Inducible nitric oxide synthase inhibition reverses pulmonary arterial dysfunction in lung transplantation

Inhibition of the cGAS-STING Pathway Attenuates Lung Ischemia/Reperfusion Injury via Regulating Endoplasmic Reticulum Stress in Alveolar Epithelial Type II Cells of Rats

Purpose

Endoplasmic reticulum stress (ERS) plays an important role in the pathogenesis of lung ischemia/reperfusion (I/R) injury. Cyclic GMP-AMP synthase (cGAS) is a cytosol dsDNA sensor, coupling with downstream stimulator of interferon genes (STING) located in the ER, which involves innate immune responses. The aim of our present study was to investigate the effects of cGAS on lung I/R injury via regulating ERS.

Methods

We used Sprague-Dawley rats to make the lung I/R model by performing left hilum occlusion-reperfusion surgery. cGAS-specific inhibitor RU.521, STING agonist SR-717, and 4-phenylbutyric acid (4-PBA), the ERS inhibitor, were intraperitoneally administered in rats. Double immunofluorescent staining was applied to detect the colocalization of cGAS or BiP, an ERS protein, with alveolar epithelial type II cells (AECIIs) marker. We used transmission electron microscopy to examine the ultrastructure of ER and mitochondria. Apoptosis and oxidative stress in the lungs were assessed, respectively. The profiles of pulmonary edema and lung tissue injury were evaluated. And the pulmonary ventilation function was measured using a spirometer system.

Results

In lung I/R rats, the cGAS-STING pathway was upregulated, which implied they were activated. After cGAS-STING pathway was inhibited or activated in lung I/R rats, the ERS was alleviated after cGAS was inhibited, while when STING was activated after lung I/R, ERS was aggravated in the AECIIs, these results suggested that cGAS-STING pathway might trigger ERS responses. Furthermore, activation of cGAS-STING pathway induced increased apoptosis, inflammation, and oxidative stress via regulating ERS and therefore resulted in pulmonary edema and pathological injury in the lungs of I/R rats. Inhibition of cGAS-STING pathway attenuated ERS, therefore attenuated lung injury and promoted pulmonary ventilation function in I/R rats.

Conclusion

Inhibition of the cGAS-STING pathway attenuates lung ischemia/reperfusion injury via alleviating endoplasmic reticulum stress in alveolar epithelial type II cells of rats.

Ischemia-Reperfusion Injury in Lung Transplantation

Lung transplantation has been established worldwide as the last treatment for end-stage respiratory failure. However, ischemia–reperfusion injury (IRI) inevitably occurs after lung transplantation. The most severe form of IRI leads to primary graft failure, which is an important cause of morbidity and mortality after lung transplantation. IRI may also induce rejection, which is the main cause of mortality in recipients. Despite advances in donor management and graft preservation, most donor grafts are still unsuitable for transplantation. Although the pulmonary endothelium is the primary target site of IRI, the pathophysiology of lung IRI remains incompletely understood. It is essential to understand the mechanism of pulmonary IRI to improve the outcomes of lung transplantation. Therefore, we reviewed the state-of-the-art in the management of pulmonary IRI after lung transplantation. Recently, the ex vivo lung perfusion (EVLP) system has been clinically introduced worldwide. Various promising therapeutic strategies for the protection of the endothelium against IRI, including EVLP, inhalation therapy with therapeutic gases and substances, fibrinolytic treatment, and mesenchymal stromal cell therapy, are awaiting clinical application. We herein review the latest advances in the field of pulmonary IRI in lung transplantation.

Organ Care System Lung resulted in lower apoptosis and iNOS expression in donor lungs

Ischemia-reperfusion (IR) injury after lung transplantation is still today an important complication in up to 25% of patients. The Organ Care System (OCS) Lung, an advanced normothermic ex vivo lung perfusion system, was found to be effective in reducing primary graft dysfunction compared to standard organ care (SOC) but studies on tissue/molecular pathways that could explain these more effective clinical results are lacking. This observational longitudinal study aimed to investigate IR injury in 68 tissue specimens collected before and after reperfusion from 17 OCS and 17 SOC preserved donor lungs. Several tissue analyses including apoptosis evaluation and inducible nitric oxide synthase (iNOS) expression (by immunohistochemistry and real-time reverse transcriptase-polymerase chain reaction) were performed. Lower iNOS expression and apoptotic index were distinctive of OCS preserved tissues at pre- and post-reperfusion times, independently from potential confounding factors. Moreover, OCS recipients had lower acute cellular rejection at the first 6-month follow-up. In conclusion, IR injury, in terms of apoptosis and iNOS expression, was less frequent in OCS- than in SOC-preserved lungs, which could eventually explain a better clinical outcome. Further studies are needed to validate our data and determine the role of iNOS expression as a predictive biomarker of the complex IR injury mechanism.

Gas Partial Pressure in Cultured Cells: Patho-Physiological Importance and Methodological Approaches

Gas partial pressures within the cell microenvironment are one of the key modulators of cell pathophysiology. Indeed, respiratory gases (O2 and CO2) are usually altered in respiratory diseases and gasotransmitters (CO, NO, H2S) have been proposed as potential therapeutic agents. Investigating the pathophysiology of respiratory diseases in vitro mandates that cultured cells are subjected to gas partial pressures similar to those experienced by each cell type in its native microenvironment. For instance, O2 partial pressures range from ∼13% in the arterial endothelium to values as low as 2-5% in cells of other healthy tissues and to less than 1% in solid tumor cells, clearly much lower values than those used in conventional cell culture research settings (∼19%). Moreover, actual cell O2 partial pressure in vivo changes with time, at considerably different timescales as illustrated by tumors, sleep apnea, or mechanical ventilation. Unfortunately, the conventional approach to modify gas concentrations at the above culture medium precludes the tight and exact control of intra-cellular gas levels to realistically mimic the natural cell microenvironment. Interestingly, well-controlled cellular application of gas partial pressures is currently possible through commercially available silicone-like material (PDMS) membranes, which are biocompatible and have a high permeability to gases. Cells are seeded on one side of the membrane and tailored gas concentrations are circulated on the other side of the membrane. Using thin membranes (50-100 μm) the value of gas concentration is instantaneously (<0.5 s) transmitted to the cell microenvironment. As PDMS is transparent, cells can be concurrently observed by conventional or advanced microscopy. This procedure can be implemented in specific-purpose microfluidic devices and in settings that do not require expensive or complex technologies, thus making the procedure readily implementable in any cell biology laboratory. This review describes the gas composition requirements for a cell culture in respiratory research, the limitations of current experimental settings, and also suggests new approaches to better control gas partial pressures in a cell culture.

Lung Ischaemia-Reperfusion Injury: The Role of Reactive Oxygen Species

Lung ischaemia-reperfusion injury (LIRI) occurs in many lung diseases and during surgical procedures such as lung transplantation. The re-establishment of blood flow and oxygen delivery into the previously ischaemic lung exacerbates the ischaemic injury and leads to increased microvascular permeability and pulmonary vascular resistance as well as to vigorous activation of the immune response. These events initiate the irreversible damage of the lung with subsequent oedema formation that can result in systemic hypoxaemia and multi-organ failure. Alterations in the production of reactive oxygen species (ROS) and reactive nitrogen species (RNS) have been suggested as crucial mediators of such responses during ischaemia-reperfusion in the lung. Among numerous potential sources of ROS/RNS within cells, nicotinamide adenine dinucleotide phosphate (NADPH) oxidases, xanthine oxidases, nitric oxide synthases and mitochondria have been investigated during LIRI. Against this background, we aim to review here the extensive literature about the ROS-mediated cellular signalling during LIRI, as well as the effectiveness of antioxidants as treatment option for LIRI.

Oxidative and nitrosative stress during pulmonary ischemia-reperfusion injury: from the lab to the OR

Oxidative and nitrosative stress are an umbrella term for pathophysiological processes that involve free radical generation during inflammation. In this review, the involvement of reactive oxygen and nitrogen species is evaluated during lung ischemia-reperfusion injury (LIRI) from a surgical point of view. The main biochemical and cellular mechanisms behind free radical generation are discussed, together with surgical procedures that may cause reperfusion injury. Finally, different therapeutic strategies are further explored. A literature search was performed, searching for "lung ischemia reperfusion injury", "reperfusion injury", "large animal model" and different search terms for each section: "surgery", "treatment", "cellular mechanism", or "enzyme". Although reperfusion injury is not an uncommon entity and there is a lot of evidence concerning myocardial ischemia-reperfusion injury, in the lung this phenomenon is less extensively described and studies in large animals are not easy to come by. With increasing number of patients on waiting lists for lung transplant, awareness for this entity should all but rise.

Electrospun poly-ε-caprolactone scaffold modified with catalytic nitric oxide generation and heparin for small-diameter vascular graft

Vascular grafts are significantly needed in peripheral vascular surgery; however, small diameter grafts are not always available, and synthetic grafts perform poorly because of acute thrombosis and neointimal proliferation after implantation.

Expression of arginase I and inducible nitric oxide synthase in the peripheral blood and lymph nodes of HIV‑positive patients

Arginase I (Arg I) and inducible nitric oxide synthase (iNOS) are important in regulating immune functions through their metabolites. Previous studies have revealed that the expression of Arg I is increased and the expression of iNOS is reduced in the serum and peripheral blood mononuclear cells of human immunodeficiency virus (HIV)-infected patients. As one of the most important immune organs and HIV replication sites, whether similar changes are present in the lymph nodes following HIV infection remains to be elucidated. To investigate this, the present study collected lymph node and blood specimens from 52 HIV-infected patients to measure the expression levels of Arg I and iNOS by immunohistochemistry and fluoresence-based flow cytometry. Compared with control subjects without HIV infection, the patients with HIV had significantly higher expression levels of Arg I in the lymph nodes and higher frequencies of Arg I⁺ CD4⁺ T cells and CD8⁺ T cells in the blood and lymph nodes, and these results were contrary the those of iNOS in the corresponding compartments. The expression levels of Arg I in the lymph nodes and blood were negatively associated with peripheral CD4⁺ T cell count and positively associated with viral load. However, the expression levels of iNOS in the lymph nodes and blood were positively associated with peripheral CD4⁺ T cell count and negatively associated with viral load. These results showed that alterations in the expression levels of Arg I and iNOS in the peripheral T cells and peripheral nodes of HIV infected patients are associated with disease progression in these patients. These results indicate a potential to therapeutic strategy for delaying disease progression through regulating and manipulating the expression levels of Arg I and iNOS in patients infected with HIV.