Skin-autofluorescence is an independent predictor of graft loss in renal transplant recipients

Role of skin autofluorescence in managing renal and cardiac diseases in outpatient dermatology

INTRODUCTION

The accumulation of tissue-advanced glycation end products in skin results from complex and consecutive reactions and can be measured by skin autofluorescence (SAF) reader devices. This overview discusses studies evaluating the utilization of SAF in screening renal and cardiac disease.

MATERIALS AND METHODS

Literature search was performed using Google Scholar, PubMed, Springer, Ovid, and ScienceDirect.

RESULTS

SAF was an independent predictor of progression of chronic kidney disease (CKD) and was elevated in subjects on hemodialysis and peritoneal dialysis. Furthermore, SAF was significantly associated with cardiovascular events, cardiovascular mortality, and all-cause mortality in CKD patients. Other studies revealed a correlation between SAF and arterial stiffness, vascular damage, and subclinical atherosclerosis. A vegetarian diet was associated with lower SAF levels, whereas malnutrition was correlated with higher levels and increased mortality.

CONCLUSIONS

SAF measurement may be useful in managing renal and cardiac disease. Future studies are needed to clarify the specific role of SAF in the management of CKD and its noninvasive office utilization to identify comorbidities in inflammatory diseases, such as psoriasis.

Methylglyoxal and Its Adducts: Induction, Repair, and Association with Disease

Metabolism is an essential part of life that provides energy for cell growth. During metabolic flux, reactive electrophiles are produced that covalently modify macromolecules, leading to detrimental cellular effects. Methylglyoxal (MG) is an abundant electrophile formed from lipid, protein, and glucose metabolism at intracellular levels of 1-4 μM. MG covalently modifies DNA, RNA, and protein, forming advanced glycation end products (MG-AGEs). MG and MG-AGEs are associated with the onset and progression of many pathologies including diabetes, cancer, and liver and kidney disease. Regulating MG and MG-AGEs is a potential strategy to prevent disease, and they may also have utility as biomarkers to predict disease risk, onset, and progression. Here, we review recent advances and knowledge surrounding MG, including its production and elimination, mechanisms of MG-AGEs formation, the physiological impact of MG and MG-AGEs in disease onset and progression, and the latter in the context of its receptor RAGE. We also discuss methods for measuring MG and MG-AGEs and their clinical application as prognostic biomarkers to allow for early detection and intervention prior to disease onset. Finally, we consider relevant clinical applications and current therapeutic strategies aimed at targeting MG, MG-AGEs, and RAGE to ultimately improve patient outcomes.

Role of Advanced Glycation Endproduct (AGE)-Receptor for Advanced Glycation Endproduct (RAGE) Axis in Cardiovascular Disease and Its Therapeutic Intervention

Despite the early loss of glycemic differences between the original intensive therapy group and conventional treatment in the DCCT/EDIC and UKPDS 80 trials, a continued reduction in microvascular risk and risk reductions for emergency myocardial infarction and all-cause death were observed 10-30 years after the end of these trials. These observations demonstrated that so-called "metabolic memory" could cause chronic abnormalities in diabetic vessels that are not easily reversed, even by subsequent improvement in blood glucose levels, thus suggesting a long-term beneficial influence of early metabolic control; that is, legacy effects on the risk of vascular complications and death in patients with both type 1 and type 2 diabetes. Formation and accumulation of advanced glycation endproducts (AGEs) are known to progress at an accelerated rate under diabetes. Furthermore, AGEs are hardly degraded and remain for a long time in diabetic vessels even after glycemic control is improved. Therefore, AGEs could explain why former cumulative diabetic exposure could contribute to current progression of vascular complications in diabetes. Here, the clinical utility of measurement of serum and tissue accumulation levels of AGEs for evaluating the prevalence and severity of numerous types of cardiovascular disease is reviewed and novel therapeutic strategies that could target the AGE-RAGE axis in CVD are discussed.

Advanced glycation end products (AGEs) estimated by skin autofluorescence are related with cardiovascular risk in renal transplant

Background

Advanced glycation end products (AGEs) accumulation, a measure of cumulative metabolic stress, constitute a novel pathogenic mechanism involved in aging, diabetes, cardiovascular (CVD) and chronic kidney disease (CKD). Despite removal of uremic toxins and AGEs after a successful renal transplant (RT), CVD remains the leading cause of mortality. We hypothesized that AGEs measurement by Skin Autofluorescence (SAF) might be useful even after a successful RT and thus reflect the high cardiovascular risk burden of these patients.

Methods

189 stable RT (61% men, aged 56±13.0 years), CKD stages 1–4 and >12 months since RT were enrolled. Variables collected comprised comorbid history, medication use, smoking habit, routine biochemistry, subclinical atheromatosis by ankle-brachial-index (ABI) and allograft resistivity index (RI), 24-h ABPM, anthropometry and handgrip strength. AGEs were measured by SAF and expressed in arbitrary units (AU). Vascular age was estimated by Koetsier´s formula (SAF-0.83/0.024) and expected 10-years cardiovascular death risk was calculated with the REGICOR score.

Results

Mean SAF was 3.00±0.83 AU and estimated vascular age 90±34.7 years (30 years above biological age). SAF was higher among men (3.10±0.91 vs 2.81±0.66), diabetic nephropathy (3.49±0.75 vs 2.96±0.83) and steroid users (3.14±0.86 vs 2.71±0.69). We observed a positive correlation of SAF with night-systolic blood pressure (r = 0.25, p = 0.001), parathormone (r = 0.20, p<0.01), phosphate (r = 0.28, p<0.001) and negative with hemoglobin (r = -0.29, p<0.001), CKD-EPI (r = -0.32, p<0.001), albumin (r = -0.17, p<0.05), and dynamometry (r = -0.20, p<0.01). Subclinical vascular atheromatosis (ABI and RI) as well as the REGICOR scale (r = 0.35 p<0.001) were also correlated with SAF. In multivariable analysis age, gender, steroid use, serum phosphate and handgrip strength remained independently associated with SAF.

Conclusions

SAF levels are elevated in RT patients and correlate with CVD risk. Besides age and male sex, our results suggest that phosphate overload, steroid use and nutritional status are important factors linking to AGEs accumulation.

A new gender-specific model for skin autofluorescence risk stratification

Advanced glycation endproducts (AGEs) are believed to play a significant role in the pathophysiology of a variety of diseases including diabetes and cardiovascular diseases. Non-invasive skin autofluorescence (SAF) measurement serves as a proxy for tissue accumulation of AGEs. We assessed reference SAF and skin reflectance (SR) values in a Saudi population (n = 1,999) and evaluated the existing risk stratification scale. The mean SAF of the study cohort was 2.06 (SD = 0.57) arbitrary units (AU), which is considerably higher than the values reported for other populations. We show a previously unreported and significant difference in SAF values between men and women, with median (range) values of 1.77 AU (0.79-4.84 AU) and 2.20 AU (0.75-4.59 AU) respectively (p-value « 0.01). Age, presence of diabetes and BMI were the most influential variables in determining SAF values in men, whilst in female participants, SR was also highly correlated with SAF. Diabetes, hypertension and obesity all showed strong association with SAF, particularly when gender differences were taken into account. We propose an adjusted, gender-specific disease risk stratification scheme for Middle Eastern populations. SAF is a potentially valuable clinical screening tool for cardiovascular risk assessment but risk scores should take gender and ethnicity into consideration for accurate diagnosis.

Skin autofluorescence as a novel marker of vascular damage in children and adolescents with chronic kidney disease

BACKGROUND

Skin autofluorescence (sAF) was examined as a marker of the accumulation of advanced glycation end products (AGEs) in tissues of children with chronic kidney disease (CKD) in relation to renal function, dialysis modality and markers of endothelial inflammation and dysfunction.

METHODS

A total of 76 children with CKD were enrolled in the study, of whom 20 children were on hemodialysis (HD), 20 were on peritoneal dialysis (PD) and 36 were treated conservatively. A control group of 26 healthy subjects was also included in the study. In all children, sAF intensity, carotid intima-media (cIMT) thickness and plasma concentrations of sE-selectin, matrix metalloproteinase 9 (MMP-9), tissue inhibitor of metalloproteinase 1 (TIMP-1), asymmetric dimethylarginine (ADMA), symmetric dimethylarginine (SDMA) and plasminogen activator inhibitor type 1 (PAI-1) were measured.

RESULTS

Compared to the controls, children with CKD had significantly elevated sAF levels. sAF in the children with CKD was positively correlated with sE-selectin, MMP-9, TIMP-1, ADMA, SDMA and PAI-1 levels. In the predialysis group (conservative treatment) sAF levels were positively correlated with sE-selectin and ADMA levels and negatively correlated with glomerular filtration rate. Multiple regression analysis showed a significant association of sAF with sE-selectin and MMP-9 in CKD children.

CONCLUSIONS

The results reveal that AGEs were accumulated in the children with CKD. This accumulation was related to early vascular changes and a number of biochemical vascular risk markers. sAF measurement, as a noninvasive method, may be useful for identification of clinical risk factors of vascular disease in CKD children.

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.

Tissue advanced glycation end product deposition after kidney transplantation

BACKGROUND

Tissue advanced glycation end products (AGEs) accumulate in chronic kidney disease (CKD) and are a measure of cumulative metabolic stress. Measurement of tissue AGEs by skin autofluorescence (SAF) correlates well with cardiovascular outcomes in dialysis patients. SAF levels in transplant recipients relative to CKD and dialysis patients have not been previously studied, and the impact of transplantation on SAF levels in dialysis patients is unknown.

METHODS

SAF was measured using an AGE reader in 66 patients who had received a kidney transplant. Values were compared to those obtained in 1,707 patients with CKD stage 3 and in 115 patients on dialysis.

RESULTS

Mean SAF in transplant recipients [2.81 ± 0.64 arbitrary units (AU)] was significantly lower than in patients on haemodialysis (3.73 ± 0.88 AU) and peritoneal dialysis (3.57 ± 0.75 AU; p < 0.001), but was no different from CKD stage 3 (2.79 ± 0.66 AU; p = 0.42). In the transplant group, SAF correlated most strongly with age (r = 0.316). There was no correlation between SAF and estimated glomerular filtration rate or renal replacement therapy vintage. A small cohort of patients with SAF recorded on dialysis and following transplantation showed a drop in SAF over a mean time of 16 months after transplantation.

DISCUSSION

Tissue AGE values in kidney transplant recipients are significantly lower than in patients receiving dialysis and similar to those in patients with CKD stage 3. Our data suggest that transplantation may be associated with a reduction in tissue AGEs, and this might be an important component of the observed reduction in cardiovascular risk in transplant recipients compared to patients on dialysis.

Advanced glycation end-products, a pathophysiological pathway in the cardiorenal syndrome

The prevalence of heart failure (HF) is increasing. A distinction is made between diastolic HF (preserved left ventricular ejection fraction (LVEF)) and systolic HF (reduced LVEF). Advanced glycation end-products (AGEs) are crystallized proteins that accumulate during ageing, but are particularly increased in patients with diabetes mellitus and in patients with renal failure. Through the formation of collagen crosslinks, and by interaction with the AGE-receptor, which impairs calcium handling and increases fibrosis, AGE-accumulation has pathophysiologically been associated with the development of diastolic and renal dysfunction. Interestingly, diastolic dysfunction is a frequent finding in elderly patients, diabetic patients and in patients with renal failure. Taken together, this suggests that AGEs are related to the development and progression of diastolic HF and renal failure. In this review, the role of AGEs as a possible pathophysiological factor that link the development and progression of heart and renal failure, is discussed. Finally, the role of AGE intervention as a possible treatment in HF patients will be discussed.

Determinants of arterial stiffness in chronic kidney disease stage 3

BACKGROUND

Early chronic kidney disease (CKD) is associated with increased cardiovascular (CV) risk but underlying mechanisms remain uncertain. Arterial stiffness (AS) is associated with increased CV risk in advanced CKD, but it is unclear whether AS is relevant to CV disease (CVD) in early CKD.

STUDY DESIGN

Cross-sectional.

SETTING AND PARTICIPANTS

1717 patients with previous estimated glomerular filtration rate (eGFR) 59-30 mL/min/1.73 m(2); mean age 73±9y, were recruited from 32 general practices in primary care.

OUTCOMES

Increased arterial stiffness.

MEASUREMENTS

Medical history was obtained and participants underwent clinical assessment, urine and serum biochemistry testing. Carotid to femoral pulse wave velocity (PWV) was determined as a measure of AS, using a Vicorder™ device.

RESULTS

Univariate analysis revealed significant correlations between PWV and risk factors for CVD including age (r = 0.456; p<0.001), mean arterial pressure (MAP) (r = 0.228; p<0.001), body mass index (r = -0.122; p<0.001), log urinary albumin to creatinine ratio (r = 0.124; p<0.001), Waist to Hip ratio (r = 0.124, p<0.001), eGFR (r = -0.074; p = 0.002), log high sensitivity c-reactive protein (r = 0.066; p = 0.006), HDL (r = -0.062; p = 0.01) and total cholesterol (r = -0.057; p = 0.02). PWV was higher in males (9.6 m/sec vs.10.3 m/sec; p<0.001), diabetics (9.8 m/sec vs. 10.3 m/sec; p<0.001), and those with previous CV events (CVE) (9.8 m/s vs. 10.3 m/sec; p<0.001). Multivariable analysis identified age, MAP and diabetes as strongest independent determinants of higher PWV (adjusted R² = 0.29). An interactive term indicated that PWV increased to a greater extent with age in males versus females. Albuminuria was a weaker determinant of PWV and eGFR did not enter the model.

LIMITATIONS

Data derived from one study visit, with absence of normal controls.

CONCLUSION

In this cohort, age and traditional CV risk factors were the strongest determinants of AS. Albuminuria was a relatively weak determinant of AS and eGFR was not an independent determinant. Long-term follow-up will investigate AS as an independent risk factor for CVE in this cohort.

Skin autofluorescence as a marker of cardiovascular risk in children with chronic kidney disease

BACKGROUND

We examined skin autofluorescence (sAF) in chronic kidney disease children (CKD) in relation to renal function and dialysis modality.

METHODS

Twenty children on hemodialysis (HD), 20 on peritoneal dialysis (PD), 36 treated conservatively, and 26 healthy subjects were enrolled into the study. In all children sAF, pulse-wave velocity indexed to height (PWV/ht), left ventricular mass index (LVMI), blood pressure (BP), serum lipid profile, phosphate (P), calcium (Ca), and homocysteine were measured.

RESULTS

sAF was significantly elevated in CKD groups vs. controls and was significantly associated with PWV/ht, LVMI, BP, P, Ca × P product and homocysteine. sAF in HD and PD groups was positively correlated with dialysis vintage, and in the predialysis group negatively correlated with glomerular filtration rate (eGFR). Multiple regression analysis showed significant association of sAF with LVMI and P in the CKD patient group, and with dialysis treatment duration and BP in dialyzed children.

CONCLUSIONS

In CKD children, tissue accumulation of advanced glycation end-products (AGEs) was observed. This was aggravated as eGFR declined and was related to early cardiovascular changes and some biochemical cardiovascular disease (CVD) risk markers. sAF as a non-invasive method may be a useful tool for identification of a clinical risk factors of cardiovascular disease in CKD children.

Increased skin autofluorescence after colorectal operation reflects surgical stress and postoperative outcome

BACKGROUND

Abdominal surgery is a major oxidative stress effector. The increase in oxidative stress has been related to postoperative complications. Oxidative stress leads to the formation and accumulation of oxidation protein end products, which exhibit autofluorescence (AF) and induce inflammatory reactions.

METHODS

Skin AF was assessed perioperatively in 40 consecutive colorectal surgery patients until discharge. Duration of surgery, estimated blood loss, and urinary production per hour were analyzed as measures of surgical stress. The clinical occurrence of anastomotic leakage, systemic infections, and cardiopulmonary complications within 30 days of surgery were analyzed.

RESULTS

A perioperative increase in skin AF of 19 ± .2% was observed. Duration of operation and blood loss were independently associated with the perioperative increase in skin AF. Skin AF correlated with C-reactive protein levels postoperatively. American Society of Anesthesiologists classification, duration of operation, and preoperative and perioperative increases in AF were independently associated with postoperative complications.

CONCLUSIONS

This is the first study to demonstrate an association between skin AF and surgical stress and outcomes, which may rate the condition of a patient after operation.

Skin autofluorescence as a measure of advanced glycation endproduct deposition: a novel risk marker in chronic kidney disease

PURPOSE OF REVIEW

Skin autofluorescence (SAF) is a new method to noninvasively assess accumulation of advanced glycation endproducts (AGEs) in a tissue with low turnover. Recent progress in the clinical application of SAF as a risk marker for diabetic nephropathy as well as cardiovascular disease in nondiabetic end-stage kidney disease, less advanced chronic kidney disease, and renal transplant recipients is reviewed.

RECENT FINDINGS

Experimental studies highlight the fundamental role of the interaction of AGEs with the receptor for AGEs (RAGEs), also called the AGE-RAGE axis, in the pathogenesis of vascular and chronic kidney disease. SAF predicts (cardiovascular) mortality in renal failure and also chronic renal transplant dysfunction. Long-term follow-up results from the Diabetes Control and Complications Trial and UK Prospective Diabetes Study suggest that AGE accumulation is a key carrier of metabolic memory and oxidative stress. Short-term intervention studies in diabetic nephropathy with thiamine, benfotiamine and angiotensin-receptor blockers aimed at reducing AGE formation have reported mixed results.

SUMMARY

SAF is a noninvasive marker of AGE accumulation in a tissue with low turnover, and thereby of metabolic memory and oxidative stress. SAF independently predicts cardiovascular and renal risk in diabetes, as well as in chronic kidney disease. Further long-term studies are required to assess the potential benefits of interventions to reduce AGE accumulation.

Reference values of skin autofluorescence

BACKGROUND

Skin autofluorescence (AF) as measured with the AGE Reader (DiagnOptics Technologies, Groningen, The Netherlands) is a noninvasive prognostic marker in diabetes mellitus and other diseases with increased cardiovascular risk. This study provides reference values of healthy Caucasian control subjects as a function of age, tobacco smoking, and gender.

METHODS

The results of skin AF measured in 428 healthy Caucasian control subjects by the AGE Reader (n = 211) and its nonautomated but otherwise similar predecessor, the Autofluorescence Reader (n = 217), were analyzed. Linear regression analysis was performed to obtain reference values for skin AF as a function of age. Further analysis was performed on the effect of tobacco smoking (n = 96) and gender.

RESULTS

Skin AF was described by a linear increase with age of approximately 0.023 arbitrary units (AU) per year for subject age up to 70 years. Tobacco smoking was associated with an absolute increase of skin AF by 0.16 AU (P < 0.01), without a significant further increase with age (P = 0.17). Gender had no influence on skin AF in nonsmokers. Among current smokers, female subjects had a 0.2 AU higher skin AF than male subjects (P = 0.02), with no further age-related increase.

CONCLUSIONS

The present results provide reference values of skin AF for healthy Caucasian control subjects over a broad age range. A major contribution of age and some interaction of smoking and gender were observed, resulting in reference values of skin AF suitable for clinical settings and future studies.