Vitamin E as an antioxidant of the lung: mechanisms of vitamin E delivery to alveolar type II cells.

Oxidants play an important role in the development of acute and chronic lung injuries. Alveolar surfactant is the first target of air-borne oxidants. Surfactant contains, besides dipalmitoyl phosphatidylcholine, cholesterol and polyunsaturated phospholipids that play an important functional role. Therefore, vitamin E could be important for protecting surfactant lipids against oxidation and subsequent lung injury. Alveolar type II cells play a central role in synthesis and secretion of surfactant lipids and also supplement the surfactant with vitamin E during intracellular assembly. High density lipoprotein (HDL) is the primary source of vitamin E for type II cells. The uptake of vitamin E by specific lipid transfer is mediated by at least three HDL-specific receptors (scavenger receptor BI, membrane dipeptidase, and HDL-binding protein-2). In addition, cubilin and megalin mediate in a cooperative manner HDL-holoparticle uptake by alveolar type II cells. A temporary vitamin E deficiency induces a reversible change of the expression of pro- and antiinflammatory markers and of markers defining apoptosis, and reduces surfactant lipid synthesis in alveolar type II cells. These metabolic changes of type II cells may prime the lung to develop clinically manifest injury in response to an additional insult, e.g., hyperoxia.