Aerosolized administration of N-acetylcysteine attenuates lung fibrosis induced by bleomycin in mice

Reactive oxygen species (ROS) play an important role in the pathogenesis of pulmonary fibrosis. We previously demonstrated that N-acetylcysteine (NAC), an antioxidant, inhibited adhesion molecule expression and cytokine production in lung cells. When NAC is inhaled into the alveolar space, it is expected to directly interact with inflammatory cells and to elevate glutathione levels in the epithelial lining fluids. We therefore examined whether inhaled NAC inhibits lung fibrosis induced by bleomycin (BLM). Male ICR mice were given a single intravenous injection of BLM (150 mg/ kg). Thirty milliliters of NAC (70 mg/ml) or saline were inhaled twice a day for 28 d using an ultrasonic nebulizer. In the inflammatory phase (Day 7), NAC administration attenuated the cellular infiltration in both bronchoalveolar lavage fluid (BALF) and alveolar tissues. At Day 28, the fibrotic changes estimated by Aschroft's criteria and hydroxyproline content in the NAC inhalation group were significantly decreased compared with the BLM-only group (p < 0.05). CXC chemokines, macrophage inflammatory protein-2 (MIP-2), cytokine-induced neutrophil chemoattractant (KC), and CC chemokines, macrophage inflammatory protein-1alpha (MIP-1alpha), in BALF were mostly elevated on Day 7 in the BLM-only group; however, these elevations were significantly repressed by NAC inhalation (p < 0.05). Lipid hydroperoxide (LPO) was also quantified in BALF. LPO was markedly increased on Day 3 in the BLM-only group, and this increase was significantly decreased by NAC inhalation (p < 0.05). These results revealed that aerosolized NAC ameliorated acute pulmonary inflammation induced by BLM injection via the repression of chemokines and LPO production, resulting in the attenuation of subsequent lung fibrosis. These findings are limited to the BLM-induced lung fibrosis animal model. However, NAC inhalation will be expected to be a potential therapy for patients with other interstitial pneumonias because ROS are involved in the pathogenesis of lung injury in most interstitial pneumonia.

Role of macrophage scavenger receptors in hepatic granuloma formation in mice

In mice homozygous for the gene mutation for type I and type II macrophage scavenger receptors (MSR-A), MSR-A-/-, the formation of hepatic granulomas caused by a single intravenous injection of heat-killed Corynebacterium parvum was delayed significantly for 10 days after injection, compared with granuloma formation in wild-type (MSR-A+/+) mice. In the early stage of granuloma formation, numbers of macrophages and their precursor cells were significantly reduced in MSR-A-/- mice compared with MSR-A+/+ mice. In contrast to MSR-A+/+ mice, no expression of monocyte chemoattractant protein-1, tumor necrosis factor-alpha, and interferon-gamma mRNA was observed in MSR-A-/- mice by 3 days after injection. Also in MSR-A-/- mice, uptake of C. parvum by Kupffer cells and monocyte-derived macrophages in the early stage of granuloma formation was lower and elimination of C. parvum from the liver was slower than in MSR-A+/+ mice. In the livers of MSR-A+/+ mice, macrophages and sinusoidal endothelial cells possessed MSR-A, but this was not seen in the livers of MSR-A-/- mice. In both MSR-A-/- and MSR-A+/+ mice, expression of other scavenger receptors was demonstrated. These data suggest that MSR-A deficiency impairs the uptake and elimination of C. parvum by macrophages and delays hepatic granuloma formation, particularly in the early stage.