Distribution of [14C]-labelled aflatoxin B1 in mice

Aflatoxin B1 induces infertility, fetal deformities, and potential therapies

Aflatoxin B1 (AFB1) is a subsidiary poisonous metabolite, archetypally spawned by Aspergillus flavus and A. parasiticus, which are often isolated in warm or tropical countries across the world. AFB1 is capable of disrupting the functioning of several reproductive endocrine glands by interrupting the enzymes and their substrates that are liable for the synthesis of various hormones in both males and females. In men, AFB1 is capable of hindering testicular development, testicular degeneration, and reduces reproductive capabilities. In women, a direct antagonistic interaction of AFB1 with steroid hormone receptors influencing gonadal hormone production of estrogen and progesterone was responsible for AFB1-associated infertility. AFB1 is potentially teratogenic and is responsible for the development of malformation in humans and animals. Soft-tissue anomalies such as internal hydrocephalus, microphthalmia, cardiac defects, augmented liver lobes, reproductive changes, immune modifications, behavioral changes and predisposition of animals and humans to neoplasm development are AFB1-associated anomalies. Substances such as esculin, selenium, gynandra extract, vitamins C and E, oltipraz, and CDDO-Im are potential therapies for AFB1. Thus, this review elucidates the pivotal pathogenic roles of AFB1 in infertility, fetal deformities, and potential therapies because AFB1 toxicity is a key problem globally.

Early exposure to food contaminants reshapes maturation of the human brain-gut-microbiota axis

Early childhood growth and development is conditioned by the consecutive events belonging to perinatal programming. This critical window of life will be very sensitive to any event altering programming of the main body functions. Programming of gut function, which is starting right after conception, relates to a very well-established series of cellular and molecular events associating all types of cells present in this organ, including neurons, endocrine and immune cells. At birth, this machinery continues to settle with the establishment of extra connection between enteric and other systemic systems and is partially under the control of gut microbiota activity, itself being under the densification and the diversification of microorganisms' population. As thus, any environmental factor interfering on this pre-established program may have a strong incidence on body functions. For all these reasons, pregnant women, fetuses and infants will be particularly susceptible to environmental factors and especially food contaminants. In this review, we will summarize the actual understanding of the consequences of repeated low-level exposure to major food contaminants on gut homeostasis settlement and on brain/gut axis communication considering the pivotal role played by the gut microbiota during the fetal and postnatal stages and the presumed consequences of these food toxicants on the individuals especially in relation with the risks of developing later in life non-communicable chronic diseases.

Effect of UV irradiation on aflatoxin reduction: a cytotoxicity evaluation study using human hepatoma cell line

In this proof-of-concept study, the efficacy of a medium-pressure UV (MPUV) lamp source to reduce the concentrations of aflatoxin B₁, aflatoxin B₂, and aflatoxin G₁ (AFB_1, AFB₂, and AFG₁) in pure water is investigated. Irradiation experiments were conducted using a collimated beam system operating between 200 to 360 nm. The optical absorbance of the solution and the irradiance of the lamp are considered in calculating the average fluence rate. Based on these factors, the UV dose was quantified as a product of average fluence rate and treatment time. Known concentrations of aflatoxins were spiked in water and irradiated at UV doses ranging from 0, 1.22, 2.44, 3.66, and 4.88 J cm^-2. The concentration of aflatoxins was determined by HPLC with fluorescence detection. LC-MS/MS product ion scans were used to identify and semi-quantify degraded products of AFB₁, AFB₂, and AFG₁. It was observed that UV irradiation significantly reduced aflatoxins in pure water (p < 0.05). Irradiation doses of 4.88 J cm^-2 reduced concentrations 67.22% for AFG₁, 29.77% for AFB₂, and 98.25% for AFB₁ (p < 0.05). Using this technique, an overall reduction of total aflatoxin content of ≈95% (p < 0.05) was achieved. We hypothesize that the formation of ˙OH radicals initiated by UV light may have caused photolysis of AFB₁, AFB₂, and AFG₁ molecules. In cell culture studies, our results demonstrated that the increase of UV dosage decreased the aflatoxin-induced cytotoxicity in HepG₂ cells. Therefore, our research finding suggests that UV irradiation can be used as an effective technique for the reduction of aflatoxins.

Aflatoxin B1-induced epigenetic alterations: An overview

Aflatoxin B1 (AFB1) is widely distributed in nature, especially in a variety of food commodities. It is confirmed to be the most toxic of all the aflatoxins. The toxicity of AFB1 has been well investigated, and it may result in severe health problems including carcinogenesis, mutagenesis, growth retardation, and immune suppression. Epigenetic modifications including DNA methylation, histone modifications and regulation of non-coding RNA play an important role in AFB1-induced disease and carcinogenesis. To better understand the evidence for AFB1-induced epigenetic alterations and the potential mechanisms of the toxicity of AFB1, we conducted a review of published studies of AFB1-induced epigenetic alterations.

Teratogenic effects in rabbits of simultaneous exposure to ochratoxin A and aflatoxin B1 with special reference to microscopic effects

To elucidate the teratogenic effects, ochratoxin A (OTA) and aflatoxin B1 (AFB1) were dissolved in corn oil and administered in combination to New Zealand White rabbits during 6-18 days of gestation orally with the dose levels of OTA+AFB1, 0.05+0.05 and 0.1+0.1mg/kg body weight. To assess pathomorphological features of the anomalies, the fetal serial sections were histologically examined. There was no mortality in any of the treated groups. Body weights and body weight gains of dams in the combined treatment groups were comparable with those of controls and individual treatments. The mean crown to rump lengths in both the combination dose groups and mean fetal weights in high dose combination group were significantly decreased. In the high dose combination, there was increase in the percent of implants resorbed and significant increase in the incidence of visceral anomalies. The combination treatment resulted in various gross, skeletal and visceral anomalies such as wrist drop, scoliosis, bent metacarpals, rudimentary ribs, cardiac defects and microphthalmia. There was a dose-related increase in the percent of litters showing the histopathological changes in the fetal tissues. The incidence of histopathological changes in the tissue sections prepared from fetal liver, kidneys, brain, heart and eyes was found increased in the high dose combination group. The comparative evaluation of the results of combination versus individual treatments revealed that certain anomalies observed in the individual treatment of OTA such as knuckling of fetlock, rudimentary tail or agenesis of tail, wavy ribs, hydrocephalus and agenesis of kidney and AFB1 as enlarged eye sockets and enlarged liver were absent in the combination treatment. However, some new manifestations such as cardiac defects and scoliosis were seen. The results of the present study indicated that in combination, OTA and AFB1 have antagonistic interaction. The presence of subtle lesions histologically due to an interference with normal development suggested that microscopic examination of the fetal tissues could provide additional, useful information to a developmental toxicity study.

Effect in rats of simultaneous prenatal exposure to ochratoxin A and aflatoxin B1. I. Maternal toxicity and fetal malformations

Ochratoxin A (OA) and Aflatoxin B1 (AFB1), the food borne mycotoxins are produced by several fungal species of the genera Aspergillus and Penicillium. To determine the teratogenic effects, these mycotoxins were administered orally either individually or in combination to the pregnant Wistar rats on days 6-15 of gestation. OA and AFB1 were dissolved in corn oil and different doses of OA (0.125, 0.25, 0.50, and 0.75 mg/kg), AFB1 (0.125, 0.25, 0.50, and 1.00 mg/kg), and a combination of OA+AFB1 (0.125+0.125; 0.25+0.50; 0.50+0.25 mg/kg) were given by gastric intubation to rats. During dosing period, the body weight and body weight gains significantly decreased at a higher dosage, in both individual and combined treatments. In all the combination treatments, the percent implants resorbed, fetal body weights, and crown-rump lengths were comparable to those of controls and with the individual mycotoxin treatment. The number of dead fetuses was significantly increased in the high OA combination (OA+AFB1 0.50+0.25) group as compared with the other two combinations. OA and AFB1 alone and in combination caused various gross, skeletal, and visceral anomalies. The occurrence was considerably less pronounced in fetuses of AFB1 and combination groups as compared with those of OA group fetuses. The exencephaly, incomplete closure of skull, wavy and fused ribs, agenesis of the ischium bone, and enlarged renal pelvis, recorded in OA treatment and ear abnormality and incomplete ossification of skull bones observed in AFB1 when given individually, were not seen in combination groups. However, new manifestations, such as gastroschisis and syndactyly were observed and the incidence of cardiac defects was increased in fetuses due to the combined treatment. The results of the present study indicated that there is some interaction between these mycotoxins that resulted in reduced teratogenic activity of OA in the presence of AFB1. Apparently, new manifestations observed in combination treatment points to the potential threat of teratogenicity in terms of public health hazards.

Effects of aflatoxin B1 on embryo fetal development in rabbits

Aflatoxin B1 (AFB1), is a food borne mycotoxin produced by fungal species of the genera Aspergillus. To elucidate the teratogenic effects, AFB1 was dissolved in corn oil and given orally to New Zealand White rabbits during 6-18 days of gestation with the dose levels of 0.025, 0.05 and 0.1 mg/kg body weight. To assess pathomorphological features of the anomalies induced by AFB1, the fetal serial sections were histologically examined. There was no maternal mortality in any group. There was non-significant decrease in percent of live fetuses and increase in the percent resorptions and post-implantation losses at 0.1 mg/kg dose group as compared with those of controls. The mean crown to rump lengths of 0.05 and 0.1 mg/kg dose groups were significantly reduced than that of the control. The mean fetal weights were significantly reduced in 0.1 mg/kg dose group than that of other treated groups. The gross anomalies observed included wrist drop and enlarged eye socket whereas, skeletal anomalies were agenesis of caudal vertebrae, incomplete ossification of skull bones and bent metacarpals. The visceral anomalies of microphthalmia and cardiac defects were seen at 0.1 mg/kg dose group. The characteristic histological findings of fetal tissues were distortion of normal hepatic cord pattern and reduced megakaryocytes in liver, fusion of auriculo-ventricular valves, mild degenerative changes in myocardial fibers, microphthalmic eyes and lenticular degeneration. The results of this study indicated that AFB1 was found to be teratogenic in rabbits when given by oral route during gestation days 6-18 and the dose of 0.1 mg/kg could be considered as the minimum oral teratogenic dose. The histological examination of the fetal tissues indicated its importance in identifying the visceral anomalies which were otherwise not visible.

Low hepatic glutathione S-transferase and increased hepatic DNA adduction contribute to increased tumorigenicity of aflatoxin B1 in newborn and partially hepatectomized mice

Low levels of hepatic glutathione S-transferase and increased formation of aflatoxin B1 (AFB1)-DNA adducts correlate with hepatocyte proliferation and increased hepatocarcinogenesis in both newborn mice and partially hepatectomized adult mice, as compared to normal, adult C57BL/6J mice. Newborn mice, which are highly susceptible to the hepatocarcinogenic effects of AFB1, have active proliferation of hepatocytes until 3 weeks of age, when hepatocyte proliferation abruptly ceases. At about this time, the mice become highly resistant to AFB1. In adult mice, AFB1 carcinogenicity is increased after stimulation of liver proliferation by partial hepatectomy. To become carcinogenic, AFB1 is activated in the liver by the P450 enzyme system to electrophilic intermediates, some of which form DNA adducts believed to be responsible for mutations leading to cancer. The most carcinogenic intermediate, AFB(1)-8,9-epoxide, is detoxified by glutathione S-transferase-mediated conjugation to glutathione. Glutathione levels, glutathione S-transferase levels, and AFB1-DNA adduct formation were measured at 4, 10, 30, 120, 245 and 365 days of age in C57BL/6J mice. There was a 5-fold increase in hepatic glutathione S-transferase levels and 13-fold decrease in hepatic AFB1-DNA adduct formation over these ages. Induction of hepatocyte proliferation following partial hepatectomy of 120-day-old mice lowered hepatic glutathione S-transferase levels and increased the extent of hepatic AFB1-DNA formation to levels similar to those measured in 4-day-old mice. These results indicate that increased susceptibility to AFB1 hepatocarcinogenesis in newborn mice, and in adult mice following partial hepatectomy, is due to decreased GST and increased adduct formation in proliferating liver.

Effect in rats of simultaneous prenatal exposure to ochratoxin A and aflatoxin B1. II. Histopathological features of teratological anomalies induced in fetuses

The histopathological features of various abnormalities induced by different doses of ochratoxin A (OA), aflatoxin B1 (AFB1), and their combination in rat fetuses were studied. The pregnant Wistar rats were orally treated during 6-15 gestation days with different doses of OA (0.125, 0.25, 0.50, 0.75 mg/kg), AFB1 (0.125, 0.25, 0.50, 1.00 mg/kg), and their combination (0.125+0.125, 0.25+0.50, 0.50+0.25 mg/kg). The fetal sections passing through liver, kidney, brain, heart, and eyes were selected from the fetuses given visceral examination representing each litter. The selected sections were processed for paraffin embedding, stained with H and E, and examined by light microscopy. The histological examination of the fetal organs revealed that OA, AFB1, and their combination treatments caused variable changes in internal organs. In the case of OA, the incidence of pathological lesions liver, kidney, brain, and eye lesions was high, whereas in AFB1 treatment, liver, brain, kidney, and heart were affected. The incidence of heart lesions, especially valvular defects, increased in the combination groups. Bile duct proliferation/new bile duct formation, defective ossification of cranial bones, exposure of the brain to the exterior, hypoplasia of cerebellum, and retinal defects observed in OA treatment and spinal cord defects in addition to liver, kidney, and brain changes observed in AFB1 were less severe in the combination groups. The present study indicates that the occurrence of brain, kidney, and liver lesions in combination treatment was less than in either individual treatment suggesting antagonism of OA-induced teratogenic effects by AFB1. The indication of subtle lesions due to an interference with normal development and arrest of differentiation in various internal organs observed in the present study suggests that microscopic examination of the tissues can provide additional useful information to a developmental toxicity study.

Disposition of 3H-aflatoxin B1 in mice: formation and retention of tissue bound metabolites in nasal glands

Whole-body autoradiography with 3H-labelled aflatoxin B1 (3H-AFB1) in C57B1-mice showed a pronounced accumulation and retention of radioactivity in some nasal glands. At long survival intervals the labelling of the nasal glands was much higher than that of the liver. Experiments in vitro showed a capacity of the nasal glands to form tissue-bound 3H-AFB1-metabolites. Incubations in the presence of glutathione decreased the levels of tissue-bound 3H-AFB1-metabolites both in the liver and in the nasal glands, but the decrease was more pronounced in the former than in the latter tissue. The 3H-AFB1-metabolite-binding to the nasal glands in vitro was inhibited by the cytochrome P-450-inhibitor metyrapone and by CO- and N2-atmospheres indicating a cytochrome P-450-dependent bioactivation of the AFB1 in these glands. Cytochrome P-450 was shown to be present in the glands although at a much lower level than in the liver. The glands in the nose, which were shown to have this AFB1-metabolizing capacity, were the lateral nasal gland (Steno's gland) situated ventrally and laterally to the maxillary sinus and the large group of glands in the lateral nasal wall ventrally to the ostium of the maxillary sinus. Our results also indicated an AFB1-metabolizing capacity of the serous glands which are present in the anterior part of the nasal septum.

Binding of aflatoxin B1 to melanin

Whole-body autoradiography of pigmented C57BL mice injected with 3H-labelled aflatoxin B1 (AFB1) showed a high degree of labelling of melanin-containing tissues, such as the melanin of eyes and hair follicles. The corresponding tissues in albino NMRI mice contained only low amounts of the label. Liquid chromatography of extracts of pigmented mouse eyes showed the presence of only non-metabolized AFB1. Analysis of the binding of AFB1 to melanin from bovine eyes using the method of Scatchard revealed two classes of binding sites. Incubations in the presence of metallic cations did not affect the binding, indicating that ionic forces play no role in the affinity. Comparisons of the binding of AFB1 to the bovine-eye pigment in media containing n-propanol, ethanol or methanol indicated that hydrophobic interactions play a role in the affinity. Apposition of the aromatic rings in AFB1 and the indole nuclei of the melanin may also result in van der Waals' forces, and the combination of these two types of forces may underly the binding of AFB1 to melanin. The melanin binding implies that AFB1 is retained in pigmented tissues at higher concentrations than in any other tissue of the body. The biological implication of this accumulation is now known, but the possibility that there may be an increased risk for the induction of melanomas is discussed.

Application of whole-body autoradiography in toxicology

Whole-body autoradiography enables the drugs and toxicants to be distributed throughout the animal. Good results are obtained with this technique. However, certain artifacts can occur that could lead to misinterpretation, and these must be known. These artifacts are described. From the metabolic point of view, autoradiography provides data on the distribution kinetics of a compound and the elimination of radioactivity in various organs. These data are a guide for quantitative research into the metabolism of a compound. From the toxicological point of view, it must be admitted that the main purpose of this technique is to reveal the sites of retention of radioactivity. Such specific organ retention could be the consequence of the activation of a minor metabolite into a very reactive compound. If this is so, it is a specific organ effect which could not be studied by other techniques and could lead the way to a more specific organ effect which could not be studied by other techniques and could lead the way to a more appropriate line of research in the study of chronic toxicity. However, it must be recalled that the fact that a compound is retained by a specific organ does not always mean that the compound exerts a toxic effect upon the said organ. With this technique, distribution study can be performed on pregnant animals, and it provides us with more data concerning the transplacental passage of radioactive metabolites. All these aspects of the technique clearly indicate that whole-body autoradiography should be insisted upon during the early stages of development of new molecules. Successive experiments could then lead to selecting the best experimental conditions for metabolic pharmacokinetics and studies in toxicology.

The distribution and intracellular translocation of aflatoxin B1 in isolated hepatocytes

The distribution and intracellular translocation of AFB1 in various subcellular fractions was investigated in isolated hepatocytes by pulse-chase experiments. After labeling the hepatocytes with [3H]-AFB1 (14.5 nM) for 15 min, the highest concentration of [3H]-AFB1 was found in the cytosolic fraction where 66% was bound noncovalently and 1.5% covalently. The lowest concentration of [3H]-AFB1 was found in the nuclear fraction; 36% and 4.9% were bound noncovalently and covalently respectively. When the [3H]-AFB1 loaded cells were chased with unlabeled AFB1 (1 microM), the radioactivity of [3H]-AFB1 in the cell lysate and cytosolic fraction decreased in time with an apparent rate of elimination (t1/2) of 93 min and 66 min, respectively. The levels of covalently bound AFB1 increased with time and reached a maximum at 60 min in nuclei (270%), and at 120 min in mitochondria (220%) and cytosol (430%) as compared to the zero time. Only in the microsomal fraction was there no significant increase with time in covalently bound AFB1. These results suggest that the toxin after activation by the microsomal mixed function oxidases was either detoxified or transported to other cellular organelles where covalent binding of macromolecules occurred.

Distal nephron function of the rat during acute aflatoxicosis

The effect of an acute intoxication with aflatoxin B1 (AFB1) on some parameters of distal nephron function was examined in rats 48 h after a single i.p. dose of 100 micrograms/kg body wt. The parameters tested were the capacity for the excretion of fixed acids and ammonium salts during metabolic acidosis and the concentration and dilution of urine applying conventional clearance techniques. The treated rats showed a glomerular filtration rate (GFR) approx. 50% lower than the controls, but they were able to reduce the urinary pH as were nonintoxicated animals. The ammonium excretion rate per ml of GFR was unimpaired in the treated rats, but the rate of excretion of fixed acids per ml of GFR was increased. The maximal urinary osmolality was significantly diminished in the intoxicated rats as was water reabsorption, when compared with data obtained in the controls. No differences between groups were seen in the free water formation although urinary excretion of electrolytes was significantly increased. The studies support the nephrotoxicity of AFB1 in the rat probably by interfering with transport function in the collecting tubule cells together with a diffuse impairment of proximal tubule function, as observed previously.

Alterations in renal function induced by aflatoxin B1 in the rat

The effects of aflatoxin B1 (AFB1) on renal function were determined in adult male Wistar rats by in vivo and in vitro studies. In vivo studies demonstrated that AFB1 decreased glomerular filtration rate, tubular reabsorption of glucose, and tubular transport for p-amino-hippurate. Furthermore, AFB1 pretreatment increased urinary excretion of sodium and potassium and urinary gamma-glutamyl transferase content. In vitro studies showed that slices of renal cortical tissue obtained from AFB1-treated rats (100 microgram/kg) exhibited a diminished capacity to accumulate p-aminohippurate. On the other hand, total water content of tissue, amount of extracellular water, and intracellular sodium were increased. Intracellular potassium was diminished by treatment with AFB1. Although the molecular species responsible for the effects is not known, these results indicated that AFB1 is nephrotoxic in the rat following a single low dose (100 microgram/kg body wt, ip).

The tissue distribution and the pattern of excretion of [14C]-13-labeled 12, 13-epoxytrichothec-9-ene in mice and rats

The distribution in the mouse tissues of 13-[14C]-12,13-epoxtrichothec-9-ene administered intravenously was determined by whole-body autoradiography and by tracing the radioactivity of the tissues oxidized in an Auto Sample Oxidizer. The appearance of the label in urine and feces was also followed by the tracer technique. The distributions of radioactivity in tissues as determined by the two methods were almost identical. On the autoradiograms of mice killed 10 min after the injection, marked blackening of the film was observed at the sites corresponding to the liver, kidney, and bladder with urine, and much less darkening at other sites. The radioactivities contained in the liver, kidney, urine and small intestine were 13.3, 2.3, 2.6 and 10.2% of the dose, respectively. The labeled toxin was rapidly excreted into urine and feces, 56.0 and 4.9% in 6 hr and 66.7 and 28.0% in 24 hr after injection, respectively. Oral administration of the labeled toxin to mother mice resulted in the appearance of radioactivity in the stomach contents of 7-day suckling mice, thus demonstrating indirectly the secretion of the toxin into the milk. An attempt to show a respiratory route of excretion in rats given the radioactive compound orally or intravenously failed to detect any radioactivity in the expired CO2 collected for 6 hr, suggesting that the 14C in the epoxy ring was intact.