Partially Reduced MIL-100(Fe) as a CO Carrier for Sustained CO Release and Regulation of Macrophage Phenotypic Polarization

Iron-MOFs for Biomedical Applications

Over the past two decades, iron-based metal-organic frameworks (Fe-MOFs) have attracted significant research interest in biomedicine due to their low toxicity, tunable degradability, substantial drug loading capacity, versatile structures, and multimodal functionalities. Despite their great potential, the transition of Fe-MOFs-based composites from laboratory research to clinical products remains challenging. This review evaluates the key properties that distinguish Fe-MOFs from other MOFs and highlights recent advances in synthesis routes, surface engineering, and shaping technologies. In particular, it focuses on their applications in biosensing, antimicrobial, and anticancer therapies. In addition, the review emphasizes the need to develop scalable, environmentally friendly, and cost-effective production methods for additional Fe-MOFs to meet the specific requirements of various biomedical applications. Despite the ability of Fe-MOFs-based composites to combine therapies, significant hurdles still remain, including the need for a deeper understanding of their therapeutic mechanisms and potential risks of resistance and overdose. Systematically addressing these challenges could significantly enhance the prospects of Fe-MOFs in biomedicine and potentially facilitate their integration into mainstream clinical practice.

CO-loaded hemoglobin/EGCG nanoparticles functional coatings for inflammation modulation of vascular implants

During the implantation process of cardiovascular implants, vascular damage caused by inflammation occurs, and the inflammatory process is accompanied by oxidative stress. Currently, carbon monoxide (CO) has been demonstrated to exhibit various biological effects including vasodilatation, antithrombotic, anti-inflammatory, apoptosis-inducing and antiproliferative properties. In this study, hemoglobin/epigallocatechin-3-gallate (EGCG) core-shell nanoparticle-containing coating on stainless steel was prepared for CO loading and inflammation modulation. Inspired by strong coordination ability with CO, hemoglobin nanoparticle was first prepared and encapsulated into EGCG metal-phenolic networks. A polydopamine (PDA) linking layer was then coated on 316 stainless steel, and the hemoglobin/EGCG nanoparticles were loaded with the subsequent PDA deposition. It showed that the maximum release amount of CO by the coating was 17.0 nmol/cm2 in 48 h. In vitro evaluations conducted in a simulated inflammatory environment revealed that the coating, which released CO from hemoglobin/EGCG nanoparticles, effectively mitigated the lipopolysaccharide-induced inflammatory response in macrophages. Specifically, it decreased the expression of tumor necrosis factor-α, increased the expression of interleukin-10, suppressed the polarization of macrophages toward the M1 phenotype and reduced intracellular reactive oxygen species (ROS). Furthermore, under simulated oxidative stress conditions, the coating decreased the apoptosis of endothelial cells induced by oxidative stress and down-regulated intracellular ROS levels. In vivo implantation results further confirmed that the coating, with its hemoglobin/EGCG nanoparticles and CO release capabilities, reduced macrophage-mediated inflammatory responses and modulated the polarization phenotype of macrophages.

FeMOFs/CO loading reduces NETosis and macrophage inflammatory response in PLA based cardiovascular stent materials

Modification of polylactic acid (PLA) is a promising strategy for the next generation of bioresorbable vascular stent biomaterials. With this focus, FeMOFs nanoparticles was incorporated in PLA, and then post loading of carbon monoxide (CO) was performed by pressurization. It showed FeMOFs incorporation increased hydrophilicity of the surface and CO loading, and CO release was sustained at least for 3 days. It is well acknowledged NETosis and macrophage mediated inflammation are the principal effectors of atherosclerosis and cardiovascular disease, and it further increases the risk of late stent thrombosis and restenosis. In this study, the effects of CO release of PLA/FeMOFs/CO on NETosis and macrophage behavior were thoroughly explored. In vitro evaluation results showed that PLA/FeMOFs/CO significantly inhibited neutrophil extracellular traps (NETs) release and neutrophil elastase expression by reducing intracellular reactive oxygen species in a simulated inflammatory environment. It reduced Lipopolysaccharide-induced macrophage inflammation with decreased tumor necrosis factor-α expression and increased IL-10 expression. Meanwhile it enhanced endothelial cell activity and growth in inflammatory environment, and inhibited platelet adhesion and activation. In vivo implantation results confirmed that PLA/FeMOFs/CO reduced the macrophages and neutrophils mediated inflammatory response, thus reduced the neointimal hyperplasia. Overall, PLA/FeMOFs/CO effectively prevented the inflammation and restenosis associated with PLA implantation. Our study provides a new strategy to improve the immunocompatibility of PLA implant materials.

Carbon monoxide-releasing Vehicle CO@TPyP-FeMOFs modulating macrophages phenotype in inflammatory wound healing

Healing of chronic wounds has been critically limited by prolonged inflammation. Carbon monoxide (CO) is a biologically active molecule with high potential based on its efficacy in modulating inflammation, promoting wound healing and tissue remodeling. Strategies to use CO as a gaseous drug to chronic wounds have emerged, but controlling the sustained release of CO at the wound site remains a major challenge. In this work, a porphyrin-Fe based metal organic frameworks, TPyP-FeMOFs was prepared. The synthesized TPyP-FeMOFs was high-temperature vacuum activated (AcTPyP-FeMOFs) and AcTPyP-FeMOFs had a relatively high Fe (II) content. CO sorption isotherms showed that AcTPyP-FeMOFs chemisorbed CO and thus CO release was sustained and prolonged. In vitro evaluation results showed that CO@TPyP-FeMOFs reduced the inflammatory level of lipopolysaccharide (LPS) activated macrophages, polarized macrophages to M2 anti-inflammatory phenotype, and promoted the proliferation of fibroblasts by altering the pathological microenvironment. In vivo study confirmed CO@TPyP-FeMOFs promoted healing in a LPS model of delayed cutaneous wound repair and reduced macrophages and neutrophils recruitment. Both in vitro and in vivo studies verified that CO@TPyP-FeMOFs acted on macrophages by modulating phenotype and inflammatory factor expression. Thus, CO release targeting macrophages and pathological microenvironment modulation presented a promising strategy for wound healing.

An organic-organometallic CO-releasing material comprising 4,4'-bipyridine and molybdenum subcarbonyl building blocks

Over the past two decades, following the discovery of the important biological roles of carbon monoxide (CO), metal carbonyl complexes have been intensively studied as CO-releasing molecules (CORMs) for therapeutic applications. To improve the properties of "bare" low molecular weight CORMs, attention has been drawn to conjugating CORMs with macromolecular and inorganic scaffolds to produce CO-releasing materials (CORMAs) capable of storing and delivering large payloads of the gasotransmitter. A significant obstacle is to obtain CORMAs that retain the beneficial features of the parent CORMs. In the present work, a crystalline metal-organic framework (MOF) formulated as Mo(CO)3(4,4'-bipyridine)3/2 (Mobpy), with a structure based on Mo(CO)3 metallic nodes and bipyridine linkers, has been prepared in near quantitative yield by a straightforward reflux method, and found to exhibit CO-release properties that mimic those typically observed for molybdenum carbonyl CORMs. Mobpy was characterized by powder X-ray diffraction (PXRD), thermogravimetric analysis (TGA), FT-IR, FT-Raman and diffuse reflectance (DR) UV-vis spectroscopies, and 13C{1H} cross-polarization (CP) magic-angle spinning (MAS) NMR. The release of CO from Mobpy was studied by the deoxy-myoglobin (deoxy-Mb)/carbonmonoxy-myoglobin (MbCO) UV-vis assay. Mobpy liberates CO upon contact with a physiological buffer in the dark, leading to a maximum released amount of 1.3-1.5 mmol g-1, after 1.5 h at 37 °C, with half-lives of 0.5-1.0 h (time to transfer 0.5 equiv. of CO to Mb). In the solid-state and under open air, Mobpy undergoes complete decarbonylation over a period of 42 days, corresponding to a theoretical CO-release of 7.25 mmol g-1.

Recent advances in carbon monoxide-releasing nanomaterials

As an endogenous signaling molecule, carbon monoxide (CO) has emerged as an increasingly promising option regarding as gas therapy due to its positive pharmacological effects in various diseases. Owing to the gaseous nature and potential toxicity, it is particularly important to modulate the CO release dosages and targeted locations to elucidate the biological mechanisms of CO and facilitate its clinical applications. Based on these, diverse CO-releasing molecules (CORMs) have been developed for controlled release of CO in biological systems. However, practical applications of these CORMs are limited by several disadvantages including low stability, poor solubility, weak releasing controllability, random diffusion, and potential toxicity. In light of rapid developments and diverse advantages of nanomedicine, abundant nanomaterials releasing CO in controlled ways have been developed for therapeutic purposes across various diseases. Due to their nanoscale sizes, diversified compositions and modified surfaces, vast CO-releasing nanomaterials (CORNMs) have been constructed and exhibited controlled CO release in specific locations under various stimuli with better pharmacokinetics and pharmacodynamics. In this review, we present the recent progress in CORNMs according to their compositions. Following a concise introduction to CO therapy, CORMs and CORNMs, the representative research progress of CORNMs constructed from organic nanostructures, hybrid nanomaterials, inorganic nanomaterials, and nanocomposites is elaborated. The basic properties of these CORNMs, such as active components, CO releasing mechanisms, detection methods, and therapeutic applications, are discussed in detail and listed in a table. Finally, we explore and discuss the prospects and challenges associated with utilizing nanomaterials for biological CO release.

The Triple Crown: NO, CO, and H2S in cancer cell biology

Nitric oxide (NO), carbon monoxide (CO), and hydrogen sulfide (H2S) are three endogenously produced gases with important functions in the vasculature, immune defense, and inflammation. It is increasingly apparent that, far from working in isolation, these three exert many effects by modulating each other's activity. Each gas is produced by three enzymes, which have some tissue specificities and can also be non-enzymatically produced by redox reactions of various substrates. Both NO and CO share similar properties, such as activating soluble guanylate cyclase (sGC) to increase cyclic guanosine monophosphate (cGMP) levels. At the same time, H2S both inhibits phosphodiesterase 5A (PDE5A), an enzyme that metabolizes sGC and exerts redox regulation on sGC. The role of NO, CO, and H2S in the setting of cancer has been quite perplexing, as there is evidence for both tumor-promoting and pro-inflammatory effects and anti-tumor and anti-inflammatory activities. Each gasotransmitter has been found to have dual effects on different aspects of cancer biology, including cancer cell proliferation and apoptosis, invasion and metastasis, angiogenesis, and immunomodulation. These seemingly contradictory actions may relate to each gas having a dual effect dependent on its local flux. In this review, we discuss the major roles of NO, CO, and H2S in the context of cancer, with an effort to highlight the dual nature of each gas in different events occurring during cancer progression.

Tricarbonyl-Pyrazine-Molybdenum(0) Metal-Organic Frameworks for the Storage and Delivery of Biologically Active Carbon Monoxide

Metal-organic frameworks (MOFs) have high potential as nanoplatforms for the storage and delivery of therapeutic gasotransmitters or gas-releasing molecules. The aim of the present study was to open an investigation into the viability of tricarbonyl-pyrazine-molybdenum(0) MOFs as carbon monoxide-releasing materials (CORMAs). A previous investigation found that the reaction of Mo(CO)₆ with excess pyrazine (pyz) in a sealed ampoule gave a mixture comprising a major triclinic phase with pyz-occupied hexagonal channels, formulated as fac-Mo(CO)₃(pyz)_3/2·1/2pyz (Mo-hex), and a minor dense cubic phase, formulated as fac-Mo(CO)₃(pyz)_3/2 (Mo-cub). In the present work, an open reflux method in toluene has been optimized for the large-scale synthesis of the pure Mo-cub phase. The crystalline solids Mo-hex and Mo-cub were characterized by powder X-ray diffraction (PXRD), scanning electron microscopy (SEM), thermogravimetric analysis (TGA), FT-IR and FT-Raman spectroscopies, and ¹³C{¹H} cross-polarization (CP) magic-angle spinning (MAS) NMR spectroscopy. The release of CO from the MOFs was studied by the deoxy-myoglobin (deoxy-Mb)/carbonmonoxy-myoglobin (MbCO) UV-vis assay. Mo-hex and Mo-cub release CO upon contact with a physiological buffer in the dark, delivering 0.35 and 0.22 equiv (based on Mo), respectively, after 24 h, with half-lives of 3-4 h. Both materials display high photostability such that the CO-releasing kinetics is not affected by irradiation of the materials with UV light. These materials are attractive as potential CORMAs due to the slow release of a high CO payload. In the solid-state and under open air, Mo-cub underwent almost complete decarbonylation over a period of 4 days, corresponding to a theoretical CO release of 10 mmol per gram of material.