The lung HETEs (and EETs) up

The association of eicosanoids and eicosanoid-related metabolites with pulmonary hypertension

BACKGROUND

Eicosanoids are bioactive lipids that regulate systemic inflammation and exert vasoactive effects. Specific eicosanoid metabolites have previously been associated with pulmonary hypertension (PH), yet their role remains incompletely understood.

METHODS

We studied 482 participants with chronic dyspnoea who underwent clinically indicated cardiopulmonary exercise testing (CPET) with invasive haemodynamic monitoring. We performed comprehensive profiling of 888 eicosanoids and eicosanoid-related metabolites using directed non-targeted mass spectrometry, and examined associations with PH (mean pulmonary arterial pressure (mPAP) >20 mmHg), PH subtypes and physiological correlates, including transpulmonary metabolite gradients.

RESULTS

Among 482 participants (mean±sd age 56±16 years, 62% women), 200 had rest PH. We found 48 eicosanoids and eicosanoid-related metabolites that were associated with PH. Specifically, prostaglandin (11β-dhk-PGF2α), linoleic acid (12,13-EpOME) and arachidonic acid derivatives (11,12-DiHETrE) were associated with higher odds of PH (false discovery rate q<0.05 for all). By contrast, epoxide (8(9)-EpETE), α-linolenic acid (13(S)-HOTrE(γ)) and lipokine derivatives (12,13-DiHOME) were associated with lower odds. Among PH-related eicosanoids, 14 showed differential transpulmonary metabolite gradients, with directionality suggesting that metabolites associated with lower odds of PH also displayed pulmonary artery uptake. In individuals with exercise PH, eicosanoid profiles were intermediate between no PH and rest PH, with six metabolites that differed between rest and exercise PH.

CONCLUSIONS

Our findings highlight the role of specific eicosanoids, including linoleic acid and epoxide derivatives, as potential regulators of inflammation in PH. Of note, physiological correlates, including transpulmonary metabolite gradients, may prioritise future studies focused on eicosanoid-related pathways as important contributors to PH pathogenesis.

Significance of Pulmonary Endothelial Injury and the Role of Cyclooxygenase-2 and Prostanoid Signaling

The endothelium plays a key role in the dynamic balance of hemodynamic, humoral and inflammatory processes in the human body. Its central importance and the resulting therapeutic concepts are the subject of ongoing research efforts and form the basis for the treatment of numerous diseases. The pulmonary endothelium is an essential component for the gas exchange in humans. Pulmonary endothelial dysfunction has serious consequences for the oxygenation and the gas exchange in humans with the potential of consecutive multiple organ failure. Therefore, in this review, the dysfunction of the pulmonary endothel due to viral, bacterial, and fungal infections, ventilator-related injury, and aspiration is presented in a medical context. Selected aspects of the interaction of endothelial cells with primarily alveolar macrophages are reviewed in more detail. Elucidation of underlying causes and mechanisms of damage and repair may lead to new therapeutic approaches. Specific emphasis is placed on the processes leading to the induction of cyclooxygenase-2 and downstream prostanoid-based signaling pathways associated with this enzyme.

The influence of Hyssopus cuspidatus Boriss extract on lipid mediators metabolism network in asthmatic mice

Current drugs do not provide an absolute cure or modify the course of asthma. Hyssopus cuspidatus Boriss extract (SXCF) has been used as Uyghur medicine for several years to treat bronchial asthma. However, very limited research has been conducted on the therapeutic mechanisms of SXCF. Disruptions in the metabolic network of lipid mediators (LMs) are closely linked to the development of asthma. Here, we explored the therapeutic mechanism of SXCF in asthma based on the metabolic network of LMs, aiming to contribute to the understanding of SXCF in asthma treatment at the molecular level. The UHPLC-MRM strategy was used for the quantitative detection of LMs in the lung tissue and in the peripheral circulatory system (serum). ELISA was used to detect IgE in serum and cytokines in BALF. The lung tissue sections were stained with H&E to observe the infiltration of inflammatory cells, and behavioural changes in mice were observed and recorded throughout the animal experiment. In contrast to the asthma group, the opposite result was observed in the SXCF groups, where the perturbed LMs metabolic network was partly restored in a dose-dependent manner with a significant elevation of anti-inflammatory metabolites, while pro-inflammatory lipids were decreased. As significant downregulation of IgE and pro-inflammatory cytokines was observed, IgE and cytokines analysis also supported the anti-inflammatory effects of SXCF. It was also noticed that SXCF treatment reduced the number of coughs and decreased the inflammatory cell infiltration around the bronchus in mice. These results suggested that SXCF has a significant ameliorative effect on ovalbumin (OVA)-induced asthma. The modulation of LMs is a possible underlying mechanism of the SXCF effects.

Glycaemic Control in Patients Undergoing Percutaneous Coronary Intervention: What Is the Role for the Novel Antidiabetic Agents? A Comprehensive Review of Basic Science and Clinical Data

Coronary artery disease (CAD) remains one of the most important causes of morbidity and mortality worldwide, and revascularization through percutaneous coronary interventions (PCI) significantly improves survival. In this setting, poor glycaemic control, regardless of diabetes, has been associated with increased incidence of peri-procedural and long-term complications and worse prognosis. Novel antidiabetic agents have represented a paradigm shift in managing patients with diabetes and cardiovascular diseases. However, limited data are reported so far in patients undergoing coronary stenting. This review intends to provide an overview of the biological mechanisms underlying hyperglycaemia-induced vascular damage and the contrasting actions of new antidiabetic drugs. We summarize existing evidence on the effects of these drugs in the setting of PCI, addressing pre-clinical and clinical studies and drug-drug interactions with antiplatelet agents, thus highlighting new opportunities for optimal long-term management of these patients.

Mass spectrometry imaging of phosphatidylcholine metabolism in lungs administered with therapeutic surfactants and isotopic tracers

Mass spectrometry imaging (MSI) visualizes molecular distributions throughout tissues but is blind to dynamic metabolic processes. Here, MSI with high mass resolution together with multiple stable isotope labeling provided spatial analyses of phosphatidylcholine (PC) metabolism in mouse lungs. Dysregulated surfactant metabolism is central to many respiratory diseases. Metabolism and turnover of therapeutic pulmonary surfactants were imaged from distributions of intact and metabolic products of an added tracer, universally 13C-labeled dipalmitoyl PC (U13C-DPPC). The parenchymal distributions of newly synthesized PC species were also imaged from incorporations of methyl-D9-choline. This dual labeling strategy demonstrated both lack of inhibition of endogenous PC synthesis by exogenous surfactant and location of acyl chain remodeling processes acting on the U13C-DPPC-labeled surfactant, leading to formation of polyunsaturated PC lipids. This ability to visualize discrete metabolic events will greatly enhance our understanding of lipid metabolism in diverse tissues and has potential application to both clinical and experimental studies.

The role of cytochrome P450 (CYP) enzymes in hyperoxic lung injury

INTRODUCTION

Hyperoxic lung injury is a condition that can occur in patients in need of supplemental oxygen, such as premature infants with bronchopulmonary dysplasia or adults with acute respiratory distress syndrome. Cytochrome P450 (CYP) enzymes play critical roles in the metabolism of endogenous and exogenous compounds.

AREAS COVERED

Through their complex pathways, some subfamilies of these enzymes may contribute to or protect against hyperoxic lung injury. Oxidative stress from reactive oxygen species (ROS) production is most likely a major contributor of hyperoxic lung injury. CYP1A enzymes have been shown to protect against hyperoxic lung injury while CYP1B enzymes seem to contribute to it. CYP2J2 enzymes help protect against hyperoxic lung injury by triggering EET production, thereby, increasing antioxidant enzymes. The metabolism of arachidonic acid to ω-terminal hydroxyeicosatetraenoic acid (20-HETEs) by CYP4A and CYP4F enzymes could impact hyperoxic lung injury via the vasodilating effects of 20-HETE. CYP2E1 and CYP2A enzymes may contribute to the oxidative stress in the lungs caused by ethanol- and nicotine-metabolism, respectively.

EXPERT OPINION

Overall, the CYP enzymes, depending upon the isoform, play a contributory or protective role in hyperoxic lung injury, and are, therefore, ideal candidates for developing drugs that can treat oxygen-mediated lung injury.

Association between CYP2C19 gene polymorphisms and susceptibility to high-altitude pulmonary edema

INTRODUCTION

High-altitude pulmonary edema (HAPE) is caused by the interaction of both genetic and environmental risk factors.

OBJECTIVES

In this study, we aimed to explore whether three single nucleotide polymorphisms (SNPs) in CYP2C19 gene influenced the HAPE susceptibility in the Chinese Han population.

METHODS

We recruited 238 cases and 230 controls between January 2018 and October 2018 from the Affiliated Hospital of Xizang Minzu University. The relationship between CYP2C19 gene polymorphisms and HAPE was studied by association analysis. Genotyping was performed using the Agena MassARRAY platform and the statistical analysis was performed using Chi-squared test, independent sample t test, genetic model analysis and haplotype analysis.

RESULTS

The main finding of our study showed that rs4494250 in CYP2C19 gene was associated with an increased risk of HAPE at age >32 years in the log-additive model (OR = 1.80, 95% CI = 1.05-3.09, P = 0.033). Also, it was observed to be associated with a reduced risk of HAPE at age ≤2 years in the dominant model (A/G-A/A vs G/G, OR = 0.55, 95% CI = 0.31-0.97, P = 0.038) and in the log-additive model (OR = 0.58, 95% CI = 0.35-0.96, P = 0.033).

CONCLUSION

Our findings demonstrated that CYP2C19 genetic variants were associated with risk of developing HAPE in Han Chinese population.

Role of epoxyeicosatrienoic acids in the lung

Epoxyeicosatrienoic acids (EETs) are synthetized from arachidonic acid by the action of members of the CYP2C and CYP2J subfamilies of cytochrome P450 (CYPs). The effects of EETs on cardiovascular function, the nervous system, the kidney and metabolic disease have been reviewed. In the lungs, the presence of these CYPs and EETs has been documented. In general, EETs play a beneficial role in this essential tissue. Among the most important effects of EETs in the lungs are the induction of vasorelaxation in the bronchi, the stimulation of Ca²⁺-activated K⁺ channels, the induction of vasoconstriction of pulmonary arteries, anti-inflammatory effects induced by asthma, and protection against infection or exposure to chemical substances such as cigarette smoke. EETs also participate in tissue regeneration, but on the downside, they are possibly involved in the progression of lung cancer. More research is necessary to design therapies with EETs for the treatment of lung disease.

EETs promote hypoxic pulmonary vasoconstriction via constrictor prostanoids

To test the hypothesis that epoxyeicosatrienoic acids (EETs) facilitate pulmonary responses to hypoxia, male wild-type (WT) and soluble-epoxide hydrolase knockout (sEH-KO) mice, and WT mice chronically fed a sEH inhibitor (t-TUCB; 1 mg·kg^-1·day^-1) were used. Right ventricular systolic pressure (RVSP) was recorded under control and hypoxic conditions. The control RVSP was comparable among all groups. However, hypoxia elicited increases in RVSP in all groups with predominance in sEH-KO and t-TUCB-treated mice. 14,15-EEZE (an EET antagonist) attenuated the hypoxia-induced greater elevation of RVSP in sEH-deficient mice, suggesting an EET-mediated increment. Exogenous 5,6-; 8,9-, or 14,15-EET (0.05 ng/g body wt) did not change RVSP in any conditions, but 11,12-EET enhanced RVSP under hypoxia. Isometric tension was recorded from pulmonary arteries isolated from WT and sEH-KO mice, vessels that behaved identically in their responsiveness to vasoactive agents and vessel stretch. Hypoxic pulmonary vasoconstriction (HPV, expressed as increases in hypoxic force) was significantly greater in vessels of sEH-KO than WT vessels; the enhanced component was inhibited by EEZE. Treatment of WT vessels with 11,12-EET enhanced HPV to the same level as sEH-KO vessels, confirming EETs as primary players. Inhibition of cyclooxygenases (COXs) significantly enhanced HPV in WT vessels, but attenuated HPV in sEH-KO vessels. Blocking/inhibiting COX-1, prostaglandin H₂ (PGH₂)/thromboxane A₂ (TXA₂) receptors and TXA synthase prevented the enhanced HPV in sEH-KO vessels but had no effects on WT vessels. In conclusion, an EET-dependent alteration in PG metabolism that favors the action of vasoconstrictor PGH₂ and TXA₂ potentiates HPV and hypoxia-induced elevation of RVSP in sEH-deficient mice.

Lung Circulation

The circulation of the lung is unique both in volume and function. For example, it is the only organ with two circulations: the pulmonary circulation, the main function of which is gas exchange, and the bronchial circulation, a systemic vascular supply that provides oxygenated blood to the walls of the conducting airways, pulmonary arteries and veins. The pulmonary circulation accommodates the entire cardiac output, maintaining high blood flow at low intravascular arterial pressure. As compared with the systemic circulation, pulmonary arteries have thinner walls with much less vascular smooth muscle and a relative lack of basal tone. Factors controlling pulmonary blood flow include vascular structure, gravity, mechanical effects of breathing, and the influence of neural and humoral factors. Pulmonary vascular tone is also altered by hypoxia, which causes pulmonary vasoconstriction. If the hypoxic stimulus persists for a prolonged period, contraction is accompanied by remodeling of the vasculature, resulting in pulmonary hypertension. In addition, genetic and environmental factors can also confer susceptibility to development of pulmonary hypertension. Under normal conditions, the endothelium forms a tight barrier, actively regulating interstitial fluid homeostasis. Infection and inflammation compromise normal barrier homeostasis, resulting in increased permeability and edema formation. This article focuses on reviewing the basics of the lung circulation (pulmonary and bronchial), normal development and transition at birth and vasoregulation. Mechanisms contributing to pathological conditions in the pulmonary circulation, in particular when barrier function is disrupted and during development of pulmonary hypertension, will also be discussed.

Soluble epoxide hydrolase inhibitor attenuates inflammation and airway hyperresponsiveness in mice

Control of airway inflammation is critical in asthma treatment. Soluble epoxide hydrolase (sEH) has recently been demonstrated as a novel therapeutic target for treating inflammation, including lung inflammation. We hypothesized that pharmacological inhibition of sEH can modulate the inflammatory response in a murine ovalbumin (OVA) model of asthma. BALB/c mice were sensitized and exposed to OVA over 6 weeks. A sEH inhibitor (sEHI) was administered for 2 weeks. Respiratory system compliance, resistance, and forced exhaled nitric oxide were measured. Lung lavage cell counts were performed, and selected cytokines and chemokines in the lung lavage fluid were measured. A LC/MS/MS method was used to measure 87 regulatory lipids mediators in plasma, lung tissue homogenates, and lung lavage fluid. The pharmacological inhibition of sEH increased concentrations of the antiinflammatory epoxy eicosatrienoic acids and simultaneously decreased the concentrations of the proinflammatory dihydroxyeicosatrienoic acids and dihydroxyoctadecenoic acids. All monitored inflammatory markers, including FeNO levels, and total cell and eosinophil numbers in the lung lavage of OVA-exposed mice were reduced by sEHI. The type 2 T helper cell (Th2) cytokines (IL-4, IL-5) and chemokines (Eotaxin and RANTES) were dramatically reduced after sEHI administration. Resistance and dynamic lung compliance were also improved by sEHI. We demonstrated that sEHI administration attenuates allergic airway inflammation and airway responsiveness in a murine model. sEHI may have potential as a novel therapeutic strategy for allergic asthma.

Endocannabinoid metabolism by cytochrome P450 monooxygenases

The endogenous cannabinoid system was first uncovered following studies of the recreational drug Cannabis sativa. It is now recognized as a vital network of signaling pathways that regulate several physiological processes. Following the initial discovery of the cannabinoid receptors 1 (CB1) and 2 (CB2), activated by Cannabis-derived analogs, many endogenous fatty acids termed "endocannabinoids" are now known to be partial agonists of the CB receptors. At present, the most thoroughly studied endocannabinoid signaling molecules are anandamide (AEA) and 2-arachidonylglycerol (2-AG), which are both derived from arachidonic acid. Both AEA and 2-AG are also substrates for the eicosanoid-synthesizing pathways, namely, certain cyclooxygenase (COX), lipoxygenase (LOX), and cytochrome P450 (CYP) enzymes. In the past, research in the endocannabinoid field focused on the interaction of AEA and 2-AG with the COX and LOX enzymes, but accumulating evidence also points to the involvement of CYPs in modulating endocannabinoid signaling. The focus of this review is to explore the current understanding of CYP-mediated metabolism of endocannabinoids.

Cytochrome P450 2J2: distribution, function, regulation, genetic polymorphisms and clinical significance

Cytochrome P450 2J2 (CYP2J2) is an enzyme mainly found in human extrahepatic tissues, with predominant expression in the cardiovascular systems and lower levels in the intestine, kidney, lung, pancreas, brain, liver, etc. During the past 15 years, CYP2J2 has attracted much attention for its epoxygenase activity in arachidonic acid (AA) metabolism. It converts AA to four epoxyeicosatrienoic acids (EETs) that have various biological effects, especially in the cardiovascular systems. In recent publications, CYP2J2 is shown highly expressed in various human tumor cells, and its EET metabolites are demonstrated to implicate in the pathologic development of human cancers. CYP2J2 is also a human CYP that involved in phase I xenobiotics metabolism. Antihistamine drugs and many other compounds were identified as the substrates of CYP2J2, and studies have demonstrated that these substrates have a broad structural diversity. CYP2J2 is found not readily induced by known P450 inducers; however, its expression could be regulated in some pathological conditions, might through the activator protein-1(AP-1), the AP-1-like element and microRNA let-7b. Several genetic mutations in the CYP2J2 gene have been identified in humans, and some of them have been shown to have potential associations with some diseases. With the increasing awareness of its roles in cancer disease and drug metabolism, studies about CYP2J2 are still going on, and various inhibitors of CYP2J2 have been determined. Further studies are needed to delineate the roles of CYP2J2 in disease pathology, drug development and clinical practice.

Quantitative metabolic profiling of lipid mediators

Lipids are heterogeneous biological molecules that possess multiple physiological roles including cell structure, homeostasis, and restoration of tissue functionality during and after inflammation. Lipid metabolism constitutes a network of pathways that are related at multiple biosynthetic hubs. Disregulation of lipid metabolism can lead to pathophysiological effects and multiple lipid mediators have been described to be involved in physiological processes, (e.g. inflammation). Accordingly, a thorough description of these pathways may shed light on putative relations in multiple complex diseases, including chronic obstructive pulmonary disease, asthma, Alzheimer's disease, multiple sclerosis, obesity, and cancer. Due to the structural complexity of lipids and the low abundance of many lipid mediators, mass spectrometry is the most commonly employed method for analysis. However, multiple challenges remain in the efforts to analyze every lipid subfamily. In this review, the biological role of sphingolipids, glycerolipids, oxylipins (e.g. eicosanoids), endocannabinoids, and N-acylethanolamines in relation to health and disease and the state-of-the-art analyses are summarized. The characterization and understanding of these pathways will increase our ability to examine for interrelations among lipid pathways and improve the knowledge of biological mechanisms in health and disease.

Eicosanoid biosynthesis during mucociliary and mucous metaplastic differentiation of bronchial epithelial cells

The purpose of this study was to examine the profile of eicosanoids secreted by human bronchial epithelial cells (HBEC) during their in vitro differentiation toward mucociliary or mucous metaplastic phenotype. Eicosanoids were measured in supernatants by mass spectrometry, and corresponding gene expression by real-time PCR. Primary HBEC produced mainly prostaglandins (PGE2, PGD2) and epoxides (e.g. 14,15-EET), but during further mucociliary differentiation we observed a gradual increase in secretion of lipoxygenase derived HETEs. Treatment with IL-13 and IL-4 induced mucous metaplasia and resulted in downregulation of PG pathway, and potent induction of 15-lipoxygenase (marked release of 15-HETE). The deficiency in PG production sustained during long term culture of mucous metaplastic epithelia. In conclusions, Th2-type cytokines induce changes in eicosanoid metabolism of airway epithelial cells, resulting in an immense induction of 15-lipoxygenase pathway, and inhibition of PG pathways. Deficient production of immunomodulatory PGs may promote chronic inflammation and airway remodeling.

Human alveolar epithelial cells attenuate pulmonary microvascular endothelial cell permeability under septic conditions

Acute lung injury (ALI) and its most severe form, acute respiratory distress syndrome (ARDS), are characterised by high-protein pulmonary edema and severe hypoxaemic respiratory failure due to increased permeability of pulmonary microvascular endothelial cells (PMVEC). Alveolar epithelial cells (AEC) contribute importantly to normal alveolar function, and AEC dysfunction in ALI/ARDS is associated with worse outcomes. We hypothesized that AEC can modulate human PMVEC barrier function, and investigated the effects of AEC presence on human PMVEC barrier under septic conditions in vitro. PMVEC isolated from human lung were treated in vitro with septic stimulation (lipopolysaccharide [LPS], a mixture of clinically-relevant cytokines [cytomix], or plasma from patients with severe sepsis), and the trans-PMVEC leak of Evans Blue dye-labeled albumin assessed. PMVEC septic responses were compared in the presence/absence of co-cultured A549 epithelial cell line or primary human AEC. Septic stimulation with LPS, cytomix, or septic plasma induced marked PMVEC hyper-permeability (10.2±1.8, 8.9±2.2, and 3.7±0.2 fold-increase vs. control, respectively, p<0.01 for all). The presence of A549 cells or primary human AEC in a non-contact co-culture model attenuated septic PMVEC hyper-permeability by 39±4% to 100±3%, depending on the septic stimulation (p<0.05). Septic PMVEC hyper-permeability was also attenuated following treatment with culture medium conditioned by previous incubation with either naïve or cytomix-treated A549 cells (p<0.05), and this protective effect of A549 cell-conditioned medium was both heat-stable and transferable following lipid extraction. Cytomix-stimulated PMN-dependent PMVEC hyper-permeability and trans-PMVEC PMN migration were also inhibited in the presence of A549 cells or A549 cell-conditioned medium (p<0.05). Human AEC appear to protect human PMVEC barrier function under septic conditions in vitro, through release of a soluble mediator(s), which are at least partly lipid in nature. This study suggests a scientific and potential clinical therapeutic importance of epithelial-endothelial cross talk in maintaining alveolar integrity in ALI/ARDS.

Biochemical pathogenesis of aspirin exacerbated respiratory disease (AERD)

Aspirin exacerbated respiratory disease (AERD) is a distinct clinical entity characterized by eosinophilic rhinosinusitis, asthma and often nasal polyposis. Exposure to aspirin or other nonsteroid anti-inflammatory drugs (NSAIDs) exacerbates bronchospasms with asthma and rhinitis. Disease progression suggests a skewing towards TH2 type cellular response along with moderate to severe eosinophil and mast cell infiltration. Alterations in upper and lower airway cellular milieu with abnormalities in eicosanoid metabolism and altered eicosanoid receptor expression are the key features underlying AERD pathogenesis. Dysregulation of arachidonic acid (AA) metabolism, notably reduced prostaglandin E2 (PGE2) synthesis compared to their aspirin tolerant counterpart and relatively increased PGD2 production, a TH2/eosinophil chemoattractant are reported in AERD. Underproduced PGE2 is metabolized by overexpression of 15 prostaglandin dehydrogenase (15-PGDH) to inactive products further reducing PGE2 at real time. This relives the inhibitory effect of PGE2 on 5-lipoxygenase (5-LOX) resulting in overproduction of cysteinyl leukotrienes (CysLTs). Diminished formation of CysLT antagonists called lipoxins (LXs) also augments CysLTs responsiveness. Occasional intake of NSAIDs favors even more 5-LOX product formation, further narrowing the bronchoconstrictive bottle neck, resulting in acute asthmatic exacerbations along with increased mucus production. This review focuses on abnormalities in biochemical and molecular mechanisms in eicosanoid biosynthesis, eicosanoid receptor dysregulation and associated polymorphisms with special reference to arachidonic acid metabolism in AERD.

Cytochrome P450-derived epoxyeicosatrienoic acids and pulmonary hypertension: central role of transient receptor potential C6 channels

Hypoxia induces the constriction of pulmonary resistance arteries, which results in the redistribution of blood from poor to better ventilated areas, thus optimizing its oxygenation. Many different oxygen-sensing mechanisms have been proposed to regulate this process, including cytochrome P450 enzymes. These enzymes, which convert substrates such as arachidonic acid into bioactive epoxides (the epoxyeicosatrienoic acids [EETs]), are highly expressed in the lung as is the soluble epoxide hydrolase which metabolizes the epoxides to their less active diols. The EETs play a well-documented role as endothelium-derived vasodilators in the systemic vasculature, but in the pulmonary circulation, they are generated in vascular smooth muscle cells and potentiate vasoconstriction. Preventing the breakdown of 11,12-EET by the inhibition or genetic deletion of the soluble epoxide hydrolase strongly augments the response to hypoxia. Mechanistically, 11,12-EET potentiates the contractile response by recruiting transient receptor potential C6 channels to caveolae. Indeed, neither 11,12-EET nor hypoxia is able to elicit pulmonary vasoconstriction in TRPC6 knockout mice. The cytochrome and soluble epoxide hydrolase enzymes are also implicated in the vascular remodeling associated with chronic hypoxia and pulmonary hypertension. Thus, targeting this pathway may be in an attractive new therapeutic approach to treat this incapacitating disease.

Hypoxic pulmonary vasoconstriction

It has been known for more than 60 years, and suspected for over 100, that alveolar hypoxia causes pulmonary vasoconstriction by means of mechanisms local to the lung. For the last 20 years, it has been clear that the essential sensor, transduction, and effector mechanisms responsible for hypoxic pulmonary vasoconstriction (HPV) reside in the pulmonary arterial smooth muscle cell. The main focus of this review is the cellular and molecular work performed to clarify these intrinsic mechanisms and to determine how they are facilitated and inhibited by the extrinsic influences of other cells. Because the interaction of intrinsic and extrinsic mechanisms is likely to shape expression of HPV in vivo, we relate results obtained in cells to HPV in more intact preparations, such as intact and isolated lungs and isolated pulmonary vessels. Finally, we evaluate evidence regarding the contribution of HPV to the physiological and pathophysiological processes involved in the transition from fetal to neonatal life, pulmonary gas exchange, high-altitude pulmonary edema, and pulmonary hypertension. Although understanding of HPV has advanced significantly, major areas of ignorance and uncertainty await resolution.

Upregulation of osmo-mechanosensitive TRPV4 channel facilitates chronic hypoxia-induced myogenic tone and pulmonary hypertension

Chronic hypoxia causes pulmonary hypertension with vascular remodeling, increase in vascular tone, and altered reactivity to agonists. These changes involve alterations in multiple Ca(2+) pathways in pulmonary arterial smooth muscle cells (PASMCs). We have previously shown that vanilloid (TRPV)- and melastatin-related transient receptor potential (TRPM) channels are expressed in pulmonary arteries (PAs). Here we found that TRPV4 was the only member of the TRPV and TRPM subfamilies upregulated in PAs of chronic hypoxic rats. The increase in TRPV4 expression occurred within 1 day of hypoxia exposure, indicative of an early hypoxic response. TRPV4 in PASMCs were found to be mechanosensitive. Osmo-mechanical stress imposed by hypotonic solution activated Ca(2+) transients; they were inhibited by TRPV4 specific short interfering RNA, the TRPV blocker ruthenium red, and the cytochrome P450 epoxygenase inhibitor N-(methylsulfonyl)-2-(2-propynyloxy)-benzenehexanamide. Consistent with TRPV4 upregulation, the Ca(2+) response induced by the TRPV4 agonist 4α-phorbol 12,13-didecanoate and hypotonicity was potentiated in hypoxic PASMCs. Moreover, a significant myogenic tone, sensitive to ruthenium red, was observed in pressurized endothelium denuded small PAs of hypoxic but not normoxic rats. The elevated basal intracellular Ca(2+) concentration in hypoxic PASMCs was also reduced by ruthenium red. In extension of these results, the development of pulmonary hypertension, right heart hypertrophy, and vascular remodeling was significantly delayed and suppressed in hypoxic trpv4(-/-) mice. These results suggest the novel concept that TRPV4 serves as a signal pathway crucial for the development of hypoxia-induced pulmonary hypertension. Its upregulation may provide a pathogenic feed-forward mechanism that promotes pulmonary hypertension via facilitated Ca(2+) influx, subsequently enhanced myogenic tone and vascular remodeling.

Epithelial cells and airway diseases

The airway epithelial cell is the initial cell type impacted both by inhaled environmental factors, such as pathogens, allergens, and pollutants, and inhaled medications for airway diseases. As such, epithelial cells are now recognized to play a central role in the regulation of airway inflammatory status, structure, and function in normal and diseased airways. This article reviews our current knowledge regarding the roles of the epithelial cell in airway inflammation and host defense. The interactions of inhaled environmental factors and pathogens with epithelial cells are also discussed, with an emphasis on epithelial innate immune responses and contributions of epithelial cells to immune regulation. Recent evidence suggesting that epithelial cells play an active role in inducing several of the structural changes, collectively referred to airway remodeling, seen in the airways of asthmatic subjects is reviewed. Finally, the concept that the epithelium is a major target for the actions of a number of classes of inhaled medications is discussed, as are the potential mechanisms by which selected drugs may alter epithelial function.

Role of arachidonic acid-derived metabolites in the control of pulmonary arterial pressure and hypoxic pulmonary vasoconstriction in rats

BACKGROUND

The roles of arachidonic acid (AA) metabolites in hypoxia-induced pulmonary vasoconstriction (HPV), a critical physiological mechanism that prevents ventilation/perfusion mismatch, are still incompletely understood.

METHODS

Pulmonary arterial pressure was measured in ventilated/perfused rat lungs. Isometric tones of rat intralobar pulmonary arteries were also measured, using a myograph.

RESULTS

Hypoxia (Po₂, 3%)-induced pulmonary arterial pressure increases (ΔPAP(hypox)) were stable with blood-mixed perfusate, but decayed spontaneously. ΔPAP(hypox) was inhibited by 29%, 16%, and 28% by the thromboxane A₂ (TXA₂) antagonist SQ-29548, the 5-lipoxygenase inhibitor, MK886, and the leukotriene D₄ antagonist, LY-171883, respectively. The prostacyclin synthase inhibitor tranylcypromine augmented ΔPAP(hypox) by 5%, whereas inhibition of cytochrome P450 did not affect ΔPAP(hypox). Consistently, the TXA₂ analogue U46619 increased ΔPAP(hypox) whereas prostacyclin abolished ΔPAP(hypox). However, leukotriene D₄ had no direct effect on ΔPAP(hypox). In the isolated pulmonary arteries, pretreatment with U46619 was essential to demonstrate hypoxia-induced contraction.

CONCLUSIONS

The above results suggest that TXA₂ and cysteinyl leukotrienes, other than leukotriene D₄, are endogenous factors that facilitate HPV in rats. The indispensable role of TXA₂-induced pretone in the HPV of isolated pulmonary arteries indicates that the signal from thromboxane receptors might be a critical component of oxygen sensation mechanisms.

Role of cytochrome P450 enzymes in the bioactivation of polyunsaturated fatty acids

Cytochrome P450 (CYP)-dependent metabolites of arachidonic acid (AA), such as epoxyeicosatrienoic acids and 20-hydroxyeicosatetraenoic acid, serve as second messengers of various hormones and growth factors and play pivotal roles in the regulation of vascular, renal and cardiac function. As discussed in the present review, virtually all of the major AA metabolizing CYP isoforms accept a variety of other polyunsaturated fatty acids (PUFA), including linoleic, eicosapentaenoic (EPA) and docosahexaenoic acids (DHA), as efficient alternative substrates. The metabolites of these alternative PUFAs also elicit profound biological effects. The CYP enzymes respond to alterations in the chain-length and double bond structure of their substrates with remarkable changes in the regio- and stereoselectivity of product formation. The omega-3 double bond that distinguishes EPA and DHA from their omega-6 counterparts provides a preferred epoxidation site for CYP1A, CYP2C, CYP2J and CYP2E subfamily members. CYP4A enzymes that predominantly function as AA ω-hydroxylases show largely increased (ω-1)-hydroxylase activities towards EPA and DHA. Taken together, these findings indicate that CYP-dependent signaling pathways are highly susceptible to changes in the relative bioavailability of the different PUFAs and may provide novel insight into the complex mechanisms that link essential dietary fatty acids to the development of cardiovascular disease.

Enhanced pulmonary expression of the TrkB neurotrophin receptor in hypoxic rats is associated with increased acetylcholine-induced airway contractility

AIM

We have recently reported that hypoxia stimulates transcription of the TrkB neurotrophin receptor in cultured cells via stabilization of hypoxia-inducible factor-1alpha. Here we investigated whether the expression of TrkB and other neurotrophin receptors is oxygen-sensitive also in vivo, and explored the functional consequences of an oxygen-regulated TrkB expression.

METHODS

Rats were exposed either to 21% O(2) or 8% O(2) for 6 h and TrkB was analysed by reverse transcription real-time PCR, in situ mRNA hybridization, and immunological techniques. The importance of the brain-derived neurotrophic factor (BDNF)-TrkB pathway in the control of mechanical airway function was assessed on isolated tracheal segments from normoxic and hypoxic rats.

RESULTS

TrkB transcripts were increased approx. 15-fold in the lungs of hypoxic rats, and the respiratory epithelium was identified as the site of enhanced TrkB expression in hypoxia. The TrkB ligand, BDNF, significantly increased the contractile response to acetylcholine (ACh) of isolated tracheal segments from hypoxic but not from normoxic rats. This effect of BDNF was prevented by pre-incubation of the tissue specimens with the tyrosine kinase inhibitor K252a and by mechanical removal of the TrkB containing airway epithelium. Likewise, the nitric oxide (NO) synthase inhibitor l-NAME abrogated the influence of BDNF on ACh-induced contractions of isolated tracheal segments from hypoxic rats.

CONCLUSION

These results demonstrate that systemic hypoxia stimulates expression of the TrkB neurotrophin receptor in the airway epithelium. Furthermore, activation of TrkB signalling by BDNF in hypoxia enhances mechanical airway contractility to ACh through a mechanism that requires NO.

Why eicosanoids could represent a new class of tocolytics on uterine activity in pregnant women

OBJECTIVE

The purpose of this study was to assess the effects of exogenous eicosanoids on spontaneous uterine contractile activity.

STUDY DESIGN

Eight uterine biopsies were performed from women who were undergoing elective cesarean delivery. Tension measurements were performed in vitro on myometrial strips. Contractile activities were quantified by the calculation of the area under the curve. The effects of eicosanoids and specific enzyme inhibitors were assessed. Fractions from various uterine tissues were analyzed by Western blot.

RESULTS

Data demonstrate the presence, in some tested tissues, of cytochrome P-450 epoxygenase and soluble epoxide hydrolase, which respectively produce and degrade epoxyeicosatrienoic acid regioisomers. Inhibition of soluble epoxide hydrolase with 12-(3-adamantan-1-yl-ureido)-dodecanoic acid or omega-hydroxylase with N-methylsulfonyl-12,12-dibromododec-11-enamide resulted in a tocolytic effect; N-methylsulfonyl-6-[2-propargyloxyphenyl] hexanamide, which is an epoxygenase inhibitor, had no effect. Exogenous epoxyeicosatrienoic acids displayed significant tocolytic effects on spontaneous contractile activities.

CONCLUSION

Epoxy- and hydroxyeicosanoids represent new bioactive, arachidonic acid by-products with in vitro tocolytic activities. These findings suggest that cytochrome P-450 isozymes may represent relevant pharmacologic targets under physiopathologic conditions.

Quantitative profiling method for oxylipin metabolome by liquid chromatography electrospray ionization tandem mass spectrometry

Cyclooxygenase, lipoxygenase, and epoxygenase derived oxylipins, especially eicosanoids, play important roles in many physiological processes. Assessment of oxidized fatty acid levels is important for understanding their homeostatic and pathophysiological roles. Most reported methods examine these pathways in isolation. The work described here employed a solid phase extraction-liquid chromatography-electrospray ionization MS/MS (SPE-LC-ESI MS/MS) method to monitor these metabolites. In 21 min, 39 oxylipins were quantified along with eight corresponding internal standards. The limits of quantification were between 0.07 and 32 pg (20 pM-10 nM). Finally, the validated method was used to evaluate oxylipin profiles in lipopolysaccharide-exposed mice, an established septic inflammatory model. The method described here offers a useful tool for the evaluation of complex regulatory oxylipin responses in in vitro or in vivo studies.

Relaxing effects of 17(18)-EpETE on arterial and airway smooth muscles in human lung

Human cytochrome P-450 epoxygenase enzymes metabolize eicosapentaenoic acid (EPA), an ω-3-polyunsaturated fatty acid (PUFA), and leads to the production of 17(18)-epoxyeicosatetraenoic acid, or 17(18)-EpETE. The aim of the present study was to delineate the mode of action of 17(18)-EpETE on human pulmonary artery (HPA) and distal bronchi. Isometric tension measurements demonstrated that 17(18)-EpETE induced concentration-dependent relaxing effects in pulmonary artery and airway smooth muscles. Iberiotoxin (IbTx) and glyburide (Glyb), known BKCa and KATP channel inhibitors, respectively, reversed the relaxation induced by 17(18)-EpETE on both tissues types. Microelectrode measurements showed that exogenous addition of 17(18)-EpETE hyperpolarized the membrane potential of HPA and bronchial smooth muscle cells. These induced electrophysiological effects were reversed by the addition of 10 nM IbTx and 10 μM Glyb. Complementary experiments performed on human bronchi, using the planar lipid bilayer reconstitution technique, demonstrated that 17(18)-EpETE activated reconstituted BKCa channels at low free Ca2+ concentration. Moreover, in bronchi, the relaxing responses induced by 17(18)-EpETE were also related to reduced Ca2+ sensitivity of the myofilaments, since free Ca2+ concentration-response curves, performed on β-escin-permeabilized cultured explants, were shifted toward higher Ca2+. Together, these results provide new insight into the mode of action of 17(18)-EpETE in lung tissues and highlight this eicosanoid as a potent modulator of tone on both HPA and distal bronchi in vitro, which may be of clinical relevance in the pathophysiology of pulmonary hypertension and airway diseases.

Oxygen dependency of hydrogen sulfide-mediated vasoconstriction in cyclostome aortas

Hydrogen sulfide (H2S) has been proposed to mediate hypoxic vasoconstriction (HVC), however, other studies suggest the vasoconstrictory effect indirectly results from an oxidation product of H2S. Here we examined the relationship between H2S and O2 in isolated hagfish and lamprey vessels that exhibit profound hypoxic vasoconstriction. In myographic studies, H2S (Na2S) dose-dependently constricted dorsal aortas (DA) and efferent branchial arteries (EBA) but did not affect ventral aortas or afferent branchial arteries; effects similar to those produced by hypoxia. Sensitivity of H2S-mediated contraction in hagfish and lamprey DA was enhanced by hypoxia. HVC in hagfish DA was enhanced by the H2S precursor cysteine and inhibited by amino-oxyacetate, an inhibitor of the H2S-synthesizing enzyme,cystathionine β-synthase. HVC was unaffected by propargyl glycine, an inhibitor of cystathionine λ-lyase. Oxygen consumption(ṀO2) of hagfish DA was constant between 15 and 115 mmHg PO2 (1 mmHg=0.133 kPa), decreased when PO2 &lt;15 mmHg, and increased after PO2 exceeded 115 mmHg. 10 μmol l–1 H2S increased and ⩾100μmol l–1 H2S decreased ṀO2. Consistent with the effects on HVC, cysteine increased and amino-oxyacetate decreased ṀO2. These results show that H2S is a monophasic vasoconstrictor of specific cyclostome vessels and because hagfish lack vascular NO, and vascular sensitivity to H2S was enhanced at low PO2, it is unlikely that H2S contractions are mediated by either H2S–NO interaction or an oxidation product of H2S. These experiments also provide additional support for the hypothesis that the metabolism of H2S is involved in oxygen sensing/signal transduction in vertebrate vascular smooth muscle.

20-HETE increases superoxide production and activates NAPDH oxidase in pulmonary artery endothelial cells

Reactive oxygen species (ROS) signal vital physiological processes including cell growth, angiogenesis, contraction, and relaxation of vascular smooth muscle. Because cytochrome P-450 family 4 (CYP4)/20-hydroxyeicosatetraenoic acid (20-HETE) has been reported to enhance angiogenesis, pulmonary vascular tone, and endothelial nitric oxide synthase function, we explored the potential of this system to stimulate bovine pulmonary artery endothelial cell (BPAEC) ROS production. Our data are the first to demonstrate that 20-HETE increases ROS in BPAECs in a time- and concentration-dependent manner as detected by enhanced fluorescence of oxidation products of dihydroethidium (DHE) and dichlorofluorescein diacetate. An analog of 20-HETE elicits no increase in ROS and blocks 20-HETE-evoked increments in DHE fluorescence, supporting its function as an antagonist. Endothelial cells derived from bovine aortas exhibit enhanced ROS production to 20-HETE quantitatively similar to that of BPAECs. 20-HETE-induced ROS production in BPAECs is blunted by pretreatment with polyethylene-glycolated SOD, apocynin, inhibition of Rac1, and a peptide-based inhibitor of NADPH oxidase subunit p47(phox) association with gp91. These data support 20-HETE-stimulated, NADPH oxidase-derived, and Rac1/2-dependent ROS production in BPAECs. 20-HETE promotes translocation of p47(phox) and tyrosine phosphorylation of p47(phox) in a time-dependent manner as well as increased activated Rac1/2, providing at least three mechanisms through which 20-HETE activates NADPH oxidase. These observations suggest that 20-HETE stimulates ROS production in BPAECs at least in part through activation of NADPH oxidase within minutes of application of the lipid.

Effects of omega-hydroxylase product on distal human pulmonary arteries

The aim of the present study was to provide a mechanistic insight into how 20-hydroxyeicosatetraenoic acid (20-HETE) relaxes distal human pulmonary arteries (HPAs). This compound is produced by omega-hydroxylase from free arachidonic acid. Tension measurements, performed on either fresh or 1 day-cultured pulmonary arteries, revealed that the contractile responses to 1 microM 5-hydroxytryptamine were largely relaxed by 20-HETE in a concentration-dependent manner (0.01-10 microM). Iberiotoxin pretreatments (10 nM) partially decreased 20-HETE-induced relaxations. However, 10 microM indomethacin and 3 microM SC-560 pretreatments significantly reduced the relaxations to 20-HETE in these tissues. The relaxing responses induced by the eicosanoid were likely related to a reduced Ca2+ sensitivity of the myofilaments since free Ca2+ concentration ([Ca2+])-response curves performed on beta-escin-permeabilized cultured explants were shifted toward higher [Ca2+]. 20-HETE also abolished the tonic responses induced by phorbol-ester-dibutyrate (a PKC-sensitizing agent). Western blot analyses, using two specific primary antibodies against the PKC-potentiated inhibitory protein CPI-17 and its PKC-dependent phosphorylated isoform pCPI-17, confirmed that 20-HETE interferes with this intracellular process. We also investigated the effect of 20-HETE on the activation of Rho-kinase pathway-induced Ca2+ sensitivity. The data demonstrated that 20-HETE decreased U-46619-induced Ca2+ sensitivity on arteries. Hence, this observation was correlated with an increased staining of p116(Rip), a RhoA-binding protein. Together, these results strongly suggest that the 20-hydroxyarachidonic acid derivative is a potent modulator of tone in HPAs in vitro.

Oxygen sensors in context

The ability to adapt to changes in the availability of O2 provides a critical advantage to all O2-dependent lifeforms. In mammals it allows optimal matching of the O2 requirements of the cells to ventilation and O2 delivery, underpins vital changes to the circulation during the transition from fetal to independent, air-breathing life, and provides a means by which dysfunction can be limited or prevented in disease. Certain tissues such as the carotid body, pulmonary circulation, neuroepithelial bodies and fetal adrenomedullary chromaffin cells are specialised for O2 sensing, though most others show for example alterations in transcription of specific genes during hypoxia. A number of mechanisms are known to respond to variations in PO2 over the physiological range, and have been proposed to fulfil the function as O2 sensors; these include modulation of mitochondrial oxidative phosphorylation and a number of O2-dependent synthetic and degradation pathways. There is however much debate as to their relative importance within and between specific tissues, whether their O2 sensitivity is actually appropriate to account for their proposed actions, and in particular their modus operandi. This review discusses our current understanding of how these mechanisms may operate, and attempts to put them into the context of the actual PO2 to which they are likely to be exposed. An important point raised is that the overall O2 sensitivity (P50) of any O2-dependent mechanism does not necessarily correlate with that of its O2 sensor, as the coupling function between the two may be complex and non-linear. In addition, although the bulk of the evidence suggests that mitochondria act as the key O2 sensor in carotid body, pulmonary artery and chromaffin cells, the signalling mechanisms by which alterations in their function are translated into a response appear to differ fundamentally, making a global unified theory of O2 sensing unlikely.

Functional effects of 20-HETE on human bronchi: hyperpolarization and relaxation due to BKCa channel activation

Airway smooth muscle (ASM) metabolizes arachidonic acid (AA) through various enzymatic pathways, including cytochrome P-450 (CYP-450) omega-hydroxylase, which leads to the production of 20-hydroxyeicosatetraenoic acid (20-HETE). The goal of this study was to delineate the mode of action of 20-HETE in human ASM cells. Isometric tension measurements demonstrated that 20-HETE induced a concentration-dependent relaxant effect in ASM on bronchi precontracted with either methacholine or AA. Relaxing effects of 20-HETE on resting tone were prevented by 10 nM iberiotoxin (IbTx), a BK(Ca) channel inhibitor. Microelectrode measurements showed that exogenous additions of 20-HETE (0.1-10 microM) hyperpolarized the membrane potential of human ASM cells. This concentration-dependent electrophysiological effect induced by the eicosanoid was prevented by 10 nM IbTx. Complementary experiments, using the planar lipid bilayer reconstitution technique, demonstrated that 20-HETE activated reconstituted BK(Ca) channels at low free Ca(2+) concentrations. Together, these results indicate that 20-HETE-dependent activation of BK(Ca) channels is responsible for the hyperpolarization and controlled relaxation of ASM in human distal bronchi.

Promoter polymorphism G-50T of a human CYP2J2 epoxygenase gene is associated with common susceptibility to asthma

BACKGROUND

Cytochrome P-450 2J2 (CYP2J2) has recently been shown to be an important enzyme in the metabolism of epoxygenase-derived eicosanoids that play important functional roles in pulmonary physiology and may contribute to the pathogenesis of asthma.

STUDY OBJECTIVE

The focus of our pilot study was to evaluate whether common polymorphism G-50T within the proximal promoter of human CYP2J2 gene is associated with the susceptibility to bronchial asthma.

DESIGN AND PARTICIPANTS

A total of 429 unrelated Russian subjects were recruited in this case-control study, including 215 sex-matched and age-matched patients with asthma and 214 healthy control subjects. The blood samples were analyzed for genetic polymorphism G-50T in the CYP2J2 gene by polymerase chain reaction followed by restriction fragment length polymorphism analysis.

RESULTS

The frequency of variant allele -50T of the CYP2J2 gene was significantly higher in asthmatic patients than in healthy subjects (odds ratio [OR], 5.04; 95% confidence interval [CI], 1.99 to 12.77; p = 0.0003). In addition, the heterozygous genotype -50GT of the CYP2J2 gene was found to be significantly associated with susceptibility to allergic asthma (OR, 5.40; 95% CI, 2.05 to 14.26; p = 0.0003) as well as nonallergic asthma (OR, 5.77; 95% CI, 1.84 to 18.10; p = 0.004). The associations of the CYP2J2 gene G-50T polymorphism with asthma remained significant after adjustment for age and gender using multiple logistic regression analysis.

CONCLUSIONS

Our data demonstrate for the first time that the CYP2J2 gene might be considered as a novel candidate gene for common susceptibility to asthma and highlight the importance of the P-450 epoxygenase pathway of metabolism of arachidonic acid in the pathogenesis of the disease.

Epoxyeicosatrienoic Acid Relaxing Effects Involve Ca2+-Activated K+Channel Activation and CPI-17 Dephosphorylation in Human Bronchi

The aim of the present study was to provide a mechanistic insight into how 14,15-epoxyeicosatrienoic acid (EET) relaxes organ-cultured human bronchi. Tension measurements, performed on either fresh or 3-d-cultured bronchi, revealed that the contractile responses to 1 microM methacholine and 10 microM arachidonic acid were largely relaxed by the eicosanoid regioisomer in a concentration-dependent manner (0.01-10 microM). Pretreatments with 14,15-epoxyeicosa-5(Z)-enoic acid, a specific 14,15-EET antagonist, prevented the relaxing effect, whereas iberitoxin pretreatments (10 nM) partially abolished EET-induced relaxations. In contrast, pretreatments with 1 microM indomethacin amplified relaxations in explants and membrane hyperpolarizations triggered by 14,15-EET on airway smooth muscle cells. The relaxing responses induced by 14,15-EET were likely related to reduced Ca2+ sensitivity of the myofilaments, because free Ca2+ concentration-response curves performed on beta-escin-permeabilized cultured explants were shifted toward higher [Ca2+] (lower pCa2+ values). 14,15-EET also abolished the tonic responses induced by phorbol-ester-dybutyrate (PDBu) (a protein kinase C [PKC]-sensitizing agent), on both fresh (intact) and beta-escin-permeabilized explants. Western blot analyses, using two specific primary antibodies against CPI-17 and its PKC-dependent phosphorylated isoform (p-CPI-17), confirmed that the eicosanoid interferes with this intracellular process. These data indicate that 14,15-EET hyperpolarizes airway smooth muscle cells and relaxes precontracted human bronchi while reducing Ca2+ sensitivity of fresh and cultured explants. The intracellular effects are related to a PKC-dependent process involving a lower phosphorylation level of CPI-17.

Hydroxyeicosatetraenoic acids released through the cytochrome P-450 pathway regulate 3T6 fibroblast growth

Eicosanoids participate in the regulation of cellular proliferation. Thus, we observed that prostaglandin E(2) interaction with membrane receptors is involved in the control of 3T6 fibroblast growth induced by serum. However, our results suggested that another arachidonic acid pathway might be implicated in these events. Our results show that 3T6 fibroblasts synthesized hydroxyeicosatetraenoic acids (HETEs) such as 12-HETE through the cytochrome P-450 (CYP450) pathway. However, 3T6 fibroblasts did not produce leukotriene B(4) (LTB(4)), and lipoxygenase inhibitors and LT antagonists failed to inhibit 3T6 fibroblast growth induced by FBS. In contrast, we observed that CYP450 inhibitors such as SKF-525A, 17-octadecynoic acid, 1-aminobenzotriazole, and 6-(2-propargyloxyphenyl)hexanoic acid reduced 12(S)-HETE levels, 3T6 fibroblast growth, and DNA synthesis induced by FBS. The impairment of DNA synthesis and 3T6 fibroblast growth induced by SKF-525A were reversed by exogenous addition of HETEs. Moreover, we report that 5-HETE, 12(S)-HETE, and 15(S)-HETE are mitogenic on 3T6 fibroblast in the absence of another growth factor, and this effect was dependent on the activation of the phosphatidylinositol-3-kinase pathway. In conclusion, our results show that HETEs, probably produced by CYP450, are involved in the control of 3T6 fibroblast growth.

Protective effects of epoxyeicosatrienoic acids on human endothelial cells from the pulmonary and coronary vasculature

Epoxyeicosatrienoic acids (EETs) are cytochrome P-450 (CYP) metabolites synthesized from the essential fatty acid arachidonic acid to generate four regioisomers, 14,15-, 11,12-, 8,9-, and 5,6-EET. Cultured human coronary artery endothelial cells (HCAECs) contain endogenous EETs that are increased by stimulation with physiological agonists such as bradykinin. Because EETs are known to modulate a number of vascular functions, including angiogenesis, we tested each of the four regioisomers to characterize their effects on survival and apoptosis of HCAECs and cultured human lung microvascular endothelial cells (HLMVECs). A single application of physiologically relevant concentration of 14,15-, 11,12-, and 8,9-EET but not 5,6-EET (0.75-300 nM) promoted concentration-dependent increase in cell survival of HLMVECs and HCAECs after removal of serum. The lipids also protected the same cells from death via the intrinsic, as well as extrinsic, pathways of apoptosis. EETs did not increase intracellular calcium concentration ([Ca2+]i) or phosphorylate mitogen-activated protein kinase p44/42 when applied to these cells, and their protective action was attenuated by the phosphotidylinositol-3 kinase inhibitor wortmannin (10 microM) but not the cyclooxygenase inhibitor indomethacin (20 microM). Our results demonstrate for the first time the capacity of EETs to enhance human endothelial cell survival by inhibiting both the intrinsic, as well as extrinsic, pathways of apoptosis, an important underlying mechanism that may promote angiogenesis and endothelial survival during atherosclerosis and related cardiovascular ailments.

Cytochrome P450 epoxygenase gene function in hypoxic pulmonary vasoconstriction and pulmonary vascular remodeling

We assessed pulmonary cytochrome P450 (CYP) epoxygenase expression and activity during hypoxia and explored the effects of modulating epoxygenase activity on pulmonary hypertension. The acute hypoxic vasoconstrictor response was studied in Swiss Webster mice, who express CYP2C29 in their lungs. Animals were pretreated with vehicle, the epoxygenase inhibitor (N-methylsulfonyl-6-[2-propargyloxyphenyl] hexanamide) or an inhibitor of the soluble epoxide hydrolase. Whereas the epoxygenase inhibitor attenuated hypoxic pulmonary constriction (by 52%), the soluble epoxide hydrolase inhibitor enhanced the response (by 39%), indicating that CYP epoxygenase-derived epoxyeicosatrienoic acids elicit pulmonary vasoconstriction. Aerosol gene transfer of recombinant adenovirus containing the human CYP2C9 significantly elevated mean pulmonary artery pressure and total pulmonary resistance indices, both of which were sensitive to the inhibitor sulfaphenazole. The prolonged exposure of mice to hypoxia increased CYP2C29 expression, and transcript levels increased 5-fold after exposure to normobaric hypoxia (FIO2 0.07) for 2 hours. This was followed by a 2-fold increase in protein expression and by a significant increase in epoxyeicosatrienoic acid production after 24 hours. Chronic hypoxia (7 days) elicited pulmonary hypertension and pulmonary vascular remodeling, effects that were significantly attenuated in animals continually treated with N-methylsulfonyl-6-[2-propargyloxyphenyl] hexanamide (-46% and -55%, respectively). Our results indicate that endogenously generated epoxygenase products are associated with hypoxic pulmonary hypertension in mice and that selective epoxygenase inhibition significantly reduces acute hypoxic pulmonary vasoconstriction and chronic hypoxia-induced pulmonary vascular remodeling. These observations indicate potential novel targets for the treatment of pulmonary hypertension and highlight a pivotal role for CYP epoxygenases in pulmonary responses to hypoxia.

Inhibition of 20-HETE abolishes the myogenic response during NOS antagonism in the ovine fetal pulmonary circulation

Mechanisms that maintain high pulmonary vascular resistance (PVR) and oppose vasodilation in the fetal lung are poorly understood. In fetal lambs, increased pulmonary artery pressure evokes a potent vasoconstriction, suggesting that a myogenic response contributes to high PVR in the fetus. In adult systemic circulations, the arachidonic acid metabolite 20-hydroxyeicosatetraenoic acid (20-HETE) has been shown to modulate the myogenic response, but its role in the fetal lung is unknown. We hypothesized that acute increases in pulmonary artery pressure release 20-HETE, which causes vasoconstriction, or a myogenic response, in the fetal lung. To address this hypothesis, we studied the hemodynamic effects of N-methylsufonyl-12,12-dibromododec-11-enamide (DDMS), a specific inhibitor of 20-HETE production, on the pulmonary vasoconstriction caused by acute compression of the ductus arteriosus (DA) in chronically prepared fetal sheep. An inflatable vascular occluder around the DA was used to increase pulmonary artery pressure under three study conditions: control, after pretreatment with nitro-l-arginine (l-NA; to inhibit shear-stress vasodilation), and after combined treatment with both l-NA and a specific 20-HETE inhibitor, DDMS. We found that DA compression after l-NA treatment increased PVR by 44 ± 12%. Although intrapulmonary DDMS infusion did not affect basal PVR, DDMS completely abolished the vasoconstrictor response to DA compression in the presence of l-NA (44 ± 12% vs. 2 ± 4% change in PVR, l-NA vs. l-NA + DDMS, P < 0.05). We conclude that 20-HETE mediates the myogenic response in the fetal pulmonary circulation and speculate that pharmacological inhibition of 20-HETE might have a therapeutic role in neonatal conditions characterized by pulmonary hypertension.

CAR and PXR expression and inducibility of CYP2B and CYP3A activities in rat and rabbit lungs

Several CYP enzymes are expressed in the lung of mammals but studies on their regulation have been rather neglected. In this study, the CAR and PXR expression and the inducibility of CYP 2B and CYP 3A isoforms in the lung rats and rabbits were investigated. Rats were treated with phenobarbital, clotrimazole or a mixture of dexametasone plus pregnenolone 16alpha-carbonitrile, whereas rabbits were treated with phenobarbital or rifampicin. A low constitutive expression of CAR mRNA was demonstrated by RT-PCR analysis in the lung of rat but not in rabbit. Phenobarbital treatment did not change the CAR expression profiles and did not induce in either rats and rabbits the pulmonary CYP 2B isoforms, as judged by western blot analysis and the marker pentoxyresorufin O-dealkylase and 7-ethoxy-4-trifluoroethylcoumarin O-deethylase activities. On the contrary, these marker activities were strongly induced by phenobarbital in the liver of both species. A low constitutive level of PXR mRNA was also detected by RT-PCR in the lung of rabbit but not in rat. However, also in this case, their expressions were not altered by the administration of strong CYP 3A inducers such as clotrimazole or a mixture of dexametasone plus pregnenolone 16alpha-carbonitrile for the rat and rifampicin or phenobarbital for the rabbit. For the first time, it was demonstrated by RT-PCR that rat lung expresses CYP 3A2, 3A9, 3A18 and 3A23 whereas the rabbit lung expresses the CYP 3A6, the only CYP 3A isoform identified in the rabbit so far. However, notwithstanding the differences observed in the constitutive presence of PXR and CYP 3A transcripts in both species, the above mentioned treatments did not affect in their lungs, unlike their livers, neither the anti-rat 3A immunoreactive proteins nor the CYP 3A marker 7-benzyloxyquinoline O-debenzylase and the 6beta-testosterone hydroxylase activities. The results obtained indicate that the role of CAR and PXR in the lung of rat and rabbit is different from that observed in the liver or other extrahepatic tissues where the induction of the CYP 2B and CYP 3A isoforms is regulated by these receptors.

Regulation and inhibition of arachidonic acid omega-hydroxylases and 20-HETE formation

Cytochrome P450-catalyzed metabolism of arachidonic acid is an important pathway for the formation of paracrine and autocrine mediators of numerous biological effects. The omega-hydroxylation of arachidonic acid generates significant levels of 20-hydroxyeicosatetraenoic acid (20-HETE) in numerous tissues, particularly the vasculature and kidney tubules. Members of the cytochrome P450 4A and 4F families are the major omega-hydroxylases, and the substrate selectivity and regulation of these enzymes has been the subject of numerous studies. Altered expression and function of arachidonic acid omega-hydroxylases in models of hypertension, diabetes, inflammation, and pregnancy suggest that 20-HETE may be involved in the pathogenesis of these diseases. Our understanding of the biological significance of 20-HETE has been greatly aided by the development and characterization of selective and potent inhibitors of the arachidonic acid omega-hydroxylases. This review discusses the substrate selectivity and expression of arachidonic acid omega-hydroxylases, regulation of these enzymes during disease, and the application of enzyme inhibitors to study 20-HETE function.

Possible pathomechanisms of sudden infant death syndrome: key role of chronic hypoxia, infection/inflammation states, cytokine irregularities, and metabolic trauma in genetically predisposed infants

Chronic hypoxia, viral infections/bacterial toxins, inflammation states, biochemical disorders, and genetic abnormalities are the most likely trigger of sudden infant death syndrome (SIDS). Autopsy studies have shown increased pulmonary density of macrophages and markedly more eosinophils in the lungs accompanied by increased T and B lymphocytes. The elevated levels of immunoglobulins, about 20% more muscle in the pulmonary arteries, increased airway smooth muscle cells, and increased fetal hemoglobin and erythropoietin are evidence of chronic hypoxia before death. Other abnormal findings included mucosal immune stimulation of the tracheal wall, duodenal mucosa, and palatine tonsils, and circulating interferon. Low normal or higher blood levels of cortisol often with petechiae on intrathoracic organs, depleted maternal IgG antibodies to endotoxin core (EndoCAb) and early IgM EndoCAb triggered, partial deletions of the C4 gene, and frequent IL-10-592*A polymorphism in SIDS victims as well as possible hypoxia-induced decreased production of antiinflammatory, antiimmune, and antifibrotic cytokine IL-10, may be responsible for the excessive reactions to otherwise harmless infections. In SIDS infants, during chronic hypoxia and times of infection/inflammation, several proinflammatory cytokines are released in large quantities, sometimes also representing a potential source of tissue damage if their production is not sufficiently well controlled, eg, by pituitary adenylate cyclase-activating polypeptide (PACAP) and vasoactive intestinal polypeptide (VIP). These proinflammatory cytokines down-regulate gene expression of major cytochrome P-450 and/or other enzymes with the specific effects on mRNA levels, protein expression, and enzyme activity, thus affecting metabolism of several endogenous lipophilic substances, such as steroids, lipid-soluble vitamins, prostaglandins, leukotrienes, thromboxanes, and exogenous substances. In SIDS victims, chronic hypoxia, TNF-alpha and other inflammatory cytokines, and arachidonic acid (AA) as well as n-3 polyunsaturated fatty acids (FA), stimulated and/or augmented superoxide generation by polymorphonuclear leukocytes, which contributed to tissue damage. Chronic hypoxia, increased amounts of nonheme iron in the liver and adrenals of these infants, enhanced activity of CYP2C9 regarded as the functional source of reactive oxygen species (ROS) in some endothelial cells, and nicotine accumulation in tissues also intensified production of ROS. These increased quantities of proinflammatory cytokines, ROS, AA, and nitric oxide (NO) also resulted in suppression of many CYP450 and other enzymes, eg, phosphoenolpyruvate carboxykinase (PEPCK), an enzyme important in the metabolism of FA during gluconeogenesis and glyceroneogenesis. PEPCK deficit found in SIDS infants (caused also by vitamin A deficiency) and eventually enhanced by PACAP lipolysis of adipocyte triglycerides resulted in an increased FA level in blood because of their impaired reesterification to triacylglycerol in adipocytes. In turn, the overproduction and release of FA into the blood of SIDS victims could lead to the metabolic syndrome and an early phase of type 2 diabetes. This is probably the reason for the secondary overexpression of the hepatic CYP2C8/9 content and activity reported in SIDS infants, which intensified AA metabolism. Pulmonary edema and petechial hemorrhages often present in SIDS victims may be the result of the vascular leak syndrome caused by IL-2 and IFN-alpha. Chronic hypoxia with the release of proinflammatory mediators IL-1alpha, IL-1beta and IL-6, and overloading of the cardiovascular and respiratory systems due to the narrowing airways and small pulmonary arteries of these children could also contribute to the development of these abnormalities. Moreover, chronic hypoxia of SIDS infants induced also production of hypoxia-inducible factor 1alpha (HIF-1alpha), which stimulated synthesis and release of different growth factors by vascular endothelial cells and intensified subclinical inflammatory reactions in the central nervous system, perhaps potentiated also by PACAP and VIP gene mutations. These processes could lead to the development of brainstem gliosis and disorders in the release of neuromediators important for physiologic sleep regulation. All these changes as well as eventual PACAP abnormalities could result in disturbed homeostatic control of the cardiovascular and respiratory responses of SIDS victims, which, combined with the nicotine effects and metabolic trauma, finally lead to death in these often genetically predisposed children.

Histamine-cytokine connection in immunity and hematopoiesis

A number of recent studies have led to a reappraisal of the functional capacities of histamine in immunity and hematopoiesis. This change of perspective was provided by the following findings: (1) the evidence for multiple cellular sources of histamine, differing from mature basophils and mast cells by their ability to newly synthesize and liberate the mediator without prior storage, (2) the discovery of a novel histamine receptor (H4R), preferentially expressed on hematopoietic and immunocompetent cells, (3) the potential intracellular activity of histamine through cytochrome P450 and (4) the demonstration of a histamine-cytokine cross-talk. Indeed, cytokines not only modulate the degranulation process of histamine but also control its neosynthesis by the histamine-forming enzyme, histidine decarboxylase (HDC), at transcriptional and post-transcriptional levels. In turn, histamine intervenes in the intricate cytokine network, regulating cytokine production by immune cells through distinct receptors signaling distinct biological effects. This type of regulation is particularly relevant in the context of TH1/TH2 differentiation, autoimmunity and tumor immunotherapy.

Soluble epoxide hydrolase is a main effector of angiotensin II-induced hypertension

The soluble epoxide hydrolase (sEH) metabolizes vasodilatory epoxyeicosatrienoic acids (EETs) to their di-hydroxy derivatives. We hypothesized that the metabolism of EETs by the sEH contributes to angiotensin II-induced hypertension and tested the effects of a water-soluble sEH inhibitor, 12-(3-adamantan-1-yl-ureido) dodecanoic acid (AUDA) on blood pressure. AUDA (130 microg/mL in drinking water) did not affect blood pressure in normotensive animals but markedly lowered it in mice with angiotensin II-induced hypertension (1 mg/kg per day). The effect of AUDA was accompanied by an increase in urinary salt and water excretion. Intravenous application of AUDA (8 mg/kg) acutely lowered blood pressure and heart rate in animals with angiotensin II-induced hypertension but failed to affect blood pressure in animals with phenylephrine-induced hypertension (29 mg/kg per day). AUDA (0.1 micromol/L) selectively lowered vascular resistance in an isolated perfused kidney preparation from angiotensin II-pretreated mice but not from control mice. In the perfused hind limb and in isolated carotid arteries from angiotensin II-treated mice, AUDA was without effect. The omega-hydroxylase inhibitor N-methylsulfonyl-12,12-dibromododec-11-enamide, which attenuates formation of the potent vasoconstrictor 20-hydroxyeicosatetraenoic acid, decreased tone in carotid arteries from angiotensin II-treated but not from control mice. These data demonstrate that the decrease in blood pressure observed after sEH inhibition in angiotensin II-induced hypertension can be attributed to an initial reduction in heart rate followed by pressure diuresis resulting from increased perfusion of the kidney. Direct vasodilatation of resistance arteries in skeletal muscles does not appear to contribute to the antihypertensive effects of sEH inhibition in mice.

Arachidonic and eicosapentaenoic acid metabolism by human CYP1A1: highly stereoselective formation of 17(R),18(S)-epoxyeicosatetraenoic acid

Human cytochrome P450 1A1 (CYP1A1) and human NADPH-cytochrome P450 reductase were expressed and purified from Spodoptera frugiperda insect cells. A reconstituted enzymatically active system metabolized polyunsaturated fatty acids such as arachidonic (AA) and eicosapentaenoic acid (EPA). CYP1A1 was an AA hydroxylase which oxidizes this substrate at a rate of 650+/-10 pmol/min/nmol CYP1A1, with over 90% of metabolites accounted for by hydroxylation products and with 19-OH-AA as major product. Epoxyeicosatrienoic acid (EET), mainly 14,15-EET, accounted for about 7% of total metabolites. Unlike rat CYP1A1, the human enzyme exhibited no 20-OH-AA as product. In contrast, with EPA as substrate CYP1A1 was mainly an epoxygenase, oxidizing with over 68% of total metabolites EPA to 17(R),18(S)-epoxyeicosatetraenoic acid (17(R),18(S)-EETeTr). 19-OH-EPA accounted for about 31% of total metabolites. Significantly, the 17,18-olefinic bond of EPA was epoxidized to 17(R),18(S)-EETeTr with nearly absolute regio- and stereoselectivity. Molecular modeling analyses provided rationale for high efficiency of AA hydroxylation at C(19) and its gradual decrease down to C(14), as well as for the limited EPA 17(S),18(R) epoxidation due to unfavorable enzyme-substrate interactions. The absence of omega-hydroxylation for both substrates is not due to steric factors, but probably a consequence of different reactivities of omega and (omega-1) carbons for hydrogen abstraction. It is suggested that the capacity of human CYP1A1 to metabolize AA and EPA and its inducibility by polycyclic aromatic hydrocarbons may affect the production of physiologically active metabolites, in particular, in the cardiovascular system and other extrahepatic tissues including lung.

Excess nitric oxide decreases cytochrome P-450 2J4 content and P-450-dependent arachidonic acid metabolism in lungs of rats with acute pneumonia

Recently, we demonstrated that pulmonary CYP2J4 content, a prominent source of EETs and HETEs formation in rat lungs, is reduced in pneumonia. Therefore, the purpose of this study was to determine the role of iNOS-derived NO in reduced pulmonary CYP2J4 protein content and decreased CYP metabolites in pneumonia. Rats were randomized to control, control plus 1400W (iNOS inhibitor), pneumonia, and pneumonia plus 1400W groups. Pseudomonas organisms were injected into lungs of pneumonia rats. At 40 h after surgery, rats were treated with either saline or 1400W for 4 h before death. Venous plasma samples were obtained for measuring nitrites/nitrates (NOx). There was no significant effect of 1400W on blood pressure measured in control or pneumonia rats, whereas 1400W reduced the elevated plasma NOx levels in pneumonia rats by half. CYP primary metabolites of AA formed at significantly lower rates in pulmonary microsomes from pneumonia rats compared with control rats. Treatment of pneumonia rats with 1400W resulted in a significant increase in the rate of formation of pulmonary EETs and omega-terminal HETEs compared with untreated pneumonia rats. The reduction in CYP2J4 protein content in pneumonia lung microsomes was also partially prevented by 1400W. Therefore, excess NO from iNOS decreases the pulmonary production of EETs and omega-HETEs in acute pneumonia. Inhibition of iNOS restores CYP2J4 protein content and CYP activity in acute pneumonia, indicating an important NO-CYP interaction in pulmonary responses to infection. We speculate CYP2J4 and its AA metabolites are involved in the modulation of pulmonary function in health and disease.

Pulmonary cytochrome P-450 2J4 is reduced in a rat model of acute Pseudomonas pneumonia

We previously reported that the levels of epoxyeicosatrienoic acids (EETs) and 20-hydroxyeicosatetraenoic acid (20-HETE) are depressed in microsomes prepared from lungs of rats with acute Pseudomonas pneumonia. We also showed a potential role for cytochrome P-450 (CYP) metabolites of arachidonic acid (AA) in contractile responses of both normal pulmonary arteries and pulmonary arteries from rats with pneumonia. The CYP2J subfamily enzymes (endogenous source of EETs and HETEs) are constitutively expressed in human and rat lungs where they are localized in vascular smooth muscle and endothelium. The purpose of this study was to determine if CYP2J proteins are modified in pneumonia. Pseudomonas organisms were injected via a tracheostomy in the lungs of rats. Later (44 h), lungs were frozen, and microsomes were prepared from pneumonia and control rat lung homogenates. Lung microsomal proteins were then immunoblotted with anti-CYP2B1/2B2, anti-CYP4A, anti-CYP2J9pep2 (which reacts with rat CYP2J3), anti-CYP2J6pep1 (which reacts with rat CYP2J4), anti-CYP2J2pep4, or anti-CYP2J2pep3 (both of which react with all known CYP2J isozymes). Western blotting revealed a prominent 55-kDa band with anti-CYP2J2pep3, anti-CYP2J2pep4, and anti-CYP2J6pep1 (but not anti-CYP2J9pep2) that was reduced in pneumonia compared with control lung microsomes. The CYP2B bands (51-52 kDa) were less prominent and not different between pneumonia and control lungs. CYP4A proteins (20-HETE sources) were not detected in rat lung microsomes. Therefore, rat lung contains a protein with immunological characteristics similar to CYP2J4, and this CYP is reduced after pneumonia. We speculate that CYP2J (but not CYP2B) enzymes and their AA metabolic products (EETs) are involved in the modulation of pulmonary vascular tone in pneumonia in rats.

Differential effects of 5,6-EET on segmental pulmonary vasoactivity in the rabbit

In the rabbit, 5,6-epoxyeicosatrienoic acid (EET) was reported both to dilate and to constrict pulmonary blood vessels. We propose that these seemingly contradictory results could be explained by differences in responses to 5,6-EET in large-conductance pulmonary arteries (PA) compared with smaller PA and resistance vessels. Thus we found that in rings of extralobar PA [>2-mm outside diameter (OD)], in which active tension had been increased with PGF(2alpha), 5,6-EET produced relaxation in a concentration- and cyclooxygenase (COX)-dependent manner. In contrast, 5,6-EET increased tension in intralobar (1- to 2-mm OD) PA. Small extralobar PA (2- to 2.5-mm OD) exhibited intermediate responses. In the intact lung, the net effect of 5,6-EET (1 x 10(-8)-1 x 10(-5) M) was an increase in pulmonary vascular resistance (PVR) from 13.0 +/- 0.5 to 47.8 +/- 4.6 mmHg. 100 ml(-1) x min(-1) (EC(50) 5.9 +/- 1.7 x 10(-7) M). The increase in PVR was accompanied by a 10-fold increase in perfusate thromboxane (TX)B(2) concentration. The 5,6-EET-induced increase in PVR was prevented with indomethacin (100 microM), a cyclooxygenase inhibitor, or ONO-3708 (20 microM), a TX/PGH(2) (TP) receptor antagonist, but not with OKY-046 (700 microM), a TX synthase inhibitor. These results demonstrate that although 5,6-EET dilates large extralobar PA segments in a COX-dependent manner, in the intact rabbit lung 5,6-EET produces constriction that requires synthesis of a COX-dependent agonist of the TP receptor other than TX.