Flogen SIPS

FLOGEN SIPS 2022: Yoshikawa International Symposium on Oxidative Stress for Sustainable Development of Human Beings (2nd international Symposium) Presenter: Prof. Christian Andre Amatore, CNRS & PSL, French Academy of Sciences, Paris, France Title: Understanding Oxidative Stress in Brain with Ultramicroelectrodes: Implications for a Possible Mechanism of Alzheimer Disease Abstract Oxidative stress is an essential metabolic outcome in aerobic organisms due to the activity of mitochondria in providing the basic energy of cells or during the operation of several enzymatic pools. It also serves to regulate the size and shape of organs or restructure them during foetal development by apoptosis. Oxidative stress is also indispensable to the immune system by allowing macrophages to eliminate virus, bacteria and impaired or dead cells through phagocytosis [1]. In fact, no aerobic organism could live without oxidative stress, a fact that explains why evolution maintained such unsafe mechanisms in aerobic organisms. Though, they are associated to highly negative issues. Indeed, oxidative stress mechanisms provide a variety of life-harmful radicals and species called generically Reactive Oxygen Species (ROS) and Reactive Nitrogen Species (RNS) whose fluxes need to be finely controlled to avoid the destruction of most organic molecules (e.g., lipids in cell membranes, enzymes, etc.) and biological ones (DNA, proteins, etc.) in cells. Thus, under normal conditions, a panoply of antioxidants and enzymatic systems ensures a fine homeostatic balance. However, rupture of this delicate balance is frequent and may provoke severe damages leading to human pathologies (aging, cancers, AIDS, hearth and brain strokes, Parkinson and Alzheimer’ diseases, etc.). Using platinized carbon fiber ultramicroelectrodes we could establish that the composition of the primary oxidative stress in macrophages [1,2] and characterize the nature of functional hyperemia in the brain.3 This led us to formulate an alternative hypothesis about the onset of Alzheimer disease when Amyloid-β and ascorbate molecules are present [4,5]. References: 1. K. Hu, Y. Li, S.A. Rotenberg, C. Amatore, M.V. Mirkin. J. Am. Chem. Soc., 141, 2019, 4564-4568. 2. C Amatore, S. Arbault, M. Guille, F. Lemaître. Chem. Rev., 108, 2008, 2585–2621. 3. C. Amatore, S. Arbault, C. Bouton, K. Coffi, J.-C. Drapier, H. Ghandour, Y. Tong. ChemBioChem, 7, 2006, 653-661. 4. R. Giacovazzi, I. Ciofini, L. Rao, C. Adamo, C. Amatore, Phys. Chem. Phys. Chem. (PCCP), 16, 2014, 10169-10174. 5. L. Lai, C. Zhao, M. Su, X. Li, X. Liu, H. Jiang, C. Amatore, X.M. Wang. Biomater. Sc., 4, 2016, 1085-1091.

FLOGEN SIPS 2022: Yoshikawa International Symposium on Oxidative Stress for Sustainable Development of Human Beings (2nd international Symposium) Presenter: Dr. Alexander Oleinick, CNRS, Paris, France Title: Modeling of quantitative nano-amperometric measurement of sub-quantal glutamate release by living neurons Abstract Glutamate (Glu) is a crucial fundamental excitatory neurotransmitter released through vesicular exocytosis in the central nervous system. Dysregulation of the glutamate uptake by neurons and glial cells result in increase of the glutamate extracellular concentration leading eventually to excitotoxicity associated with increased oxidative stress and neurodegeneration [1]. Hence, quantitative measurements and interpretation of intravesicular Glu and of transient exocytotic release contents directly from individual living neurons are highly desired for understanding the mechanisms (full or sub-quantal release?) of synaptic transmission and plasticity. However, this could not be achieved so far due to the lack of adequate experimental strategies relying on selective and sensitive Glu nanosensors. We will show that a novel electrochemical Glu nanobiosensor based on a single SiC nanowire [2] is prone to selectively measure in real-time Glu fluxes released via exocytosis by large Glu vesicles (ca. 125 nm diameter) present in single hippocampal axonal varicosities as well as their intravesicular content before exocytosis by IVIEC. Combination of these two series of measurements revealed a sub-quantal release mode in living hippocampal neurons, viz., only ca. one third to one half of intravesicular Glu molecules are released by individual vesicles during exocytotic events. Importantly, this fraction remained practically the same when hippocampal neurons were pretreated with L-Glu-precursor L-glutamine, while it significantly increased after zinc treatment, although in both cases the intravesicular contents before release were drastically affected. Finally, the simulations of the electrochemical monitoring of the glutamate release events will be presented. The obtained theoretical results support the quantitative measurements with the enzymatic electrode. In addition, simulation results will also serve to discuss the meaning and adequacy of pre-calibrations performed in bulk solutions [3] to assess the analytical properties of enzyme-based electrochemical nanosensors aimed to detect fast transient release events. References: [1] A.A. Kritis et al. Front. Cell. Neurosci. 9 (2015) 91. [2] X. Yang, et al. Angew. Chem. Int. Ed. 60 (2021) 15803–15808. [3] C.P. McMahon, et al. Analyst 131 (2006) 68–72.

FLOGEN SIPS 2022: Yoshikawa International Symposium on Oxidative Stress for Sustainable Development of Human Beings (2nd international Symposium) Presenter: Prof. Shigeru Hirano, Kyoto Prefectural University of Medicine, Kyoto, Japan Title: Role of Anti-Oxidant Twendee X for Maintenance of Voice and Swallow Abstract Voice and swallowing function are critical functions for human life which is supported by intriguing motion of pharynx and larynx. Swallowing function is complicated consisting of the motion of tongue, soft palate, pharyngeal muscles, laryngeal elevation, and the vocal folds. Reactive oxygen species (ROS) affects the whole organs and their functions, which deteriorate vocal and swallowing function with age or diseases. Dysphagia causes sarcopenia, frail, and aspiration pneumonia which occasionally causes death. It is important to maintain swallowing function as well as vocal function to keep the body in healthy status. Twendee X, the strongest anti-oxidant, can maintain the function of the pharynx and larynx by reducing ROS. Our previous data indicated that reduction of ROS leads to maintenance of the vocal folds against aging or injury. We have also confirmed that Twendee X can maintain the vocal function of professional singers. To date, we have established a dysphagia model of guinea pig by resecting nerve branches to the thyropharyngeal muscle. This model represents motor-related dysphagia which is often observed in elderly or patients with neuromuscular diseases. In this model, the animals became unable to eat immediately after the surgery, and lost weight for about 1 week, but they recovered by compensation. When the animals were fed with Twendee x, the immediate reduction of food intake was prevented possibly because of maintenance of the muscles. Twendee X is thought to be effective for maintenance of voice and swallowing function.

FLOGEN SIPS 2022: Yoshikawa International Symposium on Oxidative Stress for Sustainable Development of Human Beings (2nd international Symposium) Presenter: Dr. Alexander Oleinick, CNRS, Paris, France Title: Modelling detection of key biomolecules with enzymatic electrodes: Diffusion towards randomly distributed active sites Abstract Monitoring of key biomolecules and/or oxidative stress at cellular or sub-cellular levels by means of electrochemistry requires electrodes with good selectivity and sensitivity. These both characteristics often achieved by employing enzymatic electrodes. At these electrodes the enzymes are generally dispersed within a polymer layer covering electrode surface, where product(s) of the enzymatic conversion are detected. Rationalization of the experimental data imply understanding mass transport towards an enzymatic electrode which is a complicated process due to random distribution of the enzymes along the electrode surface. This process can be considered through the framework of random arrays, that is a set of active sites distributed randomly, which is also useful for description of many practical micro- and nanoscale systems [1]. As shown previously these systems can be efficiently addressed theoretically by using Voronoi diagrams [1, 2] which allows facile tessellation of the system into the unit cells around each active sites. The overall current flowing in the system can then be evaluated by modelling diffusion-reaction processes inside every unit cell and summing the contributions from individual active sites. Although this approach is tempting by its simplicity and efficiency [1] one should bear in mind that Voronoi diagram representing the unit cells by polygonal prisms remains approximation and as each approximation remains valid only under certain conditions. We have shown [3] that even for the case of diffusion limited electron transfer (ET) the actual shapes of the unit cells are more complicated and depend on the local configuration of the neighbouring active sites. This was exemplified on the small patches of the random arrays with band-like and disk-like active sites via simulations and analytical derivations. Importantly, by comparing the total and individual electrode currents obtained by employing Voronoi tessellation and simulation of the system without any approximations we found that the former are reproduced with a good accuracy while the latter are evaluated with a much larger relative error [3], thus demonstrating the limits of Voronoi tessellation for representation of such systems. Moreover, diffusion interaction between the neighbouring sites compensate the differences in unit cell sizes leading to a more uniform unit cell sizes then predicted by Voronoi tessellation [4]. This, in particular explains why the early theory of random arrays using uniform representation of the system were quantitatively successful [5]. References: [1] O. Sliusarenko, A. Oleinick, I. Svir, C. Amatore. J. Electrochem. Soc. 167, 2020, 013530. [2] T. J. Davies and R. G. Compton. J. Electroanal. Chem. 585, 2005, 63. [3] G. Pireddu, I. Svir, C. Amatore, A. Oleinick, ChemElectroChem 8, 2021, 2413. [4] G. Pireddu, I. Svir, C. Amatore, A. Oleinick, Electrochim. Acta 365, 2021, 137338. [5] C. Amatore, J.-M. Savéant, D. Tessier, J. Electroanal. Chem. 147, 1983, 39.