ß-Cell Insulin Resistance Plays a Causal Role in Fat-Induced ß-Cell Dysfunction In Vitro and In Vivo.

In the classical insulin target tissues of liver, muscle, and adipose tissue, chronically elevated levels of free fatty acids (FFA) impair insulin signaling. Insulin signaling molecules are also present in ß-cells where they play a role in ß-cell function. Therefore, inhibition of the insulin/insulin-like growth factor 1 pathway may be involved in fat-induced ß-cell dysfunction. To address the role of ß-cell insulin resistance in FFA-induced ß-cell dysfunction we co-infused bisperoxovanadate (BPV) with oleate or olive oil for 48 hours in rats. BPV, a tyrosine phosphatase inhibitor, acts as an insulin mimetic and is devoid of any antioxidant effect that could prevent ß-cell dysfunction, unlike most insulin sensitizers. Following fat infusion, rats either underwent hyperglycemic clamps for assessment of ß-cell function in vivo or islets were isolated for ex vivo assessment of glucose-stimulated insulin secretion (GSIS). We also incubated islets with oleate or palmitate and BPV for in vitro assessment of GSIS and Akt (protein kinase B) phosphorylation. Next, mice with ß-cell specific deletion of PTEN (phosphatase and tensin homolog; negative regulator of insulin signaling) and littermate controls were infused with oleate for 48 hours, followed by hyperglycemic clamps or ex vivo evaluation of GSIS. In rat experiments, BPV protected against fat-induced impairment of ß-cell function in vivo, ex vivo, and in vitro. In mice, ß-cell specific deletion of PTEN protected against oleate-induced ß-cell dysfunction in vivo and ex vivo. These data support the hypothesis that ß-cell insulin resistance plays a causal role in FFA-induced ß-cell dysfunction.

Comparison of Effects of Injectable Semaglutide and Dulaglutide on Oxidative Stress and Glucose Variability in Patients with Type 2 Diabetes Mellitus: A Prospective Preliminary Study.

INTRODUCTION: Recent trials have shown that glucagon-like peptide-1 receptor agonists considerably reduce atherosclerotic cardiovascular disease in patients with type 2 diabetes mellitus (T2DM). Oxidative stress, a surrogate marker of cardiovascular risk, is associated with glucose variability. However, to the best of our knowledge, no studies have compared the effects of injectable semaglutide and dulaglutide therapies on oxidative stress and glucose variability assessed via continuous glucose monitoring (CGM). This study aimed to analyze and compare the effects of semaglutide and dulaglutide therapies on oxidative stress and glucose variability as assessed through CGM. METHODS: This is an open-label, multicenter, randomized, prospective, parallel-group comparison study. Overall, 37 patients with T2DM treated with dulaglutide for at least 12 weeks were randomized into two groups: one receiving continuous dulaglutide therapy (n = 19) and one receiving injectable semaglutide therapy (n = 18) groups. The coprimary endpoints were changes in the results of the diacron-reactive oxygen metabolites test, an oxidative stress marker, and CGM-evaluated glucose variability after 24 weeks. The secondary endpoint was changes in the Diabetes Treatment Satisfaction Questionnaire (DTSQ) scores. RESULTS: Switching to semaglutide therapy was better than continuous dulaglutide therapy in reducing oxidative stress, glucose variability, and glycated hemoglobin levels. Conversely, continuous dulaglutide therapy was better than semaglutide therapy in terms of DTSQ scores for "Convenience" and "Recommend." CONCLUSION: Injectable semaglutide therapy may be more effective than dulaglutide therapy in ameliorating oxidative stress and regulating glucose metabolism, including glucose variability, in patients with T2DM, while dulaglutide therapy may be more effective in terms of treatment satisfaction. CLINICAL TRIAL REGISTRATION: UMIN-CRT ID: UMIN000042670 (registered 7 December 2020).

Subcutaneous Infusion of DNA-Aptamer Raised against Advanced Glycation End Products Prevents Loss of Skeletal Muscle Mass and Strength in Accelerated-Aging Mice.

We have developed DNA aptamers that can inhibit the toxic effects of advanced glycation end products (AGE-Apts). We herein evaluated the effects of AGE-Apts on muscle mass and strength in senescence-accelerated mouse prone 8 (SAMP8) mice. Eight-month-old male SAMP8 mice received subcutaneous infusion of control DNA aptamers (CTR-Apts) or AGE-Apts. Mice in an age-matched senescence-accelerated mouse resistant strain 1 (SAMR1) group were treated with CTR-Apts as controls. The soleus muscles were collected after the 8-week intervention for weight measurement and histological, RT-PCR, and immunofluorescence analyses. Grip strength was measured before and after the 8-week intervention. AGE-Apt treatment inhibited the progressive decrease in the grip strength of SAMP8 mice. SAMP8 mice had lower soleus muscle weight and fiber size than SAMR1 mice, which was partly restored by AGE-Apt treatment. Furthermore, AGE-Apt-treated SAMP8 mice had a lower interstitial fibrosis area of the soleus muscle than CTR-Apt-treated SAMP8 mice. The soleus muscle levels of AGEs, oxidative stress, receptor for AGEs, and muscle ring-finger protein-1 were increased in the CTR-Apt-treated mice, all of which, except for AGEs, were inhibited by AGE-Apt treatment. Our present findings suggest that the subcutaneous delivery of AGE-Apts may be a novel therapeutic strategy for aging-related decrease in skeletal muscle mass and strength.

Prospective randomized comparative study of the effect of pemafibrate add-on or double statin dose on small dense low-density lipoprotein-cholesterol in patients with type 2 diabetes and hypertriglyceridemia on statin therapy.

AIMS/INTRODUCTION: Small dense low-density lipoprotein (sdLDL) is a more potent atherogenic lipoprotein than LDL. As sdLDL-cholesterol (C) levels are determined by triglyceride and LDL-C levels, pemafibrate and statins can reduce sdLDL-C levels. However, it remains unclear whether adding pemafibrate or increasing statin doses would more effectively reduce sdLDL-C levels in patients receiving statin therapy. MATERIALS AND METHODS: A total of 97 patients with type 2 diabetes and hypertriglyceridemia who were treated with statins were randomly assigned to the pemafibrate 0.2 mg/day addition or statin dose doubled, and followed for 12 weeks. sdLDL-C was measured by our established homogenous assay. RESULTS: The percentage and absolute reductions of sdLDL-C levels were significantly greater in the pemafibrate add-on group than the statin doubling group (-32.8 vs -8.1%; -16 vs -3 mg/dL, respectively). Triglyceride levels were reduced only in the pemafibrate add-on group (-44%), and LDL-C levels were reduced only in the statin doubling group (-8%), whereas levels of non-high-density lipoprotein-C and apolipoprotein B were similarly decreased (7-9%) in both groups. The absolute reductions of sdLDL-C levels were closely associated with decreased triglyceride, LDL-C, non-high-density lipoprotein-C and apolipoprotein B. In the subgroup analysis, the effect of pemafibrate add-on on sdLDL-C reductions was observed irrespective of baseline lipid parameters or statin type. No serious adverse effects were observed in both groups. CONCLUSIONS: In patients with type 2 diabetes and hypertriglyceridemia, the addition of pemafibrate to a statin is superior to doubling a statin in reducing sdLDL-C without increasing adverse effects.

SMTP-44D Inhibits Atherosclerotic Plaque Formation in Apolipoprotein-E Null Mice Partly by Suppressing the AGEs-RAGE Axis.

SMTP-44D has been reported to have anti-oxidative and anti-inflammatory reactions, including reduced expression of receptor for advanced glycation end products (RAGE) in experimental diabetic neuropathy. Although activation of RAGE with its ligands, and advanced glycation end products (AGEs), play a crucial role in atherosclerotic cardiovascular disease, a leading cause of death in diabetic patients, it remains unclear whether SMTP-44D could inhibit experimental atherosclerosis by suppressing the AGEs-RAGE axis. In this study, we investigated the effects of SMTP-44D on atherosclerotic plaque formation and expression of AGEs in apolipoprotein-E null (Apoe-/-) mice. We further studied here whether and how SMTP-44D inhibited foam cell formation of macrophages isolated from Apoe-/- mice ex vivo. Although administration of SMTP-44D to Apoe-/- mice did not affect clinical or biochemical parameters, it significantly decreased the surface area of atherosclerotic lesions and reduced the atheromatous plaque size, macrophage infiltration, and AGEs accumulation in the aortic roots. SMTP-44D bound to immobilized RAGE and subsequently attenuated the interaction of AGEs with RAGE in vitro. Furthermore, foam cell formation evaluated by Dil-oxidized low-density lipoprotein (ox-LDL) uptake, and gene expression of RAGE, cyclin-dependent kinase 5 (Cdk5) and CD36 in macrophages isolated from SMTP-44D-treated Apoe-/- mice were significantly decreased compared with those from saline-treated mice. Gene expression levels of RAGE and Cdk5 were highly correlated with each other, the latter of which was also positively associated with that of CD36. The present study suggests that SMTP-44D may inhibit atherosclerotic plaque formation in Apoe-/- mice partly by blocking the AGEs-RAGE-induced ox-LDL uptake into macrophages via the suppression of Cdk5-CD36 pathway.

Comparison of positive rates between glutamic acid decarboxylase antibodies and ElisaRSR™ 3 Screen ICA™ in recently obtained sera from patients who had been previously diagnosed with slowly progressive type 1 diabetes.

AIMS/INTRODUCTION: This study aimed to compare the positivity rates of glutamic acid decarboxylase autoantibodies (GADA) and ElisaRSR™ 3 Screen ICA™ (3 Screen ICA), a newly developed assay for the simultaneous measurement of GADA, insulinoma-associated antigen-2 autoantibodies (IA-2A), and zinc transporter 8 autoantibodies (ZnT8A), in recently obtained sera from patients who had been previously diagnosed with slowly progressive type 1 diabetes (SPIDDM). MATERIALS AND METHODS: We enrolled 53 patients with SPIDDM who were positive for GADA at the diagnosis and 98 non-diabetic individuals, and investigated the diagnostic accuracy of the 3 Screen ICA (cutoff index ≥30 units) compared with that of GADA. In addition, we compared the clinical characteristics of patients with SPIDDM who were negative or positive on 3 Screen ICA. RESULTS: The positivity rates of 3 Screen ICA, GADA, IA-2A, and ZnT8A were 88.7, 86.8, 24.5, and 13.2%, respectively. The respective sensitivity, specificity, and positive and negative predictive values for SPIDDM were 88.7, 100, 100, and 94.2% by 3 Screen ICA and 86.8, 100, 100.0, and 93.3% by GADA. There were no significant differences in age at onset, duration of diabetes, body mass index, glycated hemoglobin and C-peptide levels, and the prevalence of autoimmune thyroiditis between patients with SPIDDM who were positive or negative on 3 Screen ICA. However, the prevalence of insulin users was significantly higher in those who were positive than in those who were negative on 3 Screen ICA. CONCLUSIONS: Similar to GADA, 3 Screen ICA may be a useful diagnostic tool for detecting patients with SPIDDM.

Efficacy of a new enzyme-linked immunosorbent assay system for three islet cell autoantibodies in Japanese patients with acute-onset type 1 diabetes.

To evaluate the clinical efficacy of a new enzyme-linked immunosorbent assay (ELISA) system for simultaneously detecting three islet cell autoantibodies against glutamic acid decarboxylase (GADA), insulinoma-associated antigen-2 (IA-2A), and zinc transporter 8 (ZnT8A) (3 Screen ICA ELISA) in Japanese patients with acute-onset type 1 diabetes (T1D). In addition, clinical factors affecting the 3 Screen ICA ELISA index were investigated. We compared the positivity values of 3 Screen ICA ELISA with that of each autoantibody alone in 97 patients with acute-onset T1D (mean age 48.7 years, 49% male) and 100 non-diabetic subjects (mean age 47.0 years, 50% male). Serum thyroid stimulating hormone receptor antibody, thyroid peroxidase antibody (TPOAb) and thyroglobulin autoantibody levels were also evaluated. The cut-off value of the 3 Screen ICA ELISA was determined based on the 97th percentile of 100 non-diabetic controls (threshold for positivity, ≥14 index). The mean age of disease onset and duration of diabetes were 34.2 years and 14.5 years, respectively. Among all T1D patients, the positivity of 3 Screen ICA ELISA was 71.1%, while that of GADA, IA-2A, and ZnT8A were 59.8%, 25.8%, and 25.8%, respectively. The median 3 Screen ICA index was 121.9 (8.7-468.2) and was associated with titers of each autoantibody, most so with GADA, and was significantly higher in TPOAb-positive patients than in TPOAb-negative patients. Our findings suggests that the 3 Screen ICA ELISA may be a time-saving diagnostic tool for evaluating islet autoantibodies in acute-onset T1D patients.

Luseogliflozin inhibits high glucose-induced TGF-ß2 expression in mouse cardiomyocytes by suppressing NHE-1 activity.

OBJECTIVE: Sodium-glucose cotransporter-2 (SGLT2) inhibitors exhibit cardioprotective properties in patients with diabetes. However, SGLT2 is not expressed in the heart, and the underlying molecular mechanisms are not fully understood. We investigated whether the SGLT2 inhibitor luseogliflozin exerts beneficial effects on high glucose-exposed cardiomyocytes via the suppression of sodium-hydrogen exchanger-1 (NHE-1) activity. METHODS: Mouse cardiomyocytes were incubated under normal or high glucose conditions with vehicle, luseogliflozin, or the NHE-1 inhibitor cariporide. NHE-1 activity and gene expression were evaluated by the SNARF assay and real-time reverse transcription-polymerase chain reaction (RT-PCR) analysis, respectively. Six-week-old male db/db mice were treated with vehicle or luseogliflozin for 6 weeks, and the hearts were collected for histological, RT-PCR, and western blot analyses. RESULTS: High glucose increased NHE-1 activity and transforming growth factor (Tgf)-ß2 mRNA levels in cardiomyocytes, both of which were inhibited by luseogliflozin or cariporide, whereas their combination showed no additive suppression of Tgf-ß2 mRNA levels. Luseogliflozin attenuated cardiac hypertrophy and fibrosis in db/db mice in association with decreased mRNA and protein levels of TGF-ß2. CONCLUSIONS: Luseogliflozin may suppress cardiac hypertrophy in diabetes by reducing Tgf-ß2 expression in cardiomyocytes via the suppression of NHE-1 activity.

Nicotinamide Mononucleotide Prevents Free Fatty Acid-Induced Reduction in Glucose Tolerance by Decreasing Insulin Clearance.

The NAD-dependent deacetylase SIRT1 improves ß cell function. Accordingly, nicotinamide mononucleotide (NMN), the product of the rate-limiting step in NAD synthesis, prevents ß cell dysfunction and glucose intolerance in mice fed a high-fat diet. The current study was performed to assess the effects of NMN on ß cell dysfunction and glucose intolerance that are caused specifically by increased circulating free fatty acids (FFAs). NMN was intravenously infused, with or without oleate, in C57BL/6J mice over a 48-h-period to elevate intracellular NAD levels and consequently increase SIRT1 activity. Administration of NMN in the context of elevated plasma FFA levels considerably improved glucose tolerance. This was due not only to partial protection from FFA-induced ß cell dysfunction but also, unexpectedly, to a significant decrease in insulin clearance. However, in conditions of normal FFA levels, NMN impaired glucose tolerance due to decreased ß cell function. The presence of this dual action of NMN suggests caution in its proposed therapeutic use in humans.

Glucose-Dependent Insulinotropic Polypeptide Suppresses Foam Cell Formation of Macrophages through Inhibition of the Cyclin-Dependent Kinase 5-CD36 Pathway.

Glucose-dependent insulinotropic polypeptide (GIP) has been reported to have an atheroprotective property in animal models. However, the effect of GIP on macrophage foam cell formation, a crucial step of atherosclerosis, remains largely unknown. We investigated the effects of GIP on foam cell formation of, and CD36 expression in, macrophages extracted from GIP receptor-deficient (Gipr-/-) and Gipr+/+ mice and cultured human U937 macrophages by using an agonist for GIP receptor, [D-Ala2]GIP(1-42). Foam cell formation evaluated by esterification of free cholesterol to cholesteryl ester and CD36 gene expression in macrophages isolated from Gipr+/+ mice infused subcutaneously with [D-Ala2]GIP(1-42) were significantly suppressed compared with vehicle-treated mice, while these beneficial effects were not observed in macrophages isolated from Gipr-/- mice infused with [D-Ala2]GIP(1-42). When macrophages were isolated from Gipr+/+ and Gipr-/- mice, and then exposed to [D-Ala2]GIP(1-42), similar results were obtained. [D-Ala2]GIP(1-42) attenuated ox-LDL uptake of, and CD36 gene expression in, human U937 macrophages as well. Gene expression level of cyclin-dependent kinase 5 (Cdk5) was also suppressed by [D-Ala2]GIP(1-42) in U937 cells, which was corelated with that of CD36. A selective inhibitor of Cdk5, (R)-DRF053 mimicked the effects of [D-Ala2]GIP(1-42) in U937 cells. The present study suggests that GIP could inhibit foam cell formation of macrophages by suppressing the Cdk5-CD36 pathway via GIP receptor.

Effects of omarigliptin on glucose variability and oxidative stress in type 2 diabetes patients: A prospective study.

AIMS: To date, no clinical studies have compared once-weekly dipeptidyl peptidase 4 (DPP-4) inhibitors with once-daily DPP-4 inhibitors in terms of glucose variability (GV) and oxidative stress (OS). METHODS: Thirty-six patients with type 2 diabetes mellitus (T2DM) treated with once-daily DPP-4 inhibitors for at least 12 weeks were randomized to either continue once-daily DPP-4 inhibitors or receive omarigliptin, a once-weekly DPP-4 inhibitor, for 24 weeks. The primary end points were changes in the diacron-reactive oxygen metabolite (d-ROMs) test, a marker of OS, and GV using flash glucose monitoring. The secondary end point was changes in the diabetes treatment satisfaction questionnaire (DTSQ) scores. RESULTS: There were no significant group differences in d-ROMs and DTSQ scores after 24 weeks of treatments. However, omarigliptin was superior to once-daily DPP-4 inhibitors in controlling fasting plasma glucose (FPG) and time in range (TIR). Although FPG and TIR were unchanged at 24 weeks after switching to omarigliptin, these parameters increased in the group receiving maintenance therapy with once-daily DPP-4 inhibitors. No statistically significant changes in hemoglobin A1c were observed between the two groups. CONCLUSIONS: Our findings suggest that switching from once-daily DPP-4 inhibitors to omarigliptin may be efficacious for maintaining FPG and TIR in T2DM patients.

Roles of vascular endothelial and smooth muscle cells in the vasculoprotective effect of insulin in a mouse model of restenosis.

BACKGROUND: Insulin exerts vasculoprotective effects on endothelial cells (ECs) and growth-promoting effects on vascular smooth muscle cells (SMCs) in vitro, and suppresses neointimal growth in vivo. Here we determined the role of ECs and SMCs in the effect of insulin on neointimal growth. METHODS: Mice with transgene CreERT2 under the control of EC-specific Tie2 (Tie2-Cre) or SMC-specific smooth muscle myosin heavy chain promoter/enhancer (SMMHC-Cre) or littermate controls were crossbred with mice carrying a loxP-flanked insulin receptor (IR) gene. After CreERT2-loxP-mediated recombination was induced by tamoxifen injection, mice received insulin pellet or sham (control) implantation, and underwent femoral artery wire injury. Femoral arteries were collected for morphological analysis 28 days after wire injury. RESULTS: Tamoxifen-treated Tie2-Cre+ mice showed lower IR expression in ECs, but not in SMCs, than Tie2-Cre- mice. Insulin treatment reduced neointimal area after arterial injury in Tie2-Cre- mice, but had no effect in Tie2-Cre+ mice. Tamoxifen-treated SMMHC-Cre+ mice showed lower IR expression in SMCs, but not in ECs, than SMMHC-Cre- mice. Insulin treatment reduced neointimal area in SMMHC-Cre- mice, whereas unexpectedly, it failed to inhibit neointima formation in SMMHC-Cre+ mice. CONCLUSION: Insulin action in both ECs and SMCs is required for the "anti-restenotic" effect of insulin in vivo.

Association between insulin-like growth factor 1 and pancreatic volume in type 1 and type 2 diabetes: cross-sectional study of a Japanese population.

AIMS/HYPOTHESIS: Although IGF-1 is known to promote organ growth, including exocrine pancreas, the association between plasma IGF-1 levels and pancreatic size remains unclear in diabetic patients. METHODS: This cross-sectional study was designed to investigate the correlations among pancreatic volume (PV) based on computed tomography, IGF-1 levels, age- and sex-adjusted IGF-1 levels (IGF-1 Z-score), and C-peptide levels in patients with type 1 diabetes (T1D) (n = 51) and type 2 diabetes (T2D) (n = 104) in a Japanese population. RESULTS: PV was significantly correlated with body weight (BW) in both types of diabetes. PV adjusted for BW (PV/BW), IGF-1 Z-score and C-peptide levels were significantly lower in patients with T1D than T2D. There was a significant positive correlation between C-peptide levels and PV/BW in both subtypes of diabetes. IGF-1 Z-scores were significantly correlated with PV/BW in patients with T1D (r = 0.37, P = 0.007), but not T2D. Although IGF-1 Z-scores were not correlated with age, age of disease onset, disease duration, HbA1c, or C-peptide levels in both types of diabetes, a multivariable liner regression analysis revealed that IGF-1 Z-score and C-peptide levels were independent correlates of PV/BW in T1D patients, while C-peptide levels were a sole correlate in T2D. CONCLUSIONS/INTERPRETATION: Decreased IGF-1 levels might be one causal factor for smaller pancreas in patients with T1D.

Very rare case of Graves' disease with resistance to methimazole: a case report and literature review.

BACKGROUND: Methimazole (MMI) is used to treat hyperthyroidism in Graves' disease. It is rare to encounter patients in whom hyperthyroidism cannot be controlled using high doses of MMI.Case presentation: A 21-year-old woman was referred to our hospital because of MMI-resistant Graves' disease. Although her MMI dose had been increased to 120 mg/day, her serum thyroid hormone concentration was too high to be measured. Additional therapy with lithium carbonate, and then with dexamethasone and inorganic iodine, was initiated. After 14 days, the patient's serum thyroid hormone concentration normalized, while she was taking 150 mg/day MMI, 800 mg/day lithium carbonate, 6 mg/day dexamethasone and 306 mg/day inorganic iodine, and total thyroidectomy was then performed. The patient was discharged 8 days after the thyroidectomy and experienced no major complications. CONCLUSIONS: We have presented a rare case of Graves' disease that was resistant to high-dose MMI. Combination therapy of MMI with lithium carbonate, dexamethasone and inorganic iodine may represent a therapeutic option for the preoperative preparation of patients with MMI-resistant Graves' disease.

Glucose Variability is Independently Correlated with Serum Level of Pigment Epithelium-Derived Factor in Type 2 Diabetes.

INTRODUCTION: Pigment epithelium-derived factor (PEDF) may play a role in cardiometabolic disorders. The aim of this study was to investigate which biochemical and clinical parameters are independently associated with serum PEDF levels in patients with type 2 diabetes mellitus (T2DM). METHODS: We performed a cross-sectional analysis of 124 patients with T2DM who underwent continuous glucose monitoring (CGM) and blood chemistry analysis, including the diacron-reactive oxygen metabolites (d-ROMs) test and serum PEDF measurement (study 1). Then we investigated whether the changes in the studied biochemical and clinical parameters after 24 weeks of treatment (Δparameters) with anti-hyperglycemic agents, including sodium-glucose cotransporter 2 inhibitors, glucagon-like peptide 1 receptor agonists, and/or insulin and anti-hypertensive drugs and statins, were independently correlated with change in PEDF (ΔPEDF) in 52 of the patients with T2DM for whom there was sufficient serum samples to perform the post-treatment analysis (study 2). Serum levels of PEDF were measured with an enzyme-linked immunosorbent assay. CGM metrics were calculated on days 2 and 3. Oxidative stress was evaluated using the d-ROMs test. RESULTS: Body mass index (BMI), triglycerides, fasting C-peptide, mean amplitude of glycemic excursions (MAGE), urinary albumin-to-creatinine ratio (UACR), and d-ROMs were positively associated with serum PEDF level, and high-density lipoprotein cholesterol (HDL-C) and estimated glomerular filtration rate (eGFR) were inversely associated with serum PEDF level. Because these parameters were correlated with each other, multivariate stepwise analysis was performed: eGFR, HDL-C, BMI, MAGE, and UACR remained significant (R2 = 0.452). Furthermore, ΔMAGE and Δd-ROMs were positively correlated with ΔPEDF in study 2. CONCLUSIONS: The results of this study suggest that MAGE may be independently correlated with elevations in serum PEDF level in patients with T2DM.

Glucose-dependent insulinotropic polypeptide inhibits cardiac hypertrophy and fibrosis in diabetic mice via suppression of TGF-ß2.

Diabetic cardiomyopathy is associated with an increased risk for heart failure and death in patients with diabetes. We investigated here whether and how GIP attenuated cardiac hypertrophy and fibrosis in diabetic mice with obesity. Diabetic db/db mice at 7 weeks old were infused with vehicle or GIP (50 nmol/kg/day) for 6 weeks, and hearts were collected for histological and RT-PCR analyzes. Cardiomyocytes isolated from neonatal mice were incubated with or without 300 nM [D-Ala2]-GIP, 30 mM glucose, or 100 µg/mL advanced glycation end products (AGEs) for RT-PCR and lucigenin assays. Compared with non-diabetic mice, diabetic mice exhibited larger left ventricle wall thickness and cardiomyocyte sizes and more fibrotic areas in association with up-regulation of myosin heavy chain ß (ß-Mhc) and transforming growth factor-beta2 (Tgf-ß2) mRNA levels, all of which were inhibited by GIP infusion. High glucose increased NADPH oxidase-driven superoxide generation and up-regulated ß-Mhc, Tgf-ß2, and receptor for AGEs mRNA levels in cardiomyocytes, and augmented the AGE-induced ß-Mhc gene expression. [D-Ala2]-GIP attenuated all of the deleterious effects of high glucose and/or AGEs on cardiomyocytes. Our present findings suggest that GIP could inhibit cardiac hypertrophy and fibrosis in diabetic mice via suppression of TGF-ß2.

AGE-RAGE Axis Stimulates Oxidized LDL Uptake into Macrophages through Cyclin-Dependent Kinase 5-CD36 Pathway via Oxidative Stress Generation.

Advanced glycation end products (AGEs) are localized in macrophage-derived foam cells within atherosclerotic lesions, which could be associated with the increased risk of atherosclerotic cardiovascular disease under diabetic conditions. Although foam cell formation of macrophages has been shown to be enhanced by AGEs, the underlying molecular mechanism remains unclear. Since cyclin-dependent kinase 5 (Cdk5) is reported to modulate inflammatory responses in macrophages, we investigated whether Cdk5 could be involved in AGE-induced CD36 gene expression and foam cell formation of macrophages. AGEs significantly increased Dil-oxidized low-density lipoprotein (ox-LDL) uptake, and Cdk5 and CD36 gene expression in U937 human macrophages, all of which were inhibited by DNA aptamer raised against RAGE (RAGE-aptamer). Cdk5 and CD36 gene expression levels were correlated with each other. An antioxidant, N-acetyl-l-cysteine, mimicked the effects of RAGE-aptamer on AGE-exposed U937 cells. A selective inhibitor of Cdk5, (R)-DRF053, attenuated the AGE-induced Dil-ox-LDL uptake and CD36 gene expression, whereas anti-CD36 antibody inhibited the Dil-ox-LDL uptake but not Cdk5 gene expression. The present study suggests that AGEs may stimulate ox-LDL uptake into macrophages through the Cdk5-CD36 pathway via RAGE-mediated oxidative stress.

Anti-inflammatory and atheroprotective properties of glucagon.

Although glucagon has been shown to exert pleiotropic actions in various types of cells and organs through the interaction with its receptor, its pathophysiological role in atherosclerotic cardiovascular disease remains unclear. Here, we examined whether and how glucagon could attenuate the progression of atherosclerotic plaques in apolipoprotein E-deficient mice (ApoE-/-), an animal model of atherosclerosis. Glucagon (138 or 413 nmol/kg/day) or vehicle was infused to mice at 16 weeks of age. After 4-week treatment, vascular samples were collected for histological and RT-PCR analyses. Human monocytic THP-1 cells were pre-incubated with or without a glucagon receptor antagonist L-168049, and then treated with or without glucagon for 7 h. Gene and protein expressions were determined by RT-PCR and western blot analyses, respectively. High-dose glucagon infusion significantly decreased aortic plaque area and volume in ApoE-/- mice, both of which were inversely correlated with plasma glucagon levels. Glucagon infusion also reduced the ratio of pro-inflammatory interleukin-1ß to anti-inflammatory interleukin-10 gene expression in aortae. Glucagon receptor was expressed in THP-1 cells, and 1 nM glucagon decreased the ratio of interleukin-1ß to interleukin-10 gene expression, which was significantly prevented by L-168049. Our present findings suggest that glucagon could exert atheroprotection partly via its anti-inflammatory property.

Resveratrol Inhibits Neointimal Growth after Arterial Injury in High-Fat-Fed Rodents: The Roles of SIRT1 and AMPK.

We have shown that both insulin and resveratrol (RSV) decrease neointimal hyperplasia in chow-fed rodents via mechanisms that are in part overlapping and involve the activation of endothelial nitric oxide synthase (eNOS). However, this vasculoprotective effect of insulin is abolished in high-fat-fed insulin-resistant rats. Since RSV, in addition to increasing insulin sensitivity, can activate eNOS via pathways that are independent of insulin signaling, such as the activation of sirtuin 1 (SIRT1) and AMP-activated kinase (AMPK), we speculated that unlike insulin, the vasculoprotective effect of RSV would be retained in high-fat-fed rats. We found that high-fat feeding decreased insulin sensitivity and increased neointimal area and that RSV improved insulin sensitivity (p < 0.05) and decreased neointimal area in high-fat-fed rats (p < 0.05). We investigated the role of SIRT1 in the effect of RSV using two genetic mouse models. We found that RSV decreased neointimal area in high-fat-fed wild-type mice (p < 0.05), an effect that was retained in mice with catalytically inactive SIRT1 (p < 0.05) and in heterozygous SIRT1-null mice. In contrast, the effect of RSV was abolished in AMKPα2-null mice. Thus, RSV decreased neointimal hyperplasia after arterial injury in both high-fat-fed rats and mice, an effect likely not mediated by SIRT1 but by AMPKα2.

A Dipeptidyl Peptidase-4 Inhibitor Inhibits Foam Cell Formation of Macrophages in Type 1 Diabetes via Suppression of CD36 and ACAT-1 Expression.

Dipeptidyl peptidase-4 (DPP-4) inhibitors have been reported to play a protective role against atherosclerosis in both animal models and patients with type 2 diabetes (T2D). However, since T2D is associated with dyslipidemia, hypertension and insulin resistance, part of which are ameliorated by DPP-4 inhibitors, it remains unclear whether DPP-4 inhibitors could have anti-atherosclerotic properties directly by attenuating the harmful effects of hyperglycemia. Therefore, we examined whether a DPP-4 inhibitor, teneligliptin, could suppress oxidized low-density lipoprotein (ox-LDL) uptake, foam cell formation, CD36 and acyl-coenzyme A: cholesterol acyltransferase-1 (ACAT-1) gene expression of macrophages isolated from streptozotocin-induced type 1 diabetes (T1D) mice and T1D patients as well as advanced glycation end product (AGE)-exposed mouse peritoneal macrophages and THP-1 cells. Foam cell formation, CD36 and ACAT-1 gene expression of macrophages derived from T1D mice or patients increased compared with those from non-diabetic controls, all of which were inhibited by 10 nmol/L teneligliptin. AGEs mimicked the effects of T1D; teneligliptin attenuated all the deleterious effects of AGEs in mouse macrophages and THP-1 cells. Our present findings suggest that teneligliptin may inhibit foam cell formation of macrophages in T1D via suppression of CD36 and ACAT-1 gene expression partly by attenuating the harmful effects of AGEs.