RESUMO
Acetylcholinesterase (AChE), the enzyme involved in the hydrolysis of the neurotransmitter acetylcholine, has been implicated in non-cholinergic actions which may play a role in neurodegenerative diseases such as Alzheimer's disease. To study the potential cytotoxicity of brain AChE, the effects of affinity purified AChE were analyzed on neuronal (Neuro 2a) and glial-like (B12) cells. LDH release and MTT reduction assays showed that AChE was toxic; the toxicity was dependent on the enzyme concentration, time of incubation and cellular density. The toxic effect of AChE was not related to its catalytic activity, since the anti-cholinesterase drug BW284C51 and heat inactivation were unable to block the effects of the enzyme. When cells were incubated at 4 degrees C, toxicity was completely blocked, in contrast to cells incubated at 37 degrees C. The presence of serum in the culture medium inhibited the toxic effects of AChE. Cytoplasmic shrinkage, condensation and fragmentation of nucleus as well as DNA strand breaks detected with the TUNEL technique indicated that apoptotic cell death is involved in the effect of AChE. Considering that we have previously shown that AChE promotes the assembly of beta-amyloid peptide into neurotoxic amyloid fibrils, it is conceivable that the neurotoxicity of AChE shown here may play a role in the neuronal degeneration observed in Alzheimer's disease.
Assuntos
Acetilcolinesterase/toxicidade , Neuroglia/efeitos dos fármacos , Neurônios/efeitos dos fármacos , Acetilcolinesterase/metabolismo , Doença de Alzheimer/metabolismo , Animais , Biotina , Proteínas Sanguíneas/farmacologia , Bovinos , Contagem de Células , Temperatura Baixa , Fragmentação do DNA , Nucleotídeos de Desoxiuracil , Ativação Enzimática/fisiologia , Camundongos , Neuroblastoma , Emaranhados Neurofibrilares/enzimologia , Neuroglia/citologia , Neurônios/citologia , Coloração e Rotulagem , Células Tumorais Cultivadas/citologia , Células Tumorais Cultivadas/efeitos dos fármacosRESUMO
Alzheimer's disease (AD) is associated with a reduction in cholinergic activity as a result of specific neuronal loss. Current potential treatments for the disease include both cholinomimetic drugs and anticholinesterase inhibitors. One of the drugs approved by the FDA is tacrine (9-amine-1,2,3,4 tetrahydroacridine; THA), a strong acetylcholinesterase (AChE) inhibitor. We have studied the effects of tacrine on glial and neuronal cells in culture assessing cell survival and viability and morphology. Lactate dehydrogenase (LDH) activity and methylthiazol-diphenyl-tetrazolium (MTT) reduction were used as toxicity indicators. We found that tacrine toxicity on rat B12 glial cells and mouse Neuro 2A cells was strongly dependent on its concentration (up to 500 microM) and time of exposure. The toxic effect was not prevented by serum factors nor by bovine serum albumin. Fluorescein-conjugated phalloidin was used to examine the arrangement of actin filaments at substrate adhesion regions and cell-cell contacts. Primary events following exposure to tacrine included changes in cell morphology, disappearance of actin filament bundles, and disruption of focal adhesion contacts. At concentrations between 10 and 50 microM, tacrine induced neurite outgrowth in Neuro 2A cells, an effect that was not observed in B12 cells, suggesting that certain tacrine effects could be specific for neuronal cells. Although similar trends of response were observed for both cell types, some differences between undifferentiated and differentiated cells were apparent.
Assuntos
Neurônios/efeitos dos fármacos , Tacrina/toxicidade , Animais , Diferenciação Celular/efeitos dos fármacos , Tamanho Celular/efeitos dos fármacos , Relação Dose-Resposta a Droga , Glioma , Camundongos , Neuroblastoma , Neuroglia/efeitos dos fármacos , Neurônios/patologia , Ratos , Células Tumorais CultivadasRESUMO
Brain acetylcholinesterase (AChE) forms stable complexes with amyloid-beta peptide (Abeta) during its assembly into filaments, in agreement with its colocalization with the Abeta deposits of Alzheimer's brain. The association of the enzyme with nascent Abeta aggregates occurs as early as after 30 min of incubation. Analysis of the catalytic activity of the AChE incorporated into these complexes shows an anomalous behavior reminiscent of the AChE associated with senile plaques, which includes a resistance to low pH, high substrate concentrations, and lower sensitivity to AChE inhibitors. Furthermore, the toxicity of the AChE-amyloid complexes is higher than that of the Abeta aggregates alone. Thus, in addition to its possible role as a heterogeneous nucleator during amyloid formation, AChE, by forming such stable complexes, may increase the neurotoxicity of Abeta fibrils and thus may determine the selective neuronal loss observed in Alzheimer's brain.