ABSTRACT
The standard C3H/10T1/2 clone 8 (C3H/10T1/2 CL8) cell transformation assay was tested for its ability to identify a variety of polycyclic hydrocarbons and alkylating agents. Dose-dependent morphologic transformation occurred with benzo[a]pyrene (BaP), 3-methylcholanthrene (MCA), 7,12-dimethylbenz[a]anthracene, BaP-7,8-dihydroxy-7,8-dihydrodiol (BaP-7,8-diol), as well as with the relatively weak in vivo carcinogen benzo[e]pyrene. Dibenz[a,h]anthracene yielded a relatively weak response, whereas anthracene and phenanthrene were negative. In contrast, treatment of C3H/10T1/2 CL8 cells with two directly acting alkylating agents, N-nitroso-N-methylnitroguanidine (MNNG) and styrene oxide, gave no transformation, whereas a third alkylating agent, ethyl methanesulfonate (EMS), gave a weak response. Treatment with MCA (2.5 micrograms/ml) yielded a reproducible positive response and, therefore, served as a positive control for routine use of the C3H/10T1/2 CL8 assay. When cells treated with the hydrocarbons BaP, BaP-7,8-diol, or MCA were analyzed for nonspecific DNA damage (single-strand breaks or alkaline-labile sites) by alkaline elution techniques, little if any DNA damage was observed. In contrast, the alkylating agents MNNG, styrene oxide, and EMS yielded substantial numbers of single-strand breaks.
Subject(s)
Alkylating Agents/toxicity , Cell Survival/drug effects , Cell Transformation, Neoplastic/chemically induced , Drug Evaluation, Preclinical/methods , Polycyclic Compounds/toxicity , Animals , Benzo(a)pyrene , Benzopyrenes/toxicity , Clone Cells , DNA Repair , Ethyl Methanesulfonate/toxicity , Methylcholanthrene/toxicity , Methylnitronitrosoguanidine/toxicity , MiceABSTRACT
Soil-applied imidacloprid exhibits exceptional efficacy as a systemic insecticide against the Colorado potato beetle, Leptinotarsa decemlineata (Say). An uneven distribution of the chemical within potato plants could result in differential concentrations, which may allow for discrimination between genotypes of varying susceptibility. In this study, susceptible and tolerant larvae were fed leaves from the lower, middle, and upper canopy of treated and untreated plants to characterize within-plant distribution of imidacloprid at 4, 6, 8, 10, 12, and 14 wk after planting. Significant differences in larval mortality and development indicated that the concentration of imidacloprid was unevenly distributed in the potato foliage during 6-14 wk after planting. The concentration of imidacloprid was lowest in the younger tissues of the upper leaves and highest in the older, lower leaves. At 6 wk, a time when the postdiapause beetles are colonizing potato fields, the lower concentration in upper leaves was toxic to susceptible larvae but did not kill a substantial portion of the tolerant larvae. Results suggest that higher concentrations of imidacloprid in the lower canopy leaves may act as a toxic barrier to colonizing susceptible beetles but may allow more tolerant individuals to reach the upper canopy with lower concentrations. Possible scenarios of how different concentrations of the systemic insecticide could influence the rate of resistance development are discussed.