Toxicity of aflatoxin B1 to Helicoverpa zea and bioactivation by cytochrome P450 monooxygenases

Ren Sen L. Zeng, Guodong Niu, Zhimou Wen, Mary A. Schuler, May R. Berenbaum

Research output: Contribution to journalArticle

Abstract

Infestation of corn (Zea mays) by corn earworm (Helicoverpa zea) predisposes the plant to infection by Aspergillus fungi and concomitant contamination with the carcinogenic mycotoxin aflatoxin B1 (AFB1). Although effects of ingesting AFB1 are well documented in livestock and humans, the effects on insects that naturally encounter this mycotoxin are not as well defined. Toxicity of AFB1 to different stages of H. zea (first, third, and fifth instars) was evaluated with artificial diets containing varying concentrations. Although not acutely toxic at low concentrations (1-20 ng/g), AFB1 had significant chronic effects, including protracted development, increased mortality, decreased pupation rate, and reduced pupal weight. Sensitivity varied with developmental stage; whereas intermediate concentrations (200 ng/g) caused complete mortality in first instars, this same concentration had no detectable adverse effects on larvae encountering AFB1 in fifth instar. Fifth instars consuming AFB1 at higher concentrations (1 μg/g), however, displayed morphological deformities at pupation. That cytochrome P450 monooxygenases (P450s) are involved in the bioactivation of aflatoxin in this species is evidenced by the effects of piperonyl butoxide (PBO), a known P450 inhibitor, on toxicity; whereas no fourth instars pupated in the presence of 1 μg/g AFB1 in the diet, the presence of 0.1% PBO increased the pupation rate to 71.7%. Pupation rates of both fourth and fifth instars on diets containing 1 μg/g AFB1 also increased significantly in the presence of PBO. Effects of phenobarbital, a P450 inducer, on AFB1 toxicity were less dramatic than those of PBO. Collectively, these findings indicate that, as in many other vertebrates and invertebrates, toxicity of AFB1 to H. zea results from P450-mediated metabolic bioactivation.

Original languageEnglish (US)
Pages (from-to)1459-1471
Number of pages13
JournalJournal of Chemical Ecology
Volume32
Issue number7
DOIs
StatePublished - Dec 1 2006

Fingerprint

Aflatoxin B1
Helicoverpa zea
aflatoxin B1
Mixed Function Oxygenases
cytochrome P-450
Cytochrome P-450 Enzyme System
Zea mays
cytochrome
Toxicity
pupation
toxicity
Piperonyl Butoxide
piperonyl butoxide
instars
Nutrition
maize
Mycotoxins
diet
mortality
Diet

Keywords

  • Aflatoxin B1
  • Bioactivation
  • Cytochrome P450 monooxygenase
  • Helicoverpa zea
  • Mycotoxin
  • Piperonyl butoxide

ASJC Scopus subject areas

  • Ecology, Evolution, Behavior and Systematics
  • Biochemistry

Cite this

Toxicity of aflatoxin B1 to Helicoverpa zea and bioactivation by cytochrome P450 monooxygenases. / Zeng, Ren Sen L.; Niu, Guodong; Wen, Zhimou; Schuler, Mary A.; Berenbaum, May R.

In: Journal of Chemical Ecology, Vol. 32, No. 7, 01.12.2006, p. 1459-1471.

Research output: Contribution to journalArticle

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abstract = "Infestation of corn (Zea mays) by corn earworm (Helicoverpa zea) predisposes the plant to infection by Aspergillus fungi and concomitant contamination with the carcinogenic mycotoxin aflatoxin B1 (AFB1). Although effects of ingesting AFB1 are well documented in livestock and humans, the effects on insects that naturally encounter this mycotoxin are not as well defined. Toxicity of AFB1 to different stages of H. zea (first, third, and fifth instars) was evaluated with artificial diets containing varying concentrations. Although not acutely toxic at low concentrations (1-20 ng/g), AFB1 had significant chronic effects, including protracted development, increased mortality, decreased pupation rate, and reduced pupal weight. Sensitivity varied with developmental stage; whereas intermediate concentrations (200 ng/g) caused complete mortality in first instars, this same concentration had no detectable adverse effects on larvae encountering AFB1 in fifth instar. Fifth instars consuming AFB1 at higher concentrations (1 μg/g), however, displayed morphological deformities at pupation. That cytochrome P450 monooxygenases (P450s) are involved in the bioactivation of aflatoxin in this species is evidenced by the effects of piperonyl butoxide (PBO), a known P450 inhibitor, on toxicity; whereas no fourth instars pupated in the presence of 1 μg/g AFB1 in the diet, the presence of 0.1{\%} PBO increased the pupation rate to 71.7{\%}. Pupation rates of both fourth and fifth instars on diets containing 1 μg/g AFB1 also increased significantly in the presence of PBO. Effects of phenobarbital, a P450 inducer, on AFB1 toxicity were less dramatic than those of PBO. Collectively, these findings indicate that, as in many other vertebrates and invertebrates, toxicity of AFB1 to H. zea results from P450-mediated metabolic bioactivation.",
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