Modification of surfactant metabolizing cells in rat lung by clofibrate, a hypolipidemic peroxisome proliferating agent. Evidence to suggest that clofibrate influences pulmonary surfactant metabolism

Alveolar Proteinosis and Phospholipidoses of the Lungs

Three pulmonary disease conditions result from the accumulation of phospholipids in the lung. These conditions are the human lung disease known as pulmonary alveolar proteinosis, the lipoproteinosis that arises in the lungs of rats during acute silicosis, and the phospholipidoses induced by numerous cationic amphiphilic therapeutic agents. In this paper, the status of phospholipid metabolism in the lungs during the process of each of these lung conditions has been reviewed and possible mechanisms for their establishment are discussed. Pulmonary alveolar proteinosis is characterized by the accumulation of tubular myelin-like multilamellated structures in the alveoli and distal airways of patients. These structures appear to be formed by a process of spontaneous assembly involving surfactant protein A and surfactant phospholipids. Structures similar to tubular myelin-like multilamellated structures can be seen in the alveoli of rats during acute silicosis and, as with the human condition, both surfactant protein A and surfactant phospholipids accumulate in the alveoli. Excessive accumulation of surfactant protein A and surfactant phospholipids in the alveoli could arise from their overproduction and hypersecretion by a subpopulation of Type II cells that are activated by silica, and possibly other agents. Phospholipidoses caused by cationic amphiphilic therapeutic agents arise as a result of their inhibition of phospholipid catabolism. Inhibition of phospholipases results in the accumulation of phospholipids in the cytoplasm of alveolar macrophages and other cells. While inhibition of phospholipases by these agents undoubtedly occurs, there are many anomalous features, such as the accumulation of extracellular phospholipids and surfactant protein A, that cannot be accounted for by this simplistic hypothesis.

Role of the lung in accumulation and metabolism of xenobiotic compounds--implications for chemically induced toxicity

The mammalian lung is exposed to and affected by many airborne and bloodborne foreign compounds. This review summarizes the role of lung in accumulation and metabolism of xenobiotics, some of which are spontaneously reactive or are metabolically activated to toxic intermediates. The specific architectural arrangement of mammalian lung favors that so-called pneumophilic drugs are filtered out of the blood and are retained within the tissue as shown in particular for amphetamine, chlorphentermine, amiodarone, imipramine, chlorpromazine, propranolol, local anaesthetics, and some miscellaneous therapeutics. There is strong evidence that intrapulmonary distribution activity and regulation of drug-metabolizing enzymes in lung is distinct from liver. This review focuses on the metabolic rate of selected compounds in lung such as 5-fluoro-2'-deoxyuridine, local anesthetics, nicotine, benzo(alpha)pyrene, ipomeanol, 4-methylnitrosamino-1-(3-pyridyl)-1-butanone. It is widely accepted that the formation of radical species is a key event in the pneumotoxic mechanisms induced by bleomycin, paraquat, 3-methylindole, butylhydroxytoluene, or nitrofurantoin. Finally, methodological approaches to assess the capacity of lung to eliminate foreign compounds as well as biochemical features of the pulmonary tissue are evaluated briefly.