Role of methylglyoxal in Alzheimer's disease

Glyceraldehyde-3-phosphate dehydrogenase is involved in the pathogenesis of Alzheimer's disease

One of important characteristics of Alzheimer's disease is a persistent oxidative/nitrosative stress caused by pro-oxidant properties of amyloid-beta peptide (Aβ) and chronic inflammation in the brain. Glyceraldehyde-3-phosphate dehydrogenase (GAPDH) is easily oxidized under oxidative stress. Numerous data indicate that oxidative modifications of GAPDH in vitro and in cell cultures stimulate GAPDH denaturation and aggregation, and the catalytic cysteine residue Cys152 is important for these processes. Both intracellular and extracellular GAPDH aggregates are toxic for the cells. Interaction of denatured GAPDH with soluble Aβ results in mixed insoluble aggregates with increased toxicity. The above-described properties of GAPDH (sensitivity to oxidation and propensity to form aggregates, including mixed aggregates with Aβ) determine its role in the pathogenesis of Alzheimer's disease.

Genomic Analysis Identifies Risk Factors in Restless Legs Syndrome

OBJECTIVE

Restless legs syndrome (RLS) is a neurological condition that causes uncomfortable sensations in the legs and an irresistible urge to move them, typically during periods of rest. The genetic basis and pathophysiology of RLS are incompletely understood. We sought to identify additional novel genetic risk factors associated with RLS susceptibility.

METHODS

We performed a whole-genome sequencing and genome-wide association meta-analysis of RLS cases (n = 9,851) and controls (n = 38,957) in 3 population-based biobanks (All of Us, Canadian Longitudinal Study on Aging, and CARTaGENE).

RESULTS

Genome-wide association analysis identified 9 independent risk loci, of which 8 had been previously reported, and 1 was a novel risk locus (LMX1B, rs35196838, OR 1.14, 95% CI 1.09-1.19, p value = 2.2 × 10-9). Furthermore, a transcriptome-wide association study also identified GLO1 and a previously unreported gene, ELFN1. A genetic correlation analysis revealed significant common variant overlaps between RLS and neuroticism (rg = 0.40, se = 0.08, p value = 5.4 × 10-7), depression (rg = 0.35, se = 0.06, p value = 2.17 × 10-8), and intelligence (rg = -0.20, se = 0.06, p value = 4.0 × 10-4).

INTERPRETATION

Our study expands the understanding of the genetic architecture of RLS, and highlights the contributions of common variants to this prevalent neurological disorder. ANN NEUROL 2024.

Is Methylglyoxal a Potential Biomarker for the Warburg Effect Induced by the Lipopolysaccharide Neuroinflammation Model?

Methylglyoxal (MG) is considered a classical biomarker of diabetes mellitus and its comorbidities. However, a role for this compound in exacerbated immune responses, such as septicemia, is being increasingly observed and requires clarification, particularly in the context of neuroinflammatory responses. Herein, we used two different approaches (in vivo and acute hippocampal slice models) to investigate MG as a biomarker of neuroinflammation and the neuroimmunometabolic shift to glycolysis in lipopolysaccharide (LPS) inflammation models. Our data reinforce the hypothesis that LPS-induced neuroinflammation stimulates the cerebral innate immune response by increasing IL-1β, a classical pro-inflammatory cytokine, and the astrocyte reactive response, via elevating S100B secretion and GFAP levels. Acute neuroinflammation promotes an early neuroimmunometabolic shift to glycolysis by elevating glucose uptake, lactate release, PFK1, and PK activities. We observed high serum and cerebral MG levels, in association with a reduction in glyoxalase 1 detoxification activity, and a close correlation between serum and hippocampus MG levels with the systemic and neuroinflammatory responses to LPS. Findings strongly suggest a role for MG in immune responses.

Molecular mechanisms linking type 2 diabetes mellitus and late-onset Alzheimer's disease: A systematic review and qualitative meta-analysis

Research evidence indicating common metabolic mechanisms through which type 2 diabetes mellitus (T2DM) increases risk of late-onset Alzheimer's dementia (LOAD) has accumulated over recent decades. The aim of this systematic review is to provide a comprehensive review of common mechanisms, which have hitherto been discussed in separate perspectives, and to assemble and evaluate candidate loci and epigenetic modifications contributing to polygenic risk linkages between T2DM and LOAD. For the systematic review on pathophysiological mechanisms, both human and animal studies up to December 2023 are included. For the qualitative meta-analysis of genomic bases, human association studies were examined; for epigenetic mechanisms, data from human studies and animal models were accepted. Papers describing pathophysiological studies were identified in databases, and further literature gathered from cited work. For genomic and epigenomic studies, literature mining was conducted by formalised search codes using Boolean operators in search engines, and augmented by GeneRif citations in Entrez Gene, and other sources (WikiGenes, etc.). For the systematic review of pathophysiological mechanisms, 923 publications were evaluated, and 138 gene loci extracted for testing candidate risk linkages. 3 57 publications were evaluated for genomic association and descriptions of epigenomic modifications. Overall accumulated results highlight insulin signalling, inflammation and inflammasome pathways, proteolysis, gluconeogenesis and glycolysis, glycosylation, lipoprotein metabolism and oxidation, cell cycle regulation or survival, autophagic-lysosomal pathways, and energy. Documented findings suggest interplay between brain insulin resistance, neuroinflammation, insult compensatory mechanisms, and peripheral metabolic dysregulation in T2DM and LOAD linkage. The results allow for more streamlined longitudinal studies of T2DM-LOAD risk linkages.

3D human stem-cell-derived neuronal spheroids for in vitro neurotoxicity testing of methylglyoxal, highly reactive glycolysis byproduct and potent glycating agent

Human-derived three-dimensional (3D) in vitro models are advanced human cell-based model for their complexity, relevance and application in toxicity testing. Intracellular accumulation of methylglyoxal (MGO), the most potent glycating agent in humans, mainly generated as a by-product of glycolysis, is associated with age-related diseases including neurodegenerative disorders. In our study, 3D human stem-cell-derived neuronal spheroids were set up and applied to evaluate cytotoxic effects after short-term (5 to 48 h) treatments with different MGO concentrations, including low levels, taking into consideration several biochemical endpoints. In MGO-treated neurospheroids, reduced cell growth proliferation and decreased cell viability occurred early from 5-10 μM, and their compactness diminished starting from 100 μM, apparently without affecting spheroid size. MGO markedly caused loss of the neuronal markers MAP-2 and NSE from 10-50 μM, decreased the detoxifying Glo1 enzyme from 50 μM, and activated NF-kB by nuclear translocation. The cytochemical evaluation of the 3D sections showed the presence of necrotic cells with loss of nuclei. Apoptotic cells were observed from 50 μM MGO after 48 h, and from 100 μM after 24 h. MGO (50-10 µM) also induced modifications of the cell-cell and cell-ECM interactions. These effects worsened at the higher concentrations (300-500 µM). In 3D neuronal spheroids, MGO tested concentrations comparable to human samples levels measured in MGO-associated diseases, altered neuronal key signalling endpoints relevant for the pathogenesis of neurodegenerative diseases and aging. The findings also demonstrated that the use of 3D neuronal spheroids of human origin can be useful in a strategy in vitro for testing MGO and other dicarbonyls evaluation.

A Mechanism of Action of Metformin in the Brain: Prevention of Methylglyoxal-Induced Glutamatergic Impairment in Acute Hippocampal Slices

Metformin, a biguanide compound (N-1,1-dimethylbiguanide), is widely prescribed for diabetes mellitus type 2 (T2D) treatment. It also presents a plethora of properties, such as anti-oxidant, anti-inflammatory, anti-apoptosis, anti-tumorigenic, and anti-AGE formation activity. However, the precise mechanism of action of metformin in the central nervous system (CNS) needs to be clarified. Herein, we investigated the neuroprotective role of metformin in acute hippocampal slices exposed to methylglyoxal (MG), a highly reactive dicarbonyl compound and a key molecule in T2D developmental pathophysiology. Metformin protected acute hippocampal slices from MG-induced glutamatergic neurotoxicity and neuroinflammation by reducing IL-1β synthesis and secretion and RAGE protein expression. The drug also improved astrocyte function, particularly with regard to the glutamatergic system, increasing glutamate uptake. Moreover, we observed a direct effect of metformin on glutamate transporters, where the compound prevented glycation, by facilitating enzymatic phosphorylation close to Lys residues, suggesting a new neuroprotective role of metformin via PKC ζ in preventing dysfunction in glutamatergic system induced by MG.

Structural perturbations induced by cumulative action of methylglyoxal and peroxynitrite on human fibrinogen: An in vitro and in silico approach

Methylglyoxal (MGO); a reducing sugar and a dicarbonyl; attaches to the biomolecules (proteins, lipids, and DNA) leading to glycation and accumulation of oxidative stress in cells and tissues. Superoxide anion formed under such conditions entraps free nitric oxide radical (NO) to form peroxynitrite (PON). Nitro-oxidative stress due to PON is well established. Human fibrinogen plays a key role in haemostasis and is a highly vulnerable target for oxidation. Modifications of fibrinogen can potentially disrupt its structure and function. Earlier evidence suggested that glycation and nitro-oxidation lead to protein aggregation by making it resistant to lysis. This study aims to reveal the structural perturbations on fibrinogen in the presence of MGO and PON synergistically. The in vitro glyco-nitro-oxidation of human fibrinogen by MGO and PON leads to substantial structural alterations, as evident by biophysical and biochemical studies. In-silico results revealed the formation of stable complexes. UV-visible, intrinsic fluorescence, and circular dichroism investigations confirmed the synergistic effect of MGO and PON caused micro-structural modifications leading to secondary structural alterations. AGEs formation in MGO-modified fibrinogen reduced the free lysine and free arginine residues which were quantified by TNBS and phenanthrenequinone assays. Enhanced oxidative status was confirmed by estimating carbonyl content. ANS fluorophore validated exposure of hydrophobic patches in modified protein and thioflavin-T showed maximum binding with synergistically modified fibrinogen, indicated the formation of β-sheet. Confocal and electron microscope results corroborated the formation of aggregates. This study, therefore, evaluated the impact of MGO and PON on the structural integrity, oxidative status and aggregate formation of fibrinogen that can aggravate metabolic complications.

Neuroprotective effects of dipeptidyl peptidase 4 inhibitor on Alzheimer's disease: a narrative review

Insulin resistance in brain and amyloidogenesis are principal pathological features of diabetes-related cognitive decline and development of Alzheimer's disease (AD). A growing body of evidence suggests that maintaining glucose under control in diabetic patients is beneficial for preventing AD development. Dipeptidyl peptidase 4 inhibitors (DDP4is) are a class of novel glucose-lowering medications through increasing insulin excretion and decreasing glucagon levels that have shown neuroprotective potential in recent studies. This review consolidates extant evidence from earlier and new studies investigating the association between DPP4i use, AD, and other cognitive outcomes. Beyond DPP4i's benefits in alleviating insulin resistance and glucose-lowering, underlying mechanisms for the potential neuroprotection with DPP4i medications were categorized into the following sections: (Ferrari et al., Physiol Rev, 2021, 101, 1,047-1,081): the benefits of DPP4is on directly ameliorating the burden of β-amyloid plaques and reducing the formation of neurofibrillary tangles; DPP4i increasing the bioactivity of neuroprotective DPP4 substrates including glucagon-like peptide-1 (GLP-1), glucose-dependent insulinotropic peptide (GIP), and stromal-derived factor-1α (SDF-1α) etc.; pleiotropic effects of DPP4is on neuronal cells and intracerebral structure including anti-inflammation, anti-oxidation, and anti-apoptosis. We further revisited recently published epidemiological studies that provided supportive data to compliment preclinical evidence. Given that there remains a lack of completed randomized trials that aim at assessing the effect of DPP4is in preventing AD development and progression, this review is expected to provide a useful insight into DPP4 inhibition as a potential therapeutic target for AD prevention and treatment. The evidence is helpful for informing the rationales of future clinical research and guiding evidence-based clinical practice.

Methylglyoxal Induced Modifications to Stabilize Therapeutic Proteins: A Review

Therapeutic proteins are potent, fast-acting drugs that are highly effective in treating various conditions. Medicinal protein usage has increased in the past 10 years, and it will evolve further as we better understand disease molecular pathways. However, it is associated with high processing costs, limited stability, difficulty in being administered as an oral medication, and the inability of large proteins to penetrate tissue and reach their target locations. Many methods have been developed to overcome the problems with the stability and chaperone activity of therapeutic proteins, viz., the addition of external agents (changing the properties of the surrounding solvent by using stabilizing excipients, e.g., amino acids, sugars, polyols) and internal agents (chemical modifications that influence its structural properties, e.g., mutations, glycosylation). However, these methods must completely clear protein instability and chaperone issues. There is still much work to be done on finetuning chaperone proteins to increase their biological efficacy and stability. Methylglyoxal (MGO), a potent dicarbonyl compound, reacts with proteins and forms covalent cross-links. Much research on MGO scavengers has been conducted since they are known to alter protein structure, which may result in alterations in biological activity and stability. MGO is naturally produced within our body, however, its impact on chaperones and protein stability needs to be better understood and seems to vary based on concentration. This review highlights the efforts of several research groups on the effect of MGO on various proteins. It also addresses the impact of MGO on a client protein, α-crystallin, to understand the potential solutions to the protein's chaperone and stability problems.

NMR analysis seeking for cognitive decline and dementia metabolic markers in plasma from aged individuals

BACKGROUND

Blood biomarkers can improve the ability to diagnose dementia, providing new information to better understand the pathophysiology and causes of the disease. Some studies with patients have already shown changes in metabolic profiles among patients with pathological cognitive decline or Alzheimer's disease, when compared to individuals with normal cognition.

METHODS

To search for new metabolic biomarkers of dementia, we analyzed serum levels of several metabolites, measured by nuclear magnetic resonance spectroscopy, in elderly individuals, a group with normal cognitive decline (control), and three other groups with cognitive decline. pathological (low, moderate, and severe).

RESULTS

Decreased plasma levels of tyrosine, glutamate, valine, leucine, and isoleucine are associated with worsening of pathological cognitive decline. However, the area under analysis of receptor operating characteristics suggests that tyrosine and glutamate have low specificity and sensitivity. Valine, leucine, and isoleucine are influenced by blood glucose or diabetes, but these conditions do not seem to be of great influence in the differences observed. Isobutyrate, histidine, acetone and unknown-1 metabolite also decrease their plasma levels with increasing CD. Isobutyrate ad histidine could have neuroprotective and antioxidant actions, respectively. To elucidate the role of decreased unknown metabolite-1 as a CD biomarker, it will be necessary to previously investigate its identity. To define and elucidate the role of acetone in pathological CD, additional laboratory and clinical studies must be performed. All these metabolites together may constitute a set of biomarkers with capability to identify pathological CD or dementia.

SIGNIFICANCE AND NOVELTY

Decrease of glutamate, tyrosine, valine, leucine, isoleucine, histidine, isobutyrate, acetone and unknown-1 metabolite together are a set of biomarkers able to identify pathological CD or dementia. Histidine, isobutyrate, acetone and unknown-1 metabolite are more specific biomarkers of CD.

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.

Synthesis and antiglycation activity of 3-phenacyl substituted thiazolium salts, new analogs of Alagebrium

After preliminary ab initio calculations, 3-phenacyl substituted thiazolium salts, analogs of Alagebrium, were synthesized and investigated in vitro as glycation reaction inhibitors. The most part of investigations focused on the potential of the title compounds to attenuate the formation of fluorescent AGEs as well on their ability to disrupt the cross-linking formation among glycated proteins. Additionally, the capability of thiazolium salts to deglycate in the reaction of early glycation products with nitroblue tetrazolium was determined. Cytotoxicological properties of the title compounds were evaluated using LDH and MTT assays. The leader compound (3-[2-(biphenyl-4-yl)-2-oxoethyl]-1,3-thiazol-3-ium bromide) in a 50 mg/kg dose (p.o. 14 days) was further tested within an in vivo carbonyl stress model (rats, methylglyoxal 86.25 mg/kg/d, i.p., 14 days). As a result, the leader-molecule revealed a high effectiveness against all three examined mechanisms of glycation reaction inhibition in in vitro tests and was able to suppress capacity of methylglyoxal to form AGEs in vivo.

Highly specific σ2R/TMEM97 ligand FEM-1689 alleviates neuropathic pain and inhibits the integrated stress response

The sigma 2 receptor (σ2R) was described pharmacologically more than three decades ago, but its molecular identity remained obscure until recently when it was identified as transmembrane protein 97 (TMEM97). We and others have shown that σ2R/TMEM97 ligands alleviate mechanical hypersensitivity in mouse neuropathic pain models with a time course wherein maximal antinociceptive effect is approximately 24 h following dosing. We sought to understand this unique antineuropathic pain effect by addressing two key questions: do these σ2R/TMEM97 compounds act selectively via the receptor, and what is their downstream mechanism on nociceptive neurons? Using male and female conventional knockout mice for Tmem97, we find that a σ2R/TMEM97 binding compound, FEM-1689, requires the presence of the gene to produce antinociception in the spared nerve injury model in mice. Using primary mouse dorsal root ganglion neurons, we demonstrate that FEM-1689 inhibits the integrated stress response (ISR) and promotes neurite outgrowth via a σ2R/TMEM97-specific action. We extend the clinical translational value of these findings by showing that FEM-1689 reduces ISR and p-eIF2α levels in human sensory neurons and that it alleviates the pathogenic engagement of ISR by methylglyoxal. We also demonstrate that σ2R/TMEM97 is expressed in human nociceptors and satellite glial cells. These results validate σ2R/TMEM97 as a promising target for further development for the treatment of neuropathic pain.

Genomic analysis identifies risk factors in restless legs syndrome

Restless legs syndrome (RLS) is a neurological condition that causes uncomfortable sensations in the legs and an irresistible urge to move them, typically during periods of rest. The genetic basis and pathophysiology of RLS are incompletely understood. Here, we present a whole-genome sequencing and genome-wide association meta-analysis of RLS cases (n = 9,851) and controls (n = 38,957) in three population-based biobanks (All of Us, Canadian Longitudinal Study on Aging, and CARTaGENE). Genome-wide association analysis identified nine independent risk loci, of which eight had been previously reported, and one was a novel risk locus (LMX1B, rs35196838, OR = 1.14, 95% CI = 1.09-1.19, p-value = 2.2 × 10-9). A genome-wide, gene-based common variant analysis identified GLO1 as an additional risk gene (p-value = 8.45 × 10-7). Furthermore, a transcriptome-wide association study also identified GLO1 and a previously unreported gene, ELFN1. A genetic correlation analysis revealed significant common variant overlaps between RLS and neuroticism (rg = 0.40, se = 0.08, p-value = 5.4 × 10-7), depression (rg = 0.35, se = 0.06, p-value = 2.17 × 10-8), and intelligence (rg = -0.20, se = 0.06, p-value = 4.0 × 10-4). Our study expands the understanding of the genetic architecture of RLS and highlights the contributions of common variants to this prevalent neurological disorder.

Methylglyoxal-induced neurotoxic effects in primary neuronal-like cells transdifferentiated from human mesenchymal stem cells: Impact of low concentrations

In the last decades, advanced glycation end-products (AGEs) have aroused the interest of the scientific community due to the increasing evidence of their involvement in many pathophysiological processes including various neurological disorders and cognitive decline age related. Methylglyoxal (MG) is one of the reactive dicarbonyl precursors of AGEs, mainly generated as a by-product of glycolysis, whose accumulation induces neurotoxicity. In our study, MG cytotoxicity was evaluated employing a human stem cell-derived model, namely, neuron-like cells (hNLCs) transdifferentiated from mesenchymal stem/stromal cells, which served as a source of human based species-specific "healthy" cells. MG increased ROS production and induced the first characteristic apoptotic hallmarks already at low concentrations (≥10 μM), decreased the cell growth (≥5-10 μM) and viability (≥25 μM), altered Glo-1 and Glo-2 enzymes (≥25 μM), and markedly affected the neuronal markers MAP-2 and NSE causing their loss at low MG concentrations (≥10 μM). Morphological alterations started at 100 μM, followed by even more marked effects and cell death after few hours (5 h) from 200 μM MG addition. Substantially, most effects occurred as low as 10 μM, concentration much lower than that reported from previous observations using different in vitro cell-based models (e.g., human neuroblastoma cell lines, primary animal cells, and human iPSCs). Remarkably, this low effective concentration approaches the level range measured in biological samples of pathological subjects. The use of a suitable cellular model, that is, human primary neurons, can provide an additional valuable tool, mimicking better the physiological and biochemical properties of brain cells, in order to evaluate the mechanistic basis of molecular and cellular alterations in CNS.

Saccharomyces cerevisiae DJ-1 paralogs maintain genome integrity through glycation repair of nucleic acids and proteins

Reactive carbonyl species (RCS) such as methylglyoxal and glyoxal are potent glycolytic intermediates that extensively damage cellular biomolecules leading to genetic aberration and protein misfolding. Hence, RCS levels are crucial indicators in the progression of various pathological diseases. Besides the glyoxalase system, emerging studies report highly conserved DJ-1 superfamily proteins as critical regulators of RCS. DJ-1 superfamily proteins, including the human DJ-1, a genetic determinant of Parkinson's disease, possess diverse physiological functions paramount for combating multiple stressors. Although S. cerevisiae retains four DJ-1 orthologs (Hsp31, Hsp32, Hsp33, and Hsp34), their physiological relevance and collective requirement remain obscure. Here, we report for the first time that the yeast DJ-1 orthologs function as novel enzymes involved in the preferential scavenge of glyoxal and methylglyoxal, toxic metabolites, and genotoxic agents. Their collective loss stimulates chronic glycation of the proteome, and nucleic acids, inducing spectrum of genetic mutations and reduced mRNA translational efficiency. Furthermore, the Hsp31 paralogs efficiently repair severely glycated macromolecules derived from carbonyl modifications. Also, their absence elevates DNA damage response, making cells vulnerable to various genotoxins. Interestingly, yeast DJ-1 orthologs preserve functional mitochondrial content, maintain ATP levels, and redistribute into mitochondria to alleviate the glycation damage of macromolecules. Together, our study uncovers a novel glycation repair pathway in S. cerevisiae and a possible neuroprotective mechanism of how hDJ-1 confers mitochondrial health during glycation toxicity.

A splicing transcriptome-wide association study identifies novel altered splicing for Alzheimer's disease susceptibility

Alzheimer's disease (AD) is a common neurodegenerative disease in aging individuals. Alternative splicing is reported to be relevant to AD development while their roles in etiology of AD remain largely elusive. We performed a comprehensive splicing transcriptome-wide association study (spTWAS) using intronic excision expression genetic prediction models of 12 brain tissues developed through three modelling strategies, to identify candidate susceptibility splicing introns for AD risk. A total of 111,326 (46,828 proxy) cases and 677,663 controls of European ancestry were studied. We identified 343 associations of 233 splicing introns (143 genes) with AD risk after Bonferroni correction (0.05/136,884 = 3.65 × 10^-7). Fine-mapping analyses supported 155 likely causal associations corresponding to 83 splicing introns of 55 genes. Eighteen causal splicing introns of 15 novel genes (EIF2D, WDR33, SAP130, BYSL, EPHB6, MRPL43, VEGFB, PPP1R13B, TLN2, CLUHP3, LRRC37A4P, CRHR1, LINC02210, ZNF45-AS1, and XPNPEP3) were identified for the first time to be related to AD susceptibility. Our study identified novel genes and splicing introns associated with AD risk, which can improve our understanding of the etiology of AD.

Inhibitory potential of N-acetylaspartate against protein glycation, AGEs formation and aggregation: Implication of brain osmolyte in glycation-related complications

Protein glycation and aggregation have a pivotal role in many diseases including diabetes and neurodegenerative disorders. N-acetyl aspartate (NAA), an osmolyte derived from L-aspartic acid, is one of the most abundant metabolites in the mammalian brain. Although NAA is supposed to be a substitute for a neuronal marker, its function is not fully elucidated. Herein, we have investigated the effect of NAA on glycation, AGEs formation and aggregation of irisin. AGE-specific fluorescence showed the strong inhibition of AGEs formation in the presence of NAA, demonstrating its anti-glycating property. The aggregates present in MG-modified irisin were also reduced by NAA, which was confirmed by Thioflavin T fluorescence and fluorescence microscopy. Further, for the explanation of the strong anti-glycating potential of NAA, the interaction between irisin and NAA was also examined. Interaction studies involving steady-state fluorescence and molecular docking demonstrated that hydrogen bonding and salt bridges by NAA stabilize the irisin. It was found that glycation-prone residues i.e., lysine and arginine are specifically involved in the interaction which might prevent them from getting modified during the process of glycation. This study for the first time reported the antiglycating potential of NAA which can be implicated in the therapeutic management of various glycation-related complications.

The C-glucosyl flavone isoorientin pretreatment attenuates the methylglyoxal-induced mitochondrial dysfunction in the human neuroblastoma SH-SY5Y cells: role for the AMPK-PI3K/Akt/Nrf2/γ-GCL/GSH axis

The reactive dicarbonyl methylglyoxal (MG) behaves as a pro-oxidant agent, causing redox dysfunction and cell death by different mechanisms in mammalian cells. MG is also a mitochondrial toxicant, impairing the oxidative phosphorylation (OXPHOS) system and leading to bioenergetics and redox collapses. MG induces glycation and exerts an important role in neurodegenerative and cardiovascular diseases. Isoorientin (ISO), a C-glucosyl flavone found in Aspalathus linearis, Fagopyrum esculentum, and Passiflora edulis, among others, is an antioxidant and anti-inflammatory molecule. ISO is a potent inducer of the transcription factor nuclear factor erythroid 2-related factor 2 (Nrf2), the master modulator of the redox environment in mammals. We investigated here whether ISO would prevent the mitochondria-related redox and bioenergetics impairments induced by MG in the human neuroblastoma SH-SY5Y cells. The cells were administrated with ISO at 20 μM for 18 h prior to the exposure to MG at 500 μM for further 24 h. It was observed that ISO efficiently prevented the mitochondrial impairments caused by MG. ISO upregulated the activity of the enzyme γ-glutamate-cysteine ligase (γ-GCL), consequently stimulating the synthesis of glutathione (GSH). The inhibition of γ-GCL, adenosine monophosphate-activated protein kinase (AMPK), and phosphoinositide 3-kinase/Akt (PI3K/Akt) suppressed the beneficial effects induced by ISO on the MG-challenged cells. Moreover, silencing of Nrf2 blocked the ISO-dependent γ-GCL and GSH upregulation and the effects on the mitochondria of the MG-challenged cells. Then, ISO caused mitochondrial protection by an AMPK-PI3K/Akt/Nrf2/γ-GCL/GSH-dependent manner in MG-administrated SH-SY5Y cells.

Behavioral and Proteomic Studies Reveal Methylglyoxal Activate Pathways Associated with Alzheimer's Disease

Diabetes is one of the major risk factors for Alzheimer's disease (AD) development. The role of elevated levels of glucose, methylglyoxal (MGO), and advanced glycation end products (AGEs) in the pathogenesis of AD is not well understood. In this pursuit, we studied the role of methylglyoxal in the pathogenesis of AD in rat models. The elevated plus-maze (EPM) behavioral study indicated that MGO induces anxiety. Treatment of telmisartan (RAGE expression inhibitor) and aminoguanidine (MGO quencher) attenuated MGO induced anxiety. Further, hippocampal proteomics demonstrated that MGO treated rats differentially regulate proteins involved in calcium homeostasis, mitochondrial functioning, and apoptosis, which may affect neurotransmission and neuronal plasticity. The hippocampal tau phosphorylation level was increased in MGO treated rats, which was reduced in the presence of aminoguanidine and telmisartan. The plasma fructosamine level was increased upon MGO treatment. Hippocampal histochemistry showed vascular degeneration and neuronal loss upon MGO treatment. This study provides mechanistic insight into the role of MGO in the diabetes-associated development of AD.

The expanding impact of methylglyoxal on behavior-related disorders

Methylglyoxal (MGO) is a reactive dicarbonyl compound formed as a byproduct of glycolysis. MGO is a major cell-permeant precursor of advanced glycation end products (AGEs), since it readily reacts with basic phospholipids and nucleotides, as well as amino acid residues of proteins, such as arginine, cysteine, and lysine. The AGEs production induced by MGO are widely associated with several pathologies, including neurodegenerative diseases. However, the impact of MGO metabolism and AGEs formation in the central nervous system (particularly in neurons, astrocytes and oligodendrocytes) on behavior and psychiatric diseases is not fully understood. Here, we briefly present background information on the biological activity of MGO in the central nervous system. It was gathered the available information on the role of MGO metabolism at the physiological processes, as well as at the neurobiology of psychiatry diseases, especially pain-related experiences, anxiety, depression, and cognition impairment-associated diseases. To clarify the role of MGO on behavior and associated diseases, we reviewed primarily the main findings at preclinical studies focusing on genetic and pharmacological approaches. Since monoamine neurotransmitter systems are implicated as pivotal targets on the pathophysiology and treatment of psychiatry and cognitive-related diseases, we also reviewed how MGO affects these neurotransmission systems and the implications of this phenomenon for nociception and pain; learning and cognition; and mood. In summary, this review highlights the pivotal role of glyoxalase 1 (Glo1) and MGO levels in modulating behavioral phenotypes, as well as related cellular and molecular signaling. Conclusively, this review signals dopamine as a new neurochemical MGO target, as well as highlights how MGO metabolism can modulate the pathophysiology and treatment of pain, psychiatric and cognitive-related diseases.

Characterization of advanced glycation end products and aggregates of irisin: Multispectroscopic and microscopic approaches

Glycation of proteins leading to the formation of advanced glycation end products (AGEs) has been demonstrated to contribute to the pathogenesis of several diseases. Irisin is a clinically significant protein, putatively involved in obesity, diabetes, and neurological disorders. This study aimed to monitor the methyl-glyoxal (MG) induced AGEs and aggregate formation of irisin, as a function of time, employing multispectroscopic and microscopic approaches. ANS fluorescence suggested a molten globule-like state on Day 6, followed by the formation of irisin AGEs adducts, as confirmed by AGE-specific fluorescence. Glycation of irisin led to aggregate formation, which was characterized by Thioflavin T fluorescence, CD spectroscopy, and microscopic studies. These aggregates were confirmed by exploiting fluorescence microscopy, confocal, and transmission electron microscopy. Molecular docking was performed to determine the crucial residues of irisin involved in irisin-MG interaction. Usually, MG is present in trace amounts as a metabolic by-product in the body, which is found to be elevated in diseased conditions viz. diabetes and Alzheimer's disease. This study characterized the AGEs and aggregates of clinically important protein, irisin; and since MG level has been found to be increased in various pathological conditions, this study provides a clinical perspective. There is a possibility that elevated MG concentrations might glycate irisin resulting in reduced irisin levels as reported in pathological conditions. However, further investigations are required to prove it.

Understanding the role of glycation in the pathology of various non-communicable diseases along with novel therapeutic strategies

Glycation refers to carbonyl group condensation of the reducing sugar with the free amino group of protein, which forms Amadori products and advanced glycation end products (AGEs). These AGEs alter protein structure and function by configuring a negative charge on the positively charged arginine and lysine residues. Glycation plays a vital role in the pathogenesis of metabolic diseases, brain disorders, aging, and gut microbiome dysregulation with the aid of 3 mechanisms: (i) formation of highly reactive metabolic pathway-derived intermediates, which directly affect protein function in cells, (ii) the interaction of AGEs with its associated receptors to create oxidative stress causing the activation of transcription factor NF-κB, and (iii) production of extracellular AGEs hinders interactions between cellular and matrix molecules affecting vascular and neural genesis. Therapeutic strategies are thus required to inhibit glycation at different steps, such as blocking amino and carbonyl groups, Amadori products, AGEs-RAGE interactions, chelating transition metals, scavenging free radicals, and breaking crosslinks formed by AGEs. The present review focused on explicitly elaborating the impact of glycation-influenced molecular mechanisms in developing and treating noncommunicable diseases.

Methylglyoxal-Modified Human Serum Albumin Binds to Leukocyte Myeloperoxidase and Inhibits its Enzymatic Activity

Hyperglycemia in diabetes mellitus induces modification of proteins by glucose and its derivative methylglyoxal (MG). Neutrophils perform their bactericidal activity mainly via reactive halogen (RHS) and oxygen (ROS) species generation catalyzed by myeloperoxidase (MPO) stored in neutrophil azurophilic granules (AGs) and membrane NADPH oxidase, respectively. Herein, we study the binding of human serum albumin (HSA) modified with MG (HSA-MG) to MPO and its effects on MPO activity and release by neutrophils. Peroxidase activity of MPO was registered by oxidation of 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) diammonium salt, and chlorinating activity by decolorization of Celestine blue B dye. Binding of HSA-MG to MPO was studied by affinity chromatography, disc-electrophoresis, ligand Western blotting and enzyme-linked solid phase immunoassay using monoclonal antibodies (mAbs) to MPO. ROS and RHS generation were detected by lucigenin (Luc) and luminol (Lum) chemiluminescence (CL), respectively. Neutrophil degranulation was assessed by flow cytometry using fluorescent labeled antibodies to the marker proteins CD63 from AGs and CD11b from peroxidase-negative granules (PNGs). NETosis was assayed by quantifying DNA network-like structures (NET-like structures) in blood smears stained by Romanowsky. HSA-MG bound to MPO, giving a stable complex (Kd = 1.5 nM) and competing with mAbs, and non-competitively inhibited peroxidase and chlorinating MPO activity and induced degranulation of PNGs but not of AGs. HSA-MG enhanced Luc-CL per se or following PMA, unlike Lum-CL, and did not affect spontaneous or PMA-stimulated NETosis. Thus, HSA modified under hyperglycemia-like conditions stimulated NADPH oxidase of neutrophils but dampened their functions dependent on activity of MPO, with no effect on its release via degranulation or NETosis. This phenomenon could underlie the downregulation of bactericidal activity of MPO and neutrophils, and hence of innate immunity, giving rise to wound healing impairment and susceptibility to infection in patients with hyperglycemia.

Arginine Reduces Glycation in γ2 Subunit of AMPK and Pathologies in Alzheimer's Disease Model Mice

The metabolism disorders are a common convergence of Alzheimer's disease (AD) and type 2 diabetes mellitus (T2DM). The characteristics of AD are senile plaques and neurofibrillary tangles (NFTs) composed by deposits of amyloid-β (Aβ) and phosphorylated tau, respectively. Advanced glycation end-products (AGEs) are a stable modification of proteins by non-enzymatic reactions, which could result in the protein dysfunction. AGEs are associated with some disease developments, such as diabetes mellitus and AD, but the effects of the glycated γ2 subunit of AMPK on its activity and the roles in AD onset are unknown.

METHODS

We studied the effect of glycated γ2 subunit of AMPK on its activity in N2a cells. In 3 × Tg mice, we administrated L-arginine once every two days for 45 days and evaluated the glycation level of γ2 subunit and function of AMPK and alternation of pathologies.

RESULTS

The glycation level of γ2 subunit was significantly elevated in 3 × Tg mice as compared with control mice, meanwhile, the level of pT172-AMPK was obviously lower in 3 × Tg mice than that in control mice. Moreover, we found that arginine protects the γ2 subunit of AMPK from glycation, preserves AMPK function, and improves pathologies and cognitive deficits in 3 × Tg mice.

CONCLUSIONS

Arginine treatment decreases glycated γ2 subunit of AMPK and increases p-AMPK levels in 3 × Tg mice, suggesting that reduced glycation of the γ2 subunit could ameliorate AMPK function and become a new target for AD therapy in the future.

Impairment of insulin signaling pathway PI3K/Akt/mTOR and insulin resistance induced AGEs on diabetes mellitus and neurodegenerative diseases: a perspective review

Insulin resistance is common in type 2 diabetes mellitus (T2DM), neurodegenerative diseases, cardiovascular diseases, kidney diseases, and polycystic ovary syndrome. Impairment in insulin signaling pathways, such as the PI3K/Akt/mTOR pathway, would lead to insulin resistance. It might induce the synthesis and deposition of advanced glycation end products (AGEs), reactive oxygen species, and reactive nitrogen species, resulting in stress, protein misfolding, protein accumulation, mitochondrial dysfunction, reticulum function, and metabolic syndrome dysregulation, inflammation, and apoptosis. It plays a huge role in various neurodegenerative diseases like Parkinson's disease, Alzheimer's disease, Huntington's disease, and Amyloid lateral sclerosis. In this review, we intend to focus on the possible effect of insulin resistance in the progression of neurodegeneration via the impaired P13K/Akt/mTOR signaling pathway, AGEs, and receptors for AGEs.

Methylglyoxal and Its Adducts: Induction, Repair, and Association with Disease

Metabolism is an essential part of life that provides energy for cell growth. During metabolic flux, reactive electrophiles are produced that covalently modify macromolecules, leading to detrimental cellular effects. Methylglyoxal (MG) is an abundant electrophile formed from lipid, protein, and glucose metabolism at intracellular levels of 1-4 μM. MG covalently modifies DNA, RNA, and protein, forming advanced glycation end products (MG-AGEs). MG and MG-AGEs are associated with the onset and progression of many pathologies including diabetes, cancer, and liver and kidney disease. Regulating MG and MG-AGEs is a potential strategy to prevent disease, and they may also have utility as biomarkers to predict disease risk, onset, and progression. Here, we review recent advances and knowledge surrounding MG, including its production and elimination, mechanisms of MG-AGEs formation, the physiological impact of MG and MG-AGEs in disease onset and progression, and the latter in the context of its receptor RAGE. We also discuss methods for measuring MG and MG-AGEs and their clinical application as prognostic biomarkers to allow for early detection and intervention prior to disease onset. Finally, we consider relevant clinical applications and current therapeutic strategies aimed at targeting MG, MG-AGEs, and RAGE to ultimately improve patient outcomes.

Acute Methylglyoxal-Induced Damage in Blood-Brain Barrier and Hippocampal Tissue

Methylglyoxal (MG) is a reactive dicarbonyl compound formed mostly via the glycolytic pathway. Elevated blood glucose levels can cause MG accumulation in plasma and cerebrospinal fluid in patients with diabetes mellitus and Alzheimer's disease. Under these disease conditions, the high reactivity of MG leads to modification of proteins and other biomolecules, generating advanced glycation end products (AGEs), which are considered mediators in neurodegenerative diseases. We investigated the integrity of the blood-brain barrier (BBB) and astrocyte response in the hippocampus to acute insult induced by MG when it was intracerebroventricularly administered to rats. Seventy-two hours later, BBB integrity was lost, as assessed by the entry of Evans dye into the brain tissue and albumin in the cerebrospinal fluid, and a decrease in aquaporin-4 and connexin-43 in the hippocampal tissue. MG did not induce changes in the hippocampal contents of RAGE in this short interval, but decreased the expression of S100B, an astrocyte-secreted protein that binds RAGE. The expression of two important transcription factors of the antioxidant response, NF-κB and Nrf2, was unchanged. However, hemeoxigenase-1 was upregulated in the MG-treated group. These data corroborate the idea that hippocampal cells are targets of MG toxicity and that BBB dysfunction and specific glial alterations induced by this compound may contribute to the behavioral and cognitive alterations observed in these animals.

Dietary Methylglyoxal Exposure Induces Alzheimer's Disease by Promoting Amyloid β Accumulation and Disrupting Autophagy in Caenorhabditis elegans

Methylglyoxal (MG) is a precursor of advanced glycation end products usually generated during cooking. The high level of MG in the brain is correlated to the pathogenesis of Alzheimer's disease (AD). However, it is not clear if MG consumed through the diet can cause AD-related toxicity. Herein, the Caenorhabditis elegans (C. elegans) AD model was used to investigate the neurotoxicity after long-term MG exposure at dietary levels. The results showed that C. elegans locomotive behaviors were significantly decreased after 0.1, 0.5, and 1 mM MG exposure (p < 0.001). In amyloid β (Aβ)-expressing transgenic C. elegans strains, 0.5 mM MG significantly promoted Aβ accumulation by around 50% in day-8 CL2006 (p < 0.001), enhanced paralysis in CL4176 (p < 0.001) and CL2006 (p < 0.01), and made CL2355 around 17% more vulnerable to 5-HT, indicating impaired serotonin reuptake (p < 0.05). Additionally, 0.5 mM MG significantly increased the reactive oxygen species level (p < 0.001) by inhibiting the expression of stress-response genes including sod-3, gst-4, and hsp-16.2 in day-8 aged worms. Moreover, the autophagic pathway was disrupted through lgg-1, vps-34, and bec-1 expression after MG exposure and Aβ accumulation. Treatment with the citrus flavonoid nobiletin reduced the MG-induced toxicity (p < 0.001). Overall, these findings imply that it is possible to exacerbate AD pathogenesis by MG exposure through the diet.

PARK7/DJ-1 as a Therapeutic Target in Gut-Brain Axis Diseases

It is increasingly known that Parkinson's (PD) and Alzheimer's (AD) diseases occur more frequently in patients with inflammatory gastrointestinal diseases including inflammatory bowel (IBD) or celiac disease, indicating a pathological link between them. Although epidemiological observations suggest the existence of the gut-brain axis (GBA) involving systemic inflammatory and neural pathways, little is known about the exact molecular mechanisms. Parkinson's disease 7 (PARK7/DJ-1) is a multifunctional protein whose protective role has been widely demonstrated in neurodegenerative diseases, including PD, AD, or ischemic stroke. Recent studies also revealed the importance of PARK7/DJ-1 in the maintenance of the gut microbiome and also in the regulation of intestinal inflammation. All these findings suggest that PARK7/DJ-1 may be a link and also a potential therapeutic target in gut and brain diseases. In this review, therefore, we discuss our current knowledge about PARK7/DJ-1 in the context of GBA diseases.

Admixture Mapping of Alzheimer's disease in Caribbean Hispanics identifies a new locus on 22q13.1

Late-onset Alzheimer's disease (LOAD) is significantly more frequent in Hispanics than in non-Hispanic Whites. Ancestry may explain these differences across ethnic groups. To this end, we studied a large cohort of Caribbean Hispanics (CH, N = 8813) and tested the association between Local Ancestry (LA) and LOAD ("admixture mapping") to identify LOAD-associated ancestral blocks, separately for ancestral components (European [EUR], African [AFR], Native American[NA]) and jointly (AFR + NA). Ancestral blocks significant after permutation were fine-mapped employing multi-ethnic whole-exome sequencing (WES) to identify rare variants associated with LOAD (SKAT-O) and replicated in the UK Biobank WES dataset. Candidate genes were validated studying (A) protein expression in human LOAD and control brains; (B) two animal AD models, Drosophila and Zebrafish. In the joint AFR + NA model, we identified four significant ancestral blocks located on chromosomes 1 (p value = 8.94E-05), 6 (p value = 8.63E-05), 21 (p value = 4.64E-05) and 22 (p value = 1.77E-05). Fine-mapping prioritized the GCAT gene on chromosome 22 (SKAT-O p value = 3.45E-05) and replicated in the UK Biobank (SKAT-O p value = 0.05). In LOAD brains, a decrease of 28% in GCAT protein expression was observed (p value = 0.038), and GCAT knockdown in Amyloid-β42 Drosophila exacerbated rough eye phenotype (68% increase, p value = 4.84E-09). In zebrafish, gcat expression increased after acute amyloidosis (34%, p value = 0.0049), and decreased upon anti-inflammatory Interleukin-4 (39%, p value = 2.3E-05). Admixture mapping uncovered genomic regions harboring new LOAD-associated loci that might explain the observed different frequency of LOAD across ethnic groups. Our results suggest that the inflammation-related activity of GCAT is a response to amyloid toxicity, and reduced GCAT expression exacerbates AD pathology.

Glycation modulates glutamatergic signaling and exacerbates Parkinson's disease-like phenotypes

Alpha-synuclein (aSyn) is a central player in the pathogenesis of synucleinopathies due to its accumulation in typical protein aggregates in the brain. However, it is still unclear how it contributes to neurodegeneration. Type-2 diabetes mellitus is a risk factor for Parkinson's disease (PD). Interestingly, a common molecular alteration among these disorders is the age-associated increase in protein glycation. We hypothesized that glycation-induced neuronal dysfunction is a contributing factor in synucleinopathies. Here, we dissected the impact of methylglyoxal (MGO, a glycating agent) in mice overexpressing aSyn in the brain. We found that MGO-glycation potentiates motor, cognitive, olfactory, and colonic dysfunction in aSyn transgenic (Thy1-aSyn) mice that received a single dose of MGO via intracerebroventricular injection. aSyn accumulates in the midbrain, striatum, and prefrontal cortex, and protein glycation is increased in the cerebellum and midbrain. SWATH mass spectrometry analysis, used to quantify changes in the brain proteome, revealed that MGO mainly increase glutamatergic-associated proteins in the midbrain (NMDA, AMPA, glutaminase, VGLUT and EAAT1), but not in the prefrontal cortex, where it mainly affects the electron transport chain. The glycated proteins in the midbrain of MGO-injected Thy1-aSyn mice strongly correlate with PD and dopaminergic pathways. Overall, we demonstrated that MGO-induced glycation accelerates PD-like sensorimotor and cognitive alterations and suggest that the increase of glutamatergic signaling may underly these events. Our study sheds new light into the enhanced vulnerability of the midbrain in PD-related synaptic dysfunction and suggests that glycation suppressors and anti-glutamatergic drugs may hold promise as disease-modifying therapies for synucleinopathies.

Effect of Cannabidiol on the Neural Glyoxalase Pathway Function and Longevity of Several C. elegans Strains Including a C. elegans Alzheimer's Disease Model

Cannabidiol is a nonpsychoactive phytocannabinoid produced by the Cannabis sativa plant and possesses a wide range of pharmacological activities, including anti-inflammatory, antioxidant, and neuroprotective activities. Cannabidiol functions in a neuroprotective manner, in part through the activation of cellular antioxidant pathways. The glyoxalase pathway detoxifies methylglyoxal, a highly reactive metabolic byproduct that can accumulate in the brain, and contributes to the severity of neurodegenerative diseases, including Alzheimer's disease. While cannabidiol's antioxidant properties have been investigated, it is currently unknown how it may modulate the glyoxalase pathway. In this research paper, we examine the effects of Cannabidiol on cerebellar neurons and in several Caenorhabditis elegans strains. We determined that a limited amount of Cannabidiol can prevent methylglyoxal-mediated cellular damage through enhancement of the neural glyoxalase pathway and extend the lifespan and survival of C. elegans, including a transgenic C. elegans strain modeling Alzheimer's disease.

The Methylglyoxal/RAGE/NOX-2 Pathway is Persistently Activated in the Hippocampus of Rats with STZ-Induced Sporadic Alzheimer's Disease

Alzheimer's disease (AD) is the leading cause of dementia in humans, with a high social and economic cost. AD is predominantly a sporadic disease, and the intracerebroventricular (ICV) administration of streptozotocin (STZ) has been widely used as an AD-like model of dementia. While the etiology of AD remains unknown, changes such as glucose metabolism and activation of receptors for advanced glycation end products (RAGE) seem to underlie its pathogenesis. We hypothesized that methylglyoxal, an endogenous toxin derived from the glycolytic pathway, could be the precursor of advanced glycated end products that activates RAGE and that, consequently, may activate membrane NADPH oxidase (NOX), contributing to the inflammatory status of the model and the disease. We administered ICV-STZ to Wistar rats and evaluated several neurochemical parameters in the hippocampus, particularly glyoxalase 1 (GLO-1) activity, which serves as an index of high levels of methylglyoxal, and the contents of RAGE and NOX-2, the most abundant brain NOX isoform. At the times evaluated (4 and 24 weeks after STZ), we observed cognitive deficit, increased beta-amyloid content, and increased tau phosphorylation. A persistent increase in GLO-1 activity was found, as well as increases in RAGE and NOX-2 contents, suggesting astroglial and microglial commitment. The increase in NOX-2 may reflect elevated microglial activity (confirmed by IBA-1 marker), which may contribute to the synaptic dysfunction and pruning described in the literature, both in this model and AD patients. Furthermore, reinforcing this possibility, we found a reduction in cholinergic communication in the hippocampus (as shown by decreased choline acetyltransferase), a reduction in BDNF, and an increase in TGF-β, the combination of which may result in synaptic deterioration.

An anthracenecarboximide-guanidine fluorescent probe for selective detection of glyoxals under weak acidic conditions

An anthracenecarboximide-guanidine based turn-on fluorescent probe ANC-DCP-1 for selective detection of glyoxals (methylglyoxal and glyoxal, GOS) over formaldehyde under weak acidic conditions around pH 6.0 was reported. The probe showed great potential in studying relative GOS levels in weak acidic biological fluids such as in urine for diabetic diagnosis and prognosis, and also found application in the food industry such as for fast unique manuka factor (UMF) scale determination of Manuka honey.

Formation of 5-membered dihydroxyimidazolidines with increased deprotonation at around pH 6.0 and enhanced intramolecular charge transfer for turn-on fluorescence detection of glyoxals.

Hallmarks of Metabolic Reprogramming and Their Role in Viral Pathogenesis

Metabolic reprogramming is a hallmark of cancer and has proven to be critical in viral infections. Metabolic reprogramming provides the cell with energy and biomass for large-scale biosynthesis. Based on studies of the cellular changes that contribute to metabolic reprogramming, seven main hallmarks can be identified: (1) increased glycolysis and lactic acid, (2) increased glutaminolysis, (3) increased pentose phosphate pathway, (4) mitochondrial changes, (5) increased lipid metabolism, (6) changes in amino acid metabolism, and (7) changes in other biosynthetic and bioenergetic pathways. Viruses depend on metabolic reprogramming to increase biomass to fuel viral genome replication and production of new virions. Viruses take advantage of the non-metabolic effects of metabolic reprogramming, creating an anti-apoptotic environment and evading the immune system. Other non-metabolic effects can negatively affect cellular function. Understanding the role metabolic reprogramming plays in viral pathogenesis may provide better therapeutic targets for antivirals.

Role of Lactate in Inflammatory Processes: Friend or Foe

During an inflammatory process, shift in the cellular metabolism associated with an increase in extracellular acidification are well-known features. This pH drop in the inflamed tissue is largely attributed to the presence of lactate by an increase in glycolysis. In recent years, evidence has accumulated describing the role of lactate in inflammatory processes; however, there are differences as to whether lactate can currently be considered a pro- or anti-inflammatory mediator. Herein, we review these recent advances on the pleiotropic effects of lactate on the inflammatory process. Taken together, the evidence suggests that lactate could exert differential effects depending on the metabolic status, cell type in which the effects of lactate are studied, and the pathological process analyzed. Additionally, various targets, including post-translational modifications, G-protein coupled receptor and transcription factor activation such as NF-κB and HIF-1, allow lactate to modulate signaling pathways that control the expression of cytokines, chemokines, adhesion molecules, and several enzymes associated with immune response and metabolism. Altogether, this would explain its varied effects on inflammatory processes beyond its well-known role as a waste product of metabolism.

TNF-ɑ Induces Methylglyoxal Accumulation in Lumbar Herniated Disc of Patients With Radicular Pain

Lumbar disc herniation (LDH) with radicular pain is a common and complicated musculoskeletal disorder. Our previous study showed that LDH-induced methylglyoxal (MG) accumulation contributed to radicular pain. The underlying mechanisms through which MG accumulates are poorly understood. In the present study, we found that both MG and tumor necrosis factor-alpha (TNF-ɑ) levels in the herniated disc of patients with radicular pain were significantly increased, and the activity of Glyoxalase 1 (GLO1), the rate-limiting enzyme that metabolizes MG, was decreased. In rats, the LDH model was mimicked by implantation of autologous nucleus pulposus (NP) to the left lumbar five spinal nerve root. The mechanical allodynia was observed in LDH rats. Besides, MG and TNF-ɑ levels were increased, and GLO1 activity was significantly decreased in the implanted NP. In cultured rat NP cells, stimulation with the inflammatory mediator TNF-ɑ reduced GLO1 activity and expression. These results suggested that TNF-ɑ-induced GLO1 activity decrease contributed to MG accumulation in the herniated disc of patients with radicular pain.

Spironolactone Attenuates Methylglyoxal-induced Cellular Dysfunction in MC3T3-E1 Osteoblastic Cells

BACKGROUND

Methylglyoxal (MG) is associated with the pathogenesis of age- and diabetes-related complications. Spironolactone is a competitive antagonist of aldosterone that is widely employed in the treatment of hypertension and heart failure. This study examined the effects of spironolactone on MG-induced cellular dysfunction in MC3T3-E1 osteoblastic cells.

METHODS

MC3T3-E1 cells were treated with spironolactone in the presence of MG. The mitochondrial function, bone formation activity, oxidative damage, inflammatory cytokines, glyoxalase I activity, and glutathione (GSH) were measured.

RESULTS

Pretreatment of MC3T3-E1 osteoblastic cells with spironolactone prevented MG-induced cell death, and improved bone formation activity. Spironolactone reduced MG-induced endoplasmic reticulum stress, production of intracellular reactive oxygen species, mitochondrial superoxides, cardiolipin peroxidation, and inflammatory cytokines. Pretreatment with spironolactone also increased the level of reduced GSH and the activity of glyoxalase I. MG induced mitochondrial dysfunction, but markers of mitochondrial biogenesis such as mitochondrial membrane potential, adenosine triphosphate, proliferator-activated receptor gamma coactivator 1α, and nitric oxide were significantly improved by treatment of spironolactone.

CONCLUSION

Spironolactone could prevent MG-induced cytotoxicity in MC3T3-E1 osteoblastic cells by reduction of oxidative stress. The oxidative stress reduction was explained by spironolactone's inhibition of advanced glycation end-product formation, restoring mitochondrial dysfunction, and anti-inflammatory effect.

Levels of Receptor for Advanced Glycation End Products and Glyoxalase-1 in the Total Circulating Extracellular Vesicles from Mild Cognitive Impairment and Different Stages of Alzheimer's Disease Patients

BACKGROUND

Growing evidence supports that receptor for advanced glycation end products (RAGE) and glyoxalase-1 (GLO-1) are implicated in the pathophysiology of Alzheimer's disease (AD). Extracellular vesicles (EVs) are nanovesicles secreted by almost all cell types, contribute to cellular communication, and are implicated in AD pathology. Recently, EVs are considered as promising tools to identify reliable biomarkers in AD.

OBJECTIVE

The aim of our study was to determine the levels of RAGE and GLO-1 in circulating EVs from mild cognitive impairment (MCI) and AD patients and to analyze their correlation with the clinical Mini-Mental State Examination and Montreal Cognitive Assessment scores. We have studied the possibility that neuronal cells could release and transfer GLO-1 through EVs.

METHODS

RAGE and GLO-1 levels were measured in circulating EVs, respectively, by Luminex assay and western blot. Released-EVs from SK-N-SH neuronal cells were isolated and GLO-1 levels were determined by western blot.

RESULTS

Our data showed higher levels of RAGE in EVs from late AD patients while GLO-1 levels in EVs from early AD were lower as compared to control and MCI patients. Interestingly, levels of RAGE and GLO-1 in EVs were correlated with the cognitive scores regardless of age. For the first time, we demonstrated that GLO-1 was released from neuronal cells through EVs.

CONCLUSION

Although more samples will be needed, our preliminary results support the use of peripheral EVs cargo as new tools for the discovery of peripheral AD biomarkers.

The Glyoxalase System in Age-Related Diseases: Nutritional Intervention as Anti-Ageing Strategy

The glyoxalase system is critical for the detoxification of advanced glycation end-products (AGEs). AGEs are toxic compounds resulting from the non-enzymatic modification of biomolecules by sugars or their metabolites through a process called glycation. AGEs have adverse effects on many tissues, playing a pathogenic role in the progression of molecular and cellular aging. Due to the age-related decline in different anti-AGE mechanisms, including detoxifying mechanisms and proteolytic capacities, glycated biomolecules are accumulated during normal aging in our body in a tissue-dependent manner. Viewed in this way, anti-AGE detoxifying systems are proposed as therapeutic targets to fight pathological dysfunction associated with AGE accumulation and cytotoxicity. Here, we summarize the current state of knowledge related to the protective mechanisms against glycative stress, with a special emphasis on the glyoxalase system as the primary mechanism for detoxifying the reactive intermediates of glycation. This review focuses on glyoxalase 1 (GLO1), the first enzyme of the glyoxalase system, and the rate-limiting enzyme of this catalytic process. Although GLO1 is ubiquitously expressed, protein levels and activities are regulated in a tissue-dependent manner. We provide a comparative analysis of GLO1 protein in different tissues. Our findings indicate a role for the glyoxalase system in homeostasis in the eye retina, a highly oxygenated tissue with rapid protein turnover. We also describe modulation of the glyoxalase system as a therapeutic target to delay the development of age-related diseases and summarize the literature that describes the current knowledge about nutritional compounds with properties to modulate the glyoxalase system.

Carbonylation of skin collagen induced by reaction with methylglyoxal

Our previous studies have shown that glycerin, which is present at high concentrations in moisturizers and skin lotions, gradually oxidizes to produce methylglyoxal (MGO). In this study, we observed that MGO-treated porcine dermis type-I collagen was carbonylated in an MGO concentration- and time-dependent manner. Furthermore, we examined the structure of advanced glycation end products (AGEs) induced by MGO reacting with type-I collagen. Our findings demonstrate that the α chains of collagen reacted with MGO and easily transformed into a modified protein containing a methylglyoxal-derived hydroimidazolone (MG-H1) moiety in a concentration- and time-dependent manner. Moreover, porcine skin proteins underwent carbonylation when the skin section was treated with MGO for four weeks. Analysis of the structure of AGEs on the carbonylated proteins extracted from MGO-treated skin sections revealed that skin collagen had been converted to MG-H1-modified protein. These novel findings suggest that continuous application of MGO to the skin leads to carbonylation of proteins, which may cause prompt accumulation of MG-H1-modified dermis collagen, thereby resulting in morphological and functional changes of collagen in the skin.

Methylglyoxal influences development of Caenorhabditis elegans via lin-41-dependent pathway

Methylglyoxal is a highly reactive dicarbonyl compound. It can be obtained either endogenously through biological enzymatic/non-enzymatic pathways or exogenously via the uptake of certain foods and beverages, such as Manuka honey. Studies about its biological properties are quite controversial, though the majority reported a positive association between methylglyoxal and certain pathologies. In this report, we tested if methylglyoxal can alter the development of animals using Caenorhabditis elegans as the in vivo model. Treatment of methylglyoxal at 0.1 and 1 mmol/L for 2 days significantly inhibited the development of Caenorhabditis elegans, particularly targeting the transition from L3 stage. Pharyngeal pumping rate, the food intake marker was also significantly reduced by methylglyoxal at both 0.1 and 1 mmol/L. Additionally, treatment of 0.1 mmol/L methylglyoxal increased, while 1 mmol/L methylglyoxal decreased the nematodes' average moving speed. The effect of methylglyoxal on development was in part due to the modulation of lin-41, which encodes a homolog of human TRIM71. The mutation of lin-41 could alleviate or abolish the effects of methylglyoxal on growth rate, body size, pumping rate and locomotive activity. In summary, these results suggested that methylglyoxal influenced the development of Caenorhabditis elegans, which is in part via the lin-41-dependent pathway.

Carnosic acid depends on glutathione to promote mitochondrial protection in methylglyoxal-exposed SH-SY5Y cells

Methylglyoxal (MG) is an endogenously produced toxicant that induces mitochondrial dysfunction leading to impaired redox biology homeostasis, bioenergetics collapse, and cell death in mammalian cells. However, MG toxicity is particularly relevant to neurons and glia given their chemical and metabolic characteristics. Here, we have investigated whether a pretreatment with carnosic acid (CA) would be able to promote mitochondrial protection in human neuroblastoma SH-SY5Y cells exposed to MG. We found that a pretreatment with CA at 1 μM for 12 h prevented the MG-induced lipid peroxidation and protein carbonylation and nitration in the membranes of mitochondria obtained from the SH-SY5Y cells. CA also prevented the MG-elicited Complexes I and V dysfunction, adenosine triphosphate (ATP) levels decline, and loss of mitochondrial membrane potential (MMP). Moreover, CA also reduced the mitochondrial production of the radical anion superoxide (O₂^-•) in the MG-challenged cells. We found that CA upregulated the synthesis of glutathione (GSH) by increasing the activity of the γ-glutamylcysteine ligase (γ-GCL). Inhibition of the GSH synthesis by buthionine sulfoximine (BSO) abolished the CA-induced mitochondrial protection. Besides, inhibition of the phosphoinositide 3-kinase (PI3K)/Akt signaling pathway, as well as silencing of the transcription factor nuclear factor erythroid 2-related factor 2 (Nrf2), suppressed the CA-stimulated protection and the synthesis of GSH. Thus, CA promoted mitochondrial protection by a PI3K/Akt/Nrf2/γ-GCL/GSH axis in MG-treated SH-SY5Y cells.

Short-Term Alterations in Behavior and Astroglial Function After Intracerebroventricular Infusion of Methylglyoxal in Rats

Methylglyoxal (MG) is a by-product of glycolysis. In pathological conditions, particularly diabetes mellitus, this molecule is unbalanced, causing widespread protein glycation. In addition to protein glycation, other effects resulting from high levels of MG in the central nervous system may involve the direct modulation of GABAergic and glutamatergic neurotransmission, with evidence suggesting that the effects of MG may be related to behavioral changes and glial dysfunction. In order to evaluate the direct influence of MG on behavioral and biochemical parameters, we used a high intracerebroventricular final concentration (3 μM/μL) to assess acute effects on memory and locomotor behavior in rats, as well as the underlying alterations in glutamatergic and astroglial parameters. MG induced, 12 h after injection, a decrease in locomotor activity in the Open field and anxiolytic effects in rats submitted to elevated plus-maze. Subsequently, 36 h after surgery, MG injection also induced cognitive impairment in both short and long-term memory, as evaluated by novel object recognition task, and in short-term spatial memory, as evaluated by the Y-maze test. In addition, hippocampal glutamate uptake decreased and glutamine synthetase activity and glutathione levels diminished during seventy-two hours after infusion of MG. Interestingly, the astrocytic protein, S100B, was increased in the cerebrospinal fluid, accompanied by decreased hippocampal S100B mRNA expression, without any change in protein content. Taken together, these results may improve our understanding of how this product of glucose metabolism can induce the brain dysfunction observed in diabetic patients, as well as in other neurodegenerative conditions, and further defines the role of astrocytes in disease and therapeutics.

Environmental exposures and the etiopathogenesis of Alzheimer's disease: The potential role of BACE1 as a critical neurotoxic target

Alzheimer's disease (AD) is a major public health crisis due to devastating cognitive symptoms, a lack of curative treatments, and increasing prevalence. Most cases are sporadic (>95% of cases) after the age of 65 years, implicating an important role of environmental factors in disease pathogenesis. Environmental neurotoxicants have been implicated in neurodegenerative disorders including Parkinson's Disease and AD. Animal models of AD and in vitro studies have shed light on potential neuropathological mechanisms, yet the biochemical and molecular underpinnings of AD-relevant environmental neurotoxicity remain poorly understood. Beta-site amyloid precursor protein cleaving enzyme 1 (BACE1) is a potentially critical pathogenic target of environmentally induced neurotoxicity. BACE1 clearly has a critical role in AD pathophysiology: It is required for amyloid beta production and expression and activity of BACE1 are increased in the AD brain. Though the literature on BACE1 in response to environmental insults is limited, current studies, along with extensive AD neurobiology literature suggest that BACE1 deserves attention as an important neurotoxic target. Here, we critically review research on environmental neurotoxicants such as metals, pesticides, herbicides, fungicides, polyfluoroalkyl substances, heterocyclic aromatic amines, advanced glycation end products, and acrolein that modulate BACE1 and potential mechanisms of action. Though more research is needed to clearly understand whether BACE1 is a critical mediator of AD-relevant neurotoxicity, available reports provide convincing evidence that BACE1 is altered by environmental risk factors associated with AD pathology, implying that BACE1 inhibition and its use as a biomarker should be considered in AD management and research.

The Isothiocyanate Sulforaphane Depends on the Nrf2/γ-GCL/GSH Axis to Prevent Mitochondrial Dysfunction in Cells Exposed to Methylglyoxal

Methylglyoxal (MG) is a reactive dicarbonyl presenting both endogenous (e.g. glycolysis) and exogenous (e.g. food cooking) sources. MG induces neurotoxicity, at least in part, by affecting mitochondrial function, including a decline in the oxidative phosphorylation (OXPHOS) system activity, bioenergetics failure, and redox disturbances. Sulforaphane (SFN) is an isothiocyanate found mainly in cruciferous vegetables and exerts antioxidant and anti-inflammatory effects in mammalian cells. SFN also decreases mitochondrial vulnerability to several chemical stressors. SFN is a potent activator of the transcription factor nuclear factor erythroid 2-related factor 2 (Nrf2), which is a master regulator of the mammalian redox biology. Here, we have investigated whether and how SFN would be able to prevent the MG-induced mitochondrial collapse in the human neuroblastoma SH-SY5Y cells. The cells were exposed to SFN at 5 µM for 24 h prior to the administration of MG at 500 µM for additional 24 h. We found that SFN prevented the MG-induced OXPHOS dysfunction and mitochondrial redox impairment. SFN stimulated the activity of the enzyme γ-glutamylcysteine ligase (γ-GCL), leading to increased synthesis of glutathione (GSH). Inhibition of γ-GCL with buthionine sulfoximine (BSO) or silencing of Nrf2 using small interfering RNA (siRNA) against this transcription factor reduced the levels of GSH and abolished the mitochondrial protection promoted by SFN in the MG-treated cells. Thus, SFN protected mitochondria of the MG-challenged cells by a mechanism involving the Nrf2/γ-GCL/GSH axis.

Spatial Transcriptomics Reveals Genes Associated with Dysregulated Mitochondrial Functions and Stress Signaling in Alzheimer Disease

Alzheimer disease (AD) is a devastating neurological disease associated with progressive loss of mental skills and cognitive and physical functions whose etiology is not completely understood. Here, our goal was to simultaneously uncover novel and known molecular targets in the structured layers of the hippocampus and olfactory bulbs that may contribute to early hippocampal synaptic deficits and olfactory dysfunction in AD mice. Spatially resolved transcriptomics was used to identify high-confidence genes that were differentially regulated in AD mice relative to controls. A diverse set of genes that modulate stress responses and transcription were predominant in both hippocampi and olfactory bulbs. Notably, we identify Bok, implicated in mitochondrial physiology and cell death, as a spatially downregulated gene in the hippocampus of mouse and human AD brains. In summary, we provide a rich resource of spatially differentially expressed genes, which may contribute to understanding AD pathology.

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Spatial transcriptomics identifies differentially expressed genes with spatial patterns

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Early application of spatial transcriptomics to olfactory bulbs from AD models

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Bok gene is spatially differentially expressed in AD mouse and patient brains

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Paip1 and Homer1 genes are regulated in a PolB-dependent manner

Cellular Signaling and Anti-Apoptotic Effects of Prolactin-Releasing Peptide and Its Analog on SH-SY5Y Cells

Prolactin-releasing peptide (PrRP), a natural ligand for the GPR10 receptor, is a neuropeptide with anorexigenic and antidiabetic properties. Due to its role in the regulation of food intake, PrRP is a potential drug for obesity treatment and associated type 2 diabetes mellitus (T2DM). Recently, the neuroprotective effects of lipidized PrRP analogs have been proven. In this study, we focused on the molecular mechanisms of action of natural PrRP31 and its lipidized analog palm¹¹-PrRP31 in the human neuroblastoma cell line SH-SY5Y to describe their cellular signaling and possible anti-apoptotic properties. PrRP31 significantly upregulated the phosphoinositide-3 kinase-protein kinase B/Akt (PI3K-PKB/Akt) and extracellular signal-regulated kinase/cAMP response element-binding protein (ERK-CREB) signaling pathways that promote metabolic cell survival and growth. In addition, we proved via protein kinase inhibitors that activation of signaling pathways is mediated specifically by PrRP31 and its palmitoylated analog. Furthermore, the potential neuroprotective properties were studied through activation of anti-apoptotic pathways of PrRP31 and palm¹¹-PrRP31 using the SH-SY5Y cell line and rat primary neuronal culture stressed with toxic methylglyoxal (MG). The results indicate increased viability of the cells treated with PrRP and palm¹¹-PrRP31 and a reduced degree of apoptosis induced by MG, suggesting their potential use in the treatment of neurological disorders.