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Maximum Cell Density (maximum + cell_density)
Selected AbstractsCell proliferation of human bone marrow mesenchymal stem cells on biodegradable microcarriers enhances in vitro differentiation potentialCELL PROLIFERATION, Issue 5 2010L.-Y. Sun Objectives:, For reasons of provision of highly-specific surface area and three-dimensional culture, microcarrier culture (MC) has garnered great interest for its potential to expand anchorage-dependent stem cells. This study utilizes MC for in vitro expansion of human bone marrow mesenchymal stem cells (BMMSCs) and analyses its effects on BMMSC proliferation and differentiation. Materials and methods:, Effects of semi-continuous MC compared to control plate culture (PC) and serial bead-to-bead transfer MC (MC bead-T) on human BMMSCs were investigated. Cell population growth kinetics, cell phenotypes and differentiation potential of cells were assayed. Results:, Maximum cell density and overall fold increase in cell population growth were similar between PCs and MCs with similar starting conditions, but lag period of BMMSC growth differed substantially between the two; moreover, MC cells exhibited reduced granularity and higher CXCR4 expression. Differentiation of BMMSCs into osteogenic and adipogenic lineages was enhanced after 3 days in MC. However, MC bead-T resulted in changes in cell granularity and lower osteogenic and adipogenic differentiation potential. Conclusions:, In comparison to PC, MC supported expansion of BMMSCs in an up-scalable three-dimensional culture system using a semi-continuous process, increasing potential for stem cell homing ability and osteogenic and adipogenic differentiation. [source] Cryopreservation and in Vitro Expansion of Chondroprogenitor Cells Isolated from the Superficial Zone of Articular CartilageBIOTECHNOLOGY PROGRESS, Issue 1 2005Juan M. Melero Martin Understanding the proliferation mechanisms of chondroprogenitor cells and their influence on cell differentiation is crucial in order to develop large-scale expansion processes for tissue engineering applications. Proliferation control mechanisms were mainly attributed to substrate limitation and cell-cell contact inhibition. The limiting substrates were found to be components of the FCS, with an optimal proliferation rate achieved in the presence of 40% FCS. In addition, the medium supply rate was found to be essential in reducing substrate limitation. In terms of FCS, 10 ,L FCS cm,2 h,1 was the threshold feed rate required to prevent substrate limitation. Above this rate, maximum cell densities of 5.3 × 105 cells/cm2 were achieved, representing a 53-fold expansion. To reduce the need for high supply rates, the effect of specific growth factors was also investigated. Cell densities of 3.3 × 105 cells/cm2 were achieved in batch cultures using 40% FCS and 1 ng/mL TGF-,1. Chondroprogenitor cells were expanded in this medium up to three passages without compromising their ability to differentiate and produce cartilage-like matrix in pellet cultures. In addition to substrate limitation, cell-cell contact, even at very sparse subconfluent densities, appeared capable of exerting some degree of growth inhibition. The cells exhibited deceleratory growth kinetics, characterized by a decrease of specific growth rates over time. [source] Growth inhibition of Listeria monocytogenes by a nonbacteriocinogenic Carnobacterium piscicolaJOURNAL OF APPLIED MICROBIOLOGY, Issue 1 2005L. Nilsson Abstract Aims:, This study elucidates the mechanisms by which a nonbacteriocinogenic Carnobacterium piscicola inhibits growth of Listeria monocytogenes. Methods and Results:,Listeria monocytogenes was exposed to live cultures of a bacteriocin-negative variant of C. piscicola A9b in co-culture, in a diffusion chamber system, and to a cell-free supernatant. Suppression of maximum cell density (0,3·5 log units) of L. monocytogenes was proportional to initial levels of C. pisciola (103,107 CFU ml,1). Cell-to-cell contact was not required to cause inhibition. The cell-free C. piscicola supernatant caused a decrease in L. monocytogenes maximum cell density, which was abolished by glucose addition but not by amino acid, vitamin or mineral addition. The fermentate also gave rise to a longer lag phase and a reduction in growth rate. These effects were independent of glucose and may have been caused by acetate production by C. piscicola. 2D gel-electrophoretic patterns of L. monocytogenes exposed to C. piscicola or to L. monocytogenes fermentate did not differ. Treatment with C. piscicola fermentate resulted in down-regulation (twofold) of genes involved in purine- or pyrimidine metabolism, and up-regulation (twofold) of genes from the regulon for vitamin B12 biosynthesis and propanediol and ethanolamine utilization. Conclusions:, A nonbacteriocinogenic C. piscicola reduced growth of L. monocytogenes partly by glucose depletion. Significance and Impact of the Study:, Understanding the mechanism of microbial interaction enhances prediction of growth in mixed communities as well as use of bioprotective principles for food preservation. [source] 293 cell cycle synchronisation adenovirus vector productionBIOTECHNOLOGY PROGRESS, Issue 1 2009Tiago B. Ferreira Abstract As the market requirements for adenovirus vectors (AdV) increase, the maximisation of the virus titer per culture volume per unit time is a key requirement. However, despite the fact that 293 cells can grow up to 8 × 106 cell/mL in simple batch mode operations, for optimal AdV infection a maximum cell density of 1 × 106 cell/mL at infection time has usually been utilized due to the so called "cell density effect". In addition, AdV titer appears to be dependent upon cell cycle phase at the time of infection. To evaluate the dependence of AdV production upon cell cycle phase, 293 cells were chemically synchronised at each phase of the cell cycle; a 2.6-fold increase on AdV cell specific titer was obtained when the percentage of cells at the S phase of the cell cycle was increased from 36 to 47%; a mathematical equation was used to relate AdV cell specific productivities with cell synchronisation at the S phase using this data. To avoid the use of chemical inhibitors, a temperature shift strategy was also used for synchronisation at the S phase. S phase synchronisation was obtained by decreasing the culture temperature to 31°C during 67 h and restoring it to 37°C during 72 h. By using this strategy we were able to synchronise 57% of the population in the S phase of the cell cycle obtaining an increase of 7.3-fold on AdV cell specific titer after infection. © 2009 American Institute of Chemical Engineers Biotechnol. Prog., 2009 [source] Cell Cycle Progression in Serum-Free Cultures of Sf9 Insect Cells: Modulation by Conditioned Medium Factors and Implications for Proliferation and Productivity,BIOTECHNOLOGY PROGRESS, Issue 5 2000Magnus Doverskog Cell cycle progression was studied in serum-free batch cultures of Spodoptera frugiperda (Sf9) insect cells, and the implications for proliferation and productivity were investigated. Cell cycle dynamics in KBM10 serum-free medium was characterized by an accumulation of 50,70% of the cells in the G2/M phase of the cell cycle during the first 24 h after inoculation. Following the cell cycle arrest, the cell population was redistributed into G1 and in particular into the S phase. Maximum rate of proliferation (,N,max) was reached 24,48 h after the release from cell cycle arrest, coinciding with a minimum distribution of cells in the G2/M phase. The following declining ,N could be explained by a slow increase in the G2/M cell population. However, at approximately 100 h, an abrupt increase in the amount of G2/M cells occurred. This switch occurred at about the same time point and cell density, irrespective of medium composition and maximum cell density. An octaploid population evolved from G2/M arrested cells, showing the occurrence of endoreplication in this cell line. In addition, conditioned medium factor(s) were found to increase ,N,max, decrease the time to reach ,N,max, and decrease the synchronization of cells in G2/M during the lag and growth phase. A conditioned medium factor appears to be a small peptide. On basis of these results we suggest that the observed cell cycle dynamics is the result of autoregulatory events occurring at key points during the course of a culture, and that entry into mitosis is the target for regulation. Infecting the Sf9 cells with recombinant baculovirus resulted in a linear increase in volumetric productivity of ,-galactosidase up to 68,75 h of culture. Beyond this point almost no product was formed. Medium renewal at the time of infection could only partly restore the lost hypertrophy and product yield of cultures infected after the transition point. The critical time of infection correlated to the time when the mean population cell volume had attained a minimum, and this occurred 24 h before the switch into the G2/M phase. We suggest that the cell density dependent decrease in productivity ultimately depends on the autoregulatory events leading to G2/M cell cycle arrest. [source] | ||||||||||