Cysteine Donor-Based Brain-Targeting Prodrug: Opportunities and Challenges

Table 1

Transporters highly expressed at the BBB.

Transporter	BBB localization	Endogenous substrate	Reference
Glucose transporter 1 (GLUT1)	Luminal and abluminal membranes of capillary endothelial cells	Glucose and some other hexoses	[37–39]
Sodium-vitamin C transporter 2 (SVCT2)	Surface of choroid plexus epithelium cells	Vitamin C	[31, 40]
Large neutral amino acid transporter 1 (LAT1)	Luminal and abluminal membranes of capillary endothelial cells and brain parenchyma cells	Large and branched neutral amino acids	[41–43]
Cationic amino acid transporter 1 (CAT1)	Astrocytes, oligodendrocytes, endothelial cells, and neurons	Arginine, lysine, and ornithine	[44, 45]
Monocarboxylic acid transporter 1 (MCT1)	Luminal and abluminal membranes of capillary endothelial cells	Lactic and pyruvic acids	[46, 47]
Organic cation/carnitine transporter 2 (OCTN2)	Basolateral membrane and cytoplasmic region	L-carnitine	[36, 48]
Concentrative nucleoside transporter 2 (CNT2)	Brain capillary endothelium	Adenosine	[49]
Choline transporters (CHTs)	Cholinergic neurons	Choline	[50, 51]
Excitatory amino acid transporters (EAATs)	Abluminal membranes of endothelial cells, astrocytes, and neurons	Glutamate and cysteine	[52, 53]