Application Of Microdialysis Research Articles

Pitfalls of the application of microdialysis in clinical oncology: Controversial findings with docetaxel

Microdialysis is a novel and minimally invasive sampling technique, based on the diffusion of analytes from the interstitial compartment through a semi-permeable membrane, and enables direct assessment of tissue disposition and penetration of drugs. Variable antitumor responses may be associated with differences in tumor vascularity, capillary permeability or tumor interstitial pressure resulting in variable delivery of anticancer agents. In preparation of pharmacokinetic studies, aimed at measuring docetaxel concentrations in healthy and malignant tissues in vivo, in pre-clinical as well as clinical studies, in vitro recovery experiments were performed. In contrast to published data, the recovery experiments suggest that docetaxel has a very low recovery as a result of non-specific binding to currently available microdialysis catheters. Here we discuss our findings with docetaxel in a historical perspective and we report on our experience using polysorbate 80 to eliminate the non-specific binding and its effects on the recovery of docetaxel.

Glutamatergic stimulation of the basal forebrain elevates extracellular adenosine and increases the subsequent sleep

A prolonged period of waking accumulates sleep pressure, increasing both the duration and the intensity of the subsequent sleep period. Delta power, which is calculated from the slow range electroencephalographic (EEG) oscillations (0.1–4 Hz), is regarded as the marker of sleep intensity. Recent findings indicate that not only the duration but also the quality of waking, determines the level of increase in the delta activity during the subsequent sleep period. Elevated levels of extracellular adenosine in the basal forebrain (BF) during prolonged waking have been proposed to act as the molecular signal of increased sleep pressure, but the role of BF neuronal activity in elevating adenosine has not been previously explored. We hypothesized that an increase in neuronal discharge in the BF would lead to increase in the extracellular adenosine and contribute to the increase in the subsequent sleep. To experimentally increase neuronal activity in the rat BF, we used 3 h in vivo microdialysis application of glutamate or its receptor agonists N-methyl- d-aspartate (NMDA) or AMPA. Samples for adenosine measurement were collected during the drug application and the EEG was recorded during and after the treatment, altogether for 24 h. All treatments increased the duration of the subsequent sleep following the application. In contrast, delta power was elevated only if both the waking EEG theta (5–9 Hz) power (which can be regarded as a marker of active waking) and the extracellular adenosine in the BF were increased during the application. These results indicate that increased neuronal activity in the BF, and particularly the type of neuronal activity coinciding with active waking, is one of the factors contributing to the buildup of the sleep pressure.

AAPS-FDA workshop white paper: Microdialysis principles, application, and regulatory perspectives report from the Joint AAPS-FDA Workshop, November 4–5, 2005, Nashville, TN

AAPS-FDA workshop white paper : Microdialysis principles, application, and regulatory perspectives report from the joint AAPS-FDA workshop, November 4-5, 2005, Nashville, TN

Application of micro-dialysis in liver transplantation

Application of micro-dialysis in liver transplantation

Application of microdialysis for pharmacokinetic-pharmacodynamic modelling

Pharmacokinetic-pharmacodynamic (PK- PD) modelling describes the relationship between the pharmacokinetics and pharmacodynamics of a drug allowing the prediction of clinically relevant parameters. PK-PD modelling has several advantages over classical dose-response studies because it allows a better pharmacodynamic characterisation of drugs and screening of dosage-regimen. However, PK-PD studies are limited by the need forsimultaneous measurement of drug tissue levels and corresponding pharmacological effects at multiple time points. The microdialysis technique is aunique research tool that allows the simultaneous determination of unbound concentrations of drugs at several tissues and its action on biochemical and clinical markers during several hours and days. Therefore, microdialysis sampling is an attractive methodology for PK- PD studies. The aim of this review is to describe the applicability of the microdialysis technique for PK-PD modelling of therapeutic agents, including a description of PK-PD modelling concepts, an overview of the microdialysis technique and an analysis of PK-PD studies using microdialysis sampling both in the preclinical and clinical setting.

The Relevance of Microdialysis for Clinical Oncology

Conventional pharmacokinetic trials in oncology measure the total amount of drug and its metabolites in the plasma of patients. These total drug concentrations are then correlated with clinical parameters such as toxicity and/or drug efficacy. However, total drug concentrations in plasma are often not directly related to tumor or tissue concentrations and the kinetics in (tumor) tissue may be very different from the kinetics of the drug in plasma. As only the unbound fraction of drugs can passively diffuse or can be actively transported across the cell membrane of endothelial cells and penetrate the tissues and tumor cells, binding of drugs to plasma components may, in part, be responsible for the variability in clinical outcomes. Also, variation in binding to cellular components may be important. As an overall consequence, in in vivo models high inter-individual variabilities of drug concentrations in the tumor have been observed, which affected drug activity. Many current cancer drug-therapies aim for a clinical benefit at the edge of acceptable toxicity, without paying attention to (variability in) plasma and tumor or tissue pharmacokinetics. This review discusses the potential applicability of microdialysis, a minimally invasive method used to determine the unbound fraction of drugs in blood or in the interstitial fluid of tissues, in clinical oncology. Although faced with some methodological challenges, the technique offers many advantages over others, and enables direct tumor assessment for pharmacokinetics and even pharmacodynamics.

An integrated microdialysis rat model for multiple pharmacokinetic/pharmacodynamic investigations of serotonergic agents

Introduction Integrated in vivo models applying intracerebral microdialysis in conjunction with automated serial blood sampling in conscious, freely moving rodents are an attractive approach for pharmacokinetic (PK) and simultaneous pharmacokinetic/pharmacodynamic (PK/PD) investigations of CNS active drugs within the same animal. In this work, the ability to obtain and correlate data in this manner was evaluated for the selective serotonin (5-HT) reuptake inhibitor (SSRI) escitalopram. Methods An instrumented rat model equipped with an intracerebral hippocampal microdialysis probe and indwelling arterial and venous catheters was applied in the studies. Concomitant with brain microdialysis, serial blood sampling was conducted by means of an automated blood sampling device. The feasibility of the rat model for simultaneous PK/PD investigations was examined by monitoring plasma and brain extracellular concentrations of escitalopram along with SSRI-associated pharmacological activity, monitored as changes in brain 5-HT levels and plasma corticosterone levels. Results Combining intracerebral microdialysis and automated blood sampling did not cause any detectable physiological changes with respect to basal levels of plasma corticosterone or brain 5-HT levels. Furthermore, the PK of escitalopram in hippocampus following intravenous injection was not influenced by the presence of vascular catheters. Conversion of escitalopram dialysate concentrations into absolute extracellular levels by means of in vivo retrodialysis was verified by the no-net-flux method, which gave similar recovery estimates. The PK of escitalopram could be characterized simultaneously in plasma and the hippocampus of conscious, freely moving rats. Concomitantly, the modulatory and functional effects of escitalopram could be monitored as increases in brain 5-HT and plasma corticosterone levels following drug administration. Discussion The applicability of intracerebral microdialysis combined with arterial blood sampling was demonstrated for simultaneous PK/PD investigations of escitalopram in individual rats under non-stressful conditions. Together, these temporal relationships provide multiple PK/PD information in individual animals, hence minimizing inter-animal variation using a reduced number of animals.

Activity-dependent feedback modulation of spike patterning of supraoptic nucleus neurons by endogenous adenosine

Neuropeptide secretion from the dendrites of hypothalamic magnocellular supraoptic nucleus (SON) neurons contributes to the regulation of neuronal activity patterning, which ultimately determines their peptide output from axon terminals in the posterior pituitary gland. SON dendrites also secrete a number of other neuromodulators, including ATP. ATP degrades to adenosine in the extracellular space to complement transported adenosine acting on pre- and postsynaptic SON A1 receptors to reduce neuronal excitability, measured in vitro. To assess adenosine control of electrical activity in vivo, we made extracellular single-unit recordings of the electrical activity of SON neurons in anesthetized male rats. Microdialysis application (retrodialysis) of the A1 receptor antagonist, 8-cyclopentyl-1,3-dimethylxanthine (CPT) increased phasic vasopressin cell intraburst firing rates progressively over the first 5 s by 4.5 +/- 1.6 Hz (P < 0.05), and increased burst duration by 293 +/- 64% (P < 0.05). Hazard function plots were generated from interval interspike histograms and revealed that these effects were associated with increased postspike excitability. In contrast, CPT had no effect on the firing rates and hazard function plot profiles of continuously active vasopressin and oxytocin cells. However, CPT significantly increased clustering of spikes, as quantified by the index of dispersion, in oxytocin cells and continuously active vasopressin cells (by 267 +/- 113% and 462 +/- 67%, respectively, P < 0.05). Indeed, in 4 of 5 continuously active vasopressin cells, CPT induced a pseudophasic activity pattern. Together, these results indicate that endogenous adenosine is involved in the local control of SON cell activity in vivo.

Coupling microdialysis to capillary electrophoresis

An overview of the most outstanding aspects of microdialysis (MD) and capillary electrophoresis (CE) separately, but especially the promising trend of their off and on-line coupling is presented here. The interfaces required and the main advantages of MD-CE arrangements as compared with those used in MD–HPLC are emphasized as well as key applications of MD–CE in pharmacokinetics, pharmacodynamics and neuroscience.

Application of Microdialysis in Clinical Pharmacology

Microdialysis has been developed during the last 25 years by several authors primarily to study brain function and changes in levels of endogenous compounds such as neurotransmitters or metabolites in different laboratory animals. However, in the last ten years microdialysis sampling has been introduced as a versatile technique in the clinical setting. Although, microdialysis sampling has been extensively used for metabolic monitoring in patients, it was also employed for the study of distribution of different therapeutic agents especially anti-infective and antineoplasic drugs. In addition, clinical effect of drugs in patients could be also determined by means of microdialysis. So, this article reviewed the vast applications of the microdialysis technique for the study of pharmacokinetic and pharmacodynamic properties of drugs in the clinical setting.

Application of microdialysis to evaluate the efflux transport of estradiol 17-β glucuronide across the rat blood–retinal barrier

The purpose of the present study was to evaluate vitreous humor/retina-to-blood efflux transport in rats and determine the efflux transport of estradiol 17-β glucuronide (E17βG) across the blood–retinal barrier (BRB) by the use of microdialysis. [ 3H]E17βG and [ 14C] d-mannitol, which were used as a model compound for amphipathic organic anions and a bulk flow marker, respectively, were injected into the vitreous humor of rat eye, and a microdialysis probe was placed in the vitreous humor. [ 3H]E17βG and [ 14C] d-mannitol were bi-exponentially eliminated from the vitreous humor after vitreous bolus injection. The elimination rate constant of [ 3H]E17βG during the terminal phase was 1.9-fold greater than that of [ 14C] d-mannitol and reduced the level of [ 14C] d-mannitol in the retinal presence of 0.3 mM E17βG, suggesting that [ 3H]E17βG is transported via a carrier-mediated efflux transport process across the BRB. The efflux transport of [ 3H]E17βG was significantly inhibited by organic anions, such as probenecid, sulfobromophthalein, digoxin, and dehydroepiandrosterone sulfate, whereas it was not inhibited by p-aminohippuric acid. In conclusion, the efflux transport of [ 3H]E17βG across the rat BRB was evaluated by microdialysis and its inhibition by organic anions suggests organic anion transporting polypeptide 1a4-mediated E17βG efflux transport at the BRB.

Microdialysis as a tool in local pharmacodynamics

In many cases the clinical outcome of therapy needs to be determined by the drug concentration in the tissue compartment in which the pharmacological effect occurs rather than in the plasma. Microdialysis is an in vivo technique that allows direct measurement of unbound tissue concentrations and permits monitoring of the biochemical and physiological effects of drugs throughout the body. Microdialysis was first used in pharmacodynamic research to study neurotransmission, and this remains its most common application in the field. In this review, we give an overview of the principles, techniques, and applications of microdialysis in pharmacodynamic studies of local physiological events, including measurement of endogenous substances such as acetylcholine, catecholamines, serotonin, amino acids, peptides, glucose, lactate, glycerol, and hormones. Microdialysis coupled with systemic drug administration also permits the more intensive examination of the pharmacotherapeutic effect of drugs on extracellular levels of endogenous substances in peripheral compartments and blood. Selected examples of the physiological effects and mechanisms of action of drugs are also discussed, as are the advantages and limitations of this method. It is concluded that microdialysis is a reliable technique for the measurement of local events, which makes it an attractive tool for local pharmacodynamic research.

Applicability of reverse microdialysis in pharmacological and toxicological studies

A recent application of microdialysis is the introduction of a substance into the extracellular space via the microdialysis probe. The inclusion of a higher amount of a drug in the perfusate allows the drug to diffuse through the microdialysis membrane to the tissue. This technique, actually called as reverse microdialysis, not only allows the local administration of a substance but also permits the simultaneous sampling of the extracellular levels of endogenous compounds. Local effects of exogenous compounds have been studied in the central nervous system, hepatic tissue, dermis, heart and corpora luteae of experimental animals by means of reverse microdialysis. In central nervous studies, reverse microdialysis has been extensively used for the study of the effects on neurotransmission at different central nuclei of diverse pharmacological and toxicological agents, such as antidepressants, antipsychotics, antiparkinsonians, hallucinogens, drugs of abuse and experimental drugs. In the clinical setting, reverse microdialysis has been used for the study of local effects of drugs in the adipose tissue, skeletal muscle and dermis. The aim of this review is to describe the principles of the reverse microdialysis, to compare the technique with other available methods and finally to describe the applicability of reverse microdialysis in the study of drugs properties both in basic and clinical research.

Application of microdialysis to study thein vivo release of pingyangmycin fromin situ gels in rabbits

Microdialysis was used together with HPLC to monitor the local concentration of pingyangmycin hydrochloride (PYM) after embolizing rabbit ear-veins with an injectable sustained release formulation, PYM-Zein/PYM-Zein-sucrose acetate isobutyrate (SAIB), in situ gel. The dialysis probe was perfused at 2 microL/min. The in vivo recovery was 46.6 3.1% (n = 4). The samples were injected directly into HPLC. PYM was detected using UV detector at 291 nm. Separation from other components in the dialysate was performed using a Discovery((R)) RP-Amide C(16) column within 12 min. The response for PYM in the dialysate was linear (r(2) > 0.996) over the range of 2.5-212 microg/mL. The limit of detection and limit of quantitation of PYM in the dialysate were 0.4 and 1.5 microg/mL, respectively. The results demonstrated that the in situ gel of PYM-Zein-SAIB could extend the release of PYM to 4 days. SAIB could significantly cut down the initial burst of PYM from the in situ gels (p < 0.05).

Urea as an endogenous surrogate in human microdialysis to determine relative recovery of drugs: Analytics and applications

During in vivo microdialysis studies time-consuming and laborious bedside calibration methods, e.g. retrodialysis, have to be performed. To reduce the burden on the patient it would be desirable to establish a reliable, time-saving calibration technique to obtain the in vivo recovery describing the relative drug transfer across the membrane of the microdialysis probe. The performed study aimed to evaluate and validate the use of urea as an endogenous reference compound to determine relative in vivo recovery of anti-infectives, e.g. linezolid used herein as model drug. In order to meet the special requirements imposed by microdialysis to measure urea concentrations in very small sample volumes (∼10 μL) a photometric assay in 96-well microtiter plates was established based on the method of Berthelot. Subsequently, concentration- and flow rate-dependence were evaluated in vitro to determine the relative recovery (RR) of urea. Finally, urea and linezolid concentrations in human microdialysis samples were measured. The developed assay was validated according to international guidelines and met all requirements. Relative in vitro recovery was found to be independent from concentration and dependent on flow rate. Subsequently, relative in vivo recovery of urea was correlated with relative in vivo recovery of linezolid obtained by the traditional retrodialysis method. In healthy volunteers, the mean ratio of the relative recovery of linezolid to the relative recovery of urea was 0.6 for the subcutaneous (s.c.: CV 33.4%, n = 48) and 0.7 for the intramuscular probe (i.m.: CV 18.8%, n = 40), respectively. In critically ill patients this ratio was 0.7 for both tissues (s.c.: CV 32.8%, n = 18; i.m.: CV 22.1%, n = 17). Successful calibration of the urea reference technique without the need to use in vitro data will further promote the application of microdialysis in clinical studies especially in critically ill patients, as it reduces the imposed burden to a minimum.

In vivo microdialysis for PK and PD studies of anticancer drugs

In vivo microdialysis technique has become one of the major tools to sample endogenous and exogenous substances in extracellular spaces. As a well-validated sampling technique, microdialysis has been frequently employed for quantifying drug disposition at the desired target in both preclinical and clinical settings. This review addresses general methodological considerations critical to performing microdialysis in tumors, highlights selected preclinical and clinical studies that characterized drug disposition in tumors by the use of microdialysis, and illustrates the potential application of microdialysis in the assessment of tumor response to cancer treatment.

Microdialysis as an Excellent Sampling Approach for Biomedical Analysis

Microdialysis is an excellent sampling technique for continuous monitoring of endogenous and exogenous compounds in the extracellular fluid. This technique has several advantages compared with conventional methods. Accordingly, this technique is extensively applied to study pharmacokinetics and pharmacodynamics both in experimental animals and human. In this mini-review, various topics related to microdialysis for the last five years will be discussed on its benefits. With the development of microdialysis technique and increasing number of applications of microdialysis for human study, this technique seems to play an important role in clinical practice, for example, bedside microdialysis as drug monitoring or diagnostic of disease. Keywords: microdialysis, pharmacokinetics, pharmacodynamics, experimental animal, human

Applicability of microdialysis as a technique for pharmacokinetic–pharmacodynamic (PK–PD) modeling of antihypertensive beta-blockers

Introduction The aim of the present work was to examine microdialysis as a technique for the study of pharmacokinetic–pharmacodynamic modeling of antihypertensive drugs. For this purpose, we studied the antihypertensive and the chronotropic effect of metoprolol and its plasma concentrations in sham operated (SO) and aortic coarctated (ACo) rats at an early hypertensive stage. Methods Plasma metoprolol concentrations were obtained by means of a “shunt” vascular microdialysis probe. Changes in mean arterial pressure and heart rate were also measured in the same experiment. Results A rapid decay of metoprolol levels was observed in both experimental groups. For the chronotropic effect, a good association between plasma levels and the chronotropic effect was observed in SO and ACo rats. ACo rats had a greater sensitivity to the chronotropic effect ( E max:−38±2%, n=5, p<0.05) than SO animals ( E max:−27±1%, n=5). A delay in the blood pressure reduction induced by metoprolol was observed in both experimental groups. A good association was observed between concentrations of metoprolol in the effect compartment and the corresponding hypotensive effect in both experimental groups. The calculated PK–PD parameters were not different between SO and ACo groups. Discussion A good correlation was found between metoprolol concentration and its chronotropic and antihypertensive effects in normotensive and ACo hypertensive rats, allowing the employment of PK–PD models. The microdialysis technique allows simultaneous determination of plasma levels of antihypertensive drugs and their cardiovascular effects, and is therefore a powerful tool for PK–PD modeling.

Brain microdialysis and its application for the study of neurotransmitter release during exercise

Physical exercise influences the central dopaminergic, noradrenergic, and serotonergic systems. A number of studies have examined brain noradrenaline (NA), serotonin (5‐hydroxytryptamine, or 5‐HT), and dopamine (DA) with exercise. The microdialysis technique employs the dialysis (from Greek: to separate) principle in which a membrane, permeable to water and small solutes, separates two fluid compartments; microdialysis can collect virtually any substance from the brains of freely moving animals with a limited amount of tissue trauma. This method allows the measurement of local neurotransmitter release in combination with on‐going behavioral changes such as exercise. Several kinds of behavior have been studied using microdialysis. The first studies were descriptive, i.e., they registered the extracellular neurotransmitter concentrations during locomotion or after application of an acute stress. Thereafter, the effects of acute and chronic stress, such as an acute bout of endurance exercise or training, on extracellular neurotransmitter concentrations were evaluated both at rest and during exercise. The latest studies evaluated the link between extracellular neurotransmitter concentrations and fatigue in running animals and their direct effect on peripheral hormonal concentrations and on the regulation of body temperature during exercise. The present paper will discuss the application of microdialysis in neuroscience, focusing on exercise and behavioral‐related studies

Translational Neurochemical Research in Acute Human Brain Injury: The Current Status and Potential Future for Cerebral Microdialysis

Microdialysis (MD) was introduced as an intracerebral sampling method for clinical neurosurgery by Hillered et al. and Meyerson et al. in 1990. Since then MD has been embraced as a research tool to measure the neurochemistry of acute human brain injury and epilepsy. In general investigators have focused their attention to relative chemical changes during neurointensive care, operative procedures, and epileptic seizure activity. This initial excitement surrounding this technology has subsided over the years due to concerns about the amount of tissue sampled and the complicated issues related to quantification. The interpretation of mild to moderate MD fluctuations in general remains an issue relating to dynamic changes of the architecture and size of the interstitial space, blood-brain barrier (BBB) function, and analytical imprecision, calling for additional validation studies and new methods to control for in vivo recovery variations. Consequently, the use of this methodology to influence clinical decisions regarding the care of patients has been restricted to a few institutions. Clinical studies have provided ample evidence that intracerebral MD monitoring is useful for the detection of overt adverse neurochemical conditions involving hypoxia/ischemia and seizure activity in subarachnoid hemorrhage (SAH), traumatic brain injury (TBI), thromboembolic stroke, and epilepsy. There is some data strongly suggesting that MD changes precede the onset of secondary neurological deterioration following SAH, hemispheric stroke, and surges of increased ICP in fulminant hepatic failure. These promising investigations have relied on MD-markers for disturbed glucose metabolism (glucose, lactate, and pyruvate) and amino acids. Others have focused on trying to capture other important neurochemical events, such as excitotoxicity, cell membrane degradation, reactive oxygen species (ROS) and nitric oxide (NO) formation, cellular edema, and BBB dysfunction. However, these other applications need additional validation. Although these cerebral events and their corresponding changes in neurochemistry are important, other promising MD applications, as yet less explored, comprise local neurochemical provocations, drug penetration to the human brain, MD as a tool in clinical drug trials, and for studying the proteomics of acute human brain injury. Nevertheless, MD has provided new important insights into the neurochemistry of acute human brain injury. It remains one of very few methods for neurochemical measurements in the interstitial compartment of the human brain and will continue to be a valuable translational research tool for the future. Therefore, this technology has the potential of becoming an established part of multimodality neuro-ICU monitoring, contributing unique information about the acute brain injury process. However, in order to reach this stage, several issues related to quantification and bedside presentation of MD data, implantation strategies, and quality assurance need to be resolved. The future success of MD as a diagnostic tool in clinical neurosurgery depends heavily on the choice of biomarkers, their sensitivity, specificity, and predictive value for secondary neurochemical events, and the availability of practical bedside methods for chemical analysis of the individual markers. The purpose of this review was to summarize the results of clinical studies using cerebral MD in neurosurgical patients and to discuss the current status of MD as a potential method for use in clinical decision-making. The approach was to focus on adverse neurochemical conditions in the injured human brain and the MD biomarkers used to study those events. Methodological issues that appeared critical for the future success of MD as a routine intracerebral sampling method were addressed.