N -acetyl- l -cysteine and Mn 2+ attenuate Cd 2+ -induced disturbance of the intracellular free calcium homeostasis in cultured cerebellar granule neurons

Mitochondrial Oxidative Stress Is the General Reason for Apoptosis Induced by Different-Valence Heavy Metals in Cells and Mitochondria

This review analyzes the causes and consequences of apoptosis resulting from oxidative stress that occurs in mitochondria and cells exposed to the toxic effects of different-valence heavy metals (Ag+, Tl+, Hg2+, Cd2+, Pb2+, Al3+, Ga3+, In3+, As3+, Sb3+, Cr6+, and U6+). The problems of the relationship between the integration of these toxic metals into molecular mechanisms with the subsequent development of pathophysiological processes and the appearance of diseases caused by the accumulation of these metals in the body are also addressed in this review. Such apoptosis is characterized by a reduction in cell viability, the activation of caspase-3 and caspase-9, the expression of pro-apoptotic genes (Bax and Bcl-2), and the activation of protein kinases (ERK, JNK, p53, and p38) by mitogens. Moreover, the oxidative stress manifests as the mitochondrial permeability transition pore (MPTP) opening, mitochondrial swelling, an increase in the production of reactive oxygen species (ROS) and H2O2, lipid peroxidation, cytochrome c release, a decline in the inner mitochondrial membrane potential (ΔΨmito), a decrease in ATP synthesis, and reduced glutathione and oxygen consumption as well as cytoplasm and matrix calcium overload due to Ca2+ release from the endoplasmic reticulum (ER). The apoptosis and respiratory dysfunction induced by these metals are discussed regarding their interaction with cellular and mitochondrial thiol groups and Fe2+ metabolism disturbance. Similarities and differences in the toxic effects of Tl+ from those of other heavy metals under review are discussed. Similarities may be due to the increase in the cytoplasmic calcium concentration induced by Tl+ and these metals. One difference discussed is the failure to decrease Tl+ toxicity through metallothionein-dependent mechanisms. Another difference could be the decrease in reduced glutathione in the matrix due to the reversible oxidation of Tl+ to Tl3+ near the centers of ROS generation in the respiratory chain. The latter may explain why thallium toxicity to humans turned out to be higher than the toxicity of mercury, lead, cadmium, copper, and zinc.

Extracellular Alkalosis Reduces the Neurotoxicity of Zinc Ions in Cultured Cerebellar Granule Neurons

Zn²⁺ is known to be important for the normal brain functions. Disruption of zinc homeostasis and zinc-induced neurotoxicity has been shown to play a role in the development of neurodegenerative diseases. In this work, we investigated the effect of extracellular alkalosis on the zinc ions neurotoxicity in the cultured rat cerebellar granule neurons. Zinc chloride (0.03-0.06 mM, 24 h) added to the culture medium of rat cerebellar granule neurons caused the dose-dependent death of these cells. According to ultrastructural morphological features, the process of cell death could be attributed to necrosis, since it was accompanied by swelling of intracellular organelles and disruption of cell membranes against the background of relatively intact nuclear membranes. Neuronal death was associated with an increase in the level of intracellular free zinc. The toxic effect of zinc ions was significantly decreased when ionotropic glutamate NMDA-receptors were blocked by MK-801 or when the extracellular pH was increased from 7.3 to 7.8, due to a decrease in the zinc overload of the cytoplasm of these cells. The presented results demonstrate that NMDA channels are one of the Zn ion entry pathways in the cultured cerebellar granule neurons. Extracellular alkalosis reduces the zinc overload of the cytoplasm and, consequently, promotes the survival of neurons. Probably, zinc's neurotoxicity is inextricably linked with changes in the intracellular concentration of protons.

Effect of zinc and copper ions on cadmium-induced toxicity in rat cultured cortical neurons

BACKGROUND

Cadmium is a highly toxic heavy metal that is capable of accumulating in the body and causing neurodegeneration. However, the effect of other trace elements on Cd²⁺ toxicity is currently poorly understood. The aim of this work was to study the effect of Zn²⁺ and Cu²⁺ ions on cadmium-induced death of neurons in the cerebral cortex.

METHODS

The work was performed on rat cortical primary cultures. The MTT test was used to determine the cytotoxicity effects. Analysis of intracellular Ca²⁺ concentration was assessed by the Fluo-4 AM calcium indicator that exhibit an increase in fluorescence upon binding Ca²⁺. MitoSOX Red (mitochondrial superoxide indicator) was used to measuring mitochondrial ROS content in live cells.

RESULTS

In this article, we show that the administration of CdCl₂ (0.005-0.02 mM) for 48 h induced an increase in dose-dependent death rate of cultured cortical neurons. Mature neurons were more sensitive to the damaging effects of Cd²⁺ than immature ones. ZnCl₂ (0.01-0.03 mM) significantly protected neurons from this toxic effect. In contrast to ZnCl₂, CuCl₂ (0.01 mM) increased cadmium neurotoxicity. Using Fluo-4 AM, measurements of intracellular calcium ions demonstrated that 24 h-exposure to Cd²⁺ induced intensive increase in Fluo-4 fluorescence in neurons, which was significantly reduced by zinc ions. CuCl₂ increased the cadmium-induced Fluo-4 and MitoSOX Red fluorescence in neurons. The chelator of intracellular Ca²⁺ BAPTA significantly decreased Cd²⁺-induced intensive increase in Fluo-4 fluorescence in cells.

CONCLUSION

The data obtained by us indicate that Zn²⁺ and Cu²⁺ can affect the neurotoxicity of cadmium in different directions: Zn²⁺ weaken the violation of intracellular calcium homeostasis caused by cadmium, preventing cell death, while Cu²⁺ potentiate the increase in the level of free intracellular calcium induced by cadmium and the development of mitochondrial dysfunction with an increase in the production of free radicals in differentiated cultured neurons of the cerebral cortex, which ultimately stimulates cytotoxicity.

Thymoquinone Induces Mitochondrial Damage and Death of Cerebellar Granule Neurons

Thymoquinone (TQ) exhibits a wide spectrum of biological activities. Most studies on the neurotoxic action of TQ have been carried out in cancer cell lines. Here, we studied the toxic effect of TQ in primary neuronal cultures in vitro. Incubation with 0.04-0.05 mM TQ for 24 h induced the death of cultured cerebellar granule neurons (CGNs) in a dose-dependent manner. Neuronal death was preceded by an increase in the reactive oxygen species (ROS) generation, as demonstrated using CellROX Green and MitoSOX Red. Confocal and electron microscopy showed that incubation with 0.05 mM TQ for 5 h induced changes in the intracellular localization of mitochondria and mitochondria hypertrophy and cell swelling. The antioxidant N-acetyl-L-cysteine (2 mM) protected CGNs from the toxic action of TQ. Taken together, these facts suggest that TQ is toxic for normal neurons, while ROS-induced changes in the mitochondria can be one of the major causes of the TQ-induced neuronal damage and death.

Effect of Manganese Chloride and of Cotreatment with Cadmium Chloride on the In Vitro Proliferative, Motile and Invasive Behavior of MDA-MB231 Breast Cancer Cells

We examined the dose⁻response effect of MnCl₂ on the proliferative behavior of triple-negative breast cancer MDA-M231 cells vs. immortalized HB2 cells from breast epithelium taken as nontumoral counterparts. We also tested the effect of MnCl₂ on tumor cell invasiveness in vitro by evaluating the relative invasion indexes through Boyden chamber assays. Moreover, we checked whether cotreatment with both MnCl₂ and CdCl₂ could modify the observed biological response by MDA-MB231 cells. Our results show a promotional impact of MnCl₂ on cell proliferation, with 5 µM concentration inducing the more pronounced increase after 96-h exposure, which is not shared by HB2 cells. Exposure to 5 µM MnCl₂ induced also an elevation of the relative invasion index of cancer cells. The Mn-mediated stimulatory effects were counteracted by cotreatment with CdCl₂. These data support the concept that human exposure to high environmental concentrations of Mn may increase the risk of carcinogenesis and metastasis by prompting the expansion and dissemination of triple-negative breast cancer cells. On the other hand, the Mn-counteracting anticancer property of Cd looks promising and deserves a more detailed characterization of the involved intracellular targets aimed to the molecular modeling of specific antineoplastic agents against malignant breast cancer spreading.

Cadmium nitrate-induced neuronal apoptosis is protected by N-acetyl-l-cysteine via reducing reactive oxygen species generation and mitochondria dysfunction

Cigarette smoking is a well-established risk factor for various diseases, such as cardiovascular diseases, neurodegeneration, and cancer. Cadmium nitrate (Cd(NO₃)₂) is one of the major products from the cigarette smoke. Up to now, no supporting evidence on Cd(NO₃)₂-induced apoptosis and its related working mechanism in neurons has been found. In present study, the mode of cell death, caspase activities, reactive oxygen species (ROS) generation, and mitochondrial dysfunction in N2a cells, which are neuron-like cells, were assessed by Annexin V-FITC and PI assays, caspase fluorometric assay, DCFH-DA fluorescence assay, and JC-1 fluorescence assay respectively. The results showed that not only Cd(NO₃)₂ induced apoptosis and necrosis but also the activities of caspase-3 and -9 expressed in a concentration-dependent manner. In addition, Cd(NO₃)₂ also induced both mitochondrial dysfunction and ROS generation in a concentration-dependent manner. All these indicated that in N2a cells parallel trends could be observed in apoptosis, caspase-3 and -9 activities, mitochondrial dysfunction, and ROS generation when induced by Cd(NO₃)₂. Furthermore, Cd(NO₃)₂-induced apoptosis, caspases activities, mitochondrial dysfunction, and ROS generation were reduced by N-acetyl-l-cysteine (NAC). These results indicated that Cd(NO₃)₂-induced neuronal apoptosis was reduced by NAC via intrinsic apoptotic caspase cascade activities and their up-stream factors, including mitochondrial dysfunction and ROS generation.

Streptozotocin toxicity in vitro depends on maturity of neurons

Streptozotocin (STZ) is a glucosamine-nitrosourea compound that is particularly toxic to the insulin-producing beta-cells of the pancreas in mammals; it is used for experimental simulation of sporadic Alzheimer's disease by means of intracerebroventricular administration in vivo. Here we show that the application of 3-4 mM STZ to primary culture for 48 h induces neuronal death in immature (2-3 days in vitro) cultures of rat cerebellar granule cells. Mature cultures (7-8 days in vitro) were poorly sensitive to this toxic treatment. Immature cultures demonstrated a high expression of the protein PSA-NCAM, the marker of immature neurons, and they were insensitive to the toxic effect of glutamate. In mature cultures, this protein was poorly expressed, whereas neurons showed a very high sensitivity to the toxic effect of glutamate. Measurements of the concentration of intracellular free calcium ions ([Ca²⁺]_i) showed that the STZ-induced [Ca²⁺]_i increase in young neurons was six times higher than that in mature neurons. Our results show that STZ is very toxic for immature neurons and probably it can significantly impair neurogenesis.