Effect of carbon monoxide-releasing molecules II-liberated CO on suppressing inflammatory response in sepsis by interfering with nuclear factor kappa B activation

MiR-107-3p Knockdown Alleviates Endothelial Injury in Sepsis via Kallikrein-Related Peptidase 5

INTRODUCTION

Endothelial injury is a major characteristic of sepsis and contributes to sepsis-induced multiple-organ dysfunction. In this study, we investigated the role of miR-107-3p in sepsis-induced endothelial injury.

METHODS

Human umbilical vein endothelial cells (HUVECs) were exposed to 20 μg/mL of lipopolysaccharide (LPS) for 6-48 h. The levels of miR-107-3p and kallikrein-related peptidase 5 (KLK5) were examined. HUVECs were treated with LPS for 12 h and subsequently transfected with miR-107-3p inhibitor, KLK5 siRNA, or cotransfected with KLK5 siRNA and miR-107-3p inhibitor/negative control inhibitor. Cell survival, apoptosis, invasion, cell permeability, inflammatory response, and the Toll-like receptor 4/nuclear factor κB signaling were evaluated. In addition, the relationship between miR-107-3p and KLK5 expression was predicted and verified.

RESULTS

LPS significantly elevated miR-107-3p levels, which peaked at 12 h. Conversely, the KLK5 level was lower in the LPS group than in the control group and was lowest at 12 h. MiR-107-3p knockdown significantly attenuated reductions in cell survival and invasion, apoptosis promotion, hyperpermeability and inflammation induction, and activation of the NF-κB signaling caused by LPS. KLK5 knockdown had the opposite effect. Additionally, KLK5 was demonstrated as a target of miR-107-3p. MiR-107-3p knockdown partially reversed the effects of KLK5 depletion in LPS-activated HUVECs.

CONCLUSIONS

Our findings indicate that miR-107-3p knockdown may protect against sepsis-induced endothelial cell injury by targeting KLK5. This study identified a novel therapeutic target for sepsis-induced endothelial injury.

Gossypol improves myocardial dysfunction caused by sepsis by regulating histone acetylation

Gossypol is a polyphenol from the cotton plant with anti-inflammatory and anti-oxidation activities and can also function as a histone deacetylase (HDAC) inhibitor. Sepsis is an inflammatory disease with high mortality. Inflammation, oxidative stress, and epigenetic factors are involved in sepsis and its complications. The biological activities of gossypol strongly suggest the potential effects of gossypol on sepsis. In the present study, the beneficial effects of gossypol on sepsis were evaluated. We established a cecal ligation and puncture (CLP) mouse model of sepsis and treated CLP mice with gossypol. The survival rate, serum level of myocardial injury markers, and myocardial level of oxidation markers were measured. We also administered gossypol to lipopolysaccharide (LPS)-treated primary cardiomyocytes. The production of pro-inflammatory cytokines, activation of protein kinase B (AKT) and IκB kinase (IKK), acetylation of histone, and expression of HDACs were measured. Gossypol prevented the death of CLP mice and ameliorated myocardial damage in CLP mice. Moreover, gossypol decreased oxidative factors, while promoting antioxidant production in CLP mice. Gossypol prevented LPS and cytosine-phosphate-guanosine-induced expression of pro-inflammatory cytokines, suppressed LPS-induced activation of AKT and IKK, inhibited histone acetylation, and decreased the expression of HDACs. In conclusion, gossypol ameliorates myocardial dysfunction in mice with sepsis.

Gases in Sepsis: Novel Mediators and Therapeutic Targets

Sepsis, a potentially lethal condition resulting from failure to control the initial infection, is associated with a dysregulated host defense response to pathogens and their toxins. Sepsis remains a leading cause of morbidity, mortality and disability worldwide. The pathophysiology of sepsis is very complicated and is not yet fully understood. Worse still, the development of effective therapeutic agents is still an unmet need and a great challenge. Gases, including nitric oxide (NO), carbon monoxide (CO) and hydrogen sulfide (H₂S), are small-molecule biological mediators that are endogenously produced, mainly by enzyme-catalyzed reactions. Accumulating evidence suggests that these gaseous mediators are widely involved in the pathophysiology of sepsis. Many sepsis-associated alterations, such as the elimination of invasive pathogens, the resolution of disorganized inflammation and the preservation of the function of multiple organs and systems, are shaped by them. Increasing attention has been paid to developing therapeutic approaches targeting these molecules for sepsis/septic shock, taking advantage of the multiple actions played by NO, CO and H₂S. Several preliminary studies have identified promising therapeutic strategies for gaseous-mediator-based treatments for sepsis. In this review article, we summarize the state-of-the-art knowledge on the pathophysiology of sepsis; the metabolism and physiological function of NO, CO and H₂S; the crosstalk among these gaseous mediators; and their crucial effects on the development and progression of sepsis. In addition, we also briefly discuss the prospect of developing therapeutic interventions targeting these gaseous mediators for sepsis.

Protective Impact of Edaravone Against ZnO NPs-induced Oxidative Stress in the Human Neuroblastoma SH-SY5Y Cell Line

Extensive applications of ZnO NPs (zinc oxide nanoparticles) in daily life have created concern about their biotoxicity. Zinc oxide nanoparticles induce oxidative stress, inflammation, and apoptosis in neurons. Edaravone applies antioxidant agent and anti-inflammatory impacts in the different cells, as evaluated in both in vitro and in vivo experimental models. This study is designed to explore, how edaravone would avert mitochondrial impairment in human neuronal cells against ZnO NPs-induced toxicity. Accordingly, we analyzed here whether a pretreatment (for 24 h) with edaravone (10-100 μM) would enhance mitochondrial protection in the human neuroblastoma cells SH-SY5Y against ZnO NPs-induced toxicity. We found that edaravone at 25 μM averted the ZnO NPs-induced decrease in the amounts of adenosine triphosphate (ATP), just as on the activity of the complexes I and V. Also, edaravone induced an antioxidant activity by diminishing the levels of lipid peroxidation, protein carbonylation, and protein nitration in the mitochondrial membranes. Edaravone blocked the ZnO NPs-induced transcription factor nuclear factor-κB (NF-κB) upregulation. The inhibition of the heme oxygenase-1 (HO-1) enzyme by zinc protoporphyrin IX (ZnPP IX, 10 μM) smothered the preventive impacts brought about by edaravone with respect to mitochondrial function and inflammation. After this examination, it can be concluded that edaravone caused cytoprotective impacts in an HO-1-dependent manner in SH-SY5Y cells against ZnO NPs-induced toxicity.

Carbon Monoxide-Releasing Molecule-3 Ameliorates Acute Lung Injury in a Model of Hemorrhagic Shock and Resuscitation: Roles of p38MAPK Signaling Pathway

OBJECTIVE

It was reported that carbon monoxide-releasing molecule-3 (CORM-3) administration immediately after hemorrhagic shock and resuscitation (HSR) ameliorates the HSR-induced acute lung injury (ALI); however, the specific mechanism of the protective effects against HSR-induced ALI remains unclear.

METHODS

To induce hemorrhagic shock, rats were bled to a mean arterial blood pressure of 30 mm Hg for 45 min and then resuscitated with shed blood via the left vein. CORM-3 (4 mg/kg or 8 mg/kg) was respectively administrated after HSR. Twelve  hours post-HSR, lung injury was assessed by wet/dry (W/D) ratio, hematoxylin-eosin staining staining, and lung ultrasound; the apoptotic and pyroptotic macrophages were measured by immunofluorescence staining; and the expression of phosphorylated p38 mitogen activated protein kinase (p-p38MAPK) and total p38MAPK was measured by western blotting. SB203580 (5 mg/kg), a special inhibitor of p-p38MAPK, was administrated by abdominal cavity to assess the roles of p38MAPK in HSR-induced ALI.

RESULTS

Increased B-line score, lung injury score, and W/D ratio indicated the fact of ALI after HSR. Twelve hours post-HSR, CORM-3 administration significantly decreased the B-line score, lung injury score, W/D ratio, apoptotic and pyroptotic macrophages, and the expressions of p-p38MAPK. Further, SB203580 not only reduced HSR-induced ALI, but also enhanced the protective effects of CORM-3 against ALI.

CONCLUSION

We identified the protective effects of CORM-3 against HSR-induced ALI. The mechanism might be related to the inhibition of p38MAPK signaling pathway in lung macrophages.

Carbon Monoxide Releasing Molecule-2-Upregulated ROS-Dependent Heme Oxygenase-1 Axis Suppresses Lipopolysaccharide-Induced Airway Inflammation

The up-regulation of heme oxygenase-1 (HO-1) is mediated through nicotinamaide adenine dinucleotide phosphate (NADPH) oxidases (Nox) and reactive oxygen species (ROS) generation, which could provide cytoprotection against inflammation. However, the molecular mechanisms of carbon monoxide-releasing molecule (CORM)-2-induced HO-1 expression in human tracheal smooth muscle cells (HTSMCs) remain unknown. Here, we found that pretreatment with CORM-2 attenuated the lipopolysaccharide (LPS)-induced intercellular adhesion molecule (ICAM-1) expression and leukocyte count through the up-regulation of HO-1 in mice, which was revealed by immunohistochemistrical staining, Western blot, real-time PCR, and cell count. The inhibitory effects of HO-1 by CORM-2 were reversed by transfection with HO-1 siRNA. Next, Western blot, real-time PCR, and promoter activity assay were performed to examine the HO-1 induction in HTSMCs. We found that CORM-2 induced HO-1 expression via the activation of protein kinase C (PKC)α and proline-rich tyrosine kinase (Pyk2), which was mediated through Nox-derived ROS generation using pharmacological inhibitors or small interfering ribonucleic acids (siRNAs). CORM-2-induced HO-1 expression was mediated through Nox-(1, 2, 4) or p47^phox, which was confirmed by transfection with their own siRNAs. The Nox-derived ROS signals promoted the activities of extracellular signal-regulated kinase 1/2 (ERK1/2). Subsequently, c-Fos and c-Jun-activator protein-1 (AP-1) subunits-were up-regulated by activated ERK1/2, which turned on transcription of the HO-1 gene by regulating the HO-1 promoter. These results suggested that in HTSMCs, CORM-2 activates PKCα/Pyk2-dependent Nox/ROS/ERK1/2/AP-1, leading to HO-1 up-regulation, which suppresses the lipopolysaccharide (LPS)-induced airway inflammation.

Protective effects of carbon monoxide releasing molecule‑2 on pancreatic function in septic mice

The present study aimed to investigate the effect of carbon monoxide (CO)‑releasing molecule‑2 (CORM‑2) on pancreatic function in sepsis‑model mice. To perform the present investigation, mice were rendered septic by cecal ligation and puncture (CLP). Then, mice were either treated with or without CORM‑2 (8 mg/kg, intravenous) for different durations (6, 12 and 24 h) immediately following CLP. The levels of serum amylase and lipase, tumor necrosis factor α, interleukin‑1β and interleukin‑6 in addition to myeloperoxidase (MPO) activity in pancreatic tissues were determined at 6, 12 and 24 h post‑CLP. Histological scores and the expression of intercellular adhesion molecule 1 (ICAM‑1), vascular cell adhesion molecule 1 (VCAM‑1), nuclear factor‑κB (NF‑κB) and phosphorylated inhibitor of κB (p‑IκB‑α) in the pancreas were also evaluated at 24 h post‑CLP. The results of the present study revealed that compared with CLP‑alone group, CORM‑2 treatment significantly (P<0.05) reduced the levels of serum amylase, lipase and pro‑inflammatory cytokines. In parallel, the severity of pancreatic histology, MPO activity and the expression levels of ICAM‑1 and VCAM‑1 in the pancreas of CORM‑2 treated CLP mice were substantially decreased compared with the untreated group. Furthermore, CORM‑2 treatment inhibited the expression levels of NF‑κB and P‑IκB‑α in the pancreas of mice following CLP compared with the untreated group. CORM‑2‑liberated CO exerted protective effects on the pancreatic function of septic mice, and the beneficial effects may be due to the suppression of NF‑κB activation and subsequent regulation of NF‑κB‑dependent expression of cytokines.

Therapeutic effect of carbon monoxide-releasing molecule-3 on acute lung injury after hemorrhagic shock and resuscitation

Hemorrhagic shock and resuscitation (HSR) induces a pulmonary inflammatory response and frequently causes acute lung injury. Carbon monoxide-releasing molecule-3 (CORM-3) has been reported to liberate and deliver CO under physiological conditions, which exerts organ-protective effects during systemic insults. The present study aimed to determine whether the administration of CORM-3 following HSR exerts a therapeutic effect against HSR-induced lung injury without any detrimental effects on oxygenation and hemodynamics. To induce hemorrhagic shock, rats were bled to a mean arterial blood pressure of 30 mmHg for 45 min and then resuscitated with the shed blood. CORM-3 or a vehicle was intravenously administered immediately following the completion of resuscitation. The rats were divided into four groups, including sham, HSR, HSR/CORM-3 and HSR/inactive CORM-3 groups. Arterial blood gas parameters and vital signs were recorded during HSR. The histopathological changes to the lungs were evaluated using a lung injury score, while pulmonary edema was evaluated on the basis of the protein concentration in bronchoalveolar lavage fluid and the lung wet/dry ratio. We also investigated the pulmonary expression levels of inflammatory mediators and apoptotic markers such as cleaved caspase-3 and transferase-mediated dUTP-fluorescein isothiocyanate nick-end labeling (TUNEL) staining. Although HSR caused significant lung histopathological damage and pulmonary edema, CORM-3 significantly ameliorated this damage. CORM-3 also attenuated the HSR-induced upregulation of tumor necrosis factor-α, inducible nitric oxide synthase and interleukin-1β genes, and the expression of interleukin-1β and macrophage inflammatory protein-2. In addition, the expression of interleukin-10, an anti-inflammatory cytokine, was inversely enhanced by CORM-3, which also reduced the number of TUNEL-positive cells and the expression of cleaved caspase-3 following HSR. Although CORM-3 was administered during the acute phase of HSR, it did not exert any influence on arterial blood gas analysis data and vital signs during HSR. Therefore, treatment with CORM-3 ameliorated HSR-induced lung injury, at least partially, through anti-inflammatory and anti-apoptotic effects, without any detrimental effects on oxygenation and hemodynamics.

Gasotransmitters and the immune system: Mode of action and novel therapeutic targets

Gasotransmitters are a group of gaseous molecules, with pleiotropic biological functions. These molecules include nitric oxide (NO), hydrogen sulfide (H₂S), and carbon monoxide (CO). Abnormal production and metabolism of these molecules have been observed in several pathological conditions. The understanding of the role of gasotransmitters in the immune system has grown significantly in the past years, and independent studies have shed light on the effect of exogenous and endogenous gasotransmitters on immune responses. Moreover, encouraging results come from the efficacy of NO-, CO- and H₂S -donors in preclinical animal models of autoimmune, acute and chronic inflammatory diseases. To date, data on the influence of gasotransmitters in immunity and immunopathology are often scattered and partial, and the scarcity of clinical trials using NO-, CO- and H₂S -donors, reveals that more effort is warranted. This review focuses on the role of gasotransmitters in the immune system and covers the evidences on the possible use of gasotransmitters for the treatment of inflammatory conditions.

Phosphatidylinositol 3-kinase-mediated HO-1/CO represses Fis1 levels and alleviates lipopolysaccharide-induced oxidative injury in alveolar macrophages

Sepsis-related acute respiratory distress syndrome is characterized by marked oxidative stress and mitochondrial dysfunction lacking of specific therapy. Heme oxygenase (HO)-1 followed by endogenous carbon monoxide (CO) exerted a cytoprotective effect against multi-organ damage during sepsis. Additionally, the phosphatidylinositol 3-kinase (PI3K)/protein kinase B (Akt) pathway, which serves as an upstream regulator of HO-1, was associated with inflammation and oxidative stress. Therefore, the purpose of the present study was to investigate whether the PI3K/Akt pathway was involved in the effects of HO-1/CO on the expression of mitochondrial fission 1 protein (Fis1). In the present study, CO releasing molecule-2 (CORM2), as the exogenous source of CO, plus LY294002, as a specific PI3K inhibitor, were pre-incubated in lipopolysaccharide (LPS)-simulated rat NR8383 alveolar macrophages. The results demonstrated that CORM2 improved cell viability, inhibited tumor necrosis factor-α levels, malondialdehyde contents, while elevating interleukin-10 levels and superoxide dismutase activities. In addition, pretreatment with CORM2 suppressed the fragmentation of mitochondria, upregulated the expressions of phosphorylated-Akt and HO-1 but downregulated the levels of Fis1 mRNA and protein in LPS-exposed cells. However, pretreatment with LY294002 significantly inhibited the phosphorylation of Akt, decreased HO-1 levels, aggravated mitochondrial fragmentation, increased Fis1 mRNA and protein levels, and reversed the above protective effects of CORM2. Collectively, the results of the present study indicated that the PI3K/Akt pathway mediated the cytoprotective effects of HO-1/CO on the transcription and translational levels of Fis1, and alleviated LPS-induced oxidative injury in alveolar macrophages.

The Carbon monoxide releasing molecule ALF-186 mediates anti-inflammatory and neuroprotective effects via the soluble guanylate cyclase ß1 in rats' retinal ganglion cells after ischemia and reperfusion injury

BACKGROUND

The endogenously produced gaseous molecule carbon monoxide is able to promote organ protection after ischemia-reperfusion injuries (IRI). The impact of carbon monoxide releasing molecules (CORM) regarding inflammation in neuronal tissues has not been studied in detail. In this investigation, we aimed to analyze the effects of the CORM ALF-186 on neuro-inflammation and hypothesized that the soluble guanylate cyclase (sGC) is playing a decisive role.

METHODS

Retinal ischemia-reperfusion injury was performed for 60 min in Sprague-Dawley rats. Thereafter, the CORM ALF-186 (10 mg/kg) in the presence or absence of the sGC inhibitor ODQ was injected via a tail vein. Retinal tissue was harvested 24 h later to analyze mRNA or protein expression of sGC-β1 subunit, transcription factors NF-κB and CREB, the inflammatory cytokines TNF-α and IL-6, as well as the heat shock proteins (HSP) HSP-70 and HSP-90. Immunohistochemistry was performed on frozen sections of the retina. The overall neuroprotective effect of ALF-186 was assessed by counting fluorogold-pre-labeled retinal ganglion cells (RGC) 7 days after IRI.

RESULTS

Ischemia-reperfusion mediated loss of vital RGC was attenuated by the administration of ALF-186 after injury. ALF-186 treatment after IRI induced sGC-ß1 leading to a decreased NF-κB and CREB phosphorylation. Consecutively, ALF-186 mitigated IRI induced TNF-α and IL-6 expression in the retina and in the rats' serum. Moreover, ALF-186 attenuated heat shock protein 70 (Hsp-70) while increasing Hsp-90. The sGC-inhibitor ODQ attenuated the anti-inflammatory effects of ALF-186 and increased retinal loss of ganglion cells. These results were confirmed by immunohistochemistry.

CONCLUSION

The CORM ALF-186 protected RGC from IRI induced loss. Furthermore, ALF-186 reduced IRI mediated neuroinflammation in the retina and in the serum by activating sGC. Inhibition of sGC stopped the beneficial and protective effects of ALF-186. ALF-186 may present a promising therapeutic alternative in treating inflammation after neuronal IRI.

LPS-induced inflammatory response is suppressed by Wnt inhibitors, Dickkopf-1 and LGK974

In this study, LPS-induced inflammatory responses in BEAS-2B human bronchial epithelial cells and human umbilical vein endothelial cell (HUVEC)s were found to be prevented by Dickkopf-1 (DKK-1), a secreted Wnt antagonist, and LGK974, a small molecular inhibitor of the Wnt secretion. LPS-induced IκB degradation and NF-κB nuclear translocation as well as the expressions of pro-inflammatory genes including IL-6, IL-8, TNF- α, IL-1β, MCP-1, MMP-9, COX-2 and iNOS, were all suppressed by DKK-1 and LGK974 in a dose-dependent manner. The suppressive effects of LGK974 on NF-κB, IκB, and pro-inflammatory gene expression were rescued by ectopic expression of β-catenin, suggesting that the anti-inflammatory activity of LGK974 is mediated by modulation of the Wnt/β-catenin pathway and not by unrelated side effects. When Wnt recombinant proteins were treated to cells, Wnt3a and Wnt5a significantly induced pro-inflammatory gene expressions, while Wnt7a and Wnt10b showed little effects. It was also found that Wnt3a and Wnt5a expressions were significantly induced by LPS treatment. Consistently, knockdown of Wnt3a and Wnt5a blocked LPS-induced inflammatory responses, while treatment of recombinant Wnt3a and Wnt5a proteins rescued the inhibition of inflammatory responses by LGK974. Findings of this study showed that DKK-1 and LGK974 suppress LPS-induced inflammatory response by modulating Wnt/β-catenin pathway.

Characteristics of exogenous carbon monoxide deliveries

Carbon monoxide (CO) has long been considered an environmental pollutant and a poison. Exogenous exposure to amounts of CO beyond the physiologic level of the body can result in a protective or adaptive response. However, as a gasotransmitter, endogenous CO is important for multiple physiologic functions. To date, at least seven distinct methods of delivering CO have been utilized in animal and clinical studies. In this mini-review, we summarize the exogenous CO delivery methods and compare their advantages and disadvantages.

Escherichia coli heme oxygenase modulates host innate immune responses

Induction of mammalian heme oxygenase (HO)-1 and exposure of animals to carbon monoxide (CO) ameliorates experimental colitis. When enteric bacteria, including Escherichia coli, are exposed to low iron conditions, they express an HO-like enzyme, chuS, and metabolize heme into iron, biliverdin and CO. Given the abundance of enteric bacteria residing in the intestinal lumen, our postulate was that commensal intestinal bacteria may be a significant source of CO and those that express chuS and other Ho-like molecules suppress inflammatory immune responses through release of CO. According to real-time PCR, exposure of mice to CO results in changes in enteric bacterial composition and increases E. coli 16S and chuS DNA. Moreover, the severity of experimental colitis correlates positively with E. coli chuS expression in IL-10 deficient mice. To explore functional roles, E. coli were genetically modified to overexpress chuS or the chuS gene was deleted. Co-culture of chuS-overexpressing E. coli with bone marrow-derived macrophages resulted in less IL-12p40 and greater IL-10 secretion than in wild-type or chuS-deficient E. coli. Mice infected with chuS-overexpressing E. coli have more hepatic CO and less serum IL-12 p40 than mice infected with chuS-deficient E. coli. Thus, CO alters the composition of the commensal intestinal microbiota and expands populations of E. coli that harbor the chuS gene. These bacteria are capable of attenuating innate immune responses through expression of chuS. Bacterial HO-like molecules and bacteria-derived CO may represent novel targets for therapeutic intervention in inflammatory conditions.

Pretreatment of Mouse Neural Stem Cells with Carbon Monoxide-Releasing Molecule-2 Interferes with NF-κB p65 Signaling and Suppresses Iron Overload-Induced Apoptosis

Neural stem cell (NSC) transplantation is a promising approach to repair the damaged brain after hemorrhagic stroke; however, it is largely limited by the poor survival of donor cells. Breakdown products of the hematoma and subsequent iron overload contribute to the impairment of survival of neural cells. There is little information regarding the mechanism involved in the death of grafted cells. Furthermore, therapeutic research targeted to improving the survival of grafted neural stem cells (NSCs) is strikingly lacking. Here, we showed that iron overload induced apoptosis of C17.2 cells, a cell line originally cloned from mouse NSCs and immortalized by v-myc. Pretreatment with carbon monoxide-releasing molecule-2 (CORM-2) markedly protected C17.2 cells against iron overload in a dose-dependent manner. Moreover, CORM-2 interfered with NF-κB signaling, including inhibition of nuclear translocation and down-regulation of NF-κB p65. TUNEL staining showed that preconditioning C17.2 cells with CORM-2 enhanced their resistance to apoptosis induced by iron overload, which was concomitant with down-regulation of the pro-apoptotic proteins (Bax and cleaved caspase-3) and up-regulation of the anti-apoptotic protein Bcl2. The protective effect of CORM-2 could be simulated by BAY11-7082, a special inhibitor of NF-κB p65. These results provide a novel and effective strategy to enhance the survival of NSCs after transplantation and, therefore, their efficacy in repairing brain injury due to hemorrhagic stroke.

Different design of enzyme-triggered CO-releasing molecules (ET-CORMs) reveals quantitative differences in biological activities in terms of toxicity and inflammation

Acyloxydiene–Fe(CO)₃ complexes can act as enzyme-triggered CO-releasing molecules (ET-CORMs). Their biological activity strongly depends on the mother compound from which they are derived, i.e. cyclohexenone or cyclohexanedione, and on the position of the ester functionality they harbour. The present study addresses if the latter characteristic affects CO release, if cytotoxicity of ET-CORMs is mediated through iron release or inhibition of cell respiration and to what extent cyclohexenone and cyclohexanedione derived ET-CORMs differ in their ability to counteract TNF-α mediated inflammation. Irrespective of the formulation (DMSO or cyclodextrin), toxicity in HUVEC was significantly higher for ET-CORMs bearing the ester functionality at the outer (rac-4), as compared to the inner (rac-1) position of the cyclohexenone moiety. This was paralleled by an increased CO release from the former ET-CORM. Toxicity was not mediated via iron as EC₅₀ values for rac-4 were significantly lower than for FeCl₂ or FeCl₃ and were not influenced by iron chelation. ATP depletion preceded toxicity suggesting impaired cell respiration as putative cause for cell death. In long-term HUVEC cultures inhibition of VCAM-1 expression by rac-1 waned in time, while for the cyclohexanedione derived rac-8 inhibition seems to increase. NFκB was inhibited by both rac-1 and rac-8 independent of IκBα degradation. Both ET-CORMs activated Nrf-2 and consequently induced the expression of HO-1.

This study further provides a rational framework for designing acyloxydiene–Fe(CO)₃ complexes as ET-CORMs with differential CO release and biological activities. We also provide a better understanding of how these complexes affect cell-biology in mechanistic terms.