Milacemide: Safety assessment in senile dementia of the Alzheimer type

The structural requirements for the design of antiepileptic-glycine derivatives

Glycine is a major inhibitory neurotransmitter and recent reports have shown that certain lipophilic derivatives of glycine demonstrate anticonvulsant activity in intact animals. In these studies, glycinamide derivatives were found to be more potent than their corresponding glycine analogues. Consequently, the objective of the current study was to investigate the pharmacokinetics and pharmacodynamics (anticonvulsant activity and neurotoxicity) of the following phenyl derivatives of glycinamide: N'-benzyl glycinamide, N-benzyloxycarbonyl glycinamide (Z-glycinamide), Z-glycine, N-Z,N'-benzyl glycinamide and N-phenylacetyl glycinamide. The antiepileptic activity and neurotoxicity was carried out in classical animal models for antiepileptic screening. The pharmacokinetics of the active compounds were studied in dogs, a common animal model for comparative crossover pharmacokinetic studies. Of the compounds investigated in this study, Z-glycinamide, N'-benzyl glycinamide and N-Z,N'-benzyl glycinamide were found to be active. Therefore, the disposition of Z-glycinamide and N-Z,N'-benzyl glycinamide in comparison to Z-glycine was studied in plasma, brain, liver and urine of rats. The disposition of Z-glycinamide and N-Z,N'-benzyl glycinamide into the brain was better than that of Z-glycine. Unlike glycine or glycinamide, Z-glycinamide and N-Z,N'-benzyl glycinamide showed antiepileptic activity in animal models due to their better pharmacodynamic and pharmacokinetic properties. The pharmacokinetics of Z-glycinamide was similar in dogs and rats. Substitution of the Z group with the analogous phenylacetyl moiety led to inactive compounds. In an analogous series of compounds, the loss of the anticonvulsant activity may be due to pharmacodynamic and pharmacokinetic reasons. This study provides certain clues concerning the structural requirements for the design of antiepileptic-active glycine derivatives.

Effects of D-cycloserine and aniracetam on spatial learning in rats with entorhinal cortex lesions

A great body of behavioural and neurophysiological evidence suggests that excitatory amino acids are involved in mechanisms of learning and memory. Moreover, degeneration of glutamatergic pathways may underlie the cognitive deficits seen in various disorders such as Alzheimer's dementia. As direct stimulation of glutamatergic receptors with agonists may increase the risk of toxicity and accelerate neuropathological changes, a more valid approach seems to be positive modulation of glutamatergic receptors that may reverse the symptoms with a lower risk of excitotoxic effects. Such a possibility offered by partial agonists of the strychnine-insensitive glycine site of the NMDA receptor (Gly-B site) or positive modulators of AMPA receptors, such as aniracetam. In the present study, the effects of d-cycloserine and aniracetam were tested in two animal models of cognitive deficits (entorhinal cortex lesion-induced deficits evaluated in the radial maze and scopolamine-induced amnesia evaluated in passive avoidance test). D-cycloserine (6 mg/kg, for 10 days) had no effect on spatial working memory deficit induced by entorhinal cortex lesions. It did, however, reverse scopolamine-induced deficits in the passive avoidance test when given acutely at the same dose. In contrast, aniracetam (50 mg/kg, for 10 days) produced beneficial effects in the radial maze test in rats with entorhinal cortex lesions, but given at the same dose acutely did not influence scopolamine-induced amnesia. The positive effect of d-cycloserine against scopolamine-induced amnesia may be probably related to the cholinergic-glutamatergic interaction in the hippocampus. The negative data obtained with d-cycloserine in the model of entorhinal cortex lesions-induced cognitive deficits could be taken as a hint that it is probably not suitable for the symptomatological therapy of Alzheimer's disease. The mechanism of positive action of aniracetam cannot be explained on the basis of AMPA receptor modulation, as the dose used (50 mg/kg) is well below that required for the effect at AMPA receptors. Other actions such as peripheral effects or modulation of metabotropic receptors seem more likely.

Fasting for 24 h reveals liver microsteatosis after continuous i.v. infusion of milacemide in the rat

Milacemide (2-n-pentylaminoacetamide) hydrochloride was administered by continuous i.v. infusion for up to 7 days, at 300 and 600 mg/kg per day to male Sprague-Dawley rats. This was intended to provide high and sustained exposure to evaluate the effect of a preterminal 24-h fast on liver lipid content. Liver lipid content, as assessed by triglyceride concentration and histopathology, was not different in saline controls or rats infused with up to 600 mg/kg per day for up to 7 days, when they had access to food up to sacrifice. When the rats were fasted for 24 h before sacrifice, milacemide produced microsteatosis in the periportal and midzonal areas. The effect was significant after 2 days of infusion at 600 mg/kg per day and increased in intensity with duration of administration. After 7 days of infusion, at 600 mg/kg per day, liver triglycerides increased by more than 4-fold in rats fasted for the last 24 h. No other differences from the controls were observed at light microscopy or in liver protein content and AST activity. Liver ALT activity was decreased by 28% and plasma ALT activity by 23%. Plasma triglyceride levels were lowered by milacemide, in both fasted and fed rats. This study demonstrates that fasting for 24 h triggers the development of liver microsteatosis in rats exposed to milacemide. Fasting has been previously described to increase liver microsteatosis after administration of sodium valproate, 4-en valproate and pentenoic acid in the rat. These findings might help to identify the mechanism of the hepatic effects of milacemide.(ABSTRACT TRUNCATED AT 250 WORDS)