Stationery Office. Published by John Wiley & Sons, Ltd.

Cholinesterases modulate cell adhesion in human neuroblastoma cells in vitro

Cholinesterases are expressed non-synaptically during embryonic development, neoplasia and neurodegeneration. We have investigated the effects of acetylcholinesterase (AChE) and butyrylcholinesterase (BChE) and, conversely, anti-AChE and -BChE antibodies and inhibitors on cell adhesion and neurite outgrowth in human neuroblastoma cells. Analysis of cholinesterase levels and isoforms in undifferentiated and differentiated cells indicated a significant rise in AChE levels on differentiation. This increase was related to both cell-associated and secreted enzyme, and was predominantly the G4 isoform. BChE levels and isoforms, on the other hand, showed no significant variation. Coating the tissue culture plate with AChE stimulated neurite outgrowth, while BChE had an anti-adhesive effect. Cell adhesion was affected by the BChE inhibitor, ethopropazine, and the AChE peripheral site inhibitor, BW284c51, but not by eserine which binds to the active site. This indicates that the adhesion function is non-cholinergic, a finding supported by the lack of effect of AE-2, a monoclonal antibody that inhibits AChE, on cell adhesion. Four out of a panel of nine anti-AChE antibodies inhibited adhesion to varying degrees. Of these antibodies, two are catalytic, with epitopes associated with the peripheral anionic site of AChE, and the remaining two have epitopes overlapping this site. Neither of the two anti-BChE antibodies used had any effect on adhesion. These results indicate the importance of AChE in neuroblastoma cell adhesion and neurite outgrowth, and suggest that the peripheral anionic site may be involved in these processes.

Effects of inescapable stress and treatment with pyridostigmine bromide on plasma butyrylcholinesterase and the acoustic startle response in rats

Pyridostigmine bromide (PB) is a reversible, peripherally active inhibitor of acetylcholinesterase (AChE) activity, and is recommended by the military as a pretreatment against potential nerve gas exposure. Recent evidence suggests that exposure to inescapable stressors allows PB to cross the blood-brain barrier, and thereby affect central AChE activity in mice. Here, we evaluated the functional impact of a stress/PB treatment interaction on acoustic startle responding and plasma butyrylcholinesterase (BuChE) activity in male Sprague-Dawley rats. To model the treatment protocol used by the military, PB was delivered in the drinking water of rats for 7 consecutive days. The morning after the start of PB treatment, and for the next 6 days, half the rats were exposed to 1 h of supine restraint stress. We therefore employed a 2 x 2 (stress x PB treatment) between-groups design. Exposure to supine stress alone induced a persistent decrease in plasma BuChE activity. Further decreases in BuChE activity were not observed in rats exposed to supine restraint and PB treatment. Exposure to stress also induced an exaggerated startle response, evident on the last day of stress and 24 h after stressor cessation. Treatment with PB alone produced an exaggerated startle response over the same time period, albeit to a lesser degree. Although treatment with PB concurrent with stress did not produce further changes in either BuChE activity or acoustic startle responding, stress-induced alterations in drinking behavior (and thereby the dose of PB ingested) may have affected these results. Persistent stress-induced reductions in BuChE activity may increase the risk of adverse reactions to cholinomimetics.

Organophosphorus poisoning and anaesthesia

Organophosphorus compounds, used as insecticides and agents of chemical warfare, are a major global cause of health problems. These irreversible inhibitors of cholinesterase produce three well-recognised clinical entities: the initial cholinergic phase, which is a medical emergency often requiring management in an intensive care unit; the intermediate syndrome, during which prolonged ventilatory care is necessary; and delayed polyneuropathy. In addition, disturbances of body temperature and endocrine function, electrolyte imbalances, immunological dysfunction and disorders of reproduction have been reported in animals and man. Vocal cord paralysis, pancreatitis, cardiac arrhythmias and a wide range of neuropsychiatric disorders are known to follow acute and chronic exposure to organophosphorus compounds. As a result of the inhibition of plasma cholinesterase, there can be increased sensitivity to drugs hydrolysed by this enzyme, e.g. suxamethonium and mivacurium. The inhibition of acetylcholinesterase causes dysfunction at the neuromuscular junction which can produce altered responses to nondepolarizing neuromuscular blockers. Anaesthetists may encounter patients exposed to organophosphorus compounds either following acute poisoning, trauma (warfare) or as patients with a wide range of nonspecific disorders presenting for surgery. The traditional use of oximes and atropine in treatment has failed to reduce the morbidity and mortality associated with poisoning. The roles of agents that have reduced the toxicity of organophosphorus compounds in animal experiments are discussed as potential therapeutic agents. There is an urgent need for accurate information on the problems associated with exposure to organophosphorus compounds. This would best be achieved by collaborative research between technologically advanced countries and developing countries, where organophosphorus compounds are a leading cause of ill health.

Antisense technologies have a future fighting neurodegenerative diseases

Our growing understanding of the role that unfavorable patterns of gene expression play in the etiology of neurodegenerative disease emphasizes the need for strategies to selectively block the biosynthesis of harmful proteins in the brain. Antisense technologies are ideally suited to this purpose. Tailor-designed to target specific RNA, antisense oligonucleotides and ribozymes offer tools to suppress the production of proteins mediating neurodegeneration. Although technical limitations must still be overcome, the antisense approach represents a novel and exciting strategy for intervention in diseases of the central nervous system.

Human erythrocyte but not brain acetylcholinesterase hydrolyses heroin to morphine

1. In human blood, heroin is rapidly hydrolysed by sequential deacylation of two ester bonds to yield first 6-monoacetylmorphine (6-MAM), then morphine. 2. Serum butyrylcholinesterase (BuChE) hydrolyses heroin to 6-MAM with a catalytic efficiency of 4.5/min per mumol/L, but does not proceed to produce morphine. 3. In vitro, human erythrocyte acetylcholinesterase (AChE) hydrolyses heroin to 6-MAM, with a catalytic efficiency of 0.5/min per mumol/L under first-order kinetics. Moreover, erythrocyte AChE, but not BuChE is capable of further hydrolysing 6-MAM to morphine, albeit at a considerably slower rate. 4. Both hydrolysis steps by erythrocyte AChE were totally blocked by the selective AChE inhibitor BW284c51 but were not blocked by the BuChE-specific inhibitor, iso-OMPA (tetraisopropylpyrophosphoramide). 5. The brain synaptic form of AChE, which differs from the erythrocyte enzyme in its C-terminus, was incapable of hydrolysing heroin. 6. Heroin suppressed substrate hydrolysis by antibody-immobilized erythrocyte but not by brain AChE. 7. These findings reveal a new metabolic role for erythrocyte AChE, the biological function of which is as yet unexplained, and demonstrate distinct biochemical properties for the two AChE variants, which were previously considered catalytically indistinguishable.

Association of low PON1 type Q (type A) arylesterase activity with neurologic symptom complexes in Gulf War veterans

Previously Haley et al. described six possible syndromes identified by factor analysis of symptoms in Gulf War veterans and demonstrated that veterans with these symptom complexes were more neurologically impaired than age-sex-education-matched well controls. They also uncovered strong associations (relative risks 4-8) suggesting that these symptom complexes were related to wartime exposure to combinations of organophosphate pesticides, chemical nerve agents, high concentration DEET insect repellant, and symptoms of advanced acute toxicity after taking pyridostigmine. Here we have shown that compared to controls, ill veterans with the neurologic symptom complexes were more likely to have the R allele (heterozygous QR or homozygous R) than to be homozygous Q for the paraoxonase/arylesterase 1 (PON1) gene. Moreover, low activity of the PON1 type Q (Gln192, formerly designated type A) arylesterase allozyme distinguished ill veterans from controls better than just the PON1 genotype or the activity levels of the type R (Arg192, formerly designated type B) arylesterase allozyme, total arylesterase, total paraoxonase, or butyrylcholinesterase. A history of advanced acute toxicity after taking pyridostigmine was also correlated with low PON1 type Q arylesterase activity. Type Q is the allozyme of paraoxonase/arylesterase that most efficiently hydrolyzes several organophosphates including sarin, soman, and diazinon. These findings further support the proposal that neurologic symptoms in some Gulf War veterans were caused by environmental chemical exposures.

Gulf War illnesses: causation and treatment

Soldiers returning from the Gulf War in 1991 described a range of symptoms, including some consistent with the chronic fatigue syndrome, fibromyalgia, and multiple chemical sensitivity. Well-defined adverse health events attributable to service in the Gulf occurred. However, controlled epidemiological studies in Gulf War veterans and controls describe significant excesses of symptoms that were not clearly associated with pathologic disease. At least 12% of veterans currently receive some form of disability from the Department of Veterans Affairs. A number of reports outline theories proposed to explain the excess, but few are scientifically supported. Management guidelines for this spectrum of disorders resembles that of many of "emerging overlap syndromes," including multiple chemical sensitivity, chronic fatigue syndrome, and fibromyalgia. They include the establishment of a trusting doctor-patient relationship, negotiations around a common ground of scientific and etiologic beliefs, non-labeling of the disorder, and work toward recovery in the absence of clear etiologic answers.

Pyridostigmine bromide and Gulf War syndrome

Gulf War Syndrome has become a growing concern of US government, military Gulf war veterans and their families. It is suggested that research on genotype/phenotype of acetylcholinesterase and butyrylcholinesterase may help to discover the role of pyridostigmine bromide in the cause of Gulf War Syndrome.

Purification, molecular characterization and catalytic properties of a Pseudomonas fluorescens enzyme having cholinesterase-like activity

An enzyme with a cholinesterase (ChE) activity, produced by Pseudomonas fluorescens, was purified to homogeneity in a three-step procedure. Analysis by non-denaturing and SDS-PAGE, and by isoelectric focusing, indicated that the enzyme was a monomer of 43 kDa, with a pI of 6.1. The N-terminal sequence, AEPLKAVGAGEGQLDIVAWPGYIEA, showed some similarities with proteins of the ChE family and a strong similarity with a protein from Escherichia coli with unknown structure and function. Cholinesterase activity at pH 7.0 and 25 degreesC was maximum with propionylthiocholine as substrate (kcat,app=670 min-1), followed by acetylthiocholine, and significantly lower with butyrylthiocholine. Catalytic specificity (kcat/Km) was the same for propionylthiocholine and acetylthiocholine, but was two orders of magnitude lower for butyrylthiocholine. Kinetics of thiocholine ester hydrolysis showed inhibition by excess substrate which was ascribed to binding of a second substrate molecule, leading to non-productive ternary complex (Km=35 microM, KSS=0.49 mM with propionylthiocholine). There was low or no reactivity with organophosphates and carbamates. The enzyme inhibited by echothiophate (kII=0.44x102 M-1 min-1) was not reactivated by pralidoxime methiodide. However, the P. fluorescens enzyme had affinity for procainamide and decamethonium, two reversible ChE inhibitors used as affinity chromatography ligand and eluant, respectively. Although similarity of the N-terminal amino acid sequence of the enzyme with an internal sequence of ChEs is weak, its catalytic activity towards thiocholine esters, and its affinity for positively charged ligands supports the contention that this enzyme may belong to the ChE family. However, we cannot rule out that the enzyme belongs to another structural family of proteins having cholinesterase-like properties. The reaction of the enzyme with organophosphates suggests that it is a serine esterase, and currently this enzyme may be termed as having a cholinesterase-like activity.

Does examination of urinary sediment identify individuals with Gulf War syndrome? A pilot study

BACKGROUND

Many veterans who were involved in the Persian Gulf theater of operations have had a variety of unexplained physical complaints, collectively called the Gulf War syndrome or similar names. There has been much debate on the issue and numerous publications, both in the medical and the lay press. A method for examining urinary sediment that was developed in an effort to identify nonculturable bacteria has been used in Gulf War veterans and was the basis for intensive antimicrobial therapy in many of them.

METHODS

We evaluated eight Gulf War veterans with complaints compatible with Gulf War syndrome. Subjects were from various parts of the United States. A detailed history and physical examination were performed. Urine was obtained before and after prostatic massage (men) or before and after pelvic examinations (women) and was tested by a previously described microscopic method as well as by culture and conventional Gram stain. Age- and sex-matched healthy control subjects were tested similarly and concurrently.

RESULTS

Two female Gulf War veterans had findings of Candida albicans and Klebsiella pneumoniae by conventional culture. The same organism types were seen both by the special method and by conventional Gram stain. All other subjects and controls were completely indistinguishable.

CONCLUSION

Examining the urinary sediment by this elaborate method does not differentiate persons with Gulf War syndrome from normal, healthy control subjects who were never in the Persian Gulf area.

Normal and atypical butyrylcholinesterases in placental development, function, and malfunction

1. In utero exposure to poisons and drugs (e.g., anticholinesterases, cocaine) is frequently associated with spontaneous absorption and placental malfunction. The major protein interacting with these compounds is butyrylcholinesterase (BuChE), which attenuates the effects of such xenobiotics by their hydrolysis or sequestration. Therefore, we studied BuChE expression during placental development. 2. RT-PCR revealed both BuChEmRNA and acetylcholinesterase (AChE) mRNA throughout gestation. However, cytochemical staining detected primarily BuChE activity in first-trimester placenta but AChE activity in term placenta. 3. As the atypical variant of BuChE has a narrower specificity for substrates and inhibitors than the normal enzyme, we investigated its interactions with alpha-solanine and cocaine, and sought a correlation between the occurrence of this variant and placental malfunction. 4. Atypical BuChE of serum or recombinant origin presented > 10-fold weaker affinities than normal BuChE for cocaine and alpha-solanine. However, BuChE in the serum of the heterozygote and a homozygous normal were similar in their drug affinities. Therefore, heterozygous serum or placenta can protect the fetus from drug or poison exposure, unlike homozygous atypical serum or placenta. 5. Genotype analyses revealed that heterozygous carriers of atypical BuChE were threefold less frequent among 49 patients with placental malfunction than among 76 controls of the entire Israeli population. These observations exclude heterozygote carriers of atypical BuChE from being at high risk for placental malfunction under exposure to anticholinesterases.

Effect of neostigmine on concentration and extraction fraction of acetylcholine using quantitative microdialysis

A quantitative microdialysis method was used to determine the effect of local perfusion of 0, 100, 200, and 300 nM neostigmine (NEO) on acetylcholine (ACh) extracellular concentration and microdialysis extraction fraction (E(d)) in the striatum of the rat. Because of the efficiency of AChE, the inhibition of this enzyme is expected to result in a substantial increase in ACh levels and a decrease in the E(d) of ACh. The extracellular concentration of ACh increased linearly with increasing concentrations of NEO. The control ACh concentration was determined to be 18.4 +/- 11.8 nM (n = 10; mean +/- S.E.M.) The ACh extracellular concentration for the remaining groups was determined to be 173 +/- 14 nM (n = 5), 329 +/- 52.5 nM (n = 13), and 581 +/- 109 nM (n = 10) for the 100, 200, and 300 nM NEO groups, respectively. Perfusion with 300 nM NEO resulted in a significant reduction in the E(d) of ACh (64.5 +/- 3.5% vs. 43.6 +/- 7.5%, P < 0.05). In contrast to ACh, perfusion with 0, 1, and 10 microM hemicholinium-3, an inhibitor of high-affinity choline uptake, increased choline levels but did not affect the E(d) of choline. The effects on E(d) are consistent with E(d) being influenced by rapid clearance mechanisms.

Pyridostigmine brain penetration under stress enhances neuronal excitability and induces early immediate transcriptional response

Pyridostigmine, a carbamate acetylcholinesterase (AChE) inhibitor, is routinely employed in the treatment of the autoimmune disease myasthenia gravis. Pyridostigmine is also recommended by most Western armies for use as pretreatment under threat of chemical warfare, because of its protective effect against organophosphate poisoning. Because of this drug's quaternary ammonium group, which prevents its penetration through the blood-brain barrier, the symptoms associated with its routine use primarily reflect perturbations in peripheral nervous system functions. Unexpectedly, under a similar regimen, pyridostigmine administration during the Persian Gulf War resulted in a greater than threefold increase in the frequency of reported central nervous system symptoms. This increase was not due to enhanced absorption (or decreased elimination) of the drug, because the inhibition efficacy of serum butyryl-cholinesterase was not modified. Because previous animal studies have shown stress-induced disruption of the blood-brain barrier, an alternative possibility was that the stress situation associated with war allowed pyridostigmine penetration into the brain. Here we report that after mice were subjected to a forced swim protocol (shown previously to simulate stress), an increase in blood-brain barrier permeability reduced the pyridostigmine dose required to inhibit mouse brain AChE activity by 50% to less than 1/100th of the usual dose. Under these conditions, peripherally administered pyridostigmine increased the brain levels of c-fos oncogene and AChE mRNAs. Moreover, in vitro exposure to pyridostigmine increased both electrical excitability and c-fos mRNA levels in brain slices, demonstrating that the observed changes could be directly induced by pyridostigmine. These findings suggest that peripherally acting drugs administered under stress may reach the brain and affect centrally controlled functions.

The significance of the activity of CSF cholinesterases in dementias

This article reviews the significance of changes in the level of cerebrospinal fluid acetylcholinesterase or cholinesterase in patients with Alzheimer's disease or other dementias. Evidence has shown that the methodology of assaying cerebrospinal fluid acetylcholinesterase or cholinesterase is reliable and the activity of the enzyme is stable. Low acetylcholinesterase or cholinesterase levels presenting in cerebrospinal fluid of a demented individual may confirm the clinical diagnosis of Alzheimer's disease or other organic dementia. A low activity of acetylcholinesterase or cholinesterase existing in cerebrospinal fluid of a non-demented individual may indicate a brain at risk, or that the person is in the preclinical stage of dementia. Recognition of the presence of the preclinical stage may be very beneficial for explaining the real meaning of the 'overlap' in the biochemistry and pathology between dementia and non-dementia, and also very important for prevention and treatment. Therefore, the strategy of prevention and of treatment should no longer be designed to inhibit acetylcholinesterase activity. In contrast, it should be designed to enhance the neuronal acetylcholinesterase activity or to delay the degeneration of brain acetylcholinesterase system.