CYP1/2 Activation and Glutathione-dependent Cytotoxicity of Four Pesticides in Hep G2 and Fa32 Cells

1-Aminobenzotriazole: A Mechanism-Based Cytochrome P450 Inhibitor and Probe of Cytochrome P450 Biology

1-Aminobenzotriazole (1-ABT) is a pan-specific, mechanism-based inactivator of the xenobiotic metabolizing forms of cytochrome P450 in animals, plants, insects, and microorganisms. It has been widely used to investigate the biological roles of cytochrome P450 enzymes, their participation in the metabolism of both endobiotics and xenobiotics, and their contributions to the metabolism-dependent toxicity of drugs and chemicals. This review is a comprehensive evaluation of the chemistry, discovery, and use of 1-aminobenzotriazole in these contexts from its introduction in 1981 to the present.

Potential of an in vitro toolbox combined with exposure data as a first step for the risk assessment of dietary chemical contaminants

In vitro risk assessment of dietary contaminants has become a priority in human food safety. This paper proposes an in vitro approach associating different complementary tools in an original toolbox and aims to improve the assessment of the toxicological impact of dietary contaminants at realistic human exposure levels, with a special focus on the intestinal compartment. The system is based on the use of four complementary cellular tools, namely stress gene induction in transgenic strains of Escherichia coli, modulation of the activity of key biotransformation enzymes (cytochrome P-450 (CYP) 1A1 and 3A4) in a human intestinal cell line, and activation of aryl hydrocarbon receptor (AhR) and oestrogenic receptor (ER)-dependent genes in agonistic and antagonistic assays with luciferase reporter cells. It was applied to four chosen model molecules: ochratoxin A (OTA) and deoxynivalenol (DON), two common food-borne mycotoxins, and imazalil (IMA) and benomyl (BEN), two fungicides widely occurring in foodstuffs. All these assays were performed at or around a realistic intestinal concentration, determined through a deterministic approach based on the calculation of a theoretical maximum daily intake (TMDI). Using the four model molecules, it is clearly highlighted that induction of CYP1A1 activity and inhibition of CYP3A4 activity occurred in Caco-2 cells at a realistic intestinal concentration of IMA. Furthermore, some bacterial stress genes were induced in a range of realistic concentrations, following exposure to DON and IMA. In addition, BEN clearly provoked an ER agonistic activity in a human oestrogen sensitive reporter cell line. All these results are in accordance with the literature, suggesting that the in vitro toolbox constitutes an interesting approach in order to obtain a first 'fingerprint' of dietary contaminants at realistic human exposure for further risk assessment.

Methyl Parathion-Induced Changes in Free and Protein-Bound SH Levels in Rat Tissues

The main objective of this study was to investigate the changes in free and protein-bound SH contents in methyl parathion-exposed rat tissues. The free and protein-bound SH levels are usually affected and depleted by oxidative stress-inducing agents. Results would indicate if methyl parathion toxicity partly results from depletion of sulfhydryl content of tissues. Six-week-old male Wistar albino rats were used in this study. Following exposure to methyl parathion for 3 months, the liver, the brain, and the kidney tissues were removed from the rats. The free and protein-bound SH contents were determined in these tissues. In addition, plasma lactate dehydrogenase levels were determined. Our results showed that methyl parathion exposure significantly lowers the free and protein-bound SH levels in rat tissues. However, lactate dehydrogenase activity in the blood plasma did not display any differences compared to the control group. The free SH concentrations in the control rat liver, brain, and kidney tissues were 3.78 +/- 0.1 mumol/100 mg tissue, 1.56 +/- 0.08 mumol/100 mg tissue, and 2.16 +/- 0.08 mumol/100 mg tissue, respectively, whereas the free SH concentrations in rats exposed to methyl parathion were determined as 0.536 +/- 0.1 mumol/100 mg tissue in the liver, 1.06 +/- 0.1 mumol/100 mg tissue in the brain, and 0.108 +/- 0.03 mumol/100 mg tissue in the kidney. The protein-bound SH concentrations in the liver and in the kidney in rats exposed to methyl parathion displayed a significant decrease also. However, the protein-bound SH level in the brain did not change significantly. These results indicate that methyl parathion exposure partially depletes the free and protein-bound SH levels. Thus, it was concluded that methyl parathion toxicity may partly result from oxidative stress.