Uncomplicating the Macrovascular Complications of Diabetes: The 2014 Edwin Bierman Award Lecture

Novel Nongenetic Murine Model of Hyperglycemia and Hyperlipidemia-Associated Aggravated Atherosclerosis

Objective

Atherosclerosis, the main pathology underlying cardiovascular diseases is accelerated in diabetic patients. Genetic mouse models require breeding efforts which are time-consuming and costly. Our aim was to establish a new nongenetic model of inducible metabolic risk factors that mimics hyperlipidemia, hyperglycemia, or both and allows the detection of phenotypic differences dependent on the metabolic stressor(s).

Methods and Results

Wild-type mice were injected with gain-of-function PCSK9D377Y (proprotein convertase subtilisin/kexin type 9) mutant adeno-associated viral particles (AAV) and streptozotocin and fed either a high-fat diet (HFD) for 12 or 20 weeks or a high-cholesterol/high-fat diet (Paigen diet, PD) for 8 weeks. To evaluate atherosclerosis, two different vascular sites (aortic sinus and the truncus of the brachiocephalic artery) were examined in the mice. Combined hyperlipidemic and hyperglycemic (HGHCi) mice fed a HFD or PD displayed characteristic features of aggravated atherosclerosis when compared to hyperlipidemia (HCi HFD or PD) mice alone. Atherosclerotic plaques of HGHCi HFD animals were larger, showed a less stable phenotype (measured by the increased necrotic core area, reduced fibrous cap thickness, and less α-SMA-positive area) and had more inflammation (increased plasma IL-1β level, aortic pro-inflammatory gene expression, and MOMA-2-positive cells in the BCA) after 20 weeks of HFD. Differences between the HGHCi and HCi HFD models were confirmed using RNA-seq analysis of aortic tissue, revealing that significantly more genes were dysregulated in mice with combined hyperlipidemia and hyperglycemia than in the hyperlipidemia-only group. The HGHCi-associated genes were related to pathways regulating inflammation (increased Cd68, iNos, and Tnfa expression) and extracellular matrix degradation (Adamts4 and Mmp14). When comparing HFD with PD, the PD aggravated atherosclerosis to a greater extent in mice and showed plaque formation after 8 weeks. Hyperlipidemic and hyperglycemic mice fed a PD (HGHCi PD) showed less collagen (Sirius red) and increased inflammation (CD68-positive cells) within aortic plaques than hyperlipidemic mice (HCi PD). HGHCi-PD mice represent a directly inducible hyperglycemic atherosclerosis model compared with HFD-fed mice, in which atherosclerosis is severe by 8 weeks.

Conclusion

We established a nongenetically inducible mouse model allowing comparative analyses of atherosclerosis in HCi and HGHCi conditions and its modification by diet, allowing analyses of multiple metabolic hits in mice.

Beneficial effects of cinnamon and its extracts in the management of cardiovascular diseases and diabetes

Cardiovascular diseases (CVDs) and diabetes are the leading causes of death worldwide, which underlines the urgent necessity to develop new pharmacotherapies. Cinnamon has been an eminent component of spice and traditional Chinese medicine for thousands of years. Numerous lines of findings have elucidated that cinnamon has beneficial effects against CVDs in various ways, including endothelium protection, regulation of immune response, lowering blood lipids, antioxidative properties, anti-inflammatory properties, suppression of vascular smooth muscle cell (VSMC) growth and mobilization, repression of platelet activity and thrombosis and inhibition of angiogenesis. Furthermore, emerging evidence has established that cinnamon improves diabetes, a crucial risk factor for CVDs, by enhancing insulin sensitivity and insulin secretion; regulating the enzyme activity involved in glucose; regulating glucose metabolism in the liver, adipose tissue and muscle; ameliorating oxidative stress and inflammation to protect islet cells; and improving diabetes complications. In this review, we summarized the mechanisms by which cinnamon regulates CVDs and diabetes in order to provide a theoretical basis for the further clinical application of cinnamon.

Gualou-Xiebai-Banxia decoction protects against type II diabetes with acute myocardial ischemia by attenuating oxidative stress and apoptosis via PI3K/Akt/eNOS signaling

Gualou-Xiebai-Banxia decoction has a long history of medical use for treating cardiovascular diseases in China. In this study, we investigated the protective effect and underlying mechanisms GXB in type II diabetes with acute myocardial ischemia (T2DM-AMI) rats. We hypothesized that GXB may display its protective effect on T2DM-AMI by reducing endothelial progenitor cells (EPCs) apoptosisviaactivating PI3K (phosphatidyl inositol 3-kinase)/Akt (serine/threonine protein kinase B)/eNOS (endothelial nitric oxide synthase) signaling. Rats were challenged with a high-fat diet and intraperitoneal injection of streptozotocin to induce a model of type II diabetes mellitus (T2DM) and coronary ligation to induce acute myocardial infarction (AMI). Changes in metabolites were assessed via enzyme-linked immunoassay and biochemical examination. The number and apoptosis rate of EPCs in peripheral blood were detected by flow cytometry. Target mRNAs and proteins in EPCs were analyzed by RT-PCR and Western blot analysis. The results demonstrated that GXB treatment decreased T2DM-AMI-associated changes in plasma fasting blood glucose, muscular enzymes, and blood lipids, and reduced oxidative stress. Furthermore, EPC apoptosis was increased in T2DM-AMI rats and was associated with decreased mRNA and protein levels of PI3K, Akt, and eNOS compared to the controls. Conversely, T2DM-AMI rats treated with GXB exhibited more circulating EPCs and downregulated levels of cell apoptosis, combined with increased mRNA and protein levels of PI3K, Akt, and eNOS compared to those of untreated T2DM-AMI rats. Our study showed that GXB treatment mitigated EPC apoptosis and promoted PI3K/Akt/eNOS signaling in T2DM-AMI rats.

Therapies for the Treatment of Cardiovascular Disease Associated with Type 2 Diabetes and Dyslipidemia

Cardiovascular disease (CVD) is the leading cause of death worldwide and is the clinical manifestation of the atherosclerosis. Elevated LDL-cholesterol levels are the first line of therapy but the increasing prevalence in type 2 diabetes mellitus (T2DM) has positioned the cardiometabolic risk as the most relevant parameter for treatment. Therefore, the control of this risk, characterized by dyslipidemia, hypertension, obesity, and insulin resistance, has become a major goal in many experimental and clinical studies in the context of CVD. In the present review, we summarized experimental studies and clinical trials of recent anti-diabetic and lipid-lowering therapies targeted to reduce CVD. Specifically, incretin-based therapies, sodium-glucose co-transporter 2 inhibitors, and proprotein convertase subtilisin kexin 9 inactivating therapies are described. Moreover, the novel molecular mechanisms explaining the CVD protection of the drugs reviewed here indicate major effects on vascular cells, inflammatory cells, and cardiomyocytes, beyond their expected anti-diabetic and lipid-lowering control. The revealed key mechanism is a prevention of acute cardiovascular events by restraining atherosclerosis at early stages, with decreased leukocyte adhesion, recruitment, and foam cell formation, and increased plaque stability and diminished necrotic core in advanced plaques. These emergent cardiometabolic therapies have a promising future to reduce CVD burden.

Lixisenatide enhances mitochondrial biogenesis and function through regulating the CREB/PGC-1α pathway

Mitochondrial dysregulation has been associated with vascular endothelial dysfunction and pathophysiological development of cardiovascular diseases. Lixisenatide is a drug approved by the US Food and Drug Administration for the treatment of type 2 diabetes (T2D). Little information regarding the effects of lixisenatide on mitochondrial function in endothelial cells has been reported before. In the current study, we found that treatment with lixisenatide significantly increased the expression of PGC-1α, a "molecular switch" of mitochondrial biogenesis in human umbilical vein endothelial cells (HUVECs). Lixisenatide treatment also promoted the expressions of NRF1 and TFAM, which are the target genes of PGC-1α and executors of mitochondrial biogenesis. Importantly, our results indicate that lixisenatide treatment promoted mitochondrial biogenesis by elevating the ratio of mitochondrial-to-nuclear DNA (mtDNA/nDNA), mitochondrial mass, cytochrome B expression, and citrate synthase activity in HUVECs. Correspondingly, we found that lixisenatide treatment led to a functional gain and improvement in mitochondria by increasing the mitochondrial respiration rate and ATP generation. Mechanistically, lixisenatide treatment induced the phosphorylation of CREB at Ser133. Blockage of CREB phosphorylation using its inhibitor H89 abolished the effects of lixisenatide on the activation of PGC-1α/NRF-1/TFAM as well as the increase in mtDNA/nDNA. These findings suggest that lixisenatide promoted mitochondrial biogenesis in endothelial cells through activating the PGC-1α signaling pathway, which is mediated by the transcriptional factor CREB.

Activated protein C reverses epigenetically sustained p66Shc expression in plaque-associated macrophages in diabetes

Impaired activated protein C (aPC) generation is associated with atherosclerosis and diabetes mellitus. Diabetes-associated atherosclerosis is characterized by the hyperglycaemic memory, e.g., failure of disease improvement despite attenuation of hyperglycaemia. Therapies reversing the hyperglycaemic memory are lacking. Here we demonstrate that hyperglycaemia, but not hyperlipidaemia, induces the redox-regulator p66Shc and reactive oxygen species (ROS) in macrophages. p66Shc expression, ROS generation, and a pro-atherogenic phenotype are sustained despite restoring normoglycemic conditions. Inhibition of p66Shc abolishes this sustained pro-atherogenic phenotype, identifying p66Shc-dependent ROS in macrophages as a key mechanism conveying the hyperglycaemic memory. The p66Shc-associated hyperglycaemic memory can be reversed by aPC via protease-activated receptor-1 signalling. aPC reverses glucose-induced CpG hypomethylation within the p66Shc promoter by induction of the DNA methyltransferase-1 (DNMT1). Thus, epigenetically sustained p66Shc expression in plaque macrophages drives the hyperglycaemic memory, which-however-can be reversed by aPC. This establishes that reversal of the hyperglycaemic memory in diabetic atherosclerosis is feasible.

Unmet Need for Adjunctive Dyslipidemia Therapy in Hypertriglyceridemia Management

Despite the important role of high-intensity statins in reducing atherosclerotic cardiovascular disease events in secondary and primary prevention, substantial residual risk persists, particularly among high-risk patients with type 2 diabetes mellitus, metabolic syndrome, and obesity. Considerable attention is currently directed to the role that elevated triglycerides (TGs) and non-high-density lipoprotein cholesterol levels play as important mediators of residual atherosclerotic cardiovascular disease risk, which is further strongly supported by genetic linkage studies. Previous trials with fibrates, niacin, and most cholesterol ester transfer protein inhibitors that targeted high-density lipoprotein cholesterol raising, and/or TG lowering, have failed to show conclusive evidence of incremental event reduction after low-density lipoprotein cholesterol levels were "optimally controlled" with statins. Although omega-3 fatty acids are efficacious in lowering TG levels and may have pleiotropic effects such as reducing plaque instability and proinflammatory mediators of atherogenesis, clinical outcomes data are currently lacking. Several ongoing randomized controlled trials of TG-lowering strategies with an optimal dosage of omega-3 fatty acids are nearing completion.

Intensive Diabetes Treatment and Cardiovascular Outcomes in Type 1 Diabetes Mellitus: Implications of the Diabetes Control and Complications Trial/Epidemiology of Diabetes Interventions and Complications Study 30-Year Follow-up

Type 1 diabetes mellitus, an autoimmune disorder characterized by beta-cell destruction and absolute insulin deficiency, is associated with significantly increased cardiovascular disease risk but the mechanisms underlying this enhanced risk are unclear. Results of the pivotal Diabetes Control and Complications Trial/Epidemiology of Diabetes Interventions and Complications study have shown that compared to conventional therapy, intensive glycemic control results in decreased cardiovascular morbidity and mortality. Evidence from this study also revealed contributions of blood pressure, renal disease, body weight, and lipids to cardiovascular disease in type 1 diabetes mellitus. Extrapolating from existing evidence, this article addresses clinical strategies to mitigate cardiovascular risks.

The GLP-1 analogue lixisenatide decreases atherosclerosis in insulin-resistant mice by modulating macrophage phenotype

AIMS/HYPOTHESIS

Recent clinical studies indicate that glucagon-like peptide-1 (GLP-1) analogues prevent acute cardiovascular events in type 2 diabetes mellitus but their mechanisms remain unknown. In the present study, the impact of GLP-1 analogues and their potential underlying molecular mechanisms in insulin resistance and atherosclerosis are investigated.

METHODS

Atherosclerosis development was evaluated in Apoe ^-/- Irs2 ^+/- mice, a mouse model of insulin resistance, the metabolic syndrome and atherosclerosis, treated with the GLP-1 analogues lixisenatide or liraglutide. In addition, studies in Apoe ^-/- Irs2 ^+/- mice and mouse-derived macrophages treated with lixisenatide were performed to investigate the potential inflammatory intracellular pathways.

RESULTS

Treatment of Apoe ^-/- Irs2 ^+/- mice with either lixisenatide or liraglutide improved glucose metabolism and blood pressure but this was independent of body weight loss. Both drugs significantly decreased atheroma plaque size. Compared with vehicle-treated control mice, lixisenatide treatment generated more stable atheromas, with fewer inflammatory infiltrates, reduced necrotic cores and thicker fibrous caps. Lixisenatide-treated mice also displayed diminished IL-6 levels, proinflammatory Ly6C^high monocytes and activated T cells. In vitro analysis showed that, in macrophages from Apoe ^-/- Irs2 ^+/- mice, lixisenatide reduced the secretion of the proinflammatory cytokine IL-6 accompanied by enhanced activation of signal transducer and activator of transcription (STAT) 3, which is a determinant for M2 macrophage differentiation. STAT1 activation, which is essential for M1 phenotype, was also diminished. Furthermore, atheromas from lixisenatide-treated mice showed higher arginase I content and decreased expression of inducible nitric oxide synthase, indicating the prevalence of the M2 phenotype within plaques.

CONCLUSIONS/INTERPRETATION

Lixisenatide decreases atheroma plaque size and instability in Apoe ^-/- Irs2 ^+/- mice by reprogramming macrophages towards an M2 phenotype, which leads to reduced inflammation. This study identifies a critical role for this drug in macrophage polarisation inside plaques and provides experimental evidence supporting a novel mechanism of action for GLP-1 analogues in the reduction of cardiovascular risk associated with insulin resistance.

Regulation of Macrophage Apoptosis and Atherosclerosis by Lipid-Induced PKCδ Isoform Activation

RATIONALE

Activation of monocytes/macrophages by hyperlipidemia associated with diabetes mellitus and obesity contributes to the development of atherosclerosis. PKCδ (protein kinase C δ) expression and activity in monocytes were increased by hyperlipidemia and diabetes mellitus with unknown consequences to atherosclerosis.

OBJECTIVE

To investigate the effect of PKCδ activation in macrophages on the severity of atherosclerosis.

METHODS AND RESULTS

PKCδ expression and activity were increased in Zucker diabetic rats. Mice with selective deletion of PKCδ in macrophages were generated by breeding PKCδ flox/flox mice with LyzM-Cre and ApoE^-/- mice (MPKCδKO/ApoE^-/- mice) and studied in atherogenic (AD) and high-fat diet (HFD). Mice fed AD and HFD exhibited hyperlipidemia, but only HFD-fed mice had insulin resistance and mild diabetes mellitus. Surprisingly, MPKCδKO/ApoE^-/- mice exhibited accelerated aortic atherosclerotic lesions by 2-fold versus ApoE^-/- mice on AD or HFD. Splenomegaly was observed in MPKCδKO/ApoE^-/- mice on AD and HFD but not on regular chow. Both the AD or HFD increased macrophage number in aortic plaques and spleen by 1.7- and 2-fold, respectively, in MPKCδKO/ApoE^-/- versus ApoE^-/- mice because of decreased apoptosis (62%) and increased proliferation (1.9-fold), and not because of uptake, with parallel increased expressions of inflammatory cytokines. Mechanisms for the increased macrophages in MPKCδKO/ApoE^-/- were associated with elevated phosphorylation levels of prosurvival cell-signaling proteins, Akt and FoxO3a, with reduction of proapoptotic protein Bim associated with PKCδ induced inhibition of P85/PI3K.

CONCLUSIONS

Accelerated development of atherosclerosis induced by insulin resistance and hyperlipidemia may be partially limited by PKCδ isoform activation in the monocytes, which decreased its number and inflammatory responses in the arterial wall.

Plasma Prekallikrein Is Associated With Carotid Intima-Media Thickness in Type 1 Diabetes

The hypothesis that plasma prekallikrein (PK) is a risk factor for the development of vascular complications was assessed in a study using the Diabetes Control and Complications Trial (DCCT)/Epidemiology and Diabetes Interventions and Complications (EDIC) cohort of subjects with type 1 diabetes. The circulating levels of plasma PK activity were measured in the plasma of 636 subjects with type 1 diabetes (EDIC years 3-5). Common and internal carotid intima-media thickness (IMT) were measured by B-mode ultrasonography in EDIC years 1 and 6. Plasma PK levels were positively and significantly associated with BMI, hemoglobin A1c, systolic blood pressure, total cholesterol, LDL cholesterol, and triglycerides but not with age, sex, duration of diabetes, or HDL cholesterol. Univariate and multivariable statistical models after controlling for other risk factors consistently demonstrated a positive association between plasma PK and progression of internal carotid IMT. Multivariate analysis using a general linear model showed plasma PK to be significantly associated with progression of both internal and combined IMT (Wilks Λ P value of 0.005). In addition, the mean internal carotid IMT levels were higher in subjects with plasma PK levels in the highest 10th percentile compared with subjects with plasma PK levels in the lower 10th percentile (P = 0.048). These novel findings implicate plasma PK as a risk factor for vascular disease in type 1 diabetes.