Glucose-dependent insulinotropic polypeptide is required for moderate high-fat diet- but not high-carbohydrate diet-induced weight gain.

Both high-fat (HFD) and high-carbohydrate (ST) diets are known to induce weight gain. Glucose-dependent insulinotropic polypeptide (GIP) is secreted mainly from intestinal K cells upon stimuli by nutrients such as fat and glucose, and it potentiates glucose-induced insulin secretion. GIP is well known to contribute to HFD-induced obesity. In this study, we analyzed the effect of ST feeding on GIP secretion and metabolic parameters to explore the role of GIP in ST-induced weight gain. Both wild-type (WT) and GIP receptor deficient ( GiprKO) mice were fed normal chow (NC), ST, or moderate (m)HFD for 22 wk. Body weight was measured, and then glucose tolerance tests were performed. Insulin secretion from isolated islets also was analyzed. WT mice fed ST or mHFD displayed weight gain concomitant with increased plasma GIP levels compared with WT mice fed NC. WT mice fed mHFD showed improved glucose tolerance due to enhanced insulin secretion during oral glucose tolerance tests compared with WT mice fed NC or ST. GiprKO mice fed mHFD did not display weight gain. On the other hand, GiprKO mice fed ST showed weight gain and did not display obvious glucose intolerance. Glucose-induced insulin secretion was enhanced during intraperitoneal glucose tolerance tests and from isolated islets in both WT and GiprKO mice fed ST compared with those fed NC. In conclusion, enhanced GIP secretion induced by mHFD-feeding contributes to increased insulin secretion and body weight gain, whereas GIP is marginally involved in weight gain induced by ST-feeding.

S100B impairs glycolysis via enhanced poly(ADP-ribosyl)ation of glyceraldehyde-3-phosphate dehydrogenase in rodent muscle cells.

S100 calcium-binding protein B (S100B), a multifunctional macromolecule mainly expressed in nerve tissues and adipocytes, has been suggested to contribute to the pathogenesis of obesity. To clarify the role of S100B in insulin action and glucose metabolism in peripheral tissues, we investigated the effect of S100B on glycolysis in myoblast and myotube cells. Rat myoblast L6 cells were treated with recombinant mouse S100B to examine glucose consumption, lactate production, glycogen accumulation, glycolytic metabolites and enzyme activity, insulin signaling, and poly(ADP-ribosyl)ation of glyceraldehyde-3-phosphate dehydrogenase (GAPDH). Glycolytic metabolites were investigated by enzyme assays or metabolome analysis, and insulin signaling was assessed by Western blot analysis. Enzyme activity and poly(ADP-ribosyl)ation of GAPDH was evaluated by an enzyme assay and immunoprecipitation followed by dot blot with an anti-poly(ADP-ribose) antibody, respectively. S100B significantly decreased glucose consumption, glucose analog uptake, and lactate production in L6 cells, in either the presence or absence of insulin. In contrast, S100B had no effect on glycogen accumulation and insulin signaling. Metabolome analysis revealed that S100B increased the concentration of glycolytic intermediates upstream of GAPDH. S100B impaired GAPDH activity and increased poly(ADP-ribosyl)ated GAPDH proteins. The effects of S100B on glucose metabolism were mostly canceled by a poly(ADP-ribose) polymerase inhibitor. Similar results were obtained in C2C12 myotube cells. We conclude that S100B as a humoral factor may impair glycolysis in muscle cells independent of insulin action, and the effect may be attributed to the inhibition of GAPDH activity from enhanced poly(ADP-ribosyl)ation of the enzyme.

Effects of clozapine on adipokine secretions/productions and lipid droplets in 3T3-L1 adipocytes.

Clozapine, a second-generation antipsychotic (SGA), is a cause of side effects related to metabolic syndrome. The participation of serotonin 5-HT2C and histamine H1 receptors in the central nervous system has been reported as a mechanism of the weight gain caused by clozapine. In the present study, we investigated the direct pharmacological action of clozapine on the 3T3-L1 adipocytes and compared it to that of blonanserin, an SGA with low affinity for both receptors. Short-term exposure to clozapine decreased secretion and mRNA expression of leptin. Long-term exposure decreased leptin as well as adiponectin secretion, and further increased lipid droplets accumulation. However, short- and long-term exposures to blonanserin did not affect these parameters. A selective serotonin 5-HT2C, but not a histamine H1, receptor antagonist enhanced the decreased secretion of leptin induced by short-term exposure to clozapine, but did not affect the increased accumulation of lipid droplets. Our findings indicate that clozapine, but not blonanserin, strongly and directly affected the secretion of adipokines, such as leptin, in adipocytes and caused adipocyte enlargement.

Endogenous GIP ameliorates impairment of insulin secretion in proglucagon-deficient mice under moderate beta cell damage induced by streptozotocin.

AIMS/HYPOTHESIS: The action of incretin hormones including glucose-dependent insulinotropic polypeptide (GIP) and glucagon-like peptide-1 (GLP-1) is potentiated in animal models defective in glucagon action. It has been reported that such animal models maintain normoglycaemia under streptozotocin (STZ)-induced beta cell damage. However, the role of GIP in regulation of glucose metabolism under a combination of glucagon deficiency and STZ-induced beta cell damage has not been fully explored. METHODS: In this study, we investigated glucose metabolism in mice deficient in proglucagon-derived peptides (PGDPs)-namely glucagon gene knockout (GcgKO) mice-administered with STZ. Single high-dose STZ (200 mg/kg, hSTZ) or moderate-dose STZ for five consecutive days (50 mg/kg × 5, mSTZ) was administered to GcgKO mice. The contribution of GIP to glucose metabolism in GcgKO mice was also investigated by experiments employing dipeptidyl peptidase IV (DPP4) inhibitor (DPP4i) or Gcg-Gipr double knockout (DKO) mice. RESULTS: GcgKO mice developed severe diabetes by hSTZ administration despite the absence of glucagon. Administration of mSTZ decreased pancreatic insulin content to 18.8 ± 3.4 (%) in GcgKO mice, but ad libitum-fed blood glucose levels did not significantly increase. Glucose-induced insulin secretion was marginally impaired in mSTZ-treated GcgKO mice but was abolished in mSTZ-treated DKO mice. Although GcgKO mice lack GLP-1, treatment with DPP4i potentiated glucose-induced insulin secretion and ameliorated glucose intolerance in mSTZ-treated GcgKO mice, but did not increase beta cell area or significantly reduce apoptotic cells in islets. CONCLUSIONS/INTERPRETATION: These results indicate that GIP has the potential to ameliorate glucose intolerance even under STZ-induced beta cell damage by increasing insulin secretion rather than by promoting beta cell survival.

Effect of hyperglycemia on hepatocellular carcinoma development in diabetes.

Compared with other cancers, diabetes mellitus is more closely associated with hepatocellular carcinoma (HCC). However, whether hyperglycemia is associated with hepatic carcinogenesis remains uncertain. In this study, we investigate the effect of hyperglycemia on HCC development. Mice pretreated with 7,12-dimethylbenz (a) anthracene were divided into three feeding groups: normal diet (Control), high-starch diet (Starch), and high-fat diet (HFD) groups. In addition, an STZ group containing mice that were fed a normal diet and injected with streptozotosin to induce hyperglycemia was included. The STZ group demonstrated severe hyperglycemia, whereas the Starch group demonstrated mild hyperglycemia and insulin resistance. The HFD group demonstrated mild hyperglycemia and severe insulin resistance. Multiple HCC were macroscopically and histologically observed only in the HFD group. Hepatic steatosis was observed in the Starch and HFD groups, but levels of inflammatory cytokines, interleukin (IL)-6, tumor necrosis factor-α, and IL-1ß, were elevated only in the HFD group. The composition of gut microbiota was similar between the Control and STZ groups. A significantly higher number of Clostridium cluster XI was detected in the feces of the HFD group than that of all other groups; it was not detectable in the Starch group. These data suggested that hyperglycemia had no effect on hepatic carcinogenesis. Different incidences of HCC between the Starch and HFD groups may be attributable to degree of insulin resistance, but diet-induced changes in gut microbiota including Clostridium cluster XI may have influenced hepatic carcinogenesis. In conclusion, in addition to the normalization of blood glucose levels, diabetics may need to control insulin resistance and diet contents to prevent HCC development.

Aripiprazole increases NADPH level in PC12 cells: the role of NADPH oxidase.

In aripiprazole-treated PC12 cells, we previously showed that the mitochondrial membrane potential (Δψm) was rather increased in spite of lowered cytochrome c oxidase activity. To address these inconsistent results, we focused the NADPH generation by glucose-6-phosphate dehydrogenase (G6PD), a rate-limiting enzyme of the pentose phosphate pathway (PPP), to titrate reactive oxygen species (ROS) that results in the Δψm maintenance. G6PD may be also involved in another inconsistent result of lowered intracellular lactate level in aripiprazole-treated PC12 cells, because PPP competes glucose-6-phosphate with the glycolytic pathway, resulting in the downregulation of glycolysis. Therefore, we assayed intracellular amounts of NADPH, ROS, and the activities of the enzymes generating or consuming NADPH (G6PD, NADP(+)-dependent isocitrate dehydrogenase, NADP(+)-dependent malic enzyme, glutathione reductase, and NADPH oxidase [NOX]) and estimated glycolysis in 50 µM aripiprazole-, clozapine-, and haloperidol-treated PC12 cells. NADPH levels were enhanced only in aripiprazole-treated ones. Only haloperidol increased ROS. However, the enzyme activities did not show significant changes toward enhancing NADPH level except for the aripiprazole-induced decrease in NOX activity. Thus, the lowered NOX activity could have contributed to the aripiprazole-induced increase in the NADPH level by lowering ROS generation, resulting in maintained Δψm. Although the aforementioned assumption was invalid, the ratio of fructose-1,6-bisphosphate to fructose-6-phosphate was decreased by all antipsychotics examined. Pyruvate kinase activity was enhanced only by aripiprazole. In summary, these observations indicate that aripiprazole possibly possesses the pharmacological superiority to clozapine and haloperidol in the ROS generation and the adjustment of glycolytic pathway.

Low-serum culture system improves the adipogenic ability of visceral adipose tissue-derived stromal cells.

In obese adipose tissue, infiltrating macrophages release proinflammatory cytokines that trigger insulin resistance. An adipocyte-based platform from visceral fat would be useful to elucidate the pathology of adipose inflammation and to develop therapeutic drugs for insulin resistance. ADSCs (adipose tissue-derived mesenchymal stromal cells) expanded from subcutaneous fat are intensively studied as sources for regenerative medicine. However, the adipocyte culture system from visceral fat tissue has not been utilized yet. We aimed to establish the bioactive adipocyte platform using ADSCs from visceral fat pad. Stromal vascular fractions were processed from epididymal fat pads of Sprague-Dawley rats and three human omental fat pads, and the ADSCs were expanded using a low-serum culture method. The responses of ADSCs and ADSC-adipocytes (their adipogenic lineages) to pioglitazone, a therapeutic drug for diabesity, were evaluated by gene expression and ELISA. ADSCs (1×108) were expanded from 10 g of rat epididymal fat pads or human omental fat pads over five passages. Cell surface marker expressions revealed that visceral ADSCs were equivalent to mesenchymal stem cells. ADSC-adipocytes expanded in the low-serum culture system significantly showed higher expression of adipogenic markers [PPAR (peroxisome proliferator-activated receptor) γ, LPL (lipoprotein lipase) and FABP4 (fatty acid-binding protein 4)] and adipocytokines [adiponectin, resistin, leptin, PAI-1 (plasminogen-activator inhibitor 1) and IL (interleukin)-10] than those expanded in a high-serum culture system. Pioglitazone accelerated the adipogenic induction and increased adiponectin expression in human ADSCs by 57.9±5.8-fold (mean±S.E.M.) relative to control cells (P<0.001). Both in rat and human ADSC-adipocytes, TNF-α significantly induced proinflammatory cytokines [MCP-1 (monocyte chemoattractant protein-1) and IL-6] and suppressed adiponectin expression, while pioglitazone antagonized these effects. The present findings suggest that visceral ADSC-adipocytes expanded in low-serum culture would be useful for adiposcience and pharmacological evaluations.

The alpha-glucosidase inhibitor miglitol increases hepatic CYP7A1 activity in association with altered short-chain fatty acid production in the gut of obese diabetic mice.

PURPOSE: Bile acids (BAs) have been shown to contribute to glucose and energy homeostasis. We have recently reported that miglitol, an alpha-glucosidase inhibitor, increases fecal BA excretion and ameliorate insulin resistance and obesity in mice. The aim of this study was to clarify the mechanisms by which miglitol affects BA metabolism. The expression of genes regulating BA metabolism, gut microbiome and short-chain fatty acids (SCFA) were examined. PROCEDURES: NSY mice, representing an obese type 2 diabetic model, were fed with a high-fat diet with or without miglitol for 4 weeks. The expression of BA-related genes in the liver and the lower intestine were measured. Alterations in fecal microbiome, fecal SCFA along with plasma lipid levels were also evaluated. MAJOR FINDINGS: Miglitol significantly increased fecal BA secretion and markedly upregulated the mRNA expression, protein levels and enzyme activity of hepatic cholesterol 7α-hydroxylase, a rate-limiting enzyme of BA synthesis. In the intestine, miglitol treatment significantly suppressed the mRNA expression of apical sodium-dependent bile acid transporter and ATP-binding cassette transporter G5 and G8. In fecal microbiome, the prevalence of prevotella was remarkably reduced and that of clostridium subcluster XIVa was increased by miglitol. Miglitol elevated formic and n-butyric acids along with total SCFA concentration in feces, while succinic acid was decreased. There was no change in plasma total cholesterol levels. CONCLUSIONS: Collectively, miglitol may affect BA metabolism via enhanced CYP7A1 activity resulting from at least in part the alterations in gut microbiome and SCFA production in obese diabetic mice.

Dipeptidyl peptidase-4 inhibitor anagliptin reduces fasting apolipoprotein B-48 levels in patients with type 2 diabetes: A randomized controlled trial.

Type 2 diabetes and dyslipidemia are diseases that collectively increase the risk of patients developing cardiovascular complications. Several incretin-based drugs are reported to improve lipid metabolism, and one of these medications, anagliptin, is a dipeptidyl peptidase-4 (DPP-4) inhibitor that has been shown to decrease serum triglyceride and low-density lipoproteins cholesterol. This study aimed to conduct an investigation into the effects of anagliptin on serum lipid profiles. This multicenter, open-label, randomized (1:1), parallel group study was designed to evaluate the effects of anagliptin on serum lipid profiles (triglycerides, lipoproteins, apolipoproteins, and cholesterol fractions). The study involved 24 patients with type 2 diabetes at two participating hospitals for a period of 24 weeks. Patients were randomly assigned to the anagliptin (n = 12) or control (n = 12) groups. Patients in the anagliptin group were treated with 200 mg of the drug twice daily. Patients in the control group did not receive anagliptin, but continued with their previous treatment schedules. Lipid metabolism was examined under fasting conditions at baseline and 24 weeks. Patients treated with anagliptin for 24 weeks exhibited significantly reduced levels of serum apolipoprotein B-48, a marker for lipid transport from the intestine, compared with the control group patients (P < 0.05). After 24 weeks of treatment, serum adiponectin levels were significantly raised, whereas glycated hemoglobin (HbA1c) levels were significantly lower compared with the baseline in the anagliptin group (P < 0.05), but not in the control group. This study showed that the DPP-4 inhibitor anagliptin reduces fasting apolipoprotein B-48 levels, suggesting that this drug may have beneficial effects on lipid metabolism possibly mediated by the inhibition of intestinal lipid transport.

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.

High glucose-induced upregulation of Rho/Rho-kinase via platelet-derived growth factor receptor-beta increases migration of aortic smooth muscle cells.

Small GTPase Rho and Rho-kinase, the target protein of Rho, play an important role in atherosclerosis. In diabetic macroangiopathy, one of the major pathogenic changes is the migration of vascular smooth muscle cells (SMCs). Platelet-derived growth factor (PDGF) is known to stimulate the migration of SMCs. In the current study, we have investigated the involvement of the Rho/Rho-kinase pathway in the increased migration of cultured human aortic SMCs under a high glucose condition. PDGF stimulated the activation and the protein level of Rho. The protein level of PDGF receptor-beta (PDGFR-beta) was increased under the high glucose condition concomitant with the increased protein level and activation of Rho. The increased protein level and activity of Rho were suppressed by an anti-PDGF neutralizing antibody or a PDGFR-beta inhibitor, AG1433, under the high glucose condition. Furthermore, high glucose significantly increased the migration of SMCs. A specific inhibitor of Rho-kinase, Y-27632, or anti-PDGF neutralizing antibody inhibited increased migration of SMCs under the high glucose condition. The protein levels of Rho were increased in aortae of diabetic rats, which were abolished by the treatment of Imatinib, the inhibitor of PDGFR. These observations indicate that the upregulation of the PDGFR-beta / Rho / Rho-kinase pathway increases the migration of SMCs under the high glucose condition. The inhibition of Rho/Rho-kinase may be a new target for the treatment of diabetic macroangiopathy.

Biochemical roles of the oligosaccharide chains in thyrostimulin, a heterodimeric hormone of glycoprotein hormone subunits alpha 2 (GPA2) and beta 5 (GPB5).

Thyrostimulin is a heterodimeric hormone composed of GPA2 and GPB5, and shares the thyroid-stimulating hormone receptor (TSHR). Thyrostimulin has three N-linked oligosaccharide chains, two in GPA2 and one in GPB5. The roles of these N-linked oligosaccharides in secretion, heterodimer formation and signal transduction were analyzed. Recombinant GPA2s lacking either of the two oligosaccharides were obtained from conditioned medium, whereas dual site-disrupted GPA2 and the GPB5 mutant were not expressed in either the conditioned medium or cell lysate. The binding between GPA2 and GPB5 was weaker than that between TSH subunits GPA1 and TSH beta. Neither of the oligosaccharides in GPA2 had significant effects on heterodimerization. Disruption of either of the oligosaccharides in GPA2 significantly decreased receptor activation, suggesting their critical role in receptor activation.

Antiglycation effect of gliclazide on in vitro AGE formation from glucose and methylglyoxal.

Gliclazide, a sulfonylurea widely used for treatment of diabetes mellitus, is known to scavenge reactive oxygen species. To clarify whether its antioxidative ability interferes with the glycation processes, we incubated bovine serum albumin (BSA) with 1 M glucose or 1 mM methylglyoxal, in the presence or absence of gliclazide, and observed the formation of advanced glycation end products (AGEs). AGE production was assessed by AGE-specific fluorescence, an enzyme-linked immunosorbent assay (ELISA), and Western blotting. The fluorescence at excitation/emission wavelengths of 320/383 nm and 335/385 nm was definitely increased by incubating BSA with 1 M glucose or 1 mM methylglyoxal, and 1 mM gliclazide significantly blunted the fluorescent augmentation, in both wavelengths, in a dose-dependent fashion. Gliclazide almost equaled to aminoguanidine, a putative antiglycation agent, in the inhibitory effect on the glucose-induced fluorescence, while the methylglyoxal-derived fluorescent formation was less suppressed by gliclazide than by aminoguanidine. The AGE concentrations determined by ELISA showed similar results. Incubation of BSA with 1 M glucose or 1 mM methylglyoxal yielded an apparent increase in carboxymethyllysine or argpyrimidine. Both AGEs were significantly lowered by 1 mM gliclazide and a reduction of glucose-derived carboxymethyllysine was comparable to that caused by aminoguanidine. The results of Western blotting supported the findings in ELISA. To our knowledge, the present study provides the first evidence of the antiglycation effect of gliclazide on in vitro AGE formation from glucose and methylglyoxal.

Effects of basic fibroblast growth factor on experimental diabetic neuropathy in rats.

Basic fibroblast growth factor (bFGF) stimulates angiogenesis and induces neural cell regeneration. We investigated the effects of bFGF on diabetic neuropathy in streptozotocin-induced diabetic rats. Diabetic rats were treated with human recombinant bFGF as follows: 1) intravenous administration, 2) intramuscular injection into thigh and soleus muscles with cross-linked gelatin hydrogel (CGH), and 3) intramuscular injection with saline. Ten or 30 days later, the motor nerve conduction velocity (MNCV) of the sciatic-tibial and caudal nerves, sensitivity to mechanical stimuli, sciatic nerve blood flow (SNBF), and retinal blood flow (RBF) were measured. Delayed MNCV in the sciatic-tibial and caudal nerves, hypoalgesia, and reduced SNBF in diabetic rats were all ameliorated by intravenous administration of bFGF after 10, but not 30, days. Intramuscular injection of bFGF with CGH also improved sciatic-tibial MNCV, hypoalgesia, and SNBF after 10 and 30 days, but caudal MNCV was not improved. However, intramuscular injection of bFGF with saline had no significant effects. bFGF did not significantly alter RBF in either normal or diabetic rats. These observations suggest that bFGF could have therapeutic value for diabetic neuropathy and that CGH could play important roles as a carrier of bFGF.

Chronic high-sucrose diet increases fibroblast growth factor 21 production and energy expenditure in mice.

Excess carbohydrate intake causes obesity in humans. On the other hand, acute administration of fructose, glucose or sucrose in experimental animals has been shown to increase the plasma concentration of anti-obesity hormones such as glucagon-like peptide 1 (GLP-1) and Fibroblast growth factor 21 (FGF21), which contribute to reducing body weight. However, the secretion and action of GLP-1 and FGF21 in mice chronically fed a high-sucrose diet has not been investigated. To address the role of anti-obesity hormones in response to increased sucrose intake, we analyzed mice fed a high-sucrose diet, a high-starch diet or a normal diet for 15 weeks. Mice fed a high-sucrose diet showed resistance to body weight gain, in comparison with mice fed a high-starch diet or control diet, due to increased energy expenditure. Plasma FGF21 levels were highest among the three groups in mice fed a high-sucrose diet, whereas no significant difference in GLP-1 levels was observed. Expression levels of uncoupling protein 1 (UCP-1), FGF receptor 1c (FGFR1c) and ß-klotho (KLB) mRNA in brown adipose tissue were significantly increased in high sucrose-fed mice, suggesting increases in FGF21 sensitivity and energy expenditure. Expression of carbohydrate responsive element binding protein (ChREBP) mRNA in liver and brown adipose tissue was also increased in high sucrose-fed mice. These results indicate that FGF21 production in liver and brown adipose tissue is increased in high-sucrose diet and participates in resistance to weight gain.

Therapeutic neovascularization using cord blood-derived endothelial progenitor cells for diabetic neuropathy.

Diabetic neuropathy is based on the impairment of nerve blood flow and the metabolic disorder. Although the vasodilating agents and anticoagulants improve nerve function and symptoms in diabetic neuropathy, more effective treatments are needed. Because endothelial progenitor cells (EPCs) have been identified in adult human peripheral blood, many studies have shown that transplantation of EPCs improves circulation to ischemic tissues. In this study, we have demonstrated that therapeutic neovascularization using human umbilical cord blood-derived EPCs reversed diabetic neuropathy. EPCs were isolated and expanded on day 7 of culture from cord blood mononuclear cells. Unilateral intramuscular injection of EPCs into hindlimb skeletal muscles significantly ameliorated impaired sciatic motor nerve conduction velocity and sciatic nerve blood flow in the EPC-injected side of streptozotocin-induced diabetic nude rats compared with the saline-injected side of diabetic nude rats. Histological study revealed an increased number of microvessels in hindlimb skeletal muscles in the EPC-injected side of diabetic rats. These findings suggest that transplantation of EPCs from cord blood may be a useful treatment for diabetic neuropathy.

Soluble adhesion molecules and C-reactive protein in the progression of silent cerebral infarction in patients with type 2 diabetes mellitus.

The purpose of this study was to investigate the association between the progression of silent cerebral infarction (SCI) and levels of soluble adhesion molecules and high-sensitivity C-reactive protein (hs-CRP) in type 2 diabetic patients. One hundred twenty middle-aged and elderly diabetic patients without histories of vascular events were followed up for a period of 3 years. We measured levels of soluble intercellular adhesion molecule 1 (sICAM-1), vascular cell adhesion molecule 1, E-selectin, and hs-CRP and assessed brain ischemic lesions by magnetic resonance imaging at baseline and 3 years later. Silent cerebral infarction was observed in 13% of the patients at baseline, and these patients were significantly older and had significantly higher blood pressure than those without SCI. Thirty-two patients had newly diagnosed SCI after 3 years. There were no significant differences in factors such as age, blood pressure, and diabetic control between patients without SCI and those in whom it was newly diagnosed. However, only sICAM-1 levels, but not the other soluble adhesion molecules or hs-CRP, were associated with the progression of SCI, and this relationship remains after adjustment for risk factors. On the other hand, higher levels of sICAM-1 and hs-CRP at baseline were observed in 7 patients who were excluded from the present study because of the onset of symptomatic cerebral infarction during follow-up. Our present study suggests that sICAM-1 levels may be a potential marker for SCI, which may lead to future stroke and vascular dementia, and that this marker could be useful in monitoring disease progression and as a surrogate marker in treatment studies.

Insulin elevates leptin secretion and mRNA levels via cyclic AMP in 3T3-L1 adipocytes deprived of glucose.

AIMS: Leptin plays an important role in the pathogenesis of obesity and diabetes, yet the regulatory mechanisms of this hormone have not been fully elucidated. In this study, we aimed to clarify the roles of insulin and glucose in leptin secretion and mRNA production using inhibitors of insulin signal transduction in adipocytes cultured under glucose-free or normal conditions. METHODS: Differentiated 3T3-L1 adipocytes were stimulated with insulin in combination with inhibitors for phosphoinositide 3-kinase (PI3K), Akt, and phosphodiesterase 3B (PDE3B), as well as epinephrine and a cyclic AMP (cAMP) analog under glucose-free or normal conditions. After 8 h of stimulation, leptin protein levels in the media and leptin mRNA expression levels in the adipocytes were measured. RESULTS: Insulin significantly increased the secretion and mRNA levels of leptin under the depletion of glucose. Glucose augmented basal leptin secretion without insulin, while glucose nullified insulin-induced leptin mRNA upregulation. The PI3K inhibitor BEZ-235, the Akt inhibitor MK-2206, and the PDE3B inhibitor cilostazol attenuated the insulin stimulation of leptin secretion, but did not suppress the insulin-induced leptin mRNA upregulation with glucose depletion. In contrast to the glucose-free condition, insulin failed to upregulate leptin mRNA in the presence of glucose. The cAMP analog dibutyryl cAMP and epinephrine decreased both leptin secretion and mRNA regardless of glucose supplementation. CONCLUSION: Insulin alone stimulates leptin secretion and elevates leptin mRNA levels via cAMP under the lack of glucose metabolism, while glucose is a significant and ambivalent effector on the insulin effects of leptin.