Effects of pirfenidone and fisetin on apoptosis and oxidative stress mechanisms in heart tissue of bleomycin-induced pulmonary fibrosis.

Bleomycin (BLM) is a chemotherapeutic agent that has been demonstrated to induce severe pulmonary and cardiac toxicity. Pirfenidone (PFD) is an established antifibrotic drug, while fisetin (FST) is a naturally occurring cardioprotective flavonol. The present study was conducted with the objective of evaluating the underlying mechanisms of BLM-induced cardiac damage and investigating the potential protective effects of combined PFD and FST treatment. Forty male Wistar albino rats were randomly divided into five groups (n = 8): Sham (intratracheal saline), and four groups that received a single intratracheal bleomycin injection (5 mg/kg) on day 1: BLM alone, BLM + PFD (50 mg/kg, oral), BLM + FST (25 mg/kg, oral), and BLM + PFD+FST (50 mg/kg PFD and 25 mg/kg FST, oral). Following induction, treatments were administered daily via gavage for 14 days. Cardiac damage was assessed using Hematoxylin and Eosin staining. ER stress-mediated apoptosis and oxidative stress were evaluated via immunohistochemistry (GADD153, Caspase-3), gene expression analysis (Bax/Bcl-2), and biochemical assays. The administration of BLM has been demonstrated to induce severe structural deterioration, characterised by the presence of persistent eosinophilic cardiomyocytes and haemorrhagic areas. While single treatments (BLM + PFD and BLM + FST) provided moderate improvements to histology, the combined treatment (BLM + PFD+FST) demonstrated superior preservation of tissue architecture. Biochemically and immunohistochemically, the BLM group exhibited a significantly increased Bax/Bcl-2 ratio, elevated caspase-3 and GADD153 expression, and exacerbated oxidative stress parameters. Conversely, the combined treatment significantly suppressed these pro-apoptotic signalling pathways and restored oxidative balance more effectively than either agent alone. Widespread cardiac fibrosis was not observed in any group during this acute phase. The combination of pirfenidone and fisetin in treatment provides superior cardiac protection against the toxicity induced by bleomycin in comparison to monotherapies. This is achieved by significantly attenuating pro-apoptotic signalling and restoring oxidative balance (GSH, MDA, MPO). These findings suggest that multi-targeted therapeutic approaches addressing both ER stress and oxidative pathways may be more effective than single-agent therapy in mitigating the cardiac complications associated with pulmonary fibrosis models.