University of Groningen Regulation of hepatic transport in experimental cholestasis Koopen, Nynke Rixt IMPORTANT NOTE: You are advised to consult the publisher's version (publisher's PDF) if you wish to cite from it. Please check the document version below. Document Version Publisher's PDF, also known as Version of record Publication date: 1998 Link to publication in University of Groningen/UMCG research database Citation for published version (APA): Koopen, N. R. (1998). Regulation of hepatic transport in experimental cholestasis. [S.n.]. Copyright Other than for strictly personal use, it is not permitted to download or to forward/distribute the text or part of it without the consent of the author(s) and/or copyright holder(s), unless the work is under an open content license (like Creative Commons). The publication may also be distributed here under the terms of Article 25fa of the Dutch Copyright Act, indicated by the “Taverne” license. More information can be found on the University of Groningen website: https://www.rug.nl/library/open-access/self-archiving-pure/taverne- amendment. Take-down policy If you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediately and investigate your claim. Downloaded from the University of Groningen/UMCG research database (Pure): http://www.rug.nl/research/portal. For technical reasons the number of authors shown on this cover page is limited to 10 maximum. Download date: 05-10-2021 Regulation of Hepatic Transport in Experimental Choles Regulation of Hepatic Transport in Experimental Cholestasis Stellingen behorend bij het proefschrift Mechanisms involved in malabsorption of dietary lipids Mini Kalivianakis Groningen, 23 september 1998 Severe fat malabsorption due to impaired lipolysis can be identified by the 13C­ MTG breath test. However, in situations of mild fat malabsorption, considerable interindividual variation in the results of the 13C-MTG breath test occurs, which 13 may be explained by a shift in the rate-limiting step in the overall process of CO2 production. (DIT PROEFSCHRIFT) The continuing fat malabsorption in cystic fibrosis patients on enzyme replacement therapy is not likely due to insufficient lipolytic enzyme activity, but rather due to either incomplete intraluminal solubilization and/or reduced mucosal uptake of long-chain fatty acids. (DIT PROEFSCHRIFT) Vrouwelijke wetenschappers moeten ongeveer 2½ maal beter presteren dan hun mannelijke collega' s voor een vergelijkbaar resultaat. (NATURE 1997;387:341) Een promotieonderzoek is niet alleen een investering is in jezelf maar ook in de universiteit. Dat dit besef ook begint door te dringen tot de universitaire wereld blijkt uit het feit dat een aantal universiteiten bereid is de promovendi meer te betalen. Mini staat voor meer dan klein. Ook voor stellingen geldt dat een hogere kwantiteit vaak niet ten goede komt aan de kwaliteit. Cover design: Margarethe II RIJKSUNNERSITEITGRONINGEN REGULATION OF HEPATIC TRANSPORTIN EXPERIMENTALCHOLESTASIS Proefschrift ter verkrijgingvan het doctoraat in de Medische Wetenschappen aan de Rijksuniversiteit Groningen op gezag van de Rector Magnificus,dr. D.F.J. Bosscher, in het openbaar te verdedigen op woensdag 9 september 1998 om 16.15 uur door Nynke RixtKoopen geboren op 31 oktober 1968 te Sneek Promotor: Prof. dr. RJ. Vonk Co-promotor: Dr. F. Kuipers Referent: Dr. M. Milller Promotiecommisie: Prof. Dr. P.L.M. Jansen Prof. Dr. P.J.J. Sauer Prof. Dr. P.J.Meier-Abt The Research described in this thesis was conducted at the laboratory of nutrition and metabolism, Groningen Institute of Drug Studies, University of Groningen, the Netherlands Financial support was provided by the Nederlandse organisatie voor Wetenschappelijk Onderzoek (NWO). The printing of this thesis was financiallysupported by Groningen Institute of Drug Studies. Hope Farms B.V. and]. Koopen Yn in om en omsjoch As ik omsjoch - by 't Joarutsjen like alles sa tsfuster - bin ik likegoed yn in omsf och de ijochtbeakensbf uster. Dussf och ik wer om en bfusterom my hinne. En wat ik ek sfoch, ik sjochek de sinne. Jk sjochyn in omsjoch - myn medisyn- runomwer ijochtyn. MeindertBylsma Contents Chapter 1 General introduction and outline of the thesis. 9 Chapter 2 Impaired activity of the bile canalicular organic anion transporter 33 (mrp2/cmoat) is not the main cause of ethinylestradiol-induced cholestasis. Chapter 3 Differentialeffects of 17a-ethinylestradiol on the neutral and acidic pathways 53 of bile salt synthesis in the rat. Chapter 4 Hepatic bile salt flux does not modulate level and activity of the sinusoidal Na+ 71 taurocholate cotransporter (ntcp) in rats. + Chapter 5 Decreased Na -dependent taurocholate uptake and low expression of the 87 sinusoidal Na +-taurocholate cotransporting protein (ntcp) in livers of mdr2- pGlycoprotein deficientmice. Chapter 6 Toxic effects of dietary cholesterol in mdr2 p-glycoprotein-deficientmice 10 Chapter 7 Biliary Fibrosis Associated with altered bile composition in a mouse model of 12 erythropoetic protoporhyria. Chapter 8 Molecular mechanisms of cholestasis: causes and consequences of impaired bile 14 formation. Chapter 9 Discussion. 16 Nederlandse samenvatting. 17 Dankwoord. 17 Chapter 1 General Introduction Chapter I 10 General introduction GENERALINTRODUCTION Cholestasis a clinical condition in which the formation of bile is impaired. The causes underlying the development of cholestasis in patients can be extremely varied. This thesis describes the relationship between bile production and composition, levels and activity of specific hepatic transport proteins involved in bile formation and the diagnostic value of cholestatic serum markers like bile salts and bilirubin in differentexperimental models. 1. Bile formation The formation of bile is an important function of the liver. Bile contains bile salts, phospholipids cholesterol, a variety of proteins and bilirubin as its main organic constituents. Electrolytes and a number of trace elements are also present in bile. Bile serves many functions in the body. In the first place, the biliary pathway represents the major route for elimination of endogenous and exogenous waste products. Bilirubin, which gives bile its bright yellow colour is produced during the breakdown of hemoglobin fromsenescent red blood cells and of other heme-containing proteins and is secreted into bile after the coupling of sugar groups, which renders this hydrophobic compound more water­ soluble. Bile also plays a role in disposition from the body of a wide variety of xenobiotics, including drugs and heavy metals. Secondly, bile formation is important in the maintenance of cholesterol homeostasis. Cholesterol leaves the body almost exclusively after its excretion into bile, either as the freecompound or after its conversion to bile salts. Thirdly, bile is essential forthe solubilization by bile salts of dietary lipid and lipid-soluble vitamins in the small intestine and for the assembly of chylomicrons by the enterocytes: both processes are required for efficient intestinal absorption of dietary fats and fat-soluble vitamins. Therefore, maintenance of bile formation is not only essential for functioning of the liver but also of the organism as a whole. Bile is formed by the liver parenchymal cells, or hepatocytes, which represent the major cell type in the liver in quantitative terms (1). Hepatocytes are polarized cells with their basolateral or sinusoidal membrane facing the blood and their apical or canalicular membrane facing the bile (figure 1). To maintain this polarization, the canalicular domain of adjacent cells is sealed from the blood compartment by means of tight junctions, through which large molecules can not pass, but which are permeable for electrolytes and water. In order to be secreted into bile, most compounds therefore have to pass through the hepatocytes. The hepatocytes are arranged in one cell thick layers that line the sinusoids in the liver-lobules, the smallest structural units of the liver according to the model of Rappaport (figure2). This lobule receives blood via branches of the portal vein and the hepatic artery. Via the sinusoids the blood then flows to the central vein. Along the sinusoids there is a functional division of the hepatocytes into three zones, i.e. the periportal, the central or intermediate and the perivenous zone. A morphological and functional heterogeneity of hepatocytes exists along these differentzones with respect to metabolic- and transport functions (2,3). 11 Chapter 1 Figure 1. Schematic representation of liver cell plate. Hepatocytes are polarized cells. Proteins and solutes fromthe blood pass the endothelialbarrier, whereas erythrocytes and other blood derived cells cannot pass. Hepatocytes absorb compounds fromthe space of Disse. 7bese compounds and waste products generated insidethe liver are secreted in the canaliculus. Bile leaves the lobule in the direction opposite to blood flow. 7be sinusoidal and canalicular compartment are separated by tightjunctions. -- ........,,, Central'. Vein } ,/ Branch Hepatic Artery Figure 2. Schematic representation of the liver lobule. Hepatocyte cell plates are radially arrangedaround the centralvein to forma hexagonal shaped liver lobule. Blood enters the lobule via branches of the portal vein and branches fromthe hepatic artery that combine to form the sinusoidal blood flow (largearrow). Bile leaves viathe bile ducts. (small arrow).Adapted from Bloom et al. (1975) A textbookof histology.