Project description:BackgroundHere, we described the presence of a neurotoxin with phospholipase A2 activity isolated from Micrurus lemniscatus venom (Mlx-8) with affinity for muscarinic acetylcholine receptors (mAChRs).MethodsThe purification, molecular mass determination, partial amino acid sequencing, phospholipase A2 activity determination, inhibition of the binding of the selective muscarinic ligand [3H]QNB and inhibition of the total [3H]inositol phosphate accumulation in rat hippocampus of the Mlx-8 were determined.ResultsThirty-one fractions were collected from HPLC chromatography, and the Mlx-8 toxin was used in this work. The molecular mass of Mlx-8 is 13.628 Da. Edman degradation yielded the following sequence: NLYQFKNMIQCTNTRSWL-DFADYG-CYCGRGGSGT. The Mlx-8 had phospholipase A2 enzymatic activity. The pKi values were determined for Mlx-8 toxin and the M1 selective muscarinic antagonist pirenzepine in hippocampus membranes via [3H]QNB competition binding assays. The pKi values obtained from the analysis of Mlx-8 and pirenzepine displacement curves were 7.32 ± 0.15, n = 4 and 5.84 ± 0.18, n = 4, respectively. These results indicate that Mlx-8 has affinity for mAChRs. There was no effect on the inhibition ability of the [3H]QNB binding in hippocampus membranes when 1 µM Mlx-8 was incubated with 200 µM DEDA, an inhibitor of phospholipase A2. This suggests that the inhibition of the phospholipase A2 activity of the venom did not alter its ability to bind to displace [3H]QNB binding. In addition, the Mlx-8 toxin caused a blockade of 43.31 ± 8.86%, n = 3 and 97.42 ± 2.02%, n = 3 for 0.1 and 1 µM Mlx-8, respectively, on the total [3H]inositol phosphate content induced by 10 µM carbachol. This suggests that Mlx-8 inhibits the intracellular signaling pathway linked to activation of mAChRs in hippocampus.ConclusionThe results of the present work show, for the first time, that muscarinic receptors are also affected by the Mlx-8 toxin, a muscarinic ligand with phospholipase A2 characteristics, obtained from the venom of the Elapidae snake Micrurus lemniscatus, since this toxin was able to compete with muscarinic ligand [3H]QNB in hippocampus of rats. In addition, Mlx-8 also blocked the accumulation of total [3H]inositol phosphate induced by muscarinic agonist carbachol. Thus, Mlx-8 may be a new pharmacological tool for examining muscarinic cholinergic function.

Project description:BackgroundEndogenous phospholipases A2 (PLA2) play a fundamental role in inflammation, neurodegenerative diseases, apoptosis and cellular senescence. Neurotoxins with PLA2 activity are found in snake venoms from the Elapidae and Viperidae families. The mechanism of action of these neurotoxins have been studied using hippocampal and cerebellar neuronal cultures showing [Ca2+]i increase, mitochondrial depolarization and cell death. Astrocytes are rarely used as a model, despite being modulators at the synapses and responsible for homeostasis and defense in the central nervous system. Preserving the cell division ability, they can be utilized to study the cell proliferation process. In the present work cultured astrocytes and glioblastoma cells were employed to characterize the action of β-micrustoxin (previously named Mlx-9), a PLA2 isolated from Micrurus lemniscatus snake venom. The β-micrustoxin structure was determined and the cell proliferation, cell cycle phases and the regulatory proteins p53, p21 and p27 were investigated.Methodsβ-micrustoxin was characterized biochemically by a proteomic approach. Astrocytes were obtained by dissociation of pineal glands from Wistar rats; glioblastoma tumor cells were purchased from ATCC and Sigma and cultured in DMEM medium. Cell viability was evaluated by MTT assay; cell proliferation and cell cycle phases were analyzed by flow cytometry; p53, p21 and p27 proteins were studied by western blotting and immunocytochemistry.ResultsProteomic analysis revealed fragments on β-micrustoxin that aligned with a PLA2 from Micrurus lemniscatus lemniscatus previously identified as transcript ID DN112835_C3_g9_i1/m.9019. β-micrustoxin impaired the viability of astrocytes and glioblastoma tumor cells. There was a reduction in cell proliferation, an increase in G2/M phase and activation of p53, p21 and p27 proteins in astrocytes.ConclusionThese findings indicate that β-micrustoxin from Micrurus lemniscatus venom could inhibit cell proliferation through p53, p21 and p27 activation thus imposing cell cycle arrest at the checkpoint G2/M.

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Cnemidophorus lemniscatus

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