Snake envenomation and protective natural endogenous proteins: a mini review of the recent developments (1991-1997).

The properties of several factors--antihaemorrhagic, antineurotoxic, antimyotoxic--isolated from the blood serum or plasma of different animals are described with more emphasis placed on the structural differences and similarities among the factors of the snake (Trimeresurus flavoviridis) and mammals (Didelphis marsupials and Herpestes edwardsii). Classification of antihaemorrhagic factors of snake and mammals according to structural homologies, and their effectiveness in neutralizing venom haemorrhagic activities in comparison with that of commercial antivenoms are also reviewed. The antineurotoxic factors isolated so far from the sera of viperid (Vipera palestinae, Daboia r. siamensis), crotalid (Crotalus d. terrificus, T. flavoviridis, Agkistrodon b. siniticus) and elapid (Naja naja atra) snakes, as reviewed, are inhibitors of phospholipase A2, and the amino acid sequences, particularly of those inhibitors from the sera of crotalid snakes, do not share significant sequence homology even within the same family Crotalidae. The amino acid sequences of antineurotoxic factors of the snake (Crotalus d. terrificus) also are not homologous to those of the antihaemorrhagic factors from the blood of the snake (T. flavoviridis) or mammals (Didelphis virginiana, Herpestes edwardsii). The mechanism of action of antihaemorrhagic and antineurotoxic factors is briefly discussed as well as the possibility that crotalids and viperids might possess both of those endogenous neutralizing factors in their blood. Some recent findings on the antimyotoxic factors from the snake serum or plasma with inhibition properties against PLA2 activity and myotoxicity of venoms or toxins are also shortly reviewed.