Papers by Rianita Van Onselen
Environmental toxicology and pharmacology, Feb 1, 2024
Neuroscience Letters, Dec 31, 2023
Toxicon, 2018
b-N-methylamino-L-alanine (BMAA) has been shown to accumulate in organisms by associating with ho... more b-N-methylamino-L-alanine (BMAA) has been shown to accumulate in organisms by associating with host proteins. It has been proposed that this association is the result of misincorporation of BMAA into the primary structure of proteins, specifically in the place of L-serine, and that this misincorporation causes protein misfolding resulting in the tangle formation typically associated with neurodegenerative diseases. However, more recent studies have questioned the validity of the BMAA misincorporation hypothesis. Furthermore, BMAA association with proteins in the absence of de novo protein synthesis has been demonstrated although the nature of these associations has not yet been characterized. We therefore sought to investigate the effects of these undescribed interactions on protein functioning, and to identify the site(s) of these interactions. We present data here to show that BMAA can inhibit the activity of certain enzymes, interfere with protein folding in the absence of de novo protein synthesis, and associate in vitro with commercial proteins to such an extent that it cannot be removed by protein precipitation or denaturation. Based on the observed effects of these interactions on protein functioning, we suggest that this might constitute an additional mechanism of toxicity that could help to explain the role of BMAA in the development of neurodegenerative diseases.
Neurotoxicity Research, 2017
The implication of β-N-methylamino-L-alanine (BMAA) in the development of neurodegenerative disea... more The implication of β-N-methylamino-L-alanine (BMAA) in the development of neurodegenerative diseases worldwide has led to several investigations of the mechanism, or mechanisms, of toxicity of this cyanobacterially produced amino acid. The primary mechanism of toxicity that was identified is excitotoxicity, with a second possible mechanism, the misincorporation of BMAA into the primary protein structure and consequent cell damage, having been more recently reported. However, studi es on excitotoxicit y and misincorporation have been conducted independently and there are therefore no data available on the relative contribution of each of these mechanisms to the total toxicity of BMAA. The rat pheochromocytoma cell line PC12 is an ideal model for a study of this type, as glutamate receptor expression is modified by cell differentiation, which can be affected by exposure to nerve growth factor. In this study, the PC12 cell line was evaluated as a model to study BMAA toxicity via the two proposed mechanisms: excitotoxicity and protein misincorporation. BMAA and canavanine treatment of cultures of PC12 were evaluated for depolarization of the mitochondrial membrane. In canavanine-treated cultures, this was evident after 9 days of treatment and was attributed to the primary mechanism of canavanine toxicity, protein misincorporation. However, no membrane depolarization was observed for BMAA-treated cultures even after 21 days of continuous treatment at 500 μM. Short-term exposure to both BMAA and canavanine resulted in a slight increase in necrosis in undifferentiated cells that was prevented in canavanine-treated cultures by co-incubation with arginine, but not in BMAA-treated cultures by co-incubation with serine. A slight increase in apoptosis was observed in undifferentiated cells treated with either BMAA or glutamate, and ROS production increased in glutamate-treated cells. However, the excitotoxicity was less pronounced than reported in previous studies with neuronal cells. In contrast, apoptosis was greatly increased in both BMAA-and glutamatetreated cells after differentiation and resulting mGluR1 increase, indicating that excitotoxicity is the main, if not only, mechanism of toxicity in PC12.
Analytical and Bioanalytical Chemistry
The presence of antiretroviral drugs (ARVDs) in the aquatic environment poses a significant healt... more The presence of antiretroviral drugs (ARVDs) in the aquatic environment poses a significant health risk to the ecosystem. The dilution of these compounds during wastewater treatment processes, followed by discharge into the environment, results in extremely low concentrations in the range of ng/L. Therefore, to enable detection of these low concentrations, it is important to determine the most efficient electrospray ionization (ESI) mode using the right mobile phase modifier and to establish a selective extraction procedure. In this study, we compared the ESI intensity in the positive and negative mode using both formic acid (FA) and ammonium hydroxide (NH4OH) as mobile phase modifiers. The results revealed a phenomenon known as the “wrong-way-round” (WWR) ESI in which high intensity [M + H]+ ions were detected under basic conditions using NH4OH as modifier and, similarly, high intensity [M-H]− ions were detected under acidic conditions using FA as modifier. Furthermore, mixed-mode ...
Toxicon, 2015
β-N-methylamino-l-alanine (BMAA), is commonly found in both a free and proteinassociated form in ... more β-N-methylamino-l-alanine (BMAA), is commonly found in both a free and proteinassociated form in various organisms exposed to the toxin. The long latency of development of neurodegeneration attributed to BMAA, is hypothesized to be the result of excitotoxicity following slow release of the toxin from protein reservoirs. It was recently suggested that these BMAA-protein associations may reflect misincorporation of BMAA in place of serine, as occurs, for example, when canavanine misincorporates in place of arginine. We therefore compared BMAA and canavanine toxicty in various bacterial species, and misincorporation of these amino acids into proteins in a bacterial protein expression system. None of the bacterial species showed any physiological stress responses to BMAA in contrast to the growth reduction observed when cultures were incubated in media containing canavanine. LC-MS analysis confirmed uptake of BMAA from growth media. However, after immobilized metal affinity chromatography and SDS-PAGE purification of proteins produced in an E scherichia coli expression system, no BMAA was detected by either LC-MS or LC-MS/MS analysis using two derivatization methods, or by orbitrap MS of trypsin digests of the protein. We therefore conclude that BMAA is not misincorporated into proteins in bacteria and that the observed BMAA-protein association in bacteria is superficial.
Toxins, Dec 14, 2017
Misincorporation of β-N-methylamino-L-alanine (BMAA) into proteins has been proposed to be a mech... more Misincorporation of β-N-methylamino-L-alanine (BMAA) into proteins has been proposed to be a mechanism of toxicity to explain the role of BMAA in neurodegenerative disease development. However, studies have shown that all detectable BMAA can be removed from proteins by SDS-PAGE purification and that the toxicity of L-canavanine cannot be reproduced in prokaryotes or in a rat pheochromocytoma cell line, strongly indicating that the misincorporation hypothesis of BMAA should be re-investigated. The aim of this study was therefore to determine if BMAA misincorporates into proteins in cells of human origin with subsequent misincorporation-type toxicity. Almost complete loss of viability in response to exposure to L-4-fluorophenylalanine and L-m-tyrosine was observed in all of the cell lines, corresponding to a concentration-dependent increase of the analogues in protein extracts from exposed cells. In contrast, BMAA exposure resulted in slight toxicity in one of the cell lines but the observed toxicity was not the result of misincorporation of BMAA into proteins, as no BMAA was detected in any of the SDS-PAGE purified protein extracts that were obtained from the cells following BMAA exposure. The results show that BMAA is not misincorporated into human proteins and that misincorporation is not a valid mechanism of toxicity.
Handbook of Neurotoxicity
Toxicology and Applied Pharmacology
International Journal of Toxicology
The naturally produced, nonprotein amino acid β- N-methylamino-l-alanine (BMAA) has been proposed... more The naturally produced, nonprotein amino acid β- N-methylamino-l-alanine (BMAA) has been proposed as a significant contributor to sporadic neurodegenerative disease development worldwide. However, the existing hypothesized mechanisms of toxicity do not adequately explain the role of BMAA in neurodegenerative disease development. There is evidence for BMAA-induced enzyme inhibition, but the effect of BMAA on human stress response enzymes has received little attention, despite the well-described role of oxidative stress in neurodegenerative disease development. The aim of this study was therefore to investigate the effect of BMAA on human catalase activity and compare it to the known inhibitor 3-amino-1,2,4-triazole. BMAA inhibited human erythrocyte catalase in a cell-free exposure to the same extent as the known inhibitor. Based on enzyme kinetics, the inhibition appears to be noncompetitive, possibly as a result of BMAA binding in the nicotinamide adenine dinucleotide phosphate (NAD...
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Papers by Rianita Van Onselen