Preclinical Testing of Living Tissue-Engineered Heart Valves for Pediatric Patients, Challenges and Opportunities.

Introduction: Pediatric patients with cardiac congenital diseases require heart valve implants that can grow with their natural somatic increase in size. Current artificial valves perform poorly in children and cannot grow; thus, living-tissue-engineered valves capable of sustaining matrix homeostasis could overcome the current drawbacks of artificial prostheses and minimize the need for repeat surgeries. Materials and Methods: To prepare living-tissue-engineered valves, we produced completely acellular ovine pulmonary valves by perfusion. We then collected autologous adipose tissue, isolated stem cells, and differentiated them into fibroblasts and separately into endothelial cells. We seeded the fibroblasts in the cusp interstitium and onto the root adventitia and the endothelial cells inside the lumen, conditioned the living valves in dedicated pulmonary heart valve bioreactors, and pursued orthotopic implantation of autologous cell-seeded valves with 6 months follow-up. Unseeded valves served as controls. Results: Perfusion decellularization yielded acellular pulmonary valves that were stable, no degradable in vivo, cell friendly and biocompatible, had excellent hemodynamics, were not immunogenic or inflammatory, non thrombogenic, did not calcify in juvenile sheep, and served as substrates for cell repopulation. Autologous adipose-derived stem cells were easy to isolate and differentiate into fibroblasts and endothelial-like cells. Cell-seeded valves exhibited preserved viability after progressive bioreactor conditioning and functioned well in vivo for 6 months. At explantation, the implants and anastomoses were intact, and the valve root was well integrated into host tissues; valve leaflets were unchanged in size, non fibrotic, supple, and functional. Numerous cells positive for a-smooth muscle cell actin were found mostly in the sinus, base, and the fibrosa of the leaflets, and most surfaces were covered by endothelial cells, indicating a strong potential for repopulation of the scaffold. Conclusions: Tissue-engineered living valves can be generated in vitro using the approach described here. The technology is not trivial and can provide numerous challenges and opportunities, which are discussed in detail in this paper. Overall, we concluded that cell seeding did not negatively affect tissue-engineered heart valve (TEHV) performance as they exhibited as good hemodynamic performance as acellular valves in this model. Further understanding of cell fate after implantation and the timeline of repopulation of acellular scaffolds will help us evaluate the translational potential of this technology.

Challenges in Perioperative Animal Care for Orthotopic Implantation of Tissue-Engineered Pulmonary Valves in the Ovine Model.

BACKGROUND: Development of valvular substitutes meeting the performance criteria for surgical correction of congenital heart malformations is a major research challenge. The sheep is probably the most widely used animal model in heart valves regenerative medicine. Although the standard cardiopulmonary bypass (CPB) technique and various anesthetic and surgical protocols are reported to be feasible and safe, they are associated with significant morbidity and mortality rates. The premise of this paper is that the surgical technique itself, especially the perioperative animal care and management protocol, is essential for successful outcomes and survival. METHODS: Ten juvenile and adult female sheep aged 7.8-37.5 months and weighing 32.0-58.0 kg underwent orthotopic implantation of tissue-engineered pulmonary valve conduits on beating heart under normothermic CPB. The animals were followed-up for 6 months before scheduled euthanasia. RESULTS: Based on our observations, we established a guide for perioperative care, follow-up, and treatment containing information regarding the appropriate clinical, biological, and ultrasound examinations and recommendations for feasible and safe anesthetic, surgical, and euthanasia protocols. Specific recommendations were also included for perioperative care of juvenile versus adult sheep. CONCLUSION: The described surgical technique was feasible, with a low mortality rate and minimal surgical complications. The proposed anesthetic protocol was safe and effective, ensuring both adequate sedation and analgesia as well as rapid recovery from anesthesia without significant complications. The established guide for postoperative care, follow-up and treatment in sheep after open-heart surgery may help other research teams working in the field of heart valves tissue regeneration.

Correlation between the increased release of catecholamines evoked by local anesthetics and their analgesic and adverse effects: Role of K(+) channel inhibition.

Because local anesthetics are known to inhibit both sodium and potassium channels, and anesthetic properties have been attributed to the former effect, we compared their effects with those of tetrodotoxin (TTX), a selective Na(+) channel inhibitor with anesthetic activity, and 4-aminopyridine (4-AP), a selective potassium channel blocker with convulsive activity, on transmitter release during rest and in response to field (axonal) stimulation using the microvolume perfusion method and isolated prefrontal cortex and spinal cord slice preparations loaded with the radioactive transmitters [(3)H]dopamine ([(3)H]DA) and [(3)H]noradrenaline ([(3)H]NA). It is also known that local anesthetics may exert analgesic effect and, rarely, some adverse effects on the central nervous system (CNS). Neurochemical evidence demonstrated that local anesthetics administered at concentrations ranging from 0.5 to 5mM, which might have been intentionally or accidentally achieved in clinical practice (e.g., during spinal and epidural anesthesia or peripheral nerve block), led to presynaptic failures during neurochemical transmission, including inhibited transmitter release associated with axonal firing and markedly enhanced extraneuronal concentrations of transmitters due to increased resting, [Ca(2+)]o-independent release. Tetrodotoxin, a toxin with selective Na(+) channel-blocking properties, inhibited the stimulation-evoked release but failed to affect the resting release. In contrast, the potassium channel inhibitor 4-AP enhanced both the resting- and action potential-evoked transmitter releases. It is concluded that effects of local anesthetics on resting catecholamine release in the spinal cord may contribute to their action during neuropathic pain relief and spinal analgesia as well as to their side effects in the CNS.