The therapeutic potential of carbon monoxide

Heme Oxygenase-1 as Therapeutic Target for Diabetic Foot Ulcers

A diabetic foot ulcer (DFU) is one of the major complications of diabetes. Wound healing under diabetic conditions is often impaired. This is in part due to the excessive oxidative stress, prolonged inflammation, immune cell dysfunction, delayed re-epithelialization, and decreased angiogenesis present at the wound site. As a result of these multifactorial impaired healing pathways, it has been difficult to develop effective therapeutic strategies for DFU. Heme oxygenase-1 (HO-1) is the rate-limiting enzyme in heme degradation generating carbon monoxide (CO), biliverdin (BV) which is converted into bilirubin (BR), and iron. HO-1 is a potent antioxidant. It can act as an anti-inflammatory, proliferative, angiogenic and cytoprotective enzyme. Due to its biological functions, HO-1 plays a very important role in wound healing, in part mediated through the biologically active end products generated by its enzymatic activity, particularly CO, BV, and BR. Therapeutic strategies involving the activation of HO-1, or the topical application of its biologically active end products are important in diabetic wound healing. Therefore, HO-1 is an attractive therapeutic target for DFU treatment. This review will provide an overview and discussion of the importance of HO-1 as a therapeutic target for diabetic wound healing.

Synthesis, docking studies, biological activity of carbon monoxide release molecules based on coumarin derivatives

In the present work, we synthesized seven complexes. All complexes were identified by ESI-HRMS, ¹H-NMR, ¹⁹F-NMR and ¹³C-NMR spectroscopies. The synthesized complexes were tested for their anticancer activities in vitro against three different human cell lines, including breast MDAMB231, cervical Hela, liver HepG2. IC₅₀ values of complexes 1-7 were 34.98–667.35 µM. Complex 5 revealed higher sensitivity towards MDAMB231 cells with IC₅₀ values 34.98 μM in comparison to 5-FU as positive control. Moreover, complex 5 caused a decrease of mitochondrial membrane potential and effectively induced ROS production against MDAMB231 cells. Western blot analysis showed that complex 5 could up-regulate the expression of Bax protein and down-regulate the expression of Bcl-2, activate Caspase-3, slightly down-regulate the expression of HO-1. The docking studies showed that complex 5 could be interacted with Bcl-2 protein through hydrophobic interactions, hydrogen bonds and salt bridges to enhance the binding affinity. All the analyzed coumarins obeyed the Lipinski’s rule of five for orally administered drugs. Based on the aforementioned results, it suggests that the complex induced apoptosis cell via mitochondria pathways. Collectively, complex 5 could be considered as a promising hit for new anti-breast cancer agents. Carbonyl cobalt CORMs, as potential anticancer therapeutic agents, provided a new idea for the development of metal anticancer drugs.

Cytotoxicity of fac-Mn(CO)3 complexes with a bidentate quinoline ligand towards triple negative breast cancer

The cytotoxicity of two tricarbonyl Mn(I) complexes of the general formula fac-[MnBr(CO)₃L] (L = quinoline-2-carboxaldehyde (A) and 8-amino quinoline (B)) towards triple negative breast cancer (MDA-MB-231) was reported. Complexes A and B released CO when exposed to 468 nm light. Compound B has a dose-dependent cytotoxicity, with half maximal inhibitory concentration values of 19.62 μM and 11.43 μM before and after illumination, respectively. Co-treatment of MDA-MB-231 with paclitaxel (30 nM) and complex B (10 μM) resulted in a 50% reduction in cell viability.

Role of Carbon Monoxide in Oxidative Stress-Induced Senescence in Human Bronchial Epithelium

Prolonged or excessive stimulation from inhaled toxins may cause oxidative stress and DNA damage that can lead to stress-induced senescence in epithelial cells, which can contribute to several airway diseases. Mounting evidence has shown carbon monoxide (CO) confers cytoprotective effects. We investigated the effects of CO on oxidative stress-induced senescence in human airway epithelium and elucidated the underlying molecular mechanisms. Here, CO pretreatment reduced H₂O₂-mediated increases in total reactive oxygen species (ROS) production and mitochondrial superoxide in a human bronchial epithelial cell line (BEAS-2B). H₂O₂ treatment triggered a premature senescence-like phenotype with enlarged and flattened cell morphology accompanied by increased SA-β-gal activity, cell cycle arrest in G0/G1, reduced cell viability, and increased transcription of senescence-associated secretory phenotype (SASP) genes. Additionally, exposure to H₂O₂ increased protein levels of cellular senescence markers (p53 and p21), reduced Sirtuin 3 (SIRT3) and manganese superoxide dismutase (MnSOD) levels, and increased p53 K382 acetylation. These H₂O₂-mediated effects were attenuated by pretreatment with a CO-containing solution. SIRT3 silencing induced mitochondrial superoxide production and triggered a senescence-like phenotype, whereas overexpression decreased mitochondrial superoxide production and alleviated the senescence-like phenotype. Air-liquid interface (ALI) culture of primary human bronchial cells, which becomes a fully differentiated pseudostratified mucociliary epithelium, was used as a model. We found that apical and basolateral exposure to H₂O₂ induced a vacuolated structure that impaired the integrity of ALI cultures, increased goblet cell numbers, decreased SCGB1A1+ club cell numbers, increased p21 protein levels, and increased SASP gene transcription, consistent with our observations in BEAS-2B cells. These effects were attenuated in the apical presence of a CO-containing solution. In summary, we revealed that CO has a pivotal role in epithelial senescence by regulating ROS production via the SIRT3/MnSOD/p53/p21 pathway. This may have important implications in the prevention and treatment of age-associated respiratory pathologies.

External stimuli-responsive gasotransmitter prodrugs: Chemistry and spatiotemporal release

Gasotransmitters like nitric oxide, carbon monoxide, and hydrogen sulfide with unique pleiotropic pharmacological effects in mammals are an emerging therapeutic modality for different human diseases including cancer, infection, ischemia-reperfusion injuries, and inflammation; however, their clinical translation is hampered by the lack of a reliable delivery form, which delivers such gasotransmitters to the action site with precisely controlled dosage. The external stimuli-responsive prodrug strategy has shown tremendous potential in developing gasotransmitter prodrugs, which affords precise temporospatial control and better dose control compared with endogenous stimuli-sensitive prodrugs. The promising external stimuli employed for gasotransmitter activation range from photo, ultrasound, and bioorthogonal click chemistry to exogenous enzymes. Herein, we highlight the recent development of external stimuli-mediated decaging chemistry for the temporospatial delivery of gasotransmitters including nitric oxide, carbon monoxide, hydrogen sulfide and sulfur dioxide, and discuss the pros and cons of different designs.

Carbon Monoxide-Releasing Molecule-3 Suppresses the Malignant Biological Behavior of Tongue Squamous Cell Carcinoma via Regulating Keap1/Nrf2/HO-1 Signaling Pathway

Carbon monoxide-releasing molecule-3 (CORM-3) is a water-soluble complex which has the ability to release carbon monoxide (CO). The study is aimed at investigating the epidemiological characters and effects of CORM-3 on tongue squamous cell carcinoma (TSCC) cells and the mechanisms involved. Firstly, CAL27 and SCC4 were treated with CORM-3 or iCORM-3. The proliferation, migration, and invasion of cells were separately evaluated by CCK-8, scratch assay, and transwell assay. We found that the optimal concentration of CORM-3 on the proliferation of CAL27 and SCC4 cells was 400 μM, and CORM-3 was significantly inhibited the proliferation, migration, and invasion of TSCC cells. Meanwhile, CORM-3 increased the protein expression of HO-1 detected by western blot. Short-hairpin RNAs (shRNAs) were constructed to manipulate the expression of HO-1 in CAL27 and SCC4 cells. Then, rescue assays were conducted to explore the reversion effect of shHO-1 on the CORM-3 function. Mechanistically, CORM-3 decreased the protein of Keap1 expression as well as increased Nrf2 expression. Upregulation of E-cadherin was observed, as well as the downregulation of N-cadherin expression significantly. The antitumor effect of CORM-3 was used to xenograft tumor in nude mice for further investigation in vivo, and the result showed that CORM-3 significantly suppressed tumor growth in xenograft nude mice. These data suggest that CORM-3 acts as a tumor suppressor by regulating the Keap1/Nrf2/HO-1 signaling pathway in TSCC, which provides a potential chemotherapeutic strategy for TSCC.

Insights into stimuli-responsive diselenide bonds utilized in drug delivery systems for cancer therapy

Due to the complexity and particularity of cancer cell microenvironments, redox responsive drug delivery systems (DDSs) for cancer therapy have been extensively explored. Compared with widely reported cancer treatment systems based on disulfide bonds, diselenide bonds have better redox properties and greater anticancer efficiency. In this review, the significance and application of diselenide bonds in DDSs are summarized, and the stimulation sensitivity of diselenide bonds is comprehensively reported. The potential and prospects for the application of diselenide bonds in next-generation anticancer drug treatment systems are extensively discussed.

Controlled therapeutic delivery of CO from carbon monoxide-releasing molecules (CORMs)

Carbon monoxide (CO) has been regarded as a "silent killer" for its toxicity toward biological systems. However, a low concentration of endogenously produced CO has shown a number of therapeutic benefits such as anti-inflammatory, anti-proliferative, anti-apoptosis, and cytoprotective activities. Carbon monoxide-releasing molecules (CORMs) have been developed as alternatives to direct CO inhalation, which requires a specialized setting for strict dose control. CORMs are efficient CO donors, with central transition metals (such as ruthenium, iron, cobalt, and manganese) surrounded by CO as a ligand. CORMs can stably store and subsequently release their CO payload in the presence of certain triggers including solvent, light, temperature, and ligand substitution. However, CORMs require appropriate delivery strategies to improve short CO release half-life and target specificity. Herein, we highlighted the therapeutic potential of inhalation and CORMs-delivered CO. The applications of conjugate and nanocarrier systems for controlling CO release and improving therapeutic efficacy of CORMs are also described in detail. The review concludes with some of the hurdles that limit clinical translation of CORMs. Keeping in mind the tremendous potential and growing interest in CORMs, this review would be helpful for designing controlled CO release systems for clinical applications.

Rational Construction of a Mitochondria-Targeted Reversible Fluorescent Probe with Intramolecular FRET for Ratiometric Monitoring Sulfur Dioxide and Formaldehyde

Sulfur dioxide (SO₂) and formaldehyde (FA) are important species that maintain redox homeostasis in life and are closely related to many physiological and pathological processes. Therefore, it is of great significance to realize the reversible monitoring of them at the intracellular level. Here, we synthesized a reversible ratiometric fluorescent probe through a reasonable design, which can sensitively monitor SO₂ derivatives and FA, and the detection limit can reach 0.16 μM. The probe can specifically target mitochondria and successfully monitor the fluctuations of SO₂ and FA in living cells. It also works well in the detection of SO₂ and FA in zebrafish. This high-performance probe is expected to find broad in vitro and in vivo applications.

Photoactive carbon monoxide-releasing coordination polymer particles

We report the synthesis of photoactive carbon monoxide-releasing coordination polymer particles through the assembly of Mn(I) carbonyl complexes with bis(imidazole) ligands. The use of Mn(I) carbonyl complexes as metallic nodes in the coordination network avoids the potential for aggregation-induced self-quenching, favouring their use in the solid state.

A new metal-free benzorhodol-based photoluminophore selective for carbon monoxide detection applicable in both in vitro and in vivo bioimaging

A new benzorhodol-based non-fluorescent organic frame (DEB-CO) detects carbon monoxide (CO) selectively through a spirolactam ring-opening mechanism. Herein, the selective off-on fluorogenic behavior of this probe towards CO has been achieved without any assistance of precious and hazardous metals (e.g. Pd²⁺) as additional substrates. Moreover, the red-emissive probe motivated us to apply in situ tracing in mice and living cells. The selective off-on fluorogenic behavior of this probe towards CO originating from CORM-3 in vitro and in vivo with a limit of detection as low as 64.29 nM (for CORM-3) has been observed. Additionally, this probe is capable of sensing toxic carbon monoxide gas. This probe has also been utilized to detect intracellular CO in MCF7 cells (in vitro) and to spot the distribution of CO in mice (in vivo) by acquiring bioimages with the help of confocal microscopy, which indicates that DEB-CO is a smart competent probe for this purpose.

Synergetic Antimicrobial Activity and Mechanism of Clotrimazole-Linked CO-Releasing Molecules

Several metal-based carbon monoxide-releasing molecules (CORMs) are active CO donors with established antibacterial activity. Among them, CORM conjugates with azole antibiotics of type [Mn(CO)₃(2,2′-bipyridyl)(azole)]⁺ display important synergies against several microbes. We carried out a structure–activity relationship study based upon the lead structure of [Mn(CO)₃(Bpy)(Ctz)]⁺ by producing clotrimazole (Ctz) conjugates with varying metal and ligands. We concluded that the nature of the bidentate ligand strongly influences the bactericidal activity, with the substitution of bipyridyl by small bicyclic ligands leading to highly active clotrimazole conjugates. On the contrary, the metal did not influence the activity. We found that conjugate [Re(CO)₃(Bpy)(Ctz)]⁺ is more than the sum of its parts: while precursor [Re(CO)₃(Bpy)Br] has no antibacterial activity and clotrimazole shows only moderate minimal inhibitory concentrations, the potency of [Re(CO)₃(Bpy)(Ctz)]⁺ is one order of magnitude higher than that of clotrimazole, and the spectrum of bacterial target species includes Gram-positive and Gram-negative bacteria. The addition of [Re(CO)₃(Bpy)(Ctz)]⁺ to Staphylococcus aureus causes a general impact on the membrane topology, has inhibitory effects on peptidoglycan biosynthesis, and affects energy functions. The mechanism of action of this kind of CORM conjugates involves a sequence of events initiated by membrane insertion, followed by membrane disorganization, inhibition of peptidoglycan synthesis, CO release, and break down of the membrane potential. These results suggest that conjugation of CORMs to known antibiotics may produce useful structures with synergistic effects that increase the conjugate’s activity relative to that of the antibiotic alone.

Time Domains of Hypoxia Responses and -Omics Insights

The ability to respond rapidly to changes in oxygen tension is critical for many forms of life. Challenges to oxygen homeostasis, specifically in the contexts of evolutionary biology and biomedicine, provide important insights into mechanisms of hypoxia adaptation and tolerance. Here we synthesize findings across varying time domains of hypoxia in terms of oxygen delivery, ranging from early animal to modern human evolution and examine the potential impacts of environmental and clinical challenges through emerging multi-omics approaches. We discuss how diverse animal species have adapted to hypoxic environments, how humans vary in their responses to hypoxia (i.e., in the context of high-altitude exposure, cardiopulmonary disease, and sleep apnea), and how findings from each of these fields inform the other and lead to promising new directions in basic and clinical hypoxia research.

Strategy for Detecting Carbon Monoxide: Cu2+-Assisted Fluorescent Probe and Its Applications in Biological Imaging

Herein, a novel strategy was proposed for identifying carbon monoxide (CO), which plays a crucial part in living systems. For the first time, we have managed to design, synthesize, and characterize successfully this new Cu²⁺-assisted fluorescent probe (DPHP) in detecting CO. Compared with the commonly adopted Pd⁰-mediated Tsuji-Trost reaction recognition method, such a new strategy did not engage costly palladium (II) salt and generated no leaving group, indicating a satisfactory anti-interference ability. The recognition mechanism was confirmed by IR, ¹H NMR titration, HR-MS, cyclic voltammetry, X-ray photoelectron spectroscopy, electron paramagnetic resonance, and optical properties. Surprisingly, it was found that the new method achieved high selectivity and rapid identification of CO with a lower limit of detection (1.7 × 10^-8 M). More intriguingly, it could recognize endogenous and exogenous CO in HeLa cells. The cytotoxicity of this new method was so low that it allowed the detection of CO in mice and zebrafish. Basically, our results trigger a novel viewpoint of rationally designing and synthesizing advanced materials for CO detection with unique features, impelling new research in detection chemistry.

Micro-Gel Ensembles for Accelerated Healing of Chronic Wound via pH Regulation

The pH value in the wound milieu plays a key role in cellular processes and cell cycle processes involved in the process of wound healing. Here, a microfluidic assembly technique is employed to fabricate micro-gel ensembles that can precisely tune the pH value of wound surface and accelerate wound healing. The micro-gel ensembles consist of poly (hydroxypropyl acrylate-co-acrylic acid)-magnesium ions (poly-(HPA-co-AA)-Mg²⁺ ) gel and carboxymethyl chitosan (CMCS) gel, which can release and absorb hydrogen ion (H⁺ ) separately at different stages of healing in response to the evolution of wound microenvironment. By regulating the wound pH to affect the proliferation and migration of cell on the wound and the activity of various biological factors in the wound, the physiological processes are greatly facilitated which results in much accelerated healing of chronic wound. This work presents an effective strategy in designing wound healing materials with vast potentials for chronic wound management.

The Role of Concomitant Nrf2 Targeting and Stem Cell Therapy in Cerebrovascular Disease

Despite the reality that a death from cerebrovascular accident occurs every 3.5 min in the United States, there are few therapeutic options which are typically limited to a narrow window of opportunity in time for damage mitigation and recovery. Novel therapies have targeted pathological processes secondary to the initial insult, such as oxidative damage and peripheral inflammation. One of the greatest challenges to therapy is the frequently permanent damage within the CNS, attributed to a lack of sufficient neurogenesis. Thus, recent use of cell-based therapies for stroke have shown promising results. Unfortunately, stroke-induced inflammatory and oxidative damage limit the therapeutic potential of these stem cells. Nuclear factor erythroid 2-related factor 2 (Nrf2) has been implicated in endogenous antioxidant and anti-inflammatory activity, thus presenting an attractive target for novel therapeutics to enhance stem cell therapy and promote neurogenesis. This review assesses the current literature on the concomitant use of stem cell therapy and Nrf2 targeting via pharmaceutical and natural agents, highlighting the need to elucidate both upstream and downstream pathways in optimizing Nrf2 treatments in the setting of cerebrovascular disease.

Low-dose carbon monoxide suppresses metastatic progression of disseminated cancer cells

Low-dose carbon monoxide (CO) is under investigation in clinical trials to treat non-cancerous diseases and has excellent safety profiles. Due to the early detection and cancer awareness, increasing cancer patients are diagnosed at early stages and potentially curative surgical resection can be done. However, many patients ultimately experience recurrence. Here, we evaluate the therapeutic effect of CO on cancer metastatic progression. We show that 250 ppm CO inhibits migration of multiple types of cancer cell lines including breast, pancreatic, colon, prostate, liver, and lung cancer and reduces the ability to adhere to fibronectin. We demonstrate that in mouse models, 250 ppm inhaled CO inhibits lung metastasis of breast cancer and liver metastasis of pancreatic cancer. Moreover, low-dose CO suppresses recurrence and increases survival after surgical removal of primary pancreatic cancer in mice. Mechanistically, low-dose CO blocks transcription of heme importers, leading to diminished intracellular heme levels and a heme-regulated enzyme, cytochrome P4501B1 (CYP1B1). Either supplementing heme or overexpressing CYP1B1 reverses the anti-migration effect of low-dose CO. Taken together, low-dose CO therapy inhibits cell migration, reduces adhesion to fibronectin, prevents disseminated cancer cells from expanding into gross metastases, and improves survival in pre-clinical mouse models of metastasis.

Mitochondrial adaptation in cancer drug resistance: prevalence, mechanisms, and management

Drug resistance represents a major obstacle in cancer management, and the mechanisms underlying stress adaptation of cancer cells in response to therapy-induced hostile environment are largely unknown. As the central organelle for cellular energy supply, mitochondria can rapidly undergo dynamic changes and integrate cellular signaling pathways to provide bioenergetic and biosynthetic flexibility for cancer cells, which contributes to multiple aspects of tumor characteristics, including drug resistance. Therefore, targeting mitochondria for cancer therapy and overcoming drug resistance has attracted increasing attention for various types of cancer. Multiple mitochondrial adaptation processes, including mitochondrial dynamics, mitochondrial metabolism, and mitochondrial apoptotic regulatory machinery, have been demonstrated to be potential targets. However, recent increasing insights into mitochondria have revealed the complexity of mitochondrial structure and functions, the elusive functions of mitochondria in tumor biology, and the targeting inaccessibility of mitochondria, which have posed challenges for the clinical application of mitochondrial-based cancer therapeutic strategies. Therefore, discovery of both novel mitochondria-targeting agents and innovative mitochondria-targeting approaches is urgently required. Here, we review the most recent literature to summarize the molecular mechanisms underlying mitochondrial stress adaptation and their intricate connection with cancer drug resistance. In addition, an overview of the emerging strategies to target mitochondria for effectively overcoming chemoresistance is highlighted, with an emphasis on drug repositioning and mitochondrial drug delivery approaches, which may accelerate the application of mitochondria-targeting compounds for cancer therapy.

Role of Heme Oxygenase in Gastrointestinal Epithelial Cells

The gastrointestinal tract is a unique organ containing both vascular and luminal routes lined by epithelial cells forming the mucosa, which play an important role in the entry of nutrients and act as a selective barrier, excluding potentially harmful agents. Mucosal surfaces establish a selective barrier between hostile external environments and the internal milieu. Heme is a major nutritional source of iron and is a pro-oxidant that causes oxidative stress. Heme oxygenases (HOs) catalyze the rate-limiting step in heme degradation, resulting in the formation of iron, carbon monoxide, and biliverdin, which are subsequently converted to bilirubin by biliverdin reductase. In gastrointestinal pathogenesis, HO-1, an inducible isoform of HO, is markedly induced in epithelial cells and plays an important role in protecting mucosal cells. Recent studies have focused on the biological effects of the products of this enzymatic reaction, which have antioxidant, anti-inflammatory, and cytoprotective functions. In this review, the essential roles of HO in the gastrointestinal tract are summarized, focusing on nutrient absorption, protection against cellular stresses, and the maintenance and regulation of tight junction proteins, emphasizing the potential therapeutic implications. The biochemical basis of the potential therapeutic implications of glutamine for HO-1 induction in gastrointestinal injury is also discussed.

Luminal Administration of a Water-soluble Carbon Monoxide-releasing Molecule (CORM-3) Mitigates Ischemia/Reperfusion Injury in Rats Following Intestinal Transplantation

BACKGROUND

The protective effects of carbon monoxide (CO) against ischemia/reperfusion (IR) injury during organ transplantation have been extensively investigated. Likewise, CO-releasing molecules (CORMs) are known to exert a variety of pharmacological activities via liberation of controlled amounts of CO in organs. Therefore, we hypothesized that intraluminal administration of water-soluble CORM-3 during cold storage of intestinal grafts would provide protective effects against IR injury.

METHODS

Orthotopic syngeneic intestinal transplantation was performed in Lewis rats following 6 h of cold preservation in Ringer solution or University of Wisconsin solution. Saline containing CORM-3 (100 µmol/L) or its inactive counterpart (iCORM-3) was intraluminally introduced in the intestinal graft before cold preservation.

RESULTS

Histopathological analysis of untreated and iCORM-3-treated grafts revealed a similar erosion and blunting of the intestinal villi. These changes in the mucosa structure were significantly attenuated by intraluminal administration of CORM-3. Intestinal mucosa damage caused by IR injury led to considerable deterioration of gut barrier function 3 h postreperfusion. CORM-3 significantly inhibited upregulation of proinflammatory mRNA levels, ameliorated intestinal morphological changes, and improved graft blood flow and mucosal barrier function. Additionally, CORM-3-treated grafts increased recipient survival rates. Pharmacological blockade of soluble guanylyl cyclase activity significantly reversed the protective effects conferred by CORM-3, indicating that CO partially mediates its therapeutic actions via soluble guanylyl cyclase activation.

CONCLUSIONS

Our study demonstrates that luminally delivered CORM-3 provides beneficial effects in cold-stored rat small intestinal grafts and could be an attractive therapeutic application of CO in the clinical setting of organ preservation and transplantation.

Carbon Monoxide Signaling: Examining Its Engagement with Various Molecular Targets in the Context of Binding Affinity, Concentration, and Biologic Response

Carbon monoxide (CO) has been firmly established as an endogenous signaling molecule with a variety of pathophysiological and pharmacological functions, including immunomodulation, organ protection, and circadian clock regulation, among many others. In terms of its molecular mechanism(s) of action, CO is known to bind to a large number of hemoproteins with at least 25 identified targets, including hemoglobin, myoglobin, neuroglobin, cytochrome c oxidase, cytochrome P450, soluble guanylyl cyclase, myeloperoxidase, and some ion channels with dissociation constant values spanning the range of sub-nM to high μM. Although CO's binding affinity with a large number of targets has been extensively studied and firmly established, there is a pressing need to incorporate such binding information into the analysis of CO's biologic response in the context of affinity and dosage. Especially important is to understand the reservoir role of hemoglobin in CO storage, transport, distribution, and transfer. We critically review the literature and inject a sense of quantitative assessment into our analyses of the various relationships among binding affinity, CO concentration, target occupancy level, and anticipated pharmacological actions. We hope that this review presents a picture of the overall landscape of CO's engagement with various targets, stimulates additional research, and helps to move the CO field in the direction of examining individual targets in the context of all of the targets and the concentration of available CO. We believe that such work will help the further understanding of the relationship of CO concentration and its pathophysiological functions and the eventual development of CO-based therapeutics. SIGNIFICANCE STATEMENT: The further development of carbon monoxide (CO) as a therapeutic agent will significantly rely on the understanding of CO's engagement with therapeutically relevant targets of varying affinity. This review critically examines the literature by quantitatively analyzing the intricate relationships among targets, target affinity for CO, CO level, and the affinity state of carboxyhemoglobin and provide a holistic approach to examining the molecular mechanism(s) of action for CO.

An all-in-one CO gas therapy-based hydrogel dressing with sustained insulin release, anti-oxidative stress, antibacterial, and anti-inflammatory capabilities for infected diabetic wounds

To effectively treat diabetic wounds, the development of versatile medical dressings that can long-term regulate blood glucose and highly effective anti-oxidative stress, antibacterial and anti-inflammatory are critical. Here, an all-in-one CO gas-therapy-based versatile hydrogel dressing (ICOQF) was developed via the dynamic Schiff base reaction between the amino groups on quaternized chitosan (QCS) and the aldehyde groups on benzaldehyde-terminated F108 (F108-CHO) micelles. CORM-401 (an oxidant-sensitive CO-releasing molecules) was encapsulated in the hydrophobic core of F108-CHO micelles and insulin was loaded in the three-dimensional network structure of ICOQF. The dynamic Schiff base bonds not only endowed ICOQF with good tissue adhesion, injectability and self-healing, but also gave it sustained and controllable insulin release ability. In addition, ICOQF could quickly generate CO in inflamed wound tissue by consuming reactive oxygen species. The generated CO could effectively anti-oxidative stress by activating the expression of heme oxygenase; antibacterial by inducing the rupture of bacterial cell membranes and mitochondrial dysfunction and inhibiting the synthesis of adenosine triphosphate; and anti-inflammatory by inhibiting the proliferation of activated macrophages and promoting the polarization of the M1 phenotype to the M2 phenotype. Due to these outstanding properties, ICOQF significantly promoted the healing of STZ-induced MRSA-infected diabetic wounds accompanied by good biocompatibility. This study clearly shows that ICOQF is a versatile hydrogel dressing with great application potential for the management of diabetic wounds. STATEMENT OF SIGNIFICANCE: The development of some versatile hydrogel dressings that can not only provide a prolonged and controlled insulin release property but also utilize a non-antibiotic treatment modality for highly effective antibacterial, anti-inflammatory, and anti-oxidative stress effects is vital for the successful treatment of diabetic wounds. Herein, we developed an all-in-one CO gas-therapy-based versatile hydrogel dressing (ICOQF) with sustained and controllable insulin release abilities. Moreover, ICOQF could not only quickly release CO in the inflamed wound tissue by consumption of reactive oxygen species but also utilize the generated CO to highly effectively anti-oxidative stress, antibacterial, and anti-inflammatory. ICOQF therapy substantially promoted the healing of STZ-induced MRSA-infected diabetic wounds. Overall, this work provides a multifunctional hydrogel dressing for the management of diabetic wounds.

Gasotransmitters in the tumor microenvironment: Impacts on cancer chemotherapy (Review)

Nitric oxide, carbon monoxide and hydrogen sulfide are three endogenous gasotransmitters that serve a role in regulating normal and pathological cellular activities. They can stimulate or inhibit cancer cell proliferation and invasion, as well as interfere with cancer cell responses to drug treatments. Understanding the molecular pathways governing the interactions between these gases and the tumor microenvironment can be utilized for the identification of a novel technique to disrupt cancer cell interactions and may contribute to the conception of effective and safe cancer therapy strategies. The present review discusses the effects of these gases in modulating the action of chemotherapies, as well as prospective pharmacological and therapeutic interfering approaches. A deeper knowledge of the mechanisms that underpin the cellular and pharmacological effects, as well as interactions, of each of the three gases could pave the way for therapeutic treatments and translational research.

Modulatory Role of Carbon Monoxide on the Inflammatory Response and Oxidative Stress Linked to Gastrointestinal Disorders

Significance: Carbon monoxide (CO) is an endogenous gaseous mediator that plays an important role in maintaining gastrointestinal (GI) tract homeostasis, acting in mucosal defense, and providing negative modulation of pathophysiological markers of clinical conditions. Recent Advances: Preclinical studies using animal models and/or cell culture show that CO can modulate the inflammatory response and oxidative stress in GI mucosal injuries and pathological conditions, reducing proinflammatory cytokines and reactive oxygen species, while increasing antioxidant defense mechanisms. Critical Issues: CO has potent anti-inflammatory and antioxidant effects. The defense mechanisms of the GI tract are subject to aggression by different chemical agents (e.g., drugs and ethanol) as well as complex and multifactorial diseases, with inflammation and oxidative stress as strong triggers for the deleterious effects. Thus, it is possible that CO acts on a variety of molecules involved in the inflammatory and oxidative signaling cascades, as well as reinforcing several defense mechanisms that maintain GI homeostasis. Future Directions: CO-based therapies are promising tools for the treatment of GI disorders, such as gastric and intestinal injuries, inflammatory bowel disease, and pancreatitis. Therefore, it is necessary to develop safe and selective CO-releasing agents and/or donor drugs to facilitate effective treatments and methods for analysis of CO levels that are simple and inexpensive. Antioxid. Redox Signal. 37, 98-114.

Does air pollution modify temperature-related mortality? A systematic review and meta-analysis

INTRODUCTION

There is an increasing interest in understanding whether air pollutants modify the quantitative relationships between temperature and health outcomes. The results of available studies were, however, inconsistent. This study aims to sum up the current evidence and provide a comprehensive understanding of this topic.

METHODS

We conducted an electronic search in PubMed (MEDLINE), EMBASE, Web of Science Core Collection, and ProQuest Dissertations and Theses. The modified Navigation Guide was applied to evaluate the quality and strength of evidence. We calculated pooled temperature-related mortality at low and high pollutant levels respectively, using the random-effects model.

RESULTS

We identified 22 eligible studies, eleven of which were included in the meta-analysis. Significant effect modification was observed on heat effects for all-cause and non-accidental mortality by particulate matter with an aerodynamic diameter of <10 μm (PM₁₀) and ozone (O₃) (p < 0.05). The excess risks (ERs) for all-cause and non-accidental mortality were 5.4% (4.4%, 6.4%) and 6.3% (4.8%, 7.8%) at the low PM₁₀ level, 8.8% (7.5%, 10.1%) and 11.4% (8.7%, 14.2%) at the high PM₁₀ level, respectively. As for O₃, the ERs for all-cause and non-accidental mortality were 5.1% (3.9%, 6.3%) and 3.6% (0.1%, 7.2%) at the low O₃ level, 7.6% (6.3%, 9.0%) and 12.5% (4.7%, 20.9%) at the high O₃ level, respectively. Surprisingly, the heat effects on cardiovascular mortality were found to be lower at high carbon monoxide (CO) levels [ERs = 5.4% (3.9%, 6.9%)] than that at low levels [ERs = 9.4% (7.0%, 11.9%)]. The heterogeneity varied, but the results of sensitivity analyses were generally robust. Significant effect modification by air pollutants was not observed for heatwave or cold effects.

CONCLUSIONS

PM₁₀ and O₃ modify the heat-related all-cause and non-accidental mortality, indicating that policymakers should consider air pollutants when establishing heat-health warning systems. Future studies with comparable designs and settings are needed.

The Advancement of Gas-Generating Nanoplatforms in Biomedical Fields: Current Frontiers and Future Perspectives

Diverse gases (NO, CO, H₂ S, H₂ , etc.) have been widely applied in the medical intervention of various diseases, including cancer, cardiovascular disease, ischemia-reperfusion injury, bacterial infection, etc., attributing to their inherent biomedical activities. Although many gases have many biomedical activities, their clinical use is still limited due to the rapid and free diffusion behavior of these gases molecules, which may cause potential side effects and/or ineffective treatment. Gas-generating nanoplatforms (GGNs) are effective strategies to address the aforementioned challenges of gas therapy by preventing gas production or release at nonspecific sites, enhancing GGNs accumulation at targeted sites, and controlling gas release in response to exogenous (UV, NIR, US, etc.) or endogenous (H₂ O₂ , GSH, pH, etc.) stimuli at the lesion site, further maintaining gas concentration within the effective range and achieving the purpose of disease treatment. This review comprehensively summarizes the advancements of "state-of-the-art" GGNs in the recent three years, with emphasis on the composition, structure, preparation process, and gas release mechanism of the nanocarriers. Furthermore, the therapeutic effects and limitations of GGNs in preclinical studies using cell/animal models are discussed. Overall, this review enlightens the further development of this field and promotes the clinical transformation of gas therapy.

Delivery of therapeutic carbon monoxide by gas-entrapping materials

Carbon monoxide (CO) has long been considered a toxic gas but is now a recognized bioactive gasotransmitter with potent immunomodulatory effects. Although inhaled CO is currently under investigation for use in patients with lung disease, this mode of administration can present clinical challenges. The capacity to deliver CO directly and safely to the gastrointestinal (GI) tract could transform the management of diseases affecting the GI mucosa such as inflammatory bowel disease or radiation injury. To address this unmet need, inspired by molecular gastronomy techniques, we have developed a family of gas-entrapping materials (GEMs) for delivery of CO to the GI tract. We show highly tunable and potent delivery of CO, achieving clinically relevant CO concentrations in vivo in rodent and swine models. To support the potential range of applications of foam GEMs, we evaluated the system in three distinct disease models. We show that a GEM containing CO dose-dependently reduced acetaminophen-induced hepatocellular injury, dampened colitis-associated inflammation and oxidative tissue injury, and mitigated radiation-induced gut epithelial damage in rodents. Collectively, foam GEMs have potential paradigm-shifting implications for the safe therapeutic use of CO across a range of indications.

Carbon monoxide mechanism of protection against renal ischemia and reperfusion injury

Carbon monoxide is quickly moving past its historic label as a molecule once feared, to a therapeutic drug that modulates inflammation. The development of carbon monoxide releasing molecules and utilization of heme oxygenase-1 inducers have shown carbon monoxide to be a promising therapy in reducing renal ischemia and reperfusion injury and other inflammatory diseases. In this review, we will discuss the developments and application of carbon monoxide releasing molecules in renal ischemia and reperfusion injury, and transplantation. We will review the anti-inflammatory mechanisms of carbon monoxide in respect to mitigating apoptosis, suppressing dendritic cell maturation and signalling, inhibiting toll-like receptor activation, promoting anti-inflammatory responses, and the effects on renal vasculature.

Glucose Metabolism Intervention-Facilitated Nanomedicine Therapy

Ordinarily, cancer cells possess features of abnormally increased nutrient intake and metabolic pathways. The disorder of glucose metabolism is the most important among them. Therefore, starvation therapy targeting glucose metabolism specifically, which results in metabolic disorders, restricted synthesis, and inhibition of tumor growth, has been developed for cancer therapy. However, issues such as inadequate targeting effectiveness and drug tolerance impede their clinical transformation. In recent years, nanomaterial-assisted starvation treatment has made significant progress in addressing these challenges, whether as a monotherapy or in combination with other medications. Herein, representative researches on the construction of nanosystems conducting starvation therapy are introduced. Elaborate designs and interactions between different treatment mechanisms are meticulously mentioned. Not only are traditional treatments based on glucose oxidase involved, but also newly sprung small molecule agents targeting glucose metabolism. The obstacles and potential for advancing these anticancer therapies were also highlighted in this review.

Chemiexcitation-Triggered Prodrug Activation for Targeted Carbon Monoxide Delivery

Photolysis-based prodrug strategy can address some critical drug delivery issues, which otherwise are very challenging to tackle with traditional prodrug strategy. However, the need for external light irradiation significantly hampers its in vivo application due to the poor light accessibility of deep tissue. Herein, we propose a new strategy of chemiexcitation-triggered prodrug activation, wherein a photoresponsive prodrug is excited for drug payload release by chemiexcitation instead of photoirradiation. As such, the bond-cleavage power of photolysis can be employed to address some critical drug delivery issues while obviating the need for external light irradiation. We have established the proof of concept by the successful development of a chemiexcitation responsive carbon monoxide delivery platform, which exhibited specific CO release at the tumor site and pronounced tumor suppression effects. We anticipate that such a concept of chemiexcitation-triggered prodrug activation can be leveraged for the targeted delivery of other small molecule-based drug payloads.

Beneficial and Detrimental Roles of Heme Oxygenase-1 in the Neurovascular System

Heme oxygenase (HO) has both beneficial and detrimental effects via its metabolites, including carbon monoxide (CO), biliverdin or bilirubin, and ferrous iron. HO-1 is an inducible form of HO that is upregulated by oxidative stress, nitric oxide, CO, and hypoxia, whereas HO-2 is a constitutive form that regulates vascular tone and homeostasis. In brains injured by trauma, ischemia-reperfusion, or Alzheimer’s disease (AD), the long-term expression of HO-1 can be detected, which can lead to cytotoxic ferroptosis via iron accumulation. In contrast, the transient induction of HO-1 in the peri-injured region may have regenerative potential (e.g., angiogenesis, neurogenesis, and mitochondrial biogenesis) and neurovascular protective effects through the CO-mediated signaling pathway, the antioxidant properties of bilirubin, and the iron-mediated ferritin synthesis. In this review, we discuss the dual roles of HO-1 and its metabolites in various neurovascular diseases, including age-related macular degeneration, ischemia-reperfusion injury, traumatic brain injury, Gilbert’s syndrome, and AD.

Naphthalimide derivatives as fluorescent probes for imaging endogenous gasotransmitters

Gasotransmitters have gained significant recognition attributed to their evident biological impacts, and is accepted as a promising and less-explored area with immense research scope. The three-member family comprising of nitric oxide, carbon monoxide and hydrogen sulphide as endogenous gaseous signaling molecules have been found to elicit a plethora of crucial biological functions, spawning a new research area. The sensing of these small molecules is vital to gain deeper insights into their functions, as they can act both as a friend or a foe in mammalian systems. The initial sections of the review present the physiological and pathophysiological roles of these endogenous gas transmitters and their synergistic interactions. Further, various detection approaches, especially the usage of fascinating features of 1,8-naphthalimide as fluorescent probe in the detection and monitoring of these small signaling molecules are highlighted. The current limitations and the future scope of improving the sensing of the three gasotransmitters are also discussed.

CORM-3 induces DNA damage through Ru(II) binding to DNA

When the ‘CO-releasing molecule-3’, CORM-3 (Ru(CO)₃Cl(glycinate)), is dissolved in water it forms a range of ruthenium complexes. These are taken up by cells and bind to intracellular ligands, notably thiols such as cysteine and glutathione, where the Ru(II) reaches high intracellular concentrations. Here, we show that the Ru(II) ion also binds to DNA, at exposed guanosine N7 positions. It therefore has a similar cellular target to the anticancer drug cisplatin, but not identical, because Ru(II) shows no evidence of forming intramolecular crossbridges in the DNA. The reaction is slow, and with excess Ru, intermolecular DNA crossbridges are formed. The addition of CORM-3 to human colorectal cancer cells leads to strand breaks in the DNA, as assessed by the alkaline comet assay. DNA damage is inhibited by growth media containing amino acids, which bind to extracellular Ru and prevent its entry into cells. We conclude that the cytotoxicity of Ru(II) is different from that of platinum, making it a promising development target for cancer therapeutics.

Photo-Responsive Micelles with Controllable and Co-Release of Carbon Monoxide, Formaldehyde and Doxorubicin

Endogenous gases have attracted much attention due to their potent applications in disease therapies. The combined therapy, including gaseous molecules and other medicines that can create synergistic effects, is a new way for future treatment. However, due to the gaseous state, gas utilization in medical service is still limited. To pave the way for future usage, in this work, an amphiphilic block copolymer containing nitrobenzyl ether, 3-hydroxyflavone (3-HF) derivatives and ether linker was constructed. The nitrobenzyl ether group endows the polymer with a photo-responsive character. Upon light illumination, 3-HF derivatives can be triggered for carbon monoxide (CO) release. The ether linker can also be released emitting formaldehyde (FA). The self-assembly induced micelle can encompass medicine, e.g., doxorubicin (DOX), into it and a controlled release of DOX can be realized upon light illumination. As far as we know, there is no report on the combination donor of CO and DOX and this is the first attempt on the co-release of CO, FA and DOX.

Activatable Fluorescent-Photoacoustic Integrated Probes with Deep Tissue Penetration for Pathological Diagnosis and Therapeutic Evaluation of Acute Inflammation in Mice

Inflammation is associated with many diseases, so the development of an excellent near infrared fluorescent (NIRF) and photoacoustic (PA) dual-modality probe is crucial for the accurate diagnosis and efficacy evaluation of inflammation. However, most of the current NIRF/PA scaffolds are based on repurposing existing fluorescent dye platforms that exhibit non-optimal properties for both NIRF and PA signal outputs. Herein, we developed a novel dye scaffold QL-OH by optimizing the NIRF and PA signal of classical hemicyanine dyes. Based on this optimized dye, we developed the first NIRF/PA dual-mode carbon monoxide (CO) probe QL-CO for noninvasive and sensitive visualization of CO levels in deep inflammatory lesions in vivo. The novel probe QL-CO exhibited rapid and sensitive NIRF₇₇₅/PA₇₃₀ dual activation responses toward CO. In addition, the CO-activated probe QL-CO was successfully used for the diagnosis of inflammation and evaluation of anti-inflammation drug efficacy in living mice though the NIRF/PA dual-mode imaging technology for the first time. More importantly, the probe QL-CO could accurately locate the deep inflammatory lesion tissues (≈1 cm) in mice and obtain 3D PA diagnostic images with deep penetration depth and spatial resolution. Therefore, the new NIRF/PA dual-mode probe QL-CO has high potential for deep-tissue diagnosis imaging of CO in vivo. These findings may provide a new tool and approach for future research and diagnosis of CO-associated diseases.

Hydrophilic CO-Releasing Material of PEGlyated Ruthenium Carbonyl Complex

The poor water-solubility and instability of Ru(II) carbonyl complex hamper the therapeutic application as CO releasing materials (CO-RMs). To enhance the hydrophilicity and bio-utility of CO, a robust Ru(I) carbonyl sawhorse skeleton was grafted with water-soluble PEGylated sidearm. In this case, 12 PEGylated sawhorse Ru₂(CO)₄ complexes were prepared with satisfactory yields and characterized by IR and ¹H- and ¹³C- NMR. X-ray diffraction analysis of CO-RM 8, 13 and 14 revealed the featured diruthenium sawhorse skeleton and PEGylated axial ligands. The flask-shaking method measures the water-solubility of CO-RMs, indicating that both bridging carboxylate ligands and PEGlyated axial ligands regulate the hydrophilicity of these CO-RMs. Under photolysis conditions, CO-RM 4–13 sustainable released therapeutic amounts of CO in the myoglobin assay. The correlation of the CO release kinetics and hydrophilicity of CO-RMs demonstrated that the more hydrophilic CO-RM released CO faster. The biological test found that the low cytotoxic CO-RM 4 showed a specific anticancer activity toward HT-29 tumour cells.

The complex photochemistry of coumarin-3-carboxylic acid in acetonitrile and methanol

Irradiation of coumarin-3-carboxylic acid in acetonitrile and methanol solutions at 355 nm results in complex multistep photochemical transformations, strongly dependent on the solvent properties and oxygen content. A number of reaction intermediates, which themselves undergo further (photo)chemical reactions, were identified by steady-state and transient absorption spectroscopy, mass spectrometry, and NMR and product analyses. The triplet excited compound in acetonitrile undergoes decarboxylation to give a 3-coumarinyl radical that traps molecular oxygen to form 3-hydroxycoumarin as the major but chemically reactive intermediate. This compound is oxygenated by singlet oxygen, produced by coumarin-3-carboxylic acid sensitization, followed by a pyrone ring-opening reaction to give an oxalic acid derivative. The subsequent steps lead to the production of salicylaldehyde, carbon monoxide, and carbon dioxide as the final products. When 3-coumarinyl radical is not trapped by oxygen in degassed acetonitrile, it abstracts hydrogen from the solvent and undergoes triplet-sensitized [2 + 2] cycloaddition. The reaction of 3-coumarinyl radical with oxygen is largely suppressed in aerated methanol as a better H-atom donor, and coumarin is obtained as the primary product in good yields. Because coumarin derivatives are used in many photophysical and photochemical applications, this work provides detailed and sometimes surprising insights into their complex phototransformations.

Switching on Cytotoxicity of Water-Soluble Diiron Organometallics by UV Irradiation

The diiron compounds [Fe₂Cp₂(CO)₂(μ-CO)(μ-CSEt)]CF₃SO₃, [1]CF₃SO₃, K[Fe₂Cp₂(CO)₃(CNCH₂CO₂)], K[2], [Fe₂Cp₂(CO)₂(μ-CO)(μ-CNMe₂)]NO₃, [3]NO₃, [Fe₂Cp₂(CO)₂(PTA){μ-CNMe(Xyl)}]CF₃SO₃, [4]CF₃SO₃, and [Fe₂Cp₂(CO)(μ-CO){μ-η:¹η³-C(4-C₆H₄CO₂H)CHCNMe₂}]CF₃SO₃, [5]CF₃SO₃, containing a bridging carbyne, isocyanoacetate, or vinyliminium ligand, were investigated for their photoinduced cytotoxicity. Specifically, the novel water-soluble compounds K[2], [3]NO₃, and [4]CF₃SO₃ were synthesized and characterized by elemental analysis and IR and multinuclear NMR spectroscopy. Stereochemical aspects concerning [4]CF₃SO₃ were elucidated by ¹H NOESY NMR and single-crystal X-ray diffraction. Cell proliferation studies on human skin cancer (A431) and nontumoral embryonic kidney (HEK293) cells, with and without a 10-min exposure to low-power UV light (350 nm), highlighted the performance of the aminocarbyne [3]NO₃, nicknamed NIRAC (Nitrate-Iron-Aminocarbyne), which is substantially nontoxic in the dark but shows a marked photoinduced cytotoxicity. Spectroscopic (IR, UV-vis, NMR) measurements and the myoglobin assay indicated that the release of one carbon monoxide ligand represents the first step of the photoactivation process of NIRAC, followed by an extensive disassembly of the organometallic scaffold.

M-CPOnes: transition metal complexes with cyclopropenone-based ligands for light-triggered carbon monoxide release

A new class of CO-releasing molecules, M-CPOnes, was prepared combining cyclopropenone-based ligands for CO release with the modular scaffold of transition metal complexes. In proof-of-concept studies, M-CPOnes based on Zn^II, Fe^II and Co^II are stable in the dark but undergo light-triggered CO release with the cyclopropenone substituents and metal ions enabling tuning of the photophysical properties. Furthermore, the choice of metal allows the use of different spectroscopic methods to monitor photodecarbonylation from fluorescence spectroscopy to UV/vis spectroscopy and paramagnetic NMR spectroscopy. The modularity of M-CPOnes from the metal ion to the cyclopropenone substitution and potential for further functionalisation of the ligand make M-CPOnes appealing for tailored functionality in applications.

Medical Gas Therapy for Tissue, Organ, and CNS Protection: A Systematic Review of Effects, Mechanisms, and Challenges

Gaseous molecules have been increasingly explored for therapeutic development. Here, following an analytical background introduction, a systematic review of medical gas research is presented, focusing on tissue protections, mechanisms, data tangibility, and translational challenges. The pharmacological efficacies of carbon monoxide (CO) and xenon (Xe) are further examined with emphasis on intracellular messengers associated with cytoprotection and functional improvement for the CNS, heart, retina, liver, kidneys, lungs, etc. Overall, the outcome supports the hypothesis that readily deliverable "biological gas" (CO, H2 , H2 S, NO, O2 , O3 , and N2 O) or "noble gas" (He, Ar, and Xe) treatment may preserve cells against common pathologies by regulating oxidative, inflammatory, apoptotic, survival, and/or repair processes. Specifically, CO, in safe dosages, elicits neurorestoration via igniting sGC/cGMP/MAPK signaling and crosstalk between HO-CO, HIF-1α/VEGF, and NOS pathways. Xe rescues neurons through NMDA antagonism and PI3K/Akt/HIF-1α/ERK activation. Primary findings also reveal that the need to utilize cutting-edge molecular and genetic tactics to validate mechanistic targets and optimize outcome consistency remains urgent; the number of neurotherapeutic investigations is limited, without published results from large in vivo models. Lastly, the broad-spectrum, concurrent multimodal homeostatic actions of medical gases may represent a novel pharmaceutical approach to treating critical organ failure and neurotrauma.

Stimuli-Responsive Antibacterial Materials: Molecular Structures, Design Principles, and Biomedical Applications

Infections are regarded as the most severe complication associated with human health, which are urgent to be solved. Stimuli-responsive materials are appealing therapeutic platforms for antibacterial treatments, which provide great potential for accurate theranostics. In this review, the advantages, the response mechanisms, and the key design principles of stimuli-responsive antibacterial materials are highlighted. The biomedical applications, the current challenges, and future directions of stimuli-responsive antibacterial materials are also discussed. First, the categories of stimuli-responsive antibacterial materials are comprehensively itemized based on different sources of stimuli, including external physical environmental stimuli (e.g., temperature, light, electricity, salt, etc.) and bacterial metabolites stimuli (e.g., acid, enzyme, redox, etc.). Second, structural characteristics, design principles, and biomedical applications of the responsive materials are discussed, and the underlying interrelationships are revealed. The molecular structures and design principles are closely related to the sources of stimuli. Finally, the challenging issues of stimuli-responsive materials are proposed. This review will provide scientific guidance to promote the clinical applications of stimuli-responsive antibacterial materials.