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Effect of airborne particulate extracts on monocyte oxidative metabolism
R Fabiani1, L Pampanella, A Minelli
1Department of Cellular and Molecular Biology, University of Perugia, Italy.
Abstract:
Alveolar macrophages lie on the air side of the alveolar-capillary barrier of the lung. They originate from circulating monocytes and are an important first-line host defense against inhaled microorganisms. In monocytes and macrophages, phagocytosis is associated with an increase in O2 consumption and superoxide anion (O2-) generation, that is, "the respiratory burst". O2- is the precursor of highly reactive, oxygen-derived free radicals that are used to kill potential pathogens. Although it is well known that airborne particulate matter inhibits the phagocytic activity of alveolar macrophages, very little is known about the effect of airborne particulate extracts on the respiratory burst. In this study, monocytes isolated from the peripheral blood were incubated for 2 hr at 37 degrees C with increasing concentrations of particulate extract and then stimulated for 30 min with phorbol 12-myristate 13 acetate (PMA) or with Zymosan. The released O2- was measured by the superoxide dismutase inhibitable reduction of cytochrome C. The results cleary showed that, at a particulate concentration of 0.17 mg/mL, the production of O2- was reduced to 22% and 40% of the control values when the cells were stimulated with PMA and Zymosan, respectively. Concomitantly, there was a release of LDH in the supernatant (50% of the total), indicating that a large proportion of cells were damaged by the treatment with the environmental pollutants, and some cytosolic components were released from the cells. Giemsa staining of the treated monocytes revealed the presence of many cells with a dispersed cytosol; the nucleus, although not destroyed, had a different shape. It was suggested that the airborne particulate matter has a toxic effect that induces the disintegration of the plasma membrane. Cytosolic factors (proteins and coenzymes) necessary for O2- production leak from the cells and superoxide generation is therefore reduced. It remains to be determined whether this phenomenon also occurs in vivo.
Insights
Airborne particulate matter damages monocytes, reducing their ability to generate superoxide anions, a key component of the respiratory burst. This cellular damage impairs host defense mechanisms against inhaled pathogens.
Area of Science:
- Environmental Toxicology
- Immunology
- Cell Biology
Background:
- Alveolar macrophages are crucial for lung defense, originating from monocytes and utilizing the respiratory burst (superoxide anion generation) to combat pathogens.
- While airborne particulate matter's effect on phagocytosis is known, its impact on the respiratory burst remains unclear.
Purpose of the Study:
- To investigate the effects of airborne particulate extracts on the respiratory burst in human monocytes.
- To determine if particulate matter exposure compromises the cellular integrity necessary for superoxide anion production.
Main Methods:
- Human peripheral blood monocytes were incubated with varying concentrations of particulate extract.
- Cells were stimulated with phorbol 12-myristate 13 acetate (PMA) or Zymosan to induce the respiratory burst.
- Superoxide anion (O2-) production was quantified, and cell damage was assessed via lactate dehydrogenase (LDH) release and Giemsa staining.
Main Results:
- Particulate extract significantly reduced O2- production by 22% (PMA) and 40% (Zymosan) at 0.17 mg/mL.
- Significant LDH release (50% of total) indicated substantial cell damage and plasma membrane disintegration.
- Giemsa staining revealed dispersed cytosol and altered nuclear morphology in treated monocytes.
Conclusions:
- Airborne particulate matter exhibits toxicity, leading to monocyte plasma membrane disintegration and leakage of essential cytosolic factors.
- This cellular damage impairs superoxide anion generation, compromising a critical component of the innate immune response.
- Further in vivo studies are needed to confirm these findings in a living organism.