Transport, utilization and biliary secretion of lysophosphatidylcholine in the rat liver

The hepatic uptake, transport and utilization of plasma lysophosphatidylcholine (lysoPC) and its contribution to biliary lipid secretion have been investigated in bile-fistula rats. The animals were given a single intravenous dose of sn-1-[1-14C]palmitoyl-lysoPC, under constant intravenous sodium taurocholate infusion (1 mumol/min), and the fate of the label was followed in blood, bile and liver for up to 3 h. The livers were excised at given time points, extracted and/or homogenized to determine the lipid distribution and subcellular location of radioactivity. LysoPC was rapidly cleared from plasma, though a consistent fraction of the label persisted in plasma over the experimental time-period in the form of either lysoPC or PC. Recovery of radioactivity in the liver varied from 15.6% after 5 min to 19.5% after 3 h. Hepatic lysoPC underwent rapid microsomal acylation to form specific PC molecular species (mainly 16:0-20:4 and, to a lesser extent, 16:0-18:2 and 16:0-16:1). Ultrafiltration, dialysis and gel-chromatographic analyses of cytosolic fractions (post 105,000 X g supernatants) indicated that lysoPC is transported to the site of acylation mostly as a macromolecular aggregate with an approx. Mr of 14,400. Small amounts of radioactivity were secreted into bile over 3 h (20% in the form of lysoPC and the remainder as 16:0-18:2 and 16:0-20:4 PC species). Plasma lysoPC, taken up by the liver, is mostly transported by a cytosolic carrier with a molecular weight close to fatty-acid-binding proteins; it then enters a distinct acylation pathway, selective for some polyunsaturated-PC species and does not contribute significantly to biliary secretion, either directly, or through its products.     

Nonparenchymal liver cells and granulomas during lamprey biliary atresia

Transmission (thin sections and freeze-fracture replicas) and scanning electron microscopy were used to describe the nonparenchymal liver cells during the seven (1-7) stages of metamorphosis in the sea lamprey, Petromyzon marinus L., when bile ducts and canaliculi degenerate. The biliary atresia is accompanied by an increased diameter of fenestrae in the endothelium, an active phagocytosis by Kupffer cells in the sinusoids, and large lipid inclusions in perisinusoidal lipocytes (fat-storing or Ito cells). Plasma-like cells and foci of nonparenchymal cells (granulomas) are present in the liver interstitium during at least four stages of metamorphosis. The fenestrae in the sinusoidal wall are wider (up to 2.8-micron diameter) than normally reported for vertebrate livers but are likely a reflection of the morphogenetic and physiological events and consequences of the biliary atresia. Kupffer cells are involved in an extensive erythrophagocytosis, the storage of iron, and perhaps the incorporation of cellular components from hepatocytes. Lipocytes are the vitamin A-storing cells of the transforming liver and may be responsible for some perisinusoidal fibrosis. Granulomas are present during stages 3-6 and are focal areas where mononuclear leukocytes (lymphocytes and plasmalike cells), macrophages, and neutrophils have infiltrated the hepatic parenchyma. The function of the granulomas is not known; but their presence may be related to the porous nature of the sinusoidal wall, the tissue degeneration, and/or the physiological change (e.g., bile stasis) during biliary atresia.     

1-Acyl-lysolecithin acyltransferase and synthesis of biliary lecithins in rat liver

The role of lysolecithin acyltransferase activities in biliary lecithin formation was investigated, using livers perfused in the presence of labeled palmitoyl-lysolecithin and albumin, overloaded or not with linoleic acid. At the end of liver perfusion, the lecithins extracted from microsomes, mitochondria and plasma membranes displayed the same specific activity. Double-labeled lysolecithin was used to prove that labeled lecithins were synthesized by lysolecithin acylation. In the absence or presence of a linoleic acid overload, the level of lysolecithin incorporation into linoleyl and arachidonyl containing lecithin was identical. Hence fatty acids did not influence phosphatidylcholine synthesis by the acylation pathway. In vitro the rate of linoleyl lecithin synthesis was the same in plasma membranes, mitochondria and microsomes provided the linoleyl-CoA concentration was lower than 30 microM. Taurocholate was essential to the excretion of lecithin synthesized from lysolecithin and stimulated its synthesis. The specific activities of the two lecithin molecular species excreted in bile (linoleyl and arachidonyl) were not significantly different. These results enabled us to evaluate the contribution of the lysolecithin pathway to the synthesis of lecithin in liver and bile: this contribution in bile was less than 2% under the perfusion conditions used.     

Immuno-isolation and culture of biliary epithelial cells from normal human liver

Summary Biliary epithelial cells (BEC) lining the intra-hepatic biliary ducts are the site of damage in several immunologically mediated liver diseases. BEC are difficult to isolate since they represent only 5% of the total cell number in normal liver. In this communication, a novel method for their isolation from normal liver is presented using a monoclonal antibody (HEA125) with specificity for an epithelial cell surface glyco-protein reported to be expressed in liver only by biliary epithelium. By combining differential density centrifugation and immuno-magnetic separation using HEA125 pure BEC (10⁵ cells/g fresh tissue) were prepared routinely. These cells were maintained in culture for up to 4 weeks with significant increases in cell numbers. The ability to prepare BEC from human liver offers an opportunity to develop In Vitro models to investigate the aetiology of diseases in intra-hepatic biliary epithelium. EDITOR’S STATEMENT This is a novel application to purification of specific liver cell types directly from tissue. It is well-suited for rapid communication because of its novelty and potential utility to investigators.