Lipoproteins in hypoxic tumor cells as traps of free radicals

Abstract

We examined the role of main cell protective mechanisms in retaining the high resistance of ascitic cells (EAC, ZAH) to lipid peroxidation with respect to different stages of tumor-organism metabolic interactions. The following mechanisms were studied: (1) the activity of main EAC enzymatic antioxidants (GSH-Px, SOD); (2) changes in lipid metabolism, especially the content of the main PUFA (linoleic and arachidonic fatty acids) in EAC cells; (3) comparison of intracellular resistance between EAC/ZAH cytoplasmic sections (containing LP-granules or not) to lipid peroxidation (initialized directly by UV-light). We found that the high resistance to lipid peroxidation was typical for cytoplasma sections (without LP-granules) on all stages of tumor development in vivo. The intracellular LP-granules become the main sensitive targets for FR-action, but only in the chronic hypoxia state of EAC/ZAH tumor cells. The latter effect developed in close correlation with the following metabolic interactions: (1) increasing the proportion of PUFA (especially, arachidonic and linoleic acids) transported to EAC tumor cells from host organs and accumulated mainly in tumor LP-granules, and (2) decreasing the alpha-tocopherol content of these hypoxic EAC cells while no activation of the main cell antioxidative enzymes (GSH-Px, SOD) took place. The vitality and high resistance of EAC stationary cells were accompanied by the 'paradoxical' state with great differences between the resistance of the intracellular PUFA-rich granules and other cytoplasmic sections. A similar state was found in stationary ZAH cells. The cell state is in good agreement with the Dormandy's suggestion that PUFA-rich granules can trap reactive radical species preventing their interaction with 'critical' PUFA-membranes.