Evaluation of Systemically Delivered Glycopeptides for the Treatment of Acute Brain Injury and Parkinson's Disease

Abstract

Parkinson’s Disease (PD) is a progressive neurodegenerative disease characterized by the loss of dopamine producing cells within the substantia nigra, and the spread and accumulation of alpha synuclein containing aggregates across the brain and even in the periphery. Individuals with PD experience classic motor symptoms such as bradykinesia, rigidity, tremor and postural instability, as well as a variety of non-motor symptoms, often including cognitive decline. Levodopa, or L-DOPA is the gold standard treatment of PD, however L-DOPA only improves the motor symptoms, and does not address the underlying pathology associated with disease. Additionally, a large percentage of individuals develop a hyperkinetic movement secondary to treatment, called L-DOPA-induced Dyskinesias. For these reasons it’s imperative that new treatments are developed that target not only the non-motor symptoms, but are disease modifying in nature. Acute brain injuries, such as ischemic stroke and traumatic brain injury (TBI) differ from PD in that rather than several converging mechanisms of pathophysiology resulting in cell death and functional loss, initial damage is caused by a single acute event. Interestingly however, post-injury sequelae is known to result in further damage, and often involve many of the same processes involved in PD. These processes represent potential points of therapeutic intervention for drugs with neuroprotective properties. Peptide based therapies are attractive because they can initiate a wide range of effects and act in a multi-modal fashion, with little chance of toxicity. However, because of their poor stability and kinetics, peptides have difficulty translating into human medicine. Glycosylation of a peptide however prevents degradation of these peptides, and enhances blood-brain barrier penetration, increasing the translatable potential of these drugs. The present dissertation explores the use of novel glycopeptides to fill this therapeutic gap in PD. The glycopeptides in reference, an Angiotensin (1-7) glycoside (PNA5) and PACAP glycosides (2ls98lac and 2ls80mel) were chosen based on a large body of literature suggesting that they could be beneficial in the context of neurodegeneration. We first demonstrated in Chapter 2 that glycosylated-PACAP did in fact cross the Blood-Brain Barrier in appreciable quantities and had better stability than the native peptide. I then explored the use of glycosylated-PACAP in PD and TBI. Glycosylated-PACAP was able to reduce cell loss in the context of mild, but not moderate nigrostriatal degeneration. In TBI, glycosylated-PACAP reduced the sleep-wake cycle abnormalities and sensorimotor deficits. In both cases, there were indications that immunomodulation was taking place. This prompted us to assess glycosylated-PACAP efficacy in another model of acute injury, ischemic stroke. In Chapter 3 it was demonstrated that glycosylated-PACAP treatment after stroke reduced infarct size in a rodent model. It was also shown that in PC12 cells, an in vitro model of neuron-like cells glycosylated-PACAP produces neurite outgrowth, indicating that glycosylated-PACAP could also potentiate long term structural remodeling of neurons and synapses. Finally, in Chapter 4 PNA5 was evaluated in the context of cognitive dysfunction in PD. A chronic, progressive, mouse-model (Thy1-Syn) was treated daily for 2 months and evaluated for behavior and brain pathology. PNA5 restored cognitive function in these animals and reduced signs of central and peripheral inflammation. Additionally, a plasma-based biomarker, MIP-1 was identified, which has potential to act as a surrogate marker for cognitive decline in PD, and target engagement after PNA5 treatment. The results of these studies provide support for the use of glycosylated peptides for the treatment of PD and brain injury. Given that the disease modifying therapeutic landscape for neurodegeneration is bleak, it is crucial to develop drugs that get into the brain and have a central effect.