Annual Meeting of the Japanese Society of Toxicology

Purpose: 1,2-Dichloropropane(DCP) is thought to induce cholangiocarcinoma(CCA) among Japanese printing workers in 2013. However no studies have shown DCP-induced CCA in rodents. Five kinds of rodents were exposed to DCP to find an appropriate animal model for DCP-induced CCA.
Methods: First, 12 C57BL/6J mice, Balb/cA mice, F344 rats, Syrian Hamsters and Guinea Pigs were divided into 4 groups equally and exposed to DCP at 0, 300, 1000 and 3000 ppm respectively. Then 32 Balb/cA mice and Syrian Hamsters were divvied into 4 groups equally and exposed to DCP at 0, 200, 400 and 800ppm respectively. After the last exposure livers were dissected out for immunohistochemistry with anti- GSTT1, GSTM1, GSTPi antibodies.
Result: Either in control or exposed group all of the animals expressed GSTT1 both at liver cells and bile duct cells.
Conclusion: GSTT1 expression cannot explain the gap between human and rodents in the case of DCP inducing CCA.

View full abstract

Domoic acid (DA) is an algal toxin which has been associated with significant neurotoxicity in human, non-human primates, rodents, and marine mammals. Developmental exposure to DA is believed to result in neurotoxicity that may persist into adulthood. DA is produced by harmful algal blooms of Pseudo-nitzcshia and thus consumption of contaminated marine seafood is of potential concern. We evaluated oral exposures to DA during pregnancy in mice where exposures occurred during early neurodevelopment. Doses of 0 (vehicle), 1, or 3 mg/kg of DA were administered by gavage to C57BL/6 mice on gestational days 10 to 17. These doses represent human relevant exposures. The offspring were tested for persisting neurobehavioral consequences during neonate, adolescence and adulthood. DA did not induce dose related decreases in body weights of dams or offspring. Neurobehavioral tests revealed both dose and sex-related differences in several neurobehavioral measures including anxiety in elevated plus maze, walking patterns in CatWalk test, home-cage behaviors, and memory in the Morris water maze. This study demonstrated significant sex-specific and persistent neurobehavioral effects of repeated prenatal exposures to DA at low-dose levels that did not induce toxicity in dams. This study adds significant new information to the literature as most previous studies have focused on exposure routes/patterns with less relevant exposure pathways. (Supported by the Pacific Northwest Center for Human Health and Ocean Studies (NIH/NIEHS: P50 ES012762 and NSF: OCE-0434087, OCE-0910624 and 1128883))

View full abstract

Show abstractHide abstract

Pharmacokinetic drug-drug interaction can significantly impact drug safety and efficacy. Prediction of this drug-drug interaction risk is a requisite in the development plan of a new drug candidate to the submission of the registration dossier. In vitro identification and measurement of the contribution of the major cytochrome P450 enzymes involved in the human metabolism of a new drug candidate, also called “CYP phenotyping assay”, allows predicting the impact of another co-administered drug (perpetrator) on the pharmacokinetics of the new chemical entity (victim). Up to now, a battery of in vitro tests (recommended by the regulatory agencies) is required for this CYP phenotyping assay. Each of these tests suffers from numerous inconvenients: no direct quantitative measurement of the contribution of each CYP in the metabolism of a drug, biologic system not fully representative of the liver situation (eg human recombinant CYP450), lack of specificity (eg antibody anti-CYP450), too specific conditions of use (eg chemical competitive CYP specific inhibitors). A new in vitro model, called, Silensomes™ has been developed to encounter the disadvantages of the current methodologies. Silensomes™ correspond to human pooled liver microsomes chemically desactivated for one specific CYP450. CYP3A4 Silensomes™ were chosen as a proof of concept of this new model. Following their preparation, the cryopreserved batches of desactivated-CYP3A4 and control pooled liver microsomes were incubated with CYP1A2, CYP2A6, CYP2B6, CYP2C8, CYP2C9, CYP2C19, CYP2D6, CYP2E1 and CYP3A4 specific substrates to measure their respective activities. Results showed that CYP3A4 Silensomes™ abolished CYP3A4 activities of testosterone, nifedipine and midazolam to more than 80 % with no impact on the other CYP450 activities tested showing the high specificity and potency of the inhibition. Silensome™ CYP3A4 desactivation was preserved after storage at -80°C. Moreover, CYP3A4 contribution measured for known multi CYP substrates, following their incubation with CYP3A4 Silensomes™ were similar to the fm values observed in vivo or in vitro. These results showed that the CYP3A4 Silensomes™ model responds to the different criteria of specificity, potency, stability and predictability to ensure a good extrapolation of the risk of pharmacokinetic drug-drug interaction. Moreover, this new “ready to use” in vitro model is very easy to handle and can be easily fully automated. This approach will be extended to all the human major CYP450 in order to provide a complete kit ready to use for the CYP450 phenotyping assay. It is therefore the model of choice for a rapid and robust determination of the CYP contribution all along the development plan of a new chemical entity.

View full abstract

Download PDF (773K)

Register with J-STAGE for free!