Crosslinking of alpha-synuclein by advanced glycation endproducts--an early pathophysiological step in Lewy body formation?

Mitigating diabetes associated with reactive oxygen species (ROS) and protein aggregation through pharmacological interventions

Diabetes mellitus, a complex metabolic disorder, presents a growing global health challenge. In 2021, there were 529 million diabetics worldwide. At the super-regional level, Oceania, the Middle East, and North Africa had the highest age-standardized rates. The majority of cases of diabetes in 2021 (>90.0%) were type 2 diabetes, which is largely indicative of the prevalence of diabetes in general, particularly in older adults (K. L. Ong, et al., Global, regional, and national burden of diabetes from 1990 to 2021, with projections of prevalence to 2050: a systematic analysis for the Global Burden of Disease Study 2021, Lancet, 2023, 402(10397), 203-234). Nowadays, slowing the progression of diabetic complications is the only effective way to manage diabetes with the available therapeutic options. However, novel biomarkers and treatments are urgently needed to control cytokine secretion, advanced glycation end products (AGEs) production, vascular inflammatory effects, and cellular death. Emerging research has highlighted the intricate interplay between reactive oxygen species (ROS) and protein aggregation in the pathogenesis of diabetes. In this scenario, the main aim of this paper is to provide a comprehensive review of the current understanding of the molecular mechanisms underlying ROS-induced cellular damage and protein aggregation, specifically focusing on their contribution to diabetes development. The role of ROS as key mediators of oxidative stress in diabetes is discussed, emphasizing their impact on cellular components and signaling. Additionally, the involvement of protein aggregation in impairing cellular function and insulin signaling is explored. The synergistic effects of ROS and protein aggregation in promoting β-cell dysfunction and insulin resistance are examined, shedding light on potential targets for therapeutic intervention.

Insight into the Effect of Methylglyoxal on the Conformation, Function, and Aggregation Propensity of α-Synuclein

It is well-known that people suffering from hyperglycemia have a higher propensity to develop Parkinson's disease (PD). One of the most plausible mechanisms linking these two pathologies is the glycation of neuronal proteins and the pathological consequences of it. α-Synuclein, a key component in PD, can be glycated at its fifteen lysine. In fact, the end products of this process have been detected on aggregated α-synuclein isolated from in vivo. However, the consequences of glycation are not entirely clear, which are of crucial importance to understand the mechanism underlying the connection between diabetes and PD. To better clarify this, we have here examined how methylglyoxal (the most important carbonyl compound found in the cytoplasm) affects the conformation and aggregation propensity of α-synuclein, as well as its ability to cluster and fuse synaptic-like vesicles. The obtained data prove that methylglyoxal induces the Lys-Lys crosslinking through the formation of MOLD. However, this does not have a remarkable effect on the averaged conformational ensemble of α-synuclein, although it completely depletes its native propensity to form soluble oligomers and insoluble amyloid fibrils. Moreover, methylglyoxal has a disrupting effect on the ability of α-synuclein to bind, cluster and fusion synaptic-like vesicles.

The Contribution of Type 2 Diabetes to Parkinson's Disease Aetiology

Type 2 diabetes (T2D) and Parkinson's disease (PD) are chronic disorders that have a significant health impact on a global scale. Epidemiological, preclinical, and clinical research underpins the assumption that insulin resistance and chronic inflammation contribute to the overlapping aetiologies of T2D and PD. This narrative review summarises the recent evidence on the contribution of T2D to the initiation and progression of PD brain pathology. It also briefly discusses the rationale and potential of alternative pharmacological interventions for PD treatment.

The RAGE Axis: A Relevant Inflammatory Hub in Human Diseases

In 1992, a transcendental report suggested that the receptor of advanced glycation end-products (RAGE) functions as a cell surface receptor for a wide and diverse group of compounds, commonly referred to as advanced glycation end-products (AGEs), resulting from the non-enzymatic glycation of lipids and proteins in response to hyperglycemia. The interaction of these compounds with RAGE represents an essential element in triggering the cellular response to proteins or lipids that become glycated. Although initially demonstrated for diabetes complications, a growing body of evidence clearly supports RAGE's role in human diseases. Moreover, the recognizing capacities of this receptor have been extended to a plethora of structurally diverse ligands. As a result, it has been acknowledged as a pattern recognition receptor (PRR) and functionally categorized as the RAGE axis. The ligation to RAGE leads the initiation of a complex signaling cascade and thus triggering crucial cellular events in the pathophysiology of many human diseases. In the present review, we intend to summarize basic features of the RAGE axis biology as well as its contribution to some relevant human diseases such as metabolic diseases, neurodegenerative, cardiovascular, autoimmune, and chronic airways diseases, and cancer as a result of exposure to AGEs, as well as many other ligands.

Communal interaction of glycation and gut microbes in diabetes mellitus, Alzheimer's disease, and Parkinson's disease pathogenesis

Diabetes and its complications, Alzheimer's disease (AD), and Parkinson's disease (PD) are increasing gradually, reflecting a global threat vis-à-vis expressing the essentiality of a substantial paradigm shift in research and remedial actions. Protein glycation is influenced by several factors, like time, temperature, pH, metal ions, and the half-life of the protein. Surprisingly, most proteins associated with metabolic and neurodegenerative disorders are generally long-lived and hence susceptible to glycation. Remarkably, proteins linked with diabetes, AD, and PD share this characteristic. This modulates protein's structure, aggregation tendency, and toxicity, highlighting renovated attention. Gut microbes and microbial metabolites marked their importance in human health and diseases. Though many scientific shreds of evidence are proposed for possible change and dysbiosis in gut flora in these diseases, very little is known about the mechanisms. Screening and unfolding their functionality in metabolic and neurodegenerative disorders is essential in hunting the gut treasure. Therefore, it is imperative to evaluate the role of glycation as a common link in diabetes and neurodegenerative diseases, which helps to clarify if modulation of nonenzymatic glycation may act as a beneficial therapeutic strategy and gut microbes/metabolites may answer some of the crucial questions. This review briefly emphasizes the common functional attributes of glycation and gut microbes, the possible linkages, and discusses current treatment options and therapeutic challenges.

Experimental and hypothetical appraisal on inhibition of glucose-induced glycation of bovine serum albumin by quercetin

BACKGROUND

The specificity of protein functions depends on its folding ability into a functional structure. Protein folding is an essential systemic phenomenon that prevents incorrect folding which could result in harmful aggregation. This harmful aggregation of proteins causes neurodegenerative diseases and systemic amyloidosis. Experimental and theoretical approaches were used in this study to explicate the probable mechanisms of action of quercetin in inhibition of glucose-induced glycation through estimations of percentage glycated protein, inhibited induced protein aggregation, and unoxidized bovine serum albumin thiol groups and assessments of molecular interactions of quercetin with the structures of bovine serum albumin, amyloid beta-peptide (1-42) and 3D amyloid-beta (1-42) fibrils retrieved from the protein databank ( http://www.rcsb.org ).

RESULTS

The results showed quercetin inhibited the formation of glycated protein, protein aggregation, and thiol oxidation in a concentration-dependent manner where 200 μg/ml showed the highest inhibition while 50 μg/ml depicted the least inhibition in all the studied assessments. From the docking analysis, it was observed that quercetin had a significantly higher binding affinities - 8.67 ± 0.09 kcal/mol, - 5.37 ± 0.05 kcal/mol and - 5.93 ± 0.13 kcal/mol for the bovine serum albumin, amyloid beta-peptide (1-42) and 3D amyloid-beta (1-42) fibrils respectively compared to the glucose, the inducer. Quercetin and glucose interacted with amino acid residues at the BSA subdomain IIA thus providing a clue that quercetin may impose its inhibition through the binding domain. Also, it is important to mention that the phytochemicals shared a similar interaction profile as that of glucose with the amyloid-beta.

CONCLUSIONS

These findings established the beneficial effects of quercetin as a potential agent that could alleviate hyperglycaemic-initiated disorders associated with elevated serum glucose levels.

Neuroprotective compounds from marine invertebrates

Background

Neuroinflammation is a key pathological feature of a wide variety of neurological disorders, including Parkinson’s, multiple sclerosis, Alzheimer’s, and Huntington’s disease. While current treatments for these disorders are primarily symptomatic, there is a growing interest in developing new therapeutics that target the underlying neuroinflammatory processes.

Main body

Marine invertebrates, such as coral, sea urchins, starfish, sponges, and sea cucumbers, have been found to contain a wide variety of biologically active compounds that have demonstrated potential therapeutic properties. These compounds are known to target various key proteins and pathways in neuroinflammation, including 6-hydroxydopamine (OHDH), caspase-3 and caspase-9, p-Akt, p-ERK, p-P38, acetylcholinesterase (AChE), amyloid-β (Aβ), HSF-1, α-synuclein, cellular prion protein, advanced glycation end products (AGEs), paraquat (PQ), and mitochondria DJ-1.

Short conclusion

This review focuses on the current state of research on the neuroprotective effects of compounds found in marine invertebrates and the potential therapeutic implications of these findings for treating neuroinflammatory disorders. We also discussed the challenges and limitations of using marine-based compounds as therapeutics, such as sourcing and sustainability concerns, and the need for more preclinical and clinical studies to establish their efficacy and safety.

Graphical abstract

Alpha synuclein post translational modifications: potential targets for Parkinson's disease therapy?

Parkinson's disease (PD) is the most common neurodegenerative disorder with motor symptoms. The neuropathological alterations characterizing the brain of patients with PD include the loss of dopaminergic neurons of the nigrostriatal system and the presence of Lewy bodies (LB), intraneuronal inclusions that are mainly composed of alpha-synuclein (α-Syn) fibrils. The accumulation of α-Syn in insoluble aggregates is a main neuropathological feature in PD and in other neurodegenerative diseases, including LB dementia (LBD) and multiple system atrophy (MSA), which are therefore defined as synucleinopathies. Compelling evidence supports that α-Syn post translational modifications (PTMs) such as phosphorylation, nitration, acetylation, O-GlcNAcylation, glycation, SUMOylation, ubiquitination and C-terminal cleavage, play important roles in the modulation α-Syn aggregation, solubility, turnover and membrane binding. In particular, PTMs can impact on α-Syn conformational state, thus supporting that their modulation can in turn affect α-Syn aggregation and its ability to seed further soluble α-Syn fibrillation. This review focuses on the importance of α-Syn PTMs in PD pathophysiology but also aims at highlighting their general relevance as possible biomarkers and, more importantly, as innovative therapeutic targets for synucleinopathies. In addition, we call attention to the multiple challenges that we still need to face to enable the development of novel therapeutic approaches modulating α-Syn PTMs.

Novel dicarbonyl metabolic pathway via mitochondrial ES1 possessing glyoxalase III activity

Glycation, caused by reactive dicarbonyls, plays a role in various diseases by forming advanced glycation end products. In live cells, reactive dicarbonyls such as glyoxal (GO) and methylglyoxal (MGO) are produced during cell metabolism, and these should be removed consistently. However, the dicarbonyl metabolic system in the mitochondria remains unclear. It has been speculated that the mammalian mitochondrial protein ES1 is a homolog of bacterial elbB possessing glyoxalase III (GLO3) activity. Therefore, in this study, to investigate ES1 functions and GLO3 activity, we generated ES1-knockout (KO) mice and recombinant mouse ES1 protein and investigated the biochemical and histological analyses. In the mitochondrial fraction obtained from ES1-KO mouse brains, the GO metabolism and cytochrome c oxidase activity were significantly lower than those in the mitochondrial fraction obtained from wildtype (WT) mouse brains. However, the morphological features of the mitochondria did not change noticeably in the ES1-KO mouse brains compared with those in the WT mouse brains. The mitochondrial proteome analysis showed that the MGO degradation III pathway and oxidative phosphorylation-related proteins were increased. These should be the response to the reduced GO metabolism caused by ES1 deletion to compensate for the dicarbonyl metabolism and damaged cytochrome c oxidase by elevated GO. Recombinant mouse ES1 protein exhibited catalytic activity of converting GO to glycolic acid. These results indicate that ES1 possesses GLO3 activity and modulates the metabolism of GO in the mitochondria. To our knowledge, this is the first study to show a novel metabolic pathway for reactive dicarbonyls in mitochondria.

Unveiling new secrets in Parkinson's disease: The glycatome

We are witnessing a considerable increase in the incidence of Parkinson's disease (PD), which may be due to the general ageing of the population. While there is a plethora of therapeutic strategies for this disease, they still fail to arrest disease progression as they do not target and prevent the neurodegenerative process. The identification of disease-causing mutations allowed researchers to better dissect the underlying causes of this disease, highlighting, for example, the pathogenic role of alpha-synuclein. However, most PD cases are sporadic, which is making it hard to unveil the major causative mechanisms of this disease. In the recent years, epidemiological evidence suggest that type-2 diabetes mellitus (T2DM) individuals have higher risk and worst outcomes of PD, allowing to raise the hypothesis that some dysregulated processes in T2DM may contribute or even trigger the neurodegenerative process in PD. One major consequence of T2DM is the unprogrammed reaction between sugars, increased in T2DM, and proteins, a reaction named glycation. Pre-clinical reports show that alpha-synuclein is a target of glycation, and glycation potentiates its pathogenicity which contributes for the neurodegenerative process. Moreover, it triggers, anticipates, or aggravates several PD-like motor and non-motor complications. A given profile of proteins are differently glycated in diseased conditions, altering the brain proteome and leading to brain dysfunction and neurodegeneration. Herein we coin the term Glycatome as the profile of glycated proteins. In this review we report on the mechanisms underlying the association between T2DM and PD, with particular focus on the impact of protein glycation.

Type 2 Diabetes and Parkinson's Disease: A Focused Review of Current Concepts

Highly reproducible epidemiological evidence shows that type 2 diabetes (T2D) increases the risk and rate of progression of Parkinson's disease (PD), and crucially, the repurposing of certain antidiabetic medications for the treatment of PD has shown early promise in clinical trials, suggesting that the effects of T2D on PD pathogenesis may be modifiable. The high prevalence of T2D means that a significant proportion of patients with PD may benefit from personalized antidiabetic treatment approaches that also confer neuroprotective benefits. Therefore, there is an immediate need to better understand the mechanistic relation between these conditions and the specific molecular pathways affected by T2D in the brain. Although there is considerable evidence that processes such as insulin signaling, mitochondrial function, autophagy, and inflammation are involved in the pathogenesis of both PD and T2D, the primary aim of this review is to highlight the evidence showing that T2D-associated dysregulation of these pathways occurs not only in the periphery but also in the brain and how this may facilitate neurodegeneration in PD. We also discuss the challenges involved in disentangling the complex relationship between T2D, insulin resistance, and PD, as well as important questions for further research. © 2022 International Parkinson and Movement Disorder Society.

Liquid-liquid Phase Separation of α-Synuclein: A New Mechanistic Insight for α-Synuclein Aggregation Associated with Parkinson's Disease Pathogenesis

Aberrant aggregation of the misfolded presynaptic protein, α-Synuclein (α-Syn) into Lewy body (LB) and Lewy neuritis (LN) is a major pathological hallmark of Parkinson's disease (PD) and other synucleinopathies. Numerous studies have suggested that prefibrillar and fibrillar species of the misfolded α-Syn aggregates are responsible for cell death in PD pathogenesis. However, the precise molecular events during α-Syn aggregation, especially in the early stages, remain elusive. Emerging evidence has demonstrated that liquid-liquid phase separation (LLPS) of α-Syn occurs in the nucleation step of α-Syn aggregation, which offers an alternate non-canonical aggregation pathway in the crowded microenvironment. The liquid-like α-Syn droplets gradually undergo an irreversible liquid-to-solid phase transition into amyloid-like hydrogel entrapping oligomers and fibrils. This new mechanism of α-Syn LLPS and gel formation might represent the molecular basis of cellular toxicity associated with PD. This review aims to demonstrate the recent development of α-Syn LLPS, the underlying mechanism along with the microscopic events of aberrant phase transition. This review further discusses how several intrinsic and extrinsic factors regulate the thermodynamics and kinetics of α-Syn LLPS and co-LLPS with other proteins, which might explain the pathophysiology of α-Syn in various neurodegenerative diseases.

A Mouse Model to Test Novel Therapeutics for Parkinson's Disease: an Update on the Thy1-aSyn ("line 61") Mice

Development of neuroprotective therapeutics for Parkinson's disease (PD) is facing a lack of translation from pre-clinical to clinical trials. One strategy for improvement is to increase predictive validity of pre-clinical studies by using extensively characterized animal models with a comprehensive set of validated pharmacodynamic readouts. Mice over-expressing full-length, human, wild-type alpha-synuclein under the Thy-1 promoter (Thy1-aSyn line 61) reproduce key features of sporadic PD, such as progressive loss of striatal dopamine, alpha-synuclein pathology, deficits in motor and non-motor functions, and elevation of inflammatory markers. Extensive work with this model by multiple laboratories over the past decade further increased confidence in its robustness and validity, especially for analyzing pathomechanisms of alpha-synuclein pathology and down-stream pathways, and for pre-clinical drug testing. Interestingly, while postnatal transgene expression is widespread in central and peripheral neurons, the extent and progression of down-stream pathology differs between brain regions, thereby replicating the characteristic selective vulnerability of neurodegenerative diseases. In-depth characterization of these readouts in conjunction with behavioral deficits has led to more informative endpoints for pre-clinical trials. Each drug tested in Thy1-aSyn line 61 enhances knowledge on how molecular targets, pathology, and functional behavioral readouts are interconnected, thereby further optimizing the platform towards predictive validity for clinical trials. Here, we present the current state of the art using Thy1-aSyn line 61 for drug target discovery, validation, and pre-clinical testing.

Receptors for Advanced Glycation End Products (RAGE): Promising Targets Aiming at the Treatment of Neurodegenerative Conditions

Advanced glycation end products (AGEs) are compounds formed after the non-enzymatic addition of reducing sugars to lipids, proteins, and nucleic acids. They are associated with the development of various clinical complications observed in diabetes and cardiovascular diseases, such as retinopathy, nephropathy, diabetic neuropathy, and others. In addition, compelling evidence indicates that these molecules participate in the progression of neurodegenerative diseases, such as Alzheimer's disease, Parkinson's disease, and amyotrophic lateral sclerosis. Multiple cellular and molecular alterations triggered by AGEs that could alter homeostasis have been identified. One of the main targets for AGE signaling is the receptor for advanced glycation end-products (RAGE). Importantly, this receptor is the target of not only AGEs, but also amyloid β peptides, HMGB1 (high-mobility group box-1), members of the S100 protein family, and glycosaminoglycans. The activation of this receptor induces intracellular signaling cascades that are involved in pathological processes and cell death. Therefore, RAGE represents a key target for pharmacological interventions in neurodegenerative diseases. This review will discuss the various effects of AGEs and RAGE activation in the pathophysiology of neurodegenerative diseases, as well as the currently available pharmacological tools and promising drug candidates.

RAGE Against the Glycation Machine in Synucleinopathies: Time to Explore New Questions

Oligomerization and aggregation of misfolded forms of α-synuclein are believed to be key molecular mechanisms in Parkinson's disease (PD) and other synucleinopathies, so extensive research has attempted to understand these processes. Among diverse post-translational modifications that impact α-synuclein aggregation, glycation may take place at several lysine sites and modify α-synuclein oligomerization, toxicity, and clearance. The receptor for advanced glycation end products (RAGE) is considered a key regulator of chronic neuroinflammation through microglial activation in response to advanced glycation end products, such as carboxy-ethyl-lysine, or carboxy-methyl-lysine. The presence of RAGE in the midbrain of PD patients has been reported in the last decades and this receptor was proposed to have a role in sustaining PD neuroinflammation. However, different PD animal models demonstrated that RAGE is preferentially expressed in neurons and astrocytes, while recent evidence demonstrated that fibrillar, non-glycated α-synuclein binds to RAGE. Here, we summarize the available data on α-synuclein glycation and RAGE in the context of PD, and discuss about the questions yet to be answered that may increase our understanding of the molecular bases of PD and synucleinopathies.

Vexed mutations promote degeneration of dopaminergic neurons through excessive activation of the innate immune response

The hallmark of Parkinson's disease (PD) is the loss of dopaminergic (DA) neurons in the brain. However, little is known about why DA neurons are selectively vulnerable to PD. We previously completed a screen identifying genes associated with the progressive degeneration of DA neurons. Here we describe the role of a previously uncharacterized gene, CG42339, in the loss of DA neurons using Drosophila Melanogaster. CG42339 mutants display a progressive loss of DA neurons and locomotor dysfunction, along with an accumulation of advanced glycation end products (AGEs) in the brain. Based on this phenotype, we refer to CG42339 as vexed. We demonstrate that vexed is specifically required within cortex glia to maintain neuronal viability. Loss of vexed function results in excessive activation of the innate immune response in the brain, leading to loss of DA neurons. We show that activation of the innate immune response leads to increased nitric oxide signaling and accumulation of AGEs, which ultimately result in neurodegeneration. These results provide further insight into the relationship between the role of the immune response in the central nervous system and how this impacts neuronal viability.

Role of post-translational modifications on the alpha-synuclein aggregation-related pathogenesis of Parkinson’s disease

Together with neuronal loss, the existence of insoluble inclusions of alpha-synuclein (α-syn) in the brain is widely accepted as a hallmark of synucleinopathies including Parkinson’s disease (PD), multiple system atrophy, and dementia with Lewy body. Because the α-syn aggregates are deeply involved in the pathogenesis, there have been many attempts to demonstrate the mechanism of the aggregation and its potential causative factors including post-translational modifications (PTMs). Although no concrete conclusions have been made based on the previous study results, growing evidence suggests that modifications such as phosphorylation and ubiquitination can alter α-syn characteristics to have certain effects on the aggregation process in PD; either facilitating or inhibiting fibrillization. In the present work, we reviewed studies showing the significant impacts of PTMs on α-syn aggregation. Furthermore, the PTMs modulating α-syn aggregation-induced cell death have been discussed. 

The Effects of Dietary Advanced Glycation End-Products on Neurocognitive and Mental Disorders

Advanced glycation end products (AGEs) are glycated proteins or lipids formed endogenously in the human body or consumed through diet. Ultra-processed foods and some culinary techniques, such as dry cooking methods, represent the main sources and drivers of dietary AGEs. Tissue accumulation of AGEs has been associated with cellular aging and implicated in various age-related diseases, including type-2 diabetes and cardiovascular disease. The current review summarizes the literature examining the associations between AGEs and neurocognitive and mental health disorders. Studies indicate that elevated circulating AGEs are cross-sectionally associated with poorer cognitive function and longitudinally increase the risk of developing dementia. Additionally, preliminary studies show that higher skin AGE accumulation may be associated with mental disorders, particularly depression and schizophrenia. Potential mechanisms underpinning the effects of AGEs include elevated oxidative stress and neuroinflammation, which are both key pathogenetic mechanisms underlying neurodegeneration and mental disorders. Decreasing dietary intake of AGEs may improve neurological and mental disorder outcomes. However, more sophisticated prospective studies and analytical approaches are required to verify directionality and the extent to which AGEs represent a mediator linking unhealthy dietary patterns with cognitive and mental disorders.

Glycation of α-synuclein hampers its binding to synaptic-like vesicles and its driving effect on their fusion

Parkinson's disease (PD) is one of the most prevalent neurodegenerative disorders affecting the worldwide population. One of its hallmarks is the intraneuronal accumulation of insoluble Lewy bodies (LBs), which cause the death of dopaminergic neurons. α-Synuclein (αS) is the main component of these LBs and in them, it commonly contains non-enzymatic post-translational modifications, such as those resulting from its reaction with reactive carbonyl species arising as side products of the intraneuronal glycolysis (mainly methylglyoxal). Consequently, lysines of the αS found in LBs of diabetic individuals are usually carboxyethylated. A precise comprehension of the effect of Nε-(carboxyethyl)lysine (CEL) on the aggregation of αS and on its physiological function becomes crucial to fully understand the molecular mechanisms underlying the development of diabetes-induced PD. Consequently, we have here used a synthetic αS where all its Lys have been replaced by CEL moieties (αS-CEL), and we have studied how these modifications could impact on the neurotransmission mechanism. This study allows us to describe how the non-enzymatic glycosylation (glycation) affects the function of a protein like αS, involved in the pathogenesis of PD. CEL decreases the ability of αS to bind micelles, although the micelle-bound fraction of αS-CEL still displays an α-helical fold resembling that of the lipid-bound αS. However, CEL completely abolishes the affinity of αS towards synaptic-like vesicles and, consequently, it hampers its physiological function as a catalyst of the clustering and the fusion of the synaptic vesicles.

Glyoxalase III enhances salinity tolerance through reactive oxygen species scavenging and reduced glycation

Methylglyoxal (MG) is a metabolically generated highly cytotoxic compound that accumulates in all living organisms, from Escherichia coli to humans, under stress conditions. To detoxify MG, nature has evolved reduced glutathione (GSH)-dependent glyoxalase and NADPH-dependent aldo-keto reductase systems. But both GSH and NADPH have been reported to be limiting in plants under stress conditions, and thus detoxification might not be performed efficiently. Recently, glyoxalase III (GLY III)-like enzyme activity has been reported from various species, which can detoxify MG without any cofactor. In the present study, we have tested whether an E. coli gene, hchA, encoding a functional GLY III, could provide abiotic stress tolerance to living systems. Overexpression of this gene showed improved tolerance in E. coli and Saccharomyces cerevisiae cells against salinity, dicarbonyl, and oxidative stresses. Ectopic expression of the E. coli GLY III gene (EcGLY-III) in transgenic tobacco plants confers tolerance against salinity at both seedling and reproductive stages as indicated by their height, weight, membrane stability index, and total yield potential. Transgenic plants showed significantly increased glyoxalase and antioxidant enzyme activity that resisted the accumulation of excess MG and reactive oxygen species (ROS) during stress. Moreover, transgenic plants showed more anti-glycation activity to inhibit the formation of advanced glycation end product (AGE) that might prevent transgenic plants from stress-induced senescence. Taken together, all these observations indicate that overexpression of EcGLYIII confers salinity stress tolerance in plants and should be explored further for the generation of stress-tolerant plants.

Glycation modulates alpha-synuclein fibrillization kinetics: a sweet spot for inhibition

Glycation is a nonenzymatic posttranslational modification (PTM) known to be increased in the brains of hyperglycemic patients. Alpha-synuclein (αSN), a central player in the etiology of Parkinson’s disease, can be glycated at lysine residues, thereby reducing αSN fibril formation in vitro and modulating αSN aggregation in cells. However, the molecular basis for these effects is unclear. To elucidate this, we investigated the aggregation of αSN modified by eight glycating agents, namely the dicarbonyl compound methylglyoxal (MGO) and the sugars ribose, fructose, mannose, glucose, galactose, sucrose, and lactose. We found that MGO and ribose modify αSN to the greatest extent, and these glycation products are the most efficient inhibitors of fibril formation. We show glycation primarily inhibits elongation rather than nucleation of αSN and has only a modest effect on the level of oligomerization. Furthermore, glycated αSN is not significantly incorporated into fibrils. For both MGO and ribose, we discovered that a level of ∼5 modifications per αSN is optimal for inhibition of elongation. The remaining sugars showed a weak but optimal inhibition at ∼2 modifications per αSN. We propose that this optimal level balances the affinity for the growing ends of the fibril (which decreases with the extent of modification) with the ability to block incorporation of subsequent αSN subunits (which increases with modification). Our results are not only relevant for other αSN PTMs but also for understanding PTMs affecting other fibrillogenic proteins and may thus open novel avenues for therapeutic intervention in protein aggregation disorders.

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.

Autophagy and Glycative Stress: A Bittersweet Relationship in Neurodegeneration

Autophagy is a fine-tuned proteolytic pathway that moves dysfunctional/aged cellular components into the lysosomal compartment for degradation. Over the last 3 decades, global research has provided evidence for the protective role of autophagy in different brain cell components. Autophagic capacities decline with age, which contributes to the accumulation of obsolete/damaged organelles and proteins and, ultimately, leads to cellular aging in brain tissues. It is thus well-accepted that autophagy plays an essential role in brain homeostasis, and malfunction of this catabolic system is associated with major neurodegenerative disorders. Autophagy function can be modulated by different types of stress, including glycative stress. Glycative stress is defined as a cellular status with abnormal and accelerated accumulation of advanced glycation end products (AGEs). It occurs in hyperglycemic states, both through the consumption of high-sugar diets or under metabolic conditions such as diabetes. In recent years, glycative stress has gained attention for its adverse impact on brain pathology. This is because glycative stress stimulates insoluble, proteinaceous aggregation that is linked to the malfunction of different neuropathological proteins. Despite the emergence of new literature suggesting that autophagy plays a major role in fighting glycation-derived damage by removing cytosolic AGEs, excessive glycative stress might also negatively impact autophagic function. In this mini-review, we provide insight on the status of present knowledge regarding the role of autophagy in brain physiology and pathophysiology, with an emphasis on the cytoprotective role of autophagic function to ameliorate the adverse effects of glycation-derived damage in neurons, glia, and neuron-glia interactions.

Role and Therapeutic Potential of RAGE Signaling in Neurodegeneration

Activation of the receptor for advanced glycation end products (RAGE) has been shown to play an active role in the development of multiple neurodegenerative diseases, including Alzheimer's disease, Parkinson's disease, and Amyotrophic Lateral Sclerosis. Although originally identified as a receptor for advanced glycation end products, RAGE is a pattern recognition receptor able to bind multiple ligands. The final outcome of RAGE signaling is defined in a context and cell type specific manner and can exert both neurotoxic and neuroprotective functions. Contributing to the complexity of the RAGE signaling network, different RAGE isoforms with distinctive signaling capabilities have been described. Moreover, multiple RAGE ligands bind other receptors and RAGE antagonism can significantly affect their signaling. Here, we discuss the outcome of celltype specific RAGE signaling in neurodegenerative pathologies. In addition, we will review the different approaches that have been developed to target RAGE signaling and their therapeutic potential. A clear understanding of the outcome of RAGE signaling in a cell type- and disease-specific manner would contribute to advancing the development of new therapies targeting RAGE. The ability to counteract RAGE neurotoxic signaling while preserving its neuroprotective effects would be critical for the success of novel therapies targeting RAGE signaling.

Essential Metals in the Brain and the Application of Laser Ablation-Inductively Coupled Plasma-Mass Spectrometry for their Detection

Metals are natural component of the ecosystem present throughout the layers of atmosphere; their abundant expression in the brain indicates their importance in the central nervous system (CNS). Within the brain tissue, their distribution is highly compartmentalized, the pattern of which is determined by their primary roles. Bio-imaging of the brain to reveal spatial distribution of metals within specific regions has provided a unique understanding of brain biochemistry and architecture, linking both the structures and the functions through several metal mediated activities. Bioavailability of essential trace metal is needed for normal brain function. However, disrupted metal homeostasis can influence several biochemical pathways in different fields of metabolism and cause characteristic neurological disorders with a typical disease process usually linked with aberrant metal accumulations. In this review we give a brief overview of roles of key essential metals (Iron, Copper and Zinc) including their molecular mechanisms and bio-distribution in the brain as well as their possible involvement in the pathogenesis of related neurodegenerative diseases. In addition, we also reviewed recent applications of Laser Ablation Inductively Couple Plasma Mass Spectrophotometry (LA-ICP-MS) in the detection of both toxic and essential metal dyshomeostasis in neuroscience research and other related brain diseases.

Structural and Functional Changes of Reconstituted High-Density Lipoprotein (HDL) by Incorporation of α-synuclein: A Potent Antioxidant and Anti-Glycation Activity of α-synuclein and apoA-I in HDL at High Molar Ratio of α-synuclein

α-synuclein (α-syn) is a major culprit of Parkinson's disease (PD), although lipoprotein metabolism is very important in the pathogenesis of PD. α-syn was expressed and purified using the pET30a expression vector from an E. coli expression system to elucidate the physiological effects of α-syn on lipoprotein metabolism. The human α-syn protein (140 amino acids) with His-tag (8 amino acids) was expressed and purified to at least 95% purity. Isoelectric focusing gel electrophoresis showed that the isoelectric point (pI) of α-syn and apoA-I were pI = 4.5 and pI = 6.4, respectively. The lipid-free α-syn showed almost no phospholipid-binding ability, while apoA-I showed rapid binding ability with a half-time (T_1/2) = 8 ± 0.7 min. The α-syn and apoA-I could be incorporated into the reconstituted HDL (rHDL, molar ratio 95:5:1:1, palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC):cholesterol:apoA-I:α-syn with the production of larger particles (92 Å) than apoA-I-rHDL (86 and 78 Å) and α-syn-rHDL (65 Å). An rHDL containing both apoA-I and α-syn showed lower α-helicity around 45% with a red shift of the Trp wavelength maximum fluorescence (WMF) from 339 nm, while apoA-I-HDL showed 76% α-helicity and 337 nm of WMF. The denaturation by urea addition showed that the incorporation of α-syn in rHDL caused a larger increase in the WMF than apoA-I-rHDL, suggesting that the destabilization of the secondary structure of apoA-I by the addition of α-syn. On the other hand, the addition of α-syn induced two-times higher resistance to rHDL glycation at apoA-I:α-syn molar ratios of 1:1 and 1:2. Interestingly, low α-syn in rHDL concentrations, molar ratio of 1:0.5 (apoA-I:α-syn), did not prevent glycation with more multimerization of apoA-I. In the lipid-free and lipid-bound state, α-syn showed more potent antioxidant activity than apoA-I against cupric ion-mediated LDL oxidation. On the other hand, microinjection of α-syn (final 2 μM) resulted in 10% less survival of zebrafish embryos than apoA-I. A subcutaneous injection of α-syn (final 34 μM) resulted in less tail fin regeneration than apoA-I. Interestingly, incorporation of α-syn at a low molar ratio (apoA-I:α-syn, 1:0.5) in rHDL resulted destabilization of the secondary structure and impairment of apoA-I functionality via more oxidation and glycation. However, at a higher molar ratio of α-syn in rHDL (apoA-I:α-syn = 1:1 or 1:2) exhibited potent antioxidant and anti-glycation activity without aggregation. In conclusion, there might be a critical concentration of α-syn and apoA-I in HDL-like complex to prevent the aggregation of apoA-I via structural and functional enhancement.

Intermediates of α-synuclein aggregation: Implications in Parkinson's disease pathogenesis

Cytoplasmic deposition of aberrantly misfolded α-synuclein (α-Syn) is a common feature of synucleinopathies, including Parkinson's disease (PD). However, the precise pathogenic mechanism of α-Syn in synucleinopathies remains elusive. Emerging evidence has suggested that α-Syn may contribute to PD pathogenesis in several ways; wherein the contribution of fibrillar species, for exerting toxicity and disease transmission, cannot be neglected. Further, the oligomeric species could be the most plausible neurotoxic species causing neuronal cell death. However, understanding the structural and molecular insights of these oligomers are very challenging due to the heterogeneity and transient nature of the species. In this review, we discuss the recent advancements in understanding the formation and role of α-Syn oligomers in PD pathogenesis. We also summarize the different types of α-Syn oligomeric species and potential mechanisms to exert neurotoxicity. Finally, we address the possible ways to target α-Syn as a promising approach against PD and the possible future directions.

Delineation of Neuroprotective Effects and Possible Benefits of AntioxidantsTherapy for the Treatment of Alzheimer's Diseases by Targeting Mitochondrial-Derived Reactive Oxygen Species: Bench to Bedside

Alzheimer's disease (AD) is considered the sixth leading cause of death in elderly patients and is characterized by progressive neuronal degeneration and impairment in memory, language, etc. AD is characterized by the deposition of senile plaque, accumulation of fibrils, and neurofibrillary tangles (NFTs) which are responsible for neuronal degeneration. Amyloid-β (Aβ) plays a key role in the process of neuronal degeneration in the case of AD. It has been reported that Aβ is responsible for the production of reactive oxygen species (ROS), depletion of endogenous antioxidants, increase in intracellular Ca²⁺ which further increases mitochondria dysfunctions, oxidative stress, release of pro-apoptotic factors, neuronal apoptosis, etc. Thus, oxidative stress plays a key role in the pathogenesis of AD. Antioxidants are compounds that have the ability to counteract the oxidative damage conferred by ROS. Therefore, the antioxidant therapy may provide benefits and halt the progress of AD to advance stages by counteracting neuronal degeneration. However, despite the beneficial effects imposed by the antioxidants, the findings from the clinical studies suggested inconsistent results which might be due to poor study design, selection of the wrong antioxidant, inability of the molecule to cross the blood-brain barrier (BBB), treatment in the advanced state of disease, etc. The present review insights into the neuroprotective effects and limitations of the antioxidant therapy for the treatment of AD by targeting mitochondrial-derived ROS. This particular article will certainly help the researchers to search new avenues for the treatment of AD by utilizing mitochondrial-derived ROS-targeted antioxidant therapies.

An Update on the Critical Role of α-Synuclein in Parkinson's Disease and Other Synucleinopathies: from Tissue to Cellular and Molecular Levels

The aggregation of alpha-synuclein (α-Syn) plays a critical role in the development of Parkinson's disease (PD) and other synucleinopathies. α-Syn, which is encoded by the SNCA gene, is a lysine-rich soluble amphipathic protein normally expressed in neurons. Located in the cytosolic domain, this protein has the ability to remodel itself in plasma membranes, where it assumes an alpha-helix conformation. However, the protein can also adopt another conformation rich in cross-beta sheets, undergoing mutations and post-translational modifications, then leading the protein to an unusual aggregation in the form of Lewy bodies (LB), which are cytoplasmic inclusions constituted predominantly by α-Syn. Pathogenic mechanisms affecting the structural and functional stability of α-Syn - such as endoplasmic reticulum stress, Golgi complex fragmentation, disfunctional protein degradation systems, aberrant interactions with mitochondrial membranes and nuclear DNA, altered cytoskeleton dynamics, disrupted neuronal plasmatic membrane, dysfunctional vesicular transport, and formation of extracellular toxic aggregates - contribute all to the pathogenic progression of PD and synucleinopathies. In this review, we describe the collective knowledge on this topic and provide an update on the critical role of α-Syn aggregates, both at the cellular and molecular levels, in the deregulation of organelles affecting the cellular homeostasis and leading to neuronal cell death in PD and other synucleinopathies.

DJ-1 Acts as a Scavenger of α-Synuclein Oligomers and Restores Monomeric Glycated α-Synuclein

Glycation of α-synuclein (αSyn), as occurs with aging, has been linked to the progression of Parkinson’s disease (PD) through the promotion of advanced glycation end-products and the formation of toxic oligomers that cannot be properly cleared from neurons. DJ-1, an antioxidative protein that plays a critical role in PD pathology, has been proposed to repair glycation in proteins, yet a mechanism has not been elucidated. In this study, we integrate solution nuclear magnetic resonance (NMR) spectroscopy and liquid atomic force microscopy (AFM) techniques to characterize glycated N-terminally acetylated-αSyn (glyc-ac-αSyn) and its interaction with DJ-1. Glycation of ac-αSyn by methylglyoxal increases oligomer formation, as visualized by AFM in solution, resulting in decreased dynamics of the monomer amide backbone around the Lys residues, as measured using NMR. Upon addition of DJ-1, this NMR signature of glyc-ac-αSyn monomers reverts to a native ac-αSyn-like character. This phenomenon is reversible upon removal of DJ-1 from the solution. Using relaxation-based NMR, we have identified the binding site on DJ-1 for glycated and native ac-αSyn as the catalytic pocket and established that the oxidation state of the catalytic cysteine is imperative for binding. Based on our results, we propose a novel mechanism by which DJ-1 scavenges glyc-ac-αSyn oligomers without chemical deglycation, suppresses glyc-ac-αSyn monomer–oligomer interactions, and releases free glyc-ac-αSyn monomers in solution. The interference of DJ-1 with ac-αSyn oligomers may promote free ac-αSyn monomer in solution and suppress the propagation of toxic oligomer and fibril species. These results expand the understanding of the role of DJ-1 in PD pathology by acting as a scavenger for aggregated αSyn.

Understanding the Role of Protein Glycation in the Amyloid Aggregation Process

Protein function and flexibility is directly related to the native distribution of its structural elements and any alteration in protein architecture leads to several abnormalities and accumulation of misfolded proteins. This phenomenon is associated with a range of increasingly common human disorders, including Alzheimer and Parkinson diseases, type II diabetes, and a number of systemic amyloidosis characterized by the accumulation of amyloid aggregates both in the extracellular space of tissues and as intracellular deposits. Post-translational modifications are known to have an active role in the in vivo amyloid aggregation as able to affect protein structure and dynamics. Among them, a key role seems to be played by non-enzymatic glycation, the most unwanted irreversible modification of the protein structure, which strongly affects long-living proteins throughout the body. This study provided an overview of the molecular effects induced by glycation on the amyloid aggregation process of several protein models associated with misfolding diseases. In particular, we analyzed the role of glycation on protein folding, kinetics of amyloid formation, and amyloid cytotoxicity in order to shed light on the role of this post-translational modification in the in vivo amyloid aggregation process.

The Nigral Coup in Parkinson's Disease by α-Synuclein and Its Associated Rebels

The risk of Parkinson's disease increases with age. However, the etiology of the illness remains obscure. It appears highly likely that the neurodegenerative processes involve an array of elements that influence each other. In addition, genetic, endogenous, or exogenous toxins need to be considered as viable partners to the cellular degeneration. There is compelling evidence that indicate the key involvement of modified α-synuclein (Lewy bodies) at the very core of the pathogenesis of the disease. The accumulation of misfolded α-synuclein may be a consequence of some genetic defect or/and a failure of the protein clearance system. Importantly, α-synuclein pathology appears to be a common denominator for many cellular deleterious events such as oxidative stress, mitochondrial dysfunction, dopamine synaptic dysregulation, iron dyshomeostasis, and neuroinflammation. These factors probably employ a common apoptotic/or autophagic route in the final stages to execute cell death. The misfolded α-synuclein inclusions skillfully trigger or navigate these processes and thus amplify the dopamine neuron fatalities. Although the process of neuroinflammation may represent a secondary event, nevertheless, it executes a fundamental role in neurodegeneration. Some viral infections produce parkinsonism and exhibit similar characteristic neuropathological changes such as a modest brain dopamine deficit and α-synuclein pathology. Thus, viral infections may heighten the risk of developing PD. Alternatively, α-synuclein pathology may induce a dysfunctional immune system. Thus, sporadic Parkinson's disease is caused by multifactorial trigger factors and metabolic disturbances, which need to be considered for the development of potential drugs in the disorder.

The concept of protein folding/unfolding and its impacts on human health

Proteins have evolved in specific 3D structures and play different functions in cells and determine various reactions and pathways. The newly synthesized amino acid chains once depart ribosome must crumple into three-dimensional structures so can be biologically active. This process of protein that makes a functional molecule is called protein folding. The protein folding is both a biological and a physicochemical process that depends on the sequence of it. In fact, this process occurs more complicated and in some cases and in exposure to some molecules like glucose (glycation), mistaken folding leads to amyloid structures and fatal disorders called conformational diseases. Such conditions are detected by the quality control system of the cell and these abnormal proteins undergo renovation or degradation. This scenario takes place by the chaperones, chaperonins, and Ubiquitin-proteasome complex. Understanding of protein folding mechanisms from different views including experimental and computational approaches has revealed some intermediate ensembles such as molten globule and has been subjected to biophysical and molecular biology attempts to know more about prevalent conformational diseases.

Advanced glycation end products (AGEs) and other adducts in aging-related diseases and alcohol-mediated tissue injury

Advanced glycation end products (AGEs) are potentially harmful and heterogeneous molecules derived from nonenzymatic glycation. The pathological implications of AGEs are ascribed to their ability to promote oxidative stress, inflammation, and apoptosis. Recent studies in basic and translational research have revealed the contributing roles of AGEs in the development and progression of various aging-related pathological conditions, such as diabetes, cardiovascular complications, gut microbiome-associated illnesses, liver or neurodegenerative diseases, and cancer. Excessive chronic and/or acute binge consumption of alcohol (ethanol), a widely consumed addictive substance, is known to cause more than 200 diseases, including alcohol use disorder (addiction), alcoholic liver disease, and brain damage. However, despite the considerable amount of research in this area, the underlying molecular mechanisms by which alcohol abuse causes cellular toxicity and organ damage remain to be further characterized. In this review, we first briefly describe the properties of AGEs: their formation, accumulation, and receptor interactions. We then focus on the causative functions of AGEs that impact various aging-related diseases. We also highlight the biological connection of AGE-alcohol-adduct formations to alcohol-mediated tissue injury. Finally, we describe the potential translational research opportunities for treatment of various AGE- and/or alcohol-related adduct-associated disorders according to the mechanistic insights presented.

Yeasts as Complementary Model Systems for the Study of the Pathological Repercussions of Enhanced Synphilin-1 Glycation and Oxidation

Synphilin-1 has previously been identified as an interaction partner of α-Synuclein (αSyn), a primary constituent of neurodegenerative disease-linked Lewy bodies. In this study, the repercussions of a disrupted glyoxalase system and aldose reductase function on Synphilin-1 inclusion formation characteristics and cell growth were investigated. To this end, either fluorescent dsRed-tagged or non-tagged human SNCAIP, which encodes the Synphilin-1 protein, was expressed in Saccharomyces cerevisiae and Schizosaccharomyces pombe yeast strains devoid of enzymes Glo1, Glo2, and Gre3. Presented data shows that lack of Glo2 and Gre3 activity in S. cerevisiae increases the formation of large Synphilin-1 inclusions. This correlates with enhanced oxidative stress levels and an inhibitory effect on exponential growth, which is most likely caused by deregulation of autophagic degradation capacity, due to excessive Synphilin-1 aggresome build-up. These findings illustrate the detrimental impact of increased oxidation and glycation on Synphilin-1 inclusion formation. Similarly, polar-localised inclusions were observed in wild-type S. pombe cells and strains deleted for either glo1⁺ or glo2⁺. Contrary to S. cerevisiae, however, no growth defects were observed upon expression of SNCAIP. Altogether, our findings show the relevance of yeasts, especially S. cerevisiae, as complementary models to unravel mechanisms contributing to Synphilin-1 pathology in the context of neurodegenerative diseases.

Protective actions of bioactive flavonoids chrysin and luteolin on the glyoxal induced formation of advanced glycation end products and aggregation of human serum albumin: In vitro and molecular docking analysis

The post-translational modification of proteins by nonenzymatic glycation (NEG) and the accumulation of AGEs are the two underlying factors associated with the long-term pathogenesis in diabetes. Glyoxal (GO) is a reactive intermediate which has the ability to modify proteins and generate AGEs at a faster rate. Human serum albumin (HSA) being the most abundant serum protein has a higher chance to be modified by NEG. The key objective of the present study is to investigate the potency of chrysin and luteolin as antiglycating and antifibrillating agents in the GO-mediated glycation and fibril formation of HSA. AGEs formation were confirmed from the absorption and fluorescence spectral measurements. Both the flavonoids were able to quench the AGEs fluorescence intensity in vitro indicating the antiglycating nature of the molecules. The formation of fibrils in the GO-modified HSA was confirmed by the Thioflavin T (ThT) fluorescence assay and the flavonoids were found to exihibit the antifibrillation properties in vitro. Docking results suggested that both the flavonoids interact with various amino acid residues of subdomain IIA including glycation prone lysines and arginines via non-covalent forces and further stabilized the structure of HSA, which further explains their mechanisms of action as antiglycating and antifibrillating agents.

Use of skin advanced glycation end product levels measured using a simple noninvasive method as a biological marker for the diagnosis of neuropsychiatric diseases

OBJECTIVES

The accumulation of advanced glycation end products (AGEs) may be involved in the pathophysiology of several neuropsychiatric diseases. In this study, the skin AGEs level of several neuropsychiatric diseases was assessed with a simple noninvasive method. Moreover, whether skin AGE level can be used as a biomarker for the diagnosis of these diseases was evaluated.

METHODS

A total of 27 patients with schizophrenia, 26 with major depressive disorder, and 10 with major neurocognitive disorders (MNDs), such as Alzheimer's disease or dementia with Lewy body, as well as 26 healthy controls were enrolled in this study. The skin AGE levels of the patients were assessed with an AGE scanner, a fluorometric method used to assay skin AGE levels.

RESULTS

One-way analysis of covariance was performed after adjusting for significant covariates, including age. Although the group with MNDs had higher skin AGE levels than the other groups, the main effect of diagnosis did not significantly affect the skin AGE levels of the groups.

CONCLUSIONS

Skin AGE levels in neuropsychiatric diseases with mild symptoms did not significantly differ. Further large-scale studies using a simple noninvasive method for the early detection and treatment of MNDs must be conducted.

Advanced glycation end products and protein carbonyl levels in plasma reveal sex-specific differences in Parkinson's and Alzheimer's disease

Neurodegenerative diseases (NDD) such as Alzheimer's (AD) and Parkinson's disease (PD) are distinct clinical entities, however, the aggregation of key neuronal proteins, presumably leading to neuronal demise appears to represent a common mechanism. It has become evident, that advanced glycation end products (AGEs) trigger the accumulation of such modified proteins, which eventually contributes to pathological aspect of NDDs. Increased levels of AGEs are found in amyloid plaques in AD brains and in both advanced and early PD (incidental Lewy body disease). The molecular mechanisms by which AGE dependent modifications may modulate the susceptibility towards NDDs, however, remain enigmatic and it is unclear, whether AGEs may serve as biomarker of NDD. In the present study, we examined AGEs (CML: Carboxymethyllysine and CEL: Carboxyethyllysine), markers of oxidative stress and micronutrients in the plasma of PD and AD patients and controls. As compared to healthy controls, AD females displayed lower levels of CEL while higher levels of CML were found in AD and PD patients. A somewhat similar pattern was observed for protein carbonyls (PC), revealing lower values exclusively in AD females, whereas AD males displayed significantly higher values compared to healthy controls and PD. Sex-specific differences were also observed for other relevant markers such as malondialdehyde, 3-nitrotyrosine, γ -tocopherols, retinol, plasma proteins and α-carotene, while α-tocopherols, β-carotene, lutein/zeaxanthin, β-cryptoxanthin and lycopene showed no relevant association. Taken together, our study suggests yet unappreciated differences of the distribution of AGEs among the sexes in NDD. We therefore suggest to make a clear distinction between sexes when analyzing oxidative (AGEs)-related stress and carbonyl-related stress and vitamins.

P301 L, an FTDP-17 Mutant, Exhibits Enhanced Glycation in vitro

BACKGROUND

Frontotemporal dementia and parkinsonism-linked to chromosome-17 are a group of diseases with tau mutations leading to primary tauopathies which include progressive supranuclear palsy, corticobasal syndrome, and frontotemporal lobar degeneration. Alzheimer's disease is a non-primary tauopathy, which displays tau neuropathology of excess tangle formation and accumulation. FTDP-17 mutations are responsible for early onset of AD, which can be attributed to compromised physiological functions due to the mutations. Tau is a microtubule-binding protein that secures the integrity of polymerized microtubules in neuronal cells. It malfunctions owing to various insults and stress conditions-like mutations and post-translational modifications.

OBJECTIVE

In this study, we modified the wild type and tau mutants by methyl glyoxal and thus studied whether glycation can enhance the aggregation of predisposed mutant tau.

METHODS

Tau glycation was studied by fluorescence assays, SDS-PAGE analysis, conformational evaluation, and transmission electron microscopy.

RESULTS

Our study suggests that FTDP-17 mutant P301 L leads to enhanced glycation-induced aggregation as well as advanced glycation end products formation. Glycation forms amorphous aggregates of tau and its mutants without altering its native conformation.

CONCLUSION

The metabolic anomalies and genetic predisposition have found to accelerate tau-mediated neurodegeneration and prove detrimental for the early-onset of Alzheimer's disease.

Temporal evolution of microglia and α-synuclein accumulation following foetal grafting in Parkinson's disease

We observed Lewy pathology in healthy embryonic dopamine neurons implanted into the striatum of patients with advanced Parkinson's disease. In the present study we examined the temporal relationship between the presence of inflammation with activated microglia and the emergence of α-synuclein pathology. Inflammation with activated microglia was observed in all grafts and at all time points examined between 18 months and 16 years as determined by both CD45 and TMEM119 staining. In contrast, α-synuclein was not detected at 18 months, only diffuse monomeric α-synuclein staining was observed at 4 years, and α-synuclein aggregates were not observed until 14-16 years after transplantation. Thus, there is evidence of inflammation and microglial activation in graft deposits long before the accumulation of α-synuclein pathology in implanted dopamine neurons. These observations raise the possibility that microglial activation contributes to the development of α-synuclein pathology, and supports the concept that microglia play an integral role in the propagation and spread of α-synuclein pathology.

Unravelling the effect of N(ε)-(carboxyethyl)lysine on the conformation, dynamics and aggregation propensity of α-synuclein

α-Synuclein (αS) aggregation is a hallmark in several neurodegenerative diseases. Among them, Parkinson's disease is highlighted, characterized by the intraneuronal deposition of Lewy bodies (LBs) which causes the loss of dopaminergic neurons. αS is the main component of LBs and in them, it usually contains post-translational modifications. One of them is the formation of advanced glycation end-products (mainly CEL and MOLD) arising from its reaction with methylglyoxal. Despite its biological relevance, there are no data available proving the effect of glycation on the conformation of αS, nor on its aggregation mechanism. This has been hampered by the formation of a heterogeneous set of compounds that precluded conformational studies. To overcome this issue, we have here produced αS homogeneously glycated with CEL. Its use, together with different biophysical techniques and molecular dynamics simulations, allowed us to study for the first time the effect of glycation on the conformation of a protein. CEL extended the conformation of the N-terminal domain as a result of the loss of transient N-/C-terminal long-range contacts while increasing the heterogeneity of the conformational population. CEL also inhibited the αS aggregation, but it was not able to disassemble preexisting amyloid fibrils, thus proving that CEL found on LBs must be formed in a later event after aggregation.

We study the effect of an advanced glycation end product (N(ε)-(carboxyethyl)lysine), found on the Lewy bodies of people suffering from Parkinson’s disease, on the conformational and aggregation features of alpha-synuclein.

Redox Signaling and Advanced Glycation Endproducts (AGEs) in Diet-Related Diseases

Diets are currently characterized by elevated sugar intake, mainly due to the increased consumption of processed sweetened foods and drinks during the last 40 years. Diet is the main source of advanced glycation endproducts (AGEs). These are toxic compounds formed during the Maillard reaction, which takes place both in vivo, in tissues and fluids under physiological conditions, favored by sugar intake, and ex vivo during food preparation such as baking, cooking, frying or storage. Protein glycation occurs slowly and continuously through life, driving AGE accumulation in tissues during aging. For this reason, AGEs have been proposed as a risk factor in the pathogenesis of diet-related diseases such as diabetes, insulin resistance, cardiovascular diseases, kidney injury, and age-related and neurodegenerative diseases. AGEs are associated with an increase in oxidative stress since they mediate the production of reactive oxygen species (ROS), increasing the intracellular levels of hydrogen peroxide (H₂O₂), superoxide (O₂⁻), and nitric oxide (NO). The interaction of AGEs with the receptor for AGEs (RAGE) enhances oxidative stress through ROS production by NADPH oxidases inside the mitochondria. This affects mitochondrial function and ultimately influences cell metabolism under various pathological conditions. This short review will summarize all evidence that relates AGEs and ROS production, their relationship with diet-related diseases, as well as the latest research about the use of natural compounds with antioxidant properties to prevent the harmful effects of AGEs on health.

Tracking Insulin Glycation in Real Time by Time-Resolved Emission Spectroscopy

The application of time-resolved fluorescence sensing to the study of heterogenic biomolecular systems remains challenging because of the complexity of the resulting photophysics. Measuring the time-resolved emission spectroscopy (TRES) spectra can provide a more informative alternative to the modeling of the fluorescence decay that is currently employed. Here, we demonstrate this approach by monitoring real-time changes in intrinsic insulin fluorescence by TRES as a straightforward probe to directly measure kinetics of insulin aggregation and glycation. Our findings hold promise for monitoring the storage of insulin and its application in the control of diabetes and may support the development of more effective therapeutics against amyloidosis.

Dicarbonyl Stress at the Crossroads of Healthy and Unhealthy Aging

Dicarbonyl stress occurs when dicarbonyl metabolites (i.e., methylglyoxal, glyoxal and 3-deoxyglucosone) accumulate as a consequence of their increased production and/or decreased detoxification. This toxic condition has been associated with metabolic and age-related diseases, both of which are characterized by a pro-inflammatory and pro-oxidant state. Methylglyoxal (MGO) is the most reactive dicarbonyl and the one with the highest endogenous flux. It is the precursor of the major quantitative advanced glycated products (AGEs) in physiological systems, arginine-derived hydroimidazolones, which accumulate in aging and dysfunctional tissues. The aging process is characterized by a decline in the functional properties of cells, tissues and whole organs, starting from the perturbation of crucial cellular processes, including mitochondrial function, proteostasis and stress-scavenging systems. Increasing studies are corroborating the causal relationship between MGO-derived AGEs and age-related tissue dysfunction, unveiling a previously underestimated role of dicarbonyl stress in determining healthy or unhealthy aging. This review summarizes the latest evidence supporting a causal role of dicarbonyl stress in age-related diseases, including diabetes mellitus, cardiovascular disease and neurodegeneration.

α-Synuclein in Parkinson's disease: causal or bystander?

Parkinson's disease (PD) comprises a spectrum of disorders with differing subtypes, the vast majority of which share Lewy bodies (LB) as a characteristic pathological hallmark. The process(es) underlying LB generation and its causal trigger molecules are not yet fully understood. α-Synuclein (α-syn) is a major component of LB and SNCA gene missense mutations or duplications/triplications are causal for rare hereditary forms of PD. As typical sporadic PD is associated with LB pathology, a factor of major importance is the study of the α-syn protein and its pathology. α-Syn pathology is, however, also evident in multiple system atrophy (MSA) and Lewy body disease (LBD), making it non-specific for PD. In addition, there is an overlap of these α-synucleinopathies with other protein-misfolding diseases. It has been proven that α-syn, phosphorylated tau protein (pτ), amyloid beta (Aβ) and other proteins show synergistic effects in the underlying pathogenic mechanisms. Multiple cell death mechanisms can induce pathological protein-cascades, but this can also be a reverse process. This holds true for the early phases of the disease process and especially for the progression of PD. In conclusion, while rare SNCA gene mutations are causal for a minority of familial PD patients, in sporadic PD (where common SNCA polymorphisms are the most consistent genetic risk factor across populations worldwide, accounting for 95% of PD patients) α-syn pathology is an important feature. Conversely, with regard to the etiopathogenesis of α-synucleinopathies PD, MSA and LBD, α-syn is rather a bystander contributing to multiple neurodegenerative processes, which overlap in their composition and individual strength. Therapeutic developments aiming to impact on α-syn pathology should take this fact into consideration.

Nitration and Glycation Diminish the α-Synuclein Role in the Formation and Scavenging of Cu2+-Catalyzed Reactive Oxygen Species

Human α-synuclein is a small monomeric protein (140 residues) essential to maintain the function of the dopaminergic neurons and the neuronal redox balance. However, it holds a dark side since it is able to clump inside the neurons forming insoluble aggregates known as Lewy bodies, which are considered the hallmark of Parkinson's disease. Sporadic mutations and nonenzymatic post-translational modifications are well-known to stimulate the formation of Lewy bodies. Yet, the effect of nonenzymatic post-translational modifications on the function of α-synuclein has been studied less intense. Therefore, here we study how nitration and glycation mediated by methylglyoxal affect the redox features of α-synuclein. Both diminish the ability of α-synuclein to chelate Cu²⁺, except when N^ε-(carboxyethyl)lysine or N^ε-(carboxymethyl)lysine (two advanced glycation end products highly prevalent in vivo) are formed. This results in a lower capacity to prevent the Cu-catalyzed ascorbic acid degradation and to delay the formation of H₂O₂. However, only methylglyoxal was able to abolish the ability of α-synuclein to inhibit the free radical release. Both nitration and glycation enhanced the α-synuclein availability to be damaged by O₂^•-, although glycation made α-synuclein less reactive toward HO^•. Our data represent the first report describing how nonenzymatic post-translational modifications might affect the redox function of α-synuclein, thus contributing to a better understanding of its pathological implications.

Neuropathology and pathogenesis of extrapyramidal movement disorders: a critical update-I. Hypokinetic-rigid movement disorders

Extrapyramidal movement disorders include hypokinetic rigid and hyperkinetic or mixed forms, most of them originating from dysfunction of the basal ganglia (BG) and their information circuits. The functional anatomy of the BG, the cortico-BG-thalamocortical, and BG-cerebellar circuit connections are briefly reviewed. Pathophysiologic classification of extrapyramidal movement disorder mechanisms distinguish (1) parkinsonian syndromes, (2) chorea and related syndromes, (3) dystonias, (4) myoclonic syndromes, (5) ballism, (6) tics, and (7) tremor syndromes. Recent genetic and molecular-biologic classifications distinguish (1) synucleinopathies (Parkinson's disease, dementia with Lewy bodies, Parkinson's disease-dementia, and multiple system atrophy); (2) tauopathies (progressive supranuclear palsy, corticobasal degeneration, FTLD-17; Guamian Parkinson-dementia; Pick's disease, and others); (3) polyglutamine disorders (Huntington's disease and related disorders); (4) pantothenate kinase-associated neurodegeneration; (5) Wilson's disease; and (6) other hereditary neurodegenerations without hitherto detected genetic or specific markers. The diversity of phenotypes is related to the deposition of pathologic proteins in distinct cell populations, causing neurodegeneration due to genetic and environmental factors, but there is frequent overlap between various disorders. Their etiopathogenesis is still poorly understood, but is suggested to result from an interaction between genetic and environmental factors. Multiple etiologies and noxious factors (protein mishandling, mitochondrial dysfunction, oxidative stress, excitotoxicity, energy failure, and chronic neuroinflammation) are more likely than a single factor. Current clinical consensus criteria have increased the diagnostic accuracy of most neurodegenerative movement disorders, but for their definite diagnosis, histopathological confirmation is required. We present a timely overview of the neuropathology and pathogenesis of the major extrapyramidal movement disorders in two parts, the first one dedicated to hypokinetic-rigid forms and the second to hyperkinetic disorders.