We thank Professor Wolf Frommer (Carnegie Institution for Science, Stanford University) for kindly providing us with the glucose FRET plasmid and Dr. Uwe Ludewig (Hohenheim University) for kindly supplying the glutamine FRET construct in the pUTKan plant expression vector. AB is funded by the BBSRC Targeted Priority Studentships program.&#160;Both CK and KP are supported by RCUK Fellowships in Biopharmaceuticals Processing.&#160;CK also wishes to thank Lonza Biologics for their financial support.&#160;The Centre for Synthetic Biology and Innovation is generously supported by the EPSRC.

1. Cell Line Revival and Maintenance
<ol>
	<li>Revive CHO cells in 9 ml&#160;CD-CHO medium supplemented with 8 mM L-Glutamine and 10 ml/L&#160;100x&#160;hypoxanthine/thymidine supplement (complete growth medium).</li>
	<li>Centrifuge at 100 x g for 5 min.</li>
	<li>Resuspend the cells in 10 ml&#160;of fresh complete growth medium.</li>
	<li>Remove a 1 ml&#160;sample and determine the viable cell concentration by light microscopy using the trypan blue dye exclusion method in a hemocytometer.</li>
	<li>Initiate a culture...

<ol>
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The FIBS enable in vivo and in situ quantitation of key molecules, in this case growth-limiting nutrients, removing uncertainties arising from quenching and extraction methods. The findings suggest that there is a good correlation between the FIBS signal and the intracellular concentrations in the range of 1-5 mM for glucose and 0.3-2 mM for glutamine. In batch CHO cell culture, these concentrations are encountered in the exponential, stationary, and early decline phases. The exponential and stationary ...

Metabolite monitoring has various applications in bioprocessing, including process development, media and feed design, and metabolic engineering. Various methods are available for concentration measurements through the use of enzymatic1, chemical2, or binding assays3. An interesting option is the use of fluorescent, protein-based in vivo biological sensors as reporters of the intracellular concentration of key metabolites. In ultra-low volume assays, fluorescence is a convenient tool as miniaturization actually improves the signal-to-noise ratio4,5 and protein-based sensors can be genetically encoded meaning that no exogenous reagents are necessary for metabolite analysis. F&#246;rster Resonance Energy Transfer (FRET) biosensors consist of two fluorescent proteins connected by a ligand binding domain. FRET is a nonradiative transfer of energy from a photo-excited donor to an acceptor fluorescent molecule located in close proximity (&#60;100). Ligand cleavage or binding causes a conformational change in the sensor, which, in turn, induces a change in the proximity of the fluorophores, leading to a change in FRET efficiency measured by the change in the emission spectrum. FRET integrated biological sensors (FIBS) are constitutively produced within the cell line and their spectral characteristics change based on the concentration of metabolite within the cell. FIBS have fast response times making them ideal for taking measurements for dynamic models6. Previous applications include monitoring single7-9 and multiple10 metabolites&#160;and providing data on spatiotemporal distribution11. FIBS can be created in two configurations: Apo-Max, where ligand binding disrupts the proximity of the fluorophores lowering energy transfer and Apo-Min, where ligand binding brings the two fluorophores into closer contact (Figure 1).
In this work, a protocol is presented for constructing Chinese hamster ovary (CHO) cell lines that constitutively express a FIBS for a metabolite, glucose or glutamine. A methodology is established for the calibration of the sensor in vivo to enable future quantitative measurements of intracellular metabolite concentration, as presented in Figure 2. Based on this, the intracellular concentration of glucose or glutamine can be determined in fed-batch CHO cell cultures, to which the two nutrients were added in high concentrations in-process. The results demonstrate that using the fluorescent signal from the FIBS and the previously constructed calibration curve, accurately prediction of the intracellular concentration is possible, as confirmed by an independent enzymatic assay. This method offers substantial advantages over current analytical technologies because it is noninvasive, low-cost and fast, giving a real-time signal of the FIBS that can be monitored throughout the culture.

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	<tbody>
		<tr height="22">
			<td height="22" style="height:22px;width:239px;">CHO-S Cells</td>
			<td style="width:120px;">Life Tecnologies</td>
			<td style="width:120px;">11619-012</td>
			<td style="width:459px;">Cell line will vary depending on the goals of the study</td>
		</tr>
		<tr height="22">
			<td height="22" style="height:22px;width:239px;">pCDNA4/TO vector&#160;</td>
			<td style="width:120px;">Life Tecnologies</td>
			<td style="width:120px;"></td>
			<td style="width:459px;"></td>
		</tr>
		<tr height="43">
			<td height="43" style="height:43px;width:239px;">TransIT-PRO Transfection Reagent</td>
			<td style="width:120px;">Mirus Bio</td>
			<td style="width:120px;">MIR 5700</td>
			<td style="width:459px;">Transfections can be accomplished using any method suitable for the cell line under study</td>
		</tr>
		<tr height="22">
			<td height="22" style="height:22px;width:239px;">Zeocin</td>
			<td style="width:120px;">Invivogen</td>
			<td style="width:120px;"></td>
			<td style="width:459px;"></td>
		</tr>
		<tr height="43">
			<td height="43" style="height:43px;width:239px;">CD-CHO medium</td>
			<td style="width:120px;">Life Technologies</td>
			<td style="width:120px;">10743-011</td>
			<td style="width:459px;">Cell growth medium is dependent upon the cells under study</td>
		</tr>
		<tr height="43">
			<td height="43" style="height:43px;width:239px;">100X HT Supplement</td>
			<td style="width:120px;">Life Technologies</td>
			<td style="width:120px;">11067-030</td>
			<td style="width:459px;"></td>
		</tr>
		<tr height="43">
			<td height="43" style="height:43px;width:239px;">L-Glutamine 200 mM (100X), Liquid</td>
			<td style="width:120px;">Life Technologies</td>
			<td style="width:120px;">25030032</td>
			<td style="width:459px;"></td>
		</tr>
		<tr height="43">
			<td height="43" style="height:43px;width:239px;">InfinitePRO 200 plate reader</td>
			<td style="width:120px;">Tecan</td>
			<td style="width:120px;">FLx800TBI</td>
			<td style="width:459px;">Any 96-well fluorescence plate reader that can access the required wavelengths can be substituted</td>
		</tr>
		<tr height="21">
			<td height="190" rowspan="6" style="height:190px;width:239px;">Filters for plate reader</td>
			<td rowspan="6" style="width:120px;">Tecan</td>
			<td align="right" style="width:120px;">30000463</td>
			<td rowspan="6" style="width:459px;"></td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:120px;">(520NM BW 10NM)</td>
		</tr>
		<tr height="21">
			<td align="right" height="21" style="height:21px;width:120px;">30022786</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:120px;">(430NM BW 35NM)</td>
		</tr>
		<tr height="21">
			<td align="right" height="21" style="height:21px;width:120px;">30022787</td>
		</tr>
		<tr height="43">
			<td height="43" style="height:43px;width:120px;">(465NM BW 35NM)</td>
		</tr>
		<tr height="22">
			<td height="22" style="height:22px;width:239px;">Maxiprep Plasmid Purification Kit</td>
			<td style="width:120px;">Qiagen</td>
			<td style="width:120px;">12163</td>
			<td style="width:459px;">Any suitable kit can be substituted</td>
		</tr>
		<tr height="43">
			<td height="43" style="height:43px;width:239px;">Amplex Red glucose/glucose oxidase assay kit</td>
			<td style="width:120px;">Invitrogen</td>
			<td style="width:120px;">A22189</td>
			<td style="width:459px;">Any suitable kit can be substituted</td>
		</tr>
		<tr height="43">
			<td height="43" style="height:43px;width:239px;">EnzyChrom&#160; Glutamine Assay Kit</td>
			<td style="width:120px;">BioAssay systems</td>
			<td style="width:120px;">EOAC-100</td>
			<td style="width:459px;">Any suitable kit can be substituted</td>
		</tr>
		<tr height="43">
			<td height="43" style="height:43px;width:239px;">Improved Neubauer haemocytometer</td>
			<td style="width:120px;">Fisher Scientific</td>
			<td style="width:120px;">MNK-420-010N</td>
			<td style="width:459px;"></td>
		</tr>
		<tr height="22">
			<td height="22" style="height:22px;width:239px;">Incubator&#160;</td>
			<td style="width:120px;">Nuaire</td>
			<td style="width:120px;">NU-5510E</td>
			<td style="width:459px;"></td>
		</tr>
	</tbody>
</table>

fibs-enabled noninvasive metabolic profiling

In the era of computational biology, new high throughput experimental systems are necessary in order to populate and refine models so that they can be validated for predictive purposes. Ideally such systems would be low volume, which precludes sampling and destructive analyses when time course data are to be obtained. What is needed is an in situ monitoring tool which can report the necessary information in real-time and noninvasively. An interesting option is the use of fluorescent, protein-based in vivo biological sensors as reporters of intracellular concentrations. One particular class of in vivo biosensors that has found applications in metabolite quantification is based on F&#246;rster Resonance Energy Transfer (FRET) between two fluorescent proteins connected by a ligand binding domain. FRET integrated biological sensors (FIBS) are constitutively produced within the cell line, they have fast response times and their spectral characteristics change based on the concentration of metabolite within the cell. In this paper, the method for constructing Chinese hamster ovary (CHO) cell lines that constitutively express a FIBS for glucose and glutamine and calibrating the FIBS in vivo in batch cell culture in order to enable future quantification of intracellular metabolite concentration is described. Data from fed-batch CHO cell cultures demonstrates that the FIBS was able in each case to detect the resulting change in the intracellular concentration. Using the fluorescent signal from the FIBS and the previously constructed calibration curve, the intracellular concentration was accurately determined as confirmed by an independent enzymatic assay.

An overview of the methodology is presented in Figure 2. In the work presented herein, CHO cells were transfected with the FIBS vector and stable cell lines were selected at an antibiotic pressure of 400 &#956;g/ml&#160;zeocin. Two separate stable cell lines constitutively expressing the glucose and glutamine sensors were therefore created. Figure 1 depicts the configurations of the two biosensors used in this study. The glucose sensor is based on the Apo-Max principle and the correspond...

Watch this Scientific Journal Video about FIBS-enabled Noninvasive Metabolic Profiling at JoVE.com

FIBS-enabled Noninvasive Metabolic Profiling

A description of how to calibrate F&#246;rster Resonance Energy Transfer integrated biological sensors (FIBS) for in situ metabolic profiling is presented.&#160;The FIBS can be used to measure intracellular levels of metabolites noninvasively aiding in the development of metabolic models and high throughput screening of bioprocess conditions.

In the era of computational biology, new high throughput experimental systems are necessary in order to populate and refine models so that they can be ...

fibs-enabled-noninvasive-metabolic-profiling

Research

JoVE Journal

Bioengineering

9.6K vistas.  Imperial College London.  Se presenta una descripción de cómo calibrar Transferencia Förster Resonance Energy sensores biológicos integrados (FIBS) en el perfil metabólico situ. Los FIBS se pueden utilizar para medir los niveles intracelulares de metabolitos de forma no invasiva ayudando en el desarrollo de modelos metabólicos y cribado de alto rendimiento de las condiciones de bioprocesos. 