In Alzheimer's disease (AD), accumulation of fibrillar fragments (Aβ) of β-amyloid precursor protein (APP) may lead to neurotoxicity by triggering oxidative and/or nitrosative injury. In 1996, two of the applicants (MBS and CFN) identified inducible nitric oxide (NO) synthase (iNOS) in lesions of AD. As catalyst of the high output pathway of NO production, iNOS was a plausible contributor to neuronal damage. To address its actual pathogenic significance, one of us (CFN) helped generate iNOS-deficient mice and then bred iNOS-null alleles into mice transgenic for the mutant human AD-related genes APP and presenilin-1. Using these mice, CFN and the third applicant, MFB, an AD investigator, found that iNOS made a major contribution to AD-related mortality, Aβ deposition, microgliosis, astrocytosis, and nitrotyrosine formation in this model.
Given that inhibitors of iNOS have been administered safely to mice and people, iNOS has emerged as a functionally important source of oxidative/nitrosative brain injury that may be a plausible target for pharmacologic inhibition in AD. Meanwhile, a team led by MBS synthesized triterpenoids that potently block induction of iNOS and at the same time induce the anti-inflammatory enzymes heme oxygenase 1 (HO 1) and "phase 2" anti-oxidants.
The goal of the present proposal is to target iNOS by clinically relevant pharmacologic interventions in transgenic mice with AD-like disease. We will administer the novel triterpenoid TP-224 in chow to test prophylactic inhibition of iNOS induction. Separately, we will administer the substrate analog inhibitor N-iminoethyl-L-lysine (L-NIL) in drinking water to test therapeutic inhibition of iNOS action. Each agent will be given to Tg19959 mice, which bear a prion promoter-driven triple-mutant (K670N/M671L/V717F) APP transgene and develop cerebral Aβ deposits by 3 months of age.
Prophylaxis with TP-224 will begin at 1 month of age and therapy with L-NIL at 4 months. Following 6 months of oral administration of test agents, experimental and vehicle-fed control groups will be monitored in a Morris water maze to evaluate learning and memory. Their brains will then be examined for cerebral plaque formation, neuritic pathology, astrocytosis, microgliosis, expression of iNOS and HO 1, and formation of nitrotyrosine. These experiments will indicate whether pharmacologic interventions directed against iNOS can ameliorate or delay the progression of AD-like disease in mice. Positive results will provide a rationale for clinical trials.