Pulmonary microsomes contain a Ca(2+)-transport system sensitive to oxidative stress

Association between lung function in adults and plasma DDT and DDE levels: results from the Canadian Health Measures Survey

BACKGROUND

Although DDT [1,1,1-trichloro-2,2-bis(4-chlorophenyl)ethane] has been banned in many countries since the 1970s, it may still pose a risk to human respiratory health. In agriculture, DDT exposures have been associated with asthma and chronic bronchitis. However, little is known about the effect of DDT on lung function.

METHODS

We used data on 1,696 participants 20-79 years of age from the Canadian Health Measures Survey (CHMS) and conducted multiple regression analysis to estimate associations between plasma p,p´-DDT/DDE and lung function.

RESULTS

Almost all participants (> 99.0%) had detectable concentrations of plasma p,p´-DDE, but only 10.0% had detectable p,p´-DDT. Participants with detectable p,p´-DDT had significantly lower mean FVC (difference = 311 mL; 95% CI: -492, -130; p = 0.003) and FEV1 (difference = 232 mL; 95% CI: -408, -55; p = 0.015) than those without. A 100-ng/g lipid increase in plasma p,p´-DDE was associated with an 18.8-mL decrease in mean FVC (95% CI: -29, -9) and an 11.8-mL decrease in mean FEV1 (95% CI: -21, -3). Neither exposure was associated with FEV1/FVC ratio or FEF25%-75%.

CONCLUSIONS

DDT exposures, which may have occurred decades ago, were still detectable among Canadians. Plasma DDT and DDE were negatively associated with lung function parameters. Additional research on the potential effects of DDT use on lung function is warranted.

Oxidative Stress - Clinical Diagnostic Significance

Elevated free radical production and/or insufficient antioxidative defense results in cellular oxidant stress responses. Sustained and/or intense oxidative insults can overcome cell defenses resulting in accumulated damage to macromolecules, leading to loss of cell function, membrane damage, and ultimately to cell death. Oxidative stress (OS) can result from conditions including excessive physical stress, exposure to environmental pollution and xenobiotics, and smoking. Oxidative stress, as a pathophysiological mechanism, has been linked to numerous pathologies, poisonings, and the ageing process. Reactive oxygen species and reactive nitrogen species, endogenously or exogenously produced, can readily attack all classes of macromolecules (proteins, DNA, unsaturated fatty acid). The disrupted oxidative-reductive milieu proceeds via lipid peroxidation, altered antioxidative enzyme activities and depletion of non-enzymatic endogenous antioxidants, several of which can de detected in the pre-symptomatic phase of many diseases. Therefore, they could represent markers of altered metabolic and physiological homeostasis. Accordingly, from the point of view of routine clinical-diagnostic practice, it would be valuable to routinely analyze OS status parameters to earlier recognize potential disease states and provide the basis for preventative advance treatment with appropriate medicines.

Protective effects of Munziq and Mushil of abnormal Savda to mitochondrial oxidative damage

Munziq and Mushil of Abnormal Savda are traditional Uighur herbal medicinal products, which could have antioxidant properties protecting mitochondria against oxidative damage. Mitochondria were isolated from rat livers. A FeSO4/VitC hydroxyl radical-generating system was used to induce mitochondrial oxidative damage. Alterations in mitochondrial membrane structure were observed by electron microscopy, and mitochondrial superoxide dismutase (SOD) activity, malondialdehyde (MDA) level and Ca2+-Mg2+-ATPase activity were measured. Muziq or Mushil were added, at concentrations ranging from 10(-5) to 10(-1) g/mL. Mitochondrial membrane structure was damaged after exposure to hydroxyl radical; mitochondrial SOD and Ca2+-Mg2+-ATPase activities decreased (by 80 and 55%, respectively, both P < 0.01), and MDA level increased 4.6-fold (P < 0.01). Munziq and Mushil protected mitochondrial membranes from structural damage. They inhibited the changes in mitochondrial functions in a dose-dependent manner. At the highest concentrations, values were equal to initial normal values. Munziq and Mushil of Abnormal Savda can reduce the oxidative damage induced by hydroxyl radical and protect the mitochondrial membrane structure and its functions.

Oxidative stress increases internal calcium stores and reduces a key mitochondrial enzyme

Fibroblasts from patients with genetic and non-genetic forms of Alzheimer's disease (AD) show many abnormalities including increased bombesin-releasable calcium stores (BRCS), diminished activities of the mitochondrial alpha-ketoglutarate dehydrogenase complex (KGDHC), and an altered ability to handle oxidative stress. The link between genetic mutations (and the unknown primary event in non-genetic forms) and these other cellular abnormalities is unknown. To determine whether oxidative stress could be a convergence point that produces the other AD-related changes, these experiments tested in fibroblasts the effects of H(2)O(2), in the presence or absence of select antioxidants, on BRCS and KGDHC. H(2)O(2) concentrations that elevated carboxy-dichlorofluorescein (c-H(2)DCF)-detectable ROS increased BRCS and decreased KGDHC activity. These changes are in the same direction as those in fibroblasts from AD patients. Acute treatments with the antioxidants Trolox, or DMSO decreased c-H(2)DCF-detectable ROS by about 90%, but exaggerated the H(2)O(2)-induced increases in BRCS by about 4-fold and did not alter the reduction in KGDHC. Chronic pretreatments with Trolox more than doubled the BRCS, tripled KGDHC activities, and reduced the effects of H(2)O(2). Pretreatment with DMSO or N-acetyl cysteine diminished the BRCS and either had no effect, or exaggerated the H(2)O(2)-induced changes in these variables. The results demonstrate that BRCS and KGDHC are more sensitive to H(2)O(2) derived species than c-H(2)DCF, and that oxidized derivatives of the antioxidants exaggerate the actions of H(2)O(2). The findings support the hypothesis that select abnormalities in oxidative processes are a critical part of a cascade that leads to the cellular abnormalities in cells from AD patients.

Cardiac ischemia oxidizes regulatory thiols on ryanodine receptors: captopril acts as a reducing agent to improve Ca2+ uptake by ischemic sarcoplasmic reticulum

We tested the hypothesis that ischemia alters sarcoplasmic reticulum (SR) Ca2+ transport by oxidizing regulatory thiols on ryanodine receptors (RyRs), and that membrane-permeable sulfhydryl-containing angiotensin-converting enzyme (ACE) inhibitors protect against ischemia-induced oxidation and explain in part, the therapeutic actions of captopril. Ca2+ uptake and adenosine triphosphatase (ATPase) activity was measured from SR vesicles isolated from control or ischemic dog and human ventricles and compared with or without sulfhydryl reductants. The rate and amount of Ca2+ uptake was lower for canine ischemic SR compared with control (6.5 +/- 0.2 --> 18.5 +/- 1.1 nmol Ca2+/mg/min and 123.1 +/- 4.7 --> 235.0 +/- 17.3 nmol Ca2+/mg; n = 8 each). Captopril, dithiothreitol (DTT), glutathione (GSH), and L-cysteine increased the rate and amount of Ca2+ uptake by canine and human ischemic SR vesicles by approximately 50%. Reducing agents had no effect on Ca2+- ATPase activity in either canine control or ischemic (approximately 40% less than control) SR. Captopril was as potent as DTT at reversing the oxidation of skeletal and cardiac RyRs induced by reactive disulfides (RDSs) or nitric oxide (NO). In neonatal rat myocytes, RDSs or NO triggered SR Ca2+ release and increased cytosolic Ca2+, an effect reversed by captopril and DTT but not GSH or cysteine. Pretreatment of myocytes with captopril (exposure and then wash) inhibited Ca2+ elevation elicited by RDSs or NO, indicating that captopril is an effective, membrane-permeable intracellular reducing agent. Thus, net SR Ca2+ accumulation is reduced by ischemia in part due to the oxidation of thiols that gate RyRs, an effect reversed by captopril.

Hydrogen peroxide attenuates store-operated calcium entry and enhances calcium extrusion in thyroid FRTL-5 cells

Redox modulation participates in the regulation of intracellular free calcium concentration ([Ca(2+)](i)) in several cell types. In thyroid cells, including FRTL-5 cells, changes in [Ca(2+)](i) regulate several important functions, including the production of H(2)O(2) (hydrogen peroxide). As H(2)O(2) is of crucial importance for the production of thyroid hormones, we investigated the effects of H(2)O(2) on [Ca(2+)](i) in thyroid FRTL-5 cells. H(2)O(2) itself did not modulate basal [Ca(2+)](i). However, H(2)O(2) attenuated store-operated calcium entry evoked by thapsigargin, both in a sodium-containing buffer and in a sodium-free buffer. The effect of H(2)O(2) was abrogated by the reducing agent beta-mercaptoethanol. H(2)O(2) also attenuated the thapsigargin-evoked entry of barium and manganese. The effect of H(2)O(2) was, at least in part, mediated by activation of protein kinase C (PKC), as H(2)O(2) enhanced the binding of [(3)H]phorbol 12,13-dibutyrate. H(2)O(2) also stimulated the translocation of the isoenzyme PKCepsilon from the cytosolic fraction to the particulate fraction. Furthermore, H(2)O(2) did not attenuate store-operated calcium entry in cells treated with staurosporine or calphostin C, or in cells with down-regulated PKC. H(2)O(2) depolarized the membrane potential in bisoxonol-loaded cells and when patch-clamp in the whole-cell mode was used. The depolarization was attenuated in cells with down-regulated PKC. This depolarization, at least in part, explained the H(2)O(2)-evoked inhibition of calcium entry. In addition, H(2)O(2) enhanced the extrusion of calcium from cells stimulated with thapsigargin and this effect was abolished in cells with down-regulated PKC and after treatment of the cells with the reducing agent beta-mercaptoethanol. In conclusion H(2)O(2) attenuates an increase in [Ca(2+)](i). As H(2)O(2) is produced in thyroid cells in a calcium-dependent manner, our results suggest that H(2)O(2) may participate in the regulation of [Ca(2+)](i) in these cells via a negative-feedback mechanism involving activation of PKC.

Ischemia-induced changes in 2'-5'-oligoadenylate synthethase mRNA levels in rat brain: comparison with changes produced by perturbations of endoplasmic reticulum calcium homeostasis in neuronal cell cultures

2'-5' Oligoadenylate synthetase (OAS) expression is induced by interferon or viral infection of cells. To better understand ischemia-induced changes in gene expression and to elucidate the possible underlying mechanisms, changes in OAS mRNA levels were evaluated after 30 min four-vessel occlusion and 2, 4, 8 or 24 h recovery and compared to the temporal profile of changes in mRNA levels induced by a transient depletion of endoplasmic reticulum (ER) calcium stores in primary neuronal cell cultures. OAS mRNA levels dropped during early recovery both in vivo and in vitro. After 6 h recovery from ER calcium pool depletion, OAS mRNA levels increased to about 350% of controls and returned to control levels after 24 h of recovery. After 24 h recovery from ischemia, OAS mRNA levels rose to about 390% of controls in the hippocampus and striatum and to 210% of the control value in the cortex. It is concluded that transient ischemia place cells into an antiviral state, most pronounced in the hippocampus and striatum, and that disturbances of ER calcium homeostasis may contribute to this process.

Sensitivity of the synaptic membrane Na+/Ca2+ exchanger and the expressed NCX1 isoform to reactive oxygen species

Two plasma membrane proteins, the Na+/Ca2+ exchanger (NCX) and the Ca2+-ATPase, are major regulators of free intraneuronal Ca2+ levels as they are responsible for extrusion of Ca2+ from the intracellular to the extracellular medium. Because disruption of cellular Ca2+ regulation plays a role in damage occurring under conditions of oxidative stress, studies were conducted to assess the sensitivity of the NCX to reactive oxygen species (ROS). Exchanger activity in brain synaptic plasma membranes and in transfected CHO-K1 cells was inhibited following brief exposure to the peroxyl radical generating azo initiator 2,2'-azobis(2-amidinopropane)dihydrochloride (AAPH) and to peroxynitrite. Incubation with hydrogen peroxide did not alter NCX activity, even at 800 microM concentration. In CHO-K1 cells transiently transfected with the NCX1 isoform of the exchanger, AAPH treatment decreased the maximal transport capacity (Vmax), whereas the K(act) remained unchanged. Peroxynitrite led to an increase in K(act) with no change in Vmax. Loss of activity following exposure to either AAPH or peroxynitrite was associated with the formation of high molecular weight aggregates of NCX, and AAPH also caused fragmentation of the exchanger protein. These findings suggest that the NCX is sensitive to biologically relevant ROS and could be involved in the loss of Ca2+ homeostasis observed under oxidative stress.

Signal transduction and regulation of lung endothelial cell permeability. Interaction between calcium and cAMP

Pulmonary endothelium forms a semiselective barrier that regulates fluid balance and leukocyte trafficking. During the course of lung inflammation, neurohumoral mediators and oxidants act on endothelial cells to induce intercellular gaps permissive for transudation of proteinaceous fluid from blood into the interstitium. Intracellular signals activated by neurohumoral mediators and oxidants that evoke intercellular gap formation are incompletely understood. Cytosolic Ca2+ concentration ([Ca2+]i) and cAMP are two signals that importantly dictate cell-cell apposition. Although increased [Ca2+]i promotes disruption of the macrovascular endothelial cell barrier, increased cAMP enhances endothelial barrier function. Furthermore, during the course of inflammation, elevated endothelial cell [Ca2+]i decreases cAMP to facilitate intercellular gap formation. Given the significance of both [Ca2+]i and cAMP in mediating cell-cell apposition, this review addresses potential sites of cross talk between these two intracellular signaling pathways. Emerging data also indicate that endothelial cells derived from different vascular sites within the pulmonary circulation exhibit distinct sensitivities to permeability-inducing stimuli; that is, elevated [Ca2+]i promotes macrovascular but not microvascular barrier disruption. Thus this review also considers the roles of [Ca2+]i and cAMP in mediating site-specific alterations in endothelial permeability.

Antioxidant depletion, lipid peroxidation, and impairment of calcium transport induced by air-blast overpressure in rat lungs

Exposure to blast overpressure, or the sudden rise in atmospheric pressure after explosive detonation, results in damage mainly of the gas-filled organs. In addition to the physical damage, in the lung, injury may proceed via a hemorrhage-dependent mechanism initiating oxidative stress and accumulation of lipid peroxidation products. Massive rupture of capillaries and red blood cells, release of hemoglobin, its oxidation to met-hemoglobin and degradation sets the stage for heme-catalyzed oxidations. The authors hypothesized that lipid hydroperoxides interact with met-hemoglobin in the lungs of exposed animals to produce ferryl-hemoglobin, an extremely potent oxidant that induces oxidative damage by depleting antioxidants and initiating peroxidation reactions. Oxidation-induced disturbance of Ca2+ homeostasis facilitates further amplification of the damage. To test this hypothesis, groups of anesthetized rats (6 rats/group) were exposed to blast at 3 peak pressures: low (61.2 kPa), medium (95.2 kPa), high (136 kPa). One group served as an unexposed control. Immediately after exposure, the rats were euthanized and the lungs were analyzed for biochemical parameters. Blast overpressure caused: (1) depletion of total and water-soluble pulmonary antioxidant reserves and individual antioxidants (ascorbate, vitamin E, GSH), (2) accumulation of lipid peroxidation products (conjugated dienes, TBARS), and (3) inhibition of ATP-dependent Ca2+ transport. The magnitude of these changes in the lungs was proportional to the peak blast overpressure. Inhibition of Ca2+ transport strongly correlated with both depletion of antioxidants and enhancement of lipid peroxidation. In model experiments, met-hemoglobin/H2O2 produced damage to Ca2+ transport in the lungs from control animals similar to that observed in the lungs from blast overpressure-exposed animals. Ascorbate, which is known to reduce ferryl-hemoglobin, protected against met-hemoglobin/H2O2-induced damage of Ca2+ transport. If ferryl-hemoglobin is the major reactive oxygen species released by hemorrhage, then its specific reductants (e.g., nitric oxide) along with other antioxidants may be beneficial protectants against pulmonary barotrauma.

Murine pulmonary Ca(2+)-transport system activated by allergic immune response retains sensitivity to oxidative stress

Exaggerated oxygen radical production by airway cells may contribute to increased airway responsiveness and heightened smooth muscle constriction in asthmatic lungs. Smooth muscle cell contractility in the lung is regulated by Ca2+ homeostasis. The contribution of inflammatory cells to these events is unclear. A murine model of allergic pulmonary hypersensitivity was developed to study the role of Ca2+ transport in allergic pulmonary reactions. Sensitization of mice was accomplished by injection with ovalbumin (OA) (1 or 50 micrograms) or OA (1 microgram) plus Al(OH)3. Pulmonary responses were elicited by inhalation provocation challenge with OA aerosol and quantified by the extent of inflammatory cell infiltrate at 24 h. Increased Ca2+ transport was found in microsomes and homogenates of the lung after antigen challenge. Activation of Ca2+ transport was correlated with the severity of the allergic pulmonary response as evidenced from specific antibody production and inflammatory cell infiltrate. The greatest increase in Ca2+ transport was noted in microsomes from mice sensitized with OA plus adjuvant. Ca2+ transport in sensitized, but not in control mice, was responsive to oxidative stress induced by addition of phenol and hydrogen peroxide. Lung homogenates from both groups of animals responded similarly to phenoxyl radical-induced oxidative stress induced by phenol plus exogenous tyrosinase. These results are the first to indicate heightened Ca2+ transport in pulmonary microsomes following an allergic lung response and emphasize the role of aluminum hydroxide in enhancing allergic reactions in the lung. The responsiveness of the system to oxidative stress suggests that oxidative mechanisms may contribute to the physiologic and pathologic manifestations, such as airway hyperreactivity, associated with allergic pulmonary disease.