Protective effects of somatostatin on mice islets injury after transplantation by pancreas exocrine cells

Abstract

Objective To investigate the protective effects of somatostatin (SS) on mice islets injury after transplantation by pancreas exocrine cells and its mechanism. Method (1) In vitro, 20 male BALB/C mice were randomly divided into the SS group (n=10) and the control group (n=10). The animals in SS group were injected with SS (10 g/g) by intraperitoneal injection (i.p) before 30 min, and those in the control group were given the same amount of normal saline (i.p). The pancreas exocrine cells and islet cells in two groups were extracted respectively, and the apoptosis was detected by flow cytometric. (2) The pancreases of mice were digested with collagenase, islets and pancreatic exocrine cells were collected, and the purity and activity of islet was detected. In vivo, 8-9-week old male BALB/C mice were induced into diabetic mice with Streptozocin (STZ) (190 mg/kg body weight, i. p). 250 islets and the equal volume of pancreatic exocrine cells were transplanted into different regions of left kidney subcapsule. Forty mice were divided into two groups randomly. The experimental group was injected with SS (10 g/g, 3 times every day, i. p) for 28 days after operation, and the control group was injected with the same amount of normal saline (3 times every day, i. p) for 28 days. Then mice in two groups were injected with 5-Ethynyl-2'-deoxyuridine (EDU) (5 g/g, once every day, i. p) for 28 days. Blood glucose 1evel was monitored continually. Glucose tolerance test was performed after 8 days, and the left kidney was removed respectively after 10 days and 28 days. The expression of anti-amylase antibodies in subcapsule was detected by irnmunohistochemieal staining. The proliferation of islet beta cells was measured by immunofluorescence staining. Result (1) The apoptosis rate of pancreas exocrine cells in the experimental group was significantly higher than in the control group (P 0.05). The purity and activity of islet were above 95%. After islets transplantation, the blood glucose levels in control and experimental groups were normal, but experimental group had the advanced islet function in reversing diabetes. The average blood glucose level in control group was significantly higher than in experimental group, and the blood glucose regulating function of islet was normal. A large number of anti-amylase antibody-positive cells were found in renal subcapsule in the control group while little seen in the experimental group after 10 days. Immunofluorescence showed that the Insulin + EDU+ β cells of islet in the experimental group were more than those in the control group. The number of anti—amylase antibody-positive cells in the experimental group was significantly less than in the control group after 28 days, but showed no obvious difference from that at 10th day. The number of increased beta cells in the experimental group was still significantly greater than in the control group after 28 day, but the proliferation rate was reduced as compared with that at 10th day. Conclusion SS can reduce pancreas exocrine cells damage in the process of mice islets transplantation. SS can induce the apoptosis of damaged pancreas exocrine cells, inhibit pancreatic acinar cells from secreting pancreatic amylase and promote proliferation of islet beta cells. Key words: Islet transplantation; Somatostatin; Pancreas exocrine cell; Apoptosis