Alveolar fluid clearance is faster in women with acute lung injury compared to men

Ventilator-Induced Lung Injury as a Dynamic Balance Between Epithelial Cell Damage and Recovery

Acute respiratory distress syndrome (ARDS) has a high mortality rate that is due in part to ventilator-induced lung injury (VILI). Nevertheless, the majority of patients eventually recover, which means that their innate reparative capacities eventually prevail. Since there are currently no medical therapies for ARDS, minimizing its mortality thus amounts to achieving an optimal balance between spontaneous tissue repair versus the generation of VILI. In order to understand this balance better, we developed a mathematical model of the onset and recovery of VILI that incorporates two hypotheses: (1) a novel multi-hit hypothesis of epithelial barrier failure, and (2) a previously articulated rich-get-richer hypothesis of the interaction between atelectrauma and volutrauma. Together, these concepts explain why VILI appears in a normal lung only after an initial latent period of injurious mechanical ventilation. In addition, they provide a mechanistic explanation for the observed synergy between atelectrauma and volutrauma. The model recapitulates the key features of previously published in vitro measurements of barrier function in an epithelial monolayer and in vivo measurements of lung function in mice subjected to injurious mechanical ventilation. This provides a framework for understanding the dynamic balance between factors responsible for the generation of and recovery from VILI.

Standardization of methods for sampling the distal airspace in mechanically ventilated patients using heat moisture exchange filter fluid

Noninvasive sampling of the distal airspace in patients with acute respiratory distress syndrome (ARDS) has long eluded clinical and translational researchers. We recently reported that fluid collected from heat moisture exchange (HME) filters closely mirrors fluid directly aspirated from the distal airspace. In the current study, we sought to determine fluid yield from different HME types, optimal HME circuit dwell time, and reliability of HME fluid in reflecting the distal airspace. We studied fluid yield from four different filter types by loading increasing volumes of saline and measuring volumes of fluid recovered. We collected filters after 1, 2, and 4 h of dwell time for measurement of fluid volume and total protein from 13 subjects. After identifying 4 h as the optimal dwell time, we measured total protein and IgM in HME fluid from 42 subjects with ARDS and nine with hydrostatic pulmonary edema (HYDRO). We found that the fluid yield varies greatly by filter type. With timed sample collection, fluid recovery increased with increasing circuit dwell time with a median volume of 2.0 mL [interquartile range (IQR) 1.2-2.7] after 4 h. Total protein was higher in the 42 subjects with ARDS compared with nine with HYDRO [median 708 µg/mL (IQR 244-2017) vs. 364 µg/mL (IQR 136-578), P = 0.047], confirming that total protein concentration in HME is higher in ARDS compared with hydrostatic edema. These studies establish a standardized HME fluid collection protocol and confirm that HME fluid analysis is a novel noninvasive tool for the study of the distal airspace in ARDS.

Demographics, management and outcome of females and males with acute respiratory distress syndrome in the LUNG SAFE prospective cohort study

Rationale

We wished to determine the influence of sex on the management and outcomes in acute respiratory distress syndrome (ARDS) patients in the Large Observational Study to Understand the Global Impact of Severe Acute Respiratory Failure (LUNG SAFE).

Methods

We assessed the effect of sex on mortality, intensive care unit and hospital length of stay, and duration of invasive mechanical ventilation (IMV) in patients with ARDS who underwent IMV, adjusting for plausible clinical and geographic confounders.

Findings

Of 2377 patients with ARDS, 905 (38%) were female and 1472 (62%) were male. There were no sex differences in clinician recognition of ARDS or critical illness severity profile. Females received higher tidal volumes (8.2±2.1 versus 7.2±1.6 mL·kg−1; p<0.0001) and higher plateau and driving pressures compared with males. Lower tidal volume ventilation was received by 50% of females compared with 74% of males (p<0.0001). In shorter patients (height ≤1.69 m), females were significantly less likely to receive lower tidal volumes. Surviving females had a shorter duration of IMV and reduced length of stay compared with males. Overall hospital mortality was similar in females (40.2%) versus males (40.2%). However, female sex was associated with higher mortality in patients with severe confirmed ARDS (OR for sex (male versus female) 0.35, 95% CI 0.14–0.83).

Conclusions

Shorter females with ARDS are less likely to receive lower tidal volume ventilation, while females with severe confirmed ARDS have a higher mortality risk. These data highlight the need for better ventilatory management in females to improve their outcomes from ARDS.

Increased TMEM16A Involved in Alveolar Fluid Clearance After Lipopolysaccharide Stimulation

Transmembrane protein 16A (TMEM16A) regulates a wide variety of cellular activities, including epithelial fluid secretion and maintenance of ion homeostasis. Lipopolysaccharide (LPS), an outer membrane component of Gram-negative bacteria, is one of the major causes of acute lung injury (ALI). In this study, we investigated the effects of LPS on the expression of TMEM16A in LA795 cells and mouse lung tissue and the potential mechanism.

RESULT

We detected the expression of TMEM16A in LA795 cells and mouse lung tissue by RT-PCR, Western blot, and RNA interference techniques. TMEM16A expression was significantly increased by LPS stimulation in LA795 cells and in mouse lung tissue. Moreover, the LPS-induced TMEM16A expression enhancement in lung tissue was much more prominent in the alveolar epithelial region than in bigger airway epithelial cells. The typical TMEM16A current was recorded, and LPS treatment significantly enhances the current amplitude in LA795 cells. TMEM16A shRNA or TMEM16A inhibitor (T16Ainh-A01) did not affect alveolar fluid clearance (AFC), while co-application of T16Ainh-A01 induced a stronger AFC inhibition than LPS alone. LPS notably and synchronously enhanced Akt phosphorylation (p-Akt) and TMEM16A expression in a time-dependent manner in LA795 cells. Taken together, our results suggest that TMEM16A maybe plays an important role in pathological conditions of LPS-induced ALI as a protective protein.

Incidence and Outcomes of Acute Respiratory Distress Syndrome: A Nationwide Registry-Based Study in Taiwan, 1997 to 2011

Most epidemiological studies of acute respiratory distress syndrome (ARDS) have been conducted in western countries, and studies in Asia are limited. The aim of our study was to evaluate the incidence, in-hospital mortality, and 1-year mortality of ARDS in Taiwan.We conducted a nationwide inpatient cohort study based on the Taiwan National Health Insurance Research Database between 1997 and 2011. A total of 40,876 ARDS patients (68% male; mean age 66 years) were identified by International Classification of Diseases, 9th edition coding and further analyzed for clinical characteristics, medical costs, and mortality.The overall crude incidence of ARDS was 15.74 per 100,000 person-years, and increased from 2.53 to 19.26 per 100,000 person-years during the study period. The age-adjusted incidence of ARDS was 15.19 per 100,000 person-years. The overall in-hospital mortality was 57.8%. In-hospital mortality decreased from 59.7% in 1997 to 47.5% in 2011 (P < 0.001). The in-hospital mortality rate was lowest (33.5%) in the youngest patients (age 18-29 years) and highest (68.2%) in the oldest patients (>80 years, P < 0.001). The overall 1-year mortality rate was 72.1%, and decreased from 75.8% to 54.7% during the study period. Patients who died during hospitalization were older (69 ± 17 versus 62 ± 19, P < 0.001) and predominantly male (69.8% versus 65.3%, P < 0.001). In addition, patients who died during hospitalization had significantly higher medical costs (6421 versus 5825 US Dollars, P < 0.001) and shorter lengths of stay (13 versus 19 days, P < 0.001) than patients who survived.We provide the first large-scale epidemiological analysis of ARDS incidence and outcomes in Asia. Although the overall incidence was lower than has been reported in a prospective US study, this may reflect underdiagnosis by International Classification of Diseases, 9th edition code and identification of only patients with more severe ARDS in this analysis. Overall, there has been a decreasing trend in in-hospital and 1-year mortality rates in recent years, likely because of the implementation of lung-protective ventilation.

Male Sex is Associated with a Reduced Alveolar Epithelial Sodium Transport

Respiratory distress syndrome (RDS) is the most frequent pulmonary complication in preterm infants. RDS incidence differs between genders, which has been called the male disadvantage. Besides maturation of the surfactant system, Na⁺ transport driven alveolar fluid clearance is crucial for the prevention of RDS. Na⁺ transport is mediated by the epithelial Na⁺ channel (ENaC) and the Na,K-ATPase, therefore potential differences in their expression or activity possibly contribute to the gender imbalance observed in RDS. Fetal distal lung epithelial (FDLE) cells of rat fetuses were separated by sex and analyzed regarding expression and activity of the Na⁺ transporters. Ussing chamber experiments showed a higher baseline short-circuit current (I_SC) and amiloride-sensitive ΔI_SC in FDLE cells of female origin. In addition, maximal amiloride-sensitive ΔI_SC and maximal ouabain-sensitive ΔI_SC of female cells were higher when measured in the presence of a permeabilized basolateral or apical membrane, respectively. The number of FDLE cells per fetus recoverable during cell isolation was also significantly higher in females. In addition, lung wet-to-dry weight ratio was lower in fetal and newborn female pups. Female derived FDLE cells had higher mRNA levels of the ENaC- and Na,K-ATPase subunits. Furthermore, estrogen (ER) and progesterone receptor (PR) mRNA levels were higher in female cells, which might render female cells more responsive, while concentrations of placenta-derived sex steroids do not differ between both genders during fetal life. Inhibition of ER-β abolished the sex differences in Na⁺ transport and female cells were more responsive to estradiol stimulation. In conclusion, a higher alveolar Na⁺ transport, possibly attributable to a higher expression of hormone receptors in female FDLE cells, provides an explanation for the well known sex-related difference in RDS occurrence and outcome.

Regulation of epithelial sodium channel expression by oestradiol and progestogen in alveolar epithelial cells

Oestrogen (E) and progestogen (P) exert regulatory effects on the epithelial Na(+) channel (ENaC) in the kidneys and the colon. However, the effects of E and P on the ENaC and on alveolar fluid clearance (AFC) remain unclear, and the mechanisms of action of these hormones are unknown. In this study, we showed that E and/or P administration increased AFC by more than 25% and increased the expression of the α and γ subunits of ENaC by approximately 35% in rats subjected to oleic acid-induced acute lung injury (ALI). A similar effect was observed in the dexamethasone-treated group. Furthermore, E and/or P treatment inhibited 11β-hydroxysteroid dehydrogenase (HSD) type 2 (11β-HSD2) activity, increased corticosterone expression and decreased the serum adrenocorticotrophic hormone (ACTH) levels. These effects were similar to those observed following treatment with carbenoxolone (CBX), a nonspecific HSD inhibitor. Further investigation showed that CBX further significantly increased AFC and α-ENaC expression after treatment with a low dose of E and/or P. In vitro, E or P alone inhibited 11β-HSD2 activity in a dose-dependent manner and increased α-ENaC expression by at least 50%, and E combined with P increased α-ENaC expression by more than 80%. Thus, E and P may augment the expression of α-ENaC, enhance AFC, attenuate pulmonary oedema by inhibiting 11β-HSD2 activity, and increase the active glucocorticoid levels in vivo and in vitro.

17β-estradiol suppresses lipopolysaccharide-induced acute lung injury through PI3K/Akt/SGK1 mediated up-regulation of epithelial sodium channel (ENaC) in vivo and in vitro

Background

17β-estradiol can suppress acute lung injury (ALI) and regulate alveolar epithelial sodium channel (ENaC). However the relationship between these two functions remains unclear. This study is conducted to assess the role of ENaC and the PI3K/Akt/SGK1 signaling pathway in 17β-estradiol therapy in attenuating LPS-induced ALI.

Methods

ALI was induced in C57BL/J male mice by intratracheal administration of lipopolysaccharide (LPS). Concurrent with LPS administration, 17β-estradiol or sterile saline was administered to ALI model with or without the phosphoinositide 3-kinase (PI3K) inhibitor wortmannin. The lung histological changes, inflammatory mediators in bronchoalveolar lavage fluid (BALF), wet/dry weight ratio (W/D) and alveolar fluid clearance (AFC) were measured 4 hours after LPS challenge in vivo. For in vitro studies, LPS-challenged MLE-12 cells were pre-incubated with or without wortmannin for 30 minutes prior to 17β-estradiol treatment. Expression of ENaC subunits was assessed by reverse transcriptase PCR, western blot, cell surface biotinylation, and immunohistochemistry. The levels of phosphorylated Akt and SGK1 in lung tissue and lung cell lines were investigated by western blot.

Results

17β-estradiol suppressed LPS-mediated ALI in mice by diminishing inflammatory mediators and enhancing AFC. 17β-estradiol promoted the expression and surface abundance of α-ENaC, and increased the levels of phosphorylated-Akt and phosphorylated-SGK1 following LPS challenge. This induction was abolished by the PI3K inhibitor wortmannin in vivo and in vitro.

Conclusion

17β-estradiol attenuates LPS-induced ALI not only by repressing inflammation, but also by reducing pulmonary edema via elevation of α-ENaC expression and membrane abundance. These effects were mediated, at least partially, via activation of the PI3K/Akt/SGK1 signaling pathway.

TIP peptide inhalation in experimental acute lung injury: effect of repetitive dosage and different synthetic variants

Background

Inhalation of TIP peptides that mimic the lectin-like domain of TNF-α is a novel approach to attenuate pulmonary oedema on the threshold to clinical application. A placebo-controlled porcine model of acute respiratory distress syndrome (ARDS) demonstrated a reduced thermodilution-derived extravascular lung water index (EVLWI) and improved gas exchange through TIP peptide inhalation within three hours. Based on these findings, the present study compares a single versus a repetitive inhalation of a TIP peptide (TIP-A) and two alternate peptide versions (TIP-A, TIP-B).

Methods

Following animal care committee approval ARDS was induced by bronchoalveolar lavage followed by injurious ventilation in 21 anaesthetized pigs. A randomised-blinded three-group setting compared the single-dosed peptide variants TIP-A and TIP-B as well as single versus repetitive inhalation of TIP-A (n = 7 per group). Over two three-hour intervals parameters of gas exchange, transpulmonary thermodilution, calculated alveolar fluid clearance, and ventilation/perfusion-distribution were assessed. Post-mortem measurements included pulmonary wet/dry ratio and haemorrhage/congestion scoring.

Results

The repetitive TIP-A inhalation led to a significantly lower wet/dry ratio than a single dose and a small but significantly lower EVLWI. However, EVLWI changes over time and the derived alveolar fluid clearance did not differ significantly. The comparison of TIP-A and B showed no relevant differences. Gas exchange and ventilation/perfusion-distribution significantly improved in all groups without intergroup differences. No differences were found in haemorrhage/congestion scoring.

Conclusions

In comparison to a single application the repetitive inhalation of a TIP peptide in three-hour intervals may lead to a small additional reduction the lung water content. Two alternate TIP peptide versions showed interchangeable characteristics.

Estrogen and the cystic fibrosis gender gap

Cystic fibrosis (CF) is the most frequent inherited disease in Caucasian populations and is due to a defect in the expression or activity of a chloride channel encoded by the cystic fibrosis transmembrane conductance regulator (CFTR) gene. Mutations in this gene affect organs with exocrine functions and the main cause of morbidity and mortality for CF patients is the lung pathology in which the defect in CFTR decreases chloride secretion, lowering the airway surface liquid height and increasing mucus viscosity. The compromised ASL dynamics leads to a favorable environment for bacterial proliferation and sustained inflammation resulting in epithelial lung tissue injury, fibrosis and remodeling. In CF, there exist a difference in lung pathology between men and women that is termed the "CF gender gap". Recent studies have shown the prominent role of the most potent form of estrogen, 17β-estradiol in exacerbating lung function in CF females and here, we review the role of this hormone in the CF gender dichotomy.

Clinical grade allogeneic human mesenchymal stem cells restore alveolar fluid clearance in human lungs rejected for transplantation

The lack of suitable donors for all solid-organ transplant programs is exacerbated in lung transplantation by the low utilization of potential donor lungs, due primarily to donor lung injury and dysfunction, including pulmonary edema. The current studies were designed to determine if intravenous clinical-grade human mesenchymal stem (stromal) cells (hMSCs) would be effective in restoring alveolar fluid clearance (AFC) in the human ex vivo lung perfusion model, using lungs that had been deemed unsuitable for transplantation and had been subjected to prolonged ischemic time. The human lungs were perfused with 5% albumin in a balanced electrolyte solution and oxygenated with continuous positive airway pressure. Baseline AFC was measured in the control lobe and if AFC was impaired (defined as <10%/h), the lungs received either hMSC (5 × 10(6) cells) added to the perfusate or perfusion only as a control. AFC was measured in a different lung lobe at 4 h. Intravenous hMSC restored AFC in the injured lungs to a normal level. In contrast, perfusion only did not increase AFC. This positive effect on AFC was reduced by intrabronchial administration of a neutralizing antibody to keratinocyte growth factor (KGF). Thus, intravenous allogeneic hMSCs are effective in restoring the capacity of the alveolar epithelium to remove alveolar fluid at a normal rate, suggesting that this therapy may be effective in enhancing the resolution of pulmonary edema in human lungs deemed clinically unsuitable for transplantation.

Estradiol activates epithelial sodium channels in rat alveolar cells through the G protein-coupled estrogen receptor

Female sex predisposes individuals to poorer outcomes during respiratory disorders like cystic fibrosis and influenza-associated pneumonia. A common link between these disorders is dysregulation of alveolar fluid clearance via disruption of epithelial sodium channel (ENaC) activity. Recent evidence suggests that female sex hormones directly regulate expression and activity of alveolar ENaC. In our study, we identified the mechanism by which estradiol (E2) or progesterone (P4) independently regulates alveolar ENaC. Using cell-attached patch clamp, we measured ENaC single-channel activity in a rat alveolar cell line (L2) in response to overnight exposure to either E2 or P4. In contrast to P4, E2 increased ENaC channel activity (NPo) through an increase in channel open probability (Po) and an increased number of patches with observable channel activity. Apical plasma membrane abundance of the ENaC α-subunit (αENaC) more than doubled in response to E2 as determined by cell surface biotinylation. αENaC membrane abundance was approximately threefold greater in lungs from female rats in proestrus, when serum E2 is greatest, compared with diestrus, when it is lowest. Our results also revealed a significant role for the G protein-coupled estrogen receptor (Gper) to mediate E2's effects on ENaC. Overall, our results demonstrate that E2 signaling through Gper selectively activates alveolar ENaC through an effect on channel gating and channel density, the latter via greater trafficking of channels to the plasma membrane. The results presented herein implicate E2-mediated regulation of alveolar sodium channels in the sex differences observed in the pathogenesis of several pulmonary diseases.

Estrogen regulation of epithelial ion transport: Implications in health and disease

Estrogen, 17β-estradiol (E2), has been shown to modulate the activity of ion channels in a diverse range of epithelial tissues. The channel activation or inhibition responses to E2 are often rapid, occurring in seconds to minutes, independent of protein synthesis and gene transcription ('non-genomic' response). These rapid effects of E2 require activation of specific protein kinases or changes in intracellular calcium and pH which in turn modulate the conductance, open probability or number of channels in the plasmamembrane. Estrogen has also been shown to affect the expression of ion transporters over days ('genotropic' response) causing long-term sustained changes in transepithelial ion transport. It is now accepted that so called non-genomic responses are not stand-alone events and are necessary to prime the latent genomic response and even be critical for the full latent response to occur. In a number of epithelia the non-genomic and genotropic responses to estrogen are sex-specific and variable in potency and sensitivity to E2 depending on the stage of the estrous cycle. Of increasing interest is the effect these rapid and latent actions of E2 on ion transporters have on the physiological functions of epithelia. For example, estrogen regulation of a class of voltage-gated K(+) channels (KCNQ1) can determine the rate of Cl(-) secretion in the intestine. In whole-body terms, the combined effects of estrogen on a variety of ion channels which control fluid and electrolyte transport in the kidney, intestine and lung may be necessary for endometrial expansion and implantation of the blastocyte.

Postoperative estradiol levels associate with development of primary graft dysfunction in lung transplantation patients

BACKGROUND

Primary graft dysfunction (PGD) frequently complicates lung transplantation in the immediate postoperative period. Both female gender and estradiol modulate the body's response to injury and can influence the rate of alveolar fluid clearance.

OBJECTIVE

We hypothesized that female gender and higher estradiol levels would be associated with a lower risk of PGD after lung transplantation.

METHODS

We measured plasma estradiol levels preoperatively, 6 hours postoperatively, and 24 hours postoperatively in a cohort of 111 lung transplant recipients at 2 institutions.

RESULTS

Mean age was 57 years (12.5) and 52% were female. Median postoperative estradiol level was 63.9 pg/mL (interquartile range, 28.8-154.3 pg/mL) in male and 65.1 pg/mL (interquartile range, 28.4-217.2 pg/mL) in female patients. Contrary to our hypothesis, higher estradiol levels at 24 hours were associated with an increased risk of PGD at 72 hours in male patients (P = 0.001). This association was preserved when accounting for other factors known to be associated with PGD. However, there was no relationship between gender and risk of PGD or between estradiol levels and PGD in females.

CONCLUSION

These findings suggest that there might be different biologic effects of estrogens in males and females, and highlight the importance of considering gender differences in future studies of PGD.

Phosphatidylinositol 4,5-bisphosphate stimulates alveolar epithelial fluid clearance in male and female adult rats

Cell membrane phospholipids, like phosphatidylinositol 4,5-bisphosphate [PI(4,5)P(2)], can regulate epithelial Na channel (ENaC) activity. Gender differences in lung ENaC expression have also been demonstrated. However, the effects in vivo on alveolar fluid clearance are uncertain. Thus PI(4,5)P(2) effects on alveolar fluid clearance were studied in male and female rats. An isosmolar 5% albumin solution was intrapulmonary instilled; alveolar fluid clearance was studied for 1 h. Female rats had a 37 ± 19% higher baseline alveolar fluid clearance than male rats. Bilateral ovariectomy attenuated this gender difference. Compared with controls, PI(4,5)P(2) instillation (300 μM) increased alveolar fluid clearance by ∼93% in both genders. Amiloride or the specific αENaC small-interfering RNA inhibited baseline and PI(4,5)P(2)-stimulated alveolar fluid clearance in both genders, indicating a dependence on amiloride-sensitive pathways. The fraction of amiloride inhibition was greater in PI(4,5)P(2)-instilled rats (male: 64 ± 10%; female: 70 ± 11%) than in controls (male: 30 ± 6%; female: 44 ± 8%). PI(4,5)P(2) instillation lacked additional alveolar fluid clearance stimulation above that of terbutaline, nor did propranolol inhibit alveolar fluid clearance after PI(4,5)P(2) instillation, indicating that PI(4,5)P(2) stimulation was not secondary to endogenous β-adrenoceptor activation. PI(4,5)P(2) amine instillation resulted in an intermediate alveolar fluid clearance stimulation, suggesting that, to reach maximal alveolar fluid clearance stimulation, PI(4,5)P(2) must reside in cell membranes. In summary, PI(4,5)P(2) instillation upregulated in vivo alveolar fluid clearance similar to short-term β-adrenoceptor upregulation of alveolar fluid clearance. PI(4,5)P(2) stimulation was mediated partly by increased amiloride-sensitive Na transport. There exist important gender-related effects suggesting a female advantage that may have clinical implications for resolution of acute lung injury.

The effect of influenza virus A on th1/th2 balance and alveolar fluid clearance in pregnant rats

ABSTRACT Pregnant women are more prone to H1N1 infection and often with severe complications. The authors studied the influence of H1N1 infection on T-helper cell type 1/type 2 (Th1/Th2) balance and alveolar fluid clearance (AFC) in pregnant rats. The pregnant rats were infected intranasally with influenza virus. Peripheral blood interferon-γ (IFN-γ) and interleukin-4 (IL-4) were measured by enzyme-linked immunosorbent assay (ELISA) and AFC was estimated by albumin concentration in alveolar lavage. The ratio of IFN-γ/IL-4 in nonpregnant rats was 21 ± 7. There was significant increase in both cytokines in infected pregnant rats compared with noninfected counterparts, with dramatic reduction in IFN-γ/IL-4 ratio (8 ± 3) compared to that (15 ± 8) in normal pregnant group. AFC of normal nonpregnant rats was 17% ± 3% and H1N1 infection reduced it to 11% ± 2%. AFC of normal pregnant rats was 22% ± 2% and H1N1 infection reduced it to 10% ± 2%. Dexamethasone reversed AFC in both nonpregnant and pregnant groups (14% ± 4% and 13% ± 2%, respectively). These results show that influenza virus A infection leads to Th2-biased immunity and reduces AFC in normal rats, and further worsens these in pregnant rats. Dexamethasone reverses these effects in both pregnant and nonpregnant rats.