Platelet Dysfunction in Asphyxiated Newborn Piglets Resuscitated with 21% and 100% Oxygen

Abstract

Hemostatic disturbances are common in asphyxiated newborns after resuscitation. We compared platelet function in hypoxic newborn piglets reoxygenated with 21% or 100% oxygen. Piglets (1-3 d, 1.5-2.1 kg) were anesthetized and acutely instrumented for hemodynamic monitoring. After stabilization, normocapnic hypoxia was induced with an inspired oxygen concentration of 10 -15% for 2 h. Piglets were then resuscitated for 1 h with 21% or 100% oxygen, followed by 3 h with 21% oxygen. Platelet counts and collagen (2, 5, and 10 g/mL)-stimulated whole blood aggregation were studied before hypoxia and at 4 h of post-hypoxia/ reoxygenation. Platelet function was studied using transmission electron microscopy and by measuring plasma thromboxane B 2 (TxB 2 ) and matrix metalloproteinase (MMP)-2 and -9 levels. Control piglets were sham-operated without hypoxia/reoxygenation. The hypoxemic (PaO 2 33 mm Hg) piglets developed hypotension with metabolic acidosis (pH 7.02-7.05). Upon reoxygenation, piglets recovered and blood gases gradually normalized. At 4 h reoxygenation, platelet aggregation ex vivo was impaired as evidenced by a rightwarddownward shifting of the concentration-response curves. Electron microscopy showed features of platelet activation. Plasma MMP-9 but not MMP-2 activity significantly increased. Resuscitation with 100% but not 21% oxygen increased plasma TxB 2 levels. Platelet counts decreased after hypoxia/reoxygenation but were not different between groups during the experiment. Resuscitation of hypoxic newborn piglets caused platelet activation with significant deterioration of platelet aggregation ex vivo and increased plasma MMP-9 levels. High oxygen concentrations may aggravate the activation of prostaglandin-thromboxane mechanistic pathway. MMP-2 (constitutive isoform, 72 kD) and MMP-9 (inducible isoform, 92 kD) are zinc-dependent endopeptidases that play an important role in the regulation of platelet aggregation (6 -9). MMPs are activated by proteolysis and oxidants including the peroxynitrite anion (6,10). Increased plasma MMP-2 and -9 activity with platelet dysfunction was observed in an animal model of extracorporeal circulation with a high oxygen environment (11). Lemke et al. (12) recently reported a surge in plasma MMP-9 activity in the first day of postnatal life, which is consistent with a change from a low to a high oxygen environment. Interestingly, in neonatal models of asphyxia, resuscitation with 100% oxygen is associated with higher oxidative stress and MMP-2 activities in the heart and brain than those with 21% oxygen (13,14). However, there is little information on the activity of MMPs in plasma and its relationship to platelet aggregatory function in the reoxygenation of asphyxiated newborns.Asphyxiated infants are often resuscitated with 100% oxygen, and this is associated with increased oxidative stress up to 28 d after birth (15). In the midst of the debate between the use of 21% or 100% oxygen in the resuscitation of asphyxiated newborns, we designed this study to examin...

The First Golden Minutes of the Extremely-Low-Gestational-Age Neonate: A Gentle Approach

“…Furthermore, in studies of term and near-term neonates, using 100% oxygen in the resuscitation has been associated with increased cardiac and renotubular damages [103] in addition to the increased oxidative stress shown in whole-blood markers (oxidized glutathione content) that persisted up to 28 days after birth [114] . In animal models of asphyxia, the increased oxidative stress has been related to impaired organ function and/or injury as in the heart, lung, brain, intestine, kidney, adrenal glands, and platelets [115][116][117][118][119][120][121] . Further, an epidemiological link between resuscitation with supplemental oxygen and childhood leukaemia has been suggested by Naumburg et al [122] and Spector et al [123] .…”

Clinical practices in neonatal oxygenation: where have we failed? What can we do?

“…57 Furthermore, the oxidative stress of pure oxygen lasts at least for 4 weeks after birth, 58 and there could be more myocardial and kidney injury. Animal studies have also shown that 100% oxygen activates transcription factors, leads to thrombocyte aggregation, 59 increases oxidative stress, neurologic and brain damage, 60,61 inflammation in the lung and heart and may also trigger pulmonary hypertension. 62 Finally, who would have imagined that only a few minutes of oxygen could be associated with childhood cancer?…”

Temporal Platelet Aggregatory Function in Hypoxic Newborn Piglets Reoxygenated With 18%, 21%, and 100% Oxygen

“…These radicals can activate arachidonic acid metabolism with the production of thromboxane (Tx) A 2 and subsequent activation of platelets (4,5). Furthermore, hypoxia and reoxygenation are associated with increases in the plasma activities of matrix metalloproteinases (MMPs) 2 and 9 (6,7), which play an important role in the regulation of platelet aggregatory function (8,9). Platelet activation and dysfunction may be related to thromboembolic complications seen in asphyxiated newborns.…”

“…We recently reported the platelet aggregatory response to collagen stimulation after life-threatening hypoxia and reoxygenation with 21% or 100% oxygen in an acutely instrumented animal model of neonatal asphyxia (7). Platelets were activated with increased plasma TxB 2 levels, and platelet aggregation was impaired similarly in both reoxygenated groups (7).…”

“…Platelets were activated with increased plasma TxB 2 levels, and platelet aggregation was impaired similarly in both reoxygenated groups (7). It is uncertain if the platelet lesion is a fundamental hypoxia-reoxygenation pathology and if less than 21% oxygen concentration would be beneficial for the platelet function.…”