Pharmacokinetic and Metabolism Studies Using Microdialysis Sampling

Abstract

Introduction ADME (adsorption, distribution, metabolism, elimination) studies on new drug entities, toxicological studies on environmental contaminants, and evaluation of chemicals in the workplace all involve gathering similar types of information. Such studies rely on a combination of in vitro, ex vivo, and in vivo techniques. Among the in vitro and ex vivo systems are isolated enzymes, microsomes, cell cultures, tissue homogenates, tissue slices, and isolated organs. Information about the role of specific enzymes and tissues, types of intermediates formed, and pathways for xenobiotic biotransformation are gained through these types of studies. However, because they represent parts rather than the whole physiological system, the types of information gained do not reflect the entire scheme of biotransformation within the intact organism.Traditional in vivo techniques include sampling blood and other biological fluids, analysis of elimination products to determine final disposition of the parent compound and metabolites, and tissue sampling requiring one or more animals per time point. These studies provide general information about the metabolism and final disposition of a compound, but do not offer details about specific enzymes, intermediates, or in vivo metabolic pathways. An overall limitation to traditional approaches is that results obtained in vitro sometimes do not correlate with those found in vivo.Microdialysis sampling has several characteristics that complement traditional in vitro and in vivo pharmacokinetic and metabolism techniques. This approach is accomplished by implanting a probe consisting of a hollow fiber dialysis membrane into the organ or biological matrix of interest. The short length of hollow fiber is affixed to pieces of narrow bore tubing that serve as inlet and oulet conduits for the probe. A solution, termed the perfusate, is pumped slowly through the probe. The perfusate is an aqueous solution that closely matches the ionic composition of the extracellular fluid (ECF). When the perfusate is correctly matched to the ECF, there should be no net exchange of water or ions across the membrane. Low molecular weight compounds can diffuse into or out of the probe lumen in response to concentration gradients and are pumped to the analysis system. NIH-PA Author ManuscriptNIH-PA Author Manuscript NIH-PA Author ManuscriptA diagram of the process is shown in Figure 1. For clarity, the diagram shows only one analyte (A), although several compounds are typically sampled at the same time in a microdialysis experiment. Large molecules such as proteins (P) and small molecules bound to proteins (P-A) are excluded by the membrane. Those molecules entering the lumen of the membrane are swept along by the perfusate and exit the probe. The solution leaving the probe, termed the dialysate, is collected for analysis. The probe can be thought of as an artificial blood vessel in that it can both deliver and remove compounds from the local area. Delivery of the parent compound via the probe permits study o...

An in vitro comparison of microdialysis relative recovery of Met- and Leu-enkephalin using cyclodextrins and antibodies as affinity agents

“…Microdialysis sampling has been used for over thirty years for chemical sampling applications in neuroscience, pharmacokinetics, and drug metabolism [4][5][6]. It is by far the most commonly used method for the collection of low molecular weight hydrophilic neurotransmitters, such as acetylcholine, dopamine, and glutamate from mammalian brain with high relative recovery [7][8][9].…”

“…Enkephalins are endogenous opioid neuropeptides that have morphinelike action or pain relief in the body and are readily associated with the neurochemistry of addiction [2]. Enkephalins also play significant roles in mediating body temperature control, food intake, reward mechanisms, and stress [3].Microdialysis sampling has been used for over thirty years for chemical sampling applications in neuroscience, pharmacokinetics, and drug metabolism [4][5][6]. It is by far the most commonly used method for the collection of low molecular weight hydrophilic neurotransmitters, such as acetylcholine, dopamine, and glutamate from mammalian brain with high relative recovery Publisher's Disclaimer: This is a PDF file of an unedited manuscript that has been accepted for publication.…”

Use of Online Microdialysis Sampling to Determine the in Vivo Rate of Phenol Glucuronidation in Rainbow Trout

“…MD sampling methods were initially developed to measure endogenous compounds in the CNS (Benveniste and Hüttemeier, 1990) but have since been used in a wide range of scientific disciplines, including studies of chemical kinetics and biotransformation. The use of MD in pharmacokinetic studies with mammals has been extensively reviewed (Ståhle, 1992;Elmquist and Sawchuk, 1997;Davies, 1999;Hansen et al, 1999;Verbeeck, 2000).…”

“…MD sampling methods were initially developed to measure endogenous compounds in the CNS (Benveniste and Hüttemeier, 1990) but have since been used in a wide range of scientific disciplines, including studies of chemical kinetics and biotransformation. The use of MD in pharmacokinetic studies with mammals has been extensively reviewed (Ståhle, 1992;Elmquist and Sawchuk, 1997;Davies, 1999;Hansen et al, 1999;Verbeeck, 2000).In a pioneering effort, McKim et al (1993) used MD probes implanted in the dorsal aorta of rainbow trout to measure blood borne concentrations of phenol (PH) and its phase II metabolic product, phenyl glucuronide (PG), during continuous PH exposures. This method was then combined with periodic urine sampling to characterize the renal elimination of PH, PG, and two additional PH metabolites, phenyl sulfate and hydroquinone (McKim et al, 1999).…”

Continuous in vivo Monitoring of Blood Diffusible Calcium Using On-line Microdialysis Sampling Coupled with Flame Atomic Absorption Spectrometry

“…For these reasons, there is a growing interest in designing and developing various types of on-line techniques for rapid, easy, and reliable analysis of Ca concentration in blood. 2,7 Microdialysis, [8][9][10][11] a powerful sampling technique used to obtain protein-free samples, has become an important technique for continuous in vivo sampling of the extracellular fluid in discrete compartments of living systems. A microdialysis system is easy to automate and can be on-line coupled with many analytical techniques, such as liquid chromatography, 12 capillary electrophoresis, 13 mass spectrometry, 14 flow-injection analysis, [15][16][17][18] and electrochemical detection.…”