Generation of a New Model Rat: Nrf2 Knockout Rats Are Sensitive to Aflatoxin B1 Toxicity

The transcription factor Nrf2 (NF-E2-related-factor 2) regulates a battery of antioxidative stress-response genes and detoxication genes, and Nrf2 knockout lines of mice have been contributing critically to the clarification of roles that Nrf2 plays for cell protection. However, there are apparent limitations in use of the mouse models. For instance, rats exhibit more suitable features for toxicological or physiological examinations than mice. In this study, we generated 2 lines of Nrf2 knockout rats by using a genome editing technology; 1 line harbors a 7-bp deletion (Lambda 7) and the other line harbors a 1-bp insertion (+1) in the Nrf2 gene. In the livers of rats homozygously deleting the Nrf2 gene, an activator of Nrf2 signaling, CDDO-Im, could not induce expression of representative Nrf2 target genes. To examine altered toxicological response, we treated the Nrf2 knockout rats with aflatoxin B-1 (AFB(1)), a carcinogenic mycotoxin that elicits gene mutations through binding of its metabolites to DNA and for which the rat has been proposed as a reasonable surrogate for human toxicity. Indeed, in the Nrf2 knockout rat livers the enzymes of the AFB(1) detoxication pathway were significantly downregulated. Single dose administration of AFB(1) increased hepatotoxicity and binding of AFB(1)-N-7-guanine to hepatic DNA in Nrf2 knockout rats compared with wild-type. Nrf2 knockout rats repeatedly treated with AFB(1) were prone to lethality and CDDO-Im was no longer protective. These results demonstrate that Nrf2 knockout rats are quite sensitive to AFB(1) toxicities and this rat genotype emerges as a new model animal in toxicology.