Methodological and analytical considerations for intra-operative microdialysis

Riviere‑Cazaux et al. Fluids and Barriers of the CNS (2023) 20:94 https://doi.org/10.1186/s12987-023-00497-2 Fluids and Barriers of the CNS Open Access RESEARCH Methodological and analytical considerations for intra‑operative microdialysis Cecile Riviere‑Cazaux1, Karishma Rajani1, Masum Rahman1, Juhee Oh2, Desmond A. Brown3, Jaclyn F. White4, Benjamin T. Himes5, Ignacio Jusue‑Torres1, Moses Rodriguez6, Arthur E. Warrington2,6, Sani H. Kizilbash7, William F. Elmquist2 and Terry C. Burns1* Abstract Background Microdialysis is a technique that can be utilized to sample the interstitial fluid of the central nervous sys‑ tem (CNS), including in primary malignant brain tumors known as gliomas. Gliomas are mainly accessible at the time of surgery, but have rarely been analyzed via interstitial fluid collected via microdialysis. To that end, we obtained an investigational device exemption for high molecular weight catheters (HMW, 100 kDa) and a variable flow rate pump to perform microdialysis at flow rates amenable to an intra-operative setting. We herein report on the lessons and insights obtained during our intra-operative HMW microdialysis trial, both in regard to methodological and ana‑ lytical considerations. Methods Intra-operative HMW microdialysis was performed during 15 clinically indicated glioma resections in four‑ teen patients, across three radiographically diverse regions in each patient. Microdialysates were analyzed via targeted and untargeted metabolomics via ultra-performance liquid chromatography tandem mass spectrometry. Results Use of albumin and lactate-containing perfusates impacted subsets of metabolites evaluated via global metabolomics. Additionally, focal delivery of lactate via a lactate-containing perfusate, induced local metabolic changes, suggesting the potential for intra-operative pharmacodynamic studies via reverse microdialysis of candidate drugs. Multiple peri-operatively administered drugs, including levetiracetam, cefazolin, caffeine, mannitol and aceta‑ minophen, could be detected from one microdialysate aliquot representing 10 min worth of intra-operative sam‑ pling. Moreover, clinical, radiographic, and methodological considerations for performing intra-operative microdialysis are discussed. Conclusions Intra-operative HMW microdialysis can feasibly be utilized to sample the live human CNS microenviron‑ ment, including both metabolites and drugs, within one surgery. Certain variables, such as perfusate type, must be considered during and after analysis. Trial registration NCT04047264 Keywords Glioma, Microdialysis, Metabolomics, IDH, Pharmacokinetic, Mass spectrometry *Correspondence: Terry C. Burns Full list of author information is available at the end of the article © The Author(s) 2023. Open Access This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if changes were made. The images or other third party material in this article are included in the article’s Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article’s Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this licence, visit http://creativecommons.org/licenses/by/4.0/. The Creative Commons Public Domain Dedication waiver (http://creativeco mmons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated in a credit line to the data. Riviere‑Cazaux et al. Fluids and Barriers of the CNS (2023) 20:94 Background Few methods exist via which the live central nervous system (CNS) can be sampled and analyzed in situ, including in the presence of a brain tumor. Gliomas are primary malignant brain tumors that inevitably recur and for which no cure currently exists [1]. The glioma and its extracellular microenvironment remain poorly understood as the tumor is only immediately accessible in the operating room, at the time of resection [2]. Studies in gliomas, as well as other CNS diseases, such as Alzheimer’s Disease and Parkinson’s Disease, often rely on animal models that incompletely recapitulate the pathology and therapeutic resistance of the disease [3–6]. Understanding and sampling this biology in situ could enable therapeutic discoveries guided by the patient’s own live disease. Microdialysis is a technique that enables sampling of candidate biomarkers from the tissue microenvironment [7]. Perfusate flows through the sampling catheter that has a semipermeable membrane with a set molecular weight cut-off. The concentration gradient between the parenchyma and the perfusate enables extracellular parenchymal analytes to diffuse across the membrane and into the recovered microdialysate. Microdialysis has been deployed in traumatic brain injury studies to identify biomarkers of tissue health and damage, including glucose [8, 9], n-acetylaspartate (NAA) [10], lactate/ pyruvate ratio [9, 11], and glutamate [12]. In glioma and other CNS diseases, microdialysis has been utilized for pharmacokinetic studies to evaluate local CNS free drug levels [13–15]. More recently, we and others have utilized microdialysis in gliomas to evaluate the extracellular metabolic and cytokine/chemokine microenvironment of these tumors [16–22]. We recently reported findings from our intra-operative high molecular weight (HMW) microdialysis trial (NCT04047264) [23]. This work identified a highly conserved signature of blood– brain barrier disruption across patients with enhancing tumors, enriched for plasma-derived analytes. As a firstin-human intra-operative study of HMW microdialysis, multiple lessons were learned from each patient about the potential pitfalls and opportunities of intra-operative HMW microdialysis. Herein, we report on (or “confess”) these lessons and surreptitious insights obtained during intra-operative HMW microdialysis. We discuss clinical, radiographic, and methodologic considerations to optimize feedback from the tumor in a relatively short period of time during ongoing resection. The impact of different perfusate components, including lactate and albumin, was retrospectively evaluated. While not intentional, we demonstrate the metabolism of focally delivered lactate via reverse microdialysis from Lactated Ringer’s-containing Page 2 of 17 perfusate into pyruvate. This finding suggested the potential to focally alter the local metabolic microenvironment via reverse microdialysis for future pharmacodynamic studies. Finally, although we did not expect that untargeted global metabolomic analyses would detect multiple drugs, we demonstrate (...truncated)