Journal of Veterinary Internal Medicine (Sep 2021)

Increased α‐tocopherol metabolism in horses with equine neuroaxonal dystrophy

  • Erin N. Hales,
  • Hadi Habib,
  • Gianna Favro,
  • Scott Katzman,
  • R. Russell Sakai,
  • Sabin Marquardt,
  • Matthew H. Bordbari,
  • Brittni Ming‐Whitfield,
  • Janel Peterson,
  • Anna R. Dahlgren,
  • Victor Rivas,
  • Carolina Alanis Ramirez,
  • Sichong Peng,
  • Callum G. Donnelly,
  • Bobbi‐Sue Dizmang,
  • Angelica Kallenberg,
  • Robert Grahn,
  • Andrew D. Miller,
  • Kevin Woolard,
  • Benjamin Moeller,
  • Birgit Puschner,
  • Carrie J. Finno

DOI
https://doi.org/10.1111/jvim.16233
Journal volume & issue
Vol. 35, no. 5
pp. 2473 – 2485

Abstract

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Abstract Background Equine neuroaxonal dystrophy/equine degenerative myeloencephalopathy (eNAD/EDM) is an inherited neurodegenerative disorder associated with a vitamin E deficiency within the first year of life. Vitamin E consists of 8 isoforms metabolized by the CYP4F2 enzyme. No antemortem diagnostic test currently exists for eNAD/EDM. Hypothesis/Objectives Based on the association of α‐tocopherol deficiency with the development of eNAD/EDM, we hypothesized that the rate of α‐tocopherol, but not γ‐tocopherol or tocotrienol metabolism, would be increased in eNAD/EDM‐affected horses. Animals Vitamin E metabolism: Proof of concept (POC) study; eNAD/EDM‐affected (n = 5) and control (n = 6) horses. Validation study: eNAD/EDM‐affected Quarter Horses (QHs; n = 6), cervical vertebral compressive myelopathy affected (n = 6) horses and control (n = 29) horses. CYP4F2 expression and copy number: eNAD/EDM‐affected (n = 12) and age‐ and sex‐matched control (n = 11‐12) horses. Methods The rates of α‐tocopherol/tocotrienol and γ‐tocopherol/tocotrienol metabolism were assessed in equine serum (POC and validation) and urine (POC only) using liquid chromatography tandem mass spectrometry (LC‐MS/MS). Quantitative reverse‐transcriptase PCR (qRT‐PCR) and droplet digital (dd)‐PCR were used to assay expression and genomic copy number of a CYP4F2 equine ortholog. Results Metabolic rate of α‐tocopherol was increased in eNAD/EDM horses (POC,P < .0001; validation, P = .03), with no difference in the metabolic rate of γ‐tocopherol. Horses with eNAD/EDM had increased expression of the CYP4F2 equine orthologue (P = .02) but no differences in copy number. Conclusions and Clinical Importance Increased α‐tocopherol metabolism in eNAD/EDM‐affected QHs provides novel insight into alterations in vitamin E processing in eNAD/EDM and highlights the need for high‐dose supplementation to prevent the clinical phenotype in genetically susceptible horses.

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