[show abstract][hide abstract] ABSTRACT: We recently demonstrated that reducing IGF-1 receptor (IGF-1R) numbers in the endothelium enhances nitric oxide (NO) bioavailability and endothelial cell insulin sensitivity. In the present report, we aimed to examine the effect of increasing IGF-1R on endothelial cell function and repair. To examine the effect of increasing IGF-1R in the endothelium, we generated mice overexpressing human IGF-1R in the endothelium (human IGF-1R endothelium-overexpressing mice [hIGFREO]) under direction of the Tie2 promoter enhancer. hIGFREO aorta had reduced basal NO bioavailability (percent constriction to N(G)-monomethyl-l-arginine [mean (SEM) wild type 106% (30%); hIGFREO 48% (10%)]; P < 0.05). Endothelial cells from hIGFREO had reduced insulin-stimulated endothelial NO synthase activation (mean [SEM] wild type 170% [25%], hIGFREO 58% [3%]; P = 0.04) and insulin-stimulated NO release (mean [SEM] wild type 4,500 AU [1,000], hIGFREO 1,500 AU ; P < 0.05). hIGFREO mice had enhanced endothelium regeneration after denuding arterial injury (mean [SEM] percent recovered area, wild type 57% [2%], hIGFREO 47% [5%]; P < 0.05) and enhanced endothelial cell migration in vitro. The IGF-1R, although reducing NO bioavailability, enhances in situ endothelium regeneration. Manipulating IGF-1R in the endothelium may be a useful strategy to treat disorders of vascular growth and repair.
[show abstract][hide abstract] ABSTRACT: Low concentrations of insulin-like growth factor (IGF) binding protein-1 (IGFBP1) are associated with insulin resistance, diabetes, and cardiovascular disease. We investigated whether increasing IGFBP1 levels can prevent the development of these disorders. Metabolic and vascular phenotype were examined in response to human IGFBP1 overexpression in mice with diet-induced obesity, mice heterozygous for deletion of insulin receptors (IR(+/-)), and ApoE(-/-) mice. Direct effects of human (h)IGFBP1 on nitric oxide (NO) generation and cellular signaling were studied in isolated vessels and in human endothelial cells. IGFBP1 circulating levels were markedly suppressed in dietary-induced obese mice. Overexpression of hIGFBP1 in obese mice reduced blood pressure, improved insulin sensitivity, and increased insulin-stimulated NO generation. In nonobese IR(+/-) mice, overexpression of hIGFBP1 reduced blood pressure and improved insulin-stimulated NO generation. hIGFBP1 induced vasodilatation independently of IGF and increased endothelial NO synthase (eNOS) activity in arterial segments ex vivo, while in endothelial cells, hIGFBP1 increased eNOS Ser(1177) phosphorylation via phosphatidylinositol 3-kinase signaling. Finally, in ApoE(-/-) mice, overexpression of hIGFBP1 reduced atherosclerosis. These favorable effects of hIGFBP1 on insulin sensitivity, blood pressure, NO production, and atherosclerosis suggest that increasing IGFBP1 concentration may be a novel approach to prevent cardiovascular disease in the setting of insulin resistance and diabetes.
[show abstract][hide abstract] ABSTRACT: In mice, haploinsufficiency of the IGF-1 receptor (IGF-1R(+/-)), at a whole-body level, increases resistance to inflammation and oxidative stress, but the underlying mechanisms are unclear. We hypothesized that by forming insulin-resistant heterodimers composed of one IGF-1Rαβ and one insulin receptor (IR), IRαβ complex in endothelial cells (ECs), IGF-1R reduces free IR, which reduces EC insulin sensitivity and generation of the antioxidant/anti-inflammatory signaling radical nitric oxide (NO).
Using a number of complementary gene-modified mice with reduced IGF-1R at a whole-body level and specifically in EC, and complementary studies in EC in vitro, we examined the effect of changing IGF-1R/IR stoichiometry on EC insulin sensitivity and NO bioavailability.
IGF-1R(+/-) mice had enhanced insulin-mediated glucose lowering. Aortas from these mice were hypocontractile to phenylephrine (PE) and had increased basal NO generation and augmented insulin-mediated NO release from EC. To dissect EC from whole-body effects we generated mice with EC-specific knockdown of IGF-1R. Aortas from these mice were also hypocontractile to PE and had increased basal NO generation. Whole-body and EC deletion of IGF-1R reduced hybrid receptor formation. By reducing IGF-1R in IR-haploinsufficient mice we reduced hybrid formation, restored insulin-mediated vasorelaxation in aorta, and insulin stimulated NO release in EC. Complementary studies in human umbilical vein EC in which IGF-1R was reduced using siRNA confirmed that reducing IGF-1R has favorable effects on NO bioavailability and EC insulin sensitivity.
These data demonstrate that IGF-1R is a critical negative regulator of insulin sensitivity and NO bioavailability in the endothelium.
[show abstract][hide abstract] ABSTRACT: Circulating angiogenic progenitor cells (APCs) participate in endothelial repair after arterial injury. Type 2 diabetes is associated with fewer circulating APCs, APC dysfunction, and impaired endothelial repair. We set out to determine whether insulin resistance adversely affects APCs and endothelial regeneration.
We quantified APCs and assessed APC mobilization and function in mice hemizygous for knockout of the insulin receptor (IRKO) and wild-type (WT) littermate controls. Endothelial regeneration after femoral artery wire injury was also quantified after APC transfusion.
IRKO mice, although glucose tolerant, had fewer circulating Sca-1(+)/Flk-1(+) APCs than WT mice. Culture of mononuclear cells demonstrated that IRKO mice had fewer APCs in peripheral blood, but not in bone marrow or spleen, suggestive of a mobilization defect. Defective vascular endothelial growth factor-stimulated APC mobilization was confirmed in IRKO mice, consistent with reduced endothelial nitric oxide synthase (eNOS) expression in bone marrow and impaired vascular eNOS activity. Paracrine angiogenic activity of APCs from IRKO mice was impaired compared with those from WT animals. Endothelial regeneration of the femoral artery after denuding wire injury was delayed in IRKO mice compared with WT. Transfusion of mononuclear cells from WT mice normalized the impaired endothelial regeneration in IRKO mice. Transfusion of c-kit(+) bone marrow cells from WT mice also restored endothelial regeneration in IRKO mice. However, transfusion of c-kit(+) cells from IRKO mice was less effective at improving endothelial repair.
Insulin resistance impairs APC function and delays endothelial regeneration after arterial injury. These findings support the hypothesis that insulin resistance per se is sufficient to jeopardize endogenous vascular repair. Defective endothelial repair may be normalized by transfusion of APCs from insulin-sensitive animals but not from insulin-resistant animals.
[show abstract][hide abstract] ABSTRACT: Background
In a similar manner to insulin, the growth promoting hormone Insulin-like Growth Factor-1 (IGF-1), may be an important regulator of endothelial nitric oxide (NO) bioavailability. We have previously reported evidence of increased basal NO production in the vasculature in two murine models of reduced IGF-1 receptor (global hemizygous knockout (IGFRKO) and endothelial cell specific IGF-1R knockout (ECIGFRKO)). Augmentation of this increase in NO is relative to progressive decrease in IGF-1R number (WT vs ECIGFRKO hemizygotes p=0.01, WT vs ECIGFRKO homozygotes p=0.001). Furthermore, by decreasing IGF-1R numbers in the insulin resistant hemizygous insulin receptor knockout (IRKO) model (IRKO × IGFRKO) we have shown insulin sensitivity in the vasculature can be restored. In this study, we have investigated further these receptor interactions with the generation of a mouse overexpressing the human IGF-1R specifically in the endothelium under control of the Tie-2 promoter-enhancer (hIGFREO), and by targeted knockdown of the IGF-1R in human umbilical vein endothelial cells (HUVECs).Methods
Metabolic function was assessed in mice by tolerance tests using whole-blood micro-sampling after insulin or glucose intraperitoneal injection. Cardiovascular function was assessed by thoracic aortic vasomotion ex vivo in the organbath. Complimentary in vitro studies were conducted by siRNA mediated downregulation of the IGF-1 receptor in HUVECs with and wihout insulin stimulation. Nitric oxide synthase activity was measured using an assay measuring conversion of [14C]-L-arginine to [14 C]-L-citrulline.ResultsGlucose and insulin tolerance testing showed no difference between hIGFREO mice and wild-type (WT) littermates. Murine thoracic aorta from hIGFREO mice were hypercontractile to phenylepherine (PE) compared to WT (Emax hIGFREO=0.91±0.045 g; WT=0.62±0.045 g, p=0.0036) with decreased response to LNMMA (Emax hIGFREO=47.70±9.87 g; WT=106.1±30.10 g, p=0.048). These data indicate reduced endothelial NO bioavailability in hIGFREO mice compared to WT. HUVECs transfected with IGF1R-siRNA showed increased basal and insulin mediated eNOS phosphorylation in the presence of insulin (Ins: 164±4.9% vs siRNA+Ins: 192±0.7%, p
[show abstract][hide abstract] ABSTRACT: IntroductionInsulin-resistance, the primary metabolic abnormality underpinning type-2-diabetes mellitus (T2DM) and obesity, is an important risk factor for the development of atherosclerotic cardiovascular disease. Circulating-angiogenic-progenitor-cells (APCs) participate in endothelial-repair following arterial injury. Type-2 diabetes is associated with fewer circulating APCs, APC dysfunction and impaired endothelial-repair. We set out to determine whether insulin-resistance per se adversely affects APCs and endothelial-regeneration.Research Design and Methods
We quantified APCs and assessed APC-mobilisation and function in mice hemizygous for knockout of the insulin receptor (IRKO) and wild-type (WT) littermate controls. Endothelial-regeneration following femoral artery wire-injury was also quantified at time intervals after denudation and following APC transfusion.ResultsThe metabolic phenotype of IRKO mice was consistent with compensated insulin resistance, with hyperinsulinaemia after a glucose challenge but a normal blood glucose response to a glucose tolerance test. IRKO mice had fewer circulating Sca-1+/Flk-1+ APCs than WT mice at baseline. Culture of mononuclear-cells demonstrated that IRKO mice had fewer APCs in peripheral-blood, but not in bone-marrow or spleen, suggestive of a mobilisation defect. Defective VEGF-stimulated APC mobilisation was confirmed in IRKO mice, consistent with reduced eNOS expression in bone marrow and impaired vascular eNOS activity. Paracrine-angiogenic-activity of APCs from IRKO mice was impaired compared to those from WT animals. Endothelial-regeneration of the femoral artery following denuding wire-injury was delayed in IRKO mice compared to WT (re-endothelialised area 35.8±4.8% vs 66.6±5.2% at day 5 following injury and 35.6±4.8% vs 59.8±6.6% at day 7; P
[show abstract][hide abstract] ABSTRACT: Circulating progenitor cells (CPC) have emerged as potential mediators of vascular repair. In experimental models, CPC mobilization is critically dependent on nitric oxide (NO). South Asian ethnicity is associated with reduced CPC. We assessed CPC mobilization in response to exercise in Asian men and examined the role of NO in CPC mobilization per se.
In 15 healthy, white European men and 15 matched South Asian men, CPC mobilization was assessed during moderate-intensity exercise. Brachial artery flow-mediated vasodilatation was used to assess NO bioavailability. To determine the role of NO in CPC mobilization, identical exercise studies were performed during intravenous separate infusions of saline, the NO synthase inhibitor L-NMMA, and norepinephrine. Flow-mediated vasodilatation (5.8%+/-0.4% vs 7.9%+/-0.5%; P=0.002) and CPC mobilization (CD34(+)/KDR(+) 53.2% vs 85.4%; P=0.001; CD133(+)/CD34(+)/KDR(+) 48.4% vs 73.9%; P=0.05; and CD34(+)/CD45(-) 49.3% vs 78.4; P=0.006) was blunted in the South Asian group. CPC mobilization correlated with flow-mediated vasodilatation and l-NMMA significantly reduced exercise-induced CPC mobilization (CD34(+)/KDR(+) -3.3% vs 68.4%; CD133(+)/CD34(+)/KDR(+) 0.7% vs 71.4%; and CD34(+)/CD45(-) -30.5% vs 77.8%; all P<0.001).
In humans, NO is critical for CPC mobilization in response to exercise. Reduced NO bioavailability may contribute to imbalance between vascular damage and repair mechanisms in South Asian men.
[show abstract][hide abstract] ABSTRACT: The number of people with the insulin-resistant conditions of type 2 diabetes mellitus (T2DM) and obesity has reached epidemic proportions worldwide. Eighty percent of people with T2DM will die from the complications of cardiovascular atherosclerosis. Insulin resistance is characterised by endothelial dysfunction, which is a pivotal step in the initiation/progression of atherosclerosis. A hallmark of endothelial dysfunction is an unfavourable imbalance between the bioavailability of the antiatherosclerotic signalling molecule nitric oxide (NO) and proatherosclerotic reactive oxygen species. In this review we discuss the mechanisms linking insulin resistance to endothelial dysfunction, with a particular emphasis on a potential role for a toxic effect of free fatty acids on endothelial cell homeostasis.
Biochimica et Biophysica Acta (BBA) - Molecular and Cell Biology of Lipids. 01/2010;
[show abstract][hide abstract] ABSTRACT: Obesity and type 2 diabetes mellitus are characterized by insulin resistance, reduced bioavailability of the antiatherosclerotic signaling molecule nitric oxide (NO), and accelerated atherosclerosis. IGF-I, the principal growth-stimulating peptide, which shares many of the effects of insulin, may, like insulin, also be involved in metabolic and vascular homeostasis. We examined the effects of IGF-I on NO bioavailability and the effect of obesity/type 2 diabetes mellitus on IGF-I actions at a whole-body level and in the vasculature. In aortic rings IGF-I blunted phenylephrine-mediated vasoconstriction and relaxed rings preconstricted with phenylephrine, an effect blocked by N(G)-monomethyl L-arginine. IGF-I increased NO synthase activity to an extent similar to that seen with insulin and in-vivo IGF-I led to serine phosphorylation of endothelial NO synthase (eNOS). Mice rendered obese using a high-fat diet were less sensitive to the glucose-lowering effects of insulin and IGF-I. IGF-I increased aortic phospho-eNOS levels in lean mice, an effect that was blunted in obese mice. eNOS activity in aortae of lean mice increased 1.6-fold in response to IGF-I compared with obese mice. IGF-I-mediated vasorelaxation was blunted in obese mice. These data demonstrate that IGF-I increases eNOS phosphorylation in-vivo, increases eNOS activity, and leads to NO-dependent relaxation of conduit vessels. Obesity is associated with resistance to IGF-I at a whole-body level and in the endothelium. Vascular IGF-I resistance may represent a novel therapeutic target to prevent or slow the accelerated vasculopathy seen in humans with obesity or type 2 diabetes mellitus.
[show abstract][hide abstract] ABSTRACT: IGF-1 is a peptide hormone that is expressed in most tissues. It shares significant structural and functional similarities with insulin, and is implicated in the pathogenesis of insulin resistance and cardiovascular disease. Recombinant human IGF-1 has been used in Type 2 diabetes to improve insulin sensitivity and aid glycemic control. There is evidence supporting IGF-1 as a vascular protective factor and it may also be beneficial in the treatment of chronic heart failure. Further understanding of the effects of IGF-1 signaling in health and disease may lead to novel approaches to the prevention and treatment of diabetes and cardiovascular disease.
Expert Review of Cardiovascular Therapy 10/2008; 6(8):1135-49.
[show abstract][hide abstract] ABSTRACT: We sought to compare mortality reduction associated with secondary prevention in patients with and without diabetes after acute coronary syndrome (ACS).
We conducted a cohort study involving 2,499 patients with ACS recruited from 11 U.K. hospitals. Multivariable analysis comparing all-cause mortality risk reduction associated with pharmacologic agents in patients with and without diabetes.
Aspirin was not associated with significant mortality benefit in diabetes sufferers (95% CI 0.50-1.08); nondiabetic patients derived a 48% mortality reduction (P < 0.001). The interaction between diabetes and aspirin use was statistically significant (P = 0.037), indicating that patients with diabetes experience less effective mortality reduction from aspirin use.
Aspirin, but not other secondary prevention agents, is associated with less effective mortality reduction in patients with diabetes and unstable coronary artery disease.
Diabetes care 02/2008; 31(2):363-5. · 7.74 Impact Factor
[show abstract][hide abstract] ABSTRACT: Diabetes Mellitus (DM) is associated with adverse cardiovascular prognosis. However, the risk associated with DM may vary between individuals according to their overall cardiovascular risk burden. Therefore, we aimed to determine whether DM is associated with poor outcome in patients presenting with Acute Coronary Syndrome (ACS) according to the index episode being a first or recurrent cardiovascular event.
We conducted a retrospective analysis of a prospective cohort study involving 2499 consecutively admitted patients with confirmed ACS in 11 UK hospitals during 2003. Usual care was provided for all participants. Demographic factors, co-morbidity and treatment (during admission and at discharge) factors were recorded. The primary outcome was all cause mortality (median 2 year follow up), compared for cohorts with and without DM according to their prior cardiovascular disease (CVD) disease status. Adjusted analyses were performed with Cox proportional hazards regression analysis. Within the entire cohort, DM was associated with an unadjusted 45% increase in mortality. However, in patients free of a history of CVD, mortality of those with and without DM was similar (18.8% and 19.7% respectively; p = 0.74). In the group with CVD, mortality of patients with DM was significantly higher than those without DM (46.7% and 33.2% respectively; p<0.001). The age and sex adjusted interaction between DM and CVD in predicting mortality was highly significant (p = 0.002) and persisted after accounting for comorbidities and treatment factors (p = 0.006). Of patients free of CVD, DM was associated with smaller elevation of Troponin I (p<0.001). However in patients with pre-existing CVD Troponin I was similar (p = 0.992).
DM is only associated with worse outcome after ACS in patients with a pre-existing history of CVD. Differences in the severity of myocyte necrosis may account for this. Further investigation is required, though our findings suggest that aggressive primary prevention of CVD in patients with DM may have beneficially modified their first presentation with (and mortality after) ACS.
PLoS ONE 01/2008; 3(10):e3483. · 3.73 Impact Factor
[show abstract][hide abstract] ABSTRACT: Both diabetes mellitus (DM) and hyperglycaemia are known to predict outcome after acute coronary syndrome (ACS). Recent work has suggested women with DM have greater baseline cardiovascular risk and poorer outcome after ACS. The interaction between sex and abnormal glucose homoeostasis in patients without diabetes is unexplored; we aimed to assess this relationship.
Retrospective analysis of data from a prospective cohort study of 1575 patients with a confirmed ACS and no previous diagnosis of DM in 11 UK hospitals. Multivariable analysis was performed to assess the value of clinical variables, including hyperglycaemia and sex, in predicting 2 year all-cause mortality. Sex and hyperglycaemia interacted in predicting mortality. In men, mortality risk increased more steeply with incremental levels of glycaemia than in women (glucose > or =11.1 mmol/l, hazard ratio, 2.19; 95% confidence interval, 1.2-4.0). In both sex groups increasing glycaemia predicted mortality at levels currently not recommended for acute therapeutic intervention (7.8-11.0 mmol/l).
In patients not known to have diabetes, hyperglycaemia is a concentration-dependent predictor of long-term mortality after ACS; this predictive value is stronger in men than women.
European Journal of Cardiovascular Prevention and Rehabilitation 10/2007; 14(5):666-71. · 2.63 Impact Factor