F.A. de Wolff

Arsenic neurotoxicity — A review:

Arsenic (As) is one of the oldest poisons known to men. Its applications throughout history are wide and varied: murder, make-up, paint and even as a pesticide. Chronic As toxicity is a global environmental health problem, affecting millions of people in the USA and Germany to Bangladesh and Taiwan. Worldwide, As is released into the environment by smelting of various metals, combustion of fossil fuels, as herbicides and fungicides in agricultural products. The drinking water in many countries, which is tapped from natural geological resources, is also contaminated as a result of the high level of As in groundwater. The environmental fate of As is contamination of surface and groundwater with a contaminant level higher than 10 particle per billion (ppb) as set by World Health Organization (WHO). Arsenic exists in both organic and inorganic species and either form can also exist in a trivalent or pentavalent oxidation state. Long-term health effects of exposure to these As metabolites are severe and highly variable: skin and lung cancer, neurological effects, hypertension and cardiovascular diseases. Neurological effects of As may develop within a few hours after ingestion, but usually are seen in 2—8 weeks after exposure. It is usually a symmetrical sensorimotor neuropathy, often resembling the Guillain—Barré syndrome. The predominant clinical features of neuropathy are paresthesias, numbness and pain, particularly in the soles of the feet. Electrophysiological studies performed on patients with As neuropathy have revealed a reduced nerve conduction velocity, typical of those seen in axonal degeneration. Most of the adverse effects of As, are caused by inactivated enzymes in the cellular energy pathway, whereby As reacts with the thiol groups of proteins and enzymes and inhibits their catalytic activity. Furthermore, As-induced neurotoxicity, like many other neurodegenerative diseases, causes changes in cytoskeletal protein composition and hyperphosphorylation. These changes may lead to disorganization of the cytoskeletal framework, which is a potential mechanism of As-induced neurotoxicity. Human & Experimental Toxicology (2007) 26, 823—832

Arsenic-induced neurotoxicity in relation to toxicokinetics: Effects on sciatic nerve proteins

In our previous study in rats acutely exposed to As, we observed an effect of As on neurofilaments in the sciatic nerve. This study deals with the effects of inorganic As in Wistar rats on the cytoskeletal protein composition of the sciatic nerve after subchronic intoxication. Sodium meta-arsenite (NaAsO2) dissolved in phosphate-buffered saline (PBS) was administered daily in doses of 0, 3 and 10 mg/kg body weight/day (n=9 rats/group) by intragastric route for 4, 8 and 12 week periods. Toxicokinetic measurements revealed a saturation of blood As in the 3- and 10-mg/kg dose groups at approximately 14 microg/ml, with an increase in renal clearance of As at increasing doses. After exsanguination, sciatic nerves were excised and the protein composition was analyzed. Analysis of the sciatic nerves showed compositional changes in their proteins. Protein expression of neurofilament Medium (NF-M) and High (NF-H) was unchanged. Neurofilament protein Low (NF-L) expression was reduced, while mu- and m-calpain protein expression was increased, both in a dose/time pattern. Furthermore, NF-H protein was hypophosphorylated, while NF-L and microtubule-associated protein tau (MAP-tau) proteins were (hyper)-phosphorylated. In conclusion, we show that expression of mu- and m-calpain protein is increased by exposure to As, possibly leading to increased NF-L degradation. In addition, hyperphosphorylation of NF-L and MAP-tau by As also contribute to destabilization and disruption of the cytoskeletal framework, which eventually may lead to axonal degeneration.

Arsenic-induced toxicity: effect on protein composition in sciatic nerve

Exposure to arsenic compounds may lead to skin and lung cancer and various disorders such as vascular disease and peripheral neuropathy in humans. Peripheral arsenic neurotoxicity has been demonstrated clinically and in electrophysiological studies. Patients intoxicated with arsenic show neurological symptoms in their feet and hands. These patients show significantly lower nerve conduction velocities (NCVs) in their peripheral nerves in comparison with controls. The mechanism of arsenic peripheral nervous system (PNS) toxicity, however, has never been described before. This is the first study to investigate the toxicity of arsenic on the PNS. Male Wistar rats were exposed to arsenite given as a single dose i.v. After sacrifice, sciatic nerves were excised and the protein composition was analysed. Protein analysis of sciatic nerves showed disappearance of neurofilament and fibroblast proteins in rats treated with arsenite doses of 15 and 20 mg/kg in comparison with the control groups. Some fibroblast protein bands had disappeared in the 20-mg/kg dose group. The analysed neurofilament-M and-L proteins decreased dose dependency over time. arsenic affects the composition of proteins in the rat sciatic nerve, especially the neurofilaments. The reduction of signals in Western blot analysis reveals changes in cytoskeletal composition, which may well lead to neurotoxic effects in vivo.

A hypertensive toddler

limit of 1 g/L. The children were last seen in September,1996, both in good health.Despite the extent of information on mercurypoisoning, the clinical similarities between acrodynia andphaeochromocytoma and an increase in adrenaline andnoradrenaline concentrations have been reported onlysporadically.

Mechanism of arsenic-induced neurotoxicity may be explained through cleavage of p35 to p25 by calpain

In recent studies we have demonstrated that arsenic (As) metabolites change the composition of neuronal cytoskeletal proteins in vivo and in vitro. To further examine the mechanism of arsenic-induced neurotoxicity with various arsenate metabolites (iAsV, MMAV and DMAV) and arsenite metabolites (iAsIII, MMAIII and DMAIII), we investigated the role of the proteolytic enzyme calpain and its involvement in the cleavage of p35 protein to p25, and also mRNA expression levels of calpain, cyclin-dependent kinase 5 (cdk5) and glycogen synthase kinase 3 beta (gsk3ss). A HeLa cell line transfected with a p35 construct (HeLa-p35) was used as a model, since all other proteins such as calpain, CDK5 and GSK3beta are already present in HeLa cells as they are in neuronal cells. HeLa-p35 cells were incubated with various As metabolites and concentrations of 0, 10 and 30 microM for duration of 4 h. Subsequently the cells were either lysed to study their relative quantification levels of these genes or to be examined on their p35-protein expression. P35-RNA expression levels were significantly (p<0.01) increased by arsenite metabolites, while p35 protein was cleaved to p25 (and p10) after incubation with these metabolites. The cleavage of p35 is caused by calcium (Ca2+) induced activation of calpain. Inhibition of calpain activity by calpeptin prevents cleavage of p35 to p25. These results suggest that cleavage of p35 to p25 by calpain, probably As-induced Ca2+-influx, may explain the mechanism by which arsenic induces its neurotoxic effects.

Determination by flameless atomic absorption of aluminium in serum and hair for toxicological monitoring of patients on chronic intermittent haemodialysis.

Determination of aluminium in serum of patients on chronic intermittent haemodialysis is of paramount importance in the prevention or early diagnosis of aluminium intoxication. We present a new method based on flameless atomic absorption spectroscopy, in which the serum matrix is destroyed by oxygen. A comparison has been made between the described method and another procedure which is used in the Laboratory of Toxicology in Gent, with favourable results. In addition, a method is presented for the determination of aluminium in hair, in which special attention has been paid to the cleaning of the hair samples prior to destruction. As yet it cannot be concluded whether aluminium concentrations in hair give a better representation of the body burden than serum levels do.

Experience with a Screening Method for Laxative Abuse

1 Abuse of laxatives may lead to a variety of serious disorders which are usually difficult to recognize because of the heterogenicity of the toxic effects. 2 In order to facilitate the diagnosis of chronic laxative poisoning, a laboratory screening method for the detection of colonic stimulants in urine has been designed and has been applied in practice over a three-year-period. 3 During this period, 157 samples from 81 patients were sent to the laboratory. Fifteen patients (18.5%) were definitely shown to use self-prescribed laxatives. 4 Next to the diphenolic compounds: bisacodyl, phenolphthalein and bisoxatin, the anthraquinone derivative rhein, a metabolite of vegetable laxatives, was found in several cases. In the urine of three patients a substance resembling rhein was found, which was shown to be aloe-emodin. 5 It is concluded that chronic self-poisoning with laxatives is a fairly common disorder that can easily be overlooked. Laboratory screening of the urine of suspected patients is an economic and reliable method for its diagnosis.

Pharmacokinetics of tiapride in patients with tardive dyskinesia and Huntington's disease

SummaryThe pharmacokinetics of tiapride were determined at steady-state in 5 patients with tardive dyskinesia and 2 patients with Huntingtons disease given tiapride 100 mg t.i.d. for 7 days. The maximum serum concentration of tiapride of 1.47±0.35 µg/ml was reached after 1.4±0.67 h. The half-life time of elimination was 229±41 min. About 50% of the dose of tiapride was excreted unchanged by the kidney. Neither protein binding nor glucuronide, sulphate or acetyl conjugation was observed. Renal clearance in the patients appeared to be lower but the other pharmacokinetic parameters did not differ from previous findings in healthy young volunteers.

Comparative toxicity of arsenite metabolites in wild type cho cells and in cells deficient in excision repair cross-complementing 1 and 2

Arsenic (As) has been shown to alter one or more DNA repair processes. Excision repair cross-complementing 1 and 2 (ERCC1 and ERCC2) have shown to be associated with arsenic-induced toxicity and carcinogenicity. In this study, we investigated cytotoxic effects of various As metabolites in relation to two nucleotide excision repair genes: ERCC1 and ERCC2. Various arsenate (pentavalent) and arsenite (trivalent) metabolites were tested in ERCC1, ERCC2 deficient and wild type cells. Our results showed that in the selected concentration range pentavalent As metabolites; iAs(V), MMA(V) and DMA(V) were not cytotoxic, unlike the trivalent As metabolites; iAs(III), MMA(III) and DMA(III). The measured LC(50) demonstrated a significant difference (p<0.01) for iAs(III) between the three cell lines, while MMA(III) and DMA(III) are more cytotoxic to all three cell lines. UV5 (ERCC2 deficient) cells also showed a lower resistance to iAs(III) in comparison to AA8 (wild type) and UV20 (ERCC2 deficient) cells. This might be explained through the generation of hydrogen peroxide (H(2)O(2)), which is generated by increase of intracellular Ca(2+) level. Generation of H(2)O(2) in UV5 cells after incubation with iAs(III) is significantly higher than AA8 and UV20 cells (p<0.01). In conclusion, absence of ERCC2 leads to a increased generation of H(2)O(2) by iAs(III) in UV5 cells, which is in contrast to AA8 and UV20 cells.

The plasma level of methylphenidate in the single-dose oral methylphenidate test

Pharmacological challenge tests are thought to be of value in pr:dicting response to a specific treatment in depression. Sabelli et al. (1983) suggested that the methylphenidate te ~t (MPT) may be useful for making a rational choice among, tricyclic antidepressants. In their study, v. mood elevation frc, m methylphcnidate (MP) p-edictec a therapeutic response to infipramine or desipramine, while ~ r~gative response favored nortriptyline, a mort: serot:>nergic-acting antidepressant. Recently. Spar and LaRue (1985~ advocated a single-dose oral MPT whic~ because of its relative simplicity and easier execution, would be preferable (in a clinical setting) to the more sophisticated procedure of Fawcetx et at. (1984), who titrated the dose of MP until a response was reached. Evaiuation of a challenge test is complicamd