The Protective Effect Of 1,25-dihydroxyvitaminD₃ On Pancreatic β Cells Damaged By Streptozotocin

Objective: To investigate the protective effect of1,25-dihydroxyvitaminD3 on streptozotocin-induced pancreatic β cellsimpairment in cultured newborn rat islet cells. Methods: 1.Groups: With culture of islet isolated from Wistar ratsof 3 to 5 days and divided into 4 groups: ①normal controlgroup;②1,25-(OH)2D3 control group: 1,25-(OH)2D3 was added to theculture medium at the concentration of 1×10-6M for 30 minutes; ③STZgroup: STZ was added to the culture medium at the concentration of2.2mmol/L for 30 minutes; ④protective group: islet cells were treated for30 minutes with 1×10-8M 1,25-(OH)2D3 (low concentration) or 1×10-6M1,25-(OH)2D3 (high concentration),then STZ was added for 30minutes ,too. Culture medium was removed at specified times and thecells were resuspended with normal culture medium, some projects wereevaluated after 18 hours. 2.Insulin content of cell supernatant wereexamined by radioimmunoassay. Apoptotic cells were identified byHoechest33258 fluorescence staining and quantitated by flow cytometry.The expression of bcl-xL and bax protein were evaluated byimmunohistochemical staining. Results: In 1,25-(OH)2D3 control group, insulin release level(173.72±8.33μIU/ml), apoptosis rate(2.52±0.54%) and expression ofapoptosis protein were unchanged compared with normal control group,P>0.05. The secretory function of pancreatic β cells was suppressed bySTZ. Insulin release level was 62.95±5.52μIU/ml in STZ group versus182.87±7.68μIU/ml in normal control group, apoptosis rate increased to25.94±2.27% from 2.09±0.22%.In both protective groups, insulin levelwas 107.05±3.33μIU/ml(10-8M group)and 114.89±7.12μIU/ml(10-6Mgroup)respectively, apoptosis rate decreased to 11.95±1.17%(10-8Mgroup)and 10.23±0.48%(10-6M group)respectively, compared with STZgroup, P<0.01. Apoptosis of β cells was correlated with expression ofbcl-xL and bax, the expression of bcl-xL in 1,25-(OH)2D3 protectivegroup was higher than that of the STZ group, while the expression of baxin 1,25-(OH)2D3 protective group was lower than that of the STZ group.But insulin release level, apoptosis rate and expression of apoptosisprotein were not difference between 10-8M group and 10-6M group, P>0.05. Conclusion: Pancreatic β cells were not affected significantly byhigh concentration 1,25-(OH)2D3 in vitro. 1,25-(OH)2D3 protect β cellsagainst apoptosis induced by STZ in vitro by up-regulates the expressionof bcl-xL and down-regulates the expression of bax. There was nodifference in low concentration and high concentration 1,25-(OH)2D3 toprotect pancreatic β cells.