AN ORGANOTYPICAL IN-VITRO MODEL OF THE LIVER PARENCHYMA FOR UPTAKE STUDIES OF DIAGNOSTIC MR RECEPTOR AGENTS

Testing of receptor-specific MR contrast agents targeted to the liver is hampered by a shortage of viable in vitro models with in vivo-like hepatocellular morphology. Coated pits are ultrastructural signs of an active receptor-mediated endocytosis in hepatocytes. Expression of co ated pits by matrix overlaid hepatocytes was studied by transmission e lectron microscopy. Binding of a rhodaminated asialoglycoprotein recep tor agent (MION-ASF-rh) was assessed by fluorescence microscopy. Fluor escence of cells exposed to MION-ASF-rh was 2.1 times above autofluore scence. Competitive blockage of MION-ASF-rh with D(+)-galactose reduce d fluorescent light emission to a level of 58% of MION-ASF-rh-induced fluorescence. After preincubation with the hepatotoxin CCl4 a dose-dep endent decrease in fluorescent light emission resulted. Hepatocytes ma intained a homogeneous cell surface expression, with microprojections, coated pits, and vesicles on both sinusoidal surfaces. Matrix overlai d primary hepatocytes constitute a viable, morphologically and functio nally differentiated model. This model can be used to study receptor b inding, uptake, and blockage of diagnostic magnetopharmaceuticals unde r controlled conditions.