The authors would like to acknowledge the contribution of Meritxell Romeu-Nadal to the rat study.

1. Animal Procedures
<ol>
	<li>All animal work should be carried out in accordance with the Home Office Animals (Scientific Procedures) Act (1986).</li>
	<li>Mate Wistar rats aged 10 weeks old by monogamous breeding, and confirm pregnancy by the appearance of a vaginal plug. Record this as day 1 of gestation, and commence experimental diet. For virgin females, house each rat individually, and commence experimental diet.</li>
	<li>After feeding the experimental diets for 20 days euthanize rats by CO2 asphyxia...

<ol>
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Chem. 52 (12), 2265-2272 (2006).</li><li>Lauritzen, L., Carlson, S. E. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Maternal+fatty+acid+status+during+pregnancy+andlactation+and+relation+to+newborn+and+infant+status.">Maternal fatty acid status during pregnancy andlactation and relation to newborn and infant status.</a> Matern. Child Health. 7 (2), 41-58 (2011).</li><li>Kelsall, C. 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=Vascular+dysfunction+induced+in+offspring+by+maternal+dietary+fat+involves+altered+arterial+polyunsaturated+fatty+acid+biosynthesis.">Vascular dysfunction induced in offspring by maternal dietary fat involves altered arterial polyunsaturated fatty acid biosynthesis.</a> PLoS One. 7 (4), (2012).</li><li>Karpe, F., Dickmann, J. R., Frayn, K. N. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Fatty+acids,+obesity,+and+insulin+resistance:+time+for+a+re-evaluation.">Fatty acids, obesity, and insulin resistance: time for a re-evaluation.</a> Diabetes. 60 (10), 2441-2449 (2011).</li><li>Mossoba, M. M., Moss, J., Kramer, J. K. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Trans+fat+labelling+and+levels+in+U.S.+foods:+assessment+of+gas+chromatographic+and+infrared+spectroscopic+techniques+for+regulatory+compliance.">Trans fat labelling and levels in U.S. foods: assessment of gas chromatographic and infrared spectroscopic techniques for regulatory compliance.</a> J. AOAC Int. 92 (5), 1284-1300 (2009).</li><li>Chee, K. 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=Fatty+acid+content+of+marine+oil+capsules.">Fatty acid content of marine oil capsules.</a> Lipids. 25 (9), 523-528 (1990).</li><li>Folch, J., Lees, M., Sloane-Stanley, G. 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+simple+method+for+the+isolation+and+purification+of+total+lipids+from+animal+tissues.">A simple method for the isolation and purification of total lipids from animal tissues.</a> J. Biol. Chem. 226 (1), 497-509 (1957).</li><li>Burdge, G. C., Wright, P., Jones, E. A., Wootton, S. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+method+for+separation+of+phosphatidylcholine,+triacylglycerol,+non-esterified+fatty+acids+and+cholesterol+esters+from+plasma+by+solid-phase+extraction.">A method for separation of phosphatidylcholine, triacylglycerol, non-esterified fatty acids and cholesterol esters from plasma by solid-phase extraction.</a> Br. J. Nutr. 84 (5), 781-787 (2000).</li><li>Sepp&#228;nen-Laakso, T., Laakso, I., Hiltunen, R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Analysis+of+fatty+acids+by+gas+chromatography,+and+its+relevance+to+research+on+health+and+nutrition.">Analysis of fatty acids by gas chromatography, and its relevance to research on health and nutrition.</a> Anal. Chim. Acta. 465 (1), 39-62 (2002).</li><li>Beesley, T. E., Buglio, B., Scott, R. P. W. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> Quantitative chromatographic analysis. , (2000).</li><li>Bartle, K. D., Myers, P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=History+of+gas+chromatography.">History of gas chromatography.</a> Trends Anal. Chem. 21 (9), 9-10 (2002).</li><li>Childs, C. E. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> The effect of gender, pregnancy and diet upon rat tissue fatty acid composition and immune function. , 378 (2008).</li><li>Harris, S. W., Pottala, J. V., Ramachandran, S. V., Larson, M. G., Robins, S. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Changes+in+erythrocyte+membrane+Trans+and+marine+fatty+acids+between+1999+and+2006+in+older+Americans.">Changes in erythrocyte membrane Trans and marine fatty acids between 1999 and 2006 in older Americans.</a> J. Nutr. 142 (7), 1297-1303 (2012).</li><li>Roberts, L. D., McCombie, G., Titman, C. M., Griffin, J. L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+matter+of+fat:+An+introduction+to+lipidomic+profiling+method.">A matter of fat: An introduction to lipidomic profiling method.</a> J. Chromatogr. B. 871 (2), 174-181 (2008).</li></ol>

Gas chromatography is an accurate technique to use for fatty acid analysis, and its high reproducibility deems this technique suitable for clinical analyses.&#160;Appropriate GC columns must be used to enable identification of fatty acids of interest, with available columns having variations in the polarity of the stationary phase, column length and internal diameter. The use of a fused silica capillary column in this method of analysis provides good thermal stability and high reproducibility of retention times due to it...

Gas chromatography (GC) is a well-established technique used to identify and quantify the incorporation of fatty acids into lipid pools and cell membranes1,2 during supplementation or physiological conditions such as obesity (and related diseases such as diabetes) or pregnancy3-5. It is also suitable for analyzing the types and quantities of fats in foods. This is useful when characterizing experimental diets, as well as ensuring that the food industry complies with regulations. For example, GC can be used to confirm the identity and quantity of fatty acids within a product such as a dietary supplement to ensure that labeling is correct and regulations are adhered to6,7. &#160;Analysis of fatty acids can provide valuable insights into lipid metabolism in health and disease, the impact of dietary change, and the effect of changes in physiological state8. Use of GC to study samples during pregnancy has provided important information on changes in fatty acid and complex lipid homeostasis3.

In advance of the chromatographic separation, lipids are typically extracted from the sample using the solubility of lipids in solvent mixtures of chloroform and methanol. Sodium chloride is added to facilitate the separation of the mixture into aqueous and organic lipid containing phases9,10. Complex lipid classes of interest can be separated from the total lipid extract by solid phase extraction (SPE). This separation technique elutes lipid classes based upon their polarity or binding affinity. Triacyglycerols (TAG) and cholesteryl esters (CE) are eluted first as a combined fraction, further classes, phosphatidylcholine (PC), Phosphatidylethanolamine (PE), and non-esterified fatty acids (NEFA) are eluted by increasing the polarity of the eluting solvent. The separation of TAG from CE exploits the binding of TAG only to a fresh SPE cartridge, allowing CE to be eluted. TAG can then be eluted by increasing the polarity of the eluting solvent9,10. This method allows multiple samples to be separated simultaneously with a higher yield than is achieved with thin layer chromatography, which means that relatively small&#160;sized samples (e.g. &#60;100 &#181;l plasma or serum, &#60;100 mg tissue) can be analyzed11,12.

GC is a well-established technique first described in the 1950s; it was suggested that the mobile phase in the then liquid-liquid systems could be replaced with vapor. It was initially used for petroleum analysis but rapidly expanded into other areas such as amino acid analysis and lipid biochemistry, which is still of major interest. Advances in GC equipment and technology such as the development of capillary columns from the previously used packed columns has led to our current techniques in which fatty acids are able to be separated more efficiently at lower temperatures resulting in GC being routinely used to identify and quantify fatty acids in a wide range of investigations13.

GC requires fatty acids to be derivatized in order that they may become sufficiently volatile to be eluted at reasonable temperatures without thermal decomposition. This usually involves the substitution of a functional group containing hydrogen to form esters, thioesters or amides for analysis. Methyl esters are commonly studied derivatives, which are produced by methylation. In this method the ester bonds in complex lipids are hydrolyzed to release free fatty acids, which are transmethylated to form fatty acid methyl esters (FAME).&#160;The resulting profile of FAME, determined by GC, is referred to as the fatty acid composition and may be easily compared between different experimental groups9,10. The technique allows both the proportions of individual fatty acids and their concentrations to be measured.

In addition to the use of GC for analyzing fatty acids in nutrition studies and within the food industry, the technique can be used across a wide range of analytical fields. For example, environmental analyses using GC include measuring water contamination by insecticides and soil analyses measuring chlorobenzene content. In toxicology, GC has also been used to identify illegal substances in urine and blood samples of individuals; such a sports performance enhancers12 and the ability to separate complex mixtures of hydrocarbons makes this technique popular in the petroleum industry for petrochemical analysis12.

Pregnancy is associated with significant changes to the fatty acid composition of maternal tissues, specifically in the content of omega-3 (n-3) and omega-6 (n-6) polyunsaturated fatty acids (PUFA)3.&#160; In the current study, we exemplify the use of GC in the measurement of fatty acids by describing its use in the analysis of the fatty acid composition of liver tissue taken from virgin and pregnant rats fed low and high fat diets with different oil sources. The experimental diets provided here were a low fat soybean oil based diet, a high-fat soybean oil-based diet (130.9 g total fat/kg total fat) or a high-fat linseed oil-based diet (130.9 g total fat/kg diet), provided for 20 days.&#160;The full nutrient and fatty acid composition of these diets have been described previously14. The soybean oil diets are rich in linoleic acid (18:2n-6) and contain some &#945;-linolenic acid (18:3n-3) while the linseed oil diet is rich in &#945;-linolenic acid. These high-fat diets represent different rations of linoleic to &#945;-linolenic acids (rations of 8:1 and 1:1, respectively). The method for isolation of individual lipid classes and analysis by GC is well established and validated, and has been published previously10 but without the detailed technical description found herein.

<table border="0" cellpadding="0" cellspacing="0">
	<tbody>
		<tr>
			<td>Methanol:</td>
			<td>Fisher Scientific</td>
			<td>M/4056/17</td>
			<td>&#39;CAUTION&#39; Fumes - HPLC Grade</td>
		</tr>
		<tr>
			<td>Chloroform:</td>
			<td>Fisher Scientific</td>
			<td>C/4966/17</td>
			<td>&#39;CAUTION&#39; Fumes - HPLC Grade</td>
		</tr>
		<tr>
			<td>BHT:</td>
			<td>Sigma- Aldrich</td>
			<td>W218405</td>
			<td>&#39;CAUTION&#39; Dust fumes - Anhydrous</td>
		</tr>
		<tr>
			<td>NaCl</td>
			<td>Sigma- Aldrich</td>
			<td>S9888</td>
			<td>Anhydrous</td>
		</tr>
		<tr>
			<td>Hexane</td>
			<td>Fisher Scientific</td>
			<td>H/0406/17</td>
			<td>&#39;CAUTION&#39; Fumes - HPLC Grade</td>
		</tr>
		<tr>
			<td>Glacial acetic acid</td>
			<td>Sigma- Aldrich</td>
			<td>695084</td>
			<td>&#39;CAUTION&#39; Burns - 99.85%</td>
		</tr>
		<tr>
			<td>Sulfuric acid</td>
			<td>Sigma- Aldrich</td>
			<td>339741</td>
			<td>&#39;CAUTION&#39; Burns - 99.999%</td>
		</tr>
		<tr>
			<td>Potassium carbonate</td>
			<td>Sigma- Aldrich</td>
			<td>209619</td>
			<td>99% ACS Reagent grade</td>
		</tr>
		<tr>
			<td>Potassium bicarbonate</td>
			<td>Sigma- Aldrich</td>
			<td>237205</td>
			<td>99.7% ACS Reasgent grade</td>
		</tr>
		<tr>
			<td>Ethyl acetate</td>
			<td>Fisher Scientific</td>
			<td>10204340</td>
			<td>&#39;CAUTION&#39; Fumes - 99+% GLC SpeciFied</td>
		</tr>
		<tr>
			<td>Toluene</td>
			<td>Fisher Scientific</td>
			<td>T/2300/15</td>
			<td>&#39;CAUTION&#39; Fumes</td>
		</tr>
		<tr>
			<td>Diethyl ether</td>
			<td>Sigma- Aldrich</td>
			<td>309966</td>
			<td>&#39;CAUTION&#39; Fumes</td>
		</tr>
		<tr>
			<td>Nitrogen (oxygen free) cylinder</td>
			<td>BOC</td>
			<td>44-w</td>
			<td>&#39;CAUTION&#39; Compressed gas - explosion risk</td>
		</tr>
		<tr>
			<td>Aminopropyl silica SPE cartridges</td>
			<td>Agilent</td>
			<td>12102014</td>
			<td>Cartridge - Bead mass 100mg</td>
		</tr>
		<tr>
			<td>Silica gel SPE cartidges</td>
			<td>Agilent</td>
			<td>14102010</td>
			<td>Cartridge - Bead mass 100mg</td>
		</tr>
		<tr>
			<td>Molecular seives</td>
			<td>Sigma- Aldrich</td>
			<td>334324</td>
			<td>Pellets, AW-300, 1.6mm</td>
		</tr>
		<tr>
			<td>Glass pasteur pipettes</td>
			<td>Fisher Scientific</td>
			<td>FB50251</td>
			<td></td>
		</tr>
		<tr>
			<td>Borosilicate glass test tube</td>
			<td>Fisher Scientific</td>
			<td>FB59527</td>
			<td>Non-screw cap</td>
		</tr>
		<tr>
			<td>Screw thread glass test tubes</td>
			<td>Fisher Scientific</td>
			<td>FB59555</td>
			<td>13mm</td>
		</tr>
		<tr>
			<td>Caps for screw thread test tubes</td>
			<td>Fisher Scientific</td>
			<td>FB51353</td>
			<td>To fit 13mm tube</td>
		</tr>
		<tr>
			<td>Solida phase extraction (SPE) tank</td>
			<td>Agilent</td>
			<td></td>
			<td>VacElut 20 Manifold</td>
		</tr>
		<tr>
			<td>Luer stopcocks for SPE tank</td>
			<td>Agilent</td>
			<td>12131005</td>
			<td></td>
		</tr>
		<tr>
			<td>Vacuum pump</td>
			<td>Sigma- Aldrich</td>
			<td>2656-194GB-1EA</td>
			<td></td>
		</tr>
		<tr>
			<td>GC vials</td>
			<td>Kinesis</td>
			<td>STV 12-03TS</td>
			<td>Short thread 9mm, TPX 0.2ml fused glass insert</td>
		</tr>
		<tr>
			<td>GC vial lids</td>
			<td>Kinesis</td>
			<td>SCC09-0.2B</td>
			<td>Short thread 9mm blue</td>
		</tr>
		<tr>
			<td>GC inlet liners</td>
			<td>SGE Analytical science</td>
			<td>092002</td>
			<td>Split/splitless Focus liner ID 4mm, OD 6.3mm length 78.5mm</td>
		</tr>
		<tr>
			<td>GC septa</td>
			<td>SGE Analytical science</td>
			<td>041856</td>
			<td>11mm, MN material</td>
		</tr>
		<tr>
			<td>GC column</td>
			<td>SGE Analytical science</td>
			<td>054612</td>
			<td>Length 30m, ID 0.22mm, Film thickness 0.25&#181;m</td>
		</tr>
		<tr>
			<td>Gas chromatograph</td>
			<td></td>
			<td></td>
			<td>HP 6890 series</td>
		</tr>
	</tbody>
</table>

the use of gas chromatography to analyze compositional changes of fatty acids in rat liver tissue during pregnancy

Gas chromatography (GC) is a highly sensitive method used to identify and quantify the fatty acid content of lipids from tissues, cells, and plasma/serum, yielding results with high accuracy and high reproducibility. In metabolic and nutrition studies GC allows assessment of changes in fatty acid concentrations following interventions or during changes in physiological state such as pregnancy. Solid phase extraction (SPE) using aminopropyl silica cartridges allows separation of the major lipid classes including triacylglycerols, different phospholipids, and cholesteryl esters (CE). GC combined with SPE was used to analyze the changes in fatty acid composition of the CE fraction in the livers of virgin and pregnant rats that had been fed various high and low fat diets. There are significant diet/pregnancy interaction effects upon the omega-3 and omega-6 fatty acid content of liver CE, indicating that pregnant females have a different response to dietary manipulation than is seen among virgin females.

The success of this method is dependent on following the protocol precisely and on using clean solvents and reagents in order to reduce &#8216;noise&#8217; and contamination that can appear on a chromatogram. Contaminated samples are more challenging to analyze, lowering the accuracy of the area under the curve calculations. If the protocol is followed successfully a chromatogram with clear symmetrical, well defined peaks and with minimal background noise should be obtained as illustrated in Figure 3. If...

Watch this Scientific Journal Video about The Use of Gas Chromatography to Analyze Compositional Changes of Fatty Acids in Rat Liver Tissue during Pregnancy at JoVE.com

The Use of Gas Chromatography to Analyze Compositional Changes of Fatty Acids in Rat Liver Tissue during Pregnancy

Pregnancy leads to significant changes to the fatty acid composition of maternal tissues. Lipid profiles can be obtained via gas chromatography to allow identification and quantification of fatty acids in individual lipid classes among rats fed various high and low fat diets during pregnancy.

Gas chromatography (GC) is a highly sensitive method used to identify and quantify the fatty acid content of lipids from tissues, cells, and plasma/serum, ...

The Use of Gas Chromatography to Analyze Compositional Changes of Fatty Acids in Rat Liver Tissue during Pregnancy

Abstract