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G S Bailey

Publications and source records attributed to G S Bailey.

At least 73 records · Page 4Linked to original sources
PubMed1991

Chemopreventive properties of chlorophyllin: inhibition of aflatoxin B1 (AFB1)-DNA binding in vivo and anti-mutagenic activity against AFB1 and two heterocyclic amines in the Salmonella mutagenicity assay.

Chlorophyllin (CHL), a sodium/copper derivative of chlorophyll, has been used to treat a number of human conditions with no toxic effects being reported. Recent studies have described the anti-mutagenic activity of CHL in several short-term genotoxicity assays; however, this compound has not been reported to inhibit carcinogen--DNA binding in vivo, and it has yet to be evaluated as an anti-carcinogen in any species. The chemopreventive properties of CHL were studied in trout using inhibition of aflatoxin B1 (AFB1)--DNA binding as an end-point. Chlorophyllin and AFB1 were coadministered in the diet, and carcinogen--DNA binding levels were determined in liver after 1, 3, 5 and 7 days. Linear increases in AFB1--DNA binding occurred with time of treatment at each CHL dose level (0, 500, 1000 and 2000 p.p.m.). Each increase in CHL dose produced a concomitant decrease in AFB1--DNA binding, resulting in a series of curves of decreasing slope. At the highest CHL dose level of 2000 p.p.m., AFB1--DNA binding was inhibited by 70%. These results suggest that CHL should be a potent inhibitor of AFB1-induced hepatocarcinogenesis in this model. In the Salmonella assay, CHL exhibited potent anti-mutagenic activity against AFB1 and two heterocyclic amines when incubated in the presence of trout liver activation systems. CHL also inhibited the mutagenic activity of AFB1-8,9-epoxide in the absence of a metabolic activation system. Dietary CHL substantially inhibited liver AFB1-DNA binding in vivo, even when AFB1 was given by i.p. injection to avoid direct AFB1--CHL interaction in the diet or gut. Collectively, these studies support a CHL inhibitory mechanism involving complex formation with the carcinogen in the gut coupled with electrophile scavenging or further complexing in the target organ.

Aflatoxin B1↗
PubMed1991

Modulation of mycotoxin and nitrosamine carcinogenesis by indole-3-carbinol: quantitative analysis of inhibition versus promotion.

The value of chemopreventive agents for reducing human response to mycotoxins and N-nitrosamines remains uncertain, especially since many such agents also can act as tumour promoters. Indole-3-carbinol (I3C) from cruciferous vegetables can inhibit DNA adduction and hepatocarcinogenesis induced by aflatoxin B1 (AFB1) or N-nitroso-diethylamine in trout if given before and with the carcinogen but promotes carcinogenesis when given after initiation. Similar results have been obtained with I3C and AFB1 in rats. In detailed studies using 10,000 trout, inhibition of AFB1 carcinogenesis was found to be saturable at high doses of I3C, approximately proportional to dose of I3C through the range of human intake and, within this range, quantitatively predicted by I3C-mediated reduction of AFB1-DNA adduction in liver. In a second study, post-initiation promotion of AFB1 carcinogenesis was approximately proportional to I3C dose, increased with duration of exposure, decreased with delayed onset of exposure, and reduced but still significant when I3C was given on alternate months or weeks or twice per week only. Hence, promotion by this common component of cruciferous vegetables required prolonged exposure but not necessarily on a daily basis.

Aflatoxin B1↗
PubMed1990

A simple and rapid purification of kallikrein from rat submandibular gland.

Rat submandibular kallikrein was isolated in an 87% yield by a very quick and simple procedure involving hydrophobic interaction chromatography. Furthermore, that purification method was superior to both aprotinin-affinity chromatography and immunoaffinity chromatography for the purification of rat submandibular kallikrein. The kallikrein purified by hydrophobic interaction chromatography consisted of a number of isoenzymes. The major component of Mr 38,000 seen on SDS-gel electrophoresis was found to be the glycosylated kallikrein, whereas the minor component of Mr 26,000 represented the non-glycosylated enzyme.

Animals↗
PubMed1990

Mechanisms of anti-carcinogenesis by indole-3-carbinol. Studies of enzyme induction, electrophile-scavenging, and inhibition of aflatoxin B1 activation.

The induction of oxidation and conjugation enzymes, the scavenging of carcinogen electrophiles, and the inhibition of aflatoxin B1 (AFB1) activation were examined as possible mechanisms of anti-carcinogenesis by indole-3-carbinol (I3C). Liver microsomal 7-ethoxycoumarin O-deethylase and 7-ethoxyresorufin O-deethylase activities were not induced significantly in rainbow trout fed diets containing 500-2000 ppm I3C for 8 days compared to trout fed the control diet. Furthermore, no detectable changes in the specific contents of cytochrome P-450 isozymes LM2 and LM4b, as measured by Western-blotting and immunoquantitation, were found in liver microsomes following dietary I3C administration. Dietary I3C had no significant effect on liver microsomal uridine diphosphate-glucuronyl-transferase activity, measured using the substrates 1-naphthol and testosterone, or on cytosolic glutathione S-transferase activity, measured using the substrate styrene oxide. The ability of I3C or its acid reaction products (RXM; generated by the reaction of I3C with HCl) to act as scavengers for the direct alkylating agent AFB1-8,9-Cl2 was examined. Addition of I3C or RXM to in vitro incubations did not inhibit the covalent binding of AFB1-8,9-Cl2 to calf thymus DNA. Kinetic analyses of microsome-mediated binding of AFB1 to DNA in vitro indicated that RXM inhibited the metabolic activation of AFB1. RXM increased the apparent Km for the AFB1-DNA binding reaction without changing the associated Vmax; the apparent Km values at 0, 3.5, 35, and 350 microM RXM were 35, 38, 66, and 86 microM for trout liver microsomes. RXM also inhibited the activation of AFB1 by rat liver microsomes, but I3C was not an effective inhibitor against AFB1-DNA binding mediated by either rat or trout liver microsomes. The results of the present study indicate that inhibition of microsome-activated AFB1 binding to DNA by I3C products may be of significant importance in I3C inhibition of hepatocarcinogenesis in trout and other species. The inhibition of carcinogen activation by I3C is contrasted with the mechanism of anti-carcinogenesis by beta-naphthoflavone, which involves induction of xenobiotic metabolizing enzymes.

7-Alkoxycoumarin O-Dealkylase↗
PubMed1990

Tumor dose-response studies with aflatoxin B1 and the ambivalent modulator indole-3-carbinol: inhibitory versus promotional potency.

Indole-3-carbinol (I3C), a natural compound from cruciferous vegetables, inhibits aflatoxin B1 (AFB1) carcinogenesis in trout when administered prior to and during carcinogen exposure, but also promotes it in the same species when given after AFB1 initiation. To provide quantitative potency information for these opposing activities, detailed tumor dose-response studies were performed with AFB1 (10-400 ppb) and I3C (0-4,000 ppm). In a plot of (logit) percent tumor response vs log AFB1 exposure, the results generated a series of parallel AFB1 dose-response curves. Increasing I3C doses displaced these curves, respectively, toward higher and lower AFB1 doses in the inhibition and promotion studies. Similar potencies were observed over the dose range 0-1,500 ppm I3C; the 50% promotion and inhibition (P50 and I50) values were 1,000 vs 1,400 ppm I3C, respectively. Differences in the protocols used in the two studies suggest that the inhibitory activity of I3C is more likely to supersede promotion under human exposure conditions.

Aflatoxin B1↗
PubMed1989

Metaplastic pancreatic cells in liver tumors induced by diethylnitrosamine.

Metaplastic pancreatic cells have been infrequently observed in fish liver tumors induced by chemical carcinogens. An investigation with nitrosamine-exposed trout was undertaken to characterize the relationships of metaplastic pancreatic cells with other cell types. Eight-week-old rainbow trout (Salmo gairdneri) were fed a control diet or diets containing 500 ppm beta-naphthoflavone (BNF), 2000 ppm indole-3-carbinol (13C), or 100 ppm Aroclor 1254 (PCB) for 6 weeks. The fish were then exposed to 250 ppm diethylnitrosamine for 24 hr in an aqueous aquarium bath and reared on control diet for 39 weeks postexposure. Livers were excised, processed to paraffin sections, and stained with hematoxylin and eosin for histological evaluation. Metaplastic pancreatic cells were found only in tumors. Of the tumors with metaplastic pancreatic cells, 100/105 (95.2%) contained neoplastic cholangiolar components. Only 5/105 (4.76%) were hepatocellular carcinomas. 13C pretreatment inhibited the incidence of cholangiolar tumors (cholangioma 3.6% vs 31.3%, cholangiocarcinoma 3.6% vs 13.0%) and metaplastic pancreatic cells (5.1% vs 19.1%), whereas BNF and PCB had no effect. A hepatocellular origin for metaplastic pancreatic cells is supported. Cholangiolar neoplasia is associated with the expression, growth, or survival of metaplastic pancreatic cells in liver tumors. Hepatocarcinogenicity should not be described entirely by hepatocellular events since cholangiolar and metaplastic pancreatic cells can respond associatively to carcinogens and dietary modulators.

Adenoma, Bile Duct↗
PubMed1989

In vivo disposition of the natural anti-carcinogen indole-3-carbinol after po administration to rainbow trout.

Indole-3-carbinol (I3C), a compound found naturally as a glucosinolate in cruciferous vegetables such as broccoli and cabbage, has been shown to modulate the carcinogenic process in a number of animal species. The lack of detailed information on the disposition of I3C in vivo provided the main impetus for the study reported here, in which the distribution and metabolic fate of I3C was assessed in selected tissues and excreta after po administration to rainbow trout (Salmo gairdneri). Animals were fasted for 3 days and given [5-3H]I3C either in the diet or by single oral gavage (40 mg/kg body weight; 15 muCi/kg body weight). Following administration, 75% of the initial 3H-dose was detected within the stomach between 0.5 and 12 hr, after which it was released to distal regions of the gut for subsequent uptake, distribution and elimination. At the end of the study (72 hr) 25% of the administered dose was recovered from the water which reflected excretion through the gills and urinary tract. Significant excretion also occurred in the bile, with approximately 5% of the initial 3H-dose recovered from the bile sacs at 72 hr. Further analyses of the radioactive components in the bile indicated that one or more derivatives of I3C, but not the parent compound itself, are excreted as glucuronide conjugates using this route. Radioactivity accumulated in the liver throughout most of the study, reaching levels of 1-1.5% between 48 and 72 hr of the administered dose. High-performance liquid chromatography analyses indicated the presence of four main radiolabelled species in these livers, one of which co-eluted with the parent compound, I3C. The major radiolabelled species recovered from the liver was tentatively identified as the dimer, 3,3'-diindolylmethane (I33'), which comprised 40% of the total hepatic radiolabel. This dimer, I33', was also found to accumulate in the diet containing I3C, which reflected a time-dependent dimerization of the parent compound in vitro. These findings are discussed in view of recent postulates of a role for I3C condensation products such as I33' in the mechanism of I3C anti-carcinogenesis.

Animals↗
PubMed1989

Quantitative inter-relationships between aflatoxin B1 carcinogen dose, indole-3-carbinol anti-carcinogen dose, target organ DNA adduction and final tumor response.

A number of recent studies have described inhibitor-mediated reductions in the covalent DNA binding and tumorigenicity of various carcinogens, in species such as rats, mice and rainbow trout (Salmo gairdneri). Since inhibitory effects have, in most cases, been reported after testing at one carcinogen and one inhibitor level only, the detailed relationships between carcinogen dose, inhibitor dose, in vivo DNA binding and final tumor response are not well understood in any species. To determine these relationships we have employed the trout model in a combined DNA binding/tumor dose-response protocol using approximately 10,000 animals. Trout were pretreated with one of five different dose-levels of indole-3-carbinol (I3C), a naturally occurring anti-carcinogen found in cruciferous vegetables such as broccoli and cabbage. After 4 weeks, animals received the same dietary level of I3C for a further 2 weeks together with [3H]aflatoxin B1 (AFB1) in the dose-range 10-320 p.p.b. From tanks containing 150 animals (three tanks per I3C-AFB1 dose-point), 15 fish were selected at random in order to assess hepatic AFB1-DNA binding levels. Remaining animals were returned to control diet for determination of tumor response at 12 months. Linear increases in DNA binding occurred with dose of AFB1 at each I3C dose-level. Successive increases in I3C dose gave dose-related decreases in AFB1-DNA binding, resulting in a series of curves of decreasing slope. Shifts in DNA-binding slopes were compared quantitatively with horizontal displacements towards higher carcinogen dose in corresponding tumor dose-response curves. At I3C doses of less than or equal to 2000 p.p.m., the inhibitor-altered tumor response was predicted precisely by changes in dose received (DNA adducts formed) in the target organ. These data constitute the first direct evidence of pure anti-initiating activity by a natural anti-carcinogen found in human diet, where all animals were treated at the same time and under identical conditions of exposure in both DNA binding and tumor studies. The data are discussed further in view of (i) their implications for DNA binding-carcinogenicity correlations and the concept of 'molecular dosimetry', and (ii) limitations in the current database on anti-carcinogenesis as regards in vivo potency information, particularly for 'ambivalent modulators' which exhibit both inhibitory and promotional activity.

Aflatoxin B1↗
PubMed1989

Iron resistance of hepatic lesions and nephroblastoma in rainbow trout (Salmo gairdneri) exposed to MNNG.

Histochemical markers are important for the early detection of chemically initiated neoplasia in experimental animal studies. The marker, iron resistance, was evaluated in the Shasta strain of rainbow trout (Salmo gairdneri). Twenty-one-day-old trout embryos were exposed to 100 ppm aqueous N-methyl-N'-nitro-N-nitrosoguanidine (MNNG) for 30 min in a static water bath. Fish were fed a semipurified diet, and sampled monthly from the 4th to the 9th month. Two days before sampling, fish were iron-loaded with a single ip dose of 0.30 mg iron dextran/100 g body weight. Livers and kidneys were conventionally processed to paraffin sections for iron, or hematoxylin and eosin (H&E) staining. Normal hepatocytes accumulated iron in pericanalicular locations, but in hepatocytes from carcinogen-altered foci and tumors, iron staining was clearly reduced or absent. Normal renal tubule cells exhibited slight to moderate iron staining, while those from nephroblastoma were iron resistant. These results establish iron resistance as a property of preneoplastic and neoplastic trout hepatocytes and nephroblastoma cells for the first time. Iron resistance may offer a practical histochemical marker in experimental fish models of hepatocellular carcinoma and nephroblastoma.

Adenoma↗
PubMed1988

Identification of human lung mast cell kininogenase as tryptase and relevance of tryptase kininogenase activity.

We have described previously the IgE-mediated release of kininogenase activity from purified human lung mast cells. Using supernatant fractions from mast cells stimulated with anti-IgE in the presence of deuterium oxide, we have purified this kininogenase to homogeneity by gel filtration and heparin-agarose chromatography and have demonstrated that it is identical to tryptase, the major neutral protease of human lung mast cells. Thus, tryptase and kininogenase activities co-chromatographed through both purification steps with equivalent yields. The final purified kininogenase was free of detectable chymotryptic and carboxypeptidase activities and was identified as tryptase on the basis of sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE), amino acid composition and inhibition profile. Three such preparations of tryptase were all capable of releasing kinin from each of two different preparations of purified, single-chain, human low molecular weight kininogen. Interestingly, kinin generation was optimal at pH 5.5 and was enhanced by heparin, which has been reported to stabilize tryptase. SDS-PAGE analysis of kininogen hydrolysis by tryptase revealed the formation of a diffusely stained region in the molecular weight range of 60,000-65,000, rather than a discrete heavy chain band. Under optimal conditions, the three tryptase preparations released 10-12 micrograms kinin/hr/mg but released only 2 micrograms kinin/hr/mg at pH 7.2. HPLC analysis revealed that the kinin released was bradykinin. We conclude that the kininogenase activity from human lung mast cells is attributable to tryptase. The unique pH optimum of this reaction of a serine protease, however, raises doubts as to the physiologic significance of this activity.

Amino Acids↗
PubMed1988

Modulation of diethylnitrosamine-induced hepatocarcinogenesis and O6-ethylguanine formation in rainbow trout by indole-3-carbinol, beta-naphthoflavone, and Aroclor 1254.

Rainbow trout were fed a diet containing indole-3-carbinol (2000 ppm), beta-naphthoflavone (500 ppm), or Aroclor 1254 (100 ppm) for 6 weeks before a single 24-hr exposure to an aqueous solution of 250 ppm diethylnitrosamine (DEN). The fish were killed 42 weeks later to determine the carcinogenic response. DEN exposure produced an 80.2% incidence of liver tumors and an average of 3.47 tumors per tumor-bearing fish, whereas no tumors were detected in the sham-treated control fish. Tumor induction was inhibited by indole-3-carbinol (27.5% incidence, 1.89 tumors per tumor-bearing fish) but enhanced by beta-naphthoflavone (91.8% incidence, 3.60 tumors per tumor-bearing fish). Aroclor 1254 had no effect on DEN-induced hepatocarcinogenesis (80.0% incidence, 3.03 tumors per tumor-bearing fish). The effects of these modulators on O6-ethylguanine and 7-ethylguanine formation (measured by HPLC and fluorescence spectrophotometry) were examined. Liver DNA ethylguanine levels were reduced in indole-3-carbinol-pretreated fish and increased in beta-naphthoflavone-pretreated fish compared to untreated controls after DEN exposure. Aroclor 1254 pretreatment had no significant effect on DNA ethylguanine formation. Similar O6-ethylguanine to 7-ethylguanine ratios were found among the control and treated groups. The results of this study indicate that modulation of DEN hepatocarcinogenesis by indole-3-carbinol and beta-naphthoflavone may be mediated by their effects on O6-ethylguanine formation and, therefore, on the initiation phase of carcinogenesis.

Animals↗
PubMed1988

Formation and persistence of ethylguanines in liver DNA of rainbow trout (Salmo gairdneri) treated with diethylnitrosamine by water exposure.

Diethylnitrosamine exposure via the water resulted in the formation of 7-ethylguanine and O6-ethylguanine in rainbow trout liver DNA. The modified bases were quantitated by high-pressure liquid chromatography and fluorescence spectrophotometry. In vivo 7-ethylguanine and O6-ethylguanine levels were directly proportional to DEN concentrations between 62.5 and 250 ppm. 7-Ethylguanine and O6-ethylguanine levels were approximately directly proportional to duration of exposure to DEN between 0 and 6 hr under the conditions used, with less than proportionate increases thereafter. Removal of ethylguanines from liver DNA following a 24-hr exposure to 250 ppm DEN (a known carcinogenic regimen) was biphasic; 24% of the O6-ethylguanine and 32% of the 7-ethylguanine found immediately after exposure were removed in 12 hr but no significant decline was found over the period from 12 to 96 hr after exposure. Alkyl acceptor protein activity in trout liver was examined to assess the role of enzymatic repair in the observed loss of O6-ethylguanine in vivo. Although an O6-alkylguanine repair system similar to the alkyltransferase system reported in rodents was found in trout liver, only 4% of the O6-ethylguanine lost from DNA after exposure to 250 ppm DEN can be accounted for by activity of the alkyl acceptor protein. The high incidence of liver tumours observed in DEN-treated rainbow trout may be related to the rapid formation and substantial persistence of the promutagenic O6-ethylguanine in liver DNA.

Animals↗
PubMed1988

The significance of glutathione conjugation for aflatoxin B1 metabolism in rainbow trout and coho salmon.

Rainbow trout are known to be more susceptible to aflatoxin B1 (AFB1) hepatocarcinogenesis than coho salmon, or trout pre-fed the carcinogenesis inhibitors beta-naphthoflavone (beta NF), Aroclor 1254 or indole-3-carbinol. The study reported here examined the relationship between AFB1-glutathione (GSH) conjugation and AFB1 carcinogenesis in salmon, trout and trout pre-fed the three inhibitors. The AFB1-glutathione (AFB1-SG) conjugate was not detected in salmon bile and was present in trout bile in amounts representing less than 0.2% of the administered dose 24 hr after injection of [3H]AFB1. The major conjugates were glucuronides of aflatoxicol and aflatoxicol M1. In incubations of isolated liver cell fractions, less than 0.5% of the original AFB1 dose was recovered as AFB1-SG in salmon and trout preparations, compared to 25% in mouse-liver cell preparations. The GSH concentration in livers of the control trout was higher than that for coho salmon but lower than that for trout pre-fed beta NF. Liver GSH-transferase activity in control trout livers was much higher than in the control salmon livers, but was only 62% of that found for trout fed beta NF. There was no apparent relationship among the various groups between liver GSH concentrations, liver GSH-transferase activity, or biliary GSH conjugate, and the degree of carcinogenic response of AFB1. Thus current evidence does not indicate a major role for aflatoxin B1 epoxide-GSH detoxification in coho salmon, or rainbow trout fed any of the three anticarcinogens tested. These results in salmonid fish are contrary to those which suggest AFB1-SG conjugation as a major determinant of AFB1 carcinogenesis and its dietary modulation in rodent models.

Aflatoxin B1↗
PubMed1988

Comparative effect of dietary butylated hydroxyanisole and beta-naphthoflavone on aflatoxin B1 metabolism, DNA adduct formation, and carcinogenesis in rainbow trout.

Butylated hydroxyanisole (BHA) and beta-naphthoflavone (BNF), both chemicals with anti-carcinogenic properties in some experimental animals, were compared for effects on aflatoxin B1 (AFB1) metabolism, hepatic DNA adduct formation and carcinogenesis in the rainbow trout. Dietary BHA had no effect on the hepatic tumor incidence when fed at 0.03 or 0.3% 4 weeks prior to and during a 4 week dietary exposure of 10 p.p.b. AFB1. BNF, when fed at 0.005 or 0.05% under similar conditions, significantly reduced tumor response, which confirms previous results in trout (Nixon et al., Carcinogenesis, 5, 615-619, 1984). BHA fed at either 0.03 or 0.3% for 8 weeks had no post-initiation effect on the 52 week hepatic tumor incidence of trout exposed to a 0.5 p.p.m. AFB1 solution as embryos. A similar post-initiation exposure to 0.05% BNF significantly enhanced AFB1 tumor response. The influence of dietary BHA and BNF on AFB1 metabolism and DNA adduct formation and persistence in trout were examined. A 3 week pre-treatment with 0.3% dietary BHA had no effect on in vivo hepatic nuclear AFB1-DNA adduct formation at 0.5, 1, 2 and 7 days after AFB1 i.p. injection. By contrast 0.05% dietary BNF reduced hepatic AFB1-DNA adducts to 33-60% of control levels at 0.5, 1, 2 and 4 days after AFB1 exposure. This was accompanied by significantly lower blood and liver levels of AFB1 during the first 24 h after i.p. injection. Livers of BNF trout also contained 4-fold more of the less carcinogenic metabolite, aflatoxin M1, and 50% less aflatoxicol (AFL), a metabolite with similar carcinogenicity as AFB1. Bile AFL-glucuronide levels were significantly decreased in BNF-fed trout, but total bile glucuronides were significantly increased due to a 15-fold increase in aflatoxicol-M1 glucuronide. Freshly isolated hepatocytes from BHA-fed fish, when incubated with AFB1 for 1 h, showed no difference in levels of AFB1-DNA adducts or ratios of AFB1 metabolites when compared to hepatocytes isolated from fish fed a control diet only. By contrast, dietary BNF has been previously shown to greatly enhance AFM1 production, reduce AFL production, and significantly reduce AFB1-DNA adduct formation in isolated trout hepatocytes (Bailey et al., Natl. Cancer Inst. Monograph, 65, 379-385, 1984). These results indicate that dietary BHA up to 0.3% does not alter AFB1 metabolism or DNA adduction in trout, nor does it inhibit or promote AFB1 hepatocarcinogenesis in this species.(ABSTRACT TRUNCATED AT 400 WORDS)

Aflatoxin B1↗
PubMed1988

Aflatoxin B1 carcinogenesis and its relation to DNA adduct formation and adduct persistence in sensitive and resistant salmonid fish.

Rainbow trout (Salmo gairdneri) and coho salmon (oncorhynchus kisutch) were exposed to aflatoxin B1 (AFB1) either by passive embryo uptake or by dietary treatment after hatching and feeding onset. Trout exposed as embryos to an aqueous solution of 0.5 p.p.m. AFB1 for 15 min showed a 62% tumor incidence 12 months later, whereas coho salmon exposed to a similar solution for 30 min showed only a 9% incidence. The difference between salmon and trout response was even greater by dietary AFB1 treatment. Trout exposed for 4 weeks to 20 p.p.b. dietary AFB1 had a 62% tumor response 12 months later, whereas salmon exposed to 40 p.p.b. dietary AFB1 for 4 weeks failed to develop tumors. A 5% tumor incidence was observed in salmon 12 months after 3 weeks exposure to 5000 p.p.b. dietary AFB1, a lethal dose for trout. In addition to a lower tumor incidence when compared to trout, the neoplastic response of salmon to AFB1 is to produce benign hepatic adenomas in contrast to the malignant hepatocellular carcinomas seen in trout. AFB1 metabolism, DNA adduct formation, adduct persistence in vivo and in vitro and cytochrome P-450 isozyme composition were compared in livers of trout and salmon to understand the role of metabolism and initiation in this species difference. AFB1-DNA binding was 7-56 times greater in trout than salmon liver at various times after AFB1 injection, 20 times greater in embryos or in freshly isolated trout hepatocyte preparations after a 1 h incubation with aflatoxin B1, and 18 times greater in trout liver after a three week dietary (80 p.p.b.) exposure. The major AFB1-DNA adduct was 8,9-dihydro-8-(N7-guanyl)-9-hydroxyaflatoxin B1 in both species. Persistence of AFB1-DNA adducts in vivo in liver was high compared to mammalian systems, implying that active enzymatic removal of bulky DNA adducts is low in both species and probably not a factor in their differential response to aflatoxin. Species differences in other phase I and phase II metabolism pathways and in AFB1 elimination were, overall, much less striking than those previously observed for trout fed inhibitors of aflatoxin carcinogenesis. Rates of bile elimination of AFB1 detoxication products, and total excretion of aflatoxins into water after AFB1 exposure, were not significantly different between trout and salmon. Since detoxication differences were not observed, the species difference in AFB1-DNA binding appears to reflect less efficient cytochrome P-450 metabolism of aflatoxin to the reactive 8,9-epoxide in salmon, compared to trout.(ABSTRACT TRUNCATED AT 400 WORDS)

Aflatoxin B1↗
PubMed1988

Mechanisms of anti-carcinogenesis by indole-3-carbinol: detailed in vivo DNA binding dose-response studies after dietary administration with aflatoxin B1.

Several recent reports have described inhibitor-mediated reductions in the covalent binding of various carcinogens to DNA in vivo. The majority of these studies show inhibitory effects after testing at one inhibitor and one carcinogen dose level only. Consequently, the detailed relationships between inhibitor dose, carcinogen dose, and in vivo inhibitory potency have not been clearly delineated in any species. To systematically determine these relationships in vivo, rainbow trout (Salmo gairdneri) were exposed to a range of carcinogen (aflatoxin B1, AFB1) and inhibitor (indole-3-carbinol, I3C) doses by concomitant dietary exposure. Inhibitory potencies were then assessed using in vivo covalent binding of AFB1 to hepatic DNA as an end-point. Linear increases in DNA binding occurred with increasing dose of AFB1 and with time of inhibitor/carcinogen co-treatment, at each I3C dose level. Successive increases in inhibitor dose resulted in corresponding dose-related decreases in AFB1--DNA binding such that a series of curves of decreasing slope was produced. AFB1--DNA binding was suppressed by almost 95% at the highest I3C dose tested. These studies describe for the first time such a degree of inhibition by I3C on covalent binding of AFB1 to DNA in vivo, where inhibitor and carcinogen are covariables administered repeatedly in the diet. Moreover, the linear inhibitory response observed at low I3C doses indicates the possible absence of any significant threshold for I3C protection against AFB1--DNA binding. Thus, even at low levels I3C may offer some protection against chemically-induced neoplasia.

Aflatoxin B1↗