Trimethyltin encephalopathy

Animal models of Alzheimer's disease: An originof innovativetreatments and insight to the disease's etiology

Alzheimer's disease (AD) is a progressive neurodegenerative disorder. The main pathogenic features are the development and depositionof senile plaques and neurofibrillary tangles in brain. Recent developments in the knowledge of the pathophysiological mechanisms behind Alzheimer's disease and other cognitive disorders have suggested new approaches to treatment development. These advancements have been significantly aided by the use of animal models, which are also essential for the assessment of therapies. Various approaches as transgenic animal model, chemical models, brain injury are used. This review will presentAD pathophysiology and emphasize several Alzheimer like dementia causingchemical substances, transgenic animal model and stereotaxy in order to enhance our existing knowledge of their mechanism of AD induction, dose, and treatment duration.

Effect of rottlerin on astrocyte phenotype polarization after trimethyltin insult in the dentate gyrus of mice

BACKGROUND

It has been demonstrated that reactive astrocytes can be polarized into pro-inflammatory A1 phenotype or anti-inflammatory A2 phenotype under neurotoxic and neurodegenerative conditions. Microglia have been suggested to play a critical role in astrocyte phenotype polarization by releasing pro- and anti-inflammatory mediators. In this study, we examined whether trimethyltin (TMT) insult can induce astrocyte polarization in the dentate gyrus of mice, and whether protein kinase Cδ (PKCδ) plays a role in TMT-induced astrocyte phenotype polarization.

METHODS

Male C57BL/6 N mice received TMT (2.6 mg/kg, i.p.), and temporal changes in the mRNA expression of A1 and A2 phenotype markers were evaluated in the hippocampus. In addition, temporal and spatial changes in the protein expression of C3, S100A10, Iba-1, and p-PKCδ were examined in the dentate gyrus. Rottlerin (5 mg/kg, i.p. × 5 at 12-h intervals) was administered 3-5 days after TMT treatment, and the expression of A1 and A2 transcripts, p-PKCδ, Iba-1, C3, S100A10, and C1q was evaluated 6 days after TMT treatment.

RESULTS

TMT treatment significantly increased the mRNA expression of A1 and A2 phenotype markers, and the increased expression of A1 markers remained longer than that of A2 markers. The immunoreactivity of the representative A1 phenotype marker, C3 and A2 phenotype marker, S100A10 peaked 6 days after TMT insult in the dentate gyrus. While C3 was expressed evenly throughout the dentate gyrus, S100A10 was highly expressed in the hilus and inner molecular layer. In addition, TMT insult induced microglial p-PKCδ expression. Treatment with rottlerin, a PKCδ inhibitor, decreased Iba-1 and C3 expression, but did not affect S100A10 expression, suggesting that PKCδ inhibition attenuates microglial activation and A1 astrocyte phenotype polarization. Consistently, rottlerin significantly reduced the expression of C1q and tumor necrosis factor-α (TNFα), which has been suggested to be released by activated microglia and induce A1 astrocyte polarization.

CONCLUSION

We demonstrated the temporal and spatial profiles of astrocyte polarization after TMT insult in the dentate gyrus of mice. Taken together, our results suggest that PKCδ plays a role in inducing A1 astrocyte polarization by promoting microglial activation and consequently increasing the expression of pro-inflammatory mediators after TMT insult.

The main mechanisms of trimethyltin chloride-induced neurotoxicity: Energy metabolism disorder and peroxidation damage

Trimethyltin chloride (TMT) is a by-product in the synthesis of organotin, a plastic stabilizer. With the rapid development of industry, the occupational hazards caused by TMT cannot be ignored. TMT is a typical neurotoxicant, which mainly damages the limbic system and brainstem of the nervous system. Previous studies have demonstrated that the neurotoxicity induced by TMT is linked to the inhibition of energy metabolism, but the underlying mechanism remains elusive. In order to investigate the mechanism of TMT-induced inhibition of energy metabolism, C57BL/6 male mice were administered by IP injection in different TMT doses (0 mg/kg, 1.00 mg/kg, 2.15 mg/kg and 4.64 mg/kg) and times (1d, 3d and 6d), and then the changes of superoxide dismutase (SOD) activity, malondialdehyde (MDA) level and Na+-K+-ATPase activity in cerebral cortex, cerebellum, hippocampus, pons, medulla oblongata of mice, the expressions of Na+-K+-ATPase protein, AMP-activated protein kinase (AMPK), phosphorylated AMP-activated protein kinase(p-AMPK)and peroxisome proliferator-activated receptor γ coactivator-1 α (PGC-1α) in hippocampus and medulla oblongata were measured; the effects of TMT on the viability, the activity of SOD, glutathione (GSH) and Na+-K+-ATPase, MDA level, and the expression of PGC-1α and Na+-K+-ATPase protein in N2a cells were measured by different TMT doses and times, in order to verify the experiments in vivo. Our results found that most of the mice showed depression, tremor, epilepsy, spasm and other symptoms after TMT exposure. Moreover, with the increase of TMT dose, the activity of Na+-K+-ATPase and the expressions of AMPK protein in the hippocampus and medulla oblongata of mice decreased, and the expressions of p-AMPK protein increased. Peroxidative damage was evident in hippocampus, medulla oblongata of mice and N2a cells, and the expression of PGC-1α and Na+-K+-ATPase protein was significantly down-regulated. Therefore, it is reasonable to believe that TMT-induced neurotoxic symptoms and inhibition of energy metabolism may be related to p-AMPK and down-regulation of PGC-1α in the hippocampus and medulla oblongata.

Tributyltin Alters Calcium Levels, Mitochondrial Dynamics, and Activates Calpains Within Dorsal Root Ganglion Neurons

Tributyltin (TBT) remains a global health concern. The primary route of human exposure to TBT is either through ingestion or skin absorption, but TBT's effects on the peripheral nervous system have still not been investigated. Therefore, we exposed in vitro sensory dorsal root ganglion (DRG) neurons to TBT at a concentration of 50-200 nM, which is similar to the observed concentrations of TBT in human blood samples. We observed that TBT causes extensive axon degeneration and neuronal death in the DRG neurons. Furthermore, we discovered that TBT causes an increase in both cytosolic and mitochondrial calcium levels, disrupts mitochondrial dynamics, decreases neuronal ATP levels, and leads to the activation of calpains. Additional experiments demonstrated that inhibition of calpain activation prevented TBT-induced fragmentation of neuronal cytoskeletal proteins and neuronal cell death. Thus, we conclude that calpain activation is the key executioner of TBT-induced peripheral neurodegeneration.

KIF5A-dependent axonal transport deficiency disrupts autophagic flux in trimethyltin chloride-induced neurotoxicity

Trimethyltin chloride (TMT) is widely used as a constituent of fungicides and plastic stabilizers in the industrial and agricultural fields, and is generally acknowledged to have potent neurotoxicity, especially in the hippocampus; however, the mechanism of induction of neurotoxicity by TMT remains elusive. Herein, we exposed Neuro-2a cells to different concentrations of TMT (2, 4, and 8 μM) for 24 h. Proteomic analysis, coupled with bioinformatics analysis, revealed the important role of macroautophagy/autophagy-lysosome machinery in TMT-induced neurotoxicity. Further analysis indicated significant impairment of autophagic flux by TMT via suppressed lysosomal function, such as by inhibiting lysosomal proteolysis and changing the lysosomal pH, thereby contributing to defects in autophagic clearance and subsequently leading to nerve cell death. Mechanistically, molecular interaction networks of Ingenuity Pathway Analysis identified a downregulated molecule, KIF5A (kinesin family member 5A), as a key target in TMT-impaired autophagic flux. TMT decreased KIF5A protein expression, disrupted the interaction between KIF5A and lysosome, and impaired lysosomal axonal transport. Moreover, Kif5a overexpression restored axonal transport, increased lysosomal dysfunction, and antagonized TMT-induced neurotoxicity in vitro. Importantly, in TMT-administered mice with seizure symptoms and histomorphological injury in the hippocampus, TMT inhibited KIF5A expression in the hippocampus. Gene transfer of Kif5a enhanced autophagic clearance in the hippocampus and alleviated TMT-induced neurotoxicity in vivo. Our results are the first to demonstrate KIF5A-dependent axonal transport deficiency to cause autophagic flux impairment via disturbance of lysosomal function in TMT-induced neurotoxicity; manipulation of KIF5A may be a therapeutic approach for antagonizing TMT-induced neurotoxicity.Abbreviations: 3-MA: 3-methyladenine; AAV: adeno-associated virus; ACTB: actin beta; AGC: automatic gain control; ATG: autophagy-related; ATP6V0D1: ATPase H+ transporting lysosomal V0 subunit D1; ATP6V1E1: ATPase H+ transporting lysosomal V1 subunit E1; CA: cornu ammonis; CQ: chloroquine; CTSB: cathepsin B; CTSD: cathepsin D; DCTN1: dynactin subunit 1; DG: dentate gyrus; DYNLL1: dynein light chain LC8-type 1; FBS: fetal bovine serum; GABARAP: GABA type A receptor-associated protein; GABARAPL1: GABA type A receptor associated protein like 1; GABARAPL2: GABA type A receptor associated protein like 2; GAPDH: glyceraldehyde-3-phosphate dehydrogenase; IPA: Ingenuity Pathway Analysis; KEGG: Kyoto Encyclopedia of Genes and Genomes; KIF5A: kinesin family member 5A; LAMP: lysosomal-associated membrane protein; MAP1LC3B/LC3B: microtubule-associated protein 1 light chain 3 beta; NBR1: NBR1 autophagy cargo receptor; OPTN: optineurin; PBS: phosphate-buffered saline; PFA: paraformaldehyde; PIK3C3/VPS34: phosphatidylinositol 3-kinase catalytic subunit type 3; PRM: parallel reaction monitoring; siRNA: small interfering RNA; SQSTM1/p62: sequestosome 1; SYP: synaptophysin; TAX1BP1: Tax1 binding protein 1; TMT: trimethyltin chloride; TUB: tubulin.

Acute Trimethyltin Poisoning Caused by Exposure to Polyvinyl Chloride Production: 8 Cases

This manuscript aimed to describe and analyze acute trimethyltin poisoning caused by exposure to polyvinyl chloride production and review the literature. Combined with an analysis of occupational hygiene survey data, the clinical data of 8 cases of acute trimethyltin poisoning were analyzed retrospectively. The clinical manifestations of acute trimethyltin poisoning are mainly related to central nervous system damage, hypokalemia and metabolic acidosis in patients with severe poisoning. Early positive potassium supplementation and symptomatic treatment are beneficial to the improvement of the condition. The early recognition of central nervous system manifestations and hypokalemia is beneficial for early diagnosis and correct treatment.

Enhanced neurogenesis is involved in neuroprotection provided by rottlerin against trimethyltin-induced delayed apoptotic neuronal damage

AIMS

We here investigated the effect of late- and post-ictal treatment with rottlerin, a polyphenol compound isolated from Mallotus philippinensis, on delayed apoptotic neuronal death induced by trimethyltin (TMT) in mice.

MAIN METHODS

Male C57BL/6N mice received a single injection of TMT (2.4 mg/kg, i.p.), and mice were treated with rottlerin after a peak time (i.e., 2 d post-TMT) of convulsive behaviors and apoptotic cell death (5.0 mg/kg, i.p. at 3 and 4 d after TMT injection). Object location test and tail suspension test were performed at 5 d after TMT injection. In addition, changes in the expression of apoptotic and neurogenic markers in the dentate gyrus were examined.

KEY FINDINGS

Late- and post-ictal treatment with rottlerin suppressed delayed neuronal apoptosis in the dentate gyrus, and attenuated memory impairments (as evaluated by object location test) and depression-like behaviors (as evaluated by tail suspension test) at 5 days after TMT injection in mice. In addition, rottlerin enhanced the expression of Sox2 and DCX, and facilitated p-ERK expression in BrdU-incorporated cells in the dentate gyrus of TMT-treated mice. Rottlerin also increased p-Akt expression, and attenuated the increase in the ratio of pro-apoptotic factors/anti-apoptotic factors, and consequent cytosolic cytochrome c release and caspase-3 cleavage. Rottlerin-mediated action was significantly reversed by SL327, an ERK inhibitor.

SIGNIFICANCE

Our results suggest that late- and post-ictal treatment with rottlerin attenuates TMT-induced delayed neuronal apoptosis in the dentate gyrus of mice via promotion of neurogenesis and inhibition of an on-going apoptotic process through up-regulation of p-ERK.

Association between 10 urinary heavy metal exposure and attention deficit hyperactivity disorder for children

Attention deficit hyperactivity disorder (ADHD) is associated with heavy metal exposure during adolescent development. However, the direct clinical evidence is limited. To investigate the possible association between environmental heavy metal exposure and ADHD, a case-control study was conducted with children aged 6-14 years in Guangzhou, China. Results showed that median concentrations of chromium (Cr), manganese (Mn), cobalt (Co), nickel (Ni), copper (Cu), molybdenum (Mo), tin (Sn), barium (Ba), and lead (Pb) in the urine of the case group were significantly higher than those of the control group. Children with ADHD had significantly higher levels of 8-OHdG and MDA compared with those from the control group. In addition, correlations between urinary Co, Ni, Cu, Mo, and Sn were significantly correlated with 8-OHdG and MDA concentrations in urine. After the case and control groups were combined together and the first quartile was used as the reference category, odds ratios (ORs) of ADHD for children increased significantly with the quartile increasing of urinary Co, Cu, and Sn. Our study provides a clinical evidence that Co, Cu, and Sn exposure, particularly Sn exposure, may be an environmental risk of the incurrence of ADHD for children. Furthermore, Co, Ni, Cu, Mo, and Sn exposures were significantly correlated with DNA and lipid damage.

Autophagy in trimethyltin-induced neurodegeneration

Autophagy is a degradative process playing an important role in removing misfolded or aggregated proteins, clearing damaged organelles, such as mitochondria and endoplasmic reticulum, as well as eliminating intracellular pathogens. The autophagic process is important for balancing sources of energy at critical developmental stages and in response to nutrient stress. Recently, autophagy has been involved in the pathophysiology of neurodegenerative diseases although its beneficial (pro-survival) or detrimental (pro-death) role remains controversial. In the present review, we discuss the role of autophagy following intoxication with trimethyltin (TMT), an organotin compound that induces severe hippocampal neurodegeneration associated with astrocyte and microglia activation. TMT is considered a useful tool to study the molecular mechanisms occurring in human neurodegenerative diseases such as Alzheimer's disease and temporal lobe epilepsy. This is also relevant in the field of environmental safety, since organotin compounds are used as heat stabilizers in polyvinyl chloride polymers, industrial and agricultural biocides, and as industrial chemical catalysts.

Protective Effects of Scolopendra Water Extract on Trimethyltin-Induced Hippocampal Neurodegeneration and Seizures in Mice

Trimethyltin (TMT) is an organotin compound with potent neurotoxic action characterized by neuronal degeneration in the hippocampus. This study evaluated the protective effects of a Scolopendra water extract (SWE) against TMT intoxication in hippocampal neurons, using both in vitro and in vivo model systems. Specifically, we examined the actions of SWE on TMT- (5 mM) induced cytotoxicity in primary cultures of mouse hippocampal neurons (7 days in vitro) and the effects of SWE on hippocampal degeneration in adult TMT- (2.6 mg/kg, intraperitoneal) treated C57BL/6 mice. We found that SWE pretreatment (0-100 μg/mL) significantly reduced TMT-induced cytotoxicity in cultured hippocampal neurons in a dose-dependent manner, as determined by lactate dehydrogenase and 3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrazolium bromide assays. Additionally, this study showed that perioral administration of SWE (5 mg/kg), from -6 to 0 days before TMT injection, significantly attenuated hippocampal cell degeneration and seizures in adult mice. Furthermore, quantitative analysis of Iba-1 (Allograft inflammatory factor 1)- and GFAP (Glial fibrillary acidic protein)-immunostained cells revealed a significant reduction in the levels of Iba-1- and GFAP-positive cell bodies in the dentate gyrus (DG) of mice treated with SWE prior to TMT injection. These data indicated that SWE pretreatment significantly protected the hippocampus against the massive activation of microglia and astrocytes elicited by TMT. In addition, our data showed that the SWE-induced reduction of immune cell activation was linked to a significant reduction in cell death and a significant improvement in TMT-induced seizure behavior. Thus, we conclude that SWE ameliorated the detrimental effects of TMT toxicity on hippocampal neurons, both in vivo and in vitro. Altogether, our findings hint at a promising pharmacotherapeutic use of SWE in hippocampal degeneration and dysfunction.

Inhibition of SERPINA3N-dependent neuroinflammation is essential for melatonin to ameliorate trimethyltin chloride-induced neurotoxicity

Trimethyltin chloride (TMT) is a potent neurotoxin that causes neuroinflammation and neuronal cell death. Melatonin is a well-known anti-inflammatory agent with significant neuroprotective activity. Male C57BL/6J mice were intraperitoneally injected with a single dose of melatonin (10 mg/kg) before exposure to TMT (2.8 mg/kg, ip). Thereafter, the mice received melatonin (10 mg/kg, ip) once a day for another three consecutive days. Melatonin dramatically alleviated TMT-induced neurotoxicity in mice by attenuating hippocampal neuron loss, inhibiting epilepsy-like seizures, and ameliorating memory deficits. Moreover, melatonin markedly suppressed TMT-induced neuroinflammatory responses and astrocyte activation, as shown by a decrease in inflammatory cytokine production as well as the downregulation of neurotoxic reactive astrocyte phenotype markers. Mechanistically, serine peptidase inhibitor clade A member 3N (SERPINA3N) was identified as playing a central role in the protective effects of melatonin based on quantitative proteome and bioinformatics analysis. Most importantly, melatonin significantly suppressed TMT-induced SERPINA3N upregulation at both the mRNA and protein levels. The overexpression of Serpina3n in the mouse hippocampus abolished the protective effects of melatonin on TMT-induced neuroinflammation and neurotoxicity. Melatonin protected cells against TMT-induced neurotoxicity by inhibiting SERPINA3N-mediated neuroinflammation. Melatonin may be a promising and practical agent for reducing TMT-induced neurotoxicity in clinical practice.

Trimethyltin (TMT) Reduces Testosterone Production in Adult Leydig Cells in Rats

Trimethyltin (TMT) is widely used as a plastic heat stabilizer and can cause severe toxicity. Here, the effects of TMT on testosterone production by adult Leydig cells and the related mechanisms of action were investigated. Eighteen adult male Sprague Dawley rats (56 days old) were randomly divided into 3 groups and given intraperitoneal injection of TMT for 21 consecutive days at the doses of 0 (vehicle control), 5, or 10 mg/kg/d. After treatment, trunk blood was collected for hormonal analysis. In addition, related gene and protein expression in testes was detected. At 10 mg/kg, TMT significantly reduced serum testosterone levels but increased serum luteinizing and follicle-stimulating hormone levels. The messenger RNA and protein levels of luteinizing hormone/chorionic gonadotropin receptor, steroidogenic acute regulatory protein, cytochrome P450 17-hydroxylase/17,20-lyase, follicle-stimulating hormone receptor, and SRY box 9 were significantly lower in the TMT-treated testes than in controls. Immunohistochemical study showed that TMT decreased adult Leydig cell number. In conclusion, these findings indicate that TMT reduced adult Leydig cell testosterone production in vivo by directly downregulating the expression of steroidogenic enzymes and decreasing adult Leydig cell number in the testis.

Styphnolobium japonicum (L.) Schott Fruits Increase Stress Resistance and Exert Antioxidant Properties in Caenorhabditis elegans and Mouse Models

Styphnolobium japonicum (L.) Schott is a popular Asian tree widely used in traditional medicine. The current study explored the potential stress resistance and antioxidant activities of its fruits. Phytochemical profiling of the hydroalcoholic fruit extract was done via high performance liquid chromatography-photodiode array-electrospray ionization-mass/mass (HPLC-PDA-ESI-MS/MS). Twenty four phenolic constituents were tentatively identified in the extract. The Caenorhabditis elegans (C. elegans) nematode model in addition to trimethyltin (TMT)-induced neurotoxicity mouse model were used for in vivo evaluation of its antioxidant properties. The ability of the extract to enhance stress resistance was manifested through increasing survival rate by 44.7% and decreasing basal reactive oxygen species (ROS) levels by 72.3% in C. elegans. In addition, the extract increased the levels of the stress response enzyme superoxide dismutase-3 (Sod-3) by 55.5% and decreased the expression of heat shock protein-16.2 (Hsp-16.2) in nematodes, which had been challenged by juglone, by 21%. Using a mouse model, the extract significantly decreased the expression of the oxidative stress marker malondialdehyde (MDA). Furthermore, an elevation in the levels of the antioxidant marker glutathione (GSH), SOD and heme oxygenase-1 (HO-1) enzymes were observed. Our findings imply that Styphnolobium japonicum has the potential to be used in future studies focusing on diseases associated with oxidative stress.

Trimethyltin chloride induces reactive oxygen species-mediated apoptosis in retinal cells during zebrafish eye development

Trimethyltin chloride (TMT), one of the most widely used organotin compounds in industrial and agricultural fields, is widespread in soil, aquatic systems, foodstuffs and household items. TMT reportedly has toxic effects on the nervous system; however, there is limited information about its effects on eye development and no clear associated mechanisms have been identified. Therefore, in the present study, we investigated eye morphology, vison-related behavior, reactive oxygen species (ROS) production, apoptosis, histopathology, and gene expression to evaluate the toxicity of TMT during ocular development in zebrafish embryos. Exposure to TMT decreased the axial length and surface area of the eye and impaired the ability of zebrafish to recognize light. 2',7'-dichlorofluorescein diacetate and acridine orange assays revealed dose-dependent increases in ROS formation and apoptosis in the eye. Furthermore, pyknosis of retinal cells was confirmed through histopathological analysis. Antioxidative enzyme-related genes were downregulated and apoptosis-inducing genes were upregulated in TMT-treated zebrafish compared to expression in controls. Retinal cell-specific gene expression was suppressed mainly in retinal ganglion cells, bipolar cells, and photoreceptor cells, whereas amacrine cell-, horizontal cell-, and Müller cell-specific gene expression was enhanced. Our results demonstrate for the first time the toxicity of TMT during eye development, which occurs through the induction of ROS-mediated apoptosis in retinal cells during ocular formation.

Organotins in Neuronal Damage, Brain Function, and Behavior: A Short Review

The consequences of exposure to environmental contaminants have shown significant effects on brain function and behavior in different experimental models. The endocrine-disrupting chemicals (EDC) present various classes of pollutants with potential neurotoxic actions, such as organotins (OTs). OTs have received special attention due to their toxic effects on the central nervous system, leading to abnormal mammalian neuroendocrine axis function. OTs are organometallic pollutants with a tin atom bound to one or more carbon atoms. OT exposure may occur through the food chain and/or contaminated water, since they have multiple applications in industry and agriculture. In addition, OTs have been used with few legal restrictions in the last decades, despite being highly toxic. In addition to their action as EDC, OTs can also cross the blood-brain barrier and show relevant neurotoxic effects, as observed in several animal model studies specifically involving the development of neurodegenerative processes, neuroinflammation, and oxidative stress. Thus, the aim of this short review is to summarize the toxic effects of the most common OT compounds, such as trimethyltin, tributyltin, triethyltin, and triphenyltin, on the brain with a focus on neuronal damage as a result of oxidative stress and neuroinflammation. We also aim to present evidence for the disruption of behavioral functions, neurotransmitters, and neuroendocrine pathways caused by OTs.

Toxin-Induced Experimental Models of Learning and Memory Impairment

Animal models for learning and memory have significantly contributed to novel strategies for drug development and hence are an imperative part in the assessment of therapeutics. Learning and memory involve different stages including acquisition, consolidation, and retrieval and each stage can be characterized using specific toxin. Recent studies have postulated the molecular basis of these processes and have also demonstrated many signaling molecules that are involved in several stages of memory. Most insights into learning and memory impairment and to develop a novel compound stems from the investigations performed in experimental models, especially those produced by neurotoxins models. Several toxins have been utilized based on their mechanism of action for learning and memory impairment such as scopolamine, streptozotocin, quinolinic acid, and domoic acid. Further, some toxins like 6-hydroxy dopamine (6-OHDA), 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) and amyloid-β are known to cause specific learning and memory impairment which imitate the disease pathology of Parkinson's disease dementia and Alzheimer's disease dementia. Apart from these toxins, several other toxins come under a miscellaneous category like an environmental pollutant, snake venoms, botulinum, and lipopolysaccharide. This review will focus on the various classes of neurotoxin models for learning and memory impairment with their specific mechanism of action that could assist the process of drug discovery and development for dementia and cognitive disorders.

Trimethyltin-induced hippocampal neurodegeneration: A mechanism-based review

Trimethyltin (TMT), a toxic organotin compound, induces neurodegeneration selectively involving the limbic system and especially prominent in the hippocampus. Neurodegeneration-associated behavioral abnormalities, such as hyperactivity, aggression, cognitive deficits, and epileptic seizures, occur in both exposed humans and experimental animal models. Previously, TMT had been used generally in industry and agriculture, but the use of TMT has been limited because of its dangers to people. TMT has also been used to make a promising in vivo rodent model of neurodegeneration because of its region-specific characteristics. Several studies have demonstrated that TMT-treated animal models of epileptic seizures can be used as tools for researching hippocampus-specific neurotoxicity as well as the molecular mechanisms leading to hippocampal neurodegeneration. This review summarizes the in vivo and in vitro underlying mechanisms of TMT-induced hippocampal neurodegeneration (oxidative stress, inflammatory responses, and neuronal death/survival). Thus, the present review may be helpful to provide general insights into TMT-induced neurodegeneration and approaches to therapeutic interventions for neurodegenerative diseases, including temporal lobe epilepsy.

Geochemistry of tin (Sn) in Chinese coals

Based on 1625 data collected from the published literature, the geochemistry of tin (Sn) in Chinese coals, including the abundance, distribution, modes of occurrence, genetic types and combustion behavior, was discussed to make a better understanding. Our statistic showed the average Sn of Chinese coal was 3.38 mg/kg, almost two times higher than the world. Among all the samples collected, Guangxi coals occupied an extremely high Sn enrichment (10.46 mg/kg), making sharp contrast to Xinjiang coals (0.49 mg/kg). Two modes of occurrence of Sn in Chinese coals were found, including sulfide-bounded Sn and clay-bounded Sn. In some coalfields, such as Liupanshui, Huayingshan and Haerwusu, a response between REEs distribution and Sn content was found which may caused by the transportation of Sn including clay minerals between coal seams. According to the responses reflecting on REEs patterns of each coalfield, several genetic types of Sn in coalfields were discussed. The enrichment of Sn in Guangxi coals probably caused by Sn-rich source rocks and multiple-stage hydrothermal fluids. The enriched Sn in western Guizhou coals was probably caused by volcanic ashes and sulfide-fixing mechanism. The depletion of Sn in Shengli coalfield, Inner Mongolia, may attribute to hardly terrigenous input and fluids erosion. As a relative easily volatilized element, the Sn-containing combustion by-products tended to be absorbed on the fine particles of fly ash. In 2012, the emission flux of Sn by Chinese coal combustion was estimated to be 0.90 × 10(9) g.

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.

In vitro models for neurotoxicology research

The nervous system has a highly complex organization, including many cell types with multiple functions, with an intricate anatomy and unique structural and functional characteristics; the study of its (dys)functionality following exposure to xenobiotics, neurotoxicology, constitutes an important issue in neurosciences.

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.

Molecular mechanisms of environmental organotin toxicity in mammals

Organotins such as tributyltin are suspected of having multiple toxic effects in mammals, in addition to their endocrine-disrupting function. Endogenous organotin concentrations in human blood range from a few to a few hundred nM. In this review, we summarize recent findings on the mechanisms of toxicity of environmental organotins such as tributyltin (TBT) and triphenyltin (TPT) in mammals. TBT and TPT are potent inhibitors of mitochondrial ATP synthase, and a recent study suggests that TBT binds directly to ATP synthase. Organotins disturb steroid biosynthesis and degradation. TBT and TPT are dual agonists of retinoid X receptor (RXR) and peroxisome proliferator-activated receptor γ (PPARγ); they also induce the differentiation of adipocytes in vitro and in vivo, probably through PPARγ activation, suggesting that they may work as obesogens. Environmental organotins are also neurotoxic; they induce behavioral abnormality and are toxic to the developing central nervous system. In vitro studies have shown that organotins induce intracellular Ca(2+) elevation and glutamate excitotoxicity. Recently, it was reported that endogenous levels of TBT decrease expression of 2-amino-3-(5-methyl-3-oxo-1,2-oxazol-4-yl)propanoic acid (AMPA) receptor subunit GluR2, leading to neuronal vulnerability. Most of the experimental studies have employed organotins at concentrations of µM order, and it remains important to clarify the molecular mechanisms of events induced by endogenous levels of environmental organotins.

Possible involvement of galectin-3 in microglial activation in the hippocampus with trimethyltin treatment

Trimethyltin (TMT) is an organotin neurotoxicant with effects that are selectively localized to the limbic system (especially the hippocampus), which produces memory deficits and temporal lobe seizures. Galectin-3 (Gal-3) is a beta-galactoside-binding lectin that is important in cell proliferation and regulation of apoptosis. The present study evaluated the temporal expression of Gal-3 in the hippocampus of adult BALB/c mice after TMT treatment (i.p., 2.5mg/kg). Western blotting analyses showed that Gal-3 immunoreactivity began to increase days after treatment; the immunoreactivity peaked significantly within days after treatment but significantly declined between days 4 and 8. Immunohistochemical analysis indicated that Gal-3 expression was very rare in the hippocampi of vehicle-treated controls. However, Gal-3 immunoreactivity appeared between 2 and 8 days after TMT treatment and was primarily localized to the hippocampal dentate gyrus (DG), in which neuronal degeneration occurred. The immunoreactivity was detected predominantly in most of the Iba1-positive microglia and in some GFAP-positive astrocytes of the hippocampal DG. Furthermore, Gal-3 expression co-localized with the pro-inflammatory enzymes cyclooxygenase-2 and inducible nitric oxide synthase in the hippocampal DG. Therefore, we suggest that Gal-3 is involved in the inflammatory process of neurodegenerative disorder induced by organotin intoxication.

Cytotoxic effects of two organotin compounds and their mode of inflicting cell death on four mammalian cancer cells

In this report, we have tested the cytotoxicity of two organotin (OT) compounds by flow cytometry on a panel of immortalized cancer cell lines of human and murine origin. Although the OT compounds exhibited varying levels of cytotoxicity, diphenylmethyltin chloride was more toxic than 1,4-bis (diphenylchlorostannyl)p-xylene on all cell lines tested. The OT compounds were found to be highly cytotoxic to lymphoma cell lines with lower toxicity toward the HeLa cervical cancer cell line. In order to discern the mechanism by which cell death was induced, additional experiments were conducted to monitor characteristic changes consistent with apoptosis and/or necrosis. Cell lines treated with the experimental compounds indicated that there was no consistent mode of cell death induction. However, both compounds induced apoptosis in the pro-B lymphocyte cell line, NFS-70. The work presented here also demonstrates that the two OT compounds possess selective cytotoxicity against distinct transformed cell lines.

Exposure to an organometal compound stimulates adipokine and cytokine expression in white adipose tissue

OBJECTIVE

White adipose tissue (WAT) is now considered a defined tissue capable of interactions with other organ systems. WAT role in elevating the level of systemic chronic inflammation suggests that alterations in this tissue as the result of disease or environmental factors may influence the development and progression of various obesity-related pathologies. This study investigated WAT cell-specific responses to an organometal compound, trimethyltin (TMT), to determine possible contribution to induced inflammation.

METHODS

Human primary mature adipocytes and macrophage differentiated THP-1 cells were cultured in TMT presence and relative toxicities and different adipokine levels were determined. The inflammatory response was examined in TMT presence for primary cells from obese ob/ob mice WAT, and after TMT injection in ob/ob mice.

RESULTS

Both adipocytes and macrophages were resistant to cell death induced by TMT. However, adipocytes cultured in TMT presence showed increased expression of TNFα and IL-6, and modified leptin levels. In macrophage cultures, TMT also increased TNFα and IL-6, while MCP-1 and MIP-1α were decreased. In vivo, a single injection of TMT in ob/ob mice, elevated TNFα, MIP-1α and adiponectin in WAT.

CONCLUSIONS

Elevation of the inflammatory related products can be induced by chemical exposure in adipocytes and macrophages, as well as murine WAT. These data suggest that numerous factors, including a systemic chemical exposure, can induce an inflammatory response from the WAT. Furthermore, when characterizing both chemical-induced toxicity and the progression of the chronic inflammation associated with elevated WAT content, such responses in this target tissue should be taken into consideration.

Enhanced neurogenesis in the olfactory bulb in adult mice after injury induced by acute treatment with trimethyltin

In adults, the subventricular zone is known to contain undifferentiated neural progenitor cells that proliferate and generate the olfactory bulb (OB) interneurons throughout life. We earlier showed that trimethyltin (TMT) causes neuronal damage in the granular cell layer of the OB in adult mice. In the current study, we examined neurogenesis in the OB in adult mice after injury induced by acute treatment with TMT. On day 2 post-TMT treatment, enhanced incorporation of 5-bromo-2'-deoxyuridine (BrdU) was seen in the granular cell layer of the OB. Many of the BrdU-labeled cells were undifferentiated cells on day 2 post-treatment. On day 30 post-TMT treatment, BrdU-labeled neuronal cells were dramatically increased in number in the granular cell layer of the OB. However, TMT treatment was ineffective in affecting the migration of BrdU-labeled cells from the subventricular zone to the OB. The results of a neurosphere assay revealed that the number of neurospheres derived from the OB was significantly increased on day 2 post-TMT treatment. The neurosphere-forming neural progenitor cells derived from the OB of TMT-treated animals were capable of differentiating into neuronal cells as well as into astrocytes. Taken together, our data suggest that the OB has the ability to undergo enhanced neurogenesis following TMT-induced neuronal injury in adult mice.

Mechanism underlying hypokalemia induced by trimethyltin chloride: Inhibition of H+/K+-ATPase in renal intercalated cells

Trimethyltin chloride (TMT), a byproduct of plastic stabilizers, has caused 67 poisoning accidents in the world; more than 98% (1814/1849) of the affected patients since 1998 have been in China. As a long-established toxic chemical, TMT severely affects the limbic system and the cerebellum; however, its relationship with hypokalemia, a condition observed in the majority of the cases in the last decade, remains elusive. To understand the mechanism underlying hypokalemia induced by TMT, Sprague-Dawley (SD) rats were administered TMT to determine the relationship between H(+)/K(+)-ATPase activity and the blood and urine K(+) concentration and pH, respectively. H(+)/K(+)-ATPase protein and mRNA were observed too. In vitro changes to intracellular pH, K(+) channels in renal cells were measured. The results showed that TMT increased potassium leakage from the kidney, raised urine pH, and inhibited H(+)/K(+)-ATPase activity both in vitro and in vivo. In the tested animals, H(+)/K(+)-ATPase activity was positively correlated with the decrease of plasma K(+) and blood pH but was negatively correlated with the increase of urine K(+) and urine pH (P<0.01), while TMT did not change the expression of H(+)/K(+)-ATPase protein and mRNA. TMT decreased intracellular pH and opened K(+) channels in renal intercalated cells. Our findings suggest TMT can directly inhibit the activity of H(+)/K(+)-ATPases in renal intercalated cells, reducing urine K(+) reabsorption and inducing hypokalemia.

Methylated Metal(loid) Species in Humans

While the metal(loid)s arsenic, bismuth, and selenium (probably also tellurium) have been shown to be enzymatically methylated in the human body, this has not yet been demonstrated for antimony, cadmium, germanium, indium, lead, mercury, thallium, and tin, although the latter elements can be biomethylated in the environment. Methylated metal(loid)s exhibit increased mobility, thus leading to a more efficient metal(loid) transport within the body and, in particular, opening chances for passing membrane barriers (blood-brain barrier, placental barrier). As a consequence human health may be affected. In this review, relevant data from the literature are compiled, and are discussed with respect to the evaluation of assumed and proven health effects caused by alkylated metal(loid) species.

Pseudoenzymatic dealkylation of alkyltins by biological dithiols

We investigated the time dependence of the degradation of three alkyltin derivatives by a nine amino acid linear peptide (I(1)LGCWCYLR(9)) containing a CXC motif derived from the primary sequence of stannin, a membrane protein involved in alkyltin toxicity. We monitored the reaction kinetics using the intrinsic fluorescence of the tryptophan residue in position 5 of the peptide and found that all of the alkyltins analyzed are progressively degraded to dialkyl derivatives, following a pseudoenzymatic reaction mechanism. The end point of the reactions is the formation of a covalent complex between the disubstituted alkyltin and the peptide cysteines. These data agree with the speciation profiles proposed for polysubstituted alkyltins in the environment and reveal a possible biotic degradation pathway for these toxic compounds.

JNK and p38 MAPK are independently involved in tributyltin-mediated cell death in rainbow trout (Oncorhynchus mykiss) RTG-2 cells

Mitogen-activated protein kinases (MAPKs) are a family of Ser/Thr protein kinases that transmit various extracellular signals to the nucleus inducing gene expression, cell proliferation, and apoptosis. Recent studies have revealed that organotin compounds induce apoptosis and MAPK phosphorylation/activation in mammal cells. In this study, we elucidated the cytotoxic mechanism of tributyltin (TBT), a representative organotin compound, in rainbow trout (Oncorhynchus mykiss) RTG-2 cells. TBT treatment resulted in significant caspase activation, characteristic morphological changes, DNA fragmentation, and consequent apoptotic cell death in RTG-2 cells. TBT exposure induced the rapid and sustained accumulation of phosphorylated MAPKs, including extracellular signal-regulated kinase (ERK), c-Jun N-terminal kinase (JNK), and p38 MAP kinase (p38 MAPK). Further analysis using pharmacological inhibitors against caspases and MAPKs showed that TBT also induced cell death in a caspase-independent manner and that p38 MAPK is involved in TBT-induced caspase-independent cell death, whereas JNK is involved in the caspase-dependent apoptotic pathway. Thus, TBT employs at least two independent signaling cascades to mediate cell death in RTG-2 cells. To our knowledge, this is the first study revealing the relationship between MAPK activation and TBT cytotoxicity in RTG-2 cells.

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.

Acute trimethyltin exposure induces oxidative stress response and neuronal apoptosis in Sebastiscus marmoratus

Trimethyltin (TMT) is a well-documented neurotoxicant that affects the function of central nervous system (CNS). In this study, we studied the neurotoxicity of TMT on the brain of marine fish Sebastiscus marmoratus. Our results showed that TMT acute exposure induced brain cell apoptosis in the telencephalon, optic tectum and cerebellum. In addition, we observed increased production of reactive oxygen species (ROS), nitric oxide (NO) and one asparate-specific cysteinyl protease named caspase-3 which are often associated with the processes of cell apoptosis, in the brain of S. marmoratus after acute treatment of TMT. Our results indicated that TMT induces neurotoxicity and oxidative stress in marine fish S. marmoratus. Our results suggested that TMT exposure in the environment may affect fish behaviors including schooling, sensory and motorial learnings, based on the observation of cell apoptosis in the cerebral regions.

Mitochondrial oxygen consumption inhibition importance for TMT-dependent cell death in undifferentiated PC12 cells

The evolving role of mitochondria as a target for different death-inducing noxae prompted us to investigate trimethyltin (TMT)-dependent effects on mitochondrial functionality. For this purpose, we used a homogeneous cell culture model represented by undifferentiated PC12 cells. Mitochondria isolated from PC12 cells treated with TMT for 6, 12 and 24h, showed a time-dependent inhibition of ADP-stimulated oxygen consumption using succinate or glutamate/malate as substrate. Using a fluorescent assay, the effect of TMT on mitochondrial membrane potential (delta Psi) in PC12 cells was also determined. After 24h in culture, a strong loss of mitochondrial membrane potential (delta Psi) was observed in TMT-treated cells. Collapse of mitochondrial membrane potential correlated with an increased expression of bax/bcl-2 ratio, as evaluated by polymerase chain reaction. Western blotting and spectrophotometric analysis showed that cytochrome c release and activation of caspase 3 were concurrently induced. Our findings suggest that inhibition of mitochondrial respiration represents the early toxic event for cell death in PC12 due to trimethyltin.

Hypoxia-like transcriptional activation in TMT-induced degeneration: microarray expression analysis on PC12 cells

To more clearly elucidate the complete network of molecular mechanisms induced by trimethyltin (TMT) toxicity, we used a homogeneous cell culture model represented by PC12 cells treated with 1 and 5 micromol/L TMT for 24 h. The gene expression profile was performed by microarray analysis, enabling us to identify 189 genes that were significantly modulated in treated cells, compared with controls. The main effects of TMT on gene expression seem to be related to the activation of metabolic processes (glycolysis and lipogenesis) along with cell death pathways, membrane remodeling and intracellular biomolecules trafficking. These alterations are triggered by the neurotoxicant earlier than a strong decrease in cell viability, which occurs at higher TMT concentrations or at later time points. Some aspects of the transcriptional modulation observed in this study resemble the gene activation known to occur during cell response to hypoxia. Other cell toxicants have also been reported to exert similar effects on gene expression. Therefore, our data help to delineate general basic adaptive mechanisms possibly shared by cells responding to different death-inducing noxae, such as TMT.

The cyto- and genotoxicity of organotin compounds is dependent on the cellular uptake capability

Organotin compounds have been widely used as stabilizers and anti-fouling agents with the result that they are ubiquitously distributed in the environment. Organotins accumulate in the food chain and potential effects on human health are disquieting. It is not known as yet whether cell surface adsorption or accumulation within the cell, or indeed both is a prerequisite for the toxicity of organotin compounds. In this study, the alkylated tin derivatives monomethyltin trichloride (MMT), dimethyltin dichloride (DMT), trimethyltin chloride (TMT) and tetramethyltin (TetraMT) were investigated for cyto- and genotoxic effects in CHO-9 cells in relation to the cellular uptake. To identify genotoxic effects, induction of micronuclei (MN), chromosome aberrations (CA) and sister chromatid exchanges (SCE) were analyzed and the nuclear division index (NDI) was calculated. The cellular uptake was assessed using ICP-MS analysis. The toxicity of the tin compounds was also evaluated after forced uptake by electroporation. Our results show that uptake of the organotin compounds was generally low but dose-dependent. Only weak genotoxic effects were observed after exposure of cells to DMT and TMT. MMT and TetraMT were negative in the test systems. After forced uptake by electroporation MMT, DMT and TMT induced significant DNA damage at non-cytotoxic concentrations. The results presented here indicate a considerable toxicological potential of some organotin species but demonstrate clearly that the toxicity is modulated by the cellular uptake capability.

Recent Studies on the Trimethyltin Actions in Central Nervous Systems

Trimethyltin (TMT) is a toxic organotin compound that produces injury to the central nervous systems of mammals. Recently, high-dose TMT (2.8 mg/kg) has been shown to produce neurodegeneration and subsequent neurogenesis specifically in the hippocampal dentate gyrus of mice, indicating that mice injected with TMT serve as a useful in vivo model to study neurogenesis as well as neurodegeneration in this brain region. In addition, gene-engineered mice have allowed research to focuse on the mechanisms of TMT toxicity. These studies have revealed the involvement of stannin, nuclear factor kappa B (NF-kappaB), presenilin-1, apolipoprotein E, and pituitary adenylyl cyclase-activating polypeptide (PACAP) in TMT toxicity and suggested the relationship between genetic mutations and neuronal susceptibility to degeneration. In this review, we briefly summarize the previous studies and discuss the current status of research on TMT.

Glutamate Excitotoxicity Is Involved in Cell Death Caused by Tributyltin in Cultured Rat Cortical Neurons

Tributyltin, an endocrine-disrupting chemical, has been used as a heat stabilizer, agricultural pesticide, and component of antifouling paints. In this study, the neurotoxicity of tributyltin was investigated in cultured rat cortical neurons. Tributyltin caused marked time- and dose-dependent increases in the number of trypan blue-stained cells. Measurement of extracellular glutamate concentration showed that glutamate release was induced by tributyltin. Application of the glutamate receptor antagonists MK-801 and CNQX decreased the neurotoxicity. These results suggest that released glutamate and glutamate receptors are involved in tributyltin toxicity. Next, we examined whether various factors, believed to be involved in glutamate excitotoxicity also influence tributyltin toxicity. Cell death induced by tributyltin was found to be reduced by alpha-tocopherol (a membrane-permeable antioxidant), SB202190 (a p38 mitogen-activated protein kinase inhibitor), and U-0126 (an extracellular signal-regulated protein kinase kinase inhibitor). MK-801 and CNQX decreased the phosphorylation of ERK, but not that of p38. A caspase-3 inhibitor had no effect on tributyltin toxicity, and tributyltin did not change the nuclear morphology. These results suggest that the glutamate excitotoxicity caused by tributyltin is unrelated to apoptosis. In conclusion, we demonstrated that tributyltin induced glutamate release and subsequent activation of glutamate receptors, leading to neuronal death. We propose two independent neuronal death pathways by tributyltin; one is glutamate receptor-dependent cell death via ERK phosphorylation, and the other may be glutamate receptor-independent cell death via p38 activation.

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.

Oxiracetam pre- but not post-treatment prevented social recognition deficits produced with trimethyltin in rats

The social recognition paradigm was used to investigate the effect of trimethyltin (TMT) in adult male rats. Consequently, the effect of chronic oxiracetam (OXI) treatment in TMT impaired animals was evaluated. In all experiments, a behavioural testing was performed 3 weeks after TMT administration. Experiment 1: A single TMT oral dose, 5 and 7.5 but not 2.5mg/kg, impaired the natural ability of the adults to recognize a juvenile conspecific that they encountered 30 min before. The dose of 5mg/kg TMT was chosen to be used in subsequent experiments. Experiment 2: Chronic OXI pre-+post-treatment, daily 3 or 30 mg/kg sc for 7 days before and 7 days after the insult, protected the adults against recognition deficit produced by TMT. Experiment 3: OXI pre- but not post-treatment (always 3 and 30 mg/kg) had beneficial effects on the social recognition. The findings suggest that social recognition ability of adult male rats pre-treated sufficiently long with OXI is resistant to the neurotoxicity effect of TMT.