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Nerve guidance conduits (NGCs) are used as an alternative to the "gold standard" nerve autografting, preventing the need for surgical intervention required to harvest autologous nerves. However, the regeneration outcomes achieved with the current NGCs are only comparable with autografting when the gap is short (less than 10 mm). In the present study, we have developed NGCs made from a blend of polyhydroxyalkanoates, a family of natural resorbable polymers. Hollow NGCs made from a 75:25 poly(3‐hydroxyoctanoate)/poly(3‐hydroxybutyrate) blend (PHA‐NGCs) were manufactured using dip‐molding. These PHA‐NGCs showed appropriate flexibility for peripheral nerve regeneration. In vitro cell studies performed using RT4‐D6P2T rat Schwann cell line confirmed that the material is capable of sustaining cell proliferation and adhesion. PHA‐NGCs were then implanted in vivo to repair 10 mm gaps of the median nerve of female Wistar rats for 12 weeks. Functional evaluation of the regenerated nerve using the grasping test showed that PHA‐NGCs displayed similar motor recovery as the autograft, starting from week 7. Additionally, nerve cross‐sectional area, density and number of myelinated cells, as well as axon diameter, fiber diameter, myelin thickness and g‐ratio obtained using the PHA‐NGCs were found comparable to an autograft. This preclinical data confirmed that the PHA‐NGCs are indeed highly promising candidates for peripheral nerve regeneration. [ABSTRACT FROM AUTHOR]

Objectives: To evaluate: (i) the neuro‐regenerative potential of chitosan membrane (CS‐Me) on acutely axotomised autonomic neurones in vitro; (ii) to exclude the possibility that a pro‐regenerative biomaterial could interfere with the proliferation activity of prostate cancer cell lines; (iii) to provide an in vivo proof of the biocompatibility and regeneration promoting effect of CS‐Me in a standardised rat model of peripheral nerve injury and repair; (iv) finally, to evaluate the tissue reaction induced by the degrading material; as previous studies have shown promising effects of CS‐Me for protection of the neurovascular bundles for potency recovery in patients that undergo nerve‐sparing radical prostatectomy (RP). Materials and Methods: Addressing aim (i), the neuro‐regenerative potential, organotypic cultures derived from primary sympathetic ganglia were cultured on CS‐Me over 3 days and neurite extension and axonal sprouting were evaluated. Addressing aim (ii), effects of CS on cancer cells, different human prostate cancer cell lines (PC3, DU‐145, LN‐Cap) were seeded on CS‐coated plates or cultured in the presence of CS‐Me dissolution products. Addressing aims (iii) and (iv), functional recovery of peripheral nerve fibres and tissue reaction with the biomaterial, CS‐Me and CS nerve guides were used to repair a median nerve injury in the rat. Functional recovery was evaluated during the post‐recovery time by the behavioural grasping test. Results: CS‐Me significantly stimulated axon elongation from autonomic ganglia in comparison to control conditions in organotypic three‐dimensional cultures. CS coating, as well as the dissolution products of CS‐Me, led to a significantly lower proliferation rate of prostate cancer cell lines in vitro. Tissue reaction towards CS‐Me and standard CS nerve guides was similar in the rat median nerve model, as was the outcome of nerve fibre regeneration and functional recovery. Conclusion: The results of this study provide the first experimental evidence in support of the clinical safety of CS‐Me and of their postulated effectiveness for improving functional recovery after RP. The presented results are coherent in demonstrating that acutely axotomised autonomic neurones show increased neurite outgrowth on CS‐Me substrate, whilst the same substrate reduces prostate cancer cell line proliferation in vitro. Furthermore, CS‐Me do not demonstrate any disadvantage for peripheral nerve repair in a standard animal model. [ABSTRACT FROM AUTHOR]

The peripheral nervous system has an intrinsic capability to regenerate, crucially related to the ability of Schwann cells (SC) to create a permissive environment, for example, through production of regeneration-promoting neurotrophic factors. Survival, proliferation, migration and differentiation of SC into a myelinating phenotype during development and after injury is regulated by different Neuregulin1 (NRG1) isoforms. This study investigates the expression of different NRG1 isoforms and of their ErbB receptors in distal rat median nerve samples under regenerating conditions after a mild (crush) and more severe (end-to-end repair) injury and under degenerating condition. The expression of the NRG1/ErbB system was evaluated at mRNA and protein level, and demonstrated to be specific for distinct and consecutive phases following nerve injury and regeneration or the progress in degeneration. For the first time a detailed analysis of expression profiles not only of soluble and transmembrane NRG1 isoforms, but also of alpha and beta as well as type a, b and c isoforms is presented. The results of mRNA and protein expression pattern analyses were related to nerve ultrastructure changes evaluated by electron microscopy. In particular, transmembrane NRG1 isoforms are differentially regulated and proteolytically processed under regeneration and degeneration conditions. Soluble NRG1 isoforms alpha and beta, as well as type a and b, are strongly upregulated during axonal regrowth, while type c NRG1 isoform is downregulated. This is accompanied by an upregulation of ErbB receptors. This accurate regulation suggests that each molecule plays a specific role that could be clinically exploited to improve nerve regeneration. [ABSTRACT FROM AUTHOR]

Quantitative estimation of myelinated nerve fiber number, together with fiber size parameters, is one of the most important tools for nerve regeneration research. In this study we used a design-based stereological method to evaluate the regenerative process in two experimental paradigms: crush injury and autograft repair. Samples were embedded in resin and morphometric counting and measurements were performed using both light and electron microscopes. Results show a significant difference in myelinated fiber number estimation between light and electron microscopes, especially after autograft repair; light microscope significantly underestimates the number of fibers because of the large number of very small axons that can be detected only in electron microscope. The analysis of the size parameters also shows a higher number of small fibers in electron microscopic analysis, especially in regenerated nerves. This comparative study shows that the integration of data obtained in light microscope with those obtained in electron microscope is necessary in revealing very small myelinated fibers that cannot be detected otherwise. Moreover, the difference in the estimation of total number of myelinated fibers between light and electron microscopes must be considered in data analysis to ensure accurate interpretation of the results. [ABSTRACT FROM AUTHOR]

Little is known on the early homing features of transplanted mesenchymal stem cells (MSCs).We used the isolated rat heart model to study the homing of MSCs injected in the ventricular wall of a beating heart. In this model all types of cells and matrix elements with their interactions are represented, while external interferences by endothelial/neutrophil interaction and neurohormonal factors are excluded.We studied the morphology and marker expression of MSCs implanted in normal hearts and in the border-zone of infarcted myocardium. Early morphological adaptation of MSC homing differs between normal and infarcted hearts over the first 6 hrs after transplantation. In normal hearts, MSCs migrate very early through the interstitial milieu and begin to show morphological changes.Yet, in infarcted hearts MSCs remain in the site of injection forming clusters of round-shaped cells in the border-zone of the infarcted area. Both in normal and infarcted hearts, immunohistochemistry and confocal imaging showed that, besides the proliferative marker proliferating cell nuclear agent (PCNA), some transplanted cells early express myoblastic maker GATA-4, and some of them show a VWF immunopositivity. Moreover, a few hours after injection connexin-43 is well evident between cardiomyocytes and injected cells. This study indicates for the first time that the isolated beating heart is a good model to study early features of MSC homing without external interferences. The results show (i ) that MSCs start to change marker expression few hours after injection into a beating heart and (ii ) that infarcted myocardium influences transplanted MSC morphology and mobility within the heart. [ABSTRACT FROM AUTHOR]