Cyclic strain induces reactive oxygen species production via an endothelial NAD(P)H oxidase

Molecular profiling of sponge deflation reveals an ancient relaxant-inflammatory response

A hallmark of animals is the coordination of whole-body movement. Neurons and muscles are central to this, yet coordinated movements also exist in sponges that lack these cell types. Sponges are sessile animals with a complex canal system for filter-feeding. They undergo whole-body movements resembling "contractions" that lead to canal closure and water expulsion. Here, we combine live 3D optical coherence microscopy, pharmacology, and functional proteomics to elucidate the sequence and detail of shape changes, the tissues and molecular physiology involved, and the control of these movements. Morphometric analysis and targeted perturbation suggest that the movement is driven by the relaxation of actomyosin stress fibers in epithelial canal cells, which leads to whole-body deflation via collapse of the incurrent and expansion of the excurrent canal system. Thermal proteome profiling and quantitative phosphoproteomics confirm the control of cellular relaxation by an Akt/NO/PKG/PKA pathway. Agitation-induced deflation leads to differential phosphorylation of proteins forming epithelial cell junctions, implying their mechanosensitive role. Unexpectedly, untargeted metabolomics detect a concomitant decrease in antioxidant molecules during deflation, reflecting an increase in reactive oxygen species. Together with the secretion of proteinases, cytokines, and granulin, this indicates an inflammation-like state of the deflating sponge reminiscent of vascular endothelial cells experiencing oscillatory shear stress. These results suggest the conservation of an ancient relaxant-inflammatory response of perturbed fluid-carrying systems in animals and offer a possible mechanism for whole-body coordination through diffusible paracrine signals and mechanotransduction.

Stretchable Oxygen-Tolerant Sensor Based on a Single-Atom Fe-N4 Electrocatalyst for Observing the Role of Oxidative Stress in Hypertension

Oxidative stress and related oxidative damage have a causal relation with the pathogenesis of hypertension. Therefore, it is crucial to determine the mechanism of oxidative stress in hypertension by applying mechanical forces on cells to simulate hypertension while monitoring the release of reactive oxygen species (ROS) from cells under an oxidative stress environment. However, cellular level research has rarely been explored because monitoring the ROS released by cells is still challenging owing to the interference of O₂. In this study, an Fe single-atom-site catalyst anchored on N-doped carbon-based materials (Fe SASC/N-C) was synthesized, which exhibits excellent electrocatalytic activity for the reduction of hydrogen peroxide (H₂O₂) at a peak potential of +0.1 V and can effectively avoid the interference of O₂. Furthermore, we constructed a flexible and stretchable electrochemical sensor based on the Fe SASC/N-C catalyst to study the release of cellular H₂O₂ under simulated hypoxic and hypertension conditions. Density functional theory calculations show that the highest transition state energy barrier from the oxygen reduction reaction (ORR), i.e., O₂ to H₂O, is 0.38 eV. In comparison, the H₂O₂ reduction reaction (HPRR) can be completed only by overcoming a lower energy barrier of 0.24 eV, endowing the HPRR to be more favorable on Fe SASC/N-C compared with the ORR. This study provided a reliable electrochemical platform for real-time investigation of H₂O₂-related underlying mechanisms of the hypertension process.

Redox Homeostasis Alteration in Endothelial Mechanotransduction Monitored by Dual Stretchable Electrochemical Sensors

In vivo, endothelial cells are permanently subjected to dynamic cyclic stretch and adapt to it through the release of vasoactive substances. Among them, reactive oxygen species (ROS) and nitric oxide (NO) are indispensable redox molecules, the contents of which and their ratio are closely implicated with endothelial redox homeostasis. However, simultaneous and quantitative monitoring of ROS and NO release in endothelial mechanotransduction remains a great challenge. Herein, a stretchable electrochemical device is developed with a dual electrode based on gold nanotubes decorated with uniform and tiny platinum nanoparticles. This hybrid nanostructure endows the sensor with high sensitivity toward both hydrogen peroxide (H₂O₂) (as the most stable ROS) and NO electrooxidation. Importantly, the two species can be well discriminated by applying different potentials, which allows simultaneous monitoring of H₂O₂ and NO release in stretch-induced endothelial mechanotransduction by the same device. The results of quantitative analysis suggest that endothelial redox homeostasis and its alteration are strongly related to vascular biomechanical and biochemical milieus. Further investigation reveals that the interplay of ROS and NO signaling has an important role in the regulation of endothelial redox state. This work will greatly facilitate the deep understanding of the molecular mechanism of endothelial dysfunction and vascular disorder.

Macrophage uptake of oxidized and acetylated low-density lipoproteins and generation of reactive oxygen species are regulated by linear stiffness of the growth surface

Macrophages are key players in the development of atherosclerosis: they scavenge lipid, transform into foam cells, and produce proinflammatory mediators. At the same time, the arterial wall undergoes profound changes in its mechanical properties. We recently showed that macrophage morphology and proinflammatory potential are regulated by the linear stiffness of the growth surface. Here we asked whether linear stiffness also regulates lipid uptake by macrophages. We cultured murine bone marrow-derived macrophages (BMMs) on polyacrylamide gels modeling stiffness of healthy (1kPa) and diseased (10-150kPa) blood vessels. In unprimed BMMs, increased linear stiffness increased uptake of oxidized (oxLDL) and acetylated (acLDL) low density lipoproteins and generation of reactive oxygen species, but did not alter phagocytosis of bacteria or silica particles. Macrophages adapted to stiff growth surfaces had increased mRNA and protein expression of two key lipoprotein receptors: CD36 and scavenger receptor b1. Regulation of the lipoprotein receptor, lectin-like receptor for ox-LDL, was more complex: mRNA expression decreased but surface protein expression increased with increased stiffness. Focal adhesion kinase was required for maximal uptake of oxLDL, but not of acLDL. Uptake of oxLDL and acLDL was independent of rho-associated coiled coil kinase. Through pharmacologic inhibition and genetic deletion, we found that transient receptor potential vanilloid 4 (TRPV4), a mechanosensitive ion channel, plays an inhibitory role in the uptake of acLDL, but not oxLDL. Together, these results implicate mechanical signaling in the uptake of acLDL and oxLDL, opening up the possibility of new pharmacologic targets to modulate lipid uptake by macrophages in vivo.

Stretchable Electrode Based on Au@Pt Nanotube Networks for Real-Time Monitoring of ROS Signaling in Endothelial Mechanotransduction

Vascular endothelial cells (ECs) are natively exposed to dynamic cyclic stretch and respond to it by the production of vasoactive molecules. Among them, reactive oxygen species (ROS) are closely implicated to the endothelial function and vascular homeostasis. However, the dynamic monitoring of ROS release during endothelial mechanotransduction remains a steep challenge. Herein, we developed a stretchable electrochemical sensor by decoration of uniform and ultrasmall platinum nanoparticles (Pt NPs) on gold nanotube (Au NT) networks (denoted as Au@Pt NTs). The orchestrated structure exhibited prominent electrocatalytic property toward the oxidation of hydrogen peroxide (H₂O₂) (as the most stable ROS) while maintaining excellent mechanical compliance of Au NT networks. Moreover, the favorable biocompatibility of Au NTs and Pt NPs promoted the adhesion and proliferation of ECs cultured thereon. These allowed in situ inducing ECs mechanotransduction and synchronously real-time monitoring of H₂O₂ release. Further investigation revealed that the production of H₂O₂ was positively correlated with the applied mechanical strains and could be boosted by other coexisting pathogenic factors. This indicates the great prospect of our proposed sensor in exploring ROS-related signaling for the deep understanding of cell mechanotransduction and vascular disorder.

Single-atom Ni-N4 provides a robust cellular NO sensor

Nitric oxide (NO) has been implicated in a variety of physiological and pathological processes. Monitoring cellular levels of NO requires a sensor to feature adequate sensitivity, transient recording ability and biocompatibility. Herein we report a single-atom catalysts (SACs)-based electrochemical sensor for the detection of NO in live cellular environment. The system employs nickel single atoms anchored on N-doped hollow carbon spheres (Ni SACs/N-C) that act as an excellent catalyst for electrochemical oxidation of NO. Notably, Ni SACs/N-C shows superior electrocatalytic performance to the commonly used Ni based nanomaterials, attributing from the greatly reduced Gibbs free energy that are required for Ni SACs/N-C in activating NO oxidation. Moreover, Ni SACs-based flexible and stretchable sensor shows high biocompatibility and low nanomolar sensitivity, enabling the real-time monitoring of NO release from cells upon drug and stretch stimulation. Our results demonstrate a promising means of using SACs for electrochemical sensing applications.

The monitoring of nitric oxide is important to a number of disease states and biomedical applications. Here, the authors report on a single nickel atom catalyst based sensor for detecting nitric oxide production from cells.

Mechanosensing and Mechanoregulation of Endothelial Cell Functions

Vascular endothelial cells (ECs) form a semiselective barrier for macromolecules and cell elements regulated by dynamic interactions between cytoskeletal elements and cell adhesion complexes. ECs also participate in many other vital processes including innate immune reactions, vascular repair, secretion, and metabolism of bioactive molecules. Moreover, vascular ECs represent a unique cell type exposed to continuous, time-dependent mechanical forces: different patterns of shear stress imposed by blood flow in macrovasculature and by rolling blood cells in the microvasculature; circumferential cyclic stretch experienced by the arterial vascular bed caused by heart propulsions; mechanical stretch of lung microvascular endothelium at different magnitudes due to spontaneous respiration or mechanical ventilation in critically ill patients. Accumulating evidence suggests that vascular ECs contain mechanosensory complexes, which rapidly react to changes in mechanical loading, process the signal, and develop context-specific adaptive responses to rebalance the cell homeostatic state. The significance of the interactions between specific mechanical forces in the EC microenvironment together with circulating bioactive molecules in the progression and resolution of vascular pathologies including vascular injury, atherosclerosis, pulmonary edema, and acute respiratory distress syndrome has been only recently recognized. This review will summarize the current understanding of EC mechanosensory mechanisms, modulation of EC responses to humoral factors by surrounding mechanical forces (particularly the cyclic stretch), and discuss recent findings of magnitude-specific regulation of EC functions by transcriptional, posttranscriptional and epigenetic mechanisms using -omics approaches. We also discuss ongoing challenges and future opportunities in developing new therapies targeting dysregulated mechanosensing mechanisms to treat vascular diseases. © 2019 American Physiological Society. Compr Physiol 9:873-904, 2019.

Poly(ADP-Ribose)Polymerase-1 in Lung Inflammatory Disorders: A Review

Asthma, acute lung injury (ALI), and chronic obstructive pulmonary disease (COPD) are lung inflammatory disorders with a common outcome, that is, difficulty in breathing. Corticosteroids, a class of potent anti-inflammatory drugs, have shown less success in the treatment/management of these disorders, particularly ALI and COPD; thus, alternative therapies are needed. Poly(ADP-ribose)polymerases (PARPs) are the post-translational modifying enzymes with a primary role in DNA repair. During the last two decades, several studies have reported the critical role played by PARPs in a good of inflammatory disorders. In the current review, the studies that address the role of PARPs in asthma, ALI, and COPD have been discussed. Among the different members of the family, PARP-1 emerges as a key player in the orchestration of lung inflammation in asthma and ALI. In addition, PARP activation seems to be associated with the progression of COPD. Furthermore, PARP-14 seems to play a crucial role in asthma. STAT-6 and GATA-3 are reported to be central players in PARP-1-mediated eosinophilic inflammation in asthma. Interestingly, oxidative stress-PARP-1-NF-κB axis appears to be tightly linked with inflammatory response in all three-lung diseases despite their distinct pathophysiologies. The present review sheds light on PARP-1-regulated factors, which may be common or differential players in asthma/ALI/COPD and put forward our prospective for future studies.

Segmental aortic stiffening contributes to experimental abdominal aortic aneurysm development

BACKGROUND

Stiffening of the aortic wall is a phenomenon consistently observed in age and in abdominal aortic aneurysm (AAA). However, its role in AAA pathophysiology is largely undefined.

METHODS AND RESULTS

Using an established murine elastase-induced AAA model, we demonstrate that segmental aortic stiffening precedes aneurysm growth. Finite-element analysis reveals that early stiffening of the aneurysm-prone aortic segment leads to axial (longitudinal) wall stress generated by cyclic (systolic) tethering of adjacent, more compliant wall segments. Interventional stiffening of AAA-adjacent aortic segments (via external application of surgical adhesive) significantly reduces aneurysm growth. These changes correlate with the reduced segmental stiffness of the AAA-prone aorta (attributable to equalized stiffness in adjacent segments), reduced axial wall stress, decreased production of reactive oxygen species, attenuated elastin breakdown, and decreased expression of inflammatory cytokines and macrophage infiltration, and attenuated apoptosis within the aortic wall, as well. Cyclic pressurization of segmentally stiffened aortic segments ex vivo increases the expression of genes related to inflammation and extracellular matrix remodeling. Finally, human ultrasound studies reveal that aging, a significant AAA risk factor, is accompanied by segmental infrarenal aortic stiffening.

CONCLUSIONS

The present study introduces the novel concept of segmental aortic stiffening as an early pathomechanism generating aortic wall stress and triggering aneurysmal growth, thereby delineating potential underlying molecular mechanisms and therapeutic targets. In addition, monitoring segmental aortic stiffening may aid the identification of patients at risk for AAA.

NADPH Oxidase Activity in Cerebral Arterioles Is a Key Mediator of Cerebral Small Vessel Disease-Implications for Prevention

Cerebral small vessel disease (SVD), a common feature of brain aging, is characterized by lacunar infarcts, microbleeds, leukoaraiosis, and a leaky blood-brain barrier. Functionally, it is associated with cognitive decline, dementia, depression, gait abnormalities, and increased risk for stroke. Cerebral arterioles in this syndrome tend to hypertrophy and lose their capacity for adaptive vasodilation. Rodent studies strongly suggest that activation of Nox2-dependent NADPH oxidase activity is a crucial driver of these structural and functional derangements of cerebral arterioles, in part owing to impairment of endothelial nitric oxide synthase (eNOS) activity. This oxidative stress may also contribute to the breakdown of the blood-brain barrier seen in SVD. Hypertension, aging, metabolic syndrome, smoking, hyperglycemia, and elevated homocysteine may promote activation of NADPH oxidase in cerebral arterioles. Inhibition of NADPH oxidase with phycocyanobilin from spirulina, as well as high-dose statin therapy, may have potential for prevention and control of SVD, and high-potassium diets merit study in this regard. Measures which support effective eNOS activity in other ways-exercise training, supplemental citrulline, certain dietary flavonoids (as in cocoa and green tea), and capsaicin, may also improve the function of cerebral arterioles. Asian epidemiology suggests that increased protein intakes may decrease risk for SVD; conceivably, arginine and/or cysteine-which boosts tissue glutathione synthesis, and can be administered as N-acetylcysteine-mediate this benefit. Ameliorating the risk factors for SVD-including hypertension, metabolic syndrome, hyperglycemia, smoking, and elevated homocysteine-also may help to prevent and control this syndrome, although few clinical trials have addressed this issue to date.

Synergistic Impact of Nicotine and Shear Stress Induces Cytoskeleton Collapse and Apoptosis in Endothelial Cells

Nicotine is the major component in cigarette smoke and has been recognized as a risk factor for various cardiovascular diseases such as atherosclerosis. However, the definite pathogenesis of nicotine-mediated endothelial dysfunction remains unclear because hemodynamic factor in most of prior in vitro studies was excluded. To understand how nicotine affects endothelium in the dynamic environment, human umbilical vein endothelial cells were treated by different laminar shear stresses (LSS; 0, 6, 8, and 12 dynes cm(-2)) with and without 10(-4) M nicotine for 12 h in a parallel plate flow system, following detections of cellular morphology and apoptotic level. Our results showed that cells sheared by 12 dynes cm(-2) LSS with nicotine excessively elongated and aligned with the flow direction, and exhibited significant apoptosis as compared to the groups with nicotine or LSS alone. We reasoned that the irregular morphological rearrangement and elevated apoptosis were resulted from the interruption of mechanostasis due to cytoskeletal collapse. Furthermore, all the impaired responses can be rescued by treatment with free radical scavenger ascorbic acid (10(-4) M), indicating oxidative stress was likely mediated with the impairments. In summary, our findings demonstrated an essential role of LSS in nicotine-mediated endothelial injury occurring in the physiological environment.

Regulation of thrombomodulin expression and release in human aortic endothelial cells by cyclic strain

Background and Objectives

Thrombomodulin (TM), an integral membrane glycoprotein expressed on the lumenal surface of vascular endothelial cells, promotes anti-coagulant and anti-inflammatory properties. Release of functional TM from the endothelium surface into plasma has also been reported. Much is still unknown however about how endothelial TM is regulated by physiologic hemodynamic forces (and particularly cyclic strain) intrinsic to endothelial-mediated vascular homeostasis.

Methods

This study employed human aortic endothelial cells (HAECs) to investigate the effects of equibiaxial cyclic strain (7.5%, 60 cycles/min, 24 hrs), and to a lesser extent, laminar shear stress (10 dynes/cm², 24 hrs), on TM expression and release. Time-, dose- and frequency-dependency studies were performed.

Results

Our initial studies demonstrated that cyclic strain strongly downregulated TM expression in a p38- and receptor tyrosine kinase-dependent manner. This was in contrast to the upregulatory effect of shear stress. Moreover, both forces significantly upregulated TM release over a 48 hr period. With continuing focus on the cyclic strain-induced TM release, we noted both dose (0–7.5%) and frequency (0.5–2.0 Hz) dependency, with no attenuation of strain-induced TM release observed following inhibition of MAP kinases (p38, ERK-1/2), receptor tyrosine kinase, or eNOS. The concerted impact of cyclic strain and inflammatory mediators on TM release from HAECs was also investigated. In this respect, both TNFα (100 ng/ml) and ox-LDL (10–50 µg/ml) appeared to potentiate strain-induced TM release. Finally, inhibition of neither MMPs (GM6001) nor rhomboids (3,4-dichloroisocoumarin) had any effect on strain-induced TM release. However, significantly elevated levels (2.1 fold) of TM were observed in isolated microparticle fractions following 7.5% strain for 24 hrs.

Conclusions

A preliminary in vitro investigation into the effects of cyclic strain on TM in HAECs is presented. Physiologic cyclic strain was observed to downregulate TM expression, whilst upregulating in a time-, dose- and frequency-dependent manner the release of TM.

Hemodynamic regulation of reactive oxygen species: implications for vascular diseases

SIGNIFICANCE

Arterial blood vessels functionally and structurally adapt to altering hemodynamic forces in order to accommodate changing needs and to provide stress homeostasis. This ability is achieved at the cellular level by converting mechanical stimulation into biochemical signals (i.e., mechanotransduction). Physiological mechanical stress helps maintain vascular structure and function, whereas pathologic or aberrant stress may impair cellular mechano-signaling, and initiate or augment cellular processes that drive disease.

RECENT ADVANCES

Reactive oxygen species (ROS) may represent an intriguing class of mechanically regulated second messengers. Chronically enhanced ROS generation may be induced by adverse mechanical stresses, and is associated with a multitude of vascular diseases. Although a causal relationship has clearly been demonstrated in large numbers of animal studies, an effective ROS-modulating therapy still remains to be established by clinical studies.

CRITICAL ISSUES AND FUTURE DIRECTIONS

This review article focuses on the role of various mechanical forces (in the form of laminar shear stress, oscillatory shear stress, or cyclic stretch) as modulators of ROS-driven signaling, and their subsequent effects on vascular biology and homeostasis, as well as on specific diseases such as arteriosclerosis, hypertension, and abdominal aortic aneurysms. Specifically, it highlights the significance of the various NADPH oxidase (NOX) isoforms as critical ROS generators in the vasculature. Directed targeting of defined components in the complex network of ROS (mechano-)signaling may represent a key for successful translation of experimental findings into clinical practice.

Inflammation and mechanical stretch promote aortic stiffening in hypertension through activation of p38 mitogen-activated protein kinase

RATIONALE

Aortic stiffening commonly occurs in hypertension and further elevates systolic pressure. Hypertension is also associated with vascular inflammation and increased mechanical stretch. The interplay between inflammation, mechanical stretch, and aortic stiffening in hypertension remains undefined.

OBJECTIVE

Our aim was to determine the role of inflammation and mechanical stretch in aortic stiffening.

METHODS AND RESULTS

Chronic angiotensin II infusion caused marked aortic adventitial collagen deposition, as quantified by Masson trichrome blue staining and biochemically by hydroxyproline content, in wild-type but not in recombination activating gene-1-deficient mice. Aortic compliance, defined by ex vivo measurements of stress-strain curves, was reduced by chronic angiotensin II infusion in wild-type mice (P<0.01) but not in recombination activating gene-1-deficient mice (P<0.05). Adoptive transfer of T-cells to recombination activating gene-1-deficient mice restored aortic collagen deposition and stiffness to values observed in wild-type mice. Mice lacking the T-cell-derived cytokine interleukin 17a were also protected against aortic stiffening. In additional studies, we found that blood pressure normalization by treatment with hydralazine and hydrochlorothiazide prevented angiotensin II-induced vascular T-cell infiltration, aortic stiffening, and collagen deposition. Finally, we found that mechanical stretch induces the expression of collagen 1α1, 3α1, and 5a1 in cultured aortic fibroblasts in a p38 mitogen-activated protein kinase-dependent fashion, and that inhibition of p38 prevented angiotensin II-induced aortic stiffening in vivo. Interleukin 17a also induced collagen 3a1 expression via the activation of p38 mitogen-activated protein kinase.

CONCLUSIONS

Our data define a pathway in which inflammation and mechanical stretch lead to vascular inflammation that promotes collagen deposition. The resultant increase in aortic stiffness likely further worsens systolic hypertension and its attendant end-organ damage.

NOX enzymes: potential target for the treatment of acute lung injury

Acute lung injury (ALI) and its more severe form, acute respiratory distress syndrome (ARDS), is characterized by acute inflammation, disruption of the alveolar-capillary barrier, and in the organizing stage by alveolar pneumocytes hyperplasia and extensive lung fibrosis. The cellular and molecular mechanisms leading to the development of ALI/ARDS are not completely understood, but there is evidence that reactive oxygen species (ROS) generated by inflammatory cells as well as epithelial and endothelial cells are responsible for inflammatory response, lung damage, and abnormal repair. Among all ROS-producing enzymes, the members of NADPH oxidases (NOXs), which are widely expressed in different lung cell types, have been shown to participate in cellular processes involved in the maintenance of lung integrity. It is not surprising that change in NOXs’ expression and function is involved in the development of ALI/ARDS. In this context, the use of NOX inhibitors could be a possible therapeutic perspective in the management of this syndrome. In this article, we summarize the current knowledge concerning some cellular aspects of NOXs localization and function in the lungs, consider their contribution in the development of ALI/ARDS and discuss the place of NOX inhibitors as potential therapeutical target.

Tyrosine nitration limits stretch-induced CD40 expression and disconnects CD40 signaling in human endothelial cells

Hemodynamic forces are important effectors of endothelial cell phenotype and function. Because CD40-CD154 interactions between endothelial cells and mononuclear leukocytes or activated platelets play an important role in vascular dysfunction, we investigated the effects of cyclic stretch on CD40 expression in human cultured endothelial cells. Short-term stretch transiently up-regulated CD40 expression while long-term stretch resulted in a distinct decline in CD40 protein which was prevented by inhibition of the 20S proteasome or scavenging of peroxynitrite. Tyrosine nitration of CD40 also occurred under static conditions on addition of authentic peroxynitrite, and according to mass spectrometry analysis Tyr-82 but not Tyr-31 was its target in the native protein. Immunofluorescence analysis of endothelial cells transduced with a control or Tyr-82 to Ala mutated AAV9-CD40-eGFP expression construct confirmed a peroxynitrite-dependent redistribution of the protein from the cell membrane to the cytoplasm, which was prevented by methyl-β-cyclodextrin. Moreover, CD154-stimulated IL-12p40 and E-selectin expression markedly decreased after exposure to authentic peroxynitrite or cyclic stretch, respectively. Coimmunoprecipitation demonstrated a decreased binding of TRAF2 and TRAF6 to the CD40 protein after tyrosine nitration. Through this posttranslational oxidative modification of an important costimulatory molecule, endothelial cells are able to quickly adapt to unfavorable hemodynamics and maintain their anti-inflammatory phenotype.

Trans-plasma membrane electron transport in mammals: functional significance in health and disease

Trans-plasma membrane electron transport (t-PMET) has been established since the 1960s, but it has only been subject to more intensive research in the last decade. The discovery and characterization at the molecular level of its novel components has increased our understanding of how t-PMET regulates distinct cellular functions. This review will give an update on t-PMET, with particular emphasis on how its malfunction relates to some diseases, such as cancer, abnormal cell death, cardiovascular diseases, aging, obesity, neurodegenerative diseases, pulmonary fibrosis, asthma, and genetically linked pathologies. Understanding these relationships may provide novel therapeutic approaches for pathologies associated with unbalanced redox state.

NADPH oxidase-mediated redox signaling: roles in cellular stress response, stress tolerance, and tissue repair

NADPH oxidase (Nox) has a dedicated function of generating reactive oxygen species (ROS). Accumulating evidence suggests that Nox has an important role in signal transduction in cellular stress responses. We have reviewed the current evidence showing that the Nox system can be activated by a collection of chemical, physical, and biological cellular stresses. In many circumstances, Nox activation fits to the cellular stress response paradigm, in that (1) the response can be initiated by various forms of cellular stresses; (2) Nox-derived ROS may activate mitogen-activated protein kinases (extracellular signal-regulated kinase, p38) and c-Jun NH(2)-terminal kinase, which are the core of the cell stress-response signaling network; and (3) Nox is involved in the development of stress cross-tolerance. Activation of the cell survival pathway by Nox may promote cell adaptation to stresses, whereas Nox may also convey signals toward apoptosis in irreversibly injured cells. At later stage after injury, Nox is involved in tissue repair by modulating cell proliferation, angiogenesis, and fibrosis. We suggest that Nox may have an integral role in cell stress responses and the subsequent tissue repair process. Understanding Nox-mediated redox signaling mechanisms may be of prominent significance at the crossroads of directing cellular responses to stress, aiming at either enhancing the stress resistance (in such situations as preventing ischemia-reperfusion injuries and accelerating wound healing) or sensitizing the stress-induced cytotoxicity for proliferative diseases such as cancer. Therefore, an optimal outcome of interventions on Nox will only be achieved when this is dealt with in a timely and disease-and stage-specific manner.

Nitric oxide alterations following acute ductal constriction in the fetal lamb: a role for superoxide

Acute partial compression of the fetal ductus arteriosus (DA) results in an initial abrupt increase in pulmonary blood flow (PBF), which is followed by a significant reduction in PBF to baseline values over the ensuing 2-4 h. We have previously demonstrated that this potent vasoconstricting response is due, in part, to an endothelin-1 (ET-1)-mediated decrease in nitric oxide synthase (NOS) activity. In addition, in vitro data demonstrate that ET-1 increases superoxide levels in pulmonary arterial smooth muscle cells and that oxidative stress alters NOS activity. Therefore, the objectives of this study were to determine the potential role of superoxide in the alterations of hemodynamics and NOS activity following acute ductal constriction in the late-gestation fetal lamb. Eighteen anesthetized near-term fetal lambs were instrumented, and a lung biopsy was performed. After a 48-h recovery, acute constriction of the DA was performed by inflating a vascular occluder. Polyethylene glycol-superoxide dismutase (PEG-SOD; 1,000-1,500 units/kg, n = 7) or PEG-alone (vehicle control group, n = 5) was injected into the pulmonary artery before ductal constriction. Six animals had a sham operation. In PEG-alone-treated lambs, acute ductal constriction rapidly decreased pulmonary vascular resistance (PVR) by 88%. However, by 4 h, PVR returned to preconstriction baseline. This vasoconstriction was associated with an increase in lung superoxide levels (82%), a decrease in total NOS activity (50%), and an increase in P-eNOS-Thr495 (52%) (P < 0.05). PEG-SOD prevented the increase of superoxide after ductal constriction, attenuated the vasoconstriction, preserved NOS activity, and increased P-eNOS Ser1177 (307%, P < 0.05). Sham procedure induced no changes. These data suggest that an acute decrease in NOS activity that is mediated, in part, by increased superoxide levels, and alterations in the phosphorylation status of the endothelial NOS isoform, underlie the pulmonary vascular response to acute ductal constriction.

Long-term cyclic strain downregulates endothelial Nox4

Endothelial cells in vivo are constantly exposed to mechanical forces such as cyclic strain. In endothelial cells, Nox4-containing NAD(P)H oxidase complexes have been identified as major sources of superoxide anion (.O(2)(-)) formation. In this study, we analyzed the effect of cyclic strain on endothelial ROS formation by electron paramagnetic resonance spectroscopy, cytochrome c assay, and dihydroethidium fluorescence, on NO formation by Griess reaction and on gene expression by RT-PCR and Western blot. Primary cultures of human umbilical vein endothelial cells were exposed to 2-18% cyclic strain for up to 24 h using the Flexercell system. Long-term application of 5-12% cyclic strain downregulated Nox4 expression and ROS formation in a time-dependent manner. Downregulation of Nox4 was further confirmed by promoter analysis using dual-luciferase assay. Cu/Zn SOD, MnSOD, and catalase expression was decreased after application of chronic 12% cyclic strain. In contrast, endothelial NO formation and eNOS were increased by cyclic strain. Strain-dependent Nox4 downregulation was abolished by eNOS inhibition with L-NAME. In conclusion, physiological levels of cyclic strain downregulate Nox4 expression and superoxide anion formation. This novel mechanism might contribute to a vasoprotective balance between NO and superoxide anions in response to physiological mechanical stimulation of endothelial cells.

Upregulation of glutathione peroxidase offsets stretch-induced proatherogenic gene expression in human endothelial cells

OBJECTIVE

Localization of atherosclerotic plaques typically correlates with areas of biomechanical strain where shear stress is decreased while stretch, thought to promote atherogenesis through enhanced oxidative stress, is increased.

METHODS AND RESULTS

In human cultured endothelial cells, nitric oxide synthase expression was exclusively shear stress-dependent whereas expression of glutathione peroxidase-1 (GPx-1), but not that of Cu(2+)/Zn(2+)-superoxide dismutase or Mn(2+)-superoxide dismutase, was upregulated solely in response to cyclic stretch. GPx-1 expression was also enhanced in isolated mouse arteries perfused at high pressure. Combined pharmacological and decoy oligodeoxynucleotide blockade revealed that activation of p38 MAP kinase followed by nuclear translocation of CCAAT/enhancer binding protein plays a pivotal role in stretch-induced GPx-1 expression in human endothelial cells. Antisense oligodeoxynucleotide knockdown of GPx-1 reinforced both their capacity to generate hydrogen peroxide and the transient stretch-induced expression of CD40, monocyte chemoatractant protein-1, and vascular cell adhesion molecule-1. Consequently, THP-1 monocyte adhesion to the GPx-1-depleted cells was augmented.

CONCLUSIONS

Stretch-induced proatherosclerotic gene expression in human endothelial cells seems to be hydrogen peroxide-mediated. The concomitant rise in GPx-1 expression, but not that of other antioxidant enzymes, may comprise an adaptive mechanism through which the cells maintain their antiatherosclerotic properties in spite of a decreased bioavailability of nitric oxide.

Effects of cyclic strain and growth factors on vascular smooth muscle cell responses

Under physiological and pathological conditions, vascular smooth muscle cells (SMC) are exposed to different biochemical factors and biomechanical forces. Previous studies pertaining to SMC responses have not investigated the effects of both factors on SMCs. Thus, in our research we investigated the combined effects of growth factors like Bfgf (basic fibroblast growth factor), TGF-β (transforming growth factor β) and PDGF (platelet-derived growth factor) along with physiological cyclic strain on SMC responses. Physiological cyclic strain (10% strain) significantly reduced SMC proliferation compared to static controls while addition of growth factors bFGF, TGF-β or PDGF-AB had a positive influence on SMC growth compared to strain alone. Microarray analysis of SMCs exposed to these growth factors and cyclic strain showed that several bioactive genes (vascular endothelial growth factor, epidermal growth factor receptor, etc.) were altered upon exposure. Further work involving biochemical and pathological cyclic strain stimulation will help us better understand the role of cyclic strain and growth factors in vascular functions and development of vascular disorders.

Cyclic stretch, reactive oxygen species, and vascular remodeling

Blood vessels respond to changes in mechanical load from circulating blood in the form of shear stress and mechanical strain as the result of heart propulsions by changes in intracellular signaling leading to changes in vascular tone, production of vasoactive molecules, and changes in vascular permeability, gene regulation, and vascular remodeling. In addition to hemodynamic forces, microvasculature in the lung is also exposed to stretch resulting from respiratory cycles during autonomous breathing or mechanical ventilation. Among various cell signaling pathways induced by mechanical forces and reported to date, a role of reactive oxygen species (ROS) produced by vascular cells receives increasing attention. ROS play an essential role in signal transduction and physiologic regulation of vascular function. However, in the settings of chronic hypertension, inflammation, or acute injury, ROS may trigger signaling events that further exacerbate smooth muscle hypercontractility and vascular remodeling associated with hypertension and endothelial barrier dysfunction associated with acute lung injury and pulmonary edema. These conditions are also characterized by altered patterns of mechanical stimulation experienced by vasculature. This review will discuss signaling pathways regulated by ROS and mechanical stretch in the pulmonary and systemic vasculature and will summarize functional interactions between cyclic stretch- and ROS-induced signaling in mechanochemical regulation of vascular structure and function.

Biomechanical stress induces novel arterial intima-enriched genes: implications for vascular adaptation to stress

BACKGROUND

The arterial vasculature is subjected to considerably greater biomechanical stress than the venous circulation. This is reflected in the difference in morphology between large arteries and veins, however little is known about the molecular differences that arise as a consequence of biomechanical stress. Previously, we identified a group of arterial intima-enriched (AIE) genes: sciellin, periplakin, SPRR3, envoplakin, galectin 7, and plakoglobin that are functionally related in that they contribute to the stress properties of stratified epithelium. We sought to test our hypothesis that these genes were regulated by biomechanical stress in vascular smooth muscle cells (VSMCs).

METHODS

Immunofluorescence was employed to determine the expression of the AIE genes in saphenous vein coronary artery bypass grafts. Furthermore, we used a model of cyclic stress to determine if the AIE genes were regulated by biomechanical stress in VSMCs in vitro.

RESULTS

Sciellin and periplakin were upregulated in saphenous vein coronary artery bypass grafts after arterialization, but were absent in non-arterialized saphenous veins. Sciellin, SPRR3, and periplakin transcripts were all upregulated (4.67-, 4.95-, 2.77-fold, respectively) by prolonged exposure to cyclic strain (24-72 h), but not at earlier time points.

CONCLUSIONS

These findings suggest a novel role for several human AIE genes in the VSMC response to arterialization and extended cyclic strain.

SUMMARY

Biomechanical stress has long been implicated in vascular pathologies. We report the novel finding of a group of genes, previously studied in stratified epithelium, that were regulated by prolonged cyclic stress in vascular smooth muscle cells. This may have important implications to vascular disease.

Mechanical stress activates proinflammatory cytokines and antioxidant defense enzymes in human dental pulp cells

This study was conducted to investigate the effects of mechanical stress, particularly cyclic strain, on proinflammatory cytokines as well as antioxidant properties and their interactions with cellular defense systems in human dental pulp (HDP) cells. Exposure of HDP cells to mechanical strain induced inflammatory cytokines such as interleukin-1 beta, tumor necrosis factor-alpha, and interleukin-6, as well as antioxidant genes such as heme oxygenase-1, superoxide dismutases, reduced nicotinamide adenine dinucleotide phosphate quinone oxidoreductase-1, and glutathione peroxidases. In addition, treatment with N-acetylcysteine, indomethacin, and heme oxygenase-1 inhibitors blocked reactive oxygen species production, antioxidant response element (ARE) gene expression, and Nrf2 accumulation that occurred in response to mechanical stress. These data demonstrate that mechanical strain activates inflammatory cytokines and oxidative stress, which then act in concert to induce the Nrf2-/ARE-mediated antioxidant enzymes. Therefore, we suggest that the activation of a compensatory adaptation or defense antioxidant system might represent a novel mechanism for protecting HDP cells against mechanical stress.

Effects of cyclic strain on endothelial cell apoptosis and tubulogenesis are dependent on ROS production via NAD(P)H subunit p22phox

OBJECTIVE

Vascular endothelial cells (ECs) are constantly exposed to blood flow associated forces such as cyclic strain due to blood pressure, which affects ECs survival and angiogenesis by producing ROS via NAD(P)H oxidase. NAD(P)H oxidase subunit p22phox is reported to be related to the development of atherosclerosis and increased levels of p22phox mRNA are correlated to ECs proliferation. However, the importance and signaling mechanism of p22phox on ECs survival and angiogenesis under cyclic strain are unclear.

METHODS

5%-20% cyclic strain were applied by the Flexercell system to simulate in vivo environment of human ECs; the effect of p22phox on mechanical ECs survival mechanism and tubulogenesis was determined by western blot and 3-D tissue culture by knocking down p22phox expression via shRNA plasmid.

RESULTS

Knockdown of p22phox induced expression of cleaved caspase-3 and decreased cell viability ratio (CVR). 5% strain increased and 20% strain decreased CVR of shp22phox cells. There were complex biphasic effects of cyclic strain on ECs survival signaling. 5% strain continuously increased Akt phosphorylation; 20% strain increased after 10min stimulation and decreased Akt phosphorylation lately. 5% strain increased and 20% strain decreased eNOS phosphorylation. Knockdown of p22phox decreased Akt and eNOS phosphorylation with or without cyclic strain. ROS production was increasingly stimulated progressively by strain via the p22phox pathway. 5% strain increased and 20% strain decreased total NO production and vascular tubulogenesis via p22phox pathway.

CONCLUSION

ROS production is pivotal to responses to physiological or pathological strain. Physiological strain increases but pathological strain decreases ECs survival and tubulogenesis, and these effects occur via the NAD(P)H subunit p22phox pathway.

Inflammatory and transcriptional roles of poly (ADP-ribose) polymerase in ventilator-induced lung injury

Introduction

Poly (ADP-ribose) polymerase (PARP) participates in inflammation by cellular necrosis and the nuclear factor-kappa-B (NF-κB)-dependent transcription. The purpose of this study was to examine the roles of PARP in ventilator-induced lung injury (VILI) in normal mice lung.

Methods

Male C57BL/6 mice were divided into four groups: sham tracheostomized (sham), lung-protective ventilation (LPV), VILI, and VILI with PARP inhibitor PJ34 pretreatment (PJ34+VILI) groups. Mechanical ventilation (MV) settings were peak inspiratory pressure (PIP) 15 cm H₂O + positive end-expiratory pressure (PEEP) 3 cm H₂O + 90 breaths per minute for the LPV group and PIP 40 cm H₂O + PEEP 0 cm H₂O + 90 breaths per minute for the VILI and PJ34+VILI groups. After 2 hours of MV, acute lung injury (ALI) score, wet-to-dry (W/D) weight ratio, PARP activity, and dynamic compliance (C_D) were recorded. Tumor necrosis factor-alpha (TNF-α), interleukin-6 (IL-6), myeloperoxidase (MPO) activity, and nitrite/nitrate (NO_X) in the bronchoalveolar lavage fluid and NF-κB DNA-binding activity in tissue homogenates were measured.

Results

The VILI group showed higher ALI score, W/D weight ratio, MPO activity, NO_X, and concentrations of TNF-α and IL-6 along with lower C_D than the sham and LPV groups (P < 0.05). In the PJ34+VILI group, PJ34 pretreatment improved all histopathologic ALI, inflammatory profiles, and pulmonary dynamics (P < 0.05). NF-κB activity was increased in the VILI group as compared with the sham and LPV groups (P < 0.05) and was decreased in the PJ34+VILI group as compared with the VILI group (P = 0.009). Changes in all parameters were closely correlated with the PARP activity (P < 0.05).

Conclusion

Overactivation of PARP plays an important role in the inflammatory and transcriptional pathogenesis of VILI, and PARP inhibition has potentially beneficial effects on the prevention and treatment of VILI.

Inhibition of NADPH oxidase-related oxidative stress-triggered signaling by honokiol suppresses high glucose-induced human endothelial cell apoptosis

Angiopathy is a major complication of diabetes. Abnormally high blood glucose is a crucial risk factor for endothelial cell damage. Nuclear factor-kappaB (NF-kappaB) has been demonstrated as a mediated signaling in hyperglycemia or oxidative stress-triggered apoptosis of endothelial cells. Here we explored the efficacy of honokiol, a small molecular weight natural product, on NADPH oxidase-related oxidative stress-mediated NF-kappaB-regulated signaling and apoptosis in human umbilical vein endothelial cells (HUVECs) under hyperglycemic conditions. The methods of morphological Hoechst staining and annexin V/propidium iodide staining were used to detect apoptosis. Submicromolar concentrations of honokiol suppressed the increases of NADPH oxidase activity, Rac-1 phosphorylation, p22(phox) protein expression, and reactive oxygen species production in high glucose (HG)-stimulated HUVECs. The degradation of IkappaBalpha and increase of NF-kappaB activity were inhibited by honokiol in HG-treated HUVECs. Moreover, honokiol (0.125-1 microM) also suppressed HG-induced cyclooxygenase (COX)-2 upregulation and prostaglandin E(2) production in HUVECs. Honokiol could reduce increased caspase-3 activity and the subsequent apoptosis and cell death triggered by HG. These results imply that inhibition of NADPH oxidase-related oxidative stress by honokiol suppresses the HG-induced NF-kappaB-regulated COX-2 upregulation, apoptosis, and cell death in HUVECs, which has the potential to be developed as a therapeutic agent to prevent hyperglycemia-induced endothelial damage.

Stretch-induced activation of AMP kinase in the lung requires dystroglycan

Lung cells are exposed to cyclic stretch during normal respiration and during positive pressure mechanical ventilation administered to support gas exchange. Dystroglycan is a ubiquitously expressed matrix receptor that is required for normal basement membrane formation during embryogenesis and for maintaining the function of skeletal muscle myocytes and neurons where it links cells to matrix. We previously reported that equibiaxial stretch of primary alveolar epithelial cells activated the MAP kinase pathway ERK1/2 through a mechanism that required an interaction between dystroglycan and matrix. We determined whether this mechanism of mechanotransduction activates other signaling cascades in lung epithelium. Exposure of rat epithelial alveolar type II cells (AEC) to cyclic mechanical stretch resulted in activation of 5' AMP-activated protein kinase (AMPK). This response was not affected by pretreatment of AEC with the ERK inhibitor PD98059 but was inhibited by knockdown in dystroglycan expression. Moreover, production of reactive oxygen species was enhanced in mechanically stimulated AEC in which dystroglycan was knocked down. This enhancement was reversed by treatment of AEC with an AMPK activator. Activation of AMPK was also observed in lung homogenates from mice after 15 minutes of noninjurious mechanical ventilation. Furthermore, knockdown of dystroglycan in the lungs of mice using an adenovirus encoding a dystroglycan shRNA prevented the stretch-induced activation of AMPK. These results suggest that exposure to cyclic stretch activates the metabolic sensing pathway AMPK in the lung epithelium and supports a novel role for dystroglycan in this mechanotransduction.

Renovascular hypertension by two-kidney one-clip enhances endothelial progenitor cell mobilization in a p47phox-dependent manner

BACKGROUND

Enhanced mechanical forces, e.g. in arterial hypertension, stimulate the formation of reactive oxygen species (ROS) by the NAD(P)H oxidase. Since bone marrow derived endothelial progenitor cells (EPCs) contribute to vascular remodeling and repair, we investigated whether renovascular hypertension stimulates EPC mobilization in a NAD(P)H oxidase-dependent manner.

METHODS

Renovascular hypertension was induced by two-kidney one-clip (2K1C) in C57BL/6 (WT) and in mice lacking the p47phox subunit of the NAD(P)H oxidase (p47phox-/-).

RESULTS

In WT, 2K1C increased blood pressure levels by 32.4 +/- 4 mmHg, which was associated with a four-fold increase in circulating EPCs (Sca-1+;Flk-1+). In p47phox-/- mice, the increase in blood pressure was significantly reduced (15.1 +/- 1.8 mmHg, P < 0.05) and not associated with increased EPCs. Inhibitors of the renin-angiotensin system (RAS) and nonspecific vasodilators normalized blood pressure and inhibited EPC mobilization in WT mice after 2K1C. In addition, p47phox deficiency and pharmacological ROS blockage abrogated 2K1C-induced blood pressure elevation and EPC mobilization. Stromal cell derived factor (SDF)-1 and matrix metalloproteinase (MMP)-9 activity in the bone marrow, required for EPC mobilization, were modulated in WT mice after 2K1C. In contrast, no alterations in SDF-1 and MMP-9 were observed in p47phox-/- mice. Moreover, enhanced migration of Lin- bone marrow mononuclear cells was observed when stimulated with plasma from 2K1C WT mice but not when stimulated with plasma from 2K1C p47phox-/- mice.

CONCLUSION

Enhanced mechanical stretch in renovascular hypertension induces EPC mobilization in a p47phox-dependent manner, involving bone marrow SDF-1 and MMP-9 which may contribute to compensatory vascular adaptation in renovascular hypertension.

Cellular stretch increases superoxide production in the thick ascending limb

Superoxide (O(2)(-)) is an important regulator of kidney function. We have recently shown that luminal flow stimulates O(2)(-) production in the thick ascending limb (TAL), attributable in part to mechanical factors. Stretch, pressure and shear stress all change when flow increases in the TAL. We hypothesized that stretch rather than shear stress or pressure per se stimulates O(2)(-) production by TALs. We measured O(2)(-) production in isolated perfused rat TALs using fluorescence microscopy and dihydroethidium. Tubules were perfused with a Na-free solution to eliminate the confounding effect of Na transport. Flow induced an increase in O(2)(-) production from 29+/-4 to 90+/-8 AU/s (P<0.002; n=5). The response to flow is rapidly reversible. O(2)(-) production by TALs perfused at 10 nL/min decreased from 113+/-6 to 25+/-10 AU/s (P<0.003; n=4) 15 minutes after flow was stopped. Increasing pressure and stretch in the absence of shear stress caused a significant increase in O(2)(-) production (40+/-6 to 118+/-17 AU/s; P<0.02; n=5). In contrast, eliminating shear stress had no effect (107+/-9 versus 108+/-10 AU/s; n=5). Increasing stretch by 27+/-2% in the presence of flow while reducing pressure stimulated O(2)(-) production from 66+/-7 to 84+/-9 AU/s (29+/-8%; P<0.02; n=5). Tempol inhibited this increase (n=5). We conclude that increasing stretch rather than pressure or shear stress accounts for the mechanical aspect of flow-induced O(2)(-) production in the TAL. Stretch of the TAL during hypertension, diabetes, and salt loading may contribute to renal damage.

Redox imbalance and ventilator-induced lung injury

Mechanical ventilation (MV) is an indispensable therapy in the care of critically ill patients with acute lung injury and the acute respiratory distress syndrome; however, it is also known to further lung injury in certain conditions of mechanical stress, leading to ventilator-induced lung injury (VILI). The mechanisms by which conventional MV exacerbates lung injury and inflammation are of considerable clinical significance. Redox imbalance has been postulated, among other mechanisms, to enhance/perpetuate susceptibility to VILI. A better understanding of these pathologic mechanisms will help not only in alleviating the side effects of mechanical forces but also in the development of new therapeutic strategies. Here, we review the relevance of oxidative stress in VILI from human studies as well as cellular and mouse models of mechanical stress. Potential therapeutic avenues for the treatment of VILI with exogenous administration of antioxidants also are discussed.

Disruption of skeletal myocytes initiates superoxide release: contribution of NADPH oxidase

Generation of reactive oxygen species (ROS) as an early local reaction to muscle crush injury has frequently been predicted. However, although it is known that severe inflammatory reactions occurring after major muscle trauma originate mainly from early local incidents within the injured tissue, no detailed studies exist on the local generation of ROS in response to myocyte destruction thus far. Therefore, in this study, ROS formation after lethal mechanical damage was examined using a model of scraping injury to cultured C2C12 skeletal myocytes and superoxide detection by lucigenin chemiluminescence, nitrotetrazolium blue chloride reduction, or electron spin resonance spectroscopy. Mechanical rupture of myocytes resulted in an immediate release of superoxide from the damaged cells that could be substantially blocked by the superoxide scavengers superoxide dismutase (51%), tiron (95%), and MAMA/NO (93%) and by hypoxia (83% inhibition). Superoxide generation was primarily confined to the myocytes' membrane fraction and 7- to 8-fold enhanced by the addition of NADH or NADPH. The NADPH-enhanced superoxide generation could largely be diminished by the NAD(P)H oxidase inhibitors diphenyleneiodonium and apocynin in cell lysates (97% and 35% inhibition, respectively) and in isolated membrane fractions (61% and 63% inhibition). We thus conclude that immediately after myocyte damage, large amounts of superoxide are formed that predominantly originate from membrane-bound electron-transferring enzymes, especially NAD(P)H oxidase. This suggests a decisive role of ROS in the pathogenesis of tissue trauma, with superoxide being an initiator of the signaling mechanism from injured myocytes to the surrounding tissue and, potentially, to the whole body.

''Iatrogenic Gilbert syndrome''--a strategy for reducing vascular and cancer risk by increasing plasma unconjugated bilirubin

The catabolism of heme, generating biliverdin, carbon monoxide, and free iron, is mediated by heme oxygenase (HO). One form of this of this enzyme, heme oxygenase-1, is inducible by numerous agents which promote oxidative stress, and is now known to provide important antioxidant protection, as demonstrated in many rodent models of free radical-mediated pathogenesis, and suggested by epidemiology observing favorable health outcomes in individuals carrying high-expression alleles of the HO-1 gene. The antioxidant impact of HO-1 appears to be mediated by bilirubin, generated rapidly from biliverdin by ubiquitously expressed biliverdin reductase. Bilirubin efficiently scavenges a wide range of physiological oxidants by electron donation. In the process, it is often reconverted to biliverdin, but biliverdin reductase quickly regenerates bilirubin, thereby greatly boosting its antioxidant potential. There is also suggestive evidence that bilirubin inhibits the activity or activation of NADPH oxidase. Increased serum bilirubin is associated with reduced risk for atherogenic disease in epidemiological studies, and more limited data show an inverse correlation between serum bilirubin and cancer risk. Gilbert syndrome, a genetic variant characterized by moderate hyperbilirubinemia attributable to reduced hepatic expression of the UDP-glucuronosyltransferase which conjugates bilirubin, has been associated with a greatly reduced risk for ischemic heart disease and hypertension in a recent study. Feasible strategies for boosting serum bilirubin levels may include administration of HO-1 inducers, supplementation with bilirubin or biliverdin, and administration of drugs which decrease the efficiency of hepatic bilirubin conjugation. The well-tolerated uricosuric drug probenecid achieves non-competitive inhibition of hepatic glucuronidation reactions by inhibiting the transport of UDP-glucuronic acid into endoplasmic reticulum; probenecid therapy is included in the differential diagnosis of hyperbilirubinemia, and presumably could be used to induce an ''iatrogenic Gilbert syndrome''. Other drugs, such as rifampin, can raise serum bilirubin through competitive inhibition of hepatocyte bilirubin uptake--although unfortunately rifampin is not as safe as probenecid. Measures which can safely achieve moderate serum elevations of bilirubin may prove to have value in the prevention and/or treatment of a wide range of disorders in which oxidants play a prominent pathogenic role, including many vascular diseases, cancer, and inflammatory syndromes. Phycobilins, algal biliverdin metabolites that are good substrates for biliverdin reductase, may prove to have clinical antioxidant potential comparable to that of bilirubin.

Flow increases superoxide production by NADPH oxidase via activation of Na-K-2Cl cotransport and mechanical stress in thick ascending limbs

Superoxide (O2−) regulates renal function and is implicated in hypertension. O2−production increases in response to increased ion delivery in thick ascending limbs (TALs) and macula densa and mechanical strain in other cell types. Tubular flow in the kidney acutely varies causing changes in ion delivery and mechanical stress. We hypothesized that increasing luminal flow stimulates O2−production by NADPH oxidase in TALs via activation of Na-K-2Cl cotransport. We measured intracellular O2−in isolated rat TALs using dihydroethidium in the presence and absence of luminal flow and inhibitors of NADPH oxidase, Na-K-2Cl cotransport, and Na/H exchange. In the absence of flow, the rate of O2−production was 5.8 ± 1.4 AU/s. After flow was initiated, it increased to 29.7 ± 4.3 AU/s ( P < 0.001). O2−production was linearly related to flow. Tempol alone and apocynin alone blocked the flow-induced increase in O2−production (3.5 ± 1.7 vs. 4.5 ± 2.8 AU/s and 8.2 ± 2.1 vs. 10.6 ± 2.8 AU/s, respectively). Furosemide decreased flow-induced O2−production by 55% (37.3 ± 5.2 to 16.8 ± 2.8 AU/s; P < 0.002); however, dimethylamiloride had no effect. Finally, we examined whether changes in mechanical forces are involved in flow-induced O2−production by using a Na-free solution to perfuse TALs. In the absence of NaCl, luminal flow enhanced O2−production (1.5 ± 0.5 to 13.5 ± 1.1 AU/s; P < 0.001), ∼50% less stimulation than when flow was increased in the presence of luminal NaCl. We conclude that flow stimulates O2−production in TALs via activation of NADPH oxidase and that NaCl absorption due to Na-K-2Cl cotransport and flow-associated mechanical factors contribute equally to this process.

Critical role of the NAD(P)H oxidase subunit p47phox for left ventricular remodeling/dysfunction and survival after myocardial infarction

Accumulating evidence suggests a critical role of increased reactive oxygen species production for left ventricular (LV) remodeling and dysfunction after myocardial infarction (MI). An increased myocardial activity of the NAD(P)H oxidase, a major oxidant enzyme system, has been observed in human heart failure; however, the role of the NAD(P)H oxidase for LV remodeling and dysfunction after MI remains to be determined. MI was induced in wild-type (WT) mice (n=46) and mice lacking the cytosolic NAD(P)H oxidase component p47(phox) (p47(phox)-/- mice) (n=32). Infarct size was similar among the groups. NAD(P)H oxidase activity was markedly increased in remote LV myocardium of WT mice after MI as compared with sham-operated mice (83+/-8 versus 16.7+/-3.5 nmol of O(2)(-) x microg(-1) x min(-1); P<0.01) but not in p47(phox)-/- mice after MI (13.5+/-3.6 versus 15.5+/-3.5 nmol of O(2)(-) x microg(-1) x min(-1)), as assessed by electron-spin resonance spectroscopy using the spin probe CP-H. Furthermore, increased myocardial xanthine oxidase activity was observed in WT, but not in p47(phox)-/- mice after MI, suggesting NAD(P)H oxidase-dependent xanthine oxidase activation. Myocardial reactive oxygen species production was increased in WT mice, but not in p47(phox)-/- mice, after MI. LV cavity dilatation and dysfunction 4 weeks after MI were markedly attenuated in p47(phox)-/- mice as compared with WT mice, as assessed by echocardiography (LV end-diastolic diameter: 4.5+/-0.2 versus 6.3+/-0.3 mm, P<0.01; LV ejection fraction, 35.8+/-2.5 versus 22.6+/-4.4%, P<0.05). Furthermore, cardiomyocyte hypertrophy, apoptosis, and interstitial fibrosis were substantially reduced in p47(phox)-/- mice as compared with WT mice. Importantly, the survival rate was markedly higher in p47(phox)-/- mice as compared with WT mice after MI (72% versus 48%; P<0.05). These results suggest a pivotal role of NAD(P)H oxidase activation and its subunit p47(phox) for LV remodeling/dysfunction and survival after MI. The NAD(P)H oxidase system represents therefore a potential novel therapeutic target to prevent cardiac failure after MI.

Cyclic strain and motion control produce opposite oxidative responses in two human endothelial cell types

The phenotype of endothelial cells (ECs) is specific to the vascular bed from which they originate. To examine how mechanical forces alter the phenotype of different ECs, we compared the effects of cyclic strain and motion control on reactive oxygen species (ROS) production and metabolism and cell adhesion molecule expression in human umbilical vein endothelial cells (HUVEC) vs. human aortic endothelial cells (HAEC). HUVEC and HAEC were subjected to cyclic strain (10% or 20%, 1 Hz), to a motion control that simulated fluid agitation over the cells without strain, or to static conditions for 24 h. We measured H(2)O(2) production with dichlorodihydrofluorescein acetate and superoxide with dihydroethidium fluorescence changes; superoxide dismutase (SOD), catalase, and glutathione peroxidase (GPx) activities spectrophotometrically; and vascular cell adhesion molecule (VCAM)-1 and intercellular adhesion molecule (ICAM)-1 protein expression with Western blot analyses. HUVEC under cyclic strain showed 1) higher intracellular H(2)O(2) levels, 2) increased SOD, catalase, and GPx activities, and 3) greater VCAM-1 and ICAM-1 protein expression, compared with motion control or static conditions. However, in HAEC, motion control induced higher levels of ROS, enzyme activities associated with ROS defense, and VCAM-1 and ICAM-1 expression than cyclic strain. The opposite responses obtained with these two human EC types may reflect their vessels of origin, in that HAEC are subjected to higher cyclic strain deformations in vivo than HUVEC.

Prostacyclin in sepsis: A systematic review

According to current literature, infective processes greatly modify both vascular hemodynamics and anti-oxidant properties of affected tissues, causing a change in homeostasis that regulates the correct functioning of all cells responsible for the physiological and metabolic balance of various organs. As a consequence, the response to the infection that has caused the change is also likely to be weaker and, in the case of septic shock, ineffective. In this review, we will take into consideration these mechanisms and then focus on a group of vasodilator drugs (prostacyclin and its analogs) which, though have been used for over 20 years mainly to treat obstructive vascular diseases, have such hemodynamic and anti-inflammatory properties which prevent homeostatic changes. It is obvious that prostacyclin does not definitively have anti-infective characteristics; however, in association with anti-infective drugs (antibiotics, etc.), the effectiveness of the latter appears improved, at least in some circumstances. Similarly, the fact that prostacyclin and its analogs have a cytoprotective effect on the liver and reduce the ischemia-reperfusion damage following liver transplant is not a novelty and evidence that they improve hepatic hemodynamics suggests their use in those pathologies characterized by possible reduced perfusion or ascertained ischemia of the liver.

Cyclic strain-mediated matrix metalloproteinase regulation within the vascular endothelium: a force to be reckoned with

The vascular endothelium is a dynamic cellular interface between the vessel wall and the bloodstream, where it regulates the physiological effects of humoral and biomechanical stimuli on vessel tone and remodeling. With respect to the latter hemodynamic stimulus, the endothelium is chronically exposed to mechanical forces in the form of cyclic circumferential strain, resulting from the pulsatile nature of blood flow, and shear stress. Both forces can profoundly modulate endothelial cell (EC) metabolism and function and, under normal physiological conditions, impart an atheroprotective effect that disfavors pathological remodeling of the vessel wall. Moreover, disruption of normal hemodynamic loading can be either causative of or contributory to vascular diseases such as atherosclerosis. EC-matrix interactions are a critical determinant of how the vascular endothelium responds to these forces and unquestionably utilizes matrix metalloproteinases (MMPs), enzymes capable of degrading basement membrane and interstitial matrix molecules, to facilitate force-mediated changes in vascular cell fate. In view of the growing importance of blood flow patterns and mechanotransduction to vascular health and pathophysiology, and considering the potential value of MMPs as therapeutic targets, a timely review of our collective understanding of MMP mechanoregulation and its impact on the vascular endothelium is warranted. More specifically, this review primarily summarizes our current knowledge of how cyclic strain regulates MMP expression and activation within the vascular endothelium and subsequently endeavors to address the direct and indirect consequences of this on vascular EC fate. Possible relevance of these phenomena to vascular endothelial dysfunction and pathological remodeling are also addressed.

Nitric oxide and atherosclerosis: an update

Nitric oxide (NO) is a molecule that has gained recognition as a crucial modulator of vascular disease. NO has a number of intracellular effects that lead to vasorelaxation, endothelial regeneration, inhibition of leukocyte chemotaxis, and platelet adhesion. Endothelium damage induced by atherosclerosis leads to the reduction in bioactivity of endothelial NO synthase (eNOS) with subsequent impaired release of NO together with a local enhanced degradation of NO by increased generation of reactive oxygen species with subsequent cascade of oxidation-sensitive mechanisms in the arterial wall. Many commonly used vasculoprotective agents have their therapeutic actions through the production of NO. L-Arginine, the precursor of NO, has demonstrated beneficial effects in atherosclerosis and disturbed shear stress. Finally, eNOS gene polymorphism might be an additional risk factor that may contribute to predict cardiovascular events. However, further studies are needed to understand the possible clinical implications of these correlations.

Energy deficiency in the failing heart: linking increased reactive oxygen species and disruption of oxidative phosphorylation rate

Heart failure is a complex syndrome of numerous dysfunctional components which converge to cause chronic progressive failure of ventricular contractile function and maintenance of cardiac output demand. The aim of this brief review is to highlight some of the mounting evidence indicating that augmented superoxide, related reactive oxygen species and other free radicals contribute to the oxidative stress evident during the progression of heart failure. While much of the source of increased reactive oxygen species is mitochondrial, there are other intracellular sources, which together are highly reactive with functional and structural cellular lipids and proteins. Bioenergetic defects limiting ATP synthesis in the failing myocardium relate not only to post-translational modification of electron transport respiratory chain proteins but also to perturbation of Krebs Cycle enzyme-dependent synthesis of NADH. Accumulation of pathological levels of lipid peroxides relate to dysfunction in the intrinsic capacity to clear and renew dysfunctional proteins. This review also features key limitations of human heart failure studies and potential clinical therapies that target the elevated oxidative stress that is a hallmark of human heart failure.

Molecular mechanisms of the vascular responses to haemodynamic forces

Blood vessels are permanently subjected to mechanical forces in the form of stretch, encompassing cyclic mechanical strain due to the pulsatile nature of blood flow and shear stress. Significant variations in mechanical forces, of physiological or physiopathological nature, occur in vivo. These are accompanied by phenotypical modulation of smooth muscle cells and endothelial cells, producing structural modifications of the arterial wall. In all the cases, vascular remodelling can be allotted to a modification of the tensional strain or shear, and underlie a trend to reestablish baseline mechanical conditions. Vascular cells are equipped with numerous receptors that allow them to detect and respond to the mechanical forces generated by pressure and shear stress. The cytoskeleton and other structural components have an established role in mechanotransduction, being able to transmit and modulate tension within the cell via focal adhesion sites, integrins, cellular junctions and the extracellular matrix. Mechanical forces also initiate complex signal transduction cascades, including nuclear factor-kappaB and mitogen-activated protein kinase pathways, leading to functional changes within the cell.

NADPH oxidase-mediated oxidative stress: genetic studies of the p22(phox) gene in hypertension

Increased vascular production of reactive oxygen species, especially superoxide anion, significantly contributes to the oxidative stress associated with hypertension. An enhanced superoxide production causes an increased inactivation of nitric oxide that diminishes nitric oxide bioavailability, thus contributing to endothelial dysfunction and hypertrophy of vascular cells. It has been shown that NADPH oxidases play a major role as the most important sources of superoxide anion in phagocytic and vascular cells. Several experimental observations have described an enhanced superoxide generation as a result of NADPH oxidase activation in hypertension. Although these enzymes respond to stimuli such as vasoactive factors, growth factors, and cytokines, recent data suggest a significant role of the genetic background in the modulation of the expression of its different components. Several polymorphisms have been identified in the promoter and in the coding region of CYBA, the gene that encodes the essential subunit of the NADPH oxidase p22phox, some of which seem to influence significantly the activity of these enzymes in the context of cardiovascular diseases. Among CYBA polymorphisms, genetic investigations have provided a novel marker, the -930(A/G) polymorphism, which determines the genetic susceptibility of hypertensive patients to oxidative stress.

INHIBITION OF CYCLIC STRAIN-INDUCED ENDOTHELIN-1 SECRETION BY TETRAMETHYLPYRAZINE

1. Chuanxiong is a Chinese herb that has been used widely in China to treat vascular disorders. 2,3,5,6-Tetramethylpyrazine (TMP) is one of the major components purified from chuanxiong. Many studies have demonstrated that TMP is effective in the treatment of cardiovascular diseases. However, the mechanism of action by which TMP exerts relaxation in vascular vessels remains unclear. 2. Endothelin (ET)-1 is a potent vasopressor synthesised by endothelial cells both in culture and in vivo. The aims of the present study were to test the hypothesis that TMP may alter strain-induced ET-1 secretion and to identify the putative underlying signalling pathways in endothelial cells. 3. We showed that TMP inhibits strain-induced ET-1 secretion. 2,3,5,6-Tetramethylpyrazine also inhibits the strain-induced formation of reactive oxygen species (ROS) and phosphorylation of extracellular signal-regulated kinases (ERK) 1/2. Furthermore, pretreating cells with TMP or the anti-oxidant N-acetyl-cysteine decreased strain-induced increases in ET-1 secretion and ERK1/2 phosphorylation. Using a reporter gene assay, TMP and N-acetyl-cysteine were demonstrated to also attenuate the strain-induced activity of the activator protein-1 reporter. 4. In summary, we have demonstrated, for the first time, that TMP inhibits strain-induced ET-1 gene expression, in part by interfering with the ERK1/2 pathway via attenuation of ROS formation. Thus, the present study provides important new insights into the molecular pathways that may contribute to the proposed beneficial effects of TMP in the vascular system.