Phospholipids of the lung in normal, toxic, and diseased states

Alveolar proteinosis syndrome: pathogenesis, diagnosis, and management

PURPOSE OF REVIEW

This review discusses the most recent clinical and basic research literature on pulmonary alveolar proteinosis (PAP) as it relates to pathogenesis, diagnosis, and management.

RECENT FINDINGS

The discovery of Granulocyte macrophage-colony stimulating factor (GM-CSF) and the alveolar macrophage as critical regulators of surfactant protein and lipid homeostasis has led to significant advances in PAP. Adults affected by PAP have circulating neutralizing anti-GM-CSF antibodies. Reduced localized GM-CSF activity in the lung (from neutralizing anti-GM-CSF antibodies), decreases alveolar macrophage surfactant degradation with surfactant excess and accumulation. Cause, source of antibodies or downstream effects of GM-CSF deficiency is speculative. GM-CSF antibodies above a threshold level have proved to be a useful diagnostic test. Research towards therapy has focused on improving the technique for therapeutic whole lung lavage as well as overcoming effects of neutralizing anti-GM-CSF, which include GM-CSF therapy (systemic and inhaled) and anecdotal reports of anti-B cell therapy. Whereas this approach has been somewhat successful for primary PAP, other causes of PAP (i.e. alveolar macrophage dysfunction, surfactant protein alterations) are still without therapy.

SUMMARY

Understanding of the pathogenesis of PAP has greatly increased in the last decade; study has brought better comprehension of lung biology and recognition of the critical role for GM-CSF and alveolar macrophage in surfactant clearance. Balance between resident immune cell population and normal lung function still needs further study. Resident alveolar macrophages have an essential role in surfactant homeostasis. With this knowledge more effective diagnostic tests (e.g. anti-GM-CSF antibody) and therapies for PAP are under investigation.

Differential lipid specificities of the repeated domains of annexin IV

The roles of the four domains of annexin IV in binding to phospholipids and glycolipids were assessed by analyzing the binding of a group of mutant annexins IV in which one or more of the four domains was inactivated by replacing a critical amino residue(s) (Asp or Glu) with the neutral residue Ala. The data reveal that individual annexin domains may have characteristic affinities for different lipids. In particular, inactivation of the fourth domain inhibits the binding to phosphatidylserine (PS) and phosphatidylinositol (PI) but not to phosphatidylglycerol (PG), suggesting that this domain specifically can accommodate the larger head groups of PS and PI whereas the other three domains may form more restricted binding pockets. In order to block binding to PG, domain 1, or both domains 2 and 3 must be inactivated in addition to domain 4, suggesting that all four domains may be able to accommodate the headgroup of PG to some extent. Binding to acidic glycolipids (sulfatides) was also sensitive to inactivation of domain 4. However, in the case of sulfatides the nature of the binding reaction is fundamentally different compared with the binding to phospholipids since the interaction with sulfatides was highly sensitive to an increase in ionic strength. The binding to sulfatides may depend therefore on charge-charge interactions whereas the binding to phospholipid may involve a more specific interaction between the lipid headgroup and the protein surface, and/or interaction of the protein with the hydrophobic portion of a lipid bilayer.

Secondary alveolar proteinosis in cancer patients

Pulmonary alveolar proteinosis (AP) is a rare cause of progressive respiratory failure in the normal host. It was first described by Rosen and coworkers in 1958 on the morphological basis of the accumulation of a PAS-positive material in the alveolar space. A couple of years later, AP was found to be unexpectedly associated with malignant diseases, especially with acute or chronic myeloid leukemias. These forms were called secondary AP in opposition to the primary forms observed in normal hosts. Probably because of its morphological definition and late diagnosis by means of histology or autopsy material, secondary AP has been considered to be life-threatening for a long time. However, recent observations show that AP can be diagnosed early in the course of the disease, especially through bronchoalveolar lavage, as long as the pathologist is aware of this possibility. Another point is that secondary AP can be reversible, both clinically and morphologically. This article summarizes the clinical features, morphological findings, and the main malignant diseases associated with secondary AP. We also comment on the hypotheses proposed in the literature to explain the association of AP, malignant disease, and immunosuppression. Alveolar macrophage is likely a key factor in the occurrence of secondary AP.

Presence of an 80 kilodalton protein, cross-reacted with monoclonal antibodies to pulmonary surfactant protein A, in the human middle ear

We report the presence of a middle ear protein that has the same epitope as human surfactant protein A. Monoclonal antibodies (PC-6 and PE-10) against human pulmonary surfactant protein A stained faint granules of the mucosal epithelial cell cytoplasm in the orifice of the eustachian tube immunohistochemically. These antibodies also reacted with middle ear effusion of patients with otitis media with effusion by dot immunoassay, and recognized an 80 kd protein by Western blot analysis. These findings indicate that a protein immunoreactive with PC-6 and PE-10 occurs in the mucosal epithelial cells of the middle ear, and is also present in middle ear effusion. It is therefore likely that this 80 kd protein might be secreted from the mucosal epithelial cells to the middle ear cavity.

Elevation of rat pulmonary, hepatic and lung surfactant lipids by fly ash inhalation

Fly ash contains many polycyclic aromatic hydrocarbons and genotoxic trace elements. In rats, fly ash exposure profoundly affects lung and liver histology. In the present study, the effect of fly ash inhalation on lung and liver lipids of rats was examined. Male Wistar strain rats were exposed daily to fly ash (0.27 +/- 0.01 mg/L air) in an inhalation chamber, 6 hr daily over a period of 15 days, and were killed on various days, i.e. 16, 30, 60, and 120. Fly ash inhalation significantly (P less than 0.05) increased total phospholipids (PL), phosphatidylcholine (PC) and phosphatidylethanolamine (PE) in lungs. PC and dipalmitoylphosphatidylcholine (DPPC) contents in microsomes and lung surfactant also were significantly (P less than 0.05) higher in rats exposed to fly ash compared to control group animals. Radiolabeled precursor incorporation studies indicated that fly ash induced the synthesis of PC and DPPC by both CDP-choline pathway and N-methylation of PE in lung microsomes and enhanced their secretion into lung surfactant. In liver, PC and PE contents were elevated significantly (P less than 0.05) by fly ash exposure on days 16 and 30 respectively. A similar elevation of PC was observed in hepatic microsomes; this increase was due to its increased synthesis. However, the increased synthesis of PC in liver occurred to a greater extent by the N-methylation pathway than by the CDP-choline pathway.

Effects of chronic exposure to ozone on pulmonary lipids in rats

Ozone is the most toxic component of photochemical oxidant air pollution. Exposure to high concentrations of ozone produces a variety of toxic effects in the lung, but it is not known to what extent prolonged exposure to low concentrations of ozone may contribute to the development of chronic lung disease. Phospholipids, important components of cellular membranes and surfactant, are necessary for the maintenance of normal lung structure and function. In order to test the effects of chronic exposure to environmentally relevant concentrations of ozone on phospholipid metabolism in the lung, rats were exposed to clean air or to 0.12, 0.25 or 0.50 ppm ozone for up to 18 months. The content and biosynthesis of phospholipids in both lung tissue and bronchopulmonary lavage fluid (surfactant) were measured. Incorporation of [14C]acetate into lung tissue phospholipids, an estimate of overall biosynthesis, decreased significantly at some time points in the study, while tissue phospholipid content tended to increase with both ozone concentration and with age. No changes were detected in phospholipid content of bronchopulmonary lavage fluid. These findings did not support the hypothesis that prolonged exposure of rats to environmentally relevant concentrations of ozone results in either qualitative or quantitative deficits in the pulmonary surfactant system.

Bioreactivity of intratracheally administered slate dust in rats: incorporation of 14C-acetate into lung lipids

The effect of intratracheally instilled slate dust on the phospholipid profile, and 14C-acetate incorporation into the lipids of lung lavage, whole lung tissue and its subcellular fractions, has been studied in rats. The acellular fraction of lung lavage showed a decrease in the phospholipid content at 4 days and then an increase at 40 days of dust exposure, whereas the cellular fraction showed the reverse. The order of 14C-acetate incorporation into total lipids and individual phospholipids showed a parallel trend. The rate of incorporation with total lipids of lung tissue was higher at the two stages of dust exposure and a similar pattern prevailed in the subcellular fractions, i.e. mitochondrial, microsomal and cytosolic fraction. Acetate incorporation was highest in mitochondria, followed by the microsomes. An increase in the microsomal and mitochondrial cholesterol levels was also observed. There was no significant change in the solvent-extracted 14C-counts of whole plasma, trichloroacetic acid (TCA) precipitate and TCA supernatant of plasma. The results indicate that slate dust causes an enhanced synthesis of pulmonary surfactant and other lung lipids and, therefore, has an effect on the metabolism of type II alveolar epithelial cells.

Changes in phospholipids in bronchoalveolar lavage fluid of patients with interstitial lung diseases

We analyzed phospholipids of human bronchoalveolar lavage (BAL) fluids from patients with interstitial lung diseases; idiopathic pulmonary fibrosis (IPF), sarcoidosis, and eosinophilic granuloma (EG) and compared them to those of normal subjects. The content of phospholipid/ml of BAL fluid was significantly decreased in IPF. There was a significant decrease in phosphatidylglycerol (PG) and an increase in phosphatidylinositol (PI) in IPF but not in sarcoidosis and EG. Thus, the PG to PI ratio was significantly decreased in IPF. The dipalmitoyl species of phosphatidylcholine (PC) was found to be significantly decreased in IPF and sarcoidosis by molecular species analysis using high performance liquid chromatography. In contrast, the unsaturated species were increased in these diseases. The decrease in dipalmitoyl PC appeared to be a common feature in interstitial lung diseases. The changes in phospholipids in BAL fluids, especially decreases in DPPC and PG to PI ratio in IPF, appear to indicate that damage of alveolar Type II cells and/or of metabolic disturbance in pulmonary surfactant occurs in IPF.

Calcium-independent phospholipase A2 in rat tissue cytosols

Cytosols (105,000 X g supernatant) from seven rat tissues were assayed for Ca2+-independent phospholipase A2 activity with either 1-acyl-2-[1-14C]linoleoyl-sn-glycero-3-phosphocholine, 1-acyl-2-[1-14C]linoleoyl-sn-glycero-3-phosphoethanolamine or 1-O-hexadecyl-2-[9,10-3H2]oleoyl-sn-glycero-3-phosphocholine as substrate. Low but consistent activities ranging from 10-120 pmol/min per mg protein were found in all tissues. The highest activities were present in liver, lung and brain. Total activities in mU/g wet weight were rather constant, ranging from 0.43 (heart) to 1.36 (liver). The soluble enzyme from rat lung cytosol was further investigated and was found to be capable of hydrolyzing microsomal membrane-associated substrates without exhibiting much selectivity for phosphatidylcholine species. Comparative gel filtration experiments of cytosol prepared from non-perfused and perfused lungs indicated that part of the Ca2+-independent phospholipase A2 originated from blood cells, but most of it was derived from lung cells. Lung cytosol also contained Ca2+-dependent phospholipase A2 activity, a small part of which originated from blood cells, presumably platelets. The major amount of Ca2+-dependent phospholipase A2 activity, however, came from lung cells. Neither this enzyme nor the Ca2+-independent phospholipase A2 from lung tissue showed immunological cross-reactivity with monoclonal antibodies against Ca2+-dependent phospholipase A2 isolated from rat liver mitochondria.

Effect of excess dietary iron on lipid composition of calf liver, heart, and skeletal muscle

Effect of excess dietary iron on lipid composition of calf liver, skeletal muscle, and heart was assessed. High dietary iron (5000 versus 100 ppm in milk replacer DM) had no effect on the relative proportion of lipid classes in liver or their unsaturated fatty acid composition. In muscle some minor lipid components were reduced and cholesterol and sphingomyelin increased. Excessive iron had a marked effect, however, on heart lipid composition, reducing total lipids and almost all lipid classes; triglycerides, sphingomyelin, and lysophosphatidylcholine were increased. Characteristically, sphingomyelin increases in cell membranes in response to aging and numerous pathological conditions. High dietary iron reduced linolenic acid in phosphatidyl-ethanolamine and phosphatidylcholine of both skeletal and cardiac muscle. This may have resulted from iron-caused ethane production from autoxidation of linolenic acid or other n-3 family fatty acids, an effect known to occur in the rat. Linoleic and arachidonic fatty acids appeared to be unaffected. Plasmalogens in muscle and heart phosphatidylethanolamine and phosphatidylcholine were increased by high iron intake. As these alk-1-enyl ethers protect cells from oxidation and radiation damage, their synthesis may have been increased in response to stress from excessive iron. The results indicate that a relatively high concentration of vitamin E may be required in calf milk replacer when excessive iron is present.

Protective role of sulfhydryl reagents in oxidant lung injury

Recently there has been a great deal of interest in exploring possible ways to protect the lung from oxidant damage. Since sulfhydryl compounds are among the most important endogenous antioxidants, their therapeutic use has been proposed. Glutathione (GSH), the main intracellular nonprotein sulfhydryl, plays an important role in the maintenance of cellular proteins and lipids in their functional state. With oxidant stress, GSH acts to protect cell constituents as evidenced by increased turnover to GSSG, formation of mixed disulfides with proteins, utilization of NADPH, and utilization of glucose in the pentose pathway. When GSH is experimentally lowered (e.g., by protein deficiency or with diethylmaleate) the toxic effects of oxidant stress are exacerbated as evidenced by increased membrane and cell damage, pulmonary edema, and mortality. Several recent investigations have shown that sulfhydryl reagents (particularly N-acetyl cysteine, a cell-permeable GSH precursor) can provide significant protection against certain pulmonary toxins. N-acetyl cysteine reduced the lethal effects of 100% O2 in rats by 65%. Therefore, the therapeutic potential of sulfhydryl reagents in the treatment and prevention of oxidant injury and the mechanisms involved are an important direction for lung research.

Pulmonary alveolar phospholipoproteinosis: experience with 34 cases and a review

A retrospective review of Mayo Clinic records through 1983 revealed 84 patients (24 male and 10 female; mean age, 41 years) with the diagnosis of pulmonary alveolar phospholipoproteinosis. The major clinical features were dyspnea, cough, fever, and chest pain. Chest roentgenograms usually showed bilateral symmetric alveolar infiltrates, but asymmetric, unilateral, and chronic patchy patterns were also noted. Diagnosis was established by thoracotomy-lung biopsy in 26 patients. Histologic analysis revealed uniform filling of the alveoli by periodic acid-Schiff-positive material and maintenance of normal alveolar architecture. Electron microscopy showed enlarged alveolar macrophages with lamellar osmiophilic inclusions, dense granules, and myeloid bodies. Of the 21 patients who underwent therapeutic bronchoalveolar lavage, 13 had no recurrence of the disease during a mean follow-up of 8.8 years. In patients who underwent pulmonary function testing both before and after lavage, significant restrictive dysfunctions present before the procedure were alleviated afterward. Three deaths occurred among the 34 patients. Pulmonary alveolar phospholipoproteinosis may result from defective clearance of phospholipids by the alveolar macrophages, excessive production of phospholipids by type II pneumocytes, or both. It is likely a nonspecific response to a variety of injuries to the alveolar macrophage or type II pneumocyte or both, including exposure to certain dusts and chemicals and occurrence of hematologic diseases or infections. The uncommon occurrence of this disorder suggests individual susceptibility.

Induction of superoxide dismutase isozymes in rabbit lung due to aniline exposure

Single exposure of rabbits to aniline vapors caused induction of superoxide dismutase isozymes and activity as evidenced by the incorporation of radioactive amino acids and prosthetic group metals into enzymatic protein zones of electrophoreograms. Induced of a new cytosolic isozyme following aniline exposure was also evident. Xenobiotic stress indicated a close relation between free radical processes and lung biotransformation mechanisms.

Enzymatic bases for the fatty acid positioning in phospholipids of Brevibacterium ammoniagenes

Positional distribution of fatty acids in phospholipids from Brevibacterium ammoniagenes was analyzed to find that phosphatidylethanolamine consisted mainly of 1-saturated acyl 2-unsaturated acyl species while phosphatidylglycerol consisted mainly of 1-unsaturated acyl 2-saturated acyl species. Three acyltransferase systems were characterized in a membrane preparation--the acylations of glycerophosphate, 1-acyl-glycerophosphate, and 2-acyl-glycerophosphate--which appeared to be catalyzed by different enzymes. The distribution of fatty acids in the phosphatidylethanolamine molecule was not correlated simply with the specificities of these enzymes, but the relatively high specificity for palmitoyl-CoA of the glycerophosphate acyltransferase system to form 2-acyl-glycerophosphate, followed the relatively high specificity for oleoyl-CoA of the 2-acyl-glycerophosphate acyltransferase system, provided a basis for producing the major molecular species of phosphatidylglycerol.

The activity and properties of an acidic triacylglycerol lipase from adult and fetal rat lung

Triacylglycerol lipase with maximal activity at pH 5 was present in adult and fetal lung. The activity was inhibited by serum concentrations used to measure lipoprotein lipase and by 0.5 M NaCl. The activity in homogenates from fetal lung was about 40% of the activity in adult lung homogenates. The activity increased to 80% of the adult levels during the first 24-48 h following birth. Acidic triacylglycerol lipase was present in all subcellular fractions from adult lung. However, the major amount of activity appeared to be associated with lysosomes. Fetal lung contained significantly more activity in the cytosolic fraction compared to the adult. The reaction produced free fatty acids (65%), 1,2(2,3)-diacylglycerol (22%) and 2-monoacylglycerol (12%). Minimal amounts of 1,3-diacylglycerol and 1(3)-monoacylglycerol were formed. Diacylglycerol lipase and monoacylglycerol hydrolase activities at pH 5 were independently determined and both were higher than the triacylglycerol lipase activity. The subcellular distribution of diacylglycerol lipase and monoacylglycerol hydrolase differed from that of triacylglycerol lipase. Overall, the results indicated that the lung has considerable intracellular lipase activity and therefore could readily hydrolyze intracellular triacylglycerol to free fatty acids. The reaction also produced significant amounts of 1,2-diacylglycerol which suggests that triacylglycerol could be a direct source of diacylglycerol for phospholipid synthesis.