Cutting Edge: Human Vagus Produces Specialized Proresolving Mediators of Inflammation with Electrical Stimulation Reducing Proinflammatory Eicosanoids

Abstract

Inflammatory resolution is a process that, when uncontrolled, impacts many organs and diseases. As an active, self-limited inflammatory process, resolution involves biosynthesis of specialized proresolving mediators (SPM) (e.g., lipoxins, resolvins [Rv], protectins, and maresins). Because vagal stimulation impacts inflammation, we examined human and mouse vagus ex vivo to determine if they produce lipid mediators. Using targeted lipid mediator metabololipidomics, we identified lipoxins, Rv, and protectins produced by both human and mouse vagus as well as PGs and leukotrienes. Human vagus produced SPM (e.g., RvE1, NPD1/PD1, MaR1, RvD5, and LXA₄) on stimulation that differed from mouse (RvD3, RvD6, and RvE3), demonstrating species-selective SPM. Electrical vagus stimulation increased SPM in both human and mouse vagus as did incubations with Escherichia coli. Electrical vagus stimulation increased SPM and decreased PGs and leukotrienes. These results provide direct evidence for vagus SPM and eicosanoids. Moreover, they suggest that this vagus SPM circuit contributes to a new proresolving vagal reflex.

Fig 1:. Human vagus produces endogenous SPMs and eicosanoids.

Fresh post-mortem human vagus were each dissected and incubated (20min, 37°C with 5% CO₂), electrically stimulated (2.5mA 18V direct DC, 20min, 37°C), or incubated with 10⁹ c.f.u. of E. coli (3h, 37°C), cold methanol added containing deuterium-labeled internal standards; LM identified and quantified using LC-MS/MS (see Materials and Methods). A) LC-MS/MS chromatographs. B) MS/MS spectra with diagnostic ions for RvD5, RvE1, LXB₄, LXA₄, MaR1, and PD1 are representative of 6 different vagus from 3 human subjects. C) LM-Network visualization of unstimulated vagus using Cytoscape 3.6.1 software and quantitation using LC-MS-MS values. Circle size in pg; Black circle, not detected; Grey square, transient intermediates not monitored. Results are mean values. A-C are representative of 6 different human vagus from 3 subjects.

Fig 2.. Vagus electrical stimulation of SPM production and reduction of eicosanoids.

Mouse vagus incubated (20min at 37°C with 5 % CO), electrically stimulated (2.5mA 18V direct DC, 20min), or with 10⁹c.f.u. E. coli (3h at 37°C), bioactive metabolomes identified and quantified as in Fig. 1A) PCA 3D score plot; B) Loading 2D plot shows endogenous LM. 3D, 3-dimensional. 2D, 2-dimensional. C) RvD3, RvD4, RvE1, RvE3, and LXB₄ (left) increased, LTB₄, PGD₂, PGE₂, PGF_2α, and TxB₂ (right) diminished. E) LM-SPM-Network pathways visualized with Cytoscape (3.6.1) with mean value changes between unstimulated and stimulated vagus. Up-regulated LM (red), down-regulated (blue). Black circles, not detected; Grey squares, not monitored. A-E are representative from 3 independent animals. Results are mean±SEM, *p<0.05, one-tailed t test.