Wolfgang Domej

Oxidative stress and free radicals in COPD – implications and relevance for treatment

Oxidative stress occurs when free radicals and other reactive species overwhelm the availability of antioxidants. Reactive oxygen species (ROS), reactive nitrogen species, and their counterpart antioxidant agents are essential for physiological signaling and host defense, as well as for the evolution and persistence of inflammation. When their normal steady state is disturbed, imbalances between oxidants and antioxidants may provoke pathological reactions causing a range of nonrespiratory and respiratory diseases, particularly chronic obstructive pulmonary disease (COPD). In the respiratory system, ROS may be either exogenous from more or less inhalative gaseous or particulate agents such as air pollutants, cigarette smoke, ambient high-altitude hypoxia, and some occupational dusts, or endogenously generated in the context of defense mechanisms against such infectious pathogens as bacteria, viruses, or fungi. ROS may also damage body tissues depending on the amount and duration of exposure and may further act as triggers for enzymatically generated ROS released from respiratory, immune, and inflammatory cells. This paper focuses on the general relevance of free radicals for the development and progression of both COPD and pulmonary emphysema as well as novel perspectives on therapeutic options. Unfortunately, current treatment options do not suffice to prevent chronic airway inflammation and are not yet able to substantially alter the course of COPD. Effective therapeutic antioxidant measures are urgently needed to control and mitigate local as well as systemic oxygen bursts in COPD and other respiratory diseases. In addition to current therapeutic prospects and aspects of genomic medicine, trending research topics in COPD are presented.

Exercise Increases the Frequency of Circulating Hematopoietic Progenitor Cells, But Reduces Hematopoietic Colony-Forming Capacity

Circulating hematopoietic progenitor cells (CPCs) may be triggered by physical exercise and/or normobaric hypoxia from the bone marrow. The aim of the study was to investigate the influence of physical exercise and normobaric hypoxia on CPC number and functionality in the peripheral blood as well as the involvement of oxidative stress parameters as possibly active agents. Ten healthy male subjects (25.3±4.4 years) underwent a standardized cycle incremental exercise test protocol (40 W+20 W/min) under either normoxic (FiO2 ∼0.21) or hypoxic conditions (FiO2<0.15, equals 3,500 m, 3 h xposure) within a time span of at least 1 week. Blood was drawn from the cubital vein before and 10, 30, 60, and 120 min after exercise. The number of CPCs in the peripheral blood was analyzed by flow cytometry (CD34/CD45-positive cells). The functionality of cells present was addressed by secondary colony-forming unit-granulocyte macrophage (CFU-GM) assays. To determine a possible correlation between the mobilization of CPCs and reactive oxygen species, parameters for oxidative stress such as malondialdehyde (MDA) and myeloperoxidase (MPO) were obtained. Data showed a significant increase of CPC release under normoxic as well as hypoxic conditions after 10 min of recovery (P<0.01). Most interestingly, although CD34+/CD45dim cells increased in number, the proliferative capacity of CPCs decreased significantly 10 min after cessation of exercise (P<0.05). A positive correlation between CPCs and MDA/MPO levels turned out to be significant for both normoxic and hypoxic conditions (P<0.05/P<0.01). Hypoxia did not provoke an additional effect. Although the CPC frequency increased, the functionality of CPCs decreased significantly after exercise, possibly due to the influence of increased oxidative stress levels.

Successful outcome after intravenous gasoline injection.

IntroductionGasoline, ingested intentionally or accidentally, is toxic. The majority of reported cases of gasoline intoxication involve oral ingestion or inhalation. Data are scarce on complications and outcomes following hydrocarbon poisoning by intravenous injection.Case ReportFollowing a suicide attempt by intravenous self-injection of 10 ml of gasoline, a 26-year-old medical student was admitted to the intensive care unit (ICU) with hemoptysis, symptoms of acute respiratory failure, chest pain, and severe abdominal cramps. Gas exchange was severely impaired and a chest x-ray indicated chemical pneumonitis. Initial treatment consisted of mechanical ventilation, supportive hyperventilation, administration of nitrogen oxide (NO), and prednisone. Unfortunately, the patient developed multi-organ dysfunction syndrome (MODS) complicated by life-threatening severe vasoplegia within 24 hours after gasoline injection. High doses of vasopressors along with massive amounts of parenteral fluids were necessary. Despite fluid replacement, renal function worsened and required hemofiltration on 5 sequential days. After 12 days of intensive care management, the patient recovered completely and was discharged to a psychiatric care facility.DiscussionIntravenous gasoline injection causes major injury to the lungs, the organ bearing the first capillary bed encountered. Treatment of gasoline poisoning is symptomatic because no specific antidote is available. Early and aggressive supportive care may be conducive to a favorable outcome with minimal residual pulmonary sequelae.

Oxidative stress caused by acute and chronic exposition to altitude

SummaryIn this article, current views on cellular and molecular biology (biochemical) mechanisms are discussed under the aspect of altitude exposition. The Andean, Tibetan, and Ethiopian patterns of adaptation to high-altitude hypoxia are known (Beal et al., Proc. Natl. Acad. Sci. USA 99: 17215–17218, 2002). The phylogenetic tree of the human species suggests that there are genetic differences in adaptation patterns to chronic hypoxic hypoxia. Five defense mechanisms are well established for lowlanders who are exposed to acute hypoxic hypoxia. Consequences of the cellular decrease in ATP are the formation of hypoxanthine and xanthine, which are the substrates for the massive formation of superoxide anion radicals and hydrogen peroxide via the oxidase activity of the xanthine oxidoreductase reaction. Under severe hypoxia, about 51% of the total inhaled oxygen is used to form superoxide anion radicals in rat liver (Gerber et al., Adv. Exp. Med. Biol. 253B, Plenum Press, New York, pp. 497–504, 1989). The reactivity and selectivity of the superoxide anion radical are modified by specific interactions and electron exchange. It is commonly accepted that the superoxide anion radical in aqueous solutions has a lifetime in the millisecond range. However, electron spin resonance spectroscopy studies in a KO2/H2O/iron ion system revealed for the first time a stabilization of a part of the initially added superoxide anion radicals lasting up to hours at room temperature (Földes-Papp, Gen. Physiol. Biophys. 11: 3–38, 1992). Superoxide anion radicals adsorbed on an oxidic iron hydrate phase in aqueous systems might function as a strong oxidant similar to that species which has been suggested to be a complex between oxygen and different valence states of iron in the initiation of lipid peroxidation by ferrous iron. There were serious doubts about the identity of alkoxy radicals. For the first time, alkoxy radicals were directly demonstrated in solution by electron spin resonance spectroscopy (Földes-Papp et al., Adv. Synth. Catal. 333: 293–301, 1991). The redox status in mammalian cells is mainly determined by the antioxidant glutathione, which is a key player in maintaining the intracellular redox equilibrium and in the metabolic regulation of the cellular defense against oxidative stress. As reactive oxygen species occupy an essential role in membrane damage, the idea of membrane-bound enzymatic defense mechanisms gets a new dimension (Földes-Papp et al., Acta Biol. Med. Ger. 40: 1129–1132, 1981; Földes-Papp and Maretzki, Acta Biol. Med. Ger. 41: 1003–1008, 1982). The steady state between antioxidants and pro-oxidants affects the gene expression via hypoxia-induced transcription activities. The transcription factor hypoxia-inducible factor 1 (HIF-1) is a global regulator of oxygen homeostasis. As discussed in this article, hypoxia or “oxidative stress” is accompanied by appropriate molecular adaptation mechanisms at the enzymatic or epigenetic level (enzymatic and non-enzymatic radical inhibitors, posttranslational modifications) and at the genetic level (transcription, translation).ZusammenfassungIn dieser Originalarbeit werden die derzeit gültigen, aktuellen Sichtweisen der zellulären und molekularbiologischen-biochemischen Mechanismen unter dem Aspekt der Höhenexposition diskutiert. Die Anden-, tibetanischen und äthiopischen Adaptationsmuster an große Höhen sind bekannt (Beal et al., Proc. Natl. Acad. Sci. USA 99: 17215–17218, 2002). Der phylogenetische Stammbaum des Menschen weist auf genetische Unterschiede in den molekularen Adaptationsmustern unter chronisch-hypoxischer Hypoxie hin. Fünf Schutzmechanismen sind bei Tieflandbewohnern, die einer akuten hypoxischen Hypoxie ausgesetzt sind, etabliert. Konsequenzen des zellulären ATP-Abfalls sind die Bildung von Hypoxanthin und Xanthin, die dann die Substrate für die massive Generierung von Superoxidanionen-Radikalen und Wasserstoffperoxid durch die Oxidaseaktivität der Xanthin-Oxidoreduktase sind. Bei schwerer Hypoxie werden ca. 51 % des eingeatmeten Sauerstoffs dazu verwendet, Superoxidanionen-Radikale in der Rattenleber zu bilden (Gerber et al., Adv. Exp. Med. Biol. 253B, Plenum Press, New York, pp. 497–504, 1989). Die Reaktivität und Selektivität des Superoxidanionen-Radikals wird durch spezifische Wechselwirkungen und Elektronenaustausch-Reaktionen modifiziert. Es gilt als allgemein akzeptiert, dass das Superoxidanionen-Radikal in wässrigen Lösungen eine Lebenszeit im Millisekundenbereich hat. Untersuchungen in einem KO2/H2O/Eisenionen-System mittels Elektronen-Spin-Resonanz-Spektroskopie haben jedoch erstmalig gezeigt, dass eine Stabilisierung des initial zugesetzten Superoxidanionen-Radikals (KO2) erfolgt, die bis zu Stunden bei Raumtemperatur anhält (Földes-Papp, Gen. Physiol. Biophys. 11: 3–38, 1992). Superoxidanionen-Radikale, die an eine oxidische Eisenhydratphase in wässrigen Systemen adsorbiert werden, können als starke Oxidantien wirken ähnlich der chemischen Verbindung, die aus einem Komplex zwischen Sauerstoff und Eisenionen unterschiedlicher Valenzen besteht und die die Initiationsreaktion der Lipidperoxidation durch Eisen(II) katalysiert. Es gab ernsthafte Zweifel an der Existenz von Alkoxy-Radikalen im wässrigen Milieu. Zum ersten Mal gelang es, Alkoxy-Radikale in wässriger Lösung direkt mittels Elektronen-Spin-Resonanz-Spektroskopie nachzuweisen (Földes-Papp et al., Adv Synth Catal 333: 293–301, 1991). Das Redoxpotential in Säugetierzellen ist wesentlich durch das Antioxidanz Glutathion bestimmt. Dem Glutathion kommt eine Schlüsselrolle bei der Aufrechterhaltung des intrazellulären Redox-Gleichgewichtes und in der metabolischen Regulation der zellulären Schutzmechanismen gegen oxidativen Stress zu. Da die reaktiven Sauerstoffspezies wesentlich zu den Membranschädigungen beitragen, erhält die ursprüngliche Idee der Membran-gebundenen enzymatischen Schutzmechanismen eine neue Dimension (Földes-Papp et al., Acta Biol. Med. Ger. 40: 1129–1132, 1981; Földes-Papp and Maretzki, Acta Biol. Med. Ger. 41: 1003–1008, 1982). Das biochemische Fließgleichgewicht zwischen Antioxidantien und Pro-Oxidantien hat Auswirkungen auf die Genexpression über Hypoxie-induzierte Transkriptionsaktivitäten. Der Transkriptionsfaktor hypoxia-inducible factor 1 (HIF-1) ist ein globales Regulativ der Sauerstoffhomeostase. Hypoxie oder „oxidativer Stress“ sind begleitet durch entsprechende molekulare Adaptationsmechanismen auf der enzymatischen bzw. epigenetischen Ebene (enzymatische und nicht-enzymatische Radikalinhibitoren, posttranslationale Modifizierungen) und auf der genetischen Ebene (Transkription, Translation).

Exercise-induced norepinephrine decreases circulating hematopoietic stem and progenitor cell colony-forming capacity.

A recent study showed that ergometry increased circulating hematopoietic stem and progenitor cell (CPC) numbers, but reduced hematopoietic colony forming capacity/functionality under normoxia and normobaric hypoxia. Herein we investigated whether an exercise-induced elevated plasma free/bound norepinephrine (NE) concentration could be responsible for directly influencing CPC functionality. Venous blood was taken from ten healthy male subjects (25.3+/−4.4 yrs) before and 4 times after ergometry under normoxia and normobaric hypoxia (FiO2<0.15). The circulating hematopoietic stem and progenitor cell numbers were correlated with free/bound NE, free/bound epinephrine (EPI), cortisol (Co) and interleukin-6 (IL-6). Additionally, the influence of exercise-induced NE and blood lactate (La) on CPC functionality was analyzed in a randomly selected group of subjects (n = 6) in vitro under normoxia by secondary colony-forming unit granulocyte macrophage assays. Concentrations of free NE, EPI, Co and IL-6 were significantly increased post-exercise under normoxia/hypoxia. Ergometry-induced free NE concentrations found in vivo showed a significant impairment of CPC functionality in vitro under normoxia. Thus, ergometry-induced free NE was thought to trigger CPC mobilization 10 minutes post-exercise, but as previously shown impairs CPC proliferative capacity/functionality at the same time. The obtained results suggest that an ergometry-induced free NE concentration has a direct negative effect on CPC functionality. Cortisol may further influence CPC dynamics and functionality.

Impact of Mental and Physical Stress on Blood Pressure and Pulse Pressure under Normobaric versus Hypoxic Conditions

Objective Hypobaric hypoxia, physical and psychosocial stress may influence key cardiovascular parameters including blood pressure (BP) and pulse pressure (PP). We investigated the effects of mild hypobaric hypoxia exposure on BP and PP reactivity to mental and physical stress and to passive elevation by cable car. Methods 36 healthy volunteers participated in a defined test procedure consisting of a period of rest 1, mental stress task (KLT-R), period of rest 2, combined mental (KLT-R) and physical task (bicycle ergometry) and a last period of rest both at Graz, Austria (353 m asl) and at the top station Dachstein (2700 m asl). Beat-to-beat heart rate and BP were analysed both during the test procedures at Graz and at Dachstein and during passive 1000 m elevation by cable car (from 1702 m to 2700 m). Results A significant interaction of kind of stress (mental vs. combined mental and physical) and study location (Graz vs. Dachstein) was found in the systolic BP (p = .007) and PP (p = .002) changes indicating that during the combined mental and physical stress task sBP was significantly higher under hypoxic conditions whereas sBP and PP were similar during mental stress both under normobaric normoxia (Graz) and under hypobaric hypoxia (Dachstein). During the passive ascent in cable car less trivialization (psychological coping strategy) was associated with an increase in PP (p = .004). Conclusion Our data show that combined mental and physical stress causes a significant higher raise in sBP and PP under hypoxic conditions whereas isolated mental stress did not affect sBP and PP under hypoxic conditions. PP-reaction to ascent in healthy subjects is not uniform. BP reactions to ascent that represents an accumulation of physical (mild hypobaric hypoxia) and psychological stressors depend on predetermined psychological traits (stress coping strategies). Thus divergent cardiovascular reactions can be explained by applying the multidimensional aspects of the biopsychosocial concept.