High conservation of both phase I and II drug-metabolizing activities in cryopreserved rat liver slices

1. Xenobiotic-metabolizing enzymes, including both cytochrome P450 and phas e II-conjugating systems, have been characterized in rat liver slices cryop reserved in 12 or 18 % dimethylsulphoxide (DMSO). 2. Several cytochrome P450 isoforms in rat liver slices metabolized testost erone to a variety of hydroxylated products. The rates of formation of thes e same products were well maintained during cryopreservation of the slices in both 12 or 18 % DMSO. 3. After cryopreservation of rat liver slices in 18 % DMSO, the rates of me tabolism of ropivacaine to 3-hydroxyropivacaine, 4-hydroxyropivacaine and P PX (all catalysed by different cytochrome P450 isoforms) were similar to 94 , 79 and 82 % respectively of the corresponding rates observed with fresh s lices. 4. The rates of conjugation of 7-hydroxycoumarin and 1-naphthol by rat live r slices were significantly decreased after cryopreservation in 12 % DMSO, but they were maintained when the concentration of this cryopreservant was increased to 18 %. 5. After cryopreservation in 12 % DMSO, the mitochondrial reduction of the tetrazolium salt MTT by rat liver slices was significantly lowered. In cont rast, slices cryopreserved in 18 % DMSO demonstrated no significant decreas e in their capacity to reduce MTT. 6. Thus, in agreement with previous studies, it was found that cytochrome P 450-dependent activities are retained after cryopreservation of liver slice s. Although phase II-conjugating enzyme activities are more sensitive to cr yopreservation, it was shown that increasing the concentration of DMSO pres ent during cryopreservation could circumvent the problem. This modification improves the usefulness of cryopreserved rat liver slices as a tool in dru g metabolism studies.