Book of Abstmcts - EURUZVX ‘94

of different test systems will be presented. Some compounds will be discussed in more detail and the question of the existence of ‘pure’ sneugens will be addressed.

Key words: genetic toxicology. aneuploidy; risk-assessment; regulatory guidelines

IMM, A Cycfosporin which Induces and tnhiblts liver CYP3A Levels

M. Alegret. E. Meyer, S. Smifey, J. Guertler. A.E.M. Vickers. Drug SafeM Sandoz Pharma, CH-4002 8asel,

Swi~erfand

SD2 IMM 125 (IMM) is a cyclosporin immunosuppressant like cyclosporin A (CSA). IMM can either induce or inhibit the liver cytochrome PrlSOs, in particular the CYPBA proteins, which primarily metabolize the drug, depending on the dose and duration of exposure. In a short term study (male Wistar rats, 190-300 g), IMM (2 week. 20 mgikglday) induces the CYP3A proteins, 2-fold compared to control and to CSA treated. fndu~tion of the CYP3A proteins persists as seen in a 26 week study at 10 mgkglday (1 B-fold increase). while at higher doses (100 mglkglday). CYP3A levels were inhibited 73%. After 52 weeks the CYP3A levels exhibited a dose dependent decrease, 4% at 8 mg/kg/day. 22% at 24 mgilcglday and 31% at 48 mglkglday. The hepatic metabolic rate of IMM in treated rats was modified following the same pattern as CYP3A levels. which would imply ?hat. as CSA. IMM is mainly metabolized in the liver by the CYP3A family.

InhIbition of the CYP3A proteins (20-C%) by IMM can be detected in vitro using human liver slice cultures (1 and 10 PM). ihese concentrations were equivalent to the blood levels of the rats in the 26 week study of the 100 mg/kg/day dose group. The extent of inhibition is similar for CSA.

IMM treatment (20 mglkglday for 2 weeks). as with CSA. increases p-glycoprotein (Pgc) levels in rat liver (1 .&fold) and kidney (1.3-fold). In the 26-week study, IMM decreased Pgp levels at all doses tested, while after 52 weeks, 48 mg IMMlkglday increased levels by 44%.

These findings demonstrate that IMM wili affect its own metabolism. by ~nduGing liver CYP3A levels at low doses or inhibiting them at higher doses or longer treatments. and its transport out of the cell by increasing Pgp levels. These effects can influence the blood levels of the drug.

Key words: cyclosporins; liver cytochrome P450; metabolism

Influence on Ethanol Within Session Tolerance by Pretrestment with Competitive and ~on~rn~~~ve Glutamate Antagonists

K. Andreas. L.-f? Giitz. A. Schiller. lnshtute of Pharmacology and ?6xicology, EXhnical University of Dresden, Germany

Motor impairment (rotarod test) and nociceptive sensitivity (tail flick test) were used to investigate whether the non-competitive N.met~yl-D-aspa~ate (NMDA) antagonist dizofcipine (MK-80~). the competitiva NMDA receptor antagonist 2-amino-5phosphonopentanoic acid (AP-5). or the competitive kainate/quisqualate (non-NMDA) receptor antagonist do influence the development of rapid tolerance to ethanol. Male albino mites (22.5 f 1.5 gms.) were the subjects for these experiments. Maximum effects of ethanol were measured 60 minutes (rotarod test) and 20 minutes (tail flick test) after i.p. injection. We found that i.p. injection of 3.3 g/kg ethanol 5 hours prior to different doses of ethanol produces rapid tolerance. EDso of ethanol altered from 1.75 g/kg to 2.45 g/kg in rotarod test and from 2.2 g/kg to 3.7 g/kg in tail flick test.

Next the animals were administered with 0.2 mg&g dizolcipine 30 minutes prior to the first injection of ethanol. which produced rapid tolerance. This pretreatment with dizolcipine showed a significant decrease of rapid tolerance to ethanol (ED50 of ethanol in rotarod test: 1.55 g/kg and in tail flick test: 2.2 g/kg). These results suggest that NMDA receptor is involved in expression of rapid tolerance to ethanol. Studies are now in progress to examine the effects of the competitive NMDA-antagonists AP-5 and the kainats/quisqualate receptor antagonist CNOX.

An Hepatocyte Culture System for Screening Hepatotoxins In Vitro

L.M. Arterburn l, K. Wallace 3. R.M. Overton I, S.E. Da Costa I, J. Zurto 2, J.M. Frazier 2, RD. Curren 3, J.W. Harbell 3. ’ Research Division, MCR. Grace 8 Co., Cofumbia. MD; 2 Div. of Toxcoiogicai Sciences. John Hopkins School of Hygiene, Baltimore, MD; 3 Microbiological Associates, Inc., Rockwile, MD

We have recently developed culture techniques for maintaining primary rat hepatocytes in a differentiated state. The hepatocytes, which are sustained in a chemically-defined medium, remain highly viable in culture for a period of at least 10 days and retain generally labile hepatocyte-specific functions including many basal and inducible cy. tochrome P450 enzyme activities, Phase II enzyme activities and physiological albumin secretion rates. The cells