Name: measuring nitrite and nitrate, metabolites in the nitric oxide pathway, in biological materials using the chemiluminescence method
Uploaded: 2016-12-25T15:00:00
Description: Watch this Scientific Journal Video about Measuring Nitrite and Nitrate, Metabolites in the Nitric Oxide Pathway, in Biological Materials using the Chemiluminescence Method at JoVE.com

Authors want to acknowledge critical contributions of Dr A. Dejam and M. M. Pelletier in developing the use of nitrite preserving solution for the nitrite measurements in blood.

All protocols including use of animals were approved for use by NIDDK Animal Care and Use Committee and human blood was obtained from NIH Blood bank from healthy donors.
1. Sample Preparation
<ol>
	<li>Preparation of nitrite preserving solution
	<ol>
		<li>Prepare a solution containing 890 mM potassium ferricyanide (K3Fe(CN)6) and 118 mM NEM (N-ethylmaleimide) in distilled water. Dissolve well until it is clear yellow with no crystals present. Add NP-40...

<ol>
	<li>Piknova, B., Schechter, A. N. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Measurement+of+Nitrite+in+Blood+Samples+Using+the+Ferricyanide-Based+Hemoglobin+Oxidation+Assay.">Measurement of Nitrite in Blood Samples Using the Ferricyanide-Based Hemoglobin Oxidation Assay.</a> Methods Mol Biol. 704, 39-56 (2011).</li><li>Nagababu, E., Rifkind, J. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Measurement+of+plasma+nitrite+by+chemiluminescence+without+interference+of+S-,+N-nitroso+and+nitrated+species.">Measurement of plasma nitrite by chemiluminescence without interference of S-, N-nitroso and nitrated species.</a> Free Radic Biol Med. 42, 1146-1154 (2007).</li><li>Pinder, A. G., Rogers, S. C., Khalatbari, A., Ingram, T. E., James, P. E., Hancock, J. T. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+measurement+of+nitric+oxide+and+its+metabolites+in+biological+samples+by+ozone-based+chemiluminescence.">The measurement of nitric oxide and its metabolites in biological samples by ozone-based chemiluminescence.</a> Methods in Molecular Biology, Redox-Mediated Signal Transduction. 476, 11-28 (2008).</li><li>Pelletier, M. M., Kleinbongard, P., Ring-wood, L., Hito, R., Hunter, C. J., Schechter, A. N., 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+measurement+of+blood+and+plasma+nitrite+by+chemiluminescence:+pitfalls+and+solutions.">The measurement of blood and plasma nitrite by chemiluminescence: pitfalls and solutions.</a> Free Radic Biol Med. 41, 541-548 (2006).</li><li>Mac Arthur, P. H., Shiva, S., Gladwin, M. T. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Measurement+of+circulating+nitrite+and+S-nitrosothiols+by+reductive+chemiluminescence.">Measurement of circulating nitrite and S-nitrosothiols by reductive chemiluminescence.</a> J Chromatogr B. 851, 93-105 (2007).</li><li>Bryan, N. S., Grisham, M. B. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Methods+to+detect+nitric+oxide+and+its+metabolites+in+biological+samples.">Methods to detect nitric oxide and its metabolites in biological samples.</a> Free Radic Biol Med. 43, 645-657 (2007).</li><li>Hendgen-Cotta, U., Grau, M., Rasaaf, T., Gharinin, P., Kelm, M., Kleinbongard, P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Reductive+gas-phase+chemiluminescence+and+flow+injection+analysis+for+measurement+of+nitric+oxide+pool+in+biological+matrices.">Reductive gas-phase chemiluminescence and flow injection analysis for measurement of nitric oxide pool in biological matrices.</a> Method Enzymol. 441, 295-315 (2008).</li><li>Yang, B. K., Vivas, E. X., Reiter, C. D., Gladwin, M. T. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Methodologies+for+the+sensitive+and+specific+measurement+of+S-nitrosothiols,+iron-nitrosyls+and+Nitrite+in+biological+samples.">Methodologies for the sensitive and specific measurement of S-nitrosothiols, iron-nitrosyls and Nitrite in biological samples.</a> Free Radic Res. 37, 1-10 (2003).</li><li>Sm&#225;rason, A. K. 1., Allman, K. G., Young, D., Redman, C. W. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Elevated+levels+of+serum+nitrate,+a+stable+end+product+of+nitric+oxide,+in+women+with+pre-eclampsia.">Elevated levels of serum nitrate, a stable end product of nitric oxide, in women with pre-eclampsia.</a> Br J Obstet Gynaecol. 104 (5), 538-543 (1997).</li><li>Beckman, J. S., Congert, K. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Direct+Measurement+of+Dilute+Nitric+Oxide+in+Solution+with+an+Ozone+Chemiluminescent+Detector.">Direct Measurement of Dilute Nitric Oxide in Solution with an Ozone Chemiluminescent Detector.</a> Methods: A companion to Methods in Enzymology. 7, 35-39 (1995).</li><li>Bates, J. N. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Nitric+oxide+measurements+by+chemiluminescence+detection.">Nitric oxide measurements by chemiluminescence detection.</a> Neuroprotocols: A companion to Methods in Neuroscience. 1, 141-149 (1992).</li></ol>

Critical Steps within the Protocol
Aliquots of all solutions (including the water) used to prepare, dilute or otherwise treat original samples have to be saved and checked for possible nitrite or (more often) nitrate contamination. We found that most contamination comes from water and many chemicals used to treat sample (ferricyanide in particular) also contain significant amount of nitrate contamination in some lots that interferes with the endogenous nitrate determination. We therefore check al...

Nitrite, and to a less extend nitrate, levels in blood reflect overall state of body NO metabolism. Nitrite concentrations in blood and most organs and tissues are only in high nanomolar or low micromolar range, nitrate is usually present in much higher amounts &#8212; in micromolar range. Changes in nitrite levels due to disease progression or changes in dietary habits are quite small and can be only measured using a very sensitive method. Because of their very different levels and different metabolic processes, separate determination of nitrite and nitrate levels is essential. So-called &#34;NOx determination&#34; where nitrite and nitrate are measured together has very little value.
Several methods for quantifying nitrite in various biological samples have been developed&#160;&#8212; the most common being the oldest one, based on the Griess reaction that had been originally described in 1879. Even with modern modifications, the sensitivity limit for nitrite attainable by Griess&#39; method is in low micromolar range. Chemiluminescence (CL), combined with tri-iodide reducing solution, is currently considered the most sensitive method, allowing quantification in the low nanomolar range of nitrite concentrations1-8,10,11. The same CL method, combined with vanadium(III) chloride reducing solution, can be used for sensitive measurements of nitrate, with precision in the nanomolar range9.
CL detects free gas NO. Therefore, nitrite, nitrate, R-nitrosothiols (R-SNO), R-nitrosoamines (R-NNO), or metal-NO compounds (later in manuscript referred as &#34;R-(X)-NO&#34;), must be converted into free NO gas in order to quantify their original amounts via CL. Conversion to NO is achieved using several different reducing solutions, depending on the nature of the NO metabolite. After conversion, free NO gas is purged from the reaction vessel by a carrier gas (He, N2 or Ar) into the reaction chamber of CL analyzer where ozone (O3) is combined with NO to form nitrogen dioxide (NO2) in its activated state. With return to the ground state, NO2* emits in infrared region and emitted photon is detected by photomultiplier (PMT) of CL instrument. The intensity of emitted light is directly proportional to NO concentration in reaction chamber, which allows calculation of the concentration of the original species using proper calibration curves.
In our protocol, we first present CL-based determination of nitrite and nitrate in the most used clinical settings &#8212; in blood and plasma, and then we discuss how to determine these ions in tissue samples. We also explain in detail how to preserve the original physiological nitrite concentration in nitrite-reactive environments, such as blood and its compartments, plasma and red blood cells.

<table border="0" cellpadding="0" cellspacing="0" width="812">
	<colgroup>
		<col />
		<col />
		<col />
		<col />
	</colgroup>
	<tbody>
		<tr height="26">
			<td height="26" style="height:26px;width:351px;">potassium ferricyanide; K3Fe(CN)6</td>
			<td style="width:135px;">Sigma</td>
			<td style="width:119px;">702587</td>
			<td style="width:207px;"></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">NEM; N-ethylmaleimide</td>
			<td style="width:135px;">Sigma</td>
			<td>4260</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">NP-40; 4-Nonylphenyl-polyethylene glycol</td>
			<td style="width:135px;">Sigma</td>
			<td style="width:119px;">74385</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">sulfanilamide; AS&#160;</td>
			<td style="width:135px;">Sigma</td>
			<td>S9251</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:351px;">HCl</td>
			<td style="width:135px;">Sigma</td>
			<td style="width:119px;">H1758</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:351px;">acetic acid, glacial</td>
			<td style="width:135px;">Sigma</td>
			<td style="width:119px;">A9967</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">ascorbic acid&#160;</td>
			<td style="width:135px;">Sigma</td>
			<td style="width:119px;">A7506</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:351px;">potassium iodide; KI</td>
			<td style="width:135px;">Sigma</td>
			<td style="width:119px;">60399</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:351px;">iodine; I2</td>
			<td style="width:135px;">Sigma</td>
			<td style="width:119px;">207772</td>
			<td>light sensitive, toxic</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:351px;">sodium nitrite; NaNO2</td>
			<td style="width:135px;">Sigma</td>
			<td>563218</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:351px;">vanadium(III) chloride; VCl3</td>
			<td style="width:135px;">Sigma</td>
			<td style="width:119px;">208272</td>
			<td>ligt sensitive, toxic</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:351px;"></td>
			<td style="width:135px;"></td>
			<td style="width:119px;"></td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:351px;"></td>
			<td style="width:135px;"></td>
			<td style="width:119px;"></td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">GentleMac</td>
			<td style="width:135px;">Miltenyi</td>
			<td style="width:119px;"></td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Sievers NOA 280i</td>
			<td style="width:135px;">GE</td>
			<td style="width:119px;"></td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">CLD 88Y</td>
			<td style="width:135px;">&#160;Ecophysics&#160;</td>
			<td style="width:119px;"></td>
			<td></td>
		</tr>
	</tbody>
</table>

measuring nitrite and nitrate, metabolites in the nitric oxide pathway, in biological materials using the chemiluminescence method

Nitric oxide (NO) is one of the main regulator molecules in vascular homeostasis and also a neurotransmitter. Enzymatically produced NO is oxidized into nitrite and nitrate by interactions with various oxy-heme proteins and other still not well known pathways. The reverse process, reduction of nitrite and nitrate into NO had been discovered in mammals in the last decade and it is gaining attention as one of the possible pathways to either prevent or ease a whole range of cardiovascular, metabolic and muscular disorders that are thought to be associated with decreased levels of NO. It is therefore important to estimate the amount of NO and its metabolites in different body compartments &#8212; blood, body fluids and the various tissues. Blood, due to its easy accessibility, is the preferred compartment used for estimation of NO metabolites. Due to its short lifetime (few milliseconds) and low sub-nanomolar concentration, direct reliable measurements of blood NO in vivo present great technical difficulties. Thus NO availability is usually estimated based on the amount of its oxidation products, nitrite and nitrate. These two metabolites are always measured separately. There are several well established methods to determine their concentrations in biological fluids and tissues. Here we present a protocol for chemiluminescence method (CL), based on spectrophotometrical detection of NO after nitrite or nitrate reduction by tri-iodide or vanadium(III) chloride solutions, respectively. The sensitivity for nitrite and nitrate detection is in low nanomolar range, which sets CL as the most sensitive method currently available to determine changes in NO metabolic pathways. We explain in detail how to prepare samples from biological fluids and tissues in order to preserve original amounts of nitrite and nitrate present at the time of collection and how to determine their respective amounts in samples. Limitations of the CL technique are also explained.

Figure 2 shows representative results collected from standards and five different samples. As shown in this figure, photomultiplier voltage increases immediately after nitrite-containing solution (standards or samples) is injected into reducing solution (injections times are indicated by red arrows below the curve) and returns to the baseline value once all nitrite present in the injected solution was reduced. It is also clear from this figure that accurate volume measure...

Watch this Scientific Journal Video about Measuring Nitrite and Nitrate, Metabolites in the Nitric Oxide Pathway, in Biological Materials using the Chemiluminescence Method at JoVE.com

Measuring Nitrite and Nitrate, Metabolites in the Nitric Oxide Pathway, in Biological Materials using the Chemiluminescence Method

Nitric oxide (NO) is an important signaling molecule in vascular homeostasis. NO production in vivo is too low for direct measurement. Chemiluminescence provides useful insight into NO cycle via measuring its precursors and oxidation products, nitrite and nitrate. Nitrite / nitrate determination in body tissues and fluids is explained.

Nitric oxide (NO) is one of the main regulator molecules in vascular homeostasis and also a neurotransmitter. Enzymatically produced NO is oxidized into ...

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