Fig. 1(A) Body weight, (B) blood glucose levels, and (C) glycosylated hemoglobin levels in the experimental groups. Body weight was increased gradually in all experimental groups, but diabetes mellitus (DM)+alpha lipoic acid (ALA) group showed less increased trend compared with other groups although significant differences were not present. Glucose levels were significant higher in DM groups than normal group; however, DM+metformin group showed lower glucose level significantly compared with other DM group. Data are presented as mean±standard deviation (n=7 to 10 per group). aP<0.05 vs. normal controls, bP<0.05 vs. DM (n=7 to 10 per group).
Fig. 2Sensory test using (A) Von Frey filament, (B) hot plate, (C) tail flick, and (D) Randall-Selitto responses in the experimental groups. Mechanical allodynia, threshold to hot sense, and pressure response were more sensitive in diabetes mellitus (DM) group during experimental period and these responses were partly blunted by metformin or alpha lipoic acid (ALA) treatment although there were no significant differences between DM+metformin and DM+ALA groups. Data are presented as mean±standard deviation (n=7 to 10 per group). aP<0.05 vs. normal controls, bP<0.05 vs. DM (n=7 to 10 per group).
Fig. 3Intraepidermal nerve fiber density (IENFD) according to the time passage (A) and metformin (MET) or alpha lipoic acid (ALA) treatment (B) in experimental groups and immunohistochemistry images (C) of the cutaneous small nerve fibers in experimental groups (a: normal; b: diabetes mellitus [DM]; c: DM+MET; d: DM+ALA). Arrows indicate immunostained small nerve fiber. Both DM+MET and DM+ALA groups showed less reduced IENFD irrespective of experimental period compared with DM group and significant differences were not present between DM+MET and DM+ALA groups. Data are presented as mean±standard deviation (n=7 to 10 per group). aP0.05 vs. normal controls, bP<0.05 vs. DM (n=7 to 10 per group).
Fig. 4The comparison of sciatic nerves in the respect of (A) axon diameter, (B) myelin sheath thickness, and (C) myelinated fiber diameter of experimental groups. There were no significant differences in the three morphometric parameters between diabetes mellitus (DM)+metformin and DM+alpha lipoic acid (ALA) groups. Data are presented as mean±standard deviation (n=7 to 10 per group). aP0.05 vs. normal controls, bP<0.05 vs. DM (n=7 to 10 per group).
Fig. 5Stained morphological findings of sciatic nerves (×1,000) using toluidine blue in the experimental groups. (A) Normal, (B) diabetes mellitus (DM), (C) DM+metformin (MET), (D) DM+alpha lipoic acid (ALA).
Fig. 6Blood levels of (A) vitamin B12, (B) glutathione, and (C) tumor necrosis factor α (TNF-α) in the experimental groups at 24 weeks. Vitamin B12 and glutathione levels were not different among experimental groups; however, TNF-α was most high in diabetes mellitus (DM) group compared with other experimental groups and DM+metformin or DM+alpha lipoic acid (ALA) groups showed reduced trend significantly compared with DM group. Data are presented as mean±standard deviation (n=7 to 10 per group). aP0.05 vs. normal controls, bP<0.05 vs. DM (n=7 to 10 per group).