EFFECT OF PHAFFIA RHODOZYMA BIOMASS AND antioxidants on the ENZYMES OF glutathione system in the tissues of albino rats under aflatoxin B1 influence

Abstract

Introduction. Aflatoxin B1 (AFB1) is one of the most hazardous mycotoxins that can be consumed by animals as a consequence of receiving feed contaminated with moulds. The toxin causes a wide range of adverse health effects and can exhibit potent carcinogenic action. Therefore working out the effective measures to reduce the toxic effects of AFB1 in animals represents an important issue in animal husbandry and veterinary medicine. AFB1 poisoning was shown to increase lipid peroxidation (LPO) and to inhibit the activities of antioxidant system enzymes in animal cells. Thus, using the antioxidants could be helpful in prevention and correction of metabolic disturbances caused by AFB1. Basidiomicetous yeast Phaffia rhodozyma is known as microorganism able to synthesize a carotenoid astaxanthin – a potent natural antioxidant. The aim of this study was to research the effectiveness of application the yeast Phaffia rhodozyma biomass as dietary additive in animal feeding in comparison to vitamin E and “E-Selenium” preparations towards the glutathione system in the liver, brain and kidneys of albino rats in the conditions of aflatoxin B1 toxicity.

Materials and methods. Adult male albino rats (180–200 g body weight) were used in the experiments. Animals were randomly divided into nine groups: control (n=10) and eight experimental groups (E1–E8, n=5). The rats of groups E1, E3, E5, E7 were treated with aflatoxin by intragastric introducing of AFB1 (dissolved in olive oil) in a dose 0.025 mg/kg body weight daily during 7 days, and the rats of groups E2, E4, E6, E8 were exposed to aflatoxin in the same dose and by the same route during 14 days. The rats of groups E3 and E4 were given additionally a preparation of yeast Phaffia rhodozyma biomass, introduced intragastrically in a dose 1.5 g/kg body weight daily during 7 and 14 days respectively. Yeast biomass was administered to animals prior to the introduction of AFB1.The rats of groups E5 and E6 received a preparation “E-Selenium” as a single intramuscular injection in a dose 0.05 ml/kg body weight prior to the beginning of treatment with AFB1. The rats of groups E7 and E8 were treated with vitamin Е as single intragastric gavage (100 mg/kg body weight) before the beginning of treatment with AFB1. Animals of control group were treated with an equivalent volume of olive oil by intragastric administration for the same period.

Fresh organs (liver, kidney, brain) were removed from euthanatized animals, and prepared homogenates were used for analysis. Glutathione peroxidase and glutathione reductase activities, as well as concentration of the reduced glutathione (GSH) were determined by using the standard methods. The results, processed as means±S.D. were analyzed using Student’s test to determine the significance level.

Results and discussion. The experimental data show, that exposure to AFB1 leads to inhibition of activities of glutathione system enzymes (glutathione reductase, glutathione peroxidase) and diminishes the GSH concentration in all analyzed tissues of the rats on the 7th and 14th days of experiment. Introducing of yeast Phaffia rhodozyma biomass to the rats treated with AFB1, contributes to normalization of functional state of glutathione system in liver, kidney and brain tissues. At the same time the activities of glutathione peroxidase and glutathione reductase, and GSH content increased significantly compared to the levels observed in the tissues of rats treated with AFB1 alone. In the conditions of treatment the rats with preparations “E-Selenium” and vitamin E prior to daily AFB1 administration, the glutathione reductase and glutathione peroxidase activities and GSH content increased on the 7th day of experiment compared to these indices in animals treated with AFB1. However, the positive effects of the antioxidants in counteracting AFB1 toxicity were not apparent on the 14th day of experiment.

The effectiveness of yeast Phaffia rhodozyma biomass in reducing the harmful effects of AFB1 towards the activities of antioxidant system enzymes can be explained by the following features: 1) the structural components of yeast cell wall are directly involved in the binding of mycotoxins, thus yeast biomass can adsorb AFB1 in the gastric tract; 2) a cellular metabolite astaxanthin produced by yeast Phaffia rhodozyma is potent antioxidant able to improve antioxidant status of the cells and to facilitate the detoxification of aflatoxin B1 in the gastrointestinal tract.

Conclusions. Application of the yeast Phaffia rhodozyma biomass as additive in animal feeding can reduce aflatoxin B1 toxicity by normalization the activities of antioxidant system enzymes (glutathione reductase, glutathione peroxidase) and content of reduced glutathione in the liver, kidney and brain cells. Besides, yeast biomass can adsorb AFB1 in the gastrointestinal tract of animals. Positive effects vitamin Е and “E-Selenium” preparations on functional state of antioxidant system in rat tissues in the conditions of AFB1 intoxication were evident only on the 7th day of experiment, while these effects were not apparent on the 14th day of experiment. Thus, preparation of yeast Phaffia rhodozyma biomass can be suggested as more effective dietary additive in counteracting AFB1 toxicity in animals in comparison to single application of vitamin Е or “E-Selenium” preparations.