Potent intracellular antibacterial activity of a marine peptide-N6NH2 and its D-enantiomer against multidrug-resistant Aeromonas veronii.

Aeromonas veronii can cause a variety of diseases such as sepsis in humans and animals. However, there has been no effective way to eradicate A. veronii. In this study, the intracellular antibacterial activities of the C-terminal aminated marine peptide N6 (N6NH₂) and its D-enantiomer (DN6NH₂) against A. veronii were investigated in macrophages and in mice, respectively. The result showed that DN6NH₂ with the minimum inhibitory concentration (MIC) of 1.62 μM is more resistant to cathepsin B than N6NH₂ (3.23 μM). The penetration percentages of the cells treated with 4–200 μg/mL fluorescein isothiocyanate (FITC)-DN6NH₂ were 52.5–99.6%, higher than those of FITC-N6NH₂ (27.0–99.1%). Both N6NH₂ and DN6NH₂ entered macrophages by macropinocytosis and an energy-dependent manner. DN6NH₂ reduced intracellular A. veronii by 34.57%, superior to N6NH₂ (19.52%). After treatment with 100 μg/mL DN6NH₂, the levels of tumor necrosis factor-α (TNF-α), interleukin-6 (IL-6), and IL-1β were reduced by 53.45%, 58.54%, and 44.62%, respectively, lower than those of N6NH₂ (15.65%, 12.88%, and 14.10%, respectively); DN6NH₂ increased the IL-10 level (42.94%), higher than N6NH₂ (7.67%). In the mice peritonitis model, 5 μmol/kg DN6NH₂ reduced intracellular A. veronii colonization by 73.22%, which was superior to N6NH₂ (32.45%) or ciprofloxacin (45.67%). This suggests that DN6NH₂ may be used as the candidate for treating intracellular multidrug-resistant (MDR) A. veronii. Key points: • DN6NH₂improved intracellular antibacterial activity against MDR A. veronii. • DN6NH₂entered macrophages by micropinocytosis and enhanced the internalization rates. • DN6NH₂effectively protected the mice from infection with A. veronii. [ABSTRACT FROM AUTHOR]