SignificanceInherited or acquired defects in mitochondria lead to devastating disorders for which we have no effective general therapies. We recently reported that breathing normobaric 11% O2 prevents neurodegeneration in a mouse model of a pediatric mitochondrial disease, Leigh syndrome. Here we provide updated survival curves of mice treated with varying doses of oxygen and explore eventual causes of death. We explore alternative hypoxia regimens and report that neither intermittent nor moderate hypoxia regimens suffice to prevent neurological disease. Finally, we show that hypoxia can not only prevent, but also reverses the brain lesions in mice with advanced neuropathology. Our preclinical studies will help guide future clinical studies aimed at harnessing hypoxia as a safe and practical therapy.

Graphical AbstractHighlights d Blocking ETC or lactate production reduces cytosolic NAD + / NADH and increases HUFAs d HUFA synthesis by D5D and D6D is a mechanism for glycolytic NAD + recycling d D5D-and D6D-mediated NAD + regeneration can be acutely adaptive in vivo d SLC16A11 and FADS1-3 may influence metabolic risk via impact on cytosolic NAD + /NADH SUMMARY The reactions catalyzed by the delta-5 and delta-6 desaturases (D5D/D6D), key enzymes responsible for highly unsaturated fatty acid (HUFA) synthesis, regenerate NAD + from NADH. Here, we show that D5D/D6D provide a mechanism for glycolytic NAD + recycling that permits ongoing glycolysis and cell viability when the cytosolic NAD + /NADH ratio is reduced, analogous to lactate fermentation. Although lesser in magnitude than lactate production, this desaturase-mediated NAD + recycling is acutely adaptive when aerobic respiration is impaired in vivo.Notably, inhibition of either HUFA synthesis or lactate fermentation increases the other, underscoring their interdependence. Consistent with this, a type 2 diabetes risk haplotype in SLC16A11 that reduces pyruvate transport (thus limiting lactate production) increases D5D/D6D activity in vitro and in humans, demonstrating a chronic effect of desaturase-mediated NAD + recycling. These findings highlight key biologic roles for D5D/D6D activity independent of their HUFA end products and expand the current paradigm of glycolytic NAD + regeneration.

Background Survivors of severe COVID-19 are at risk of impaired health-related quality of life (HRQoL) and persistent physical and psychological disability after ICU and hospital discharge. The subsequent social burden is a major concern. We aimed to assess the short-term HRQoL, physical function and prevalence of post-traumatic stress symptoms of invasively mechanically ventilated COVID-19 patients treated in our ICU. Methods Prospective, observational cohort study in a follow-up clinic. Patients completed a 6-min walking test (6MWT) to assess their cardio-pulmonary function around 2 months (early follow-up) from hospital discharge, the EQ-5D-5L questionnaire for quality of life assessment around 2 months and at 6 months from hospital discharge and an anonymous web-based Impact of Event Scale-Revised (IES-R) questionnaire for Post-Traumatic Stress symptoms at 2 months. Results 47 patients attended our follow-up program, mean age 59 ± 10 years, median pre-morbid Clinical Frailty Scale (CFS) 2 [2–3]. The median distance walked in 6 min was 470 [406–516] m, 83 [67–99]% of the predicted value. Overall 1 out 3 patients and 4/18 (22%) among those with a good functional baseline prior to COVID-19 (CFS of 1 or 2) had lower (84%) than predicted 6MWT. EQ-5D-5L quality of life VAS was 80 [70–90] out of 100 at early follow-up with a slight improvement to 85 [77.5–90] at 6 months. Mobility, self-care and usual activities improved between the two timepoints, while pain/discomfort and depression/anxiety did not improve or got worse. The IES-R total score was greater than the threshold for concern of 1.6 in 27/41(66%) respondents. Conclusions Patients recovering from severe COVID-19 requiring invasive mechanical ventilation surviving hospital discharge present with early mild to moderate functional impairment, mildly reduced quality of life from hospital discharge with an overall improvement of mobility, self-care and the ability of performing usual activities, while a worsening of pain and depression/anxiety symptoms at 6 months and a large proportion of symptoms of post-traumatic distress soon after hospital discharge.

Background International guidelines suggest using a higher (>10 cmH 2 O) positive end-expiratory pressure (PEEP) in patients with moderate-to-severe acute respiratory distress syndrome (ARDS) due to the novel coronavirus disease (COVID-19). However, even if oxygenation generally improves with a higher PEEP, compliance and arterial carbon dioxide tension (PaCO 2 ) frequently do not, as if recruitment was small. Research question Is the potential for lung recruitment small in patients with early ARDS due to COVID-19? Study design and methods Forty patients with ARDS due to COVID-19 were studied in the supine position within three days of endotracheal intubation. They all underwent a PEEP trial, where oxygenation, compliance, and PaCO 2 were measured with 5, 10, and 15 cmH 2 O of PEEP and all other ventilatory settings unchanged. Twenty underwent a whole-lung static computed tomography at 5 and 45 cmH 2 O, and the other twenty at 5 and 15 cmH 2 O of airway pressure. Recruitment and hyperinflation were defined as a decrease in the volume of the non-aerated (density above -100 HU) and an increase in the volume of the over-aerated (density below -900 HU) lung compartments, respectively. Results From 5 to 15 cmH 2 O, oxygenation improved in thirty-six (90%) patients but compliance only in eleven (28%) and PaCO 2 only in fourteen (35%). From 5 to 45 cmH 2 O, recruitment was 351 (161-462) ml and hyperinflation 465 (220-681) ml. From 5 to 15 cmH 2 O, recruitment was 168 (110-202) ml and hyperinflation 121 (63-270) ml. Hyperinflation variably developed in all patients and exceeded recruitment in more than half of them. Interpretation Patients with early ARDS due to COVID-19, ventilated in the supine position, present with a large potential for lung recruitment. Even so, their compliance and PaCO 2 do not generally improve with a higher PEEP, possibly due to hyperinflation.

Intravenous fluid administration is a medical intervention performed worldwide on a daily basis. Nevertheless, only a few physicians are aware of the characteristics of intravenous fluids and their possible effects on plasma acid-base equilibrium. According to Stewart's theory, pH is independently regulated by three variables: partial pressure of carbon dioxide, strong ion difference (SID), and total amount of weak acids (ATOT). When fluids are infused, plasma SID and ATOT tend toward the SID and ATOT of the administered fluid. Depending on their composition, fluids can therefore lower, increase, or leave pH unchanged. As a general rule, crystalloids having a SID greater than plasma bicarbonate concentration (HCO₃-) cause an increase in plasma pH (alkalosis), those having a SID lower than HCO₃- cause a decrease in plasma pH (acidosis), while crystalloids with a SID equal to HCO₃- leave pH unchanged, regardless of the extent of the dilution. Colloids and blood components are composed of a crystalloid solution as solvent, and the abovementioned rules partially hold true also for these fluids. The scenario is however complicated by the possible presence of weak anions (albumin, phosphates and gelatins) and their effect on plasma pH. The present manuscript summarises the characteristics of crystalloids, colloids, buffer solutions and blood components and reviews their effect on acid-base equilibrium. Understanding the composition of intravenous fluids, along with the application of simple physicochemical rules best described by Stewart's approach, are pivotal steps to fully elucidate and predict alterations of plasma acid-base equilibrium induced by fluid therapy.

Sickle cell disease is an inherited disorder of hemoglobin (Hb). During a sickle cell crisis, deoxygenated sickle hemoglobin (deoxyHbS) polymerizes to form fibers in red blood cells (RBCs), causing the cells to adopt "sickled" shapes. Using small molecules to increase the affinity of Hb for oxygen is a potential approach to treating sickle cell disease, because oxygenated Hb interferes with the polymerization of deoxyHbS. We have identified a triazole disulfide compound (4,4'-di(1,2,3-triazolyl)disulfide, designated TD-3), which increases the affinity of Hb for oxygen. The crystal structures of carboxy- and deoxy-forms of human adult Hb (HbA), each complexed with TD-3, revealed that one molecule of the monomeric thiol form of TD-3 (5-mercapto-1H-1,2,3-triazole, designated MT-3) forms a disulfide bond with β-Cys93, which inhibits the salt-bridge formation between β-Asp94 and β-His146. This inhibition of salt bridge formation stabilizes the R-state and destabilizes the T-state of Hb, resulting in reduced magnitude of the Bohr effect and increased affinity of Hb for oxygen. Intravenous administration of TD-3 (100 mg/kg) to C57BL/6 mice increased the affinity of murine Hb for oxygen, and the mice did not appear to be adversely affected by the drug. TD-3 reduced in vitro hypoxia-induced sickling of human sickle RBCs. The percentage of sickled RBCs and the P of human SS RBCs by TD-3 were inversely correlated with the fraction of Hb modified by TD-3. Our study shows that TD-3, and possibly other triazole disulfide compounds that bind to Hb β-Cys93, may provide new treatment options for patients with sickle cell disease.

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Background Prone positioning improves survival in moderate-to-severe acute respiratory distress syndrome (ARDS) unrelated to the novel coronavirus disease (COVID-19). This benefit is probably mediated by a decrease in alveolar collapse and hyperinflation and a more homogeneous distribution of lung aeration, with fewer harms from mechanical ventilation. In this preliminary physiological study we aimed to verify whether prone positioning causes analogue changes in lung aeration in COVID-19. A positive result would support prone positioning even in this other population. Methods Fifteen mechanically-ventilated patients with COVID-19 underwent a lung computed tomography in the supine and prone position with a constant positive end-expiratory pressure (PEEP) within three days of endotracheal intubation. Using quantitative analysis, we measured the volume of the non-aerated, poorly-aerated, well-aerated, and over-aerated compartments and the gas-to-tissue ratio of the ten vertical levels of the lung. In addition, we expressed the heterogeneity of lung aeration with the standardized median absolute deviation of the ten vertical gas-to-tissue ratios, with lower values indicating less heterogeneity. Results By the time of the study, PEEP was 12 (10–14) cmH2O and the PaO2:FiO2 107 (84–173) mmHg in the supine position. With prone positioning, the volume of the non-aerated compartment decreased by 82 (26–147) ml, of the poorly-aerated compartment increased by 82 (53–174) ml, of the normally-aerated compartment did not significantly change, and of the over-aerated compartment decreased by 28 (11–186) ml. In eight (53%) patients, the volume of the over-aerated compartment decreased more than the volume of the non-aerated compartment. The gas-to-tissue ratio of the ten vertical levels of the lung decreased by 0.34 (0.25–0.49) ml/g per level in the supine position and by 0.03 (− 0.11 to 0.14) ml/g in the prone position (p < 0.001). The standardized median absolute deviation of the gas-to-tissue ratios of those ten levels decreased in all patients, from 0.55 (0.50–0.71) to 0.20 (0.14–0.27) (p < 0.001). Conclusions In fifteen patients with COVID-19, prone positioning decreased alveolar collapse, hyperinflation, and homogenized lung aeration. A similar response has been observed in other ARDS, where prone positioning improves outcome. Therefore, our data provide a pathophysiological rationale to support prone positioning even in COVID-19.