ABSTRACT
Aflatoxin B1 (AFB1) is a fungal toxin and contaminant that has been implicated in human liver carcinogenesis. In this study we evaluated the effect of a 65% of total calories from sucrose diet (HSD) for 90 days on hepatic cytochrome P450 (CYP450) and glutathione-S-transferase (GST) activity compared to rats maintained on standard lab chow (0% sucrose). There was a statistically significant increase in the number of S. typhimurium His+ revertants (p < 0.001) generated from the incubation of AFB1 with hepatic microsomes from rats fed a HSD. The HSD did not affect the total microsomal CYP450 content nor content of CYP450 1A2, 2B1, 2 isoforms which activate AFB1. Alkoxyresorufin O-dealkylase activity (MROD, PROD) of microsomes from animals fed HSD was decreased by 73% and 49%, respectively. MROD activity is linked to CYP 1A2 activity while PROD is linked to CYP 2B1,2 activity. Although the amount of CYP 3A was significantly decreased in rats fed a HSD, its activity, determined by the presence of the fluorometric metabolite 7-hydroxyquinidine, was unchanged. GST activity was significantly lower in the rats fed HSD.
Subject(s)
Aflatoxin B1/toxicity , Dietary Sucrose/administration & dosage , Food-Drug Interactions , Liver/drug effects , Mutagenesis/drug effects , Mutagens/toxicity , Aflatoxin B1/metabolism , Animals , Cytochrome P-450 Enzyme System/metabolism , Glutathione Transferase/metabolism , Isoenzymes , Liver/enzymology , Microsomes, Liver/drug effects , Microsomes, Liver/enzymology , Mutagens/metabolism , Rats , Rats, Inbred F344 , Salmonella typhimurium/drug effects , Salmonella typhimurium/geneticsABSTRACT
To assess the effect of dietary sucrose on liver cytochrome P450 1A content and activity, male F344 rat weanlings were randomized into two diet groups for a period of 90 days. One group was fed a diet containing 65% of total calories from sucrose (HSD) while the other was fed standard lab chow (0% sucrose). Microsomal fractions from each of 10 animals in each group were used in Western immunoblot, mutagenesis and 7-alkoxyresorufin-0-deethylase (AROD) assays. No statistically significant difference in the mean quantity of liver CYP 1A2 was detected by Western blot analysis, while a significant decrease in mean liver CYP 1A1 was observed in the rats fed the HSD. Liver microsomal-dependent mutagenesis of two heterocyclic amines (HCAs), 2-amino-3,8-dimethyl-imadazo[4,5-f]quinoxaline (MeIQx) and 2-amino-3-methyl-imidazo[4,5-f]quinoline (IQ), in Salminella typhimurium TA98 was decreased in animals on the HSD compared to those on the control diet by 33% (p < 0.001) and 25% (p < 0.001), respectively. In addition, rats on the HSD had significantly decreased ethoxyresorufin-0-deethylase (EROD) and methoxyresorufin-0-deethylase (MROD) activity over a range of substrate concentrations. These results show that a HSD alters hepatic CYP 1A content and activity and suggests that the metabolism of substrates for this P450 subfamily may be significantly altered.
Subject(s)
Carbolines/toxicity , Cytochrome P-450 CYP1A1/metabolism , Cytochrome P-450 CYP1A2/metabolism , Quinolines/toxicity , Quinoxalines/toxicity , Sucrose/pharmacology , Animals , Cytochrome P-450 Enzyme System/metabolism , Diet , Liver/drug effects , Liver/enzymology , Male , Mutagenicity Tests , Oxidoreductases/metabolism , Quinolines/antagonists & inhibitors , Quinoxalines/antagonists & inhibitors , Random Allocation , Rats , Rats, Inbred F344 , Sucrose/administration & dosageABSTRACT
The effect of sucrose on the induction of hepatic and peripheral insulin resistance is well-documented. Studies show that, although oral administration of glucose does not significantly decrease total hepatic microsomal cytochrome P450 content, it causes an increase in cytosolic protein and in microsomal phospholipid and fatty acid content. In this study we examined the effects of a chronic high sucrose diet (HSD) on liver enzyme activity. Male Fisher 344 weanling rats were randomly assigned to a control diet (0% sucrose by calories, n = 10) or a diet in which starch was replaced by sucrose (65% sucrose, by calories, n = 10) for 90 days. The effects of HSD on weight gain, liver weight, hepatic microsomal cytochrome P450 (CYP450) content and glutathione-S-transferase (GST) activity were measured and compared with those fed standard lab chow. A small but statistically significant decrease in body weight (g) was seen in the sucrose-fed rats after day 50. Liver GST activity (nmol/mg protein/min) at the end of 90 days was decreased in animals maintained on HSD compared to those on the control diet, (181.7 +/- 8.0, 234.7 +/- 5.5), respectively. The liver weight and total CYP450 content in the two diet groups were not significantly different. The ratios of liver weight to body weight at the end of 90 days suggested that the livers of the HSD-fed animals were larger per gram of body weight. In addition, rats on the HSD had significantly smaller amounts of liver CYP450 1A1 and 3A2 than the rats on the control diet. These results suggest that a HSD may alter the hepatic enzyme activity which may affect the metabolism of substrates for these enzyme systems.
