Impact of the Hydroperoxyl Radical (•OOH) on the Redox Metabolism of Mononuclear Cells During Phagocytosis: An In Vitro Experimental Study

The hydroperoxyl radical (•OOH), a reactive oxygen species (ROS), plays a critical role in regulating physiological processes. Its involvement in cellular redox pathways and association with pathological processes make it a key molecule for understanding how excessive free radicals modulate cellular metabolism. This study investigated the effects of exogenous •OOH on the redox metabolism of mononuclear cells during phagocytosis. Rat-derived mononuclear cells were treated with different concentrations of •OOH (generated via spark-discharge non-coherent radiation), and phagocytosis was induced using latex particles. The effect of •OOH on cell membrane integrity was assessed by trypan-blue-staining, while redox metabolites were quantified by spectrofluorimetry and spectrophotometry at 1-, 30-, and 60-minutes post-phagocytosis induction. In unexposed cells, free FAD and NADH levels increased during phagocytosis, tryptophan-containing proteins remained stable, and glycation end-products (AGEs) rose significantly by 60 minutes post-phagocytosis induction. •OOH at concentrations of (3.6 ± 0.9) × 10⁻⁵ and (1.8 ± 0.45) × 10⁻⁴ mol/L did not alter redox metabolism. However, exposure to higher concentrations ((5.4 ± 1.35) × 10⁻⁴ mol/L) induced significant cytotoxic effects. At the metabolic level, this dose triggered a marked redox imbalance, evidenced by a 1.4-fold increase in FAD, altered coenzyme ratios (NADH/FAD and NADH/NAD), and a significant decrease in tryptophan-related protein fluorescence, indicating extensive macromolecular damage. All •OOH concentrations tested suppressed the formation of AGEs 60 minutes after phagocytosis induction. We propose that this inhibition is not due to a protective effect, but to fragmentation of the protein backbone or modifications in the side chains induced by radicals.