Laurence Barrier

Synthesis and antioxidant activity of new tetraarylpyrroles.

The synthesis and in vitro antioxidant activity of 17 new tetraarylpyrroles are investigated by 2 tests highly documented in the literature: capability to prevent Fe(2+)-induced lipid peroxidation on microsomes, which is a membrane preparation rich in polyunsaturated fatty acids, and direct scavenging effect on a stable free radical, 1,l-diphenyl-2-picryl-hydrazyl (DPPH). For the Fe(2+)-induced microsomal lipid peroxidation system, the results show that molecules which possess 2-pyrazinyl or 2-pyridyl in the 3- and 4-positions on the pyrrole ring are the most efficient. Introduction of methoxy groups on the phenyl ring in the 2- and 5-positions increases the effects but the higher activity is obtained with 2-furyl or 2-thienyl. The only compounds which possess a direct scavenger effect on trapping the stable free radical DPPH are those which have 2-pyridyl in the 3- and 4-positions and 2-furyl or 2-thienyl in the 2- and 5-positions.

Radical scavenging activity and antioxidant properties of tannins from Guiera senegalensis (Combretaceae)

The antioxidant properties of nine tannins isolated and characterized from different parts of Guiera senegalensis were evaluated. Interesting results showed that galloylquinic acids (hydrolysable tannins), resulting from a tri‐ or tetra‐substitution of galloyl groups on the quinic acid skeleton, played a crucial role in the inhibitory effect on Fe2+‐induced lipid peroxidation in rat liver microsomes and radical scavenger activity in the 1,1‐diphenyl‐2‐picrylhydrazyl (DPPH) test. The effects of all tannins were markedly higher than that of gallic acid. Condensed tannins such as epicatechin and epigallocatechin gallate also showed fairly significant effects in both tests.

Fluoro-Jade B staining as useful tool to identify activated microglia and astrocytes in a mouse transgenic model of Alzheimer's disease.

Fluoro-Jade B is known as a high affinity fluorescent marker for the localization of neuronal degeneration during acute neuronal distress. However, one study suggested that fluoro-Jade B stains reactive astroglia in the primate cerebral cortex. In this study, we analyzed the staining of fluoro-Jade B alone or combined with specific markers for detection of glial fibrillary acidic protein (GFAP) or activated CD68 microglia in the double APP(SL)/PS1 KI transgenic mice of Alzheimers disease (AD), which display a massive neuronal loss in the CA1 region of the hippocampus. Our results showed that fluoro-Jade B did not stain normal and degenerating neurons in this double mouse transgenic model. Fluoro-Jade B was co-localized with Abeta in the core of amyloid deposits and in glia-like cells expressing Abeta. Furthermore, fluoro-Jade B was co-localized with CD68/macrosialin, a specific marker of activated microglia, and with GFAP for astrocytes in APP(SL)/PS1 KI transgenic mice of AD. Taken together, these findings showed that fluoro-Jade B can be used to label activated microglia and astrocytes which are abundant in the brain of these AD transgenic mice. It could stain degenerating neurons as a result of acute insult while it could label activated microglia and astrocytes during a chronic neuronal degenerative process such as AD for example.

Group I metabotropic glutamate receptors activate the p70S6 kinase via both mammalian target of rapamycin (mTOR) and extracellular signal-regulated kinase (ERK 1/2) signaling pathways in rat striatal and hippocampal synaptoneurosomes

Group I metabotropic glutamate receptors (mGluRs) have been demonstrated to play a role in synaptic plasticity via a rapamycin-sensitive mRNA translation signaling pathway. Various growth factors can stimulate this pathway, leading to the phosphorylation and activation of mammalian target of rapamycin (mTOR), a serine/threonine protein kinase that modulates the activity of several translation regulatory factors, such as p70S6 kinase. However, little is known about the cellular and molecular mechanisms that bring the plastic changes of synaptic transmission after stimulation of group I mGluRs. Here, we investigated the role of the mTOR-p70S6K and the ERK1/2-p70S6K pathways in rat striatal and hippocampal synaptoneurosomes after group I mGluR stimulation. Our findings show that (S)-3,5-dihydroxyphenylglycine (DHPG) increases significantly the activation of mTOR and p70S6K (Thr389, controlled by mTOR) in both brain areas. The mTOR activation is dose-dependent and requires the stimulation of mGluR1 subtype receptors as for the p70S6K activation observed in striatum and hippocampus. In addition, the p70S6K (Thr421/Ser424) activation via the ERK1/2 activation is increased and involved also mGluR1 receptors. These results demonstrate that group I mGluRs are coupled to mTOR-p70S6K and ERK1/2-p70S6K pathways in striatal and hippocampal synaptoneurosomes. The translational factor p70S6K could be involved in the group I mGluRs-modulated synaptic efficacy.

The oxindole/imidazole derivative C16 reduces in vivo brain PKR activation

Inhibition of double‐stranded RNA‐dependent protein kinase (PKR) represents an interesting strategy for neuroprotection. However, inhibiting this kinase which triggers the apoptotic process could favour in counterpart cell proliferation and tumorigenesis. Here, we use an in vivo model of 7‐day‐old rat displaying a high activation of brain PKR to investigate the effects of a new PKR inhibitor identified as an oxindole/imidazole derivative (C16). We show for the first time that acute systemic injection of C16 specifically inhibits the apoptotic PKR/eIF2α signaling pathway without stimulating the proliferative mTOR/p70S6K signaling mechanism.

Origin of 4-hydroxynonenal incubation-induced inhibition of dopamine transporter and Na+/K+ adenosine triphosphate in rat striatal synaptosomes

Previous experiments reported that an incubation of striatal synaptosomes with 4-hydroxynonenal (4-HNE) resulted in an inhibition of dopamine (DA) uptake and Na+/K+ adenosine triphosphate (ATPase) activity. The present work investigated whether theses inhibitions are related to a 4-HNE binding to the DA transporter (DAT) and the Na+/K+ ATPase. The number of specific [125I]-PE21 binding sites on the DAT was significantly reduced after incubation with 4-HNE. The Na+/K+ ATPase activity decrease induced by 4-HNE was partially reversed, in a dose-dependent manner, by veratridine, a pump stimulator agent. Our previous data (Morel, P., Tallineau, C., Pontcharraud, R., Piriou, A. and Huguet, F., Effects of 4-hydroxynonenal, a lipid peroxidation product, on dopamine transport and Na+/K+ ATPase in rat striatal synaptosomes. Neurochem. Int., 33 (1999) 531-540) combining with the data observed in this study suggest that changes in DA uptake in striatal synaptosomes are directly related to 4-HNE binding to the DAT, whereas the decrease in Na+/K+ ATPase activity resulted only partially from 4-HNE binding to the pump and is mainly secondary to membrane lipid disruption.

Gender-dependent accumulation of ceramides in the cerebral cortex of the APPSL/PS1Ki mouse model of Alzheimer’s disease

Altered sphingolipid metabolism plays an emergent role in the etiology of Alzheimers disease (AD). In this study, we determined the levels of ceramides and other related-sphingolipids (sphingomyelins, sulfatides and galactosylceramides) in the cerebral cortex of an APP(SL)/PS1Ki mouse model of AD. The results demonstrate that ceramides accumulated in the cortex of APP(SL)/PS1Ki mice, but not in PS1Ki mice, whereas all others major sphingolipids (except galactosylceramides) were not altered in comparison with those from age-matched wild-type mice. Furthermore, as early as 3 months of age, female mice but not males, exhibit a strong increase in 2-hydroxy fatty acid-containing ceramides, whereas males display a significant elevation of non-hydroxy fatty acid ceramide species. Therefore, the gender differences in ceramide accumulation in the brain of mice expressing APP(SL) suggest that additional factors like modified ceramide metabolism may contribute to the increased propensity of females to develop AD.

Impairment of the neuronal dopamine transporter activity in MPP+-treated rat was not prevented by treatments with nitric oxide synthase or poly(ADP-ribose) polymerase inhibitors

The neurotoxin 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) causes, via its metabolite MPP(+), damages of the nigrostriatal dopaminergic pathway, similar to those observed in Parkinsons disease. An intranigral injection of 10 microg MPP(+) in rat induced a decrease of about 30% of the neuronal dopamine transporter (DAT) activity 21 days after lesion. Based on the hypothesis that MPTP/MPP(+) neurotoxicity involves the nitric oxide (NO) production and/or an activation of poly(ADP-ribose) polymerase (PARP), we investigated the preventive effects of a treatment either with L-Name, a NO synthase (NOS) inhibitor or 3-aminobenzamide, a PARP inhibitor on the reduction of dopamine uptake induced by MPP(+). Rats received a daily injection i.p. of 50 mg/kg L-Name or 10 mg/kg 3-aminobenzamide 3 days before and during 21 days after the MPP(+) lesion. The results showed that inhibitors of NOS and PARP did not prevent the alteration of DAT activity induced by 10 microg MPP(+), indicating that NO and PARP were not involved in the biochemical cascade leading to the inhibition of rat DAT activity by MPP(+) in our experimental conditions.

Relevance of different striatal markers in assessment of the MPP+-induced dopaminergic nigrostriatal injury in rat.

Many striatal dopaminergic markers are available for estimating the degree of the nigrostriatal lesion by MPTP/MPP+, but the changes of these markers are not perfectly matched. In this study we investigated different striatal markers and determined which ones closely reflected the nigrostriatal alteration. The in vivo binding of (E)‐N‐(3‐iodoprop‐2‐enyl)‐ 2‐β‐carbomethoxy‐3β‐(4′‐methylphenyl)nortropane (PE2I), a selective and potent inhibitor of the neuronal dopamine transporter (DAT) was considered as the reference index of injury of striatal dopaminergic nerve‐endings. Rats received a 10‐µg MPP+ injection in the right substantia nigra and were killed at 7 days after lesion. The results were as follows: (i) a decrease (66%) of the biodistribution of [125I]PE2I; (ii) a great reduction of the DAT expression measured by the binding of [125I]PE2I in striatal membranes (Bmax decreased by 54%) and in cerebral slices (88%); (iii) an 80% inhibition of the vesicular monoamine transporter expression revealed by the binding of [3H]dihydrotetrabenazine in cerebral slices; (iv) a robust decrease in the quantity of DA and its metabolites (about 50–60%); (v) a slight modification of the DAT activity with a decreased number of functional sites (Vmax decreased by 12%, p < 0.05) without change of the affinity in striatal synaptosomes. Among these markers the binding of [125I]PE2I in membrane homogenates and the content of DA, and its metabolites, in striatum could be the most relevant in vitro indexes of the degenerative state of the nigrostriatal pathway after MPP+ lesion.

Autoxidation of Rat Brain Homogenate: Evidence for Spontaneous Lipid Peroxidation. Comparison with the Characteristics of Fe2+- and Ascorbic Acid-Stimulated Lipid Peroxidation

Aerobically-incubated brain homogenates are known to undergo autoxidation characterized by spontaneous TBARS production, presumably as a result of lipid peroxidation. However, TBARS measurement alone, because of its lack of specificity, is not sufficient to demonstrate the occurrence of lipid peroxidation in complex biological systems. This study, undertaken to determine whether or not spontaneous oxidation of rat brain homogenate is due to lipid peroxidation, measured different specific markers of this process (fatty acids, lipid aldehydes and the formation of fluorescence products) and studied changes in alpha-tocopherol. Incubation of rat brain homogenates at 37 degrees C under air led to spontaneous TBARS formation, which was accompanied by lipid aldehydes and lipid fluorescence products as well as polyunsaturated fatty acid (PUFA) degradation. Alpha-tocopherol was also consumed. On the whole, these results demonstrate that autoxidation of brain homogenate is a spontaneous lipid peroxidation process. When homogenates were exposed to Fe2+ and ascorbic acid-induced oxidative stress, lipid peroxidation was enhanced. However, spontaneous and stimulated peroxidation showed similar patterns not characteristic of classical lipid peroxidation, i.e. without the lag and accelerating phases typical of a propagating chain reaction. PUFA degradation was limited despite stimulation of peroxidation.