Metabolic consequences of inflammatory disruption of the blood-brain barrier in an organ-on-chip model of the human neurovascular unit

Abstract

BackgroundUnderstanding blood-brain barrier responses to inflammatory stimulation (such as lipopolysaccharide mimicking a systemic infection or a cytokine cocktail that could be the result of local or systemic inflammation) is essential to understanding the effect of inflammatory stimulation on the brain. It is through the filter of the blood-brain barrier that the brain responds to outside influences, and the blood-brain barrier is a critical point of failure in neuroinflammation. It is important to note that this interaction is not a static response, but one that evolves over time. While current models have provided invaluable information regarding the interaction between cytokine stimulation, the blood-brain barrier, and the brain, these approaches—whether in vivo or in vitro—have often been only snapshots of this complex web of interactions.MethodsWe utilize new advances in microfluidics, organs-on-chips, and metabolomics to examine the complex relationship of inflammation and its effects on blood-brain barrier function ex vivo and the metabolic consequences of these responses and repair mechanisms. In this study, we pair a novel dual-chamber, organ-on-chip microfluidic device, the NeuroVascular Unit, with small-volume cytokine detection and mass spectrometry analysis to investigate how the blood-brain barrier responds to two different but overlapping drivers of neuroinflammation, lipopolysaccharide and a cytokine cocktail of IL-1β, TNF-α, and MCP1,2.ResultsIn this study, we show that (1) during initial exposure to lipopolysaccharide, the blood-brain barrier is compromised as expected, with increased diffusion and reduced presence of tight junctions, but that over time, the barrier is capable of at least partial recovery; (2) a cytokine cocktail also contributes to a loss of barrier function; (3) from this time-dependent cytokine activation, metabolic signature profiles can be obtained for both the brain and vascular sides of the blood-brain barrier model; and (4) collectively, we can use metabolite analysis to identify critical pathways in inflammatory response.ConclusionsTaken together, these findings present new data that allow us to study the initial effects of inflammatory stimulation on blood-brain barrier disruption, cytokine activation, and metabolic pathway changes that drive the response and recovery of the barrier during continued inflammatory exposure.Electronic supplementary materialThe online version of this article (doi:10.1186/s12974-016-0760-y) contains supplementary material, which is available to authorized users.

Tissue chips – innovative tools for drug development and disease modeling

“…To address this, as well as to assess the ability of candidate therapeutics for treatment of brain disorders, a number of microfluidic devices have been developed to model the BBB 51 . One of these systems from the VIBRE Center at Vanderbilt consists of chambers of neurons cultured separately from chambers of endothelial cells, to mimic the neurovascular environment and enable study of BBB function and dysfunction 25, 26 .…”

“…Together with the flexibility with complexity and design, there is a growing interest in MPS development, and support from governmental funding agencies 13, 14 and private industry has led to a wide, and ever-expanding, range of organ tissues being modeled. These include liver 15, 16 , skin 17 , heart 18–20 , vasculature 21, 22 , brain 23, 24 , blood-brain barrier 25, 26 , bone 27 , the female reproductive system 28–30 , gut 31 , muscle 32 , kidney 33, 34 , pancreas 35, 36 , and cornea 37 , amongst others (see Bhatia and Ingber 38 ).…”

Fitting tissue chips and microphysiological systems into the grand scheme of medicine, biology, pharmacology, and toxicology

“…In recent MPS studies, we are seeing functional measurements such as contractility, calcium signaling, and electrophysiological responses of cardiac and skeletal muscle, 37,[69][70][71][72][73][74][75] electrical resistance and molecular permeability of barriers, [76][77][78][79][80][81][82] and metabolomic responses to inflammatory challenges. 78 In this issue, the Parker group uses a variety of measures, including gene expression profiling, to quantify factors that affect maturation of neonatal rat cardiomyocytes into a more mature phenotype. 83 As TCs continue to recapitulate more tissue-level functions, we will see more functional measurements that could not be possible with monolayer monocultures.…”

“…The MPS community should consider comparing, for example, a mouse with a mouse-on-a-chip to confirm that the appropriate physiology is being recapitulated and to inform the extrapolation from existing animal assays to in vitro and in vivo human studies, as discussed by Ewart et al 46 Knudsen et al 47 85 Metabolomics is rapidly moving into prominence as the instrumentation improves and the databases expand, but the annotation of the databases and the interpretation of the resulting metabolic and signaling networks have not yet proven useful to many potential end users. Metabolomic analysis techniques are just now being applied to OoCs, 78 and ultimately the MPS effort could benefit from untargeted multiomics studies of mechanism of action. 86 As the analytical approaches are broadened, it will be important to develop mathematical methodologies to interpret data from TCs and MPS homunculi.…”

PEG-<em>b</em>-(PELG-<em>g</em>-PLL) nanoparticles as TNF-&alpha; nanocarriers: potential cerebral ischemia/reperfusion injury therapeutic applications

“…Substances produced by immune responses (such as inflammatory mediators) are able to cross the BBB and affect central nervous system function. [43][44][45] These data indicate that cytokines often cross the BBB with relatively high efficacy. IL-4 can promote activation of type 2 macrophages, which is usually coupled with secretion of IL-10, which in turn results in diminution of pathological inflammation.…”