Polydopamine nanoparticles as multitasking nanoplatforms against neurodegenerative diseases

Neurodegenerative diseases, like Alzheimer's, Parkinson's and amyotrophic lateral sclerosis (ALS), present significant challenges to global health due to their debilitating effects and the growing prevalence in ageing populations. These conditions are closely linked to an imbalance expression in the microglia phenotypes and an overproduction of reactive oxygen species (ROS), which leads to oxidative stress and subsequent neuronal damage. Due to their high reactivity, ROS can interact with various intracellular macromolecules, compromising their structure and leading to serious impairment of cellular functions. In this regard, microglia, immune cells of the central nervous system, can exhibit pro-inflammatory (M1) or anti-inflammatory (M2) phenotypes, playing a central role as inflammatory mediators. Recent studies have shown that in many neurodegenerative diseases the overexpression of M1-activated microglia exacerbates oxidative stress, leading to a vicious cycle of inflammation and neurodegeneration. Therefore, targeting microglial activation and ROS production is crucial for developing effective treatments. Polydopamine (PDA), a synthetic polymer derived from dopamine, has emerged as a promising material for contrasting ROS due to its strong antioxidant properties and excellent biocompatibility. PDA can effectively scavenge free radicals and reduce oxidative stress, making it a potential therapeutic agent for neurodegenerative diseases. This thesis explores the potential of polydopamine nanoparticles (PDNPs) as versatile nanoplatforms to reduce ROS production in the human brain. First, an in vitro model using human microglia cells (HMC3) was developed and various concentrations of PDNPs were tested to assess internalisation and cell viability. After determining the optimal concentration, experiments were conducted to observe how PDNPs interacted with the phenotypes expressed by the HMC3 cells and their effects on ROS production. Additionally, the ability of PDNPs to convert near-infrared (NIR) radiation into heat was exploited to test whether a localized temperature increase could induce HMC3 cells to adopt an anti-inflammatory phenotype. Once the in vitro model was optimized, the study progressed to a more complex one. Due to the high costs and ethical concerns associated with in vivo models, the choice fell on the in ovo model, which involves grafting cells or tissues onto the avian chorioallantoic membrane (CAM) of developing embryos. The CAM model offers several advantages, including being a cost-effective and more ethically acceptable alternative to mammalian models, along with rapid development and ease of observation. Finally, HMC3 spheroids were created and, after optimization, transplanted onto the CAM of quail embryos. This setup enabled the study of the impact of PDNPs on a three-dimensional, vascularized structure.