Use of differential DNA-repair host mediated assays to investigate the biotransformation of xenobiotics in Drosophila melanogaster. I. Genotoxic effects of nitrosamines.

A rapid differential DNA-repair assay procedure was developed to investigate the biotransformation of xenobiotics in Drosophila melanogaster in vivo. Indicator of genotoxic activity was a pair of streptomycin-dependent Escherichia coli strains differing vastly in DNA repair capacity (uvr+/rec+ vs. uvrB/recA). Prior to the experiments with test compounds, mixtures of the two strains were injected into the abdomina of untreated animal hosts (male Berlin-K flies) and the time-dependent recovery kinetics determined. Subsequently, different aliphatic and aromatic nitrosamines were tested. Solutions of the compounds were injected simultaneously with the indicator cells. Three hours later, the flies were killed, homogenized and the induction of (repairable) DNA damage determined by comparison of the survival rates of the two strains in single animals. Eight carcinogenic compounds (nitrosodiethylamine, NDEA; nitrosodimethylamine, NDMA; nitrosodi-npropylamine, NDPA; nitrosodiethanolamine, NDELA; nitrosomethylaniline, NMA; 4-methyl-nitrosopiperidine, MNPIP; nitrosopyrrolidine, NPYR; nitrosomorpholine, NMOR) and one whose tumorigenic activities are still controversially discussed (nitrosodiphenylamine, NDPhA) induced dose-dependent differential killing effects in the present system. One agent which has not been found carcinogenic in rodents (2.6-dimethyl-nitrosopiperidiine. NDMPIP) gave negative results. The ranking order of genotoxic activities of the nitrosamines found in Drosophila in vivo is in good agreement with those of carcinogenic potencies established on the basis of experiments with rats. The most pronounced exceptions are the rather weak response towards NMA and the stronger DNA damaging activity of NMPIP compared to NDMA. Phenobarbital (5-ethyl-5-phenyl-2,4,6-trioxohepatahydropyramidine) (PB) feeding of the flies resulted in an increase of the DNA damaging potencies of all nitrosamines tested. Substantial enhancement of the induction of DNA damage was however, restricted to NDEA, NPYR and NMOR, whereas with nitrosodiphenylamine (NDPhA), NDELA and NDMA only a moderate (less than 25%) increase of differential killing effects was found. In the case of the two latter compounds, these results might be due to the fact that enzymes other than the MFO are involved in their activation. Attempts to localize the formation and/or distribution of metabolites in the bodies of fruitflies by separation of the tagmata of chemically treated animals and determination of genotoxic effects in the different segments indicate that the most pronounced effects occur in the abdomina whereas in heads and thoraxes comparatively lower activities are detectable.