Tissue injury following inhalation of fine particulate matter and hydrogen peroxide is associated with altered production of inflammatory mediators and antioxidants by alveolar macrophages

On the performance of carbon-based screen-printed electrodes for (in)organic hydroperoxides sensing in rainwater

Hydroperoxides play important roles in atmospheric chemical processes since they act as strong oxidants. This paper details with the modification, characterization and performance of different carbon-based screen-printed electrodes to develop a sensor that allows to analyze organic and inorganic hydroperoxides in atmospheric samples. Commercial electrodes made up of graphite, graphene, carbon nanotubes and graphene oxide were electrochemically activated and subsequently modified by layer-by-layer method with a conducting polymer of azure-A and electrodeposited platinum nanoparticles. Characterization of modified electrodes was performed by FE-SEM, XPS, Raman spectroscopy, cyclic voltammetry, and impedance spectroscopy. Even though all modified carbonaceous substrates enabled the development of competitive electrochemical sensors for (in)organic hydroperoxides detection, carbon nanotubes underlying substrate exhibited the best performances in terms of sensitivity, stability, limit of detection and linear range. This amperometric sensor displayed linear responses to hydroperoxides over 0.081-450 μM with detection limits in the range of 24-558 nM and sensitivity values among 0.0628±1.6E-4 and 0.0112±0.71E-4 μA/μM for the different hydroperoxides herein studied. The developed electrochemical sensor was successfully applied to the analysis of (in)organic hydroperoxides in rainwater samples. Measurements in rainwater were performed in a city located in the East of Spain and collected at two different sites (downtown and suburban area) on two different dates (July and November 2020). The presented results demonstrated high sensitivity and selectivity for the detection of hydroperoxides among a plethora of substances naturally present in rainwater.

Cytotoxicity induced by fine particulate matter (PM2.5) via mitochondria-mediated apoptosis pathway in rat alveolar macrophages

Although positive associations exist between ambient particulate matter (PM_2.5; diameter ≤ 2.5 μm) and the morbidity and mortality rates for respiratory diseases, the biological mechanisms of the reported health effects are unclear. Considering that alveolar macrophages (AM) are the main cells responsible for phagocytic clearance of xenobiotic particles that reach the airspaces of the lungs, the purpose of this study was to investigate whether PM_2.5 induced AM apoptosis, and investigate its possible mechanisms. Freshly isolated AM from Wistar rats were treated with extracted PM_2.5 at concentrations of 33, 100, or 300 μg/mL for 4 h; thereafter, the cytotoxic effects were evaluated. The results demonstrated that PM_2.5 induced cytotoxicity by decreasing cell viability and increasing lactate dehydrogenase (LDH) levels in AMs. The levels of reactive oxygen species (ROS) and intracellular calcium cations (Ca²⁺) markedly increased in higher PM_2.5 concentration groups. Additionally, the apoptotic ratio increased, and the apoptosis-related proteins BCL2-associated X (Bax), caspase-3, and caspase-9 were upregulated, whereas B cell lymphoma-2 (Bcl-2) protein levels were downregulated following PM_2.5 exposure. Cumulative findings showed that PM_2.5 induced apoptosis in AMs through a mitochondrial-mediated pathway, which indicated that PM_2.5 plays a significant role in lung injury diseases.

Alveolar macrophage reaction to PM2.5 of hazy day in vitro: Evaluation methods and mitochondrial screening to determine mechanisms of biological effect

Hazy weather in China has recently become a major public health concern due to high levels of atmospheric fine particulate matter (PM_2.5) with a large amount of polycyclic aromatic hydrocarbon (PAHs). In this study, the mass concentration of PAHs in hazy PM_2.5 in urban Taiyuan city, China was determined and toxicities of different dosage of the hazy PM_2.5 on rat alveolar macrophages (AMs) were examined. It was found that the hazy PM_2.5, bounded with many species of PAHs (CHR, BbF, BaP, BaA, and etc.), significantly increased cellular malondialdehyde (MDA) content followed by the decreasing in superoxide (SOD) and glutathione peroxidase (GPx) in AMs. They induced mitochondrial changes in ultrastructure as evidenced by mitochondrial swelling and cristae disorganization, and a dose-dependent decrease in mitochondrial profile density. Also, the mRNA expression levels of mitochondrial fusion-related genes were modified. The Mfn1 and Mfn2 which are essential for mitochondrial fusion increased significantly in hazy PM_2.5-treated group compared to the control in a dose-dependent manner, OPA1 was significantly increased at the highest PM_2.5 dose delivered. These findings suggested that exposure to hazy PM_2.5 could activate oxidative stress pathways in AMs, resulting in abnormal mitochondrial morphology and fusion/fission frequency. Possibly, the toxic effects were mostly attributed to the high burden of varied PAHs in hazy PM_2.5.

Liver kinase B1 suppresses lipopolysaccharide-induced nuclear factor κB (NF-κB) activation in macrophages

Liver kinase B1 (LKB1), a serine/threonine kinase, is a tumor suppressor and metabolic regulator. Recent data suggest that LKB1 is essential in regulating homeostasis of hematopoietic cells and immune responses. However, its role in macrophages and innate immune system remains unclear. Here we report that macrophage LKB1 inhibits pro-inflammatory signaling in response to LPS. LPS-induced pro-inflammatory cytokines and pro-inflammatory enzymes were monitored in bone marrow-derived macrophages isolated from myeloid cell-specific LKB1 knock out mice and their wild type littermate control mice. LPS induced higher levels of pro-inflammatory cytokines and pro-inflammatory enzymes in bone marrow-derived macrophages from LKB1 KO than those from wild type mice. Consistently, LPS induced higher levels of NF-κB activation in LKB1-deficient macrophages than those in wild type. Further, LPS stimulation significantly increased LKB1 phosphorylation at serine 428, which promoted its binding to IκB kinaseβ (IKKβ), resulting in the inhibition of NF-κB. Finally, LPS injection caused higher levels of cytokine release and more severe tissue injury in the lung tissues of LKB1 KO mice than in those of control mice. We conclude that LKB1 inhibits LPS-induced NF-κB activation in macrophages.

Direct photolysis of α-pinene ozonolysis secondary organic aerosol: effect on particle mass and peroxide content

Primary and secondary organic aerosols (POA and SOA) contain a complex mixture of multifunctional chemicals, many of which are photolabile. Much of the previous work that aimed to understand the chemical evolution (aging) of POA and SOA has focused on the reactive uptake of gas-phase oxidants by particles. By stripping volatile compounds and ozone from α-pinene ozonolysis SOA with three 1-m-long denuders, and exposing the residual particles in a flow cell to near-ultraviolet (λ>300 nm) radiation, we find that condensed-phase photochemistry can induce significant changes in SOA particle size and chemical composition. The particle-bound organic peroxides, which are highly abundant in α-pinene ozonolysis SOA (22 ± 5% by weight), have an atmospheric photolysis lifetime of about 6 days at a 24-h average solar zenith angle (SZA) of 65° experienced at 34° latitude (Los Angeles) in the summer. In addition, the particle diameter shrinks 0.56% per day under these irradiation conditions as a result of the loss of volatile photolysis products. Experiments with and without the denuders show similar results, suggesting that condensed-phase processes dominate over heterogeneous reactions of particles with organic vapors, excess ozone, and gas-phase free radicals. These condensed-phase photochemical processes occur on atmospherically relevant time scales and should be considered when modeling the evolution of organic aerosol in the atmosphere.

Toxic effect of different ZnO particles on mouse alveolar macrophages

To study the toxicity mechanism of ZnO nanoparticles on mouse macrophages, the toxic effect of different ZnO nanoparticles on mouse alveolar macrophages (MH-S) was investigated in this study. The results showed that the 24h IC(50) of four ZnO particles were 48.53, 47.37, 45.43 and 26.74 μg/ml for bulk ZnO, 100 nm, 30 nm and 10-30 nm ZnO particles, respectively. At the concentration of 10 μg/ml and below, dissolved zinc ions induced metallothionein synthesis, enhanced cellular resistance to oxidative stress. ZnO particles mainly induced cell apoptosis. When the concentration of ZnO particles was 20 μg/ml and above, excessive zinc destroyed mitochondrial function and cell membrane, caused cell necrosis. Dissolved zinc ions first cause toxicity in MH-S cells. However, the toxic effect of dissolved zinc ions may exist a threshold on mouse macrophages, inducing about 50% cell death. The toxic difference of different ZnO particles mainly depended on the effect of nondissolved ZnO particles.

Effects of ischemic acute kidney injury on lung water balance: nephrogenic pulmonary edema?

Pulmonary edema worsens the morbidity and increases the mortality of critically ill patients. Mechanistically, edema formation in the lung is a result of net flow across the alveolar capillary membrane, dependent on the relationship of hydrostatic and oncotic pressures. Traditionally, the contribution of acute kidney injury (AKI) to the formation of pulmonary edema has been attributed to bulk fluid accumulation, increasing capillary hydrostatic pressure and the gradient favoring net flow into the alveolar spaces. Recent research has revealed more subtle, and distant, effects of AKI. In this review we discuss the concept of nephrogenic pulmonary edema. Pro-inflammatory gene upregulation, chemokine over-expression, altered biochemical channel function, and apoptotic dysregulation manifest in the lung are now understood as “extra-renal” and pulmonary effects of AKI. AKI should be counted as a disease process that alters the endothelial integrity of the alveolar capillary barrier and has the potential to overpower the ability of the lung to regulate fluid balance. Nephrogenic pulmonary edema, therefore, is the net effect of fluid accumulation in the lung as a result of both the macroscopic and microscopic effects of AKI.

SOLUBLE AND INSOLUBLE AIR PARTICLE FRACTIONS INDUCE DIFFERENTIAL PRODUCTION OF TUMOR NECROSIS FACTOR α IN RAT LUNG

Altered cytokine production in the lung follows the deposition of urban air particles. The present study was designed to measure changes in tumor necrosis factoralpha (TNFalpha) and endothelin-1 (ET-1) levels in rat lung after instilling various fractions of the dust EHC-93, while in vitro, alveolar macrophages (AMs) and type 2 epithelial cells were studied to determine relative production of these molecules in response to the same particles. Whole dust and its soluble and leached components were instilled into rat lung and the animals were killed at intervals to 2 weeks; they received tritiated thymidine by intraperitoneal injection 1 hour before death. All samples induced some inflammation, with the highest cellular efflux being found by bronchoalveolar lavage 1 day after leached particles. Lung injury, illustrated by protein levels in lavage fluid, was maximal after instilling the soluble fraction and subsequently epithelial regeneration was also maximal in this group. TNFalpha levels were highest after instilling whole dust or its leached fraction at 4 hours and 1 day, and cell culture studies indicated a predominant AM source for this cytokine. ET-1 levels were also increased in BAL from 4 hours to 3 days and were mostly associated with the instillation of leached particles. The results demonstrate that the rapid production/release of TNFalpha and ET-1 after particle deposition is largely due to the insoluble particulate fraction. There appears to be a differential response to whole dust where the soluble components cause some inflammation and epithelial cell necrosis, whereas the leached particles are more likely to react with macrophages to induce the production of proinflammatory cytokines such as TNFalpha.

Hydrogen peroxide induces the production of tumor necrosis factor-alpha in RAW 264.7 macrophage cells via activation of p38 and stress-activated protein kinase

The effect of hydrogen peroxide (H(2)O(2)) on production of tumor necrosis factor (TNF)-alpha was examined in RAW 264.7 murine macrophage cells. H(2)O( 2) led to production of TNF-alpha up to 24 h after the treatment, but not nitric oxide in RAW 264.7 cells. H(2)O(2) induced TNF-alpha production in mouse peritoneal macrophages as well as RAW 264.7 cells. The H(2)O(2)induced TNF-alpha production was prevented by inhibitors of p38 and stress-activated protein kinase (SAPK/JNK), and H(2)O( 2) induced the phosphorylation of p38 and SAPK. Further, H(2)O( 2) significantly augmented the AP-1 activity, but not nuclear factor (NF)-kappaB activity in RAW 264.7 cells. A high level of intracellular reactive oxygen radicals (ROS) was detected in H(2)O(2)-exposed RAW 264.7 cells. Ebselen, a cell permeable antioxidant, prevented the H( 2)O(2)-induced TNFalpha production. H(2)O(2) significantly enhanced lipopolysaccharide (LPS)-induced TNF-alpha production. Therefore, H( 2) O(2) was suggested to induce TNF-alpha production in macrophages via activating p38 and SAPK/JNK as oxidative stress-related signal pathways.

Evidence of Health Impacts of Sulfate-and Nitrate-Containing Particles in Ambient Air

Ambient particulate matter (PM) is a complex mixture of inorganic and organic compounds. The U.S. Environmental Protection Agency (EPA) regulates PM as a criteria pollutant and promulgates National Ambient Air Quality Standards for it. The PM indicator is based on mass concentration, unspecified as to chemical composition, for specific size fractions. The numerical standards are based on epidemiologic evidence of associations between the various size-related particle mass concentrations as indicators and excess mortality and cardiorespiratory health effects as endpoints. The U.S. National Research Council has stated that more research is needed to differentiate the apparent health effects associated with different particle chemical constituents. Sulfate and nitrate constitute a significant portion of the particle mass in the atmosphere, but are accompanied by similar amounts of carbonaceous material, along with low concentrations of various species, including bioactive organic compounds and redox cycling metals. Extensive animal and human toxicology data show no significant effects for particles consisting only of sulfate and nitrate compounds at levels in excess of ambient air concentrations. A few epidemiologic studies, including both short-term time-series studies and long-term cohort studies, have included the sulfate content of PM as a specific variable in health effect analyses. There are much less data for nitrate. The results from the epidemiologic studies with PM sulfate are inconsistent. A detailed analysis of the time-series epidemiological studies shows that PM sulfate has a weaker "risk factor" than PM2.5 for health effects. Since sulfate is correlated with PM2.5, this result is inconsistent with sulfate having a strong health influence. However, there are many limitations with these types of studies that warrant caution for any comparison between a chemical component and mass concentration. In total, the epidemiologic and toxicologic evidence provide little or no support for a causal association of PM sulfate and health risk at ambient concentrations. For nitrate-containing PM, virtually no epidemiological data exist. Limited toxicological evidence does not support a causal association between particulate nitrate compounds and excess health risks. There are some possible indirect processes through which sulfate and nitrate in PM may affect health-related endpoints, including interactions with certain metal species and a linkage with production of secondary organic matter. There is insufficient evidence to include or exclude these processes as being potentially important to PM-associated health risk.

Decreased lung function after inhalation of ultrafine and fine particulate matter during exercise is related to decreased total nitrate in exhaled breath condensate

This study was designed to investigate PM(1) inhalation during exercise on lung function, exhaled nitric oxide (eNO), and total nitrate (NO3), S-nitrosoglutathione (GSNO), and malondialdehyde (MDA) in exhaled breath condensate (EBC). Inhalation of combustion-derived PM is associated with adverse respiratory health. A mechanistic action of PM on lung function is not defined; however, nitrosative/oxidative stress is likely. Prior to and after two 30-min exercise bouts 4-5 days apart, inhaling low (7382 +/- 1727 particles cm(- 3)) or high (252,290 +/- 77,529 particles cm(- 3)) PM(1), 12 nonasthmatic males performed spirometry and eNO and EBC collection. Normal resting lung function did not change after low PM(1) exercise. After high PM(1) exercise, FEV(1) and FEF(25-75) fell significantly (p = .0005, p = .002) and was related to [PM(1)] (r = -.55, p = .005 and r =-.61, p = .002; respectively); 11- and 52-ml decreases were calculated for each 20,000 particles cm(- 3) increase for FEV and FEF(25-75). NO3 did not change after low PM(1) exercise (30.5% increase), but significantly decreased by 43.8% after high PM(1) exercise, and correlated with lung function changes (r = .63, and r = .54 for FEV(1) and FEF(25-75), respectively; p = .001 and p = .007). No change in GSNO was observed. Alveolar NO decreased after high PM(1) conditions (p = .02); eNO pre-to-post difference was related to changes in FEV(1) (r = .60, p = .002). MDA increased 40% after low PM exercise (NS) and increased 208% after high PM exercise (p = .06). Thus, high PM(1) inhalation during exercise caused a reduced alveolar contribution to eNO; NO3 and eNO variables were decreased and were related to impaired lung function. Decreased NO(3) and eNO may be due to superoxide/NO formation of peroxynitrite, resulting in lipid peroxidation.

Pulmonary effects of inhaled limonene ozone reaction products in elderly rats

d-Limonene is an unsaturated volatile organic chemical found in cleaning products, air fresheners and soaps. It is oxidized by ozone to secondary organic aerosols consisting of aldehydes, acids, oxidants and fine and ultra fine particles. The lung irritant effects of these limonene ozone reaction products (LOP) were investigated. Female F344 rats (2- and 18-month-old) were exposed for 3 h to air or LOP formed by reacting 6 ppm d-limonene and 0.8 ppm ozone. BAL fluid, lung tissue and cells were analyzed 0 h and 20 h later. Inhalation of LOP increased TNF-alpha, cyclooxygenase-2, and superoxide dismutase in alveolar macrophages (AM) and Type II cells. Responses of older animals were attenuated when compared to younger animals. LOP also decreased p38 MAP kinase in AM from both younger and older animals. In contrast, while LOP increased p44/42 MAP kinase in AM from younger rats, expression decreased in AM and Type II cells from older animals. NF-kappaB and C/EBP activity also increased in AM from younger animals following LOP exposure but decreased or was unaffected in Type II cells. Whereas in younger animals LOP caused endothelial cell hypertrophy, perivascular and pleural edema and thickening of alveolar septal walls, in lungs from older animals, patchy accumulation of fluid within septal walls in alveolar sacs and subtle pleural edema were noted. LOP are pulmonary irritants inducing distinct inflammatory responses in younger and older animals. This may contribute to the differential sensitivity of these populations to pulmonary irritants.

Chemical and physical properties of ultrafine diesel exhaust particles sampled downstream of a catalytic trap

The chemical and physical properties of exhaust particles produced by a Caterpillar 3176 C-12 heavy duty diesel engine equipped with a catalytic trap (CRT) are reported. The engine was operated at 600 Nm and 1500 rpm, using fuels containing 15 and 49 ppm sulfur. A two-stage dilution tunnel designed to simulate the reactions that occur when hot combustion products mix with cooler atmospheric air was used. Particle size distributions were measured using a scanning mobility particle sizer (SMPS) and nano-scanning mobility particle sizer (nano SMPS); a nanomicro-orifice uniform deposit impactor (nano MOUDI) collected size-resolved samples for gravimetric and chemical analysis. A nanometer tandem differential mobility analyzer (nano TDMA) was used to measure the volatility and hygroscopicity of 4-15 nm particles. These measurements confirm that the particles consisted primarily of sulfates.

Exceeding of Henry's law by hydrogen peroxide associated with urban aerosols

Simultaneous measurements of gas- and aerosol-phase hydrogen peroxide (H2O2) have been made at two sites in Los Angeles, one near the Pacific coast at the University of California at Los Angeles (UCLA), and the other in downtown Los Angeles with close proximity to a heavily traveled freeway (freeway site). At both the freeway and UCLA sites, gas-phase H2O2 levels were similar, averaging 1.17 +/- 1.0 and 1.05 +/- 0.6 ppb, respectively. The particle-associated H2O2 in both fine (PM2.5) and coarse (>PM2.5) modes was higher at the freeway site, as compared to UCLA, by a factor of 2. However, when aerosol-phase H2O2 is normalized to particle mass loadings, the fine-mode H2O2 levels are very similar at the two sites: 0.42 +/- 0.3 and 0.58 +/- 0.3 ng H2O2/microg particle mass at the freeway and UCLA sites, respectively. The normalized coarse-mode H2O2 levels were significantly higher at the freeway site than at UCLA, 1.05 +/- 0.3 and 0.51 +/- 0.3 ng/microg, respectively. Estimating aerosol liquid water content on the basis of relative humidity and aerosol mass, a calculated equivalent H2O2 in aerosol liquid water averages 70 mM, more than 2 orders of magnitude higher than concentrations predicted by gas-particle partitioning (Henry's law), which averages 0.1 mM. This indicates that the sampled particles are capable of generating H2O2 in aqueous solution. These corresponding aqueous-phase H2O2 concentrations in aerosol liquid water exceed levels that have been observed to produce cellular damage to lung epithelial cells in laboratory experiments by at least 3 orders of magnitude. Although most measurements of H2O2 in particles were made using an extraction solution adjusted to pH 3.5, a set of measurements indicates that H2O2 from fine-mode particles extracted in the physiologically relevant pH range 5-7.5 also generate H2O2 with only slightly lowered efficiency; coarse-mode H2O2 production dropped by 75% at the upper end of this range. Finally, a small set of measurements was performed to investigate the degree to which the recently developed Versatile Aerosol Concentrator Enrichment System (VACES) affects H2O2 levels in concentrated ambient aerosols. The VACES appeared to a have minimal impact on particulate H2O2.

Aerosol-borne quinones and reactive oxygen species generation by particulate matter extracts

The mass loadings of quinones and their ability to generate reactive oxygen species (ROS) were investigated in total suspended particulate samples collected in Fresno, CA, over a 12-month period. Particles were collected on Teflon filters and were analyzed for the presence of 12 quinones containing one to four aromatic rings by gas chromatography with mass spectrometry. Measured levels are generally greater than mass loadings reported at other locations. The mass loadings were highest during winter months and were strongly anticorrelated with temperature. ROS generation was investigated by measuring the rate of hydrogen peroxide production from the reaction of laboratory standards and ambient samples with dithiothreitol (DTT). ROS generation from ambient samples shows a strong positive correlation with the mass loadings of the three most reactive quinones and may account for all of the ROS formed in the DTT test.

Response of intestinal cells and macrophages to an orally administered cellulose-PEG based polymer as a potential treatment for intractable edemas

The elimination of water from the body represents a fundamental therapeutic goal in those diseases in which oedemas occur. Aim of this work is the design of a material able to absorb large amount of water to be used, by oral administration, in those cases in which resistance to diuretics appears. Sorption and mechanical properties of the cellulose based superabsorbent hydrogel acting as a water elimination system have been modulated through the insertion of molecular spacers between the crosslinks. Starting polymers are the sodium salt of carboxymethylcellulose (CMCNa), a polyelectrolyte cellulose derivative, and the hydroxyethylcellulose (HEC), a non-polyelectrolyte derivative. Polyethyleneglycol (PEG) with various molecular weights, has been linked by its free ends at two divinylsulfone (DVS) crosslinker molecules, in order to increase the average distance between two crosslinking sites and thus acting as spacer. Both the effect of concentration and molecular weight of the spacer resulted to significantly affect the hydrogel final sorption properties and thus the efficiency of the body water elimination system. Biocompatibility studies have been performed to test the hydrogel compatibility with respect to intestinal and macrophages cell lines. To investigate the effects of intestinal cells conditioned media after the contact with the gel on macrophages nitric oxide release tests have been carried out.

Association between particulate matter and emergency room visits, hospital admissions and mortality in Spokane, Washington

There is conflicting evidence regarding the association between different size fractions of particulate matter (PM) and cardiac and respiratory morbidity and mortality. We investigated the short-term associations of four size fractions of particulate matter (PM(1), PM(2.5), PM(10), and PM(10-2.5)) and carbon monoxide with hospital admissions and emergency room (ER) visits for respiratory and cardiac conditions and mortality in Spokane, Washington. We used a log-linear generalized linear model to compare daily averages of PM and carbon monoxide with daily counts of the morbidity and mortality outcomes from January 1995 to June 2001. We examined pollution lags ranging from 0 to 3 days and compared our results to a similar log-linear generalized additive model. Effect estimates tended to be smaller and have larger standard errors for the generalized linear model. Overall, we saw no association with respiratory ER visits and any size fraction of PM. However, there was a suggestion of greater respiratory effect from fine PM when compared to coarse fraction. Carbon monoxide was associated with both all respiratory ER visits and visits for asthma at the 3-day lag. We feel that carbon monoxide may be serving as a marker for combustion-derived pollutants, which is one large component of the diverse air pollutant mixture. We also found no association with any size fraction of PM or CO with cardiac hospital admissions or mortality at the 0- to 3-day lag. We found no consistent associations between any size fraction of PM and cardiac or respiratory ER visits or hospital admissions.

Nitric oxide mitigates peroxide-induced iron-signaling, oxidative damage, and apoptosis in endothelial cells: role of proteasomal function?

In this mini-review, oxidant-induced transferrin receptor-mediated iron-signaling and apoptosis are described in endothelial and neuronal cells exposed to a variety of oxidative stresses. The role of nitric oxide and nitration in the regulation of iron homeostasis and oxidant-induced apoptosis is described. The interrelationship between oxidative stress, iron-signaling, and nitric oxide-dependent proteasomal function provides a rational mechanism that connects both oxidative and nitrative modifications.

Multiple pathways of peroxynitrite cytotoxicity

Peroxynitrite is a reactive oxidant produced from nitric oxide (NO) and superoxide, which reacts with a variety of biomolecules including proteins, lipids and DNA. Peroxynitrite is produced by the body in response to a variety of toxicologically relevant molecules including environmental toxins. It is also produced by the body in response to environmental toxins, as well as in reperfusion injury and inflammation. Here we overview the multiple pathways of peroxynitrite cytotoxicity. Initiation of lipid peroxidation, direct inhibition of mitochondrial respiratory chain enzymes, inactivation of glyceraldehyde-3-phosphate dehydrogenase, inhibition of membrane Na(+)/K(+) ATP-ase activity, inactivation of membrane sodium channels, and other oxidative protein modifications contribute to the cytotoxic effect of peroxynitrite. In addition, peroxynitrite is a potent trigger of DNA strand breakage, with subsequent activation of the nuclear enzyme poly-ADP ribosyl synthetase or polymerase (PARP), with eventual severe energy depletion and necrosis of the cells. Studies conducted with peroxynitrite decomposition catalysts suggest that neutralization of peroxynitrite is of significant therapeutic benefit after exposure to various environmental toxins as well as in a variety of inflammatory and reperfusion disease conditions.

Induction of cyclooxygenase-2 by heat shock protein 60 in macrophages and endothelial cells

The 60-kDa heat shock protein (HSP60), an endogenous ligand for the toll-like 4 receptor, is generated in response to inflammation, tissue injury, and/or stress and stimulates macrophages to produce cytotoxic and proinflammatory mediators including nitric oxide, tumor necrosis factor (TNF)-alpha, interleukin (IL)-6, and IL-12. In the present studies we report that HSP60 is an effective inducer of cyclooxygenase-2 (COX-2) in macrophages, as well as endothelial cells. In both cell types, the synthesis of COX-2 was coordinate with induction of nitric oxide synthase (NOS)-2 and with nitric oxide production. With the use of promoter constructs in transient transfection assays, optimal expression of COX-2 in macrophages was found to require nuclear factor (NF)-kappaB, the cAMP-response element (CRE), and NF-IL-6, but not the E-box. Mobility shift assays revealed that HSP60 induced NF-kappaB and CRE binding activity, while CCAAT/enhancer binding protein (C/EBP), which binds to NF-IL-6, was constitutively active in the cells. Both c-Jun and CRE binding protein (CREB) bound to the CRE, while C/EBP-beta bound to NF-IL-6. These data indicate that NF-kappaB, C/EBP-beta, c-Jun, and CREB are important in HSP60-induced expression of COX-2. The c-Jun-NH(2)-terminal kinase (JNK), p44/42 mitogen-activated protein (MAP) kinase [extracellular signal-regulated kinase 1/2 (ERK1/2)], and p38 MAP kinase were rapidly activated by HSP60 in the macrophages. PD-98059, an inhibitor of phosphorylation of ERK1/2, caused a marked inhibition of HSP60-induced COX-2 and NOS-2 expression. Unexpectedly, SB-203580, a p38 kinase antagonist, was found to block HSP60-induced expression of COX-2, but not NOS-2. These data indicate that both ERK1/2 kinase and p38 kinase play a role in regulating HSP60-induced expression of COX-2.

Indoor hydrogen peroxide derived from ozone/d-limonene reactions

In this pilot study, performed in an office manipulated to resemble an environment with a strong indoor ozone source or a significant influx of outdoor air during a smog event, reactions between ozone and d-limonene produced hydroperoxides. Hydrogen peroxide (H202) presumably constituted the majority of the measured hydroperoxides, although a small amount of organic hydroperoxides (ROOH) may have contributed to the signal. Total hydroperoxides were 1.0-1.5 ppb at low air exchange rates (0.5-4 h(-1)) and 0.6-0.8 ppb at high air exchange rates (12-18 h-1). The net estimated yield ranged from 1.5 to 3.2%, consistent with values reported in the literature. Based on these yields and typical indoor scenarios, peak indoor concentrations of H202 are projected to be comparable with, but not significantly larger than, peak outdoor concentrations. Hygroscopic secondary organic aerosols (SOA; 10-100 microg m(-3)) were simultaneously generated by the ozone/d-limonene reactions; their co-occurrence with H202 provides a mechanism whereby H2O2 can be transported into the lower respiratory tract. The results demonstrate that reduced air exchange rates lead to increased concentrations of H2O2 and SOA as well as a shift in the size-distribution toward larger particles (0.3-0.7 microm diameter), potentially increasing the amount of H2O2 delivered to the lower respiratory region. This study increases our understanding of H2O2 exposures, including exposures to H2O2 associated with co-occurring hygroscopic aerosols. It also re-emphasizes the potential of ozone-driven chemistry to alter indoor environments, often producing products more irritating than their precursors.