Gaseous therapeutics in acute lung injury

Systematic review and meta-analysis of studies between short-term exposure to ambient carbon monoxide and non-accidental, cardiovascular, and respiratory mortality in China

Although a growing number of original epidemiological studies imply a link between ambient pollution exposure and mortality risk, the findings associated with carbon monoxide (CO) exposure are inconsistent. Thus, we conducted a systematic review and meta-analysis of epidemiological studies to evaluate the correlations between ambient CO and non-accidental, cardiovascular, and respiratory mortality in China. Eight databases were searched from inception to 15 May 2021. A random-effect model was used to calculate the pooled relative risks (RRs) and 95% confidence intervals (CIs). Subgroup analyses as well as sensitivity analyses were performed. The I square value (I²) was used to assess heterogeneity among different studies. The assessment of publication bias on included studies was examined by funnel plot and Egger's test. The influence of a potential publication bias on findings was explored by using the trim-and-fill procedure. Ultimately, a total of 19 studies were included in our analysis. The pooled relative risk for each 1 mg/m³ increase of ambient carbon monoxide was 1.0220 (95%CI: 1.0102-1.0339) for non-accidental mortality, 1.0304 (95%CI:1.0154-1.0457) for cardiovascular mortality, and 1.0318 (95%CI:1.0132-1.0506) for respiratory mortality. None of subgroup analyses could explain the source of heterogeneity. Exclusion of any single study did not materially alter the pooled effect estimates. Although it was suggestive of publication bias, findings were generally similar with principal findings when we explored the influence of a potential publication bias using the trim-and-fill method. Our meta-analysis demonstrated that exposure to ambient CO was positive with risk of deaths from all non-accidental causes, total cardiovascular, and respiratory diseases. Based on these findings, tougher intervention policies and initiatives to reduce the health effects of CO exposure should be established.

Activation of Resolution Pathways to Prevent and Fight Chronic Inflammation: Lessons From Asthma and Inflammatory Bowel Disease

Formerly considered as a passive process, the resolution of acute inflammation is now recognized as an active host response, with a cascade of coordinated cellular and molecular events that promotes termination of the inflammatory response and initiates tissue repair and healing. In a state of immune fitness, the resolution of inflammation is contained in time and space enabling the restoration of tissue homeostasis. There is increasing evidence that poor and/or inappropriate resolution of inflammation participates in the pathogenesis of chronic inflammatory diseases, extending in time the actions of pro-inflammatory mechanisms, and responsible in the long run for excessive tissue damage and pathology. In this review, we will focus on how resolution can be the target for therapy in "Th1/Th17 cell-driven" immune diseases and "Th2 cell-driven" immune diseases, with inflammatory bowel diseases (IBD) and asthma, as relevant examples. We describe the main cells and mediators stimulating the resolution of inflammation and discuss how pharmacological and dietary interventions but also life style factors, physical and psychological conditions, might influence the resolution phase. A better understanding of the impact of endogenous and exogenous factors on the resolution of inflammation might open a whole area in the development of personalized therapies in non-resolving chronic inflammatory diseases.

Carbon Monoxide Improves Efficacy of Mesenchymal Stromal Cells During Sepsis by Production of Specialized Proresolving Lipid Mediators

Supplemental Digital Content is available in the text.

Objectives:

Mesenchymal stromal cells are being investigated as a cell-based therapy for a number of disease processes, with promising results in animal models of systemic inflammation and sepsis. Studies are ongoing to determine ways to further improve the therapeutic potential of mesenchymal stromal cells. A gas molecule that improves outcome in experimental sepsis is carbon monoxide. We hypothesized that preconditioning of mesenchymal stromal cells with carbon monoxide ex vivo would promote further therapeutic benefit when cells are administered in vivo after the onset of polymicrobial sepsis in mice.

Design:

Animal study and primary cell culture.

Setting:

Laboratory investigation.

Subjects:

BALB/c mice.

Interventions:

Polymicrobial sepsis was induced by cecal ligation and puncture. Mesenchymal stromal cells, mesenchymal stromal cells-conditioned with carbon monoxide, fibroblasts, or fibroblasts-conditioned with carbon monoxide were delivered by tail vein injections to septic mice. The mice were assessed for survival, bacterial clearance, and the inflammatory response during sepsis in each of the groups. Mesenchymal stromal cells were also assessed for their ability to promote bacterial phagocytosis by neutrophils, the production of specialized proresolving lipid mediators, and their importance for mesenchymal stromal cells function using gene silencing.

Measurements and Main Results:

Ex vivo preconditioning with carbon monoxide allowed mesenchymal stromal cells to be administered later after the onset of sepsis (6 hr), and yet maintain their therapeutic effect with increased survival. Carbon monoxide preconditioned mesenchymal stromal cells were also able to alleviate organ injury, improve bacterial clearance, and promote the resolution of inflammation. Mesenchymal stromal cells exposed to carbon monoxide, with docosahexaenoic acid substrate, produced specialized proresolving lipid mediators, particularly D-series resolvins, which promoted survival. Silencing of lipoxygenase pathways (5-lipoxygenase and 12/15-lipoxygenase), which are important enzymes for specialized proresolving lipid mediator biosynthesis, resulted in a loss of therapeutic benefit bestowed on mesenchymal stromal cells by carbon monoxide.

Conclusions:

Taken together, these data suggest that production of specialized proresolving lipid mediators contribute to improved mesenchymal stromal cell efficacy when exposed to carbon monoxide, resulting in an improved therapeutic response during sepsis.

Novel Endogenous Proresolving Molecules:Essential Fatty Acid-Derived and Gaseous Mediators in the Resolution of Inflammation

Acute inflammation is a fundamental, protective response that orchestrates immune system to address harmful stimuli both from within and via invasion. New evidences indicate that the resolution of acute inflammation is not simply passive but active and highly regulated processes coordinated by new families of potent bioactive lipid mediators (LMs), coined specialized proresolving mediators (SPMs). These SPMs are biosynthesized from n-3 polyunsaturated fatty acids. Low concentrations of SPM (nM range) stimulate proresolving cellular processes, such as inhibition of neutrophil infiltration, enhancement of macrophage phagocytosis of bacteria and efferocytosis of cellular debris, and reduction of inflammatory pain through specific G-protein coupled receptors.Of the many bioactive mediators that regulate inflammation resolution, low-dose carbon monoxide (CO) functions as a tissue-protective gaso-transmitter that is endogenously produced by the heme oxygenase (HO) system. Specific SPMs activate the HO system, which in turn enhances endogenous CO production locally, thus establishing a protective feed-forward circuit between SPMs and CO. In addition, treatment with low-dose CO and SPMs exerts protective effects against ischemia/reperfusion injury by decreasing leukocyte-platelet interaction and proinflammatory LM levels.Recent studies reviewed herein assessed the impact of SPMs and low-dose inhaled CO on inflammatory diseases. LM metabololipidomics approach allows the assessment of the efficacy of novel treatments with SPMs and low-dose CO. Moreover, this approach indicates the regions where the action of individual LMs may be physiologically relevant and when these LMs are produced in vivo to serve their proresolving mediator functions that may also permit new directions for treating human diseases.

Hydrogen Sulfide as a Potential Therapeutic Target in Fibrosis

Hydrogen sulfide (H₂S), produced endogenously by the activation of two major H₂S-generating enzymes (cystathionine β-synthase and cystathionine γ-lyase), plays important regulatory roles in different physiologic and pathologic conditions. The abnormal metabolism of H₂S is associated with fibrosis pathogenesis, causing damage in structure and function of different organs. A number of in vivo and in vitro studies have shown that both endogenous H₂S level and the expressions of H₂S-generating enzymes in plasma and tissues are significantly downregulated during fibrosis. Supplement with exogenous H₂S mitigates the severity of fibrosis in various experimental animal models. The protective role of H₂S in the development of fibrosis is primarily attributed to its antioxidation, antiapoptosis, anti-inflammation, proangiogenesis, and inhibition of fibroblasts activities. Future studies might focus on the potential to intervene fibrosis by targeting the pathway of endogenous H₂S-producing enzymes and H₂S itself.

Cell-cell interactions and bronchoconstrictor eicosanoid reduction with inhaled carbon monoxide and resolvin D1

Polymorphonuclear leukocyte (PMN)-mediated acute lung injury from ischemia/reperfusion (I/R) remains a major cause of morbidity and mortality in critical care medicine. Here, we report that inhaled low-dose carbon monoxide (CO) and intravenous resolvin D1 (RvD1) in mice each reduced PMN-mediated acute lung injury from I/R. Inhaled CO (125-250 ppm) and RvD1 (250-500 ng) each reduced PMN lung infiltration and gave additive lung protection. In mouse whole blood, CO and RvD1 attenuated PMN-platelet aggregates, reducing leukotrienes (LTs) and thromboxane B2 (TxB2) in I/R lungs. With human whole blood, CO (125-250 ppm) decreased PMN-platelet aggregates, expression of adhesion molecules, and cysteinyl LTs, as well as TxB2. RvD1 (1-100 nM) also dose dependently reduced platelet activating factor-stimulated PMN-platelet aggregates in human whole blood. In nonhuman primate (baboon) lung infection with Streptococcus pneumoniae, inhaled CO reduced urinary cysteinyl LTs. These results demonstrate lung protection by low-dose inhaled CO as well as RvD1 that each reduced PMN-mediated acute tissue injury, PMN-platelet interactions, and production of both cysteinyl LTs and TxB2. Together they suggest a potential therapeutic role of low-dose inhaled CO in organ protection, as demonstrated using mouse I/R-initiated lung injury, baboon infections, and human whole blood.

Carbon monoxide: present and future indications for a medical gas

Gaseous molecules continue to hold new promise in molecular medicine as experimental and clinical therapeutics. The low molecular weight gas carbon monoxide (CO), and similar gaseous molecules (e.g., H2S, nitric oxide) have been implicated as potential inhalation therapies in inflammatory diseases. At high concentration, CO represents a toxic inhalation hazard, and is a common component of air pollution. CO is also produced endogenously as a product of heme degradation catalyzed by heme oxygenase enzymes. CO binds avidly to hemoglobin, causing hypoxemia and decreased oxygen delivery to tissues at high concentrations. At physiological concentrations, CO may have endogenous roles as a signal transduction molecule in the regulation of neural and vascular function and cellular homeostasis. CO has been demonstrated to act as an effective anti-inflammatory agent in preclinical animal models of inflammation, acute lung injury, sepsis, ischemia/reperfusion injury, and organ transplantation. Additional experimental indications for this gas include pulmonary fibrosis, pulmonary hypertension, metabolic diseases, and preeclampsia. The development of chemical CO releasing compounds constitutes a novel pharmaceutical approach to CO delivery with demonstrated effectiveness in sepsis models. Current and pending clinical evaluation will determine the usefulness of this gas as a therapeutic in human disease.