Effects of kynurenine on CD3+ and macrophages in wound healing

Abstract

As prolongation of the inflammation phase in a healing process frequently leads to wound impairment, here we queried whether kynurenine (Kyn) could modulate this phase of wound healing. To address this, a protein microarray, quantitative polymerase chain reaction (qPCR), flow cytometry for immune cells and immune cell proliferation in the presence and absence of Kyn were conducted and compared. The result of a protein microarray revealed that the expression of 12 pro-inflammatory cytokines and chemokines was modulated in Kyn-treated mouse splenocytes as compared with those of control. These findings were then evaluated by conducting a qPCR for the gene expression of these factors and showed a significant reduction in the gene expression of majority of these cytokines and chemokines (interleukin [IL]-2, IL-17, C-X-C motif chemokine ligand [CXCL] 10, CXCL1, C-C motif ligand [CCL] 12, CXCL9, CCL4, CXCL2, and CCL5) in response to Kyn treatment. To test the anti-inflammatory effect of Kyn in an animal model, dorsal surface wounds were generated in a mouse model and wounds received daily topical application of either nothing (control), dermal cream (second control), or Kyn cream using uninjured skin tissue as another control. The wounded tissues were harvested on days 3, 6, and 10 postwounding. As anticipated, the results of fluorescence-activated cell sorting analysis revealed that upon wounding, the number of total infiltrated CD3+ cells and macrophages (CD11b+) significantly increased on day 3, peaked on day 6, and reduced on day 10 post-wounding. Interestingly, as compared with those of uninjured and dermal cream alone-treated wounds, Kyn treatment significantly reduced the number of infiltrated CD3+ cells, but not CD11b+ cells, at different time intervals examined. These findings collectively suggest that Kyn, as a small molecule, can potentially be used to overcome the difficulties associated with persistency of inflammation in healing wounds.

Examination of Kynurenine Toxicity on Corneal and Conjunctival Epithelium: In vitro and in vivo Studies

“…Thus, these results suggest that KYN possesses properties that can be considered beneficial in the healing of the corneal epithelium. Indeed, there are reports showing that KYN can facilitate and modulate healing processes [7, 11, 36]. Interestingly, wounds that received IDO genetically modified dermal fibroblasts healed more quickly than those of the controls [7].…”

“…In comparison, the concentration of KYN in human cerebrospinal fluid is 134.5 nM [26] and in serum 1.8 μM [27, 28]. A topical application of KYN is considered to be safe [7]. However, the use of relatively higher than physiological doses of KYN raises the question of consumer safety.…”

“…Moreover, KYN reduced scar formation due to its antifibrogenic action [12]. It was postulated that KYN may modulate the inflammation phase in the healing process and can potentially be used to overcome difficulties associated with persistency of inflammation in skin wounds healing [7]. These facts justified a topical use of KYN in skin wound healing therapies, and a registered clinical trial on human subjects was conducted (https://clinicaltrials.gov/ct2/show/NCT02340325).…”

“…IDO is present at low levels in many extrahepatic tissues including the cornea, where it was detected in stroma and endothelium [2-5]. The activity of IDO markedly increases during an infection or inflammation, induced by cytokines, lipopolysaccharide or other agents [6, 7]. …”

“…Compounds that promote normal corneal regeneration rather than fibrosis are being sought [13, 14]. KYN is a small molecule (208 Da) and therefore it can penetrate different tissues [7] including the corneal stroma [6]. Therefore, KYN seems to be a prospective agent for the treatment of corneal and ocular surface diseases.…”