This work has been partially supported by the research grants FIS (PS12/00866) from Instituto de Salud Carlos III, Madrid, Spain; Fondo Europeo para el Desarrollo Regional (FEDER); Red de Investigaci&#243;n en SIDA (RIS), ISCIII-RETIC (RD16/0025/0002) and CERCA Programme / Generalitat de Catalunya. The authors thank the Retrovirology and Viral Immunopathology Laboratory of the Institut d&#39;Investigacions Biom&#232;diques August Pi I Sunyer (IDIBAPS). We thank T. Escrib&#224;, C. Rovira, and C. Hurtado for their assistance and S. Cuf&#237; from the Knowledge and Technology Transfer Office for her guidance in protecting the invention.

For this study, ethical committee approval (Comit&#232; &#200;tic d&#39;Investigaci&#243; Cl&#237;nica, Hospital Clinic, Barcelona; approval number HCB/2014/0756) and written, informed consent from all subjects were obtained.
1. NBD-cholesterol Preparation
<ol>
	<li>Dissolve the NBD-cholesterol (MW 494.63; see Table of Materials) in pure ethanol to obtain the stock (2 mM). For a 10 mg vial, dissolve the entire vial contents in a 10.1 mL volume of ethanol to obtain a 2 mM stock.</li>
	<li>Dilute the NBD-cholesterol from the stock in RPMI 1640 supplemented with 10% fetal bovine serum and 5% penicillin/streptomycin (R10 medium) to reach a final concentration of 5 &#956;M (e.g., obtain 10 mL of NBD-cholesterol at 5 &#956;M final concentration) by diluting 25 &#956;L of NBD-cholesterol stock (2 mM) in R10 medium. This volume is sufficient for a 96-well plate.</li>
</ol>
2. Cell Culture and Seeding (Day-2)
<ol>
	<li>Culture THP-1 cells in R10 medium at 37 &#176;C, 5% CO2. Adjust to 0.3 x 106 cells/mL every 3 days.</li>
	<li>Seed the cells in a white 96-well plate with a flat, clear bottom at 0.2 x 106 cells/well in R10 medium (100 &#956;L per well).</li>
	<li>Treat the cells with 100 nM phorbol 12-myristate 13-acetate (PMA; from a 10 &#956;M stock) for 48&#8211;72 h, incubating at 37 &#176;C, 5% CO2 to differentiate THP-1 cells into dmTHP-1. 
	NOTE: It is recommended to use 5 &#956;L of PMA stock (10 &#956;M) in 500 &#956;L of R10 medium. Prior to this, prepare a 10 &#956;M PMA stock by dissolving a lyophilized 1 g vial in 10 mL of dimethyl sulfoxide (DMSO), aliquot, and stock at -20 &#176;C.</li>
	<li>Alternatively (suggestion) combine steps 2.2 and 2.3 for better homogenization. Prepare 10 mL of THP-1 cells in a 15 mL tube, add 200 &#956;L of PMA stock (10 &#956;M), mix gently, and immediately seed 100 &#956;L per well onto the plate. Incubate the cells as described in step 2.3.</li>
</ol>
3. Apolipoprotein B Depleted Serum (ABDS) Preparation (Day 2 or 3)
<ol>
	<li>To prepare a polyethylene glycol (PEG) solution, dilute glycine in 10% PBS (with sterile H2O) to a concentration of 200 mM at pH 7.4. Add 40 mL of 200 mM glycine to 10 g of PEG 8000 to obtain PEG 20% (w/v). Mix the solution vigorously to homogenize.</li>
	<li>Apply 4 parts of 20% PEG per 10 parts of serum/plasma on each serum/plasma sample in a 1.5 mL tube and leave the mixture on ice for 25 min17 (e.g., for 100 &#956;L of plasma or serum, add 40 &#956;L of 20% PEG solution).</li>
	<li>Centrifuge the PEG-apolipoprotein B precipitate at 13,000 x g for 15 min at 4 &#176;C.</li>
	<li>Discard the precipitate. Transfer the supernatant to a new tube. 
	NOTE: We suggest preparing the ABDS on day 3 (fresh). If it is not possible, prepare the ABDS on day 2 and keep it at 4 &#176;C overnight.</li>
</ol>
4. NBD-cholesterol Cell Loading (Day 2)
<ol>
	<li>Discard the culture medium of the dmTHP-1 and wash the cells twice with 1x phosphate-buffered saline (PBS).</li>
	<li>Load the cells with 5 &#956;M NBD-cholesterol (100 &#956;L per well) in R10 medium and incubate overnight at 37 &#176;C, 5% CO2.</li>
</ol>
5. Incubation with Cholesterol Acceptors (Day 3)
<ol>
	<li>Discard the medium and wash the cells twice with PBS.</li>
	<li>Incubate the cells with 2&#8211;5% ABDS or the desired concentration of purified lipid acceptor (HDL, ApoA, ApoE, etc.) diluted in colorless RPMI 1640 medium (100 &#956;L per well) for 4&#8211;6 h at 37 &#176;C. 
	NOTE: Include a negative control (C-) consisting of colorless RPMI 1640 medium without acceptors and a positive control (C+) (e.g., ABDS from a pool of healthy donors or purified HDLs). Note that the positive control applies particularly when patient samples (disease conditions) are analyzed (Supplementary Figure 1).</li>
	<li>Prepare a 200 mL stock of the cell lysis solution 1 (50 mM Tris buffer, 150 mM NaCl, H2O). Mix the cell lysis solution 1 at 1:1 (v:v) ratio with pure ethanol to obtain the lysis solution 2.</li>
</ol>
6. Fluorescent Signal Capture (Day 3)
<ol>
	<li>Media NBD-cholesterol detection
	<ol>
		<li>Remove the cell medium from the plates and collect it in a new white 96-well plate with an opaque flat bottom.</li>
		<li>For an optimal fluorescence signal detection in the media samples, add 100 &#956;L of pure ethanol to 100 &#956;L of each medium sample to obtain a 1:1 ratio in the 96-well white plate.</li>
		<li>Keep the plate with the treated media to further measure the fluorescence intensity (FI) at a 463&#8260;536 nm (excitation/emission) wavelength in the luminometer.</li>
	</ol>
	</li>
	<li>Intracellular NBD-cholesterol detection
	<ol>
		<li>Wash the cells twice with PBS.</li>
		<li>To obtain the intracellular cholesterol, lyse the cells by incubating them with 100 &#956;L of lysis solution 2 per well and shake the plate at room temperature (RT) for 25 min.</li>
		<li>For an optimal fluorescence signal detection in the cell lysate samples, capture the fluorescence intensity of the cell lysates in the same white 96-well plate with clear flat bottom (the same plate in which cells were seeded in step 2.2).</li>
	</ol>
	</li>
	<li>6.3 Measure the fluorescence intensity (FI) in the luminometer while adjusting the sensitivity parameter to 50 in the software (see Table of Materials).</li>
</ol>
7. Results Analysis
<ol>
	<li>Express the cholesterol efflux rate of a sample as a percentage calculated by the formula: 
	<img alt="Equation" src="/files/ftp_upload/58891/58891eq1.jpg" /></li>
	<li>Obtain the final measure of cholesterol efflux (CE) by subtracting the CE of the negative control (sample loaded with NBD-cholesterol but incubated with colorless RPMI 1640 medium, without cholesterol acceptors) from the CE of a given samples: 
	<img alt="Equation 2" src="/files/ftp_upload/58891/58891eq2.jpg" /></li>
</ol>

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R., Gordon, S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Immunity,+atherosclerosis+and+cardiovascular+disease.">Immunity, atherosclerosis and cardiovascular disease.</a> Trends Immunol. 22, (2001).</li><li>Yamamoto, S., Narita, I., Kotani, K. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+macrophage+and+its+related+cholesterol+efflux+as+a+HDL+function+index+in+atherosclerosis.">The macrophage and its related cholesterol efflux as a HDL function index in atherosclerosis.</a> Clinica Chimica Acta. 457, 117-122 (2016).</li><li>Escol&#224;-Gil, J. 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L., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Fluorescent+Sterols+for+the+Study+of+Cholesterol+Trafficking+in+Living+Cells.">Fluorescent Sterols for the Study of Cholesterol Trafficking in Living Cells.</a> Probes and Tags to Study Biomolecular Function: for Proteins, RNA, and Membranes. , 1-33 (2008).</li><li>Osta&#353;ov, P., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=FLIM+studies+of+22-+and+25-NBD-cholesterol+in+living+HEK293+cells:+Plasma+membrane+change+induced+by+cholesterol+depletion.">FLIM studies of 22- and 25-NBD-cholesterol in living HEK293 cells: Plasma membrane change induced by cholesterol depletion.</a> Chemistry and Physics of Lipids. 167, 62-69 (2013).</li><li>Song, W., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Characterization+of+fluorescent+NBD-cholesterol+efflux+in+THP-1-derived+macrophages.">Characterization of fluorescent NBD-cholesterol efflux in THP-1-derived macrophages.</a> Molecular Medicine Reports. 12 (4), 5989-5996 (2015).</li><li>Liu, N., Wu, C., Sun, L., Zheng, J., Guo, P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Sesamin+enhances+cholesterol+efflux+in+RAW264.7+macrophages.">Sesamin enhances cholesterol efflux in RAW264.7 macrophages.</a> Molecules. 19 (6), 7516-7527 (2014).</li><li>Qin, Z. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+use+of+THP-1+cells+as+a+model+for+mimicking+the+function+and+regulation+of+monocytes+and+macrophages+in+the+vasculature.">The use of THP-1 cells as a model for mimicking the function and regulation of monocytes and macrophages in the vasculature.</a> Atherosclerosis. 221 (1), 2-11 (2012).</li><li>Low, H., Hoang, A., Sviridov, D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Cholesterol+Efflux+Assay.">Cholesterol Efflux Assay.</a> Journal of Visualized Experiments. (61), 5-9 (2012).</li><li>Gimpl, G., Gehrig-Burger, K. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Cholesterol+reporter+molecules.">Cholesterol reporter molecules.</a> Bioscience Reports. 27 (6), 335-358 (2007).</li><li>Zhang, J., Cai, S., Peterson, B. R., Kris-Etherton, P. M., Heuvel, J. P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Vanden+Development+of+a+Cell-Based,+High-Throughput+Screening+Assay+for+Cholesterol+Efflux+Using+a+Fluorescent+Mimic+of+Cholesterol.">Vanden Development of a Cell-Based, High-Throughput Screening Assay for Cholesterol Efflux Using a Fluorescent Mimic of Cholesterol.</a> ASSAY and Drug Development Technologies. 9 (2), 136-146 (2011).</li><li>Rader, D. D. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Molecular+regulation+of+HDL+metabolism+and+function:+implications+for+novel+therapies.">Molecular regulation of HDL metabolism and function: implications for novel therapies.</a> Journal of Clinical Investigation. 116 (12), 3090-3100 (2006).</li><li>Davidson, W. S., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+effects+of+apolipoprotein+B+depletion+on+HDL+subspecies+composition+and+function.">The effects of apolipoprotein B depletion on HDL subspecies composition and function.</a> Journal of Lipid Research. 57 (4), 674-686 (2016).</li><li>Park, S. H., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Sage+weed+(Salvia+plebeia)+extract+antagonizes+foam+cell+formation+and+promotes+cholesterol+efflux+in+murine+macrophages.">Sage weed (Salvia plebeia) extract antagonizes foam cell formation and promotes cholesterol efflux in murine macrophages.</a> International Journal of Molecular Medicine. 30 (5), 1105-1112 (2012).</li><li>Litvinov, Y., Savushkin, E. V., Garaeva, E. A. D. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Cholesterol+Efflux+and+Reverse+Cholesterol+Transport:+Experimental+Approaches.">Cholesterol Efflux and Reverse Cholesterol Transport: Experimental Approaches.</a> Current Medicinal Chemistry. 371 (25), 2383-2393 (2016).</li><li>Phillips, A., Mucksavage, M. L., Wilensky, R. L., Mohler, E. 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The authors wish to declare that they are inventors of the patent application (EPO; 18382337.6-1118; 17th May 2018) entitled &#34;Method for determining cholesterol efflux&#34; based on this method.

Fluorescent-labelled cholesterol is a promising strategy to analyze and investigate the properties and metabolism of natural cholesterol in vitro. Its main advantages are that it can be taken up by cells, allows for intracellular and membrane distribution studies, and can be applied to cholesterol efflux assays such as in this protocol (Figure 7). Some fluorescent-labelled sterols allow cholesterol tracking in vitro including BODIPY-cholesterol, dansyl-cholesterol, dehydroegrosterol, and 22-...

According to the World Health Organization, the current principal causes of death worldwide are ischemic heart disease and stroke (accounting for a total of 15.2 million deaths)1. Both are cardiovascular diseases (CVD) that can be preceded by atherosclerosis and the rupture of atheroma plaques in the blood vessels2,3.
Atherosclerosis is a vessel wall inflammatory disease in which macrophages, T cells, mast cells, and dendritic cells infiltrate the endothelium and accumulate from the blood, eventually forming atherosclerotic plaques. Atherosclerotic plaques present a lipid core and cholesterol crystals, evidenced by high-resolution B-mode ultrasonography measurements of the carotid intima media thickness4,5. In macrophages, cholesterol efflux towards lipid acceptor particles is carried out by means of the ATP-binding cassette (ABC) receptors ABCA1, ATP binding cassette subfamily G member 1 (ABCG1), and the scavenger receptor SR-BI. The imbalance of cholesterol influx and efflux in macrophages is considered a key process in atherosclerosis initiation6. Cholesterol efflux is considered a key step in cholesterol elimination from peripheral tissue to the plasma and liver in a process called reverse cholesterol transport (RCT). Cholesterol is transferred from macrophages mainly to apolipoprotein A1 (ApoA1) found on the surface of high-density lipoprotein (HDL) particles. HDLs then transport cholesterol to the liver for excretion and re-utilization7,8,9.
Traditionally, tritium (3H) radio-labelled cholesterol has been used in cholesterol efflux10. The emission signal of radioisotopes is highly sensitive10; however, radio-labelled cholesterol presents obvious handicaps such as long protocols, risk of exposure to ionizing radiation, and the need for special radioactivity facilities and equipment to ensure safe handling of radioactive emission. On the contrary, fluorescence has been successfully incorporated in diagnostic techniques due to its simplicity in fluorescent signal detection, the wide variety of fluorophores available, and its safety11. Several fluorescent-labelled sterols have been used to study cholesterol metabolism including dehydroergosterol (with intrinsic fluorescence), dansyl cholesterol, 4,4-difluoro-3a,4adiaza-s-indacene (BODIPY)-cholesterol, and 22-(N-(7-Nitrobenz-2-Oxa-1,3-Diazol-4-yl)Amino)-23,24-Bisnor-5-Cholen-3&#946;-Ol (NBD-cholesterol). Particularly, NBD-cholesterol presents an efficient uptake in human cells12. Two different NBD labelled-cholesterol are currently available: 22-(N-(7-nitrobenz-2-oxa-1,3-diazol-4-yl)amino)-23,24-bisnor-5-cholen-3b-ol (22-NBD) and 25-(N-[(7-nitrobenz-2-oxa-1,3-diazol-4-yl)-methyl]amino)-27-norcholesterol (25-NBD; Figure 1). Cholesterol labelled with 22-NBD moiety may best suit cholesterol efflux studies, while 25-NBD-cholesterol is mainly used in cellular membrane dynamics research13,14.
Cell lines typically used in in vitro cholesterol efflux assays are monocyte-like cells such as human leukemia-derived THP-1 cells, murine Raw 264.7 cells15, or J774.1. All of these cells can be differentiated into macrophages in vitro using phorbol 12-myristate 13-acetate (PMA), but THP-1-derived macrophages (dmTHP-1) best reflect and mimic the human macrophages16.
In the present study, we optimize and standardize a fluorescent high-throughput method to determine the cholesterol efflux capacity of serum samples on dmTHP-1, using 22-NBD-cholesterol as an alternative to [3H]-cholesterol. In addition, we compare the optimized fluorescent technique with the standard radioactive analog.

<table>
	<tbody>
		<tr>
			<td>96-well collecting plate</td>
			<td>Corning Inc</td>
			<td>Costar 3912</td>
			<td>white 96-well plate with opaque clear bottom</td>
		</tr>
		<tr>
			<td>96-well culture plate</td>
			<td>Corning Inc</td>
			<td>Costar 3610</td>
			<td>white 96-well plate with flat clear bottom</td>
		</tr>
		<tr>
			<td>Cholesterol Efflux Assay Kit (Cell-based)</td>
			<td>Abcam</td>
			<td>ab196985</td>
			<td>commercial high-throughput cell-based assay kit aimed to determine the cholesterol efflux</td>
		</tr>
		<tr>
			<td>colorless RPMI 1640</td>
			<td>Sigma-Aldrich</td>
			<td>R7509</td>
			<td>RPMI 1640 with no pehnol-red</td>
		</tr>
		<tr>
			<td>Gen5 Data Analysis Software</td>
			<td>BioTek</td>
			<td></td>
			<td>Version 2.0</td>
		</tr>
		<tr>
			<td>Glycine</td>
			<td>Sigma-Aldrich</td>
			<td>G8790-100G</td>
			<td>Glycine, non-animal use</td>
		</tr>
		<tr>
			<td>Luminometer</td>
			<td>Biotek</td>
			<td>SYNERGY HT</td>
			<td>Multi-Detection Microplate Reader</td>
		</tr>
		<tr>
			<td>Lysis Solution 1</td>
			<td>in-house</td>
			<td></td>
			<td>50 mM Tris Buffer, 150 mM NaCl and H2O</td>
		</tr>
		<tr>
			<td>Lysis Solution 2</td>
			<td>in-house</td>
			<td></td>
			<td>Pure ethanol and Cell Lysis Solution 1:1 (v:v)</td>
		</tr>
		<tr>
			<td>NBD-cholesterol</td>
			<td>Thermo-Fisher</td>
			<td>N1148</td>
			<td>22-(N-(7-Nitrobenz-2-Oxa-1,3-Diazol-4-yl)Amino)-23,24-Bisnor-5-Cholen-3&#946;-Ol</td>
		</tr>
		<tr>
			<td>PBS</td>
			<td>Sigma-Aldrich</td>
			<td>P3813</td>
			<td>Phosphate-buffered&#160;saline</td>
		</tr>
		<tr>
			<td>PEG 8000</td>
			<td>Sigma-Aldrich</td>
			<td>202452-250G</td>
			<td>polyethylene glycol</td>
		</tr>
		<tr>
			<td>PMA</td>
			<td>Sigma-Aldrich</td>
			<td>79346</td>
			<td>Phorbol 12-merystate B-acetate.</td>
		</tr>
		<tr>
			<td>R10</td>
			<td>in-house</td>
			<td></td>
			<td>RPMI 1640 supplemented with 10 % fetal bovine serum and 5 % Penicillin/Streptomycin.</td>
		</tr>
		<tr>
			<td>RPMI 1640</td>
			<td>Sigma-Aldrich</td>
			<td>R8758</td>
			<td>RPMI 1640 with 2mM L-glutamine containing 1.5 g/L sodium bicarbonate and 4.5 g/L glucose</td>
		</tr>
		<tr>
			<td>THP-1 cells</td>
			<td>Sigma-Aldrich</td>
			<td>ATCC, #TIB-202</td>
			<td>monocyte-like line derived from leukemia from a one year old baby</td>
		</tr>
		<tr>
			<td>Tween 80</td>
			<td>Sigma-Aldrich</td>
			<td>P1754</td>
			<td></td>
		</tr>
	</tbody>
</table>

high-throughput nitrobenzoxadiazole-labeled cholesterol efflux assay

Atherosclerosis leads to cardiovascular disease (CVD). It is still unclear whether cholesterol-HDL (cHDL) concentration plays a causal role in atherosclerosis development. However, an important factor in early stages of atheroma plaque formation is cholesterol efflux capacity to HDL (the ability of HDL particles to accept cholesterol from macrophages) in order to avoid foam cell formation. This is a key step in avoiding the accumulation of cholesterol in the endothelium and a part of reverse cholesterol transport (RCT) to eliminate cholesterol through the liver. Cholesterol efflux capacity to serum or plasma in macrophage cell models is a promising tool that can be used as biomarker for atherosclerosis. Traditionally, [3H]-cholesterol has been used in cholesterol efflux assays. In this study, we aim to develop a safer and faster strategy using fluorescent labelled-cholesterol (NBD-cholesterol) in a cellular assay to trace the cholesterol uptake and efflux process in THP-1-derived macrophages. Finally, we optimize and standardize the NBD-cholesterol efflux method and develop a high-throughput analysis using 96-well plates.

The aim of the cholesterol efflux assay is to determine in vitro the cholesterol efflux capacity of a given serum, plasma, or supernatant containing HDL particles. The method consists of loading labelled-cholesterol into a culture of a standard macrophage cell line and inducing contact with the testing sample diluted into FBS-free media with the cells. Finally, the fluorescent levels from the NBD are measured in the media and cell lysate. To optimize measurements, the effluxed cholesterol from the cells to media is mixed...

Watch this Scientific Journal Video about High-throughput Nitrobenzoxadiazole-labeled Cholesterol Efflux Assay at JoVE.com

High-throughput Nitrobenzoxadiazole-labeled Cholesterol Efflux Assay

Measurement of in vitro cholesterol efflux capacity to serum or plasma in macrophage cell models is a promising tool as a biomarker for atherosclerosis. In the present study, we optimize and standardize a fluorescent NBD-cholesterol efflux method and develop a high-throughput analysis using 96-well plates.

Atherosclerosis leads to cardiovascular disease (CVD). It is still unclear whether cholesterol-HDL (cHDL) concentration plays a causal role in ...

high-throughput-nitrobenzoxadiazole-labeled-cholesterol-efflux-assay

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JoVE Journal

Medicine

8.9K Views.  Hospital Clínic de Barcelona. Measurement of in vitro cholesterol efflux capacity to serum or plasma in macrophage cell models is a promising tool as a biomarker for atherosclerosis. In the present study, we optimize and standardize a fluorescent NBD-cholesterol efflux method and develop a high-throughput analysis using 96-well plates.

Video: High-throughput Nitrobenzoxadiazole-labeled Cholesterol Efflux Assay

A High-throughput Automated Platform for the Development of Manufacturing Cell Lines for Protein Therapeutics

The fast-growing biopharmaceutical industry demands speedy development of highly efficient and reliable production systems to meet the increasing requirement for drug supplies. The generation of production cell lines has traditionally involved manual operations that are labor-intensive, low-throughput and vulnerable to human errors. We report here an integrated high-throughput and automated platform for development of manufacturing cell lines for the production of protein therapeutics.
The combination of BD FACS Aria Cell Sorter, CloneSelect Imager and TECAN Freedom EVO liquid handling system has enabled a high-throughput and more efficient cell line development process. In this operation, production host cells are first transfected with an expression vector carrying the gene of interest 1, followed by the treatment with a selection agent. The stably-transfected cells are then stained with fluorescence-labeled anti-human IgG antibody, and are subsequently subject to flow cytometry analysis 2-4. Highly productive cells are selected based on fluorescence intensity and are isolated by single-cell sorting on a BD FACSAria. Colony formation from single-cell stage was detected microscopically and a series of time-laps digital images are taken by CloneSelect Imager for the documentation of cell line history. After single clones have formed, these clones were screened for productivity by ELISA performed on a TECAN Freedom EVO liquid handling system. Approximately 2,000 - 10,000 clones can be screened per operation cycle with the current system setup.
This integrated approach has been used to generate high producing Chinese hamster ovary (CHO) cell lines for the production of therapeutic monoclonal antibody (mAb) as well as their fusion proteins. With the aid of different types of detecting probes, the method can be used for developing other protein therapeutics or be applied to other production host systems. Comparing to the traditional manual procedure, this automated platform demonstrated advantages of significantly increased capacity, ensured clonality, traceability in cell line history with electronic documentation and much reduced opportunity in operator error.

A high-throughput, automated platform of manufacturing cell line development for producing protein therapeutics is described. Implementation of BD FACS Aria Cell Sorter, CloneSelect Imager and TECAN Freedom EVO liquid handling system has demonstrated significantly increased processing capacity in cell line development with improved cell line quality and high reproducibility.

The fast-growing biopharmaceutical industry demands speedy development of highly efficient and reliable production systems to meet the increasing ...

Mouse Eye Enucleation for Remote High-throughput Phenotyping

The mouse eye is an important genetic model for the translational study of human ophthalmic disease. Blinding diseases in humans, such as macular degeneration, photoreceptor degeneration, cataract, glaucoma, retinoblastoma, and diabetic retinopathy have been recapitulated in transgenic mice.1-5 Most transgenic and knockout mice have been generated by laboratories to study non-ophthalmic diseases, but genetic conservation between organ systems suggests that many of the same genes may also play a role in ocular development and disease. Hence, these mice represent an important resource for discovering new genotype-phenotype correlations in the eye. Because these mice are scattered across the globe, it is difficult to acquire, maintain, and phenotype them in an efficient, cost-effective manner. Thus, most high-throughput ophthalmic phenotyping screens are restricted to a few locations that require on-site, ophthalmic expertise to examine eyes in live mice. 6-9 An alternative approach developed by our laboratory is a method for remote tissue-acquisition that can be used in large or small-scale surveys of transgenic mouse eyes. Standardized procedures for video-based surgical skill transfer, tissue fixation, and shipping allow any lab to collect whole eyes from mutant animals and send them for molecular and morphological phenotyping. In this video article, we present techniques to enucleate and transfer both unfixed and perfusion fixed mouse eyes for remote phenotyping analyses.

The dissection technique illustrates enucleation of the mouse eye for tissue fixation to perform phenotyping in high-throughput screens.

The mouse eye is an important genetic model for the translational study of human ophthalmic disease. Blinding diseases in humans, such as macular ...

Cholesterol Efflux Assay

Cholesterol content of cells must be maintained within the very tight limits, too much or too little cholesterol in a cell results in disruption of cellular membranes, apoptosis and necrosis 1. Cells can source cholesterol from intracellular synthesis and from plasma lipoproteins, both sources are sufficient to fully satisfy cells' requirements for cholesterol. The processes of cholesterol synthesis and uptake are tightly regulated and deficiencies of cholesterol are rare 2. Excessive cholesterol is more common problem 3. With the exception of hepatocytes and to some degree adrenocortical cells, cells are unable to degrade cholesterol. Cells have two options to reduce their cholesterol content: to convert cholesterol into cholesteryl esters, an option with limited capacity as overloading cells with cholesteryl esters is also toxic, and cholesterol efflux, an option with potentially unlimited capacity. Cholesterol efflux is a specific process that is regulated by a number of intracellular transporters, such as ATP binding cassette transporter proteins A1 (ABCA1) and G1 (ABCG1) and scavenger receptor type B1. The natural acceptor of cholesterol in plasma is high density lipoprotein (HDL) and apolipoprotein A-I. 
The cholesterol efflux assay is designed to quantitate the rate of cholesterol efflux from cultured cells. It measures the capacity of cells to maintain cholesterol efflux and/or the capacity of plasma acceptors to accept cholesterol released from cells. The assay consists of the following steps. Step 1: labelling cellular cholesterol by adding labelled cholesterol to serum-containing medium and incubating with cells for 24-48 h. This step may be combined with loading of cells with cholesterol. Step 2: incubation of cells in serum-free medium to equilibrate labelled cholesterol among all intracellular cholesterol pools. This stage may be combined with activation of cellular cholesterol transporters. Step 3: incubation of cells with extracellular acceptor and quantitation of movement of labelled cholesterol from cells to the acceptor. If cholesterol precursors were used to label newly synthesized cholesterol, a fourth step, purification of cholesterol, may be required.
The assay delivers the following information: (i) how a particular treatment (a mutation, a knock-down, an overexpression or a treatment) affects the capacity of cell to efflux cholesterol and (ii) how the capacity of plasma acceptors to accept cholesterol is affected by a disease or a treatment. This method is often used in context of cardiovascular research, metabolic and neurodegenerative disorders, infectious and reproductive diseases.

The cholesterol assay is designed to quantitate the rate of cholesterol efflux from cultured cells and the capacity of plasma acceptors to accept cholesterol released from cells. The assay consists of labelling cells with cholesterol, equilibration of cholesterol among intracellular pools and release of cholesterol to an extracellular acceptor.

Cholesterol content of cells must be maintained within the very tight limits, too much or too little cholesterol in a cell results in disruption of ...

High Throughput Sequential ELISA for Validation of Biomarkers of Acute Graft-Versus-Host Disease

Unbiased discovery proteomics strategies have the potential to identify large numbers of novel biomarkers that can improve diagnostic and prognostic testing in a clinical setting and may help guide therapeutic interventions. When large numbers of candidate proteins are identified, it may be difficult to validate candidate biomarkers in a timely and efficient fashion from patient plasma samples that are event-driven, of finite volume and irreplaceable, such as at the onset of acute graft-versus-host disease (GVHD), a potentially life-threatening complication of allogeneic hematopoietic stem cell transplantation (HSCT).
Here we describe the process of performing commercially available ELISAs for six validated GVHD proteins: IL-2R&alpha;5, TNFR16, HGF7, IL-88, elafin2, and REG3&alpha;3 (also known as PAP1) in a sequential fashion to minimize freeze-thaw cycles, thawed plasma time and plasma usage. For this procedure we perform the ELISAs in sequential order as determined by sample dilution factor as established in our laboratory using manufacturer ELISA kits and protocols with minor adjustments to facilitate optimal sequential ELISA performance. The resulting plasma biomarker concentrations can then be compiled and analyzed for significant findings within a patient cohort. While these biomarkers are currently for research purposes only, their incorporation into clinical care is currently being investigated in clinical trials.
This technique can be applied to perform ELISAs for multiple proteins/cytokines of interest on the same sample(s) provided the samples do not need to be mixed with other reagents. If ELISA kits do not come with pre-coated plates, 96-well half-well plates or 384-well plates can be used to further minimize use of samples/reagents.

High throughput validation of multiple candidate biomarkers can be performed by sequential ELISA in order to minimize freeze/thaw cycles and use of precious plasma samples. Here, we demonstrate how to sequentially perform ELISAs for six different validated plasma biomarkers1-3 of graft-versus-host disease (GVHD)4 on the same plasma sample.

Unbiased discovery proteomics strategies have  the potential to identify large numbers of novel biomarkers that can improve  diagnostic and prognostic ...

High-throughput Flow Cytometry Cell-based Assay to Detect Antibodies to N-Methyl-D-aspartate Receptor or Dopamine-2 Receptor in Human Serum

Over the recent years, antibodies against surface and conformational proteins involved in neurotransmission have been detected in autoimmune CNS diseases in children and adults. These antibodies have been used to guide diagnosis and treatment. Cell-based assays have improved the detection of antibodies in patient serum. They are based on the surface expression of brain antigens on eukaryotic cells, which are then incubated with diluted patient sera followed by fluorochrome-conjugated secondary antibodies. After washing, secondary antibody binding is then analyzed by flow cytometry. Our group has developed a high-throughput flow cytometry live cell-based assay to reliably detect antibodies against specific neurotransmitter receptors. This flow cytometry method is straight forward, quantitative, efficient, and the use of a high-throughput sampler system allows for large patient cohorts to be easily assayed in a short space of time. Additionally, this cell-based assay can be easily adapted to detect antibodies to many different antigenic targets, both from the central nervous system and periphery. Discovering additional novel antibody biomarkers will enable prompt and accurate diagnosis and improve treatment of immune-mediated disorders.

Over the recent years, live cell-based assays have been used successfully to detect antibodies against surface and conformational antigens. Here, we describe a method using high-throughput flow cytometry enabling the analysis of large cohorts of patients. Detection of novel antibodies will improve diagnosis and treatment of immune-mediated disorders.

Over the recent years, antibodies against surface and conformational proteins involved in neurotransmission have been detected in autoimmune CNS diseases ...

High Throughput Characterization of Adult Stem Cells Engineered for Delivery of Therapeutic Factors for Neuroprotective Strategies

Mesenchymal stem cells (MSCs) derived from bone marrow are a powerful cellular resource and have been used in numerous studies as potential candidates to develop strategies for treating a variety of diseases. The purpose of this study was to develop and characterize MSCs as cellular vehicles engineered for delivery of therapeutic factors as part of a neuroprotective strategy for rescuing the damaged or diseased nervous system. In this study we used mouse MSCs that were genetically modified using lentiviral vectors, which encoded brain-derived neurotrophic factor (BDNF) or glial cell-derived neurotrophic factor (GDNF), together with green fluorescent protein (GFP). 
Before proceeding with in vivo transplant studies it was important to characterize the engineered cells to determine whether or not the genetic modification altered aspects of normal cell behavior. Different culture substrates were examined for their ability to support cell adhesion, proliferation, survival, and cell migration of the four subpopulations of engineered MSCs. High content screening (HCS) was conducted and image analysis performed. 
Substrates examined included: poly-L-lysine, fibronectin, collagen type I, laminin, entactin-collagen IV-laminin (ECL). Ki67 immunolabeling was used to investigate cell proliferation and Propidium Iodide staining was used to investigate cell viability. Time-lapse imaging was conducted using a transmitted light/environmental chamber system on the high content screening system.
Our results demonstrated that the different subpopulations of the genetically modified MSCs displayed similar behaviors that were in general comparable to that of the original, non-modified MSCs. The influence of different culture substrates on cell growth and cell migration was not dramatically different between groups comparing the different MSC subtypes, as well as culture substrates. 
This study provides an experimental strategy to rapidly characterize engineered stem cells and their behaviors before their application in long-term in vivo transplant studies for nervous system rescue and repair.

This study describes an experimental platform to rapidly characterize engineered stem cells and their behaviors before their application in long-term in vivo transplant studies for nervous system rescue and repair.

Mesenchymal stem cells (MSCs) derived from bone marrow are a powerful cellular resource and have been used in numerous studies as potential candidates to ...

An Organotypic High Throughput System for Characterization of Drug Sensitivity of Primary Multiple Myeloma Cells

In this work we describe a novel approach that combines ex vivo drug sensitivity assays and digital image analysis to estimate chemosensitivity and heterogeneity of patient-derived multiple myeloma (MM) cells. This approach consists in seeding primary MM cells freshly extracted from bone marrow aspirates into microfluidic chambers implemented in multi-well plates, each consisting of a reconstruction of the bone marrow microenvironment, including extracellular matrix (collagen or basement membrane matrix) and stroma (patient-derived mesenchymal stem cells) or human-derived endothelial cells (HUVECs). The chambers are drugged with different agents and concentrations, and are imaged sequentially for 96 hr through bright field microscopy, in a motorized microscope equipped with a digital camera. Digital image analysis software detects live and dead cells from presence or absence of membrane motion, and generates curves of change in viability as a function of drug concentration and exposure time. We use a computational model to determine the parameters of chemosensitivity of the tumor population to each drug, as well as the number of sub-populations present as a measure of tumor heterogeneity. These patient-tailored models can then be used to simulate therapeutic regimens and estimate clinical response.

We describe a high-throughput drug sensitivity assay for primary multiple myeloma cells. It consists of a reconstruction of the bone marrow microenvironment (including extracellular matrix and stroma) in multi-well plates, and a non-invasive method for longitudinal quantification of cell viability.

In this work we describe a novel approach that combines ex vivo drug sensitivity assays and digital image analysis to estimate chemosensitivity and ...

A High Throughput, Multiplexed and Targeted Proteomic CSF Assay to Quantify Neurodegenerative Biomarkers and Apolipoprotein E Isoforms Status

Many neurodegenerative diseases are&#160;still lacking effective treatments. Reliable biomarkers for identifying and classifying these diseases will be important in the development of future novel therapies. Often&#160;potential new biomarkers do not make it&#160;into the clinic&#160;due to limitations&#160;in their development and&#160;high costs.&#160;However,&#160;targeted proteomics using Multiple Reaction Monitoring Liquid Chromatography-tandem/Mass Spectrometry (MRM LC-MS/MS), specifically using triple quadrupole mass spectrometers, is one method that can be used to rapidly evaluate and validate biomarkers&#160;for clinical translation into diagnostic laboratories. Traditionally, this platform has been used extensively for measurement of small molecules&#160;in clinical laboratories, but it is the potential to analyze proteins, that makes it an attractive alternative to ELISA (Enzyme-Linked Immunosorbent Assay)-based methods. We describe here how targeted proteomics can be used to measure multiplexed markers of dementia, including the detection and quantitation of the known risk factor apolipoprotein E isoform 4 (ApoE4).
In order to make the assay suitable for translation, it is designed to be rapid, simple, highly specific and cost effective. To achieve this, every step in the development of the assay must be optimized for the individual proteins and tissues they are analyzed in. This method describes a typical workflow including various tips and tricks to developing a targeted proteomics MRM LC-MS/MS for translation.
The method development is optimized using custom synthesized versions of tryptic quantotypic peptides, which calibrate&#160;the MS for detection and then spiked into CSF to determine correct identification of the endogenous peptide in the chromatographic separation prior to analysis in the MS. To achieve absolute quantitation, stable isotope-labeled internal standard versions of the peptides with short amino acid sequence tags and containing a trypsin cleavage site, are included in the assay.

We describe a high-throughput, multiplex, and targeted proteomic cerebrospinal fluid (CSF) assay developed with potential for clinical translation. The test can quantitate potential markers and risk factors for neurodegeneration, such as the apolipoprotein E variants (E2, E3 and E4), and measure their allelic expression.

Many neurodegenerative diseases are&#160;still lacking effective treatments. Reliable biomarkers for identifying and classifying these diseases will be ...

Optimized LC-MS/MS Method for the High-throughput Analysis of Clinical Samples of Ivacaftor, Its Major Metabolites, and Lumacaftor in Biological Fluids of Cystic Fibrosis Patients

Defects in the cystic fibrosis trans-membrane conductance regulator (CFTR) are the cause of cystic fibrosis (CF), a disease with life-threatening pulmonary manifestations. Ivacaftor (IVA) and ivacaftor-lumacaftor (LUMA) combination are two new breakthrough CF drugs that directly modulate the activity and trafficking of the defective CFTR-protein. However, there is still a dearth of understanding on pharmacokinetic/pharmacodynamic parameters and the pharmacology of ivacaftor and lumacaftor. The HPLC-MS technique for the simultaneous analysis of the concentrations of ivacaftor, hydroxymethyl-ivacaftor, ivacaftor-carboxylate, and lumacaftor in biological fluids in patients receiving standard ivacaftor or ivacaftor-lumacaftor combination therapy has previously been developed by our group and partially validated to FDA standards. However, to allow the high-throughput analysis of a larger number of patient samples, our group has optimized the reported method through the use of a smaller pore size reverse-phase chromatography column (2.6 &#181;m, C8 100 &#197;; 50 x 2.1 mm) and a gradient solvent system (0-1 min: 40% B; 1-2 min: 40-70% B; 2-2.7 min: held at 70% B; 2.7-2.8 min: 70-90% B; 2.8-4.0 min: 90% B washing; 4.0-4.1 min: 90-40% B; 4.1-6.0 min: held at 40% B) instead of an isocratic elution. The goal of this study was to reduce the HPLC-MS analysis time per sample dramatically from ~15 min to only 6 min per sample, which is essential for the analysis of a large amount of patient samples. This expedient method will be of considerable utility for studies into the exposure-response relationships of these breakthrough CF drugs.

Ivacaftor and ivacaftor-lumacaftor combination are two new CF drugs. However, there is still a dearth of understanding on their PK/PD and pharmacology. We present an optimized HPLC-MS technique for the simultaneous analysis of ivacaftor and its major metabolites, and lumacaftor.

Defects in the cystic fibrosis trans-membrane conductance regulator (CFTR) are the cause of cystic fibrosis (CF), a disease with life-threatening ...

Differential Effects of Lipid-lowering Drugs in Modulating Morphology of Cholesterol Particles

Treatment of dyslipidemia patients with lipid-lowering drugs leads to a significant reduction in low-density lipoproteins (LDL) level and a low to moderate level of increase in high-density lipoprotein (HDL) cholesterol in plasma. However, a possible role of these drugs in altering morphology and distribution of cholesterol particles is poorly understood. Here, we describe the in vitro evaluation of lipid-lowering drug effects in modulating morphological features of cholesterol particles using the plaque array method in combination with imaging flow cytometry. Image analyses of the cholesterol particles indicated that lovastatin, simvastatin, ezetimibe, and atorvastatin induce the formation of both globular and linear strand-shaped particles, whereas niacin, fibrates, fluvastatin, and rosuvastatin induce the formation of only globular-shaped particles. Next, purified very low-density lipoprotein (VLDL) and LDL particles incubated with these drugs showed changes in the morphology and image texture of cholesterol particles subpopulations. Furthermore, screening of 50 serum samples revealed the presence of a higher level of linear shaped HDL cholesterol particles in subjects with dyslipidemia (mean of 18.3%) compared to the age-matched normal (mean of 11.1%) samples. We also observed considerable variations in lipid-lowering drug effects on reducing linear shaped LDL and HDL cholesterol particles formation in serum samples. These findings indicate that lipid-lowering drugs, in addition to their cell-mediated hypolipidemic effects, may directly modulate morphology of cholesterol particles by a non-enzymatic mechanism of action. The outcomes of these results have potential to inform diagnosis of atherosclerosis and predict optimal lipid-lowering therapy.

The objective of this study was to evaluate in vitro lipid-lowering drug effects in modulating the morphology of cholesterol particles. Comparison of lipid-lowering drugs revealed variations in their effect in modulating the morphological features of cholesterol particles.