Advanced glycation end product cross-linking: pathophysiologic role and therapeutic target in cardiovascular disease

Diabetes-related heart failure

As the link between heart failure (HF) and diabetes mellitus (DM) becomes unignorable, so the need is further increasing for pathological comprehension: What is "diabetic cardiomyopathy (DMC)?" In response to current concern, the most updated guidelines stated by the ACCF/AHA and by the ESC/EASD take one step further, including the definition of DMC, although it is a matter yet to be completed. For more than 40 years, coronary artery disease and hypertension have been considered as the main causes of diabetes-related cardiac dysfunction. HF was originally considered as a result of reduced left ventricular ejection fraction (HF-REF); however, it has been recognized that HF symptoms are often observed in patients with preserved EF (HF-PEF). DMC includes HF with both reduced and preserved entities independent of coronary stenosis and hypertension. Cardiologists are thus facing a sort of chaos without clear guidelines for the "deadly intersection" of DM and HF. Today, the increasing interest and concern have caused DMC to be revisited and the first step in controlling the chaos around DMC is to organize and analyze all of the available evidence from preclinical and clinical studies. This review aims to illustrate the current concepts of DMC by shedding light on the new molecular mechanisms.  (Circ J 2014; 78: 576-583).

Heart failure with preserved ejection fraction: emerging drug strategies

Approximately half of heart failure patients have a normal ejection fraction, a condition designated as heart failure with preserved ejection fraction (HFpEF). This heart failure subtype disproportionately affects women and the elderly and is commonly associated with other cardiovascular comorbidities, such as hypertension and diabetes. HFpEF is increasing at a steady rate and is predicted to become the leading cause of heart failure within a decade. HFpEF is characterized by impaired diastolic function, thought to be due to concentric remodeling of the heart along with increased stiffness of both the extracellular matrix and myofilaments. In addition, oxidative stress and inflammation are thought to have a role in HFpEF progression, along with endothelial dysfunction and impaired nitric oxide-cyclic guanosine monophosphate-protein kinase G signaling. Surprisingly a number of clinical studies have failed to demonstrate any benefit of drugs effective in heart failure with systolic dysfunction in HFpEF patients. Thus, HFpEF is one of the largest unmet needs in cardiovascular medicine, and there is a substantial need for new therapeutic approaches and strategies that target mechanisms specific for HFpEF. This conclusion is underscored by the recently reported disappointing results of the RELAX trial, which assessed the use of phosphodiesterase-5 inhibitor sildenafil for treating HFpEF. In animal models, endothelial nitric oxide synthase activators and If current inhibitors have shown benefit in improving diastolic function, and there is a rationale for assessing matrix metalloproteinase 9 inhibitors and nitroxyl donors. LCZ696, a combination drug of angiotensin II receptor blocker and neprilysin inhibitor, and the aldosterone receptor antagonist spironolactone are currently in clinical trial for treating HFpEF. Here we present an overview of the etiology and diagnosis of HFpEF that segues into a discussion of new therapeutic approaches emerging from basic research and drugs currently in clinical trial that primarily target diastolic dysfunction or imbalanced ventricular-arterial coupling.

AGEs, contributors to placental bed vascular changes leading to preeclampsia

Glycation of proteins or other biomolecules and their further long-term degradation result in the formation of advanced glycation end products, AGEs. AGEs and other ligands interact with their receptors, RAGEs, localized to a variety of tissues, but mainly in endothelium and vascular wall cells. This interaction triggers diverse signaling pathways that converge on the activation of NF-κB and the initiation of a local inflammatory reaction that, when prolonged, results in dysfunctional features. Preeclampsia is a serious vascular disorder centred at the placenta-uterine interface, the placental bed, but the condition extends to the mother's circulation. RAGEs have notorious expression in the placental bed tissues along pregnancy but, in addition, RAGEs and their ligands are expressed in the fetal membranes and are found in the amniotic fluid and the mother's serum. Disorders complicating pregnancies and having an important vascular involvement, as preeclampsia and diabetes mellitus, have additional enhanced AGE/RAGE expression variation. This indicates that for their assessment, the assay of RAGEs or their ligands may become useful diagnostic or prognostic procedures.

Advanced glycation endproducts in food and their effects on health

Advanced glycation endproducts (AGEs) form by Maillard-reactions after initial binding of aldehydes with amines or amides in heated foods or in living organisms. The mechanisms of formation may include ionic as well as oxidative and radical pathways. The reactions may proceed within proteins to form high-molecular weight (HMW) AGEs or among small molecules to form low-molecular weight (LMW) AGEs. All free amino acids form AGEs, but lysine or arginine side chains dominate AGE formation within proteins. The analysis of AGEs in foods and body fluids is most often performed by ELISA or LC-MS; however, none of the methodologies cover all HMW and LMW AGEs. Most research is, therefore, carried out using 'representative' AGE compounds, most often N(ε)-carboxymethyl-lysine (CML). Only LMW AGEs, including peptide-bound forms, and carbonyls may be absorbed from the gut and contribute to the body burden of AGEs. Some AGEs interact with specific pro- or anti-inflammatory receptors. Most studies on the biological effects of AGEs have been carried out by administering heated foods. The pro-inflammatory and deteriorating biological effects of AGEs in these studies, therefore, need further confirmation. The current review points out several research needs in order to address important questions on AGEs in foods and health.

Oxidative stress in cardiovascular diseases and obesity: role of p66Shc and protein kinase C

Reactive oxygen species (ROS) are a byproduct of the normal metabolism of oxygen and have important roles in cell signalling and homeostasis. An imbalance between ROS production and the cellular antioxidant defence system leads to oxidative stress. Environmental factors and genetic interactions play key roles in oxidative stress mediated pathologies. In this paper, we focus on cardiovascular diseases and obesity, disorders strongly related to each other; in which oxidative stress plays a fundamental role. We provide evidence of the key role played by p66(Shc) protein and protein kinase C (PKC) in these pathologies by their intracellular regulation of redox balance and oxidative stress levels. Additionally, we discuss possible therapeutic strategies aimed at attenuating the oxidative damage in these diseases.

Thrombospondin-4, tumour necrosis factor-like weak inducer of apoptosis (TWEAK) and its receptor Fn14: novel extracellular matrix modulating factors in cardiac remodelling

Cardiac remodelling is defined as changes in the size, shape, and function of the heart, which are most commonly caused by hypertension-induced left ventricular hypertrophy and myocardial infarction. Both neurohumoral and inflammatory factors have critical roles in the regulation of cardiac remodelling. A characteristic feature of cardiac remodelling is modification of the extracellular matrix (ECM), often manifested by fibrosis, a process that has vital consequences for the structure and function of the myocardium. In addition to established modulators of the ECM, the matricellular protein thrombospondin-4 (TSP-4) as well as the tumour necrosis factor-like weak inducer of apoptosis (TWEAK) and its receptor Fn14 has been recently shown to modulate cardiac ECM. TSP-4 null mice develop pronounced cardiac hypertrophy and fibrosis with defects in collagen maturation in response to pressure overload. TWEAK and Fn14 belong to the tumour necrosis factor superfamily of proinflammatory cytokines. Recently it was shown that elevated levels of circulating TWEAK via Fn14 critically affect the cardiac ECM, characterized by increasing fibrosis and cardiomyocyte hypertrophy in mice. Here we review the literature concerning the role of matricellular proteins and inflammation in cardiac ECM remodelling, with a special focus on TSP-4, TWEAK, and its receptor Fn14.

Role of Dietary Advanced Glycation End Products in Diabetes Mellitus

Dietary advanced glycation end products (AGEs) can be formed via the Maillard reaction and several alternative pathways. AGEs exert their deleterious effects by damaging protein structure and function, as well as through activation of cellular mechanisms. At the cellular level, the damaging effects of AGEs have been attributed to several AGE-binding proteins. Increased levels of AGEs have been implicated in several chronic diseases, including diabetes-related complications such as renal diseases, retinopathy, neuropathy, and cardiovascular diseases, as well as delayed wound healing. To investigate the role of AGEs thoroughly, a reliable assessment of dietary AGEs is needed. Varying methodology, diverse food preparation, and quantification of a variety of dietary AGEs makes this a complex goal. In addition, some antiglycation food products may balance or offset the negative impact of dietary AGEs.

Aging and atherosclerosis: mechanisms, functional consequences, and potential therapeutics for cellular senescence

Atherosclerosis is classed as a disease of aging, such that increasing age is an independent risk factor for the development of atherosclerosis. Atherosclerosis is also associated with premature biological aging, as atherosclerotic plaques show evidence of cellular senescence characterized by reduced cell proliferation, irreversible growth arrest and apoptosis, elevated DNA damage, epigenetic modifications, and telomere shortening and dysfunction. Not only is cellular senescence associated with atherosclerosis, there is growing evidence that cellular senescence promotes atherosclerosis. This review examines the pathology of normal vascular aging, the evidence for cellular senescence in atherosclerosis, the mechanisms underlying cellular senescence including reactive oxygen species, replication exhaustion and DNA damage, the functional consequences of vascular cell senescence, and the possibility that preventing accelerated cellular senescence is a therapeutic target in atherosclerosis.

Alagebrium in combination with exercise ameliorates age-associated ventricular and vascular stiffness

Advanced glycation end-products (AGEs) initiate cellular inflammation and contribute to cardiovascular disease in the elderly. AGE can be inhibited by Alagebrium (ALT), an AGE cross-link breaker. Moreover, the beneficial effects of exercise on aging are well recognized. Thus, we investigated the effects of ALT and exercise (Ex) on cardiovascular function in a rat aging model. Compared to young (Y) rats, in sedentary old (O) rats, end-systolic elastance (Ees) decreased (0.9±0.2 vs 1.7±0.4mmHg/μL, P<0.05), dP/dt(max) was attenuated (6054±685 vs 9540±939mmHg/s, P<0.05), ventricular compliance (end-diastolic pressure-volume relationship (EDPVR)) was impaired (1.4±0.2 vs 0.5±0.4mmHg/μL, P<0.05) and diastolic relaxation time (tau) was prolonged (21±3 vs 14±2ms, P<0.05). In old rats, combined ALT+Ex (4weeks) increased dP/dt(max) and Ees (8945±665 vs 6054±685mmHg/s, and 1.5±0.2 vs 0.9±0.2 respectively, O with ALT+Ex vs O, P<0.05 for both). Diastolic function (exponential power of EDPVR and tau) was also substantially improved by treatment with Alt+Ex in old rats (0.4±0.1 vs 0.9±0.2 and 16±2 vs 21±3ms, respectively, O with ALT+EX vs O, P<0.05 for both). Pulse wave velocity (PWV) was increased in old rats (7.0±0.7 vs 3.8±0.3ms, O vs Y, P<0.01). Both ALT and Ex alone decreased PWV in old rats but the combination decreased PWV to levels observed in young (4.6±0.5 vs 3.8±0.3ms, O with ALT+Ex vs Y, NS). These results suggest that prevention of the formation of new AGEs (with exercise) and breakdown of already formed AGEs (with ALT) may represent a therapeutic strategy for age-related ventricular and vascular stiffness.

Vascular damage in kidney disease: beyond hypertension

Chronic kidney disease (CKD) is highly prevalent and a multiplier of cardiovascular disease (CVD) and cannot be completely explained by traditional Framinghan risk factors. Consequently, greater emphasis has been placed in nontraditional risk factors, such as inflammation, endothelial dysfunction, sympathetic overactivation, protein-energy wasting oxidative stress, vascular calcification, and volume overload. The accumulation of uremic toxins (and the involvement of genetic factors) is responsible for many of the clinical consequences of a condition known as uremia. In this brief paper, we discuss mechanisms involved in the vascular damage of CKD patients, aiming to point out that important factors beyond hypertension are largely responsible for endothelial activation and increased CVD risk, with potential impact on risk stratification and development of novel therapeutic options.

Increasing duration of type 1 diabetes perturbs the strength-structure relationship and increases brittleness of bone

Type 1 diabetes (T1DM) increases the likelihood of a fracture. Despite serious complications in the healing of fractures among those with diabetes, the underlying causes are not delineated for the effect of diabetes on the fracture resistance of bone. Therefore, in a mouse model of T1DM, we have investigated the possibility that a prolonged state of diabetes perturbs the relationship between bone strength and structure (i.e., affects tissue properties). At 10, 15, and 18 weeks following injection of streptozotocin to induce diabetes, diabetic male mice and age-matched controls were examined for measures of skeletal integrity. We assessed 1) the moment of inertia (I(MIN)) of the cortical bone within diaphysis, trabecular bone architecture of the metaphysis, and mineralization density of the tissue (TMD) for each compartment of the femur by micro-computed tomography and 2) biomechanical properties by three-point bending test (femur) and nanoindentation (tibia). In the metaphysis, a significant decrease in trabecular bone volume fraction and trabecular TMD was apparent after 10 weeks of diabetes. For cortical bone, type 1 diabetes was associated with decreased cortical TMD, I(MIN), rigidity, and peak moment as well as a lack of normal age-related increases in the biomechanical properties. However, there were only modest differences in material properties between diabetic and normal mice at both whole bone and tissue-levels. As the duration of diabetes increased, bone toughness decreased relative to control. If the sole effect of diabetes on bone strength was due to a reduction in bone size, then I(MIN) would be the only significant variable explaining the variance in the maximum moment. However, general linear modeling found that the relationship between peak moment and I(MIN) depended on whether the bone was from a diabetic mouse and the duration of diabetes. Thus, these findings suggest that the elevated fracture risk among diabetics is impacted by complex changes in tissue properties that ultimately reduce the fracture resistance of bone.

Dietary advanced glycation end products and aging

Advanced glycation end products (AGEs) are a heterogeneous, complex group of compounds that are formed when reducing sugar reacts in a non-enzymatic way with amino acids in proteins and other macromolecules. This occurs both exogenously (in food) and endogenously (in humans) with greater concentrations found in older adults. While higher AGEs occur in both healthy older adults and those with chronic diseases, research is progressing to both quantify AGEs in food and in people, and to identify mechanisms that would explain why some human tissues are damaged, and others are not. In the last twenty years, there has been increased evidence that AGEs could be implicated in the development of chronic degenerative diseases of aging, such as cardiovascular disease, Alzheimer’s disease and with complications of diabetes mellitus. Results of several studies in animal models and humans show that the restriction of dietary AGEs has positive effects on wound healing, insulin resistance and cardiovascular diseases. Recently, the effect of restriction in AGEs intake has been reported to increase the lifespan in animal models. This paper will summarize the work that has been published for both food AGEs and in vivo AGEs and their relation with aging, as well as provide suggestions for future research.

The carbonyl scavenger carnosine ameliorates dyslipidaemia and renal function in Zucker obese rats

The metabolic syndrome is a risk factor that increases the risk for development of renal and vascular complications. This study addresses the effects of chronic administration of the endogenous dipeptide carnosine (β-alanyl-L-histidine, L-CAR) and of its enantiomer (β-alanyl-D-histidine, D-CAR) on hyperlipidaemia, hypertension, advanced glycation end products, advanced lipoxidation end products formation and development of nephropathy in the non-diabetic, Zucker obese rat. The Zucker rats received a daily dose of L-CAR or D-CAR (30 mg/kg in drinking water) for 24 weeks. Systolic blood pressure was recorded monthly. At the end of the treatment, plasma levels of triglycerides, total cholesterol, glucose, insulin, creatinine and urinary levels of total protein, albumin and creatinine were measured. Several indices of oxidative/carbonyl stress were also measured in plasma, urine and renal tissue. We found that both L- and D-CAR greatly reduced obese-related diseases in obese Zucker rat, by significantly restraining the development of dyslipidaemia, hypertension and renal injury, as demonstrated by both urinary parameters and electron microscopy examinations of renal tissue. Because the protective effect elicited by L- and D-CAR was almost superimposable, we conclude that the pharmacological action of L-CAR is not due to a pro-histaminic effect (D-CAR is not a precursor of histidine, since it is stable to peptidic hydrolysis), and prompted us to propose that some of the biological effects can be mediated by a direct carbonyl quenching mechanism.

Role of lysyl oxidase in myocardial fibrosis: from basic science to clinical aspects

Because of its dynamic nature, the composition and structure of the myocardial collagen network can be reversibly modified to adapt to transient cardiac injuries. In response to persistent injury, however, irreversible, maladaptive changes of the network occur leading to fibrosis, mostly characterized by the excessive interstitial and perivascular deposition of collagen types I and III fibers. It is now becoming apparent that myocardial fibrosis directly contributes to adverse myocardial remodeling and the resulting alterations of left ventricular (LV) anatomy and function present in the major types of cardiac diseases. The enzyme lysyl oxidase (LOX) is a copper-dependent extracellular enzyme that catalyzes lysine-derived cross-links in collagen and elastin. LOX-mediated cross-linking of collagen types I and III fibrils leads to the formation of stiff collagen types I and III fibers and their subsequent tissue deposition. Evidence from experimental and clinical studies shows that the excess of LOX is associated with an increased collagen cross-linking and stiffness. It is thus conceivable that LOX upregulation and/or overactivity could underlie myocardial fibrosis and altered LV mechanics and contribute to the compromise of LV function in cardiac diseases. This review will consider the molecular aspects related to the regulation and actions of LOX, namely, in the context of collagen synthesis. In addition, it will address the information related to the role of myocardial LOX in heart failure and the potential benefits of controlling its expression and function.

Carotid plaque, arterial stiffness gradient, and remodeling in hypertension

The analysis of plaque mechanics along the longitudinal axis (bending strain) may provide useful information because repetitive bending strain of an atherosclerotic plaque can fatigue the wall material and result in plaque rupture. Whether essential hypertension is associated with a specific pattern of bending strain has not yet been determined. The study included 92 patients with an atherosclerotic plaque on the common carotid artery: 66 patients with essential hypertension, either treated or not, and 26 normotensive patients. A novel noninvasive echotracking system (ArtLab; Esaote, The Netherlands) was used to measure intima-media thickness, diameter, and distensibility at 128 sites on a 4-cm-long carotid segment. Carotid plaque was either less elastic than adjacent carotid artery (inward strain) or more elastic (outward strain). Inward strain was more frequently associated with an inward plaque remodeling, whereas an outward strain was more frequently associated with an outer remodeling. In multivariate logistic regression analysis, patients with essential hypertension were more likely to exhibit an inward strain of carotid plaque (odds ratio=6.9 [1.4 to 34.9]; P<0.02), independently of 2 factors favoring inward strain: an outer remodeling (odds ratio=4.6 [1.7 to 13.4]; P<0.005) and the absence of renin-angiotensin system blockers (odds ratio=4.8 [1.1 to 20.4]; P<0.05). In conclusion, arterial wall material of hypertensive patients was less elastic at the site of the plaque than upstream, and carotid was inwardly strained in the zone affected by plaque. This may generate a high level of stress concentrations and fatigue, exposing the plaque to a greater risk of rupture.

Heart failure with preserved ejection fraction: hypertension, diabetes, obesity/sleep apnea, and hypertrophic and infiltrative cardiomyopathy

The detailed pathophysiology of heart failure with preserved ejection fraction (HF-PEF) remains an area of active research and controversy; however, abnormalities of diastolic function are generally believed to play an important role. Most commonly, diastolic dysfunction occurs as a consequence of myocyte hypertrophy, endomyocardial fibrosis, and abnormalities of intracellular calcium handling that are related to normal myocardial aging and accelerated by comorbidities such as hypertension, diabetes, coronary artery disease, and obesity. In this article, three fundamental risk factors are considered for "secondary" diastolic dysfunction and HF-hypertension, diabetes, and obesity-with an emphasis on the clinical epidemiology, pathophysiologic mechanisms, and treatment implications of each. The article concludes with a brief discussion of "primary" diastolic HF due to infiltrative or restrictive cardiomyopathies.

Structural and functional remodeling of the left atrium: clinical and therapeutic implications for atrial fibrillation

Left atrial (LA) structural and functional remodeling reflects a spectrum of pathophysiological changes that have occurred in response to specific stressors. These changes include alterations at the levels of ionic channels, cellular energy balance, neurohormonal expression, inflammatory response, and physiologic adaptations. There is convincing evidence demonstrating an important pathophysiological association between LA remodeling and atrial fibrillation (AF). Measures that will prevent, attenuate, or halt these processes of LA remodeling may have a major public health impact with respect to the epidemic of AF. In this review, we describe the mechanisms involved in LA remodeling and highlight the existing and potential therapeutic options for its reversal, and implications for AF development.

Age-related effect on the concentration of collagen crosslinks in human osteonal and interstitial bone tissue

Collagen crosslinks are important to the quality of bone and may be contributors to the age-related increase in bone fracture. This study was performed to investigate whether age and gender effects on collagen crosslinks are similar in osteonal and interstitial bone tissues. Forty human cadaveric femurs were collected and divided into two age groups: middle-aged (42-63 years of age) and elderly (69-90 years of age) with ten males and ten females in each group (n = 10). Micro-cores of bone tissue from both secondary osteons and interstitial regions in the medial quadrant of the diaphysis were extracted using a custom-modified, computer-controlled milling machine. The bone specimens were then analyzed using high performance liquid chromatography to determine the effects of age and gender on the concentration of mature, enzymatic crosslinks (hydroxylysyl-pyridinoline-HP and lysyl-pyridinoline-LP) and a non-enzymatic crosslink (pentosidine-PE) at these two microstructural sites. The results indicate that age has a significant effect on the concentration of LP and PE, while gender has a significant effect on HP and LP. In addition, the concentration of the crosslinks in the secondary osteons is significantly different from that in the interstitial bone regions. These results suggest that the amount of non-enzymatic crosslinking may increase while that of mature enzymatic crosslinking may decrease with age. Such changes could potentially reduce the inherent quality of the bone tissue in the elderly skeleton.

Ventricular Pump Function in Heart Failure with Normal Ejection Fraction: Insights from Pressure-Volume Measurements

The syndrome of heart failure in the setting of normal ejection fraction (HFNEF) is manifest in a clinically heterogeneous group of patients with multiple and varied comorbid conditions. In this report, we review available data derived from pressure-volume (PV) analyses in patients with and in animal models of HFNEF. Pressure-volume analysis of ventricular function is challenging in the clinical setting but provides unique insights into the systolic, diastolic, and overall pumping characteristics of the heart. Results of such analyses have thus far been limited to small cohorts of patients but suggest that different cohorts of patients with HFNEF having PV relations that imply different pathophysiologic mechanisms exist. This emphasizes the need to take a view of this syndrome, which extends beyond diastolic dysfunction, particularly when it comes to proposing and investigating therapeutic targets. We therefore propose that progress can be made in advancing therapeutics for HFNEF if it is appreciated that different underlying pathophysiologic mechanisms may be important in different cohorts and if attention expands beyond diastolic dysfunction as the sole target. Similar to the success that was achieved in advancing therapeutics for systolic heart failure when attention shifted away from the heart to the neurohormonal and renal axes, our interpretation of data in human beings and in animal models suggests that addressing similar targets (perhaps not in exactly the same manner) may prove to be fruitful, at least for some patients with HFNEF as well.