MAPT and Alzheimer disease: QA, for example, is an excitotoxin that can induce oxidative stress and neuronal death, while KYNA has neuroprotective properties and its dysregulation can contribute to cognitive deficits.42,43 In AD, increased levels of IDO1 and Kyn have been associated with enhanced amyloid-beta (Aβ) deposition and tau hyperphosphorylation, two hallmark features of AD pathology.