A molecular MRI probe to detect treatment of cardiac apoptosis in vivo

Abstract

Cell death by apoptosis is critical in myocardial diseases, and noninvasive detection of early, reversible apoptosis might be useful clinically. Exogenous Annexin-V (ANX) protein binds membrane phosphatidylserine, which is externalized in early apoptosis. A molecular MRI probe was constructed with superparamagnetic iron oxide (SPIO) conjugated to recombinant human ANX (ANX-SPIO). Apoptosis was induced with doxorubicin, a cardiotoxic cancer drug, in culture in neonatal rat ventricular myocytes, cardiac fibroblasts, and mesenchymal stem cells, and in vivo in the mouse heart. ANX-SPIO was validated using T2*-weighted 3T MRI. ANX-SPIO produced T2* signal loss, reflecting iron content, that correlated highly with independent apoptosis markers; bound with high affinity to apoptotic myocytes by competition assay (Ki 69 nM); detected apoptosis in culture much earlier than did TUNEL stain; and revealed fibroblast resistance to apoptosis. With apoptosis in vivo, ANX-SPIO produced diffuse myocardial T2* signal loss that correlated with increased iron stain and caspase activity. Treatment with an alpha-1-adrenergic agonist in vivo reversed apoptosis and eliminated the ANX-SPIO MRI signal. It is concluded that cardiac MRI of ANX-SPIO detects early, nonischemic cardiac apoptosis in culture and in vivo, and can identify reversibly injured cardiac cells in diseased hearts, when treatment is still possible. Magn Reson Med 66:1152-1162,

Cardiac Alpha1-Adrenergic Receptors: Novel Aspects of Expression, Signaling Mechanisms, Physiologic Function, and Clinical Importance

“…However, pharmacology and knockouts argue against the results seen in certain cardiac transgenics. Specifically, studies with a 1 -agonists in mouse (Chan et al, 2008;Dash et al, 2011) and human (Cleveland et al, 1996Galinanes, 2001, 2002), as well as in loss-of-function mouse models (O'Connell et al, , 2006Huang et al, 2007) as reviewed above, support a 1 -mediated cardioprotective effects.…”

“…In support of the finding that the a 1 A-subtype is both sufficient and necessary to prevent cardiac myocyte death, long-term infusion of a subpressor concentration of the a 1 A-subtype-specific agonist A61603 [N-[5-(4,5-dihydro-1H-imidazol-2yl)-2-hydroxy-5,6,7,8-tetrahydronaphthalen-1-yl]methanesulphonamide hydrobromide] prevents cell death and pathologic remodeling associated with doxorubicin-induced cardiotoxicity (Chan et al, 2008;Dash et al, 2011).…”

“…However, in mice, subpressor doses of an a 1 A-subtype-specific ligand prevent doxorubicin cardiotoxicity (Chan et al, 2008;Dash et al, 2011); in humans, some small trials Cardiac a 1 -Adrenergic Receptors indicate a 1 -ARs agonists might improve function in heart failure (Cabanes et al, 1992;Zakir et al, 2009); and numerous studies identify adaptive hypertrophy with subpressor a 1 -agonist infusion, as reviewed in the section on hypertrophy. These data provide a preliminary proof-of-principle demonstration of the efficacy of a 1 -agonists in heart failure, and justify further study.…”

Traditional and novel methods to assess and prevent chemotherapy-related cardiac dysfunction noninvasively

“…86 A new superparamagnetic iron oxide probe conjugated to recombinant human annexin has demonstrated diffuse myocardial signal loss in rats treated with doxorubicin, suggestive of apoptosis by CMR. 87,88 Myocardial fibrosis detected as delayed enhancement (DE) by CMR has proven prognostic value in coronary heart disease, 89 and restrictive myocardial diseases including aortic stenosis, 90 hypertrophic cardiomyopathy, 91,92 and the infiltrative diseases of sarcoidosis 93 and amyloidosis. 94 CMR studies in larger populations of patients receiving potentially cardiotoxic agents are needed to see whether the presence of fibrosis detected by gadolinium enhancement identifies a cohort of patients more vulnerable to the cardiotoxic effects of chemotherapy, who may benefit from more frequent and long-term follow-up, and earlier treatment with ACE inhibitors and beta blockade to reduce the incidence and severity of chemotherapy-induced heart failure.…”

Remote magnetic targeting of iron oxide nanoparticles for cardiovascular diagnosis and therapeutic drug delivery: where are we now?

“…To increase their specificity, IONs can be functionalized to bind certain target structures, as shown for early cardiomyocyte apoptosis in rats, for instance. 73 Apart from the use of pure ION formulations, such functionalized ION approaches are highly promising, given that appropriate ION-based compounds get legal approval as diagnostic CAs. Ferumoxytol, the only remaining ION complex that is still Food and Drug Administration approved for IV application in the US, was recently withdrawn from the European Union market due to commercial reasons.…”