INS and Parkinson disease: For instance, insulin modulates α-Syn expression and aggregation (Sharma et al., 2015b,c), regulates vesicular monoamine transporter 2 (VMAT2; Kong et al., 2020) and intranasal administration of insulin ameliorated mitochondrial function, motor impairment and dopaminergic neuron death in a rat model of PD (Iravanpour et al., 2021).