Role of PLA2 activity in the hemolytic and histopathological effects induced by the venom of the „fire coral“ Millepora complanata
The „fire coral“ Millepora complanata, a regular resident of coral reefs in the Mexican Caribbean, produces severe skin lesions in humans as a result of the release of toxins from their nematocysts. At present, very little is known regarding the process of envenomation due to Millepora's sting, the proper treatment, the structure of the toxins and their mechanism of action. In this study we report the purification of a protein with hemolytic and PLA2 activities from the extract of this hydrocoral. In addition, the systemic toxic effects and histopathological changes induced by the extract in mice are presented. Intravenous administration of the extract, at the highest dose tested (5.33µg protein/g), produced convulsions and death within 1min (LD50=4.62µg protein/g). Histologically, no abnormality was observed in brain and liver tissue samples. However, kidney and lung sections showed infiltration of erythrocytes and proteinaceous material within glomerular apparatus and bronchial alveoli. M. complanata extract had a PLA2 activity of 7.23±0.1 mmol min-1 mg-1, but it did not display protease activity. Both, enzymatic activity and histopathological changes were completely eliminated after incubation of the extract in denaturing conditions. Unexpectedly, the denatured extract conserved its lethal effect. Analysis of the extract, using ion exchange and size-exclusion chromatography, afforded a fraction containing a 28 kDa protein, which displays PLA2 and hemolytic activities. Our results suggest that the M. complanata extract contains hemolysins with PLA2 activity that might be responsible for the histopathological changes observed in kidney and lung. Additionally, this extract contains other unidentified thermostable toxins that have lethal effects in mice.
Acknowledgements: Posgrado en Ciencias del Mar y Limnología- UNAM, CONACYT (Grant SEP-2004-C01–47432 to A. Rojas).