Bothropstoxin‐I from Bothrops jararacussu snake venom is a lysine‐49 phospholipase A₂ with myotoxic and neurotoxic activities. In this study, we used mouse phrenic nerve‐diaphragm preparations in the absence and presence of manganese (Mn²⁺), a presynaptic blocker, to investigate a possible presynaptic action of bothropstoxin‐I. At concentrations of 0.9 mM and 1.8 mM, Mn²⁺ produced 50% neuromuscular blockade in less than 4 min., which was spontaneously reversible at the lower concentration. Bothropstoxin‐I (1.4 μM) irreversibly inhibited neuromuscular blockade by 50% in 31±4 min. (mean±S.E.M., n=9). Pretreating preparations with 0.9 mM Mn²⁺ prevented the blockade by bothropstoxin‐I. When added after bothropstoxin‐I, Mn²⁺ produced its characteristic blockade and, after washing, the twitch tension returned to pre‐Mn²⁺ levels, indicating that bothropstoxin‐I caused irreversible damage before the addition of Mn²⁺. Electrophysiological measurements showed that a concentration of bothropstoxin‐I (0.35 μM), which did not produce neuromuscular blockade, caused the appearance of giant miniature end‐plate potentials with no change in the membrane resting potential but increased the quantal content. Preparations preincubated with Mn²⁺ (0.9 mM, 30 min.) were protected against the depolarizing action of bothropstoxin‐I (0.7 μM). These results show that, in addition to its well‐known myotoxic effect, bothropstoxin‐I also has a presynaptic action.

Extracts from Dipteryx alata bark obtained with different solvents (hexane, dichloromethane, ethyl acetate and methanol) were mixed in vitro with Bothrops jararacussu (Bjssu, 40 μg/mL) and Crotalus durissus terrificus (Cdt, 15 μg/mL) snake venoms, and applied to a mouse phrenic nerve-diaphragm preparation to evaluate the possible neutralization of venom effects. Cdt venom neurotoxic effect was not inhibited by any of the extracts, while the neurotoxic and myotoxic actions of Bjssu venom were decreased by the methanolic extract. This inhibition appears to be augmented by tannins. Dichloromethane bark extract inhibited ~40% of Bjssu venom effects and delayed blockade induced by Cdt. The methodology used to determine which extract was active allows inferring that: (i) phenolic acids and flavonoids contained in the methanolic extract plus tannins were responsible mostly for neutralization of Bjssu effects; (ii) terpenoids from the dichloromethane extract may participate in the anti-Cdt and anti-Bjssu venom effects; (iii) a given extract could not inhibit venoms from different species even if those belong to the same family, so it is improper to generalize a certain plant as antiophidian; (iv) different polarity extracts do not present the same inhibitory capability, thus demonstrating the need for characterizing both venom pharmacology and the phytochemistry of medicinal plant compounds

Snakebite is a neglected disease and serious health problem in Brazil, with most bites being caused by snakes of the genus Bothrops. Although serum therapy is the primary treatment for systemic envenomation, it is generally ineffective in neutralizing the local effects of these venoms. In this work, we examined the ability of 7,8,3'-trihydroxy-4'-methoxyisoflavone (TM), an isoflavone from Dipteryx alata, to neutralize the neurotoxicity (in mouse phrenic nerve-diaphragm preparations) and myotoxicity (assessed by light microscopy) of Bothrops jararacussu snake venom in vitro. The toxicity of TM was assessed using the Salmonella microsome assay (Ames test). Incubation with TM alone (200 μg/mL) did not alter the muscle twitch tension whereas incubation with venom (40 μg/mL) caused irreversible paralysis. Preincubation of TM (200 μg/mL) with venom attenuated the venom-induced neuromuscular blockade by 84% ± 5% (mean ± SEM; n = 4). The neuromuscular blockade caused by bothropstoxin-I (BthTX-I), the major myotoxic PLA₂ of this venom, was also attenuated by TM. Histological analysis of diaphragm muscle incubated with TM showed that most fibers were preserved (only 9.2% ± 1.7% were damaged; n = 4) compared to venom alone (50.3% ± 5.4% of fibers damaged; n = 3), and preincubation of TM with venom significantly attenuated the venom-induced damage (only 17% ± 3.4% of fibers damaged; n = 3; p < 0.05 compared to venom alone). TM showed no mutagenicity in the Ames test using Salmonella strains TA98 and TA97a with (+S9) and without (−S9) metabolic activation. These findings indicate that TM is a potentially useful compound for antagonizing the neuromuscular effects (neurotoxicity and myotoxicity) of B. jararacussu venom.