Generation Of Active Oxygen Species Research Articles

Some biochemical reactions of strawberry plants to infection with Botrytis cinerea and salicylic acid treatment

The reactions of strawberry plants to infection with <i>B. cinerea</i> and treatment with salicylic acid has been studied. Infection of leaves with <i>B. cinerea</i> resulted in early increases in active oxygen species generation, superoxide dismutase and peroxidase activities and phenolic compounds content. Some increases of the above reactions were noticed in plants treated with salicylic acid but not in the plants treated with SA and then later infected with <i>B. cinerea</i>.

Ameliorated Effect of Shading Treatment in Strong Light Period on Senescence and Photosynthesis in Cucumber ^|^lsquo;Jinchun No. 5^|^rsquo; Seedlings

To gain a physiological understanding of the effects of light intensity on the cucumber (Cucumis sativus L.), we subjected ‘Jinchun No. 5’ seedlings to shading treatment in three plots with light transmission of 100% (unshaded), 80%, and 60% in strong light periods for 45 days, and examined active oxygen species, senescence indicators and photosynthetic properties on the 15th, 30th, and 45th days of shading treatment respectively. The amounts of active oxygen species superoxide anions and hydrogen peroxide in leaves fell with decreasing light intensity on each of the 15th, 30th, and 45th days of shading treatment respectively. The amounts of chlorophyll and protein also decreased and that of malondialdehyde increased — all indicators of senescence — with decreasing light intensity on each of the 15th, 30th, and 45th days of shading treatment respectively. The photosynthetic property stomatal conductance in the 80% and 60% transmission plots exceeded that in the 100% transmission plot on the 15th and 30th days of shading treatment. No significant difference was seen in sub-stomatal CO2 concentration between all three light transmission plots. Both transpiration and net photosynthesis rates rose with decreasing light intensity. These results suggest that the shading treatment during strong light periods may suppress the generation and accumulation of active oxygen species, inhibit senescence and also ameliorate photosynthesis in cucumber ‘Jinchun No. 5’ seedlings.

The influence of glucose on the free radical peroxidation of low density lipoproteins in vitro and in vivo

It was shown that glucose in concentration 12.5-100 mM stimulated of Cu(2+)-mediated free radical peroxidation of low density lipoproteins (LDL) from human blood plasma. On the base investigation of kinetic parameters of LDL peroxidation it was stated that intensification of this process in the conditions of our experiments is caused by formation of free radical intermediates of glucose autoxidation during active oxygen species generation in the presence of metal ions with variable valence. It was found that glucose level normalization in the blood of patients with type 2 diabetes during therapy accompanied by significant decreasing of LDL oxidizing. During therapy with sugar-lowering drug metformin which utilizate methylglyoxal the LDL peroxidation from blood diabetes mellitus in vivo inhibited in more higher degree probably in consequence of decreasing of methylglyoxal-dependent generation of superoxide anion radicals as was shown by us early [Biochemistry (Moscow), 2007, 72: 1081-1090; Biochemistry (Moscow), 20(09, 74: 461-466].

The antioxidative activity of oral hypoglycemic agents

Oral hypoglycemic agents, such as glibenclamide, gliclazide, metformin, rosiglitazone maleate, and diabenol, are known to exert in vitro a mild direct antioxidatove action. Rosiglitazone maleate showed moderate activity only on the hemiluminescence model with generation of active oxygen species while diabenol behaves as a scavenger of superoxide anion and hydroxyl radical in model hemiluminescence systems. Gliclazide exhibited dose-dependent activity only with respect to stable diphenyl-1-picrylhydrazyl (DPPG) radicals. Metformin and glibenclamide were inactive under in vitro conditions. It is hypothesized that the antioxidative action of hypoglycemic agents used for long-term pharmacotherapy should be attributed to their direct effect on the activity of enzymes of the antioxdative system.

Morphological, physiological and biochemical responses of plants to drought stress

Plants in nature are continuously exposed to several biotic and abiotic stresses. Among these stresses, drought stress is one of the most adverse factors of plant growth and productivity and considered a severe threat for sustainable crop production in the conditions on changing climate. Drought triggers a wide variety of plant responses, ranging from cellular metabolism to changes in growth rates and crop yields. Understanding the biochemical and molecular responses to drought is essential for a holistic perception of plant resistance mechanisms to water-limited conditions. This review describes some aspects of drought induced changes in morphological, physiological and biochemical changes in plants. Drought stress progressively decreases CO2 assimilation rates due to reduced stomatal conductance. It reduces leaf size, stems extension and root proliferation, disturbs plant water relations and reduces water-use efficiency. It disrupts photosynthetic pigments and reduces the gas exchange leading to a reduction in plant growth and productivity. The critical roles of osmolyte accumulation under drought stress conditions have been actively researched to understand the tolerance of plants to dehydration. In addition, drought stress-induced generation of active oxygen species is well recognized at the cellular level and is tightly controlled at both the production and consumption levels, through increased antioxidative systems. This review focuses on the ability and strategies of higher plants to respond and adapt to drought stress. Key words: Drought stress, growth, yield, gas exchange, photosynthetic pigments, antioxidative system.

Efficient and selective formation of methanol from methane in a fuel cell-type reactor

Direct oxidation of methane to methanol at low temperatures was investigated using a fuel cell-type reactor, where a mixture of methane and H 2O vapor was supplied to the anode and air to the cathode. Methanol was scarcely produced over a Pt/C anode from 50 to 250 °C. However, through trial and error, the production of methanol over a V 2O 5/SnO 2 anode was significant at 100 °C; the current efficiency for methanol production and the selectivity toward methanol were as high as 61.4% and 88.4%, respectively. Methanol was produced by the reaction of methane with an active oxygen species over the V 2O 5 catalyst. Cyclic voltammetry of the anode indicated that the generation of such active oxygen species was strongly dependent on the anode potential. Moreover, X-ray diffraction, transmission electron microscopy, and X-ray photoelectron spectroscopy measurements confirmed that highly dispersed and partially reduced vanadium species were present on the SnO 2 surface. These vanadium species are considered to be active sites for the formation of the active oxygen species, probably anion radicals ( O 2 - and O −).

Effects of Dalargin on Free Radical Processes in the Blood of Rats Exposed to Moderate Hypothermia

Moderate hypothermia stimulates LPO processes in rat plasma and erythrocytes and simultaneously increases antioxidant activity in the plasma and SOD activity erythrocyte. Dalargin prevents stimulation of LPO in the blood in hypothermia by reducing the generation of active oxygen species and maintaining the level of low-molecular antioxidants.

Neutrophils exhibit distinct phenotypes toward chitosans with different degrees of deacetylation: implications for cartilage repair

IntroductionOsteoarthritis is characterized by the progressive destruction of cartilage in the articular joints. Novel therapies that promote resurfacing of exposed bone in focal areas are of interest in osteoarthritis because they may delay the progression of this disabling disease in patients who develop focal lesions. Recently, the addition of 80% deacetylated chitosan to cartilage microfractures was shown to promote the regeneration of hyaline cartilage. The molecular mechanisms by which chitosan promotes cartilage regeneration remain unknown. Because neutrophils are transiently recruited to the microfracture site, the effect of 80% deacetylated chitosan on the function of neutrophils was investigated. Most studies on neutrophils use preparations of chitosan with an uncertain degree of deacetylation. For therapeutic purposes, it is of interest to determine whether the degree of deacetylation influences the response of neutrophils to chitosan. The effect of 95% deacetylated chitosan on the function of neutrophils was therefore also investigated and compared with that of 80% deacetylated chitosan.MethodsHuman blood neutrophils from healthy donors were isolated by centrifugation on Ficoll-Paque. Chemotaxis was performed using the chemoTX system. Production of superoxide anions was evaluated using the cytochrome c reduction assay. Degranulation was determined by evaluating the release of myeloperoxidase and lactoferrin. The internalization of fluorescently labelled 80% deacetylated chitosan by neutrophils was studied by confocal microscopy.ResultsNeutrophils were dose dependently attracted to 80% deacetylated chitosan. In contrast, 95% deacetylated chitosan was not chemotactic for neutrophils. Moreover, the majority of the chemotactic effect of 80% deacetylated chitosan was mediated by phospholipase-A2-derived bioactive lipids. Contrary to the induction of chemotaxis, neither 80% nor 95% deacetylated chitosan activated the release of granule enzymes or the generation of active oxygen species. Despite the distinct response of neutrophils toward 80% and 95% deacetylated chitosan, both chitosans were internalized by neutrophils.ConclusionsEighty per cent deacetylated chitosan induces a phenotype in neutrophils that is distinct from the classical phenotype induced by pro-inflammatory agents. Our observations also indicate that the degree of deacetylation is an important factor to consider in the use of chitosan as an accelerator of repair because neutrophils do not respond to 95% deacetylated chitosan.

Early Responses of Tobacco Suspension Cells to Rhizobacterial Elicitors of Induced Systemic Resistance

Colonization of roots by selected strains of fluorescent Pseudomonas spp. can trigger induced systemic resistance (ISR) against foliar pathogens in a plant species-specific manner. It has been suggested that early responses in cell suspension cultures in response to rhizobacterial elicitors, such as generation of active oxygen species (AOS) and extracellular medium alkalinization (MA), are linked to the development of ISR in whole plants. Perception of flagellin was demonstrated to elicit ISR in Arabidopsis, and bacterial lipopolysaccharides (LPS) have been shown to elicit several defense responses and to act as bacterial determinants of ISR in various plant species. In the present study, the LPS-containing cell walls, the pyoverdine siderophores, and the flagella of Pseudomonas putida WCS358, P. fluorescens WCS374, and P. fluorescens WCS417, which are all known to act as elicitors of ISR in selected plant species, were tested for their effects on the production of AOS, MA, elevation of cytoplasmic Ca(2+) ([Ca(2+)](cyt)), and defense-related gene expression in tobacco suspension cells. The LPS of all three strains, the siderophore of WCS374, and the flagella of WCS358 induced a single, transient, early burst of AOS, whereas the siderophores of WCS358 and WCS417 and the flagella of WCS374 and WCS417 did not. None of the compounds caused cell death. Once stimulated by the active compounds, the cells became refractory to further stimulation by any of the active elicitors, but not to the elicitor cryptogein from the oomycete Phytophthora cryptogea, indicating that signaling upon perception of the different rhizobacterial compounds rapidly converges into a common response pathway. Of all compounds tested, only the siderophores of WCS358 and WCS417 did not induce MA; the flagella of WCS374 and WCS417, although not active as elicitors of AOS, did induce MA. These results were corroborated by using preparations from relevant bacterial mutants. The active rhizobacterial elicitors led to a rapid increase in [Ca(2+)](cyt), peaking at 6 min, whereas the inactive siderophores of WCS358 and WCS417 elicited a single spike at 1 min. Elicitation of the cells by cell-wall LPS of WCS358 or the siderophore of WCS374 induced a weak, transient expression of several defense-related genes, including PAL and GST. The spectrum of early responses of the suspension cells was not matched by the expression of ISR in whole tobacco plants against Erwinia carotovora pv. carotovora. Of the live bacterial strains, only WCS358 elicited significant ISR, but application of the LPS or the siderophore of all three strains also elicited ISR. Notably, the absence of elicitation of AOS and MA in suspension-cultured cells but induction of ISR in whole plants by the siderophore of WCS358, which was lost upon treatment with the siderophore-minus mutant of WCS358, indicates that the early responses in suspension cells are not predictive of the ability to induce ISR in whole plants. Possible explanations for these discrepancies are discussed.

One-step synthesis of nanostructured Pd-doped mixed oxides MOx-CeO2 (M = Mn, Fe, Co, Ni, Cu) for efficient CO and C3H8 total oxidation

A series of nanostructured Pd-doped mixed oxides MOx-CeO2 (M=Mn, Fe, Co, Ni, Cu), with uniform mesoporous structure and large surface area exceeding 115m2g−1, were synthesized in one step by a surfactant-assisted co-precipitation. Their catalytic performance was investigated using total oxidation of CO and C3H8 as the model reactions. The results show that, a synergism exists between even trace amounts of exposed Pd and 3d-transition metal oxides for CO oxidation, whereas such an effect is absent for C3H8 oxidation. In situ diffuse reflectance infrared spectroscopy (DRIFTS) study reveals that the synergistic essential for CO oxidation should be the interaction-assisted generation of active oxygen species between Pd and MOx, which react readily with CO, forming bidentate carbonate (1587 and 1285cm−1) as intermediates. Moreover, structural characterization results indicate that a solid solution is formed between CeO2 and Mn2O3 or Fe2O3, resulting in the very strong interaction between Pd and MOx, as well as the greatly improved CO oxidation. The light-off temperatures for Pd-doped Mn and Fe-containing catalysts, as compared with the Pd-free catalysts, are decreased by more than 70 and 100°C, respectively. In particular, a CO conversion as high as 80% can be achieved even at room temperature on Pd-doped Mn-containing catalyst. While for C3H8 oxidation, the C–H bond activation, but not the oxygen activation, plays a crucial role. The C–H bond activation ability of the catalysts is largely determined by the d-electron configurations of the M cations. A ‘double-peak’ phenomenon can be derived with the increase of d-electron number.

Evaluation of the role of fMLF chemotaxic peptide receptors in umbilical cord blood granulocytes from newborns at risk of infectious inflammatory diseases

We studied the role of receptors with high and low affinity for fMLF chemotaxic peptide in the generation of active oxygen species by umbilical cord blood granulocytes from newborns with normal neonatal period, born after normal or complicated gestation, in children with manifestations of bacterial infection born after complicated pregnancy, and in granulocytes of non-pregnant women with normal reproductive function. Granulocytes of children born after complicated pregnancy exhibited high reactivity in induction of respiratory burst in a wide range of fMLF concentrations. The presentation of receptors with high and low affinity on granulocytes during initiation of the respiratory burst differs in children born after complicated pregnancy and in healthy babies born after normal gestation. Presumably, the detected differences result from high expression of receptors with low affinity for fMLF and disorders or immaturity of mechanisms responsible for receptor inactivation.

Neural networks modeling signal responses and taxol production of cultured Taxus chinensis cells induced by bio-elicitor

Quantitatively describing the signal transduction process is important for understanding the mechanism of signal regulation in cells, and thus, poses both a challenge and an opportunity for chemical and biochemical engineers. An artificial neural network (ANN), in which we took the signal molecules as neural nodes, was constructed to simulate the generation of active oxygen species (AOS) in Taxus chinensis cells induced by a bio-elicitor. The relative contents of AOS in cells predicted by the ANN model agreed well with the experimental data and three notable stages of AOS increase were observed from the 3D figure of AOS generation. The robustness of AOS trajectories indicated that signal regulation in vivo was an integral feedback control model that ensured the adaptation of Taxus chinensis to environmental stress. The artificial neural network was able to predict taxol production as well as determine the optimal concentration of oligosaccharides needed for it.

Study of Compounds Suppressing Free Radical Generation from UV-Exposed Ketoprofen

Ketoprofen [(RS)-2-(3-benzoylphenyl)propanoic acid] is widely used for the treatment of inflammatory diseases and musculoskeletal injury. However, there is concern regarding its potential for photosensitization as a side effect. Free radicals and active oxygen species generated from ketoprofen on exposure to ultraviolet (UV) light have been implicated in phototoxicity and photosensitization. In this study, we examined the suppressing ability of some compounds for the free radicals and active oxygen species generated by the photodynamic reaction of ketoprofen, to determine a new resist of photosensitization by ketoprofen. Eight compounds, including six known free radical scavengers were individually mixed with ketoprofen, and the mixtures were exposed to UV. Then, the free radicals and the active oxygen species were determined by the electron spin resonance spectrometry to estimate suppressing and scavenging ability of compounds. The compounds that show promise in suppressing superoxide anion generation from UV-exposed ketoprofen were further evaluated using the on-line photo-irradiated superoxide anion detection system. It was confirmed that quercetin, a flavonoid, strongly suppresses the generation of free radicals and active oxygen species from UV-exposed ketoprofen. The experiments using the experimental formulation of an adhesive skin patch of ketoprofen containing quercetine and the Chemiluminescence analyzer (CLA) indicated that quercetin has high potential for use as an excipient in ketoprofen ointments to suppress phototoxicity and photosensitization by ketoprofen.

Effect of glutaphen on generation of active oxygen species, photosynthetic electron transport, and the functional activity of photosystem 2 in Chlorella cells

Treatment of chlorella green algae (Chlorella sp.) for 2 h in the dark with the photodynamic herbicide glutaphen (GTP), consisting of 0.3 mM 1,10-phenanthroline and 0.6 mM glutamic acid, followed by illumination leads to efficient generation of active oxygen species (AOS). After 15 min of illumination, AOS accumulation reaches 200% compared with the level in cells of the control culture, then it decreases down to 130% and 115% after 1 day and 3 days of illumination. During the first few days after treatment, we observe inhibition of synthesis of a specific precursor of chlorophyll (Chl): 5-aminolevulinic acid molecules, and then we observe stimulation of the synthesis. The effect of GTP on the photosynthetic activity of chlorella does not depend on the AOS level but rather remains uniform, in contrast to its effect on the Chl biosynthesis system. GTP does not change the efficiency of light harvesting and charge separation at the reaction centers of photosystem (PS) 2, but significantly lowers the functional efficiency of the electron transport chain: the photochemical quenching constants for Chl a fluorescence and the effective quantum yield of photochemical reactions in photosystem 2 decrease. The major mechanism of action for GTP is probably displacement of the secondary quinone acceptor QB from its binding site on the D1 protein by the 1,10-phenanthroline, consequent inhibition of electron efflux from Q A − and increase in the fraction of QB-nonreducing centers of PS 2. The active oxygen species generated in the cells have a photodegradative effect on the Chl biosynthesis system, in particular on its initial steps, and do not involve already formed pigment-protein complexes of PS 2.

PLS versus zeolites as sorbents and catalysts: Part 9. An unexpected reaction of Al-PILC sorbed CCl 4 with benzene

Reactivity of CCl 4 on alumina-pillared clays (PILCs) has been exploited to investigate if benzene activation is possible under both static and dynamic conditions. PILC-encapsulated CCl 4 indeed reacts, giving chlorobenzene (PhCl) and biphenyl as main products (with benzoyl chloride as a side-product). Although overall yields are low (2–4%, calculated on starting benzene) they increase when a transition metal-containing pillar is present (e.g. FAZA, which has Fe 2+/Fe 3+-alumina pillars and activity comparable with the mid-pore zeolite ZSM-5). Yields increase further (e.g. PhCl > 5%) when the PILC is also cation-exchanged, as in Cu-FAZA. Trends in yields on changing reaction parameters show that the reaction giving PhCl occurs via a cation-intermediate, whereas biphenyl is formed via a free-radical mechanism. Finally, chlorohydroxybenzenes can be obtained in both mid-pore zeolites and PILCs, which is rationalised in terms of generation of active oxygen species at the Lewis acid sites. It is suggested that benzoyl chloride forms from interaction between in situ-generated COCl 2 and Lewis acid sites.

Influence of O 2 and H 2 on NO reduction by NH 3 over Ag/Al 2O 3: A transient isotopic approach

Mechanistic aspects of low-temperature (423–723 K) selective catalytic reduction of NO with NH 3 (NH 3-SCR) over an Ag(1.7 wt%)/Al 2O 3 (2Ag/Al 2O 3) catalyst in the presence and absence of O 2 and H 2 were studied using a transient low-pressure (peak pressure < 10 Pa) technique, the temporal analysis of products (TAP) reactor, in combination with isotopic traces. Preoxidized 2Ag/Al 2O 3 showed very low activity in the NH 3-SCR reaction. The activity increased tremendously after ex situ reduction of 2Ag/Al 2O 3 in a hydrogen flow (5 vol% H 2 in Ar) at 373 K for 30 min. This observation was related to the creation of reduced Ag species, which catalyze O 2 and NO dissociation, yielding adsorbed oxygen species. O 2 is a better supplier of oxygen species. Oxygen species played a key role in NH 3 dehydrogenation, yielding reactive NH x fragments that are important intermediates for nitrogen formation via a coupling reaction between NO and NH 3. This reaction pathway predominated over direct NO decomposition to N 2 in the presence of O 2. In addition to generation of active oxygen species, gas-phase oxygen accelerated transformation of surface N-containing intermediates into gas-phase reaction products. The role of hydrogen in the NH 3-SCR reaction is to transform oxidized Ag species into reduced species that are active sites for O 2 and NO adsorption. Our findings suggest that the reduction of oxidized Ag is responsible for the boosting effect of H 2 in the NH 3-SCR reaction, and also that H 2 helps decrease total N 2O production.

Effects of oxalate exposure on Madin-Darby canine kidney cells in culture: renal prothrombin fragment-1 mRNA expression

It has been suggested that renal tubular cell damage induced by oxalic acid, one of the components of urinary calculi, may be involved in a variety of ways in the development of urolithiasis. During our study on a calculus related protein, renal prothrombin fragment-1 (RPTF-1), we noted that this is an inflammation related substance that mediates an acute inflammatory reaction, one of the original roles of prothrombin. RPTF-1 is a part of prothrombin that is a coagulation factor known to be expressed in the renal tubule. We examined whether oxalic acid may cause cytotoxic effects on tubular epithelial cells and whether such chemical stimulation may promote the translation of RPTF-1 mRNA into RPTF-1 proteins. We used Madin-Darby canine kidney (MDCK) cells derived from the distal tubule of a dog kidney. In this study, the effects of oxalic acid in culture solution at different concentrations on cytotoxicity were assessed using a MTT assay. The location of active oxygen species was identified using dichlorofluorescein diacetate. After the prothrombin sequence of RPTF-1 was confirmed in MDCK cells, RPTF-1 mRNA expression was determined by RT-PCR. The gene sequence of the same promoter area was ligated, and a luciferase sequence was inserted downstream of the vector. The target sequence was transfected into MDCK cells and the relation between oxalic acid and prothrombin promoter was examined. In addition, the variable expression of RPTF-1 mRNA was quantitatively compared depending on oxalic acid concentrations using real-time PCR. When cytotoxicity was investigated, cells were not damaged but, by contrast, were stimulated and activated under oxalic acid below a certain concentration. The relation between cytotoxicity on the cultured MDCK cell membrane and active oxygen species was confirmed. Luminescence in MDCK cells containing the luciferase gene was detected by the addition of oxalic acid, which activated the prothrombin promoter. A part of the prothrombin gene sequence in the MDCK cells was detected and an increase in the expression of RPTF-1 mRNA in MDCK cells by the addition of oxalic acid was confirmed using real-time PCR. Increased expression of prothrombin by adding oxalic acid has already been demonstrated in previous studies. In this study, however, RPTF-1 mRNA was promoted by oxalic acid and a direct association between oxalic acid and RPTF-1 is indicated. This finding shows that increased oxalic acid in urine induces the expression of RPTF-1 in tubular epithelial cells and thereby causes the generation of active oxygen species.

Synthesis and Type I/Type II photosensitizing properties of a novel amphiphilic zinc phthalocyanine

A novel amphiphilic zinc phthalocyanine (ZnPcLTs) has been synthesized, which possesses good amphiphilicity, and low aggregation. The generation efficiency of singlet oxygen and other active oxygen species' trapping rate studies were studied by electron spin resonance (ESR) spectroscopy. The results indicated that the photosensitizer possessed a higher active oxygen species generation efficiency than that of hematoporphyrin. The results of photodamage experiments towards calf-thymus DNA indicated that ZnPcLTs is a promising photosensitizer candidate for photodynamic therapy.

Determination of free radicals generated from light exposed ketoprofen

Ketoprofen [(RS)-2-(3-benzoylphenyl)propanoic acid] has been widely used for the treatment of inflammatory diseases and musculoskeletal injury. However, there is concern over its phototoxicity and photosensitization potential as side effects. In the present study, we examined photodynamic action of ketoprofen, determined free radicals and active oxygen species generated from ketoprofen by photo-irradiation, which have been implicated as the phototoxicity and photosensitization. The generation of superoxide anion, hydroxyl radical and singlet oxygen were determined by electron spin resonance (ESR), chemiluminescence analyzer (CLA) and the on-line photo irradiated superoxide anion detection system, when ketoprofen was exposed by the ultraviolet lamp or the chemical lamp. The on-line light exposed superoxide anion detection system was developed to catch superoxide anions generated at an instant and estimate quantitatively risk of the light-sensitive disease of drugs. These radicals were maintained for 20 min at the ESR spectrum measurement using the spin trapping reagent, 5,5-dimethyl-1-pyrroline- N-oxide (DMPO), though these signals were declining gradually. The degradation products were analyzed to identify the chemical structures. The pathway of the photo degradation and generation of the active oxygen species was estimated by the experimental results obtained in this study.

Air pollution particles activate NF-κB on contact with airway epithelial cell surfaces

Air pollution particles (PM) are known to elicit an acute inflammatory response in vivo that is mediated in part through PM-induced activation of the NF-κB signaling pathway. Many of the details of this process and particularly where in the cell it occurs are unclear. To determine whether contact of PM particles with an epithelial cell surface activates NF-κB, rat tracheal explants were exposed to Ottawa Urban Air Particles or iron-loaded fine TiO 2, a model PM particle, for up to 2 h. During this period, there was no evidence of particle entry into the tracheal epithelial cells by light or electron microscopy, but both types of particle activated NF-κB as assayed by gel shifts. NF-κB activation could be inhibited by the active oxygen species scavenger, tetramethylthiourea; the redox-inactive metal chelator, deferoxamine; the Src inhibitor, PP2; and the epidermal growth factor (EGF) receptor inhibitor AG1478. An iron-containing citrate extract of both dusts also produced NF-κB activation. Both dusts and a citrate extract caused phosphorylation of the EGF receptor on tyrosine 845, an indicator of Src activity. We conclude that iron-containing PM particles can activate NF-κB via a pathway involving Src and the EGF receptor. This process does not require entry of particles into the airway epithelial cells but is dependent on the presence of iron and generation of active oxygen species by the dusts. These findings imply that even brief contact of PM with a pulmonary epithelial cell surface may produce deleterious effects in vivo.