Sodium nitroprusside-induced seizure and taurine release from rat hippocampus

Spermidine influence on the nitric oxide synthase and arginase activity relationship during experimentally induced seizures

Nitric oxide (NO), a potential candidate for a modulator of convulsive activity, is a mediator in several pathological events in the central nervous system. The polyamines, spermidine (Spd) and spermine, are neuromodulators influencing the metabolism of L-arginine and NO production. Here we examined the effects of Spd on NO production and arginase activity during convulsions induced by pentylenetetrazol (PTZ). Male Wistar rats were allocated into four experimental groups of 8 animals each and received the following treatments: I (control)--saline, intraperitoneally (i.p.); II (PTZ)--seizures induced by pentylenetetrazol (100mg/kg bw i.p); III (Spd)--Spd (1 mg/kg bw i.p.) 50 min before PTZ application; IV (Mid)--antiepileptic Midazolam (100 mg/kg bw) 45 min before PTZ. In brain cortex, striatum, hippocampus, cerebellum, and brainstem homogenates, nitrite + nitrate levels and arginase activity were determined. Spermidine showed proepileptic effects. shortening seizure latency and inducing a more profound increase of NO production than PTZ in all brain structures. PTZ reduced arginase activity, whereas Spd pretreatment increased enzyme activity, with the most profound effects in cerebellum and brainstem. The results point out the importance of polyamine and arginine metabolism in the brain during seizures, suggesting a regulatory role for polyamines and arginase in NO production.

Coupling between neuronal nitric oxide synthase and glutamate receptor 6-mediated c-Jun N-terminal kinase signaling pathway via S-nitrosylation contributes to ischemia neuronal death

S-nitrosylation, as a post-translational protein modification, recently has been paid more and more attention in stroke research. S-nitrosylation regulates protein function by the mechanisms of covalent attachment that control the addition or the removal of nitric oxide (NO) from a cysteine thiol. The derivation of NO is established by the demonstration that, in cerebral neurons, NO mainly generates from neuronal nitric oxide synthase (nNOS) during the early stages of reperfusion. In the past researches, we demonstrate that global ischemia-reperfusion facilitates the activation of glutamate receptor 6 (GluR6) -mediated c-Jun N-terminal kinase (JNK) signaling pathway. The objective of this study is primarily to determine, during the early stages of reperfusion in rat four-vessel occlusion (4-VO) ischemic model, whether nNOS-derived NO affects the GluR6-mediated JNK signaling route via S-nitrosylation which is performed mainly by the biotin switch assay. Here, we show that administration of 7-nitroindazole, an inhibitor of nNOS, or ketamine, an antagonist of N-methyl-d-aspartate receptor (NMDAR), diminishes the increased S-nitrosylation of GluR6 induced by cerebral ischemia-reperfusion. In contrast, 2-amion-5,6-dihydro-6-methyl-4H-1,3-thiazine, an inhibitor of inducible NO synthase does not affect S-nitrosylation of GluR6. Moreover, treatment with sodium nitroprusside (SNP), an exogenous NO donor, increases the S-nitrosylation and phosphorylation of nNOS, leading to the attenuation of the increased S-nitrosylation of GluR6 and the assembling of GluR6* postsynaptic density protein 95 (PSD95)* mixed lineage kinase 3 (MLK3) signaling module induced by cerebral ischemia-reperfusion. The results also show that GluR6 downstream MLK3* mitogen activated protein kinase kinase 4/7* JNK signaling module and nuclear or non-nuclear apoptosis pathways are involved in the above signaling route. However, dithiothreitol (DTT) antagonizes the neuroprotection of SNP. Treatment with DTT alone, as a negative control, prevents S-nitrosylation of proteins, which indicates the existence of endogenously produced S-nitrosylation. These data suggest that GluR6 is S-nitrosylated by endogenous NO in cerebral ischemia-reperfusion, which is possibly correlated with NMDAR* PSD95* nNOS signaling module, and further activates GluR6* PSD95* MLK3 signaling module and JNK signaling pathway. In contrast, exogenous NO donor antagonizes the above action of endogenous NO generated from nNOS. Thus, our results provide the coupling of nNOS with GluR6 by S-nitrosylation during the early stages of ischemia-reperfusion, which can be a new approach for stroke therapy.

Inhibition of high K+-evoked gamma-aminobutyric acid release by sodium nitroprusside in rat hippocampus

To clarify whether nitric oxide (NO) modifies high K(+)-evoked gamma-aminobutyric acid (GABA) release, we examined the effects of sodium nitroprusside, an NO donor; diethyldithiocarbamate, an NO trapper; dithiothreitol, a superoxide radical scavenger; and 1H-(1,2,4)oxadiazole(4,3-a)quinoxalin-1-one, a specific guanylyl cyclase inhibitor, on high (100 mM) K(+)-evoked GABA release from rat hippocampus in vivo using microdialysis. Perfusion with 0.5 or 5 mM sodium nitroprusside significantly reduced high K(+)-evoked GABA release. Co-perfusion with 0.5 mM sodium nitroprusside and 5 mM diethyldithiocarbamate or 0.5 mM 1H-(1,2,4)oxadiazole(4,3-a)quinoxalin-1-one significantly enhanced high K(+)-evoked GABA release. Co-perfusion with 0.5 mM sodium nitroprusside and 1 mM dithiothreitol tended to increase it. These results demonstrate that sodium nitroprusside reduces high K(+)-evoked GABA release both via an NO/cyclic GMP-dependent pathway and via an NO-dependent, but cyclic GMP-independent, pathway in rat hippocampus in vivo.

Acid-promoted DNA-cleaving activities and total synthesis of varacin C

The first total synthesis of the antibiotic varacin C has been accomplished. In addition, it has been demonstrated that this antibiotic exhibits potent antitumor activity and is capable of causing efficient DNA cleavage under acidic conditions.

Benzotrithiole 2-oxide: a new family of thiol-activated DNA-cleaving functionalities

It was demonstrated in our studies that benzotrithiole 2-oxide was capable of causing efficient DNA cleavage in the presence of 2-mercaptoethanol or glutathione and exhibited potent cytotoxic properties against certain cancer cell lines.

Sodium nitroprusside-induced seizures and adenosine release in rat hippocampus

In the present study, we examined the effects of nitric oxide (NO)-related compounds, i.e. sodium nitroprusside (NO donor), diethyldithiocarbamate (NO trapper) and dithiothreitol (superoxide radical scavenger) on release of aspartate and adenosine from rat hippocampus using electrophysiological and microdialysis methods. Perfusion with 0.05 or 0.5 mM sodium nitroprusside significantly reduced high K(+)-evoked release of aspartate during high K(+) perfusion. Perfusion with 0.5 mM sodium nitroprusside always induced seizures and significantly increased release of aspartate and adenosine during washout of sodium nitroprusside. Diethyldithiocarbamate (5 mM) reversed the effects of sodium nitroprusside. Dithiothreitol (1 mM) significantly reduced the increase in adenosine release by sodium nitroprusside. These findings indicate that adenosine release is closely related to development of seizures, which are triggered by an increase in both NO itself and in part peroxynitrite, which results in reaction with superoxide radicals.