Glucose-Dependent Insulinotropic Polypeptide Suppresses Peripheral Arterial Remodeling in Male Mice.

Glucose-dependent insulinotropic polypeptide (GIP) exhibits direct cardiovascular actions in addition to its well-known insulinotropic effect. However, the role of GIP in peripheral artery disease remains unclear. In this study, we evaluated the effects of GIP against peripheral arterial remodeling in mouse models. The genetic deletion of GIP receptor (GIPR) led to exaggerated neointimal hyperplasia after transluminal femoral artery wire injury. Conversely, chronic GIP infusion suppressed neointimal hyperplasia and facilitated endothelial regeneration. The beneficial effects of GIP were abrogated by inhibiting nitric oxide (NO) synthase, suggesting a possible mechanism mediated by NO. In cultured human umbilical vein endothelial cells (HUVECs), GIP elevated cytosolic calcium levels without affecting intracellular cAMP levels. Furthermore, GIP dose-dependently increased NO production, whereas this effect was abolished by inhibiting AMP-activated protein kinase (AMPK). GIP induced AMPK phosphorylation, which was abrogated by inhibiting phospholipase C and calcium-calmodulin-dependent protein kinase kinase but not by adenylate cyclase or liver kinase B1, suggesting the existence of a calcium-mediated GIPR signaling pathway. These effects of GIP were retained in severe hyperglycemic Leprdb/ Leprdb mice and in high-glucose-cultured HUVECs. Overall, we demonstrated the protective effects of GIP against peripheral arterial remodeling as well as the involvement of a calcium-mediated GIPR signaling pathway in vascular endothelial cells. Our findings imply the potential vascular benefits of multiple agonists targeting G protein-coupled receptors, including GIPR, which are under development for the treatment of type 2 diabetes.

A Dipeptidyl Peptidase-4 Inhibitor Suppresses Macrophage Foam Cell Formation in Diabetic db/db Mice and Type 2 Diabetes Patients.

Dipeptidyl peptidase-4 (DPP-4) inhibitors could have antiatherosclerotic action, in addition to antihyperglycemic roles. Because macrophage foam cells are key components of atherosclerosis, we investigated the effect of the DPP-4 inhibitor teneligliptin on foam cell formation and its related gene expression levels in macrophages extracted from diabetic db/db (C57BLKS/J Iar -+Leprdb/+Leprdb ) mice and type 2 diabetes (T2D) patients ex vivo. We incubated mouse peritoneal macrophages and human monocyte-derived macrophages differentiated by 7-day culture with oxidized low-density lipoprotein in the presence/absence of teneligliptin (10 nmol/L) for 18 hours. We observed remarkable suppression of foam cell formation by teneligliptin treatment ex vivo in macrophages isolated from diabetic db/db mice (32%) and T2D patients (38%); this effect was accompanied by a reduction of CD36 (db/db mice, 43%; T2D patients, 46%) and acyl-coenzyme A: cholesterol acyltransferase-1 (ACAT-1) gene expression levels (db/db mice, 47%; T2D patients, 45%). Molecular mechanisms underlying this effect are associated with downregulation of CD36 and ACAT-1 by teneligliptin. The suppressive effect of a DPP-4 inhibitor on foam cell formation in T2D is conserved across species and is worth studying to elucidate its potential as an intervention for antiatherogenesis in T2D patients.

The role of endothelial nitric oxide in the anti-restenotic effects of liraglutide in a mouse model of restenosis.

BACKGROUND: Previous animal studies have shown that glucagon-like peptide-1 receptor agonists (GLP-1RAs) suppress arterial restenosis, a major complication of angioplasty, presumably through their direct action on vascular smooth muscle cells. However, the contribution of vascular endothelial cells (VECs) to this process remains unknown. In addition, the potential interference caused by severe hyperglycemia and optimal treatment regimen remain to be determined. METHODS: Nine-week-old male C57BL6 (wild-type) and diabetic db/db mice were randomly divided into vehicle or liraglutide treatment groups (Day 1), and subject to femoral artery wire injuries (Day 3). The injured arteries were collected on Day 29 for morphometric analysis. Human umbilical vein endothelial cells (HUVECs) were used for in vitro experiments. One-way ANOVA, followed by Tukey's test, was used for comparisons. RESULTS: In wild-type mice, liraglutide treatment (5.7, 17, or 107 nmol/kg/day) dose-dependently reduced the neointimal area (20, 50, and 65%) without inducing systemic effects, and caused an associated decrease in the percentage of vascular proliferating cells. However, these effects were completely abolished by the nitric oxide synthase (NOS) inhibitor N-omega-nitro-L-arginine methyl ester. Next, we investigated the optimal treatment regimen. Early treatment (Days 1-14) was as effective in reducing the neointimal area and vascular cell proliferation as full treatment (Days 1-29), whereas delayed treatment (Days 15-29) was ineffective. In HUVECs, liraglutide treatment dose-dependently stimulated NO production, which was dependent on GLP-1R, cAMP, cAMP-dependent protein kinase, AMP-activated protein kinase (AMPK), and NOS. Subsequently, we investigated the role of liver kinase B (LKB)-1 in this process. Liraglutide increased the phosphorylation of LKB-1, and siRNA-induced LKB-1 knockdown abolished liraglutide-stimulated NO production. In severe hyperglycemic db/db mice, liraglutide treatment also suppressed neointimal hyperplasia, which was accompanied by reductions in vascular cell proliferation and density. Furthermore, liraglutide treatment suppressed hyperglycemia-enhanced vascular inflammation 7 days after arterial injury. CONCLUSIONS: We demonstrate that endothelial cells are targets of liraglutide, and suppress restenosis via endothelial NO. Furthermore, the protective effects are maintained in severe hyperglycemia. Our findings provide an evidence base for a future clinical trial to determine whether treatment with GLP-1RAs represents potentially effective pharmacological therapy following angioplasty in patients with diabetes.

Combination Therapy with a Sodium-Glucose Cotransporter 2 Inhibitor and a Dipeptidyl Peptidase-4 Inhibitor Additively Suppresses Macrophage Foam Cell Formation and Atherosclerosis in Diabetic Mice.

Dipeptidyl peptidase-4 inhibitors (DPP-4is), in addition to their antihyperglycemic roles, have antiatherosclerotic effects. We reported that sodium-glucose cotransporter 2 inhibitors (SGLT2is) suppress atherosclerosis in a glucose-dependent manner in diabetic mice. Here, we investigated the effects of combination therapy with SGLT2i and DPP-4i on atherosclerosis in diabetic mice. SGLT2i (ipragliflozin, 1.0 mg/kg/day) and DPP-4i (alogliptin, 8.0 mg/kg/day), either alone or in combination, were administered to db/db mice or streptozotocin-induced diabetic apolipoprotein E-null (Apoe-/- ) mice. Ipragliflozin and alogliptin monotherapies improved glucose intolerance; however, combination therapy did not show further improvement. The foam cell formation of peritoneal macrophages was suppressed by both the ipragliflozin and alogliptin monotherapies and was further enhanced by combination therapy. Although foam cell formation was closely associated with HbA1c levels in all groups, DPP-4i alone or the combination group showed further suppression of foam cell formation compared with the control or SGLT2i group at corresponding HbA1c levels. Both ipragliflozin and alogliptin monotherapies decreased scavenger receptors and increased cholesterol efflux regulatory genes in peritoneal macrophages, and combination therapy showed additive changes. In diabetic Apoe-/- mice, combination therapy showed the greatest suppression of plaque volume in the aortic root. In conclusion, combination therapy with SGLT2i and DPP4i synergistically suppresses macrophage foam cell formation and atherosclerosis in diabetic mice.

Suppressive Effects of Glucose-Dependent Insulinotropic Polypeptide on Cardiac Hypertrophy and Fibrosis in Angiotensin II-Infused Mouse Models.

BACKGROUND: Activation of glucose-dependent insulinotropic polypeptide receptor (GIPR) has been shown to be protective against atherosclerosis. However, effects of GIP on the heart have remained unclear. To address this question, in vitro and in vivo experiments were conducted. METHODS AND RESULTS: In isolated mouse cardiomyocytes, GIPR mRNA was detected by reverse transcription-polymerase chain reaction, and GIP stimulation increased adenosine 3',5'-cyclic monophosphate production. In apolipoprotein E-knockout mice, infusion of angiotensin II (AngII; 2,000 ng·kg(-1)·min(-1)) significantly increased the heart weights, and co-administration of GIP (25 nmol·kg(-1)·day(-1)) reversed this increase (both P<0.01). In the left ventricular walls, GIP suppressed AngII-induced cardiomyocyte hypertrophy by 34%, apoptosis by 77%, and interstitial fibrosis by 79% (all P<0.01). Furthermore, GIP reduced AngII-induced expression of transforming growth factor-ß1 (TGF-ß1) and hypoxia inducible factor-1α. In wild-type mice, cardiac hypertrophy was induced by AngII to a lesser extent, and prevented by GIP. In contrast, GIP did not show any cardioprotective effect against AngII-induced cardiac hypertrophy in GIPR-knockout mice. In an in vitro experiment using mouse cardiomyocytes, GIP suppressed AngII-induced mRNA expression of B-type natriuretic peptide and TGF-ß1. CONCLUSIONS: It was demonstrated that cardiomyocytes represent a direct target of GIP action in vitro, and that GIP ameliorated AngII-induced cardiac hypertrophy via suppression of cardiomyocyte enlargement, apoptosis, and fibrosis in vivo. (Circ J 2016; 80: 1988-1997).

A Dipeptidyl Peptidase-4 Inhibitor but not Incretins Suppresses Abdominal Aortic Aneurysms in Angiotensin II-Infused Apolipoprotein E-Null Mice.

AIM: The main pathophysiology of abdominal aortic aneurysm (AAA) considerably overlaps with that of atherosclerosis. We reported that incretins [glucagon-like peptide (GLP)-1 and glucose-dependent insulinotropic polypeptide (GIP)] or a dipeptidyl peptidase-4 inhibitor (DPP-4I) suppressed atherosclerosis in apolipoprotein E-null (Apoe－/－) mice. Here we investigated the effects of incretin-related agents on AAA in a mouse model. METHODS: Apoe－/－ mice maintained on an atherogenic diet were subcutaneously infused with saline, Ang II (2000 ng/kg/min), Ang II, and native GLP-1 (2.16 nmol/kg/day) or Ang II and native GIP (25 nmol/kg/day) for 4 weeks. DPP-4I (MK0626, 6 mg/kg/day) was provided in the diet to the Ang II-infused mice with or without incretin receptor antagonists [(Pro3) GIP and exendin (9-39)]. RESULTS: AAA occurred in 70% of the animals receiving Ang II. DPP-4I reduced this rate to 40% and significantly suppressed AAA dilatation, fibrosis, and thrombosis. In contrast, incretins failed to attenuate AAA. Incretin receptor blockers did not reverse the suppressive effects of DPP-4I on AAA. In the aorta, DPP-4I significantly reduced the expression of Interleukin-1ß and increased that of tissue inhibitor of metalloproteinase (TIMP)-2. In addition, DPP-4I increased the ratio of TIMP-2 to matrix metalloproteinases-9. CONCLUSIONS: DPP-4I, MK0626, but not native incretins has protective effects against AAA in Ang II-infused Apoe－/－ mice via suppression of inflammation, proteolysis, and fibrosis in the aortic wall.

Amelioration of Hyperglycemia with a Sodium-Glucose Cotransporter 2 Inhibitor Prevents Macrophage-Driven Atherosclerosis through Macrophage Foam Cell Formation Suppression in Type 1 and Type 2 Diabetic Mice.

Direct associations between hyperglycemia and atherosclerosis remain unclear. We investigated the association between the amelioration of glycemia by sodium-glucose cotransporter 2 inhibitors (SGLT2is) and macrophage-driven atherosclerosis in diabetic mice. We administered dapagliflozin or ipragliflozin (1.0 mg/kg/day) for 4-weeks to apolipoprotein E-null (Apoe-/-) mice, streptozotocin-induced diabetic Apoe-/- mice, and diabetic db/db mice. We then determined aortic atherosclerosis, oxidized low-density lipoprotein (LDL)-induced foam cell formation, and related gene expression in exudate peritoneal macrophages. Dapagliflozin substantially decreased glycated hemoglobin (HbA1c) and glucose tolerance without affecting body weight, blood pressure, plasma insulin, and lipids in diabetic Apoe-/- mice. Aortic atherosclerotic lesions, atheromatous plaque size, and macrophage infiltration in the aortic root increased in diabetic Apoe-/- mice; dapagliflozin attenuated these changes by 33%, 27%, and 20%, respectively. Atherosclerotic lesions or foam cell formation highly correlated with HbA1c. Dapagliflozin did not affect atherosclerosis or plasma parameters in non-diabetic Apoe-/- mice. In db/db mice, foam cell formation increased by 4-fold compared with C57/BL6 mice, whereas ipragliflozin decreased it by 31%. Foam cell formation exhibited a strong correlation with HbA1c. Gene expression of lectin-like ox-LDL receptor-1 and acyl-coenzyme A:cholesterol acyltransferase 1 was upregulated, whereas that of ATP-binding cassette transporter A1 was downregulated in the peritoneal macrophages of both types of diabetic mice. SGLT2i normalized these gene expressions. Our study is the first to demonstrate that SGLT2i exerts anti-atherogenic effects by pure glucose lowering independent of insulin action in diabetic mice through suppressing macrophage foam cell formation, suggesting that foam cell formation is highly sensitive to glycemia ex vivo.

Preventive effect of dipeptidyl peptidase-4 inhibitor on atherosclerosis is mainly attributable to incretin's actions in nondiabetic and diabetic apolipoprotein E-null mice.

AIM: Several recent reports have revealed that dipeptidyl peptidase (DPP)-4 inhibitors have suppressive effects on atherosclerosis in apolipoprotein E-null (Apoe (-/-)) mice. It remains to be seen, however, whether this effect stems from increased levels of the two active incretins, glucagon-like peptide-1 (GLP-1) and glucose-dependent insulinotropic polypeptide (GIP). METHODS: Nontreated Apoe (-/-) mice, streptozotocin-induced diabetic Apoe (-/-) mice, and db/db diabetic mice were administered the DPP-4 inhibitor vildagliptin in drinking water and co-infused with either saline, the GLP-1 receptor blocker, exendin(9-39), the GIP receptor blocker, (Pro(3))GIP, or both via osmotic minipumps for 4 weeks. Aortic atherosclerosis and oxidized low-density lipoprotein-induced foam cell formation in exudate peritoneal macrophages were determined. RESULTS: Vildagliptin increased plasma GLP-1 and GIP levels without affecting food intake, body weight, blood pressure, or plasma lipid profile in any of the animals tested, though it reduced HbA1c in the diabetic mice. Diabetic Apoe (-/-) mice exhibited further-progressed atherosclerotic lesions and foam cell formation compared with nondiabetic counterparts. Nondiabetic and diabetic Apoe (-/-) mice showed a comparable response to vildagliptin, namely, remarkable suppression of atherosclerotic lesions with macrophage accumulation and foam cell formation in peritoneal macrophages. Exendin(9-39) or (Pro(3))GIP partially attenuated the vildagliptin-induced suppression of atherosclerosis. The two blockers in combination abolished the anti-atherosclerotic effect of vildagliptin in nondiabetic mice but only partly attenuated it in diabetic mice. Vildagliptin suppressed macrophage foam cell formation in nondiabetic and diabetic mice, and this suppressive effect was abolished by infusions with exendin(9-39)+(Pro(3))GIP. Incubation of DPP-4 or vildagliptin in vitro had no effect on macrophage foam cell formation. CONCLUSIONS: Vildagliptin confers a substantial anti-atherosclerotic effect in both nondiabetic and diabetic mice, mainly via the action of the two incretins. However, the partial attenuation of atherosclerotic lesions by the dual incretin receptor antagonists in diabetic mice implies that vildagliptin confers a partial anti-atherogenic effect beyond that from the incretins.