Effect of aflatoxin on rat liver lysosomes

Dose-related increase in liver heme catabolism during rabbit aflatoxicosis

Aflatoxin B1 (AFB1) has been reported to decrease microsomal hepatic cytochrome P450 (P450) content and increase both total plasma bilirubin concentration and liver heme oxygenase activity. The purposes of this study were to determine whether liver hemoproteins contents and heme catabolizing enzymes were affected by the mycotoxin and whether these alterations were linked to hyperbilirubinemia. Male New Zealand rabbits were divided into three groups of five animals, each receiving for 5 days either arabic gum as vehicle or AFB1 at a daily oral dose of 0.05 or 0.10 mg/kg. These treatments affected neither cytochrome b5 content nor NADPH-cytochrome reductase activity. A linear dose-dependent decrease in cytochrome P450 content and increases in both heme oxygenase and biliverdin reductase activities were observed. Bilirubin UDP-glucuronyltransferase activity was dramatically decreased at both doses, whereas cholestasis occurred only at 0.10 mg/kg. An exponential dose-dependent increase in plasma bilirubin concentration was also observed. Both the simultaneous exponential increase in bilirubinemia associated to a reduced bilirubin UDP-glucuronyltransferase activity and the absence of cholestasis at 0.05 mg/kg, suggested that the hyperbilirubinemia is more probably related to an increased heme catabolism than to an altered bile duct permeability.

Dose-related effect of aflatoxin B1 on liver drug metabolizing enzymes in rabbit

The effects of chronic administration of aflatoxin B1 (AFB1) on liver drug metabolism enzymes were measured in New Zealand rabbits divided into three groups of 5 animals, each receiving over 5 days either arabic gum or AFB1 in arabic gum at a daily oral dose of 0.05 or 0.10 mg/kg. These treatments did not lead to any lethality in any of the treated groups, but the body weight gain was altered. Biochemical exploration of plasma components revealed a dose-dependent hepatotoxicity characterized by cytolysis and cholestasis. At 0.10 mg/kd/day of AFB1, significant decreases were observed in total liver microsomal cytochrome P450, several P450-dependent monooxygenase activities, all individual P450 isoenzymes levels analysed by Western-blotting and glutathione S-transferase activities. By contrast, at 0.05 mg/kg/day of AFB1, even though total cytochrome P450 was decreased by 30%, only P450 1A1 and 3A6 isoenzymes, and aniline hydroxylation, pentoxyresorufin O-depentylation, aminopyrine, erythromycin, ethylmorphine and dimethylnitrosamine N-demethylations were affected. In the same animal group, the only glutathione S-transferase accepting CDNB (1-chloro-2,4-dinitrobenzene) as substrate was decreased by 22%. UDP-glucuronyltransferase accepting p-nitrophenol as substrate was increased in both groups of animals (33-62%). The mechanisms that could contribute to the observed changes in drug metabolizing enzymes are discussed.

Hepatic mitochondrial function and lysosomal enzyme activity in ethanol-potentiated aflatoxin B1 hepatotoxicity

The possible role of hepatic mitochondrial function and lysosomal enzyme activity in ethanol-enhanced aflatoxin B1 (AFB1) hepatotoxicity was studied in male rats. Hepatic ATP content was significantly decreased in rats treated with ethanol (4.0 g/kg body wt.) and AFB1 (2.0 mg/kg body wt.) compared with rats treated with AFB1 alone at 12-72 h after AFB1 administration. The decrease in hepatic ATP content was due to the decrease in the activity of NADH-cytochrome c reductase whereas cytochrome oxidase activity did not differ in rats treated with ethanol and AFB1 when compared to AFB1 alone. Total and free activities of hepatic lysosomal enzymes (glucuronidase, arylsulfatase and acid phosphatase) were significantly increased in rats treated with ethanol and AFB1 at 24-36 h after AFB1 administration when compared to AFB1 alone. The increase in hepatic lysosomal enzyme activities correlated well with the increase in the lipid peroxide level of lysosomes in rats treated with ethanol and AFB1. These findings indicate that the decrease in hepatic mitochondrial respiratory enzyme activities and the increase in lipid peroxide level of lysosomes might lead to a decrease in hepatic ATP content, and that the increase in the activities of hepatic lysosomal enzymes, respectively, enhance the AFB1 hepatotoxicity of ethanol.

Effects of T-2 mycotoxin on gastrointestinal tissues: a review of in vivo and in vitro models

T-2 mycotoxin, a trichothecene, is the principal toxic component of Fusarium sp. Agricultural products and food are frequently contaminated with this toxin. Various animal models have been used to determine its metabolic fate, rate of excretion, and distribution. A modulation effect on cell-mediated immunity and alterations in gastrointestinal propulsion have been demonstrated. The toxin has been shown to produce some similar pathologic alterations in various animal species studied. The consistent alteration appears to mainly affect mitotic cells of the gastrointestinal tract and the lymphoid system. A host of bioassay systems are now being used as alternative methods to the use of animals for testing of the mycotoxin. These tests may accurately assess and define the role of the subject-toxin interactions following consumption of T-2 mycotoxin contaminated food sources. T-2 mycotoxin, as observed above with in vivo and in vitro models, promotes a chemically-induced change in structure and function of affected gastrointestinal cells from a transient and reversible aberration in a single enzymatic reaction to cell death. Regardless of the end point measured, the toxic response brought about in cells appears to involve the interactions of virtually all subcellular processes--membrane transport and permeability, chemical metabolism, DNA function, and energy production/expenditure--as cells attempt to maintain their functional integrity while disposing of the toxicant. The variation in the quality of the toxic response with dose suggests that more cellular processes are perturbed as the chemical dose is increased.

The relationship of certain blood parameters to aflatoxin resistance in Japanese quail

Blood chemistry profiles were obtained for two lines of Japanese quail selected for resistance to aflatoxin, and for a nonselected control line. Nine of the 18 plasma components measured in samples taken at 4 weeks of age changed as a result of selection. Plasma concentrations of total protein, albumin, cholesterol, and potassium, and the activities of lactic dehydrogenase, glutamic-oxalacetic transaminase, and cholinesterase were significantly elevated in aflatoxin-resistant quail compared with the nonselected line. The activities of beta-glucuronidase and alpha-amylase changed most dramatically; both activities were much lower in the resistant lines than in the control line. In another experiment, serum total protein, albumin, alpha-amylase, and beta-glucuronidase were tested as identifiers of aflatoxin-resistant individuals within a nonselected population of quail. Serum samples obtained from 150 nonselected quail immediately before and 24 hr after administration of an oral dose of aflatoxin were analyzed for each of the four components. The acute toxicosis decreased body weight, serum alpha-amylase activity, total protein, and albumin; whereas, serum beta-glucuronidase activity and the coefficients of variation for each parameter were increased. Correlations between measurements made prior to dosing and parameters reflecting aflatoxin susceptibility were not significant. However, postdose determinations of albumin, protein, and beta-glucuronidase were significantly related to susceptibility parameters. These data indicate that the four blood components tested cannot be utilized to identify resistant birds within a nonselected population of quail without an aflatoxin challenge; but albumin, protein, and beta-glucuronidase are correlated with resistance when measured during an aflatoxin stress.

Comparative responses of genetically resistant and nonselected Japanese quail to dietary aflatoxin

Two lines of Japanese quail (AR2.5 and AR3) selected for resistance to aflatoxin and a nonselected control line (NS) were fed diets containing 0, 10, and 20 micrograms of aflatoxin/g of feed. Line-related reductions in mortality and growth inhibition clearly demonstrated the resistance of the AR lines to dietary aflatoxin. Two-week cumulative mortality percentages for the NS, AR2.5, and AR3 lines fed the 10 micrograms/g diet were 13.9, 7.7, and 2.6%, respectively, and 44.4, 17.9, and 12.8% at 20 micrograms/g. Average growth reduction percentages resulting from feeding the 10 and 20 micrograms/g diets to the NS, AR2.5, and AR3 lines were: 17.3 and 27.5%, 10.7 and 20.1%, and 4.3 and 10.5%, respectively. In addition, AR quail were resistant in varying degrees to the following aflatoxin-induced effects: liver lipid accumulation and enlargement, hepatic protein depletion, elevated hepatic beta-glucuronidase activity, bursal regression, and hypoproteinemia. Comparisons of the AR and NS lines fed the control diet revealed no detrimental physiological or biochemical response to selection for aflatoxin resistance. Genetic resistance to aflatoxin was associated with increased relative liver weight, higher liver protein content, and elevated plasma concentrations of protein and lipid compared with NS quail. One or more of these differences may be related to the mechanism of genetic resistance to aflatoxin in AR quail.

Effects of T-2 toxin on glucose and tryptophan uptake and intestinal mucosal enzymes

We studied the uptake of D-glucose and L-tryptophan by the small intestine and estimated the activities of the intestinal brush border enzymes (sucrase, lactase, NA+-K+-ATPase and alkaline phosphatase) and lysosomal enzymes in rats receiving T-2 toxin orally. considerable decrease occurred in glucose and tryptophan uptake and in brush border sucrase, lactase and (Na+-K+)-ATPase. Alkaline phosphatase activity and release of lysosomal enzymes (acid phosphatase and acid ribonuclease) was unchanged.

Immune studies with T-2 toxin: effect of feeding and withdrawal in monkeys

Ingestion of T-2 toxin, a product of Fusarium fungi, has been reported to have a variety of effects leading to morbidity and mortality in animals and humans. Semi-purified T-2 toxin was given to monkeys by gastric intubation at a level of 100 microgram/kg body weight/day for 4-5 wk and the haematological and immune parameters were studied before and after the treatment. Leucocyte counts were depressed at the end of wk 4 of treatment. The immunological studies studies showed suppression of the bactericidal activity of neutrophils, of cell-mediated immune status as assessed by T-cell number and lymphocyte transformation, and of humoral immunity as reflected in B-cell number and IgG and IgM levels. However serum complement (CH50) did not show any change. Investigations carried out 5 months after withdrawal of the toxin indicated that these parameters had returned almost to the initial, pretreatment levels. These data suggest that the greater incidence of infection seen in mycotoxin-ingesting animals may be due to immune suppression. Withdrawal of the mycotoxin results in improvement of haematological and immune functions.