Cerebrovascular glycocalyx damage and microcirculation impairment in patients with temporal lobe epilepsy

Abstract

Temporal lobe epilepsy (TLE) is increasingly associated with blood-brain barrier dysfunction and microvascular alterations, yet the pathophysiological link is missing. An important barrier function is exerted by the glycocalyx, a gel-like layer coating the endothelium. To explore such associations, we used intraoperative videomicroscopy to quantify glycocalyx and microcirculation properties of the neocortex and hippocampus of 15 patients undergoing resective brain surgery as treatment for drug-resistant TLE, and 15 non-epileptic controls. Fluorescent lectin staining of neocortex and hippocampal tissue was used for blood vessel surface area quantification. Neocortical perfused boundary region, the thickness of the glycocalyx' impaired layer, was higher in patients (2.64 ± 0.52 µm) compared to controls (1.31 ± 0.29 µm), P < 0.01, indicative of reduced glycocalyx integrity in patients. Moreover, erythrocyte flow velocity analysis revealed an impaired ability of TLE patients to (de-)recruit capillaries in response to changing metabolic demands (R² = 0.75, P < 0.01), indicating failure of neurovascular coupling mechanisms. Blood vessel quantification comparison between intraoperative measurements and resected tissue showed strong correlation (R² = 0.94, P < 0.01). This is the first report on in vivo assessment of glycocalyx and microcirculation properties in TLE patients, confirming the pivotal role of cerebrovascular changes. Further assessment of the cerebral microcirculation in relation to epileptogenesis might open avenues for new therapeutic targets for drug-resistant epilepsy.

Keywords: Blood-brain barrier; capillary recruitment; glycocalyx; microcirculation; temporal lobe epilepsy.

Figure 1.

Perfused Boundary Region (PBR) values in µm. (a) comparison of cortical PBR values between patients and controls. The significantly higher PBR values in patients are indicative of a more damaged glycocalyx and (b) comparison of cortical and hippocampal PBR values in patients.

Figure 2.

Vascular density per vessel diameter class. (a) cortical vascular density of patients and controls; there were no significant differences detected in any of the diameter classes, albeit a trend can be observed for diameter classes 5 µm (+74%), 6 µm (+58%), and 7 µm (+49%) in patients compared to controls and (b) comparison of patient cortical and patient hippocampal vascular density; no significant difference was observed.

Figure 3.

Scatter dot plots and linear regression of cortical V_RBC in capillaries (diameter classes 4–7 µm) plotted against cortical V_RBC in feed vessels (diameter classes 10–25 µm) of patients and controls. A strong dependency between cortical capillaries and feed vessels was found only in patients.

Figure 4.

Capillary recruitment capacity of the microcirculation in patients and controls. A clear decrease in capillary recruitment capacity was found in the cortical blood vessels of patients compared to controls. Hippocampal recruitment capacity was high (96%), though no control data is available.

Figure 5.

Example of a visualized Ulex Europaeus Agglutinin I (UEA-I) lectin-stained neocortical sample. Left before and right after automated annotation of vessels (purple delineations). Inset image on the left shows the entire slice and magnified area (red box).

Figure 6.

Scatter dot plot and linear regression of Cerebral Blood Surface Area (CBSA) and Blood vessel Stained Surface Area (BSSA). Quantification of blood vessel results are in 10⁻² µm²/µm². Linear regression showing a good fit (R² = 0.94). The function describing the relation between these two measurements shows a 3.01 times higher blood vessel surface area count.