The role of platelets in hemostasis and the effects of snake venom toxins on platelet function.

The human body has a set of physiological processes, known as hemostasis, which keeps the blood fluid and free of clots in normal vessels; in the case of vascular injury, this process induces the local formation of a hemostatic plug, preventing hemorrhage. The hemostatic system in humans presents complex physiological interactions that involve platelets, plasma proteins, endothelial and subendothelial structures. Disequilibrium in the regulatory mechanisms that control the growth and the size of the thrombus is one of the factors that favors the development of diseases related to vascular disorders such as myocardial infarction and stroke, which are among the leading causes of death in the western world. Interfering with platelet function is a strategy for the treatment of thrombotic diseases. Antiplatelet drugs are used mainly in cases related to arterial thrombosis and interfere in the formation of the platelet plug by different mechanisms. Aspirin (acetylsalicylic acid) is the oldest and most widely used antithrombotic drug. Although highly effective in most cases, aspirin has limitations compared to other drugs used in the treatment of homeostatic disorders. For this reason, research related to molecules that interfere with platelet aggregation are of great relevance. In this regard, snake venoms are known to contain a number of molecules that interfere with hemostasis, including platelet function. The mechanisms by which snake venom components inhibit or activate platelet aggregation are varied and can be used as tools for the diagnosis and the treatment of several hemostatic disorders. The aim of this review is to present the role of platelets in hemostasis and the mechanisms by which snake venom toxins interfere with platelet function.

Comparative analysis of local effects caused by Bothrops alternatus and Bothrops moojeni snake venoms: enzymatic contributions and inflammatory modulations.

Bothropic envenomation is characterised by severe local damage caused by the toxic action of venom components and aggravated by induced inflammation. In this comparative study, the local inflammatory effects caused by the venoms of Bothrops alternatus and Bothrops moojeni, two snakes of epidemiological importance in Brazil, were investigated. The toxic action of venom components induced by bothropic venom was also characterised. Herein, the oedema, hyperalgesia and myotoxicity induced by bothropic venom were monitored for various lengths of time after venom injection in experimental animals. The intensity of the local effects caused by B. moojeni venom is considerably more potent than B. alternatus venom. Our results also indicate that metalloproteases and phospholipases A2 have a central role in the local damage induced by bothropic venoms, but serine proteases also contribute to the effects of these venoms. Furthermore, we observed that specific anti-inflammatory drugs were able to considerably reduce the oedema, the pain and the muscle damage caused by both venoms. The inflammatory reaction induced by B. moojeni venom is mediated by eicosanoid action, histamine and nitric oxide, with significant participation of bradykinin on the hyperalgesic and myotoxic effects of this venom. These mediators also participate to inflammation caused by B. alternatus venom. However, the inefficient anti-inflammatory effects of some local modulation suggest that histamine, leukotrienes and nitric oxide have little role in the oedema or myotoxicity caused by B. alternatus venom.

Histological and ultrastructural analyses of muscle damage induced by a myotoxin isolated from Bothrops alternatus snake venom.

Muscular necrosis is a serious consequence of Bothrops snake bites that may lead to permanent loss of tissue or function. Myonecrosis may be due to injury to blood vessels, destabilization and/or rupture of plasma membrane, and inflammatory mechanisms triggered by different proteins from the snake venom. In this work we describe the isolation and partial functional characterization of a myotoxin from B. alternatus snake venom. The myotoxin was isolated by a combination of ion exchange and gel filtration chromatography and displayed a molecular weight of approximately 15,000, as estimated by SDS-PAGE under reducing conditions. In non-reducing conditions a protein band of approximately 25,000 was also observed, suggesting that its native form is a homodimer. The myotoxin induced myonecrosis, but had no proteolytic and phospholipase A2 activities. The myotoxic activity was assessed on the basis of the histological and ultrastructural alterations induced by the toxin in the gastrocnemius skeletal muscle of Swiss mice. The toxin led to a series of drastic degenerative events characterized by extensive cellular destruction, loss of the arrangements of skeletal fibers, intense infiltration of inflammatory cells, fatty degeneration and hemorrhage. Electron microscopy analyses revealed that the myotoxin caused cell swelling, mitochondrial alterations and dilation of the sarcoplasmic reticulum, but did not affect the integrity of the muscle cell membranes. The myonecrosis caused by this toxin was related to the perturbation in the membrane permeability, intracellular alterations and inflammatory reaction.