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Contact with Lonomia achelous caterpillars venom induces a severe bleeding syndrome in humans. A constant finding in all reported cases is a marked decrease of blood coagulation factor XIII (FXIII), which has been attributed to the presence of a proteolytic enzyme, isolated and named Lonomin V, in the hemolymph and hair secretion. In this study, the effect of Lonomin V on transglutaminase activity from human plasma, rabbit plasma, and platelet FXIII was analyzed. The decrease of activity was more pronounced in platelet (A2) when compared with rabbit plasma (AB) and human plasma FXIII (A2B2). This finding might be explained by the differences in FXIII molecular structure. In addition, platelet FXIII molecule was degraded by Lonomin to several fragments of low molecular mass. Lonomin V was stable over a wide range of pH (6-8.5) and temperatures of -70 degrees C, -20 degrees C and between 4 to 24 degrees C, with a progressive decrease at 37 degrees C and total inactivation at 60 degrees C after 2 hours incubation. Diisopropyl fluoro-phosphate, phenylmethylsulfonyl fluoride, tosyl-l-lysine chloromethyl ketone, and iodoacetamide abolished the effect of Lonomin V on FXIII; in contrast dithiothreitol and EDTA-Na enhance the activity. We concluded that Lonomin V is a serine proteinase with a free Cys essential for the enzymatic activity. Due to its proteolytic activity on FXIII, with concomitant impairment of fibrin cross-linking, Lonomin V might be useful in association with thrombolytic drugs for preventing rethrombosis.

Lonomia achelous caterpillar venom (LACV) causes a severe bleeding diathesis in humans. A constant finding in these cases is a profound depression of blood clotting Factor XIII (FXIII) activity. The molecular mechanisms by which LONOMIN V (a chromatographically purified fraction from LACV) alters the FXIII complex is the subject of the present study. Incubation of human purified FXIII with Lonomin V shows that both the zymogen and the activated forms of FXIII were proteolytically degraded, with the generation of peptidic fragments of low molecular weight. Both the A and B subunits of FXIII were degraded in a progressive, dose dependent manner. The B subunit was more resistant to the action of Lonomin V, requiring higher concentrations in order to achieve complete degradation. On the basis of these findings we postulate that the proteolysis of FXIII in vivo is one of the pathophysiological factors behind this bleeding syndrome.

Lonomia Achelous Caterpillar Venom (LACV) causes a severe acquired bleeding diathesis in exposed persons. The condition is characterized by prolonged bleeding from superficial wounds and mucous membranes. Intracranial or intra-abdominal hemorrhage is a common and often fatal complication. A constant finding in these cases is a profound decrease of clotting Factor XIII (FXIII) activity. In the present study, the effects of LACV on plasmatic and purified human FXIII has been evaluated. The results show that native LACV and one of its chromatographically purified fractions (termed FIID) produce a dose dependent decrease of FXIII activity accompanied with an impairment of fibrin(ogen) crosslinking. We conclude that the inactivation of FXIII by fraction FIID (which will be named Lonomin V), is one of the principal patho-physiological mechanisms behind the acquired bleeding diathesis seen in these cases.