The effect of heptyl-physostigmine,a new cholinesterase inhibitor,on the central cholinergic system of the rat

Heptyl-physostigmine (Heptyl-Phy; MF-201) is a new carbamate derivative of physostigmine (Phy) with greater lipophilicity and longer inhibitory action on cholinesterase (ChE) activity than the parent compound. Following single dose administration of 5 mg/kg heptyl-Phy i.m., maximal whole brain acetylcholinesterase (AChE) inhibition (82%) if reached at 60 min. Inhibition of plasma BuChE butyrylcholinesterase (BuChE) remains close to the steady state level (60%) between 120 and 360 min. At 360 min, whole brain AChE activity is still 67% inhibited compared to controls. Inhibition of AChE activity displays brain regional differences which are more significant at 360 min. At this time point, AChe activity in cerebellum is only 40% inhibited while frontal cortex and medial septum are still 80% inhibited. Increases in acetycholine (ACh) levels also show regional differences, however, there is no direct relationship between AChE inhibition and ACh increase. The electrically evoked ³H]ACh release in cortical slices was inhibited only by the highest concentration of heptyl-Phy tested (10^–4M). At this concentration ChE activity was 97% inhibited in vitro. In conclusion, our results demonstrate that heptyl-Phy compares favorably to other reversible cholinesterase inhibitors (ChEI), particularly to Phy as far as producing a more long-lasting inhibition of AChE and a more prolonged increase of ACh in brain with less severe side effects. Therefore, it represents an interesting candidate for cholinomimetic therapy of Alzheimer disease (AD).Dept. of Pharmacology, Shanghai Institute of Materia Medica Chinese Academy of Sciences Shanghai 20031 China.Special issue dedicated to Dr. Paola S. Timiras