Isolation of viable human hepatic progenitors from adult livers is possible even after 48 hours of cold ischemia

Biological, Medical, and Other Tissue Variables Affecting Biospecimen Utilization

Bioresources are critical resources that support biomedical research because of their ability to appropriately collect, process, store, and distribute a wide range of high-quality biospecimens that meet the needs of specific investigators. Of note, some biorepositories are concerned by their growing inventories and their low rates of tissue utilization. This review discusses the technical characteristics of biospecimens that can cause morphological and molecular variability and/or limit the usefulness of biospecimens in research. This article also describes current challenges related to biospecimen characteristics that may affect biospecimen utilization. These include inadequate awareness of investigators about the availability of biospecimens with specific morphologic and molecular features, donor variability, preanalytical variables, technical problems inherent with an investigator's request for biospecimens, limited tissue availability from a biorepository based on requested sizes and/or numbers of available biospecimens, effects of times of warm and cold ischemia, damage of tissues during surgery, and molecular changes during storage. To ensure maximal biospecimen utilization of all types of biospecimens requires continual education of investigators from diverse fields, particularly on factors that cause variability in the morphological and molecular characteristics of tissues. The investigators' requests for biospecimens and associated data should be reviewed carefully, including by a bioresource-associated pathologist. Queries arising from the request/application form should be resolved by bioresource personnel directly with the investigator.

Response of Human Fetal Liver Progenitor Cell Types to Temperature and pH Stresses In Vitro

Prolonged physiological stresses, including abnormal pH and temperature, are deleterious. However, human hepatic progenitors have been shown to be quite tolerant of temporary temperature stress such as in cold ischemia. We aimed at identifying how various stresses affect liver progenitors, and at determining whether distinct effects exist on different progenitor cells of the human liver. Total fetal liver cells were exposed to low (25°C), normal (37°C), or high (40°C) temperatures, or low (6.76), normal (7.35), or high (7.88) pH in vitro. Culture at 25°C increased cell numbers and percentages of proliferation marker Ki67⁺ total cells. In total cell cultures, percentages of CD326⁺ hepatic progenitors co-expressing DLK1 (delta-like 1 homolog), SSEA4, or CD90 increased, as well as proliferation of SSEA4⁺ and CD235a⁺ progenitors. Analyses of presorted hepatic progenitors revealed that culture at 25°C increased cell numbers of CD326⁺ hepatic stem/progenitor cells but not DLK⁺ hepatoblasts. The expression of several mesenchymal genes was reduced, and distinct hepatic stem/progenitor cell colonies emerged. At 40°C, numbers of adherent hepatic cells decreased but those of hematopoietic nonadherent cells increased. High pH did not cause major effects. Acidic pH resulted in decreased total cell numbers and affected hematopoietic cells. Percentages of DLK1⁺ hepatoblasts were increased, but those of hematopoietic mature CD45⁺ cells were decreased. In particular, proliferation of adherent hepatic CD326⁺, SSEA4⁺ progenitors, and hematopoietic CD45⁺ cells and CD235a⁺ erythroblasts was reduced. Conclusively, our data indicate that low-temperature stress stimulates hepatic progenitor and erythroblast proliferation, whereas acidic pH promotes hepatic maturation and reduces hematopoietic cells.

Isolation, characterization and cold storage of cells isolated from diseased explanted livers

INTRODUCTION

Livers discarded after standard organ retrieval are commonly used as a cell source for hepatocyte transplantation. Due to the scarcity of organ donors, this leads to a shortage of suitable cells for transplantation. Here, the isolation of liver cells from diseased livers removed during liver transplantation is studied and compared to the isolation of cells from liver specimens obtained during partial liver resection.

METHODS

Hepatocytes from 20 diseased explanted livers (Ex-group) were isolated, cultured and stored at 4°C for up to 48 hours, and compared to hepatocytes isolated from the normal liver tissue of 14 liver lobe resections (Rx-group). The nonparenchymal cell fraction (NPC) was analyzed by flow cytometry to identify potential liver progenitor cells, and OptiPrep™ (Sigma-Aldrich) density gradient centrifugation was used to enrich the progenitor cells for immediate transplantation.

RESULTS

There were no differences in viability, cell integrity and metabolic activity in cell culture and survival after cold storage when comparing the hepatocytes from the Rx-group and the Ex-group. In some cases, the latter group showed tendencies of increased resistance to isolation and storage procedures. The NPC of the Ex-group livers contained considerably more EpCAM+ and significantly more CD90+ cells than the Rx-group. Progenitor cell enrichment was not sufficient for clinical application.

CONCLUSIONS

Hepatocytes isolated from diseased explanted livers showed the essential characteristics of being adequate for cell transplantation. Increased numbers of liver progenitor cells can be isolated from diseased explanted livers. These results support the feasibility of using diseased explanted livers as a cell source for liver cell transplantation.

Effects of Cold Ischemia on Gene Expression: A Review and Commentary

Frequently investigators request that tissues be collected and processed in less than one hour following removal from a patient. Some biorepositories expend significant personnel time and other resources in trying to meet such goals; however, it is unclear whether the perceived benefits of relatively short cold ischemia times warrant these added costs. The literature of human surgical tissues prospectively exposed to cold ischemia at several time points was reviewed to compare the changes in transcripts/genes and microRNA with time of cold ischemia. Also, reports of protein changes in response to cold ischemia were correlated to changes in genes. The literature is limited; however, for most tissues, only a small proportion of transcripts/genes (<1%) changes up to 3 hours following surgery and most transcripts increase rather than decrease in less than 2 hours of cold ischemia. Biorepositories and investigators must consider the literature for evidence of significant changes in molecular results from tissues before spending significant resources on relatively rapid collection of tissues to meet cold ischemia times of less than 3 hours. Instead, those using human tissues in research must consider if the cold ischemia times affect their use in specific research; hence are these tissues "fit for purpose?"

EpCAM and the biology of hepatic stem/progenitor cells

Epithelial cell adhesion molecule (EpCAM) is a transmembrane glycoprotein, which is frequently and highly expressed on carcinomas, tumor-initiating cells, selected tissue progenitors, and embryonic and adult stem cells. During liver development, EpCAM demonstrates a dynamic expression, since it can be detected in fetal liver, including cells of the parenchyma, whereas mature hepatocytes are devoid of EpCAM. Liver regeneration is associated with a population of EpCAM-positive cells within ductular reactions, which gradually lose the expression of EpCAM along with maturation into hepatocytes. EpCAM can be switched on and off through a wide panel of strategies to fine-tune EpCAM-dependent functional and differentiative traits. EpCAM-associated functions relate to cell-cell adhesion, proliferation, maintenance of a pluripotent state, regulation of differentiation, migration, and invasion. These functions can be conferred by the full-length protein and/or EpCAM-derived fragments, which are generated upon regulated intramembrane proteolysis. Control by EpCAM therefore not only depends on the presence of full-length EpCAM at cellular membranes but also on varying rates of the formation of EpCAM-derived fragments that have their own regulatory properties and on changes in the association of EpCAM with interaction partners. Thus spatiotemporal localization of EpCAM in immature liver progenitors, transit-amplifying cells, and mature liver cells will decisively impact the regulation of EpCAM functions and might be one of the triggers that contributes to the adaptive processes in stem/progenitor cell lineages. This review will summarize EpCAM-related molecular events and how they relate to hepatobiliary differentiation and regeneration.