Effect of Insulin Sensitizer Metformin on AD Biomarkers

Inclusion Criteria: * • Ages 55-80. * 2 Sex distribution: male and female * Diagnosis of MCI due to AD127 or early dementia due to AD128 with: a) age 55 - 80, b) complaint of cognitive decline, c) abnormal performance on the Logical Memory subtest of the Wechsler Memory Scale, d) MMSE \> 21, e) CDR 0.5-1, f) positive topographic (MRI, FDG-PET) or molecular (CSF, amyloid imaging) biomarker consistent with AD, and g) no history of diabetes or other exclusions. * Fluent in English or Spanish * Education \>5, literate, and/or good working history that precludes consideration of mental retardation * Visual and auditory acuity sufficient for neuropsychological testing and auditory evoked potential EEG * Geriatric Depression Scale \< 6 * Modified Hachinski Ischemic Score \< 4 * No major health issues or diseases expected to interfere with the study * Willing to complete all baseline assessments and study procedures * Stable on all permitted medications for 8 weeks * Not pregnant, lactating or of child-bearing potential (women must be \>2 years post-menopausal or surgically sterile) * No history of diabetes * Fasting blood glucose \<126 and/or HgbA1c \< 6.4 * Study partner with frequent contact with patient willing to accompany patient to visits and complete partner study forms * No contraindication to metformin Exclusion Criteria: * • Any CNS disease other than suspected incipient AD, such as clinical stroke, brain tumor, normal pressure hydrocephalus, brain tumor, multiple sclerosis, significant head trauma with persistent neurological of cognitive deficits or complaints, Parkinson's disease, frontotemporal dementia, or other neurodegenerative diseases * Screening/baseline MRI scans with evidence of infarction or other focal lesions in critical memory structures that may be related to cognitive dysfunction * Major active psychiatric illness (e.g., depression, bipolar disorder, obsessive compulsive disorder, schizophrenia) within the previous year * History of alcohol or other substance abuse or dependence within the past two years * Pacemakers, aneurysm clips, artificial heart valves, ear implants, metal fragments or foreign objects in the eyes, skin or body or claustrophobia that would preclude MRI scanning * History of past or current diabetes, pancreatic or liver disease, renal disease * Any significant systemic illness or unstable medical condition that could affect compliance with study * Laboratory abnormalities in B12, TFTs, RPR, Lyme or other common lab parameters that might contribute to cognition or participation in study * Coagulopathy or anti-coagulant therapy (such as coumadin) increasing the risk for LP resulting in PT/PTT and INR within 1.5 standard deviations over the upper normal limit. * Compromised renal function at screening as determined by creatinine clearance \<30mL/min based on Cockcroft-Gault calculation * Liver dysfunction at screening as evidenced by alanine transaminase (ALT/SGPT) values \> 2X upper limit of normal or aspartate transaminase (AST/SGOT) values \> 3X or total bilirubin \> 2X. * Has received acetylcholinesterase inhibitor and/or memantine and/or any other medicine that affects the central nervous system for less than 4 months or has less than 2 months stable therapy on these treatments by baseline visit. * Current use of specified medications with psychoactive properties that deleteriously affect cognition (e.g., certain antidepressants, anticholinergics, anti-histamines, antipsychotics, sedative hypnotics, anxiolytics) * Use of investigational agents one month prior to entry and for the duration of the trial * Exceptions to these guidelines may be considered on a case-by-case basis at the discretion of the protocol director.