Serum pentosidine as an indicator of Alzheimer's disease

Skin autofluorescence, reflecting accumulation of advanced glycation end products, and the risk of dementia in a population-based cohort

Conditions such as hyperglycemia and oxidative stress lead to the formation of advanced glycation end products (AGEs), which are harmful compounds that have been implicated in dementia. Within the Rotterdam Study, we measured skin AGEs as skin autofluorescence, reflecting long-term accumulation of AGEs, and determined their association with the risk of dementia and with brain magnetic resonance imaging (MRI) measures. Skin autofluorescence was measured between 2013 and 2016 in 2922 participants without dementia. Of these, 1504 also underwent brain MRI, on which measures of brain atrophy and cerebral small vessel disease were assessed. All participants were followed for the incidence of dementia until 2020. Of 2922 participants (mean age 72.6 years, 57% women), 123 developed dementia. Higher skin autofluorescence (per standard deviation) was associated with an increased risk of dementia (hazard ratio 1.21 [95% confidence interval 1.01-1.46]) and Alzheimer's disease (1.19 [0.97-1.47]), independently of age and other studied potential confounders. Stronger effects were seen in apolipoprotein E (APOE) ε4 carriers (1.34 [0.98-1.82]) and in participants with diabetes (1.35 [0.94-1.94]). Participants with higher skin autofluorescence levels also had smaller total brain volumes and smaller hippocampus volumes on MRI, and they had more often lacunes. These results suggest that AGEs may be involved in dementia pathophysiology.

Anti-Glucotoxicity Effect of Phytoconstituents via Inhibiting MGO-AGEs Formation and Breaking MGO-AGEs

The therapeutic benefits of phytochemicals in the treatment of various illnesses and disorders are well documented. They show significant promise for the discovery and creation of novel medications for treating a variety of human diseases. Numerous phytoconstituents have shown antibiotic, antioxidant, and wound-healing effects in the conventional system. Traditional medicines based on alkaloids, phenolics, tannins, saponins, terpenes, steroids, flavonoids, glycosides, and phytosterols have been in use for a long time and are crucial as alternative treatments. These phytochemical elements are crucial for scavenging free radicals, capturing reactive carbonyl species, changing protein glycation sites, inactivating carbohydrate hydrolases, fighting pathological conditions, and accelerating the healing of wounds. In this review, 221 research papers have been reviewed. This research sought to provide an update on the types and methods of formation of methylglyoxal-advanced glycation end products (MGO-AGEs) and molecular pathways induced by AGEs during the progression of the chronic complications of diabetes and associated diseases as well as to discuss the role of phytoconstituents in MGO scavenging and AGEs breaking. The development and commercialization of functional foods using these natural compounds can provide potential health benefits.

In Vitro Methodologies to Study the Role of Advanced Glycation End Products (AGEs) in Neurodegeneration

Advanced glycation end products (AGEs) can be present in food or be endogenously produced in biological systems. Their formation has been associated with chronic neurodegenerative diseases such as Alzheimer’s disease, Parkinson’s disease, multiple sclerosis, and amyotrophic lateral sclerosis. The implication of AGEs in neurodegeneration is related to their ability to bind to AGE-specific receptors and the ability of their precursors to induce the so-called “dicarbonyl stress”, resulting in cross-linking and protein damage. However, the mode of action underlying their role in neurodegeneration remains unclear. While some research has been carried out in observational clinical studies, further in vitro studies may help elucidate these underlying modes of action. This review presents and discusses in vitro methodologies used in research on the potential role of AGEs in neuroinflammation and neurodegeneration. The overview reveals the main concepts linking AGEs to neurodegeneration, the current findings, and the available and advisable in vitro models to study their role. Moreover, the major questions regarding the role of AGEs in neurodegenerative diseases and the challenges and discrepancies in the research field are discussed.

Identification of key long non-coding RNA-associated competing endogenous RNA axes in Brodmann Area 10 brain region of schizophrenia patients

Schizophrenia (SCZ) is a serious mental condition with an unknown cause. According to the reports, Brodmann Area 10 (BA10) is linked to the pathology and cortical dysfunction of SCZ, which demonstrates a number of replicated findings related to research on SCZ and the dysfunction in tasks requiring cognitive control in particular. Genetics' role in the pathophysiology of SCZ is still unclear. Therefore, it may be helpful to understand the effects of these changes on the onset and progression of SCZ to find novel mechanisms involved in the regulation of gene transcription. In order to determine the molecular regulatory mechanisms affecting the SCZ, the long non-coding RNA (lncRNA)-associated competing endogenous RNAs (ceRNAs) axes in the BA10 area were determined using a bioinformatics approach in the present work. A microarray dataset (GSE17612) consisted of brain post-mortem tissues of the BA10 area from SCZ patients and matched healthy subjects was downloaded from the Gene Expression Omnibus (GEO) database. This dataset included probes for both lncRNAs and mRNAs. Using the R software's limma package, the differentially expressed lncRNAs (DElncRNAs) and mRNAs (DEmRNAs) were found. The RNA interactions were also discovered using the DIANA-LncBase and miRTarBase databases. In the ceRNA network, positive correlations between DEmRNAs and DElncRNAs were evaluated using the Pearson correlation coefficient. Finally, lncRNA-associated ceRNA axes were built by using the co-expression and DElncRNA-miRNA-DEmRNA connections. We identified the DElncRNA-miRNA-DEmRNA axes, which included two key lncRNAs (PEG3-AS1, MIR570HG), seven key miRNAs (hsa-miR-124-3p, hsa-miR-17-5p, hsa-miR-181a-5p, hsa-miR-191-5p, hsa-miR-26a-5p, hsa-miR-29a-3p, hsa-miR-29b-3p), and eight key mRNAs (EGR1, ETV1, DUSP6, PLOD2, CD93, SERPINB9, ANGPTL4, TGFB2). Furthermore, DEmRNAs were found to be enriched in the "AGE-RAGE signaling pathway in diabetic complications", "Amoebiasis", "Transcriptional misregulation in cancer", "Human T-cell leukemia virus 1 infection", and "MAPK signaling pathway". This study offers research targets for examining significant molecular pathways connected to the pathogenesis of SCZ, even though the function of these ceRNA axes still needs to be investigated.

Advanced glycation end products and cognitive impairment in schizophrenia

Advanced glycation end products play a key role in the pathophysiology of schizophrenia. Cognitive impairment is one of the central features of schizophrenia; however, the association between advanced glycation end products and cognitive impairment remains unknown. This study investigated whether advanced glycation end products affect the cognitive domain in patients with schizophrenia. A total of 58 patients with chronic schizophrenia were included in this cross-sectional study. Plasma advanced glycation end products were measured using high-performance liquid chromatography (HPLC). Neuropsychological and cognitive functions were assessed using the Wechsler Adult Intelligence Scale, Third Version, and the Wisconsin Card Sorting Test Keio-FS version. Multiple regression analysis adjusted for age, sex, body mass index, educational years, daily dose of antipsychotics, and psychotic symptoms revealed that processing speed was significantly associated with plasma pentosidine, a representative advanced glycation end product (standardized β = -0.425; p = 0.009). Processing speed is the cognitive domain affected by advanced glycation end products. Considering preceding evidence that impaired processing speed is related to poor functional outcome, interventions targeted at reducing advanced glycation end products may contribute to promoting recovery of patients with schizophrenia as well as cognitive function improvement.

Assessment of Advanced Glycation End Products and Receptors and the Risk of Dementia

Importance

Advanced glycation end products (AGEs) and their receptor (RAGE) are implicated in the pathophysiological processes of dementia and potentially underlie the association of diabetes with neurodegeneration. However, longitudinal studies examining this association are lacking.

Objective

To determine whether markers of the AGE-RAGE system are associated with prevalent and incident dementia and with cognition.

Design, Setting, and Participants

In this population-based cohort study including participants from the prospective Rotterdam Study, extracellular newly identified RAGE binding protein (EN-RAGE) and soluble RAGE (S-RAGE) were measured in plasma collected between 1997 and 1999 in a random selection of participants, and additionally in participants with prevalent dementia. Participants without dementia were followed up for dementia until 2016. Skin AGEs, measured as skin autofluorescence, and cognition were measured between 2013 and 2016 in participants without dementia. Data analysis was performed from June 2019 to December 2019.

Exposures

EN-RAGE, S-RAGE, and skin autofluorescence.

Main Outcomes and Measures

Prevalent and incident dementia and cognition, adjusted for potential confounders, including age, sex, diabetes, educational level, APOE ε4 carrier status, smoking, and estimated glomerular filtration rate.

Results

Of 3889 included participants (mean [SD] age, 72.5 [8.9] years; 2187 [56.2%] women), 1021 participants had data on plasma markers (mean [SD] age 73.6 [7.8] years; 564 [55.2%] women), 73 participants had dementia at baseline, and during 10 711 person-years of follow-up, 161 participants developed incident dementia. Compared with low levels, high EN-RAGE level was associated with a higher prevalence of dementia (odds ratio [OR], 3.68 [95% CI, 1.50-8.03]; P = .003), while high S-RAGE level was associated with a lower prevalence of dementia (OR, 0.37 [95% CI, 0.17-0.78]; P = .01). These associations attenuated in a longitudinal setting, with hazard ratios of 0.65 (95% CI, 0.42-1.01) for high EN-RAGE (P = .05) and 1.22 (95% CI, 0.82-1.81) for high S-RAGE (P = .33). Among 2890 participants without dementia (mean [SD] age, 72.5 [9.4] years; 1640 [57%] women), higher skin autofluorescence was associated with lower global cognitive function (adjusted difference in z score per 1-SD higher skin autofluorescence, -0.07 [95% CI, -0.11 to -0.04]), especially among carriers of the APOE ε4 allele (adjusted difference in z score per 1-SD higher skin autofluorescence, -0.15 [95% CI, -0.22 to -0.07]).

Conclusions and Relevance

These findings suggest that the AGE-RAGE system is associated with cognitive decline and dementia cross-sectionally but not longitudinally. This indicates either a short-term association or reverse causality. Findings of cross-sectional associations between higher skin autofluorescence and lower cognitive function and an association with APOE status also warrant replication and prospective studies.

The potential role of dietary advanced glycation endproducts in the development of chronic non-infectious diseases: a narrative review

Increasing clinical and experimental evidence accumulated during the past few decades supports an important role for dietary advanced glycation endproducts (AGE) in the pathogenesis of many chronic non-infectious diseases, such as type 2 diabetes, CVD and others, that are reaching epidemic proportions in the Western world. Although AGE are compounds widely recognised as generated in excess in the body in diabetic patients, the potential importance of exogenous AGE, mostly of dietary origin, has been largely ignored in the general nutrition audience. In the present review we aim to describe dietary AGE, their mechanisms of formation and absorption into the body as well as their main mechanisms of action. We will present in detail current evidence of their potential role in the development of several chronic non-infectious clinical conditions, some general suggestions on how to restrict them in the diet and evidence regarding the potential benefits of lowering their consumption.

Circulating and Extracellular Vesicles Levels of N-(1-Carboxymethyl)-L-Lysine (CML) Differentiate Early to Moderate Alzheimer's Disease

BACKGROUND

Both advanced glycation end products (AGEs) N-(1-carboxymethyl)-L-lysine (CML) and pentosidine were found in the brain from Alzheimer's disease (AD) patients and were associated with the neuropathological hallmarks of AD. In AD patients, the circulating level of both AGEs remains unknown. Moreover, their levels in peripheral extracellular vesicles (EVs) and their association with AD remain to be determined. Finally, it is not known if neuronal cells can release AGEs via EVs and propagate AGEs.

OBJECTIVE

To determine the levels of circulating CML and pentosidine during the progression of AD. Moreover, their levels in circulating EVs were determined and their association with the clinical cognitive scores were analyzed. Finally, we have studied the possibility that neuronal cells eliminate and transfer these AGEs through EVs.

METHODS

CML and pentosidine levels were measured in serum and in circulating EVs. Released-EVs from SK-N-SH neuronal cells were isolated and CML levels were also determined.

RESULTS

The levels of CML in albumin-free serum proteins were higher in the early stage of AD while the levels of pentosidine remained unchanged. In contrast, the levels of CML in the EVs were lower in the moderate stage of AD. Interestingly, the levels of CML in serum were negatively correlated with the clinical cognitive scores MMSE and MoCA. For the first time, we were able to demonstrate that CML was present in EVs released from neuronal cells in culture.

CONCLUSION

Peripheral and circulating EVs levels of CML can differentiate early to moderate AD. In the brain, neuronal CML can propagate from cells-to-cells via EVs.

Benfotiamine and Cognitive Decline in Alzheimer's Disease: Results of a Randomized Placebo-Controlled Phase IIa Clinical Trial

BACKGROUND

In preclinical models, benfotiamine efficiently ameliorates the clinical and biological pathologies that define Alzheimer's disease (AD) including impaired cognition, amyloid-β plaques, neurofibrillary tangles, diminished glucose metabolism, oxidative stress, increased advanced glycation end products (AGE), and inflammation.

OBJECTIVE

To collect preliminary data on feasibility, safety, and efficacy in individuals with amnestic mild cognitive impairment (aMCI) or mild dementia due to AD in a placebo-controlled trial of benfotiamine.

METHODS

A twelve-month treatment with benfotiamine tested whether clinical decline would be delayed in the benfotiamine group compared to the placebo group. The primary clinical outcome was the Alzheimer's Disease Assessment Scale-Cognitive Subscale (ADAS-Cog). Secondary outcomes were the clinical dementia rating (CDR) score and fluorodeoxyglucose (FDG) uptake, measured with brain positron emission tomography (PET). Blood AGE were examined as an exploratory outcome.

RESULTS

Participants were treated with benfotiamine (34) or placebo (36). Benfotiamine treatment was safe. The increase in ADAS-Cog was 43% lower in the benfotiamine group than in the placebo group, indicating less cognitive decline, and this effect was nearly statistically significant (p = 0.125). Worsening in CDR was 77% lower (p = 0.034) in the benfotiamine group compared to the placebo group, and this effect was stronger in the APOEɛ4 non-carriers. Benfotiamine significantly reduced increases in AGE (p = 0.044), and this effect was stronger in the APOEɛ4 non-carriers. Exploratory analysis derivation of an FDG PET pattern score showed a treatment effect at one year (p = 0.002).

CONCLUSION

Oral benfotiamine is safe and potentially efficacious in improving cognitive outcomes among persons with MCI and mild AD.

Crucial players in Alzheimer's disease and diabetes mellitus: Friends or foes?

Alzheimer's disease (AD) and diabetes mellitus, especially type 2 (T2DM), are very common and widespread diseases in contemporary societies, and their incidence is steadily on the increase. T2DM is a multiple metabolic disorder, with several mechanisms including hyperglycaemia, insulin resistance, insulin receptor and insulin growth factor disturbances, glucose toxicity, formation of advanced glycation end products (AGEs) and the activity of their receptors. AD is the most common form of dementia, characterized by the accumulation of extracellular beta amyloid peptide aggregates and intracellular hyper-phosphorylated tau proteins, which are thought to drive and/or accelerate inflammatory and oxidative stress processes leading to neurodegeneration. The aim of this paper is to provide a comprehensive review of the evidence linking T2DM to the onset and development of AD and highlight the unknown or poorly studied "nooks and crannies" of this interesting relationship, hence providing an opportunity to stimulate new ideas for the analysis of comorbidities between AD and DM. Despite, indication of possible biomarkers of early diagnosis of T2DM and AD, this review is also an attempt to answer the question as to whether the crucial factors in the development of both conditions support the link between DM and AD.

Insight of brain degenerative protein modifications in the pathology of neurodegeneration and dementia by proteomic profiling

Dementia is a syndrome associated with a wide range of clinical features including progressive cognitive decline and patient inability to self-care. Due to rapidly increasing prevalence in aging society, dementia now confers a major economic, social, and healthcare burden throughout the world, and has therefore been identified as a public health priority by the World Health Organization. Previous studies have established dementia as a 'proteinopathy' caused by detrimental changes in brain protein structure and function that promote misfolding, aggregation, and deposition as insoluble amyloid plaques. Despite clear evidence that pathological cognitive decline is associated with degenerative protein modifications (DPMs) arising from spontaneous chemical modifications to amino acid side chains, the molecular mechanisms that promote brain DPMs formation remain poorly understood. However, the technical challenges associated with DPM analysis have recently become tractable due to powerful new proteomic techniques that facilitate detailed analysis of brain tissue damage over time. Recent studies have identified that neurodegenerative diseases are associated with the dysregulation of critical repair enzymes, as well as the misfolding, aggregation and accumulation of modified brain proteins. Future studies will further elucidate the mechanisms underlying dementia pathogenesis via the quantitative profiling of the human brain proteome and associated DPMs in distinct phases and subtypes of disease. This review summarizes recent developments in quantitative proteomic technologies, describes how these techniques have been applied to the study of dementia-linked changes in brain protein structure and function, and briefly outlines how these findings might be translated into novel clinical applications for dementia patients. In this review, only spontaneous protein modifications such as deamidation, oxidation, nitration glycation and carbamylation are reviewed and discussed.

The regulation of soluble receptor for AGEs contributes to carbonyl stress in schizophrenia

Our previous study showed that enhanced carbonyl stress is closely related to schizophrenia. The endogenous secretory receptor for advanced glycation end-products (esRAGE) is a splice variant of the AGER gene and is one of the soluble forms of RAGE. esRAGE is considered to be a key molecule for alleviating the burden of carbonyl stress by entrapping advanced glycation end-products (AGEs). In the current study, we conducted genetic association analyses focusing on AGER, in which we compared 212 schizophrenic patients to 214 control subjects. We also compared esRAGE levels among a subgroup of 104 patients and 89 controls and further carried out measurements of total circulating soluble RAGE (sRAGE) in 25 patients and 49 healthy subjects. Although the genetic association study yielded inconclusive results, multiple regression analysis indicated that a specific haplotype composed of rs17846798, rs2071288, and a 63 bp deletion, which were in perfect linkage disequilibrium (r² = 1), and rs2070600 (Gly82Ser) were significantly associated with a marked decrease in serum esRAGE levels. Furthermore, compared to healthy subjects, schizophrenia showed significantly lower esRAGE (p = 0.007) and sRAGE (p = 0.03) levels, respectively. This is the first study to show that serum esRAGE levels are regulated by a newly identified specific haplotype in AGER and that a subpopulation of schizophrenic patients are more vulnerable to carbonyl stress.

High dietary advanced glycation end products are associated with poorer spatial learning and accelerated Aβ deposition in an Alzheimer mouse model

There is growing evidence of the involvement of advanced glycation end products (AGEs) in the pathogenesis of neurodegenerative processes including Alzheimer's disease (AD) and their function as a seed for the aggregation of Aβ, a hallmark feature of AD. AGEs are formed endogenously and exogenously during heating and irradiation of foods. We here examined the effect of a diet high in AGEs in the context of an irradiated diet on memory, insoluble Aβ₄₂, AGEs levels in hippocampus, on expression of the receptor for AGEs (RAGE), and on oxidative stress in the vasculature. We found that AD‐like model mice on high‐AGE diet due to irradiation had significantly poorer memory, higher hippocampal levels of insoluble Aβ₄₂ and AGEs as well as higher levels of oxidative stress on vascular walls, compared to littermates fed an isocaloric diet. These differences were not due to weight gain. The data were further supported by the overexpression of RAGE, which binds to Aβ₄₂ and regulates its transport across the blood–brain barrier, suggesting a mediating pathway. Because exposure to AGEs can be diminished, these insights provide an important simple noninvasive potential therapeutic strategy for alleviating a major lifestyle‐linked disease epidemic.

Clinical features of schizophrenia with enhanced carbonyl stress

Accumulating evidence suggests that advanced glycation end products, generated as a consequence of facilitated carbonyl stress, are implicated in the development of a variety of diseases. These diseases include neurodegenerative illnesses, such as Alzheimer disease. Pyridoxamine is one of the 3 forms of vitamin B6, and it acts by combating carbonyl stress and inhibiting the formation of AGEs. Depletion of pyridoxamine due to enhanced carbonyl stress eventually leads to a decrease in the other forms of vitamin B6, namely pyridoxal and pyridoxine. We previously reported that higher levels of plasma pentosidine, a well-known biomarker for advanced glycation end products, and decreased serum pyridoxal levels were found in a subpopulation of schizophrenic patients. However, there is as yet no clinical characterization of this subset of schizophrenia. In this study, we found that these patients shared many clinical features with treatment-resistant schizophrenia. These include a higher proportion of inpatients, low educational status, longer durations of hospitalization, and higher doses of antipsychotic medication, compared with patients without carbonyl stress. Interestingly, psychopathological symptoms showed a tendency towards negative association with serum vitamin B6 levels. Our results support the idea that treatment regimes reducing carbonyl stress, such as supplementation of pyridoxamine, could provide novel therapeutic benefits for this subgroup of patients.

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.

Serum concentration of an inflammatory glycotoxin, methylglyoxal, is associated with increased cognitive decline in elderly individuals

BACKGROUND

Advanced glycations end products increase oxidant stress, inflammation, and neurotoxicity. Serum levels are increased in diabetes and aging. We examined the relationship between serum methylglyoxal derivatives (sMG), and cognitive decline, in 267 non-demented elderly.

METHODS

Tobit mixed regression models assessed the association of baseline sMG with cognitive decline in the Mini Mental State Exam (MMSE) over time, controlling for sociodemographic factors (age, sex, and years of education), cardiovascular risk factors (diabetes and presence of an ApoE4 allele), and kidney function. sMG was assessed by ELISA.

RESULTS

The fully adjusted model showed an annual decline of 0.26 MMSE points per unit increase in baseline sMG (p = 0.03). Significance was unchanged as additional risk factors were added to the model. The interactions of sMG with diabetes, sex, age, kidney function, and ApoE4 genotype were not significant.

CONCLUSIONS

Higher levels of baseline sMG were associated with a faster rate of cognitive decline, after adjusting for several sociodemographic and clinical characteristics. This relationship did not differ by sex, ApoE4 genotype, or diabetes status suggesting its generality. Since subjects were cognitively normal at the beginning of the study, elevated sMG may be indicative of brain cell injury initiated before clinically evident cognitive compromise.

Advanced glycation end product level, diabetes, and accelerated cognitive aging

OBJECTIVE

Several studies report that diabetes increases risk of cognitive impairment; some have hypothesized that advanced glycation end products (AGEs) underlie this association. AGEs are cross-linked products that result from reactions between glucose and proteins. Little is known about the association between peripheral AGE concentration and cognitive aging.

METHODS

We prospectively studied 920 elders without dementia, 495 with diabetes and 425 with normal glucose (mean age 74.0 years). Using mixed models, we examined baseline AGE concentration, measured with urine pentosidine and analyzed as tertile, and performance on the Modified Mini-Mental State Examination (3MS) and Digit Symbol Substitution Test (DSST) at baseline and repeatedly over 9 years. Incident cognitive impairment (a decline of >1.0 SD on each test) was analyzed with logistic regression.

RESULTS

Older adults with high pentosidine level had worse baseline DSST score (p=0.05) but not different 3MS score (p=0.32). On both tests, there was a more pronounced 9-year decline in those with high and mid pentosidine level compared to those in the lowest tertile (3MS 7.0, 5.4, and 2.5 point decline, p overall <0.001; DSST 5.9, 7.4, and 4.5 point decline, p=0.03). Incident cognitive impairment was higher in those with high or mid pentosidine level than those in the lowest tertile (3MS: 24% vs 17%, odds ratio=1.55; 95% confidence interval 1.07-2.26; DSST: 31% vs 22%, odds ratio=1.62; 95% confidence interval 1.13-2.33). There was no interaction between pentosidine level, diabetes status, and cognitive decline. Multivariate adjustment for age, sex, race, education, hypertension, cardiovascular disease, estimated glomerular filtration rate, and diabetes diminished results somewhat but overall patterns remained similar.

CONCLUSION

High peripheral AGE level is associated with greater cognitive decline in older adults with and without diabetes.

Plasma pentosidine: a potential biomarker in the management of multiple sclerosis

Background: The chronic inflammation associated with multiple sclerosis (MS) may lead to the upregulation of pentosidine.

Objectives: This cross-sectional study compares plasma pentosidine levels among healthy controls (HCs) and patients with MS at different disease stages. The study also determines pentosidine's usefulness as a biomarker of MS disease activity and/or severity via its correlation with a number of indicators of MS disease.

Methods: Pentosidine levels were analyzed in 98 MS patients and 43 HCs using reverse-phase high-pressure liquid chromatography with fluorescence detection.

Results: Plasma pentosidine levels were significantly higher in MS patients when compared with HCs ( p = 0.02). Patients on disease-modifying therapies (DMTs) had lower plasma pentosidine levels when compared with DMT-naïve patients ( p =  0.01). Pentosidine plasma levels correlated with indicators of MS disease severity, including Extended Disability Status Scale ( p = 0.03), MS Severity Scale ( p = 0.01), and MS Functional Composite ( p = 0.03). No correlation between pentosidine levels and age, rate of clinical relapse, and disease duration was observed.

Conclusions: Our results suggest that pentosidine could be a novel, inflammatory biomarker in MS clinical practice. Longitudinal studies are warranted to determine any causal relationship between changes in plasma pentosidine levels and MS disease pathology. These studies may pave the way for use of advanced glycation end product (AGE) inhibitors and AGE-breaking agents as new therapeutic modalities in MS.

AGEs/RAGE complex upregulates BACE1 via NF-κB pathway activation

Although the pathogenesis of sporadic Alzheimer disease (AD) is not clearly understood, it is likely dependent on several age-related factors. Diabetes is a risk factor for AD, and multiple mechanisms connecting the 2 diseases have been proposed. Hyperglycemia enhances the formation of advanced glycation end products (AGEs) that result from the auto-oxidation of glucose and fructose. The interaction of AGEs with their receptor, named RAGE, elicits the formation of reactive oxygen species that are also believed to be an early event in AD pathology. To investigate a functional link between the disorders diabetes and AD, the effect of 2 AGEs, pentosidine and glyceraldehydes-derived pyridinium (GLAP), was studied on BACE1 expression both in vivo, in streptozotocin treated rats, and in vitro in differentiated neuroblastoma cells. We showed that pentosidine and GLAP were able to upregulate BACE1 expression through their binding with RAGE and the consequent activation of NF-κB. In addition, both pentosidine and GLAP were found to be increased in the brain in sporadic AD patients. Our findings demonstrate that activation of the AGEs/RAGE axis, by upregulating the key enzyme for amyloid-β production, provides a pathologic link between diabetes mellitus and AD.

Hyperglycemia and glycation in diabetic complications

Diabetes mellitus is a multifactorial disease, classically influenced by genetic determinants of individual susceptibility and by environmental accelerating factors, such as lifestyle. It is considered a major health concern,as its incidence is increasing at an alarming rate, and the high invalidating effects of its long-term complications affect macro- and microvasculature, heart, kidney, eye, and nerves. Increasing evidence indicates that hyperglycemia is the initiating cause of the tissue damage occurring in diabetes, either through repeated acute changes in cellular glucose metabolism, or through the long-term accumulation of glycated biomolecules and advanced glycation end products (AGEs). AGEs represent a heterogeneous group of chemical products resulting from a nonenzymatic reaction between reducing sugars and proteins, lipids, nucleic acids, or a combination of these.The glycation process (glucose fixation) affects circulating proteins (serum albumin, lipoprotein, insulin, hemoglobin),whereas the formation of AGEs implicates reactive intermediates such as methylglyoxal. AGEs form cross-links on long-lived extracellular matrix proteins or react with their specific receptor RAGE, resulting inoxidative stress and proinflammatory signaling implicated in endothelium dysfunction, arterial stiffening, and microvascular complications. This review summarizes the mechanism of glycation and of AGEs formation and the role of hyperglycemia, AGEs, and oxidative stress in the pathophysiology of diabetic complications.

[Biomarkers for early diagnosis of Alzheimer's disease: current update and future directions]

INTRODUCTION

The increased prevalence of the sporadic form of Alzheimer's disease (AD) has become a significant health issue in the elderly population. The need for early diagnosis is imperative because this, along with the development of novel therapeutic treatments, would permit the rapid and perhaps more efficient treatment of these debilitating disorders early on.

BACKGROUND

Over the last decade, the potential use of certain biomarkers in the cerebrospinal fluid (CSF), and more recently, in the plasma has been investigated. Among the candidates studied includes the neurotoxic amyloid beta peptide and the Tau protein. However, although these two proteins have been clearly shown to be directly related to the pathophysiology of this disorder, it has proven difficult to establish a clear relationship between plasma or CSF levels of Abeta and Tau and the incidence and severity of AD in patients. This is due in part to differences in methodologies related to the detection sensitivity, as well as the variations in the biological data and consequent interpretation of the biochemical and biological data. Peripheral cells, in particular platelets and skin fibroblasts, could be an alternative solution as peripheral biological markers for the early diagnosis of AD. These cells are easily accessible from patients. Furthermore, they would provide a means not only to validate potential therapeutic strategies, but also to study the mechanisms involved in the development of AD, including APP processing.

PERSPECTIVES

A combined strategy using both a fundamental mechanistic and an analytical approach of patient peripheral cells will allow the identification of new biological markers for AD, and hence permit immediate therapeutic strategies to be implemented.