Blockade of neuronal nitric oxide synthase abolishes the toxic effects of Tx2-5, a lethal Phoneutria nigriventer spider toxin.
The primary goal of this study was to determine whether Tx2-5, a sodium channel selective toxin obtained from the venom of the spider Phoneutria nigriventer, produced penile erection by means of nitric oxide mechanism. Toxin identity was analyzed by MALDI-TOF, ES-MS and N-terminal amino acid sequencing. Pretreating mice with the non-selective nitric oxide synthase (NOS) inhibitor N(omega)-Nitro-L-arginine methyl ester hydrochloride (L-NAME) and the selective neuronal-NOS inhibitor 7-Nitroindazole (7-NI) prior to Tx2-5 i.p. (10 microg/25 g mouse) injection challenged the hypothesis above. Controls were injected with the D-isomer or DMSO or saline. Results demonstrated that L-NAME inhibited penile erections in about half the animals treated, while 7-NI completely abolished this effect. Interestingly 7-NI also abolished all the other symptoms of intoxication induced by Tx2-5, including salivation, respiratory distress and death. Tx2-5 killed all the animals of the control group and no one in the 7-NI-treated group. We conclude that (1) intraperitoneal injections of Tx2-5 induce a toxic syndrome that include penile erection, hypersalivation and death by respiratory distress or pulmonary edema; (2) pretreatment with the non-selective NOS inhibitor L-NAME reduces the penile erection and partially protects from the lethal effects of Tx2-5; (3) pretreatment with the nNOS-selective inhibitor 7-NI completely abolishes all the toxic effects of Tx2-5, including penile erection and death suggesting that nNOS is the major player in this intoxication; (4) toxins from other animals that affect sodium channels in the same way as Tx2-5 and induce similar toxic syndromes may have as a major common target, the activation of nitric oxide synthases.
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Molecular Biology Center, Instituto de Pesquisas Energéticas e Nucleares (IPEN), Cidade Universitária, Av. Prof. Lineu Prestes 2242, São Paulo, SP 05508-900, Brazil.
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Camillo
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D000704:Analysis of Variance; D000818:Animals; D004791:Enzyme Inhibitors / Q000494:pharmacology; D007191:Indazoles / Q000494:pharmacology; D008171:Lung Diseases / Q000139:chemically induced / Q000201:enzymology; D008297:Male; D051379:Mice; D008807:Mice, Inbred BALB C; D019331:NG-Nitroarginine Methyl Ester / Q000494:pharmacology; D009479:Neuropeptides / Q000633:toxicity*; D009498:Neurotoxins / Q000633:toxicity; D019001:Nitric Oxide Synthase / Q000037:antagonists & inhibitors*; D052248:Nitric Oxide Synthase Type I; D011317:Priapism / Q000139:chemically induced / Q000201:enzymology; D013111:Spider Venoms / Q000633:toxicity*; D013112:Spiders
D004791:Enzyme Inhibitors; D007191:Indazoles; D009479:Neuropeptides; D009498:Neurotoxins; D013111:Spider Venoms; C076902:Tx2 neurotoxin; D019001:Nitric Oxide Synthase; D052248:Nitric Oxide Synthase Type I; C496321:Nos1 protein, mouse; C080122:7-nitroindazole; D019331:NG-Nitroarginine Methyl Ester