The action of aflatoxin B1 on the rat liver

Aflatoxin B₁⁻Formamidopyrimidine DNA Adducts: Relationships between Structures, Free Energies, and Melting Temperatures

Thermal stabilities of DNA duplexes containing Gua (g), α- (a) or β-anomer of formamidopyrimidine-N7-9-hydroxy-aflatoxin B₁ (b) differ markedly (T_m: a<g<b), but the underlying molecular origin of this experimentally observed phenomenon is yet to be identified and determined. Here, by employing explicit-solvent molecular dynamics simulations coupled with free-energy calculations using a combined linear-interaction-energy/linear-response-approximation approach, we explain the quantitative differences in Tm in terms of three structural features (bulkiness, order, and compactness) and three energetical contributions (non-polar, electrostatic, and preorganized-electrostatic), and thus advance the current understanding of the relationships between structures, free energies, and thermal stabilities of DNA double helices.

Ganoderma lucidum and Auricularia polytricha Mushrooms Protect against Carbofuran-Induced Toxicity in Rats

The current study aimed to investigate the ameliorative effects of two types of mushrooms, Ganoderma lucidum (GL) and Auricularia polytricha (AP), against carbofuran- (CF) induced toxicity in rats. Male Wistar rats (n = 42) were divided into six equal groups. The rats in the negative control group received oral administration of CF at 1 mg/kg with the normal diet for 28 days. The treatment groups received oral administration of ethanolic extract of GL or AP at 100 mg/kg followed by coadministration of CF at 1 mg/kg with the normal diet for the same experimental period, respectively. In the CF alone treated group, there were significant decreases in the erythrocytic and thrombocytic indices but increases in the concentrations of the total leukocytes, including the agranulocytes. A significant increase in all of the liver function biomarkers except albumin, in lipid profiles except high-density lipoprotein, and in the kidney function markers occurred in the negative control group compared to the rats of the normal control and positive control groups. The coadministration of mushroom extracts significantly ameliorated the toxic effects of the CF. The GL mushroom extract was more efficacious than that of the AP mushroom, possibly due to the presence of high levels of phenolic compounds and other antioxidants in the GL mushroom.

Toxicity Assessment of Cadinene Sesquiterpenes from Eupatorium adenophorum in Mice

This study evaluated toxic efficacy of Eupatorium adenophorum extracts, against the Kunming mice. In acute study, we firstly tested median lethal dose (LD50) in mice of three cadinene sesquiterpenes 2-deoxo-2-(acetyloxy)-9-oxoageraphorone (DAOA), 9-oxo-agerophorone (OA) and 9-oxo-10,11-dehydro-agerophorone (ODA) from Eupatorium adenophorum (Ea). DAOA (215-4640 mg/kg BW, given orally) showed lowest LD50 at 926 mg/kg BW for male mice in contrast with OA (1470 mg/kg BW) and ODA (1470 mg/kg BW). In sub-acute study, repeated doses (75-300 mg/kg BW, for 7 days) of DAOA/OA increased blood parameters, liver and spleen index in dose dependent relationship, along with decrease in thymus index. The blood biochemical and histopathological examination showed that DAOA/OA dose 300 mg/kg BW significantly causes pathological changes of hepatic lobules and hepatocytes, which are consistent with cholestasis and hepatic injury. 75 mg/kg dose of DAOA/OA was found to be approximately/totally safe over the span of 7 days treatment showing no change in all above described parameters. Cadinene sesquiterpenes guarantee low risk to environment as a type of low toxic botanical components, which may find potential application in biopesticides development field.

Short-term safety and efficacy of calcium montmorillonite clay (UPSN) in children

Recently, an association between childhood growth stunting and aflatoxin (AF) exposure has been identified. In Ghana, homemade nutritional supplements often consist of AF-prone commodities. In this study, children were enrolled in a clinical intervention trial to determine the safety and efficacy of Uniform Particle Size NovaSil (UPSN), a refined calcium montmorillonite known to be safe in adults. Participants ingested 0.75 or 1.5 g UPSN or 1.5 g calcium carbonate placebo per day for 14 days. Hematological and serum biochemistry parameters in the UPSN groups were not significantly different from the placebo-controlled group. Importantly, there were no adverse events attributable to UPSN treatment. A significant reduction in urinary metabolite (AFM1) was observed in the high-dose group compared with placebo. Results indicate that UPSN is safe for children at doses up to 1.5 g/day for a period of 2 weeks and can reduce exposure to AFs, resulting in increased quality and efficacy of contaminated foods.

Integrative toxicopathological evaluation of aflatoxin B₁ exposure in F344 rats

In this study, male F344 rats were orally exposed to a single dose of aflatoxin B₁ (AFB₁) at 0, 50, 250, or 1,000 µg/kg body weight (BW) or repeated dose of 0, 5, 10, 25, or 75 µg/kg BW for up to 5 weeks. Biochemical and histological changes were assessed together with the formation of AFB1-lysine adduct (AFB-Lys) and liver foci positive for placental form glutathione S transferase (GST-P⁺). In single-dose protocol, serum aspartate transaminase (AST), alanine transaminase (ALT), and alkaline phosphatase (ALP) showed dose-related elevation, with maximal changes observed (>100-fold) at day 3 after treatment. Animals that received 250 µg/kg AFB₁ showed concurrent bile duct proliferation, necrosis, and GST-P⁺ hepatocytes at 3 day, followed by liver GST-P⁺ foci appearance at 1 week. In repeated-dose protocol, bile duct proliferation and liver GST-P⁺ foci co-occurred after 3-week exposure to 75 µg/kg AFB₁, followed by proliferation foci formation after 4 week and dramatic ALT, AST, and CK elevations after 5 weeks. Liver GST-P⁺ foci were induced temporally and in a dose-related manner. Serum AFB-Lys increased temporally at low doses (5-25 µg/kg), and reached the maximum after 2-week exposure at 75 µg/kg. This integrative study demonstrated that liver GST-P⁺ cells and foci are sensitive biomarkers for AFB₁ toxic effect and correlated with bile duct proliferation and biochemical alterations in F344 rats.

Oxidative stress, hematological and biochemical alterations in farmers exposed to pesticides

In this study, a cohort of farmers from the Mateur region in the North of Tunisia, were interviewed and examined for the biochemical effects of pesticides. We studied their haematological profile, lipid parameters, serum markers of nephrotoxicity and hepatotoxicity. We also evaluated the activities of Butyrylcholinesterase (BChE), Acetylcholinesterase (AChE) and thiolactonase-paroxonase (PON). Moreover, lipid peroxidation and activities of antioxidant enzymes superoxide dismutase (SOD) and catalase (CAT) were determined. The duration of pesticide use and the farmers' age were considered in the analysis. Our results revealed significant differences in some haematological parameters, in liver and kidney functions, in the lipidic status of the pesticide-exposed group. We also reported an increase in the index of incidence of cardiovascular risk in farmer populations. A significant decrease in AChE, BChE and PON levels was found among farmers. Lipid peroxidation, however, increased. The activities of SOD and CAT were remarkably elevated in farmer populations. There was a significant relation between changes in biological markers, the duration of pesticide use and the farmers' age. This study indicates that a long-term exposure to pesticides may play an important role in the development of vascular diseases via metabolic disorders of lipoproteins, lipid peroxidation and oxidative stress, inhibition of BChE and decrease in thiolactonase-PON levels.

The glucocorticoid receptor: a revisited target for toxins

The hypothalamic-pituitary-adrenal (HPA) axis activation and glucocorticoid responses are critical for survival from a number of bacterial, viral and toxic insults, demonstrated by the fact that removal of the HPA axis or GR blockade enhances mortality rates. Replacement with synthetic glucocorticoids reverses these effects by providing protection against lethal effects. Glucocorticoid resistance/insensitivity is a common problem in the treatment of many diseases. Much research has focused on the molecular mechanism behind this resistance, but an area that has been neglected is the role of infectious agents and toxins. We have recently shown that the anthrax lethal toxin is able to repress glucocorticoid receptor function. Data suggesting that the glucocorticoid receptor may be a target for a variety of toxins is reviewed here. These studies have important implications for glucocorticoid therapy.

Deltamethrin-induced oxidative damage and biochemical alterations in rat and its attenuation by Vitamin E

Deltamethrin is a synthetic pyrethroid insecticide used worldwide in agriculture, home pest control, protection of foodstuff and disease vector control. The objective of this study was to investigate the propensity of deltamethrin to induce oxidative stress and changes in biochemical parameters and enzyme activities in male rats following a short-term (30 days) oral exposure and its possible attenuation by Vitamin E (Vit. E). Rats were assigned to 1 of 4 treatment groups: 0mg Vit. E and 0mg deltamethrin/kg body weight (BW) (control); 100mg Vit. E/kg BW; 1.28mg deltamethrin/kg BW; 100mg Vit. E plus 1.28mg deltamethrin/kg BW. Results obtained showed that deltamethrin significantly (P<0.05) induced thiobarbituric acid-reactive substances (TBARS; the marker of lipid peroxidation) in plasma. The activities of glutathione S-transferase (GST) and superoxide dismutase (SOD) were significantly decreased due to deltamethrin administration. On the other hand, treatment with Vitamin E alone increased the activities of GST and SOD, and decreased the levels of TBARS. Also, Vitamin E alleviated the harmful effect of deltamethrin in the combination group. Enzymatic activities of aminotransferases (AST and ALT), phosphatases (AcP and AlP) and lactate dehydrogenase (LDH) in plasma were significantly increased, while acetylcholinesterase (AChE) was inhibited. Deltamethrin significantly (P<0.05) increased the levels of plasma total lipid (TL), cholesterol, triglyceride (TG), low density lipoprotein (LDL) and very low density lipoprotein (VLDL), while the level of high density lipoprotein (HDL) decreased. Vitamin E alone decreased the levels of lipids and lipoproteins, and alleviated the harmful effects of deltamethrin. Concentrations of glucose, urea, creatinine and total bilirubin were increased. While, plasma total protein (TP), albumin (A) and globulin (G) were significantly (P<0.05) decreased. The present study revealed that the presence of Vitamin E could diminish the adverse effects of deltamethrin on most of biochemical parameters, lipid peroxidation and enzyme activities in rats.

Use of proteomic methods to identify serum biomarkers associated with rat liver toxicity or hypertrophy

BACKGROUND

Our objectives were to identify serum marker proteins in rats that might serve as sensitive indicators of hepatomegaly, hepatocellular necrosis, or hepatobiliary injury and to use them to analyze data from a collaborative proteomics project.

METHODS

In each of 4 studies comprising the collaborative project, rats were given 1 of 4 compounds that target the liver through different mechanisms. Sera and liver samples were collected by terminal bleeds at 1 of 3 postdose time points. Sera were depleted of major secretory proteins and then separated into protein features by 2-dimensional gel electrophoresis (2DGE). Liver specimens were also processed and subjected to 2DGE. Protein spots that significantly increased or decreased in quantity after drug treatment were recovered, digested, analyzed by mass spectroscopy, and compared with available databases for identification. Criteria for further consideration were (a) temporal expression (i.e., increase or decrease at early, fulminant, or recovery periods), (b) known biological function, (c) probable hepatic origin, and (d) any previous association with toxicity in published studies. Markers that changed significantly at the early time point were important because of their potential sensitivity for signaling minimal damage.

RESULTS

Vitamin D-binding protein, paraoxonase, cellular retinol-binding protein, malate dehydrogenase, F-protein, and purine nucleoside phosphorylase were identified as empirically confirmed serum markers for hepatic effects in drug-treated rats.

CONCLUSION

Proteomics can be applied for the identification and confirmation of peripheral biomarkers for altered liver function after toxicant exposure.

Changes in some hematological and biochemical indices of rabbits induced by isoflavones and cypermethrin

Protective effect of isoflavones on cypermethrin-induced changes in blood hematology, and plasma lipids, lipoproteins, glucose, urea, creatinine, total bilirubin and protein concentrations of male New Zealand White rabbits was studied. Rabbits were orally given sublethal dose of cypermethrin (24 mg/kg BW; 1/100 LD50), while isoflavones (2 mg/kg BW) was given alone or in combination with cypermethrin. The tested doses were given to rabbits every other day for 12 weeks. Results showed that cypermethrin caused a significant (P<0.05) increase in the levels of plasma total lipids (TL), cholesterol, triglyceride (TG), low density lipoprotein (LDL) and very low density lipoprotein (VLDL), while the level of high density lipoprotein (HDL) decreased. Isoflavones alone significantly (P<0.05) decreased the levels of TL, cholesterol, TG, LDL and VLDL, and increased HDL, and alleviated the harmful effects of cypermethrin on lipid profiles. Cypermethrin caused a significant (P<0.05) increase in glucose, urea, creatinine and total bilirubin. The concentrations of plasma total protein (TP) and albumin (A) were significantly (P<0.05) decreased in plasma of rabbits treated with cypermethrin, while globulin concentration and A/G ratio were not affected. Results showed that cypermethrin significantly (P<0.05) decreased hemoglobin (Hb), total erythrocytic count (TEC) and packed cell volume (PCV), while total leukocyte count (TLC) increased. Isoflavones alone did not cause any significant change in these parameters, but minimized the toxic effect of cypermethrin. Results demonstrated the beneficial influences of isoflavones in reducing the negative effects of cypermethrin on blood hematology and biochemical parameters of male rabbits.

Influence of ascorbic acid supplementation on the haematological and clinical biochemistry parameters of male rabbits exposed to aflatoxin B1

This study was undertaken to evaluate the effectiveness of L-ascorbic acid (AA) in alleviating the toxicity of aflatoxin B1 (AFB1) in male New-Zealand white rabbits. Five rabbits (6 months of age and mean body weight 3.12 kg) per group were assigned to 1 of 6 treatment groups: 0 mg AA and 0 mg AFB1/kg BW (control); 20 mg AA/kg BW; 15 microg AFB1/kg BW; 15 microg AFB1 plus 20 mg AA/kg BW; 30 pg AFB1/kg BW; 30 pg AFB1 plus 20 mg AA/kg BW. Rabbits were orally administered their respective doses every other day for 9 weeks, followed by a 9-week recovery period where all drugs were withdrawn. Evaluations were made for hemato-biochemical parameters and enzymatic activities. Results showed that AFB1 significantly (p < 0.05) decreased hemoglobin (Hb), total erythrocytic count (TEC) and packed cell volume (PCV), in a dose-dependent manner, and these effects were continued during the recovery period. Ascorbic acid caused an increase in these parameters, and alleviated the negative effect of AFB1 during the treatment period. Additionally, serum concentrations of total protein, albumin and glucose were significantly (P < 0.05) declined by treatment with the high dose of aflatoxin and these effects were continued during the recovery period. Ascorbic acid caused non-significant increases in these parameters and alleviated the harmful effect of AFB1. On the other hand, aflatoxin treatment caused significant increases (P < 0.05) in the activities of serum aspartate aminotransferase (AST), alanine aminotransferase (ALT) and alkaline phosphatase (AlP) during the treatment period in a dose dependent manner, and this effect was continued during the recovery period, especially with the high dose. Also, treatment with the high dose of aflatoxin caused significant increases (P<0.05) in cholesterol and total bilirubin. Ascorbic acid caused significant decreases in these parameters and alleviated the harmful effects of AFB1. Whereas, Total leukocyte count (TLC), urea and creatinine were not significantly affected by aflatoxin-treatment. Generally, it is interesting feature that the treatment with AA alone had no negative effects on most of the previous parameters. Also, the presence of AA could diminished the adverse effects of AFB1 on most of hematological and biochemical values, and enzymatic activities in rabbits.

Effect of aflatoxin ingestion in feed on body weight gain and tissue residues in rabbits

The effect of a subclinical dose of aflatoxin on body weight gain and risk assessment of aflatoxin in muscle tissue for food safety were the focus of the study. Thirty New Zealand rabbits, 2 months old, were used. A group of 24 rabbits was fed aflatoxin 2 p.p.m. day-1 for a period of 4 months. The weights of the individual aflatoxin-fed rabbits and those of the control group were recorded weekly. Aflatoxin was withdrawn from a group of six rabbits chosen at random for a period of 4 weeks before the termination of the experiment. All rabbits were necropsied at the end of the study for gross and microscopic changes of the internal organs. Samples of muscle tissue were also collected and analysed chemically for aflatoxin using thin-layer chromatography. Significant weight loss equivalent to 13% mortality was found in the aflatoxin-fed rabbits. Characteristic pathological changes were found. Aflatoxins B1 and G2 were detected in muscle tissue at alarming concentrations far exceeding the permissible levels in food for human consumption in the aflatoxin-fed group. No detectable aflatoxins were found in the aflatoxin-withdrawal group.

RNA transcription and lysosomal activation during xenotransplant hyperacute rejection: inhibition of RNA polymerase

In summary, our data indicates that AFB1 has no effect on LyAct during XTHAR. Although these results are from short-term incubation studies, they nevertheless suggest that inhibition of RNA transcription by AFB1 may be of no consequence in LyAct during XTHAR. Hence, our results appear to support the view that, in general, XTHAR recruits preformed components and may not require de novo synthesis of lysosomal proteins. Additional studies using long-term incubation (days to weeks) and other protein synthesis blockers are suggested to further elucidate the effects of protein synthesis inhibition of LyAct during XTHAR.

Blood biochemical profiles in induced aflatoxicosis of cockerels

1. Experimental intoxication induced in cockerels with varying doses of aflatoxin fed at the rate of 2.5 micrograms, 5.0 micrograms, and 10.0 micrograms per g of food resulted in appreciable changes in blood biochemical profiles. 2. At all doses the aflatoxin caused decreases in serum total proteins, albumin: globulin ratio, serum total cholesterol, serum calcium and phosphorus and increase in serum globulins, alanine amino transferase (ALT) and aspartate amino transferase (AST) concentrations. 3. No changes in serum bilirubin were observed. 4. Possible mechanisms for such blood biochemical changes are discussed and related to liver cellular damage caused by the aflatoxin toxicity.

Toxicity of aflatoxin B1 in broiler chicks and its reduction by activated charcoal

A study was conducted on 60 broiler chicks of the effect of activated charcoal (200 ppm) on the toxicity of 0.5 ppm aflatoxin B1 (AFB1) in feed fed from day 1 to day 42. Activated charcoal was found to be moderately effective in reducing the harmful effects of AFB1 as assessed by growth response and various biochemical parameters. The feeding of activated charcoal along with AFB1 reduced the inhibitory effect of AFB1 on bodyweights and feed intake. There was also a significant improvement in the serum aspartate aminotransferase, alkaline phosphatase, total proteins, calcium and phosphorus levels. However, no significant improvement was observed in cholesterol levels.

Synergism between aflatoxin B1 and oxytetracycline on fatty acid esterification in isolated rat hepatocytes

The individual and combined effects of aflatoxin B1 (AFB1) and oxytetracycline (OXT) on the synthesis and secretion of triacylglycerols in isolated rat hepatocytes maintained in suspension during 2.5 h were studied. Secretion of triacylglycerols was inhibited by both drugs when administered separately. This inhibition was accompanied by a concomitant elevation of intracellular triacylglycerols only at the highest AFB1 dose tested. Total synthesis of triacylglycerols was not inhibited by AFB1 or by OXT. When the two drugs were simultaneously added to the incubation medium, the AFB1-induced accumulation of intracellular triacylglycerols was no longer observed; the inhibition of secretion was nevertheless identical to that observed with AFB1 alone. Finally, total esterification of palmitate was inhibited by 20% compared to the AFB1-treated cells. These data suggest that OXT inhibits lipid accumulation induced by AFB1 but that this effect is due to an inhibition of total synthesis of triacylglycerols. The mechanism of AFB1's effect and of the interaction between both molecules is discussed.

The in vivo disposition of aflatoxin B1 in rat liver

The disposition of a non-toxic i.p. dose of [3H]-aflatoxin B1 (0.70 micrograms/kg) in the blood, plasma, and liver was studied in male Wistar rats. Uptake into the blood, plasma, and liver was biphasic; there was an initial rapid rise (0-2 hr) followed by a second phase (2-12 hr) of a gradual increase. Most of the radioactivity in the blood was bound noncovalently to albumin. Distribution of radioactivity in the subcellular fractions of liver showed that the microsomes exhibited the highest labeling which increased over the time course; labeling of the cytosol reached a maximum at 2 hr then decreased to a new steady state, whereas the mitochondria and nuclei reached a plateau. When the content of aflatoxin B1 in the nuclear subfractions was examined, greater than 92% of the total radioactivity was found in the deoxyribonucleoprotein fraction, and 84% of this was bound noncovalently. These results suggest that aflatoxin B1 is transported from the site of injection through the blood to the liver and its subcellular and subnuclear fractions primarily in a noncovalent form.

Interaction of aflatoxin B1 with the rat monooxygenase system and relationships to its acute toxic effect

The effect of aflatoxin B1 (AFB1) on the liver microsomal and nuclear mixed function oxidase system (MFO) of adult male rats was studied at oral doses of 1 and 3 mg/kg. At first both doses increased the activities and concentrations of all P450 components followed. The maximum values were observed between 24 and 48 h and were dose- and enzyme-dependent. After 72 h the values dropped to 15-55% of the initial values. Inhibition of the MFO system lasted even after 120 h, when a trend to return to the normal values was already noticeable. We assume that AFB1 acts as an inductor of the monooxygenase system and the reactive electrophilic intermediate(s) bind irreversibly to or autocatalytically inactivate P450.

Immunosuppression due to chronic ochratoxicosis in broiler chicks

Crystalline ochratoxin A (OA) was added to the feed of broiler chicks at 0.5 ppm and 2.0 ppm, and humoral and cell-mediated immunity (CMI) were studied. CMI was assessed by skin sensitivity testing, graft versus host (GVH) reaction and T lymphocyte count. Humoral immunity was examined by measuring the haemagglutinin (HA) response to sheep RBC (SRBC). In addition, total lymphocyte counts, total serum protein, albumin and globulin were determined and the phagocytic activity of splenic macrophages was measured in the nitroblue tetrazolium test (NBT). The weights of lymphoid organs were also recorded at post-mortem examination of the birds. Highly significant reductions in CMI were indicated by diminished skin sensitivity, GVH reactions and T lymphocyte counts. On the other hand, only the overall HA titres differed significantly between the various treatment groups. Total lymphocyte counts, total serum protein, serum albumin and serum globulin were significantly depressed on the 21st day of intoxication. The number of NBT-positive cells was drastically reduced in both the intoxicated groups compared with controls (P less than 0.05) and the weights of thymus, bursa of Fabricius and spleen of intoxicated birds were significantly reduced. The study illustrated the immunosuppressive effects of ochratoxicosis in broiler chicks.

Interaction between aflatoxin B1 and oxytetracycline in isolated rat hepatocytes

Isolated rat hepatocytes were used as an in vitro model to investigate a possible interaction between oxytetracycline (OXT) and aflatoxin B1 (AFB1). LDH leakage, RNA and protein synthesis and glycogen accumulation were measured in the presence of both drugs, either separately or in combination. The evolution of LDH leakage during the incubation was identical in untreated and treated cells. AFB1 inhibited RNA and protein synthesis at a concentration of 10(-7) M and 10(-6) M, respectively, and higher, whereas OXT did not influence RNA synthesis but inhibited protein synthesis at the highest tested concentration, 10(-3) M. As far as glycogen is concerned, rats were injected with glucagon before sacrifice in order to obtain a constant synthesis rate in isolated hepatocytes. AFB1 inhibited the accumulation of glycogen from 10(-6) M upward. This effect was never observed before 90 min of incubation. OXT had no effect on glycogen synthesis. In the presence of both drugs, no interaction was demonstrated as far as RNA and protein synthesis were concerned, but OXT opposed the inhibition induced by AFB1 on glycogen accumulation. If the "in vivo" protection, provided by OXT against AFB1-induced toxicity, is due to a direct interference in the toxic mechanisms of the mycotoxin, these results show that OXT does not influence the AFB1-inhibition of RNA and protein synthesis. The latter are early and sensitive parameters inhibited by AFB1. On the contrary, taking into consideration the results on glycogen accumulation, it seems more interesting to investigate further this metabolism.

Hepatic protection by 16, 16-dimethyl prostaglandin E2 (DMPG) against acute aflatoxin B1-induced injury in the rat

Studies were conducted to assess the possible protective action of 16,16-dimethyl prostaglandin E2 (DMPG) against acute aflatoxin B1 (AFB1) induced hepatic injury in the rat. Evaluation of liver damage by histopathologic techniques and clinical chemistry indicated that hepatic necrosis was ameliorated by treatment with DMPG even though binding of radiolabeled (3H)-AFB1 to hepatic DNA was unaffected by this prostaglandin. However, DMPG did not protect rats against AFB1-induced mortality. These data suggest that hepatic protection by DMPG was due to mechanisms other than an interference with the activation or hepatic binding of AFB1.

Toxic synergism between aflatoxin and T-2 toxin in broiler chickens

The individual and combined effects of aflatoxin and T-2 toxin were studied in male broiler chicks (Hubbard X Hubbard). The experimental design was a 2 X 2 factorial design with dietary treatments of 0 and 2.5 micrograms/g aflatoxin and 0 and 4.0 micrograms/g T-2 toxin. The broilers were obtained at 1 day of age and housed in electrically heated batteries with feed and water available ad libitum until they reached 3 wk of age. Aflatoxicosis in this study was characterized by a significant (P less than .05) reduction in body weight, changes in red blood cell counts and serum levels of protein, albumin, glucose, cholesterol, and calcium, and magnesium, activity of the serum enzymes lactic dehydrogenase and alkaline phosphatase, and a significant (P less than .05) increase in relative weights of the liver, kidney, spleen, pancreas, proventriculus, and heart. Dietary T-2 toxin alone caused oral lesions, a significant (P less than .05) decrease in serum protein, albumin, potassium, and magnesium levels, and a significant (P less than .05) decrease in the activity of the serum enzymes lactic dehydrogenase and alkaline phosphatase. In the combination treatment of aflatoxin and T-2 toxin, significant (P less than .05) interactive effects were seen through a decrease in body weights, increase in the relative weights of the kidney, gizzard, and heart, and decrease in mean corpuscular volume and serum levels of potassium. These data indicate that aflatoxin and T-2 toxin can interact to produce synergistic toxicity. This synergism is a threat to poultry production due to the prevalence of these mycotoxins and severity of the interactive toxicity of these mycotoxins.

Modification of protein synthetic components by aflatoxin B1

Molecular sites of perturbation by the hepatocarcinogen aflatoxin B1 (AFB1) in the protein synthesis initiation complex were assessed using isolated hepatocytes and a cell-free activating system containing microsomes and cytoplasmic ribonucleoprotein complexes (cRPC). Ribosomal proteins showed no detectable modification by the toxin in either system. With hepatocytes, initiation factors demonstrated only slight modification by AFB1. RNAs from both hepatocytes and the cell-free system with microsomes and cRPC were modified, with poly(A)-containing RNA exhibiting at least a 5-fold higher modification than poly(A)-lacking RNA. The poly(A)-lacking RNAs were modified in the order 28S rRNA greater than 18S rRNA greater than 5-6S rRNA greater than 4S tRNA. Guanine was the target base of AFB1, but only 10% of the AFB1-GMP adducts were on guanines located in a poly(G) region. These results suggest that guanine modification in RNAs may be responsible for the observed inhibition of translational initiation by AFB1 to a greater extent than modification of either ribosomal intrinsic or associated proteins.

Hepatocellular uptake of aflatoxin B1 by non-ionic diffusion. Inhibition of bile acid transport by interference with membrane lipids

Aflatoxin B1 permeates isolated rat hepatocytes by non-ionic diffusion. Its uptake is neither saturable nor influenced by metabolic energy and not inhibited by treatment of cells with proteases. The initial rate of aflatoxin B1 uptake measured at 7 degrees C is between 40 and 50% compared to that at 37 degrees C. However, after an incubation period of 7 minutes identical equilibrium uptake is reached at both temperatures. The apparent activation energies, calculated for aflatoxin B1 uptake by Arrhenius diagrams ranged between 1.69 and 4.5 kcal/mol. A Q10 value of 1.34 was calculated for a temperature interval of 7-17 degrees C but decreased to 1.05 for the interval of 27-37 degrees C. Liposomes or lipoproteins added to the cell suspension inhibited the aflatoxin B1 uptake into hepatocytes. Liposomes mainly composed of unsaturated fatty acids bind twice as much aflatoxin B1 as those composed of saturated ones, indicating that the lipophilicity of the mycotoxin is crucial in the determination of its uptake into liver cells. At concentrations above 5 micrograms/ml, aflatoxin B1 inhibited the carrier-mediated uptake of cholic acid and of phalloidin into hepatocytes. This effect was reversible and abolished by washing the cells after preincubation with aflatoxin. In concentrations below 5 micrograms/ml the uptake of phallotoxin and cholic acid was however stimulated by 15-25%. These results indicate, that a carrier-mediated uptake into hepatocytes via the multispecific bile salt transporter is not responsible for the organoselective clearance of aflatoxins by the liver. On the other hand, the cholestatic effect of aflatoxin B1 results at least partially from the inhibition of the multispecific bile acid transport system. This inhibition may arise from affinity of aflatoxins to lipid domains of the cell membrane.

Liver lipid metabolism in T-2 toxicosis. I. Effects of a single dose feeding of T-2 toxin to rats

The acute effects of oral administration of a single dose of T-2 toxin (2.0 mg/kg body wt) to rats on whole liver lipid metabolism were studied at 8, 16 and 24 h post-treatment. Administration of T-2 toxin significantly increased liver and microsomal total lipids, free cholesterol, esterified cholesterol and triglycerides initially at 8 h, which subsequently returned to control values at 24 h. However, no significant alterations were observed in the contents of whole liver and liver microsomal total phospholipids and phosphatidyl choline, except that phosphatidyl ethanolamine and sphingomyelin + lysophosphatidyl ethanolamine contents in liver at 16 and 24 h and sphingomyelin + lysophosphatidyl ethanolamine content in liver microsomes at all three periods were significantly lower. The incorporation of 1-14C-acetate into whole liver and liver microsomal total lipids was reduced at 16 and 24 h post feeding. However, the incorporation of 1-14C-acetate into liver and microsomal free cholesterol, esterified cholesterol and triglycerides was significantly higher at 8 h, subsequently returning to the control value at 24 h; incorporation was significantly lower even into microsomal triglycerides. The incorporation of 1-14C-acetate into liver and its microsomal total phospholipids, phosphatidyl choline, phosphatidyl ethanolamine and sphingomyelin + lysophosphatidyl ethanolamine, was significantly decreased at all three periods post toxin treatment. The results suggested that T-2 toxin inhibited the incorporation of 14C-acetate mainly into liver and its microsomal phospholipids and their subfractions in rats.

Progression of aflatoxicosis in broiler chickens

The progression of aflatoxicosis was evaluated in young broiler chickens (Hubbard X Hubbard). The experimental design consisted of four dietary treatments of aflatoxin (0, 1.25, 2.5, and 5.0 micrograms of aflatoxin/g of feed, ppm) and 11 replicates of 10 broilers/replicate. The broilers were maintained in electrically heated batteries with feed and water available ad libitum from hatching to 3 weeks of age. The broilers were weighed, bled, killed by cervical dislocation, and necropzied at 3, 6, 9, 12, 15, 17, and 21 days of age. Body weights were significantly decreased by 5.0 ppm aflatoxin at 6 days of age and by 2.5 ppm at 17 days of age. Aflatoxin induced a significant increase in the relative weight of the proventriculus, gizzard, spleen, and kidney. Liver atrophy was indicated in the early stages of aflatoxicosis by a decrease in the relative weight of this organ. As aflatoxicosis progressed, hepatomegaly became apparent due to lipid accumulation in the liver. Packed-cell volume and hemoglobin levels were significantly decreased by 5.0 ppm aflatoxin at 12 days and by 2.5 ppm aflatoxin at 21 days of age. Serum levels of albumin and total protein were significantly reduced at 5.0 and 2.5 ppm aflatoxin by 3 and 6 days of age, respectively. Serum levels of uric acid, triglycerides, and cholesterol were significantly decreased from control values from 12 through 21 days of age by 5.0 ppm aflatoxin and, to a lesser extent, by 2.5 ppm aflatoxin. The activity of serum lactic dehydrogenase was significantly decreased at all aflatoxin treatment levels from 12 through 21 days of age.(ABSTRACT TRUNCATED AT 250 WORDS)

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.

Inhibition of oxygen uptake in liver slices of three mammalian species (rat, rabbit, guinea-pig) by aflatoxin B1 (AFB1)

Oxygen uptake in liver slices of rats, rabbits and guinea pigs were determined manometrically in the presence of different concentrations of aflatoxin B1 (AFB1). AFB1 inhibited oxygen uptake at all concentrations of AFB1 tested (3.2 microM, 16.0 microM, 48.1 microM, 64.1 microM, 80.0 microM, 112.2 microM). Inhibition was directly proportional to the concentration of AFB1 inducing the inhibition. The degree of inhibition of oxygen uptake in the 3 mammalian species seems to correlate with their respective susceptibilities to AFB1 toxicity. The highest inhibition was in guinea pig and the least in rat; that in the rabbit was intermediate between rat and guinea pig.

Biochemical and physiological responses of growing chickens and ducklings to dietary aflatoxins

Two-week-old ducks and chickens were fed for a 14-day period diets containing either groundnut meal (GNM) or fish meal (FM) contaminated with the following aflatoxin (AF) levels: 0, 50, 100, 200 and 400 micrograms AF B1 equivalent per kg ration; nitrogen and energy balances were measured, liver lesions assessed, and various biochemical analyses in blood, livers and muscles were made. Both ducks and chickens fed diets containing GNM were more affected by dietary AF than those fed diets with FM. In ducks, in addition to the reduction in growth and utilization of protein, dietary AF caused liver damage and significantly affected most of the blood constituents; chickens were either not affected or affected to a lesser degree, but no liver damage was recorded. Individual blood tests or enzyme ratios did not provide a sufficiently precise diagnosis of aflatoxicosis. However, blood clotting time and De Riti's ratio, when used in a multivariate regression. allowed projection of a degree of liver damage caused by AF in ducks fed GNM diet with 83.6% of variance being accounted for.

Evaluation of immunity of young broiler chickens during simultaneous aflatoxicosis and ochratoxicosis

A 2 X 2 factorial experimental design consisting of the treatments 0 and 2.5 micrograms/g aflatoxin and 0 and 2.0 micrograms/g ochratoxin A with 12 replicates of 10 birds per treatment level was used to evaluate the effects of these mycotoxins on various aspects of immunity. Male chicks (Hubbard X Hubbard) were maintained on these treatments from one day of age to 3 weeks of age at which time six replicate pens per treatment were sacrificed and various parameters measured. The additional six replicate pens per treatment were maintained on toxin feed beyond 3 weeks of age, and at 4 weeks of age, three replicate pens were immunized with sheep red blood cells (SRBC) and Brucella abortus. Antibody titers were measured up to 10 days postimmunization. Aflatoxin and ochratoxin A, individually, significantly (P less than .05) decreased body weight, and a synergistic toxicity was evident by a significant (P less than .05) decrease in body weight. Antibody titers and phagocytic activity of heterophils were not significantly (P less than .05) altered by any treatments. The relative weight of the bursa of Fabricius and the number of follicles for a given area of the folds of the bursa of Fabricius were significantly (P less than .05) decreased only by the interaction treatment. Complement activity was significantly (P less than .05) decreased by aflatoxin and the combination of aflatoxin and ochratoxin A and depressed, although not significantly (P less than .05), by ochratoxin A.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of inhibitors of microsomal enzymes on aflatoxin B1-induced cytotoxicity and inhibition of RNA synthesis in isolated rat hepatocytes

Previous studies conducted in this laboratory demonstrated that AFB1 activation and deactivation was effectively inhibited by metyrapone and TCPO in isolated hepatocytes. The present study was undertaken to study the toxic effect of AFB1 on hepatocyte and RNA synthesis, and to assess the influence of the inhibitors on AFB1-induced cytotoxicity and AFB1-inhibited RNA synthesis. AFB1 at 50 microM was toxic and inhibited macromolecular synthesis by greater than 70% at 180 min of incubation whereas at lower concentrations of AFB1 (0.05-10 microM) dose-and time-dependent decreases in cell viability, protein and RNA synthesis were observed. Using [3H]-AFB1 (0.1.5 microM), the uptake and covalent binding of the toxin were also dose-and time-dependent. Initial rates of these processes to reach half-maximum was found to be 0.25 microM AFB1. In cells treated with AFB1 (5 microM) and metyrapone (1.0 mM) or SKF-525A (10 microM), the cell viability was similar to the control and [3H]-uridine incorporation was significantly higher than AFB1 treated cells. AFB1 and TCPO (0.5 mM) treated cells exhibited further decreases in cell viability and RNA synthesis. Results suggest that the binding of AFB1 to DNA and impairment of transcriptional activity may lead to cell death.

Inhibition of rat liver aminoacyl-tRNA synthetases in vitro after acute and chronic aflatoxin B1 administration in vivo

In a cell-free system the influence of acute aflatoxin B1 administration on the fractions of the hepatic microsomal translation complex of female rats was examined and compared with the influence of chronic aflatoxin B1 treatment. Polypeptide synthesis determined by [14C]leucine incorporation with the postmitochondrial supernatant was inhibited by 80% 24 h after acute aflatoxin B1 administration whereas inhibition was only 17% in animals 30 weeks after chronic treatment. After acute aflatoxin B1 administration inhibition of protein synthesis was by 67%, mainly on the polysomal level, whereas inhibition with the pH 5 enzyme was only by 22%. After chronic aflatoxin B1 administration inhibition was by 18%, mainly with the pH 5 enzyme and by only 6% on the polysomes. The inhibition by pH 5 enzyme was further investigated with regard to aminoacyl-tRNA synthetases, components of pH 5 enzyme. Leucine-specific aminoacyl-tRNA synthesis was inhibited by 20% 24 h after acute and by 12% 30 weeks after chronic aflatoxin B1 treatment. Aminoacyl-tRNA synthetase activities in a crude synthetase preparation tested with 5 amino acids were found to be noncompetitively inhibited. It is concluded that the inhibition of protein synthesis after acute and chronic aflatoxin B1 administration is in part due to decreased aminoacyl-tRNA levels caused by inhibited aminoacyl-tRNA synthetases.

Experimental aflatoxicosis in swine: morphological and clinical pathological results

The morphological changes in livers of 30 feeder pigs fed diets containing corn contaminated by aflatoxins (0.0 microgram aflatoxins/g feed, 0.4 microgram aflatoxin/g feed, and 0.8 microgram aflatoxin/g feed) were compared with changes in hematology, liver specific serum enzymes, serum proteins, and lymphocyte stimulation indices. Histologically, the livers were classified into five groups. Pigs fed the 0.8 microgram/g diets had the most severe histological lesions of karyomegaly, bile ductule proliferation and hepatocellular degeneration plus elevated gamma-glutamyl transpeptidase, aspartate aminotransferase, and alkaline phosphatase. This group also had significantly lower total protein and albumin values compared to the control pigs. Variation in the severity of the histological lesions was seen in pigs fed 0.4 microgram/g diets as well as variation in lymphocyte indices, liver specific serum enzymes, and electrophoretic results in the affected pigs in that group.

Steatorrhea during aflatoxicosis in chickens

Graded levels of dietary aflatoxin (0, .625, 1.25, 2.5, 5 and 10 microgram/g) were tested for their effect on lipid excretion in feces of young broiler chickens. There was a highly significant (P less than .01) increase at 1.25 microgram/g and above including a threefold increase at 10 microgram/g, while growth rate was decreased only at levels of 2.5 microgram/g and above. Pancreatic lipase, the primary fat digestive enzyme, was decreased significantly (P less than .05) at all levels of aflatoxin and at 10 microgram/g was only 40% of the control value, Bile, which is required for lipid digestion and absorption, was decreased highly significantly (P less than .01) in concentration by all growth inhibition levels of aflatoxin. A slight but significant ( P less than .05) increase in bladder size at growth inhibitory levels of aflatoxin appeared adequate to compensate for decreased bile concentration. A pair feeding technique showed the effect of aflatoxin on fecal lipids and pancreatic lipase occurred in diets low (2%) or high (17%) in fat. The steatorrhea caused by aflatoxin apparently reflects a lipid malabsorption syndrome caused by an impaired ability to digest lipids.