Ferenc Puskas

Left versus right atrial difference in dominant frequency, K+ channel transcripts, and fibrosis in patients developing atrial fibrillation after cardiac surgery

BACKGROUND The development of atrial fibrillation (AF) after cardiac surgery is associated with adverse outcomes; however, the mechanism(s) that trigger and maintain AF in these patients are unknown. OBJECTIVE The purpose of this study was to test our hypothesis that postoperative AF is maintained by high-frequency sources in the left atrium (LA) resulting from ion channel and structural features that differ from the right atrium (RA). METHODS Forty-four patients with no previous history of AF who underwent cardiac surgery consented to LA and RA biopsies. Histologic sections evaluated fatty infiltration, fibrosis, and iron deposition; quantitative reverse transcription-polymerase chain reaction (RT-PCR) assessed ion channel expression. In a subset of 27 patients, LA and RA unipolar recording leads were also placed. In patients who developed AF, the dominant frequency (DF) for each lead was calculated using fast Fourier transform. RESULTS DFs during AF were LA 6.26 +/- 0.8 Hz, RA 4.56 +/- 0.7 Hz (P <.01). RT-PCR revealed LA-to-RA differences in mRNA abundance for Kir2.3 (1.8:1) and Kir3.4 (2.3:1). While LA fibrosis was greater in patients developing AF compared with those remaining in normal sinus rhythm (10.8% +/- 11% vs. 3.8% +/- 3.5%; P = .03), the amount of LA fibrosis inversely correlated with the LA DF. CONCLUSIONS This is the first demonstration of LA-to-RA frequency differences during postoperative AF, which are associated with LA-to-RA differences in mRNA levels for potassium channel proteins and LA fibrosis. These results strongly suggest that sources of AF after cardiac surgery are located in the LA and are stabilized by LA fibrosis.

On the role of 4-hydroxynonenal in health and disease

Polyunsaturated fatty acids are susceptible to peroxidation and they yield various degradation products, including the main α,β-unsaturated hydroxyalkenal, 4-hydroxy-2,3-trans-nonenal (HNE) in oxidative stress. Due to its high reactivity, HNE interacts with various macromolecules of the cell, and this general toxicity clearly contributes to a wide variety of pathological conditions. In addition, growing evidence suggests a more specific function of HNE in electrophilic signaling as a second messenger of oxidative/electrophilic stress. It can induce antioxidant defense mechanisms to restrain its own production and to enhance the cellular protection against oxidative stress. Moreover, HNE-mediated signaling can largely influence the fate of the cell through modulating major cellular processes, such as autophagy, proliferation and apoptosis. This review focuses on the molecular mechanisms underlying the signaling and regulatory functions of HNE. The role of HNE in the pathophysiology of cancer, cardiovascular and neurodegenerative diseases is also discussed.

Toll-Like Receptor 4–Dependent Microglial Activation Mediates Spinal Cord Ischemia–Reperfusion Injury

Background— Paraplegia continues to complicate thoracoabdominal aortic interventions. The elusive mechanism of spinal cord ischemia–reperfusion injury has delayed the development of pharmacological adjuncts. Microglia, the resident macrophages of the central nervous system, can have pathological responses after a variety of insults. This can occur through toll-like receptor 4 (TLR-4) in stroke models. We hypothesize that spinal cord ischemia–reperfusion injury after aortic occlusion results from TLR-4–mediated microglial activation in mice. Methods and Results— TLR-4 mutant and wild-type mice underwent aortic occlusion for 5 minutes, followed by 60 hours of reperfusion when spinal cords were removed for analysis. Spinal cord cytokine production and microglial activation were assessed at 6 and 36 hours after surgery. Isolated microglia from mutant and wild-type mice were subjected to oxygen and glucose deprivation for 24 hours, after which the expression of TLR-4 and proinflammatory cytokines was analyzed. Mice without functional TLR-4 demonstrated decreased microglial activation and cytokine production and had preserved functional outcomes and neuronal viability after thoracic aortic occlusion. After oxygen and glucose deprivation, wild-type microglia had increased TLR-4 expression and production of proinflammatory cytokines. Conclusions— The absence of functional TLR-4 attenuated neuronal injury and microglial activation after thoracic aortic occlusion in mice. Furthermore, microglial upregulation of TLR-4 occurred after oxygen and glucose deprivation, and the absence of functional TLR-4 significantly attenuated the production of proinflammatory cytokines. In conclusion, TLR-4–mediated microglia activation in the spinal cord after aortic occlusion is critical in the mechanism of paraplegia after aortic cross-clamping and may provide targets for pharmacological intervention.

Cytokine Expression Profile in Human Lungs Undergoing Normothermic Ex-Vivo Lung Perfusion

BACKGROUND A donor lung shortage prevents patients from receiving life-saving transplants. Ex-vivo lung perfusion (EVLP) is a viable means of expanding the donor pool by evaluating and potentially improving donor lung function. The metabolic and inflammatory effects of EVLP on human lung tissue are currently unknown. We sought to establish representative cytokine expression in human donor lungs meeting acceptable lung transplant criteria after prolonged normothermic EVLP. METHODS Seven single human lungs not meeting traditional transplantation criteria for various reasons underwent normothermic EVLP. Lungs were perfused with deoxygenated colloid, rewarmed, and ventilated per standard protocol. Lung function was evaluated every hour. Biopsies were taken at 1, 6, and 12 hours. Inflammatory cytokines were quantitatively measured using a human cytokine magnetic bead-based multiplex assay. RESULTS All lungs met traditional transplant criteria after EVLP. The partial pressure of arterial oxygen and physiologic lung function significantly improved (p<0.05). No pulmonary edema was formed, and histology demonstrated no evidence of acute lung injury. Interleukin (IL)-6, IL-8, granulocyte colony-stimulating factor, and monocyte chemotactic protein-1 were upregulated, while granulocyte macrophage colony-stimulating factor was downregulated during EVLP (p<0.05). IL-1β, IL-4, IL-7, IL-12, interferon-γ, macrophage inflammatory protein-1β, and tumor necrosis factor-α were detectable and unchanged. CONCLUSIONS Ex-vivo lung perfusion demonstrates the ability to improve oxygenation and physiologic lung function in donor lungs unacceptable for transplantation without injury to the lung. We establish here a cytokine expression profile in human lungs undergoing normothermic EVLP. These data can be used in the future to explore novel targeted therapies for ischemia-reperfusion injury.

Attenuation of spinal cord ischemia and reperfusion injury by erythropoietin

BACKGROUND Paraplegia remains a devastating complication for patients undergoing thoracic aortic procedures. Although surgical adjuncts have evolved to reduce the risk of paraplegia, no pharmacologic therapies have proven efficacious in attenuating spinal cord ischemia-reperfusion injury. Effects of erythropoietin in spinal cord ischemia-reperfusion injury, however, have not yet been elucidated. We hypothesized that pretreatment with erythropoietin would attenuate functional and cytoarchitectural spinal cord injury related to high-risk aortic procedures. METHODS Adult male mice were subjected to ischemia-reperfusion. Aortic arch and proximal left subclavian arteries were clamped for 5 minutes; animals were observed for 48 hours. Neurologic scores of hind limb function were assessed every 12 hours. Experimental groups consisted of treatment with erythropoietin 4 hours before crossclamping (n = 7), ischemic controls (n = 7), and sham ischemia (operation without crossclamping, n = 6). Thoracolumbar sections of spinal cord were removed after 48 hours and preserved for cytoarchitectural analysis. RESULTS Mice pretreated with erythropoietin exhibited significant preservation of hind limb motor function. All mice without pretreatment were paralyzed at 48 hours. Mice with erythropoietin pretreatment had improved motor function; 3 had no measurable neurologic deficit at 48 hours. Histologic analysis in mice treated with erythropoietin showed markedly reduced neuronal cell injury. CONCLUSIONS Erythropoeitin preserves both function and histologic appearance in mice undergoing spinal cord ischemia-reperfusion. With further elucidation of mechanisms of protection and optimal administration, erythropoietin could become an important adjunct in reducing the incidence and severity of spinal cord injury related to aortic interventions.

Left Ventricular Assist Device Outflow Cannula Obstruction by the Rare Environmental Fungus Myceliophthora thermophila

Left ventricular assist devices are used to provide mechanical circulatory support during end-stage heart failure either as a destination therapy or as a bridge to heart transplantation. Perioperative transesophageal echocardiography is becoming an invaluable tool to investigate device function during implantation and in case of mechanical malfunction. Most malfunctions are due to inflow graft occlusion, or device malfunction, while outflow graft dysfunction is rare. Here, we present a case of severe outflow conduit obstruction by a rare environmental fungus, Myceliophthora thermophila. After replacement of the infected device and intensive antifungal treatment, heart transplantation was performed 2 yr later.

Transesophageal echocardiography in noncardiac thoracic surgery.

In high-risk surgeries with medically complicated patients, transesophageal echocardiography (TEE) adds an additional level of monitoring with which few can disagree. This article presents multiple applications of TEE that can assist both the anesthesiologist and the surgeon through major noncardiac thoracic surgery. It highlights how TEE can be used as an adjuvant to lung resection surgery; TEE as a monitor during lung transplantation; TEE to assess patients for extracorporeal membrane oxygenation; TEE for thoracic aortic surgery; and TEE in the assessment of patients with acute pulmonary hypertension undergoing noncardiac thoracic surgery.

Spinal cord protection via alpha-2 agonist-mediated increase in glial cell-line–derived neurotrophic factor

OBJECTIVES Delayed paraplegia secondary to ischemia-reperfusion injury is a devastating complication of thoracoabdominal aortic surgery. Alpha-2 agonists have been shown to attenuate ischemia-reperfusion injury, but the mechanism for protection has yet to be elucidated. A growing body of evidence suggests that astrocytes play a critical role in neuroprotection by release of neurotrophins. We hypothesize that alpha-2 agonism with dexmedetomidine increases glial cell-line-derived neurotrophic factor in spinal cord astrocytes to provide spinal cord protection. METHODS Spinal cords were isolated en bloc from C57BL/6 mice, and primary spinal cord astrocytes and neurons were selected for and grown separately in culture. Astrocytes were treated with dexmedetomidine, and glial cell-line-derived neurotrophic factor was tested for by enzyme-linked immunosorbent assay. The 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay was used to assess neuronal viability. RESULTS Spinal cord primary astrocytes treated with dexmedetomidine at 1 μmol/L and 10 μmol/L had significantly increased glial cell-line-derived neurotrophic factor production compared with control (P < .05). Neurons subjected to oxygen glucose deprivation had significant preservation (P < .05) of viability with use of dexmedetomidine-treated astrocyte media. Glial cell-line-derived neurotrophic factor neutralizing antibody eliminated the protective effects of the dexmedetomidine-treated astrocyte media (P < .05). CONCLUSIONS Astrocytes have been shown to preserve neuronal viability via release of neurotrophic factors. Dexmedetomidine increases glial cell-derived neurotrophic factor from spinal cord astrocytes via the alpha-2 receptor. Treatment with alpha-2 agonist dexmedetomidine may be a clinical tool for use in spinal cord protection in aortic surgery.

Spinal Cord Ischemia-Reperfusion Injury Induces Erythropoietin Receptor Expression

BACKGROUND Paraplegia remains a devastating complication of aortic surgery, occurring in up to 20% of complex thoracoabdominal repairs. Erythropoietin (EPO) attenuates this injury in models of spinal cord ischemia. Upregulation of the beta-common receptor (βcR) subunit of the EPO receptor is associated with reduced damage in murine models of neural injury. This receptor activates anti-apoptotic pathways including signaling transducer and activator of transcription 3 (STAT3). We hypothesized that spinal cord ischemia-reperfusion injury upregulates the βcR subunit with a subsequent increase in activated STAT3. METHODS Adult male C57/BL6 mice received an intraperitoneal injection of 0.5 mL of EPO (10 U/kg) or 0.9% saline after induction of anesthesia. Spinal cord ischemia was induced through sternotomy and 4-minute thoracic aortic cross-clamp. Sham mice underwent sternotomy without cross-clamp placement. Four groups were studied: ischemic and sham groups, each with and without EPO treatment. After 4 hours of reperfusion, spinal cords were harvested and homogenized. The βcR subunit expression and STAT3 activation were evaluated by immunoblot. RESULTS Ischemia reperfusion increased βcR subunit expression in spinal cords of ischemia + saline and ischemia + EPO mice compared with shams (3.4 ± 1.39 vs 1.31 ± 0.3, p = 0.01 and 3.80 ± 0.58 vs 1.56 ± 0.32, p = 0.01). Additionally, both ischemic groups demonstrated increased STAT3 activation compared with shams (1.35 ± 0.14 vs 1.09 ± 0.07, p = 0.01 and 1.66 ± 0.35 vs 1.08 ± 0.17, p = 0.02). CONCLUSIONS Ischemia-reperfusion injury induces EPO receptor βcR subunit expression and early downstream anti-apoptotic signaling through STAT3 activation. Further investigation into the role of the βcR subunit is warranted to determine tissue protective functions of EPO. Elucidation of mechanisms involved in spinal cord protection is essential for reducing delayed paraplegia.

Interruption of spinal cord microglial signaling by alpha-2 agonist dexmedetomidine in a murine model of delayed paraplegia

BACKGROUND Despite investigation into preventable pharmacologic adjuncts, paraplegia continues to complicate thoracoabdominal aortic interventions. The alpha 2a adrenergic receptor agonist, dexmedetomidine, has been shown to preserve neurologic function and neuronal viability in a murine model of spinal cord ischemia reperfusion, although the mechanism remains elusive. We hypothesize that dexmedetomidine will blunt postischemic inflammation in vivo following thoracic aortic occlusion with in vitro demonstration of microglial inhibition following lipopolysaccharide (LPS) stimulation. METHODS Adult male C57BL/6 mice underwent 4 minutes of aortic occlusion. Mice received 25 μg/kg intraperitoneal dexmedetomidine (n = 8) or 0.9% normal saline (n = 7) at reperfusion and 12-hour intervals postoperatively until 48 hours. Additionally, sham mice (n = 3), which had aortic arch exposed with no occlusion, were included for comparison. Functional scoring was done at 6 hours following surgery and 12-hour intervals until 60 hours when spinal cords were removed and examined for neuronal viability and cytokine production. Additional analysis of microglia activation was done in 12 hours following surgery. Age- and sex-matched mice had spinal cord removed for microglial isolation culture. Cells were grown to confluence and stimulated with toll-like receptor-4 agonist LPS 100 ng/mL in presence of dexmedetomidine or vehicle control for 24 hours. Microglia and media were then removed for analysis of protein expression. RESULTS Dexmedetomidine treatment at reperfusion significantly preserved neurologic function with mice in treatment group having a Basso Score of 6.3 in comparison to 2.3 in ischemic control group. Treatment was associated with a significant reduction in microglia activation and in interleukin-6 production. Microglial cells in isolation when stimulated with LPS had an increased production of proinflammatory cytokines and markers of activation. Treatment with dexmedetomidine significantly attenuated microglial activation and proinflammatory cytokine production in vitro with a greater than twofold reduction in tumor necrosis factor-α. CONCLUSIONS Alpha 2a agonist, dexmedetomidine treatment at reperfusion preserved neurologic function and neuronal viability. Furthermore, dexmedetomidine treatment resulted in an attenuation of microglial activation and proinflammatory cytokine production both in vivo and in vitro following LPS stimulation. This finding lends insight into the mechanism of paralysis following thoracic aortic interventions and may guide future pharmacologic targets for attenuating spinal cord ischemia and reperfusion.