Lonomia obliqua Caterpillar Spicules Trigger Human Blood Coagulation via Activation of Factor X and Prothrombin

Abstract

SummaryIn southern Brazil, envenomation by larvae of the moth Lonomia obliqua (Walker) may result in blood clotting factor depletion, leading to disseminated intravascular coagulation with subsequent haemorrhage and acute renal failure which may prove fatal. We have examined the effect of a crude extract of spicules from these caterpillars on in vitro hemostasis. The extract alone did not aggregate platelets and had no detectable effect on purified fibrinogen, suggesting that extract induces clot formation by triggering activation of the clotting cascade. In agreement with the presence of thrombin-mediated activity, hirudin prevented clot formation. The extract was found to activate both prothrombin and factor X, suggesting that the depletion of blood clotting factors results from the steady activation of factor X and prothrombin. Heating and diisopropylfluorophosphate abolished the procoagulant activity of the extract, indicating that the active component involved is a protein that may belong to the serine protease family of enzymes. The ability of hirudin to inhibit this coagulant activity suggests that this inhibitor could be beneficial in the treatment of patients envenomed by L. obliqua caterpillars.

A catalog for the transcripts from the venomous structures of the caterpillar Lonomia obliqua: Identification of the proteins potentially involved in the coagulation disorder and hemorrhagic syndrome

“…A cladogram for LOqua-SP1 and these serine proteases is shown in Figure 3b, available for download and in the Supplemental Data. Consistent with a pro-hemostatic function for these sequences, previous studies have described a prothrombin activator from bristle extract of L. obliqua (Donato et al, 1998). Cloning and expression of LOqua-SP1 may help to elucidate its substrate specificity and role in envenomation.…”

“…The coagulation disorder presented by these patients appears to be related to the action of many caterpillar toxins acting in a redundant manner on the hemostatic system. Accordingly, molecules that activate factor X and prothrombin (Donato et al, 1998) and likely coded by sequences such as LOqua-SP1 and LOqua-SP6, among others, may play an important role in envenomation. The action of these enzymes leads ultimately to thrombin formation that, among other effects, induces platelet aggregation and fibrin formation.…”

“…A diagram for the potential targets of L. obliqua toxins (section 3.6). "L. obliqua FXactivator" and "L. obliqua prothrombin-activator" acts on Factor X (FX) and prothrombin, respectively, leading ultimately to thrombin generation and fibrin formation (Donato et al, 1998). Fibrin is cross-linked by FXIIIa in a thrombin-dependent manner, and is subsequently degraded by plasmin with D-dimers formation (Williams, 1998).…”

“…In the latter case, the insect's cuticle is broken and many secretions, including hemolymph, penetrate the human skin and enter the circulation (Veiga et al, 2001). While some toxic principles are found in bristle extract, others are present in the hemolymph of L. obliqua (Donato et al, 1998;Veiga et al, 2003). Some of the active principles produced by Lonomia sp.…”

“…Some of the active principles produced by Lonomia sp. that interfere with the hemostatic system have been characterized: fibrinolytic proteases in the hemolymph of L. achelous (Amarant et al, 1991), prothrombin or factor X activators in L. obliqua bristle (Donato et al, 1998) and α-fibrinogenases found in both bristles and in a secretion obtained after freezing L. obliqua caterpillars (Veiga et al, 2003;Pinto et al, 2004). Other active compounds such as phospholipases were also described in Lonomia sp.…”