Abstract

Glutamate is the major excitatory amino acid in the vertebrate brain, playing an important role in most brain functions. It exerts its activity through plasma membrane receptors and transporters, expressed both in neurons and glia cells. Overstimulation of neuronal glutamate receptors is linked to cell death in a process known as excitotoxicity, that is prevented by the efficient removal of the neurotransmitter through glutamate transporters enriched in the glia plasma membrane and in the components of the blood–brain barrier (BBB). Silica nanoparticles (SiO₂-NPs) have been widely used in biomedical applications and directed to enter the circulatory system; however, little is known about the potential adverse effects of SiO₂-NPs exposure on the BBB transport systems that support the critical isolation function between the central nervous system (CNS) and the peripheral circulation. In this contribution, we investigated the plausible SiO₂-NPs-mediated disruption of the glutamate transport system expressed by BBB cell components. First, we evaluated the cytotoxic effect of SiO₂-NPs on human brain endothelial (HBEC) and Uppsala 87 Malignant glioma (U-87MG) cell lines. Transport kinetics were evaluated, and the exposure effect of SiO₂-NPs on glutamate transport activity was determined in both cell lines. Exposure of the cells to different SiO₂-NP concentrations (0.4, 4.8, 10, and 20 µg/ml) and time periods (3 and 6 h) did not affect cell viability. We found that the radio-labeled D-aspartate ([³H]-D-Asp) uptake is mostly sodium-dependent, and downregulated by its own substrate (glutamate). Furthermore, SiO₂-NPs exposure on endothelial and astrocytes decreases [³H]-D-Asp uptake in a dose-dependent manner. Interestingly, a decrease in the transporter catalytic efficiency, probably linked to a diminution in the affinity of the transporter, was detected upon SiO₂-NPs. These results favor the notion that exposure to SiO₂-NPs could disrupt BBB function and by these means shed some light into our understanding of the deleterious effects of air pollution on the CNS.

中文翻译：

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二氧化硅纳米颗粒减少血脑屏障成分中谷氨酸的吸收

摘要

谷氨酸是脊椎动物大脑中主要的兴奋性氨基酸，在大多数大脑功能中发挥着重要作用。它通过在神经元和神经胶质细胞中表达的质膜受体和转运蛋白发挥其活性。神经元谷氨酸受体的过度刺激与兴奋性毒性过程中的细胞死亡有关，通过富含神经胶质质膜和血脑屏障（BBB）成分的谷氨酸转运蛋白有效去除神经递质可以防止这种情况。二氧化硅纳米颗粒（SiO ₂ -NPs）已广泛应用于生物医学应用并直接进入循环系统；_{然而，关于 SiO 2} -NP 暴露对 BBB 运输系统的潜在不利影响知之甚少，而 BBB 运输系统支持中枢神经系统 (CNS) 和外周循环之间的关键隔离功能。在这篇文章中，我们研究了 SiO ₂ -NPs 介导的 BBB 细胞成分表达的谷氨酸转运系统的可能破坏。_{首先，我们评估了 SiO 2} -NPs 对人脑内皮 (HBEC) 和乌普萨拉 87 恶性胶质瘤 (U-87MG) 细胞系的细胞毒性作用。评估了两种细胞系中的转运动力学，并确定了 SiO ₂ -NP 的暴露对谷氨酸盐转运活性的影响。将细胞暴露于不同的 SiO ₂ -NP 浓度（0.4、4.8、10 和 20 µg/ml）和时间段（3 和 6 小时）不会影响细胞活力。我们发现放射性标记的 D-天冬氨酸 ([ ³ H]-D-Asp) 的摄取主要依赖于钠，并受到其自身底物（谷氨酸）的下调。此外，内皮细胞和星形胶质细胞上的SiO ₂ -NPs暴露以剂量依赖性方式降低[ ^{3 H]-D-Asp摄取。}_{有趣的是，在 SiO 2} -NP上检测到转运蛋白催化效率的降低，这可能与转运蛋白亲和力的降低有关。这些结果支持这样的观点，即暴露于 SiO ₂ -NPs 可能会破坏 BBB 功能，并通过这些方式为我们理解空气污染对中枢神经系统的有害影响提供一些线索。