Pirfenidone Injection to Prevent Vocal Fold Scarring in a Canine Model: A Pilot Preclinical Study

This pilot study investigated the safety and efficacy of pirfenidone (PFD) injection for vocal fold (VF) scarring after laser cordectomy in a canine model. We evaluated safe PFD concentrations and its preventive effects on postoperative VF scarring using laryngoscopic, histological, immunohistochemical (IHC), and high-speed imaging analyses.

To assess toxicity, 0.3 mL of saline or PFD solution at six serial concentrations (0, 0.5, 1.0, 2.5, 5.0, and 10.0 mg/mL; 0 mg/mL = saline) was injected into the VFs of three dogs, and histological evaluation was performed 2 weeks later. For efficacy testing, saline, 1.0 mg/mL PFD, or 2.5 mg/mL PFD was injected into the right VFs of three dogs before type III laser cordectomy. The left VFs remained untreated. Wound status was assessed by laryngoscopy at 4 and 8 weeks. At 8 weeks, vibratory function was assessed using high-speed imaging, followed by histological and IHC analyses for collagen type I (COL1) and α-smooth muscle actin (α-SMA).

In the toxicity test, VFs injected with ≤ 2.5 mg/mL PFD showed complete epithelial healing, whereas those injected with ≥ 5.0 mg/mL PFD showed epithelial detachment from the lamina propria. In the efficacy test, high-speed imaging demonstrated greater vibratory amplitudes in PFD-injected VFs than in control VFs, with more pronounced improvement at 2.5 mg/mL PFD. Hematoxylin and eosin (H&E), Masson's trichrome, and Alcian blue staining showed that VFs injected with 2.5 mg/mL PFD exhibited reduced fibrotic changes and collagen deposition compared with saline- and 1.0 mg/mL PFD-injected VFs. IHC analysis showed attenuated α-SMA and COL1 immunoreactivity in PFD-treated VFs, particularly in the 2.5 mg/mL PFD-injected VF.

This pilot study suggests that PFD injection before laser cordectomy may mitigate VF scarring and help preserve VF vibratory function in a canine model. These findings provide preliminary evidence supporting the potential of PFD as a preventive strategy against fibrosis during VF surgery.