Triethyl Lead Research Articles

The Biochemical Evaluation of Neurotoxic Damage

The Biochemical Evaluation of Neurotoxic Damage. BONDY, S. C. (1986). Fundam. Appl. Toxicol. 6, 208–216. The specific problems related to the study of chemicals that damage the nervous system are discussed. Such damage may be direct or may occur by a series of sequential events. Such a series of events may involve other organs and biochemical targets not confined to nerve tissue. The complexity of investigation of the mode of action of rather nonspecific toxic agents requires that a circumscribed objective be defined and examples of such goals are given. One of these is to attempt to determine which neuronal circuits are damaged by a given toxic agent and how this might cause alterations of behavior. Acrylamide and triethyl lead are used to exemplify the application of neurotransmitter receptor analysis to correlation of deranged nerve activity patterns with modulation of behavior. Such evaluation can set the stage for more detailed biochemical studies of neurotoxic mechanisms.

Potentially toxic concentrations of triethyl lead in Black Forest rainwater samples

Recently, speculation has grown that the European forest damage may be caused by the continual exposure of trees to rainwater containing trialkyl lead salts1 (R3PbX; R = ethyl, methyl). These are degradation products of tetraalkyl lead (R4Pb) which are added to petroleum as anti-knock agents; they inhibit tubulin polymerization2,3 and are highly toxic to mammalian and plant cells4. Here we describe the analysis of rainwater samples collected at two sites in the Black Forest, FRG. Total lead content was measured by atomic absorption and found to be in the range previously determined for rural areas5. The portion of R3PbX was assayed by the inhibition of pork brain tubulin polymerization. R3PbX was present in one-third of all rainwater samples. The highest concentration was 0.3 µM, that is 103 times higher than previously reported5. For comparison, 1 µM R3PbX killed soybean cells or neuroblastoma cells in culture4.

Effect of transition or heavy metals on [ 3H]haloperidol binding in rat striatal membranes in vitro

Our previous experiments have shown that several metal cations affect dopaminergic uptake and release processes in synaptosomes in vitro. It is thus possible that other membrane-related steps of neurotransmission, such as receptor binding, are affected as well. We studied the effect of Mn 2+, Cu 2+, Cd 2+, Zn 2+, Hg 2+, Pb 2+ and of two organometals, methyl mercury and triethyl lead, on [ 3H]haloperidol binding in the striatal P 2 fraction assuming that such a study would reveal direct effects of the ions on dopaminergic D 2 receptor binding. According to non-linear curve fitting and Scatchard analysis, [ 3H]haloperidol bound to two sites in striatal tissue. The K d of the higher affinity site was 0.14 ± 0.05 nM and the B max 226.3 ± 50.3 fmol/mg protein. The respective values for the lower affinity sites were 2.49 ± 0.56 nM and 678.3 ± 111.4 fmol/mg protein. Among the divalent cations, Hg 2+ (IC 50 0.7 μM) and Cu 2+ (IC 50 2.9 μM) inhibited the high affinity [ 3H]haloperidol binding most potently. The inhibition by Cu 2+ was due to a decrease in the binding affinity (increase in the K d) while the number of binding sites remained unchanged. Zn 2+ inhibited the binding by 41.8% and Cd 2+ by 38.7% at 10 μM concentration while Pb 2+ and Mn 2+ did not affect binding significantly at this or lower concentrations. Methyl mercury (IC 50 0.9 μM) and triethyl lead (IC 50 2.6 μM) inhibited binding as well. Both these organometallic cations decreased the binding affinity but did not change significantly the number of binding sites. The results suggest that particularly Cu 2+, Hg 2+, methyl mercury and triethyl lead are able to decrease striatal dopaminergic D 2 receptor binding if they reach the receptors in the brain.

Central neurotoxicity after exposure to organic lead: Susceptibility to seizures

Organic leads are present in the environment from a variety of sources and produce metabolites such as triethyl lead (TEL) which have relatively long half-lives in the brain. However, little is known at present about the possible neurological consequences of exposure to these compounds. The susceptibility of an animal to experimentally induced seizures has been used as a reliable index of neural function to assess neurotoxic insult, and the present study assessed the effect of TEL upon this index. Adult male rats of the Fischer-344 strain were divided into groups and treated with 7.88 mg/kg of TEL or the control vehicle at 1, 7, 14 or 28 days prior to a single challenge with 35 mg/kg of pentylenetetrazole (PTZ). The rats treated with TEL were more susceptible to PTZ-induced seizures than were the controls. This effect was statistically significant on days 7, 14 and 28 after treatment, although some elevation of seizure scores was observed among TEL-treated animals on day 1. These results demonstrate a functional change in the central nervous system after exposure to TEL, which persists for at least 4 weeks after exposure.

Effects of triethyl lead on hot-plate responsiveness and biochemical properties of hippocampus

Rats treated with a single dose of triethyl lead chloride (TEL) by subcutaneous injection (7.9 mg/kg) showed a transient increase in latencies to lick the hind paw during hot-plate testing. The time course of triethyl lead-induced antinociception was temporally associated with depressed binding capacity of benzodiazepine receptor sites and reduced levels of Substance P. Both of these changes appeared to be confined to the hippocampus and were not apparent in the cortex or striatum of treated rats. Met-enkephalin levels were not altered in any region studied at any time during the 21-day postdosing period. Lead levels within the brain were higher than blood levels 1 week after triethyl lead injection. Although changes in more than one factor may account for the antinociceptive effect of triethyl lead, the hippocampus seems especially vulnerable to this amphiphilic organometal.

Experimental design considerations: a determinant of acute neonatal toxicity.

Few studies have investigated the potential developmental differences resulting from treating neonatal rat pups in either split-litter or whole-litter (nested) experimental designs. We directly compared rat pups dosed with triethyl lead (TEL) via both split-litter (representing all dosage groups within a single litter) and nested (all pups randomly assigned to a single litter receive the same dose) designs. The nested design was chosen to produce a uniform behavioral pattern across pups within each litter, whereas the split-litter design was chosen to promote pup competition and differential maternal care. On postpartum day 5, pups were administered either 12, 13, 14, or 15 mg/kg TEL, with each design represented by 12 litters. Although the LD50 values for the two designs were not significantly different, there were significantly more deaths in the 12 mg/kg dosage group within the split-litter design than in the nested design group. Preweaning survival times for split-litter dosed animals were also decreased. In addition, significant growth reduction (7-16%) was observed in the split-litter group, relative to the nested design animals during the preweaning period. These results suggest that neonatal toxicity is not independent from experimental design considerations, and that the factors of littermate competition and/or pup-induced maternal care deserve further study.

Influence of triethyl lead on the activity of enzymes of the ascites tumor cell plasma membrane and its microviscosity

The influence of triethyl lead (TriEL) on the activity of plasma membrane-bound enzymes of Ehrlich ascites tumor cells and on membrane fluidity has been investigated. TriEL completely inhibits the (Na + -K +)-ATPase in its membrane-bound and even more pronounced in its solubilized form between 5 and about 20 μM. It also alters the microviscosity of the isolated plasma membrane up to a temperature of about 30°C, but it does not have any influence on the fluidity of the membrane-derived liposomes. From these data it is concluded that the inhibitor may interact directly with the catalytic subunit of the (Na ++ K +)-ATPase, and may not exert its influence by interfering with the membrane lipids.

Organometal-induced antinociception: A time- and dose-response comparison of triethyl and trimethyl lead and tin

Recent reports have demonstrated that organolead and -tin compounds can alter behavioral reactivity to noxious stimuli. To further define the dose response and temporal characteristics of these neurobehavioral effects, male Fischer 344 rats were injected sc with either one-fourth, one-half, or three-fourths the acute LD50 of triethyl lead (TEL), triethyl tin (TET), trimethyl lead (TML), trimethyl tin (TMT), or distilled water and tested on a 57.5°C hot plate 1, 7, 14, 21, and 28 days after dosing. All four organometals altered hot plate latencies, but the magnitude and time course of these effects differed among the compounds. TEL produced a dose-related increase in latencies which was maximal 1 and 7 days postdosing and had dissipated by 28 days. In contrast, the group administered TML ( 3 4 LD50) exhibited a late developing antinocioception which became evident 14 days after dosing and persisted throughout the period of testing. The intermediate dose of TMT ( 1 2 LD50) also produced a delayed increase in response times which was observed 21 and 28 days post-treatment. The 3 4 LD50 dose of TMT produced increased hot plate latencies on all post-treatment test days except Day 14. TET ( 1 2 LD50) produced increased hot plate latencies 1, 7, 14, and 21 days postdosing and also induced a reversible ataxia and akinesia. Higher doses of TET proved lethal to 80% of the animals and lower doses failed to alter response times in the hot plate. These data demonstrate that trialkyl lead and tin compounds can produce time- and dose-related increases in hot plate latencies.

On the toxic effects of tetraethyl lead and its derivatives on the chrysophyte Poterioochromonas malhamensis—V. Electron microscopical studies

The unicellular alga Poterioochromonas malhamensis was treated for 2–7 days with toxic concentrations of lead nitrate (Pb, 1000 μM), triethyl lead (TriEL, 10 μM) and tetraethyl lead (TEL, 100 μM) and examined by transmission electron microscopy. 1000 μM Pb caused deformations of nuclei, structural alterations of mitochondria and an increase of autolytic activity. Both organic lead compounds were considerably more toxic than inorganic lead and the resultant ultrastructural alterations were highly complex, generally involving all cell organelles. The most prominent ultrastructural effects of organolead were an increase in the number and/or size of nuclei, contractile vacuoles, chloroplasts and dictyosomes. A marked accumulation of lipid droplets and of lysosomes was observed as well as the occurrence of (lipofuscin-like) residual bodies. Mitochondria were not remarkably affected. Basal body complexes consisting of up to four basal bodies without visible contacts to the cell membrane or to flagellae were found in the cytoplasm of giant cells. The described toxic effects of TEL and TriEL in P. malhamensis closely resemble the structural damages caused by organolead in other plant organisms or in tissues of experimental animals.

On the toxic effects of tetraethyl lead and its derivatives on the chrysophyte poterioochromonas malhamensis. IV. influence of lead antidotes and related agents

The unicellular alga Poterioochromonas malhamensis was exposed to 12.5 μM of inorganic or triethyl lead and simultaneously treated with lead antidotes and related agents at concentrations of 12.5, 31.25 and 62.5 μM. With increasing concentrations some of the antidotes alone slightly to severely inhibited algal growth (BAL ∗, CaNa 2EDTA, EDTA, Na 2EDTA), whereas others (DPA, EGTA, DIZO) were non-toxic at the concentrations tested. EGTA and CaNa 2EDTA, at all concentrations tested, completely suppressed the growth inhibition caused by inorganic lead; Na 2EDTA and EDTA were protective at the lower or medium concentrations, but DIZO. DPA and BAL considerably enhanced lead toxicity with increasing concentrations. None of the tested agents was able to reduce the toxic effects of triethyl lead. All antidotes markedly increased inhibition of algal growth caused by triethyl lead and some were even lethal to the poisoned algae either at the highest (Na 2EDTA, EDTA, DPA) or at all concentrations used (DIZO, BAL). P. malhamensis proved to be a highly sensitive and valuable tests system and the results obtained exhibited striking parallels to medical and clinical experience in therapy of human poisoning with inorganic and organic lead compounds.

Effect of triethyl lead on the placental uptake and transfer of the non-metabolisable α-aminoisobutyric acid in guinea pigs

In order to study the effect of organolead on the placental transfer of amino acids, triethyl lead chloride was administered by i.p. injections to pregnant guinea-pigs. The following day, the fetal part of the placenta was perfused in situ during i.v. infusion of α-aminoisobutyric acid (AIB) to the dam. It was found that triethyl lead treatment (2.5 mg/kg body wt) decreased the AIB-concentration in perfusion media compared with that of the control group. Treatment with 1 mg/kg body wt has no effect. It was also shown that the placental uptake of AIB in animals receiving 2.5 mg/kg body wt is significantly reduced compared with that of the control group. No such effect was obtained in animals receiving 1 mg/kg body wt. It is suggested that triethyl lead may inhibit placental Na +-K +-adenosinetriphosphatase, an enzyme involved with placental amino acid transport. Another possible explanation is a reduction in maternal placental blood flow.

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.

Metabolism of tetraorganolead compounds by rat-liver microsomal mono-oxygenase. II. Enzymic dealkylation of tetraethyl lead.

The biological degradation of tetraethyl lead to the triethyl lead cation by rat-liver microsomes from untreated, phenobarbital-pretreated and methylcholanthrene-pretreated rats has been studied; NADPH and oxygen are essential. The reaction is inhibited by CO and can be reactivated in the presence of O2 by irradiation with u.v. light with a max. at 450 nm. Substrate binding to cytochrome P-450 is of type 1. Apparent Km values for triethyl lead formation in microsomes were determined. The highest activities (i.e. about 2 nmol triethyl lead per nmol cytochrome P-450 per min) and the lowest apparent Km values (i.e. 7 X 10(-6) M) are found in microsomes from methylcholanthrene-pretreated rats. In microsomes from control and phenobarbital-pretreated rats Ks values from substrate-binding studies (about 2 X 10(-6) M) are one order of magnitude lower than the apparent Km values (3 X 10(-5) M).

Metabolism of tetraorganolead compounds by rat-liver microsomal mono-oxygenase. I. Analytical methods for quantitative determination of dealkylation products.

Different methods have been examined for the separation and determination of the triethyl lead ion in the presence of tetraethyl lead in biological material. Quantitative recovery of triethyl lead, and a limit of detection of less than 10(-8)M, were obtained with selective chromatography on kieselguhr (Extrelut) in combination with atomic absorption spectrometry.

Triethyl lead toxicity in relation to brain glutathione and glutathione 5-transferase

A dose-dependent decrease in the content of reduced glutathione (GSH) was found in the brain of rats following treatment with Pb(Et)3 for varying time intervals. Maximum inhibition of 19% was observed 3 h after the last dose of Pb(Et) 3 (8 mg/kg) daily for 3 days. Glutathione S-transferase activity did not change significantly. In vitro, there was no conjugation of GSH with PbEt 3 and the addition of brain cytosol did not catalyse the conjugation.

Progesterone and oestrogen concentrations in plasma during blastocyst implantation in mice exposed to triethyl lead.

Abstract: Female mice were injected intraperitoneally with triethyl lead chloride (3.0 or 6.0 mg/kg body weight, respectively) once a day on days 3–4 after mating. At the time of blastocyst implantation the plasma level of progesterone was significantly lower in females given 3.0 mg/kg body weight and the plasma levels of 17β‐oestradiol and progesterone were significantly lower in females given 6.0 mg/kg body weight than in control females.

On the toxic effects of tetraethyl lead and its derivatives on the chrysophyte Poterioochromonas malhamensis. III. Chemical analyses

Abstract The photolytic decomposition of tetraethyl lead (TEL) into the derivatives triethyl lead (TriEL), diethyl lead (DiEL) and into inorganic lead (Pb) in aqueous environment has been examined by using a single‐step dithizone extraction method. In cell‐free medium, TEL decomposes rapidly upon illumination to form TriEL, which accumulates in the medium. DiEL is formed in very small quantities only and without any significant accumulation, whereas the concentration of Pb increases slightly but continuously. In darkness the formation of TriEL amounts, as compared to light, to a maximum of 10 %, and DiEL as well as Pb are below the analytical threshold. There is a considerable loss of the initially added TEL: after 98 hr of incubation 96 % of the total lead are eliminated from the illuminated medium and 99.5 % from the non‐illuminated one. In illuminated tap water, where the creation of TriEL takes place much faster than in cultivation medium, the loss of total lead amounts to only 84 %. The formation kinetics for TriEL during the first 72 hr of incubation were determined as follows: tap water/ light: y = 0.18 x; cultivation medium/light: y = ln(l + 0.924 x); cultivation medium/darkness: y = ln(l + 0.006 x), with y being TriEL as ppm Pb and x the hours of incubation. Compared to previous biological experiments, these data conclusively indicate that TriEL is the toxic derivative of TEL which is created upon illumination and causes the severe inhibitory effects in cultures of Poterioochromonas malhamensis poisoned by TEL. The significance of these findings for polluted natural environments and for the metabolic pathway of organolead in intoxicated mammalia is discussed briefly, and a diagrammatical model is presented describing the presumed fate of TEL and its derivatives under experimental conditions.

On the toxic effects of tetraethyl lead and its derivatives on the chrysophyte Poterioochromonas malhamensis: II. Triethyl lead, diethyl lead, and inorganic lead

The toxic effects of the tetraethyl lead (TEL) derivatives triethyl lead (TriEL), diethyl lead (DiEL), and of inorganic lead (Pb 2+) on the Chrysophyte Poterioochromonas malhamensis were studied. The algae's parameters of interest were cell growth, and the formation of giant cells and of polyploid nuclei. (1) Based on their zero-growth-inducing concentrations, the tested lead compounds reveal the following relative toxicities to the algae: Pb 2+, light/darkness = 1 1 ; DiEL, light/darkness = 11 10 ; TriEL, light/darkness = 55 33 ; TEL, light/darkness = 7 0 . (2) The lead compounds differ greatly in the concentration ranges which cause slight inhibitory to lethal effects. The ranges are: Pb 2+ = 5 to >1000 μ m (>200×); DiEL = 5 to 100 μ m (20×); TriEL = 5 to 25 μ m (5×). (3) Pb 2+ is the least toxic TEL derivative. Its growth-inhibiting effect is remarkably high at very low concentrations (10μ m) but it increases only slightly with rising concentrations. Even 3-day treatment with 1000 μ m Pb 2+ is not lethal to the whole culture. Between 10 to 500 μ m Pb 2+, the nuclear indices of the cultures stay nearly unaffected, whereas there is a moderate but distinct increase in the percentage of polyploids, with maxima of 10% in the light and 6% in darkness. (4) DiEL is about ten times more toxic to Poterioochromonas than Pb 2+. It inhibits cellular growth and leads to the formation of giant cells and of polyploid nuclei under light and dark conditions. DiEL is much less stable to light than TriEL. In the course of the experiments it obviously tends to decompose upon illumination to a less active and less water-soluble compound. (5) Among the tested TEL derivatives, TriEL is the most toxic. In light as well as in darkness it inhibits algal growth and leads to the formation of giant multinucleated cells and of polyploid nuclei. The effects of TriEL are identical to those which were observed in TEL-treated illuminated cultures of Poterioochromonas. (6) Although DiEL has TriEL-like activity, there is evidence suggesting that in these experiments DiEL is not formed from TEL in critical amounts. The present studies further support the idea that TriEL is the primary derivative of TEL in illuminated algal cultures and that TriEL is the agent which causes the severe inhibitory effects in TEL toxicity to Poterioochromonas malhamensis.

Organometalloidal derivatives of the transition metals : VII. The thermal and photochemical properties of trialkyllead derivatives of Cr, Mo and W

Trimethyl- and tri ethyllead derivatives (η 5-C 5H 5)M(CO) 3PbR 3 (M  Cr, Mo, and W) have been synthesized. The trimethyllead derivatives are photochemically, and to a lesser extent, thermally unstable with respect to methyl transfer reactions that yield the corresponding (η 5-C 5H 5)M(CO) 3CH 3 complex. The related triethyllead complexes behave in a distinctly different fashion exhibiting rearrangements to [(η 5-C 5H 5)M(CO) 3] 3PbEt 2 (M  W, Mo). The reactions of the Cr, Mo, and W complexes with SO 2 yielded the corresponding alkyl sulphinato complexes as did the reaction of the related Fe complex [(η 5-C 5H 5)Fe(CO) 2PbEt 3].

Excretion of triethyl lead, diethyl lead and inorganic lead after injection of tetraethyl lead in rabbits (author's transl)

Rabbits were dosed with tetraethyl lead at 12 mg/kg; their organs, bloods, urines and feces were then assayed for tetraehyl lead, triethyl lead, diethyl lead, inorganic lead and total lead, and the chemical species of the lead excreted in the urines and feces were also studied. 1) One day after the dosing, the total lead in the urine was made up of about 69% diethyl lead, about 27% inorganic lead and about 4% triethyl lead. This ratio of the chemical species of lead to total lead remained unchanged even 7 days after the dosing. 2) Two days after the dosing, the total lead in the feces consisted of about 85% inorganic lead, about 9% diethyl lead and about 6% triethyl lead. Seven days after the dosing, the total lead in the feces comprised about 95% inorganic lead, about 4% triethyl lead and about 1% diethyl lead. 3) Intravisceral levels of lead were also measured 24 hours after the dosing. Triethyl lead accounted for about 84% of the total lead in the liver, about 68% in the kidneys, and about 59% in the blood. 4) Lead levels in B bile and intestinal contents were determined 24 hours after the dosing. Diethyl lead accounted for about 93% of total lead in B bile, while inorganic lead made up about 90% of the total lead in the cecal, the colonic and the rectal contents. 5) Conversion of diethyl lead by intestinal contents was studied in vitro by adding diethyl lead to the intestinal contents of normal rabbits. Incubation of the mixtures in the presence of N2 at 38°C for 180 minutes resulted in the conversion of 16% of the diethyl lead into inorganic lead in the cecal, the colonic and the rectal contents. The conversion of diethyl lead into inorganic lead in the cencal contents was followed up and it was found that the inorganic lead output increased with the passage of time. Diethyl lead proved to be the principal chemical species of lead that is eliminated into the urine and bile after dosing rabbits with tetraethyl lead. However, inorganic lead accounted for the major portion of the lead excreted into the feces. This finding suggested that the diethyl lead eliminated into the bile could be converted into inorganic lead in the intestines.