Activation of alveolar macrophages after plutonium oxide inhalation in rats: involvement in the early inflammatory response.

Alveolar macrophages play an important role in the distribution, clearance and inflammatory reactions after particle inhalation, which may influence long-term events such as fibrosis and tumorigenesis. The objectives of the present study were to investigate the early inflammatory events after plutonium oxide inhalation in rats and involvement of alveolar macrophages. Lung changes were studied from 3 days to 3 months after inhalation of PuO2 of different isotopic compositions (70% or 97% 239Pu) and initial lung deposits (range 2.1 to 43.4 kBq/rat). Analyses of bronchoalveolar lavages showed early increases in the numbers of granulocytes, lymphocytes and multinucleated macrophages. The activation of macrophages was evaluated ex vivo by measurement of inflammatory mediator levels in culture supernatants. TNF-alpha and chemokine MCP-1, MIP-2 and CINC-1 production was elevated from 7 days after inhalation and remained so up to 3 months. In contrast, IL-1beta, IL-6 and IL-10 production was unchanged. At 6 weeks, pulmonary macrophage numbers and activation state were increased as observed from an immunohistochemistry study of lung sections with anti-ED1. Similarly, histological analyses of lung sections also showed evidence of inflammatory responses. In conclusion, our results indicate early inflammatory changes in the lungs of PuO2-contaminated animals and the involvement of macrophages in this process. A dose-effect relationship was observed between the amount of radionuclide inhaled or retained at the time of analysis and inflammatory mediator production by alveolar macrophages 14 days after exposure. For similar initial lung deposits, the inflammatory manifestation appears higher for 97% 239Pu than for 70% 239Pu.

In vitro radiation-induced effects on rat tracheal epithelial cells. I) Different radiosensitivity of cell inactivation after alpha and gamma irradiations.

In order to compare the radiotoxicity of alpha- and gamma-irradiations, primary cultures of tracheal epithelial cells from two rat strains, Sprague Dawley (SD) and Wistar Furth/Fisher F344 (WF/Fi) rats, were irradiated with 241Am alpha-particles or 60 Co gamma-rays. The survival ratio for each of the two rat strain cells appeared to be statistically different after high-LET irradiation. WF/Fi rat cells were 1.7-times more radiosensitive than SD rat cells, whereas no difference was observed following low-LET irradiation. A comparison of the cell survival yielded RBEs of 2.8 and 4.5 for SD and WF/Fi rat cells, respectively. As previously observed, with increasing LET of particles, the cell-survival curves approximate an exponential function of the dose. On the contrary, for low-LET, the survival curves showed a marked initial shoulder. This in vitro cellular model, using epithelial cells of the upper airway, provides a suitable system to estimate the mechanism involved in radiosensitivity after high-LET irradiation. The responses to radiation-induced lethal effects within a same type of cell were dependent on the irradiation parameters, but might be modulated by the individual sensitivity under genetic or epigenetic factor controls.

In vitro radiation-induced effects on rat tracheal epithelial cells. II) Different preneoplastic cell transformation after alpha and gamma irradiations.

In order to compare the cell transformation induced by alpha- and gamma-irradiation, primary cultures of tracheal epithelial cells from two rat strains, Sprague Dawley (SD) and Wistar Furth/Fisher F344 (WF/Fi) rats, were irradiated with 241Am alpha-particles or 60 Co gamma-rays. The relative transformation frequency (RTF) for WF/Fi primary cells was very close to the level of the spontaneous incidence and independent on the two irradiation types used. On the contrary, the RTF for the SD primary cells increased with a decrease of the LET radiation when the relative survival was higher than about 40%. Therefore, the RTF values reached 4-5 for alpha-particles and 10-12 for gamma-rays. The RTF can be related to the intrinsic radiosensitivity of the rat epithelial cells. However, the difference in the radiation-induced RTF for SD or WF/Fi primary cells seems to be due to the development, under genetic control, of the initial lesion to the neoplastic state.

Plutonium behavior after pulmonary administration according to solubility properties, and consequences on alveolar macrophage activation.

The physico-chemical form in which plutonium enters the body influences the lung distribution and the transfer rate from lungs to blood. In the present study, we evaluated the early lung damage and macrophage activation after pulmonary contamination of plutonium of various preparation modes which produce different solubility and distribution patterns. Whatever the solubility properties of the contaminant, macrophages represent a major retention compartment in lungs, with 42 to 67% of the activity from broncho-alveolar lavages being associated with macrophages 14 days post-contamination. Lung changes were observed 2 and 6 weeks post-contamination, showing inflammatory lesions and accumulation of activated macrophages (CD68 positive) in plutonium-contaminated rats, although no increased proliferation of pneumocytes II (TTF-1 positive cells) was found. In addition, acid phosphatase activity in macrophages from contaminated rats was enhanced 2 weeks post-contamination as compared to sham groups, as well as inflammatory mediator levels (TNF-α, MCP-1, MIP-2 and CINC-1) in macrophage culture supernatants. Correlating with the decrease in activity remaining in macrophages after plutonium contamination, inflammatory mediator production returned to basal levels 6 weeks post-exposure. The production of chemokines by macrophages was evaluated after contamination with Pu of increasing solubility. No correlation was found between the solubility properties of Pu and the activation level of macrophages. In summary, our data indicate that, despite the higher solubility of plutonium citrate or nitrate as compared to preformed colloids or oxides, macrophages remain the main lung target after plutonium contamination and may participate in the early pulmonary damage.