Blockade of Neuronal Nitric Oxide Synthase Abolishes the Toxic Effects of TX2-5, a Lethal Phoneutria nigriventer Spider Toxin

^1Yonamine, C.M.; ²Troncone, L.R.P. & ¹Camillo, M,A,P.

1 Molecular Biology Center, IPEN, Av.Prof.Lineu Prestes 2242; SP; CEP 05508-900; Brazil; 2 Laboratory of Pharmacology; Instituto Butantan, Av.Vital Brasil, 1500; SP; CEP.05503-900; Brazil.

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 purity and identity were analyzed by MALDI-TOF and ES-MS yielding a main component with 5116 Da and N- terminal amino acid sequence identical to Tx2-5. Pre-treating mice with the non-selective NOS inhibitor L-NAME and the selective nNOS inhibitor 7-Nitroindazole (7-NI) prior to TX2-5 i.p (10 micrograms/25g mouse) injection challenged the hypothesis above. 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, hipersalivation 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 sythase.

Finacial support of LRPT: FAPESP 02/04545-7

Financial support CMY: CNPq

Correspondence to: ltronc@usp.br