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.
In vivo assessment of corneal barrier function through non-invasive impedance measurements using a flexible probe
