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.