Chemical reactivity of the carbon-centered free radicals and ferrous iron in coals: role of bioavailable Fe2+ in coal workers pneumoconiosis.

Striking differences in the prevalence of coal workers' pneumoconiosis (CWP) exist between different coal mine regions. The major factors responsible for the observed regional differences in CWP have not yet been identified. In the present study, chemical reactivity of the carbon-centered free radicals in coals and lung tissues, as well as ferrous iron in the coals, were studied by ESR techniques. The ESR spectra clearly demonstrated the presence of at least two types of carbon-centered free radical species, which might respectively attribute to the macromolecular phase and the molecular phase of coal. Grinding produced free radicals in coals. Exposure of freshly ground coal to air for 28 h induced a slight increase of free radicals for most of the coals, and a slight decrease after 4 months' exposure. The lung tissue samples of coal workers deceased of CWP showed similar ESR spectra as coal samples, and these radicals were highly stable in the lung. After incubation of coals with glutathione, hydrogen peroxide, sodium formate or oxygen, the coal sample from the Gardanne mine which has never induced CWP, and thus is the least hazardous coal, showed the most significant change in the carbon-centered free radical concentration. No significant changes were observed among other coals reported to induce CWP. On the other hand, we found that the coals released different amounts of Fe2+ in an acidic medium. Interestingly, the prevalence of CWP correlates positively with the released Fe2+ content in these coals and with the amount of oxygen radicals produced by the interaction of Fe2+ with O2 in the acidified coal filtrates. Our studies indicate that the carbon-centered free radicals may not be biologically relevant to coal dust-induced pneumoconiosis, whereas the acid soluble Fe2+, which may be dissolved in the phagolysosomes of macrophages, can then lead to Fe2+-induced oxidative stress and eventual CWP development.

Cytotoxic and transforming effects of some iron-containing minerals in Syrian hamster embryo cells.

Four physicochemically characterized iron-containing minerals, one fibrous (a nemalite [brucite]) and three nonfibrous (a biotite [phyllosilicate], a magnetite (Fe3O4), and a goethite [FeOOH alpha]), were studied for cytotoxicity and morphological transformation of Syrian hamster embryo (SHE) cells. When colony-forming efficiency was used as a measure of cytotoxicity, it appeared that the nemalite was about 1.7-fold more cytotoxic than the biotite and magnetite. However, if the inhibitory effect on the cell growth was considered the nemalite appeared to be 8-fold more effective. The analysis of the cell cycle kinetics by flow cytometry revealed a time- and dose-dependent delay in the progression of cells through the cell cycle, with the accumulation of cells in S and G2-M phases, more particularly in the cultures treated with nemalite. While the goethite was neither cytotoxic nor transforming, the other three dusts were, in a dose-dependent manner, efficient in inducing morphological transformation of SHE cells. According to their transforming potency they ranged as follows: nemalite > biotite > magnetite. A 18-fold higher treatment concentration of magnetite than that of nemalite was necessary to induce the same transformation frequency. The iron chelator desferrioxamine abolished the transforming effect of nemalite. The results suggest that (i) the cytotoxicity and the transformation are induced by some divalent iron-containing minerals and that they are two distinct processes; (ii) there is a varying ability among these dusts to induce cell transformation; and (iii) the bioavailability of divalent iron leading to formation of reactive iron-oxygen species could mediate the transforming potency of a mineral. Physicochemical studies correlated to biological effects of many metallic mine dusts are the only approach for understanding their mechanisms of action and their role in occupational pathology.

Factors that influence the formation and stability of hydrated ferrous sulfate in coal dusts. Possible relation to the emphysema of coal miners.

Epidemiological studies have shown that a causal relationship may exist between coal dust exposure and emphysema in coal miners. Emphysema can be considered as one of the human pathologies associated with oxidative stress, resulting from oxidant-induced alpha 1-antitrypsin (alpha 1-AT) inactivation and uncontrolled proteolysis of lung tissue. We have previously reported that certain coal dusts contained hydrated ferrous sulfate (FeSO4) that inactivated alpha 1-AT [Huang et al. (1993) Chem. Res. Toxicol. 6, 452-458]. In the present study, we have shown that the FeSO4 originated from oxidation of pyrite (FeS2), which is a typical contaminant of coal dusts. The relative humidity and microenvironment around individual pyrite particles influence the formation of FeSO4 in the coal. However, the subsequent human exposure to coal dust containing FeSO4 depends on the stability of the formed FeSO4. We found that pH played the most important role in stabilizing the FeSO4, such that a final pH < 4.5 after oxidation of pyrite stabilized FeSO4, whereas at high pH the conversion of reactive Fe2+ to Fe3+ was immediate. Sulfuric acid (H2SO4), which is also produced by the oxidation of pyrite, can lower the pH, but it can also be neutralized by other minerals in coal dusts, such as calcite (CaCO3). The stability of FeSO4 in coal dust can also be influenced by the length of exposure to air. Our studies demonstrated that coal samples differed in their capacity to stabilize FeSO4. This current study strengthens our previous reported hypothesis that emphysema, which occurs irregularly in coal miners, could be directly related to exposure to coal dust containing FeSO4.

Effect of mineral particles containing iron on primary cultures of rabbit tracheal epithelial cells: possible implication of oxidative stress.

Environmental mineral particles such as asbestos are responsible for numerous respiratory diseases. In addition to effects related to their geometry, particles are now assumed to act by triggering an oxidative stress process. Iron-containing particles, in particular, can produce oxygen-activated species by oxidizing their iron. To evaluate the involvement of iron-containing particles in respiratory diseases, three mineral particles (chrysotile, nemalite, and hematite) were tested in primary cultures of tracheal epithelium. Because of the ciliary beat, the three mineral particles were quickly concentrated at the periphery of the mucociliary epithelium, reconstituted in vitro where they induced cellular lesions. Endocytosis of the three types of particles was observed. Cytotoxicity studies have indicated that among the tested particles, the most cytostatic after 24 hr of treatment was the one that contained more Fe2+ available on the surface, nemalite. Moreover, the effect of nemalite was reduced by pretreatment with desferrioxamine. As mineral particles, especially asbestos, are suspected to induce squamous metaplasia, we chose to study two specific transformations of the epithelium: the expression of cytokeratin-13 and the formation of cross-linked envelopes. Under our culture conditions, nemalite and chrysotile increased the expression of the cytokeratin-13, a specific marker of squamous metaplasia, whereas nemalite was the only particle able to strongly induce the formation of cross-linked envelopes. Nemalite was the most cytostatic particle and the most efficient at inducing squamous metaplasia. Measures of oxidizing power by electron-spin resonance revealed that nemalite produced the most oxygen-activated species.(ABSTRACT TRUNCATED AT 250 WORDS)

Inactivation of alpha 1-antitrypsin by aqueous coal solutions: possible relation to the emphysema of coal workers.

Increasing evidence demonstrates that emphysema in coal workers may be related to their exposure to coal dusts. The hypothesis that emphysema could be related to the production of reactive oxygen species (ROS) generated by inhaled coal dusts was examined in the present study. Using ESR, we investigated whether the interaction of different coals with dissolved oxygen in aqueous medium could generate ROS. Indeed, we found that one of the five examined French coal samples, Vouters coal, was effective in oxidizing formate anions or ethanol by a radical pathway. Inactivation of alpha 1-antitrypsin (alpha 1-AT) in vitro was then examined for all five coal filtrates. The Vouters coal filtrate, which exhibits oxidative activity, can also inactivate alpha 1-AT. When this coal filtrate was crystallized and redissolved, its oxidative activity was found to be conserved. By use of various analytical techniques, the active component of this coal filtrate was identified to be primarily ferrous sulfate. We confirmed that pure ferrous sulfate can effectively reduce oxygen to produce ROS in aqueous medium in vitro and can also inactivate alpha 1-AT. In this report, the nature of the coal-generated oxidative species, the origin of ferrous sulfate, and the stability of ferrous sulfate in the different coal samples are discussed. These results offer evidence that some inhaled coal dusts are capable of producing ROS, which may play an important role in the development of coal workers' emphysema.

Free radical production during photo-assisted NADPH reduction of four alpha-nitroarenofurans.

Generation of radical anions during NADPH reduction of four mutagenic and genotoxic alpha-nitroarenofurans was examined. ESR showed that free radicals were generated during reduction solely in the presence of light. Computer simulations of ESR spectra were in good agreement with the experimental ones.

Microsomal lipid peroxidation and oxy-radicals formation are induced by insoluble iron-containing minerals.

Lipid peroxidation, measured by malondialdehyde formation is induced in rat liver microsomes by insoluble iron-containing minerals (pyrite, magnetite, nemalite and an iron ore, minette de Lorraine) which are generally found either in iron mines or as contaminants of asbestos fibers. In spin-trapping studies using DMPO as a spin trap those minerals are also found to catalyze the oxidation of formate to carboxylate radicals by oxygen, via the formation of hydroxyl radicals. The two processes are mainly due to the presence of redox active iron at the surface of the solid particles and thus are greatly inhibited by desferrioxamine, a strong iron chelator. However, these reactions are not correlated.

Production of free radicals arising from the surface activity of minerals and oxygen. Part I. Iron mine ores.

The excess incidence of lung cancers observed in many metal mines probably is not only correlated with radioactivity but also with the inhaled dusts. In an attempt to determine a possible mechanism of carcinogenicity related to the surface activity of dusts, using the spin-trapping agent and ESR spectroscopy, one can demonstrate that some mineral dusts from iron ore mines are very active in an oxidative process in aqueous medium, implying the formation of radical oxygen species on reducing surface sites of the solid. This reducing surface activity of the dusts depends on the presence of Fe2+ ion in the lattice and on the process of activation and passivation of the surface sites. The more simple process of activation is the dissolution of the oxidized coating on the particle surface. Among the oxides, oxyhydroxides, carbonates, and silicates, the magnesium-iron phyllosilicates (chlorite, biotite, berthierine) appear the most active. The siderite FeCO3 is also active, but the iron oxides and oxyhydroxides are generally nonactive.

Production of oxygen radicals by the reduction of oxygen arising from the surface activity of mineral fibres.

According to certain hypotheses, the production of oxygen radicals within the biological medium (the phenomenon of oxidative stress) may play an important role in fibrosis and in certain steps of carcinogenesis. The mineral fibres of various materials are capable of participating in this phenomenon, owing to the reducing nature of their surface activity, so that OH. radicals can be produced from oxygen in 3 steps. The surface activity of inorganic materials which are insoluble or only very slightly soluble is due to the presence of electron donor active sites, generally linked to Fe2+ ions found in the neighbourhood of the surface. In biological systems, these sites may emerge on the surface as a result of the partial dissolution of the particle, the action of a biological reducing agent, the phenomenon of deposition on the surfaces or cation exchange. We have explored the reducing properties of the surfaces of a certain number of mineral fibres, in aqueous buffer medium, by electron paramagnetic resonance (EPR) measurement of the adduct with the radical-trapping agent 5,5'-dimethyl-l-pyrrolidine-N-oxide (DMPO), produced from the radicals initially formed (OH. or R.). We have found certain fibres to be highly effective in producing radicals from dissolved oxygen (Canadian chrysotile, nemalite, freshly ground amphiboles) while others have little effect. The reducing activity of certain fibres may be markedly increased by prior treatment in the presence of a ferrous salt (as in the case of erionite) or by the addition of glutathione to the reaction medium (as in the case of UICC crocidolite). It is suggested that the carcinogenic activity of certain inorganic materials at the pulmonary level is the result of their surface reducing properties. These reducing properties may either be present at the time of inhalation or acquired in the biological medium. This hypothesis is not in conflict with the observation of the role of the dimensional characteristics of fibres in mesothelioma.

Studies on surface properties of asbestos. IV. Catalytic role of asbestos in fluorene oxidation.

To determine whether asbestos is a basic catalyst, catalytic oxidation of fluorene to fluorenone in a heterogeneous system was tested. It was shown that oxidation was quantitatively possible on the surface of all basic minerals, such as asbestos (chrysotile and crocidolite) and magnesia, but was not possible with acidic mineral materials such as silica. The effects of different factors are discussed.

The relationship of hand dominance to the motor corrdination, mental ability, and right-left awareness of young normal children.

Normal children who had established hand dominance, as measured by the McCarthy Scales, were compared on mental and motor variables with youngsters who did not give evidence of dominance. Using the McCarthy normative sample (N = 1,032) as the data source, significant differences in cognitive and motor ability were found for 2(1/2)--4(1/2)-year-olds but not for 5--8(1/2)-year-olds. However, a significant relationship between handedness and right versus left awareness was obtained for the older group.