Dietrich Kluth

Nitrofen-induced diaphragmatic hernias in rats : an animal model

In embryological terms, pathogenesis of congenital diaphragmatic hernia (CDH) associated with pulmonary hypoplasia is still unclear. However, it is known since 1971 that Nitrofen (2,4-dichloro-phenyl-p-nitrophenyl ether) can induce anatomical malformations in rats including diaphragmatic hernias. On order to establish an animal model of the embryogenesis of CDH, the effect of Nitrofen on the developing diaphragm was studied. Thirty-three pregnant female rats were exposed to Nitrofen. Five unexposed pregnant rats served as controls. In the first set of experiments, single doses of Nitrofen were given between the 9th and 13th day of pregnancy. In the second set of experiments, dosages of 50, 100, and 150 mg per animal were given on day 11 of pregnancy only. Postnatally the litters (469 newborn rats) were dissected to record the incidence of diaphragmatic malformations. The results were: (1) most hernias occurred after administration of 100 mg Nitrofen on day 9 (42%) and 11 (59%); (2) left-sided hernias were observed only after exposure to Nitrofen on day 9; (3) after exposure on day 10 or later all hernias were on the right side; and (4) Fifty-nine percent of the newborn rats exposed on day 11 had CDH. These results show that this model is suitable for further embryological investigations on the development of CDH.

Hepatic tissue engineering: from transplantation to customized cell-based liver directed therapies from the laboratory

•  Introduction •  Development of cell isolation and primary culture for hepatocytes •  Three–dimensional culture using matrices •  Development of bioreactor systems for liver cells •  First clinical application of bioreactors with liver cells •  Development of matrix‐based hepatocyte transplantation •  Outlook: future perspective for the development of successful tissue engineering approaches for transplantation

Long-term differentiated function of heterotopically transplanted hepatocytes on three-dimensional polymer matrices.

Hepatocyte transplantation using porous matrices is under investigation as an alternative therapy for certain liver diseases. For this purpose, long-term function of transplanted hepatocytes is mandatory. This problem has not been sufficiently investigated yet. In this study Lewis rats were used as donors and recipients. Stimulated (group A, portocaval shunt) or unstimulated (group B) hepatocytes were transplanted into prevascularized polyvinyl-alcohol matrices. Cell-free matrices served as controls (group C). Matrices were harvested between 1 h and 1 year after implantation and analyzed by morphometry; albumin RNA in situ hybridization; and cytokeratin-, actin-, desmin-, and macrophage-specific antigen immunohistology. The hepatocyte number significantly decreased within the first week following implantation. Between 1 month and 1 year after transplantation a significant increase in hepatocyte number was noted in groups A and B. Albumin transcripts of transplanted hepatocytes were at normal levels at all times except for group B after 1 year. The immunohistology suggested engraftment of nonparenchymal liver cells. We conclude that 3-dimensional matrices provide a sufficient environment for long-term engraftment of transplanted liver cells. The hepatocytes are able, despite suboptimal initial engraftment, to repopulate the scaffold for at least half of the recipients life span and maintain cell-specific function after sufficient stimulation.

The natural history of congenital diaphragmatic hernia and pulmonary hypoplasia in the embryo

Up to now, descriptions of the natural history of congenital diaphragmatic hernia (CDH) associated with pulmonary hypoplasia (PH) are based exclusively on observations made in the fetal period. However, nothing is known about the events that take place in an embryo with CDH. Recently, an animal model of CDH and PH has been established in rat embryos to study the embryology and natural history of this lesion. We exposed 36 pregnant Sprague-Dawley rats to a single dose of 100 mg nitrofen on day 11 of pregnancy. A total of 356 staged embryos and fetuses from day 13 to day 21 were studied by light and scanning electronmicroscopy. The litters of 9 untreated rats (124 normal age-matched embryos and fetuses) served as controls. The abnormal development of the diaphragmatic anlage was first seen in embryos aged 13 to 14 days. A defect appeared in the dorsal part of the diaphragm, normally on the right side. The liver grew through this defect early on. Gut was found in an intrathoracic position only in the very late stages (day 21/22) and newborns. Compared to controls, lungs of nitrofen-embryos with CDH were smaller, depending on the size of liver found in the thoracic cavity. Histologically, compression of lung was absent at these stages. Most authors speculate that CDH results because the pleuroperitoneal canals fail to close at the end of the embryonic period (ie, week 8 to 10 in human development) leading to a defect in the dorsolateral region of the diaphragm. However, contradictory to this assumption, our findings indicate that diaphragmatic defects develop in early embryonic life.(ABSTRACT TRUNCATED AT 250 WORDS)

Fetal and adult liver stem cells for liver regeneration and tissue engineering

For the development of innovative cell‐based liver directed therapies, e.g. liver tissue engineering, the use of stem cells might be very attractive to overcome the limitation of donor liver tissue. Liver specific differentiation of embryonic, fetal or adult stem cells is currently under investigation. Different types of fetal liver (stem) cells during development were identified, and their advantageous growth potential and bipotential differentiation capacity were shown. However, ethical and legal issues have to be addressed before using fetal cells. Use of adult stem cells is clinically established, e.g. transplantation of hematopoietic stem cells. Other bone marrow derived liver stem cells might be mesenchymal stem cells (MSC). However, the transdifferentiation potential is still in question due to the observation of cellular fusion in several in vivo experiments. In vitro experiments revealed a crucial role of the environment (e.g. growth factors and extracellular matrix) for specific differentiation of stem cells. Co‐cultured liver cells also seemed to be important for hepatic gene expression of MSC. For successful liver cell transplantation, a novel approach of tissue engineering by orthotopic transplantation of gel‐immobilized cells could be promising, providing optimal environment for the injected cells. Moreover, an orthotopic tissue engineering approach using bipotential stem cells could lead to a repopulation of the recipients liver with healthy liver and biliary cells, thus providing both hepatic functions and biliary excretion. Future studies have to investigate, which stem cell and environmental conditions would be most suitable for the use of stem cells for liver regeneration or tissue engineering approaches.

Embryology of bladder exstrophy

A hypothesis in respect to the teratogenesis of bladderexstrophy and its variants is offered. The central feature of this hypothesis is the abnormal persistance of the caudal position of the insertion of the body stalk on the embryo. As a consequence of this, the normal advance and interposition of mesenchymal tissue to the midline becomes impossible. The cloaca cannot be translocated backwards into the body cavity and the cranial end of the cloacal membrane remains in contact with the inferior aspect of the low-set body stalk. This, in contrast to the previously proposed abnormal rostral extention of the cloacal membrane, causes a wedge-effect resulting in the lateralization of the abdominal wall structures and also in the prevention of the midline fusion of the genital hillocks (labioscrotal or genital folds). A cloacal membrane normally is an unstable structure lacking mesoderm, and it retains these characteristics in the superficial and infraumbilical position to be described. It has a strong tendency to disintegrate. It may rupture at variable times and to a variable extent. The consequence of such an embryonic event is either a typical bladder exstrophy or one of the variants of the exstrophy malformation. Three different variants are presented that the proposed embryologic hypothesis can readily explain.

Influence of flow conditions and matrix coatings on growth and differentiation of three-dimensionally cultured rat hepatocytes.

Maintenance of liver-specific function of hepatocytes in culture is still difficult. Improved culture conditions may enhance the cell growth and function of cultured cells. We investigated the effect of three-dimensional culture under flow conditions, and the influence of surface modifications in hepatocyte cultures. Hepatocytes were harvested from Lewis rats. Cells were cultured on three-dimensional polymeric poly-lactic-co-glycolic acid (PLGA) matrices in static culture, or in a pulsatile flow-bioreactor system. Different surface modifications of matrices were investigated: coating with collagen I, collagen IV, laminin, or fibronectin; or uncoated matrix. Hepatocyte numbers, DNA content, and albumin secretion rate were assessed over the observation period. Culture under flow condition significantly enhanced cell numbers. An additional improvement of this effect was observed, when matrix coating was used. Cellular function also showed a significant increase (4- to 5-fold) under flow conditions when compared with static culture. Our data showed that culture under flow conditions improves cell number, and strongly enhances cellular function. Matrix modification by coating with extracellular matrix showed overall an additive stimulatory effect. Our conclusion is that combining three-dimensional culture under flow conditions and using matrix modification significantly improves culture conditions and is therefore attractive for the development of successful culture systems for hepatocytes.

Stem-like Cells in Human Hepatoblastoma

Hepatoblastoma is a pediatric liver tumor with epithelial components resembling embryonal and fetal liver cells. The existence of teratoid hepatoblastoma suggests the presence of stem cells in hepatoblastoma. The aim of this study was to analyze the expression of stem cell markers in hepatoblastomas. We studied specimens from 10 hepatoblastomas. Five of the hepatoblastomas were of epithelial and five of mixed type. Immunohistochemistry (IHC) for the stem cell markers CD34, Thy1, c-kit, and the hepatic or biliary lineage markers CK-18, OCH, CK-7, and CD56 was performed. Double IHC for stem cell and lineage markers was used to identify putative liver stem cells. The different markers showed distinct distributions on the tumor cells. Cells in atypical ducts were found to express simultaneously stem cell markers and hepatocytic or biliary lineage markers. Other cells in connective tissue showed c-kit expression, but not hepatic or biliary marker expression. The data show the presence of different cell populations bearing stem cell markers in human hepatoblastoma. Ductal cells co-expressing stem cell markers and hepatic lineage markers phenotypically resemble hepatic stem-like cells. These findings support the thesis that stem cells play a role in the histogenesis of hepatoblastoma.

The embryology of the foregut

Until today, several theories have been developed to explain the occurrence of common foregut malformations as esophageal atresia and tracheoseophageal fistula. Most researchers believe that these malformations are the result of an impaired process of septation of the early foregut. However, a detailed review of the literature makes clear that a unified embryologic concept of the normal foregut development is still missing. This statement is still true after the development of an animal model, the so-called Adriamycin model in rats, which allows the reproduction of embryos, fetuses, and newborns with a huge spectrum of malformations, including foregut malformations. In the first part of this review, data from the literature are presented and analyzed critically, which deal with the differentiation of the foregut into the esophagus and the respiratory tract. In general, it is a shortcoming that reliable illustrations of these crucial embryologic processes still are missing in most of these reports. Therefore, in the second part, scanning electron microscopy pictures of the developing foregut are presented in a series of chicken embryos. In these pictures, signs of a septum are completely missing as an important structure during the differentiation of the foregut. In the third part, the spectrum of theories that should explain abnormal foregut malformations is presented and critically discussed. In the last section, the Adriamycin model and its implications for the current understanding of the foregut malformations is discussed.

Optimization of hepatocyte spheroid formation for hepatic tissue engineering on three-dimensional biodegradable polymer within a flow bioreactor prior to implantation

We hypothesize that in vitro conditioning of hepatocytes within biodegradable poly-L-lactic acid (PLLA) polymer matrices prior to implantation may increase hepatocyte survival and function after transplantation. The purpose of this study was to optimize the culture conditions of hepatocytes in a pulsatile flow bioreactor. PLLA discs were seeded with rat hepatocytes in a concentration of 2.5, 5, 10, 20 and 40 × 106 cells/ml. Seeded discs were exposed to recirculated perpendicular flow of 0, 7, 15, 24, 32, 52 ml/min of supplemented Williams’ Medium E and harvested after 6 days in flow culture. Only under flow conditions the hepatocytes formed spheroidal aggregates (SphA) of 50–260 µm in diameter with a liver-like morphology and active metabolic function. The number of SphA was examined by phase contrast microscopy and the reductive enzyme function of the hepatocytes was tested using MTT. Hematoxylin and eosin histology showed vital hepatocytes within the SphA less than 200 µm in diameter but central necrosis in the SphA exceeding this size. Immunohistochemical staining confirmed albumin production of hepatocytes within the SphA. The optimal cell seeding concentration was 10 × 106 cells/ml with a flow speed of 24 ml/min. SphA of hepatocytes cultured with this flow bioreactor method may prove useful as a functional unit for tissue engineering of an in vivo liver substitute.