Hydrolytic Decomposition of S-Aroylthiooximes: Effect of pH and N-Arylidene Substitution on Reaction Rate

Multifunctional injectable hydrogel with self-supplied H2S release and bacterial inhibition for the wound healing with enhanced macrophages polarization via interfering with PI3K/Akt pathway

Hydrogen sulfide (H2S) gas therapy is beneficial for accelerating wound healing and alleviating the inflammatory process, but is seriously hindered by insufficient delivery and unsustainable release in vivo. This study presents a multifunctional injectable hydrogel, OC@ε-PL-SATO, composed of oxidized hyaluronic acid and N-acetylcysteine (NAC) as an initiator, carboxymethyl chitosan and S-aroylthiooxime modified ε-Poly-(l-lysine) (ε-PL-SATO). ε-PL-SATO is a NAC-responsive H2S donor. OC@ε-PL-SATO hydrogel is designed for the desired wound healing process, with rapid gelation (<30 s) and a sustained H2S release. After mixing and gelling, H2S could be long-term released from the hydrogel and effectively drives macrophages toward M2 polarization, thereby ameliorating the inflammatory response. Revealed by transcriptome analysis, the underlying mechanism is that OC@ε-PL-SATO hydrogel releasing H2S inhibits LPS-mediated inflammatory responses in RAW264.7 cells by interfering with phosphatidylinositol 3-kinase/protein kinase B (PI3K/Akt) signaling and NF-κB activation. Furthermore, the OC@ε-PL-SATO hydrogel effectively eliminates the bacterial burden and alleviates the accompanying inflammation in a rat model of cutaneous wound infection. Importantly, the sustained generation of H2S gas significantly promotes angiogenesis and collagen deposition, ultimately accelerating the wound repair. In conclusion, this study provides a multifunctional injectable hydrogel with rapid gelatinization and continuous H2S release for accelerating the infected wound healing.

Thiobenzophenones: tunable hydrolysis-based donors for intracellular H2S delivery

H2S, the third gasotransmitter, is involved in many physiological and pathological processes. Compounds that can release H2S slowly under physiological conditions are useful chemical tools for studying H2S biology as...

A combined experimental and computational approach reveals how aromatic peptide amphiphiles self-assemble to form ion-conducting nanohelices

Reported here is a combined experimental-computational strategy to determine structure-property-function relationships in persistent nanohelices formed by a set of aromatic peptide amphiphile (APA) tetramers with the general structure K S XEK S , where KS= S-aroylthiooxime modified lysine, X = glutamic acid or citrulline, and E = glutamic acid. In low phosphate buffer concentrations, the APAs self-assembled into flat nanoribbons, but in high phosphate buffer concentrations they formed nanohelices with regular twisting pitches ranging from 9-31 nm. Coarse-grained molecular dynamics simulations mimicking low and high salt concentrations matched experimental observations, and analysis of simulations revealed that increasing strength of hydrophobic interactions under high salt conditions compared with low salt conditions drove intramolecular collapse of the APAs, leading to nanohelix formation. Analysis of the radial distribution functions in the final self-assembled structures led to several insights. For example, comparing distances between water beads and beads representing hydrolysable KS units in the APAs indicated that the KS units in the nanohelices should undergo hydrolysis faster than those in the nanoribbons; experimental results verified this hypothesis. Simulation results also suggested that these nanohelices might display high ionic conductivity due to closer packing of carboxylate beads in the nanohelices than in the nanoribbons. Experimental results showed no conductivity increase over baseline buffer values for unassembled APAs, a slight increase (0.4 × 102 μS/cm) for self-assembled APAs under low salt conditions in their nanoribbon form, and a dramatic increase (8.6 × 102 μS/cm) under high salt conditions in their nanohelix form. Remarkably, under the same salt conditions, these self-assembled nanohelices conducted ions 5-10-fold more efficiently than several charged polymers, including alginate and DNA. These results highlight how experiments and simulations can be combined to provide insight into how molecular design affects self-assembly pathways; additionally, this work highlights how this approach can lead to discovery of unexpected properties of self-assembled nanostructures.

The evolving landscape for cellular nitric oxide and hydrogen sulfide delivery systems: A new era of customized medications

Nitric oxide (NO) and hydrogen sulfide (H2S) are industrial toxins or pollutants; however, both are produced endogenously and have important biological roles in most mammalian tissues. The recognition that these gasotransmitters have a role in physiological and pathophysiological processes has presented opportunities to harness their intracellular effects either through inhibition of their production; or more commonly, through inducing their levels and or delivering them by various modalities. In this review article, we have focused on an array of NO and H2S donors, their hybrids with other established classes of drugs, and the various engineered delivery platforms such a fibers, polymers, nanoparticles, hydrogels, and others. In each case, we have reviewed the rationale for their development.

H2S-releasing amphiphilic dipeptide hydrogels are potent S. aureus biofilm disruptors

As a gasotransmitter, hydrogen sulfide (H2S) has been studied to treat wounds and inflammation, but its potential antimicrobial effects in this context have not been evaluated. An H2S-releasing dipeptide hydrogel (S-FE), and several non-H2S-releasing control dipeptides, (C-FE, C-GE, FBA-FE, and FE where S = S-aroylthiooxime, an H2S donor; C = control, an oxime incapable of H2S release; FBA = 4-formylbenzamide, also incapable of H2S release; and E, F, G = glutamic acid, phenylalanine, and glycine, respectively), were studied to correlate differences in their chemical structures and H2S-releasing abilities with their antimicrobial effects on Staphylococcus aureus bacteria. Dipeptides with Phe (S-FE, C-FE, and FE) self-assembled into nanoribbons in water and displayed β-sheet formation and enhanced fluorescence, while the other two dipeptides (FBA-FE and C-GE) did not form assemblies in water. In vitro experiments with Staphylococcus aureus, which is a commonly found bacterium associated with wounds, showed significant antimicrobial effects from some of the dipeptides. Dipeptide S-FE inhibited bacterial growth more effectively than any of the controls, thereby limiting biofilm formation or disrupting established biofilms. These antimicrobial H2S-releasing dipeptide hydrogels provide a promising new approach to treat wound infections.

Linker-Regulated H2S Release from Aromatic Peptide Amphiphile Hydrogels

Controlled release is an essential requirement for delivery of hydrogen sulfide (H₂S) because of its reactive nature, short half-life in biological fluids, and toxicity at high concentrations. In this context, H₂S delivery via hydrogels may be beneficial as they can deliver H₂S locally at the site of interest. Herein, we employed hydrogels based on aromatic peptide amphiphiles (APAs) with tunable mechanical properties to modulate the rates of H₂S release. The APAs contained an aromatic S-aroylthiooxime (SATO) H₂S donor attached with a linker to a short IAVEEE hexapeptide. Linker units included carbonyl, substituted O-methylenes, alkenyl, and alkyl segments with the goal of evaluating the role of linker structure on self-assembly, capacity for hydrogelation, and H₂S release rate. We studied each peptide by transmission electron microscopy, circular dichroism spectroscopy, and rheology, and we measured H₂S release rates from each gel, triggering SATO decomposition and release of H₂S by addition of cysteine (Cys). Using an H₂S-selective electrode probe as well as a turn-on fluorescent H₂S probe in the presence of H9C2 cardiomyocytes, we found that the rate of H₂S release from the hydrogels depended on the rate of Cys penetration into the nanofiber core with stiffer gels showing longer overall release.

The Benefits of Macromolecular/Supramolecular Approaches in Hydrogen Sulfide Delivery: A Review of Polymeric and Self-Assembled Hydrogen Sulfide Donors

Significance: Cell homeostasis and redox balance are regulated in part by hydrogen sulfide (H2S), a gaseous signaling molecule known as a gasotransmitter. Given its biological roles, H2S has promising therapeutic potential, but controlled delivery of this reactive and hazardous gas is challenging due to its promiscuity, rapid diffusivity, and toxicity at high doses. Macromolecular and supramolecular drug delivery systems are vital for the effective delivery of many active pharmaceutical ingredients, and H2S stands to benefit greatly from the tunable physical, chemical, and pharmacokinetic properties of polymeric and/or self-assembled drug delivery systems. Recent Advances: Several types of H2S-releasing macro- and supramolecular materials have been developed in the past 5 years, and the field is expanding quickly. Slow-releasing polymers, polymer assemblies, polymer nano- and microparticles, and self-assembled hydrogels have enabled triggered, sustained, and/or localized H2S delivery, and many of these materials are more potent in biological assays than analogous small-molecule H2S donors. Critical Issues: H2S plays a role in a number of (patho)physiological processes, including redox balance, ion channel regulation, modulation of inducible nitric oxide synthase, angiogenesis, blood pressure regulation, and more. Chemical tools designed to (i) deliver H2S to study these processes, and (ii) exploit H2S signaling pathways for treatment of diseases require control over the timing, rate, duration, and location of release. Future Directions: Development of new material approaches for H2S delivery that enable long-term, triggered, localized, and/or targeted delivery of the gas will enable greater understanding of this vital signaling molecule and eventually expedite its clinical application.

Supramolecular nanostructures with tunable donor loading for controlled H2S release

Hydrogen sulfide (H₂S), an endogenously generated and regulated signaling gas, plays a vital role in a variety of (patho)physiological processes. In the past few years, different kinds of H₂S-releasing compounds (often referred to as H₂S donors) have been developed for H₂S delivery, but it is still challenging to make H₂S donors with tunable payloads in a simple and efficient manner. Herein, a series of peptide-H₂S donor conjugates (PHDCs) with tunable donor loadings are designed for controlled H₂S release. The PHDCs self-assemble into nanoribbons with different geometries in aqueous solution. Upon addition of cysteine, these nanostructures release H₂S, delivering their payload into H9C2 cells, as visualized using an H₂S-selective fluorescent probe. Beyond imaging, in vitro studies show that the ability of PHDCs to mitigate doxorubicin-induced cardiotoxicity in H9C2 cardiomyocytes depends on their nanostructures and H₂S release profiles. This strategy may enable the development of sophisticated H₂S-releasing biomaterials for drug delivery and regenerative medicine.

Supramolecular Tuning of H2S Release from Aromatic Peptide Amphiphile Gels: Effect of Core Unit Substituents

H₂S is a gasotransmitter with several physiological roles, but its reactivity and short half-life in biological media make its controlled delivery difficult. For biological applications of the gas, hydrogels have the potential to deliver H₂S with several advantages over other donor systems, including localized delivery, controlled release rates, biodegradation, and variable mechanical properties. In this study, we designed and evaluated peptide-based H₂S-releasing hydrogels with controllable H₂S delivery. The hydrogels were prepared from short, self-assembling aromatic peptide amphiphiles (APAs), functionalized on their N-terminus with S-aroylthiooximes (SATOs), which release H₂S in response to a thiol trigger. The APAs were studied both in solution and in gel forms, with gelation initiated by addition of CaCl₂. Various substituents were included on the SATO component of the APAs in order to evaluate their effects on self-assembled morphology and H₂S release rate in both the solution and gel phases. Transmission electron microscopy (TEM) images confirmed that all H₂S-releasing APAs self-assembled into nanofibers above a critical aggregation concentration (CAC) of ∼0.5 mg/mL. Below the CAC, substituents on the SATO group affected H₂S release rates predictably in line with electronic effects (Hammett σ values) according to a linear free energy relationship. Above the CAC, circular dichroism, infrared, and fluorescence spectroscopies demonstrated that substituents influenced the self-assembled structures by affecting hydrogen bonding (β-sheet formation) and π-π stacking. At these concentrations, electronic control over release rates diminished, both in solution and in the gel form. Rather, the release rate depended primarily on the degree of organization in the β-sheets and the amount of π-π stacking. This supramolecular control over release rate may enable the evaluation of H₂S-releasing hydrogels with different release rates in biological applications.