Tacrolimus reduces scar formation and promotes sciatic nerve regeneration

Abstract

A sciatic nerve transection and repair model was established in Sprague-Dawley rats by transecting the tendon of obturator internus muscle in the greater sciatic foramen and suturing with nylon sutures. The models were treated with tacrolimus gavage (4 mg/kg per day) for 0, 2, 4 and 6 weeks. Specimens were harvested at 6 weeks of intragastric administration. Masson staining revealed that the collagen fiber content and scar area in the nerve anastomosis of the sciatic nerve injury rats were significantly reduced after tacrolimus administration. Hematoxylin-eosin staining showed that tacrolimus significantly increased myelinated nerve fiber density, average axon diameter and myelin sheath thickness. Intragastric administration of tacrolimus also led to a significant increase in the recovery rate of gastrocnemius muscle wet weight and the sciatic functional index after sciatic nerve injury. The above indices were most significantly improved at 6 weeks after of tacrolimus gavage. The myelinated nerve fiber density in the nerve anastomosis and the sciatic nerve functions had a significant negative correlation with the scar area, as detected by Spearman's rank correlation analysis. These findings indicate that tacrolimus can promote peripheral nerve regeneration and accelerate the recovery of neurological function through the reduction of scar formation.

Keywords: myelinated nerve fiber; neural regeneration; neurological function; peripheral nerve injury; scar; sciatic nerve; tacrolimus.

Figure 1

Collagen fiber proliferation in longitudinal sections of injured sciatic nerve at the nerve anastomosis site (Masson staining, light microscope, × 40). In the model group (A), a large amount of collagen fibers were dyed dark blue. In the tacrolimus gavage groups for 2 (B), 4 (C), 6 weeks (D), the number of blue collagen fibers gradually decreased, while of the number of red nuclei increased. In the normal control group (E), the vast majority of staining was nuclear.

Figure 2

Myelinated nerve fiber formation in the transverse sciatic nerve at the site of anastomosis (hematoxylin-eosin staining, light microscope, × 40). In the model group (A), blue myelinated nerve nuclei were rarely visible. In the tacrolimus gavage groups for 2 (B), 4 (C), and 6 weeks (D), the number of blue myelinated nerve nuclei was gradually increased. In the normal control group (E), many blue myelinated nerve nuclei were observed.

Figure 3

Correlation of sciatic nerve myelinated nerve fiber density and sciatic functional index with scar area (Spearman's rank correlation analysis). (A) Myelinated nerve fiber density (n/mm²) showed a significant negative correlation with scar area (mm²; r_s = -1.0, P < 0.01); (B) Sciatic functional index (%) absolute value was apparently positively correlated with scar area (mm²; r_s = 1.0, P < 0.01).