Systemic pirfenidone treatment fails to mitigate fibrosis and compromises functional recovery in a porcine model of volumetric muscle loss

Repurposing clinically approved antifibrotic agents presents a potential near-term therapeutic strategy to mitigate the extensive fibrotic scarring that follows severe volumetric muscle loss (VML) injury and inhibits functional recovery. We hypothesized that daily oral administration of pirfenidone, an FDA-approved antifibrotic, would mitigate the overwhelming fibrotic response and facilitate functional recovery in a clinically relevant porcine VML model. Yorkshire-cross pigs (n = 12) underwent VML or sham surgery in the peroneus tertius muscle and were subsequently allocated to pirfenidone treatment or untreated controls. At the 4-week study endpoint, the affected muscles underwent comprehensive histological, biochemical, transcriptional and neuromuscular functional assessments. Transcription profiling demonstrated that pirfenidone downregulated key pro-inflammatory cytokine and chemokine regulators involved in excessive fibrosis, including TNF, CCL3L1 and CCL2. While pirfenidone treatment failed to reduce total collagen deposition, evidenced by picrosirius red quantification and hydroxyproline content, it did result in a less dense collagen fibre architecture, suggestive of altered tissue remodelling. However, pirfenidone treatment impaired functional recovery through reduced contractile output and resulted in stagnant weight gain compared to the untreated cohort. This work demonstrates that systemic pirfenidone administration failed to meaningfully reduce fibrosis and subsequently worsened functional capacity following VML, similar to previous antifibrotic studies. The functional deficits and stagnant weight gains observed here underscore a critical knowledge gap regarding the impact of systemic antifibrotics on contractile recovery, necessitating a rigorous re-evaluation of delivery routes, dosages and administration timelines to ensure that future therapies for fibrotic scarring do not inadvertently hinder the physiological recovery of VML-injured muscle.