Viability of coronary arteries cultured in an ex-vivo vascular bioreactor

Funding Acknowledgements

Type of funding sources: Public grant(s) – National budget only. Main funding source(s): ZonMW

Introduction

Cardiovascular diseases (CVD) are the leading cause of death globally. The CVD that causes most of the deaths annually is atherosclerosis [1]. The treatment of choice for acute symptoms like myocardial infarction is percutaneous coronary intervention with the implantation of a stent. Despite successful clinical results, there are still complications [2]. Current pre-clinical research to assess safety and efficacy of stents is primarily based on healthy animal models [3]. However, these are limited to the number of simultaneous experiments and ethical concerns. Several in-vitro and ex-vivo models are available to evaluate and assess medical devices and treatments. In particular, ex-vivo systems represent an important class, because the presence of native tissue guarantees biological response as a result of cell-cell interaction within a physiological extracellular matrix.

Purpose

The main goal of this research is to culture coronary arteries long-term in order to maintain them viable for assessment of safety and efficacy of stents, by mimicking physiological conditions.

Methods

The ex-vivo vascular bioreactor was used and data were acquired as described before [4]. Culture experiments were performed on porcine right coronary arteries (RCA) (n=9). Duration of culture was set to 2 (n=3), 4 (n=3), and 9 days (n=3). Hearts harvested from a local slaughterhouse were kept on Krebs-buffer (4°C) until dissection within 2 hours. The bioreactor containing the dissected RCA was placed in a 38°C incubator with 100% humidity and 5% CO2. The RCA was cultured in a blood-mimicking culture medium [4]. To assess cultured blood vessel morphology, diameter and structure during the culture period, ultrasound imaging was performed. Pressure (60-100 mmHg), flow rate (± 60 ml/min), and diameter measurements were monitored every day. The flow rate was adjusted to ensure a physiological peak endothelial shear stress of around 0.8 – 1.8 Pa. After 2, 4 or 9 days of culture, the RCA was fixed in buffered formaldehyde for 24 hours, embedded in paraffin and sectioned. Histology was performed using hematoxylin and eosin (H&E) and resorcin fuchsin (RF).

Results

Ultrasound imaging showed that the morphology and structure of cultured arteries was maintained during the cultures (average diameter 3.5±1.1 mm). Extracellular matrix was preserved as shown by histology (RF stain, Figure 1). Endothelial cells (ECs) coverage was incomplete at 2, but after 4 days it was completely restored. After 9 days of culture, a minimal layer of newly formed neointima was visible (Figure 1).

Conclusions

The cultured RCAs maintained their physiological morphology up to 9 days of culture. The endothelium was completely restored after 4 days, making the system suitable for ex-vivo interventions like stenting. The investigated model represents a useful tool for testing vascular therapies and devices, supporting the translational phase between in-vitro and ex-vivo studies.

Relation between pre-existing plaque size and neointimal healing in an adult porcine model of familial hypercholesterolemia

Background

Despite the efficacy of novel drug eluting stents (DES) in preventing restenosis, this complication still occurs, as do neo-atherosclerosis development and poor stent strut coverage that are associated with stent thrombosis. Safety and efficacy of novel coronary stents are preclinically being tested using an established porcine coronary model. However, the use of young healthy animal only allow limited conclusions to be drawn on the long-term effects, as the artieries do not reflect human pathology of advanced atherosclerosis. A key unresolved question is whether and how the presence, size and composition of pre-existing atherosclerotic plaque affect neointimal healing.

Purpose

The objective of this study is to understand the role of atherosclerotic plaque in neointimal response following DES placement in a large animal model of coronary artery disease by using optical coherence tomography (OCT) analysis.

Methods

The study was approved by the animal ethics committee. Familial hypercholesterolemia (FH) swine (n=6 Bretoncelles-Meishan) were given a high fat diet for 12 months to develop atherosclerosis. Stents (n=14) were implanted in n=14 coronary arteries under guidance of OCT with a stent-artery ratio of 1.1:1 at sites of atherosclerotic plaque, and animals were sacrificed after 28 days. Two types of Sirolimus eluting stents with different release profiles were implanted. Serial OCT pullbacks were taken before and after stent placement and after 28 days (follow-up), quantitatively analyzed and compared using dedicated software. The lumen area, stent area, plaque size (calculated as external elastic lamina (EEL) area - lumen area) and neointima (calculated as stent area – lumen area) were evaluated for each frame and averaged per stent. The plaque burden before stent implantation was evaluated at the same site of stent placement using coronary side branches as reference.

Results

The graph shows the association between the pre-existing plaque size before stenting and neointima formation after 28 days. Surprisingly, more pre-existing plaque size resulted in less neointima (P<0.01). There was one outlier, a stent with long dissection and extensive malapposition at baseline which showed an excessive tissue response at follow-up. The response in this animal model shows similarity to human vessel response as both regions with thin neointima formation as well as poor strut coverage were observed for both stent types.

Conclusion

The novel model of adult FH swine shows long-term vessel response to DES, that is similar to human response. This work shows that pre-existing atherosclerotic plaque affects the neointima after DES implantation. This insight highlights the necessity to use relevant disease models for safety and efficacy testing.

Plaque size and neointima relation

Funding Acknowledgement

Type of funding source: Public grant(s) – National budget only. Main funding source(s): The Netherlands Organisation for Health Research and Development (ZonMw)

Immunomodulation of surface biofunctionalized 3D printed porous titanium implants

Additive manufacturing (AM) techniques have provided many opportunities for the rational design of porous metallic biomaterials with complex and precisely controlled topologies that give rise to unprecedented combinations of mechanical, physical, and biological properties. These favorable properties can be enhanced by surface biofunctionalization to enable full tissue regeneration and minimize the risk of implant-associated infections (IAIs). There is, however, an increasing need to investigate the immune responses triggered by surface biofunctionalized AM porous metals. Here, we studied the immunomodulatory effects of AM porous titanium (Ti-6Al-4V) printed using selective laser melting, and of two additional groups consisting of AM implants surface biofunctionalized using plasma electrolytic oxidation (PEO) with/without silver nanoparticles. The responses of human primary macrophages and human mesenchymal stromal cells (hMSCs) were studied in terms of cell viability, cell morphology and biomarkers of macrophage polarization. Non-treated AM porous titanium triggered a strong pro-inflammatory response in macrophages, albeit combined with signs of anti-inflammatory effects. The PEO treatment of AM porous titanium implants showed a higher potential to induce polarization towards a pro-repair macrophage phenotype. We detected no cytotoxicity against hMSCs in any of the groups. However, the incorporation of silver nanoparticles resulted in strong cytotoxicity against attached macrophages. The results of this study indicate the potential immunomodulatory effects of the AM porous titanium enhanced with PEO treatment, and point towards caution and further research when using silver nanoparticles for preventing IAIs.

[Our experience with antibiotic therapy in children hospitalized between 1979 and 1981]

The use of antibiotics in the Children Hospital of Florence has been studied considering the whole hospital for 1979 and only one department for 1980-81. 7832 clinical records of children admitted to the Hospital have been analyzed in order to get more informations about the quality of antibiotic treatment and to understand the causes of use and misuse of this kind of drugs in pediatric practice.