Neuropathology of trimethyltin intoxication. IV. Changes in the spinal cord

Role of autophagy inhibitors and inducers in modulating the toxicity of trimethyltin in neuronal cell cultures

Trimethyltin (TMT) is a triorganotin compound which determines neurodegeneration of specific brain areas particularly damaging the limbic system. Earlier ultrastructural studies indicated the formation of autophagic vacuoles in neurons after TMT intoxication. However, no evaluation has been attempted to determine the role of the autophagic pathway in TMT neurotoxicity. To assess the contribution of autophagy to TMT-induced neuronal cell death, we checked the vulnerability of neuronal cultures to TMT after activation or inhibition of autophagy. Our results show that autophagy inhibitors (3-methyladenine and L-asparagine) greatly enhanced TMT neurotoxicity. Conversely, known activators of autophagy, such as lithium and rapamycin, displayed neuroprotection against this toxic compound. Due to its diverse targets, the action of lithium was complex. When lithium was administered according to a chronic treatment protocol (6 days pretreatment) it was able to rescue both hippocampal and cortical neurons from TMT (or from glutamate toxicity used as reference). This effect was accompanied by an increased phosphorylation of glycogen synthase kinase 3 which is a known target for lithium neuroprotection. If the pre-incubation time was reduced to 2 h (acute treatment protocol), lithium was still able to counteract TMT toxicity in hippocampal but not in cortical neurons. The neuroprotective effect of lithium acutely administered against TMT in hippocampal neurons can be completely reverted by an excess of inositol and is possibly related to the inactivation of inositol monophosphatase, a key regulator of autophagy. These data indicate that TMT neurotoxicity can be dramatically modified, at least in vitro, by lithium addition which seems to act through different mechanisms if acutely or chronically administered.

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.

Neurotoxicological effects of trimethyltin on the stellate ganglion

Hamsters treated with trimethyltin (TMT), 3 or 4 mg/kg IP, developed neurological symptoms, including tremor, within 24 hours. Postganglionic action potentials were recorded from isolated stellate ganglia of untreated hamsters (control ganglia) and TMT-treated hamsters (TMT ganglia). Compound action potentials (nicotinic transmission) of control and TMT ganglia were not significantly different. The afterdischarges induced by preganglionic stimulation at 30 Hz for 2 sec in the presence of 10(-3) M hexamethonium (muscarinic transmission) were significantly smaller in TMT ganglia than in control ganglia. The discharges induced by the muscarinic cholinoceptor agonist. McN-A-343, were also smaller in the TMT ganglia. Two other muscarinic processes, posttetanic potentiation and potentiation of the compound action potential by McN-A-343, were not significantly reduced in the TMT ganglia. Morphological studies of the ganglia revealed marked changes in the TMT ganglia with severe neuronal degeneration including vacuole formations and accumulations of lysosomes in the cytoplasm. These results demonstrate that TMT has marked anatomical effects on the stellate ganglion that may lead to the reduction in muscarinic cholinergic transmission.

Biological activity of organotin compounds--an overview

As a consequence of the rapid expansion of the uses and applications of the organotin compounds, the concern about their environmental and health effects is increasing. The main subject of this overview is the current understanding of the mammalian toxicity of the organotin compounds. Four different types of target organ toxicity, namely neurotoxicity, hepatoxicity, immunotoxicity, and cutaneous toxicity, are discussed in more detail. The effects of the organotin compounds on the mitochondrial and cellular level are summarized and discussed in relation to the mode of action of these compounds on the central nervous system, the liver and bile duct, the immune system, and the skin.

Possible pathogenic mechanisms on trimethyltin-induced lesions in the hippocampus of adult and neonatal rats : An overview

The extent of trimethyltin (TMT) induced lesions in the rat hippocampal formation was reviewed. Adult rats were treated with a single dose of 6.0 mg TMT/kg body wt and were sacrificed between 3-60 d following exposure. In the hippocampal formation, the granule cells of fascia dentata showed early changes, which subsided considerably at a later time of the intoxication. On the other hand, destruction of the pyramidal neurons in the Ammon's horn became more pronounced with time, resulting in an extensive destruction of this structure. It is interesting to note that the CA3 neurons in the septal portion of the Ammon's horn were more vulnerable than those located more temporally, whereas the reverse pattern was observed for the dentate granule cells as well as for the CA1,2 neurons of the Ammon's horn. Special stain for zinc (Timm's method) also revealed a progressive depletion of zinc in the mossy fibers. When neonatal rats were treated at various times with a single injection of TMT, rapid and progressive destruction of the Ammon's horn was observed in animals injected between postnatal day (PND) 5-15. The progression of neuronal involvement was CA3b →CA3a, b →CA3(a,b,c)→CA3+CA2→entire Ammon's horn (CA1,2,3). This pattern of pathological lesion was in good concert with morphological development and functional maturity of the hippocampal formation. Destruction of the Ammon's horn neurons was proposed to be the result of hyperexcitation of the dentate granule neurons under the influence of TMT. Other possible mechanisms are also discussed.

Trimethyltin as a selective adrenal chemosympatholytic agent in vivo: effect precedes both clinical and histopathological evidence of toxicity

Trimethyltin (TMT) is a potent neuronotoxiciant but there is little data regarding its systemic effects. In this study, female BALB/c mice were administered either 0.9% saline or 2.75 mg TMT/kg intraperitoneally (i.p.). The animals were then housed in room air or in glass chambers flushed with either 10%, 40%, or 100% oxygen. Mice were sacrificed at 4, 8, 24, and 48 h after treatment and adrenals analyzed for various neurotransmitters by ion-pairing HPLC with electrochemical detection. In addition, adrenal S-adenosylmethionine (SAM) and blood ketone bodies were determined Sections of adrenals were evaluated by electron microscopy for histopathological changes. In vivo treatment with the toxicant resulted in a significant decrease in adrenal epinephrine and norepinephrine levels as early as 8 h following treatment. This effect preceded the appearance of both clinical signs and histopathological changes in the hippocampus by 12-24 h. With exposure to TMT in room air, mouse adrenal content of epinephrine fell from 1861.3 +/- 97.3 ng/4 mg to 1493.3 +/- 137.0 ng/4 mg while norepinephrine levels fell from 779.6 +/- 32.3 ng/4 mg to 503.4 +/- 44.3 ng/4 after 8 h. Supplementation with 40% oxygen did not attenuate this effect but in the case of mice treated with TMT and housed in 100% oxygen for 48 h, actually exacerbated the adrenal epinephrine depletion. Housing in approximately half normal atmospheric oxygen (10%) neither prevented nor enhanced the effects of TMT. The epinephrine/norepinephrine ratios were: control, 2.44; TMT (room air), 1.56; TMT (10% O2), 1.72; TMT (40% O2), 1.44; TMT (100% O2), 1.07. None of the conditions used in this study caused a decrease in adrenal dopamine, 5-hydroxyindole acetic acid (5-HIAA), 5-hydroxytryptamine (5-HT) or in the level of SAM. TMT treatment significantly increased blood ketone bodies indicating additional metabolic dysfunction. The significance of these findings in relation to TMT neuronotoxicity and fatty liver syndrome are discussed.

Behavioral effects of trimethyltin in two strains of mice. II. Multiple fixed ratio, fixed interval

Adult male C57BL/6N and BALB/c mice were trained to respond under a multiple fixed-ratio 30, fixed-interval 600-sec schedule of milk presentation. After performance had stabilized, each mouse received a single dose of trimethyltin X Cl (TMT) by ip administration. Three hours after administration, behavioral testing was started and continued at 24-hr intervals thereafter. The behavior of mice receiving 0.3 mg/kg was unaffected at 3, 27, and 51 hr after administration. Likewise, no effects were seen at 3 and 27 hr after 1 mg/kg. However, at 51 hr after administration there was a significant change in the temporal patterning of fixed-interval responding in the C57BL/6N strain, as shown by a decrease in the fixed-interval quarter-life. There was no significant change in the BALB/c strain at this dose. At 3 mg/kg the responding of both strains was greatly affected, and responding remained disrupted for at least 6 to 7 weeks. Neuropathological examination of the brains of both strains of mice showed no significant lesions (light microscopy) at 0.3 and 1 mg/kg. At 3 mg/kg, severe neuronal necrosis was observed in the fascia dentata region in both strains. Thus, in mice receiving TMT, the behavioral deficits were closely paralleled by the presence or absence of significant neuropathology.

Behavioral effects of trimethyltin in two strains of mice. I. Spontaneous motor activity

Adult male mice (C57BL/6N and BALB/c) were administered single doses of trimethyltin X Cl (TMT) by the ip route. The effects of TMT administration were determined on lethality (3-6 mg/kg), spontaneous motor activity (SMA), and the physical appearance of the mice (0.3-3 mg/kg). The effects of TMT on lethality were strain dependent in that a single dose of 3 mg/kg, ip, produced approximately 35% lethality in the C57BL/6N strain during the first 72 hr following administration. Less than 15% lethality was observed at this dose in the BALB/c strain. In both strains, 3.5 mg/kg, ip, produced more than 70% lethality during the first 144 hr after administration. Higher doses produced proportionally greater lethality. The SMA of both strains was not affected significantly at doses below 1 mg/kg, ip. At 1 mg/kg a small decrease in activity was observed during the first 24 hr. At 3 mg/kg, SMA was initially decreased in both strains. However, the decrease was of smaller magnitude in the C57BL strain and was followed by a large increase in SMA which did not return to control levels for approximately 1 week. An increase in SMA was observed in the BALB/c strain on the fifth day following TMT but returned to control values by Day 6. At 3 mg/kg, ip, the C57BL mice were observed to have severe whole body tremors and were hypersensitive to external stimuli. The whole body tremor was not as marked in the BALB/c strain. Neuropathological studies on the treated mice indicated that the behavioral studies paralleled the pathology produced by TMT. These data confirm the initial observation of greater sensitivity of the mouse to toxic effects of TMT compared to the rat.