(1/33) Effects of dietary oltipraz and ethoxyquin on aflatoxin B1 biotransformation in non-human primates.
Following aflatoxin B1 (AFB) exposure, rats readily develop liver tumors. However, treatment of rats with a variety of compounds, including the synthetic dithiolthione oltipraz and the antioxidant ethoxyquin, protects these rodents from AFB-induced hepatocarcinogenesis. Several epidemiological studies strongly suggest that AFB is also a causative agent of liver cancer in humans. However, relatively little is known about the efficacy of cancer chemoprevention in human and non-human primates. To this end, we examined the effects of chemopreventive agents on AFB metabolism in non-human primates. Hepatic aflatoxin B1 metabolism profiles of macaque (Macaca nemestrina) and marmoset (Callithrix jacchus) monkeys were determined and compared to humans. Quantitatively, the oxidative metabolism of this mycotoxin was similar in the three primate species. In contrast to macaques, both humans and marmosets lacked AFB-glutathione conjugating activity. It was concluded that marmosets resembled human AFB metabolism more closely than the macaques, and therefore, marmoset monkeys were chosen for this study. Eleven adult male marmosets were randomly assigned to three groups. Animals received the synthetic dithiolthione oltipraz, the antioxidant ethoxyquin, or vehicle only. In addition, two single doses of AFB were also administered orally before and after animals were treated with aforementioned compounds. Both oltipraz and ethoxyquin induced aflatoxin B1-glutathione conjugating activity in the livers of some but not all marmosets. In addition, 10 microM oltipraz inhibited cytochrome P450-mediated activation of AFB to the ultimate carcinogenic metabolite, aflatoxin B1-8,9-epoxide, in vitro, up to 51%. Furthermore, animals treated in vivo with oltipraz, but not ethoxyquin, exhibited a significant reduction (53% average) in AFB-DNA adduct formation relative to the control animals (p < 0.05). Together, our data suggest that chemoprevention is also effective in primates; however, most likely to a lesser degree than in rodents. (+info)
(2/33) Regulation of rat glutamate-cysteine ligase (gamma-glutamylcysteine synthetase) subunits by chemopreventive agents and in aflatoxin B(1)-induced preneoplasia.
Certain dietary constituents can protect against chemically induced carcinogenesis in rodents. A principal mechanism by which these chemopreventive compounds exert their protective effects is likely to be via induction of carcinogen detoxification. This can be mediated by conjugation with glutathione, which is synthesized by the sequential actions of glutamate-cysteine ligase (GLCL) and glutathione synthetase. We have demonstrated that dietary administration of the naturally occurring chemopreventive agents, ellagic acid, coumarin or alpha-angelicalactone caused an increase in GLCL activity of between approximately 3- and 5-fold in rat liver. Treatment with the synthetic antioxidant ethoxyquin or the classic inducer phenobarbital caused < 2-fold induction of GLCL activity in rat liver, which was not found to be significant. The increases in GLCL activity were accompanied by increases (between 2- and 4-fold) in levels of both the catalytic heavy subunit (GLCLC) and regulatory light subunit (GLCLR). No substantial induction of GLCL was observed in rat kidney. The glutathione S-transferase (GST) subunits A1, A3, A4, A5, P1 and M1 were all found to be inducible in rat liver by most of the agents. The greatest levels of induction were observed for GST P1, following treatment with coumarin (20-fold), alpha-angelicalactone (10-fold) or ellagic acid (6-fold), and GST A5, following treatment with coumarin (7-fold), alpha-angelicalactone (6-fold) and ethoxyquin (6-fold). Glutathione synthetase was induced approximately 1.5-fold by coumarin, alpha-angelicalactone, ellagic acid and ethoxyquin. The expression of glutathione-related enzymes was also examined in preneoplastic lesions induced in rat liver by aflatoxin B(1). The majority of gamma-glutamyltranspeptidase (GGT)-positive preneoplastic foci contained increased levels of GLCLC relative to the surrounding tissue. This was usually found to be accompanied by an increase in GLCLR. Cells in the inner cortex of rat kidney were found to contain the highest levels of both GLCLC and GLCLR. The same cells showed the strongest staining for GGT activity. (+info)
(3/33) Comparative xenobiotic metabolism between Tg.AC and p53+/- genetically altered mice and their respective wild types.
The use of transgenic animals, such as v-Ha-ras activated (TG:AC) and p53+/- mice, offers great promise for a rapid and more sensitive assay for chemical carcinogenicity. Some carcinogens are metabolically activated; therefore, it is critical that the altered genome of either of these model systems does not compromise their capability and capacity for metabolism of xenobiotics. The present work tests the generally held assumption that xenobiotic metabolism in the TG:AC and p53+/- mouse is not inherently different from that of the respective wild type, the FVB/N and C57BL/6 mouse, by comparing each genotype's ability to metabolize benzene, ethoxyquin, or methacrylonitrile. Use of these representative substrates offers the opportunity to examine arene oxide formation, aromatic ring opening, hydroxylation, epoxidation, O-deethylation, and a number of conjugation reactions. Mice were treated by gavage with (14)C-labeled parent compound, excreta were collected, and elimination routes and rates, as well as (14)C-derived metabolite profiles in urine, were compared between relevant treatment groups. Results of this study indicated that metabolism of the 3 parent compounds was not appreciably altered between either FVB/N and TG:AC mice or C57BL/6 and p53+/- mice. Further, expression of CYP1A2, CYP2E1, CYP3A, and GST-alpha in liver of naive genetically altered mice was similar to that of corresponding wild-type mice. Thus, these results suggest that the inherent ability of TG:AC and p53+/- mice to metabolize xenobiotics is not compromised by their altered genomes and would not be a factor in data interpretation of toxicity studies using either transgenic mouse line. (+info)
(4/33) High-performance liquid chromatography coupled with chemiluminescence nitrogen detection for the study of ethoxyquin antioxidant and related organic bases.
The Chemiluminescent Nitrogen Detector (CLND) for use with high-performance liquid chromatography (HPLC) allows for the low-level detection of nitrogen-containing compounds with simple quantitation. The nitrogen selective detector's equimolar response (i.e., equal response for nitrogen independent of its chemical environment) allows for any nitrogen-containing compound to be quantitated as long as the number of nitrogens are known. The HPLC-CLND provides a new detection method for analytes that are not available in large quantities or have unknown chemical or physical characteristics such as oxidation products, metabolites, or impurities. Ethoxyquin is a primary antioxidant that is used to preserve many food products and animal feeds. HPLC-CLND is used in the study of the oxidation products of ethoxyquin because limited quantities of these compounds are available and subsequent calibration curves are difficult to maintain. HPLC-CLND as a new method of detection has been evaluated for its equimolarity of response, linear range, limit of detection, and limit of quantitation. (+info)
(5/33) Induction of glutathione S-transferase activity and protein expression in brown bullhead (Ameiurus nebulosus) liver by ethoxyquin.
The inducibility of hepatic cytosolic glutathione S-transferases (GSTs) was examined in brown bullheads, a freshwater fish that is highly susceptible to hepatic neoplasia following exposure to carcinogen-contaminated sediments. Juvenile bullheads were fed a semi-purified antioxidant-free diet supplemented with ethoxyquin (0.5% w/w dissolved in 3% corn oil), a prototypical rodent GST-inducing agent, twice daily for 14 days. Control bullheads received the antioxidant-free diet supplemented with corn oil (3% w/w). A significant increase (1.6-fold, p < or = 0.01) in hepatic cytosolic GST activity toward 1-chloro-2,4-dinitrobenzene (CDNB) was observed in the ethoxyquin-treated bullheads relative to control fish. A trend toward increased GST-NBC activity was observed in the ethoxyquin-treated fish (1.2-fold, p = 0.06), whereas no treatment-related effects were observed on GST activities toward ethacrynic acid (ECA). In contrast, GST activity toward (+/-)-anti-benzo[a]pyrene-trans-7,8-dihydrodiol-9,10-epoxide (BPDE) was repressed in affinity-purified cytosolic fractions prepared from ethoxyquin-treated bullheads relative to control bullheads. Silver staining and densitometric analysis of isoelectric-focused, affinity-purified GST proteins revealed increased expression of two basic GST-like isoforms in ethoxyquin-treated fish. In summary, exposure to ethoxyquin increases brown bullhead GST-CDNB catalytic activity and hepatic cationic GST protein expression. However, the increase in overall GST-CDNB activity by ethoxyquin is associated with repression of GST-BPDE activity, suggesting differential effects on hepatic bullhead GST isoforms by ethoxyquin. The potential repression of bullhead GST isoforms that conjugate the carcinogenic metabolites of PAH metabolism under conditions of environmental chemical exposure could be a contributing factor in the sensitivity of bullheads to pollutant-associated neoplasia. (+info)
(6/33) Carbohydrate fermentation and nitrogen metabolism of a finishing beef diet by ruminal microbes in continuous cultures as affected by ethoxyquin and(or) supplementation of monensin and tylosin.
Long-term feedlot studies have shown positive effects (i.e., improved ADG and reduced morbidity and mortality) of dietary supplementation with ethoxyquin (AGRADO). This may be due to improving the antioxidant capacity at the ruminal, postruminal, or postabsorption levels. This study was designed to investigate the role of ethoxyquin at the rumen level. A finishing diet (12.5% CP; DM basis) was formulated to contain (on a DM basis) 77.5% flaked corn, 10% corn cobs, 10% protein/vitamin/mineral supplement, and 2.5% tallow. In a randomized complete block design experiment, the treatments were arranged as a 2 x 2 factorial. The main factors were two ethoxyquin treatments (without or with 150 ppm) and two monensin/tylosin treatments (without or with monensin and tylosin at 0.0028 and 0.0014% of dietary DM, respectively). Eight dual-flow, continuous culture fermenters were used in two experimental periods (blocks; 8 d each with 5 d for adjustment and 3 d for sample collection) to allow for four replications for each treatment. No interactions (P > 0.05) were detected for any of the measurements evaluated. Therefore, results of the main factors were summarized. Ethoxyquin supplementation improved (P < 0.05) true digestibility of OM (from 38.8 to 45.0%) but it did not alter (P > 0.05) concentrations of total VFA (averaging 131 mM) or acetate (averaging 58.8 mM). Ethoxyquin decreased (P < 0.05) propionate concentration from 51.1 to 42.4 mM and increased (P < 0.05) butyrate concentration from 18.4 to 22.9 mM. Digestion of total nonstructural carbohydrates was not altered (P > 0.05) by the treatments and averaged 86%. With the exception of increased (P < 0.05) concentration of propionate (from 42.0 to 51.5 mM) and decreased (P < 0.05) concentration of butyrate (from 25.9 to 16.3 mM), no effects (P > 0.05) were detected for monensin/tylosin. Ruminal N metabolism, including efficiency of bacterial protein synthesis (averaging 21.2 g N/kg OM truly digested), was not affected (P > 0.05) by the treatments. Results suggest positive effects of ethoxyquin on ruminal digestion of OM and unique changes in VFA production. (+info)
(7/33) Characterisation of a novel mouse liver aldo-keto reductase AKR7A5.
We have characterised a novel aldo-keto reductase (AKR7A5) from mouse liver that is 78% identical to rat aflatoxin dialdehyde reductase AKR7A1 and 89% identical to human succinic semialdehyde (SSA) reductase AKR7A2. AKR7A5 can reduce 2-carboxybenzaldehyde (2-CBA) and SSA as well as a range of aldehyde and diketone substrates. Western blots show that it is expressed in liver, kidney, testis and brain, and at lower levels in skeletal muscle, spleen heart and lung. The protein is not inducible in the liver by dietary ethoxyquin. Immunodepletion of AKR7A5 from liver extracts shows that it is one of the major liver 2-CBA reductases but that it is not the main SSA reductase in this tissue. (+info)
(8/33) Proteomic analysis of oxidative stress-resistant cells: a specific role for aldose reductase overexpression in cytoprotection.
We are using a proteomic approach that combines two-dimensional electrophoresis and tandem mass spectrometry to detect and identify proteins that are differentially expressed in a cell line that is resistant to oxidative stress. The resistant cell line (OC14 cells) was developed previously through chronic exposure of a parent cell line (HA1 cells) to increasing hydrogen peroxide concentrations. Biochemical analyses of this system by other investigators have identified elevated content and activity of several classical antioxidant proteins that have established roles in oxidative stress resistance, but do not provide a complete explanation of this resistance. The proteomics studies described here have identified the enzyme aldose reductase (AR) as 4-fold more abundant in the resistant OC14 cells than in the HA1 controls. Based on this observation, the role of AR in the resistant phenotype was investigated by using a combination of AR induction with ethoxyquin and AR inhibition with Alrestatin to test the cytotoxicity of two oxidation-derived aldehydes: acrolein and glycolaldehyde. The results show that AR induction in HA1 cells provides protection against both acrolein- and glycolaldehyde-induced cytotoxicity. Furthermore, glutathione depletion sensitizes the cells to the acrolein-induced toxicity, but not the glycolaldehyde-induced toxicity, while AR inhibition sensitizes the cells to both acrolein- and glycolaldehyde-induced. These observations are consistent with a significant role for AR in the oxidative stress-resistant phenotype. These studies also illustrate the productive use of proteomic methods to investigate the molecular mechanisms of oxidative stress. (+info)