gamma-Hydroxybutyric acid and 5-fluorouracil, metabolites of UFT, inhibit the angiogenesis induced by vascular endothelial growth factor

UFT, a drug composed of uracil and tegafur at the molar ratio of 4:1, is an orally active agent for the treatment of a wide variety of malignant tumours. Using a murine dorsal air sac (DAS) assay, we have previously shown that UFT and its metabolites, gamma-hydroxybutyric acid (GHB) and 5-fluorouracil (5-FU), inhibited the angiogenesis induced by murine renal cell carcinoma. Here we report that UFT was more effective than other fluorinated pyrimidines such as 5-FU and doxifluridine (5'-DFUR) in blocking the angiogenic responses elicited by five human cancer cell lines which produced high levels of vascular endothelial growth factor (VEGF), but no detectable fibroblast growth factor-2 (FGF-2) in vitro. In contrast, UFT was unable to block the angiogenic response to one human gastric cancer cell line which produced both VEGF and FGF-2 in vitro. However, the production or secretion of VEGF by these cells was unaffected by GHB and 5-FU treatment. Interestingly, GHB suppressed the chemotactic migration and tube formation of human umbilical vein endothelial cells (HUVECs) stimulated by VEGF, without inhibiting their DNA synthesis. Since GHB did not affect the FGF-2-driven activities in HUVECs, its action appears to be VEGF-selective. On the other hand, 5-FU inhibited DNA synthesis and migration of HUVECs stimulated by both VEGF and FGF-2, and tube formation driven by VEGF, suggesting that 5-FU is cytotoxic to endothelial cells. The inhibitory effects of 5-FU, and especially those GHB, were reproduced under in vivo condition using the DAS assay. The VEGF-mediated angiogenesis was significantly inhibited by UFT, 5-FU, and especially by GHB. We propose that the selective inhibitory effects of GHB on VEGF-mediated responses of endothelial cells are involved in the anti-angiogenic activity of UFT.

Tri-n-butyltin delays the cell death induced by hydrogen peroxide in rat thymocytes

Tri-n-butyltin (TBT), one of environmental pollutants accumulated in mollusks, at nanomolar concentrations decreases cellular content of glutathione (GSH), suggesting that TBT increases cell vulnerability to oxidative stress because GSH has a role in catabolizing hydrogen peroxide (H(2)O(2)). In order to examine this possibility, the effect of tri-n-butyltin chloride (TBTCl) on rat thymocytes suffering from oxidative stress induced by H(2)O(2) was examined using a flow cytometer with four fluorescent probes; ethidium bromide, 2',7'-dichlorofluorescin diacetate, 5-chloromethylfluorescein diacetate and annexin-V-FITC. TBTCl at concentrations ranging from 100 nM to 1 μM attenuated H(2)O(2)-induced decrease in cell viability in a dose-dependent manner. It was unlikely that TBTCl reduced H(2)O(2)-induced oxidative stress because TBTCl failed to affect H(2)O(2)-induced oxidation of intracellular molecule (2',7'-dichlorofluorescin) and H(2)O(2)-induced decrease in cellular content of GSH. Results suggest that TBTCl may inhibit the pathway of cell death induced by H(2)O(2) or that TBTCl may induce a protective substance against the oxidative stress produced by H(2)O(2).

Tri-n-butyltin-induced change in cellular level of glutathione in rat thymocytes: a flow cytometric study

Since some of organotins, accumulated in edible mollusks of aquatic environments, exert a variety of toxic actions on experimental animals, it causes concern for the health of humans. We examined the effects of tri-n-butyltin chloride (TBT) and other organotins (triethyltin chloride, trimethyltin chloride, triphenyltin chloride and tetrabutyltin) on cellular content of glutathione (GSH) in rat thymocytes using a flow cytometer to further characterize the toxicity of TBT. When the cells were incubated with TBT at concentrations of 3 nM or more for 15 min, the cellular content of GSH dose-dependently decreased. However, it completely or partly recovered until 180 min even in the continued presence of TBT. This recovery was temperature-sensitive, suggesting an involvement of metabolic process. The efficacy of TBT to decrease the cellular content of GSH was greater than those of other organotins. Results suggest that TBT and some organotins at environmentally relevant (nanomolar) concentrations significantly reduce the cellular content of GSH, suggesting that they increase the vulnerability to some biological and chemical insults.

UFT and its metabolites inhibit cancer-induced angiogenesis. Via a VEGF-related pathway

Treatment with UFT for spontaneous lung metastasis of murine renal carcinoma (RENCA) after resection of the primary tumor has resulted in significant prolongation of the life span of tumor-bearing animals. UFT inhibited the growth of metastatic nodules in the lung, apparently via decreased density of microvessels in the metastatic foci. Subsequent experiments used dorsal air sac assay to directly trace newly forming microvessels. UFT abrogated the process of angiogenesis, induced by the RENCA cells, in a dose-dependent manner. The inhibitory effect appeared to originate from tegafur, a component of UFT, and from its known metabolites: fluorouracil (5-FU), gamma-hydroxybutyric acid (GHB), and gamma-butyrolactone (GBL). The inhibition of angiogenesis by UFT appeared to be a common phenomenon, also observed in other human cancer cell lines characterized by an excessive production of vascular endothelial growth factor (VEGF)--such as gastric, lung, and colon cancers. In vitro analysis revealed that 5-FU and gamma-hydroxybutyric acid regulated VEGF-dependent responses of human umbilical vein endothelial cells. Dorsal air sac assay revealed that UFT, 5-FU, and gamma-hydroxybutyric acid strongly inhibited the angiogenesis induced by recombinant human VEGF. These data suggest that the antiangiogenic activity of UFT is at least partially associated with an ability of the metabolites of UFT to interfere with VEGF-dependent responses of vascular endothelial cells.

Modulation of tumor cell motility by plasmin

Using a pure chemotactic model, we investigated the effect of plasmin on tumor cell motility. In the presence of various extracellular matrix proteins, plasmin facilitated motility of human melanoma LOX and lung cancer Lu-99 cells. Laminin contributed most to the action of plasmin. The cell motility induced by plasmin and laminin was chemokinetic in nature and was almost completely suppressed by alpha2-antiplasmin. To further characterize the action of plasmin, various signal transduction kinase inhibitors were tried out. The results suggested that plasmin may modulate cell motility through protein kinase C and mitogen-activated protein kinase cascades in cooperation with laminin.

[Anti-angiogenic activities of UFT and its metabolites, GHB and GBL, in the dorsal air sac (DAS) model in mice]

We investigated the effects of UFT and its metabolites, GHB and GBL, on angiogenesis induced by tumor cells in a dorsal air sac (DAS) assay in mice. Five tumor cell lines (murine renal carcinoma; RENCA, human gastric cancer; 4-1ST, human small-cell lung carcinoma; LX-1, and human colon carcinoma; DLD-1, KM-20C) were used in the DAS assay. In this model, UFT demonstrated a significant anti-angiogenic activity in a dose-dependent manner while 5-FU (19 mg/kg/day) and 5'-DFUR (200 mg/kg/day) were less effective. Moreover, tegafur (FT), a component of UFT, and gamma-hydroxybutyric acid (GHB) and gamma-butyrolactone (GBL), in vivo metabolites of UFT, inhibited angiogenesis induced by RENCA cells. The inhibitory effects of 5-FU, GHB, and GBL on angiogenesis were increased with administration by continuous infusion, providing a suitable pharmacokinetic profile. These results suggest that GHB and GBL are involved in the expression of anti-angiogenic activity of UFT.

Exposure of rat thymocytes to hydrogen peroxide increases annexin V binding to membranes: inhibitory actions of deferoxamine and quercetin

Effects of hydrogen peroxide (H(2)O(2)) on rat thymocytes were examined, using a flow cytometer and three fluorescent probes, annexin V-fluorescein isothiocyanate (annexin V-FITC) for detecting phosphatidylserine expressed on the membrane surface, ethidium bromide for estimating dead cells, and fluo-3-acetoxymethyl ester (fluo-3-AM) for monitoring changes in intracellular Ca(2+) concentration ([Ca(2+)](i)), to characterize H(2)O(2)-induced cytotoxicity. Exposure to H(2)O(2) (30 microM or more) increased the number of annexin V-positive live cells dose- and time-dependently while the number of dead cells increased at concentrations of 1 mM or more. H(2)O(2) (30 microM or more) increased [Ca(2+)](i) in a dose-dependent manner. Threshold concentration of H(2)O(2) to increase [Ca(2+)](i) was similar to that to increase annexin V binding to membranes. The H(2)O(2)-induced change in cell membranes was attenuated under Ca(2+)-free conditions. Therefore, it is likely that Ca(2+) is involved in the H(2)O(2)-induced cytotoxicity. Deferoxamine was effective to protect the cells suffering from H(2)O(2)-induced oxidative stress, suggesting a contribution of hydroxyl radicals generated by the Fenton reaction. Quercetin also exerted a potent protective action on cells suffering from H(2)O(2)-induced oxidative stress. The results indicate that the exposure of rat thymocytes to H(2)O(2) at micromolar concentrations increases annexin V binding to cell membranes in a Ca(2+)-dependent manner, suggesting the possibility that the oxidative stress caused by H(2)O(2) (and/or hydroxyl radicals) induces apoptosis via increasing [Ca(2+)](i).

Flow cytometric analysis on tri-n-butyltin-induced increase in annexin V binding to membranes of rat thymocytes

Effects of tri-n-butyltin chloride (TBT) on rat thymocytes were examined by using a flow cytometer and three fluorescent dyes (annexin V-FITC, ethidium bromide and fluo-3-AM) to further characterize its cytotoxic action. TBT at concentrations of 100 nM or greater, time- and dose-dependently increased the population of annexin V-positive live cells in the cell suspension. Most of cells became to be annexin V-positive within 60 min after the start of application of 300 nM TBT. Some of annexin V-positive live cells were further stained with ethidium, indicating that some of the cells were killed, in continued presence of TBT at 300 nM or greater. When the cells were exposed to 300 nM TBT only for 15 min, the population of annexin V-positive live cells increased after removal of TBT from incubation medium. TBT-induced increase in the population of annexin V-positive live cells was partly attenuated under Ca(2+)-free condition, although that was not the case for the dead cells. TBT at 30 nM or greater increased [Ca(2+)]i in a dose-dependent manner. Triethyltin and trimethyltin even at 1 μM did not increase the [Ca(2+)]i and the population of annexin V-positive live cells. The population of annexin V-positive live cells increased as the [Ca(2+)]i was increased by ionomycin, a calcium ionophore. Results suggest an involvement of Ca(2+) in some of TBT-induced cytotoxicity.

UFT and its metabolites inhibit the angiogenesis induced by murine renal cell carcinoma, as determined by a dorsal air sac assay in mice

UFT, an anticancer agent that is composed of tegafur (FT) and uracil at a molar ratio of 1:4, is widely used in clinical practice in Japan to treat cancer patients requiring a long-term chemotherapy, and it is associated with few side effects, if any. In this study, we have evaluated the inhibitory effect of UFT against RENCA cell-induced angiogenesis by a dorsal air sac assay. Marked angiogenesis is induced by implantation of a chamber containing RENCA cells into mice. In this model, UFT showed a strong angiogenesis-inhibitory effect, whereas 5-fluorouracil (5-FU) and doxifluridine were less effective. Additional experiments revealed FT to be effective component of UFT; uracil remained ineffective in the inhibition of angiogenesis. Moreover, we have found that gamma-hydroxybutyric acid and gamma-butyrolactone, the metabolites of FT, possess a potent angiogenesis inhibitory effect that is amplified when the compounds are administered by a continuous infusion. This may reflect a transition in blood concentration of each metabolite resulting from the administration of UFT. Similar results were also obtained with respect to 5-FU. It was suggested that UFT has a stronger angiogenesis-inhibitory effect than did other fluorinated pyrimidines, partly due to its pharmacokinetic properties characterized by maintaining of higher and long-lasting blood levels of 5-FU and partly due the inhibitory effects derived from gamma-hydroxybutyric acid and gamma-butyrolactone, UFT-specific metabolites.

Methylmercury toxicity in dissociated rat brain neurons: modification by l-cysteine and trimethylbenzylmercaptan and comparison with dimethylmercury and N-ethylmaleimide

The effects of methylmercury (MeHg) on dissociated rat cerebellar neurons were compared with those of MeHg conjugated with l-cysteine (MeHg-Cys conjugate), dimethylmercury (DiMeHg), N-ethylmaleimide (NEM) and ionomycin using a flow cytometer and two fluorescent dyes, fluo-3-AM and ethidium bromide. The efficacies of MeHg to increase intracellular concentration of Ca(2+) ([Ca(2+)]i) and to decrease cell viability were greatly reduced by conjugating MeHg with l-cysteine. It was not due to a decreased lipophilic property of MeHg-Cys because the conjugation of MeHg with trimethylbenzylmercaptane, a lipophilic substance, also reduced the efficacies. It seems that the reactivity of MeHg to SH-groups is responsible for the MeHg-induced toxicity since NEM increased [Ca(2+)]i and decreased cell viability while DiMeHg did not significantly affect them. However, the toxicity of MeHg was not explained only by the reactivity of MeHg to SH-groups since NEM-induced changes in fluo-3 and ethidium fluorescence were different from MeHg-induced ones. Ionomycin-induced changes in those fluorescence were also different although ionomycin decreased cell viability after increasing [Ca(2+)]i. Therefore, it is suggested that the mechanism of MeHg toxicity is more complicated than those of NEM and ionomycin.

Effects of triphenyltin on growth and viability of K562 leukemia cells

The effects of triphenyltin on growth and viability of K562 human leukemia cells were examined using a flow cytometer with fluorescent dyes, ethidium bromide, fluo-3-AM, and propidium iodide. Triphenyltin at concentrations ranging from 30 nM to 1 μM inhibited the growth of K562 cells in a dose-dependent manner when the cells were incubated with triphenyltin at respective concentrations for 72 h. Triphenyltin at 100 nM slowed the rate of growth without affecting the viability. Triphenyltin at 300 nM or higher greatly decreased the viability of K562 cells. Triphenyltin at 300 nM increased the concentration of intracellular Ca(2+) and induced cell cycle arrest in G2/M phase and apoptosis in K562 cells. The concentration of triphenyltin inducing 50% inhibition of growth of K562 cells was lower than those of cisplatin, diphenyltin, monophenyltin, triethyltin and trimethyltin. However, tributyltin was equally toxic. Results suggest that there are several types of mechanisms for the inhibitory action of triphenyltin on the growth of K562 cells, being dependent on its concentration.

Protective actions of 5'-n-alkylated curcumins on living cells suffering from oxidative stress

To elucidate the roles of 5'-n-alkyl chains of curcumin derivatives in their protective actions on cells against oxidative stress, we compared the efficacy of curcumin and 5'-alkylated curcumins to inhibit the peroxidation of linoleic acid and to protect rat thymocytes suffering from H2O2-induced oxidative stress with their permeation into cells. The inhibitory action of 5'-n-alkylated curcumins on lipid peroxidation increased as the length of hydrocarbon chains of 5'-n-alkylated curcumins was prolonged. This potency order was not confirmed for the protective actions of 5'-n-alkylated curcumins on cells against oxidative stress. Among 5'-alkylated curcumins, the most potent protective action was observed for 5'-n-C3H7-curcumin because it had the greatest permeation into the cells. Further increases in the length of hydrocarbon chains (up to n-C19H39) of 5'-n-alkylated curcumins greatly attenuated their protective actions by reducing their permeation into the cells.

Cytotoxic actions of FTY720, a novel immunosuppressant, on thymocytes and brain neurons dissociated from the rat

Effects of FTY720 (2-amino-2-(2-[4-octylphenyl]ethyl)-1,3-propanediol HCl), a novel immunosuppressant, were examined on neurons and thymocytes respectively dissociated from rat brains and thymus glands using a flow cytometer to see if FTY720 exerts cytotoxic actions not only on spleen cells as previously reported but also on the other cells. FTY720 at a concentration of 10 microM deteriorated almost all of the thymocytes, while it was not the case for brain neurons. FTY720 increased the intracellular concentration of Ca2+ ([Ca2+]i) of thymocytes in both the presence and absence of external Ca2+, although the [Ca2+]i increased by FTY720 in the presence of external Ca2+ was much greater than that in the absence of external Ca2+. Thus, FTY720 may increase the membrane permeability of Ca2+ and release Ca2+ from intracellular Ca2+ stores in thymocytes. Furthermore, the number of thymocytes stained with ethidium, a dye impermeant to intact membranes, time-dependently increased after drug application. Therefore, FTY720 at concentrations of 3 - 10 microM non-specifically increases the membrane permeability of thymocytes, resulting in necrotic cell death, although FTY720 at micromolar concentrations was reported to induce apoptosis of spleen cells.

New curcuminoids isolated from Zingiber cassumunar protect cells suffering from oxidative stress: a flow-cytometric study using rat thymocytes and H2O2

Effects of new complex curcuminoids (cassumunin A and cassumunin B) isolated from tropical ginger, Zingiber cassumunar, were examined in dissociated rat thymocytes suffering from oxidative stress induced by 3 mM hydrogen peroxide by using a flow cytometer and ethidium bromide. The effects were compared with those of curcumin, a natural antioxidant, whose chemical structure is included in those of cassumunins A and B. Pretreatment of rat thymocytes with the respective cassumunins at concentrations ranging from 100 nM to 3 microM dose-dependently prevented the hydrogen peroxide (H2O2)-induced decrease in cell viability. It had the same action, although less effective, against the treatment with cassumunin A or B (3 microM) immediately after or 60 min after start of the oxidative stress. Respective potencies of cassumunins A and B in protecting the cells suffering from H2O2-induced oxidative stress were greater than that of curcumin. It is suggested that cassumunins A and B may possess a potent protective action on living cells suffering from oxidative stress.

Fluorescent estimation on cytotoxicity of methylmercury in dissociated rat cerebellar neurons: its comparison with ionomycin

To study the cellular basis of the neurotoxicity of methylmercury, the effects of methylmercury on dissociated rat cerebellar neurons were examined using a flow cytometer, a confocal laser microscope and three fluorescent dyes, fluo-3 for monitoring the changes in intracellular Ca(2+) concentration ([Ca(2+)](i)) and for detecting live neurons, ethidium for assessing the neurons that are dead or have compromised membranes, and 5-chloromethylfluorescein (CMF) for estimating the cellular content of nonprotein thiols. Methylmercury at concentrations of 1 μM or greater increased the [Ca(2+)](i) of almost all neurons. Prolonged exposure to methylmercury (3 and 10 μM) produced a further increase in [Ca(2+)](i), in association with compromising membranes in some neurons. Thereafter, methylmercury induced blebs on membranes of some neurons with increased [Ca(2+)](i). Methylmercury at concentrations of 0.3 μM or greater dose-dependently decreased the cellular content of nonprotein thiols. Results suggest that methylmercury may induce the loss of membrane integrity through destabilized Ca(2+) homeostasis and oxidative stress in mammalian brain neurons.

Flow-cytometric analysis on kainate-induced decrease in the cellular content of non-protein thiols in dissociated rat brain neurons

In order to study the kainate-induced oxidative stress on brain neurons, the effect of kainate on cellular content of glutathione in rat cerebellar neurons were examined using a flow cytometer and 5-chloromethylfluorescein, a fluorescent dye for cellular non-protein thiols (mainly glutathione). Kainate at concentrations ranging from 30 microM to 1 mM produced a dose-dependent decrease in cellular content of glutathione. Exposure of neurons to kainate at concentrations of 300 microM or greater seemed to deplete cellular glutathione. Potency of kainate in reducing cellular content of glutathione was greater than those of glutamate and N-methyl-D-aspartate (NMDA). Kainate-induced decrease in cellular content of glutathione was partly attenuated by 6-nitro-7-cyano-quinoxaline-2,3-dione, a blocker of non-NMDA receptors and removal of external Ca2+. Results indicate that kainate causes Ca2(+)-dependent oxidative stress that decreases the cellular content of glutathione via activation of non-NMDA type of glutamate receptors.

Oxidative stress-induced increase in intracellular Ca2+ and Ca(2+)-induced increase in oxidative stress: an experimental model using dissociated rat brain neurons

In order to study the oxidative stress-induced change in intracellular concentration of Ca2+ ([Ca2+]i) and Ca(2+)-induced oxidative stress, effects of hydrogen peroxide and ionomycin, a calcium ionophore, on rat cerebellar neurons were examined using a flow cytometer and fluorescent dyes: fluo-3 for monitoring [Ca2+]i; 2',7'-dichlorofluorescin, for reactive oxygen species; and 5-chloromethylfluorescein, for cellular nonprotein thiols. Oxidative stress induced by hydrogen peroxide dose-dependently increased [Ca2+]i and decreased the content of nonprotein thiols. Ionomycin increased oxidative metabolism and decreased the content of nonprotein thiols. Results suggest that oxidative stress induces an increase in [Ca2+]i while an increase in [Ca2+]i increases oxidative stress in neurons.

Fluorescent estimation of H2O2-induced changes in cell viability and cellular nonprotein thiol level of dissociated rat thymocytes

We have developed a procedure to simultaneously estimate cell viability and the cellular level of nonprotein thiol (presumably glutathione) using two fluorescent dyes, 5-chloromethylfluorescein (5CMF) and ethidium, and rat thymocytes. Diethylmaleate and N-ethylmaleimide reduced, respectively, the intensity of 5CMF fluorescence to 0.23 and 0.1, relative to the control. Incubation with buthionine sulfoximine, an inhibitor of glutathione synthesis, decreased the intensity of 5CMF fluorescence to 0.61. Results indicate that 5CMF fluorescence can be attenuated by agents that decrease the level of cellular nonprotein thiols, suggesting that 5CMF fluorescence is utilized for estimating the level of cellular glutathione. Hydrogen peroxide (10 microM to 3 mM) reduced the intensity of 5CMF fluorescence in a dose-dependent manner and increased the number of thymocytes stained with ethidium (presumably dead cells or cells with compromised membranes) at concentrations of 300 microM or greater. Reduction of cellular glutathione level seems to precede cell death in which oxidative stress is involved.

Flow cytometric analysis of the H2O2-induced increase in intracellular Ca2+ concentration of rat thymocytes

The effect of hydrogen peroxide (H2O2) on the intracellular Ca2+ concentration ([Ca2+]i) of rat thymocytes was examined by a flow cytometer and two fluorescent dyes, fluo-3-AM and ethidium bromide, a dye impermeant to intact membranes, to characterize the H2O2-induced increase in [Ca2+]i. H2O2 at concentrations greater than 30 microM dose-dependently increased the [Ca2+]i of thymocytes which were not stained with ethidium. Removal of external Ca2+ greatly reduced the degree of H2O2-induced increase in [Ca2+]i. However, H2O2 still increased the [Ca2+]i under the external Ca(2+)-free condition. Diethylmaleate, which is known to produce a chemical depletion of cellular nonprotein thiol, significantly increased the [Ca2+]i. Dithiothreitol, which is used to protect cellular nonprotein thiol, slightly decreased the [Ca2+]i, but greatly reduced the H2O2-induced increase in [Ca2+]i. Therefore, it is considered that H2O2 may increase the [Ca2+]i through a mechanism related to the effects of H2O2 on the cellular nonprotein thiol.

Flow-cytometric estimation on glutamate- and kainate-induced increases in intracellular Ca2+ of brain neurons: a technical aspect

Effects of glutamate and kainate on the intracellular Ca2+ concentration ([Ca2+]i) in a large population (several thousand) of dissociated cerebellar granule cell neurons were evaluated using a flow-cytometer and a combination of two fluorescent dyes, fluo-3-AM for estimating [Ca2+]i and ethidium bromide for removing neurons that had compromised membranes from the cell population examined. The number of neurons responding to glutamate or kainate in augmenting the fluo-3 fluorescence increased in a dose-dependent manner. The number of neurons responding to kainate was much greater than that to glutamate. CNQX, a blocker of non-NMDA receptors, completely blocked the response elicited by kainate while the complete blockade of this glutamate-induced response was made by a combination of MK-801, a NMDA receptor blocker, and CNQX. Nicardipine, a calcium antagonist, decreased the number of neurons responding to glutamate and kainate, suggesting involvement of voltage-dependent calcium channels. These results indicate that the flow-cytometric measurement of glutamate and kainate responses has the potential to provide answers to such questions as what percentage of the population of neurons respond to these amino acids and what is the resulting distribution of [Ca2+]i.

Ginkgo biloba extract protects brain neurons against oxidative stress induced by hydrogen peroxide

Effect of Ginkgo biloba extract was examined on dissociated rat cerebellar neurons suffering from oxidative stress induced by hydrogen peroxide using a flow cytometer and ethidium bromide. Hydrogen peroxide at a concentration of 3 mM increased the number of neurons stained with ethidium (presumably dead neurons) in a time-dependent manner. Pretreatment of neurons with G. biloba extract (10 micrograms/ml) greatly delayed a time-dependent increase in number of dead neurons during exposure to hydrogen peroxide. It was true, but less effective, in the case of treatment with G. biloba extract immediately or 60 min after start of oxidative stress. Results implicate G. biloba extract as a potential agent in protecting the neurons suffering from oxidative stress induced by hydrogen peroxide.

Change in membrane permeability induced by amyloid beta-protein fragment 25-35 in brain neurons dissociated from rats

Effects of amyloid beta-protein fragment 25-35, A beta P(25-35), on the membrane permeability of organic molecules were examined in the brain neurons dissociated from rats by using an argon laser (equipped in flow cytometer and laser microscope) and a combination of two fluorescent dyes, fluo-3-AM and ethidium bromide. A beta P(25-35) at concentrations of 1 microM or greater induced both leakage of fluo-3 from the neurons and permeation of ethidium across the membrane in a dose-dependent manner, although both dyes are highly impermeant to the intact plasma membrane. Thus, A beta P(25-35) seems to increase not only membrane permeability of inorganic ions such as Ca2+, Na+ and K+, as previously suggested, but also that of organic molecules. Therefore, the brain neuron membrane is suggested to lose its integrity in the presence of A beta P(25-35) that leads to neuronal death.

Attenuation of Ca(2+)-induced increase in oxidative metabolism by cooling and calmodulin antagonist in mammalian brain neurons: a flow-cytometric study

Effects of cooling and calmodulin antagonist on ionomycin-induced increase in oxidative metabolism (or formation of reactive oxygen species) of rat cerebellar neurons was examined using a flow cytometer and 2',7'-dichlorofluorescin diacetate, a fluorescent dye for intracellular hydrogen peroxide. Cooling neurons to temperatures below 16 degrees C greatly attenuated ionomycin-induced augmentation of oxidative metabolism without affecting the Ca2+ influx produced by ionomycin. Rewarming neurons to 36 degrees C in presence of ionomycin increased the oxidative metabolism, indicating a temperature-sensitive metabolic process. Substitution of Ca2+ with Ba2+ or Sr2+ completely abolished an ionomycin-induced increase in the oxidative metabolism. Pretreatment with W-7, a calmodulin antagonist, at concentrations of 10 microM or higher (up to 100 microM) produced a dose-dependent attenuation of ionomycin-induced increase in oxidative metabolism. Results suggest that calmodulin is involved in the ionomycin-induced increase in oxidative metabolism of dissociated cerebellar neurons.

Flow cytometric analysis on cytotoxic action of amyloid beta protein fragment 25-35 on brain neurons dissociated from the rats

Effects of amyloid beta protein fragment 25-35, A beta P(25-35), on membrane permeability and cell viability were examined in the brain neurons dissociated from the rats using a flow cytometer and two fluorescent dyes, fluo-3 to monitor intracellular Ca2+ concentration ([Ca2+]i) of neurons and ethidium which is impermeant to membranes of intact neurons to stain dead and dying neurons. A beta P(25-35) augmented fluo-3 fluorescence of some neurons at concentrations greater than 1 microM, indicating an increase in [Ca2+]i although other neurons (about 80% of total neurons) did not respond to A beta P(25-35) even at 10 microM. A beta P(25-35) at 1 microM or greater increased dose-dependently the number of ethidium-stained neurons, suggesting a dose-dependent increase in number of dead and dying neurons. Results suggest that A beta P(25-35) increases the membrane permeability of brain neurons, resulting in a destabilized intracellular homeostasis that leads to neuonal death.

Methylmercury-induced augmentation of oxidative metabolism in cerebellar neurons dissociated from the rats: its dependence on intracellular Ca2+

Effect of methylmercury chloride on oxidative metabolism of cerebellar neurons dissociated from the rats was examined using 2',7'-dichlorofluorescin (DCFH) which is oxidized by cellular hydrogen peroxide to be a fluorescent compound (DCF) and fluo-3, an indicator for intracellular Ca2+ concentration ([Ca2+]i). Methylmercury at 1 microM or less did not affect DCF fluorescence of cerebellar neurons. Further increase in concentration of methylmercury (up to 30 microM) induced changes in DCF fluorescence. Thus, DCF fluorescence was slightly attenuated during 5 min after applying methylmercury to the neurons, indicating a decrease in oxidation of DCFH. Thereafter, DCF fluorescence was time-dependently augmented in continued presence of methylmercury, indicating an increase in DCFH oxidation. Although methylmercury-induced augmentation of DCF fluorescence was greatly suppressed under external Ca(2+)-free condition, it was not the case for methylmercury-induced attenuation of DCF fluorescence. Methylmercury at 3 microM or more dose-dependently increased the [Ca2+]i. Results suggest that methylmercury increases intracellular Ca2+ in cerebellar neurons, resulting in an increase in formation of reactive oxygen species that may contribute to cell injury.

Effect of N,N-diethyldithiocarbamate on ionomycin-induced increase in oxidation of cellular 2',7'-dichlorofluorescin in dissociated cerebellar neurons

Effect of N,N-diethyldithiocarbamate (DDC), an inhibitor for cytosolic superoxide dismutase, on an ionomycin-induced increase in oxidative metabolism was examined in cerebellar neurons dissociated from the rats, using a flow cytometer and 2',7'-dichlorofluorescin diacetate and fluo-3-AM, fluorescent dyes for intracellular hydrogen peroxide and Ca2+, respectively. DDC reduced the ionomycin-induced augmentation of 2',7'-dichlorofluorescin fluorescence in a dose-dependent manner. DDC did not affect cellular content of 2',7'-dichlorofluorescin and ionomycin-induced increase in intracellular Ca2+ concentration. Results indicate that ionomycin increases the formation of superoxide anion in brain neuron.

Effect of tri-n-butyltin on intracellular Ca2+ concentration of mouse thymocytes under Ca(2+)-free condition

Effect of tri-n-butyltin at concentrations ranging from 100 nM to 1 microM on the intracellular Ca2+ concentration of mouse thymocytes was examined under Ca(2+)-free conditions in comparison with those of 50 nM A23187, 100 nM thapsigargin and 10 microM cyclopiazonic acid, using the fluorescent dye for intracellular Ca2+, fluo-3. Tri-n-butyltin persistently increased the intensity of fluo-3 fluorescence while A23187, thapsigargin and cyclopiazonic acid produced a transient augmentation of the fluorescence. Pretreatment with A23187 greatly decreased the fluorescence responses induced by 1 microM tri-n-butyltin. However, the effect of thapsigargin and cyclopiazonic acid on the tri-n-butyltin-induced response was much weaker than that of A23187. In the presence of tri-n-butyltin, the transient response produced by A23187 was greatly prolonged. Results may suggest that tri-n-butyltin increases the membrane Ca2+ permeability of the intracellular organelles (cellular calcium stores) and decreases the Ca2+ pump activity of thymocyte membrane, resulting in a sustained increase in the intracellular Ca2+ concentration under Ca(2+)-free concentration.

Fluorescent estimation on the effect of Ca2+ antagonists on the oxidative metabolism in dissociated mammalian brain neurons

Effect of organic Ca2+ antagonists on the oxidative metabolism or the formation of reactive oxygen species was estimated on dissociated mammalian neurons using a flow cytometer and 2',7'-dichlorofluorescin which is oxidized to be fluorescent by cellular oxidants. Of the organic Ca2+ antagonists used, flunarizine and nifedipine decreased the intensity of fluorescence at 1 microM or more while it was not the case for verapamil and diltiazem, suggesting one of the favourable actions of flunarizine and nifedipine on ischemic brain damage.

Flow cytometric estimation of the effect of Ginkgo biloba extract on the content of hydrogen peroxide in dissociated mammalian brain neurons

The effect of Ginkgo biloba extract (GBE) on the content of hydrogen peroxide was estimated in cerebellar neurons dissociated from rats, by means of a flow-cytometer and 2',7'-dichlorofluorescein (DCF) diacetate, a fluorescent dye for intracellular hydrogen peroxide. The GBE started to reduce the DCF fluorescence of the neuron at 0.1 microgram/ml to 0.3 microgram/ml. Further increases in the GBE concentration (up to 3 micrograms/ml) produced a dose-dependent decrease in the DCF fluorescence, suggesting that GBE reduces the content of hydrogen peroxide or suppresses the reactive oxygen species (ROS) formation of cerebellar neurons. The present technique may be useful for preliminary evaluations of agents affecting the ROS formation in mammalian brain neurons.

Characterization of the triphenyltin-induced increase in intracellular Ca2+ of mouse thymocytes: comparison with the action of A23187

The properties of triphenyltin (TPT) in increasing intracellular Ca2+ ([Ca2+]i) of thymocytes was studied, in comparison with those of A23187, by the use of fluorescent dyes to monitor membrane potential and [Ca2+]i. Both 1 microM TPT and 30 nM A23187 increased the [Ca2+]i associated with the hyperpolarization mediated by Ca(2+)-dependent K+ conductance. The time course for the TPT-induced increase in the [Ca2+]i was much slower than that of A23187. When the external Ca2+ ([Ca2+]o) was removed, TPT produced a slight, but persistent, increase in the [Ca2+]i while A23187 caused only a transient increase in the [Ca2+]i. Reintroduction of Ca2+ to the external solution produced an increase in [Ca2+]i in both cases. Therefore, these results suggested that the increase in the [Ca2+]i of thymocytes induced by TPT and A23187 was dependent on the presence of [Ca2+]o and an intracellular Ca store. The potency of TPT in increasing the [Ca2+]i was greater than those of diphenyltin and monophenyltin, suggesting an involvement of the lipophilic property of organotins in increasing [Ca2+]i. The TPT-induced increase in the [Ca2+]i may be partly responsible for the toxicity of TPT on organs and/or organ systems.

Tri-n-butyltin increases intracellular Ca2+ in mouse thymocytes: a flow-cytometric study using fluorescent dyes for membrane potential and intracellular Ca2+

Effects of tri-n-butyltin (TBT) on mouse thymocytes were examined using a flow-cytometer and fluorescent dyes for membrane potential and intracellular Ca2+ ([Ca2+]i). TBT at concentrations from 1 x 10(-7) M to 3 x 10(-7) M caused hyperpolarization in thymocytes during 30 min. after drug application in a time- and dose-dependent manner. Further increase in TBT concentration (to 1 x 10(-6) M) made hyperpolarization of thymocytes more profound within 5 min. after application, thereafter gradually depolarized them during the next 25 min. TBT at 3 x 10(-8) M or more (up to 1 x 10(-6) M) increased the [Ca2+]i of thymocytes. After reaching maximum [Ca2+]i at the various TBT concentrations used within 5 min. after drug application, the [Ca2+]i slightly decreased in a time-dependent manner. Effects of TBT on membrane potential and the [Ca2+]i were greatly reduced under nominal external Ca(2+)-free condition. Results suggest that TBT can promote Ca(2+)-influx to thymocytes, resulting in hyperpolarization by activation of Ca(2+)-dependent K+ current. The increase in [Ca2+]i by TBT may be related to its cytotoxic action on thymocytes.

Triphenyltin-induced increase in the intracellular Ca2+ of dissociated mammalian CNS neuron: its independence from voltage-dependent Ca2+ channels

To test the possibility that triphenyltin (TPT) increases the intracellular Ca2+ ([Ca2+]i) in neurons as found previously in thymocytes, the effect of TPT on [Ca2+]i was examined in rat cerebellar neurons by a flow-cytometer with fluorescent dyes. TPT at concentrations ranging from 3 x 10(-7) M to 1 x 10(-5) M dose-dependently increased the [Ca2+]i. The TPT-induced increase in [Ca2+]i was not attenuated by a Ca2+ channel blocker, suggesting that it was not dependent on voltage-dependent Ca2+ channels. As the concentration of external Ca2+ ([Ca2+]e) increased, TPT produced a more profound increase in the [Ca2+]i. However, the increase in the [Ca2+]i by TPT was observed even in nominally [Ca2+]e-free solution. These results suggest two possibilities. First, TPT may promote Ca(2+)-influx to the neuron. Secondly, TPT may affect the intracellular Ca-store sites. This study is relevant to the neurotoxicity of organotins because it has become progressively clear that sustained increases in the [Ca2+]i can activate various Ca(2+)-dependent degradative processes.