Vol. 29, Issue 7, 1042-1050, July 2001

SHORT COMMUNICATION
Studies Comparing in Vivo:in Vitro Metabolism of Three Pharmaceutical Compounds in Rat, Dog, Monkey, and Human Using Cryopreserved Hepatocytes, Microsomes, and Collagen Gel Immobilized Hepatocyte Cultures

Nicola J. Hewitt, Karl-Uhlrich Bühring, Johannes Dasenbrock, Jutta Haunschild, Bernhard Ladstetter, and Dietmar Utesch

Institute of Toxicology, Merck KGaA, Darmstadt, Germany (N.J.H., D.U.); and Institute of Pharmacokinetics and Metabolism, Merck KGaA, Grafing, Germany (K.-U.B., J.D., J.H., B.L.)

The in vivo metabolism of three pharmaceutical compounds, EMD68843, EMD96785, and EMD128130, was compared in fresh and cryopreserved hepatocyte (CPH) suspensions and microsomes from rat, dog, monkey, and human livers and fresh human and rat hepatocyte collagen gel immobilized cultures (GICs). Half of the major in vivo metabolites was produced by phase 1 (hydroxylation, oxidation, hydrolysis, N-dealkylation) and half by phase 2 metabolism (mostly glucuronidation but also sulfation and glycine conjugation). The identity and percentage of phase 1 and 2 metabolites from each compound produced in hepatocytes compared well with that in each species in vivo. Glucuronidation was more extensive in GICs than in CPHs. In contrast, CPHs but not GICs, produced sulfate metabolites. Microsomes (supplemented with NADPH only) produced most of the phase 1 but no phase 2 metabolites. Metabolism in CPHs was the same as in fresh hepatocyte suspensions. Discrete species differences in metabolism were detected by CPHs and microsomes. Cytochrome P450 and glucuronosyl S-transferase contents of CPHs did not account for species differences in the percentage of phase 1 and 2 metabolites or the rate of disappearance of the parent compounds in these cells. These data show a good correlation between major metabolites formed in vivo and in vitro. CPHs and GICs, unlike microsomes, carried out sequential phase 1 and 2 metabolism. Each in vitro system has its own advantages, however, for short-term metabolism studies CPHs may be more useful since they are readily available, easier and quicker to prepare than GICs, and have more comprehensive enzyme systems than microsomes.