Delayed application of silver nanoparticles reveals the role of early inflammation in burn wound healing.

Burn injury is common, and antimicrobial agents are often applied immediately to prevent wound infection and excessive inflammatory response. Although inflammation is essential for clearing bacteria and creating an environment conducive to the healing process, it is unclear what time-frame inflammation should be present for optimal wound healing. This study critically investigated the role of early inflammation in burn wound healing, and also revealed the molecular mechanisms underlying the pro-healing effects of silver nanoparticles (AgNPs). We created a burn injury mouse model using wild-type and Smad3-/- mice, which were topically treated with AgNPs at different post-burn days, and examined the healing processes of the various groups. We also delineated the molecular pathways underlying the anti-inflammation and pro-healing effects of AgNPs by morphological and histological analysis, immuno-histochemistry, and western blotting. Our results showed that (1) AgNPs regulated pro-inflammatory cytokine IL-6 production of keratinocytes and neutrophils infiltration through KGF-2/p38 signaling pathway, (2) Topical AgNPs treatment immediately after burn injury significantly supressed early inflammation but resulted in delayed healing, (3) A short delay in AgNPs application (post-burn day 3 in our model) allowed early inflammation in a controlled manner, and led to optimal burn wound healing. Thus, our current study showed that some degree of early inflammation was beneficial, but prolonged inflammation was detrimental for burn wound healing. Further evaluation and clinical translation of this finding is warranted.