Abstract
To clarify the mechanism of oral toxicity of ricin, the interaction of ricin with the epithelial cells isolated from rat small intstine was compared in vitro with those of other plant lectins by two different determinations, i.e., viability and cytotoxicity. After incubatino of the cells for 1h at 37°C with ricin, ricin B-chain, castor bean hemagglutinin (CBH), soybean agglutinin (SBA), wheat germ agglutinin (WGA), concanvalin A (Con A), and peanut agglutinin (PNA), respectively, followed by staining with tyrpan blue, ricin and ricin B-chain as well as CBH and SBA were found to have effectively reduced the number of viable cells. On the contrary, only ricin inhibited protein synthesis in the cells and the effect was blocked by D-galactose. Additional experiments employing [125I]-labeled ricin strongly suggested that ricin was first bound via its B-chain to the galactosyl residues on the cell surface followed by internalization into cells as the whole 62kDa molecule.These results infer first that ricin, as well as other lectins mentioned above, was able to reduced viability of the epithelial cells of rat small intestine by direct binding to the cell surface. The second effect, specific to ricin, was the inhibition of cellular protein synthesis.
