Effect of vitamin D on bone metabolism in diabetic rats and its related mechanism

Objective To study the effect of 1,25-dihydroxyvitamin D3 on bone metabolism in diabetic rats and the related molecular mechanism.Methods A total of 45 healthy 6-8 weeks old male Sprague Dawley (SD) rats were treated with streptozotocin.The streptozotocin-induced diabetic rats were randomly assigned to diabetic group (DM),low dose vitamin D treated group(LD),and high dose vitamin D treated group(HD).Another 12 healthy SD rats were used as normol control group(NC).The rats in NC group and DM group were fed with 0.05 ml/d nut oil;those in the LD group and HD group were fed respectively with 0.03 and0.10 μg · kg-1 · d-1 1,25-dihydroxyvitamin D3 dissolved in 0.05 ml nut oil.12 weeks later,serum calcium,phosphorus,osteocalcin,type Ⅰ collagen cross-linked telopeptide (NTX),and 24 h urinary calcium were determined.Right femurs were harvested for pathohistological analysis by hematoxylin-eosin (HE) staining.Expressions of osteoprotegerin,receptor activator nuclear factor κB ligand (RANKL),core binding factor α1(Cbfa1) were detected by immunohistochemical staining.The osteoprotegerin,RANKL,Cbfa1,osteocalcin mRNA levels of bone tissue were performed by realtime quantitative reverse transcription polymerase chain reaction assay.Results (1) Compared with the NC group,serum calcium and 24 h urinary calcium in LD and HD groups were significantly higher (P＜0.05) ; 24 h urinary calcium in DM group was significantly higher than that in NC group (P ＜ 0.05).(2) Serum osteocalcin level in DM and LD groups was significantly lower than that in NC group (P＜0.05) ; there was no significant difference between the serum NTX levels of all groups (P＞0.05).(3) There was no significant difference in the mRNA expression of Cbfa1 in all groups (P＞0.05).The mRNA expression of osteocalcin in DM group was significantly lower than that in NC group (P ＜0.05).The mRNA expression of RANKL in DM group was significantly lower than that in NC group (P＜0.05) ; and that in LD and HD group was significantly higher than that in DM group (P＜0.05),and that in HD group was significantly higher than that in LD group (P＜0.05).The mRNA expression of osteoprotegerin in DM group was significantly lower than that in NC group (P＜0.05).The ratio of RANKL to osteoprotegerin in HD group was significantly higher than that in DM group (P＜0.05).Conclusions Vitamin D may promote bone metabolism in diabetic rats by up-regulating the expressions of osteocalcin and RANKL or in addition to other means. Key words: Diabetes mellitus ;  Rats ;  Vitamin D ;  Bone metabolism