Pathogenesis-Driven Drug Repurposing with a Self-Nanoemulsifying Delivery System for Parkinson’s Disease

Background/Objectives: The aim of the present study was to investigate the mechanisms in Parkinson’s disease (PD), a progressive neurodegenerative disorder characterized by loss of dopaminergic neurons, aggregation of α-synuclein, mitochondrial dysfunction, oxidative stress, neuroinflammation, gut dysbiosis, and blood–brain barrier (BBB) impairment. Although there are several approved therapies that have been developed, their aqueous solubility, oral bioavailability, first-pass metabolism, and inability to penetrate the BBB make them less effective over time. This review is intended to critically analyze the potential of self-nanoemulsifying drug delivery systems (SNEDDSs) as a pathogenesis-related approach to enhance the delivery and therapeutic activity of repurposed drugs and conventional drugs for PD. Methods: A comprehensive literature search was conducted to address the pathogenic mechanisms of PD, the deficiencies of current pharmacotherapy, recent developments in SNEDDS formulation strategies and their application in improving oral bioavailability, lymphatic transport, BBB penetration and targeted brain delivery. A special focus was dedicated to drug repurposing, functionalized SNEDDSs, PEGylation, and gut–brain axis modulation. Results: SNEDDSs significantly enhance the water solubility, stability, intestinal absorption and systemic exposure of poorly water-soluble therapeutic agents and, to a certain extent, lymphatic uptake to avoid first-pass metabolism. These systems include improved brain delivery, decreased pharmacokinetic variability, and prolonged drug levels within the therapeutic range. Moreover, SNEDDSs can be used to deliver multiple molecules that are found to be neuroprotective, antioxidant, anti-inflammatory and probiotic, all at once, which can act on multiple pathogenic mechanisms associated with PD. Functionalized and PEGylated SNEDDSs add further to formulation stability, extend systemic circulation and increase efficiency of brain targeting. Conclusions: SNEDDSs are a promising translational nanomedicine platform for enhancing the effectiveness of conventional and repurposed therapeutics in PD, which address key pharmacokinetic and biological challenges. The next generation of oral therapies with targeted surface engineering, precision drug repurposing and clinical validation will be expected to bring about a faster advancement of drugs that can alter the course of disease rather than giving only symptomatic relief.