Pyruvate-fortified cardioplegia evokes myocardial erythropoietin signaling in swine undergoing cardiopulmonary bypass

Relevance and Recommendations for the Application of Cardioplegic Solutions in Cardiopulmonary Bypass Surgery in Pigs

Cardioplegic solutions play a major role in cardiac surgery due to the fact that they create a silent operating field and protect the myocardium against ischemia and reperfusion injury. For studies on cardioplegic solutions, it is important to compare their effects and to have a valid platform for preclinical testing of new cardioplegic solutions and their additives. Due to the strong anatomical and physiological cardiovascular similarities between pigs and humans, porcine models are suitable for investigating the effects of cardioplegic solutions. This review provides an overview of the results of the application of cardioplegic solutions in adult or pediatric pig models over the past 25 years. The advantages, disadvantages, limitations, and refinement strategies of these models are discussed.

Impact of High Altitude on Cardiovascular Health: Current Perspectives

Globally, about 400 million people reside at terrestrial altitudes above 1500 m, and more than 100 million lowlanders visit mountainous areas above 2500 m annually. The interactions between the low barometric pressure and partial pressure of O2, climate, individual genetic, lifestyle and socio-economic factors, as well as adaptation and acclimatization processes at high elevations are extremely complex. It is challenging to decipher the effects of these myriad factors on the cardiovascular health in high altitude residents, and even more so in those ascending to high altitudes with or without preexisting diseases. This review aims to interpret epidemiological observations in high-altitude populations; present and discuss cardiovascular responses to acute and subacute high-altitude exposure in general and more specifically in people with preexisting cardiovascular diseases; the relations between cardiovascular pathologies and neurodegenerative diseases at altitude; the effects of high-altitude exercise; and the putative cardioprotective mechanisms of hypobaric hypoxia.

HIF-1α stabilization reduces retinal degeneration in a mouse model of retinitis pigmentosa

Retinitis pigmentosa (RP) is a group of inherited retinal dystrophies characterized by progressive and irreversible loss of vision due to rod and cone degeneration. Evidence suggests that an inappropriate oxygen level could contribute to its pathogenesis. Rod cell death could increase oxygen concentration, reduce hypoxia-inducible factor 1 (HIF-1α) and contribute to cone cell death. The purposes of this study were: 1) to analyze the temporal profile of HIF-1α, its downstream effectors VEGF, endothelin-1 (ET-1), iNOS, and glucose transporter 1 (GLUT1), and neuroinflammation in retinas of the murine model of rd10 ( retinal degeneration 10) mice with RP; 2) to study oxygen bioavailability in these retinas; and 3) to investigate how stabilizing HIF-1α proteins with dimethyloxaloglycine (DMOG), a prolyl hydroxylase inhibitor, affects retinal degeneration, neuroinflammation, and antioxidant response in rd10 mice. A generalized down-regulation of HIF-1α and its downstream targets was detected in parallel with reactive gliosis, suggesting high oxygen levels during retinal degeneration. At postnatal d 18, DMOG treatment reduced photoreceptor cell death and glial activation. In summary, retinas of rd10 mice seem to be exposed to a hyperoxic environment even at early stages of degeneration. HIF-1α stabilization could have a temporal neuroprotective effect on photoreceptor cell survival, glial activation, and antioxidant response at early stages of RP.-Olivares-González, L., Martínez-Fernández de la Cámara, C., Hervás, D., Millán, J. M., Rodrigo, R. HIF-1α stabilization reduces retinal degeneration in a mouse model of retinitis pigmentosa.

Pyruvate enhancement of cardiac performance: Cellular mechanisms and clinical application

Cardiac contractile function is adenosine-5'-triphosphate (ATP)-intensive, and the myocardium's high demand for oxygen and energy substrates leaves it acutely vulnerable to interruptions in its blood supply. The myriad cardioprotective properties of the natural intermediary metabolite pyruvate make it a potentially powerful intervention against the complex injury cascade ignited by myocardial ischemia-reperfusion. A readily oxidized metabolic substrate, pyruvate augments myocardial free energy of ATP hydrolysis to a greater extent than the physiological fuels glucose, lactate and fatty acids, particularly when it is provided at supra-physiological plasma concentrations. Pyruvate also exerts antioxidant effects by detoxifying reactive oxygen and nitrogen intermediates, and by increasing nicotinamide adenine dinucleotide phosphate reduced form (NADPH) production to maintain glutathione redox state. These enhancements of free energy and antioxidant defenses combine to augment sarcoplasmic reticular Ca²⁺ release and re-uptake central to cardiac mechanical performance and to restore β-adrenergic signaling of ischemically stunned myocardium. By minimizing Ca²⁺ mismanagement and oxidative stress, pyruvate suppresses inflammation in post-ischemic myocardium. Thus, pyruvate administration stabilized cardiac performance, augmented free energy of ATP hydrolysis and glutathione redox systems, and/or quelled inflammation in a porcine model of cardiopulmonary bypass, a canine model of cardiac arrest-resuscitation, and a caprine model of hypovolemia and hindlimb ischemia-reperfusion. Pyruvate's myriad benefits in preclinical models provide the mechanistic framework for its clinical application as metabolic support for myocardium at risk. Phase one trials have demonstrated pyruvate's safety and efficacy for intravenous resuscitation for septic shock, intracoronary infusion for heart failure and as a component of cardioplegia for cardiopulmonary bypass. The favorable outcomes of these trials, which argue for expanded, phase three investigations of pyruvate therapy, mirror findings in isolated, perfused hearts, underscoring the pivotal role of preclinical research in identifying clinical interventions for cardiovascular diseases. Impact statement This article reviews pyruvate's cardioprotective properties as an energy-yielding metabolic fuel, antioxidant and anti-inflammatory agent in mammalian myocardium. Preclinical research has shown these properties make pyruvate a powerful intervention to curb the complex injury cascade ignited by ischemia and reperfusion. In ischemically stunned isolated hearts and in large mammal models of cardiopulmonary bypass, cardiac arrest-resuscitation and hypovolemia, intracoronary pyruvate supports recovery of myocardial contractile function, intracellular Ca²⁺ homeostasis and free energy of ATP hydrolysis, and its antioxidant actions restore β-adrenergic signaling and suppress inflammation. The first clinical trials of pyruvate for cardiopulmonary bypass, fluid resuscitation and intracoronary intervention for congestive heart failure have been reported. Receiver operating characteristic analyses show remarkable concordance between pyruvate's beneficial functional and metabolic effects in isolated, perfused hearts and in patients recovering from cardiopulmonary bypass in which they received pyruvate- vs. L-lactate-fortified cardioplegia. This research exemplifies the translation of mechanism-oriented preclinical studies to clinical application and outcomes.

Pyruvate alleviates lipid peroxidation and multiple-organ dysfunction in rats with hemorrhagic shock

OBJECTIVE

Pyruvate can reduce lipid peroxidation, which plays a critical role in organ injury, in various models. However, it is not fully understood if this inhibition occurs in resuscitation of hemorrhagic shock (HS). This study examines effects of pyruvate Ringer solution (PR) in this respect in rats.

METHODS

Rats, subjected to 45% blood loss, were randomly allocated to the 3 groups (n = 18): HS with no fluid resuscitation (group NR), HS resuscitated with lactated Ringer solution (LR) (group LR), and HS resuscitated with PR (group PR). Mean arterial pressure, plasma levels of thiobarbituric acid reactive substances (TBARS), and superoxide dismutase were measured at various time points until 360 minutes after hemorrhage. Visceral organs were harvested at the end for evaluations of the TBARS, antioxidant enzyme, and tissue water content. Other 54 rats with identical procedures without sampling were documented for 24-hour survival rates (n = 18) after fluid resuscitation.

RESULTS

Pyruvate Ringer solution significantly increased mean arterial pressure and decreased blood TBARS levels after lethal HS. It also reduced TBARS concentrations and glutathione peroxidase activities but significantly enhanced glutathione reductase activities in most organs and greatly improved the ratios of reduced glutathione over oxidized glutathione in various organs in group PR, compared to group LR. Furthermore, PR significantly improved various organ function and water contents relative to LR. Group PR showed a more than 2-fold higher 24-hour survival rate of group LR.

CONCLUSIONS

Pyruvate Ringer solution alleviated organ edema and injury and prompted survival partially through inhibition of lipid peroxidation in various organs in severe HS rats.

Methylene blue-induced neuronal protective mechanism against hypoxia-reoxygenation stress

Brain ischemia and reperfusion (I/R) injury occurs in various pathological conditions, but there is no effective treatment currently available in clinical practice. Methylene blue (MB) is a century-old drug with a newly discovered protective function in the ischemic stroke model. In the current investigation we studied the MB-induced neuroprotective mechanism focusing on stabilization and activation of hypoxia-inducible factor-1α (HIF-1α) in an in vitro oxygen and glucose deprivation (OGD)-reoxygenation model.

METHODS

HT22 cells were exposed to OGD (0.1% O2, 6h) and reoxygenation (21% O2, 24h). Cell viability was determined with the calcein AM assay. The dynamic change of intracellular O2 concentration was monitored by fluorescence lifetime imaging microscopy (FLTIM). Glucose uptake was quantified using the 2-[N-(7-Nitrobenz-2-Oxa-1,3-Diazol-4-yl)Amino]-2-Deoxy-d-Glucose (2-NBDG) assay. ATP concentration and glycolytic enzyme activity were examined by spectrophotometry. Protein content changes were measured by immunoblot: HIF-1α, prolyl hydroxylase 2 (PHD2), erythropoietin (EPO), Akt, mTOR, and PIP5K. The contribution of HIF-1α activation in the MB-induced neuroprotective mechanism was confirmed by blocking HIF-1α activation with 2-methoxyestradiol-2 (2-MeOE2) and by transiently transfecting constitutively active HIF-1α.

RESULTS

MB increases cell viability by about 50% vs. OGD control. Compared to the corresponding control, MB increases intracellular O2 concentration and glucose uptake as well as the activities of hexokinase and G-6-PDH, and ATP concentration. MB activates the EPO signaling pathway with a corresponding increase in HIF-1α. Phosphorylation of Akt was significantly increased with MB treatment followed by activation of the mTOR pathway. Importantly, we observed, MB increased nuclear translocation of HIF-1α vs. control (about three folds), which was shown by a ratio of nuclear:cytoplasmic HIF-1α protein content.

CONCLUSION

We conclude that MB protects the hippocampus-derived neuronal cells against OGD-reoxygenation injury by enhancing energy metabolism and increasing HIF-1α protein content accompanied by an activation of the EPO signaling pathway.

Pyruvate Is Superior to Citrate in Oral Rehydration Solution in the Protection of Intestine via Hypoxia-Inducible Factor-1 Activation in Rats With Burn Injury

BACKGROUND

Recent studies have suggested that pyruvate-enriched oral rehydration solution (Pyr-ORS) may be superior to the standard bicarbonate-based ORS in the protection of intestine from ischemic injury. The aim of this study was to compare the effects of Pyr-ORS with citrate-enriched ORS (Cit-ORS) on the intestinal hypoxia-inducible factor-1 (HIF-1)-erythropoietin (EPO) signaling pathway for enteral rehydration in a rat model of burn injury.

METHODS

Rats were randomly assigned to 4 groups (N = 20, 2 subgroups each: n = 10): scald sham (group SS), scald with no fluid resuscitation (group SN), scald and resuscitation with enteral Cit-ORS (group SC), and scald and resuscitation with enteral Pyr-ORS (group SP). At 2.5 and 4.5 hours after a 35% total body surface area (TBSA) scald, intestinal mucosal blood flow (IMBF), contents of HIF-1, EPO, endothelial nitric oxide synthase (eNOS), nitric oxide (NO), barrier protein (ZO-1), levels of serum diamine oxidase (DAO), and intestinal mucosal histology injury score were determined.

RESULTS

Serum DAO activities in the scalded groups were significantly elevated, but less raised in group SP than in group SC, at 2.5 hours and at 4.5 hours after the scald. Further, group SP more profoundly preserved intestinal HIF-1 expression compared with group SC at the 2 time points. Compared with group SC, group SP had markedly elevated intestinal EPO, eNOS, and NO levels at the same time points, respectively (P < .05). Similarly, IMBF and ZO-1 levels were significantly higher in group SP than in group SC. Intestinal mucosal histopathological scores were statistically higher at 2.5 hours and 4.5 hours after scalding but were more attenuated in group SP than in group SC (P < .05). Immunofluorescence expression of intestinal mucosal ZO-1 was consistent with the above changes. The above parameters were also significantly different between groups SC and SN (all P < .05).

CONCLUSION

Pyr-ORS provides a superior option to Cit-ORS for the preservation of intestinal blood flow and barrier function and the attenuation of histopathological alterations in enteral resuscitation of rats with burn injury. Its underlying mechanism may be closely related to the pyruvate in activation of intestinal HIF-1-EPO signaling cascades.

Cerebral metabolism following traumatic brain injury: new discoveries with implications for treatment

Because it is the product of glycolysis and main substrate for mitochondrial respiration, lactate is the central metabolic intermediate in cerebral energy substrate delivery. Our recent studies on healthy controls and patients following traumatic brain injury (TBI) using [6,6-(2)H2]glucose and [3-(13)C]lactate, along with cerebral blood flow (CBF) and arterial-venous (jugular bulb) difference measurements for oxygen, metabolite levels, isotopic enrichments and (13)CO2 show a massive and previously unrecognized mobilization of lactate from corporeal (muscle, skin, and other) glycogen reserves in TBI patients who were studied 5.7 ± 2.2 days after injury at which time brain oxygen consumption and glucose uptake (CMRO2 and CMRgluc, respectively) were depressed. By tracking the incorporation of the (13)C from lactate tracer we found that gluconeogenesis (GNG) from lactate accounted for 67.1 ± 6.9%, of whole-body glucose appearance rate (Ra) in TBI, which was compared to 15.2 ± 2.8% (mean ± SD, respectively) in healthy, well-nourished controls. Standard of care treatment of TBI patients in state-of-the-art facilities by talented and dedicated heath care professionals reveals presence of a catabolic Body Energy State (BES). Results are interpreted to mean that additional nutritive support is required to fuel the body and brain following TBI. Use of a diagnostic to monitor BES to provide health care professionals with actionable data in providing nutritive formulations to fuel the body and brain and achieve exquisite glycemic control are discussed. In particular, the advantages of using inorganic and organic lactate salts, esters and other compounds are examined. To date, several investigations on brain-injured patients with intact hepatic and renal functions show that compared to dextrose + insulin treatment, exogenous lactate infusion results in normal glycemia.

Erythropoietin: powerful protection of ischemic and post-ischemic brain

Ischemic brain injury inflicted by stroke and cardiac arrest ranks among the leading causes of death and long-term disability in the United States. The brain consumes large amounts of metabolic substrates and oxygen to sustain its energy requirements. Consequently, the brain is exquisitely sensitive to interruptions in its blood supply, and suffers irreversible damage after 10-15 min of severe ischemia. Effective treatments to protect the brain from stroke and cardiac arrest have proven elusive, due to the complexities of the injury cascades ignited by ischemia and reperfusion. Although recombinant tissue plasminogen activator and therapeutic hypothermia have proven efficacious for stroke and cardiac arrest, respectively, these treatments are constrained by narrow therapeutic windows, potentially detrimental side-effects and the limited availability of hypothermia equipment. Mounting evidence demonstrates the cytokine hormone erythropoietin (EPO) to be a powerful neuroprotective agent and a potential adjuvant to established therapies. Classically, EPO originating primarily in the kidneys promotes erythrocyte production by suppressing apoptosis of proerythroid progenitors in bone marrow. However, the brain is capable of producing EPO, and EPO's membrane receptors and signaling components also are expressed in neurons and astrocytes. EPO activates signaling cascades that increase the brain's resistance to ischemia-reperfusion stress by stabilizing mitochondrial membranes, limiting formation of reactive oxygen and nitrogen intermediates, and suppressing pro-inflammatory cytokine production and neutrophil infiltration. Collectively, these mechanisms preserve functional brain tissue and, thus, improve neurocognitive recovery from brain ischemia. This article reviews the mechanisms mediating EPO-induced brain protection, critiques the clinical utility of exogenous EPO to preserve brain threatened by ischemic stroke and cardiac arrest, and discusses the prospects for induction of EPO production within the brain by the intermediary metabolite, pyruvate.

Pyruvate minimizes rtPA toxicity from in vitro oxygen-glucose deprivation and reoxygenation

Clinical application of recombinant tissue plasminogen activator (rtPA) for stroke is limited by hemorrhagic transformation, which narrows rtPA's therapeutic window. In addition, mounting evidence indicates that rtPA is potentially neurotoxic if it traverses a compromised blood brain barrier. Here, we demonstrated that pyruvate protects cultured HT22 neuronal and primary microvascular endothelial cells co-cultured with primary astrocytes from oxygen glucose deprivation (OGD)/reoxygenation stress and rtPA cytotoxicity. After 3 or 6h OGD, cells were reoxygenated with 11mmol/L glucose±pyruvate (8mmol/L) and/or rtPA (10µg/ml). Measured variables included cellular viability (calcein AM and annexin-V/propidium iodide), reactive oxygen species (ROS; mitosox red and 2',7'-dichlorofluorescein diacetate), NADPH, NADP(+) and ATP contents (spectrophotometry), matrix metalloproteinase-2 (MMP2) activities (gelatin zymography), and cellular contents of MMP2, tissue inhibitor of metalloproteinase-2 (TIMP2), and phosphor-activation of anti-apoptotic p70s6 kinase, Akt and Erk (immunoblot). Pyruvate prevented the loss of HT22 cells after 3h OGD±rtPA. After 6h OGD, rtPA sharply lowered cell viability; pyruvate dampened this effect. Three hours OGD and 4h reoxygenation with rtPA increased ROS formation by about 50%. Pyruvate prevented this ROS formation and doubled cellular NADPH/NADP(+) ratio and ATP content. In endothelial cell monolayers, 3h OGD and 24h reoxygenation increased FITC-dextran leakage, indicating disruption of intercellular junctions. Although rtPA exacerbated this effect, pyruvate prevented it while sharply lowering MMP2/TIMP2 ratio and increasing phosphorylation of p70s6 kinase, Akt and Erk. Pyruvate protects neuronal cells and microvascular endothelium from hypoxia-reoxygenation and cytotoxic action of rtPA while reducing ROS and activating anti-apoptotic signaling. These results support the proposed use of pyruvate as an adjuvant to dampen the side effects of rtPA treatment, thereby extending rtPA's therapeutic window.

Epo and non-hematopoietic cells: what do we know?

The hematopoietic growth factor erythropoietin (Epo) circulates in plasma and controls the oxygen carrying capacity of the blood (Fisher. Exp Biol Med (Maywood) 228:1-14, 2003). Epo is produced primarily in the adult kidney and fetal liver and was originally believed to play a role restricted to stimulation of early erythroid precursor proliferation, inhibition of apoptosis, and differentiation of the erythroid lineage. Early studies showed that mice with targeted deletion of Epo or the Epo receptor (EpoR) show impaired erythropoiesis, lack mature erythrocytes, and die in utero around embryonic day 13.5 (Wu et al. Cell 83:59-67, 1995; Lin et al. Genes Dev. 10:154-164, 1996). These animals also exhibited heart defects, abnormal vascular development as well as increased apoptosis in the brain suggesting additional functions for Epo signaling in normal development of the central nervous system and heart. Now, in addition to its well-known role in erythropoiesis, a diverse array of cells have been identified that produce Epo and/or express the Epo-R including endothelial cells, smooth muscle cells, and cells of the central nervous system (Masuda et al. J Biol Chem. 269:19488-19493, 1994; Marti et al. Eur J Neurosci. 8:666-676, 1996; Bernaudin et al. J Cereb Blood Flow Metab. 19:643-651, 1999; Li et al. Neurochem Res. 32:2132-2141, 2007). Endogenously produced Epo and/or expression of the EpoR gives rise to autocrine and paracrine signaling in different organs particularly during hypoxia, toxicity, and injury conditions. Epo has been shown to regulate a variety of cell functions such as calcium flux (Korbel et al. J Comp Physiol B. 174:121-128, 2004) neurotransmitter synthesis and cell survival (Velly et al. Pharmacol Ther. 128:445-459, 2010; Vogel et al. Blood. 102:2278-2284, 2003). Furthermore Epo has neurotrophic effects (Grimm et al. Nat Med. 8:718-724, 2002; Junk et al. Proc Natl Acad Sci U S A. 99:10659-10664, 2002), can induce an angiogenic phenotype in cultured endothelial cells and is a potent angiogenic factor in vivo (Ribatti et al. Eur J Clin Invest. 33:891-896, 2003) and might enhance ventilation in hypoxic conditions (Soliz et al. J Physiol. 568:559-571, 2005; Soliz et al. J Physiol. 583, 329-336, 2007). Thus multiple functions have been identified breathing new life and exciting possibilities into what is really an old growth factor.This review will address the function of Epo in non-hematopoietic tissues with significant emphasis on the brain and heart.

Pyruvate effects on red blood cells during in vitro cardiopulmonary bypass with dogs' blood

To investigate the effects of pyruvate (Pyr) on adenosine triphosphate (ATP), endothelial nitric oxide synthase (eNOS), and nitric oxide (NO) in red blood cells (RBCs) during the cardiopulmonary bypass procedure (CPB), blood, 500 mL, was collected from each of 10 healthy dogs (weight 12-18 kg). The blood was divided into two parts (250 mL each) and randomly assigned into the control group (Group C, n = 10) or the Pyr group (Group P, n = 10). The blood was commingled with an equal volume of 0.9% NaCl and pyruvated isotonic solution (Pyr 50 mM) in the extracorporeal circuit in the two groups, respectively. The CPB procedure was fixed at 120 min, and the transferring flow was 4 L/min. Contents of ATP in RBCs, eNOS activities, and NO productions in plasma were measured before CPB and during CPB at 30, 60, 90, and 120 min in both groups. The ATP level, eNOS activity, and NO production were not different prior to CPB between the two groups. A decline of ATP levels was shown in both groups but remained significantly higher in Group P than in Group C at the same time points during in vitro CPB (P < 0.01). Values of eNOS and NO were significantly increased in Group C but markedly reduced in Group P during CPB, compared with pre-CPB (P < 0.01). The CPB procedure significantly damaged dogs' RBCs in the ATP level, eNOS activity, and NO production, in vitro, but Pyr effectively protected RBCs in these functions during CPB. Pyr would be clinically protective for RBCs during CPB.

Pyruvate protects the brain against ischemia-reperfusion injury by activating the erythropoietin signaling pathway

BACKGROUND AND PURPOSE

Pyruvate is known to be cytoprotective through antioxidant and anti-inflammatory mechanisms. We tested the hypothesis that pyruvate protects the brain against ischemia-reperfusion injury by inducing endogenous erythropoietin (EPO) expression.

METHODS

Pyruvate's protective effect was evaluated in C6 glioma cells and HT22 neuronal cells subjected to transient oxygen glucose deprivation. Cell viability (calcein AM assay) and expression of hypoxia-inducible factor-1α, EPO, Akt and Erk (immunoblot), and EPO receptor (reverse transcription-polymerase chain reaction) were analyzed. Transient focal cerebral ischemia in rats was induced by 2 hours middle cerebral artery occlusion followed by 24 hours reperfusion. Pyruvate or saline was infused from 60 minutes occlusion until 30 minutes reperfusion. Lesion volume and DNA fragmentation were assessed by 2,3,5-triphenyltetrazolium staining and terminal deoxynucleotidyl transferase-mediated dUTP nick end-labeling assay, respectively. Immunoblots were conducted to determine cerebral EPO contents.

RESULTS

Pyruvate increased cell viability, hypoxia-inducible factor-1α, EPO, and Akt phosphorylation. Small interfering RNA suppression of hypoxia-inducible factor-1α and EPO abolished pyruvate-induced cytoprotection. In the rat stroke model, pyruvate reduced lesion volume by 84% and DNA fragmentation by 77% versus controls; increased EPO content paralleled these cerebroprotective actions of pyruvate.

CONCLUSIONS

Pyruvate activation of the hypoxia-inducible factor-1α-EPO signaling cascade in neurons and glia could protect the brain from ischemia-reperfusion injury.

Acute Vhl gene inactivation induces cardiac HIF-dependent erythropoietin gene expression

Von Hippel Lindau (Vhl) gene inactivation results in embryonic lethality. The consequences of its inactivation in adult mice, and of the ensuing activation of the hypoxia-inducible factors (HIFs), have been explored mainly in a tissue-specific manner. This mid-gestation lethality can be also circumvented by using a floxed Vhl allele in combination with an ubiquous tamoxifen-inducible recombinase Cre-ER^T2. Here, we characterize a widespread reduction in Vhl gene expression in Vhl^floxed-UBC-Cre-ER^T2 adult mice after dietary tamoxifen administration, a convenient route of administration that has yet to be fully characterized for global gene inactivation. Vhl gene inactivation rapidly resulted in a marked splenomegaly and skin erythema, accompanied by renal and hepatic induction of the erythropoietin (Epo) gene, indicative of the in vivo activation of the oxygen sensing HIF pathway. We show that acute Vhl gene inactivation also induced Epo gene expression in the heart, revealing cardiac tissue to be an extra-renal source of EPO. Indeed, primary cardiomyocytes and HL-1 cardiac cells both induce Epo gene expression when exposed to low O₂ tension in a HIF-dependent manner. Thus, as well as demonstrating the potential of dietary tamoxifen administration for gene inactivation studies in UBC-Cre-ER^T2 mouse lines, this data provides evidence of a cardiac oxygen-sensing VHL/HIF/EPO pathway in adult mice.

Pyruvate-enriched cardioplegia suppresses cardiopulmonary bypass-induced myocardial inflammation

BACKGROUND

Cardiopulmonary bypass-induced oxidative stress initiates inflammation that can damage the myocardium. This study tested whether cardioplegia enriched with the intermediary metabolite and antioxidant pyruvate dampens postbypass myocardial inflammation.

METHODS

Pigs were maintained on cardiopulmonary bypass while their hearts were arrested for 60 minutes with 4:1 blood:crystalloid cardioplegia, in which the crystalloid contained 188 mM glucose ± 24 mM pyruvate. Pigs were weaned from bypass after 30 minutes of whole blood reperfusion and recovered for 4 hours. Glutathione (GSH) and glutathione disulfide (GSSG) were measured in coronary sinus plasma to indirectly monitor myocardial GSH redox state (GSH/GSSG). Left ventricular myocardium was sampled 4 hours after cardiopulmonary bypass for analyses of C-reactive protein, matrix metalloproteinases 2 and 9 and tissue inhibitor of metalloproteinase-2 (TIMP-2), and to assess neutrophil infiltration by histology and myeloperoxidase assay.

RESULTS

Coronary sinus GSH/GSSG fell 70% after cardiopulmonary bypass with control cardioplegia, but pyruvate cardioplegia produced a robust increase in coronary sinus GSH/GSSG that persisted for 4 hours after bypass. Myocardial C-reactive protein content increased 5.6-fold after control bypass, and neutrophil infiltration and myeloperoxidase activity also increased, but pyruvate-fortified cardioplegia prevented these inflammatory effects. Control cardioplegia lowered myocardial TIMP-2 content by 59% and increased matrix metalloproteinase-9 activity by 35% versus nonbypass sham values, but pyruvate cardioplegia increased TIMP-2 content ninefold versus control cardioplegia and prevented the increase in matrix metalloproteinase-9. Matrix metalloproteinase-2 was not affected by bypass ± pyruvate.

CONCLUSIONS

Pyruvate-enriched cardioplegia dampens cardiopulmonary bypass-induced myocardial inflammation. Increased GSH/GSSG and TIMP-2 may mediate pyruvate's effects.