Biomedical subjects

A J Ghio

Publications and source records attributed to A J Ghio.

At least 55 records · Page 3Linked to original sources

PubMed1999

Resistance of hypotransferrinemic mice to hyperoxia-induced lung injury.

Oxidative stress plays a central role in the pathogenesis of acute and chronic pulmonary diseases. Safe sequestration of iron, which participates in the formation of the hydroxyl radical, is crucial in the lung's defense. We used a mouse line defective in the major iron transport protein transferrin to investigate the effect of aberrant iron metabolism on the lung's defense against oxidative injury. The tolerance to hyperoxic lung injury was greater in the hypotransferrinemic than in wild-type mice as documented by histopathology and biochemical indexes for lung damage. There was no increase in the levels of intracellular antioxidants, inflammatory cytokines, and heme oxygenase-1 in the hypotransferrinemic mouse lung compared with those in wild-type mice. However, there were elevated expressions of ferritin and lactoferrin in the lung of hypotransferrinemic mice, especially in the alveolar macrophages. Our results suggest that pulmonary lactoferrin and ferritin protect animals against oxidative stress, most likely via their capacity to sequester iron, and that alveolar macrophages are the key participants in iron detoxification in the lower respiratory tract.

Animals↗

PubMed1999

Cellular and biochemical response of the human lung after intrapulmonary instillation of ferric oxide particles.

Bronchoalveolar lavage (BAL) was used to sample lung cells and biochemical components in the lung air spaces at various times from 1 to 91 d after intrapulmonary instillation of 2.6 microm-diameter iron oxide particles in human subjects. The instillation of particles induced transient acute inflammation during the first day post instillation (PI), characterized by increased numbers of neutrophils and alveolar macrophages as well as increased amounts of protein, lactate dehydrogenase, and interleukin-8 in BAL fluids. This response was subclinical and was resolved within 4 d PI. A similar dose-dependent response was seen in rats 1 d after intratracheal instillation of the same particles. The particles contained small amounts of soluble iron (240 ng/mg) and possessed the capacity to catalyze oxidant generation in vitro. Our findings indicate that the acute inflammation after particle exposure may, at least partially, be the result of oxidant generation catalyzed by the presence of residual amounts of ferric ion, ferric hydroxides, or oxyhydroxides associated with the particles. These findings may have relevance to the acute health effects associated with increased levels of ambient particulate air pollutants.

Adult↗

PubMed1998

In vivo evidence of free radical formation after asbestos instillation: an ESR spin trapping investigation.

It has been postulated that the in vivo toxicity of asbestos results from its catalysis of free radical generation. We examined in vivo radical production using electron spin resonance (ESR) coupled with the spin trap alpha-(4-pyridyl-1-oxide)-N-t-butylnitrone (4-POBN); 180 day-old rats were intratracheally instilled with either 500 microg crocidolite or saline. Twenty-four hours later, histologic examination revealed a neutrophilic inflammatory response. ESR spectroscopy of the chloroform extract from lungs exposed to asbestos gave a spectrum consistent with a carbon-centered radical adduct, while those spectra from lungs instilled with saline revealed a much weaker signal. This same radical formation persisted and, even one month after instillation, could be detected in the lungs of rats exposed to asbestos. The 4-POBN adducts detected by ESR are very similar to, if not identical with, ethyl and pentyl radical adducts, providing evidence of in vivo lipid peroxidation resulting from asbestos exposure. We conclude that, after instillation of crocidolite in the rat, ESR analysis of lung tissue demonstrates in vivo free radical production.

Animals↗

PubMed1998

The release of iron from different asbestos structures by hydrogen peroxide with concomitant O2 generation.

Treatment of aqueous suspensions of different asbestos fibers (amosite, anthophyllite, chrysotile, and crocidolite) at 0-4 degrees C and pH 7.2 with H2O2 results in the consumption of H2O2 with concomitant release of iron and production of O2. During incubations, [H2O2] decreased in proportion to the mass of the suspended fiber, the duration of incubation, and the initial [H2O2]. The consumption of H2O2, production of O2 and release of iron all vary synergistically with the structure of the asbestos fiber. Release of silicon during the incubation was small relative to the decrement in [H2O2], reflecting a lack of dissolution of the fiber. The data are consistent with a redox process for the release of surface bound iron and it is significant that iron release occurs in the absence of a Fe(II) or Fe(III) chelator. The implications of iron release from the asbestos surface may be important in inflammatory disorders in which both silicate bound iron and H2O2 accumulate.

Asbestos↗

PubMed1998

Disruption of normal iron homeostasis after bronchial instillation of an iron-containing particle.

The atmosphere constitutes a prime vehicle for the movement and redistribution of metals. Metal exposure can be associated with an oxidative stress. We tested the hypothesis that, in response to an iron-containing particle, the human respiratory tract will demonstrate an increased expression of both lactoferrin and ferritin as the host attempts to transport and store the metal in a chemically less-reactive form and therefore diminish the oxidative stress the particle presents. Subjects (n = 22) were instilled with 20 ml of saline and 20 ml of an iron-containing particle suspended in saline in a right middle lobe bronchus and a lingular bronchus, respectively. At either 1, 2, or 4 days after this exposure, the volunteer was lavaged for a sample of the lower respiratory tract, and concentrations of L-ferritin, transferrin, and lactoferrin were measured by enzyme immunoassay, immunoprecipitin analysis, and enzyme-linked immunosorbent assay (ELISA), respectively. Transferrin receptor was also quantified by ELISA. The concentrations of L-ferritin in the lavage fluid of lung exposed to particles were significantly increased relative to the levels of the protein in the segment exposed to saline. Relative to saline instillation, transferrin was significantly diminished after exposure to the iron-containing particle, whereas both lactoferrin and transferrin receptor concentrations in the segment of the lung exposed to the particle were significantly elevated. We conclude that instillation of an iron-containing particle was associated with a disequilibrium in iron metabolism in the lower respiratory tract. The response included increased ferritin and lactoferrin concentrations, whereas transferrin concentrations diminished. This coordinated series of reactions by the host effects a decrease in the availability of catalytically reactive iron to likely diminish the consequent oxidative stress to the human host.

Adolescent↗

PubMed1998

Metal-dependent expression of ferritin and lactoferrin by respiratory epithelial cells.

Increased availability of catalytically active metal has been associated with an oxidative injury. The sequestration of transition metals within intracellular ferritin confers an antioxidant function to this protein. Such storage by ferritin requires that the metal be transported across a cell membrane. We tested the hypothesis that, in response to in vitro exposures to catalytically active metal, respiratory epithelial cells increase the production of lactoferrin and ferritin to bind, transport, and store this metal with their coordination sites fully complexed. Residual oil fly ash is an emission source air pollution particle with biological effects that, both in vitro and in vivo, correspond with its metal content. Cell cultures were exposed to 0-200 micrograms/ml of oil fly ash for 2 and 24 h. Concentrations of ferritin and lactoferrin mRNA were estimated by reverse transcription-polymerase chain reaction, and concentrations of ferritin and lactoferrin proteins were measured in parallel. mRNA for ferritin did not change with exposure to oil fly ash. However, ferritin protein concentrations increased. Although mRNA for transferrin receptor decreased, mRNA for lactoferrin increased after incubation with the particle. Similar to changes in mRNA, transferrin concentration decreased, whereas that of lactoferrin increased. Deferoxamine, a metal chelator, inhibited these responses, and exposure of the cells to vanadium compounds alone reproduced elevations in lactoferrin mRNA. We conclude that increases in ferritin and lactoferrin expression can be metal dependent. This response can function to diminish the oxidative stress a metal chelate presents to a living system.

Air Pollutants↗

PubMed1998

Activation of MAPKs in human bronchial epithelial cells exposed to metals.

We have previously shown that in vitro exposure to metallic compounds enhances expression of interleukin (IL)-6, IL-8, and tumor necrosis factor-alpha in human bronchial epithelial cells. To characterize signaling pathways involved in metal-induced expression of inflammatory mediators and to identify metals that activate them, we studied the effects of As, Cr, Cu, Fe, Ni, V, and Zn on the mitogen-activated protein kinases (MAPK) extracellular receptor kinase (ERK), c-Jun NH2-terminal kinase (JNK), and P38 in BEAS cells. Noncytotoxic concentrations of As, V, and Zn induced a rapid phosphorylation of MAPK in BEAS cells. Activity assays confirmed marked activation of ERK, JNK, and P38 in BEAS cells exposed to As, V, and Zn. Cr and Cu exposure resulted in a relatively small activation of MAPK, whereas Fe and Ni did not activate MAPK under these conditions. Similarly, the transcription factors c-Jun and ATF-2, substrates of JNK and P38, respectively, were markedly phosphorylated in BEAS cells treated with As, Cr, Cu, V, and Zn. The same acute exposure to As, V, or Zn that activated MAPK was sufficient to induce a subsequent increase in IL-8 protein expression in BEAS cells. These data suggest that MAPK may mediate metal-induced expression of inflammatory proteins in human bronchial epithelial cells.

Activating Transcription Factor 2↗

PubMed1998

Induction of ferritin and heme oxygenase-1 by endotoxin in the lung.

Heme oxygenase (HO)-1 expression is increased by forms of oxidative stress that also induce ferritin. Even though this could result from release of iron by heme degradation, we hypothesized that ferritin expression in the lung after endotoxin [lipopolysaccharide (LPS)] would occur independently of HO-1 because iron sequestration is an important response to infection. We tested this hypothesis by instilling saline or LPS (1 mg) into lungs of rats and measuring ferritin expression, HO-1 expression and activity, and HO-1 and ferritin mRNAs at different times. Lungs were also inflation fixed for immunohistochemistry for HO-1 and ferritin. Studies were performed with and without the HO inhibitor tin protoporphyrin. Ferritin and HO-1 labeling were minimal (macrophages only) in control lungs. By 4 h after LPS instillation, ferritin staining was present in bronchial epithelium and macrophages, became diffuse at 16 h, and was nearly gone by 48-72 h. HO-1 was detectable in macrophages 4 and 16 h after LPS instillation, increased in macrophages and bronchial epithelium at 24 h, and diffusely increased in bronchial epithelium and the alveolar region at 48-72 h. Lung ferritin content increased significantly by 4 h and peaked at 16 h before declining. HO-1 protein was present by Western blot in control lung, stable at 4 h, and increased by 24 h after LPS instillation, whereas HO enzyme activity had increased by 4 h after LPS instillation. After complete inhibition of HO enzyme activity with tin protoporphyrin, ferritin increased threefold at 4 h and sixfold at 24 h after LPS instillation. HO-1 mRNA increased by 4 h and was sustained at 24 h, whereas ferritin mRNA did not change after LPS instillation. These results indicate that intratracheal LPS rapidly induces ferritin protein in the lung independently of its mRNA synthesis or HO enzyme activity. LPS induces HO-1 mRNA, which is followed by increased expression of protein.

Animals↗

PubMed1998

Copper-dependent inflammation and nuclear factor-kappaB activation by particulate air pollution.

Particulate air pollution causes increased cardiopulmonary morbidity and mortality, but the chemical determinants responsible for its biologic effects are not understood. We studied the effect of total suspended particulates collected in Provo, Utah, an area where an increase in respiratory symptoms in relation to levels of particulate pollution has been well documented. Provo particulates caused cytokine-induced neutrophil chemoattractant-dependent inflammation of rat lungs. Provo particulates stimulated interleukin-6 (IL-6) and IL-8 production, increased IL-8 messenger RNA (mRNA) and enhanced expression of intercellular adhesion molecule-1 (ICAM-1) in cultured BEAS-2B cells, and stimulated IL-8 secretion in primary cultures of human bronchial epithelium. Cytokine secretion was preceded by activation of the transcription factor nuclear factor-kappaB (NF-kappaB) and was reduced by treatment of cultures with superoxide dismutase, deferoxamine, or N-acetylcysteine. These biologic effects were replicated by culturing BEAS cells with quantities of Cu2+ found in Provo extract. IL-8 secretion by BEAS cells could be modified by addition of normal constituents of airway lining fluid to the culture medium. Mucin significantly reduced IL-8 secretion, and ceruloplasmin significantly increased IL-8 secretion and activation of NF-kappaB. These findings suggest that copper ions may cause some of the biologic effects of inhaled particulate air pollution in the Provo region of the United States, and may provide an explanation for the sensitivity of asthmatic individuals to Provo particulates that has been observed in epidemiologic studies.

Air Pollution↗

PubMed1997

Soluble transition metals mediate residual oil fly ash induced acute lung injury.

Identification of constituents responsible for the pulmonary toxicity of fugitive combustion emission source particles may provide insight into the adverse health effects associated with exposure to these particles as well as ambient air particulate pollution. Herein, we describe results of studies conducted to identify constituents responsible for the acute lung injury induced by residual oil fly ash (ROFA) and to assess physical-chemical factors that influence the pulmonary toxicity of these constituents. Biochemical and cellular analyses performed on bronchoalveolar lavage fluid obtained from rats following intratracheal instillation of ROFA suspension demonstrated the presence of severe inflammation, an indicator of pulmonary injury, which included recruitment of neutrophils, eosinophils, and monocytes into the airway. A leachate prepared from ROFA, containing predominantly Fe, Ni, V, Ca, Mg, and sulfate, produced similar lung injury to that induced by ROFA suspension. Depletion of Fe, Ni, and V from the ROFA leachate abrogated its pulmonary toxicity. Correspondingly, minimal lung injury was observed in animals exposed to saline-washed ROFA particles. A surrogate transition metal sulfate solution containing Fe, V, and Ni largely reproduced the lung injury induced by ROFA. Metal interactions and pH were found to influence the severity and kinetics of lung injury induced by ROFA and soluble transition metals. These findings provide direct evidence for the role of soluble transition metals in the pulmonary injury induced by the combustion emission source particulate, ROFA.

Acute Disease↗

PubMed1997

In vivo accumulation of iron on crocidolite is associated with decrements in oxidant generation by the fiber.

In vivo exposures to fibrous silicates are characterized by the formation of asbestos bodies. These structures consist of the original fiber with a coating of inexact composition, but it will include iron and protein. We tested the hypothesis that this iron, accumulated on asbestos bodies, participates in electron transport and oxidant generation. Thirty-day-old, male guinea pigs were intratracheally instilled with 1.0 mg crocidolite. Six months later, the animals were anesthetized, euthanized, and the fibers were isolated from the lungs. Energy-dispersive x-ray analysis and x-ray photoelectron spectroscopy confirmed an accumulation of metal onto the fiber after in vivo exposure. Stains for iron demonstrated a heterogeneous distribution of the metal on the silicate, while the uptake of a commercially available polyclonal antibody to ferritin localized to beaded enlargements along the coated fibers. Chelatable [Fe3+] associated with the fiber increased after in vivo exposure. However, oxidant generation by asbestos bodies was decreased relative to uncoated fibers despite the elevation in the concentration of metal associated with the crocidolite. We conclude that iron is accumulated onto fibers in the lungs of guinea pigs. Some portion of this accumulation of iron is in the form of ferritin, and this metal is not chemically reactive in oxidant production. Asbestos bodies may represent a successful attempt by the host to sequester the metal adsorbed to the surface of a fiber and diminish the oxidative challenge introduced by a fibrous silicate. Subsequently, the generation of free radicals by the fibrous silicate is diminished.

Animals↗

PubMed1997

Cytokine production by human airway epithelial cells after exposure to an air pollution particle is metal-dependent.

Despite the many epidemiological studies supporting the contention that ambient air pollution particles can adversely affect human health, there is no clear agreement as to a biologically plausible mechanism which can explain the acute mortality and morbidity associated with exposure to particles less than 10 microm in size. We tested the hypothesis that metals present in an air pollution particle can induce the synthesis and expression of the inflammatory cytokines IL-8, IL-6, and TNFalpha. A residual oil fly ash (ROFA) containing the transition metals vanadium, nickel, and iron was used as a model emission source air pollution particle. Normal human bronchial epithelial (NHBE) cells were exposed for either 2 or 24 hr to 0, 5, 50, or 200 microg/ml ROFA. Concentrations of IL-8, IL-6, and TNF-alpha proteins were measured with commercially available ELISA kits. mRNA for these same cytokines was quantified by RT-PCR. NHBE cells exposed to ROFA produced significant amounts of IL-8, IL-6, and TNF, as well as mRNAs coding for these cytokines. Cytokine production was inhibited by the inclusion of either the metal chelator deferoxamine (1.0 mM) or the free radical scavenger dimethylthiourea (1.0 mM). In addition, vanadium containing compounds, but not iron or nickel sulfates, mimicked the effects of intact ROFA. These results demonstrate that metals present in ROFA may be responsible for production and release of inflammatory mediators by the respiratory tract epithelium and suggest that these mediators may contribute to the toxic effects of particulate air pollutants reported in epidemiology studies.

Air Pollutants, Occupational↗

PubMed1997

Non-heme (Fe3+) in the lung increases with age in both humans and rats.

Increasing non-heme iron concentrations in host tissues are potentially significant, because they can be associated with an increased risk of injury including infections, fibrosis, and neoplasms. We tested the hypothesis that non-heme (Fe3+) in the lung increases with age in both humans and rats. Human tissue was collected at autopsy before fixation occurred. The total number of specimens was 131 with 78 nonsmokers and 53 smokers. Tissue was hydrolyzed in 3 N hydrochloric acid and 10% trichloroacetic acid. Supernatant (Fe3+) was measured with a thiocyanate assay. Non-heme (Fe3+) increased with age in nonsmokers. The correlation coefficient between lung (Fe3+) and age in the nonsmokers was 0.58 (p < 0.0001). Iron stains were negative, whereas those for ferritin demonstrated increased uptake with aging. Smokers had significantly greater non-heme (Fe3+) relative to nonsmokers (101.1 and 46.0 micromol/L respectively; T = 11.44, p < 0.0001). Lung non-heme (Fe3+) in smokers also increased with age (r = 0.75; p < 0.0001). Iron stains demonstrated uptake in the proximity of retained pigmented material. Ferritin stains demonstrated intense uptake in both the macrophages and the airway and alveolar epithelium of smokers. An animal model was also analyzed for an effect of aging on lung non-heme (Fe3+). At specified times between 30 and 186 days of age, rats (n = 48) were anesthetized and exsanguinated, and the lungs were excised. In rats, similar to humans, a positive correlation was seen between lung non-heme (Fe3+) and age (r = 0.73; p = 0.007). Stains for iron in rat lung were uniformly negative, whereas those for ferritin demonstrated increased uptake by airway and alveolar epithelium in older rats. We conclude that non-heme (Fe3+) in lung tissue increases with age in both humans and rats. Elevations in lung non-heme (Fe3+) could contribute to an increased incidence of pneumonias, pulmonary fibrosis, and bronchogenic carcinoma observed among older individuals.

Adolescent↗

PubMed1997

In vivo evidence of free radical formation in the rat lung after exposure to an emission source air pollution particle.

Exposure to air pollution particles can be associated with increased human morbidity and mortality. The mechanism(s) of lung injury remains unknown. We tested the hypothesis that lung exposure to oil fly ash (an emission source air pollution particle) causes in vivo free radical production. Electron spin resonance (ESR) in conjunction with the spin trap alpha-(4-pyridyl 1-oxide)-N-tert-butylnitrone (4-POBN) was used to detect radical adducts. Rats were instilled with 500 micrograms of either oil fly ash or saline. Twenty-four hours later, ESR spectroscopy of the chloroform extract from lungs of animals exposed to the oil fly ash gave a spectrum consistent with a carbon-centered radical adduct (hyperfine coupling constants alpha N = 15.0 G and alpha H beta = 2.5 G), while those spectra from lungs instilled with saline revealed a much weaker signal. This signal was reproduced by instilling animals with the soluble fraction of the oil fly ash, which contains soluble metal compounds. The same signal was observed after instillation of either a mixture of vanadium, nickel, and iron sulfates or VOSO4 alone. We conclude that, after instillation of an air pollution particle in the rat, ESR analysis of lung tissue demonstrates in vivo free radical production. This generation of free radicals appears to be associated with soluble metals in the oil fly ash.

Air Pollution↗

PubMed1997

Hypothesis: iron chelation plays a vital role in neutrophilic inflammation.

Neutrophil influx into tissues occurs in many diverse diseases and can be associated with both beneficial and injurious effects. We hypothesize that the stimulus for certain neutrophilic inflammatory responses can be reduced to a series of competing reactions for iron, with either a labile or reactive coordination site available, between host chelators and chelators not indigenous to that specific living system. The iron focuses the transport of host phagocytic cells through a metal catalyzed generation of oxidant sensitive mediators including cytokines and eicosanoids. Many of these products are chemotactic for neutrophils. We also postulate that the iron increases the activity of the phagocyte associated NADPH oxidoreductase in the neutrophil. The function of this enzyme is likely to be the generation of superoxide in the host's attempt to chemically reduce and dislodge the iron from its chelate complex. After the reoxidation of Fe2+ in an aerobic environment, Fe3+ will be coordinated by host lactoferrin released by the neutrophil. When complexed by this glycoprotein, the metal does not readily undergo oxidation/reduction and is safely transported to the macrophages of the reticuloendothelial system where it is stored in ferritin. Finally, we propose that the neutrophil will attempt to destroy the chelator not indigenous to the host by releasing granular contents other than lactoferrin. Inability to eliminate the chelator allows this sequence to repeat itself, which can lead to tissue injury. Such persistence of a metal chelate in the host may be associated with biomineralization, fibrosis, and cancer.

Animals↗

PubMed1997

Disruption of protein tyrosine phosphate homeostasis in bronchial epithelial cells exposed to oil fly ash.

Residual oil fly ash (ROFA) is a toxic air pollutant that we have previously shown induces inflammatory mediator expression in human bronchial epithelial cells. To identify intracellular signaling mechanisms activated by ROFA, we studied its effect on protein tyrosine phosphate metabolism in the human bronchial epithelial cell line BEAS. Noncytotoxic levels of ROFA induced significant dose- and time-dependent increases in protein tyrosine phosphate levels in BEAS cells. ROFA-induced increases in protein phosphotyrosines were associated with its soluble fraction and were mimicked by vanadyl [V(IV)]- and vanadate [V(V)]-containing solutions. Ferrous, ferric, and nickel (II) ion solutions failed to increase phosphotyrosine levels. Tyrosine phosphatase activity, which was known to be inhibited by vanadium ions, was markedly diminished after ROFA treatment. Tyrosine kinase activity was unaffected. We conclude that ROFA exposure induces vanadium ion-mediated inhibition of tyrosine phosphatase activity, leading to accumulation of protein phosphotyrosines in BEAS cells. These findings demonstrate that ROFA exposure disrupts protein tyrosine phosphate homeostasis in BEAS cells and suggest a possible mechanism that leads to increased synthesis of proinflammatory proteins in airway epithelial cells exposed to PM10.

Air Pollutants↗

PubMed1997

Genetic variability in combustion particle-induced chronic lung injury.

Occupational exposure to anthropogenic particles is associated with lung injury in humans. We hypothesized that residual oil fly ash (ROFA), an emission source particulate, may induce acute lung injury and fibrosis in sensitive rat strains and that fibronectin (Fn) gene expression will correspond to the development of fibrosis. Male Sprague-Dawley (SD), Wistar (WIS), and Fischer 344 (F-344) rats (60 days old) were exposed to saline or ROFA (8.3 mg/kg) by intratracheal instillation and examined for up to 12 wk. Histology indicated focal areas of lung damage showing inflammatory cell infiltration as well as alveolar, airway, and interstitial thickening in all three rat strains during 1-7 days postexposure. Trichrome staining of the lung sections indicated a sporadic incidence of focal alveolar fibrosis at 1, 3, and 12 wk in SD rats, whereas WIS and F-344 rats showed only a modest increase in trichrome staining in the septal areas. Of all Fn mRNA isoforms examined by polymerase chain reaction, only EIIIA(+) was upregulated during 6 h-1 wk in ROFA-exposed SD and WIS rats but not in F-344 rats. In situ hybridization analysis in SD rats revealed Fn mRNA expression by macrophage and alveolar and airway epithelium and within fibrotic areas. Immunohistochemical analysis revealed increased presence of Fn EIIIA(+) protein in the areas of fibrotic injury and basally to the airway epithelium. In summary, Fn EIIIA(+) increases early in the course of particle-induced lung injury and remodeling, which may or may not result in discernible alveolar fibrosis. There is a rat strain variation in ROFA-induced fibrosis and associated Fn EIIIA(+) expression.

Air Pollutants↗

PubMed1997

Ferritin expression after in vitro exposures of human alveolar macrophages to silica is iron-dependent.

The increased availability of catalytically active iron after silica exposure can present an oxidative injury to a living system. Sequestration of reactive iron would, therefore, confer a protective effect. The intracellular storage of iron by ferritin within macrophages can limit the potential for radical generation and cellular injury resulting from exposure to a metal chelate. We tested the hypothesis that in vitro exposure of human alveolar macrophages to silica increases the expression of ferritin through a posttranscriptional mechanism. Exposure of 1.0 x 10(6) macrophages to 100 microg/ml silica for 4 h increased light-subunit (L)-ferritin protein concentrations in both cell supernatants and lysates. Inclusion of 1.0 mM deferoxamine in the reaction mixtures inhibited increases in ferritin after silica. To test for a posttranscriptional regulation of ferritin protein expression, cells were incubated with acid-washed particles, silica with complexed zinc cation, and silica with complexed iron cation. L-ferritin protein concentrations were increased in both cell supernatants and lysates after 4 h of exposure to silica with complexed iron cation. There were no increases in L-ferritin after incubations with acid-washed particles or silica with complexed zinc cation. There were no significant differences in levels of L-ferritin cDNA between any of the exposures, suggesting a posttranscriptional control of ferritin expression.

Cells, Cultured↗