Application of Hydrogels in Cardiac Regeneration

Myocardial infarction (MI) is a leading cause of death globally. Due to limited cardiac regeneration, infarcted myocardial tissue is gradually replaced by cardiac fibrosis, causing cardiac dysfunction, arrhythmia, aneurysm, free wall rupture, and sudden cardiac death. Thus, the development of effective methods to promote cardiac regeneration is extremely important for MI treatment. In recent years, hydrogels have shown promise in various methods for cardiac regeneration. Hydrogels can be divided into natural and synthetic types. Different hydrogels have different features and can be cross-linked in various ways. Hydrogels are low in toxicity and highly stable. Since they have good biocompatibility, biodegradability, and transformability, moderate mechanical properties, and proper elasticity, hydrogels are promising biomaterials for promoting cardiac regeneration. They can be used not only as scaffolds for migration of stem cells, but also as ideal carriers for delivery of drugs, genetic materials, stem cells, growth factors, cytokines, and small molecules. In this review, the application of hydrogels in cardiac regeneration during or post-MI is discussed in detail. Hydrogels open a promising new area in cardiac regeneration for treating MI.

Characterization and Evaluation of Rapamycin-Loaded Nano-Micelle Ophthalmic Solution

Rapamycin-loaded nano-micelle ophthalmic solution (RAPA-NM) offers a promising application for preventing corneal allograft rejection; however, RAPA-NM has not yet been fully characterized. This study aimed to evaluate the physicochemical properties, biocompatibility, and underlying mechanism of RAPA-NM in inhibiting corneal allograft rejection. An optimized RAPA-NM was successfully prepared using a polyvinyl caprolactam-polyvinyl acetate-polyethylene glycol (PVCL-PVA-PEG) graft copolymer as the excipient at a PVCL-PVA-PEG/RAPA weight ratio of 18:1. This formulation exhibited high encapsulation efficiency (99.25 ± 0.55%), small micelle size (64.42 ± 1.18 nm), uniform size distribution (polydispersity index = 0.076 ± 0.016), and a zeta potential of 1.67 ± 0.93 mV. The storage stability test showed that RAPA-NM could be stored steadily for 12 weeks. RAPA-NM also displayed satisfactory cytocompatibility and high membrane permeability. Moreover, topical administration of RAPA-NM could effectively prevent corneal allograft rejection. Mechanistically, a transcriptomic analysis revealed that several immune- and inflammation-related Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways were significantly enriched in the downregulated genes in the RAPA-NM-treated allografts compared with the rejected allogenic corneal grafts. Taken together, these findings highlight the potential of RAPA-NM in treating corneal allograft rejection and other ocular inflammatory diseases.

Defective autophagy triggered by arterial cyclic stretch promotes neointimal hyperplasia in vein grafts via the p62/nrf2/slc7a11 signaling pathway

Autophagy is an adaptation mechanism to keep cellular homeostasis, and its deregulation is implicated in various cardiovascular diseases. After vein grafting, hemodynamic factors play crucial roles in neointimal hyperplasia, but the mechanisms are poorly understood. Here, we investigated the impacts of arterial cyclic stretch on autophagy of venous smooth muscle cells (SMCs) and its role in neointima formation after vein grafting. Rat jugular vein graft were generated via the 'cuff' technique. Autophagic flux in venous SMCs is impaired in 3-day, 1-week and 2-week grafted veins. 10%-1.25 Hz cyclic stretch (arterial stretch) loaded with FX5000 stretch system on venous SMCs blocks cellular autophagic flux in vitro and shows no significant impact on activity of mTORC1 and AMPK. Microtubule depolymerization but not lysosome dysfunction nor autophagosome/amphisome-lysosomal membrane fusion blockade is involved in the impairment of autophagic flux. Microtubule stabilization, induced by paclitaxel treatment and external stents intervention respectively, restores venous SMC autophagy and ameliorates neointimal hyperplasia in vivo. Moreover, autophagy impairment causes accumulation of the cargo receptor p62, which sequesters keap1 to p62 aggregates and results in the stabilization and nuclear translocation of nrf2 to modulate its target antioxidative gene SLC7A11. p62 silencing abrogates the increases of nrf2 and slc7a11 protein expression, glutathione level and venous SMC proliferation triggered by arterial cyclic stretch in vitro, and further hinders nrf2 nuclear translocation, reduces neointimal thickness after vein grafting in vivo. p62 (T349A) mutation also inhibited venous SMC proliferation and alleviated neointimal formation in vivo. These findings suggest that stabilization of microtubules to rescue autophagic flux or direct silencing of p62 are potential therapeutic strategies for neointimal hyperplasia.

Targeted Nanoparticles for the Binding of Injured Vascular Endothelium after Percutaneous Coronary Intervention

Percutaneous coronary intervention (PCI) is a common procedure for the management of coronary artery obstruction. However, it usually causes vascular wall injury leading to restenosis that limits the long-term success of the PCI endeavor. The ultimate objective of this study was to develop the targeting nanoparticles (NPs) that were destined for the injured subendothelium and attract endothelial progenitor cells (EPCs) to the damaged location for endothelium regeneration. Biodegradable poly(lactic-co-glycolic acid) (PLGA) NPs were conjugated with double targeting moieties, which are glycoprotein Ib alpha chain (GPIbα) and human single-chain antibody variable fragment (HuscFv) specific to the cluster of differentiation 34 (CD34). GPIb is a platelet receptor that interacts with the von Willebrand factor (vWF), highly deposited on the damaged subendothelial surface, while CD34 is a surface marker of EPCs. A candidate anti-CD34 HuscFv was successfully constructed using a phage display biopanning technique. The HuscFv could be purified and showed binding affinity to the CD34-positive cells. The GPIb-conjugated NPs (GPIb-NPs) could target vWF and prevent platelet adherence to vWF in vitro. Furthermore, the HuscFv-conjugated NPs (HuscFv-NPs) could capture CD34-positive cells. The bispecific NPs have high potential to locate at the damaged subendothelial surface and capture EPCs for accelerating the vessel repair.

Nanoparticles in the diagnosis and treatment of vascular aging and related diseases

Aging-induced alternations of vasculature structures, phenotypes, and functions are key in the occurrence and development of vascular aging-related diseases. Multiple molecular and cellular events, such as oxidative stress, mitochondrial dysfunction, vascular inflammation, cellular senescence, and epigenetic alterations are highly associated with vascular aging physiopathology. Advances in nanoparticles and nanotechnology, which can realize sensitive diagnostic modalities, efficient medical treatment, and better prognosis as well as less adverse effects on non-target tissues, provide an amazing window in the field of vascular aging and related diseases. Throughout this review, we presented current knowledge on classification of nanoparticles and the relationship between vascular aging and related diseases. Importantly, we comprehensively summarized the potential of nanoparticles-based diagnostic and therapeutic techniques in vascular aging and related diseases, including cardiovascular diseases, cerebrovascular diseases, as well as chronic kidney diseases, and discussed the advantages and limitations of their clinical applications.

Nanospheres encapsulated everolimus delivery into arterial wall-the tissue pharmacokinetics and vascular response experimental study

OBJECTIVE

This study aimed to evaluate the pharmacokinetic profile and tissue effects of everolimus delivered into arterial wall using biodegradable nanospheres.

BACKGROUND

Delivery of everolimus into the arterial wall is challenging due to its low-lipophilic profile.

METHODS

A pharmacokinetic study included 28 porcine coronary arterial segments initially injured with balloon angioplasty followed by the local delivery of everolimus encapsulated in nanospheres (EEN) via injection through a microporous delivery catheter. The animals were sacrificed at 1 hour, 1,7,28, and 90-day follow-up. In the tissue effects study 16 coronary bare metal stent (BMS) were implanted following EEN delivery, 15 BMS following nanospheres delivery without the drug (reference group) and 16 implanted BMS served as a control. Angiographic and histology follow-up was scheduled at 28 and 90-day.

RESULTS

The study showed high-everolimus concentrations in arterial tissue early after nanoparticles delivery followed by its gradual decrease to 1.15 ± 0.40 ng/mg at 90 days. Histology analysis showed favorable biocompatibility and healing profile with comparable area stenosis between groups at both time-points.

CONCLUSIONS

The present study demonstrates for the first time the safety, biocompatibility, and long-term retention of everolimus in arterial tissue after single local delivery of biodegradable nanospheres.

Targeted Delivery of Bioactive Molecules for Vascular Intervention and Tissue Engineering

Cardiovascular diseases are the leading cause of death in the United States. Treatment often requires surgical interventions to re-open occluded vessels, bypass severe occlusions, or stabilize aneurysms. Despite the short-term success of such interventions, many ultimately fail due to thrombosis or restenosis (following stent placement), or incomplete healing (such as after aneurysm coil placement). Bioactive molecules capable of modulating host tissue responses and preventing these complications have been identified, but systemic delivery is often harmful or ineffective. This review discusses the use of localized bioactive molecule delivery methods to enhance the long-term success of vascular interventions, such as drug-eluting stents and aneurysm coils, as well as nanoparticles for targeted molecule delivery. Vascular grafts in particular have poor patency in small diameter, high flow applications, such as coronary artery bypass grafting (CABG). Grafts fabricated from a variety of approaches may benefit from bioactive molecule incorporation to improve patency. Tissue engineering is an especially promising approach for vascular graft fabrication that may be conducive to incorporation of drugs or growth factors. Overall, localized and targeted delivery of bioactive molecules has shown promise for improving the outcomes of vascular interventions, with technologies such as drug-eluting stents showing excellent clinical success. However, many targeted vascular drug delivery systems have yet to reach the clinic. There is still a need to better optimize bioactive molecule release kinetics and identify synergistic biomolecule combinations before the clinical impact of these technologies can be realized.

Nanoparticles administered intrapericardially enhance payload myocardial distribution and retention

Pharmacological therapies for cardiovascular diseases are limited by short-term pharmacokinetics and extra-cardiac adverse effects. Improving delivery selectivity specifically to the heart, wherein therapeutic drug levels can be maintained over time, is highly desirable. Nanoparticle (NP)-based pericardial drug delivery could provide a strategy to concentrate therapeutics within a unique, cardiac-restricted compartment to allow sustained drug penetration into the myocardium. Our objective was to explore the kinetics of myocardial penetration and retention after pericardial NP drug delivery. Fluorescently-tagged poly(lactic-co-glycolic acid) (PLGA) NPs were loaded with BODIPY, a fluorophore, and percutaneously administered into the pericardium via subxiphoid puncture in rabbits. At distinct timepoints hearts were examined for presence of NPs and BODIPY. PLGA NPs were found non-uniformly distributed on the epicardium following pericardial administration, displaying a half-life of ~2.5days in the heart. While NPs were mostly confined to epicardial layers, BODIPY was capable of penetrating into the myocardium, resulting in a transmural gradient. The distinct architecture and physiology of the different regions of the heart influenced BODIPY distribution, with fluorophore penetrating more readily into atria than ventricles. BODIPY proved to have a long-term presence within the heart, with a half-life of ~7days. Our findings demonstrate the potential of utilizing the pericardial space as a sustained drug-eluting reservoir through the application of nanoparticle-based drug delivery, opening several exciting avenues for selective and prolonged cardiac therapeutics.

Drug loaded nanoparticle coating on totally bioresorbable PLLA stents to prevent in-stent restenosis

Biodegradable polymer poly (dl-lactide) (PDLLA) has been used as drug coating material for drug-eluting stents due to its excellent biocompatibility and sustained drug release ability. However, the uniform thin layer drug eluting coating on a stent not only inhibits the blood vessel's smooth muscle cell overgrowth but also delay the endotheliation process which is often associated with the occurrence of acute thrombosis. Therefore, in this study, we developed a novel coating method using PDLLA nanoparticles (NPs) as a coating to overcome this issue. The average 300 nm sized sirolimus-loaded PDLLA nanoparticles were prepared by a conventional emulsion solvent evaporation method. A low temperature plasma polymerization technology to graft hydrophilic polymers on to poly (l-lactide) stent was used to increase the surface coating efficiency of nanoparticles on the stent. Results showed that sirolimus-loaded nanoparticles can be successfully coated on to the stents with sustained drug release properties. In vitro cell culture study showed the drug loaded nanoparticle coating effectively inhibited the proliferation of smooth muscle cells while still allowed a faster proliferation of endothelial cells, suggesting that the new NP coated bioresorbable stents have the potential to reduce both the occurrence of in-stent restenosis and acute thrombosis. © 2016 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 106B: 88-95, 2018.

Paclitaxel-coated balloon plus bare-metal stent for de-novo coronary artery disease: final 5-year results of a randomized prospective multicenter trial

BACKGROUND

The PERfECT Stent Study compared paclitaxel-coated balloon (PCB) angioplasty plus bare-metal stent (BMS) implantation with BMS alone in de-novo lesions in native coronary artery disease. Angiographic follow-up after 6 months showed the superiority of the additional PCB. We evaluated a potential late catch-up phenomenon with the use of PCB.

METHODS AND RESULTS

In the prospective, multicenter, single-blind, randomized PERfECT Stent trial, 120 patients were assigned to either PCB angioplasty plus BMS implantation or BMS alone. For BMS, the endothelial progenitor cell capturing stent was used. Dual antiplatelet therapy was recommended for 3 months. The clinical endpoint for 5-year follow-up was a composite of cardiac death, myocardial infarction attributed to the target vessel, or target lesion revascularization. The follow-up rate after 5 years was 97%. Baseline and procedural characteristics did not differ. At the 5-year follow-up, clinically driven target lesion revascularization was 23.2% in the BMS group versus 15% with PCB plus BMS (P=0.26). The clinical endpoint (major adverse cardiac event) was 30.4% with BMS and with 23.5% lower with PCB plus BMS. No definite or probable stent thrombosis was found in either group with a dual antiplatelet therapy for 3 months for the total period.

CONCLUSION

PCB angioplasty plus BMS was superior to BMS alone for the treatment of de-novo lesions. The combined clinical endpoint was lower with PCB plus BMS at 6 months and remained lower after 5 years. There was no late catch-up phenomenon (http://www.clinicaltrials.gov; NCT 00732953).

An In Vitro Thrombolysis Study Using a Mixture of Fast-Acting and Slower Release Microspheres

PURPOSE

To test the hypothesis that a mixture combining fast and slower release rate microspheres can restore blood flow rapidly and prevent formation of another blockage in thrombolysis.

METHODS

We used polyethylene glycol (PEG) microspheres which provide the release of the encapsulated streptokinase (SK) on the scale of minutes, and Eudragit FS30D (Eud), a polymethacrylate polymer, for development of delayed release microspheres which were desirable to prevent a putative second thrombus. Eud microspheres were coated with chitosan (CS) to further extend half-life. Experiments included the development, characterization of Eud/SK and CS-Eud/SK microspheres, and in vitro thrombolytic studies of the mixtures of PEG/SK and Eud /SK microspheres and of PEG/SK and CS-Eud/SK microspheres.

RESULTS

CS-Eud/SK microspheres have slightly lower encapsulation efficiency, reduced activity of SK, and a much slower release of SK when compared with microspheres of Eud/SK microspheres. Counter-intuitively, slower release leads to faster thrombolysis after reocclusion as a result of greater retention of agent and the mechanism of distributed intraclot thrombolysis.

CONCLUSIONS

A mixture of PEG/SK and CS-Eud/SK microspheres could break up the blood clot rapidly while providing clot-lytic efficacy in prevention of a second blockage up to 4 h.

In situ re-endothelialization via multifunctional nanoscaffolds

The endothelium monolayer lining in the luminal side of blood vessels provides critical antithrombotic functions. Damage to these cells will expose a highly thrombogenic subendothelium, which leads to pathological vascular changes. Using combined tissue engineering and ligand-receptor targeting strategy, we developed a biodegradable urethane-doped polyester (UPE) multifunctional targeting nanoparticle (MTN) scaffold system with dual ligands: (1) glycoprotein 1b (GP1b) to target the injured arterial endothelium and subendothelium and (2) anti-CD34 antibodies to capture endothelial progenitor cells for endothelium regeneration. The fabricated spherical MTNs of 400 nm were found to be cytocompatible and hemocompatible. Both the in vitro and ex vivo targeting of these nanoscaffolds not only showed binding specificity of MTNs onto the von Willebrand factor -coated surfaces that simulate the injured arterial walls but also competed with platelets for binding onto these injured sites. Further in vivo study has revealed that a single delivery of MTNs upon vascular injury reduced neointimal hyperplasia by 57% while increased endothelium regeneration by ∼ 60% in 21 days. These results support the promise of using MTN nanoscaffolds for treating vascular injury in situ.

Autophagy regulates vascular endothelial cell eNOS and ET-1 expression induced by laminar shear stress in an ex vivo perfused system

Vascular endothelial cell function responds to steady laminar shear stress; however, the underlying mechanisms are not fully elucidated. In the present study, we examined the effect of steady laminar shear stress on vascular endothelial cell autophagy and endothelial cell nitric oxide synthase (eNOS) and endothelin-1 (ET-1) expression using an ex vivo perfusion system. Human vascular endothelial cells and common arteries of New Zealand rabbits were pretreated with or without rapamycin or 3-MA for 30 min. These were then placed in an ex vivo cell perfusion system or an ex vivo organ perfusion system under static conditions (0 dynes/cm2) or steady laminar shear stress (5 or 15 dynes/cm2) for 1 h. In both ex vivo perfusion vascular endothelial cells and vascular vessel segment, steady laminar shear stress promoted autophagy and eNOS expression and inhibited ET-1 expression. Compared with steady laminar shear stress treatment alone, the pretreatment of autophagy inducer rapamycin obviously strengthened the expression of eNOS and decreased the expression of ET-1 in both the 5 and 15 dynes/cm2 treatment groups. Moreover, when pretreated with the autophagy inhibitor 3-MA, the eNOS expression was obviously inhibited and the ET-1 expression was reversed. These findings demonstrate that autophagy is upregulated under steady laminar shear stress, improving endothelial cell maintenance of vascular tone function.