Majidah Shadid

Effect of deferoxamine and allopurinol on non-protein-bound iron concentrations in plasma and cortical brain tissue of newborn lambs following hypoxia-ischemia.

Reduction of non-protein-bound iron (NPBI) using iron chelators may attenuate hypoxia-ischemia-induced reperfusion injury of the brain. This study investigated whether administration of low-dose deferoxamine and allopurinol, both having NPBI-chelating properties, reduced hypoxia-ischemia-induced NPBI formation in plasma effluent from the brain and in cerebral cortical tissue. Twenty-one newborn lambs underwent severe hypoxia-ischemia. Upon reperfusion and reoxygenation the lambs received either a placebo (n = 7), or deferoxamine 2.5 mg/kg (n = 7) or allopurinol 20 mg/kg (n = 7). The post-hypoxic-ischemic NPBI levels in plasma were significantly lower after deferoxamine but not after allopurinol as compared to placebo-treated lambs. Cortical NPBI levels in both deferoxamine and allopurinol-treated lambs were significantly lower than NPBI levels in placebo-treated lambs. We conclude that deferoxamine effectively lowers NPBI in plasma effluent from the brain, and that both, deferoxamine and allopurinol, lower NPBI in cortical brain tissue.

The Effect of Antioxidative Combination Therapy on Post Hypoxic-Ischemic Perfusion, Metabolism, and Electrical Activity of the Newborn Brain

Reoxygenation and reperfusion after severe hypoxia and ischemia (HI) contribute substantially to birth asphyxia-related brain injury. Excess production of free radicals via metabolization of arachidonic acid, xanthine oxidase, and non-protein-bound iron play an important role. Cerebral reperfusion injury is characterized by a decrease in perfusion, oxygen consumption, and electrical activity of the brain. Reduction of free radical production may attenuate these features. We therefore induced severe HI in 35 newborn lambs, and upon reperfusion the lambs received a placebo [control(CONT), n = 7], the cyclooxygenase inhibitor indomethacin (INDO, 0.3 mg/kg/i.v., n = 7), the xanthine oxidase inhibitor allopurinol(ALLO, 20 mg/kg/i.v., n = 7), the iron chelator deferoxamine (DFO, 2.5 mg/kg/i.v., n = 7), or a combination of these drugs (COMB,n = 7). In each group changes (%) from pre-HI values were investigated for brain perfusion [measured by carotid artery flow(Qcar, mL/min)], (relative) cerebral O2 metabolism(CMRO2), and electrocortical brain activity (ECBA, µV) at 15, 60, 120, and 180 min post-HI. Qcar decreased significantly at 120 and 180 min post-HI in CONT (p < 0.05), but not in INDO, ALLO, DFO, and COMB groups. CMRO2 decreased significantly in CONT at 60 min post-HI (p < 0.05), remained stable in DFO and INDO, and was significantly higher in ALLO and COMB (p < 0.05) at 120 and 180 min post-HI. ECBA was significantly lower in CONT during the whole post-HI period (p < 0.05), ECBA in INDO and COMB were significantly decreased at 60 and 120 min post-HI (p < 0.05), but recovered afterward, whereas DFO and ALLO remained stable during the post-HI period. In conclusion preservation of Qcar and CMRO2, and recovery of ECBA occurred after treatment with INDO, ALLO, and DFO; combination of these drugs did not have an additional positive effect.

Effect of Post-Hypoxic-lschemic Inhibition of Nitric Oxide Synthesis on Cerebral Blood Flow, Metabolism and Electrocortical Brain Activity in Newborn Lambs

Since an excessive production of nitric oxide upon reperfusion/reoxygenation may play an important role in post-hypoxic-ischemic (HI) brain injury, we investigated whether immediate post-HI blockade of nitric oxide synthesis by N-omega-nitro-L-arginine (NLA) may reduce this injury. In 18 newborn lambs, subjected to severe HI, changes from pre-HI values were measured for carotid blood flow (Qcar [ml/min]) as a measure of changes in brain blood flow, (relative) cerebral metabolic rate of oxygen (CMRO2), and electrocortical brain activity (ECBA) at 15, 60, 120 and 180 min after HI. Upon completion of HI, at the onset of reperfusion and reoxygenation, 6 lambs received a placebo (control group), 6 low-dose NLA (10 mg/kg i.v., NLA-10 group), and 6 high-dose NLA (40 mg/kg i.v., NLA-40 group). Histological damage to cerebellar Purkinje cells was assessed after termination of the experiment. Only the control group showed a distinct initial post-HI cerebral hyperperfusion. From 60 min after HI onward Qcar was decreased to about 75% of pre-HI Qcar in all 3 groups, although none of these changes in Qcar reached statistical significance. Despite the decreased Qcar in all 3 groups, only the control group showed a significantly decreased CMRO2. ECBA and its bandwidth decreased in all groups, but only recovered in the NLA-10 group 180 min after HI. The brain to body mass ratio (%) and percentage necrotic Purkinje cells were, respectively: 15.3 +/- 0.8 and 56 +/- 10 (control group); 12.5 +/- 1.2 and 36 +/- 9 (NLA-10 group), and 11.3 +/- 1.0 (p < 0.05 vs. the control group) and 35 +/- 14 (NLA-40 group). Since post-HI reperfusion injury of the brain has been characterized by a decreased CMRO2 and electrical brain activity, we conclude that preservation of CMRO2 in both NLA groups, but a recovery of ECBA and its bandwidth only in the NLA-10 group, suggests that NLA, and especially low-dose NLA, may reduce post-HI brain injury.

Near infrared spectroscopy-measured changes in cerebral blood volume and cytochrome aa3 in newborn lambs exposed to hypoxia and hypercapnia, and ischemia: a comparison with changes in brain perfusion and O2 metabolism ☆

OBJECTIVES Validation of near infrared spectroscopy (NIRS)-measured changes in cerebral blood volume (deltaCBV) and cytochrome aa3 (deltaCytaa3) as estimators of changes in brain perfusion and oxygenation in the newborn lamb during hypoxia and hypercarbia, and additional hypotension. METHODS AND MATERIALS In 33 newborn lambs brain perfusion assessed by carotid artery blood flow (deltaQcar: ml/min)and cerebral metabolic rate of oxygen (deltaCMRO2: ml O2/min) were related to NIRS-derived deltaCBV (ml/100 g) and deltaCytaa3 (microM) during combined hypoxia and hypercarbia and additional hypotension. Combined hypoxia and hypercapnia was induced by ventilation with 6-8% of O2 and 10% of CO2 during 30 min, and additional hypotension ( < 35 mmHg for 5 min) was induced by careful withdrawal of blood. RESULTS CBV increased during hypoxia and hypercarbia, decreased during additional hypotension and was related to deltaQcar: (0.009 ml/100 g change per ml/min Qcar: P < 0.0001). Cytaa3 increased during hypoxia and hypercarbia, decreased during subsequent additional hypotension andshowed a reverse relationship with deltaCMRO2 (-1.65 microM change per ml O2/min CMRO2: P <0.0001). Cytaa3 remained above baseline during reperfusion. CONCLUSIONS deltaCBV estimates changes in brain perfusion, but overestimates brain perfusion during hypotension. The pattern of deltaCytaa3 suggests less oxygen utilisation by brain tissue during hypoxia and subsequent reperfusion.

Oxidative stress during post-hypoxic-ischemic reperfusion in the newborn lamb: the effect of nitric oxide synthesis inhibition.

Post-hypoxic-ischemic (HI) reperfusion induces endothelium and neurons to produce excessive amounts of nitric oxide and superoxide, leading to peroxynitrite formation, release of protein-bound metal ions (i.e. iron), and cytotoxic oxidants. We produced severe HI in 18 newborn lambs and serially determined plasma prooxidants (non-protein-bound iron), lipid peroxidation (malondialdehyde), and antioxidative capacity [ratio of ascorbic acid/dehydroascorbic acid (AA/DHA), α-tocopherol, sulfhydryl groups, allantoin/uric acid ratio, and vitamin A] in blood effluent from the brain before and at 15, 60, 120, and 180 min after HI. The lambs were divided in three groups: six received a placebo (CONT), six received low dose (10 mg/kg/i.v.) Nω-nitro-L-arginine (NLA-10) to block nitric oxide production, and six received high dose NLA (40 mg/kg/iv; NLA-40), immediately after completion of HI. Non-protein-bound iron increased in all groups after HI but was significantly lower in both NLA groups at 180 min post-HI (p < 0.05), the AA/DHA ratio showed a consistent decrease in CONT (at 60 min post-HI, p < 0.05), but remained stable in NLA lambs. α-Tocopherol decreased steadily in the CONT, but not in the NLA lambs [180 post-H: 1.9 ± 0.9 versus 4.2 ± 0.7 μM(NLA-40), p < 0.05). Malondialdehyde was significantly higher in CONT lambs 120 min post-H compared with NLA groups [0.61 ± 017versus 0.44 ± 0.05 μM (NLA-40), p < 0.05]. Vitamin A and sulfhydryl groups did not differ among groups. We conclude that post-H inhibition of nitric oxide synthesis diminishes non-protein-bound iron increment and preserves antioxidant capacity.

Pretreatment with allopurinol in cardiac hypoxic-ischemic reperfusion injury in newborn lambs exerts its beneficial effect through afterload reduction.

Abstract The aim of this study was to determine whether allopurinol (ALLO) reduces reperfusion injury inflicted upon the heart resulting from excess production of free oxygen radicals after hypoxia and ischemia (HI) in newborn animals. We, therefore, produced severe HI in 13 newborn lambs by low O2-ventilation and blood volume reduction. One hour before HI seven lambs received ALLO (20 mg/kg i.v.), six received a placebo (CONT). Cardiac function and hemodynamic parameters were assessed by sequential measurement of left ventricular (LV) contractility through the end-systolic pressure-volume relation (ESPVR) using the conductance catheter method. Stroke volume (SV), cardiac output (CO), and aortic pressure (Pao) were measured and ejection fraction and total peripheral resistance (TPR) were calculated before HI, upon resuscitation (UR), and at 60 and 120 min post-HI. To estimate the effect of ALLO on redox status and anti-oxidative capacity, we measured concentrations of uric acid, sulfhydryl (SH), malondialdehyde (MDA), ascorbic acid (AA), and dehydroxylated ascorbic acid (DHAA) in plasma obtained from the coronary sinus and calculated the AA/DHAA ratio. Compared to CONT lambs, TPR in ALLO treated lambs decreased significantly, accompanied by a rise in CO and SV. ALLO did not affect myocardial contractility, because the ESPVR showed no significant differences between groups. AA/DHAA and SH showed a significant decrease in ALLO animals vs pre-HI, but not in CONT animals. Uric acid was significantly decreased in ALLO as compared to pre-HI and CONT animals. MDA was significantly increased in CONT animals at 15 min post-HI as compared to pre-HI, whereas in ALLO animals MDA showed a significant increase at 120 min post-HI vs CONT. We conclude that pretreatment with ALLO has a beneficial effect on the pump function by afterload reduction but not by changes in contractility. Furthermore, ALLO inhibited uric acid formation with a consequent decrease in anti-oxidative capacity.

Effect of Deferoxamine on Post-Hypoxic-Ischemic Reperfusion Injury of the Newborn Lamb Heart

Post-hypoxic-ischemic (HI) reperfusion induces excess production of non-protein-bound iron (NPBI), leading to formation of the highly reactive hydroxyl radical. We investigated whether the iron-chelator deferoxamine (DFO) could reduce reperfusion injury and improve left ventricular (LV) function. We produced severe HI in 14 newborn lambs and measured pre-HI, upon reperfusion, 60 and 120 min after HI the following parameters: mean aortic blood pressure, total peripheral resistance, stroke volume (SV), ejection fraction (EF) and LV contractility (pre-HI, 60 and 120 min post-HI). These parameters were assessed by measuring LV pressure (tip manometer) and volume (conductance catheter), using inflow occlusion to obtain slope (Ees) and volume intercept of the end-systolic P-V relationship (V10). We determined the antioxidative capacity, i.e. the ratio of ascorbic acid and dehydroascorbic acid (AA/DHAA) and malondialdehyde from coronary sinus blood at pre-HI and at 15, 60 and 120 min post-HI. Seven lambs received DFO (10 mg/kg i.v.) immediately after HI, 6 control lambs received a placebo. While neither Ees nor EF changed significantly in either group, the volume intercept V10 in the DFO-treated group was significantly smaller (0.25 ± 0.03 vs. 0.70 ± 0.09, p < 0.05), whereas SV was larger (3.6 ± 0.6 vs. 2.2 ± 0.2 ml, p < 0.05) and the AA/DHAA ratio was significantly lower at 15 min post-HI (p < 0.05) providing evidence for HI damage and for the protective effect of DFO. In conclusion: post-HI treatment of the newborn lamb with DFO has a modifying effect on free radical-induced damage to the myocardium and protects myocardial performance.

Influence of Inhibition of Nitric Oxide Synthesis on Cardiac Function in the Newborn Lamb after Hypoxic-Ischemic Injury

The aim of the present study was to investigate the effect of immediate post-hypoxic-ischemic (HI) inhibition of nitric oxide synthesis by Nω-nitro-L-arginine (NLA) on cardiac function and reactive oxygen species production. Fifteen newborn lambs were subjected to severe HI. Upon resuscitation 5 received 10 mg NLA/kg, 4 40 mg NLA/kg and 6 a placebo. Left ventricular (LV) contractility, cardiac output (CO), non-protein-bound iron (NPBI), ratio of reduced/oxidized ascorbic acid, α-tocopherol, sulfhydryl groups and malondialdehyde were measured before and 15, 60 and 120 min after resuscitation. There was a significant decrease in CO in all 3 groups at 60 min post-HI (p < 0.05). Reactive oxygen species production was also highest at 60 min post-HI (significantly increased NPBI and decrease in sulfhydryl groups in control lambs; p < 0.05). These results suggest neither a positive nor a negative effect of nitric oxide synthesis inhibition on post-HI myocardial performance but may suggest a positive effect of NLA on reactive oxygen species-mediated post-HI damage.

Effect of Deferoxamine on Na+,K+-ATPase Activity and Electrocortical Brain Activity after Hypoxia-Ischemia in Newborn Lambs

Effect of Deferoxamine on Na + ,K + -ATPase Activity and Electrocortical Brain Activity after Hypoxia-Ischemia in Newborn Lambs

Nitric Oxide (NO)-Inhibition After Hypoxia-Ischemia (HI) Restores Brain Blood Flow Autoregulation |[bull]| 1863

Birth asphyxia impairs brain blood flow autoregulation (BBF-A). Inappropriate NO-synthesis of vasodilator NO may be important in this respect. We investigated if NO-synthase-inhibition by N-ω-nitro-L-arginin (NLA) could restore BBF-A after HI. Severe HI was induced in 16 newborn lambs and brain blood flow (carotid flow [mL/min]: Qcar) and aortic blood pressure[mmHg]: Pao) were measured over a 30 min period before HI (pre-HI), 0-30 min after completion of HI (0-30 post-HI) and from 60 to 120 min post-HI (60-120 post-HI). Immediately after completion of HI, 5 lambs received a placebo(CONT), 6 a low dose NLA (10 mg/kg/iv: NLA-10) and 5 high dose NLA (40 mg/kg/iv: NLA-40).