ncx1, ncx2, and ncx3 gene product expression and function in neuronal anoxia and brain ischemia.

Over the last few years, although extensive studies have focused on the relevant function played by the sodium-calcium exchanger (NCX) during focal ischemia, a thorough understanding of its role still remains a controversial issue. We explored the consequences of the pharmacological inhibition of this antiporter with conventional pharmacological approach, with the synthetic inhibitory peptide, XIP, or with an antisense strategy on the extent of brain damage induced by the permanent occlusion of middle cerebral artery (pMCAO) in rats. Collectively, the results of these studies suggest that ncx1 and ncx3 genes could be play a major role to limit the severity of ischemic damage probably as they act to dampen [Na+]i and [Ca2+]i overload. This mechanism seems to be normally activated in the ischemic brain as we found a selective upregulation of NCX1 and NCX3 mRNA levels in regions of the brain surviving to an ischemic insult. Despite this transcript increase, NCX1, NCX2, and NCX3 proteins undergo an extensive proteolytic degradation in the ipsilateral cerebral hemisphere. All together these results suggest that a rescue program centered on an increase NCX function and expression could halt the progression of the ischemic damage. On the basis of this evidence we directed our attention to the understanding of the transductional and transcriptional pathways responsible for NCX upregulation. To this aim, we are studying whether the brain isoform of Akt, Akt1, which is a downstream effector of neurotrophic factors, such as NGF can, in addition to affecting the other prosurvival cascades, also exert its neuroprotective effect by modulating the expression and activity of ncx1, ncx2, and ncx3 gene products.

The 2-oxopyrrolidinacetamide piracetam reduces infarct brain volume induced by permanent middle cerebral artery occlusion in male rats.

In this study, the temporal development of focal cerebral infarction induced by permanent middle cerebral artery occlusion (pMCAO) and the effects of piracetam, a derivative of gamma-aminobutyric acid widely used in clinical practice as a nootropic agent, on infarct area and volume were investigated. pMCAO caused a cerebral infarct whose size progressively increased after 3, 6, 9, and 24 h. Piracetam (125 mg/kg i.p.), administered 6, 9, and 22 h after pMCAO, did not reduce pMCAO-induced brain infarct area size detected at the 24th hour. By contrast, when this agent was administered at the doses of 250 and 500 mg/kg, it caused a marked reduction of the infarct area size. This reduction was observed in almost every brain slice affected by pMCAO, although statistical differences (p <0.05) were detected in slices located at 3-5.5 mm posterior to the anterior pole in animals treated with 250 mg/kg piracetam and in slices located at 3.5-5 mm in those receiving 500 mg/kg. When the mean total volumes of brain infarct resulting from pMCAO were calculated, it was observed that in animals which had received piracetam (250 or 500 mg/kg) infarction volume was markedly ( approximately 50%) and significantly (p <0.05) reduced in comparison with saline injected rats. Finally, piracetam (250 mg/kg administered i.p. 6, 9, and 22 h after the ischemic insult) significantly reduced brain infarct area evaluated 48 h and 7 days after pMCAO.

Differential vulnerability of cortical and cerebellar neurons in primary culture to oxygen glucose deprivation followed by reoxygenation.

The effects of glucose and O2 deprivation (OGD) on the survival of cortical and cerebellar neurons were examined to characterize the biochemical mechanisms involved in OGD and OGD followed by reoxygenation. To this aim, neurons were kept for different time periods in a hypoxic chamber with a controlled atmosphere of 95% N(2) and 5% CO2 in a glucose-free medium. After OGD, reoxygenation was achieved by exposing the cells to normal O2 and glucose levels. Neither MTT, an index of mitochondrial oxidative phosphorylation, nor malondialdehyde (MDA) production, a parameter measuring lipid peroxidation, were affected by 1 hr of OGD in cortical neurons. When OGD was followed by 24 hr of reoxygenation, MTT levels were reduced by 40% and MDA was significantly increased, whereas cellular ATP content did not change. Cerebellar granule cells, on the other hand, did not show any reduction of mitochondrial activity after exposure to 1 hr OGD or to 1 hr OGD plus 24 hr of reoxygenation. When OGD was prolonged for 2 hr, a significant reduction of the mitochondrial activity and of cellular ATP content occurred, coupled to a significant MDA increase in cerebellar granule cells, whereas in cortical neurons a reduction of MTT levels after 2 hr OGD was not accompanied by a decrease of cellular ATP content nor by an increase of MDA production. Moreover, 24 hr of reoxygenation further reinforced lipid peroxidation, LDH release, propidium iodide positive neurons and the reduction of ATP content in cerebellar granule cells. The results of the present study collectively show that cortical and cerebellar neurons display different levels of vulnerability to reoxygenation followed by OGD. Furthermore, the impairment of mitochondrial activity and the consequent overproduction of free radicals in neurons were observed for the first time occurring not only during the reoxygenation phase, but already beginning during the OGD phase.

Sodium nitroprusside prevents chemical hypoxia-induced cell death through iron ions stimulating the activity of the Na+-Ca2+ exchanger in C6 glioma cells.

In C6 glioma cells exposed to chemical hypoxia, an increase of extracellular lactate dehydrogenase (LDH) activity, cell death, and intracellular Ca2+ concentration ([Ca2+]i) occurred. Sodium nitroprusside (SNP), a nitric oxide donor and an iron-containing molecule, reduced chemical hypoxia-induced LDH release and cell death. These effects were counteracted by bepridil and by 5-(N-4-chlorobenzyl)-2',4'-dimethylbenzamil (CB-DMB), two specific inhibitors of the Na+-Ca2+ exchanger. SNP also increased the activity of the Na+-Ca2+ exchanger as a Na+ efflux pathway, stimulated by Na+-free conditions and evaluated by monitoring [Ca2+]i in single cells. In addition, SNP produced a further increase of chemical hypoxia-elicited [Ca2+]i elevation, and this effect was blocked by bepridil. Chemical hypoxia-evoked cell death and LDH release were counteracted by the ferricyanide moiety of the SNP molecule, K3Fe(CN)6, and by ferric chloride (FeCl3), and this effect was counteracted by CB-DMB. In addition, the iron ion chelator deferoxamine reversed the protective effect exerted by SNP on cell injury. Collectively, these findings suggest that the protective effect of SNP on C6 glioma cells exposed to chemical hypoxia is due to the activation of the Na+-Ca2+ exchanger operating as a Na+ efflux-Ca2+ influx pathway induced by iron present in the SNP molecule.