Skin autofluorescence is increased in patients with carotid artery stenosis and peripheral artery disease

A physically active lifestyle is related to a lower level of skin autofluorescence in a large population with chronic-disease (LifeLines cohort)

BACKGROUND

Physical activity (PA) has substantial health benefits and is important in combatting chronic diseases, which have been associated with elevated levels of advanced glycation endproducts (AGEs). AGEs play a role in the aging process, and an association between PA and AGEs has been reported. We aimed to investigate the relationship between PA and AGE accumulation in a general population and in a population with chronic diseases.

METHODS

This large cross-sectional population study used data from adult participants in the LifeLines project, with participant information drawn from the LifeLines database as well data from patients with diabetes mellitus or renal and/or cardiovascular diseases. Tissue AGE accumulation was assessed non-invasively by skin-autofluorescence (SAF) using an AGE reader (DiagnOptics Technologies BV, Groningen, the Netherlands). PA was assessed using the short questionnaire to assess health-enhancing physical activity (SQUASH). Multivariate linear regression analyses were adjusted for age, body mass index, sex, and smoking status.

RESULTS

Data from 63,452 participants (general population n = 59,177, chronic disease n = 4275) were analyzed. The general population was significantly younger (43.58 ± 11.77 years, mean ± SD) and had significantly lower SAF (1.90 ± 0.42 arbitrary units (AU)) compared to the population with chronic disease (age: 55.51 ± 12.07 years; SAF: 2.27 ± 0.51 AU). In the group with chronic disease, more hours of moderate to vigorous physical activities per week were associated with lower SAF (β = -0.002, 95% confidence interval (95%CI): -0.002 to -0.001). For the general population, there was no association between hours of moderate to vigorous activity and SAF (β = 3.2  × 10^-5, 95%CI: 0.000-0.001, p = 0.742). However, there was an association in the general population between total hours of PA per week and SAF (β = 4.2 × 10^-4, 95%CI: 0.000-0.001, p < 0.001), but this association was not found in the chronic disease population (β = -3.2 × 10^-4, 95%CI: -0.001 to 0.000, p = 0.347).

CONCLUSION

Our study demonstrates that an inverse relationship exists between PA and AGE accumulation in the population with chronic disease. More hours of moderate to vigorous activity is associated with a significantly decreased SAF. More PA is associated with a lower SAF, even after adjusting for the established predictors (age, body mass index, smoking status, and sex). Our findings could help to promote health and prolong longevity.

Hemodialysis Patients with Higher Serum Levels of Soluble Receptor for Advanced Glycation End Products Have an Increased Risk for Arteriovenous Fistula Failure

BACKGROUND

Arteriovenous fistula (AVF) failure due to thrombosis is a major cause of morbidity in patients undergoing regular hemodialysis (HD). Advanced glycation end products (AGEs) and their receptor (RAGE) might contribute to inflammation, neointimal hyperplasia, and thrombosis. RAGE has a C-truncated secretory receptor form, called soluble RAGE (sRAGE). In this study, we aimed to evaluate the association of serum sRAGE with AVF failure due to thrombosis in HD patients.

METHODS

Eighty-eight prevalent HD patients with functional AVF were included in the study. The presence of stenosis, clinical and laboratory data, and serum sRAGE was evaluated at inclusion. sRAGE concentration was measured by a competitive enzyme-linked immunosorbent assay, and stenosis was detected by ultrasound. Patients were prospectively followed up for 36 months. During this period, AVF failure (defined as the absence of blast or palpable thrill and impossible cannulation with 2 needles because of complete thrombosis) was noted and thrombosis was certified by ultrasound examination.

RESULTS

During follow-up, 16 (18.18%) patients lost their vascular access due to thrombosis. In multivariate Cox regression analysis, sRAGE was a significant predictor of vascular access thrombosis (hazard ratio = 1.15, 95% confidence interval: 1.03-1.25, p = 0.012). Kaplan-Meier analysis showed a significantly lower AVF patency time in patients with sRAGE >16.78 ng/mL than those with sRAGE <16.78 ng/mL (p = 0.02). In the subgroup of patients with stenosis at baseline, sRAGE, serum albumin, obesity, and ischemic heart disease were associated with thrombosis.

CONCLUSION

In our study, baseline, systemic sRAGE is associated with the occurrence of thrombosis of AVF, and this marker has a significant impact on AVF survival.

AGE-RAGE Axis in the Pathophysiology of Chronic Lower Limb Ischemia and a Novel Strategy for Its Treatment

This review focuses on the role of advanced glycation end products (AGEs) and its cell receptor (RAGE) and soluble receptor (sRAGE) in the pathogenesis of chronic lower limb ischemia (CLLI) and its treatment. CLLI is associated with atherosclerosis in lower limb arteries. AGE-RAGE axis which comprises of AGE, RAGE, and sRAGE has been implicated in atherosclerosis and restenosis. It may be involved in atherosclerosis of lower limb resulting in CLLI. Serum and tissue levels of AGE, and expression of RAGE are elevated, and the serum levels of sRAGE are decreased in CLLI. It is known that AGE, and AGE-RAGE interaction increase the generation of various atherogenic factors including reactive oxygen species, nuclear factor-kappa B, cell adhesion molecules, cytokines, monocyte chemoattractant protein-1, granulocyte macrophage-colony stimulating factor, and growth factors. sRAGE acts as antiatherogenic factor because it reduces the generation of AGE-RAGE-induced atherogenic factors. Treatment of CLLI should be targeted at lowering AGE levels through reduction of dietary intake of AGE, prevention of AGE formation and degradation of AGE, suppression of RAGE expression, blockade of AGE-RAGE binding, elevation of sRAGE by upregulating sRAGE expression, and exogenous administration of sRAGE, and use of antioxidants. In conclusion, AGE-RAGE stress defined as a shift in the balance between stressors (AGE, RAGE) and antistressor (sRAGE) in favor of stressors, initiates the development of atherosclerosis resulting in CLLI. Treatment modalities would include reduction of AGE levels and RAGE expression, RAGE blocker, elevation of sRAGE, and antioxidants for prevention, regression, and slowing of progression of CLLI.

Skin Autofluorescence-Indicated Advanced Glycation End Products as Predictors of Cardiovascular and All-Cause Mortality in High-Risk Subjects: A Systematic Review and Meta-analysis

Background

Chronic deposits of advanced glycation end products produced by enzymatic glycation have been suggested as predictors of atherosclerotic‐related disorders. This study aimed to estimate the relationship between advanced glycation end products indicated by skin autofluorescence levels and the risk of cardiovascular and all‐cause mortality based on data from observational studies.

Methods and Results

We systematically searched Medline, Embase, the Cochrane Central Register of Controlled Trials, the Cochrane Database of Systematic Reviews, and the Web of Science databases from their inceptions until November 2017 for observational studies addressing the association of advanced glycation end products by skin autofluorescence levels with cardiovascular and all‐cause mortality. The DerSimonian and Laird random‐effects method was used to compute pooled estimates of hazard ratios and their respective 95% confidence intervals for the risk of cardiovascular and all‐cause mortality associated with levels of advanced glycation end products by skin autofluorescence. Ten published studies were included in the systematic review and meta‐analysis. Higher skin autofluorescence levels were significantly associated with a higher pooled risk estimate for cardiovascular mortality (hazard ratio: 2.06; 95% confidence interval, 1.58–2.67), which might not be important to moderate heterogeneity (I²=34.7%; P=0.163), and for all‐cause mortality (hazard ratio: 1.91; 95% confidence interval, 1.42–2.56) with substantial heterogeneity (I²=60.8%; P=0.0.18).

Conclusions

Our data suggest that skin autofluorescence levels could be considered predictors of all‐cause mortality and cardiovascular mortality in patients at high and very high risk.

Effects of Long-Term Physical Activity and Diet on Skin Glycation and Achilles Tendon Structure

Advanced glycation end-products (AGEs) accumulate with aging and have been associated with tissue modifications and metabolic disease. Regular exercise has several health benefits, and the purpose of this study was to investigate the effect of regular long-term exercise and diet on skin autofluorescence (SAF) as a measure of glycation and on Achilles tendon structure. In connection with the 2017 European Masters Athletics Championships Stadia, high-level male athletes (n = 194) that had regularly trained for more than 10 years were recruited, in addition to untrained controls (n = 34). SAF was non-invasively determined using an AGE Reader. Achilles tendon thickness and vascular Doppler activity were measured by ultrasonography, and diet was assessed by a questionnaire. There was no significant difference in SAF between the athletes and controls. However, greater duration of exercise was independently associated with lower SAF. Diet also had an effect, with a more "Western" diet in youth being associated with increased SAF. Furthermore, our data demonstrated that greater Achilles tendon thickness was associated with aging and training. Together, our data indicate that long-term exercise may yield a modest reduction in glycation and substantially increase Achilles tendon size, which may protect against injury.

When the skin is in the center of interest: An aging issue

The skin represents the first bearer of marks of time as well as an easily accessible model for the assessment and determination of the involved molecular mechanisms. The deterioration of important skin functions due to intrinsic and extrinsic aging leads to clinical manifestations, which mirror several internal age-associated diseases, such as neurodegenerative, cardiovascular, skeletal, and endocrine/metabolic skin diseases. Current molecular data indicate that skin aging, especially intrinsic aging, mirrors age-related deficiencies in the entire human body. These data and the development of new biologic technologies highlight the importance of the skin in aging research and should enable future interdisciplinary projects on internal diseases, which could barely have been performed until recently due mainly to the lack of respective tissue.

Oxidative stress and antioxidant treatment in patients with peripheral artery disease

Peripheral artery disease is an atherosclerotic disease of arterial vessels that mostly affects arteries of lower extremities. Effort induced cycles of ischemia and reperfusion lead to increased reactive oxygen species production by mitochondria. Therefore, the pathophysiology of peripheral artery disease is a consequence of metabolic myopathy, and oxidative stress is the putative major operating mechanism behind the structural and metabolic changes that occur in muscle. In this review, we discuss the evidence for oxidative damage in peripheral artery disease and discuss management strategies related to antioxidant supplementation. We also highlight the major pathways governing oxidative stress in the disease and discuss their implications in disease progression. Potential therapeutic targets and diagnostic methods related to these mechanisms are explored, with an emphasis on the Nrf2 pathway.

Assessment of advanced glycation end-products as a biomarker of diabetic outcomes

There are substantial differences in the onset and severity of diabetes complications that are not fully explained by HbA1c levels and other risk factors. HbA1c is the gold standard for assessing metabolic control, but has limited value to identify patients at risk of developing diabetic complications. The main disadvantage of HbA1c is that it does not provide information about glycemic variability and does not reflect long-term exposure to hyperglycemia. One of the main pathogenetic mechanisms of diabetic complications is the generation and accumulation of advanced glycation end-products (AGEs). Based on its fluorescence properties, AGEs may be measured in tissues such as the skin or lens. These non-invasive measurements of AGE accumulation may be considered as promising biomarkers of late diabetic complications, and our objective is to summarize the available evidence supporting this statement. However, further translational research and prospective clinical trials are needed before these new biomarkers may be incorporated into clinical practice.

Critical Appraisal of Advanced Glycation End Products (AGEs) and Circulating Soluble Receptors for Advanced Glycation End Products (sRAGE) as a Predictive Biomarkers for Cardiovascular Disease in Hemodialysis Patients

The interaction of advanced glycation end products (AGE) and their receptors promote vascular complications of diabetes in hemodialysis (HD) patients. The soluble form of the receptor for the advanced glycation end-products (sRAGE) has been studied as a vascular biomarker in various diseases with controversial results. Our aim was to evaluate the association of the serum levels of the AGEs and their receptor sRAGE with cardiovascular disease (CVD) and the cardiovascular risk factors among HD patients. There were 130 HD patients and 80 age and gender matched control subjects were involved; 31.5% of the HD group were diabetic, which was an underlying cause of renal impairment; 36.1% had CVD, which was comprising 44.7% of diabetics and 55.3% of non-diabetic patients. The AGEs and sRAGE were assessed by enzyme linked immunosorbent assay (ELISA). In addition, the lipid profile, glycemic indices, pre-dialysis renal function tests, and hemoglobin % (Hb) were evaluated. The results show that the circulating AGEs and sRAGE levels were significantly higher in the HD patients. Those with underlying diabetes displayed higher sRAGE levels, which were positively correlated with hyperglycemia, HbA1C, and total cholesterol (TC). The HD patients with an increased serum sRAGE exhibited more cardiovascular risk factors (hypercholesterolemia and anemia) with a high prevalence of CVD. Using a linear regression analysis, we found a significant association of sRAGE with CVD and TC among HD patients, regardless of whether associating diabetes was an underlying cause of renal impairment. Overall, the HD patients displayed significantly higher serum AGEs with a concomitant increase in the circulating sRAGE levels, mainly in the diabetic HD, which were significantly associated with the CVD (independent predictors) and CV risk factors (hypercholesterolemia), mainly sRAGEs, regardless of the underlying diabetes mellitus. This highlights the prognostic role of AGEs and sRAGE in HD patients regardless of underlying cause in order to predict the risk for CVD.

Role of Ligands of Receptor for Advanced Glycation End Products (RAGE) in Peripheral Artery Disease

Atherosclerotic cardiovascular disease, including peripheral artery disease (PAD), is more common and severe in diabetic patients compared with nondiabetic individuals. Indeed, diabetes is associated with the increased risk of limb amputation and all-cause mortality in patients with symptomatic PAD. Proteins and lipids are nonenzymatically modified by sugars, resulting in the formation and accumulation of advanced glycation end products (AGEs), whose process is accelerated under diabetic conditions, especially patients with a long duration of diabetes. Accumulating evidence shows that nonenzymatic modification by sugars alters the structural integrity of collagens and lipoproteins in large vessels, thereby being involved in vascular stiffness and atherosclerotic plaque instability. Furthermore, engagement of receptor for AGEs (RAGE) with its ligands, such as AGEs, high mobility group box 1, and S100A proteins evokes inflammatory and thrombotic reactions, thus playing a central role in the development and progression of atherosclerotic cardiovascular disease. In this article, we review the pathophysiological role of RAGE ligands in PAD and discuss the clinical utility of measurement of plasma, serum, or tissue RAGE ligands for assessment of the severity and prognosis of PAD. This review suggests that RAGE ligands may be a novel biomarker and also a therapeutic target of PAD, especially in patients with diabetes.

Sickle Cell Disease is Associated With Elevated Levels of Skin Advanced Glycation Endproducts

Sickle cell disease (SCD) is associated with increased oxidative stress which potentially enhances generation of advanced glycation endproducts (AGEs). We estimated skin accumulation of AGEs in SCD patients and assessed their relationship with hemolysis and nephropathy. Skin intrinsic fluorescence (SIF), an estimate of AGEs, was assessed in African American patients with and without SCD. After skin excitation with light at 375, 405, and 420 nm, raw autofluorescence was adjusted using specific intrinsic corrections. Group differences in SIF were evaluated by multiple variable regression using chronological age and sex as covariates. The relationship of SIF with reticulocyte count, serum lactate dehydrogenase, estimated glomerular filtration rate (GFR), plasma creatinine, bilirubin, and urine microalbumin was assessed. There were 48 SCD patients (29 male/19 female, age=13.4±3.6 y) and 51 controls (25 male/26 female, age=10.4±5.0 y). SIF375(1.0,0.0), SIF405(0.5,0.5), and SIF420(0.5,0.5) were significantly higher in SCD patients. There was no difference in SIF between SCD patients with and without microalbuminuria. SIF 420(0.5,0.5) was correlated with reticulocyte count (r=0.33; P=0.03). Skin AGEs as estimated by SIF were higher in children with SCD and weakly associated with 1 measure of hemolysis. Further study is needed to determine whether chronic increased deposition of AGEs is associated with development of complications of SCD.

Accumulation of advanced glycation end products is associated with macrovascular events and glycaemic control with microvascular complications in Type 2 diabetes mellitus

AIM

The United Kingdom Prospective Diabetes Study (UKPDS) study showed that glycaemic control (HbA1c ) can predict vascular complications in Type 2 diabetes mellitus. The Diabetes Control and Complications Trial (DCCT) study showed that accumulation of advanced glycation end products (AGEs) from skin biopsies predicts vascular complications in Type 1 diabetes. Previously, we showed that tissue AGEs can be measured non-invasively using skin autofluorescence (SAF). The aim of this study was to compare the predictive value of HbA1c and SAF for new macrovascular events and microvascular complications in people with Type 2 diabetes.

METHODS

A prospective cohort study of 563 participants, median age 64 years [interquartile range (IQR) 57-72], diabetes duration of 13 years, from five Dutch hospitals was performed.

RESULTS

After a median follow-up of 5.1 (IQR 4.3-5.9) years, 79 (15%) participants had died and 49 (9%) were lost to follow-up. Some 133 (26%) developed a microvascular complication and 189 (37%) a macrovascular event. Tertiles of HbA1c were significantly associated with development of microvascular complications (log rank P = 0.022), but not with macrovascular events. Tertiles of SAF were significantly associated with macrovascular events (log rank P = 0.003). Cox regression analysis showed SAF was associated with macrovascular events: crude hazard ratio (HR) 1.53 (P < 0.001) per unit increase, HR 1.28 (P = 0.03) after correction for UKPDS score. HbA1c was predictive for microvascular complications: crude HR 1.20 (P = 0.004), HR 1.20 (P = 0.004) after correction for UKPDS score.

CONCLUSION

This study shows that tissue accumulation of AGEs, assessed by SAF, is associated with development of macrovascular events in people with Type 2 diabetes, whereas HbA1c is associated with the development of microvascular complications.

The AGE-RAGE Axis: Implications for Age-Associated Arterial Diseases

The process of advanced glycation leads to the generation and accumulation of an heterogeneous class of molecules called advanced glycation endproducts, or AGEs. AGEs are produced to accelerated degrees in disorders such as diabetes, renal failure, inflammation, neurodegeneration, and in aging. Further, AGEs are present in foods and in tobacco products. Hence, through both endogenous production and exogenous consumption, AGEs perturb vascular homeostasis by a number of means; in the first case, AGEs can cause cross-linking of long-lived molecules in the basement membranes such as collagens, thereby leading to “vascular stiffening” and processes that lead to hyperpermeability and loss of structural integrity. Second, AGEs interaction with their major cell surface signal transduction receptor for AGE or RAGE sets off a cascade of events leading to modulation of gene expression and loss of vascular and tissue homeostasis, processes that contribute to cardiovascular disease. In addition, it has been shown that an enzyme, which plays key roles in the detoxification of pre-AGE species, glyoxalase 1 (GLO1), is reduced in aged and diabetic tissues. In the diabetic kidney devoid of Ager (gene encoding RAGE), higher levels of Glo1 mRNA and GLO1 protein and activity were observed, suggesting that in conditions of high AGE accumulation, natural defenses may be mitigated, at least in part through RAGE. AGEs are a marker of arterial aging and may be detected by both biochemical means, as well as measurement of “skin autofluorescence.” In this review, we will detail the pathobiology of the AGE-RAGE axis and the consequences of its activation in the vasculature and conclude with potential avenues for therapeutic interruption of the AGE-RAGE ligand-RAGE pathways as means to forestall the deleterious consequences of AGE accumulation and signaling via RAGE.

Skin accumulation of advanced glycation end products is increased in patients with an abdominal aortic aneurysm

OBJECTIVE

Advanced glycation end products (AGEs) are implicated in the pathogenesis of cardiovascular disease. Accumulation of AGEs is driven by oxidative or glycemic stress and can be assessed by skin autofluorescence (SAF). SAF is increased in patients with peripheral artery disease (PAD) and independently associated with mortality and major adverse cardiovascular events in these patients. PAD and abdominal aortic aneurysm (AAA) share several risk factors. Inflammation is an important process in AAA formation and increases levels of oxidative stress. We therefore hypothesized that SAF would be increased in AAA patients compared with controls.

METHODS

A case-control study was performed in 248 AAA patients and 124 controls without AAA or PAD matched for age and presence of diabetes mellitus. SAF was noninvasively assessed with the AGE Reader (Diagnoptics Technologies BV, Groningen, The Netherlands).

RESULTS

SAF was higher in AAA patients than in controls: 2.89 ± 0.63 vs 2.68 ± 0.63 arbitrary units (P = .003). PAD comorbidity was associated with increased SAF within the AAA patient group (P = .01). After correction for known factors influencing SAF (age, current smoking, hypertension, and estimated glomerular filtration rate), PAD comorbidity remained an independent determinant of SAF. Logistic regression analysis of the total cohort showed an unadjusted odds ratio (OR) of 1.74 (95% confidence interval [CI], 1.20-2.51) for the presence of AAA with each unit increase of SAF and an adjusted OR of 1.78 (95% CI, 1.22-2.60) after correction for cardiovascular comorbidity (cerebrovascular disease and coronary artery disease). After additional correction for sex, current smoking, hypertension, and use of lipid-lowering drugs, this significance was lost (adjusted OR, 1.53; 95% CI, 0.94-2.48).

CONCLUSIONS

Skin accumulation of AGEs, measured by SAF, is increased in patients with AAA compared with controls without AAA or PAD, independent of the presence of coronary artery disease and cerebrovascular disease. In AAA patients, SAF is closely associated with the presence of PAD and cardiovascular risk factors.

Advanced Glycation End Products and Risks for Chronic Diseases: Intervening Through Lifestyle Modification

Advanced glycation end products (AGEs) are a family of compounds of diverse chemical nature that are the products of nonenzymatic reactions between reducing sugars and proteins, lipids, or nucleic acids. AGEs bind to one or more of their multiple receptors (RAGE) found on a variety of cell types and elicit an array of biologic responses. In this review, we have summarized the data on the nature of AGEs and issues associated with their measurements, their receptors, and changes in their expression under different physiologic and disease states. Last, we have used this information to prescribe lifestyle choices to modulate AGE-RAGE cycle for better health.

Skin autofluorescence, a non-invasive marker of advanced glycation end products: clinical relevance and limitations

Advanced glycation end products (AGEs) are protein-bound compounds derived from glycaemic and oxidative stress that contain fluorescent properties, which can be non-invasively measured as skin autofluorescence (SAF) by the AGE Reader. SAF has been demonstrated to be a biomarker of cumulative skin AGEs and potentially may be a better predictor for the development of chronic complications and mortality in diabetes than glycated haemoglobin A1c. However, there are several confounding factors that should be assessed prior to its broader application: these include presence of other fluorescent compounds in the skin that might be measured (eg, fluorophores), skin pigmentation and use of skin creams. The aim of this article is to provide a theoretical background of this newly developed method, evaluate its clinical relevance and discuss the potential confounding factors that need further analysis.

Effect of glycation inhibitors on aging and age-related diseases

Vast evidence supports the view that glycation of proteins is one of the main factors contributing to aging and is an important element of etiopathology of age-related diseases, especially type 2 diabetes mellitus, cataract and neurodegenerative diseases. Counteracting glycation can therefore be a means of increasing both the lifespan and healthspan. In this review, accumulation of glycation products during aging is presented, pathophysiological effects of glycation are discussed and ways of attenuation of the effects of glycation are described, concentrating on prevention of glycation. The effects of glycation and glycation inhibitors on the course of selected age-related diseases, such as Alzheimer's disease, Parkinson's disease and cataract are also reviewed.

Skin Autofluorescence is Associated with Early-stage Atherosclerosis in Patients with Type 1 Diabetes

AIM

Accumulation level of fluorescent advanced glycation end products (AGEs) in the skin can be measured non-invasively as skin autofluorescence (skin AF) by autofluorescence reader. The aim of this study was to assess possible associations between skin AF and diabetic complications, especially early-stage atherosclerosis, in Japanese type 1 diabetic patients.

METHODS

Skin AF was measured by AGE reader® in 105 Japanese type 1 diabetic patients (34 men and 71 women, aged 37.4±12.4 years (±SD)) and 23 age-matched healthy non-diabetic subjects. Ultrasonic carotid intima-media thickness (IMT), ankle-brachial index (ABI), and brachial ankle pulse wave velocity (baPWV) were evaluated as indices of early-stage diabetic macroangiopathy. Urinary albumin-to-creatinine ratio (UACR), the coefficient of variation of R-R intervals (CVR-R), and presence of retinopathy were also evaluated.

RESULTS

Skin AF values were significantly higher in type 1 diabetic patients than in healthy controls (2.07±0.50 (mean±SD) and 1.90±0.26, respectively, p=0.024). Skin AF was associated with carotid IMT (r=0.446, p＜0.001) and baPWV (r=0.450, p＜0.001), but not with ABI (r=－0.019, p=0.8488). Notably, skin AF was an independent risk factor for IMT thickening. Similarly, skin AF was associated with log (UACR) (r=0.194, p=0.049) and was an independent risk factor for UACR. Furthermore, skin AF values were significantly higher in patients with diabetic retinopathy than in those without (2.21±0.08 and 1.97±0.06, respectively, p=0.020).

CONCLUSIONS

Skin AF was significantly associated with the presence and/or severity of diabetic complications and was an independent risk factor for carotid atherosclerosis.

Association of Skin Autofluorescence Levels With Kidney Function Decline in Patients With Peripheral Artery Disease

Objective—

Skin autofluorescence (SAF), a measure of advanced glycation end product accumulation, is associated with kidney function. We investigated the association of SAF with rate of kidney function decline in a cohort of patients with peripheral artery disease.

Approach and Results—

We performed a post hoc analysis of an observational longitudinal cohort study. We included 471 patients with peripheral artery disease, and SAF was measured at baseline. Primary end point was rate of estimated glomerular filtration rate (eGFR) decline. Secondary end points were incidence of eGFR <60 and <45 mL/min/1.73 m 2 and rapid eGFR decline, defined as a decrease in eGFR of >5 mL/min/1.73 m 2 /y. During a median follow-up of 3 years, the mean change in eGFR per year was −1.8±4.4 mL/min/1.73 m 2 /y. No significant difference in rate of eGFR decline was observed per 1 arbitrary unit increase in SAF (−0.1 mL/min/1.73 m 2 /y; 95% confidence interval, −0.7 to 0.5; P =0.8). Analyses of the secondary end points showed that there was an association of SAF with incidence of eGFR <60 and <45 mL/min/1.73 m 2 (hazard ratio, 1.54; 95% confidence interval, 1.13–2.10; P =0.006 and hazard ratio, 1.76; 95% confidence interval, 1.20–2.59; P =0.004, respectively), but after adjustment for age and sex, significance was lost. There was no association of SAF with rapid eGFR decline.

Conclusions—

In conclusion, in this cohort of patients with peripheral artery disease, elevated SAF was associated with lower baseline eGFR. Although SAF has previously been established as a predictor for cardiovascular disease and mortality, it did not predict the rate of kidney function decline during follow-up in this study.

Cellular mechanisms and consequences of glycation in atherosclerosis and obesity

Post-translational modification of proteins imparts diversity to protein functions. The process of glycation represents a complex set of pathways that mediates advanced glycation endproduct (AGE) formation, detoxification, intracellular disposition, extracellular release, and induction of signal transduction. These processes modulate the response to hyperglycemia, obesity, aging, inflammation, and renal failure, in which AGE formation and accumulation is facilitated. It has been shown that endogenous anti-AGE protective mechanisms are thwarted in chronic disease, thereby amplifying accumulation and detrimental cellular actions of these species. Atop these considerations, receptor for advanced glycation endproducts (RAGE)-mediated pathways downregulate expression and activity of the key anti-AGE detoxification enzyme, glyoxalase-1 (GLO1), thereby setting in motion an interminable feed-forward loop in which AGE-mediated cellular perturbation is not readily extinguished. In this review, we consider recent work in the field highlighting roles for glycation in obesity and atherosclerosis and discuss emerging strategies to block the adverse consequences of AGEs. This article is part of a Special Issue entitled: The role of post-translational protein modifications on heart and vascular metabolism edited by Jason R.B. Dyck & Jan F.C. Glatz.

Skin collagen fluorophore LW-1 versus skin fluorescence as markers for the long-term progression of subclinical macrovascular disease in type 1 diabetes

BACKGROUND

Skin collagen Long Wavelength Fluorescence (LWF) is widely used as a surrogate marker for accumulation of advanced glycation end-products. Here we determined the relationship of LWF with glycemia, skin fluorescence, and the progression of complications during EDIC in 216 participants from the DCCT.

METHODS

LW-1 and collagen-linked fluorescence (CLF) were measured by either High Performance Liquid Chromatography (HPLC) with fluorescence detection (LW-1) or total fluorescence of collagenase digests (CLF) in insoluble skin collagen extracted from skin biopsies obtained at the end of the DCCT (1993). Skin intrinsic fluorescence (SIF) was noninvasively measured on volar forearm skin at EDIC year 16 by the SCOUT DS instrument.

RESULTS

LW-1 levels significantly increased with age and diabetes duration (P < 0.0001) and significantly decreased by intensive vs. conventional glycemic therapy in both the primary (P < 0.0001) and secondary (P < 0.037) DCCT cohorts. Levels were associated with 13-16 year progression risk of retinopathy (>3 sustained microaneurysms, P = 0.0004) and albumin excretion rate (P = 0.0038), the latter despite adjustment for HbA1c. Comparative analysis for all three fluorescent measures for future risk of subclinical macrovascular disease revealed the following significant (P < 0.05) associations after adjusting for age, diabetes duration and HbA1c: coronary artery calcium with SIF and CLF; intima-media thickness with SIF and LW-1; and left ventricular mass with LW-1 and CLF.

CONCLUSIONS

LW-1 is a novel risk marker that is robustly and independently associated with the future progression of microvascular disease, intima-media thickness and left ventricular mass in type 1 diabetes. Trial registration NCT00360815 and NCT00360893 at clinicaltrials.gov.

Skin Autofluorescence Is Associated with Endothelial Dysfunction in Uremic Subjects on Hemodialysis

BACKGROUND

Elevated levels of advanced glycation end products (AGEs) within tissues may contribute to endothelial dysfunction, an early indicator of atherosclerosis. We aimed to investigate whether levels of skin AGEs could be a useful marker to predict endothelial dysfunction in uremic subjects on hemodialysis.

METHODS AND RESULTS

One hundred and nineteen uremic patients on hemodialysis and 57 control subjects with moderate-to-high cardiovascular risk factors and without chronic kidney disease (CKD) were enrolled. We used ultrasound to measure flow-mediated vasodilation (FMD). An AGE reader measured skin autoflurorescence (AF). We then compared differences in FMD and skin AF values between the two groups. The uremic subjects had significantly higher levels of skin AF (3.47±0.76 AU vs. 2.21±0.45 arbitrary units; P<0.01) and significantly lower levels of FMD (4.79%±1.88% vs. 7.19%±2.17%; P<0.01) than the non-CKD subjects. After adjusting for all potential covariates, we found that skin AF level independently predicted FMD in both the hemodialysis and the non-CKD groups. In the hemodialysis group, skin AF ≥ 3.05 arbitrary units predicted abnormal FMD at a sensitivity of 87.9% and a specificity of 78.6% (P<0.01).

CONCLUSIONS

Skin AF could be a useful marker to predict endothelial dysfunction in uremic subjects on hemodialysis.

Skin autofluorescence as a measure of advanced glycation end products deposition predicts 5-year amputation in patients with peripheral artery disease

OBJECTIVE

Patients with peripheral artery disease are at risk for critical limb ischemia and amputation. Accumulation of advanced glycation end products is increased and predictive for coronary and cerebrovascular events in several high cardiovascular risk groups. We hypothesized that accumulation of tissue advanced glycation end products, measured by skin autofluorescence (SAF), predicts amputation in patients with peripheral artery disease.

APPROACH AND RESULTS

Between October 2007 and June 2008, 252 patients with peripheral artery disease were included at the outpatient clinic. During a 5-year follow-up, 22 (9%) had an amputation because of critical limb ischemia. Competing risks regression analysis showed a subproportional hazard ratio of 3.05 (95% confidence interval [CI], 1.87-4.96); P<0.0001 for amputation per unit incease of SAF. After correction for diabetes mellitus and Fontaine stage, subproportional hazard ratio was 2.72 (95% CI, 1.38-5.39); P=0.004. In patients with Fontaine stage I and II only (n=215), SAF was the only predictor for amputation, subproportional hazard ratio 4.05 (95% CI, 2.09-7.83); P<0.0001. Fontaine stage multiplied by SAF resulted in a significant increase of the area under the curve for prediction of amputation when compared with Fontaine stage only: area under the curve increased from 0.74 (95% CI, 0.63-0.86) to 0.83 (95% CI, 0.74-0.92); P=0.003.

CONCLUSIONS

Skin autofluorescence, as a measure of tissue advanced glycation end products deposition, predicts amputation in patients with peripheral artery disease during a 5-year follow-up, independent from the presence of diabetes mellitus and Fontaine stage. Even at lower Fontaine stage (I or II), SAF is a strong predictor of amputation. The multiplication of Fontaine stage by SAF results in a good prediction model of amputation.

Skin Autofluorescence - A Non-invasive Measurement for Assessing Cardiovascular Risk and Risk of Diabetes

The results of the Diabetes Control and Complications Trial-Epidemiology of Diabetes Interventions and Complications (DCCT-EDIC) study have strengthened the 'glycaemic memory' concept, postulating that the quality of metabolic control over several years predicts the development of diabetic complications. To mirror long-term metabolic control, the degree of glycated haemoglobin (HbA_1c) might not represent the optimal biomarker. Other substances with a longer persistence, like the so-called advanced glycation end-products (AGEs), which probably form the substrate of the glycaemic memory, might perform better. Newly developed methods such as the assessment of skin autofluorescence (SAF), enable fast, uncomplicated and non-invasive AGEs assessment. SAF was validated for diabetes screening and shows a good predictive value for the development of diabetic and cardiovascular complications. This article deals with the theoretical background and with available clinical data on this new variable.

Reference values of skin autofluorescence as an estimation of tissue accumulation of advanced glycation end products in a general Slovak population

AIMS

For decades, Slovakia has maintained a prominent place in mortality rates from cardiovascular diseases among European Union (EU-27) countries. Determination of skin autofluorescence serves as an estimate of tissue accumulation of advanced glycation end products--substances accumulating in tissues and body fluids that play a pathophysiological role in age-related diseases and their complications, such as diabetes.

METHODS

In 1385 apparently healthy Slovakian subjects aged from a few days old to 77 years, skin autofluorescence was determined using an advanced glycation end product reader and compared with reference data from Dutch Caucasians. The impact of the weekly frequency of recreational physical exercise on skin autofluorescence was investigated in the adults, and the impact of feeding regimen in the infants.

RESULTS

With the exception of 10- to 19-year-olds, Slovaks had lower skin autofluorescence values in comparison with the Dutch Caucasians. In healthy non-smokers, physical exercise for > 30 min/day performed ≥ 3 times/week was associated with lower skin autofluorescence levels. In infants, breastfeeding (advanced glycation end product-poor diet) was associated with lower skin autofluorescence levels in comparison with consumption of infant formulas (advanced glycation end product-rich diet).

CONCLUSIONS

Reference ranges of skin autofluorescence in Slovak Caucasians, detailed for paediatric age groups, are provided. Our data show that, in healthy adults, regular physical exercise associates with lower skin autofluorescence. Infants fed or weaned from infant formulas (advanced glycation end product-rich diet) have higher skin autofluorescence than their breast milk-consuming counterparts. It is unclear why Slovaks have lower skin autofluorescence compared with a Dutch population with lower cardiovascular mortality rates. Reference data on skin autofluorescence from diverse populations are needed for the precise clinical interpretation of skin autofluorescence measurements.

Skin autofluorescence is associated with 5-year mortality and cardiovascular events in patients with peripheral artery disease

OBJECTIVE

Advanced glycation end products play a pivotal role in atherosclerosis. Recently, we showed that tissue advanced glycation end products deposition, noninvasively assessed by skin autofluorescence (SAF), is increased in patients with peripheral artery disease. The aim of the present study was to establish whether SAF is associated with all-cause mortality and with fatal or nonfatal major adverse cardiovascular events (MACE) in patients with peripheral artery disease.

APPROACH AND RESULTS

We performed a single-center prospective cohort study of 252 patients with peripheral artery disease (mean age, 66±11 years), recruited from the outpatient clinic (October 2007 to June 2008) who were followed until June 2013. SAF was measured with the AGE Reader. The primary end point was all-cause mortality, and the secondary end point was fatal or nonfatal MACE, defined as cardiovascular death and nonfatal myocardial infarction or stroke. During a median follow-up of 5.1 (interquartile range, 5.0-5.3) years, 62 (25%) patients died. Fatal or nonfatal MACE occurred in 62 (25%) patients. A higher SAF was associated with increased risk for all-cause mortality (hazard ratio per unit increase, 2.01; 95% confidence interval, 1.40-2.88; P=0.0002) and fatal or nonfatal MACE (hazard ratio, 1.82; 95% confidence interval, 1.28-2.60; P=0.001), also after adjustment for cardiovascular risk factors and the use of lipid-lowering drugs (hazard ratio, 1.63; 95% confidence interval, 1.13-2.34; P=0.009 and hazard ratio, 1.50; 95% confidence interval, 1.04-2.17; P=0.03, for all-cause mortality and fatal and nonfatal MACE, respectively).

CONCLUSIONS

SAF as a measure of advanced glycation end products deposition is independently associated with all-cause mortality and fatal or nonfatal MACE in patients with peripheral artery disease after a 5-year follow-up.

Skin autofluorescence, a non-invasive marker for AGE accumulation, is associated with the degree of atherosclerosis

Introduction

Advanced glycation endproducts (AGEs) may be involved in the development of atherosclerosis, beyond diabetes and renal disease. Skin autofluorescence (AF) is a non-invasive marker for AGEs. We examined whether skin AF is increased in (subclinical) atherosclerosis and associated with the degree of atherosclerosis independent of diabetes and renal function.

Methods

A cross-sectional study of 223 patients referred for primary (n = 163) or secondary (n = 60) prevention between 2006 and 2012 was performed. Skin AF was measured using the AGE-Reader. Ultrasonography was used to assess plaques in carotid and femoral arteries and computed tomography for the calculation of the coronary artery calcium score (CACS; in primary prevention only). Primary prevention patients were divided into a group with subclinical atherosclerosis defined as >1 plaque or CACS>100 (n = 67; age 53 year [interquartile range 48–56]; 49% male) and without (controls; 96; 43 [38–51]; 55%). Secondary prevention were patients with peripheral arterial disease (60; 64 [58–70]; 73%).

Results

Skin AF was higher in subclinical and clinical atherosclerosis compared with controls (skin AF 2.11 [interquartile range 1.83–2.46] and 2.71 [2.15–3.27] vs. 1.87 [1.68–2.12] respectively; P = 0.005 and <0.001). In a multivariate analysis, the association of skin AF with the atherosclerosis categories was independent of age, sex, diabetes, presence of the metabolic syndrome, Framingham Risk Score, and renal function. Skin AF correlated with most cardiovascular risk factors, Framingham risk score, and IMT and CACS.

Conclusions

Skin AF is increased in documented subclinical and clinical atherosclerosis, independent of known risk factors such as diabetes and renal disease. These data suggest that AGEs may be associated with the burden of atherosclerosis and warrant a prospective study to investigate its clinical usability as a risk assessment tool for primary prevention.

Vascular effects of advanced glycation endproducts: Clinical effects and molecular mechanisms

The enhanced generation and accumulation of advanced glycation endproducts (AGEs) have been linked to increased risk for macrovascular and microvascular complications associated with diabetes mellitus. AGEs result from the nonenzymatic reaction of reducing sugars with proteins, lipids, and nucleic acids, potentially altering their function by disrupting molecular conformation, promoting cross-linking, altering enzyme activity, reducing their clearance, and impairing receptor recognition. AGEs may also activate specific receptors, like the receptor for AGEs (RAGE), which is present on the surface of all cells relevant to atherosclerotic processes, triggering oxidative stress, inflammation and apoptosis. Understanding the pathogenic mechanisms of AGEs is paramount to develop strategies against diabetic and cardiovascular complications.

The AGE-RAGE pathway and its relation to cardiovascular disease in patients with chronic kidney disease

Chronic kidney disease (CKD) carries an unequivocal high risk for cardiovascular disease (CVD) contributing to high morbimortality; however, the underlying reasons are not fully known. Among mechanisms involved in the pathophysiology of CVD, chronic overstimulation of the advanced glycation end-products (AGE)-receptor for AGE (RAGE) pathway is likely a major contributor in patients with CKD. This review describes briefly some of the components of this pathway, highlighting especially differences between circulating AGE and tissue AGE and how activation of the AGE-RAGE pathway may promote CVD in CKD.

Variability of skin autofluorescence measurement over 6 and 12 weeks and the influence of benfotiamine treatment

BACKGROUND

Measurements of skin autofluorescence (SAF) allow for a simple and noninvasive quantification of tissue advanced glycation end-products (AGEs), a marker linked to the risk of diabetes complications. The aim of this study was to test the repeatability of SAF over 6 and 12 weeks and to test whether benfotiamine, a thiamine prodrug suggested to reduce AGEs formation under hyperglycemic conditions, is able to attenuate SAF when administered over 6 weeks.

PATIENTS AND METHODS

In a double-blind, placebo-controlled, randomized, crossover study, 22 patients with type 2 diabetes mellitus (T2DM) received 900 mg/day benfotiamine or placebo for 6 weeks (washout period of 6 weeks between). At the beginning and at the end of each treatment period, SAF was assessed in the fasting state, as well as 2, 4, and 6 h following a mixed test meal.

RESULTS

The respective intra-individual and inter-individual variability of fasting SAF was 6.9% and 24.5% within 6 weeks and 10.9% and 23.1% within 12 weeks. The respective variability calculated for triplicate comparisons was 9.9% and 27.7%. A short-term therapy with benfotiamine did not influence SAF significantly, nor did we find a significant postprandial SAF increase.

CONCLUSIONS

In patients with T2DM, repeated, timely spaced SAF measurements have an intra-subject variability of below 11%. Using these data, sample sizes were calculated for interventional studies aiming at reducing SAF. Benfotiamine treatment for 6 weeks did not significantly influence SAF; for this, a longer-term therapy is probably needed.

Skin Autofluorescence as a Measure of Advanced Glycation End Products Deposition Is Elevated in Peripheral Artery Disease

Objective—

Evidence for an important role of advanced glycation end products (AGEs) in the development of atherosclerosis and cardiovascular disease beyond diabetes mellitus and renal disease is growing. Skin autofluorescence (SAF) is a validated noninvasive measure of tissue AGEs. We hypothesized that SAF is elevated in peripheral artery disease (PAD).

Methods and Results—

A case–control study was performed in 492 patients with PAD and 164 controls, matched for age (mean 66±10 years) and presence of diabetes mellitus. Cardiovascular risk factors and comorbidity (coronary artery disease, cerebrovascular disease, abdominal aortic aneurysm) were assessed. SAF was measured with the AGE Reader. SAF was higher in patients compared with controls: geometric mean 2.77 (95% confidence interval [CI], 2.71–2.83) versus 2.44 (95% CI, 2.35–2.53) arbitrary units, P =0.4×10 −8 . In logistic regression, the adjusted odds ratio for the presence of PAD was 2.47 (95% CI, 1.66–3.69) per 1 unit increase of SAF. PAD patients with cardiovascular comorbidity had a higher SAF compared with those without: geometric mean 2.93 (95% CI, 2.85–3.02) versus 2.63 (95% CI, 2.55–2.71) arbitrary units, P =0.4×10 −6 , also after correction for confounders. Regression analysis showed that age, smoking, diabetes mellitus, chronic kidney disease, and a history of cerebrovascular disease or abdominal aortic aneurysm were independently associated with SAF in the patients with PAD.

Conclusion—

Accumulation of tissue AGEs is increased in patients with PAD, independent of cardiovascular risk factors and comorbidity, although these conditions are associated with a further increase. These findings underscore the importance of AGEs in PAD, irrespective of the presence of diabetes mellitus and renal insufficiency.

Skin autofluorescence and the association with renal and cardiovascular risk factors in chronic kidney disease stage 3

BACKGROUND AND OBJECTIVES

Tissue advanced glycation end products (AGE) accumulation is a measure of cumulative metabolic stress. Assessment of tissue AGE by skin autofluorescence (SAF) correlates well with cardiovascular (CV) outcomes in diabetic, transplant, and dialysis patients, and may be a useful marker of CV risk in earlier stages of chronic kidney disease (CKD).

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

1707 patients with estimated GFR 59 to 30 ml/min per 1.73 m(2) were recruited from primary care practices for the Renal Risk In Derby (RRID) study. Detailed medical history was obtained, and each participant underwent clinical assessment as well as urine and serum biochemistry tests. SAF was assessed (mean of three readings) as a measure of skin AGE deposition using a cutaneous AF device (AGE Reader™, DiagnOptics, Groningen, The Netherlands).

RESULTS

Univariate analysis revealed significant correlations between AF readings and several potential risk factors for cardiovascular disease (CVD) and progression of CKD. SAF readings (arbitrary units) were also significantly higher among males (2.8 ± 0.7 versus 2.7 ± 0.6), diabetics (3.0 ± 0.7 versus 2.7 ± 0.6), patients with evidence of self-reported CVD (2.9 ± 0.7 versus 2.7 ± 0.6), and those with no formal educational qualifications (2.8 ± 0.6 versus 2.6 ± 0.6; P < 0.01 for all). Multivariable linear regression analysis identified hemoglobin, diabetes, age, and eGFR as the most significant independent determinants of higher SAF (standardized coefficients -0.16, 0.13, 0.12, and -0.10, respectively; R(2) = 0.17 for equation).

CONCLUSION

Increased SAF is independently associated with multiple CV and renal risk factors in CKD 3. Long-term follow-up will assess the value of SAF as a predictor of CV and renal risk in this population.