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Home » Archive » 2015

TDK conference 2015

Drug metabolism analysis in rabbits using in vitro and in vivo models
Nagy Tamás - year 4
SzIU, Faculty of Veterinary Science, Department of Pharmacology and Toxicology
Supervisor: Palócz Orsolya

Abstract:

The cytochrome P450 (CYP450) enzymes catalyze the metabolism of numerous endogenous and exogenous compounds. The enzymes of the CYP1, CYP2 and CYP3 families primarily take part in the transformation of drugs and other xenobiotics. Any alterations occurring in the activity of the CYP450 enzymes have an effect on the formation of the drug metabolites in the body. These hem containing, endoplasmic reticulum bound enzymes can be found in basically any organism although their quantity and activity is species specific. The liver contains CYP enzymes in the highest amount therefore the liver cell cultures provide a great model to examine them. It is important though that the results gained from in vitro examinations should be comparable to the ones from living organizations.

The purpose of our project is to measure the CYP450 activity in rabbits after the utilization of different inducer and inhibitor compounds and to compare the results from in vitro tests to those from in vivo. We have used phenobarbital to evoke the inducer effect, while ketoconazole and alpha-naphtoflavone were applied to examine the inhibition.

Twelve New-Zealand white rabbits were divided into three groups: untreated controls, the ones treated with 80 mg/kg bw. phenobarbital for three days and the ones which were given 40 mg/kg bw. ketoconazole for three days. Microsomes were separated from the livers to measure CYP450 activity. During our in vitro experiments we treated primary hepatocyte cultures obtained from rabbits with 500 µM phenobarbital, 25 µM ketoconazole and 50 µM alpha-naphtoflavone for 2 hours. The activity of the CYP1A1, CYP1A2 and CYP3A6 isoenzymes were measured with the luminescence method.

The results from the phenobarbital treatment revealed a significant increase in each analyzed isoenzyme’s activity both in vitro and in vivo. While ketoconazole notably decreased the activity of CYP3A6 both in vitro and in vivo and we observed the same effect in case of the CYP1A1 under in vitro circumstances, yet in the in vivo tests the CYP1A1 activity increased.

According to our results the stimulating effect in the established in vitro model can be examined the same way as under in vivo conditions. Based on our experiments one of our most important observations is that inhibition occurs differently in case of in vitro and in vivo models to the different isoenzymes. One possible explanation for this is the steric inhibitory effect of ketoconazole.



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