The attenuating effect of ursodeoxycholic acid on endoplasmic reticulum stress-mediated pancreatic β-cell apoptosis in streptozotocin-induced diabetic rats

Abstract

Objective To clarify the protective effect of nrsodeoxycholic acid ( UDCA ) on endoplasmic reticulum stress-mediated apoptosis in pancreatic β-cell of streptozotocin ( STZ )-induced diabetic rats.Methods Rats( n =40) received a single injection STZ( 50 mg/kg) intra-peritoneally and formed a β-cell injury model.Weight-matched normal rats( the control group,n =10 ) were injected with the buffer alone.STZ-treated rats with persistent random blood glucose higher than 16.7 mmol/L for 1 week were considered as diabetic status( n=14 ),then divided randomly into STZ-induced diabetes mellitus ( DM ) group ( n =7 ) and UDCA-treated DM group ( n =7 ).UDCA (40 mg· kg- 1,d-1 ) was administered daily by intragastric intubations throughout the experimental period (30 d).During the entire experiment,blood glucose in all rats was assessed.By the end of the experiment,all rats were sacrificed with the pancreas removed and the blood sample collected immediately.Fasting insulin levels were assayed by radioimmunoassay.The morphological changes of pancreatic β-cells apoptosis were determined by TUNEL assay.RNA in pancreas was abstracted and microarray containing 89 pieces of apoptosis related genes was applied.The related gene expressions were detected by RT-PCR and Western blot.Results The concentration of blood glucose in diabetic rats was gradually decreased after UDCA treatment,but at the end of the experiment it was still higher than that in the normal control group.The treatment with UDCA raised the fasting insulin level in diabetic rats,but this concentration was significantly lower as compared to the control group.Based on TUNEL stained tissue sections,the percentage of β-cell apoptosis of UDCA-treated DM group was significantly lower than that of STZ-induced diabetic group(P＜0.05 ).Among 89 genes,42 genes up-regulated and 46 genes down-regulated in diabetic rats,some of which were ameliorated by UDCA treatment.The expressions of Caspase-3,Bax,Bip,and CHOP mRNA in pancreas of DM group were significantly up-regulated as compared with those in the control group ( P ＜ 0.05 ) ; while the expression of Bcl-2 mRNA was markedly down-regulated (P＜0.05 ).However,these parameters in the U DCA-treated animals showed a marked improvement.Conclusion Ursodeoxycholic acid seems to protect pancreatic β-cell from apoptosis in STZ-induced diabetes by attenuating the severity of endoplasmic reticulum stress. Key words: Ursodeoxycholic acid ; Pancreatic β-cells; Apoptosis; Endoplasmic reticulum stress