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PubMed1980

The effects of aflatoxin B1 on some testicular and kidney enzyme activity in rat.

The effects of chronic intra-peritoneal administration of aflatoxin B1 on the activity of alkaline and acid phosphatases; glutamic oxaloacetate (GOT) and pyruvate transaminases (GPT); 5'-nucleotidase and lactic dehydrogenase enzymes were monitored in the testis and kidney of adult albino rats. Results showed that aflatoxin B1 depressed the activity of alkaline phosphatase in both tissues, but increased that of acid phosphatase in only the testis. While GOT and 5'-nucleotidase were inhibited, GPT and lactic dehydrogenase activity was enhanced by this carcinogen. These responses were similar for the testis and kidney. The above findings coupled with the microscopical observation of the testis tissue seem to indicate that the essential lesion of this toxin on the testis may be a modification of the enzymes of germinal cells resulting from a gradual depletion of the latter. Furthermore, the results appear to show that by and large, aflatoxin B1 exerts only slightly different effects on the testis and kidney at the enzyme level.

Acid Phosphatase↗
PubMed1981

Determination of aflatoxin B1 in corn, wheat, and peanut butter by enzyme-linked immunosorbent assay and solid phase radioimmunoassay.

Determinations of aflatoxin B1 in corn, wheat, and peanut butter by an enzyme-linked immunoassay (ELISA) and a solid-phase radioimmunoassay (RIA) were compared. Samples spiked with 2.9-43.2 ppb B1 were subjected to AOAC extraction procedure 26.017 or 26.023. The extracts were concentrated, redissolved in methanol, diluted in phosphate-buffered saline with Tween 20, and directly analyzed for B1 by either ELISA or RIA. At 5.8 ppb or greater, recoveries for B1 in corn, wheat, and peanut butter samples were 80.0, 86.6, and 94.8% by ELISA and 61.0, 93.3, and 110.0% by RIA, respectively. Recoveries greater than 120% were obtained for the wheat and peanut butter samples spiked with 2.9 ppb aflatoxin B1 by the RIA method but not by ELISA. Overall results indicated that ELISA gave more consistent data, relatively lower standard deviations, and lower coefficients of variation than did RIA. Analysis of 3 samples naturally contaminated with aflatoxins revealed that the ELISA data were comparable to those obtained by other established chemical methods.

Aflatoxin B1↗
PubMed1992

Effect of dietary aflatoxin B1 on the growth response and haematologic changes of young Japanese quail.

Feeding of aflatoxin B1 at the rate of 0.5 ppm to young Japanese quail resulted in significant (p less than 0.01) decrease in body weight gain that became apparent on the third week. There was no significant difference in the mean values of haemoglobin, packed cell volume and total erythrocyte counts of quail chicks given aflatoxin B1 in feed in comparison to those fed on a similar diet without aflatoxin. However, the total leucocyte count revealed an increase on the third week which was due to an increase in the percentage of heterophils and decrease in lymphocytes.

Aflatoxin B1↗
PubMed1975

[The mycotoxin sensitivity of several Bacillus thuringiensis (Berliner) strains sensitive and resistant to aflatoxin B1].

Antimicrobial activity of pure preparations of seven mycotoxins, coumarin and dicoumarin, was studied against various strains of Bacillus thuringiensis (Berliner). The acquisition of resistance to Aflatoxin B1, by a new strain designated "stable variant", obtained in the presence of mycotoxin lethal dose, is very specific. However, a relation seems to exist between Aflatoxin B1 susceptibility and sensitivity to compounds which possess a double furan ring. In vitro, coumarin exhibits an inhibitory effect against antibacterial activity of Aflatoxin B1.

Aflatoxins↗
PubMed2005

Fecal and urinary excretion of aflatoxin B1 metabolites (AFQ1, AFM1 and AFB-N7-guanine) in young Chinese males.

Our study was designed to assess the fecal and urinary excretion of 3 aflatoxin B1 (AFB1) metabolites, aflatoxins M1 (AFM1) and Q1 (AFQ1) and aflatoxin B1-N7-guanine (AFB-N7-guanine) that are produced by the predominant forms of cytochrome P450 enzymes responsible for the biotransformation of AFB1. Fecal and urinary AFM1, AFQ1 and urinary AFB-N7-guanine were assessed in 83 young Chinese males selected from a larger population (n = 300) based on detectable urinary AFM1. The concentration of fecal AFQ1 (median 137 ng/g fresh weight, IQR 9.1 to 450) was approximately 60 times higher than that of AFM1 (2.3 ng/g, IQR 0.0 to 7.3). In urine, the median AFQ1 was 10.4 ng/ml (IQR 3.4 to 23.3), and the median AFM1 and AFB-N7-guanine 0.04 ng/ml (IQR 0.01 to 0.33) and 0.38 ng/ml (IQR 0.0 to 2.15), respectively. A subgroup (n = 14) with hepatitis B virus (HBV) infection had significantly higher fecal concentrations of AFQ1 (p = 0.043) and AFM1 (p = 0.001) than those who were hepatitis B-virus antigen (HBsAg) negative, and the respective differences in urinary AFQ1 and AFM1 concentrations approached statistical significance (p = 0.054, p = 0.138). Our study demonstrates that AFQ1 is excreted in urine and feces at higher levels than AFM1, and feces are an important route of excretion of these AFB1 metabolites. AFQ1 should be further assessed for its predictive value as a marker for exposure and risk of dietary aflatoxins.

Aflatoxin B1↗
PubMed1989

The effect of inducers of mixed-function oxidases on hepatic microsome-mediated aflatoxin B1 transformation in C3H/10T1/2 cells.

The potent hepatotoxin and hepatocarcinogen aflatoxin B1 (AFB1) is metabolized by different forms of cytochrome P450 associated with the hepatic mixed-function oxidase system. C3H/10T1/2(10T1/2) cells, which have limited inherent capacity to metabolize AFB1, were treated with AFB1 in the presence of hepatic microsomes isolated from chemically treated rats to investigate the effects of the induction of specific cytochromes P450 on AFB1-mediated toxicity and transformation. Relative to uninduced microsomes, phenobarbital (PB) treatment induced AFB1-DNA binding (essentially representing the formation of AFB1-8,9-oxide bound to DNA) 3.2-fold, while pretreatment with Aroclor 1254, 3-methylcholanthrene (3-MC), or 5,6-benzoflavone (beta-NF) preferentially induced aflatoxin M1 (AFM1) formation from 2- to 5-fold. 10T1/2 cells were exposed to a multiple treatment regimen with 4 microM AFB1 and hepatic microsomes from uninduced, PB-, Aroclor 1254-, 3-MC-, or beta-NF-treated rats; respective cumulative toxicities of approximately 90, 95, 70, 60, and 40% control (no microsomes) values resulted. An enhanced AFB1 transformation response correlated with the increasing toxicities observed for the different treatments, with uninduced or PB-induced microsomes yielding approximately four foci/dish, while treatments with Aroclor 1254-, 3-MC-, or beta-NF-induced microsomes resulted in only one to two foci/dish. These results demonstrate that AFB1 is a complete carcinogen in the 10T1/2 system when repetitive incubations are used in conjunction with an appropriate hepatic microsomal activation system. These data also correlate the induction of AFB1-4-hydroxylase with a decrease in AFB1-mediated toxicity and transformation of 10T1/2 cells, and support the hypothesis that the Phase I metabolic conversion of AFB1 to AFM1 in the liver represents an effective detoxification pathway per se.

Aflatoxin B1↗
PubMed1994

Ultrastructural changes in murine lymphocytes induced by aflatoxin B1.

This investigation sought to determine whether splenic lymphocytes obtained from Balb/C mice exposed to aflatoxin B1 (AFB1) showed any ultrastructural changes which could account for the immunodysfunction attributable to aflatoxins. Lymphocytes obtained from Balb/C mice administered aflatoxin B1 in olive oil daily for three weeks were studied using both transmission and scanning electron microscopy. The lymphocytes demonstrated ultrastructural changes primarily in the mitochondria where marked internal dissociation of the cristae was revealed by transmission electron microscopy. All other cellular organelles were unaffected. No significant alterations in external structure were observed under scanning electron microscopy. The findings of this study indicate that AFB1 administration does not affect the surface topography of lymphocytes, but AFB1, by causing extensive mitochondrial damage, may affect the way in which these cells function. This could be a possible explanation for the immunodysfunction associated with AFB1.

Aflatoxin B1↗
PubMed2001

Cytotoxicity of aflatoxin B1 and its chemically synthesised epoxide derivative on the A549 human epithelioid lung cell line.

Aflatoxin B1 (AFB1 ) is a carcinogenic mycotoxin found in feeds and in airborne grain dusts. Aflatoxin B1 requires biotransformation to the AFB1-8,9 epoxide (AFBO) by a bioactivation system and subsequent covalent binding to DNA or proteins, to exert its carcinogenic potential. The lung contains cytochrome P450, prostaglandin-H-synthase, lipoxygenase, epoxide hydrolase and other bioactivation enzymes, and is thus a potential target for the effects of AFB1 via the routes of inhalation and ingestion. The A549 human epithelioid lung cell line and the methylthiazol tetrazolium (MTT) bioassay were used to investigate the cytotoxicity of AFB1 and its chemically synthesised epoxide (AFBO) in vitro. Statistical analysis of the MTT results indicated that there were overall significant differences between the control and both the AFB1-treated (p < 0.0001) and AFBO-treated cells (p = 0.002). However, there was no significant difference between AFB1 and AFBO-treated cells, when the entire range of concentrations were assessed against each other (p = 0.2877). When analysed at each concentration, only at 0.01 mM was there a significant difference between the effects of AFB1 and AFBO (p = 0.0358). The results of this investigation show that AFB1 and AFBO are both cytotoxic in the A549 cell line.

Aflatoxin B1↗
PubMed1990

Aflatoxin-B1 inhibition of spermatogenesis in the toad Bufo regularis.

Aflatoxin-B1 was injected in a dose of 0.01 mg/50 g body weight into the dorsal lymph sac of male toads (Bufo regularis) to evaluate its effect on the testes. After three and six weeks' treatment the diameters of the seminiferous tubules were significantly reduced. Furthermore, spermatogenic cells were almost completely absent. The histological evidence also showed complete suppression of spermatogenesis. It is suggested that one or several AFB1 metabolites may be responsible for suppression of spermatogenesis in the given toads, through inhibition of testicular androgenic activity.

Aflatoxin B1↗
PubMed1984

Quantitation of aflatoxin B1 adduction within the ribosomal RNA gene sequences of rat liver DNA.

The in vivo formation of covalent aflatoxin B1 (AFB1)-DNA adducts within the rRNA gene sequences of nuclear DNA has been studied in AFB1-treated rats. Liver nuclear DNA, enriched in ribosomal DNA (rDNA) by one round of cesium salt density gradient centrifugation, was treated under buffered alkaline conditions to convert unstable AFB1-N7-guanine adducts to stable AFB1-formamidopyrimidine derivatives. The alkali-treated DNA was hybridized to 18S and 28S rRNA in 70% formamide buffer to form rRNA X rDNA hybrids. These hybrids were separated from the bulk of nuclear DNA by two rounds of centrifugation in CsCl, and the level of AFB1 adduction to rDNA versus total nuclear DNA was compared as a function of dose 2 hr after AFB1 administration. Over an 8-fold dose range (0.25-2.0 mg of AFB1 per kg of body weight), rDNA contained 4- to 5-fold more AFB1 residues than nuclear DNA, indicating that rDNA is preferentially accessible to carcinogen modification in vivo. While aflatoxin B1 forms adducts with DNA principally at guanine residues, the guanine enrichment of rDNA was insufficient to explain the magnitude of observed preferential AFB1 modification of rDNA. These results support the hypothesis that rDNA regions are preferentially accessible to carcinogen modification because of the diffuse conformation maintained within transcribed genes. This experimental approach permits the quantitative description of carcinogen modification within a defined gene sequence; further refinement of this approach may be useful in defining the precise relationships between covalent chemical-DNA interactions and the alterations in gene expression that result.

Aflatoxin B1↗
PubMed1988

Effects of cortisol pretreatment on the acute hepatotoxicity of aflatoxin B1.

Effects of cortisol pretreatment on acute hepatotoxicity induced by aflatoxin B1 (AFB1) were investigated in female rats. Pretreatment of cortisol (1.0-10.0 mg/kg body weight) for 7 consecutive days markedly increased mortality rate, activity of plasma glutamic pyruvic transaminase (PGPT), plasma glutamic oxaloacetic transaminase (PGOT) and liver triglycerides induced by AFB1 (3.0 mg/kg body weight). The potentiating action of cortisol on hepatic necrosis of AFB1 showed a dose-dependent pattern. The possible mechanism of its action may be related to an increase in the activity of aniline hydroxylase and formation of AFB1-2,3-epoxide which in turn caused a marked increase in AFB1 binding to hepatic DNA and proteins, and lipid peroxide formation. Therefore, the potentiating action of cortisol on AFB1 hepatotoxicity may possibly increase the damage to DNA and membranes of various organelles.

Aflatoxin B1↗
PubMed1982

Ultrastructural changes in the liver of rats treated with aflatoxin B1 and undernutrition.

White male Wistar rats were treated with Aflatoxin B1 for 2 months while on standard pellet food ad libitum or 80% undernutrition. Although each animal received 400 micrograms of AFB1 no cancer in the liver or elsewhere developed. Histologically the findings in the groups treated with the mycotoxin were the well known until now. Undernutrition led to atrophic and degenerative changes in the liver. Electronmicroscopically there were found marked changes in the nucleus, with microsegregation of the nucleolus; diminution and disorganization of endoplasmic reticulum and mitochondria; changes in the lysosomes, abundance of microbodies etc. with difference according to the intoxication, nutrition, or both of them. However, the combination of the 2 etiologic factors did not lead to a simple summation of the deleterious effect. At the same time, we do not have the right to claim a real "anticarcinogenic" action of undernutrition.

Aflatoxin B1↗
PubMed1981

Effects of activated aflatoxin B1 and caffeine on DNA replicon initiation in HeLa cells.

Aflatoxin B1 (AFB1) is activated by a rat microsomal extract (S-9) to form a product that inhibits DNA synthesis in HeLa cells. At 10(-7) M, AFB1 inhibited initiation of replicons, as shown in alkaline sucrose gradient profiles 30 min after incubation with the drug. Ninety minutes later, the profile of treated cells was similar to that of control, but 4 h later there was another effect on replicon initiation. At 10(-6) M, the inhibition of initiation was greater than at 10(-7) M and increased progressively. Four hours after removal of the drug, the gradient profile showed low amounts of radioactivity in all size classes of DNA. When cells were incubated in medium containing caffeine (2mM) even as late as 60 min after incubation with AFB1, the inhibition of replicon initiation was prevented. If caffeine was later removed from the medium, replicon initiation was then inhibited. At 10(-7) M or 10(-6) M, AFB1 had little immediate effect on chain elongation, but at 10(-5) M, the gradient profiles showed an accumulation of low molecular weight DNA molecules, with no radioactivity in the region of high molecular weight DNA, owing to a block to chain elongation; this was not affected by caffeine. These results suggest that AFB1 induces damage that changes the conformation of chromatin so that initiation of new replicons cannot occur; in the presence of caffeine this change does not occur and DNA replication is not inhibited.

Aflatoxin B1↗
PubMed1989

Influence of dietary protein, fat or amino acids on the response of weanling swine to aflatoxin B1.

Two experiments were conducted using corn from clean or aflatoxin B1 (AFB1)-contaminated (182 ppb) sources. Weanling pigs (28 d) were fed one of eight dietary treatments arranged in a 2 x 2 x 2 factorial design. In Exp. 1 (192 pigs), treatments varied in corn source (clean or AFB1-contaminated), CP level (18 or 20%) and added fat (0 or 5%). At the end of the 28-d growth trials, plasma samples were obtained. An AFB1 x CP level interaction was detected (P less than .05) for growth rate (ADG), feed intake (FI) and feed/gain ratio (F/G). Feeding AFB1 reduced (P less than .05) ADG (.30 vs .37 kg/d) and FI (.57 vs .66 kg/d) and increased F/G (1.88 vs 1.78) of pigs fed 18% CP diets. Performance of pigs fed 20% CP diets was not altered by AFB1. Adding 5% fat to diets improved (P less than .05) F/G but did not improve ADG of pigs fed AFB1. There was an AFB1 x CP x fat interaction (P less than .05) for plasma cholesterol. Adding fat or increasing the CP level prevented the depression of plasma cholesterol in pigs fed AFB1. In Exp. 2 (96 pigs), all diets contained 18% CP and the treatments varied in corn source (clean or AFB1-contaminated), added L-lysine HCl (0 or .25%) and added DL-methionine (0 or .15%). Feeding AFB1 reduced (P less than .05) ADG of pigs fed the 18% CP diet (.44 vs .50 kg/d) but not of pigs fed diets supplemented with .25% lysine.(ABSTRACT TRUNCATED AT 250 WORDS)

Aflatoxin B1↗
PubMed1991

Transcriptional effect of aflatoxin B1 on cytosine and/or hypoxanthine containing DNAs.

The effect of aflatoxin B1 (AFB1) on the template function for RNA synthesis of several single and double-stranded synthetic DNAs containing cytosine (C) and/or hypoxanthine (H) bases is studied in vitro. The results indicate that AFB1, after liver microsome activation, strongly inhibits the template function of poly[d(I-C)] and has little, if any, effect on polydI.polydC, polydI, or polydC. This conclusion is reached whether rat liver nuclear free RNA polymerase or E. coli RNA polymerase is used for the transcription. The mechanism of this inhibition is believed mainly due to the inhibition of elongation of RNA synthesis, because autoradiography of the [alpha-32 P]GTP labeled RNAs after polyacrylamide gel electrophoresis clearly shows that the size of the RNA from AFB1 treated group is dramatically reduced. The evidence that the selective inhibition of poly[d(I-C)] template function is a direct reflection of the binding of AFB1 to poly[d(I-C)] is provided by the use of radioactive [3H]AFB1 for the binding and by spectrum analysis of the appearance of a broad AFB1-DNA adduct peak between 300 nm and 400 nm right after the typical DNA peak at 260 nm. These data, which are in direct support to our recent report (F.L. Yu, et al., Carcinogenesis, 11, 475-478, 1990), suggest that the binding of AFB1 prefers alternating, double-stranded DNA, and the binding affinity of AFB1 to DNA is greatly reduced when the bases are in either single- or double-stranded homopolymer forms.(ABSTRACT TRUNCATED AT 250 WORDS)

Aflatoxin B1↗
PubMed1985

Tigroid cell foci and neoplastic nodules in the liver of rats treated with a single dose of aflatoxin B1.

In rats treated orally with a single dose of aflatoxin B1 (5 mg/kg body weight) characteristic focal and nodular liver lesions developed which differed in their fine structure, enzyme histochemical pattern and growth behaviour from other types of carcinogen-induced hepatic foci and nodules described earlier. The foci were composed of a distinct cell population which showed specific structural changes of the cytoplasm. Typically, unusually large and abundant basophilic bodies consisting of highly ordered stacks of cisternae of the rough endoplasmic reticulum (ER) were arranged in long, striped bands and stood out against an acidophilic background which was due to hypertrophy of the smooth ER. We propose the descriptive terms 'tigroid cells', and 'tigroid cell foci' for this population of altered hepatocytes. Correlative cytochemical investigations on the tigroid cell foci revealed characteristic changes in carbohydrate metabolism, such as a decrease in the activity of glycogen synthetase and glycogen phosphorylase and an increase in the activity of glucose-6-phosphate dehydrogenase and glyceraldehyde-3-phosphate dehydrogenase. The activity of glucose-6-phosphatase and ATPase was normal (or partially reduced) and that of the gamma-glutamyl-transpeptidase was always lacking. A progressive increase in the number and size of the tigroid cell foci and transitions from tigroid cell foci to neoplastic nodules with similar morphological and cytochemical features were observed during the time period of 104 weeks. The mitotic index within tigroid cell foci and nodules was approximately 100 times higher than that of the surrounding hepatic tissue or the liver parenchyma of untreated control animals. The important question whether the tigroid cell foci represent a specific pre-neoplastic or early neoplastic cell population requires further investigations.

Aflatoxin B1↗
PubMed2003

Excretion of aflatoxin M1 in milk of dairy ewes treated with different doses of aflatoxin B1.

Two experiments were conducted to study the amount of aflatoxin M1 (AFM1) in milk in response to feeding aflatoxin B1 (AFB1). In experiment 1, four dairy ewes in early lactation received a single dose of pure AFB1 (2 mg). Individual milk samples were collected during the following 5 d to measure AFM1 concentration. The average excretion of AFM1 in milk followed an exponential decreasing pattern, with two intermediate peaks at 24 and 48 h. No AFM1 was detected in milk at 96 h after dosing. The mean rate of transfer of AFB1 into AFM1 in milk was 0.032%, with a high individual variability (SD = 0.017%). In experiment 2, 16 dairy ewes in midlactation were divided into four groups that received different daily doses of AFB1 (0, 32, 64, and 128 microgram for control and groups T1, T2, and T3, respectively) for 14 d. Pure AFB1 was administered to each animal divided in two daily doses. Individual milk samples were collected at 12, 24, 36, 48, 72, 96, 144, 216, and 312 h after the first AFB1 administration, during the intoxication period, and every 24 h for 7 d after the withdrawal of AFB1. AFM1 was detected in the milk of all animals of the treated groups at 12 h after the administration of AFB1. In all treated groups, milk AFM1 concentration increased from 12 to 144 h after the beginning of administration. It then decreased, reaching a stable concentration at 216 and 312 h after the first administration. No AFM1 was detected in milk 3 d after the last administration of AFB1. Milk AFM1 concentration measured at steady-state condition was significantly affected by the AFB1 dose (0.031, 0.095, and 0.166 in T1, T2, and T3 groups, respectively), with a linear relationship between AFB1 dose and milk AFM1 concentration (R2 = 77.2%). The carryover (AFM1/AFB1 ratio) was not significantly affected by treatment, and its mean value was 0.112% (SE = 0.011). The carryover was lower than that reported for dairy cattle and goats, suggesting a better ability of sheep to degrade AFB1.

Aflatoxin B1↗
PubMed1988

Correlation studies between the binding of aflatoxin B1 to chromatin components and the inhibition of RNA synthesis.

Aflatoxin B1 (AFB1) is a potent inhibitor of rat liver nuclear and nucleolar RNA synthesis. However, since after activation AFB1 binds to both DNA and chromosomal proteins, the question is which form of binding is responsible for the inhibition of RNA synthesis. Male Sprague-Dawley rats (200 g) were given i.p. injections of 10, 50, 100, 300 and 500 micrograms AFB1 per 100 g body wt containing 50 microCi [3H]AFB1 (sp. act. 25 Ci/mmol), and the animals sacrificed 2 h later. Liver nuclei, nucleoli and P-3 (a transcriptionally active subnucleolar fraction that is 3.4-fold enriched in active rDNA) were isolated and the binding of AFB1 to DNA and protein of each fraction was determined by DNase I digestion and 5% trichloracetic acid (TCA) hydrolysis. We found that the binding of AFB1 to both nuclear and nucleolar DNA plateaus at 300 micrograms AFB1 per 100 g body wt with values around 100 and 400 pmol AFB1 per mg nuclear and nucleolar DNA, respectively. On the other hand, the binding to protein is linear, although with different slopes, for both nuclear and nucleolar fractions even at 500 micrograms AFB1 per 100 g body wt, the highest dose used. Since AFB1 inhibition of nuclear and nucleolar RNA synthesis plateaus respectively at 60% and 90% inhibition levels at the dose of 300 micrograms AFB1 per 100 g body wt, these results suggest the binding of AFB1 to DNA, but not to protein, is responsible for the inhibition of RNA synthesis. Further support for this contention is obtained by comparing the binding and the inhibition data between P-3 and nucleoli. P-3 is three times more transcriptionally active than nucleoli and, as a result, is more sensitive to AFB1 inhibition. This greater sensitivity is reflected by the specific binding activity of AFB1 to P-3 DNA, which is greater than 50% higher than to nucleolar DNA. In contrast, this effect is not reflected by the specific binding activity of AFB1 to protein which is exactly the same for both fractions.

Aflatoxin B1↗