Montelukast Therapy on Alzheimer's Disease

Inclusion Criteria: 1. Age: 50 years or older 2. MCI group will be defined based on: (i) Subjective memory concern; (ii) Abnormal memory function documented using the Logical Memory subscale (Delayed Paragraph Recall, Paragraph A only) from the Wechsler Memory Scale-Revised (the maximum score is 25): \[\<11 for 16 or more years of education; \<9 for 8-15 years of education; \<6 for \<7 years of education\]; (iii) Montreal Cognitive Assessment (MoCA) \< 26; (iv) Clinical Dementia Rating (CDR) scale /Memory box score=0.5; (v) General functional performance sufficiently preserved (Functional Assessment Questionnaire ≤5). 3. Early AD dementia group will be defined based on: (i) Subjective memory concern; (ii) Abnormal memory function documented using the Logical Memory subscale (Delayed Paragraph Recall, Paragraph A only) from the Wechsler Memory Scale-Revised (the maximum score is 25): \[\<11 for 16 or more years of education; \<9 for 8-15 years of education; \<6 for \<7 years of education\]; (iii) Montreal Cognitive Assessment (MoCA) \<26; (iv) Clinical Dementia Rating scale/Memory box score 1 or 2; (v) Early AD dementia defined as Functional Assessment Staging Test (FAST) of 4 or 5 Exclusion Criteria: 1. Intolerance to Montelukast; 2. Current diagnosis of bronchial asthma or exercise-induced bronchospasm and currently on Montelukast or other leukotriene receptor antagonists (Zafirlukast, Pranlukast); 3. Liver disease (elevated liver enzymes (\>2x normal): Alanine aminotransferase (ALT), AST, alkaline phosphatase, total bilirubin); 4. Renal disease (Creatinine \>2.0 mg/dl), platelets\<50,000/μl, or INR\>1.9; 5. Diagnosis of any neurological or psychiatric disorders that affects cognition such as uncontrolled depression, schizophrenia, Parkinson's disease or use of anti-Parkinsonian therapies (unless used for essential tremor), multiple sclerosis, or other active medical condition that in the judgment of the study physicians would affect the safety of the subject or scientific integrity of the study; 6. Other contributing factors to cognitive impairment such as uncontrolled hypothyroidism (TSH \>10 mU/l) or untreated low vitamin B12 (\<250 ng/mL); 7. Uncontrolled congestive heart failure reflected by poor exercise tolerance and shortness of breath at rest or with some exertion; 8. Actively undergoing chemotherapy or radiation therapy for cancer treatment; 9. History of stroke in the past 3 years; 10. Severely impaired cognition (MoCA ≤10, FAST \>5 or CDR \>2); 11. Inability to have MRI and LP e.g. for MRI, metal implants or cardiac pacemaker or for LP, bleeding diathesis from disease states or from use of anticoagulants such as warfarin, heparin and related products, Rivaroxaban or Xarelto, Apixaban or Eliquis, Edoxaban or Savaysa, Dabigatran or Pradaxa. Subjects who can have either one lumbar puncture (LP) or MRI will be enrolled; 12. Inability to have cognitive assessment due to hearing, vision, or language issues or due to severe impairment; 13. History of increased intracranial pressure (ICP); 14. In those who are unable to demonstrate that they understood the details of the study using the University of California, San Diego Brief Assessment of Capacity to Consent (UBACC) instrument modified for EMERALD (i.e. lack of decisional-capacity to consent), a study partner/surrogate who can sign on their behalf will be required; otherwise, they will be excluded; 15. Use of phenobarbital or rifampin due to drug interaction.