The efficacy of switching basal-bolus insulin therapy to basal insulin-supported oral therapy with a glinide and an α-glucosidase inhibitor in patients with type 2 diabetes depends on insulin secretory capacity, but not on blood glucose profiles and insulin dosages prior to the switching.

Aims: We aimed to identify patients who would benefit from basal insulin-supported oral therapy (BOT) with a glinide and an α-glucosidase inhibitor (a fixed-dose combination tablet of mitiglinide 10 mg and voglibose 0.2 mg) in Japanese type 2 diabetic patients. Methods: Patients who were hospitalized to improve hyperglycemia received basal-bolus insulin therapy. After the reduction of glucose toxicity, a 75 g oral glucose tolerance test and a glucagon test were performed. Thereafter, the basal-bolus insulin therapy was switched to BOT with mitiglinide, followed by further addition of voglibose. Interstitial glucose levels were continuously monitored throughout the study period. Diurnal glucose profile was recorded and analyzed. Patients were divided into two groups according to whether their percentage of time in range (TIR, 70-180 mg/dL) under BOT with mitiglinide/voglibose was higher than 70% or not, and the differences in clinical characteristics between the groups were analyzed. Results: Twenty patients were enrolled, and 19 of them completed the study. BOT with mitiglinide/voglibose achieved ≥ 70% of TIR in thirteen patients. The area under the curve of serum C-peptide levels during the oral glucose tolerance test was significantly higher in the patients with ≥ 70% of TIR. The daily insulin dosages and blood glucose profiles were comparable between the two groups. Conclusions: The efficacy of BOT with mitiglinide/voglibose depended on residual insulin secretory abilities. This therapy would be a useful therapeutic option for patients with type 2 diabetes.

Clinical parameters correlated with the psoas muscle index in Japanese individuals with type 2 diabetes mellitus.

Aims: Muscle atrophy is a diabetic complication, which results in a deterioration in glycemic control in type 2 diabetes mellitus (T2DM) individuals. The psoas muscle mass index (PMI) is a reliable indicator for estimating whole-body muscle mass. We aimed to examine the relationship between clinical parameters and the PMI to clarify the mechanism underlying muscle atrophy in diabetes. Methods: This retrospective, cross-sectional study examined 51 patients (31 men and 20 women) with T2DM and a mean HbA1c value of 9.9 ± 1.7%. These patients were admitted to Aichi Medical University Hospital and underwent abdominal computed tomography imaging from July 2020 to April 2021. Multiple clinical parameters were assessed with the PMI. Results: In a multiple regression analysis adjusted for age and sex, the PMI was correlated with body weight, body mass index, serum concentrations of corrected calcium, aspartate aminotransferase, alanine aminotransferase, creatine kinase, thyroid-stimulating hormone (TSH), urinary C-peptide concentrations, the free triiodothyronine/free thyroxine (FT3/FT4) ratio, and the young adult mean score at the femur neck. Receiver operating characteristic curves were created using TSH concentrations and the FT3/FT4 ratio for diagnosing a low PMI. The area under the curve was 0.593 and 0.699, respectively. The cut-off value with maximum accuracy for TSH concentrations was 1.491 µIU/mL, sensitivity was 56.1%, and specificity was 80.0%. Corresponding values for the FT3/FT4 ratio were 1.723, 78.0, and 66.7%, respectively. Conclusion: TSH concentrations and the FT3/FT4 ratio are correlated with the PMI, and their thresholds may help prevent muscle mass loss in Japanese individuals with T2DM.

Protocol to image and analyze the morphology of mouse peripheral nerves using transmission electron microscopy.

Morphological analysis of peripheral nerves in mouse models can be used to characterize the pathophysiology of peripheral nerve disease, but obtaining high-quality electron micrographs can be challenging. Here, we present a protocol to obtain electron micrographs of mouse peripheral nerves. We detail the procedures of sampling, fixation, and embedding of peripheral nerves. We then outline the steps for ultrathin sectioning and transmission electron microscopy imaging. Finally, we describe morphological evaluation of nerve fibers in these images using ImageJ and AxonSeg. For complete details on the use and execution of this protocol, please refer to Nakai-Shimoda et al. (2021).

Thermal gradient ring reveals thermosensory changes in diabetic peripheral neuropathy in mice.

Diabetic peripheral neuropathy (DPN) includes symptoms of thermosensory impairment, which are reported to involve changes in the expression or function, or both, of nociceptive TRPV1 and TRPA1 channels in rodents. In the present study, we did not find changes in the expression or function of TRPV1 or TRPA1 in DPN mice caused by STZ, although thermal hypoalgesia was observed in a murine model of DPN or TRPV1-/- mice with a Plantar test, which specifically detects temperature avoidance. With a Thermal Gradient Ring in which mice can move freely in a temperature gradient, temperature preference can be analyzed, and we clearly discriminated the temperature-dependent phenotype between DPN and TRPV1-/- mice. Accordingly, we propose approaches with multiple behavioral methods to analyze the progression of DPN by response to thermal stimuli. Attention to both thermal avoidance and preference may provide insight into the symptoms of DPN.

O-GlcNAcylation of myocyte-specific enhancer factor 2D negatively regulates insulin secretion from pancreatic ß-cells.

Patients with type 2 diabetes often exhibit impairments in both glucose-induced insulin secretion (GIIS) and incretin-induced insulin secretion (IIIS). These phenotypes are associated with altered glucose metabolism in pancreatic ß-cells, although the molecular mechanisms remain unclear. Here, we used MIN6-K8 pancreatic ß-cell lines as a model to examine the effect of O-linked N-acetylglucosamine glycosylation (O-GlcNAcylation), a glucose-induced protein posttranslational modification, on insulin secretion. O-GlcNAcylation was enhanced in high-glucose-treated MIN6-K8 cells, and high levels of O-GlcNAcylation attenuated PKA-dependent phosphorylation, suggesting that the two protein modifications may compete with each other. Immunoprecipitation proteomic analysis identified six candidate proteins that were O-GlcNAcylated by high-glucose treatment, whereas the O-GlcNAcylations were removed by treatment with an incretin mimetic, exendin-4. Among these proteins, knockdown of myocyte enhancer factor 2D (Mef2d) enhanced insulin secretion, and high-glucose treatment increased the level of O-GlcNAcylation of Mef2d in MIN6-K8 cells. Furthermore, knockout of Mef2d promoted GIIS in MIN6-K8 cells, whereas adenovirus-mediated rescue of Mef2d decreased GIIS in the knockout cells. These results suggest that Mef2d negatively regulates insulin secretion through O-GlcNAcylation.

Increased glycolysis affects ß-cell function and identity in aging and diabetes.

OBJECTIVE: Age is a risk factor for type 2 diabetes (T2D). We aimed to elucidate whether ß-cell glucose metabolism is altered with aging and contributes to T2D. METHODS: We used senescence-accelerated mice (SAM), C57BL/6J (B6) mice, and ob/ob mice as aging models. As a diabetes model, we used db/db mice. The glucose responsiveness of insulin secretion and the [U-13C]-glucose metabolic flux were examined in isolated islets. We analyzed the expression of ß-cell-specific genes in isolated islets and pancreatic sections as molecular signatures of ß-cell identity. ß cells defective in the malate-aspartate (MA) shuttle were previously generated from MIN6-K8 cells by the knockout of Got1, a component of the shuttle. We analyzed Got1 KO ß cells as a model of increased glycolysis. RESULTS: We identified hyperresponsiveness to glucose and compromised cellular identity as dysfunctional phenotypes shared in common between aged and diabetic mouse ß cells. We also observed a metabolic commonality between aged and diabetic ß cells: hyperactive glycolysis through the increased expression of nicotinamide mononucleotide adenylyl transferase 2 (Nmnat2), a cytosolic nicotinamide adenine dinucleotide (NAD)-synthesizing enzyme. Got1 KO ß cells showed increased glycolysis, ß-cell dysfunction, and impaired cellular identity, phenocopying aging and diabetes. Using Got1 KO ß cells, we show that attenuation of glycolysis or Nmnat2 activity can restore ß-cell function and identity. CONCLUSIONS: Our study demonstrates that hyperactive glycolysis is a metabolic signature of aged and diabetic ß cells, which may underlie age-related ß-cell dysfunction and loss of cellular identity. We suggest Nmnat2 suppression as an approach to counteract age-related T2D.

Alterations of retinal thickness measured by optical coherence tomography correlate with neurophysiological measures in diabetic polyneuropathy.

AIMS/INTRODUCTION: Diabetic polyneuropathy (DPN) and diabetic retinopathy (DR) are traditionally regarded as microvascular complications. However, these complications may share similar neurodegenerative pathologies. Here we evaluate the correlations in the severity of DPN and changes in the thickness of neuroretinal layers to elucidate whether these complications exist at similar stages of progression. MATERIALS AND METHODS: A total of 43 patients with type 2 diabetes underwent a nerve conduction study (NCS), a macular optical coherence tomography, and a carotid artery ultrasound scan. Diabetic polyneuropathy was classified according to Baba's classification using NCS. The retina was automatically segmented into four layers; ganglion cell complex (GCC), inner nuclear layer/outer plexiform layer (INL/OPL), outer nuclear layer/photoreceptor inner and outer segments, and retinal pigment epithelium (RPE). The thickness of each retinal layer was separately analyzed for the fovea and the parafovea. RESULTS: Fourteen patients were classified as having moderate to severe diabetic polyneuropathy. The thicknesses of the foveal and parafoveal INL/OPL increased in patients with diabetic polyneuropathy compared with patients without. The thickness of the parafoveal retinal pigment epithelium decreased in patients with diabetic polyneuropathy. The thinning of parafoveal ganglion cell complex and foveal and parafoveal retinal pigment epithelium were positively correlated with deterioration of nerve functions in the nerve conduction study, but the thickening of INL/OPL was positively correlated with the nerve function deterioration. The thinning of parafoveal ganglion cell complex and foveal retinal pigment epithelium were positively correlated with the thickening of the carotid intima-media. CONCLUSIONS: Depending on the progression of diabetic polyneuropathy, the ganglion cell complex and retinal pigment epithelium became thinner and the INL/OPL became thicker. These retinal changes might be noteworthy for pathological investigations and for the assessment of diabetic polyneuropathy and diabetic retinopathy.

Secreted Factors from Stem Cells of Human Exfoliated Deciduous Teeth Directly Activate Endothelial Cells to Promote All Processes of Angiogenesis.

Diabetes is a major risk factor for atherosclerosis and ischemic vascular diseases. Recently, regenerative medicine is expected to be a novel therapy for ischemic diseases. Our previous studies have reported that transplantation of stem cells promoted therapeutic angiogenesis for diabetic neuropathy and ischemic vascular disease in a paracrine manner, but the precise mechanism is unclear. Therefore, we examined whether secreted factors from stem cells had direct beneficial effects on endothelial cells to promote angiogenesis. The soluble factors were collected as conditioned medium (CM) 48 h after culturing stem cells from human exfoliated deciduous teeth (SHED) in serum-free DMEM. SHED-CM significantly increased cell viability of human umbilical vein endothelial cells (HUVECs) in MTT assays and accelerated HUVECs migration in wound healing and Boyden chamber assays. In a Matrigel plug assay of mice, the migrated number of primary endothelial cells was markedly increased in the plug containing SHED-CM or SHED suspension. SHED-CM induced complex tubular structures of HUVECs in a tube formation assay. Furthermore, SHED-CM significantly increased neovascularization from the primary rat aorta, indicating that SHED-CM stimulated primary endothelial cells to promote comprehensive angiogenesis processes. The angiogenic effects of SHED-CM were the same or greater than the effective concentration of VEGF. In conclusion, SHED-CM directly stimulates vascular endothelial cells to promote angiogenesis and is promising for future clinical application.

Tumor-like features of gene expression and metabolic profiles in enlarged pancreatic islets are associated with impaired incretin-induced insulin secretion in obese diabetes: A study of Zucker fatty diabetes mellitus rat.

AIMS/INTRODUCTION: Pancreatic islets are heterogenous. To clarify the relationship between islet heterogeneity and incretin action in the islets, we studied gene expression and metabolic profiles of non-large and enlarged islets of the Zucker fatty diabetes mellitus rat, an obese diabetes model, as well as incretin-induced insulin secretion (IIIS) in these islets. MATERIALS AND METHODS: Pancreatic islets of control (fa/+) and fatty (fa/fa) rats at 8 and 12 weeks-of-age were isolated. The islets of fa/fa rats at 12 weeks-of-age were separated into non-large islets (≤200 µm in diameter) and enlarged islets (>300 µm in diameter). Morphological analyses, insulin secretion experiments, transcriptome analysis, metabolome analysis and oxygen consumption analysis were carried out on these islets. RESULTS: The number of enlarged islets was increased with age in fatty rats, and IIIS was significantly reduced in the enlarged islets. Markers for ß-cell differentiation were markedly decreased in the enlarged islets, but those for cell proliferation were increased. Glycolysis was enhanced in the enlarged islets, whereas the tricarboxylic acid cycle was suppressed. The oxygen consumption rate under glucose stimulation was reduced in the enlarged islets. Production of glutamate, a key signal for IIIS, was decreased in the enlarged islets. CONCLUSIONS: The enlarged islets of Zucker fatty diabetes mellitus rats, which are defective for IIIS, show tumor cell-like metabolic features, including a dedifferentiated state, accelerated aerobic glycolysis and impaired mitochondrial function. The age-dependent increase in such islets could contribute to the pathophysiology of obese diabetes.

Ranirestat Improved Nerve Conduction Velocities, Sensory Perception, and Intraepidermal Nerve Fiber Density in Rats with Overt Diabetic Polyneuropathy.

Distal sensory-motor polyneuropathy is one of the most frequent diabetic complications. However, few therapies address the etiology of neurodegeneration in the peripheral nervous systems of diabetic patients. Several metabolic mechanisms have been proposed as etiologies of this polyneuropathy. In this study, we revisited one of those mechanisms, the polyol pathway, and investigated the curative effects of a novel strong aldose reductase inhibitor, ranirestat, in streptozotocin-induced diabetic rats with preexisting polyneuropathy. Twelve weeks after the onset of diabetes, rats which had an established polyneuropathy were treated once daily with a placebo, ranirestat, or epalrestat, over 6 weeks. Before and after the treatment, nerve conduction velocities and thermal perception threshold of hindlimbs were examined. After the treatment, intraepidermal fiber density was evaluated. As an ex vivo assay, murine dorsal root ganglion cells were dispersed and cultured with or without 1 µmol/l ranirestat for 48 hours. After the culture, neurite outgrowth was quantified using immunological staining. Sensory nerve conduction velocity increased in diabetic rats treated with ranirestat (43.3 ± 3.6 m/s) compared with rats treated with placebo (39.8 ± 2.3). Motor nerve conduction velocity also increased in the ranirestat group (45.6 ± 3.9) compared with the placebo group (38.9 ± 3.5). The foot withdrawal latency to noxious heating was improved in the ranirestat group (17.7 ± 0.6 seconds) compared with the placebo group (20.6 ± 0.6). The decrease in the intraepidermal fiber density was significant in the diabetic placebo group (21.6 ± 1.7/mm) but not significant in the diabetic ranirestat group (26.2 ± 1.2) compared with the nondiabetic placebo group (30.3 ± 1.5). Neurite outgrowth was promoted in the neurons supplemented with ranirestat (control 1446 ± 147 µm/neuron, ranirestat 2175 ± 149). Ranirestat improved the peripheral nervous dysfunctions in rats with advanced diabetic polyneuropathy. Ranirestat could have potential for regeneration in the peripheral nervous system of diabetic rats.

Functional adenosine triphosphate-sensitive potassium channel is required in high-carbohydrate diet-induced increase in ß-cell mass.

AIMS/INTRODUCTION: A high-carbohydrate diet is known to increase insulin secretion and induce obesity. However, whether or not a high-carbohydrate diet affects ß-cell mass (BCM) has been little investigated. MATERIALS AND METHODS: Both wild-type (WT) mice and adenosine triphosphate-sensitive potassium channel-deficient (Kir6.2KO) mice were fed normal chow or high-starch (ST) diets for 22 weeks. BCM and the numbers of islets were analyzed by immunohistochemistry, and gene expression levels in islets were investigated by quantitative real-time reverse transcription polymerase chain reaction. MIN6-K8 ß-cells were stimulated in solution containing various concentrations of glucose combined with nifedipine and glimepiride, and gene expression was analyzed. RESULTS: Both WT and Kir6.2KO mice fed ST showed hyperinsulinemia and body weight gain. BCM, the number of islets and the expression levels of cyclinD2 messenger ribonucleic acid were increased in WT mice fed ST compared with those in WT mice fed normal chow. In contrast, no significant difference in BCM, the number of islets or the expression levels of cyclinD2 messenger ribonucleic acid were observed between Kir6.2KO mice fed normal chow and those fed ST. Incubation of MIN6-K8 ß-cells in high-glucose media or with glimepiride increased cyclinD2 expression, whereas nifedipine attenuated a high-glucose-induced increase in cyclinD2 expression. CONCLUSIONS: These results show that a high-starch diet increases BCM in an adenosine triphosphate-sensitive potassium channel-dependent manner, which is mediated through upregulation of cyclinD2 expression.

Inhibition of SNAT5 Induces Incretin-Responsive State From Incretin-Unresponsive State in Pancreatic ß-Cells: Study of ß-Cell Spheroid Clusters as a Model.

ß-Cell-ß-cell interactions are required for normal regulation of insulin secretion. We previously found that formation of spheroid clusters (called K20-SC) from MIN6-K20 clonal ß-cells lacking incretin-induced insulin secretion (IIIS) under monolayer culture (called K20-MC) drastically induced incretin responsiveness. Here we investigated the mechanism by which an incretin-unresponsive state transforms to an incretin-responsive state using K20-SC as a model. Glutamate production by glucose through the malate-aspartate shuttle and cAMP signaling, both of which are critical for IIIS, were enhanced in K20-SC. SC formed from ß-cells deficient for aspartate aminotransferase 1, a critical enzyme in the malate-aspartate shuttle, exhibited reduced IIIS. Expression of the sodium-coupled neutral amino acid transporter 5 (SNAT5), which is involved in glutamine transport, was downregulated in K20-SC and pancreatic islets of normal mice but was upregulated in K20-MC and islets of rodent models of obesity and diabetes, both of which exhibit impaired IIIS. Inhibition of SNAT5 significantly increased cellular glutamate content and improved IIIS in islets of these models and in K20-MC. These results suggest that suppression of SNAT5 activity, which results in increased glutamate production, and enhancement of cAMP signaling endows incretin-unresponsive ß-cells with incretin responsiveness.

Essential roles of aspartate aminotransferase 1 and vesicular glutamate transporters in ß-cell glutamate signaling for incretin-induced insulin secretion.

Incretins (GLP-1 and GIP) potentiate insulin secretion through cAMP signaling in pancreatic ß-cells in a glucose-dependent manner. We recently proposed a mechanistic model of incretin-induced insulin secretion (IIIS) that requires two critical processes: 1) generation of cytosolic glutamate through the malate-aspartate (MA) shuttle in glucose metabolism and 2) glutamate transport into insulin granules by cAMP signaling to promote insulin granule exocytosis. To directly prove the model, we have established and characterized CRISPR/Cas9-engineered clonal mouse ß-cell lines deficient for the genes critical in these two processes: aspartate aminotransferase 1 (AST1, gene symbol Got1), a key enzyme in the MA shuttle, which generates cytosolic glutamate, and the vesicular glutamate transporters (VGLUT1, VGLUT2, and VGLUT3, gene symbol Slc17a7, Slc17a6, and Slc17a8, respectively), which participate in glutamate transport into secretory vesicles. Got1 knockout (KO) ß-cell lines were defective in cytosolic glutamate production from glucose and showed impaired IIIS. Unexpectedly, different from the previous finding that global Slc17a7 KO mice exhibited impaired IIIS from pancreatic islets, ß-cell specific Slc17a7 KO mice showed no significant impairment in IIIS, as assessed by pancreas perfusion experiment. Single Slc17a7 KO ß-cell lines also retained IIIS, probably due to compensatory upregulation of Slc17a6. Interestingly, triple KO of Slc17a7, Slc17a6, and Slc17a8 diminished IIIS, which was rescued by exogenously introduced wild-type Slc17a7 or Slc17a6 genes. The present study provides direct evidence for the essential roles of AST1 and VGLUTs in ß-cell glutamate signaling for IIIS and also shows the usefulness of the CRISPR/Cas9 system for studying ß-cells by simultaneous disruption of multiple genes.

Case of ketoacidosis by a sodium-glucose cotransporter 2 inhibitor in a diabetic patient with a low-carbohydrate diet.

We present a case of a 32-year-old diabetic woman with Prader-Willi syndrome who developed severe ketoacidosis caused by a sodium-glucose cotransporter 2 (SGLT2) inhibitor, a novel class of antihyperglycemic agents, during a strict low-carbohydrate diet. At admission, a serum glucose level of 191 mg/dL was relatively low, though laboratory evaluations showed severe ketoacidosis. This is the first report of ketoacidosis caused by a SGLT2 inhibitor. It is necessary to not only pay attention when using a SGLT2 inhibitor in patients following a low-carbohydrate diet, but also to start a low-carbohydrate diet in patients treated with a SGLT2 inhibitor because of a high risk for developing ketoacidosis.