György Seprényi

Ionic mechanisms limiting cardiac repolarization reserve in humans compared to dogs.

•  Cardiac repolarization, through which heart‐cells return to their resting state after having fired, is a delicate process, susceptible to disruption by common drugs and clinical conditions. •  Animal models, particularly the dog, are often used to study repolarization properties and responses to drugs, with the assumption that such findings are relevant to humans. However, little is known about the applicability of findings in animals to man. •  Here, we studied the contribution of various ion‐currents to cardiac repolarization in canine and human ventricle. •  Humans showed much greater repolarization‐impairing effects of drugs blocking the rapid delayed‐rectifier current IKr than dogs, because of lower repolarization‐reserve contributions from two other important repolarizing currents (the inward‐rectifier IK1 and slow delayed‐rectifier IKs). •  Our findings clarify differences in cardiac repolarization‐processes among species, highlighting the importance of caution when extrapolating results from animal models to man.

Na+/Ca2+ exchanger inhibition exerts a positive inotropic effect in the rat heart, but fails to influence the contractility of the rabbit heart

Background and purpose: The Na+/Ca2+ exchanger (NCX) may play a key role in myocardial contractility. The operation of the NCX is affected by the action potential (AP) configuration and the intracellular Na+ concentration. This study examined the effect of selective NCX inhibition by 0.1, 0.3 and 1.0 μM SEA0400 on the myocardial contractility in the setting of different AP configurations and different intracellular Na+ concentrations in rabbit and rat hearts.

Restraint Stress-Induced Morphological Changes at the Blood-Brain Barrier in Adult Rats

Stress is well-known to contribute to the development of both neurological and psychiatric diseases. While the role of the blood-brain barrier is increasingly recognized in the development of neurodegenerative disorders, such as Alzheimers disease, dysfunction of the blood-brain barrier has been linked to stress-related psychiatric diseases only recently. In the present study the effects of restraint stress with different duration (1, 3, and 21 days) were investigated on the morphology of the blood-brain barrier in male adult Wistar rats. Frontal cortex and hippocampus sections were immunostained for markers of brain endothelial cells (claudin-5, occluding, and glucose transporter-1) and astroglia (GFAP). Staining pattern and intensity were visualized by confocal microscopy and evaluated by several types of image analysis. The ultrastructure of brain capillaries was investigated by electron microscopy. Morphological changes and intensity alterations in brain endothelial tight junction proteins claudin-5 and occludin were induced by stress. Following restraint stress significant increases in the fluorescence intensity of glucose transporter-1 were detected in brain endothelial cells in the frontal cortex and hippocampus. Significant reductions in GFAP fluorescence intensity were observed in the frontal cortex in all stress groups. As observed by electron microscopy, 1-day acute stress induced morphological changes indicating damage in capillary endothelial cells in both brain regions. After 21 days of stress thicker and irregular capillary basal membranes in the hippocampus and edema in astrocytes in both regions were seen. These findings indicate that stress exerts time-dependent changes in the staining pattern of tight junction proteins occludin, claudin-5, and glucose transporter-1 at the level of brain capillaries and in the ultrastructure of brain endothelial cells and astroglial endfeet, which may contribute to neurodegenerative processes, cognitive and behavioral dysfunctions.

Are Granulocytes the Main Effector Cells of Natural Cytotoxicity in Chickens

Purified peripheral blood granulocytes from chicken were tested for cytotoxic activity against two types of virus-transformed chicken cell line, LSCC-H32 and LSCC-RP9. Strong cytotoxicity could be demonstrated, as measured in a 4-hr 51Cr-release assay, especially against the fibroblastoid LSCC-H32 cells. The degree of cytotoxicity was dependent on the E:T ratio. Normal CEF cells were completely resistant to the cytotoxicity. No cytotoxicity of human granulocytes could be observed against a variety of adherent and non-adherent target cells, as measured by the same microcytotoxicity technique. The priority of granulocytes in the natural cytotoxicity in the avian system is, therefore, suggested.

Modulation of gap junctions by nitric oxide contributes to the anti-arrhythmic effect of sodium nitroprusside?

Background and purpose:  Nitric oxide (NO) donors provide a preconditioning‐like anti‐arrhythmic protection in the anaesthetized dog. As NO may modulate gap junction (GJ) function, the present study investigated whether this anti‐arrhythmic effect is due to a modification of GJs by NO, derived from the NO donor sodium nitroprusside (SNP).

A novel transgenic rabbit model with reduced repolarization reserve: long QT syndrome caused by a dominant-negative mutation of the KCNE1 gene

The reliable assessment of proarrhythmic risk of compounds under development remains an elusive goal. Current safety guidelines focus on the effects of blocking the KCNH2/HERG ion channel‐in tissues and animals with intact repolarization. Novel models with better predictive value are needed that more closely reflect the conditions in patients with cardiac remodelling and reduced repolarization reserve.

The role of nitric oxide, superoxide and peroxynitrite in the anti‐arrhythmic effects of preconditioning and peroxynitrite infusion in anaesthetized dogs

Background and purpose:  Both ischaemia preconditioning (PC) and the intracoronary infusion of peroxynitrite (PN) suppress ischaemia and reperfusion (I/R)‐induced arrhythmias and the generation of nitrotyrosine (NT, a marker of PN). However, it is still unclear whether this latter effect is due to a reduction in nitric oxide (NO) or superoxide (O2‐) production.

IL-17A and IL-17F induce autophagy in RAW 264.7 macrophages

Autophagy is an important cellular catabolic process for the lysosomal degradation of cytoplasmic organelles, proteins and microorganisms. The autophagic process is intertwined with the immune response: autophagy regulates both innate and adaptive immunity, conversely, cytokines produced during the course of the immune response modulate various functions of the autophagic cascade. The IL-17 family member cytokines play a pivotal role in immune protection against extra- and intracellular bacterial pathogens. Since the effects of IL-17A and IL-17F on autophagy have not yet been reported, we have evaluated the autophagic activity in the RAW 264.7 cell line treated with either IL-17A or IL-17F. Both IL-17A and IL-17F proved to promote microtubule-associated protein 1 light chain 3 B-II (LC3B-II) accumulation, enhance the autophagic flux, facilitate the intracellular redistribution of LC3B, increase both the average number and the size of autophagosomes per cell, and foster the formation of acidic vesicular organelles. IL-17F was considerably more efficient than IL-17A in promoting the autophagic process. Further experiments to determine the potential effect of IL-17-induced autophagy on the antibacterial activity of RAW macrophages revealed that IL-17F significantly decreased the intracellular counts of Mycobacterium terrae, while the colony-forming unit values remained comparable in the IL-17A-treated cells and the control cultures. In conclusion, these results demonstrate that IL-17A and IL-17F are capable of inducing autophagy in macrophages, and thereby contribute to the elimination of Mycobacterium terrae. These data may bear on the pathogenesis of infections caused by Mycobacterium terrae, as IL-17 plays a pivotal role in the immune response to mycobacteria. IL-17-mediated activation of autophagy may also be implicated in various infections and other pathological conditions.

Induction of human defensins by intestinal Caco-2 cells after interactions with opportunistic Candida species.

In this study we investigated the effects of Candida albicans, Candida krusei, Candida tropicalis and Candida parapsilosis on human beta-defensin 2 (HBD-2) production in Caco-2 intestinal cell line, and the production of alpha-defensins (human neutrophil peptides, HNP 1-3) in peripheral blood. Opportunistic pathogen yeasts can modulate the host immune function by inducing defensins, the natural antimicrobial peptides. Here we show that Candida spp. stimulated HBD-2 expression in and release from Caco-2 cells, with C. albicans inducing the highest levels of HBD-2. Similarly, HNP 1-3 secretion was significantly increased in whole blood after exposure to Candida yeast cells, with C. albicans producing the greatest effect. Our investigations underscore the important role of beta and alpha defensins produced by intestinal epithelial cells locally and neutrophils systemically in the antifungal defense against Candida.

High Mobility Group Box 1 Protein Induction by Mycobacterium Bovis BCG

High mobility group box 1 protein (HMGB1), a nuclear protein, is a critical cytokine that mediates the response to infection, injury, and inflammation. The aim of our study was to elaborate a reliable in vitro model to investigate whether Mycobacterium bovis BCG is able to induce HMGB1 secretion from the monocytic U-937 cells. Western blot technique was applied for the detection of HMGB1 from supernatants of cells, following induction with Mycobacterium bovis BCG. Densitometric analysis revealed higher concentrations of HMGB1 in cell supernatants stimulated with BCG than in the supernatants of the control, nonstimulated cells. Further quantitation of the secreted HMGB1 was performed by ELISA. The BCG strain resulted in a higher amount of secreted HMGB1 (450 ± 44 ng/mL) than that of LPS (84 ± 12 ng/mL) or Staphylococcus aureus (150 ± 14 ng/mL). BCG and Phorbol −12-myristate −13 acetate (PMA), added together, resulted in the highest HMGB1 secretion (645 ± 125 ng/mL). The translocation of the HMGB1 towards the cytoplasm following infection of cells with BCG was demonstrated by immunofluorescence examinations. Conclusion: Our pilot experiments draw attention to the HMGB1 inducing ability of Mycobacterium bovis. Assesment of the pathophysiological role of this late cytokine in mycobacterial infections demands further in vitro and in vivo examinations.