Metabolism and carcinogenic potential of inorganic arsenic in humanized-liver mice

Inorganic arsenic is a known human carcinogen associated with liver and bladder cancer. Among its species, sodium arsenite (iAs III ) undergoes complex hepatic biotransformation, producing methylated metabolites such as monomethylated (MMA) and dimethylated (DMA) forms. However, its human-relevant mechanisms of metabolism and carcinogenicity remain unclear due to species differences in arsenic biotransformation. To clarify these differences, we employed a humanized-liver (HL) mouse model, in which mouse hepatocytes are replaced with human hepatocytes, to investigate the metabolism and carcinogenic potential of iAs III . HL and wild type (WT) mice were administrated 50 ppm of iAs III in drinking water for 4 weeks. Urine, liver, and bladder samples were collected for analysis. Urinary arsenic speciation was determined using high-performance liquid chromatography coupled with inductively coupled plasma mass spectrometry (HPLC-ICP-MS). Histopathology and immunohistochemistry were performed on both liver and bladder tissue, and gene expression profiles were analyzed using RNA sequencing and microarray, respectively. Urinary arsenic speciation revealed distinct species-dependent differences. Dimethylarsinic acid (DMA V ) was the predominant urinary arsenic metabolite in both HL and WT mice. Total urinary arsenic in HL mice was lower than in WT mice, but the distribution of metabolites differed markedly. The proportion of MMA V in HL mice (26.4%) was substantially higher than in WT mice (4.7%), whereas DMA V accounted for 58.5% in HL and 80.7% in WT mice. This urinary metabolite pattern more closely resembled that observed in humans exposed to inorganic arsenic. Hepatic arsenic methyltransferase (As3MT) expression was significantly elevated in WT mice treated with iAs III but tended to decrease in HL mice. Gene expression profiles of liver and bladder tissues of HL mice also differed from those of WT mice. Immunohistochemical analysis of proliferation markers is currently underway to evaluate whether iAs III promotes hepatocellular and urothelial proliferative response. Arsenic content in the liver is also currently under investigation, and pathway analysis of the transcriptomic data using Ingenuity Pathway Analysis (IPA) is ongoing to identify key molecular alterations for further validation. In conclusion, these findings indicate that human hepatocytes exhibit lower methylation capacity, resulting in higher proportions of toxic MMA species, suggesting that humans may be more susceptible to arsenic than mice. Furthermore, the HL mouse model effectively reflects human arsenic metabolism and provides a valuable in vivo platform for elucidating human-relevant metabolic, toxicological, and molecular mechanisms underlying arsenic-induced hepatotoxicity and carcinogenicity.