Effects of phalloidin and colchicine on diethylmaleate-induced choleresis and ultrastructural appearance of rat hepatocytes

Loss of a Candidate Biliary Atresia Susceptibility Gene, add3a, Causes Biliary Developmental Defects in Zebrafish

OBJECTIVES

Biliary atresia (BA) is a progressive fibroinflammatory cholangiopathy affecting the bile ducts of neonates. Although BA is the leading indication for pediatric liver transplantation, the etiology remains elusive. Adducin 3 (ADD3) and X-prolyl aminopeptidase 1 (XPNPEP1) are 2 genes previously identified in genome-wide association studies as potential BA susceptibility genes. Using zebrafish, we investigated the importance of ADD3 and XPNPEP1 in functional studies.

METHODS

To determine whether loss of either gene leads to biliary defects, we performed morpholino antisense oligonucleotide (MO) knockdown studies targeting add3a and xpnpep1 in zebrafish. Individuals were assessed for decreases in biliary function and the presence of biliary defects. Quantitative polymerase chain reaction was performed on pooled 5 days postfertilization larvae to assess variations in transcriptional expression of genes of interest.

RESULTS

Although both xpnpep1 and add3a are expressed in the developing zebrafish liver, only knockdown of add3a produced intrahepatic defects and decreased biliary function. Similar results were observed in homozygous add3a mutants. MO-mediated knockdown of add3a also showed higher mRNA expression of hedgehog (Hh) targets. Inhibition of Hh signaling rescued biliary defects caused by add3a knockdown. Combined knockdown of add3a and glypican-1 (gpc1), another mediator of Hh activity that is also a BA susceptibility gene, resulted in more severe biliary defects than knockdown of either alone.

CONCLUSIONS

Our results support previous studies identifying ADD3 as a putative genetic risk factor for BA susceptibility. Our results also provide evidence that add3a may be affecting the Hh pathway, an important factor in BA pathogenesis.

Protective effect of bile acid derivatives in phalloidin-induced rat liver toxicity

Phalloidin causes severe liver damage characterized by marked cholestasis, which is due in part to irreversible polymerization of actin filaments. Liver uptake of this toxin through the transporter OATP1B1 is inhibited by the bile acid derivative BALU-1, which does not inhibit the sodium-dependent bile acid transporter NTCP. The aim of the present study was to investigate whether BALU-1 prevents liver uptake of phalloidin without impairing endogenous bile acid handling and hence may have protective effects against the hepatotoxicity induced by this toxin. In anaesthetized rats, i.v. administration of BALU-1 increased bile flow more than taurocholic acid (TCA). Phalloidin administration decreased basal (-60%) and TCA-stimulated bile flow (-55%) without impairing bile acid output. Phalloidin-induced cholestasis was accompanied by liver necrosis, nephrotoxicity and haematuria. In BALU-1-treated animals, phalloidin-induced cholestasis was partially prevented. Moreover haematuria was not observed, which was consistent with histological evidences of BALU-1-prevented injury of liver and kidney tissue. HPLC-MS/MS analysis revealed that BALU-1 was secreted in bile mainly in non-conjugated form, although a small proportion (<5%) of tauro-BALU-1 was detected. BALU-1 did not inhibit the biliary secretion of endogenous bile acids. When highly choleretic bile acids, - ursodeoxycholic (UDCA) and dehydrocholic acid (DHCA) - were administered, they were found less efficient than BALU-1 in preventing phalloidin-induced cholestasis. Biliary phalloidin elimination was low but it was increased by BALU-1>TCA>DHCA>UDCA. In conclusion, BALU-1 is able to protect against phalloidin-induced hepatotoxicity, probably due to an inhibition of the liver uptake and an enhanced biliary secretion of this toxin.

Bilirubin in clinical practice: a review

Bilirubin is an endogenous compound that can be toxic under certain conditions but, on the other hand, mild unconjugated hyperbilirubinaemia might protect against cardiovascular diseases and tumour development. Serum bilirubin levels are often enhanced under a variety of clinical conditions. These are discussed and the mechanisms are outlined.

Effects of colchicine on liver functions of cirrhotic rats: beneficial effects result from stellate cell inactivation and inhibition of TGF beta1 expression

Liver cirrhosis (LC) is a chronic disease with high mortality rate and its pathophysiology includes hepatic parenchymal cell destruction, connective tissue formation, and nodular regeneration. Colchicine has been used in liver diseases as an anti-inflammatory and anti-fibrotic drug. However, there is controversy over the beneficial effects of colchicine in LC treatment. In the present study, we injected rats with multiple doses of dimethylnitrosamine for 4 weeks and used rats with severe LC to determine whether colchicine treatment improved liver functions and resolved cirrhotic nodules. Colchicine (30-150microg/kg per day, i.p., for 4 weeks) failed to significantly increase the survival rate of LC rats. Animals were subjected to blood biochemical, liver histopathological and immunochemical analyses. The plasma albumin level, decreased in cirrhotic rats, was restored by colchicine treatment along with reduction of ascites. Colchicine decreased the accumulated extracellular matrix and the multiple fibrotic nodules formed in cirrhotic liver, and eliminated alpha-smooth muscle actin (alpha-SMA)-positive cells. In activated stellate cells, colchicine inhibited alpha-SMA and transforming growth factor-beta1 (TGFbeta1) expression. The results of the present study showed that colchicine resolves cirrhotic nodules and accumulated fibers in the liver of LC rats, but failed to significantly improve the survival rate of LC animals, and that the beneficial effects of colchicine in cirrhotic animals result from stellate cell inactivation and inhibition of TGFbeta1 expression.

Role of glutathione and oxidative stress in phalloidin-induced cholestasis

BACKGROUND/AIMS

Biliary glutathione is an important generator of the bile-salt independent flow, and is known to be regulated by the hepatic glutathione availability. We investigated, in an acute model of phalloidin-induced cholestasis, biliary glutathione secretion and the role of hepatic glutathione, oxidative stress, and protein kinase c activation, which have been implicated in many hepatotoxin-induced hepatic dysfunctions.

METHODS

Rats were given a single dose of 80 microg/100 g body weight of phalloidin and the hepatic thiols and glutathione content, redox state and vesicular activity were evaluated during both development of and recovery from cholestasis. The prophylactic effect of N-acetylcysteine (a precursor of glutathione synthesis and an antioxidant) was also examined. In addition, in the isolated perfused rat liver, we studied the prophylactic effect of the PKc inhibitor H7 on phalloidin-induced cholestasis.

RESULTS

In the early stages of cholestasis, phalloidin induced a decline in bile flow, mainly related to a disruption of biliary glutathione secretion. The decline in biliary glutathione content was not associated with increased glutathione degradation, indicated by a parallel decline in biliary non-protein thiols and by the lack of an increase in biliary gamma-glutamyltranspeptidase. There was also no evidence of hepatic depletion of glutathione or of oxidative stress, as measured by the oxidized-to-reduced glutathione ratio. Moreover, phalloidin resulted in inhibition of vascular transcytosis as assessed by horseradish peroxidase labeling. Pre-treatment with N-acetylcysteine did not counteract the decline in biliary glutathione secretion and bile flow produced by phalloidin, supporting the view that the hepatic availability of glutathione and oxidative stress injury are not implicated in the early stages of cholestatic injury. Moreover, treatment with H-7 did not alter the biliary glutathione output, or the decline in bile flow induced by the toxin.

CONCLUSIONS

This study suggests that the phalloidin-induced inhibition of bile formation may be attributed to rapid disruption of the hepatocanalicular transport of glutathione.

Effect of diethylmaleate on bile secretion and ultrastructural appearance of hepatocytes in normal rats and mutant rats with defective organic anion secretion

Diethylmaleate is an organic anion secreted into bile as a glutathione conjugate. Its transport by the hepatocyte is associated with dilatation of the Golgi apparatus and the appearance of small vesicles in the pericanalicular area. It has been speculated that the Golgi apparatus could play a role in the intracellular transport and/or the biliary canalicular secretion of diethylmaleate. The purpose of this work was to determine whether the alterations in the Golgi apparatus and the pericanalicular vesicles could mediate the canalicular secretion of diethylmaleate. Diethylmaleate biliary secretion and diethylmaleate-induced bile flow were measured in Sprague-Dawley rats, and in TR- rats which have an inherited defect in the excretion into bile of organic anions, including glutathione conjugates. Livers of both Sprague-Dawley and TR-rats were examined by electron microscopy, to characterize the changes in intracellular organelles. In Sprague-Dawley rats, as previously described, diethylmaleate administration was associated with an increase in bile flow, which was parallel in time to the secretion into bile of diethylmaleate conjugates. Electron microscopic examination of the liver after diethylmaleate administration showed dilatation of the Golgi saccules. In contrast, in TR- rats, the increase in bile flow and the secretion of diethylmaleate conjugated were nearly absent. Nevertheless, electron microscopic examination showed a dilatation of the Golgi saccules similar to that observed in Sprague-Dawley rats. TR- rats, in addition to the changes in the Golgi apparatus, had marked dilatation of the endoplasmic reticulum. These results show that biliary secretion of diethylmaleate conjugates was severely impaired in TR- rats, in spite of a dilatation of the Golgi apparatus and of the endoplasmic reticulum. We conclude that it is unlikely that the alterations in the Golgi apparatus (and the endoplasmic reticulum) induced by diethylmaleate play a role in the canalicular secretion of diethylmaleate. We do not exclude the possibility that these organelles could play a role in intracellular transport of this compound. Alternatively, these alterations could be due to a "toxic" effect of diethylmaleate accumulation in hepatocytes.