Allopurinol-induced effects in premature baboons with respiratory distress syndrome

Effects of Hypothermia and Allopurinol on Oxidative Status in a Rat Model of Hypoxic Ischemic Encephalopathy

Hypoxic ischemic encephalopathy (HIE) is one of the main causes of morbidity and mortality during the neonatal period, despite treatment with hypothermia. There is evidence that oxidative damage plays an important role in the pathophysiology of hypoxic-ischemic (HI) brain injury. Our aim was to investigate whether postnatal allopurinol administration in combination with hypothermia would reduce oxidative stress (OS) biomarkers in an animal model of HIE. Postnatal 10-day rat pups underwent unilateral HI of moderate severity. Pups were randomized into: Sham operated, hypoxic-ischemic (HI), HI + allopurinol (HIA), HI + hypothermia (HIH), and HI + hypothermia + allopurinol (HIHA). Biomarkers of OS and antioxidants were evaluated: GSH/GSSG ratio and carbonyl groups were tested in plasma. Total antioxidant capacity (TAC) was analyzed in plasma and cerebrospinal fluid, and 8-iso-prostaglandin F2α was measured in brain tissue. Plasma 2,2′–azinobis-(3-ethyl-benzothiazoline-6-sulfonic acid) (ABTS) levels were preserved in those groups that received allopurinol and dual therapy. In cerebrospinal fluid, only the HIA group presented normal ferric reducing ability of plasma (FRAP) levels. Protein oxidation and lipid peroxidation were significantly reduced in all groups treated with hypothermia and allopurinol, thus enhancing neuroprotection in HIE.

Results of and further prevention of hypoxic fetal brain damage by inhibition of xanthine oxidase enzyme with allopurinol

Several experimental models on adult and newborn animals showed that in cerebral hypoxic-ischemic conditions similar to clinical states the main source of the excessive production of free oxygen radicals is the highly activated xanthine oxidase (XO) enzyme reaction. Long before this data were available, it became known that the main role of allopurinol (AP) is the inhibition of XO. On the basis of these results, many therapeutic trials with AP were performed both in experimental and clinical studies of ischemia and reperfusion. However, it has been shown that only preventive administration of AP has favorable effects. The explanation for the poor results of AP treatment in human fetal brain damage (FBD) cases is that the drug was applied postnatally. The clinical studies performed in healthy laboring mothers whose deliveries were complicated with FBD showed that placental transfer after prenatal administration of AP may be effective in protecting newborns at increased risk of hypoxic-ischemic cerebral damage. Further controlled trials are required to determine if the prophylactic use of the drug might prevent hypoxic-ischemic injuries when the drug is administered immediately prior to impending fetal hypoxia, or even in deliveries at risk of developing hypoxia.

Effect of oxygen on lung superoxide dismutase activities in premature baboons with bronchopulmonary dysplasia

We investigated the effects of gestational age and oxygen exposure on superoxide dismutase (SOD) activities in distal fetal lung tissue in primate models of bronchopulmonary dysplasia. During the final third of fetal life, lung coppper-zinc SOD (Cu,ZnSOD) specific activity decreased, whereas lung manganese SOD (MnSOD) specific activity tended to increase. In the premature newborn (140 days, 78% of term gestation), lung total SOD and Cu,ZnSOD specific activities decreased after 6-10 days of ventilation with as needed [pro re nada (PRN)] or 100% oxygen compared with fetal control animals. Neither Cu,ZnSOD mRNA nor protein expression changed after either oxygen exposure at this gestation (140 days) relative to fetal control animals. At this age (6-10 days), lung MnSOD specific activity did not change in oxygen-exposed relative to fetal control animals, even though lung expression of MnSOD mRNA and protein increased after PRN or 100% oxygen exposure. In the very premature 125-day newborn (69% of term), lung Cu,ZnSOD specific activity and protein decreased, whereas Cu,ZnSOD mRNA increased, after 6-10 days of ventilation with PRN oxygen compared with fetal control animals. In fetal lung explants, hyperoxia also decreased expression of SOD activity acutely (16-h exposure, 125 and 140 days gestation). To conclude, expression of SOD activity in the premature primate lung did not increase in response to elevated oxygen tension, apparently due to effects occurring subsequent to the expression of these mRNAs.

Pharmacologic adjuncts to mechanical ventilation in acute respiratory distress syndrome

This article reviews pharmacologic approaches to treating acute respiratory distress syndrome (ARDS). The authors discuss the therapeutic effects of ketoconazole, antioxidants, corticosteroids, surfactant, ketanserin, pentoxifylline, bronchodilators, and almitrine in ARDS. Current animal data and proposed mechanics which may foster future pharmacologic therapies are also examined.

Early albumin leakage in pulmonary endothelial monolayers exposed to varying levels of hyperoxia

We assessed the effect of varying levels of hyperoxia on 14C-albumin flux across bovine pulmonary artery endothelial cell (BPAEC) monolayers. Endothelialized nitrocellulose filters were mounted in Ussing-type chambers which were filled with cell culture medium (M 199). Equimolar amounts of 14C-labeled and unlabeled albumin were added to the "hot" and "cold" chambers, respectively, and the monolayers were exposed to 3 hours of varying levels of oxygen (16%, 30%, 40%, 60%, and 95%). When compared to 16% O2, exposure to hyperoxic gas mixtures of 40% or greater progressively increased albumin permeability across endothelial monolayers within 3 hours to a value 2.5 times higher at 95% O2 compared to 16% O2 (p < 0.001). Hyperoxia-induced permeability increases were prevented by catalase, superoxide dismutase, desferrioxamine, and allopurinol. Our data indicate that hyperoxia induces endothelial permeability changes more rapidly than previously reported even at O2 concentrations as low as 40%.

Randomised controlled trial of allopurinol prophylaxis in very preterm infants

Allopurinol, an inhibitor of xanthine oxidase (an enzyme capable of generating superoxide radicals following hypoxiaischaemia), was investigated in preterm infants to determine its ability to prevent the complications of neonatal intensive care which may be associated with oxidative injury. Four hundred infants of between 24 and 32 weeks' gestation were randomly allocated to receive enteral allopurinol (20 mg/ml) or an equivalent dose of placebo for seven daily doses. At admission, plasma hypoxanthine concentrations were significantly higher in infants who subsequently developed periventricular leucomalacia (PVL), bronchopulmonary dysplasia (BPD), or retinopathy of prematurity (ROP), but there was no difference in the primary endpoint (PVL) between the treated and control groups. The failure of allopurinol prophylaxis in this group of infants is probably related to the complex nature of the pathological processes and to the timing of treatment. If oxidant injury is an important mechanism of cellular injury in these preterm infants, an alternative biochemical modulator would be required, or a combination of agents might be effective.

Antioxidants and neonatal lung disease

Bronchopulmonary dysplasia (BPD) remains a clinical problem in survivors of neonatal intensive care despite recent advances which include surfactant replacement. Oxygen toxicity may well be a component in the pathogenesis of BPD and disturbance of the oxidant-antioxidant balance constitutes a biochemical problem which should be addressed in the management of preterm babies. Preterm babies appear to have inadequate antioxidant potential and yet when delivered may experience considerable oxidant stress. This imbalance may be ameliorated by antenatal steroid therapy which augments pulmonary antioxidants as well as surfactant production. Augmentation of antioxidants by administration of exogenous enzymes such as superoxide dismutase and catalase is possible in animal models but the clinical use of such therapies awaits further research.

Magnitude of hyperoxic stress and degree of lung maturity determine the nature of pulmonary antioxidant response in the guinea pig

The ability of the immature lung to induce antioxidant defences in response to hyperoxic stress was examined. Preterm guinea pigs (65 days gestation, term = 68 d) were exposed to either 21% O2, 85% O2 or 95% O2 for 72 hours. Exposure to 85% O2 increased lung catalase, glutathione peroxidase and manganese superoxide dismutase activities in comparison to air controls. Exposure to 95% O2 resulted only in an increase in glutathione peroxidase activity. Bronchoalveolar lavage fluid GSH concentration was increased by a similar amount by both exposure regimes, while lung copper/zinc superoxide dismutase activity was unchanged by either treatment. Comparison of the antioxidant response of term and preterm animals exposed to 85% O2 for 72 hours indicated a greater response in the lung of the preterm animals. Manganese superoxide dismutase activity was elevated in both term and preterm animals, while catalase and glutathione peroxidase activities were elevated only in preterm animals. The extent of microvascular permeability as indicated by bronchoalveolar lavage fluid protein concentration, was lower in preterm animals than in term animals. We conclude that the immature lung can respond to hyperoxic stress by antioxidant induction and that the nature of the response is dependent, in part, both on the severity of the stress and on the maturity of the lung.