Acetaminophen for Oxidative Stress After Cardiopulmonary Bypass

Infants with complex congenital cardiac defects frequently undergo cardiopulmonary bypass
(CBP) during surgical repair of their cardiac lesions (1). CBP exposes infants and children
to endothelial damage, hyperoxia, hemolysis, and systemic inflammatory response (2-7). The
systemic inflammatory response contributes to the organ dysfunction and is initiated by
exposure of blood to the artificial surfaces of the extracorporeal circuit resulting in
significant hemolysis and activation of complement. Hyperoxia has been shown to cause
oxidative stress and the production of free radical molecules, which contributes to the
morbidity of CPB. Hemolysis leads to free hemoglobin and the subsequent release of free iron
in the plasma, which can catalyze redox reactions and has been shown to be another source of
severe oxidant injury in children following bypass (8, 9). Additionally, the release of
proinflammatory cytokines, hypothermia, hemorrhage requiring multiple transfusions, and
activation of neutrophils leading to an enhancement of the respiratory burst contribute to
oxidative injury and worsening inflammation (9).

Myoglobin and hemoglobin contain ferrous iron (Fe2+), which normally transports reversibly
bound oxygen molecules to tissues. When muscle or red blood cells are damaged, the
iron-chelating heme molecules are released into the plasma, and the ferrous iron is oxidized
to the ferric (Fe3+) state. In the higher oxidation state, the ferric hemoproteins are able
to reduce other molecules, notably hydrogen peroxide and lipid hydroperoxides, producing
lipid peroxides and ferryl (Fe4+) hemoproteins. The ferryl hemoproteins can then enter an
oxidation-reduction cycle with lipid molecules, causing further lipid peroxide production,
leading to a cascade of oxidative damage to cellular membranes (10-12).

With increasing oxidative stress, oxygen free radicals attack esterified arachidonate
layered within cell membrane lipid bilayers, resulting in the production of multiple lipid
peroxidation products called isoprostanes (Iso-P) and isofurans (IsoF) (13-17). Many forms
of IsoF and IsoP have been shown to be powerful vasoconstrictors, and have been shown to
contribute to the pathogenesis and organ dysfunction associated with rhabdomyolysis,
subarachnoid hemorrhage and hemolytic disorders (10, 16, 18-21). F2-isoprostanes are
sensitive and specific markers of oxidative stress in vivo. (4) The mechanism/s causing
increased oxidative stress during CPB are incompletely understood and the relationship
between free hemoglobin and F2-isoprostanes in humans undergoing CPB is unknown.

Inhibition of hemoprotein-induced oxidative stress may have important clinical applications
in humans. Hemolysis, in addition to contributing to the oxidative stress response, is also
associated with acute kidney injury (AKI) in patients undergoing CPB or extracorporeal life
support (5-6). In fact, plasma free hemoglobin has been shown to be an independent predictor
of AKI in the early postoperative period (5). We have recently demonstrated that
acetaminophen, through inhibition of prostaglandin H2-synthases (PGHS), inhibits the
oxidation of free arachidonic acid catalyzed by myoglobin and hemoglobin. Moreover, in an
animal model of rhabdomyolysis-induced kidney injury, acetaminophen significantly attenuated
the decrease in creatinine clearance compared to control (10).

The current proposal tests the central hypothesis that acetaminophen will attenuate the
oxidative stress response associated with CPB-induced hemolysis in children undergoing
cardiac surgery. If acetaminophen attenuates the oxidative stress response associated with
CPB-induced hemolysis the potential therapeutic benefit extends to all cardiac surgery
patients requiring CPB. Based on the outcome of this pilot study we will design a
prospective randomized trial to test the hypothesis that acetaminophen will reduce AKI
associated with hemoprotein-induced oxidative stress following CPB.

Patients will be eligible for enrollment based on the following inclusion criteria:

1) Infants or children (newborn to 17years of age) undergoing cardiopulmonary bypass for
biventricular surgical correction of their congenital heart lesions.

Patients will not be eligible for this study based on the following exclusion criteria:

1. Patients scheduled for single ventricle palliation will be excluded, in an effort to
standardize the time of repair, time on CPB, and surgical procedure.

2. Patients with severe neurological abnormalities at baseline.

3. Patients with major non-cardiac congenital malformations, developmental disorders or
serious chronic disorders. Benign congenital malformations (such as club foot, ear
tags, etc.) will not exclude the subject from the study.

4. Non-English speaking patients, or parent/legal guardians.

5. Patients less than 3 kg, to limit risk of excessive blood loss from lab draws.

6. Previous adverse reaction to acetaminophen

7. History of acute or chronic kidney disease

8. History of chronic liver disease

9. Emergency surgery