Background: Cells are exposed to elevated levels of CO 2 (hypercapnia) in many diseases. Results: Hypercapnia decreased cell proliferation, which was prevented with ␣-ketoglutarate, IDH2 overexpression, and microRNA-183 inhibition. Conclusion: Hypercapnia causes mitochondrial dysfunction by up-regulation of microRNA-183, which decreases the levels of IDH2. Significance: Hypercapnia causes mitochondrial dysfunction, which is relevant for patients with lung diseases.

Hypercapnia, an elevation of the level of carbon dioxide (CO 2 ) in blood and tissues, is a marker of poor prognosis in chronic obstructive pulmonary disease and other pulmonary disorders. We previously reported that hypercapnia inhibits the expression of TNF and IL-6 and phagocytosis in macrophages in vitro. In the present study, we determined the effects of normoxic hypercapnia (10% CO 2 , 21% O 2 , and 69% N 2 ) on outcomes of Pseudomonas aeruginosa pneumonia in BALB/c mice and on pulmonary neutrophil function. We found that the mortality of P. aeruginosa pneumonia was increased in 10% CO 2 -exposed compared with air-exposed mice. Hypercapnia increased pneumonia mortality similarly in mice with acute and chronic respiratory acidosis, indicating an effect unrelated to the degree of acidosis. Exposure to 10% CO 2 increased the burden of P. aeruginosa in the lungs, spleen, and liver, but did not alter lung injury attributable to pneumonia. Hypercapnia did not reduce pulmonary neutrophil recruitment during infection, but alveolar neutrophils from 10% CO 2 -exposed mice phagocytosed fewer bacteria and produced less H 2 O 2 than neutrophils from air-exposed mice. Secretion of IL-6 and TNF in the lungs of 10% CO 2 -exposed mice was decreased 7 hours, but not 15 hours, after the onset of pneumonia, indicating that hypercapnia inhibited the early cytokine response to infection. The increase in pneumonia mortality caused by elevated CO 2 was reversible when hypercapnic mice were returned to breathing air before or immediately after infection. These results suggest that hypercapnia may increase the susceptibility to and/or worsen the outcome of lung infections in patients with severe lung disease.Keywords: carbon dioxide; pulmonary infection; reactive oxygen species; phagocytosis; inflammation Hypercapnia occurs in patients with severe acute and chronic lung diseases such as chronic obstructive pulmonary disease (COPD), currently the third leading cause of death in the United States (1). Individuals with COPD and other chronic respiratory disorders are also at risk for the development of acute respiratory failure, which may be accompanied by acute or acute-on-chronic hypercapnia. In addition, patients with acute respiratory distress syndrome (ARDS) and status asthmaticus may develop hypercapnia.Hypercapnia has long been recognized as a marker of poor prognosis in patients with COPD, among whom pulmonary infections are a major cause of morbidity and mortality (2-6). Hypercapnia is also an independent risk factor for mortality in hospitalized patients with community-acquired pneumonia and in patients with cystic fibrosis awaiting lung transplantation (7-10). Moreover, hypercapnic patients with acute respiratory failure can develop ventilatorassociated pneumonia, which prolongs intensive care unit and hospital stays, and carries a mortality rate of 33-50% (11). On the other hand, in some studies, hypercapnia accompanying low tidal volume mechanical ventilation ("permissive hypercapnia") has been associated with reduced mor...

Smith-Lemli-Opitz syndrome (SLOS) is a malformation syndrome caused by deficiency of 7-dehydrocholesterol reductase catalysing the last step of cholesterol biosynthesis. This results in an accumulation of 7- and 8-dehydrocholesterol (7 + 8-DHC) and, in most patients, a deficiency of cholesterol. Current therapy consists of dietary cholesterol supplementation, which raises plasma cholesterol levels, but clinical effects have been reported in only a few patients. Hydroxymethylglutaryl-coenzyme A (HMG-CoA) reductase inhibitors were shown to reduce 7 + 8-DHC levels and increase cholesterol concentrations in two small trials with divergent clinical outcome. This retrolective study evaluates the effects of cholesterol only and of cholesterol plus the HMG-CoA reductase inhibitor simvastatin on plasma sterols in 39 SLOS patients and on anthropometric measures in 20 SLOS patients. Cholesterol as well as additional simvastatin decreased the plasma (7 + 8-DHC)/cholesterol ratio. However, the mechanism leading to the decreasing ratio was different. Whereas it was due to an increasing cholesterol concentration in the cholesterol-only cohort, a decreasing 7 + 8-DHC concentration was demonstrated in the cohort receiving additional simvastatin. We could not confirm a positive effect of simvastatin treatment on anthropometric measures or behaviour, as previously reported.

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