3-nitrotyrosine and Acidosis

The effectiveness of sodium bicarbonate (SB) has recently been questioned although it is often used to correct metabolic acidosis of neonates. The aim of the present study was to examine its effect on hemodynamic changes and hydrogen peroxide (H(2)O(2)) generation in the resuscitation of hypoxic newborn animals with severe acidosis.. Newborn piglets were block-randomized into a sham-operated control group without hypoxia (n = 6) and two hypoxia-reoxygenation groups (2 h normocapnic alveolar hypoxia followed by 4 h room-air reoxygenation, n = 8/group). At 10 min after reoxygenation, piglets were given either i.v. SB (2 mEq/kg), or saline (hypoxia-reoxygenation controls) in a blinded, randomized fashion. Hemodynamic data and blood gas were collected at specific time points and cerebral cortical H(2)O(2) production was continuously monitored throughout experimental period. Plasma superoxide dismutase and catalase and brain tissue glutathione, superoxide dismutase, catalase, nitrotyrosine and lactate levels were assayed.. Two hours of normocapnic alveolar hypoxia caused cardiogenic shock with metabolic acidosis (PH: 6.99 ± 0.07, HCO(3)(-): 8.5 ± 1.6 mmol/L). Upon resuscitation, systemic hemodynamics immediately recovered and then gradually deteriorated with normalization of acid-base imbalance over 4 h of reoxygenation. SB administration significantly enhanced the recovery of both pH and HCO(3-) recovery within the first hour of reoxygenation but did not cause any significant effect in the acid-base at 4 h of reoxygenation and the temporal hemodynamic changes. SB administration significantly suppressed the increase in H(2)O(2) accumulation in the brain with inhibition of superoxide dismutase, but not catalase, activity during hypoxia-reoxygenation as compared to those of saline-treated controls.. Despite enhancing the normalization of acid-base imbalance, SB administration during resuscitation did not provide any beneficial effects on hemodynamic recovery in asphyxiated newborn piglets. SB treatment also reduced the H(2)O(2) accumulation in the cerebral cortex without significant effects on oxidative stress markers presumably by suppressing superoxide dismutase but not catalase activity.

Topics: Acid-Base Equilibrium; Acidosis; Animals; Animals, Newborn; Blood Gas Analysis; Catalase; Cerebral Cortex; Disease Models, Animal; Female; Glutathione; Hemodynamics; Hydrogen Peroxide; Hypoxia; Infusions, Intravenous; Lactic Acid; Male; Oxidation-Reduction; Oxidative Stress; Oxygen; Pulmonary Alveoli; Resuscitation; Sodium Bicarbonate; Superoxide Dismutase; Swine; Tyrosine

Postconditioning (PostC) modifies the early post-ischemic pH, redox environment, and activity of enzymes. We hypothesized that early acidosis in PostC may affect superoxide dismutase (SOD) and catalase (CAT) activities, may reduce 3-nitrotyrosine (3-NT) protein levels, and may increase S-nitrosylated (SNO) protein levels, thus deploying its protective effects. To verify this hypothesis, we studied the early (7(th) min) and late (120(th) min) phases of reperfusion (a) endogenous SOD and CAT activities and (b) 3-NT protein levels and SNO protein levels. Isolated rat hearts underwent 30-min ischemia/120-min reperfusion (I/R) or PostC (5 cycles of 10-s I/R at the beginning of 120-min reperfusion) either with or without exogenous CAT or SOD infused during the initial 3 min of reperfusion. The effects of early reperfusion with acid buffer (AB, pH 6.8) on endogenous antioxidant enzymes were also tested. Pressure, infarct size, and lactate dehydrogenase release were also measured. At the 7(th) min, PostC induced a significant decrease in SOD activity with no major change both in Mn and Cu/Zn SOD levels and in CAT activity and level. PostC also reduced 3-NT and increased SNO levels. Exogenous SOD, but not CAT, abolished PostC cardioprotection. In late reperfusion (120-min), I/R increased SOD activity but decreased CAT activity and Cu/Zn SOD levels; these effects were reversed by PostC; 3-NT was not affected, but SNO was increased by PostC. AB reproduced PostC effects on antioxidant enzymes. The conclusions are as follows: PostC downregulates endogenous SOD and preserves CAT activity, thus increasing SNO and reducing 3-NT levels. These effects are triggered by early post-ischemic acidosis. Yet acidosis-induced SOD downregulation may limit denitrosylation, thus contributing to PostC triggering. Hence, exogenous SOD, but not CAT, interferes with PostC triggering. Prolonged SOD downregulation and SNO increase may contribute to PostC and AB beneficial effects.

Topics: Acidosis; Animals; Catalase; Male; Myocardial Ischemia; Myocardial Reperfusion Injury; Rats; Rats, Wistar; Superoxide Dismutase; Tyrosine

Nitrotyrosine produced by NO-mediated reaction is a possible marker for cytotoxicity in brain ischemia. In this study, we aimed to determine whether iNOS is responsible for the nitrotyrosine formation and which type of cell is predominantly nitrated. Fifty-eight wild-type and 28 iNOS knockout male mice were used. Under halothane anesthesia the left middle cerebral artery was occluded for 2 h and reperfused for 0.5 or 15 h. The ratio of nitrotyrosine to total tyrosine (%NO2-Tyr) was measured by means of a hydrolysis/HPLC. After 0.5-h reperfusion, %NO2-Tyr in the ischemic cortex of wild-type and knockout mice amounted to 0.037 +/- 0.040% (n = 8) and 0.064 +/- 0.035% (n = 6), respectively, being significantly higher than that in the sham operation group (n = 7) (P < 0.05). After 15-h reperfusion, nitrotyrosine was detected only in wild-type mice (0.039 +/- 0.025%, n = 7), not in knockout or sham-operated mice (P < 0.05). Immunohistochemical reaction for nitrotyrosine was seen predominantly in the vascular wall in the peri-infarct region of the cerebral cortex in wild-type mice after 15-h reperfusion, but not in corresponding knockout mice. Our data suggest that iNOS is responsible for nitrotyrosine formation in the later phase of reperfusion, and that vascular endothelium is the major site of this reaction, at least in the case of 15-h reperfusion.

Topics: Acidosis; Animals; Blood Glucose; Blood Pressure; Carbon Dioxide; Cerebral Cortex; Cerebrovascular Circulation; Chromatography, High Pressure Liquid; Endothelium, Vascular; Infarction, Middle Cerebral Artery; Ischemic Attack, Transient; Male; Mice; Mice, Inbred C57BL; Mice, Knockout; Nitrates; Nitric Oxide; Nitric Oxide Synthase; Nitric Oxide Synthase Type II; Oxygen; Reperfusion Injury; Tyrosine