Photostability studies of GarKS peptides for topical formulation development.

There is a growing interest in the use of antimicrobial peptides (AMPs) as potent alternatives for conventional antibiotics, especially in chronic infected wounds. The development of a suitable topical formulation requires a thorough assessment of the photostability profiles of AMPs. In this study, we sought to investigate the photostability of novel Garvicin KS (GarKS; composed of three peptides GakA, GakB, and GakC) peptides either as an individual peptide or in combinations. The photostability of the aqueous peptide solution was determined using Suntest (indoor and outdoor conditions). Furthermore, the antimicrobial efficacy of the peptides was evaluated following UVA irradiations. Photodegradation of the peptides under indoor and outdoor conditions followed first-order kinetics. Individual peptides (GakA, GakB, and GakC) were more prone to photodegradation as compared to combination peptides (GakA+GakB, GakB+GakC, and GakA+GakC) both under indoor and outdoor conditions where the GakA+GakB combination was the most photostable. A combination of GakA+GakB+GakC enhanced photostability under indoor conditions but was reduced under outdoor conditions. A combination of three peptides with an antioxidant (glutathione) or superoxide/hydrogen peroxide scavenger (trehalose) enhanced the photostability of peptides with the highest stability achieved at a peptide:photostabilizer molar ratio of 1:0.8 for glutathione. A nominal increase in the MIC value for the peptide combinations as opposed to a larger increase for individual peptides further supports the photostability effects of combination peptides following UVA irradiations. These results suggest that the GakA+GakB or GakA+GakB+GakC combinations exhibited the highest photostability with excellent antimicrobial efficacy deemed suitable for the development of a potent AMP formulation for topical applications.