Calcium signals and caspase-12 participated in paraoxon-induced apoptosis in EL4 cells

Harpagide exerts a neuroprotective effect by inhibiting endoplasmic reticulum stress via SERCA following oxygen-glucose deprivation/reoxygenation injury

Cerebrovascular diseases endanger human health, and the physiological and pathological processes of cerebral ischemia/reperfusion injury (CIRI) are critical for the occurrence of these diseases and as targets for their treatment. Here, we evaluated the effects of harpagide-mediated pharmacological and genetic inhibition of sarco-endoplasmic reticulum Ca²⁺-ATPase (SERCA) in vitro in PC12 cells. The molecular mechanism by which harpagide protects PC12 cells against oxygen-glucose deprivation/reoxygenation (OGD/R) injury was investigated by evaluating the cell survival rate with the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide (MTT) assay, assessing apoptosis by flow cytometry, determining the intracellular Ca²⁺ concentration ([Ca²⁺]_i) by laser scanning confocal microscopy (LSCM), and measuring the expression of proteins related to SERCA and endoplasmic reticulum stress (ERS) by Western blotting. The results revealed that harpagide significantly decreased thapsigargin (TG)-induced apoptosis of PC12 cells, downregulated the expression of ERS-related markers, considerably improved the TG-induced expression of SERCA-related proteins and reduced the [Ca²⁺]_i, suggesting that harpagide effectively inhibited ERS directly. Moreover, harpagide did not significantly reduce OGD/R-induced apoptosis but increased the expression of ERS markers in PC12/SERCA^- cells, indicating that harpagide targets SERCA to protect against CIRI by suppressing ERS-mediated apoptosis.

In-vitro effect of diazoxon, a metabolite of diazinon, on proliferation, signal transduction, and death induction in mononuclear cells of Nile tilapia fish (Oreochromis niloticus)

The immune response of teleosts (bonefish) is altered by diazinon (DZN), an organophosphate pesticide. It has been suggested that such alteration is due to the extraneuronal cholinergic system in fish leukocytes that renders these cells a target of pesticides. Diazoxon (DZO), the oxon metabolite of DZN, has been attributed immunotoxic effects. Still, to date there are no reports on the effects of DZO upon parameters involved in the signaling cascade of immune response cells. Therefore, this work evaluated the effect of DZO on key parameters of cell signaling (intracellular Ca²⁺ flux, ERK 1/2 phosphorylation), cell proliferation, and antiproliferative processes (apoptosis, senescence, mitochondrial membrane potential) in spleen mononuclear cells of Nile tilapia fish. The results obtained show that DZO does not affect cell proliferation but causes a lack of response to stimulation with PMA and ionomycin to release intracellular calcium. In addition, it inhibits ERK 1/2 phosphorylation and causes loss of mitochondrial membrane potential, apoptosis, and senescence. These results suggest that the lack of cell response to release intracytoplasmic Ca²⁺ inhibits ERK which disrupts the mitochondrial membrane potential, leading to cell apoptosis and senescence. These findings prove that DZO significantly affects key parameters involved in the survival of immune response cells.

Protective effects of calbindin‑D28K on the UVB radiation‑induced apoptosis of human lens epithelial cells

Calbindin-D28K (Calb1) may protect human lens epithelial cells (HLECs) from apoptosis, which is a process resulting in individual cell death. The protective effects of Calb1 may be attributed to buffering high concentrations of Ca²⁺. The present study investigated the mechanisms through which Calb1 protects SRA01/04 cells (a human lens epithelial cell line) against apoptosis induced by ultraviolet B (UVB) exposure. Cells transfected with a lentivirus overexpressing Calb1 and control cells were treated with 40 µW/cm² irradiation for 15 min and then cultured for 24 h. The changes in intracellular Ca²⁺ were detected by colorimetry, and the protein expression levels of Bad, Bcl-2 and caspase-12 were measured by western blot analysis. The intracellular Ca²⁺ concentration of control HLECs increased significantly following UVB irradiation, whereas in Calb1-overexpressing cells, the Ca²⁺ levels remained steady. In the control cells, the expression of Bad and caspase-12 was upregulated, and that of Bcl-2 was down-regulated. Notably, during UVB radiation-induced apoptosis, the overexpression of Calb1 inhibited cell death, resulting in the decreased expression of Bad and caspase-12, and in the upregulated expression of Bcl-2. These results suggested that Calb1 inhibited the upregulation of genes involved in apoptosis. The siRNA-mediated knockdown of Calb1 resulted in increased rates of UVB radiation-induced apoptosis, the increased expression of Bad and caspase-12, and the decreased expression of Bcl-2, further demonstrating that Calb1 may mediate UVB radiation-mediated apoptosis by regulating Ca²⁺. On the whole, the findings of the present study indicate that UVB exposure can lead to an imbalance in the intracellular Ca²⁺ homeostasis in HLECs and that Calb1 protein exerts a negative effect on the expression of pro-apoptotic genes in HLECs. Calb1 may thus inhibit the UVB radiation-induced apoptosis of HLECs by regulating Ca²⁺.

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.

Effects of paraoxon on serum biochemical parameters and oxidative stress induction in various tissues of Wistar and Norway rats

This study investigates the effects of different doses of paroxon (POX), an active metabolite of the organophosphate pesticide parathion, on some serum biochemical parameters and induction of oxidative stress in various tissues of female Wistar and Norway rats. The rats were intraperitoneally treated with 0.3, 0.7, 1 and 1.5 mg/kg of POX. The parameters were evaluated after 24h. The results showed that the decreased glutathione level and catalase, glutathione-S-transferase and lactate dehydrogenase activities in tissues of Wistar rat were higher than Norway rat at higher doses of POX. At these concentrations, POX increased superoxide dismutase activity, malondialdehyde level and some serum biochemical indices. In conclusion, POX induces the production of free radicals and oxidative stress in a dose-dependent manner. Induction of oxidative stress in POX-treated rats is in the order of brain > liver > heart > kidney>spleen. Wistar rat is found to be more sensitive to the toxicity of POX compared to Norway rat.

Lead-induced ER calcium release and inhibitory effects of methionine choline in cultured rat hippocampal neurons

Lead, a ubiquitous neurotoxicant, can result in learning and memory dysfunction. Long term potentiation in the hippocampus, a potential neural substrate for learning and memory, is thought to be linked to calcium-triggered intracellular events. In this study, laser scanning confocal microscopy was used to examine the effects of Pb(2+) on intracellular and endoplasmic reticulum free calcium concentration ([Ca(2+)](i) and [Ca(2+)](ER)) in cultured neonatal rat hippocampal neurons and their possible antagonism by methionine choline; understanding these effects would help explain the lead-induced cognitive and learning dysfunction and explore efficient safety and relief strategies. The results showed that Pb(2+) increased [Ca(2+)](i) and decreased [Ca(2+)](ER) linearly in a time- and concentration-dependant manner, and Pb(2+) addition after the applying of a ryanodine receptor (RyR) antagonist and an inositol-1,4,5-triphosphate receptor (IP(3)R) antagonist did not increase [Ca(2+)](i). The addition of 10, 20, or 40 mmol/L methionine choline simultaneously with addition of 10 μmol/L Pb(2+) decreased [Ca(2+)](i) in Ca(2+)-free culture medium by 39.0%, 66.0%, and 61.6%, respectively, in a concentration-dependant manner in a certain dose range. Our results suggest that Pb(2+) induces ER calcium release to increase the resting [Ca(2+)](i); and methionine choline inhibit this increase in [Ca(2+)](i).

A cembranoid protects acute hippocampal slices against paraoxon neurotoxicity

Many neurotoxic organophosphates (OPs) inhibit acetylcholinesterase (AChE) and as a result can cause a life threatening cholinergic crisis. Current medical countermeasures, which typically include atropine and oximes target the cholinergic crisis and are effective in decreasing mortality but do not sufficiently protect against delayed neurological deficits. There is, therefore, a need to develop neuroprotective drugs to prevent long-term neurological deficits. We used acute hippocampal slices to test the hypothesis that 4R,6R-cembratrienediol (4R) protects against functional damage caused by the OP paraoxon (POX). To assess hippocampal function, we measured synaptically evoked population spikes (PSs). Application of 4R reversed POX inhibition of PSs and the EC(50) of this effect was 0.8 μM. Atropine alone did not protect against POX neurotoxicity, but it did enhance protection by 4R. Pralidoxime partially regenerated AChE activity and protected against POX inhibition of PSs. 4R did not regenerate AChE suggesting that under our experimental conditions, the deleterious effect of POX on hippocampal function is not directly related to AChE inhibition. In conclusion, 4R is a promising neuroprotective compound against OP neurotoxins.

Effects of paraoxon on neuronal and lymphocytic cholinergic systems

The cholinergic system in lymphocytes is hypothesized to be a key target for neurotoxic organophosphates (OPs). The present study determined the comparative effects of paraoxon, the active metabolite of OP-parathion, which is detected in the human neuroblastoma line, SH-SY5Y, and leukemic T-lymphocytes, MOLT-3, in vitro. Paraoxon induced cytotoxic effects in a dose- and time-dependent manner in both cells. Further, the paraoxon-induced modulatory effects were comparable despite different cell types, including over-expression of N-terminus acetylcholinesterase (N-AChE) protein, a marker of apoptosis, down-regulations of mRNA encoding M1, M2, and M3 muscarinic acetylcholine receptors (mAChRs), and induction in expression of c-Fos gene, an indication of certain mAChR subtype(s) activation. Furthermore, the non-selective cholinergic antagonist atropine partially attenuated the paraoxon-induced N-AChE and c-Fos activations in both types of cells. These results provide initial and additional information that OPs may similarly induce neuro- and immuno-toxic effects through mAChRs activation, and they underline the potential of using lymphocytes for assessing OPs-induced neurotoxicity.