IN-VIVO UPTAKE OF LECITHIN-COATED POLYSTYRENE BEADS BY RAT HEPATOCYTES AND SINUSOIDAL ENDOTHELIAL-CELLS

Background: While phagocytosis by Kupffer cells (stellate perisinusoid al macrophages) is well known and that by endothelial cells also is th ought to occur under certain conditions, the uptake of large particles by hepatocytes has not been well studied. We reported previously the selective phagocytic uptake of material by hepatocytes using egg lecit hin-coated silicon particles. In the present work, we describe more pr ecisely this process following the injection of lecithin-coated polyst yrene beads. Additionally, we consider the possible significance of th e transcytotic action by endothelial cells. Methods: Polystyrene latex beads (240 nm in diameter) composed of two layers of polystyrene and methyl methacrylate with a central void cavity and diameter of 140 nm were injected into male Wister-Imamichi rats, The injections were admi nistered through the hepatic portal vein in a volume of 3 ml (concentr ation of the lecithin-coated or uncoated beads was 2 mg/ml), Controls received the lecithin alone at a concentration of 2 mg/ml, Liver sampl es were taken 5, 10, or 15 min after injection, fixed, and processed f or ultrastructural analysis. Results: Both lecithin-coated and noncoat ed beads were mainly incorporated in the Kupffer cells as well as in t he endothelial cells. Bristle-coated invaginations were observed in th e uptake by both cell types; however, noncoated invaginations were als o active in the endothelial cells, especially on the surface facing th e perisinusoidal space of Disse. Only coated beads were observed withi n the space or in the hepatocytes. Once taken up by the hepatocytes, t he lecithin-coated beads were found either within lysosomes or in a fr ee state in the cytoplasm. Conclusions: Uptake of 240 nm lecithin-coat ed polystyrene beads was observed by Kupffer cells, endothelial cells and hepatocytes. These beads were considered to be transported across the endothelial cells by transcytosis, Pseudopodia and bristle-coated invaginations were not employed by the hepatocytes when incorporating the beads. (C) 1996 Wiley-Liss, Inc.