Person:

Polizzotti, Brian

Background: Administration of a recombinant peptide of Periostin (rPN) has recently been shown to stimulate cardiomyocyte proliferation and angiogensis after myocardial infarction (MI). However, strategies for targeting the delivery of rPN to the heart are lacking. Intrapericardial administration of drug-eluting hydrogels may provide a clinically viable strategy for increasing myocardial retention, therapeutic efficacy, and bioactivity of rPN and to decrease systemic re-circulation. Methods and Results: We investigated the ability of intrapericardial injections of drug-eluting hydrogels to deliver and prolong the release of rPN to the myocardium in a large animal model of myocardial infarction. Gelfoam is an FDA-approved hemostatic material commonly used in surgery, and is known to stimulate fibrin clot formation. We show that Gelfoam disks loaded with rPN, when implanted within the pericardium or peritoneum of mammals becomes encapsulated within a non-fibrotic fibrin-rich hydrogel, prolonging the in vitro and in vivo release of rPN. Administration into the pericardial cavity of pigs, following a complete occlusion of the left anterior descending artery, leads to greater induction of cardiomyocyte mitosis, increased cardiomyocyte cell cycle activity, and enhanced angiogenesis compared to direct injection of rPN alone. Conclusions: The results of this study suggest that intrapericardial drug delivery of Gelfoam, enhanced by triggered clot formation, can be used to effectively deliver rPN to the myocardium in a clinically relevant model of myocardial infarction. The work presented here should enhance the translational potential of pharmaceutical-based strategies that must be targeted to the myocardium.

Background: We previously developed and validated a strategy for stimulating heart regeneration by administration of recombinant neuregulin (rNRG1), a growth factor, in mice. rNRG1 stimulated proliferation of heart muscle cells, cardiomyocytes, and was most effective when administration began during the neonatal period. Our results suggested the use of rNRG1 to treat pediatric patients with heart failure. However, administration in this age group may stimulate growth outside of the heart. Methods: NRG1 and ErbB receptor expression was determined by RT-PCR. rNRG1 concentrations in serum were quantified by ELISA. Mice that received protocols of recombinant neuregulin1-β1 administration (rNRG1, 100 ng/g body weight, daily subcutaneous injection for the first month of life), previously shown to induce cardiac regeneration, were examined at pre-determined intervals. Somatic growth was quantified by weighing. Organ growth was quantified by MRI and by weighing. Neoplastic growth was examined by MRI, visual inspection, and histopathological analyses. Phospho-ERK1/2 and S6 kinase were analyzed with Western blot and ELISA, respectively. Results: Lung, spleen, liver, kidney, brain, and breast gland exhibited variable expression of the NRG1 receptors ErbB2, ErbB3, ErbB4, and NRG1. Body weight and tibia length were not altered in mice receiving rNRG1. MRI showed that administration of rNRG1 did not alter the volume of the lungs, liver, kidneys, brain, or spinal cord. Administration of rNRG1 did not alter the weight of the lungs, spleen, liver, kidneys, or brain. MRI, visual inspection, and histopathological analyses showed no neoplastic growth. Follow-up for 6 months showed no alteration of somatic or organ growth. rNRG1 treatment increased the levels of phospho-ERK1/2, but not phospho-S6 kinase. Conclusions: Administration protocols of rNRG1 for stimulating cardiac regeneration in mice during the first month of life did not induce unwanted growth effects. Further studies may be required to determine whether this is the case in a corresponding human population.

After birth cardiomyocytes undergo terminal differentiation, characterized by binucleation and centrosome disassembly, rendering the heart unable to regenerate. Yet, it has been suggested that newborn mammals regenerate their hearts after apical resection by cardiomyocyte proliferation. Thus, we tested the hypothesis that apical resection either inhibits, delays, or reverses cardiomyocyte centrosome disassembly and binucleation. Our data show that apical resection rather transiently accelerates centrosome disassembly as well as the rate of binucleation. Consistent with the nearly 2-fold increased rate of binucleation there was a nearly 2-fold increase in the number of cardiomyocytes in mitosis indicating that the majority of injury-induced cardiomyocyte cell cycle activity results in binucleation, not proliferation. Concurrently, cardiomyocytes undergoing cytokinesis from embryonic hearts exhibited midbody formation consistent with successful abscission, whereas those from 3 day-old cardiomyocytes after apical resection exhibited midbody formation consistent with abscission failure. Lastly, injured hearts failed to fully regenerate as evidenced by persistent scarring and reduced wall motion. Collectively, these data suggest that should a regenerative program exist in the newborn mammalian heart, it is quickly curtailed by developmental mechanisms that render cardiomyocytes post-mitotic.