5-HT7 receptor antagonism (SB-269970) attenuates bleomycin-induced pulmonary fibrosis in rats via downregulating oxidative burden and inflammatory cascades and ameliorating collagen deposition: Comparison to terguride

The neurotransmitter 5-hydroxytryptamine (5-HT) is involved in regulation of local tissue inflammation and repair through a set of receptors (5-HT1-7 receptors), which are expressed in the lung. Considering the protective importance of 5-HT receptor antagonists against development of pulmonary fibrosis, we evaluated whether 5-HT7 receptor antagonist (SB-269970) modulates lung inflammatory and fibrogenic processes in comparison with 5-HT2A/B receptor antagonist (terguride), in bleomycin (BLM)-induced idiopathic pulmonary fibrosis (IPF) model. IPF model induced by a single dose of intra-tracheal BLM instillation (5 mg/kg), and rats were treated with intraperitoneal injection of SB-269970 (1 mg/kg day) or terguride (1.2 mg/kg/d). The experiment was carried out on two separate sets of rats that were killed at day 7th and day 21st to evaluate the endpoint of the IPF inflammatory and fibrogenic phases, respectively. During the inflammatory phase 5-HT2A/B and 5-HT7 receptor antagonists attenuated the BLM-induced increase in the lung fluid content, the inflammatory cytokines levels and oxidative stress burden. In the fibrogenic phase, both SB-269970 and terguride reduced the serotonin concentrations in lung homogenates and significantly protected against IPF fibrogenic phase by attenuating collagen deposition and mRNA expression of both transforming growth factor-β1 (TGF- β1), and procollagen type Ӏ (PINP). 5-hydroxytryptamine 5-HT7 receptor antagonist showed more benefits than 5-HT2A/B receptor antagonist on the deleterious effects accompanied BLM instillation. The present study showed involvement of 5-HT7 receptor in the pathophysiology of BLM-induced IPF in rats and identified it as a potential therapeutic target in lung fibrotic disorders.