Effects of Mlx-8, a phospholipase A2 from Brazilian coralsnake Micrurus lemniscatus venom, on muscarinic acetylcholine receptors in rat hippocampus

Autor(es)

Roberta Tancredi Francesco dos Santos ^[1] ; Marcelo Florencio Passos Silva ^[2] ; Rafael Marques Porto ^[3] ; Ivo Lebrun ^[4] ; Luís Roberto de Camargo Gonçalves ^[5] ; Isabel de Fátima Correia Batista ^[6] ; Maria Regina Lopes Sandoval ^[7] ; Fernando Maurício Francis Abdalla ^[8]

Afiliação do(s) autor(es)

^[1] Butantan Institute. Laboratory of Pharmacology - Brasil

^[2] Butantan Institute. Laboratory of Pharmacology - Brasil

^[3] Butantan Institute. Laboratory of Biochemistry and Biophysics - Brasil

^[4] Butantan Institute. Laboratory of Biochemistry and Biophysics - Brasil

^[5] Butantan Institute. Laboratory of Pathophysiology - Brasil

^[6] Butantan Institute. Laboratory of Biochemistry and Biophysics - Brasil

^[7] Butantan Institute. Laboratory of Pharmacology - Brasil

^[8] Butantan Institute. Laboratory of Pharmacology - Brasil

• Tipo de documento: Artigo Científico
• Fonte: Journal of Venomous Animals and Toxins including Tropical Diseases; v. 26, 2020-01-27.

Resumo

Abstract Background: Here, 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). Methods: The 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. Results: Thirty-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. Conclusion: The 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. (AU)

• Processo FAPESP: 11/51600-2 - Caracterização farmacológica e funcional de componentes isoladas do veneno da serpente Micrurus lemniscatus com atividade fosfolipásica a2 e componentes ativos em receptores muscarínicos no sistema nervoso de ratos
• Beneficiário: Maria Regina Lopes Sandoval
• Modalidade de apoio: Auxílio à Pesquisa - Regular