Roles of intracellular and extracellular ROS formation in apoptosis induced by cold atmospheric helium plasma and X-irradiation in the presence of sulfasalazine.

Sulfasalazine (SSZ) is a well-known anti-inflammatory drug and also an inhibitor of the cystine-glutamate antiporter that is known to reduce intracellular glutathione (GSH) level and increase cellular oxidative stress, indicating its anti-tumor potential. However, the combination of SSZ with other physical modalities remains unexplored. Here, the effects of SSZ on cold atmospheric helium plasma (He-CAP), which produces approximately 24 x higher concentration of hydroxyl radicals (. OH) compared to X-irradiation (IR) in aqueous solution, and on IR-induced apoptosis in human leukemia Molt-4 cells were studied to elucidate the mechanism of apoptosis enhancement. Both the Annexin V-FITC/PI and DNA fragmentation assay revealed that pre-treatment of cells with SSZ significantly enhanced He-CAP and IR-induced apoptosis. Similar enhancement was observed during the loss of mitochondrial membrane potential, intracellular Ca2+ ions, and mitochondria- and endoplasmic reticulum-related proteins. The concentration of intracellular reactive oxygen species (ROS) was much higher in He-CAP treated cells than in X-irradiated cells. On the other hand, strong enhancement of Fas expression and caspase-8 and -3 activities were only observed in X-irradiated cells. It might be possible that the higher concentration of intracellular and extracellular ROS suppressed caspase activities and Fas expression in He-CAP-treated cells. Notably, pretreating the cells with an antioxidant N-acetyl-L-cysteine (NAC) dramatically decreased apoptosis in cells treated by He-CAP, but not by IR. These results suggest that IR-induced apoptosis is due to specific and effective ROS distribution since intracellular ROS formation is marginal and the high production of ROS inside and outside of cells plays unique roles in He-CAP induced apoptosis. We conclude that our data provides efficacy and mechanistic insights for SSZ, which might be helpful for establishing SSZ as a future sensitizer in He-CAP or IR therapy for cancer.

The Role of the Glutathione System in Oxidative Modification of Proteins and Dysregulation of Apoptosis in Jurkat Tumor Cells.

We compared changes in the redox status and intensity of oxidative modification of proteins in intact Jurkat tumor cells and cells cultured with buthionine sulfoximine, an inhibitor of the key enzyme of glutathione synthesis γ-glutamylcysteine synthetase. The glutathione system components play a role in modulation of the content of protein-bound glutathione, protein carbonyl derivatives, bityrosine, and oxidized tryptophan, and in dysregulation of apoptosis in Jurkat tumor cells. Inhibition of de novo synthesis of glutathione in Jurkat tumor cells was followed by accumulation of hydroxyl radical, a reduction in the level of protein-bound glutathione and oxidized tryptophan, and a rise in the concentration of protein carbonyl derivatives. These changes were accompanied by activation of programmed cell death.

Dimercapto-1-propanesulfonic acid (DMPS) induces metaphase II mouse oocyte deterioration.

In light of the recent lead contamination of the water in Flint, Michigan and its potential adverse outcomes, much research and media attention has turned towards the safety profile of commonly used chelators. Dimercapto-1-propanesulfonic acid (DMPS) typically used in the treatment of lead, mercury and arsenic poisoning also displays a high affinity towards transition metals such as zinc and copper, essential for biological functioning. It is given in series of dosages (0.2-0.4g/day) over a long period, and has the ability to enter cells. In this work, we investigated the mechanism through which increasing concentrations of DMPS alter oocyte quality as judged by changes in microtubule morphology (MT) and chromosomal alignment (CH) of metaphase II mice oocyte. The oocytes were directly exposed to increasing concentration of DMPS (10, 25, 50, 100 and 300µM) for four hours (time of peak plasma concentration after administration) and reactive oxygen species (mainly hydroxyl radical and superoxide) and zinc content were measured. This data showed DMPS plays an important role in deterioration of oocyte quality through a mechanism involving zinc deficiency and enhancement of reactive oxygen species a major contributor to oocyte damage. Our current work, for the first time, demonstrates the possibility of DMPS to negatively impact fertility. This finding can not only help in counseling reproductive age patients undergoing such treatment but also in the development of potential therapies to alleviate oxidative damage and preserve fertility in people receiving heavy metal chelators.

Iron Supplements and Magnesium Peroxide: An Example of a Hazardous Combination in Self-Medication.

The use of self-medication, which includes dietary supplements and over-the-counter drugs, is still on the rise, while safety issues are not well addressed yet. This especially holds for combinations. For example, iron supplements and magnesium peroxide both produce adverse effects via the formation of reactive oxygen species (ROS). This prompted us to investigate the effect of the combination of three different iron supplements with magnesium peroxide on ROS formation. Hydroxyl radical formation by the three iron supplements either combined with magnesium peroxide or alone was determined by performing a deoxyribose assay. Free iron content of iron supplements was determined using ferrozine assay. To determine hydrogen peroxide formation by magnesium peroxide, a ferrous thiocyanate assay was performed. Finally, electron spin resonance spectroscopy (ESR) was performed to confirm the formation of hydroxyl radicals. Our results show that magnesium peroxide induces the formation of hydrogen peroxide. All three iron supplements induced the formation of the extremely reactive hydroxyl radical, although the amount of radicals formed by the different supplements differed. It was shown that combining iron supplements with magnesium peroxide increases radical formation. The formation of hydroxyl radicals after the combination was confirmed with ESR. All three iron supplements contained labile iron and induced the formation of hydroxyl radicals. Additionally, magnesium peroxide in water yields hydrogen peroxide, which is converted into hydroxyl radicals by iron. Hence, iron supplements and magnesium peroxide is a hazardous combination and exemplifies that more attention should be given to combinations of products used in self-medication.

Peculiarities of the free radical processes in rat liver mitochondria under toxic hepatitis on the background of alimentary protein deficiency.

The rate of superoxide anion radical, hydroxyl radical and hydrogen peroxide generation, the level of oxidative modification of mitochondrial proteins in the liver of rats with toxic hepatitis was investigated on the background of alimentary protein deficiency. We did not find significant increases of the intensity of free radical processes in liver mitochondria of rats maintained on the protein-deficient ration. The most significant intensification of free radical processes in liver mitochondria is observed under the conditions of toxic hepatitis, induced on the background of alimentary protein deprivation. Under these conditions the aggravation of all studied forms of reactive oxygen species generation was observed in liver mitochondria. The generation rates were increased as follows: O2 ­ by 1.7 times, Н2О2 ­ by 1.5 times, •ОН ­ practically double on the background of accumulation of oxidized mitochondria-derived proteins. The established changes in thiol groups' redox status of respiratory chain proteins insoluble in 0.05 M sodium-phosphate buffer (pH 11.5), and changes of their carbonyl derivatives content may be considered as one of the regulatory factors of mitochondrial energy-generating function.

Oxidative stress, mitochondrial permeability transition pore opening and cell death during hypoxia-reoxygenation in adult cardiomyocytes.

Reactive oxygen species production is necessary to induce cell death following hypoxia/reoxygenation but the effect of reactive oxygen species produced during hypoxia on mitochondrial permeability transition pore (mPTP) opening and cell death is not established. Here we designed a model of hypoxia/reoxygenation in isolated cardiomyocytes measuring simultaneously reactive oxygen species production, mPTP opening and cell death in order (i) to establish a causal relationship between them, and (ii) to investigate the roles of various reactive oxygen species in mPTP opening. The percentage of cardiomyocytes exhibiting mPTP opening during reoxygenation increased with the duration of hypoxia. Antioxidants increased the time to mPTP opening when present during hypoxia but not at reoxygenation. This was associated with a drop in hydroxyl radical and hydrogen peroxide during hypoxia and the first minutes of reoxygenation. The increase in time to mPTP opening was accompanied by an improvement in cell viability reflected by maintenance of superoxide production at reoxygenation. Cyclosporin A delayed both the time to mPTP opening and cell death despite maintenance of reactive oxygen species production during hypoxia. These findings demonstrate that reactive oxygen species production precedes mPTP opening and that reactive oxygen species produced during hypoxia, particularly hydroxyl radicals and hydrogen peroxide, are necessary to induce mPTP opening which depends on hypoxia duration.

On the mechanism of Cr (VI)-induced carcinogenesis: dose dependence of uptake and cellular responses.

Cr (VI) compounds are widely used industrial chemicals and are recognized human carcinogens. The mechanisms of carcinogenesis associated with these compounds remain to be investigated. The present study focused on dose-dependence of Cr (VI)-induced uptake and cellular responses. The results show that Cr (VI) is able to enter the cells (human lung epithelial cell line A549) at low concentration (< 10 microM) and that the Cr (VI) uptake appears to be a combination of saturable transport and passive diffusion. Electron spin resonance (ESR) trapping measurements showed that upon stimulation with Cr (VI), A549 cells were able to generate reactive oxygen species (ROS). The amount of ROS generated depended on the Cr (VI) concentration. ROS generation involved NADPH-dependent flavoenzymes. Cr (VI) affected the following cellular parameters in a dose-dependent manner, (a) activation of nuclear transcription factors NF-kappaB, and p53, (b) DNA damage, (c) induction of cell apoptosis, and (d) inhibition of cell proliferation. The activation of transcription factors was assessed by electrophoretic mobility shift assay and western blot analysis, DNA damage by single cell gel electrophoresis assay, cell apoptosis by DNA fragmentation assay, and cell proliferation by a non-radioactive ELISA kit. At the concentration range used in the present study, no thresholds were found in all of these cell responses to Cr (VI). The results may guide further research to better understand and evaluate the risk of Cr (VI)-induced carcinogenesis at low levels of exposure.

Effect of iron and manganese on hydroxyl radical production by 6-hydroxydopamine: mediation of antioxidants.

6-Hydroxydopamine (6-OHDA) neurotoxicity has often been related to the generation of free radicals. Here we examined the effect of the presence of iron (Fe(2+) and Fe(3+)) and manganese and the mediation of ascorbate, L-cysteine (CySH), glutathione (GSH), and N-acetyl-CySH on hydroxyl radical (*OH) production during 6-OHDA autoxidation. In vitro, the presence of 800 nM iron increased (> 100%) the production of *OH by 5 microM 6-OHDA while Mn(2+) caused a significant reduction (72%). The presence of ascorbate (100 microM) induced a continuous generation of *OH while the presence of sulfhydryl reductants (100 microM) limited this production to the first minutes of the reaction. In general, the combined action of metal + antioxidant increased the *OH production, this effect being particularly significant (> 400%) with iron + ascorbate. In vivo, tyrosine hydroxylase immunohistochemistry revealed that intrastriatal injections of rats with 6-OHDA (30 nmol) + ascorbate (600 nmol), 6-OHDA + ascorbate + Fe(2+) (5 nmol), and 6-OHDA + ascorbate + Mn(2+) (5 nmol) caused large striatal lesions, which were markedly reduced (60%) by the substitution of ascorbate by CySH. Injections of Fe(2+) or Mn(2+) alone showed no significant difference to those of saline. These results clearly demonstrate the role of ascorbate as an essential element for the neurotoxicity of 6-OHDA, as well as the diminishing action of sulfhydryl reductants, and the negligible effect of iron and manganese on 6-OHDA neurotoxicity.

Increased vulnerability of neurones and glial cells to low concentrations of methylmercury in a prooxidant situation.

Using reaggregating rat brain cell cultures at two different stages of differentiation, we examined the biochemical effects of a 10-day treatment with nanomolar concentrations of methylmercuric chloride (monomethylmercury), in the presence or absence of promoters of hydroxyl radical formation (10 microM copper sulphate plus 100 microM ascorbate). A decrease in total protein content accounted for the general cytotoxicity of these compounds, whereas selective effects were assessed by determining the activities of cell type-specific enzymes. Methylmercury, up to 100 nM, as well as the copper ascorbate mixture, when applied separately, induced no general cytotoxicity, and only slight effects on neuronal parameters. However, when applying 100 nM methylmercury and the copper-ascorbate mixture together, a drastic decrease in neuronal and glial parameters was found. Under these conditions, the content of reactive oxygen species, assessed by 2',7'-dichlorofluorescin oxidation, increased greatly, while the activities of antioxidant enzymes decreased. In the presence of copper and ascorbate, differentiated cultures appeared more resistant than immature ones to low methylmercury concentrations (1-10 mM), but did undergo similar changes in both cell type-specific and antioxidant enzyme activities at 100 nM methylmercury. These results suggest that in prooxidant conditions low doses of mercury can become much more deleterious for the central nervous system.