A semicompartmental modeling approach for pharmacodynamic data assessment

Evaluating and predicting the correlations of hepatic concentration and pyrrole-protein adduction with hepatotoxicity induced by retrorsine based on pharmacokinetic/pharmacodynamic model

Retrosine (RTS) is a pyrrolozidine alkaloid and a known hepatotoxin that widely exist in nature. The mechanisms involved in toxic action of pyrrolizidine alkaloids need further investigation. The objective of the present study was to evaluate the correlation of RTS hepatotoxicity with hepatic RTS concentration and pyrrole-protein adduction. Mice were intragastrically treated with RTS alone or RTS and ketoconazole (KTZ) simultaneously. Sera and liver tissues were collected at various time points after administration, followed by the determination of changes in serum transaminase activity, hepatic RTS concentration and pyrrole-protein adduction. The correlation of RTS hepatotoxicity with hepatic RTS concentration and hepatic pyrrole-protein adduction were examined by use of Sigmoid-Emax PK/PD models. Dose-dependent hepatotoxicity, hepatic RTS concentration and pyrrole-protein adduction were observed in the animals, which could be modulated by co-treatment with KTZ. The fit parameters indicated pyrrole-protein adduction was more closely related with liver injury than hepatic RTS concentration. Similar correlation was observed in mice given low-dose of RTS for 4 consecutive days. RTS hepatotoxicity is correlated with hepatic pyrrole-protein adduction derived from RTS rather than hepatic RTS concentration. The observed protein modification would be a good indicator to predict the hepatoxicity of RTS at low dose.

A semi-compartmental model describing the pharmacokinetic-pharmacodynamic relationship

Frequently, we encounter the phenomenon of hysteresis in kinetic-dynamic modeling. The hysteresis loop in the concentration-effect curve suggests a time discrepancy caused by various pharmacokinetic and pharmacodynamic factors. To collapse the hysteresis loop and to simplify the concentration-effect relationship, several kinetic-dynamic modeling approaches including the effect compartment link model, turnover model (indirect response model), and tolerance/rebound model, have been used. The semicompartmental model is one method to describe the hysteresis of the pharmacokinetic-pharmacodynamic relationship. Furthermore, this semi-compartmental model differs from other models (full parametric approaches) as it does not require pharmacokinetic parameters to estimate pharmacodynamic parameters and k_e0. Therefore, we could employ a semi-compartmental approach in case it is difficult to apply the compartment model to pharmacokinetic data, as required for the pharmacodynamic analysis of inhalational anesthetics.