Metabolic basis of the species difference to aflatoxin B1 induced hepatotoxicity

Protective activity of different hepatic cytosolic glutathione S-transferases against DNA-binding metabolites of aflatoxin B1

To evaluate the role of glutathione S-transferase (GST) isoenzymes in induced resistance of hepatocytes to aflatoxin B1 (AFB1), we compared DNA protective activities of different hepatic cytosol preparations and purified GSTs from normal rats, rats exposed to different polychlorinated biphenyls (PCBs), and rats with carcinogen-induced hepatocellular neoplasms, with cytosols or purified GSTs from mouse, rainbow trout, and human livers. These comparisons were performed in an in vitro assay for [3H]AFB1-DNA binding after activation by rat liver microsomes. Cytosol and S-hexylglutathione-affinity-purified GST preparations from livers of mice consistently had strong protective activity against AFB1-DNA binding. The majority of this activity was dependent on the presence of reduced glutathione (GSH) but some GSH-independent protection was observed in mouse hepatic cytosol, but not in purified GST preparations. We found that all of the GSH-dependent DNA-protective activity in mouse liver eluted as a single GST isoenzyme by hydroxyapatite chromatography. Preparations of cytosol and purified GSTs from normal rat liver, rainbow trout liver, and human liver had much less AFB1-specific DNA protective activity than GSTs found in mouse liver preparations. Cytosol from rats with carcinogen-generated liver neoplasms and livers induced with 3,3',4,4'-tetrachlorobiphenyl and 2,2',4,4',5,5'-hexachlorobiphenyl had more GST activity toward CDNB than cytosol from normal rat liver. When equivalent units of GST activity (CDNB) were compared, there was little difference observed between the DNA-protective activities of PCB-induced and normal rat liver cytosols, yet cytosol from rat liver neoplasms was more protective. Purified GST-P (7-7), the GST isoenzyme most induced in carcinogen-generated rat liver neoplasms, was not protective when added at protein concentrations found to be protective for total GSTs isolated from these neoplasms. These studies demonstrate that the resistance of mouse liver to AFB1 can be explained primarily by a single constitutive GST isoenzyme (YaYa or 4-4) with a relatively high activity toward DNA-binding metabolites of AFB1. GST isoenzymes with such high specific DNA protective activity against AFB1 metabolites were not evident in human, rat, or rainbow trout liver or in PCB-induced or neoplastic rat liver preparations.

Effect of glucose administration on hamster liver S9-mediated mutagenesis, metabolism and DNA-binding of benzo[a]pyrene and aflatoxin B1

Hamster liver S9 prepared from control animals and animals given 30% glucose in drinking water 48 h before killing was used in studies of benzo[a]pyrene (BaP) and aflatoxin (AFB1)-induced mutagenesis, metabolism of BaP and AFB1, and metabolite binding to calf thymus DNA. BAP-induced mutagenesis in Salmonella typhimurium TA100 was reduced 38.5% while AFB1-induced mutagenesis was increased 36% by S9 from glucose-treated hamsters. The reduction of [3H]BaP metabolite binding to calf thymus DNA in incubations with S9 from glucose-treated hamsters correlated with a decrease in unknown BP metabolite-deoxyribonucleoside adducts isolated by high performance liquid chromatography (HPLC). Differences in the 7R and 7S-diol epoxide-1 and 2 deoxyguanosine adducts of BaP between control and glucose-treated S9 were not observed. HPLC analysis of AFB1-DNA adducts showed a 25% increase in [3H]AFB1-N7-guanine in incubations of glucose-treated S9 with [3H]AFB1 and calf thymus DNA. HPLC analysis of the organosoluble fraction of incubations with [3H]BaP and [3H]AFB1 indicated a significant effect by glucose-treated S9 on metabolism. The effect of glucose on metabolism was further reflected in the reduction of both BaP and AFB1 metabolite conjugation with glucuronide and glutathione as determined by separation on an alumina column. These results indicate that the oral administration of 30% glucose in drinking water alters hamster liver S9-mediated mutagenesis and binding of BaP and AFB1 metabolites to DNA through an effect on the metabolism of these two carcinogens.

Comparative uptake, vascular transport, and cellular internalization of aflatoxin-B1 and benzo(a)pyrene

Studies of the uptake of benzo(a)pyrene (BaP) and aflatoxin-B1 (AFB1) after gastric instillation showed that BaP was absorbed via the intestinal lymphatic drainage and transported to the vascular circulation sequestered within lipoproteins in thoracic duct lymph, while AFB1 was absorbed with water soluble compounds into the gastrointestinal venous drainage and was not transported in association with lipoproteins. BaP was taken up into plasma lipoproteins over a broad concentration range, while AFB1 was not sequestered within lipoproteins over the same concentration range. Low density lipoproteins (LDL) facilitated BaP uptake into fibroblasts and impeded BaP uptake into hepatocytes. High density lipoproteins (HDL) facilitated BaP uptake into hepatocytes and impeded BaP uptake into fibroblasts. The uptake of AFB1 into either fibroblasts or hepatocytes was not affected by lipoproteins.

Aflatoxin B1-specific cytochrome P-450 isozyme (P-450-AFB) inducible by 3-methylcholanthrene in golden hamsters

Hepatic microsomes of polychlorinated biphenyl (PCB)-treated Syrian Golden hamsters possessed a higher potency toward aflatoxin B1 activation, based on the Ames test, than other animal species. This activity was induced in hamsters preferentially by treatment with 3-methylcholanthrene rather than phenobarbital. The contribution of an isozyme of cytochrome P-450 (P-450-AFB) to the activity of hamster livers for aflatoxin B1 was studied. P-450-AFB, purified from 3-methylcholanthrene-treated hamster livers, was shown to possess the highest activation of aflatoxin B1 in the Ames test. The quantification of this isozyme by a fluorometric sandwich enzyme-linked immunosorbent assay (ELISA) demonstrated that P-450-AFB was induced mainly in Syrian Golden hamsters but not in Chinese hamsters, or in other species. This isozyme constitutes approximately 40% of the total cytochrome P-450 of the hepatic microsomes from 3-methylcholanthrene-treated Golden hamsters but only 1% in the microsomes of phenobarbital-treated hamsters. Thus, we conclude that the high activity of Golden hamster livers towards aflatoxin B1 activation was due presumably to this distinct and unique cytochrome P-450 isozyme which was induced mainly by 3-methylcholanthrene in Golden hamsters.

Influence of electrophilic character and glutathione depletion on chemical dysmorphogenesis in cultured rat embryos

To examine the importance of reduced intracellular glutathione (GSH) in the modulation of dysmorphogenesis and to gain insight into the electrophilic character of the embryotoxic intermediates generated in the rat embryo from N-acetoxy-2-acetylaminofluorene (AAAF) and acetaminophen (APAP) in cultured embryos, the effects of GSH depletion on the embryotoxicity, dysmorphogenesis and covalent binding of these agents were examined. Both AAAF (90 microM) and APAP (500 microM) produced concentration-dependent, statistically significant (P less than or equal to 0.05) decreases in embryonic length as well as embryonic and visceral yolk sac protein content when rat embryos were exposed in vitro between days 10 and 11 of gestation. The predominant malformations observed upon exposure to AAAF and APAP were prosencephalic hypoplasia and abnormal neurulation respectively. Exposure of conceptuses to [3H]APAP followed by separation and fractionation of the cellular RNA, DNA and protein via density gradient centrifugation resulted in detectable binding in fractions that contained protein, but not DNA or RNA. This suggested that the rat conceptus is capable of bioactivating APAP to a soft electrophile that selectively arylates protein. In contrast, conceptuses exposed to [3H]AAAF exhibited detectable binding to RNA, DNA and protein, indicative of conversion to both hard and soft electrophiles. Depletion of GSH was accomplished by pretreating conceptuses with 500 microM L-buthionine-S,R-sulfoximine (BSO) from the start of the culture period (day 9.5) until the morning of day 10. When conceptuses were depleted previously of GSH by BSO, exposure to APAP resulted in significant potentiation (relative to APAP alone) of the observed embryotoxicity. These conceptuses displayed further decreases in both embryonic size and protein content of the embryo and yolk sac, as well as increased incidence of abnormally open anterior neuropores and increased binding (3-fold) of [3H]APAP to protein. In contrast, pretreatment with BSO did not potentiate the AAAF-elicited decreases in embryonic size or protein content, nor the severity of prosencephalic hypoplasia, although a slight increase in binding of [3H]AAAF to DNA was observed. Taken together, these data are consistent with the concept that abnormal neurulation elicited by APAP results from the generation of one or more soft electrophilic species, whereas elicitation of prosencephalic hypoplasia by AAAF appears to be a consequence of conversion to a relatively hard electrophile(s).

Effects of modulation of hepatic glutathione on biotransformation and covalent binding of aflatoxin B1 to DNA in the mouse

Relative to the rat and most other species tested, the mouse is resistant to the carcinogenic effects of aflatoxin B1 (AFB). Previous investigations in our laboratory demonstrated that mouse liver cytosol has 52 times greater hepatic glutathione S-transferase (GST) activity toward the AFB-epoxide, compared with rat liver cytosol. To determine the importance of GST-mediated detoxification of the AFB-epoxide in the mouse in vivo, we examined the effects of glutathione (GSH) depletion on the covalent binding of AFB to hepatic DNA in control and 2(3)-butyl-4-hydroxyanisole (BHA)-treated mice. Male Swiss-Webster mice were fed control or 0.75% BHA diet for 14 days. Depletion of hepatic GSH was accomplished with D,L-buthionine-S-sulfoximine (BSO, 0.6 g/kg in saline) and diethyl maleate (DEM, 0.75 ml/kg), administered by ip injection at 2 and 1.5 hr, respectively, prior to administration of 3H-AFB (0.25 mg/kg, ip in DMSO). The combined BSO-DEM treatment depleted hepatic GSH by 97 and 70% in control and BHA-treated mice, respectively. In mice receiving the control diet, GSH depletion was associated with a 30-fold increase in the covalent binding of AFB to hepatic DNA. AFB-DNA binding in mice treated with dietary BHA alone was reduced to 54% of control. In BHA-treated mice, BSO-DEM treatment increased AFB-DNA binding by 62%. Dietary BHA increased hepatic S-9 mediated activation of AFB to the AFB-epoxide by eightfold in both control and BSO-DEM mice. BHA also increased GST activity toward the AFB-epoxide by 52 and 68% in control and BSO-DEM mice, respectively. The BSO-DEM treatment alone had no significant effect on the in vitro biotransformation of AFB. These results support the hypothesis that GST is the principal determinant of species differences in susceptibility to AFB-induced hepatocarcinogenicity. The results also support the hypothesis that BHA may protect against the toxic and carcinogenic effects of xenobiotics in part by preventing the depletion of hepatic GSH.

Conjugation of model substrates or microsomally-activated aflatoxin B1 with reduced glutathione, catalysed by cytosolic glutathione-S-transferases in livers of rats, mice and guinea pigs

Glutathione-S-transferase (GST) activity has been examined in liver cytosol fractions from guinea pigs, mice, control fed rats or rats with pre-neoplastic nodular liver lesions. The levels of activity in unfractionated cytosols have been assayed using the model substrates 1-chloro-2,4-dinitrobenzene (CDNB), 3,4-dichloronitrobenzene (DCNB) and monobromobimane (mBrB) with reduced glutathione (GSH). The order of activities in the various liver fractions using CDNB as substrate were: mouse greater than pre-neoplastic nodular rat greater than guinea pig greater than control rat and paralleled the capacities of the cytosols to catalyse the formation of aflatoxin B1-GSH from microsomally-activated aflatoxin B1 (AFB1) and GSH. Quantitative differences between the activities of the cytosols using the three model substrates were observed. In the mouse fractionation of GST activity by isoelectric focusing (I.E.F.) on preparative granular gels showed that the most basic component (isoelectric point pH 9.4) with the highest conjugating activity with respect to microsomally-activated AFB1 did not correspond with the peak of most activity for conjugating CDNB. In the pre-neoplastic nodular rat liver the CDNB conjugating activities of all fractions separated on granular I.E.F. gels, were higher than the corresponding fractions isolated from control rat liver, with particular enhancement of the peak containing the 3:3 isoenzyme. In contrast to control rat liver the 7:7 isoenzyme was detected in pre-neoplastic nodular liver preparations. These isoenzymes (3:3 and 7:7) did not contribute significantly to the enhanced level of AFB1-GSH formation catalysed by cytosol fractions prepared from pre-neoplastic nodular rat liver. The microsomally-activated AFB1-conjugating activity of unfractionated rat liver cytosols was increased to a relatively greater extent than CDNB conjugating activity during the induction of pre-neoplastic nodular liver lesions, and the elevated level of the activated AFB1-conjugating activity was found to be associated with the most basic fraction (isoelectric point pH 9.0). Analytical isoelectric focusing gels using mBrB as substrate demonstrated the presence of a basic GST isoenzyme in the pre-neoplastic nodular rat liver, not detected in preparations from the livers of control rats. The low level of activated AFB1-conjugating activity present in unfractionated guinea-pig cytosol was found to correspond with the fraction containing the peak of CDNB conjugating activity on preparative isoelectric focusing (isoelectric point pH 7.5). The lack of correlation between the conjugation of model substrates and the conjugation of xenobiotics could be of import

Comparative effects of butylated hydroxyanisole on hepatic in vivo DNA binding and in vitro biotransformation of aflatoxin B1 in the rat and mouse

To determine the mechanisms which mediate species- and treatment-related differences in susceptibility to aflatoxin B1 (AFB), we conducted a comparative study of the effects of dietary butylated hydroxyanisole (BHA) on the hepatic in vivo DNA binding and in vitro biotransformation of AFB in the rat and mouse. Mice are resistant to the hepatocarcinogenic effects of AFB, and BHA pretreatment has been shown to inhibit the carcinogenic effects of AFB in the highly susceptible rat. Rats and mice were fed a control diet or an identical diet containing 0.75% BHA for 10 days. On the 11th day, one-half of the control and BHA animals were administered [3H]AFB (0.25 mg/kg in dimethyl sulfoxide) via intraperitoneal injection. Animals were killed 2 hr later and covalent binding of AFB to hepatic DNA was determined. The remaining animals were killed for preparation of hepatic subcellular fractions used in in vitro assays. BHA treatment resulted in a decrease in in vivo hepatic AFB-DNA adduct formation in mice to 68% of control, but, in rats, treatment decreased AFB-DNA binding to 18% of control. Furthermore, hepatic AFB-DNA binding in control mice was only 1.2% of that measured in control rats. The rate of in vitro activation of AFB to the epoxide was 3.4-fold greater in control mice relative to control rats. BHA pretreatment increased the activation of AFB in mice 3.3-fold, but had no effect on oxidative metabolism in rats. Control mice had 52 times greater glutathione S-transferase (GST) activity toward the AFB-epoxide, but only 2.6 times greater GST activity toward 1-chloro-2,4-dinitrobenzene (CDNB), compared to that of control rats. In mice, BHA did not significantly increase GST activity toward the AFB-epoxide, but increased GST activity toward CDNB 3.1-fold. In rats, BHA increased GST activity toward the AFB-epoxide and CDNB by 3.2- and 2.1-fold, respectively. Epoxide hydrolase activity toward p-nitrostyrene oxide in mice was only 52% of the activity in rats. BHA increased epoxide hydrolase activity 3.8- and 2.5-fold in mice and rats, respectively. These data indicate that mice have high levels of an AFB-epoxide-specific GST activity relative to that of the rat. The rate of formation of the AFB-epoxide and the activity of epoxide hydrolase appear to be relatively unimportant under conditions of high GST activity, whereas elevated GST activity, and thus inactivation of the AFB-epoxide, appears to be the critical component in species- and BHA-induced differences in AFB-DNA adduct formation and, presumably, AFB hepatocarcinogenicity.

Strain differences in the metabolic activation of aflatoxin B1 in the rat

It has been reported that female Fischer rats are much more susceptible to the hepatocarcinogenic effects of aflatoxin B1 than female DA rats. Female Fischer rats are approximately twice as active as female DA rats in producing adducts of aflatoxin B1 with DNA in vivo, in freshly isolated hepatocytes and with hepatic microsomal fractions. There was no difference between the hepatic microsomal fractions from Fischer and DA rats in the production of adducts between aflatoxin B1 and microsomal protein. The difference between the strains in the formation of adducts with DNA was not due to either the activity of glutathione S-transferases or to the selective destruction of cytochrome P-450 in the DA strain. None of the differences reported here was of sufficient magnitude to explain the difference in susceptibility of the rat strains to the hepatocarcinogenic effects of aflatoxin B1.

Aetiological factors in hepatocellular cancer

The major risk factors for HCC are outlined in Table 2. Each factor may contribute to the multistep process of hepatocarcinogenesis. Hepatitis B virus and aflatoxins are the principal aetiological candidates and may be considered as initiators of the malignant state (see Figure 1). The majority of HCC arises via the cirrhotic pathway; the associated changes in the hormonal milieu may alter the handling of environmental carcinogens and the rounds of cell proliferation may increase sensitivity to sub-threshold doses of carcinogens. Exogenous androgens and oestrogens may operate through a similar mechanism to promote clonal expansion of preneoplastic cells. The importance of identifying the major aetiological factors lies in the possibility of prevention. The prognosis of HCC is dismal and it represents a major scourge in developing Third World countries. It is encouraging to think that the majority of cases could be prevented by the widespread use of hepatitis B vaccines and the development of intervention programmes against aflatoxin contamination of foodstuffs.

Variables influencing DNA-binding in mouse liver

The suitability of certain mouse strains for carcinogenicity testing has been questioned. Some chemicals increase the incidence of liver tumors above a relatively high background, an effect not seen in rats. This raises the question whether species and tissue specific effects are involved which are reflected in the DNA binding of metabolites. DNA binding indices in mouse liver have been determined in only a few instances. They are comparable to those found for rat liver DNA with aniline, benzo(a)-pyrene, butadiene, dimethylnitrosamine, methylnitrosourea and they are lower in the mouse with aflatoxin B1, trans-4-acetylaminostilbene and 2-aminofluorene derivatives. The available data on DNA binding in mouse liver suggest that the same adducts are formed as in rats but that metabolism and repair are variables which can modify the extent of DNA damage. However, the extent of DNA binding does not always correlate with the susceptibility of this tissue to carcinogenesis. But mouse liver is no exception in this respect. It is concluded that the formation of mouse liver tumors in long term studies with genotoxic chemicals indicates tumor initiating potential. In contrast, there are other chemicals such as chlorinated hydrocarbon insecticides which do not bind to DNA to any extent and which are not genotoxic in common short term tests and yet give rise to liver tumors in mice but not in rats. Positive results in long term studies are suggested to indicate promoting properties of such compounds.

DNA damage and repair in mouse liver

The formation of DNA adducts in mouse liver has been demonstrated for numerous chemicals including members of most major classes of carcinogens. Considerably less is known about the persistence and repair of DNA adducts in mouse liver. Likewise, major gaps in present knowledge exist regarding the molecular dosimetry of DNA adducts and their potential for miscoding during continuous exposure to high versus low doses of carcinogens. A prime example of this is 2-acetylaminofluorene (2-AAF), the carcinogen used in the ED01 megamouse study. There are no molecular dosimetry studies on the DNA adducts of 2-AAF, even though such a unique data base exists for the dose-response relationship of mouse liver tumors. Reviewing the pertinent literature, identifying deficiencies, and conducting the required research will hopefully permit a better determination of the relevance of mouse liver tumors to man.

Differential effects on the metabolism of dimethylnitrosamine and aflatoxin B1 by hepatic microsomes from senescent rats

The ability of hepatic microsomes from senescent rats to metabolize the two potent hepatocarcinogens dimethylnitrosamine (DMN) and aflatoxin B1 (AFB1) was investigated. Seven and 24-month-old male Sprague-Dawley rats were used. Liver weights, and microsomal protein per gram tissue weight were higher, whereas cytochrome P-450 and cytochrome b5 were significantly lower in older rats. Glutathione S-transferases and NADPH cytochrome c reductase activities were dramatically reduced in senescent rats. There was no difference in the formation of formaldehyde from DMN in vitro (31 vs. 34 pmol/nmol P-450) between the young and old rats. In contrast, increased microsome mediated binding of AFB1 to DNA was observed in older rats (116 vs. 228 pmol/nmol P-450) suggesting the possibility of either quantitative or qualitative changes in P-450 species. Additionally the cytoplasmic GSH S-transferases from older rats affected lower inhibition of binding of AFB1 to DNA. These results indicated differential abilities in the hepatic microsomal metabolism of these two carcinogens which may cause differential effects of these carcinogens in senescent rats.

Effects of single-dose and repeated-dose pretreatment with 2(3)-tert-butyl-4-hydroxyanisole (BHA) on the hepatobiliary disposition and covalent binding to DNA of aflatoxin B1 in the rat

The effects of two distinctive BHA pretreatment regimens on the biliary excretion of aflatoxin B1 (AFB) metabolites and the covalent binding of AFB to hepatic DNA were studied in vivo in the rat. To differentiate between enzyme induction effects and direct antioxidant effects, BHA was given to rats for 9 days (500 mg/kg/day, sc) or as a single dose (500 mg/kg, po), and [3H]AFB was administered ip. Repeated treatment with BHA enhanced the biliary excretion of both the glutathione conjugate of AFB and the AFP1-glucuronide to 200% of control values, reduced the amount of AFB remaining in the liver to 53% of control and reduced the covalent binding of AFB to hepatic DNA to 16% of control. A single BHA treatment had no effect on the biliary excretion of AFB or the binding of AFB to hepatic macromolecules, even though high concentrations of BHA were present in the liver during the period of AFB metabolism. These results support the hypothesis that BHA inhibits AFB carcinogenesis via the induction of phase II biotransformation pathways such as glutathione S-transferase, which act to reduce the amount of AFB-epoxide available for binding to DNA. We found no evidence of a direct antioxidant effect of BHA in altering the hepatobiliary disposition of AFB.

Acute aflatoxicosis in genetically resistant and nonselected Japanese quail

Aflatoxin B1 (AFB1) was administered by either oral intubation or intravenous (IV) injection to two lines of Japanese quail selected for aflatoxin resistance (AR2.5 and AR3) and a nonselected control line (NS). Pretreatment feed consumption did not vary significantly between lines; however, normal water intake of AR quail was 25% greater than that of NS quail. Oral AFB1 dosing (1.0 mg/kg body wt) elicited 53 and 25% decreases in feed and water consumption of NS quail within 24 hr. The only postdose change detected in the selected lines was a 10% increase in AR2.5 water intake. Oral AFB1 dosing also caused a significant reduction in excreta dry matter of NS quail. Twenty-four hr after IV AFB1 injection (.75 mg/kg body wt), feed and water consumption of the NS line were depressed by 93 and 75%, respectively, but only feed intake was decreased (13%) in the AR2.5 line. Intravenously injected AFB1 did not affect 24-hr parameters in the AR3 line. Body weight loss was noted in NS quail after both oral and IV dosing, while the AR lines maintained pretreatment body weights. Both AR lines also exhibited resistance to AFB1-induced hepatic lesions observed in NS birds. Biliary output was also studied during a 12-hr period following IV administration of AFB1. Cholecystic bile measurements taken at 1.5- and 3-hr after dosing averaged 34 and 50% higher in the AR lines than in the NS line. These results demonstrate the resistance of the selected quail to AFB1 whether administered orally or intravenously and therefore, indicate the AR line resistance is unrelated to intestinal absorption of the toxin.(ABSTRACT TRUNCATED AT 250 WORDS)

Modulation by certain factors of metabolic activation of aflatoxin B1 as detected in vitro in a simple fluorimetric assay

Forty compounds belonging to various chemical groups have been tested for their ability to suppress metabolic activation of aflatoxin B1 (AFB1) mediated by rat liver microsome. Microsomal activation has been carried out in an in vitro system containing Tris-buffer at pH 7.2. Production of the reactive metabolite, AFB1 8,9-epoxide, has been measured by separation and detection of its hydrolysis product AFB1 8,9-dihydrodiol as the Tris-diol complex. The complex is separated using simple procedures of biphasic extraction and deproteinization, and detected by its characteristic fluorescence. Quantitation is made by direct comparison of its fluorescence with that of an authentic Tris-diol prepared synthetically. The method is rapid and proved to be highly sensitive and reproducible. A large number of compounds have been observed to modulate at varying degrees the activation of AFB1 in this in vitro system. Many compounds have been tested at several concentration ranges and inhibition curve is constructed in each case from which ID50 values, i.e., the dose needed to bring about 50% inhibition can be obtained. These values expressed as nmol afford a direct and realistic comparison of the inhibitory potential of various modulators. Factors having great inhibitory potential have been identified as retinoids (retinol, retinal, retinoic acid, retinyl acetate), beta-carotene, riboflavin, ascorbic acid, copper, zinc, linoleic acid, p-hydroxy benzoic acid, butylated hydroxyanisole, butylated hydroxytoluene, disulfiram, and phenothiazine. Several other compounds have shown moderate inhibitory potential. The strong inhibition on Tris-diol formation by several vitamins, antioxidants and trace metals shows similarity with their effect on AFB1-DNA adduct formation. It is suggested that these agents may have potential anticarcinogenic activity against AFB1.

Effect of butylated hydroxyanisole on in vivo and in vitro hepatic aflatoxin B1-DNA binding in rats

Butylated hydroxyanisole (BHA) pretreatment of male rats has been examined for its effect on in vivo and in vitro hepatic aflatoxin B1-DNA binding (AFB1-DNA) in these animals. No difference either in cytochrome P-450 content or microsome-mediated AFB1-DNA was observed between livers from control and treated rats. However, cytosols from treated animals showed severalfold more inhibition of microsome mediated AFB1 binding to either exogenous or endogenous DNA than cytosols from controls. Presence of 1 mM level of either trichloropropene oxide or styrene oxide partially reversed the cytosolic inhibition of binding. Intraperitoneal administration of AFB1 2h before killing produced 50% less AFB1 binding to nuclear DNA in treated than in control animals. The role of induced glutathione S-transferases in treated rats in modulating hepatic AFB1-DNA binding is discussed.