Microdialysis for pharmacokinetic analysis of drug transport to the brain

doi:10.1016/S0169-409X(98)00089-1

Advanced Drug Delivery Reviews

Volume 36, Issues 2–3, 5 April 1999, Pages 211-227

https://doi.org/10.1016/S0169-409X(98)00089-1 Get rights and content

Abstract

The intracerebral microdialysis technique represents an important tool for monitoring free drug concentrations in brain extracellular fluid (brain_EcF) as a function of time. With knowledge of associated free plasma concentrations, it provides information on blood–brain barrier (BBB) drug transport. However, as the implantation of the microdialysis probe evokes tissue reactions, it should be established if the BBB characteristics are maintained under particular microdialysis experimental conditions. Several studies have been performed to evaluate the use of intracerebral microdialysis as a technique to measure drug transport across the BBB and to measure regional pharmacokinetics of drugs in the brain. Under carefully controlled conditions, the intracerebral microdialysis data did reflect passive BBB transport under normal conditions, as well as changes induced by hyperosmolar opening or by the presence of a tumor in the brain. Studies on active BBB transport by the mdr1a-encoded P-glycoprotein (Pgp) were performed, comparing mdr1a(−/−) with wild-type mice. Microdialysis surgery and experimental procedures did not affect Pgp functionality, but the latter did influence in vivo concentration recovery, which was in line with theoretical predictions. It is concluded that intracerebral microdialysis provides meaningful data on drug transport to the brain, only if appropriate methods are applied to determine in vivo concentration recovery.

Introduction

Numerous drugs have an action on the central nervous system (CNS), either desired or not, and their activity–time profile will be greatly determined by the pharmacokinetics of the drug in the fluid around the target brain tissue. The pharmacokinetics of a drug in the brain will depend on transport across the blood–brain barrier (BBB). Transport of drugs between brain and blood can take place by diffusion, with the concentration gradient of the free drug between both sides of the BBB membrane as the driving force. Another possibility is transport by energy-dependent mechanisms (active transporters), with, in this case, the direction of transport being dependent on the location of the transporter at the brain's endothelial cells, and the extent of transport being determined by the capacity of the transporter.

Physiological and anatomical considerations dictate that the brain should not be considered as a single compartment. Drug disposition into the brain is determined by exchange between blood, brain extracellular fluid (brain_EcF), brain cells and cerebrospinal fluid (CSF). In this review, we consider techniques used in in vivo animal research, by which brain pharmacokinetic data can be obtained. These include brain homogenization, CSF sampling, autoradiography (QAR), in vivo voltammetry, nuclear magnetic resonance (NMR), positron emission spectroscopy (PET) and intracerebral microdialysis. The most important characteristics of these methods will be described briefly. The use of intracerebral microdialysis should be the method of choice if one were interested in determining the (local) extracellular concentrations of a free drug as a function of time in individual freely moving animals.

With knowledge of the associated concentration–time profiles of the free drug in blood, intracerebral microdialysis can be used to characterize drug transport across the BBB under different conditions. However, and this is very important to realize, the intracerebral microdialysis technique involves the implantation of a microdialysis probe into the brain. This inevitably causes brain tissue trauma and may therefore affect BBB characteristics. Therefore, we considered it necessary to determine if intracerebral microdialysis provides meaningful data on brain pharmacokinetics. Several studies have been performed, dealing with passive as well as active transport across the BBB.

An important issue that was addressed was the relationship between dialysate concentrations and brain_EcF concentrations (defined as in vivo concentration recovery). In our early microdialysis studies dealing with the evaluation of passive BBB transport characteristics, in vitro calibration of the microdialysis probe was considered to be a good method for calculating brain_EcF from dialysate concentrations. The results of these studies are described and have been qualitatively re-interpreted here because we now know that the relation between dialysate concentrations and brain_EcF concentration cannot be predicted by in vitro calibration. Mathematical methods 1, 2have provided a great deal of insight into all processes that may affect in vivo concentration recovery. One of these is described here, together with two practical approaches to estimate in vivo concentration recovery (and thereby brain_EcF concentrations); the no-net-flux (NNF) [3]and the dynamic-no-net-flux (DNNF) method [4]. Then, studies on active BBB transport by the mdr1a-encoded P-glycoprotein (Pgp), comparing mdr1a(−/−) with wild-type mice, are reviewed. In these studies, the NNF and DNNF methods have been applied, showing interesting differences in in vivo concentration recovery between the absence and presence of Pgp.

Section snippets

In vivo other than intracerebral microdialysis

A number of in vivo techniques exists that can be used to determine the brain pharmacokinetics of drugs, like brain homogenization, CSF sampling, in vivo voltammetry, QAR, NMR and PET scan.

Concentration recovery

The relationship between the concentrations in dialysate and ECF concentrations (in vivo concentration recovery) may be complex. Over the years, knowledge and insight into all of these processes have increased, especially through mathematical modelling 1, 2. Thus, in early microdialysis articles, the use of in vitro calibration of the probes was considered to be sufficient. Then, gradually, investigators became aware of the fact that in vivo concentration recovery may deviate importantly from

Lipophilicity

By using the brain perfusion technique and initial uptake of a drug after intravenous administration, it was observed that a good relationship exists between BBB permeability and the log P/[molecular weight (MW)]^1/2 for many compounds that cross the BBB by passive diffusion. Such transport across the BBB occurs via the paracellular and/or the transcellular route. Hydrophilic drugs can only diffuse paracellularly and are therefore restricted by the presence of the tight junctions between the

Mdr1a-encoded P-glycoprotein at the BBB and the use of mdr1a(−/−) mice

Multidrug resistance (MDR) is defined as the ability of cells to develop resistance to a broad range of structurally and functionally unrelated drugs after being exposed to these drugs. MDR can be mediated by the (increased) activity of Pgps. [54]. These 170 kDa proteins act as ATP-dependent drug efflux pumps, leading to lower intracellular concentrations of a variety of natural, toxic products, such as anthracyclines, taxanes, epipodophyllotoxins and vinca-alkaloids (Pgp substrates). In

Discussion and conclusions

About a decade ago, the intracerebral microdialysis technique entered the field of pharmacokinetics in brain research. Since then, the number of publications in this field has increased exponentially. Within this period, much has been learned about the proper use of this technique. Today, it has outgrown its childhood diseases and its potentials and limitations have been more-or-less well defined. Numerous data points can be obtained from individual animals, which makes the technique attractive

Abbreviations

AUC	Area under the concentration–time curve
BBB	Blood–brain barrier
brain_ECF	Brain extracellular fluid
C_dialysate	Concentration in the dialysate
C_ECF	Bulk ECF concentration outside the microdialysis probe
C_in	Concentration in the perfusate
CNS	Central nervous system
CSF	Cerebrospinal fluid
D_eff	Effective diffusion coefficient in the brain
ECF	Extracellular fluid
F	Flow rate of the perfusate
k_ep	Rate constant for extracellular–microvascular exchange
k_em	Rate constant for irreversible extracellular metabolism
k_e→im

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Microdialysis for pharmacokinetic analysis of drug transport to the brain

Abstract

Introduction

Section snippets

In vivo other than intracerebral microdialysis

Concentration recovery

Lipophilicity

Mdr1a-encoded P-glycoprotein at the BBB and the use of mdr1a(−/−) mice

Discussion and conclusions

Abbreviations

Life Sci.

Brain Res.

Exp. Neurol.

J. Neurosci. Methods

Biol. Psychiatry

Prog. Neurobiol.

J. Neurosci. Methods

J. Pharm. Methods

J. Pharm. Methods

Brain Res.

Brain Res. Rev.

Brain. Res.

Brain Res.

J. Biol. Chem.

Cell

J. Biol. Chem.

Quantitative microdialysis: analysis of transients and application to pharmacokinetics in brain

J. Neurochem.

Quantitative microdialysis under transient conditions

Anal. Chem.

Brain efflux index as a novel method of analyzing efflux transport at the blood–brain barrier

J. Pharmacol. Exp. Ther.

An in situ brain perfusion technique to study cerebrovascular transport in the rat

Am. J. Physiol.

Effects of benzylpenicillin on the disposition of cefodizine in rats: no net effect on total clearance due to increased hepatobiliary clearance and increased renal clearance

J. Pharmacol. Exp. Ther.

Kinetics of drug action in disease states. Effect of infusion rate on phenobarbital concentrations in serum, brain and cerebrospinal fluid of normal rats at onset of loss of righting reflex

J. Pharmacol. Exp. Ther.

Kinetic model for disposition of 6-mercaptopurine in monkey plasma and cerebrospinal fluid

Am. J. Physiol.

Enzyme modified microelectrode with millisecond response time

Curr. Sep.

Autoradiographic analysis of 3H-MK-801 (dizocilpine) in vivo uptake and in vitro binding after focal cerebral ischemia in the rat

J. Neurosurg.

Quantitation of blood–brain barrier permeability by positron emission tomography

Phys. Med. Biol.

Synthesis of carbon-11 labeled ionidated cocaine derivatives and their distribution in baboon brain measured using positron emission tomography

J. Med. Chem.

Drug equilibration across the blood–brain-barrier — pharmacokinetic considerations based on the microdialysis method

Pharm. Res.

Coupling of microdialysis with capillary electrophoresis: a new approach to the study of drug transfer between two compartments of the body in freely moving rats

J. Chromatogr.

Pharmaceutical and biomedical application of capillary electrophoresis/electrochemistry

Electrophoresis

Comparison of in vitro and in vivo calibration of microdialysis probes using retrodialysis

Curr. Sep.

Autoradiographic analysis of ³H-MK-801 (dizocilpine) in vivo uptake and in vitro binding after focal cerebral ischemia in the rat