Financial support for the experiments presented in the study was provided by the Marie Heim-V&#246;gtlin program of the Swiss National Science Foundation.
We thank Ms. Johanna Nyffeler for developing a set of modified MATLAB programs for screening for statistically significant differences in real-time cell analyzer&#8217;s data and Dr. Yama Abassi for helpful discussion.

1. Preparation
<ol>
	<li>Place the real-time cell analyzer&#8217;s station in a tissue culture incubator set at 37 &#176;C and with 5% CO2. Carry out all cell culture handling and pharmacological treatments in a tissue culture hood under sterile conditions.</li>
	<li>NOTE: Neuronal cell lines requiring different temperature settings compared to standard conditions for culture, should be adjusted accordingly. For weakly adherent cell lines, use coating agents to facilitate the interaction of cells with the gold microelectrodes in the bottom of the wells of the E-Plate 96.</li>
	<li>Prepare 1,000X stock solutions of the pharmacological compounds for cell culture treatment (neuroprotective agents or second messenger pathways inhibitors in the appropriate solvent &#8211; dimethylsulfoxide or sterile water) and store them at -20 &#176;C. Use the solvent as vehicle in the following treatments.</li>
	<li>Culture human neuroblastoma SK-N-SH cells in DMEM/F12 medium supplemented with 10% fetal bovine serum (FBS) (proliferation medium) in cell culture flasks with 175 cm2 surface to density of about 75%. Keep cell passage number within a range (of about 10 passages) to ascertain consistency between experiments in terms of rate of cell proliferation and response to cytotoxicity. Lower passage numbers are preferred.</li>
	<li>Wash the adherent SK-N-SH cell layer with PBS, and trypsinize with 0.05% trypsin-EDTA solution for 5 min at 37 &#730;C. Centrifuge the cells at 170 &#215; g for 5 min to remove trypsin. Resuspend the cells in 10 ml proliferation medium. Count the cells with Scepter cell counter and adjust cell number to 300,000 cells/ml by diluting cells with proliferation medium.</li>
</ol>
2. Plating and Proliferation of SK-N-SH Cells
<ol>
	<li>Add 100 &#181;l proliferation medium to each well of the E-Plate 96 and leave it for 30 min in the tissue culture hood at RT to equilibrate. Insert the E-Plate 96 in the real-time cell analyzer station in the CO2 incubator at 37 &#176;C.</li>
	<li>Start the real-time cell analyzer software. On the Layout page select the wells included in the experiment and enter in the edit boxes the information about cell type, cell number, names and concentrations of chemical compounds used for cell treatment. 
	NOTE: For the purposes of this protocol at least 4 replicates are recommended for each treatment.</li>
	<li>On the Schedule software page determine &#8220;Steps&#8221; included in the experiment, by selecting the number of sweeps measuring Cell Index and the interval between sweeps for each step. Since Step 1 is predetermined for background measurement, select &#8220;Add a step&#8221; and set Step 2 to measure the Cell Index every 15 min for 96 hr. 
	NOTE: For treatments, in which effects with fast kinetics are expected, set sweeps at shorter intervals.</li>
	<li>Click Start to initiate the automatically predetermined Step 1 and measure the background impedance of the media. This value is automatically subtracted by the software at each data point once the cells are added to the wells.</li>
	<li>Use the previously prepared in step 1.5) cell suspension of 300,000 cells/ml in proliferation medium. 30,000 cells/well for cell toxicity/neuroprotection studies and 15,000 cells/well for cell proliferation studies. Take out the E-Plate and add 100 &#181;l cell suspension per well for cell toxicity/neuroprotection studies and add 50 &#181;l cell suspension and 50 &#181;l proliferation medium per well for cell proliferation studies. The number of cells plated per well needs to be optimized for each cell line empirically.</li>
	<li>Gently swirl the E-Plate 96 for even plating of the cells. Leave the E-Plate 96 for 30 min in the tissue culture hood at RT to allow the cells settle evenly to the bottom of the wells.</li>
	<li>Insert the E-Plate 96 in the real-time cell analyzer station and start Step 2 on the Schedule page. Monitor Cell Index values throughout the experiment by viewing the cell curves on the Plot page and the raw Cell Index data on the Cell Index page of the software.</li>
</ol>
3. Serum Deprivation
<ol>
	<li>24 hr after plating the cells, pause the experiment, and remove the E-Plate 96 from the real-time cell analyzer station. Dilute second messenger inhibitors from 1,000X stocks with DMEM/F12 serum-free medium &#8211; to 200&#215; the final concentration. Treat cells with 1 &#956;l inhibitors of second messenger pathways to be tested for their involvement in neurotoxicity/neuroprotection 30 min before initiating cytotoxicity, to inhibit the respective pathways. Return the E-Plate 96 to the station and resume experimental Cell Index measurements.</li>
	<li>After 30 min pause the experiment again. Carefully remove proliferation medium fully from the E-Plate 96 wells with a pipette (or multi-channel pipette), taking care not to disrupt the adherent cell layer by directing the edge of the pipette tip to the corner of the well. Add 200 &#181;l/well of serum-free DMEM/F12 medium (serum deprivation medium). Ensure rapid exchange of cell culture medium to minimize mechanical agitation of the cells.</li>
	<li>Dilute compounds to be tested for their neuroprotective effects from 1,000X stock with serum-free DMEM/F12 medium to 200&#215; the final concentration. Add 1 &#956;l compounds to be tested for their neuroprotective effects and 1 &#956;l inhibitors of second messenger pathways in the individual wells according to the experimental plan.</li>
	<li>In cells for proliferation studies do not change medium. Dilute compounds to be tested from 1,000X stock to 200&#215; the final concentration in proliferation medium, treat with 1 &#956;l per well and continue to culture in proliferation medium.</li>
	<li>Resume the experiment to continue with Cell Index measurements every 15 min for 96 hr as previously set.</li>
</ol>
4. Data Analysis
<ol>
	<li>For neurotoxicity/neuroprotection data normalize Cell Index to the last time point before pharmacological treatment or medium change to reduce variation between experiments by selecting &#8220;normalized Cell Index&#8221; and &#8220;normalize Time&#8221; on the Plot page.</li>
	<li>Highlight the wells on the Plot page for the experimental conditions of interest and click &#8220;Add&#8221; to plot the normalized Cell Index curves. Observe the kinetics of the neurotoxic/neuroprotective effect, or of second messengers inhibition as normalized Cell Index curves as a function of time.</li>
	<li>Observe the Cell Index curves for the tested drug treatments in proliferation medium as a function of time to assess whether an effect on proliferation is involved in the neuroprotective/neurotoxic effect.</li>
	<li>Export the experimental info for all Cell Index time points from the Cell Index software page into an Excel file to initiate statistical evaluation of the results 
	NOTE: As an initial step in the statistical analysis a set of modified MATLAB programs that use the Welch&#39;s t-test, with the p-value plotted semilogarithmically, utilize inverted axis against the time scale (provided as supplementary code files). These programs allow detection of p-values over the time-course of an entire real-time cell analyzer experiment, and thus aid the selection of time points for more detailed statistical analysis. See the supplementary material for detailed information on the programs.</li>
	<li>For statistical analysis of differences in Cell Index values under different treatment conditions at specific time points, select Cell Index values at respective time points from the exported Excel file. Analyze the Cell Index values for the selected time points with one-way or two-way analysis of variance (ANOVA) followed by a post-hoc test using statistical software.</li>
</ol>

<ol>
	<li>Cavallucci, V., D'Amelio, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Matter+of+life+and+death:+the+pharmacological+approaches+targeting+apoptosis+in+brain+diseases.">Matter of life and death: the pharmacological approaches targeting apoptosis in brain diseases.</a> Curr. Pharm. Des. 17 (3), 215-229 (2011).</li><li>Bull, S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=HPA+CHaPD+001:+Review+of+Environmental+Chemicals+and+Neurotoxicity.">HPA CHaPD 001: Review of Environmental Chemicals and Neurotoxicity.</a> Focus on Neurological Diseases. , (2007).</li><li>Ke, N., Wang, X., Xu, X., Abassi, Y. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+xCELLigence+system+for+real-time+and+label-free+monitoring+of+cell+viability.">The xCELLigence system for real-time and label-free monitoring of cell viability.</a> Methods Mol. Biol. 740, 33-43 (2011).</li><li>Limame, R., 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=Comparative+analysis+of+dynamic+cell+viability,+migration+and+invasion+assessments+by+novel+real-time+technology+and+classic+endpoint+assays.">Comparative analysis of dynamic cell viability, migration and invasion assessments by novel real-time technology and classic endpoint assays.</a> PLoS One. 7 (10), e46536 (2012).</li><li>Diemert, 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=Impedance+measurement+for+real-time+detection+of+neuronal+cell+death.">Impedance measurement for real-time detection of neuronal cell death.</a> J. Neurosci. Methods. 203 (1), 69-77 (2012).</li><li>Kustermann, 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=A+label-free,+impedance-based+real+time+assay+to+identify+drug-induced+toxicities+and+differentiate+cytostatic+from+cytotoxic+effects.">A label-free, impedance-based real time assay to identify drug-induced toxicities and differentiate cytostatic from cytotoxic effects.</a> Toxicol In Vitro. 27 (5), 1589-1595 (2013).</li><li>Marinova, Z., Walitza, S., Gr&#252;nblatt, E. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=5-HT2A+serotonin+receptor+agonist+DOI+alleviates+cytotoxicity+in+neuroblastoma+cells:+role+of+the+ERK+pathway.">5-HT2A serotonin receptor agonist DOI alleviates cytotoxicity in neuroblastoma cells: role of the ERK pathway.</a> Prog. Neuropsychopharmacol. Biol. Psychiatry. 44, 64-72 (2013).</li><li>Gonz&#225;lez-Maeso, J., 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=Hallucinogens+recruit+specific+cortical+5-HT(2A)+receptor-mediated+signaling+pathways+to+affect+behavior.">Hallucinogens recruit specific cortical 5-HT(2A) receptor-mediated signaling pathways to affect behavior.</a> Neuron. 53 (3), 439-452 (2007).</li><li>Tsuchioka, M., Takebayashi, M., Hisaoka, K., Maeda, N., Nakata, Y. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Serotonin+(5-HT)+induces+glial+cell+line-derived+neurotrophic+factor+(GDNF)+mRNA+expression+via+the+transactivation+of+fibroblast+growth+factor+receptor+2+(FGFR2)+in+rat+C6+glioma+cells.">Serotonin (5-HT) induces glial cell line-derived neurotrophic factor (GDNF) mRNA expression via the transactivation of fibroblast growth factor receptor 2 (FGFR2) in rat C6 glioma cells.</a> J. Neurochem. 106 (1), 244-257 (2008).</li><li>Galante, D., 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=Differential+toxicity,+conformation+and+morphology+of+typical+initial+aggregation+states+of+A&#946;1-42+and+A&#946;py3-42+beta-amyloids.">Differential toxicity, conformation and morphology of typical initial aggregation states of A&#946;1-42 and A&#946;py3-42 beta-amyloids.</a> Int. J. Biochem. Cell. Biol. 44 (11), 2085-2093 (2012).</li><li>Sheline, C. T., Cai, A. L., Zhu, J., Shi, C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Serum+or+target+deprivation-induced+neuronal+death+causes+oxidative+neuronal+accumulation+of+Zn2+and+loss+of+NAD.">Serum or target deprivation-induced neuronal death causes oxidative neuronal accumulation of Zn2+and loss of NAD.</a> Eur. J. Neurosci. 32, 894-904 (2010).</li></ol>

Publication costs for the current video-article were sponsored by &#8220;ACEA Biosciences&#8221;.

The current protocol presents the utility of a real-time cell analyzer to assess continuously and under label-free conditions the neuroprotective/neurotoxic effects of compounds in neuronal cell lines and to gain insight into the second messenger pathways involved in the effect.
Even though the real-time cell analyzer&#8217;s utility to study cytotoxicity and effects of drugs on cell proliferation is generally recognized, only a few studies have used it in neuronal related cell types. We have ...

Neuronal cell death plays a critical role in the pathophysiology of many brain-related disorders1. The availability of reliable and high-throughput in vitro toxicity assays is critical to gain better insight into the mechanisms of neurotoxicity and to help select neuroprotective molecules as therapeutic candidates in drug development2. However, there are many limitations to most widely used in vitro neurotoxicity assays.They assess neurotoxicity/neuroprotection at a single time-point not allowing kinetic resolution; often use label or probe which can interfere with the signaling pathways and limit additional studies in the same cell population, and are often labor-intensive, and in many cases do not provide mechanistic insight. In the present study we demonstrate the utility of a real-time impedance-based cell analyzer to determine neurotoxicity and neuroprotection in a neuronal cell line in real-time and under label-free conditions and to provide insight into downstream mechanisms through analysis of second messenger pathways involved in the effect.
Previous studies have confirmed the validity of the real-time cell analyzer to determine cytotoxicity as well as effects on cell proliferation in cell lines in comparison with standard techniques3,4,5,6. For example, a good correlation was observed between readouts of the standard cell viability WST-1 assay and Cell Index values at several time points under basal proliferation conditions and after two different toxic paradigms in HeLa cells3. In A549 and MDA-MB-231 cells proliferation and cytotoxicity provoked with the microtubule stabilizer paclitaxel showed very similar values when assessed by Cell Index measurements and the standardly used sulforhodamine B (SRB) assay4. In the neuronal cell line of immortalized hippocampal neurons HT-22 Cell Index measurements were validated for their ability to detect cell proliferation, glutamate cytotoxicity and cytoprotection against the widely used 3-(4,5-dimethylthiazol-2-yl)2,5-diphenyltetrazolium-bromide (MTT) assay5. In the same study the MTT assay results and Cell Index measurements also correlated well in measuring neuronal progenitor cells proliferation, cytotoxicity after growth factors deprivation and rescue of cytotoxicity by the pan-caspase inhibitor QVD5. Cytotoxicity induced in NIH 3T3 cells by Vandetanib (vascular endothelial growth factor receptor and epidermal growth factor receptor inhibitor) showed similar results measured with Cell Index values or neutral red uptake assay6.
We have recently used the real-time cell analyzer system to assess neuroprotective effects of the serotonin 2A (5-HT2A) receptor agonist (&#177;)-2,5-dimethoxy-4-iodoamphetamine hydrochloride (DOI) in a neuronal cell line (SK-N-SH cells) and screened for the involvement of second messenger pathways through monitoring the effect of their chemical inhibition on the observed neuroprotection7. Interestingly, the 5-HT2A receptor has both hallucinogenic and nonhallucinogenic agonists (like DOI and lisuride, respectively), which may activate both common and distinct second messenger pathways8.
The advantages of the presented technique are that it allows to collect real-time information on cell survival in the course of days, to delineate second-messenger pathways involved, to assess the possible contribution of proliferation effects to neuroprotection, and to select an optimal time for additional end-point studies on the same cell population. A schematic diagram of the workflow in the current protocol is presented in Figure 1.

<table border="0" cellpadding="0" cellspacing="0" width="1015">
	<tbody>
		<tr height="21">
			<td height="21" style="height:21px;width:279px;">Name of Material/ Equipment</td>
			<td style="width:161px;">Company</td>
			<td style="width:119px;">Catalog Number</td>
			<td style="width:457px;">Comments/Description</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:279px;">xCELLigence&#160; RTCA SP system bundle</td>
			<td style="width:161px;">ACEA Biosciences</td>
			<td style="width:119px;">No: 00380601030</td>
			<td>consists of RTCA Analyzer, RTCA SP Station and RTCA Control Unit</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:279px;">E-plate 96</td>
			<td style="width:161px;">ACEA Biosciences</td>
			<td style="width:119px;">No: 05232368001</td>
			<td>for culturing the cells, inserted in the RTCA SP Station</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:279px;">SK-N-SH cells</td>
			<td style="width:161px;">ATCC - (in partnership with LGC Standards)</td>
			<td style="width:119px;">HTB-11</td>
			<td>can be replaced by another adherent neuronal cell line of interest</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:279px;">DMEM/F12&#160;</td>
			<td style="width:161px;">Sigma-Aldrich</td>
			<td style="width:119px;">D8437</td>
			<td>cell culture medium</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:279px;">fetal bovine serum</td>
			<td style="width:161px;">Life Technologies</td>
			<td style="width:119px;">16140-063</td>
			<td>supplements proliferation, but not serum deprivation medium</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:279px;">tisue culture flask T175</td>
			<td style="width:161px;">Sarstedt</td>
			<td style="width:119px;">83.1812.302&#160;</td>
			<td>for culturing cells, which will be later plated on the E-Plate 96</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:279px;">0.05% Trypsin-EDTA</td>
			<td style="width:161px;">Life Technologies</td>
			<td style="width:119px;">25300-054</td>
			<td>for trypsinization of cells cultured in tissue culture flasks</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:279px;">Scepter 2.0 cell counter</td>
			<td style="width:161px;">Merck Millipore</td>
			<td style="width:119px;">PHCC20060</td>
			<td>automated cell counter</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:279px;">phosphate-buffered saline</td>
			<td style="width:161px;">Life Technologies</td>
			<td style="width:119px;">10010-015</td>
			<td>for washing the cells</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:279px;">(&#177;)-DOI hydrochloride</td>
			<td style="width:161px;">Sigma-Aldrich</td>
			<td style="width:119px;">D101</td>
			<td>5-HT2A agonist for cell culture treatment</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:279px;">LY-294,002 hydrochloride</td>
			<td style="width:161px;">Sigma-Aldrich</td>
			<td style="width:119px;">L9908</td>
			<td>PI3-K inhibitor for cell culture treatment&#160;</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:279px;">lisuride maleate</td>
			<td style="width:161px;">Tocris Bioscience</td>
			<td align="right" style="width:119px;">4052</td>
			<td>compound with 5-HT2A agonistic activity for cell culture treatment</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:279px;">dimethyl sulfoxide</td>
			<td style="width:161px;">Sigma-Aldrich</td>
			<td style="width:119px;">D4540</td>
			<td>for dissolving LY-294,002 and lisuride maleate</td>
		</tr>
	</tbody>
</table>

real-time impedance-based cell analyzer as a tool to delineate molecular pathways involved in neurotoxicity and neuroprotection in a neuronal cell line

Many brain-related disorders have neuronal cell death involved in their pathophysiology. Improved in vitro models to study neuroprotective or neurotoxic effects of drugs and downstream pathways involved would help gain insight into the molecular mechanisms of neuroprotection/neurotoxicity and could potentially facilitate drug development. However, many existing in vitro toxicity assays have major limitations &#8211; most assess neurotoxicity and neuroprotection at a single time point, not allowing to observe the time-course and kinetics of the effect. Furthermore, the opportunity to collect information about downstream signaling pathways involved in neuroprotection in real-time would be of great importance. In the current protocol we describe the use of a real-time impedance-based cell analyzer to determine neuroprotective effects of serotonin 2A (5-HT2A) receptor agonists in a neuronal cell line under label-free and real-time conditions using impedance measurements. Furthermore, we demonstrate that inhibitors of second messenger pathways can be used to delineate downstream molecules involved in the neuroprotective effect. We also describe the utility of this technique to determine whether an effect on cell proliferation contributes to an observed neuroprotective effect. The system utilizes special microelectronic plates referred to as E-Plates which contain alternating gold microelectrode arrays on the bottom surface of the wells, serving as cell sensors. The impedance readout is modified by the number of adherent cells, cell viability, morphology, and adhesion. A dimensionless parameter called Cell Index is derived from the electrical impedance measurements and is used to represent the cell status. Overall, the real-time impedance-based cell analyzer allows for real-time, label-free assessment of neuroprotection and neurotoxicity, and the evaluation of second messenger pathways involvement, contributing to more detailed and high-throughput assessment of potential neuroprotective compounds in vitro, for selecting therapeutic candidates.

Serum deprivation leads to decrease in Cell Index values, which can be monitored continuously with the real-time cell analyzer
Neurotoxic stimuli to the cells lead to a decrease in Cell Index values, which can be monitored in real-time with the presented technique and the dynamics of which is dependent on the specific neurotoxic stimulus and the cell type studied. Figure 2 demonstrates the increase in Cell Index when SK-N-SH cells are grown in proliferation me...

Watch this Scientific Journal Video about Real-Time Impedance-based Cell Analyzer as a Tool to Delineate Molecular Pathways Involved in Neurotoxicity and Neuroprotection in a Neuronal Cell Line at JoV

Real-Time Impedance-based Cell Analyzer as a Tool to Delineate Molecular Pathways Involved in Neurotoxicity and Neuroprotection in a Neuronal Cell Line

Improved in vitro neurotoxicity assays would aid the identification of new neuroprotective compounds. The utility of a real-time impedance-based cell analyzer to determine cytotoxicity and cytoprotection in neuronal cell lines and to delineate the involvement of second messenger pathways, thus gaining insight in the mechanism of neuroprotection is presented.

Many brain-related disorders have neuronal cell death involved in their pathophysiology. Improved in vitro models to study neuroprotective or neurotoxic ...

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Neuroscience

11.3K Views.  University of Zürich. Improved in vitro neurotoxicity assays would aid the identification of new neuroprotective compounds. The utility of a real-time impedance-based cell analyzer to determine cytotoxicity and cytoprotection in neuronal cell lines and to delineate the involvement of second messenger pathways, thus gaining insight in the mechanism of neuroprotection is presented.

Video: Real-Time Impedance-based Cell Analyzer as a Tool to Delineate Molecular Pathways Involved in Neurotoxicity and Neuroprotection in a Neuronal Cell Line