Effects of hydromethylthionine mesylate and rivastigmine in a pharmacological mouse model of Alzheimer's disease.

The results from clinical trials have indicated that the tau aggregation inhibitor hydromethylthionine mesylate (HMTM) produces disease-modifying effects in Alzheimer's disease (AD) patients when administered alone, but less of an effect when administered in conjunction with cholinesterase inhibitors (ChEIs). The use of ChEIs for AD has been supported by their ability to reverse scopolamine-induced cognitive impairments in rodents reminiscent of those seen in AD patients. We have previously shown that another tau aggregation inhibitor, methylthionine chloride (MTC), is able to reverse scopolamine-induced deficits in spatial learning and memory. The objective here was to determine the symptomatic efficacy of HMTM and rivastigmine, alone or in combination, in a scopolamine model of AD. Female NMRI mice were treated systemically with scopolamine (0.5 mg/kg) or vehicle in combination with ChEI rivastigmine (0.5 mg/kg) or HMTM (5 or 15 mg/kg) daily before assessment of spatial learning and memory performance in a reference memory task in the water maze. Systemic administration of scopolamine induced significant impairments in the spatial learning of the mice compared to vehicle treatment. These deficits were reversed by treatment with HMTM at both doses and with rivastigmine when given alone. Furthermore, coadministration of rivastigmine with HMTM ameliorated the impairments induced by scopolamine. These findings extend our previous observations with MTC and confirm that HMTM also has a dual mode of action, disease modification through tau aggregation inhibition, but also having symptomatic effects through its normalisation of cholinergic activity.