Intravenous sulforhodamine B reduces alveolar surface tension, improves oxygenation, and reduces ventilation injury in a respiratory distress model

The fix is not yet in: recommendation for fixation of lungs within physiological/pathophysiological volume range in preclinical pulmonary structure-function studies

Quantitative characterization of lung structures by morphometrical or stereological analysis of histological sections is a powerful means of elucidating pulmonary structure-function relations. The overwhelming majority of studies, however, fix lungs for histology at pressures outside the physiological/pathophysiological respiratory volume range. Thus, valuable information is being lost. In this perspective article, we argue that investigators performing pulmonary histological studies should consider whether the aims of their studies would benefit from fixation at functional transpulmonary pressures, particularly those of end-inspiration and end-expiration. We survey the pressures at which lungs are typically fixed in preclinical structure-function studies, provide examples of conditions that would benefit from histological evaluation at functional lung volumes, summarize available fixation methods, discuss alternative imaging modalities, and discuss challenges to implementing the suggested approach and means of addressing those challenges. We aim to persuade investigators that modifying or complementing the traditional histological approach by fixing lungs at minimal and maximal functional volumes could enable new understanding of pulmonary structure-function relations.

A gene polymorphism at SP-B 1580 site regulates the pulmonary surfactant tension of viral pneumonia through the cellular pyroptosis signaling pathway

BACKGROUND

Viral pneumonias, such as SARS and MERS, have been a recurrent challenge for the public healthcare system. COVID-19 posed an unprecedented global crisis. The primary impact of viral pneumonia is pathologic changes of lung tissue. However, the effect of SP-B site gene polymorphism on alveolar surface tension in viral pneumonia remains unexplored.

OBJECTIVE

To explore the molecular mechanism of how the gene polymorphism at SP-B 1580 site regulates the pulmonary surfactant tension of viral pneumonia through the cellular pyroptosis signaling pathway using an in vivo animal experiment and a clinical trial.

METHODS

We constructed a genetically modified mouse model of viral pneumonia and administered H5N1 influenza virus through intratracheal injection. After 48 hours, the survival rate of each mouse group was evaluated. Lung tissue, blood, and bronchoalveolar lavage fluid samples were collected for histopathologic analysis. Inflammatory factor concentrations were measured using ELISA. The level of apoptosis was determined using TUNEL assay. Changes in the expression of cell death-related factors were assessed using qRT-PCR and protein blotting. Additionally, blood samples from patients with viral pneumonia were analyzed to detect single nucleotide polymorphisms and explore their correlation with disease severity, inflammatory factor levels, and pulmonary surfactant protein expression.

RESULTS

Following H5N1 infection of mice, the model group and hSP-B-C group showed high mortality rates within 24 hours. The survival rates in the blank control group, virus model group, hSP-B-C group, and hSP-B-T group were 100%, 50%, 37.5%, and 75%, respectively. Histologic analysis revealed significant lung tissue damage, congestion, alveolar destruction, and thickened alveolar septa in the model and hSP-B-C groups. However, these pulmonary lesions were significantly alleviated in the hSP-B-T group. Inflammatory factor levels were elevated in the model and hSP-B-C groups but reduced in the hSP-B-T group. TUNEL assay demonstrated a decrease in apoptotic cells in the lungs of the hSP-B-T group. Furthermore, the expression of SP-B and cell death-related proteins was downregulated in all three groups, with the lowest expression observed in the hSP-B-C group. The clinical trial found that patients with severe viral pneumonia exhibited a higher frequency of CC genotype and C allele in, along with increased inflammatory factor levels and decreased SP-B expression compared to those with mild-to-moderate viral pneumonia.

CONCLUSION

SP-B polymorphism at the 1580 site regulates lung surfactant tension through the cell pyroptosis signaling pathway, thus affecting the progression of viral pneumonia.

The mitochondrial calcium uniporter of pulmonary type 2 cells determines severity of acute lung injury

Acute Lung Injury (ALI) due to inhaled pathogens causes high mortality. Underlying mechanisms are inadequately understood. Here, by optical imaging of live mouse lungs we show that a key mechanism is the viability of cytosolic Ca²⁺ buffering by the mitochondrial Ca²⁺ uniporter (MCU) in the lung’s surfactant-secreting, alveolar type 2 cells (AT2). The buffering increased mitochondrial Ca²⁺ and induced surfactant secretion in wild-type mice, but not in mice with AT2-specific MCU knockout. In the knockout mice, ALI due to intranasal LPS instillation caused severe pulmonary edema and mortality, which were mitigated by surfactant replenishment prior to LPS instillation, indicating surfactant’s protective effect against alveolar edema. In wild-type mice, intranasal LPS, or Pseudomonas aeruginosa decreased AT2 MCU. Loss of MCU abrogated buffering. The resulting mortality was reduced by spontaneous recovery of MCU expression, or by MCU replenishment. Enhancement of AT2 mitochondrial buffering, hence endogenous surfactant secretion, through MCU replenishment might be a therapy against ALI.

Acute lung injury caused by inhalation of pathogens leads to mortality, but the mechanisms are unclear. Here, the authors show in mice that that loss of the mitochondrial calcium uniporter (MCU) of alveolar type 2 cells (AT2) impaired mitochondrial Ca²⁺ buffering and surfactant secretion, and increased mortality, in response to LPS instillation, suggesting the MCU as a potential therapeutic target in ALI.

Nanoparticle-mediated surfactant therapy in patients with severe COVID-19: a perspective

Coronavirus disease 2019 (COVID-19) is an RNA virus-based disease that can be deadly. For critically ill patients, mechanical ventilation is an important life-saving treatment. However, mechanical ventilation shows a trade-off between supporting respiratory function and ventilator-induced lung injury (VILI). Surfactant therapy is a medical administration of exogenous surfactant to supplement or replace deficient or dysfunctional endogenous surfactant. Surfactant therapy can be used to postpone or shorten the use of mechanical ventilation to minimize or avoid VILI, because surfactants can reduce surface tension, improve lung compliance, and enhance oxygenation. In addition, nanotechnology can be applied to improve the therapeutic effect and reduce the adverse effects of surfactants. In this perspective, we discussed how nanoparticles deliver surfactants through intravenous injection and inhalation to the expected lung disease regions where surfactants are mostly needed, and discussed the prospects of nanoparticle-mediated surfactant therapy in the treatment of patients with severe COVID-19.

The Mitochondrial Calcium Uniporter of Pulmonary Type 2 Cells Determines Severity of ARDS

Acute lung immunity to inhaled pathogens elicits defensive pneumonitis that may convert to the Acute Respiratory Distress Syndrome (ARDS), causing high mortality. Mechanisms underlying the conversion are not understood, but are of intense interest because of the ARDS-induced mortality in the ongoing Covid-19 pandemic. Here, by optical imaging of live lungs we show that key to the lethality is the functional status of mitochondrial Ca2+ buffering across the mitochondrial Ca2+ uniporter (MCU) in the alveolar type 2 cells (AT2), which protect alveolar stability. In mice subjected to ARDS by airway exposure to lipopolysaccharide (LPS), or to Pseudomonas aeruginosa, there was marked loss of MCU expression in AT2. The ability of mice to survive ARDS depended on the extent to which the MCU expression recovered, indicating that the viability of Ca2+ buffering by AT2 mitochondria critically determines ARDS severity. Mitochondrial transfer to enhance AT2 MCU expression might protect against ARDS.

Sulforhodamine B and exogenous surfactant effects on alveolar surface tension under acute respiratory distress syndrome conditions

In the acute respiratory distress syndrome (ARDS), alveolar surface tension, T, may be elevated. Elevated T should increase ventilation-induced lung injury. Exogenous surfactant therapy, intended to lower T, has not reduced mortality. Sulforhodamine B (SRB) might, alternatively, be used to lower T. We test whether substances suspected of elevating T in ARDS raise T in the lungs and test the abilities of exogenous surfactant and SRB to reduce T. In isolated rat lungs, we micropuncture a surface alveolus and instill a solution of a purported T-raising substance: control saline, cell debris, secretory phospholipase A₂ (sPLA₂), acid, or mucins. We test each substance alone; with albumin, to model proteinaceous edema liquid; with albumin and exogenous surfactant; and with albumin and SRB. We determine T in situ in the lungs by combining servo-nulling pressure measurement with confocal microscopy and applying the Laplace relation. With control saline, albumin does not alter T, additional surfactant raises T, and additional SRB lowers T. The experimental substances, without or with albumin, raise T. Excepting under aspiration conditions, addition of surfactant or SRB lowers T. Exogenous surfactant activity is concentration and ventilation dependent. Sulforhodamine B, which could be delivered intravascularly, holds promise as an alternative therapeutic.NEW & NOTEWORTHY In the acute respiratory distress syndrome (ARDS), lowering surface tension, T, should reduce ventilation injury yet exogenous surfactant has not reduced mortality. We show with direct T determination in isolated lungs that substances suggested to elevate T in ARDS indeed raise T, and exogenous surfactant reduces T. Further, we extend our previous finding that sulforhodamine B (SRB) reduces T below normal in healthy lungs and show that SRB, too, reduces T under ARDS conditions.