Name: use of electron paramagnetic resonance in biological samples at ambient temperature and 77 k
Uploaded: 2019-01-11T13:30:00
Description: Watch this Scientific Journal Video about Use of Electron Paramagnetic Resonance in Biological Samples at Ambient Temperature and 77 K at JoVE.com

This work was supported by the University of Colorado School of Medicine Dean&#39;s Strategic Research Infrastructure award, R01 HL086680-09 and 1R35HL139726-01, to E.N.G. and UCD CFReT fellowship award (HE). The authors thank Dr. Sandra Eaton and Dr. Gareth Eaton (University of Denver), Dr. Gerald Rosen and Dr. Joseph P. Kao (University of Maryland), and Dr. Sujatha Venkataraman (University of Colorado Denver) for helpful discussions, and Joanne Maltzahn,&#160;Ashley Trumpie and Ivy McDermott (University of Colorado Denver) for technical support.

All animal studies were approved by the University of Colorado Denver Institutional Animal Care and Use Committee.
1. Preparation of Reagents
<ol>
	<li>Diethylenetriaminepentaacetic acid (DTPA) stock (150 mM)
	<ol>
		<li>Add 2.95 g of DTPA (393.35 g/mol) to 10 mL of deionized water.</li>
		<li>To dissolve DTPA, add 1 M NaOH dropwise and bring to a pH of 7.0.</li>
		<li>Bring the volume to 50 mL with water for a final DTPA concentration of 150 mM, and store at 4 &#176;C.</li>...

<ol>
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B., 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=Electron+spin+relaxation+times+and+rapid+scan+EPR+imaging+of+pH-sensitive+amino-substituted+trityl+radicals.">Electron spin relaxation times and rapid scan EPR imaging of pH-sensitive amino-substituted trityl radicals.</a> Magnetic Resonance in Chemistry. 53 (4), 280-284 (2015).</li><li>Elajaili, 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=Imaging+disulfide+dinitroxides+at+250+MHz+to+monitor+thiol+redox+status.">Imaging disulfide dinitroxides at 250 MHz to monitor thiol redox status.</a> Journal of Magnetic Resonance. 260, 77-82 (2015).</li><li>Halpern, H. 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=Oxymetry+Deep+in+Tissues+with+Low-Frequency+Electron-Paramagnetic-Resonance.">Oxymetry Deep in Tissues with Low-Frequency Electron-Paramagnetic-Resonance.</a> Proceedings of the National Academy of Sciences of the United States of America. 91 (26), 13047-13051 (1994).</li><li>Epel, B., 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=Imaging+thiol+redox+status+in+murine+tumors+in+vivo+with+rapid-scan+electron+paramagnetic+resonanc.">Imaging thiol redox status in murine tumors in vivo with rapid-scan electron paramagnetic resonanc.</a> Journal of Magnetic Resonance. 276, 31-36 (2017).</li><li>Legenzov, E. A., Sims, S. J., Dirda, N. D. A., Rosen, G. M., Kao, J. P. 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I., 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=Distinct+roles+of+Nox1+and+Nox4+in+basal+and+angiotensin+II-stimulated+superoxide+and+hydrogen+peroxide+production.">Distinct roles of Nox1 and Nox4 in basal and angiotensin II-stimulated superoxide and hydrogen peroxide production.</a> Free Radical Biology and Medicine. 45 (9), 1340-1351 (2008).</li><li>Dikalov, S. I., Kirilyuk, I. A., Voinov, M., Grigor'ev, I. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=EPR+detection+of+cellular+and+mitochondrial+superoxide+using+cyclic+hydroxylamines.">EPR detection of cellular and mitochondrial superoxide using cyclic hydroxylamines.</a> Free Radical Research. 45 (4), 417-430 (2011).</li><li>Dikalova, A. E., 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=Therapeutic+Targeting+of+Mitochondrial+Superoxide+in+Hypertension.">Therapeutic Targeting of Mitochondrial Superoxide in Hypertension.</a> Circulation Research. 107 (1), 106-116 (2010).</li><li>Dikalov, S. I., Polienko, Y. F., Kirilyuk, I. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Electron+Paramagnetic+Resonance+Measurements+of+Reactive+Oxygen+Species+by+Cyclic+Hydroxylamine+Spin+Probes.">Electron Paramagnetic Resonance Measurements of Reactive Oxygen Species by Cyclic Hydroxylamine Spin Probes.</a> Antioxidants &amp; Redox Signaling. , (2017).</li><li>Sharma, 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=L-Carnitine+preserves+endothelial+function+in+a+lamb+model+of+increased+pulmonary+blood+flow.">L-Carnitine preserves endothelial function in a lamb model of increased pulmonary blood flow.</a> Pediatric Research. 74 (1), 39-47 (2013).</li><li>Berg, K., Ericsson, M., Lindgren, M., Gustafsson, H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+High+Precision+Method+for+Quantitative+Measurements+of+Reactive+Oxygen+Species+in+Frozen+Biopsies.">A High Precision Method for Quantitative Measurements of Reactive Oxygen Species in Frozen Biopsies.</a> PloS One. 9 (3), (2014).</li><li>Kozlov, A. V., 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=EPR+analysis+reveals+three+tissues+responding+to+endotoxin+by+increased+formation+of+reactive+oxygen+and+nitrogen+species.">EPR analysis reveals three tissues responding to endotoxin by increased formation of reactive oxygen and nitrogen species.</a> Free Radical Biology and Medicine. 34 (12), 1555-1562 (2003).</li><li>Van Rheen, Z., 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=Lung+Extracellular+Superoxide+Dismutase+Overexpression+Lessens+Bleomycin-Induced+Pulmonary+Hypertension+and+Vascular+Remodeling.">Lung Extracellular Superoxide Dismutase Overexpression Lessens Bleomycin-Induced Pulmonary Hypertension and Vascular Remodeling.</a> American Journal of Respiratory Cell and Molecular Biology. 44 (4), 500-508 (2011).</li><li>Mouradian, G. C., 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=Superoxide+Dismutase+3+R213G+Single-Nucleotide+Polymorphism+Blocks+Murine+Bleomycin-Induced+Fibrosis+and+Promotes+Resolution+of+Inflammation.">Superoxide Dismutase 3 R213G Single-Nucleotide Polymorphism Blocks Murine Bleomycin-Induced Fibrosis and Promotes Resolution of Inflammation.</a> American Journal of Respiratory Cell and Molecular Biology. 56 (3), 362-371 (2017).</li><li>Dikalov, S. I., Li, W., Mehranpour, P., Wang, S. S., Zafari, A. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Production+of+extracellular+superoxide+by+human+lymphoblast+cell+lines:+comparison+of+electron+spin+resonance+techniques+and+cytochrome+C+reduction+assay.">Production of extracellular superoxide by human lymphoblast cell lines: comparison of electron spin resonance techniques and cytochrome C reduction assay.</a> Biochem Pharmacol. 73 (7), 972-980 (2007).</li><li>Kozuleva, M., 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=Quantification+of+superoxide+radical+production+in+thylakoid+membrane+using+cyclic+hydroxylamines.">Quantification of superoxide radical production in thylakoid membrane using cyclic hydroxylamines.</a> Free Radical Biology and Medicine. 89, 1014-1023 (2015).</li><li>Chen, K., Swartz, H. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Oxidation+of+Hydroxylamines+to+Nitroxide+Spin+Labels+in+Living+Cells.">Oxidation of Hydroxylamines to Nitroxide Spin Labels in Living Cells.</a> Biochimica Et Biophysica Acta. 970 (3), 270-277 (1988).</li></ol>

The assessment of free radical production in biological settings is important in understanding redox regulated signaling in health and disease, but the measure of these species is highly challenging due to the short half-life of free radical species and technical limitations with commonly used methods. EPR is a valuable and powerful tool in redox biology, as it is the only unambiguous method for detecting free radicals. In this project, we demonstrate practical EPR methods for designing experiments and preparing samples ...

While measures of oxidative stress and reactive oxygen species are important to the study of diverse diseases across all organ systems, the detection of reactive oxygen species (ROS) is challenging due to a short half-life and high reactivity. An electron paramagnetic resonance (EPR) technique is the most unambiguous method for detecting free radicals. Spin probes have advantages over the more commonly used fluorescent probes. Though fluorescent probes are relatively inexpensive and easy to use and provide rapid, sensitive detection of ROS, they do have serious limitations due to artifactual signals, an inability to calculate ROS concentrations, and a general lack of specificity1.
To facilitate the use of EPR for biological studies, a variety of spin probes have been synthesized that can measure a range of biologically relevant free radical species as well as pO2, pH, and redox states2,3,4,5,6,7. Spin traps have also been developed to capture short-lived radicals and form long-living adducts, which facilitates detection by EPR8. Both classes (spin probes and spin traps) have advantages and limitations. One commonly used class of spin probes are cyclic hydroxylamines, which are EPR-silent and react with short-lived radicals to form a stable nitroxide. Cyclic hydroxylamines react with superoxide 100 times faster than spin traps, enabling them to compete with cellular antioxidants, but they lack specificity and require the use of appropriate controls and inhibitors to identify the radical species or source responsible for the nitroxide signal. While spin traps exhibit specificity, with distinct spectral patterns depending on the trapped species, they have slow kinetics for superoxide spin trapping and are prone to biodegradation of the radical adducts. Applications for spin trapping have been well-documented in biomedical research9,10,11,12,13.
The goal of this project is to demonstrate practical EPR methods for designing experiments and preparing samples to detect superoxide using spin probes in different cellular compartments in vitro and in different tissue compartments in vivo. Several manuscripts have published protocols relevant to these goals, using cell-permeable, cell-impermeable, and mitochondrial targeted spin probes to target different cellular compartments in vitro and process tissue for analysis in mouse models14,15. We build upon this body of literature by validating an approach to measure superoxide using a 1-hydroxy-3-methoxycarbonyl-2,2,5,5-tetramethylpyrrolidine (CMH) spin probe in different cellular compartments in vitro to ensure accurate measurements, highlighting potential technical problems that may skew results. We also provide methods to perform EPR measurements in blood, bronchoalveolar lavage fluid, and lung tissue using the CMH spin probe. These studies compare different methods to process the tissues as well as present a method to inject another spin probe, CPH, into mice prior to harvesting tissue. Finally, we develop a practical method to store samples in polytetrafluoroethylene (PTFE) tubing to allow for the storage and transfer of samples before EPR measurements at 77 K.

<table border="0" cellpadding="0" cellspacing="0" style="width:1993px;" width="1994">
	<tbody>
		<tr height="20">
			<td height="20" style="height:20px;width:931px;">DMEM</td>
			<td style="width:196px;">LifeTech</td>
			<td style="width:224px;">10566-016</td>
			<td style="width:643px;">cell culture media</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">Diethylenetriaminepentaacetic acid (DTPA)</td>
			<td>Sigma Aldrich</td>
			<td>D6518-5G</td>
			<td></td>
		</tr>
		<tr height="23">
			<td height="23" style="height:23px;">sodium chloride (NaCl)&#160;</td>
			<td>Fisher Scientific&#160;</td>
			<td>&#160;BP358-212</td>
			<td>used to prepare 50 mM phosphate saline buffer&#160; according to Sigma aldrish&#160;&#160;</td>
		</tr>
		<tr height="24">
			<td height="24" style="height:24px;">potassium phosphate dibasic (HK2PO4 )</td>
			<td>Fisher Scientific&#160;</td>
			<td>&#160;BP363-500</td>
			<td>used to prepare 50 mM phosphate saline buffer&#160; according to Sigma aldrish&#160;&#160;</td>
		</tr>
		<tr height="24">
			<td height="24" style="height:24px;">potassium phosphate monobasic (KH2PO4 )</td>
			<td>Sigma Aldrich</td>
			<td>P-5379</td>
			<td>used to prepare 50 mM phosphate saline buffer&#160; according to Sigma aldrish&#160;&#160;</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">Krebs-Henseleit buffer (KHB)&#160;</td>
			<td>(Alfa Aesar, Hill)</td>
			<td>J67820</td>
			<td></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">Bovine erythrocyte superoxide dismutase (SOD)</td>
			<td>Sigma Aldrich</td>
			<td>&#160;S7571-30KU</td>
			<td></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">Phorbol 12-myristate 13-acetate (PMA)&#160;</td>
			<td>Sigma Aldrich</td>
			<td>P1585-1MG</td>
			<td>Dissolve in DMSO</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">Antimycin A (AA)</td>
			<td>Sigma Aldrich</td>
			<td>A8674-25MG</td>
			<td>Dissolve in Ethanol and store in glass vials(MW used is the averaged molecular weights for four lots)</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">1-Hydroxy-3-methoxycarbonyl-2,2,5,5-tetramethylpyrrolidine . HCl (CMH)</td>
			<td>Enzo Life Sciences</td>
			<td>ALX-430-117-M050</td>
			<td></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">1-Hydroxy-3-carboxy-2,2,5,5-tetramethylpyrrolidine . HCl (CPH)</td>
			<td>Enzo Life Sciences</td>
			<td>ALX-430-078-M250</td>
			<td></td>
		</tr>
		<tr height="49">
			<td height="49" style="height:49px;width:931px;">1-Hydroxy-4-[2-triphenylphosphonio)-acetamido]-2,2,6,6-tetramethylpiperidine, 1-Hydroxy-2,2,6,6-tetramethyl-4-[2-(triphenylphosphonio)acetamido]piperidinium dichloride ( mito-TEMPO-H)</td>
			<td style="width:196px;">Enzo Life Sciences</td>
			<td style="width:224px;">ALX-430-171-M005</td>
			<td style="width:643px;"></td>
		</tr>
		<tr height="49">
			<td height="49" style="height:49px;width:931px;">1-Hydroxy-2,2,6,6-tetramethylpiperidin-4-yl-trimethylammonium chloride . HCl (CAT1H)</td>
			<td style="width:196px;">Enzo Life Sciences</td>
			<td style="width:224px;">ALX-430-131-M250</td>
			<td style="width:643px;"></td>
		</tr>
		<tr height="32">
			<td height="32" style="height:32px;width:931px;">Heparin&#160;</td>
			<td style="width:196px;">Sagent Pharmaceuticals</td>
			<td style="width:224px;">NDC 25021-400-10</td>
			<td style="width:643px;"></td>
		</tr>
		<tr height="30">
			<td height="30" style="height:30px;">Diphenyliodonium chloride&#160;</td>
			<td style="width:196px;">Sigma Aldrich</td>
			<td>43088</td>
			<td style="width:643px;"></td>
		</tr>
		<tr height="26">
			<td height="26" style="height:26px;width:931px;">Deferoxamin mesylate salt</td>
			<td>Sigma Aldrich</td>
			<td style="width:224px;">D9533-1G</td>
			<td style="width:643px;"></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">Critoseal</td>
			<td>Leica</td>
			<td>39215003</td>
			<td></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">BRAND disposable BLAUBRAND&#160;micropipettes, intraMark</td>
			<td>Sigma Aldrich</td>
			<td>708733</td>
			<td>Capillaries</td>
		</tr>
		<tr height="40">
			<td height="40" style="height:40px;width:931px;">PTFE FRACTIONAL FLUOROPOLYMER TUBING 
			3/16&#8221; OD x 1/8&#8221; ID</td>
			<td>NORELL</td>
			<td>1598774A</td>
			<td>Teflon tubing&#160;</td>
		</tr>
		<tr height="35">
			<td height="35" style="height:35px;">SILICONE RUBBER STOPPERS FOR NMR SAMPLE TUBES&#160; FOR THIN WALL TUBES HAVING AN OD OF 4mm-5mm (3.2mm TO 4.2mm ID) TS-4-5-SR</td>
			<td>NORELL</td>
			<td>94987</td>
			<td></td>
		</tr>
		<tr height="35">
			<td height="35" style="height:35px;">EMXnano Bench-Top EPR spectrometer&#160;</td>
			<td>Bruker BioSpin GmbH</td>
			<td>E7004002</td>
			<td></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">EMX NANO TISSUE CELL</td>
			<td>Bruker BioSpin GmbH</td>
			<td>E7004542</td>
			<td></td>
		</tr>
	</tbody>
</table>

use of electron paramagnetic resonance in biological samples at ambient temperature and 77 k

The accurate and specific detection of reactive oxygen species (ROS) in different cellular and tissue compartments is essential to the study of redox-regulated signaling in biological settings. Electron paramagnetic resonance spectroscopy (EPR) is the only direct method to assess free radicals unambiguously. Its advantage is that it detects physiologic levels of specific species with a high specificity, but it does require specialized technology, careful sample preparation, and appropriate controls to ensure accurate interpretation of the data. Cyclic hydroxylamine spin probes react selectively with superoxide or other radicals to generate a nitroxide signal that can be quantified by EPR spectroscopy. Cell-permeable spin probes and spin probes designed to accumulate rapidly in the mitochondria allow for the determination of superoxide concentration in different cellular compartments.
In cultured cells, the use of cell permeable 1-hydroxy-3-methoxycarbonyl-2,2,5,5-tetramethylpyrrolidine (CMH) along with and without cell-impermeable superoxide dismutase (SOD) pretreatment, or use of cell-permeable PEG-SOD,&#160;allows for the differentiation of extracellular from cytosolic superoxide. The mitochondrial 1-hydroxy-4-[2-triphenylphosphonio)-acetamido]-2,2,6,6-tetramethyl-piperidine,1-hydroxy-2,2,6,6-tetramethyl-4-[2-(triphenylphosphonio)acetamido] piperidinium dichloride (mito-TEMPO-H) allows for measurement of mitochondrial ROS (predominantly superoxide).
Spin probes and EPR spectroscopy can also be applied to in vivo models. Superoxide can be detected in extracellular fluids such as blood and alveolar fluid, as well as tissues such as lung tissue. Several methods are presented to process and store tissue for EPR measurements and deliver intravenous 1-hydroxy-3-carboxy-2,2,5,5-tetramethylpyrrolidine (CPH) spin probe in vivo. While measurements can be performed at room temperature, samples obtained from in vitro and in vivo models can also be stored at -80 &#176;C and analyzed by EPR at 77 K. The samples can be stored in specialized tubing stable at -80 &#176;C and run at 77 K to enable a practical, efficient, and reproducible method that facilitates storing and transferring samples.

Superoxide detection using CMH was validated using the X/XO superoxide generating system to demonstrate that the nitroxide (CM.) signal was fully inhibited by SOD, while catalase had no effect&#160;(Figure 1A). The total, extracellular superoxide was then evaluated in RAW 264.7 cells by incubating cells with the cell-permeable CMH spin probe +/- SOD pretreatment. The nitroxide concentration was measured in both the cell suspension and buffer, which...

Watch this Scientific Journal Video about Use of Electron Paramagnetic Resonance in Biological Samples at Ambient Temperature and 77 K at JoVE.com

Use of Electron Paramagnetic Resonance in Biological Samples at Ambient Temperature and 77 K

Electron paramagnetic resonance (EPR) spectroscopy is an unambiguous method to measure free radicals. The use of selective spin probes allows for detection of free radicals in different cellular compartments. We present a practical, efficient method to collect biological samples that facilitate treating, storing, and transferring samples for EPR measurements.

The accurate and specific detection of reactive oxygen species (ROS) in different cellular and tissue compartments is essential to the study of ...

Dysregulated redox signaling is implicated in the pathogenesis of diverse diseases. The study of redox biology requires the accurate detection of reactive oxygen species in different cellular and tissue compartments. EPR spectroscopy is the only method that measures free radicals unambiguously.This protocol demonstrates a practical method for handling and storage of biologic samples for EPR spectroscopy. These protocols illustrate the use of EPR and spin probes in two representative models. Although they can be adapted to evaluate the active species in other biological settings.The design of the experiment and the handling of the sample are critical for its reproducibility. We recommend considering cell density and ensuring appropriate time-matched controls. Begin by gently washing raw 264.7 cells with one milliliter of Krebs-Henseleit Buffer or KHB, per well.And treat the cells with 500 microliters of KHB, supplemented with 100 micromil of DTPA per well. To pretreat with superoxide dismutase, add 15 microliters of superoxide dismutase stock, or vehicle, to each well, and place the plate at 37 degrees Celsius for 10 minutes. At the end of the superoxide dismutase pretreatment, add 12.5 microliters of 10 millimolar CMH and 40 microliters of 125 micromolar PMA working solution to the appropriate wells, and incubate at 37 degrees Celsius for 50 minutes.Immediately place the plates on ice and collect the buffer from each well into individual 1.5 milliliter tubes on ice. Next, add 100 microliters of fresh KHB plus DTPA to each well and gently scrape the cells from the bottom of each well. Then resuspend the cell suspensions with pipetting and transfer the cells into individual 1.5 milliliter tubes on ice.For superoxide detection at room temperature, first load 50 microliters of one buffer or cell sample into a capillary tube and seal the tube. Immediately place the tube into the electron paramagnetic resonance, or EPR, spectrometer and set the EPR acquisition parameters for room temperature measurements. Always test a blank sample of buffer containing the same concentration of probe treated under the same experimental conditions as a control.For superoxide detection at 77 degrees Kelvin, load 150 microliters of one sample into a one to two inch piece of straight polytetrafluoroethylene, or PTFE, tubing, with a rubber stopper at one end. Seal the other end of the tube with a second stopper and flash freeze the sample in liquid nitrogen. Then quickly remove the stoppers and place the PTFE tubing in a labeled cryotube for liquid nitrogen storage.For EPR measurements, fill the finger dewar of the EPR spectrometer with liquid nitrogen and place the PTFE tubing containing the sample in the liquid nitrogen. Place the finger dewar into the EPR spectrometer and set the EPR acquisition parameters for measurements at 77 degrees Kelvin. For ROS detection in frozen lung tissue, place the tissue on dry ice and use tweezers to stabilize the flash-frozen tissue on dry ice.Cut the sample into five 15 milligram pieces, and weigh the pieces in a tared 1.5 milliliter tube. Add 196 microliters of KHB plus DTPA and four microliters of CMH to the sample, and incubate the lung sample for one hour in a 37 degree Celsius water bath before pelleting the tissue fragments with a brief centrifugation. Then place the sample on ice before transferring 150 microliters of the supernatant into a piece of PTFE tubing for flash freezing in preparation of EPR measurement as just demonstrated.Evaluation of the total superoxide production in raw 264.7 cells stimulated with PMA as demonstrated, reveals that the nitroxide concentration in both the cell suspension and the buffer of the PMA-treated cells is similar, due to the permeable nature and rapid equilibration of the spin probe. The nitroxide radicals signal increases in raw 264.7 cells stimulated with PMA, compared to control cells, but not in cells pretreated with cell-impermeable superoxide dismutase. The concentration of nitroxide obtained at low temperatures in raw 264.7 cells after stimulation with PMA is also attenuated in the presence of superoxide dismutase consistent with the room temperature data.The nitroxide concentration is increased in the blood and bronchoalveolar lavage fluid of bleo mice and treated mice, as well as within the supernatants of harvested lung tissue pieces from bleo mice and injured animals, compared to PBS-treated controls. Further, after retro-orbital spin probe injection, bleo mice and treated animals demonstrate a higher spin probe signal compared to controls. These practical protocols will allow researchers to test free radical production in different cellular compartments and biological samples by EPR, including low temperature measurements.

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