Conditionally immortalized cell lines as a new in vitro model for the study of barrier functions

Conditionally immortalized brain and retinal capillary endothelial and chor oid plexus epithelial cell lines were established from a transgenic rat (Tg rat) and mouse (Tg mouse) harboring the temperature-sensitive simian virus 40 (ts SV 40) large T-antigen. These cell lines exhibit temperature-sensit ive cell growth due to the expression of ts SV 40 large T-antigen. Mouse br ain (TM-BBB) and rat brain (TR-BBB) and rat retinal (TR-iBRB) capillary end othelial cell lines appear to have a spindle-fiber shaped morphology and ex hibit the typical endothelial markers, such as von Willebrand factor and ac etylated low-density lipoprotein uptake. These cell lines express in vivo i nflux and efflux transporters, such as P-glycoprotein (P-gp) and GLUT1, whi ch is capable of 3-O-methyl-D-glucose transport. TM-BBB cells are able to u ndergo efflux transport of cyclosporin A, which is a substrate for P-gp tra nsport activity. They may also express oatp2 and exhibit dehydroepiandroste rone sulfate and digoxin uptake activity. TR-BBB cells express the mRNA of multidrug resistance associated protein 1 (MRP1) and a large neutral amino acid transporter, which consists of LAT1 and 4F2hc. TR-iBRB cells exhibit p H-dependent L-lactic acid transport activity and express the mRNA of monoca rboxylate transporter (MCT) 1 and 2. The choroid plexus epithelial cell lin e (TR-CSFB) has polygonal cell morphology, expresses the typical choroid pl exus epithelial cell marker, transthyretin, and has Na+,K+-ATPase located o n the apical side. TR-CSFB cells also exhibit amino acid transport activity which has been observed in vivo. These barrier cell lines established from the Tg rat and Tg mouse have in vitro transport functions and are good in vitro models for drug transport to the brain and retina and as a screen for drugs which might be capable of delivery to the brain and retina.