Photobiomodulation Therapy with Zinc Oxide/Pheophorbide-a Nanoflakes Enhances Neurovascular Repair in Spinal Cord Injury Evidenced Using Photoacoustic Imaging

Spinal cord injury (SCI) and its accompanying neurodegenerative processes lead to devastating impairments, with limited treatment options. Our study investigates the synthesis and evaluation of Pheophorbide-a conjugated zinc oxide nanoflakes (Phei-Zn NFs) as a nanotheranostic platform combined with near-infrared (NIR) photobiomodulation (PBM) therapy for SCI treatment. The Phei-Zn NFs demonstrated photothermal stability, neuronal cell uptake, antioxidant, and anti-inflammatory properties when tested in in vitro models. Further mechanistic studies displayed an upregulation of regenerative markers Collapsin response mediator protein 2 (CRMP2) and Beta-tubulin III following treatment with Phei-Zn NFs combined with NIR light-based PBM therapy. The in vivo acute rat SCI model indicated that the Phei-Zn NFs provided enhanced micro-CT contrast imaging and augmented vascularization, as evidenced by noninvasive photoacoustic imaging. Molecular analyses confirmed suppression of pro-inflammatory cytokines and promotion of anti-inflammatory microglial polarization and improved blood-spinal cord barrier integrity. These findings highlight Phei-Zn NFs coupled with PBMT (photobiomodulation therapy) as a promising noninvasive strategy to mitigate inflammation, promote neuroregeneration, and improve functional outcomes after SCI.