Particulate matter properties and health effects: consistency of epidemiological and toxicological studies

Identifying the ambient particulate matter (PM) fractions or constituents, critically involved in eliciting adverse health effects, is crucial to the implementation of more cost-efficient abatement strategies to improve air quality. This review focuses on the importance of different particle properties for PM-induced effects, and whether there is consistency in the results from epidemiological and experimental studies. An evident problem for such comparisons is that epidemiological and experimental data on the effects of specific components of ambient PM are limited. Despite this, some conclusions can be drawn. With respect to the importance of the PM size-fractions, experimental and epidemiological studies are somewhat conflicting, but there seems to be a certain consistency in that the coarse fraction (PM10-2.5) has an effect that should not be neglected. Better exposure characterization may improve the consistency between the results from experimental and epidemiological studies, in particular for ultrafine particles. Experimental data indicate that surface area is an important metric, but composition may play an even greater role in eliciting effects. The consistency between epidemiological and experimental findings for specific PM-components appears most convincing for metals, which seem to be important for the development of both pulmonary and cardiovascular disease. Metals may also be involved in PM-induced allergic sensitization, but the epidemiological evidence for this is scarce. Soluble organic compounds appear to be implicated in PM-induced allergy and cancer, but the data from epidemiological studies are insufficient for any conclusions. The present review suggests that there may be a need for improvements in research designs. In particular, there is a need for better exposure assessments in epidemiological investigations, whereas experimental data would benefit from an improved comparability of studies. Combined experimental and epidemiological investigations may also help answer some of the unresolved issues.

Abstract 5431: Effects of various dietary fibers on intestinal carcinogenesis in Min mice

Colorectal cancer is among the most prevalent types of cancers and its development has been associated with components in the diet. Dietary fibers seem to display a protective role, and in the search for what mechanisms may be involved increased focus has been directed at the effect of fibers on the gut micro flora. This project has included studies aimed at generating new knowledge about how various types of dietary fibers influence the intestinal tumorigenesis, inflammatory status, composition of bacteria in various intestinal segments and the interrelationships between these factors. Three different fibers were tested; a finely ground cellulose preparate, inulin and mask (a dried and finely milled brewers spent grain). All fibers were present in the diet in a lower and a higher concentration (5 % and 15%). The test diets were given to multiple intestinal neoplasia (Min) and wild type (Wt) mice from weaning until euthanation at week 11. The Min mice carry the same mutation as seen in the human familial adenomatous polyposis (FAP) syndrome that results in spontaneous development of colorectal tumors. The majority of sporadic human colorectal tumors are also mutated in the same signaling pathway. Colon carcinogenesis was induced by two subcutaneous injections of azoxymethan (day 7 ±1 and14 ±1 after birth). At euthanation a blood sample from the hepatic portal vein was obtained and the small (Min mice) and large intestine (Min and Wt mice) were removed and fixed. The coecum and spleen were weighed and snap frozen. Individual weights and diet consumption were recorded. Scoring of tumors in the small and large intestine displayed a weak but significant difference in tumor development between the different diet groups. The inulin 5% diet resulted in reduced tumor number compared to the cellulose (small and large intestine) and the mask (large intestine) fibers. Analysis by Multiplex of a large range of inflammatory cytokines in plasma revealed the presence of individual animals with high levels of certain cytokines. This variation seems to be independent of fiber type in the diet. However, analysis of several data from the individual animals with respect to any correlation between cancer development and cytokine level is presently under evaluation. Furthermore, a pilot screening of the micro flora in feces from selected representative animals demonstrated interesting differences in species variation when related to the various fibers tested and the two different doses included. All animal recordings in this study are done on the individual level; correlations between tumor development, inflammatory status and intestinal micro flora will therefore be made at several levels. In summary, our results demonstrate that various types of fibers influence the development of tumors to various degrees. Further evaluation of the data is in progress and may reveal associations between tumor development, inflammatory status and the intestinal micro flora.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 5431. doi:1538-7445.AM2012-5431

Fish liver and seagull eggs, vitamin D-rich foods with a shadow: results from the Norwegian Fish and Game Study

SCOPE

Fish liver, fish liver oil, oily fish and seagull eggs have been major sources of vitamin D for the coastal population of Norway. They also provide dioxin and polychlorinated dioxin-like compounds (dl-compounds), which may interfere with vitamin D homeostasis. We investigated whether serum 25-hydroxyvitamin D (25(OH)D) might be compromised by concomitant intake of dl-compounds.

METHODS AND RESULTS

We studied 182 adults participating in the Norwegian Fish and Game Study. Participants who consumed fish liver and/or seagull eggs had higher dl-compound intake and blood concentrations than non-consumers (p < 0.001). Vitamin D intake was higher (p < 0.001), whereas serum 25(OH)D was lower (p = 0.029) in consumers than in non-consumers. Among non-consumers, vitamin D intake was associated with serum 25(OH)D (β=1.06; 95% CI: 0.48, 1.63). This association was weaker among consumers (β = 0.52; 95% CI: -0.05, 1.08), but strengthened when adjusted for retinol intake (β = 0.66; 95% CI: 0.12, 1.21). The association between vitamin D intake and serum 25(OH)D did not seem to be compromised by intake of dl-compounds.

CONCLUSION

To secure adequate vitamin D status while keeping the intake of dioxins and dl-polychlorinated biphenyls low, a healthy diet should include both supplemental vitamin D and oily fish. Despite high nutrient content, dietary fish liver and seagull eggs should be restricted, due to dl-compounds and possible vitamin A-D antagonism.

Helseeffekter av byluftpartikler

Svevestøv i byluft består av forbrenningspartikler og mineralpartikler med svært forskjellige størrelser og kjemiske egenskaper. Svevestøvet kan deles inn i størrelsesfraksjoner som PMAmbient particulate matter (PM) comprises particles from different combustion processes and a variety of mineral particles. The particles vary widely in size distribution and chemical/physical characteristics. PM is often divided into size fractions with different aerodynamic diameters: PM10 (PM ! 10 mm), PM2.5 (PM ! 2.5 mm) and PM0.1 (PM ! 0.1 mm). Recent population studies have found an association between an increase in mortality and morbidity due to lung and/or cardiovascular disease and short-term increases in PM. The relative risk (RR) was approximately 1.005 for an increase in 10 mg/m3 PM10, without an observed threshold even at concentrations below 10 mg/m3. Chronic exposure has been investigated to a lesser extent, but longterm exposure to PM2.5 has been found to be associated with an approximately 10-fold greater increase in RR than short-term exposures. Experimental studies with volunteers in chamber and field studies show mild lung or cardiovascular responses at concentrations of ambient particles (PM2.5/PM10: 100-200 mg/m3) that may occur during episodes of air pollution. Animal studies at higher concentrations have shown stronger responses. The experimental studies support the epidemiological evidence for an adverse health effect of PM. Both population- and experimental studies indicate the existence of vulnerable individuals. At low to average ambient concentrations there seems to exist a discrepancy between the results of population- and experimental studies that might be due to the absence of the most vulnerable individuals in the experimental studies. Together with cell culture experiments, human and animal studies indicate the importance of physical and chemical properties of the particles (size, content of metals, organics, endotoxins, etc.) for the observed effects. More knowledge about adverse health effects induced by low concentrations of PM and the critical particle characteristics, is required.10 (PM £ 10 mm), PM2,5 (PM £ 2,5 mm) og PM0,1 (PM £ 0,1 mm). Nyere befolkningsstudier viser en assosiasjon mellom økning i dødelighet og sykelighet (pga. lunge- og hjertekarsykdommer) og kortvarige økninger i svevestøvskonsentrasjoner i byluft. Den relative risikoen (RR) er rundt 1,005 ved en økning av PM10 på 10 mg/m3, uten noen observert terskelverdi, selv ved nivåer under 10 mg/m3. Kronisk eksponering for svevestøv er mindre undersøkt, men årelang eksponering for PM2,5 er assosiert med en RR som er omlag 10 ganger større enn ved korttidseksponering. Befolkningsstudiene indikerer at enkelte grupper synes å være spesielt følsomme (lungesyke, hjertesyke og barn). Hos frivillige individer i kammer- og feltstudier, fant man effekter både i luftveiene og i hjerte-karsystemet ved konsentrasjoner av svevestøv (PM2,5/PM10: 100-200 mg/m3) som kan forekomme i episoder med økt luftforurensning. Dyreforsøk med høyere konsentrasjoner ga kraftigere responser. De eksperimentelle studiene understøtter befolkningsstudiene i at byluftpartikler representerer et helseproblem. Både befolkningsstudiene og eksperimentelle studier indikerer at enkelte individer er mer sårbare enn andre. Ved lave til middels konsentrasjoner av byluftpartikler synes det å foreligge en diskrepans mellom disse studietypene som kan skyldes at de mest sårbare individene ikke er inkludert i eksperimentelle forsøk. Studier med mennesker, dyr og celler viser at fysisk/kjemiske egenskaper ved partiklene (størrelse, innhold av metaller, organiske forbindelser, endotoksiner etc.) er sentrale for de observerte effektene av svevestøvet. Mer kunnskap både om helseeffekter ved lave konsentrasjoner, samt egenskaper ved partikler, er nødvendig.

Importance of Size and Composition of Particles for Effects on Cells In Vitro

A primary goal of current research on particle-induced health effects is to reveal the critical characteristics that determine their biological effects. Experimental studies have shown that smaller particles induce stronger biological effects than larger particles of similar composition, due to their larger surface area to mass ratio. However, correlation for variations in surface area could not account for variation in biological reactivity among particles of differential composition. Hence, the importance of size and surface area does not override the importance of particle composition. Moreover, different particle characteristics appear to be involved in different biological effects in vitro. Our studies show that mineral particle-induced apoptosis mostly seems to depend on particle size, whereas composition and surface reactivity appeared to be most important for the proinflammatory potential of the particles. The ability of the particles to generate reactive oxygen species in vitro was not correlated with either inflammatory markers or apoptosis, suggesting that other mechanisms are at play. A single, specific component of the mineral particles, explaining the differences in response, has not been identified. In European-wide studies such as the Respiratory Allergy and Inflammation due to Air Pollution (RAIAP) study, particles have been sampled in different locations to study season- and site-dependent variations in responses particles, such as markers of inflammatory and allergic reactions in cells and animals. The data indicate that coarse particles can induce at least as strong inflammatory responses as fine particles. The allergic responses tended to be more associated with the organic fraction (PAH) of particles, whereas the inflammatory reactions seemed to be more associated with metals and endotoxin. Overall, coarse PM was found to have an inflammatory potential similar to fine PM on an equal mass basis. Even though one has to take into account different concentrations in ambient air as well as differences in respiratory system deposition of the size fractions, the potential of coarse particles to induce pulmonary effects should not be neglected.

Iron release and ROS generation from mineral particles are not related to cytokine release or apoptosis in exposed A549 cells

The generation of reactive oxygen species (ROS) by mineral particles is believed to be central to their toxicity and their ability to induce inflammation. Surface bound or soluble iron may contribute to the particle-effects by enhancing the ROS generation through the Fenton reaction. Nevertheless, the importance of ROS and transition metals to mineral particle-induced effects is still unclear and further investigations are needed. In the present study we have investigated different mineral particles for their total iron content, amount of soluble iron at pH 7.0 and 4.0, their ability to generate ROS in a cell-free environment, and their ability to induce cytokine release and apoptosis in a human alveolar epithelial cell line (A549). All the investigated parameters varied considerably between the different particles, with the exception of ability to induce apoptosis. Total iron content did not reflect the amount of soluble iron, and neither total nor soluble iron was correlated with ROS generation. Moreover, iron content and ROS was not correlated with the ability of particles to induce cytokine release or apoptosis. The present results suggest that there is no clear relationship between the particles iron content and ability to generate ROS. Moreover, neither iron content nor the ability to induce ROS generation appears to be a prerequisite for the inflammatory potential or cytotoxicity of mineral particles.

Relation between sources of particulate air pollution and biological effect parameters in samples from four European cities: an exploratory study

Given that there are widely different prevalence rates of respiratory allergies and asthma between the countries of Europe and that exposure to ambient particulate matter (PM) is substantial in urban environments throughout Europe, an EU project entitled "Respiratory Allergy and Inflammation Due to Ambient Particles" (RAIAP) was set up. The project focused on the role of physical and chemical composition of PM on release of cytokines of cells in vitro, on respiratory inflammation in vivo, and on adjuvant potency in allergy animal models. Coarse (2.5-10 microm) and fine (0.15-2.5 microm) particles were collected during the spring, summer and winter in Rome (I), Oslo (N), Lodz (PL), and Amsterdam (NL). Markers within the same model were often well correlated. Markers of inflammation in the in vitro and in vivo models also showed a high degree of correlation. In contrast, correlation between parameters in the different allergy models and between allergy and inflammation markers was generally poor. This suggests that various bioassays are needed to assess the potential hazard of PM. The present study also showed that by clustering chemical constituents of PM based on the overall response pattern in the bioassays, five distinct groups could be identified. The clusters of traffic, industrial combustion and/or incinerators (TICI), and combustion of black and brown coal/wood smoke (BBCW) were associated primarily with adjuvant activity for respiratory allergy, whereas clusters of crustal of material (CM) and sea spray (SS) are predominantly associated with measures for inflammation and acute toxicity. The cluster of secondary inorganic aerosol and long-range transport aerosol (SIALT) was exclusive associated with systemic allergy. The present study has shown that biological effect of PM can be linked to one or more PM emission sources and that this linkage requires a wide range of bioassays.

Different particle determinants induce apoptosis and cytokine release in primary alveolar macrophage cultures

Background

Particles are known to induce both cytokine release (MIP-2, TNF-α), a reduction in cell viability and an increased apoptosis in alveolar macrophages. To examine whether these responses are triggered by the same particle determinants, alveolar macrophages were exposed in vitro to mineral particles of different physical-chemical properties.

Results

The crystalline particles of the different stone types mylonite, gabbro, basalt, feldspar, quartz, hornfels and fine grain syenite porphyr (porphyr), with a relatively equal size distribution (≤ 10 μm), but different chemical/mineral composition, all induced low and relatively similar levels of apoptosis. In contrast, mylonite and gabbro induced a marked MIP-2 response compared to the other particles. For particles of smaller size, quartz (≤ 2 μm) seemed to induce a somewhat stronger apoptotic response than even smaller quartz (≤ 0.5 μm) and larger quartz (≤ 10 μm) in relation to surface area, and was more potent than hornfels and porphyr (≤ 2 μm). The reduction in cell viability induced by quartz of the different sizes was roughly similar when adjusted to surface area. With respect to cytokines, the release was more marked after exposure to quartz ≤ 0.5 μm than to quartz ≤ 2 μm and ≤ 10 μm. Furthermore, hornfels (≤ 2 μm) was more potent than the corresponding hornfels (≤ 10 μm) and quartz (≤ 2 μm) to induce cytokine responses. Pre-treatment of hornfels and quartz particles ≤ 2 μm with aluminium lactate, to diminish the surface reactivity, did significantly reduce the MIP-2 response to hornfels. In contrast, the apoptotic responses to the particles were not affected.

Conclusion

These results indicate that different determinants of mineral/stone particles are critical for inducing cytokine responses, reduction in cell viability and apoptosis in alveolar macrophages. The data suggest that the particle surface reactivity was critical for cytokine responses, but contributed less to cell death for the types of particles tested. The size-dependent variations, specially in cytokine release, seem not to be explained only by particle surface area.

Cytokine release from alveolar macrophages exposed to ambient particulate matter: heterogeneity in relation to size, city and season

Background

Several studies have demonstrated an association between exposure to ambient particulate matter (PM) and respiratory and cardiovascular diseases. Inflammation seems to play an important role in the observed health effects. However, the predominant particle component(s) that drives the inflammation is still not fully clarified. In this study representative coarse (2.5–10 μm) and fine (0.1–2.5 μm) particulate samples from a western, an eastern, a northern and a southern European city (Amsterdam, Lodz, Oslo and Rome) were collected during three seasons (spring, summer and winter). All fractions were investigated with respect to cytokine-inducing potential in primary macrophages isolated from rat lung. The results were related to the physical and chemical parameters of the samples in order to disclose possible connections between inflammatory potential and specific characteristics of the particles.

Results

Compared on a gram-by gram basis, both site-specific and seasonal variations in the PM-induced cytokine responses were demonstrated. The samples collected in the eastern (Lodz) and southern (Rome) cities appeared to be the most potent. Seasonal variation was most obvious with the samples from Lodz, with the highest responses induced by the spring and summer samples. The site-specific or seasonal variation in cytokine release could not be attributed to variations in any of the chemical parameters. Coarse fractions from all cities were more potent to induce the inflammatory cytokines interleukin-6 and tumour necrosis factor-α than the corresponding fine fractions. Higher levels of specific elements such as iron and copper, some polycyclic aromatic hydrocarbons (PAHs) and endotoxin/lipopolysaccaride seemed to be prevalent in the coarse fractions. However, variations in the content of these components did not reflect the variation in cytokine release induced by the different coarse fractions. Addition of polymyxin B did not affect the particle-induced cytokine release, indicating that the variations in potency among the coarse fractions are not explained by endootoxin.

Conclusion

The inflammatory potential of ambient PM demonstrated heterogeneity in relation to city and season. The coarse particle fractions were consistently more potent than the respective fine fractions. Though a higher level of some elements, PAH and endotoxin was found in the coarse fractions, the presence of specific components was not sufficient to explain all variations in PM-induced cytokine release.

Mineral Particles of Varying Composition Induce Differential Chemokine Release from Epithelial Lung Cells: Importance of Physico-chemical Characteristics

Presently, little is known about the potential health effects of mineral particles other than asbestos and quartz. In this study, a human epithelial lung cell line (A549), primary human small airway epithelial cells (SAECs) and primary rat type 2 (T2) cells were exposed to stone quarry particles of two size fractions (<10 and <2.5 microm) from nine different rock samples. The ability to induce the release of chemokines from lung cells was investigated and compared with the particles' mineral and element composition and the amount of soluble elements. The stone particles induced the release of only low levels of interleukin (IL)-8 from A549 cells. In contrast, some of the other particles induced the release of high levels of macrophage inflammatory protein (MIP)-2 from T2 cells, and high levels of IL-8 from SAECs. Differences in particle surface area could account for differences in activity between the <10 and <2.5 microm fractions of six out of the nine rock samples. For two samples the <2.5 microm fraction was most active and for one sample the <10 microm fraction was most active. Content of the mineral plagioclase displayed a strong, negative correlation with the potential to induce MIP-2, whereas the mineral pyroxene was positively correlated with MIP-2 induction. However, neither plagioclase nor pyroxene content was sufficient to explain differences in bioactivity between the particles. No statistically significant correlation was found between the amounts of total or soluble elements and MIP-2 release. In conclusion, the results suggest that mineral particles with a high content of plagioclase have a low potential to induce a pro-inflammatory response. However, a particular mineral or element responsible for eliciting strong increases in chemokine release could not be identified. Thus, at present it appears that analysing mineral and element content is insufficient to predict stone particle bioactivity, and that biological testing is a necessity.

Release of inflammatory cytokines, cell toxicity and apoptosis in epithelial lung cells after exposure to ambient air particles of different size fractions

Several studies have shown that particles of smaller size may be more potent than larger to induce inflammatory and toxic responses in cultured lung cells. However, the relative importance of different size fractions of ambient PM to induce such effects is still not known. In this study, we investigated the potency of different size fractions of urban ambient air particles to induce release of inflammatory cytokines in the human alveolar cell line A549 and primary rat type 2 cells. A mineral-rich ambient air PM10 sample collected in a road tunnel (road PM10) was also included. The coarse fraction of the urban ambient air particles demonstrated a similar or higher potency to induce release of the proinflammatory cytokines IL-8/MIP-2 and IL-6 compared to the fine and ultrafine fractions. The coarse fraction was also the most toxic in both cell systems. In contrast to the A549 cells, no induction of cytokine release was induced by the ultrafine particles in the primary type 2 cells. The mineral-rich road PM10 may be equally or more potent than the various size fractions of the ambient air particles to induce cytokines in both cell types. In conclusion, the coarse fraction of ambient particles may be at least as potent by mass as smaller fractions to induce inflammatory and toxic effects in lung cells.

Mineral composition other than quartz is a critical determinant of the particle inflammatory potential

The aim of this study was to examine the inflammatory potential of stone quarry particles with differing mineral and metal composition and if the effects could be related to the leaching of metals from the particles and if antioxidants would reduce the cytokine release. After intratracheal instillation of rats with a type of mylonite (median size 8 microns) we found a stronger inflammatory potential of mylonite than of quartz at 20 h after treatment. In isolated rat type 2 cells and human epithelial lung cells (A549) mylonite induced a much greater release of MIP-2/IL-8 than quartz or a type of basalt and a feldspar. The mylonite particles were more potent even when compared to smaller size fractions of quartz. Thus mineral composition can be more important than size in eliciting acute inflammatory responses. The content of metals in basalt and mylonite showed minor variations with somewhat more metals present in basalt. The release of metals from the two particle types varied, but in general more metals were released from basalt than from mylonite particles. However, metal release was not related to the differences in proinflammatory effect. Antioxidants seemed to decrease the release of cytokines induced by mylonite particles, but a suppression of basal cytokine release by antioxidants was also observed, questioning the involvement of oxygen radicals in the mylonite-induced effects.

Rat lung inflammatory responses after in vivo and in vitro exposure to various stone particles

Rat lung alveolar macrophages and type 2 cells were exposed for 20 h in vitro to various stone particles with differing contents of metals and minerals (a type of mylonite, gabbro, feldspar, and quartz). The capability to induce the release of the inflammatory cytokines interleukin-6 (IL-6), tumour necrosis factor-alpha (TNF-alpha), and macrophage inflammatory protein-2 (MIP-2) was investigated. We found marked differences in potency between the various particles, with mylonite being most potent overall, followed by gabbro, and with feldspar and quartz having an approximately similar order of lower potency. The results also demonstrated differences in cytokine release pattern between the two cell types. For all particle types including quartz, type 2 cells showed the most marked increase in MIP-2 and IL-6 secretion, whereas the largest increase in TNF-alpha release was observed in macrophages. To investigate possible correlations between in vitro and in vivo inflammatory responses, rats were instilled with the same types of particles and bronchoalveolar lavage (BAL) fluid was collected after 20 h. The results demonstrated a correlation between the in vitro cytokine responses and the number of neutrophilic cells in the BAL fluid. The BAL fluid also showed a strong MIP-2 response to mylonite. However, this was the only particle type to give a significant cytokine response in the BAL fluid. We further examined whether a similar graded inflammatory response would be continued in type 2 cells and alveolar macrophages isolated from the exposed animals. Again a differential cytokine release pattern was observed between type 2 cells and macrophages, although the order of potency between particle types was altered. In conclusion, various stone particles caused differential inflammatory responses after both in vitro and in vivo exposure, with mylonite being the most potent stone particle. The results suggest the alveolar type 2 cell to be an important participant in the inflammatory response following exposure to particles.

Importance of soluble metals and reactive oxygen species for cytokine release induced by mineral particles

The mechanisms for particle-induced health effects are not well understood, but inflammation seems to be of importance. Previously, we have shown that stone quarry particles with various mineral and metal content differed widely in potency to induce inflammatory cytokines (IL-6, IL-8 and TNF-alpha) in different types of lung cells. In this study we investigated if the observed cytokine responses were associated with the soluble or insoluble components of the stone particles and if there was a relationship between the differential cytokine release and generation of reactive oxygen species (ROS). Exposure of the human alveolar cell line A549 to the different particle leachates (pH 7.4 and 4.0) did not induce corresponding differential increases in the IL-8 release as observed with whole particles. Increase in ROS production, measured as dichlorofluorescein-fluorescence, was only demonstrated after exposure of A549 cells to the pH 4.0 extract from basalt. Furthermore, generation of ROS was found in neutrophils but not in A549 cells and primary macrophages after exposure to suspensions of the solid particles. However, no obvious differences in potency among the different particles were demonstrated. In summary, other mechanisms than particle-induced ROS formation seem to be responsible for the differential induction of IL-8. Furthermore, our findings indicate that the differential ability to induce IL-8 release in lung cells is attributed to the solid components of the stone particles.

Silica-induced cytokine release from A549 cells: importance of surface area versus size

Physical and chemical properties such as structure, composition and surface reactivity determine the biological activity of mineral particles. Long-term exposure to crystalline silica is known to cause persistent pulmonary inflammation leading to adverse health effects. There is less information about the potential health effects of amorphous (noncrystalline) silica. In this study, the inflammatory and cytotoxic potency of crystalline and amorphous silica in relation to particle size and surface area was assessed. Human epithelial lung cells (A549) were exposed to different size fractions of quartz ( aerodynamic diameter 0.5, 2 and 10 microm) and amorphous silica (diameter 0.3 microm). All particles induced increased release of the proinflammatory cytokines interleukin (IL)-6 and IL-8. When cells were exposed to equal masses of quartz, the smallest size fraction was the most potent. These differences, however, disappeared when cytokine release was related to equal surface areas. When amorphous silica and quartz were compared, the amorphous silica was most potent to induce IL - 6 regardless of how exposure was expressed, whereas the smallest size fraction of quartz was the most potent inducer of IL-8. Thus, the surface area seems to be the critical determinant when potency of different sizes of quartz is compared.

Mineral and/or metal content as critical determinants of particle-induced release of IL-6 and IL-8 from A549 cells

Mineral particles in occupational exposure and ambient air particles may cause adverse health effects in humans. In this study the ability of different stone quarry particles to induce release of the proinflammatory cytokines interleukin-6 (IL-6) and interleukin-8 (IL-8) from human epithelial lung cells (A549) was investigated. Size distribution within the PM10 fractions was quite similar for all particle samples, whereas mineral content and metal composition differed. Particles, containing minerals such as quartz, amphibole, chlorite, and epidote, induced a marked increase in IL-6 and IL-8 release. Particles composed mainly of plagioclase were much less effective. The most potent particle samples exhibited a relatively high content of transition metals such as iron. Exposure to identical masses or surface areas resulted in the same order of potency among the different particle samples. Significant cytotoxicity was observed only at higher concentrations of particle exposure. Thus, mineral composition and/or metal contents of particles from different stone quarries were critical determinants for the marked differences in potency to induce cytokine responses in human epithelial lung cells.

Role of signal transduction pathways in lung inflammatory responses

A variety of cell types participate in lung inflammation. Macrophages and epithelial cells play an important role in the inflammatory process by releasing cytokines in a complex cell to cell network. Interleukins are important mediators of this cell signalling. The interleukins IL-6 and IL-8 are released from epithelial cells in response to noxious agents such as particles, bacterial and fungal toxins and various chemicals. Though the involvement of, e.g. NF-IL-6 (C/EBP-beta) in the regulation of interleukins has been reported, the role of different signal transduction pathways in the regulation of these mediators has not been thoroughly investigated in lung epithelial cells. The involvement of different signal transduction pathways in the release of inflammatory markers is discussed with special emphasis on the effect of lung toxic compounds in human and rat lung epithelial cells.