Rapid structural transformation of ionizable lipid nanoparticles involving Omega-3 polyunsaturated fatty acids enhances antioxidant defense and mitochondrial proteins activity in pH-responsive drug delivery

Inefficient intracellular delivery remains a major bottleneck in the development of nanomedicines targeting brain disorders. To address this challenge, we present a dynamic structural nanomedicine platform based on ionizable liquid crystalline lipid nanoparticles (LC-LNPs) incorporating omega-3 polyunsaturated fatty acids (PUFAs), enabling pH-responsive transformation and neuroprotective drug delivery. The created multidrug-loaded nonlamellar LC-LNP co-encapsulated the antioxidants ginkgolide B and quercetin and were functionalized with the bioactive cell-penetrating pituitary adenylate cyclase-activating polypeptide (PACAP) for targeted neuronal delivery. The time-resolved synchrotron SAXS study revealed that the PUFA-LNPs exploit the inherent pH-sensitivity of DHA and EPA to undergo a rapid, millisecond-timescale pH-dependent structural transformation from a hexagonal mesophase (lattice parameter shrinkage from 6.14 nm to ∼5.57 nm within 200 ms). This dynamic mechanism, triggered by acidic pH, induces a more compact LNP nanostructure that promotes the efficient release of poorly soluble antioxidant compounds. The in vivo safety study following intranasal administration in C57BL/6 J mice established excellent biocompatibility for nose-to-brain drug delivery. The multidrug-loaded LC-LNPs induced significant neuroprotective transcriptomic changes, including the upregulation of mitochondrial, antioxidant, and neurotrophic markers alongside suppression of pro-apoptotic genes. The in vitro studies confirmed that PUFA-LNPs effectively modulate mitochondrial protein activity (e.g., a 1.5-fold increase in ATP synthase expression), enhance mitochondrial resilience, antioxidant enzyme function (GSH-Px), and positively influence ROS-associated signaling pathways. Thanks to the ionizable carboxyl groups of PUFAs, which confer their intrinsic pH-sensitive properties, we achieved precisely characterized, pH-responsive structural reorganization of the LNPs, enabling enhanced intracellular drug delivery and synergistic neuroprotection of neuronal cells.