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Comparative Metabolic Analysis of Lactate for CHO Cells in Glucose and Galactose
Camila A. Wilkens,Claudia Altamirano,Ziomara P. Gerdtzen 한국생물공학회 2011 Biotechnology and Bioprocess Engineering Vol.16 No.4
t-PA producing CHO cells have been shown to undergo a metabolic shift when the culture medium is supplemented with a mixture of glucose and galactose. This metabolic change is characterized by the reincorporation of lactate and its use as an additional carbon source. The aim of this work is to understand lactate metabolism. To do so,Chinese hamster ovary cells were grown in batch cultures in four different conditions consisting in different combinations of glucose and galactose. In experiments supplemented with glucose, only lactate production was observed. Cultures with glucose and galactose consumed glucose first and produced lactate at the same time, after glucose depletion galactose consumption began and lactate uptake was observed. Comparison of the metabolic state of cells with and without the shift by metabolic flux analysis show that the metabolic fluxes distribution changes mostly in the reactions involving pyruvate metabolism. When not enough pyruvate is being produced for cells to support their energy requirements, lactate dehydrogenase complex changes the direction of the reaction yielding pyruvate to feed the TCA cycle. The slow change from high fluxes during glucose consumption to low fluxes in galactose consumption generates intracellular conditions that allow the influx of lactate. Lactate consumption is possible in cell cultures supplemented with glucose and galactose due to the low rates at which galactose is consumed. Evidence suggests that an excessive production and accumulation of pyruvate during glucose consumption leads to lactate production and accumulation inside the cell. Other internal conditions such as a decrease in internal pH, forces the flow of lactate outside the cell. After metabolic shift the intracellular pool of pyruvate, lactate and H+ drops permitting the reversal of the monocarboxylate transporter direction, therefore leading to lactate uptake. Metabolic analysis comparing glucose and galactose consumption indicates that after metabolic shift not enough pyruvate is produced to supply energy metabolism and lactate is used for pyruvate synthesis. In addition, MFA indicates that most carbon consumed during low carbon flux is directed towards maintaining energy metabolism.
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Karen A. Flores,J. Cristian Salgado,Gerald Zapata-Torres,Ziomara P. Gerdtzen,María-Julieta Gonzalez,Marcela A. Hermoso 한국생물공학회 2012 Biotechnology and Bioprocess Engineering Vol.17 No.3
In order to develop future therapeutic applications for cell penetrating peptides (CPPs), it is essential to characterize their internalization mechanisms, as they might affect the stability and the accessibility of the carried drug. Several internalization mechanisms have been described in literature, such as endocytosis and transduction. In this work we study the internalization mechanism in HeLa cells of two TIRAP derived peptides: pepTIRAP and pepTIRAPALA, where some of the cationic amino acids were replaced with alanines. Detailed analysis of internalization and the peptides electrostatic potential was carried out, to shed light on the internalization mechanism involved. Molecular modeling studies showed that the main difference identified between pepTIRAP and pepTIRAPALA is the distribution of their electrostatic potential field. The structure of pepTIRAP displays a predominantly positive potential when compared to pepTIRAPALA, which has a more balanced potential distribution. In addition, docking experiments show that interactions between pepTIRAP and negatively charged molecules on the cellular surface such as heparan sulfate are stronger than the ones exhibited by pepTIRAPALA. A mathematical model was proposed to quantify the amount of peptide internalized or non-specifically bound to the membrane. The model indicates a stronger interaction of pepTIRAP with the plasma membrane, compared to pepTIRAPALA. We propose these discrepancies are related to the differences in the electrostatic potential characteristics of each peptide. In the case of pepTIRAP, these interactions lead to the formation of nucleation zones,which are the first stage of the transduction internalization mechanism. These results should be considered for effective design of a cell penetrating peptide.
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