Elevated serum levels of AGEs, sRAGE, and pentosidine in Tunisian patients with severity of diabetic retinopathy

Impacts of regular consumption of grapes on macular pigment accumulation in Singapore older adults: a randomized controlled trial

Background: Oxidative stress is a key risk factor for visual impairment and consuming dietary antioxidant-rich foods may help in managing visual impairments. However, a limited number of studies have investigated the effect of dietary antioxidant-rich food including grapes on eye health in older adults. Objectives: To assess the effects on macular pigment accumulation of regular consumption of grapes in Singapore older adults. Methods: This was a 16 week, double-blind, randomized, placebo-controlled trial. Thirty-four Singapore older adults were randomized into regularly consuming either 46 g day-1 of freeze-dried table grape powder (the intervention group) or the same amount of placebo powder (the control group). Macular pigment optical density (MPOD), skin carotenoid status, advanced glycation end product (AGEs) status and dietary lutein intake were assessed every 4 weeks, and plasma lutein concentration, total antioxidant capacity and total phenolic content were measured every 8 weeks. Results: A significant time effect (p = 0.007) was observed for MPOD, and this is largely attributed to the improvement in the MPOD for the intervention group, as a significant increase was observed only in this group (week 0: 0.56 ± 0.04 D.U.; week 16: 0.61 ± 0.04 D.U., p < 0.01). Additionally, a significant increase in plasma total antioxidant capacity (week 0: 0.26 ± 0.13 mM TEAC; week 16: 0.36 ± 0.20 mM TEAC, p < 0.01) and total phenolic content (week 0: 10.50 ± 0.44 mg L-1 GAE; week 16: 12.58 ± 0.55 mg L-1 GAE, p < 0.001) was observed for the intervention group only. In contrast, a significant increase in skin AGE status was observed in the control group (week 0: 2.47 ± 0.24; week 16: 2.99 ± 0.12, p < 0.05) while this was mitigated in the intervention group. There were no differences in dietary lutein intake, plasma lutein concentration and skin carotenoid status between groups throughout the study. Conclusions: Regular intake of grapes may improve eye health in Singapore older adults, specifically in augmenting MPOD, which can be explained by an increase in plasma total antioxidant capacity and phenolic content, and the downregulation of AGEs. This study was registered at clinicatrials.gov as NCT05064865.

The AGE-RAGE Axis and the Pathophysiology of Multimorbidity in COPD

Chronic obstructive pulmonary disease (COPD) is a disease of the airways and lungs due to an enhanced inflammatory response, commonly caused by cigarette smoking. Patients with COPD are often multimorbid, as they commonly suffer from multiple chronic (inflammatory) conditions. This intensifies the burden of individual diseases, negatively affects quality of life, and complicates disease management. COPD and comorbidities share genetic and lifestyle-related risk factors and pathobiological mechanisms, including chronic inflammation and oxidative stress. The receptor for advanced glycation end products (RAGE) is an important driver of chronic inflammation. Advanced glycation end products (AGEs) are RAGE ligands that accumulate due to aging, inflammation, oxidative stress, and carbohydrate metabolism. AGEs cause further inflammation and oxidative stress through RAGE, but also through RAGE-independent mechanisms. This review describes the complexity of RAGE signaling and the causes of AGE accumulation, followed by a comprehensive overview of alterations reported on AGEs and RAGE in COPD and in important co-morbidities. Furthermore, it describes the mechanisms by which AGEs and RAGE contribute to the pathophysiology of individual disease conditions and how they execute crosstalk between organ systems. A section on therapeutic strategies that target AGEs and RAGE and could alleviate patients from multimorbid conditions using single therapeutics concludes this review.

IFI44L and C1QTNF5 as promising biomarkers of proliferative diabetic retinopathy

Proliferative diabetic retinopathy (PDR) is a world-wide leading cause of blindness among adults and may be associated with the influence of genetic factors. It is significant to search for genetic biomarkers of PDR. In our study, we collected genomic data about PDR from gene expression omnibus (GEO) database. Differentially expressed gene (DEG) analysis and weighted gene co-expression network analysis (WGCNA) were carried out. The gene module with the highest gene significance (GS) was defined as the key module. Hub genes were identified by Venn diagram. Then we verified the expression of hub genes in validation data sets and built a diagnostic model by least absolute shrinkage and selection operator (LASSO) regression. Enrichment analysis, including gene ontology (GO), Kyoto Encyclopedia of Genes and Genomes (KEGG), gene set enrichment analysis (GSEA) and construction of a protein-protein interaction (PPI) network were conducted. In GSE60436, we identified 466 DEGs. WGCNA established 14 gene modules, and the blue module (GS = 0.64), was the key module. Interferon (IFN)-induced protein 44-like (IFI44L) and complement C1q tumor necrosis factor-related protein 5 (C1QTNF5) were identified as hub genes. The expression of hub genes in GEO datasets was verified and a diagnostic model was constructed by LASSO as follows: index = IFI44L * 0.0432 + C1QTNF5 * 0.11246. IFI44L and C1QTNF5 might affect the disease progression of PDR by regulating metabolism-related and inflammatory pathways. IFI44L and C1QTNF5 may play important roles in the disease process of PDR, and a LASSO regression model suggested that the 2 genes could serve as promising biomarkers of PDR.

Diagnostic circulating biomarkers to detect vision-threatening diabetic retinopathy: Potential screening tool of the future?

With the increasing prevalence of diabetes in developing and developed countries, the socio-economic burden of diabetic retinopathy (DR), the leading complication of diabetes, is growing. Diabetic retinopathy (DR) is currently one of the leading causes of blindness in working-age adults worldwide. Robust methodologies exist to detect and monitor DR; however, these rely on specialist imaging techniques and qualified practitioners. This makes detecting and monitoring DR expensive and time-consuming, which is particularly problematic in developing countries where many patients will be remote and have little contact with specialist medical centres. Diabetic retinopathy (DR) is largely asymptomatic until late in the pathology. Therefore, early identification and stratification of vision-threatening DR (VTDR) is highly desirable and will ameliorate the global impact of this disease. A simple, reliable and more cost-effective test would greatly assist in decreasing the burden of DR around the world. Here, we evaluate and review data on circulating protein biomarkers, which have been verified in the context of DR. We also discuss the challenges and developments necessary to translate these promising data into clinically useful assays, to detect VTDR, and their potential integration into simple point-of-care testing devices.

Impact of Dietary Advanced Glycation End Products on Female Reproduction: Review of Potential Mechanistic Pathways

Advanced glycation end products (AGEs), a heterogenous group of products formed by the reaction between protein and reducing sugars, can form endogenously due to non-enzymatic reactions or by exogenous sources such as diet where considerable increase in AGEs is observed due to the modification of food mainly by thermal processing. Recent studies have suggested that AGEs could impact, via inducing inflammation and oxidative stress, the reproductive health and fertility in both males and females. This review presents a summary of recently published data pertaining to the pathogenesis of dietary AGEs and their receptors as well as their potential impact on female reproductive health. More specifically, it will present data pertaining to dietary AGEs’ involvement in the mechanistic pathogenesis of polycystic ovary syndrome, ovarian dysfunction, as well as the AGEs’ effect perinatally on the female offspring reproduction. Understanding the mechanistic impact of dietary AGEs on female reproduction can help contribute to the development of targeted pharmacological therapies that will help curb rising female infertility.

Impact of Type 2 Diabetes Mellitus and Antidiabetic Medications on Bone Metabolism

PURPOSE OF REVIEW

This review focuses on the complex interactions between hyperglycemia and bone fragility and the effects of antidiabetic medications on bone metabolism.

RECENT FINDINGS

Type 2 diabetes (T2D) is associated with increased risk of bone fracture even in those with increased or normal bone mineral density (BMD). The pathophysiology of diabetic bone disease is not completely understood, but it is thought to be multifactorial and associated with complex cross talk among factors such as AGEs, IGF-1, enteric hormones, and pro-inflammatory cytokines. Treatment for T2D may have an impact on bone metabolism. Diabetic bone disease should be considered a serious complication of long-standing T2D.

Type 1 diabetes and hearing loss: Audiometric assessment and measurement of circulating levels of soluble receptor for advanced glycation end products

BACKGROUND

We examined the hearing function in adults with and without type 1 diabetes (T1D) to investigate whether an association exists between hearing loss and duration of diabetes, haemoglobin A1C level, diabetes complications and levels of select serum and urinary biomarkers.

METHODS

We measured pure tone audiometry (PTA) thresholds; serum levels of C-reactive protein (CRP), vascular endothelial growth factor (VEGF), soluble receptors for advanced glycation end-product (sRAGE); and urinary isoprostane in 30 adults with T1D (age 43.8 ± 11.4 years). We also measured PTA thresholds in 11 adults without diabetes (age 53 ± 5.5 years).

RESULTS

63.3% of adults with T1D had high-frequency hearing loss. Among adults with T1D, those with hearing loss were older (48.2 vs 36.2 years old, P < .01), had a longer duration of diabetes (30.7 vs 21.2 years, P = .02), a greater prevalence of peripheral neuropathy (57.9 vs 9.1%, P = .02) and significantly lower median levels of sRAGE (1054.27 vs 1306.83 pg/mL, P = .03) compared to those with normal hearing. Adults with T1D between the ages of 40 and 60 years old, who had diabetes for ≥35 years, had significantly higher PTA thresholds at both 500and 8000 Hz than age-matched adults without diabetes.

CONCLUSIONS

A significant proportion of adults with T1D have high-frequency hearing loss before age of 60 that is positively associated with age, duration of diabetes and presence of peripheral neuropathy. Our results are in support of previous studies suggesting a potential protective role of sRAGE against AGE toxicity and diabetes complications.

Syzygium aromaticum Reduces Diabetes-induced Glucotoxicity via the NRF2/Glo1 Pathway

Advanced glycation end products and methylglyoxal are known to show increased levels in diabetic conditions and induce diverse metabolic disorders. However, the antiglycation ability of the bark of Syzygium aromaticum is not yet studied. In this study, we determined the inhibitory effects of S. aromaticum on AGE formation. Moreover, S. aromaticum showed breakage and inhibitory ability against the formation of AGE-collagen crosslinks. In SV40 MES13 cells, treatment with the S. aromaticum extract significantly ameliorated MG-induced oxidative stress as well as cytotoxicity. Furthermore, in the S. aromaticum extract-treated group, there was a reduction in levels of several diabetic markers, such as blood glucose, kidney weight, and urinary albumin to creatinine ratio in streptozotocin-induced diabetic rats. Treatment with the S. aromaticum extract significantly increased the expression of nuclear factor erythroid 2-related factor 2, a transcription factor involved in the expression of antioxidant enzymes. Moreover, the treatment significantly upregulated the expression of glyoxalase 1 and downregulated the expression of receptor for AGEs. These results suggest that the S. aromaticum extract might ameliorate diabetes-induced renal damage by inhibiting the AGE-induced glucotoxicity and oxidative stress through the Nrf2/Glo1 pathway.

Diabetes and bone

Bone disease is a serious complication to diabetes. Patients with type 1 diabetes (T1D) and type 2 diabetes (T2D) suffer from an increased risk of fracture, most notably at the hip, compared with patients without diabetes. Confounders such as patient sex, age, body mass index, blood glucose status, fall risk, and diabetes medications may influence the fracture risk. Different underlying mechanisms contribute to bone disease in patients with diabetes. Bone quality is affected by low bone turnover in T1D and T2D, and furthermore, incorporation of advanced glycation end-products, changes in the incretin hormone response, and microvascular complications contribute to impaired bone quality and increased fracture risk. Diagnosis of bone disease in patients with diabetes is a challenge as current methods for fracture prediction such as bone mineral density T-score and fracture risk assessment tools underestimate fracture risk for patients with T1D and T2D. This review focuses on bone disease and fracture risk in patients with diabetes regarding epidemiology, underlying disease mechanisms, and diagnostic methods, and we also provide considerations regarding the management of diabetes patients with bone disease in terms of an intervention threshold and different treatments.

The relationship of blood cell-associated inflammatory indices and diabetic retinopathy: a Meta-analysis and systematic review

AIM

To explore the correlation between several blood cell-associated inflammatory indices including mean platelet volume (MPV), platelet distribution width (PDW), neutrophil to lymphocyte ratio (NLR) and platelet-lymphocyte ratio (PLR), and the presence and severity of diabetic retinopathy (DR).

METHODS

We searched for eligible studies from PubMed, EMBASE, Web of Science and CNKI up to December 13, 2017. Standardized mean difference (SMD) calculated with confidence interval (CI) of 95% was used to estimate the values of those indices.

RESULTS

A total of 31 studies were included in the present Meta-analysis. As compared with type 2 diabetes mellitus (T2DM) patients without DR, the values of MPV, PDW, NLR, and PLR were higher in patients with DR (SMD=0.67; 95%CI: 0.36 to 0.98; SMD=0.51; 95%CI: 0.27 to 0.75; SMD=0.77; 95%CI: 0.49 to 1.05 and SMD=1.18; 95%CI: 0.07 to 2.28). Additionally, it was also observed that MPV was closely correlated with the severity of DR.

CONCLUSION

MPV, PDW, NLR, and PLR could be recommended as diagnostic biomarkers for DR, and MPV could be applied to assess the severity of DR.

Relationship between serum-soluble receptor for advanced glycation end products (sRAGE) and disease activity in rheumatoid arthritis patients

Objective: Considering the important role of serum soluble receptor for advanced glycation end product (sRAGE/RAGE)-ligand system in rheumatoid arthritis (RA), this study aimed to evaluate serum sRAGE levels in RA patients compared to healthy subjects and to assess whether there is an association between sRAGE levels and disease characteristics in RA.Methods: In this cross-sectional study, 60 RA patients according to the ACR/EULAR 2010 criteria and 30 age- and sex-matched healthy controls were included. In patients, clinical examination was performed and disease activity score 28 (DAS-28) measure of disease activity was assessed. Serum sRAGE level was measured using ELISA kit.Results: The mean ± SD age of patients and controls was 54.86 ± 11.65 and 50.71 ± 3.72 years, respectively). Serum sRAGE level was significantly higher in RA patients (median [25th and 75th percentiles], 1000.3 [792.00, 1486.8]) compared to healthy controls (median [25th and 75th percentiles], 293.25 [220.35, 364.24]) (p < .001). There was significant difference in serum sRAGE level according to the activity of disease (p < .001). There were significant positive correlations between serum sRAGE level with disease activity (r = 0.67, p < .001), ESR (r = 0.411, p = .001) and CRP (r = 0.273, p = .035). There were no significant correlations between serum sRAGE level with demographic characteristics as well as biochemical measurements including serum creatinine, BUN, RF, and Anti-CCP (p > .05).Conclusions: Our study revealed higher serum sRAGE levels in RA patients compared to healthy controls, which correlated positively with disease activity.

Diagnosis and management of bone fragility in diabetes: an emerging challenge

Fragility fractures are increasingly recognized as a complication of both type 1 and type 2 diabetes, with fracture risk that increases with disease duration and poor glycemic control. Yet the identification and management of fracture risk in these patients remains challenging. This review explores the clinical characteristics of bone fragility in adults with diabetes and highlights recent studies that have evaluated bone mineral density (BMD), bone microstructure and material properties, biochemical markers, and fracture prediction algorithms (i.e., FRAX) in these patients. It further reviews the impact of diabetes drugs on bone as well as the efficacy of osteoporosis treatments in this population. We finally propose an algorithm for the identification and management of diabetic patients at increased fracture risk.

Short-Term Administration of Astaxanthin Attenuates Retinal Changes in Diet-Induced Diabetic Psammomys obesus

OBJECTIVES

Psammomys obesus is a high-fat diet (HFD)-fed animal model of obesity and type 2 diabetes recently explored as a model of non-proliferative diabetic retinopathy. This study tested the protective effect of the pigment astaxanthin (AST) in the P. obesus diabetic retina.

METHODS

Young adult P. obesus were randomly assigned to two groups. The control group received a normal diet consisting of a plant-based regimen, and the HFD group received an enriched laboratory chow. After 3 months, control and diabetic rodents were administered vehicle or AST, daily for 7 days. Body weight, blood glucose, and plasma pentosidine were assessed. Frozen sections of retinas were immunolabeled for markers of oxidative stress, glial reactivity and retinal ganglion cell bodies, and imaged by confocal microscopy.

RESULTS

Retinal tissue from AST-treated control and HFD-diabetic P. obesus showed a greater expression of the antioxidant enzyme heme oxygenase-1 (HO-1). In retinas of HFD-diabetic AST-treated P. obesus, cellular retinaldehyde binding protein and glutamine synthetase in Müller cells were more intense compared to the untreated HFD-diabetic group. HFD-induced diabetes downregulated the expression of glial fibrillary acidic protein in astrocytes, the POU domain protein 3A in retinal ganglion cells, and synaptophysin throughout the plexiform layers.

DISCUSSION

Our results show that type 2-like diabetes induced by HFD affected glial and neuronal retinal cell homeostasis. AST treatment induced the antioxidant enzyme HO-1 and reduced glial reactivity. These findings suggest that diabetic P. obesus is a useful model of HFD-induced obesity and diabetes to evaluate early neuroglial retinal alterations and antioxidant neuroprotection mechanisms in DR.

Advanced glycation end products alter steroidogenic gene expression by granulosa cells: an effect partially reversible by vitamin D

STUDY QUESTION

Does vitamin D attenuate the adverse effects of advanced glycation end products (AGEs) on steroidogenesis by human granulosa cells (GCs)?

SUMMARY ANSWER

AGEs alter the expression of genes important in steroidogenesis while 1,25-dihydroxyvitamin D3 (vit D3) in vitro attenuates some of the actions of AGEs on steroidogenic gene expression, possibly by downregulating the expression of the pro-inflammatory cell membrane receptor for AGEs (RAGE).

WHAT IS KNOWN ALREADY

Vitamin D attenuates the pro-inflammatory effects of AGEs in non-ovarian tissues.

STUDY DESIGN, SIZE, DURATION

Women who were undergoing IVF were enrolled. Follicular fluid samples (n = 71) were collected and cumulus GCs (n = 12) were treated in culture.

PARTICIPANTS/MATERIALS, SETTING, METHODS

Follicular fluid levels of the anti-inflammatory soluble RAGE (sRAGE), AGEs and 25-hydroxyvitamin D (25-OHD) were quantified for possible correlations. GCs of each participant were split equally and treated with either media alone (control) or with human glycated albumin (HGA as a precursor for AGEs) with or without vit D3 after which RT-PCR and immunofluorescence were performed and cell culture media estradiol (E2) levels were compared.

MAIN RESULTS AND THE ROLE OF CHANCE

In follicular fluid, sRAGE levels were positively correlated with 25-OHD levels. HGA treatment (i) increased CYP11A1 (by 48%), 3β-HSD (by 38%), StAR (by 42%), CYP17A1 (by 30%) and LHR (by 37%) mRNA expression levels (P < 0.05 for all) but did not alter CYP19A1 or FSHR mRNA expression levels; and (ii) increased E2 release in cell culture media (P = 0.02). Vit D3 treatment (i) downregulated RAGE mRNA expression by 33% and RAGE protein levels by 44% (P < 0.05); (ii) inhibited the HGA-induced increase in CYP11A1, StAR, CYP17A1 and LHR mRNA levels, but not the increase in 3β-HSD mRNA levels; and (iii) did not inhibit the HGA-induced E2 release in cell culture media.

LIMITATIONS REASONS FOR CAUTION

This study used luteinized GCs that were collected from women who received gonadotropins thus the results obtained may not fully extrapolate to non-luteinized GCs in vivo.

WIDER IMPLICATIONS OF THE FINDINGS

This study suggests that there is a relationship between AGEs and their receptors (RAGE and sRAGE) with vitamin D. Understanding the interaction between AGEs and vitamin D in ovarian physiology could lead to a more targeted therapy for the treatment of ovarian dysfunction.

STUDY FUNDING/COMPETING INTEREST(S)

Funding was received from NIH (R01 NS045940), American Society for Reproductive Medicine, Ferring Pharmaceuticals Inc., and University of Vermont College of Medicine Bridge Funds. All authors have nothing to disclose.

Methylglyoxal: A Relevant Marker of Disease Activity in Patients with Rheumatoid Arthritis

Background

The contribution of methylglyoxal (MGO) and soluble receptor for advanced glycation end products (sRAGE) in the presence of rheumatoid arthritis (RA) is still unknown. We investigated whether serum MGO and sRAGE were related to the presence of disease activity in RA.

Methods

80 patients with RA and 30 control subjects were included in a cross-sectional study. The severity of RA was assessed using the disease activity score for 28 joints (DAS28). Serum MGO and sRAGE were measured by ELISA.

Results

Serum MGO levels were significantly higher in patients with RA versus control subjects (P < 0.001) and were increased in RA patients with higher disease activity versus RA patients with moderate disease activity (P = 0.019). Serum sRAGE concentrations were significantly decreased in RA patients with higher disease activity versus RA patients with moderate disease activity and versus control subjects (P = 0.004; P = 0.002, resp.). A multiple logistic regression analysis demonstrated that MGO was independently associated with the presence of activity disease in RA (OR = 1.17, 95% CI: 1.02–1.31, P = 0.01).

Conclusion

Serum MGO and sRAGE levels are inversely related to the activity of RA, and MGO is independently associated with a higher disease activity of RA.

Increased serum concentrations of Nɛ-carboxymethyllysine are related to the presence and the severity of rheumatoid arthritis

Background There are limited data regarding the contribution of advanced glycation end products in the presence of rheumatoid arthritis. We investigated whether serum N^ɛ-carboxymethyllysine and pentosidine were related to the presence and the severity of rheumatoid arthritis. Methods Eighty patients with rheumatoid arthritis and 30 control subjects were included in a cross-sectional study. The severity of rheumatoid arthritis was assessed using the disease activity score for 28 joints. Serum N^ɛ-carboxymethyllysine and pentosidine were measured by enzyme-linked immunosorbent assay. Results Serum N^ɛ-carboxymethyllysine and pentosidine concentrations were significantly higher in patients with rheumatoid arthritis vs. control subjects ( P < 0.001). Serum N^ɛ-carboxymethyllysine and pentosidine concentrations were significantly higher in rheumatoid arthritis patients with high disease activity vs. rheumatoid arthritis patients with moderate disease activity ( P < 0.001, P = 0.019, respectively). A multiple logistic regression analysis demonstrated that N^ɛ-carboxymethyllysine was independently associated with the presence of rheumatoid arthritis (OR = 1.21, 95% CI: 1.05-1.39, P = 0.006). Furthermore, in a multivariate stepwise regression analysis, N^ɛ-carboxymethyllysine was independently correlated with disease activity score for 28 joints (standardized β = 0.43, P = 0.001). Conclusion Serum N^ɛ-carboxymethyllysine and pentosidine were increased during rheumatoid arthritis, and N^ɛ-carboxymethyllysine was independently associated with the presence and the severity of rheumatoid arthritis.

Correlation between follicular fluid levels of sRAGE and vitamin D in women with PCOS

PURPOSE

The pro-inflammatory advanced glycation end products (AGEs) and their anti-inflammatory soluble receptors, sRAGE, play a role in the pathogenesis of PCOS. There is a correlation between vitamin D (vit D) and sRAGE in the serum, whereby vit D replacement increases serum sRAGE levels in women with PCOS, thus incurring a protective anti-inflammatory role.

OBJECTIVE

This study aims to compare levels of sRAGE, N-carboxymethyl-lysine (CML; one of the AGEs), and 25-hydroxy-vit D in the follicular fluid (FF) of women with or without PCOS, and to evaluate the correlation between sRAGE and 25-hydroxy-vit D in the FF.

MATERIAL AND METHODS

Women with (n = 12) or without (n = 13) PCOS who underwent IVF were prospectively enrolled.

RESULTS

Women with PCOS had significantly higher anti-Mullerian hormone levels, higher number of total retrieved and mature oocytes, and higher number of day 3 and day 5 embryos formed. Compared to women without PCOS, women with PCOS had significantly lower FF sRAGE levels. In women with PCOS, in women without PCOS, and in all participants together, there was a significant positive correlation between sRAGE and 25-hydroxy-vit D. sRAGE positively correlated with CML in women without PCOS but not in women with PCOS.

CONCLUSIONS

In women with PCOS, the low ovarian levels of the anti-inflammatory sRAGE suggest that sRAGE could represent a biomarker and a potential therapeutic target for ovarian dysfunction in PCOS. Whether there is a direct causal relationship between sRAGE and vit D in the ovaries remains to be determined.

Mechanisms of diabetes mellitus-induced bone fragility

The risk of fragility fractures is increased in patients with either type 1 diabetes mellitus (T1DM) or type 2 diabetes mellitus (T2DM). Although BMD is decreased in T1DM, BMD in T2DM is often normal or even slightly elevated compared with an age-matched control population. However, in both T1DM and T2DM, bone turnover is decreased and the bone material properties and microstructure of bone are altered; the latter particularly so when microvascular complications are present. The pathophysiological mechanisms underlying bone fragility in diabetes mellitus are complex, and include hyperglycaemia, oxidative stress and the accumulation of advanced glycation endproducts that compromise collagen properties, increase marrow adiposity, release inflammatory factors and adipokines from visceral fat, and potentially alter the function of osteocytes. Additional factors including treatment-induced hypoglycaemia, certain antidiabetic medications with a direct effect on bone and mineral metabolism (such as thiazolidinediones), as well as an increased propensity for falls, all contribute to the increased fracture risk in patients with diabetes mellitus.

Curcumin and Boswellia serrata Modulate the Glyco-Oxidative Status and Lipo-Oxidation in Master Athletes

Background: Chronic intensive exercise is associated with a greater induction of oxidative stress and with an excess of endogenous advanced glycation end-products (AGEs). Curcumin can reduce the accumulation of AGEs in vitro and in animal models. We examined whether supplementation with curcumin and Boswellia serrata (BSE) gum resin for 3 months could affect plasma levels of markers of oxidative stress, inflammation, and glycation in healthy master cyclists. Methods. Forty-seven healthy male athletes were randomly assigned to Group 1, consisting of 22 subjects given a Mediterranean diet (MD) alone (MD group), and Group 2 consisted of 25 subjects given a MD plus curcumin and BSE (curcumin/BSE group). Interleukin-6 (IL-6), tumor necrosis factor-α (TNFα), high-sensitivity c-reactive protein (hs-CRP), total AGE, soluble receptor for AGE (sRAGE), malondialdehyde (MDA), plasma phospholipid fatty acid (PPFA) composition, and non-esterified fatty acids (NEFA) were tested at baseline and after 12 weeks. Results: sRAGE, NEFA, and MDA decreased significantly in both groups, while only the curcumin/BSE group showed a significant decline in total AGE. Only the changes in total AGE and MDA differed significantly between the curcumin/BSE and MD groups. Conclusions. Our data suggest a positive effect of supplementation with curcumin and BSE on glycoxidation and lipid peroxidation in chronically exercising master athletes.

Plasma Levels of Pentosidine, Carboxymethyl-Lysine, Soluble Receptor for Advanced Glycation End Products, and Metabolic Syndrome: The Metformin Effect

Metabolic syndrome (MetS) is considered one of the most important public health problems. Several and controversial studies showed that the role of advanced glycation end products (AGEs) and their receptor in the development of metabolic syndrome and therapeutic pathways is still unsolved. We have investigated whether plasma pentosidine, carboxymethyl-lysine (CML), and soluble receptor for advanced glycation end products (sRAGE) levels were increased in patients with MetS and the effect of metformin in plasma levels of pentosidine, CML, and sRAGE. 80 control subjects and 86 patients were included in this study. Pentosidine, CML, and sRAGE were measured in plasma by enzyme-linked immunosorbent assay (ELISA). Plasma pentosidine, CML, and sRAGE levels were significantly increased in patients compared to control subjects (P < 0.001, P < 0.001, and P = 0.014, resp.). Plasma levels of pentosidine were significantly decreased in patients who received metformin compared to untreated patients (P = 0.01). However, there was no significant difference between patients treated with metformin and untreated patients in plasma CML levels. Plasma levels of sRAGE were significantly increased in patients who received metformin and ACE inhibitors (P < 0.001 and P = 0.002, resp.). However, in a multiple stepwise regression analysis, pentosidine, sRAGE, and drugs treatments were not independently associated. Patients with metabolic syndrome showed increased levels of AGEs such as pentosidine and CML. Metformin treatment showed a decreased level of pentosidine but not of CML. Therapeutic pathways of AGEs development should be taken into account and further experimental and in vitro studies merit for advanced research.

Circulating Biomarkers of Diabetic Retinopathy: An Overview Based on Physiopathology

Diabetic retinopathy (DR) is the main cause of working-age adult-onset blindness. The currently available treatments for DR are applicable only at advanced stages of the disease and are associated with significant adverse effects. In early stages of DR the only therapeutic strategy that physicians can offer is a tight control of the risk factors for DR. Therefore, new pharmacological treatments for these early stages of the disease are required. In order to develop therapeutic strategies for early stages of DR new diagnostic tools are urgently needed. In this regard, circulating biomarkers could be useful to detect early disease, to identify those diabetic patients most prone to progressive worsening who ought to be followed up more often and who could obtain the most benefit from these therapies, and to monitor the effectiveness of new drugs for DR before more advanced DR stages have been reached. Research of biomarkers for DR has been mainly based on the pathogenic mechanism involved in the development of DR (i.e., AGEs, oxidative stress, endothelial dysfunction, inflammation, and proangiogenic factors). This review focuses on circulating biomarkers at both early and advanced stages that could be relevant for the prediction or detection of DR.

Molecular Markers of Diabetic Retinopathy: Potential Screening Tool of the Future?

Diabetic retinopathy (DR) is among the leading causes of new onset blindness in adults. Effective treatment may delay the onset and progression of this disease provided it is diagnosed early. At present retinopathy can only be diagnosed via formal examination of the eye by a trained specialist, which limits the population that can be effectively screened. An easily accessible, reliable screening biomarker of diabetic retinopathy would be of tremendous benefit in detecting the population in need of further assessment and treatment. This review highlights specific biomarkers that show promise as screening markers to detect early diabetic retinopathy or even to detect patients at increased risk of DR at the time of diagnosis of diabetes. The pathobiology of DR is complex and multifactorial giving rise to a wide array of potential biomarkers. This review provides an overview of these pathways and looks at older markers such as advanced glycation end products (AGEs), inflammatory markers, vascular endothelial growth factor (VEGF) as well as other newer proteins with a role in the pathogenesis of DR including neuroprotective factors such as brain derived neurotrophic factor (BDNF) and Pigment Epithelium Derived Factor (PEDF); SA100A12, pentraxin 3, brain natriuretic peptide, apelin 3, and chemerin as well as various metabolites such as lipoprotein A, folate, and homocysteine. We also consider the possible role of proteins identified through proteomics work whose levels are altered in the sera of patients with DR as screening markers though their role in pathophysiology remains to be characterized. The role of microRNA as a promising new screening marker is also discussed.

Biomarkers in Diabetic Retinopathy

There is a global diabetes epidemic correlating with an increase in obesity. This coincidence may lead to a rise in the prevalence of type 2 diabetes. There is also an as yet unexplained increase in the incidence of type 1 diabetes, which is not related to adiposity. Whilst improved diabetes care has substantially improved diabetes outcomes, the disease remains a common cause of working age adult-onset blindness. Diabetic retinopathy is the most frequently occurring complication of diabetes; it is greatly feared by many diabetes patients. There are multiple risk factors and markers for the onset and progression of diabetic retinopathy, yet residual risk remains. Screening for diabetic retinopathy is recommended to facilitate early detection and treatment. Common biomarkers of diabetic retinopathy and its risk in clinical practice today relate to the visualization of the retinal vasculature and measures of glycemia, lipids, blood pressure, body weight, smoking, and pregnancy status. Greater knowledge of novel biomarkers and mediators of diabetic retinopathy, such as those related to inflammation and angiogenesis, has contributed to the development of additional therapeutics, in particular for late-stage retinopathy, including intra-ocular corticosteroids and intravitreal vascular endothelial growth factor inhibitors ('anti-VEGFs') agents. Unfortunately, in spite of a range of treatments (including laser photocoagulation, intraocular steroids, and anti-VEGF agents, and more recently oral fenofibrate, a PPAR-alpha agonist lipid-lowering drug), many patients with diabetic retinopathy do not respond well to current therapeutics. Therefore, more effective treatments for diabetic retinopathy are necessary. New analytical techniques, in particular those related to molecular markers, are accelerating progress in diabetic retinopathy research. Given the increasing incidence and prevalence of diabetes, and the limited capacity of healthcare systems to screen and treat diabetic retinopathy, there is need to reliably identify and triage people with diabetes. Biomarkers may facilitate a better understanding of diabetic retinopathy, and contribute to the development of novel treatments and new clinical strategies to prevent vision loss in people with diabetes. This article reviews key aspects related to biomarker research, and focuses on some specific biomarkers relevant to diabetic retinopathy.

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.

Increased serum concentrations of pentosidine are related to presence and severity of coronary artery disease

BACKGROUND

There are limited data regarding the contribution of advanced glycation end products (AGEs) in the presence of coronary artery disease (CAD). We investigated whether serum pentosidine and Nε-carboxymethyllysine (CML) were related to the presence and the severity of CAD.

METHODS

69 Tunisian patients with CAD (≥ 50% obstruction in ≥ 1 coronary artery), 32 Tunisian patients without CAD but with potential cardiovascular risk factors and 60 Tunisian control subjects were included in a cross-sectional study. Patients were classified as CAD and non CAD patients according to angiographic results. The severity of CAD was assessed using the Gensini score. Serum pentosidine and CML were measured by LC-MS/MS.

RESULTS

Serum pentosidine and CML concentrations were significantly higher in non-CAD patients vs control subjects (P<0.001). Serum pentosidine concentrations were significantly higher in CAD patients vs non-CAD patients (P<0.001). A multiple logistic regression analysis demonstrated that pentosidine was independently associated with the presence of CAD (OR=1.52, 95% CI: 1.12-2.07, P=0.007). The area under curve (AUC) determined by ROC analysis was 0.74 (95% CI: 0.64-0.84, P<0.001) and the optimal cut-off value of pentosidine to predict the presence of CAD was 3.2 μmol/mol Lys, with 64% sensitivity and 78% specificity. Furthermore, in a multivariate stepwise regression analysis, pentosidine was independently correlated with Gensini score (standardized β= 0.46, 95% CI: 0.70-1.99, P<0.001).

CONCLUSIONS

High concentrations of pentosidine show the presence and the severity of CAD with high sensitivity.

Unlocking the biology of RAGE in diabetic microvascular complications

The discovery of the receptor for advanced glycation end-products (RAGE) set the stage for the elucidation of important mechanisms underpinning diabetic complications. RAGE transduces the signals of advanced glycation end-products (AGEs), proinflammatory S100/calgranulins, and high mobility group box 1 (HMGB1), and is a one of a family of receptors for lysophosphatidic acid (LPA). These ligand tales weave a theme of vascular perturbation and inflammation linked to the pathogenesis of the chronic complications of diabetes. Once deemed implausible, this concept of inflammatory cues participating in diabetic complications is now supported by a plethora of experimental evidence in the macro- and microvasculature. We review the biology of ligand-RAGE signal transduction and its roles in diabetic microvascular complications, from animal models to human subjects.

Biomarkers in diabetic retinopathy and the therapeutic implications

The main problem both in type 1 (T1DM) and type 2 (T2DM) diabetes is the development of chronic vascular complications encompassing micro- as well as macrocirculation. Chronic complications lower the quality of life, lead to disability, and are the cause of premature death in DM patients. One of the chronic vascular complications is a diabetic retinopathy (DR) which leads to a complete loss of sight in DM patients. Recent trials show that the primary cause of diabetic retinopathy is retinal neovascularization caused by disequilibrium between pro- and antiangiogenic factors. Gaining knowledge of the mechanisms of action of factors influencing retinal neovascularization as well as the search for new, effective treatment methods, especially in advanced stages of DR, puts special importance on research concentrating on the implementation of biological drugs in DR therapy. At present, it is antivascular endothelial growth factor and antitumor necrosis factor that gain particular significance.

Usefulness of non-enzymatic post-translational modification derived products (PTMDPs) as biomarkers of chronic diseases

Molecular aging of proteins results from the complex association of different reactions that lead to the progressive alteration of their structural and functional properties. These reactions, which include oxidation, glycoxidation, carbonylation and carbamylation, occur during aging and are amplified in various chronic diseases such as diabetes or chronic renal failure. Specific compounds generated throughout this process called post-translational modification derived products (PTMDPs) have been suggested to be promising biomarkers for the management of chronic diseases. During the last decades, the emergence of mass spectrometry and proteomics has largely contributed to the development of sensitive and specific analytical methods devoted to PTMDP quantification in biological fluids. This review aimed at providing evidences for the clinical relevance of PTMDPs as biomarkers in chronic diseases, and at emphasizing on the contribution of mass spectrometric and proteomic methods in this field. Different issues that should be addressed in order to ensure the implementation of these biomarkers in clinical practice have been highlighted. This article is part of a Special Issue entitled: Posttranslational Protein modifications in biology and Medicine.