Intranasal delivery of DPSC-derived small extracellular vesicles-encased phloroglucinol attenuates non-motor and motor deficits and promotes neurogenesis in an in vivo rat model of Parkinson's disease.

Abstract

Background: Parkinson's disease (PD) is characterized by dopaminergic (DA) neuron degeneration in the substantia nigra pars compacta (SNpc) driven by oxidative stress, inflammation, and impaired neurogenesis. Phloroglucinol, a polyphenolic antioxidant, has demonstrated neuroprotective effects in PD models but suffers from limited clinical applicability due to poor blood-brain barrier (BBB) permeability. Small extracellular vesicles (sEV) derived from dental pulp stem cells (DPSCs) exhibit neuroprotective and immunomodulatory properties and serve as promising vehicles for targeted drug delivery across the BBB. This study aimed to evaluate the therapeutic efficacy of intranasally administered sEV-encased phloroglucinol (sEV-Phl) in a chronic MPTP rat model of PD.

Methods: DPSC-derived sEV were isolated via density gradient ultracentrifugation and characterized using Transmission Electron Microscopy (TEM), Dynamic-Light-Scattering (DLS), and CD marker expression. Phloroglucinol was encased in sEV (sEV-Phl) using sonication. Antioxidant properties were tested in vitro using an H₂DCF.DA assay in SH-SY5Y cells exposed to 6-OHDA. Chronic MPTP-treated male Wistar rats received intranasal sEV-Phl, with motor and non-motor behaviours evaluated up to 4-weeks post-MPTP treatment. TH-positive neurons, neurogenesis (Ki67, BrdU and FOXA2), lipid-peroxidation, and neurotransmitter-levels were analyzed. sEV biodistribution was tracked via near-infrared imaging and localization in neuronal and glial cells was confirmed with PKH-26 labelling, with confocal-imaging further verifying localization in neuronal and glial cells. TNF-α expression was assessed as a marker of neuroinflammation.

Results: sEV displayed high purity and homogeneity. sEV-Phl significantly reduced oxidative stress both in vitro and in vivo, as indicated by decreased ROS and lipid peroxidation levels. sEV-Phl treated MPTP rats demonstrated marked improvement in motor and non-motor behaviours compared to MPTP rats. Immunohistochemical analysis revealed increased TH-positive neurons and enhanced neurogenesis in the SNpc of sEV-Phl-treated animals. Biodistribution studies confirmed efficient midbrain targeting of sEV, which were localized to dopaminergic-neurons, astrocytes and microglia. sEV-Phl also significantly reduced TNF-α expression, indicating decreased neuroinflammation.

Conclusion: This study provides the first instance of using DPSC-derived sEV as a delivery vehicle for phloroglucinol in a PD model. sEV-Phl demonstrated significant neuroprotective-effects, enhanced DA-neuron survival and neurogenesis, and reduced neuroinflammation. Intranasal delivery of sEV-Phl represents a promising non-invasive therapeutic strategy for PD, offering a dual benefit of antioxidative and neurogenic support.