Role of sirtuin-1 (SIRT1) in hypoxic injury in pancreatic ß-cells.

Islet transplantation (ITx) is being developed as a treatment for type 1 diabetes mellitus, but hypoxic damage to transplanted islet grafts is an important factor affecting successful transplantation. To investigate the role of sirtuin-1 (SIRT1) under hypoxic injury in INS-1 cells, one type of pancreatic ß-cell lines, we used SRT1720 and GW4064 for SIRT1 activation. The small interfering RNA SIRT1 (si-SIRT1) was used to suppress SIRT1 gene expression. We measured cell viability, apoptosis, and the levels of inflammatory cytokines, including tumour necrosis factor-α (TNF-α), interleukin-6 (IL-6), and reactive oxygen species (ROS), under hypoxic conditions. Real-time PCR and Western blot analysis were performed. Cell viability was significantly reduced to 71% and 40% after 4 and 6 h of hypoxic conditions, respectively. Apoptosis increased significantly 2.8-fold and 5.3-fold after 4 and 6 h of hypoxia, respectively. SIRT1 expression was significantly reduced at the mRNA and protein levels during hypoxia. Hypoxic damage significantly increased the TNF-α, IL-6 and ROS levels in INS-1 cells. However, the reduced cell viability and increased inflammatory cytokines from hypoxic damage were ameliorated by SIRT1 activation in INS-1 cells. These results suggest that SIRT1 is a potential target for the protection of pancreatic ß-cells against hypoxic damage during ITx.

The Anti-Inflammatory Effects of Glucagon-Like Peptide Receptor Agonist Lixisenatide on the Retinal Nuclear and Nerve Fiber Layers in an Animal Model of Early Type 2 Diabetes.

This study explored the anti-inflammatory effects of a glucagon-like peptide-1 receptor agonist (GLP-1RA), known as lixisenatide, on the eyes of early type 2 diabetic mice. Diabetic (db/db) mice were divided into three groups: GLP-1RA [lixisenatide (LIX)], insulin (INS) with controlled hyperglycemia based on the glucose concentration of lixisenatide, and diabetic control (D-CON). Nondiabetic control mice (db/dm) were also characterized for comparison. After 8 weeks of treatment, mRNA levels of inflammatory markers, terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling, immunohistochemical staining; Western blot of glial fibrillary acidic protein (GFAP) and thioredoxin-interacting protein; and retinal thickness were assessed in the central and peripheral neurosensory retina. LIX showed decreased immunohistochemical staining for both thioredoxin-interacting protein and GFAP in the central and peripheral neurosensory retina compared with D-CON and INS, and decreased expression of these proteins in the neurosensory retina and immunohistochemical staining in the optic nerve head for GFAP compared with D-CON. The inner nuclear layer in the peripheral retina in LIX was only thinner than those of D-CON and INS. In an early type 2 diabetic mouse model, lixisenatide treatment showed superior anti-inflammatory effects on the retina and optic nerve head independent of hyperglycemia. Thus, the neuroprotective effects of lixisenatide treatment in the peripheral inner nuclear layer should be evaluated in early type 2 diabetic retinopathy.

Effect of the Sodium-Glucose Cotransporter 2 Inhibitor, Dapagliflozin, on Genitourinary Infection in an Animal Model of Type 2 Diabetes.

PURPOSE: To investigate the effect of dapagliflozin, a sodium-glucose cotransporter 2 inhibitor, on inflammatory cytokines of urogenital tissue in a rat model of type 2 diabetes (T2DM) to infer pharmaceutical influence of dapagliflozin on genitourinary infection or inflammation. METHODS: Study animals were divided into the following 4 groups of 10 animals each: (1) the Otsuka Long-Evans Tokushima Fatty (OLETF)-DA group treated with dapagliflozin at 1.0 mg/kg/day, (2) the OLETF-VO group treated with voglibose at 0.6 mg/kg/day, (3) the control group (OLETF-CO) given water, and (4) the Long-Evans Tokushima Otsuka (LETO) rats were included as nondiabetic control group. Changes in blood glucose, 24-hour urine volume, and urine glucose were measured. The interleukin-1ß (IL-1ß) and interleukin-18 (IL-18) levels in the bladder and the urethra were quantified, respectively. RESULTS: The urine glucose level and the 24-hour urine volume at 12 weeks of treatment were significantly higher in the OLETF-DA group than that in any other group (P<0.05). The cytokine analysis of the bladder and urethra showed higher IL18 and IL-1ß in the OLETF-DA and the OLETF-CO groups than that in the OLETF-VO and LETO groups (P<0.05). The cytokine levels did not differ between the OLETF-DA and the OLETF-CO groups, and the level of IL-18 in the OLETF-DA group was higher in the urethra than in the bladder. CONCLUSION: This study revealed that dapagliflozin increased the urine glucose concentration, resulting in an inflammatory response remain in the urogenital tract as the untreated diabetic rats. Therefore, when treating patients with T2DM with dapagliflozin, careful attention should be paid to genitourinary infection or inflammation.

Effect of sodium-glucose cotransporter 2 inhibitor, empagliflozin, and α-glucosidase inhibitor, voglibose, on hepatic steatosis in an animal model of type 2 diabetes.

OBJECTIVE: We investigated the effects of sodium-glucose cotransporter 2 inhibitor, empagliflozin, and α-glucosidase inhibitor, voglibose, on hepatic steatosis in an animal model of type 2 diabetes (T2DM). METHODS: Empagliflozin (OLETF-EMPA) or voglibose (OLETF-VOG) was administered to Otsuka Long-Evans Tokushima fatty (OLETF) rats once daily for 12 weeks. Control Long-Evans Tokushima Otsuka (LETO) and OLETF (OLETF-C) rats received saline. RESULTS: Blood glucose levels were significantly suppressed in OLETF-EMPA and OLETF-VOG compared with the OLETF-C group. The liver fat content was significantly higher in the OLETF-C group than in the OLETF-EMPA and OLETF-VOG. Hepatic gene expressions involved in gluconeogenesis (glucose 6-phosphatase [G6Pase], fructose-1,6-bisphosphatase [FBP1], and phosphoenolpyruvate carboxykinase [PEPCK]) and lipogenesis (acetyl-CoA carboxylase [ACC], fatty acid synthase [FAS], and sterol regulatory element-binding transcription factor 1c [SREBP-1c]) were significantly decreased in the OLETF-EMPA group compared with other OLETF groups (OLETF-C and OLETF-VOG). Sirtuin 1 (SIRT1) expression level and SIRT1 activity were markedly reduced in OLETF-C rats; however, its expression increased in the OLETF-EMPA and OLETF-VOG. AMP-activated protein kinase (AMPK) phosphorylation level was remarkably increased by empagliflozin treatment in OLETF rats compared with other OLETF groups. Long-term empagliflozin and voglibose treatment reduced hepatic steatosis with suppression of gluconeogenesis and lipogenesis pathway in OLETF rats. CONCLUSION: We suggest that this metabolic improvement might be related to SIRT1 and AMPK pathway in T2DM. But empagliflozin is thought to have more advantage to prevent hepatic steatosis than voglibose in T2DM.

Effect of resveratrol treatment on graft revascularization after islet transplantation in streptozotocin-induced diabetic mice.

We evaluated the effect of resveratrol (RSV) on graft survival after islet transplantation (ITx) in diabetic mice. Isolated islets from Balb/c mice (200 IEQ) were transplanted under the kidney capsule of diabetic Balb/c mice. Vehicle or RSV (200 mg/kg/day, orally) was given for 14 days after ITx. Two more control groups [STZ-treated (No-ITx-Control) and STZ+RSV-treated (No-ITx-RSV) mice without ITx] were added. Glucose tolerance tests (GTT) was performed at 14 days after ITx. In vitro, isolated islets pretreated with vehicle or RSV (1 µM) were incubated in a hypoxic chamber (O2 1%, 1hr). Some of the ITx was performed in mouse insulin 1 gene promoter-green fluorescent protein (MIP-GFP) transgenic mice and analyzed using an in vivo imaging system. After 14 days of ITx, 2-hr glucose levels on GTT in the RSV-treated group were significantly lower than those of other control groups. But the glucose status was not improved in No-ITx mice with RSV. At day 3, the percentage of Ki-67/insulin co-stained cells in islet graft was significantly increased in the RSV-ITx group. Immunostaining with anti-insulin and anti-BS-1 antibodies revealed significantly higher insulin-stained area and vascular density in RSV-treated islet grafts. The mean vessel volume per islet graft measured by in vivo imaging was significantly higher in the RSV-treated group at day 3. In isolated islets cultured in hypoxic conditions, the cell death rate and oxidative stress were significantly attenuated with RSV pretreatment. Hypoxic treatment for isolated islets decreased the expression of SIRT-1 mRNA, and this attenuation was recovered by RSV pretreatment. Our data suggest that RSV treatment improved glycemic control, beta-cell proliferation, reduced oxidative stress, and enhanced islet revascularization and the outcome of ITx in diabetic mice.