Increased production of nitrotyrosine in lung tissue of rats with radiation-induced acute lung injury

Protective Effects of Hydrogen against Irradiation

Radiation-induced lung injury is characterized by an acute pneumonia phase followed by a fibrotic phase. At the time of irradiation, a rapid, short-lived burst of reactive oxygen species (ROS) such as hydroxyl radicals (•OH) occurs, but chronic radiation-induced lung injury may occur due to excess ROS such as H₂O₂, O2•-, ONOO-, and •OH. Molecular hydrogen (H₂) is an efficient antioxidant that quickly diffuses cell membranes, reduces ROS such as •OH and ONOO-, and suppresses damage caused by oxidative stress in various organs. In 2011, through the evaluation of electron-spin resonance and fluorescent indicator signals, we had reported that H₂ can eliminate •OH and can protect against oxidative stress-related apoptotic damage induced by irradiation of cultured lung epithelial cells. We had explored for the first time the radioprotective effects of H₂ treatment on acute and chronic radiation-induced lung damage in mice by inhaled H2 gas (for acute) and imbibed H₂-enriched water (for chronic). Thus, we had proposed that H₂ be considered a potential radioprotective agent. Recent publications have shown that H₂ directly neutralizes highly reactive oxidants and indirectly reduces oxidative stress by regulating the expression of various genes. By regulating gene expression, H₂ functions as an anti-inflammatory and anti-apoptotic molecule and promotes energy metabolism. The increased evidence obtained from cultured cells or animal experiments reveal a putative place for H₂ treatment and its radioprotective effect clinically. This review focuses on major scientific advances in the treatment of H₂ as a new class of radioprotective agents.

Radiation-Induced Normal Tissue Damage: Oxidative Stress and Epigenetic Mechanisms

Radiotherapy (RT) is currently one of the leading treatments for various cancers; however, it may cause damage to healthy tissue, with both short-term and long-term side effects. Severe radiation-induced normal tissue damage (RINTD) frequently has a significant influence on the progress of RT and the survival and prognosis of patients. The redox system has been shown to play an important role in the early and late effects of RINTD. Reactive oxygen species (ROS) and reactive nitrogen species (RNS) are the main sources of RINTD. The free radicals produced by irradiation can upregulate several enzymes including nicotinamide adenine dinucleotide phosphate oxidase (NADPH oxidase), lipoxygenases (LOXs), nitric oxide synthase (NOS), and cyclooxygenases (COXs). These enzymes are expressed in distinct ways in various cells, tissues, and organs and participate in the RINTD process through different regulatory mechanisms. In recent years, several studies have demonstrated that epigenetic modulators play an important role in the RINTD process. Epigenetic modifications primarily contain noncoding RNA regulation, histone modifications, and DNA methylation. In this article, we will review the role of oxidative stress and epigenetic mechanisms in radiation damage, and explore possible prophylactic and therapeutic strategies for RINTD.

Persistent Oxidative Stress in Vestibular Schwannomas After Stereotactic Radiation Therapy

OBJECTIVE

Stereotactic radiation therapy is increasingly used to treat vestibular schwannomas (VSs) primarily and to treat tumor remnants following microsurgery. Little data are available regarding the effects of radiation on VS cells. Tyrosine nitrosylation is a marker of oxidative stress following radiation in malignant tumors. It is not known how long irradiated tissue remains under oxidative stress, and if such modifications occur in benign neoplasms such as VSs treated with significantly lower doses of radiation. We immunostained sections from previously radiated VSs with an antibody that recognizes nitrosylated tyrosine residues to assess for ongoing oxidative stress.

STUDY DESIGN

Immunohistochemical analysis.

METHODS

Four VSs, which recurred after excision, were treated with stereotactic radiation therapy. Ultimately each tumor required salvage reresection for regrowth. Histologic sections of each tumor before and after radiation were immunolabeled with a monoclonal antibody specific to nitrotyrosine and compared. Two VSs that underwent reresection of a growing tumor remnant without previous radiation therapy served as additional controls.

RESULTS

Irradiated tumors enlarged in volume by 3.16 to 8.62 mL following radiation. Preradiation sections demonstrated little to no nitrotyrosine immunostaining. Three of four of irradiated VSs demonstrated increased nitrotyrosine immunostaining in the postradiation sections compared with preradiation tumor sections. Nonirradiated VSs did not label with the antinitrotyrosine antibody.

CONCLUSIONS

VSs exhibit oxidative stress up to 7 years after radiotherapy, yet these VSs continued to enlarge. Thus, VSs that grow following radiation appear to possess mechanisms for cell survival and proliferation despite radiation-induced oxidative stress.

Hyper-activation of pp60Src limits nitric oxide signaling by increasing asymmetric dimethylarginine levels during acute lung injury

The molecular mechanisms by which the endothelial barrier becomes compromised during lipopolysaccharide (LPS) mediated acute lung injury (ALI) are still unresolved. We have previously reported that the disruption of the endothelial barrier is due, at least in part, to the uncoupling of endothelial nitric oxide synthase (eNOS) and increased peroxynitrite-mediated nitration of RhoA. The purpose of this study was to elucidate the molecular mechanisms by which LPS induces eNOS uncoupling during ALI. Exposure of pulmonary endothelial cells (PAEC) to LPS increased pp60^Src activity and this correlated with an increase in nitric oxide (NO) production, but also an increase in NOS derived superoxide, peroxynitrite formation and 3-nitrotyrosine (3-NT) levels. These effects could be simulated by the over-expression of a constitutively active pp60^Src (Y527FSrc) mutant and attenuated by over-expression of dominant negative pp60^Src mutant or reducing pp60^Src expression. LPS induces both RhoA nitration and endothelial barrier disruption and these events were attenuated when pp60^Src expression was reduced. Endothelial NOS uncoupling correlated with an increase in the levels of asymmetric dimethylarginine (ADMA) in both LPS exposed and Y527FSrc over-expressing PAEC. The effects in PAEC were also recapitulated when we transiently over-expressed Y527FSrc in the mouse lung. Finally, we found that the pp60-^Src-mediated decrease in DDAH activity was mediated by the phosphorylation of DDAH II at Y207 and that a Y207F mutant DDAH II was resistant to pp60^Src-mediated inhibition. We conclude that pp60^Src can directly inhibit DDAH II and this is involved in the increased ADMA levels that enhance eNOS uncoupling during the development of ALI.

Antioxidant strategies in respiratory medicine

Pulmonary oxidant stress plays an important pathogenetic role in disease conditions including acute lung injury/adult respiratory distress syndrome (ALI/ARDS), hyperoxia, ischemia-reperfusion, sepsis, radiation injury, lung transplantation, COPD, and inflammation. Reactive oxygen species (ROS), released from activated macrophages and leukocytes or formed in the pulmonary epithelial and endothelial cells, damage the lungs and initiate cascades of pro-inflammatory reactions propagating pulmonary and systemic stress. Diverse molecules including small organic compounds (e.g. gluthatione, tocopherol (vitamin E), flavonoids) serve as natural antioxidants that reduce oxidized cellular components, decompose ROS and detoxify toxic oxidation products. Antioxidant enzymes can either facilitate these antioxidant reactions (e.g. peroxidases using glutathione as a reducing agent) or directly decompose ROS (e.g. superoxide dismutases [SOD] and catalase). Many antioxidant agents are being tested for treatment of pulmonary oxidant stress. The administration of small antioxidants via the oral, intratracheal and vascular routes for the treatment of short- and long-term oxidant stress showed rather modest protective effects in animal and human studies. Intratracheal and intravascular administration of antioxidant enzymes are being currently tested for the treatment of acute oxidant stress. For example, intratracheal administration of recombinant human SOD is protective in premature infants exposed to hyperoxia. However, animal and human studies show that more effective delivery of drugs to cells experiencing oxidant stress is needed to improve protection. Diverse delivery systems for antioxidants including liposomes, chemical modifications (e.g. attachment of masking pegylated [PEG]-groups) and coupling to affinity carriers (e.g. antibodies against cellular adhesion molecules) are being employed and currently tested, mostly in animal and, to a limited extent, in humans, for the treatment of oxidant stress. Further studies are needed, however, in order to develop and establish effective applications of pulmonary antioxidant interventions useful in clinical practice. Although beyond the scope of this review, antioxidant gene therapies may eventually provide a strategy for the management of subacute and chronic pulmonary oxidant stress.

Radiation-induced lung injury and inflammation in mice: role of inducible nitric oxide synthase and surfactant protein D

Reactive nitrogen species (RNS) generated after exposure to radiation have been implicated in lung injury. Surfactant protein D (SP-D) is a pulmonary collectin that suppresses inducible nitric oxide synthase (iNOS)-mediated RNS production. Herein, we analyzed the role of iNOS and SP-D in radiation-induced lung injury. Exposure of wild-type (WT) mice to γ-radiation (8 Gy) caused acute lung injury and inflammation, as measured by increases in bronchoalveolar lavage (BAL) protein and cell content at 24 h. Radiation also caused alterations in SP-D structure at 24 h and 4 weeks post exposure. These responses were blunted in iNOS(-/-) mice. Conversely, loss of iNOS had no effect on radiation-induced expression of phospho-H2A.X or tumor necrosis factor (TNF)-α. Additionally, at 24 h post radiation, cyclooxygenase expression and BAL lipocalin-2 levels were increased in iNOS(-/-) mice, and heme oxygenase (HO)-1(+) and Ym1(+) macrophages were evident. Loss of SP-D resulted in increased numbers of enlarged HO-1(+) macrophages in the lung following radiation, along with upregulation of TNF-α, CCL2, and CXCL2, whereas expression of phospho-H2A.X was diminished. To determine if RNS play a role in the altered sensitivity of SP-D(-/-) mice to radiation, iNOS(-/-)/SP-D(-/-) mice were used. Radiation-induced injury, oxidative stress, and tissue repair were generally similar in iNOS(-/-)/SP-D(-/-) and SP-D(-/-) mice. In contrast, TNF-α, CCL2, and CXCL2 expression was attenuated. These data indicate that although iNOS is involved in radiation-induced injury and altered SP-D structure, in the absence of SP-D, it functions to promote proinflammatory signaling. Thus, multiple inflammatory pathways contribute to the pathogenic response to radiation.

Non-invasive whole-body plethysmograph for assessment and prediction of radiation-induced lung injury using simultaneously acquired nitric oxide and lung volume measurements

Radiation-induced lung injury (RILI) is a prevalent side effect in patients who undergo thoracic irradiation as part of their cancer treatment. Preclinical studies play a major role in understanding disease onset under controlled experimental conditions. The aim of this work is to develop a single-chambered optimized, non-invasive, whole-body plethysmograph prototype for unrestrained small animal lung volume measurements for preclinical RILI studies. The system is also designed to simultaneously obtain nitric oxide (NO) measurements of the expired breath. The device prototype was tested using computer simulations, phantom studies and in vivo measurements in experimental animal models of RILI. The system was found to improve resemblance to true breathing signal characteristics as measured by improved skewness (21.83%) and kurtosis (51.94%) in addition to increased overall signal sensitivity (3.61%) of the acquired breath signal, when compared to matching control data. NO concentration data was combined with breath measurements in order to predict early RILI onset. The system was evaluated using serial weekly measurements in hemi-thorax irradiated rats (n = 8) yielding a classification performance of 50.0%, 62.5%, 87.5% using lung volume only, NO only, and combined measurements of both, respectively. Our results indicate that improved performance could be achieved when measurements of lung volume are combined with those of NO. This would provide the overall plethysmography system with the ability to provide useful diagnostic and prognostic information for preclinical and, potentially, clinical thoracic dose escalation studies.

Radiation-modifying abilities of Nigella sativa and thymoquinone on radiation-induced nitrosative stress in the brain tissue

To investigate Nigella sativa oil (NSO) and Thymoquinone (TQ) for their antioxidant effects on the brain tissue of rats exposed to ionizing radiation. Fifty-four male albino Wistar rats, divided into six groups, were designed as group I (normal control group) did not receive NSO, TQ or irradiation; group II (control group of TQ) received dimethyl sulfoxide and sham irradiation; group III (control group of NSO) received saline and sham irradiation; group IV (irradiation plus NSO group) received both 5 Gray of gamma irradiation to total cranium and NSO; group V (irradiation plus TQ group) received both irradiation and TQ; group VI (irradiation alone group) received irradiation plus saline. Alterations in nitric oxide (NO·) and peroxynitrite (ONOO(-)) levels, and nitric oxide synthase (NOS) enzyme activity were measured by biochemical methods in homogenized brain tissue of rats. Levels of NO· and ONOO(-), and enzyme activity of NOS in brain tissue of the rats treated with NSO or TQ were found to be lower than in received IR alone (p<0.002) Nigella sativa oil (NSO) and its active component, TQ, clearly protect brain tissue from radiation-induced nitrosative stress.

Superoxide mediates acute liver injury in irradiated mice lacking sirtuin 3

AIMS

This study determined whether acute radiation-induced liver injury seen in Sirtuin3(-/-) mice after exposure to Cs-137 γ-rays was mediated by superoxide anion (O2(•-)).

RESULTS

Male wild-type (WT) and SIRT3(-/-) mice were given 2×2 Gy whole-body radiation doses separated by 24 h and livers were harvested 20 h after the second dose. Ex vivo measurements in fresh frozen liver sections demonstrated 50% increases in dihydroethidium oxidation from SIRT3(-/-) animals, relative to WT animals, before irradiation, but this increase was not detected 20 h after radiation exposure. In addition, irradiated livers from SIRT3(-/-) animals showed significant hydropic degeneration, loss of MitoTracker Green FM staining, increased immunohistochemical staining for 3-nitrotyrosine, loss of Ki67 staining, and increased mitochondrial localization of p53. These parameters of radiation-induced injury were significantly attenuated by an intraperitoneal injection of 2 mg/kg of the highly specific superoxide dismutase mimic, GC4401, 30 min before each fraction.

INNOVATION

Sirtuin 3 (SIRT3) is believed to regulate mitochondrial oxidative metabolism and antioxidant defenses in response to acute radiation-induced liver injury. This work provides strong evidence for the causal role of O2(•-) in the liver injury process initiated by whole-body irradiation in SIRT3(-/-) mice.

CONCLUSION

These results support the hypothesis that O2(•-) mediates acute liver injury in SIRT3(-/-) animals exposed to whole-body γ-radiation and suggest that GC4401 could be used as a radio-protective compound in vivo.

In vivo study of radioprotective effect of NO-synthase inhibitors and acetyl-L-carnitine

This study investigated the protective effect of two nitric oxide synthase inhibitors N(omega)-nitro-L-arginine methyl ester (L-NAME, 100 mg/kg i.p.) and aminoguanidine (AG, 400 mg/kg i.p.), and an antioxidant acetyl-L-carnitine (ALC, 250 mg/kg i.p., once daily for five days) against radiation-induced damage in Wistar rats. Blood samples were collected 6 h after whole-body irradiation with 8 Gy. Plasma concentrations of nitrite+nitrate (NO(x)) and malondialdehyde (MDA) were measured by high-performance liquid chromatography. A single injection of L-NAME one hour before exposure effectively prevented the radiation-induced elevation of plasma NO(x) and it reduced 2.6-fold the risk for death during the subsequent 30-day period. Pretreatment with ALC prevented the radiation-induced increase in plasma MDA and it had similar effect on mortality as L-NAME did. Presumably due to its short half-life, the partially iNOS-selective inhibitor and antioxidant AG given in a single dose before exposure did not attenuate MDA and NO(x) and it failed to significantly improve the 30-day survival. In conclusion, pretreatment with both the nonspecific NOS inhibitor L-NAME and the antioxidant ALC markedly reduce mortality to radiation sickness in rats. The radioprotective effect may be directly related to effective attenuation of the radiation-induced elevation of NO production by L-NAME and of oxidative stress by ALC.

Radiation mitigating properties of the lignan component in flaxseed

BACKGROUND

Wholegrain flaxseed (FS), and its lignan component (FLC) consisting mainly of secoisolariciresinol diglucoside (SDG), have potent lung radioprotective properties while not abrogating the efficacy of radiotherapy. However, while the whole grain was recently shown to also have potent mitigating properties in a thoracic radiation pneumonopathy model, the bioactive component in the grain responsible for the mitigation of lung damage was never identified. Lungs may be exposed to radiation therapeutically for thoracic malignancies or incidentally following detonation of a radiological dispersion device. This could potentially lead to pulmonary inflammation, oxidative tissue injury, and fibrosis. This study aimed to evaluate the radiation mitigating effects of FLC in a mouse model of radiation pneumonopathy.

METHODS

We evaluated FLC-supplemented diets containing SDG lignan levels comparable to those in 10% and 20% whole grain diets. 10% or 20% FLC diets as compared to an isocaloric control diet (0% FLC) were given to mice (C57/BL6) (n=15-30 mice/group) at 24, 48, or 72-hours after single-dose (13.5 Gy) thoracic x-ray treatment (XRT). Mice were evaluated 4 months post-XRT for blood oxygenation, lung inflammation, fibrosis, cytokine and oxidative damage levels, and survival.

RESULTS

FLC significantly mitigated radiation-related animal death. Specifically, mice fed 0% FLC demonstrated 36.7% survival 4 months post-XRT compared to 60-73.3% survival in mice fed 10%-20% FLC initiated 24-72 hours post-XRT. FLC also mitigated radiation-induced lung fibrosis whereby 10% FLC initiated 24-hours post-XRT significantly decreased fibrosis as compared to mice fed control diet while the corresponding TGF-beta1 levels detected immunohistochemically were also decreased. Additionally, 10-20% FLC initiated at any time point post radiation exposure, mitigated radiation-induced lung injury evidenced by decreased bronchoalveolar lavage (BAL) protein and inflammatory cytokine/chemokine release at 16 weeks post-XRT. Importantly, neutrophilic and overall inflammatory cell infiltrate in airways and levels of nitrotyrosine and malondialdehyde (protein and lipid oxidation, respectively) were also mitigated by the lignan diet.

CONCLUSIONS

Dietary FLC given early post-XRT mitigated radiation effects by decreasing inflammation, lung injury and eventual fibrosis while improving survival. FLC may be a useful agent, mitigating adverse effects of radiation in individuals exposed to incidental radiation, inhaled radioisotopes or even after the initiation of radiation therapy to treat malignancy.

Elevation in exhaled nitric oxide predicts for radiation pneumonitis

PURPOSE

Radiation pneumonitis is a major toxicity after thoracic radiotherapy (RT), with no method available to accurately predict the individual risk. This was a prospective study to evaluate exhaled nitric oxide as a predictive biomarker for radiation pneumonitis in esophageal cancer patients.

PATIENTS AND METHODS

A total of 34 patients prescribed neoadjuvant chemoradiotherapy for esophageal cancer were enrolled in the present trial. Each patient underwent respiratory surveys and exhaled nitric oxide (NO) measurements before, at the end of, and 1 to 2 months after completing RT. Pneumonitis toxicity was scored using the Common Terminology Criteria for Adverse Events, version 4.0. The demographics, dosimetric factors, and exhaled NO levels were evaluated for correlation with symptomatic patients (scores ≥ 2).

RESULTS

Of the 34 patients, 28 were evaluable. All had received 50.4 Gy RT with concurrent chemotherapy. The pneumonitis toxicity score was Grade 3 for 1, Grade 2 for 3, Grade 1 for 7, and Grade 0 for 17. The dosimetric factors were not predictive of symptoms. The mean exhaled NO level measured before, at completion, and at restaging was 17.3 ± 8.5 (range, 5.5-36.7), 16.0 ± 14.2 (range, 5.8-67.7), and 14.7 ± 6.2 (range, 5.5-28.0) parts per billion, respectively. The ratio of exhaled NO at the end of RT vs. before treatment was 3.4 (range, 1.7-6.7) for the symptomatic and 0.8 (range, 0.3-1.3) for the asymptomatic (p = .0017) patients. The elevation in exhaled NO preceded the peak symptoms by 33 days (range, 21-50). The interval to peak symptoms was inversely related to the exhaled NO elevation.

CONCLUSIONS

Elevations in exhaled NO at the end of RT was found to predict for radiation pneumonitis symptoms.

Exhaled nitric oxide predicts radiation pneumonitis in esophageal and lung cancer patients receiving thoracic radiation

BACKGROUND AND PURPOSE

Radiation pneumonitis is a significant toxicity following thoracic radiotherapy with no method to predict individual risk.

MATERIALS AND METHODS

Sixty-five patients receiving thoracic radiation for lung or esophageal cancer were enrolled in a phase II study. Each patient received respiratory surveys and exhaled nitric oxide measurements before, on the last day of, and 30-60 days after completing radiotherapy (RT). Pneumonitis toxicity was scored using the common terminology criteria for adverse events, version 4.0. The demographics, dosimetric factors, and nitric oxide ratio (NOR) of end RT/pre-RT were evaluated for correlation with symptomatic patients (Grade ≥ 2).

RESULTS

Fifty patients completed the trial. The pneumonitis toxicity score was: Grade 3 for 1 patient, Grade 2 for 6 patients, Grade 1 for 18 patients, and Grade 0 for 25 patients. Dosimetric factors were not predictive of symptoms. The NOR was 3.0 ± 1.8 (range 1.47-6.73) for the symptomatic and 0.78 ± 0.29 (range 0.33-1.37) for the asymptomatic patients (p=0.006). A threshold NOR of 1.4 separated symptomatic and asymptomatic patients (p<0.001). The average error was 4%.

CONCLUSIONS

Elevation in eNO on the last day of radiotherapy predicted subsequent symptomatic radiation pneumonitis weeks to months after treatment.

Hydrogen therapy attenuates irradiation-induced lung damage by reducing oxidative stress

Molecular hydrogen (H(2)) is an efficient antioxidant that diffuses rapidly across cell membranes, reduces reactive oxygen species (ROS), such as hydroxyl radicals and peroxynitrite, and suppresses oxidative stress-induced injury in several organs. ROS have been implicated in radiation-induced damage to lungs. Because prompt elimination of irradiation-induced ROS should protect lung tissue from damaging effects of irradiation, we investigated the possibility that H(2) could serve as a radioprotector in the lung. Cells of the human lung epithelial cell line A549 received 10 Gy irradiation with or without H(2) treatment via H(2)-rich PBS or medium. We studied the possible radioprotective effects of H(2) by analyzing ROS and cell damage. Also, C57BL/6J female mice received 15 Gy irradiation to the thorax. Treatment groups inhaled 3% H(2) gas and drank H(2)-enriched water. We evaluated acute and late-irradiation lung damage after H(2) treatment. H(2) reduced the amount of irradiation-induced ROS in A549 cells, as shown by electron spin resonance and fluorescent indicator signals. H(2) also reduced cell damage, measured as levels of oxidative stress and apoptotic markers, and improved cell viability. Within 1 wk after whole thorax irradiation, immunohistochemistry and immunoblotting showed that H(2) treatment reduced oxidative stress and apoptosis, measures of acute damage, in the lungs of mice. At 5 mo after irradiation, chest computed tomography, Ashcroft scores, and type III collagen deposition demonstrated that H(2) treatment reduced lung fibrosis (late damage). This study thus demonstrated that H(2) treatment is valuable for protection against irradiation lung damage with no known toxicity.

Early changes in L-arginine-nitric oxide metabolic pathways in response to the whole-body gamma irradiation of rats

PURPOSE

Nitric oxide (NO), a reactive radical, is formed in higher amounts from L-arginine by inducible NO synthase (iNOS) during early response to ionizing radiation presumably as a part of signal transduction pathways. This study investigated the changes in L-arginine-NO metabolic pathways within a 24-hour period after whole-body gamma irradiation of rats with the range of low to supra-lethal doses.

MATERIALS AND METHODS

Young adult female Wistar rats received either 0-50 Gy whole-body irradiation or an intraperitoneal injection of bacterial lipopolysaccharide (LPS, 10 mg/kg). Exhaled NO was monitored using chemiluminiscence, nitrite + nitrate (NO(x)) and L-arginine were assayed by high-performance liquid chromatography, and expression of iNOS was determined using Western blot.

RESULTS

Irradiation resulted in a dose-dependent increase of plasma NO(x) to maximum levels which were 4-fold higher compared to controls (p < 0.001). The NO(x) levels increased less in the bronchoalveolar lavage fluid (BAL) (1.7-fold, p < 0.001) and liver homogenate (2.5-fold, p < 0.05), respectively, and were dose-independent. Exhaled NO, lung NO(x), plasma and BAL L-arginine, and the expression of iNOS in lung and liver tissues of irradiated rats and controls were similar. LPS caused a considerable increase (p < 0.001) in exhaled NO (61-fold), NO(x) levels (plasma 34-fold, BAL 6-fold, lung 5-fold, liver 4-fold), and in iNOS expression, respectively.

CONCLUSION

In contrast to the LPS treatment of rats, the radiation-induced changes in L-arginine-NO metabolic pathways are modest, particularly in the airways and lungs. Noninvasive measurement of exhaled NO within a 24-h period following the exposure of rats to ionizing radiation has no value for biodosimetry.

Mechanisms of nitric oxide synthase uncoupling in endotoxin-induced acute lung injury: role of asymmetric dimethylarginine

Acute lung injury (ALI) is associated with severe alterations in lung structure and function and is characterized by hypoxemia, pulmonary edema, low lung compliance and widespread capillary leakage. Asymmetric dimethylarginine (ADMA), a known cardiovascular risk factor, has been linked to endothelial dysfunction and the pathogenesis of a number of cardiovascular diseases. However, the role of ADMA in the pathogenesis of ALI is less clear. ADMA is metabolized via hydrolytic degradation to l-citrulline and dimethylamine by the enzyme, dimethylarginine dimethylaminohydrolase (DDAH). Recent studies suggest that lipopolysaccharide (LPS) markedly increases the level of ADMA and decreases DDAH activity in endothelial cells. Thus, the purpose of this study was to determine if alterations in the ADMA/DDAH pathway contribute to the development of ALI initiated by LPS-exposure in mice. Our data demonstrate that LPS exposure significantly increases ADMA levels and this correlates with a decrease in DDAH activity but not protein levels of either DDAH I or DDAH II isoforms. Further, we found that the increase in ADMA levels cause an early decrease in nitric oxide (NO(x)) and a significant increase in both NO synthase (NOS)-derived superoxide and total nitrated lung proteins. Finally, we found that decreasing peroxynitrite levels with either uric acid or Manganese (III) tetrakis (1-methyl-4-pyridyl) porphyrin (MnTymPyp) significantly attenuated the lung leak associated with LPS-exposure in mice suggesting a key role for protein nitration in the progression of ALI. In conclusion, this is the first study that suggests a role of the ADMA/DDAH pathway during the development of ALI in mice and that ADMA may be a novel therapeutic biomarker to ascertain the risk for development of ALI.

Protein tyrosine nitration: selectivity, physicochemical and biological consequences, denitration, and proteomics methods for the identification of tyrosine-nitrated proteins

Protein tyrosine nitration (PTN) is a post-translational modification occurring under the action of a nitrating agent. Tyrosine is modified in the 3-position of the phenolic ring through the addition of a nitro group (NO2). In the present article, we review the main nitration reactions and elucidate why nitration is not a random chemical process. The particular physical and chemical properties of 3-nitrotyrosine (e.g., pKa, spectrophotometric properties, reduction to aminotyrosine) will be discussed, and the biological consequences of PTN (e.g., modification of enzymatic activity, sensitivity to proteolytic degradation, impact on protein phosphorylation, immunogenicity and implication in disease) will be reviewed. Recent data indicate the possibility of an in vivo denitration process, which will be discussed with respect to the different reaction mechanisms that have been proposed. The second part of this review article focuses on analytical methods to determine this post-translational modification in complex proteomes, which remains a major challenge.

Oxidative damage pathways in relation to normal tissue injury

Given the increasing population of long-term cancer survivors, the need to mitigate or treat late effects has emerged as a primary area of radiation biology research. Once thought to be irreversible, radiation-induced late effects are now viewed as dynamic multicellular interactions between multiple cell types within a particular program that can be modulated. The molecular, cellular and biochemical pathways responsible for radiation-induced late morbidity remain ill-defined. This review provides data in support of the hypothesis that these late effects are driven, in part, by a chronic oxidative stress. Irradiating late responding normal tissues leads to chronic increases in reactive oxygen/reactive nitrogen oxide species that serve as intracellular signaling species to alter cell function/phenotype, resulting in chronic inflammation, organ dysfunction, and ultimate fibrosis and/or necrosis. Furthermore, we hypothesize that the effectiveness of renin-angiotensin system blockers in preventing or mitigating the severity of radiation-induced late effects reflects, in part, inhibition of reactive oxygen species generation and the resultant chronic oxidative stress. These findings provide a robust rationale for anti-inflammatory-based interventional therapies in the treatment of late normal tissue injury.

Peroxynitrite formation in radiation-induced salivary gland dysfunction in mice

Xerostomia frequently arises in patients with head and neck malignancies that are treated by radiation. However, the mechanisms responsible for the destruction of the salivary gland remain unknown. We previously established a xerostomia model of mice and identified the pathway through which nitric oxide (NO) affects the pathogenesis of radiation-induced salivary gland dysfunction. Although the toxicity of NO alone is modest, NO with superoxide anion (O2(*-)) rapidly forms peroxynitrite (ONOO), a more powerful toxic oxidant. In this study, we used the experimental model to examine: 1) when NO and O2(*-) production is maximum in the salivary gland after irradiation;2) whether peroxynitrite, as assessed by nitrotyrosine production, is responsible for salivary gland dysfunction; and 3) the effect of the iNOS selective inhibitor, aminoguanidine (AG), on nitrotyrosine formation. The increases in production of NO and O2(*-) in the salivary gland peaked on day 7 after irradiation. Nitrotyrosine detected immunohistochemically was significantly reduced by AG in the salivary gland. On the basis of these results, we concluded that NO together with O2(*-) forms the more reactive ONOO, which might be an important pathogenic factor in radiation-induced salivary gland dysfunction.

Lung Injury and Recovery After Exposure to Blast Overpressure

BACKGROUND

A critical immediate determinant of survival after exposure to blast overpressure (BOP) is pulmonary damage, but mechanisms of injury and the course of recovery are not well understood. The objective of this study was to characterize the progression of oxidative and inflammatory responses in lungs as well as the activation of consequent protective mechanisms after exposure to medium intensity BOP.

METHODS

Rats were exposed to a moderate (approximately 120 kPa) level of BOP in a pneumatically driven shock tube. At different times (2-192 hours) after exposure, lungs were examined for pathologic signs of injury, markers of inflammatory responses, and indicators of oxidative and nitrative damage.

RESULTS

The results showed a postblast activation of inflammatory response (increase of myeloperoxidase activity, CINC-1, ICAM-1, and iNOS), increase in protein oxidation and nitration, and development of gross diffused hemorrhage in lungs. The initial phase of lung damage that peaked at 24 to 48 hours after exposure to BOP was followed by gradual dissolution of inflammation and oxidation that were complete by 192 hours. Resolution of morphologic damage and inflammation in lungs concurred with activation of expression of antioxidant enzymes heme oxygenase-1 (HO-1) and manganese superoxide dismutase (MnSOD). Plasma level of gelsolin, a marker of acute lung damage was decreased at 24 hours postblast and later returned to the control level.

CONCLUSIONS

The study shows the role of adaptive anti-oxidant and anti- inflammatory mechanisms in lung recovery after injury caused by exposure to BOP.

Free radical theory of autoimmunity

Background

Despite great advances in clinical oncology, the molecular mechanisms underlying the failure of chemotherapeutic intervention in treating lymphoproliferative and related disorders are not well understood.

Hypothesis

A hypothetical scheme to explain the damage induced by chemotherapy and associated chronic oxidative stress is proposed on the basis of published literature, experimental data and anecdotal observations. Brief accounts of multidrug resistance, lymphoid malignancy, the cellular and molecular basis of autoimmunity and chronic oxidative stress are assembled to form a basis for the hypothesis and to indicate the likelihood that it is valid in vivo.

Conclusion

The argument set forward in this article suggests a possible mechanism for the development of autoimmunity. According to this view, the various sorts of damage induced by chemotherapy have a role in the pattern of drug resistance, which is associated with the initiation of autoimmunity.

The effects of nitric oxide in acute lung injury

Acute lung injury (ALI) is a common clinical problem associated with significant morbidity and mortality. Ongoing clinical and basic research and a greater understanding of the pathophysiology of ALI have not been translated into new anti-inflammatory therapeutic options for patients with ALI, or into a significant improvement in the outcome of ALI. In both animal models and humans with ALI, there is increased endogenous production of nitric oxide (NO) due to enhanced expression and activity of inducible NO synthase (iNOS). This increased presence of iNOS and NO in ALI contributes importantly to the pathophysiology of ALI. However, inhibition of total NO production or selective inhibition of iNOS has not been effective in the treatment of ALI. We have recently suggested that there may be differential effects of NO derived from different cell populations in ALI. This concept of cell-source-specific effects of NO in ALI has potential therapeutic relevance, as targeted iNOS inhibition specifically to key individual cells may be an effective therapeutic approach in patients with ALI. In this paper, we will explore the potential role for endogenous iNOS-derived NO in ALI. We will review the evidence for increased iNOS expression and NO production, the effects of non-selective NOS inhibition, the effects of selective inhibition or deficiency of iNOS, and this concept of cell-source-specific effects of iNOS in both animal models and human ALI.

Oxidative stress in radiology staff

Excessive production of reactive oxygen species has been observed following acute and chronic exposure to radiation in animal models which can lead to several detrimental and irreversible outcomes in vital organs. Aim of this study was to determine the oxidative stress status in radiology unit workers which are exposed to persistent low-dose radiation.

METHODS

: A group of 32 radiology unit employees along with 32 sex- and age-matched hospital workers, not exposed to low-dose radiation were recruited from two separate hospitals for the study. Exposed subjects showed higher levels of lipid peroxidation (P=0.009), total antioxidant capacity (P=0.0006) and thiol groups (P=0.03). It is concluded that occupationally exposed individuals are oxidatively stressed and precautions such as antioxidant therapy seems reasonable.

Thalidomide reduces lipopolysaccharide/zymosan-induced acute lung injury in rats

Pharmacological therapies targeting fulminant lung inflammation in acute lung injury (ALI) need to be improved. We evaluated the effect of thalidomide, a chemical modulating both acute and chronic inflammation, on ALI induced by intravenous administration of lipopolysaccharide (LPS) and zymosan in male Sprague-Dawley rats. Injection of LPS and zymosan induced significant lung inflammation, as evidenced by increased neutrophil sequestration in lung tissue as well as enhanced nitric oxide metabolite (NO(x)(-)) production in the serum and bronchoalveolar lavage (BAL) fluid. Lactate dehydrogenase (LDH) activity and protein concentration in BAL fluid were significantly increased after administration of LPS and zymosan. Pulmonary microvascular permeability was determined using the Evans blue retention method, which showed a significant increase in microvascular permeability after LPS and zymosan administration, indicating the development of ALI. Animals that received thalidomide (100 mg/kg) 2 h prior to LPS injection had significantly reduced pulmonary NO(x)(-) production, pulmonary microvascular permeability, and LDH activity and protein concentration in BAL fluid. We therefore conclude that thalidomide ameliorates lung inflammation and reduces ALI induced by combined LPS and zymosan administration in rats.

Morphological and functional changes induced by the amino acid analogue 3-nitrotyrosine in mouse neuroblastoma and rat glioma cell lines

The amino acid analogue 3-nitrotyrosine (3-NT) is formed in neural cells as a result of the intense stimulation of NMDA glutamate receptors. 3-NT is involved in the pathology of diverse neurodegenerative disorders. The aim of our work is to investigate the sensitivity of cultured neural and glial cells to 3-NT. We report the morphological changes detected on mouse neuroblastoma (C1300) and rat glioma (C6) cell lines cultured in a medium supplemented with different 3-NT concentrations. Western blot displayed a selective incorporation of 3-NT into a single protein that co-migrated with tubulin. Both cell lines showed morphological changes, nuclear suffering, decreased viability and growth inhibition (starting from 90 and 360 microM for C1300 and C6, respectively). Such effects were dose-dependent, though glioma cells showed severe alterations at higher 3-NT concentrations. Our results point out a higher 3-NT sensitivity in the neural cells studied in comparison with those of glial origin. The dramatic toxicity of 3-NT in neural cells suggests further investigations focused on the biochemical mechanisms at the roots of neurodegenerative diseases.

Anti-inflammatory effect of Pelteobagrus nudiceps extract on rat model of CFA-induced pulmonary tuberculous granuloma

We investigated the effectiveness of supportive therapy with a fish-oil extract called repair tuberculosis (RTB) in anti-tuberculosis treatment, and the underlying mechanism of action. The active component of RTB is the unsaturated fatty acid docosatetraenoic acid (C(22)H(36)O(2)), which was reported to induce the resorption and healing of pulmonary lesions in patients with severe pulmonary tuberculosis. We administered RTB to a rat model of CFA-induced pulmonary tuberculous granuloma (RTB group), and compared the results with those in a control group, which did not receive RTB. Histological examination of the lungs showed a significantly smaller area of granuloma in the RTB group than in the control group. IFN-gamma levels in bronchoalveolar lavage fluid (BALF) were higher in the RTB group than in the control group, suggesting that Th1-type immune reaction is activated in the RTB group. Moreover, significantly enhanced expression of inducible nitric oxide synthase mRNA in lung tissue was observed in the RTB group. Superoxide production by cells recovered from BALF was attenuated in the RTB group. There were no difference in IL-4 levels in BALF, or in expression of TNF-alpha mRNA in lung tissue between the RTB and control groups. The above results suggest that RTB activates Th1-type cellular immune reaction, promotes absorption of lesions, and inhibits the generation of cytotoxic substances.

Chlorine-induced injury to the airways in mice

Exposure to chlorine gas (Cl2) causes occupational asthma that we hypothesized occurs through the induction of airway inflammation and airway hyperresponsiveness by oxidative damage. Respiratory mechanics and airway responsiveness to methacholine were assessed in A/J mice 24 hours after a 5-minute exposure to 100, 200, 400, or 800 ppm Cl2 and 2 and 7 days after inhalation of 400 ppm Cl2. Airway responsiveness was higher 24 hours after 400 and 800 ppm Cl2. Responsiveness after inhalation of 400 ppm Cl2 returned to normal by 2 days but was again elevated at 7 days. Airway epithelial loss, patchy alveolar damage, proteinaceous exudates, and inflammatory cells within alveolar walls were observed in animals exposed to 800 ppm Cl2. Macrophages, granulocytes, epithelial cells, and nitrate/nitrite levels increased in lung lavage fluid. Increased inducible nitric oxide synthase expression and oxidation of lung proteins were observed. Epithelial cells and alveolar macrophages from mice exposed to 800 ppm Cl2 stained for 3-nitrotyrosine residues. Inhibition of inducible nitric oxide synthase with 1400W (1 mg/kg) abrogated the Cl2-induced changes in responsiveness. We conclude that chlorine exposure causes functional and pathological changes in the airways associated with oxidative stress. Inducible nitric oxide synthase is involved in the induction of changes in responsiveness to methacholine.

Type 2 nitric oxide synthase and protein nitration in chronic lung infection

Inflammation in the lung can lead to increased expression of inducible nitric oxide synthase (iNOS) and enhanced NO production. It has been postulated that the resultant highly reactive NO metabolites may have an important role in host defence, although they might also contribute to tissue damage. However, in a number of inflammatory lung diseases, including bronchiectasis, iNOS expression is increased but no elevation of airway NO can be detected. A potential explanation for this finding is that NO is rapidly scavenged by reaction with superoxide radicals, forming peroxynitrite, which is preferentially metabolized via nitration and nitrosation reactions. To test this hypothesis, anaesthetized, specific pathogen-free rats were inoculated with Pseudomonas aeruginosa incorporated into agar beads (chronically infected group) or sterile agar beads (control group). Ten to 15 days later, the lungs were isolated and fixed. Pseudomonas organisms were isolated from the lungs of the chronically infected group. These lungs showed extensive inflammatory cell infiltration and tissue damage, which were not observed in control lungs. Expression of iNOS was increased in the chronically infected group when compared with the control group. However, the mean number of cells staining for nitrotyrosine in the chronically infected group was not significantly different from that in the controls, nor was there an excess of nitrotyrosine, nitrate, nitrite or nitrosothiol concentrations in the infected lungs. Thus, no evidence was found of increased NO metabolites in chronically infected lungs, including products of the peroxynitrite pathway. These findings suggest that chronic infection does not cause increased iNOS activity in the lung, despite increased expression of iNOS.

Incorporation of 3-nitrotyrosine into the C-terminus of alpha-tubulin is reversible and not detrimental to dividing cells

The C-terminus of the alpha-chain of tubulin is subject to reversible incorporation of tyrosine by tubulin tyrosine ligase and removal by tubulin carboxypeptidase. Thus, microtubules rich in either tyrosinated or detyrosinated tubulin can coexist in the cell. Substitution of the terminal tyrosine by 3-nitrotyrosine has been claimed to cause microtubule dysfunction and consequent injury of epithelial lung carcinoma A549 cells. Nitrotyrosine is formed in cells by nitration of tyrosine by nitric oxide-derived species. We studied properties of tubulin modified by in vitro nitrotyrosination at the C-terminus of the alpha-subunit, and the consequences for cell functioning. Nitrotyrosinated tubulin was a good substrate of tubulin carboxypeptidase, and showed a similar capability to assemble into microtubules in vitro to that of tyrosinated tubulin. Tubulin of C6 cells cultured in F12K medium in the presence of 500 micro m nitrotyrosine became fully nitrotyrosinated. This nitrotyrosination was shown to be reversible. No changes in morphology, proliferation, or viability were observed during cycles of nitrotyrosination, denitrotyrosination, and re-nitrotyrosination. Similar results were obtained with CHO, COS-7, HeLa, NIH-3T3, NIH-3T3(TTL-), and A549 cells. C6 and A549 cells were subjected to several passages during 45 days or more in the continuous presence of 500 micro m nitrotyrosine without noticeable alteration of morphology, viability, or proliferation. The microtubular networks visualized by immunofluorescence with antibodies to nitrotyrosinated and total tubulin were identical. Furthermore, nitrotyrosination of tubulin in COS cells did not alter the association of tubulin carboxypeptidase with microtubules. Our results demonstrate that substitution of C-terminal tyrosine by 3-nitrotyrosine has no detrimental effect on dividing cells.

Inducible nitric oxide synthase plays a role in LPS-induced hyperglycemia and insulin resistance

The molecular mechanisms underlying endotoxin-induced insulin resistance remain unclear. Endotoxin or lipopolysaccharide (LPS) injection is a potent stimulator of inducible nitric oxide synthase (iNOS). This study in rats, using the specific iNOS inhibitor aminoguanidine, investigated the role of iNOS in endotoxin-induced hyperglycemia and insulin resistance. LPS injection led to hyperglycemia, insulin resistance, and increased iNOS protein expression and activity. Aminoguanidine prevented LPS-induced hyperglycemia without affecting insulin levels or iNOS expression. Aminoguanidine attenuated the LPS-induced insulin resistance, reflected by the requirement for a higher glucose infusion rate to maintain euglycemia during a hyperinsulinemic clamp study. Aminoguanidine completely blocked the LPS-elevated hepatic glucose output and also inhibited LPS-induced increases in hepatic glycogen phosphorylase activities and phosphoenolpyruvate carboxykinase (PEPCK) mRNA expression, key enzymes for glycogenolysis and gluconeogenesis, respectively. Thus, these data demonstrate an important role for iNOS in LPS-induced insulin resistance, evidenced by the attenuation of LPS-induced hyperglycemia and reversal of increased hepatic glucose output by aminoguanidine. The protective effect of aminoguanidine on insulin resistance is probably by attenuation of hepatic glucose output via its inhibition of key enzymes for glycogenolysis and gluconeogenesis, including glycogen phosphorylase and PEPCK.

Tyrosine nitration: localisation, quantification, consequences for protein function and signal transduction

The nitration of free tyrosine or protein tyrosine residues generates 3-nitrotyrosine the detection of which has been utilised as a footprint for the in vivo formation of peroxynitrite and other reactive nitrogen species. The detection of 3-nitrotyrosine by analytical and immunological techniques has established that tyrosine nitration occurs under physiological conditions and levels increase in most disease states. This review provides an updated, comprehensive and detailed summary of the tissue, cellular and specific protein localisation of 3-nitrotyrosine and its quantification. The potential consequences of nitration to protein function and the pathogenesis of disease are also examined together with the possible effects of protein nitration on signal transduction pathways and on the metabolism of proteins.

Nitric oxide: a pro-inflammatory mediator in lung disease?

Inflammatory diseases of the respiratory tract are commonly associated with elevated production of nitric oxide (NO*) and increased indices of NO* -dependent oxidative stress. Although NO* is known to have anti-microbial, anti-inflammatory and anti-oxidant properties, various lines of evidence support the contribution of NO* to lung injury in several disease models. On the basis of biochemical evidence, it is often presumed that such NO* -dependent oxidations are due to the formation of the oxidant peroxynitrite, although alternative mechanisms involving the phagocyte-derived heme proteins myeloperoxidase and eosinophil peroxidase might be operative during conditions of inflammation. Because of the overwhelming literature on NO* generation and activities in the respiratory tract, it would be beyond the scope of this commentary to review this area comprehensively. Instead, it focuses on recent evidence and concepts of the presumed contribution of NO* to inflammatory diseases of the lung.