The focus of the described research in this thesis is on the oxidative stress response (Nrf2 pathway). The aim of the research presented in this thesis is to obtain more information concerning... Show moreThe focus of the described research in this thesis is on the oxidative stress response (Nrf2 pathway). The aim of the research presented in this thesis is to obtain more information concerning microRNAs which are involved in the Nrf2 pathway, to determine and evaluate the application of microRNAs for the construction of novel mechanistic biomarkers. Furthermore, we aimed to obtain a better understandingwith respect to the dynamics of the Nrf2 pathway to repeated xenobiotic exposure.To investigate the effect of overexpression of microRNAs on the Nrf2 pathway response in general and in combination with chemical exposure, a microRNA mimic screen was performed. In this screen overexpression of microRNAs was induced by using synthetic microRNA mimics. Since repeated exposure may drive adaptation programs and may lead to different responses between single and repeated exposures. The effect of a second exposure on the dynamics of the Nrf2 pathway activation was conducted. Final, results of a study are shown where a panel of structurally different phenolic compounds were used to demonstrate the proof-of-concept that Nrf2 pathway reporters can successfully be applied as biomarkers to characterize the specific pro-oxidant responses of chemicals. Show less
Stel W. van der, Carta G., Eakins J., Darici S., Delp J., Forsby A., Bennekou S.H., Gardner I., Leist M., Danen E.H.J., Walker P., Water B. van de, Jennings P. 2020
Evidence is mounting for the central role of mitochondrial dysfunction in several pathologies including metabolic diseases, accelerated ageing, neurodegenerative diseases and in certain xenobiotic... Show moreEvidence is mounting for the central role of mitochondrial dysfunction in several pathologies including metabolic diseases, accelerated ageing, neurodegenerative diseases and in certain xenobiotic-induced organ toxicity. Assessing mitochondrial perturbations is not trivial and the outcomes of such investigations are dependent on the cell types used and assays employed. Here we systematically investigated the effect of electron transport chain (ETC) inhibitors on multiple mitochondrial-related parameters in two human cell types, HepG2 and RPTEC/TERT1. Cells were exposed to a broad range of concentrations of 20 ETC-inhibiting agrochemicals and capsaicin, consisting of inhibitors of NADH dehydrogenase (Complex I, CI), succinate dehydrogenase (Complex II, CII) and cytochrome bc1 complex (Complex III, CIII). A battery of tests was utilised, including viability assays, lactate production, mitochondrial membrane potential (MMP) and the Seahorse bioanalyser, which simultaneously measures extracellular acidification rate [ECAR] and oxygen consumption rate [OCR]. CI inhibitors caused a potent decrease in OCR, decreased mitochondrial membrane potential, increased ECAR and increased lactate production in both cell types. Twenty-fourhour exposure to CI inhibitors decreased viability of RPTEC/TERT1 cells and 3D spheroid-cultured HepG2 cells in the presence of glucose. CI inhibitors decreased 2D HepG2 viability only in the absence of glucose. CII inhibitors had no notable effects in intact cells up to 10 µM. CIII inhibitors had similar effects to the CI inhibitors. Antimycin A was the most potent CIII inhibitor, with activity in the nanomolar range. The proposed CIII inhibitor cyazofamid demonstrated a mitochondrial uncoupling signal in both cell types. The study presents a comprehensive example of a mitochondrial assessment workflow and establishes measurable key events of ETC inhibition. Show less
Bischoff, L.J.M.; Kuijper, I.A.; Schimming, J.P.; Wolters, L.; Braak, B. ter; Langenberg, J.P.; ... ; Water, B. van de 2018
Oxidative stress leads to the activation of the Nuclear factor-erythroid-2-related factor 2 (Nrf2) pathway. While most studies have focused on the activation of the Nrf2 pathway after single... Show moreOxidative stress leads to the activation of the Nuclear factor-erythroid-2-related factor 2 (Nrf2) pathway. While most studies have focused on the activation of the Nrf2 pathway after single chemical treatment, little is known about the dynamic regulation of the Nrf2 pathway in the context of repeated exposure scenarios. Here we employed single cell live imaging to quantitatively monitor the dynamics of the Nrf2 pathway during repeated exposure, making advantage of two HepG2 fluorescent protein reporter cell lines, expressing GFP tagged Nrf2 or sulfiredoxin 1 (Srxn1), a direct downstream target of Nrf2. High throughput live confocal imaging was used to measure the temporal dynamics of these two components of the Nrf2 pathway after repeated exposure to an extensive concentration range of diethyl maleate (DEM) and tert-butylhydroquinone (tBHQ). Single treatment with DEM or tBHQ induced Nrf2 and Srxn1 over time in a concentration-dependent manner. The Nrf2 response to a second treatment was lower than the response to the first exposure with the same concentration, indicating that the response is adaptive. Moreover, a limited fraction of individual cells committed themselves into the Nrf2 response during the second treatment. Despite the suppression of the Nrf2 pathway, the second treatment resulted in a three-fold higher Srxn1-GFP response compared to the first treatment, with all cells participating in the response. While after the first treatment Srxn1-GFP response was linearly related to Nrf2-GFP nuclear translocation, such a linear relationship was less clear for the second exposure. siRNA-mediated knockdown demonstrated that the second response is dependent on the activity of Nrf2. Several other, clinically relevant, compounds (i.e., sulphorophane, nitrofurantoin and CDDO-Me) also enhanced the induction of Srxn1-GFP upon two consecutive repeated exposure. Together the data indicate that adaptation towards pro-oxidants lowers the Nrf2 activation capacity, but simultaneously primes cells for the enhancement of an antioxidant response which depends on factors other than just Nrf2. These data provide further insight in the overall dynamics of stress pathway activation after repeated exposure and underscore the complexity of responses that may govern repeated dose toxicity. Show less
Karkampouna, S.; Helm, D. van der; Gray, P.C.; Chen, L.; Klima, I.; Grosjean, J.; ... ; Kruithof-de Julio, M. 2018
