Towards functionalised nanoparticle-based therapies for oxidative stress following partial injury to the central nervous system

[Truncated] The loss of undamaged but vulnerable tissue in the central nervous system (CNS) following neurotrauma contributes to long term deterioration of functional outcomes. A range of biochemical cascades occur resulting in the loss of intact tissue beyond the injury site in a process referred to as secondary degeneration. This cascade is thought to include an increase in extracellular levels of the neurotransmitter glutamate, which leads to glutamate excitotoxicity, causing an increased influx of Ca2+ into neurons and glia. The movement of Ca2+ into cells following injury is facilitated by activation of Ca2+ permeable membrane-bound ion channels. These include glutamate activated NMDA and AMPA receptors, voltage gated calcium channels and ATP activated purinergic receptors P2X7 and P2Y1 Along with changes in Ca2+ dynamics, secondary degeneration also results in other changes in the CNS, such as microglial activation and the increase of AQP4 expression in astrocytes, which leads to an influx of water into the cell causing swelling and cell death.

Whilst Ca2+ is essential for cellular function, excessive and rapid increases in the intracellular concentrations are linked to the overproduction of reactive oxygen species (ROS) via the mitochondria. Excess ROS contributes to the degradation of vital cellular machinery including proteins, lipids as well as DNA, leading to disruption of cellular function and cell death. This ROS and Ca2+ imbalance following neurotrauma leads to a self-amplifying biochemical cascade resulting in the spread of injury to undamaged cells and exacerbating the severity of the initial injury. It is currently hypothesised that the astrocytic syncytium is involved in the movement of Ca2+ and ROS between neurons and glia. However, Ca2+ microdomain changes within astrocytes following injury are currently not fully understood.

This PhD thesis is split into two parts. The first describes the use of a combination of fluorescence microscopy and nanoscale secondary ion mass spectrometry (NanoSIMS) to investigate Ca2+ microdomain dynamics in untreated rat optic nerve vulnerable to secondary degeneration, up to three months following partial injury. The second part describes the development of a nanoparticle-based system for delivery of the antioxidant resveratrol to astrocytes of rat optic nerve susceptible to secondary degeneration, tracking both the nanoparticle and resveratrol (using a 13C-enriched form) by NanoSIMS, as well as an investigation of the effect of the nanoparticle-based treatment on Ca2+ microdomain dynamics in the optic nerve in vivo.