Blood, sweat and fatty acids

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  • Published: Nov 1, 2016
  • Author: Ryan De Vooght-Johnson
  • Channels: Gas Chromatography
thumbnail image: Blood, sweat and fatty acids

Non-invasive

A new non-invasive method of sampling fatty acid methyl esters using filter paper to collect sweat could simplify the diagnosis of disrupted lipid metabolism.

‘Non-invasive’ is the current buzzword in molecular diagnostics. After all, why would you subject your patient to a barrage of painful and obtrusive tests when the oil “spills” of the human body allow us to look underneath the bonnet?

Urine, saliva, sweat, sputum and stools? Non-invasive. Blood and biopsies? Invasive. In general, a test that requires a breach of the skin or to poke within orifices is considered invasive. The hope, therefore, is that markers of interest seep over into our bodily secretions, where they can then be probed without cause of distress to the patient.

For Roman Kanď´ar and colleagues studying lipid metabolism at the University of Pardubice in the Czech Republic, sweat has caught their eye. Fatty acids, for instance, are released by the apocrine glands in the epidermis, which exploits the antimicrobial traits of these hydrophobic chains. Where better to look for these fatty acids then than within the skin’s sweaty secretions?

‘Currently there is great interest in simple and non-invasive methods of sample collection,’ explains Kanďár. However, he concedes that ‘only a few methods’ for sampling fatty acids in sweat exist.

Blood versus sweat

Writing in the Journal of Separation Science, Kanďár draws on the advantages of blood spots dried on a special filter paper: only a tiny drop of blood is required, the samples are easily transported and stored on a membrane, and the analytes remain stable for a long time. However, drying sweat on the same, treated filter would carry all those benefits in addition to being non-invasive, non-contagious, and practically available on tap (exertion willing).

Seizing the opportunity, the Czech researchers assembled 30 subjects who would donate their blood and then break a sweat on an exercise bike. His team collected their beads of salty secretions onto paper soaked with butylated hydroxytoluene, allowed them to dry over three hours, and then either analysed them or placed them on long-term storage at −20 °C.

To analyse the fatty acid profiles, Kanďár first converted the fatty acids to their methyl esters (FAMEs) under optimized conditions with acetyl chloride, separated these by gas chromatography (100-mm length HP-88 capillary column, 62-minute 120–197 °C gradient), and detected with a flame ionisation detector. FAMEs were identified by their retention times.

Stable, accurate and linear

Polyunsaturated fatty acids tend to oxidise and therefore new methods of sampling fatty acids must prove that oxidation is not a problem during the analysis. Although not discussed at great length, Kanďár states that degradation of FAMEs suspended in sweat samples stored on paper at −20 °C was minimal for up to three months.

Their method was able to detect and determine both short- and long-chain saturated and unsaturated fatty acids of 14–24-carbon length, some as low as 0.04 μg per 1-mL drop of sweat. Recovery of FAMEs with their optimised sample preparation strategy was generally good (92.6–99.3%).

Finally, Kanďár compared the determinations of FAMEs within the blood and sweat from each subject side-by-side—a correlation not studied hitherto—finding a strong and statistically significant linearity between the two, although admittedly determinations did not exactly match.

‘With more sensitive and specific techniques such as GC-MS, LC-MS, and MS/MS,’ the authors conclude, ‘we can improve and simplify the diagnosis of disturbances in lipid metabolism.’

Related Links

J. Sep. Sci., 2016, Early View paper. Kanď´ar et al. Determination of selected fatty acids in dried sweat spot using gas chromatography with flame ionization detection.

Experience L!fe: Everything You Always Wanted to Know About Sweat.

Article by Ryan De Vooght-Johnson

The views represented in this article are solely those of the author and do not necessarily represent those of John Wiley and Sons, Ltd.

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