Intracellular storage of surfactant and proinflammatory cytokines in co-cultured alveolar epithelium and macrophages in response to increasing CO2 and cyclic cell stretch

Reduced Surfactant Contributes to Increased Lung Stiffness Induced by Rapid Inspiratory Flow

INTRODUCTION

The mechanism of fast inspiratory flow rate (V_I') induced lung injury is unclear. As fast V_I' increases hysteresis, a measure of surface tension at the air-liquid interface, surfactant release or function may be important. This experimental study examines the contribution of impaired surfactant release or function to dynamic-VILI.

METHODS

Isolated perfused lungs from male Sprague Dawley rats were randomly allocated to four groups: a long or short inspiratory time (Ti = 0.5 s; slow V_I' or Ti = 0.1 s; fast V_I') at PEEP of 2 or 10 cmH₂O. Tidal volume was constant (7 ml/kg), with f = 60 breath/min. Forced impedance mechanics (tissue elastance (Htis), tissue resistance (Gtis) and airway resistance (Raw) were measured at 30, 60 and 90 min following which the lung was lavaged for surfactant phospholipids (PL) and disaturated PL (DSP).

RESULTS

Fast V_I' resulted in a stiffer lung. Concurrently, PL and DSP were decreased in both tubular myelin rich and poor fractions. Phospholipid decreases were similar with PEEP. In a subsequent cohort, laser confocal microscopy-based assessment demonstrated increased cellular injury with increased V_I' at both 30 and 90 min ventilation.

CONCLUSION

Rapid V_I' may contribute to ventilator induced lung injury (VILI) through reduced surfactant release and/or more rapid reuptake despite unchanged tidal stretch.

Mechanosensing and Mechanoregulation of Endothelial Cell Functions

Vascular endothelial cells (ECs) form a semiselective barrier for macromolecules and cell elements regulated by dynamic interactions between cytoskeletal elements and cell adhesion complexes. ECs also participate in many other vital processes including innate immune reactions, vascular repair, secretion, and metabolism of bioactive molecules. Moreover, vascular ECs represent a unique cell type exposed to continuous, time-dependent mechanical forces: different patterns of shear stress imposed by blood flow in macrovasculature and by rolling blood cells in the microvasculature; circumferential cyclic stretch experienced by the arterial vascular bed caused by heart propulsions; mechanical stretch of lung microvascular endothelium at different magnitudes due to spontaneous respiration or mechanical ventilation in critically ill patients. Accumulating evidence suggests that vascular ECs contain mechanosensory complexes, which rapidly react to changes in mechanical loading, process the signal, and develop context-specific adaptive responses to rebalance the cell homeostatic state. The significance of the interactions between specific mechanical forces in the EC microenvironment together with circulating bioactive molecules in the progression and resolution of vascular pathologies including vascular injury, atherosclerosis, pulmonary edema, and acute respiratory distress syndrome has been only recently recognized. This review will summarize the current understanding of EC mechanosensory mechanisms, modulation of EC responses to humoral factors by surrounding mechanical forces (particularly the cyclic stretch), and discuss recent findings of magnitude-specific regulation of EC functions by transcriptional, posttranscriptional and epigenetic mechanisms using -omics approaches. We also discuss ongoing challenges and future opportunities in developing new therapies targeting dysregulated mechanosensing mechanisms to treat vascular diseases. © 2019 American Physiological Society. Compr Physiol 9:873-904, 2019.

Influence of static forces on the expression of selected parameters of inflammation in periodontal ligament cells and alveolar bone cells in a co-culture in vitro model

OBJECTIVE

Aim of this study was to investigate the impact of human PDL-derived fibroblasts (HPDF) and human alveolar bone-derived osteoblasts (HABO) co-culture on the expression of cytokines involved in tissue remodeling using an in vitro compressive force (CF) model.

MATERIALS AND METHODS

Static compressive force (CF) of 47.4 g/cm² was applied on mono- and co-cultured HPDFs and HABOs for 1, 2, or 4 h at 30 °C. TNFA, PTGS2, and IL6 gene expressions were determined by quantitative real-time polymerase chain reaction. TNF, PGE₂, and IL6 concentrations were measured using enzyme-linked immunosorbent assay.

RESULTS

In mono-culture, TNFA, PTGS2, and IL6 gene expressions were upregulated under CF as compared to controls for each time period in both cell types. PGE₂ increased at 1 and 2 h in both cell types, and IL6 increased only at 2 and 4 h in HPDFs. Co-culture alleviated the force-induced increase of the expression of TNFA, PTGS2, IL6, PGE2, and IL6 in HPDFs at any time point. In HABOs, co-cultivation decreased the expression of PGE₂ after 1 h and 4 h, and that of IL6 after 1 h compared to mono-culture.

CONCLUSIONS

CF application on co-cultures of HPDFs and HABOs causes significant changes of TNFA, PTGS2, and IL6 gene expressions and PGE₂ and IL6 production in comparison to mono-culture indicating intercellular communication.

CLINICAL RELEVANCE

Mechanical stimulation of HPDFs and HABOs in co-culture induces a different gene expression pattern than stimulation of individual cell types alone. Co-culture might therefore be a relevant method to elucidate periodontal regeneration during orthodontic therapy.

Pediatric acute respiratory distress syndrome - current views

Acute respiratory distress syndrome (ARDS) mainly involves acute respiratory failure. In addition to this affected patients feel progressive arterial hypoxemia, dyspnea, and a marked increase in the work of breathing. The only clinical solution for the above pathological state is ventilation. Mechanical ventilation is necessary to support life in ARDs but it itself worsen lung injury and the term is known clinically as ‘ventilation induced lung injury’ (VILI). At the cellular level, respiratory epithelial cells are subjected to cyclic stretch, i.e. repeated cycles of positive and negative strain, during normal tidal ventilation. In aerated areas of diseased lungs, or even normal lungs subjected to injurious positive pressure mechanical ventilation, the cells are at risk of being over distended, and worsening injury by disrupting the alveolar epithelial barrier. Further, hypercapnic acidosis (HCA) in itself confers protection from stretch injury, potentially via a mechanisms involving inhibition of nuclear factor κB (NF-κB), a transcription factor central to inflammation, injury and repair. Mesenchymal stem cells are the latest in the field and are being investigated as a possible therapy for ARDS.

Effects of hypercapnia in acute respiratory distress syndrome

In patients with acute respiratory distress syndrome (ARDS) hypercapnia is a marker of poor prognosis, however there is controversial information regarding the effect of hypercapnia on outcomes. Recently two studies in a large population of mechanical ventilation patients showed higher mortality associated independently to hypercapnia. Key roles responsible for the poor clinical outcomes observed in critically ill patients exposed to hypercapnia are not well known, two possible mechanisms involved are the effect of CO2 on the muscle and the alveolar epithelium. Hypercapnia frequently coexists with muscle atrophy and dysfunction, moreover patients surviving ARDS present reduced muscle strength and decreased physical quality of life. One of the possible mechanisms responsible for these abnormalities could be the effects of hypercapnia during the course of ARDS. More over controversy persists about the hypercapnia role in the alveolar space, in the last years there is abundant experimental information on its deleterious effects on essential functions of the alveolar epithelium.

Integrated Stress Response Mediates Epithelial Injury in Mechanical Ventilation

Ventilator-induced lung injury (VILI) is a severe complication of mechanical ventilation that can lead to acute respiratory distress syndrome. VILI is characterized by damage to the epithelial barrier with subsequent pulmonary edema and profound hypoxia. Available lung-protective ventilator strategies offer only a modest benefit in preventing VILI because they cannot impede alveolar overdistension and concomitant epithelial barrier dysfunction in the inflamed lung regions. There are currently no effective biochemical therapies to mitigate injury to the alveolar epithelium. We hypothesize that alveolar stretch activates the integrated stress response (ISR) pathway and that the chemical inhibition of this pathway mitigates alveolar barrier disruption during stretch and mechanical ventilation. Using our established rat primary type I-like alveolar epithelial cell monolayer stretch model and in vivo rat mechanical ventilation that mimics the alveolar overdistension seen in acute respiratory distress syndrome, we studied epithelial responses to mechanical stress. Our studies revealed that the ISR signaling pathway is a key modulator of epithelial permeability. We show that prolonged epithelial stretch and injurious mechanical ventilation activate the ISR, leading to increased alveolar permeability, cell death, and proinflammatory signaling. Chemical inhibition of protein kinase RNA-like endoplasmic reticulum kinase, an upstream regulator of the pathway, resulted in decreased injury signaling and improved barrier function after prolonged cyclic stretch and injurious mechanical ventilation. Our results provide new evidence that therapeutic targeting of the ISR can mitigate VILI.

Induced hypernatraemia is protective in acute lung injury

BACKGROUND

Sucrose induced hyperosmolarity is lung protective but the safety of administering hyperosmolar sucrose in patients is unknown. Hypertonic saline is commonly used to produce hyperosmolarity aimed at reducing intra cranial pressure in patients with intracranial pathology. Therefore we studied the protective effects of 20% saline in a lipopolysaccharide lung injury rat model. 20% saline was also compared with other commonly used fluids.

METHODS

Following lipopolysaccharide-induced acute lung injury, male Sprague Dawley rats received either 20% hypertonic saline, 0.9% saline, 4% albumin, 20% albumin, 5% glucose or 20% albumin with 5% glucose, i.v. During 2h of non-injurious mechanical ventilation parameters of acute lung injury were assessed.

RESULTS

Hypertonic saline resulted in hypernatraemia (160 (1) mmol/l, mean (SD)) maintained through 2h of ventilation, and in amelioration of lung oedema, myeloperoxidase, bronchoalveolar cell infiltrate, total soluble protein and inflammatory cytokines, and lung histological injury score, compared with positive control and all other fluids (p ≤ 0.001). Lung physiology was maintained (conserved PaO2, elastance), associated with preservation of alveolar surfactant (p ≤ 0.0001).

CONCLUSION

Independent of fluid or sodium load, induced hypernatraemia is lung protective in lipopolysaccharide-induced acute lung injury.

Congenital ureteropelvic junction obstruction: human disease and animal models

Ureteropelvic junction (UPJ) obstruction is the most frequently observed cause of obstructive nephropathy in children. Neonatal and foetal animal models have been developed that mimic closely what is observed in human disease. The purpose of this review is to discuss how obstructive nephropathy alters kidney histology and function and describe the molecular mechanisms involved in the progression of the lesions, including inflammation, proliferation/apoptosis, renin-angiotensin system activation and fibrosis, based on both human and animal data. Also we propose that during obstructive nephropathy, hydrodynamic modifications are early inducers of the tubular lesions, which are potentially at the origin of the pathology. Finally, an important observation in animal models is that relief of obstruction during kidney development has important effects on renal function later in adult life. A major short-coming is the absence of data on the impact of UPJ obstruction on long-term adult renal function to elucidate whether these animal data are also valid in humans.

[Permissive and non-permissive hypercapnia: mechanisms of action and consequences of high carbon dioxide levels]

Acute lung injury is a disease with high incidence of mortality and its treatment is still controversial. Increasing the levels of CO2 beyond the physiological range has been proposed as a potential protective strategy for patients on mechanical ventilation, as it could moderate the inflammatory response. In this article we review the published evidence on the role of CO2 during acute lung injury. We conclude that although there are reports suggesting benefits from hypercapnia, more recent evidence suggests that hypercapnia could be deleterious, contributing to worsening of the lung injury.