Na+ -taurocholate cotransporting polypeptide inhibition has hepatoprotective effects in cholestasis in mice.

Accumulation of bile salts (BSs) during cholestasis leads to hepatic and biliary injury, driving inflammatory and fibrotic processes. The Na+ -Taurocholate Cotransporting Polypeptide (NTCP) is the major hepatic uptake transporter of BSs, and can be specifically inhibited by myrcludex B. We hypothesized that inhibition of NTCP dampens cholestatic liver injury. Acute cholestasis was induced in mice by a 3.5-diethoxycarbonyl-1.4-dihydrocollidine (DDC) diet or by bile duct ligation (BDL). Chronic cholestasis was investigated in Atp8b1-G308V and Abcb4/Mdr2 deficient mice. Mice were injected daily with myrcludex B or vehicle. Myrcludex B reduced plasma alkaline phosphatase (ALP) levels in DDC-fed, Atp8b1-G308V and BDL mice by 39%, 27% and 48% respectively. Expression of genes involved in fibrosis, proliferation and inflammation was reduced by myrcludex B treatment in DDC-fed and Atp8b1-G308V mice. NTCP-inhibition increased plasma BS levels from 604±277 to 1746±719 µm in DDC-fed mice, 432±280 to 762±288 µm in Atp8b1-G308V mice and from 522±130 to 3625±378 µm in BDL mice. NTCP-inhibition strongly aggravated weight loss in BDL mice, but not in other cholestatic models studied. NTCP-inhibition reduced biliary BS output in DDC-fed and Atp8b1-G308V mice by ∼50% while phospholipid (PL) output was maintained, resulting in a higher PL/BS ratio. Conversely, liver injury in Abcb4 deficient mice, lacking biliary phospholipid output, was aggravated after myrcludex B treatment. Conclusion: NTCP-inhibition by myrcludex B has hepatoprotective effects, by reducing BS load in hepatocytes and increasing the biliary PL/BS ratio. High micromolar plasma BS levels after NTCP-inhibition were well tolerated. NTCP-inhibition may be beneficial in selected forms of cholestasis. (Hepatology 2018).

Hydroethanolic extract of Baccharis trimera ameliorates alcoholic fatty liver disease in mice.

Ethanol abuse is a serious public health problem that is associated with several stages of alcoholic liver disease (ALD) and a high incidence of morbidity and mortality. Alcoholic fatty liver disease (AFLD), the earliest stage of ALD, is a multifactorial injury that involves oxidative stress and disruptions of lipid metabolism. Although benign and reversible, no pharmacological treatments are available for this condition. In the present study, we induced AFLD in mice with 10% ethanol and a low-protein diet and then orally treated them with a hydroethanolic extract of Baccharis trimera (HEBT; 30 mg kg-1). HEBT reversed ethanol-induced oxidative stress in the liver, reduced lipoperoxidation, normalized GPx, GST, SOD and Cat activity, and GSH and total ROS levels. The reverser effect of HEBT was observed upon ethanol-induced increases in the levels of plasma and hepatic triglycerides, plasma cholesterol, plasma high-density lipoprotein, and plasma and hepatic low-density lipoprotein. Moreover, HEBT increased fecal triglycerides and reduced the histological ethanol-induced lesions in the liver. HEBT also altered the expression of genes that are involved in ethanol metabolism, antioxidant systems, and lipogenesis (i.e., CypE1, Nrf2, and Scd1, respectively). No signs of toxicity were observed in HEBT-treated mice. We propose that HEBT may be a promising pharmacological treatment for AFLD.

Hepatic cytochrome P450 deficiency in mouse models for intrahepatic cholestasis predispose to bile salt-induced cholestasis.

Progressive familial intrahepatic cholestasis (PFIC) types 1 and 3 are severe cholestatic liver diseases caused by deficiency of ATB8B1 and ABCB4, respectively. Mouse models for PFIC display mild phenotypes compared with human patients, and this can be explained by the difference in bile salt pool composition. Mice, unlike humans, have the ability to detoxify hydrophobic bile salts by cytochrome P450-mediated (re)hydroxylation and thus have a less toxic bile salt pool. We have crossed mouse models for PFIC1 and PFIC3 with Hrn mice that have a reduced capacity to (re)hydroxylate bile salts. Double transgenes were obtained by backcrossing Atp8b1(G308V/G308V) and Abcb4(-/-) mice with Hrn mice that have a liver-specific disruption of the cytochrome P450 reductase gene and therefore have markedly reduced P450 activity. In these mice, a more hydrophobic bile salt pool was instilled by cholic acid supplementation of the diet, and bile formation and liver pathology was studied. As opposed to single transgenes, Atp8b1(G308V/G308V)/Hrn and Abcb4(-/-)/Hrn mice rapidly developed strong cholestasis that was evidenced by increased plasma bilirubin and bile salt levels. The bile salt pool was more toxic in both models; Atp8b1(G308V/G308V)/Hrn mice had a more hydrophobic plasma pool compared with the single transgene, whereas Abcb4(-/-)/Hrn mice had a more hydrophobic biliary pool compared with the single transgene. In line with these findings, liver damage was not aggravated in Atp8b1(G308V/G308V)/Hrn but was more severe in Abcb4(-/-)/Hrn mice. These data indicate that bile salt pool composition is a critical determinant in the initiation and progression of cholestasis and liver pathology in PFIC1 and PFIC3. Most importantly, our data suggest that the hydrophobicity of the plasma bile salt pool is an important determinant of the severity of cholestasis, whereas the hydrophobicity of the biliary bile salt pool is an important determinant of the severity of liver pathology.

Advances in pathogenesis and management of pruritus in cholestasis.

Chronic pruritus is a burdensome feature of numerous hepatobiliary disorders such as primary biliary cirrhosis, primary sclerosing cholangitis, cholangiocarcinoma, inherited forms of cholestasis and intrahepatic cholestasis of pregnancy. Bile salts, µ-opioids, serotonin, histamine and steroids have been controversially discussed in the pathogenesis of cholestatic pruritus. However, for these substances neither a correlation with itch severity nor a causative link has ever been established. Recent findings indicate that the potent neuronal activator lysophosphatidic acid and autotaxin, the enzyme forming lysophosphatidic acid, may play a key element in the pathogenesis of cholestatic pruritus. Serum activity of autotaxin correlated with itch intensity and response to antipruritic treatment in patients with cholestatic pruritus, but not other forms of pruritus. Autotaxin activity thereby represents the first biomarker for pruritus and had a positive predictive value of 70% in differentiating cholestatic pruritus from other forms of pruritus. Treatment options for patients with cholestatic pruritus include the anion exchange resin colestyramine, the PXR agonist rifampicin, the µ-opioid antagonist naltrexone, and the serotonin reuptake inhibitor sertraline. These drugs are recommended by evidence-based guidelines as a stepwise therapeutic approach. Patients unresponsive to these drugs should be referred to specialized centers to receive experimental approaches such as UVB phototherapy, albumin dialysis, plasmapheresis or nasobiliary drainage. This review discusses pruritogen candidates in cholestasis, gives novel insights into the neuronal signaling pathway of pruritus and summarizes evidence-based treatment options for patients suffering from pruritus in cholestasis.

ABCC6-mediated ATP secretion by the liver is the main source of the mineralization inhibitor inorganic pyrophosphate in the systemic circulation-brief report.

OBJECTIVE: Mutations in ABCC6 underlie the ectopic mineralization disorder pseudoxanthoma elasticum (PXE) and some forms of generalized arterial calcification of infancy, both of which affect the cardiovascular system. Using cultured cells, we recently showed that ATP-binding cassette subfamily C member 6 (ABCC6) mediates the cellular release of ATP, which is extracellularly rapidly converted into AMP and the mineralization inhibitor inorganic pyrophosphate (PPi). The current study was performed to determine which tissues release ATP in an ABCC6-dependent manner in vivo, where released ATP is converted into AMP and PPi, and whether human PXE ptients have low plasma PPi concentrations. APPROACH AND RESULTS: Using cultured primary hepatocytes and in vivo liver perfusion experiments, we found that ABCC6 mediates the direct, sinusoidal, release of ATP from the liver. Outside hepatocytes, but still within the liver vasculature, released ATP is converted into AMP and PPi. The absence of functional ABCC6 in patients with PXE leads to strongly reduced plasma PPi concentrations. CONCLUSIONS: Hepatic ABCC6-mediated ATP release is the main source of circulating PPi, revealing an unanticipated role of the liver in systemic PPi homeostasis. Patients with PXE have a strongly reduced plasma PPi level, explaining their mineralization disorder. Our results indicate that systemic PPi is relatively stable and that PXE, generalized arterial calcification of infancy, and other ectopic mineralization disorders could be treated with PPi supplementation therapy.

Advances in pathogenesis and treatment of pruritus.

The pathogenesis of itch during cholestasis is largely unknown and treatment options are limited. Lysophosphatidate, female steroid hormones, and endogenous opioids are among the agents discussed as potential pruritogens in cholestasis. The itch-alleviating action of guideline-based therapeutic interventions with anion exchanger resins, rifampicin, opioid antagonists, and serotonin reuptake inhibitors are studied to unravel the molecular pathogenesis of itch. Still, a considerable part of the patients is in need of alternative experimental therapeutic approaches (eg, UV-B phototherapy, extracorporeal albumin dialysis, nasobiliary drainage), providing additional information about the enigmatic pathophysiology of cholestatic pruritus.

Complementary functions of the flippase ATP8B1 and the floppase ABCB4 in maintaining canalicular membrane integrity.

BACKGROUND & AIMS: Progressive familial intrahepatic cholestasis can be caused by mutations in ABCB4 or ATP8B1; each encodes a protein that translocates phospholipids, but in opposite directions. ABCB4 flops phosphatidylcholine from the inner to the outer leaflet, where it is extracted by bile salts. ATP8B1, in complex with the accessory protein CDC50A, flips phosphatidylserine in the reverse direction. Abcb4(-/-) mice lack biliary secretion of phosphatidylcholine, whereas Atp8b1-deficient mice have increased excretion of phosphatidylserine into bile. Each system is thought to have a role protecting the canalicular membrane from bile salts. METHODS: To investigate the relationship between the mechanisms of ABCB4 and ATP8B1, we expressed the transporters separately and together in cultured cells and studied viability and phospholipid transport. We also created mice with disruptions in ABCB4 and ATP8B1 (double knockouts) and studied bile formation and hepatic damage in mice fed bile salts. RESULTS: Overexpression of ABCB4 was toxic to HEK293T cells; the toxicity was counteracted by coexpression of the ATP8B1-CDC50A complex. In Atp8b1-deficient mice, bile salts induced extraction of phosphatidylserine and ectoenzymes from the canalicular membrane; this process was not observed in the double-knockout mice. CONCLUSIONS: ATP8B1 is required for hepatocyte function, particularly in the presence of ABCB4. This is most likely because the phosphatidylserine flippase complex of ATP8B1-CDC50A counteracts the destabilization of the membrane that occurs when ABCB4 flops phosphatidylcholine. Lipid asymmetry is therefore important for the integrity of the canalicular membrane; ABCB4 and ATP8B1 cooperate to protect hepatocytes from bile salts.

[Pruritus in liver disease. Pathogenesis and treatment]. / Pruritus bij leverziekten. Pathogenese en behandeling.

Pruritus is a severe symptom in patients with cholestatic hepatobiliary disease; it can greatly reduce the quality of life. Cholestatic itching often peaks in the evening and early night. It mainly occurs on the palms of the hands and soles of the feet but can also occur more generalised. The pathogenesis of cholestatic pruritus has not yet been completely clarified. Possible contributors are bile salts, histamine, progesterone metabolites and opioids. A relationship between these elements and the intensity of the itch has not, however, been demonstrated. Autotaxin, an enzyme that produces lysophosphatidic acid, has recently been identified as a possible pruritogen caused by cholestasis. Treatment is aimed at eliminating pruritogens with bile acid sequestrants (cholestyramine), managing the metabolism of pruritogens (rifampicin), and influencing the perception of itch by the central nervous system with µ-opioid antagonists or SSRIs. In cases of unbearable, treatment-resistant itching, consideration may be given to experimental therapies such as UV light therapy or nasobiliary drainage.

Regulation of direct transintestinal cholesterol excretion in mice.

Biliary secretion is generally considered to be an obligate step in the pathway of excess cholesterol excretion from the body. We have recently shown that an alternative route exists. Direct transintestinal cholesterol efflux (TICE) contributes significantly to cholesterol removal in mice. Our aim was to investigate whether the activity of this novel pathway can be influenced by dietary factors. In addition, we studied the role of cholesterol acceptors at the luminal side of the enterocyte. Mice were fed a Western-type diet (0.25% wt/wt cholesterol; 16% wt/wt fat), a high-fat diet (no cholesterol; 24% wt/wt fat), or high-cholesterol diet (2% wt/wt), and TICE was measured by isolated intestinal perfusion. Bile salt-phospholipid mixtures served as cholesterol acceptor. Western-type and high-fat diet increased TICE by 50 and 100%, respectively. In contrast, the high-cholesterol diet did not influence TICE. Intestinal scavenger receptor class B type 1 (Sr-B1) mRNA and protein levels correlated with the rate of TICE. Unexpectedly, although confirming a role for Sr-B1, TICE was significantly increased in Sr-B1-deficient mice. Apart from the long-term effect of diets on TICE, acute effects by luminal cholesterol acceptors were also investigated. The phospholipid content of perfusate was the most important regulator of TICE; bile salt concentration or hydrophobicity of bile salts had little effect. In conclusion, TICE can be manipulated by dietary intervention. Specific dietary modifications might provide means to stimulate TICE and, thereby, to enhance total cholesterol turnover.

ATP8B1 requires an accessory protein for endoplasmic reticulum exit and plasma membrane lipid flippase activity.

UNLABELLED: Mutations in ATP8B1 cause progressive familial intrahepatic cholestasis type 1 and benign recurrent intrahepatic cholestasis type 1. Previously, we have shown in mice that Atp8b1 deficiency leads to enhanced biliary excretion of phosphatidylserine, and we hypothesized that ATP8B1 is a flippase for phosphatidylserine. However, direct evidence for this function is still lacking. In Saccharomyces cerevisiae, members of the Cdc50p/Lem3p family are essential for proper function of the ATP8B1 homologs. We have studied the role of two human members of this family, CDC50A and CDC50B, in the routing and activity of ATP8B1. When only ATP8B1 was expressed in Chinese hamster ovary cells, the protein localized to the endoplasmic reticulum. Coexpression with CDC50 proteins resulted in relocalization of ATP8B1 from the endoplasmic reticulum to the plasma membrane. Only when ATP8B1 was coexpressed with CDC50 proteins was a 250%-500% increase in the translocation of fluorescently labeled phosphatidylserine observed. Importantly, natural phosphatidylserine exposure in the outer leaflet of the plasma membrane was reduced by 17%-25% in cells coexpressing ATP8B1 and CDC50 proteins in comparison with cells expressing ATP8B1 alone. The coexpression of ATP8B1 and CDC50A in WIF-B9 cells resulted in colocalization of both proteins in the canalicular membrane. CONCLUSION: Our data indicate that CDC50 proteins are pivotal factors in the trafficking of ATP8B1 to the plasma membrane and thus may be essential determinants of ATP8B1-related disease. In the plasma membrane, ATP8B1 functions as a flippase for phosphatidylserine. Finally, CDC50A may be the potential beta-subunit or chaperone for ATP8B1 in hepatocytes.

Orlistat treatment of unconjugated hyperbilirubinemia in Crigler-Najjar disease: a randomized controlled trial.

Unconjugated hyperbilirubinemia in Crigler-Najjar (CN) disease is conventionally treated with phototherapy and phenobarbital. Orlistat treatment increases fecal fat excretion and decreases plasma unconjugated bilirubin (UCB) concentrations in Gunn rats, the animal model for CN disease. We determined in CN patients the effects of orlistat treatment on plasma UCB concentrations, and on fecal excretion of fat and UCB. A randomized, placebo-controlled, double-blind, cross-over trial was conducted in 16 patients, simultaneous with their regular treatment (phototherapy, n = 11, and/or phenobarbital, n = 6). Patients received orlistat or placebo, each for 4-6 wk. Compared with placebo, orlistat increased fecal fat excretion (+333%) and fecal UCB excretion (+43%). Orlistat treatment significantly decreased plasma UCB concentration (-9%). In 7 of 16 patients, the decrease in plasma UCB levels was clinically relevant (>10%, mean 21%). In patients with a clinically relevant response, plasma UCB concentrations during orlistat were strongly, negatively correlated with fecal fat excretion (r = -0.93). Clinically relevant response to orlistat treatment was not correlated with age, sex, CN type, BMI, or co-treatment with phototherapy or phenobarbital, but appeared correlated with a relatively lower dietary fat intake. In conclusion, orlistat treatment decreases plasma UCB concentrations, particularly in a subgroup of CN patients. Dietary fat intake may determine the responsiveness to orlistat treatment.

Increased serum concentrations of secondary bile salts during cholate feeding are due to coprophagy. A study with wild-type and Atp8b1-deficient mice.

Coprophagy (i.e., consumption of feces) is a behavior seen in rodents and other animal species. This behavior can substantially influence the enterohepatic cycling of compounds, including bile salts. Since many studies involve the feeding of rodents with bile salt supplemented diets, it is of importance to know the influence of coprophagy on bile salt composition in such studies. We compared the peripheral and portal bile salt composition of mice in conventional and metabolic cages when fed a control diet or a diet containing 0.5% cholate. We also performed these experiments with Atp8b1-deficient mice as it has been suggested that in the absence of this transporter bile salt absorption in the intestine would be increased. In mice on a control diet there is little difference in bile salt composition between conventional housing and metabolic housing. Metabolic housing led to a near complete disappearance of the low levels of dihydroxy bile salts (i.e., deoxycholate + chenodeoxycholate) in peripheral serum. In mice fed a control diet, the portal blood concentration of unconjugated dihydroxy bile salts was extremely low (<2%), but these rose to about 10% when mice were fed a cholate-supplemented diet. In metabolic cages the portal blood content of these unconjugated dihydroxy bile salts was reduced to undetectable levels. Whether housed in conventional cages or in metabolic cages, wild-type and Atp8b1-deficient mice had similar concentrations in portal blood, suggesting that intestinal bile salt absorption is not altered in Atp8b1-deficient mice.