The Linoleic Acid Content of the Stratum Corneum of Ichthyotic Golden Retriever Dogs Is Reduced as Compared to Healthy Dogs and a Significant Part Is Oxidized in Both Free and Esterified Forms.

Iuliana Popa,Didier Pin,Marek Haftek,Audrey Solgadi,Adrian L Watson,Jacques Portoukalian

doi:10.3390/metabo11120803

Abstract

Golden Retrievers may suffer from Pnpl1-related inherited ichthyosis. Our study shows that in the stratum corneum (SC) of ichthyotic dogs, linoleic acid (LA) is also present in the form of 9-keto-octadecadienoic acid (9-KODE) instead of the acylacid form as in normal dogs. The fatty acids purified from SC strips (LA, acylacids) were characterized by liquid chromatography-tandem mass spectrometry (LC-MS) and atmospheric pressure chemical ionization (APCI). Electrospray ionization (ESI) and MS2(MS/MS Tandem mass spectrum/spectra)/M3 (MS/MS/MS Tandem mass spectrum/spectra) fragmentation indicated the positions of the double bonds in 9-KODE. We showed that ichthyotic dogs have a threefold lower LA content in the form of acylacids. The MS2 fragmentation of acyl acids showed in some peaks the presenceof an ion at the m/z 279, instead of an ion at m/z 293 which is characteristic of LA. The detected variant was identified upon MS3 fragmentation as 9-keto-octadecadienoic acid (9-KODE), and the level of this keto-derivative was increased in ichthyotic dogs. We showed by the APCI that such keto forms of LA are produced from hydroperoxy-octadecadienoic acids (HpODE) upon dehydration. In conclusion, the free form of 9-KODE was detected in ichthyotic SC up to fivefold as compared to unaffected dogs, and analyses by HPLC (High performance liquid chromatography) and ESI-MS (Electrospray Ionization-Mass Spectrometry) indicated its production via dehydration of native 9-HpODE.

Highlights

Linoleic acid is one of the two essential fatty acids for humans and other mammals, the second being alpha-linolenic acid
As reported in our recent study [2], the free fatty acid fractions of canine stratum corneum (SC) analyzed by mass spectrometry with APC showed that the major part of linoleic acid (LA) was esterified to ω-OH-VLCFA in acylacids that produce ions in the m/z 700 to m/z 830 range
The present study shows the presence of oxygenated derivatives of LA esterified onto ω-OH-VLCFA in canine SC, mostly in the 9-hydroperoxy-octadecadienoic acid (9-KODE) form, which is dehydrated to the 9-keto-derivative during the analyses by mass spectrometry

Summary

Introduction

Linoleic acid is one of the two essential fatty acids for humans and other mammals, the second being alpha-linolenic acid. As shown in our recent study [2], LA is found in canine SC mainly as an ester to omega-hydroxy very long chain fatty acids (ω-OH-VLCFA) in acylacids [3] that form the fatty acid moieties of acylceramides [4]. The occurrence of the latter compounds in the epidermis is critical to ensure an optimal cutaneous barrier function [5]. We report here the presence of significant levels of oxidized derivatives of LA in acylacids of ichthyotic dogs, much higher than in control dogs

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