6-Month Follow-Up of a Novel Biodegradable Drug-Eluting Stent Composed of Poly-L-Lactic Acid and Amorphous Calcium Phosphate Nanoparticles in Porcine Coronary Artery

The lysine methyltransferase SMYD2 facilitates neointimal hyperplasia by regulating the HDAC3-SRF axis

Coronary restenosis is an important cause of poor long-term prognosis in patients with coronary heart disease. Here, we show that lysine methyltransferase SMYD2 expression in the nucleus is significantly elevated in serum- and PDGF-BB-induced vascular smooth muscle cells (VSMCs), and in tissues of carotid artery injury-induced neointimal hyperplasia. Smyd2 overexpression in VSMCs (Smyd2-vTg) facilitates, but treatment with its specific inhibitor LLY-507 or SMYD2 knockdown significantly inhibits VSMC phenotypic switching and carotid artery injury-induced neointima formation in mice. Transcriptome sequencing revealed that SMYD2 knockdown represses the expression of serum response factor (SRF) target genes and that SRF overexpression largely reverses the inhibitory effect of SMYD2 knockdown on VSMC proliferation. HDAC3 directly interacts with and deacetylates SRF, which enhances SRF transcriptional activity in VSMCs. Moreover, SMYD2 promotes HDAC3 expression via tri-methylation of H3K36 at its promoter. RGFP966, a specific inhibitor of HDAC3, not only counteracts the pro-proliferation effect of SMYD2 overexpression on VSMCs, but also inhibits carotid artery injury-induced neointima formation in mice. HDAC3 partially abolishes the inhibitory effect of SMYD2 knockdown on VSMC proliferation in a deacetylase activity-dependent manner. Our results reveal that the SMYD2-HDAC3-SRF axis constitutes a novel and critical epigenetic mechanism that regulates VSMC phenotypic switching and neointimal hyperplasia.

Clinical implications of inflammation in atheroma formation and novel therapies in cardiovascular diseases

Cardiovascular diseases (CVD) are the leading causes of death and disability in the world. Among all CVD, the most common is coronary artery disease (CAD). CAD results from the complications promoted by atherosclerosis, which is characterized by the accumulation of atherosclerotic plaques that limit and block the blood flow of the arteries involved in heart oxygenation. Atherosclerotic disease is usually treated by stents implantation and angioplasty, but these surgical interventions also favour thrombosis and restenosis which often lead to device failure. Hence, efficient and long-lasting therapeutic options that are easily accessible to patients are in high demand. Advanced technologies including nanotechnology or vascular tissue engineering may provide promising solutions for CVD. Moreover, advances in the understanding of the biological processes underlying atherosclerosis can lead to a significant improvement in the management of CVD and even to the development of novel efficient drugs. To note, over the last years, the observation that inflammation leads to atherosclerosis has gained interest providing a link between atheroma formation and oncogenesis. Here, we have focused on the description of the available therapy for atherosclerosis, including surgical treatment and experimental treatment, the mechanisms of atheroma formation, and possible novel therapeutic candidates such as the use of anti-inflammatory treatments to reduce CVD.

Methyltransferase-like 3 suppresses phenotypic switching of vascular smooth muscle cells by activating autophagosome formation

Prevention of neointima formation is the key to improving long-term outcomes after stenting or coronary artery bypass grafting. RNA N⁶ -methyladenosine (m⁶ A) methylation has been reported to be involved in the development of various cardiovascular diseases, but whether it has a regulatory effect on neointima formation is unknown. Herein, we revealed that methyltransferase-like 3 (METTL3), the major methyltransferase of m⁶ A methylation, was downregulated during vascular smooth muscle cell (VSMC) proliferation and neointima formation. Knockdown of METTL3 facilitated, while overexpression of METTL3 suppressed the proliferation of human aortic smooth muscle cells (HASMCs) by arresting HASMCs at G2/M checkpoint and the phosphorylation of CDC2 (p-CDC2) was inactivated by METTL3. On the other hand, the migration and synthetic phenotype of HASMCs were enhanced by METTL3 knockdown, but inhibited by METTL3 overexpression. The protein levels of matrix metalloproteinase 2 (MMP2), MMP7 and MMP9 were reduced, while the expression level of tissue inhibitor of metalloproteinase 3 was increased in HASMCs with METTL3 overexpression. Moreover, METTL3 promoted the autophagosome formation by upregulating the expression of ATG5 (autophagy-related 5) and ATG7. Knockdown of either ATG5 or ATG7 largely reversed the regulatory effects of METTL3 overexpression on phenotypic switching of HASMCs, as evidenced by increased proliferation and migration, and predisposed to synthetic phenotype. These results indicate that METTL3 inhibits the phenotypic switching of VSMCs by positively regulating ATG5-mediated and ATG7-mediated autophagosome formation. Thus, enhancing the level of RNA m⁶ A or the formation of autophagosomes is the promising strategy to delay neointima formation.

Synthetic amorphous calcium phosphates (ACPs): preparation, structure, properties, and biomedical applications

Amorphous calcium phosphates (ACPs) represent a metastable amorphous state of other calcium orthophosphates (abbreviated as CaPO₄) possessing variable compositional but rather identical glass-like physical properties, in which there are neither translational nor orientational long-range orders of the atomic positions. In nature, ACPs of a biological origin are found in the calcified tissues of mammals, some parts of primitive organisms, as well as in the mammalian milk. Manmade ACPs can be synthesized in a laboratory by various methods including wet-chemical precipitation, in which they are the first solid phases, precipitated after a rapid mixing of aqueous solutions containing dissolved ions of Ca²⁺ and PO₄^3- in sufficient amounts. Due to the amorphous nature, all types of synthetic ACPs appear to be thermodynamically unstable and, unless stored in dry conditions or doped by stabilizers, they tend to transform spontaneously to crystalline CaPO₄, mainly to ones with an apatitic structure. This intrinsic metastability of the ACPs is of a great biological relevance. In particular, the initiating role that metastable ACPs play in matrix vesicle biomineralization raises their importance from a mere laboratory curiosity to that of a reasonable key intermediate in skeletal calcifications. In addition, synthetic ACPs appear to be very promising biomaterials both for manufacturing artificial bone grafts and for dental applications. In this review, the current knowledge on the occurrence, structural design, chemical composition, preparation, properties, and biomedical applications of the synthetic ACPs have been summarized.

Surface engineering at the nanoscale: A way forward to improve coronary stent efficacy

Coronary in-stent restenosis and late stent thrombosis are the two major inadequacies of vascular stents that limit its long-term efficacy. Although restenosis has been successfully inhibited through the use of the current clinical drug-eluting stent which releases antiproliferative drugs, problems of late-stent thrombosis remain a concern due to polymer hypersensitivity and delayed re-endothelialization. Thus, the field of coronary stenting demands devices having enhanced compatibility and effectiveness to endothelial cells. Nanotechnology allows for efficient modulation of surface roughness, chemistry, feature size, and drug/biologics loading, to attain the desired biological response. Hence, surface topographical modification at the nanoscale is a plausible strategy to improve stent performance by utilizing novel design schemes that incorporate nanofeatures via the use of nanostructures, particles, or fibers, with or without the use of drugs/biologics. The main intent of this review is to deliberate on the impact of nanotechnology approaches for stent design and development and the recent advancements in this field on vascular stent performance.

Long-Term Arterial Remodeling After Bioresorbable Scaffold Implantation 4-Year Follow-up of Quantitative Coronary Angiography, Histology and Optical Coherence Tomography

PURPOSE

Our previous studies have confirmed the safety and efficacy of the novel fully bioresorbable PLLA scaffold (PowerScaffold®) at 12 months implantation. In the present study, the scaffold absorption and coronary vessel remodeling at 4 years were evaluated.

METHODS

After PowerScaffold® were implanted into 13 coronary arteries of 6 miniature pigs, quantitative coronary angiography (QCA) was performed at 15 days and 4 years follow-up to measure the mean lumen diameter (MLD), late lumen loss (LLL), and % stenosis of the coronary arteries. Optical coherence tomography (OCT) was performed to obtain the strut footprints at 4 years before euthanization for histological analysis. In addition, 2 PowerScaffold® were implanted into 2 miniature pigs for 2 years as supplementary data. All stented arteries were dissected and stained with HE, Masson, EVG, and Alcian blue to observe struts, cells, fibrinoid, elastin, and proteoglycans, respectively.

RESULTS

There were no significant differences in MLD, LLL and % stenosis in stented coronary arteries between 15 days and 4 years by QCA. At 4 years, most strut sites were indiscernible and replaced by extracellular matrix and connective tissue by histology. Both strut/vessel wall interaction and strut coverage were shown 100% by OCT.

CONCLUSION

At 4 years, the scaffold struts were completely embedded into vessel wall and mostly replaced by regenerated tissue. There was no sign of in-stent stenosis in all stented arteries.

Effect of novel bioresorbable scaffold composed of poly-L-lactic acid and amorphous calcium phosphate nanoparticles on inflammation and calcification of surrounding tissues after implantation

To study the effect of novel bioresorbable scaffold composed of poly-L-lactic acid (PLLA) and amorphous calcium phosphate (ACP) nanoparticles on inflammation and calcification of surrounding tissues after implantation. Ninety six PLLA/ACP scaffolds and 96 PLLA scaffolds were randomly implanted in the back muscle tissue of 48 SD rats. At the 1st, 2nd, 4th, and 12th weeks after implantation, the calcium, phosphorus, and alkaline phosphatase levels in the blood serum and the contents of calcium and alkaline phosphatase in the tissue surrounding the scaffolds were measured. Hematoxylin-eosin staining was performed to count the inflammatory cells. Von kossa staining was performed to observe calcification of the surrounding tissue around the scaffold. NF-κB staining was performed by immunohistochemistry to calculate the positive expression index of inflammatory cells. Western blot was used to detect the expression of IL-6 and BMP-2 in the tissues surrounding the scaffolds. At the 1st, 2nd, 4th, and 12th weeks after scaffold implantation, there were no significant difference in the serum concentration of calcium, phosphorus, alkaline phosphatase and in the tissue homogenate concentration of alkaline phosphatase between the two groups (P > 0.05). The level of calcium in tissue homogenates was lower in the PLLA/ACP group than in the PLLA group at 12-week (P < 0.05). The hematoxylin-eosin staining results showed that the inflammatory cell count in the PLLA/ACP group was lower than the PLLA group at 4-week and 12-week (P < 0.05). The results of NF-kB positive expression index showed that the PLLA group was significantly more than the PLLA/ACP group at 4-week and 12-week (P < 0.01). Western blot results showed that IL-6 expression levels in the PLLA/ACP group scaffolds were significantly lower than those in the control group at the 2-week, 4-week and 12-week (P < 0.05). The expression of BMP-2 in the PLLA group was significantly lower than that in the control group at 4-week and 12-week (P < 0.05). The PLLA/ACP composite material has good histocompatibility. The integration of nanoscale ACPs reduces the inflammatory response induced by acidic metabolites of PLLA material and may inhibit tissue calcification by reducing the amount of calcification factors in the body.