1,25（OH）₂D3Prevent High Glucose-induced Pancreatic Beta-cells Dysfunction Through Inhibition Of NLRP3Inflammasome Activation

ObjectiveDiabetes is a metabolic disease which characterized as high blood glucose the mainlypathophysiological basis is insufficient insulin secretion or action which cause disorder of bloodglucose, protein and fat metabolism, and secondary lead to water and electrolyte metabolismimbalance. Pancreatic β-cells are the only insulin secretory cells in the body, number, size and thefunctional status of β-cell determines the level of insulin secretion, then, plays an important role inmaintenance of blood glucose homeostasis. Therefore, to explore the mechanism of islet β-celldysfunction is important. In addition to its traditional function of maintain homeostasis of calciumand phosphorus, vitamin D3contains a wide range of biological effects of non calcium adjustmenteffects. In this study, we explore the relationship between vitamin D3and pancreatic β-cell function,whether the effect of vitamin D3islet β-cell dysfunction and possible mechanisms for protectionunder high glucose with clinical investigations, animal experiments and cell experiments.MethodsClinical investigations: we selected556subjects recruited from the outpatient clinic of theShanghai Clinical Center for Diabetes (Shanghai, China) from January,2011to April,2012,comprising78NGT volunteers,59type1DM patients and419type2DM subjects. We compareserum levels of25(OH) D3between the three groups, and then to explore the relationship betweenvitamin D levels and pancreatic β-cell function in each group according to diabetes type. Becauseof the influence of gender on serum25(OH)D3, type2diabetic subjects of men and women wereseparated analyzed. Animal experiments: male SD rats are grouped fed with normal diet and high-glucose diet, inthe meanwhile, vitamin D3intervention (233.3U/kg/wk) are given. After5weeks, intraperitonealglucose tolerance test (IPGTT) is conducted to detect whether high glucose induced impairedglucose tolerance rat model is successfully build, and observe the effects of vitamin D3on bloodglucose and insulin secretion at the same time.Cell experiments: In vitro, we first detect the effect of1,25(OH)2D3on glucose-stimulatedinsulin secretion (GSIG) in INS-1E cells and isolated islets. Then, INS-1E cells are incubated innormal glucose concentration (5.6mmol/L) or high glucose concentration (30mmol/L) for48hoursand divided into control group (Ctr), control plus VD group (Ctr+VD), High-glucose group (HG)and High-glucose plus VD group (HG+VD) according to whether given1,25(OH)2D3intervention.We detect1,25(OH)2D3on reactive oxygen species (ROS) generation, apoptosis, and furtherexplore its possible mechanisms.ResultsClinical investigations: the proportion of vitamin D deficiency in NGT, the T1DM and T2DMgroup are85.9%,93.9%and88.5%. Serum25(OH) D3levels are significantly lower in T1DMpatients than it in NGT group and T2DM patients. Male has significantly higher vitamin D3levelthan female. Serum25(OH) D3levels are independently associated FCP in patients with type1diabetes, independently associated with2h-0CP levels in male T2DM patients and associated with2hCP level in femaleT2DM patients.Animal experiments: Compared with the normal diet fed rats, high-glucose diet fed ratsshowed a significantly increased body weight and blood glucose levels after5-6weeks. Whilegiving vitamin D3intervention found that, compared with the high-sugar diet group, vitamin D3intervention can significantly reduce blood glucose levels and improve insulin secretion duringglucose load.Cell experiments: in vitro,1,25(OH)2D3can significantly improve GSIS level in INS-1E cellsand isolated islets.1,25(OH)2D3can significantly prevent high glucose induced ROS productionand apoptosis in INS-1E cells.1,25(OH)2D3significantly reverse high glucose induced NLRP3inflammasome expression at mRNA and protein levels, and decrease expression of ASC,TXNIP, IL-1β and IL-18at the same time.Conclusion1. Serum25(OH) D3levels are independently associated with pancreatic β-cell function in type1diabetes and male type2diabetic patients.2. Vitamin D3can significantly reverse increased high glucose and deceased insulin release inhigh-glucose diet induced impaired glucose tolerance rat model during glucose load.3.1,25(OH)2D3prevent high glucose induced INS-1E cell dysfunction by blocking activation ofNLRP3inflammasome.