Skin autofluorescence and complications of diabetes: does ethnic background or skin color matter?

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.

Genetic glucocorticoid receptor variants differ between ethnic groups but do not explain variation in age of diabetes onset, metabolic and inflammation parameters in patients with type 2 diabetes

Aims

The effect of excess glucocorticoid receptor (GR) stimulation through glucocorticoid medication or cortisol on glucose metabolism is well established. There are genetic GR variants that result in increased or decreased GR stimulation. We aimed to determine the prevalence of genetic GR variants in different ethnic groups in a cohort of patients with type 2 diabetes, and we aimed to determine their association with age of diabetes onset and metabolic and inflammation parameters.

Methods

A cross-sectional analysis was performed in a multiethnic cohort (n = 602) of patients with established type 2 diabetes. Polymorphisms in the GR gene that have previously been associated with altered glucocorticoid sensitivity (TthIIII, ER22/23EK N363S, BclI and 9β) were determined and combined into 6 haplotypes. Associations with age of diabetes onset, HbA1c, hs-CRP and lipid values were evaluated in multivariate regression models.

Results

The prevalence of the SNPs of N363S and BclI was higher in Dutch than in non-Dutch patients. We observed a lower prevalence of the SNP 9β in Dutch, South(East) Asian and Black African patients versus Turkish and Moroccan patients. We did not detect an association between SNPs and diabetes age of onset or metabolic parameters. We only found a trend for lower age of onset and higher HbA1c in patients with 1 or 2 copies of haplotype 3 (TthIIII + 9β).

Conclusions

The prevalence of genetic GR variants differs between patients of different ethnic origins. We did not find a clear association between genetic GR variants and age of diabetes onset or metabolic and inflammation parameters. This indicates that the clinical relevance of GR variants in patients with established type 2 diabetes is limited.

A Prospective Analysis of Skin and Fingertip Advanced Glycation End-Product Devices in Healthy Volunteers

Background: Advanced glycation end products (AGEs) have been shown to accumulate in bone and are gaining interest in connective tissue research. Aims: To investigate the intrarater reliability, two-timepoint agreement and correlations within and between two commercially available skin autofluorescence (SAF) AGE devices. Methods: Healthy volunteers were enrolled in a prospective study at a single academic institution. Each participant underwent SAF analysis by two different, commercially available devices on two occasions, 14 days apart. Upon enrollment, a general survey about the participant’s lifestyle and health status was completed and followed up on for any changes at timepoint two. Results: In total, 40 participants (F:M ratio 5:3) with an average age of 39.0 ± 12.5 years were analyzed. For the AGE reader (skin) and AGE sensor (fingertip), both intrarater reliability and two-timepoint agreement were excellent with an interclass correlation coefficient (ICC) > 0.90 and a strong correlation within both machines. However, there was no correlation between both machines for either timepoint. In total, 4 participants were identified as outliers above the +2SD. Additionally, 5 participants with dark-colored skin could not be measured with the AGE reader at timepoint one and 4 at timepoint two. In contrast, all participants were able to undergo SAF analysis with the AGE sensor, irrespective of their skin type. Conclusions: Both machines showed excellent intrarater reliability and two-timepoint agreement, but the skin AGE reader might have limited applicability in individuals with dark-colored skin. Future research on AGEs might take our findings into consideration.

Clinical Significance of Non-invasive Skin Autofluorescence Measurement in Patients with Diabetes: A Systematic Review and Meta-analysis

BACKGROUND

Advanced glycation end products (AGE), one of the main factors causing diabetic end-organ damage, accumulate in long half-life proteins, such as skin and cartilage collagen. AGE measurement may offer additional evidence to predict diabetic vascular complications. Skin autofluorescence (SAF) is suggested as a non-invasive, quick, and reliable method to measure tissue AGE level. The aim of this study was to review and evaluate evidence on the clinical validation of SAF measurement in diabetes mellitus (DM) patients.

METHODS

In this systematic review and meta-analysis, we searched "PubMed" (MEDLINE) and "Cochrane" databases from their inception to 10 August 2021 for observational studies concerning SAF measurement in diabetic patients. The following key terms were used in advanced searching: "Diabetes", "Diabetes Mellitus"," DM", "Glycation ", "Advanced Glycation End product", "AGE", "skin autofluorescence", "SAF". Published studies that included DM patients and estimated their AGE using SAF were considered eligible for meta-analysis. Articles that were editorials, study proposals, congress posters, or case reports and were not on human subjects were excluded. We used a random-effect models for meta-analyzing the clinical validation of SAF in DM with particular emphasis on chronic diabetes complications.

FINDINGS

We identified 881 records and twenty-nine records fulfilled our eligibility criteria and were included in the systematic review and meta-analysis. A statistically significant correlation was found between SAF and diabetes last HbA1c 0.21(0.13,0.28) in studies with substantial heterogeneity (I2=77.99%, p<0.05). Nevertheless, a significant positive association between SAF level and diabetic retinopathy (DR) [(OR= 1.05, 95% CI=1.03,1.08), (I2=63.78%, p<0.05)], diabetic peripheral neuropathy (DPN) [(OR= 1.11, 95%CI= 1.06,1.16), (I2=79.17%, p<0.05)], diabetic nephropathy (DNP) [(OR= 1.08, 95%CI: 1.05,1.11), (I 2 =65.36%, p<0.05)] and diabetic macrovascular events (D-MVE) [(OR=1.08, 95%CI=1.05,1.11) (I2=67.32, p<0.05)] were found.

INTERPRETATION

Our study confirmed the significance of SAF measurement as a non-invasive surrogate marker of DM micro and macrovascular complications. Skin AGE estimation may be a useful factor for the prediction and early detection of irreversible DM complications. More studies with larger populations and longer follow-up periods are required.

Cellular origin and microRNA profiles of circulating extracellular vesicles in different stages of diabetic nephropathy

BACKGROUND

Diabetic nephropathy (DN) is a major complication of diabetes and the main cause of end-stage renal disease. Extracellular vesicles (EVs) are small cell-derived vesicles that can alter disease progression by microRNA (miRNA) transfer.

METHODS

In this study, we aimed to characterize the cellular origin and miRNA content of EVs in plasma samples of type 2 diabetes patients at various stages of DN. Type 2 diabetes patients were classified in three groups: normoalbuminuria, microalbuminuria and macroalbuminuria. The concentration and cellular origin of plasma EVs were measured by flow cytometry. A total of 752 EV miRNAs were profiled in 18 subjects and differentially expressed miRNAs were validated.

RESULTS

Diabetic patients with microalbuminuria and/or macroalbuminuria showed elevated concentrations of total EVs and EVs from endothelial cells, platelets, leucocytes and erythrocytes compared with diabetic controls. miR-99a-5p was upregulated in macroalbuminuric patients compared with normoalbuminuric and microalbuminuric patients. Transfection of miR-99a-5p in cultured human podocytes downregulated mammalian target of rapamycin (mTOR) protein expression and downregulated the podocyte injury marker vimentin.

CONCLUSIONS

Type 2 diabetes patients with microalbuminuria and macroalbuminuria display differential EV profiles. miR-99a-5p expression is elevated in EVs from macroalbuminuria and mTOR is its validated mRNA target.

Is skin autofluorescence (SAF) representative of dermal advanced glycation endproducts (AGEs) in dark skin? A pilot study

Aims

Non-invasively assessed skin autofluorescence (SAF) measures advanced glycation endproducts (AGEs) in the dermis. SAF correlates with dermal AGEs in Caucasians and Asians, but studies in dark-skinned subjects are lacking. In this pilot we aimed to assess whether SAF signal is representative of intrinsic fluorescence (IF) and AGE accumulation in dark skin.

Methods

Skin biopsies were obtained in 12 dark-skinned subjects (6 healthy subjects, median age 22 years; 6 diabetes mellitus (DM) subjects, 65 years). SAF was measured with the AGE Reader, IF using confocal microscopy, and AGE distribution with specific antibodies. CML and MG-H1 were quantified with UPLC-MS/MS and pentosidine with HPLC and fluorescent detection.

Results

SAF correlated with IF from the dermis (405nm, r = 0.58, p < 0.05), but not with CML (r = 0.54, p = 0.07). CML correlated with IF from the dermis (405nm, r = 0.90, p < 0.01). UV reflectance and the coefficient of variation of SAF were negatively correlated (r = -0.80, p < 0.01). CML and MG-H1 were predominantly present around blood vessels, in collagen and fibroblasts in the dermis.

Conclusion

This proof of concept study is the first to compare non-invasive SAF with AGE levels measured in skin biopsies in dark-skinned subjects. SAF did not correlate with individual AGEs from biopsies, but was associated with IF. However, the intra-individual variance was high, limiting its application in dark-skinned subjects on an individual basis.

Recent Advances and the Potential for Clinical Use of Autofluorescence Detection of Extra-Ophthalmic Tissues

The autofluorescence (AF) characteristics of endogenous fluorophores allow the label-free assessment and visualization of cells and tissues of the human body. While AF imaging (AFI) is well-established in ophthalmology, its clinical applications are steadily expanding to other disciplines. This review summarizes clinical advances of AF techniques published during the past decade. A systematic search of the MEDLINE database and Cochrane Library databases was performed to identify clinical AF studies in extra-ophthalmic tissues. In total, 1097 articles were identified, of which 113 from internal medicine, surgery, oral medicine, and dermatology were reviewed. While comparable technological standards exist in diabetology and cardiology, in all other disciplines, comparability between studies is limited due to the number of differing AF techniques and non-standardized imaging and data analysis. Clear evidence was found for skin AF as a surrogate for blood glucose homeostasis or cardiovascular risk grading. In thyroid surgery, foremost, less experienced surgeons may benefit from the AF-guided intraoperative separation of parathyroid from thyroid tissue. There is a growing interest in AF techniques in clinical disciplines, and promising advances have been made during the past decade. However, further research and development are mandatory to overcome the existing limitations and to maximize the clinical benefits.

Increased Circulating and Urinary Levels of Soluble TAM Receptors in Diabetic Nephropathy

TAM receptors (Tyro3, Axl, and Mer) have been implicated in innate immunity. Circulating TAM receptor soluble forms (sTyro3, sAxl, sMer) are related to autoimmune disorders. We investigated TAM and their ligand protein S in patients with diabetes. Urinary and plasma levels of protein S, sTyro3, sAxl, and sMer were determined in 126 patients with diabetes assigned to a normoalbuminuric or macroalbuminuric (urinary albumin excretion <30 mg/24 hours and >300 mg/24 hours, respectively) study group and 18 healthy volunteers. TAM and protein S immunostaining was performed on kidney biopsy specimens from patients with diabetic nephropathy (n = 9) and controls (n = 6). TAM expression and shedding by tubular epithelial cells were investigated by PCR and enzyme-linked immunosorbent assay in an in vitro diabetes model. Patients with macroalbuminuria diabetes had higher circulating levels of sMer and more urinary sTyro3 and sMer than normoalbuminuric diabetics. Increased clearance of sTyro3 and sMer was associated with loss of tubular Tyro3 and Mer expression in diabetic nephropathy tissue and glomerular depositions of protein S. During in vitro diabetes, human kidney cells had down-regulation of Tyro3 and Mer mRNA and increased shedding of sTyro3 and sMer. Renal injury in diabetes is associated with elevated systemic and urine levels of sMer and sTyro3. This is the first study reporting excretion of sTAM receptors in urine, identifying the kidney as a source of sTAM.

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.

Oral health information from the dentist to the diabetologist

BACKGROUND

Diabetes care includes annual evaluation of micro- and macrovascular complications, however, oral pathologies are not included. We studied retrieving oral health information, in particular periodontal disease, from the dentist and studied the association between the reported periodontal condition and variables of both diabetes and dental care.

METHODS

During their annual comprehensive diabetes evaluation, patients were asked to deliver an oral health questionnaire (OHQ) to their dentist. Based on the returned OHQs, the process of retrieving oral health information from the dentist was analyzed. In addition, reported oral health measures with special emphasis to periodontitis, using a Periodontal Screening Index (PSI), were related to diabetes-related variables.

RESULTS

We included 889 patients of whom 102 patients (11%) did not visit a dentist at all and 252 (28%) were edentulous. The response rate was <50% for oral information on patients with diabetes. For the second aim, OHQs of 207 patients could be further analyzed. A moderate to high PSI-score was found in 106 patients, of whom 65% were untreated for periodontitis. Furthermore high PSI-scores were associated with poor oral hygiene, soft tissue pathologies and periodontal treatment, but not significantly with glycemic control and presence of diabetes complications.

CONCLUSION

The transfer of information from the dentist to the diabetologist is far from optimal. An OHQ can be a valuable tool for the identification of patients with diabetes with poor oral health especially untreated periodontal disease, which is helpful for proper diabetes management.