Zearalenone induces apoptosis and cytoprotective autophagy in primary Leydig cells

Endoplasmic Reticulum Stress Cooperates in Zearalenone-Induced Cell Death of RAW 264.7 Macrophages

Zearalenone (ZEA) is a fungal mycotoxin that causes cell apoptosis and necrosis. However, little is known about the molecular mechanisms of ZEA toxicity. The objective of this study was to explore the effects of ZEA on the proliferation and apoptosis of RAW 264.7 macrophages and to uncover the signaling pathway underlying the cytotoxicity of ZEA in RAW 264.7 macrophages. This study demonstrates that the endoplasmic reticulum (ER) stress pathway cooperated in ZEA-induced cell death of the RAW 264.7 macrophages. Our results show that ZEA treatment reduced the viability of RAW 264.7 macrophages in a dose- and time-dependent manner as shown by the 3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrazolium bromide assay (MTT) and flow cytometry assay. Western blots analysis revealed that ZEA increased the expression of glucose-regulated protein 78 (GRP78) and CCAAT/enhancer binding protein homologous protein (CHOP), two ER stress-related marker genes. Furthermore, treating the cells with the ER stress inhibitors 4-phenylbutyrate (4-PBA) or knocking down CHOP, using lentivirus encoded short hairpin interfering RNAs (shRNAs), significantly diminished the ZEA-induced increases in GRP78 and CHOP, and cell death. In summary, our results suggest that ZEA induces the apoptosis and necrosis of RAW 264.7 macrophages in a dose- and time-dependent manner via the ER stress pathway in which the activation of CHOP plays a critical role.

Hepatotoxic effects of mycotoxin combinations in mice

This study was performed to assess the individual and combined toxic effects of aflatoxin B1 (AFB1), zearalenone (ZEA) and deoxynivalenol (DON) within the liver of mice. A total of 56 4-week-old weanling female mice were divided into seven groups (n = 8). For 2 weeks, each group received an oral administration of either solvent (control), AFB1, ZEA, DON, AFB1 + ZEA, AFB1 + DON or ZEA + DON per day. The results showed that AFB1, ZEA and DON induced liver injury, indicated by elevated relative liver weight, activities of alanine aminotransferase (ALT) and/or aspartate aminotransferase (AST), as well as decreased albumin (ALB) and/or total protein (TP) concentration in the serum. These mycotoxins also decreased hepatic total antioxidant capacity (T-AOC), and/or increased the concentration of malondialdehyde (MDA). Moreover, AFB1 + DON displayed synergistic effects, while AFB1 + ZEA displayed antagonistic effects on those parameters previously described. Furthermore, the apoptotic potential was demonstrated associated with an upregulation of the apoptotic genes Caspase-3 and Bax, along with a downregulation of the antiapoptotic gene Bcl-2 in liver. In conclusion, this study provides a better understanding of the toxic effects of AFB1, ZEA, DON, alone or in combinations on the liver of mice, which could contribute to the risk assessment of these mycotoxins in food and feed.

Food contaminant zearalenone and its metabolites affect cytokine synthesis and intestinal epithelial integrity of porcine cells

The intestinal epithelium is the first barrier against food contaminants. Zearalenone (ZEN) is an estrogenic mycotoxin that was identified as a common contaminant of cereal grains and food and feedstuffs. In the present study, we have investigated the in vitro effects of ZEN and some of its metabolites (α-ZOL, β-ZOL) in concentrations of 10–100 µM on a swine epithelial cell line: Intestinal porcine epithelial cells (IPEC-1). We demonstrated that both ZEN metabolites were more toxic for IPEC cells as resulted from the XTT test, while for doses lower than 10 µM, only β-ZOL showed a more pronounced cytotoxicity versus epithelial cells as resulted from neutral red assay. ZEN has no effect on TER values, while α-ZOL significantly decreased the TER values, starting with day 4 of treatment. β-ZOL had a dual effect, firstly it induced a significant increase of TER, and then, starting on day 6, it induced a dramatic decrease of TER values as compared with on day 0. Concerning the cytokine synthesis, our results showed that ZEN has a tendency to increase the synthesis of IL-8 and IL-10. By contrast, α- and β-ZOL decreased the expression of both IL-8 and IL-10, in a dose dependent manner. In conclusion, our results showed that ZEN and its metabolites differently affected porcine intestinal cell viability, transepithelial resistance and cytokine synthesis with important implication for gut health.

Aflatoxin B1 is toxic to porcine oocyte maturation

As a toxic secondary metabolite of Aspergillus species, Aflatoxin B1 (AFB1) is a major food and feed contaminant in tropical and sub-tropical regions with high temperature and humidity. It has been reported to be toxic to the female reproductive system in laboratory and domestic animals. In the present study, the influence of acute exposure to AFB1 (10 and 50 μM, 44h) on porcine oocyte maturation and its possible mechanism were investigated. The maturation rates of oocytes decreased significantly in the presence of 50 μM of AFB1. Cell cycle analysis showed that most oocytes were arrested at germinal vesicle breakdown or meosis I stage. However, actin assembly, spindle structure and chromosome alignment were not disrupted after exposure to 50 μM AFB1. Further study showed that DNA methylation levels increased in treated oocytes (50 μM). Histone methylation levels were also analysed after treatment (50 μM): H3K27me3 and H3K4me2 levels decreased, whereas H3K9me3 level increased, indicating that epigenetic modification was affected. AFB1 treatment (50 μM) also induced oxidative stress and further led to autophagy, as shown by accumulation of reactive oxygen species, up-regulated LC3 protein expression and increased mRNA levels of ATG3, ATG5 and ATG7. Annexin V-FITC staining assay revealed that AFB1 treatment (50 μM) resulted in oocyte early apoptosis, which was confirmed by increased Bak, Bax, Bcl-xl mRNA levels. Collectively, our results suggest that AFB1 disrupts porcine oocyte maturation through changing epigenetic modifications as well as inducing oxidative stress, excessive autophagy and apoptosis.

Elaborating the role of natural products-induced autophagy in cancer treatment: achievements and artifacts in the state of the art

Autophagy is a homeostatic process that is highly conserved across different types of mammalian cells. Autophagy is able to relieve tumor cell from nutrient and oxidative stress during the rapid expansion of cancer. Excessive and sustained autophagy may lead to cell death and tumor shrinkage. It was shown in literature that many anticancer natural compounds and extracts could initiate autophagy in tumor cells. As summarized in this review, the tumor suppressive action of natural products-induced autophagy may lead to cell senescence, provoke apoptosis-independent cell death, and complement apoptotic cell death by robust or target-specific mechanisms. In some cases, natural products-induced autophagy could protect tumor cells from apoptotic death. Technical variations in detecting autophagy affect data quality, and study focus should be made on elaborating the role of autophagy in deciding cell fate. In vivo study monitoring of autophagy in cancer treatment is expected to be the future direction. The clinical-relevant action of autophagy-inducing natural products should be highlighted in future study. As natural products are an important resource in discovery of lead compound of anticancer drug, study on the role of autophagy in tumor suppressive effect of natural products continues to be necessary and emerging.

Mycotoxin zearalenone induces apoptosis in mouse Leydig cells via an endoplasmic reticulum stress-dependent signalling pathway

Zearalenone (ZEN) is a Fusarium mycotoxin that causes several reproductive disorders and genotoxic effects. This study demonstrated the involvement of endoplasmic reticulum (ER) stress in ZEN-induced mouse Leydig cell death. Our study showed that ZEN reduced cell proliferation in a murine Leydig tumour cell line in a dose-dependent manner. The involvement of apoptosis as a major cause of ZEN-induced cell death was further confirmed by the results of a caspase-3 activity assay, which showed a ZEN dose-dependent increase in cell death. Treatment of MLTC-1 and primary mouse Leydig cells with ZEN upregulated the expression of the ER stress-typical markers GRP78, CHOP and caspase-12 protein. Further, pre-treating the cells with 4-phenylbutyrate or knocking down GRP78 using lentivirus-encoded shRNA significantly diminished ZEN-induced apoptosis and inhibited the expression of CHOP and caspase-12. In summary, these results suggest that the activation of an ER stress pathway plays a key role in ZEN-induced apoptosis in the mouse Leydig cells.

Altered oxidative stress, apoptosis/autophagy, and epigenetic modifications in Zearalenone-treated porcine oocytes

ZEN affected porcine oocyte maturation and early embryonic development. Oxidative stress, autophagy and apoptosis occurred. Aberrant epigenetic modifications were also observed.

Autophagy and senescence, stress responses induced by the DNA-damaging mycotoxin alternariol

The mycotoxin alternariol (AOH), a frequent contaminant in fruit and grain, is known to induce cellular stress responses such as reactive oxygen production, DNA damage and cell cycle arrest. Cellular stress is often connected to autophagy, and we employed the RAW264.7 macrophage model to test the hypothesis that AOH induces autophagy. Indeed, AOH treatment led to a massive increase in acidic vacuoles often observed upon autophagy induction. Moreover, expression of the autophagy marker LC3 was markedly increased and there was a strong accumulation of LC3-positive puncta. Increased autophagic activity was verified biochemically by measuring the degradation rate of long-lived proteins. Furthermore, AOH induced expression of Sestrin2 and phosphorylation of AMPK as well as reduced phosphorylation of mTOR and S6 kinase, common mediators of signaling pathways involved in autophagy. Transmission electron microscopy analyzes of AOH treated cells not only clearly displayed structures associated with autophagy such as autophagosomes and autolysosomes, but also the appearance of lamellar bodies. Prolonged AOH treatment resulted in changed cell morphology from round into more star-shaped as well as increased β-galactosidase activity. This suggests that the cells eventually entered senescence. In conclusion, our data identify here AOH as an inducer of both autophagy and senescence. These effects are suggested to be to be linked to AOH-induced DSB (via a reported effect on topoisomerase activity), resulting in an activation of p53 and the Sestrin2-AMPK-mTOR-S6K signaling pathway.