The neurotoxicology and pathology of organomercury, organolead, and organotin

Aquaporin Inhibitors

Aquaporins (AQP) working as membrane channels facilitated water transport, play vital roles in various physiological progress including cell migration, energy metabolism, inflammation, etc. They are quite important drug targets, but elusive for discovery due to their undruggable properties. In this chapter, we summarized most fluently used methods for screening AQP inhibitors, including cell swelling assay, cell shrinking assay, and stopped-flow assay. And three classes of AQP inhibitors have been discussed, including metal-related inhibitors, quaternary ammonium salts, and small molecule inhibitors which further divided into four parts, sulfanilamide analogies, TGN-020, antiepileptic drugs, and others. It has been suggested that although they showed inhibition effects on AQP1, AQP3, AQP4, AQP7, or AQP9 in some researches, none of them could be asserted as AQP inhibitors to some extent. Discovering AQP inhibitors is a big challenge, but if successful, it will be a great contribution for human health.

Recent Trends and Future Perspectives of Emergent Analytical Techniques for Mercury Sensing in Aquatic Environments

Environmental emissions of mercury from industrial waste and natural sources, even in trace amounts, are toxic to organisms and ecosystems. However, industrial-scale mercury detection is limited by the high cost, low sensitivity/specificity, and poor selectivity of the available analytical tools. This review summarizes the key sensors for mercury detection in aqueous environments: colorimetric-, electrochemical-, fluorescence-, and surface-enhanced Raman spectroscopy-based sensors reported between 2014-2021. It then compares the performances of these sensors in the determination of inorganic mercury (Hg²⁺ ) and methyl mercury (CH₃ Hg⁺ ) species in aqueous samples. Mercury sensors for aquatic applications still face serious challenges in terms of difficult deployment in remote areas and low robustness, reliability, and selectivity in harsh environments. We provide future perspectives on the selective detection of organomercury species, which are especially toxic and reactive in aquatic environments. This review is intended as a valuable resource for scientists in the field of mercury sensing.

Serum trace metal association with response to erythropoiesis stimulating agents in incident and prevalent hemodialysis patients

Alterations in hemodialysis patients' serum trace metals have been documented. Early studies addressing associations levels of serum trace metals with erythropoietic responses and/or hematocrit generated mixed results. These studies were conducted prior to current approaches for erythropoiesis stimulating agent (ESA) drug dosing guidelines or without consideration of inflammation markers (e.g. hepcidin) important for regulation of iron availability. This study sought to determine if the serum trace metal concentrations of incident or chronic hemodialysis patients associated with the observed ESA response variability and with consideration to ESA dose response, hepcidin, and high sensitivity C-reactive protein levels. Inductively-coupled plasma-mass spectrometry was used to measure 14 serum trace metals in 29 incident and 79 prevalent dialysis patients recruited prospectively. We compared these data to three measures of ESA dose response, sex, and dialysis incidence versus dialysis prevalence. Hemoglobin was negatively associated with ESA dose and cadmium while positively associated with antimony, arsenic and lead. ESA dose was negatively associated with achieved hemoglobin and vanadium while positively associated with arsenic. ESA response was positively associated with arsenic. Vanadium, nickel, cadmium, and tin were increased in prevalent patients. Manganese was increased in incident patients. Vanadium, nickel, and arsenic increased with time on dialysis while manganese decreased. Changes in vanadium and manganese were largest and appeared to have some effect on anemia. Incident and prevalent patients' chromium and antimony levels exceeded established accepted upper limits of normal.

Protein pathway analysis to study development-dependent effects of acute and repeated trimethyltin (TMT) treatments in 3D rat brain cell cultures

Trimethyltin is an organometallic compound, described to be neurotoxic and to trigger neuroinflammation and oxidative stress. Previous studies associated TMT with the perturbation of mitochondrial function, or neurotransmission. However, the mechanisms of toxicity may differ depending on the duration of exposure and on the stage of maturation of brain cells. This study aim at elucidating whether the toxicity pathways triggered by a known neurotoxicant (TMT) differs depending on cell maturation stage or duration of exposure. To this end omics profiling of immature and differentiated 3D rat brain cell cultures exposed for 24 h or 10 days (10-d) to 0.5 and 1 μM of TMT was performed to better understand the underlying mechanisms of TMT associated toxicity. Proteomics identified 55 and 17 proteins affected by acute TMT treatment in immature and differentiated cultures respectively, while 10-day treatment altered 96 proteins in immature cultures versus 353 in differentiated. The results suggest different sensitivity to TMT depending on treatment duration and cell maturation. In accordance with known TMT mechanisms oxidative stress and neuroinflammation was observed after 10-d treatment at both maturation stages, whereas the neuroinflammatory process was more prominent in differentiated cultures than in the immature, no development-dependent difference could be detected for oxidative stress or synaptic neurodegeneration. Pathway analysis revealed that both vesicular trafficking and the synaptic machinery were strongly affected by 10-d TMT treatment in both maturation stages, as was GABAergic and glutamatergic neurotransmission. This study shows that omics approaches combined with pathway analysis constitutes an improved tool-set in elucidating toxicity mechanisms.

In vitro models to study insulin and glucocorticoids modulation of trimethyltin (TMT)-induced neuroinflammation and neurodegeneration, and in vivo validation in db/db mice

Brain susceptibility to a neurotoxic insult may be increased in a compromised health status, such as metabolic syndrome. Both metabolic syndrome and exposure to trimethyltin (TMT) are known to promote neurodegeneration. In combination the two factors may elicit additive or compensatory/regulatory mechanisms. Combined effects of TMT exposure (0.5-1 μM) and mimicked metabolic syndrome-through modulation of insulin and glucocorticoid (GC) levels-were investigated in three models: tridimensional rat brain cell cultures for neuron-glia effects; murine microglial cell line BV-2 for a mechanistic analysis of microglial reactivity; and db/db mice as an in vivo model of metabolic syndrome. In 3D cultures, low insulin condition significantly exacerbated TMT's effect on GABAergic neurons and promoted TMT-induced neuroinflammation, with increased expression of cytokines and of the regulator of intracellular GC activity, 11β-hydroxysteroid dehydrogenase 1 (11β-Hsd1). Microglial reactivity increased upon TMT exposure in medium combining low insulin and high GC. These results were corroborated in BV-2 microglial cells where lack of insulin exacerbated the TMT-induced increase in 11β-Hsd1 expression. Furthermore, TMT-induced microglial reactivity seems to depend on mineralocorticoid receptor activation. In diabetic BKS db mice, a discrete exacerbation of TMT neurotoxic effects on GABAergic neurons was observed, together with an increase of interleukin-6 (IL-6) and of basal 11β-Hsd1 expression as compared to controls. These results suggest only minor additive effects of the two brain insults, neurotoxicant TMT exposure and metabolic syndrome conditions, where 11β-Hsd1 appears to play a key role in the regulation of neuroinflammation and of its protective or neurodegenerative consequences.

Organotin Compounds Toxicity: Focus on Kidney

Organotin compounds (OTs) are synthetic persistent organometallic xenobiotics widely used in several commercial applications. They exert well-described harmful effects in brain, liver, adipose tissue, and reproductive organs, as they are endocrine-disrupting chemicals (EDCs), but the effects in the kidneys are less known. The kidneys are especially vulnerable to environmental contaminants because they are a metabolizing site of xenobiotics, therefore, pollutants can accumulate in renal tissue, leading to impaired renal function and to several renal abnormalities. Individuals chronically exposed to OTs present a threefold increase in the prevalence of kidney stones. These compounds can directly inhibit H⁺/K⁺-ATPase in renal intercalated cells, resulting in hypokalemia, renal tubular acidity, and increased urinary pH, which is a known risk factor for kidney stones formation. OTs effects are not only limited to induce nephrolithiasis, its nephrotoxicity is also due to increased reactive oxygen species (ROS). This increase leads to lipid peroxidation, abnormal cellular function, and cell death. Combined, the enzymatic and non-enzymatic antioxidant defense systems become deficient and there is a consequent uncontrolled generation of ROS that culminates in renal tissue damage. Still, few epidemiological and experimental studies have reported renal impact correlated to OTs exposure. This lack of investigation of the complete effect of OTs in renal function and structure led us to perform this review reporting the main researches about this subject.

Maskless wafer-level microfabrication of optical penetrating neural arrays out of soda-lime glass: Utah Optrode Array

Borrowing from the wafer-level fabrication techniques of the Utah Electrode Array, an optical array capable of delivering light for neural optogenetic studies is presented in this paper: the Utah Optrode Array. Utah Optrode Arrays are micromachined out of sheet soda-lime-silica glass using standard backend processes of the semiconductor and microelectronics packaging industries such as precision diamond grinding and wet etching. 9 × 9 arrays with 1100μ m × 100μ m optrodes and a 500μ m back-plane are repeatably reproduced on 2i n wafers 169 arrays at a time. This paper describes the steps and some of the common errors of optrode fabrication.

Experimental Evaluation of Proposed Small-Molecule Inhibitors of Water Channel Aquaporin-1

The aquaporin-1 (AQP1) water channel is a potentially important drug target, as AQP1 inhibition is predicted to have therapeutic action in edema, tumor growth, glaucoma, and other conditions. Here, we measured the AQP1 inhibition efficacy of 12 putative small-molecule AQP1 inhibitors reported in six recent studies, and one AQP1 activator. Osmotic water permeability was measured by stopped-flow light scattering in human and rat erythrocytes that natively express AQP1, in hemoglobin-free membrane vesicles from rat and human erythrocytes, and in plasma membrane vesicles isolated from AQP1-transfected Chinese hamster ovary cell cultures. As a positive control, 0.3 mM HgCl2 inhibited AQP1 water permeability by >95%. We found that none of the tested compounds at 50 µM significantly inhibited or increased AQP1 water permeability in these assays. Identification of AQP1 inhibitors remains an important priority.

Neurotoxicity of metals

Metals are frequently used in industry and represent a major source of toxin exposure for workers. For this reason governmental agencies regulate the amount of metal exposure permissible for worker safety. While essential metals serve physiologic roles, metals pose significant health risks upon acute and chronic exposure to high levels. The central nervous system is particularly vulnerable to metals. The brain readily accumulates metals, which under physiologic conditions are incorporated into essential metalloproteins required for neuronal health and energy homeostasis. Severe consequences can arise from circumstances of excess essential metals or exposure to toxic nonessential metal. Herein, we discuss sources of occupational metal exposure, metal homeostasis in the human body, susceptibility of the nervous system to metals, detoxification, detection of metals in biologic samples, and chelation therapeutic strategies. The neurologic pathology and physiology following aluminum, arsenic, lead, manganese, mercury, and trimethyltin exposures are highlighted as classic examples of metal-induced neurotoxicity.

Chronic trimethyltin chloride exposure and the development of kidney stones in rats

We recently reported that occupational exposure to trimethyltin (TMT) is a risk factor for developing kidney stones. To further examine the association between TMT exposure and the formation of kidney stones, we conducted a 180-day animal study and exposed the randomly grouped Sprague-Dawley (SD) rats to TMT in the drinking water at doses of 0, 8.2, 32.8 and 131.3 µg kg(-1) day(-1). Transient behavioral changes were observed in the high-dose group during the first 2 weeks of exposure. TMT exposure led to a significant dose-dependent inhibition of renal H(+)/K(+)-ATPase and an increase in urinary pH. In comparison to no kidney stones being identified in the control and the lowest dose group, 1 rat in the 32.8 µg kg(-1) day(-1) dose group and 3 out of 9 rats in the 131.3 µg kg(-1) day(-1) dose group were found to have stones in the kidney/urinary tract. Pathological analysis showed that more wide spread calcium disposition was observed in kidneys of rats with TMT exposure compared with the rats in the control group. However, X-ray diffraction (XRD) analysis found that the kidney stones were mainly composed of struvite with the formula: NH4MgPO4 6H2O, while calcium-containing components were also detected. Together, this study further demonstrates through animal studies that chronic exposure to a relatively low level of TMT induces nephrotoxicity and increases the risk for developing kidney stones.

Developmental and degenerative modulation of brain-derived neurotrophic factor transcript variants in the mouse hippocampus

Brain-derived neurotrophic factor (BDNF) is regarded as an important factor for neurogenesis, synaptic plasticity, and neuronal network organization in brain circuits. However, little is known about the regulation of BDNF transcript variants in the hippocampus during postnatal development and following chemically induced neurotoxicity. In the present study, we examined the expression of individual BDNF transcript variants in the mouse hippocampus on postnatal day (PD) 3, 7, 14, 21, and 56, as well as in the adult hippocampus 1, 2, 4, and 8 days after trimethyltin (TMT) treatment. During postnatal development, the expression levels of common BDNF-coding transcripts and BDNF transcript variants increased gradually in the hippocampus, but the temporal patterns of each exon transcript showed significant differences. In the TMT-treated hippocampus, the levels of common BDNF-coding transcripts and exon I, IIC, III, VII, VIII, and IXA transcripts were significantly increased 1 day post-treatment. These observations suggest that the differential regulation of BDNF exon transcripts may be associated with neuronal and synaptic maturation during postnatal development, and neuronal survival and synaptic plasticity in chemically induced neurodegeneration.

Cisplatin inhibits hippocampal cell proliferation and alters the expression of apoptotic genes

The hippocampus, which is critical for memory and spatial navigation, contains a proliferating stem cell niche that is especially vulnerable to antineoplastic drugs such as cisplatin. Although the damaging effects of cisplatin have recently been recognized, the molecular mechanisms underlying its toxic effects on this vital region are largely unknown. Using a focused apoptosis gene array, we analyzed the early cisplatin-induced changes in gene expression in the hippocampus of adult Sprague-Dawley rats and compared the results to those from the inferior colliculus, a non-mitotic auditory region resistant to cisplatin-induced cell death. Two days after a 12 mg/kg dose of cisplatin, significant increases were observed in five proapoptotic genes: Bik, Bid, Bok, Trp53p2, and Card6 and a significant decrease in one antiapoptotic gene Bcl2a1. In contrast, Nol3, an antiapoptotic gene, showed a significant increase in expression. The cisplatin-induced increase in Bid mRNA and decrease in Bcl2a1 mRNA were accompanied by a corresponding increase and decrease of their respective proteins in the hippocampus. In contrast, the cisplatin-induced changes in Bcl2a1, Bid, Bik, and Bok gene expression in the inferior colliculus were strikingly different from those in the hippocampus consistent with the greater susceptibility of the hippocampus to cisplatin toxicity. Cisplatin also significantly reduced immunolabeling of the cell proliferation marker Ki67 in the subgranular zone of the hippocampus 2 days post-treatment. These results indicate that cisplatin-induced hippocampal cell death is mediated by increased expression of proapoptotic and decreased antiapoptotic genes and proteins that likely inhibit hippocampal cell proliferation.

Gene expression profiling as a tool to investigate the molecular machinery activated during hippocampal neurodegeneration induced by trimethyltin (TMT) administration

Trimethyltin (TMT) is an organotin compound exhibiting neurotoxicant effects selectively localized in the limbic system and especially marked in the hippocampus, in both experimental animal models and accidentally exposed humans. TMT administration causes selective neuronal death involving either the granular neurons of the dentate gyrus or the pyramidal cells of the Cornu Ammonis, with a different pattern of localization depending on the different species studied or the dosage schedule. TMT is broadly used to realize experimental models of hippocampal neurodegeneration associated with cognitive impairment and temporal lobe epilepsy, though the molecular mechanisms underlying the associated selective neuronal death are still not conclusively clarified. Experimental evidence indicates that TMT-induced neurodegeneration is a complex event involving different pathogenetic mechanisms, probably acting differently in animal and cell models, which include neuroinflammation, intracellular calcium overload, and oxidative stress. Microarray-based, genome-wide expression analysis has been used to investigate the molecular scenario occurring in the TMT-injured brain in different in vivo and in vitro models, producing an overwhelming amount of data. The aim of this review is to discuss and rationalize the state-of-the-art on TMT-associated genome wide expression profiles in order to identify comparable and reproducible data that may allow focusing on significantly involved pathways.

Possible role of the glycogen synthase kinase-3 signaling pathway in trimethyltin-induced hippocampal neurodegeneration in mice

Trimethyltin (TMT) is an organotin compound with potent neurotoxic effects characterized by neuronal destruction in selective regions, including the hippocampus. Glycogen synthase kinase-3 (GSK-3) regulates many cellular processes, and is implicated in several neurodegenerative disorders. In this study, we evaluated the therapeutic effect of lithium, a selective GSK-3 inhibitor, on the hippocampus of adult C57BL/6 mice with TMT treatment (2.6 mg/kg, intraperitoneal [i.p.]) and on cultured hippocampal neurons (12 days in vitro) with TMT treatment (5 µM). Lithium (50 mg/kg, i.p., 0 and 24 h after TMT injection) significantly attenuated TMT-induced hippocampal cell degeneration, seizure, and memory deficits in mice. In cultured hippocampal neurons, lithium treatment (0–10 mM; 1 h before TMT application) significantly reduced TMT-induced cytotoxicity in a dose-dependent manner. Additionally, the dynamic changes in GSK-3/β-catenin signaling were observed in the mouse hippocampus and cultured hippocampal neurons after TMT treatment with or without lithium. Therefore, lithium inhibited the detrimental effects of TMT on the hippocampal neurons in vivo and in vitro, suggesting involvement of the GSK-3/β-catenin signaling pathway in TMT-induced hippocampal cell degeneration and dysfunction.

Toxicity of trimethyltin and dimethyltin in rats and mice

Extensive uses of methyltin compounds in polyvinyl chloride (PVC) production have led to a dramatic increase of occupational-related methyltin poisoning accidents and the widespread contamination of methyltins in various environmental media. Here, we conducted studies to compare the acute toxicity induced by trimethyltin (TMT) and dimethyltin (DMT), and investigated the cumulative toxic effects of TMT in rats and mice. Neurobehavioral changes were observed in rats and mice treated with either DMT or TMT, but we also observed that both TMT and DMT exposure in rats significantly lowered the blood potassium level. Moreover, the cumulative toxic coefficient factor of TMT was 1.7 in rats versus 3.8 in mice, suggesting a high cumulative risk for rats and a moderate risk for mice. In summary, we demonstrated that acute and chronic exposure to methyltin compounds induced neurotoxicity and hypokalemia. Moreover, our study suggests that TMT can accumulate in the body and pose a risk for workers chronically exposed to a low dose of TMT.

Safe Management of Mass Fatalities following Chemical, Biological, and Radiological Incidents

Contaminated mass fatalities following the release of chemical, biological, or radiological agents pose a potential major health hazard. A United Kingdom government investigation has identified a number of areas of risk. This paper presents an outline of the findings of the study and describes specific pathways for the management of contaminated and non-contaminated fatalities. Factors determining the choice between cremation and burial are discussed. Effective decontamination remains a neglected area of study for both fatalities and casualties.

Trimethyltin initially activates the caspase 8/caspase 3 pathway for damaging the primary cultured cortical neurons derived from embryonic mice

The organotin trimethyltin (TMT) is well known to cause neuronal damage in the central nervous system. To elucidate the mechanisms underlying the toxicity of TMT toward neurons, we prepared primary cultures of neurons from the neocortex of mouse embryos. A continuous exposure to TMT produced a decrease in cell viability as well as an increase in the number of cells with nuclear condensation/shrinkage at the exposure time window up to 24 hr. In addition to the events at the early time window, lactate dehydrogenase released was significantly elevated at the later exposure time from 36 to 48 hr. With a 3-hr exposure to TMT, a significant increase was observed in the activity of caspase 8, but not in that of caspase 9. TMT exposure produced no elevation in the level of cytochrome c released from mitochondria until 12 hr of exposure, with a significant facilitation of cytochrome c release at the exposure times of 16 and 24 hr. After the activation of caspase 8 by TMT exposure, caspase 3 activation and nuclear translocation of caspase-activated DNase were caused by exposure for 6 hr or longer. However, nuclear DNase II was elevated at the later time window of exposure. A caspase inhibitor completely prevented TMT from damaging the cells in any time window. Taken together, our data are the first demonstration that TMT toxicity is initially caused by activation of the caspase 8/caspase 3 pathway for nuclear translocation of DNases in cortical neurons in primary culture.

Severe neurotoxicity following ingestion of tetraethyl lead

Organic lead compounds are potent neurotoxins which can result in death even from small exposures. Traditionally, these compounds are found in fuel stabilizers, anti-knock agents, and leaded gasoline. Cases of acute organic lead intoxication have not been reported for several decades. We report a case of a 13-year-old Iraqi male who unintentionally ingested a fuel stabilizer containing 80-90% tetraethyl lead, managed at our combat support hospital. The patient developed severe neurologic symptoms including agitation, hallucinations, weakness, and tremor. These symptoms were refractory to escalating doses of benzodiazepines and ultimately required endotracheal intubation and a propofol infusion. Adjunctive therapies included chelation, baclofen, and nutrition provided through a gastrostomy tube. The patient slowly recovered and was discharged in a wheelchair 20 days after ingestion, still requiring tube feeding. Follow-up at 62 days post-ingestion revealed near-resolution of symptoms with residual slurred speech and slight limp. This case highlights the profound neurotoxic manifestations of acute organic lead compounds.

Impact of gasoline inhalation on some neurobehavioural characteristics of male rats

BACKGROUND

This paper examines closely and compares the potential hazards of inhalation of two types of gasoline (car fuel). The first type is the commonly use leaded gasoline and the second is the unleaded type enriched with oxygenate additives as lead substituent in order to raise the octane number. The impacts of gasoline exposure on Na+, K+-ATPase, superoxide dismutase (SOD), acetylcholinesterase (AChE), total protein, reduced glutathione (GSH), and lipid peroxidation (TBARS) in the cerebral cortex, and monoamine neurotransmitters dopamine (DA), norepinephrine (NE) and serotonin (5-HT) in the cerebral cortex, hippocampus, cerebellum and hypothalamus were evaluated. The effect of gasoline exposure on the aggressive behaviour tests was also studied.

RESULTS

The present results revealed that gasoline inhalation induced significant fluctuations in the levels of the monoamine neurotransmitters in the studied brain regions. This was concomitant with a decrease in Na+, K+-ATPase activity and total protein content. Moreover, the group exposed to the unleaded gasoline exhibited an increase in lipid peroxidation and a decrease in AChE and superoxide dismutase activities. These physiological impairments were accompanied with a higher tendency towards aggressive behaviour as a consequence to gasoline inhalation.

CONCLUSION

It is concluded from the present work that chronic exposure to either the leaded or the unleaded gasoline vapours impaired the levels of monoamine neurotransmitters and other biochemical parameters in different brain areas and modulated several behavioural aspects related to aggression in rats.

The sequential magnetic resonance images of tri-methyl tin leukoencephalopathy

Organotin compounds are commonly used in industrial and agriculture. It causes toxic effects on skin, eyes, respiratory system, gastrointestinal system, and nervous system. After cleaning a di-methyl tin tank, 43-year-old man showed a dizziness, disorientation, visual hallucination, and agitation. Through a measurement by liquid chromatography and inductively coupled plasma-mass spectrometry, di-methyl tin and tri-methyl tin was detected. Although magnetic resonance (MR) image 3 days after exposure showed no abnormal signal intensity, follow-up MR images 15 days after exposure revealed abnormal extensive signal intensities in the white matter that was not ever coincident with previous reports. It was hardly explainable that previous abnormal signal intensities of MR image nearly disappeared 4 months later. We present a case of a patient who developed acute toxic leukoencephalopathy from an acute inhalational exposure to methyl tin with sequential MR images showing an involvement of white matter that was not ever reported.

High susceptibility of cortical neural progenitor cells to trimethyltin toxicity: involvement of both caspases and calpain in cell death

Neural progenitor cells play an essential role in both the developing embryonic nervous system and in the adult brain, where the capacity for self-renewal would be important for normal brain functions. In the present study, we used embryonic cortical neural progenitor cells to investigate the effects of trimethyltin chloride (TMT) on the survival of neural progenitor cells. In cultures of cortical neural progenitor cells, the formation of round neurospheres was observed in the presence of epidermal growth factor and basic fibroblast growth factor within 9 days in vitro. The neurospheres were then harvested for subsequent replating and culturing for assessment of cell viability in either the presence or absence of TMT at the concentration of 5microM. Lasting exposure to TMT produced not only nuclear condensation in the cells in a time-dependent manner over a period of 6-24h, but also the release of lactate dehydrogenase into the culture medium. Immunoblot and immunocytochemical analyses revealed that TMT had the ability to activate both caspase-3 and calpain, as well as to cause nuclear translocation of deoxyribonuclease II, which is located within cytoplasm in intact cells. Additionally, treatment with a calpain inhibitor [trans-epoxysuccinyl-l-leucylamido-(4-guanidino) butane] and a caspase inhibitor [Z-Val-Ala-Asp(OMe)-CH2F] produced a significant reduction in damaged cells induced by TMT. Taken together, our data indicate that neural progenitor cells are highly susceptible to TMT in undergoing cell death via the activation of 2 parallel pathways, ones involving calpain and the other, caspase-3.

Oral lead exposure induces dysbacteriosis in rats

OBJECTIVES

Lead's (Pb(II)) possible role in intestinal pathologies of microbial etiology remains mostly unknown. The aim of this study was to examine the effects of lead on the gut microbial community and its interactions with rat intestinal epithelium.

METHODS

The lead-induced changes in different intestinal microbial groups (lactose-positive lac(+) and -negative lac(-) E.coli strains, lactobacilli and yeasts) were followed separately by the colony-forming unit (CFU) method. Samples were taken from outbred white rats subjected to different exposure schedules. Additionally, the impact of different lead doses on microbial adhesion to cultured intestinal cells (IEC-6) was investigated. Finally, the lead accumulation and distribution were measured by means of atomic absorption spectrometry.

RESULTS

For the first time it was shown that oral lead exposure causes drastic changes in the gut microbial community. Proportional to the lead dose received, the relative number of lactose-negative E.coli cells increased dramatically (up to 1,000-fold) in comparison to the other microbial groups during 2 wk of exposure. Considering the number of microbes in the intestine, such a shift in intestinal microflora (dysbacteriosis) is very significant. Adhesion studies showed certain stimulating effects of lead on E. coli attachment to rat intestinal epithelium as compared to Lactobacillus attachment.

CONCLUSIONS

The mechanisms providing the apparent competitive success of the lac(-) group are unclear but could be related to changes in surface interactions between microbial and host cells. This study may provide important clues for understanding the pathological effects of metal dietary toxins in human beings.

Speciation of alkyllead in aqueous samples with application of liquid membrane probe for extraction and preconcentration

Lead is known to be toxic, especially in its organic forms (organolead, OL). In the environment tetraalkyllead species are rapidly degraded by sunlight and atmospheric constituents like ozone or hydroxyl radicals. Such breakdown yields the soluble forms such as trialkyllead and dialkyllead and finally ionic lead species. The liquid membrane extraction probe (LMP) device has been developed and used as an extraction and preconcentration tool for the speciation analysis of organolead compounds by GC/MS. It allows analysis of OL species at low concentrations in complicated matrices of environmental samples. The effect of pH, stirring rate, and time that influence the extraction efficiency of OL extraction by the LMP method were optimized. The transformation of tetramethyllead in aqueous media at different concentrations of major ions K(+), Na(+), Ca(2+), Mg(2+), Cl(-), SO(4)(2-) and the application of LMP to environmental samples are presented. It was found that degradation of tetramethyllead takes between 24 and 37 days. The detection limit (LOD) of the method for all organolead species investigated is around 4.7 microg/L, with a limit of quantitation of 15 microg/L.

Effects of tri butyl tin acetate on dopamine biosynthesis and l-dopa-lnduced cytotoxicity in pc12 cells

The effects of tributyltin acetate (TBTA) on dopamine biosynthesis and L-3,4-dihydroxyphenylalanine (L-DOPA)-induced cytotoxicity in PC12 cells were examined. TBTA at concentrations of 0.1-0.2 microM inhibited dopamine biosynthesis by reducing tyrosine hydroxylase (TH) activity and TH gene expression in PC12 cells. TBTA at 0.1-0.4 microM also reduced L-DOPA (20-50 microM)-induced increases in dopamine content for 24 h in PC12 cells. TBTA at concentrations up to 0.3 microM did not affect cell viability. However, TBTA at concentrations higher than 0.4 microM caused apoptotic cytotoxicity. Exposure of PC12 cells to non-cytotoxic (0.1 and 0.2 microM) or cytotoxic (0.4 microM) concentrations of TBTA with L-DOPA (20, 50 and 100 microM) significantly increased the cell loss and the percentage of apoptotic cells after 24 or 48 h compared with TBTA or L-DOPA alone. These data suggest that TBTA inhibits dopamine biosynthesis and enhances L-DOPA-induced cytotoxicity in PC12 cells.

Efficacy of moclobemide in a rat model of neurotoxicant-induced edema

The potent antidepressant effect of moclobemide, a selective and reversible type A monoamine oxidase (MAO) inhibitor, is clinically established. In view of the ongoing debate on the neuroprotective properties of MAO inhibitors, the present study was undertaken to further define the protective effect of moclobemide in a rat model of neurotoxicant-induced edema. In this model, daily oral triethyltin (TET) administration for 5 consecutive days strongly perturbed the rat behaviour and induced a cerebral edema at the 5th day. Oral coadministration of moclobemide (2 × 100 mg·kg–1·day–1) with TET blocked the development of brain edema and the increase in the cerebral chloride content induced by TET. Moreover, moclobemide reduced the increase in the cerebral sodium content and attenuated the neurological deficit. In conclusion, moclobemide possesses potent protective properties in this rat model of cerebral edema, suggesting potential clinical utility as a neuroprotectant.

Effects of a biodegradable polymer synthesized with inorganic tin on the chondrogenesis of human articular chondrocytes

Recent study has shown that biodegradable polymers are attractive candidates for chondrocyte fixation and further transplantation in cartilage tissue engineering. Poly (glycolic acid) (PGA), a polymer of glycolic acid, is widely used in orthopedic applications as a biodegradable polymer. Organotin, lead, antimony, and zinc are catalysts commonly used in synthesizing PGA. Here, we investigated the biocompatibility of PGA, synthesized with and without inorganic tin as a catalyst in chondrogenesis of human articular chondrocytes in a micromass culture system. Significant enhancement of chondrocyte proliferation and expression of the collagen type II protein gene were observed in cultures treated with PGA synthesized with a tin catalyst. However, aggrecan gene expression was very similar to the control culture. Amount of collagen type II protein was also increased in the same group of cultured chondrocytes. In contrast, PGA without a catalyst caused overall inhibition of chondrogenesis. Despite several positive findings, extensive investigations are essential for the feasibility of this PGA(Sn) in future clinical practice.

Structure, dynamics, and membrane topology of stannin: a mediator of neuronal cell apoptosis induced by trimethyltin chloride

Organotin compounds or alkyltins are ubiquitous environmental toxins that have been implicated in cellular death. Unlike other xenobiotic compounds, such as organomercurials and organoleads, alkyltins activate apoptotic cascades at low concentrations. Trimethyltin (TMT) chloride is amongst the most toxic organotin compounds, and is known to selectively inflict injury to specific regions of the brain. Stannin (SNN), an 88-residue mitochondrial membrane protein, has been identified as the specific marker for neuronal cell apoptosis induced by TMT intoxication. This high specificity of TMT makes SNN an ideal model system for understanding the mechanism of organotin neurotoxicity at a molecular level. Here, we report the three-dimensional structure and dynamics of SNN in detergent micelles, and its topological orientation in lipid bilayers as determined by solution and solid-state NMR spectroscopy. We found that SNN is a monotopic membrane protein composed of three domains: a single transmembrane helix (residues 10-33) that transverses the lipid bilayer at approximately a 20 degrees angle with respect to the membrane normal; a 28 residue unstructured linker, which includes a conserved CXC metal-binding motif and a putative 14-3-3zeta binding domain; and a distorted cytoplasmic helix (residues 61-79) that is partially absorbed into the plane of the lipid bilayer with a tilt angle of approximately 80 degrees from the membrane normal. The structure and architecture of SNN within the lipid environment provides insight about how this protein transmits toxic insults caused by TMT across the membrane.

Cytometric analysis of adverse action of diphenyl ditelluride on rat thymocytes: cell shrinkage as a cytotoxic parameter

Despite the growing use of organotellurium compounds in the chemical and biomedical fields, there has been no great concern about their toxicity until now. To test the possibility that diphenyl ditelluride (DPDT) and tellurium chloride (TeCl2), organic and inorganic tellurium compounds, may exert adverse action on mammals, their effects on rat thymocytes were examined under in vitro conditions using a flow cytometer with fluorescent probes. Incubation of thymocytes with DPDT at 300 nM or more for 24 h significantly increased the populations of shrunken cells and of cells with hypodiploidal DNA. Z-VAD-FMK, a paninhibitor of caspases, greatly suppressed the DPDT-induced increase in the hypodiploidal cell population, suggesting the involvement of caspase activation in DPDT toxicity. Hence, it is possible that DPDT would increase the population of thymocytes undergoing apoptosis if the blood concentration in mammals reached at least 300 nM or more. TeCl2 was much less potent than DPDT in increasing the population of hypodiploidal cells.

Interactions of Alkyltin Salts with Biological Dithiols: Dealkylation and Induction of a Regular β-Turn Structure in Peptides

Organotin compounds specifically target vicinal dithiols, thereby inhibiting the function of essential enzymes. Here, we present the NMR binding studies of trimethyltin (TMT) and dimethyltin (DMT) chlorides with a linear peptide (ILGCWCYLR) derived from the membrane protein stannin (SNN). We show that this peptide is able to dealkylate TMT and bind DMT, adopting a stable type-I beta-turn conformation. Both the NMR data and the calculated structures indicate that the two cysteines coordinate the tin atom in a distorted tetrahedral geometry. The molecular geometries and tin coordination state were confirmed using density functional theory (DFT). In addition, NMR spectral parameters back calculated from the DFT minimized structure compared well with experimental data. These results in conjunction with studies on peptide variants (i.e., C4S, C6S, and Y7F) demonstrate unequivocally the key role of biological dithiols in both the dealkylation and binding of organotin compounds. This peptide serves as a model system for alkyltin-protein interactions and gives new insights into the biological fate of alkyltin compounds.

Neurotoxic effects of trimethyltin and triethyltin on human fetal neuron and astrocyte cultures: a comparative study with rat neuronal cultures and human cell lines

Trimethyltin (TMT) and triethyltin (TET) caused cell death in cultures of primary human neurons and astrocytes, rat neurons and human neuroblastoma cell lines. Human neurons and astrocytes showed a delayed response to TMT cytotoxicity. After 24h of TMT exposure, LC50 values were 148.1, 335.5 and 609.7 microM for SK-N-MC neuroblastoma cell line, neurons and astrocytes, respectively. Over 5 days of exposure, the cytotoxic potency of TMT increased about 70-fold in human cortical neurons. Rat hippocampal neurons were the most vulnerable cells to TMT cytotoxicity, exhibiting an LC50 value 30-fold lower (1.4 microM) than that of rat cerebellar granule cells (44.28 microM). With the exception of rat hippocampal neurons, TET was more potent than TMT in inducing cell death (LC50 values of 3.5-16.9 microM). Moreover, TET was more effective than TMT in increasing intracellular free Ca2+ concentration in human and rat neurons. This work shows that human fetal neuron and astrocyte cultures are a useful model for studying the neurotoxic effects of these environmental contaminants and, thus, predicting their impact on human health.

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

Neuropeptide Y and somatostatin participate differently in the seizure-generating mechanisms following trimethyltin-induced hippocampal damage

Trimethyltin (TMT) is an organic metal known to induce neuronal degeneration in the hippocampus, and abnormal behavior characterized by seizures, increased aggression and memory deficits. We administered TMT to rats and studied the changes of neuropeptide Y (NPY) and somatostatin (SOM) in the hippocampus. Phenobarbital (PB) was administered as an anticonvulsant to assess the effect of seizures on neuropeptide expressions in both dorsal and ventral hippocampus. Histochemically, NPY-immunoreactivity increased 4 days after TMT treatment in the hilus of the hippocampus, then progressively decreased and dropped to a level below control 16 days after TMT treatment. Detection of NPY mRNA by in situ hybridization preceded the detection of NPY by immunohistochemistry. NPY mRNA signals increased in the hilus 2 days after TMT treatment. SOM-immunoreactivity also increased in the hilus of the hippocampus 2 days after TMT treatment, then decreased rapidly to a normal level. Similar changes in SOM mRNA were demonstrated by in situ hybridization. PB treatment significantly inhibited changes of NPY in terms of both immunoreactivity and mRNA expression; however, the same treatment failed to affect changes in SOM expression. This suggests that NPY and SOM act by different mechanisms in TMT-induced neurodegeneration.

Neurotoxicologic sequelae of tributyltin intoxication in rats

Tributyltin oxide (TBTO) is a commonly used biocide. The purpose of this study is to correlate the toxicity of TBTO with the alterations of brain neurotransmitters and ATPases. TBTO was given by stomach tube to rats at either 37.5 or 75 mg x kg (-1)for 3 consecutive days. Nervous signs appeared in treated animals and the mortality reached 12 and 30%, respectively. The levels of brain dopamine, norepinephrine and serotonin decreased in a dose-dependent manner. The activities of brain total ATPase, Mg (2+)-ATPase and Na (+)/K (+)- ATPase were suppressed. The activity of Na (+)/K (+)- ATPase was more severely affected than that of Mg (2+)-ATPase. Histopathological changes in brain included hyperaemia, focal haemorrhages in vacuolated myelinated fibres, chromatolysis, or complete necrosis of neurons, degenerative changes, or complete absence of purkinje cells in the cerebellum.

Trimethyltin and triethyltin differentially induce spontaneous noradrenaline release from rat hippocampal slices

The environmental contaminants trimethyltin (TMT) and triethyltin (TET) stimulated the spontaneous release of [(3)H]noradrenaline ([(3)H]NA) from hippocampal slices in a time- and concentration-dependent manner. TMT was the most potent compound, exhibiting an EC50 value 10-fold lower (3.8 microM) than that of TET (39.5 microM). Metal-evoked [(3)H]NA release did not increase in the absence of desipramine and was completely blocked by reserpine preincubation, indicating a vesicular origin of [(3)H]NA release but not a mechanism involving reversal of the transmitter transporter. The voltage-gated Na(+) channel blocker tetrodotoxin (TTX) did not affect metal-evoked [(3)H]NA release. [(3)H]NA release elicited by TMT was partially extracellular Ca(2+)-dependent, since it was significantly decreased in a Ca(2+)-free EGTA-containing medium, whereas TET induced an extracellular Ca(2+)-independent release of [(3)H]NA. Neither inhibitors of Ca(2+)-entry through Na(+)/Ca(2+)exchanger and voltage-gated calcium channels, nor agents that interfere with Ca(2+)-mobilization from intracellular stores affected [(3)H]NA release induced by TMT. TET-evoked [(3)H]NA release was reduced by ruthenium red, which depletes mitochondrial Ca(2+)stores, but was not modified by caffeine and thapsigargin, which interfere with Ca(2+)mobilization from endoplasmic reticulum. The fact that TET effect was also attenuated by DIDS, an inhibitor of anion exchange, indicates that the effect of TET on spontaneous [(3)H]NA release may be mediated by intracellular mobilization of Ca(2+) from mitochondrial stores through a Cl(-) dependent mechanism.

An integrative approach to neurotoxicology

Exposure of human populations to a wide variety of chemicals has generated concern about the potential neurotoxicity of new and existing chemicals. Experimental studies conducted in laboratory animals remain critical to the study of neurotoxicity. An integrative approach using pharmacokinetic, neuropathological, neurochemical, electrophysiological, and behavioral methods is needed to determine whether a chemical is neurotoxic. There are a number of factors that can affect the outcome of a neurotoxicity study, including the choice of animal species, dose and dosage regimen, route of administration, and the intrinsic sensitivity of the nervous system to the test chemical. The neurotoxicity of a chemical can vary at different stages of brain development and maturity. Evidence of neurotoxicity may be highly subjective and species specific and can be complicated by the presence of systemic disease. The aim of this paper is to give an overview of these and other factors involved in the assessment of the neurotoxic potential for chemicals. This article discusses the neurotoxicity of several neurotoxicants (eg, acrylamide, trimethyltin, 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine, manganese, and ivermectin), thereby highlighting a multidisciplinary approach to the assessment of chemically induced neurotoxicity in animals. These model chemicals produce a broad range of effects that includes peripheral axonopathy, selective neuronal damage within the nervous system, and impaired neuronal-glial metabolism.