Preclinical Evaluation of Tacrolimus in a Canine Model of Alzheimer's Disease

This project uses aging beagles and a longitudinal treatment design to test the potential of a calcineurin (CN) inhibiting strategy in Alzheimer¡¦s disease (AD). Beagles are metabolically similar to humans and spontaneously develop amyloid-ƒÒ (AƒÒ) deposition with advanced age. Consequently, the aging beagle model has shown exceptional predictive validity in regard to several high-profile anti-AD drug trials. The molecular target of our treatment strategy, CN, has recently emerged as a key mechanism for AD pathophysiology. Signs of CN hyperactivity are found during early stages of cognitive decline in humans and in mouse models of AD. Studies across numerous laboratories, using a variety of experimental models, suggest that CN activity is both necessary and sufficient for the progression of key AD biobehavioral markers including AƒÒ deposition, neurodegeneration, neuroinflammation/glial activation, synapse dysfunction, and cognitive loss. To inhibit CN, we will use tacrolimus, an FDA-approved drug for the prophylaxis of allograft rejection and a second line treatment for numerous immune/inflammatory disorders. In animal models, tacrolimus exhibits potent anti-inflammatory, neuroprotective, and perhaps lifespan extending properties. Moreover, a recent epidemiological study found that the incidence of dementia was strikingly reduced in human kidney transplant patients taking tacrolimus, relative to age-matched subjects in the general population. In this project, 5-6 month old beagles will undergo 1 year of behavioral/cognitive screening. At 6-7 months-of age (prior to the development of significant amyloid pathology), dogs will be sorted into two groups matched for cognitive status. One group will received tacrolimus (.075mg/kg/day, orally) continuously for the next two years, while the other group will receive placebo. Aim 1 will assess multidomain cognition and measure blood and CSF biomarkers (e.g. AƒÒ and cytokines) at multiple time points across the tacrolimus treatment period. Aim 2 will use MRI/MRS to measure longitudinal changes in cerebral perfusion, brain metabolism, and structural integrity. Aim 3 will use immunohistochemistry and a variety of biochemical assays to assess AD biomarkers (e.g. AƒÒ deposition, glial activation, synapse loss, and neurodegeneration) and CN-related signaling parameters (e.g. cell-type specific expression, CN proteolysis, and NFAT activation) in postmortem brain tissue. These studies will provide a rigorous test of the CN hypothesis of AD and possibly pave the way for investigating CN inhibition has a primary or complimentary treatment strategy in human AD clinical trials.