Longitudinal changes in inflammatory markers in nasal lavage of cotton workers. Relation to endotoxin exposure and lung function changes

OBJECTIVES

The aim of this study was to evaluate time-related changes in inflammatory markers in nasal lavage (NAL) in relation to endotoxin exposure and lung function changes.

METHODS

Endotoxin in cotton dust is well known to elicit proinflammatory mediators involved in acute or chronic respiratory inflammation due to cotton dust. We applied nasal lavage as well as lung function and exposure measurements in a small group (n = 11) of cotton workers during 6 weeks of observation (after 2 weeks free of exposure). Several inflammatory markers in NAL, such as interleukin 8 (IL-8), IL-6, and down-stream mediators, including soluble tumor necrosis factor receptor 75 (sTNF-R75) and soluble intercellular adhesion molecule 1 (ICAM-1), cell counts, marker of epithelial response (uric acid), and marker of plasma exudation (albumin) were measured.

RESULTS

At the exposure levels examined in this study [cotton dust, geometric mean (GM) = 1.10 mg/m3; endotoxin, GM = 2,869 EU/m3], several inflammatory markers in NAL such as IL-8, sTNF-R75, and albumin tended to increase through the measurement period with increasing airborne endotoxin concentration (in six workers who had paired measurements in weeks 1 and 6). Although no statistical significance was reached, airborne endotoxin exposure and all inflammatory markers in NAL were relatively higher in cotton workers with a 6-week lung function decrease.

CONCLUSION

The data suggest that inflammatory markers in NAL are associated with repeated airborne endotoxin exposure.

Blood interleukin-8 production is increased in chemical workers with bronchitic symptoms

Chemical exposure may result in respiratory conditions such as chronic bronchitis, bronchial hyperresponsiveness, and chronic airway obstruction. Clinical studies have shown that during the course of disease, cytokine networks are changed. In order to study the relationship between blood cytokines and respiratory symptoms in an occupational setting, we investigated 106 chemical workers during a routine yearly medical examination in 1995. Lung function was measured with flow volume curves and impedance using the forced oscillation technique (FOT). Smoking-status and respiratory symptoms were determined by questionnaires. Cytokines were selected on biological plausibility and measured both in a whole blood assay (TNF-alpha, IL-8) and in serum (IL-4, IL-5, IL-6, IFN-gamma). The hypothesis is that blood levels of TNF-alpha and IL-8 are increased in bronchitis, while serum levels of IL4, IL-5 are increased and IFN-gamma is decreased in asthmatic workers. Spontaneous IL-8 release was significantly higher in workers with bronchitis (P < 0.05) or chronic bronchitis (P < 0.01) compared to workers without those respiratory symptoms, also after correction for age, pack-years, and blood lymphocyte numbers or compared to a matched control group. No correlation was present between specific cytokines and asthmatic symptoms. These data suggest that blood IL-8 may be considered as a useful marker for bronchitis.

Toxicity and occupational health hazards of coal fly ash (CFA). A review of data and comparison to coal mine dust

Coal fly ashes (CFA) are complex particles of a variable composition, which is mainly dependent on the combustion process, the source of coal and the precipitation technique. Toxic constituents in these particles are considered to be metals, polycyclic aromatic hydrocarbons and silica. The purpose of this review was to study the in vitro and in vivo data on coal fly ash and relate the studied endpoints to the role of (crystalline) silica, considering its recent classification as a human carcinogen. For most of the effects coal mine dust was chosen as a reference, since it contains up to 10% of crystalline silica (alpha-quartz) and is well studied both in vivo and in vitro. Most studies on fly ash toxicity were not designed to elucidate the effect of its silica-content nor did they include coal mine dust as a reference. Taking this into account, both in vitro and in vivo experimental studies show lower toxicity, inflammatory potential and fibrogenicity of CFA compared to silica and coal mine dust. Although in vitro and in vivo studies suggest genotoxic effects of fly ash, the data are limited and do not clarify the role of silica. Epidemiological studies in fly ash exposed working populations have found no evidence for effects commonly seen in coal workers (pneumoconiosis, emphysema) with the exception of airway obstruction at high exposure. In conclusion, the available data suggest that the hazard of coal fly ash is not to be assessed by merely adding the hazards of individual components. A closer investigation of 'matrix' effects on silica's toxicity in general seems an obligatory step in future risk assessment on fly ashes and other particles that incorporate silica as a component.

Neutrophils amplify the formation of DNA adducts by benzo[a]pyrene in lung target cells

Inflammatory cells and their reactive oxygen metabolites can cause mutagenic effects in lung cells. The purpose of this study was to investigate the ability of activated neutrophils to modulate DNA binding of benzo[a]pyrene (B[a]P), a known carcinogen, in lung target cells. Equivalent numbers of rat lung epithelial cells (RLE-6TN cell line) and freshly isolated human blood neutrophils (PMN) were coincubated in vitro for 2 hr after addition of benzo[a]pyrene (0.5 microM) or two of its trans-diol metabolites, with or without stimulation with phorbol myristate acetate (PMA). DNA adducts of B[a]P-metabolites were determined in target cells using 32P-postlabeling; oxidative DNA damage (7-hydro-8-oxo-2'-deoxyguanosine [8-oxodG]) was evaluated by high performance liquid chromatography with electrochemical detection. Increased DNA adducts were observed in lung cells coincubated with polymorphonuclear leukocytes (PMN). Activation of PMN with PMA, or addition of more activated PMN in relation to the number of lung cells, further increased the number of adducts, the latter in a dose-response manner. Incubation with B[a]P-4,5-diol did not result in any adduct formation, while B[a]P-7,8-diol led to a significant number of adducts. Moreover, PMA-activated PMN strongly enhanced adduct formation by B[a]P-7,8-diol, but not 8-oxodG, in lung cells. The addition of antioxidants to the coincubations significantly reduced the number of adducts. Results suggest that an inflammatory response in the lung may increase the biologically effective dose of polycyclic aromatic hydrocarbons (PAHs), and may be relevant to data interpretation and risk assessment of PAH-containing particulates.

Particles, inflammation and respiratory tract carcinogenesis

Particle-induced carcinogenesis is a non-specific outcome of many different particles. It was the purpose of this study, (i) to comprehensively review some of the mechanisms through which particles and particle-associated carcinogens can cause mutagenic/carcinogenic effects, and (ii) to indicate how this affects risk assessment studies. Data are presented that demonstrate the crucial role of a chronic inflammatory response in mutagenic effects of both silica and carbon black particles on the HPRT gene in lung target cells. The concept of inflammation in particle-induced genotoxicity is put into the context of other mechanisms, such as the release of cytokines and reactive oxygen species. It is concluded that interpretation of rat inhalation studies should certainly include this concept.

A five year follow-up of lung function among chemical workers using flow-volume and impedance measurements

Impedance of the respiratory system, measured using the forced oscillation technique (FOT), has repeatedly been proposed as a tool for occupational health screening. The aim of this study was to compare the outcome of impedance measurements and flow-volume curves, and to study relationships between lung function decline and specific exposures and smoking. Both measurements were applied in 136 chemical workers from seven main production/personnel groups during a 5 year follow-up (1990-1995). The prevalence of airway obstruction (forced expiratory volume in one second (FEV1) < 80% of predicted) at both time-points was about 5% but did not necessarily include the same subjects. The average decline in FEV1 over 5 yrs was 200 mL (predicted decline 160 mL). Although most impedance parameters correlated to flow-volume parameters in both years, a rapid 5 year decline of FEV1 (> 330 mL) was only accompanied by a significant decrease in the reactance at 8 Hz (X8) and an increase in the resonance frequency (f0). Interestingly, decline in FEV1 was significantly dependent on age, years of employment, pack-years, FEV1, and all impedance parameters at the start in 1990 (r = 0.35; p = 0.01). Similarly, the increase in f0 was significantly dependent on age, years of employment, pack-years, f0, FEV1, forced vital capacity (FVC), peak expiratory flow (PEF) and maximal mid-expiratory flow (MMEF) at the start (r = 0.56; p < 0.01). Those with a rapid decline in FEV1, were relatively more represented among acid workers (relative risk (RR) = 2.14), maintenance workers (RR = 2.1) and bulk/transport workers (RR = 1.78), but none of these was significant. Lung function, however, was significantly lower in the bulk/transport workers (n = 14) compared to the rest, based both on flow-volume (FEV1, FVC) and impedance (X8, f0) measurements. Smoking had a significant effect on most flow-volume parameters but only for frequency dependence among the impedance outcomes. It is concluded that alterations in impedance parameters do reflect changes in flow-volume curves induced by age. smoking and occupational exposure. Therefore, these data are a valuable extension to current cross-sectional data.

Cross-shift changes in blood inflammatory markers occur in the absence of airway obstruction in workers exposed to grain dust

Grain dust is well known to cause both acute and chronic respiratory disorders, and endotoxins are considered key components in this. Since endotoxins are known to elicit proinflammatory mediators, we investigated cytokine (tumor necrosis factor [TNF], interleukin-6, interleukin-8) release and a number of proinflammatory and anti-inflammatory proteins (soluble TNF receptors, lipopolysaccharide (LPS) binding protein, bactericidal permeability increasing protein (BPI), C-reactive protein) in plasma of workers exposed to grain dust. In two surveys during 1 week, lung function was measured daily before and after the shift, using flow-volume curves and/or forced oscillation measurements. On Monday and Friday, blood samples (30 mL) were drawn and cytokine release was determined by enzyme-linked immunosorbent assay in supernatant of isolated monocytes or whole blood culture, either unstimulated or on the ex vivo stimulation with 3 ng/mL or 1,000 ng/mL endotoxin. Individual exposures were determined from stationary dust measurements at every workplace combined with personal task analysis during all shifts. In both surveys, no cross-week change in lung function parameters was observed. In the first survey (average exposure: 20.2 mg/m3), monocyte spontaneous TNF release was increased sevenfold cross week (p<0.001) and was significantly related both to individual dust exposure (r=0.62) of that week and the increase in soluble TNF receptor 75 kD (r=0.85). In the second survey, where average exposure was much lower (3.67 mg/m3), impedance parameters indicated a significant improvement of airway function, and cross-week changes in inflammatory markers were minimal. Therefore, we conclude that inflammatory events can be used to monitor adverse respiratory effects of moderate grain dust exposure.

Plasma levels of soluble tumour necrosis factor receptors are increased in coal miners with pneumoconiosis

Among other cytokines, tumour necrosis factor (TNF)-alpha is considered to play a key role in the development of mineral dust related fibrosis. Previously, we showed that ex-vivo release of TNF by peripheral blood monocytes is a marker for progression of coal workers' pneumoconiosis (CWP). Since soluble TNF receptors (sTNF-Rs) are believed to play an important regulatory role in systemic effects of TNF, we measured plasma levels of sTNF-R55 and sTNF-R75 in coal miners with (n = 28) or without (n = 76) CWP and in nonexposed controls (n = 29). sTNF-R75 levels were significantly increased in miners with CWP (2.09 +/- 0.44 ng.mL-1) versus the nonexposed controls (1.86 +/- 0.23 ng.mL-1). Neither sTNF-R55 nor sTNF-R75 were related to exposure, stage of pneumoconiosis, smoking, or (spontaneous or ex-vivo induced) monocyte TNF-release. sTNF-R55 was increased in subjects with medication (especially those using cardiovascular drugs); upon exclusion of these subjects, sTNF-R55 was found also to be significantly increased in CWP. In conclusion, bearing in mind a confounding effect of medication, soluble TNF receptors are elevated in plasma of retired miners with coal workers' pneumoconiosis. These observations further support the important role of TNF-mediated pathways in the pathogenesis of mineral dust related fibrosis.

Epidemiological evaluation of release of monocyte TNF-alpha as an exposure and effect marker in pneumoconiosis: a five year follow up study of coal workers

OBJECTIVES

To determine (a) reproducibility with previous cross sectional findings, and (b) the predictive value of initial release of tumour necrosis factor-alpha (TNF-alpha) towards later progression of coalworkers' pneumoconiosis (CWP).

METHODS

Release of monocyte TNF-alpha after in vitro stimulation with coal mine dust, silica, and endotoxin was measured in 104 retired miners and was related to stage of CWP (chest radiograph) and cumulative exposure. A subgroup of 46 miners was screened by high resolution computed tomography (HRCT). Prospective analysis of TNF-alpha (40 out of 104 miners involved in the previous TNF-alpha study) was done by relating initial TNF-alpha to five year progression of CWP measured by comparison of paired chest radiographs.

RESULTS

As observed previously, dust stimulated release of TNF-alpha was increased in miners, especially in the early stages of pneumoconiosis. Cumulative exposure was related to pneumoconiotic stage but not to release of TNF-alpha. This excluded TNF-alpha as an exposure marker. Initial concentrations (1987) of TNF-alpha were related to later progression of CWP. Miners who showed abnormally high dust stimulated release of TNF-alpha had an increased risk of progression in CWP (relative risk 8.1).

CONCLUSIONS

These results show (a) the significant involvement of TNF-alpha in pneumoconiosis in humans induced by coal dust and (b) that this routine test possibly constitutes a powerful tool to estimate individual prognosis of pneumoconiotic disease, even after the end of occupational exposure.

Oxidant resistance of cadmium-adapted human lung fibroblasts

Metallothionein (MT) is a metal and thiol-rich protein readily induced by cadmium (Cd) exposure. In vitro experiments have demonstrated that MT is able to serve as a scavenger of hydroxyl radicals as well as superoxide anions, albeit to a lesser extent. The role of MT as a mediator in Cd induced oxidant resistance was investigated in a nontransformed human lung fibroblast cell line (IMR-90). Cells were passaged three times either in a Cd-containing medium (8.9 microM CdCl2) or in a medium which lacked Cd. Cellular MT content, as quantitated by a modification of the heme/109Cd binding assay, increased significantly with each passage in Cd. Immunocytochemistry studies revealed that all Cd-pretreated cells contained MT and that MT was localized in both cytoplasmic and nuclear compartments. Immunolabeling was more intense in some cells compared to others. Very slight immunolabeling was observed in physiological control cells, grown in the absence of Cd, and virtually no staining was observed in Cd-adapted or non-adapted cells when primary antibody was omitted. Using the xanthine/xanthine oxidase system as a generating system for active oxygen species, we found that the magnitude of cell injury for Cd-adapted and non-adapted fibroblasts was dependent upon oxidant concentration and duration of oxidant exposure. Cd-adapted fibroblasts, which were characterized by over-expression of MT, were significantly more resistant to injury by active oxygen species and also exhibited a greater ability to scavenge extracellular hydrogen peroxide compared to cells with no previous history of Cd exposure. Experiments with aminotriazole demonstrated that catalase was not a major contributor to the additional hydrogen peroxide scavenging capacity of Cd-adapted cells. The data presented in this report are consistent with involvement of MT in protecting critical cellular targets from reactive oxygen species.

Evaluation of serum type III procollagen peptide as an exposure marker in retired coal workers

Serum type III procollagen peptide (PIIIP), a degradation product of the type III collagen precursor, has been put forward as an exposure marker for mineral dust. We evaluated PIIIP levels as a marker of exposure to and effects of coal dust in retired coal miners (n = 104). To this end: (a) the individual cumulative dust exposure was calculated from job-exposure matrices, and (b) in addition to routine chest radiography (CR) of all miners according to the criteria of the International Labour Organisation (ILO), a subgroup (n = 46) was screened by high-resolution computed tomography (HRCT). Profusion score (CR and HRCT) tended to increase with cumulative dust exposure, even in the absence of CR evidence for pneumoconiosis (i.e. CR < or = 0/1, n = 35). In contrast to our previous findings in active miners, PIIIP levels were not increased in miners as compared with non-dust-exposed controls (n = 29), and no differences were observed between miners without (ILO = 0/0) and miners with coal workers' pneumoconiosis (CWP; ILO > or = 0/1). No trend in PIIIP versus pneumoconiosis stage was present, either by CR or by the more sensitive HRCT score. PIIIP was also unrelated to any lung function parameter (FEV1, FVC, impedance, diffusion capacity). Age, medication, medical history and smoking habits had no significant effect on PIIIP levels. In the miners with CWP (i.e. ILO > 0/0, n = 28) a significant negative correlation was present between PIIIP values and (log) cumulative dust exposure. This decrease in serum PIIIP levels with increasing cumulative exposure may be due to chronic adaptive changes in type III collagen deposition and/or breakdown. Other relations between exposure and PIIIP were not observed. In conclusion, the present findings do not support the use of serum type III procollagen peptide as a marker of exposure to and (early) interstitial or respiratory effects of coal dust.

Induction of c-fos and c-jun proto-oncogenes in target cells of the lung and pleura by carcinogenic fibers

To study mechanisms of cell proliferation by asbestos and nonasbestos fibers, we examined the effects of these agents on the mRNA levels of c-fos and c-jun and ornithine decarboxylase (ODC) in hamster tracheal epithelial (HTE) cells and rat pleural mesothelial (RPM) cells, the progenitor cells of bronchogenic carcinoma and mesothelioma, respectively. In comparison with crocidolite asbestos, increases in c-jun mRNA were less striking in HTE cells after exposure to man-made vitreous fiber-10 (MMVF-10) or refractory ceramic fiber-1 (RCF-1). No c-fos mRNA was detected in HTE cells after exposure to particulates, but exposure of HTE cells to H2O2 caused striking increases in c-fos and c-jun, which preceded increases in ODC mRNA. Increases in ODC mRNA were also observed in HTE cells after exposure to nonasbestos fibers, whereas only crocidolite asbestos caused elevations in ODC mRNA in RPM cells. In RPM cells, crocidolite and chrysotile asbestos caused increases in mRNA levels of both c-fos and c-jun. No increases in proto-oncogene induction were observed using MMVF-10 or RCF-1 at nontoxic concentrations (< or = 5 micrograms/cm2 dish). Moreover, erionite, a fiber extremely potent in the causation of mesothelioma in humans, caused more dramatic elevations in c-fos and c-jun. Nonfibrous particles (riebeckite, polystyrene beads) did not alter proto-oncogene expression in these cell types, suggesting that the fibrous geometry of particulates is critical in the induction of c-fos and c-jun.

Respiratory symptoms and lung function in animal feed workers

In a study among 194 male workers exposed to endotoxin-containing organic dust in animal feed mills, lung function was measured by flow volume curves and impedance measurements and respiratory symptoms were recorded by means of a validated questionnaire. The aims were to detect and localize airway obstruction caused by fodder dust and endotoxin, and to relate respiratory symptoms to both types of lung function measurements. Flow volume and impedance parameters were significantly related to present exposure. All impedance parameters, of the spirometric measures only FEF25, were significantly related to cumulative dust or endotoxin exposure. The changes in impedance parameters were for overall increasing resistance at 8 Hz and decreasing reactance at 8 Hz, reflecting an increase in peripheral airflow obstruction, with increasing exposure. The changes in all lung function parameters were more strongly related to (cumulative) endotoxin exposure than to inspirable dust exposure. All impedance parameters and FEV1 showed a good correlation with complaints of chronic bronchitis and breathlessness. Impedance measurement of the respiratory system proved to be a useful tool for objectively assessing (early) airflow obstruction in workers exposed to inspirable dust and endotoxin and in localizing airflow obstruction.

Respiratory effects and serum type III procollagen in potato sorters exposed to diatomaceous earth

Exposure to diatomaceous earth with low crystalline silica content (< 1%) is rarely reported to cause pneumoconiotic disease, whereas airway obstruction and bronchitis are more frequently reported. We investigated the occurrence of pneumoconiosis and airflow limitation in 172 male workers from 5 potato sorting plants (55 controls, 29 salesmen, 72 currently exposed, and 16 retired exposed) exposed to inorganic dust from former sea terraces (7.7-15.4 mg/m3), high in diatomaceous earth. The presence of fibrosis was evaluated by chest radiographs (exposed only) and serum levels of type III procollagen (P-III-P) were measured as an estimate of fibrogenetic activity. Lung function was assessed by flow volume curves and impedance measurements. A validated questionnaire was used to record respiratory symptoms. No pneumoconiotic abnormalities were demonstrated by chest radiographs. In line with this finding, serum P-III-P levels were not elevated in exposed workers as compared to controls, suggesting no differences in fibrogenetic activity. In fact, serum P-III-P levels decreased significantly (P < 0.03) with increasing cumulative exposure. Flow volume parameters indicated airflow obstruction, dose-related to (cumulative) dust exposure; the annual decline in forced expiratory flow volume (FEV1) was estimated at 10.5 ml/year (P < 0.05). Airway obstruction was confirmed by impedance analysis: In the retired group impedance changes were compatible with airway obstruction extending into the peripheral airways. We conclude that this exposure to quartz during potato sorting does not result in an increased risk for pneumoconiosis, but that (prolonged) surveillance in this group is desirable in order to detect early indications of airflow obstruction.

Biological markers and occupational lung disease: mineral dust-induced respiratory disorders

There is a need for methods to monitor early adverse effects, exposure, and/or susceptibility of individual subjects due to occupational and environmental causes. This paper discusses the experimental origin, value, and validity of several biological indicators, termed biomarkers, that were used to study coal dust-induced respiratory disorders. The findings are presented in a framework to visualize problems and challenges when developing biomarkers. Taking the framework of mineral dust-induced lung disorders as an example, it is demonstrated how carefully designed follow-up studies are a prerequisite to test the validity and use of events often put forward as biomarkers. It is concluded from the data that serum type III procollagen is neither an exposure nor an (early) effect marker, antioxidant enzyme expression is related to the early inflammatory response after mineral dust inhalation, while the evidence is accumulating that tumor necrosis factor-alpha is a susceptibility marker for progression in mineral dust-induced lung fibrosis.

Airflow obstruction and monocyte TNF release in coal workers

Respiratory health of 102 retired coal miners was assessed by chest radiographs, lung function measurements, and questionnaires, and related to tumor necrosis factor-alpha (TNF-alpha) production by blood monocytes upon priming with different stimuli. The objective was to assess a possible relationship between airflow obstruction and TNF-alpha production in retired coal workers. No significant differences in lung function were observed between cases of coal workers' pneumoconiosis (CWP) (n = 27; > %) and references (n = 75; = > %), nor was the effect of cumulative exposure on flow volume or impedance parameters significant. TNF-alpha release upon stimulation of blood monocytes with coal mine dust was significantly increased in cases with International Labour Organisation (ILO) score 0/1 (doubtful cases) compared to references and cases with a higher ILO score. Airflow limitation defined either as a FEV1 < 80% (N = 10; 5 cases of CWP) or as a resonance frequency > 15 Hz accompanied by a negative frequency dependence of resistance (N = 9; 4 cases of CWP) was significantly related to high levels of TNF-alpha release upon stimulation with endotoxin and silica, with silica showing the strongest relation. These data suggest that in this group airflow limitation is associated with an increased expression of inflammatory mediators indifferent of the presence of pneumoconiosis.

Serum procollagen type III peptide in coal workers' pneumoconiosis: a five-year follow-up study

Several studies have suggested the use of serum type III procollagen peptide (PIIIP) as a marker in fibrotic lung disease. To test serum PIIIP as a biomarker for progression of coal workers' pneumoconiosis (CWP), a follow-up study was conducted among 156 coal miners. A five-year progression of simple CWP was determined from paired chest X-ray readings and related to serum PIIIP measured in 1987 (n = 73) and in 1992 (n = 104). Although in eight subjects CWP had progressed, none of these subjects had abnormal levels of serum PIIIP, nor were they different from nonprogressed miners with regard to exposure, age, or smoking habits. The results suggest that the use of serum PIIIP as a biomarker to screen for coal workers' pneumoconiosis is limited.

Oxidant stress responses in human pleural mesothelial cells exposed to asbestos

The generation of oxidants is a proposed mechanism of cell injury by asbestos fibers. To determine whether human pleural mesothelial cells (HMC) respond to asbestos and active oxygen species (AOS) by induction of antioxidant enzymes, cells obtained from pleural effusion were exposed to crocidolite or chrysotile asbestos or xanthine/xanthine oxidase (X/XO), a chemical-generating system of AOS. Gene expression of manganese-containing superoxide dismutase (MnSOD) and heme oxygenase (HO), endogenous enzymes involved in cell defense against oxidant stresses, was then determined. Dosage-dependent increases in steady-state mRNA levels of MnSOD and HO were observed in HMC exposed to asbestos or X/XO. However, increases in gene expression of MnSOD or HO did not occur in HMC after exposure to particulates such as polystyrene beads or riebeckite, the nonfibrous analog of crocidolite asbestos. Comparative experiments with human adult lung fibroblasts (HAL) showed less striking increases in mRNA levels of MnSOD and HO in response to asbestos, but steady-state mRNA levels for HO were increased more than fivefold in response to X/XO. To determine whether increases in mRNA levels of MnSOD were translated into protein, Western blot analyses were performed on HMC and HAL cells exposed to asbestos or X/XO. Slight increases in MnSOD immunoreactive protein were observed in HMC in response to both agents. In contrast, X/XO caused striking elevations in MnSOD protein levels in HAL cells. These results suggest that certain antioxidant enzymes are inducible in HMC after exposure to asbestos and other oxidants.

Increased expression of manganese-containing superoxide dismutase in rat lungs after inhalation of inflammatory and fibrogenic minerals

Steady-state mRNA levels and immunoreactive protein for manganese-containing superoxide dismutase (MnSOD) were assayed in rat lungs after subchronic inhalation of the fibrogenic silicon dioxide, cristobalite, or preparations of titanium dioxide (TiO2) of different inflammatory and fibrogenic potential. Total and differential cell counts recoverable by bronchoalveolar lavage (BAL) were also measured to ascertain whether induction of certain antioxidant enzymes (AOE) correlated with inflammatory responses. Inhalation of cristobalite and ultra-fine TiO2, a particle causing pulmonary inflammation and fibrosis, caused dramatic increases in MnSOD mRNA levels in rat lung which correlated with increases in MnSOD immunoreactive protein. Increases in gene expression of other AOE [catalase, glutathione peroxidase (GPX), copper-zinc containing superoxide dismutase (CuZnSOD)] were less striking and did not correlate precisely with inflammatory potential of minerals. Inflammatory changes in BAL correlated directly with steady-state MnSOD mRNA levels in lung. Inhalation of TiO2-F, a noninflammatory, nonfibrogenic mineral, failed to induce MnSOD or mRNAs for other AOE. Our data suggest that particles causing inflammation and pulmonary fibrosis increase expression of AOE in lung, most notably MnSOD. Thus, elevations of MnSOD mRNA levels in lung or BAL may be predictive of lung disease.

Effects of Aramid, a high strength synthetic fiber, on respiratory cells in vitro

Industry continues to develop synthetic fibers for new technologies and as replacements for asbestos, a toxic and carcinogenic fiber. To determine whether the in vitro effects of the aromatic polyamide fiber, Aramid (Kevlar, Twaron), resembled those induced by asbestos, fibers were surveyed for (1) cytotoxicity as measured by total cell protein, and (2) proliferative capacity as measured by [3H]thymidine incorporation, colony forming efficiency (CFE), and ornithine decarboxylase (ODC) activity in two target cells of mineral dust-induced lung damage, hamster tracheal epithelial (HTE) cells and rat lung (RL90) fibroblasts. Results of cytotoxicity tests indicated that Aramid was as toxic to HTE and RL90 cells as were crocidolite and chrysotile asbestos when expressed on both an equal mass and equal fiber number basis. In HTE cells, Aramid caused a statistically significant increase in [3H]thymidine incorporation and CFE and produced a dose-dependent induction of ODC enzyme activity. Proliferative effects by asbestos or Aramid were not observed in RL90 fibroblasts. Thus, when tested over a respirable size range, Aramid exhibited many of the same effects on epithelial cells in vitro as did asbestos, including increased radiolabeled nucleotide incorporation into DNA and induction of ODC enzyme activity.

Physiologically based toxicokinetic modeling of 1,3-butadiene lung metabolism in mice becomes more important at low doses

This paper describes a physiologically based toxicokinetic model for 1,3-butadiene uptake, distribution, and metabolic clearance in mice. Model parameters for metabolic activity were estimated from the correspondence between computer simulation studies and experimental results as published in the literature. The parameterized model was validated with independent literature data. With the resulting model, the relative importance of lung metabolism as compared to metabolism in the liver increased with decreasing ambient air concentrations. This was due to saturation of metabolism in the alveolar area of the lung, which occurred in the simulations at ambient air concentrations well below current threshold limit values. At higher air concentration, liver metabolism became relatively more important. The tendency toward increased importance of lung metabolism at low doses indicates the necessity of careful extrapolation of in vivo results to low doses. Moreover, this trend may also contribute to species difference in susceptibility to the carcinogenic activity of butadiene.

Cell and tissue responses to oxidative damage

A broad array of oxidative stresses modulates gene expression in a variety of mammalian cells. One goal of this review was to characterize cellular responses to oxidative injury, how these processes are regulated, and the outcome for a particular cell or tissue. Many genes induced in response to specific oxidant stresses have been identified and include transcription factors, replication proteins, proteases, protease inhibitors, proteins affecting cell proliferation and various antioxidants, i.e. heme oxygenase, MT, and MnSOD. The latter enzyme is induced after a number of cytokines and oxidant stresses including hyperoxia and mineral dusts causing inflammation. Moreover, increases in mRNA levels of TNF and IL-1, cytokines inducing MnSOD, are observed after exposure to UV and ionizing radiation. Since increased electron flow could lead to generation of more AOS within mitochondria, increased levels of MnSOD might be necessary to maintain normal functioning of the mitochondria after oxidative stress. Alterations in cell growth are intrinsically related to the pathogenesis of many diseases. Paradoxically, some of the responses of cells to oxidative stress reflect cytotoxicity and cytostasis, whereas others result in increased cell proliferation. For example, induction of gadd genes observed after oxidative stress is related to growth arrest of cells, a response which might enable the cell to repair oxidative damage prior to replication. This phenomenon might prevent fixation of mutations associated with oxidative DNA damage. On the other hand, increased mRNA expression and activity of ODC, observed after exposure of cells to UV or asbestos is associated with increased cell proliferation. In addition, increased mRNA expression of cellular proto-oncogenes observed after exposure to oxidants could also be related to increased DNA synthesis or proliferation. Figure 5 provides a general scheme of cell responses to oxidative stress and possible ramifications. AOS can react with a number of target molecules including proteins, lipids, and DNA. These interactions elicit a number of signals including activation of gene regulatory factors (transcription factors) which in turn activate oxidative stress-responsive genes or regulons. Consequently, a number of proteins are produced with distinctive functions including DNA repair enzymes, antioxidants, proteases inhibitors, cytokines and proteins affecting cell proliferation. These cellular responses to AOS can lead to restoration of normal cellular function and adaptation to oxidative stress, cell death or aberrant proliferation. It is the latter two responses which can lead to a variety of disease states including cancer.(ABSTRACT TRUNCATED AT 400 WORDS)

Decreased glutathione content and glutathione S-transferase activity in red blood cells of coal miners with early stages of pneumoconiosis

Blood samples of miners heavily exposed to coal dust were examined for changes in glutathione S-transferase (GST) activity. Decreased GST activity was found in red blood cells of subjects with early stages of coal workers' pneumoconiosis (International Labour Office classification 0/1-1/2) when compared with control miners. At further progression of coal workers' pneumoconiosis (> or = 2/1), the activity of GST was not different from controls. In the same group with moderate coal workers' pneumoconiosis a decrease in GSH in red blood cells occurred. Decreases in GST activity in early stages of coal workers' pneumoconiosis, as well as the decreases in glutathione peroxidase (GPx) activity and in GSH concentrations reported earlier, may originate from damage caused by reactive oxygen species. These changes might imply an impairment of the detoxification capacity for electrophilic and oxidative compounds during this stage of the disease.