Practical method for endothelial glycocalyx imaging in formalin-fixed, paraffin-embedded tissues in vascular pathology.

Abstract

The endothelial glycocalyx (eGCX), a delicate carbohydrate-rich layer coating the vascular endothelium, critically regulates vascular homeostasis, controlling permeability, thrombosis, and inflammation. Despite its fundamental importance, assessing the morphology of the eGCX remains technically challenging because of its fragile structure, which collapses during conventional fixation. Existing visualization methods require complex preparation, expensive equipment, and fresh tissues, severely limiting accessibility and clinical applicability. Here, we present a practical approach for visualizing and semi-quantitatively phenotyping the eGCX using formalin-fixed, paraffin-embedded (FFPE) tissue sections prepared via specialized Alcian blue fixation, followed by strategic integration of silver enhancement staining and low-vacuum scanning electron microscopy. The proposed method enabled robust visualization of eGCX across multiple vascular beds, including brain parenchymal vessels, choroid plexus fenestrated capillaries, and retinal vasculature, along with a thickness-based index suitable for between-condition comparisons among FFPE sections. The technique demonstrated high sensitivity in detecting pathological alterations, evidenced by near-complete eGCX loss in retinal vein occlusion models with significant reductions in thickness and lectin fluorescence intensity. Finally, the workflow was successfully applied to human colorectal surgical specimens processed via immediate Alcian blue immersion fixation, enabling visualization of vascular eGCX in FFPE clinical sections. Overall, these findings support an accessible FFPE-compatible approach for wide-field eGCX imaging and pathology-oriented phenotyping.