Topical substance P increases inflammatory cell density in genetically diabetic murine wounds

The neuropeptide substance P (SP) is a known inflammatory mediator released from cutaneous peripheral nerve terminals. SP effects on cellular composition in the cutaneous response to injury remain unclear. Based on our previous observations about SP effects on wound repair, we hypothesized that topical SP increases inflammatory cell density infiltration early after injury. A full‐thickness 1.5 × 1.5 cm2 wound was created on the dorsum of 8–9‐week‐old C57BL/6J‐m+Leprdb mice (db/db). Wounds were treated daily with 300 μL of either normal saline (0.9% NaCl) or 10−9 M SP for 7 days. Three wounds from each group were harvested at 2, 3, 7, 14, and 28 days. Samples underwent enzymatic digestion and were incubated with fluorescent‐labeled antibodies. Using flow cytometry, cellular content and density for each sample was derived. Masson Trichrome stained histology specimens were prepared to confirm results. Cell density in the SP‐treated wounds (11.3 × 107 cells/g tissue, standard deviation [SD]±1.5 × 107) was greater than in NaCl‐treated wounds (7 × 107 cells/g tissue, SD±2.3 × 107, p<0.05) at day 7 postwounding. SP significantly increased the density of leukocytes (2.1 × 107, SD ±3.6 × 106 vs. 1.8 × 107, SD±4.9 × 105, p<0.02) 3 days after wounding and the density of macrophages (2.9 × 107, SD±7.5 × 106 vs. 1.3 × 107, SD±1.4 × 106, p<0.05) 7 days after wounding. There were no significant differences in endothelial cell, leukocyte, or macrophage density at later time points. Topical SP treatment increases early inflammatory density in the healing wounds of db/db mice. These data support a role for nerve‐mediated inflammation in cutaneous wound repair.