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Rapid increases in respiratory epithelial permeability occur after intratracheal instillation of PMA
Abstract:
We measured pulmonary epithelial permeability by quantifying the disappearance of two water-soluble compounds, [14C]mannitol and [3H]inulin, after their instillation, with and without phorbol myristate acetate (PMA), into gas-filled perfused (50 ml/min) rabbit lungs in situ. Both tracers disappeared in a monoexponential fashion over 30 min with calculated first-order rate constants (control; n = 11) of 0.0008 +/- 0.0002 and 0.0027 +/- 0.0008 min-1 for inulin and mannitol, respectively. The ratio of the rate constants (3.1 +/- 0.5) was not significantly different from the ratio of diffusivities of mannitol:inulin (3.7). Addition of PMA (250 micrograms) significantly (n = 9, P less than 0.05) increased the rate constants for both inulin and mannitol to 0.0024 +/- 0.0007 and 0.0087 +/- 0.0025 min-1, respectively, while not affecting their ratio (4.3 +/- 0.5). Addition of human leukocytes (4-8 X 10(8)/l) to the perfusate did not exacerbate the effect of 250 micrograms PMA (n = 3). The addition of catalase (n = 7) completely inhibited the effect of 250 micrograms PMA. PMA (250 micrograms) did not significantly affect perfusion pressure but increased wet-to-dry weight ratios. Light microscopic histology showed damage to epithelial and endothelial cells after 250 micrograms PMA which was not seen after coinstillation of catalase. Catalase sensitivity of functional and structural effects of PMA suggests that the effect was secondary to production of hydrogen peroxide. Since this effect was noted in lungs not perfused with neutrophils and addition of leukocytes did not exacerbate the increase in permeability, we hypothesize that an undetermined pulmonary cell type was the source of hydrogen peroxide. Finally, we found no evidence for restrictive pores with radii of 0.4-1.4 nm.
Insights
Phorbol myristate acetate (PMA) increases pulmonary epithelial permeability by inducing hydrogen peroxide production, likely from an unknown lung cell. Catalase treatment completely blocks this effect, suggesting a role for oxidative stress in lung injury.
Area of Science:
- Pulmonary physiology
- Cell biology
- Toxicology
Background:
- Pulmonary epithelial permeability is crucial for lung function.
- Phorbol myristate acetate (PMA) is known to induce inflammation and cell damage.
- The specific mechanisms by which PMA affects lung permeability are not fully understood.
Purpose of the Study:
- To investigate the effect of PMA on pulmonary epithelial permeability in isolated rabbit lungs.
- To determine the role of hydrogen peroxide in PMA-induced lung permeability changes.
- To identify potential cellular sources of hydrogen peroxide in the lung.
Main Methods:
- Isolated rabbit lungs were perfused in situ with gas.
- Pulmonary epithelial permeability was measured using radiolabeled tracers ([14C]mannitol and [3H]inulin).
- The effects of PMA, human leukocytes, and catalase on permeability, perfusion pressure, and lung histology were assessed.
Main Results:
- PMA significantly increased pulmonary epithelial permeability, as indicated by increased tracer clearance rates.
- The PMA-induced increase in permeability was completely inhibited by catalase, suggesting hydrogen peroxide involvement.
- PMA caused histological damage to lung cells, which was prevented by catalase.
- Leukocyte addition did not enhance PMA's effect on permeability.
Conclusions:
- PMA increases pulmonary epithelial permeability through a mechanism involving hydrogen peroxide production.
- An undetermined pulmonary cell, not neutrophils, is likely the source of PMA-induced hydrogen peroxide.
- Oxidative stress plays a significant role in PMA-induced lung injury and permeability changes.