Activity testing of alveolar macrophages and changes in surfactant phospholipids after irradiation in bronchoalveolar lavage: experimental and clinical data

Cytotoxicity induced by fine particulate matter (PM2.5) via mitochondria-mediated apoptosis pathway in rat alveolar macrophages

Although positive associations exist between ambient particulate matter (PM_2.5; diameter ≤ 2.5 μm) and the morbidity and mortality rates for respiratory diseases, the biological mechanisms of the reported health effects are unclear. Considering that alveolar macrophages (AM) are the main cells responsible for phagocytic clearance of xenobiotic particles that reach the airspaces of the lungs, the purpose of this study was to investigate whether PM_2.5 induced AM apoptosis, and investigate its possible mechanisms. Freshly isolated AM from Wistar rats were treated with extracted PM_2.5 at concentrations of 33, 100, or 300 μg/mL for 4 h; thereafter, the cytotoxic effects were evaluated. The results demonstrated that PM_2.5 induced cytotoxicity by decreasing cell viability and increasing lactate dehydrogenase (LDH) levels in AMs. The levels of reactive oxygen species (ROS) and intracellular calcium cations (Ca²⁺) markedly increased in higher PM_2.5 concentration groups. Additionally, the apoptotic ratio increased, and the apoptosis-related proteins BCL2-associated X (Bax), caspase-3, and caspase-9 were upregulated, whereas B cell lymphoma-2 (Bcl-2) protein levels were downregulated following PM_2.5 exposure. Cumulative findings showed that PM_2.5 induced apoptosis in AMs through a mitochondrial-mediated pathway, which indicated that PM_2.5 plays a significant role in lung injury diseases.

Phospholipid concentration in lung lavage fluid as biomarker for pulmonary fibrosis

Pulmonary surfactant comprised primarily of phospholipids is a phospholipid-protein complex synthesized by type II alveolar epithelial cells or Clara cells and secreted to the pulmonary alveoli. As changes have been found in phospholipid concentrations in the bronchoalveolar lavage fluid (BALF) of patients with pulmonary fibrosis, phospholipid is considered to be involved in the process of fibrois/fibrotic process. Therefore, we made a crystalline silica rat model and measured phospholipid concentrations in lung lavage fluid in order to study the relationship of phospholipid to particle-induced pulmonary fibrosis. Eight-week-old Wistar male rats (n = 35) were injected with 2 mg crystalline silica particles suspended in 0.4 ml physiological saline. Rats in the control group (n = 35) were injected with physiological saline only. There were 7 rats in each of the ten subgroups. Rats were sacrificed and dissected at 3 days, 1 wk, 1 mo, 3 mo, and 6 mo after injection. Bronchoalveolar lavage was conducted on bronchoalveoli recovered from the right lung of each rat, the lavage fluid was centrifuged, and the supernatant was used to measure phospholipid concentration. The results were compared with previously reported inflammation scores. Phospholipid concentrations in lung lavage fluid for the exposed group showed a statistically significant increase compared to the control group throughout the observation period. Moreover, when compared to histopathologically examined inflammation scores, a positive correlation was found between the two. Judging from the facts that phospholipid concentrations in lung lavage fluid increased and that this increase correlated with the severity of inflammation, this experiment indicated that phospholipids are involved in particle-induced lung disorders.

Decreased phagocytic capacity of rat peritoneal macrophages following photon abdominal irradiation

Photon irradiation of the abdomen may be accompanied by complications due to a decrease in the immune defense of the recipient. Since peritoneal macrophages are an important component of the immune system, we examined the phagocytic activity and oxygen superoxide anion generation by peritoneal macrophages from rats 2 and 4 weeks after abdominal irradiation with 6 MV photons applying a single dose of 2 Gy. Two and 4 weeks after irradiation, peritoneal macrophages were harvested and their capacity to engulf latex particles and to produce oxygen superoxide anions was determined. Non-irradiated rats, treated identically otherwise, served as controls. Two weeks after irradiation the phagocytic capacity and oxygen superoxide anion generation decreased by 61 and 70%, respectively, compared with controls. This tendency persisted after 4 weeks post irradiation, the decrease in both functions being 50 and 74%, respectively. It is suggested that the altered function of peritoneal macrophages following irradiation may further compromise the immune defense in patients receiving abdominal radiotherapy.

Consequences of gamma-irradiation on inflammatory cytokine regulation in human monocytes/macrophages

Inflammation is a frequent result of radiation damage, especially after therapeutic irradiation. Monocytes and macrophages play an important role in inflammatory cytokine secretion. However, knowledge of monocyte/ macrophage involvement in the pathogenesis of inflammation is still incomplete. In this study, we investigated the inflammatory cytokine regulation after in vitro gamma-irradiation of monocytes/macrophages. Semiquantitative RT-PCR after irradiation revealed no significant induction of interleukin 1 beta or tumour necrosis factor-alpha mRNA expression. When induction was observed, for only two donors out of seven, only interleukin 6 gene expression was affected by irradiation, with a 5-14-fold increase in level according to the donor, 2h after irradiation compared with sham-irradiated cells. For only one of seven donors tested, monocytes/macrophages responded to 10-Gy gamma-rays by releasing inflammatory cytokines.

Oxidative stress in radiation-induced interstitial pneumonitis in the rat

The involvement of free radical metabolism in the pathogenesis of interstitial pneumonitis was investigated in an animal model. Male Wistar rats were irradiated at the thoracic region by gamma-rays from a 60Co source. Histopathological examination confirmed that 50% of the rats developed pneumonitis between 2 and 8 weeks following a single dose of 14 Gy. Parallel biochemical studies in the lung of these rats showed that mitochondria and microsomes had higher levels of lipid peroxidation. In the cytoplasmic fraction of the lung the activities of superoxide dismutase and catalase were markedly reduced in the pneumonitic rat. In lung mitochondria, however, the levels of these two enzymes were not significantly altered. On the contrary, lipid peroxidation and superoxide dismutase, as well as catalase activities in lung tissue in the non-pneumonitic group of the irradiated rat were comparable with that of control animals. The results indicate that free radical-induced oxidative stress following thoracic irradiation may be one of the causative factors in the development of interstitial pneumonitis.