Increased Alveolar Epithelial Damage Markers and Inflammasome-Regulated Cytokines Are Associated with Pulmonary Superinfection in ARDS.

Acute respiratory distress syndrome (ARDS) is a life-threatening form of respiratory failure defined by dysregulated immune homeostasis and alveolar epithelial and endothelial damage. Up to 40% of ARDS patients develop pulmonary superinfections, contributing to poor prognosis and increasing mortality. Understanding what renders ARDS patients highly susceptible to pulmonary superinfections is therefore essential. We hypothesized that ARDS patients who develop pulmonary superinfections display a distinct pulmonary injury and pro-inflammatory response pattern. Serum and BALF samples from 52 patients were collected simultaneously within 24 h of ARDS onset. The incidence of pulmonary superinfections was determined retrospectively, and the patients were classified accordingly. Serum concentrations of the epithelial markers soluble receptor for advanced glycation end-products (sRAGE) and surfactant protein D (SP-D) and the endothelial markers vascular endothelial growth factor (VEGF) and angiopoetin-2 (Ang-2) as well as bronchoalveolar lavage fluid concentrations of the pro-inflammatory cytokines interleukin 1ß (IL-1ß), interleukin 18 (IL-18), interleukin 6 (IL-6), and tumor necrosis factor-alpha (TNF-a) were analyzed via multiplex immunoassay. Inflammasome-regulated cytokine IL-18 and the epithelial damage markers SP-D and sRAGE were significantly increased in ARDS patients who developed pulmonary superinfections. In contrast, endothelial markers and inflammasome-independent cytokines did not differ between the groups. The current findings reveal a distinct biomarker pattern that indicates inflammasome activation and alveolar epithelial injury. This pattern may potentially be used in future studies to identify high-risk patients, enabling targeted preventive strategies and personalized treatment approaches.

Impaired ketogenesis ties metabolism to T cell dysfunction in COVID-19.

Anorexia and fasting are host adaptations to acute infection, and induce a metabolic switch towards ketogenesis and the production of ketone bodies, including ß-hydroxybutyrate (BHB)1-6. However, whether ketogenesis metabolically influences the immune response in pulmonary infections remains unclear. Here we show that the production of BHB is impaired in individuals with SARS-CoV-2-induced acute respiratory distress syndrome (ARDS) but not in those with  influenza-induced ARDS. We found that BHB promotes both the survival of and the production of interferon-γ by CD4+ T cells. Applying a metabolic-tracing analysis, we established that BHB provides an alternative carbon source to fuel oxidative phosphorylation (OXPHOS) and the production of bioenergetic amino acids and glutathione, which is important for maintaining the redox balance. T cells from patients with SARS-CoV-2-induced ARDS were exhausted and skewed towards glycolysis, but could be metabolically reprogrammed by BHB to perform OXPHOS, thereby increasing their functionality. Finally, we show in mice that a ketogenic diet and the delivery of BHB as a ketone ester drink restores CD4+ T cell metabolism and function in severe respiratory infections, ultimately reducing the mortality of mice infected with SARS-CoV-2. Altogether, our data reveal that BHB is an alternative source of carbon that promotes T cell responses in pulmonary viral infections, and highlight impaired ketogenesis as a potential confounding factor in severe COVID-19.

Tetracycline ameliorates silica-induced pulmonary inflammation and fibrosis via inhibition of caspase-1.

BACKGROUND: Inhalation of dust containing silica particles is associated with severe pulmonary inflammation and lung injury leading to chronic silicosis including fibrotic remodeling of the lung. Silicosis represents a major global health problem causing more than 45.000 deaths per year. The inflammasome-caspase-1 pathway contributes to the development of silica-induced inflammation and fibrosis via IL-1ß and IL-18 production. Recent studies indicate that tetracycline can be used to treat inflammatory diseases mediated by IL-1ß and IL-18. Therefore, we hypothesized that tetracycline reduces silica-induced lung injury and lung fibrosis resulting from chronic silicosis via limiting IL-1ß and IL-18 driven inflammation. METHODS: To investigate whether tetracycline is a therapeutic option to block inflammasome-caspase-1 driven inflammation in silicosis, we incubated macrophages with silica alone or combined with tetracycline. The in vivo effect of tetracycline was determined after intratracheal administration of silica into the mouse lung. RESULTS: Tetracycline selectively blocks IL-1ß production and pyroptotic cell death via inhibition of caspase-1 in macrophages exposed to silica particles. Consistent, treatment of silica-instilled mice with tetracycline significantly reduced pulmonary caspase-1 activation as well as IL-1ß and IL-18 production, thereby ameliorating pulmonary inflammation and lung injury. Furthermore, prolonged tetracycline administration in a model of chronic silicosis reduced lung damage and fibrotic remodeling. CONCLUSIONS: These findings suggest that tetracycline inhibits caspase-1-dependent production of IL-1ß in response to silica in vitro and in vivo. The results were consistent with tetracycline reducing silica-induced pulmonary inflammation and chronic silicosis in terms of lung injury and fibrosis. Thus, tetracycline could be effective in the treatment of patients with silicosis as well as other diseases involving silicotic inflammation.

SP-D Serum Levels Reveal Distinct Epithelial Damage in Direct Human ARDS.

Acute respiratory distress syndrome (ARDS) is a heterogeneous syndrome with multiple underlying diseases. Particularly epithelial damage results from direct (e.g., pneumonia) rather than indirect lung injury (e.g., nonpulmonary sepsis), which is more likely associated with endothelial damage. Hence, targeting ARDS patients based on their molecular phenotypes is a promising approach to improve outcome. With regard to distinct inflammatory responses and subsequent lung damage in direct ARDS due to the causing pathogen, we quantified markers of epithelial and endothelial damage and pro-inflammatory cytokines in patients with ARDS triggered by bacterial, viral, and atypical pathogen pneumonia or indirect ARDS. The serum levels of interleukin-6 (IL-6) and interleukin-8 (IL-8), lung epithelial injury markers surfactant protein D (SP-D), and soluble receptor for advanced glycation end-products (sRAGE) as well as endothelial injury marker angiopoietin-2 (Ang-2) from 49 patients with distinct types of ARDS were analyzed by multiplex immunoassay. Epithelial damage marker SP-D was significantly higher in direct ARDS caused by viral and atypical pathogens in contrast to ARDS caused by typical bacterial pneumonia and nonpulmonary sepsis. In contrast, sRAGE levels did not differ due to the causing pathogen. Patients with atypical pathogen pneumonia related ARDS showed significantly lower Ang-2 levels compared to patients with viral and indirect ARDS. Patients with viral and atypical pneumonia related ARDS possessed significantly lower serum IL-6 levels compared to bacterial pneumonia related ARDS and IL-6 levels in atypical pneumonia related ARDS were significantly lower than in indirect ARDS. Current findings report a potential difference in ARDS biomarkers due to the underlying disease and pathogen.

Inhibition of Caspase-1 with Tetracycline Ameliorates Acute Lung Injury.

Rationale: Acute respiratory distress syndrome (ARDS) is a heterogeneous syndrome with a mortality of up to 40%. Precision medicine approaches targeting patients on the basis of their molecular phenotypes of ARDS might help to identify effective pharmacotherapies. The inflammasome-caspase-1 pathway contributes to the development of ARDS via IL-1ß and IL-18 production. Recent studies indicate that tetracycline can be used to treat inflammatory diseases mediated by IL-1ß and IL-18, although the molecular mechanism by which tetracycline inhibits inflammasome-caspase-1 signaling remains unknown. Objectives: To identify patients with ARDS characterized by IL-1ß and IL-18 expression and investigate the ability of tetracycline to inhibit inflammasome-caspase-1 signaling in ARDS. Methods: IL-1ß and IL-18 concentrations were quantified in BAL fluid from patients with ARDS. Tetracycline's effects on lung injury and inflammation were assessed in two mouse models of direct (pulmonary) acute lung injury, and its effects on IL-1ß and IL-18 production were assessed by alveolar leukocytes from patients with direct ARDS ex vivo. Murine macrophages were used to further characterize the effect of tetracycline on the inflammasome-caspase-1 pathway. Measurements and Main Results: BAL fluid concentrations of IL-1ß and IL-18 are significantly higher in patients with direct ARDS than those with indirect (nonpulmonary) ARDS. In experimental acute lung injury, tetracycline significantly diminished lung injury and pulmonary inflammation by selectively inhibiting caspase-1-dependent IL-1ß and IL-18 production, leading to improved survival. Tetracycline also reduced the production of IL-1ß and IL-18 by alveolar leukocytes from patients with direct ARDS. Conclusions: Tetracycline may be effective in the treatment of direct ARDS in patients with elevated caspase-1 activity. Clinical Trial registered with www.clinicaltrials.gov (NCT04079426).