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

Adjunct Fenofibrate Up-regulates Bile Acid Glucuronidation and Improves Treatment Response For Patients With Cholestasis

Accumulation of cytotoxic bile acids (BAs) during cholestasis can result in liver failure. Glucuronidation, a phase II metabolism pathway responsible for BA detoxification, is regulated by peroxisome proliferator-activated receptor alpha (PPARα). This study investigates the efficacy of adjunct fenofibrate therapy to up-regulate BA-glucuronidation and reduce serum BA toxicity during cholestasis. Adult patients with primary biliary cholangitis (PBC, n = 32) and primary sclerosing cholangitis (PSC, n = 23), who experienced an incomplete response while receiving ursodiol monotherapy (13-15 mg/kg/day), defined as serum alkaline phosphatase (ALP) ≥ 1.5 times the upper limit of normal, received additional fenofibrate (145-160 mg/day) as standard of care. Serum BA and BA-glucuronide concentrations were measured by liquid chromatography-mass spectrometry. Combination therapy with fenofibrate significantly decreased elevated serum ALP (-76%, P < 0.001), aspartate transaminase, alanine aminotransferase, bilirubin, total serum BAs (-54%), and increased serum BA-glucuronides (+2.1-fold, P < 0.01) versus ursodiol monotherapy. The major serum BA-glucuronides that were favorably altered following adjunct fenofibrate include hyodeoxycholic acid-6G (+3.7-fold, P < 0.01), hyocholic acid-6G (+2.6-fold, P < 0.05), chenodeoxycholic acid (CDCA)-3G (-36%), and lithocholic acid (LCA)-3G (-42%) versus ursodiol monotherapy. Fenofibrate also up-regulated the expression of uridine 5'-diphospho-glucuronosyltransferases and multidrug resistance-associated protein 3 messenger RNA in primary human hepatocytes. Pearson's correlation coefficients identified strong associations between serum ALP and metabolic ratios of CDCA-3G (r2  = 0.62, P < 0.0001), deoxycholic acid (DCA)-3G (r2  = 0.48, P < 0.0001), and LCA-3G (r2  = 0.40, P < 0.001), in ursodiol monotherapy versus control. Receiver operating characteristic analysis identified serum BA-glucuronides as measures of response to therapy. Conclusion: Fenofibrate favorably alters major serum BA-glucuronides, which correlate with reduced serum ALP levels and improved outcomes. A PPARα-mediated anti-cholestatic mechanism is involved in detoxifying serum BAs in patients with PBC and PSC who have an incomplete response on ursodiol monotherapy and receive adjunct fenofibrate. Serum BA-glucuronides may serve as a noninvasive measure of treatment response in PBC and PSC.

Role of glucuronidation for hepatic detoxification and urinary elimination of toxic bile acids during biliary obstruction

Biliary obstruction, a severe cholestatic condition, results in a huge accumulation of toxic bile acids (BA) in the liver. Glucuronidation, a conjugation reaction, is thought to protect the liver by both reducing hepatic BA toxicity and increasing their urinary elimination. The present study evaluates the contribution of each process in the overall BA detoxification by glucuronidation. Glucuronide (G), glycine, taurine conjugates, and unconjugated BAs were quantified in pre- and post-biliary stenting urine samples from 12 patients with biliary obstruction, using liquid chromatography-tandem mass spectrometry (LC-MS/MS). The same LC-MS/MS procedure was used to quantify intra- and extracellular BA-G in Hepatoma HepG2 cells. Bile acid-induced toxicity in HepG2 cells was evaluated using MTS reduction, caspase-3 and flow cytometry assays. When compared to post-treatment samples, pre-stenting urines were enriched in glucuronide-, taurine- and glycine-conjugated BAs. Biliary stenting increased the relative BA-G abundance in the urinary BA pool, and reduced the proportion of taurine- and glycine-conjugates. Lithocholic, deoxycholic and chenodeoxycholic acids were the most cytotoxic and pro-apoptotic/necrotic BAs for HepG2 cells. Other species, such as the cholic, hyocholic and hyodeoxycholic acids were nontoxic. All BA-G assayed were less toxic and displayed lower pro-apoptotic/necrotic effects than their unconjugated precursors, even if they were able to penetrate into HepG2 cells. Under severe cholestatic conditions, urinary excretion favors the elimination of amidated BAs, while glucuronidation allows the conversion of cytotoxic BAs into nontoxic derivatives.

Profiling serum bile acid glucuronides in humans: gender divergences, genetic determinants, and response to fenofibrate

Glucuronidation, catalyzed by UDP-glucuronosyltransferase (UGT) enzymes detoxifies cholestatic bile acids (BAs). We aimed at i) characterizing the circulating BA-glucuronide (-G) pool composition in humans, ii) evaluating how sex and UGT polymorphisms influence this composition, and iii) analyzing the effects of lipid-lowering drug fenofibrate on the circulating BA-G profile in 300 volunteers and 5 cholestatic patients. Eleven BA-Gs were determined in pre- and post-fenofibrate samples. Men exhibited higher BA-G concentrations, and various genotype/BA-G associations were discovered in relevant UGT genes. The chenodeoxycholic acid-3G concentration was associated with the UGT2B7 802C>T polymorphism. Glucuronidation assays confirmed the predominant role of UGT2B7 and UGT1A4 in CDCA-3G formation. Fenofibrate exposure increased the serum levels of 5 BA-G species, including CDCA-3G, and up-regulated expression of UGT1A4, but not UGT2B7, in hepatic cells. This study demonstrates that fenofibrate stimulates BA glucuronidation in humans, and thus reduces bile acid toxicity in the liver.

Effect of genipin on cholestasis induced by estradiol-17beta-glucuronide and lithocholate-3-O-glucuornide in rats

AIM

Genipin is reported to stimulate the insertion of multidrug resistance protein 2 (Mrp2) in the bile canalicular membrane, thereby causing choleresis by the increased the biliary excretion of glutathione, which has been considered to be a substrate of Mrp2. In the present study, we examined the effect of genipin on cholestasis induced by estradiol-17beta-glucuronide and lithocholate-3-O-glucuronide, Mrp2 substrates, in rats. Further, the effect of genipin on the biliary excretion of substrates of P-glycoprotein (P-gp), vinblastine and erythromycin, was also studied.

METHODS

The effect of genipin infusion at the rate of 0.5 micromol/min/100 g on cholestasis induced by estradiol-17beta-glucuronide (0.075 micromol/min/100 g for 20 min) and lithocholate-3-O-glucuronide (0.15 micromol/min/100 g for 40 min) was studied. The effect of genipin infusion on the biliary excretion of a tracer dose of vinblastine and erythromycin infused at the rate of 0.1 micromol/min/100 g was also studied.

RESULTS

Genipin relieved estradiol-17beta-glucuronide-induced cholestasis, and cumulative biliary estradiol-17beta-glucuronide excretion for 120 min was increased from 50 +/- 20%-81 +/- 20% dose. In contrast, genipin had no effect on lithocholate-3-O-glucuronide-induced cholestasis. Biliary excretion of a tracer dose of vinblastine and the maximum biliary excretion of erythromycin were significantly decreased by genipin.

CONCLUSIONS

Genipin protected estradiol-17beta-glucuronide-induced cholestasis. The mechanism of the protection of cholestasis by genipin is unknown, but it is speculated to be due to a conformational change of P-gp by genipin, in addition to the stimulation of Mrp2 insertion into the bile canaliculi.

Integration of hepatic drug transporters and phase II metabolizing enzymes: Mechanisms of hepatic excretion of sulfate, glucuronide, and glutathione metabolites

The liver is the primary site of drug metabolism in the body. Typically, metabolic conversion of a drug results in inactivation, detoxification, and enhanced likelihood for excretion in urine or feces. Sulfation, glucuronidation, and glutathione conjugation represent the three most prevalent classes of phase II metabolism, which may occur directly on the parent compounds that contain appropriate structural motifs, or, as is usually the case, on functional groups added or exposed by phase I oxidation. These three conjugation reactions increase the molecular weight and water solubility of the compound, in addition to adding a negative charge to the molecule. As a result of these changes in the physicochemical properties, phase II conjugates tend to have very poor membrane permeability, and necessitate carrier-mediated transport for biliary or hepatic basolateral excretion into sinusoidal blood for eventual excretion into urine. This review summarizes sulfation, glucuronidation, and glutathione conjugation reactions, as well as recent progress in elucidating the hepatic transport mechanisms responsible for the excretion of these conjugates from the liver. The discussion focuses on alterations of metabolism and transport by chemical modulators, and disease states, as well as pharmacodynamic and toxicological implications of hepatic metabolism and/or transport modulation for certain active phase II conjugates. A brief discussion of issues that must be considered in the design and interpretation of phase II metabolite transport studies follows.

Effect of organic anions and bile acid conjugates on biliary excretion of taurine-conjugated bile acid sulfates in the rat

Biliary organic anion excretion is mediated by an ATP-dependent primary active transporter, canalicular multispecific organic anion transporter/multidrug resistance protein 2. On the other hand, a multiplicity of canalicular organic anion transporter/multidrug resistance protein 2 has been suggested. Therefore, to examine the effect of hydrophobicity on the substrate specificity of canalicular multispecific organic anion transporter/multidrug resistance protein 2, we examined the effect of organic anions and bile acid conjugates on biliary excretion of three taurine-conjugated bile acid sulfates with different hydrophobicity, taurolithocholate-3-sulfate, taurochenodeoxycholate3-sulfate, and taurocholate-3-sulfate in rats. Biliary excretions of these bile acid conjugates were delayed in Eisai hyperbilirubinemic rats. Biliary excretion of these bile acid conjugates was inhibited by sulfobromophthalein, whereas biliary excretion and taurocholate-3-sulfate was not inhibited by phenolphthalein glucuronide. Taurolithocholate-3-sulfate and ursodeoxycholate-3-glucuronide decreased biliary excretion of taurochenodeoxycholate-3-sulfate and taurocholate-3-sulfate, but ursodeoxycholate-3,7-disulfate did not affect biliary excretion of taurochenodeoxycholate-3-sulfate and taurocholate-3-sulfate. These findings indicate that very hydrophilic organic anions are not good substrates of canalicular multispecific organic anion transporter/multidrug resistance protein 2.

Absorption of unconjugated bile acids and tauroursodeoxycholate in the rat intestine

The absorption of ursodeoxycholate and its tauro-conjugate by the jejunum and the terminal ileum of rat intestine was compared with that of other unconjugated bile acids and taurocholate. In the ligated jejunum, the efficacy of absorption of unconjugated bile acids was in the following order: ursodeoxycholate = deoxycholate > chenodeoxycholate = cholate > lithocholate. This order cannot be explained by the theory that the passive diffusion of bile acids is faster the less hydroxyl bonds in the molecule. These findings on the unconjugated bile acids in the ligated jejunum were further confirmed by perfusion experiments. In the ligated terminal ileum, ursodeoxycholate, cholate and deoxycholate were absorbed as fast as taurocholate or tauroursodeoxycholate, whereas absorption of chenodeoxycholate was significantly slower. The Na+-dependency of the absorption of ursodeoxycholate and cholate in the terminal ileum was confirmed by perfusion studies. In conclusion, intestinal absorption of ursodeoxycholate was efficient in both the jejunum and ileum and these results may contribute to the high availability of ursodeoxycholate in various hepatobiliary diseases.

Effect of taurolithocholate-3-sulphate on biliary excretion of sulphobromophthalein and dibromosulphophthalein in the Eisai hyperbilirubinaemic rat

We previously reported that biliary lithocholate-3-sulphate excretion was inhibited by dibromosulphophthalein, not by sulphobromophthalein in Eisai hyperbilirubinaemic rats (EHBR); instead its excretion was inhibited by both organic anions in control rats. In the present study, the effect of taurolithocholate-3-sulphate on the excretion of sulphobromophthalein and dibromosulphophthalein was studied in EHBR and control Sprague-Dawley rats. Taurolithocholate-3-sulfate infusion inhibited biliary excretion of sulphobromophthalein and dibromosulphophthalein in both EHBR and control rats. These findings indicate that in control rats biliary excretion of taurolithocholate-3-sulphate is mediated by a carrier common for both organic anions, and that in EHBR, in which the canalicular multispecific organic anion transporter is impaired, the excretory pathway for taurolithocholate-3-sulphate is also partly identical to that for both organic anions.

Effect of tauro-alpha-muricholate and tauro-beta-muricholate on oestradiol-17 beta-glucuronide-induced cholestasis in rats

The effect of tauro-beta-muricholate (beta MC-tau) and tauro-alpha-muricholate (alpha MC-tau) on oestradiol-17 beta-glucuronide (E217G)-induced cholestasis was compared with that of tauroursodeoxycholate (UDC-tau) in rats. Like UDC-tau, alpha MC-tau and beta MC-tau infused at the rate of 0.2 mumol/min per 100 g bodyweight (BW) completely inhibited the cholestasis induced by E217G infused at the rate of 0.06 mumol/min per 100 g BW for 20 min. These findings indicate that beta MC-tau and alpha MC-tau are useful in protecting against various types of experimental cholestasis, as well as against bile acid-induced cholestasis.

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.

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.

The interaction of hydrophobic bile acids with the alpha 1-proteinase inhibitor

An in vitro complex formation between cholesterol and human alpha 1-proteinase inhibitor (alpha 1-antitrypsin, alpha 1-Pi) has been described. Hydrophobic bile acids were studied for a similar interaction using lithocholic acid (LC) as a prototype of a hydrophobic acid. At a molar ratio of 5:1, LC induced conformational changes of alpha 1-Pi reflected in an abnormal gel-electrophoretic appearance, loss of anodal immunoreactivity on crossed immunoelectrophoresis, exposition of new antigenic determinant(s) on immunodiffusion, and loss of antiproteinase activity. After 6 h incubation, LC and alpha 1-Pi form a complex of approximately 200 kDa molecular mass seen following gel-filtration. After prolonged (24 h) interaction a series of large alpha 1-Pi polymers were seen on SDS-PAGE under reducing conditions followed by Western blotting. Glycolitho-, sulfolitho-, deoxycholic and 3-beta-hydroxy-5-cholenoic acids induced similar but less pronounced changes of alpha 1-Pi, whereas transferrin remained unaffected. Hydrophilic acids lacked effect on alpha 1-Pi. The results are compatible with a specific, irreversible interaction of alpha 1-Pi with hydrophobic bile acids affecting its physical and proteinase inhibitory properties. The cholestatic potency of the hydrophobic acids studied and their ability to induce alpha 1-Pi polymerization may be important in cholestatic conditions.