Tracking the inflammatory response in stroke in vivo by sensing the enzyme myeloperoxidase

Abstract

Inflammation can extend ischemic brain injury and adversely affect outcome in experimental animal models. A key difficulty in translating animal studies to humans is the lack of a definitive method to confirm and track inflammation in the brain in vivo. Myeloperoxidase (MPO), a key inflammatory enzyme secreted by activated neutrophils and macrophages/microglia, can generate highly reactive oxygen species to cause additional damage in cerebral ischemia. We report here that a functional, enzyme-activatable MRI agent can accurately track the oxidative activity of MPO noninvasively in stroke in living animals. We found that MPO is widely distributed in ischemic tissues, correlates positively with infarct size, and is detected even 3 weeks postinfarction. The peak level of MPO activity, determined by activation of the MPO-sensing agent in vivo and confirmed by MPO activity and quantitative RT-PCR assays, occurred on day 3 after ischemia. Both neutrophils and macrophages/microglia contribute to secrete MPO in the ischemic brain, although neutrophils peak earlier (days 1-3) whereas macrophages/microglia are most abundant later (days 3-7). In contrast to the conventional MRI agent diethylenetriaminepentatacetate gadolinium, which reports blood-brain barrier disruption, MPO imaging is able to additionally track MPO activity and confirm inflammation on the molecular level in vivo, information that was previously only possible to obtain on ex vivo brain sections and impossible to assess in living human patients. Our findings could allow efficient noninvasive serial screening of therapies targeting inflammation and the use of MPO imaging as an imaging biomarker to risk-stratify patients.inflammation ͉ ischemia ͉ molecular imaging ͉ MRI ͉ brain

G-CSF Induces Membrane Expression of a Myeloperoxidase Glycovariant that Operates as an E-selectin Ligand on Human Myeloid Cells

“…Our in vitro studies of myeloid cells coincubated with HUVECs indicate that G-CSFtreated myeloid cells are angiotoxic to E-selectin-expressing endothelial cells; this effect is ameliorated by interruption of E-selectin receptor/ligand interactions and by inhibition of MPO activity. Although further studies are necessary to directly assess the role(s) of MPO-EL in vasculopathy, these findings offer novel perspectives on the association between MPO expression and vascular injury: in vivo, MPO-EL could serve as a key effector of sickle cell crises (28), myocardial infarction and coronary artery disease (29,30), atherosclerosis (31,32), and stroke (33), conditions which have all been linked to MPO. Indeed, G-CSF administration can trigger angina and myocardial infarction (34,35).…”

The roles of myeloperoxidase in coronary artery disease and its potential implication in plaque rupture

“…In vitro studies suggest that unlike MPO, eosinophil peroxidase is inefficient in oxidizing, and hence 'activating' MPO-Gd [162]. Moreover, in vivo studies employing MPO-deficient mice and models of MI and stroke showed no agent activation [160,163], indicating that MPO-Gd is a relatively specific imaging agent for assessment of MPO activity. Furthermore, MPO-Gd is highly sensitive and able to detect MPO concentrations as low as 0.005 U/mg, which is substantially lower than levels present in many pathological conditions (e.g.…”

Immunopathogenetic Aspects of Ischemic Stroke

“…Рекрутирование циркулирующих моноцитов в зону инфаркта и пенумбры в модели инсульта происходит через 24 часа после окклюзии арте-рии, и моноциты детектируются в зоне повреж-дения в течение 14 дней с пиком на 3-7 сутки [11]. Первоначально считалось, что рекрутируемые моноциты/макрофаги усиливают ишемическое повреждение и способствуют прогрессии вто-ричных повреждений [26].…”