In this video, Holden Janssens from Charles River South San Francicso site describes the microdialysis method.
Holden Janssens (00:07) My name is Holden Janssens, and I'm the Associate Director of Vivo Pharmacology here at Charles River. I've been with Charles River Brains On-Line for almost five years. So we can measure a lot of different things using microdialysis. We can measure things like neurotransmitters, looking at serotonin, dopamine or norepinephrine. We can also measure other analytes that are in the brain such as kynurenine and in its metabolites, as well as exogenous compounds, such as client compounds. We can measure the PK of compounds that are being administered to the animals over time. (00:38) So push-pull microdialysis is a technique that allows us to measure larger molecules, such as proteins, such as A-beta, Tau , α-Synuclein as well as antibodies using microdialysis. We're able to measure proteins or large molecules that are in the interstitial space and the pore size as larger in the microdialysis membrane. And so we're able to pull those proteins or larger molecules through the microdialysis probe and be able to measure them using a microdialysis technique. (01:04) Push-pull microdialysis is a technique that's very applicable in neurodegenerative diseases. So when you're looking at levels of A-beta in or Tau in Alzheimer's disease, you can measure how levels change over time and how administration of such things like antibodies can decrease those levels. So the MediQuant microdialysis probe is a proprietary microdialysis probe that was developed many years ago to measure quantitative levels of primarily drugs in the brain. So this technique allows us to have a very slow flow through the microdialysis probe, which allows as high, close to a 100% of drug to pass from the outside of the microdialysis probe in the brain, through the membrane, which is then picked up by the carrier flow. And then it's diluted at a known concentration. And with this really slow flow, we're able to get close to a 100% recovery with a microdialysis probe. When you're grinding up tissue and looking at brain levels, you're measuring bound and unbound concentrations in the brain, but what the power of the MediQuant technique is that we're able to measure the free fraction compound that's in the brain, not the unbound and we're able to measure that over time. (02:14) So one of the powers of the MediQuant technique is that we're able to measure pharmacokinetic changes within the same animal in multiple compartments. So in the past, when you've done a simple PK study, it requires a lot of animals and you're having to collect tissues from animals and be able to compare across multiple animals. With MediQuant technique, we're able to measure free fraction compound in the brain. You can also put a MediQuant microdialysis probe in the jugular vein and be able to measure free compound levels in the blood. So one thing we can do with microdialysis is combine it with behavioral assays and other techniques that we do in house. We can use microdialysis coupled with different behavioral assays and look at behaviorally, both changes in neurotransmitters and how different compounds may increase or decrease those changes in neurotransmitters, in response to different behaviors, such as novel object recognition. (03:00) We can also couple microdialysis with the EEG. So within the same animal, we can measure the levels of neurotransmitter changes in response to administration of a compound, and be able to compare that with the EEG activity all within the same animal at the same time. And this multimodal approach may help our clients make better decisions moving forward in the clinic. So microdialysis is a technique that can be used in many different tissues. We can measure free compound levels in other tissues, besides the brain, including tumors. We can also look at changes in analytes in other organs of the body, including the gut, the liver, the lung and the heart. So microdialysis while in theory may be simple, but in practicality can be rather challenging. Being able to place the microdialysis probe in a specific brain region sample from that region, collect the samples in a consistent way, makes it for a very challenging technique.