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Current blood biomarkers are suboptimal in detecting drug-induced liver injury (DILI) and predicting its outcome. We sought to characterize the natural variabilty and performance characteristics of 14 promising DILI biomarker candidates. Serum or plasma from multiple cohorts of healthy volunteers (n = 192 and n = 81), subjects who safely took potentially hepatotoxic drugs without adverse effects (n = 55 and n = 92) and DILI patients (n = 98, n = 28, and n = 143) were assayed for microRNA-122 (miR-122), glutamate dehydrogenase (GLDH), total cytokeratin 18 (K18), caspase cleaved K18, glutathione S-transferase α, alpha-fetoprotein, arginase-1, osteopontin (OPN), sorbitol dehydrogenase, fatty acid binding protein, cadherin-5, macrophage colony-stimulating factor receptor (MCSFR), paraoxonase 1 (normalized to prothrombin protein), and leukocyte cell-derived chemotaxin-2. Most candidate biomarkers were significantly altered in DILI cases compared with healthy volunteers. GLDH correlated more closely with gold standard alanine aminotransferase than miR-122, and there was a surprisingly wide inter- and intra-individual variability of miR-122 levels among healthy volunteers. Serum K18, OPN, and MCSFR levels were most strongly associated with liver-related death or transplantation within 6 months of DILI onset. Prediction of prognosis among DILI patients using the Model for End-Stage Liver Disease was improved by incorporation of K18 and MCSFR levels. Conclusion: GLDH appears to be more useful than miR-122 in identifying DILI patients, and K18, OPN, and MCSFR are promising candidates for prediction of prognosis during an acute DILI event. Serial assessment of these biomarkers in large prospective studies will help further delineate their role in DILI diagnosis and management., (© 2018 by the American Association for the Study of Liver Diseases.)

Recent progress in research on drug-induced liver injury (DILI) has been determined by key developments in two areas. First, new technologies allow the identification of genetic risk factors with improved sensitivity, specificity, and efficiency. Second, new mechanistic concepts of DILI emphasize the importance of unspecific "downstream" events following drug-specific initial "upstream" hepatocyte injury and of complex interactions between environmental and genetic risk factors. The integration of genetic and mechanistic concepts is essential for current research approaches, and genetic studies of DILI now focus on targets that affect the function and transcriptional regulation of genes relating not only to drug metabolism but also to human leukocyte antigens (HLAs), cytokines, oxidative stress, and hepatobiliary transporters. Risk factors affecting unspecific downstream mechanisms may be identified using pooled DILI cases caused by various drugs. The power to detect variants that confer a low risk can be increased by recruitment of strictly selected cases through large networks, whereas controls may also be obtained from genotyped reference populations. The first genomewide studies of DILI identified HLA variants as risk factors for hepatotoxicity associated with flucloxacillin and ximelagatran, and their design has defined a new standard for pharmacogenetic studies. From a clinical and regulatory point of view, there is a need for genetic tests that identify patients at increased hepatotoxic risk. However, DILI is a rare complex disease, and pharmacogenetic studies have so far not been able to identify interactions of several risk factors defining a high population-attributable risk and clinically relevant absolute risk for DILI.

Unlabelled: Intrahepatic cholestasis of pregnancy (ICP) is defined as pruritus and elevated bile acid serum concentrations in late pregnancy. Splicing mutations have been described in the multidrug resistance p-glycoprotein 3 (MDR3, ABCB4) gene in up to 20% of ICP women. Pedigrees studied were not large enough for linkage analysis. Ninety-seven family members of a woman with proven ICP were asked about pruritus in earlier pregnancies, birth complications and symptomatic gallstone disease. The familial cholestasis type 1 (FIC1, ATP8B1) gene, bile salt export pump (BSEP, ABCB11) and MDR3 gene were analyzed in 55 relatives. We identified a dominant mode of inheritance with female restricted expression and a new intronic MDR3 mutation c.3486+5G>A resulting in a 54 bp (3465-3518) inframe deletion via cryptic splicing site activation. Linkage analysis of the ICP trait versus this intragenic MDR3 variant yielded a LOD score of 2.48. A Bayesian analysis involving MDR3, BSEP, FIC1 and an unknown locus gave a posterior probability of >0.9966 in favor of MDR3 as causative ICP locus. During the episode of ICP the median gamma-glutamyl transpeptidase (gamma-GT) activity was 10 U/l (95% CI, 6.9 to 14.7 U/l) in the index woman. Four stillbirths were reported in seven heterozygous women (22 pregnancies) and none in five women (14 pregnancies) without MDR3 mutation. Symptomatic gallstone disease was more prevalent in heterozygous relatives (7/21) than in relatives without the mutation (1/34), (P = 0.00341)., Conclusion: This study demonstrates that splicing mutations in the MDR3 gene can cause ICP with normal gamma-GT and may be associated with stillbirths and gallstone disease.

Primary biliary cirrhosis (PBC) and primary sclerosing cholangitis (PSC) are characterized by a cholestatic pattern of liver damage, also observed in hereditary or acquired dysfunction of the canalicular membrane transporters bile salt export pump (BSEP, ABCB11) and multidrug resistance protein type 3 (MDR3, ABCB4). Controversy exists whether a genetically determined dysfunction of BSEP and MDR3 plays a pathogenic role in PBC and PSC. Therefore, 149 healthy Caucasian control individuals (control group) were compared to 76 PBC and 46 PSC patients with respect to genetic variations in BSEP and MDR3. Sequencing spanned approximately 10,000 bp including promoter and coding regions as well as 50-350 bp of flanking intronic regions. In all, 46 and 45 variants were identified in BSEP and MDR3, respectively. No differences between the groups were detected either in the total number of variants (BSEP: control group: 37, PBC: 37, PSC: 31; and MDR3: control group: 35; PBC: 32, PSC: 30), or in the allele frequency of the common variable sites. Furthermore, there were no significant differences in haplotype distribution and linkage disequilibrium. In conclusion, this study provides an analysis of BSEP and MDR3 variant segregation and haplotype structure in a Caucasian population. Although an impact of rare variants on BSEP and MDR3 function cannot be ruled out, our data do not support a strong role of BSEP and MDR3 genetic variations in the pathogenesis of PBC and PSC.

Hepatobiliary transporters are down-regulated in toxic and cholestatic liver injury. Cytokines such as tumor necrosis factor alpha (TNF-alpha) and interleukin 1 beta (IL-1 beta) are attributed to mediate this regulation, but their particular contribution in vivo is still unknown. Thus, we studied the molecular mechanisms by which Ntcp, Oatp1, Oatp2, and Mrp2 are regulated by proinflammatory cytokines during liver injury. Rats were injected intraperitoneally with either carbon tetrachloride or endotoxin. Inactivation of TNF-alpha and IL-1 beta was achieved by repetitive intraperitoneal injection of etanercept and anakinra, respectively. Messenger RNA (mRNA) levels of transporters and binding activities as well as nuclear protein levels of Ntcp, Oatp2, and Mrp2 transactivators were determined 20 to 24 hours later. In contrast to IL-1 beta, TNF-alpha inactivation alone fully prevented down-regulation of Ntcp, Oatp1, and Oatp2 mRNA as well as reduced binding activity of hepatocyte nuclear factor 1 (HNF-1) in CCl(4)-induced toxic injury. In endotoxemia, down-regulation of Mrp2, and partially in case of Ntcp, could be prevented by IL-1 beta but not TNF-alpha blockade. However, inactivation of either cytokine led to preservation of HNF1 and partially of retinoid X receptor/retinoic acid receptor (RXR/RAR) binding activity. No effect of anticytokines was seen on pregnane X receptor (PXR) and constitutive androstane receptor (CAR) binding activity as well as nuclear protein mass. In conclusion, TNF-alpha represents the master cytokine responsible for HNF1-dependent down-regulation of Ntcp, Oatp1, and Oatp2 in CCl(4)-induced toxic liver injury. IL-1 beta predominates in a complex signaling network of Ntcp and Mrp2 regulation in cholestatic liver injury. In contrast to in vitro studies, HNF1 and RXR/RAR-independent mechanisms appear to be more important in regulation of Mrp2 and Ntcp gene expression in endotoxemia.

Bile acids regulate the expression of genes involved in cholesterol homeostasis. They are ligands of the farnesoid X receptor, which induces small heterodimer partner (SHP)-1, a transcriptional repressor of bile acid synthetic enzymes. In cholestatic liver disease, hepatic bile acid concentrations are elevated and expression of the major Na+-independent bile acid uptake system, organic anion transporting polypeptide (OATP)-C (solute carrier gene family SLC21A6), is markedly decreased. Because the OATP-C gene is transcriptionally dependent on the hepatocyte nuclear factor (HNF) 1 alpha, we hypothesized that bile acids decrease OATP-C expression through direct repression of HNF1 alpha. To test this hypothesis, we studied the regulation of the human HNF1 alpha gene by bile acids. HNF1 alpha expression in cultured hepatoma cells was decreased approximately 50% after 12 hours' exposure to 100 micromol/L chenodeoxycholic acid (CDCA). Characterization of the human HNF1 alpha gene promoter identified a consensus bile acid response element that binds and is activated by HNF4 alpha. Mutagenesis of the HNF4 alpha site abolished baseline HNF1 alpha promoter activity. The central mechanism by which bile acids repress HNF1 alpha is decreased activation by HNF4 alpha. SHP directly inhibits HNF4 alpha-mediated transactivation of the HNF1 alpha promoter in cotransfection assays. In addition, HNF4 alpha nuclear binding activity is decreased by CDCA and the human HNF4 alpha gene promoter is repressed by CDCA through an SHP-independent mechanism. In conclusion, we show that repression of HNF1 alpha is an important new mechanism by which bile acids regulate the expression of HNF1 alpha-dependent genes in man. This explains the suppressive effect of bile acids on the OATP-C gene promoter, leading to decreased expression in cholestatic liver disease.

Ursodeoxycholic acid (UDCA) exerts anticholestatic effects by undefined mechanisms. Previous work suggested that UDCA stimulates biliary exocytosis via Ca(++)- and protein kinase C (PKC)-dependent mechanisms. Therefore, the effect of taurine-conjugated UDCA (TUDCA) was studied in the experimental model of taurolithocholic acid (TLCA)-induced cholestasis on bile flow, hepatobiliary exocytosis, distribution of PKC isoforms, and density of the apical conjugate export pump, Mrp2, in canalicular membranes. Isolated perfused rat livers were preloaded with horseradish peroxidase (HRP), a marker of vesicular exocytosis, and were perfused with bile acids or dimethylsulfoxide (control) only. PKC isoform distribution and membrane density of Mrp2 were studied using immunoblotting and immunoelectron-microscopic techniques. Biliary secretion of the Mrp2 substrate, 2,4-dinitrophenyl-S-glutathione (GS-DNP), was studied in the presence or absence of the PKC inhibitor, bisindolylmaleimide I (BIM-I; 1 micromol/L). TLCA (10 micromol/L) impaired bile flow by 51%; biliary secretion of HRP and GS-DNP by 46% and 95%, respectively; membrane binding of the Ca(++)-sensitive alpha-isoform of PKC by 32%; and density of Mrp2 in the canalicular membrane by 79%. TUDCA (25 micromol/L) reversed the effects of TLCA on bile flow, secretion of HRP and GS-DNP, and distribution of alpha-PKC. TUDCA reduced membrane binding of epsilon-PKC and increased Mrp2 density 4-fold in canalicular membranes of cholestatic hepatocytes. BIM-I inhibited the effect of TUDCA on GS-DNP secretion in cholestatic livers by 49% without affecting secretion in controls. In conclusion, TUDCA may enhance the secretory capacity of cholestatic hepatocytes by stimulation of exocytosis and insertion of transport proteins into apical membranes via PKC-dependent mechanisms.

The protein kinase C (PKC) family of isoenzymes plays a key role in the regulation of hepatocellular secretion. The hydrophobic and cholestatic bile acid, taurolithocholic acid (TLCA), acts as a potent Ca++ agonist in isolated hepatocytes. However, its effect on PKC isoforms has not been elucidated. Here we investigate the effects of TLCA at low micromolar concentrations on the distribution of PKC isoforms and on membrane-associated PKC activity. The distribution of PKC isoforms was determined in isolated rat hepatocytes in short-term culture using Western blotting and immunofluorescence techniques. PKC activity was measured radiochemically. TLCA (10 micromol/L) induced selective translocation of epsilon-PKC by 47.9% +/- 20.5% (P <.02 vs. controls; n = 7), but not of alpha-, delta-, and zeta-PKC to the hepatocellular membranes, whereas the phorbol ester, phorbol 12-myristate 13-acetate (PMA) (1 micromol/L) caused translocation of all mobile isoforms, alpha-, delta-, and epsilon-PKC, as shown by immunoblotting. Immunofluorescence studies demonstrated selective translocation of epsilon-PKC to the canalicular membranes of isolated rat hepatocyte couplets by TLCA (10 micromol/L), but predominant translocation to intracellular and basolateral membranes by PMA (1 micromol/L). Both TLCA (10 micromol/L) and PMA (1 micromol/L) stimulated membrane-bound PKC activity by 60.5% +/- 45. 8% (P <.05 vs. controls; n = 5) and 72.4% +/- 37.2% (P <.05; n = 5), respectively. TLCA at lower concentrations (5 micromol/L) was less effective. Because activation of epsilon-PKC has been associated with impairment of vesicle-mediated targeting and insertion of membrane proteins in secretory cells, it is attractive to speculate that TLCA reduces bile secretory capacity of the liver cell by activation of epsilon-PKC at the canalicular membrane.

The organic anion transporting polypeptide (OATP) of the basolateral hepatocyte membrane mediates multispecific uptake of anionic and other amphipathic substrates from sinusoidal blood plasma. To investigate the mechanisms controlling OATP expression, the 5'-flanking region of the human OATP gene was isolated from a P1-derived artificial chromosome genomic clone. Sequence analysis of the OATP promoter showed a number of consensus binding sites for both ubiquitous and liver-enriched transcription factors. Transfection of HepG2 cells with a series of 5'-deleted promoter-luciferase constructs identified the minimal promoter region within 91 base pairs relative to the transcription initiation site. A putative silencer element was localized in the -662/-440 region. The minimal promoter was also active in Chang liver, Madin-Darby canine kidney, and Chinese hamster ovary cells, indicating that basal promoter function is independent of liver-specific regulatory mechanisms. In transfected HepG2 cells, taurocholate (100 micromol/L) stimulated and triiodothyronine (1 micromol/L) inhibited OATP promoter activity, whereas hydrocortisone, dexamethasone, beta-estradiol, estrone-3-sulfate, and testosterone had no significant effect. Reverse-transcription polymerase chain reaction analysis showed an increase in OATP messenger RNA in the livers of four patients with chronic cholestatic liver disease compared with three noncholestatic controls. The up-regulation of OATP expression by taurocholate could serve to enhance the sinusoidal efflux of toxic intracellular compounds during chronic cholestasis.

A phospholipid translocating protein from rat liver has been expressed in Xenopus laevis oocytes. Injection of oocytes with total rat liver messenger RNA (mRNA) resulted in the function expression of saturable uptake of the water soluble phophatidylcholine derivative L-alpha-dibutyroylglycero-3-phophatidylcholine (diC4PC), Kinetic studies revealed an apparent Km value of approximately 10 mmol/L, which is similar to the value previously obtained in isolated rat liver canalicular plasma membrane vesicles for an adenosine triphosphate (ATP)-independent phosphatidylcholine translocator. Size fractionation of total rat liver mRNA yielded an active mRNA species between 1.8 and 2.6 kb, that stimulated the expressed phophatidylcholine uptake activity approximately fivefold as compared with differently sized mRNA subfractions. This active mRNA size class is too small to code for the mdr2 P-glycoprotein, which has been suggested to function as an ATP-dependent canalicular phosphatidylcholine translocator. Hence, the data indicate that there are at least two separate polypeptides involved in phospholipid translocation from hepatocytes into bile.

Bile acids are taken up into human liver by Na+-dependent and Na+-independent transport mechanisms. In hepatocarcinogenesis, numerous liver-specific functions are lost and the uptake of organic anions is markedly reduced. We have investigated the molecular and functional derangements of bile acid transport in the human hepatoblastoma cell line HepG2. Uptake of [3H]-taurocholic acid was saturable and entirely Na+ independent, with the kinetic characteristics of the human liver organic anion transporting polypeptide (OATP). OATP, but not the Na+-dependent bile acid transporter (Na+-taurocholate-cotransporting polypeptide [NTCP]), was detectable by reverse-transcription polymerase chain reaction (RT-PCR) analysis of HepG2 RNA. The level of OATP expression in HepG2 cells was determined by Northern blot analysis and was found to be 40% in comparison with normal liver. Transfection of an OATP-derived phosphorothioate (PTO)-antisense oligonucleotide into HepG2 cells resulted in 77% inhibition of temperature-dependent bile acid uptake. Injection of HepG2 messenger RNA (mRNA) into Xenopus laevis oocytes significantly stimulated Na+-independent taurocholate uptake, indicating the expression of a bile acid transport protein. We conclude that bile acid uptake into human hepatoblastoma HepG2 cells is mediated by the multi-specific organic anion transporting polypeptide OATP. Therapeutic strategies employing bile acid-derived cytostatic agents for the treatment of hepatocellular carcinomas may therefore depend upon the expression of the Na+-independent bile acid transporter OATP in hepatic malignancies.

Comparative studies between different patient groups have suggested that cholecystectomy enhances bacterial dehydroxylation of the primary bile acid cholic acid (CA) to the secondary bile acid deoxycholic acid (DCA). DCA may exert a cocarcinogenic effect on the colonic mucosa. In a short-term follow-up study on nine female patients we found no alterations of the CA or DCA pools after cholecystectomy. However, in the long term, cholecystectomy could promote changes of the intestinal bacterial flora and thereby lead to enhanced conversion of CA to DCA, causing an expansion of the DCA pool size and a reduction of the CA pool size. To test this hypothesis, pool sizes, fractional turnover rates (FTR), and synthesis or input rates of CA, chenodeoxycholic acid (CDCA) and DCA were determined in 12 female patients before and again 5 to 8 years after cholecystectomy. In the long term, pool size and synthesis rate of CA had not changed and DCA pool size had expanded by only 7.5% (not significant [NS]). DCA input increased by 32% (NS) but was balanced by an increase in FTR of 36%. Pool size (-17%) and synthesis rate (-5%) of CDCA were not significantly diminished. Overall, the sizes of the total bile acid pool (-6%, NS; 50 +/- 8 vs. 53 +/- 13 mumol/kg) and the pool fractions of CA (44.7 +/- 10.3% vs. 42.8 +/- 7.6%) and DCA (25.5 +/- 14.1% vs. 23.6 +/- 9.3%) remained similar. In conclusion, cholecystectomy causes no changes in bile acid pool composition and thus has no adverse effects on bile acid metabolism in the long term.

To characterize the transport functions of a recently cloned basolateral organic anion transporting polypeptide of rat hepatocytes we performed further kinetic transport and substrate cis-inhibition studies in organic anion-transporting polypeptide-cRNA injected Xenopus laevis oocytes. The studies demonstrate saturable Na(+)-independent sulfobromophthalein (Michaelis-Menten constant, 1.5 mumol/L) and taurocholate (Michaelis-Menten constant, 50 mumol/L) uptake by organic anion-transporting polypeptide. Sulfobromophthalein uptake was inhibited by the following organic anions: 0.01 mmol/L bilirubin (43%), 0.1 mmol/L indocyanine green (81%), 0.1 mmol/L 4,4'-diisothiocyanatostilbene-2,2'-disulfonic acid (DIDS; 52%) and 1 mmol/L probenecid (74%). Competitive inhibition was shown for indocyanine green (inhibition constant about 1.3 mumol/L). Sulfobromophthalein and taurocholate uptakes were also inhibited by cholate, chenodeoxycholate, deoxycholate and ursodeoxycholate, as well as their glycine and taurine conjugates. Organic anion-transporting polypeptide also mediated uptake of glycocholate, tauroursodeoxycholate and taurochenodeoxycholate. No cis-inhibition of sulfobromophthalein uptake was seen in the presence of ATP, para-aminohippuric acid, bumetanide, digitoxin, reduced glutathione, leukotriene C4, nicotinic acid, ouabain, oxalate, rifampicin, succinate or sulfate. Furthermore, radioactively labeled para-aminohippuric acid, alpha-ketoglutarate and reduced glutathione were not taken up by organic anion-transporting polypeptide in cRNA-injected frog oocytes. These data confirm that organic anion-transporting polypeptide represents a novel hepatocellular organic anion uptake system that can mediate Na(+)-independent transport of monovalent (e.g., bile acids) and divalent (e.g., sulfobromophthalein and indocyanine green) cholephilic organic anions.(ABSTRACT TRUNCATED AT 250 WORDS)