Walnut Oil Prevents Scopolamine-Induced Memory Dysfunction in a Mouse Model

For thousands of years, it has been widely believed that walnut is a kind of nut that has benefits for the human body. Walnut oil, accounting for about 70% of walnut, mainly consists of polyunsaturated fatty acids. To investigate the effect of walnut oil on memory impairment in mice, scopolamine (3 mg/kg body weight/d) was used to establish the animal model during Morris Water Maze (MWM) tests. Walnut oil was administrated orally at 10 mL/kg body weight/d for 8 consecutive weeks. The results showed that walnut oil treatment ameliorated the behavior of the memory-impaired mice in the MWM test. Additionally, walnut oil obviously inhibited acetylcholinesterase activity (1.26 ± 0.12 U/mg prot) (p = 0.013) and increased choline acetyltransferase activity (129.75 ± 6.76 U/mg tissue wet weight) in the brains of scopolamine-treated mice (p = 0.024), suggesting that walnut oil could prevent cholinergic function damage in mice brains. Furthermore, walnut oil remarkably prevented the decrease in total superoxide dismutase activity (93.30 ± 5.50 U/mg prot) (p = 0.006) and glutathione content (110.45 ± 17.70 mg/g prot) (p = 0.047) and the increase of malondialdehyde content (13.79 ± 0.96 nmol/mg prot) (p = 0.001) in the brain of scopolamine-treated mice, indicating that walnut oil could inhibit oxidative stress in the brain of mice. Furthermore, walnut oil prevented histological changes of neurons in hippocampal CA1 and CA3 regions induced by scopolamine. These findings indicate that walnut oil could prevent memory impairment in mice, which might be a potential way for the prevention of memory dysfunctions.

Urtica dioica leaves modulates muscarinic cholinergic system in the hippocampus of streptozotocin-induced diabetic mice

Diabetes mellitus is a chronic metabolic disorder and has been associated with cognitive dysfunction. In our earlier study, chronic Urtica dioica (UD) treatment significantly ameliorated diabetes induced associative and spatial memory deficit in mice. The present study was designed to explore the effect of UD leaves extract on muscarinic cholinergic system, which has long been known to be involved in cognition. Streptozotocin (STZ) (50 mg/kg, i.p., consecutively for 5 days) was used to induce diabetes followed by treatment with UD extract (50 mg/kg, oral) or rosiglitazone (5 mg/kg, oral) for 8 weeks. STZ-induced diabetic mice showed significant reduction in hippocampal muscarinic acetylcholine receptor-1 and choline acetyltransferase expressions. Chronic diabetes significantly up-regulated the protein expression of acetylcholinesterase associated with oxidative stress in hippocampus. Besides, STZ-induced diabetic mice showed hypolocomotion with up-regulation of muscarinic acetylcholine receptor-4 expression in striatum. Chronic UD treatment significantly attenuated the cholinergic dysfunction and oxidative stress in the hippocampus of diabetic mice. UD had no effect on locomotor activity and muscarinic acetylcholine receptor-4 expression in striatum. In conclusion, UD leaves extract has potential to reverse diabetes mediated alteration in muscarinic cholinergic system in hippocampus and thereby improve memory functions.

Effects of zinc on SN56 cholinergic neuroblastoma cells

Zinc is a trace element necessary for proper development and function of brain cells. However, excessive accumulation of zinc exerts several cytotoxic effects in the brain. The aim of this work was to see whether cytotoxic effects of zinc are quantitatively correlated with changes in acetyl-CoA metabolism. The zinc levels up to 0.20 mmol/L caused concentration-dependent inhibition of pyruvate dehydrogenase (PDH) activity that correlated with the increase in trypan blue-positive fraction and the decrease in cultured cell number (r = 0.96, p = 0.0001). Chronic exposure of cells to 0.15 mmol/L zinc decreased choline acetyltransferase and aconitase activities, cytoplasmic acetyl-CoA and whole cell ATP level by 38%, 57%, 35%, and 62%, respectively but caused no change in mitochondrial acetyl-CoA level and activities of other enzymes of glycolytic and tricarboxylic acid cycle. dl-alpha-lipoamide when added simultaneously with zinc to cultured cells or their homogenates attenuated its chronic or acute suppressive effects. In homogenates of chronically Zn-treated cells, lipoamide overcame PDH but not aconitase inhibition. Presented data indicate that acute-transient elevation of zinc caused reversible inhibition of PDH, aconitase activities and acetyl-CoA metabolism, which when prolonged could lead to irreversible enzyme inactivation yielding decrease in cell viability and secondary suppression of their cholinergic phenotype.

A single nucleotide polymorphism in CHAT influences response to acetylcholinesterase inhibitors in Alzheimer's disease

BACKGROUND

Alzheimer's disease (AD) is a devastating neurodegeneration with a characteristic deficit in cholinergic neurotransmission. Treatment with acetylcholinesterase (AChE) inhibitors aims to reverse this deficit and does ameliorate the decline in cognition in some AD patients, although response is variable.

OBJECTIVE

To examine whether sequence variation in the gene encoding choline acetyltransferase (CHAT), which encodes the major catalytic enzyme of the cholinergic pathway, predicts response to AChE inhibitors.

METHODS

Alzheimer's disease patients (121) were treated with cholinesterase inhibitors and the effect of treatment on cognition was measured using the Mini Mental State Examination (MMSE). Six polymorphisms in CHAT were analysed for association with change in MMSE score.

RESULTS

After correction for multiple testing, we found one SNP, rs733722, in a promoter region of CHAT, is associated with response of AD patients to cholinesterase inhibitors (P = 0.03) and accounts for 6% of the variance in response to AChE inhibitors.

CONCLUSION

Rs733722 represents a putative marker of response to AChE inhibitors in AD patients.

Temporal memory in mature and aged rats is sensitive to choline acetyltransferase inhibition

The effects of a potent inhibitor of choline acetyltransferase (ChAT), BW813U, on timing behavior in mature (6-10 months) and aged (26-30 months) male rats were assessed. Twenty rats were trained on a discrete trial 20-s peak-interval (PI) procedure. During baseline (non-drug) training, the time of the maximum response rate (peak time) for mature rats was approximately at the time of scheduled reinforcement, but peak time for aged rats was reliably later. A single administration of BW813U (100 mg/kg, ip) produced a long-lasting increase in peak time for both mature and aged rats that occurred gradually and was synergistic with age. These horizontal shifts in peak time indicate a change in the content of reference memory for the remembered time of reinforcement that is similar for both aging processes and BW813U administration. When a 5-s gap was imposed in the signal, PI-GAP procedure, control rats of both ages summed the signal durations before and after the gap, whereas rats given BW813U showed no retention of the signal duration prior to the gap. This loss of trial-specific temporal information suggests a drug-induced working memory dysfunction. Taken together, these results demonstrate that both working and reference memory for temporal information are sensitive to choline acetyltransferase inhibition in rats.

Three-dimensional quantitative structure-activity relationship (3D-QSAR) analyses of choline acetyltransferase inhibitors

As a basis for predicting structural features that may lead to the design of more potent and selective inhibitors of choline acetyltransferase (ChAT), the three-dimensional quantitative structure-activity relationship (3D-QSAR) studies were carried out on a series of trans-1-methyl-4-(1-naphthylvinyl)pyridinium (MNVP+) analogs, which are known ChAT inhibitors. 3D-QSAR studies were carried out using the comparative molecular field analysis (CoMFA) and comparative molecular similarity indices analysis (CoMSIA) methods. Since these inhibitors have extremely shallow potential energy minimum energy wells and low barriers to rotation, two dihedral angles unique to these inhibitors were systematically modified to reflect the energetically preferred conformations as determined by force field calculations. An optimum alignment rule was devised based on the conformations obtained from the molecular mechanics studies, using a common substructure alignment method. The studies involve a set of 21 compounds and experimentally determined molar IC50 values were used as the dependent variable in the analysis. The 3D-QSAR models have conventional r2-values of 0.953 and 0.954 for CoMFA and CoMSIA, respectively; similarly, cross-validated coefficient q2-values of 0.755 and 0.834 for CoMFA and CoMSIA, respectively, were obtained. On the basis of these predictive r2-values the model was tested using previously determined IC50 values. CoMSIA 3D-QSAR yielded better results than CoMFA.

The neurotransmitter noradrenaline rescues septal cholinergic neurons in culture from degeneration caused by low-level oxidative stress

We have developed a model system in which rat basal forebrain cholinergic neurons degenerate progressively when maintained in culture conditions that make them susceptible to low-level oxidative stress. In this study, we showed that cholinergic neurons identified by acetylcholinesterase cytochemistry or choline acetyl transferase immunocytochemistry are rescued efficiently by the neurotransmitter noradrenaline (NA). The effect of NA required neither adrenoceptor activation nor intracellular accumulation. NA operated via a mechanism that precluded activation of a cell death pathway in which reactive oxygen species (ROS) and proapoptotic caspases were crucially involved. It is noteworthy that NA remained protective even when applied late in the degenerative process but before intracellular ROS began to increase. The high efficacy of iron chelators and catalase in preventing the death of cholinergic neurons in this model suggested that NA neutralized the effects of hydroxyl radicals produced through a Fenton-type reaction. Pyrocatechol [the diphenolic moiety of NA] was sufficient in itself to prevent ROS production and cholinergic cell demise, indicating that the catechol structure was instrumental for the neuroprotective function of NA. Therefore, the noncatecholic neurotransmitter GABA failed to prevent neurodegeneration. Nerve growth factor and brain derived neurotrophic factor, two trophic peptides for septal cholinergic neurons, did not afford protection by themselves and did not improve neuroprotection provided by NA. However, in the presence of NA, they both retained their efficacy to stimulate cholinergic parameters. These data indicate that NA-based therapeutic strategies may be of interest in such neurodegenerative conditions as Alzheimer's disease, where progressive cholinergic deficits occur.

Regulation of cholinergic gene expression by nerve growth factor depends on the phosphatidylinositol-3'-kinase pathway

Nerve growth factor (NGF) exerts anti-apoptotic, trophic and differentiating actions on sympathetic neurons and cholinergic cells of the basal forebrain and activates the expression of genes regulating the synthesis and storage of the neurotransmitter acetylcholine (ACh). We have been studying the intracellular signaling pathways involved in this process. Although, in the rat pheochromocytoma cell line PC12, NGF strongly activates the mitogen-activated protein kinase (MAPK) pathway, prolonged inhibition of MAPK kinase (MEK) activity by PD98059 or U0126 did not affect the ability of NGF to up-regulate choline acetyltransferase (ChAT) or to increase intracellular ACh levels. In contrast, the treatment with the phosphatidylinositol 3'-kinase (PI3K) inhibitor LY294002, but not with its inactive analogue LY303511, completely abolished the NGF-induced production of ACh. Inhibition of PI3K also eliminated the NGF effect on the intracellular ACh level in primary cultures of septal neurons from E18 mouse embryos. Blocking the PI3K pathway prevented the activation of cholinergic gene expression, as demonstrated in RT/PCR assays and in transient transfections of PC12 cells with cholinergic locus promoter-luciferase reporter constructs. These results indicate that the PI3K pathway, but not the MEK/MAPK pathway, is the mediator of NGF-induced cholinergic differentiation.

The endogenous, immunologically active peptide apelin inhibits lymphocytic cholinergic activity during immunological responses

We investigated the effects of apelin, an immunologically active peptide ligand for orphan receptor APJ, on acetylcholine (ACh) synthesis in MOLT-3 human leukemic T cells. We initially confirmed expression of APJ mRNA in several human T- and B-cell lines by reverse transcription-polymerase chain reaction (RT-PCR). We also found that in phytohemagglutinin (PHA)-stimulated MOLT-3 cells, an active apelin fragment, apelin-13, down-regulates expression of choline acetyltransferase (ChAT) mRNA and significantly reduces ChAT activity and cellular ACh content and release. It thus appears that apelin inhibits lymphocytic cholinergic activity via APJ during immunological responses.

Estrogen enhances retrograde transport of brain-derived neurotrophic factor in the rodent forebrain

The neurotrophins and their receptors activate signaling molecules to regulate neural function in development and adulthood. Neurons in the septum-diagonal band complex (or basal forebrain) derive neurotrophins through retrograde transport of these peptides from their forebrain targets. The present study tests the hypothesis that the gonadal hormone estrogen enhances retrograde transport of the neurotrophin brain-derived neurotrophic factor (BDNF). Estrogen increases BDNF expression in the horizontal limb of the diagonal band of Broca (hlDBB) and its forebrain target the olfactory bulb. In the present study, rhodamine-labeled (Rho-) BDNF injected into the olfactory bulb was rapidly transferred to neurons in the hlDBB. Significantly greater numbers of hlDBB neurons were retrogradely labeled with Rho-BDNF in animals pretreated with estrogen, compared with placebo-replaced controls. Anti-tyrosine kinase (trk) B antibodies injected into the olfactory bulb attenuated retrograde transport of Rho-BDNF in a dose-dependent manner, suggesting that estrogen may enhance BDNF transport in this circuit through regulation of its trk receptor. Anti-trkB antibodies also reduced cAMP response element binding protein phosphorylation in the hlDBB and combined injections of anti-trkA and trkB in the olfactory bulb reduced estrogen-induced increases in basal forebrain choline acetyltransferase. These studies support the hypothesis that estrogen facilitates neurotrophin transport in forebrain circuits.

Magnetic resonance imaging of the neuroprotective effect of xaliproden in rats

RATIONALE AND OBJECTIVES

The neurotrophic effect of Xaliproden has been followed using sequential cerebral magnetic resonance imaging (MRI) in rats with vincristine-induced brain lesion as a model of Alzheimer disease.

METHODS

Nineteen rats received an intraseptal injection of vincristine on day 0, followed by a daily gavage with either the vehicle (Tween-20 1%) (n = 10) or Xaliproden (10 mg/kg) (n = 9). Eight sham-operated controls received a daily gavage with either the vehicle (n = 4) or Xaliproden (n = 4). Brain MR imaging was performed at 4.7 T on a Biospec 47/30 MR system before surgery then 3, 7, 10, and 14 days after surgery.

RESULTS

At day 3 following vincristine injection, an increase in MR signal intensity in the septum was observed on T2-weighted images. This increase was maximal at day 10, and remained stable until day 14. Daily treatment with Xaliproden delayed the appearance of hypersignals until day 7 and reduced by Ca. 50% the magnitude of the increase in signal intensity from day 10. No changes were observed in the hippocampus.

CONCLUSION

Quantitative MRI objectifies noninvasively the neuroprotective effect of Xaliproden on rat brain anatomy.

Inhibition of choline acetyltransferase by excitatory amino acids as a possible mechanism for cholinergic dysfunction in the central nervous system

Choline acetyltransferase (ChAT) activity was reduced by more than 85% in cultured retina cells after 16 h treatment with 150 microM kainate (T(1/2) : 3.5 h). Glutamate, AMPA and quisqualate also inhibited the enzyme in equivalent proportion. Cell lesion measured by lactate dehydrogenase (LDH) release, 3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrazolium bromide - thiazolyl blue (MTT) reduction and microscopic observation was not detected even after 48 h with kainate. Other retina neurochemical markers were not affected by kainate and full recovery of the enzyme was achieved 9 days after kainate removal. Moreover, hemicolinium-3 sensitive choline uptake and hemicolinium-3 binding sites were maintained intact after kainate treatment. The immunoblot and immunohistochemical analysis of the enzyme revealed that ChAT molecules were maintained in cholinergic neurons. The use of antagonists showed that ionotropic and group 1 metabotropic receptors mediated the effect of glutamate on ChAT inhibition, in a calcium dependent manner. The quisqualate mediated ChAT inhibition and part of the kainate effect (30%) was prevented by 5 mM N(G)-nitro-L-arginine methyl ester (L-NAME). Veratridine (3 microM) also reduced ChAT by a Ca(2+) dependent, but glutamate independent mechanism and was prevented by 1 microM tetrodotoxin.

Molecular mechanism of cholinergic dysfunction and cognitive deficits induced by amyloid beta-peptide

Amyloid beta-peptide (A beta) plays a critical role in the development of Alzheimer's disease (AD). Much progress has been made in understanding this age-related neurodegenerative disorder; thus an insight into the cellular actions of A beta and resulting functional consequences may contribute to preventive and therapeutic approaches for AD. In this review, recent evidence of A beta-induced brain dysfunction, especially cholinergic impairment and memory deficits, is summarized. Moreover, proposed mechanisms for A beta-induced neurotoxicity such as oxidative stress, ion-channel formation, and A beta-receptor interaction are discussed.

Inhibition of acetylcholine synthesis and tyrosine nitration induced by peroxynitrite are differentially prevented by antioxidants

Evidence of an overload of reactive oxygen species and peroxynitrite, a derivative of nitric oxide, in sporadic amyotrophic lateral sclerosis suggests that peroxynitrite could impair cholinergic functions. Because of the impossibility of obtaining synaptosomes from vertebrate neuromuscular junctions, we used cholinergic synaptosomes purified from Torpedo marmorata electroneurons to characterize the defects triggered by peroxynitrite in more detail. Addition of peroxynitrite or its donor 3-morpholinosydnonimine abolished high-affinity choline uptake and synthesis of acetylcholine from acetate. T. marmorata choline acetyltransferase (ChAT) was impaired to the same extent as bovine brain ChAT. A hallmark of peroxynitrite action is the nitration of tyrosine residues in proteins. Peroxynitrite induced a concentration-dependent appearance of nitrotyrosines in several neuronal proteins from synaptosomes and, more readily, from synaptic vesicles. Peroxynitrite also triggered tyrosine nitrations in purified ChAT. Peroxynitrite-dependent nitrations were impaired when synaptosomes were pretreated with thioreductants (glutathione, N-acetyl cysteine, dithiothreitol) or antioxidants (uric acid, melatonin, bovine serum albumin, desferrioxamine). Deleterious effects of peroxynitrite on choline transport and ChAT activity were prevented by the thioreductants but only partially by the antioxidants, suggesting a mechanism other than tyrosine nitration, which may involve cysteine oxidation. Further development of protective agents acting on choline transport and on ChAT activity may offer interesting therapeutic possibilities with respect to cholinergic dysfunction occurring in neurodegenerative diseases.

Sustained, long-lasting inhibition of nitric oxide synthase aggravates the neural damage in some models of excitotoxic brain injury

Brain nitric oxide (NO) can be a mediator of physiological and neuroprotective actions and an effector of neural damage. The effectiveness of acute or chronic inhibition of NO production in in vivo experiments of neurotoxicity/neuroprotection is controversial. We report here on the effects of a chronic, sustained inhibition of nitric oxide synthase (NOS) on the neurodegenerative damage caused by three different excitotoxic lesions. The damage caused by intrastriatal injection of ibotenic or kainic acid was aggravated in rats subjected to chronic NOS inhibition. On the contrary, the drop of cortical cholinergic input consequent to ibotenic acid-mediated degeneration of basal forebrain neurons was not altered by chronic NOS inhibition. The worsening of the damage was not related to any overt differential sensitivity to excitotoxicity of NOS-containing striatal neurons under conditions of NOS inhibition. These results suggest that, contrary to what has been often reported for short-term, mild inhibition of NO production, chronic and sustained NOS inhibition may exacerbate neuropathology. Thus, long-lasting shortage of NO may be detrimental when neuroprotective mechanisms related to the physiological action of this free radical are severely impaired. Although we cannot exclude that inhibition of the endothelial NOS isoform could have contributed to the worsening of neuropathology, differences among the paradigms of neurotoxicity used in the present study suggest a primary involvement of the neuronal NOS isoform. In view of the potential therapeutic use of NOS inhibitors, the effects of a too drastic alteration of the balance between neuroprotective and neurodegenerative actions of NO should be carefully considered.

Effects of chronic metrifonate treatment on cholinergic enzymes and the blood-brain barrier

After an acute (4 h) treatment with an irreversible cholinesterase inhibitor organophosphate, metrifonate (100 mg/kg i.p.), the activities of both acetyl- and butyrylcholinesterase were inhibited (66.0-70.7% of the control level) in the rat brain cortex and hippocampus. There were no significant changes in the acetyl- and butyrylcholinesterase activities in the olfactory bulb, or in the choline acetyltransferase activity in all three brain areas. After chronic (2 or 5 week) metrifonate treatment (100 mg/kg daily i.p.), the activities of both cholinesterases were substantially inhibited in the rat brain cortex and hippocampus (15.8-31.8% of the control levels), but there was no inhibition of the choline acetyltransferase activity. Moreover, chronic metrifonate treatment did not have any effect on the distribution of the acetylcholinesterase molecular forms. In vitro, metrifonate proved to be a more potent inhibitor of butyryl- than of acetylcholinesterase in both the cortex and the hippocampus. In the hippocampus, the butyrylcholinesterase activity was twice as sensitive to metrifonate inhibition as that in the cortex (IC50 values 0.22 and 0.46 microM, respectively). The effects of chronic (5 week) metrifonate treatment on the blood-brain barrier of the adult rat were examined. The damage to the blood-brain barrier was judged by the extravasation of Evans' blue dye in three brain regions: the cerebral cortex, the hippocampus, and the striatum. No extravasation of Evans' blue dye was found in the brain by fluorometric quantitation. These data indicate that chronic metrifonate treatment may increase the extracellular acetylcholine level via cholinesterase inhibition, but it does not have any effects on the blood-brain barrier. Therefore, it appears reasonable to hypothesize that cholinesterase activities do not play a role in the blood-brain barrier permeability.

Par-4 induces cholinergic hypoactivity by suppressing ChAT protein synthesis and inhibiting NGF-inducibility of ChAT activity

Profound reductions in choline acetyl-transferase (ChAT) activity are reliable markers for cholinergic hypoactivity associated with cognitive function deficit in Alzheimer's disease (AD). Par-4 (prostate apoptosis response-4) is a novel mediator of neuronal apoptosis associated with the pathogenesis of AD. Par-4 contains a leucine zipper domain (Leu.zip) that presumably mediates protein-protein interactions critical for its functions in apoptosis. Par-4 activity can be effectively blocked by overexpression of Leu. zip because it exerts a dominant negative action possibly by competitively blocking the interaction of Par-4 with other proteins. Whether Par-4 participates in regulation of cholinergic signaling has not been determined. We report that overexpression of Par-4 results in apoptotic and non-apoptotic reductions in ChAT activity in transfected PC12 cells following exposure to a toxic concentration (50 microM) of aggregated amyloid beta peptide 1-42 (Abeta 1-42) and a non-toxic concentration (1 microM) of soluble Abeta 1-42, respectively. Non-apoptotic reduction in ChAT activity induced by Par-4 can be completely blocked by co-overexpression of Leu.zip, indicating that enhanced Par-4 activity is a necessary event for cholinergic hypoactivity in PC12 cells. Further studies found that Par-4 induces non-apoptotic reduction in ChAT activity by: (1) reducing ChAT protein levels following exposure to non-toxic concentration of Abeta, and (2) blocking the cellular capability to increase ChAT activity following exposure to nerve growth factor (NGF). The role of Par-4 in inducing cholinergic hypoactivity may have significant implications in the understanding and the treatment of memory impairment in AD.

Choline acetyltransferase, acetylcholinesterase, and nicotinic acetylcholine receptors of human gingival and esophageal epithelia

A non-neuronal cholinergic system that includes neuronal-like nicotinic acetylcholine receptors (nAChRs) has recently been described in epithelial cells that line the skin and the upper respiratory tract. Since the use of nicotine-containing products is associated with morbidity in the upper digestive tract, and since nicotine may alter cellular functions directly via nAChRs, we sought to identify and characterize a non-neuronal cholinergic system in the gingival and esophageal epithelia. mRNA transcripts for alpha3, alpha5, alpha7, and beta2 nAChR subunits, choline acetyltransferase, and the asymmetric and globular forms of acetylcholinesterase were amplified from gingival keratinocytes (KC) by means of polymerase chain-reactions. These proteins were visualized in the gingival and esophageal epithelia by means of specific antibodies. Variations in distribution and intensity of immunostaining were found, indicating that the repertoire of cholinergic enzymes and receptors expressed by the cells changes during epithelial maturation, and that an upward concentration gradient of free acetylcholine exists. Blocking of the nAChRs with mecamylamine resulted in reversible loss of cell-to-cell adhesion, and shrinking and rounding of cultured gingival KC. Activation of the receptors with acetylcholine or carbachol caused stretching and peripheral ruffling of the cytoplasmic aprons, and formation of new intercellular contacts. These results demonstrate that both the keratinizing epithelium of attached gingiva and the non-keratinizing epithelium lining the upper two-thirds of the esophageal mucosa possess a non-neuronal cholinergic system. The nAChRs expressed by these epithelia are coupled to regulation of cell adhesion and motility, and may provide a target for the deleterious effects of nicotine.

Antidotal efficacy of pyridinium oximes and cholineacetyltransferase inhibitors against organophosphorus intoxication in rodents

In an attempt to develop effective antidote against organophosphorus intoxication, some new imidazole-pyridinium mono-oximes, long chain pyridinium mono-oximes and cholineacetyltransferase inhibitors were synthesised. These compounds were evaluated for their in vivo therapeutic protection and neuromuscular function studies in rodents. The results indicate that SPK-series oximes may be useful against sarin poisoning without any beneficial effect against VX (O-Ethyl S-2-NN-diisopropylaminoethyl methylphosphonofluoridate) intoxication. The cholineacetyltransferase (ChAT) inhibitors may not be of any help against any of the OP compounds studied in this study.

Enzyme activity and protein of multiple forms of choline acetyltransferase: effects of calyculin A and okadaic acid

Choline acetyltransferase (ChAT) appears to exist in multiple forms, three of which can be isolated biochemically as cytosolic (cChAT), ionically-membrane bound (ibChAT) and non-ionic membranous (mChAT). In this study, we first examined whether the quantitative distribution of enzyme protein and enzyme activity was the same. Enzyme activity and ChAT protein distributed similarly: the majority of ChAT activity and protein were found in cChAT followed by mChAT and least activity and amount were in ibChAT. Our second objective was to investigate the effects of calyculin A or okadaic acid on the subcellular distribution of ChAT activity and amount from rat hippocampal formation. Calyculin A and okadaic acid decreased significantly (p < 0.01) cytosolic and membranous ChAT activity; ionically-bound ChAT was not significantly (p > 0.67) different from control. Removal of calyculin A or okadaic acid restored cytosolic ChAT activity (p > 0.9 as compared to control), but not membranous enzyme activity (p < 0.05 as compared to control). The immunoreactive cytosolic ChAT was reduced significantly (p < 0.01) by calyculin A and okadaic acid. Enzyme amount of membranous ChAT was decreased significantly by calyculin A (p < 0.01) and okadaic acid (p < 0.001). Enzyme amount of ionically-bound ChAT was not changed (p > 0.99) by either of these two phosphatase inhibitors. This investigation demonstrates that alterations in ChAT activity of each subfraction parallel changes in enzyme amounts in the same fractions.

Higher activities of acetylcholinesterase and choline acetyltransferase in jaw-opening than jaw-closing motoneurones in the rat

The activities of acetylcholinesterase (AChE) and choline acetyltransferase (ChAT) in rat masticatory motoneurones were measured. Anterior digastric (jaw-opening) and masseter (jaw-closing) motoneurones were retrogradely labelled with the fluorescent tracers nuclear yellow and bisbenzimide, respectively. The animals were pretreated with an irreversible AChE inhibitor, diisopropyl fluorophosphate, for the measurement of AChE activities. After transcardial perfusion, serial frozen sections, 20-microm thick, of the brainstem were prepared and processed for AChE histochemical analysis. Sections of 30-microm thickness were also prepared and processed for ChAT immunohistochemical analysis using anti-ChAT antibodies and the peroxidase-antiperoxidase complex. The AChE and ChAT activities in motoneurones identified by their fluorescence were determined by measuring their absorbance in the cytoplasm at 470 and 450 nm, respectively. Each of the enzymatic activities was significantly higher in the anterior digastric than in masseter motoneurones (p < 0.001, student t-test).

The lipid peroxidation product 4-hydroxynonenal impairs glutamate and glucose transport and choline acetyltransferase activity in NSC-19 motor neuron cells

Both oxidative stress and excitotoxicity are implicated in the pathogenesis of a number of neurodegenerative disorders, such as amyotrophic lateral sclerosis. We previously reported increased modification of proteins by 4-hydroxynonenal (HNE), a product of membrane lipid peroxidation, in the spinal cords of patients with amyotrophic lateral sclerosis relative to controls. In the current study, we examined the functional consequences of protein modification by HNE in a cell line with a motor neuron phenotype, NSC-19. Treatment of NSC-19 cells with FeSO4, which catalyzes lipid peroxidation, or HNE induced concentration-dependent decreases in glucose and glutamate transport. Vitamin E and propyl gallate blocked the impairment of glucose and glutamate transport caused by FeSO4 in these cells, but not that caused by HNE, whereas glutathione blocked the effects of FeSO4 as well as HNE. Both FeSO4 and HNE caused an increase in the number of apoptotic nuclei in NSC-19 cultures, but this occurred subsequent to the impairment of glucose and glutamate transport. Reductions in choline acetyltransferase activity were also observed in FeSO4- or HNE-treated NSC-19 cells before induction of apoptosis. Our results suggest that, prior to cell death, oxidative stress and HNE down-regulate cholinergic markers and impair glucose and glutamate transport in motor neurons, the latter of which may lead to excitotoxic degeneration of the cells.

Inhibition of choline acetyltransferase activity by serum albumin modified with octanoic acid and other fatty acids

In this study, we examined the effect of fatty acids on choline acetyltransferase (ChAT) activity. ChAT is unstable in a solution of low protein concentration, so serum albumin (BSA) is usually added to stabilize the enzyme. However, we found that ChAT from bovine caudate nucleus rapidly lost its activity when diluted with a buffer containing commercial preparations of BSA. This effect was caused by octanoic acid, which was found in the gas chromatography/mass spectrometry system of lipid extract in commercial BSAs. The inhibition of ChAT activity by octanoic acid depended on the concentrations of the octanoic acid and of the albumin. We also found that ChAT activity was decreased by some long-chain fatty acids, arachidonic acid having exhibited the strongest effect. The extent to which arachidonic acid inhibited ChAT activity depended on the molar ratio of arachidonic acid and albumin, rather than upon the concentration of arachidonic acid. The effect of octanoic acid and arachidonic acid on ChAT activity appeared to increase in the presence of albumin.

Inhibition of dopamine and choline acetyltransferase concentrations in rat CNS neurons by rat alpha 1- and alpha 2-macroglobulins

Previous studies have implicated human alpha-2-macroglobulin (alpha2M) as a potential regulator of neuronal development and function. Rat alpha-1-macroglobulin (alpha1M) and acute-phase alpha-2-macroglobulin (alpha2M) are murine homologues of human alpha2M. In this report, we tested the effect of intracranially infused serotonin-activated rat alpha1M (5HT-alpha1M) on the concentration of dopamine (DA) in the corpus striatum in vivo and the effect of 5HT-activated rat alpha1M and alpha2M on the choline acetyltransferase (ChAT) activity upon embryonic basal forebrain neurons in culture. The results show that direct infusion of 0.65 nmole rat 5HT-alpha1M into the adult rat corpus striatum produced a consistent attenuation upon striatal DA concentrations. This decrease was particularly prominent at 5-7 days post-infusion. In addition, rat 5HT-alpha1M and rat 5HT-alpha2M, like human 5HT-alpha2M, all significantly inhibited ChAT activity of embryonic rat cerebral cortex neurons. Although normal human alpha2M and rat alpha2M were either marginally or insignificantly inhibitory in this preparation, normal rat alpha1M dose-dependently inhibited ChAT activity. These results demonstrate that monoamine-activated alpha-macroglobulins from rat depress dopaminergic and cholinergic neurotransmitter systems in the CNS, and this suggests a potential regulatory role of these alpha-macroglobulins in neurotransmitter metabolism.

Nerve growth factor-independent reduction in choline acetyltransferase activity in PC12 cells expressing mutant presenilin-1

Mutations in the presenilin genes (PS-1 and PS-2) are linked to early onset familial Alzheimer's disease (AD), but the mechanisms by which these mutations cause the cognitive impairment characteristic of AD are unknown. Basal forebrain cholinergic neurons are involved in learning and memory processes, and reductions in choline acetyl-transferase (ChAT) activity are a characteristic feature of AD brain. We therefore hypothesized that presenilin mutations suppress expression of the cholinergic phenotype. In rat PC12 cells stably transfected with the human PS-1 gene containing the Leu --> Val mutation at codon 286 (L286V), we observed a drastic reduction (>90%) in basal ChAT activity compared with cells transfected with vector alone. By immunocytochemistry, a similar decrease in ChAT protein levels was found in the mutant transfectants. In cells differentiated with nerve growth factor, ChAT activity was again markedly lower in L286V-expressing cells than in control cells. We also observed reductions in ChAT activity in PC12 cells expressing the wild-type human PS-1 gene but to a lesser extent than in L286V-expressing cells. The viability of cells transfected with either the wild-type or the mutant PS-1 gene was not compromised. Our results suggest that PS-1 mutations may contribute to the cognitive impairment in AD by causing a nontoxic suppression of the cholinergic phenotype.

Effects of organophosphate and carbamate pesticides on acetylcholinesterase and choline acetyltransferase activities of the polychaete Nereis diversicolor

A toxicity test for organophosphates (OP) and carbamates (C) was improved with the adult ragworm Nereis diversicolor. Animals were maintained in U-shaped glass tubes of 4-mm inner diameter fixed vertically on a plastic plate and placed in glass aquaria. Each tank was covered with glass in order to reduce evaporation and heat dissipation. Temperature varied between 15 and 16 degrees C and salinity was constant (34 per thousand) during the entire length of the experiment. Experiments were performed with a fixed day length of 12 h and seawater was gently aerated. The maintenance system allowed the administration of OP and C compounds via the seawater. An acclimatization period of 48 h was not sufficient to accomodate worms to their artificial burrows; accordingly, we chose to acclimate worms for a week before beginning the exposure. Choline acetyltransferase (ChAT) activity was very low and was not significantly modified by two OP compounds: malathion and parathion-ethyl. ChAT is not a target for these pesticides and should not be used for future studies about OP and C toxicity. On the other hand, inhibitory effects on acetylcholinesterase (AChE) activity were determined at concentrations of 10(-6) M for three OP compounds-malathion, parathion-ethyl, and phosalone-and a carbamate pesticide-carbaryl. We measured only short-term effects and no cumulative effect was determined, the maximum percentage of AChE activity inhibition being between 2 (carbaryl) and 7 (OP compounds) days after exposure and then remaining stable. Mortality occured only after a period of intoxication of 14 days. N diversicolor, which can be easily maintained at the laboratory, seems to be a good candidate for future laboratory studies to test the toxicity of other pollutants.

Microglia from the developing rat medial septal area can affect cholinergic and GABAergic neuronal differentiation in vitro

The normal development of the central nervous system is regulated by glia. In this regard, we have reported that astrocytes, stimulated by epidermal growth factor or transforming growth factor alpha, suppress the biochemical differentiation of rat medial septal cholinergic neurons in vitro, as evidenced by a decrease in choline acetyltransferase activity. In this study, we found that, in contrast to astrocytes, microglia enhance rather than suppress this aspect of cholinergic cell expression. When in excess, microglia can revert the effects of epidermal growth factor on the septal cholinergic neurons without altering the astroglial proliferative response to this growth factor. In the absence of growth factors or other glial cell types, microglia increase choline acetyltransferase activity above control levels and thus, may be a source of cholinergic differentiating activity. The increase in enzyme activity induced by microglia is rapid in onset, detected as early as 2 h after their addition to the septal neurons and maintained up to six or seven days in vitro. Furthermore, in the absence or presence of other glial cell types, microglia also influence septal GABAergic neurons by significantly increasing glutamate decarboxylase activity. As microglia affect neither septal cholinergic nor GABAergic neuronal cell survival, they appear to enhance the biochemical differentiation of these two neuronal cell types. Specific immunoneutralizing antibodies were used to identify the microglia-derived factors affecting these two neuronal types. In this regard, we found that the microglia-derived cholinergic differentiating activity is significantly suppressed by antibodies raised against interleukin-3. Furthermore, interleukin-3 was detected in both conditioned media and cell homogenates from septal neuronal-microglial co-cultures by western blotting. Finally, although basic fibroblast growth factor and interleukin-3 significantly increase septal glutamate decarboxylase activity, neither appears to be implicated in the GABAergic cell response to the microglia. In conclusion, these results demonstrate that microglia can enhance the biochemical differentiation of developing cholinergic and GABAergic neurons in vitro.

Continuous infusion of beta-amyloid protein into the rat cerebral ventricle induces learning impairment and neuronal and morphological degeneration

To investigate the toxicity of beta-amyloid protein, a component of the senile plaques in Alzheimer's disease, it was infused into the cerebral ventricle of rats for 14 days by a mini-osmotic pump. Performances in the water maze and passive avoidance tasks in beta-amyloid protein-treated rats were impaired. Choline acetyltransferase activity significantly decreased in the hippocampus both immediately and 2 weeks after the cessation of the infusion. However, the learning impairment was recoverable 2 weeks after cessation of the infusion. Both immediately and 2 weeks after the cessation of the infusion, glial fibrillary acidic protein immunoreactivity increased. Furthermore, beta-amyloid protein altered the staining in the nuclei of hippocampal cells for only 2 weeks after the cessation. These results suggest that beta-amyloid protein produces some damage in the central nervous system in vivo.

Biochemical activities of berberine, palmatine and sanguinarine mediating chemical defence against microorganisms and herbivores

The alkaloids berberine, palmatine and sanguinarine are toxic to insects and vertebrates and inhibit the multiplication of bacteria, fungi and viruses. Biochemical properties which may contribute to these allelochemical activities were analysed. Acetylcholine esterase, butyrylcholinesterase, choline acetyl transferase, alpha 1- and alpha 2-adrenergic, nicotinergic, muscarinergic and serotonin2 receptors were substantially affected. Sanguinarine appears to be the most effective inhibitor of choline acetyl-transferase (IC50 284 nM), while the protoberberines were inactive at this target. Berberine and palmatine were most active at the alpha 2-receptor (binding with IC50 476 and 956 nM, respectively). Furthermore, berberine and sanguinarine intercalate DNA, inhibit DNA synthesis and reverse transcriptase. In addition, sanguinarine (but not berberine) affects membrane permeability and berberine protein biosynthesis. In consequence, these biochemical activities may mediate chemical defence against microorganisms, viruses and herbivores in the plants producing these alkaloids.

Ameliorating effects of SDZ ENA 713 on age-associated decreases in learning performance and brain choline acetyltransferase activity in rats

In the present study, we have investigated the effects of SDZ ENA 713 on spatial learning deficits in aged rats. Using the same animals, the effect of SDZ ENA 713 on choline acetyltransferase was simultaneously studied to obtain a basis for the behavioral study. In the aged rats, the spatial learning and choline acetyltransferase activity in the frontal cortex were significantly deteriorated compared with young adult rats. SDZ ENA 713 (0.2 mg/kg) significantly shortened the time to reach a hidden platform without affecting swim rates in the water maze task. SDZ ENA 713 (0.1 and 0.2 mg/kg) inhibited aging-induced decreases in choline acetyltransferase activity in the frontal cortex. These results suggest that SDZ ENA 713 ameliorates aging-induced learning deficits and cholinergic dysfunction in rats.

Inhibition of lysoPAF acetyltransferase activity by flavonoids

OBJECTIVE AND DESIGN

Several kinds of flavonoids, widely distributed natural products of the vegetable kingdom which possess anti-inflammatory activity, were examined for inhibitory effects on the acetyl-CoA: 1-alkyl-2-lyso-sn-glycero-3-phosphocholine (lysoPAF) acetyltransferase activity.

METHODS

Acetyl-CoA:lysoPAF acetyltransferase activity was determined using homogenates of a rat mucosal-type mastocytoma cell line, RBL-2H3 as an enzyme source. The production of platelet-activating factor (PAF) in rat peripheral white blood cells stimulated with the calcium ionophore A23187 was studied.

RESULTS

Of the flavonoids tested, luteolin and quercetin exhibited significant inhibitory effects (IC50, 45 microM and 80 microM, respectively), whereas other structurally-related flavonoids failed to affect the lysoPAF acetyltransferase activity. Luteolin did not suppress the activity of choline acetyltransferase, suggesting that the inhibition observed here was specific. Luteolin also inhibited the production of PAF in rat peripheral white blood cells.

CONCLUSIONS

These results indicate that luteolin could become a leading compound for developing a novel type of anti-inflammatory, anti-allergic drugs that target lysoPAF acetyltransferase.

Differential action of NMDA antagonists on cholinergic neurotoxicity produced by N-methyl-D-aspartate and quinolinic acid

1. Injections of N-methyl-D-aspartate (NMDA) and quinolinic acid (Quin), agonists that activate NMDA receptors, into the rat nucleus basalis magnocellularis (nbM) produced a dose-related decrease in cholineacetyltransferase (ChAT) activity in the cerebral cortex and amygdala 7 days after injection. 2. In order to examine the possibility that NMDA and Quin activate different sub-types of NMDA receptors to produce central cholinergic neurotoxicity, the sensitivity of these agonists to the action of three different NMDA receptor antagonists, 2-amino-7-phosphonoheptanoate (AP-7), 7-chlorokynurenate and dizolcipine (MK801) was examined by injecting a fixed dose of NMDA (60 nmol) or Quin (120 nmol) in combination with different doses of the antagonists into the nbM. 3. Both AP-7 (0.6-15 nmol) and 7-chlorokynurenate (3.75-200 nmol), which block the NMDA receptor recognition site and glycine modulatory site respectively, produced a dose-related attenuation of the NMDA or Quin-induced decrease in ChAT activity in both the cortex and amygdala. Both antagonists showed a greater potency against the action of NMDA than against Quin. 4. MK801 (2-200 nmol), an NMDA receptor-linked channel blocker, attenuated the Quin and NMDA response only at a high dose. Unlike AP-7 and 7-chlorokynurenate, MK801 did not exhibit a consistent difference in its potency as an antagonist against NMDA and Quin. 5. The differential antagonist actions of AP-7 or 7-chlorokynurenate against NMDA and Quin-induced cholinergic neurotoxicity suggest that the excitotoxic actions of these two agonists are mediated via distinct NMDA receptor sub-types. The NMDA- and Quin-sensitive receptors appear to differ with respect to properties of the receptor recognition and glycine modulatory sites that are associated with these receptors.

A protective effect of lithium on rat behaviour altered by ibotenic acid lesions of the basal forebrain cholinergic system

Lithium was tested on an animal model of a brain cholinergic excitotoxic lesion. Male Wistar rats received unilaterally 50 nmol ibotenic acid in the nucleus basalis magnocellularis. Some were treated intraperitoneally with LiCl from two days before to six days after lesioning. Such treated rats showed less deficits than untreated lesioned animals on passive avoidance, ambulatory behaviour and choline acetyltransferase activity in the lesioned cortex. Lithium protection against excitatory amino acid neurotoxicity is suggested.

192IGG-saporin-induced selective lesion of cholinergic basal forebrain system: neurochemical effects on cholinergic neurotransmission in rat cerebral cortex and hippocampus

A novel cholinergic immunotoxin (conjugate of the monoclonal antibody 192IgG against the low-affinity nerve growth factor receptor with the cytotoxin saporin) producing selective lesions of cholinergic neurons in rat basal forebrain was applied to study its effect on hippocampal and cerebral cortical cholinergic neurotransmission. Intracerebroventricular injection of 4 micrograms 192IgG-saporin conjugate resulted in a selective loss of cholinergic cells in the basal forebrain nuclei 1 week after application, which was accompanied by decreased activities of choline acetyltransferase and by reduced high-affinity uptake of [3H]choline into cholinergic nerve terminals in the cerebral cortex and hippocampus, as well as by a significant activation of micro- and to a lesser extent of astroglial cells in the hippocampus, but hardly in the cerebral cortex.. The K(+)-stimulated release of [3H]acetylcholine from cortical and hippocampal slices of immunolesioned rats was found to be markedly decreased 1 week after injection. Cholinergic immunolesion led to enhanced cortical M1-muscarinic acetylcholine receptor numbers, but did not alter muscarinic receptor sensitivity as measured by carbachol-stimulated inositol phosphate production or phorbol ester binding to membrane-bound protein kinase C. In the hippocampal formation differential enhancements in binding levels of M1-muscarinic cholinergic receptor sites in the CA1 region and in the dentate gyrus were observed, whereas the nicotinic and M2-muscarinic receptor subtype are seemingly not affected by the immunotoxin in either of the subfields studied. Cholinergic immunolesioning did not result in any alterations in the hybridization signals for m1 through m4 muscarinic acetylcholine receptor mRNA in any region or layer of the hippocampus. The data suggest that (i) the novel cholinergic immunotoxin 192IgG-saporin is an appropriate tool to mimic cholinergic hypofunction in the hippocampal formation and cerebral cortex, and (ii) selective and specific immunolesion of cholinergic cells in medial septal nuclei differentially affects cholinergic receptors in particular hippocampal subfields.

Molecular modeling studies of some choline acetyltransferase inhibitors

Choline acetyltransferase (ChAT) inhibitors related to trans-1-methyl-4- (1-naphthylvinyl)-pyridinium (NVP+) have been assumed to depend upon a nearly or completely planar conformation for their enzyme-inhibitor interaction. In an effort to investigate the geometries and preferred conformations for these compounds, geometry optimizations using the semiempirical molecular orbital method AM1 and a modified version of the molecular mechanics method MM2(92) have been carried out. The results indicate that the active inhibitors are either planar or nearly coplanar, lying in relatively flat potential wells in the vicinity of the corresponding planar structures. When nonplanarity is favored, one ring is twisted out of the plane by approximately 30 degrees. Where steric features significantly deter assumption of a nearly planar conformation, the analogs are inactive. The inactivity of analogs bearing tricyclic aryl groups appears to result from bulk-related hindrance to ChAT receptor binding rather than lack of coplanarity.

Endogenous inhibitors of human choline acetyltransferase present in Alzheimer's brain: preliminary observation

We have previously demonstrated the presence in Alzheimer's disease brain of an endogenous inhibitor of choline acetyltransferase activity. Selected properties of these compounds were investigated. There appear to be two distinct classes of inhibitor present, both phosphomonoesters and nonphosphorylated substances. They are not proteins, pass through 500 mm dialyses membranes and are not lipoidal. There are both different sensitivities of individual control cytosotic activity to inhibition and differences in intrinsic inhibitory activity present in individual Alzheimer's disease brain samples. There is a competitive type of inhibition with respect to acetyl CoA as substrate and a noncompetitive type with respect to choline as substrate.

Monoamine-activated alpha 2-macroglobulin inhibits choline acetyltransferase of embryonic basal forebrain neurons and reversal of the inhibition by NGF and BDNF but not NT-3

Monoamine-activated alpha 2-macroglobulin (alpha 2M) has recently been shown to inhibit the growth and survival of cholinergic neurons of the basal forebrain (Liebl and Koo: J Neurosci Res 35:170-182, 1993). The mechanism of this inhibitory effect is believed to involve the regulation of growth factor activities by alpha 2M. The objectives of this study are to determine whether monoamine-activated alpha 2M can inhibit choline acetyltransferase (ChAT) activity of cholinergic basal forebrain neurons, and whether some common neurotrophins in the CNS can reverse the inhibition. This study demonstrates that both methylamine-activated alpha 2M (MA-alpha 2M) and serotonin-activated alpha 2M (5HT-alpha 2M) can dose-dependently suppress the expression of normal basal levels of ChAT activity in embryonic rat basal forebrain cells in vitro, while normal alpha 2M has little or no effect. As little as 0.35 microM monoamine-activated alpha 2M can suppress the ChAT activity, whereas either nerve growth factor (NGF) or brain-derived neurotrophic factor (BDNF), but not neurotrophin-3 (NT-3), stimulates ChAT expression of these cells. The addition of either NGF or BDNF to the alpha 2M-suppressed cells can increase ChAT activity back to its normal levels, while NT-3 can not. These results demonstrate that (1) monoamine-activated alpha 2M is a potent non-cytotoxic inhibitor of the ChAT activity in cholinergic basal forebrain neurons, and (2) NGF and BDNF are capable of not only stimulating the ChAT activity but can also specifically reverse the alpha 2M inhibition.(ABSTRACT TRUNCATED AT 250 WORDS)

Hydrophilic and amphiphilic forms of Drosophila choline acetyltransferase are encoded by a single mRNA

We have previously shown that the enzyme choline-O-acetyltransferase (ChAT) exists in a hydrophilic and an amphiphilic form in Drosophila head. A complementary DNA clone of 4.2 kb containing the entire coding region of ChAT was isolated from a cDNA library of Drosophila heads. The cDNA was subcloned in an expression vector and injected into the nucleus of Xenopus oocytes. Injected oocytes expressed high levels of ChAT activity. This activity was inhibited by bromoacetylcholine, a specific inhibitor of the enzyme. In the present study the non-ionic detergent Triton X-114 was used to analyse whether the expression of hydrophilic and amphiphilic ChAT was or was not directed by a single cDNA. The two forms of ChAT were found to be synthesized in injected oocytes. Approximately 9% of the recombinant enzyme partitioned as amphiphilic activity. This value was similar to that found for native amphiphilic ChAT in Drosophila heads. Sedimentation in sucrose gradients of amphiphilic enzyme was found to be influenced by the type of detergent present in the gradient whereas this was not the case for hydrophilic ChAT. Hydrophilic and amphiphilic enzyme activities differed in some of their biochemical properties. Amphiphilic ChAT was less sensitive to inhibition by the product acetylcholine than was hydrophilic ChAT. Moreover, amphiphilic ChAT was found to be more resistant than hydrophilic ChAT to heat inactivation at 45 degrees C. These properties were observed for the native as well as for recombinant ChAT. These results demonstrate that the hydrophilic and amphiphilic forms of ChAT are derived from one mRNA.

In vitro effect of aluminum chloride on choline acetyltransferase activity of the rat brain during postnatal growth

A decrease in the activity of choline acetyltransferase (ChAT) has been well documented in brains from individuals with Alzheimer's disease (AD) (Bird et al., 1983; McGeer, 1984). Decreased ChAT activity was also found in dialysis encephalopathy victims, but this reduction was less marked than that observed in AD (Yates et al., 1980). The involvement of aluminum in the etiology of AD has been proposed by some authors on the basis of abnormal concentration of aluminum in autopsied brain samples from AD patients (Krishnan et al., 1987), in the neurofibrillary tangles (Perl and Pendlebury, 1986) and the neuritic plaques (Candy et al., 1986). King (1984) hypothesized that elevated levels of aluminum contribute to the cholinergic deficits in AD. Aluminum is considered to be the causal factor in dialysis encephalopathy (Alfrey et al., 1976), particularly in young children with azotemia (Andreoli et al., 1984). Several animal studies demonstrate in vivo an aluminum effect on ChAT (Yates et al., 1980; Hofstetter et al., 1987). The distribution of the cholinergic perikarya in the rat CNS has been established immunohistochemically using antisera to ChAT (Sofroniev et al., 1982). From the basal forebrain, ChAT positive fiber bundles could be followed to the olfactory bulb, neocortex and hippocampus (Ichikawa and Hirata, 1986). This paper examines the influence of aluminum chloride at different concentrations on the activity of ChAT in homogenates from basal forebrain and neostriatum of rats during postnatal growth.

Time course of cholinergic and monoaminergic changes in rat brain after immunolesioning with 192 IgG-saporin

192 IgG-saporin, an immunotoxin targeted at the low affinity NGF receptor, was infused into the lateral ventricle of rat brain. Three days and one week post lesion, choline acetyltransferase activity was markedly decreased in cortex, hippocampus, olfactory bulbs, and septum (brain regions innervated by the cholinergic neurons of the basal forebrain) with no change in cerebellum, striatum or pons. Measurement of monoamine levels revealed increases in HVA, DOPAC and dopamine, primarily in the olfactory bulbs at the 28-day time point only, suggesting a compensation for cholinergic inactivity. High levels of basal forebrain cholinergic lesioning can be obtained with this immunotoxin with minimal or no effects on monoaminergic or other cholinergic systems.

Retinal cholinergic system: characterization of rat retinal acetyltransferases using specific inhibitors of choline- and carnitine-acetyltransferases

Choline acetyltransferase catalyzes the synthesis of acetylcholine from choline and acetylcoenzyme A (ACoA) in both nervous and non-nervous tissues. Carnitine acetyltransferase occurs in several tissues and transfers acetyl groups from ACoA to carnitine forming acetylcarnitine and exhibits weak choline acetyltransferase activity. Several haloacetylcholines and haloacetylcarnitines were synthesized to develop selective inhibitors of choline acetyltransferase and carnitine acetyltransferase. Acetylcholine is a transmitter for some presynaptic neurons and/or amacrine cells in retina. Selective inhibitors of choline acetyltransferase and carnitine acetyltransferase were used in the evaluation of choline acetyltransferase and carnitine acetyltransferase activities in the rat retina. Choline acetyltransferase and carnitine acetyltransferase activities were assayed by transferring of [14C]acetyl group from [14C]ACoA to choline or carnitine and estimating [14C]-acetylcholine or [14C]acetylcarnitine. This study gave the following results: (a) Bromoacetylcholine (BrACh) was a selective inhibitor of purified choline acetyltransferase (I50, 2.2 microM); (b) (R)-bromoacetylcarnitine [(R)-BrACa] was more potent for inhibiting purified carnitine acetyltransferase (I50, 4 microM) than purified choline acetyltransferase (I50, 46 microM); (c) Rat retinal sonicate gave choline acetyltransferase activity of 98 +/- 6 nmol of ACh formed/mg/10 min. When the carnitine acetyltransferase was completely inhibited by (R)-BrACa, the activity for choline acetyltransferase decreased to 47 +/- 1 nmol, and this decrease was possibly due to the formation of some [14C]acetylcholine by carnitine acetyltransferase. The net retinal choline acetyltransferase activity was 51 nmol acetylcholine/mg protein/10 min; (d) Rat retinal sonicate contained carnitine acetyltransferase activity of 102 +/- 7 nmol acetylcarnitine formed/mg protein/10 min. This was not altered by inhibition of choline acetyltransferase with BrACh. This means that choline acetyltransferase did not use carnitine as a substrate. Choline acetyltransferase and carnitine acetyltransferase activities did not change after dialysis of retinal sonicates at 4 degrees C for 24 hrs. These observations suggest that BrACh and (R)-BrACa are useful for assessing the correct values for choline acetyltransferase and carnitine acetyltransferase activities in retinal tissues.

Muscarinic cholinergic receptor density following small intestinal transplantation in rats

After small intestinal transplantation, intestinal isografts can organize migrating myoelectric complexes, and we have shown that migrating myoelectric complex frequency in the fasted state was reduced compared with controls after transplantation of the distal 50% of small intestine. We hypothesized that changes in motor activity after transplantation were related to alteration of cholinergic nerve activity or receptor density. With use of standard microsurgical techniques, the distal 50% of small intestine was orthotopically transplanted in a Lewis-to-Lewis donor-recipient combination. Resection controls were prepared by resecting the proximal 50% of small intestine, and sham controls were prepared by performing a sham laparotomy. Two months after surgery, small intestine was harvested. Choline acetyltransferase activity among the three groups was similar, suggesting that intrinsic cholinergic nerves remained intact. There was a strong trend toward decreased acetylcholinesterase activity [analysis of variance (ANOVA), P = 0.16] after transplantation, consistent with loss of extrinsic vagal nerve fibers. There were no differences in histochemical distribution of acetylcholinesterase among these groups. Muscarinic receptor density, as determined by binding to [N-methyl-3H]scopolamine, was decreased after transplantation (ANOVA, P = 0.02). There was a trend toward decreased receptor density in animals with resected small intestine. Surgical interruption of intrinsic nerve pathways rather than ischemia or extrinsic denervation might be the mechanism for diminished receptor density after transplantation, and reduced small bowel motor activity may be related to decreased density of muscarinic cholinergic receptors.

Effect of the choline acetyltransferase inhibitor (2-benzoylethyl)-trimethylammonium iodide (BETA) on human placental prostaglandin release and phospholipase A2 activity

We investigated the effect of an inhibitor of acetylcholine (ACh) synthesis, (2-benzoylethyl)trimethylammonium iodide (BETA), on prostaglandin (PG)E2 and PGF2 alpha release from incubated placental explants in the presence or absence of ACh or arachidonic acid (AA). BETA alone (100 microM) significantly reduced both PGE2 and PGF2 alpha release. However, this inhibitory effect of BETA was not reversed in the presence of ACh (10 microM to 1 mM). The addition of AA (10 to 100 microM) increased both PGE2 and PGF2 alpha release, and simultaneously overcame the inhibition of PGE2 but not PGF2 alpha release by BETA. These results are compatible with the hypothesis that BETA may be inhibiting the phospholipase A2 (PLA2) step rather than prostaglandin H synthase (PGHS) step in the enzymatic pathway of PG generation. This hypothesis was supported by evidence showing a lack of effect of BETA (10 and 100 microM) on ovine placental microsome PGHS activity. Moreover, human placental homogenate PLA2 activity was reversibly inhibited by BETA (100 microM). In the presence of BETA (100 microM), addition of exogenous ACh (100 microM) had no significant effect on placental PLA2 activity. These results indicate that the inhibitory effect of BETA on placental PG release was unlikely to be via an action on ACh synthesis, but rather via a reversible effect on PLA2 activity.

Inhibition of cytosolic human forebrain choline acetyltransferase activity by phospho-L-serine: a phosphomonoester that accumulates during early stages of Alzheimer's disease

There is no satisfactory explanation for the cholinergic deficit characteristic of Alzheimer's disease. We have performed a series of experiments which demonstrate that (a) an inhibitor of cytosolic human brain choline acetyltransferase is present in the cytosol of Alzheimer brain tissue, (b) human brain cytosolic choline acetyltransferase activity is inhibited by phospho-L-serine in a competitive manner. Cytosol was prepared from human forebrain or amygdala and the Km for choline and acetyl CoA of the choline acetyltransferase were 750 microM and 12.5 microM, respectively. Phospho-L-serine was found to be a competitive inhibitor of this enzyme with respect to choline but not with respect to acetyl CoA with a Ki of 750 microM for the human forebrain and 3 mM for human amygdala. These concentrations of phospho-L-serine are present in brain tissue at early stages of Alzheimer's disease. Several other phosphomonoesters and phosphodiesters that are increased in Alzheimer's disease were either less inhibitory or without effect. The addition of heat denatured and non-heat denatured cytosol from Alzheimers forebrain inhibited the choline acetyltransferase activity present in control human brain cytosol. The inhibitory activity of the Alzheimers cytosol was retained in TCA deproteinized samples and removed by dialysis or by alkaline phosphatase treatment. Dialysis of the cytosol increased the choline acetyltransferase activity of 5 of 8 Alzheimer's disease samples from 21 to 118% with p values of < 0.025 or < 0.001, respectively. These observations provide evidence that an endogenous non-proteinaceous, dialyzable, phosphomonoester, present in Alzheimers brain inhibits the choline acetyltransferase of both control and Alzheimers brain.(ABSTRACT TRUNCATED AT 250 WORDS)

Inhibition and inactivation of presynaptic cholinergic markers using redox-reactive choline analogs

Inhibition and inactivation of two presynaptic cholinergic "markers", choline acetyltransferase and high affinity choline transporter, has been investigated using inhibitors designed with a redox-reactive catechol tethered to a quaternary ammonium group. Two quaternary ammonium alkyl-substituted catechols, 3[(trimethylammonio)methyl]catechol (TMC, 1) and N,N-dimethylepinephrine (catecholine, 2) were shown to bind weakly and noncompetitively to bovine choline acetyltransferase yet inactivated the enzyme in a time course consistent with the involvement of early intermediates in the spontaneous oxidation of these catechols. Both agents also inhibited high-affinity choline uptake. The time course of TMC and catecholine spontaneous oxidation-dependent inactivation of high affinity choline uptake sites was slower than, if it occurred at all, the spontaneous degradation of measurable choline transport in synaptosomes. When compared with inhibition of uptake of other neurotransmitters, it was shown that catecholine demonstrated more selectivity than TMC toward inhibition of choline transport. Km (microM) and Vmax (pmol/min per mg of protein) were measured for high affinity transport of choline, dopamine, and serotonin and were observed to be Km = 2.04 +/- 0.31, Vmax = 22 +/- 1; Km = 1.4, Vmax = 53; and Km = 0.15, Vmax = 23, respectively, in good agreement with published literature values. Ki's (mM) for catecholine and TMC, calculated from experimentally determined IC50's, were for catecholine 0.13 +/- 0.06, 0.53 +/- 0.09, and 0.39 +/- 0.10, and for TMC 0.06 +/- 0.03, 0.09 +/- 0.03, and 0.09 +/- 0.08, for choline, dopamine, and serotonin transport, respectively. In vivo studies using catecholine suggest that this compound impairs learning ability associated with long-term memory. Thus, catecholine represents a lead compound in a potential series of redox-reactive choline analogs, which may become useful irreversible antagonists of the critical cholinergic macromolecular targets underlying cholinergic hypofunction in disorders such as Alzheimer's disease.

[Assessment of the activity of choline acetyltransferase in heart tissues]

A procedure is described for the radioisotope assay of acetylcholine transferase activity (EC 2.3.1.6), which involved specific synthesis of acetylcholine in vivo. Bromine acetylcholine was used as an inhibitor of the enzyme; 14C-AcCoA was used as a substrate and product of the enzymatic reaction. 14C-acetylcholine was separated from the substrate by means of anion exchange chromatography. The procedure described was 5 times more sensitive than the methods developed by F. Fonnum (1975) and S. Tucek (1983) being similarly reproducible. The assay was tested in experiments with rats under various conditions of hyperbaric oxygenation, in simulation of myocardial infarction as well as in moderate immobilization stress. The findings suggest that estimation of the acetylcholine transferase activity may be involved in complex evaluation of the cholinergic system state in tissues, which is essential for the study of pathogenesis of their dysfunctions and development of respective approaches to eliminate these impairments.

Effects of nefiracetam, DM-9384 on amnesia and decrease in choline acetyltransferase activity induced by cycloheximide

The effects of nefiracetam, [N-(2,6-dimethyl-phenyl)-2-(2-oxo-pyrrolidinyl)acetamide, DM-9384], a cyclic derivative of GABA, were investigated in the cycloheximide (CXM)-induced amnesia animal model using the passive avoidance task. Pre-training administration of DM-9384 attenuated the CXM-induced amnesia as indicated by prolongation of step-down latency. It protected against CXM-induced inhibition of choline acetyltransferase activity in the cerebral cortex. These results suggest that DM-9384 attenuates CXM-induced amnesia by interacting with AChergic neuronal system and enhancing protein synthesis in the brain.