ABSTRACT
BACKGROUND: Diabetes causes abnormal insulin like growth factor-1 (IGF-1) gene expression, which contributes to initiation and development of peripheral neuropathy.OBJECTIVE: To investigate the efficacy of a single dose of methylcabalamin on prevention of experimental diabetic neuropathy and the possible molecular mechanism of its involvement in IGF-1 gene expression.DESIGN: Completely randomized and controlled experiment.SETTING: Endocrinology Department of the First Affiliated Hospital of Nanjing Medical University.MATERIALS: The study was carried out in an Animal Center of Nanjing Medical University. Totally 80 male Sprague Dawley rats (sanitary degree)were randomly selected.METHODS: ① Totally 64 rats were chosen to be induced diabetic. They were injected intravenously with alloxan dissolved in saline solutions, at the dose of 240 mg/kg. ② Of 16 rats were chosen as normal control group who were injected intravenously with equivalent volume of saline solution. ③ Of 64 established diabetic rats were treated with daily subcutaneous injection of pork regular insulin in combination of protamine zinc insulin (2:1) then further divided into 2 groups as insulin-treatment diabetic control groups based on different blood glucose levels: group 1 with relatively better control of diabetes, group 2 with relatively worse control of diabetes, with 32 rats in each group. Totally 16 rats of each group were treated with methylcobalamin injection intramuscularly with 500 μg/kg body weight, thus correspondingly divided into insulin +methylcobalamin group 1 and insulin+methylcobalamin group 2. The remaining 16 rats of each group as respective insulin-treatment diabetic control groups were treated with equivalent volume of saline. ④ Initiate weight and end weight were measured at beginning of the experiment and after diabetic model was established. Glucose oxidase was used to detect glucose level. 1-deoxy-1-malin was used to detect fructose level. ⑤ Parameters were measured as follows: Sensory/motor nerve conduction velocity (SNCV, MNCV) and evoked potential amplitude (EPA) of sciatic nerves detected by evoked electromyogram; IGF-I mRNA by reverse-transcriptase polymerase chain reaction (RT-PCR); IGF-1 peptide by enzyme-linked immunosorbent assay (ELISA). ⑥ One-way analysis of variance was used to analyze the Significance of differences among groups.MAIN OUTCOME MEASURES: ① Tissue IGF-1 mRNA/ IGF-1 peptide, electrophysiological data of individual groups at different points of the experiment. ② Comparison between individual groups in glucose metabolic parameters and body weights at different points of the experiment.RESULTS: Three rats died for diabetic infection or other acute complications and only 77 rats were included in the final statistical analysis.① Body weight and glucose metabolic parameter changes: After diabetic model, glucose, fructose level and body weight change between methylcobalamin+insulin treated groups and insulin treated groups were not significant. ② IGF-1 mRNA/peptide changes: Tissue IGF-1 mRNA increased significantly in methylcobalamin + insulin treated groups than that in insulin treated groups, respectively (P ＜ 0.05-0.01). Two weeks after diabetic model was established, the sciatic tissue IGF-1 mRNA contents were obviously higher in methylcobalamin + insulin treated group 1 than that in insulin treated group 1 (P ＜ 0.05), but not significantly different from that in NC group; Similarly, tissue IGF-1 mRNA contents were obviously higher in methylcobalamin + insulin treated group 2 than that in insulin treated group 2 (P ＜ 0.05), but lower than that in NC group (P ＜ 0.01); Month 2, tissue IGF-1 contents in methylcobalamin+ insulin treated groups were lower signiiicantly than NC groups, but higher than insulin treated groups (P ＜ 0.05-0.01). By month 3, IGF-1 mRNA level in methylcobalamin+ insulin treated group 2 was not significantly different from that in insulin treated group 2. The IGF-1 peptide levels in nerve tissue changed approximately parallel to IGF-1 mRNA level over time course. ③ Nerve electrophysiological data changes: Month 2 and 3, SNCV, MNCV and EPA were significantly higher in methylcobal-amin+ insulin treated group 1 than in insulin treated group 1 (P ＜ 0.05);Month 2, SNCV and EPA were higher in methylcobalamin+ insulin treated group 2 than in insulin treated group 2 (P ＜ 0.05); Month 3, SNCV, MNCV and EPA were significantly lower in methylcobalamin + insulin treated group 2 than in control group (P ＜ 0.05-0.01), whereas no difference was observed between methylcobalamin + insulin treated group 2 and insulin treated group 2.CONCLUSION: ① Methylcobal has not effect on blood glucose. ②Methylcobal could prevent occurrence of experimental neuropathy through its effect on nerve IGF-1 gene expression of diabetic rats. ③ A better efficacy could be achieved by Methylcobal with a good control of blood glucose level in prevention of diabetic peripheral neuropathy.