Compared to infected mice treated with PBS, a marked reduction in the expression level of pro-inflammatory chemokines (e.g. CXCL-1, CXCL-2), cytokines (i.e. IL-6 and IL-17), and other inflammatory-related genes (Tnf-α, Nf-κb) was detected in the lungs of mice at 24 hours after treatment with a single or a double dosage of Esc(1–21)-1c at 0.1 mg/kg (Fig. 6a). Indeed, the gene-expression level was similar to that of untreated non-infected mice (control, Fig. 6a). This suggests that therapeutic treatments with the diastereomer led to a substantially attenuated inflammatory response upon P. aeruginosa-induced respiratory infection. Furthermore, bacterial infection resulted in noticeable induction of airway epithelial gene Ccsp but only mild changes in Pseudomonas-induced lung infection, after administration of Esc(1–21)-1c (Fig. 6b). Ccsp gene encodes for Clara/Club cell secretory protein, and serves as a marker for assessing the cellular integrity and permeability of the lung epithelium that could be induced after epithelial injury38. Our results clearly supported that bacterial infection-induced lung injury was significantly less after one or two dosage of Esc(1–21)-1c administration. The gene expression difference in foxj1 among various treatments was not significant.Figure 6Effect of Esc(1–21)-1c on the expression level of different inflammatory-related genes (panel a) and airway epithelial-associated genes (panel b). Gene expression in the lungs of P. aeruginosa infected mice after a single or a double peptide administration (at 0.1 mg/kg) was investigated at 24 hours after bacterial infection. Mice were intra-tracheally infected with 3 million PAO1 cells. The peptides were administered intra-tracheally at 2 μg (0.1 mg/kg) at 2 hours and 12 hours after the infection. After 24 hours from bacterial challenge, the RNA was extracted from the lung tissue and quantitative PCR was performed as described54. Results are mean ± SEM from three independent experiments; n = 4–6 mice for each treatment group. The t-test was used to compare the means of PBS-receiving non-infected mice (control) versus PBS-treated infected animals. One-way analysis of variance (ANOVA) was used peptide-treated infected mice and PBS-treated infected animals, posthoc comparisons were made using the Dunnett’s multiple comparison test when the P-value was significant (p < 0.05). *p < 0.05, **p < 0.01, ***p < 0.001 for peptide-treated infected mice or PBS-receiving non-infected mice (control) versus PBS-treated infected animals.