INS and Parkinson disease: Multiple pre-clinical studies have demonstrated the neuroprotective effects of insulin, insulin-like growth factor and GLP-1 analogues administered by the intranasal route in animal models of AD and PD, including a reduction in AD hallmarks (e.g. amyloid plaque load), restoration of synaptic plasticity, lowered chronic inflammation response, reduced functional impairment, and improved synaptogenesis or neuronal functionality [4, 7, 11, 15–17].