Date Published: January 29, 2012
Publisher: Hindawi Publishing Corporation
Author(s): Tamotsu Imanishi, Muhammad Mubarak Hossain, Tadahiko Suzuki, Ping Xu, Itaru Sato, Haruo Kobayashi.
Anticholinesterases (antiChEs) are used to treat Alzheimer’s disease. The comparative effects of two antiChEs, methanesulfonyl fluoride (MSF) and donepezil, on the extracellular levels of ACh in the hippocampus were investigated by in vivo microdialysis in freely moving rats. MSF at 1 and 2 mg/kg produced a dose-dependent increase in ACh efflux from 10 min to at least 3 hrs after injection. At 2 mg/kg, the increase was still present at 24 hr. Donepezil at 1 mg/kg showed a similar but smaller effect, and, paradoxically, 2 mg/kg showed no consistent effect. MSF at 1 and 2 mg/kg decreased acetylcholinesterase activity in the hippocampus to 54.8 and 20.1% of control, respectively. These results suggest that MSF is a suitable candidate for the treatment of Alzheimer’s disease.
Alzheimer’s disease (AD) is a slowly progressive neurodegenerative illness characterized by the presence of senile plaques containing β-amyloid protein (Aβ) in brain tissue, tau-neurofibrillary tangles in neurons and, the loss of different transmitter-containing axons, especially cholinergic nerves [1, 2]. Unfortunately, therapeutic strategies targeting amyloid plaques with plaque-removing vaccines or gamma-secretase modulators have been disappointing [3, 4].
Male Sprague-Dawley rats (Japan SLC, Hamamatsu, Japan) weighting 200–250 g were housed one per cage under the standard laboratory conditions (23 ± 1°C, 55 ± 5% humidity) with free access to standard pellet diet (MEQ, Oriental Yeast Co., Tokyo) and drinking water ad libitum with lights on at 08:00 and off at 20:00. Animal handling and procedures were conducted in accordance with the Animal Welfare Act and with the Guide for the Care and Use of Laboratory Animals approved by the Animal Experiment Committee in Iwate University, Japan. Five rats were used in each group.
The injections of MSF and donepezil (1 and 2 mg/kg i.p.) did not produce any observable clinical signs or symptoms in the rats. The basal rates of efflux from the hippocampus of vehicle-only injected control rats were 5.2 ± 0.2 pmol ACh/10 μL/10 min and 180.8 ± 2.6 pmol choline/10 μL/10 min (n = 15). The response of ACh in the hippocampus to vehicle treatment was not significantly different throughout the experiment.
We have previously reported that a single dose of MSF at 1.5 mg/kg s.c. significantly increased the concentrations of extraterminal ACh and cytoplasmic ACh in the cortex of mice . In these experiments, an increase in the fractional ACh content of brain tissues taken ex vivo and homogenized for analysis was found to be elevated at 180 min, and the increase persisted to 24 hr. The extraterminal ACh determined in that earlier ex vivo experiment may approximately correspond to extracellular ACh in the current in vivo experiment at those same time points. The present experiment confirmed the earlier results and showed that doses of either 1 mg/kg or 2 mg/kg MSF strongly increase extracellular ACh during the first 180 min after administration and the effect persists for 24 hr after the higher dose of 2 mg/kg.
The present study showed that MSF at doses 1 and 2 mg/kg produced a consistent increase in the efflux of ACh in freely moving rats as measured by microdialysis throughout the first 3 hrs at both doses and a persistent increase was still present at 24 hr at the higher dose. Since ChE inhibitors are the major therapeutic agents used in AD patients, the agent-like MSF, which increases extracellular ACh in the hippocampus with a long-lasting efficacy but without excess stimulation, may serve as an effective therapy to alleviate or prevent the central cholinergic deficits which are reported to cause cognitive impairments.