[Evaluation of blood esterases in Alzheimer's disease]

The aim of this work was to evaluate a possible correlation between erythrocyte acetylcholinesterase activity (AChE) and membrane fluidity expressed by fluorescence polarization of--1,6--diphenyl 1,3,5--hexatriene (DPH). Blood samples of 34 Alzheimer's patients (18F and 16M) were obtained and haemoglobin concentration, haematocrit, plasma (butyrylcholinesterase, BuChE) and erythrocyte (AChE) esterase activities and fluorescence polarization after introduction of DPH in erythrocyte membrane have been determined. Results were compared with values obtained from blood samples of 34 apparently healthy volunteers with the same age variation (53-82 years). There was no correlation between AChE activity and fluorescence polarization in the control group nor in the patients' group. There was a significant negative correlation (r = -0.82; p < 0.001) between mean corpuscular hemoglobin concentration (MCHG) and erythrocyte acetylcholinesterase activity in Alzheimer's patients. This correlation suggests that any variation of internal globular viscosity (or MCHG) may indirectly affect AChE enzymatic activity and consequently contribute to the loss of interrelation between AChE activity and membrane lipid fluidity, verified in the present work. A biological marker for Alzheimer's disease diagnosis remains to be discovered.