Neostriatal and cortical quinolinate levels are increased in early grade Huntington's disease

Abstract

Huntington's disease (HD), an inherited neurodegenerative disorder, is caused by an abnormal polyglutamine expansion in the huntingtin protein. This genetic defect may result in heightened neuronal susceptibility to excitotoxic injury, a mechanism that has been postulated to play a critical role in HD. Quinolinate (QUIN) and kynurenate (KYNA), two endogenous neuroactive metabolites of the kynurenine pathway of tryptophan degradation, have been proposed to modulate excitotoxic neuronal death in HD. A third kynurenine pathway metabolite, the free radical generator 3-hydroxykynurenine (3-HK), has also been hypothesized to play a causal role in the pathogenesis of HD. We show here that the brain levels of both 3-HK and QUIN are increased three to four-fold in low-grade (grade 0/1) HD brain. These changes were seen in the neocortex and in the neostriatum, but not in the cerebellum. In contrast, brain 3-HK and QUIN levels were either unchanged or tended to decrease in grade 2 and advanced grade (grades 3-4) HD brain. Brain kynurenine and KYNA levels fluctuated only modestly as the illness progressed. These results support a possible involvement of 3-HK and QUIN in the early phases of HD pathophysiology and indicate novel therapeutic strategies against the disease.