William Chau

Cardioprotective Effects of Selective Mitochondrial-Targeted Antioxidants in Myocardial Ischemia/Reperfusion (I/R) Injury

Cardioprotective Effects of Mitochondrial-Targeted Antioxidants in Myocardial Ischemia/Reperfusion (I/R) Injury Reactive oxygen species (ROS) generated during myocardial I/R contribute to post-reperfused cardiac contractile dysfunction. Damaged cardiomyocyte mitochondria are major sites of excess ROS generation during reperfusion. We hypothesized that reducing mitochondrial ROS formation should attenuate myocardial I/R injury and thereby improve function of isolated perfused rat hearts subjected to I(30min)/R(45min) compared to untreated I/R hearts. Mitoquinone (MitoQ, MW=579g/mol; complexed with cyclodextrin (MW=1135g/mol) to improve water solubility, total MW=1714g/mol), a coenzyme Q derivative, and SS-31 (Szeto-Schiller) peptide ((D-Arg)-Dmt-LysPhe-Amide, MW=639g/mol, Genemed Synthesis, Inc., San Antonio, TX), an alternating cationic-aromatic peptide, are selective mitochondrial ROS inhibitors which significantly improved post-reperfused cardiac function compared to untreated I/R controls in this study (p<0.05). MitoQ elicits antioxidant effects through the recycling of ubiquinone to ubiquinol, whereas SS-31 utilizes an antioxidant dimethyltyrosine residue. Improvement in postreperfused cardiac function by MitoQ or SS-31 was associated with a significant decrease in myocardial tissue infarct size compared to untreated I/R hearts (p<0.01). These results suggest mitochondrial-derived ROS are important contributors to I/R injury, and MitoQ or SS-31 when administered at reperfusion may potentially augment the benefits of angioplasty or

Apocynin Exerts Dose-Dependent Cardioprotective Effects by Attenuating Reactive Oxygen Species in Ischemia/Reperfusion

Ischemia/reperfusion results in cardiac contractile dysfunction and cell death partly due to increased reactive oxygen species and decreased endothelial-derived nitric oxide bioavailability. NADPH oxidase normally produces reactive oxygen species to facilitate cell signalling and differentiation; however, excessive release of such species following ischemia exacerbates cell death. Thus, administration of an NADPH oxidase inhibitor, apocynin, may preserve cardiac function and reduce infarct size following ischemia. Apocynin dose-dependently (40 μM, 400 μM and 1 mM) attenuated leukocyte superoxide release by 87 ± 7%. Apocynin was also given to isolated perfused hearts after ischemia, with infarct size decreasing to 39 ± 7% (40 μM), 28 ± 4% (400 μM; p < 0.01) and 29 ± 6% (1 mM; p < 0.01), versus the control’s 46 ± 2%. This decrease correlated with improved final post-reperfusion left ventricular end-diastolic pressure, which decreased from 60 ± 5% in control hearts to 56 ± 5% (40 μM), 43 ± 4% (400 μM; p < 0.01) and 48 ± 5% (1 mM; p < 0.05), compared to baseline. Functionally, apocynin (13.7 mg/kg, I.V.) significantly reduced H2O2 by nearly four-fold and increased endothelial-derived nitric oxide bioavailability by nearly four-fold during reperfusion compared to controls (p < 0.01), which was confirmed in in vivo rat hind limb ischemia/reperfusion models. These results suggest that apocynin attenuates ischemia/reperfusion-induced cardiac contractile dysfunction and infarct size by inhibiting reactive oxygen species release from NADPH oxidase.

Comparing the effectiveness of TAT and Myristoylation of gp91ds on Leukocyte Superoxide (SO) Release

SO release from leukocytes via NADPH oxidase activation contributes to oxidative stress under various diseases, such as ischemia/reperfusion (I/R) injury and vascular complications in diabetes. NADPH oxidase has seven isoforms with NOX2 being the predominant isoform of NADPH oxidase in polymorphonuclear leukocytes (PMNs). Activation of NOX2 requires the assembly of cytosolic subunits (p47, p40, p67, Rac) to plasma membrane subunits (gp91 and p22) [1]. NADPH oxidase is activated during I/R injury via cytokine receptor stimulation or chemotactic factor (N-formyl-L-methionyl-L-leucyl-L-phenylalanine (fMLP, MW= 438 g/mol) and utilizes molecular oxygen to produce SO [2] (Figure 1).

Protein Kinase C Beta II (PKC ßII) Peptide Inhibitor Exerts Cardioprotective Effects in Myocardial Ischemia/Reperfusion Injury

Coronary heart disease is the leading cause of death worldwide, and is primarily attributable to the detrimental effects of tissue infarct after an ischemic insult. The most effective therapeutic intervention for reducing infarct size associated with myocardial ischemia injury is timely and effective reperfusion of blood flow back to the ischemic heart tissue. However, the reperfusion of blood itself can induce additional cardiomyocyte death that can account for up to 50% of the final infarction size. Currently, there are no effective clinical pharmacologic treatments to limit myocardial ischemia/reperfusion (MI/R) injury in heart attack patients [1]. Reperfusion injury is initiated by decreased endothelialderived nitric oxide (NO) which occurs within 5 min of reperfusion [2], and may in part be explained by PKC II mediated activation of NADPH oxidase, which occurs upon cytokine release during MI/R [3]. PKC II activity is increased in animal models of MI/R and known to exacerbate tissue injury [4,5]. PKC II is known to increase NADPH oxidase activity in leukocytes, endothelial cells and cardiac myocytes via phox47 phosphorylation, and decrease endothelial NO synthase (eNOS) activity via phosphorylation of Thr 495 [6-8]. NADPH oxidase produces superoxide (SO) and quenches endothelial derived NO in cardiac endothelial cells. Moreover, PKC II phosphorylation of p66Shc at Ser 36 leads to increased mitochondrial reactive active oxygen species (ROS) production, opening of the mitochondrial permeability transition pore (MPTP), and pro-apoptotic factors leading to cell death and increased infarct size [9] (Figure 1 left). Therefore, using a pharmacologic agent that inhibits the rapid release of PKC II mediated ROS, would attenuate endothelial dysfunction and downstream pro-

Cardioprotective Effects of Cell Permeable NADPH oxidase inhibitors in Myocardial Ischemia/Reperfusion Injury

Cardioprotective Effects of Cell Permeable NADPH oxidase inhibitors in Myocardial Ischemia/Reperfusion (I/R) Injury Issachar Devine, Qian Chen, Regina Ondrasik, William Chau, Katelyn Navitsky, On Say Lau, Christopher W. Parker, Kyle D. Bartol, Brendan Casey, Robert Barsotti, Lindon H. Young Department of Pathology, Microbiology, Immunology & Forensic Medicine, Philadelphia College of Osteopathic Medicine