Induction of micronuclei by lambda-cyhalothrin in Wistar rat bone marrow and gut epithelial cells.

We have investigated the genotoxicity of lambda-cyhalothrin (LCT) (CAS registry No. 91465-08-06), a pyrethroid insecticide, in bone marrow cells and in colonic crypt epithelial cells of groups of four rats per dose treated in vivo by gavage at doses of 0.8, 3.06 and 6.12 mg/kg body weight (body wt). We measured genotoxicity using the micronucleus (MN) assay, scoring 2000 polychromatic erythrocytes (PCEs) per animal for bone marrow and 1000 colonic crypt epithelial cells per animal for the colon. We assessed cytotoxicity in bone marrow by calculating the ratio of PCEs to normochromatic erythrocytes, and in the colonic crypt epithelium by observing the frequency of binucleate cells and the mitotic index in 1000 cells. Apoptosis in colonic crypt epithelial cells was measured by observing the frequency of karyorrhexis and karyolysis in 1000 cells. We found that LCT induced a statistically significant dose-related increase in MN formation in the bone marrow and the colonic crypt. The colonic epithelium was more sensitive to the clastogenic effects of LCT than the bone marrow as judged by the significantly higher frequencies of MN in the colon than in the bone marrow at doses of 3.06 and 6.12 mg/kg body wt.