Cardiac function, myocardial glutathione, and matrix metalloproteinase-2 levels in hypoxic newborn pigs reoxygenated by 21%, 50%, or 100% oxygen

Attenuation of Acute Renal Injury After the Post-resuscitation Administration of Doxycycline in Surviving Newborn Piglets With Severe Hypoxia-Reoxygenation

Background: Asphyxiated neonates often have myocardial dysfunction and renal insufficiency. Previously we demonstrated that doxycycline improved cardio-renal function through matrix metalloproteinase (MMP)-2 inhibition in an acute swine model of neonatal hypoxia-reoxygenation. The prolonged cardio-renal protective effects of doxycycline in neonates still remained unknown. We therefore hypothesized that the protective effects of doxycycline persisted in surviving subjects. Methods: Newborn piglets were instrumented and subjected to 1 h of hypoxia followed by reoxygenation with 21-25% oxygen and observed for 4 days. Intravenous doxycycline (30 mg/kg) or normal saline (1 mL, saline-control group) was given at 5 min of reoxygenation (n = 8/group) in a randomized, blinded fashion. Sham-operated piglets (n = 5) received no hypoxia-reoxygenation. At 96 h after reoxygenation, the left ventricular function was assessed by Millar® catheter. Renal injury was investigated by measuring plasma creatinine, urinary N-acetyl-D-glucosaminidase activity, renal tissue lactate and MMP-2 activity. Results: Both hypoxia-reoxygenation groups had similar hypoxic stress with severe lactate acidosis, and hemodynamic recovery. Doxycycline-treated piglets had higher urine output with lower urine N-acetyl-D-glucosaminidase, plasma creatinine, and renal MMP-2 activity (vs. saline-controls; all p < 0.05). These markers were all negatively correlated with urine output. Conclusions: In newborn piglets surviving hypoxia-reoxygenation, we observed a weak but significant and persistent attenuation of renal injury and improved recovery with the post-resuscitation administration of doxycycline.

Role for Functional SOD2 Polymorphism in Pulmonary Arterial Hypertension in a Chinese Population

The superoxide dismutase 2 (SOD2) gene is a pivotal part of oxidative stress system, which could induce the onset of pulmonary arterial hypertension (PAH). In this study, we quantified the influence of a SOD2 exonic polymorphism (rs4880) on PAH susceptibility. We genotyped this single nucleotide polymorphism (SNP) by TaqMan, and evaluated its association with PAH susceptibility in a case-control study of 460 patients and 530 controls in China. There were significant differences between PAH cases and controls in both CC and TC+CC genotypes (p = 0.013 and p = 0.010, respectively). Furthermore, the number of variant alleles followed a dose-response manner (p trend was 0.023). Besides, the mRNA level and protein expression also indicated that the C allele of this variant decreased the expression of SOD2 gene (p = 0.004 in mRNA level and p = 0.012 in protein level) after the transfection of plasmids containing the different genotype of rs4480. There is significant association between SOD rs4880 polymorphism and the PAH susceptibility, and this polymorphism influenced PAH susceptibility by altering the expression of SOD2.

Doxycycline attenuates renal injury in a swine model of neonatal hypoxia-reoxygenation

Acute kidney injury in asphyxiated neonates is common. The renal protective effects of doxycycline, a known matrix metalloproteinase (MMP) inhibitor, have been demonstrated in rat ischemic-reperfusion models of injury. These effects have not been tested in large-animal models designed to reflect true clinical scenarios of neonatal hypoxia-reoxygenation (H-R). Newborn piglets were surgically instrumented for hemodynamic monitoring and subjected to 2 h of hypoxia followed by 4 h of normoxic reoxygenation. Piglets were blindly randomized to receive i.v. saline or doxycycline (3, 10, or 30 mg/kg) 5 min into reoxygenation (n = 7 per group). Sham-operated piglets (n = 5) received no H-R. Renal injury was investigated by histologic examination and measuring serum creatinine, urinary N-acetyl-D-glucosaminidase activity and renal tissue lactate with enzyme-linked immunosorbent assay. Renal tissue oxidative stress (lipid hydroperoxides) and total MMP-2 activity were measured with enzyme-linked immunosorbent assay and gelatin zymography, respectively. Piglets treated with doxycycline had significantly improved cardiac index, systemic arterial pressure, renal artery blood flow, and oxygen delivery, with no difference observed in heart rate compared with controls. The H-R piglets had significantly higher urinary N-acetyl-D-glucosaminidase activity, renal tissue lipid hydroperoxides, lactate, and MMP-2 activity, which were attenuated to varied degrees in a dose-related manner in piglets treated with doxycycline (P = 0.08 to P < 0.05). Serum creatinine and histologic features of H-R were not different among groups. Postresuscitation administration of doxycycline improved renal perfusion, attenuated renal injury, and reduced tissue oxidative stress and MMP-2 activity in a clinically translatable newborn swine model of H-R.

Inhibition of MMP-2 expression with siRNA increases baseline cardiomyocyte contractility and protects against simulated ischemic reperfusion injury

Matrix metalloproteinases (MMPs) significantly contribute to ischemia reperfusion (I/R) injury, namely, by the degradation of contractile proteins. However, due to the experimental models adopted and lack of isoform specificity of MMP inhibitors, the cellular source and identity of the MMP(s) involved in I/R injury remain to be elucidated. Using isolated adult rat cardiomyocytes, subjected to chemically induced I/R-like injury, we show that specific inhibition of MMP-2 expression and activity using MMP-2 siRNA significantly protected cardiomyocyte contractility from I/R-like injury. This was also associated with increased expression of myosin light chains 1 and 2 (MLC1/2) in comparison to scramble siRNA transfection. Moreover, the positive effect of MMP-2 siRNA transfection on cardiomyocyte contractility and MLC1/2 expression levels was also observed under control conditions, suggesting an important additional role for MMP-2 in physiological sarcomeric protein turnover. This study clearly demonstrates that intracellular expression of MMP-2 plays a significant role in sarcomeric protein turnover, such as MLC1 and MLC2, under aerobic (physiological) conditions. In addition, this study identifies intracellular/autocrine, cardiomyocyte-produced MMP-2, rather than paracrine/extracellular, as responsible for the degradation of MLC1/2 and consequent contractile dysfunction in cardiomyocytes subjected to I/R injury.

Intracellular regulation of matrix metalloproteinase-2 activity: new strategies in treatment and protection of heart subjected to oxidative stress

Much is known regarding cardiac energy metabolism in ischemia/reperfusion (I/R) injury. Under aerobic conditions, the heart prefers to metabolize fatty acids, which contribute to 60-80% of the required ATP. During ischemia, anaerobic glycolysis increases and becomes an important source of ATP for preservation of ion gradients. With reperfusion, fatty acid oxidation quickly recovers and again predominates as the major source of mitochondrial oxidative metabolism. Although a number of molecular mechanisms have been implicated in the development of I/R injury, their relative contributions remain to be determined. One such mechanism involves the proteolytic degradation of contractile proteins, such as troponin I (TnI), myosin heavy chain, titin, and the myosin light chains (MLC1 and MLC2) by matrix metalloproteinase-2 (MMP-2). However, very little is known about intracellular regulation of MMP-2 activity under physiological and pathological conditions. Greater understanding of the mechanisms that govern MMP-2 activity may lead to the development of new therapeutic strategies aimed at preservation of the contractile function of the heart subjected to myocardial infarction (MI) or I/R. This review discusses the intracellular mechanisms controlling MMP-2 activity and highlights a new intracellular therapeutic direction for the prevention and treatment of heart injury.

The role of oxygen in the delivery room

As recently as the year 2000, 100% oxygen was recommended to begin resuscitation of depressed newborns in the delivery room. However, the most recent recommendations of the International Liaison Committee on Resuscitation counsel the prudent use of oxygen during resuscitation. In term and preterm infants, oxygen therapy should be guided by pulse oximetry that follows the interquartile range of preductal saturations of healthy term babies after vaginal birth at sea level. This article reviews the literature in this context, which supports the radical but judicious curtailment of the use of oxygen in resuscitation at birth.

Early versus delayed cyclosporine treatment in cardiac recovery and intestinal injury during resuscitation of asphyxiated newborn piglets

PURPOSE

We previously demonstrated that treating asphyxiated newborn piglets with cyclosporine immediately following resuscitation can improve cardiac and intestinal recovery. However, immediate treatment may not be feasible for a large portion of neonates delivered in peripheral or rural hospitals. Therefore, our objective was to determine if delayed cyclosporine treatment remained effective in treating neonatal asphyxia. We hypothesized that early and delayed cyclosporine treatment would improve cardiac and intestinal recovery during resuscitation of asphyxiated newborn piglets.

METHODS

Thirty piglets (1-4 days old) were instrumented for continuous monitoring of cardiac output and mesenteric hemodynamics. After stabilization, normocapnic alveolar hypoxia (10-15 % oxygen) was instituted for 2 h followed by reoxygenation with 100 % oxygen for 0.5 h, then 21 % for 5.5 h. Piglets were block-randomized to receive either intravenous bolus of cyclosporine A (10 mg/kg) or normal saline (control) at 5 or 120 min of reoxygenation (early or delayed, respectively; n = 8/group). Myocardial and intestinal lactate concentrations as well as histological examinations were determined.

RESULTS

Hypoxic piglets had cardiogenic shock (cardiac output 52 ± 1 % of baseline, mean arterial pressure 32 ± 1 mmHg) and acidosis (pH 6.98 ± 0.1). Although both cyclosporine treatments improved cardiac output (p < 0.05 vs. controls), only early cyclosporine treatment improved stroke volume and systemic oxygen delivery (p < 0.05 vs. controls). Left ventricle and intestinal lactate were lowered in both cyclosporine-treated groups (p < 0.05 vs. controls). Early, but not delayed, cyclosporine treatment also attenuated intestinal injury (p < 0.05 vs. controls).

CONCLUSION

This study demonstrates that treating asphyxiated newborn piglets with cyclosporine within 2 h of resuscitation is effective with superior cardioprotection and intestinal injury attenuation with early treatment.

Cyclosporine treatment improves cardiac function and systemic hemodynamics during resuscitation in a newborn piglet model of asphyxia: a dose-response study

OBJECTIVES

Asphyxiated neonates often have myocardial depression, which is a significant cause of morbidity and mortality. Cardioprotective effects of cyclosporine have been observed in adult patients and animals with myocardial infarction. However, the cardioprotective effect of cyclosporine in neonates has not yet been studied. We hypothesize that cyclosporine will improve cardiac function and reduce myocardial injury in asphyxiated newborn piglets.

DESIGN

Thirty-six piglets (1-4 days old, weighing 1.4-2.5 kg) were acutely instrumented for continuous monitoring of cardiac output and systemic arterial pressure. After stabilization, normocapnic alveolar hypoxia (10% to 15% oxygen) was instituted for 2 hrs followed by reoxygenation with 100% oxygen for 0.5 hrs and then 21% for 3.5 hrs. A nonasphyxiated, sham-operated group was included (n = 4) to control for effects of the surgical model. Plasma troponin and myocardial lactate concentrations were determined as well as morphologic examinations.

SETTING

Neonatal asphyxia and reoxygenation.

SUBJECTS

Newborn (1-4 days old) piglets.

INTERVENTIONS

Piglets were block-randomized to receive intravenous boluses of cyclosporine A (2.5, 10, or 25 mg/kg) or normal saline (control) at 5 mins of reoxygenation (n = 8/group).

MEASUREMENTS AND MAIN RESULTS

Cardiac index, heart rate, systemic oxygenation, plasma troponin, and left ventricular lactate were measured. Hypoxic piglets had cardiogenic shock (cardiac output 40% to 48% of baseline), hypotension (mean arterial pressure 27-31 mm Hg), and acidosis (pH 7.04). Cyclosporine treatment caused bell-shaped improvements in cardiac output, stroke volume, and systemic oxygen delivery (p < .05 vs. controls). Plasma troponin and left ventricle lactate were higher in controls than that of 2.5 and 10 mg/kg cyclosporine-treated groups (p < .05). Although histologic features of myocardial injury were not different among groups, severe damage was observed in mitochondria of control piglets but attenuated in that of cyclosporine (10 mg/kg) treatment.

CONCLUSIONS

Postresuscitation administration of cyclosporine causes preservation of cardiac function and attenuates myocardial injury in newborn piglets after asphyxia-reoxygenation.

Therapeutic strategies to protect the immature newborn myocardium during resuscitation following asphyxia

Perinatal asphyxia contributes to over one million newborn deaths worldwide annually, and may progress to multiorgan failure. Cardiac dysfunction, of varying severity, is seen in 50%-70% of asphyxiated newborns. Resuscitation is necessary to restore oxygenation to deprived tissues, including the heart. However, reoxygenation of asphyxiated newborns may lead to generation of reactive oxygen species (ROS) and further myocardial damage, termed reperfusion injury. The newborn heart is especially vulnerable to oxidative stress and reperfusion injury due to immature antioxidant defense mechanisms and increased vulnerability to apoptosis. Currently, newborn myocardial protective strategies are aimed at reducing the generation of ROS through controlled reoxygenation, boosting antioxidant defenses, and attenuating cellular injury via mitochondrial stabilization.

Impaired diastolic function and disruption of the force-frequency relationship in the right ventricle of newborn pigs resuscitated with 100% oxygen

BACKGROUND

Resuscitation with 100% oxygen increases oxidative stress and is detrimental for organ function.

OBJECTIVE

To study the effects of resuscitation with 100% oxygen compared to room-air on myocardial function.

METHODS

Twenty-eight newborn pigs underwent global hypoxia (8% oxygen/N2) until base excess reached -20 mmol/l. The animals were randomized into two groups and resuscitated with either 100% or room air for 30 min. Myocardial tissue Doppler velocities and acceleration of the mitral and tricuspid valve annuli during systole and diastole were assessed before global hypoxia and after resuscitation together with troponin I.

RESULTS

Peak early diastolic velocity (E') and acceleration (pEac) in the septum and pEac in the lateral tricuspid valve annulus were lower after resuscitation with 100% oxygen, suggesting impaired diastolic relaxation in the right ventricle. Lower systolic velocities and acceleration in the right ventricle relative to heart rate indicate disruption of the right ventricular force-frequency relationship after resuscitation with 100% oxygen. Troponins were higher in the 100% oxygen group, suggesting increased myocardial damage in this group.

CONCLUSION

Resuscitation with 100% oxygen compared to room air induces diastolic dysfunction, disrupts the systolic force-frequency relationship and increases myocardial damage in the newborn pig.

Neonatal asphyxia induces the nitration of cardiac myosin light chain 2 that is associated with cardiac systolic dysfunction

Hypoxia followed by reoxygenation (H-R) observed during perinatal asphyxia is a serious complication with high mortality and morbidity rates that may cause adverse cardiovascular effects in neonates. Our aim was to determine if oxidative stress related to H-R induces peroxynitrite-dependent modifications of the cardiac contractile protein, myosin regulatory light chain 2 (MLC2), and whether this is associated with development of cardiac systolic dysfunction. Twelve newborn piglets were acutely instrumented for hemodynamic monitoring and randomized to a control group ventilated with only atmospheric air or to the H-R study group exposed to alveolar normocapnic hypoxia followed by reoxygenation. Afterward, animals were euthanized, and the hearts were harvested for biochemical analyses. Systolic function as well as cardiac MLC2 levels decreased in H-R animals, whereas nitrates and nitrotyrosine levels increased. Negative correlations between nitrates, nitrotyrosine, and MLC2 levels were observed. Moreover, H-R induced nitration of two tyrosine residues within the MLC2 protein. Similarly, in vitro exposure of MLC2 to peroxynitrite resulted in the nitration of tyrosine, which increased the susceptibility of MLC2 to subsequent degradation by matrix metalloproteinase 2. Substitution of this tyrosine with phenylalanine prevented the matrix metalloproteinase 2-dependent degradation of MLC2. In addition, a large decrease in MLC2 phosphorylation caused by H-R was observed. Oxidative stress related to asphyxia induces nitration of cardiac MLC2 protein and thus increases its degradation. This and a large decrease in MLC2 phosphorylation contribute to the development of systolic dysfunction. Inhibition of MLC2 nitration and/or direct inhibition of its degradation by MMP-2 could be potential therapeutic targets aiming at reduction of myocardial damage during resuscitation of asphyxiated newborns.

Differential contribution of mitochondria, NADPH oxidases, and glycolysis to region-specific oxidant stress in the anoxic-reoxygenated embryonic heart

The ability of the developing myocardium to tolerate oxidative stress during early gestation is an important issue with regard to possible detrimental consequences for the fetus. In the embryonic heart, antioxidant defences are low, whereas glycolytic flux is high. The pro- and antioxidant mechanisms and their dependency on glucose metabolism remain to be explored. Isolated hearts of 4-day-old chick embryos were exposed to normoxia (30 min), anoxia (30 min), and hyperoxic reoxygenation (60 min). The time course of ROS production in the whole heart and in the atria, ventricle, and outflow tract was established using lucigenin-enhanced chemiluminescence. Cardiac rhythm, conduction, and arrhythmias were determined. The activity of superoxide dismutase, catalase, gutathione reductase, and glutathione peroxidase as well as the content of reduced and oxidized glutathione were measured. The relative contribution of the ROS-generating systems was assessed by inhibition of mitochondrial complexes I and III (rotenone and myxothiazol), NADPH oxidases (diphenylene iodonium and apocynine), and nitric oxide synthases ( N-monomethyl-l-arginine and N-iminoethyl-l-ornithine). The effects of glycolysis inhibition (iodoacetate), glucose deprivation, glycogen depletion, and lactate accumulation were also investigated. In untreated hearts, ROS production peaked at 10.8 ± 3.3, 9 ± 0.8, and 4.8 ± 0.4 min (means ± SD; n = 4) of reoxygenation in the atria, ventricle, and outflow tract, respectively, and was associated with arrhythmias. Functional recovery was complete after 30–40 min. At reoxygenation, 1) the respiratory chain and NADPH oxidases were the main sources of ROS in the atria and outflow tract, respectively; 2) glucose deprivation decreased, whereas glycogen depletion increased, oxidative stress; 3) lactate worsened oxidant stress via NADPH oxidase activation; 4) glycolysis blockade enhanced ROS production; 5) no nitrosative stress was detectable; and 6) the glutathione redox cycle appeared to be a major antioxidant system. Thus, the glycolytic pathway plays a predominant role in reoxygenation-induced oxidative stress during early cardiogenesis. The relative contribution of mitochondria and extramitochondrial systems to ROS generation varies from one region to another and throughout reoxygenation.

Shock: a common consequence of neonatal asphyxia

Neonatal asphyxia is associated with multi-organ hypoxia-ischemia and subsequent dysfunction. The cardiovascular system is frequently affected, causing signs of shock and complicating the neonatal circulatory transition. Hypothermia therapy can improve outcome from neonatal asphyxia without adversely affecting cardiovascular stability. Therapy directed at the cardiovascular system can improve short-term measures of systemic blood flow, but to date has not been demonstrated to improve long-term outcome.

Hydrocortisone administration increases pulmonary artery pressure in asphyxiated newborn piglets reoxygenated with 100% oxygen

In severely asphyxiated neonates developing vasopressor-resistant shock, hydrocortisone is commonly used to improve perfusion. However, its acute haemodynamic effects in asphyxiated neonates are largely unknown. In a swine model of neonatal asphyxia, effects of hydrocortisone on systemic and pulmonary circulations were examined. Piglets (1-3d, 1.5-2.4kg) were acutely instrumented to measure heart rate, systemic and pulmonary artery pressures, and pulmonary artery flow. After 2h of normocapnic hypoxia, animals were resuscitated with 100% oxygen for 1h followed by 21% oxygen for 3h. Intravenous hydrocortisone (1mg/kg) or saline was given in a blinded, randomized fashion 2h after reoxygenation (n=6/group). Haemodynamic parameters, blood gases, plasma cortisol, as well as levels of endothelin-1, nitrite/nitrate, nitrotyrosine, matrix metalloproteinases-2 and -9 in the lung were analysed. Severe hypoxia caused metabolic acidosis (mean pH: 6.91-6.97, mean plasma lactate: 17.2-18.3mM), tachycardia and shock. Hydrocortisone did not affect systemic haemodynamics which recovered with reoxygenation, but it increased pulmonary artery pressure at 90-120min after administration (36±3 vs. 27±2 and 26±1mmHg for hypoxia-reoxygenation control and sham-operated piglets, respectively, P<0.05). In the lung tissue, hydrocortisone significantly increased endothelin-1 and nitrite/nitrate levels, but had no effect on nitrotyrosine. Further, it decreased lung matrix metalloproteinase-9, but not matrix metalloproteinase-2, activity, which were both elevated with hypoxia-reoxygenation. It is most likely that the increase in pulmonary artery pressure observed after hydrocortisone treatment was associated with increased endothelin-1 level in the lung. Our findings caution the use of hydrocortisone as a first-intention treatment of shock in asphyxiated neonates.

Plasma cortisol response to ACTH challenge in hypoxic newborn piglets resuscitated with 21% and 100% oxygen

Although the use of supplemental oxygen to resuscitate asphyxiated neonates remains controversial, the effects of hypoxia and reoxygenation (room air versus pure oxygen) on the hypothalamo-pituitary-adrenal axis are unknown. We aimed to evaluate the effect of hypoxia and reoxygenation with either 21% or 100% oxygen on plasma cortisol before and after an adrenocorticotrophin (ACTH) challenge in newborn piglets. Thirty-five piglets (aged 1-3 days, weighing 1.5-2.4 kg) were instrumented to measure heart rate, MAP, and cardiac output. After 2 h of normocapnic hypoxia (PaO2, 20-30 mmHg; pH, <6.95), piglets were resuscitated with 21% or 100% oxygen for 1 h and then 21% oxygen for 3 h. Sham-operated piglets had no hypoxia-reoxygenation (H-R). Serial plasma cortisol levels were determined after a blinded randomized administration of ACTH (4 microg/kg, i.v.) or saline at 2 h reoxygenation. The expression of steroidogenic factor 1 in the adrenals was studied. Cardiac output decreased with hypoxia and recovered with resuscitation. Piglets developed hypotension similarly in 21% and 100% H-R groups during reoxygenation (versus sham-operated group, P < 0.05). Both H-R groups had increased plasma cortisol levels (versus sham-operated group, P < 0.05) at 2 h of reoxygenation after hypoxia, with a further increase in levels in 21% H-R piglets at 4 h reoxygenation (versus 100% H-R piglets, P < 0.05). The response to ACTH was delayed in H-R groups, with the maximum increase at 120 min post-ACTH administration (versus 30-60 min post-ACTH for sham-operated piglets). Plasma cortisol levels increased significantly post-ACTH administration in 21% H-R and sham-operated piglets (115% +/-50% and 126% +/- 25% at 120 min, respectively, P < 0.05 vs. pre-ACTH baselines) but not in 100% H-R piglets (51% +/-14%), which had a lower expression of steroidogenic factor 1 than the other groups. Although the clinical significance of high cortisol levels and cortisol response to ACTH in H-R newborn piglets is uncertain, a preserved cortisol response may support using room air in neonatal resuscitation.

Post-resuscitation NOS inhibition does not improve hemodynamic recovery of hypoxic newborn pigs

BACKGROUND

Significant improvement in myocardial recovery has been shown previously with interventions to decrease reactive oxygen species after ischemia/hypoxia. We investigated whether co-administration of N-acetylcysteine (NAC, a scavenger for reactive oxygen species) and N (G)-monomethyl-L: -arginine (L-NMMA, a non-selective nitric oxide synthase inhibitor) results in better hemodynamic recovery.

DESIGN

Controlled, block-randomized study.

SETTING

University research laboratory.

SUBJECT

Mixed breed piglets (1-4d, 1.6-2.4 kg).

INTERVENTIONS

Acutely instrumented piglets received normocapnic alveolar hypoxia (10-15% oxygen) for 2 h followed by reoxygenation with 100% oxygen (1 h) then 21% oxygen (3 h). After reoxygenation, hypoxic-reoxygenated piglets were given either saline (controls), NAC [30 mg/kg bolus + 20 mg/(kg h) infusion], NMMA [0.1 mg/kg bolus + 0.1 mg/(kg h) infusion] or NAC + L-NMMA via intravenous infusion in a blinded, randomized fashion (n = 8/group). Sham-operated piglets had no hypoxia-reoxygenation (n = 5).

MEASUREMENTS AND RESULTS

Both cardiac index and stroke volume of hypoxia-reoxygenation controls remained depressed during reoxygenation (vs. normoxic baseline, p < 0.05). Post-resuscitation treatment with L-NMMA alone did not improve systemic hemodynamic recovery, but caused pulmonary hypertension (vs. controls). In contrast, treating the piglets with either NAC or NAC + L-NMMA improved cardiac index and stroke volume, with no effect on heart rate and blood pressure (vs. controls). These treatments also decreased various oxidative stress markers in myocardial tissues (vs. controls). However, there was no significant difference between NAC- and NAC + L-NMMA groups in all examined parameters.

CONCLUSIONS

Post-resuscitation administration of NAC improved cardiac function and reduced oxidative stress in newborn pigs with hypoxia-reoxygenation insult. Low-dose, non-selective inhibitor of nitric oxide synthase activity did not provide any further beneficial effect.

High brain tissue oxygen tension during ventilation with 100% oxygen after fetal asphyxia in newborn sheep

The optimal inhaled oxygen fraction for newborn resuscitation is still not settled. We hypothesized that short-lasting oxygen ventilation after intrauterine asphyxia would not cause arterial or cerebral hyperoxia, and therefore be innocuous. The umbilical cord of fetal sheep was clamped and 10 min later, after delivery, ventilation with air (n = 7) or with 100% oxygen for 3 (n = 6) or 30 min (n = 5), followed by air, was started. Among the 11 lambs given 100% oxygen, oxygen tension (PO2) was 10.7 (1.8-56) kPa [median (range)] in arterial samples taken after 2.5 min of ventilation. In those ventilated with 100% oxygen for 30 min, brain tissue PO2 (PbtO2) increased from less than 0.1 kPa in each lamb to individual maxima of 56 (30-61) kPa, whereas in those given oxygen for just 3 min, PbtO2 peaked at 4.2 (2.9-46) kPa. The maximal PbtO2 in air-ventilated lambs was 2.9 (0.8-5.4) kPa. Heart rate and blood pressure increased equally fast in the three groups. Thus, prolonged ventilation with 100% oxygen caused an increase in PbtO2 of a magnitude previously only reported under hyperbaric conditions. Reducing the time of 100% oxygen ventilation to 3 min did not consistently avert systemic hyperoxia.

Achievement of targeted saturation values in extremely low gestational age neonates resuscitated with low or high oxygen concentrations: a prospective, randomized trial

OBJECTIVE

Extremely low gestational age neonates have very low oxygen saturation in utero and an immature antioxidant defense system. Abrupt increases in oxygen saturation after birth may cause oxidative stress. We compared achievement of a targeted oxygen saturation of 85% at 10 minutes of life when resuscitation was initiated with low or high fractions of inspired oxygen and levels were adjusted according to preductal pulse oxygen saturation values.

METHODS

A prospective, randomized, clinical trial was performed in 2 level III neonatal referral units. Patients of < or = 28 weeks of gestation who required active resuscitation were randomly assigned to the low-oxygen group (fraction of inspired oxygen: 30%) or the high-oxygen group (fraction of inspired oxygen: 90%). Every 60 to 90 seconds, the fraction of inspired oxygen was increased in 10% steps if bradycardia occurred (< 100 beats per minute) or was decreased in similar steps if pulse oxygen saturation reached values of > 85%. Preductal pulse oxygen saturation was continuously monitored.

RESULTS

The fraction of inspired oxygen in the low-oxygen group was increased stepwise to 45% and that in the high-oxygen group was reduced to 45% to reach a stable pulse oxygen saturation of approximately 85% at 5 to 7 minutes in both groups. No differences in oxygen saturation in minute-to-minute registers were found independent of the initial fraction of inspired oxygen used 4 minutes after cord clamping. No differences in mortality rates in the early neonatal period were detected.

CONCLUSIONS

Resuscitation can be safely initiated for extremely low gestational age neonates with a low fraction of inspired oxygen (approximately 30%), which then should be adjusted to the infant's needs, reducing the oxygen load to the neonate.

Epinephrine versus dopamine to treat shock in hypoxic newborn pigs resuscitated with 100% oxygen

Shock and tissue hypoperfusion are common after asphyxia. We compared systemic and regional hemodynamic effects of epinephrine and dopamine in the treatment of shock and hypotension in asphyxiated newborn piglets resuscitated with 100% oxygen. Twenty-four piglets (1-3 days old; weight, 1.4-2.6 kg) were acutely instrumented to measure cardiac index (CI), carotid, mesenteric and renal arterial blood flows, and mean systemic (SAPs) and pulmonary arterial pressures (PAPs). Piglets had normocapnic alveolar hypoxia (F(IO2)=0.08-0.10) for 50 min and reoxygenated with F(IO2)=1.0 for 1 h then F(IO2)=0.21 for 3.5 h. After 2 h reoxygenation, either dopamine (2 microg kg(-1) min(-1)) or epinephrine (0.2 microg kg(-1) min(-1)) was given for 30 min in a blinded randomized manner, which was then increased to maintain SAP (within 10% of baseline, pressure-driven dose) for 2 h. Hypoxia caused hypotension (SAP, 44%+/-3% of baseline), cardiogenic shock (CI, 41%+/-4%), and metabolic acidosis (mean pH, 7.04-7.09). Upon reoxygenation, hemodynamic parameters immediately recovered but gradually deteriorated during 2 h with SAP at 45+/-1 mmHg, CI at 74+/-9% of baseline, and pH 7.32+/-0.03. Low doses of either drug had no significant systemic and renal hemodynamic response. Epinephrine (0.3-1.5 microg kg(-1) min(-1)) for 2 h increased SAP and CI (with higher stroke volume) and decreased pulmonary vascular resistance (with reduced PAP-SAP ratio), whereas the responses with dopamine (10-25 microg kg(-1) min(-1)) were modest. Low-dose epinephrine improved mesenteric and carotid arterial flows, whereas the pressure-driven doses of epinephrine and dopamine increased carotid and mesenteric arterial flows, respectively. To treat shock in asphyxiated newborn piglets resuscitated with 100% oxygen, epinephrine exhibits an inotropic action compared with dopamine, whereas both catecholamines can increase carotid and mesenteric perfusion.

Oxidative stress and matrix metalloproteinase-9 activity in the liver after hypoxia and reoxygenation with 21% or 100% oxygen in newborn piglets

We designed a randomized controlled study to identify and compare the liver tissue responses in systemic hypoxia and resuscitation with 21% and 100% oxygen using an animal model of neonatal hypoxia and reoxygenation. Twenty-seven piglets (1-3 days old, weight 1.5-2.0 kg) were acutely instrumented and mechanically ventilated. The animals underwent 2 h of normocapnic alveolar hypoxia (10-15% oxygen) then reoxygenation with 21% or 100% oxygen for 1 h, then 1 h with 21% oxygen. Controls were sham-operated without hypoxia-reoxygenation. After 2 h of reoxygenation liver tissue samples were immediately processed for histological and biochemical analyses of markers of oxidative stress and tissue injury. Two hours of hypoxia caused a significant reduction in mean arterial pressure with cardiogenic shock and metabolic acidemia, with similar recovery upon resuscitation with 21% and 100% oxygen. After 2 h of reoxygenation, the hepatic GSSG:total glutathione ratio and matrix metalloproteninase-9 activity, which correlated with the portal venous oxygenation at 15 min of reoxygenation, were greater in the 100% group and hepatic lactate level was higher in the 21% group than the controls (all P<0.05). Both hypoxic-reoxygenated groups had similarly elevated hepatic Bcl-2 levels. Apart from more non-distinct mitochondria identified in the 100% group, hepatic tissue adenylate energy charge and plasma transaminases levels did not differ among groups. We concluded that in this acute model of neonatal hypoxia and reoxygenation, resuscitation using 21% oxygen avoids the excess oxidative stress and elevated matrix metalloproteninase-9 activity in the liver when 100% oxygen was used. The study supports the conservative use of oxygen in optimizing post-hypoxic hepatic recovery.

The hemodynamic effects of dobutamine during reoxygenation after hypoxia: a dose-response study in newborn pigs

Asphyxiated neonates usually have myocardial stunning and hypotension and require inotropic support. A randomized controlled study was designed to examine the dose-response effect of dobutamine (5-20 microg x kg(-1) x min(-1)) on systemic and regional circulations and oxygen metabolism in a neonatal swine model of hypoxia/reoxygenation. Thirty-eight anesthetized newborn piglets were acutely instrumented for continuous monitoring of heart rate, systemic and pulmonary arterial pressures, and pulmonary (surrogate for cardiac index), right common carotid, and superior mesenteric and left renal arterial flows. After stabilization, they were exposed to normocapnic alveolar hypoxia (10%-15% oxygen) for 2 h followed by reoxygenation with 100% oxygen for 1 h, then 21% for 3 h. Piglets were block randomized to receive dobutamine infusion (5, 10, or 20 microg x kg(-1) x min(-1)) or saline (control) at 2 to 4 h of reoxygenation (n = 8 each). A nonasphyxiated, sham-operated group was included (n = 6). Blood samples were collected for blood gas analysis, arterial and venous co-oximetry, and plasma lactate concentration determination. At 2-h reoxygenation after hypoxia, there was hypotension (systemic arterial pressure, 27 to 36 mmHg) and myocardial dysfunction (cardiac index from 178-209 to 134-156 mL x kg(-1) x min(-1)). Cardiac index improved significantly with 20 microg x kg(-1) x min(-1) of dobutamine (P < 0.05) and modestly in the treatment groups of 5 and 10 microg x kg(-1) x min(-1) (P < 0.1) (at 120 min, 172 +/- 35, 160 +/- 30, and 158 +/- 56 mL x kg(-1) x min(-1) vs. 119 +/- 33 mL x kg(-1) x min(-1) of controls, respectively), with corresponding increases in stroke volume. Pulmonary vascular resistance was lower in all dobutamine-treated groups (vs. controls, P < 0.05) There were no differences in heart rate, systemic and pulmonary arterial pressures, systemic vascular resistance, and regional flows between groups. The group of 20 mug.kg.min of dobutamine also had higher systemic oxygen delivery (at 120 min, 18 +/- 5 vs. 11 +/- 3 O(2) mL x kg(-1) x min(-1) of controls, P < 0.05) with no significant differences in systemic oxygen consumption and regional oxygen delivery between groups. After the reoxygenation of newborn piglets with severe hypoxia, high dose of dobutamine is effective to treat myocardial stunning and low cardiac output with no significant effect on blood pressure or regional circulation. Further clinical studies are needed to confirm these findings in the human neonate.

RESUSCITATION WITH 21% OR 100% OXYGEN IS EQUALLY EFFECTIVE IN RESTORING PERFUSION AND OXYGEN METABOLISM IN THE LIVER OF HYPOXIC NEWBORN PIGLETS

The differential effects of the use of high or low oxygen levels during resuscitation on the neonatal liver are unknown. We compared the hepatic hemodynamics and oxygen metabolism in hypoxic newborn piglets resuscitated with 21% or 100% oxygen. Twenty-seven piglets (age, 1-3 days; weight, 1.5-2.0 kg) were acutely instrumented to measure cardiac output, hepatic artery, and portal venous blood flows (hepatic artery flow index [HAFI] and portal venous flow index [PVFI], respectively). The animals underwent 2 h of hypoxia (fraction of inspired oxygen, 0.10-0.15), then reoxygenation with 21% (n = 9) or 100% (n = 9) oxygen for 1 h, then 1 h with 21% oxygen. The controls (n = 9) were sham-operated without hypoxia-reoxygenation. Oxygen transport and plasma lactate concentrations were studied. Hypoxic animals had hypotension and decreased cardiac index with metabolic acidosis (mean pH, 7.00-7.02; P < 0.05 vs. controls). The PVFI and the total hepatic blood flow (THFI = PVFI + HAFI), despite the absence of significant change in HAFI, decreased to 16 +/- 2 mL/min/kg and 19 +/- 3 mL/min/kg, respectively (versus 24 +/- 2 mL/min/kg and 28 +/- 2 mL/min/kg of controls; P < 0.05). Fifteen minutes after reoxygenation, the cardiac index improved, PVFI recovered, HAFI was maintained, and THFI was not different between the groups. The hepatic oxygen consumption decreased (59%; P < 0.05) and the extraction increased (89%; P < 0.001) during hypoxia. Similarly, on reoxygenation, the hepatic oxygen consumption improved; however, extraction decreased versus controls on 100% but not on 21% oxygen (P < 0.05). The plasma lactate concentrations increased in both groups with hypoxia and were not different during reoxygenation between the group administered with 21% oxygen and the group administered with 100% oxygen. The hypoxic neonatal liver has reduced hepatic blood flow but has relatively preserved HAFI, and oxygen consumption recovered similarly on reoxygenation with 21% and 100% oxygen. The increased oxygen extraction during hypoxia normalized in 21% but reduced in 100% reoxygenation, with no differences in plasma lactate concentrations.

Tissue-specific changes in glutathione content of hypoxic newborn pigs reoxygenated with 21% or 100% oxygen

We compared the responses towards oxidative stress in the liver, lung, brain, heart, kidney and small intestine of hypoxic newborn animals resuscitated with 21% or 100% oxygen. After stabilization, piglets (1-3 days, 1.6-2.0 kg, n=8/group) were randomized to receive 2 h of alveolar hypoxia (FiO(2)=0.10-0.14) followed by reoxygenation with 21% or 100% oxygen for 1 h and then another hour with 21% oxygen. Controls were sham-operated without hypoxia-reoxygenation. At the end of the experiment, tissues from liver, lung, brain, heart, kidney and small intestine were collected and tested for GSH, GSSG and lipid peroxidation levels and histological examination. In normoxic controls, liver had the highest GSH level, followed by brain, heart, lung, small intestine and kidney which had the highest level of oxidative stress markers (GSSG level and GSSG:GSH ratio). Hypoxic-reoxygenated piglets had the highest GSSG levels and GSSG:GSH ratio in the kidney. Hypoxic piglets resuscitated with 100% oxygen had higher GSSG:GSH ratios in the lung and liver, but not in the kidney, brain, heart and small intestine, than controls, which were not different from the 21% group. No significant differences in peroxidation and histological tissue damage were found between groups in the liver and lung. We concluded that although hypoxic piglets resuscitated with 100% oxygen have higher oxidative stress in the liver and lung than with 21% oxygen, there are no significant differences in peroxidation and histological tissue damage acutely.

Inhibition of sulfur compounds and antioxidants on MMP-2 and -9 at the activity level found during neonatal hypoxia–reoxygenation

The inhibitory effect of different sulfur compounds and antioxidants at the activity level of matrix metalloproteinase (MMP)-2 and -9 during neonatal hypoxia-reoxygenation is unknown. The tissue activity of MMP-2 and -9 was first determined by gelatin zymography in different tissues of 6 newborn piglets that underwent alveolar hypoxia and reoxygenation. The in vitro inhibitory effects of sulfur compounds and antioxidants with or without the thiol group were compared at the highest concentrations of MMP-2 and -9 found. These compounds included: amino acids containing sulfur [cysteine, DL-homocysteine, L-methionine] and not containing sulfur [L-histidine], antioxidants containing sulfur [L-glutathione and N-acetyl-cysteine] and not containing sulfur [ascorbic acid], and oxidized glutathione. Lung had the highest activity of MMP-2 and -9 among the tissues studied. The compounds showed differential effects on the activity of MMP-2 and -9. The order of the potency of inhibition of these compounds for MMP-2 was cysteine> or =histidine> or =ascorbic acid> or =glutathione> or =oxidized glutathione> or =homocysteine> or =N-acetyl-cysteine>methionine, whereas for MMP-9, it was cysteine> or =ascorbic acid> or =histidine>glutathione>homocysteine>N-acetyl-cysteine>oxidized glutathione>methionine. The IC50 values of these compounds on MMP-2 were significantly lower than the corresponding IC50 values on MMP-9. In conclusions, at the activity level of MMP-2 and -9 measured after neonatal hypoxia-reoxygenation, cysteine showed the highest potency of inhibition. The compounds showed different potencies of inhibition, regardless of the presence or absence of the thiol group or the antioxidant property of the compound.

EFFECT OF NOS INHIBITION ON RAT GASTRIC MATRIX METALLOPROTEINASE PRODUCTION DURING ENDOTOXEMIA

Matrix metalloproteinases (MMPs) degrade the extracellular matrix and contribute to LPS-induced gastric injury. MMPs are closely modulated by their activators, membrane type-MMP (MT-MMPs) and their endogenous inhibitors, the tissue inhibitors of metalloproteinases (TIMPs). As LPS-induced gastric injury is mediated in part by iNOS, and NO modulates MMP production in vitro, we hypothesized that NOS inhibition would similarly modulate LPS-induced gastric MMP production. Therefore, the purpose of these studies was to compare the effects of selective and nonselective NOS inhibition on LPS-induced gastric MMP production.

METHODS

Sprague-Dawley rats were given either the nonselective NOS inhibitor NG-nitro-L-arginine methyl ester (L-NAME; 5 mg/kg, s.c.), a selective iNOS inhibitor, aminoguanidine (45 mg/kg, i.p.) or L-N-iminoethyl-lysine (L-NIL; 10 mg/kg, i.p.), or vehicle 15 min before saline or LPS (20 mg/kg, i.p.) and killed 24 h after LPS administration. Stomachs were assessed for macroscopic injury (computed planimetry), and gastric mucosal MMP production was assessed by gelatin zymography, in situ zymography, and Western analysis for MMP-2, MT1-MMP, and TIMP-2. (n > or = 4/group; ANOVA).

RESULTS

Aminoguanidine treatment decreased LPS-induced macroscopic gastric injury as well as MMP-2 and MT1-MMP protein production while having no effect on TIMP-2 protein levels. L-NIL similarly attenuated the induction of MMP-2 and MT1-MMP by LPS. L-NAME failed to attenuate LPS induced gastric injury or MT1-MMP protein induction and increased MMP-2 levels. L-NAME similarly had no effect on gastric TIMP-2 production.

CONCLUSIONS

Selective iNOS inhibition decreases gastric MMP-2 activity after LPS administration, whereas nonselective inhibition increases MMP-2 levels. The ability of selective iNOS inhibition to ameliorate LPS-induced gastric injury may be due in part to its inhibition of active MMP-2 production, whereas nonselective NOS inhibitors increase MMP-2 levels and maintain gastric injury after LPS administration.

A dose-response study of graded reoxygenation on the carotid haemodynamics, matrix metalloproteinase-2 activities and amino acid concentrations in the brain of asphyxiated newborn piglets

PURPOSE

It is controversial to choose an appropriate oxygen concentration to resuscitate asphyxiated newborns regarding the clinical and biochemical oxidative effects. We examined the vasomotor response to reoxygenation with graded reoxygenation and the effects on matrix metalloproteinases and amino acids of the immature brain.

METHODS

Thirty-two piglets (1-3 days, 1.5-2.1 kg) were instrumented for continuous monitoring of left common carotid and pulmonary arterial flows (Transonic). Piglets were randomized to a sham-operated control group (without hypoxia/reoxygenation) or 2 h hypoxia induced by decreasing the inspired oxygen concentration to 10-15%, followed by reoxygenation with 21, 50 or 100% oxygen for 1 h and then 21% oxygen for 3 h (n=8 each). The brains were then flash frozen and analyzed for matrix metalloproteinases and amino acid levels by zymography and HPLC, respectively.

RESULTS

After 2 h oxygen deprivation, the absolute carotid flow remained similar but accounted for 38% of cardiac output (increased from 17% at baseline, p=0.001). During early reoxygenation, the flow rose in the piglets resuscitated with air (p<0.05), but not in those with supplemental oxygen. Carotid vascular resistance correlated significantly with the arterial partial pressure of oxygen (r=0.7). There was an oxygen-dependent increase in global cerebral activity of matrix metalloproteinase-2 with specific increases in the basal ganglia of all hypoxic-reoxygenated brains. There were no significant differences in glutamate and other amino acids in any brain regions.

CONCLUSIONS

Although using high oxygen concentration to resuscitate asphyxiated newborn piglets increased carotid vascular resistance and cerebral matrix metalloproteinase-2 activity, there is no detrimental effect observed in this acute model of hypoxia-reoxygenation.