Abstract 3366: Imaging of Peroxidase Activity in Injured Myocardium

Ischemic myocardial injury causes timed recruitment of neutrophils and monocyte/macrophages, which produce significant amounts of myeloperoxidase (MPO). MPO leads to the formation of reactive chlorinating species capable of oxidizing proteins. We developed a small molecule based MPO substrate for MRI, Gd-bis-5-HT-DPTA, which is first radicalized, and then oligomerized and covalently bound to matrix proteins, all leading to enhanced R1-relaxivity and delayed wash out kinetics. Mice were subjected to coronary artery ligation and injected with 0.3mmol/kg Gd-bis-5-HT-DPTA (or Gd-DTPA as control). We performed T1-weighted cardio-respiratory gated MRI 10–120min later, followed by immunoreactive staining for MPO. 3 mice each were studied at day 1, 2, 4, 8, and >1 month after MI. Subsequently, MPO tissue activity was determined with the guaiacol method. MPO activity peaked 2 days after MI (contrast-to-noise-ratio (CNR) day 1, 26+/−4; day 2, 39+/−10; day 4, 29+/−3), and tissue levels of MPO over time correlated well with probe activity in vivo (r2=0.65, p<0.01). CNR following Gd-DTPA peaked ten minutes after injection (10.5+/−0.2), and returned to pre-injection values at 60min. In contradistinction, following injection Gd-bis-5-HT-DPTA, CNR was higher and peaked later (p<0.05 vs. Gd-DTPA, arrows depict MI in figure ). Immunoreactive staining for MPO correlated well with enhancement (r2=0.92, p<0.05). Gd-bis-5-HT-DPTA facilitates in-vivo assessment of MPO activity in injured myocardium. This approach allows non-invasive probing of the inflammatory response to ischemia and has the potential to guide the development and application of novel cardioprotective therapies.

Neutrophil-mediated accumulation of 2-ClHDA during myocardial infarction: 2-ClHDA-mediated myocardial injury

The pathophysiological sequelae of myocardial infarction include neutrophil infiltration into the infarct zone that contributes to additional damage to viable tissue and removal of cellular debris from necrosed tissue. Reactive chlorinating species produced by myeloperoxidase amplify the oxidant capacity of activated neutrophils. Plasmalogens are a major phospholipid subclass of both endothelial cells and cardiac myocytes. Recent studies have shown that plasmalogens are targeted by neutrophil-derived reactive chlorinating species that lead to the production of α-chloro fatty aldehydes. Results herein demonstrate that the α-chloro fatty aldehyde 2-chlorohexadecanal (2-ClHDA) accumulates in rat hearts subjected to left anterior descending coronary artery occlusion. Myocardia from rats subjected to surgical infarction had increased 2-ClHDA and neutrophil infiltration levels compared with myocardia from rats subjected to sham surgery. Additionally, infarcted myocardia from rats rendered neutropenic by treatments with an anti-neutrophil antibody had diminished 2-ClHDA and neutrophil infiltration levels compared with infarcted myocardia from normopenic rats; 2-ClHDA was shown to elicit myocardial damage as determined by lactate dehydrogenase release in isolated perfused rat hearts. Additionally, 2-ClHDA treatment of hearts resulted in decreased heart rate and ventricular performance. Taken together, the present results demonstrate a novel neutrophil-dependent myeloperoxidase-based mechanism that results in 2-ClHDA production in response to regional myocardial infarction that may also contribute to cardiac dysfunction.