Background Increased levels of plasma lipopolysaccharide (LPS) have been found in obesity and diabetes patients.This study was to investigate the effect of LPS on pancreatic beta-cell viability and the involvement of caspase 3 in NIT-1 cell line.Methods Mouse insulinoma NIT-1 cells were treated with LPS for the indicated time and dose.Cell viability was measured by cell counting kit-8 reagent.Toll-like receptor 4 (TLR4),caspase 3 and cleaved caspase 3 were detected by Western blotting.Insulin was determined by radioimmunoassay (RIA).Results LPS promoted NIT-1 cell proliferation at 1 μg/ml,peaked at 72 hours of incubation.A reduction in cleavage of caspase 3 was observed upon LPS treatment.Bay11-7082,a specific inhibitor of nuclear factor (NF)-κB,blunted LPS-induced inhibition of caspase 3 cleavage.Reduction in chronic insulin secretion was observed after treatment with LPS at 1 μg/ml for 48 and 72 hours,not for 24 hours.TLR4 protein was upregulated when NIT-1 cells were treated with LPS at 1 pg/ml for 24 hours.Conclusions LPS promotes early NIT-1 cell proliferation in association with NF-κB-mediated inhibition of caspase 3 cleavage.LPS exerts a time-dependent inhibitory effect on chronic insulin secretion from NIT-1 cells.