Cyclooxygenase metabolites contribute to oleic acid-induced lung edema by a pressure effect

Alteration in the Lipid Profile and the Desaturases Activity in Patients With Severe Pneumonia by SARS-CoV-2

The kidnapping of the lipid metabolism of the host's cells by severe acute respiratory syndrome (SARS-CoV-2) allows the virus to transform the cells into optimal machines for its assembly and replication. Here we evaluated changes in the fatty acid (FA) profile and the participation of the activity of the desaturases, in plasma of patients with severe pneumonia by SARS-CoV-2. We found that SARS-CoV-2 alters the FA metabolism in the cells of the host. Changes are characterized by variations in the desaturases that lead to a decrease in total fatty acid (TFA), phospholipids (PL) and non-esterified fatty acids (NEFAs). These alterations include a decrease in palmitic and stearic acids (p ≤ 0.009) which could be used for the formation of the viral membranes and for the reparation of the host's own membrane. There is also an increase in oleic acid (OA; p = 0.001) which could modulate the inflammatory process, the cytokine release, apoptosis, necrosis, oxidative stress (OS). An increase in linoleic acid (LA) in TFA (p = 0.03) and a decreased in PL (p = 0.001) was also present. They result from damage of the internal mitochondrial membrane. The arachidonic acid (AA) percentage was elevated (p = 0.02) in the TFA and this can be participated in the inflammatory process. EPA was decreased (p = 0.001) and this may decrease of pro-resolving mediators with increase in the inflammatory process. The total of NEFAs (p = 0.03), PL (p = 0.001), cholesterol, HDL and LDL were decreased, and triglycerides were increased in plasma of the COVID-19 patients. Therefore, SARS-CoV-2 alters the FA metabolism, the changes are characterized by alterations in the desaturases that lead to variations in the TFA, PL, and NEFAs profiles. These changes may favor the replication of the virus but, at the same time, they are part of the defense system provided by the host cell metabolism in its eagerness to repair damage caused by the virus to cell membranes.

In VitroModels to Study Mechanisms of Lung Toxicity

Several functioning in vitro systems of varying complexity are currently in use for the study of mechanisms of lung toxicity. The isolated perfused lung is the model closest to the in vivo situation. It is a suitable model for combining metabolic and functional studies. It is, for instance, possible to relate changes in lung mechanics and lung perfusion flow to the release of various mediators during exposure of the lung to various agents. A simpler model may be constructed from lung slices which are less viable but suitable for uptake as well as metabolism studies.

Specific lung cells such as Clara cells and type II pneumocytes have been isolated and cultured and are valuable tools for studies of the molecular mechanisms of lung toxicity, particularly in cases of cell-specific toxicity. There is, however, a great need to develop techniques for the isolation and culture of other types of lung cells and also to improve the culturing techniques for those already isolated.

Participation of Arachidonic Acid Metabolism in the Aortic Aneurysm Formation in Patients with Marfan Syndrome

Marfan syndrome (MFS) is a pleiotropic genetic disease involving the cardiovascular system where a fibrillin-1 mutation is present. This mutation is associated with accelerated activation of transforming growth factor β (TGFβ1) which contributes to the formation of aneurysms in the root of the aorta. There is an imbalance in the synthesis of thromboxane A₂ (TXA₂) and prostacyclin, that is a consequence of a differential protein expression of the isoforms of cyclooxygenases (COXs), suggesting an alteration of arachidonic acid (AA) metabolism. The aim of this study was to analyze the participation of AA metabolism associated with inflammatory factors in the dilation and dissection of the aortic aneurysm in patients with MFS. A decrease in AA (p = 0.02), an increase in oleic acid (OA), TGFβ1, tumor necrosis factor alpha (TNFα), prostaglandin E₂ (PGE₂) (p < 0.05), and COXs activity (p = 0.002) was found. The expressions of phospholipase A₂ (PLA₂), cytochrome P450 (CYP450 4A), 5-lipoxygenase (5-LOX), COX2 and TXA2R (p < 0.05) showed a significant increase in the aortic aneurysm of patients with MFS compared to control subjects. COX1, 6-keto-prostaglandin 1 alpha (6-keto-PG_1α) and 8-isoprostane did not show significant changes. Histological examination of the aortas showed an increase of cystic necrosis, elastic fibers and collagen in MFS. The results suggest that there are inflammatory factors coupled to genetic factors that predispose to aortic endothelial dysfunction in the aortic tissue of patients with MFS. There is a decrease in the percentage of AA, associated with an increase of PLA₂, COX2/TXA2R, CYP450 4A, and 5-LOX which leads to a greater synthesis of PGE₂ than of 6-keto-PGF_1α, thus contributing to the formation of the aortic aneurysm. The evident loss of the homeostasis in these mechanisms confirms that there is a participation of the AA pathway in the aneurysm progression in MFS.

Update on pulmonary edema: the role and regulation of endothelial barrier function

Discovery of the pathophysiologic mechanisms leading to pulmonary edema and identification of effective strategies for prevention remain significant clinical concerns. Endothelial barrier function is a key component for maintenance of the integrity of the vascular boundary in the lung, particularly since the gas exchange surface area of the alveolar-capillary membrane is large. This review is focused on new insights in the pulmonary endothelial response to injury and recovery, reversible activation by edemagenic agents, and the biochemical/structural basis for regulation of endothelial barrier function. This information is discussed in the context of fundamental concepts of lung fluid balance and pulmonary function.

Role of cyclooxygenase-2 in oleic acid-induced acute lung injury

Eicosanoid production appears to be important to both edemagenesis and the pattern of pulmonary perfusion in experimental acute lung injury (ALI). We hypothesized that these effects could be mediated by the inducible form of cyclooxygenase (COX-2). We used positron emission tomography to evaluate the pulmonary perfusion pattern in dogs given oleic acid (OA) only (n = 6), the novel COX-2 inhibitor SC-236 50 min before OA (n = 3), and SC-236 given 20 min before endotoxin (Etx), followed by OA given 30 min after Etx (n = 5). Thromboxane B(2) (TXB(2)) and prostacyclin (6-keto prostaglandin F(1alpha); 6-keto PGF(1alpha)) metabolite concentrations in plasma and lung tissue were measured in these groups and in another group given Etx + OA (n = 4). Inhibition of COX-2 before administration of OA alone or before administration of Etx and OA did not have any significant effect on plasma or lung tissue concentrations of TXB(2). However, inhibition of COX-2 prior to Etx and OA significantly reduced the plasma and lung tissue concentrations of 6-keto PGF(1alpha) as compared with those in the group given only Etx + OA. Moreover, SC-236 prevented the expected loss of perfusion redistribution associated with Etx + OA only. The effect of endotoxin on pulmonary perfusion in ALI is therefore the result of a COX-2-mediated increase in prostacyclin production in lung tissue.

Response to inhaled nitric oxide in acute lung injury depends on distribution of pulmonary blood flow prior to its administration

Responses to inhaled nitric oxide (iNO) in acute lung injury (ALI), as evidenced by improvements in oxygenation, are variable. We hypothesized that the effect of iNO may be related to the pre-iNO distribution of pulmonary blood flow (PBF). In the present study we evaluated the effect of iNO on PBF in normal healthy dogs and in a canine model of ALI induced by oleic acid (OA). In Group "OA only" (n = 5), ALI was induced by central venous injection of 0.08 ml/kg OA. In Group "E+OA" (n = 5), hypoxic pulmonary vasoconstriction after ALI was blocked with low-dose endotoxin (15 microg/kg of Escherichia coli endotoxin) administered 30 min before giving the same dose of OA. Measurements of regional PBF and lung water concentration (LWC) using positron emission tomography (PET) and H215O were performed before and after OA or placebo, and then again at concentrations of 10, 40, and 0 ppm iNO. One hundred twenty minutes after OA injury, PaO2/FIO2 fell significantly in Group OA only, from 567 +/- 32 to 437 +/- 67 mm Hg. In these animals, PBF redistributed from the dorsal edematous regions of the lungs to the nondependent zones, thus partially preserving normal ventilation/ perfusion relationships. As in the normal animals, in Group OA only, iNO did not significantly change either PBF or oxygenation. In Group E+OA, the administration of low-dose endotoxin eliminated perfusion redistribution from the dorsal edematous lung regions. As a result, PaO2/FIO2 fell from 558 +/- 70 to 119 +/- 53 mm Hg, a decrease that was significantly greater than that in Group OA only. In Group E+OA, administration of iNO restored perfusion redistribution to a similar level as in Group OA only, which was associated with a significant improvement in PaO2/FIO2, from 119 +/- 53 to 251 +/- 159 (10 ppm iNO), and 259 +/- 165 mm Hg (40 ppm iNO). We conclude that the effect of iNO on oxygenation after ALI depends on the pre-iNO perfusion pattern, which may help explain the variable response to iNO often observed in patients with acute respiratory distress syndrome.

Synergistic hemodynamic effects of low-dose endotoxin and acute lung injury

We evaluated the effects of low-dose endotoxin (15 microg/kg) on the pulmonary and systemic responses to oleic acid (OA)-induced acute lung injury in dogs. Animals given endotoxin alone (n = 5) showed a modest decrease in arterial blood pressure, but no effects on pulmonary hemodynamics, blood gases, cardiac output, or lung water accumulation. Animals (n = 6) given only OA (0.08 ml/kg) showed the expected development of mild-moderate pulmonary hypertension, a comparable reduction in arterial blood pressure, hypoxemia, increased lung water concentration, and an altered intrapulmonary perfusion pattern, as assessed by positron emission tomography. Animals (n = 7) given the same dose of endotoxin, followed 30 min later by the same dose of OA, developed a similar increase in lung water concentration as the group given OA alone, but failed to develop pulmonary hypertension or to redistribute pulmonary blood flow away from the edematous lung regions. In addition, arterial blood pressure fell significantly more than in the other groups. These responses were associated with a 30-fold increase in circulating prostacyclin (assayed as 6-keto prostaglandin F1 alpha [PGF1alpha]). The effects on systemic blood pressure, intrapulmonary blood flow redistribution, and eicosanoid production were eliminated by pretreating (n = 5) animals with meclofenamate (2 mg/kg). The results are consistent with a "priming" effect of low-dose endotoxin on the pulmonary endothelium, with exaggerated prostacyclin production in response to a subsequent lung injury. This interaction leads to altered intrapulmonary hemodynamics that exacerbate the development of hypoxemia, and to significant decreases in systemic blood pressure. To the extent that the lung is the most likely source of the increased prostacyclin production, the synergistic effects of low-dose endotoxin and lung injury may produce a kind of "lung shock."

Measuring the weight of the isolated perfused rat lung during negative pressure ventilation

Weight measurement represents a means of quantitating edema formation in isolated lungs and following its time course. During ventilation by negative pressure measurements with commonly used weight transducers are impossible because the pressure changes inside the artificial thoracic chamber affect the weight reading. Therefore, we have developed a weight transducer that can be used during negative pressure ventilation. Its design and applicability for assessing weight gain induced by various agents in the negative-pressure-ventilated isolated perfused rat lung is presented here.

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

Alterations in the lipid composition of lung microsomal membranes occur in oleic acid-induced respiratory distress. The marked decrease in the phosphatidylcholine/lysophosphatidylcholine molar ratio could be related with an altered metabolism of lysophosphatidylcholine in these membranes. Results revealed that the activity of phospholipase A increased whereas that of acyl-CoA:lysophosphatidylcholine acyltransferase decreased. Microsomal lysophospholipase activity remained unchanged. On the other hand, the microsomal enzyme system involved in the de novo synthesis of diacylglycerol was impaired, and cholinephosphotransferase activity was lowered. These changes in the activity of some membrane-bound enzymes were not caused by changes in the membrane lipid fluidity since lipid structural order parameter (SDPH) did not change and neither did the major factors on which the fluidity depends. The possible significance of microsomal lipid alterations in the pathogenesis of respiratory distress induced by oleic acid is discussed.

The role of activation of neutrophils and microvascular pressure in acute pulmonary edema

Activated polymorphonuclear neutrophils (PMN) can mediate vascular injury in the lung. This study compared activated aggregate PMN (emboli) to activated PMN that were previously adhered to the microvasculature (non-embolic) in the isolated perfused rat lung. Permeability and microvascular pressure (Pmv), components of PMN-induced edema, were examined by continuous measurement of wet weight, pulmonary arterial and left atrial pressures, and by intermittent determination of double occlusion pressure. PMN that were activated with phorbol myristate acetate and then perfused into the lung formed aggregates that lodged primarily in the precapillary bed, increasing arterial resistance. Although these PMN had minimal direct contact with the capillary endothelium, edema rapidly developed and Pmv was progressively elevated. If PMN were allowed to adhere in the capillary bed, a minimal and nonprogressive increase in Pmv and lung weight occurred. When these adherent PMN were then activated, there was a progressive rise in both Pmv and lung weight. The free radical scavenger catalase prevented this edema formation but not the rise in pressure. In control lungs with matched elevation of Pmv, edema did not develop. In another group of lungs with activation of pre-adherent PMN in which Pmv was maintained at control levels, edema formation was greatly delayed. These data show that: (1) the activated PMN free radical products alone caused permeability injury in the lung because neither contact of the PMN with the capillary endothelium nor embolization was necessary, and (2) increased Pmv does not cause edema but greatly increases the rate of edema formation when the endothelium is injured.

Acute lung injury monitored with radiolabeled transferrin and lung volume measurements

Anesthetized pigs (n = 12) were given oleic acid (OA) to induce acute lung injury. Three additional pigs were used as uninjured controls. Six of the animals were pretreated with terbutaline before OA infusion. 113mIn-labeled transferrin and 99mTc-labeled erythrocytes were used for tracing of extravascular plasma leakage. A computerized gamma camera supplied image analysis of the radioactivities over the heart and lungs. A lung transferrin index (LTI), which describes the net accumulation of plasma equivalents in the lung, was calculated. OA caused an immediate increase in LTI and concurrent, correlated decreases in functional residual capacity, lung thorax compliance and arterial PO2. LTI was also correlated to the content of plasma equivalents in lung tissue samples and also to the wet weight/dry weight-ratios of the same tissue samples. Finally, LTI was correlated to the calculated plasma loss from the circulation. Changes in all these parameters were correlated to the dose of OA. We conclude that this noninvasive double radioisotope technique can detect plasma protein leakage in lung injury of different degrees. We found no significant anti-edema effect of terbutaline.

Comparison between intra- and extracellular surfactant in respiratory distress induced by oleic acid

The present study compares the phospholipid distribution and protein content in bronchoalveolar lavage, purified extracellular surfactant and lamellar bodies isolated from rabbits killed at intervals of 2.5, 12 and 24 h after oleic acid administration. The data suggest that the alteration of pulmonary surfactant could be partially due to the type II cell response to the injury.