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Lysosomal enzyme activities in pulmonary macrophages from rabbits breathing iron oxide
Abstract:
The effects of an in vivo exposure to a nontoxic particle, iron oxide, on lysosomal hydrolases in pulmonary macrophages were examined. Rabbits breathed a submicron-sized aerosol of iron oxide for 3 h (mass concentration, 186 to 222 mg/m3). Macrophages were recovered by lung lavage 0, 12, 18, and 24 h later. The number of cells lavaged after iron oxide was significantly greater than the control number, whereas the amount of protein recovered per 10(8) cells decreased, suggesting the influx of smaller cells. Macrophages from animals exposed to iron oxide reacted histochemically for acid phosphatase showed increased stain intensity and redistribution of enzyme within the cytoplasm. Considerable cell-to-cell variability in enzyme activity was evident in these macrophages. Homogenates of cells exposed to iron oxide assayed for 6 lysosomal acid hydrolases showed little change in specific activity or in total enzyme per 10(8) cells when compared to homogenates of cells from control animals. Sucrose density gradient centrifugation demonstrated that exposure to iron oxide caused an increase in lysosome heterogeneity over that seen in control preparations and the appearance of a population of lysosomes of increased density. An aerosol of iron oxide did not greatly alter the average concentrations of lysosomal enzymes in pulmonary macrophages, but did stimulate recruitment of new cells and thus increases the total amount of some enzymes in the lung.
Insights
Inhaling iron oxide particles increases pulmonary macrophage numbers and lysosome density in rabbits. While average enzyme activity per cell is unchanged, total lung enzyme content rises due to cell recruitment.
Area of Science:
- Pulmonary toxicology
- Cell biology
- Immunology
Background:
- Pulmonary macrophages are crucial for lung defense.
- Lysosomal hydrolases are key enzymes involved in cellular degradation.
- Understanding particle effects on macrophages is vital for respiratory health.
Purpose of the Study:
- To investigate the impact of in vivo iron oxide exposure on lysosomal hydrolases in rabbit pulmonary macrophages.
- To assess changes in macrophage number, enzyme activity, and lysosome characteristics.
Main Methods:
- Rabbits inhaled submicron iron oxide aerosol.
- Pulmonary macrophages were collected via lung lavage at various time points.
- Histochemistry, enzyme assays, and sucrose density gradient centrifugation were performed.
Main Results:
- Iron oxide exposure increased macrophage cell count, indicating recruitment.
- Histochemistry revealed increased acid phosphatase intensity and redistribution.
- Lysosome density heterogeneity increased, with a population of denser lysosomes appearing.
- Specific activity and total enzyme per cell showed minimal changes, but total lung enzyme increased.
Conclusions:
- Iron oxide inhalation stimulates pulmonary macrophage recruitment.
- While average lysosomal enzyme concentrations per cell are not significantly altered, the increased cell numbers lead to a higher total enzyme content in the lung.
- Iron oxide exposure alters lysosome characteristics within macrophages.