Comparison of peripheral nerve protection between insulin-based glucose control and alpha lipoic acid (ALA) in the streptozotocin (STZ)-induced diabetic rat

Strict glucose control is a well-proven therapeutic approach for peripheral neuropathies in patients with diabetes. Alpha lipoic acid (ALA) has also been accepted as a therapeutic agent for diabetic peripheral neuropathy (DPN) in the respect of pathogenesis. However, the potential of ALA as a treatment for DPN in comparison to that of glucose control is unclear. In this study, we compared the neuroprotective potential of glucose control and ALA. Animals were divided into 6 groups based on the intervention used, as follows: normal, diabetes (DM), DM+racemic form of ALA, DM+R form of ALA, DM+once daily insulin glargine, and DM+once daily insulin glargine with twice daily insulin glulisine. Various sensory tests were performed after 12 weeks of treatment, and immunohistochemistry of nerve fibers obtained from the sciatic and cutaneous nerves was performed after 24 weeks of treatment. There were no significant differences between the ALA-treated and insulin-treated DM groups in the sensory tests or in antioxidant activity. The axonal diameters and myelin sheath area of the sciatic nerves and the cutaneous small nerves, as assessed based on intraepidermal nerve fiber density, were similar in the ALA-treated and insulin-treated animals, although there was a non-significant trend for a mild increase in the both basal and rapid-acting insulin group compared with non-treated DM group. In conclusion, our results suggest that the neuroprotective benefits of ALA and insulin-based glucose control may be similar, although glucose control may have had slightly more beneficial effects in this animal model of diabetes. Of note, glucose levels should be strictly controlled, including corrections for fluctuations in the glucose level, to obtain therapeutic benefits in DPN.