Effect of NEP1-40/PLGA on facial nerve repair in rats

To investigate the effect of neurite outgrowth inhibitor extracellular peptide residues 1-40 (NEP1-40) combined with poly (lactic-co-glycolic acid) (PLGA) and gelatin electrospun fiber membrane on facial nerve repair in rats.

According to the principle of random grouping, 108 male SD rats were divided into four groups (n = 27 in each group, approved by the ethics committee), namely, the sham group, control group, PLGA group, and NEP1-40 + PLGA group. A facial nerve fracture model was established for all of the groups except for the sham group. The control group received no further treatment, the PLGA group and the NEP1-40+PLGA group were supported by PLGA membrane, and the NEP1-40+PLGA group received one immediate local injection of NEP1-40 (5 μg/μL) at a dose of 10 μL. Facial nerve function analysis, electrophysiological examination, transmission electron microscope observation, HE staining, and immunohistochemical staining of myelin marker S100β and axonal marker β3-tubulin were used to evaluate the recovery of injured facial nerves of rats at 2, 4 and 8 weeks.

At 8 weeks, the facial nerve function score of the NEP1-40+PLGA group was better than that of the control group and PLGA group (P < 0.001), and facial nerve function was significantly restored. Electrophysiological examination of nerve action potentials at the injured facial nerve showed that the amplitude in the NEP1-40+PLGA group was higher than that of the control group and PLGA group (P < 0.001), but there was no significant difference in latency and conduction velocity results between the groups (P > 0.05). At 2, 4, and 8 weeks, transmission electron microscopy showed that the number of myelinated nerve fibers and myelin sheath thickness in the cross-section of the injured facial nerve in the NEP1-40+PLGA group were greater than those in the other groups (P < 0.05). At 8 weeks, HE staining showed that the facial nerves in the control group had partially recovered, but the overall cell distribution was uneven and the boundary with surrounding tissues was slightly blurred. In contrast, the NEP1-40+PLGA group had a relatively uniform cell distribution and a clearer boundary with surrounding tissues. At 2, 4, and 8 weeks, the immunohistochemical results showed that in the cross-section of the injuried facial nerve, NEP1-40 increased the expression of neural markers S100 β and β3-tubulin, especially β3-tubulin, which was close to normal levels (P > 0.05).

NEP1-40 is beneficial for the generation of new myelin sheaths and axons at the site of injury, and it can promote the repair and regeneration of injured facial nerves to a certain extent, thus accelerating the recovery of injured nerve function.