Manuka honey and its component, methyl syringate, shift neutrophil release profiles from pro-inflammatory while preserving pro-regenerative growth factor release in vitro

Evan Norman MainSamantha Cherie HallGary Lee Bowlin^*

• The University of Memphis, Memphis, United States

Neutrophils, traditionally viewed as short-lived effector cells of acute inflammation, are now recognized as multifunctional contributors to immune regulation, tissue repair, and pathology. Upon activation, they elicit robust oxidative and cytokine responses, including the release of myeloperoxidase (MPO) and interleukin-8 (IL-8), which amplify neutrophil recruitment, prolong survival, and reinforce inflammatory signaling. Neutrophils also secrete regenerative mediators, including hepatocyte growth factor (HGF), vascular endothelial growth factor A (VEGF-A), and matrix metalloproteinase-9 (MMP-9). Manuka honey and its principal phenolic constituent, methyl syringate, have recently been shown to reduce neutrophil inflammatory activity, including intracellular reactive oxygen species (ROS) production and neutrophil extracellular trap formation (NETosis). However, their effects on primary human neutrophil signaling, enzyme release, and growth-factor secretion have not been characterized. To address this, peripheral blood neutrophils were isolated from healthy donors using density gradient separation and seeded into 96-well plates. Cells were stimulated with PMA and treated for 3 or 6 hours with 5% or 10% Manuka honey or 600 or 1300 µM methyl syringate; unstimulated cells served as negative controls, and PMA-stimulated cells served as positive controls. Supernatants were collected and analyzed using magnetic bead-based multiplex ELISAs. Both Manuka honey and methyl syringate reduced the release of inflammatory mediators in PMA-activated neutrophils, with dose-and time-dependent effects. Most treatments significantly reduced MPO levels at 3 hours and, across all treatments, at 6 hours, typically achieving ≥50% reductions and ≥70% suppression at higher doses. IL-8 release showed the most potent and most consistent inhibition, with Manuka honey reducing levels to near baseline by 6 hours. MMP-9 showed modest responsiveness, particularly to methyl syringate. HGF secretion remained unchanged across treatments. VEGF-A release was markedly decreased by Manuka honey at both time points (≥70%), whereas methyl syringate produced more minor but statistically significant reductions only at 6 hours. In conclusion, the data suggest that Manuka honey and methyl syringate are both efficacious at reducing pro-inflammatory cytokines and enzymes. However, methyl syringate alone preserved factors associated with pro-angiogenic and remodeling despite reduced inflammation.