Heart transplantation outcomes in cardiac sarcoidosis.

BACKGROUND: Cardiac sarcoidosis (CS) is a progressive inflammatory cardiomyopathy that can lead to heart failure, arrhythmia, and death. There is limited data on Orthotopic Heart Transplantation (OHT) outcomes in patients with CS. Here we examine outcomes in patients with CS who have undergone OHT at centers throughout the United States from 1987 to 2019. METHODS: This was an analysis of 63,947 adult patients undergoing OHT captured in the United Network for Organ Sharing (UNOS) registry. Patients were characterized as cardiac sarcoidosis (CS) or Non-CS. Baseline characteristics were compared using chi-square and Kruskal-Wallis Tests. Outcomes of interest included primary graft failure, patient survival, treated graft rejection, hospitalization for infection, and post-transplant malignancy. RESULTS: During the study period 227 patients with CS underwent OHT. Patients with CS were younger, had higher proportion of non-white patients, and received transplants at more urgent statuses. After multivariable modeling there was no difference in survival (HR 0.86, CI 0.59-1.3, p = 0.446) or graft failure (HR 0.849, CI 0.58-1.23, p = 0.394) between patients with CS and Non-CS. Patients with CS had lower odds of rejection (OR 0.558, CI 0.315- 0.985, p = 0.0444). Patients with CS had similar odds of hospitalization for infection and post-transplant malignancy, as Non-CS patients. CONCLUSIONS: Patients with CS and Non-CS had similar post OHT survival, odds of graft failure, hospitalizations for infection, and post-transplant malignancy. Results of this study confirm the role of heart transplantation as a viable option for patients with CS.

A mechanism of benefit of soy genistein in asthma: inhibition of eosinophil p38-dependent leukotriene synthesis.

BACKGROUND: Dietary intake of the soy isoflavone genistein is associated with reduced severity of asthma, but the mechanisms responsible for this effect are unknown. OBJECTIVE: To determine whether genistein blocks eosinophil leukotriene C(4) (LTC(4)) synthesis and to evaluate the mechanism of this effect, and to assess the impact of a 4-week period of soy isoflavone dietary supplementation on indices of eosinophilic inflammation in asthma patients. METHODS: Human peripheral blood eosinophils were stimulated in the absence and presence of genistein, and LTC(4) synthesis was measured. 5-lipoxygenase (5-LO) nuclear membrane translocation was assessed by confocal immunofluorescence microscopy. Mitogen-activated protein (MAP) kinase activation was determined by immunoblot. Human subjects with mild-to-moderate persistent asthma and minimal or no soy intake were given a soy isoflavone supplement (100 mg/day) for 4 weeks. The fraction of exhaled nitric oxide (FE(NO)) and ex vivo eosinophil LTC(4) production were assessed before and after the soy isoflavone treatment period. RESULTS: Genistein inhibited eosinophil LTC(4) synthesis (IC(50) 80 nm), blocked phosphorylation of p38 MAP kinase and its downstream target MAPKAP-2, and reduced translocation of 5-LO to the nuclear membrane. In patients with asthma, following 4 weeks of dietary soy isoflavone supplementation, ex vivo eosinophil LTC(4) synthesis decreased by 33% (N=11, P=0.02) and FE(NO) decreased by 18% (N=13, P=0.03). CONCLUSION: At physiologically relevant concentrations, genistein inhibits eosinophil LTC(4) synthesis in vitro, probably by blocking p38- and MAPKAP-2-dependent activation of 5-LO. In asthma patients, dietary soy isoflavone supplementation reduces eosinophil LTC(4) synthesis and eosinophilic airway inflammation. These results support a potential role for soy isoflavones in the treatment of asthma.

Prostaglandin E(2) regulates wound closure in airway epithelium.

Repair of the airway epithelium after injury is critical for the maintenance of barrier function and the limitation of airway hyperreactivity. Airway epithelial cells (AECs) metabolize arachidonic acid to biologically active eicosanoids via the enzyme cyclooxygenase (COX). We investigated whether stimulating or inhibiting COX metabolites would affect wound closure in monolayers of cultured AECs. Inhibiting COX with indomethacin resulted in a dose-dependent inhibition of wound closure in human and feline AECs. Specific inhibitors for both COX-1 and COX-2 isoforms impaired wound healing. Inhibitors of 5-lipoxygenase did not affect wound closure in these cells. The addition of prostaglandin E(2) (PGE(2)) eliminated the inhibition due to indomethacin treatment, and the exogenous application of PGE(2) stimulated wound closure in a dose-dependent manner. Inhibition of COX with indomethacin only at initial time points resulted in a sustained inhibition of wound closure, indicating that prostanoids are involved in early wound repair processes such as spreading and migration. These differences in wound closure may be important if arachidonic acid metabolism and eicosanoid concentrations are altered in disease states such as asthma.

Keratinocyte growth factor stimulates bronchial epithelial cell proliferation in vitro and in vivo.

Airway epithelial cell (AEC) proliferation is crucial to the maintenance of an intact airway surface and the preservation of host defenses. The factors that regulate AEC proliferation are not known. Keratinocyte growth factor (KGF), also known as FGF-7, is a member of the fibroblast growth factor family and a known epithelial cell mitogen. We studied the influence of KGF on the growth of cultured human bronchial epithelial cells and on bronchial cells of rats treated with KGF in vivo. First, we demonstrated the mRNA for the KGF receptor (KGFR) in both normal human bronchial epithelial (NHBE) cells and BEAS-2B cells (a human bronchial epithelial cell line). KGF caused a dose-dependent increase in DNA synthesis, as assessed by thymidine incorporation, in both cell types, with a maximal twofold increase in NHBE cells after 50 ng/ml KGF (P < 0.001). KGF also induced a doubling in NHBE cell number at 10 ng/ml (P < 0.001). Finally, we determined the effect of intratracheal administration of KGF to rats on proliferation of AEC in vivo. Measuring bromodeoxyuridine (BrdU) incorporation in AEC nuclei, KGF increased BrdU labeling of rat AEC in both large and small airways by approximately threefold compared with PBS-treated controls (P < 0.001). Thus KGF induces proliferation of bronchial epithelial cells both in vitro and in vivo.

Decreased leukotriene C4 synthesis accompanies adherence-dependent nuclear import of 5-lipoxygenase in human blood eosinophils.

The enzyme 5-lipoxygenase (5-LO) catalyzes the synthesis of leukotrienes (LTs) from arachidonic acid (AA). Adherence or recruitment of polymorphonuclear neutrophils (PMN) induces nuclear import of 5-LO from the cytosol, which is associated with enhanced LTB4 synthesis upon subsequent cell stimulation. In this study, we asked whether adherence of human eosinophils (EOS) causes a similar redistribution of 5-LO and an increase in LTC4 synthesis. Purified blood EOS examined either in suspension or after adherence to fibronectin for 5 min contained only cytosolic 5-LO. Cell stimulation resulted in activation of 5-LO, as evidenced by its translocation to membranes and LTC4 synthesis. As with PMN, adherence of EOS to fibronectin for 120 min caused nuclear import of 5-LO. Unexpectedly, however, adherence also caused a time-dependent decrease in LTC4 synthesis: EOS adhered for 120 min produced 90% less LTC4 than did cells adhered for 5 min. Adherence did not diminish the release of [3H]AA from prelabeled EOS or reduce the synthesis of the prostanoids thromboxane and PGE2. Also, inhibition of LTC4 production caused by adherence could not be overcome by the addition of exogenous AA. Adherence increased, rather than decreased, LTC4 synthase activity. However, the stimulation of adherent EOS failed to induce translocation of 5-LO from the nucleoplasm to the nuclear envelope. This resistance to activation of the nuclear pool of 5-LO with diminished LT production represents a novel mode of regulation of the enzyme, distinct from the paradigm of up-regulated LT synthesis associated with intranuclear localization of 5-LO observed in PMN and other cell types.

Regulation of 5-lipoxygenase activity in mononuclear phagocytes: characterization of an endogenous cytosolic inhibitor.

The proinflammatory leukotrienes (LT) play important roles in host defense and disease states. However, no endogenous mechanisms to downregulate 5-lipoxygenase (5-LO), the enzyme catalyzing LT synthesis, have been described. We observed that the cytosolic fraction of rat alveolar macrophages (AMs) and peritoneal macrophages (PMs), and of peripheral blood monocytes (PBMs) contain substantial amounts of 5-LO protein, but little detectable 5-LO activity. We therefore examined these mononuclear phagocyte (MNP) cytosolic fractions for inhibitory activity against 5-LO. MNP cytosol dose-dependently reduced the 5-LO activity in neutrophil (PMN) cytosol and AM membrane. Furthermore, MNP cytosol dose-dependently prolonged the lag phase of soybean lipoxygenase (LO) without affecting the rate of product formation. This effect was overcome by subsequent addition of 13(S)-hydroperoxy-9-cis-11-trans-octadecadienoic acid (13-HpOD), suggesting that the active factor scavenges hydroperoxides. Inactivation by boiling and roteinase K suggest that is a protein. We speculate that this cytosolic factor(s) may serve as an endogenous means for the down-regulation of 5-LO in macrophages.

Keratinocyte growth factor promotes alveolar epithelial cell DNA repair after H2O2 exposure.

Alveolar epithelial cell (AEC) injury and repair are important in the pathogenesis of oxidant-induced lung damage. Keratinocyte growth factor (KGF) prevents lung damage and mortality in animals exposed to various forms of oxidant stress, but the protective mechanisms are not yet established. Because DNA strand break (DNA-SB) formation is one of the earliest cellular changes that occurs after cells are exposed to an oxidant stress, we determined whether KGF reduces H2O2-induced pulmonary toxicity by attenuating AEC DNA damage. KGF (10-100 ng/ml) decreased H2O2 (0.05-0.5 mM)-induced DNA-SB formation in cultured A549 and rat alveolar type II cells measured by an alkaline unwinding, ethidium bromide fluorometric technique. The protective effects of KGF were independent of alterations in catalase, glutathione (GSH), or the expression of bcl-2 and bax, two protooncogenes known to regulate oxidant-induced apoptosis. Actinomycin D and cycloheximide abrogated protective effects of KGF. Furthermore, protection by KGF was completely blocked by 1) genistein, a tyrosine kinase inhibitor; 2) staurosporine and calphostin C, protein kinase C (PKC) inhibitors; and 3) aphidicolin, butylphenyl dGTP, and 2',3'-dideoxythymidine 5'-triphosphate, inhibitors of DNA polymerase. We conclude that KGF attenuates H2O2-induced DNA-SB formation in cultured AECs by mechanisms that involve tyrosine kinase, PKC, and DNA polymerases. These data suggest that the ability of KGF to protect against oxidant-induced lung injury is partly due to enhanced AEC DNA repair.

Cyclic stretch of airway epithelium inhibits prostanoid synthesis.

Airway epithelial cells (AEC) metabolize arachidonic acid (AA) to biologically active eicosanoids, which contribute to regulation of airway smooth muscle tone and inflammatory responses. Although in vivo the airways undergo cyclical stretching during ventilation, the effect of cyclic stretch on airway epithelial AA metabolism is unknown. In this study, cat and human AEC were grown on flexible membranes and were subjected to cyclic stretch using the Flexercell strain unit. Cyclic stretch downregulated synthesis of prostaglandin (PG) E2, PGI2, and thromboxane A2 by both cell types in a frequency-dependent manner. The percent inhibition of prostanoid synthesis in both cell types ranged from 53 +/- 7 to 75 +/- 8% (SE; n = 4 and 5, respectively). Treatment of cat AEC with exogenous AA (10 micrograms/ml) had no effect on the stretch-induced inhibition of PGE2 synthesis, whereas treatment with exogenous PGH2 (10 micrograms/ml) overcame the stretch-induced decrease in PGE2 production. These results indicate that stretch inhibits prostanoid synthesis by inactivating cyclooxygenase. When cells were pretreated with the antioxidants catalase (100 micrograms/ml, 150 U/ml) and N-acetylcysteine (1 mM), there was a partial recovery of eicosanoid production, suggesting that cyclic stretch-induced inactivation of cyclooxygenase is oxidant mediated. These results may have important implications for inflammatory diseases in which airway mechanics are altered.

Reduced superoxide dismutase in lung cells of patients with asthma.

Lung cells recovered from symptomatic patients with asthma generate increased amounts of reactive oxygen species (ROS). Animal and in vitro studies indicate that ROS can reproduce many of the features of asthma. The ability of ROS to produce the clinical features of asthma may depend on an individual's lung antioxidant defenses. Patients with asthma are reported to have reduced antioxidant defenses in peripheral blood, but little is known about the antioxidant defenses of their lung cells. To define lung cell antioxidant defenses in asthma, the glutathione concentration and the glutathione reductase, glutathione peroxidase, catalase, and superoxide dismutase (SOD) activities were measured in cells recovered by bronchoalveolar lavage (BAL cells) and by bronchial brushing (bronchial epithelial cells, HBEC) from normal subjects and patients with asthma. Superoxide dismutase activity was reduced 25% in BAL cells (p < .05) and nearly 50% in HBEC (p < .02) from patients with asthma. Alterations in the other antioxidants were not identified. A direct relationship was found between airway reactivity to methacholine, measured as PC(20)FEV(1), and HBEC SOD activity (r2 = 89; p < .005), but not between airway reactivity and the other antioxidants. The finding of reduced SOD activity in lung cells of patients with asthma suggests that diminished SOD activity serves as a marker of the inflammation characterizing asthma. Alternatively, it may play a role in the development or severity of the disease.

Increased 5-lipoxygenase metabolism in the lungs of human subjects exposed to ozone.

The environmental pollutant ozone, at sufficiently high levels, is known to induce pulmonary inflammation with resultant airway obstruction in normal subjects. Eicosanoids comprise one group of mediators released from alveolar macrophages which are involved in the pathogenesis of inflammatory lung diseases. We compared the effects of 2-h exposures to 0.4 ppm ozone and filtered air on pulmonary function and eicosanoid levels in bronchoalveolar lavage fluid in 11 normal healthy volunteers. Subjects were exposed to a 6-fold increase in minute ventilation using an adjusted work load on a cycle ergometer. All subjects complained of cough and dyspnea, and demonstrated increased airway obstruction, and increased specific airway resistance following ozone exposure as compared to air exposure. Bronchoalveolar lavage cell count demonstrated a 9-fold increase in the number of neutrophils with a lesser reduction in the number of alveolar macrophages following ozone exposure. Notably, bronchoalveolar lavage fluid leukotriene (LT) C4 (8-fold) and to a lesser extent LTB4 (1.5-fold) levels were higher following ozone exposure compared to air control, with no change in prostaglandins. In a subset of four subjects, alveolar macrophage arachidonic acid metabolism was studied in vitro following separate in vivo exposures to both ozone and air. Alveolar macrophages obtained following ozone exposure released more 5-lipoxygenase (1.5-fold) metabolites, with no change in cyclooxygenase metabolites, than did cells obtained following air exposure. These observations document activation of the 5-lipoxygenase pathway in the lung following ozone exposure, and suggest that alveolar macrophages may participate in the generation of LT, whose actions promote airway inflammation and obstruction.

Hydrogen peroxide increases the availability of arachidonic acid for oxidative metabolism by inhibiting acylation into phospholipids in the alveolar macrophage.

Reactive oxygen species stimulate metabolism of arachidonic acid (AA) to eicosanoids in a variety of cells and tissues, yet the pathway(s) by which oxidants increase the availability of AA for oxidative metabolism are not known. Thus, we explored the effects of hydrogen peroxide (H2O2) on deacylation and reacylation of AA to determine the enzymatic mechanism(s) by which this oxidant increases levels of free, unesterified AA, and thereby its oxidative metabolism to eicosanoids, in the rat alveolar macrophage (AM). Over the range from 0.1 to 0.5 mM, H2O2 caused marked time- and dose-dependent inhibition of incorporation of [3H]AA into macrophage phospholipids, whereas calcium ionophore A23187 and zymosan particles did not cause such inhibition. Within this concentration range, there was an almost exact reciprocal correlation between inhibition of [3H]AA acylation and H2O2-stimulated accumulation of free [3H]AA in prelabeled AM cultures. Thimerosal, which blocks AA reacylation but spares deacylation via phospholipase A2 (PLA2), did not affect accumulation of free [3H]AA in prelabeled cells stimulated with H2O2, while markedly augmenting [3H]AA release in response to A23187 and to zymosan. Despite its ability to block AA acylation almost completely, H2O2 did not directly inhibit arachidonoyl CoA synthetase or arachidonoyl CoA:lysophosphatide acyltransferase, which catalyze AA incorporation into phospholipids. However, H2O2 (0.1 to 0.5 mM) markedly depleted AMs of ATP, required for synthesis of the acylation intermediate arachidonoyl CoA, suggesting that this was the means by which H2O2 inhibited acylation. Notably, H2O2 (0.03 to 3 mM) failed to stimulate macrophage PLA2 activity. We conclude that H2O2, in contrast to A23187 and zymosan, inhibits incorporation of AA into phospholipids, and that this represents the major mechanism by which the oxidant increases the availability of free AA for oxidative metabolism in the AM. This may be an important basis for release of eicosanoids in oxidant-induced inflammation and injury of the lung.

Membrane association of active 5-lipoxygenase in resting cells. Evidence for novel regulation of the enzyme in the rat alveolar macrophage.

The enzyme 5-lipoxygenase (5-LO) catalyzes the first two steps in the metabolism of arachidonic acid to leukotrienes, substances which play pivotal roles both in normal host defense and in pathologic states of inflammation. Recent studies in granulocytic cells have shown that activation of 5-LO involves its Ca(2+)-dependent translocation from cytosol to membrane compartments. However, little information exists about the molecular regulation of 5-LO in macrophages, even though these cells comprise the resident effector cell population of most organs. We therefore examined the levels of 5-LO activity and immunoreactive protein in cytosol and membrane fractions of resident rat alveolar (AM) and peritoneal macrophages (PM) and compared them with the well studied human neutrophil (polymorphonuclear leukocyte). In the resting state, PM resembled polymorphonuclear leukocyte in that most of their cell-free 5-LO activity, as well as protein content, were localized to the cytosol fraction. By contrast, resting AM contained most of their activity and almost half of their immunoreactive protein in the crude membrane fraction. The inability of the drug MK-886 to reverse this membrane association suggested that the 5-LO-activating protein was not the site of binding in the resting cell; however, this drug completely inhibited leukotriene B4 synthesis in ionophore A23187-stimulated AM, indicating that an interaction between 5-LO and 5-LO-activating protein was nonetheless required for product synthesis upon stimulation. Translocation of cytosolic 5-LO protein could not be convincingly demonstrated in A23187-stimulated AM, suggesting that the pool of 5-LO enzyme responsible for product formation originated in the membrane rather than the cytosol fraction of the resting cell. The AM therefore represents the first mammalian cell in which 5-LO has been recovered from the membrane fraction (a) of a resting cell and (b) in active form. These novel findings extend our understanding of the molecular regulation of 5-LO and may be of importance in designing strategies to limit inflammation in the lung and other sites.

Basal activation of protein kinase C in rat alveolar macrophages: implications for arachidonate metabolism.

Alveolar macrophages (AM) exhibit numerous functional differences from other mononuclear phagocyte populations, even though they are derived from a common circulating monocytic precursor. Yet no differences in fundamental signaling mechanisms uniquely expressed by AM have been elucidated to date. Protein kinase C (PKC) is one signal transduction mechanism thought to have an important role in regulating macrophage function and about which little information exists for AM. This study was undertaken to assess the state of activation of PKC in cultured resident rat AM compared with resident rat peritoneal macrophages (PM) and the means by which active PKC regulates arachidonic acid (AA) metabolism in the two cell types. As assessed by a histone phosphorylation assay, resting AM, in contrast to PM, exhibited constitutive activation of PKC as evidenced by localization of a majority of PKC activity to the membrane fraction. Ionophore A23187-stimulated release and metabolism of AA were attenuated by depletion of or inhibition of cellular PKC activity in AM but not in PM. In contrast, A23187-stimulated AA metabolism was augmented by activation of PKC to a greater extent in PM than in AM. Results from both cell types indicated that the 5-lipoxygenase pathway was particularly upregulated by PKC activation. We conclude that activation of PKC occurs uniquely during macrophage residence in the alveolar space and that this property as well as the downregulation of PKC which results have profound consequences for the regulation of at least one important macrophage function, the synthesis of bioactive eicosanoids.

Differential dependence on protein kinase C of arachidonic acid metabolism stimulated by hydrogen peroxide and by zymosan in the alveolar macrophage.

The dependence on protein kinase C (PKC) of arachidonic acid (AA) metabolism stimulated by the biologically important oxidant H2O2, as compared to zymosan particles, was investigated in the rat alveolar macrophage. The PKC inhibitor staurosporine markedly reduced AA release and eicosanoid synthesis stimulated by zymosan, but only slightly inhibited AA release and metabolism induced by H2O2. Furthermore, in macrophages depleted of PKC by extended exposure to phorbol 12-myristate 13-acetate, AA release in response to zymosan was greatly inhibited, whereas that stimulated by H2O2 was attenuated to a significantly lesser degree. Thus, zymosan-stimulated AA metabolism requires active PKC, whereas H2O2-induced metabolism is largely PKC-independent. This provides direct evidence for the existence of two pathways of agonist-stimulated AA metabolism, which differ in their dependence on PKC, in the alveolar macrophage.

Glucocorticoids fail to inhibit arachidonic acid metabolism stimulated by hydrogen peroxide in the alveolar macrophage.

We have previously demonstrated that the biologically important oxidant hydrogen peroxide (H2O2) triggers release and metabolism of arachidonic acid (AA) in the alveolar macrophage (AM). In this study, we evaluated the ability of glucocorticoids to inhibit rat AM AA metabolism stimulated by H2O2, as compared to the particulate zymosan. Methylprednisolone and other glucocorticoids failed to significantly inhibit release of AA stimulated by H2O2, while markedly reducing AA release in response to zymosan. Similarly, methylprednisolone only weakly inhibited synthesis of thromboxane (Tx)B2 stimulated by H2O2, while inhibiting zymosan-induced eicosanoid synthesis to a marked degree. On the other hand, the phospholipase inhibitor mepacrine strongly inhibited AA release and TxB2 formation stimulated by both H2O2 and zymosan, indicating that H2O2 induced AA metabolism is indeed susceptible to pharmacologic inhibition. The failure of glucocorticoids to inhibit AA metabolism stimulated by H2O2 in the AM may in part explain their inability to ameliorate oxidant-mediated lung inflammation and injury.

Complex effects of in vitro hyperoxia on alveolar macrophage arachidonic acid metabolism.

Metabolites of arachidonic acid (AA) released into bronchoalveolar lavage fluid of animals exposed to hyperoxia have previously been implicated as mediators of pulmonary oxygen toxicity. The alveolar macrophage (AM) represents an important potential source of these eicosanoids. We have therefore investigated the effects of in vitro hyperoxia (95% O2/5% CO2) versus normoxia (95% air/5% CO2) on the metabolism of AA in the AM of the rat. Exposure to 95% O2 for up to 72 h did not impair the viability or affect the protein content of cultured AMs. Hyperoxia for 24 to 72 h increased the accumulation of free AA liberated from endogenous stores in cultures of resting AMs. Despite this increase in free AA, no changes in synthesis of thromboxane B2, prostaglandin (PG) E2, PGF2 alpha, leukotriene (LT) B4, or LTC4 were observed in resting AMs exposed to hyperoxia for up to 72 h. This was not due to degradation of eicosanoids in hyperoxia. However, formation of cyclooxygenase metabolites from exogenously supplied AA was reduced in hyperoxia-incubated AMs, suggesting that hyperoxia inhibited the cyclooxygenase enzyme. In AMs stimulated with calcium ionophore A23187, both AA release and synthesis of cyclooxygenase and lipoxygenase eicosanoids were augmented after incubation in hyperoxia for 24 to 72 h. The increase in A23187-stimulated LTB4 synthesis caused by hyperoxia was inhibited by the antioxidants catalase, superoxide dismutase, and the intracellular cysteine loading agent L-2-oxothiazolidine-4-carboxylic acid, suggesting that the augmentation by hyperoxia of A23187-induced AA metabolism was mediated by reactive oxygen metabolites. Thus, hyperoxia has complex effects on AA metabolism in the AM, which include the ability to augment the release of AA and formation of bioactive eicosanoids. These findings support a possible role for eicosanoid synthesis by the AM in the pathogenesis of oxygen toxicity of the lung.

Hydrogen peroxide inhibits alveolar macrophage 5-lipoxygenase metabolism in association with depletion of ATP.

We have previously shown that the biologically important reactive oxygen metabolite hydrogen peroxide (H2O2) stimulates arachidonic acid (AA) release and thromboxane A2 synthesis in the rat alveolar macrophage. We have now investigated the effects of H2O2 on alveolar macrophage 5-lipoxygenase metabolism. H2O2 failed to stimulate detectable synthesis of leukotriene B4, leukotriene C4, or 5-hydroxyeicosatetraenoic acid (5-HETE) as determined by reverse-phase high performance liquid chromatography (RP-HPLC) and sensitive radioimmunoassays (RIAs). This was not explained by oxidative degradation of leukotrienes by H2O2 at the concentrations used. Moreover, RIA and RP-HPLC analyses demonstrated that H2O2 dose-dependently inhibited synthesis of leukotriene B4, leukotriene C4, and 5-HETE induced by the agonists A23187 (10 microM) and zymosan (100 micrograms/ml), over the same concentration range at which it augmented synthesis of the cyclooxygenase products thromboxane A2 and 12-hydroxy-5,8,10-heptadecatrienoic acid. Four lines of evidence suggested that H2O2 inhibited alveolar macrophage leukotriene and 5-HETE synthesis by depleting cellular ATP, a cofactor for 5-lipoxygenase. 1) H2O2 depleted ATP in A23187- and zymosan-stimulated alveolar macrophages with a dose dependence very similar to that for inhibition of agonist-induced leukotriene synthesis. 2) The time courses of ATP depletion and inhibition of leukotriene B4 synthesis by H2O2 were compatible with a rate-limiting effect of ATP on leukotriene synthesis in H2O2-exposed cultures. 3) Treatment of alveolar macrophages with the electron transport inhibitor antimycin A prior to A23187 stimulation depleted ATP and inhibited leukotriene B4 and C4 synthesis to equivalent degrees, while thromboxane A2 production was spared. 4) Incubation with the ATP precursors inosine plus phosphate attenuated both ATP depletion and inhibition of leukotriene B4 and C4 synthesis in alveolar macrophages stimulated with A23187 in the presence of H2O2. Our results show that H2O2 has the capacity to act both as an agonist for macrophage AA metabolism, and as a selective inhibitor of the 5-lipoxygenase pathway, probably as a result of its ability to deplete ATP. Depletion of cellular energy stores by oxidants generated during inflammation in vivo may be a means by which the inflammatory response is self-limited.

Discontinuation of mechanical ventilation.

The vast majority of patients who undergo mechanical ventilation are able to discontinue ventilatory assistance within a few days. Typically, patients who require only short-term mechanical ventilation do not have severe underlying lung disease, and the problem for which they require ventilatory support is most commonly rapidly reversible. In these patients on short-term ventilatory support, parameters of spontaneous ventilatory requirements and respiratory muscle strength, including minute ventilation, maximal voluntary ventilation, vital capacity, and maximal inspiratory pressure, are useful in predicting the success of discontinuation of mechanical ventilation. Ventilatory support can generally be discontinued by a variety of techniques in these patients without the need for weaning from the ventilator per se. The smaller group of patients in whom it is not possible to discontinue mechanical ventilation within less than 7 days comprises individuals who frequently have severe acute or chronic lung disease, multisystem extrapulmonary disease, or neuromuscular disease. After a period of prolonged mechanical ventilatory support, these complicated patients require a process of progressive weaning in which they gradually become able to support spontaneous ventilation. Spontaneous ventilatory parameters do not correlate well with weaning ability in patients on long-term ventilatory support. A systematic and comprehensive approach in which attention is focused on optimizing pulmonary and nonpulmonary factors that affect the weaning process provides the best chance for successful withdrawal of ventilatory support after long-term mechanical ventilation. Inadequate ventilatory drive, respiratory muscle weakness and fatigue, increased work of breathing, excessive CO2 production, and cardiac failure are potential mechanisms that may play a role in inhibiting successful weaning. Adverse factors relevant to each of these mechanisms must be addressed and corrected to whatever extent possible. Studies have not demonstrated the superiority of either classic T-piece weaning or IMV weaning methods in difficult-to-wean patients on long-term ventilatory support. Both techniques may be used successfully as long as all patient variables that may adversely affect weaning ability are corrected or optimized and close care and attention to the details of the weaning process itself are provided.(ABSTRACT TRUNCATED AT 400 WORDS)

Hydrogen-peroxide-induced arachidonic acid metabolism in the rat alveolar macrophage.

Mounting evidence suggests that reactive oxygen metabolites can initiate the release and metabolism of arachidonic acid (AA). We therefore examined the effects of hydrogen peroxide (H2O2), a biologically relevant oxygen metabolite, on AA release and cyclooxygenase metabolism by the rat alveolar macrophage (AM). At concentrations between 10(-4) and 10(-3) M, which were largely noncytotoxic as assessed by chromium release, H2O2 exposure for 30 min caused a steep dose-dependent increase in AA release that peaked at approximately 5-fold stimulation at 10(-3) M H2O2. AA release induced by H2O2 was inhibited by the H2O2 scavenger catalase, but not by inactivated catalase or by scavengers of superoxide anion, hydroxyl radical, or ferric iron. An evaluation of cyclooxygenase metabolite formation by specific radioimmunoassays and high performance liquid chromatography demonstrated a greater than 2-fold increment in thromboxane (Tx)A2 (measured as TxB2) synthesis at 10(-4) M H2O2, but no increment in prostaglandin (PG) E2 synthesis. H2O2-induced TxB2 synthesis was cyclooxygenase-dependent, since it was inhibited by indomethacin (1 microM). There was no significant degradation of either PGE2 or TxB2 in AM cultures by H2O2 at concentrations to 10(-2) M. The effect of H2O2 on agonist-induced cyclooxygenase metabolism was also examined. H2O2 at 10(-4) M inhibited PGE2 synthesis induced by zymosan and A23187, whereas agonist-induced TxB2 synthesis was either unaffected (zymosan) or augmented (A23187) by H2O2. These findings suggest inhibition by H2O2 of PGE2 synthesis.(ABSTRACT TRUNCATED AT 250 WORDS)