Skin autofluorescence: an emerging biomarker in persons with kidney disease

Epigenetic clocks indicate that kidney transplantation and not dialysis mitigate the effects of renal ageing

BACKGROUND

Chronic kidney disease (CKD) is an age-related disease that displays multiple features of accelerated ageing. It is currently unclear whether the two treatment options for end-stage kidney disease (dialysis and kidney transplantation [KT]) ameliorate the accelerated uremic ageing process.

METHODS

Data on clinical variables and blood DNA methylation (DNAm) from CKD stage G3-G5 patients were used to estimate biological age based on blood biomarkers (phenotypic age [PA], n = 333), skin autofluorescence (SAF age, n = 199) and DNAm (Horvath, Hannum and PhenoAge clocks, n = 47). In the DNAm cohort, we also measured the change in biological age 1 year after the KT or initiation of dialysis. Healthy subjects recruited from the general population were included as controls.

RESULTS

All three DNAm clocks indicated an increased biological age in CKD G5. However, PA and SAF age tended to produce implausibly large estimates of biological age in CKD G5. By contrast, DNAm age was 4.9 years (p = 0.005) higher in the transplantation group and 5.9 years (p = 0.001) higher in the dialysis group compared to controls. This age acceleration was significantly reduced 1 year after KT, but not after 1 year of dialysis.

CONCLUSIONS

Kidney failure patients displayed an increased biological age as estimated by DNAm clocks compared to population-based controls. Our results suggest that KT, but not dialysis, partially reduces the age acceleration.

Topical glutathione amino acid precursors protect skin against environmental and oxidative stress

BACKGROUND

Although glutathione (GSH) has long been considered a master antioxidant, poor stability and bioavailability limit its application in skin protection. To overcome the challenges, Unilever R&D formulated a Glutathione Amino acid Precursors blend (named GAP) to boost GSH de novo synthesis.

OBJECTIVE

Determine whether GAP can boost GSH levels and provide skin protection against stressors.

METHODS

Normal human epidermal keratinocytes were treated with GAP, with or without stressors, namely, menadione, blue light or pollutants. Ascorbic acid was used as a benchmark. The levels of GSH, glutathione disulfide (GSSG), adenosine triphosphate (ATP) and reactive oxygen species (ROS) were quantified. A placebo-controlled clinical study was conducted on 21 female subjects who received product applications and subsequent UV radiation. Tape strip samples were collected from the subjects for GSH and GSSG quantification using ultra-performance liquid chromatography-mass spectrometry/mass spectrometry (UPLC-MS/MS). The UV-protective effect of GAP was investigated using ex vivo skin. Biomarkers related to DNA damage and the skin barrier were analysed using immunohistochemistry.

RESULTS

Glutathione amino acid precursors significantly increased the GSH levels and GSH/GSSG ratio in normal human epidermal keratinocytes. Menadione treatment resulted in excessive ROS production and a decline in ATP levels, which were effectively abrogated by GAP. The protective effects of GAP against menadione-induced oxidative stress were superior to those of ascorbic acid. In addition, GAP effectively protected the cells against blue light-induced ROS production and pollutant-induced ATP depletion. Topical application of the GAP formulation significantly elevated the skin GSH/GSSG ratio in a clinical study. Ex vivo skin treated with the GAP formulation displayed a reduction in DNA damage and high levels of barrier proteins after UV exposure.

CONCLUSIONS

Glutathione amino acid precursors effectively increases cellular GSH levels to protect the skin from oxidative and environmental stresses.

Expression of genes with biomarker potential identified in skin from DSLD-affected horses increases with age

Degenerative Suspensory Ligament Desmitis (DSLD) negatively impacts connective tissues in horses, which often leads to progressive chronic pain and lameness. DSLD has been shown to be a systemic disorder that affects multiple body systems, including tendons, sclerae, and the aorta. Currently, the diagnosis is confirmed by post mortem histological examination of a tendon or suspensory ligament. Histology reveals inappropriate accumulations of proteoglycans in the tendons and other tissues in DSLD-affected horses. Unfortunately, there is no reliable method to diagnose DSLD in living horses. Recently, bone morphogenetic protein 2 (BMP2) was identified in active DSLD lesions. In addition, recent data from RNA sequencing (RNA-seq) showed overexpression of numerous genes, among them BMP2, FOS and genes for keratins in DSLD skin biopsies-derived RNA. We hypothesized that some of these genes can be used as biomarkers for diagnosis of DSLD in a panel. Overexpression of some of them was verified in quantitative real time PCR. Immunohistochemistry and RNAscope in-situ hybridization (ISH) assays were used to determine the level of overexpression of specific genes in skin biopsies from control and DSLD-affected horses. The RNAscope ISH assay has shown to be more reliable and more specific that immunohistochemistry. ISH confirmed a significant increase in KRT83 and BMP-2 in hair follicles in DSLD cases, as well as abnormally high expression of FOS in the epidermis, especially in aging horses. Because statistically relevant specificity and sensitivity was documented only for FOS and BMP2, but not KRT83 we recommend the use of FOS and BMP2 panel to diagnose DSLD. We conclude that a panel of two markers from the studied group (BMP2 and FOS) can serve as an additional diagnostic tool for DSLD in living horses, especially in older animals. Further studies are necessary to confirm if this biomarker panel could be used as a prospective tool to identify DSLD in horses as they age.

Accelerated AGEing: The Impact of Advanced Glycation End Products on the Prognosis of Chronic Kidney Disease

Advanced glycation end products (AGEs) are aging products. In chronic kidney disease (CKD), AGEs accumulate due to the increased production, reduced excretion, and the imbalance between oxidant/antioxidant capacities. CKD is therefore a model of aging. The aim of this review is to summarize the present knowledge of AGEs in CKD onset and progression, also focusing on CKD-related disorders (cardiovascular diseases, sarcopenia, and nutritional imbalance) and CKD mortality. The role of AGEs as etiopathogenetic molecules, as well as potential markers of disease progression and/or therapeutic targets, will be discussed.

Advanced glycation end products in skeletal muscle health and sarcopenia: A systematic review of observational studies

BACKGROUND

Advanced glycation end products (AGEs) and AGEs receptor (RAGE) may play a role in sarcopenia. This systematic review evaluated the associations between AGEs measured in tissues (skin) by autofluorescence (SAF) and/or circulation (blood, urine) and muscle health outcomes (strength, mass, function) and sarcopenia in observational studies.

METHODS

MEDLINE, Embase, Scopus and Web of Science were searched for studies reporting associations between AGEs and muscle-related outcomes in community-dwelling adults aged ≥ 30 years (until March 2022).

RESULTS

Fourteen cross-sectional and one prospective study were included in the narrative summary. SAF was negatively associated with muscle strength, mass, and physical functioning in adults aged ≥ 30 years (four studies), and muscle mass (three studies), strength, and sarcopenia (one study) in adults aged ≥ 65 years. Circulating AGEs were negatively associated with muscle strength and physical functioning (four studies) and predicted the risk of walking disability (one prospective study), and sarcopenia (one study) in older adults. The role of RAGE in muscle health was inconclusive.

CONCLUSIONS

SAF and circulating AGEs were negatively associated with muscle-related outcomes in adults aged ≥ 30 years in cross-sectional studies. This finding should be confirmed in well-designed prospective studies investigating sarcopenia, as AGEs represent a potentially modifiable target for intervention.

Skin Autofluorescence Measurement as Initial Assessment of Hepatic Parenchyma Quality in Patients Undergoing Liver Resection

Skin autofluorescence (SAF) can detect advanced glycation end products (AGEs) that accumulate in tissues over time. AGEs reflect patients’ general health, and their pathological accumulation has been associated with various diseases. This study aimed to determine whether its measurements can correlate with the liver parenchyma quality. This prospective study included 186 patients who underwent liver resections. Liver fibrosis and/or steatosis > 10% were found in almost 30% of the patients. ROC analysis for SAF revealed the optimal cutoff point of 2.4 AU as an independent predictor for macrovesicular steatosis ≥ 10% with an AUC of 0.629 (95% CI 0.538−0.721, p = 0.006), 59.9% sensitivity, 62.4% specificity, and positive (PPV) and negative (NPV) predictive values of 45.7% and 74.1%, respectively. The optimal cutoff point for liver fibrosis was 2.3 AU with an AUC of 0.613 (95% CI 0.519−0.708, p = 0.018), 67.3% sensitivity, 55.2% specificity, and PPV and NPV of 37.1% and 81.2%, respectively. In the multivariable logistic regression model, SAF ≥ 2.4 AU (OR 2.16; 95% CI 1.05−4.43; p = 0.036) and BMI (OR 1.21; 95% CI 1.10−1.33, p < 0.001) were independent predictors of macrovesicular steatosis ≥ 10%. SAF may enhance the available non-invasive methods of detecting hepatic steatosis and fibrosis in patients prior to liver resection.

Skin autofluorescence as a novel predictor of acute kidney injury after liver resection

Abstract

Background

Skin autofluorescence (SAF) reflects accumulation of advanced glycation end-products (AGEs). The aim of this study was to evaluate predictive usefulness of SAF measurement in prediction of acute kidney injury (AKI) after liver resection.

Methods

This prospective observational study included 130 patients undergoing liver resection. The primary outcome measure was AKI. SAF was measured preoperatively and expressed in arbitrary units (AU).

Results

AKI was observed in 32 of 130 patients (24.6%). SAF independently predicted AKI (p = 0.047), along with extent of resection (p = 0.019) and operative time (p = 0.046). Optimal cut-off for SAF in prediction of AKI was 2.7 AU (area under the curve [AUC] 0.611), with AKI rates of 38.7% and 20.2% in patients with high and low SAF, respectively (p = 0.037). Score based on 3 independent predictors (SAF, extent of resection, and operative time) well stratified the risk of AKI (AUC 0.756), with positive and negative predictive values of 59.3% and 84.0%, respectively. In particular, SAF predicted AKI in patients undergoing major and prolonged resections (p = 0.010, AUC 0.733) with positive and negative predictive values of 81.8%, and 62.5%, respectively.

Conclusions

AGEs accumulation negatively affects renal function in patients undergoing liver resection. SAF measurement may be used to predict AKI after liver resection, particularly in high-risk patients.

Methods to assess advanced glycation end-products

PURPOSE OF REVIEW

Advanced glycation end-products (AGEs) resulting from protein glycoxidation constitute biomarkers of interest in different pathological situations. Several methods for quantifying AGEs in biological fluids or tissues have been developed without any real consensus on a gold standard method. The aim of this review is to provide an overview of recent publications in the field helping to decide if these markers could find their place as diagnostic tools in clinical practice.

RECENT FINDINGS

This update shows that new AGEs are regularly discovered and new analytical methods (especially mass spectrometry-based methods) regularly described. Skin autofluorescence measurement is increasingly performed due to the practicability of the dedicated devices, in spite of its questionable specificity. In biological fluids, carboxymethyllysine remains the most frequently measured AGE. However, to date, it is still difficult to compare results obtained from different studies because measured AGEs and modes of expression are different and because no method standardization has been initiated.

SUMMARY

Despite their potential interest as biomarkers and the availability of unfortunately non-standardized assay methods, AGEs remain confined to clinical research studies without really being used in daily clinical practice. These challenges must be addressed in order to allow their implementation.

The association of skin autofluorescence with cardiovascular events and all-cause mortality in persons with chronic kidney disease stage 3: A prospective cohort study

BACKGROUND

Tissue advanced glycation end product (AGE) accumulation has been proposed as a marker of cumulative metabolic stress that can be assessed noninvasively by measurement of skin autofluorescence (SAF). In persons on haemodialysis, SAF is an independent risk factor for cardiovascular events (CVEs) and all-cause mortality (ACM), but data at earlier stages of chronic kidney disease (CKD) are inconclusive. We investigated SAF as a risk factor for CVEs and ACM in a prospective study of persons with CKD stage 3.

METHODS AND FINDINGS

Participants with estimated glomerular filtration rate (eGFR) 59 to 30 mL/min/1.73 m2 on two consecutive previous blood tests were recruited from 32 primary care practices across Derbyshire, United Kingdom between 2008 and 2010. SAF was measured in participants with CKD stage 3 at baseline, 1, and 5 years using an AGE reader (DiagnOptics). Data on hospital admissions with CVEs (based on international classification of diseases [ICD]-10 coding) and deaths were obtained from NHS Digital. Cox proportional hazards models were used to investigate baseline variables associated with CVEs and ACM. A total of 1,707 of 1,741 participants with SAF readings at baseline were included in this analysis: The mean (± SD) age was 72.9 ± 9.0 years; 1,036 (60.7%) were female, 1,681 (98.5%) were of white ethnicity, and mean (±SD) eGFR was 53.5 ± 11.9 mL/min/1.73 m2. We observed 319 deaths and 590 CVEs during a mean of 6.0 ± 1.5 and 5.1 ± 2.2 years of observation, respectively. Higher baseline SAF was an independent risk factor for CVEs (hazard ratio [HR] 1.12 per SD, 95% CI 1.03-1.22, p = 0.01) and ACM (HR 1.16, 95% CI 1.03-1.30, p = 0.01). Additionally, increase in SAF over 1 year was independently associated with subsequent CVEs (HR 1.11 per SD, 95% CI 1.00-1.22; p = 0.04) and ACM (HR 1.24, 95% CI 1.09-1.41, p = 0.001). We relied on ICD-10 codes to identify hospital admissions with CVEs, and there may therefore have been some misclassification.

CONCLUSIONS

We have identified SAF as an independent risk factor for CVE and ACM in persons with early CKD. These findings suggest that interventions to reduce AGE accumulation, such as dietary AGE restriction, may reduce cardiovascular risk in CKD, but this requires testing in prospective randomised trials. Our findings may not be applicable to more ethnically diverse or younger populations.

Comparison of skin autofluorescence, a marker of tissue advanced glycation end-products in the fistula and non-fistula arms of patients treated by hemodialysis

Advanced glycosylation end-products (AGEs) are reported to be a risk factor for cardiovascular mortality in hemodialysis (HD) patients. As serum AGEs can change with dialysis, measurement of AGEs deposited in the skin by autofluorescence (SAF) is now a recognized method of measuring AGEs. An arteriovenous fistula (AVF) is the preferred way to access blood in HD patients, and as the creation of an AVF changes blood flow distribution in the arm, we wished to determine whether this affected SAF deposition in the skin. SAF was measured using the AGE reader, which directs ultraviolet light at an intensity range of 300-420 nm (peak 370 nm) in the arms of HD patients dialyzing with an AVF. We measured SAF in 267 patients, 60.3% male, 46.1% diabetic, median duration of dialysis 34.7 (15.1-64.2) months with AVF. The median SAF was lower in the AVF arm (median 3.4 (2.9-4.2) vs. 3.7 (3.2-4.5) AU, P < .001), and for the 160 patients with an upper arm AVF (3.5 (2.9-4.3) vs. 3.8 (3.2-4.5) AU, P < .001), but not for the 107 patients dialyzing with a forearm AVF ((3.4 (2.8-4.2) vs. 3.6 (3.0-4.5) AU, P = .085). Blood flow was greater for upper arm AVF compared to forearm AVFs (1190 (770-1960) vs. (930 (653-1250) mL/min, P = .007), but there was no association between blood flow and SAF (P > .05). AVF alters blood flow in the arm, and we found that SAF measurements were lower in the arm with AVF. We suggest that SAF measurements are made in the non-AVF arm.

Enzymatic and non-enzymatic crosslinks found in collagen and elastin and their chemical synthesis

This review summarized the enzymatic and non-enzymatic crosslinks found in collagen and elastin and their organic synthesis.