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Abstract: Myocardial oxidative stress and Ca2+ overload induced by ischemia-reperfusion may be involved in the development and progression of myocardial dysfunction in heart failure. Xanthine oxidase, which is capable of producing reactive oxygen species, is considered as a culprit regarding ischemia-reperfusion injury of cardiomyocytes. Even though inhibition of xanthine oxidase by allopurinol in failing hearts improves cardiac performance, the regulatory mechanisms are not known in detail. We therefore hypothesized that allopurinol may prevent the xanthine oxidase-induced reactive oxygen species production and Ca2+ overload, leading to decreased calcium-responsive signaling in myocardial dysfunction. Allopurinol reversed the increased xanthine oxidase activity in ischemia-reperfusion injury of neonatal rat hearts. Hypoxia-reoxygenation injury, which simulates ischemia-reperfusion injury, of neonatal rat cardiomyocytes resulted in activation of xanthine oxidase relative to that of the control, indicating that intracellular xanthine oxidase exists in neonatal rat cardiomyocytes and that hypoxia-reoxygenation induces xanthine oxidase activity. Allopurinol (10 μM) treatment suppressed xanthine oxidase activity induced by hypoxia-reoxygenation injury and the production of reactive oxygen species. Allopurinol also decreased the concentration of intracellular Ca2+ increased by enhanced xanthine oxidase activity. Enhanced xanthine oxidase activity resulted in decreased expression of protein kinase C and sarcoendoplasmic reticulum calcium ATPase and increased the phosphorylation of extracellular signal-regulated protein kinase and p38 kinase. Xanthine oxidase activity was increased in both ischemia-reperfusion-injured rat hearts and hypoxia-reoxygenation-injured cardiomyocytes, leading to reactive oxygen species production and intracellular Ca2+ overload through mechanisms involving p38 kinase and extracellular signal-regulated protein kinase (ERK) via sarcoendoplasmic reticulum calcium ATPase (SERCA) and protein kinase C (PKC). Xanthine oxidase inhibition with allopurinol modulates reactive oxygen species production and intracellular Ca2+ overload in hypoxia-reoxygenation-injured neonatal rat cardiomyocytes. [Copyright &y& Elsevier]

Reactive oxygen species-mediated cellular injury is involved in the pathogenesis of many diseases, including those affecting the cardiovascular system, such as myocardial ischemia–reperfusion injury, inflammation, and atheroscleosis. Raxofelast (IRFI-016; (±)-5-acetoxy-2, 3-dihydro-4, 6, 7-trimethyl-2-benzofuran-acetic acid) was designed with the aim of maximizing the antioxidant potency of phenols chemically related to vitamin E. The antioxidant activity of raxofelast has been convincingly demonstrated in several in vitro studies and in various models of ischemia–reperfusion injury. In this study, the antiproliferative effects of raxofelast were investigated to determine whether transduction signals and protooncogenes are affected in H2O2-stimulated rat aortic smooth muscle cells. In a tetrazolium-based colorimetric assay, the proliferation of rat aortic smooth muscle cells was increased by 3-fold in 0.1% fetal bovine serum/Dulbecco''s modified Eagle''s medium (DMEM) containing 500 μM H2O2, indicating that exogenous 500 μM H2O2 was a growth stimulator of rat aortic smooth muscle cells. Exogenous H2O2 significantly activated extracellular signal-regulated kinases (ERKs) activity within 30 min and raxofelast inhibited the ERKs activation dose dependently in 500 μM H2O2-stimulated rat aortic smooth muscle cells (IC50: 200 μM). Raxofelast reduced the intracellular reactive oxygen species generated by exogenous H2O2 in a dose-dependent manner. In 500 μM H2O2-stimulated rat aortic smooth muscle cells, raxofelast dramatically attenuated the activation of mitogen-activating protein kinase (MAPK)/ERK kinase 1, 2 (MEK1,2) and protein kinase C (PKC) without affecting Ras expression. Induction of c-myc mRNA was significantly reduced dose dependently up to 100 μM by raxofelast in concentrations. These data indicate that the antiproliferative effects of raxofelast in H2O2-stimulated rat aortic smooth muscle cells may involve the suppression of intracellular reactive oxygen species formation and the inhibition of ERKs by inactivation through PKC and MEK1,2 and down-regulation of c-myc expression, regardless of Ras activation. [Copyright &y& Elsevier]

In cardiac myocytes, stimulation of α1-adrenoceptor (AR) leads to a hypertrophic phenotype. The Gh protein (transglutaminase II, TGII) is tissue type transglutaminase and transmits the α1B-adrenoceptor signal with GTPase activity. Recently, it has been shown that the calreticulin (CRT) down-regulates both GTP binding and transglutaminase activities of TGII. To elucidate whether Gh mediates norepinephrine-stimulated intracellular signal transductions leading to activation of extracellular signal-regulated kinases (ERKs) and neonatal rat cardiomyocyte hypertrophy, we examined the effects of Gh on the activation of ERKs and inhibitory effects of CRT on α1-adrenoceptor/Gh signaling. In neonatal rat cardiomyocytes, norepinephrine-induced ERKs activation was inhibited by an α1-adrenoceptor blocker (prazosin), but not by an β-adrenoceptor blocker (propranolol). Overexpression of the Gh protein stimulated norepinephrine-induced ERKs activation, which was inhibited by α-adrenoceptor blocker (prazosin). Co-overexpression of Gh and CRT abolished norepinephrine-induced ERKs activation. Taken together, norepinephrine induces hypertrophy in neonatal rat cardiomyocytes through α1-AR stimulation and Gh is partly involved in norepinephrine-induced MEK1,2/ERKs activation. Activation of Gh-mediated MEK1,2/ERKs was completely inhibited by CRT. [Copyright &y& Elsevier]