Effect of nafenopin (SU-13,437) on liver function: influence on the hepatic transport of organic anions

Role of enterohepatic recirculation in drug disposition: cooperation and complications

Enterohepatic recirculation (EHC) concerns many physiological processes and notably affects pharmacokinetic parameters such as plasma half-life and AUC as well as estimates of bioavailability of drugs. Also, EHC plays a detrimental role as the compounds/drugs are allowed to recycle. An in-depth comprehension of this phenomenon and its consequences on the pharmacological effects of affected drugs is important and decisive in the design and development of new candidate drugs. EHC of a compound/drug occurs by biliary excretion and intestinal reabsorption, sometimes with hepatic conjugation and intestinal deconjugation. EHC leads to prolonged elimination half-life of the drugs, altered pharmacokinetics and pharmacodynamics. Study of the EHC of any drug is complicated due to unavailability of the apposite model, sophisticated procedures and ethical concerns. Different in vitro and in vivo methods for studies in experimental animals and humans have been devised, each having its own merits and demerits. Involvement of the different transporters in biliary excretion, intra- and inter-species, pathological and biochemical variabilities obscure the study of the phenomenon. Modeling of drugs undergoing EHC has always been intricate and exigent models have been exploited to interpret the pharmacokinetic profiles of drugs witnessing multiple peaks due to EHC. Here, we critically appraise the mechanisms of bile formation, factors affecting biliary drug elimination, methods to estimate biliary excretion of drugs, EHC, multiple peak phenomenon and its modeling.

The hepatocellular transport of sulfobromophthalein-glutathione by clofibrate treated, perfused rat liver

The hypolipidemic drug clofibrate is known to affect the hepatic transport of various organic anions including bilirubin, fatty acids and sulfobromophthalein. Changes in the rate of metabolism and/or intracellular transport have been claimed responsible for the effect. To evaluate these possibilities, the transport of sulfobromophthalein-glutathione, a model compound that does not require metabolism for biliary excretion, was studied in perfused livers isolated from clofibrate-treated and control rats. Cytosolic fatty acid binding protein and glutathione S-transferase activity were also measured. Clofibrate treatment significantly increased liver weight; as a result glutathione S-transferase activity (toward 1-chloro-2,4-dinitrobenzene) fell if expressed per gram of liver (4560 +/- 420 (SE) vs 7010 +/- 260 nmoles/min for clofibrate treated and controls respectively, p less than 0.002), but was unchanged when expressed per total liver (60.8 +/- 6.5 vs 64.6 +/- 3.5 mumoles/min for clofibrate and controls p greater than 0.5). Irrespective of how it was expressed fatty acid binding protein was significantly increased by the drug treatment. Steady state sulfobromophthalein-glutathione removal velocity was saturable with increasing concentrations of sulfobromophthalein-glutathione in both control and clofibrate-treated livers. Steady state extraction ratio, as well as Vmax and Km for removal, did not differ between the two groups. In keeping with other observations, these data collectively indicate that the hepatic steady state removal of nonmetabolized compounds is not affected by clofibrate.(ABSTRACT TRUNCATED AT 250 WORDS)

Selective hepatobiliary transport defect for organic anions and neutral steroids in mutant rats with hereditary-conjugated hyperbilirubinemia

Mutant rats (TM rats) with abnormal hepatic excretory function were used to study biliary transport of dibromosulfophthalein, ouabain, tributylmethyl ammonium, cholate and taurocholate. In whole animals, dibromosulfophthalein and ouabain clearance is reduced to 7 and 37% of normal, respectively, due to severely impaired excretion from liver to bile. Initial uptake rates of these agents are relatively little affected. In the isolated perfused liver preparation, dibromosulfophthalein is retained within liver and perfusion medium, and the 60-min recovery on bile is reduced to 1.5 vs 75% in normal controls. Biliary excretion of cholate, taurocholate and the quaternary ammonium cation, [14C]tributylmethyl ammonium, is not impaired. These results provide evidence for a selective defect of organic anion and neutral steroid transport in TM rats and confirm that multiple pathways exist for the hepatobiliary excretion of organic anions, neutral steroids, bile acids and cations. Bile flow in whole animals and in the isolated perfused liver is reduced to 50 and 30% of normal, respectively. This suggests that a normal function of the excretory systems for organic anions and neutral steroids is important for the maintenance of normal bile flow.

Impairment of hepatic glutathione S-transferase activity as a cause of reduced biliary sulfobromophthalein excretion in clofibrate-treated rats

Administration of clofibrate reduced the maximal excretion rate of bile sulfobromophthalein (BSP) in rats but left that of phenol-3,6-dibromophthalein (DBSP) unchanged. This decrease in liver transport of BSP was due to reduced bile excretion of conjugated BSP. Hepatic uptake and storage of this dye were not impaired. Liver glutathione S-transferase activity in vitro, measured with BSP, 1,2-dichloro-4-nitrobenzene (DCNB) or 1-chloro-2, 4-dinitrobenzene (CDNB) was significantly reduced. This alteration in liver conjugating activity was probably not related to a modification of the hepatic GSH pool, since the GSH level was unchanged or only increased slightly after clofibrate treatment. Detection of this inhibition required at least two daily doses of clofibrate. Inhibition was dose-related and lasted for several days after cessation of the drug. In clofibrate-treated rats, Lineweaver-Burk plots showed a reduced Vmax for both the BSP and GSH substrates. These results suggest that clofibrate decreases hepatobiliary transport of BSP by lowering glutathione S-transferase activity in the liver.

Hepatic drug transport in the rat. A comparison between isolated hepatocytes, the isolated perfused liver and the liver in vivo

The hepatic transport of three different drugs, the organic anion dibromosulphophthalein, the organic cation d-tubocurarine and the uncharged compound ouabain was studied in vivo in the isolated perfused rat liver and isolated hepatocytes. The respective clearances by uptake were determined for the various substrates and corrected for differences in hepatic blood flow and extracellular protein binding in the three liver preparations. The corrected uptake values in the intact organ, in vivo and in the isolated perfused liver were highly comparable; for dibromosulphophthalein a clearance of 2.1 ml/min per 10(6) hepatocytes was found in vivo, whereas in perfusion a value of 2.4 ml/min per 10(6) cells was calculated. For d-tubocurarine, the values were 34 x 10 (-4) and 55 x 10(-4) ml/min per 10(6) cells obtained in vivo and in the isolated perfused organ, respectively. With ouabain as the substrate, the in vivo clearance amounted to 5.1 x 10(-2), whereas in the isolated perfused liver a value of 4.8 x 10(-2) ml/min per 10(6) cells was calculated. The clearance by uptake obtained for dibromosulphophthalein was ouabain in the isolated hepatocytes appeared to be a factor of 2-3 lower than in the intact organ. In the case of d-tubocurarine however the clearance was identical to that in vivo and the isolated perfused liver. The rate of secretion from isolated hepatocytes was, for dibromosulphophthalein identical to, and for d-tubocurarine and ouabain lower than that in the intact organ, especially as compared with the in vivo preparation. It is concluded that transport function is well preserved in the isolated perfused liver and isolated hepatocytes. For certain substrates freshly isolated hepatocytes may exhibit a somewhat lower uptake and/or secretion rate, in spite of a good cell quality as judged by generally accepted criteria for cell viability. Whether this is due to changes in membrane composition (not detected by our viability tests) or a selection of a subpopulation of hepatocytes, is discussed.U

Biliary and urinary excretion of drug conjugates: effect of diuresis and choleresis on excretion of harmol sulphate and harmol glucuronide in the rat

1. Harmol (7-hydroxy-1-methyl-9H-pyrido [3,4b] indole) is converted to harmol sulphate and harmol glucuronide in the rat in vivo. Harmol sulphate is excreted mainly in urine, while harmol glucuronide is excreted about equally in bile and urine, when harmol is given intravenously. 2. In rats with ligated kidneys, only choleresis produced by glycodehydrocholate and dehydrocholate caused enhanced biliary excretion of harmol sulphate; harmol glucuronide was unaffected. Several other bile salts had no effect. 3. Mannitol diuresis markedly increased urinary excretion of harmol sulphate, and decreased its biliary excretion. Harmol glucuronide was much less affected. 4. Nafenopin pretreatment increased liver weight and bile flow, and enhanced biliary excretion of harmol sulphate at the expense of its urinary excretion. 5. For harmol sulphate, urine and bile are compensatory pathways of elimination that can be influenced by urine and bile flow changes through diuresis and choleresis.