Microdialysis is a minimally-invasive sampling technique that is used for continuous measurement of free, unbound analyte concentrations in extracellular fluid and was initially developed for CNS research. It can be performed in any tissue type to assess the physiological or pharmacological functions of biochemicals (e.g., neurotransmitters, hormones, glucose) or perform metabolite ID/metabolite profiling, or determine the distribution of new chemical entities within the body. Microdialysis sampling is an excellent way to model the pharmacokinetics of a given therapeutic compound.
The microdialysis technique involves the implantation of a semi-permeable membrane in the target issue. The hollow fiber membrane is connected to inlet and outlet tubing, and the probe is continuously perfused with a solution that resembles the sampled tissue of interest (e.g., artificial CSF). Molecules that are small enough to diffuse across the pores of the membrane will diffuse from the in vivo sampling site to the inside of the membrane across a diffusion gradient and will be collected at time points for analysis. While microdialysis was originally developed as a method to sample the CNS, it has been used in oncology tumor models.
Figures 1 & 2: Measurement of Glutamine in the CSF or spinal cord of rodents via CSF sampling Norepinephrine
Measurement of neurotransmitters (glutamine and norepinephrine) in the CSF and spinal cord of anaesthetized or freely moving rodents is shown.
Figure 3: Measurement of Norepinephrine in Gut Tissues
Measurement of norepinephrine in gut tissues sampled using microdialysis is shown.
Apart from conventional microdialysis that sample small molecular weight analytes and support metabolite profiling, Charles River offers a push-pull method to sample high molecular weight analytes (peptides, proteins including tau and alpha-synuclein and interleukins and interleukins). The push-pull probes have a higher membrane cut-off and due to the bigger pores, a “pull” flow in the outlet is needed to ensure that the perfusion liquid is not lost along with the “push” flow in the inlet tube.
Figure 4: Measurement of Abeta in APP Transgenic Rodent Models
Conventional and push-pull microdialysis for Abeta peptides is compared. ELN 44989 is a nonselective gamma-secretase inhibitor.
The MetaQuant method is a proprietary microdialysis method that uses customizable probes to perform metabolite profiling and identification. developed by Brainlink. This method is used in various tissues including the GI tract, heart, liver, bone, kidney, lung, eye, and skin tissue and is a modified regular microdialysis probe combining measurement of absolute levels in the tissue of interest with sampled volume collection equal to the regular microdialysis technique. Ultraslow flows are applied in this technique.
Case Study: Customized Microdialysis
Client-developed compound showed clear behavioral phenotype, but mechanism of action was unclear.
A study was designed to combine conventional microdialysis with MetaQuant, plasma, and CSF sampling to monitor a range of neurotransmitters, potential biomarkers, and free-drug concentrations in different compartments simultaneously.
One particular biomarker was elevated in a dose-related manner and increased in-brain CSF and plasma as peak drug concentrations were achieved. Based on this study, the compound was taken forward into development. Later, the marker was subsequently used as a clinical biomarker in later-stage trials.
Microdialysis Services Frequently Asked Questions (FAQs)
Can this method be combined with other testing methods?
Yes, microdialysis is a noninvasive method where a probe is inserted to sample from the target tissue and the same animal can be used to perform behavioral studies or other assays.
Can this method be used to measure multiple endpoints simultaneously?
Microdialysis can be used to monitor a range of neurotransmitters, bloodborne biomarkers and most importantly, free drug concentrations in different tissues in the body as well as different compartments of the brain.
How can the recovered drug concentration be maximized?
One approach is to use the proprietary MetaQuant microdialysis method, that uses custom built probes for sampling combined with an ultra slow flow to maximize recovery of free drug concentrations or metabolites.