Victor A Robinson

Centers for Disease Control and Prevention, Druid Hills, GA, United States

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Publications (27)72.27 Total impact

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    ABSTRACT: Consequent to the 2010 Deepwater Horizon oil spill in the Gulf of Mexico, there is an emergent concern about the short- and long-term adverse health effects of exposure to crude oil, weathered-oil products, and oil dispersants among the workforce employed to contain and clean up the spill. Oil dispersants typically comprise of a mixture of solvents and surfactants that break down floating oil to micrometer-sized droplets within the water column, thus preventing it from reaching the shorelines. As dispersants are generally sprayed from the air, workers are at risk for exposure primarily via inhalation. Such inhaled fractions might potentially permeate or translocate to the brain via olfactory or systemic circulation, producing central nervous system (CNS) abnormalities. To determine whether oil dispersants pose a neurological risk, male Sprague-Dawley rats were exposed by whole-body inhalation exposure to a model oil dispersant, COREXIT EC9500A (CE; approximately 27 mg/m(3) × 5 h/d × 1 d), and various molecular indices of neural dysfunction were evaluated in discrete brain areas, at 1 or 7 d postexposure. Exposure to CE produced partial loss of olfactory marker protein in the olfactory bulb. CE also reduced tyrosine hydroxylase protein content in the striatum. Further, CE altered the levels of various synaptic and neuronal intermediate filament proteins in specific brain areas. Reactive astrogliosis, as evidenced by increased expression of glial fibrillary acidic protein, was observed in the hippocampus and frontal cortex following exposure to CE. Collectively, these findings are suggestive of disruptions in olfactory signal transduction, axonal function, and synaptic vesicle fusion, events that potentially result in an imbalance in neurotransmitter signaling. Whether such acute molecular aberrations might persist and produce chronic neurological deficits remains to be ascertained.
    Journal of Toxicology and Environmental Health Part A 11/2011; 74(21):1405-18. · 1.73 Impact Factor
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    ABSTRACT: Nanoparticles agglomerate and clump in solution, making it difficult to accurately deliver them for in vivo or in vitro experiments. Thus, experiments were conducted to determine the best method to suspend nanosized particles. Ultrafine and fine carbon black and titanium dioxide were suspended in phosphate buffered saline (PBS), rat and mouse bronchoalveolar lavage fluid (BALF), and PBS containing dipalmitoyl phosphatidylcholine (DPPC) and/or mouse serum albumin. To assess and compare how these various suspension media dispersed the nanoparticles, images were taken using light microscopy, scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The results of this study show that PBS is not a satisfactory medium to prepare nanoparticle suspensions. However, BALF was an excellent media in which to suspend nanoparticles. The use of PBS containing protein or DPPC alone, in concentrations found in BALF, did not result in satisfactory particle dispersion. However, PBS-containing protein plus DPPC was satisfactory, although less effective than BALF.
    07/2009; 1(2):118-129.
  • Nanotechnology: Characterization, Dosing and Health Effects, Edited by N Monteiro-Riviere, L Tran, 01/2007: chapter 14; Informa Healthcare.
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    ABSTRACT: Our laboratory has previously reported results from a rat silica inhalation study which determined that, even after silica exposure ended, pulmonary inflammation and damage progressed with subsequent fibrosis development. In the present study, the relationship between silica exposure, nitric oxide (NO) and reactive oxygen species (ROS) production, and the resultant pulmonary damage is investigated in this model. Rats were exposed to silica (15 mg/m3, 6 h/day) for either 20, 40, or 60 days. A portion of the rats from each exposure were sacrificed at 0 days postexposure, while another portion was maintained without further exposure for 36 days to examine recovery or progression. The major findings of this study are: (1) silica-exposed rat lungs were in a state of oxidative stress, the severity of which increased during the postexposure period, (2) silica-exposed rats had significant increase in lung NO production which increased in magnitude during the postexposure period, and (3) the presence of silica particle(s) in an alveolar macrophage (AM) was highly associated with inducible nitric oxide synthase (iNOS) protein. These data indicate that, even after silica exposure has ended, and despite declining silica lung burden, silica-induced pulmonary NO and ROS production increases, thus producing a more severe oxidative stress. A quantitative association between silica and expression of iNOS protein in AMs was also determined, which adds to our previous observation that iNOS and NO-mediated damage are associated anatomically with silica-induced pathological lesions. Future studies will be needed to determine whether the progressive oxidative stress, and iNOS activation and NO production, is a direct result of silica lung burden or a consequence of silica-induced biochemical mediators.
    Toxicological Sciences 04/2006; 90(1):188-97. · 4.33 Impact Factor
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    ABSTRACT: Human epidemiologic studies have found that silicosis may develop or progress even after occupational exposure has ended, suggesting that there is a threshold lung burden above which silica-induced pulmonary disease progresses without further exposure. We previously described the time course of rat pulmonary responses to silica inhalation as biphasic, the initial phase characterized by increased but controlled pulmonary inflammation and damage. However, after a threshold lung burden was exceeded, rapid progression of silica-induced pulmonary disease occurred. To test the hypothesis that there is a threshold lung burden above which silica-induced pulmonary disease progresses without further exposure we initiated a study to investigate the relationship between silica exposure, the initiation and progression of silica-induced pulmonary disease, and recovery. Rats were exposed to silica (15 mg/m(3), 6 h/day) for either 20, 40, or 60 days. A portion of the rats from each exposure were maintained without further exposure for 36 days to examine recovery. The major findings of this study are: (1) silica-exposed rats were not in pulmonary overload, and lung silica burden decreased with recovery; (2) pulmonary inflammation, damage and lipidosis increased with recovery for rats exposed to silica for 40 and 60 days, but not 20 days; (3) histopathology revealed changes in silica-induced alveolitis, epithelial hypertrophy and hyperplasia, and alveolar lipoproteinosis consistent with bronchoalveolar lavage (BAL) endpoints; and (4) pulmonary fibrosis developed even when exposure was stopped prior to its initial development.
    Toxicological Sciences 07/2004; 79(2):370-80. · 4.33 Impact Factor
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    ABSTRACT: The role of nitric oxide (NO) in pulmonary disease has been controversial with both antiinflammatory (scavenging radicals and inhibiting NF-êB activation) and proinflammatory (forming highly reactive peroxynitrite and augmenting NF-êB activation by inflammatory agents) actions reported. Therefore, a study has been initiated to determine whether deletion of the inducible nitric oxide synthase (iNOS) gene in the C57BL/6J mouse alters the pulmonary macrophage response to lipopolysaccharide (LPS) or silica. The objective of the initial phase of this study was to determine the difference in responsiveness of alveolar macrophages (AMs), harvested from naive wild-type (WT) or iNOS knockout (iNOS KO) mice, to an in vitro LPS or silica exposure. Primary AMs were obtained by bronchoalveolar lavage (BAL) from age- and weight-matched iNOS KO and WT mice. The cells were treated with interferon-gamma (IFN-ã) (50 U/ml), IFN-ã (50 U/ml) + LPS (1 microg/ml), LPS (0.01-100 microg/ml), or silica (25-250 microg/ml). The following parameters were measured: nitrate and nitrite (NOx), tumor necrosis factor-á (TNF-á), macrophage inflammatory protein-2 (MIP-2), intracellular generation of the reactive oxygen species (ROS) hydrogen peroxide (H(2)O(2) and superoxide (O(*-2)), and basal (unstimulated) total antioxidant capacity. Data show a significant increase in NOx production upon exposure to IFN-ã +/- LPS in the WT but not iNOS KO AMs. NOx production by iNOS KO or WT AMs was not altered by in vitro exposure to LPS or silica alone. LPS, but not silica, induced TNF-á and MIP-2 production in both iNOS KO and WT AMs. Statistical analysis of concentration response curves found a significant tendency for greater mediator production in the iNOS KO versus WT AMs. Basal intracellular production of H(2)O(2) and O(*- 2) was significantly greater in the iNOS KO compared to WT AMs. In contrast, LPS- (10 microg/ml) or silica- (100 microg/ml) stimulated intracellular oxidant production was lower in iNOS KO AMs, but overall (basal + stimulated) inflammatory capacity was similar between the cell types. The basal total antioxidant production of the iNOS KO AMs was approximately twofold higher than the WT AMs. In conclusion, certain compensatory changes appear to occur in AMs from iNOS KO mice. In response to the inability to induce NO production, iNOS KO AMs exhibit significantly higher basal generation of H(2)O(2) and (O(*- 2)) as well as higher total antioxidant levels. In addition, LPS induced TNF-á and MIP-2 production tend to be higher in AMs from iNOS KO mice. Such compensatory changes in the AM response may affect the response of iNOS KO mice to inflammatory exposures.
    Journal of Toxicology and Environmental Health Part A 07/2003; 66(11):995-1013. · 1.73 Impact Factor
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    ABSTRACT: 1-->3-beta-Glucans produce pulmonary inflammation in rats and are commonly found in indoor air dust samples. Conformation is an important factor determining the biological activity of 1-->3-beta-glucans. The partially opened triple-helix conformation induced by NaOH treatment and the annealed triple-helix conformation have been identified by fluorescence resonance energy transfer spectroscopy in our previous study. The objective of this study was to examine the role of these conformations of 1-->3-beta-glucans in the induction of pulmonary inflammation in rats. A partially opened triple-helix conformation of the known inflammatory 1-->3-beta-glucan zymosan was prepared by treating zymosan with NaOH followed by neutralization and dialysis. The annealed triple-helix conformation was prepared by allowing the partially opened triple-helix conformation to anneal for 9 d at room temperature. Rats were exposed to fresh or annealed NaOH-treated zymosan via intratracheal instillation. The results show that the zymosan-induced pulmonary inflammatory responses were significantly reduced after the 9-d annealing period, which suggests that this inflammatory response was dependent on the conformation of zymosan. Freezing NaOH-treated zymosan (for 7 d) inhibited the annealing process. Exposure of rats to thawed preparations of zymosan resulted in the same inflammatory responses as the freshly prepared partially opened triple-helix zymosan. In contrast, the potency of untreated zymosan did not change significantly following a 7-d annealing period, indicating that annealing occurs only after the conformation has been modified by NaOH treatment. This study indicates that the partially opened triple helix of 1-->3-beta-glucans is more active than the closed conformation in inducing pulmonary inflammation in rats.
    Journal of Toxicology and Environmental Health Part A 03/2003; 66(6):551-63. · 1.73 Impact Factor
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    ABSTRACT: 1-->3-beta-Glucans, derived from the inner cell wall of yeasts and fungi, are commonly found in indoor air dust samples and have been implicated in organic dust toxic syndrome. In a previous study, it was reported that 1-->3-beta-glucan (zymosan A) induced acute pulmonary inflammation in rats. This study investigates which form of 1-->3-beta-glucans, particulate or soluble, is more potent in inducing pulmonary inflammation. Zymosan A was suspended in 0.25 N NaOH for 30 min, neutralized, dialyzed for 2 d using deionized water, and particulate and soluble fractions were collected. Male Sprague-Dawley rats were exposed via intratracheal instillation to NaOH-soluble or NaOH-insoluble zymosan A. At 18 h postexposure, various indicators of pulmonary response were monitored, including indicators of lung damage, such as serum albumin concentration and lactate dehydrogenase (LDH) activity in acellular bronchoalveolar lavage fluid. Inflammation was characterized by an increase in lavageable polymorphonuclear leukocytes (PMN). Pulmonary irritation (breathing frequency increase) and oxidant production (nitric oxide and chemiluminescence, CL) were also monitored. Exposure to the particulate form of NaOH-treated zymosan produced a significant increase in all these indicators. In contrast, rats exposed to the NaOH-soluble fraction were not markedly affected except for LDH, PMN, and CL. However, these increases were significantly less than with exposure to NaOH-insoluble zymosan. Therefore, results demonstrate that particulate zymosan A is more potent in inducing pulmonary inflammation and damage in rats than the soluble form of this beta-glucan.
    Journal of Toxicology and Environmental Health Part A 01/2003; 66(1):25-38. · 1.73 Impact Factor
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    ABSTRACT: In previous reports from this study, measurements of pulmonary inflammation, bronchoalveolar lavage cell cytokine production and nuclear factor-kappa B activation, cytotoxic damage, and fibrosis were detailed. In this study, we investigated the temporal relationship between silica inhalation, nitric oxide (NO), and reactive oxygen species (ROS) production, and damage mediated by these radicals in the rat. Rats were exposed to a silica aerosol (15 mg/m(3) silica, 6 h/day, 5 days/wk) for 116 days. We report time-dependent changes in 1) activation of alveolar macrophages and concomitant production of NO and ROS, 2) immunohistochemical localization of inducible NO synthase and the NO-induced damage product nitrotyrosine, 3) bronchoalveolar lavage fluid NO(x) and superoxide dismutase concentrations, and 4) lung lipid peroxidation levels. The major observations made in this study are as follows: 1) NO and ROS production and resultant damage increased during silica exposure, and 2) the sites of inducible NO synthase activation and NO-mediated damage are associated anatomically with pathological lesions in the lungs.
    AJP Lung Cellular and Molecular Physiology 09/2002; 283(2):L485-93. · 3.52 Impact Factor
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    ABSTRACT: Blasting sand is used for abrasive blasting, but its inhalation is associated with pulmonary inflammation and fibrosis. Consequently, safer substitute materials for blasting sand are needed. In a previous study from this laboratory, the comparative pulmonary toxicity of five abrasive blasting substitutes and blasting sand was reported. In this study, the pulmonary toxicity of blasting sand was compared to five additional abrasive blasting substitutes: steel grit, copper slag, nickel slag, crushed glass, and olivine. Exposed rats received by intratracheal instillation 10 mg of respirable-size particles of blasting sand or an abrasive blasting substitute, while controls were instilled with vehicle. Pulmonary inflammation, damage, and fibrosis were examined 28 d postexposure. Pulmonary inflammation was monitored by determining bronchoalveolar lavage polymorphonuclear cell counts and alveolar macrophage activation by chemiluminescence. Pulmonary damage was assessed by acellular bronchoalveolar (BAL) fluid serum albumin concentrations and lactate dehydrogenase activities. Histological examination of lung tissue samples was made to assess the severity and distribution of pulmonary fibrosis, alveolitis, and alveolar epithelial cell hypertrophy and hyperplasia. In comparison to blasting sand, olivine exposed rats had higher levels of pulmonary inflammation and damage with a similar level of fibrosis. Steel grit-exposed rats had lower levels of pulmonary inflammation and damage, and did not develop fibrosis. However, steel grit-exposed rats had a level of epithelial cell hypertrophy and hyperplasia similar to blasting sand. The other abrasive blasting substitutes gave a mixed profile of toxicity. The data demonstrate that steel grit produced less acute pulmonary toxicity than blasting sand or any of the other abrasive blasting substitutes. Notwithstanding, the data also suggest that chronic exposure to steel grit may pose a health risk due to its effects on epithelial cell proliferation in the lung.
    Journal of Toxicology and Environmental Health Part A 09/2002; 65(16):1121-40. · 1.73 Impact Factor
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    ABSTRACT: Most previous studies of silica toxicity have used relatively high exposure doses of silica. In this study, male rats received by intratracheal instillation either vehicle, aged or freshly fractured silica at a dose of either 5 microg/rat once a week for 12 weeks (total dose=60 microg) or 20 microg/rat once a week for 12 weeks (total dose=240 microg). One week after the last exposure, bronchoalveolar lavage (BAL) was conducted and markers of pulmonary inflammation, alveolar macrophage (AM) activation and pulmonary damage were examined. For rats exposed to a total of 60 microg silica, both aged and freshly fractured silica increased polymorphonuclear leukocytes (PMN) yield and AM activation above control to a similar degree, but no evidence of pulmonary damage, as measured by BAL fluid lactate dehydrogenase activity or albumin concentration, was detected. For rats exposed to 240 microg silica, aged or freshly fractured silica increased PMN yield and AM activation above control. However, zymosan-stimulated and L-NAME sensitive AM chemiluminescence was greater for rats exposed to freshly fractured silica compared to aged silica. Exposure to 240 microg aged or freshly fractured silica also resulted in pulmonary damage, but the extent of this damage did not differ between the two types of silica. The results suggest that exposure of rats to silica levels far lower than those previously examined can cause pulmonary inflammation. In addition, exposure to freshly fractured silica causes greater generation of reactive oxygen species from AM, measured as AM chemiluminescence, in comparison to aged silica, but there is an apparent threshold below which this difference does not occur.
    Toxicology 07/2002; 175(1-3):63-71. · 4.02 Impact Factor
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    ABSTRACT: In vitro studies suggest that silica-induced lung disease may be linked to processes regulated by nuclear factor-kappa B (NF-kappa B) activation, but this has not been examined in vivo. Rats were exposed to a silica aerosol of 15 mg/m(3) (6 h/day, 5 days/wk) for 116 days, and bronchoalveolar lavage (BAL) was conducted at various times during the exposure. Silica-induced pulmonary inflammation and damage were determined by measuring BAL cell differentials and first BAL fluid lactate dehydrogenase (LDH) activity and serum albumin concentrations, respectively. NF-kappa B activation and production of tumor necrosis factor-alpha (TNF-alpha) and interleukin-1 (IL-1) by BAL cells were also measured. The results demonstrate that NF-kappa B activation occurred after 5 days exposure, and continued to increase thereafter. BAL cell production of IL-1 and TNF-alpha had increased incrementally by 10 and 30 days of exposure, respectively. This elevation continued through 79 days of exposure before further increasing at 116 days of exposure. Pulmonary inflammation and damage in silica-exposed rats were also significantly elevated at 5 days of exposure, further increased at a slow rate through 41 days of exposure, and dramatically increased thereafter. Taken together, the results indicate that the initial molecular response of NF-kappa B activation in BAL cells occurs in response to low levels of silica deposition in the lung and increases more rapidly versus exposure duration than silica-induced pulmonary inflammation, cellular damage, and cytokine production by BAL cells. This suggests that NF-kappa B activation in BAL cells may play an important role in the initiation and progression of silica-induced pulmonary inflammation, cellular damage, and fibrosis.
    Inhalation Toxicology 05/2002; 14(4):349-67. · 1.89 Impact Factor
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    ABSTRACT: The present study investigates whether 1-->3-beta-glucans (zymosan particles) modify the pulmonary response of rats to endotoxin (lipopolysaccharide, LPS). Initial experiments were conducted to establish appropriate doses of LPS and regimens for exposure to zymosan and LPS. Interaction between zymosan and LPS exposures was determined to be the deviation from the sum of the individual effects of these agents. Treatment with zymosan on Day 1 and LPS on Day 2 modified several indices of pulmonary responsiveness, including tumor necrosis factor-alpha, albumin, and lactate dehydrogenase activity (LDH) in first acellular lavage fluid as well as the levels of chemiluminescence (CL), NO-dependent CL, and nitric oxide production in cultured lavaged alveolar macrophage cells determined 1 day after exposure. No significant deviation from additivity was found for breathing rate increase and polymorphonuclear leukocytes infiltration. Simultaneous administration of zymosan and LPS or administration of LPS before zymosan did not change these indices of pulmonary responsiveness. These data suggest that the inhibitory effect of 1-->3-beta-glucans on pulmonary responsiveness to endotoxin exposure was apparent only when rats were pretreated with 1-->3-beta-glucan. These results suggest that complex interaction of components may exist in exposure to organic dusts. Therefore, hazard may not be defined by measuring endotoxin or 1-->3-beta-glucans alone.
    Toxicology and Applied Pharmacology 02/2002; 178(3):172-9. · 3.98 Impact Factor
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    ABSTRACT: Although endotoxin is a known potent stimulant of inflammatory responses, the magnitude of pulmonary response following exposure to various organic dusts does not always correlate with endotoxin content of the dusts alone. Other components, such as 1-->3-beta-glucans, derived from the inner cell wall of yeasts and fungi, have been implicated in organic dust toxic syndrome. However, animal studies report conflicting results concerning the inflammatory potency of 1-->3-beta-glucan. In this experiment, the pulmonary reaction of rats to 1-->3-beta-glucan (zymosan A) exposure was assessed. Male Sprague-Dawley rats were exposed via intratracheal instillation (IT) to zymosan A (dose range 0-5 mg/kg body weight). Rats were sacrificed 1-7 d postexposure and the following pulmonary responses were monitored: (1) breathing frequency, (2) differential cell counts of hronchoalveolar lavage (BAL) cells, (3) chemiluminescence (CL) as a measure of alveolar macrophage activation, (4) nitric oxide production by alveolar macrophages, (5) albumin levels, and (6) lactate dehydrogenase (LDH) activity in the first acellular lavage fluid. Upon challenge with zymosan A, rats exhibited a dose-dependent pulmonary response at 1 d post IT that was significantly higher than the control level at a dose of 1-2.5 mg/kg body weight for each of these pulmonary parameters. Post-IT enhancement of breathing frequencies and polymorphonuclear leukocytes (PMN) obtained by BAL both correlated very well with zymosan A concentration (r = .95 and .99, respectively). Elevation of albumin levels and LDH activity of the acellular BAL fluid also correlated (r = .80) with the dose of zymosan. The recovery from a single intratracheal administration of zymosan A (2.5 mg/kg body weight) was monitored over 7 d. PMN and CL showed significant recovery from d 1 level by 3 d postexposure. Breathing frequencies and nitric oxide production showed significant recovery from d 1 level by 4 d postexposure. A good correlation (r2= .8) between recovery of PMN in BAL, CL, or nitric oxide production and the days postexposure was observed.
    Journal of Toxicology and Environmental Health Part A 10/2001; 64(4):311-325. · 1.73 Impact Factor
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    ABSTRACT: Inhalation of silica dust is associated with pulmonary fibrosis. Therefore, substitute abrasive materials have been suggested for use in abrasive blasting operations. To date, toxicological evaluation of most substitute abrasives has been incomplete. Therefore, the objective of this study was to compare the pulmonary toxicity of a set of substitute abrasives (garnet, staurolite, coal slag, specular hematite, and treated sand) to that of blasting sand. Rats were exposed to blasting sand or an abrasive substitute by intratracheal instillation and pulmonary responses to exposure were monitored 4 weeks postexposure. Pulmonary damage was monitored as lactate dehydrogenase (LDH) in the acellular lavage fluid. Pulmonary inflammation was evaluated from the yield of polymorphonuclear leukocytes (PMN) obtained by bronchoalveolar lavage. The activity of alveolar macrophages was determined by measuring zymosan-stimulated chemiluminescence. Blasting sand caused lung damage and showed histologic evidence for inflammation and fibrosis. Garnet, staurolite, and treated sand exhibited toxicity and inflammation that were similar to blasting sand, while coal slag caused greater pulmonary damage and inflammation than blasting sand. In contrast, specular hematite did not significantly elevate LDH or PMN levels and did not stimulate macrophage activity 4 weeks postexposure.
    Toxicological Sciences 06/2001; 61(1):135-43. · 4.33 Impact Factor
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    ABSTRACT: In a previous study, we demonstrated that the length of glass fibers was a critical determinant of fiber potency in induction of tumor necrosis factor (TNF)-alpha and that activation of NF-kappaB was an important factor in this response. In the present study, we analyzed the role of mitogen-activated protein (MAP) kinases in the induction of TNF-alpha by glass fibers. Glass fibers induced phosphorylation of MAP kinases, p38, and ERK in primary rat alveolar macrophages, and this phosphorylation was associated with TNF-alpha gene expression. Long fibers were more potent than short fibers in activation of MAP kinases. Results from mechanistic analysis support that MAP kinases activate transcription factor c-Jun. The activated c-Jun acts on the TNF-alpha gene promoter through two binding sites, the cyclic AMP response element and the activator protein 1-binding site. These results suggest that in addition to the NF-kappaB pathway for TNF-alpha production, glass fibers are able to activate c-Jun through MAP kinase pathways that lead to induction of TNF-alpha expression.
    Journal of Biological Chemistry 03/2001; 276(7):5360-7. · 4.65 Impact Factor
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    ABSTRACT: We studied the adsorption of hydroxyl radicals and superoxide anion radicals on a hydroxylated alpha-quartz surface using cluster and periodic slab models by means of density functional calculations. Models of two hydroxylated alpha-quartz surfaces--(0001) and (0111)--have been used in the simulations. The hydroxyl radical adsorbs readily on both surfaces. The subsurface Si-O bonds are weakened during the adsorption resulting in surface layer destabilization. This destabilization leads directly to surface disintegration in the case of *OH/(0111) adsorption. The product of the surface disintegration and reconstruction is a surface terminated by silanol groups (Si-OH) and siloxyl radicals (Si-O*). The model calculations suggest that adsorption of *OH on a hydroxylated quartz surface transforms a chemically inert, aged, silanol terminated surface to a very reactive, silicon-based radical terminated surface. The activated surface may then cause oxidative damage to the adsorbed biomaterial. The superoxide anion radical adsorbs on both surfaces, but the adsorption products are only weakly bonded to the surface. The calculated energy barrier for the O2*- activated subsurface Si-O bond dissociation is 10 kcal/mol, which is higher than for the *OH activated process (4 kcal/mol). The calculated weaker bonding to the surface and higher activation energy barrier suggest that the superoxide anion radical will be less efficient in reactivation of an aged, hydroxylated quartz surface than the hydroxyl radical. The importance of the specific geometry of the surface silicon atoms on the surface reactivity and adsorption properties is also discussed. The theoretical predictions are supported experimentally using chemiluminescence to monitor reactivation of the aged silica surface by superoxide anion radicals.
    Journal of Environmental Pathology Toxicology and Oncology 02/2001; 20 Suppl 1:119-32. · 0.92 Impact Factor
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    ABSTRACT: Previous studies have determined that alpha-quartz (crystalline silica) can cause pulmonary inflammation, damage, and fibrosis. However, the temporal relationship between silica inhalation and pulmonary inflammation, damage, and fibrosis has not been fully examined. To address this gap in our knowledge of silica-induced pulmonary fibrosis, a chronic inhalation study using rats was designed. Specifically, rats were exposed to a silica aerosol (15 mg/m3 silica, 6 h/d, 5 d/wk, 116 d), and measurements of pulmonary inflammation, damage, and fibrosis were monitored throughout the study. We report (1) data demonstrating that the silica aerosol generation and exposure system produced a consistent silica aerosol of respirable size particles; (2) the time course of silica deposition in the lung; (3) calculations that demonstrate that the rats were not in pulmonary overload; (4) histopathological data demonstrating time-dependent enhancement of silica-induced alveolitis, epithelial hypertrophy and hyperplasia, alveolar lipoproteinosis, and pulmonary fibrosis in the absence of overload; and (5) biochemical data documenting the development of lipidosis, lung damage, and fibrosis.
    Journal of Environmental Pathology Toxicology and Oncology 02/2001; 20 Suppl 1:1-14. · 0.92 Impact Factor
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    ABSTRACT: A major route of exposure to allergens is through the respiratory tract. Comparatively few animal studies have used aerosolized high-molecular-weight allergens for sensitization, and in these studies, proper characterization of the aeroallergen exposure was usually missing. The purpose of this study was to profile the exposure-response relationship in Brown Norway rats (BNR) to well-characterized ovalbumin (OVA) aerosols. Rats were exposed 30 min/wk x 6 wk to respirable OVA aerosols from <1 mg/m(3) to 64 mg/m(3) air. Ovalbumin-specific circulating immunoglobulin (Ig)E, IgG, and IgA were measured throughout the study period. Rats were sacrificed 1 day after the last exposure. Pulmonary tissue was processed for histopathological and histochemical analysis. Tracheas were isolated, perfused, and assessed for in vitro responsiveness to methacholine. Serum concentrations of OVA-specific antibodies increased with both exposure concentration and number of exposures. The number of BNR with measurable titers also increased with both dose and time. Pulmonary inflammatory changes were noted only in BNR exposed to higher OVA concentrations (15 and 64 mg/m(3) air). Increased tracheal reactivity to methacholine was not found in any of the sensitized BNR. In summary, sustained aeroallergen concentration-dependent changes in specific antibody responses and pulmonary inflammation have been demonstrated.
    Inhalation Toxicology 03/2000; 12(3):245-61. · 1.89 Impact Factor
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    ABSTRACT: Apoptosis is a physiological mechanism for the control of DNA integrity in mammalian cells. Vanadium induces both DNA damage and apoptosis. It is suggested that vanadium-induced apoptosis serves to eliminate DNA-damaged cells. This study is designed to clarify a role of reactive oxygen species in the mechanism of apoptosis induced by vanadium. We established apoptosis model with murine epidermal JB6 P+ cells in the response to vanadium stimulation. Apoptosis was detected by a cell death ELISA assay and morphological analysis. The result shows that apoptosis induced by vanadate is dose-dependent, reaching its saturation level at a concentration of 100 microM vanadate. Vanadyl (IV) can also induce apoptosis albeit with lesser potency. A role of reactive oxygen species was analyzed by multiple reagents including specific scavengers of different reactive oxygen species. The result shows that vanadate-induced apoptosis is enhanced by NADPH, superoxide dismutase and sodium formate, but was inhibited by catalase and deferoxamine. Cells exposed to vanadium consume more molecular oxygen and at the same time, produce more H2O2 as measured by the change in fluorescence of scopoletin in the presence of horseradish peroxidase. This change in oxygen consumption and H2O2 production is enhanced by NADPH. Taken together, these results show that vanadate induces apoptosis in epidermal cells and H2O2 induced by vanadate plays a major role in this process.
    Molecular and Cellular Biochemistry 01/2000; 202(1-2):9-17. · 2.33 Impact Factor