Assessing the therapeutic potential of lab-made hepatocytes.

Hepatocyte transplantation has potential as a bridge or even alternative to whole-organ liver transplantation. Because donor livers are scarce, realizing this potential requires the development of alternative cell sources. To be therapeutically effective, surrogate hepatocytes must replicate the complex function and ability to proliferate of primary human hepatocytes. Ideally, they are also autologous to eliminate the need for immune suppression, which can have severe side effects and may not be sufficient to prevent rejection long term. In the past decade, several methods have been developed to generate hepatocytes from other readily and safely accessible somatic cells. These lab-made hepatocytes show promise in animal models of liver diseases, supporting the feasibility of autologous liver cell therapies. Here, we review recent preclinical studies exemplifying different types of lab-made hepatocytes that can potentially be used in autologous liver cell therapies. To define the therapeutic efficacy of current lab-made hepatocytes, we compare them to primary human hepatocytes, focusing on engraftment efficiency and posttransplant proliferation and function. In addition to summarizing published results, we discuss animal models and assays effective in assessing therapeutic efficacy. This analysis underscores the therapeutic potential of current lab-made hepatocytes, but also highlights deficiencies and uncertainties that need to be addressed in future studies aimed at developing liver cell therapies with lab-made hepatocytes. (Hepatology 2016;64:287-294).

Safety Findings in Pediatric Patients During Long-Term Treatment With Teduglutide for Short-Bowel Syndrome-Associated Intestinal Failure: Pooled Analysis of 4 Clinical Studies.

BACKGROUND: This analysis assessed combined safety data from 4 clinical studies of teduglutide in pediatric patients with short-bowel syndrome-associated intestinal failure (SBS-IF). METHODS: Safety data from teduglutide-treated patients in 4 clinical trials were pooled. The completed 12-week and 24-week phase 3 core studies (NCT01952080/EudraCT 2013-004588-30 and NCT02682381/EudraCT 2015-002252-27) enrolled children aged 1-17 years with SBS-IF. Patients could elect to enroll in ongoing open-label extensions (NCT02949362/EudraCT 2016-000863-17 and NCT02954458/EudraCT 2016-000849-30). Interim data from ongoing studies were included. RESULTS: Safety data are reported for 89 pediatric patients treated with teduglutide for a median (range) of 51.7 (5.0-94.7) weeks. Adverse events (AEs) were reported in all patients; the most common were vomiting (51.7%), pyrexia (43.8%), upper respiratory tract infection (41.6%), and cough (33.7%). Thirty-five patients (39.3%) had AEs considered related to teduglutide treatment; abdominal pain and vomiting were most frequent (5.6% each). Three serious AEs in 3 patients (3.4%) were considered related to teduglutide treatment: ileus, d-lactic acidosis, and gastrointestinal obstruction due to hard stools. All 3 events resolved. One cecal polyp was detected, which was not biopsied or found on repeat colonoscopy. No cases of neoplasia occurred. CONCLUSION: Based on integrated data from 4 clinical studies, including long-term follow-up for ≤161 weeks, teduglutide had a safety profile consistent with the individual core pediatric studies and as expected for pediatric patients with SBS-IF who never received teduglutide. The most frequent AEs reflected treatment with teduglutide, complications of the underlying disease, and typical childhood illnesses.

Increased dosage of mammalian Sir2 in pancreatic beta cells enhances glucose-stimulated insulin secretion in mice.

Sir2 NAD-dependent deacetylases connect transcription, metabolism, and aging. Increasing the dosage or activity of Sir2 extends life span in yeast, worms, and flies and promotes fat mobilization and glucose production in mammalian cells. Here we show that increased dosage of Sirt1, the mammalian Sir2 ortholog, in pancreatic beta cells improves glucose tolerance and enhances insulin secretion in response to glucose in beta cell-specific Sirt1-overexpressing (BESTO) transgenic mice. This phenotype is maintained as BESTO mice age. Pancreatic perfusion experiments further demonstrate that Sirt1 enhances insulin secretion in response to glucose and KCl. Microarray analyses of beta cell lines reveal that Sirt1 regulates genes involved in insulin secretion, including uncoupling protein 2 (Ucp2). Isolated BESTO islets also have reduced Ucp2, increased ATP production, and enhanced insulin secretion during glucose and KCl stimulation. These findings establish the importance of Sirt1 in beta cell function in vivo and suggest therapeutic interventions for type 2 diabetes.

Safety and Efficacy of Teduglutide in Pediatric Patients With Intestinal Failure due to Short Bowel Syndrome: A 24-Week, Phase III Study.

BACKGROUND: This study evaluated the safety and efficacy of teduglutide in pediatric patients with short bowel syndrome-associated intestinal failure (SBS-IF). METHODS: A 24-week, phase III trial with 2 randomized, double-blind teduglutide dose groups and a nonblinded standard of care (SOC) arm was used; patients received 0.025 mg/kg or 0.05 mg/kg teduglutide once daily. Safety end points included treatment-emergent adverse events (TEAEs) and growth parameters. The primary efficacy/pharmacodynamic end point was the number of patients who achieved a ≥20% reduction in parenteral support (PS) from baseline at week 24. RESULTS: All 59 enrolled patients completed the study (0.025 mg/kg, n = 24; 0.05 mg/kg, n = 26; SOC, n = 9). Baseline demographics and disease characteristics were comparable among groups. TEAEs were reported by 98% and 100% of patients in the teduglutide and SOC groups, respectively. The most common TEAEs in the teduglutide-treated groups were pyrexia and vomiting. The primary end point was achieved by 13 (54.2%), 18 (69.2%), and 1 (11.1%) patients who received 0.025 mg/kg teduglutide, 0.05 mg/kg teduglutide, and SOC, respectively (P < 0.05 vs SOC). Both 0.025-mg/kg and 0.05-mg/kg teduglutide groups showed clinically significant reductions in PS volume (P < 0.05 vs SOC), PS calories, days per week and hours per day of PS infusions, and increases in enteral nutrition and plasma citrulline at week 24 compared with baseline. Two (8.3%, 0.025 mg/kg teduglutide) and 3 patients (11.5%, 0.05 mg/kg teduglutide) achieved enteral autonomy. CONCLUSION: The safety profile of teduglutide was similar to that reported previously in children and adults. Treatment with teduglutide was associated with significant reductions in PS for pediatric patients with SBS-IF over 24 weeks.

In Vivo Hepatic Reprogramming of Myofibroblasts with AAV Vectors as a Therapeutic Strategy for Liver Fibrosis.

Liver fibrosis, a form of scarring, develops in chronic liver diseases when hepatocyte regeneration cannot compensate for hepatocyte death. Initially, collagen produced by myofibroblasts (MFs) functions to maintain the integrity of the liver, but excessive collagen accumulation suppresses residual hepatocyte function, leading to liver failure. As a strategy to generate new hepatocytes and limit collagen deposition in the chronically injured liver, we developed in vivo reprogramming of MFs into hepatocytes using adeno-associated virus (AAV) vectors expressing hepatic transcription factors. We first identified the AAV6 capsid as effective in transducing MFs in a mouse model of liver fibrosis. We then showed in lineage-tracing mice that AAV6 vector-mediated in vivo hepatic reprogramming of MFs generates hepatocytes that replicate function and proliferation of primary hepatocytes, and reduces liver fibrosis. Because AAV vectors are already used for liver-directed human gene therapy, our strategy has potential for clinical translation into a therapy for liver fibrosis.

A nutrient-sensitive interaction between Sirt1 and HNF-1α regulates Crp expression.

Silent information regulator 2 (Sir2) orthologs are an evolutionarily conserved family of NAD-dependent protein deacetylases that regulate aging and longevity in model organisms. The mammalian Sir2 ortholog Sirt1 regulates metabolic and stress responses through the deacetylation of many transcriptional regulatory factors. To elucidate the mechanism by which Sirt1 controls gene expression in response to nutrient availability, we devised a bioinformatic screen combining gene expression analysis with phylogenetic footprinting to identify transcription factors as new candidate partners of Sirt1. One candidate target was HNF-1α, a homeodomain transcription factor that regulates pancreatic ß-cell and hepatocyte functions and is commonly mutated in patients with maturity-onset diabetes of the young (MODY). Interestingly, Sirt1 physically interacts with HNF-1αin vitro but does so in vivo only in nutrient-restricting conditions. This interaction requires 12-24 h of nutrient restriction and is dependent on protein synthesis. Both nutrient restriction and Sirt1 suppress HNF-1α transcriptional activity and the expression of one of its target genes, C-reactive protein (Crp), in mouse primary hepatocytes. Pharmacological inhibition of Sirt1 blocks the suppression of Crp by nutrient restriction. Similarly, Crp expression is also suppressed in fasted and diet-restricted liver. Furthermore, Sirt1 and HNF-1α co-localize on two HNF-1α binding sites on the Crp promoter, leading to decreased acetylation of lysine 16 of histone H4 at these sites only in response to nutrient restriction. These findings reveal a novel nutrient-dependent interaction between Sirt1 and HNF-1α and provide important insight into the molecular mechanism by which Sirt1 mediates the anti-aging effects of diet restriction.

The regulation of nicotinamide adenine dinucleotide biosynthesis by Nampt/PBEF/visfatin in mammals.

PURPOSE OF REVIEW: Nicotinamide adenine dinucleotide (NAD) is a classic coenzyme in cellular redox reactions. Recently, NAD biochemistry has also been implicated in a broader range of biological functions in mammals, but the regulation of NAD biosynthesis has been poorly investigated. Recent progress in the field of NAD biochemistry has fueled new interest in the NAD biosynthetic pathways from its precursors and their physiological roles in metabolism. This review summarizes the latest knowledge on the NAD biosynthetic pathways and focuses on one of the key NAD biosynthetic enzymes, namely, nicotinamide phosphoribosyltransferase. RECENT FINDINGS: Mammals predominantly use nicotinamide rather than nicotinic acid as a precursor for NAD biosynthesis. Nicotinamide phosphoribosyltransferase (Nampt) is the rate-limiting enzyme that converts nicotinamide to nicotinamide mononucleotide in the NAD biosynthetic pathway from nicotinamide in mammals. The same protein has also been identified as a cytokine (pre-B-cell colony-enhancing factor or PBEF) or an insulin-mimetic hormone (visfatin). SUMMARY: We propose that the presumed multiple effects of Nampt/PBEF/visfatin may be entirely explained by its role as an intra and extracellular NAD biosynthetic enzyme. We also propose a new model of Namp/PBEF/visfatin-mediated systemic NAD biosynthesis and its possible physiological significance. Our model provides an important insight into developing preventive/therapeutic interventions for metabolic complications, such as obesity and diabetes.

The NAD biosynthesis pathway mediated by nicotinamide phosphoribosyltransferase regulates Sir2 activity in mammalian cells.

Recent studies have revealed new roles for NAD and its derivatives in transcriptional regulation. The evolutionarily conserved Sir2 protein family requires NAD for its deacetylase activity and regulates a variety of biological processes, such as stress response, differentiation, metabolism, and aging. Despite its absolute requirement for NAD, the regulation of Sir2 function by NAD biosynthesis pathways is poorly understood in mammals. In this study, we determined the kinetics of the NAD biosynthesis mediated by nicotinamide phosphoribosyltransferase (Nampt) and nicotinamide/nicotinic acid mononucleotide adenylyltransferase (Nmnat), and we examined its effects on the transcriptional regulatory function of the mouse Sir2 ortholog, Sir2alpha, in mouse fibroblasts. We found that Nampt was the rate-limiting component in this mammalian NAD biosynthesis pathway. Increased dosage of Nampt, but not Nmnat, increased the total cellular NAD level and enhanced the transcriptional regulatory activity of the catalytic domain of Sir2alpha recruited onto a reporter gene in mouse fibroblasts. Gene expression profiling with oligonucleotide microarrays also demonstrated a significant correlation between the expression profiles of Nampt- and Sir2alpha-overexpressing cells. These findings suggest that NAD biosynthesis mediated by Nampt regulates the function of Sir2alpha and thereby plays an important role in controlling various biological events in mammals.