Academisch Medisch Centrum Universiteit van Amsterdam

Hepatic transport processes

• Focus of research is the role of transporter proteins in the canalicular membrane, which are involved in the formation of bile, particularly the mechanism of bile salt and lipid excretion across the canalicular membrane. This process is unique in the sense that bile salt (=detergent) concentrations are reached which are high enough to dissolve any biological membrane. Hence, the canalicular membrane needs to harness itself against this highly toxic fluid. We study inherited liver diseases in which this mechanism of self defense is compromised.
• Many cholestatic patients suffer from itch (pruritus) and this can develop into an enormous burden to the patient. Nevertheless, the mechanism of cholestatic itch is completely unresolved and therapy therefore remains problematic. We have initiated a study into the fundamental basis of this clinical problem and discovered that autotaxin, the enzyme that is responsible for formation of lysophosphatidic acid plays a role in this process. We are currently unravelling the mechanism by which this potent signalling molecule induces or aggravates itch.
• The plasma membrane of hepatocytes harbors several drug extrusion pumps, such as MRP2 (ABCC2), ABCG2 and MDR1 (ABCB1) in the canalicular membrane and MRP3 (ABCC3) and MRP4 (ABCC4) in the basolateral membrane. These ATP-dependent transporters are expressed both in liver and in the intestine; therefore they determine to a large extent the pharmacokinetic behaviour of drugs. In mouse strains with disruptions of the various transporter genes (as well as combined gene disruptions) we determine the role of these transporters in pharmacokinetics of various classes of drugs. These issues will become increasingly important for drug development as well as the elucidation of drug-drug interactions.
• Primary biliary cirrhosis is a relatively frequent liver disease that occurs mainly in middle aged women. It is regarded as an autoimmune disease, but the mechanism by which it develops remains obscure. Most likely it involves a combination of dysregulation of the immune ssystem and dysfunction of bile duct epithelial cells. We are currently developing animal models for this disease.

Training
'74 - '81 Study Biochemistry at the University of Amsterdam (graduation cum laude)

'81 - '85 PhD-student at the Dept. of Biochemistry University of Amsterdam (PhD. thesis: "Biosynthesis, transport and processing of lysosomal α-glucosidase" (promotor: prof. J.M. Tager)

'85 - '86 post-doc at the Biotechnological Center, University of Amsterdam (project: In vitro immunisation of B-cells for production of monoclonal antibodies)

Position
'86 - '99 staff member (biochemist) of the Dept. of Gastrointestinal and Liver Diseases, Academic Medical Center, Amsterdam

'99 - '00 Associate professor and head of the Laboratory for Experimental Hepatology, Academic Medical Center, Amsterdam

2000-present Professor of Experimental Hepatology, Academic Medical Center Amsterdam

2002-present Head of the Tytgat Institute for Liver and Intestinal Research.
 

1. The physiological function of ATP8B1 and other members of the P4 ATPase subfamily. We have discovered that this lipid flippase (which is deficient in an inherited form of cholestasis) needs at least one accessory protein from the small family of CDC50 proteins to be properly targeted to the plasma membrane. In the presence of this protein flippase activity can be assayed enabling us to screen the effect of mutations. Also the CDC50 genes are now candidates as causative genes for cholestatic disorders. The human genome harbours 14 P4 ATPases, all of which are thought to be phospholipid flippases. However, most of these gene products have not been studied yet. We are currently exploring the function of these flippases and their CDC50 partners.

2. Hepatic transport functions. Many aspects of bile formation have been elucidated in the past decades. However, several aspects of normal bile formation and especially of biliary dyfunction and cholestasis are not well understood. We are improving animal models for cholestatic diseases; not only with respect to defects in transport function but also with respect to the role of bile salt signalling and the role of biliary bicarbonate secretion. In addition, we are trying to unravel the factors that contribute to the development of autoimmunitiy against bile duct epithelial cells as occurs in primary biliary cirrhosis (collaboration with prof. Ulrich Beuers)

3. Cholestatic pruritus. Patients with various forms of cholestasis often suffer from chronic itch (pruritus). This can be a very heavy burden to the patient. The mechanism of cholestatic itch is unknown. Bile salts and endogenous opioids have been implicated but we have found no evidence to support this contetnion. We have set up assays  to analyze the effect of cholestatic factors on neuronal signalling. Currently, we are analyzing the factors that we have identified and we are trying to elucidate the mechanism by which they cause itch. This will provide means to implement existing drugs or develop new drugs against this agonizing problem (collaboration with prof. Ulrich Beuers).
4. Development of a liver function test. In collaboration with a pharmaceutical company we have analyzed the mechanism of clearance of a fluorescent bile salt analog that is under development as a liver function test.

5. Bioartificial liver support; hardware: The AMC bioartificial liver has been evaluated by 3D numerical modeling and computational simulation: resulting in improved oxygenation capacity by increased oxygen capillaries and thinner matrix. Comparable function of AMC-BAL and Berlin BAL (MELSS); cells: Immortalised human fetal liver cell line (cBAL111), patent pending. Improvement of differentiation grade

This research group participates in the AMC Liver Center and the Amsterdam Center for Metabolism