Phagocytosis is associated with respiratory burst producing reactive oxygen and nitrogen species. Several studies imply that erythrocytes can inhibit the respiratory burst during erythrophagocytosis. In this work we studied the mechanisms of this effect using control and in vitro peroxidized erythrocyte membranes. We demonstrated that autofluorescence of peroxidation products can be used for visualization of phagocytozed membranes by fluorescence microscopy. We also found that respiratory burst induced by a phorbol ester was inhibited by control membranes (5 mg/ml) to 63 % (P0.001), and to 40 % by peroxidized membranes (P0.001). We proved that this effect is not caused by the direct interaction of membranes with free radicals or by the interference with luminol chemiluminescence used for the detection of respiratory burst. There are indications of the inhibitory effects of iron ions and free radical products. Macrophages containing ingested erythrocyte membranes do not contain protein-bound nitrotyrosine. These observations imply a specific mechanism of erythrocyte phagocytosis.
Although nitrated proteins have been repeatedly used as markers of lung injury, little is known about their formation and metabolism under hyperoxia. We therefore measured 3-nitrotyrosine (3NTYR) concentrations in lung tissue and serum of rats with carrageenan-induced pneumonia exposed to hyperoxia. Twenty-nine Wistar male rats were assigned to one of 4 groups. Two experimental groups were treated by intratracheal application of carrageenan (0.5 ml of 0.7 % solution) and then one was exposed to hyperoxia for 7 days (FIO2 0.8), the other to air. Rats of two control groups breathed either hyperoxic gas mixture or air for 7 days. At the end of exposure the ventilation was determined in anesthetized, intubated animals in which 3NTYR concentrations were measured in the lung tissue and nitrites and nitrates (NOx) were estimated in the serum. Carrageenan instillation increased 3NTYR concentrations in lung tissue (carrageenan-normoxic group 147±7 pmol/g protein, control 90±10 pmol/g protein) and NOx concentration in the serum (carrageenan-normoxic group 126±13 ppb, control 78±9 ppb). Hyperoxia had no effect on lung tissue 3NTYR concentration in controls (control-hyperoxic 100±14 pmol/g protein) but blocked the increase of lung tissue 3NTYR in carrageenan-treated rats (carrageenan-hyperoxic 82±13 pmol/g protein), increased NOx in serum (control-hyperoxic 127±19 ppb) and decreased serum concentration of 3NTYR in both hyperoxic groups (carrageenan-hyperoxic 51±5 pmol/g protein, control-hyperoxic 67±7 pmol/g protein, carrageenan-normoxic 82±9 pmol/g protein, control 91±7 pmol/g protein). The results suggest that hyperoxia affects nitration of tyrosine residues, probably by increasing 3NTYR degradation.