Biomedical subjects

Gabor Varbiro

Publications and source records attributed to Gabor Varbiro.

7 recordsLinked to original sources

PubMed2006

Induction of necrotic cell death and mitochondrial permeabilization by heme binding protein 2/SOUL.

We found that heme-binding protein 2/SOUL sensitised NIH3T3 cells to cell death induced by A23187 and etoposide, but it did not affect reactive oxygen species formation. In the presence of sub-threshold calcium, recombinant SOUL provoked mitochondrial permeability transition (mPT) in vitro that was inhibited by cyclosporine A (CsA). This effect was verified in vivo by monitoring the dissipation of mitochondrial membrane potential. Flow cytometry analysis showed that SOUL promoted necrotic death in A23187 and etoposide treated cells, which effect was prevented by CsA. These data suggest that besides its heme-binding properties SOUL promotes necrotic cell death by inducing mPT.

Animals↗

PubMed2006

A novel SOD-mimetic permeability transition inhibitor agent protects ischemic heart by inhibiting both apoptotic and necrotic cell death.

In ischemia-reperfusion injuries, elevated calcium and reactive oxygen species (ROS) induce mitochondrial permeability transition (mPT), which plays a pivotal role in mediating damages and cell death. Inhibition of mPT decreases necrotic cell death; however, during reperfusion, the continuous production of ROS may contribute to the temporary opening of the pore and thus the onset of the delayed apoptotic cell death. Based on amiodarone structure, we developed the first SOD-mimetic mPT inhibitor (HO-3538) that can eliminate ROS in the microenvironment of the permeability pore. In isolated mitochondria, HO-3538 inhibited mPT and the release of proapoptotic mitochondrial proteins. It had a ROS scavenging effect and antiapoptotic effect in a cardiomyocyte line and it diminished release of mitochondrial proapoptotic proteins. Furthermore, HO-3538 significantly enhanced the recovery of mitochondrial energy metabolism and functional cardiac parameters; decreased infarct size, lipid peroxidation, and protein oxidation; and suppressed necrotic as well as apoptotic cell death pathways in Langendorff-perfused hearts. In these respects it was somewhat superior to its two constituents, amiodarone and a pyrrol-derivative free radical scavenger. These data suggest that the SOD-mimetic mPT inhibitors are ideal candidates for drug development for the alleviation of postinfarct myocardial injuries.

Amiodarone↗

PubMed2005

Pivotal role of Akt activation in mitochondrial protection and cell survival by poly(ADP-ribose)polymerase-1 inhibition in oxidative stress.

According to the classical view, the cytoprotective effect of inhibitors of poly(ADP-ribose)polymerase (PARP) in oxidative stress was based on the prevention of NAD+ and ATP depletion, thus the attenuation of necrosis. Our previous data on PARP inhibitors in an inflammatory model suggested that PARP-catalyzed ADP-ribosylations may affect signaling pathways, which can play a significant role in cell survival. To clarify the molecular mechanism of cytoprotection, PARP activity was inhibited pharmacologically by suppressing PARP-1 expression by a small interfering RNA (siRNA) technique or by transdominantly expressing the N-terminal DNA-binding domain of PARP-1 (PARP-DBD) in cultured cells. Cell survival, activation of the phosphatidylinositol 3-kinase (PI3-kinase)/Akt system, and the preservation of mitochondrial membrane potential were studied in hydrogen peroxide-treated WRL-68 cells. Our data showed that suppression of the single-stranded DNA break-induced PARP-1 activation by pharmacological inhibitor, siRNA, or by the transdominant expression of PARP-DBD protected cells from oxidative stress and induced the phosphorylation and activation of Akt. Furthermore, prevention of Akt activation by inhibiting PI3-kinase counteracted the cytoprotective effect of PARP inhibition. Microscopy data showed that PARP inhibition-induced Akt activation was responsible for protection of mitochondria in oxidative stress because PI3-kinase inhibitors diminished the protective effect of PARP inhibition. Similarly, Src kinase inhibitors, which decrease Akt phosphorylation, also counteracted the protection of mitochondrial membrane potential supporting the pivotal role of Akt in cytoprotection. These data together with the finding that PARP inhibition in the absence of oxidative stress induced the phosphorylation and activation of Akt indicate that PARP inhibition-induced Akt activation is dominantly responsible for the cytoprotection in oxidative stress.

Acetylcysteine↗

PubMed2004

Regulation of kinase cascades and transcription factors by a poly(ADP-ribose) polymerase-1 inhibitor, 4-hydroxyquinazoline, in lipopolysaccharide-induced inflammation in mice.

Activation of the nuclear enzyme poly(ADP-ribose) polymerase (PARP) is involved in numerous pathophysiological conditions. Because PARP-1 knockout mice are resistant to endotoxin-induced shock and inhibitors of the enzyme were reported to have similar beneficial properties, we investigated the effect of 4-hydroxyquinazoline (4-HQN), a potent PARP-1 inhibitor, on the modulation of kinase cascades and the regulation of transcription factors in a rodent septic shock model. T2-weighted magnetic resonance imaging showed the pattern of anatomical localization of the inflammatory response in bacterial lipopolysaccharide (LPS)-treated mice and the anti-inflammatory effect of the PARP-1 inhibitor. We have found that 4-HQN activated the phosphatidylinositol 3 (PI3)-kinase/Akt pathway in lung, liver, and spleen, and down-regulated two elements of the MAP kinase system. Namely, it dramatically attenuated the activation of the LPS-induced extracellular signal-regulated kinase (ERK)1/2 and p38 mitogen-activated protein (MAP) kinase in a tissue-specific manner. Furthermore, phosphorylation of p90RSK, a downstream target of ERK1/2, showed a similar pattern of down-regulation as did the phosphorylation of ERK1/2 and p38 after LPS and 4-HQN treatment. As a consequence of the aforementioned effects on the kinase pathways, 4-HQN decreased the activation of transcription factor nuclear factor-kappaB (NF-kappaB) and activator protein 1 (AP-1) in LPS-induced endotoxic shock. Our results provide evidence for the first time that the beneficial effects of PARP inhibition in endotoxic shock, such as attenuation of NF-kappaB- and AP-1 transcription factor activation, are mediated, at least partially, through the regulation of the PI3-kinase/Akt pathway and MAP kinase cascades.

Animals↗

PubMed2003

Protective effect of amiodarone but not N-desethylamiodarone on postischemic hearts through the inhibition of mitochondrial permeability transition.

Amiodarone is a widely used and potent antiarrhythmic agent that is metabolized to desethylamiodarone. Both amiodarone and its metabolite possess antiarrhythmic effect, and both compounds can contribute to toxic side effects. Here, we compare the effect of amiodarone and desethylamiodarone on mitochondrial energy metabolism, membrane potential, and permeability transition and on mitochondria-related apoptotic events. Amiodarone but not desethylamiodarone protects the mitochondrial energy metabolism of the perfused heart during ischemia in perfused hearts. At low concentrations, amiodarone stimulated state 4 respiration due to an uncoupling effect, inhibited the Ca2+-induced mitochondrial swelling, whereas it dissipated the mitochondrial membrane potential (Deltapsi), and prevented the ischemia-reperfusion-induced release of apoptosis-inducing factor (AIF). At higher concentrations, amiodarone inhibited the mitochondrial respiration and simulated a cyclosporin A (CsA)-independent mitochondrial swelling. In contrast to these, desethylamiodarone did not stimulate state 4 respiration, did not inhibit the Ca2+-induced mitochondrial permeability transition, did not induce the collapse of Deltapsi in low concentrations, and did not prevent the nuclear translocation of AIF in perfused rat hearts, but it induced a CsA-independent mitochondrial swelling at higher concentration, like amiodarone. That is, desethylamiodarone lacks the protective effect of amiodarone seen at low concentrations, such as the inhibition of calcium-induced mitochondrial permeability transition and inhibition of the nuclear translocation of the proapoptotic AIF. On the other hand, both amiodarone and desethylamiodarone at higher concentration induced a CsA-independent mitochondrial swelling, resulting in apoptotic death that explains their extracardiac toxic effect.

Amiodarone↗

PubMed2003

Decrease of the inflammatory response and induction of the Akt/protein kinase B pathway by poly-(ADP-ribose) polymerase 1 inhibitor in endotoxin-induced septic shock.

The lack of efficacy of anti-inflammatory drugs, anti-coagulants, anti-oxidants, etc. in critically ill patients has shifted interest towards developing alternative treatments. Since inhibitors of the nuclear enzyme poly-(ADP-ribose) polymerase (PARP) were found to be beneficial in many pathophysiological conditions associated with oxidative stress and PARP-1 knock-out mice proved to be resistant to bacterial lipopolysaccharide (LPS)-induced septic shock, PARP inhibitors are candidates for such a role. In this study, the mechanism of the protective effect of a potent PARP-1 inhibitor, PJ34 was studied in LPS-induced (20mg/kg, i.p.) septic shock in mice. We demonstrated a significant inflammatory response by magnetic resonance imaging in the dorsal subcutaneous region, in the abdominal regions around the kidneys and in the inter-intestinal cavities. We have found necrotic and apoptotic histological changes as well as obstructed blood vessels in the liver and small intestine. Additionally, we have detected elevated tumor necrosis factor-alpha levels in the serum and nuclear factor kappa B activation in liver of LPS-treated mice. Pre-treating the animals with PJ34 (10mg/kg, i.p.), before the LPS challenge, besides rescuing the animals from LPS-induced death, attenuated all these changes presumably by activating the phosphatidylinositol 3-kinase-Akt/protein kinase B cytoprotective pathway.

Animals↗

PubMed2003

Concentration dependent mitochondrial effect of amiodarone.

Although, the antiarrhythmic effect of amiodarone is well characterized, its effect on post-ischemic heart and cardiomyocytes, as well as the mechanism of its toxicity on extracardiac tissues is still poorly understood. In this study, we analyzed energy metabolism in situ during ischemia-reperfusion in Langendorff-perfused heart model by measuring the high-energy phosphate metabolites using 31P NMR spectroscopy. The toxicity of amiodarone on cardiomyocytes and cell lines of extracardiac origin, as well as direct effect of the drug on mitochondrial functions in isolated mitochondria was also analyzed. Amiodarone, when was present at low concentrations and predominantly in membrane bound form, protected heart and mitochondrial energy metabolism from ischemia-reperfusion-induced damages in Langendorff-perfused heart model. Toxicity of the drug was significantly higher on hepatocytes and pancreatic cells than on cardiomyocytes. In isolated mitochondria, amiodarone did not induce reactive oxygen species formation, while it affected mitochondrial permeability transition in a concentration dependent way. Up to the concentration of 10 microM, the drug considerably inhibited Ca(2+)-induced permeability transition, while at higher concentrations it induced a cyclosporin A independent permeability transition of its own. At concentrations where it inhibited the Ca(2+)-induced permeability transition (IC(50)=3.9+/-0.8 microM), it did not affect, between 6 and 30 microM it uncoupled, while, at higher concentrations it inhibited the respiratory chain. Thus, the concentration dependent nature of amiodarone's effect on permeability transition together with the different sensitivities of the tissues toward amiodarone can be involved in the beneficial cardiac and the simultaneous toxic extracardiac effects of the drug.

Amiodarone↗