NYX-458 in Subjects With Mild Cognitive Impairment or Mild Dementia Due to Parkinson's Disease or Lewy Body Dementia (Cognition, Memory, Attention, Thinking)

Change from baseline in physical examination

Physical examination

Time frame: Subjects will be followed up to 14 days post-dose

Rates of adverse events and serious adverse events

Adverse events and serious adverse events

Time frame: Subjects will be followed up to 14 days post-dose

Rates of early termination due to adverse events

Early termination due to adverse events

Time frame: Subjects will be followed up to 14 days post-dose

Change from baseline in vital signs, clinical laboratory values, and electrocardiogram results

Vital signs, clinical laboratory values, and electrocardiogram results

Time frame: Subjects will be followed up to 14 days post-dose

Change from baseline dissociative effects, psychosis, and hallucinatory symptoms as measured by the Neuropsychiatric Inventory (NPI-12)

Neuropsychiatric Inventory (NPI-12) - NPI-12 assesses 12 behavioral domains common in dementia. Higher scores indicate more severe illness.

Time frame: Subjects will be followed up to 14 days post-dose

Change from baseline in suicidal ideation and behavior as measured by the Sheehan Suicidality Tracking Scale (S-STS)

Sheehan Suicidality Tracking Scale (S-STS) is a 16-item scale that assesses the seriousness of suicidality phenomena on a likert-type scale (0 to 4) ranging from 0 = not at all to 4 = extremely

Time frame: Subjects will be followed up to 14 days post-dose

Change from baseline in motor complications as measured by the Movement Disorder Society Unified Parkinson's Disease Rating Scale (MDS-UPDRS) Part 4