Advances in Understanding Stroke-Induced Blood-Brain Barrier Disruption: Pathophysiology and Inspection Technique
At a glance
Introduction of Stroke-Induced Blood-Brain Barrier Disruption
The blood-brain barrier (BBB) is integral microvasculature of brain which preserves CNS homeostatic, its unique properties protects the brain from damage compounds. Disruption of the BBB and increased vascular permeability are central processes in various neuropathological conditions including stroke. Following stroke traces the BBB breakdown that causes a number of factors including cytotoxic edema, vasogenic cerebral edema and hemorrhagic transformation. Consequently, the majority of current research is aimed at describing how BBB breakdown occurs after stroke and establishing therapeutic approaches to decrease secondary clinicopathologic effects stemming from post-stroke disruption of the BBB.
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Pathophysiology of BBB Dysfunction in Stroke
A key feature of stroke is the associated destruction of the BBB, which begins as a result of ischemia but worsens with prolonged inadequate perfusion. Major contributors to this deterioration include nutrient deprivation (particularly hypoxia and glucose deprivation) and altered mechanotransduction, as evidenced by the persistence of BBB permeability even after partial restoration of blood flow.
Mechanisms of BBB damage during stroke include modification of tight junction (TJ) proteins, modulation of transporter protein expression, and inflammatory damage, ultimately leading to disruption of ion homeostasis and transporter protein function in the brain. To better understand the increase in BBB permeability after stroke, we describe these mechanisms in detail.
Junctional Proteins
The general increase in BBB permeability after stroke is mainly due to changes of junctional proteins that are a considerable part of our research. The first change that occurs to junctional protein expression is mediated by matrix metalloproteinases (MMPs) and reactive oxygen species (ROS). Moreover, inflammatory factors TNF-α and IL-1β combined with neutrophils are also recognized in contributing to the maintenance of BBB integrity following stroke. Consequently, interest has grown in therapeutic strategies to target these factors as a means of protecting BBB integrity.
Endogenous BBB Transporters
Changes in the expression and function of endogenous BBB transporters also affect stroke-induced BBB permeability and resulting pathophysiological processes, such as edema. The major BBB transporters associated with stroke include glucose transporters and ion transporters.
Other Mechanisms
There are also other molecules, for example the integrins and adhesion molecule regulating BBB permeability to a lesser extent following stroke. Additionally, endothelial cell adhesion molecules (such as intercellular adhesion molecule 1; ICAM-1) are known to contribute in the transport regulations within BBB largely through mediation of leukocyte transendothelial migration.
Fig.1. Possible microglia/macrophages polarization signaling following stroke and response to BBB. (Kassner, et al., 2015)
Assessment of BBB Permeability in Stroke
An increasing number of preclinical and clinical studies are incorporating assessment of BBB disruption into their study design. Several methods are available to assess BBB disruption. These methods cover a wide range of temporal and spatial resolutions and allow for the simultaneous assessment of cell morphology, protein expression and localization, cellular electrophysiology, and overall neural function. Understanding the characteristics and limitations of BBB injury assessment methods is essential for designing effective studies.
Fig.2. Representative images depicting methods of assessing BBB disruption in preclinical stroke models. (Okada, et al., 2020)
Assessment of BBB Permeability in In-Vitro Studies
Measurement of transendothelial electrical resistance (TEER)
TEER is a widely used technique to assess the integrity of tight junctions in cultured endothelial monolayers TEER measurements involve assessing the electrical resistance of cell monolayers consisting of brain endothelial cell lines (e.g., rat RBE4, rat GP8, and human hCMEC/D3) and co-cultured models of pericytes, and astrocytes and brain endothelial cell to examine BBB function in TEER. The main advantage of TEER is that it is a non-invasive method that allows continuous monitoring of living cells at all stages from BBB disruption to post-stroke repair.
BBB organoids are used for permeability assays and drug pharmacokinetic studies
BBB organoids consist of primary human brain endothelial cells, pericytes, and astrocytes, which have better characteristics of BBB integrity, including tight junctions and adherens junctions, as well as more life-like functions related to the expression of molecular transporter proteins and drug efflux pumps, compared to traditional static culture systems.
Assessment of BBB Permeability in In-Vivo Studies
| Assessment Methods | Details | Advantages | Disadvantages |
|---|---|---|---|
| Measurement of extravasated Evans blue dye | Extravasated Evans blue-albumin complex is identified macroscopically and as red fluorescence microscopically, and is measured by colorimetric and spectrophotometric methods. |
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| Immunohistochemical or immunofluorescence staining of blood components | This method measures the leakage of blood components from the intravascular area into the brain parenchyma. Albumin, fibrinogen, and immunoglobulins (Igs; IgG and IgM) staining are used for this method. |
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| Measurement of transendothelial leukocyte migration | By measuring the leakage of radioisotope-labeled sucrose and inulin to evaluate the BBB disruption. | Can show the severity of brain injury after stroke as well as BBB disruption. | This method may be influenced depending on the function of leukocyte to cross into the brain parenchyma. |
Assessment of BBB Disruption in Humans
| Assessment Methods | Details | Advantages | Disadvantages |
|---|---|---|---|
| Dynamic Contrast-enhanced Computed Tomography (DCE-CT) | Images are acquired by scanning during an intravenous injection of an iodinated contrast agent, which cannot pass the intact BBB. | Can scan faster than other imaging modalities | Include risks related to radiation, and adverse reactions due to an injection of iodinated contrast agent. |
| DCE-Magnetic Resonance Imaging (MRI) | This method commonly uses contrast agents containing gadolinium. The MR images acquired by dynamic T1-weighted imaging (T1WI) following a contrast agent injection reflect the quantitative extravasation caused by the BBB breakdown. |
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Longer scanning time. It takes up to 1 h for processing full brain permeability by DCE-MRI scans. |
| Single Photon Emitting Computed Tomography (SPECT) | 99mTc-diethylenetriaminepentaacetic acid (99mTc-DTPA) brain scintigraphy is the common technique for the assessment of BBB integrity. | 99mTc-DTPA SPECT is more cost-effective compared with DCE-MRI. | The low anatomical resolution and ionizing agent. |
BBB disruption is a pathological change causing brain edema, hemorrhagic transformation, and neuroinflammation after stroke. Stroke-induced neuroinflammation and apoptosis of endothelial cells are involved in BBB disruption. Thus, BBB disruption is considered as a major factor to determine functional outcome and an important therapeutic target to prevent further brain injury in acute stroke.
- Okada, T., et al. (2020). The stroke-induced blood-brain barrier disruption: current progress of inspection technique, mechanism, and therapeutic target. Current Neuropharmacology, 18(12), 1187-1212.
- Kassner, A., & Merali, Z. (2015). Assessment of blood–brain barrier disruption in stroke. Stroke, 46(11), 3310-3315.
