Focal release of neurotrophic factors by biodegradable microspheres enhance motor and sensory axonal regeneration in vitro and in vivo

Abstract

Neurotrophic factors (NTFs) promote nerve regeneration and neuronal survival after peripheral nerve injury. However, drawbacks related with administration and bioactivity during long periods limit their therapeutic application. In this study, PLGA microspheres (MPs) were used to locally release different NTFs and evaluate whether they accelerate axonal regeneration in comparison with free NTFs or controls. ELISA, SEM, UV/visible light microscopy, organotypic cultures of DRG explants and spinal cord slices were used to characterize MP properties and the bioactivity of the released NTFs. Results of organotypic cultures showed that encapsulated NTFs maintain longer bioactivity and enhance neurite regeneration of both sensory and motor neurons compared with free NTFs. For in vivo assays, the rat sciatic nerve was transected and repaired with a silicone tube filled with collagen gel or collagen mixed with PBS encapsulated MPs (control groups) and with free or encapsulated NGF, BDNF, GDNF or FGF-2. After 20 days, a retrotracer was applied to the regenerated nerve to quantify motor and sensory axonal regeneration. NTF encapsulation in MPs improved regeneration of both motor and sensory axons, as evidenced by increased numbers of retrolabeled neurons. Hence, our results show that slow release of NTFs with PLGA MP enhance nerve regeneration.

Dose-Dependent Differential Effect of Neurotrophic Factors on In Vitro and In Vivo Regeneration of Motor and Sensory Neurons

“…Organotypic cultures were prepared as previously described [14]. Briefly, collagen I (rat tail, #354236, Corning) diluted in basal Eagle's medium (Gibco) and sodium bicarbonate at 0.3 mg/mL was prepared as control condition.…”

The role of growth factors in nerve regeneration

“…It is well acknowledged that BDNF plays a role as a survival factor for damaged neurons (38). This survival increasing effect of exogen BDNF is temporary and dependent on functional trkB receptors (39,40).…”

“…It has been shown that, following nerve injury, BDNF does not increase functional recovery in tests such as sciatic function index, however, it has triggering effects. Although exogenous BDNF has inefficacies in postinjury functional recovering, endogenous BDNF is known to play an important role in peripheral nerve regeneration (38,55). Anti BDNF antibody application after damage has been reported both to diminish axonal elongation and to decrease the axonal density and number (56).…”

“…During regeneration, a time-dependent decrease is seen in the total number of regenerated axons and reinnervation of muscle fibers (25,47). However, it is suggested that low dose and long term BDNF application increases both axonal regeneration and neural cell repair and thus it is very effective in reversing the negative effects caused by chronic axotomy (38). Moreover, similarly, low dose BDNF application has been shown to increase the number of reinnervated muscle fibers significantly (9).…”

Recovery of erectile function comparing autologous nerve grafts, unseeded conduits, Schwann cell seeded guidance tubes and GDNF-overexpressing Schwann cell grafts

“…Adherent molecules on the surface of SCs can secrete extracellular matrix and guide the growth of axons. Neurotrophic factors secreted by SCs might be the most important factors in the microenvironment for regenerating axons (Santos et al, 2016). Growth factors enhance axonal regrowth and promote neuron survival.…”