Aim: The aim of the study was to characterize the plasma pharmacokinetics of the cyclic peptide Kalata B1 as well as performing a first study of the delivery of kalata B1 to the brain. This included the development of a quantitative LC-MS method for the analysis of Kalata B1 in plasma and brain homogenate
Methods: Six male Sprague Dawley rats (267±16 g) were given a Kalata B1 dose of 1 mg/kg as a short bolus infusion over 10 minutes at an infusion speed of 200 µl/min/kg. Blood samples were taken over 240 minutes. Brain delivery was assessed by giving four rats a steady state infusion over four hours, and sampling brain and plasma after infusion.
Samples were analysed with the developed LC-MS method for quantification of Kalata B1 concentrations in plasma. The LC-MS method monitored the double charged Kalata B1 with an m/z-value of 1446.8. Non-compartmental calculation of pharmacokinetic parameters was performed.
Results and Discussion: The AUC of kalata B1, calculated using the trapezoidal method, was 180 ± 54. Kalata B1 had a plasma clearance of 5.09 ± 0.76 ml/min/kg, a volume of distribution of 339 ± 112 ml/kg. The terminal half-life of Kalata B1 was calculated to be 1.56 hours. The brain concentrations were measured and the unbound brain to plasma ratio, Kp,uu, was calculated. The Kp,uu was determined to 0.015 ± 0.007, or 1.5 %.
Conclusions: The analytical method was able to accurately quantify concentrations of Kalata B1 in plasma. Kalata B1 shows a pharmacokinetic profile with a relatively long half-life for a peptide and a high volume of distribution indicating partition to tissue. The low Kp,uu suggests that kalata B1 is effectively kept out of the brain by the blood-brain barrier.