Role of OX/OXR cascade in insomnia and sleep deprivation link Alzheimer's disease and Parkinson's disease: Therapeutic avenue of Dual OXR Antagonist (DORA).

Sleep plays a role in the elimination of neurotoxic metabolites that are accumulated in the waking brain as a result of neuronal activity. Long-term insomnia and sleep deprivation are associated with oxidative stress, neuroinflammation, amyloid beta (Aβ) deposition, and Lewy body formation, which are known to increase the risk of mild cognitive impairment (MCI) and dementia. Orexin A (OXA) and orexin B (OXB), two neuropeptides produced in the lateral hypothalamus, are known to influence the sleep-wake cycle and the stress responses through their interactions with OX receptor 1 (OX1R) and OX receptor 2 (OX2R), respectively. OX/OXR cascade demonstrates intricate neuroprotective and anti-inflammatory effects by inhibiting nuclear factor-kappa B (NF-kB) and PLC/Ca pathway activation. OX1R binds OXA more strongly than OXB by one-order ratio, whereas OX2R binds both OXA and OXB with equal strengths. Overexpression of OXs in individuals experiences sleep deprivation, circadian rhythm disturbances, insomnia-associated MCI, Parkinson's disease (PD), and Alzheimer's disease (AD). Many dual OXR antagonists (DORAs) have been effective in their clinical studies, with suvorexant and daridorexant receiving FDA clearance for insomnia therapy in 2014 and 2022 respectively. The results of clinical studies suggested that there is a new pharmaceutical option for treating insomnia and the sleep deprivation-AD/PD relationship by targeting the OXR system. DORAs treatment reduces Aβ deposition in the brain and improves synaptic plasticity and circadian expression. This review indicates the link between sleep disorders and MCI, DORAs are an appropriate medication category for treating insomnia, and sleep deprivation links AD and PD.