Trialkyllead compounds induce the opening of the MTP pore in rat liver mitochondria.

The interactions of the tributyl, triethyl and trimethyllead compounds with energized mitochondria have been investigated in this paper. It has been shown that the (alkyl)(3)Pb-Cl compounds induce swelling in mitochondria suspended in a sucrose medium. The phenomenon is more marked the higher the lipophilicity and occurs in the following order: (Bu)(3)Pb>(Et)(3)Pb>(Me)(3)Pb. As swelling is inhibited by cyclosporine, this suggests that the swelling is due to the opening of a trans-membrane pore (MTP pore) in the mitochondria. As this pore can be responsible for the inhibition of the ATP synthesis, and, consequently for cell death, the opening of the pore could be one of the reasons for the toxicity of the (alkyl)(3)Pb-X compounds.

Organotypic spinal cord culture in serum-free fibrin gel: a new approach to study three-dimensional neurite outgrowth and of neurotoxicity testing: Effects of modulating the actin and tubulin dynamics and protein kinase activities.

Spinal cord explants from embryonic day seven (E7) chicken embryos were cultured without serum and in the presence of aprotinine, in a three-dimensional fibrin matrix. These conditions promote a robust, radial, unfasciculated outgrowth of neurites that are tipped by elaborate growth cones. Routinely after 5 days, the neurite outgrowth intensity (NOI) was determined by measuring the optical density of the immunostained neurites (image analysis program OPTIMAS version 5.2) within defined areas, extending radially for up to 3 mm from the explant border. A dose-dependent inhibition of NOI was determined for the cytoskeleton-affecting drugs nocodazole (half maximal inhibition ([I50]), 0.02 microM), taxol ([I50], 0.016 microM), cytochalasin D ([I50], 0.006 microM), and tetramethyl lead ([I50], 0.05 microM). Likewise, NOI was decreased in a dose-dependent fashion by ML-9 and RO-31-8220, inhibitors of myosin-light chain kinase and protein kinase C (PKC), respectively. The addition of 1,2-dioctanoyl-s,n-glycerol, a potent activator of PKC, led, at 5 microM, to an increase and at 30 and 60 microM to a decrease in NOI. The described system provides a rapid, reproducible, and quantitative assay for the effects of exogenous factors on the mode and intensity of neurite outgrowth.

Inhibition of cytokinesis by lead (Pb2+) in a centric diatom.

Effect of inorganic and organo lead has been studied on the mitosis of a centric diatom Cyclotella meneghiniana f. unipunctata. Binucleate cells were formed in the presence of different concentrations of Pb2+ (1.0, 2.0, 3.0 and 5.0 mM) due to inhibition of cell plate formation. Lead at 5.0 mM concentration was more inhibitory than the other concentrations. Organo lead was a powerful depressant of cytokinesis than inorganic lead. Failure of cytokinesis might be due to disruption of microtubules. Formation of distinct nuclei delayed post incubation cell divisions suggest partial damage of mitotic spindles.

Metal inhibition of ferrochelatase activity in human lymphocytes.

The activity of the terminal enzyme of haem biosynthesis, ferrochelatase (EC 4.99.1.1) was measured in sonicates of human lymphocytes. We used a sensitive method with zinc and mesoporphyrin as substrates and quantification of the product zinc-mesoporphyrin by HPLC. A variety of metal ions and organometal compounds were examined as possible inhibitors of ferrochelatase activity. Inhibition was observed with copper and mercury (but not with lead) and with tributyltin and methylmercury. The kinetics of ferrochelatase inhibition were examined for each of the four inhibitors identified.

Central sympathoplegic and norepinephrine-depleting effects of antioxidants.

Carbon disulfide (CS2), tetraethyl lead (TEL), tetraethyl tin (TeET), dithiothreitol (DTT), and gossypol acetic acid (GAA) significantly decreased brain norepinephrine (NE) in rats. The central dopamine (DA) increased after ip administration of CS2, TEL, and DTT, but decreased after TeET and GAA. The brain serotonin decreased only after TeET. Two doses of DTT decreased the NE longer than one dose (24 vs 2 hr) but did not increase DA. L-DOPA, given SC with DTT, delayed the decrease in NE by 24 hr. The similar behavioral and autonomic effects of each of these compounds suggest a central sympatholytic effect and an antipsychotic type of sedation and rigidity. A possible mechanism is reversible inhibition of dopamine beta-hydroxylase through the reduction of the copper ion of the enzyme. Each of these reducing agents, together with the boranes previously studied, has similar behavioral and autonomic effects and a common effect on NE concentration, suggesting that the agents act through a physicochemical property rather than by combination with a cellular component. These data have applications to the toxicity of the single agents. They also provide an index of activity, previously lacking, of systemic antioxidant effect.

The relation of the neurotoxicity of organic tin and lead compounds to neurotubule disaggregation.

The effect of organic lead and tin compounds upon the integrity of cerebral neurotubules has been studies in vitro and in vivo, using 3H-colchicine binding as an index of tubulin aggregation. Triethyl tin, trimethyl lead and triethyl lead chlorides at concentrations above 5 X 10(-5)M, all prevented the polymerization of tubulin. Inorganic lead had a similar effect. Trimethyl tin had a much lesser capacity to prevent such polymerization. Rats received a single dose of each organometal, by subcutaneous injection and the capacity of hippocampal soluble protein to bind 3H colchicine was assessed. At organometal doses sufficient to cause morphological damage and behavioral change, no significant differences of colchicine binding capacity were apparent.

Incorporation of 14C from glucose into amino acids in brain in vitro in the presence of organo- and inorganic lead and pyridoxal phosphate.

The incorporation of label from U14C glucose into glutamic acid, glutamine and GABA remained unaltered with the presence of lead acetate in the medium whereas tetraethyl lead (TEL) affected the incorporation in a characteristic manner in different regions of brain. Glucose uptake however was not influenced by TEL. Pyridoxal phosphate was found to reverse the effect of TEL on the incorporation especially in cerebellum and brainstem but with little effect in cerebral cortex. These findings suggest that the alterations in the GABA metabolism in TEL toxicity could be restored to some extent by pyridoxine in discrete brain areas.

Increase in dopamine uptake in rat striatal synaptosomes after an acute in vivo administration of organic and inorganic lead.

Adult male Wistar rats were administered acute toxic doses of lead (Pb), triethyl lead (TriEL) or tetraethyl lead (TEL) by gavage. The ability of striatal, hypothalamic and cortical synaptosomes to take up tritiated monoamines was assayed 24 hours later. Pb, TriEL as well as TEL increased dopamine (DA) uptake into striatal synaptosomes at least at some dose level. Pb increased, but TEL decreased 5-hydroxytryptamine(5-HT) uptake into hypothalamic synaptosomes, while TEL increased noradrenaline (NA) uptake into cortical synaptosomes. After a 3 week administration to initially 4 week old rats of even toxic doses of Pb in drinking water, monoamine uptake was not significantly affected. On the contrary, the neurotoxicity of TEL was cumulative in that a much lower dose decreased 5-HT uptake when divided over a 3 week period than acutely. In vitro TriEL inhibited DA uptake (IC50; 0.8 microM) into striatal and 5-HT uptake (5.0 microM) into hypothalamic synaptosomes but TEL and delta-aminolevulinic acid did not. The results suggest that dopaminergic and serotonergic neurones differ in their response to alkyl lead in vivo. The differences could be due to basic differences in the neurochemical behaviour of these two types of nerve endings.

Genetics of resistance to tetraethyllead.

A Drosophila melanogaster population was exposed for 25 generations to 60 micrograms tetraethyllead per gram of medium. Selection over this period resulted in an increase in fecundity, hatchability and larva-to-adult viability. Chromosome assay showed that response in these traits was generally under additive genetic control in conformity with existing results in the literature on the genetics of resistance to acute environmental stress in D. melanogaster.

Effect of tetraethyl lead and restricted food intake on locomotor activity in the rat.

The effect of tetraethyl lead (TEL) and restricted food intake on spontaneous locomotor activity in male albino rats was investigated. Forty animals were injected intraperitoneally with 4, 7, 10 or 13 mg/kg body weight of TEL in peanut oil, or a peanut oil placebo. Forty additional animals were food yoked to lead treated animals as a control procedure to hold food intake constant between lead treated and lead free animals. A comparison of pre- and posttreatment measures revealed significant decreases in food intake and increases in activity levels at dosages of 7, 10 and 13 mg/kg of TEL. In addition, food intake and activity were significantly correlated in both lead treated and yoked groups. The issue of factors associated with reduced food intake playing a role in observed activity level increases was raised.

Effect of tetramethyl lead on freshwater green algae.

The toxicity of tetramethyl lead (Me4Pb) towards freshwater algae was studied by bubbling biologically generated Me4Pb from one flask containing 5 mg of Pb 1-1 as Me3PbOAc into the culture medium in another flask where a test alga Scenedesmus quadricauda was grown. As Me4Pb is not soluble in water and is volatile, the exposure of an alga to this lead compound was only momentary. It was estimated that less than 0.5 mg of Pb(Me4Pb) had passed through the culture medium. The primary productivity and cell growth (determined by dry weight), however, decreased by 85% and 32% respectively, as compared with the controls without exposure to Me4Pb. Furthermore, cells exposed to Me4Pb tended to clump together and striking alterations in cell fine-structure were observed. An electron microscopic analysis by an energy dispersive spectrometer revealed that Pb ions had penetrated the cell and were deposited within concretion bodies. Similar results were obtained with the green algae Ankistrodesmus falcatus and Chlorella pyrenoidosa.

Effect of tetraethyl lead on food and water intake in the rat.

The effect of tetraethyl lead (TEL) on food and water intake in adult male albino rats was studied. Animals received 1, 4, 7, 10, or 13 mg/kg body weight of TELin peanut oil, or a peanut oil placebo, via either intragastric (IG) intubation or intraperitoneal (IP) injection. For food intake, route of administration was a significant factor and, compared to baseline levels, food intake was significantly depressed at dosage levels of 7, 10, and 13 mg/kg for both IP and IG administration. Further, the time course of food intake differed significantly across route of administration. Water intake was also significantly depressed at 7, 10, and 13 mg/kg, but route of administration was not a critical factor. Results were discussed in relation to clinical and experimental data on lead intoxication, and were viewed as severely limiting the utility of employing food and/or water as motivational variables in assessment of behavioral effects linked to TEL poisoning.