Differentiation of the human liver progenitor cell line (HepaRG) on a microfluidic-based biochip

HepaRG is a bipotent stem cell line that can be differentiated towards hepatocyte-like and biliary-like cells. The entire cultivation process requires 1 month and relies on the addition of 2% dimethyl sulfoxide (DMSO) to the culture. Our motivation in this research is to differentiate HepaRG cells (progenitor cells and undifferentiated cells) towards hepatocyte-like cells by minimizing the cultivation time and without using DMSO treatment by instead using a microfluidic device combined with the following strategies: (a) comparison of extracellular matrices (matrigel and collagen I), (b) types of flow (one or both sides), and (c) effects of DMSO. Our results demonstrate that matrigel promotes the differentiation of progenitor cells towards hepatocytes and biliary-like cells. Moreover, the frequent formation of HepaRG cell clusters was observed by a supply of both sides of flow, and the cell viability and liver specific functions were influenced by DMSO. Finally, differentiated HepaRG progenitor cells cultured in a microfluidic device for 14 days without DMSO treatment yielded 70% of hepatocyte-like cells with a highly polarized organization that reacted to stimulation with IL-6 to produce C-reactive protein (CRP). This culture model has high potential for investigating cell differentiation and liver pathophysiology research.

Melatonin or ramelteon therapy differentially affects hepatic gene expression profiles after haemorrhagic shock in rat--A microarray analysis

BACKGROUND & AIMS

Melatonin has been demonstrated to reduce liver damage in different models of stress. However, there is only limited information on the impact of this hormone on hepatic gene expression. The aim of this study was, to investigate the influence of melatonin or the melatonergic agonist ramelteon on hepatic gene expression profiles after haemorrhagic shock using a whole genome microarray analysis.

METHODS

Male Sprague-Dawley rats (200-300 g, n=4/group) underwent haemorrhagic shock (mean arterial pressure 35±5 mmHg). After 90 min of shock, animals were resuscitated with shed blood and Ringer's and treated with vehicle (5% dimethyl sulfoxide), melatonin or ramelteon (each 1.0 mg/kg intravenously). Sham-operated animals were treated likewise but did not undergo haemorrhage. After 2 h of reperfusion, the liver was harvested, and a whole genome microarray analysis was performed. Functional gene expression profiles were determined using the Panther® classification system; promising candidate genes were evaluated by quantitative polymerase chain reaction (PCR).

RESULTS

Microarray and PCR data showed a good correlation (r(2)=0.84). A strong influence of melatonin on receptor mediated signal transduction was revealed using the functional gene expression profile analysis, whereas ramelteon mainly influenced transcription factors. Shock-induced upregulation of three candidate genes with relevant functions for hepatocytes (ppp1r15a, dusp5, rhoB) was significantly reduced by melatonin (p<0.05 vs. shock/vehicle), but not by ramelteon. Two genes previously known as haemorrhage-induced (il1b, s100a8) were transcriptionally repressed by both drugs.

CONCLUSIONS

Melatonin and ramelteon appear to induce specific hepatic gene expression profiles after haemorrhagic shock in rats. The observed differences between both substances are likely to be attributable to a distinct mechanism of action in these agents.

On-chip three-dimensional cell culture in phaseguides improves hepatocyte functions in vitro

The in vitro study of liver functions and liver cell specific responses to external stimuli deals with the problem to preserve the in vivo functions of primary hepatocytes. In this study, we used the biochip OrganoPlate(TM) (MIMETAS) that combines different advantages for the cultivation of hepatocytes in vitro: (1) the perfusion flow is achieved without a pump allowing easy handling and placement in the incubator; (2) the phaseguides allow plating of matrix-embedded cells in lanes adjacent to the perfusion flow without physical barrier; and (3) the matrix-embedding ensures indirect contact of the cells to the flow. In order to evaluate the applicability of this biochip for the study of hepatocyte's functions, Matrigel(TM)-embedded HepG2 cells were cultured over three weeks in this biochip and compared to a static Matrigel culture (3D) and a monolayer culture (2D). Chip-cultured cells grew in spheroid-like structures and were characterized by the formation of bile canaliculi and a high viability over 14 days. Hepatocyte-specific physiology was achieved as determined by an increase in albumin production. Improved detoxification metabolism was demonstrated by strongly increased cytochrome P450 activity and urea production. Additionally, chip-cultured cells displayed increased sensitivity to acetaminophen. Altogether, the OrganoPlate seems to be a very useful alternative for the cultivation of hepatocytes, as their behavior was strongly improved over 2D and static 3D cultures and the results were largely comparable and partly superior to the previous reports on biochip-cultured hepatocytes. As for the low technical needs, this platform has the appearance of being highly applicable for further studies of hepatocytes' responses to external stimuli.

No effect of thromboxane A2 on the attachment of tumor cell lines MDA MB 231, DU145, and U937 to the basement membrane in an in-vitro model

PURPOSE

A broad body of evidence indicates the involvement of P450 TxA2 (thromboxane A2 synthetase) in tumor metastasis formation. A distinct function of the enzyme in this multistep process, however, is still unknown. Therefore the effect of TxA2 (thromboxane A2) on tumor cell adhesion to the basement membrane, a key event in metastasis formation, was investigated.

METHODS

A wide variety of compounds designed in our work group and identified as P450 TxA2 inhibitors were applied to several P450 TxA2-positive tumor cell lines to test their influence on tumor cell adhesion. For this purpose an in-vitro basement membrane adhesion model with the matrix gel preparation Matrigel was used.

RESULTS

Most of the P450 TxA2 inhibitors tested had no effect on cell adhesion. Although two compounds significantly reduced tumor cell adhesion in a concentration-dependent manner, this was not related to P450 TxA2 inhibition.

CONCLUSION

These data indicate that TxA2 might not be involved in the attachment of tumor cell lines to the basement membrane.

Spectrofluorimetric quantification of malondialdehyde for evaluation of cyclooxygenase-1/thromboxane synthase inhibition

The in vitro assay developed by Hartmann and Ledergerber (1995) utilizing the spectrofluorimetric quantification of malondialdehyde after reaction with thiobarbituric acid was modified and used for further investigations. The human whole blood was replaced by a platelet suspension of pig blood, and calcium ionophore A23187 was used instead of collagen for inducing the arachidonic acid cascade. The modified assay represents a simple, time and cost saving method for the evaluation of cyclooxygenase-1/thromboxane synthase inhibition. The reproducibility and comparability of results is given. Additional experiments allow classification of selective phospholipase A2, cyclooxygenase-1, and thromboxane synthase inhibitors. Further studies of malondialdehyde formation show that the cyclooxygenase and/or the thromboxane synthase are competitively inhibited by reaction products of the cyclooxygenase pathway by a negative feedback mechanism.

Mutational analysis of the Streptomyces lividans recA gene suggests that only mutants with residual activity remain viable

Temperature-sensitive integration plasmids carrying internal fragments of the Streptomyces lividans TK24 recA gene were constructed and used to inactivate the chromosomal recA gene of S. lividans by gene disruption and gene replacement. Integration of these plasmids resulted in recA mutants expressing C-terminally truncated RecA proteins, as deduced from Southern hybridization experiments. Mutants FRECD2 in which the last 42 amino acids, comprising the variable part of bacterial RecA proteins, had been deleted retained the wild-type phenotype. The S. lividans recA mutant FRECD3 produced a RecA protein lacking 87 amino acids probably including the interfilament contact site. FRECD3 was more sensitive to UV and MMS than the wild-type. Its ability to undergo homologous recombination was impaired, but not completely abolished. Integration of the disruption plasmid pFRECD3 in S. coelicolor "Müller" caused the same mutant phenotype as S. lividans FRECD3. In spite of many attempts no S. lividans recA mutants with deletions of 165 C-terminal amino acids or more were isolated. Furthermore, the recA gene could not be replaced by a kanamycin resistance cassette. These experiments indicate a crucial role of the recA gene in ensuring viability of Streptomyces.