Elucidation of the species differences of epyrifenacil-induced hepatotoxicity between mice and humans by mass spectrometry imaging analysis in chimeric mice with humanized liver

Abstract

Epyrifenacil, one of the protoporphyrinogen oxidase (PPO)-inhibiting herbicides, is hepatotoxic in rodents. Previous in vitro assays detected species differences in both kinetics (active hepatic uptake) and dynamics (PPO inhibitory activity) of S-3100-CA, which is a causal metabolite of the hepatotoxicity, suggesting that humans are less sensitive to the epyrifenacil-induced hepatotoxicity than are rats and mice. To elucidate the species differences in the epyrifenacil-induced hepatotoxicity between mice and humans simultaneously, this study fed epyrifenacil to chimeric mice with humanized liver with low replacement index of human hepatocytes. The distribution of S-3100-CA in the liver and subsequent protoporphyrin IX (PPIX) accumulation, an index of PPO inhibition, were compared between human and host mouse hepatocytes using mass spectrometry imaging (MSI) analysis of chimeric liver. The results showed that S-3100-CA and PPIX were significantly colocalized in regions of the liver slice containing host mouse hepatocytes, and thus it was suggested that epyrifenacil had significantly less effect on human livers than mouse livers because of the species differences in both kinetics and dynamics of S-3100-CA. Moreover, the hepatic uptake assay using cryopreserved primary hepatocytes of rats, mice and humans with inhibitors revealed that S-3100-CA is a substrate of organic anion transporting polypeptides (OATPs). These data corroborate the contribution of OATPs to hepatocellular uptake of S-3100-CA, especially in mice, and subsequent PPIX accumulation by more potent S-3100-CA-induced PPO inhibition in mice. MSI analysis of chimeric mice with humanized liver is a useful technique for elucidating species differences in pharmacokinetics and subsequent changes in toxicological biomarkers.