Quantification of the Therapeutic Antibody Ocrelizumab in Mouse Brain Interstitial Fluid Using Cerebral Open Flow Microperfusion and Simultaneous Monitoring of the Blood-Brain Barrier Integrity.

The increasing relevance of improved therapeutic monoclonal antibodies (mAbs) to treat neurodegenerative diseases has strengthened the need to reliably measure their brain pharmacokinetic (PK) profiles. The aim of this study was, therefore, to absolutely quantify the therapeutic antibody ocrelizumab (OCR) as a model antibody in mouse brain interstitial fluid (ISF), and to record its PK profile by using cerebral open flow microperfusion (cOFM). Further, to monitor the blood-brain barrier (BBB) integrity using an endogenous antibody with a similar molecular size as OCR. The study was conducted on 13 male mice. Direct and absolute OCR quantification was performed with cOFM in combination with zero flow rate, and subsequent bioanalysis of the obtained cerebral ISF samples. For PK profile recording, cerebral ISF samples were collected bi-hourly, and brain tissue and plasma were collected once at the end of the sampling period. The BBB integrity was monitored during the entire PK profile recording by using endogenous mouse immunoglobulin G1. We directly and absolutely quantified OCR and recorded its brain PK profile over 96 h. The BBB remained intact during the PK profile recording. The resulting data provide the basis for reliable PK assessment of therapeutic antibodies in the brain thus favoring the further development of therapeutic monoclonal antibodies.

Atraumatic access to human glioblastoma in a xenograft animal model by cerebral open flow microperfusion.

BACKGROUND: Orthotopic xenograft studies promote the development of targeted/personalized therapies to improve the still poor life expectancy of glioblastoma patients. NEW METHOD: We implemented an atraumatic access to glioblastoma with cerebral Open Flow Microperfusion (cOFM) by implantation of xenograft cells in rat brain with intact blood brain barrier (BBB) and subsequent development of a xenograft glioblastoma at the interface between the cOFM probe and surrounding brain tissue. Human glioma U87MG cells were implanted at a well-defined position into immunodeficient Rowett nude rat´s brain via cOFM (cOFM group) and syringe (control group). Characteristics of the mature tumors from both groups were assessed. RESULTS: For the first time xenograft cells were successfully introduced into rat brain with intact BBB using cOFM, and the tumor tissue developing around the cOFM probe was unaffected by the presence of the probe. Thereby an atraumatic access to the tumor was created. The success rate of glioblastoma development in the cOFM group was high (>70%). The mature cOFM-induced tumors (20-23 days after cell-implantation) resembled the syringe-induced ones and showed typical features of human glioblastoma. COMPARISON WITH EXISTING METHOD: Examining xenograft tumor microenvironment with currently available methods inevitably causes trauma that could affect the reliability of obtained data. CONCLUSION: This novel atraumatic access to human glioblastoma in rat brain provides the possibility to collect interstitial fluid from functional tumor tissue in vivo without trauma generation. Thereby, reliable data can be generated promoting drug research, biomarker identification, and enabling investigation of the BBB of an intact tumor.

In vivo monitoring of brain pharmacokinetics and pharmacodynamics with cerebral open flow microperfusion.

In vivo investigation of brain pharmacokinetics and pharmacodynamics (PK/PD) is an integral part of neurological drug development. However, drugs intended to act in the brain may reach it at very low concentrations due to the protective effect of the blood-brain barrier (BBB). Consequently, very sensitive measurement methods are required to investigate PK/PD of drugs in the brain. Also, these methods must be capable of continuously assessing cerebral drug concentrations with verifiable intact BBB, as disrupted BBB may lead to compound efflux from blood into brain and to biased results. To date, only a few techniques are available that can sensitively measure drug concentrations in the brain over time; one of which is cerebral open flow microperfusion (cOFM). cOFM's key features are that it enables measurement of cerebral compound concentrations with intact BBB, induces only minor tissue reactions, and that no scar formation occurs around the probe. The membrane-free cOFM probes collect diluted cerebral interstitial fluid (ISF) samples that are containing the whole molecule spectrum of the ISF. Further, combining cOFM with an in vivo calibration protocol (e.g. Zero Flow Rate) enables absolute quantification of compounds in cerebral ISF. In general, three critical aspects have to be considered when measuring cerebral drug concentrations and recording PK/PD profiles with cOFM: (a) the BBB integrity during sampling, (b) the status of the brain tissue next to the cOFM probe during sampling, and (c) the strategy to absolutely quantify drugs in cerebral ISF. This work aims to review recent applications of cOFM for PK/PD assessment with a special focus on these critical aspects.

Insulin Distribution in Human Adipose Tissue via a Novel Insulin Infusion Catheter.

Continuous subcutaneous insulin infusion (CSII) is a widely used treatment for diabetes patients. Insulin infusion sets (CSII-catheters) are continuously optimized regarding size, handling and safety, but recurring dysfunction (kinking or occlusion), due to different user situations, behavior or chain of events, demand new ways to improve the functionality and safety in patients experiencing these issues. A novel CSII-catheter design (Lantern) features additional lateral perforations, which guarantee functionality even in case of kinking or occlusion. This study aimed to compare functionality, insulin distribution, and failure rate of Lantern and standard catheters using excised human adipose tissue samples. Novel Lantern CSII-catheters (open and artificially occluded) and commercially available standard CSII-catheters were inserted into adipose tissue samples. A mixture of insulin and contrast agent was infused as single bolus (7 IU) with an insulin infusion pump at highest flow rate (1 IU/s). Microtomography images and surface-to-volume ratios were used to assess insulin distribution and depot volume indicating the functionality of CSII-catheters. Failure rate was measured by flow-stop alerts of the pump. We found no difference in the volume of insulin depots compared with the nominal volume of 70 µL. Surface-to-volume ratios showed no significant difference among CSII-catheters. None of the catheters triggered any flow-stop alarm. The novel Lantern CSII-catheter design achieved similar insulin distribution as commercially available CSII-catheters. Moreover, functionality of Lantern CSII-catheters was guaranteed during occlusion, which is an improvement compared with standard CSII-catheters. We conclude that the novel CSII-catheter design has the potential to provide a valuable contribution to patient well-being and safety.

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

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.

Comparison of cerebral Open Flow Microperfusion and Microdialysis when sampling small lipophilic and small hydrophilic substances.

BACKGROUND: Assessment of drug concentration in the brain interstitial fluid (ISF) is crucial for development of brain active drugs, which are mainly small, lipophilic substances able to cross the blood-brain barrier (BBB). We aimed to compare the applicability of cerebral Open Flow Microperfusion (cOFM) and Microdialysis (MD) to sample the lipophilic substance amitriptyline (AMI), its metabolites Hydroxyamitriptyline (HYA), Nortriptyline (NOR), Amitriptyline-N-Oxide (ANO), deuterated water (D2O) and the hydrophilic substance sodium fluorescein (Naf) in brain ISF. NEW METHOD: cOFM has been refined to yield increased spatial resolution and performance. COMPARISON OF COFM AND MD AND RESULTS: Performance of cOFM and MD was assessed by in vivo AUC ratios of probe samples (AUCCOFM/AUCMD) and the in vivo relative recovery of D2O (RRvv,D2O). Adsorption of AMI and Naf to MD and cOFM was assessed by the in vitro relative recovery (RRvt) prior to the in vivo experiments. The in vivo AUC ratio of AMI and RRvv,D2O was about two times higher for cOFM than for MD (AUCOFM/AUCMD = 2.0, RRvv,D2O(cOFM)/RRvv,D2O(MD) = 2.1). cOFM detected all investigated AMI metabolites except NOR. MD did not detect HYA, NOR, ANO and Naf. In vitro adsorption of AMI and Naf to the MD membrane was strong (RRvt,AMI = 4.4%, RRvt,Naf = 1.5%) but unspecific adsorption to cOFM was negligibly small (RRvt,AMI = 98% and RRvt,Naf = 98%). CONCLUSIONS: cOFM showed better performance when sampling AMI and its metabolites, Naf and D2O, and had an about two times higher RRvv,D2O than MD. MD did not detect HYA, NOR, ANO and Naf, most likely due to membrane adsorption.

Time-resolved hypothalamic open flow micro-perfusion reveals normal leptin transport across the blood-brain barrier in leptin resistant mice.

OBJECTIVE: The inability of leptin to suppress food intake in diet-induced obesity, sometimes referred to as leptin resistance, is associated with several distinct pathological hallmarks. One prevailing theory is that impaired transport of leptin across the blood-brain barrier (BBB) represents a molecular mechanism that triggers this phenomenon. Recent evidence, however, has challenged this notion, suggesting that leptin BBB transport is acquired during leptin resistance. METHODS: To resolve this debate, we utilized a novel cerebral Open Flow Microperfusion (cOFM) method to examine leptin BBB transport in male C57BL/6J mice, fed a chow diet or high fat diet (HFD) for 20 days. RESULTS: Basal plasma leptin levels were 3.8-fold higher in HFD-fed mice (p < 0.05). Leptin administration (2.5 mg/kg) elicited similar pharmacokinetic profiles of circulating leptin. However, while leptin reduced food intake by 20% over 22 h in chow-fed mice, it did not affect food intake in HFD-fed mice. In spite of this striking functional difference, hypothalamic leptin levels, as measured by cOFM, did not differ between chow-fed mice and HFD-fed mice following leptin administration. CONCLUSIONS: These data suggest that leptin transport across the BBB is not impaired in non-obese leptin resistant mice and thus unlikely to play a direct role in the progression of pharmacological leptin resistance.

Determination of (2)H-enrichment of rat brain interstitial fluid and rat plasma by headspace-gas-chromatography - quadrupole-mass-spectrometry.

(2)H2O as nonradioactive, stable marker substance is commonly used in preclinical and clinical studies and the precise determination of (2)H2O concentration in biological samples is crucial. However, aside from isotope ratio mass spectrometry (IRMS), only a very limited number of methods to accurately measure the (2)H2O concentration in biological samples are routinely established until now. In this study, we present a straightforward method to accurately measure (2)H-enrichment of rat brain interstitial fluid (ISF) and rat plasma to determine the relative recovery of a cerebral open flow microperfusion (cOFM) probe, using headspace-gas-chromatography - quadrupole-mass-spectrometry. This method is based on basic-catalyzed hydrogen/deuterium exchange in acetone and detects the (2)H-labelled acetone directly by the headspace GC-MS. Small sample volumes and limited number of preparation steps make this method highly competitive. It has been fully validated. (2)H enriched to 8800 ppm in plasma showed an accuracy of 98.9% and %Relative Standard Deviation (RSD) of 3.1 with n = 18 over three days and with two operators. Similar performance was obtained for cerebral ISF enriched to 1100 ppm (accuracy: 96.5%, %RSD: 3.1). With this highly reproducible method we demonstrated the successful employment of (2)H2O as performance marker for a cOFM probe.

Assessment of blood-brain barrier function and the neuroinflammatory response in the rat brain by using cerebral open flow microperfusion (cOFM).

Blood-brain barrier (BBB) impairment in systemic inflammation leads to neuroinflammation. Several factors including cytokines, chemokines and signal transduction molecules are implicated in BBB dysfunction in response to systemic inflammation. Here, we have adopted a novel in vivo technique; namely, cerebral open flow microperfusion (cOFM), to perform time-dependent cytokine analysis (TNF-alpha, IL-6 and IL-10) in the frontal cortex of the rat brain in response to a single peripheral administration of lipopolysaccharide (LPS). In parallel, we monitored BBB function using sodium fluorescein as low molecular weight reporter in the cOFM sample. In response to the systemic LPS administration, we observed a rapid increase of TNF-alpha in the serum and brain, which coincides with the BBB disruption. Brain IL-6 and IL-10 synthesis was delayed by approximately 1 h. Our data demonstrate that cOFM can be used to monitor changes in brain cytokine levels and BBB disruption in a rat sepsis model.

Enhanced doxorubicin delivery to the brain administered through glutathione PEGylated liposomal doxorubicin (2B3-101) as compared with generic Caelyx,(®)/Doxil(®)--a cerebral open flow microperfusion pilot study.

The neuroprotective blood-brain barrier (BBB) keeps many drug candidates below therapeutic levels in the central nervous system. Glutathione PEGylated liposomal doxorubicin (2B3-101) has been developed to safely enhance the delivery of doxorubicin to brain tumors. However, doxorubicin concentration in extracellular brain fluid cannot yet be reliably measured using conventional techniques. Cerebral open flow microperfusion (cOFM), a recently developed sampling technique, allows monitoring of drug concentrations in the brain independent of molecular weight and lipophilicity. In combination with cOFM sampling, sodium fluorescein (NaF) is used as a marker for BBB integrity. Rats received one intravenous dose of 7 mg/kg of either 2B3-101 or PEGylated liposomal doxorubicin (generic Caelyx(®)). Blood and cOFM sampling was performed for 5 h after dose injection. NaF concentration in the brain was monitored and remained low indicating an intact BBB. The brain-to-blood ratio of doxorubicin was 4.8-fold higher after administration of 2B3-101 as compared with generic Caelyx(®) (p = 0.0016). In conclusion, by using cOFM it was possible to show that 2B3-101 leads to enhanced doxorubicin concentration in the brain without affecting the BBB integrity.

Long-term implanted cOFM probe causes minimal tissue reaction in the brain.

This study investigated the histological tissue reaction to long-term implanted cerebral open flow microperfusion (cOFM) probes in the frontal lobe of the rat brain. Most probe-based cerebral fluid sampling techniques are limited in application time due to the formation of a glial scar that hinders substance exchange between brain tissue and the probe. A glial scar not only functions as a diffusion barrier but also alters metabolism and signaling in extracellular brain fluid. cOFM is a recently developed probe-based technique to continuously sample extracellular brain fluid with an intact blood-brain barrier. After probe implantation, a 2 week healing period is needed for blood-brain barrier reestablishment. Therefore, cOFM probes need to stay in place and functional for at least 15 days after implantation to ensure functionality. Probe design and probe materials are optimized to evoke minimal tissue reaction even after a long implantation period. Qualitative and quantitative histological tissue analysis revealed no continuous glial scar formation around the cOFM probe 30 days after implantation and only a minor tissue reaction regardless of perfusion of the probe.

Cerebral open flow microperfusion: a new in vivo technique for continuous measurement of substance transport across the intact blood-brain barrier.

The blood-brain barrier (BBB) limits substance transport to the brain and is therefore the major hurdle to overcome when developing neuroactive drugs. Herein, we report on cerebral open flow microperfusion (cOFM) as a new membrane-free technique for measuring substance transport across the intact BBB. The cOFM technique is based on a probe that is inserted into the brain, rupturing the BBB. The BBB is re-established within 15 days, which then allows sampling of interstitial brain fluid under physiological conditions. The aims of the present proof-of-concept study were to: (i) determine the time between cOFM probe insertion and BBB re-establishment; and (ii) demonstrate the ability of cOFM to sample the interstitial cerebral fluid with an intact BBB. The cOFM probe was inserted into the frontal lobe of Sprague-Dawley rats, resulting in BBB rupture. Re-establishment of the BBB was determined using Evans blue (EB) dye, which is an established marker for BBB intactness because it does not cross the intact BBB. Evaluating EB levels in the brain tissue indicated that the BBB was healed 11 days after probe insertion. To demonstrate transport across the healed BBB, we used sodium fluorescein (Naf), a sensitive, low molecular weight marker that can cross the intact BBB and can be used to monitor changes in BBB permeability. Significantly increased Naf levels were found in the interstitial fluid when hyperosmolar mannitol (known to open the BBB) was introduced via cOFM, which indicated partial opening of the BBB surrounding the cOFM probe. In conclusion, we show herein that cOFM allows monitoring of BBB permeability, which should be useful for measuring pharmacokinetics across the BBB and pharmacodynamics in the brain.