Covid-19 Interstitial Pneumonia: Histological and Immunohistochemical Features on Cryobiopsies

Kynurenine Pathway in Respiratory Diseases

The kynurenine pathway is the primary route for tryptophan catabolism and has received increasing attention as its association with inflammation and the immune system has become more apparent. This review provides a broad overview of the kynurenine pathway in respiratory diseases, from the initial observations to the characterization of the different cell types involved in the synthesis of kynurenine metabolites and the underlying immunoregulatory mechanisms. With a focus on respiratory infections, the various attempts to characterize the kynurenine/tryptophan (K/T) ratio as an inflammatory marker are reviewed. Its implication in chronic lung inflammation and its exacerbation by respiratory pathogens is also discussed. The emergence of preclinical interventional studies targeting the kynurenine pathway opens the way for the future development of new therapies.

Lung Ultrasound Score as a Predictor of Failure to Wean COVID-19 Elderly Patients off Mechanical Ventilation: A Prospective Observational Study

Background

The lung ultrasound score was developed for rapidly assessing the extent of lung ventilation, and it can predict failure to wean various types of patients off mechanical ventilation. Whether it is also effective for COVID-19 patients is unclear.

Methods

This single-center, prospective, observational study was conducted to assess the ability of the 12-region lung ultrasound score to predict failure to wean COVID-19 patients off ventilation. In parallel, we assessed whether right hemidiaphragmatic excursion or previously published predictors of weaning failure can apply to these patients. Predictive ability was assessed in terms of the area under the receiver operating characteristic curve (AUC).

Results

The mean age of the 35 patients in the study was (75 ± 9) years and 12 patients (37%) could not be weaned off mechanical ventilation. The lung ultrasound score predicted these failures with an AUC of 0.885 (95% CI 0.770-0.999, p < 0.001), and a threshold score of 10 provided specificity of 72.7% and sensitivity of 92.3%. AUCs were lower for previously published predictors of weaning failure, and right hemidiaphragmatic excursion did not differ significantly between the two groups.

Conclusion

The lung ultrasound score can accurately predict failure to wean critically ill COVID-19 patients off mechanical ventilation, whereas assessment of right hemidiaphragmatic excursion does not appear helpful in this regard.

Trial Registration

https://clinicaltrials.gov/ct2/show/NCT05706441.

Utility of bronchoalveolar lavage for COVID-19: a perspective from the Dragon consortium

Diagnosing COVID-19 and treating its complications remains a challenge. This review reflects the perspective of some of the Dragon (IMI 2-call 21, #101005122) research consortium collaborators on the utility of bronchoalveolar lavage (BAL) in COVID-19. BAL has been proposed as a potentially useful diagnostic tool to increase COVID-19 diagnosis sensitivity. In both critically ill and non-critically ill COVID-19 patients, BAL has a relevant role in detecting other infections or supporting alternative diagnoses and can change management decisions in up to two-thirds of patients. BAL is used to guide steroid and immunosuppressive treatment and to narrow or discontinue antibiotic treatment, reducing the use of unnecessary broad antibiotics. Moreover, cellular analysis and novel multi-omics techniques on BAL are of critical importance for understanding the microenvironment and interaction between epithelial cells and immunity, revealing novel potential prognostic and therapeutic targets. The BAL technique has been described as safe for both patients and healthcare workers in more than a thousand procedures reported to date in the literature. Based on these preliminary studies, we recognize that BAL is a feasible procedure in COVID-19 known or suspected cases, useful to properly guide patient management, and has great potential for research.

Transbronchial lung cryobiopsy for peripheral pulmonary lesions. A narrative review

An increasing number of peripheral pulmonary lesions (PPLs) requiring tissue verification to establish a definite diagnosis for further individualized management are detected due to the growing adoption of lung cancer screening by chest computed tomography (CT), especially low-dose CT. However, the morphological diagnosis of PPLs remains challenging. Transbronchial lung cryobiopsy (TBLC) that can retrieve larger specimens with more preserved cellular architecture and fewer crush artifacts in comparison with conventional transbronchial forceps biopsy (TBFB), as an emerging technology for diagnosing PPLs, has been demonstrated to have the potential to resolve the clinical dilemma pertaining to currently available sampling devices (e.g., forceps, needle and brush) and become a diagnostic cornerstone for PPLs. Of note, with the introduction of the 1.1 mm cryoprobe that will be more compatible with advanced bronchoscopic navigation techniques, such as radial endobronchial ultrasound (r-EBUS), virtual bronchoscopic navigation (VBN) and electromagnetic navigation bronchoscopy (ENB), the use of TBLC is expected to gain more popularity in the diagnosis of PPLs. While much remains for exploration using the TBLC technique for diagnosing PPLs, it can be envisaged that the emergence of additional studies with larger data accrual will hopefully add to the body of evidence in this field.

COVID-19. Biology, pathophysiology, and immunology: a pathologist view

Even if the SARS-CoV-2 pandemic has been declared over, several risks and clinical problems remain to be faced, including long-COVID sequelae and possible outbreaks of pathogenic variants. Intense research on COVID-19 has provided in these few years a striking amount of data covering different fields and disciplines, which can help to provide a knowledge shield against new potential infective spreads, and may also potentially be applied to other fields of medicine, including oncology and neurology. Nevertheless, areas of uncertainty still remain regarding the pathogenic mechanisms that subtend the multifaceted manifestations of the disease. To better clarify the pathogenesis of the disease, a systematic multidisciplinary evaluation of the many mechanisms involved in COVID-19 is mandatory, including clinical, physiological, radiological, immunological and pathological studies. In COVID-19 syndrome the pathological studies have been mainly performed on autopsy cases, and only a few studies are available on biopsies. Nevertheless, these studies have provided relevant information that can substantially contribute to decipher the complex scenario characterizing the different forms of COVID-19 and long-COVID-19. In this review the data provided by pathological investigations are recapitulated and discussed, in the light of different hypothesis and data provided by clinical, physiological and immunological data.

Post-COVID-19 pulmonary fibrosis: An ongoing concern

Coronavirus disease (COVID-19) caused by severe acute respiratory syndrome coronavirus 2 rapidly spread across the globe causing over 6 million deaths and major compromization of health facilities. The vast majority of survivors post-COVID-19 are left with variable degrees of health sequelae including pulmonary, neurological, psychological, and cardiovascular complications. Post-COVID-19 pulmonary fibrosis is one of the major concerns arising after the recovery from this pandemic. Risk factors for post-COVID-19 pulmonary fibrosis include age, male sex, and the severity of COVID-19 disease. High-resolution computed tomography provides diagnostic utility to diagnose pulmonary fibrosis as it provides more details regarding the pattern and the extent of pulmonary fibrosis. Emerging data showing similarities between post-COVID-19 pulmonary fibrosis and idiopathic pulmonary fibrosis, finding that needs further exploration. The management of post-COVID-19 pulmonary fibrosis depends on many factors but largely relies on excluding other causes of pulmonary fibrosis, the extent of fibrosis, and physiological impairment. Treatment includes immunosuppressants versus antifibrotics or both.

COVID-19 and lung cancer

COVID-19 pandemic had affected health services around the world, also reducing the diagnosis of lung cancer. On the other hand, examination of surgical specimens in patients with lung cancer and SARS-CoV-2 gave the opportunity to evidence early histologic features related to this emerging pandemic.

Different prioritization of health organizations during COVID-19 pandemic resulted in a significant decline of lung cancer screening (up to 56%), delayed diagnosis (up to 30-40%) and higher advanced stage, with some exceptions (i.e., Canada). Increased use of stereotactic radiation treatments in stage I-IIA have been noticed in better-organized health systems. Surgical specimens performed for lung cancer in patients with incipient SARS-CoV-2 permitted to appreciate early histologic findings of COVID-19 with hyperplastic pneumocytes with/without fibrin exudate, alveolar macrophages/myeloid cells, perivascular T-lymphocytic infiltrate and lack of hyaline membrane.

While the COVID-19 pandemic has declined the rate of lung cancer diagnosis worldwide, some institutions have significantly limited detrimental effects. Histology related to early SARS-CoV-2 infection in surgical samples for lung cancer revealed specific histologic changes.

Exploring the pathologist's role in understanding COVID-19: from pneumonia to long-COVID lung sequelae

The crucial role of pathologists in enhancing our understanding of SARS-CoV-2-related disease, from initial pneumonia manifestations to persistent long COVID lung symptoms, is the focus of this review. Pathological explorations have offered unprecedented insights into the early stages of severe COVID-19, shedding light on the interplay between the virus and subsequent complications, thereby shaping clinical approaches. Growing interest is directed to residual lung abnormalities of COVID-19 survivors. Although various radiological studies reported long-lasting pulmonary changes (e.g., ground glass opacities, reticulations, and bronchiectasis), the true incidence of pulmonary fibrosis and corresponding pathological findings in these patients remains largely unknown. There are a few high-impact and knowledgeable works on late complications in COVID-19 survivors, several coming from explant or autopsy cases, and rare cases from in vivo sampling. The study of biopsy samples has further deepened our knowledge of the aftermath of COVID-19 on lung tissue, uncovering alterations at the cellular level and shifts in vascular and epithelial dynamics. Despite the substantial progress made, future research is needed to devise a uniform strategy for interpreting lung biopsies, with a focus on leveraging advanced tools such as molecular and digital pathology techniques, along with artificial intelligence.

Mesenchymal Stem Cells in the Treatment of COVID-19

Since the emergence of the coronavirus disease 2019 (COVID-19) pandemic, many lives have been tragically lost to severe infections. The COVID-19 impact extends beyond the respiratory system, affecting various organs and functions. In severe cases, it can progress to acute respiratory distress syndrome (ARDS) and multi-organ failure, often fueled by an excessive immune response known as a cytokine storm. Mesenchymal stem cells (MSCs) have considerable potential because they can mitigate inflammation, modulate immune responses, and promote tissue regeneration. Accumulating evidence underscores the efficacy and safety of MSCs in treating severe COVID-19 and ARDS. Nonetheless, critical aspects, such as optimal routes of MSC administration, appropriate dosage, treatment intervals, management of extrapulmonary complications, and potential pediatric applications, warrant further exploration. These research avenues hold promise for enriching our understanding and refining the application of MSCs in confronting the multifaceted challenges posed by COVID-19.

Amino acid metabolism in health and disease

Amino acids are the building blocks of protein synthesis. They are structural elements and energy sources of cells necessary for normal cell growth, differentiation and function. Amino acid metabolism disorders have been linked with a number of pathological conditions, including metabolic diseases, cardiovascular diseases, immune diseases, and cancer. In the case of tumors, alterations in amino acid metabolism can be used not only as clinical indicators of cancer progression but also as therapeutic strategies. Since the growth and development of tumors depend on the intake of foreign amino acids, more and more studies have targeted the metabolism of tumor-related amino acids to selectively kill tumor cells. Furthermore, immune-related studies have confirmed that amino acid metabolism regulates the function of effector T cells and regulatory T cells, affecting the function of immune cells. Therefore, studying amino acid metabolism associated with disease and identifying targets in amino acid metabolic pathways may be helpful for disease treatment. This article mainly focuses on the research of amino acid metabolism in tumor-oriented diseases, and reviews the research and clinical research progress of metabolic diseases, cardiovascular diseases and immune-related diseases related to amino acid metabolism, in order to provide theoretical basis for targeted therapy of amino acid metabolism.

COVID-19 and interstitial lung diseases: A multifaceted look at the relationship between the two diseases

Coronavirus disease 2019 (COVID-19) is an infectious disease caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Although it has been a fatal disease for many patients, the development of treatment strategies and vaccines have progressed over the past 3 years, and our society has become able to accept COVID-19 as a manageable common disease. However, as COVID-19 sometimes causes pneumonia, post-COVID pulmonary fibrosis (PCPF), and worsening of preexisting interstitial lung diseases (ILDs), it is still a concern for pulmonary physicians. In this review, we have selected several topics regarding the relationships between ILDs and COVID-19. The pathogenesis of COVID-19-induced ILD is currently assumed based mainly on the evidence of other ILDs and has not been well elucidated specifically in the context of COVID-19. We have summarized what has been clarified to date and constructed a coherent story about the establishment and progress of the disease. We have also reviewed clinical information regarding ILDs newly induced or worsened by COVID-19 or anti-SARS-CoV-2 vaccines. Inflammatory and profibrotic responses induced by COVID-19 or vaccines have been thought to be a risk for de novo induction or worsening of ILDs, and this has been supported by the evidence obtained through clinical experience over the past 3 years. Although COVID-19 has become a mild disease in most cases, it is still worth looking back on the above-reviewed information to broaden our perspectives regarding the relationship between viral infection and ILD. As a representative etiology for severe viral pneumonia, further studies in this area are expected.

COVID-19 in Patients with Pre-Existing Interstitial Lung Disease: Potential Value of a Steroid-Based Treatment Strategy

The prognosis of patients with coronavirus disease 2019 (COVID-19) and pre-existing interstitial lung disease (preILD) is poor, and no effective treatment strategy has been determined. The aim of this study was to assess the effectiveness of a steroid-based treatment strategy for patients with COVID-19 and preILD. We retrospectively reviewed the medical records of 610 consecutive patients with COVID-19 treated at our institution between 1 March 2020 and 30 October 2021 and identified 7 patients with preILD, all of whom were treated with corticosteroids and remdesivir. All the patients were men with a median age of 63 years. Three of four patients with severe disease required invasive positive-pressure ventilation (n = 2) or nasal high-flow therapy (n = 1). All three patients could be weaned from respiratory support; however, one died in hospital. The remaining patient with severe COVID-19 had a do-not-resuscitate order in place and died while hospitalized. All three patients with moderate COVID-19 were discharged. The 30-day mortality was 0%, and the mortality rate during the entire observation period was 28.5%. The prognosis of our patients with COVID-19 and preILD has been better than in previous reports. Our management strategy using corticosteroids may have improved these patients' prognosis.

Lung Expression of Macrophage Markers CD68 and CD163, Angiotensin Converting Enzyme 2 (ACE2), and Caspase-3 in COVID-19

Background and Objectives: The coronavirus (SARS-CoV-2) damages all systems and organs. Yet, to a greater extent, the lungs are particularly involved, due to the formation of diffuse exudative inflammation in the form of acute respiratory distress syndrome (ARDS) with next progression to pulmonary fibrosis. SARS-associated lung damage is accompanied by the pronounced activation of mononuclear cells, damage of the alveoli and microvessels, and the development of organized pneumonia. To study the expression of macrophage markers (CD68 and CD163), angiotensin-converting enzyme-2 (ACE2), and caspase-3 on the results of two fatal clinical observations of COVID-19. Materials and Methods: In both clinical cases, the female patients died from complications of confirmed COVID-19. Conventional morphological and immunohistochemical methods were used. Results: There was an acute exudative hemorrhagic pneumonia with the formation of hyaline membranes, focal organization of fibrin, stromal sclerosis, stasis, and thrombus formation in the lung vessels. Signs such as the formation of hyaline membranes, organization, and fibrosis were more pronounced in severe disease activity. The activation of CD68+/CD163+ macrophages could cause cell damage at an early stage of pneumonia development, and subsequently cause fibrotic changes in lung tissue. ACE2 expression in lung tissue was not detected in severe pneumonia, while in moderate pneumonia, weak expression was noted in individual cells of the alveolar epithelium and vascular endothelium. Conclusions: This finding could show the dependence of ACE2 expression on the severity of the inflammatory process in the lungs. The expression of caspase-3 was more pronounced in severe pneumonia.

Cellular Immune Profiling of Lung and Blood Compartments in Patients with SARS-CoV-2 Infection

Background: SARS-CoV-2 related immunopathology may be the driving cause underlying severe COVID-19. Through an immunophenotyping analysis on paired bronchoalveolar lavage fluid (BALF) and blood samples collected from mechanically ventilated patients with COVID-19-associated Acute Respiratory Distress Syndrome (CARDS), this study aimed to evaluate the cellular immune responses in survivors and non-survivors of COVID-19. Methods: A total of 36 paired clinical samples of bronchoalveolar lavage fluid (BALF) mononuclear cells (BALF-MC) and peripheral blood mononuclear cells (PBMC) were collected from 18 SARS-CoV-2-infected subjects admitted to the intensive care unit (ICU) of the Policlinico Umberto I, Sapienza University Hospital in Rome (Italy) for severe interstitial pneumonia. The frequencies of monocytes (total, classical, intermediate and non-classical) and Natural Killer (NK) cell subsets (total, CD56bright and CD56dim), as well as CD4+ and CD8+ T cell subsets [naïve, central memory (TCM) and effector memory (TEM)], and those expressing CD38 and/or HLADR were evaluated by multiparametric flow cytometry. Results: Survivors with CARDS exhibited higher frequencies of classical monocytes in blood compared to non-survivors (p < 0.05), while no differences in the frequencies of the other monocytes, NK cell and T cell subsets were recorded between these two groups of patients (p > 0.05). The only exception was for peripheral naïve CD4+ T cells levels that were reduced in non-survivors (p = 0.04). An increase in the levels of CD56bright (p = 0.012) and a decrease in CD56dim (p = 0.002) NK cell frequencies was also observed in BALF-MC samples compared to PBMC in deceased COVID-19 patients. Total CD4+ and CD8+ T cell levels in the lung compartment were lower compared to blood (p = 0.002 and p < 0.01, respectively) among non-survivors. Moreover, CD38 and HLA-DR were differentially expressed by CD4+ and CD8+ T cell subsets in BALF-MC and in PBMC among SARS-CoV-2-infected patients who died from COVID-19 (p < 0.05). Conclusions: These results show that the immune cellular profile in blood and pulmonary compartments was similar in survivors and non-survivors of COVID-19. T lymphocyte levels were reduced, but resulted highly immune-activated in the lung compartment of patients who faced a fatal outcome.

Relevance of TMPRSS2, CD163/CD206, and CD33 in clinical severity stratification of COVID-19

Background

Approximately 13.8% and 6.1% of coronavirus disease 2019 (COVID-19) patients require hospitalization and sometimes intensive care unit (ICU) admission, respectively. There is no biomarker to predict which of these patients will develop an aggressive stage that we could improve their quality of life and healthcare management. Our main goal is to include new markers for the classification of COVID-19 patients.

Methods

Two tubes of peripheral blood were collected from a total of 66 (n = 34 mild and n = 32 severe) samples (mean age 52 years). Cytometry analysis was performed using a 15-parameter panel included in the Maxpar® Human Monocyte/Macrophage Phenotyping Panel Kit. Cytometry by time-of-flight mass spectrometry (CyTOF) panel was performed in combination with genetic analysis using TaqMan® probes for ACE2 (rs2285666), MX1 (rs469390), and TMPRSS2 (rs2070788) variants. GemStone™ and OMIQ software were used for cytometry analysis.

Results

The frequency of CD163+/CD206- population of transitional monocytes (T-Mo) was decreased in the mild group compared to that of the severe one, while T-Mo CD163-/CD206- were increased in the mild group compared to that of the severe one. In addition, we also found differences in CD11b expression in CD14dim monocytes in the severe group, with decreased levels in the female group (p = 0.0412). When comparing mild and severe disease, we also found that CD45- [p = 0.014; odds ratio (OR) = 0.286, 95% CI 0.104–0.787] and CD14dim/CD33+ (p = 0.014; OR = 0.286, 95% CI 0.104–0.787) monocytes were the best options as biomarkers to discriminate between these patient groups. CD33 was also indicated as a good biomarker for patient stratification by the analysis of GemStone™ software. Among genetic markers, we found that G carriers of TMPRSS2 (rs2070788) have an increased risk (p = 0.02; OR = 3.37, 95% CI 1.18–9.60) of severe COVID-19 compared to those with A/A genotype. This strength is further increased when combined with CD45-, T-Mo CD163+/CD206-, and C14dim/CD33+.

Conclusions

Here, we report the interesting role of TMPRSS2, CD45-, CD163/CD206, and CD33 in COVID-19 aggressiveness. This strength is reinforced for aggressiveness biomarkers when TMPRSS2 and CD45-, TMPRSS2 and CD163/CD206, and TMPRSS2 and CD14dim/CD33+ are combined.

Post-COVID Interstitial Lung Disease and Other Lung Sequelae

As the world emerges from the COVID-19 pandemic, clinicians and researchers across the world are trying to understand the sequelae in patients recovered from COVID-19 infection. In this article, the authors review post-acute sequelae of SARS-COV-2, interstitial lung disease, and other lung sequelae in patients recovering from COVID-19 infection.

An Integrated Radiologic-Pathologic Understanding of COVID-19 Pneumonia

This article reviews the radiologic and pathologic findings of the epithelial and endothelial injuries in COVID-19 pneumonia to help radiologists understand the fundamental nature of the disease. The radiologic and pathologic manifestations of COVID-19 pneumonia result from epithelial and endothelial injuries based on viral toxicity and immunopathologic effects. The pathologic features of mild and reversible COVID-19 pneumonia involve nonspecific pneumonia or an organizing pneumonia pattern, while the pathologic features of potentially fatal and irreversible COVID-19 pneumonia are characterized by diffuse alveolar damage followed by fibrosis or acute fibrinous organizing pneumonia. These pathologic responses of epithelial injuries observed in COVID-19 pneumonia are not specific to SARS-CoV-2 but rather constitute universal responses to viral pneumonia. Endothelial injury in COVID-19 pneumonia is a prominent feature compared with other types of viral pneumonia and encompasses various vascular abnormalities at different levels, including pulmonary thromboembolism, vascular engorgement, peripheral vascular reduction, a vascular tree-in-bud pattern, and lung perfusion abnormality. Chest CT with different imaging techniques (eg, CT quantification, dual-energy CT perfusion) can fully capture the various manifestations of epithelial and endothelial injuries. CT can thus aid in establishing prognosis and identifying patients at risk for deterioration.

SARS-CoV-2 cellular tropism and direct multiorgan failure in COVID-19 patients: Bioinformatic predictions, experimental observations, and open questions

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), the virus that causes coronavirus disease 2019 (COVID-19), has led to an unprecedented public health emergency worldwide. While common cold symptoms are observed in mild cases, COVID-19 is accompanied by multiorgan failure in severe patients. Organ damage in COVID-19 patients is partially associated with the indirect effects of SARS-CoV-2 infection (e.g., systemic inflammation, hypoxic-ischemic damage, coagulopathy), but early processes in COVID-19 patients that trigger a chain of indirect effects are connected with the direct infection of cells by the virus. To understand the virus transmission routes and the reasons for the wide-spectrum of complications and severe outcomes of COVID-19, it is important to identify the cells targeted by SARS-CoV-2. This review summarizes the major steps of investigation and the most recent findings regarding SARS-CoV-2 cellular tropism and the possible connection between the early stages of infection and multiorgan failure in COVID-19. The SARS-CoV-2 pandemic is the first epidemic in which data extracted from single-cell RNA-seq (scRNA-seq) gene expression data sets have been widely used to predict cellular tropism. The analysis presented here indicates that the SARS-CoV-2 cellular tropism predictions are accurate enough for estimating the potential susceptibility of different cells to SARS-CoV-2 infection; however, it appears that not all susceptible cells may be infected in patients with COVID-19.

Immune Response Gaps Linked to SARS-CoV-2 Infection: Cellular Exhaustion, Senescence, or Both?

The COVID-19 pandemic, promoted by the SARS-CoV-2 respiratory virus, has resulted in widespread global morbidity and mortality. The immune response against this pathogen has shown a thin line between protective effects and pathological reactions resulting from the massive release of cytokines and poor viral clearance. The latter is possibly caused by exhaustion, senescence, or both of TCD8+ cells and reduced activity of natural killer (NK) cells. The imbalance between innate and adaptive responses during the early stages of infection caused by SARS-CoV-2 contributes to the ineffective control of viral spread. The present study evaluated the tissue immunoexpression of the tissue biomarkers (Arginase-1, CCR4, CD3, CD4, CD8, CD20, CD57, CD68, CD138, IL-4, INF-α, INF-γ, iNOS, PD-1, Perforin and Sphingosine-1) to understand the cellular immune response triggered in patients who died of COVID-19. We evaluated twenty-four paraffin-embedded lung tissue samples from patients who died of COVID-19 (COVID-19 group) and compared them with ten lung tissue samples from patients who died of H1N1pdm09 (H1N1 group) with the immunohistochemical markers mentioned above. In addition, polymorphisms in the Perforin gene were genotyped through Real-Time PCR. Significantly increased tissue immunoexpression of Arginase, CD4, CD68, CD138, Perforin, Sphingosine-1, and IL-4 markers were observed in the COVID-19 group. A significantly lower immunoexpression of CD8 and CD57 was also found in this group. It is suggested that patients who died from COVID-19 had a poor cellular response concerning viral clearance and adaptive response going through tissue repair.

The fatal trajectory of pulmonary COVID-19 is driven by lobular ischemia and fibrotic remodelling

BACKGROUND

COVID-19 is characterized by a heterogeneous clinical presentation, ranging from mild symptoms to severe courses of disease. 9-20% of hospitalized patients with severe lung disease die from COVID-19 and a substantial number of survivors develop long-COVID. Our objective was to provide comprehensive insights into the pathophysiology of severe COVID-19 and to identify liquid biomarkers for disease severity and therapy response.

METHODS

We studied a total of 85 lungs (n = 31 COVID autopsy samples; n = 7 influenza A autopsy samples; n = 18 interstitial lung disease explants; n = 24 healthy controls) using the highest resolution Synchrotron radiation-based hierarchical phase-contrast tomography, scanning electron microscopy of microvascular corrosion casts, immunohistochemistry, matrix-assisted laser desorption ionization mass spectrometry imaging, and analysis of mRNA expression and biological pathways. Plasma samples from all disease groups were used for liquid biomarker determination using ELISA. The anatomic/molecular data were analyzed as a function of patients' hospitalization time.

FINDINGS

The observed patchy/mosaic appearance of COVID-19 in conventional lung imaging resulted from microvascular occlusion and secondary lobular ischemia. The length of hospitalization was associated with increased intussusceptive angiogenesis. This was associated with enhanced angiogenic, and fibrotic gene expression demonstrated by molecular profiling and metabolomic analysis. Increased plasma fibrosis markers correlated with their pulmonary tissue transcript levels and predicted disease severity. Plasma analysis confirmed distinct fibrosis biomarkers (TSP2, GDF15, IGFBP7, Pro-C3) that predicted the fatal trajectory in COVID-19.

INTERPRETATION

Pulmonary severe COVID-19 is a consequence of secondary lobular microischemia and fibrotic remodelling, resulting in a distinctive form of fibrotic interstitial lung disease that contributes to long-COVID.

FUNDING

This project was made possible by a number of funders. The full list can be found within the Declaration of interests / Acknowledgements section at the end of the manuscript.

Interstitial lung disease following coronavirus disease 2019

PURPOSE OF REVIEW

The aim of this review was to summarize the recent data concerning interstitial lung disease after COVID-19, a field where knowledge is evolving very quickly.

RECENT FINDINGS

It has been found that a proportion of patients displayed fibrotic-like pattern on chest computed tomography shortly after COVID-19 pneumonia. Those lesions can potentially represent precursors of fibrosis, although most of them will resolve until 1 year postinfection. There was a wide range of the prevalence of post-COVID-19 interstitial lung disease detected in the literature, which can be attributed to the heterogeneous definition of lung abnormalities and the discrepancy of study design. The severity of acute COVID-19 disease has been linked to increased risk of residual imaging and functional abnormalities, while reduced DLco was the most common functional abnormality in long-term survivors. Studies indicated that pathophysiology of post-COVID interstitial lung disease shares common mechanisms with idiopathic pulmonary fibrosis. Regarding therapeutic strategies of post-COVID-19 interstitial lung disease, the role of immunosuppressive and antifibrotic treatment is currently under investigation.

SUMMARY

We still need to learn about the natural history of COVID-19 disease, allowing for a better targeting of therapeutic interventions through a multidisciplinary approach.

Mechanism of selenomethionine inhibiting of PDCoV replication in LLC-PK1 cells based on STAT3/miR-125b-5p-1/HK2 signaling

There are no licensed therapeutics or vaccines available against porcine delta coronavirus (PDCoV) to eliminate its potential for congenital disease. In the absence of effective treatments, it has led to significant economic losses in the swine industry worldwide. Similar to the current coronavirus disease 2019 (COVID-19) pandemic, PDCoV is trans-species transmissible and there is still a large desert for scientific exploration. We have reported that selenomethionine (SeMet) has potent antiviral activity against PDCoV. Here, we systematically investigated the endogenous immune mechanism of SeMet and found that STAT3/miR-125b-5p-1/HK2 signalling is essential for the exertion of SeMet anti-PDCoV replication function. Meanwhile, HK2, a key rate-limiting enzyme of the glycolytic pathway, was able to control PDCoV replication in LLC-PK1 cells, suggesting a strategy for viruses to evade innate immunity using glucose metabolism pathways. Overall, based on the ability of selenomethionine to control PDCoV infection and transmission, we provide a molecular basis for the development of new therapeutic approaches.

Incidental discovery of interstitial lung disease: diagnostic approach, surveillance and perspectives

The incidental discovery of pre-clinical interstitial lung disease (ILD) has led to the designation of interstitial lung abnormalities (ILA), a radiological entity defined as the incidental finding of computed tomography (CT) abnormalities affecting more than 5% of any lung zone. Two recent documents have redefined the borders of this entity and made the recommendation to monitor patients with ILA at risk of progression. In this narrative review, we will focus on some of the limits of the current approach, underlying the potential for progression to full-blown ILD of some patients with ILA and the numerous links between subpleural fibrotic ILA and idiopathic pulmonary fibrosis (IPF). Considering the large prevalence of ILA in the general population (7%), restricting monitoring only to cases considered at risk of progression appears a reasonable approach. However, this suggestion should not prevent pulmonary physicians from pursuing an early diagnosis of ILD and timely treatment where appropriate. In cases of suspected ILD, whether found incidentally or not, the pulmonary physician is still required to make a correct ILD diagnosis according to current guidelines, and eventually treat the patient accordingly.

In patients with interstitial lung abnormalities (ILA), monitoring of those at risk of progression is currently recommended, and pulmonary physicians should pursue an early diagnosis when ILA become clinically significant to facilitate timely treatment https://bit.ly/3HKOQc8

Unbalanced IDO1/IDO2 Endothelial Expression and Skewed Keynurenine Pathway in the Pathogenesis of COVID-19 and Post-COVID-19 Pneumonia

Despite intense investigation, the pathogenesis of COVID-19 and the newly defined long COVID-19 syndrome are not fully understood. Increasing evidence has been provided of metabolic alterations characterizing this group of disorders, with particular relevance of an activated tryptophan/kynurenine pathway as described in this review. Recent histological studies have documented that, in COVID-19 patients, indoleamine 2,3-dioxygenase (IDO) enzymes are differentially expressed in the pulmonary blood vessels, i.e., IDO1 prevails in early/mild pneumonia and in lung tissues from patients suffering from long COVID-19, whereas IDO2 is predominant in severe/fatal cases. We hypothesize that IDO1 is necessary for a correct control of the vascular tone of pulmonary vessels, and its deficiency in COVID-19 might be related to the syndrome’s evolution toward vascular dysfunction. The complexity of this scenario is discussed in light of possible therapeutic manipulations of the tryptophan/kynurenine pathway in COVID-19 and post-acute COVID-19 syndromes.

Is the epithelial barrier hypothesis the key to understanding the higher incidence and excess mortality during COVID-19 pandemic? The case of Northern Italy

The high incidence and increased mortality of COVID-19 make Italy among the most impacted countries by SARS-CoV-2 outbreak. In the beginning of the pandemic, Northern regions accounted for 40% of cases and 45% of deaths from COVID-19 in Italy. Several factors have been suggested to explain the higher incidence and excess mortality from COVID-19 in these regions. It is noticed that Northern Italian regions, and particularly the cities in Po Valley, are the areas with the highest air pollution due to commercial vehicle traffic, industry and a stagnant meteorological condition, with one of the highest levels in Italy and Europe of fine particulate matter 2.5 micron or smaller in size (PM2.5). PM2.5, the major environmental pollutant deriving mainly by factory and automobile exhaust emissions and coal combustion, increases the expression of angiotensin-converting enzyme 2, the epithelial cell entry receptor for SARS-CoV-2, and thus increase the susceptibility to this virus. The epithelial barrier hypothesis proposes that many diverse diseases may rise from the disruption of epithelial barrier of skin, respiratory tract and gastrointestinal system, including allergic diseases, metabolic and autoimmune diseases, and chronic neuropsychiatric conditions. There is evidence of a close correlation between air pollution and airway epithelial barrier dysfunction. Air pollution, causing lung epithelial barrier dysfunction, may contribute to local chronic inflammation, microbiome dysbiosis and impaired antiviral immune response against SARS-CoV-2, all of which contribute to the high incidence and excess mortality from COVID-19. In addition, air pollution and epithelial barrier dysfunction contribute also to the higher prevalence of several comorbidities of COVID-19, such as diabetes, chronic obstructive pulmonary disease and obesity, which have been identified as risk factors for mortality of COVID-19. In this article, on the basis of epidemiological and environmental monitoring data in Northern Italy, it is suggested that epithelial barrier hypothesis may help to understand the excess burden and mortality from COVID-19.

Chest CT of Lung Injury 1 Year after COVID-19 Pneumonia: The CovILD Study

Background

The long-term pulmonary sequelae of COVID-19 is not well known.

Purpose

To characterize patterns and rates of improvement of chest CT abnormalities 1 year after COVID-19 pneumonia.

Materials and Methods

This was a secondary analysis of a prospective, multicenter observational cohort study conducted from April 29 to August 12, 2020, to assess pulmonary abnormalities at chest CT approximately 2, 3, and 6 months and 1 year after onset of COVID-19 symptoms. Pulmonary findings were graded for each lung lobe using a qualitative CT severity score (CTSS) ranging from 0 (normal) to 25 (all lobes involved). The association of demographic and clinical factors with CT abnormalities after 1 year was assessed with logistic regression. The rate of change of the CTSS at follow-up CT was investigated by using the Friedmann test.

Results

Of 142 enrolled participants, 91 underwent a 1-year follow-up CT examination and were included in the analysis (mean age, 59 years ± 13 [SD]; 35 women [38%]). In 49 of 91 (54%) participants, CT abnormalities were observed: 31 of 91 (34%) participants showed subtle subpleural reticulation, ground-glass opacities, or both, and 18 of 91 (20%) participants had extensive ground-glass opacities, reticulations, bronchial dilation, microcystic changes, or a combination thereof. At multivariable analysis, age of more than 60 years (odds ratio [OR], 5.8; 95% CI: 1.7, 24; P = .009), critical COVID-19 severity (OR, 29; 95% CI: 4.8, 280; P < .001), and male sex (OR, 8.9; 95% CI: 2.6, 36; P < .001) were associated with persistent CT abnormalities at 1-year follow-up. Reduction of CTSS was observed in participants at subsequent follow-up CT (P < .001); during the study period, 49% (69 of 142) of participants had complete resolution of CT abnormalities. Thirty-one of 49 (63%) participants with CT abnormalities showed no further improvement after 6 months.

Conclusion

Long-term CT abnormalities were common 1 year after COVID-19 pneumonia.

© RSNA, 2022

Online supplemental material is available for this article.

See also the editorial by Leung in this issue.

Pre- and post-COVID practice of interventional pulmonology in adults in Portugal

INTRODUCTION AND OBJECTIVES

There is a lack of information regarding bronchoscopy practice in adults in Portugal. Our objective was to obtain an overview of the characteristics, resources, techniques and behaviors in national interventional pulmonology (IP) units, before and after SARS-CoV-2 outbreak.

MATERIALS AND METHODS

An online survey was developed by an expert panel with a total of 46 questions comprising the specifications of each unit, namely physical space, equipment, staff, procedure planning, monitoring, technical differentiation, and numbers pre- and post-COVID-19. Forty-one interventional pulmonology centers were invited to participate between April and May 2021.

RESULTS

37 units (90.2%) responded to the survey. The majority (64.9%) have a fully dedicated space with a weekly presence of ≥3 chest physicians (82.1%) and support of an anesthesiologist on specific days (48.6%). There is marked heterogeneity in the IP unit's equipment, and 56.8% acquired disposable bronchoscopes after COVID-19 pandemics. Pre-bronchoscopy hemogram, platelet count and coagulation tests are regularly asked by more than 90% of the units, even when deep sedation or biopsies are not planned. In 97.3% of cases, topical anesthesia and midazolam are utilized. Propofol (21.6%) and fentanyl (29.7%) are occasionally employed in some institutions. Most units use ancillary sampling techniques to diagnose central or peripheral lesions, with radial EBUS being used for guidance of distal procedures in 37.8% of centers, linear EBUS and EUS-B-FNA for mediastinal diagnosis and/or staging in 45.9% and 27.0% of units, respectively. Cryobiopsies are used by 21.6% of respondents to diagnose diffuse lung diseases. Rigid bronchoscopy is performed in 37.8% of centers. There was a decrease in the number of flexible (p < 0.001) and rigid (p = 0.005) bronchoscopies and an upscale of personal protective equipment (PPE) during the COVID-19 outbreak.

CONCLUSIONS

IP units have variable bronchoscopic practices, but during the COVID-19 pandemic, they complied with most international recommendations, as elective procedures were postponed and PPE levels increased.

Clinical, radiological, and transbronchial biopsy findings in patients with long COVID-19: a case series

This brief communication demonstrates the correlation of persistent respiratory symptoms with functional, tomographic, and transbronchial pulmonary biopsy findings in patients with COVID-19 who had a long follow-up period. We report a series of six COVID-19 patients with pulmonary involvement who presented with persistent dyspnea within 4-15 months of discharge. We performed transbronchial biopsies, and the histopathological pattern consistently demonstrated peribronchial remodeling with interstitial pulmonary fibrosis. Therefore, lung biopsy may be useful in the approach of patients with long COVID-19, although the type of procedure, its precise indication, and the moment to perform it are yet to be clarified.

(Brazilian Registry of Clinical Trials-ReBEC; identifier: RBR-8j9kqy [http://www.ensaiosclinicos.gov.br])

Clinical, radiological, and pathological findings in patients with persistent lung disease following SARS-CoV-2 infection

Some patients experience pulmonary sequelae after SARS-CoV-2 infection, ranging from self-limited abnormalities to major lung diseases. Morphological analysis of lung tissue may help our understanding of pathogenic mechanisms and help to provide consistent personalised management. The aim of this study was to ascertain morphological and immunomolecular features of lung tissue. Transbronchial lung cryobiopsy was carried out in patients with persistent symptoms and computed tomography suggestive of residual lung disease after recovery from SARS-CoV-2 infection. 164 patients were referred for suspected pulmonary sequelae after COVID-19; 10 patients with >5% parenchymal lung disease underwent lung biopsy. The histological pattern of lung disease was not homogeneous and three different case clusters could be identified, which was mirrored by their clinical and radiological features. Cluster 1 (“chronic fibrosing”) was characterised by post-infection progression of pre-existing interstitial pneumonias. Cluster 2 (“acute/subacute injury”) was characterised by different types and grades of lung injury, ranging from organising pneumonia and fibrosing nonspecific interstitial pneumonia to diffuse alveolar damage. Cluster 3 (“vascular changes”) was characterised by diffuse vascular increase, dilatation and distortion (capillaries and venules) within otherwise normal parenchyma. Clusters 2 and 3 had immunophenotypical changes similar to those observed in early/mild COVID-19 pneumonias (abnormal expression of STAT3 in hyperplastic pneumocytes and PD-L1, IDO and STAT3 in endothelial cells). This is the first study correlating histological/immunohistochemical patterns with clinical and radiological pictures of patients with post-COVID lung disease. Different phenotypes with potentially different underlying pathogenic mechanisms have been identified.

Post-COVID lung disease is not a single entity, but includes different subtypes, each of them potentially requiring separate and different managementhttps://bit.ly/3BJDeUF

Evolution of pathological findings in surveillance biopsies of lung transplant recipients infected with SARS-CoV-2

Background

Previous reports of coronavirus disease 2019 (COVID‐19) following lung transplantation generally described a grim prognosis, but these were anecdotal case series of symptomatic patients. A systematic study of the outcomes and pathology of SARS‐CoV‐2 infection in a large cohort of lung transplant patients is lacking.

Methods

To determine the histopathologic evolution of COVID‐19 in lung transplant recipients, we identified all patients who underwent surveillance transbronchial biopsies at our institution, tested positive for SARS‐CoV‐2, and had multiple pathology specimens available for evaluation. Histology was reviewed and immunofluorescence for SARS‐CoV‐2 nucleocapsid protein was performed.

Results

Ten patients met inclusion criteria. Half (5/10) had incidental diagnosis on routine respiratory pathogen testing at the time of transbronchial biopsy. Six patients were hospitalized, with three requiring intensive care unit (ICU) admission. One patient died. Two specimens showed new onset International Society for Heart and Lung Transplantation (ISHLT) Grade A2 rejection at or following diagnosis. One patient developed bronchiolitis obliterans 111 days following diagnosis and 1 year post transplant. Two patients had organizing pneumonia at diagnosis and three patients showed evolving lung injury following diagnosis. The SARS‐CoV‐2 nucleocapsid protein was detected in a subset of samples at diagnosis and up to 111 days following diagnosis.

Conclusions

Overall, the pathology of SARS‐CoV‐2 infection in lung transplant patients is varied, ranging from no pathologic alterations to organizing pneumonia and lung injury. The pathology findings did not necessarily correlate with clinical acuity, as one patient admitted to the ICU had normal pathology. These findings may be generalizable to non‐transplant patients and require more follow‐up regarding long‐term outcomes.

How COVID-19 interacts with interstitial lung disease

The global pandemic caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has had far-reaching impacts on patients with interstitial lung disease (ILD), from diagnosis to management. In addition, after infection, persistent parenchymal change is associated with ongoing symptoms and functional impairment even in patients without pre-existing lung disease. The challenge of investigating and treating these patients has often fallen to ILD physicians. This review therefore seeks to explore the relationship between COVID-19 and the interstitium, as well as the model of care for patients with pre-existing ILD and those patients with persistent disease following recovery from their initial infection.

COVID-19 has had profound effects on patients with pre-existing interstitial lung disease, and there is growing interest in the effect on the lung parenchyma in patients recovering from acute infection. https://bit.ly/33M5s4x

Pathophysiology of coronavirus-19 disease acute lung injury

PURPOSE OF REVIEW

More than 230 million people have tested positive for severe acute respiratory syndrome-coronavirus-2 infection globally by September 2021. The infection affects primarily the function of the respiratory system, where ∼20% of infected individuals develop coronavirus-19 disease (COVID-19) pneumonia. This review provides an update on the pathophysiology of the COVID-19 acute lung injury.

RECENT FINDINGS

In patients with COVID-19 pneumonia admitted to the intensive care unit, the PaO2/FiO2 ratio is typically <26.7 kPa (200 mmHg), whereas lung volume appears relatively unchanged. This hypoxaemia is likely determined by a heterogeneous mismatch of pulmonary ventilation and perfusion, mainly associated with immunothrombosis, endothelialitis and neovascularisation. During the disease, lung weight, elastance and dead space can increase, affecting respiratory drive, effort and dyspnoea. In some severe cases, COVID-19 pneumonia may lead to irreversible pulmonary fibrosis.

SUMMARY

This review summarises the fundamental pathophysiological features of COVID-19 in the context of the respiratory system. It provides an overview of the key clinical manifestations of COVID-19 pneumonia, including gas exchange impairment, altered pulmonary mechanics and implications of abnormal chemical and mechanical stimuli. It also critically discusses the clinical implications for mechanical ventilation therapy.

Fatal cytokine release syndrome by an aberrant FLIP/STAT3 axis

Inflammatory responses rapidly detect pathogen invasion and mount a regulated reaction. However, dysregulated anti-pathogen immune responses can provoke life-threatening inflammatory pathologies collectively known as cytokine release syndrome (CRS), exemplified by key clinical phenotypes unearthed during the SARS-CoV-2 pandemic. The underlying pathophysiology of CRS remains elusive. We found that FLIP, a protein that controls caspase-8 death pathways, was highly expressed in myeloid cells of COVID-19 lungs. FLIP controlled CRS by fueling a STAT3-dependent inflammatory program. Indeed, constitutive expression of a viral FLIP homolog in myeloid cells triggered a STAT3-linked, progressive, and fatal inflammatory syndrome in mice, characterized by elevated cytokine output, lymphopenia, lung injury, and multiple organ dysfunctions that mimicked human CRS. As STAT3-targeting approaches relieved inflammation, immune disorders, and organ failures in these mice, targeted intervention towards this pathway could suppress the lethal CRS inflammatory state.

Sildenafil for treating patients with COVID-19 and perfusion mismatch: a pilot randomized trial

BACKGROUND

SARS-CoV-2 seems to affect the regulation of pulmonary perfusion. Hypoperfusion in areas of well-aerated lung parenchyma results in a ventilation-perfusion mismatch that can be characterized using subtraction computed tomography angiography (sCTA). This study aims to evaluate the efficacy of oral sildenafil in treating COVID-19 inpatients showing perfusion abnormalities in sCTA.

METHODS

Triple-blinded, randomized, placebo-controlled trial was conducted in Chile in a tertiary-care hospital able to provide on-site sCTA scans and ventilatory support when needed between August 2020 and March 2021. In total, 82 eligible adults were admitted to the ED with RT-PCR-confirmed or highly probable SARS-COV-2 infection and sCTA performed within 24 h of admission showing perfusion abnormalities in areas of well-aerated lung parenchyma; 42 were excluded and 40 participants were enrolled and randomized (1:1 ratio) once hospitalized. The active intervention group received sildenafil (25 mg orally three times a day for seven days), and the control group received identical placebo capsules in the same way. Primary outcomes were differences in oxygenation parameters measured daily during follow-up (PaO₂/FiO₂ ratio and A-a gradient). Secondary outcomes included admission to the ICU, requirement of non-invasive ventilation, invasive mechanical ventilation (IMV), and mortality rates. Analysis was performed on an intention-to-treat basis.

RESULTS

Totally, 40 participants were enrolled (20 in the placebo group and 20 in the sildenafil group); 33 [82.5%] were male; and median age was 57 [IQR 41-68] years. No significant differences in mean PaO₂/FiO₂ ratios and A-a gradients were found between groups (repeated-measures ANOVA p = 0.67 and p = 0.69). IMV was required in 4 patients who received placebo and none in the sildenafil arm (logrank p = 0.04). Patients in the sildenafil arm showed a significantly shorter median length of hospital stay than the placebo group (9 IQR 7-12 days vs. 12 IQR 9-21 days, p = 0.04).

CONCLUSIONS

No statistically significant differences were found in the oxygenation parameters. Sildenafil treatment could have a potential therapeutic role regarding the need for IMV in COVID-19 patients with specific perfusion patterns in sCTA. A large-scale study is needed to confirm these results.

TRIAL REGISTRATION

Sildenafil for treating patients with COVID-19 and perfusion mismatch: a pilot randomized trial, NCT04489446, Registered 28 July 2020, https://clinicaltrials.gov/ct2/show/NCT04489446 .

Acute lung injury-from cannabis to COVID

Recent world events have refocused attention on the pathology associated with clinical acute respiratory distress syndrome (ARDS). The vast majority of cases of clinical ARDS will have diffuse alveolar damage (DAD) histologically, but other histologies may occur less frequently. The aim of this paper is to provide a review of the pathology of DAD and acute fibrinous and organizing pneumonia and provide insights into the pathologic features associated with the E-cigarette/vaping-associated lung-injury outbreak and the ongoing SARS-CoV-2 pandemic.

Recovering from a pandemic: pulmonary fibrosis after SARS-CoV-2 infection

Acute manifestations of SARS-CoV-2 infection continue to impact the lives of many across the world. Post-acute sequelae of coronavirus disease 2019 (COVID-19) may affect 10–30% of survivors of COVID-19, and post-acute sequelae of COVID-19 (PASC)-pulmonary fibrosis is a long-term outcome associated with major morbidity. Data from prior coronavirus outbreaks (severe acute respiratory syndrome and Middle East respiratory syndrome) suggest that pulmonary fibrosis will contribute to long-term respiratory morbidity, suggesting that PASC-pulmonary fibrosis should be thoroughly screened for through pulmonary function testing and cross-sectional imaging. As data accumulates on the unique pathobiologic mechanisms underlying critical COVID-19, a focus on corollaries to the subacute and chronic profibrotic phenotype must be sought as well. Key aspects of acute COVID-19 pathobiology that may account for increased rates of pulmonary fibrosis include monocyte/macrophage–T-cell circuits, profibrotic RNA transcriptomics, protracted elevated levels of inflammatory cytokines, and duration of illness and ventilation. Mechanistic understanding of PASC-pulmonary fibrosis will be central in determining therapeutic options and will ultimately play a role in transplant considerations. Well-designed cohort studies and prospective clinical registries are needed. Clinicians, researchers and healthcare systems must actively address this complication of PASC to minimise disability, maximise quality of life and confront a post-COVID-19 global health crisis.

A complication of COVID-19, PASC-pulmonary fibrosis, has the potential to become a global respiratory health crisis. Dedicated surveillance, mechanistic understanding and clinical and research efforts are needed to confront this emerging sequela of COVID-19.https://bit.ly/3GEyB04

Alveolar type II cells and pulmonary surfactant in COVID-19 era

In this review, we discuss the role of pulmonary surfactant in the host defense against respiratory pathogens, including novel coronavirus SARS-CoV-2. In the lower respiratory system, the virus uses angiotensin-converting enzyme 2 (ACE2) receptor in conjunction with serine protease TMPRSS2, expressed by alveolar type II (ATII) cells as one of the SARS-CoV-2 target cells, to enter. ATII cells are the main source of surfactant. After their infection and the resulting damage, the consequences may be severe and may include injury to the alveolar-capillary barrier, lung edema, inflammation, ineffective gas exchange, impaired lung mechanics and reduced oxygenation, which resembles acute respiratory distress syndrome (ARDS) of other etiology. The aim of this review is to highlight the key role of ATII cells and reduced surfactant in the pathogenesis of the respiratory form of COVID-19 and to emphasize the rational basis for exogenous surfactant therapy in COVID-19 ARDS patients.

The microglial NLRP3 inflammasome is involved in human SARS-CoV-2 cerebral pathogenicity: A report of three post-mortem cases

We herein report, by using confocal immunofluorescence, the colocalization of the SARS-CoV-2 nucleocapsid within neurons, astrocytes, oligodendrocytes and microglia in three deceased COVID-19 cases, of between 78 and 85 years of age at death. The viral nucleocapsid was detected together with its ACE2 cell entry receptor, as well as the NLRP3 inflammasome in cerebral cortical tissues. It is noteworthy that NLRP3 was colocalized with CD68 + macrophages in the brain and lung of the deceased, suggesting the critical role of this type of inflammasome in SARS-CoV-2 lesions of the nervous system/lungs and supporting its potential role as a therapeutic target.

Lung histopathologic clusters in severe COVID-19: a link between clinical picture and tissue damage

BACKGROUND

Autoptic pulmonary findings have been described in severe COVID-19 patients, but evidence regarding the correlation between clinical picture and lung histopathologic patterns is still weak.

METHODS

This was a retrospective cohort observational study conducted at the referral center for infectious diseases in northern Italy. Full lung autoptic findings and clinical data of patients who died from COVID-19 were analyzed. Lung histopathologic patterns were scored according to the extent of tissue damage. To consider coexisting histopathologic patterns, hierarchical clustering of histopathologic findings was applied.

RESULTS

Whole pulmonary examination was available in 75 out of 92 full autopsies. Forty-eight hospitalized patients (64%), 44 from ICU and four from the medical ward, had complete clinical data. The histopathologic patterns had a time-dependent distribution with considerable overlap among patterns. Duration of positive-pressure ventilation (p < 0.0001), mean positive end-expiratory pressure (PEEP) (p = 0.007), worst serum albumin (p = 0.017), interleukin 6 (p = 0.047), and kidney SOFA (p = 0.001) differed among histopathologic clusters. The amount of PEEP for long-lasting ventilatory treatment was associated with the cluster showing the largest areas of early and late proliferative diffuse alveolar damage. No pharmacologic interventions or comorbidities affected the lung histopathology.

CONCLUSIONS

Our study draws a comprehensive link between the clinical and pulmonary histopathologic findings in a large cohort of COVID-19 patients. These results highlight that the positive end-expiratory pressures and the duration of the ventilatory treatment correlate with lung histopathologic patterns, providing new clues to the knowledge of the pathophysiology of severe SARS-CoV-2 pneumonia.

Comorbidity-associated glutamine deficiency is a predisposition to severe COVID-19

SARS-CoV-2 vaccinations have greatly reduced COVID-19 cases, but we must continue to develop our understanding of the nature of the disease and its effects on human immunity. Previously, we suggested that a dysregulated STAT3 pathway following SARS-Co-2 infection ultimately leads to PAI-1 activation and cascades of pathologies. The major COVID-19-associated metabolic risks (old age, hypertension, cardiovascular diseases, diabetes, and obesity) share high PAI-1 levels and could predispose certain groups to severe COVID-19 complications. In this review article, we describe the common metabolic profile that is shared between all of these high-risk groups and COVID-19. This profile not only involves high levels of PAI-1 and STAT3 as previously described, but also includes low levels of glutamine and NAD+, coupled with overproduction of hyaluronan (HA). SARS-CoV-2 infection exacerbates this metabolic imbalance and predisposes these patients to the severe pathophysiologies of COVID-19, including the involvement of NETs (neutrophil extracellular traps) and HA overproduction in the lung. While hyperinflammation due to proinflammatory cytokine overproduction has been frequently documented, it is recently recognized that the immune response is markedly suppressed in some cases by the expansion and activity of MDSCs (myeloid-derived suppressor cells) and FoxP3+ Tregs (regulatory T cells). The metabolomics profiles of severe COVID-19 patients and patients with advanced cancer are similar, and in high-risk patients, SARS-CoV-2 infection leads to aberrant STAT3 activation, which promotes a cancer-like metabolism. We propose that glutamine deficiency and overproduced HA is the central metabolic characteristic of COVID-19 and its high-risk groups. We suggest the usage of glutamine supplementation and the repurposing of cancer drugs to prevent the development of severe COVID-19 pneumonia.

Clinical Utility of Surgical Lung Biopsy for Patients with Acute Respiratory Distress Syndrome: A Systematic Review and Meta-Analysis

BACKGROUND

Surgical lung biopsy (SLB) is performed in patients with acute respiratory distress syndrome (ARDS); however, its clinical utility remains unclear.

OBJECTIVES

We categorized the pathological diagnoses and investigated the predictive value for short-term mortality.

METHOD

Three electronic databases (MEDLINE, the Cochrane Central Register of Controlled Trials, and ClinicalTrials.gov) were searched for the included studies. The QUADAS-2 was used to evaluate the risk of bias and its applicability. The types and populations of pathological diagnoses were investigated. The pooled sensitivity, positive likelihood ratio (LR+), negative likelihood ratio (LR-), and diagnostic odds ratio (DOR) were estimated at a fixed specificity. Hierarchical summary receiver operating characteristic curves were drawn.

RESULTS

A total of 16 studies that enrolled 758 patients were included. The pathological diagnoses were as follows: diffuse alveolar damage (DAD) 29.9%; infection 24.7%; interstitial lung disease 17.2%; malignancy 3.6%; cardiovascular disease 3.6%; drug toxicity 2.3%; connective tissue disease 2.2%; allergic disease 1.1%; and nonspecific diagnosis 15.4%. To predict short-term mortality, 13 studies that enrolled 613 patients used DAD as an index test and recorded a mortality rate of 56.9% (349 of 613 patients). A total of 3 studies that used index tests other than DAD were excluded. The pooled sensitivity, fixed specificity, LR+, LR-, and DOR were 0.46 (95% confidence interval [CI]: 0.29-0.56), 0.69, 1.48 (95% CI: 0.92-1.81), 0.78 (95% CI: 0.63-1.03), and 1.90 (95% CI: 0.89-2.86), respectively.

CONCLUSIONS

SLB is unlikely to provide a specific diagnosis and should not be recommended for confirming DAD or predicting ARDS prognosis.

Post-COVID-19 interstitial lung disease presenting with profound hypoxemia: Report of three cases demonstrating a good response to high-dose corticosteroid therapy

Coronavirus disease 2019 (COVID-19) is caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), which leads to critical pneumonia, although the clinical courses vary. In some cases, COVID-19 pneumonia causes secondary pulmonary fibrosis, which can retain radiological changes and prolong respiratory symptoms. Interstitial lung disease (ILD) secondary to COVID-19 is thought to be caused by multiple pathologies, such as excessive cytokines and abnormal repair processes elaborated by lung cells (epithelium, mesenchyme, and alveolar macrophages) after lung injury rather than viral invasion itself. Immunosuppression therapy may improve chronic respiratory symptoms and radiological changes in post-COVID-19 ILD, although the treatment is not yet established. Herein, we report three patients with post-COVID-19 ILD who presented with profound hypoxemia that had a good response to high-dose corticosteroid therapy. Further and larger studies are needed to establish post-COVID-19 ILD.

Characteristics of COVID-19 Pneumonia Survivors With Resting Normoxemia and Exercise-Induced Desaturation

BACKGROUND

Survivors of coronavirus disease 2019 (COVID-19) associated pneumonia may show exercise-induced desaturation. We wondered whether these individuals show physiologic and symptom characteristics similar to individuals with chronic respiratory diseases with exercise-induced desaturation, namely COPD or interstitial lung diseases (ILD). We evaluated lung function, exercise capacity, and symptoms in these individuals compared with individuals with COPD or ILD and exercise-induced desaturation.

METHODS

Survivors of COVID-19 associated pneumonia (study individuals), normoxemic at rest with exercise-induced desaturation, underwent assessment of dyspnea, dynamic lung volumes, carbon monoxide diffusion capacity, and the 6-min walk test. Data of individuals with COPD or with ILD and exercise-induced desaturation were also retrospectively analyzed.

RESULTS

FVC was lower in individuals with COVID-19 or ILD than in those with COPD. Individuals who had COVID-19 walked < 70% of predicted and, as a whole, had a 6-min walk test performance similar to individuals with ILD but walked significantly less, showed more severe leg fatigue and dyspnea during exercise, and more exercise-induced desaturation than individuals with COPD.

CONCLUSIONS

Survivors of COVID-19 associated pneumonia, who were normoxemic at rest with exercise-induced desaturation, had alterations in lung function, exercise capacity, and symptoms similar to individuals with ILD but more severe than individuals with COPD and exercise-induced desaturation.

The role of endotheliitis in COVID-19: Real-world experience of 11 190 patients and literature review for a pathophysiological map to clinical categorisation

OBJECTIVE

COVID-19 may yield a variety of clinical pictures, differing from pneumonitis to Acute Respiratory Distress Syndrome along with vascular damage in the lung tissue, named endotheliitis. To date, no specific treatment strategy was approved for the prevention or treatment of COVID-19 in terms of endotheliitis-related comorbidities. Here, we presented our treatment strategies for 11 190 COVID-19 patients depending on categorisation by the severity of both the respiratory and vascular distress and presented the manifestations of endotheliitis in skin, lung and brain tissues according to the different phases of COVID-19.

METHODS

After a retrospective examination, patients were divided into three groups according to their repercussions of vascular distress, which were represented by radiological, histopathological and clinical findings. We presented the characteristics and courses of seven representative and complicated cases which demonstrate different phases of the disease and discussed the treatment strategies in each group.

RESULTS

Among 11 190 patients, 9294 patients met the criteria for Group A, and 1376 patients were presented to our clinics with Group B characteristics. Among these patients, 1896 individuals (Group B and Group C) were hospitalised. While 1220 inpatients were hospitalised within the first 10 days after the diagnosis, 676 of them were worsened and hospitalised 10 days after their diagnosis. Among hospitalised patients, 520 of them did not respond to group A and B treatments and developed hypoxemic respiratory failure (Group C) and 146 individuals needed ventilator support and were followed in the intensive care unit, and 43 (2.2%) patients died.

CONCLUSION

Distinctive manifestations in each COVID-19 patient, including non-respiratory conditions in the acute phase and the emerging risk of long-lasting complications, suggest that COVID-19 has endotheliitis-centred thrombo-inflammatory pathophysiology. Daily evaluation of clinical, laboratory and radiological findings of patients and deciding appropriate pathophysiological treatment would help to reduce the mortality rate of COVID-19.