Long-term culture of functional hepatocytes on chemically modified collagen gels

Reconstruction of a Hard Connective Tissue Utilizing a Pressed Silk Sheet and Type-I Collagen as the Scaffold for Fibroblasts

A pressed silk sheet is a new biomaterial composed of a network of numerous cocoon filaments and having excellent mechanical strength and shape stability compared to a cotton-gauze sheet. To reconstruct a hard connective tissue using the silk sheet and type-I collagen as the scaffold for fibroblasts, three different three-dimensional floating culture systems were designed. "On sheet" system: fibroblasts were seeded on the silk sheet coated with collagen and the cell-attached sheet was cultured. "In gel" system: fibroblasts and the silk sheet were co-embedded in a collagen gel and the gel was cultured. "On vitrigel" system: fibroblasts were seeded on both sides of a collagen vitrigel involving the silk sheet and the vitrigel was cultured. The fibroblasts in all culture systems grew and formed disk-shaped connective tissue models involving the silk sheet by 14 days of culture. The "on sheet" and "on vitrigel" models retained a maximum elastic load of about 23 kgf and an ultimate tensile load of about 3.6 kgf, which were almost the same as for the individual silk sheet. However, the "in gel" system showed a low value for the tensile load. Cell damage following application of mechanical stress was lowest in the "on vitrigel" system. These data demonstrated the advantage of the "on vitrigel" system in reconstructing hard connective tissues. Such a novel culture method would contribute to a regenerative medicine for the failure of ligaments, tendons, and other connective tissues.

Collagen vitrigel: a novel scaffold that can facilitate a three-dimensional culture for reconstructing organoids

Three-dimensional reconstructed organoids in vitro are valuable for not only regenerative medicine but also drug development. However, the manipulation of conventional three-dimensional cultures is not simple. We describe a nylon membrane ring-embedded or a pressed silk sheet-embedded scaffold made of collagen "vitrigel" that can facilitate three-dimensional cultures for reconstructing an epithelial-mesenchymal model or a hard connective tissue model, respectively. Here we define vitrigel as a gel in a stable state produced by rehydration after the vitrification of a traditional hydrogel. The collagen vitrigel was successfully prepared in three steps involving a gelation process in which a cold and clear neutral salt solution containing type I collagen formed an opaque and soft gel by incubation at 37 degrees C, a vitrification process in which the gel becomes a rigid material like glass after sufficient drying out, and finally a rehydration process to convert the vitrified material into a thin and transparent gel membrane with enhanced gel strength. The framework-embedded collagen vitrigel scaffold that can be easily reversed by forceps was prepared by inserting a nylon ring or a silk sheet in the collagen solution prior to the gelation. The scaffold enabled culturing anchorage-dependent cells on both surfaces of the collagen vitrigel by the manipulation of two-dimensional cultures and consequently resulted in reconstructing a three-dimensional organoid. An intestinal epithelial-mesenchymal model was reconstructed by coculturing fibroblasts on the opposite side of monolayered Caco-2 cells on the nylon ring-embedded collagen vitrigel. Also, fibroblasts seeded on both surfaces of the silk sheet-embedded collagen vitrigel proliferated well and formed multilayers and some cells invaded into the vitrigel framed by the network of numerous strong silk filaments, suggesting a reconstruction of a hard connective tissue model. These data demonstrate that the collagen vitrigel is a valuable scaffold for tissue engineering.

Reconstruction of renal glomerular tissue using collagen vitrigel scaffold

The construction of renal glomerular tissue has provided an important tool not only for the understanding of renal physiology and pathology in blood ultrafiltration and cell dysfunction, but also in the application of tissue engineering to glomeruli regeneration and nephritic therapy. In this study, a novel method to reconstruct glomerular tissue combining cultured cells on a collagen vitrigel scaffold is described. The method consists of two newly developed techniques, one to isolate glomerular epithelial and mesangial cells rapidly from kidney, which facilitates the prolongation of cell population doublings and allows a long-term cell culture without losing cellular features, and another to prepare a stable and thin transparent collagen gel membrane termed collagen vitrigel that can facilitate three-dimensional cultures for reconstructing an epithelial-mesenchymal model. By combining the two methods, we cocultured glomerular epithelial and mesangial cells on both surfaces of the collagen vitrigel by the manipulation of two-dimensional cultures, resulting in the successful reconstruction of a three-dimensional glomerular organoid. The coculture results showed that the collagen vitrigel maintains cell growth and cell viability for more than 1 month, and surprisingly, the epithelial layer demonstrated polarity formation, which usually appears in in vivo normal epithelial cells existing at the glomerular basement membrane, but seldom appears in epithelial cells cultured in vitro. Moreover, the coculture results showed that fibronectin, an extracellular matrix component, and integrin beta1, a receptor of fibronectin, were detected in high amounts on both cells, suggesting our collagen vitrigel can provide a suitable environment for cell-cell interactions that stabilize the cell structure and may contribute to the polarity formation of epithelial cells.

Enhanced production of carcinoembryonic antigen by CW-2 cells cultured on polymeric membranes immobilized with extracellular matrix proteins

Cell growth and the production of carcinoembryonic antigen (CEA) were investigated in human colorectal adenocarcinoma tumor (CW-2) cells cultured on extracellular matrix (ECM) protein membranes, heat-treated poly(vinyl alcohol-co-ethylamine) (PVA-EA) membranes, and PVA-EA membranes containing immobilized ECM proteins. The highest concentration of CEA was found in the cell culture media of CW-2 cells on collagen (COL)-immobilized PVA-EA membranes. This is explained by the flexible mobility of COL on the COL-immobilized PVA-EA membranes causing a specific cell response for the production of CEA. An inverse relationship was observed between either the cell density or the CEA concentration in the cell culture media and the amount of fibronectin (FN) adsorbed on the COL-immobilized membranes. The CEA concentration in the cell culture media was directly related to the cell density, which, in turn, is inversely related to the amount of FN secreted by CW-2 cells. These findings indicate that cells tend to attach to the surface by secreting ECM proteins such as FN when they are grown on substrates that provide weak cell attachment.

Morphological comparison and functional reconstitution of rat hepatic parenchymal cells on various matrices

Four types of materials, type I collagen coat (Coat), acid-soluble type I collagen gel (Hardgel), pepsin-treated acid-soluble type I collagen gel (Softgel), and an extract of extracellular matrix of the murine Engelbreth-Holm-Swarm sarcoma (Matrigel), were used as matrices to culture rat hepatic parenchymal cells, and their morphological changes and adhesion were compared to the matrices by electron microscopic observations. Hepatic parenchymal cells cultured on Coat and Hardgel were extended and flattened, whereas cells cultured on Softgel and Matrigel assembled and formed aggregates. Such aggregates consisted of several hepatic parenchymal cells, with a recognizable bile duct-like alveolus on the inside. Morphologically, the aggregates were more spherical on Matrigel and oval shaped on Softgel. Microvilli of the cell surface were parallel to the matrix on Matrigel, but invaded into the gel on Softgel. Subsequently, investigation into how these morphological features affected the liver-specific functions, including secretion of albumin and induction of P450 by 3-methylcholanthrene, demonstrated that a high level of liver function was maintained in a long-term culture in hepatic parenchymal cells on Softgel. These results suggest that hepatic parenchymal cell interactions were stronger with Softgel than with Matrigel, and that Softgel appears to closely mimic the in vivo environment.

Sensitivity of human hepatocytes in culture to reactive nitrogen intermediates

The cytotoxic effects of 3-morpholinosydnonimine (Sin-1) and S-nitroso-N-acetylpenicillamine-amine (SNAP) on replicatively active human hepatocyte cells in culture was determined as a function of oxidant type. Both Sin-1 which yields nitric oxide and peroxynitrite following the generation of superoxide anion plus nitric oxide, and SNAP which generates nitric oxide, induced dose dependent decreases in the colony forming capabilities of the human hepatocytes. Sin-1 was much more cytotoxic (LD50 = 400 microM) than SNAP (LD50 = 1250 microM). Comparatively, both compounds were much less cytotoxic than H2O2 (LD50 = 96 microM). Sin-1 induced 4-fold higher levels of cellular nitrite than that generated by the chemical in cell free medium. Nitrotyrosine, a marker of peroxynitrite formation in cells, was immunohistochemically detected in hepatocytes treated with both Sin-1 and SNAP. The formation of 3-nitrotyrosine by hepatocytes incubated with SNAP, suggests that hepatocytes generate intracellular superoxide which reacts with the exogenous nitric oxide derived from SNAP to produce intracellular peroxynitrite, resulting in the SNAP cytotoxicity. The enhanced levels of Sin-1 cytotoxicity on the hepatocytes is suggested to be due both to the chemical generation of peroxynitrite and superoxide anion by Sin-1. These data indicate that peroxynitrite is formed in cultured human hepatocytes inhibiting their replication, and that peroxynitirite may play a significant role in the pathogenesis of liver disease.