Ochratoxin a lowers mRNA levels of genes encoding for key proteins of liver cell metabolism.

Ochratoxin A (OTA) is a nephro- and hepatotoxic mycotoxin that frequently contaminates food and feedstuffs. Although recent studies have indicated that OTA modulates renal gene expression, little is known regarding its impact on differential gene expression in the liver. Therefore a microarray study of the HepG2 liver cell transcriptome in response to OTA exposure (0, 0.25, 2.5 micromol/l for 24 h) was performed using Affymetrix GeneChip technology. Selected microarray results were verified by real-time PCR and Western blotting as independent methods. Out of 14,500 genes present on the microarray, 13 and 250 genes were down-regulated by 0.25 and 2.5 micromol/l OTA, respectively. Reduced mRNA levels of calcineurin A beta (PPP3CB), which regulates inflammatory signalling pathways in immune cells, and of the uncoupling protein 2 (UCP2), which has been suggested to control the production of reactive oxygen species (ROS), were observed in response to 0.25 micromol/l OTA. A particularly strong down-regulation due to 2.5 micromol/l OTA was evident for the mRNA levels of insulin-like growth factor binding protein 1 (IGFBP1) and tubulin beta 1 (TUBB1) which have been demonstrated to function as a pro-survival factor in hepatocytes and as an important cytoskeletal component, respectively. In addition, many genes involved in energy and xenobiotic metabolism, including phosphoglycerate kinase 1 (PGK1), stearoyl-Coenzyme A desaturase 1 (SCD), and glutathione S-transferase omega 1 (GSTO1), were down-regulated by OTA. Furthermore, OTA significantly inhibited the capacitative calcium entry into the HepG2 cells, indicating an alteration of calcium homeostasis. Overall, OTA dose-dependently affects multiple genes encoding for key proteins of liver cell metabolism.