Association of changes in lysophosphatidylcholine metabolism and in microsomal membrane lipid composition to the pulmonary injury induced by oleic acid

The Anionic Phospholipids of Bovine Pulmonary Surfactant

The only known compositional change in the phospholipids (PL) of pulmonary surfactant in response to a physiologic stimulus occurs around the time of birth. In most species, the predominant anionic PL changes from phosphatidylinositol (PtdIns) to phosphatidylglycerol (PtdGro). Because prior studies have shown that the change in the headgroup itself is functionally insignificant, we tested the hypothesis that the PtdIns and PtdGro contain different diacyl pairs. Experiments used electrospray-ionization mass spectrometry to determine the molecular species in PtdIns, PtdGro, and phosphatidylcholine (PtdCho) in surfactant from newborn calves and cows. The profiles for the two anionic PL were distinct. The PtdIns contained long, unsaturated fatty acid chains and no disaturated species. The PtdGro more closely resembled the profile from PtdCho. For each headgroup, the molecular species for calf and cow were similar. The differences between the two anionic PL indicate that the switch from PtdIns to PtdGro during maturation involves more than simple substitution of the headgroup, and suggest that the functional significance of the shift may reflect the different pool of diacyl pairs.

Folding and Intramembraneous BRICHOS Binding of the Prosurfactant Protein C Transmembrane Segment

Surfactant protein C (SP-C) is a novel amyloid protein found in the lung tissue of patients suffering from interstitial lung disease (ILD) due to mutations in the gene of the precursor protein pro-SP-C. SP-C is a small α-helical hydrophobic protein with an unusually high content of valine residues. SP-C is prone to convert into β-sheet aggregates, forming amyloid fibrils. Nature's way of solving this folding problem is to include a BRICHOS domain in pro-SP-C, which functions as a chaperone for SP-C during biosynthesis. Mutations in the pro-SP-C BRICHOS domain or linker region lead to amyloid formation of the SP-C protein and ILD. In this study, we used an in vitro transcription/translation system to study translocon-mediated folding of the WT pro-SP-C poly-Val and a designed poly-Leu transmembrane (TM) segment in the endoplasmic reticulum (ER) membrane. Furthermore, to understand how the pro-SP-C BRICHOS domain present in the ER lumen can interact with the TM segment of pro-SP-C, we studied the membrane insertion properties of the recombinant form of the pro-SP-C BRICHOS domain and two ILD-associated mutants. The results show that the co-translational folding of the WT pro-SP-C TM segment is inefficient, that the BRICHOS domain inserts into superficial parts of fluid membranes, and that BRICHOS membrane insertion is promoted by poly-Val peptides present in the membrane. In contrast, one BRICHOS and one non-BRICHOS ILD-associated mutant could not insert into membranes. These findings support a chaperone function of the BRICHOS domain, possibly together with the linker region, during pro-SP-C biosynthesis in the ER.

Adenovector-mediated gene transfer of lysophosphatidylcholine acyltransferase 1 attenuates oleic acid-induced acute lung injury in rats

OBJECTIVE

Lysophosphatidylcholine is generated through the hydrolysis of phosphatidylcholine by phospholipase A2 and reversely converted to phosphatidylcholine by lysophosphatidylcholine acyltransferase 1. Although lysophosphatidylcholine is a potent proinflammatory mediator and increased in several types of acute lung injuries, the role of lysophosphatidylcholine acyltransferase 1 has not yet been addressed. We aimed to investigate whether the exogenous expression of lysophosphatidylcholine acyltransferase 1 could attenuate acute lung injury.

DESIGN

Randomized, prospective animal study, including in vitro primary cell culture test.

SETTING

University medical center research laboratory.

SUBJECTS

Adult male Sprague-Dawley rats.

INTERVENTIONS

Recombinant adenoviruses carrying complementary DNA encoding lysophosphatidylcholine acyltransferase 1 or lacZ (Ad-lacZ) as a control was constructed. Alveolar type II cells were isolated from rats and cultured on tissue-culture inserts. Rats were pretreated with an endobronchial administration of the recombinant adenovirus. One week later, they were IV injected with oleic acid. The lungs were examined 4 hours post oleic acid.

MEASUREMENTS AND MAIN RESULTS

Adenoviruses carrying complementary DNA encoding lysophosphatidylcholine acyltransferase 1-infected alveolar type II cells showed lower lysophosphatidylcholine levels and a decreased percentage of cell death compared with Ad-lacZ-infected cells or noninfected cells after exposure to hydrogen peroxide for 1 hour. Compared with Ad-lacZ plus oleic acid-treated lungs, adenoviruses carrying complementary DNA encoding lysophosphatidylcholine acyltransferase 1 plus oleic acid-treated lungs showed a lower wet-to-dry lung weight ratio, a higher lung compliance, lower lysophosphatidylcholine contents, higher phosphatidylcholine contents, and a lower apoptosis ratio of alveolar type II cells. Histological scoring revealed that the adenoviruses carrying complementary DNA encoding lysophosphatidylcholine acyltransferase 1-treated lungs developed oleic acid-induced lung injuries that were attenuated compared with those of Ad-lacZ-treated lungs.

CONCLUSIONS

Exogenous expression of lysophosphatidylcholine acyltransferase 1 protects alveolar type II cells from oxidant-induced cell death in vitro, and endobronchial delivery of a lysophosphatidylcholine acyltransferase 1 transgene effectively attenuates oleic acid-induced acute lung injury in vivo. These results suggest that lysophosphatidylcholine acyltransferase 1 plays a protective role in acute lung injury.

Large-animal models of acute respiratory distress syndrome

Acute respiratory distress syndrome (ARDS) is characterized by an acute inflammatory response that compromises alveolar-capillary membrane integrity. Clinical symptoms include refractory hypoxemia, noncardiogenic edema, and decreased lung compliance. The purpose of this review is to summarize the different ARDS large-animal models in terms of similarity to the clinical disease and underlying pathophysiology. The repeated lavage, oleic acid, endotoxin, and smoke/burn ARDS models will be discussed in this review. While each model has significant benefits, none is without weaknesses. Thus, the choice of large-animal ARDS model must be carefully considered based upon the study focus and investigative team experience.

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.

Crucial role of group IIA phospholipase A(2) in oleic acid-induced acute lung injury in rabbits

Group IIA secretory phospholipase A(2) (sPLA(2)) has been implicated in a variety of inflammatory diseases including acute lung injury (ALI); however, the role of sPLA(2) in this disorder remains unclear. The aim of the present investigation was to examine the role of this enzyme in a model of ALI induced by oleic acid (OA) in rabbits by testing human group IIA phospholipase A(2) (PLA(2)) inhibitor, S-5920/LY315920Na. Experimental groups consisted of a saline control group (n = 8), an OA control group (n = 10) infused intravenously with OA (0.1 ml/kg/h for 2 h), and three groups given OA + S-5920/LY315920Na (three different doses, n = 8, respectively). Infusion of OA provoked pulmonary hemorrhage and edema formation, protein leakage, and massive neutrophil infiltration, resulting in severe hypoxemia and impaired lung compliance. PLA(2) activity was detected in the bronchoalveolar lavage fluid (BALF), but not plasma, which correlated well with severity of lung injury in this model. Pretreatment with S-5920/LY315920Na diminished the OA-induced PLA(2) activity in the BALF and dose-dependently attenuated the previously described lung injury induced by OA, accompanied by protection against lung surfactant degradation and production of thromboxane A(2) (TXA(2)) and leukotriene B(4) (LTB(4)). S-5920/LY315920Na also inhibited the OA-induced production of interleukin-8 (IL-8), both in plasma and BALF. Thus, sPLA(2) appears to play a key role in OA-induced lung injury, suggesting that the group IIA PLA(2) inhibitor may be a promising agent for patients with acute respiratory distress syndrome (ARDS).

Hypothesis: are fatty acid patterns characteristic of essential fatty acid deficiency indicative of oxidative stress?

Several unrelated diseases show plasma and tissue fatty acid patterns characteristic of those seen in Essential Fatty Acid Deficiency Disease (EFADD). A common feature occurring in all these diseases is oxidative stress. We hypothesize that reactive oxygen species or products of oxidative damage, particularly those derived from lipids, act as signal molecules to alter desaturase enzymes and induce the fatty acid patterns characteristic of EFADD.

Bioactivation of leukotoxins to their toxic diols by epoxide hydrolase

Leukotoxin is a linoleic acic oxide produced by leukocytes and has been associated with the multiple organ failure and adult respiratory distress syndrome seen in some severe burn patients. Leukotoxin has been reported to be toxic when injected into animals intravenously. Herein, we report that this lipid is not directly cytotoxic in at least two in vitro systems. Using a baculovirus expression system we demonstrate that leukotoxin is only cytotoxic in the presence of epoxide hydrolases. In addition, it is the diol metabolite that proves toxic to pulmonary alveolar epithelial cells, suggesting a critical role for the diol in leukotoxin-associated respiratory disease. In vivo data also support the toxicity of leukotoxin diol. For the first time we demonstrate that soluble epoxide hydrolase can bioactivate epoxides to diols that are apparently cytotoxic. Thus leukotoxin should be regarded as a protoxin corresponding to the more toxic diol. This clearly has implications for designing new clinical interventions.

Direct effects of meconium on rat tracheal smooth muscle tension in vitro

Increased airway resistance is a component of the meconium aspiration syndrome. Experiments were done to determine whether meconium can have a direct affect on tracheal smooth muscle tension. Tracheal segments (4-5 mm long) were isolated from male Sprague-Dawley rats and suspended in organ baths with physiologic salt solution at 37 degrees C gassed with 95% O2-5% CO2. Each segment was attached to a fixed glass rod on one side and to a force displacement transducer on the other side to measure transverse tension. The segments were stretched to 1.5 g of tension and equilibrated for 2-5 h. Human meconium was diluted in physiologic salt solution (20 g/100 mL) and filtered through gauze. Tension was generated in the segments by adding acetylcholine (10(-6) M) to the tissue bath. Addition of meconium to the organ bath (0.1-5 mg/mL) caused tracheal smooth muscle relaxation in 44% of tracheal segments tested. Contraction occurred in 8% of tested segments, but only at the intermediate and low doses. The amount of relaxation increased significantly in a concentration-dependent manner. These responses were not affected by pretreating segments with indomethacin, removing the tracheal epithelium, using KCl to generate tone, or by heating meconium above 60 degrees C for 1 h. Addition of oleic acid to the organ bath (3.5 x 10(-6) to 3.5 x 10(-4) M) caused concentration-dependent tracheal smooth muscle responses (with relaxation predominating at 3.5 x 10(-4) M and contraction predominating at 3.5 x 10(-6) M). These results suggest that meconium can cause tracheal smooth muscle relaxation by a mechanism that does not appear to be mediated by cyclooxygenase products, by the tracheal epithelium, or a protein. The direct action of meconium on tracheal smooth muscle, which may in part be mediated by a fatty acid, does not appear to contribute significantly to the increased airway tone associated with the meconium aspiration syndrome.

Changes by progesterone derivatives in fatty acids from phosphatidylcholine and phosphatidylethanolamine fractions in rat liver endoplasmic reticulum

The effects of two progesterone metabolites on fatty acid composition of phosphatidylcholine (PC) and phosphatidylethanolamine (PE) from total liver and liver microsomes were studied in female rats. 16 alpha-Hydroxyprogesterone significantly increased the amount of fatty acids esterified to PC and PE fractions in total liver and liver microsomes. Both saturated and unsaturated fatty acyl components were enhanced. In contrast, 5 beta-pregnan-3 alpha-ol-20-one caused a reduction of fatty acids bound to PC and PE fractions from total liver and liver microsomes. Pregnanolone decreased both saturated and unsaturated fatty acids. Changes in specific fatty acids occurred in palmitic and stearic acids among saturated components, and palmitoleic, oleic, linoleic, eicosatrienoic, arachidonic and docosahexenoic acids among unsaturated ones. The unsaturated: saturated fatty acid ratio was raised by 16-alpha-hydroxyprogesterone and lowered by 5 beta-pregnan-3 alpha-ol-20-one in all phospholipid fractions. The induction of drug metabolizing enzymes by 16 alpha-hydroxyprogesterone may be related to an enhanced synthesis of microsomal phospholipids containing unsaturated fatty acids, particularly arachidonic and docosahexenoic acids. In contrast, the inhibition of drug metabolism by 5 beta-pregnan-3 alpha-ol-20-one is associated with reduced formation of unsaturated fatty acyl side chains.