Insecticidal Cry toxins, which are derived from Bacillus thuringiensis, have been considered to be safe for mammals. However, the reason that the toxins do not affect the mammalian epithelium remains unconfirmed as of yet. In this study, we investigated in vitro whether Cry1Ab toxin, a Cry1 type toxin, has an affinity to the cellular brush border membrane vesicle (BBMV) of the mammalian intestinal cell, as well as whether the toxin affects the membrane potential in the cell, in comparison with the toxin effects on the silkworm midgut cell. We found that Cry1Ab toxin bound to the bovine and porcine BBMV but far more weakly than it did to the silkworm midgut BBMV. Furthermore, although the silkworm midgut cells developed severe membrane potential changes within one hour following the toxin treatment at a final concentration of 2μg/ml, no such membraneous changes were observed on the bovine and porcine intestinal cells. The present in vitro results suggest that, although Cry1Ab toxin may bind weakly or nonspecifically to certain BBMV components in the mammalian intestinal cell, it does not damage the cell's membrane integrity, thus exerting no subsequent adverse effects on the cell.
(Safety Evaluation Section, Department of Safety Research TEL +81-29-838-7823)
