In vitro and in vivo cytotoxicity of zearalenone

Abstract

Zearalenone (ZEA), a mycoestrogen produced by Fusarium fungal species, is mainly found in contaminated corns and maize. Despite ZEA has been reported in air and waters, little is known about the toxic effects induced by ZEA in vitro or in vivo. As ZEA has a similar structure to estrogen, its potential risk as an endocrine disrupting chemical (EDC) has thus aroused both environmental and public health concerns. The purpose of the first part of the study is to identify the responses and underlying molecular changes that occur when human bronchial epithelial BEAS-2B cells are exposed to ZEA. Differential gene expression profiles were identified in cells that were treated with 40μM ZEA for 6h and 24h by high-throughput microarray analysis using Affymetrix Human Gene 2.0 GeneChip. The array results showed 262 genes at 6h and 1073 genes at 24h were differentially expressed (fold change ≥1.5, p<0.05). Pathway analysis of the differentially expressed genes revealed that diverse cellular processes, which include the induction of oxidative stress, impaired response to DNA damage, cell cycle arrest, suppression of inflammatory responses, altered responses of nuclear hormone receptors and epigenetic changes, were affected. esults of further experiments indicated that 40μM ZEA decreased cell viability, induced apoptosis and promoted reactive oxygen species (ROS) generation in a time-dependent manner. Immunomodulatory effects of ZEA were revealed through the suppression of lipopolysaccharide (LPS)-induced expression of pro-inflammatory cytokines (IL-6, IL-8 and IL-1β). Interestingly, the level of global DNA methylation was markedly decreased after 24h exposure to ZEA. In vitro study using BEAS-2B cell line over-expressing a free radical scavenger, cytoglobin, showed significant attenuation of ZEA-induced ROS and cell death confirming that ZEA is a potent free radical producer. Taken together, these observations suggested that a broad range of toxic effects are elicited by ZEA. Particularly, ROS may play a pivotal role in ZEA-induced cell death. These adverse consequences observed in lung cells suggest that exposure to ZEA may lead to the pathogenesis in lung tissues. Previous studies have shown that growth and reproduction of early life stages of fish are susceptible to a variety of EDCs. However, the ecotoxicological risk of ZEA to aquatic wildlife is still poorly understood. Using marine medaka (Oryzias melastigma) as a model, the disrupting effects of ZEA on the physio-biochemical and endocrine function in vivo were studied. No effects were observed on hatching success, time to hatching and mortality after incubation of medaka embryos with ZEA at sublethal concentration of 50μg/L. No changes were observed in the Bax/Bcl2 mRNA ratio or apoptotic patterns. These results suggest that ZEA do not affect the development of the medaka embryos. However, the expression of key steroidogenic enzymes (CYP19A, CYP19B) as well as known estrogenic biomarkers (ERβ and VTG) were up-regulated at mRNA levels in newly hatched fry, indicating ZEA can potentially cause endocrine disruption in fish and posed a risk on aquatic life.