148 J BIOCHEM MOLECULAR TOXICOLOGY Volume 14, Number 3, 2000 The Influence of Diet on the Regional Distribution of Glutathione S-Transferase Activity in Channel Catfish Intestine Bernard K.-M. Gadagbui and Margaret O. James Department of Medicinal Chemistry, P.O. Box 100485, College of Pharmacy, University of Florida, Gainesville, FL 32610–0485. Tel: 352–846– 1952; Fax: 352–846–1972; E-mail: MOJAMES@UFL.EDU Received 25 June 1999; revised 7 September 1999; accepted 14 September 1999 ABSTRACT: There is evidence that glutathione con- jugates are the major metabolites formed following systemic uptake of carcinogenic contaminants from the intestine. The effect of commercial diet versus a semi- purified diet on the distribution of glutathione S-trans- ferase (GST) activity was examined in proximal, me- dial, and distal sections of catfish intestine. The bulk of GST activity with 1-chloro-2,4-dinitrobenzene, ethacrynic acid, and 3 H-benzo[a]pyrene-4,5-oxide, and the percent cytosolic protein cross-reacting with anti- catfish GST-p were in the more proximal segments and dropped off distally in the two diet groups. However, the total GST-p cross-reacting protein in the proximal section was significantly higher in fish fed a chow diet. Western blot analysis revealed p-class GST to be ex- pressed principally in the proximal intestine. Cytosol samples cross-reacted with antibodies to human GST- ,-l, and -p, but not -h, classes. Alpha-like GST iso- forms of MW 26,200 and 24,600, absent in sections from fish fed a purified diet, were differentially expressed only in the distal section of chow-fed fish. These re- sults indicate that diet significantly elicits regional dif- ferences in GST protein levels, that components of the commercial chow affect GST protein expression in the distal intestine, and that maintenance diet should be taken into consideration during dietary exposure stud- ies. @ 2000 John Wiley & Sons, Inc. J Biochem Toxicol 14:148–154, 2000 KEY WORDS: Glutathione S-Transferase; Channel Cat- fish; Intestine; Biomarkers; Diet INTRODUCTION The intestinal mucosa provides the first line of metabolic defense against dietary chemical contami- Correspondence to: Margaret O. James. Contract Grant Sponsor: National Institute of Environmental Health Sciences, National Institutes of Health. Contract Grant Number: ES-05781. Contract Grant Number: ES-07375. @ 2000 John Wiley & Sons, Inc. nants. However, its role in the first-pass biotransfor- mation of dietary xenobiotics is poorly understood. Al- though the capacity of the intestine for xenobiotic biotransformation is easily saturated, low concentra- tions of xenobiotics may be readily transformed in the intestine. Since environmental chemicals are usually presented in the diet at low levels, intestinal enzymes are likely to be important in their presystemic biotrans- formation. The few studies reported on dietary induc- tion in fish indicated increased expression of intestinal cytochrome P4501A (CYP1A) and its associated 7- ethoxyresorufin-O-deethylase (EROD) and aryl hydro- carbon hydroxylase (AHH) activities [1,2]. Studies by Clarke et al. [3] have shown that conjugating enzymes are not induced in intestine in response to intraperi- toneally injected polycyclic aromatic hydrocarbon (PAH) and polychlorinated biphenyl (PCB) while mon- ooxygenase activity is induced. Other investigators have also reported induction of intestinal monooxy- genase activity in mammals when PAHs were incor- porated in the diet, with minimal effects on intestinal conjugating activities, even when such activities were induced in the liver [4–6]. Kleinow and coworkers [7] provided evidence of intestinal formation and sys- temic uptake of potentially hazardous metabolites and detoxification products of BaP, and that glutathione conjugates were major metabolites. Although it is rec- ognized that chemicals may enter fish through the gills, the skin or gastrointestinal tract from water, sed- iments or contaminated food, studies with fish, when considered in natural settings, indicate food as an im- portant contaminant source [8–10]. Glutathione-S-transferases (GST, EC 2.5.1.18) are a group of cytosolic or microsomal enzymes that cata- lyze the conjugation of xenobiotics and endogenous molecules to glutathione. The predominant cytosolic enzymes are commonly classified as , l, p, s, or zeta [11–13]. The expression of certain GST isoenzymes has