VX-induced cell death involves activation of caspase-3 in cultured rat cortical neurons

Calcium plays a key role in paraoxon-induced apoptosis in EL4 cells by regulating both endoplasmic reticulum- and mitochondria-associated pathways

CONTEXT AND OBJECTIVE

Paraoxon (POX) is one of the most toxic organophosphorus pesticides, but its toxic mechanisms associated with apoptosis remain unclear. The aim of this study was to investigate calcium-associated mechanisms in POX-induced apoptosis in EL4 cells.

MATERIALS AND METHODS

EL4 cells were exposed to POX for 0-16 h. EGTA was used to chelate Ca(2+ ) in extracellular medium, and heparin and procaine were used to inhibit Ca(2+ )efflux from the endoplasmic reticulum (ER). Z-ATAD-FMK was used to inhibit caspase-12 activity. The apoptotic rate assay, western blotting and immunocytochemistry (ICC) were used to reveal the mechanisms of POX-induced apoptosis.

RESULTS AND DISCUSSION

POX significantly increased the expression and activation of caspase-12 and caspase-3, enhanced expression of calpain 1 and calpain 2, and induced the release of cyt c, but did not change the expression of Grp 78. Inhibiting caspase-12 activity alleviated POX-induced upregulation of calpain 1 and caspase-3, promoted POX-induced upregulation of calpain 2, and reduced POX-induced cyt c release, suggesting that there was a cross-talk between the ER-associated pathway and mitochondria-associated apoptotic signals. Attenuating intracellular calcium concentration with EGTA, heparin or procaine decreased POX-induced upregulation of calpain 1, calpain 2, caspase-12 and caspase-3, and reduced POX-induced cyt c release. After pretreatment with EGTA or procaine, POX significantly promoted expression of Grp 78.

CONCLUSIONS

Calcium played a key role in POX-induced apoptosis in EL4 cells by regulating both ER- and mitochondria-associated pathways. The cross-talk of ER- and mitochondria-associated pathways was accomplished through calcium signal.

Evaluation of diazinon-induced hepatotoxicity and protective effects of crocin

Diazinon (DZN) is one of the most widely used insecticides in agricultural pest control. Previous studies have shown that DZN may induce hepatotoxicity. Reactive oxygen species and apoptosis pathways are involved in the toxicity of DZN. Crocin, a constituent of saffron, has hepatoprotective effects due to its antioxidant activity. In this study, we examined the effects of subacute DZN exposure and ameliorating effect of crocin on lipid peroxidation and pathological changes in rat liver. Moreover, protein levels of activated and total caspases-3 and -9 and Bax/Bcl-2 ratio were measured. Five groups of rats were used in the experiment. Corn oil (control), DZN (15 mg/kg per day, orally) and crocin (12.5, 25 and 50 mg/kg per day, intraperitoneally in combination with DZN) were given to male Wistar rats ( n = 6) for 4 weeks. The level of malondialdehyde (MDA) increased significantly in DZN group compared with the control group ( p < 0.05). MDA level decreased significantly in the group that received DZN plus 25 mg crocin ( p < 0.001). No gross or histological evidence of treatment-related damage to the liver after oral exposure to DZN was observed. DZN also induced apoptosis through activation of caspases-9 and -3 and increasing Bax/Bcl-2 ratio. Crocin attenuated the activation of caspases and reduced the Bax/Bcl-2 ratio. It is concluded that subacute exposure to DZN induces oxidative stress-mediated apoptosis and crocin may reduce DZN-induced hepatotoxicity.

Cyclooxygenase-2 contributes to VX-induced cell death in cultured cortical neurons

The link between cell death and increased cyclooxygenases-2 (COX-2) activity has not been clearly established. In this study, we examined whether COX-2 activation contributed to the mechanism of neurotoxicity produced by an organophosphorous nerve agent in cultured rat cortical neurons. Exposure of neuronal cells to the nerve agent, VX resulted in an increase in COX enzyme activity in the culture media. A concentration dependent increase in the activity levels of COX-2 enzyme was observed while there was little to no effect on COX-1. In addition, COX-2 mRNA and protein levels increased several hours post-VX exposure. Pre-treatment of the cortical cells with the COX-2 selective inhibitor, NS 398 resulted in a decrease in both the enzyme activity and prostaglandin (PGE(2) and PGF(2α)) release, as well as in a reduction in cell death. These findings indicate that the increase in COX-2 activity may contribute to the mechanism of VX-induced neurotoxicity in cultured rat cortical neuron.

Hypothermia attenuates protective effects of ginkgolides on astrocytes from ischemia/reperfusion injury

The neuroprotective roles of both hypothermia and ginkgolides have been well confirmed. We first examined whether hypothermia (32 or 28 degrees C) or ginkgolides have a protective effect on astrocytes against ischemia and reperfusion-induced injury. We demonstrated that ginkgolides, but not hypothermia, have a significantly time- and concentration-dependent protective role in ischemic astrocytes. We then investigated whether co-treatment with hypothermia and ginkgolides has a synergistic role to protect astrocytes against ischemia and reperfusion-induced injury. Cells were incubated with 18.75, 37.5 or 75 microg/ml of ginkgolides at 37, 32 or 28 degrees C for 24, 48 or 72 h before exposure to ischemia (24h) and then reperfusion (24h). Data showed that the co-treatment induced a significant decrease, rather than an increase as we had expected, in their cellular viabilities and anti-apoptotic abilities as compared with the cells treated by ginkgolides only. Western blot analysis demonstrated that hypothermia (32 or 28 degrees C for 24h) has no effect on the expression of Hypoxia-inducible factor-1 alpha (HIF-1 alpha) protein, suggesting that HIF-1 alpha is not associated with the adverse effect of hypothermia on ginkgolides. The findings imply the importance of further investigating the effects of hypothermia on the pharmacological role or therapeutic efficacy of drugs commonly used clinically.

Protective effects of N-methyl-D-aspartate receptor antagonism on VX-induced neuronal cell death in cultured rat cortical neurons

Exposure of the central nervous system to organophosphorus (OP) nerve agents induces seizures and neuronal cell death. Here we report that the OP nerve agent, VX, induces apoptotic-like cell death in cultured rat cortical neurons. The VX effects on neurons were concentration-dependent, with an IC(50) of approximately 30 microM. Blockade of N-methyl-D-aspartate receptors (NMDAR) with 50 microM. D-2-amino-5-phosphonovalerate (APV) diminished 30 microM VX-induced total cell death, as assessed by alamarBlue assay and Hoechst staining. In contrast, neither antagonists of alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid receptors (AMPARs) nor metabotropic glutamate receptors (mGluRs) had any effect on VX-induced neurotoxicity. VX-induced neuronal cell death could not be solely attributed to acetylcholinesterase (AChE) inhibition, since neither the reversible pharmacological cholinesterase inhibitor, physostigmine, nor the muscarinic receptor antagonist, atropine, affected VX-induced cell death. Importantly, APV was found to be therapeutically effective against VX-induced cell death up to 2 h post VX exposure. These results suggest that NMDARs, but not AMPARs or mGluRs, play important roles in VX-induced cell death in cultured rat cortical neurons. Based on their therapeutic effects, NMDAR antagonists may be beneficial in the treatment of VX-induced neurotoxicities.