Effects of nivalenol on hepatic drug-metabolizing activity in rats

Nitric oxide mediates apoptosis and mitochondrial dysfunction and plays a role in growth hormone deficiency by nivalenol in GH3 cells

Nivalenol (NIV), a type B trichothecenes commonly found in cereal crops, can cause growth impairment in animals. However, limited information about its mechanisms is available. Trichothecenes have been characterized as an inhibitor of protein synthesis and induce apoptosis in cells. Oxidative stress is considered an underlying mechanism. However, whether NIV can induce oxidative stress and apoptosis in rat pituitary cells line GH3 is unclear. The present study showed that NIV significantly reduced the viability of cells and caused oxidative stress in GH3 cells. Further experiments showed that nitric oxide (NO), but not ROS, mediated NIV-induced oxidative stress. Additionally, NIV induced caspase-dependent apoptosis, decrease in mitochondrial membrane potential and mitochondrial ultrastructural changes. However, NIV-induced caspase activation, mitochondrial damage and apoptosis were partially alleviated by Z-VAD-FMK or NO scavenger hemoglobin. Finally, NIV changed the expression of growth-associated genes and pro-inflammatory cytokines. NIV also reduced the GH secretion in GH3 cells, which was reversed by hemoglobin. Taken together, these results suggested that NIV induced apoptosis in caspase-dependent mitochondrial pathway in GH3 cells, which might be an underlying mechanism of NIV-induced GH deficiency. Importantly, NO played a critical role in the induction of oxidative stress, apoptosis and GH deficiency in NIV-treated GH3 cells.

Effects of fusarium infection on the phenolics in emmer and naked barley

Inoculated or non-inoculated naked barley and emmer cultivars were investigated with regard to their influence on phenolic acid profiles and their arabinoxylan content. Two groups of phenolic compounds were differentiated-methanol-soluble and hydrolyzable covalent-bound phenolic compounds. Chromatographic methods were applied for their analysis. The results showed ferulic acid as the predominant phenol in both total and covalent-bound fractions. The inoculation significantly reduced the ferulic acid content within a range of 5.6-6.6% in the two cereals and all their cultivars. Naked barley cultivars additionally contained the flavonoid catechin in the soluble fraction. The innoculation led here to a significant increase in the catechin content of about 4.5%. These results document an induction of the synthesis of catechin in naked barley after artificial Fusarium infection, whereas the ferulic acid content declined.

Nivalenol and the targeting of the female reproductive system as well as haematopoietic and immune systems in rats after 90-day exposure through the diet

Nivalenol (NIV) is considered to be an important trichothecene mycotoxin produced by Fusarium species because of its frequent contamination in wheat and barley worldwide. The present study examined the subchronic toxicity of NIV in male and female F344 rats fed diets containing 0, 6.25, 25 and 100 mg kg(-1) of the toxin for 90 days. During the experimental period there was a decrease in the white blood cell count at 100 mg kg(-1) in males and at > or =6.25 mg kg(-1) in females. Histopathologically, treatment-related changes were observed in the haematopoietic and immune systems in both sexes and in the female reproductive system at 100 mg kg(-1). Flow cytometric analysis of splenic cells revealed an elevation in the ratio of helper/cytotoxic T-lymphocytes at 100 mg kg(-1). In summary, NIV targets the female reproductive system as well as haematopoietic and immune systems in rats fed NIV for 90 days. Based on a significant decrease in white blood cells in female rats relative to controls, the lowest observable effect level was calculated as 0.4 mg kg(-1) body weight day(-1).

Effect of subacute oral doses of nivalenol on immune and metabolic defence systems in mice

Nivalenol (NIV) is a toxic Fusarium secondary trichothecene metabolite occurring naturally in cereal grains. In order to evaluate the no observed adverse effect level (NOAEL), we tested the effects of a large array of oral doses of this toxin for responses on plasma biochemistry, the immune system and hepatic drug metabolism in mice. C57Bl6 mice received oral doses of toxin (0.014, 0.071, 0.355, 1.774 or 8.87 mg/kg bw) 3 days a week for 4 weeks. Only the highest dose of NIV induced an increase in plasma phosphate, decreases in plasma urea and immunoglobulin M and additional changes like increases in plasma alkaline phosphatase and immunoglobulin G. Interleukin 4 production was increased in cultured murine splenocytes. Regarding liver drug metabolising enzymes, the only glutathione transferase activity accepting 1-chloro-2,4-dinitro-benzene as substrate was transiently increased in mice receiving low doses (0.071 and 0.355 mg/kg bw) of NIV. Regarding the cytochrome P450 monooxygenases, no significant change was observed in ethoxyresorufin O-deethylase activity whereas both methoxyresorufin and pentoxyresorufin O-dealkylase activities were decreased by 38-45% for the highest dose (8.87 mg/kg bw) of NIV. However, when analysed by Western blot analysis, the protein expression of mouse P450 1a, 2b, 2c, 3a and 4a subfamilies was unchanged in animals receiving NIV. In conclusion, the NOAEL of this toxin in our study was 1.774 mg/kg bw, corresponding to an exposure to 5 ppm contaminated food. Indeed hepatotoxicity appears in the only mice treated with a five fold higher oral dose of 8.87 mg/kg bw of NIV. Such exposure levels appear to be by far higher than the maximal natural occurrence measured in European cereals, known to range from 0.34 to 1.86 ppm.

Effect of various doses of deoxynivalenol on liver xenobiotic metabolizing enzymes in mice

DON is one of the major mycotoxic contaminant of cereal grains throughout the world. The purpose of this investigation was to characterize the effects of a range of environmentally relevant doses of DON in mice exposed through a subchronic toxicological assay. Animals received 3 days per week for 4 weeks, 0.014, 0.071, 0.355 or 1.774 mg of toxin/kg b.w. All doses, except 0.014 mg/kg, provoked increases in plasma immunoglobulin A whereas there was no change in plasma biochemical parameters such as alkaline phosphatase, electrolytes or other immunoglobulins. Administration of 0.071 or 0.355 mg/kg doses led to increased liver microsomal pentoxyresorufin depentylase and cytosolic glutathione transferase activities. Examining protein modulation, western blot analyses liver fractions from mice receiving these doses revealed increased levels in both P450 2b, GST alpha and pi isoenzymes without any change in P450 1a expression. A significant competitive inhibition of deoxynivalenol on CDNB conjugation in vitro suggests that the mycotoxin is a putative substrate for glutathione S-transferases. These changes in liver xenobiotic metabolizing enzymes are discussed by considering the structural nature of deoxynivalenol and previous reports on similar effects exerted by other trichothecenes. These results suggest that a subchronic exposure to low doses of deoxynivalenol causes changes in the normal liver metabolism of xenobiotics.

Effects of trichothecene mycotoxins on eukaryotic cells: A review

The major products of the trichothecene mycotoxin biosynthetic pathway produced in a species- and sometimes isolate-specific manner by cereal-pathogenic Fusarium fungi include T-2 toxin, diacetoxyscirpenol, deoxynivalenol and nivalenol. This paper briefly reviews the major effects of such trichothecenes on the gross morphology, cytology and molecular signalling within eukaryotic cells. The gross toxic effects of select trichothecenes on animals include growth retardation, reduced ovarian function and reproductive disorders, immuno-compromization, feed refusal and vomiting. The phytotoxic effects of deoxynivalenol on plants can be summarized as growth retardation, inhibition of seedling and green plant regeneration. Trichothecenes are now recognized as having multiple inhibitory effects on eukaryote cells, including inhibition of protein, DNA and RNA synthesis, inhibition of mitochondrial function, effects on cell division and membrane effects. In animal cells, they induce apoptosis, a programmed cell death response. Current knowledge about the eukaryotic signal transduction cascades and downstream gene products activated by trichothecenes is limited, especially in plants. In mammalian cells, certain trichothecenes trigger a ribotoxic stress response and activate mitogen-activated protein kinases. DON mediates the inflammatory response by modulating the binding activities of specific transcription factors and subsequently inducing cytokine gene expression. Several genes are up-regulated in wheat in response to trichothecene mycotoxins; the significance, if any, of these genes in the host response to trichothecenes has yet to be elucidated.

Cytotoxicity assays for mycotoxins produced by Fusarium strains: a review

Mycotoxins are naturally occurring toxic secondary metabolites of fungi that may be present in food and feed. Several of these mycotoxins have been associated with human and animal diseases. Fusarium species, found worldwide in cereals and other food types for human and animal consumption, are the most important toxigenic fungi in northern temperate regions. The overall economical loss and the detrimental health effects in humans and animals of mycotoxin contamination are enormous and therefore, rapid screening methods will form an important tool in the protection of humans and animals as well as to minimize economical losses by early detection. An overview of methods for the determination of cytotoxicity and the application of such bioassays to screen solid fungal cultures, cereals, respectively, food/feedstuffs for the presence and toxic potential of Fusarium mycotoxins is presented. Various cell lines including different endpoints of toxicity using vertebrate cells and the predictive value of the in vitro assays are reviewed. Bioassays are compared with existing chemical analytical methods and the possibilities and limitations of such systems are discussed. The review is based on 149 references.