Characterization of 7-ethoxycoumarin-O-deethylase from malathion resistant and susceptible strains of Drosophila melanogaster

The expression of insecticide resistance-related cytochrome P450 forms is regulated by molting hormone in Drosophila melanogaster

The expression and enzymatic activities of insecticide resistance-related cytochrome P450B are increased by the treatment with 20-hydroxyecdysone (20HE) in D. melanogaster Oregon R flies. We have explored the role of this hormone in the maintenance of P450B basal expression. Arrest of ecdysone synthesis led to a decrease in CYP6A2 mRNA level, as well as in P450B expression and activities. This effect occurred both in insecticide susceptible (ecd1) and resistant (IRED) strains carrying the temperature-sensitive ecd mutation. The role of the 20HE in the regulation of cytochrome P450-mediated insecticide resistance has been proposed.

Inducibility of various cytochrome P450 isozymes by phenobarbital and some other xenobiotics in Drosophila melanogaster

The inducibility of cytochrome P450 isozymes has been investigated in the Drosophila melanogaster insecticide susceptible (Oregon R) and insecticide resistant (91R) strains. Both the level and induction kinetics of 7-ethoxycoumarin O-deethylase activity were stimulated by phenobarbital (PB) to a lower extent than that of aryl hydrocarbon hydroxylase in the Oregon R strain. The basal level of the cytochrome P450-linked activities in insecticide resistant flies was higher than that noted in susceptible ones. However, treatment with PB has increased levels of 7-ethoxycoumarin O-deethylase and aryl hydrocarbon hydroxylase activities more in susceptible flies than in resistant ones. In contrast to PB, the polycyclic aromatic hydrocarbon benzo[a]pyrene induced both activities in 91R flies to a greater extent than in Oregon R ones. The potent PB-like inducer in mice but not in rats 1.4-bis[2-(dichloropyridyloxy)]-benzene failed to induce the cytochrome P450 system in D. melanogaster, when triphenyldioxane (PB-like inducer in rats but not in mice) markedly affected this system in a PB-like manner. The SDS-PAGE followed by immunoblotting analysis using monoclonal antibodies 13-2e and 8-1d have shown that the level of the 56,000 and 54,000 Da insecticide resistance-related forms has increased in the susceptible strain by PB and some other PB like inducers. The relationship between these isozymes appearance and 7-ethoxycoumarin O-deethylase activity has been discussed.

The effect of the cytochrome P-450 system inducers on the development of Drosophila melanogaster

D. melanogaster development was markedly retarded and its survival decreased by larvae treatment with compounds being strong inducers of the cytochrome P-450 2B in mammals--phenobarbital (PB*), perfluorodecaline (PFD), transtilbene oxide (TSO), and triphenyldioxane (TPD). At the same time, the weak inducer hexobarbital or the selective cytochrome P-450 inducer in mice but not in rats 1,4-bis[2-(dichloropyridyl-oxy)]-benzene (DPB) did not affect the larvae development. The cytochrome P-450 1A1 inducers benzo(a)anthracene (BA) and beta-naphtoflavone (BNF) were also not effective. The toxicity of phenobarbital was shown to be decreased by the cytochrome P-450 inhibitor piperonyl butoxide by adding 20-hydroxyecdysone or by treatment with aminophylline--the indirect enhancer of ecdysone production in the larval prothoracic gland. The hypothesis of the moulting hormone degradation as the cause of elevated larvae mortality resulting from the induced high mixed function oxidase activity has been discussed.

Laboratory colonization has not reduced constitutive or induced polysubstrate monooxygenase activity in velvetbean caterpillars

We evaluated whether velvetbean caterpillars (Anticarsia gemmatalis) from a laboratory colony had reduced constitutive (basal) and/or induced activities of their polysubstrate monooxygenase (PSMO) detoxification enzyme system as a result of long-term rearing (> 100 generations) on artificial diet without introduction of field-collected individuals. Larvae from the laboratory colony and those from a recently collected field strain were fed either a standard artificial diet (control), one containing the inducing allelochemical, flavone, or foliage ofIndigofera hirsuta (a host plant of this species), and their midgut PSMO activity was assessed by measuring the in vitro rate of aldrin epoxidation. Compared with the field-strain larvae, caterpillars from the laboratory colony had 1.9-fold greater constitutive activity (standard artificial diet) and 2.3-fold greater induced activity (flavone-treated diet). In addition, the magnitude of induction was somewhat greater for the laboratory-colony larvae (induced activity was 2.0-fold greater than constitutive activity) compared with those from the field-strain (1.6-fold). In contrast, no difference in strain activity was found when larvae were fedI. hirsuta foliage. The lower PSMO activity of the field-strain larvae when fed artificial diet may have been caused by their reduced feeding and growth performance compared with laboratory-colony larvae, and it may explain their greater sensitivity to allelochemicals incorporated in the artificial diet, as we found previously. The results of this study indicate that long-term rearing of theA. gemmatalis laboratory colony on artificial diet, without the introduction of field individuals, apparently has not selected for low constitutive activity or decreased inducibility of PSMO, and thus these larvae provide a suitable model for studying xenobiotic detoxication. In addition, they suggest that using an artificial diet to evaluate resistance to pesticides or other xenobiotics in fieldcollected insects, as is frequently done, may underestimate the level of resistance if the diet, through various causes, reduces the activity of detoxification enzymes contributing to the resistance.