Effect of strain and diet upon constitutive and chemically induced activities of several xenobiotic-metabolizing enzymes in rats

doi:10.1016/j.yrtph.2004.02.007

Regulatory Toxicology and Pharmacology

Volume 39, Issue 3, June 2004, Pages 325-333

https://doi.org/10.1016/j.yrtph.2004.02.007 Get rights and content

Abstract

The response of animals in toxicity studies reflects a complex interaction of a number of variables, some intrinsic to a particular study design and others resulting from the treatment itself. The influences of strain and diet upon constitutive and benzo(a)pyrene (B(a)P) induced activities of several hepatic Phase I and II enzymes were studied in a multifactoral design. Male and female CDF and Crl:CD rats were fed a standard rodent diet ad libitum, a 75% of ad libitum restricted feeding regimen or a phytoestrogen-free diet for approximately 3 weeks. During the last five days of the study, rats were administered either corn oil (vehicle) or 15 mg/kg/day B(a)P via oral gavage. The constitutive activities of hepatic CYP1A1, CYP1A2, CYP2B1/2, and mixed isoforms of UDP-glucuronosyl transferase, sulfotransferase, and glutathione-S-transferase varied significantly by feeding regimen and strain. Responses to B(a)P administration were also observed to be influenced by diet and strain in a manner similar to that observed for constitutive activities. These findings point out the potentially significant interactions of relatively commonly encountered variables that may affect results of hazard testing, especially when employing near metabolically saturating dosages of test chemicals.

Introduction

The response of animals to administered chemicals in toxicity studies reflects a complex interaction of a number of variables, some intrinsic to a particular study design and others resulting from the treatment itself. Most studies on the impact of experimental variables upon functional changes in key enzymes and genotoxic or pathological endpoints reported to-date have been designed to evaluate effects of a single variable under tightly controlled conditions. However, hazard identification studies often involve a more complex and less controlled scenario. Commonly encountered variables include the use of different strains, dietary regimens, reduced feed intake, and/or primary and secondary effects of test materials or metabolites. It has long been accepted that these factors may affect the metabolism and pharmacokinetics and subsequent adaptation to and toxicity of administered test materials (Bidlack et al., 1986; Campbell and Hayes, 1975; Conney, 1967; Ioannides, 1999; Ronis and Ingelman-Sundberg, 1999). In particular, alterations in the activities of several so-called Phases I and II drug metabolizing enzymes have the potential to alter the toxicity of a wide range of xenobiotics. The numerous mixed-function oxygenases (MFO) comprising most of the Phase I enzymes metabolize and are often induced by a number of chemicals. The conjugative enzymes that comprise most of the Phase II enzymes are critical to the detoxification of many xenobiotics but also the activation of others, may also undergo at least limited substrate-induced increases in activity. The net effects of these changes are believed to dictate the body burden and to a large extent subsequent systemic toxicity of test materials undergoing hazard evaluation.

The objective of this study was to evaluate the influences of strain and diet upon constitutive and benzo(a)pyrene (B(a)P) induced activities of several hepatic Phases I and II enzymes in a multifactoral study design. This study was undertaken to complement gene expression profiles utilizing the same groups of animals (Kan et al., 2003).

Section snippets

Test materials

Benzo(a)pyrene (97% purity) and all biochemicals used in enzyme assays were purchased from Sigma Chemical (St. Louis, Missouri).

Animals and in-life data collection

Male and female CDF (Fischer 344)/CrlBR and Crl:CD (SD)BR rats were purchased from Charles River Laboratories (Raleigh, North Carolina and Portage, Michigan, respectively). Animals were evaluated by a laboratory veterinarian upon arrival at the laboratory,

Body and liver weights

Groups of rats ingesting approximately 75% of an ad libitum feed regimen (FR) had statistically identified lower body weights than either ad libitum fed groups (AL or PEF) from test day 2 to 3. Body weights of FR group animals were approximately 15–20% lower by the midpoint in the study (Figs. 1A and B). Administration of B(a)P had no effect upon the body weights for any group of rats. Similar results were obtained for nonfasted, terminal body weights (data not presented).

When averaged across

Discussion

The use of a multifactoral design and statistical evaluation employed in the present study provided a means of investigating the impact of multiple variables potentially encountered in the hazard evaluation of chemicals upon several xenobiotic metabolizing enzymes. Variations in genome expression patterns for the same experimental groups examined in the present study have been presented separately by Kan et al. (2003). As noted, constitutive activity data were examined statistically relative to

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Effect of strain and diet upon constitutive and chemically induced activities of several xenobiotic-metabolizing enzymes in rats

Abstract

Introduction

Section snippets

Test materials

Animals and in-life data collection

Body and liver weights

Discussion

J. Am. Diet Assoc.

Toxicol. Lett.

Methods Enzymol.

Fundam. Appl. Toxicol.

Anal. Biochem.

Mech. Aging Dev.

Mech. Aging Dev.

Mutat. Res.

Toxicol. Appl. Pharmacol.

Mutat. Res.

Continuous fluorometric assay of phenol sulfotransferase

Anal. Biochem.

Nutritional parameters that alter hepatic drug metabolism, conjugation, and toxicity

Fed. Proc.

Ethoxy-, pentoxy- and benzyloxypenoxazomes and homologues: a series of substrates to distinguish between different induced cytochromes P-450

Biochem. Pharmacol.

Role of nutrition in the drug-metabolizing enzyme system

Pharmacol. Rev.

Induction of microsomal enzymes by foreign chemicals and carcinogenesis by polycyclic aromatic hydrocarbons: G.A.A. Clowes Memorial Lecture

Cancer Res.