Investigation of the preservation effect of canagliflozin on pancreatic beta cell mass using SPECT/CT imaging with 111In-labeled exendin-4

Radiolabeled exendin derivatives are promising for non-invasive quantification of pancreatic beta cell mass (BCM); longitudinal observation of BCM for evaluation of therapeutic effects has not been achieved. The aim of this study is to demonstrate the usefulness of our developing method using [Lys12(111In-BnDTPA-Ahx)]exendin-4 to detect longitudinal changes in BCM. We performed a longitudinal study with obese type 2 diabetes model (db/db) mice administered canagliflozin, which is reported to preserve BCM. Six-week-old mice were assigned to a canagliflozin-administered group or a control group. Blood glucose levels of the canagliflozin group were significantly lower than those of the control group. Plasma insulin levels, insulin secretion during OGTT and insulin content in the pancreas were preserved in the canagliflozin group in comparison with those in the control group. According to SPECT/CT imaging analysis using [Lys12(111In-BnDTPA-Ahx)]exendin-4, pancreatic uptake was significantly decreased in the control group, whereas there was no significant change in the canagliflozin group. After nine weeks, both pancreatic uptake and BCM of the canagliflozin group were significantly higher than those of the control group, and a correlation between them was observed. In conclusion, our imaging method confirmed the BCM-preservation effect of canagliflozin, and demonstrated its potential for longitudinal evaluation of BCM.

Vascular endothelial PDPK1 plays a pivotal role in the maintenance of pancreatic beta cell mass and function in adult male mice

Aims/hypothesisThe aim of this study was to elucidate the impact of 3′-phosphoinositide-dependent protein kinase-1 (PDPK1) in vascular endothelial cells on the maintenance of pancreatic beta cell mass and function.MethodsMale vascular endothelial cell-specificPdpk1-knockout mice (Tie2+/−/Pdpk1flox/floxmice) and their wild-type littermates (Tie2−/−/Pdpk1flox/floxmice; control) were used for this study. At 12 weeks of age, an IPGTT and OGTT were conducted. Pancreatic blood flow was measured under anaesthesia. Thereafter, islet blood flow was measured by the microsphere method. Mice were killed for islet isolation and further functional study and mRNA was extracted from islets. Pancreases were sampled for immunohistochemical analyses.ResultsDuring the IPGTT, the blood glucose level was comparable between knockout mice and controlfloxmice, although serum insulin level was significantly lower in knockout mice. During the OGTT, glucose tolerance deteriorated slightly in knockout mice, accompanied by a decreased serum insulin level. During an IPGTT after pre-treatment with exendin-4 (Ex-4), glucose tolerance was significantly impaired in knockout mice. In fact, glucose-stimulated insulin secretion of isolated islets from knockout mice was significantly reduced compared with controlfloxmice, and addition of Ex-4 revealed impaired sensitivity to incretin hormones in islets of knockout mice. In immunohistochemical analyses, both alpha and beta cell masses were significantly reduced in knockout mice. In addition, the CD31-positive area was significantly decreased in islets of knockout mice. The proportion of pimonidazole-positive islets was significantly increased in knockout mice. mRNA expression levels related to insulin biosynthesis (Ins1,Ins2,Mafa,Pdx1andNeurod[also known asNeurod1]) and beta cell function (such asGckandSlc2a2) were significantly decreased in islets of knockout mice. Microsphere experiments revealed remarkably reduced islet blood flow. In addition, mRNA expression levels ofHif1α(also known asHif1a) and its downstream factors such asAdm,Eno1,Tpi1(also known asEts1),Hmox1andVegfa, were significantly increased in islets of knockout mice, indicating that islets of knockout mice were in a more hypoxic state than those of controlfloxmice. As a result, mRNA expression levels related to adaptive unfolded protein response and endoplasmic reticulum stress-related apoptotic genes were significantly elevated in islets of knockout mice. In addition, inflammatory cytokine levels were increased in islets of knockout mice. Electron microscopy revealed reduced endothelial fenestration and thickening of basal membrane of vascular endothelium in islets of knockout mice.Conclusions/interpretationVascular endothelial PDPK1 plays an important role in the maintenance of pancreatic beta cell mass and function by maintaining vascularity of pancreas and islets and protecting them from hypoxia, hypoxia-related endoplasmic reticulum stress, inflammation and distortion of capillary structure.