Abstract

A time course study was carried out to elucidate the mechanisms for antifibrotic effect of pirfenidone (PD). Hamsters were intratracheally (i.t.) instilled with saline (SA) or bleomycin (BL) (7.5 units/kg/5 ml). The animals were fed a diet containing 0.5% PD or the same control diet (CD) without the drug 2 days before and throughout the study. The animals were sacrificed at various times after instillation. The lung hydroxyproline level in BL + CD groups was gradually increased and peaked at 21 days to 181% of the SA + CD control. The BL + PD-treated groups showed a gradual decrease in their lung collagen content, showing a maximum reduction of 40% at day 21. The lung malondialdehyde levels of the BL + CD groups were increased by several-fold of the corresponding SA + CD groups at various times. The lung prolyl hydroxylase (PH) activities in the BL + CD groups were also increased by several-fold of the corresponding SA + CD groups at these time points. The hamsters in the BL + PD showed a gradual decrease in the lung malondialdehyde levels from 10 to 21days compared with their corresponding BL + CD groups. Treatment with PD also reduced the lung PH activities in the BL + PD groups compared with the corresponding BL + CD groups. However, PD failed to manifest any direct inhibitory effect on PH activity in vitro. BL treatment increased the lung procollagen I and III gene expressions in the BL + CD groups by several-fold at varying times compared with the corresponding SA + CD, and treatment with PD in the BL + PD groups significantly down-regulated the BL-induced overexpression of these genes. Studies evaluating the regulation of these genes at the transcriptional level revealed PD significantly reduced the transcription of PC I at 14 days. Our results indicate that the antifibrotic effect of PD was partly due to suppression of the BL-induced inflammatory events and partly due to down-regulation of BL-induced overexpression of lung procollagen I and III genes.