Prediction of human metabolism of the sedative-hypnotic zaleplon using chimeric mice transplanted with human hepatocytes

Abstract

1. Human chimeric mice (h-PXB mice) having humanized liver, constructed by transplantation of human hepatocytes, were evaluated as an experimental model for predicting human drug metabolism. Metabolism of zaleplon in h-PXB mice was compared with that in rat chimeric mice (r-PXB mice) constructed by transplantation of rat hepatocytes.

2. Zaleplon is metabolized to 5-oxo-zaleplon by aldehyde oxidase and to desethyl-zaleplon by cytochrome P450 (CYP3A4) in rat and human liver preparations.

3. Liver S9 fraction of h-PXB mice metabolized zaleplon to 5-oxo-zaleplon and desethyl-zaleplon in similar amounts. However, liver S9 fractions of r-PXB and control (urokinase-type plasminogen activator-transgenic severe combined immunodeficient) mice predominantly metabolized zaleplon to desethyl-zaleplon. 5-Oxo-zaleplon was detected as a minor metabolite.

4. Oxidase activity of h-PXB mouse liver cytosol toward zaleplon was about 10-fold higher than that of r-PXB or control mice. In contrast, activities for desethyl-zaleplon formation were similar in liver microsomes from these mice, as well as rat and human liver microsomes.

5. In vivo, the level of 5-oxo-zaleplon in plasma of h-PXB mice was about 7-fold higher than that in r-PXB or control mice, in agreement with the in vitro data. Thus, aldehyde oxidase in h-PXB mice functions as human aldehyde oxidase, both in vivo and in vitro.

6. In contrast, the plasma level of desethyl-zaleplon in r-PXB and control mice was higher than that in h-PXB mice.

7. These results suggest h-PXB mice with humanized liver could be a useful experimental model to predict aldehyde oxidase- and CYP3A4-mediated drug metabolism in humans.

• Aldehyde oxidase
• cytochrome P450
• human liver
• human-chimeric mice
• mouse liver
• rat-chimeric mice
• zaleplon

Acknowledgements

The authors thank Dr. Chise Tateno, PhoenixBio Co., Ltd., for supplying chimeric mice.