New generation of nitric oxide-releasing porous materials: Assessment of their potential to regulate biological functions

Ultra-Microporous Fe-MOF with Prolonged NO Delivery in Biological Media for Therapeutic Application

Nitric oxide (NO), a key element in the regulation of essential biological mechanisms, presents huge potential as therapeutic agent in the treatment and prevention of chronic diseases. Metal-organic frameworks (MOFs) with open metal sites are promising carriers for NO therapies but delivering it over an extended period in biological media remains a great challenge due to i) a fast degradation of the material in body fluids and/or ii) a rapid replacement of NO by water molecules onto the Lewis acid sites. Here, a new ultra-narrow pores Fe bisphosphonate MOF, denoted MIP-210(Fe) or Fe(H2O)(Hmbpa) (H4mbpa = p-xylenediphosphonic acid) is described that adsorbs NO due to an unprecedented sorption mechanism: coordination of NO through the Fe(III) sites is unusually preferred, replacing bound water, and creating a stable interaction with the free H2O and P-OH groups delimiting the ultra-narrow pores. This, associated with the high chemical stability of the MOF in body fluids, enables an unprecedented slow replacement of NO by water molecules in biological media, achieving an extraordinarily extended NO delivery time over at least 70 h, exceeding by far the NO kinetics release reported with others porous materials, paving the way for the development of safe and successful gas therapies.

Utilization of an aqueous two-phase emulsification to prepare bimodal porous cellulose monolith for efficient adsorption of bovine serum albumin

Cellulose monolith has garnered significant interest in the field of biochromatography, which lies in its interconnected porous structure, large surface area and biocompatibility. In this context, we propose a novel approach for preparing cellulose monoliths using an aqueous two-phase system devoid of any organic solvents and surfactants. In this strategy, emulsifying cellulose solution into PEG 20,000 solution gives bicontinuous aqueous phases and further porous cellulose monolith after regeneration of dissolved cellulose. And the macroporous channels are derived from the removal of the PEG 20,000 aqueous phase while the micropores are from the phase separation of the cellulose phase. Physical characterizations reveal the obtained cellulose monolith exhibits exceptional column permeability of 1.36 × 10-11 m2 and a substantial surface area of 39.34 m2/g. Furthermore, cellulose monolith is functionalized with diethyl ethylamine hydrochloride (DEAE-HCl) to evaluate its potential as an anion adsorbent. Experimental results reveal that the DEAE-modified cellulose monolith possesses of adsorptive capacity of 316.58 mg/g of bovine serum albumin, along with fast adsorption kinetic. This study introduces an innovative strategy for fabricating porous cellulose monoliths tailored for biochromatography applications.

Evaluation of an Imine-Linked Polymer Organic Framework for Storage and Release of H2S and NO

Hydrogen sulfide (H₂S) and nitric oxide (NO) are especially known as toxic and polluting gases, yet they are also endogenously produced and play key roles in numerous biological processes. These two opposing aspects of the gases highlight the need for new types of materials to be developed in addition to the most common materials such as activated carbons and zeolites. Herein, a new imine-linked polymer organic framework was obtained using the inexpensive and easy-to-access reagents isophthalaldehyde and 2,4,6-triaminopyrimidine in good yield (64%) through the simple and catalyst-free Schiff-base reaction. The polymeric material has microporosity, an A_BET surface area of 51 m²/g, and temperature stability up to 300 °C. The obtained 2,4,6-triaminopyrimidine imine-linked polymer organic material has a higher capacity to adsorb NO (1.6 mmol/g) than H₂S (0.97 mmol/g). Release studies in aqueous solution showed that H₂S has a faster release (3 h) from the material than NO, for which a steady release was observed for at least 5 h. This result is the first evaluation of the possibility of an imine-linked polymer organic framework being used in the therapeutic release of NO or H₂S.

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.

Current Advances of Nitric Oxide in Cancer and Anticancer Therapeutics

Nitric oxide (NO) is a short-lived, ubiquitous signaling molecule that affects numerous critical functions in the body. There are markedly conflicting findings in the literature regarding the bimodal effects of NO in carcinogenesis and tumor progression, which has important consequences for treatment. Several preclinical and clinical studies have suggested that both pro- and antitumorigenic effects of NO depend on multiple aspects, including, but not limited to, tissue of generation, the level of production, the oxidative/reductive (redox) environment in which this radical is generated, the presence or absence of NO transduction elements, and the tumor microenvironment. Generally, there are four major categories of NO-based anticancer therapies: NO donors, phosphodiesterase inhibitors (PDE-i), soluble guanylyl cyclase (sGC) activators, and immunomodulators. Of these, NO donors are well studied, well characterized, and also the most promising. In this study, we review the current knowledge in this area, with an emphasis placed on the role of NO as an anticancer therapy and dysregulated molecular interactions during the evolution of cancer, highlighting the strategies that may aid in the targeting of cancer.

A Comparison of Different Approaches to Quantify Nitric Oxide Release from NO-Releasing Materials in Relevant Biological Media

The development of solid materials that deliver nitric oxide (NO) are of interest for several therapeutic applications. Nevertheless, due to NO’s reactive nature, rapid diffusion and short half-life, reporting their NO delivery characteristics is rather complex. The full knowledge of this parameter is fundamental to discuss the therapeutic utility of these materials, and thus, the NO quantification strategy must be carefully considered according to the NO-releasing scaffold type, to the expected NO-releasing amounts and to the medium of quantification. In this work, we explore and discuss three different ways of quantifying the release of NO in different biological fluids: haemoglobin assay, Griess assay and NO electrochemical detection. For these measurements, different porous materials, namely zeolites and titanosilicates were used as models for NO-releasing platforms. The oxyhaemoglobin assay offers great sensitivity (nanomolar levels), but it is only possible to monitor the NO release while oxyhaemoglobin is not fully converted. On the other hand, Griess assay has low sensitivity in complex biological media, namely in blood, and interferences with media make NO measurements questionable. Nevertheless, this method can measure micromolar amounts of NO and may be useful for an initial screening for long-term release performance. The electrochemical sensor enabled real-time measurements in a variety of biological settings. However, measured NO is critically low in oxygenated and complex media, giving transient signals, which makes long-term quantification impossible. Despite the disadvantages of each method, the combination of all the results provided a more comprehensive NO release profile for these materials, which will help to determine which formulations are most promising for specific therapeutic applications. This study highlights the importance of using appropriate NO quantification tools to provide accurate reports.

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.

Nanoscale lipid vesicles functionalized with a nitro-aniline derivative for photoinduced nitric oxide (NO) delivery

Nanoscale vesicles functionalized with a nitric oxide (NO) releasing molecule 4-nitro-3-(trifluoromethyl)aniline have been reported. The new NO-nano-vesicular donor material shows an effective photo-release of NO upon irradiation with blue light at 410 nm. The kinetics of NO release has been monitored by using simple spectroscopic techniques such as UV-Vis and fluorescence methods. Colorimetric Griess assay and fluorescence DAF assay have been used for the detection and quantification of NO released from vesicles. This new vesicular nanoscale NO donor has the advantages of facile preparation in water, capable of releasing NO in a pure aqueous medium, photo-controlled NO release, bio-compatibility and capacity to modulate the NO donor loading to achieve an essential amount of NO.

Porous materials as carriers of gasotransmitters towards gas biology and therapeutic applications

This review highlights the strategies employed to load and release gasotransmitters such as NO, CO and H₂S from different kinds of porous materials, including zeolites, mesoporous silica, metal–organic frameworks and protein assemblies.