A stereotypic, transplantable liver tissue-culture system

A method of coculturing adult rat hepatic parenchymal cells (PC) and stromal cells in a three-dimensional framework of nylon filtration screens or biodegradable polymer meshes was developed in our laboratory. Rat liver stroma, which includes vascular and bile duct endothelial cells, fat-storing cells, fibroblasts, and Kupffer cells, were isolated by gradient centrifugation after in situ liver perfusion and expanded in monolayer culture prior to seeding onto nylon screens or bioresorbable polyglycolic acid (PGA) polymers oriented into a felt-like construct. A second inoculum of freshly isolated PC was applied after the stromal cells became established. Histological analyses revealed that PC proliferation occurred until all available space for expansion within the template was exhausted. These cells retained their rounded morphology, and after 4-5 wk 7-9 "layers" of PC filled the 140-microns deep template. Dioxin-inducible cytochrome P450 activity was detected for up to 58 d in culture, and albumin, fibrinogen, transferrin, and soluble fibronectin were detected in the medium by enzyme-linked immunosorbent assay (ELISA) for 48 d in vitro. Immunohistochemical analysis of sections through the cultures confirmed the presence of these proteins as well as cytokeratin at the cellular level; the extracellular matrix stained for both collagen type III and laminin. Long-term PC proliferation and function were enhanced by the presence of stromal cells as well as by a meshwork template whose geometry allows the interaction of PC with stroma and matrix on several different planes. To permit transplantation, cocultures of hepatic PC and stromal cells were established on PGA felt constructs instead of nylon screens. After approximately 24 d in vitro, these constructs were grafted into sites in the mesentery, omentum, and subcutaneous tissues of adult Long-Evans rats. The growth of hepatocytes after 30 d in situ was evident by histological analysis; grafts of cocultures regenerated a liver-like architecture consisting of sinusoids and putative biliary structures. In addition, PC at these extrahepatic graft sites were positive for albumin, transferrin, and fibrinogen synthesis by immunohistochemistry. Graft survival was enhanced when recipients were subjected to approximately 40% hepatectomy. Hepatic PC:stromal cell cocultures may prove useful in the restoration of liver function either by direct transplantation using PGA or similar templates, or as extracorporeal devices, using nylon screens.