High cytotoxicity and membrane permeability of Et3Pb+ in mammalian and plant cells

Lead Concentration in Rain Water Used for Drinking in the Area Surrounding Bangkok

Lead concentrations in jar water, originating from rain and used for drinking, were measured in 1990 in some of the villages surrounding Bangkok, Thailand. There were differences in lead concentrations among the villages: the values were 2.32, 1.38, 1.05 and 3.48 μg/liter in Maptaphut, Rai-Noong, Leam-Chabang and Rangsit-Pathumtani, respectively. As to direct health effects, these lead levels in the water were acceptably low at that point in time in 1990 when the study was conducted. The lead concentration in rain water was considered to be an appropriate indicator representing environmental quality under rapid industrialization. Considering that further advancement of industrialization and urbanization is expected in these areas in the near future, periodic measurement is needed for longitudinal environmental monitoring. The values presented herein can be used as background data before extensive urbanization.

Metal toxicity at the synapse: presynaptic, postsynaptic, and long-term effects

Metal neurotoxicity is a global health concern. This paper summarizes the evidence for metal interactions with synaptic transmission and synaptic plasticity. Presynaptically metal ions modulate neurotransmitter release through their interaction with synaptic vesicles, ion channels, and the metabolism of neurotransmitters (NT). Many metals (e.g., Pb(2+), Cd(2+), and Hg(+)) also interact with intracellular signaling pathways. Postsynaptically, processes associated with the binding of NT to their receptors, activation of channels, and degradation of NT are altered by metals. Zn(2+), Pb(2+), Cu(2+), Cd(2+), Ni(2+), Co(2+), Li(3+), Hg(+), and methylmercury modulate NMDA, AMPA/kainate, and/or GABA receptors activity. Al(3+), Pb(2+), Cd(2+), and As(2)O(3) also impair synaptic plasticity by targeting molecules such as CaM, PKC, and NOS as well as the transcription machinery involved in the maintenance of synaptic plasticity. The multiple effects of metals might occur simultaneously and are based on the specific metal species, metal concentrations, and the types of neurons involved.

Folic acid, ascorbic acid and sodium selenite restore the motility of Dictyostelium discoideum inhibited by triethyllead

The effect of triethyllead (TriEL) on motile activity, structure of cytoskeleton and chemotaxis of Dictyostelium discoideum amoebae in developing concentration gradients of folic acid (FA) and cAMP has been studied. It was observed that 3 microM TriEL had little or no effect on locomotion and chemotactic response of cells, whereas 5 microM TriEL strongly reduced the motile activity of Dictyostelium discoideum amoebae and inhibited their chemotaxis towards cAMP, but not towards FA. FA was found to restore the motile activity of Dictyostelium discoideum, inhibited by TriEL. A similar effect was observed in the presence of other antioxidants, i.e. ascorbic acid and sodium selenite, suggesting that oxidative stress may be involved in the action of TriEL. Moreover, the treatment of Dictyostelium amoebae with 5 microM TriEL caused disruption of microtubules while 3 microM TriEL had little effect on their structure. FA caused restoration of microtubules only in some cells within 1 h of incubation, i.e. when the directional movement of cells towards this chemoattractant was already observed. However, their organization was significantly different from that observed in the untreated cells, suggesting that microtubule undisturbed organisation may be not necessary for Dictyostelium discoideum amoebae locomotion and chemotaxis

High sensitivity of leukemic peripheral blood lymphocytes to triethyllead action

In a previous study we reported that triethyllead (Et3Pb+) inhibits cell proliferation of normal human lymphocytes. To further characterize this interaction, we studied herein the effects of Et3Pb+ on the cell viability of normal and leukemic human lymphocytes and analysed the expression and dynamics of the monomer/polymer equilibrium of tubulin in these cells. Short- and long-term cell culture experiments demonstrated significantly different dose-dependent effects of Et3Pb+ on cell viability of leukemic compared to normal lymphocytes. Indeed, in the presence of increasing concentrations of Et3Pb+ (10(-12)-10(-5) M), primary cultures of chronic lymphocytes (CLL) and acute lymphoblastic (ALL) leukemic human Lymphocytes were much more sensitive to Et3Pb+ treatment when compared to normal peripheral blood lymphocytes (PBL). The IC50 values were approximately 5 x 10(-6) M for PBL and 8 x 10(-10) M for both CLL and ALL respectively, when cells were preincubated for 3 h with this agent. These experiments revealed a 1000-fold higher responsiveness of leukemic cells to Et3Pb+ treatment. Quantitative immunoblot analysis showed that leukemic cells express up to 4-fold higher total tubulin amounts. However, the proportion of polymerized tubulin in leukemic compared to normal lymphocytes increased only slightly (up to 1.4-fold). These findings reveal a significant decrease in the polymeric to total tubulin ratio in leukemic lymphocytes, indicating important modifications in tubulin dynamics and reorganization of the microtubular structures. Our results demonstrate that leukemic cells are much more sensitive than normal lymphocytes to Et3Pb+ action. This effect may be due to the altered monomer/polymer dynamic equilibrium of tubulin shown in leukemic cells. It is, therefore, worthwhile exploring future applied uses of Et3Pb+ as a potential suppressor of leukemic cell growth.

Alterations of hepatocyte Ca2+ homeostasis by triethylated lead (Et3Pb+): are they correlated with cytotoxicity?

Isolated rat hepatocytes were used to investigate the biochemical mechanisms of toxicity of triethyllead (Et3Pb+), a highly neurotoxic degradation product of the antiknocking petrol additive tetraethyllead. As early as 5 min from the addition of 50 microM Et3Pb+ to hepatocyte suspensions a decrease of mitochondrial membrane potential and of the capacity of mitochondria and microsomes to retain Ca2+ occurred. A dose-dependent release of mitochondrial Ca2+ as well as an inhibition of microsomal Ca(2+)-ATPase activity were also evident when Et3Pb+ (from 2.5 microM up to 50 microM) was added to, respectively, isolated liver mitochondria and microsomes. Further experiments using hepatocytes loaded with the Ca2+ indicator Fura-2AM demonstrate that 1 min from addition of Et3Pb+ the cytosolic free Ca2+ levels increased by about 3-fold. High affinity plasma membrane Ca(2+)-ATPase activity was also significantly inhibited in hepatocytes treated with Et3Pb+, suggesting that an impairement of the mechanisms controlling the efflux of extracellular Ca2+ was concomitantly involved in the rise in cytosolic Ca2+ concentration. The increase in the cytosolic Ca2+ levels caused by Et3Pb+ was followed by a rapid decline of cell viability. However, the addition of EGTA or of the intracellular Ca2+ chelator BAPTA/AM did not affect either the time-course or the extent of cytotoxicity. Conversely, fructose, a glycolytic substrate that was able to support ATP production, prevented hepatocyte death. Thus, the depletion of cellular energy stores rather than the increase in cytosolic Ca2+ appears to be the mechanism by which Et3Pb+ causes irreversible injury in isolated hepatocytes.

Interaction of captan with mammalian microtubules

Using turbidometry, electron microscopy and immunofluorescent microscopy experiments we studied the effect of captan, a widely used pesticide on mammalian microtubules and microfilaments. Turbidometry at 350 nm showed a dose-dependent inhibition of tubulin assembly incubated with captan. The pesticide, given at equimolar concentration with tubulin (30 microM), caused the total inhibition of microtubule formation, while at lower concentrations (5-20 microM) the inhibition of tubulin polymerization was less extensive. At the same concentration range (5-30 microM), captan also promoted the disassembly of performed microtubules. The results of the in vitro effects of captan with microtubules were confirmed in parallel by electron microscopic studies. In vivo, captan caused also depolymerization of microtubules in cultured mouse fibroblasts as shown by indirect immunofluorescent staining of tubulin. The extent of microtubules disassembly was concentration- and time-dependent. While incubation of the cells with 10 microM captan for 3 h disturbs totally the microtubular structures, incubation with 5 microM captan needs 12 h for the same effect. Recovery of microtubules was observed, when preincubated cells were extensively washed. No interaction of this drug with equimolar concentration of G- or F-actin could be observed in vitro, as shown by polymerization experiments. In line with this, the fluorescent actin pattern in mouse fibroblasts incubated with 10 mM captan for up to 12 h did not seem to be altered. From these results it is concluded that captan interacts in equimolar concentrations with tubulin affecting the assembly and disassembly of microtubules in vitro and in cultures of mammalian cells.

Triethyllead-induced inhibition of proliferation of normal human lymphocytes through decreased expression of the Tac chain of interleukin 2 receptor

Triethyllead (Et3Pb+) in concentrations 10(-5) to 10(-6) M has been shown to inhibit several key cellular molecular systems. In order to evaluate the effect of Et3Pb+ on the human immune system, the mitogen-induced cell proliferation of peripheral blood mononuclear cells was studied in the presence of Et3Pb+. Preincubation of normal T-lymphocytes with 10(-6) M Et3Pb+ for 1-4 h, which has been shown to be non-cytotoxic, was sufficient to inhibit subsequent mitogenic-induced cell growth. The Et3Pb(+)-induced impairement of the in vitro proliferation of mitogen-activated normal T-cells was due to a dose-dependent decreased expression of the p55 polypeptide chain (Tac molecule) of the interleukin-2 receptor (IL-2-R), which could not be enhanced by exogeneously added recombinant interleukin 2 (rIL-2). Conversely, the same concentrations of Et3Pb+ could not inhibit the mitogen-induced expression of MHC class II molecules and the transferin receptor on activated T-cells. The impaired membrane expression of p55 on T-cells induced by Et3Pb+ was due to a decrease of Tac mRNA transcripts as showed by Northern blot analysis. This effect seems to be specific since in parallel experiments Et3Pb+ could not inhibit both the accumulation of actin mRNA and the production of IL-2 by Et3Pb(+)-treated mitogen-activated cells. The effect of this organolead compound was also associated with a dose-dependent decrease of the Na(+)-K(+)-ATPase activity of normal lymphocytes. These results indicate that Et3Pb+ could affect specifically T-cell proliferative responses through an imbalance of the IL-2/IL-2-R system.

Inhibition of cellular activities by triethyllead. Role of glutathione and accumulation of triethyllead in vitro

We investigated the interaction of triethyllead with ATP-coupled cellular enzymatic activities and the role of GSH to reverse the observed inhibition of these enzymes. Triethyllead inhibited the membrane bound Na+-K+-ATPase from HeLa cells (IC50 12 microM) and the ATP-hydrolysing activity of the mitochondrial F0-F1-ATPase complex (IC50 17 microM). Addition of 1 mM GSH reversed both enzyme activities totally, whereas lower GSH concentrations showed a less pronounced effect. Surprisingly, in freshly isolated rat liver mitochondria the ATP-synthesizing activity was also inhibited by triethyllead (IC50 16 microM), in spite of a measured high intramitochondrial GSH concentration (up to 10 mM). Further experiments in isolated submitochondrial particles revealed that ATP-synthesis and ATP-hydrolysis were inhibited by triethyllead with similar IC50 values, and both activities could be protected in vitro from the organolead compound in the presence of 1 mM GSH. Thus in all activities tested in vitro a high excess of GSH over triethyllead (greater than or equal to 25-fold) is necessary to restore the inhibited enzymes. The intramitochondrial triethyllead concentration was further determined after incubation of intact mitochondria with 10 microM of the organolead compound. The organolead concentration measured was as high as 600 microM. This means that in intact mitochondria there exists only a ca. 16-fold excess of GSH, which has been shown to be insufficient to protect ATP-synthesizing and ATP-hydrolyzing activities of the F0-F1-ATPase from triethyllead in vitro. We concluded that in intact mitochondria the F0-F1-ATPase complex is inhibited by triethyllead due to its accumulation in the matrix.

The interaction of triethyl lead with tubulin and microtubules

The impact of triethyl lead chloride was studied on: (i) the in vitro assembly and disassembly of microtubules from porcine brain by turbidometry and electron microscopy, (ii) the microtubule system of living mammalian cells using immunofluorescence microscopy, (iii) cell motility and chemotaxis employing the methods of phagokinetic track formation and the Boyden chamber assay, respectively, and (iv) thiol groups of the protein tubulin by their titration in the presence and absence of the organic lead compound. Triethyl lead chloride inhibited microtubule assembly and depolymerized preformed microtubules in vitro and in living cells. Random motility of cells was not markedly inhibited by triethyl lead chloride, whereas chemotaxis (directed cellular movement) was strongly inhibited. Triethyl lead chloride was found to interact with 2 thiol groups of the tubulin dimer. The interaction of triethyl lead chloride with the tubulin/microtubule system in vivo likely causes aneuploidy and is at least partly responsible for the cytotoxicity of the drug.