Thorough QT/QTc study to evaluate the effect of a single supratherapeutic dose of islatravir on QTc interval prolongation in healthy adults.

Islatravir is a deoxynucleoside analog being developed for the treatment of HIV-1 infection. Clinical studies are being conducted to evaluate islatravir, administered in combination with other antiretroviral therapies, at doses of 0.25 mg once daily and 2 mg once weekly. In multiple previous clinical studies, islatravir was generally well tolerated, with no clear trend in cardiac adverse events. A trial was conducted to evaluate the effect of islatravir on cardiac repolarization. A randomized, double-blind, active- and placebo-controlled phase 1 trial was conducted, in which a single dose of islatravir 0.75 mg, islatravir 240 mg (supratherapeutic dose), moxifloxacin 400 mg (active control), or placebo was administered. Continuous 12-lead electrocardiogram monitoring was performed before dosing through 24 hours after dosing. QT interval measurements were collected, and safety and pharmacokinetics were evaluated. Sixty-three participants were enrolled, and 59 completed the study. Fridericia's QT correction for heart rate was inadequate; therefore, a population-specific correction was applied (QTcP). The placebo-corrected change from baseline in QTcP (ΔΔQTcP) interval at the observed geometric mean maximum plasma concentration associated with islatravir 0.75 mg and islatravir 240 mg was <10 ms at all time points. Assay sensitivity was confirmed because the use of moxifloxacin 400 mg led to a ΔΔQTcP >10 ms. The pharmacokinetic profile of islatravir was consistent with that of previous studies, and islatravir was generally well tolerated. Results from the current trial suggest that single doses of islatravir as high as 240 mg do not lead to QTc interval prolongation.

Considerations for Cell and Gene Therapy Programs Entering the Clinical Space.

Cell and gene therapy (CGT) describes a broad category of medicinal products with potential applications to prevent and treat human disease in multiple therapeutic areas. These therapies leverage the use of modified nucleic acids, altered cells or tissue, or both. The modality, mechanism, route of administration, and therapeutic indication for a CGT product will influence the challenges and opportunities for early clinical development, some of which may be highly specific to the product under consideration. Both the European Medicines Agency (EMA) and the US Food and Drug Administration (FDA) encourage early interaction between sponsor and health authority to align on key elements of the CGT development program.

A Randomized, Double-Blind, Placebo-Controlled, Phase 1 Trial of Radiopaque Islatravir-Eluting Subdermal Implants for Pre-exposure Prophylaxis Against HIV-1 Infection.

BACKGROUND: Islatravir (MK-8591) is a deoxyadenosine analog in development for the treatment and prevention of HIV-1 infection. An islatravir-eluting implant could provide an additional option for pre-exposure prophylaxis (PrEP). SETTING: Previous data support a threshold islatravir triphosphate concentration for PrEP of 0.05 pmol/10 6 cells in peripheral blood mononuclear cells. Prototype islatravir-eluting implants were previously studied to establish general tolerability and pharmacokinetics (PKs) of islatravir relative to the threshold level. METHODS: In this randomized, double-blind, placebo-controlled, phase 1 trial, a next-generation radiopaque islatravir-eluting implant (48 mg, 52 mg, or 56 mg) or placebo implant was placed for a duration of 12 weeks in participants at low risk of HIV infection. Safety and tolerability, as well as PK for islatravir parent and islatravir triphosphate from plasma and peripheral blood mononuclear cells, were assessed throughout placement and 8 weeks after removal. RESULTS: In total, 36 participants (8 active and 4 placebo per dose arm) were enrolled and completed this study. Implants were generally well tolerated, with no discontinuations due to an adverse event, and no clear dose-dependence in implant-related adverse events. No clinically meaningful relationships were observed for changes in laboratory values, vital signs, or electrocardiogram assessments. Mean islatravir triphosphate levels at day 85 (0.101-0.561 pmol/10 6  cells) were above the PK threshold for all dose levels. CONCLUSION: Islatravir administered using a subdermal implant has the potential to be an effective and well-tolerated method for administering PrEP to individuals at risk of acquiring HIV-1.

Safety and Pharmacokinetics of Islatravir in Individuals with Severe Renal Insufficiency.

Islatravir (MK-8591) is a high-potency reverse transcriptase translocation inhibitor in development for the treatment of HIV-1 infection. Data from preclinical and clinical studies suggest that ~30% to 60% of islatravir is excreted renally and that islatravir is not a substrate of renal transporters. To assess the impact of renal impairment on the pharmacokinetics of islatravir, an open-label phase 1 trial was conducted with individuals with severe renal insufficiency (RI). A single dose of islatravir 60 mg was administered orally to individuals with severe RI (estimated glomerular filtration rate [eGFR] <30 mL/min/1.73 m2) and to healthy individuals without renal impairment (matched control group; eGFR ≥90 mL/min/1.73 m2). Safety and tolerability were assessed, and blood samples were collected to measure the pharmacokinetics of islatravir and its major metabolite 4'-ethynyl-2-fluoro-2'deoxyinosine (M4) in plasma, as well as active islatravir-triphosphate (TP) in peripheral blood mononuclear cells (PBMCs). Plasma islatravir and M4 area under the concentration-time curve from zero to infinity (AUC0-∞) were ~2-fold and ~5-fold higher, respectively, in participants with severe RI relative to controls, whereas islatravir-TP AUC0-∞ was ~1.5-fold higher in the RI group than in the control group. The half-lives of islatravir in plasma and islatravir-TP in PBMCs were longer in participants with severe RI than in controls. These findings are consistent with renal excretion playing a major role in islatravir elimination. A single oral dose of islatravir 60 mg was generally well tolerated. These data provide guidance regarding administration of islatravir in individuals with impaired renal function. (This study has been registered at ClinicalTrials.gov under registration no. NCT04303156.).

Incorporating protein precipitation to resolve hybrid IP-LC-MS assay interference for ultrasensitive quantification of intact therapeutic insulin dimer in human plasma.

For pharmacokinetics characterization of a therapeutic insulin dimer, an ultrasensitive plasma method was required due to the expected low circulating levels in humans. A bioanalytical strategy combining immunoprecipitation enrichment with liquid chromatography - tandem mass spectrometry (LC-MS/MS) analysis of the intact protein offers the opportunity to resolve the analyte from endogenous and exogenous insulin and insulin analogs. Nonetheless, interference from complex background matrix was observed limiting reliable measurements at the low concentration range. A sample preparation approach incorporating protein precipitation and immunoprecipitation was developed and optimized to further reduce sample complexity prior to LC-MS/MS analysis. This approach enabled a deeper level of selectivity and presented a cleaner mass spectrometric detection that may otherwise be confounded. Sample preparation was automated to allow high throughput analysis. The method reached a limit of quantitation at 0.3 ng/mL (25 pM), and a linear dynamic range from 0.3 to 300 ng/mL. Results were highly reproducible, with intra-day and inter-day precision and bias below 11%. Furthermore, the organic solvent treatment involved in protein precipitation is expected to improve assay resistance to the bias introduced by endogenous protein binding such as that exerted by anti-drug antibodies. The method was successfully applied to support clinical pharmacokinetics studies. This approach may potentially be adapted to bioanalysis of low abundance proteins.

A phase 1, open-label study to evaluate the drug interaction between islatravir (MK-8591) and the oral contraceptive levonorgestrel/ethinyl estradiol in healthy adult females.

INTRODUCTION: Hormonal contraceptives are among the most effective forms of reversible contraception, but many other compounds, including some antiretrovirals, have clinically meaningful drug-drug interactions (DDIs) with hormonal contraceptives. Islatravir is a novel human immunodeficiency virus nucleoside reverse transcriptase translocation inhibitor currently in clinical development for treatment and prevention of HIV infection. A phase 1 clinical trial was conducted to evaluate the DDI of islatravir and the combination of oral contraceptive levonorgestrel (LNG)/ethinyl estradiol (EE). METHODS: This was an open-label, two-period, fixed-sequence, DDI clinical trial in healthy, postmenopausal or bilaterally oophorectomized females aged 18 through 65 years in the United States between October 2016 and January 2017. A single dose of LNG 0.15 mg/EE 0.03 mg was given followed by a 7-day washout. Islatravir, 20 mg, was then dosed once weekly for 3 weeks; a single dose of LNG 0.15 mg/EE 0.03 mg was given concomitantly with the third dose of islatravir. Pharmacokinetic samples for plasma LNG and EE concentrations were collected pre-dose and up to 120 hours post-dose in each period. Safety and tolerability were assessed throughout the trial by clinical assessments, laboratory evaluations and examination of adverse events. RESULTS AND DISCUSSION: Fourteen participants were enrolled. The pharmacokinetics of LNG and EE were not meaningfully altered by co-administration with islatravir. For the comparison of (islatravir + LNG/EE)/(LNG/EE alone), the geometric mean ratios (GMRs) (90% confidence intervals [CIs]) for LNG AUC0-inf and Cmax were 1.13 (1.06, 1.20) and 0.965 (0.881, 1.06), respectively. For EE, the GMRs (90% CI) for AUC0-inf and Cmax were 1.05 (0.981, 1.11) and 1.02 (0.971, 1.08), respectively. Co-administration of all three drugs was generally well tolerated. CONCLUSIONS: The results of this trial support the use of LNG/EE contraceptives in combination with islatravir without dose adjustment.

Safety and Pharmacokinetics of Once-Daily Multiple-Dose Administration of Islatravir in Adults Without HIV.

BACKGROUND: Islatravir (MK-8591) is a novel nucleoside analog in development for the treatment and prevention of HIV-1 infection. Islatravir has potent antiviral activity and a long intracellular half-life. SETTING: A 3-panel, randomized, double-blind, placebo-controlled, multiple-dose study in 36 adults without HIV evaluated the safety, tolerability, and pharmacokinetics of islatravir after daily administration. METHODS: Islatravir or placebo was administered orally once daily for 42 days (5 mg) or 28 days (0.25 mg; 0.75 mg). Blood samples were taken at prespecified time points for pharmacokinetic analysis of islatravir (plasma) and islatravir-triphosphate (ISL-TP; peripheral blood mononuclear cells [PBMCs]). Rectal and vaginal tissue samples were also collected in a subset of participants. Safety and tolerability were evaluated throughout. RESULTS: The pharmacokinetics of islatravir were approximately dose proportional, with concentrations approaching a steady state between days 14 and 21 in plasma and by day 28 for ISL-TP in PBMCs. Plasma exposure accumulation was 1.5-fold to 1.8-fold, and ISL-TP exposure accumulation was ∼10-fold. The apparent terminal half-life of ISL-TP was 177-209 hours. The ISL-TP pharmacokinetic trough threshold-the minimal concentration required for efficacy-of 0.05 pmol/106 cells was achieved after a single administration at all dose levels. Rectal and vaginal tissue also exhibited potentially therapeutic concentrations. Islatravir was generally well tolerated at all doses. CONCLUSIONS: ISL-TP levels in PBMCs were above the threshold projected for antiviral efficacy against wild-type HIV after a single 0.25-mg dose. Multiple once-daily dosing of islatravir in adults without HIV was generally well tolerated up to doses of 5 mg administered for up to 6 weeks.

Lack of a Clinically Meaningful Drug Interaction Between the HIV-1 Antiretroviral Agents Islatravir, Dolutegravir, and Tenofovir Disoproxil Fumarate.

Islatravir, an investigational nucleoside reverse transcriptase translocation inhibitor, is in clinical development for the treatment and prevention of HIV-1 infection. Because islatravir may be coadministered with other antiretroviral agents, assessment of potential drug-drug interactions are warranted. This phase 1, open-label, fixed-sequence, 2-period trial in adults without HIV (N = 12) assessed the safety and pharmacokinetic interactions of islatravir administered with dolutegravir and tenofovir disoproxil fumarate (TDF). In period 1, participants received a single oral dose of islatravir (20 mg). In period 2, participants received oral doses of dolutegravir (50 mg) and TDF (300 mg) once daily on days 1 through 11, with a single oral dose of islatravir (20 mg) coadministered on day 8. There were no clinically significant changes in islatravir, dolutegravir, or TDF pharmacokinetics following coadministration. Islatravir was generally well tolerated when administered alone or in combination with dolutegravir and TDF. Coadministration of islatravir, dolutegravir, and TDF is supported, with no clinically meaningful effect on pharmacokinetics, safety, or tolerability in participants without HIV.

Safety and pharmacokinetics of islatravir subdermal implant for HIV-1 pre-exposure prophylaxis: a randomized, placebo-controlled phase 1 trial.

Islatravir (MK-8591) is a highly potent type 1 human immunodeficiency virus (HIV-1) nucleoside reverse transcriptase translocation inhibitor with a long intracellular half-life that is in development for the prevention and treatment of HIV-1. We conducted a randomized, double-blind, placebo-controlled, phase 1 trial in adults without HIV-1 infection. Participants received islatravir or placebo subdermal implants for 12 weeks and were monitored throughout this period and after implant removal. The co-primary end points were safety and tolerability of the islatravir implant and pharmacokinetics, including concentration at day 85, of islatravir triphosphate in peripheral blood mononuclear cells (PBMCs). Secondary end points included additional pharmacokinetic parameters for islatravir triphosphate in PBMCs and the plasma pharmacokinetic profile of islatravir. Based on preclinical data, two doses were assessed: 54 mg (n = 8, two placebo) and 62 mg (n = 8, two placebo). The most frequently reported adverse events were mild-to-moderate implant-site reactions (induration, hematoma, pain). Throughout the 12-week trial, geometric mean islatravir triphosphate concentrations were above a pharmacokinetic threshold of 0.05 pmol per 106 PBMCs, which was estimated to provide therapeutic reverse transcriptase inhibition (concentration at day 85 (percentage of geometric coefficient of variation): 54 mg, 0.135 pmol per 106 cells (27.3); 62 mg, 0.272 pmol per 106 cells (45.2)). Islatravir implants at both doses were safe and resulted in mean concentrations above the pharmacokinetic threshold through 12 weeks, warranting further investigation of islatravir implants as a potential HIV prevention strategy.

Safety, tolerability, and pharmacokinetics of single- and multiple-dose administration of islatravir (MK-8591) in adults without HIV.

Islatravir (MK-8591) is a nucleoside analogue in development for the treatment and prevention of HIV-1. Two phase 1 trials were conducted during initial evaluation of islatravir: rising single doses (Study 1) and rising multiple doses (Study 2) of oral islatravir in male and female participants without HIV (aged 18-60 years). Safety, tolerability, and pharmacokinetics of islatravir (plasma) and islatravir-triphosphate (peripheral blood mononuclear cells) were assessed. In Study 1, 24 participants, assigned to 1 of 3 panels, received alternating single doses of islatravir in a fasted state from 5 mg to 400 mg, or placebo, over 3 dosing periods; a 30 mg dose was additionally assessed following a high-fat meal. In Study 2, 8 participants per dose received 3 once-weekly doses of 10, 30, or 100 mg islatravir or placebo in a fasted state. For each panel in both trials, 6 participants received active drug and 2 received placebo. Islatravir was generally well-tolerated, with no serious adverse events or discontinuations due to adverse events. Islatravir was rapidly absorbed (median time to maximum plasma concentration 0.5 hours); plasma half-life was 49-61 h; intracellular islatravir-triphosphate half-life was 118-171 h. Plasma exposure increased in an approximately dose-proportional manner; there was no meaningful food effect. There was a modest degree of intracellular islatravir-triphosphate accumulation after multiple weekly dosing. After single oral doses of islatravir greater than or equal to 5 mg, intracellular islatravir-triphosphate levels were comparable to levels associated with efficacy in preclinical studies. These results warrant continued clinical investigation of islatravir.

A Phase 1 Study to Evaluate the Drug Interaction Between Islatravir (MK-8591) and Doravirine in Adults Without HIV.

BACKGROUND AND OBJECTIVES: Islatravir (MK-8591) is a novel nucleoside analogue in development for the treatment and prevention of HIV-1 infection. Doravirine is a non-nucleoside reverse transcriptase inhibitor indicated for the treatment of HIV-1 infection. This study evaluated the pharmacokinetics, safety, and tolerability of islatravir and doravirine coadministration in a double-blind, placebo-controlled, randomized, fixed-sequence study. METHODS: Adult participants without HIV infection were administered oral doravirine 100 mg (n = 10) or placebo (n = 4) once daily (QD) for 5 days, immediately followed by oral islatravir 2.25 mg (n = 10) or placebo QD (n = 4) for 14 days; islatravir 2.25 mg and doravirine 100 mg QD, or placebo QD, were then coadministered for 5 days. Pharmacokinetic and safety data were collected. RESULTS: Doravirine geometric least-squares mean ratios (90% confidence intervals (CIs)) of (doravirine + islatravir)/doravirine for the area under the plasma drug concentration-time curve over 24 h (AUC0-24h), maximum plasma concentration (Cmax), and plasma concentration at 24 h post-dose (C24h) were not meaningfully impacted. Islatravir geometric least-squares mean ratios (90% CI) of (islatravir + doravirine)/islatravir for AUC0-24h and Cmax were both close to unity, 1.06 (1.01, 1.12) and 1.08 (0.91, 1.27), respectively. All study regimens were generally well tolerated. CONCLUSION: These results indicate that coadministration of islatravir and doravirine had no clinically meaningful effect on the pharmacokinetics of either drug, and support further clinical investigation of islatravir in combination with doravirine for the treatment of HIV-1 infection.

Safety, pharmacokinetics, and antiretroviral activity of islatravir (ISL, MK-8591), a novel nucleoside reverse transcriptase translocation inhibitor, following single-dose administration to treatment-naive adults infected with HIV-1: an open-label, phase 1b, consecutive-panel trial.

BACKGROUND: Islatravir (also known as ISL and MK-8591) is a unique nucleoside reverse transcriptase translocation inhibitor in clinical development for treatment of people with HIV-1 infection. In preclinical studies, intracellular islatravir-triphosphate exhibits a long half-life and prolonged virological effects. In this study, we aimed to assess islatravir safety, pharmacokinetics, and antiretroviral activity in treatment-naive adults with HIV-1 infection. METHODS: This open-label, consecutive-panel, phase 1b trial was done at Charité Research Organisation (Berlin, Germany) and included men and women (aged 18-60 years, inclusive) with HIV-1 infection who were ART naive. Participants were required to have plasma HIV-1 RNA counts of at least 10 000 copies per mL within 30 days before the trial treatment phase, without evidence of resistance to nucleoside reverse transcriptase inhibitors. Participants were enrolled in one of five consecutive dosing panels, receiving a single oral dose of islatravir (0·5-30 mg). The primary outcomes were safety and tolerability of islatravir and change from baseline in HIV-1 plasma RNA; secondary outcomes were islatravir plasma and islatravir-triphosphate intracellular pharmacokinetics. We obtained descriptive safety and pharmacokinetics statistics, and estimated efficacy results from a longitudinal data analysis model. This study is registered with ClinicalTrials.gov, NCT02217904, and EudraCT, 2014-002192-28. FINDINGS: Between Sept 17, 2015, and May 11, 2017, we enrolled 30 participants (six per panel). Islatravir was generally well tolerated. 27 (90%) participants had 60 adverse events after receipt of drug, of which 21 (35%) were deemed to be drug related. The most common (n>1) drug-related adverse events were headache (in nine [30%] participants) and diarrhoea (in two [7%]). No serious adverse events were reported, and no participants discontinued due to an adverse event. Plasma islatravir pharmacokinetics and intracellular islatravir-triphosphate pharmacokinetics were approximately dose proportional. The islatravir-triphosphate intracellular half-life was 78·5-128·0 h. Least-squares mean HIV-1 RNA at 7 days after dose decreased from 1·67 log10 copies per mL (95% CI 1·42-1·92) at 10 mg dose to 1·20 log10 copies per mL (0·95-1·46) at 0·5 mg dose. No genetic changes consistent with development of viral resistance were detected. INTERPRETATION: Single doses of islatravir as low as 0·5 mg significantly suppressed HIV-1 RNA by more than 1·0 log at day 7 in treatment-naive adults with HIV-1 infection and were generally well tolerated, supporting the further development of islatravir as a flexible-dose treatment for individuals with HIV-1 infection. FUNDING: Merck Sharp & Dohme Corp, a subsidiary of Merck & Co Inc, Kenilworth, NJ, USA.

Assessment of Bezlotoxumab Immunogenicity.

Bezlotoxumab is a fully human monoclonal antibody that binds and neutralizes Clostridium difficile toxin B. This analysis investigated the potential of bezlotoxumab to induce immunogenicity in healthy phase 1 trial participants and in phase 2/3 trial participants receiving oral antibacterial therapy for primary or recurrent C difficile infection. Immunogenicity to bezlotoxumab was evaluated following a single intravenous dose (≤20 mg/kg) or 2 consecutive doses (10 mg/kg) given 84 days apart in healthy participants across 3 phase 1 trials (Protocol MK-3415A-004, N = 30; Protocol CA-GCDX-05-01, N = 54; Protocol MK-3415A-006, N = 12) and following a single 10 mg/kg dose in 1 phase 2 trial (Protocol CA-GCDX-06-02, ClinicalTrials.gov identifier: NCT00350298; N = 97) and 2 phase 3 trials (Protocols MK-3415A-001 and MK-3415A-002, ClinicalTrials.gov identifiers: NCT01241552 and NCT01513239; N = 1414). No treatment-emergent antidrug antibodies were observed following single or repeated dosing of bezlotoxumab. No phase 1 participants and only 1 phase 2 participant tested positive before bezlotoxumab exposure (non-treatment-emergent positive). Nine participants tested non-treatment-emergent positive in phase 3 trials, 1 of whom was neutralizing antibody-positive. Overall, the immunogenicity potential of bezlotoxumab is considered to be low.

Population Pharmacokinetics and Pharmacodynamics of Bezlotoxumab in Adults with Primary and Recurrent Clostridium difficile Infection.

The fully human monoclonal antibody bezlotoxumab is indicated for preventing the recurrence of Clostridioides difficile (formerly Clostridium difficile) infection (CDI) in adults who receive antibacterial treatment for CDI and who are at high risk for a CDI recurrence. The efficacy and safety of 10-mg/kg of body weight bezlotoxumab were demonstrated in two phase 3 trials: the MODIFY I (ClinicalTrials.gov registration number NCT01241552) and MODIFY II (ClinicalTrials.gov registration number NCT01513239) trials. Here, a population pharmacokinetic (popPK) analysis, performed using data from the MODIFY I and II trials (n = 1,515) and from three phase 1 trials (n = 72) to characterize bezlotoxumab pharmacokinetics (PK) in phase 3 clinical trial participants and in healthy subjects, is reported. A stepwise covariate search was conducted to identify factors influencing PK. Post hoc-estimated bezlotoxumab exposures from the popPK model were used to conduct an exposure-response analysis for CDI recurrence. Bezlotoxumab PK were described by a two-compartment model with linear elimination and allometric scaling for clearance and the volume of distribution by body weight. Although the final popPK model included gender, ethnicity (Japanese descent), race (black versus nonblack), and albumin level as significant covariates, the impact of these factors was not clinically meaningful, based on the totality of the PK and clinical experience. Exposure-response analysis of CDI recurrence demonstrated a similar low rate of CDI recurrence over the entire range of exposures achieved in the phase 3 trials, indicating that exposures were on the maximal response plateau of the exposure-response curve. Overall, the analyses confirmed the appropriateness of the 10-mg/kg dose across the phase 3 trial population with no dose adjustments necessary over a broad demographic background.

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.

Methylation Microarray Studies Highlight PDGFA Expression as a Factor in Biliary Atresia.

Biliary atresia (BA) is a progressive fibro-inflammatory disorder that is the leading indication for liver transplantation in children. Although there is evidence implicating genetic, infectious, environmental, and inflammatory causes, the etiology of BA remains unknown. We have recently reported that cholangiocytes from BA patients showed decreased DNA methylation relative to disease- and non-disease controls, supporting a potential role for DNA hypomethylation in BA etiopathogenesis. In the current study, we examined the methylation status of specific genes in human BA livers using methylation microarray technology. We found global DNA hypomethylation in BA samples as compared to disease- and non-disease controls at specific genetic loci. Hedgehog pathway members, SHH and GLI2, known to be upregulated in BA, were both hypomethylated, validating this approach as an investigative tool. Another region near the PDGFA locus was the most significantly hypomethylated in BA, suggesting potential aberrant expression. Validation assays confirmed increased transcriptional and protein expression of PDGFA in BA livers. We also show that PDGF-A protein is specifically localized to cholangiocytes in human liver samples. Injection of PDGF-AA protein dimer into zebrafish larvae caused biliary developmental and functional defects. In addition, activation of the Hedgehog pathway caused increased expression of PDGF-A in zebrafish larvae, providing a previously unrecognized link between PDGF and the Hedgehog pathway. Our findings implicate DNA hypomethylation as a specific factor in mediating overexpression of genes associated with BA and identify PDGF as a new candidate in BA pathogenesis.

Fructose leads to hepatic steatosis in zebrafish that is reversed by mechanistic target of rapamycin (mTOR) inhibition.

UNLABELLED: Nonalcoholic fatty liver disease (NAFLD), the accumulation of lipid within hepatocytes, is increasing in prevalence. Increasing fructose consumption correlates with this increased prevalence, and rodent studies directly support fructose leading to NAFLD. The mechanisms of NAFLD and in particular fructose-induced lipid accumulation remain unclear, although there is evidence for a role for endoplasmic reticulum (ER) stress and oxidative stress. We have evidence that NAFLD models demonstrate activation of the target of rapamycin complex 1 (Torc1) pathway. We set out to assess the contribution of ER stress, oxidative stress, and Torc1 up-regulation in the development of steatohepatitis in fructose-treated larval zebrafish. Zebrafish were treated with fructose or glucose as a calorie-matched control. We also treated larvae with rapamycin, tunicamycin (ER stress), or valinomycin (oxidative stress). Fish were stained with oil red O to assess hepatic lipid accumulation, and we also performed quantitative polymerase chain reaction (qPCR)and western blot analysis. We performed immunostaining on samples from patients with NAFLD and nonalcoholic steatohepatitis (NASH). Treatment with fructose induced hepatic lipid accumulation, mitochondrial abnormalities, and ER defects. In addition, fructose-treated fish showed activation of inflammatory and lipogenic genes. Treatment with tunicamycin or valinomycin also induced hepatic lipid accumulation. Expression microarray studies of zebrafish NAFLD models showed an elevation of genes downstream of Torc1 signaling. Rapamycin treatment of fructose-treated fish prevented development of hepatic steatosis, as did treatment of tunicamycin- or valinomycin-treated fish. Examination of liver samples from patients with hepatic steatosis demonstrated activation of Torc1 signaling. CONCLUSION: Fructose treatment of larval zebrafish induces hepatic lipid accumulation, inflammation, and oxidative stress. Our results indicate that Torc1 activation is required for hepatic lipid accumulation across models of NAFLD, and in patients.

p53-mediated biliary defects caused by knockdown of cirh1a, the zebrafish homolog of the gene responsible for North American Indian Childhood Cirrhosis.

North American Indian Childhood Cirrhosis (NAIC) is a rare, autosomal recessive, progressive cholestatic disease of infancy affecting the Cree-Ojibway first Nations of Quebec. All NAIC patients are homozygous for a missense mutation (R565W) in CIRH1A, the human homolog of the yeast nucleolar protein Utp4. Utp4 is part of the t-Utp subcomplex of the small subunit (SSU) processome, a ribonucleoprotein complex required for ribosomal RNA processing and small subunit assembly. NAIC has thus been proposed to be a primary ribosomal disorder (ribosomopathy); however, investigation of the pathophysiologic mechanism of this disease has been hindered by lack of an animal model. Here, using a morpholino oligonucleotide (MO)-based loss-of-function strategy, we have generated a model of NAIC in the zebrafish, Danio rerio. Zebrafish Cirhin shows substantial homology to the human homolog, and cirh1a mRNA is expressed in developing hepatocytes and biliary epithelial cells. Injection of two independent MOs directed against cirh1a at the one-cell stage causes defects in canalicular and biliary morphology in 5 dpf larvae. In addition, 5 dpf Cirhin-deficient larvae have dose-dependent defects in hepatobiliary function, as assayed by the metabolism of an ingested fluorescent lipid reporter. Previous yeast and in vitro studies have shown that defects in ribosome biogenesis cause stabilization and nuclear accumulation of p53, which in turn causes p53-mediated cell cycle arrest and/or apoptosis. Thus, the nucleolus appears to function as a cellular stress sensor in some cell types. In accordance with this hypothesis, transcriptional targets of p53 are upregulated in Cirhin-deficient zebrafish embryos, and defects in biliary function seen in Cirhin-deficient larvae are completely abrogated by mutation of tp53. Our data provide the first in vivo evidence of a role for Cirhin in biliary development, and support the hypothesis that congenital defects affecting ribosome biogenesis can activate a cellular stress response mediated by p53.

CCBE1 mutation in two siblings, one manifesting lymphedema-cholestasis syndrome, and the other, fetal hydrops.

BACKGROUND: Lymphedema-cholestasis syndrome (LCS; Aagenaes syndrome) is a rare autosomal recessive disorder, characterized by 1) neonatal intrahepatic cholestasis, often lessening and becoming intermittent with age, and 2) severe chronic lymphedema, mainly lower limb. LCS was originally described in a Norwegian kindred in which a locus, LCS1, was mapped to a 6.6cM region on chromosome 15. Mutations in CCBE1 on chromosome 18 have been reported in some cases of lymphatic dysplasia, but not in LCS. METHODS: Consanguineous parents of Mexican ancestry had a child with LCS who did not exhibit extended homozygosity in the LCS1 region. A subsequent pregnancy was electively terminated due to fetal hydrops. We performed whole-genome single nucleotide polymorphism genotyping to identify regions of homozygosity in these siblings, and sequenced promising candidate genes. RESULTS: Both siblings harbored a homozygous mutation in CCBE1, c.398 T>C, predicted to result in the missense change p.L133P. Regions containing known 'cholestasis genes' did not demonstrate homozygosity in the LCS patient. CONCLUSIONS: Mutations in CCBE1 may yield a phenotype not only of lymphatic dysplasia, but also of LCS or fetal hydrops; however, the possibility that the sibling with LCS also carries a homozygous mutation in an unidentified gene influencing cholestasis cannot be excluded.

Interferon-gamma directly mediates developmental biliary defects.

Biliary atresia (BA) is the most common identifiable hepatobiliary disease affecting infants, in which there are defects in intra- and extrahepatic bile ducts and progressive fibrosis. Activation of interferon-gamma (IFNγ) appears to be critical in both patients with BA and in rodent models of BA. We have recently reported a zebrafish model of biliary disease that shares features with BA, in which inhibition of DNA methylation leads to intrahepatic biliary defects and activation of IFNγ target genes. Here we report that ifng genes are hypomethylated and upregulated in zebrafish larvae treated with azacytidine (azaC), an inhibitor of DNA methylation. Injection of IFNγ protein into developing zebrafish larvae leads to biliary defects, suggesting that activation of the IFNγ pathway is sufficient to cause developmental biliary defects. These defects are associated with decreased cholangiocyte proliferation and with a decrease in the expression of vhnf1 (hnf1b, tcf2), which encodes a homeodomain protein with previously reported roles in biliary development in multiple models. These results support an importance of IFNγ in mediating biliary defects, and also demonstrate the feasibility of direct injection of intact protein into developing zebrafish larvae.