Cuminaldehyde Potentiates Antiproteolytic Peptide Efficacy via Parallel Pathways of Enhanced Inner Membrane-Damaging Activity and Inhibition of Bacterial Energy Metabolism

Antimicrobial peptides (AMPs) offer potential as antibiotic
alternatives,
but high cost, off-site cytotoxicity, and poor stability limit their
application. Combining AMPs with adjuvants holds promise in surmounting
these limitations. Among potentiators, terpenoids account for the
highest proportion, yet their potential to enhance the AMPs efficacy
and underlying mechanism remain unclear. Hence, we investigated the
potential of monoterpenoids to enhance the efficacy of antiproteolytic
AMPs N1 (NalAArIILrWrFR). Cuminaldehyde potentiated N1 activity against
all tested strains, with FICI from 0.375 to 0.094. N1/cuminaldehyde
combination also worked synergistically against drug-resistant bacteria,
exhibited a low incidence of resistance development, and was not synergistically
toxic to eukaryotes. Furthermore, cuminaldehyde enhanced N1 stability
in salts, serum, and proteases. Mechanistically, cuminaldehyde enhanced
the inner-membrane-damaging activity of N1 and inhibited bacterial
energy metabolism. Finally, cuminaldehyde enhanced the efficacy of
N1 against ETEC K88-induced enteritis in mice. Collectively, cuminaldehyde
may be a promising N1 adjuvant to combat bacterial infections and
circumvent antibiotic resistance.