Papers by Remco Westerink
Environmental Science Technology, Dec 13, 2011
Current hypotheses link long-term environmental exposure of humans to persistent organochlorine (... more Current hypotheses link long-term environmental exposure of humans to persistent organochlorine (OC) insecticides lindane (HCH) and dieldrin (HEOD) to the development of neurodegenerative disorders, such as Parkinson's disease. Primary adverse neurological effects of these insecticides are directed at inhibition of GABA A and glycine receptors, although GABAindependent effects have also been reported. In this paper we describe the effect of dieldrin and a binary mixture of dieldrin and lindane on a critical parameter of neuronal function and survival, i.e., intracellular calcium homeostasis. The intracellular calcium concentration ([Ca 2+ ] i ) has been monitored using real-time single-cell fluorescence microscopy in dopaminergic PC12 cells loaded with the calcium-sensitive dye Fura-2. The results demonstrate that nanomolar concentrations of dieldrin time-and concentration-dependently inhibit depolarizationevoked influx of Ca 2+ . Co-exposure of PC12 cells to a mixture of dieldrin and lindane revealed an additive inhibition of the depolarization-evoked increase in [Ca 2+ ] i , whereas the lindane-induced increase in basal [Ca 2+ ] i is inhibited by dieldrin. The combined findings indicate that dieldrin and binary mixtures of organochlorines affect [Ca 2+ ] i already at concentrations below commonly accepted effect concentrations and close to human internal dose levels. Consequently, current findings illustrate the need to take mixtures of OC insecticides into account in human risk assessment.
F1000posters, Nov 9, 2010
Figure 2. Occurrence of different types of [Ca 2+ ] i disturbances during exposure to OH-PBDEs. B... more Figure 2. Occurrence of different types of [Ca 2+ ] i disturbances during exposure to OH-PBDEs. Bars indicate the percentage of cells showing an initial transient increase in [Ca 2+ ] i (open bars) and those showing a late increase in [Ca 2+ ] i (closed bars). For 6-OH-BDE-47 (B) and 5-OH-BDE-47 (C), which show initial and late increases of [Ca 2+ ] i at 2 µM, more concentrations are tested. Significant increases in the percentage of cells showing initial or late increases in [Ca 2+ ] i are indicated at the lowest-observed-effect concentration. Conclusion I: Atom groups adjacent to the OH affect the ability of OH-PBDEs to disturb [Ca 2+ ] i Figure 4A. Molecular structures of OH-PBDEs illustrating the shielding of the OH-group on one or both sides with Br-atoms and/or an aromatic ring. Shielding decreases the ability of OH-PBDEs to disturb [Ca 2+ ] i while the location of the OH-group is less important. B. All OH-PBDEs increased [Ca 2+ ] i . This was not observed for parent PBDEs and 6-MeO-BDE-47. Table shows lowest-observed effect concentrations for the observed effects and resulting NOECs. When investigating fluctuations in [Ca 2+ ] i effects were detected at lower concentrations of 6-OH-BDE-47, 4'-OH-BDE-49 and BDE-47.
Toxicology in Vitro, Sep 30, 2008
Ethylbenzene and para-xylene (p-xylene), but not the chemically closely related organic solvents ... more Ethylbenzene and para-xylene (p-xylene), but not the chemically closely related organic solvents orthoxylene (o-xylene) and meta-xylene (m-xylene), are known to cause ototoxicity and irreversible hearing loss, though the underlying mechanisms are still unknown. In this study, effects of ethylbenzene and of p-, o-, and m-xylene on human heteromeric a9a10 nicotinic acetylcholine receptors (nAChRs) expressed in Xenopus oocytes were investigated using the two-electrode voltage clamp technique. ACh dose-dependently evoked an a9a10 nAChR-mediated ion current with an EC 50 of 137 lM. When ACh is applied at a low concentration (10 lM), the nAChR-mediated ion current is inhibited by a low concentration (10 lM) of ethylbenzene and p-xylene, but not by the same concentration of the non-ototoxic solvents. At a high solvent concentration (300 lM), all solvents cause inhibition of the ion currents evoked by 10 lM ACh. Ion currents evoked by a near maximum-effective concentration ACh (1 mM) are inhibited by the selected organic solvents only at 300 lM. These results demonstrate that low concentrations of the known ototoxic solvents ethylbenzene and p-xylene inhibit a9a10 nAChR-mediated ion currents, whereas the structurally related, non-ototoxic solvents m-xylene and o-xylene do not, indicating that the a9a10 nAChR is a potential target for solvent-induced ototoxicity.
Neurotoxicology and Teratology, 2015
Journal of Neurochemistry
Effects of Pb(2+) on vesicular catecholamine release in intact and ionomycin-permeabilized PC12 c... more Effects of Pb(2+) on vesicular catecholamine release in intact and ionomycin-permeabilized PC12 cells were investigated using carbon fibre microelectrode amperometry. Changes in intracellular Pb(2+) and Ca(2+) were measured from indo-1 fluorescence by confocal laser scanning microscopy. Depolarization of intact cells and superfusion of permeabilized cells with saline containing > or = 100 microm Ca(2+) rapidly evokes quantal catecholamine release. Superfusion with up to 10 microm Pb(2+) -containing saline evokes release of similar catecholamine quanta after a concentration-dependent delay. Thresholds to induce exocytosis within 30 min of exposure are between 1 and 10 microm Pb(2+) in intact cells and between 10 and 30 nm Pb(2+) in permeabilized cells. Additional inhibition of exocytosis occurs in permeabilized cells exposed to 10 microm Pb(2+). Using membrane-impermeable and -permeable chelators it is demonstrated that intracellular Ca(2+) is not required for Pb(2+) -induced exoc...
Neurotoxicology and Teratology, 2015
The Veterinary quarterly, 2014
Around the globe, chemical compounds are used to treat or repel pests and plagues that pose a thr... more Around the globe, chemical compounds are used to treat or repel pests and plagues that pose a threat to food and feed production. From epidemiological studies, it is known that there is a link between exposure to certain chemical classes of these so-called pesticides and the prevalence of neurodegenerative disorders such as Parkinson's disease in humans. However, which particular compound(s) account for this link or what underlying mechanisms are involved is still largely unresolved. The degenerative process in Parkinson's disease is largely limited to the dopaminergic neurons in the basal ganglia. Cellular mechanisms that are implicated in parkinsonian neurodegeneration include mitochondrial dysfunction, oxidative stress, disturbance of intracellular calcium homeostasis and endoplasmic reticulum (ER) stress. A major characteristic that distinguishes the dopaminergic neurons in the basal ganglia from other dopaminergic neurons is a particular reliance on intracellular calciu...
Toxicological sciences : an official journal of the Society of Toxicology, 2014
Humans are exposed to distinct structural classes of insecticides with different neurotoxic modes... more Humans are exposed to distinct structural classes of insecticides with different neurotoxic modes of action. Because calcium homeostasis is essential for proper neuronal function and development, we investigated the effects of insecticides from different classes (pyrethroid: (α-)cypermethrin; organophosphate: chlorpyrifos; organochlorine: endosulfan; neonicotinoid: imidacloprid) and mixtures thereof on the intracellular calcium concentration ([Ca(2+)]i). Effects of acute (20 min) exposure to (mixtures of) insecticides on basal and depolarization-evoked [Ca(2+)]i were studied in vitro with Fura-2-loaded PC12 cells and high resolution single-cell fluorescence microscopy. The data demonstrate that cypermethrin, α-cypermethrin, endosulfan, and chlorpyrifos concentration-dependently decreased depolarization-evoked [Ca(2+)]i, with 50% (IC50) at 78nM, 239nM, 250nM, and 899nM, respectively. Additionally, acute exposure to chlorpyrifos or endosulfan (10μM) induced a modest increase in basal ...
European Neuropsychopharmacology, 2014
Hallucinogen persisting perception disorder (HPPD) is a drug-induced condition associated with in... more Hallucinogen persisting perception disorder (HPPD) is a drug-induced condition associated with inaccurate visual representations. Since the underlying mechanism(s) are largely unknown, this review aims to uncover aspects underlying its etiology. Available evidence on HPPD and drugrelated altered visual processing was reviewed and the majority of HPPD cases were attributed to drugs with agonistic effects on serotonergic 5-HT 2A receptors. Moreover, we present 31 new HPPD cases that link HPPD to the use of ecstasy (MDMA), which is known to reverse serotonin reuptake and acts as agonist on 5-HT 2A receptors. The available evidence suggests that HPPD symptoms may be a result from a misbalance of inhibitory-excitatory activity in low-level visual processing and GABA-releasing inhibitory interneurons may be involved. However, high co-morbidities with anxiety, attention problems and derealization symptoms add complexity to the etiology of HPPD. Also, other perceptual disorders that show similarity to HPPD cannot be ruled out in presentations to clinical treatment. Taken together, evidence is still sparse, though www.elsevier.com/locate/euroneuro http://dx.
Toxicology and Applied Pharmacology, 2011
Calcium plays a crucial role in virtually all cellular processes, including neurotransmission. Th... more Calcium plays a crucial role in virtually all cellular processes, including neurotransmission. The intracellular Ca(2+) concentration ([Ca(2+)](i)) is therefore an important readout in neurotoxicological and neuropharmacological studies. Consequently, there is an increasing demand for high-throughput measurements of [Ca(2+)](i), e.g. using multi-well microplate readers, in hazard characterization, human risk assessment and drug development. However, changes in [Ca(2+)](i) are highly dynamic, thereby creating challenges for high-throughput measurements. Nonetheless, several protocols are now available for real-time kinetic measurement of [Ca(2+)](i) in plate reader systems, though the results of such plate reader-based measurements have been questioned. In view of the increasing use of plate reader systems for measurements of [Ca(2+)](i) a careful evaluation of current technologies is warranted. We therefore performed an extensive set of experiments, using two cell lines (PC12 and B35) and two fluorescent calcium-sensitive dyes (Fluo-4 and Fura-2), for comparison of a linear plate reader system with single cell fluorescence microscopy. Our data demonstrate that the use of plate reader systems for high-throughput real-time kinetic measurements of [Ca(2+)](i) is associated with many pitfalls and limitations, including erroneous sustained increases in fluorescence, limited sensitivity and lack of single cell resolution. Additionally, our data demonstrate that probenecid, which is often used to prevent dye leakage, effectively inhibits the depolarization-evoked increase in [Ca(2+)](i). Overall, the data indicate that the use of current plate reader-based strategies for high-throughput real-time kinetic measurements of [Ca(2+)](i) is associated with caveats and limitations that require further investigation.
Toxicology Letters, 2012
Toxicological and ecological concern associated with BFRs argues for replacement. The toxic poten... more Toxicological and ecological concern associated with BFRs argues for replacement. The toxic potential of alternative halogen-free flame retardants (HFFRs) is unknown. Some HFFRs act as potent inhibitors of human nicotinic acetylcholine receptors. Our in vitro study indicates high neurotoxic potential of some HFFRs. We made an initial rank-order potency to prioritize viable HFFRs.
Toxicology in Vitro, 2008
Ethylbenzene and para-xylene (p-xylene), but not the chemically closely related organic solvents ... more Ethylbenzene and para-xylene (p-xylene), but not the chemically closely related organic solvents orthoxylene (o-xylene) and meta-xylene (m-xylene), are known to cause ototoxicity and irreversible hearing loss, though the underlying mechanisms are still unknown. In this study, effects of ethylbenzene and of p-, o-, and m-xylene on human heteromeric a9a10 nicotinic acetylcholine receptors (nAChRs) expressed in Xenopus oocytes were investigated using the two-electrode voltage clamp technique. ACh dose-dependently evoked an a9a10 nAChR-mediated ion current with an EC 50 of 137 lM. When ACh is applied at a low concentration (10 lM), the nAChR-mediated ion current is inhibited by a low concentration (10 lM) of ethylbenzene and p-xylene, but not by the same concentration of the non-ototoxic solvents. At a high solvent concentration (300 lM), all solvents cause inhibition of the ion currents evoked by 10 lM ACh. Ion currents evoked by a near maximum-effective concentration ACh (1 mM) are inhibited by the selected organic solvents only at 300 lM. These results demonstrate that low concentrations of the known ototoxic solvents ethylbenzene and p-xylene inhibit a9a10 nAChR-mediated ion currents, whereas the structurally related, non-ototoxic solvents m-xylene and o-xylene do not, indicating that the a9a10 nAChR is a potential target for solvent-induced ototoxicity.
Toxicology and Applied Pharmacology, 2010
Garcia-Ratés et al. (2010) recently reported effects of 3,4- methylenedioxy-methamphetamine (MDMA... more Garcia-Ratés et al. (2010) recently reported effects of 3,4- methylenedioxy-methamphetamine (MDMA) on intracellular calcium levels ([Ca2+]i) in PC12 cells as well as on α7 and α4β2 nicotinic acetylcholine receptors (nACh-Rs) expressed in Xenopus oocytes. Their data on [Ca2+]i, obtained by determination of fluo-4 fluorescence in a plate-reader, indicate an apparent contradiction (Figs. 1 and 2). MDMA attenuated the increase in
Toxicology and Applied Pharmacology, 2002
Westerink, R. H. S., and Vijverberg, H. P. M. (2002). Toxicol. Appl. Pharmacol. 183, 153-159.
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Papers by Remco Westerink