Beneficial effects of nerve growth factor on islet transplantation

Neurotrophic Factors: An Overview

The neurotrophins are a family of closely related proteins that were first identified as survival factors for sympathetic and sensory neurons and have since been shown to control a number of aspects of survival, development, and function of neurons in both the central and peripheral nervous systems. Limiting quantities of neurotrophins during development control the numbers of surviving neurons to ensure a match between neurons and the requirement for a suitable density of target innervation. Biological effects of each of the four mammalian neurotrophins are mediated through activation of one or more of the three members of the tropomyosin-related kinase (Trk) family of receptor tyrosine kinases (TrkA, TrkB, and TrkC). In addition, all neurotrophins activate the p75 neurotrophin receptor (p75^NTR), a member of the tumor necrosis factor receptor superfamily. Neurotrophin engagement of Trk receptors leads to activation of Ras, phosphatidylinositol 3-kinase, phospholipase C-γ1, and signaling pathways controlled through these proteins, including the mitogen-activated protein kinases. Neurotrophin availability is required into adulthood, where they control synaptic function and plasticity and sustain neuronal cell survival, morphology, and differentiation. This article will provide an overview of neurotrophin biology, their receptors, and signaling pathways.

Nerve growth factor: a neuroimmune crosstalk mediator for all seasons

Neurotrophic factors comprise a broad family of biomolecules - most of which are peptides or small proteins - that support the growth, survival and differentiation of both developing and mature neurons. The prototypical example and best-characterized neurotrophic factor is nerve growth factor (NGF), which is widely recognized as a target-derived factor responsible for the survival and maintenance of the phenotype of specific subsets of peripheral neurons and basal forebrain cholinergic nuclei during development and maturation. In addition to being active in a wide array of non-nervous system cells, NGF is also synthesized by a range of cell types not considered as classical targets for innervation by NGF-dependent neurons; these include cells of the immune-haematopoietic lineage and populations in the brain involved in neuroendocrine functions. NGF concentrations are elevated in numerous inflammatory and autoimmune states such as multiple sclerosis, chronic arthritis, systemic lupus erythematosus and mastocytosis, in conjunction with increased accumulation of mast cells. Intriguingly, NGF seems to be linked also with diabetic pathology and insulin homeostasis. Mast cells and NGF appear involved in neuroimmune interactions and tissue inflammation. As mast cells are capable of producing and responding to NGF, this suggests that alterations in mast cell behaviour could provoke maladaptive neuroimmune tissue responses, including those of an autoimmune nature. Moreover, NGF exerts a modulatory role on sensory nociceptive nerve physiology in the adult, which appears to correlate with hyperalgesic phenomena occurring in tissue inflammation. NGF can therefore be viewed as a multifactorial modulator of neuro-immune-endocrine functions.

Neurotrophic Factors and Their Potential Applications in Tissue Regeneration

Neurotrophic factors are growth factors that can nourish neurons and promote neuron survival and regeneration. They have been studied as potential drug candidates for treating neurodegenerative diseases. Since their identification, there are more and more evidences to indicate that neurotrophic factors are also expressed in non-neuronal tissues and regulate the survival, anti-inflammation, proliferation and differentiation in these tissues. This mini review summarizes the characteristics of the neurotrophic factors and their potential clinical applications in the regeneration of neuronal and non-neuronal tissues.

The protective effects of Achyranthes bidentata polypeptides on rat sciatic nerve crush injury causes modulation of neurotrophic factors

Pharmacological treatment is a therapeutic approach to improving nerve regeneration and functional recovery after peripheral nerve crush injury. The objective of the present study was to investigate the effects of the polypeptides isolated from Achyranthes bidentata Blume (abbreviated as ABPP) on rat sciatic crush injury and to test the possible involvement of neurotrophic factors. After surgical crush injury, rats received daily intraperitoneal injection of 0.2 ml saline containing 2 mg ABPP, 1 μg nerve growth factor (NGF) or no additive. The results from walking track analysis, electrophysiological assessment and histological evaluation indicated that the repair outcomes by ABPP treatment were close to those by NGF treatment, but better than those by treatment with saline alone. The quantitative real-time RT-PCR was used to monitor the mRNA expression of growth associated protein in the crush nerves and the mRNA expression of NGF, brain-derived neurotrophic factor (BDNF), ciliary neurotrophic factor (CNTF), tyrosine kinase (Trk)A and TrkB in the dorsal root ganglia (DRGs) at L4-L6. The mRNA expression of these genes in the crush nerve sample and DRGs sample was higher after treatment with ABPP or NGF than after treatment with saline alone. Our findings suggest that ABPP might protect peripheral nerve against crush injury through stimulating release of neurotrophic factors and the other cytokines.

Multilayered microcapsules for the sustained-release of angiogenic proteins from encapsulated cells

BACKGROUND

Multilayered alginate microcapsules with a permselective poly-L-ornithine membrane can be used for the dual purpose of encapsulating cells in the inner core and sustained release of angiogenic proteins from the outer layer. The aim of this study was to examine the encapsulation and release of a novel chimeric form of fibroblast growth factor-1 (FGF-1) from the outer layer of alginate microcapsules.

METHODS

Heparin-binding growth-associated molecule bound to FGF-1 (HB-GAM/FGF-1) was encapsulated in the outer layer of multilayered alginate microbeads constructed using varying alginate conditions. The encapsulation and release of the chimera was quantified.

RESULTS

The outer layer was able to encapsulate and release HB-GAM/FGF-1 for up to 30 days. The outer layer made with 1% alginate of high mannuronic acid content provided the fastest release, while 1.25% high guluronic acid content alginate displayed the longest duration of release.

CONCLUSIONS

The outer layer of multilayered alginate microbeads can be used for the encapsulation and long-term release of HB-GAM/FGF-1.

Fibroblast growth factor-1 (FGF-1) loaded microbeads enhance local capillary neovascularization

BACKGROUND

Growth of new blood vessels (neovascularization) occurs naturally in the body, but the slow rate of the process may not be sufficient for survival of engineered tissues and transplanted cells, such as pancreatic islets. For transplanted islets, it is crucial that the transplantation site has sufficient vasculature to support the needs of the islets. Therefore, the specific aim of this research was quantify the effect of FGF-1 incorporation into alginate microbeads on neovascularization of such capsules in an in vivo rat transplant model.

MATERIALS AND METHODS

Microbeads loaded with FGF-1 or control beads (beads without FGF-1) were implanted in the rat omental pouch model. Animals were sacrificed 7 d post-implantation.

RESULTS

Microbeads loaded with FGF-1 stimulated a significant increase in vascular density compared with control rats implanted with control beads.

CONCLUSIONS

These results indicate that alginate microbeads loaded with FGF-1 enhance local neovascularization around implanted microbeads. These data provide a compelling impetus for experimental pursuit of FGF-loaded alginate microcapsules for vascularization of transplanted islets.