The fate and acute toxicity of aflatoxin B1 in the mastomys and rat

How does active yeast supplementation reduce the deleterious effects of aflatoxins in Wistar rats? A radiolabeled assay and histopathological study

The aim of this study was to investigate the mechanisms by which yeasts (Saccharomyces cerevisiae) control the toxic effects of aflatoxins, which are not yet fully understood. Radiolabeled aflatoxin B1 (AFB13H) was administered by gavage to Wistar rats fed with aflatoxin (AflDiet) and aflatoxin supplemented with active dehydrated yeast Y904 (AflDiet + Yeast). The distribution of AFB13H and its metabolites were analyzed at 24, 48 and 72 h by tracking back of the radioactivity. No significant differences were observed between the AflDiet and AflDiet + Yeast groups in terms of the distribution of labeled aflatoxin. At 72 h, for the AflDiet group the radiolabeled aflatoxin was distributed as following: feces (79.5%), carcass (10.5%), urine (1.7%), and intestine (7.4%); in the AflDiet + Yeast the following distribution was observed: feces (76%), carcass (15%), urine (2.9%), and intestine (4.9%). These values were below 1% in other organs. These findings indicate that even after 72 h considerable amounts of aflatoxins remains in the intestines, which may play a significant role in the distribution and metabolism of aflatoxins and its metabolites over time. The presence of yeast may not significantly affect this process. Furthermore, histopathological examination of hepatic tissues showed that the presence of active yeast reduced the severity of liver damage caused by aflatoxins, indicating that yeasts control aflatoxin damage through biochemical mechanisms. These findings contribute to a better understanding of the mechanisms underlying the protective effects of yeasts against aflatoxin toxicity.

New Insights Into the Persistent Effects of Acute Exposure to AFB1 on Rat Liver

Aflatoxin B₁ (AFB₁) has mutagenesis, carcinogenesis and teratogenesis effects and mainly found in food crops and their processed foods. AFB₁ exposure can cause acute or chronic liver poisoning, but there were few studies on the persistent effects of acute AFB₁ exposure on the liver. In this study, rat liver injury models were established 2 and 7 days after single exposure to high and low doses of AFB₁. The persistent effects of AFB₁ single acute exposure (ASAE) on rat liver were analyzed from the phenotypic and genetic levels. The results showed that compared with the control group, liver function indexes, MDA content in liver and the number of apoptotic hepatocytes in model groups increased to the highest on the 2nd day after ASAE (p < 0.001). However, the changes of liver coefficient were most significant on the 7th day after ASAE (p < 0.01). The results of liver pathology showed that the liver injury was not alleviated and the activities of antioxidant enzymes GSH-Px and SOD were the lowest on the 7th day (p < 0.001). RNA-Seq results indicated that there were 236, 33, 679, and 78 significantly differentially expressed genes (DEGs) in the model groups (LA-2d, LA-7d, HA-2d, HA-7d) compared with the control group. Among them, the Gtse1 gene related to the proliferation, differentiation and metastasis of liver cancer cells, the Lama5 and Fabp4 gene related to the inflammatory response were significantly DEGs in the four model groups, and the differential expression of the immune system-related Bcl6 gene increased with the prolonged observation time after ASAE. In conclusion, ASAE can cause persistent liver damage in rats. The persistently affected genes Lama5, Gtse1, Fabp4, and Bcl6 possess the potential to be therapeutic targets for liver disease induced by AFB₁.

Hemoadsorption Improves Survival of Rats Exposed to an Acutely Lethal Dose of Aflatoxin B1

Mycotoxins, such as aflatoxin B1 (AFB1), pose a serious threat as biological weapons due to their high toxicity, environmental stability, easy accessibility and lack of effective therapeutics. This study investigated if blood purification therapy with CytoSorb (CS) porous polymer beads could improve survival after a lethal aflatoxin dose (LD90). The effective treatment window and potential therapeutic mechanisms were also investigated. Sprague Dawley rats received a lethal dose of AFB1 (0.5-1.0 mg/kg) intravenously and hemoperfusion with a CS or Control device was initiated immediately, or after 30, 90, or 240-minute delays and conducted for 4 hours. The CS device removes AFB1 from circulation and significantly improves survival when initiated within 90 minutes of toxin administration. Treated subjects exhibited improved liver morphology and health scores. Changes in the levels of cytokines, leukocytes and platelets indicate a moderately-severe inflammatory response to acute toxin exposure. Quantitative proteomic analysis showed significant changes in the level of a broad spectrum of plasma proteins including serine protease/endopeptidase inhibitors, coagulation factors, complement proteins, carbonic anhydrases, and redox enzymes that ostensibly contribute to the therapeutic effect. Together, these results suggest that hemoadsorption with CS could be a viable countermeasure against acute mycotoxin exposure.

Changes in serum cytokine levels, hepatic and intestinal morphology in aflatoxin B1-induced injury: modulatory roles of melatonin and flavonoid-rich fractions from Chromolena odorata

Aflatoxins are known to produce chronic carcinogenic, mutagenic, and teratogenic effects, as well as acute inflammatory effects, especially in the gastrointestinal tract. The potentials of the flavonoid-rich extract from Chromolena odorata (FCO) and melatonin (a standard anti-oxidant and anti-inflammatory agent) against aflatoxin B1 (AFB1)-induced alterations in pro-inflammatory cytokine levels and morphology of liver and small intestines were evaluated in this study. We utilized Wistar albino rats (200-230 g) randomly divided into five groups made up of group A, control rats; group B, rats given AFB1 (2.5 mg/kg, intraperitoneal) twice on days 5 and 7; rats in groups C, D, and E were treated with melatonin (10 mg/kg, intraperitoneal) or oral doses of FCO1 (50 mg/kg) and FCO2 (100 mg/kg) for 7 days, respectively, along with AFB1 injection on days 5 and 7. Serum levels of interleukin 1 beta (IL-1β) and tumor necrosis factor alpha (TNF-α) were determined using commercial ELISA kits and histopathological evaluation of the liver, duodenum, and ileum were also carried out. We observed significant elevation (p < 0.05) in serum IL-1β correlating with hemorrhages and leucocytic and lymphocytic infiltration in the liver and intestines as evidences of an acute inflammatory response to AFB1 administration. All treatments yielded significant reduction (p < 0.05) in IL-1β levels, although TNF-α levels were not significantly altered in all rats that received AFB1, irrespective of the treatments. Melatonin and FCO2 produced considerable protection of hepatic tissues, although melatonin was not quite effective in protecting the intestinal lesions. Our findings suggest a modulation of cytokine expression that may, in part, be responsible for the abilities of C. odorata or melatonin in amelioration of hepatic and intestinal lesions associated with aflatoxin B1 injury.

Modification of aflatoxin B1 and ochratoxin A toxicokinetics in rats administered a yeast cell wall preparation

The cell wall of Saccharomyces cerevisiae can bind mycotoxins in vitro, but there is scarce information on whether this property decreases the absorption of mycotoxins in vivo. The effect of a yeast cell wall preparation (YCW) on toxicokinetics and balance excretion (urine and faeces) of aflatoxin B(1) (AFB1) and ochratoxin A (OTA) was tested in rats after oral administration of each toxin. The (3)H-labelled mycotoxins were used at low doses. Co-administration of YCW with AFB1 decreased the extent, but not the rate, of absorption. Concurrently, radioactivity excreted in faeces increased by up to 55% when compared with controls, whilst the excretion in urine decreased (p < 0.05). The effect of YCW on OTA was less marked, although it increased radioactivity excretion in faeces (up to 16%; p < 0.05) it did not result in changes in urine and toxicokinetic parameters. The in vivo effect is in agreement with the reported in vitro binding ability for these toxins (AFB1 > OTA). In conclusion, these results indicate that YCW could be used to protect monogastric animals against exposure to low dietary levels of selected mycotoxins.

Comparative activities of glutathione-S-transferase and dialdehyde reductase toward aflatoxin B1 in livers of experimental and farm animals

In order to gain a better understanding of the relative activities of glutathione-S-transferase (GST) and aldehyde reductase toward aflatoxin B1 (AFB1) in relation to the variation of species susceptibilities, we studied the in vitro cytosolic GST and reductase activities in liver tissues from male Fischer rats, ICR mice and golden hamsters, adult male rainbow trouts and female piglets. The GST activity was determined by incubating the liver cytosol with glutathione (GSH) and AFB1 in the presence of the hamster liver microsomes to metabolize AFB1 to AFB1-8, 9-epoxide. The reaction product, AFB1 and GSH conjugate (AFB1-GSH), was quantified with HPLC. The reductase activity was determined by incubating liver cytosol with AFB1-dialdehyde, followed by the quantification of the metabolic product, AFB1-dialcohol, with HPLC. All the animal species possessed the GST activities, and AFB1-GSH formed increasingly with the increase of the AFB1 concentration according to the model of first-order enzyme reaction kinetics. The V(max) and K(m) values of the GST activities in rodent species were higher and lower, respectively, than those in the trout and pig, being consistent with the relative susceptibilities to AFB1 of these animal species. However, no relationship was noted between the reductase activity and species susceptibility. Thus, the result of this study shows that GST toward AFB1, but not aldehyde reductase, is a determinant of the variation of species susceptibilities.

Aflatoxin B1-induced changes of glutathione-S-transferase activity in the plasma and liver of the rat

BACKGROUND

The influence of low doses of aflatoxin B1(AFB1) and partial hepatectomy (PH) on glutathione-S-transferase (GST) activity was studied in the plasma and liver of the rat.

METHODS

The animals were divided into four groups. The first (I) and the second (II) group were treated with AFB1 freshly dissolved in dimethyl sulphoxide (DMSO), and administered as a single intraperitoneal dose of 50 micrograms/rat 24 hrs after the rats had undergone either sham operation or, 40% PH, respectively. The third group (III) of animals was treated with a total dose of 1 mg AFB1-5 days per week during a period of 8 weeks. The non-treated animals were used as controls (C).

RESULTS

We observed a significant increase of GST activity in the plasma of all experimental groups compared to the controls (C), (p < 0.02 to p < 0.005). In the liver, the GST activity of all experimental groups was also significantly increased, compared to the controls (from p < 0.02 to p < 0.005).

CONCLUSION

The administration of both single and multiple doses of AFB1 led to long term increase of GST activity in the rat plasma and liver, and partial hepatectomy had no significant effect on this phenomenon.

Glutathione-S-transferase activity toward aflatoxin epoxide in livers of mastomys and other rodents

In order to study the liver glutathione-S-transferase (GST) activity toward aflatoxin B1 (AFB1) epoxide in mastomys in comparison with other rodents, we performed in vitro studies of the cytosolic GST activity toward AFB1-epoxide using mastomys, rat, mouse and hamster liver. Also AFB1 metabolism by liver microsomes including formation of AFB1-DNA adducts was studied. Cytosolic GST activity toward AFB1-epoxide was highest in mastomys liver, and higher in the hamster and mouse livers than in the rat liver, correlating well with the differences of the sensitivity of these species to the toxicity of AFB1. However, no relationship was noted between the sensitivity of a given species to the toxicity of AFB1 and the microsomal activity of binding of AFB1 to DNA or metabolizing AFB1 to AFM1, AFQ1 and AFP1. These results demonstrate the importance of the GST mediated AFB1-epoxide conjugation with glutathione in determining the differing sensitivities of these species to AFB1 toxicity. The extremely high activity of GST in mastomys indicates that this species would be a good model animal for studying GST toward AFB1-epoxide.

Stimulation of guinea pig isolated atria by aflatoxins

Acute effects of aflatoxins (AF), and in particular cardiac actions, have not been examined as much as chronic toxicity. Thus, in the present study we evaluated the effects of specific AF on isolated guinea pig atria. Isoprenaline (ISO, 4x10(-9)), AFB(1) (3x10(-6) and 6x10(-5) M) and AFG(1) (3x10(-6) and 6x10(-6) M) contracted the isolated guinea pig atria, leaving the preparation hyperresponsive to ISO. These properties of AF are of interest as they could be responsible of certain cardiotoxic effects described in the literature.

Serum biochemical values in two inbred strains of mastomys (Praomys coucha)

Serum samples collected from 119 (72 male and 47 female) mastomys (Praomys coucha) of 2 specific-pathogen-free inbred strains (RI4 and RI7) were analyzed for 12 serum biochemical parameters. Sex-related differences (p < 0.01) were noted in alkaline phosphatase and glucose; the both higher in females than in males. Age-related changes (p < 0.01) were observed in total protein, albumin, total cholesterol, and alkaline phosphatase, with higher values for the first three parameters in the older group (200-250 days of age) than in the younger group (90-140 days of age). Four out of 12 parameters showed strain-related differences (p < 0.01), consistent with the large amount of genetic heterogeneity reported in this species. These serum biochemical reference values should provide information for the use of mastomys in laboratory research.