Fig. 3
From: Neurological manifestations of SARS-CoV-2: complexity, mechanism and associated disorders
Schematic representation of methods of transport across the blood–brain barrier (i) Paracellular transport, which is obstructed by transmembrane proteins and tight junctions. The enzymes released by endothelial cells deactivate the molecules transported by paracellular means. (ii) Transcellular diffusion of hydrophobic and lipophilic molecules with the help of proteins, such as claudins. (iii) Transcytosis aided by intracellular vesicle trafficking. (iv) Carrier-mediated transcytosis with the help of transporter proteins. Transport proteins mediated transfer without making use of endocytosis and exocytosis. (vi) Multidrug resistance efflux pumps rarely undergo transport from inside to outside of the blood–brain barrier [53]