Evidence for the role of p38 MAP kinase in hypoxia-induced pulmonary vasoconstriction

In Vivo and Ex Vivo Experimental Approach for Studying Functional Role of Notch in Pulmonary Vascular Disease

Pulmonary arterial hypertension (PAH) is a severe disease characterized by sustained vasoconstriction, concentric wall thickening and vascular remodeling leading to increased pulmonary vascular resistance, causing right heart failure and death. Acute alveolar hypoxia causes pulmonary vasoconstriction, while sustained hypoxia causes pulmonary hypertension (PH). Activation of Notch signaling is implicated in the development of PAH and chronic hypoxia induced PH via partially its enhancing effect on Ca²⁺ signaling in pulmonary arterial smooth muscle cells (PASMCs). Pharmacological experiments and genetic approach using animal models of experimental PH (e.g., chronic hypoxia-induced PH) have been routinely utilized to study pathogenic mechanisms of PAH/PH and identify novel therapeutic targets. In this chapter, we describe protocols to investigate the role of Notch by measuring pulmonary hemodynamics in vivo and pulmonary arterial pressure ex vivo in mouse models of experimental PH. Using these experimental protocols, one can study the role of Notch or Notch signaling pathway in the pathogenic mechanisms of pulmonary vascular disease and develop novel therapies by targeting Notch ligands and receptors.

Revisiting the mechanism of hypoxic pulmonary vasoconstriction using isolated perfused/ventilated mouse lung

Hypoxic Pulmonary Vasoconstriction (HPV) is an important physiological mechanism of the lungs that matches perfusion to ventilation thus maximizing O2 saturation of the venous blood within the lungs. This study emphasizes on principal pathways in the initiation and modulation of hypoxic pulmonary vasoconstriction with a primary focus on the role of Ca2+ signaling and Ca2+ influx pathways in hypoxic pulmonary vasoconstriction. We used an ex vivo model, isolated perfused/ventilated mouse lung to evaluate hypoxic pulmonary vasoconstriction. Alveolar hypoxia (utilizing a mini ventilator) rapidly and reversibly increased pulmonary arterial pressure due to hypoxic pulmonary vasoconstriction in the isolated perfused/ventilated lung. By applying specific inhibitors for different membrane receptors and ion channels through intrapulmonary perfusion solution in isolated lung, we were able to define the targeted receptors and channels that regulate hypoxic pulmonary vasoconstriction. We show that extracellular Ca2+ or Ca2+ influx through various Ca2+-permeable channels in the plasma membrane is required for hypoxic pulmonary vasoconstriction. Removal of extracellular Ca2+ abolished hypoxic pulmonary vasoconstriction, while blockade of L-type voltage-dependent Ca2+ channels (with nifedipine), non-selective cation channels (with 30 µM SKF-96365), and TRPC6/TRPV1 channels (with 1 µM SAR-7334 and 30 µM capsazepine, respectively) significantly and reversibly inhibited hypoxic pulmonary vasoconstriction. Furthermore, blockers of Ca2+-sensing receptors (by 30 µM NPS2143, an allosteric Ca2+-sensing receptors inhibitor) and Notch (by 30 µM DAPT, a γ-secretase inhibitor) also attenuated hypoxic pulmonary vasoconstriction. These data indicate that Ca2+ influx in pulmonary arterial smooth muscle cells through voltage-dependent, receptor-operated, and store-operated Ca2+ entry pathways all contribute to initiation of hypoxic pulmonary vasoconstriction. The extracellular Ca2+-mediated activation of Ca2+-sensing receptors and the cell-cell interaction via Notch ligands and receptors contribute to the regulation of hypoxic pulmonary vasoconstriction.

Hypoxia Exacerbates Inflammatory Acute Lung Injury via the Toll-Like Receptor 4 Signaling Pathway

Acute lung injury (ALI) is characterized by non-cardiogenic diffuse alveolar damage and often leads to a lethal consequence, particularly when hypoxia coexists. The treatment of ALI remains a challenge: pulmonary inflammation and hypoxia both contribute to its onset and progression and no effective prevention approach is available. Here, we aimed to investigate the underlying mechanism of hypoxia interaction with inflammation in ALI and to evaluate hypoxia-inducible factor 1 alpha (HIF-1α)—the crucial modulator in hypoxia—as a potential therapeutic target against ALI. First, we developed a novel ALI rat model induced by a combined low-dose of lipopolysaccharides (LPS) with acute hypoxia. Second, we used gene microarray analysis to evaluate the inflammatory profiles of bronchi alveolar lavage fluid cells of ALI rats. Third, we employed an alveolar macrophage cell line, NR8383 as an in vitro system together with a toll-like receptor 4 (TLR4) antagonist TAK-242, to verify our in vivo findings from ALI animals. Finally, we tested the therapeutic effects of HIF-1α augmentation against inflammation and hypoxia in ALI. We demonstrated that (i) LPS upregulated inflammatory genes, tumor necrosis factor alpha (TNF-α), interleukin-1 beta (IL-1β), and interleukin-6 (IL-6), in the alveolar macrophages of ALI rats, which were further enhanced when ALI combined with hypoxia; (ii) hypoxia exposure could further enhance the upregulation of alveolar macrophageal TLR4 that was noticed in LPS-induced inflammatory ALI, conversely, TLR4 antagonist TAK-242 could suppress the macrophageal expression of TLR4 and inflammatory cytokines, including TNF-α, IL-1β, and IL-6, suggesting that the TLR4 signaling pathway as a central link between inflammation and hypoxia in ALI; (iii) manipulation of HIF-1α in vitro could suppress TLR4 expression induced by combined LPS and hypoxia, via suppressing promoter activity of the TLR4 gene; (iv) preconditioning augmentation of HIF-1α in vivo by HIF hydroxylase inhibitor, DMOG excreted protection against inflammatory, and hypoxic processes in ALI. Together, we see that hypoxia can exacerbate inflammation in ALI via the activation of the TLR4 signaling pathway in alveolar macrophages and predispose impairment of the alveolar-capillary barrier in the development of ALI. Targeting HIF-1α can suppress TLR4 expression and macrophageal inflammation, suggesting the potential therapeutic and preventative value of HIF-1α/TLR4 crosstalk pathway in ALI.

Reactive Oxygen Species and Pulmonary Vasculature During Hypobaric Hypoxia

An increasing number of people are living or working at high altitudes (hypobaric hypoxia) and therefore suffering several physiological, biochemical, and molecular changes. Pulmonary vasculature is one of the main and first responses to hypoxia. These responses imply hypoxic pulmonary vasoconstriction (HPV), remodeling, and eventually pulmonary hypertension (PH). These events occur according to the type and extension of the exposure. There is also increasing evidence that these changes in the pulmonary vascular bed could be mainly attributed to a homeostatic imbalance as a result of increased levels of reactive oxygen species (ROS). The increase in ROS production during hypobaric hypoxia has been attributed to an enhanced activity and expression of nicotinamide adenine dinucleotide phosphate oxidase (NADPH oxidase), though there is some dispute about which subunit is involved. This enzymatic complex may be directly induced by hypoxia-inducible factor-1α (HIF-1α). ROS has been found to be related to several pathways, cells, enzymes, and molecules in hypoxic pulmonary vasculature responses, from HPV to inflammation, and structural changes, such as remodeling and, ultimately, PH. Therefore, we performed a comprehensive review of the current evidence on the role of ROS in the development of pulmonary vasculature changes under hypoxic conditions, with a focus on hypobaric hypoxia. This review provides information supporting the role of oxidative stress (mainly ROS) in the pulmonary vasculature’s responses under hypobaric hypoxia and depicting possible future therapeutics or research targets. NADPH oxidase-produced oxidative stress is highlighted as a major source of ROS. Moreover, new molecules, such as asymmetric dimethylarginine, and critical inflammatory cells as fibroblasts, could be also involved. Several controversies remain regarding the role of ROS and the mechanisms involved in hypoxic responses that need to be elucidated.

Involvement of Ca2+-activated K+ channel 3.1 in hypoxia-induced pulmonary arterial hypertension and therapeutic effects of TRAM-34 in rats

Pulmonary artery hypertension (PAH) is an incurable disease associated with the proliferation of pulmonary artery smooth muscle cells (PASMCs) and vascular remodeling. The present study examined whether TRAM-34, a highly selective blocker of calcium-activated potassium channel 3.1 (Kca3.1), can help prevent such hypertension by reducing proliferation in PASMCs. Rats were exposed to hypoxia (10% O₂) for 3 weeks and treated daily with TRAM-34 intraperitoneally from the first day of hypoxia. Animals were killed and examined for vascular hypertrophy, Kca3.1 expression, and downstream signaling pathways. In addition, primary cultures of rat PASMCs were exposed to hypoxia (3% O₂) or normoxia (21% O₂) for 24 h in the presence of TRAM-34 or siRNA against Kca3.1. Activation of cell signaling pathways was examined using Western blot analysis. In animal experiments, hypoxia triggered significant medial hypertrophy of pulmonary arterioles and right ventricular hypertrophy, and it significantly increased pulmonary artery pressure, Kca3.1 mRNA levels and ERK/p38 MAP kinase signaling. These effects were attenuated in the presence of TRAM-34. In cell culture experiments, blocking Kca3.1 using TRAM-34 or siRNA inhibited hypoxia-induced ERK/p38 signaling. Kca3.1 may play a role in the development of PAH by activating ERK/p38 MAP kinase signaling, which may then contribute to hypoxia-induced pulmonary vascular remodeling. TRAM-34 may protect against hypoxia-induced PAH.

Redox regulation of protein kinases as a modulator of vascular function

Reactive oxygen species (ROS) are continuously generated in vascular tissues by various oxidoreductase enzymes. They contribute to normal cell signaling, and modulate vascular smooth muscle tone and endothelial permeability in response to physiological agonists and to various cellular stresses and environmental factors, such as hypoxia. While concentrations of ROS are normally tightly controlled by cellular redox buffer systems, if produced in excess they may contribute to vascular disease. Protein kinases are essential components of most cell signaling pathways, including those involving ROS. The functioning of several members of this highly diverse group of enzymes, which include receptor and nonreceptor tyrosine kinases, protein kinase C, mitogen-activated kinases, and Rho-kinase, are modified by ROS, either through direct oxidative modification or indirectly through modification of associated proteins such as tyrosine phosphatases and monomeric G proteins. In this review, we discuss the molecular mechanisms of redox modification of these proteins, the downstream pathways affected, the often complex interaction between major kinase pathways, and feedback to ROS production itself. We also discuss complicating factors such as differential actions of superoxide anion and hydrogen peroxide, questions concerning concentration dependence, and the significance of signaling microdomains.

Hypoxia divergently regulates production of reactive oxygen species in human pulmonary and coronary artery smooth muscle cells

Acute hypoxia causes pulmonary vasoconstriction and coronary vasodilation. The divergent effects of hypoxia on pulmonary and coronary vascular smooth muscle cells suggest that the mechanisms involved in oxygen sensing and downstream effectors are different in these two types of cells. Since production of reactive oxygen species (ROS) is regulated by oxygen tension, ROS have been hypothesized to be a signaling mechanism in hypoxia-induced pulmonary vasoconstriction and vascular remodeling. Furthermore, an increased ROS production is also implicated in arteriosclerosis. In this study, we determined and compared the effects of hypoxia on ROS levels in human pulmonary arterial smooth muscle cells (PASMC) and coronary arterial smooth muscle cells (CASMC). Our results indicated that acute exposure to hypoxia (Po(2) = 25-30 mmHg for 5-10 min) significantly and rapidly decreased ROS levels in both PASMC and CASMC. However, chronic exposure to hypoxia (Po(2) = 30 mmHg for 48 h) markedly increased ROS levels in PASMC, but decreased ROS production in CASMC. Furthermore, chronic treatment with endothelin-1, a potent vasoconstrictor and mitogen, caused a significant increase in ROS production in both PASMC and CASMC. The inhibitory effect of acute hypoxia on ROS production in PASMC was also accelerated in cells chronically treated with endothelin-1. While the decreased ROS in PASMC and CASMC after acute exposure to hypoxia may reflect the lower level of oxygen substrate available for ROS production, the increased ROS production in PASMC during chronic hypoxia may reflect a pathophysiological response unique to the pulmonary vasculature that contributes to the development of pulmonary vascular remodeling in patients with hypoxia-associated pulmonary hypertension.

Clinical perspective of hypoxia-mediated pulmonary hypertension

Pulmonary hypertension is a condition associated with a variety of pulmonary disorders whose common denominator is alveolar hypoxia. Such disorders include chronic obstructive pulmonary disease, pulmonary fibrosis, sleep-disordered breathing, and exposure to high altitude. Acute hypoxia is characterized by vasoconstriction of small pulmonary arteries, a phenomenon called hypoxic pulmonary vasoconstriction. With prolonged hypoxia, thickening of the smooth vascular layer of the small pulmonary arteries occurs, a phenomenon described as pulmonary vascular remodeling. Although the core mechanisms of both vasoconstriction and remodeling are thought to reside in the smooth muscle cell layer, the endothelium modulates these two processes. The purpose of this review is briefly to (a) discuss the mechanisms of hypoxic pulmonary hypertension as it pertains to certain disease states, and (b) examine the pathways that have potential therapeutic applications for this condition.

Therapeutic concepts for hypoxic pulmonary vasoconstriction involving ion regulation and the smooth muscle contractile apparatus

Hypoxic pulmonary vasoconstriction (HPV) and pulmonary hypertension present a common and formidable clinical problem for practicing intensivists, thoracic, transplant, and trauma surgeons. The Redox Theory for the mechanisms of HPV has provided researchers with a new understanding of the etiology behind HPV that has opened the door to many new avenues of therapy for the disease. Potassium channels have been proposed to be the main mediator contributing to HPV, and treatment concepts that attempt to manipulate the function and number of those channels have been explored. Additionally, attempts to transfer genes that express the formation of specific potassium channels directly into pulmonary hypertensive lungs have proven to be very promising. Finally, rho kinase (ROK) has been discovered to play a very central role in the formation of hypoxia-induced pulmonary hypertension, and the advent of very specific ROK inhibitors has shown positive clinical results. The purposes of this review are to: (1) briefly discuss some of the basic mechanisms that undergird HPV, including the Redox Theory for the mechanisms of HPV; (2) address current research involving treatments concepts related to ion channels; (3) report on research involving gene therapy to combat pulmonary hypertension; and (4) examine potential therapeutic avenues associated with inhibition of rho kinase.

p38 mitogen-activated protein kinase mediates the sustained phase of hypoxic pulmonary vasoconstriction and plays a role in phase I vasodilation

Hypoxic pulmonary vasoconstriction (HPV) and pulmonary hypertension present common and formidable clinical problems for thoracic, transplant, and trauma surgeons. We hypothesized that acute hypoxia causes pulmonary artery (PA) contraction and that p38 mitogen-activated protein (MAP) kinase is a key mediator in that process. To test this hypothesis, we measured isometric force displacement in isolated rat pulmonary artery rings during hypoxia in the presence and absence of the selective p38 MAP kinase inhibitor SB-20358, and stimulator anisomycin. In separate experiments, we measured the functional effects in isolated rat pulmonary artery rings of inhibiting p38 MAP kinase during normoxic conditions. p38 MAP kinase inhibition significantly attenuated the delayed, but not early, contractile phase of HPV. Additionally, stimulation of p38 MAP kinase significantly decreased the phase I vasodilation of HPV. Under normoxia conditions, there was no statistically significant difference in isometric force displacement between control and p38 MAPK inhibitor-treated pulmonary artery rings. We conclude that p38 MAP kinase may be a key mediator in the pathogenesis of HPV and that further understanding may lead to new therapies for HPV associated with acute lung injury.

EXPERIMENTAL THERAPIES FOR HYPOXIA-INDUCED PULMONARY HYPERTENSION DURING ACUTE LUNG INJURY

Hypoxic pulmonary vasoconstriction (HPV) and pulmonary hypertension present a common and formidable clinical problem for practicing thoracic, transplant, and trauma surgeons. The recent discovery of efficacious drugs that are selective for the pulmonary vasculature has brought about the potential for very powerful therapeutic agents. Inhaled nitric oxide (NO) therapy has already found broad clinical utility, yet its use is limited by potential toxicities. Rho kinase (ROK) has been discovered to play a very central role in the formation of hypoxia induced pulmonary hypertension, and the advent of very specific ROK inhibitors has shown positive clinical results. Finally, phosphodiesterase-5 inhibitors have been found to selectively vasodilate the pulmonary vasculature in the midst of HPV. The purposes of this review are to: 1) discuss the advantages and disadvantages of inhaled preparations of NO; 2) address experimental alternatives to inhaled preparations of NO to treat HPV; 3) explore potential therapeutic avenues associated with inhibition of Rho-kinase; and, 4) examine the use of phosphodiesterase-5 (PDE-5) inhibitors and combination therapy in the treatment of HPV.

Modulation of PGF2alpha- and hypoxia-induced contraction of rat intrapulmonary artery by p38 MAPK inhibition: a nitric oxide-dependent mechanism

The mechanisms through which p38 mitogen-activated protein kinase (p38 MAPK) is involved in smooth muscle contraction remain largely unresolved. We examined the role of p38 MAPK in prostaglandin F(2alpha) (PGF(2alpha))-induced vasoconstriction and in hypoxic pulmonary vasoconstriction (HPV) of rat small intrapulmonary arteries (IPA). The p38 MAPK inhibitors SB-203580 and SB-202190 strongly inhibited PGF(2alpha)-induced vasoconstriction, with IC(50)s of 1.6 and 1.2 microM, whereas the inactive analog SB-202474 was approximately 30-fold less potent. Both transient and sustained phases of HPV were suppressed by SB-203580, but not by SB-202474 (both 2 microM). Western blot analysis revealed that PGF(2alpha) (20 microM) increased phosphorylation of p38 MAPK and of heat shock protein 27 (HSP27), and this was abolished by SB-203580 but not by SB-202474 (both 2 microM). Endothelial denudation or blockade of endothelial nitric oxide (NO) synthase with N(omega)-nitro-L-arginine methyl ester (L-NAME) significantly suppressed the relaxation of PGF(2alpha)-constricted IPA by SB-203580, but not by SB-202474. Similarly, the inhibition of HPV by SB-203580 was prevented by prior treatment with L-NAME. SB-203580 (2 microM), but not SB-202474, enhanced relaxation-induced by the NO donor S-nitroso-N-acetylpenicillamine (SNAP) in endothelium-denuded IPA constricted with PGF(2alpha). In alpha-toxin-permeabilized IPA, SB-203580-induced relaxation occurred in the presence but not the absence of the NO donor sodium nitroprusside (SNP); SB-202474 was without effect even in the presence of SNP. In intact IPA, neither PGF(2alpha)- nor SNAP-mediated changes in cytosolic free Ca(2+) were affected by SB-203580. We conclude that p38 MAPK contributes to PGF(2alpha)- and hypoxia-induced constriction of rat IPA primarily by antagonizing the underlying Ca(2+)-desensitizing actions of NO.

Protein kinases in vascular smooth muscle tone--role in the pulmonary vasculature and hypoxic pulmonary vasoconstriction

Hypoxic pulmonary vasoconstriction (HPV) is an adaptive mechanism that in the normal animal diverts blood away from poorly ventilated areas of the lung, thereby maintaining optimal ventilation-perfusion matching. In global hypoxia however, such as in respiratory disease or at altitude, it causes detrimental increases in pulmonary vascular resistance and pulmonary artery (PA) pressure. The precise intracellular pathways and mechanisms underlying HPV remain unclear, although it is now recognised that both an elevation in smooth muscle intracellular [Ca2+] and a concomitant increase in Ca2+ sensitivity are involved. Several key intracellular protein kinases have been proposed as components of the signal transduction pathways leading to development of HPV, specifically Rho kinase, non-receptor tyrosine kinases (NRTK), p38 mitogen activated protein (MAP) kinase, and protein kinase C (PKC). All of these have been implicated to a greater or lesser extent in pathways leading to Ca2+ sensitisation, and in some cases regulation of intracellular [Ca2+] as well. In this article, we review the role of these key protein kinases in the regulation of vascular smooth muscle (VSM) constriction, applying what is known in the systemic circulation to the pulmonary circulation and HPV. We conclude that the strongest evidence for direct involvement of protein kinases in the mechanisms of HPV concerns a central role for Rho kinase in Ca2+ sensitisation, and a potential role for Src-family kinases in both modulation of Ca2+ entry via capacitative Ca2+ entry (CCE) and activation of Rho kinase, though others are likely to have indirect or modulatory influences. In addition, we speculate that Src family kinases may provide a central interface between the proposed hypoxia-induced generation of reactive oxygen species by mitochondria and both the elevation in intracellular [Ca2+] and Rho kinase mediated Ca2+ sensitisation.

Calcium, mitochondria and oxygen sensing in the pulmonary circulation

A key event in hypoxic pulmonary vasoconstriction (HPV) is the elevation in smooth muscle intracellular Ca2+ concentration. However, there is controversy concerning the source of this Ca2+, the signal transduction pathways involved, and the identity of the oxygen sensor. Although there is wide support for the hypothesis that hypoxia elicits depolarisation via inhibition of K+ channels, and thus promotes Ca2+ entry through L-type channels, a significant number of studies are inconsistent with this mechanism being either the sole or even major means by which Ca2+ is elevated during HPV. There is strong evidence that intracellular Ca2+ stores play a critical role, and voltage-independent Ca2+ entry mechanisms including capacitative Ca2+ entry (CCE) have also been implicated. There is renewed interest in the role of mitochondria in HPV, both in terms of modulators of Ca2+ homeostasis per se and as oxygen sensors. There is however considerable uncertainty concerning the mechanisms involved in the latter, with proposals for changes in redox couples and both an increase and decrease in mitochondrial production of reactive oxygen species (ROS). In this article we review the evidence for and against involvement of such mechanisms in HPV, and propose a model for the regulation of intracellular [Ca2+] in pulmonary artery during hypoxia in which the mitochondria play a central role.

Involvement of p38-mitogen-activated protein kinase in adenosine receptor-mediated relaxation of coronary artery

The purpose of this study was to explore the involvement of adenosine receptor(s) in porcine coronary artery (PCA) relaxation and to define the role of MAPK signaling pathways. Isometric tensions were recorded in denuded PCA rings. 5'-(N-ethylcarboxamido)adenosine (NECA), a nonselective adenosine receptor agonist, induced a concentration-dependent relaxation (EC(50) = 16.8 nM) of PGF(2alpha) (10 microM)-preconstricted arterial rings. NECA-induced relaxation was completely blocked by 0.1 microM SCH-58261 (A(2A) antagonist) at lower doses (1-40 nM) but not at higher doses (80-1,000 nM). MRS-1706 (1 microM, A(2B) antagonist) was able to shift the NECA concentration-response curve to the right. CGS-21680 (selective A(2A) agonist) induced responses similarly to NECA, whereas N(6)-cyclopentyladenosine (A(1) agonist) and Cl-IB-MECA (A(3) agonist) did not. Furthermore, the effect of NECA was attenuated by the addition of SB-203580 (10 microM, p38 MAPK inhibitor) but not by PD-98059 (10 microM, MEK inhibitor). Interestingly, SB-203580 had no effect on CGS-21680-induced relaxation. Western blot analysis demonstrated that PGF(2alpha) and adenosine agonists stimulated p38 MAPK at a concentration of 40 nM in PCA smooth muscle cells. MRS-1706 (1 microM) significantly reduced NECA-induced p38 MAPK phosphorylation. Addition of NECA and SB-203580 alone or in combination inhibited PGF(2alpha)-induced p38 MAPK. Western blot data were further confirmed by p38 MAPK activity measurement using activating transcription factor-2 assay. Our results suggest that the adenosine receptor subtype involved in causing relaxation of porcine coronary smooth muscle is mainly A(2A) subtype, although A(2B) also may play a role, possibly through p38 MAPK pathway.

Hypoxic pulmonary vasoconstriction in cardiothoracic surgery: basic mechanisms to potential therapies

Hypoxic pulmonary vasoconstriction is postulated to be an adaptive mechanism to match lung perfusion with ventilation; however, the consequences of the maladaptive effects of pulmonary vasoconstriction represent formidable therapeutic challenges. Understanding the basic mechanisms of hypoxic pulmonary vasoconstriction will enhance the assimilation of translational research into clinical practice. The purposes of this review are to (1) define basic mechanisms of pulmonary vasoconstriction and vasorelaxation; (2) delineate the biphasic contractile response to hypoxia; (3) critically examine data that support the mediator hypothesis versus the ion channel hypothesis; and (4) explore potential mechanistic-based therapies for hypoxic pulmonary vasoconstriction.

Activation of pulmonary mitogen-activated protein kinases during cardiopulmonary bypass

PURPOSE

Cardiopulmonary bypass (CPB) produces an inflammatory response associated with pulmonary dysfunction. Mitogen-activated protein kinases (MAPK) have been shown to mediate pulmonary injury. We hypothesized that MAPK are activated during CPB and potentially contribute to lung injury.

METHODS

Pigs were placed on CPB (n = 6) for 90 min, which included 80 min of cardioplegic arrest, followed by 180 min of post-CPB reperfusion. Control animals (n = 6) underwent sternotomy and heparinization only. Lung samples were collected at baseline, during CPB, and during post-CPB reperfusion. Activated forms of extracellular signal-regulated kinases 1/2 (ERK1/2) and p38 were measured by Western blot. Immunohistochemistry was used for tissue localization of activated MAPK. Pulmonary inflammation was determined by histology. Pulmonary edema was estimated by tissue water percentage.

RESULTS

Activated ERK1/2 and p38 were increased after 90 min of CPB compared with controls (3.94 +/- 0.61- and 2.49 +/- 0.15-fold increase, respectively; both P < 0.01). At 180 min of post-CPB reperfusion, ERK1/2 activity was increased by nearly 5-fold compared with controls (P < 0.01), whereas p38 activity returned to baseline levels. By immunohistochemistry, activated ERK1/2 and p38 in the CPB group were localized to alveolar epithelial cells, vascular endothelial cells, and bronchial smooth muscle. Histologic signs of lung injury included leukocyte infiltration in the CPB group. Tissue water percentage was increased with CPB (89.9 +/- 1.5% versus 82.5 +/- 1.0%, CPB versus control, P < 0.05).

CONCLUSIONS

The results of our study demonstrate that CPB increases pulmonary p38 activity and causes sustained activation of ERK1/2. MAPK activation thus may in part mediate the pulmonary inflammatory response and provide a potential site of intervention to prevent pulmonary dysfunction due to CPB.