Oxidative Stress Induces Impairment of Human Erythrocyte Energy Metabolism through the Oxygen Radical-mediated Direct Activation of AMP-deaminase

Abstract

The effect of oxidative stress on human red blood cell AMP-deaminase activity was studied by incubating either fresh erythrocytes or hemolysates with H 2 O 2 (0.5, 1, 2, 4, 6, 8, and 10 mM) or NaNO 2 (1, 5, 10, 20, and 50 mM), for 15 min at 37°C. AMP-deaminase tremendously increased by increasing H 2 O 2 or NaNO 2 at up to 4 and 20 mM, respectively (maximal effect for both oxidants was 9.5 and 6.5 times higher enzymatic activity than control erythrocytes or hemolysates, respectively). The incubation of hemolysates with iodoacetate (5-100 mM), N-ethylmaleimide (0.1-10 mM), or p-hydroxymercuribenzoate (0.1-5 mM) mimicked the effect of oxidative stress on AMP-deaminase, indicating that sulfhydryl group modification is involved in the enzyme activation. Reactive oxygen species (ROS) 1 are dangerous molecules generated physiologically and pathologically from various intracellular and extracellular sources (1). Several ROS-induced irreversible modifications of biologically fundamental macromolecules have been described, including oxidation of protein -SH groups (2), oxidation of purine nucleotides of nucleic acids (3), and initiation of lipid peroxidation reaction chain (4, 5). Due to their very high ferrous iron concentration, human erythrocytes might be exposed to risks of increased oxidative stress, mainly through the formation of ferrylhemoglobin (6) and, in part, through the Fenton reaction of hydrogen peroxide with Fe 2ϩ of hemoglobin, which generates the powerful oxidant hydroxyl radical (7). Although provided with efficient enzymatic systems for H 2 O 2 removal (catalase, glutathione peroxidase), several ROS-mediated erythrocyte damages have been reported to occur in different in vitro experimental conditions, including challenge with hydrogen peroxide (8, 9), incubation with redox-cycling drugs (10), and during the aging process (11). Nevertheless, data available in the literature give very little information on alteration of erythrocyte energy metabolism (in terms either of metabolites or of enzymatic activities) following oxidative stress, except for results reporting only modest effects of iron-ascorbate (as a ROS-generating system) on hexokinase (12), thus suggesting that enzymes involved in red blood cell energy production are scarcely affected by oxidative stress.Very recently, we have shown, on the contrary, that oxidative stress, induced by increasing the addition of H 2 O 2 concentrations to intact red blood cells, provoked a progressive ATP depletion, which was unexpectedly paralleled by a marked IMP (but neither AMP nor ADP) increase. Such a phenomenon was very probably linked to AMP-deaminase 2 activation (13). This enzyme plays a critical role in energy metabolism, catalyzing the deamination of AMP into IMP in the purine nucleotide cycle, and it is present in mammals in three different isoforms.

Medicinal activities of the leaves of Musa sapientum var. sylvesteris in vitro

“…Inhibition of H 2 O 2 induced red blood cell hemolysis of methanolic extract was examined by the in vitro method described previously by Tavazzi et al [13] . The erythrocytes from human blood were separated by centrifugation and washed with saline or isotonic sodium phosphate buffer (pH 7.4) until the supernatant was colorless.…”

Vitamin C Deficiency Activates the Purine Nucleotide Cycle in Zebrafish

“…The stimulation of physical activity in the skeletal muscle of both rats (36) and trout (34) has also been shown to affect the distribution of AMPD between free and bound forms. In human erythrocytes, Tavazzi et al (37) demonstrated that reactive oxygen species are directly responsible for activation of AMPD through sulfhydryl group modification.…”

Metalloproteinase Inhibitor Counters High-Energy Phosphate Depletion and AMP Deaminase Activity Enhancing Ventricular Diastolic Compliance in Subacute Heart Failure

“…Cardiac AMPD may help regulate adenine nucleotide catabolism during myocardial ischemia (Thakkar et al, 1994) under oxidative stress conditions (Tavazzi et al, 2001), increased ADP (Chung and Bridger, 1976), and sustained ␤-stimulation (Hohl, 1999). In skeletal muscle in vivo, AMPD activity increase during muscular work is mediated by ADP, AMP, and pH (Wheeler and Lowenstein, 1979).…”