Effects of L-carnosine on NIT-1 islet cells

AIM: To investigate the protective effect of L-carnosine on insulin secretion, proliferation and apoptosis of β-cells impaired by high glucose. METHODS: NIT-1 cells were pre-treated with glucose at concentrations of 11.1 mmol/L (control level) and 33.3 mmol/L (high level) for 72 h, and then the cells were stimulated with various concentrations of glucose (0, 5 and 25 mmol/L) and/or L-carnosine (0, 1 and 20 mmol/L). The level of insulin in the medium was measured by radioimmunoassay. To detect the effect of L-carnosine on proliferation and apoptosis, NIT-1 cells were divided into 4 groups according to different culture conditions for 72 h: group C (with 11.1 mmol/L glucose), group H (with 33.3 mmol/L glucose), group H+A (with 33.3 mmol/L glucose+ 1 mmol/L L-carnosine) and group H+B (with 33.3 mmol/L glucose +20 mmol/L L-carnosine). Proliferous or apoptotic cells were identified by BrdU labeling and flow cytometry (labeling with annexin V-FITC/PI),respectively. Total RNA was extracted and the mRNA expression of caspase-3 and bcl-2 was measured by RT-PCR. The caspase-3 activity was also checked by fluorometric assay kit. RESULTS: The insulin in high-level glucose group was lower than that in control-level glucose group. L-carnosine at concentration of 20 mmol/L notably increased the insulin secretion of the cells pre-treated with glucose at control level or high level. The proliferation and apoptosis were both increased in group H compared with group C, but the total cell counts declined because the apoptotic rate was higher than the proliferation rate. L-carnosine at concentration of 1 mmol/L significantly increased the proliferation rate and decreased the apoptotic rate. The mRNA level of caspase-3 was decreased and the mRNA level of bcl-2 was increased after the cells were treated with L-carnosine at concentration of 1 mmol/L. L-carnosine at concentrations of both 1 mmol/L and 20 mmol/L significantly decreased the caspase-3 activity. CONCLUSION: L-carnosine at high level directly stimulates insulin secretion in NIT-1 cells, and L-carnosine at normal level promotes the cell proliferation and inhibits apoptosis induced by high concentration of glucose. Caspsase-3 and Bcl-2 may be partly involved in this process.