Effects of Juglone on Neutrophil Degranulation and Myeloperoxidase Activity Related to Equine Laminitis.
Authors: Mouithys-Mickalad Ange, Storms Nazaré, Franck Thierry, Ceusters Justine, de la Rebière de Pouyade Geoffroy, Deby-Dupont Ginette, Serteyn Didier
Journal: Frontiers in veterinary science
Summary
# Editorial Summary Black walnut extract–induced laminitis in horses involves early neutrophil activation and release of myeloperoxidase (MPO), an enzyme that generates damaging reactive oxygen species in the dermal-epidermal junction; this study investigated whether juglone, the naphthoquinone compound present in walnuts and historically implicated in laminitis pathogenesis, directly triggers this neutrophil response. Using in vitro neutrophil models with multiple activation stimuli (cytochalasin B and formyl-methionyl-leucyl-phenylalanine), the researchers found that juglone actually *inhibited* neutrophil degranulation and MPO release by over 90% at physiologically relevant concentrations (25–50 μM), and further suppressed the peroxidase activity of released MPO through direct molecular interaction with its active site—findings confirmed by molecular docking studies and electron paramagnetic resonance spectroscopy. These results fundamentally challenge the prevailing assumption that juglone is the causative agent in black walnut laminitis, suggesting instead that other compounds in walnut extract or secondary mechanisms (possibly involving endotoxins or metabolic effects) drive the inflammatory cascade. For practitioners, this reframes the mechanistic understanding of black walnut toxicity and opens questions about whether juglone's antioxidant properties might actually be protective rather than pathogenic—potentially relevant considerations for future nutritional and therapeutic strategies in managing laminitis risk.
Read the full abstract on PubMed
Practical Takeaways
- •Juglone itself does not appear to be the direct trigger of black walnut-induced laminitis based on neutrophil activation mechanisms, suggesting other compounds in walnut extract may be responsible
- •Understanding that juglone actually suppresses rather than amplifies neutrophil-mediated inflammation may redirect focus to other mechanisms in laminitis pathogenesis
- •Further investigation needed to identify the actual causative agent in black walnut extract that induces the severe dermal-epidermal separation seen clinically
Key Findings
- •Juglone inhibited neutrophil degranulation by >90% at concentrations of 25 and 50 μM, contrary to the hypothesis that it triggers laminitis
- •Juglone directly inhibited myeloperoxidase (MPO) peroxidase activity by interacting with the π cation radical intermediate
- •Molecular docking confirmed juglone positioning in the MPO active site with binding to Arg-239 of the apoprotein
- •Juglone suppressed reactive oxygen species and superoxide anion production from activated polymorphonuclear neutrophils via chemiluminescence and electron paramagnetic resonance analysis