OBJECTIVE To investigate the protective effect and mechanism of vincamine derivative Vin24 on the pathological symptoms of diabetic peripheral neuropathy (DPN) in mice.

METHODS Forty 8-week-old male C57BL/6N mice were randomly divided into control group (Control), model group (STZ), vincamine group (STZ+Vin) and Vin24 group (STZ+Vin24). Except the control group, the rest three groups of mice were intraperitoneally injected with streptozocin (STZ, 150 mg ·kg^-1) to induce type 1 diabetes and administration was started six weeks later. Thirty 18-week-old male db/db mice were randomly divided into model group (db/db), vincamine group (db/db+Vin) and Vin24 group (db/db+Vin24). Ten age-matched wild-type mice were used as a control group (db/m). The vincamine group were gavaged 30 mg ·kg^-1 of vincamine daily. The Vin24 group was gavaged 46.8 mg ·kg^-1 of Vin24, while the control and model group were given the same amount of saline daily, for four weeks. Sensory functions of the mice were assessed by assays against tactile and thermal allodynia threshold. A Laser Speckle Imaging System was used to detect the peripheral blood flow. The epidermal tissues of foot pads were collected for PGP9.5 immunofluorescence to measure the intraepidermal nerve fiber (IENF) density. Primary dorsal root ganglia (DRG) neurons were isolated for β-tubulin Ⅲ immunofluorescence to evaluate neurite outgrowth. Additionally, DRG tissues were extracted for ATF3 immunofluorescence for the evaluation of DRG neuronal apoptosis, and Western blot analysis was used to measure the protein levels of Bcl-2, Bax, Cleaved-Caspase3 and Caspase3.

RESULTS The tactile and thermal allodynia thresholds were decreased (P < 0.01, P < 0.001), and peripheral blood flow was increased (P < 0.001) in Vin24-treated DPN mice. The IENF density was increased (P < 0.05, P < 0.01) and DRG neurite outgrowth was improved (P < 0.001) in Vin24 group compared with that in the model group. Immunofluorescence assay results indicated that the number of ATF3 (a marker of neuronal apoptosis)-positive neurons was obviously decreased (P < 0.01, P < 0.001) in DRG tissues of Vin24-treated DPN mice. Western blot results demonstrated that the protein level of anti-apoptotic protein Bcl-2 was significantly increased (P < 0.05), and the protein levels of pro-apoptotic proteins Bax and Cleaved-Caspase3 were significantly decreased (P < 0.05) in DRG tissues of Vin24-treated DPN mice.

CONCLUSION Vincamine derivative Vin24 inhibits the activation of Cleaved-Caspase3 and reduces the neuronal apoptosis levels by regulating Bcl-2/Bax/Caspase3 pathway, and eventually alleviates DRG neuronal damage and improves peripheral neuropathy in diabetic mice.