Priscila Randazzo-Moura

Pharmacological and partial biochemical characterization of Bmaj-9 isolated from Bothrops marajoensis snake venom

Bmaj-9, a basic PLA2 (13679.33 Da), was isolated from Bothrops marajoensis snake venom through only one chromatographic step in reversed phase HPLC on ¼-Bondapak C-18 column. The amino acid composition showed that Bmaj-9 had a high content of Lys, His, and Arg, typical of a basic PLA2. The sequence of Bmaj-9 contains 124 amino acid residues with a pI value of 8.55, such as DLWQWGQMIL KETGKLPFSY YTAYGCYCGW GGRGGKPKAD TDRCCFVHDC, revealing a high homology with Asp49 PLA2 from other snake venoms. It also exhibited a pronounced phospholipase A2 activity when compared with crude venom. In chick biventer cervicis preparations, the time for 50% and 100% neuromuscular paralysis was respectively (in minutes): 110 ± 10 (1 µg/mL); 40 ± 6 and 90 ± 2 (5 µg/mL); 30 ± 3 and 70 ± 5 (10 µg/mL); 42 ± 1 and 60 ± 2 (20 µg/mL), with no effect on the contractures elicited by either exogenous ACh (110 µM) or KCl (20 mM). Bmaj-9 (10 µg/mL) neither interfered with the muscular response to direct electrical stimulation in curarized preparations nor significantly altered the release of CK at 0, 15, 30 and 60 minutes incubations (27.4 ± 5, 74.2 ± 8, 161.0 ± 21 and 353.0 ± 47, respectively). The histological analysis showed that, even causing blockade at the maximum dosage (5 µg/mL), the toxin does not induce significant morphological alterations such as necrosis or infiltration of inflammatory cells. These results identified Bmaj-9 as a new member of the basic Asp49 PLA2 family able to interact with the motor nerve terminal membrane, thereby inducing a presynaptic neuromuscular blockade.

Shared structural determinants for the calcium-independent liposome membrane permeabilization and sarcolemma depolarization in bothropstoxin-I, a Lys49-PLA2 from the venom of Bothrops jararacussu.

The structural determinants of myotoxicity of bothropstoxin-I (BthTX-I), a Lys49 phospholipase A(2) from Bothrops jararacussu venom, were studied by measuring the resting membrane potential in the mouse phrenic nerve-diaphragm preparation. This method proved to be around 100-fold more sensitive than the creatine kinase release assay, and was used to evaluate a total of 31 site-directed BthTX-I alanine scanning mutants. Mutants that reduced the resting membrane potential were located in a surface patch defined by residues in the C-terminal loop (residues 115-129), positions 37-39 in the membrane interfacial recognition surface (Y46 and K54), and residue K93. These results expand the known structural determinants of the biological activity as evaluated by previous creatine kinase release experiments. Furthermore, a strong correlation is observed between the structural determinants of sarcolemma depolarization and calcium-independent disruption of liposome membranes, suggesting that a common mechanism of action underlies the permeabilization of the biological and model membranes.

Beneficial effect of crotamine in the treatment of myasthenic rats

Introduction: Crotamine is a basic, low‐molecular‐weight peptide that, at low concentrations, improves neurotransmission in isolated neuromuscular preparations by modulating sodium channels. In this study, we compared the effects of crotamine and neostigmine on neuromuscular transmission in myasthenic rats. Methods: We used a conventional electromyographic technique in in‐situ neuromuscular preparations and a 4‐week treadmill program. Results: During the in‐situ electromyographic recording, neostigmine (17 μg/kg) caused short‐term facilitation, whereas crotamine induced progressive and sustained twitch‐tension enhancement during 140 min of recording (50 ± 5%, P < 0.05). On the treadmill evaluation, rats showed significant improvement in exercise tolerance, characterized by a decrease in the number of fatigue episodes after 2 weeks of a single‐dose treatment with crotamine. Conclusions: These results indicate that crotamine is more efficient than neostigmine for enhancing muscular performance in myasthenic rats, possibly by improving the safety factor of neuromuscular transmission. Muscle Nerve, 2013

Bothrops fonsecai snake venom activities and cross-reactivity with commercial bothropic venom.

In this work, we examined some biochemical and biological activities of Bothrops fonsecai venom, a pitviper endemic to southeastern Brazil, and assessed their neutralization by commercial bothropic antivenom (CAv). Cross-reactivity of venom with CAv was also assessed by immunoblotting and size-exclusion high performance chromatography (SE-HPLC). Bothrops fonsecai venom had PLA2, proteolytic and esterase activities that were neutralized to varying extents by venom:antivenom ratios of 5:1 and 5:2 (PLA2 and esterase activities) or not significantly by either venom:antivenom ratio (proteolytic activity). The minimum hemorrhagic dose (69.2μg) was totally neutralized by both ratios. Clotting time in rat citrated plasma was 33±10.5s (mean±SD; n=5) and was completely neutralized by a 5:2 ratio. Edema formation was dose-dependent (1-30μg/site) and significantly inhibited by both ratios. Venom (10-300μg/mL) caused neuromuscular blockade in extensor digitorum longus preparations; this blockade was inhibited best by a 5:2 ratio. Venom caused myonecrosis and creatine kinase release in vivo (gastrocnemius muscle) and in vitro (extensor digitorum longus) that was effectively neutralized by both venom:antivenom ratios. Immunoblotting showed that venom components of ~25-100kDa interacted with CAv. SE-HPLC profiles for venom incubated with CAv or specific anti-B. fonsecai antivenom raised in rabbits (SAv) indicated that CAv had a higher binding capacity than SAv, whereas SAv had higher affinity than CAv. These findings indicate that B. fonsecai venom contains various activities that are neutralized to different extents by CAv and suggest that CAv could be used to treat envenoming by B. fonsecai.

Bp-13 PLA2: Purification and Neuromuscular Activity of a New Asp49 Toxin Isolated from Bothrops pauloensis Snake Venom

A new PLA2 (Bp-13) was purified from Bothrops pauloensis snake venom after a single chromatographic step of RP-HPLC on μ-Bondapak C-18. Amino acid analysis showed a high content of hydrophobic and basic amino acids and 14 half-cysteine residues. The N-terminal sequence showed a high degree of homology with basic Asp49 PLA2 myotoxins from other Bothrops venoms. Bp-13 showed allosteric enzymatic behavior and maximal activity at pH 8.1, 36°–45°C. Full Bp-13 PLA2 activity required Ca2+; its PLA2 activity was inhibited by Mg2+, Mn2+, Sr2+, and Cd2+ in the presence and absence of 1 mM Ca2+. In the mouse phrenic nerve-diaphragm (PND) preparation, the time for 50% paralysis was concentration-dependent (P < 0.05). Both the replacement of Ca2+ by Sr2+ and temperature lowering (24°C) inhibited the Bp-13 PLA2-induced twitch-tension blockade. Bp-13 PLA2 inhibited the contractile response to direct electrical stimulation in curarized mouse PND preparation corroborating its contracture effect. In biventer cervicis preparations, Bp-13 induced irreversible twitch-tension blockade and the KCl evoked contracture was partially, but significantly, inhibited (P > 0.05). The main effect of this new Asp49 PLA2 of Bothrops pauloensis venom is on muscle fiber sarcolemma, with avian preparation being less responsive than rodent preparation. The study enhances biochemical and pharmacological characterization of B. pauloensis venom.