Reproducible and time-dependent modification of serum protein binding in Wistar Kyoto rats

IntroductionThe theoretical basis of the influence of (alterations in) plasma protein binding on pharmacokinetics (PK) is well-established. In contrast, the impact of protein binding on pharmacodynamics has not been examined in a systematic manner. Here we present an experimental approach to modify serum protein levels and binding in the rat, in a robust, reproducible, and time-dependent manner.MethodMale Wistar Kyoto rats were divided into three different groups. The control group (n = 4) did not receive treatment. In the cannulation(−) group (n = 6) the rats were instrumented with three permanent blood cannulas. The rats in the cannulation(+) group received in addition to the cannulation a subcutaneous injection of turpentine oil of 100 μl/100 g bodyweight. The effects were characterized in terms of 1) the time course of serum levels of albumin and α1-acid glycoprotein (AGP), and 2) the effect on the ex vivo serum protein binding of S(−)-propranolol.ResultsIn control rats the AGP serum concentration was stable at a value of 169 ± 16 μg/ml. In the cannulation(−) group a maximum ten- to fifteen-fold increase in serum AGP concentration was observed at 48 h post surgery, followed by a gradual return back to baseline within 1 week. In the cannulation(+) group a similar concentration–time profile for AGP was found, but without a complete return to baseline within 1 week and with a much higher variability. Ex vivo, an increase in AGP serum concentration from 55 to 675 μg/ml resulted in a profound decrease in the free fraction of S(−)-propranolol from 14 ± 0.6 to 1.9 ± 0.3%.ConclusionsIn conclusion, through cannulation alone the serum protein levels and binding were modified in a robust, reproducible and time-dependent manner. Therefore this experimental approach is suitable for the investigation of the influence of protein binding on both pharmacokinetics and pharmacodynamics.