Cerebral Open Flow Microperfusion to Monitor Drug Transport Across the Blood‐Brain Barrier

Abstract

Drugs for neurological diseases have to cross the blood‐brain barrier (BBB) to induce their therapeutic effect. In vivo drug quantification in the brain is challenging, because invasive methods damage the BBB and measurement results may be confounded by drug leakage from the blood into the brain through the disrupted BBB. Cerebral open flow microperfusion (cOFM) is an in vivo sampling technique that allows BBB healing and re‐establishment after probe implantation and before sampling is performed. It therefore provides the opportunity to sample compounds in cerebral interstitial fluid with an intact BBB. This article comprehensively describes the experimental setup and procedures, perfusate requirements, critical parameters, common problems that may occur, and their causes and solutions. Typical results from a cOFM sampling experiment are presented and discussed. This protocol provides a tool for performing pharmacokinetic and pharmacodynamic studies in mouse or rat brain with an intact BBB. © 2019 by John Wiley & Sons, Inc.

Innovative Platform for the Advanced Online Monitoring of Three-Dimensional Cells and Tissue Cultures

“…In this study, we established an innovative platform for cultivation and online monitoring of 3D cell and tissue cultures. Integrating OFM, a proven probe-based in vivo sampling method [21,22] that is used to evaluate the pharmacokinetics and pharmacodynamics of drugs directly in skin [23], adipose [24], and brain [25] tissue in vivo, in a bioreactor opens new horizons for its applicability in in vitro models and tissues. The further implementation of sensors to the OFM in the bioreactor complements the monitoring platform enabling the sampling and online monitoring of the interstitial fluid.…”

Current Approaches to Monitor Macromolecules Directly from the Cerebral Interstitial Fluid

“…Technically, the membrane-free cOFM probe body construct itself contains the open exchange area necessary to perform the sampling experiments and is implanted directly into the brain in (not above, as for the microdialysis guide) the region of interest, as illustrated in Figure 2 b. It is recommended by the manufacturer to implant the probe body 14 days before initiating the sampling experiments [ 45 ]. This recovery period should ensure re-establishment of the BBB (for detailed discussion, see Section 3.1.1 ) and can be appraised as a third major feature of the probe design [ 41 , 42 ].…”

“…A healing dummy prevents tissue growing into the probe during this period. Sampling experiments can be initiated after 14 days by replacement of the healing dummy with a sampling insert [ 45 ].…”

“…Immediately before cOFM sampling, the healing dummy is replaced by the sampling insert, creating limited new damage according to the manufacturer as the cOFM probe body is implanted in the region of interest and the sampling insert is exactly in-line with the previously implanted guide. The probe is flushed at a high flow (typically 2 min at 5 µL/min) and a 1 h run-in phase is taken into account as an equilibration period [ 45 ]. In Custers et al [ 44 ], serotonin and ɣ-aminobutyric acid levels were determined 2 h and 20–24 h after sampling insert replacement to gain insight into possible disturbance of the brain environment, demonstrating that the 1 h run-in phase does not suffice.…”

“…The BBB is probably disrupted again after insertion of the sampling insert and flushing with the perfusate as it is in direct contact with the brain tissue (because of the absence of a membrane). Most cOFM studies in the literature are performed under anesthesia, which restricts the duration of the sampling experiment itself and makes a longer run-in phase impossible [ 41 , 43 , 45 , 80 , 83 , 84 ]. In an awake setup, the equilibration period can and should be prolonged [ 25 , 44 ].…”