In situ normothermic perfusion of livers in controlled circulatory death donation may prevent ischemic cholangiopathy and improve graft survival.

Livers from controlled donation after circulatory death (DCD) donors suffer a higher incidence of nonfunction, poor function, and ischemic cholangiopathy. In situ normothermic regional perfusion (NRP) restores a blood supply to the abdominal organs after death using an extracorporeal circulation for a limited period before organ recovery. We undertook a retrospective analysis to evaluate whether NRP was associated with improved outcomes of livers from DCD donors. NRP was performed on 70 DCD donors from whom 43 livers were transplanted. These were compared with 187 non-NRP DCD donor livers transplanted at the same two UK centers in the same period. The use of NRP was associated with a reduction in early allograft dysfunction (12% for NRP vs. 32% for non-NRP livers, P = .0076), 30-day graft loss (2% NRP livers vs. 12% non-NRP livers, P = .0559), freedom from ischemic cholangiopathy (0% vs. 27% for non-NRP livers, P < .0001), and fewer anastomotic strictures (7% vs. 27% non-NRP, P = .0041). After adjusting for other factors in a multivariable analysis, NRP remained significantly associated with freedom from ischemic cholangiopathy (P < .0001). These data suggest that NRP during organ recovery from DCD donors leads to superior liver outcomes compared to conventional organ recovery.

Paediatric obesity and renal transplantation: current challenges and solutions.

The increased incidence of obesity in the paediatric population poses significant challenges to renal transplantation. Whilst the body mass index appears to be widely used as a measure of obesity in adults, there are no standardised definitions in the paediatric population, making comparative analyses difficult. In the paediatric transplant population, obesity is associated with an increased incidence of surgical complications, diabetes, hyperlipidaemia and cardiovascular morbidity, leading to diminished graft function and impacting patient and graft survival. Management of obesity in renal transplantation requires multiple interventions starting with life-style and behavioural modification combined with medical and possibly surgical therapies, representing a unique challenge in the childhood setting. In this review we discuss the current challenges of obesity and potential solutions in the setting of paediatric transplantation.

Portal venous endothelium in developing human liver contains haematopoietic and epithelial progenitor cells.

Future treatments for chronic liver disease are likely to involve manipulation of liver progenitor cells (LPCs). In the human, data characterising the regenerative response is limited and the origin of adult LPCs is unknown. However, these remain critical factors in the design of cell-based liver therapies. The developing human liver provides an ideal model to study cell lineage derivation from progenitors and to understand how foetal haematopoiesis and liver development might explain the nature of the adult LPC population. In 1st trimester human liver, portal venous endothelium (PVE) expressed adult LPC markers and markers of haematopoietic progenitor cells (HPCs) shared with haemogenic endothelium found in the embryonic dorsal aorta. Sorted PVE cells were able to generate hepatoblast-like cells co-expressing CK18 and CK19 in addition to Dlk/pref-1, E-cadherin, albumin and fibrinogen in vitro. Furthermore, PVE cells could initiate haematopoiesis. These data suggest that PVE shares phenotypical and functional similarities both with adult LPCs and embryonic haemogenic endothelium. This indicates that a temporal relationship might exist between progenitor cells in foetal liver development and adult liver regeneration, which may involve progeny of PVE.

Highly efficient differentiation of hESCs to functional hepatic endoderm requires ActivinA and Wnt3a signaling.

Human embryonic stem cells (hESCs) are a valuable source of pluripotential primary cells. To date, however, their homogeneous cellular differentiation to specific cell types in vitro has proven difficult. Wnt signaling has been shown to play important roles in coordinating development, and we demonstrate that Wnt3a is differentially expressed at critical stages of human liver development in vivo. The essential role of Wnt3a in hepatocyte differentiation from hESCs is paralleled by our in vitro model, demonstrating the importance of a physiologic approach to cellular differentiation. Our studies provide compelling evidence that Wnt3a signaling is important for coordinated hepatocellular function in vitro and in vivo. In addition, we demonstrate that Wnt3a facilitates clonal plating of hESCs exhibiting functional hepatic differentiation. These studies represent an important step toward the use of hESC-derived hepatocytes in high-throughput metabolic analysis of human liver function.

Side population cells in developing human liver are primarily haematopoietic progenitor cells.

Side population (SP) cells have recently been identified in a number of tissues although their phenotype and functional abilities are poorly understood. Surface marker characterisation and functional assessment of developing liver SP cells might allow for their isolation and manipulation using clinically relevant techniques. It was hypothesised that SP cells are present early during human liver development and contribute to haematopoietic and epithelial lineage generation. Whilst the SP population remained positive for CD34 during the 1st and 2nd trimester, 1st trimester SP cells were more highly enriched for haematopoietic and epithelial progenitor activity than those from the 2nd trimester in vitro. Marker expression and functional similarities indicate that SP cells in developing human liver may share a temporal relationship with oval/progenitor cells, responsible for liver regeneration after massive or chronic hepatic injury. Furthermore, modification of SP integrin expression during development suggests a potential adaptive interaction with niche components such as fibronectin. Improved understanding of developing human liver SP cells will contribute to the generation of novel cell-based therapies for liver disease.

The inhibitory role of stromal cell mesenchyme on human embryonic stem cell hepatocyte differentiation is overcome by Wnt3a treatment.

Pluripotent stem cells are derived from the inner cell mass of preimplantation embryos, and display the ability of the embryonic founder cells by forming all three germ lineages in vitro. It is well established that the cellular niche plays an important role in stem cell maintenance and differentiation. Stem cells generally have limited function without the specialized microenvironment of the niche that provides key cell-cell contact, soluble mediators, and extracellular matrices. We were interested in the role that Wnt signaling, in particular Wnt3a, played in human embryonic stem cell (hESC) differentiation to hepatic endoderm in vitro. hESC differentiation to hepatic endoderm was efficient in pure stem cell populations. However, in younger hESC lines, generating stromal cell mesenchyme, our model was very inefficient. The negative effect of stroma could be reversed by pretreating hESCs with Wnt3a prior to the onset of hepatocyte differentiation. Wnt3a pretreatment reinstated efficient hESC differentiation to hepatic endoderm. These studies represent an important step in understanding hepatocyte differentiation from hESCs and the role played by the cellular niche in vitro.

Progenitor cell characterization and location in the developing human liver.

Tissue-derived stem cells may offer future liver disease therapies. The developing human liver provides an excellent model to examine normal hepatic progenitor cell maturation, but candidate populations are poorly characterized. We sought to identify putative progenitor phenotypes in first-trimester human liver, by characterizing the architectural relationship between developing epithelial, mesenchymal, and hematopoietic lineages. Bipotential hepatoblasts were identified by co-expression of hepatocytic (cytokeratin 18, albumin) and biliary(cytokeratin 19) specific markers and epithelial-specific E-cadherin. Restriction of dlk/pref-1 expression to hepatoblasts identifies this as a novel human marker allowing for hepatoblast sorting for in vitro analysis. Furthermore, the liver stem cell and haematopoietic marker Thy-1 was co-expressed with markers of hematopoietic (CD34) and mesenchymal (vimentin) lineage restriction on portal vein endothelium. Therefore, this structure may constitute a novel progenitor compartment with hemangioblast-like properties.

Hepatic progenitor cells in human fetal liver express the oval cell marker Thy-1.

Hepatic progenitor cells play a major role in regenerating diseased liver. In rodents, progenitors forming hepatocytes or cholangiocytes are identified by the stem cell marker Thy-1. The aim of this study was to ascertain whether progenitor cells expressing Thy-1 could be identified in human fetal liver. Midtrimester human fetal liver was immunostained for Thy-1, cytokeratins 18 and 19, vimentin, CD34, CD45, and fibrinogen. Thy-1+ and Thy-1+CD34+ populations were purified using fluorescence-activated cell sorting (FACS). Immunofluorescence and mRNA expression were used to examine the bipotential nature of purified stem cells. We found that Thy-1+ cells were concentrated in portal tracts but were also scattered in parenchyma. In FACS-prepared cells, 0.18-3.08% (median 0.65%, n = 14) of cells were Thy-1+. Immunophenotyping revealed that some Thy-1+ cells coexpressed cytokeratins 18 and 19, others, fibrinogen and cytokeratin 19. RT-PCR demonstrated that Thy-1+ cells expressed mRNA for Thy-1, cytokeratin 18, and cytokeratin 19, and Thy-1+CD34+ cells expressed mRNA for alpha-fetoprotein, transferrin, and hepatocyte nuclear factor-4alpha. Thy-1+ cells were identified in fetal liver. These cells expressed several lineage markers, including coexpression of biliary and hepatocellular proteins and mRNA. These data suggest that Thy-1 is a marker of liver stem cells in human fetal liver.