The role of nitric oxide in ocular surface physiology and pathophysiology

Dissecting NO Association and Dissociation Dynamics of Myoglobin, Hemoglobin, and Heme-Model Compounds

Nitric oxide (NO) binding to heme-proteins is a physiologically relevant molecular process, contributing to regulate blood pressure and flow to provide an adequate O2 supply to all body compartments. This appears to be relevant for energy-demanding tissues, characterized by high O2-consuming rates, such as the eye's retina and striated muscles under physical effort. The reaction of NO with the ferrous heme-Fe atom (heme-Fe(II)) is characterized by very fast association rate constants and very slow dissociation kinetics, which drastically differ from those observed for other gaseous ligands, such as O2 and CO. Since the heme-Fe(II)-NO bond is photosensitive, it is possible to investigate both the bimolecular dynamics of the NO pathway from the bulk solution to the metal center and ligand trapping within cavities, located in the protein matrix and affecting heme-Fe(II)-NO complex formation and dissociation. Here, dynamics of NO binding to human hemoglobin and sperm whale and horse heart myoglobin, both involved in the supply of O2 to tissues and organs, are reported and compared with heme-model compounds, dissecting the various steps of the ligand migration from the bulk solution through the protein matrix to the heme active center, correlating dynamics with structural features to clarify the structural determinants of heme-Fe(II) nitrosylation steps.

Nitrite binding to myoglobin and hemoglobin: Reactivity and structural aspects

Nitrite (NO2-) interacts with myoglobin (Mb) and hemoglobin (Hb) behaving as a ligand of both the ferrous (i.e., Mb(II) and Hb(II)) and ferric (i.e., Mb(III) and Hb(III)) forms. However, while the binding to the Fe(III) species corresponds to the formation of a stable complex (i.e., Mb(III)-NO2- and Hb(III)-NO2-), in the case of the ferrous forms the reaction proceeds with a nitrite reductase redox process, leading to the oxidation of the heme-protein with the reduction of NO2- to NO. This event is of the utmost importance for the rapid production of NO in vivo in the blood stream and in striated muscles, being crucial for the regulation of the blood flow, and thus for O2 supply to poorly oxygenated tissues, such as the eye's retina. Further, NO2- interacts with Mb(II)-O2 and Hb(II)-O2, inducing their oxidation with a complex mechanism, which has been only partially elucidated. Mb and Hb form the complex with NO2- through the O-nitrito binding mode (i.e., Fe-ONO-), which is regulated by residues paving the heme distal side; thus, in a site-directed mutant, where HisE7 is substituted by Val, the interaction occurs in the N-nitro binding mode (i.e., Fe-N(O)O-), like in most other heme-proteins. The structure-function relationships of the interaction of NO2- with both ferric and ferrous forms of Mb and Hb are discussed here.

Real-world impact of latanoprostene bunod ophthalmic solution 0.024% in glaucoma therapy: a narrative review

Latanoprostene bunod ophthalmic solution (LBN) 0.024% is a topical nitric oxide (NO)-donating prostaglandin F2α (PGF2α) analog first approved in November 2017 for reduction of intraocular pressure (IOP) in patients with ocular hypertension (OHT) or open-angle glaucoma (OAG). This narrative review describes the unique mechanism of action of LBN and summarizes available real-world data. Upon instillation, LBN is metabolized into latanoprost acid and butanediol mononitrate, which is further reduced to NO and an inactive metabolite. Latanoprost acid increases aqueous humor outflow primarily through the uveoscleral (unconventional) pathway, whereas NO increases outflow through the trabecular (conventional) pathway. Eight studies were identified: 2 studies in newly diagnosed, treatment-naïve patients with OHT or OAG, 4 studies of adjunctive therapy in patients with glaucoma receiving other IOP-lowering therapies, and 2 studies in which patients with glaucoma switched to LBN monotherapy or adjunctive therapy. Decreases in IOP after initiating LBN in newly diagnosed patients or adding/switching to LBN were generally consistent with reductions observed in clinical trials and sustained throughout the studies. Rates of discontinuation due to inadequate IOP lowering ranged from 12.2% to 17.1%. LBN was generally well tolerated in real-world studies; the most common adverse events were consistent with the known safety profile of LBN. Data from real-world studies provide important insights regarding the potential effectiveness and tolerability of LBN in the clinical setting and suggest that LBN is well tolerated and associated with significant, clinically meaningful, and durable reductions in IOP.

Value of Serum Asymmetric Dimethylarginine (ADMA) As a Novel Biomarker for Uveitis in Behçet's Disease

PURPOSE

To evaluate the serum asymmetric dimethylarginine (ADMA) level as a biomarker for uveitis in Behçet's Disease (BD).

METHODS

In this cross-sectional study, two groups of BD patients were examined: 33 with uveitis and 27 without uveitis. All patients were clinically evaluated, with disease activity measured by Behçet's Disease Current Activity Form (BDCAF) score. They also underwent thorough ophthalmic evaluation, and routine laboratory investigations, including serum ADMA.

RESULTS

Patients with BD who experienced active or inactive uveitis had higher levels of serum ADMA compared to those without uveitis. Anterior (ρ = 0.34, p < 0.01), posterior (ρ = 0.3, p < 0.05), and pan uveitis (ρ = 0.35, p < 0.01) were significantly correlated with serum ADMA levels. However, there was no significant correlation between ADMA and other BD manifestations. ROC curve analysis showed that increased serum ADMA levels in BD patients predicted uveitis with a sensitivity of 61.8%, specificity of 96.2%, and AUC of 0.78(95% CI: 0.66-0.9, p < 0.001).

CONCLUSION

Serum ADMA level can serve as a novel biomarker of uveitis in BD and its severity with good diagnostic accuracy, regardless of its site or activity.

Rational design of antibiotic-free antimicrobial contact lenses: Trade-offs between antimicrobial performance and biocompatibility

Microbial keratitis associated with contact lenses (CLs) wear remains a significant clinical concern. Antibiotic therapy is the current standard of care. However, the emergence of multidrug-resistant pathogens necessitates the investigation of alternative strategies. Antibiotic-free antimicrobial contact lenses (AFAMCLs) represent a promising approach in this regard. The effectiveness of CLs constructed with a variety of antibiotic-free antimicrobial strategies against microorganisms has been demonstrated. However, the impact of these antimicrobial strategies on CLs biocompatibility remains unclear. In the design and development of AFAMCLs, striking a balance between robust antimicrobial performance and optimal biocompatibility, including safety and wearing comfort, is a key issue. This review provides a comprehensive overview of recent advancements in AFAMCLs technology. The focus is on the antimicrobial efficacy and safety of various strategies employed in AFAMCLs construction. Furthermore, this review investigates the potential impact of these strategies on CLs parameters related to wearer comfort. This review aims to contribute to the continuous improvement of AFAMCLs and provide a reference for the trade-off between resistance to microorganisms and wearing comfort. In addition, it is hoped that this review can also provide a reference for the antimicrobial design of other medical devices.

Moringa oleifera hydroalcoholic leaf extracts mitigate valproate-induced oxidative status in the extraorbital lacrimal gland in a rat model

Dysfunction of the extraorbital lacrimal gland (ELG) can lead to loss of vision due to damage to the epithelium of cornea. The broad-spectrum anti-epileptic drug sodium valproate (SV) has numerous side effects. Moringa oleifera (M.oleifera) is widely used as a food and in folk medicine. The effects of orally administered SV and M. oleifera hydroalcoholic leaf extract on rat ELG were investigated in this study by analysing both antioxidant and oxidant parameters. Additionally, boron level and tissue factor (TF) activity were determined. Protein changes were detected by sodium dodecyl sulfate gel electrophoresis (SDS-PAGE). Significantly lower values of glutathione (GSH), superoxide dismutase (SOD), catalase (CAT) and total antioxidant status (TAS) were observed in the SV group compared to the control group. Treatment with Moringa extract significantly increased SOD, CAT and TAS values in the Moringa given SV group (SVM). While no significant differences were observed between the sialic acid values of the groups, lipid peroxidation (LPO), nitric oxide (NO) and total oxidant status (TOS) values were significantly elevated in the SV group compared to the control group. Due to the effect of Moringa extract, LPO, NO and TOS levels were significantly decreased in the SVM group compared to the SV group. TF activity was not meaningfully altered between groups. Compared to control rats, oxidative stress index (OSI) level significantly increased, whereas the boron level decreased in the SV group. Moringa extract treatment noticeably reduced OSI in the SVM group. According to SDS-PAGE, decreases in the density of protein bands with molecular weights of 51, 83, and 90 kDa were observed in SV given rats compared to the other groups. These decreases were reversed by the administration of Moringa extract. Moringa extract has shown protective properties arising from antioxidant potential, especially with its very low OSI value. Individuals undergoing SV treatment and having ELG complications might consider using Moringa extract to mitigate valproate induced damage.

Paper-based Electrochemical Sensor Integrated with Gold Nanoparticle-Decorated Carbon Cloth as a Working Electrode for Nitric Oxide Detection in Artificial Tears

Nitric oxide (NO) in human tears regulates numerous ocular surface processes, such as tear generation, corneal wound healing, conjunctival vascular tone, and so forth. Any deviation from its normal concentration is linked to various ocular syndromes, including microbial keratitis, conjunctivitis, pterygium, dry eye, retinitis, glaucoma, and so forth. Therefore, precise monitoring of NO in tears can be considered as a potential biomarker for ocular diseases. Here, we report a highly sensitive and selective electrochemical NO sensor using carbon ink-based electrodes. Counter, working (WE), and reference electrodes have been designed and painted on a butter paper by using carbon ink. To improve the sensing performance, the WE has been modified with a gold nanoparticle (Au NP)-deposited carbon cloth (CC). Such a paper-based sensor demonstrated high sensitivity of ∼0.34 μA μM-1 cm-2, ultralow detection limit of ∼2.35 nM, wide linear range of 10 nM-0.4 mM, and fast response time (0.35 s). The sensor also showed excellent stability and selectivity toward the interfering agents in human body fluids. Such a low-cost, flexible paper-based sensor was employed for the detection of NO in artificial tears.

Adverse effects of meteorological factors and air pollutants on dry eye disease: a hospital-based retrospective cohort study

Although previous studies have suggested that meteorological factors and air pollutants can cause dry eye disease (DED), few clinical cohort studies have determined the individual and combined effects of these factors on DED. We investigated the effects of meteorological factors (humidity and temperature) and air pollutants [particles with a diameter ≤ 2.5 μ m (PM2.5), ozone (O3), nitrogen dioxide (NO2), and carbon monoxide (CO)] on DED. A retrospective cohort study was conducted on 53 DED patients. DED was evaluated by Symptom Assessment in Dry Eye (SANDE), tear secretion, tear film break-up time (TBUT), ocular staining score (OSS), and tear osmolarity. To explore the individual, non-linear, and joint associations between meteorological factors, air pollutants, and DED parameters, we used generalized linear mixed model (GLMM) and Bayesian kernel machine regression (BKMR). After adjusting for all covariates, lower relative humidity or temperature was associated with a higher SANDE (p < 0.05). Higher PM2.5, O3, and NO2 levels were associated with higher SANDE and tear osmolarity (p < 0.05). Higher O3 levels were associated with lower tear secretion and TBUT, whereas higher NO2 levels were associated with higher OSS (p < 0.05). BKMR analyses indicated that a mixture of meteorological factors and air pollutants was significantly associated with increased SANDE, OSS, tear osmolarity, and decreased tear secretion.

INOS ablation promotes corneal wound healing via activation of Akt signaling

Corneal injury leads to impaired normal structure of the cornea. Improving the wound healing process in epithelial cells significantly contributes to ocular damage treatments. Here, we aimed to investigate the potential mechanisms of nitric oxide (NO) and its mediator, inducible nitric oxide synthase (iNOS), in the process of corneal wound healing. We established a corneal injury model of iNOS-/- mice, and treated human corneal epithelial cell lines (HCE-2) with the iNOS inhibitor L-INL, with or without NO replenishment by supplying sodium nitroferricyanide dihydrate (SNP). Our findings showed that inhibition of NO/iNOS accelerated corneal repair, enhanced uPAR (a receptor protein indicating the migration ability), and improved epithelial cell migration. Furthermore, NO/iNOS ablation activated Akt phosphorylation, reduced neutrophil marker protein MPO expression, and downregulated the transcription of inflammation cytokines CXCL-1, CXCL-2, IL-1β, IL-6, and TNF-α. However, the protective effects of NO/iNOS inhibition are significantly reduced by NO replenishment when treated with SNP. Therefore, we confirmed that inhibiting NO/iNOS improved the corneal wound healing by facilitating epithelial cell migration and reducing inflammatory reactions, which might be related to the activation of the Akt signaling pathway.

Nitric Oxide Binding Geometry in Heme-Proteins: Relevance for Signal Transduction

Nitric oxide (NO) synthesis, signaling, and scavenging is associated to relevant physiological and pathological events. In all tissues and organs, NO levels and related functions are regulated at different levels, with heme proteins playing pivotal roles. Here, we focus on the structural changes related to the different binding modes of NO to heme-Fe(II), as well as the modulatory effects of this diatomic messenger on heme-protein functions. Specifically, the ability of heme proteins to bind NO at either the distal or proximal side of the heme and the transient interchanging of the binding site is reported. This sheds light on the regulation of O2 supply to tissues with high metabolic activity, such as the retina, where a precise regulation of blood flow is necessary to meet the demand of nutrients.

Dietary Nitrate Metabolism in Porcine Ocular Tissues Determined Using 15N-Labeled Sodium Nitrate Supplementation

Nitrate (NO3-) obtained from the diet is converted to nitrite (NO2-) and subsequently to nitric oxide (NO) within the body. Previously, we showed that porcine eye components contain substantial amounts of nitrate and nitrite that are similar to those in blood. Notably, cornea and sclera exhibited the capability to reduce nitrate to nitrite. To gain deeper insights into nitrate metabolism in porcine eyes, our current study involved feeding pigs either NaCl or Na15NO3 and assessing the levels of total and 15N-labeled NO3-/NO2- in various ocular tissues. Three hours after Na15NO3 ingestion, a marked increase in 15NO3- and 15NO2- was observed in all parts of the eye; in particular, the aqueous and vitreous humor showed a high 15NO3- enrichment (77.5 and 74.5%, respectively), similar to that of plasma (77.1%) and showed an even higher 15NO2- enrichment (39.9 and 35.3%, respectively) than that of plasma (19.8%). The total amounts of NO3- and NO2- exhibited patterns consistent with those observed in 15N analysis. Next, to investigate whether nitrate or nitrite accumulate proportionally after multiple nitrate treatments, we measured nitrate and nitrite contents after supplementing pigs with Na15NO3 for five consecutive days. In both 15N-labeled and total nitrate and nitrite analysis, we did not observe further accumulation of these ions after multiple treatments, compared to a single treatment. These findings suggest that dietary nitrate supplementation exerts a significant influence on nitrate and nitrite levels and potentially NO levels in the eye and opens up the possibility for the therapeutic use of dietary nitrate/nitrite to enhance or restore NO levels in ocular tissues.

Simultaneous real-time detection of fractional exhaled nitric oxide and end-tidal carbon dioxide by quantum cascade laser absorption spectroscopy

The simultaneous detection of fractional exhaled nitric oxide (FeNO) and end-tidal carbon dioxide (ETCO2) is of great importance for the distinguishing and diagnosis of asthma and chronic obstructive pulmonary disease (COPD), providing more comprehensive information on respiratory disorders. This work demonstrates a simultaneous ETCO2 and FeNO detection system based on quantum cascade laser absorption spectroscopy (QCLAS) technology was presented. The system employs wavelength modulation spectroscopy (WMS) technology and the Herriott multi-pass cell, achieving a detection limit of 2.82 ppb for nitric oxide (NO) and 0.05 % for carbon dioxide (CO2). Real-time exhalation measurements were performed on volunteers with varying ETCO2 and FeNO levels, and the results of the test can accurately distinguish whether the corresponding volunteer was healthy, had asthma or COPD. The effect of exhalation flow rate on the concentration of the two gases was explored. A range of expiratory flow rates were tested in the flow rate interval from 1 to 4 L/min, and there was always an inverse relationship between expiratory flow rate and FeNO concentration, but flow rate changes did not affect ETCO2 concentration. The results indicate that this detection system can simultaneously and effectively measure ETCO2 and FeNO concentrations in real-time.

Nitrobindin versus myoglobin: A comparative structural and functional study

Most hemoproteins display an all-α-helical fold, showing the classical three on three (3/3) globin structural arrangement characterized by seven or eight α-helical segments that form a sandwich around the heme. Over the last decade, a completely distinct class of heme-proteins called nitrobindins (Nbs), which display an all-β-barrel fold, has been identified and characterized from both structural and functional perspectives. Nbs are ten-stranded anti-parallel all-β-barrel heme-proteins found across the evolutionary ladder, from bacteria to Homo sapiens. Myoglobin (Mb), commonly regarded as the prototype of monomeric all-α-helical globins, is involved along with the oligomeric hemoglobin (Hb) in diatomic gas transport, storage, and sensing, as well as in the detoxification of reactive nitrogen and oxygen species. On the other hand, the function(s) of Nbs is still obscure, even though it has been postulated that they might participate to O2/NO signaling and metabolism. This function might be of the utmost importance in poorly oxygenated tissues, such as the eye's retina, where a delicate balance between oxygenation and blood flow (regulated by NO) is crucial. Dysfunction in this balance is associated with several pathological conditions, such as glaucoma and diabetic retinopathy. Here a detailed comparison of the structural, spectroscopic, and functional properties of Mb and Nbs is reported to shed light on the similarities and differences between all-α-helical and all-β-barrel heme-proteins.

Nanozyme-Cosmetic Contact Lenses for Ocular Surface Disease Prevention

Efficiently balancing excess reactive oxygen species (ROS) caused by various factors on the ocular surface is a promising strategy for preventing the development of ocular surface diseases (OSDs). Nevertheless, the conventional topical administration of antioxidants is limited in efficacy due to poor absorption, rapid metabolism, and irreversible depletion, which impede their performance. To address this issue, contact lenses embedded with antioxidant nanozymes that can continuously scavenge ROS, thereby providing an excellent preventive effect against OSDs are developed. Specifically, Prussian blue family nanozymes are chosen based on their multiple antioxidant enzyme-like activities and excellent biocompatibility. The diverse range of colors made them promising candidates for the development of cosmetic contact lenses (CCLs) as a substitute for conventional pigments. The efficacy of nanozyme-CCLs is demonstrated in rabbits and rats exposed to a high risk of developing OSDs. These OSDs' prevention nanozyme-CCLs can pave the way for CCLs toward powerful wearable biomedical devices and provide novel strategies for the rational utilization of nanomaterials in clinical practice.

Ocular Surface Evaluation after Switch from Latanoprost 0.005% to Latanoprostene Bunod 0.024

Aim and background

To evaluate the ocular surface of patients treated with latanoprost (LT) 0.005% who switched to latanoprostene bunod (LBN) 0.024%.

Materials and methods

A prospective and nonrandomized clinical study of a case series was performed, including patients with chronic open-angle glaucoma who were on previous LT-only treatment and, after a washout period, switched to LBN, with a 3-month follow-up. The main parameter to be evaluated was the ocular surface disease index (OSDI) test. In addition, best-corrected visual acuity (BCVA), intraocular pressure (IOP), biomicroscopic aspect of the ocular surface, measuring tear breakup time, fluorescein staining (grading performed on Oxford scale) and Schirmer I test were evaluated.

Results

A total of 36 patients (72 eyes) were included, 21 women (58.3%) and 15 men (41.7%, with a mean age of 65.6 ± 10.9 years (37-86). The initial OSDI score was 17.8 ± 12.1 and improved to 11.1 ± 10.5 (p < 0.01). From the data evaluated at biomicroscopy, an improvement was observed in the Oxford scale from 0.6 ± 0.7 to 0.2 ± 0.8 (p: 0.01), but no statistically significant changes were observed in the break-up time (BUT) and Schirmer. BCVA remained stable, as did IOP, which was initially 13.4 ± 2.1 mm Hg and, after performing the LBN treatment change, went to 13.1 ± 1.7 mm Hg.

Conclusion

After the change of treatment from LT 0.005% to LBN 0.024%, the patients had an improvement in the ocular surface, maintaining control of their IOP. The need to investigate possible beneficial mechanisms on the ocular surface in glaucoma patients treated with LBN, potentially related to nitric oxide, is raised.

Clinical significance

Patients treated with LT 0.005% who switched to LBN 0.024% had an improvement in ocular surface symptoms and signs, keeping IOP under control.Latanoprostene bunod (LBN) 0.024% may have beneficial effects on the ocular surface, which should be further studied.

How to cite this article

Zanutigh V, Galetto L, Valvecchia F, et al. Ocular Surface Evaluation after Switch from Latanoprost 0.005% to Latanoprostene Bunod 0.024%. J Curr Glaucoma Pract 2023;17(4):205-209.

Toxic External Exposure Leading to Ocular Surface Injury

The surface of the eye is directly exposed to the external environment, protected only by a thin tear film, and may therefore be damaged by contact with ambient particulate matter, liquids, aerosols, or vapors. In the workplace or home, the eye is subject to accidental or incidental exposure to cleaning products and pesticides. Organic matter may enter the eye and cause infection. Ocular surface damage can trigger a range of symptoms such as itch, discharge, hyperemia, photophobia, blurred vision, and foreign body sensation. Toxin exposure can be assessed clinically in multiple ways, including via measurement of tear production, slit-lamp examination, corneal staining, and conjunctival staining. At the cellular level, environmental toxins can cause oxidative damage, apoptosis of corneal and conjunctival cells, cell senescence, and impaired motility. Outcomes range from transient and reversible with complete healing to severe and sight-compromising structural changes. Classically, evaluation of tolerance and safety was carried out using live animal testing; however, new in vitro and computer-based, in silico modes are superseding the gold standard Draize test. This review examines how environmental features such as pollutants, temperature, and seasonality affect the ocular surface. Chemical burns to the eye are considered, and approaches to protect the ocular surface are detailed.

Nitrite Reductase Activity of Ferrous Nitrobindins: A Comparative Study

Nitrobindins (Nbs) are all-β-barrel heme proteins spanning from bacteria to Homo sapiens. They inactivate reactive nitrogen species by sequestering NO, converting NO to HNO2, and promoting peroxynitrite isomerization to NO3−. Here, the nitrite reductase activity of Nb(II) from Mycobacterium tuberculosis (Mt-Nb(II)), Arabidopsis thaliana (At-Nb(II)), Danio rerio (Dr-Nb(II)), and Homo sapiens (Hs-Nb(II)) is reported. This activity is crucial for the in vivo production of NO, and thus for the regulation of blood pressure, being of the utmost importance for the blood supply to poorly oxygenated tissues, such as the eye retina. At pH 7.3 and 20.0 °C, the values of the second-order rate constants (i.e., kon) for the reduction of NO2− to NO and the concomitant formation of nitrosylated Mt-Nb(II), At-Nb(II), Dr-Nb(II), and Hs-Nb(II) (Nb(II)-NO) were 7.6 M−1 s−1, 9.3 M−1 s−1, 1.4 × 101 M−1 s−1, and 5.8 M−1 s−1, respectively. The values of kon increased linearly with decreasing pH, thus indicating that the NO2−-based conversion of Nb(II) to Nb(II)-NO requires the involvement of one proton. These results represent the first evidence for the NO2 reductase activity of Nbs(II), strongly supporting the view that Nbs are involved in NO metabolism. Interestingly, the nitrite reductase reactivity of all-β-barrel Nbs and of all-α-helical globins (e.g., myoglobin) was very similar despite the very different three-dimensional fold; however, differences between all-α-helical globins and all-β-barrel Nbs suggest that nitrite reductase activity appears to be controlled by distal steric barriers, even though a more complex regulatory mechanism can be also envisaged.

Isolation, structural and bioactivities of polysaccharides from Anoectochilus roxburghii (Wall.) Lindl.: A review

Anoectochilus roxburghii (Wall.) Lindl. (A. roxburghii), a valuable herbal medicine in China, has great medicinal and edible value. Polysaccharides, as one of the main active components of A. roxburghii, comprise glucose, arabinose, xylose, galactose, rhamnose, and mannose in different molar ratios and glycosidic bond types. By varying the sources and extraction methods of A. roxburghii polysaccharides (ARPS), different structural characteristics and pharmacological activities can be elucidated. ARPS has been reported to exhibit antidiabetic, hepatoprotective, anti-inflammatory, antioxidant, antitumor, and immune regulation activities. This review summarizes the available literature on the extraction and purification methods, structural features, biological activities, and applications of ARPS. The shortcomings of the current research and potential focus in future studies are also highlighted. This review provides systematic and current information on ARPS to promote their further exploitation and application.

Gasotransmitter-Induced Therapeutic Angiogenesis: A Biomaterial Prospective

Gasotransmitters such as NO, H₂S, and CO have emerged as key players in the regulation of various pathophysiological functions, prompting the development of gas therapy for various pathogeneses. Deficient production of gasotransmitters has been linked to various diseases such as hypertension, endothelial dysfunction, myocardial infarction, ischemia, and impaired wound healing, as they are involved in the regulatory action of angiogenesis. A better understanding of the regulatory mechanisms has given new hope to address the vascular impairment caused by the breakthroughs in gasotransmitters as therapeutics. However, the unstable nature and poor target specificity of gas donors limit the full efficacy of drugs. In this regard, biomaterials that possess excellent biocompatibility and porosity are ideal drug carriers to deliver the gas transmitters in a tunable manner for therapeutic angiogenesis. This review article provides a comprehensive discussion of biomaterial-based gasotransmitter delivery approaches for therapeutic angiogenesis. The critical role of gasotransmitters in modulating angiogenesis during tissue repair as well as their challenges and future directions are demonstrated.

Nitrosylation of ferric zebrafish nitrobindin: A spectroscopic, kinetic, and thermodynamic study

Nitrobindins (Nbs) are all-β-barrel heme-proteins present in all the living kingdoms. Nbs inactivate reactive nitrogen species by sequestering NO, converting NO to HNO₂, and isomerizing peroxynitrite to NO₃^- and NO₂^-. Here, the spectroscopic characterization of ferric Danio rerio Nb (Dr-Nb(III)) and NO scavenging through the reductive nitrosylation of the metal center are reported, both processes being relevant for the regulation of blood flow in fishes through poorly oxygenated tissues, such as retina. Both UV-Vis and resonance Raman spectroscopies indicate that Dr-Nb(III) is a mixture of a six-coordinated aquo- and a five-coordinated species, whose relative abundancies depend on pH. At pH ≤ 7.0, Dr-Nb(III) binds reversibly NO, whereas at pH ≥ 7.8 NO induces the conversion of Dr-Nb(III) to Dr-Nb(II)-NO. The conversion of Dr-Nb(III) to Dr-Nb(II)-NO is a monophasic process, suggesting that the formation of the transient Dr-Nb(III)-NO species is lost in the mixing time of the rapid-mixing stopped-flow apparatus (∼ 1.5 ms). The pseudo-first-order rate constant for the reductive nitrosylation of Dr-Nb(III) is not linearly dependent on the NO concentration but tends to level off. Values of the rate-limiting constant (i.e., k_lim) increase linearly with the OH^- concentration, indicating that the conversion of Dr-Nb(III) to Dr-Nb(II)-NO is limited by the OH^--based catalysis. From the dependence of k_lim on [OH^-], the value of the second-order rate constant k_OH- was obtained (5.2 × 10³ M^-1 s^-1). Reductive nitrosylation of Dr-Nb(III) leads to the inactivation of two NO molecules: one being converted to HNO_2, and the other being tightly bound to the heme-Fe(II) atom.

Dissociation of the proximal His-Fe bond upon NO binding to ferrous zebrafish nitrobindin

Nitrobindins (Nbs) are all-β-barrel heme-proteins present in prokaryotes and eukaryotes. Although the physiological role(s) of Nbs are still unclear, it has been postulated that they are involved in the NO/O₂ metabolism, which is particularly relevant in fishes for the oxygen supply. Here, the reactivity of ferrous Danio rerio Nb (Dr-Nb(II)) towards NO has been investigated from the spectroscopic and kinetic viewpoints and compared with those of Mycobacterium tuberculosis Nb, Arabidopsis thaliana Nb, Homo sapiens Nb, and Equus ferus caballus myoglobin. Between pH 5.5 and 9.1 at 22.0 °C, Dr-Nb(II) nitrosylation is a monophasic process; values of the second-order rate constant for Dr-Nb(II) nitrosylation and of the first-order rate constant for Dr-Nb(II)-NO denitrosylation are pH-independent ranging between 1.6 × 10⁶ M^-1 s^-1 and 2.3 × 10⁶ M^-1 s^-1 and between 5.3 × 10^-2 s^-1 and 8.2 × 10^-2 s^-1, respectively. Interestingly, both UV-Vis and EPR spectroscopies indicate that the heme-Fe(II) atom of Dr-Nb(II)-NO is five-coordinated. Kinetics of Dr-Nb(II) nitrosylation may reflect the ligand accessibility to the metal center, which is likely impaired by the crowded network of water molecules which shields the heme pocket from the bulk solvent. On the other hand, kinetics of Dr-Nb(II)-NO denitrosylation may reflect an easy pathway for the ligand escape into the outer solvent.

The Balancing of Peroxynitrite Detoxification between Ferric Heme-Proteins and CO2: The Case of Zebrafish Nitrobindin

Nitrobindins (Nbs) are all-β-barrel heme proteins and are present in prokaryotes and eukaryotes. Although their function(s) is still obscure, Nbs trap NO and inactivate peroxynitrite. Here, the kinetics of peroxynitrite scavenging by ferric Danio rerio Nb (Dr-Nb(III)) in the absence and presence of CO₂ is reported. The Dr-Nb(III)-catalyzed scavenging of peroxynitrite is facilitated by a low pH, indicating that the heme protein interacts preferentially with peroxynitrous acid, leading to the formation of nitrate (~91%) and nitrite (~9%). The physiological levels of CO₂ dramatically facilitate the spontaneous decay of peroxynitrite, overwhelming the scavenging activity of Dr-Nb(III). The effect of Dr-Nb(III) on the peroxynitrite-induced nitration of L-tyrosine was also investigated. Dr-Nb(III) inhibits the peroxynitrite-mediated nitration of free L-tyrosine, while, in the presence of CO₂, Dr-Nb(III) does not impair nitro-L-tyrosine formation. The comparative analysis of the present results with data reported in the literature indicates that, to act as efficient peroxynitrite scavengers in vivo, i.e., in the presence of physiological levels of CO₂, the ferric heme protein concentration must be higher than 10⁻⁴ M. Thus, only the circulating ferric hemoglobin levels appear to be high enough to efficiently compete with CO₂/HCO₃⁻ in peroxynitrite inactivation. The present results are of the utmost importance for tissues, like the eye retina in fish, where blood circulation is critical for adaptation to diving conditions.

Application of Metal–Organic Framework in Diagnosis and Treatment of Diabetes

Diabetes-related chronic wounds are often accompanied by a poor wound-healing environment such as high glucose, recurrent infections, and inflammation, and standard wound treatments are fairly limited in their ability to heal these wounds. Metal–organic frameworks (MOFs) have been developed to improve therapeutic outcomes due to their ease of engineering, surface functionalization, and therapeutic properties. In this review, we summarize the different synthesis methods of MOFs and conduct a comprehensive review of the latest research progress of MOFs in the treatment of diabetes and its wounds. State-of-the-art in vivo oral hypoglycemic strategies and the in vitro diagnosis of diabetes are enumerated and different antimicrobial strategies (including physical contact, oxidative stress, photothermal, and related ions or ligands) and provascular strategies for the treatment of diabetic wounds are compared. It focuses on the connections and differences between different applications of MOFs as well as possible directions for improvement. Finally, the potential toxicity of MOFs is also an issue that we cannot ignore.

Reduced graphene oxide-supported CuO nanoparticles with synergistically enhanced electrocatalytic activity for nitric oxide sensing

This work reports a NO electrochemical sensor based on rGO/CuO composites with excellent electrochemical performance.