Loxoscelism or necrotic arachnidism are terms used to describe lesions and
reactions induced by bites (envenomation) from spiders of the genus Loxosce
les. Envenomation has been reported to provoke dermonecrosis and haemorrhag
e at the bite site and haemolysis, disseminated intravascular coagulation a
nd renal failure. The purpose of this work was to study the effect of the v
enom of the brown spider Loxosceles intermedia on basement membrane structu
res and on its major constituent molecules. Light microscopy observations s
howed that L. intermedia venom obtained through electric shock, which repro
duces two major signals of Loxoscelism in the laboratory, exhibits activity
toward basement membrane structures in mouse Engelbreth-Holm-Swarm (EHS) s
arcoma. Basement degradation was seen by a reduced periodic acid-Schiff (PA
S) and alcian blue staining as well as by a reduced immunostaining for lami
nin when compared to control experiments. Electron microscopy studies confi
rmed the above results, showing the action of the venom on EHS-basement mem
branes and demonstrating that these tissue structures are susceptible to th
e venom. Using purified components of the basement membrane, we determined
through SDS-PAGE and agarose gel that the venom is not active toward lamini
n or type IV collagen, but is capable of cleaving entactin and endothelial
heparan sulphate proteoglycan. In addition, when EHS tissue was incubated w
ith venom we detected a release of laminin into the supernatant, corroborat
ing the occurrence of some basement membrane disruption. The venom-degradin
g effect on entactin was blocked by 1,10-phenanthroline, but not by other p
rotease inhibitors such as PMSF, NEM or pepstatin-A. By using light microsc
opy associated with PAS staining we were able to identify that 1,10-phenant
hroline also inhibits EHS-basement membrane disruption evoked by venom, cor
roborating that a metalloprotease of venom is involved in these effects. De
gradation of these extracellular matrix molecules and the observed suscepti
bility of the basement membrane could lead to loss of vessel and glomerular
integrity, resulting in haemorrhage and renal problems after envenomation.