Enrichment with a polyunsaturated fatty acid enhances the survival of Saccharomyces cerevisiae in the presence of tributyltin

The toxicity of inorganic metal species towards Saccharomyces cerevisiae has been shown to be markedly dependent on cellular fatty acid composition. In this investigation, the influence of fatty acid supplementation on the toxicity of the lipophilic organometal, tributyltin was investigated. Growth of S. cerevisiae was increasingly inhibited when the tributyltin concentration was increased from 0 to 10 microM. However, the inhibitory effect was partly alleviated by supplementation of the medium with 1 mM linoleate (18:2), a treatment that leads to large-scale incorporation of this polyunsaturated fatty acid (to > 60% of total fatty acids) in yeast membrane lipids. Cells that were previously enriched with 18:2 also showed reduced loss of vitality compared to cells grown in the absence of a fatty acid supplement, when exposed to tributyltin. For example, addition of tributyltin to a concentration of 0.1 microM was associated with an approximate 10% reduction in the H+ efflux activity of 18:2-enriched cells, but a 70% reduction in that of fatty acid-unsupplemented cells. Despite the increased tributyltin resistance of 18:2-enriched S. cerevisiae, the level of cell-associated tributyltin was found to be approximately two-fold higher in these organisms than in fatty acid-unsupplemented cells. These results demonstrate an increased resistance of 18:2-enriched membranes to the direct toxic action(s) of tributyltin. This is in contrast to the previously reported effect of 18:2 enrichment on sensitivity of S. cerevisiae to inorganic metal cations.

Cytochrome c release and caspase activation in hydrogen peroxide- and tributyltin-induced apoptosis

The ability of H2O2 and tributyltin (TBT) to trigger pro-caspase activation via export of cytochrome c from mitochondria to the cytoplasm was investigated. Treatment of Jurkat T lymphocytes with H2O2 resulted in the appearance of cytochrome c in the cytosol within 2 h. This was at least 1 h before caspase activation was observed. TBT caused cytochrome c release already after 5 min, followed by caspase activation within 1 h. Measurement of mitochondrial membrane potential (delta psi(m)) showed that both H2O2 and TBT dissipated delta psi(m), but with different time courses. TBT caused a concomitant loss of delta psi(m) and release of cytochrome c, whereas cytochrome c release and caspase activation preceded any apparent delta psi(m) loss in H2O2-treated cells. Thus, our results suggest that different mechanisms are involved in triggering cytochrome c release with these apoptosis-inducing agents.

Cell volume regulation in proximal renal tubules from trout (Salmo trutta)

Regulatory volume decrease (RVD) following hypo-osmotic stimulation was studied using videometric methods in isolated proximal renal tubules from trout (Salmo trutta). The relative tubule diameter increased by 132.0+/-4.8 % (maximum swelling within 1 min at 15 and 25 degrees C and within 4 min at 10 degrees C) following a change from iso-osmotic (290 mosmol kg-1) to hypo-osmotic (160 mosmol kg-1) Ringer's solution. The tubule diameter subsequently decreased to approximately one-quarter of the maximal value. Ouabain (1 mmol l-1) reduced cell swelling and inhibited the RVD response by 28.0+/-10.5 %. Furthermore, increasing the bath K+ concentration by 30 mmol l-1 inhibited RVD by 76.5+/-3.6 %. The K+ channel blocker quinine, but not Ba2+ (1 and 2 mmol l-1), significantly decreased the RVD response (by 25.0+/-5.4 and 72.3+/-5.1 % at 0.1 and 0.5 mmol l-1, respectively). Similarly, increasing the Cl- concentration in the bath from 47 to 102 mmol l-1 induced a significant reduction (45. 2+/-7.9 %) in RVD. The RVD response was also markedly reduced (by 54. 7+/-5.3 %) by the Cl- channel blocker indacrinone (MK-196; 0.5 mmol l-1), but only marginally by 5-nitro-2-(3-phenylpropylamino)benzoic acid (NPPB; 1, 5, 8 and 10 micromol l-1). Addition of the K+/Cl- symport inhibitor furosemide (0.1 mmol l-1) resulted in a 39.8+/-3.9 % inhibition of RVD. This inhibition could be completely overcome by simultaneous administration of 1 micromol l-1 tributyltin (anion exchanger) and furosemide. Chelation of either extracellular (1 mmol l-1 EGTA) or both extra- and intracellular Ca2+ (1 mmol l-1 EGTA, 10 micromol l-1 A23187) had no effect on this RVD process. Furthermore, as measured using the fluorescent dye Fura-2/AM, there was no increase in the intracellular free Ca2+ concentration upon hypo-osmotic stimulation. Administration of the 5-lipoxygenase antagonist ETH 615-139 (20 micromol l-1), however, induced a 60 % inhibition of RVD. Simultaneous addition of ETH-615 and either the K+ ionophore gramicidin (0.5 mmol l-1) or the anion exchanger tributyltin (1 micromol l-1) could not reverse the ETH 615-139 inhibition. Finally, administration of the cycloxygenase inhibitor indomethacin had only a small, but significant, effect on RVD. We conclude that RVD following hypo-osmotic swelling is in these cells a temperature- and ouabain-sensitive process that appears to be the result of K+ efflux through quinine-sensitive, Ba2+-insensitive K+ channels and Cl- efflux through an MK-196- and furosemide-sensitive Cl- conductance that is relatively unaffected by NPPB. This KCl efflux seems to be regulated by eicosanoids produced by the 5-lipoxygenase. Arachidonic acid metabolites from the cycloxygenase pathway are not involved in this process. Similarly, neither extra- nor intracellular Ca2+ appears to be important for the signalling of RVD.

Macrophage secretory function is enhanced by low doses of tributyltin-oxide (TBTO), but not tributyltin-chloride (TBTCl)

Numerous studies suggest that tributyltin (TBT) is a potent immunotoxicant in nontarget organisms with lymphoid atrophy being a hallmark response. Two of the most common formulations of TBT are bis (tri-n-butyl)-tin oxide (TBTO) and tri-n-butyl-tin chloride (TBTCl). Most of studies investigating TBT-related immunotoxicity have used relatively high doses of both compounds, but little is known about the effects of very low doses. In addition, no studies have directly compared the effects of both formulations on immune function(s). We exposed female B6C3F1 mice to a single dose of TBTO or TBTCl at 0.3, 3.0, 30 mM/kg or corn oil as a carrier control. Forty-eight h later mice received a 4% solution of thioglycolate intraperitoneally to elicit peritoneal macrophages. Ninety-six h later macrophages were harvested and stimulated with a mixture of gamma-interferon (IFN-gamma) and lipopolysaccharide (LPS). Nitric oxide (NO), tumor necrosis factor-alpha (TNF-alpha), transforming growth factor beta-1 (TGF-beta1), and phorbol ester-stimulated oxidative burst activity were then measured. Nitric oxide and TNF-alpha production were significantly elevated in the 0.3 and 3.0 mM TBTO/kg-treated groups but not in those treated by TBTCl. Background TNF-alpha production (without stimulation) was also elevated at these two doses but suppressed in TBTCl-treated animals. Oxidative burst activity was elevated at 0.3 mM TBTO/kg but not by TBTCl. TGF-beta1 production was not altered by either treatment, nor were body wts and organ-body wt ratios. To further evaluate the difference between the effects of TBTO and TBTCl on macrophage function, the in vitro toxicity of the two was determined using elicited peritoneal macrophages from untreated mice. Following a 24-h exposure to increasing concentrations of TBTO or TBTCl, functional viability was evaluated using the MTT assay. There were no differences between the two compounds in terms of treatment-related viability except that at the very highest concentrations (10(-6) M) TBTO was more toxic than TBTCl.

Effect of butyrate analogues on proliferation and differentiation in human neuroblastoma cell lines

Butyric acid has been shown in vitro to produce cytodifferentiation of a wide variety of neoplastic cells. The potential clinical use of this compound as a therapeutic agent is limited by its rapid metabolism. This has led to the examination, as potential antineoplastic agents, of compounds structurally correlated to butyrate, with longer biological half lives. In this study we investigated the effect in vitro of two butyrate analogues, tributyrin and butyramide, on inducing growth inhibition and expression of morphological and immunophenotypic properties, in human neuroblastoma cell lines. Treatment with tributyrin resulted in a strong inhibition of cell proliferation and in induction of extensive differentiation; on the contrary butyramide was scarcely effective or quite ineffective. These results demonstrate that tributyrin retains the effectiveness of butyrate and suggest that this analogue could have utility for cytodifferentiation therapy.

Effects of in vivo exposure to bis(tri-n-butyltin)oxide, hexachlorobenzene, and benzo(a)pyrene on cytokine (receptor) mRNA levels in cultured rat splenocytes and on IL-2 receptor protein levels

Analysis of cytokine (receptor) mRNA levels has been suggested to be a sensitive technique for predicting the immunomodulatory potential of drugs and chemicals. Furthermore, this type of analysis is thought to be important in unraveling mechanisms of immunotoxicity. To study these issues, male Wistar rats were exposed to the immunotoxic environmental contaminants bis(tri-n-butyltin) oxide (TBTO; 5, 20, or 80 mg/kg diet for 6 weeks), hexachlorobenzene (HCB; 50, 150, or 450 mg/kg diet for 6 weeks), or benzo(a)pyrene (B(a)P; 3, 10, 30, or 90 mg/kg body wt for 5 weeks by a daily (5 times a week) oral intubation). Spleen cells were cultured with Con A and analyzed by dot blot hybridization for IL-2, IFN-gamma, IL-2 receptor alpha-chain (IL-2R alpha; CD25), and IL-4 mRNA levels. In addition, spleen and thymus sections of TBTO-exposed animals were assayed immunohistochemically for CD25 expression. Exposure to TBTO resulted in a dose-dependent decrease in IL-2R alpha mRNA levels from 5 mg/kg, a dose-dependent increase in IFN-gamma mRNA levels from 20 mg/kg, and increased IL-2 mRNA levels at 80 mg/kg diet. Exposure to HCB resulted in a dose-dependent increase in IL-2 and IFN-gamma mRNA levels from 150 mg/kg and increased IL-2R gamma mRNA levels at 450 mg/kg diet. Exposure to B(a)P resulted in a dose-dependent increase in IL-2 and IFN-gamma mRNA levels from 10 mg/kg and increased IL-2R alpha mRNA levels at 90 mg/kg body wt. No effects were seen on IL-4 mRNA levels. Spleen and thymus sections of TBTO-exposed animals showed reduced CD25 expression from 5 mg/kg diet. These results show that (1) the correlation between altered cytokine (receptor) mRNA levels and functional endpoints is variable, depending on the type of functional endpoint tested and the compound studied, (2) these assays are among the most sensitive ones for TBTO and HCB immunotoxicity, and among the more sensitive ones for B(a)P immunotoxicity, and (3) for TBTO, these assays provide a possible clue to a mechanism for thymus atrophy, resulting from exposure to this compound: reduced IL-2R expression may impede thymocyte maturation, resulting in thymus atrophy.

Alteration of [14C]-testosterone metabolism after chronic exposure of Daphnia magna to tributyltin

Tributyltin (TBT) is a marine biocide that has been shown to alter the activity of cytochrome P450 monooxygenases and elicit toxicity indicative of androgenization in some species. The present study was conducted to determine whether TBT altered P450-, reductase-, and transferase-mediated testosterone metabolic processes in Daphnia magna at sublethal exposure concentrations. Two generations of daphnids were continuously exposed for 21 days to nominal TBT concentrations ranging from 0.31 to 2.5 microg/L TBT. The highest TBT concentration (2.5 microg/L) was lethal to 60% of the exposed organisms. Lower TBT concentrations elicited no adverse effects on molting or reproduction of the daphnids. No differences were observed in the response of the first- and second-generation daphnids to the toxicity of TBT. The ability of daphnids to metabolize [14C]-testosterone in vivo was assessed following exposure of each generation to TBT. Production of hydroxylated, reduced/dehydrogenated, and glucose-conjugated metabolites of testosterone were all elevated following exposure of both generations to 1.25 microg/L TBT. These findings indicate that, under these conditions, TBT elicits no discernible effects on molting and reproduction of daphnids at sublethal concentrations, and testosterone metabolism is enhanced at concentrations approaching those that are lethal to organisms. Alterations of steroid metabolism by xenobiotics can be used as a more sensitive indicator of sublethal exposure in daphnids than reproductive endpoints.

Effect of organotin compounds on trout hemoglobins

The stability of trout hemoglobin was examined in the presence of some organotin compounds. Tributyltin chloride (TBTC) and triphenyltin chloride (TPTC) protect HbI most efficently from the oxidation. On the other hand, the same compounds accelerate the precipitation process in HbIV to a great extent. Parahydroxymercuribenzoate (PMB), an agent blocking free SH-groups of the protein, abolished the ability of TPTC to decrease the oxidation rate of HbI.

Tributyltin oxide affects energy production in the yeast Rhodotorula ferulica, a utilizer of phenolic compounds

Rhodotorula ferulica, a yeast able to utilize phenolic compounds, was chosen for evaluating the effects of tributyltin oxide (TBTO) on this utilization. TBTO reduced respiratory capacity when vanillic or benzoic acid was the energy source. The ATP level of the cells was severely affected by 2 microM TBTO. The mitochondrial ATPase was strongly inhibited by 0.5 microM TBTO, whereas the activity of the plasma membrane ATPase was not affected by concentrations of TBTO up to 30 microM. Our data support the hypothesis that the target for TBTO action is the mitochondrial ATPase, resulting in a severe disturbance of the yeast utilization of aromatic compounds.

Induction of tumor necrosis factor-alpha in vivo by a skin irritant, tributyltin, through activation of transcription factors: its pharmacological modulation by anti-inflammatory drugs

Skin irritant reactions are under the control of a network of cytokines and lipid mediators. This study characterized the production of tumor necrosis factor-alpha (TNF) induced by a skin irritant treatment, tributyltin (TBT), in mice through transcription factor activation and its pharmacologic modulation by anti-inflammatory agents. The ears of BALB/c mice were painted with different amounts of TBT (67-536 nmol in acetone) or with acetone alone. At different times thereafter, TNF production was analyzed both at the mRNA and protein level, by semiquantitative RT-PCR and L929 cytotoxicity assay, respectively. TBT induced rapid (1 h) TNF gene expression and protein synthesis. Maximal TNF production was observed 2 h after treatment. The production of TNF was paralleled by accumulation of skin water; this was partially prevented by intraperitoneal injection of antibody against murine TNF. These data indicate that skin irritation induced by TBT is attributable, in addition to the actions of other inflammatory mediators, to the action of keratinocyte-derived TNF. TNF production was preceded by a rapid (5 min) activation of nuclear factor-kappaB (NF-kappaB), which was also maximal 30 min after treatment. TBT-induced accumulation of skin water and TNF production were significantly reduced by topical treatment with dexamethasone and pentamidine, two anti-inflammatory agents. Interestingly, dexamethasone, but not pentamidine, decreased TBT-induced NF-kappaB activation, confirming in vivo that the glucocorticoid receptor interacts functionally within the nucleus with other transcription factors opposing one another's activity.

Glutathione-doxorubicin conjugate expresses potent cytotoxicity by suppression of glutathione S-transferase activity: comparison between doxorubicin-sensitive and -resistant rat hepatoma cells

The cytotoxic mechanism of a conjugate of doxorubicin (DXR) and glutathione (GSH) via glutaraldehyde (GSH-DXR) was investigated using DXR-sensitive (AH66P) and -resistant (AH66DR) rat hepatoma cells. GSH-DXR accumulated in AH66DR cells as well as in AH66P cells without efflux by P-gp and exhibited the potent cytocidal activity against both cells compared with DXR. To examine whether thiol from GSH-DXR affected the expression of cytotoxicity, two conjugates of DXR, with modified peptides containing alanine or serine substituted for cysteine in GSH were prepared and their cytotoxicities determined. Substitution of these amino acids for cysteine resulted in an approximately two- to fourfold reduction in cytotoxic activity against both cell lines compared with the effect of GSH-DXR. Depletion of intracellular GSH by treatment of both cells with buthionine sulphoximine did not change the cytotoxic activity of DXR, BSA-DXR or GSH-DXR. By co-treating the cells with tributyltin acetate, an inhibitor of glutathione S-transferase (GST), and either DXR, BSA-DXR or GSH-DXR, the cytotoxicity was markedly increased. Interestingly, GSH-DXR showed non-competitive inhibition of GST activity and its IC50 value was 1.3 microM. These results suggested that the inhibition of GST activity by GSH-DXR must be an important contribution to the expression of potent cytotoxicity of the drug.

Effect of in vitro exposure to tributyltin on generation of oxygen metabolites by oyster hemocytes

Mollusks depend chiefly on hemocyte-mediated cytotoxic mechanisms such as reactive oxygen species (ROS) to defend against pathogenic microorganisms. The effect of in vitro tributyltin chloride (TBT) exposure on ROS generation by oyster (Crassostrea virginica) blood phagocytes is quantified in this study. Luminol-augmented chemiluminescence (LCL) was used to measure ROS activity of resting and zymosan-stimulated cells after 1 or 20 hr TBT exposure. LCL is thought to measure primarily the activity of the myeloperoxidase/hydrogen peroxide/ halide antimicrobial pathway. Hemocytes in TBT-free medium (controls) produced low level LCL, which was markedly stimulated by the addition of zymosan particles. Both resting and zymosan-stimulated LCL values were significantly inhibited by > or = 80 ppb TBT after either 1 or 20 hr of exposure. Exposure to < or = 2 ppb TBT concentrations for 20 hr produced slightly enhanced LCL activity, suggesting a hormesis-like effect. Partial reversibility of TBT suppression of LCL took place when previously exposed cells were put in TBT-free medium. The TBT concentrations used in these studies were not cytolethal in vitro and were considerably less than oyster tissue levels recorded after chronic, sublethal in vitro exposures. The data suggest that the common aquatic contaminant TBT can interact rapidly with C. virginica hemocytes to produce a partially reversible immunotoxicological lesion. Xenobiotic-induced suppression of ROS production by hemocytes may increase host susceptibility to infectious diseases.

Effects of tri-, di- and monobutyltin on synaptic parameters of the cholinergic system in the cerebral cortex of mice

Triorganotin compounds like tributyltin have been reported to be biodegraded to diorganotin, monoorganotin and then inorganic tin in animals after they have been ingested. Effects of tributyltin, dibutyltin and monobutyltin on various cholinergic parameters that are involved in synaptic transmission in the mouse cerebral cortex were investigated in vitro. Tributyltin and dibutyltin, but not monobutyltin, inhibited the activity of choline acetyltransferase, both the high-affinity and low-affinity uptakes of choline into synaptosomes, and the binding of [3H]quinuclidinyl benzilate to muscarinic acetylcholine receptors. Tributyltin and dibutyltin, but not monobutyltin, had a slightly suppressive effect on the K(+)-induced release and synthesis of acetylcholine in slices of the cortex. All three butyltins at concentrations from 10(-6) to 10(-4) M had no effect on the activity of acetylcholinesterase. The extent of the inhibitory effects on the cholinergic parameters, apart from the activity of acetylcholinesterase, was slightly greater in the case of tributyltin than dibutyltin, in particularly at the highest concentration (10(-4) M) tested. Therefore, it is concluded that tributyltin metabolites inhibit various parameters of cholinergic activity with a potency ranking of tributyltin > dibutyltin > monobutyltin.

Effects of hyperthermia on intracellular chloride

Hyperthermia induces transient changes in [Na+]i and [K+]i in mammalian cells. Since Cl- flux is coupled with Na+ and K+ in several processes, including cell volume control, we have measured the effects of heat on [Cl-]i using the chloride indicator, MQAE, with flow cytometry. The mean basal level of [Cl-]i in Chinese hamster ovary cells was 12 mM. Cells heated at 42.0 degrees or 45.0 degrees C for 30 min had about a 2.5-fold increase in [Cl-]i above unheated control values when measured immediately after heating. There was about a 3-fold decrease in [Na+]i under the same conditions, as measured by Sodium Green. The magnitude of the increase in [Cl-]i depended upon time and temperature. The [Cl-]i recovered in a time-dependent fashion to control values by 30 min after heating. When cells were heated at 45.0 degrees C for 30 min in the presence of 1.5 mM furosemide, the heat-induced [Cl-]i increase was completely blocked. Since furosemide inhibits the Na+/K+/2Cl- cotransporter, Cl- channels, and even Cl-HCO3 exchange, these ion transporters may be involved in the heat-induced increase in [Cl-]i.

Effects of extracellular pH on intracellular pH-regulation and growth in a human colon carcinoma cell-line

Mechanisms of intracellular pH (pHi) regulation seem to be involved in cellular growth and cell division. Little is known about how extracellular acidosis, known to occur in central regions of solid tumors, or alkaline conditions affect pHi regulation in colonic tumors. pHi changes in the colonic adenocarcinoma cell-line SW-620 were recorded by spectrofluorimetric monitoring of the pH-sensitive, fluorescent dye BCECF, and proliferative activity was assessed by [3H]thymidine uptake. Resting pHi in Hepes-buffered solution was 7.53 +/- 0.01 (n = 36). Both 1 mM amiloride and Na(+)-free solution inhibited pHi recovery from acidification and decreased pHi in resting cells. In HCO3-/CO2-buffered media resting pH1 was 7.42 +/- 0.01 (n = 36). Recovery from acidification was Na(+)-dependent, CI(-)-independent, and only partially blocked by 1 mM amiloride. In the presence of amiloride and 200 microM H2DIDS pHi recovery was completely inhibited. In Na(+)-free solution pHi decreased from 7.44 +/- 0.04 to 7.29 +/- 0.03 (n = 6) and no alkalinization was observed in CI(-)-free medium. Addition of 5 microM tributyltin bromide (an anion/OH-exchange ionophore) caused pHi to decrease from 7.43 +/- 0.05 to 7.17 +/- 0.08 (n = 5). The effects of pH0 on steady-state pHi, pHi recovery from acidification and proliferative activity after 48 h were investigated by changing buffer [CO2] and [HCO3-]. In general, increases in pH0 between 6.7 and 7.4 increased pHi recovery, steady-state pHi and growth rates. In summary, SW-620 cells have a resting pHi > 7.4 at 25 degrees C, which is higher than other intestinal cells. Acid extrusion in physiological bicarbonate media is accomplished by a pHi-sensitive Na+/H+ exchanger and a pHi-insensitive Na(+)-HCO3-cotransporter, both of which are operational in control cells at the resting pHi. No evidence for activity of a CI-/HCO3- exchanger was found in these cells, which could account for the high pHi observed and may explain why the cells continue to grow in acidic tumor environments.

Protease inhibitors block apoptosis at intermediate stages: a compared analysis of DNA fragmentation and apoptotic nuclear morphology

The possible correlation between DNA digestion and changes in nuclear morphology in apoptosis was studied by blocking the apoptotic process at intermediate stages. The apoptogenic action of three drugs: etoposide, puromycin, tributyltin, was contrasted with protease inhibitors with different specificity on U937 cells. The inhibitors interfered with the development of the apoptotic features without shifting cell death to necrosis: treated cells showed abnormal morphologies, which could be recognized as intermediate stages of apoptosis; accordingly, DNA analysis showed an inhibitor-dependent block of the apoptotic DNA digestion. The comparison between size of DNA fragments and nuclear morphology suggested the following correlations: loss of normal nuclear shape with the appearance of a > or = 2 Mb DNA band; ongoing chromatin condensation with the progressive DNA digestion up to 50 kb; nuclear fragmentation with DNA laddering. Protease inhibitors in etoposide-treated cells did not allow the formation of 700-300 kb fragments, suggesting that they possibly derive from a cell-mediated effect.

A non-radioactive, sensitive method for the detection of DNA fragmentation in apoptotic cells (rat pheochromocytoma PC12 and rat cortical cells)

A new method is described which is suitable for reliably analysing apoptotic fragmentation in small amounts of DNA. After isolation, DNA was labelled with biotin-4-dUTP using Klenow polymerase. Then DNA was size-separated by agarose gel electrophoresis, blot transferred and subsequently visualized by the streptavidin alkaline phosphatase-BCIP/NBT procedure. This non-radioactive method was used to detect apoptotic DNA in rat pheochromocytoma PC12 cells, treated with tributyltin (1 nM). While only 30 ng of DNA is required for analysis of apoptotic DNA using the new blot technique, 100-fold more material is needed to identify the fragmentation of DNA after separation by agarose gel electrophoresis and direct staining with ethidium bromide. In a further set of experiments, rat cortical cells were incubated with human immunodeficiency virus type 1 viral glycoprotein of M(r) of 120 kDa (gp120) to induce apoptosis. More than 0.3 ng of gp 120/ml are required to detect apoptotic DNA by the direct procedure; only 0.1 ng gp120/ml or less were sufficient to document clear DNA fragmentation using the non-radioactive blotting technique described here. These results demonstrate that the new procedure can be used to analyse very small amounts of apoptotic DNA and shows that gp120-induced apoptosis can be measured at low concentrations of the viral protein.

Intracellular calcium and pH alterations induced by tri-n-butyltin chloride in isolated rainbow trout hepatocytes: a flow cytometric analysis

The effects of tri-n-butyltin chloride (TBT) on ionic homeostasis on isolated trout hepatocytes were investigated by flow cytometry (FCM), using the Ca(2+)-sensitive and pH-sensitive fluorescent probes Indo-1 and SNARF-1, respectively. Cell viability was monitored concurrently. Treatment of hepatocytes with 1 and 5 microM TBT caused a rapid and sustained elevation of cytosolic free Ca2+ concentration [Ca2+]i and an important cytoplasmic acidification. These changes were dependent upon TBT concentration and were maintained over 60 min, the maximum exposure period investigated. At 0.5 microM TBT, there was a slight but not significant increase in [Ca2+]i and a significant reduction in intracellular pH (pHi) only after 60 min of exposure. A rise in [Ca2+]i and cytoplasmic acidification were observed before loss of viability was detectable. Experiments carried out in Ca(2+)-free medium suggest that TBT mainly mobilizes Ca2+ from intracellular stores in trout hepatocytes. The cytoplasmic acidification following TBT exposure seems to be caused by the combination of intracellular Ca2+ mobilization and by direct action of TBT. The present results suggest that ionic homeostasis perturbations could be early events in the mechanism of cell injury by TBT.

Tributyltin and dexamethasone induce apoptosis in rat thymocytes by mutually antagonistic mechanisms

The nuclei of apoptotic thymocytes can be identified by flow cytometry as a subpopulation exhibiting reduced DNA content. We observed that rat thymocyte cultures exposed to 1.0-2.5 microM tri-n-butyltin methoxide (TBT) exhibited a rapid time- and concentration-dependent induction of apoptosis, with > 85% of cells exhibiting reduced DNA content within 1 hr after exposure to 2.0-2.5 microM TBT. In contrast, exposure to 1.0 microM dexamethasone phosphate (DEX) resulted in a gradual time-dependent increase to approximately 45% induction of apoptosis by 6 hr versus approximately 15% spontaneous induction in controls. However, simultaneous exposure to TBT and DEX resulted in a decreased response: although TBT concentrations between 0.1 and 0.5 microM did not induce apoptosis, they reduced the ability of DEX to initiate apoptosis; while at TBT concentrations > or = 1.0 microM, simultaneous exposure to DEX substantially decreased the extent of TBT-induced apoptosis and cytotoxicity. Furthermore, while treatment with the protein synthesis inhibitor cycloheximide or the protein kinase C inhibitor H-7 completely blocked DEX-induced apoptosis, neither significantly reduced induction of apoptosis by TBT. Taken together, the toxicant-specific differences in the timing and extent of apoptotic induction and the dissimilar responses to CHX and H-7 suggest that TBT and DEX initiate endonuclease-mediated apoptotic cell death through different mechanisms. Moreover, the ability of each agent to retard the action of the other suggests that these mechanisms are directly or indirectly antagonistic.

Deactivation of F0F1 ATPase in intact plant mitochondria. Effect of pH and inhibitors

By using a method especially adapted to intact (pea leaf) mitochondria, we studied the regulation of the F0F1 ATPase by the electrochemical proton gradient (delta mu H+) and by the matricial pH. The kinetics of decay of the ATP hydrolase activity was studied immediately after the collapse of the electrochemical proton gradient by an uncoupler. At pH 7.5, three inhibitors of the ATPase (venturicidin, tri-n-butyl tin and aurovertin), used at non-saturating concentrations, inhibited ATP hydrolysis to the same extent throughout the decay. This showed that the activity was totally controlled by the ATPase during all the decay and rules out any involvement of the phosphate or nucleotide carriers. This interpretation was confirmed by the fact that carboxyatractyloside, an inhibitor of the ATP/ADP antiporter, had a strong effect only on the initial rate of ATP hydrolysis, but not on the rate measured after some tens of seconds of decay. Oligomycin, at variance with the other ATPase inhibitors, interfered with the deactivation process, suggesting that its effect depends on the conformational state of the enzyme. Between pH 6.5 and 7.5, the hydrolase activity rose continuously and was still kinetically controlled by the ATPase. At higher pH value, the activity slightly decreased and appeared limited by at least one of the carriers. The activity of the ATPase itself, free of any transport process, seemed to increase monotonously with pH from 6.5 to 8. The electrochemical proton gradient is required to maintain the ATPase active, whereas no effect can be observed on transport processes. Matricial pH, while modulating the apparent catalytic turnover, has no marked effect on the rate of deactivation. These results, obtained with intact mitochondria, extend previous observations on the isolated enzyme and question the binding of IF1 as a rate-limiting step for ATPase deactivation.

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.

Comparison of cellular and nuclear flow cytometric techniques for discriminating apoptotic subpopulations

We compared cellular flow cytometric methods employing carboxyfluorescein (CF), Höechst 33342, and Höechst 33258 with a nuclear method in their ability to discriminate apoptotic subpopulations in rat thymocyte cultures exposed to dexamethasone or tributyltin. In the nuclear technique, apoptotic cells appeared as a single population containing reduced DNA content, while in the cellular techniques, apoptotic cells appeared as two or more subpopulations exhibiting increased fluorescence. Of these subpopulations, early apoptotic cells [which excluded propidium iodide (PI), indicating maintenance of membrane integrity] exhibited higher fluorescence but the same level of axial light loss (i.e., size/refractive index) as viable cells; late apoptotic and dead cells (which incorporated PI) exhibited decreased axial light loss. However, while the Höechst dyes allowed discrimination of late apoptotic from dead cells, CF did not. In comparing sensitivity to staining conditions, Höechst 33258 fluorescence was the most stable over time, Höechst 33342 the least, and CF fluorescence not only varied with time, but with tri-n-butyltin methoxide concentration. Comparison of single-parameter analyses revealed that axial light loss was sensitive only to late apoptotic changes; nuclear fluorescence was a better indicator of apoptotic subpopulations, but still underestimated the total percentage of affected cells, and Höechst 33342 distinguished early apoptotic cells as those with elevated fluorescence. Early apoptotic cells stained with Höechst 33258 also exhibited increased fluorescence, but could not be distinguished from late apoptotic and dead cells without a second parameter. These findings indicate that of the methods investigated, the method of choice for detecting apoptosis depends on the goal of analysis: Höechst 33258 was best for discriminating apoptotic subpopulations, and CF was best for assessing alterations of membrane fluidity. For single-parameter analyses, Höechst 33258 was best for determining the total percentage of affected cells, while Höechst 33342 could be used to determine the percentage in early apoptosis.

Rapid reduction of mRNA coding for 2'-5'-oligoadenylate synthetase in rat pheochromocytoma PC12 cells during apoptosis

Apoptosis is a form of physiological cell death, characterized by DNA fragmentation, which often depends on RNA and protein synthesis. Because cellular RNA is also degraded during apoptosis we studied the role of the 2'-5'-oligoadenylate (2-5A) synthetase in this process. The product of the synthetase, 2-5A, stimulates endoribonuclease-L-mediated controlled RNA degradation. Here we show that apoptosis is induced in rat phenochromocytoma PC12 cells by tributyltin (TBT) at low concentrations (1 nM); already 5-10 min. after addition of this compound DNA fragmentation resulting in a stepladder-like gel pattern was observed. The level of mRNA coding for 2-5A synthetase was determined using a cloned cDNA from rats. Sequence analyses of the rat 2-5A synthetase (M(r) 40-46,000) revealed high homology to other members of class I synthetase cloned from mouse and human. Applying the rat cDNA as a probe we found that parallel with degradation of DNA the level of mRNA coding for 2-5A synthetase decreased already 7.5 min. after induction of apoptosis by TBT the amount of 2-5A synthetase mRNA was reduced by 60%. This finding indicates that this enzyme is among those mRNAs which are degraded during apoptosis and it suggests that 2-5A synthetase, which is involved in the antiviral response of cells and most likely in the control of cell growth and differentiation, does not play an active role during this process.

[Effect of bis(n-tributyltin)-oxide on the brain GABA-ergic system in vitro]

Wide concentration range (10(-14)-10(-4) M) of bis-(n-tributyltin)-oxide effect on Na(+)-dependent uptake, spontaneous and K(+)-stimulated release, specific receptor binding and GABA metabolism were studied in vitro experiments using brain slices, synaptic membrane fraction and brain tissue homogenates. It is shown that the dependence "concentration-effect" is of non-linear character in all cases. Prevailing suppression of Na(+)-dependent uptake and specific receptor binding during K(+)-stimulated release and metabolism (production and utilization) of GABA activation were marked as a general tendency. Mechanisms of TBTO effect on the studied processes and the involvement of GABA-ergic system in realization of TBTO neurotoxic effects are discussed.

The 16S rRNA sequence and genome sizing of tributyltin resistant marine bacterium, strain M-1

The 16S rRNA of the tributyltin resistant marine bacterium, strain M-1, was partly sequenced to confirm the taxonomic status. The results indicated that this bacterium should be classified under the genus Alteromonas, instead of a previous report in which this strain was identified as a Vibrio. The genome size of this strain was also measured by pulsed field gel electrophoresis (PFGE) using a contoureclamped homogeneous electric field. The strain was found to contain a genome size of 2,240 kilo base pairs, whereas Alteromonas nigrifaciens and Shewanella putrefaciens had 2,040 and 2,383 kilo base pairs, respectively. This is the first report of the genome sizing of the genus Alteromonas by PFGE.