Animal toxins and the kidney.

Envenomation or poisoning by toxins from animals poses an important health hazard in the tropics. Animal toxins are complex mixtures of proteins, peptides, enzymes and chemicals. These toxins exert their effects through modulation of ion channels and receptors, and via direct enzyme action. Depolarization or hyperpolarization of ion channels--caused by most marine toxins, and some snake and insect venoms--results in neuromuscular symptoms that can be associated with hemodynamic changes. Toxin enzymes, especially proteases and phospholipase A2, initiate inflammatory processes that involve the generation of proinflammatory cytokines and vasoactive mediators, resulting in systemic and renal hemodynamic alterations. Toxin enzymes also have direct effects on erythrocytes, myocytes, blood coagulation factors, vascular endothelium and epithelial cells. As a result, disseminated intravascular coagulation, bleeding diathesis, intravascular hemolysis and rhabdomyolysis are common after exposure to animal toxins. The renal manifestations of animal toxin envenomation, which are usually acute, result mainly from these enzymatic effects. All renal structures can be affected by animal toxins, and tubular necrosis is common. Acute kidney injury is attributed to decreased renal blood flow (associated with intravascular hemolysis or rhabdomyolysis), disseminated intravascular coagulation or direct tubular toxicity. Immunologic mechanisms have a minor role in the pathophysiology of nephropathy caused by animal toxins.