Acute Toxic Insult Research Articles

Role of DAPK in neuronal cell death

Neuronal cell death happens as a result of the normal physiological process that occurs during development, or as part of the pathological process that occurs during disease. Death-associated protein kinase (DAPK) is an intracellular protein that mediates cell death by its serine/threonine kinase activity, and transmits apoptotic cell death signals in various cells, including neurons. DAPK is elevated in injured neurons in acute models of injury such as ischemia and seizure. The absence of DAPK has been shown to protect neurons from a wide variety of acute toxic insults. Moreover, DAPK also regulates neuronal cell death during central nervous system development. Neurons are initially overproduced in the developing nervous system, following which approximately one-half of the original cell population dies. This "naturally-occurring" or "programmed" cell death is essential for the construction of the developing nervous system. In this review, we focus on the role of DAPK in neuronal cell death after neuronal injury. The participation of DAPK in developmental neuronal death is also explained.

Uncommon reaction to a common prescription

In May, 2010, a 50 year-old man presented to us with a 10 day history of abdominal pain, fever, and shivering with elevated C reactive protein and leucocytes. He had a past history of congestive subvalvular aortic stenosis which had not required surgical treatment. He weighed 85 kg, had normal renal and hepatic function, and was not on any regular medication. CT of the abdomen suggested an abscess of the appendix. He was treated with intravenous cefotaxime 1 g three times a day and metro nidazole 1 g daily for 2 days and discharged with oral metronidazole 400 mg three times a day and cipro fl oxacin 500 mg twice a day. 5 days later, he returned with a complete loss of hearing, fatigue, dizziness, vomiting, impaired balance, ataxia and dysarthria. He was afebrile and CT of the brain was normal. We suspected an encephalopathy caused by an adverse eff ect of metro nidazole and/or ciprofl oxacin, and both drugs were discontinued. Within one hour after admission he became unconscious. He was transferred to the intensive care unit and was intubated. MRI of the brain showed bilateral and symmetric swellings of the cerebellar dentate nuclei, dorsal medulla, dorsal pons, midbrain, corpus callosum and increased signal intensity in the supratentorial periventricular white matter (fi gure A), which was in accordance with previously described cases of metro nidazole induced encephalopathy. Meropenem, aciclovir and betamethasone were started to cover possible meningitis and encephalitis. The electroencephalogram, lumbar puncture, infl ammatory markers, microbiological and viral testing, autoimmune markers, and thyroid function tests were all normal. Although the metronidazole concentration in plasma was not measured, an overdose was unlikely because our patient had only been prescribed one box containing 30 pills of 400 mg, and had followed the prescription accordingly. His symptoms and MRI fi nd ings were not found to correlate with earlier described cases of ciprofl oxacin-induced encephalopathy. Wernicke’s encepha lopathy may produce similar clinical symptoms, however without MRI lesions of cerebellar dentate nuclei. Furthermore, thiamine was not admin istered to our patient. Viral encephalitis and bacterial meningitis were ruled out. According to the Naranjo probability scale our patient’s symptoms were classifi ed as probably caused by metronidazole (Naranjo Score 5/13). The case was reported to and confi rmed by the Swedish adverse eff ect register institute “SWEDIS” as a probable case of metronidazoleinduced encephalopathy. His symptoms gradually resolved and an MRI two months later, showed a clear resolution of the earlier described signal changes (fi gure B and webappendix). At fi nal follow-up in September, 2010, he was well with only residual hearing impairment. Metronidazole has been used clinically for more than 30 years and is regarded as a safe antibiotic with few adverse reactions Encephalopathy is an extremely rare but serious, neurological side-eff ect. The pathophysiology of metronidazole encephalopathy is unknown, but an acute toxic insult producing axonal swelling may be responsible and the encephalopathy may be completely reversible. There are only twenty cases of metronidazole-induced encephalopathy currently reported in English medical literature. In these cases, neurological adverse eff ects of metronidazole occurred particularly with doses exceeding 2 g daily or when used for prolonged periods. Although MRI fi ndings are typical for this condition, ignorance of metronidazole-induced encephalopathy may result in clinical misjudgment and delay of the diagnosis.

Erythema Multiforme-like Irritant Contact Dermatitis after Application of an Antiscabies Treatment

We describe the case of an irritant contact dermatitis due to an antiscabies treatment in a man who presented to our clinic with an important cutaneous reaction with many hemorrhagic, "target" erythema multiforme-like lesions, as the result of an acute toxic insult of the skin by permethrin 5%. This is a possible, but very uncommon symptom of non-eczematous contact dermatitis and an unusual drug causing the acute hypersensitivity reaction typical of erythema multiforme.

Myelin‐associated glycoprotein protects neurons from excitotoxicity

In addition to supporting rapid nerve conduction, myelination nurtures and stabilizes axons and protects them from acute toxic insults. One myelin molecule that protects and sustains axons is myelin-associated glycoprotein (MAG). MAG is expressed on the innermost wrap of myelin, apposed to the axon surface, where it interacts with axonal receptors that reside in lateral membrane domains including gangliosides, the glycosylphosphatidylinositol-anchored Nogo receptors, and β1-integrin. We report here that MAG protection extends beyond the axon to the neurons from which those axons emanate, protecting them from excitotoxicity. Compared to wild type mice, Mag-null mice displayed markedly increased seizure activity in response to intraperitoneal injection of kainic acid, an excitotoxic glutamate receptor agonist. Mag-null mice also had larger lesion volumes in response to intrastriatal injection of the excitotoxin NMDA. Prior injection of a soluble form of MAG partially protected Mag-null mice from NMDA-induced lesions. Hippocampal neurons plated on proteins extracted from wild-type rat or mouse myelin were resistant to kainic acid-induced excitotoxicity, whereas neurons plated on proteins from Mag-null myelin were not. Protection was reversed by anti-MAG antibody and replicated by addition of soluble MAG. MAG-mediated protection from excitotoxicity was dependent on Nogo receptors and β1-integrin. We conclude that MAG engages membrane-domain resident neuronal receptors to protect neurons from excitotoxicity, and that soluble MAG mitigates excitotoxic damage in vivo.

Organophosphates induce distal axonal damage, but not brain oedema, by inactivating neuropathy target esterase

Single doses of organophosphorus compounds (OP) which covalently inhibit neuropathy target esterase (NTE) can induce lower-limb paralysis and distal damage in long nerve axons. Clinical signs of neuropathy are evident 3 weeks post-OP dose in humans, cats and chickens. By contrast, clinical neuropathy in mice following acute dosing with OPs or any other toxic compound has never been reported. Moreover, dosing mice with ethyloctylphosphonofluoridate (EOPF) – an extremely potent NTE inhibitor – causes a different (subacute) neurotoxicity with brain oedema. These observations have raised the possibility that mice are intrinsically resistant to neuropathies induced by acute toxic insult, but may incur brain oedema, rather than distal axonal damage, when NTE is inactivated. Here we provide the first report that hind-limb dysfunction and extensive axonal damage can occur in mice 3 weeks after acute dosing with a toxic compound, bromophenylacetylurea. Three weeks after acutely dosing mice with neuropathic OPs no clinical signs were observed, but distal lesions were present in the longest spinal sensory axons. Similar lesions were evident in undosed nestin- cre:NTEfl/fl mice in which NTE had been genetically-deleted from neural tissue. The extent of OP-induced axonal damage in mice was related to the duration of NTE inactivation and, as reported in chickens, was promoted by post-dosing with phenylmethanesulfonylfluoride. However, phenyldipentylphosphinate, another promoting compound in chickens, itself induced in mice lesions different from the neuropathic OP type. Finally, EOPF induced subacute neurotoxicity with brain oedema in both wild-type and nestin - cre:NTEfl/fl mice indicating that the molecular target for this effect is not neural NTE.

Myelin-Associated Glycoprotein (MAG) Protects Neurons from Acute Toxicity Using a Ganglioside-Dependent Mechanism

Myelin-associated glycoprotein (MAG), a protein expressed on the innermost wrap of myelin, contributes to long-term axon stability as evidenced by progressive axon degeneration in Mag-null mice. Recently, MAG was also found to protect axons from acute toxic insults. In the current study, rat dorsal root ganglion neurons were cultured on control substrata and substrata adsorbed with myelin proteins. Neurons on myelin-adsorbed surfaces were resistant to acute degeneration of neurites induced by vincristine, a cancer chemotherapeutic agent with neuropathic side effects. Myelin-mediated protection was reversed by anti-MAG antibody and was absent when cells were cultured on extracts from Mag-null mouse myelin, confirming the protective role of MAG. Gangliosides (sialylated glycosphingolipids) are one functional class of axonal receptors for MAG. In the current studies, a direct role for gangliosides in mediating the acute protective effects of MAG was established. Treatment of neurons with sialidase, an enzyme that cleaves the terminal sialic acids required for MAG binding, reversed MAG's protective effect, as did treatment with (1R,2R)-1-phenyl-2-hexadecanoylamino-3-pyrrolidino-1-propanol, an inhibitor of glycosphingolipid biosynthesis. In contrast, treatment with phosphatidylinositol-specific phospholipase C, an enzyme that cleaves Nogo receptors (NgR, another class of MAG receptor), or with a peptide inhibitor of an NgR-associated signaling molecule p75(NTR), failed to diminish MAG-mediated protection. Inhibiting the Rho-associated protein kinase ROCK reversed protection. We conclude that MAG protects neurites from acute toxic insult via a ganglioside-mediated signaling pathway that involves activation of RhoA. Understanding MAG-mediated protection may provide opportunities to reduce axonal damage and loss.

P53-dependent cell death signaling in neurons.

The p53 tumor suppressor gene is a sequence-specific transcription factor that activates the expression of genes engaged in promoting growth arrest or cell death in response to multiple forms of cellular stress. p53 expression is elevated in damaged neurons in acute models of injury such as ischemia and epilepsy and in brain tissue samples derived from animal models and patients with chronic neurodegenerative diseases. p53 deficiency or p53 inhibition protects neurons from a wide variety of acute toxic insults. Signal transduction pathways associated with p53-induced neuronal cell death are being characterized, suggesting that intervention may prove effective in maintaining neuronal viability and restoring function following neural injury and disease.

Molecular and cellular mechanisms of cardiotoxicity.

Cardiotoxicity resulting from detrimental environmental insults has been recognized for a long time. However, extensive studies of the mechanisms involved had not been undertaken until recent years. Advances in molecular biology provide powerful tools and make such studies possible. We are gathering information about cellular events, signaling pathways, and molecular mechanisms of myocardial toxicologic responses to environmental toxicants and pollutants. Severe acute toxic insults cause cardiac cell death instantly. In the early response to mild environmental stimuli, biochemical changes such as alterations in calcium homeostasis occur. These may lead to cardiac arrhythmia, which most often is reversible. Prolonged stimuli activate transcription factors such as activator protein-1 through elevation of intracellular calcium and the subsequent activation of calcineurin. Upregulation by activated transcription factors of hypertrophic genes results in heart hypertrophy, which is a short-term adaptive response to detrimental factors. However, further development of hypertrophy will lead to severe and irreversible cardiomyopathy, and eventually heart failure. From cardiac hypertrophy to heart failure, myocardial cells undergo extensive biochemical and molecular changes. Cardiac hypertrophy causes tissue hypoperfusion, which activates compensatory mechanisms such as production of angiotensin II and norepinephrine. Both further stimulate cardiac hypertrophy and, importantly, activate counterregulatory mechanisms including overexpression of atrial natriuretic peptide and b-type natriuretic peptide, and production of cytokines such as tumor necrosis factor-alpha. This counterregulation leads to myocardial remodeling as well as cell death through apoptosis and necrosis. Cell death through activation of mitochondrial factors and other pathways constitutes an important cellular mechanism of heart failure. Our current knowledge of cardiotoxicity is limited. Further extensive studies are warranted for a comprehensive understanding of this field.

The role of p53 in neuronal cell death.

The p53 tumor suppressor gene is a sequence-specific transcription factor that activates the expression of genes engaged in promoting growth arrest or cell death in response to genotoxic stress. A possible role for p53-related modulation of neuronal viability has been suggested by the finding that p53 expression is elevated in damaged neurons in acute models of injury such as ischemia and epilepsy and in brain tissue samples derived from patients with chronic neurodegenerative diseases. Moreover, the absence of p53 has been shown to protect neurons from a wide variety of acute toxic insults. Signal transduction pathways associated with p53-induced cell death are being unraveled and suggest that intervention may prove fruitful in maintaining neuronal viability and restoring function following cytopathic insults.

The Delayed Lung Responses to Single and Repeated Intratracheal Administration of Pure Cobalt and Hard Metal Powder in the Rat

Epidemiological and clinical studies suggest that inhalation of cobalt metal dust (Go) mixed with tungsten carbide particles (WC), but not of cobalt dust alone, may cause interstitial pulmonary lesions (hard metal disease). In previous experimental studies in the rat, we have demonstrated the greater acute pulmonary toxicity of a WC-Co mixture compared to Co or WC alone. The present study was undertaken to compare in the same animal model the delayed lung response after intratracheal administration of Co or WC-Co particles (cobalt particle 6.3 wt%). The responses were also compared with those obtained after treatment with arsenic trioxide and crystalline silica used as reference materials producing an acute toxic insult and a progressive fibrogenic response, respectively. Cellular (total and differential counts) and biochemical parameters (LDH, N-acetyl-β-D-glucosaminidase, total protein, albumin, fibronectin, and hyaluronic acid) were measured in bronchoalveolar lavage fluid following single and repeated intratracheal instillations. The results indicate that the delayed lung response observed after WC-Co is different from that after cobalt metal alone. A single intratracheal dose of WC-Co (1, 5, or 10 mg/100 g body wt) induced an acute alveolitis which persisted for at least 1 month. Four months after a single instillation of WC-Co, no clear histological lung fibrosis could however be evidenced, indicating a reversibility of the lesions. The effects of cobalt (0.06, 0.3, or 0.6 mg/100 g body wt) or tungsten carbide alone (1, 5, or 10 mg/100 g body wt) were very modest, if any. Following repeated intratracheal instillations (four administrations at 1-month interval), increased lung hydroxyproline content and histopathological evidence of interstitial fibrosis were observed after WC-Co (4 × 1 mg/100 g body wt), but not after administration of each component separately, i.e., Co (4 × 0.06 mg/100 g body wt) or WC (4 × 1 mg/100 g body wt). The mechanism of the fibrotic reaction induced by WC-Co seems different from the progressive inflammatory reaction induced by crystalline silica. We suggest that it might result from a scarring reaction elicited by repeated acute insults as observed after repeated administration of arsenic trioxide.

Aspiration Cytological and Cytochemical Study of Changes Induced in Rat Liver Cells by Carbon Tetrachloride (CCl 4)

The effect of a single and several repeated exposures to CCl 4 on the rat liver was studied in aspiration smears. The cytological and cytochemical findings were correlated with the histological changes in order to establish the reliability of the cytological examination of aspirates for the diagnosis of acute and chronic lesions of the liver. It was found that there is an almost complete correlation between the data obtained from aspiration smears and histological findings but only after an acute single exposure to CCk. In animals exposed repeatedly to the vapors of CCl 4 , the liver changes showed histologically a grudual transition to postnecrotic cirrhosis. Cytologically this course of the hepatic lesions could not be followed as exactly as it was in histological sections. It was nevertheless possible to establish the diagnostic criteria for differentiating cirrhotic lesions from the less adcanced ones as well as from the acute toxic insult. This study has shown that aspiration cytology can give a valuable and reliable insight into the liver changes induced by CCl 4 .