Apomorphine-induced myocardial protection is due to antioxidant and not adrenergic/dopaminergic effects

Discovery of Novel Small-Molecule Inducers of Heme Oxygenase-1 That Protect Human iPSC-Derived Cardiomyocytes from Oxidative Stress

Oxidative injury to cardiomyocytes plays a critical role in cardiac pathogenesis following myocardial infarction. Transplantation of stem cell-derived cardiomyocytes has recently progressed as a novel treatment to repair damaged cardiac tissue but its efficacy has been limited by poor survival of transplanted cells owing to oxidative stress in the post-transplantation environment. Identification of small molecules that activate cardioprotective pathways to prevent oxidative damage and increase survival of stem cells post-transplantation is therefore of great interest for improving the efficacy of stem cell therapies. This report describes a chemical biology phenotypic screening approach to identify and validate small molecules that protect human-induced pluripotent stem cell cardiomyocytes (hiPSC-CMs) from oxidative stress. A luminescence-based high-throughput assay for cell viability was used to screen a diverse collection of 48,640 small molecules for protection of hiPSC-CMs from peroxide-induced cell death. Cardioprotective activity of "hit" compounds was confirmed using impedance-based detection of cardiomyocyte monolayer integrity and contractile function. Structure-activity relationship studies led to the identification of a potent class of compounds with 4-(pyridine-2-yl)thiazole scaffold. Examination of gene expression in hiPSC-CMs revealed that the hit compound, designated cardioprotectant 312 (CP-312), induces robust upregulation of heme oxygenase-1, a marker of the antioxidant response network that has been strongly correlated with protection of cardiomyocytes from oxidative stress. CP-312 therefore represents a novel chemical scaffold identified by phenotypic high-throughput screening using hiPSC-CMs that activates the antioxidant defense response and may lead to improved pharmacological cardioprotective therapies.

Contribution of calpains to myocardial ischaemia/reperfusion injury

Loss of calcium (Ca(2+)) homeostasis contributes through different mechanisms to cell death occurring during the first minutes of reperfusion. One of them is an unregulated activation of a variety of Ca(2+)-dependent enzymes, including the non-lysosomal cysteine proteases known as calpains. This review analyses the involvement of the calpain family in reperfusion-induced cardiomyocyte death. Calpains remain inactive before reperfusion due to the acidic pHi and increased ionic strength in the ischaemic myocardium. However, inappropriate calpain activation occurs during myocardial reperfusion, and subsequent proteolysis of a wide variety of proteins contributes to the development of contractile dysfunction and necrotic cell death by different mechanisms, including increased membrane fragility, further impairment of Na(+) and Ca(2+) handling, and mitochondrial dysfunction. Recent studies demonstrating that calpain inhibition contributes to the cardioprotective effects of preconditioning and postconditioning, and the beneficial effects obtained with new and more selective calpain inhibitors added at the onset of reperfusion, point to the potential cardioprotective value of therapeutic strategies designed to prevent calpain activation.

Activation of dopamine D4 receptors is protective against hypoxia/reoxygenation-induced cell death in HT22 cells

Several reports have shown that some dopamine receptor ligands modulate the ischemia-reperfusion injury in animal models; however, its underling mechanisms are still unclear. In this study, we sought to establish an in vitro experimental model of hypoxia/reoxygenation (H/R) using HT22 cells that originated from mouse hippocampal neurons and to examine protective the effect of dopamine-receptor ligands against H/R-induced cell injury. The treatment with hypoxia for 18 h followed by reoxygenation for 6 h induced the elevation of intracellular reactive oxygen species (ROS) and reduction of mitochondrial membrane potential; however, lactate dehydrogenase (LDH) release was not changed at this time point. LDH release was increased after reoxygenation for 18 h and longer, and this increase in LDH release was suppressed by dopamine receptor agonists such as apomorphine and apocodeine. The suppressive effects of these agonists were reversibly inhibited by L750667, a D(4)-receptor antagonist but not by D(2)- or D(3)-receptor antagonists. In addition, PD168077, a selective dopamine D(4)-receptor agonist, also protected against H/R-induced cell death. These results suggest that H/R causes oxidative stress-induced cell death and that the activation of dopamine D(4) receptors protects against H/R-induced cell death in HT22 cells.

Molecular Mechanism of Neuroprotective Drugs against Oxidative Stress-Induced Neuronal Cell Death

NF-E2-related factor-2 (Nrf2), a basic leucine zipper transcription factor, is involved in the expression of numerous detoxifying and antioxidant genes via the antioxidant response element (ARE). Keap1, a cytoplasmic protein, sequesters Nrf2 in the cytoplasm under normal conditions. Various stimuli, including electrophiles and oxidative stress, liberate Nrf2 from Keap1, allowing Nrf2 to translocate into the nucleus and to bind to the ARE. Recently, there is increasing evidence that compounds that stimulate the activation of the Nrf2-ARE pathway may become useful therapeutic drugs for neurodegenerative diseases associated with oxidative stress. Apomorphine (Apo), a dopamine D(1)/D(2) receptor agonist, is used for clinical therapy of Parkinson's disease. On the other hand, Apo is a potent radical scavenger and has protective effects on oxidative stress-induced cell death. We previously reported that pretreatment of human neuroblastoma SH-SY5Y cells with Apo enhanced the protective effects. In addition, we have recently demonstrated that Apo stimulates the translocation of Nrf2 into the nucleus and the transactivation of the ARE. Our findings suggest that not only the function as a radical scavenger, but also the function as an Nrf2-ARE pathway activator may be involved in the neuroprotective effects of Apo on oxidative stress-induced neuronal cell death. In this review, our recent studies on the mechanism underlying Apo-induced neuroprotection are summarized.