Organ distribution of liposomal formulations following intracarotid infusion in rats

The blood-brain barrier (BBB) limits the ability of many hydrophilic solutes to pass from the circulatory system into the nervous system and significantly restricts brain drug delivery. This study examined brain uptake of liposomal formulations in rats. Radiolabeled liposomes less than 1 micron in diameter, prepared from phosphatidylcholine, cholesterol and containing p-aminophenyl-alpha-mannopyranoside or sulfatide, or covalently linked to cationized albumin were injected into the right carotid arteries of rats and organ distribution determined 10 min and 1 h after injection. In all formulations, liposomal retention in brain did not exceed one-tenth of 1% of the injected dose. It seems unlikely that liposomes can significantly bind to or cross the BBB; however, apparent brain uptake could result from liposomal entrapment in the small capillaries of the brain by liposomes larger than 1 micron in diameter.