Endoplasmic reticulum transporter OAT2 regulates drug metabolism and interaction.

Xenobiotic metabolic reactions in the hepatocyte endoplasmic reticulum (ER) including UDP-glucuronosyltransferase and carboxylesterase play central roles in the detoxification of medical agents with small- and medium-sized molecules. Although the catalytic sites of these enzymes exist inside of ER, the molecular mechanism for membrane permeation in the ER remains enigmatic. Here, we investigated that organic anion transporter 2 (OAT2) regulates the detoxification reactions of xenobiotic agents including anti-cancer capecitabine and antiviral zidovudine, via the permeation process across the ER membrane in the liver. Pharmacokinetic studies in patients with colorectal cancer revealed that the half-lives of capecitabine in rs2270860 (1324C > T) variants was 1.4 times higher than that in the C/C variants. Moreover, the hydrolysis of capecitabine to 5'-deoxy-5-fluorocytidine in primary cultured human hepatocytes was reduced by OAT2 inhibitor ketoprofen, whereas capecitabine hydrolysis directly assessed in human liver microsomes were not affected. The immunostaining of OAT2 was merged with ER marker calnexin in human liver periportal zone. These results suggested that OAT2 is involved in distribution of capecitabine into ER. Furthermore, we clarified that OAT2 plays an essential role in drug-drug interactions between zidovudine and valproic acid, leading to the alteration in zidovudine exposure to the body. Our findings contribute to mechanistically understanding medical agent detoxification, shedding light on the ER membrane permeation process as xenobiotic metabolic machinery to improve chemical changes in hydrophilic compounds.

Coculture with hiPS-derived intestinal cells enhanced human hepatocyte functions in a pneumatic-pressure-driven two-organ microphysiological system.

Examining intestine-liver interactions is important for achieving the desired physiological drug absorption and metabolism response in in vitro drug tests. Multi-organ microphysiological systems (MPSs) constitute promising tools for evaluating inter-organ interactions in vitro. For coculture on MPSs, normal cells are challenging to use because they require complex maintenance and careful handling. Herein, we demonstrated the potential of coculturing normal cells on MPSs in the evaluation of intestine-liver interactions. To this end, we cocultured human-induced pluripotent stem cell-derived intestinal cells and fresh human hepatocytes which were isolated from PXB mice with medium circulation in a pneumatic-pressure-driven MPS with pipette-friendly liquid-handling options. The cytochrome activity, albumin production, and liver-specific gene expressions in human hepatocytes freshly isolated from a PXB mouse were significantly upregulated via coculture with hiPS-intestinal cells. Our normal cell coculture shows the effects of the interactions between the intestine and liver that may occur in vivo. This study is the first to demonstrate the coculturing of hiPS-intestinal cells and fresh human hepatocytes on an MPS for examining pure inter-organ interactions. Normal-cell coculture using the multi-organ MPS could be pursued to explore unknown physiological mechanisms of inter-organ interactions in vitro and investigate the physiological response of new drugs.