Daily Respiratory Research Analysis

The mitochondrial respiratory chain comprises four multimeric complexes (CI-CIV) that drive oxidative phosphorylation by transferring electrons to oxygen and generating the proton gradient required for ATP synthesis. These complexes can associate into supercomplexes (SCs), such as the CI + CIII₂ + CIV respirasome, but how SCs form, by joining preassembled complexes or by engaging partially assembled intermediates, remains unresolved. Here, we use cryo-electron microscopy to determine high-resolution structures of native human CI + CIII₂ + CIV late-assembly intermediates. Together with biochemical analyses, these structures show that respirasome biogenesis concludes with the final maturation of CIV while it is associated with fully assembled CI and CIII₂. We identify HIGD2A as a placeholder factor within isolated and supercomplexed CIV that is replaced by subunit NDUFA4 during the last step of CIV and respirasome assembly. This mechanism suggests that placeholders such as HIGD2A act as molecular timers, preventing premature incorporation of NDUFA4 or its isoforms and ensuring the orderly progression of pre-SC particles into functional respirasomes. Since defects in CIV assembly, including NDUFA4 deficiencies, cause severe encephalomyopathies and neurodegenerative disorders, understanding the molecular architecture and assembly pathways of isolated and supercomplexed CIV offers insight into the pathogenic mechanisms underlying these conditions.

BACKGROUND: The COVID-19 pandemic highlighted a global shortage of, and inequity of access to, medical oxygen. Understanding patient outcomes and the capacities of health facilities to provide respiratory support including oxygen is key to matching need and demand. We report results from a global study including 23 low-income and middle-income countries. METHODS: For this prospective, observational cohort study, consecutive patients aged 12 years or older with suspected or confirmed COVID-19 and evidence of respiratory distress were prospectively recruited within 24 h of hospital admission. Hospitals from 23 low-income and middle-income countries were included, representing all WHO regions. Baseline demographic and clinical data were collected, and daily follow-ups were recorded for in-hospital outcomes and respiratory support types. At the facility level, we assessed sources of oxygen and electricity, infrastructural and staffing capacity for critical care provision, and the capabilities of the facility for advanced respiratory support. The primary outcome was 30-day in-hospital mortality. This study was registered on ClinicalTrials.gov (NCT04918875). FINDINGS: Between Jan 24 and Nov 22, 2022, 56 sites took part. Of 53 726 patients screened, 3070 were enrolled. 1814 (61·6%) of 2947 patients had two or more underlying medical conditions and initially received oxygen through nasal cannula or non-rebreather face masks with reservoir. Invasive mechanical ventilation was most frequently used in patients recruited in the Americas (75 [26·4%] of 284 patients) and in the Eastern Mediterranean (90 [18·0%] of 499 patients). The overall mortality was 649 (23·4%) of 2779 patients, varying by region from 53 (10·5%) of 506 patients in South-East Asia to 286 (37·6%) of 760 patients in Africa. Mortality was associated with the maximum level of respiratory support received: from 17 (8·6%) of 198 patients who received no oxygen, 99 (38·4%) of 258 patients for non-rebreather reservoir bags, and 205 (62·9%) of 326 for invasive ventilation. INTERPRETATION: The availability and use of oxygen support options in low-income and middle-income countries are highly variable but appear significantly less in the African region. Mortality might be associated with a lack of access to oxygen, which varied across WHO regions but was highest in Africa. Despite many lessons learned from the COVID-19 pandemic, inequity in access to medical oxygen remains a challenge that WHO and partners must address in the post-pandemic era to avoid preventable deaths. FUNDING: UNITAID.

Excessive activation of the NLRP3 inflammasome drives the pathogenesis of diverse inflammatory diseases. However, the clinical application of NLRP3 inflammasome inhibitors remains a significant challenge. Here, we screen a natural product library of 126 compounds and identify Nimbolide (NIM), a triterpenoid from Azadirachta indica, as a potent suppressor of IL-1β secretion. Cellular studies reveal that NIM dose-dependently suppresses NLRP3 inflammasome activation, thereby the blocking Caspase-1 cleavage, IL-1β release, and pyroptosis in macrophages. Importantly, NIM exhibits high selectivity for NLRP3 inflammasome, showing no significant inhibition of non-NLRP3 inflammasomes. Mechanistically, NIM exerts dual effects by suppressing both NF-κB-dependent priming and NLRP3 inflammasome assembly. Molecular investigations reveal that NIM directly targets the Lys565 within the NLRP3 NACHT domain, thereby hindering inflammasome assembly. Using male C57BL/6 and Nlrp3-knockout mice, we demonstrate that NIM administration effectively alleviates inflammation and pathological damage in models of LPS-induced acute respiratory distress syndrome (ARDS) and DSS-induced ulcerative colitis. Collectively, our findings highlight NIM as a natural inhibitor that targets both the priming and assembly phases of NLRP3 inflammasome activation, offering a dual-modulatory strategy for treating NLRP3-driven inflammatory disorder.