Regulating H₂S release from self-assembled peptide H₂S-donor conjugates using cysteine derivatives

Self-assembled peptides provide a modular and diverse platform for drug delivery, and innovative delivery methods are needed for delivery of hydrogen sulfide (H₂S), an endogenous signaling molecule (gasotransmitter) with significant therapeutic potential. Of the available types of H₂S donors, peptide/protein H₂S donor conjugates (PHDCs) offer significant versatility. Here we discuss the design, synthesis, and in-depth study of a PHDC containing three covalently linked components: a thiol-triggered H₂S donor based on an S-aroylthiooxime (SATO), a GFFF tetrapeptide, and a tetraethylene glycol (TEG) dendron. Conventional transmission electron microscopy showed that the PHDC self-assembled into spherical structures without heat or stirring, but it formed nanofibers with gentle heat (37 °C) and stirring. Circular dichroism (CD) spectroscopy data collected during self-assembly under nanofiber-forming conditions suggested an increase in β-sheet character and a decrease in organization of the SATO units. Release of H₂S from the nanofibers was studied through triggering with various thiols. The release rate and total amount of H₂S released over both short (5 h) and long (7 d) time scales varied with the charge state: negatively charged and zwitterionic thiols (e.g., Ac-Cys-OH and H-Cys-OH) triggered release slowly while a neutral thiol (Ac-Cys-OMe) showed ∼10-fold faster release, and a positively charged thiol (H-Cys-OMe) triggered H₂S release nearly 50-fold faster than the negatively charged thiols. CD spectroscopy studies monitoring changes in secondary structure over time during H₂S release showed similar trends. This study sheds light on the driving forces behind self-assembling nanostructures and offers insights into tuning H₂S release through thiol charge state modulation.