Nitroprusside increases intracellular Zn2+ concentration without affecting cellular thiol content : A model experiment using rat thymocytes and FluoZin-3

Nitric oxide (NO) is cytotoxic under some conditions although it has physiological roles. It is recently proposed that the cytotoxicity of NO is resulted from its interaction with glutathione and zinc. Since we have revealed that a decrease in cellular content of non-protein thiols, presumably glutathione, induces intracellular Zn2+ release, there is a possibility that the cytotoxicity of nitroprusside, a donor of NO, is resulted from the interaction of NO with cellular thiols, leading to an increase in intracellular Zn2+ concentration. To test the possibility, the effects of nitroprusside on cell lethality, intracellular thiol content, and intracellular Zn2+ concentration were examined in rat thymocytes by using a flow cytometer with propidium iodide and FluoZin-3. Nitroprusside at concentrations of 0.3 mM or more (up to 10 mM) significantly augmented FluoZin-3 fluorescence, indicating an increase in intracellular Zn2+ concentration. It was also the case under external Zn2+-free condition, suggesting nitroprusside-induced release of intracellular Zn2+. However, nitroprusside at 10 mM did not affect cell lethality and cellular thiol content. Thus, it can be concluded that nitroprusside-induced increase in intracellular Zn2+ concentration is not related to its cytotoxicity

ZnCl2 and vitamin C, known as antioxidants, differently potentiate the cytotoxicity of H2O2 in rat thymocytes : Cytometric analysis using forward and side scatters

The ‘antioxidant hypothesis’ proposes that antioxidant nutrients afford protection against chronic diseases by decreasing oxidative damages. The ability of zinc to retard oxidative processes has been recognized for many years. However, the application of ZnCl2 potentiates the cytotoxicity of H2O2. Thus, some antioxidants may be cytotoxic under certain oxidative conditions. Therefore, in this study, the effect of vitamin C, one of antioxidant nutrients, on the cells treated with H2O2 has been examined to see if vitamin C potentiates the cytotoxicity of H2O2. Experiments were carried out with flow cytometer and rat thymocytes. Vitamin C also potentiated the cytotoxicity of H2O2. The increase in cell lethality induced by the combination of H2O2 and ZnCl2 was associated with the increase in population of shrunken cells with increased intensity of side scatter. However, it was not the case for the combination of H2O2 and vitamin C. The profile of cytotoxicity induced by H2O2 and vitamin C was different from that by H2O2 and ZnCl2. It may be suggested that the effects of zinc and vitamin C varies from cytoprotective to cytotoxic, being dependent on the type of oxidative stress

Tetracaine decreases intracellular Zn2+ concentration by inhibiting Zn2+ influx in rat thymocytes

In this study to examine the cytotoxic property of tetracaine, we cytometrically examined the effect of tetracaine on intracellular Zn2+ concentration by the use of FluoZin-3, a fluorescent indicator of intracellular Zn2+. Lidocaine was used as a reference drug. The incubation of rat thymocytes with tetracaine decreased the intensity of FluoZin-3 fluorescence while that with lidocaine increased the intensity. The incubation with 10 μM DTPA, a chelator for extracellular Zn2+, attenuated the tetracaine-induced decrease in fluorescence intensity. The application of ZnCl2 augmented FluoZin-3 fluorescence. The augmentation by ZnCl2 was a temperature-sensitive. Tetracaine attenuated the ZnCl2-induced augmentation of FluoZin-3 fluorescence. Taken together, the results suggest that tetracaine attenuates membrane Zn2+ influx, resulting in a decrease in intracellular Zn2+ concentration in rat thymocytes. Although the cells in this study are not targets for actions of local anesthetics, the result may give one clue to explain the difference between the cytotoxicity of local anesthetics since the action of tetracaine on FluoZin-3 fluorescence was opposite to that of lidocaine

Effects of Zn2+ chelators, DTPA and TPEN, and ZnCl2 on the cells treated with hydrogen peroxide: a flow-cytometric study using rat thymocytes

Recently, we have revealed that trace Zn2+ partly attenuates Ca2+-dependent cell death induced by A23187, a calcium ionophore, in rat thymocytes. In this study, to see if Zn2+ attenuates the H2O2-induced cell death that is also Ca2+-dependent, the effects of ZnCl2 and chelators for Zn2+ have been examined by using a flowcytometer with propidium iodide. The incubation with H2O2 increased the cell lethality. Simultaneous application of ZnCl2 greatly augmented the H2O2-induced increase in lethality. DTPA, a chelator for extracellular Zn2+, did not affect the increase in cell lethality by H2O2. However, the H2O2-induced increase in cell lethality was greatly attenuated by TPEN, a chelator for extracellular and intracellular Zn2+. Taken together, it may be likely that intracellular Zn2+ modifies the H2O2-induced cytotoxicity. However, it cannot be ruled out the possibility that TPEN chelates intracellular Fe2+, resulting in inhibiting the formation of hydroxyl radical from H2O2 that leads to an attenuation of H2O2 cytotoxicity

NOR-3, a donor of nitric oxide, increases intracellular Zn²⁺ concentration and decreases cellular thiol content: A model experiment using rat thymocytes, FluoZin-3, and 5-chloromethylfluorescein

Our previous study showed that nitroprusside, a donor of nitric oxide (NO), increased intracellular Zn2+ concentration without affecting cellular content of glutathione (GSH) although it has been proposed that the cytotoxicity of NO is resulted from its interaction with glutathione and zinc. Nitroprusside releases not only NO but also cyanides (Fe(II)CN and Fe(III)CN), CN-, Fe2+, and Fe3+. Therefore, such decomposition products may mask NO-induced action on cellular GSH content. In this study, we used NOR-3 as a donor of NO to reveal the effects of NO on intracellular Zn2+ concentration and cellular GSH content in a cytometric manner with fluorescent probes, FluoZin-3-AM and 5-chloromethylfluorescein diacetate. NOR-3 at 1-3 mM significantly increased intracellular Zn2+ concentration and decreased cellular GSH content. After the removal of extracellular Zn2+ by diethylenetriamine-N,N,N',N",N"-pentaacetic acid (DTPA, a chelator for Zn2+), the increase in intracellular Zn2+ concentration by NOR-3 was still observed although DTPA significantly attenuated the increase in intracellular Zn2+ concentration by NOR-3. Results suggest an involvement of both intracellular Zn2+ release and increase in membrane Zn2+ permeability. It is likely that NO induces oxidative stress, leading to an increase in intracellular Zn2+ concentration

Impaired extinction of cued fear memory and abnormal dendritic morphology in the prelimbic and infralimbic cortices in VPAC2 receptor (VIPR2)-deficient mice.

The structurally related neuropeptides vasoactive intestinal peptide (VIP) and pituitary adenylate cyclase-activating polypeptide (PACAP) have been implicated in stress regulation and learning and memory. Several bodies of research have shown the impact of the PACAP specific receptor PAC1 on fear memory, but the roles of other PACAP receptors in regulating fear stress responses remain to be elucidated. Here we aimed to investigate the effects of genetic deletion of VIPR2 encoding the VPAC2 receptor, which binds both VIP and PACAP, on fear-related memory and on dendritic morphology in the brain regions of the fear circuitry. Male VPAC2 receptor knockout (VPAC2-KO) and littermate wild-type control mice were subjected to Pavlovian fear conditioning paradigm. VPAC2-KO mice displayed normal acquisition of fear conditioning, contextual and cued fear memory, but impaired extinction of cued fear memory. Morphological analyses revealed reductions in cell body size and total branch number and length of apical and basal dendrites of prelimbic cortex neurons in VPAC2-KO mice. In addition, Sholl analysis indicated that the amount of dendritic material distal to the soma was decreased, while proximal dendritic material was increased. In the infralimbic cortex, the amount of apical dendritic material proximal to the soma was increased in VPAC2-KO mice, while other indices of morphology did not differ. Finally, there were no differences in dendritic morphology in basolateral amygdala neurons between genotypes. These findings suggest that the VPAC2 receptor plays an important role in the fear extinction processes and the regulation of the dendritic morphology in the prelimbic and infralimbic cortices

Impaired extinction of cued fear memory and abnormal dendritic morphology in the prelimbic and infralimbic cortices in VPAC2 receptor (VIPR2)-deficient mice.

The structurally related neuropeptides vasoactive intestinal peptide (VIP) and pituitary adenylate cyclase-activating polypeptide (PACAP) have been implicated in stress regulation and learning and memory. Several bodies of research have shown the impact of the PACAP specific receptor PAC1 on fear memory, but the roles of other PACAP receptors in regulating fear stress responses remain to be elucidated. Here we aimed to investigate the effects of genetic deletion of VIPR2 encoding the VPAC2 receptor, which binds both VIP and PACAP, on fear-related memory and on dendritic morphology in the brain regions of the fear circuitry. Male VPAC2 receptor knockout (VPAC2-KO) and littermate wild-type control mice were subjected to Pavlovian fear conditioning paradigm. VPAC2-KO mice displayed normal acquisition of fear conditioning, contextual and cued fear memory, but impaired extinction of cued fear memory. Morphological analyses revealed reductions in cell body size and total branch number and length of apical and basal dendrites of prelimbic cortex neurons in VPAC2-KO mice. In addition, Sholl analysis indicated that the amount of dendritic material distal to the soma was decreased, while proximal dendritic material was increased. In the infralimbic cortex, the amount of apical dendritic material proximal to the soma was increased in VPAC2-KO mice, while other indices of morphology did not differ. Finally, there were no differences in dendritic morphology in basolateral amygdala neurons between genotypes. These findings suggest that the VPAC2 receptor plays an important role in the fear extinction processes and the regulation of the dendritic morphology in the prelimbic and infralimbic cortices