Purpose: Microdialysis is a technique that has been used to monitor drug brain pharmacokinetics as well as change of endogenous neurotransmitters which could serve as an indicator of pharmacodynamics. So far, microdialysis is the only approach that could evaluate the unbound therapeutic concentration change with respect to time in the same animal and remain physiolocial and anatomical feature of brain to be intact. Based on previous findings by our group, DB213 (an HIV-1 replication inhibitor) could achieve significant brain uptake in Sprague-Dawley rats after intranasal administration. Therefore, we chose DB213 as model drug. Our current study aims to compare i) unbound DB213 CSF uptake kinetics by microdialysis and cisterna magna puncture; ii) DB213 striatum uptake kinetics by microdialysis and brain dissection to investigate if microanalysis could provide more information on its CSF and striatum uptake kinetics.
Methods: Two batches of SD rats were employed. SD rats in Batch 1 will received DB213 water solution through intranasal route at 50 mg/kg. CSF and striatum will be collected at 15, 30, 60, 90, 120, 240, 360, and 480 min post-dosing via cisterna magna puncture and brain dissection, respectively (n=5 per time interval). SD rats in Batch 2 will receive a surgery of microdialysis probe implantation (CMA microdialysis probe 12, 4 mm) in lateral ventricle or striatum one day prior to the experiment and followed by determination of in-vivo DB213 recovery of microdialysis probe (n=3-5). On experiment day, SD rats in Batch 2 will receive DB213 water solution through intranasal route at 50 mg/kg followed by collection of dialysate samples every 15 min till 360 min post-dosing. DB213 concentration in striatum and dialysate samples will be determined by a previous reported LC-MS/MS assay. DB213 unbound concentration in striatum at different time intervals in Batch 1 will be calculated by using the total concentration detected and unbound fraction of DB213 in brain tissue reported previously whereas those in batch 2 will be corrected by in-vivo recovery of microdialysis probe.
Results: DB213 unbound striatum and CSF concentration versus time profile in batch 1 and 2 were summarized in Figure 1. In batch 1, after drug administration, DB213 reached peak concentration in CSF and striatum of 66.3±15.1 ng/mL at 15 min post-dosing and 166.4±20.9 ng/mL at 60 min post-dosing, respectively. In batch 2, comparable in vivo probe recovery was observed in each rat. DB213 reached peak concentration in CSF and striatum of 128.1±11.1 ng/mL at 120 min post-dosing and 214.9±14.9 ng/mL at 30 min post-dosing, respectively.
It was found that DB213 unbound concentration in striatum versus time profile obtained by both microdialysis and brain dissection is comparable with similar pharmacokinetic parameters. Therefore, in the case of unbound DB213 striatum uptake kinetics, using microdialysis approach cannot provide more information than brain dissection approach. However, the CSF concentration versus time profiles of DB213 were different between microdialysis (probe inserted in lateral ventricle) and cisterna magna puncture, which could be due to the circulation of CSF in different ventricles in the CNS. Therefore, in the case of unbound DB213 CSF uptake kinetics, using microanalysis can tell more detailed information on DB213 CSF concentration in a single ventricle as well as its circulation in brain whereas cisterna magna puncture can only obtain the mean value of DB213 CSF concentration.
Conclusion: In the case of DB213, microdialysis cannot provide more information on its striatum uptake kinetics in comparison to that of brain dissection whereas it can reflect unbound DB213 CSF uptake and circulation kinetics comparison to that of cisterna magna puncture.
Chun-Ho Wong– Chinese University of Hong Kong
H.Y. Edwin Chan– Professor, Chinese University of Hong Kong
Zhong Zuo– Director and Professor, School of Pharmacy, Faculty of Medicine, The Chinese University of Hong Kong