Efficient Synergistic Antibacterial Activity of ?-MSH Using Chitosan- Based Versatile Nanoconjugates

The application of antimicrobial peptides has emerged as an alternative therapeutic tool to encounter against multidrug resistance of different pathogenic organisms. alpha-Melanocyte stimulating hormone (alpha-MSH), an endogenous neuropeptide, is found to be efficient in eradicating infection of various kinds of Staphylococcus aureus, including methicillin-resistant Staphylococcus aureus (MRSA). However, the chemical stability and efficient delivery of these biopharmaceuticals (i.e., alpha-MSH) to bacterial cells with a significant antibacterial effect remains a key challenge. To address this issue, we have developed a chitosan-cholesterol polymer using a single-step, one-pot, and simple chemical conjugation technique, where alpha-MSH is loaded with a significantly high amount (37.7%), and the final product is obtained as chitosan-cholesterol alpha-MSH polymer-drug nanoconjugates. A staphylococcal growth inhibition experiment was performed using chitosan-cholesterol alpha-MSH and individual controls. alpha-MSH and chitosancholesterol both show bacterial growth inhibition by a magnitude of 50 and 79%, respectively. The killing efficiency of polymer- drug nanoconjugates was very drastic, and almost no bacterial colony was observed (similar to 100% inhibition) after overnight incubation. Phenotypic alternation was observed in the presence of alpha-MSH causing changes in the cell structure and shape, indicating stress on Staphylococcus aureus. As a further consequence, vigorous cell lysis with concomitant release of the cellular material in the nearby medium was observed after treatment of chitosan-cholesterol alpha-MSH nanoconjugates. This vigorous lysis of the cell structure is associated with extensive aggregation of the bacterial cells evident in scanning electron microscopy (SEM). The dose-response experiment was performed with various concentrations of chitosan-cholesterol alpha-MSH nanoconjugates to decipher the degree of the bactericidal effect. The concentration of alpha-MSH as low as 1 pM also shows significant inhibition of bacterial growth (similar to 40% growth inhibition) of Staphylococcus aureus. Despite playing an important role in inhibiting bacterial growth, our investigation on hemolytic assay shows that chitosan-cholesterol alpha-MSH is significantly nontoxic at a wide range of concentrations. In a nutshell, our analysis demonstrated novel antimicrobial activity of nanoparticle-conjugated alpha-MSH, which could be used as future therapeutics against multidrug-resistant Staphylococcus aureus and other types of bacterial cells.

Automated summary

The application of antimicrobial peptides, such as alpha-melanocyte stimulating hormone (alpha-MSH), has been effective in eradicating different pathogenic organisms, including methicillin-resistant Staphylococcus aureus (MRSA). However, the chemical stability and efficient delivery of these peptides remain a major challenge. To address this issue, a chitosan-cholesterol alpha-MSH polymer-drug nanoconjugate was developed, which showed significant inhibition of bacterial growth and extensive cell lysis. The nanoparticle-conjugated alpha-MSH demonstrated novel antimicrobial activity and could be a potential therapeutic for multidrug-resistant Staphylococcus aureus and other bacteria.