The Preclinical Pharmacology of Metrifonate, Along-Acting and Well Tolerated Cholinesterase Inhibitor for Alzheimer Therapy

Characterization of learning and memory behaviors and the effects of metrifonate in the C57BL strain of mice

In the near future, a number of transgenic mouse models with neuropathological characteristics of Alzheimer's disease are expected to become widely available. It will be important to characterize their behavior in models for learning and memory. As a first step, we have characterized normal, medial septal-lesioned and hippocampal-lesioned C57BL mice, in different behavioral tests, i.e., water maze spatial navigation, Y-maze and passive avoidance behavior. These experiments were complemented by an investigation of the effects of acute treatment with an acetylcholinesterase inhibitor, metrifonate, in these behavioral tests. Normal C75BL mice perform very well in the water maze and the Y-maze, but suboptimally in the passive avoidance task. Lesioning of the medial septum or the dorsal hippocampus clearly impaired the performance of the mice. In medial septal-lesioned mice, metrifonate stimulated spatial navigation and alleviated the loss of activity in the Y-maze and passive avoidance. In hippocampal-lesioned mice, metrifonate had no effect on spatial navigation. It is concluded that C75BL mice are useful for testing in classical models for learning and memory, and that septohippocampal pathology is very likely to induce cognitive deficits in some of these models.

Effect of subchronic treatment with metrifonate and tacrine on brain cholinergic function in aged F344 rats

The effects of 21-day treatment with the acetylcholinesterase inhibitors metrifonate (80 mg kg(-1) per os (p.o.)) and tacrine (3 mg kg(-1) p.o.), twice daily, on cortical and hippocampal cholinergic systems were investigated in aged rats (24-26 months). Extracellular acetylcholine levels were measured by transversal microdialysis in vivo; choline acetyltransferase and acetylcholinesterase activities were measured ex vivo by means of radiometric methods. Basal cortical and hippocampal extracellular acetylcholine levels, measured 18 h after the last metrifonate treatment, were about 15 and two folds higher, respectively, than in control and tacrine-treated rats. A challenge with metrifonate further increased cortical and hippocampal acetylcholine levels by about three and four times, respectively. Basal extracellular acetylcholine levels, measured 18 h after the last treatment with tacrine were not statistically different from those of the control rats. A challenge with tacrine increased cortical and hippocampal extracellular acetylcholine levels by about four and two times. A 75% inhibition of cholinesterase activity was found 18 h after the last metrifonate administration, while only a 15% inhibition was detectable 18 h after the last tacrine administration. The challenge with metrifonate or tacrine resulted in 90 and 80% cholinesterase inhibition, respectively. These results demonstrate that in aging rats a subchronic treatment with metrifonate results in a long-lasting, cholinesterase inhibition, and a persistent increase in acetylcholine extracellular levels which compensate for the age-associated cholinergic hypofunction. Metrifonate is therefore a potentially useful agent for the cholinergic deficit accompanying Alzheimer's disease.