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Biomedical subjects

H Takikawa

Publications and source records attributed to H Takikawa.

At least 55 records · Page 3Linked to original sources
PubMed1996

Evidence that interference with binding to hepatic cytosol binders can inhibit bile acid excretion in rats.

We previously identified that Y' bile acid binders (3alpha-hydroxysteroid dehydrogenases) interact with bile acids in intact rat hepatocytes using [3beta-3H, C24-14C]bile acids and that indomethacin, a competitive inhibitor of 3alpha-hydroxysteroid dehydrogenase, inhibits 3H-loss from the C3-position of bile acids as well as inhibits hepatic bile acid removal and excretion. To study the kinetics of these inhibitory effects, glycocholate transport was studied in the absence and presence of indomethacin in the single-pass perfused rat liver. Indomethacin decreased net hepatic glycocholate uptake in the perfused liver, which was confirmed in isolated hepatocytes and basolateral liver plasma membrane vesicles. However, indomethacin markedly increased the sinusoidal efflux and decreased the biliary excretion of glycocholate in the perfused liver. These observations indicate that the effect of indomethacin to delay biliary glycocholate excretion is related to either intracellular or canalicular glycocholate transport. The latter possibility seemed unlikely because indomethacin did not inhibit electrogenic or adenosine triphosphate (ATP)-dependent glycocholate uptake by canalicular liver plasma membrane vesicles. Thus, the current data support an important role for binding of bile acids to cytosolic proteins in overall hepatic transport and suggest that specific interference with cytosolic binding can interfere with the excretion of bile acids.

3-Hydroxysteroid Dehydrogenases↗
PubMed1996

Alterations in glutathione homeostasis in mutant Eisai hyperbilirubinemic rats.

Eisai hyperbilirubinemic rats (EHBR) are mutant Sprague-Dawley rats that exhibit impaired biliary organic anion and reduced glutathione (GSH) secretion. In addition, liver GSH levels are twice that of age-matched controls. The mechanisms for the defect in biliary GSH secretion and the increase in cell GSH are not fully understood. We previously showed that canalicular membrane-enriched vesicles isolated from EHBR livers exhibited normal GSH transport. In the present study, we examined the steady-state rat canalicular reduced glutathione transporter (RcGshT) messenger RNA (mRNA) and protein levels, as well as the mechanisms for the increase in cell GSH. Both Northern and Western blot analyses of EHBR livers showed nearly identical RcGshT mRNA and polypeptide levels, respectively, as compared with controls. Treatment with phenobarbital, which increased steady-state RcGshT mRNA by five- to sixfold, RcGshT polypeptide, and biliary GSH secretion by onefold in controls, had a smaller effect on steady-state RcGshT-mRNA level in EHBR (by 1.5-fold) and did not increase RcGshT polypeptide or biliary GSH secretion. In examining possible mechanisms for increased liver GSH, both cysteine level and gamma-glutamylcysteine synthetase (GCS) activity were significantly higher than controls, while the activity of GSH synthetase was unchanged. Northern and Western blot analyses also showed increased steady-state GCS heavy subunit (GCS-HS) mRNA and polypeptide levels, respectively. In addition to liver, GSH levels in kidney, duodenal, jejunal, and ileal mucosa of EHBR were 200% to 300% of age-matched control rats. GCS activity was also increased in kidney cytosol of EHBR. Thus, the defect in biliary GSH secretion in EHBR most likely is either at the posttranslational level of RcGshT or in the inhibition exerted by retained endogenous organic anions. In addition, there is a widespread up-regulation of GSH synthesis capacity in the tissues of EHBR.

Analysis of Variance↗
PubMed1996

Effects of ursodeoxycholate and its conjugates on biliary glutathione excretion in rats.

The effects of ursodeoxycholate and its conjugates on biliary glutathione excretion were studied in rats. Ursodeoxycholate had no effect on glutathione excretion, but tauroursodeoxycholate (10 mumol/100 g body wt) transitionally increased biliary glutathione excretion. Ursodeoxycholate-3-O-glucuronide (2 and 10 mumol/100 g body wt) markedly inhibited biliary glutathione excretion, but ursodeoxycholate-3-sulfate (2 mumol/100 g body wt) and ursodeoxycholate-3,7-disulfate (10 mumol/100 g body wt) did not. These findings indicate the existence of several biliary excretion pathways for bile acid glucuronides and sulfates and that one of them for the glucuronides is shared by biliary glutathione excretion.

Animals↗
PubMed1996

Changes in biliary excretory mechanisms in bile duct-ligated rat.

The effects of bile duct ligation on biliary excretion of bile acids, glutathione, and lipids were studied in the rat. The bile duct of the rat was ligated for three days. The biliary bile acid excretion after bile duct cannulation was higher at first, but after 90 min became lower than that in the control rat. The bile flow in the bile duct-ligated rat was higher after bile duct cannulation and gradually decreased to the same level as in the control rat. Biliary glutathione excretion, which has been suggested to be a driving force for the bile acid-independent canalicular bile flow, was markedly decreased in the bile duct-ligated rat. The mannitol clearance was increased and the bile ductules showed proliferation in the bile duct-ligated rat, suggesting an increase in the ductular bile flow. Biliary excretion of lithocholate glucuronide was more markedly impaired than that of taurocholate. When taurocholate was infused at higher rates, which increases bile flow and biliary excretion of bile acid and lipids in the control rat, biliary bile acid and lipid excretion remained constant in the bile duct-ligated rat. These findings indicate that, in the bile duct-ligated rat, the ductular bile flow was increased and bile acid-independent canalicular bile flow was decreased and that, although the biliary excretion of bile acids was not as impaired as that of organic anions, the capacity of bile acid and lipid excretion was markedly decreased.

Animals↗
PubMed1996

Biliary excretion of estradiol-17 beta-glucuronide in the rat.

Estradiol-17beta-glucuronide (E217G) is a cholestatic agent and is considered to be related to the pathogenesis of intrahepatic cholestasis of pregnancy. In the current study, we examined the mechanism of the biliary excretion of E217G and estradiol metabolites in rats. Biliary excretion of tracer doses of [3H]estradiol-17beta-glucuronide and [14C]estradiol or [3H]taurocholate and ]14C]vinblastine, a P-glycoprotein (P-GP) substrate, intravenously administered as a bolus to bile-drained control rats or EHBR was studied. Biliary excretion of E217G and estradiol metabolites EHBR was markedly delayed. Analyses of biliary metabolites after estradiol injection showed less polar conjugates in EHBR. In contrast, the excretion of taurocholate and vinblastine (VLB) was only slightly delayed in EHBR. Although phenothiazine treatment to induce the expression of P-GP increased biliary vinblastine excretion, it did not affect biliary excretion of a tracer dose of [3H]estradiol-17beta-glucuronide. However, phenothiazine treatment inhibited the cholestasis induced by E217G infused at the rate of 0.075 micromol/min/100g for 20 minutes and increased biliary E217G excretion. Sulfobromophthalein infusion (0.2 micromol/min/100 g body 0 weight) markedly inhibited the biliary excretion of E217G and estradiol metabolites, whereas dibromosulfophthalein (DBSP) at the same infusion rate had no effect. These findings indicate that EG17G is excreted into bile by a canalicular organic anion carrier for sulfobromopthalein (BSP), not for DBSP, under physiological conditions, and that P-GP influences E217G excretion only at a high dose. under physiological conditions, and that P-GP influence s E217G excretion only at a high dose.

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMed1996

Effects of organic anions on biliary glutathione excretion in rats.

The effects of various organic anions (2 mumol/100 g body weight) on biliary glutathione excretion were studied in rats. Bromosulfophthalein markedly inhibited glutathione excretion, whereas dibromosulfophthalein was a less potent inhibitor. Experiments with different bromosulfophthalein doses revealed that the extent of inhibition of glutathione excretion was related to the total bromosulfophthalein excretion. Indocyanine green also inhibited biliary glutathione excretion. Dinitrophenyl glutathione and pravastatin did not inhibit biliary glutathione excretion. These findings indicate the existence of several pathways of biliary excretion of organic anions and suggest that one of them is a pathway for biliary glutathione excretion.

Animals↗
PubMed1996

[Organic anion carriers].

Recent studies using molecular biological techniques elucidated various organic anion carriers at the sinusoidal and the canalicular liver plasma membrane. Two sinusoidal membrane carrier have been cloned; Na+/taurocholate cotransporting polypeptide (Ntcp, 51 kDa), which mediates secondary active transport of bile acids, and Cl- -dependent organic anion-transporting protein (oatp, 74 kDa), which transports organic anions and bile acids. The existance of at least two canalicular membrane carriers for bile acids and organic anions have been identified. Both carriers transport substrates by the ATP-dependent primary active transport. As a bile acid carrier, a 110 kDa protein has been purified. Recently, the multidrug resistance protein (MRP), a member of the ATP binding cassette (ABC) transporter superfamily, is reported to closely relate to an ATP-dependent canalicular organic anion carrier.

ATP-Binding Cassette Transporters↗
PubMed1996

[Early liver cancer].

There is no definition for early liver cancers. However, solitary liver cancers smaller than 2 cm in diameter are defined as small liver cancers and this term is often used as the meaning of early cancers. Small liver cancers are diagnosed by US, US-guided biopsies, computed tomography (CT), magnetic resonance imaging (MRI), and angiography. They are successfully treated by percutaneous ethanol injection (PEI), subsegmental transcatheter arterial embolization (TAE), operations and percutaneous microwave coagulation therapy (PMCT), 3-years survival rates being more than 70%. The choice of treatments depends on the techniques available in each institute and liver function, since most cases are complicated with liver cirrhosis.

Electrocoagulation↗
PubMed1995

Binding of lithocholate and its glucuronide and sulfate by human serum albumin.

In the present study, the binding affinities of lithocholate sulfate and glucuronide by human serum albumin were compared to that of lithocholate by equilibrium dialysis, and the binding sites of these bile acids on those of various fluorescent probes and bilirubin were also studied. The dissociation constants for the primary binding sites for lithocholate sulfate and glucuronide on human serum albumin were 0.057 and 0.24 microM, respectively, which were lower than that for lithocholate (0.82 microM). Lithocholate sulfate and glucuronide, as well as lithocholate, did not simply inhibit the binding of the site II and III fluorescent probes or bilirubin to albumin. Inhibition by these bile acids of the site I fluorescent probe binding to albumin suggested that the secondary binding sites of these bile acids are equal to site I. The results of simultaneous equilibrium dialysis using [3H]lithocholate and [14C]lithocholate sulfate indicated that these compounds have the same primary binding site. In conclusion, sulfation and glucuronidation may increase the binding affinities of bile acids to human serum albumin without changing their binding site.

Bilirubin↗
PubMed1995

Mechanisms of biliary excretion of lithocholate-3-sulfate in Eisai hyperbilirubinemic rats (EHBR).

Biliary excretion of lithocholate-3-sulfate is markedly impaired in EHBR. To examine the mechanism of biliary lithocholate-3-sulfate excretion in EHBR, the effects of colchicine treatment, a vesicular transport inhibitor, and infusion of taurocholate and organic anions were studied in EHBR and Sprague-Dawley rats. Colchicine treatment and taurocholate infusion had no effect of biliary lithocholate-3-sulfate excretion in EHBR, suggesting that biliary lithocholate-3-sulfate excretion is not mediated by the vesicular transport or by the bile acid excretory pathway. In control Sprague-Dawley rats, both sulfobromophthalein and dibromosulfophthalein infusion inhibited biliary lithocholate-3-sulfate excretion. In contrast, in EHBR dibromosulfophthalein infusion inhibited biliary lithocholate-3-sulfate excretion but BSP infusion did not. Indocyanine green and pravastatin infusion did not affect biliary lithocholate-3-sulfate excretion but pravastatin infusion had no effect in EHBR. These findings indicate that, whether physiologically important or not, two of more excretory pathways for organic anions exist at the canalicular membrane other than the ATP-dependent one.

Animals↗
PubMed1995

Colchicine inhibits lithocholate-3-O-glucuronide-induced cholestasis in rats.

BACKGROUND/AIMS: It has been suggested that vesicular transport of bile acids in hepatocytes occurs, especially at high-dose loads. METHODS: The effect was studied of colchicine, a vesicular transport inhibitor, on lithocholate-3-O-glucuronide-induced cholestasis in rats. Cholestasis was induced by an intravenous infusion of lithocholate-3-O-glucoronide at the rate of 0.1 mumol.min-1.100 g-1 for 40 min. RESULTS: Colchicine treatment almost completely inhibited cholestasis and increased biliary excretion of lithocholate-3-O-glucoronide, whereas lumicolchicine had no effect. Treatment with vinblastine, another vesicular transport inhibitor, also reduced the cholestasis. Colchicine did not affect biliary excretion of taurocholate infused at the rate of 0.3 mumol.min-1.100 g-1 for 40 min, but markedly inhibited its biliary excretion when infused at the rate of 1.5 mumol.min-1.100 g-1 for 40 min. Colchicine had no effect on biliary excretion of tauroursodeoxycholate (1.5 mumol.min-1.100 g-1 for 40 min), lithocholate-3-sulfate (0.3 mumol.min-1.100 g-1 for 40 min), or a trace amount of lithocholate-3-O-glucuronide. CONCLUSIONS: These findings indicate that lithocholate-3-O-glucoronide-induced cholestasis is caused by its increased access to the vesicular transport pathway, possibly beyond the capacity of the transport by the cytosolic binders, and that the transport of lithocholate-3-O-glucoronide via the vesicular pathway induces cholestasis. Furthermore, the contribution of the vesicular pathway to hepatic transport may be different among bile acids, and lithocholate-3-O-glucuronide seems to have higher accessibility to this transport system.

Animals↗
PubMed1995

Biliary cefpiramide excretion: its relation to biliary excretion of bile acids and sulfobromophthalein.

Cefpiramide, a beta-lactam antibiotic, has been reported to be excreted from hepatocytes into the bile by a carrier-mediated system. Herein, the relationship of biliary cefpiramide excretion to the excretion of bile acids and sulfobromophthalein was studied in rats. Biliary cefpiramide excretion was markedly inhibited by sulfobromophthalein, lithocholate-3-O-glucuronide and taurolithocholate-3-sulfate, whereas it was not inhibited by ursodeoxycholate or taurocholate. However, the inhibitory effect of cefpiramide on the biliary excretion of sulfobromophthalein or lithocholate-3-sulfate was very small. These findings indicate that, although cefpiramide is excreted by a process common to organic anions and bile acid sulfate and glucuronide, two or more excretory pathways for organic anions exist and cefpiramide has affinity for only one of these carriers.

Animals↗
PubMed1994

Distribution of 3 alpha-hydroxysteroid dehydrogenase (bile acid binder) in rat small intestine: comparison with glutathione S-transferase subunits.

We identified and quantitated the Y' bile acid binder, i.e., 3 alpha-hydroxysteroid dehydrogenase (3 alpha-HSD), in rat small intestinal mucosa, and compared its longitudinal distribution with that of glutathione S-transferases (GST). The enzyme activity of 3 alpha-HSD in intestinal mucosa was approximately one-third of that in liver, and it had similar activity in the proximal, middle, and distal portions of the intestine. Immunoreactive protein corresponding to hepatic bile acid binder was detected in all segments of rat small intestine mucosal cytosol by Western blot analysis. There was no significant difference in the concentration of bile acid binder, assayed by enzyme-linked immunosorbent assay (ELISA), between the proximal and the distal intestine, this being 2.93 +/- 0.03 and 3.29 +/- 0.95 nmol/g tissue, respectively (mean +/- SD of four animals). On the other hand, the concentration of GST 1-1 showed sharp longitudinal decline and that of GST 3-4 was negligible in the small intestine, as we previously reported, indicating that bile acid binder was a prominent cytosol binding protein in the distal intestine. These results suggested the possible role of bile acid binder in the intracellular transport of bile acids in the ileum.

3-Hydroxysteroid Dehydrogenases↗
PubMed1993

cDNA cloning and expression of the human hepatic bile acid-binding protein. A member of the monomeric reductase gene family.

In human liver, we previously identified one isoform of dihydrodiol dehydrogenase activity that expresses high affinity bile acid binding (HBAB) with minimal 3 alpha-hydroxysteroid dehydrogenase (3 alpha-HSD) activity for bile acids. This protein may assist in the rapid intracellular transport of bile acids from the sinusoidal to the canalicular pole of the cell. We now report the cDNA cloning and bacterial expression of this novel, multifunctional protein. A 1252-base pair HBAB cDNA was cloned from a HepG2 lambda GT11 library using a rat hepatic bile acid binder cDNA probe. Bacterial expressed recombinant HBAB oxidized racemic trans dihydrodiol benzene (0.455 mumol NADPH/mg/min) with minimal 3 alpha-HSD activity for bile acids (< 0.003 mumol NADPH/mg/min). Lithocholic acid and chenodeoxycholic acid dissociation constants as determined by displacement of the fluorescent probe, bis-1-anilino-8 sulfonate, were higher than those previously reported for the native protein (1 microM versus 10 nM). Significant amino acid sequence homology was found with the human chlordecone reductase, bovine prostaglandin F synthetase, and rat hepatic-3 alpha-HSD suggesting, that HBAB is also a member of the recently identified, monomeric oxidoreductase gene family. Future studies will define the physiologic significance of this novel, multifunctional protein in bile acid transport and xenobiotic metabolism.

3-Hydroxysteroid Dehydrogenases↗
PubMed1993

Lithocholate-3-O-glucuronide-induced cholestasis. A study with congenital hyperbilirubinemic rats and effects of ursodeoxycholate conjugates.

The mechanism of lithocholate-3-O-glucuronide-induced cholestasis is unknown. In this study, we investigated the cholestatic effects of this agent in a congenital hyperbilirubinemic rat, EHBR. We also studied the effects of ursodeoxycholate-3-O-glucuronide and tauroursodeoxycholate on lithocholate-3-O-glucuronide-induced cholestasis in rats. Lithocholate-3-O-glucuronide, administered at the rate of 0.1 mumol/min/100 g for 40 min, a cholestatic dose in control rats, failed to cause cholestasis in EHBR, and biliary lithocholate-3-O-glucuronide excretion was delayed. Biliary concentrations of this agent did not correlate with the severity of cholestasis. Both tauroursodeoxycholate and ursodeoxycholate-3-O-glucuronide, infused at the rate of 0.2 mumol/min/100 g for 120 min, completely inhibited cholestasis induced by lithocholate-3-O-glucuronide administered at the rate of 0.1 mumol/min/100 g for 40 min. Only tauroursodeoxycholate enhanced biliary lithocholate-3-O-glucuronide excretion. These findings indicate that lithocholate-3-O-glucuronide-induced cholestasis is induced by damage at the level of the bile canalicular membrane. Ursodeoxycholate-3-O-glucuronide inhibits this cholestasis, possibly by inhibiting the access of lithocholate-3-O-glucuronide to the bile canalicular membrane.

Animals↗