European Heart Journal (2013) 34, 24362446 REVIEW

doi:10.1093/eurheartj/eht149

Clinical update

Diabetes and vascular disease: pathophysiology,

clinical consequences, and medical therapy: part I
Francesco Paneni 1,2, Joshua A. Beckman 3, Mark A. Creager 3,
and Francesco Cosentino 1,4*
1
Cardiology and Cardiovascular Research, University of Zurich, Zurich, Switzerland; 2IRCCS Neuromed, Pozzilli, Italy; 3Cardiovascular Division, Brigham and Womens Hospital and
Harvard Medical School, Boston, MA 02115, USA; and 4Cardiology, Department of Clinical and Molecular Medicine, University of Rome Sapienza, Rome, Italy

Received 14 September 2012; revised 18 October 2012; accepted 12 March 2013; online publish-ahead-of-print 2 May 2013

Hyperglycemia and insulin resistance are key players in the development of atherosclerosis and its complications. A large body of evidence suggest
that metabolic abnormalities cause overproduction of reactive oxygen species (ROS). In turn, ROS, via endothelial dysfunction and inflammation,
play a major role in precipitating diabetic vascular disease. A better understanding of ROS-generating pathways may provide the basis to develop
novel therapeutic strategies against vascular complications in this setting. Part I of this review will focus on the most current advances in the patho-
physiological mechanisms of vascular disease: (i) emerging role of endothelium in obesity-induced insulin resistance; (ii) hyperglycemia-dependent
microRNAs deregulation and impairment of vascular repair capacities; (iii) alterations of coagulation, platelet reactivity, and microparticle release;
(iv) epigenetic-driven transcription of ROS-generating and proinflammatory genes. Taken together these novel insights point to the development
of mechanism-based therapeutic strategies as a promising option to prevent cardiovascular complications in diabetes.
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Keywords Diabetes Vascular disease Pathophysiology

Introduction
Hyperglycemia, oxidative stress,
The number of people with diabetes mellitus is alarmingly increasing
due to the growing prevalence of obesity, genetic susceptibility, ur-
and vascular disease
banization, and ageing.1,2 The alterations in vascular homeostasis due to endothelial and
Type 2 diabetes, the most common form of the disease, may remain smooth muscle cell dysfunction are the main features of diabetic
undetected for many years and its diagnosis is often made incidentally vasculopathy favouring a pro-inflammatory/thrombotic state
through an abnormal blood or urine glucose test. Hence, physicians which ultimately leads to atherothrombosis. Macro- and micro-
often face this disease at an advanced stage when vascular complica- vascular diabetic complications are mainly due to prolonged expos-
tions have already occurred in most of patients. Macrovascular compli- ure to hyperglycemia clustering with other risk factors such as
cations are mainly represented by atherosclerotic disease and its arterial hypertension, dyslipidemia as well as genetic susceptibility.3
sequelae. Diabetes-related microvascular disease such as retinopathy Interestingly, nephropathy, retinopathy, and diabetic vascular
and nephropathy are major causes of blindness and renal insufficiency.1 disease are in line with the notion that endothelial, mesangial, and
Based on this scenario, a better understanding of the mechanisms retinal cells are all equipped to handle high sugar levels when com-
underlying diabetic vascular disease is mandatory because it may pared with other cell types.4 The detrimental effects of glucose
provide novel approaches to prevent or delay the development of already occur with glycemic levels below the threshold for the
its complications. This review will focus on the most current advances diagnosis of diabetes. This is explained by the concept of glycemic
in the pathophysiology of vascular disease (Part I) and will address continuum across the spectrum of prediabetes, diabetes, and cardio-
clinical manifestations and management strategies of patients with vascular risk.5 8 Early disglycemia caused by obesity-related insulin re-
diabetes (Part II). sistance or impaired insulin secretion is responsible for functional and

* Corresponding author. Tel: +39 06 33775979, Fax: +39 06 33775061, Email: f_cosentino@hotmail.com
& The Author 2013. Published by Oxford University Press on behalf of the European Society of Cardiology.
This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by-nc/3.0/), which permits non-commercial
re-use, distribution, and reproduction in any medium, provided the original work is properly cited. For commercial re-use, please contact journals.permissions@oup.com
Diabetes and vascular disease 2437

structural alterations of the vessel wall culminating with diabetic vascular downstream targets. The hyperglycemic environment induces a
complications. chronic elevation of diacyglycerol levels in endothelial cells with sub-
The initial trigger whereby high glucose concentrations alter vas- sequent membrane translocation of conventional (a, b1, b2) and
cular function is the imbalance between nitric oxide (NO) bioavail- non-conventional (d) PKC isoforms. Once activated, PKC is respon-
ability and accumulation of reactive oxygen species (ROS), leading sible for different structural and functional changes in the vasculature
to endothelial dysfunction.9 Indeed, hyperglycemia-induced gener- including alterations in cellular permeability, inflammation, angiogen-
ation of superoxide anion (O2 2 ) inactivates NO to form peroxynitrite esis, cell growth, extracellular matrix expansion, and apoptosis.14 An
(ONOO2), a powerful oxidant which easily penetrates across important consequence of PKC activation is ROS generation. In vas-
phospholipid membranes and induces substrate nitration.9 Protein cular endothelial cells, hyperglycemia-induced activation of PKC
nitrosylation blunts activity of antioxidant enzymes and endothelial increases superoxide production via NADPH oxidase15 (Figure 1).
NO synthase10 (eNOS, Figure 1). Importantly, reduced NO bioavail- Indeed, treatment with a PKCb inhibitor suppresses NADPH-
ability is a strong predictor of cardiovascular outcomes.10,11 dependent ROS generation.16
Overproduction of ROS by mitochondria is considered as a causal More recently, it has been reported that glucose-induced activa-
link between elevated glucose and the major biochemical pathways tion of PKC b2 isoform phosphorylates p66Shc at serine 36 leading
involved in the development of vascular complications of diabetes.12 to its translocation to the mitochondria, cytochrome c oxidation
Indeed, hyperglycemia-induced ROS production triggers several cel- and accumulation of ROS into the organelle.17,18 The p66Shc
lular mechanisms including polyol and hexosamine flux, advanced gly- adaptor protein functions as a redox enzyme implicated in mito-
cation end products (AGEs), protein kinase C (PKC) activation, and chondrial ROS generation and translation of oxidative signals into
NF-kB-mediated vascular inflammation.12,13 One of the main sources apoptosis.17 Interestingly, diabetic p66Shc2/2 mice are protected
of ROS in the setting of hyperglycemia is represented by PKC and its against hyperglycemia-induced endothelial dysfunction and oxidative

Figure 1 Mechanisms of hyperglycemia-induced vascular damage. High intracellular glucose concentrations lead to PKC activation and subse-
quent ROS production by NADPH oxidase and p66Shc adaptor protein. Increased oxidative stress rapidly inactivates NO leading to formation
of the pro-oxidant ONOO2 responsible for protein nitrosylation. Reduced NO availability is also due to PKC-dependent eNOS deregulation.
Indeed, PKC triggers enzyme up-regulation thus enhancing eNOS uncoupling and leading to a further accumulation of free radicals. On the
other hand, hyperglycemia reduces eNOS activity blunting activatory phosphorylation at Ser1177. Together with the lack of NO, glucose-induced
PKC activation causes increased synthesis of ET-1 favouring vasoconstriction and platelet aggregation. Accumulation of superoxide anion also trig-
gers up-regulation of pro-inflammatory genes MCP-1, VCAM-1, and ICAM-1 via activation of NF-kB signalling. These events lead to monocyte ad-
hesion, rolling, and diapedesis with formation of foam cells in the sub-endothelial layer. Foam cell-derived inflammatory cytockines maintain vascular
inflammation as well as proliferation of smooth muscle cells, accelerating the atherosclerotic process. Endothelial dysfunction in diabetes also derives
from increased synthesis of TXA2 via up-regulation of COX-2 and inactivation of PGIS by increased nitrosylation. Furthermore, ROS increase the
synthesis of glucose metabolite methylglyoxal leading to activation of AGE/RAGE signalling and the pro-oxidant hexosamine and polyol pathway flux.
PKC, protein kinase C; eNOS, endothelial nitric oxide synthase; ET1, endothelin 1; ROS, reactive oxygen species; NO, nitric oxide; MCP-1, mono-
cyte chemoattractant protein-1; VCAM-1, vascular cell adhesion molecule-1; ICAM-1, intracellular cell adhesion molecule-1; AGE, advanced glyca-
tion end product.
2438 F. Paneni et al.

stress.19 The relevance of p66Shc in the clinical setting of diabetes is Insulin resistance
supported by the notion that p66Shc gene expression is increased
in peripheral blood mononuclear cells obtained from patients with and atherothrombosis
type 2 diabetes and correlates with plasma 8-isoprostane levels, an Insulin resistance is a major feature of type 2 diabetes and develops in
in vivo marker of oxidative stress.20 Moreover, p66Shc protein has re- multiple organs, including skeletal muscle, liver, adipose tissue, and
cently emerged as an upstream modulator of NADPH activation heart.37 The onset of hyperglycemia and diabetes is often preceded
further strengthening its pivotal role in ROS generation.21,22 by many years of insulin resistance. Obesity plays a pivotal role in
PKC affects NO availability not only via intracellular accumulation this phenomenon providing an important link between type 2 dia-
of ROS but also by decreasing eNOS activity.23 25 PKC also leads to betes and fat accumulation.38 Indeed, a substantial proportion of dia-
increased production of endothelin-1 (ET-1) favouring vasoconstric- betic patients are obese.39 Obesity is a complex disorder leading to
tion and platelet aggregation14 (Figure 1). The role of ET-1 in the alterations in lipid metabolism, deregulation of hormonal axes, oxida-
pathophysiology of diabetic complications is confirmed by the obser- tive stress, systemic inflammation, and ectopic fat distribution.
vation that the activity of endogenous ET-1 on ET(A) receptors is Adipose tissue is an active source of inflammatory mediators and
enhanced in the resistance vessels of patients with diabetes.26 free fatty acids (FFAs).40 Accordingly, obese patients with type 2 dia-
In the vessel wall, PKC-dependent ROS production also partici- betes display increased plasma levels of inflammatory markers.41 Free
pates in the atherosclerotic process by triggering vascular inflamma- fatty acids bind Toll-like receptor (TLR) activating NF-kB through
tion.13,27 Indeed, ROS lead to up-regulation and nuclear translocation degradation of the inhibitory complex IkBa by IKKb-kinase.42 As a
of NF-kB subunit p65 and, hence, transcription of pro-inflammatory result, NF-kB triggers tissue inflammation due to up-regulation of in-
genes encoding for monocyte chemoattractant protein-1 (MCP-1), flammatory genes IL-6 and TNF-a.
selectins, vascular cell adhesion molecule-1 (VCAM-1), and intracel- Toll-like receptor activation by FFA leads to phosphorylation of
lular cell adhesion molecule-1 (ICAM-1). This latter event facilitates insulin receptor substrate-1 (IRS-1) by c-Jun amino-terminal kinase
adhesion of monocytes to the vascular endothelium, rolling, and dia- (JNK) and PKC, thereby altering its ability to activate downstream
pedesis in the sub-endothelium with subsequent formation of foam targets PI3-kinase and Akt. These molecular events result in the
cells (Figure 1). Secretion of IL-1 and TNF-a from active macrophages down-regulation of the glucose transporter GLUT-4 and, hence,
maintains up-regulation of adhesion molecules by enhancing NF-kB insulin resistance43 (Figure 2). Insulin resistance is critically involved
signalling in the endothelium and also promotes smooth muscle in vascular dysfunction in subjects with type 2 diabetes.42 Indeed,
cells growth and proliferation10 (Figure 1). Consistently, inhibition down-regulation of PI3-kinase/Akt pathway leads to eNOS inhibition
of PKC b2 isoform blunts VCAM-1 up-regulation in human endothe- and decreased NO production.44 Together with reduced NO syn-
lial cells upon glucose exposure.27 thesis, intracellular oxidation of stored FFA generates ROS leading
Endothelial dysfunction in diabetes is not only the result to vascular inflammation, AGEs synthesis, reduced PGI2 synthase ac-
of impaired NO availability but also of increased synthesis of vaso- tivity, and PKC activation13,44 (Figure 2).
contrictors and prostanoids.10 PKC-mediated cyclooxygenase-2 Increased ROS levels associated with insulin resistance scavenge
(COX-2) up-regulation is associated with an increase of thromb- NO production and produce peroxynitrite, with a further reduction
oxane A2 and a reduction of prostacyclin (PGI2) release28 of NO bioavailability. Reduced cellular levels of NO facilitate
(Figure 1). These findings suggest that PKC is the upstream signalling pro-inflammatory pathways triggered by increased cytokine produc-
molecule affecting vascular homeostasis in the setting of hypergly- tion. Indeed, TNF-a and IL-1 increase NF-kB activity and expression
cemia28 (Figure 1). Mitochondrial ROS also increase intracellular of adhesion molecules. TNF-a also stimulates the expression of C-
levels of the glucose metabolite methylglyoxal and AGEs synthe- reactive protein which down-regulates eNOS and increases the pro-
sis.12,29,30 In experimental diabetes, methylglyoxal is a key player in duction of adhesion molecules and endothelin-1.26,42 A recent study
the pathophysiology of diabetic complications through oxidative clearly demonstrated that loss of insulin signalling in the vascular
stress, AGEs accumulation, and endothelial dysfunction.29,31 Gener- endothelium leads to endothelial dysfunction, expression of adhe-
ation of AGEs leads to cellular dysfunction by eliciting activation of sion molecules, and atherosclerotic lesions in mice.45
the AGEs receptor (RAGE).30,32 AGE-RAGE signalling in turn acti- Although insulin resistance development has been attributed to
vates ROS-sensitive biochemical pathways such as the hexosamine adipocyte-derived inflammation, recent evidence is overturning the
flux.13 In the hyperglycemic environment, an increased flux of adipocentric paradigm.43 Indeed, inflammation and macrophage acti-
fructose-6-phosphate activates a cascade of events resulting in dif- vation seem to primarily occur in non-adipose tissue in obesity.46,47
ferent glycosilation patterns which are responsible for deregulation This concept is supported by the notion that suppression of inflam-
of enzymes involved in vascular homeostasis. Specifically, O- mation in the vasculature prevents insulin resistance in other
GlcNAcylation at the Akt site of eNOS protein leads to reduced organs and prolongs lifespan.48 Consistently, transgenic mice with
eNOS activity and endothelial dysfunction.13,33 Moreover, glycosyla- endothelium-specific overexpression of the inhibitory NF-kB
tion of transcription factors causes up-regulation of inflammatory subunit IkBa were protected from the development of insulin resist-
(TGFa, TGFb1) and pro-thrombotic genes (plasminogen activator ance. In these mice, obesity-induced macrophage infiltration of
inhibitor-1).33,34 Glucose induced-ROS production also activates adipose tissue and plasma oxidative stress markers were reduced
the polyol pathway flux involved in vascular redox stress.12,35 Ac- whereas blood flow, muscle mitochondrial content, and locomotor
cordingly, hyperactivation of this pathway has been associated with activity were increased, confirming the pivotal role of the transcrip-
increased atherosclerotic lesions in diabetic mice.36 tion factor NFkB in oxidative stress, vascular dysfunction, and inflam-
Diabetes and vascular disease 2439

Figure 2 Insulin resistance as trigger of atherothrombosis. In subjects with obesity or type 2 diabetes the increase in FFA activates TLR leading
NF-kB nuclear translocation and subsequent up-regulation of inflammatory genes IL-6 and TNF-a. On the other hand, JNK and protein kinase C
phosphorylate insulin receptor substrate-1 (IRS-1), thus blunting its downstream targets PI3-kinase and Akt. This results in down-regulation of
glucose transporter GLUT-4 and, hence, insulin resistance. Impaired insulin sensitivity in the vascular endothelium leads to increased FFA oxidation,
ROS formation, and subsequent activation of detrimental biochemical pathways such as AGE synthesis, PKC activation, protein glicosylation as well
as down-regulation of PGI2. These events blunt eNOS activity thereby leading to endothelial dysfunction. Lack of insulin signalling in platelets impairs
the IRS1/PI3K pathway resulting in Ca2+ accumulation and increased platelet aggregation. FFA, free fatty acids; TLR, toll-like receptor; JNK, c-Jun
amino-terminal kinase; IRS-1, Insulin receptor substrate-1; NO, nitric oxide; eNOS, endothelial nitric oxide shyntase; IL-6, interleukin-6; TNF-a,
tumor necrosis factor.
2440 F. Paneni et al.

mation.48 Another study confirmed these findings, showing that profile. Adipokines linked to vascular disease are leptin, adipocyte
genetic disruption of the insulin receptor substrate 2 (IRS-2) in endo- fatty acid-binding protein, interleukins, and novel ones like lipocalin-2
thelial cells reduces glucose uptake by skeletal muscle.49 These novel and pigment epithelium-derived factor. These molecules may drive
findings strengthen the central role of endothelium in obesity- vascular dysfunction via increased proliferation/migration of
induced insulin resistance, suggesting that blockade of vascular in- smooth muscle cells, eNOS inhibition, and activation of NFkB signal-
flammation and oxidative stress may be a promising approach to ling with subsequent expression of adhesion molecules and athero-
prevent metabolic disorders. Notably, pharmacological improve- sclerosis.64 Future work will need to address the potential role of
ment in insulin sensitivity in patients with type 2 diabetes and meta- these molecules as biomarkers and/or drug targets.
bolic syndrome is associated with restoration of flow-mediated
vasodilation.50 52
The atherogenic effects of insulin resistance are also due to MicroRNA and diabetic
changes in lipid profile such as high triglycerides, low HDL choles-
terol, increased remnant lipoproteins, elevated apolipoprotein B
vascular disease
(ApoB) as well as small and dense LDL.53 Once circulating FFA MicroRNAs (miRs) are a newly identified class of small non-coding
reach the liver, very low density lipoprotein (VLDL) are assembled RNAs emerging as key players in the pathogenesis of hypergly-
and made soluble by increased synthesis of ApoB. VLDL are pro- cemia-induced vascular damage.65,66 These small non-coding RNAs
cessed by cholesteryl ester transfer protein allowing transfer of trigly- orchestrate different aspects of diabetic vascular disease by regulat-
cerides to LDL, which become small and dense and, hence, more ing gene expression at the post-transcriptional level. Microarray
atherogenic. Atherogenic dyslipidemia is a reliable predictor of car- studies have shown an altered profile of miRs expression in subjects
diovascular risk and its pharmacological modulation reduces vascular with type 2 diabetes.67 69 Indeed, diabetic patients display a signifi-
events in subjects with type 2 diabetes and metabolic syndrome.54 56 cant deregulation of miRs involved in angiogenesis, vascular repair,
Coronary events in patients with insulin resistance are triggered by and endothelial homeostasis.67 Over the last few years, different
virtue of a prothrombotic state. Under physiological conditions, studies have explored the mechanisms whereby deregulation of
insulin inhibits platelet aggregation and thrombosis via tissue factor miRs expression may contribute to vascular disease in subjects
(TF) inhibition and enhanced fibrinolytic action due to modulation with diabetes. In endothelial cells exposed to high glucose miR-320
of plasminogen activator inhibitor-1 (PAI-1) levels. Indeed, patients is highly expressed and targets several angiogenic factors and their
with acute myocardial infarction receiving fibrinolityic therapy plus receptors, including vascular endothelial growth factor and insulin-
48 h insulin infusion displayed a marked decrease in PAI-1 levels.57 like growth factor-1 (IGF-1). Elevated levels of this miR are associated
In contrast, insulin resistance facilitates atherothrombosis through with decreased cell proliferation and migration, while its down-
increased cellular synthesis of PAI-1 and fibrinogen and reduced pro- regulation restores these properties and increases IGF-1 expression,
duction of tissue plasminogen activator. In platelets, lack of insulin promoting angiogenesis and vascular repair70 (Figure 3).
leads to a down-regulation of the IRS-1/Akt pathway resulting in Hyperglycemia also increases the expression of miR-221, a regula-
calcium accumulation upon basal conditions58 (Figure 2). This latter tor of angiogenesis targeting c-kit receptor which is responsible for
mechanism may explain why platelets from diabetic patients show migration and homing of endothelial progenitor cells (EPCs).71
faster response and increased aggregation compared with those miR-221 and 222 were also found to mediate AGE-induced vascular
from healthy subjects.59 Moreover, platelet reactivity and excretion damage.72 Indeed, down-regulation of miR-222 both in human endo-
of tromboxane metabolites are increased in obese patients with thelial cells exposed to high glucose and in diabetic mice elicits
insulin resistance and this phenomenon is reversed by weight loss AGE-related endothelial dysfunction via targeting, cyclin-dependent
or 3-week treatment with pioglitazone.60 Body weight as well as kinase proteins involved in cell cycle inhibition (P27KIP1 and
impaired insulin sensitivity may also account for the faster recovery P57KIP2).72 A recent study demonstrated that miR-503 is critically
of cyclooxygenase activity despite aspirin treatment.61 Indeed, involved in hyperglycemia-induced endothelial dysfunction in diabet-
higher body mass index was an independent predictor of inadequate ic mice and is up-regulated in ischaemic limb muscles of diabetic sub-
suppression of tromboxane biosynthesis in non-diabetics subjects jects.73 The detrimental effects of miR-503 in the setting of diabetes
treated with aspirin.61 In this study, the increase of aspirin dosage have been explained by its interaction with CCNE and cdc25A, crit-
was sufficient to warrant platelet inhibition. This clinical observation ical regulators of cell cycle progression affecting endothelial cell mi-
may explain the residual cardiovascular risk in obese patients treated gration and proliferation. Interestingly, miR-503 inhibition was able
with anti-platelet medications. to normalize post-ischaemic neovascularization and blood flow re-
Hyperglycemia and insulin resistance alone may not explain the covery in diabetic mice. These findings provide the rationale to
persistent cardiovascular risk burden associated with type 2 diabetes. foresee a protective effect of the modulation of miR-503 expression
Indeed, normalization of glycemia does not reduce macrovascular against diabetic vascular complications.
events suggesting that mediators of vascular risk other than glucose Plasma miR profiling showed a profound down-regulation of
significantly participate to increase the residual cardiovascular risk miR-126 in a cohort of diabetic patients.67 Recent evidence suggest
in diabetic patients.62 In this regard, adipose tissue dysfunction, in- that reduced miR-126 expression levels are partially responsible
flammation, and aberrant adipokine release may be particularly rele- for impaired vascular repair capacities in diabetes.74,75 miR-126 ex-
vant.63 In patients with abdominal obesity, an increased lipid storage pression was reduced in EPCs isolated from diabetics and transfec-
leads to hypoxia, chronic inflammation together with changes in the tion with anti-miR-126 blunted EPCs proliferation and
cellular components of adipose tissue, leading to an altered secretory migration.74,75 In contrast, restored expression of this miR promoted
Diabetes and vascular disease 2441

Figure 3 MicroRNAs involved in diabetic vascular disease. Schematic representation of microRNAs and their relative targets contributing to
reduced vascular repair and, hence, diabetes-related vascular dysfunction. VEGF, vascular endothelial growth factor; IGF-1, insulin-like growth
factor-1; ECs, endothelial cells; AGEs, advanced glycation end-products.

EPCs-related repair capacities and inhibited apoptosis. miR-126 role procoagulant activity and thrombin generation.83 These events are
in EPCs function is mediated by Spred-1, an inhibitor of Ras/ERK sig- enhanced by hyperglycemia83,84 (Figure 4). Low-grade inflammation
nalling pathway, a critical regulator of cell cycle. induces TF expression also in the vascular endothelium of diabetic
Collectively, these studies support the notion that miRs drive subjects contributing to atherothrombosis.81,83
complex signalling networks by targeting the expression of genes Microparticles (MPs), vescicles released in the circulation from
involved in cell differentiation, migration, and survival. various cell types following activation or apoptosis, are increased in
diabetic patients and predict cardiovascular outcome.85,86 Micropar-
ticles from patients with type 2 diabetes have shown to increase co-
Thrombosis and coagulation agulation activity in endothelial cells85 (Figure 4). Moreover, MPs
Individuals affected by diabetes display an increased risk of coronary carrying TF promote thrombus formation at sites of injury represent-
events and cardiovascular mortality when compared with non- ing a novel and additional mechanisms of coronary thrombosis in dia-
diabetic subjects.76 78 This phenomenon is largely explained by a betes.85
deregulation of factors involved in coagulation and platelet activa- Among the factors contributing to the diabetic prothrombotic
tion.79,80 Both insulin resistance and hyperglycemia participate to state, platelet hyperreactivity is of major relevance.87 A number of
the pathogenesis of this prothrombotic state.81 Insulin resistance mechanisms contribute to platelet dysfunction affecting adhesion, ac-
increases PAI-1 and fibrinogen and reduces tissue plasminogen tivation as well as aggregation phases of platelet-mediated throm-
activator levels. The largest increase in PAI-1 has been reported bosis (Figure 4). Hyperglycemia alters platelet Ca2+ homeostasis
in diabetic patients with poor glycemic control and treatment leading to cytoskeleton abnormalities and increased secretion of
with glucose-lowering agents glipizide or metformin comparably proaggregant factors.58 Moreover, up-regulation of glycoproteins
decreased PAI-1.82 Hyperinsulinemia induces TF expression in Ib and IIb/IIIa in diabetic patients triggers thrombus via interacting
monocytes of patients with type 2 diabetes leading to increased TF with Von Willebrand factor (vWF) and fibrin molecules (Figure 4).
2442 F. Paneni et al.

Figure 4 Coagulation and platelet reactivity in diabetes. In patients with diabetes chronic hyperglycemia and insulin resistance determine a sig-
nificant alteration in the coagulation factors as well as increased platelet aggregation, leading to a prothrombotic state. Diabetes-induced increase
of TF levels activates thrombin converting fibrinogen into fibrin. Fibrin organization is further enhanced due to high PAI-1 and reduced t-PA levels.
Increased Ca2+ content, thrombin stimulation as well as interaction with vWF via gpIIb/IIIa receptor lead to platelet shape change, granule release,
and aggregation. Release of MPs from injured endothelium and circulating platelets contribute to accelerate thrombus development. Endothelial
dysfunction precipitates rupture of the endothelial layer leading to exposure of collagen and vWF thereby activating platelets and favouring vascular
thrombosis. TF, tissue factor; t-PA, tissue plasminogen activator; PAI-1, plasminogen activator inhibitor -1; MPs, microparticles; vWF, von Willebrand
factor; ECs, endothelial cells.

Vascular hyperglycemic memory have recently identified the source of ROS perpetuating vascular dys-
function despite normoglycemia restoration.18
Recent prospective clinical trials have shown that normalization of In diabetic mice and human endothelial cells, glucose normaliza-
glycemia failed to reduce cardiovascular burden in the diabetic tion did not revert up-regulation of p66Shc protein, a mitochondrial
population.88 91 In these trials, intensive glucose-lowering therapy adaptor critically involved in ROS generation.18 Persistent p66Shc
was started after a median duration of diabetes ranging from 8 to expression is driven by epigenetic changes as reduced promoter
11 years.88 91 In contrast, early treatment of hyperglycemia was methylation and acetylation of histone 3 (Figure 5). Moreover,
shown to be beneficial.92,93 These findings support the concept p66Shc-dependent ROS generation maintains up-regulation of
that hyperglycemic environment may be remembered in the PKCbII and inhibits eNOS activity, thus feeding a detrimental
vasculature. Reactive oxygen species are probably involved in this vicious cycle despite restoration of normoglycemia18 (Figure 5). Per-
phenomenon.94,95 sistent oxidative stress is also responsible for sustained vascular
The persistence of hyperglycemic stress despite blood glucose apoptosis via caspase 3 activation. Gene silencing of p66Shc blunted
normalization has recently been defined hyperglycemic memory. persistent endothelial dysfunction and oxidative stress in the vascu-
A substantial understanding of its mechanisms has been achieved lature of diabetic mice, suggesting that this protein drives hypergly-
only in recent years.96,97 It has been recently demonstrated that tran- cemic memory18 (Figure 5). In addition, other studies have shown
sient hyperglycemia activates NF-kB, and this effect persists despite that both mammalian deacetylase SIRT-1 and tumour suppressor
subsequent normalization of glucose levels. This finding is explained p53 have a strong memory effect despite glucose normalization.99,100
by epigenetic changes occurring at the level of DNA and histone- Interestingly enough, these findings are in line with the notion that
binding promoter of pro-oxidant and pro-inflammatory genes. both SIRT-1 and p53 control p66Shc transcription.101,102 Indeed,
Specifically, methylation and acetylation are critical epigenetic reduced SIRT-1 activity in diabetes favours acetylation of histone
mark modulated by the hyperglycemic environment. Methylation 3-binding p66Shc promoter. Moreover, increased p53 activity main-
of p65/NFkB promoter by the ROS-dependent methyltransferase tains p66Shc memory effect (Figure 5).101,102 All together, these path-
Set7/9 is indeed the mechanisms whereby vascular inflammation is ways might be involved in self-perpetuating vascular damage of
not reverted by restoration of normoglycemia98 (Figure 5). We patients with diabetes despite optimal glycemic control.
Diabetes and vascular disease 2443

Figure 5 Intracellular signalling of vascular hyperglycemic memory. Hyperglycemia causes a deregulation of SIRT1 resulting in increased acetyl-
ation of histone 3-binding p66Shc promoter. Together with these changes, hypomethylation of p66Shc promoter leads to persistent overexpression
of the adaptor protein despite glucose normalization. SIRT1 down-regulation also causes increased p53 activation further promoting p66Shc gene
transcription. Overexpression of p66Shc causes mitochondrial ROS accumulation leading to vascular apoptosis, vascular inflammation (Set7/
9-dependent methylation of p65 promoter and expression of inflammatory genes) and endothelial dysfunction via a detrimental vicious cycle involv-
ing ROS, PKCb2 and eNOS inhibiting phosphorylation at Thr-495. H3, histone 3; ROS, reactive oxygen species; PKCbII, protein kinase C bII; NO,
nitric oxide; MCP-1, monocyte chemoattractant protein 1; VCAM-1, vascular cell adhesion molecule 1.

Future perspectives Funding

This work was supported by grants from the Swiss Heart Foundation,
Oxidative stress plays a major role in the development of micro- and Fondazione Roma, Italy (to F.C.).
macrovascular complications. Accumulation of free radicals in the
vasculature of diabetic patients is responsible for the activation of Conflict of interest: F.P is the recipient of a fellowship from the Italian
detrimental biochemical pathways, miRs deregulation, release of Society of Hypertension.
MPs, and epigenetic changes contributing to vascular inflammation
and ROS generation. Since cardiovascular risk burden is not eradi- References
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