The Predictive Factors of Good Clinical Response to Cholinesterase Inhibitors in Alzheimer Disease and Mixed Dementia

Overview

Background and objectives: The aims of this naturalistic study were: to analyze factors which could be predictive of good response to cholinesterase inhibitors (ChEI), such as: age, sex, schooling, mild (CDR 1) or moderate Alzheimer's disease (AD),(CDR 2), Apoliprotein epsilon 4 (APOE Ɛ4), among others, in their cognitive and clinical response. We also classified patients according to their response to Mini mental State of Examination (MMSE). Finally we saw the polymorphisms of APO E and cytochrome P450 2D6 (CYP2D6) and tried to correlate the response with different allelic forms of Apo E and among others with wild type homozygotes (wt/wt) and their polymorphisms (CYP2D6\*3,\*4, \*5, \*6 and 10) of CYP 2D6. Patients and Methods: 129 patients were diagnosed as AD or AD+cerebrovascular disease (CVD) mild or moderate. After 12 month-treatment, 97 patients completed the study. They were assessed (four) times. In the first visit, without taking ChEI, after 3, 6 and 12 month-treatment, they were taking donepezil or rivastigmine or galantamine. We also extracted 5 mL of blood sample to genotype the DNA. In each visit, we applied cognitive, functional, mood and behavior scales. Good responders were defined as those who scored \> 2 in MMSE. Results and Conclusion: In longitudinal analysis, patients with mild AD and good responders at 3 months were considered good responders at 12 months. We obtained a higher rate of good responders comparing with other researches (27.8%). There was no correlation between dose, APOE and CYP 2D6 polymorphisms, although we already obtained clinical results with the dose dosage of 5mg.

Genomic DNA for genotyping was extracted from total blood samples collected in ethylenediaminetetraacetic acid (EDTA) (Wizard Genomic DNA Purification Kit: Promega®, USA) and kept frozen at seventy degrees Celsius negative (-70ºC) until analysis. For APOE genotyping (alleles Ɛ2, Ɛ3 and Ɛ4), DNA samples were amplified by polymerase chain reaction (PCR), followed by digestion with Haemophilus haemolyticus restriction endonuclease I (HhaI) and restriction fragment length polymorphism (RFLP) analysis, as previously described by Hixson and Vernier. The CYP2D6\*3, CYP2D6\*4 and CYP2D6\*6 alleles were investigated by tetra-primer PCR and the CYP2D6\*5 allele, which presents the entire CYP2D6 gene deletion, was identified by long PCR reaction, according to the method described by Hersberger et al. The CYP2D6\*10 allele was amplified by PCR following Baclig et al. and the RFLP analysis was performed with Type II restriction enzyme (HphI). For all analysis a positive and negative controls were included. Subjects carrying Epsilon 3, Epsilon 3 (Ɛ3Ɛ3), CYP2D6\*3/4/5/6/10-nor specific mutations are classified as wild-type and functional allele carriers. The subjects carrying two defective alleles were classified as poor metabolizers (PM) and those heterozygous were classified as extensive metabolizers (EM).