Formation of Reactive Oxygen Species in Lung Alveolar Cells: Effect of Vitamin E Deficiency

Nutrition and Lung Growth

Experimental evidence from animal models and epidemiology studies has demonstrated that nutrition affects lung development and may have a lifelong impact on respiratory health. Chronic restriction of nutrients and/or oxygen during pregnancy causes structural changes in the airways and parenchyma that may result in abnormal lung function, which is tracked throughout life. Inadequate nutritional management in very premature infants hampers lung growth and may be a contributing factor in the pathogenesis of bronchopulmonary dysplasia. Recent evidence seems to indicate that infant and childhood malnutrition does not determine lung function impairment even in the presence of reduced lung size due to delayed body growth. This review will focus on the effects of malnutrition occurring at critical time periods such as pregnancy, early life, and childhood, on lung growth and long-term lung function.

Vitamin E deficiency impairs the somatostatinergic receptor-effector system and leads to phosphotyrosine phosphatase overactivation and cell death in the rat hippocampus

Vitamin E plays an essential role in maintaining the structure and function of the nervous system, and its deficiency, commonly associated with fat malabsorption diseases, may reduce neuronal survival. We previously demonstrated that the somatostatinergic system, implicated in neuronal survival control, can be modulated by α-tocopherol in the rat dentate gyrus, increasing cyclic adenosine monophosphate response element binding protein phosphorylation. To gain a better understanding of the molecular actions of tocopherols and examine the link among vitamin E, somatostatin and neuronal survival, we have investigated the effects of a deficiency and subsequent administration of tocopherol on the somatostatin signaling pathway and neuronal survival in the rat hippocampus. No changes in somatostatin expression were detected in vitamin-E-deficient rats. These rats, however, showed a significant increase in the somatostatin receptor density and dissociation constant, which correlated with a significant increase in the protein levels of somatostatin receptors. Nevertheless, vitamin E deficiency impaired the ability of the somatostatin receptors to couple to the effectors adenylyl cyclase and phosphotyrosine phosphatase by diminishing Gi protein functionality. Furthermore, vitamin E deficiency significantly increased phosphotyrosine phosphatase activity and PTPη expression, as well as PKCδ activation, and decreased extracellular-signal-regulated kinase phosphorylation. All these changes were accompanied by an increase in neuronal cell death. Subsequent α-tocopherol administration partially or completely reversed all these values to control levels. Altogether, our results prove the importance of vitamin E homeostasis in the somatostatin receptor-effector system and suggest a possible mechanism by which this vitamin may regulate the neuronal cell survival in the adult hippocampus.

Phospholipase A2 subclasses in acute respiratory distress syndrome

Phospholipases A2 (PLA2) catalyse the cleavage of fatty acids esterified at the sn-2 position of glycerophospholipids. In acute lung injury-acute respiratory distress syndrome (ALI-ARDS) several distinct isoenzymes appear in lung cells and fluid. Some are capable to trigger molecular events leading to enhanced inflammation and lung damage and others have a role in lung surfactant recycling preserving lung function: Secreted forms (groups sPLA2-IIA, -V, -X) can directly hydrolyze surfactant phospholipids. Cytosolic PLA2 (cPLA2-IVA) requiring Ca2+ has a preference for arachidonate, the precursor of eicosanoids which participate in the inflammatory response in the lung. Ca(2+)-independent intracellular PLA2s (iPLA2) take part in surfactant phospholipids turnover within alveolar cells. Acidic Ca(2+)-independent PLA2 (aiPLA2), of lysosomal origin, has additionally antioxidant properties, (peroxiredoxin VI activity), and participates in the formation of dipalmitoyl-phosphatidylcholine in lung surfactant. PAF-AH degrades PAF, a potent mediator of inflammation, and oxidatively fragmented phospholipids but also leads to toxic metabolites. Therefore, the regulation of PLA2 isoforms could be a valuable approach for ARDS treatment.

Hyperoxia impairs postnatal alveolar epithelial development via NADPH oxidase in newborn mice

Hyperoxia disrupts postnatal lung development in part through inducing inflammation. To determine the contribution of leukocyte-derived reactive oxygen species, we exposed newborn wild-type and NADPH oxidase p47(phox) subunit null (p47(phox-/-)) mice to air or acute hyperoxia (95% O(2)) for up to 11 days. Hyperoxia-induced pulmonary neutrophil influx was similar in wild-type and p47(-/-) mice at postnatal days (P) 7 and 11. Macrophages were decreased in wild-type hyperoxia-exposed mice compared with p47(phox-/-) mice at P11. Hyperoxia impaired type II alveolar epithelial cell and bronchiolar epithelial cell proliferation, but depression of type II cell proliferation was significantly less in p47(-/-) mice at P3 and P7, when inflammation was minimal. We found reciprocal results for the expression of the cell cycle inhibitor p21(cip/waf) in type II cells, which was induced in 95% O(2)-exposed wild-type mice, but significantly less in p47(phox-/-) littermates at P7. Despite partial preservation of type II cell proliferation, deletion of p47(phox) did not prevent the major adverse effects of hyperoxia on alveolar development estimated by morphometry at P11, but hyperoxia impairment of elastin deposition at alveolar septal crests was significantly worse in wild-type vs. p47(phox-/-) mice at P11. Since we found that p47(phox) is expressed in a subset of alveolar epithelial cells, its deletion may protect postnatal type II alveolar epithelial proliferation from hyperoxia through effects on epithelial as well as phagocyte-generated superoxide.