1,377 research outputs found
Monitoring of Extracellular TCA Cycle Intermediates in Mammalian Cell Culture
In recent years, monitoring of metabolites such as glucose, lactate, ammonia, glutamine, glutamate, and other amino acids has been introduced for many cell cultivations. Assaying intracellular metabolites might reveal further insights into metabolism. However, some of the mainly intracellular or even mitochondrial appearing metabolites can also be found in the medium supernatant at micromolar concentrations. Since no active transport mechanisms for excretion of these intermediates are known for most mammalian production cell lines, they might leak out of the cells and thus could be correlated to intracellular concentrations. In this work, we are investigating extracellular concentrations of five organic acids (succinic, malic, fumaric, citric, isocitric acid) during growth looking at different media and cell lines. Moreover, clear influences on concentrations were also expected to occur after viral infection of MDCK cells. The analysis is performed using an anion-exchange chromatography system (DX-320, Dionex, Idstein, Germany) with a conductivity detector. Due to high protein content of the medium, sample preparation posed some problems. Several strategies have been investigated for an optimal recovery of the abovementioned organic acids. Experiments showed that certain amounts of these organic acids already occurred in fresh medium, coming from both serum and peptone being supplements for the culture medium. Nevertheless, first results indicate significant changes of concentrations during the course of cultivation, probably not correlated to dead cells. In batch cultivation, malic, fumaric and citric acid show an almost linear increase after the lag phase, whereas isocitric and succinic acid seem to reach a constant level during stationary phase
Warping the young stellar disc in the Galactic Centre
We examine influence of the circum-nuclear disc (CND) upon the orbital
evolution of young stars in the Galactic Centre. We show that gravity of the
CND causes precession of the orbits which is highly sensitive upon the
semi-major axis and inclination. We consider such a differential precession
within the context of an ongoing discussion about the origin of the young stars
and suggest a possibility that all of them have originated in a thin disc which
was partially destroyed due to the influence of the CND during the period of
~6Myr.Comment: proc. conf. "The Universe Under the Microscope - Astrophysics at High
Angular Resolution", 21-25 April 2008, Bad Honnef, German
Detection of the Sgr A* activity at 3.8 and 4.8 microns with NACO
L'-band (lambda=3.8 microns) and M'-band (lambda=4.8 microns) observations of
the Galactic Center region, performed in 2003 at VLT (ESO) with the adaptive
optics imager NACO, have lead to the detection of an infrared counterpart of
the radio source Sgr A* at both wavelengths. The measured fluxes confirm that
the Sgr A* infrared spectrum is dominated by the synchrotron emission of
nonthermal electrons. The infrared counterpart exhibits no significant short
term variability but demonstrates flux variations on daily and yearly scales.
The observed emission arises away from the position of the dynamical center of
the S2 orbit and would then not originate from the closest regions of the black
hole.Comment: 5 pages, 3 figures, accepted in Astronomy & Astrophysic
Bioreactors for high cell density and continuous multi-stage cultivations: options for process intensification in cell culture-based viral vaccine production
With an increasing demand for efficacious, safe, and affordable vaccines for human and animal use, process intensification in cell culture-based viral vaccine production demands advanced process strategies to overcome the limitations of conventional batch cultivations. However, the use of fed-batch, perfusion, or continuous modes to drive processes at high cell density (HCD) and overextended operating times has so far been little explored in large-scale viral vaccine manufacturing. Also, possible reductions in cell-specific virus yields for HCD cultivations have been reported frequently. Taking into account that vaccine production is one of the most heavily regulated industries in the pharmaceutical sector with tough margins to meet, it is understandable that process intensification is being considered by both academia and industry as a next step toward more efficient viral vaccine production processes only recently. Compared to conventional batch processes, fed-batch and perfusion strategies could result in ten to a hundred times higher product yields. Both cultivation strategies can be implemented to achieve cell concentrations exceeding 10(7) cells/mL or even 10(8) cells/mL, while keeping low levels of metabolites that potentially inhibit cell growth and virus replication. The trend towards HCD processes is supported by development of GMP-compliant cultivation platforms, i.e., acoustic settlers, hollow fiber bioreactors, and hollow fiber-based perfusion systems including tangential flow filtration (TFF) or alternating tangential flow (ATF) technologies. In this review, these process modes are discussed in detail and compared with conventional batch processes based on productivity indicators such as space-time yield, cell concentration, and product titers. In addition, options for the production of viral vaccines in continuous multi-stage bioreactors such as two- and three-stage systems are addressed. While such systems have shown similar virus titers compared to batch cultivations, keeping high yields for extended production times is still a challenge. Overall, we demonstrate that process intensification of cell culture-based viral vaccine production can be realized by the consequent application of fed-batch, perfusion, and continuous systems with a significant increase in productivity. The potential for even further improvements is high, considering recent developments in establishment of new (designer) cell lines, better characterization of host cell metabolism, advances in media design, and the use of mathematical models as a tool for process optimization and control
Impact of Influenza A Virus Infection on Growth and Metabolism of Suspension MDCK Cells Using a Dynamic Model
Cell cultured-based influenza virus production is a viable option for vaccine manufacturing. In order to achieve a high concentration of viable cells, is requirement to have not only optimal process conditions, but also an active metabolism capable of intracellular synthesis of viral components. Experimental metabolic data collected in such processes are complex and difficult to interpret, for which mathematical models are an appropriate way to simulate and analyze the complex and dynamic interaction between the virus and its host cell. A dynamic model with 35 states was developed in this study to describe growth, metabolism, and influenza A virus production in shake flask cultivations of suspension Madin-Darby Canine Kidney (MDCK) cells. It considers cell growth (concentration of viable cells, mean cell diameters, volume of viable cells), concentrations of key metabolites both at the intracellular and extracellular level and virus titers. Using one set of parameters, the model accurately simulates the dynamics of mock-infected cells and correctly predicts the overall dynamics of virus-infected cells for up to 60 h post infection (hpi). The model clearly suggests that most changes observed after infection are related to cessation of cell growth and the subsequent transition to apoptosis and cell death. However, predictions do not cover late phases of infection, particularly for the extracellular concentrations of glutamate and ammonium after about 12 hpi. Results obtained from additional in silico studies performed indicated that amino acid degradation by extracellular enzymes resulting from cell lysis during late infection stages may contribute to this observed discrepancy
Flares and variability from Sagittarius A*: five nights of simultaneous multi-wavelength observations
Aims. We report on simultaneous observations and modeling of mid-infrared
(MIR), near-infrared (NIR), and submillimeter (submm) emission of the source
Sgr A* associated with the supermassive black hole at the center of our Galaxy.
Our goal was to monitor the activity of Sgr A* at different wavelengths in
order to constrain the emitting processes and gain insight into the nature of
the close environment of Sgr A*. Methods. We used the MIR instrument VISIR in
the BURST imaging mode, the adaptive optics assisted NIR camera NACO, and the
sub-mm antenna APEX to monitor Sgr A* over several nights in July 2007.
Results. The observations reveal remarkable variability in the NIR and sub-mm
during the five nights of observation. No source was detected in the MIR, but
we derived the lowest upper limit for a flare at 8.59 microns (22.4 mJy with
A_8.59mu = 1.6+/- 0.5). This observational constraint makes us discard the
observed NIR emission as coming from a thermal component emitting at sub-mm
frequencies. Moreover, comparison of the sub-mm and NIR variability shows that
the highest NIR fluxes (flares) are coincident with the lowest sub-mm levels of
our five-night campaign involving three flares. We explain this behavior by a
loss of electrons to the system and/or by a decrease in the magnetic field, as
might conceivably occur in scenarios involving fast outflows and/or magnetic
reconnection.Comment: 10 pages, 7 figures, published in A&
Mid-infrared and optical spectroscopy of ultraluminous infrared galaxies: A comparison
New tools from Infrared Space Observatory (ISO) mid-infrared spectroscopy
have recently become available to determine the power sources of dust-obscured
ultraluminous infrared galaxies (ULIRGs). We compare ISO classifications -
starburst or active galactic nucleus (AGN) - with classifications from optical
spectroscopy, and with optical/near-infrared searches for hidden broad-line
regions. The agreement between mid-infrared and optical classification is
excellent if optical LINER spectra are assigned to the starburst group. The
starburst nature of ULIRG LINERs strongly supports the suggestion that LINER
spectra in infrared-selected galaxies, rather than being an expression of the
AGN phenomenon, are due to shocks that are probably related to galactic
superwinds. Differences between ISO and optical classification provide clues on
the evolution of ULIRGs and on the configuration of obscuring dust. We find few
ISO AGN with optical HII or LINER identification, suggesting that highly
obscured AGN exist but are not typical for the ULIRG phenomenon in general.
Rather, our results indicate that strong AGN activity, once triggered, quickly
breaks the obscuring screen at least in certain directions, thus becoming
detectable over a wide wavelength range.Comment: aastex, 1 eps figure. Accepted by ApJ (Letters
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