Navigating into the Paradigm of Nose-to-brain Delivery of Nanotherapeutics and their Repurposing as Nanotheranostics for Neurodegenerative Diseases.

Repurposing drugs for neurodegenerative diseases using the nose-to-brain route of administration is an intriguing concept with potential benefits. The nose-to-brain route involves delivering drugs directly to the brain via the olfactory or trigeminal pathways, bypassing the blood-brain barrier, which can improve drug efficacy and reduce systemic side effects. Treatment of numerous neurodegenerative diseases such as Multiple sclerosis, Amyotrophic lateral sclerosis, Huntington's, Alzheimer's, and Parkinson's diseases has been attempted using this route of administration. These drugs may include neuroprotective agents, anti-inflammatory drugs, antioxidants, or diseasemodifying therapies. Nanotheranostics, which integrates therapeutic and diagnostic functions in a nanosystem, improves treatment precision and efficacy. Repurposing nanotherapeutics as nanotheranostics for neurodegenerative diseases through the nose-to-brain route of administration holds great potential for both diagnosis and treatment. This review highlights the various mechanisms engaged in transporting nanocarriers from nose-to-brain and the proposed fate of these nanocarriers using different live imaging techniques. Additionally, the discussion covers the recent combinatorial therapeutic approaches and theranostic applications of various nanocarriers used for neurodegenerative diseases through the nose-to-brain. Toxicity to the CNS and nasal mucosa and regulatory considerations about these delivery systems are also deliberated. Overall, repurposed nanoparticles designed as nanotheranostic agents offer a versatile platform for precise diagnosis, targeted therapy, and personalized management of neurodegenerative diseases, holding great promise for improving patient care and advancing our understanding of these complex disorders.