Folic acid-tagged protein nanoemulsions loaded with CORM-2 enhance the survival of mice bearing subcutaneous A20 lymphoma tumors

Drug-Loaded Biomimetic Carriers for Non-Hodgkin's Lymphoma Therapy: Advances and Perspective

Chemotherapy remains the mainstay of treatment for the lymphoma patient population, despite its relatively poor therapeutic results, high toxicity, and low specificity. With the advancement of biotechnology, the significance of drug-loading biomimetic materials in the medical field has become increasingly evident, attracting extensive attention from the scientific community and the pharmaceutical industry. Given that they can cater to the particular requirements of lymphoma patients, drug-loading biomimetic materials have recently become a potent and promising delivery approach for various applications. This review mainly reviews the recent advancements in the treatment of tumors with biological drug carrier-loaded drugs, outlines the mechanisms of lymphoma development and the diverse treatment modalities currently available, and discusses the merits and limitations of biological drug carriers. What is more, the practical application of biocarriers in tumors is explored by providing examples, and the possibility of loading such organisms with antilymphoma drugs for the treatment of lymphoma is conceived.

Novel Toxicodynamic Model of Subcutaneous Envenomation to Characterize Snake Venom Coagulopathies and Assess the Efficacy of Site-Directed Inorganic Antivenoms

Venomous snake bite adversely affects millions of people yearly, but few animal models allow for the determination of toxicodynamic timelines with hemotoxic venoms to characterize the onset and severity of coagulopathy or assess novel, site-directed antivenom strategies. Thus, the goals of this investigation were to create a rabbit model of subcutaneous envenomation to assess venom toxicodynamics and efficacy of ruthenium-based antivenom administration. New Zealand White rabbits were sedated with midazolam via the ear vein and had viscoelastic measurements of whole blood and/or plasmatic coagulation kinetics obtained from ear artery samples. Venoms derived from Crotalus scutulatus scutulatus, Bothrops moojeni, or Calloselasma rhodostoma were injected subcutaneously, and changes in coagulation were determined over three hours and compared to samples obtained prior to envenomation. Other rabbits had ruthenium-based antivenoms injected five minutes after venom injection. Viscoelastic analyses demonstrated diverse toxicodynamic patterns of coagulopathy consistent with the molecular composition of the proteomes of the venoms tested. The antivenoms tested attenuated venom-mediated coagulopathy. A novel rabbit model can be used to characterize the onset and severity of envenomation by diverse proteomes and to assess site-directed antivenoms. Future investigation is planned involving other medically important venoms and antivenom development.

A Structural Analysis of Proteinaceous Nanotube Cavities and Their Applications in Nanotechnology

Protein nanotubes offer unique properties to the materials science field that allow them to fulfill various functions in drug delivery, biosensors and energy storage. Protein nanotubes are chemically diverse, modular, biodegradable and nontoxic. Furthermore, although the initial design or repurposing of such nanotubes is highly complex, the field has matured to understand underlying chemical and physical properties to a point where applications are successfully being developed. An important feature of a nanotube is its ability to bind ligands via its internal cavities. As ligands of interest vary in size, shape and chemical properties, cavities have to be able to accommodate very specific features. As such, understanding cavities on a structural level is essential for their effective application. The objective of this review is to present the chemical and physical diversity of protein nanotube cavities and highlight their potential applications in materials science, specifically in biotechnology.

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.

Sawhorse-type ruthenium complexes with triazolopyrimidine ligands - what do they represent in terms of cytotoxic and CORM compounds?

Three sawhorse-type ruthenium(I) complexes containing purine analogs such as triazolopyrimidines of the general formula [Ru₂(CO)₄(μ-OOCCH₃)₂(L)₂], where L is 1,2,4-triazolo[1,5-a]pyrimidine (tp for 1), 5,7-ditertbutyl-1,2,4-triazolo[1,5-a]pyrimidine (dbtp for 2) and 5,7-diphenyl-1,2,4-triazolo[1,5-a]pyrimidine (dptp for 3), have been synthesized and characterized by elemental analysis, infrared analysis, multinuclear magnetic resonance spectroscopic techniques (¹H, ¹³C, ¹⁵N), and single-crystal X-ray diffraction (for 1 and 2). By assay with myoglobin, the photo-activated CO-releasing molecule (PhotoCORM) character of (1-3) has been confirmed, thus indicating the possibility of use in CO-based therapies. The importance of UV-induced modification has been investigated in the context of anticancer properties. Complexes (1) and (2) have been thoroughly screened for their in vitro cytotoxicity against various cancer cell lines: MCF-7 (breast cancer), HeLa (cervical cancer) and C32 (melanoma), as well as L929 normal fibroblasts in the dark and presence of UV-A light (365 nm). The results were compared with those for cisplatin and two reference ruthenium complexes, namely NAMI-A and KP1019. The most hydrophilic [Ru₂(CO)₄(μ-OOCCH₃)₂(tp)₂] (1) (log P = -1.12) was found to be more cytotoxic than (2), despite the lower cellular uptake measured by ICP-MS toward HeLa cells. Importantly, photo-induced stimulation of cells with (1) resulted in a lower decrease in the viability of L929 normal cells (IC₅₀ = 154.7 ± 6.5 μM) in comparison with HeLa cancer cells (IC₅₀ = 66.7 ± 3.4 μM). The photo-induced stimulation of (1) and (2) increases ROS generation, and their anticancer activity may be a partially ROS-dependent phenomenon.

Nanomedicine as a magic bullet for combating lymphoma

Hematological malignancy like lymphoma originates in lymph tissues and has a propensity to spread across other organs. Managing such tumors is challenging as conventional strategies like surgery and local treatment are not plausible options and there are high chances of relapse. The advent of novel targeted therapies and antibody-mediated treatments has proven revolutionary in the management of these tumors. Although these therapies have an added advantage of specificity in comparison to the traditional chemotherapy approach, such treatment alternatives suffer from the occurrence of drug resistance and dose-related toxicities. In past decades, nanomedicine has emerged as an excellent surrogate to increase the bioavailability of therapeutic moieties along with a reduction in toxicities of highly cytotoxic drugs. Nanotherapeutics achieve targeted delivery of the therapeutic agents into the malignant cells and also have the ability to carry genes and therapeutic proteins to the desired sites. Furthermore, nanomedicine has an edge in rendering personalized medicine as one type of lymphoma is pathologically different from others. In this review, we have highlighted various applications of nanotechnology-based delivery systems based on lipidic, polymeric and inorganic nanomaterials that address different targets for effectively tackling lymphomas. Moreover, we have discussed recent advances and therapies available exclusively for managing this malignancy.

Different Serum, Different Protein Corona! The Impact of the Serum Source on Cellular Targeting of Folic Acid-Modified Chitosan-Based Nanoparticles

The nanoparticle (NP) protein corona represents an interface between biological components and NPs, dictating their cellular interaction and biological fate. To assess the success of cellular targeting, NPs modified with targeting ligands are incubated with target cells in serum-free culture medium or in the presence of fetal bovine serum (FBS). In the former, the role of the corona is overlooked, and in the latter, the effects of a corona that does not represent the one forming in humans nor the respective disease state are considered. Via proteomic analysis, we demonstrate how the difference in the composition of FBS, sera from healthy human volunteers, and breast cancer patients (BrCr Pt) results in the formation of completely different protein coronas around the same NP. Successful in vitro targeting of breast cancer cells was only observed when NPs were incubated with target cells in the presence of BrCr Pt sera only. In such cases, the success of targeting was not attributed to the targeting ligand itself, but to the adsorption of specific serum proteins that facilitate NP uptake by cancer cells in the presence of BrCr Pt sera. This work therefore demonstrates how the serum source affects the reliability of in vitro experiments assessing NP-cell interactions and the consequent success or failure of active targeting and may in fact indicate an additional reason for the limited clinical success of drug targeting by NPs in cancer.

The potentials of carbon monoxide-releasing molecules in cancer treatment: An outlook from ROS biology and medicine

Carbon monoxide (CO) is now well recognized a pivotal endogenous signaling molecule in mammalian lives. The proof-of-concept employing chemical carriers of exogenous CO as prodrugs for CO release, also known as CO-releasing molecules (CO-RMs), has been appreciated. The major advantage of CO-RMs is that they are able to deliver CO to the target sites in a controlled manner. There is an increasing body of experimental studies suggesting the therapeutic potentials of CO and CO-RMs in different cancer models. This review firstly presents a short but crucial view concerning the characteristics of CO and CO-RMs. Then, the anticancer activities of CO-RMs that target many cancer hallmarks, mainly proliferation, apoptosis, angiogenesis, and invasion and metastasis, are discussed. However, their anticancer activities are varying and cell-type specific. The aerobic metabolism of molecular oxygen inevitably generates various oxygen-containing reactive metabolites termed reactive oxygen species (ROS) which play important roles in both physiology and pathophysiology. Although ROS act as a double-edged sword in cancer, both sides of which may potentially have been exploited for therapeutic benefits. The main focus of the present review is thus to identify the possible signaling network by which CO-RMs can exert their anticancer actions, where ROS play the central role. Another important issue concerning the potential effect of CO-RMs on the aerobic glycolysis (the Warburg effect) which is a feature of cancer metabolic reprogramming is given before the conclusion with future prospects on the challenges of developing CO-RMs into clinically pharmaceutical candidates in cancer therapy.

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CO-RMs as pro-drugs for controlled CO delivery are potentially beneficial in cancer treatment.

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Anticancer activities of CO-RMs are varying and cell-type specific.

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Anti-proliferative, pro-apoptotic, and anti-angiogenic effects are major niches.

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ROS may play a central role in the molecular pathways underlying anticancer activities of CO-RMs.

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CO-RMs can act against Warburg effect, a feature of cancer metabolic reprogramming.

Impact of carbon monoxide poisoning on the risk of breast cancer

Carbon monoxide (CO) is a toxic gas and an endogenous signaling molecule. Some studies involving cell lines have revealed the potential antibreast cancer effects of CO. Data on such effects in humans, however, are limited. Thus, we conducted a study on patients with CO poisoning (COP) to evaluate the effects of CO on the risk of breast cancer. We identified female patients who were diagnosed with COP over the period of 2002 and 2009 from the Nationwide Poisoning Database of Taiwan. For comparison, we selected females without COP from the National Health Insurance Research Database. Participants in the COP and comparison cohorts were matched on the index year, age, monthly income, and geographic region of residence at a 1:6 ratio. We followed up the two cohorts until the end of 2014 and compared their risks of developing breast cancer. We included 7053 participants with COP and 42,318 participants without COP. Participants with COP were at a lower risk of developing breast cancer than those without COP (0.7% vs. 1.0%, p < 0.001). Cox proportional hazard regression analyses revealed that COP was associated with a hazard ratio of 0.67 (95% confidence interval [95% CI] 0.50–0.90) for breast cancer after we adjusted for age, monthly income, geographic region, and comorbidities of hypertension, diabetes, and hyperlipidemia. Our result provides evidence for the potential protective effects of CO against breast cancer in humans. Further studies that directly evaluate the potential effects are warranted.

Construction of biomimetic silver nanoparticles in the treatment of lymphoma

Lymphoma is a well-known malignant tumor in the human body. Although many anticancer drugs have been developed to improve the survival rate of patients, about 40% of patients continue to be recurrent or refractory, a key issue needing remedy. Therefore, it is necessary to identify alternative treatments to reduce the disease's mortality. To this effect, a new type of anti-lymphoma nanocomplex FA@RBCm-AgNPs was prepared using AgNPs as the core of nanoparticles along with the targeting molecule folic acid inserted erythrocyte membrane as the shell. The biomimetic properties of red blood cell membrane (RBCm) endow F-RAN with good biocompatibility as well as the ability to evade clearance of the reticuloendothelial system. In addition, F-RAN was modified with folic acid to actively and selectively identify tumor cells. In vivo and in vitro experiments demonstrate that F-RAN can inhibit lymphoma cells and induce apoptosis of stem cells while promoting apoptosis of lymphoma with no obvious side effects. Hence, F-RAN may serve as a new treatment for lymphoma.

Lipid-Stabilized Double Emulsions Generated in Planar Microfluidic Devices

Microemulsions have found a wide range of applications exploiting their chemical and physical properties. Development of microfluidic-based approaches has allowed for the controlled production of highly monodispersed emulsions, including the formation of multiple and hierarchical emulsions. Conventional poly(dimethylsiloxane)-based microfluidic systems require tight spatial control over the surface chemistry when used for double emulsion generation, which can be challenging to achieve on the micrometer scale. Here, we present a two-dimensional device design, which can selectively be surface-treated in a straightforward manner and allows for the formation of uniform water/oil/water double emulsions by combining two distinct hydrophilic and hydrophobic surface properties. These surfaces are sufficiently separated in space to allow for imparting their functionalization without the requirement for lithographic approaches or complex flow control. We demonstrate that a mismatch between the wettability requirements of the continuous phase and the channel wall inherent in this approach can be tolerated over several hundreds of micrometers, opening up the possibility to use simple pressure-driven flows to achieve surface functionalization. The design architecture exhibits robust efficiency in emulsion generation while retaining simple device fabrication. We finally demonstrate the potential of this approach by generating water in oil in water emulsions with lipid molecules acting as surfactants.

Emerging Delivery Strategies of Carbon Monoxide for Therapeutic Applications: from CO Gas to CO Releasing Nanomaterials

Carbon monoxide (CO) therapy has emerged as a hot topic under exploration in the field of gas therapy as it shows the promise of treating various diseases. Due to the gaseous property and the high affinity for human hemoglobin, the main challenges of administrating medicinal CO are the lack of target selectivity as well as the toxic profile at relatively high concentrations. Although abundant CO releasing molecules (CORMs) with the capacity to deliver CO in biological systems have been developed, several disadvantages related to CORMs, including random diffusion, poor solubility, potential toxicity, and lack of on-demand CO release in deep tissue, still confine their practical use. Recently, the advent of versatile nanomedicine has provided a promising chance for improving the properties of naked CORMs and simultaneously realizing the therapeutic applications of CO. This review presents a brief summarization of the emerging delivery strategies of CO based on nanomaterials for therapeutic application. First, an introduction covering the therapeutic roles of CO and several frequently used CORMs is provided. Then, recent advancements in the synthesis and application of versatile CO releasing nanomaterials are elaborated. Finally, the current challenges and future directions of these important delivery strategies are proposed.

Styrene-maleic acid copolymer-encapsulated carbon monoxide releasing molecule-2 (SMA/CORM-2) suppresses proliferation, migration and invasion of colorectal cancer cells in vitro and in vivo

Although increasing evidence have confirmed that carbon monoxide release molecule-2(CORM-2) plays an active role in the treatment of inflammation and tumors, poor aqueous solubility and short CO-release duration restrict its extensive application. Our previous work synthesized styrene-maleic acid copolymer-encapsulated CORM-2 (SMA/CORM-2) to overcome above-mentioned deficiencies and demonstrated satisfactory effects in colitis. This study is to investigate the function of SMA/CORM-2 on colorectal cancer proliferation and metastasis. CCK-8 experiment is used to clarify the half maximal inhibitory concentration (IC50) of SMA/CORM-2 and to detect cell proliferation. Transwell assay coated with or without matrigel was to detect cell invasion and migration. Western blot was used to detect β-catenin, AKT, p-AKT, VEGF, MMP-2 and MMP-9 proteins. At last, nude mice xenograft was used to further investigate the anti-tumor effect of SMA/CORM-2 in vivo. After SW480 and C26 cells were treated with 0.5 mg/ml SMA/CORM-2, CRC cells proliferation, migration and invasion were inhibited. In vivo, SMA/CORM-2 treatment remarkably suppressed tumor growth and lung metastasis in nude mice. Furthermore, the expression of β-catenin, p-AKT, VEGF, MMP-2 and MMP-9 proteins could be down-regulated after SMA/CORM-2 treatment. SMA/CORM-2 exerted both in vitro and in vivo anti-proliferation and anti-metastatic effects, which may yield a novel therapeutic strategy for CRC.

An Overview of the Potential Therapeutic Applications of CO-Releasing Molecules

Carbon monoxide (CO) has long been known as the “silent killer” owing to its ability to form carboxyhemoglobin—the main cause of CO poisoning in humans. Its role as an endogenous neurotransmitter, however, was suggested in the early 1990s. Since then, the biological activity of CO has been widely examined via both the direct administration of CO and in the form of so-called “carbon monoxide releasing molecules (CORMs).” This overview will explore the general physiological effects and potential therapeutic applications of CO when delivered in the form of CORMs.

Lymphoma-targeted treatment using a folic acid-decorated vincristine-loaded drug delivery system

Purpose

B-cell lymphoma is the most frequently diagnosed lymphoid tumor. Folic acid (FA)-decorated systems were found to be preferentially internalized on the B-cell lymphoma cell line which is reported to express the folate receptor. This study was designed to develop an FA-decorated vincristine (VCR)-loaded system for targeted lymphoma treatment.

Methods

FA-decorated lipid was synthesized. VCR-loaded lipid-polymer hybrid nanoparticles (LPNs) were fabricated. In vitro cell lines and an in vivo lymphoma animal model was used to evaluate the anti B-cell lymphoma effect.

Results

FA-decorated, VCR-loaded LPNs (FA-VCR/LPNs) have shown a targeted effect in delivery to B-cell lymphoma cells. FA-VCR/LPNs also showed the highest anti-tumor effect in murine-bearing lymphoma xenografts.

Conclusion

FA-VCR/LPNs can achieve targeted delivery of VCR, bring about an outstanding therapeutic effect to treat lymphoma, and also reduce the systemic toxicity. FA-VCR/LPNs could be an excellent system for lymphoma therapy.

Diiron Hexacarbonyl Complex Induces Site-Specific Release of Carbon Monoxide in Cancer Cells Triggered by Endogenous Glutathione

In this study, we have evaluated a water-soluble, nontarget reagent and a carrier-free diiron hexacarbonyl complex, [Fe₂{μ-SCH₂CH(OH)CH₂(OH)}₂(CO)₆] (TG-FeCORM), that can induce the site-specific release of carbon monoxide (CO) in cancer cells triggered by endogenous glutathione (GSH). The releasing rate of CO was dependent on the amount of endogenous GSH. Being the amount of endogenous GSH higher in cancer cells than in normal cells, the CO-releasing rate resulted faster in cancer cells. Moreover, the anti-inflammatory properties related to the intracellular CO release of TG-FeCORM were also confirmed in the living HeLa cells.

Protein-lipid nanohybrids as emerging platforms for drug and gene delivery: Challenges and outcomes

Nanoparticulate drug delivery systems have been long used to deliver a vast range of drugs and bioactives owing to their ability to demonstrate novel physical, chemical, and/or biological properties. An exponential growth has spurred in research and development of these nanocarriers which led to the evolution of a great number of diverse nanosystems including liposomes, nanoemulsions, solid lipid nanoparticles (SLNs), micelles, dendrimers, polymeric nanoparticles (NPs), metallic NPs, and carbon nanotubes. Among them, lipid-based nanocarriers have made the largest progress whether commercially or under development. Despite this progress, these lipid-based nanocarriers suffer from several limitations that led to the development of many protein-coated lipid nanocarriers. To less extent, protein-based nanocarriers suffer from limitations that led to the fabrication of some lipid bilayer enveloping protein nanocarriers. This review discusses in-depth some limitations associated with the lipid-based or protein-based nanocarriers and the fruitful outcomes brought by protein-lipid hybridization. Also discussed are the various hybridization techniques utilized to formulate these protein-lipid nanohybrids and the mechanisms involved in the drug loading process.

Lymph cancer chemotherapy: delivery of doxorubicin-gemcitabine prodrug and vincristine by nanostructured lipid carriers

PURPOSE

Radiation and chemotherapy are the most common course of treatment for B-cell lymphoma. Doxorubicin (DOX), gemcitabine (GEM), and vincristine (VCR) are the commonly used antilymphoma chemotherapeutic drugs. The aim of this study is to construct a novel drug delivery system for the combination delivery of the three drugs on lymphoma.

MATERIALS AND METHODS

DOX-GEM prodrug was synthesized. Novel nanostructured lipid carriers (NLCs) containing DOX-GEM prodrug and VCR were prepared and used to treat B-cell lymphoma through in vivo treatment to a lymph cancer animal model. The systemic toxicity of the nanomedicine was also evaluated during the treatment.

RESULTS

DOX-GEM prodrug and VCR-loaded NLCs (DOX-GEM VCR NLCs) exhibited the highest antitumor effect in B-cell lymphoma cells and lymphoma animal xenografts when compared with the single drug-loaded NLCs and the drug solutions.

CONCLUSION

It could be concluded that the highest antitumor effect can be achieved by the system due to the stable drug-loading capacity, attractive anticancer therapeutic effects, and reduced toxicities in human Burkitt's lymphoma cell line and mice-bearing cancer model. The resulting DOX-GEM VCR NLCs could be an efficient antilymph cancer agent and could be developed further for the treatment of other tumors.

Aspects of Carbon Monoxide in Form of CO-Releasing Molecules Used in Cancer Treatment: More Light on the Way

Carbon monoxide (CO) has always been recognised as a toxic gas, due to its higher affinity for haemoglobin than oxygen. However, biological studies have revealed an intriguing role for CO as an endogenous signalling molecule, a gasotransmitter. CO is demonstrated to exert many cellular activities including anti-inflammatory, antiapoptotic, and antiproliferative activities. In animal studies, CO gas administration can prevent tissues from hypoxia or ischemic-reperfusion injury. As a result, there are a plethora of reports dealing with the biological applications of CO and CO-releasing molecules (CORMs) in inflammatory and vascular diseases. CORMs have already been tested as a therapeutic agent in clinical trials. More recently, an increased interest has been drawn to CO's potential use as an anticancer agent. In this review, we will aim to give an overview of the research focused on the role of CO and CORMs in different types of cancer and expand to the recent development of the next generation CORMs for clinical application in cancer treatment.

Paulo T, de França Lopes LG, Sousa EHS. A biphosphinic ruthenium complex with potent anti-bacterial and anti-cancer activity

Photorelease of CO and moderate binding to DNA did not seem to be essential features for potent biological activities.

Albumin/asparaginase capsules prepared by ultrasound to retain ammonia

Asparaginase reduces the levels of asparagine in blood, which is an essential amino acid for the proliferation of lymphoblastic malign cells. Asparaginase converts asparagine into aspartic acid and ammonia. The accumulation of ammonia in the bloodstream leads to hyperammonemia, described as one of the most significant side effects of asparaginase therapy. Therefore, there is a need for asparaginase formulations with the potential to reduce hyperammonemia. We incorporated 2 % of therapeutic enzyme in albumin-based capsules. The presence of asparaginase in the interface of bovine serum albumin (BSA) capsules showed the ability to hydrolyze the asparagine and retain the forming ammonia at the surface of the capsules. The incorporation of Poloxamer 407 in the capsule formulation further increased the ratio aspartic acid/ammonia from 1.92 to 2.46 (and 1.10 from the free enzyme), decreasing the levels of free ammonia. This capacity to retain ammonia can be due to electrostatic interactions and retention of ammonia at the surface of the capsules. The developed BSA/asparaginase capsules did not cause significant cytotoxic effect on mouse leukemic macrophage cell line RAW 264.7. The new BSA/asparaginase capsules could potentially be used in the treatment of acute lymphoblastic leukemia preventing hyperammonemia associated with acute lymphoblastic leukemia (ALL) treatment with asparaginase.

Mitochondria and carbon monoxide: cytoprotection and control of cell metabolism - a role for Ca(2+) ?

Carbon monoxide (CO) is an endogenously produced gasotransmitter with important biological functions: anti-inflammation, anti-apoptosis, vasomodulation and cell metabolism modulation. The most recognized cellular target for CO is the mitochondria. Physiological concentrations of CO generate mitochondrial reactive oxygen species (ROS), which are signalling molecules for CO-induced pathways. Indeed, small amounts of ROS promote cytoprotection by a preconditioning effect. Furthermore, CO prevents cell death by limiting mitochondrial membrane permeabilization, which inhibits the release of pro-apoptotic factors into the cytosol; both events are ROS dependent. CO also increases the ability of mitochondria to take up Ca(2+) . Mitochondrial metabolism is modulated by CO, namely by increasing TCA cycle rate, oxidative phosphorylation and mitochondrial biogenesis, which, in turn, increases ATP production. CO's modulation of metabolism might be important for cellular response to diseases, namely cancer and ischaemic diseases. Finally, another cytoprotective role of CO involves the control of Ca(2+) channels. By limiting the activity of T-type and L-type Ca(2+) channels, CO prevents excitotoxicity-induced cell death and modulates cell proliferation. Several questions concerning Ca(2+) signalling, mitochondria and CO can be asked, for instance whether CO modulation of cell metabolism would be dependent on the mitochondrial Ca(2+) uptake capacity, since small amounts of Ca(2+) can increase mitochondrial metabolism. Whether CO controls Ca(2+) communication between mitochondria and endoplasmic reticulum is another open field of research. In summary, CO emerges as a key gasotransmitter in the control of several cellular functions of mitochondria: metabolism, cell death and Ca(2+) signalling.