Nano-medicine improving the bioavailability of small molecules for the prevention of neurodegenerative diseases

Neurodegenerative diseases, including Parkinson's and Alzheimer's, are a heterogeneous group of brain disorders characterized by the progressive degeneration of the structure and function of the central or peripheral nervous system. It is thought that the number of people affected by these pathologies will increase in future decades, particularly in the more economically developed countries, where the populations are experiencing a demographic shift towards older ages. For many of these pathologies, and in particular for Alzheimer's disease, no effective treatments are available, and the consequent economic and social costs are very high. Scientific progress in recent decades has provided a better understanding of the genetic and biological mechanisms responsible for these neurodegenerative diseases, and offers the hope for new therapeutic approaches in the near future. Meanwhile, the lack of effective therapies for these diseases has caused researchers to focus attention on the powerful opportunity of prevention, seen on the one hand as a series of healthcare measures and patient behaviors, and on the other hand as treatments exploiting several molecules or compounds with the potential to slow down the appearance of the first signs of pathology or even to prevent these diseases. Among these, curcumin, flavonoids, such as quercetin, Gingko biloba, and folic acid have attracted the attention of scientists, and ways are being explored to increase their effectiveness and bioavailability in the site of action. Most molecules suffer from problems of solubility, or bioavailability, or the ability to cross the blood brain barrier, and one solution to this limitation being explored is nanomedicine. Polymeric nanoparticles, as well as liposomes, and functionalized nanosystems may overcome several bioavailability limits of active molecules and increase their effectiveness in the brain. This review offers an overview of small molecules that may prove effective in preventing neurodegenerative diseases, and describes the strategies in nanomedicine that are being studied to improve their bioavailability.