Exogenous nitric oxide negatively regulates the S-nitrosylation p38 mitogen-activated protein kinase activation during cerebral ischaemia and reperfusion

AIMS

A number of studies have suggested that nitric oxide (NO) plays an important role in the reactive phosphorylation of p38MAPKα (p38). However, whether S-nitrosylation of p38 is activated by NO and the details remain unclear. The aim of the present work was to assess the activation of p38, the S-nitrosylation site and the p38 signalling pathway in rat hippocampus and in HEK293 cell induced by exogenous NO.

METHODS

Primary hippocampal cultures, HEK293 cells and rat model of cerebral ischaemia/reperfusion (brain ischaemia was induced by four-vessel occlusion procedure) were used in this study. Biotin-switch method and immunoblotting were performed to study the S-nitrosylation and phosphorylation of p38, and neuronal loss was observed by histology.

RESULTS

Endogenous NO increased p38 phosphorylation and S-nitrosylation, and the activation of p38 was dependent on the S-nitrosylation of Cys-211, which was critical for the NO-mediated activation of p38. The exogenous NO donor sodium nitroprusside, S-nitrosoglutathione, 7-nitroindazole, the inhibitor of the neuronal nitric oxide synthase, inhibited the activation of p38 signal pathway induced by cerebral ischaemia/reperfusion and attenuated the damage in rat hippocampal neurones. Moreover, the N-methyl-D-aspartate receptor (NMDAR) is probably involved in the p38 activation process of S-nitrosylation and phosphorylation.

CONCLUSION

Endogenous NO induces the S-nitrosylation and phosphorylation of p38 and mediates p38 signalling pathway by NMDAR, and as exogenous NO inhibits this process and is neuroprotective in rat cerebral ischaemia/reperfusion, it may make a contribution to stroke therapy.

Activation and involvement of JNK1/2 in hydrogen peroxide-induced neurotoxicity in cultured rat cortical neurons

AIM

To investigate the role of c-Jun N-terminal protein kinase 1 and 2 (JNK1/2) and the main signal pathway for its activation in hydrogen peroxide (H(2)O(2)) induced apoptotic-like cortical cell death.

METHODS

Using the model of oxidative stress induced by H(2)O(2), the expression and diphosphorylation of JNK1/2 was examined by immunoblotting analysis, and neuronal apoptotic like cell death was determined by 4',6-diamidino-2-phenylindole (DAPI) staining.

RESULTS

The elevation in diphosphorylation level of JNK1/2 (4.40-/5.61-fold vs sham control) was associated with the concentration of H(2)O(2) (0-100 micromol/L) and the development of apoptotic-like cell death (11.04 %-81.01 %). There was no alteration of JNK1/2 protein expression following H(2)O(2) treatment and recovery at different time points. Administration with JNK1/2 antisense oligonucleotides not only significantly decreased JNK1/2 protein expression and activation level, but also significantly reduced cortical cell death induced by H(2)O(2) exposure. Furthermore, both JNK1/2 diphosphorylation and apoptotic-like cell death were largely prevented by pretreatment with (5S,10R)-(-)-5-methyl-10,11-dihydro-5H-dibenzo[a,d]cyclohepten-5,10-imine hydrogen maleate (MK-801) or omission of Ca(2+) in incubation medium with ethylene glycol-bis(2-aminoethylether)-N,N,N',N'-tetraacetic acid (EGTA).

CONCLUSION

JNK1/2 is activated and participates in H(2)O(2)-induced apoptotic-like death in cultured rat cortical neurons mainly via N-methyl-D-aspartate (NMDA) receptor-mediated influx of extracellular Ca(2+).

[Ketamine and nifedipine protect cultured cortical neurons against injurious effect of glutamate]

The effects of glutamate on cultured cortical neurons and the protective effect of ketamine and nifedipine were studied. On day 10 after plating of the cortical cells from 16-18 day-old fetal rats, the cultures were exposed to 50 mumol.L-1 glutamate and low glucose (1 g.L-1) for 10 min-24 h. The results showed that a release of lactate dehydrogenase (LDH) into the culture supernatant was observed as a function of time. The values of LDH efflux in culture medium was significantly lower than those of controls when the cells were pretreated with ketamine or nifedipine 10 min prior to addition of glutamate. More significant decrease of LDH activity in culture medium was observed when the two drugs were used in combination. These results demonstrate that the dissociated cultured cortical neurons from fetal rat are seriously damaged by glutamate. Such damage could be attenuated by ketamine and nifedipine, suggesting that ketamine and nifedipine may protect neurons from the glutamate toxicity, and the effect of combining ketamine and nifedipine was greater than either ketamine or nifedipine alone.

[Studies on mechanism of the inhibition of Ca2+/CaM PKII activity induced by hypoxia in rat hippocampal slices]

The effects of Ca2+ and ketamine on Ca2+/CaM PK II activity in rat hippocampal slices under in vitro hypoxic states have been studied and the effect of hypoxia on glutamate accumulation was also investigated. The results were as follows: (1) Ca2+/CaM PK II activity decreased gradually with increasing hypoxic time in culture medium with or without 1.3 Ca2- mmol/L, with the former case being much more pronounced. (2) Extracellular accumulation of GLU increased about two-fold after hypoxia for 30 min in vitro. (3) When slices were incubated for 30 min under conditions in excess of exogenous GLU the enzyme activity markedly decreased, a finding suggesting that the inhibition of enzyme activity induced by hypoxia may result from excitotoxicity. (4) The inhibition of the enzyme activity induced by either hypoxia or excess exogenous glutamate alone could be antagonized markedly by pretreatment with ketamine, suggesting that the hypoxia induced inhibition of the enzyme activity is mediated by NMDA receptor.

Determination of strychnine and brucine by capillary zone electrophoresis

A procedure for quantitative estimation of strychnine and brucine in the extracts of Strychnos nux-vomica seeds by capillary zone electrophoresis (CZE) was developed. The buffer solution used was 10mM phosphate buffer-MeOH (9:1), pH 2.5. The linear calibration range was 0.01-0.15 mg/ml. This method is useful for the qualitative and quantitative determination of strychnine and brucine in plant drug samples, as well as in human plasma.