Hepatic disposition of cationic drugs bound to asialoorosomucoid (ASOR): Lack of co-endocytosis and evidence for intrahepatic disposition

DIAGNOSIS AND TREATMENT OF PATIENTS WITH CRIGLER NAJJAR SYNDROME. Sinaasappel M*, Jansen PLM, Peters WHM, Bouquet J* Division of Gastroenterology, Sophia Children's Hospital, Rotterdam*, and St. Radboud Hospital, Nijmegen Crigler Najjar (CN) syndrome is a congenital disorder with unconjugated hyperbilirubinaemia due to hepatic UDP-glucuronyltransferase deficiency. Despite bilirubin isomerisation by phototherapy and enzyme induction with phenobarbital (PB) serum billrubin tends to increase with age and can reach toxic levels around puberty. The aim of our study was to develop new diagnostic and treatment modalities for these patients. Bilirubin (UCB) and conjugates (BMG, BDG) were determined by HPLC. Bilirubin (TB)/bile acid (BA) clearance ratio was determined usin~ [TB]bile/[TBlserum x IBAlserum/[BA]bile ~Diagnosis I N ] UCB (%)~ BMG (%)I BDG (%)ITB/BA clearance x 10-31 ~CN, type I I 3 ~ 88+Ii I 12+11 ~ i+i ~ 0,14+0,09 I ICN, type II ~ 4 ~ 28513 I 60~12 I 12~4 I 0,I0~0,02 I IGilbert's S I 3 I 4~I I 35~3 I 62~4 I 1,57+0,20 I INormals I 8 I 2~.i ~ 16~_2 I 82~2 ~ i0,34~_3~46 I PB treatment of CN type II patients resulted in a 29+1% decrease of serum bilirubin but no change of TB/BA clearance. With the purpose to interrupt the enterohepatic clrculation of bilirubin four patients were treated with charcoal. In two CN patients who were not treated with PB this resulted in a 35% and 24% decrease of serum bilirubin but in two patients who were on PB, charcoal caused 39% and 23% increase of serum bilirubin. Conclusions: I. Diagnosis of CN and Gilbert's syndrom can be made by bilirubin metabolite analysis of bile and calculation of TB/BA clearance ratio. 2. PB treatment of CN patients causes a reduction of serum bilirubin not by increasing bilirubin clearance but most probably by a shift of bilirubin distribution from serum to hapatic stores. 3. Reduction of serum bilirubin by activated charcoal p.o. is only seen in CN patients not treated with PB.

HEPATIC DISPOSITION OF CATIONIC DRUGS BOUND TO ASIALOOROSOMUCOID CO-ENDOCYTOSIS AND EVIDENCE FOR INTRAHEPATIC DISPOSITION*

(ASOR): LACK OF

P. van der Sluijs and D.K.F. Meijer Department of Pharmacology and Therapeutics, University of Groningen, Groningen, The Netherlands. Plasma levels of orosomucoid (OR) and its asialo derivative ASOR undergo marked elevations in a variety of hepato-biliary diseases. Since ASOR, in contrast to OR is rapidly cleared by the liver via a receptor mediated process, this might affect hepatic disposition of drugs bound to ASOR. Equilibrium binding of 12 cationic drugs was investigated. Binding of Thiazinamium, d-Tubocurarine (dTc), N-methylimipramine and N-methyldeptropine (NND) correlated excellently with the log partitioncoefficient (r=0.99). Scatchard analysis revealed a high affinity binding site for NMD on ASOR (K=60~M-]). Subsequently we studied the influence of ASOR on hepatic uptake and intrahepatic distribution of N ~ and dTc in the isolated perfused rat liver, in perfusates containing 75uM albumin. Perfusate clearance was 25.7+3.8 ml/min for NMD and 1.51+0.08 ml/min for dTc, protein bound fractions were 0.]9 and 0.03 resp. In the presence of TT~M ASOR the bound fractions were significantly increased to 0.65 and 0.]7 resp., clearances were 27.8+3.4 and J.70+0.07 ml/min resp. The similarity with controls suggests dissociation of the drug-protein ~omplex, or alternatively that decreased transport depending on unbound fraction is compensated for by increased uptake of drug associated with ASOR. This issue was addressed in subcellular fractionation studies performed with livers that were previously pulsed with ]~mol drug in the perfusion setup. No extra enrichment of the lysosomal fraction was seen as compared with controls in which ASOR was omitted. It is concluded that cationic drugs bound to ASOR are not co-endocytosed, and that dissociation of drug occurs within the sinusoidal/Disse spaces, since the same result was found with OR it is concluded that dissociation occurs spontaneously by progressive removal of free drug or due to a nonspecific surface interaction. *This study was granted by the Netherlands Foundation for Medical Research (Grant 132878).

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