Letter to the Editor regarding “Identification of the oleic acid ethanolamide (OEA) isomer cis-vaccenic acid ethanolamide (VEA) as a highly abundant 18:1 fatty acid ethanolamide in blood plasma from rats and humans”
Letter to the Editor regarding BIdentification of the oleic acid ethanolamide (OEA) isomer cis-vaccenic acid ethanolamide (VEA) as a highly abundant 18:1 fatty acid ethanolamide in blood plasma from rats and humans^
Dimitrios Tsikas 0
0 Centre of Pharmacology and Toxicology, Hannover Medical School , Carl-Neuberg-Str. 1, 30625 Hannover , Germany
Dear Editors, dear authors:
I read with great interest the recent research paper by
Röhrig et al. in Anal Bioanal Chem 2016 , which
reported on the unequivocal identification of cis-vaccenic acid
ethanolamide (VEA) in blood plasma from rats and
humans. VEA is an isomer of cis-oleic acid ethanolamide
(OEA). OEA, palmitic acid ethanolamide (PAE) and
stearic acid ethanolamide (SEA) were found to occur
physiologically in several biological samples in addition to the
endocannabinoid arachidonic acid ethanolamide
anandamide (AEA; reviewed in Ref. ). OEA, VEA, PEA, and
SEA are not endocannabinoids. Previously, we observed
by GC-MS/MS in the selected-reaction monitoring
(SRM) mode two chromatographic peaks with very similar
retention times. We identified the compound eluting at
17.86 min as OEA, yet the peak eluting at 17.92 remained
unknown . The findings by Röhrig et al.  suggest that
the unknown peak we observed in our study  is likely to
be VEA. Interestingly, the mean peak area ratio of OEA to
VEA in plasma samples from our group of about 3.5 is
close to the mean value of 2.4 reported by Röhrig et al.
for human plasma samples . In plasma of 16 apparently
healthy humans, we measured by GC-MS/MS OEA
concentrations of 18 ± 6 nM, which suggest an approximate
VEA mean concentration of 5 nM. Even this concentration
is higher than the plasma AEA concentration of 1.4 nM .
Previously, we demonstrated that a considerable fraction of
plasma OEA but not of AEA is due to laboratory
contamination . Yet, we did not investigate whether the putative
VEA may also originate from laboratory contamination or
from OEA derivatization and GC-MS/MS analysis, which
require must more drastic conditions compared with
Reply by the authors of :
We thank Dr. Dimitrios Tsikas for this highly
interesting comment, which provides an important link between
our study and Dr. Tsikas’ own excellent contributions in
Compliance with Ethical Standards
1. Röhrig W , Waibel R , Perlwitz C , Pischetsrieder M , Hoch T. Identification of the oleic acid ethanolamide (OEA) isomer cisvaccenic acid ethanolamide (VEA) as a highly abundant 18:1 fatty acid ethanolamide in blood plasma from rats and humans . Anal Bioanal Chem . 2016 ; 408 ( 22 ): 6141 - 51 .
2. Zoerner AA , Gutzki FM , Batkai S , May M , Rakers C , Engeli S , et al. Quantification of endocannabinoids in biological systems by chromatography and mass spectrometry: a comprehensive review from an analytical and biological perspective . Biochim Biophys Acta . 2011 ; 1811 (11): 706 - 23 .
3. Zoerner AA , Gutzki FM , Suchy MT , Beckmann B , Engeli S , Jordan J , et al. Targeted stable-isotope dilution GC-MS/MS analysis of the endocannabinoid anandamide and other fatty acid ethanol amides in human plasma . J Chromatogr B . 2009 ; 877 ( 26 ): 2909 - 23 .
4. Tsikas D. Identifying and quantifying contaminants contributing to endogenous analytes in gas chromatography/mass spectrometry . Anal Chem . 2010 ; 82 ( 18 ): 7835 - 41 .