TESTING THE EFFECT OF A NOVEL HYDROGEN SULFIDE RELEASING PEPTIDE ON INFECTED BURN WOUNDS
Afnan Altamimi, MD1, Yun Qian, PhD2, Shaina Yates, BS1, Santu Sarkar, PhD1, John Matson, PhD2, Nicole Levi-Polyachenko, PhD1.
1Wake forest school of medicine, Winston salem, NC, USA, 2Virginia Tech, Blacksburg, VA, USA.
PURPOSE: To evaluate the antimicrobial effects of an H2S releasing dipeptide on Staphylococcus aureus.
METHODS: An H2S releasing peptide hydrogel (S-FE) was synthesized and characterized by standard methodology prior to beginning studies with S. aureus. A control peptide that does not release H2S (C-FE) was also developed. The gels were evaluated against two variants of S. aureus, Xen29, which is bioluminescent and UAMS-1, which is known to form robust biofilms. Cysteine was used as the trigger for release of the H2S from the S-FE. Thus, the first experiment evaluated the effect of increasing concentrations of cysteine on the growth of S. aureus. Secondly, the effect the peptide gels on planktonic S. aureus was evaluated with using optical absorption of the culture, complemented by serial dilution and enumeration of the colony forming units (CFUs). The gels were then evaluated against developing or established biofilms to evaluate the potential for the H2S gels to be bacteriocidal or bacteriostatic. Biofilm mass was quantified using crystal violet assay, and bacterial viability was determined by in vivo imaging and CFU enumeration. An ex vivo porcine skin model was then used to evaluate the potential for the peptide gels to disrupt S. aureus biofilms in burns, and this was then translated into an in vivo porcine burn model to evaluate the safety of the peptides gels and reduction of bacterial burden compared to silver sulfadiazine. The impact of H2S on blood perfusion and wound healing were evaluated using laser Doppler scanning of the burns and histopathological imaging.
RESULTS: Both the S-FE and C-FE peptide hydrogels exhibited reduction in S. aureus in planktonic or biofilm form, Indicating an antimicrobial effect of the peptide itself. H2S-releasing S-FE gel which had a better antimicrobial effect in general, suggesting the inhibitory effects of H2S gas. The S-FE and C-FE dipeptide gels suppressed the bacterial ability to grow biofilm. Moreover, the S-FE had a significant antimicrobial effect on an established biofilm compared to C-Fe and a bacterial only group which could indicate the gas ability to infiltrate the biofilm to impact the bacteria directly. The impact of the gels in infected ex vivo porcine skin shows a significant decrease in bacterial burden determined by reductions in both CFUs and photon count emitted from the bioluminescent bacteria. An antimicrobial effect was noticed with the S-FE group compared to the other groups as the infection was cleared before day 14 compared to its control which persisted to day 21. There was no clear acceleration of wound healing with any of the treatments. There were no negative impacts of the dipeptide hydrogels on the health of the animals.
CONCLUSION: The S-FE and C-FE inhibited bacterial growth, thereby limiting biofilm formation or disrupting established biofilms, and S-FE showed better effects than C-FE. These antimicrobial H2S-releasing dipeptide hydrogels provide a promising new approach to treat wound infections.
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