Molecular Imaging for Efficacy of Pharmacologic Intervention in Myocardial Remodeling

ObjectivesUsing molecular imaging techniques, we examined interstitial alterations during postmyocardial infarction (MI) remodeling and assessed the efficacy of antiangiotensin and antimineralocorticoid intervention, alone and in combination.BackgroundThe antagonists of the renin-angiotensin-aldosterone axis restrict myocardial fibrosis and cardiac remodeling after MI and contribute to improved survival. Radionuclide imaging with technetium-99m–labeled Cy5.5 RGD imaging peptide (CRIP) targets myofibroblasts and indirectly allows monitoring of the extent of collagen deposition post-MI.MethodsCRIP was intravenously administered for gamma imaging after 4 weeks of MI in 63 Swiss-Webster mice and in 6 unmanipulated mice. Of 63 animals, 50 were treated with captopril (C), losartan (L), spironolactone (S) alone, or in combination (CL, SC, SL, and SCL), 8 mice received no treatment. Echocardiography was performed for assessment of cardiac remodeling. Hearts were characterized histopathologically for the presence of myofibroblasts and thick and thin collagen fiber deposition.ResultsAcute MI size was similar in all groups. The quantitative CRIP percent injected dose per gram uptake was greatest in the infarct area of untreated control mice (2.30 ± 0.14%) and decreased significantly in animals treated with 1 agent (C, L, or S; 1.71 ± 0.35%; p = 0.0002). The addition of 2 (CL, SC, or SL 1.31 ± 0.40%; p < 0.0001) or 3 agents (SCL; 1.16 ± 0.26%; p < 0.0001) demonstrated further reduction in tracer uptake. The decrease in echocardiographic left ventricular function, strain and rotation parameters, as well as histologically verified deposition of thin collagen fibers, was significantly reduced in treatment groups and correlated with CRIP uptake.ConclusionsRadiolabeled CRIP allows for the evaluation of the efficacy of neurohumoral antagonists after MI and reconfirms superiority of combination therapy. If proven clinically, molecular imaging of the myocardial healing process may help plan an optimal treatment for patients susceptible to heart failure

Myocardial remodeling after infarction: the role of myofibroblasts

Myofibroblasts have characteristics of fibroblasts and smooth muscle cells: they produce extracellular matrix and are able to contract. In so doing, they can contribute to tissue replacement and interstitial fibrosis following cardiac injury. The scar formed after myocardial injury is no longer considered to be passive tissue; it is an active playground where myofibroblasts play a role in collagen turnover and scar contraction. Maintaining the extracellular matrix in the scar is essential and can prevent dilatation of the infarct area leading to heart failure. On the other hand, extracellular matrix deposition at sites remote from the infarct area can lead to cardiac stiffness, an inevitable process of myocardial remodeling that occurs in the aftermath of myocardial infarction and constitutes the basis of the development of heart failure. Defining molecular targets on myofibroblasts in conjunction with establishing the feasibility of molecular imaging of these cells might facilitate the early detection and treatment of patients who are at risk of developing heart failure after myocardial infarction