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 (N6NH 2 ) and its D-enantiomer (DN6NH 2 ) against A. veronii were investigated in macrophages and in mice, respectively. The result showed that DN6NH 2 with the minimum inhibitory concentration (MIC) of 1.62 μM is more resistant to cathepsin B than N6NH 2 (3.23 μM). The penetration percentages of the cells treated with 4–200 μg/mL fluorescein isothiocyanate (FITC)-DN6NH 2 were 52.5–99.6%, higher than those of FITC-N6NH 2 (27.0–99.1%). Both N6NH 2 and DN6NH 2 entered macrophages by macropinocytosis and an energy-dependent manner. DN6NH 2 reduced intracellular A. veronii by 34.57%, superior to N6NH 2 (19.52%). After treatment with 100 μg/mL DN6NH 2 , 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 N6NH 2 (15.65%, 12.88%, and 14.10%, respectively); DN6NH 2 increased the IL-10 level (42.94%), higher than N6NH 2 (7.67%). In the mice peritonitis model, 5 μmol/kg DN6NH 2 reduced intracellular A. veronii colonization by 73.22%, which was superior to N6NH 2 (32.45%) or ciprofloxacin (45.67%). This suggests that DN6NH 2 may be used as the candidate for treating intracellular multidrug-resistant (MDR) A. veronii . Key points • DN6NH 2 improved intracellular antibacterial activity against MDR A. veronii. • DN6NH 2 entered macrophages by micropinocytosis and enhanced the internalization rates. • DN6NH 2 effectively protected the mice from infection with A. veronii. Graphical abstract