STRUCTURES OF THE BLOOD-BRAIN BARRIER THAT CONFERS ITS IMPERMEABILITY AND INNOVATIONS IN DRUG DELIVERY TO THE CENTRAL NERVOUS SYSTEM

The blood-brain barrier (BBB) is a critical regulatory structure that maintains neural homeostasis by selectively controlling the substances that enter the central nervous system. While this impermeability protects the brain from harmful agents, it poses a formidable challenge for delivering drugs to treat neurological disorders such as Alzheimer's, Parkinson's, and brain cancers. This review analyzes the structural components contributing to the BBB's restrictive nature, including endothelial cells with tight junctions, astrocytic end-feet, and pericytes, and highlights their implications for drug delivery. Two primary approaches to overcoming the BBB are examined: invasive techniques such as hyperosmotic agents and inflammatory mediators, and non-invasive methods including liposomal carriers and intranasal delivery. While invasive techniques can effectively enhance BBB permeability, they carry risks of adverse side effects, such as neuronal damage or exposure to harmful substances. Among non-invasive strategies, liposomal drug delivery systems show promise due to their ability to encapsulate both hydrophilic and hydrophobic drugs. However, these systems still face challenges due to limitations in current molecular drug design. Liposomes require fine-tuning to meet the BBB's molecular weight and hydrogen bonding restrictions, and advancements in medicinal chemistry are essential to develop effective carrier systems that can efficiently target the CNS without compromising safety. Furthermore, discrepancies in findings across studies, attributed to methodological and species differences, underscore the complexity of achieving consistent results. This review emphasizes the necessity for innovative research to refine these methods and mitigate their shortcomings, with the ultimate goal of enabling safe and effective treatment for currently intractable neurological diseases.