Genetic analysis of collagen Q: roles in acetylcholinesterase and butyrylcholinesterase assembly and in synaptic structure and function. (1/406)

Acetylcholinesterase (AChE) occurs in both asymmetric forms, covalently associated with a collagenous subunit called Q (ColQ), and globular forms that may be either soluble or membrane associated. At the skeletal neuromuscular junction, asymmetric AChE is anchored to the basal lamina of the synaptic cleft, where it hydrolyzes acetylcholine to terminate synaptic transmission. AChE has also been hypothesized to play developmental roles in the nervous system, and ColQ is also expressed in some AChE-poor tissues. To seek roles of ColQ and AChE at synapses and elsewhere, we generated ColQ-deficient mutant mice. ColQ-/- mice completely lacked asymmetric AChE in skeletal and cardiac muscles and brain; they also lacked asymmetric forms of the AChE homologue, butyrylcholinesterase. Thus, products of the ColQ gene are required for assembly of all detectable asymmetric AChE and butyrylcholinesterase. Surprisingly, globular AChE tetramers were also absent from neonatal ColQ-/- muscles, suggesting a role for the ColQ gene in assembly or stabilization of AChE forms that do not themselves contain a collagenous subunit. Histochemical, immunohistochemical, toxicological, and electrophysiological assays all indicated absence of AChE at ColQ-/- neuromuscular junctions. Nonetheless, neuromuscular function was initially robust, demonstrating that AChE and ColQ do not play obligatory roles in early phases of synaptogenesis. Moreover, because acute inhibition of synaptic AChE is fatal to normal animals, there must be compensatory mechanisms in the mutant that allow the synapse to function in the chronic absence of AChE. One structural mechanism appears to be a partial ensheathment of nerve terminals by Schwann cells. Compensation was incomplete, however, as animals lacking ColQ and synaptic AChE failed to thrive and most died before they reached maturity.  (+info)

The anticancer prodrug CPT-11 is a potent inhibitor of acetylcholinesterase but is rapidly catalyzed to SN-38 by butyrylcholinesterase. (2/406)

Patients treated with high doses of CPT-11 rapidly develop a cholinergic syndrome that can be alleviated by atropine. Although CPT-11 was not a substrate for acetylcholinesterase (AcChE), in vitro assays confirmed that CPT-11 inhibited both human and electric eel AcChE with apparent K(i)s of 415 and 194 nM, respectively. In contrast, human or equine butyryl-cholinesterase (BuChE) converted CPT-11 to SN-38 with K(m)s of 42.4 and 44.2 microM for the human and horse BuChE, respectively. Modeling of CPT-11 within the predicted active site of AcChE and BuChE corroborated experimental results indicating that, although the drug was oriented correctly for activation, the constraints dictated by the active site gorge were such that CPT-11 would be unlikely to be activated by AcChE.  (+info)

Cholinesterases in neural development: new findings and toxicologic implications. (3/406)

Developing animals are more sensitive than adults to acute cholinergic toxicity from anticholinesterases, including organophosphorus pesticides, when administered in a laboratory setting. It is also possible that these agents adversely affect the process of neural development itself, leading to permanent deficits in the architecture of the central and peripheral nervous systems. Recent observations indicate that organophosphorus exposure can affect DNA synthesis and cell survival in neonatal rat brain. New evidence that acetylcholinesterase may have a direct role in neuronal differentiation provides additional grounds for interest in the developmental toxicity of anticholinesterases. For example, correlative anatomic studies show that transient bursts of acetylcholinesterase expression often coincide with periods of axonal outgrowth in maturing avian, rodent, and primate brain. Some selective cholinesterase inhibitors effectively suppress neurite outgrowth in model systems like differentiating neuroblastoma cells and explanted sensory ganglia. When enzyme expression is altered by genetic engineering, acetylcholinesterase levels on the outer surface of transfected neurons correlate with ability to extend neurites. Certain of these "morphogenic" effects may depend on protein-protein interactions rather than catalytic acetylcholinesterase activity. Nonetheless, it remains possible that some pesticides interfere with important developmental functions of the cholinesterase enzyme family.  (+info)

Failure to confirm a synergistic effect between the K-variant of the butyrylcholinesterase gene and the epsilon4 allele of the apolipoprotein gene in Japanese patients with Alzheimer's disease. (4/406)

To confirm a synergistic effect between the polymorphic K variant of the butyrylcholinesterase (BChE-K) gene and the epsilon4 allele of the apolipoprotein E (APOE) gene in Alzheimer's disease, the frequency of the BChE-K allele was re-examined in a large series of Japanese patients with Alzheimer's disease and controls. Two hundred and three patients with Alzheimer's disease and 288 age and sex matched controls were genotyped by polymerase chain reaction and restriction fragment length polymorphism for BChE-K and APOE. No changes were found in the frequency of BChE-K, either in the Alzheimer's disease group as a whole (0.17 v 0.14; p=0.36) or in early (0.16 v 0.16; p=0.98) or late (0.17 v 0.13; p=0.24) onset patients compared with age matched controls. The study failed to confirm the findings of a previous study which found a significantly higher incidence of BChE-K in patients with Alzheimer's disease with APOE epsilon4 allele than in controls. In the Japanese population studied here, there was no association between BChE-K and Alzheimer's disease, nor an interaction between BChE-K and APOE epsilon4 allele.  (+info)

Anticholinesterase effects of huperzine A, E2020, and tacrine in rats. (5/406)

AIM: To compare the anticholinesterase effects of huperzine A (Hup A), E2020, and tacrine in rats. METHODS: Spectrophotometry was used to determine AChE activity in brain and BuChE activity in serum. RESULTS: Following intragastric gavage, Hup A, E2020, and tacrine all produced dose-dependent inhibitions of brain AChE. Oral Hup A exhibited a higher inhibition than E2020 and tacrine. Tacrine was more effective in inhibiting serum BuChE correlated with severe peripheral adverse effects. The BuChE activity was less affected by Hup A and E2020. After a single oral dose of Hup A, a relatively steady state of AChE inhibition produced, which was longer than that after E2020 and tacrine. No change in the cholinesterase inhibition was seen for the 3 drugs following repeated i.g. medications. CONCLUSION: Hup A i.g. exhibited a higher efficacy, a longer duration of action, and a more selective inhibition on AChE than E2020 and tacrine.  (+info)

Effects of synthetic (-)-huperzine A on cholinesterase activities and mouse water maze performance. (6/406)

AIM: To compare the effects of synthetic and natural (-)-huperzine A (Hup A) on cholinesterase and mouse water maze performance. METHODS: Spectrophotometry was used to determine cholinesterase activity. Mouse water maze was used to evaluate nootropic effect. RESULTS: The IC50 of synthetic Hup A for acetylcholinesterase (AChE) of rat cortex and rat erythrocyte membrane determined in vitro were 64.7 (52.6-79.5) and 53.9 (43.6-66.6) nmol.L-1, respectively, and for butyrylcholinesterase of rat serum was 53.6 (44.9-63.8) mumol.L-1. Synthetic Hup A 0.12-0.48 mg.kg-1 ig produced a dose-dependent inhibition of brain AChE in mice. Synthetic Hup A 0.05 mg.kg-1 ig attenuated scopolamine-induced impairment of spatial memory. The efficacy of synthetic Hup A was the same as natural Hup A. CONCLUSION: Synthetic Hup A yielded an in vitro and in vivo pharmacological profile of activities similar to that of natural Hup A.  (+info)

Characteristics of recombinant human butyrylcholinesterase. (7/406)

AIM: To study the biochemical-pharmacological properties of the recombinant human butyrylcholinesterase (rhBChE) and thereby to size up the potential possibility of using it as a detoxifying agent in succinylcholine intoxication. METHODS: CHO-dhfr cells were transfected with plasmids by electroporation. BChE activity was determined colorimetrically by 5, 5'-dithiobis-(2-nitrobenzoic acid) (DTNB) method. Antigenicity was estimated by enzyme-linked immunosorbent assay and Western blot. RESULTS: The maximal expression amounted to 25.83 ng.h-1/10(6) cells. The rhBChE was highly similar to the native human BChE (nhBChE) in terms of its catalytic property, substrate affinity, inhibitor sensitivity, reactivation, stability, and immunoreactivity with anti-nhBChE antibodies. Mice challenged with 1.5 lethal dose of succinylcholine preincubated with rhBChE survived without any symptoms of intoxication. CONCLUSION: The rhBChE and nhBChE exhibit similar biochemical-pharmacological features. It is of potential value in practical use.  (+info)

Inhibitory effects of huperzine B on cholinesterase activity in mice. (8/406)

AIM: To determine the anticholinesterase properties of huperzine B (Hup B) and compare with tacrine in vitro and in vivo. METHODS: Spectrophotometry was used to determine ChE activity. RESULTS: Hup B showed much more selective inhibition to acetylcholinesterase (AChE) than tacrine. The IC50 ratios of Hup B and tacrine for butyrylcholinesterase (BuChE): AChE were 65.8 and 0.54, respectively. Hup B ig exhibited higher efficacy on the inhibition of brain AChE than that of tacrine. Tacrine was more effective in the inhibition of serum BuChE in mice with severe concomitant peripheral adverse effects than Hup B. A single ig dose of Hup B produced steady state of AChE inhibition in 4 h. CONCLUSION: Hup B exhibits higher selectivity and efficacy in the inhibition of AChE, and lower toxicity in mice than tacrine.  (+info)

• 1
• 2
• 3
• 4
• 5
• 6
• 7
• 8
• 9
• 10