Effect of ALA on preventing diabetic peripheral neuropathy in rats through mitochondrial axonal transport

PURPOSE: To explore the mechanism by which alpha-lipoic acid (ALA) regulates mitochondrial axonal transport to protect the sciatic nerve in diabetic rats. METHODS: Among 55 healthy male Sprague‒Dawley rats, 40 were randomly selected, fed a high-carbohydrate/high-fat diet and intraperitoneally injected with streptozotocin (STZ) to induce diabetes. Diabetic rats were randomly divided into diabetic peripheral neuropathy (DPN) and alpha lipoic acid (ALA) groups, with 15 rats in each group, excluding the rats in which diabetes failed to be induced and the dead rats. The other 15 rats were used as the control group. The rats in the ALA group were administered an ALA suspension (60 mg/kg/day) by gavage for 12 weeks. The rats in the control group and DPN group were gavaged with an equal volume of distilled water every day for 12 weeks. After the intervention was complete, the motor nerve conduction velocity (MNCV) and paw withdrawal threshold (PWT) were measured. Morphological changes in the sciatic nerve were observed by HE staining. Immunofluorescence staining and Western blotting were performed to measure protein expression levels. In vitro, a model of NSC34 cell injury was established by treating cells with high concentrations of glucose and palmitic acid sodium. NSC34 cells were randomly divided into the control group, DPN group and ALA group. The ALA group was treated with ALA for 24 hours. Changes in the axons of NSC34 cells were assessed by measuring the length of the axons. Immunofluorescence staining was performed to determine the fluorescence intensity of the cells, and Western blotting was performed to determine the grayscale value of each band. RESULTS: ALA increased the MNCV and PWT in DPN rats and increased the levels of phosphorylated AMP-activated protein kinase (p-AMPK) and phosphorylated cAMP-response element-binding protein (p-CREB). The expression of a motor protein involved in anterograde axonal mitochondrial transport, kinesin family member 5A (KIF5A), was upregulated, whereas the expression of a dynein protein involved in mitochondrial retrograde transport, Dynein cytoplasmic 1 intermediate chain 2 (DYNC1I2), was downregulated by ALA. CONCLUSION: The results of this study suggest that ALA alleviates peripheral nerve injury in diabetic rats by promoting the anterograde axonal transport of mitochondria, which may be related to AMPK/CREB signaling.