Abstract
The paracloacal glands are the most prevalent scent glands in marsupials, and previous investigation of their secretions in the brushtail possum (Trichosurus vulpecula) has identified many odorous compounds together with large amounts of neutral lipids. We have examined the lipids by LC–MS, generating ammonium adducts of acylglycerols by electrospray ionisation. Chromatograms showed a complex mixture of coeluting acylglycerols, with m/z from about 404 to 1048. Plots of single [M + NH4]+ ions showed three groups of lipids clearly separated by retention time. MS–MS enabled triacylglycerols and diacylglycerol ethers to be identified from neutral losses and formation of diacylglycerols and other product ions. The earliest-eluting lipids were found to be triacylglycerol estolides, in which a fourth fatty acid forms an ester link with a hydroxy fatty acid attached to the glycerol chain. This is the first report of triacylglycerol estolides in animals. They form a complex mixture with the triacylglycerols and diacylglycerol ethers of lipids with short- and long-chain fatty acids with varying degrees of unsaturation. This complexity suggests a functional role, possibly in social communication.
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Abbreviations
- FA:
-
Fatty acid(s)
- hFA:
-
Hydroxy fatty acid(s)
- FAME:
-
Fatty acid methyl ester(s)
- TMS:
-
Trimethylsilyl derivative
- TAG:
-
Triacylglycerol(s)
- DAGE:
-
Diacylglycerol ether(s)
- EST:
-
Estolide(s), an ester formed from a FA and an hFA; also the abbreviation for TAG-estolide
- Lyso:
-
Diacylglycerol product ion
- NL:
-
Neutral loss
- GC–MS:
-
Gas chromatography–mass spectrometry
- LC–MS:
-
Liquid chromatography–mass spectrometry
- UPLC:
-
Ultra high performance liquid chromatography
- EI:
-
Electron ionisation
- ESI:
-
Electrospray ionisation
- RT:
-
Retention time
- ESM:
-
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Acknowledgments
We thank Euan Thompson and Taryn Skinner (AgResearch Invermay, Mosgiel, New Zealand) for the capture and care of the possums and for dissection of the glands. We also thank Dr. Richard Wilson (Central Science Laboratory, University of Tasmania) for generating the accurate mass data. Funding for this study was provided by the Division of Pharmacy, School of Medicine, University of Tasmania. We are grateful to the anonymous referees for their comments which improved the manuscript.
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The number of carbon atoms and double bonds in fatty acids and acyl groups is indicated as Cn:x. The total number of radyl (acyl or alkyl) carbons attached to glycerol for each lipid type is given with the total number of acyl double bonds, e.g. TAG 30:1, DAGE 31:1, EST 50:3. The fatty acid composition is shown as a list which does not specify the sn-positions, e.g. 7:0/9:0/17:0. The alkyl substituent in DAGE is marked with the ether link, e.g. 7:0/7:0/e16:0. The fourth acyl substituent in TAG-estolides is similarly indicated as 7:0/7:0/h18:1–18:2.
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McLean, S., Davies, N.W., Nichols, D.S. et al. Triacylglycerol Estolides, a New Class of Mammalian Lipids, in the Paracloacal Gland of the Brushtail Possum (Trichosurus vulpecula). Lipids 50, 591–604 (2015). https://doi.org/10.1007/s11745-015-4025-9
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DOI: https://doi.org/10.1007/s11745-015-4025-9