A-066 Does essential fatty acid deficiency alter ethanolamine plasmalogen concentrations in red blood cells? Implications for clinical testing

Abstract

Abstract Background Plasmalogens are glycerophospholipids characterized by a fatty alcohol at the sn-1 position, a polyunsaturated fatty acid at the sn-2 position, most commonly docosahexaenoic acid (DHA) or arachidonic acid, and a polar head group at the sn-3 position, mainly phosphoethanolamine. Markedly reduced plasmalogens are seen in peroxisome biogenesis defects, including Zellweger spectrum disorders (ZSD), since the first two steps of plasmalogen synthesis occur in peroxisomes. Disruption of the peroxisomal β-oxidation pathway also causes DHA deficiency in ZSD patients. Since plasmalogens are composed of fatty acids, the deficiency of DHA or other essential fatty acids could further decrease the plasmalogen level in ZSD patients and lower the results of plasmalogen testing in patients without ZSD. To test this hypothesis, we evaluated the impact of essential fatty acid (EFA) deficiency on plasmalogens in patients with ZSD and individuals with EFA deficiency due to unrelated causes. Methods Red blood cell (RBC) samples were obtained from individuals without ZSD referred to ARUP laboratories for clinical EFA testing (n = 80; age range: birth - 89 years), and from patients with ZSD (n = 7; age range birth - 9 years). Three ZSD patients were older and with a less severe phenotype. A total of 18 intact ethanolamine plasmalogen species were extracted from packed RBCs and quantified using a XEVO TQ-XS Mass Spectrometer in conjunction with Ultra-High Performance Liquid Chromatography (Waters). Total plasmalogen values were also calculated; plasmalogen deficiency was defined as ≤60% of age-matched control median. Fatty acids (FAs) were quantified by gas chromatography negative chemical ionization-mass spectrometry (GC-NCI-MS). EFA deficiency was diagnosed by increased Triene/Tetraene ratio (Mead acid/Arachidonic acid). Data was analyzed using Prism v.8.3.0 software (La Jolla, CA). The study was approved by the Institutional Review Board of the University of Utah. Results Out of the 80 samples from individuals without ZSD referred for EFA testing, 18% had normal fatty acid profile, 57% were receiving dietary supplements and 25% had elevated Triene/Tetraene ratio suggesting EFA deficiency. EFA deficiency was accompanied by low DHA only in two individuals without ZSD, whereas it was present in most of the samples from ZSD patients evaluated (5/7). None of the individuals without ZSD were deficient in plasmalogens. Moreover, when compared to individuals without ZSD with a normal FA profile, there was no significant difference observed with EFA deficiency or FA supplementation. Although our ZSD cohort is small, no correlation between EFA deficiency and plasmalogen levels was also seen in ZSD: 2 patients with milder phenotype had EFA deficiency but normal plasmalogens, 2 patients had EFA deficiency and low plasmalogens, 2 patients with low plasmalogens had low DHA without EFA deficiency, and 1 patient had low plasmalogens but normal EFA. Conclusions Plasmalogen quantitation in RBCs by LC-MS/MS is not significantly affected by EFA deficiency. Although more data is warranted to elucidate the correlation between plasmalogen levels and ZSD phenotype, plasmalogens can be within normal reference intervals in ZSD regardless of EFA status.