Yih Sharng Chen

Down-regulation of L-type calcium channel and sarcoplasmic reticular Ca2+-ATPase mRNA in human atrial fibrillation without significant change in the mRNA of ryanodine receptor, calsequestrin and phospholamban: An insight into the mechanism of atrial electrical remodeling

OBJECTIVES We investigated the gene expression of calcium-handling genes including L-type calcium channel, sarcoplasmic reticular calcium adenosine triphosphatase (Ca(2+)-ATPase), ryanodine receptor, calsequestrin and phospholamban in human atrial fibrillation. BACKGROUND Recent studies have demonstrated that atrial electrical remodeling in atrial fibrillation is associated with intracellular calcium overload. However, the changes of calcium-handling proteins remain unclear. METHODS A total of 34 patients undergoing open heart surgery were included. Atrial tissue was obtained from the right atrial free wall, right atrial appendage, left atrial free wall and left atrial appendage, respectively. The messenger ribonucleic acid (mRNA) amount of the genes was measured by reverse transcription-polymerase chain reaction and normalized to the mRNA levels of glyceraldehyde 3-phosphate dehydrogenase. RESULTS The mRNA of L-type calcium channel and of Ca(2+)-ATPase was significantly decreased in patients with persistent atrial fibrillation for more than 3 months (0.36+/-0.26 vs. 0.90+/-0.88 for L-type calcium channel; 0.69+/-0.42 vs. 1.21+/-0.68 for Ca(2+)-ATPase; both p < 0.05, all data in arbitrary unit). We further demonstrated that there was no spatial dispersion of the gene expression among the four atrial tissue sampling sites. Age, gender and underlying cardiac disease had no significant effects on the gene expression. In contrast, the mRNA levels of ryanodine receptor, calsequestrin and phospholamban showed no significant change in atrial fibrillation. CONCLUSIONS L-type calcium channel and the sarcoplasmic reticular Ca(2+)-ATPase gene were down-regulated in atrial fibrillation. These changes may be a consequence of, as well as a contributory factor for, atrial fibrillation.

Preoperative Proteinuria Predicts Adverse Renal Outcomes after Coronary Artery Bypass Grafting

Whether preoperative proteinuria associates with adverse renal outcomes after cardiac surgery is unknown. Here, we performed a secondary analysis of a prospectively enrolled cohort of adult patients undergoing coronary artery bypass grafting (CABG) at a medical center and its two affiliate hospitals between 2003 and 2007. We excluded patients with stage 5 CKD or those who received dialysis previously. We defined proteinuria, measured with a dipstick, as mild (trace to 1+) or heavy (2+ to 4+). Among a total of 1052 patients, cardiac surgery-associated acute kidney injury (CSA-AKI) developed in 183 (17.4%) patients and required renal replacement therapy (RRT) in 50 (4.8%) patients. In a multiple logistic regression model, mild and heavy proteinuria each associated with an increased odds of CSA-AKI, independent of CKD stage and the presence of diabetes mellitus (mild: OR 1.66, 95% CI 1.09 to 2.52; heavy: OR 2.30, 95% CI 1.35 to 3.90). Heavy proteinuria also associated with increased odds of postoperative RRT (OR 7.29, 95% CI 3.00 to 17.73). In summary, these data suggest that preoperative proteinuria is a predictor of CSA-AKI among patients undergoing CABG.

Novel role for the δ-opioid receptor in hypoxic preconditioning in rat retinas

δ‐Opioid receptor (DOR) is an oxygen‐sensitive protein whose function in the rat retina is unknown. We examined whether DOR is involved in hypoxic preconditioning (HPC)‐mediated retinoprotection following intraocular pressure (IOP) elevation. Rats were exposed to intermittent hypoxia (10% oxygen) to induce HPC. Unilateral retinal ischemia/reperfusion injury was induced by elevating IOP to 100 mmHg for 1 h. HPC attenuated the loss of neuronal marker expression and increased pro‐apoptotic caspase 3 activity in the IOP retina. Excess superoxide production and 8‐iso‐prostaglandin F2α accumulation caused by enhanced oxidant protein expression and reduced antioxidant enzyme level after IOP elevation were largely abrogated by HPC. HPC markedly increased the expression of hypoxia‐inducible factor‐1α (HIF‐1α) and DOR, but intravitreal administration of HIF‐1α‐specific small interfering RNA abrogated the up‐regulation of DOR. This suggested that DOR functions downstream of HIF‐1α. However, the endogenous content of leucine enkephalin in retinas was not affected by HPC or IOP. Treatment of retinas with the DOR antagonist naltrindole attenuated the HPC‐induced protection and activation of extracellular signal‐regulated kinase. These results suggest a novel mechanism of HPC‐mediated retinoprotection whereby HIF‐1α induces the expression of DOR, and DOR‐mediated activation of extracellular signal‐regulated kinase triggers cellular events that correct the redox imbalance in the post‐ischemic retina.

Changes in the mRNA levels of delayed rectifier potassium channels in human atrial fibrillation

Introduction: We measured mRNA levels of delayed rectifier potassium channels in human atrial tissue to investigate the mechanism of the shortening of the atrial effective refractory period and the loss of rate-adaptive shortening of the atrial effective refractory period in human atrial fibrillation. Methods and Results: A total of 34 patients undergoing open heart surgery were included. Atrial tissue was obtained from the right atrial free wall, right atrial appendage, left atrial free wall and left atrial appendage, respectively. The mRNA amounts of KVLQT1 (IKs), minK (β-subunit of IKs), HERG (IKr), and KV1.5 (IKur) were measured by reverse transcription-polymerase chain reaction and normalized to the mRNA amount of GAPDH. We found that the mRNA levels of KV1.5, HERG and KVLQT1 were all significantly decreased in patients with persistent atrial fibrillation for more than 3 months. In contrast, the mRNA level of minK was significantly increased in patients with persistent atrial fibrillation for more than 3 months. We further showed that these changes were independent of the underlying cardiac disease, atrial filling pressure, gender and age. We also found that there was no spatial dispersion of mRNA levels among the four atrial sampling sites. Conclusions: Because the decrease in potassium currents results in a prolonged action potential, the shortening of the atrial effective refractory period in atrial fibrillation should be attributed to other factors. However, the decrease in IKs might contribute, at least in part, to the loss of rate-adaptive shortening of the atrial refractory period.

Quality of life in adults with congenital heart disease: biopsychosocial determinants and sex-related differences

Objectives To assess the quality of life (QoL) in adults with congenital heart disease (ACHD) and to explore the sex-related differences and biopsychosocial determinants in an Asian cohort. Design Prospective cross-sectional clinical study. Setting One tertiary medical centre in Taiwan. Patients and methods The QoL of ACHD (≥20 years) was investigated using the Taiwanese version of the QoL questionnaire designed by the WHO, which assesses four domains of QoL (physical, psychological, social and environmental). Personality, psychological distress and family support were assessed using the Maudsley Personality Inventory, Brief Symptom Rating Scale, and the Family APGAR score, respectively. Results A total of 289 patients (age 33.2±10.6 years; 36% men) were studied. ACHD women had significantly lower QoL scores in the physical and psychological domains compared to the age-matched general population, whereas no differences were observed between ACHD men and the general population. Multivariate analysis showed that female gender was associated with poorer physical QoL; the sex difference in the psychological QoL was mediated by psychological distress. Interaction analysis showed that the effect of family support on the psychological domain of QoL may be different by sex. The determinants of QoL varied between different domains. Extroversion personality trait, psychological distress and family support were common determinants of most domains of QoL. Conclusions In ACHD, female gender was associated with poor physical and psychological QoL. The common denominators for QoL were primarily personality trait, psychological distress and family support, but not disease severity.

Phaeochromocytoma crisis – a rare indication for extracorporeal membrane oxygenation

We report on a case of phaeochromocytoma whose initial presentation mimicked an acute myocardial infarction. Veno‐arterial extracorporeal membrane oxygenation was used for the management of refractory cardiogenic shock and massive lung oedema. Suspicion and diagnosis of a phaeochromocytoma were made due to its unique clinical presentation during extracorporeal membrane oxygenation. Stabilisation of the crisis and recovery of cardiopulmonary function were achieved using the support of extracorporeal membrane oxygenation. This case highlights the difficulty in the differential diagnosis of cardiogenic shock secondary to phaeochromocytoma and the important role of extracorporeal membrane oxygenation can have in the successful resuscitation and management of these patients.

Mechanosensitive transient receptor potential vanilloid type 1 channels contribute to vascular remodeling of rat fistula veins

OBJECTIVE We previously showed that matrix metalloproteinases (MMPs) contribute to tremendous blood flow-induced venous wall thickening during the maturation of an arteriovenous fistula (AVF). However, how veins in the fistula sense a dramatic change in the blood flow remains unknown. Because mechanosensitive transient receptor potential vanilloid channels (TRPVs) are present in the endothelium, we examined whether the Ca2+-permeable TRPVs play a role in remodeling of fistula veins. METHODS The fistula veins were generated at femoral AVF of Wistar rats. Changes in the hemodynamics and the width and internal radius of the iliac vein were studied at 3, 7, 14, and 28 days, then the iliac vein was removed and examined for changes in wall thickness and protein or mRNA expression by immunofluorecent stain, Western blot, or real time PCR. Changes in MMP2 activity was examined by gelatin zymography. Two ligatures were performed in iliac vein to prevent venodilatation to confirm the effect of dramatic changes in hemodynamics on TRPV expression. The specific role of TRPV was studied in another group of fistula veins given with capsazepine via a subcutaneous mini-osmotic pump for 28 days. RESULTS The fistula veins demonstrated high flow/wall shear stress (WSS), wall thickening, and venodilatation compared with control veins. The WSS increase was positively correlated with upregulation of TRPV1, but not TRPV4. Narrowing fistula veins prevented TRPV1 upregulation, indicating that high flow directly upregulates TRPV1. We examined the underlying signaling components and found that enhanced Ca2+/calmodulin-dependent protein kinase II (CaMK II) activity upregulated endothelial nitric oxide synthase (eNOS) and downregulated arginase I in the fistula veins. These changes were reversed by a CaMK II inhibitor. The relative levels of eNOS and arginase I activity consequently augmented NO formation, which coincided with an increase in MMP2 activity. Chronic inhibition of TRPV1 in the fistula veins by capsazepine showed no effect on high flow and TRPV1 expression, but markedly attenuated WSS, which was concomitantly associated with attenuation of CaMK II activity, NO-dependent MMP2 activation, and remodeling. CONCLUSION These findings indicate that TRPV1 is essential in the remodeling of AVFs and that WSS leads to TRPV1 upregulation, which then enhances remodeling, therefore, inhibition of TRPV1 pathway may prolong the lifespan of an AVF by decreasing WSS and vein wall remodeling.

Mechanosensitive N-Methyl-d-Aspartate Receptors Contribute to Sensory Activation in the Rat Renal Pelvis

The N-methyl-d-aspartate (NMDA) subtype of the ionotropic glutamate receptor is found in the periphery. The present study tested whether NMDA receptors (NMDARs) are present in the ends of afferent renal nerves in the renal pelvis, an area concerned mainly with transmitting sensation and the to reflex regulation of body fluid. The main NMDAR subunit, NMDA&zgr;1, was found to be more abundant in the renal pelvis than the renal cortex and medulla, and was mainly colocalized with the pan-neuronal marker PGP9.5 or the sensory nerve marker, the neurokinin-1 receptor. However, NMDA&zgr;1 mRNA was undetectable, suggesting that it might be synthesized outside the renal pelvis. Intrarenal arterial administration of the specific ion channel blocker (+)-MK-801, but not the inactive enantiomer (−)-MK-801, decreased urine output and sodium excretion. High doses of (+)-MK-801 also caused regional vasoconstriction in the renal cortex, as determined by laser-Doppler flowmetry. Intrapelvic administration of the NMDAR ligand D-serine caused a dose-dependent increase in substance P (SP) release and afferent renal nerve activity, but had no effect on arterial pressure. The D-serine–induced sensory activation and SP release were abrogated by (+)-MK-801, the SP receptor blocker L-703,606, or dorsal rhizotomy. Increasing intrapelvic pressure resulted in an increase in afferent renal nerve activity and a diuretic/natriuretic response. Interestingly, these effects were attenuated by prior administration of (+)-MK-801. These results indicate that NMDAR-positive sensory nerves are present in the renal pelvis and contribute to the renorenal reflex control of body fluid.

Erythropoietin alleviates post-ischemic injury of rat hearts by attenuating nitrosative stress

AIMS Nitrosative stress caused by ischemia contributes to poor functional recovery in hearts. A previous study showed that recombinant human erythropoietin (EPO) activates the Janus-tyrosine kinase 2/extracellular signal-regulated kinase (Jak2/ERK) pathway to protect myocardium against ischemia/reperfusion (IR) injury. However, it is not clear how pro-survival signals triggered by EPO affect the nitric oxide (NO) system in post-ischemic myocardial tissue. MAIN METHODS Isolated rat hearts were subjected to IR injury and changes in protein expression in the myocardium were evaluated by immunostaining. KEY FINDINGS Compared with untreated hearts, EPO-treated IR hearts showed significant improvements in contractility and reduced myocardial injury and infarction; this was associated with attenuated caspase-3 activation. Excess formation of NO metabolites and nitrotyrosine, which cause nitrosative stress, was markedly suppressed by EPO. The mechanism underlying EPO-mediated alleviation of nitrosative stress was related to an increase in arginase II expression and to the suppression of heat shock protein 90 (HSP90)-dependent upregulation of endothelial and inducible NO synthase (NOS). Myocardial EPO content was restored after EPO treatment, which in turn recruited signal transducer and activator of transcription (STAT) 3 protein and induced ERK signaling downstream of Jak2, which increased arginase II levels and suppressed HSP90 expression, respectively. Inhibition of STAT3 and ERK specifically reversed the effects of EPO on arginase II and HSP90 expression. SIGNIFICANCE These results indicate that EPO triggers the Jak2-STAT3/ERK pathway to restore the balance between arginase and NOS and, thus, reduces nitrosative stress. This may form the basis of myocardial protection following IR.

H2O2 generated by NADPH oxidase 4 contributes to transient receptor potential vanilloid 1 channel-mediated mechanosensation in the rat kidney

The presence of NADPH oxidase (Nox) in the kidney, especially Nox4, results in H2O2 production, which regulates Na(+) excretion and urine formation. Redox-sensitive transient receptor potential vanilloid 1 channels (TRPV1s) are distributed in mechanosensory fibers of the renal pelvis and monitor changes in intrapelvic pressure (IPP) during urine formation. The present study tested whether H2O2 derived from Nox4 affects TRPV1 function in renal sensory responses. Perfusion of H2O2 into the renal pelvis dose dependently increased afferent renal nerve activity and substance P (SP) release. These responses were attenuated by cotreatment with catalase or TRPV1 blockers. In single unit recordings, H2O2 activated afferent renal nerve activity in response to rising IPP but not high salt. Western blots revealed that Nox2 (gp91(phox)) and Nox4 are both present in the rat kidney, but Nox4 is abundant in the renal pelvis and originates from dorsal root ganglia. This distribution was associated with expression of the Nox4 regulators p22(phox) and polymerase δ-interacting protein 2. Coimmunoprecipitation experiments showed that IPP increases polymerase δ-interacting protein 2 association with Nox4 or p22(phox) in the renal pelvis. Interestingly, immunofluorescence labeling demonstrated that Nox4 colocalizes with TRPV1 in sensory fibers of the renal pelvis, indicating that H2O2 generated from Nox4 may affect TRPV1 activity. Stepwise increases in IPP and saline loading resulted in H2O2 and SP release, sensory activation, diuresis, and natriuresis. These effects, however, were remarkably attenuated by Nox inhibition. Overall, these results suggest that Nox4-positive fibers liberate H2O2 after mechanostimulation, thereby contributing to a renal sensory nerve-mediated diuretic/natriuretic response.