Interspecies Comparision

Purpose

The interspecies comparison study is conducted in order to highlight the potential metabolic differences between the species and aid in the selection of the best species to conduct subsequent in vivo toxicology and pharmacokinetic studies.

Assay Protocol

These studies are conducted in liver microsomes from toxicological species and man. The test article is dissolved in a suitable solvent and pre-warmed at 37°C for 5 minutes with phosphate buffer and NADPH. The incubations are initiated by the addition of ice-cold microsomes. Following an appropriate incubation period, an equal volume of cold organic solvent is added to stop the reaction and the supernatants isolated by centrifugation. A negative control incubation is conducted in the same manner, with heat deactivated microsomes. An appropriate positive control is also incubated in order to confirm the metabolic viability of the microsomes.

The incubation mixtures are analyzed by an appropriate analytical method. Typical analyses are conducted using an aqueous organic solvent mixture with a reverse phase HPLC column. The method of detection, dependent on the structure of the compounds, is one or more of the following: evaporative light scattering, radiochemical or mass spectrometric detection. The patterns of metabolites and their approximate quantities are compared to one another.

Confirmation Data

The metabolism of a model drug (estradiol) in liver microsomes from five species is shown.