Claire Masterson

Effects of Intratracheal Mesenchymal Stromal Cell Therapy during Recovery and Resolution after Ventilator-induced Lung Injury

Background:Mesenchymal stromal cells (MSCs) have been demonstrated to attenuate acute lung injury when delivered by intravenous or intratracheal routes. The authors aimed to determine the efficacy of and mechanism of action of intratracheal MSC therapy and to compare their efficacy in enhancing lung repair after ventilation-induced lung injury with intravenous MSC therapy. Methods:After induction of anesthesia, rats were orotracheally intubated and subjected to ventilation-induced lung injury (respiratory rate 18 min−1, Pinsp 35 cm H2O,) to produce severe lung injury. After recovery, animals were randomized to receive: (1) no therapy, n = 4; (2) intratracheal vehicle (phosphate-buffered saline, 300 µl, n = 8); (3) intratracheal fibroblasts (4 × 106 cells, n = 8); (4) intratracheal MSCs (4 × 106 cells, n = 8); (5) intratracheal conditioned medium (300 µl, n = 8); or (6) intravenous MSCs (4 × 106 cells, n = 4). The extent of recovery after acute lung injury and the inflammatory response was assessed after 48 h. Results:Intratracheal MSC therapy enhanced repair after ventilation-induced lung injury, improving arterial oxygenation (mean ± SD, 146 ± 3.9 vs. 110.8 ± 21.5 mmHg), restoring lung compliance (1.04 ± 0.11 vs. 0.83 ± 0.06 ml·cm H2O−1), reducing total lung water, and decreasing lung inflammation and histologic injury compared with control. Intratracheal MSC therapy attenuated alveolar tumor necrosis factor-&agr; (130 ± 43 vs. 488 ± 211 pg·ml−1) and interleukin-6 concentrations (138 ± 18 vs. 260 ± 82 pg·ml−1). The efficacy of intratracheal MSCs was comparable with intravenous MSC therapy. Intratracheal MSCs seemed to act via a paracine mechanism, with conditioned MSC medium also enhancing lung repair after injury. Conclusions:Intratracheal MSC therapy enhanced recovery after ventilation-induced lung injury via a paracrine mechanism, and was as effective as intravenous MSC therapy.

Human mesenchymal stromal cells decrease the severity of acute lung injury induced by E. coli in the rat

Background Mesenchymal stromal cells (MSCs) demonstrate considerable promise in preclinical acute respiratory distress syndrome models. We wished to determine the efficacy and mechanisms of action of human MSCs (hMSCs) in the setting of acute lung injury induced by prolonged Escherichia coli pneumonia in the rat. Methods Adult male Sprague Dawley rats underwent intratracheal instillation of E. coli bacteria in all experiments. In Series 1, animals were randomised to intravenous administration of: (1) vehicle (phosphate buffered saline (PBS), 300 μL); (2) 1×107 fibroblasts/kg; (3) 1×107 hMSCs/kg or (4) 2×107 hMSCs/kg. Series 2 determined the lowest effective hMSC dose. Series 3 compared the efficacy of intratracheal versus intravenous hMSC administration, while Series 4 examined the efficacy of cryopreserved hMSC. Series 5 examined the efficacy of the hMSC secretome. Parallel in vitro experiments further assessed the potential for hMSCs to secrete LL-37 and modulate macrophage phagocytosis. Results hMSC therapy reduced the severity of rodent E. coli pneumonia, improving survival, decreasing lung injury, reducing lung bacterial load and suppressing inflammation. Doses as low as 5×106 hMSCs/kg were effective. Intratracheal hMSC therapy was as effective as intravenous hMSC. Cryopreserved hMSCs were also effective, while the hMSC secretome was less effective in this model. hMSC therapy enhanced macrophage phagocytic capacity and increased lung and systemic concentrations of the antimicrobial peptide LL37. Conclusions hMSC therapy decreased E. coli induced pneumonia injury and reduced lung bacterial burden, potentially via enhanced macrophage phagocytosis and increased alveolar LL-37 concentrations.

Therapeutic Efficacy of Human Mesenchymal Stromal Cells in the Repair of Established Ventilator-induced Lung Injury in the Rat

Background:Rodent mesenchymal stem/stromal cells (MSCs) enhance repair after ventilator-induced lung injury (VILI). We wished to determine the therapeutic potential of human MSCs (hMSCs) in repairing the rodent lung. Methods:In series 1, anesthetized rats underwent VILI (series 1A, n = 8 to 9 per group) or protective ventilation (series 1B, n = 4 per group). After VILI, they were randomized to intravenous administration of (1) vehicle (phosphate-buffered saline); (2) fibroblasts (1 × 107 cells/kg); or (3) human MSCs (1 × 107 cells/kg) and the effect on restoration of lung function and structure assessed. In series 2, the efficacy of hMSC doses of 1, 2, 5, and 10 million/kg was examined (n = 8 per group). Series 3 compared the efficacy of both intratracheal and intraperitoneal hMSC administration to intravascular delivery (n = 5–10 per group). Series 4 examined the efficacy of delayed hMSC administration (n = 8 per group). Results:Human MSC’s enhanced lung repair, restoring oxygenation (131 ± 19 vs. 103 ± 11 vs. 95 ± 11 mmHg, P = 0.004) compared to vehicle or fibroblast therapy, respectively. hMSCs improved lung compliance, reducing alveolar edema, and restoring lung architecture. hMSCs attenuated lung inflammation, decreasing alveolar cellular infiltration, and decreasing cytokine-induced neutrophil chemoattractant-1 and interleukin-6 while increasing keratinocyte growth factor concentrations. The lowest effective hMSC dose was 2 × 106 hMSC/kg. Intraperitoneal hMSC delivery was less effective than intratracheal or intravenous hMSC. hMSCs enhanced lung repair when administered at later time points after VILI. Conclusions:hMSC therapy demonstrates therapeutic potential in enhancing recovery after VILI.

Permissive hypercapnia: what to remember.

Purpose of review Hypercapnia is a central component of diverse respiratory disorders, while ‘permissive hypercapnia’ is frequently used in ventilatory strategies for patients with severe respiratory failure. This review will present data from recent studies relating to hypercapnia, focusing on issues that are of importance to anesthesiologists caring for the surgical and/or critically ill patient. Recent findings Protective ventilatory strategies involving permissive hypercapnia are widely used in patients with severe respiratory failure, particularly in acute respiratory distress syndrome, status asthmaticus, chronic obstructive pulmonary disease and neonatal respiratory failure. The physiologic effects of hypercapnia are increasingly well understood, and important recent insights have emerged regarding the cellular and molecular mechanisms of action of hypercapnia and acidosis. Acute hypercapnic acidosis is protective in multiple models of nonseptic lung injury. These effects are mediated in part through inhibition of the NF-&kgr;B pathway. Hypercapnia-mediated NF-&kgr;B inhibition may also explain several deleterious effects, including delayed epithelial wound healing and decreased bacterial killing, which has been demonstrated to cause worse lung injury in prolonged untreated pneumonia models. Summary The mechanisms of action of hypercapnia and acidosis continue to be elucidated, and this knowledge is central to determining the safety and therapeutic utility of hypercapnia in protective lung ventilatory strategies.

Inhibition of pulmonary nuclear factor kappa-B decreases the severity of acute Escherichia coli pneumonia but worsens prolonged pneumonia

IntroductionNuclear factor (NF)-κB is central to the pathogenesis of inflammation in acute lung injury, but also to inflammation resolution and repair. We wished to determine whether overexpression of the NF-κB inhibitor IκBα could modulate the severity of acute and prolonged pneumonia-induced lung injury in a series of prospective randomized animal studies.MethodsAdult male Sprague-Dawley rats were randomized to undergo intratracheal instillation of (a) 5 × 109 adenoassociated virus (AAV) vectors encoding the IκBα transgene (5 × 109 AAV-IκBα); (b) 1 × 1010 AAV-IκBα; (c) 5 × 1010 AAV-IκBα; or (d) vehicle alone. After intratracheal inoculation with Escherichia coli, the severity of the lung injury was measured in one series over a 4-hour period (acute pneumonia), and in a second series after 72 hours (prolonged pneumonia). Additional experiments examined the effects of IκBα and null-gene overexpression on E. coli-induced and sham pneumonia.ResultsIn acute pneumonia, IκBα dose-dependently decreased lung injury, improving arterial oxygenation and lung static compliance, reducing alveolar protein leak and histologic injury, and decreasing alveolar IL-1β concentrations. Benefit was maximal at the intermediate (1 × 1010) IκBα vector dose; however, efficacy was diminished at the higher (5 × 1010) IκBα vector dose. In contrast, IκBα worsened prolonged pneumonia-induced lung injury, increased lung bacterial load, decreased lung compliance, and delayed resolution of the acute inflammatory response.ConclusionsInhibition of pulmonary NF-κB activity reduces early pneumonia-induced injury, but worsens injury and bacterial load during prolonged pneumonia.

Stem cell therapy for acute respiratory distress syndrome: a promising future?

Purpose of review Acute respiratory distress syndrome (ARDS) is a devastating disease process with a 40% mortality rate, and for which there is no therapy. Stem cells are an exciting potential therapy for ARDS, and are currently the subject of intensive ongoing research efforts. We review data concerning the therapeutic promise of cell-based therapies for ARDS. Recent findings Recent experimental studies suggest that cell-based therapies, particularly mesenchymal stem/stromal cells (MSCs), endothelial progenitor cells, and embryonic or induced pluripotent stem cells all offer considerable promise for ARDS. Of these cell types, mesenchymal stromal cells offer the greatest potential for allogeneic therapy, given the large body of preclinical data supporting their use, and the advanced state of our understanding of their diverse mechanisms of action. Although other stem cells such as EPCs also have therapeutic potential, greater barriers exist, particularly the requirement for autologous EPC therapy. Other stem cells, such as ESCs and iPSCs, are at an earlier stage in the translational process, but offer the hope of directly replacing injured lung tissue. Ultimately, lung-derived stem cells may offer the greatest hope for lung diseases, given their homeostatic role in replacing and repairing damaged native lung tissues. MSCs are currently in early phase clinical trials, the results of which will be of critical importance to subsequent translational efforts for MSCs in ARDS. A number of translational challenges exist, including minimizing variability in cell batches, developing standard tests for cell potency, and producing large amounts of clinical-grade cells for use in patients. Summary Cell-based therapies, particularly MSCs, offer considerable promise for the treatment of ARDS. Overcoming translational challenges will be important to fully realizing their therapeutic potential for ARDS.

Cryopreserved, Xeno-free Human Umbilical Cord Mesenchymal Stromal Cells Reduce Lung Injury Severity and Bacterial Burden in Rodent escherichia coli –induced Acute Respiratory Distress Syndrome

Objective: Although mesenchymal stem/stromal cells represent a promising therapeutic strategy for acute respiratory distress syndrome, clinical translation faces challenges, including scarcity of bone marrow donors, and reliance on bovine serum during mesenchymal stem/stromal cell proliferation. We wished to compare mesenchymal stem/stromal cells from human umbilical cord, grown in xeno-free conditions, with mesenchymal stem/stromal cells from human bone marrow, in a rat model of Escherichia coli pneumonia. In addition, we wished to determine the potential for umbilical cord-mesenchymal stem/stromal cells to reduce E. coli–induced oxidant injury. Design: Randomized animal study. Setting: University research laboratory. Subjects: Male Sprague-Dawley rats. Interventions: Acute respiratory distress syndrome was induced in rats by intratracheal instillation of E. coli (1.5–2 × 109 CFU/kg). “Series 1” compared the effects of freshly thawed cryopreserved umbilical cord-mesenchymal stem/stromal cells with bone marrow-mesenchymal stem/stromal cells on physiologic indices of lung injury, cellular infiltration, and E. coli colony counts in bronchoalveolar lavage. “Series 2” examined the effects of cryopreserved umbilical cord-mesenchymal stem/stromal cells on survival, as well as measures of injury, inflammation and oxidant stress, including production of reactive oxidative species, reactive oxidative species scavenging by superoxide dismutase-1 and superoxide dismutase-2. Measurements and Main Results: In “Series 1,” animals subjected to E. coli pneumonia who received umbilical cord-mesenchymal stem/stromal cells had improvements in oxygenation, respiratory static compliance, and wet-to-dry ratios comparable to bone marrow-mesenchymal stem/stromal cell treatment. E. coli colony-forming units in bronchoalveolar lavage were reduced in both cell therapy groups, despite a reduction in bronchoalveolar lavage neutrophils. In series 2, umbilical cord-mesenchymal stem/stromal cells enhanced animal survival and decreased alveolar protein and proinflammatory cytokine concentrations, whereas increasing interleukin-10 concentrations. Umbilical cord-mesenchymal stem/stromal cell therapy decreased nicotinamide adenine dinucleotide phosphate-oxidase 2 and inducible nitric oxide synthase and enhanced lung concentrations of superoxide dismutase-2, thereby reducing lung tissue reactive oxidative species concentrations. Conclusions: Our results demonstrate that freshly thawed cryopreserved xeno-free human umbilical cord-mesenchymal stem/stromal cells reduce the severity of rodent E. coli–induced acute respiratory distress syndrome. Umbilical cord-mesenchymal stem/stromal cells, therefore, represent an attractive option for future clinical trials in acute respiratory distress syndrome.

Hypercapnia: clinical relevance and mechanisms of action.

Purpose of reviewMultiple clinical and laboratory studies have been conducted to illustrate the effects of hypercapnia in a range of injuries, and to understand the mechanisms underlying these effects. The aim of this review is to highlight and interpret information obtained from these recent reports and discuss how they may inform the clinical context. Recent findingsIn the last decade, several important articles have addressed key elements of how carbon dioxide interacts in critical illness states. Among them the most important insights relate to how hypercapnia affects critical illness and include the effects and mechanisms of carbon dioxide in pulmonary hypertension, infection, inflammation, diaphragm dysfunction, and cerebral ischemia. In addition, we discuss molecular insights that apply to multiple aspects of critical illness. SummaryExperiments involving hypercapnia have covered a wide range of illness models with varying degrees of success. It is becoming evident that deliberate hypercapnia in the clinical setting should seldom be used, except wherever necessitated to avoid ventilator-associated lung injury. A more complete understanding of the molecular mechanisms must be established.

Effects and Mechanisms by Which Hypercapnic Acidosis Inhibits Sepsis-Induced Canonical Nuclear Factor-κB Signaling in the Lung.

Objective:Diverse effects of hypercapnic acidosis are mediated via inhibition of nuclear factor-&kgr;B, a pivotal transcription factor, in the setting of injury, inflammation, and repair, but the underlying mechanisms of action of hypercapnic acidosis on this pathway is unclear. We aim to examine the effect of hypercapnic acidosis on the nuclear factor-&kgr;B pathway in the setting of Escherichia coli–induced lung injury and characterize the underlying mechanisms in subsequent in vitro studies. Design:In vivo animal study and subsequent in vitro studies. Setting:University Research Laboratory. Subjects:Adult male Sprague-Dawley rats and pulmonary epithelial cells. Interventions:Following pulmonary I&kgr;B&agr;-SuperRepressor transgene overexpression or sham and intratracheal E. coli inoculation, rats underwent 4 hours of mechanical ventilation under normocapnia or hypercapnic acidosis, and nuclear factor-&kgr;B activation, animal survival, lung injury, and cytokine profile were assessed. Subsequent in vitro studies examined the effect of hypercapnic acidosis on specific nuclear factor-&kgr;B canonical pathway kinases via overexpression of these components and in vitro kinase activity assays. The effect of hypercapnic acidosis on the p50/p65 nuclear factor-&kgr;B heterodimer was then assessed. Measurements and Main Results:Hypercapnic acidosis and I&kgr;B&agr;-SuperRepressor transgene overexpression reduced E. coli–induced lung inflammation and injury, decreased nuclear factor-&kgr;B activity, and increased animal survival. Hypercapnic acidosis inhibited canonical nuclear factor-&kgr;B signaling via reduced phosphorylative activation, reducing I&kgr;B kinase-&bgr; activation and intrinsic activity, thereby decreasing I&kgr;B&agr; degradation, and subsequent nuclear factor-&kgr;B translocation. Hypercapnic acidosis also directly reduced DNA binding of the nuclear factor-&kgr;B p65 subunit, although this effect was less marked. Conclusions:Hypercapnic acidosis reduced E. coli inflammation and lung injury in vivo and reduced nuclear factor-&kgr;B activation predominantly by inhibiting the activation and intrinsic activity of I&kgr;B kinase-&bgr;.

Cell therapy in acute respiratory distress syndrome

Acute respiratory distress syndrome (ARDS) is driven by a severe pro-inflammatory response resulting in lung damage, impaired gas exchange and severe respiratory failure. There is no specific treatment that effectively improves outcome in ARDS. However, in recent years, cell therapy has shown great promise in preclinical ARDS studies. A wide range of cells have been identified as potential candidates for use, among these are mesenchymal stromal cells (MSCs), which are adult multi-lineage cells that can modulate the immune response and enhance repair of damaged tissue. The therapeutic potential of MSC therapy for sepsis and ARDS has been demonstrated in multiple in vivo models. The therapeutic effect of these cells seems to be due to two different mechanisms; direct cellular interaction, and paracrine release of different soluble products such as extracellular vesicles (EVs)/exosomes. Different approaches have also been studied to enhance the therapeutic effect of these cells, such as the over-expression of anti-inflammatory or pro-reparative molecules. Several clinical trials (phase I and II) have already shown safety of MSCs in ARDS and other diseases. However, several translational issues still need to be addressed, such as the large-scale production of cells, and their potentiality and variability, before the therapeutic potential of stem cells therapies can be realized.