Targeting Inducible Nitric Oxide Synthase (iNOS) to Delay Progression of Alzheimer's- Like Disease in Mice

Carl Nathan, M.D.

Weill Medical College of Cornell University

Funded in September, 2005: $300000 for 3 years
LAY SUMMARY . ABSTRACT . BIOGRAPHY .

LAY SUMMARY

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Targeting Inducible Nitric Oxide Synthase (iNOS) to Delay Progression of Alzheimer's- Like Disease in Mice

These collaborators will determine whether drugs that target a specific enzyme, which has been implicated in damage to brain cells in Alzheimer's disease, confer protection in a mouse model. If so, the findings could lead to human clinical drug trials.

How does amyloid protein damage brain cells in Alzheimer's? Evidence suggests that amyloid triggers brain cells to produce an enzyme called "iNOS." Normal brains lack this enzyme; Alzheimer's disease brains contain it. This enzyme produces nitric oxide, which normally helps the body fight some kinds of infection, such as tuberculosis. However, expression of iNOS in the brain in people with Alzheimer's disease is inappropriate because there is not thought to be any infection, and large amounts of nitric oxide can damage neurons. Preliminary data were obtained in mice that were engineered to express altered human genes that cause Alzheimer's-like disease. Some of these mice were further engineered so that the genes encoding iNOS were disrupted. As in humans with Alzheimer's disease, the brains of mice with Alzheimer's-like disease and normal iNOS genes expressed iNOS and suffered extensive damage to their brain cells. In contrast, the mice with Alzheimer's-like disease that were genetically unable to express iNOS suffered much less damage. Now the researchers will test drugs that either stop the brain from expressing iNOS in the first place or inhibit iNOS from making its brain cell-killing molecules.

Significance: If drugs are found that target this enzyme and protect brain cells in the animal model, the research could lead to development of clinical trials of these compounds or compounds with similar actions in patients with Alzheimer's disease. Such trials would require special precautions for patients at risk of tuberculosis.

ABSTRACT

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Targeting Inducible Nitric Oxide Synthase (iNOS) to Delay Progression of Alzheimer's- Like Disease in Mice

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.

INVESTIGATOR BIOGRAPHIES

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Carl Nathan, M.D.

Carl Nathan graduated from Harvard College, majoring in East Asian history, and from Harvard Medical School, concentrating in immunology. After training at Massachusetts General Hospital, the National Cancer Institute, and Yale, he was board-certified in internal medicine and oncology. He spent nine years on the faculty at the Rockefeller University before joining what is now Weill Medical College of Cornell University as the Stanton Griffis Distinguished Professor of Medicine in 1985. Service as founding director of the Tri-Institutional M.D.-Ph.D. Program, Senior Associate Dean for Research, and Acting Dean was followed by his current appointment as Chairman, Department of Microbiology and Immunogy, and co-chairman, Graduate Program in Immunology and Microbial Pathogenesis.

Nathan's research furnished some of the first molecular explanations for immunologic macrophage activation and the antimicrobial mechanisms of macrophages. He discovered that cytokines from antigen-stimulated lymphocytes activate macrophages (1971), that activation of macrophages heightens their capacity to release reactive oxygen intermediates (1977), that interferon-γ is a principal macrophage activating factor (1983), including in man (1986), and that a major mechanism of host defense is expression of inducible nitric oxide (NO) synthase (iNOS). Nathan's lab identified NO as a cytotoxic product of macrophages; discovered the roles of the key cofactors in NO synthesis; purified (1991), cloned and named iNOS (1992); explained its high-output state (1992); produced the first iNOS-deficient mice (1995); showed the essential contribution of iNOS to control of experimental tuberculosis (1997); and identified novel mechanisms for mycobacterial resistance to NO, including peroxynitrite reductase (2000) and the proteasome (2003). Nathan is a member of the Institute of Medicine of the National Academies and a Fellow of the American Academy of Microbiology. He serves as an editor of the Journal of Experimental Medicine, an advisor for the Cancer Research Institute and Cambridge University's Institute for Medical Research, and a trustee of the Hospital for Special Surgery.

Dr. M. Flint Beal is an internationally recognized authority on neurodegenerative disorders. He is the Anne Parrish Titzell Professor and Chairman of the Department of Neurology and Neuroscience at the Weill Medical College of Cornell University and Director of the Neurology service at the New York Presbyterian Cornell Campus. Dr. Beal received his medical degree from the University of Virginia in 1976 and did his internship and first year residency in Medicine at New York-Cornell before completing his residency in Neurology at  Massachusetts General Hospital. He joined the neurology faculty at Harvard in 1983. Dr. Beal was Professor of Neurology at the Harvard Medical School and Chief of the Neurochemistry laboratory at Massachusetts General Hospital before moving to Cornell.

Dr. Beal's research has focused on the mechanism of neuronal degeneration in Alzheimer's disease, Huntington's disease, Parkinson's disease, and amyotrophic lateral sclerosis (ALS). Dr. Beal is the author or co-author of more than 350 scientific articles and more than 125 books, book chapters and reviews. He serves on the editorial boards of seven journals, including the Journal of Neurochemistry, Journal of Neurological Sciences, Journal of Molecular Neuroscience, Experimental Neurology, and Neurobiology of Disease. He is a co-editor of the Dana Guide to Brain Health. Dr. Beal is a member of the Alpha Omega Alpha Medical Honorary Society and received the Derek Denny-Brown Neurological Scholar Award of the American Neurologic Association. He has served on the Council of the American Neurologic Association and on the Science Advisory Committees of the Hereditary Disease Foundation, Huntington's Disease Society of America, Parkinson's Disease Study Group, Parkinson' Disease Foundation, Bachman-Strauss Foundation, The ALS Association, and the American Health Assistance Foundation. Dr. Beal is a member of the Institute of Medicine of the National Academy of Sciences.