Cytoprotective Action of Sodium Fumarate in an in vitro Model of Hypoxia Using Sodium Dithionite

Hypoxia is a part of many pathological and some physiological processes. It also occurs as a result of surgical techniques associated with limiting the blood supply to the operated organs and tissues. Hypoxia leads to a significant decrease in the ability of cells to implement energy-dependent processes due to a reduced contribution of mitochondria to the synthesis of adenosine triphosphate (ATP). In order to protect cells and increase the time of surgery, infusion of a solution of sodium fumarate for several days before the surgical procedure is suggested. However, the mechanism of the observed protective effect is still a subject of discussion. The aim of the research was to study the mechanism of the sodium fumarate cytoprotective effect on renal epithelial cells in acute hypoxia modeling in vitro by reducing oxygen in the medium using sodium dithionite. The study was conducted using the MDCK renal epithelial cell line with sodium dithionite at a concentration of 5 mM to create hypoxic conditions. The parameters of cellular metabolism (including the value of mitochondrial membrane potential, the state of mitochondrial NADH and FAD, the content of Ca2+ and Mg2+ and the pH level in the cytosol, the rate of glucose absorption by cells, and cell death) were assessed by means of confocal and wide-field fluorescence microscopy. The concentration of dissolved oxygen was established using the polarographic method with a Clark electrode. It was demonstrated that the use of sodium dithionite allows modeling acute hypoxia in vitro with a rapid decrease in the oxygen concentration in the cell incubation medium, which resulted in a change in mitochondrial function and the apoptosis progression. At that, sodium fumarate reduces the level of cell death, which is associated not with the restoration of the ATP-producing ability of mitochondria, but rather with an increase in the contribution of alternative sources of high-energy compounds. At the cellular level, using an optimized hypoxia model, the study revealed the mechanism of the protective role of sodium fumarate, which explained the antihypoxant effectiveness in assisted ischemia of organs and tissues.