Advanced glycation end products assessed by skin autofluorescence in type 1 diabetics are associated with nephropathy, but not retinopathy

Non-invasive skin autofluorescence as a screening method for diabetic retinopathy

Diabetic retinopathy (DR) is a public health problem and a common cause of blindness. It is diagnosed by fundus examination; however, this is a costly and time-consuming method. Non-invasive skin autofluorescence (SAF) may be an accessible, fast and simple alternative for screening and early diagnosis of DR. The aim of this study was to evaluate the accuracy of SAF as a screening method for DR. A systematic search of MEDLINE, Scopus, and Web of Science databases was performed. Random effects models for sensitivity, specificity, positive likelihood ratio (PLR) and negative likelihood ratio (NLR), diagnostic odds ratio (dOR) value and 95% CIs were used to calculate test accuracy. In addition, hierarchical summary receiver operating characteristic curves (HSROC) were used to summarise the overall test performance. Four studies were included in the meta-analysis. Pooled sensitivity and specificity were 0.79 (95% CI 0.72-0.88; I2  = 0.0%) and 0.54 (95% CI 0.32-0.92; I2  = 97.0%), respectively. The dOR value for the diagnosis of DR using SAF was 5.11 (95% CI 1.81-14.48: I2  = 85.9%). The PRL was 2.17 (95% CI 0.62-7.64) and the NRL was 0.27 (95% CI 0.07-1.03). Heterogeneity was not relevant in sensitivity and considerable in specificity. The 95% confidence region of the HSROC included all studies. SAF as a screening test for DR shows sufficient accuracy for its use in clinical settings. SAF may be an appropriate method for DR screening, and further research is needed to recommend it as a diagnostic method.

AGEs accumulation with vascular complications, glycemic control and metabolic syndrome: A narrative review

BACKGROUND

Multiple pathogenetic mechanisms are involved in the genesis of various microvascular and macrovascular complications of diabetes mellitus. Of all these, advanced glycation end products (AGEs) have been strongly implicated.

OBJECTIVES

The present narrative review aims to summarize the available literature on the genesis of AGEs and their potential role in the causation of both micro- and macrovascular complications of diabetes mellitus.

RESULTS

Uncontrolled hyperglycemia triggers the formation of AGEs through non-enzymatic glycation reactions between reducing sugars and proteins, lipids, or nucleic acids. AGEs accumulate in bloodstream and bodily tissues under chronic hyperglycemia. AGEs create irreversible cross-linkages of various intra- and extracellular molecules and activate the receptor for advanced glycation end products (RAGE), which stimulates downstream signaling pathways that generate reactive oxygen species (ROS) and contribute to oxidative stress. Additionally, intracellular glycation of mitochondrial respiratory chain proteins by AGEs contributes to the further generation of ROS, which, in turn, sets a vicious cycle that further promotes the production of endogenous AGEs. Through these pathways, AGEs play a principal role in the pathogenesis of various diabetic complications, including diabetic retinopathy, nephropathy, neuropathy, bone disease, atherosclerosis and non-alcoholic fatty liver disease. Multiple clinical studies and meta-analyses have revealed a positive association between tissue or circulating levels of AGEs and development of various diabetic complications. Besides, exogenous AGEs, primarily those derived from diets, promote insulin resistance, obesity, and metabolic syndrome.

CONCLUSIONS

AGEs, triggered by chronic hyperglycemia, play a pivotal role in the pathogenesis of various complications of diabetes mellitus.

Association Between the Tissue and Circulating Advanced Glycation End-Products and the Micro- and Macrovascular Complications in Type 1 Diabetes: The DIABAGE Study

INTRODUCTION

Type 1 diabetes is associated with an increased risk of vascular complications. We aimed to investigate the association between serum and tissue advanced glycation end-products (AGEs) and micro- and macrovascular complications in type 1 diabetes (T1D).

METHODS

We conducted a cross-sectional study on 196 adults with T1D (mean age 44.53 ± 16, mean duration of diabetes 22 ± 12 years, mean HbA1c 8 ± 1.2%). AGEs were measured in blood serum (i.e., carboxymethyllysine (CML), methylglyoxal-hydroimidazolone-1 (MGH1), and pentosidine) and by measurement of skin autofluorescence (SAF). Associations between AGEs levels and vascular complications were analyzed using binary logistic regression. Correlations between AGEs and pulse wave velocity (PWV) were also assessed by linear regressions. Significant differences were set for p values less than 0.05.

RESULTS

We found positive associations between different AGEs and vascular complications. SAF was associated with both microangiopathy (retinopathy: OR = 1.92, p = 0.011; neuropathy: OR = 2.02, p = 0.04; any microangiopathy: OR = 2.83, p < 0.0001) and macroangiopathy (coronaropathy: OR = 3.11, p = 0.009; any macroangiopathy: OR = 2.78, p = 0.003). For circulating AGEs, pentosidine was significantly associated with coronaropathy (OR = 1.61, p = 0.01) and any macroangiopathy (OR = 1.52, p = 0.005) while MGH1 was associated with nephropathy (OR 1.72, p = 0.03). Furthermore, a significant linear correlation was found between PWV and SAF (r = 0.43, p < 0.001), pentosidine (r = 0.28, p < 0.001), and MGH1 (r = 0.16, p = 0.031), but not for CML (r = 0.03, p = 0.598).

CONCLUSIONS

Skin autofluorescence appears to be a useful marker for investigating both micro- and macrovascular complications in T1D. In this study, pentosidine was associated with macroangiopathy and MGH1 with nephropathy among the circulating AGEs. Furthermore, the correlations between PWV and AGEs may suggest their value in early prediction of vascular complications in T1D.

Advanced Glycations End Products in the Skin as Biomarkers of Cardiovascular Risk in Type 2 Diabetes

The incidence and prevalence of diabetes are increasing worldwide, and cardiovascular disease (CVD) is the leading cause of death among subjects with type 2 diabetes (T2D). The assessment and stratification of cardiovascular risk in subjects with T2D is a challenge. Advanced glycation end products are heterogeneous molecules produced by non-enzymatic glycation of proteins, lipids, or nucleic acids. Accumulation of advanced glycation end products is increased in subjects with T2D and is considered to be one of the major pathogenic mechanism in developing complications in diabetes. Skin AGEs could be assessed by skin autofluorescence. This method has been validated and related to the presence of micro and macroangiopathy in individuals with type 2 diabetes. In this context, the aim of this review is to critically summarize current knowledge and scientific evidence on the relationship between skin AGEs and CVD in subjects with type 2 diabetes, with a brief reference to other diabetes-related complications.

Skin autofluorescence in people with type 1 diabetes and people without diabetes: An eight-decade cross-sectional study with evidence of accelerated aging and associations with complications

AIM

To measure skin autofluorescence in youth (<18 y.o.) and adults (≥18 y.o.) and to assess its relationship with type 1 diabetes, chronic complications and smoking.

METHODS

In a cross-sectional study (n = 383) skin autofluorescence was measured in 269 people with type 1 diabetes (67 with vascular complications) and 114 people without diabetes, covering eight decades of age. Associations of skin autofluorescence with demographics and traditional risk factors were assessed.

RESULTS

Skin autofluorescence increased with age in people with diabetes: for those with complications it increased by a mean ± se of 0.029 ± 0.003 arbitrary units per year (r = 0.76) and, for those without complications, it increased by 0.028 ± 0.002 arbitrary units (r = 0.77). These increases were higher than for people without diabetes, whose skin autofluorescence increased by 0.022 ± 0.002 arbitrary units (r = 0.78) per year (p = 0.004). Mean ±se age-adjusted skin autofluorescence was higher in people with diabetes complications vs people without diabetes complications (1.85 ± 0.04 vs 1.66 ± 0.02 arbitrary units) and people without diabetes (1.48 ± 0.03 arbitrary units; all P < 0.0001). Age-adjusted skin autofluorescence was higher in current smokers and recent ex-smokers vs non-smokers and longer-term ex-smokers (1.86 ± 0.06 vs 1.63 ± 0.02 arbitrary units; P = 0.0005). Skin autofluorescence area under the receiver-operating characteristic curve was 0.89 (95% CI 0.85-0.94) for retinopathy and 0.56 (95% CI 0.47-0.65) for nephropathy.

CONCLUSIONS

Skin autofluorescence increases with age, but faster in people with diabetes, particularly in those with complications and in smokers, consistent with accelerated aging. Skin autofluorescence may facilitate complication screening and prediction. Longitudinal studies are merited.

Skin AGEs and diabetic neuropathy

Advanced glycation end-products (AGEs) are heterogeneous molecules produced by the non-enzymatic glycation of proteins, lipids, or nucleic acids during hyperglycaemia. Accumulation of AGEs in the peripheral nerves has recently been proposed as an additional risk factor for the development of diabetic neuropathy (DN). The gold standard for measurement of tissue-bound AGEs is tissue biopsy. However, their assessment with the newer, fast and simple method of skin autofluorescence (sAF) has recently gained special interest by virtue of its non-invasive, highly reproducible nature and its acceptable correlation with the reference method of skin biopsy. Accumulation of tissue AGEs evaluated by sAF has been shown to independently correlate with DN. Importantly, increasing evidence underscores their potential value as early biomarkers of the latter. Further important associations include diabetic nephropathy, diabetic retinopathy and cardiovascular autonomic neuropathy. However, the value of the implementation of screening with skin AGEs for DN remains unclear. The aim of the present review is to critically summarise current evidence on the association between skin AGEs and diabetic microvascular complications, with a particular emphasis on diabetic neuropathy, and to note the most important limitations of existing knowledge. Longer follow-up studies are also highly anticipated to clarify its role and provide data on patient selection and cost-effectiveness.

Skin autofluorescence: Correlation with measures of diabetic sensorimotor neuropathy

OBJECTIVE

Advanced glycation end products (AGE) contribute to the development of diabetes complications. Their accumulation in skin can be non-invasively assessed by measurement of skin autofluorescence (SAF). Our study investigated whether SAF correlates with measures of diabetic peripheral neuropathy (DPN).

METHODS

In a multi-center study (8 centers), 497 consecutive individuals with diabetes mellitus were investigated. Forearm SAF was measured using the AGE Reader (Groningen, The Netherlands). DPN was assessed using the Toronto Clinical Neuropathy Score (TCNS), the Neuropathy Symptoms Score (NSS) and the Neuropathy Disability Score (NDS). RESULTS (MEAN ± SD): According to the TCNS, SAF (arbitrary units - AU) was increased in individuals with DPN (TCNS > 5): 2.59 ± 0.56 AU compared with those without DPN (TCNS ≤ 5): 2.45 ± 0.53 AU, (p = 0.04) and significantly increased with the severity of DPN (p = 0.028). Higher SAF was detected in individuals with neuropathic deficits (NDS > 2): 2.58 ± 0.56 AU vs. those without deficits (NDS ≤ 2): 2.45 ± 0.53 AU, (p = 0.009) as well as in individuals with symptoms (NSS > 2): 2.54 ± 0.56 AU vs. those without symptoms (NSS ≤ 2): 2.40 ± 0.47 AU, (p = 0.022).

CONCLUSIONS

Accumulation of AGE in skin is increased in individuals with DPN and progresses with the severity of DPN. Therefore, SAF measurement, an easy-to-use, quick and non-invasive method, might help in identifying subjects at high risk for having DPN.

Progression of skin autofluorescence of AGEs over 4 years in patients with type 1 diabetes

BACKGROUND

The deposit of advanced glycation end-products is involved in diabetic complications. It can be evaluated by measuring the skin autofluorescence (sAF). We searched whether sAF progressed over 4 years in type 1 diabetes and analysed its relationship with the development of nephropathy.

METHODS

Two measurements of skin autofluorescence (sAF) were completed on 154 patients during years 2009 and 2013. Baseline factors associated with the progression of sAF were analysed by multivariate regression analysis. The relations among sAF progression, microalbuminuria, and impaired estimated glomerular filtration rate (eGFR) were analysed by logistic regression analysis.

RESULTS

The patients were 51 ± 16 years old, with duration of diabetes of 23 ± 13 years, HbA1c: 7.7 ± 1.0%, 20.7% were treated by continuous subcutaneous insulin infusion (CSII). The sAF progressed by +18.1% over 4 years. Two interacting (P = .04) variables were associated with the later progression of sAF: mildly impaired eGFR and treatment by CSII. The patients with mildly impaired eGFR had the highest progression of sAF (+11.5% P = .01). Continuous subcutaneous insulin infusion was associated with a reduced progression of sAF in patients without kidney impairment (ß = -7.2%, P = .01). A +10% progression of sAF during the follow-up was associated with more microalbuminuria: OR = 1.45, P = .02, and more mildly impaired eGFR (<90 mL/min/1.73 m² ): OR 1.22, P = .03 at 4 years of follow-up.

CONCLUSIONS

The skin autofluorescence of advanced glycation end-products progresses in patients with type 1 diabetes, more if they have diabetic nephropathy, less if they are treated by continuous subcutaneous insulin infusion. This progression is associated with the development of nephropathy.

Advanced glycation end products among patients maintained on antipsychotics

The aim of this study was to measure advanced glycation end products (AGEs) among participants maintained on antipsychotics using the AGE Reader and to compare them with controls from the general population. Participants maintained on antipsychotics for at least 6 months were recruited from the Psychiatry Department at Rumailah Hospital, Doha, Qatar. Healthy controls were recruited from the primary healthcare centers in Doha, Qatar. AGEs of a total of 86 participants (48 patients and 38 controls) were recorded. Among the group maintained on antipsychotics, women, smokers, and Arabs had significantly higher AGEs levels compared with men, nonsmokers, and non-Arabs, respectively (P<0.05). The levels of AGEs were higher among the group of patients maintained on antipsychotics in comparison to controls; however, the difference did not reach statistical significance. This is the first study to examine AGEs in patients maintained on antipsychotics. Our findings showed that such patients do not differ significantly from controls comparing AGEs levels. Future investigations might need to consider recruiting a larger sample size using a prospective design.

Higher skin autofluorescence in young people with Type 1 diabetes and microvascular complications

AIM

To test the hypothesis that non-invasive skin autofluorescence, a measure of advanced glycation end products, would provide a surrogate measure of long-term glycaemia and be associated with early markers of microvascular complications in adolescents with Type 1 diabetes.

METHODS

Forearm skin autofluorescence (arbitrary units) was measured in a cross-sectional study of 135 adolescents with Type 1 diabetes [mean ± sd age 15.6 ± 2.1 years, diabetes duration 8.7 ± 3.5 years, HbA_1c 72 ± 16 mmol/mol (8.7 ± 1.5%)]. Retinopathy, assessed using seven-field stereoscopic fundal photography, was defined as ≥1 microaneurysm or haemorrhage. Cardiac autonomic function was measured by standard deviation of consecutive RR intervals on a 10-min continuous electrocardiogram recording, as a measure of heart rate variability.

RESULTS

Skin autofluorescence was significantly associated with age (R² = 0.15; P < 0.001). Age- and gender-adjusted skin autofluorescence was associated with concurrent HbA_1c (R² = 0.32; P < 0.001) and HbA_1c over the previous 2.5-10 years (R² = 0.34-0.43; P < 0.002). Age- and gender-adjusted mean skin autofluorescence was higher in adolescents with retinopathy vs those without retinopathy [mean 1.38 (95% CI 1.29, 1.48) vs 1.22 (95% CI 1.17, 1.26) arbitrary units; P = 0.002]. In multivariable analysis, retinopathy was significantly associated with skin autofluorescence, adjusted for duration (R² = 0.19; P = 0.03). Cardiac autonomic dysfunction was also independently associated with skin autofluorescence (R² = 0.11; P = 0.006).

CONCLUSIONS

Higher skin autofluorescence is associated with retinopathy and cardiac autonomic dysfunction in adolescents with Type 1 diabetes. The relationship between skin autofluorescence and previous glycaemia may provide insight into metabolic memory. Longitudinal studies will determine the utility of skin autofluorescence as a non-invasive screening tool to predict future microvascular complications.

Skin autofluorescence, renal insufficiency and retinopathy in patients with type 2 diabetes

OBJECTIVES

Advanced glycation end-products (AGEs) are involved in diabetic retinopathy (DR). Their accumulation in tissues can be analyzed by measuring the skin autofluorescence (sAF). We hypothesized that renal insufficiency, another cause of high sAF, may disturb the relation between sAF and DR.

RESEARCH DESIGN AND METHODS

We measured sAF with an AGE-Reader in 444 patients with type 2 diabetes (T2D), and we analyzed their retinal status. The associations of sAF with DR, and interaction with renal insufficiency were estimated by multivariate logistic regression analysis.

RESULTS

Mean age was 62years (standard deviation (SD) 10years), diabetes duration 13 (9) years and mean HbA1C 8.9% (1.8). The prevalence of DR was 21.4% and increased with age, diabetes duration, arterial hypertension, renal parameters (serum creatinine and albumin excretion rates), and sAF. The prevalence of macular edema (ME) was 8.6% and increased with the duration of diabetes, but not with sAF (p=0.11). There was a significant interaction between renal insufficiency and sAF for the relation with DR or ME (p=0.02). For the 83% patients without renal insufficiency (estimated GFR>60mL/min/1.73m2), sAF was related to DR or ME after multivariate adjustment: OR 1.87 (1.09-3.19). The 17% patients with renal insufficiency had the highest rates of DR or ME (38.6%) and the highest sAF, unrelated to each other.

CONCLUSIONS

In T2D patients with renal insufficiency, the high sAF does not relate to retinopathy, which should be systematically searched due to its high frequency. For other patients, a high sAF argues for DR screening.

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.

Skin advanced glycation end products in HIV infection are increased and predictive of development of cardiovascular events

OBJECTIVE

HIV-1 infection is associated with an increased cardiovascular disease (CVD) risk. Advanced glycation end products are formed as stable markers of glycaemic and oxidative stress. Skin autofluorescence (SAF) as marker of accumulated advanced glycation end products is increased and predictive of CVD events in diabetes mellitus, chronic kidney disease (CKD), and preexisting CVD. We determined SAF levels in HIV-1 infected patients, testing the hypothesis that SAF predicts CVD events in HIV infection.

DESIGN

Single-centre prospective cohort study.

METHODS

In 2010-2011, SAF was measured in 91 patients. Development of CVD events was monitored during a median follow-up of 4.8 years. SAF values of the patients were expressed as a ratio (rSAF) to expected SAF levels in age-matched healthy volunteers.

RESULTS

Seventy-nine men and 12 women were included, mean age 47 years; 81 patients were on combination antiretroviral therapy. With a mean rSAF of 1.155, SAF levels in patients were 15.5% higher than predicted for their age (95% confidence interval, 10.0-20.0; P < 0.001). In multivariate regression analysis, rSAF was associated with nadir CD4 cell count less than 200 cells/μl (β -0.274; P = 0.01), smoking (β 0.240; P = 0.03), and men who have sex with men (MSM) (β 0.202; P = 0.07). CVD events occurred in six patients (7%). In Cox regression analysis including age, SAF, smoking, diabetes, hypertension and CKD, SAF (P = 0.01), and (Wet Medisch-wetenschappelijk Onderzoek met mensen; WMO) CKD (P = 0.03) remained as independent predictors of CVD events.

CONCLUSION

SAF is increased in HIV-infected patients, and related with smoking, low nadir CD4 cell count, and MSM. Larger studies are needed to confirm whether SAF is an independent predictor of CVD events.

Skin advanced glycation end-products evaluation in infants according to the type of feeding and mother's smoking habits

OBJECTIVES

This study was conducted to assess whether formula-fed infants had increased skin advanced glycation end-products compared with breastfed ones. We also evaluated the effect of maternal smoke during pregnancy and lactation on infant skin advanced glycation end-products accumulation.

METHODS

Advanced glycation end-product-linked skin autofluorescence was measured in 101 infants.

RESULTS

In infants born from non-smoking mothers, advanced glycation end-products were higher in formula-fed subjects than in breastfed subjects (0.80 (0.65-0.90) vs 1.00 (0.85-1.05), p < 0.001). Advanced glycation end-products in breastfed infants from smoking mothers were higher than in those from non-smoking mothers (0.80 (0.65-0.90) vs 1.00 (0.90-1.17), p = 0.009).

CONCLUSION

Formula-fed infants had increased amounts of advanced glycation end-products compared with the breastfed ones, confirming that breast milk represents the best food for infants. Breastfed infants from mothers smoking during pregnancy and lactation had increased skin advanced glycation end-products, suggesting that smoke-related advanced glycation end-products transfer throughout breast milk. Moreover, advanced glycation end-products may already increase during gestation, possibly affecting fetal development. Thus, we reinforced that smoking must be stopped during pregnancy and lactation.

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.

Advanced glycation end products, measured in skin, vs. HbA1c in children with type 1 diabetes mellitus

BACKGROUND AND OBJECTIVE

Advanced glycation end products (AGEs) are considered major contributors to microvascular and macrovascular complications in adult patients with diabetes mellitus. AGEs can be measured non-invasively with skin autofluorescence (sAF). The primary aim was to determine sAF values in children with type 1 diabetes mellitus and to study correlations between sAF values and HbA1c and mean HbA1c over the year prior to measurement

RESEARCH DESIGN AND METHODS

In children with type 1 diabetes mellitus, sAF values were measured using the AGE Reader®. Laboratory and anthropometric values were extracted from medical charts. Correlations were studied using Pearson's correlation coefficient. Multivariable linear regression analysis was conducted to evaluate the effect of multiple study parameters on sAF values.

RESULTS

The mean sAF value was 1.33 ± 0.36 arbitrary units (AU) in children with type 1 diabetes mellitus (n = 144). sAF values correlated positively with HbA1c measured at the same time (r = 0.485; p < 0.001), mean HbA1c over the year prior to measurement (r = 0.578; p < 0.001), age (r = 0.337; p < 0.001), duration of type 1 diabetes mellitus (r = 0.277; p = 0.001), serum triglycerides (r = 0.399; p < 0.001), and total cholesterol (r = 0.352; p = 0.001). sAF values were significantly higher in patients with non-white skin (1.56 vs. 1.27 AU, respectively, p = 0.001).

CONCLUSIONS

In children with type 1 diabetes, sAF values correlate strongly with single HbA1c and mean HbA1c, making the non-invasive sAF measurement an interesting alternative to provide information about cumulative hyperglycemic states. To determine the value of sAF measurement in predicting long-term microvascular and macrovascular complications, further prospective follow-up studies are needed.

Skin fluorescence as a clinical tool for non-invasive assessment of advanced glycation and long-term complications of diabetes

Glycation is important in the development of complications of diabetes mellitus and may have a central role in the well-described glycaemic memory effect in developing these complications. Skin fluorescence has emerged over the last decade as a non-invasive method for assessing accumulation of advanced glycation endproducts. Skin fluorescence is independently related to micro- and macrovascular complications in both type 1 and type 2 diabetes mellitus and is associated with mortality in type 2 diabetes. The relation between skin fluorescence and cardiovascular disease also extends to other conditions with increased tissue AGE levels, such as renal failure. Besides cardiovascular complications, skin fluorescence has been associated, more recently, with other prevalent conditions in diabetes, such as brain atrophy and depression. Furthermore, skin fluorescence is related to past long-term glycaemic control and clinical markers of cardiovascular disease. This review will discuss the technique of skin fluorescence, its validation as a marker of tissue AGE accumulation, and its use as a clinical tool for the prediction of long-term complications in diabetes mellitus.

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.

Non-invasive measurement of skin autofluorescence to evaluate diabetic complications

Although the accumulation of advanced glycation end-products (AGEs) of the Maillard reaction in our body is reported to increase with aging and is enhanced by the pathogenesis of lifestyle-related diseases such as diabetes, routine measurement of AGEs is not applied to regular clinical diagnoses due to the lack of conventional and reliable techniques for AGEs analyses. In the present study, a non-invasive AGEs measuring device was developed and the association between skin AGEs and diabetic complications was evaluated. To clarify the association between the duration of hyperglycemia and accumulation of skin fluorophores, diabetes was induced in mice by streptozotocin. As a result, the fluorophore in the auricle of live mice was increased by the induction of diabetes. Subsequent studies revealed that the fingertip of the middle finger in the non-dominant hand is suitable for the measurement of the fluorescence intensity by the standard deviation value. Furthermore, the fluorescence intensity was increased by the presence of diabetic microvascular complications. This study provides the first evidence that the accumulation of fluorophore in the fingertip increases with an increasing number of microvascular complications, demonstrating that the presence of diabetic microvascular complications may be predicted by measuring the fluorophore concentration in the fingertip.

AGEs and chronic subclinical inflammation in diabetes: disorders of immune system

Chronic subclinical inflammation represents a risk factor of type 2 diabetes and several diabetes complications, including neuropathy and atherosclerosis including macro-vasculopathy and micro-vasculopathy. However, the inflammatory response in the diabetic wound was shown to be remarkably hypocellular, unregulated and ineffective. Advanced glycation end products (AGEs) and one of its receptors, RAGE, were involved in inducing chronic immune imbalance in diabetic patients. Such interactions attracts immune cell into diffused glycated tissue and activates these cells to induce inflammatory damage, but disturbs the normal immune rhythm in diabetic wound. Traditional measurements of AGEs are high-performance liquid chromatography and immunohistochemistry staining, but their application faces the limitations including complexity, cost and lack of reproducibility. A new noninvasive method emerged in 2004, using skin autofluorescence as indicator for AGEs accumulation. It had been reported to be informative in evaluating the chronic risk of diabetic patients. Studies have indicated therapeutic potentials of anti-AGE recipes. These recipes can reduce AGE absorption/de novo formation, block AGE-RAGE interaction and arrest downstream signaling after RAGE activation.

Autofluorescence of Skin Advanced Glycation End Products: Marker of Metabolic Memory in Elderly Population

BACKGROUND

Advanced glycation end products are involved in the vascular complications of diabetes, in chronic kidney disease, and in the aging process. Their accumulation in the elderly people, as reflected by skin autofluorescence (sAF), may be a marker of metabolic memory. We aimed to examine the association of sAF with glycemic and renal status 10 years earlier in older persons.

METHODS

In retrospective cohort study, 328 elderly community dwellers aged of 75 years and over had sAF measurement 10 years after their inclusion in the Three-City cohort. Fasting plasma glucose and serum creatinine were measured at baseline and at 10-year follow-up. In 125 participants, HbA1c was available at these two times. Associations between sAF and the glycemic and renal status 10 years before were analyzed by multivariate linear regression adjusted for age, sex, hypertension, body mass index, hypertriglyceridemia, and smoking.

RESULTS

Participants were 82.4 (standard deviation = 4.1) years on average, and their mean sAF was 2.8 (standard deviation = 0.7) arbitrary units (AU). After adjustment, sAF was higher in participants with long-standing diabetes (+0.38 AU, p = .01) or chronic kidney disease (+0.29 AU, p = .02) compared with healthy participants. sAF was related to fasting plasma glucose (+1 mmol/L associated with +0.08 AU, p = .01) and HbA1c (+1% associated with +0.15 AU, p = .03) 10 years earlier, but not to the current fasting plasma glucose (p = .82) and HbA1c (p = .32). sAF was also related to the distal and current estimated glomerular filtration rates (p = .002 and .004, respectively).

CONCLUSIONS

sAF reflects glycemic and renal status 10 years before, supporting its value as a marker of metabolic memory in the elderly people.

Skin autofluorescence is associated with carotid intima-media thickness, diabetic microangiopathy, and long-lasting metabolic control in type 1 diabetic patients. Results from Poznan Prospective Study

AIMS

Our aim was to assess the association between skin autofluorescence (AF) related to advanced glycation end products (AGEs) accumulation and long-term metabolic control, microvascular complications and carotid intima-media thickness (IMT) in an observational cohort of type 1 diabetes (DM1).

METHODS

The analysis included 77 patients with DM1 (28 women and 49 men) aged 38 (IQR: 34-41), diabetes duration 15 (14-17), participating in Poznan Prospective Study (PoProStu). Skin AF was measured with AGE Reader (DiagnOptics).

RESULTS

We found 50% of any microvascular complication; 37% of retinopathy, 37% of diabetic kidney disease and 22% of distal symmetrical neuropathy. Median carotid IMT was 0.57 (0.52-0.67) mm and skin AF 2.2 (IQR: 1.9-2.6). We found positive correlation between skin AF and patients' age (r=0.31, p=0.006), mean HbA1c from the observation time (r=0.35, p=0.001) and IMT (r=0.39, p<0.001). In multivariate logistic regression presence of microvascular complications was independently associated with skin AF: for retinopathy (OR 3.49; 95% CI: 1.08-11.28, p=0.03), for diabetic kidney disease (OR 3.62; 95% CI: 1.16-11.28, p=0.02), for neuropathy (OR 5.01; 95% CI: 1.21-20.77, p=0.02) and for any microangiopathy (OR 3.13; 95% CI: 1.06-9.18, p=0.03).

CONCLUSION

Skin AF is a reliable marker of past glycemic control of diabetes. Increased accumulation of AGEs is related to the presence of diabetic microangiopathy as well as subclinical macroangiopathy in patients with type 1.

Correlation between diabetic retinopathy severity and elevated skin autofluorescence as a marker of advanced glycation end-product accumulation in type 2 diabetic patients

AIMS

We evaluated skin autofluorescence (AF) as a marker of tissue advanced glycation end-product (AGE) accumulation and examined whether it was related to the prevalence and severity of diabetic retinopathy (DR) and of diabetic macular edema (DME) in patients with type 2 diabetes mellitus (DM).

METHODS

This study included 138 type 2 DM patients consisting of 31 patients with proliferative DR, 71 patients with non-proliferative DR, and 36 patients without retinopathy, in addition to 111 non-DM control subjects. At the time of skin AF and HbA1c measurement, self-assessed duration of DM was also determined. DR and DME stages were classified according to international guidelines.

RESULTS

Skin AF was significantly increased in patients with DM as compared with non-DM controls. Furthermore, skin AF was correlated with the severity of DR, whereas single measurement of HbA1c and self-assessed DM duration were not. None of these 3 factors showed a correlation with DME prevalence or severity.

CONCLUSIONS

Skin AF levels, which can be measured non-invasively on a screening basis without skin biopsy or blood sampling, have a greater predictive ability for the presence and severity of DR than single measurement of HbA1c or self-assessed DM duration in patients with type 2 DM.

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.

GWAS identifies an NAT2 acetylator status tag single nucleotide polymorphism to be a major locus for skin fluorescence

AIMS/HYPOTHESIS

Skin fluorescence (SF) is a non-invasive marker of AGEs and is associated with the long-term complications of diabetes. SF increases with age and is also greater among individuals with diabetes. A familial correlation of SF suggests that genetics may play a role. We therefore performed parallel genome-wide association studies of SF in two cohorts.

METHODS

Cohort 1 included 1,082 participants, 35-67 years of age with type 1 diabetes. Cohort 2 included 8,721 participants without diabetes, aged 18-90 years.

RESULTS

rs1495741 was significantly associated with SF in Cohort 1 (p < 6 × 10(-10)), which is known to tag the NAT2 acetylator phenotype. The fast acetylator genotype was associated with lower SF, explaining up to 15% of the variance. In Cohort 2, the top signal associated with SF (p = 8.3 × 10(-42)) was rs4921914, also in NAT2, 440 bases upstream of rs1495741 (linkage disequilibrium r (2) = 1.0 for rs4921914 with rs1495741). We replicated these results in two additional cohorts, one with and one without type 1 diabetes. Finally, to understand which compounds are contributing to the NAT2-SF signal, we examined 11 compounds assayed from skin biopsies (n = 198): the fast acetylator genotype was associated with lower levels of the AGEs hydroimidazolones of glyoxal (p = 0.017).

CONCLUSIONS/INTERPRETATION

We identified a robust association between NAT2 and SF in people with and without diabetes. Our findings provide proof of principle that genetic variation contributes to interindividual SF and that NAT2 acetylation status plays a major role.

Relationship of skin autofluorescence to severity of retinopathy in type 2 diabetes

PURPOSE

To evaluate the relationship between skin autofluorescence (SAF), which reflects the accumulation of advanced glycation end products (AGEs), and the severity of diabetic retinopathy (DR) in patients with type 2 diabetes.

METHODS

Sixty-seven eyes of 67 patients with type 2 diabetes were enrolled. Sixty-seven age-matched non-diabetic subjects served as controls. Diabetic patients were classified by the severity of their DR: no DR (NDR), non-proliferative DR (NPDR), and proliferative DR (PDR). SAF was measured with an autofluorescence reader.

RESULTS

SAF in the diabetes patients was significantly higher than in the controls (median 2.5 (interquartile range 2.3-2.7) and 1.8 (1.6-2.3) arbitrary unit (AU), respectively, p < 0.001). There was a statistically significant increase in SAF along with the increasing severity of DR (from NDR to NPDR: p = 0.034; NPDR to PDR: p < 0.01). Logistic regression analysis revealed that SAF (OR, 17.2; p < 0.05) was an independent factor indicating the presence of PDR.

CONCLUSIONS

SAF has an independent relationship with PDR in patients with type 2 diabetes. SAF measurement with an autofluorescence reader is a non-invasive way to assess the risk of DR. SAF may, therefore, be a surrogate marker candidate for the non-invasive evaluation of DR.

Clinical and technical factors associated with skin intrinsic fluorescence in subjects with type 1 diabetes from the Diabetes Control and Complications Trial/Epidemiology of Diabetes Interventions and Complications Study

BACKGROUND

The Diabetes Control and Complications Trial (DCCT)/Epidemiology of Diabetes Interventions and Complications(EDIC) studies have established multiyear mean hemoglobin A1c (HbA1c) as predictive of microvascular complications in persons with type 1 diabetes. However, multiyear mean HbA1c is not always available in the clinical setting. Skin advanced glycation end products (AGEs) are thought to partially reflect effects of hyperglycemia over time, and measurement of skin AGEs might be a surrogate for multiyear mean HbA1c. As certain AGEs fluoresce and skin fluorescence has been demonstrated to correlate with the concentration of skin AGEs, noninvasive measurement by skin intrinsic fluorescence(SIF) facilitates the exploration of the association of mean HbA1c and other clinical/technical factors with SIF using the detailed phenotypic database available in DCCT/EDIC.

SUBJECTS AND METHODS

Of the subjects, 1,185 (53% male) had measurements of SIF during years 16/17 of EDIC with mean age and diabetes duration of 51.5 and 29.8 years, respectively. SIF measurements were obtained on the underside of the forearm near the elbow using a skin fluorescence spectrometer. Demographic data and health history were self-reported, and an annual standardized examination measured clinical status. Linear regression models were constructed to identify significant clinical and technical factors associated with SIF, and the final models only used factors that were significant.

RESULTS

SIF ranged from 8.7 to 54.0 arbitrary units and was log-normally distributed. Log(SIF) correlated more with mean HbA1c as the time period increased. In multivariate analyses log(SIF) was significantly associated with mean HbA1c, age,estimated glomerular filtration rate < 60mL/min/m2, smoking status, skin tone, and clinic latitude <37 N.

CONCLUSIONS

SIF reflects age, mean HbA1c over time, smoking, and renal damage, which are known risk factors for diabetes complications.

Skin autofluorescence is associated with past glycaemic control and complications in type 1 diabetes mellitus

As skin autofluorescence (AF) can assess subcutaneous accumulation of fluorescent advanced glycation end-products (AGEs), this study aimed to investigate whether it was linked to glycaemic control and complications in patients with type 1 diabetes mellitus (T1DM). Using the AGE Reader™, AF was measured in T1DM patients referred to Haut-Levêque Hospital (Bordeaux, France); data on their HbA1c levels measured every 6months as far back as the last 5years were also collected. The association of AF with the patients' past glucose control, based on their latest HbA1c values, and the means of the last five and 10 HbA1c values, and with diabetic complications was also examined by linear regression analysis. The sample included 300 patients: 58% were male; the mean age was 49 (SD 17) years and the mean diabetes duration was 21 (SD 13) years. The median skin AF measurement was 2.0 [25th-75th percentiles: 1.7-2.4] arbitrary units (AU), and this was associated with age (β=0.15 per 10years, P<0.001) and diabetes duration (β=0.17 per 10years, P<0.001). After adjusting for age and estimated glomerular filtration rate (eGFR), the skin AF measurement was also related to the means of the last five and 10 HbA1c values (β=0.10 per 1% of HbA1c, P=0.005, and β=0.13 per 1% of HbA1c, P=0.001, respectively). In addition, the skin AF was associated with retinopathy (P<0.001), albuminuria (P<0.001) and decreased eGFR (P<0.001). In conclusion, the skin AF is related to the long-term glucose control and diabetic complications.

Verification of skin autofluorescence values by mass spectrometry in adolescents with type 1 diabetes: brief report

BACKGROUND

Accumulation of advanced glycation end products (AGEs) in tissues is a major risk factor for diabetes-associated complications. Skin autofluorescence (SAF) values measured by a specific noninvasive approach (AGE Reader; DiagnOptics Technologies B.V., Gröningen, The Netherlands) reflect the overall AGE exposure in skin.

SUBJECTS AND METHODS

In 16 adolescents with type 1 diabetes (age range, 11-18 years) we tested the association between SAF measured with an AGE Reader and the presence of glucuronic acid, 3-indoxyl sulfate, 3-hydroxybutyrate, phenol sulfate, and pentosidine in skin tissue determined with desorption electrospray ionization mass spectrometry (DESI-MS). These compounds are implicated in long-term diabetes complications.

RESULTS

SAF values significantly correlated with levels of compounds measured by DESI-MS (r>0.9 and P<0.001 for each).

CONCLUSIONS

The strong correlation between adolescents' SAF values measured with the AGE Reader and some glycation products measured with DESI-MS indicates that SAF values may be used as surrogate markers of skin exposure to glycemic end products in type 1 diabetes.

Cross-sectional evaluation of noninvasively detected skin intrinsic fluorescence and mean hemoglobin a1c in type 1 diabetes

BACKGROUND

This study evaluated the relationship between skin intrinsic fluorescence (SIF) and long-term mean hemoglobin A1c (HbA1c) in individuals with type 1 diabetes.

SUBJECTS AND METHODS

We undertook a cross-sectional analysis of 172 individuals with type 1 diabetes followed longitudinally with HbA1c data available over an average of 16.6 years. SIF was evaluated cross-sectionally using the SCOUT DS device (VeraLight Inc., Albuquerque, NM) and correlated with most recent HbA1c and long-term mean HbA1c. Potential determinants of this relationship, including age, gender, smoking status, duration of diabetes, and renal function, were also evaluated.

RESULTS

Age-adjusted skin intrinsic fluorescence significantly correlated with long-term mean HbA1c (R=0.44, P<0.0001). In contrast, there was no significant relationship between SIF and most recent HbA1c (R=0.14, P=0.075). The best-fit model describing the relationship between SIF and mean HbA1c controlled for factors of age, duration of disease, renal function, and site of study conduct. Controlling for these factors was also important in understanding the relationship between most recent HbA1c and SIF. Evaluating longer-term HbA1c data also strengthened the relationship between SIF and mean HbA1c. In the presence of renal dysfunction or damage, as indicated by an estimated glomerular filtration rate of <60 mL/min/1.73 m2 or presence of gross proteinuria, there was no significant correlation between SIF and mean HbA1c.

CONCLUSIONS

Noninvasive detection of SIF significantly correlates with long-term mean HbA1c, providing insight into long-term glycemic exposure. Age, duration of diabetes, and renal function are potential contributors to this relationship.

Skin autofluorescence and risk of micro- and macrovascular complications in patients with Type 2 diabetes mellitus-a multi-centre study

AIMS

Skin autofluorescence is a non-invasive marker of advanced glycation end product accumulation. In a previous study, skin autofluorescence correlated with and predicted micro- and macrovascular complications in Type 2 diabetes in a primary care setting. The present cross-sectional study aims to confirm the association between skin autofluorescence and diabetic complications in patients with Type 2 diabetes in a multi-centre secondary care setting.

METHODS

We analysed 563 subjects with Type 2 diabetes mellitus from five Dutch hospitals.

RESULTS

  Median age was 64 years, median duration of diabetes 13 years and median HbA(1c) 58 mmol/mol (7.5%). Sixty-one per cent of patients had microvascular complications (38% nephropathy, 36% retinopathy, 35% neuropathy) and 42% had macrovascular complications. Median UK Prospective Diabetes Study 10-year risk for coronary events was 19%. Median skin autofluorescence was elevated compared with age-matched healthy control subjects: 2.77 (interquartile range 2.39-3.28) vs. 2.46 (2.08-2.84) arbitrary units. Skin autofluorescence was particularly increased in patients with complications: no complications, median 2.56 (2.26-2.90); microvascular complications, 2.79 (2.38-3.29); macrovascular complications, 2.85 (2.41-3.41); both micro- and macrovascular complications, 2.96 (2.56-3.60) arbitrary units, P < 0.001. Logistic regression analysis showed that age, duration of diabetes, renal function, gender, atrial fibrillation and skin autofluorescence were independently associated with macrovascular complications. Multiple regression analysis identified age, smoking, renal function, macrovascular complications and the number of microvascular complications as the determinants of skin autofluorescence.

CONCLUSIONS

This study confirms that skin autofluorescence is increased in patients with Type 2 diabetes in a secondary care setting. Skin autofluorescence was associated with macrovascular complications in patients with diabetes and this association was independent of classical risk factors.

Advanced glycation end products, measured as skin autofluorescence, during normal pregnancy and pregnancy complicated by diabetes mellitus

BACKGROUND

Advanced glycation end products (AGEs) accumulate with age and in diabetes mellitus (DM). AGEs can be measured by the AGE Reader (DiagnOptics Technologies BV, Groningen, The Netherlands) using skin autofluorescence (SAF). SAF is related to chronic diabetes complications. In a previous study we reported that SAF is comparable in patients with gestational DM (GDM) and controls at 27 weeks of gestation. In the current study we investigated SAF at multiple time points during pregnancy in pregnancies complicated by DM (type 1 or type 2) or GDM and in controls. Furthermore, the relation between SAF levels and adverse pregnancy outcomes was investigated.

SUBJECTS AND METHODS

In this single-center prospective observational study SAF was measured during pregnancy from 26 gestational weeks onward in 79 GDM patients, 21 patients with preexistent DM (type 1 or type 2), and 55 women without diabetes. Adverse pregnancy outcomes were recorded.

RESULTS

SAF decreased slightly but significantly (β = -0.018) during normal pregnancy but not in pregnancies complicated with hyperglycemia. At the end of pregnancy SAF was higher in patients with preexistent DM (1.91 arbitrary [AU] units) compared with patients with GDM (1.71 AU) or normal pregnancy (1.66 AU) but did not differ between the latter two groups. SAF was not related to adverse pregnancy outcomes.

CONCLUSIONS

The decrease in SAF during normal pregnancy could be the result of physiological changes. Because SAF was not related to adverse pregnancy outcomes, it is unlikely that the AGE Reader will be of use in daily clinical practice for GDM patients as a marker for identifying high-risk pregnancy outcomes.

Elevated skin autofluorescence is strongly associated with foot ulcers in patients with diabetes: a cross-sectional, observational study of Chinese subjects

OBJECTIVE

This study was designed to evaluate the association between skin autofluorescence (AF), an indicator of advanced glycation end-products (AGEs), and foot ulcers in subjects with diabetes.

METHODS

In this study, 195 Chinese diabetic subjects were examined. Their feet were examined regardless of whether an ulcer was present or not. Skin AF was measured with an AGE reader. Demographic characteristics and blood data were recorded.

RESULTS

The mean values of skin AF were 2.29 ± 0.47 for subjects without foot ulcers, and 2.80 ± 0.69 for those with foot ulcers, a significant difference (P<0.05). Skin AF was strongly correlated with age and duration of diabetes. After adjusting for these factors, multivariate logistic regression showed that skin AF was independently associated with foot ulcerations.

CONCLUSIONS

Skin AF is independently associated with diabetic foot ulcerations. It might be a useful screening method for foot ulceration risk of diabetic patients.

Combined effects of treatment with vitamin C, vitamin E and selenium on the skin of diabetic rats

The aim of this study was to investigate the effects of vitamin C, vitamin E and selenium (Se) on the skin tissue of streptozotocin-induced diabetic rats. Swiss albino rats were divided into four groups: control, control + antioxidants, diabetic, diabetic + antioxidants groups. Diabetes was induced by intraperitoneal injection of 65 mg/kg streptozotocin. Vitamin C (250 mg/kg), vitamin E (250 mg/kg) and Se (0.2 mg/kg) were given by gavage technique to rats of one diabetic and one control group for 30 days. In the diabetic group, the levels of serum urea and creatinine, skin lipid peroxidation and nonenzymatic glycosylation levels increased, but skin glutathione levels decreased. Treatment with vitamin C, vitamin E and Se reversed these effects. The present study showed that vitamin C, vitamin E and Se exerted antioxidant effects and consequently may prevent skin damage caused by streptozotocin-induced diabetes.

Non-invasive measures of tissue autofluorescence are increased in Type 1 diabetes complications and correlate with a non-invasive measure of vascular dysfunction

OBJECTIVE

To determine if ocular and skin autofluorescence, reflecting advanced glycation end-products, and vascular stiffness correlate in non-diabetic and Type 1 diabetic subjects and if levels differ by diabetes status.

RESEARCH DESIGN AND METHODS

Patients with Type 1 diabetes (n = 69, 19 with and 50 without vascular complications) and 60 subjects without diabetes (control) had ocular and skin autofluorescence and pulse-wave analysis performed in the fasted state. Correlations between measures within groups used the Pearson or Spearman correlation-coefficient and measures between groups were compared by ANOVA.

RESULTS

Lens and skin autofluorescence correlated in control (r = 0.58, P = 0.0001) and in Type 1 diabetes (r = 0.53, P = 0.001). Corneal autofluorescence correlated with lens (r = 0.53, r = 0.52, P = 0.0001) and skin autofluorescence (r = 0.34, P = 0.01 and r = 0.49, P = 0.00001) in control and Type 1 diabetes respectively. In Type 1 diabetes, small and large artery elasticity correlated inversely and systemic vascular resistance correlated positively with skin autofluorescence (all P = 0.001), and with lens and corneal autofluorescence (all P < 0.03). In Type 1 diabetes tissue advanced glycation end-products correlated with C-reactive protein and inversely with the estimated glucose disposal rate and with circulating advanced glycation end-product levels. Relative to non-diabetic subjects, lens, corneal and skin fluorescence were increased (all P < 0.001) and small artery elasticity was decreased in diabetes (P = 0.04). Lens, corneal and skin autofluorescence were greater (all P = 0.0001) in patients with Type 1 diabetes with complications compared to those without complications, but small artery elasticity did not differ significantly.

CONCLUSIONS

Ocular and skin autofluorescence and vascular stiffness correlate in non-diabetic and Type 1 diabetes subjects and are increased in Type 1 diabetes. Tissue advanced glycation end-products correlate with vascular risk factors, including circulating advanced glycation end-products.

Advanced glycation end products, measured as skin autofluorescence, at diagnosis in gestational diabetes mellitus compared with normal pregnancy

BACKGROUND

Advanced glycation end products (AGEs) are tissue proteins that accumulate with age and in diabetes mellitus (DM). AGEs can be measured by the AGE-Reader (DiagnOptics Technologies BV, Groningen, The Netherlands), which measures skin autofluorescence (SAF). SAF has been suggested as a measure to screen for undiagnosed DM or impaired glucose tolerance. SAF has never been investigated in gestational DM (GDM). Therefore we compared SAF at diagnosis in GDM patients with normal pregnancy. If SAF is elevated in GDM, future research could focus on the possible use of the AGE-Reader as a screening method for GDM.

METHODS

In this monocenter observational study SAF was measured in 60 GDM patients at diagnosis and 44 pregnant women without diabetes.

RESULTS

SAF did not differ between GDM at diagnosis (mean [SD], 1.74 [0.31] arbitrary units) and normal pregnancy (1.76 [0.32] arbitrary units). SAF was lower in white European patients than in patients with other ethnicity.

CONCLUSIONS

This first study of tissue AGE accumulation in pregnancy shows no differences in SAF between women with GDM at diagnosis and normal pregnancy. This is most likely due to mild severity and short duration of hyperglycemia in GDM at diagnosis, but it does not exclude potential differences in SAF later in pregnancy. However, the fact that no differences are detected at diagnosis makes it unlikely that the AGE-Reader can be developed as a screening method for GDM in the future. Furthermore, we found that ethnicity should be taken into account when measuring SAF.

Increased accumulation of skin advanced glycation end products is associated with microvascular complications in type 1 diabetes

BACKGROUND

Skin autofluorescence (AF) measured with an AF reader device is a noninvasive tool to measure the tissue accumulation of advanced glycation end products (AGEs). The aim of the study was to assess the association between AF and microvascular complications in type 1 diabetes mellitus (DM1).

METHODS

The study population consisted of 140 DM1 patients, 28 years old (interquartile range [IQR], 23-35), 76 of whom were women, with disease duration of 13 years (IQR, 8-19). We used the AGE Reader (DiagnOptics, Groningen, The Netherlands) to measure the AF phenomenon, which occurs because of fluorescent properties of AGEs. The patients were divided according to the presence or absence of diabetes-associated microvascular complications: retinopathy, nephropathy, and neuropathy and any microangiopathy.

RESULTS

The median AF was 2.0 (IQR, 1.7-2.4). In the univariate logistic regression AF was significantly associated with retinopathy (odds ratio [OR] 2.47, 95% confidence interval [CI] 1.26-4.84, P = 0.008), nephropathy (OR 3.15, 95% CI 1.34-7.39, P = 0.008), neuropathy (OR 3.17, 95% CI 1.46-6.90, P = 0.003), and any microvascular complication (OR 2.94, 95% CI 1.46-5.92, P = 0.002). Multivariate logistic regression showed that skin AF was independently associated only with diabetic neuropathy (OR 2.98, 95% CI 0.99-8.90, P = 0.05).

CONCLUSIONS

The tissue accumulation of AGE is significantly associated with microvascular complications in DM1.

Characterisation of glyoxalase I in a streptozocin-induced mouse model of diabetes with painful and insensate neuropathy

AIMS/HYPOTHESIS

Diabetic peripheral neuropathy (DN) is a common complication of diabetes; however, the mechanisms producing positive or negative symptoms are not well understood. The enzyme glyoxalase I (GLO1) detoxifies reactive dicarbonyls that form AGEs and may affect the way sensory neurons respond to heightened AGE levels in DN. We hypothesised that differential GLO1 levels in sensory neurons may lead to differences in AGE formation and modulate the phenotype of DN.

METHODS

Inbred strains of mice were used to assess the variability of Glo1 expression by quantitative RT-PCR. Non-diabetic C57BL/6 mice were used to characterise the distribution of GLO1 in neural tissues by immunofluorescence. Behavioural assessments were conducted in diabetic A/J and C57BL/6 mice to determine mechanical sensitivity, and GLO1 abundance was determined by western blot.

RESULTS

GLO1 immunoreactivity was found throughout the nervous system, but selectively in small, unmyelinated peptidergic dorsal root ganglia (DRG) neurons that are involved in pain transmission. GLO1 protein was present at various levels in DRG from different inbred mice strains. Diabetic A/J and C57BL/6 mice, two mouse strains with different levels of GLO1, displayed dramatically different behavioural responses to mechanical stimuli. Diabetic C57BL/6 mice also had a reduced abundance of GLO1 following diabetes induction.

CONCLUSIONS/INTERPRETATION

These findings reveal that the abundance of GLO1 varies between different murine strains and within different sensory neuron populations. These differences could lead to different responses of sensory neurons to the toxic effects of hyperglycaemia and reactive dicarbonyls associated with diabetes.

Advanced glycation end products, measured as skin autofluorescence and diabetes complications: a systematic review

BACKGROUND

Advanced glycation end products (AGEs) are long-lived tissue proteins that accumulate in diabetes. Skin AGEs measured in biopsy specimens strongly correlated with complications of diabetes. AGEs can also be measured noninvasively by the AGE Reader™ (DiagnOptics B.V., Groningen, The Netherlands). The aim of this review was to systematically review all articles on the association between skin autofluorescence (SAF), measured by the AGE Reader, and complications of diabetes.

METHODS

We screened PubMed for studies on SAF and complications in diabetes mellitus type 1 and type 2. Seven articles met the inclusion criteria.

RESULTS

All studies showed positive associations of SAF with one or more complications (all-cause mortality, cardiovascular mortality, micro- and macrovascular complications, neuropathy, and nephropathy), except retinopathy. Only three studies were of prospective design, with a follow-up of 3-5 years; the other four studies were cross-sectional. Studies were of large clinical heterogeneity.

CONCLUSIONS

This systematic review of literature showed an association of SAF with end-organ complications in diabetes, except retinopathy, in all seven studies. However, studies were of large clinical heterogeneity, only three studies had a prospective design, and five studies were from the same research group. More prospective studies, with a longer period of follow-up, larger group size, and strict definitions of complications and end points, are needed to demonstrate the potential role and benefit in clinical management before the widespread use of the AGE Reader can be recommended.

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.