Sankar Rathinam, Kasper K. Sørensen, Martha Á. Hjálmarsdóttir, Mikkel B. Thygesen and Már Másson
Introduction:
Antimicrobial peptides (AMPs) are crucial elements of innate immune systems. They combat diverse microbial infections by disrupting membranes and essential processes. With their broad activity spectrum, AMPs offer a promising alternative to antibiotics. CRAMP (Cathelicidin-Related Antimicrobial Peptide) is one such AMP found in mouse immune cells. Chitosan, derived from crustacean exoskeletons and fungal cell walls, is a versatile polysaccharide with wide-ranging applications in pharmaceuticals, food, cosmetics, agriculture, and wastewater treatments.
Methods:
Using azide transfer reactions and copper-catalyzed azide-alkyne cycloadditions (CuAAC) to conjugate antimicrobial peptides (CRAMP-18) to chitosan and hydroxypropyl chitosan (HPC). Chitosan-azide and HPC-azide were prepared by using imidazolesulfonyl azide, followed by a click reaction to obtain the desired product. Conjugates were characterized using IR and NMR spectroscopy. The antibacterial effectiveness of the chitosan-peptide conjugates was tested against four bacterial species: S. aureus, E. faecalis, E. coli, and P. aeruginosa.
Results:
The CuAAC reaction successfully grafted pentynoyl-CRAMP18 onto chitosan and HPC, creating a triazole ring between the peptide and the polymers. Proton NMR spectroscopy confirmed the conversion of azide groups to 1,2,3-triazole linkages and the assessment of the degree of substitution (DS) in chitosan-peptide conjugates. The DS values for chitosan-CRAMP18 (1) and HPC-CRAMP18 (2) were 0.2 and 0.13, respectively, indicating successful peptide incorporation into both polymers. Importantly, chitosan peptide conjugates 1 and 2 demonstrated significant efficacy against Gram-negative bacteria, particularly E. coli.
Conclusion:
We successfully grafted the chitosan-CRAMP-18 peptide to chitosan via the CuAAC reaction. This study suggests that chitosan-peptide conjugates have the potential to exhibit antibacterial properties.
