Bumetanide Inhibition of the Blood-Brain Barrier Na-K-Cl Cotransporter Reduces Edema Formation in the Rat Middle Cerebral Artery Occlusion Model of Stroke

Department of Physiology and Membrane Biology, School of Medicine, University of California, Davis 95616, USA.
Journal of Cerebral Blood Flow & Metabolism (Impact Factor: 5.41). 10/2004; 24(9):1046-56. DOI: 10.1097/01.WCB.0000130867.32663.90
Source: PubMed


Increased transport of Na+ across an intact blood-brain barrier (BBB) participates in edema formation during the early hours of cerebral ischemia. In previous studies, the authors showed that the BBB Na-K-Cl cotransporter is stimulated by factors present during ischemia, suggesting that the cotransporter may contribute to the increased brain Na+ uptake in edema. The present study was conducted to determine (1) whether the Na-K-Cl cotransporter is located in the luminal membrane of the BBB, and (2) whether inhibition of the BBB cotransporter reduces brain edema formation. Perfusion-fixed rat brains were examined for cotransporter distribution by immunoelectron microscopy. Cerebral edema was evaluated in rats subjected to permanent middle cerebral artery occlusion (MCAO) by magnetic resonance diffusion-weighted imaging and calculation of apparent diffusion coefficients (ADC). The immunoelectron microscopy studies revealed a predominant (80%) luminal membrane distribution of the cotransporter. Magnetic resonance imaging studies showed ADC ratios (ipsilateral MCAO/contralateral control) ranging from 0.577 to 0.637 in cortex and striatum, indicating substantial edema formation. Intravenous bumetanide (7.6-30.4 mg/kg) given immediately before occlusion attenuated the decrease in ADC ratios for both cortex and striatum (by 40-67%), indicating reduced edema formation. Bumetanide also reduced infarct size, determined by TTC staining. These findings suggest that a luminal BBB Na-K-Cl cotransporter contributes to edema formation during cerebral ischemia.

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    • "Then the TTC stained slices were photoed by Olympus fe-240 digital camera (Pooher Photoelectric Technology Co., Ltd., Shanghai, China) and analyzed by Image Analysis Software (Image-pro Plus 6.0, Media Cybernetics, Inc., Bethesda, MD, USA). The infarction volume was presented as a percentage of the total ipsilateral hemispheric volume which can be calculated by following equation: [(contralateral hemispheric volume − ipsilateral hemispheric volume)/contralateral hemispheric volume] × 100% [18, 19]. "
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    ABSTRACT: 170 SD rats were randomly divided to five groups. Rats in model group, no-acupuncture group, and acupuncture group were subjected to MCAO surgery. Acupuncture group received 3 consecutive acupuncture treatments at a parameter that deep in 2 mm towards apex nasi and thrust/lifted at 3 times per second for 1 minute, while model group and no-acupuncture group were no-intervention control groups. Serious neural functional damage and sharp decrease of cerebral blood flow, obvious infarction volume, increased nestin mRNA expression, and immunopositive cells population (nestin(+), BrdU(+) and nestin/BrdU(+)) were found in MCAO rats which had not been observed in normal group and sham-operated group. However, the damage was attenuated by rat's "self-healing" capacity 3 days after MCAO. And the "self-healing" capacity can be strengthen by acupuncture treatment through increasing cerebral blood flow, neurogenesis, and regulation of gene transcription or GSK-3β and PP2A expression. In conclusion, the present study indicates that the underlying mechanism of acupuncture treatment on neural functional damage caused by focal ischemia injury is a multiple interaction which may involve improved cerebral blood supply, neurogenesis, and regulation of gene transcription or GSK-3β and PP2A expression in MCAO rats.
    Evidence-based Complementary and Alternative Medicine 07/2014; 2014:962343. DOI:10.1155/2014/962343 · 1.88 Impact Factor
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    • "It has been found that sodium, chloride and other solutes influx intracellularly caused by up-regulated NKCC1 results in cell swelling [12-14]. This is why NKCC1 plays an important role in astrocyte swelling/cerebral edema in ischemia and trauma [15,16]. Some studies have shown that administration of the NKCC1 blocker bumetanide can attenuate the cell swelling and injury, suggesting that sodium and chloride transport via NKCC1 is involved in ischemia-induced cell swelling and injury [17,18]. "
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    ABSTRACT: Background Hypertonic saline (HS) has been successfully used clinically for treatment of various forms of cerebral edema. Up-regulated expression of Na-K-Cl Cotransporter 1 (NKCC1) and inflammatory mediators such as tumor necrosis factor alpha (TNF-α) and interleukin-1 beta (IL-1β) has been demonstrated to be closely associated with the pathogenesis of cerebral edema resulting from a variety of brain injuries. This study aimed to explore if alleviation of cerebral edema by 10% HS might be effected through down-regulation of inflammatory mediator expression in the microglia, and thus result in decreased NKCC1 expression in astrocytes in the cerebral cortex bordering the ischemic core. Methods The Sprague-Dawley (SD) rats that underwent right-sided middle cerebral artery occlusion (MCAO) were used for assessment of NKCC1, TNF-α and IL-1β expression using Western blotting, double immunofluorescence and real time RT-PCR, and the model also was used for evaluation of brain water content (BWC) and infarct size. SB203580 and SP600125, specific inhibitors of the p38 and JNK signaling pathways, were used to treat primary microglia cultures to determine whether the two signaling pathways were required for the inhibition of HS on microglia expressing and secreting TNF-α and IL-1β using Western blotting, double immunofluorescence and enzyme-linked immunosorbent assay (ELISA). The effect of TNF-α and IL-1β on NKCC1 expression in primary astrocyte cultures was determined. In addition, the direct inhibitory effect of HS on NKCC1 expression in primary astrocytes was also investigated by Western blotting, double immunofluorescence and real time RT-PCR. Results BWC and infarct size decreased significantly after 10% HS treatment. TNF-α and IL-1β immunoexpression in microglia was noticeably decreased. Concomitantly, NKCC1 expression in astrocytes was down-regulated. TNF-α and IL-1β released from the primary microglia subjected to hypoxic exposure and treatment with 100 mM HS were decreased. NKCC1 expression in primary astrocytes was concurrently and progressively down-regulated with decreasing concentration of exogenous TNF-α and IL-1β. Additionally, 100 mM HS directly inhibited NKCC1 up-regulation in astrocytes under hypoxic condition. Conclusions The results suggest that 10% HS alleviates cerebral edema through inhibition of the NKCC1 Cotransporter, which is mediated by attenuation of TNF-α and IL-1β stimulation on NKCC1.
    Journal of Neuroinflammation 06/2014; 11(1):102. DOI:10.1186/1742-2094-11-102 · 5.41 Impact Factor
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    • "The ion transporters identified in the present study may be inserted into the current model of blood–brain barrier transport as shown in Fig. 8. The primary route for Na+ entails entry from the blood via NKCC1 [26, 54, 72]; however some must also enter in conjunction with HCO3− transport. Net exit of Na+ into the brain occurs primarily via Na+, K+–ATPases [5, 6, 25, 26, 48, 65], but possibly some Na+ could exit by cotransport with HCO3−. "
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    ABSTRACT: Ions and water transported across the endothelium lining the blood-brain barrier contribute to the fluid secreted into the brain and are important in maintaining appropriate volume and ionic composition of brain interstitial fluid. Changes in this secretion process may occur after stroke. The present study identifies at transcript and protein level ion transporters involved in the movement of key ions and examines how levels of certain of these alter following oxidative stress. Immunohistochemistry provides evidence for Cl(-)/HCO3 (-) exchanger, AE2, and Na(+), HCO3 (-) cotransporters, NBCe1 and NBCn1, on brain microvessels. mRNA analysis by RT-PCR reveals expression of these transporters in cultured rat brain microvascular endothelial cells (both primary and immortalized GPNT cells) and also Na(+)/H(+) exchangers, NHE1 (primary and immortalized) and NHE2 (primary cells only). Knock-down using siRNA in immortalized GPNT cells identifies AE2 as responsible for much of the Cl(-)/HCO3 (-) exchange following extracellular chloride removal and NHE1 as the transporter that accounts for most of the Na(+)/H(+) exchange following intracellular acidification. Transcript levels of both AE2 and NHE1 are increased following hypoxia/reoxygenation. Further work is now required to determine the localization of the bicarbonate transporters to luminal or abluminal membranes of the endothelial cells as well as to identify and localize additional transport mechanisms that must exist for K(+) and Cl(-).
    Pflügers Archiv - European Journal of Physiology 09/2013; 466(5). DOI:10.1007/s00424-013-1342-9 · 4.10 Impact Factor
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