Topical nitric oxide releasing nanoparticles are effective in a murine model of dermal Trichophyton rubrum dermatophytosis

Applications of nitric oxide-releasing nanomaterials in dermatology: Skin infections and wound healing

Nitric oxide (NO) is produced in most cells in the skin and is an important regulator of essential cutaneous functions, including responses to UV irradiation, microbial defense, wound healing, melanogenesis and epidermal permeability barrier homeostasis. Harnessing the physiological activities of NO for therapeutic use is difficult because the molecule is highly reactive and unstable. A variety of exogenous NO delivery platforms have been developed and evaluated; however, they have limited clinical applications in dermatology due to instability and poor cutaneous penetration. NO-releasing nanomaterials overcome these limitations, providing targeted tissue delivery, and sustained and controlled NO release. This review provides a comprehensive and up-to-date evaluation of the use of NO-releasing nanomaterials in dermatology for the treatment of skin and soft tissue infections and wound healing.

Potential Treatment of Dermatophyte Trichophyton rubrum in Rat Model Using Topical Green Biosynthesized Silver Nanoparticles with Achillea santolina Extract

Trichophyton rubrum is the most common dermatophyte, and can cause cutaneous infections in humans and animals (dermatophytosis). In this study, we investigated the anti-dermatophytic potential of green synthesized silver nanoparticles using Achillea santolina extract (AS-AgNPs) in an in vitro and in vivo rat model of dermal T. rubrum dermatophytosis (TRD). The green synthesis of AS-AgNPs was performed using A. santolina extract and characterized by UV-VIS spectroscopy, zeta potential, imaging (transmission electron microscopy (TEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and Energy dispersive X-ray analysis (EDX). The antifungal activity of AS-AgNPs was determined by the broth microdilution method, conidial germination, and hyphal growth inhibition. TEM and SEM were used to study the mode of the antifungal action of AS-AgNPs. AS-AgNPs inhibited the growth of T. rubrum with an MIC of 128 μg/mL, and suppressed the conidial germination and hyphal growth by 55.3% 84.6%, respectively. AS-AgNPs caused modified mycelial structures, increased cell membrane permeability, and cell wall damage. AS-AgNPs significantly increase the permeability of the fungal membrane, as revealed by reducing ergosterol biosynthesis. An increase in the intracellular ROS and the induction of apoptosis were also observed during AS-AgNP treatment. In addition, AS-AgNPs reduced the cell wall integrity, as shown by the reduction in the β-(1,3)-d-glucan synthase and chitin synthase activities. AS-AgNPs showed very low toxicity on primary human dermal fibroblasts (HDF) at the MIC. The topical treatment of the infected skin in the TRD rat model with AS-AgNPs showed a significant reduction in the fugal burden after 7 days and a complete clearance of fungal conidia, with a high recovery of epidermal and dermal structures after 14 days, compared to control rats. Interestingly, AS-AgNPs significantly attenuated the infiltrated inflammatory cells, in association with reducing the tissue proinflammatory cytokines including TNF-α, IL-1, IL-6, MOP and IL-17. In conclusion, our data prove AS-AgNPs to be a novel green topical therapy for dermatophytosis caused by T. rubrum.

Emerging Nitric Oxide and Hydrogen Sulfide Releasing Carriers for Skin Wound Healing Therapy

Nitric oxide (NO) and hydrogen sulfide (H₂ S) have been recognized as important signalling molecules involved in multiple physiological functions, including wound healing. Their exogenous delivery has been established as a new route for therapies, being the topical application the nearest to commercialization. Nevertheless, the gaseous nature of these therapeutic agents and their toxicity at high levels imply additional challenges in the design of effective delivery systems, including the tailoring of their morphology and surface chemistry to get controllable release kinetics and suitable lifetimes. This review highlights the increasing interest in the use of these gases in wound healing applications by presenting the various potential strategies in which NO and/or H₂ S are the main therapeutic agents, with focus on their conceptual design, release behaviour and therapeutic performance. These strategies comprise the application of several types of nanoparticles, polymers, porous materials, and composites as new releasing carriers of NO and H₂ S, with characteristics that will facilitate the application of these molecules in the clinical practice.

Nitric Oxide-Releasing Nanoparticles Are Similar to Efinaconazole in Their Capacity to Eradicate Trichophyton rubrum Biofilms

Filamentous fungi such as Trichophyton rubrum and T. mentagrophytes, the main causative agents of onychomycosis, have been recognized as biofilm-forming microorganisms. Nitric oxide-releasing nanoparticles (NO-np) are currently in development for the management of superficial and deep bacterial and fungal infections, with documented activity against biofilms. In this context, this work aimed to evaluate, for the first time, the in vitro anti-T. rubrum biofilm potential of NO-np using standard ATCC MYA-4438 and clinical BR1A strains and compare it to commonly used antifungal drugs including fluconazole, terbinafine and efinaconazole. The biofilms formed by the standard strain produced more biomass than those from the clinical strain. NO-np, fluconazole, terbinafine, and efinaconazole inhibited the in vitro growth of planktonic T. rubrum cells. Similarly, NO-np reduced the metabolic activities of clinical strain BR1A preformed biofilms at the highest concentration tested (SMIC₅₀ = 40 mg/mL). Scanning electron and confocal microscopy revealed that NO-np and efinaconazole severely damaged established biofilms for both strains, resulting in collapse of hyphal cell walls and reduced the density, extracellular matrix and thickness of the biofilms. These findings suggest that biofilms should be considered when developing and testing new drugs for the treatment of dermatophytosis. Development of a biofilm phenotype by these fungi may explain the resistance of dermatophytes to some antifungals and why prolonged treatment is usually required for onychomycosis.

Synthetic, Natural, and Semisynthetic Polymer Carriers for Controlled Nitric Oxide Release in Dermal Applications: A Review

Nitric oxide (NO•) is a free radical gas, produced in the human body to regulate physiological processes, such as inflammatory and immune responses. It is required for skin health; therefore, a lack of NO• is known to cause or worsen skin conditions related to three biomedical applications- infection treatment, injury healing, and blood circulation. Therefore, research on its topical release has been increasing for the last two decades. The storage and delivery of nitric oxide in physiological conditions to compensate for its deficiency is achieved through pharmacological compounds called NO-donors. These are further incorporated into scaffolds to enhance therapeutic treatment. A wide range of polymeric scaffolds has been developed and tested for this purpose. Hence, this review aims to give a detailed overview of the natural, synthetic, and semisynthetic polymeric matrices that have been evaluated for antimicrobial, wound healing, and circulatory dermal applications. These matrices have already set a solid foundation in nitric oxide release and their future perspective is headed toward an enhanced controlled release by novel functionalized semisynthetic polymer carriers and co-delivery synergetic platforms. Finally, further clinical tests on patients with the targeted condition will hopefully enable the eventual commercialization of these systems.

More than skin deep: using polymers to facilitate topical delivery of nitric oxide

Skin, the largest organ in the human body, provides several important functions, including providing protection from mechanical impacts, micro-organisms, radiation and chemicals; regulation of body temperature; the sensations of touch and temperature; and the synthesis of several substances including vitamin D, melanin, and keratin. Common dermatological disorders (CDDs) include inflammatory or immune-mediated skin diseases, skin infection, skin cancer, and wounds. In the treatment of skin disorders, topical administration has advantages over other routes of administration, and polymers are widely used as vehicles to facilitate the delivery of topical therapeutic agents, serving as matrices to keep therapeutic agents in contact with the skin. Nitric oxide (NO), a cellular signalling molecule, has attracted significant interest in treating a broad spectrum of diseases, including various skin disorders. However, there are a number of challenges in effectively delivering NO. It must be delivered in a controlled manner at sufficient concentrations to be efficacious and the delivery system must be stable during storage. The use of polymer-based systems to deliver NO topically can be an effective strategy to overcome these challenges. There are three main approaches for incorporating NO with polymers in topical delivery systems: (i) physical incorporation of NO donors into polymer bases; (ii) covalent attachment of NO donors to polymers; and (iii) encapsulation of NO donors in polymer-based particles. The latter two approaches provide the greatest control over NO release and have been used by numerous researchers in treating CDDs, including chronic wounds and skin cancer.

In Vivo Antibacterial Efficacy of Nitric Oxide-Releasing Hyperbranched Polymers against Porphyromonas gingivalis

The in vivo antibacterial activity of NO-releasing hyperbranched polymers was evaluated against Porphyromonas gingivalis, a key oral pathogen associated with periodontitis, using a murine subcutaneous chamber model. Escalating doses of NO-releasing polymers (1.5, 7.5, and 37.5 mg/kg) were administered into a P. gingivalis-infected chamber once a day for 3 days. Chamber fluids were collected on day 4, with microbiological evaluation indicating a dose-dependent bactericidal action. In particular, NO-releasing polymers at 37.5 mg/kg (1170 μg of NO/kg) achieved complete bacterial eradication (>6-log reduction in bacterial viability), demonstrating greater efficacy than amoxicillin (∼4-log reduction in bacterial viability), a commonly used antibiotic. Time-kill assays further revealed that largest dose (37.5 mg/kg; 1170 μg of NO/kg) resulted in ∼3-log killing of P. gingivalis after only a single dose. Based on these results, the potential clinical utility of NO-releasing hyperbranched polymers appears promising, particularly for oral health applications.

The potential of respiration inhibition as a new approach to combat human fungal pathogens

The respiratory chain has been proposed as an attractive target for the development of new therapies to tackle human fungal pathogens. This arises from the presence of fungal-specific electron transport chain components and links between respiration and the control of virulence traits in several pathogenic species. However, as the physiological roles of mitochondria remain largely undetermined with respect to pathogenesis, its value as a potential new drug target remains to be determined. The use of respiration inhibitors as fungicides is well developed but has been hampered by the emergence of rapid resistance to current inhibitors. In addition, recent data suggest that adaptation of the human fungal pathogen, Candida albicans, to respiration inhibitors can enhance virulence traits such as yeast-to-hypha transition and cell wall organisation. We conclude that although respiration holds promise as a target for the development of new therapies to treat human fungal infections, we require a more detailed understanding of the role that mitochondria play in stress adaption and virulence.

Nitric oxide-releasing microparticles as a potent antimicrobial therapeutic against chronic rhinosinusitis bacterial isolates

BACKGROUND

Bacteria, particularly in the biofilm state, may be implicated in the pathogenesis of chronic rhinosinusitis (CRS) and enhance antibiotic resistance. Nitric oxide (NO) is a gaseous immunomodulator with antimicrobial activity and a short half-life, complicating achievement of therapeutic concentrations. We hypothesized that a novel microparticle-based delivery platform, which allows for adjustable release of NO, could exhibit potent antibacterial effects.

METHODS

Porous organosilica microparticles (SNO-MP) containing nitrosylated thiol groups were formulated. Dissociation of the nitrosothiol groups generates NO at body temperature. The susceptibility of bacterial isolates from CRS patients to SNO-MP was evaluated through a colony forming unit (CFU) assay. Serial dilutions of SNO-MP in triplicate were incubated with isolates in suspension for 6 hours followed by plating on tryptic soy agar and overnight incubation followed by CFU quantification. Statistical analysis was performed with SPSS using one-way analysis of variance with Bonferroni correction.

RESULTS

SNO-MP displayed antibacterial activity against gram-positive (methicillin-resistant and -sensitive Staphylococcus aureus) and gram-negative (Pseudomonas aeruginosa, Enterobacter aerogenes, and Proteus mirabilis) isolates. SNO-MP induced dose-dependent reductions in CFU across all strains. Compared with controls and blank nanoparticles, SNO-MP (10 mg/mL) induced a 99.99%-100% reduction in CFU across all isolates, equivalent to a 5-9 log kill (p < 0.005). There was no statistically significant difference in CFU concentration between controls and blank microparticles.

CONCLUSION

SNO-MP demonstrates potent bactericidal effect against antibiotic-resistant CRS bacterial strains.

The First Whole-Cell Proteome- and Lysine-Acetylome-Based Comparison between Trichophyton rubrum Conidial and Mycelial Stages

Trichophyton rubrum is the most common fungal pathogen in the world, which has been studied as an important dermatophyte model organism. Despite the prevalence of T. rubrum, the available antifungal therapies are not sufficiently efficient. In this study, we performed the first comparison between the two major growth stages of T. rubrum: conidial and mycelial stages, based on their whole-cell proteomes and lysine acetylomes. In total, 4343 proteins were identified in both stages, and 1879 proteins were identified as differentially expressed between the two stages. The results showed that secretory proteases were more abundant in conidia, while aerobic metabolism and protein synthesis were significantly activated in the mycelial stage. In addition, 386 acetylated sites on 285 proteins and 5414 acetylated sites on 2335 proteins were identified in conidia and mycelia, respectively. The acetylation modifications were highly involved in metabolism and protein synthesis in both stages but differentially involved in Kyoto Encyclopedia of Genes and Genomes pathways and in epigenetic regulation between the two stages. Furthermore, inhibition of acetyltransferases or deacetylases significantly inhibited fungal growth and induced apoptosis. These results will enhance our understanding of the biological and physiological characteristics of T. rubrum and facilitate the development of improved therapies targeting these medically important pathogenic fungi.