Interictal Seizure Resections Show Two Configurations of Endothelial Glut1 Glucose Transporter in the Human Blood–Brain Barrier

Abstract

Immunogold electron microscopy was used to analyze and quantify the Glut1 glucose transporter in brain tissue from five patients undergoing surgery for treatment of seizures. Samples were prepared from two different regions of each resection: (1) the most actively spiking epileptogenic site, and (2) the least actively spiking region, as indicated by intraoperative EEG monitoring. Two configurations of endothelial cell Glut1 were observed. About one half of the capillary profiles examined displayed abundant Glut1 immunoreactivity on both luminal and abluminal endothelial membranes. In the remainder of the profiles, reduced Glut1 labeling was seen, but adjacent erythrocyte membranes remained highly Glut1 immunoreactive, suggesting that reduced endothelial Glut1 reactivity was not attributable to method artifacts. Immunogold studies using antisera to human glial fibrillary acidic protein and human serum albumin demonstrated increased quantities of these two epitopes in the extravascular regions in which more EEG spiking activity had been demonstrated. These observations were consistent with the hypotheses that capillary integrity was more compromised, and gliosis was quantitatively increased, in the more actively spiking region of the resection. Altered glucose transporter activity in the blood-brain barrier was characterized by a bimodal Glut1 distribution in which the smaller (type B) endothelial cells displayed low Glut1 immunoreactivity, whereas adjacent (and even contiguous) larger (type A) endothelial cells showed 5- to 10-fold greater expression of membrane Glut1 transporter protein. Because this transporter facilitates glucose entry to the brain, small pericapillary volumes of brain tissue may have quite different concentrations of glucose. We hypothesize that in complex partial seizures and other forms of brain insult, an alteration of blood-brain barrier Glut1 glucose transporter activity is indicated by the appearance of these two subpopulations of endothelial cells. In comparison with previous studies of human brain capillaries in hemangioblastoma and brain injury, endothelial Glut1 density was apparently reduced (interictally) in affected temporal lobes of patients with complex partial seizures.

The Blood-Brain Barrier in Epilepsy

“…In turn, cerebral blood flow rises and large cerebral arteries dilate, which leads to increased blood pressure in brain capillaries, small arteries and veins (Ndode-Ekane et al, 2010), and triggers barrier leakage. Consistent with this, extravasation of blood albumin into the brain was found specifically in regions with more EEG spiking activity in humans (Cornford et al, 1998). However, the duration of increased blood pressure is critical and determines the severity of barrier leakage.…”

“…As a consequence, impaired bloodbrain barrier integrity causes transient barrier leakage, which allows entry of blood borne molecules into the brain (Ndode-Ekane et al, 2010;Seiffert et al, 2004;Sokrab et al, 1989;Van Vliet et al, 2007). It has been shown that seizure duration correlates with reduced barrier function (Cornford & Oldendorf, 1986), and it has been demonstrated that increased blood-brain barrier permeability in epilepsy is limited to anatomically specific brain regions (Bradbury, 1979;Cornford et al, 1998;Nitsch & Klatzo, 1983;Oztas & Sandalci, 1984). Interestingly, brain regions with increased barrier permeability are often anatomically congruent with the brain regions that are implicated in the development and propagation of seizures.…”

Localization of brain endothelial luminal and abluminal transporters with immunogold electron microscopy

“…2), the contiguous larger type A endothelial cells showed a 5-to 10-fold greater expression of membrane GLUT1 transporter protein. 2 The fact that red cells seen in the lumens of both type A and B capillaries exhibited identical concentrations of membrane GLUT1 emphasized that the phenomenon was not an artifact of fixation or immunogold staining (FIG. 2).…”

“…The distance separating the luminal and abluminal capillary membranes is 300 -500 nm in human brain microvessels. 2 The association of abluminal capillary cell membrane with the surrounding glial end-foot processes is equally intimate in normal brain, but it can be reduced 3 or significantly thickened 4 in pathological conditions. The basal lamina is an acellular membrane composed of type IV collagen, fibronectin, and laminin interposed between endothelial cells and astrocytic end feet.…”

Glucose Transporter Distribution in the Vessels of the Central Nervous System of the Axolotl Ambystoma mexicanum (Urodela: Ambystomatidae)

“…that GLUT-1 immunoreactive epitopes in the mammalian CNS are only found at the brain capillary or pericyte. Other electron microscopy studies on human brain have shown with colabeled GLUT-1 and glial fibrillary acidic protein, distinct and separate expression of (10-nm gold) GLUT-1 in the endothelia, and (20-nm gold) GFAP in glial cells (Cornford et al, 1998b;Cornford and Hyman, 2005).…”