Different pharmacological profile of two closely related endocannabinoid ester analogs.

The pharmacological and neuroprotective properties of two ester analogs of the endocannabinoids, arachidonoylethyleneglycol (AA-EG) and alpha,alpha,-dimethyl arachidonoylethyleneglycol (DMA-EG), were investigated. We examined the interaction of both compounds with cannabinoid receptors (CB1 and CB2) and their efficacy in functional assays. In competition binding assays, AA-EG and DMA-EG had low potency to displace the CB1/CB2 agonist [3H]CP-55,940 in membrane preparations expressing rodent or human receptors. Binding data correlate with low efficacy of both compounds as regards to inhibition of adenylyl cyclase activity. It was also shown that DMA-EG resists hydrolysis by rat brain membranes while AA-EG undergo complete splitting under these conditions. In the cannabinoid tetrad, AA-EG induced hypomotility, analgesia, catalepsy and decreased rectal temperature indicating cannabimimetic activity. By contrast, DMA-EG was completely inactive in the same models. DMA-EG and AA-EG potently protected rat cortical neurons in culture against oxygen deprivation at nanomolar concentrations. In glutamate-induced damage, the compounds were less active protecting neurons at micromolar concentrations. The data obtained indicate that the ester endocannabinoid template can be used for the development of new compounds with potent biological activity lacking some of the undesirable behavioral side effects.

Anti-excitotoxic activity of trimetazidine in the retina.

The purpose of this study was to investigate the mechanism of the neuroprotective activity of trimetazidine in animal retina stressed by ischemia or kainate. Flash electroretinograms were recorded in guinea pigs after ischemia, induced by an acute increase in the intraocular pressure (IOP), or after an intravitreal injection of kainate. Treatment with trimetazidine per os afforded a significant protection of the electroretinogram against the ischemic as well as the excitotoxic insult as an antioxidant (dimethylthiourea) and a nitric oxide synthase inhibitor (nitroarginine) did. The effect of the drug on the extracellular accumulation of glutamate induced by chemical ischemia was studied by incubating rat retina in vitro. Trimetazidine was able to inhibit the extracellular glutamate accumulation, which represents the first step of the excitotoxic phenomenon. Then the compound activity on the glial uptake of glutamate was studied in a rat Müller cell line (rMC-1) in culture. Chemical ischemia inhibited the active 3H-glutamate transport, an effect that was reversed by trimetazidine, at micromolar concentrations. These results demonstrate that trimetazidine which is recognized as an efficient drug against ischemic injuries, is also capable of protecting the retina against excitotoxicity by reducing ischemia-induced accumulation of glutamate due in particular to glial transporter inhibition.

Hypoxia stimulates glutamate uptake in whole rat retinal cells in vitro.

Glutamate uptake in neurons and glial cells is essential to prevent the persistence of excitotoxic levels of glutamate observed during ischemia. We demonstrated that a short period of hypoxia stimulated the apparent glutamate transport rate in isolated rat retinal cells. The observed increase in glutamate uptake was not affected by glutamate receptor antagonists, protein kinase inhibitors, antioxidant or neo-synthesis inhibitors. However, inhibition of actin polymerization reversed the hypoxia-induced increase in glutamate uptake, suggesting a mobilization of transporters to the cell membrane. Moreover, the depletion in cell glutathione stimulated in the same manner the glutamate uptake and emphasized the key role of glutamate in the control of the level of this antioxidant. This rapid up-regulation of glutamate transport could be considered as an adaptative mechanism of neuroprotection.