Nitric oxide releasing nanoparticles for treatment of Candida albicans burn infections

Nanosponge hydrogel of octadecyl 3-(3,5-di-tert-butyl-4-hydroxyphenyl) propanoate of Alcaligenes faecalis

Octadecyl 3-(3,5-di-tert-butyl-4-hydroxyphenyl) propanoate (ODHP) was extracted in a previous study from the culture broth of soil isolate Alcaligenes faecalis MT332429 and showed a promising antimycotic activity. This study was aimed to formulate ODHP loaded β-cyclodextrins (CD) nanosponge (NS) hydrogel (HG) to control skin fungal ailments since nanosponges augment the retention of tested agents in the skin. Box-Behnken design was used to produce the optimized NS formulation, where entrapment efficiency percent (EE%), polydispersity index (PDI), and particle size (PS) were assigned as dependent parameters, while the independent process parameters were polyvinyl alcohol % (w/v %), polymer-linker ratio, homogenization time, and speed. The carbopol 940 hydrogel was then created by incorporating the nanosponges. The hydrogel fit Higuchi's kinetic release model the best, according to in vitro drug release. Stability and photodegradation studies revealed that the NS-HG remained stable under tested conditions. The formulation also showed higher in vitro antifungal activity against Candida albicans compared to the control fluconazole. In vivo study showed that ODHP-NS-HG increased survival rates, wound contraction, and healing of wound gap and inhibited the inflammation process compared to the other control groups. The histopathological examinations and Masson's trichrome staining showed improved healing and higher records of collagen deposition. Moreover, the permeability of ODHP-NS-HG was higher through rats' skin by 1.5-folds compared to the control isoconazole 1%. Therefore, based on these results, NS-HG formulation is a potential carrier for enhanced and improved topical delivery of ODHP. Our study is a pioneering research on the development of a formulation for ODHP produced naturally from soil bacteria. KEY POINTS: • Octadecyl 3-(3,5-di-tert-butyl-4-hydroxyphenyl) propanoate was successfully formulated as a nanosponge hydrogel and statistically optimized. • The new formula exhibited in vitro good stability, drug release, and higher antifungal activity against C. albicans as compared to the fluconazole. • Ex vivo showed enhanced skin permeability, and in vivo analysis showed high antifungal activity as evidenced by measurement of various biochemical parameters and histopathological examination.

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.

Impact of Nitric Oxide-Release Kinetics on Antifungal Activity

Pathogenic fungi are an increasing health threat due to the rise in drug resistance. The limited number of antifungals currently available and growing incidence of multi-drug-resistant fungi has caused rising healthcare costs and a decreased quality of life for patients with fungal infections. Nitric oxide (NO) has previously been shown to act as an antimicrobial agent, albeit with a limited understanding of the effects of the NO-release kinetics against pathogenic fungi. Herein, the antifungal effects of four nitric oxide-releasing small molecules were studied against the pathogenic fungi Candida albicans, Candida auris, Cryptococcus neoformans, and Aspergillus fumigatus, to demonstrate the broad-spectrum antifungal activity of NO. A bolus dose of NO was found to eradicate fungi after 24 h, where nitric oxide donors with shorter half-lives achieved antifungal activity at lower concentrations and thus had wider selectivity indexes. Each NO donor was found to cause a severe surface destruction of fungi, and all NO donors exhibited compatibility with currently prescribed antifungals against several different fungi species.

Nitric oxide-loaded nano- and microparticle platforms serving as potential new antifungal therapeutics

Fungal diseases are a leading threat to human health, especially in individuals with compromised immunity. Although there have been recent important advances in antifungal drug development, antifungal resistance, drug-drug interactions and difficulties in delivery remain major challenges. Among its pleiotropic actions, nitric oxide (NO) is a key molecule in host defense. We have developed a flexible nanoparticle platform that delivers sustained release of NO and have demonstrated the platform's efficacy against diverse bacteria as well as some fungal species. In this work, we investigate the effects of two NO-releasing particles against a panel of important human yeast. Our results demonstrate that the compounds are both effective against diverse yeast, including ascomycota and basidiomycota species, and that NO-releasing particles may be a potent addition to our armamentarium for the treatment of focal and disseminated mycoses.

Antifungal biofilm strategies: a less explored area in wound management

Background- The treatment of wound associated infections has always remained a challenge for clinicians with the major deterring factor being microbial biofilms, majorly bacterial or fungal. Biofilm infections are becoming a global concern owing to resistance against antimicrobials. Fungal biofilms are formed by a wide variety of fungal pathogens namely Candida sp., Aspergillus fumigates, Trichosporon sp., Saccharomyces cerevisiae, Cryptococcus neoformans, among others. The rising cases of fungal biofilm resistance add to the burden of wound care. Additionally, with increase in the number of surgical procedures, transplantation and the exponential use of medical devices, fungal bioburden is on the rise. Objectives- The review discusses the methods of biofilm formation and the resistance mechanisms against conventional treatments. The potential of novel delivery strategies and the mechanisms involved therein are highlighted. Further, the prospects of nanotechnology based medical devices to combat fungal biofilm resistance have also been explored. Some of the clinical trials and up-to-date patent technologies to eradicate the biofilms are also mentioned. Conclusion- Due to the many challenges faced in preventing/eradicating biofilms, only a handful of approaches have been able to make it to the market. Fungal biofilms are a fragmentary area which needs further exploration.

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.

Development of Novel Amphotericin B-Immobilized Nitric Oxide-Releasing Platform for the Prevention of Broad-Spectrum Infections and Thrombosis

Indwelling medical devices currently used to diagnose, monitor, and treat patients invariably suffer from two common clinical complications: broad-spectrum infections and device-induced thrombosis. Currently, infections are managed through antibiotic or antifungal treatment, but the emergence of antibiotic resistance, the formation of recalcitrant biofilms, and difficulty identifying culprit pathogens have made treatment increasingly challenging. Additionally, systemic anticoagulation has been used to manage device-induced thrombosis, but subsequent life-threatening bleeding events associated with all available therapies necessitates alternative solutions. In this study, a broad-spectrum antimicrobial, antithrombotic surface combining the incorporation of the nitric oxide (NO) donor S-nitroso-N-acetylpenicillamine (SNAP) with the immobilization of the antifungal Amphotericin B (AmB) on polydimethylsiloxane (PDMS) was developed in a two-step process. This novel strategy combines the key advantages of NO, a bactericidal agent and platelet inhibitor, with AmB, a potent antifungal agent. We demonstrated that SNAP-AmB surfaces significantly reduced the viability of adhered Staphylococcus aureus (99.0 ± 0.2%), Escherichia coli (89.7 ± 1.0%), and Candida albicans (93.5 ± 4.2%) compared to controls after 24 h of in vitro exposure. Moreover, SNAP-AmB surfaces reduced the number of platelets adhered by 74.6 ± 3.9% compared to controls after 2 h of in vitro porcine plasma exposure. Finally, a cytotoxicity assay validated that the materials did not present any cytotoxic side effects toward human fibroblast cells. This novel approach is the first to combine antifungal surface functionalization with NO-releasing technology, providing a promising step toward reducing the rate of broad-spectrum infection and thrombosis associated with indwelling medical devices.

Cutaneous candidiasis caused by Candida kefyr

Candidiasis is an acute or subacute fungal infection caused by fungi that belongs to candida genus, with Candida albicansbeing the most frequent causative agent. Candida kefyr is a rare cause of candidiasis which has been reported in systemic candidiasis and deep infections. However, to date, it has never been reported as a cause in dermatophytosis. We report a case of candidiasis caused by Candida kefyr in a 72-year-old woman with a chief complaint of pruritic erythematous rash on the back from one day prior to admission. Diagnosis was established based on clinical features, direct microscopic examination with 10% potassium hydroxide solution, gram staining. The fungal species was determined by carbohydrate fermentation test which showed a positive result for Candida kefyr. The patient was treated with miconazole cream and fusidic cream and showed significant clinical improvement.

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.

Multiple biological active 4-aminopyrazoles containing trifluoromethyl and their 4-nitroso-precursors: Synthesis and evaluation

4-Nitroso-3-trifluoromethyl-5-alkyl[(het)aryl]pyrazoles were synthesized via one-pot nitrosation of 1,3-diketones or their lithium salts followed by treatment of hydrazines. Reduction of nitroso-derivatives made it possible to obtain 4-amino-3-trifluoromethylpyrazoles chlorides. According to computer-aided calculations, all synthesized compounds are expected to have acceptable ADME profile for drug design. Tuberculostatic, antibacterial, antimycotic, antioxidant and cytotoxic activities of the compounds were evaluated in vitro, while their analgesic and anti-inflammatory action was tested in vivo along with acute toxicity studies. N-Unsubstituted 4-nitrosopyrazoles were the most effective tuberculostatics (MIC to 0.36 μg/ml) and antibacterial agents against Streptococcus pyogenes (MIC to 7.8 μg/ml), Staphylococcus aureus,S. aureus MRSA and Neisseria gonorrhoeae (MIC to 15.6 μg/ml). 4-Nitroso-1-methyl-5-phenylpyrazole had the pronounced antimycotic action against a wide range of fungi (Trichophytonrubrum, T. tonsurans, T. violaceum, T. interdigitale, Epidermophytonfloccosum, Microsporumcanis with MIC 0.38-12.5 μg/ml). N-Unsubstituted 4-aminopyrazoles shown high radical-scavenging activity in ABTS test, ORAC/AAPH and oxidative erythrocyte hemolysis assays. 1-Methyl-5-phenyl-3-trifluoromethylpyrazol-4-aminium chloride revealed potential anticancer activity against HeLa cells (SI > 1351). The pronounced analgesic activity was found for 4-nitroso- and 4-aminopyrazoles having phenyl fragment at the position 5 in "hot plate" test. The most of the obtained pyrazoles had a moderate acute toxicity.

Nitric Oxide-Releasing S-Nitrosoglutathione-Conjugated Poly(Lactic-Co-Glycolic Acid) Nanoparticles for the Treatment of MRSA-Infected Cutaneous Wounds

S-nitrosoglutathione (GSNO) has emerged as a potent agent for the treatment of infected cutaneous wounds. However, fabrication of GSNO-containing nanoparticles has been challenging due to its high hydrophilicity and degradability. The present study aimed to fabricate nanoparticles using newly synthesized GSNO-conjugated poly(lactic-co-glycolic acid) (PLGA) (GSNO-PLGA; GPNPs). Since hydrophilic GSNO was covalently bound to hydrophobic PLGA, loss of GSNO during the nanoparticle fabrication process was minimized, resulting in sufficient loading efficiency (2.32% of GSNO, 0.07 μmol/mg of NO). Real-time NO release analysis revealed biphasic NO release by GPNPs, including initial burst release within 3 min and continuous controlled release for up to 11.27 h, due to the differential degradation rates of the –SNO groups located at the surface and inside of GPNPs. Since GPNPs could deliver NO more efficiently than GSNO in response to increased interaction with bacteria, the former showed enhanced antibacterial effects against methicillin-resistant Staphylococcus aureus (MRSA) at the same equivalent concentrations of NO. Finally, the facilitating effects of GPNPs on infected wound healing were demonstrated in MRSA-challenged full-thickness wound mouse model. Collectively, the results suggested GPNPs as an ideal nanoparticle formulation for the treatment of MRSA-infected cutaneous wounds.

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.

Recent Advances in Nanomaterial-Based Wound-Healing Therapeutics

Nanomaterial-based wound healing has tremendous potential for treating and preventing wound infections with its multiple benefits compared with traditional treatment approaches. In this regard, the physiochemical properties of nanomaterials enable researchers to conduct extensive studies on wound-healing applications. Nonetheless, issues concerning the use of nanomaterials in accelerating the efficacy of existing medical treatments remain unresolved. The present review highlights novel approaches focusing on the recent innovative strategies for wound healing and infection controls based on nanomaterials, including nanoparticles, nanocomposites, and scaffolds, which are elucidated in detail. In addition, the efficacy of nanomaterials as carriers for therapeutic agents associated with wound-healing applications has been addressed. Finally, nanomaterial-based scaffolds and their premise for future studies have been described. We believe that the in-depth analytical review, future insights, and potential challenges described herein will provide researchers an up-to-date reference on the use of nanomedicine and its innovative approaches that can enhance wound-healing 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.

PEI/NONOates-doped PLGA nanoparticles for eradicating methicillin-resistant Staphylococcus aureus biofilm in diabetic wounds via binding to the biofilm matrix

Wounds infected with methicillin-resistant Staphylococcus aureus (MRSA) biofilm represent a high risk in patients with diabetes. Nitric oxide (NO) has shown promise in dispersing biofilm and wound healing. For an effective treatment of MRSA biofilm-infected wounds, however, NO needs to be supplied to the biofilm matrix in a sustainable manner due to a short half-life and limited diffusion distance of NO. In this study, polyethylenimine/diazeniumdiolate (PEI/NONOate)-doped PLGA nanoparticles (PLGA-PEI/NO NPs) with an ability to bind to the biofilm matrix are developed to facilitate the NO delivery to MRSA biofilm-infected wound. In simulated wound fluid, PLGA-PEI/NO NPs show an extended NO release over 4 days. PLGA-PEI/NO NPs firmly bind to the MRSA biofilm matrix, resulting in a greatly enhanced anti-biofilm activity. Moreover, PLGA-PEI/NO NPs accelerate healing of MRSA biofilm-infected wounds in diabetic mice along with complete biofilm dispersal and reduced bacterial burden. These results suggest that the biofilm-binding NO-releasing NPs represent a promising NO delivery system for the treatments of biofilm-infected chronic wounds.

Inhibition of Classical and Alternative Modes of Respiration in Candida albicans Leads to Cell Wall Remodeling and Increased Macrophage Recognition

The human fungal pathogen Candida albicans requires respiratory function for normal growth, morphogenesis, and virulence. Mitochondria therefore represent an enticing target for the development of new antifungal strategies. This possibility is bolstered by the presence of characteristics specific to fungi. However, respiration in C. albicans, as in many fungal organisms, is facilitated by redundant electron transport mechanisms, making direct inhibition a challenge. In addition, many chemicals known to target the electron transport chain are highly toxic. Here we made use of chemicals with low toxicity to efficiently inhibit respiration in C. albicans We found that use of the nitric oxide donor sodium nitroprusside (SNP) and of the alternative oxidase inhibitor salicylhydroxamic acid (SHAM) prevents respiration and leads to a loss of viability and to cell wall rearrangements that increase the rate of uptake by macrophages in vitro and in vivo We propose that treatment with SNP plus SHAM (SNP+SHAM) leads to transcriptional changes that drive cell wall rearrangement but which also prime cells to activate the transition to hyphal growth. In line with this, we found that pretreatment of C. albicans with SNP+SHAM led to an increase in virulence. Our data reveal strong links between respiration, cell wall remodeling, and activation of virulence factors. Our findings demonstrate that respiration in C. albicans can be efficiently inhibited with chemicals that are not damaging to the mammalian host but that we need to develop a deeper understanding of the roles of mitochondria in cellular signaling if they are to be developed successfully as a target for new antifungals.IMPORTANCE Current approaches to tackling fungal infections are limited, and new targets must be identified to protect against the emergence of resistant strains. We investigated the potential of targeting mitochondria, which are organelles required for energy production, growth, and virulence, in the human fungal pathogen Candida albicans Our findings suggest that mitochondria can be targeted using drugs that can be tolerated by humans and that this treatment enhances their recognition by immune cells. However, release of C. albicans cells from respiratory inhibition appears to activate a stress response that increases the levels of traits associated with virulence. Our results make it clear that mitochondria represent a valid target for the development of antifungal strategies but that we must determine the mechanisms by which they regulate stress signaling and virulence ahead of successful therapeutic advance.

Liposomes with Silk Fibroin Hydrogel Core to Stabilize bFGF and Promote the Wound Healing of Mice with Deep Second-Degree Scald

How to maintain the stability of basic fibroblast growth factor (bFGF) in wounds with massive wound fluids is important to accelerate wound healing. Here, a novel liposome with hydrogel core of silk fibroin (SF-LIP) is successfully developed by the common liposomal template, followed by gelation of liquid SF inside vesicle under sonication. SF-LIP is capable of encapsulating bFGF (SF-bFGF-LIP) with high efficiency, having a diameter of 99.8 ± 0.5 nm and zeta potential of -9.41 ± 0.10 mV. SF-LIP effectively improves the stability of bFGF in wound fluids. After 8 h of incubation with wound fluids at 37 °C, more than 50% of free bFGF are degraded, while only 18.6% of the encapsulated bFGF in SF-LIP are destroyed. Even after 3 d of preincubation with wound fluids, the cell proliferation activity and wound healing ability of SF-bFGF-LIP are still preserved but these are severely compromised for the conventional bFGF-liposome (bFGF-LIP). In vivo experiments reveal that SF-bFGF-LIP accelerates the wound closure of mice with deep second-degree scald. Moreover, due to the protective effect and enhanced penetration ability, SF-bFGF-LIP is very helpful to induce regeneration of vascular vessel in comparison with free bFGF or bFGF-LIP. The liposome with SF hydrogel core may be a potential carrier as growth factors for wound healing.

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

Systemic therapies are preferred for treating dermal dermatophytosis due to inadequate penetration of topical agents. However, systemic antifungals are associated with off-target effects and limited tissue penetration, and antimicrobial resistance is a growing concern. To address this, we investigated topical nitric oxide-releasing nanoparticles (NO-np), which have been used against superficial fungal infections and bacterial abscesses. In addition to enhanced penetration and permeation conferred by nanoparticles, nitric oxide, a broad-spectrum multi-mechanistic antimicrobial agent, offers decreased likelihood of resistance development. In the current study, NO-np inhibited Trichophyton rubrum in vitro, as well as in a murine model of dermal dermatophytosis. In mice, NO-np reduced fungal burden after three days, with complete clearance after seven. Furthermore, NO-np decreased tissue IL-2, 6, 10 and TNFα, indicating earlier attenuation of the host inflammatory response and decreased tissue morbidity. Thus, topical NO-np represent an attractive alternative to systemic therapy against dermal T. rubrum infection.

Characterization of a novel antibiofilm effect of nitric oxide-releasing aspirin (NCX-4040) on Candida albicans isolates from denture stomatitis patients

Candida albicans biofilms play a key role in denture stomatitis, one of the most common oral pathologies in elderly people. Because biofilms are highly resistant to antifungals, new pharmacological strategies are needed. Aspirin and nitric oxide-donor molecules have both shown antibiofilm effects on C. albicans, making them promising candidates for treatment. In this study, we evaluated the antifungal/antibiofilm effect of a nitric-oxide releasing aspirin (NO-ASA) on C. albicans isolates from denture stomatitis patients in vitro. Disk diffusion assays showed that while NO-ASA had no antifungal effect, the drug potentiated fluconazole inhibition zone diameters, increasing the effect of fluconazole by 20–30% (p<0.05). The effect of NO-ASA on the morphogenesis of C. albicans was evaluated using light microscopy after inducing hyphae formation. For all clinical strains assayed, 125 μM NO-ASA significantly decreased the number of filamentous cells present (p<0.01). Adhesion to abiotic surfaces, a critical event for biofilm formation, was evaluated in 96-well polystyrene plates using crystal violet assay; 125 μM NO-ASA significantly inhibited adhesion. Biofilms were observed with scanning electron microscopy (SEM) and quantified using XTT reduction assay. NO-ASA decreased biofilm formation (IC₅₀ ranging from 300 μM to 700 μM), consistent with SEM findings of altered biofilm microarchitecture. PGE₂ and carboxy-PTIO (an NO scavenger) both blocked the antibiofilm effects of NO-ASA, suggesting that the efficacy of NO-ASA may be associated with both inhibition of PGE₂ synthesis and release of NO. NO-ASA is a promising novel antibiofilm agent for treating fluconazole-resistant strains of C. albicans.

Sustained Nitric Oxide-Releasing Nanoparticles Interfere with Methicillin-Resistant Staphylococcus aureus Adhesion and Biofilm Formation in a Rat Central Venous Catheter Model

Staphylococcus aureus is frequently isolated in the setting of infections of indwelling medical devices, which are mediated by the microbe's ability to form biofilms on a variety of surfaces. Biofilm-embedded bacteria are more resistant to antimicrobial agents than their planktonic counterparts and often cause chronic infections and sepsis, particularly in patients with prolonged hospitalizations. In this study, we demonstrate that sustained nitric oxide-releasing nanoparticles (NO-np) interfere with S. aureus adhesion and prevent biofilm formation on a rat central venous catheter (CVC) model of infection. Confocal and scanning electron microscopy showed that NO-np-treated staphylococcal biofilms displayed considerably reduced thicknesses and bacterial numbers compared to those of control biofilms in vitro and in vivo, respectively. Although both phenotypes, planktonic and biofilm-associated staphylococci, of multiple clinical strains were susceptible to NO-np, bacteria within biofilms were more resistant to killing than their planktonic counterparts. Furthermore, chitosan, a biopolymer found in the exoskeleton of crustaceans and structurally integrated into the nanoparticles, seems to add considerable antimicrobial activity to the technology. Our findings suggest promising development and translational potential of NO-np for use as a prophylactic or therapeutic against bacterial biofilms on CVCs and other medical devices.

Recent Nanotechnology Approaches for Prevention and Treatment of Biofilm-Associated Infections on Medical Devices

Bacterial colonization in the form of biofilms on surfaces causes persistent infections and is an issue of considerable concern to healthcare providers. There is an urgent need for novel antimicrobial or antibiofilm surfaces and biomedical devices that provide protection against biofilm formation and planktonic pathogens, including antibiotic resistant strains. In this context, recent developments in the material science and engineering fields and steady progress in the nanotechnology field have created opportunities to design new biomaterials and surfaces with anti-infective, antifouling, bactericidal, and antibiofilm properties. Here we review a number of the recently developed nanotechnology-based biomaterials and explain underlying strategies used to make antibiofilm surfaces.

Endogenous nitric oxide accumulation is involved in the antifungal activity of Shikonin against Candida albicans

The aim of the present study was to investigate the role of nitric oxide (NO) in the antifungal activity of Shikonin (SK) against Candida albicans (C. albicans) and to clarify the underlying mechanism. The results showed that the NO donors S-nitrosoglutathione (GSNO) and L-arginine could enhance the antifungal activity of SK, whereas the NO production inhibitor Nω-nitro-L-arginine methyl ester (L-NAME) attenuated antifungal action. Using the fluorescent dye 3-amino,4-aminomethyl-2′, 7-difluorescein, diacetate (DAF-FM DA), we found that the accumulation of NO in C. albicans was increased markedly by SK in a time- and dose-dependent manner. In addition, the results of real-time reverse transcription-PCR (RT-PCR) demonstrated that the transcription level of YHB1 in C. albicans was greatly increased upon incubation of SK. Consistently, the YHB1-null mutant (yhb1Δ/Δ) exhibited a higher susceptibility to SK than wild-type cells. In addition, although the transcription level of CTA4 in C. albicans was not significantly changed when exposed to SK, the CTA4-null mutant (cta4Δ/Δ) was more susceptible to SK. Collectively, SK is the agent found to execute its antifungal activity directly via endogenous NO accumulation, and NO-mediated damage is related to the suppression of YHB1 and the function of CTA4.

Sustained Nitric Oxide-Releasing Nanoparticles Induce Cell Death in Candida albicans Yeast and Hyphal Cells, Preventing Biofilm Formation In Vitro and in a Rodent Central Venous Catheter Model

Candida albicansis a leading nosocomial pathogen. Today, candidal biofilms are a significant cause of catheter infections, and such infections are becoming increasingly responsible for the failure of medical-implanted devices.C. albicansforms biofilms in which fungal cells are encased in an autoproduced extracellular polysaccharide matrix. Consequently, the enclosed fungi are protected from antimicrobial agents and host cells, providing a unique niche conducive to robust microbial growth and a harbor for recurring infections. Here we demonstrate that a recently developed platform comprised of nanoparticles that release therapeutic levels of nitric oxide (NO-np) inhibits candidal biofilm formation, destroys the extracellular polysaccharide matrices of mature fungal biofilms, and hinders biofilm development on surface biomaterials such as the lumen of catheters. We found NO-np to decrease both the metabolic activity of biofilms and the cell viability ofC. albicansin vitroandin vivo Furthermore, flow cytometric analysis found NO-np to induce apoptosis in biofilm yeast cellsin vitro Moreover, NO-np behave synergistically when used in combination with established antifungal drug therapies. Here we propose NO-np as a novel treatment modality, especially in combination with standard antifungals, for the prevention and/or remediation of fungal biofilms on central venous catheters and other medical devices.

Nanoparticle-Based Therapies for Wound Biofilm Infection: Opportunities and Challenges

Clinical data from human chronic wounds implicates biofilm formation with the onset of wound chronicity. Despite the development of novel antimicrobial agents, the cost and complexity of treating chronic wound infections associated with biofilms remain a serious challenge, which necessitates the development of new and alternative approaches for effective anti-biofilm treatment. Recent advancement in nanotechnology for developing a new class of nanoparticles that exhibit unique chemical and physical properties holds promise for the treatment of biofilm infections. Over the last decade, nanoparticle-based approaches against wound biofilm infection have been directed toward developing nanoparticles with intrinsic antimicrobial properties, utilizing nanoparticles for controlled antimicrobials delivery, and applying nanoparticles for antibacterial hyperthermia therapy. In addition, a strategy to functionalize nanoparticles towards enhanced penetration through the biofilm matrix has been receiving considerable interest recently by means of achieving an efficient targeting to the bacterial cells within biofilm matrix. This review summarizes and highlights the recent development of these nanoparticle-based approaches as potential therapeutics for controlling wound biofilm infection, along with current challenges that need to be overcome for their successful clinical translation.

Developments in the management of Chagas cardiomyopathy

Over 100 years have elapsed since the discovery of Chagas disease and there is still much to learn regarding pathogenesis and treatment. Although there are antiparasitic drugs available, such as benznidazole and nifurtimox, they are not totally reliable and often toxic. A recently released negative clinical trial with benznidazole in patients with chronic Chagas cardiomyopathy further reinforces the concerns regarding its effectiveness. New drugs and new delivery systems, including those based on nanotechnology, are being sought. Although vaccine development is still in its infancy, the reality of a therapeutic vaccine remains a challenge. New ECG methods may help to recognize patients prone to developing malignant ventricular arrhythmias. The management of heart failure, stroke and arrhythmias also remains a challenge. Although animal experiments have suggested that stem cell based therapy may be therapeutic in the management of heart failure in Chagas cardiomyopathy, clinical trials have not been promising.

Nitric oxide therapy for dermatologic disease

Nitric oxide (NO) plays an important role in the maintenance and regulation of the skin and the integrity of its environment. Derangement of NO production is implicated in the etiology of a multitude of dermatologic diseases, indicating future therapeutic directions. In an era of increasing resistance rates to available antibiotics and subpar development of new agents, NO is promising as a prospective topical broad-spectrum antimicrobial agent with small likelihood of resistance development. Because the greatest strides have been made in the setting of infectious disease and skin and soft-tissue infection, this will be a major focus of this article. In addition, we will review NO's role in skin regulation and dysregulation, immune function, the various topical release systems that have been devised and tested, NO's relation to UV radiation and skin pigmentation, and finally, its potential applications as a cosmeceutical.

An S-(hydroxymethyl)glutathione dehydrogenase is involved in conidiation and full virulence in the rice blast fungus Magnaporthe oryzae

Magnaporthe oryzae is a hemibiotrophic fungal pathogen that causes rice blast disease. A compatible interaction requires overcoming plant defense responses to initiate colonization during the early infection process. Nitric oxide (NO) plays important roles in defense responses during host-pathogen interactions. Microbes generally protect themselves against NO-induced damage by using enzymes. Here, we characterized an S-(hydroxymethyl)-glutathione dehydrogenase gene in M. oryzae, MoSFA1, the homologs of which are involved in NO metabolism by specifically catalyzing the reduction of S-nitrosoglutathione (GSNO) in yeasts and plants. As expected from the activities of S-(hydroxymethyl)glutathione dehydrogenase in formaldehyde detoxification and GSNO reduction, MoSFA1 deletion mutants were lethal in formaldehyde containing medium, sensitive to exogenous NO and exhibited a higher level of S-nitrosothiols (SNOs) than that of the wild type. Notably, the mutants showed severe reduction of conidiation and appressoria turgor pressure, as well as significantly attenuated the virulence on rice cultivar CO-39. However, the virulence of MoSFA1 deletion mutants on wounded rice leaf was not affected. An infection assay on barley leaf further revealed that MoSFA1 deletion mutants exhibited a lower infection rate, and growth of infectious hyphae of the mutants was retarded not only in primary infected cells but also in expansion from cell to cell. Furthermore, barley leaf cell infected by MoSFA1 deletion mutants exhibited a stronger accumulation of H2O2 at 24 and 36 hpi. MoSFA1 deletion mutants displayed hypersensitivity to different oxidants, reduced activities of superoxide dismutases and peroxidases, and lower glutathione content in cells, compared with the wild type. These results imply that MoSFA1-mediated NO metabolism is important in redox homeostasis in response to development and host infection of M. oryzae. Taken together, this work identifies that MoSFA1 is required for conidiation and contributes to virulence in the penetration and biotrophic phases in M. oryzae.

Fidgetin-Like 2: A Microtubule-Based Regulator of Wound Healing

Wound healing is a complex process driven largely by the migration of a variety of distinct cell types from the wound margin into the wound zone. In this study, we identify the previously uncharacterized microtubule-severing enzyme, Fidgetin-like 2 (FL2), as a fundamental regulator of cell migration that can be targeted in vivo using nanoparticle-encapsulated small interfering RNA (siRNA) to promote wound closure and regeneration. In vitro, depletion of FL2 from mammalian tissue culture cells results in a more than twofold increase in the rate of cell movement, in part due to a significant increase in directional motility. Immunofluorescence analyses indicate that FL2 normally localizes to the cell edge, importantly to the leading edge of polarized cells, where it regulates the organization and dynamics of the microtubule cytoskeleton. To clinically translate these findings, we utilized a nanoparticle-based siRNA delivery platform to locally deplete FL2 in both murine full-thickness excisional and burn wounds. Topical application of FL2 siRNA nanoparticles to either wound type results in a significant enhancement in the rate and quality of wound closure both clinically and histologically relative to controls. Taken together, these results identify FL2 as a promising therapeutic target to promote the regeneration and repair of cutaneous wounds.

Wound healing and antibacterial activities of chondroitin sulfate- and acharan sulfate-reduced silver nanoparticles

For topical applications in wound healing, silver nanoparticles (AgNPs) have attracted much attention as antibacterial agents. Herein, we describe a green-synthetic route for the production of biocompatible and crystalline AgNPs using two glycosaminoglycans, chondroitin sulfate (CS) and acharan sulfate (AS), as reducing agents. The synthetic approach avoids the use of toxic chemicals, and the yield of AgNPs formation is found to be 98.1% and 91.1% for the chondroitin sulfate-reduced silver nanoparticles (CS-AgNPs) and the acharan sulfate-reduced silver nanoparticles (AS-AgNPs), respectively. Nanoparticles with mostly spherical and amorphous shapes were observed, with an average diameter of 6.16 ± 2.26 nm for CS-AgNPs and 5.79 ± 3.10 nm for AS-AgNPs. Images of the CS-AgNPs obtained from atomic force microscopy revealed the self-assembled structure of CS was similar to a densely packed woven mat with AgNPs sprinkled on the CS. These nanoparticles were stable under cell culture conditions without any noticeable aggregation. An approximately 128-fold enhancement of the antibacterial activities of the AgNPs was observed against Enterobacter cloacae and Escherichia coli when compared to CS and AS alone. In addition, an in vivo animal model of wound healing activity was tested using mice that were subjected to deep incision wounds. In comparison to the controls, the ointments containing CS-AgNPs and AS-AgNPs stimulated wound closure under histological examination and accelerated the deposition of granulation tissue and collagen in the wound area. The wound healing activity of the ointments containing CS-AgNPs and AS-AgNPs are comparable to that of a commercial formulation of silver sulfadiazine even though the newly prepared ointments contain a lower silver concentration. Therefore, the newly prepared AgNPs demonstrate potential for use as an attractive biocompatible nanocomposite for topical applications in the treatment of wounds.

Antimicrobial strategies centered around reactive oxygen species--bactericidal antibiotics, photodynamic therapy, and beyond

Reactive oxygen species (ROS) can attack a diverse range of targets to exert antimicrobial activity, which accounts for their versatility in mediating host defense against a broad range of pathogens. Most ROS are formed by the partial reduction in molecular oxygen. Four major ROS are recognized comprising superoxide (O2•-), hydrogen peroxide (H2O2), hydroxyl radical (•OH), and singlet oxygen ((1)O2), but they display very different kinetics and levels of activity. The effects of O2•- and H2O2 are less acute than those of •OH and (1)O2, because the former are much less reactive and can be detoxified by endogenous antioxidants (both enzymatic and nonenzymatic) that are induced by oxidative stress. In contrast, no enzyme can detoxify •OH or (1)O2, making them extremely toxic and acutely lethal. The present review will highlight the various methods of ROS formation and their mechanism of action. Antioxidant defenses against ROS in microbial cells and the use of ROS by antimicrobial host defense systems are covered. Antimicrobial approaches primarily utilizing ROS comprise both bactericidal antibiotics and nonpharmacological methods such as photodynamic therapy, titanium dioxide photocatalysis, cold plasma, and medicinal honey. A brief final section covers reactive nitrogen species and related therapeutics, such as acidified nitrite and nitric oxide-releasing nanoparticles.

Amphotericin B releasing nanoparticle topical treatment of Candida spp. in the setting of a burn wound

Candida spp. infection in the context of burn wounds leads to invasive disease with a 14-70% mortality rate. Unfortunately, current administrations of AmB, an important therapeutic demonstrating minimal resistance, are only available via potentially cytotoxic IV infusions. In order to circumvent these sequelae, we investigated the efficacy of nanoparticle encapsulated AmB (AmB-np) as a topical therapeutic against Candida spp. (drug release equilibrated solubilized AmB [AmB-sol] included as control). Clinical strains demonstrated equal or enhanced killing efficacy with 72.4-91.1% growth reduction by 4 hours. AmB-nps resulted in statistically significant reduction of fungal biofilm metabolic activity ranging from 80% to 95% viability reduction (P<0.001). Using a murine full-thickness burn model, AmB-np exhibited a quicker efficiency in fungal clearance versus AmB-sol by day three, although wound healing rates were similar. These data support the concept that AmB-np can function as a topical antifungal in the setting of a burn wound.

FROM THE CLINICAL EDITOR

The control of fungal infections with Candida species remains a challenge in the context of burn wounds. A nanoencapsulated topical amphotericin-B compound was studied in a murine model of full thickness burn injury, showing remarkable efficacy in controlling Candida infection. This may become a viable alternative to the potentially toxic intravenous formulations.

Use of nitric oxide nanoparticulate platform for the treatment of skin and soft tissue infections

The incidence of skin and soft tissue infections (SSTI) due to multi‐drug resistant pathogens is increasing. The concomitant increase in antibiotic use along with the ease with which organisms develop mechanisms of resistance have together become a medical crisis, underscoring the importance of developing innovative and effective antimicrobial strategies. Nitric oxide (NO) is an endogenously produced molecule with many physiologic functions, including broad spectrum antimicrobial activity and immunomodulatory properties. The risk of resistance to NO is minimized because NO has multiple mechanisms of antimicrobial action. NO's clinical utility has been limited largely because it is highly reactive and lacks appropriate vehicles for storage and delivery. To harness NO's antimicrobial potential, a variety exogenous NO delivery platforms have been developed and evaluated, yet limitations preclude their use in the clinical setting. Nanotechnology represents a paradigm through which these limitations can be overcome, allowing for the encapsulation, controlled release, and focused delivery of NO for the treatment of SSTI. WIREs Nanomed Nanobiotechnol 2013. doi: 10.1002/wnan.1230

This article is categorized under: 1

Therapeutic Approaches and Drug Discovery > Nanomedicine for Infectious Disease

2

Nanotechnology Approaches to Biology > Nanoscale Systems in Biology