Thermal and photochemical nitric oxide release from S-nitrosothiols incorporated in Pluronic F127 gel: potential uses for local and controlled nitric oxide release

Spraying with encapsulated nitric oxide donor reduces weight loss and oxidative damage in papaya fruit

The combination of nitric oxide (NO) donors with nanomaterials has emerged as a promising approach to reduce postharvest losses. The encapsulation of NO donors provides protection from rapid degradation and controlled release, enhancing the NO effectiveness in postharvest treatments. Moreover, the application method can also influence postharvest responses. In this study, two application methods were evaluated, spraying and immersion, using S-nitrosoglutathione (GSNO, a NO donor) in free and encapsulated forms on papaya fruit. Our hypothesis was that GSNO encapsulated in chitosan nanoparticles would outperform the free form in delaying fruit senescence. In addition, this study marks the pioneering characterization of chitosan nanoparticles containing GSNO within the framework of a postharvest investigation. Overall, our findings indicate that applying encapsulated GSNO (GSNO-NP-S) through spraying preserves the quality of papaya fruit during storage. This method not only minimizes weight loss, ethylene production, and softening, but also stimulates antioxidant responses, thereby mitigating oxidative damage. Consequently, it stands out as the promising technique for delaying papaya fruit senescence. This innovative approach holds the potential to enhance postharvest practices and advance sustainable agriculture.

Hydrogels for Gasotransmitter Delivery: Nitric Oxide, Carbon Monoxide, and Hydrogen Sulfide

Gasotransmitters, gaseous signaling molecules including nitric oxide (NO), carbon monoxide (CO), and hydrogen sulfide (H2 S), maintain myriad physiological processes. Low levels of gasotransmitters are often associated with specific problems or diseases, so NO, CO, and H2 S hold potential in treating bacterial infections, chronic wounds, myocardial infarction, ischemia, and various other diseases. However, their clinical applications as therapeutic agents are limited due to their gaseous nature, short half-life, and broad physiological roles. One route toward the greater application of gasotransmitters in medicine is through localized delivery. Hydrogels are attractive biomedical materials for the controlled release of embedded therapeutics as they are typically biocompatible, possess high water content, have tunable mechanical properties, and are injectable in certain cases. Hydrogel-based gasotransmitter delivery systems began with NO, and hydrogels for CO and H2 S have appeared more recently. In this review, the biological importance of gasotransmitters is highlighted, and the fabrication of hydrogel materials is discussed, distinguishing between methods used to physically encapsulate small molecule gasotransmitter donor compounds or chemically tether them to a hydrogel scaffold. The release behavior and potential therapeutic applications of gasotransmitter-releasing hydrogels are also detailed. Finally, the authors envision the future of this field and describe challenges moving forward.

Exploring the power of nitric oxide and nanotechnology for prolonging postharvest shelf-life and enhancing fruit quality

Nitric oxide (NO) is a versatile signaling molecule that plays a crucial role in regulating postharvest fruit quality. The utilization of NO donors to elevate endogenous NO levels and induce NO-mediated responses represents a promising strategy for extending fruit shelf-life after harvest. However, the effectiveness of NO treatment is influenced by various factors, including formulation and application methods. In this review, we investigate the impact of NO supply on different fruits, aiming to prolong postharvest shelf-life and enhance fruit quality. Furthermore, we delve into the underlying mechanisms of NO action, particularly its interactions with ethylene and reactive oxygen species (ROS). Excitingly, we also highlight the emerging field of nanotechnology in postharvest applications, discussing the use of nanoparticles as a novel approach for achieving sustained release of NO and enhancing its effects. By harnessing the potential of nanotechnology, our review is a starting point to help identify gaps and future directions in this important, emerging field.

Chitosan-GSNO nanoparticles: a positive modulator of drought stress tolerance in soybean

BACKGROUND

Chitosan biopolymer is an emerging non-toxic and biodegradable plant elicitor or bio-stimulant. Chitosan nanoparticles (CSNPs) have been used for the enhancement of plant growth and development. On the other hand, NO is an important signaling molecule that regulates several aspects of plant physiology under normal and stress conditions. Here we report the synthesis, characterization, and use of chitosan-GSNO nanoparticles for improving drought stress tolerance in soybean.

RESULTS

The CSGSNONPs released NO gas for a significantly longer period and at a much lower rate as compared to free GSNO indicating that incorporation of GSNO in CSNPs can protect the NO-donor from rapid decomposition and ensure optimal NO release. CS-GSNONPs improved drought tolerance in soybean plants reflected by a significant increase in plant height, biomass, root length, root volume, root surface area, number of root tips, forks, and nodules. Further analyses indicated significantly lower electrolyte leakage, higher proline content, higher catalase, and ascorbate peroxidase activity, and reduction in MDA and H2O2 contents after treatment with 50 μM CS-GSNONPs under drought stress conditions. Quantitative real-time PCR analysis indicated that CS-GSNONPs protected against drought-induced stress by regulating the expression of drought stress-related marker genes such as GmDREB1a, GmP5CS, GmDEFENSIN, and NO-related genes GmGSNOR1 and GmNOX1.

CONCLUSIONS

This study highlights the potential of nano-technology-based delivery systems for nitric oxide donors to improve plant growth, and development and protect against stresses.

Candidate molecules as alternative nitric oxide donors with better antibacterial property against Escherichia coli and Staphylococcus aureus

AIMS

Four nitric oxide (NO) donors, S-nitrosoglutathione (GSNO), S-nitrosocysteine (CySNO), S-nitroso-N-acetylcysteine (SNAC), and 2-(2-S-nitroso propionamide) acetic acid (GAS) were prepared and their physicochemical characteristics were analyzed. Besides, the antibacterial properties of NO donors were investigated against Escherichia coli and Staphylococcus aureus.

METHODS AND RESULTS

UV-visible absorption spectrum and Fourier transform infrared spectrum verified the successful preparation of RSNOs. All NO donors (10 mmol l-1) could release NO continuously, and the amount of NO release was from 80.22 μmol l-1 to 706.63 μmol l-1, in which the release of NO from SNAC was the highest, and the release of NO from NaNO2 was the least. The inhibition zone indicated that all NO donors showed stronger antibacterial activity against E. coli and S. aureus, and the antibacterial ability was in the order of SNAC > GSNO > CySNO > GAS > NaNO2 for both E. coli and S. aureus (P < 0.05). Scanning electron microscopy(SEM) showed that all NO donors could result in varying degrees of damage to cell wall and membrane of both E. coli and S. aureus and the damage of E. coli was more severe.

CONCLUSION

Four alternative NO donors were successfully synthesized. All alternative NO donors showed better antibacterial properties against E. coli and S. aureus than NaNO2.

Controllable release of nitric oxide from an injectable alginate hydrogel

Currently, the controlled release of nitric oxide (NO) plays a crucial role in various biomedical applications. However, injectable NO-releasing materials remain an underexplored research field to date. In this study, via the incorporation of S-nitroso-N-acetyl-penicillamine (SNAP) as an NO donor, a family of NO-releasing injectable hydrogels was synthesized through the in situ cross-linking between sodium alginate and calcium ion induced by D-(+)-gluconate δ-lactone as an initiator. Initially, the organic functional groups and the corresponding morphologies of the resulting injectable hydrogels were characterized by IR and SEM spectroscopies, respectively. The NO release times of hydrogels with different SNAP loading amounts could reach up to 36-47 h. Due to the release of NO, the highest antibacterial rates of these injectable hydrogels against Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus) were up to 95 %, respectively. Furthermore, the matrix of these hydrogels demonstrated great water absorption ability, swelling behavior, and degradation performance. Finally, we expect that these NO-releasing injectable hydrogels could have great potential applications various biomedical material fields.

Smart Magnetic Nanocarriers for Codelivery of Nitric Oxide and Doxorubicin for Enhanced Apoptosis in Cancer Cells

Extremely short half-life therapeutic molecule nitric oxide (NO) plays significant roles in the functioning of various physiological and pathological processes in the human body, whereas doxorubicin hydrochloride (DOX) is a clinically important anticancer drug widely used in cancer chemotherapy. Thus, the intracellular delivery of these therapeutic molecules is tremendously important to achieve their full potential. Herein, we report a novel approach for the development of highly water-dispersible magnetic nanocarriers for codelivery of NO and DOX. Primarily, bifunctional magnetic nanoparticles enriched with carboxyl and thiol groups were prepared by introducing cysteine onto the surface of citrate-functionalized Fe3O4 nanoparticles. DOX was electrostatically conjugated onto the surface of bifunctional nanoparticles via carboxyl moieties, whereas the thiol group was further nitrosated to provide NO-releasing molecules. The developed magnetic nanocarrier exhibited good aqueous colloidal stability, protein resistance behavior, and high encapsulation efficacy for NO (65.5%) and DOX (85%), as well as sustained release characteristics. Moreover, they showed superior cytotoxicity toward cancer (A549 and MCF-7) cells via apoptosis induction over normal (WI26VA4) cells. Specifically, we have developed magnetic nanocarriers having the capability of dual delivery of NO and DOX, which holds great potential for combinatorial cancer treatment.

Advances in Nitric Oxide-Releasing Hydrogels for Biomedical Applications

Hydrogels provide a plethora of advantages to biomedical treatments due to their highly hydrophilic nature and tissue-like mechanical properties. Additionally, the numerous and widespread endogenous roles of nitric oxide have led to an eruption in research developing biomimetic solutions to the many challenges the biomedical world faces. Though many design factors and fabrication details must be considered, utilizing hydrogels as nitric oxide delivery vehicles provides promising materials in several applications. Such applications include cardiovascular therapy, vasodilation and angiogenesis, antimicrobial treatments, wound dressings, and stem cell research. Herein, a recent update on the progress of NO-releasing hydrogels is presented in depth. In addition, considerations for the design and fabrication of hydrogels and specific biomedical applications of nitric oxide-releasing hydrogels are discussed.

Cytotoxicity towards Breast Cancer Cells of Pluronic F-127/Hyaluronic Acid Hydrogel Containing Nitric Oxide Donor and Silica Nanoparticles Loaded with Cisplatin

The incorporation of both nitric oxide (NO) donor (S-nitrosoglutathione, GSNO) and silica nanoparticles loaded with cisplatin (SiO₂@CisPt NPs) into a polymeric matrix represents a suitable approach to creating a drug-delivery system with sustained and localized drug release against tumor cells. Herein, we report the synthesis, characterization, and cytotoxicity evaluation of Pluronic F-127/hyaluronic acid hydrogel containing GSNO and SiO₂@CisPt NPs against breast cancer cells. SiO₂@CisPt NPs were successfully synthesized, revealing a spherical morphology with an average size of 158 ± 20 nm. Both GSNO and SiO₂@CisPt NPs were incorporated into the thermoresponsive Pluronic/hyaluronic hydrogel for sustained and localized release of both NO and cisplatin. The kinetics of NO release from a hydrogel matrix revealed spontaneous and sustained release of NO at the millimolar range for 24 h. The MTT assay showed concentration-dependent cytotoxicity of the hydrogel. The combination of GSNO and SiO₂@CisPt incorporated into a polymeric matrix decreased the cell viability 20% more than the hydrogel containing only GSNO or SiO₂@CisPt. At 200 µg/mL, this combination led to a critical cell viability of 30%, indicating a synergistic effect between GSNO and SiO₂@CisPt NPs in the hydrogel matrix, and, therefore, highlighting the potential application of this drug-delivery system in the field of biomedicine.

Recent progress in nitric oxide-generating nanomedicine for cancer therapy

Nitric oxide (NO) is an endogenous, multipotent biological signaling molecule that participates in several physiological processes. Recently, exogenous supplementation of tumor tissues with NO has emerged as a potential anticancer therapy. In particular, it induces synergistic effects with other conventional therapies (such as chemo-, radio-, and photodynamic therapies) by regulating the activity of P-glycoprotein, acting as a vascular relaxant to relieve tumor hypoxia, and participating in the metabolism of reactive oxygen species. However, NO is highly reactive, and its half-life is relatively short after generation. Meanwhile, NO-induced anticancer activity is dose-dependent. Therefore, the targeted delivery of NO to the tumor is required for better therapeutic effects. In the past decade, NO-generating nanomedicines (NONs), which enable sustained and specific NO release in tumor tissues, have been developed for enhanced cancer therapy. This review describes the recent efforts and preclinical achievements in the development of NON-based cancer therapies. The chemical structures employed in the fabrication of NONs are summarized, and the strategies involved in NON-based cancer therapies are elaborated.

Opportunities for Nitric Oxide in Potentiating Cancer Immunotherapy

Despite nearly 30 years of development and recent highlights of nitric oxide (NO) donors and NO delivery systems in anticancer therapy, the limited understanding of exogenous NO's effects on the immune system has prevented their advancement into clinical use. In particular, the effects of exogenously delivered NO differing from that of endogenous NO has obscured how the potential and functions of NO in anticancer therapy may be estimated and exploited despite the accumulating evidence of NO's cancer therapy-potentiating effects on the immune system. After introducing their fundamentals and characteristics, this review discusses the current mechanistic understanding of NO donors and delivery systems in modulating the immunogenicity of cancer cells as well as the differentiation and functions of innate and adaptive immune cells. Lastly, the potential for the complex modulatory effects of NO with the immune system to be leveraged for therapeutic applications is discussed in the context of recent advancements in the implementation of NO delivery systems for anticancer immunotherapy applications. SIGNIFICANCE STATEMENT: Despite a 30-year history and recent highlights of nitric oxide (NO) donors and delivery systems as anticancer therapeutics, their clinical translation has been limited. Increasing evidence of the complex interactions between NO and the immune system has revealed both the potential and hurdles in their clinical translation. This review summarizes the effects of exogenous NO on cancer and immune cells in vitro and elaborates these effects in the context of recent reports exploiting NO delivery systems in vivo in cancer therapy applications.

Recent Advances in Hydrogel-Mediated Nitric Oxide Delivery Systems Targeted for Wound Healing Applications

Despite the noticeable evolution in wound treatment over the centuries, a functional material that promotes correct and swift wound healing is important, considering the relative weight of chronic wounds in healthcare. Difficult to heal in a fashionable time, chronic wounds are more prone to infections and complications thereof. Nitric oxide (NO) has been explored for wound healing applications due to its appealing properties, which in the wound healing context include vasodilation, angiogenesis promotion, cell proliferation, and antimicrobial activity. NO delivery is facilitated by molecules that release NO when prompted, whose stability is ensured using carriers. Hydrogels, popular materials for wound dressings, have been studied as scaffolds for NO storage and delivery, showing promising results such as enhanced wound healing, controlled and sustained NO release, and bactericidal properties. Systems reported so far regarding NO delivery by hydrogels are reviewed.

Dual Action Nitric Oxide and Fluoride Ion-Releasing Hydrogels for Combating Dental Caries

Demineralization and breakdown of tooth enamel are characterized by a condition called dental caries or tooth decay, which is caused by two main factors: (1) highly acidic food intake without proper oral hygiene and (2) overactive oral bacteria generating acidic metabolic byproducts. Fluoride treatments have been shown to help rebuild the hydroxyapatite structures that make up 98% of enamel but do not tackle the bacterial overload that continues to threaten future demineralization. Herein, we have created a dual-function Pluronic F127-alginate hydrogel with nitric oxide (NO)- and fluoride-releasing capabilities for the two-pronged treatment of dental caries. Analysis of the hydrogels demonstrated porous, shear-thinning behaviors with tunable mechanical properties. Varying the weight percent of the NO donor S-nitrosoglutathione (GSNO) within the hydrogel enabled physiologically actionable NO release over 4 h, with the fabricated gels demonstrating storage stability over 21 days. This NO-releasing capability resulted in a 97.59% reduction of viable Streptococcus mutans in the planktonic state over 4 h and reduced the preformed biofilm mass by 48.8% after 24 h. Delivery of fluoride ions was confirmed by a fluoride-sensitive electrode, with release levels resulting in the significant prevention of demineralization of hydroxyapatite discs after treatment with an acidic demineralization solution. Exposure to human gingival fibroblasts and human osteoblasts showed cytocompatibility of the hydrogel, demonstrating the potential for the successful treatment of dental caries in patients.

Nitric oxide-releasing biomaterials for promoting wound healing in impaired diabetic wounds: State of the art and recent trends

Impaired diabetic wounds are serious pathophysiological complications associated with persistent microbial infections including failure in the closure of wounds, and the cause of a high frequency of lower limb amputations. The healing of diabetic wounds is attenuated due to the lack of secretion of growth factors, prolonged inflammation, and/or inhibition of angiogenic activity. Diabetic wound healing can be enhanced by supplying nitric oxide (NO) endogenously or exogenously. NO produced inside the cells by endothelial nitric oxide synthase (eNOS) naturally aids wound healing through its beneficial vasculogenic effects. However, during hyperglycemia, the activity of eNOS is affected, and thus there becomes an utmost need for the topical supply of NO from exogenous sources. Thus, NO-donors that can release NO are loaded into wound healing patches or wound coverage matrices to treat diabetic wounds. The burst release of NO from its donors is prevented by encapsulating them in polymeric hydrogels or nanoparticles for supplying NO for an extended duration of time to the diabetic wounds. In this article, we review the etiology of diabetic wounds, wound healing strategies, and the role of NO in the wound healing process. We further discuss the challenges faced in translating NO-donors as a clinically viable nanomedicine strategy for the treatment of diabetic wounds with a focus on the use of biomaterials for the encapsulation and in vivo controlled delivery of NO-donors.

Optimizing Comprehensive Performance of Aggregation-Induced Emission Nanoparticles through Molecular Packing Modulation for Multimodal Image-Guided Synergistic Phototherapy

Fluorescent nanoparticles (NPs) with aggregation-induced emission (AIE) characteristics hold remarkable potential for image-guided phototherapy. The molecular packing is the key point for optimizing the performance of AIE luminogens (AIEgens) in the aggregated or solid state. However, so far, the packing mode of AIEgens in NPs is still vague, causing some challenges for understanding the relationship between the photophysical property and packing mode, as well as further optimizing the performance of NPs for biomedical applications. In this contribution, by simply controlling the length of alkoxy chains in the donor-acceptor conjugated OPTPA, a packing balance between the twisted molecular structure and effective π-conjugation is actualized. Subsequently, the possibility of amorphous-crystalline transition of AIEgens in the polymer-encapsulated NPs is presented for the first time, and the comprehensive performance of NPs is further optimized. Both in vitro and in vivo experiments indicate that crystalline AIEgen-based NPs are remarkably effective in trimodal imaging-guided synergistic phototherapy.

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.

A Synergistic New Approach Toward Enhanced Antibacterial Efficacy via Antimicrobial Peptide Immobilization on a Nitric Oxide-Releasing Surface

Despite technological advancement, nosocomial infections are prevalent due to the rise of antibiotic resistance. A combinatorial approach with multimechanistic antibacterial activity is desired for an effective antibacterial medical device surface strategy. In this study, an antimicrobial peptide, nisin, is immobilized onto biomimetic nitric oxide (NO)-releasing medical-grade silicone rubber (SR) via mussel-inspired polydopamine (PDA) as a bonding agent to reduce the risk of infection. Immobilization of nisin on NO-releasing SR (SR-SNAP-Nisin) and the surface characteristics were characterized by Fourier transform infrared spectroscopy and scanning electron microscopy with energy-dispersive X-ray spectroscopy and contact angle measurements. The NO release profile (7 days) and diffusion of SNAP from SR-SNAP-Nisin were quantified using chemiluminescence-based nitric oxide analyzers and UV-vis spectroscopy, respectively. Nisin quantification showed a greater affinity of nisin immobilization toward SNAP-doped SR. Matrix-assisted laser desorption/ionization mass spectrometry analysis on surface nisin leaching for 120 h under physiological conditions demonstrated the stability of nisin immobilization on PDA coatings. SR-SNAP-Nisin shows versatile in vitro anti-infection efficacy against Gram-negative Escherichia coli and Gram-positive Staphylococcus aureus in the planktonic and adhered states. Furthermore, the combination of NO and nisin has a superior ability to impair biofilm formation on polymer surfaces. SR-SNAP-Nisin leachates did not elicit cytotoxicity toward mouse fibroblast cells and human umbilical vein endothelial cells, indicating the biocompatibility of the material in vitro. The preventative and therapeutic potential of SR-SNAP-Nisin dictated by two bioactive agents may offer a promising antibacterial surface strategy.

3D printed nitric oxide-releasing poly(acrylic acid)/F127/cellulose nanocrystal hydrogels

Hydrogels have been used as matrices for the topical delivery of nitric oxide (NO) for achieving vasodilation, wound healing and analgesic actions. More recently, supramolecular hydrogels comprised of poly(acrylic acid) (PAA) and micellar Pluronic F127 (F127), prepared by thermal reaction, emerged as a suitable matrix for the incorporation of hydrophilic NO donors, such as S-nitrosoglutathione (GSNO). Herein, we describe an innovative method for the three-dimensional (3D) printing of cellulose nanocrystal (CNC)-containing and semi-interpenetrating PAA/F127 hydrogels by PAA photopolymerization via digital light processing (DLP), in the absence of organic solvents. Scanning electron microscopy showed that, differently from typical porous PAA-based hydrogels, the 3D printed PAA/F127/CNC hydrogels have dense morphology. By using transmission electron microscopy we confirmed for the first time the presence of F127 micelles in the printable resin, and their preservation after the photopolymerization process. The F127 micelles conferred compressive recoverability to the 3D printed PAA/F127/CNC hydrogels, widening their potential applications as soft biomaterials. PAA/F127/CNC hydrogels charged with GSNO are shown to release NO spontaneously upon hydration at initial rates that depend on the GSNO charge and are higher in the presence of CNC. As local NO release may exert cell proliferation action, 3D printed PAA/F127/CNC/GSNO hydrogels may serve as a versatile soft biomaterial for local NO delivery in regenerative medicine and other biomedical applications.

Ag@S-nitrosothiol core-shell nanoparticles for chemo and photothermal synergistic tumor targeted therapy

Along with the development of controlled delivery systems for targeted therapy, 'single-strategy' therapy often fails to achieve the desired performance in real body internal environments. In such a case, it is necessary to develop synergistic therapy strategies. Herein, for the first time, we designed and synthesized hyaluronic acid (HA) modified Ag@S-nitrosothiol core-shell nanoparticles for synergistic tumor cell targeted therapy based on photothermal therapy (PTT) and nitric oxide (NO) based chemotherapy. Triggered by near-infrared irradiation (NIR), the Ag core nanoparticle would convert the light to cytotoxic heat via a surface plasmon resonance mechanism for cancer cell apoptosis. Meanwhile, responding to NIR as well as the generated heat, the S-nitrosothiol polymeric shells would give off free NO at high concentration, inducing NO based chemotherapy. Tumor cell selective cytotoxicity assay in vitro as well as tumor bearing mouse experiments in vivo demonstrated the effective photothermal and NO based chemical synergistic tumor targeted therapy. This spatiotemporally controllable system could provide a new option and era for tumor targeted therapy in the future.

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.

Nitric Oxide-Releasing Thermoresponsive Pluronic F127/Alginate Hydrogel for Enhanced Antibacterial Activity and Accelerated Healing of Infected Wounds

Nitric oxide (NO), a highly reactive and lipophilic molecule, is one of the molecules present in the wound environment and implicated as an important regulator in all phases of wound healing. Here, we developed an NO-releasing thermoresponsive hydrogel (GSNO-PL/AL) composed of S-nitrosoglutathione (GSNO), pluronic F127 (PL), and alginate (AL) for the treatment of infected wounds. The GSNO was incorporated into the thermoresponsive PL/AL hydrogel, and differential scanning calorimetry techniques were used for the hydrogel characterization. The hydrogel was assessed by in vitro NO release, antibacterial activity, cytotoxicity, and wound-healing activity. The GSNO-PL/AL hydrogel demonstrated thermal responsiveness and biocompatibility, and it showed sustained NO release for 7 days. It also exhibited potent bactericidal activity against Gram-positive methicillin-resistant Staphylococcus aureus and Gram-negative multidrug-resistant Pseudomonas aeruginosa (MRPA). Moreover, the GSNO-PL/AL treatment of MRPA-infected wounds accelerated healing with a reduced bacterial burden in the wounds. The GSNO-PL/AL hydrogel would be a promising option for the treatment of infected wounds.

S-Nitroso-N-acetylpenicillamine impregnated endotracheal tubes for prevention of ventilator-associated pneumonia

The chances of ventilator-associated pneumonia (VAP) increases 6-20 folds when an endotracheal tube (ETT) is placed in a patient. VAP is one of the most common hospital-acquired infections and comprises 86% of the nosocomial pneumonia cases. This study introduces the idea of nitric oxide-releasing ETTs (NORel-ETTs) fabricated by the incorporation of the nitric oxide (NO) donor S-nitroso-N-acetylpenicillamine (SNAP) into commercially available ETTs via solvent swelling. The impregnation of SNAP provides NO release over a 7-day period without altering the mechanical properties of the ETT. The NORel-ETTs successfully reduced the bacterial infection from a commonly found pathogen in VAP, Pseudomonas aeruginosa, by 92.72 ± 0.97% when compared with the control ETTs. Overall, this study presents the incorporation of the active release of a bactericidal agent in ETTs as an efficient strategy to prevent the risk of VAP.

Effects of nitric oxide-releasing nanoparticles on neotropical tree seedlings submitted to acclimation under full sun in the nursery

Polymeric nanoparticles have emerged as carrier systems for molecules that release nitric oxide (NO), a free radical involved in plant stress responses. However, to date, nanoencapsulated NO donors have not been applied to plants under realistic field conditions. Here, we verified the effects of free and nanoencapsulated NO donor, S-nitroso-mercaptosuccinic acid (S-nitroso-MSA), on growth, physiological and biochemical parameters of neotropical tree seedlings kept under full sunlight in the nursery for acclimation. S-nitroso-MSA incorporation into chitosan nanoparticles partially protected the NO donor from thermal and photochemical degradation. The application of nanoencapsulated S-nitroso-MSA in the substrate favoured the growth of seedlings of Heliocarpus popayanensis, a shade-intolerant tree. In contrast, free S-nitroso-MSA or nanoparticles containing non-nitrosated mercaptosuccinic acid reduced photosynthesis and seedling growth. Seedlings of Cariniana estrellensis, a shade-tolerant tree, did not have their photosynthesis and growth affected by any formulations, despite the increase of foliar S-nitrosothiol levels mainly induced by S-nitroso-MSA-loaded nanoparticles. These results suggest that depending on the tree species, nanoencapsulated NO donors can be used to improve seedling acclimation in the nursery.

Tumor vasodilation by N-Heterocyclic carbene-based nitric oxide delivery triggered by high-intensity focused ultrasound and enhanced drug homing to tumor sites for anti-cancer therapy

Nitric oxide (NO) is widely known as an effective vasodilator at low concentrations. Drug delivery systems combined with NO can dilate blood vessels surrounding tumor tissues, and the drug accumulation in tumors is accelerated by the enhanced permeability and retention effect, leading to an improvement in the anti-tumor effect. N-heterocyclic carbene-based NO donors (e.g., 1,3-bis-(2,4,6-trimethylphenyl)imidazolylidene nitric oxide (IMesNO) have been developed for stable NO storing in air and water, and NO release by thermolysis. Herein, we demonstrated on-demand NO release by high-intensity focused ultrasound (HIFU) as a stimulus, which generated high heat and exerted an ablation effect when treated in vivo. We demonstrated IMesNO to be a HIFU-responsive NO donor and its potential application in vivo using IMesNO-loaded micelles. Moreover, IMesNO-loaded micelles mixed with drug-loaded micelles (IMesNO/DOX@MCs) showed acceleration of drug accumulation in tumor sites and enhanced tumor growth inhibition. Thus, our findings suggest a potential clinical bioapplication of NO-releasing drug-loaded micelles owing to the therapeutic function of NO and HIFU treatment for anti-cancer therapy.

Nitric Oxide Therapy for Diabetic Wound Healing

Nitric oxide (NO) represents a potential wound therapeutic agent due to its ability to regulate inflammation and eradicate bacterial infections. Two broad strategies exist to utilize NO for wound healing; liberating NO from endogenous reservoirs, and supplementing NO from exogenous sources. This progress report examines the efficacy of a variety of NO-based methods to improve wound outcomes, with particular attention given to diabetes-associated chronic wounds.

Nanoscale Coordination Polymers for Synergistic NO and Chemodynamic Therapy of Liver Cancer

Nitric oxide (NO) induces a multitude of antitumor activities, encompassing the induction of apoptosis, sensitization to chemo-, radio-, or immune-therapy, and inhibition of metastasis, drug resistance, angiogenesis, and hypoxia, thus attracting much attention in the area of cancer intervention. To improve the precise targeting and treatment efficacy of NO, a glutathione (GSH)-sensitive NO donor (1,5-bis[(l-proline-1-yl)diazen-1-ium-1,2-diol- O²-yl]-2,4-dinitrobenzene, BPDB) coordinates with iron ions to form the nanoscale coordination polymer (NCP) via a simple precipitation and then partial ion exchange process. The obtained Fe(II)-BNCP shows desirable solubility, biocompatibility, and circulation stability. Quick NO release triggered by high concentrations of GSH in tumor cells improves the specificity of NO release in situ, thus avoiding side effects in other tissues. Meanwhile, under high concentrations of H₂O₂ in tumors, Fe²⁺ ions in BPDB-based NCP, named Fe(II)-BNCP, exert Fenton activity to generate hydroxyl radicals (·OH), which is the main contribution for chemodynamic therapy (CDT). In addition, ·O₂^- generated by the Haber-Weiss reaction of Fe²⁺ ions with H₂O₂ can quickly react with NO to produce peroxynitrite anion (ONOO^-) that is more cytotoxic than ·O₂^- or NO only. This synergistic NO-CDT effect has been proved to retard the tumor growth in Heps xenograft ICR mouse models. This work not only implements a synergistic effect of NO-CDT therapy but also offers a simple and efficient strategy to construct a coordination polymer nanomedicine via rationally designed prodrug molecules such as NO donors.

Extended Nitric Oxide-Releasing Polyurethanes via S-Nitrosothiol-Modified Mesoporous Silica Nanoparticles

S-Nitrosothiol (RSNO)-modified mesoporous silica nanoparticles (MSNs) were doped into polyurethane (PU) to achieve extended NO-releasing coatings. Parameters influencing the synthesis of RSNO-functionalized nitric oxide (NO)-releasing MSNs were evaluated to elucidate the impact of pore structure on NO release characteristics. The porous particles were characterized as having larger NO payloads and longer NO release durations than those of nonporous particles, a feature attributed to the recombination of the NO radical in confined intraporous microenvironments. NO release kinetics, particle leaching, and thermal stability of the RSNO-modified MSNs dispersed in PU were evaluated as a function of PU structure to determine the feasibility of preparing a range of NO-releasing polymers for biomedical device-coating applications. The NO release kinetics from the PUs proved to be highly extended (>30 d) and consistent over a range of PU properties. Furthermore, RSNO-modified MSN leaching was not observed from the PUs. The NO release payloads were also maintained for 4 days for polymers stored at 0 °C.

Long-term decomposition of aqueous S-nitrosoglutathione and S-nitroso-N-acetylcysteine: Influence of concentration, temperature, pH and light

Primary S-nitrosothiols (RSNOs) have received significant attention for their ability to modulate NO signaling in many physiological and pathophysiological processes. Such actions and their potential pharmaceutical uses demand a better knowledge of their stability in aqueous solutions. Herein, we investigated the effects of concentration, temperature, pH, room light and metal ions on the long-term kinetic behavior of two representative primary RSNOs, S-nitrosoglutathione (GSNO) and S-nitroso-N-acetylcysteine (SNAC). The thermal decomposition of GSNO and SNAC were shown to be affected by the auto-catalytic action of the thiyl radicals. At 25 °C in the dark and protected from the catalytic action of metal ions, GSNO and SNAC solutions 1 mM showed half-lives of 49 and 76 days, and apparent activation energies of 84 ± 14 and 90 ± 6 kJ mol^-1, respectively. Both GSNO and SNAC exhibited increased stability in the pH range 5-7. At high pH the decomposition pathway of GSNO involves the formation of an intermediate (GS-NO₂^2-), which decomposes generating GSH and nitrite. GSNO solutions displayed lower sensitivity to the catalytic action of metal ions than SNAC and the exposure to room light led to a 5-fold increase in the initial rates of decomposition of both RSNOs. In all comparisons, SNAC solutions showed higher stability than GSNO solutions. These findings provide strategic information about the stability of GSNO and SNAC and may open new perspectives for their use as experimental or therapeutic NO donors.

Nitric oxide-releasing semi-crystalline thermoplastic polymers: preparation, characterization and application to devise anti-inflammatory and bactericidal implants

Semi-crystalline thermoplastics are an important class of biomaterials with applications in creating extracorporeal and implantable medical devices. In situ release of nitric oxide (NO) from medical devices can enhance their performance via NO's potent anti-thrombotic, bactericidal, anti-inflammatory, and angiogenic activity. However, NO-releasing semi-crystalline thermoplastic systems are limited and the relationship between polymer crystallinity and NO release profile is unknown. In this paper, the functionalization of poly(ether-block-amide) (PEBA), Nylon 12, and polyurethane tubes, as examples of semi-crystalline polymers, with the NO donor S-nitroso-N-acetylpenicillamine (SNAP) within, is demonstrated via a polymer swelling method. The degree of crystallinity of the polymer plays a crucial role in both SNAP impregnation and NO release. Nylon 12, which has a relatively high degree of crystallinity, exhibits an unprecedented NO release duration of over 5 months at a low NO level, while PEBA tubing exhibits NO release over days to weeks. As a new biomedical application of NO, the NO-releasing PEBA tubing is examined as a cannula for continuous subcutaneous insulin infusion. The released NO is shown to enhance insulin absorption into the bloodstream probably by suppressing the tissue inflammatory response, and thereby could benefit insulin pump therapy for diabetes management.

Single-Molecular Near-Infrared-II Theranostic Systems: Ultrastable Aggregation-Induced Emission Nanoparticles for Long-Term Tracing and Efficient Photothermal Therapy

Second near-infrared (NIR-II, 1000-1700 nm) fluorescence bioimaging has attracted tremendous scientific interest and already been used in many biomedical studies. However, reports on organic NIR-II fluorescent probes for in vivo photoinduced imaging and simultaneous therapy, as well as the long-term tracing of specific biological objects, are still very rare. Herein we designed a single-molecular and NIR-II-emissive theranostic system by encapsulating a kind of aggregation-induced emission luminogen (AIEgen, named BPN-BBTD) with amphiphilic polymer. The ultra-stable BPN-BBTD nanoparticles were employed for the NIR-II fluorescence imaging and photothermal therapy of bladder tumors in vivo. The 785 nm excitation triggered photothermal therapy could completely eradicate the subcutaneous tumor and inhibit the growth of orthotopic tumors. Furthermore, BPN-BBTD nanoparticles were capable of monitoring subcutaneous and orthotopic tumors for a long time (32 days). Single-molecular and NIR-II-emitted aggregation-induced emission nanoparticles hold potential for the diagnosis, precise treatment, and metastasis monitoring of tumors in the future.

Supramolecular poly(acrylic acid)/F127 hydrogel with hydration-controlled nitric oxide release for enhancing wound healing

Topical nitric oxide (NO) delivery has been shown to accelerate wound healing. However, delivering NO to wounds at appropriate rates and doses requires new biomaterial-based strategies. Here, we describe the development of supramolecular interpolymer complex hydrogels comprising PEO-PPO-PEO (F127) micelles embedded in a poly(acrylic acid) (PAA) matrix, with S-nitrosoglutathione (GSNO) molecules dissolved in the hydrophilic domain. We show that PAA:F127/GSNO hydrogels start releasing NO upon hydration at rates controlled by their rates of water absorption. SAXS measurements indicate that the supramolecular structure of the hydrogels retains long-range order domains of F127 micelles. The PAA/F1227 hydrogels displayed dense morphologies and reduced rates of hydration. The NO release rates remain constant over the first 200 min, are directly correlated with the hydration rates of the PAA:F127/GSNO hydrogels, and can be modulated in the range of 40 nmol/g h to 1.5 μmol/g h by changing the PAA:F127 mass ratio. Long-term NO-release profiles over 5 days are governed by the first-order exponential decay of GSNO, with half-lives in the range of 0.5-3.4 days. A preliminary in vivo study on full-thickness excisional wounds in mice showed that topical NO release from the PAA:F127/GSNO hydrogels is triggered by exudate absorption and leads to increased angiogenesis and collagen fiber organization, as well as TGF-β, IGF-1, SDF-1, and IL-10 gene expressions in the cicatricial tissue. In summary, these results suggest that hydration-controlled NO release from topical PAA:F127/GSNO hydrogels is a potential strategy for enhancing wound healing.

STATEMENT OF SIGNIFICANCE

The topical delivery of nitric oxide (NO) to wounds may provide significant beneficial results and represent a promising strategy to treat chronic wounds. However, wound dressings capable of releasing NO after application and allowing the modulation of NO release rates, demand new platforms. Here, we describe a novel strategy to overcome these challenges, based on the use of supramolecular poly(acrylic acid) (PAA):F127 hydrogels charged with the NO donor S-nitrosoglutathione (GSNO) from whereby the NO release can be triggered by exudate absorption and delivered to the wound at rates controlled by the PAA:F127 mass ratio. Preliminary in vivo results offer a proof of concept for this strategy by demonstrating increased angiogenesis; collagen fibers organization; and TGF-β, IGF-1, SDF-1, and IL-10 gene expressions in the cicatricial tissue after topical treatment with a PAA:F127/GSNO hydrogel.

Biocompatible and Antibacterial Nitric Oxide-Releasing Pluronic F-127/Chitosan Hydrogel for Topical Applications

Nitric oxide (NO) is involved in physiological processes, including vasodilatation, wound healing and antibacterial activities. As NO is a free radical, designing drugs to generate therapeutic amounts of NO in controlled spatial and time manners is still a challenge. In this study, the NO donor S-nitrosoglutathione (GSNO) was incorporated into the thermoresponsive Pluronic F-127 (PL)-chitosan (CS) hydrogel, with an easy and economically feasible methodology. CS is a polysaccharide with known antimicrobial properties. Scanning electron microscopy, rheology and differential scanning calorimetry techniques were used for hydrogel characterization. The results demonstrated that the hydrogel has a smooth surface, thermoresponsive behavior and good mechanical stability. The kinetics of NO release and GSNO diffusion from GSNO-containing PL/CS hydrogel demonstrated a sustained NO/GSNO release, in concentrations suitable for biomedical applications. The GSNO-PL/CS hydrogel demonstrated a concentration-dependent toxicity to Vero cells, and antimicrobial activity to Pseudomonas aeruginosa (minimum inhibitory concentration and minimum bactericidal concentration values of 0.5 µg·mL-1 of hydrogel, which corresponds to 1 mmol·L-1 of GSNO). Interestingly, the concentration range in which the NO-releasing hydrogel demonstrated an antibacterial effect was not found to be toxic to the Vero mammalian cell. Thus, the GSNO-PL/CS hydrogel is a suitable biomaterial for topical NO delivery applications.

Use of gasotransmitters for the controlled release of polymer-based nitric oxide carriers in medical applications

Nitric Oxide (NO) is a small molecule gasotransmitter synthesized by nitric oxide synthase in almost all types of mammalian cells. NO is synthesized by NO synthase by conversion of l-arginine to l-citrulline in the human body. NO then stimulates soluble guanylate cyclase, from which various physiological functions are mediated in a concentration-dependent manner. High concentrations of NO induce apoptosis or antibacterial responses whereas low NO circulation leads to angiogenesis. The bidirectional effect of NO has attracted considerable attention, and efforts to deliver NO in a controlled manner, especially through polymeric carriers, has been the topic of much research. This naturally produced signaling molecule has stood out as a potentially more potent therapeutic agent compared to exogenously synthesized drugs. In this review, we will focus on past efforts of using the controlled release of NO via polymer-based materials to derive specific therapeutic results. We have also added studies and our future suggestions on co-delivery methods with other gasotransmitters as a step towards developing multifunctional carriers.

Bright AIE Nanoparticles with F127 Encapsulation for Deep-Tissue Three-Photon Intravital Brain Angiography

Deep-tissue imaging is of great significance to biological applications. In this paper, a deep-red emissive luminogen 2,3-bis(4'-(diphenylamino)-[1,1'-biphenyl]-4-yl) fumaronitrile (TPATCN) with aggregation-induced emission (AIE) feature is prepared. TPATCN molecules were then encapsulated within a polymeric matrix of Pluronic F-127 to form nanoparticles (NPs). TPATCN NPs exhibit bright three-photon fluorescence (3PF) in deep-red region, together with high chemical stability, good photostability, and biocompatibility. They are further utilized for in vivo 3PF imaging of the brain vasculature of mice, under the excitation of a 1550 nm femtosecond laser. A vivid 3D reconstruction of the brain vasculature is then built with a penetration depth of 875 µm, which is the largest in ever reported 3PF imaging based on AIE NPs. After that, by collecting both of the 3PF and third-harmonic generation signals, multichannel nonlinear optical imaging of the brain blood vessels is further realized. These results will be helpful to study the structures and functions of the brain in the future.

Liquid-infused nitric oxide-releasing (LINORel) silicone for decreased fouling, thrombosis, and infection of medical devices

Recent reports on liquid-infused materials have shown promise in creating ultra-low fouling surfaces, but are limited in their ability to prevent bacterial proliferation and prevent platelet activation in blood-contacting applications. In this work, a liquid-infused nitric oxide-releasing (LINORel) material is created by incorporating the nitric oxide (NO) donor S-nitroso-acetylpenicillamine (SNAP) and silicone oil in commercial medical grade silicone rubber tubing through a solvent swelling process. This combination provides several key advantages over previous NO-releasing materials, including decreased leaching of NO donor, controlled release of NO, and maintenance of ultra-low fouling property of liquid-infused materials. The LINORel tubing reduces protein adhesion as observed using fluorescence imaging, and platelet adhesion (81.7 ± 2.5%) in vitro over a 2 h period. The LINORel combination greatly reduces bacterial adhesion and biofilm formation of two most common pathogens responsible for hospital acquired infections: gram-positive Staphylococcus aureus and gram-negative Pseudomonas aeruginosa (99.3 ± 1.9% and 88.5 ± 3.3% respectively) over a 7-day period in a CDC bioreactor environment. Overall, the LINORel approach provides a synergistic combination of active and passive non-fouling approaches to increase biocompatibility and reduce infection associated with medical devices.

Chitosan nanoparticles for nitric oxide delivery in human skin

The use of nanoparticle-based transdermal delivery systems is a promising approach to efficiently carry and deliver therapeutic agents for dermal and systemic administration. Nitric oxide (NO) is a key molecule that plays important roles in human skin such as the control of skin homeostasis, skin defense, control of dermal blood flow, and wound healing. In addition, human skin contains stores of NO derivatives that can be mobilized and release free NO upon UV irradiation with beneficial cardiovascular effects, for instance the control of blood pressure. In this work, the NO donor precursor glutathione (GSH) was encapsulated (encapsulation efficiency of 99.60%) into ultra-small chitosan nanoparticles (CS NPs) (hydrodynamic size of 30.65 ± 11.90 nm). GSH-CS NPs have a core-shell structure, as revealed by atomic force microscopy and X-ray photoelectron spectroscopy, in which GSH is protected in the nanoparticle core. Nitrosation of GSH by nitrous acid led to the formation of the NO donor S-nitrosogluthathione (GSNO) into CS NPs. The GSNO release from the CS NPs followed a Fickian diffusion described by the Higuchi mathematical model. Topical application of GSNO-CS NPs in intact human skin significantly increased the levels of NO and its derivatives in the epidermis, as assayed by confocal microscopy, and this effect was further enhanced by skin irradiation with UV light. Therefore, NO-releasing CS NPs are suitable materials for transdermal NO delivery to local and/or systemic therapies.

Dual crosslinked chondroitin sulfate injectable hydrogel formed via continuous Diels-Alder (DA) click chemistry for bone repair

In the present work, a thermosensetive copolymer with a low gelation concentration under 37°C, F127@ChS (F127 crosslinked chondroitin sulfate) was synthesized via DA click chemistry between F127-AMI (maleimido terminated F127) and ChS-furan (furfurylamine grafted chondroitin sulfate). Then, dual crosslinked hydrogels were prepared based on F127@ChS and PEG-AMI (maleimido terminated polyethylene glycol). The physical crosslinking of F127@ChS affords the hydrogel fast gelation behavior, while in situ DA click reaction occurred between F127@ChS and PEG-AMI affords the hydrogel system covalent crosslinking. The dual crosslinked injectable hydrogel was applied as scaffold to load BMP-4 for rat cranial defect repair. As indicated by X-ray imaging, cranial digital images and histological (HE and Masson) staining analysis, new bone tissues were formed in the defected area after 12 weeks repair. The results demonstrate that the novel dual crosslinked injectable hydrogel offer an interesting option for cranial bone tissue engineering.