Histopathological changes caused by venom of urutu snake (Bothrops alternatus) in mouse skeletal muscle

Venoms and Isolated Toxins from Snakes of Medical Impact in the Northeast Argentina: State of the Art. Potential Pharmacological Applications

Among the ophidians that inhabit the Northeast of Argentina, the genus Bothrops such as B. alternatus and B. diporus species (also known as yararás) and Crotalus durisus terrificus (named cascabel), represent the most studied snake venom for more than thirty years. These two genera of venomous snakes account for the majority of poisonous snake envenomations and therefore, constitute a medical emergency in this region. This review presents a broad description of the compiled knowledge about venomous snakebite: its pathophysiological action, protein composition, isolated toxins, toxin synergism, toxin-antitoxin cross-reaction assays. Properties of some isolated toxins support a potential pharmacological application.

Why is Skeletal Muscle Regeneration Impaired after Myonecrosis Induced by Viperid Snake Venoms?

Skeletal muscle regeneration after myonecrosis involves the activation, proliferation and fusion of myogenic cells, and a coordinated inflammatory response encompassing phagocytosis of necrotic cell debris, and the concerted synthesis of cytokines and growth factors. Myonecrosis often occurs in snakebite envenomings. In the case of venoms that cause myotoxicity without affecting the vasculature, such as those of many elapid snakes, regeneration proceeds successfully. In contrast, in envenomings by most viperid snakes, which affect the vasculature and extracellular matrix in addition to muscle fibers, regeneration is largely impaired and, therefore, the muscle mass is reduced and replaced by fibro-adipose tissue. This review discusses possible causes for such poor regenerative outcome including: (a) damage to muscle microvasculature, which causes tissue hypoxia and affects the inflammatory response and the timely removal of necrotic tissue; (b) damage to intramuscular nerves, which results in atrophy of regenerating fibers; (c) degradation of muscle cell basement membrane, compromising the spatial niche for proliferating myoblasts; (d) widespread degradation of the extracellular matrix; and (e) persistence of venom components in the damaged tissue, which may affect myogenic cells at critical points in the regenerative process. Understanding the causes of poor muscle regeneration may pave the way for the development of novel therapeutic interventions aimed at fostering the regenerative process in envenomed patients.

Unresolved issues in the understanding of the pathogenesis of local tissue damage induced by snake venoms

Snakebite envenoming by viperid species, and by some elapids, is characterized by a complex pattern of tissue damage at the anatomical site of venom injection. In severe cases, tissue destruction may be so extensive as to lead to permanent sequelae, with serious pathophysiological, social and psychological consequences. Significant advances have been performed in the study of venom-induced tissue damage, including identification and characterization of the toxins involved, insights into the mechanisms of action of venoms and toxins, and study of tissue responses to venom-induced injury. Nevertheless, much remains to be known and understood on the pathogenesis of these alterations. This review focuses on some of the pending issues in the topic of snake venom-induced local tissue damage. The traditional 'reductionist' approach, which has predominated in the study of snake venoms and their actions, needs to be complemented by more integrative and holistic perspectives aimed at capturing the complexity of these pathological alterations. Future advances in the study of these topics will certainly pave the way for innovative therapeutic interventions, with the goal of reducing the impact of this aspect of snakebite envenoming.

Homogenates of skeletal muscle injected with snake venom inhibit myogenic differentiation in cell culture

INTRODUCTION

Viperid snakebite envenomings are characterized by muscle necrosis and a deficient regenerative response.

METHODS

Homogenates from gastrocnemius muscles of mice injected with the venom of the snake Bothrops asper or with 2 tissue-damaging toxins were added to cultures of C2C12 myogenic cells. Myoblasts proliferation and fusion were assessed. Venom was detected by immunoassay in mouse muscle during the first week after injection.

RESULTS

Homogenates from venom-injected muscle induced a drop in the number of proliferating myoblasts and a complete elimination of myotube formation. The inhibitory effect induced by homogenates from venom-injected mice was abrogated by preincubation of the homogenate with antivenom antibodies but not with control antibodies. This finding provides evidence that the effect is due to the action of venom in the tissue.

CONCLUSIONS

Our observations suggest that traces of venom in muscle tissue might inhibit myotube formation and preclude a successful regenerative response.

Comparison of the neurotoxic and myotoxic effects of Brazilian Bothrops venoms and their neutralization by commercial antivenom

The venoms of some Bothrops species produce neuromuscular blockade in avian and mammalian nerve-muscle preparations in vitro. In this study, we compared the neuromuscular activities (myotoxicity and neurotoxicity) of venoms from several Brazilian species of Bothrops (B. jararaca, B. jararacussu, B. moojeni, B. erythromelas and B. neuwiedi) in chick isolated biventer cervicis muscle preparations and examined their neutralization by commercial antivenom. All of the venoms (50-200 microg/ml, n = 3 - 7 each) induced long-lasting, concentration-dependent muscle contracture and twitch-tension blockade, and also inhibited the muscle responses to acetylcholine and KCl. Preincubation of the venoms (200 microg/ml) with bothropic antivenom (0.2 ml) for 30 min at 37 degrees C prevented the twitch-tension blockade to different extents, with the protection varying from 0.5% (B. neuwiedi) to 88% (B. moojeni). Complete protection against the neuromuscular action of B. neuwiedi venom was observed only with a mixture of bothropic and crotalic antivenoms. The venoms caused either high (B. jararacussu, B. neuwiedi and B. moojeni) or low (B. jararaca and B. erythromelas) creatine kinase release. Morphologically, myonecrosis was greatest with B. jararacussu venom (98-100% of fibers damaged) and least with B. jararaca venom (74% damage). The extent of neutralization by bothropic antivenom was B. jararaca (93%)>B. erythromelas (65.8%)>B. moojeni (30.7%)>B. neuwiedi (20%)>B. jararacussu (no neutralization). Despite this variation in neutralization, enzyme-linked immunosorbent assays indicated similar immunoreactivities for the venoms, although immunoblots revealed quantitative variations in the bands detected. These results show that Bothrops venoms produce varying degrees of neuromuscular blockade in chick nerve-muscle preparations. The variable protection by antivenom against neuromuscular activity indicates that the components responsible for the neuromuscular action may differ among the venoms.

Effects of Bothrops pirajai venom on the mouse extensor digitorum longus (EDL) muscle preparation

The effects of Bothrops pirajai snake venom on the mouse extensor digitorum longus (EDL) preparation were examined using myographic, histopathological and biochemical approaches. B. pirajai venom (10, 25 or 50 microg/ml) dose dependently and irreversibly blocked the contractile response of indirectly stimulated EDL muscle. Histopathological analysis of EDL muscle incubated with venom showed dose-dependent damage with a loss of the normal tissue structure and the appearance of highly dark, edematous fibers together with myofibrils in various stages of condensation. At high doses of venom (50 microg/ml), loss of muscle cells was observed. In non-stimulated EDL, B. pirajai venom (10 and 50 microg/ml) caused a time-dependent release of CK which was maximal after 120 min. These results suggest that a component(s) present in the B. pirajai venom has a direct myolytic action on the skeletal muscle.

[Hemorrhagic and edema-forming activity and histologic changes in the mouse footpad induced by venoms from Argentinian Bothrops and Crotalus genuses]

Hemorrhagic, oedema-forming activities and histopathological alterations in the mouse footpad induced by Bothrops and Crotalus snake venoms from Argentina. Hemorrhagic and oedema-forming activities of various Bothrops and Crotalus snake venoms from Argentina were studied, together with histological alterations in the mouse footpad. The highest oedema-forming activity was found in the venom of B. jararaca, followed by B. jararacussu, B. neuwiedii diporus, B. alternatus, and Crotalus durissus terrificus. Regarding hemorrhage, the highest activity was found in the venom of B. neuwiedii diporus, followed by B. jararacussu, B. alternatus, and B. jararaca. No hemorrhage was observed after injection of Crotalus durissus terrificus venom, in agreement with histological observations of injected footpads. Histological analysis revealed a conspicuous inflammatory reaction in the injected footpad, characterized by oedema and an inflammatory infiltrate rich in polymorphonuclear leucocytes. Necrotic blood vessels and dilated lymphatic vessels were observed after injection of B. jararaca and B. jararacussu venoms, and myonecrosis was evident in tissue of mice injected with B. alternatus and B. neuwiedii diporus.

Skeletal muscle degeneration and regeneration after injection of bothropstoxin-II, a phospholipase A2 isolated from the venom of the snake Bothrops jararacussu

A myotoxic phospholipase A2, named bothropstoxin II (BthTX-II), was isolated from the venom of the South American snake Bothrops jararacussu and the pathogenesis of myonecrosis induced by this toxin was studied in mice. BthTX-II induced a rapid increase in plasma creatine kinase levels. Histological and ultrastructural observations demonstrate that this toxin affects muscle fibers by first disrupting the integrity of plasma membrane, as "delta lesions" were the earliest morphological alteration and since the plasma membrane was interrupted or absent in many portions. In agreement with this hypothesis, BthTX-II released peroxidase entrapped in negatively charged multilamellar liposomes and behaved as an amphiphilic protein in charge shift electrophoresis, an indication that its mechanism of action might be based on the interaction and disorganization of plasma membrane phospholipids. Membrane damage was followed by a complex series of morphological alterations in intracellular structures, most of which are probably related to an increase in cytosolic calcium levels. Myofilaments became hypercontracted into dense clumps which alternated with cellular spaces devoid of myofibrillar material. Later on, myofilaments changed to a hyaline appearance with a more uniform distribution. Mitochondria were drastically affected, showing high amplitude swelling, vesiculation of cristae, formation of flocculent densities, and membrane disruption. By 24 hr, abundant polymorphonuclear leucocytes and macrophages were observed in the interstitial space as well as inside necrotic fibers. Muscle regeneration proceeded normally, as abundant myotubes and regenerating myofibers were observed 7 days after BthTX-II injection. By 28 days regenerating fibers had a diameter similar to that of adult muscle fibers, although they presented two distinctive features: central location of nuclei and some fiber splitting. This good regenerative response may be explained by the observation that BthTX-II does not affect blood vessels, nerves, or basal laminae.

Isolation of basic myotoxins from Bothrops moojeni and Bothrops atrox snake venoms

Three myotoxins, one from the venom of Bothrops atrox and two from the venom of B. moojeni, were isolated by ion-exchange chromatography on CM-Sephadex C-25. The three toxins are basic proteins with an estimated mol. wt of about 13,500, and similar amino acid compositions. When injected into the gastrocnemius muscle of mice, the three toxins induce drastic myonecrosis of rapid onset, as judged by histological observation and quantitation of plasma creatine kinase levels. B. atrox myotoxin also has phosphlipase A2 and anticoagulant activities, whereas B. moojeni myotoxins I and II lack these effects. The three toxins are antigenically similar to each other, and to previously isolated myotoxins I and II from the venom of B. asper, when tested by gel immunodiffusion against rabbit antiserum to B. asper myotoxin I. Two monoclonal antibodies against B. asper myotoxins were tested against the newly purified proteins. MAb-3 recognizes all of them, whereas MAb-4 recognizes only B. atrox myotoxin, by enzyme-immunoassay. B. atrox and B. moojeni myotoxins can be tentatively classified within a group of myotoxins having phospholipase A2 structure present in Bothrops venoms.