Advanced glycation endproduct precursor alters intracellular amyloid-beta/A beta PP carboxy-terminal fragment aggregation and cytotoxicity

Integrating High-Resolution Mass Spectral Data, Bioassays and Computational Models to Annotate Bioactives in Botanical Extracts: Case Study Analysis of C. asiatica Extract Associates Dicaffeoylquinic Acids with Protection against Amyloid-β Toxicity

Rapid screening of botanical extracts for the discovery of bioactive natural products was performed using a fractionation approach in conjunction with flow-injection high-resolution mass spectrometry for obtaining chemical fingerprints of each fraction, enabling the correlation of the relative abundance of molecular features (representing individual phytochemicals) with the read-outs of bioassays. We applied this strategy for discovering and identifying constituents of Centella asiatica (C. asiatica) that protect against Aβ cytotoxicity in vitro. C. asiatica has been associated with improving mental health and cognitive function, with potential use in Alzheimer's disease. Human neuroblastoma MC65 cells were exposed to subfractions of an aqueous extract of C. asiatica to evaluate the protective benefit derived from these subfractions against amyloid β-cytotoxicity. The % viability score of the cells exposed to each subfraction was used in conjunction with the intensity of the molecular features in two computational models, namely Elastic Net and selectivity ratio, to determine the relationship of the peak intensity of molecular features with % viability. Finally, the correlation of mass spectral features with MC65 protection and their abundance in different sub-fractions were visualized using GNPS molecular networking. Both computational methods unequivocally identified dicaffeoylquinic acids as providing strong protection against Aβ-toxicity in MC65 cells, in agreement with the protective effects observed for these compounds in previous preclinical model studies.

A strategic tool to improve the study of molecular determinants of Alzheimer's disease: The role of glyceraldehyde

Alzheimer's disease (AD) is the most prevalent form of dementia and is characterized by progressive neurodegeneration leading to severe cognitive, memory, and behavioral impairments. The onset of AD involves a complex interplay among various factors, including age, genetics, chronic inflammation, and impaired energy metabolism. Despite significant efforts, there are currently no effective therapies capable of modifying the course of AD, likely owing to an excessive focus on the amyloid hypothesis and a limited consideration of other intracellular pathways. In the present review, we emphasize the emerging concept of AD as a metabolic disease, where alterations in energy metabolism play a critical role in its development and progression. Notably, glucose metabolism impairment is associated with mitochondrial dysfunction, oxidative stress, Ca2+ dyshomeostasis, and protein misfolding, forming interconnected processes that perpetuate a detrimental self-feeding loop sustaining AD progression. Advanced glycation end products (AGEs), neurotoxic compounds that accumulate in AD, are considered an important consequence of glucose metabolism disruption, and glyceraldehyde (GA), a glycolytic intermediate, is a key contributor to AGEs formation in both neurons and astrocytes. Exploring the impact of GA-induced glucose metabolism impairment opens up exciting possibilities for creating an easy-to-handle in vitro model that recapitulates the early stage of the disease. This model holds great potential for advancing the development of novel therapeutics targeting various intracellular pathways implicated in AD pathogenesis. In conclusion, looking beyond the conventional amyloid hypothesis could lead researchers to discover promising targets for intervention, offering the possibility of addressing the existing medical gaps in AD treatment.

Efficacy of Glucose Metabolism-Related Indexes on the Risk and Severity of Alzheimer’s Disease: A Meta-Analysis

Background: Considering the strong correlation made between Alzheimer’s disease (AD) and the pathology of glucose metabolism disorder, we sought to analyze the effects of fasting blood glucose (FBG) level, fasting plasma insulin (FINS) level, and insulin resistance index (HOMA-IR) on the risk and severity of AD. Objective: Reveal the pathological relationship between AD and insulin resistance. Methods: We searched 5 databases from inception through April 4, 2022. Meta-regression was conducted to identify if there were significant differences between groups. Shapiro-Wilk test and the Q-Q diagram were applied to evaluate the normality of variables. A multiple logistic regression model was employed to explore the association between FBG, FINS, HOMA-IR, and Mini-Mental State Examination scale score (MMSE). Results: 47 qualified articles including 2,981 patients were enrolled in our study. FBG (p < 0.001), FINS (p < 0.001), and HOMA-IR (p < 0.001) were higher in AD patients than in controls. HOMA-IR was negatively correlated with MMSE (p = 0.001) and positively related to the sex ratio (male versus female) (p < 0.05). HOMA-IR obeyed lognormal distribution (p > 0.05), and the 95% bilateral boundary values were 0.73 and 10.67. FBG (p = 0.479) was positively correlated to MMSE, while FINS (p = 0.1657) was negatively correlated with MMSE. Conclusion: The increase in the levels of FBG, FINS, and HOMA-IR served as precise indicators of the risk of AD. HOMA-IR was found to be correlated to the increasing severity of AD, especially in male AD patients.

A systematic review and meta-analysis of cognitive and behavioral tests in rodents treated with different doses of D-ribose

BACKGROUND

D-ribose is an aldehyde sugar and a necessary component of all living cells. Numerous reports have focused on D-ribose intervention in animal models to assess the negative effects of D-ribose on cognition. However, the results across these studies are inconsistent and the doses and actual effects of D-ribose on cognition remain unclear. This systematic review aimed to evaluate the effect of D-ribose on cognition in rodents.

METHODS

The articles from PubMed, Embase, Sciverse Scopus, Web of Science, the Chinese National Knowledge Infrastructure, SinoMed, Wanfang, and Cqvip databases were screened. The results from the abstract on cognitive-related behavioral tests and biochemical markers from the included articles were extracted and the reporting quality was assessed.

RESULTS

A total of eight trials involving 289 rodents met the eligibility criteria, and both low- and high-dose groups were included. Meta-analyses of these studies showed that D-ribose could cause a significant decrease in the number of platform crossings (standardized mean difference [SMD]: -0.80; 95% CI: -1.14, -0.46; p < 0.00001), percentage of distance traversed in the target quadrant (SMD: -1.20; 95% CI: -1.47, -0.92; p < 0.00001), percentage of time spent in the target quadrant (SMD: -0.93; 95% CI: -1.18, -0.68; p < 0.00001), and prolonged escape latency (SMD: 0.41; 95% CI: 0.16, 0.65; p = 0.001) in the Morris water maze test. Moreover, D-ribose intervention increased the levels of advanced glycation end products (AGEs) in the brain (SMD: 0.49; 95% CI: 0.34, 0.63; p < 0.00001) and blood (SMD: 0.50; 95% CI: 0.08, 0.92; p = 0.02). Subsequently, subgroup analysis for the dose of D-ribose intervention revealed that high doses injured cognitive function more significantly than low D-ribose doses.

CONCLUSION

D-ribose treatment caused cognitive impairment, and cognition deteriorated with increasing dose. Furthermore, the increase in AGEs in the blood and brain confirmed that D-ribose may be involved in cognitive impairment through non-enzymatic glycosylation resulting in the generation of AGEs. These findings provide a new research idea for unveiling basic mechanisms and prospective therapeutic targets for the prevention and treatment of patients with cognitive impairment.

Alzheimer's Disease as Type 3 Diabetes: Common Pathophysiological Mechanisms between Alzheimer's Disease and Type 2 Diabetes

Globally, the incidence of type 2 diabetes mellitus (T2DM) and Alzheimer's disease (AD) epidemics is increasing rapidly and has huge financial and emotional costs. The purpose of the current review article is to discuss the shared pathophysiological connections between AD and T2DM. Research findings are presented to underline the vital role that insulin plays in the brain's neurotransmitters, homeostasis of energy, as well as memory capacity. The findings of this review indicate the existence of a mechanistic interplay between AD pathogenesis with T2DM and, especially, disrupted insulin signaling. AD and T2DM are interlinked with insulin resistance, neuroinflammation, oxidative stress, advanced glycosylation end products (AGEs), mitochondrial dysfunction and metabolic syndrome. Beta-amyloid, tau protein and amylin can accumulate in T2DM and AD brains. Given that the T2DM patients are not routinely evaluated in terms of their cognitive status, they are rarely treated for cognitive impairment. Similarly, AD patients are not routinely evaluated for high levels of insulin or for T2DM. Studies suggesting AD as a metabolic disease caused by insulin resistance in the brain also offer strong support for the hypothesis that AD is a type 3 diabetes.

Alzheimer's Disease and Protein Kinases

Alzheimer's disease (AD) is the most common neurodegenerative disorder and accounts for more than 60-80% of all cases of dementia. Loss of pyramidal neurons, extracellular amyloid beta (Abeta) accumulated senile plaques, and neurofibrillary tangles that contain hyperphosphorylated tau constitute the main pathological alterations in AD.Synaptic dysfunction and extrasynaptic N-methyl-D-aspartate receptor (NMDAR) hyperactivation contributes to excitotoxicity in patients with AD. Amyloid precursor protein (APP) and Abeta promoted neurodegeneration develop through the activation of protein kinase signaling cascade in AD. Furthermore, ultimate neuronal death in AD is under control of protein kinases-related signaling pathways. In this chapter, critical check-points within the cross-talk between neuron and protein kinases have been defined regarding the initiation and progression of AD. In this context, amyloid cascade hypothesis, neuroinflammation, oxidative stress, granulovacuolar degeneration, loss of Wnt signaling, Abeta-related synaptic alterations, prolonged calcium ions overload and NMDAR-related synaptotoxicity, damage signals hypothesis and type-3 diabetes are discussed briefly.In addition to clinical perspective of AD pathology, recommendations that might be effective in the treatment of AD patients have been reviewed.

Combatting Nitrosative Stress and Inflammation with Novel Substituted Triazinoindole Inhibitors of Aldose Reductase in PC12 Cells Exposed to 6-Hydroxydopamine Plus High Glucose

Cellular redox dysregulation produced by aldose reductase (AR) in the presence of high blood sugar is a mechanism involved in neurodegeneration commonly observed in diabetes mellitus (DM) and Parkinson's disease (PD); therefore, AR is a key target for treatment of both diseases. The substituted triazinoindole derivatives 2-(3-thioxo-2H-[1,2,4]triazino[5,6-b]indol-5(3H)-yl) acetic acid (cemtirestat or CMTI) and 2-(3-oxo-2H-[1,2,4]triazino[5,6-b]indol-5(3H)-yl) acetic acid (COTI) are well-known AR inhibitors (ARIs). The neuroprotective properties of CMTI, COTI, the clinically used epalrestat (EPA), and the pyridoindole antioxidants stobadine and SMe1EC2 were all tested in the neurotoxic models produced by hyperglycemic glucotoxicity (HG, 75 mM D-glucose, 72 h), 6-hydroxydopamine (6-OHDA), and HG+6-OHDA models in PC12 cells. Cell viability decreased in all toxic models, increased by 1-5 μM EPA, and decreased by COTI at ≥ 2.5 μM. In the HG model alone, where compounds were present in the medium for 24 h after a continuous 24-h exposure to HG, cell viability was improved by 100 nM-5 μM EPA, 1-10 μM ARIs, and the antioxidants studied, but decreased by EPA at ≥ 10 μM. In the 6-OHDA model alone, where cells were treated with compounds for 24 h and further exposed to 100 μM 6-OHDA (8 h), only the antioxidants protected cell viability. In the HG+6-OHDA model, where cells were treated with all compounds (1 nM to 50 μM) for 48 h and exposed to 75 mM glucose for 24 h followed by incubation with 6-OHDA for 8 h, cell viability was protected by 100 nM-10 μM ARIs and 100-500 nM EPA, but not by antioxidants. All ARIs inhibited the HG+6-OHDA-induced increase in iNOS, IL-1β, TNF-α, 3-NT, and total oxidant status at 1-50 μM, while increased SOD, CAT, GPx, and total antioxidant status at 1-10 μM. EPA and CMTI also reduced the HG+6-OHDA-induced increase in the cellular levels of nuclear factor kB (NF-KB). The neuroprotective potential of the novel ARIs and the pyridoindole antioxidants studied constitutes a promising tool for the development of therapeutic strategies against DM-induced and PD-related neurodegeneration.

Glycation in Huntington's Disease: A Possible Modifier and Target for Intervention

Glycation is the non-enzymatic reaction between reactive dicarbonyls and amino groups, and gives rise to a variety of different reaction products known as advanced glycation end products (AGEs). Accumulation of AGEs on proteins is inevitable, and is associated with the aging process. Importantly, glycation is highly relevant in diabetic patients that experience periods of hyperglycemia. AGEs also play an important role in neurodegenerative diseases including Alzheimer’s (AD) and Parkinson’s disease (PD). Huntington’s disease (HD) is a hereditary neurodegenerative disease caused by an expansion of a CAG repeat in the huntingtin gene. The resulting expanded polyglutamine stretch in the huntingtin (HTT) protein induces its misfolding and aggregation, leading to neuronal dysfunction and death. HD patients exhibit chorea and psychiatric disturbances, along with abnormalities in glucose and energy homeostasis. Interestingly, an increased prevalence of diabetes mellitus has been reported in HD and in other CAG triplet repeat disorders. However, the mechanisms underlying the connection between glycation and HD progression remain unclear. In this review, we explore the possible connection between glycation and proteostasis imbalances in HD, and posit that it may contribute to disease progression, possibly by accelerating protein aggregation and deposition. Finally, we review therapeutic interventions that might be able to alleviate the negative impact of glycation in HD.

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.

Therapeutic Potential of Carnosine and Its Derivatives in the Treatment of Human Diseases

Despite significant progress in the pathogenesis, diagnosis, treatment, and prevention of cancer and neurodegenerative diseases, their occurrence and mortality are still high around the world. The resistance of cancer cells to the drugs remains a significant problem in oncology today, while in the case of neuro-degenerative diseases, therapies reversing the process are still yet to be found. Furthermore, it is important to seek new chemotherapeutics reversing side effects of currently used drugs or helping them perform their function to inhibit progression of the disease. Carnosine, a dipeptide constisting of β-alanine and l-histidine, has a variety of functions to mention: antioxidant, antiglycation, and reducing the toxicity of metal ions. It has therefore been proposed to act as a therapeutic agent for many pathological states. The aim of this paper was to find if carnosine and its derivatives can be helpful in treating various diseases. Literature search presented in this review includes review and original papers found in SciFinder, PubMed, and Google Scholar. Searches were based on substantial keywords concerning therapeutic usage of carnosine and its derivatives in several diseases including neurodegenerative disorders and cancer. In this paper, we review articles and find that carnosine and its derivatives are potential therapeutic agents in many diseases including cancer, neurodegenerative diseases, diabetes, and schizophrenia. Carnosine and its derivatives can be used in treating neurodegenerative diseases, cancer, diabetes, or schizophrenia, although their usage is limited. Therefore, there's an urge to synthesize and analyze new substances, overcoming the limitation of carnosine itself.

Advanced glycation end products (AGEs), protein aggregation and their cross talk: new insight in tumorigenesis

Protein glycation and protein aggregation are two distinct phenomena being observed in cancer cells as factors promoting cancer cell viability. Protein aggregation is an abnormal interaction between proteins caused as a result of structural changes in them after any mutation or environmental assault. Protein aggregation is usually associated with neurodegenerative diseases like Alzheimer's and Parkinson's, but of late, research findings have shown its association with the development of different cancers like lung, breast and ovarian cancer. On the contrary, protein glycation is a cascade of irreversible nonenzymatic reaction of reducing sugar with the amino group of the protein resulting in the modification of protein structure and formation of advanced glycation end products (AGEs). These AGEs are reported to obstruct the normal function of proteins. Lately, it has been reported that protein aggregation occurs as a result of AGEs. This aggregation of protein promotes the transformation of healthy cells to neoplasia leading to tumorigenesis. In this review, we underline the current knowledge of protein aggregation and glycation along with the cross talk between the two, which may eventually lead to the development of cancer.

Neural Glyoxalase Pathway Enhancement by Morin Derivatives in an Alzheimer's Disease Model

The glyoxalase pathway (GP) is an antioxidant defense system that detoxifies metabolic byproduct methylglyoxal (MG). Through sequential reactions, reduced glutathione (GSH), glyoxalase I (glo-1), and glyoxalase II (glo-2) convert MG into d-lactate. Spontaneous reactions involving MG alter the structure and function of cellular macromolecules through the formation of inflammatory advanced glycation endproducts (AGEs). Accumulation of MG and AGEs in neural cells contributes to oxidative stress (OS), a state of elevated inflammation commonly found in neurodegenerative diseases including Alzheimer's disease (AD). Morin is a common plant-produced flavonoid polyphenol that exhibits the ability to enhance the GP-mediated detoxification of MG. We hypothesize that structural modifications to morin will improve its inherent GP enhancing ability. Here we synthesized a morin derivative, dibromo-morin (DBM), formulated a morin encapsulated nanoparticle (MNP), and examined their efficacy in enhancing neural GP activity. Cultured mouse primary cerebellar neurons and Caenorhabditis elegans were induced to a state of OS with MG and treated with morin, DBM, and MNP. Results indicated the morin derivatives were more effective compared to the parent compound in neural GP enhancement and preventing MG-mediated OS in an AD model.

D-ribose and pathogenesis of Alzheimer's disease

It is estimated that the global prevalence of dementia will rise as high as 24 million and predicted to be double in every 20 years which is attributed to the fact that the ageing population is increasing and so more individuals are at risk of developing neurodegenerative diseases like Alzheimer's. Many scientists favored glycation of proteins such as tau, amyloid beta (Aβ) etc. as one of the important risk factor in Alzheimer's disease (AD). Since, D-ribose shows highest glycation ability among other sugars hence, produces advanced glycation end products (AGEs) rapidly. However, there are several other mechanisms suggested by researchers through which D-ribose may cause cognitive impairments. There is a concern related to diabetic patients since they also suffer from D-ribose metabolism, may be more prone to AD risk. Thus, it is imperative that the pathogenesis and the pathways involved in AD progression are explored in the light of ribosylation and AGEs formation for identifying suitable diagnostics marker for early diagnosis or finding promising therapeutic outcomes.

Sex-specific hippocampal metabolic signatures at the onset of systemic inflammation with lipopolysaccharide in the APPswe/PS1dE9 mouse model of Alzheimer's disease

Systemic inflammation enhances the risk and progression of Alzheimer's disease (AD). Lipopolysaccharide (LPS), a potent pro-inflammatory endotoxin produced by the gut, is found in excess levels in AD where it associates with neurological hallmarks of pathology. Sex differences in susceptibility to inflammation and AD progression have been reported, but how this impacts on LPS responses remains under investigated. We previously reported in an APP/PS1 model of AD that systemic LPS administration rapidly altered hippocampal metabolism in males. Here, we used untargeted metabolomics to comprehensively identify hippocampal metabolic processes occurring at onset of systemic inflammation with LPS (100 µg/kg, i.v.) in APP/PS1 mice, at an early pathological stage, and investigated the sexual dimorphism in this response. Four hours after LPS administration, pathways regulating energy metabolism, immune and oxidative stress responses were simultaneously recruited in the hippocampi of 4.5-month-old mice with a more protective response in females despite their pro-inflammatory and pro-oxidant metabolic signature in the absence of immune stimulation. LPS induced comparable behavioural sickness responses in male and female wild-type and APP/PS1 mice and comparable activation of both the serotonin and nicotinamide pathways of tryptophan metabolism in their hippocampi. Elevations in N-methyl-2-pyridone-5-carboxamide, a major toxic metabolite of nicotinamide, correlated with behavioural sickness regardless of sex, as well as with the LPS-induced hypothermia seen in males. Males also exhibited a pro-inflammatory-like downregulation of pyruvate metabolism, exacerbated in APP/PS1 males, and methionine metabolism whereas females showed a greater cytokine response and anti-inflammatory-like downregulation of hippocampal methylglyoxal and methionine metabolism. Metabolic changes were not associated with morphological markers of immune cell activation suggesting that they constitute an early event in the development of LPS-induced neuroinflammation and AD exacerbation. These data suggest that the female hippocampus is more tolerant to acute systemic inflammation.

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.

The Role of Advanced Glycation End Products in Aging and Metabolic Diseases: Bridging Association and Causality

Accumulation of advanced glycation end products (AGEs) on nucleotides, lipids, and peptides/proteins are an inevitable component of the aging process in all eukaryotic organisms, including humans. To date, a substantial body of evidence shows that AGEs and their functionally compromised adducts are linked to and perhaps responsible for changes seen during aging and for the development of many age-related morbidities. However, much remains to be learned about the biology of AGE formation, causal nature of these associations, and whether new interventions might be developed that will prevent or reduce the negative impact of AGEs-related damage. To facilitate achieving these latter ends, we show how invertebrate models, notably Drosophila melanogaster and Caenorhabditis elegans, can be used to explore AGE-related pathways in depth and to identify and assess drugs that will mitigate against the detrimental effects of AGE-adduct development.

α‑lipoic acid can greatly alleviate the toxic effect of AGES on SH‑SY5Y cells

The aim of the study was to explore the influence of α‑lipoic acid (α‑LA) on the cytotoxicity of advanced glycation end‑products (AGEs) against SH‑SY5Y cells. AGE‑bovine serum albumin (BSA) was incubated in vitro using SH‑SY5Y cells as a target model, and the control group was set. Cells were exposed to AGE‑BSA, and α‑LA was selectively added to the cells. Cell growth and death was determined by the MTT assay, which measures cellular metabolic rate, lactate dehydrogenase (LDH) leakage rate and cellular axonal length. Immunocytochemistry was employed to detect the expression of β‑amyloid (Aβ) protein in cells, and mRNA expression of amyloid precursor protein (APP) and the receptor for AGE (RAGE) were assayed by PT‑PCR. The metabolism of MTT was clearly increased, the rate of LDH leakage was significantly decreased, and axonal length was significantly increased in cells treated with α‑LA (0.1 g/l) as compared to untreated cells. Furthermore, the expression levels of Aβ protein were also decreased. In addition, α‑LA (0.1 g/l) markedly inhibited the expression of RAGE mRNA, and did not influence APP mRNA expression as compared the control group. α‑LA (0.1 g/l) was effective at dampening the cytotoxicity of AGE‑BSA, a preliminary observation that confirms the ability of α‑LA to significantly alleviate the cytotoxicity of AGEs against SH‑SY5Y cells.

The Anti-Amyloid-β and Neuroprotective Properties of a Novel Tricyclic Pyrone Molecule

There is an urgent unmet need for new therapeutics for Alzheimer's disease (AD), the most common cause of dementia in the elderly. Therapeutic approaches targeting amyloid-β (Aβ) and its downstream toxicities have become major strategies in AD drug development. We have taken a rational design approach and synthesized a class of tricyclic pyrone (TP) compounds that show anti-Aβ and other neuroprotective actions. The in vivo efficacy of a lead TP named CP2 to ameliorate AD-like pathologies has been shown in mouse models. Here we report the selection and initial characterization of a new lead TP70, which exhibited an anti-Aβ therapeutic index even higher than CP2. Moreover, TP70 was able to reduce oxidative stress, inhibit acyl-coenzyme A:cholesterol acyltransferase (ACAT), and upregulate the expression of ATP-binding cassette subfamily A, member 1 (ABCA1), actions considered neuroprotective in AD. TP70 further showed excellent pharmacokinetic properties, including brain penetration and oral availability. When administered to 5xFAD mice via intraperitoneal or oral route, TP70 enhanced the overall solubility and decreased the level of cerebral Aβ, including both fibrillary and soluble Aβ species. Interestingly, TP70 enhanced N-methyl-D-aspartate (NMDA) receptor-mediated excitatory post-synaptic potential (EPSP) in the hippocampal CA1 area, increased the magnitude of NMDA-dependent hippocampal long-term potentiation (LTP), a cellular model of learning and memory, and prevented the Aβ oligomer-impaired LTP. Significantly, a single dose of TP70 administered to aged 5xFAD mice was effective in mitigating the impaired LTP induction, recorded at 24 h after administration. Our results support a potential of TP70 in clinical development for AD in view of its synergistic neuroprotective actions, ability to positively modulate NMDA receptor-mediated hippocampal plasticity, and favorable pharmacokinetic properties in rodents.

Is Alzheimer's disease a Type 3 Diabetes? A critical appraisal

Recently researchers proposed the term 'Type-3-Diabetes' for Alzheimer's disease (ad) because of the shared molecular and cellular features among Type-1-Diabetes, Type-2-Diabetes and insulin resistance associated with memory deficits and cognitive decline in elderly individuals. Recent clinical and basic studies on patients with diabetes and AD revealed previously unreported cellular and pathological among diabetes, insulin resistance and AD. These studies are also strengthened by various basic biological studies that decipher the effects of insulin in the pathology of AD through cellular and molecular mechanisms. For instance, insulin is involved in the activation of glycogen synthase kinase 3β, which in turn causes phosphorylation of tau, which involved in the formation of neurofibrillary tangles. Interestingly, insulin also plays a crucial role in the formation amyloid plaques. In this review, we discussed significant shared mechanisms between AD and diabetes and we also provided therapeutic avenues for diabetes and AD. This article is part of a Special Issue entitled: Oxidative Stress and Mitochondrial Quality in Diabetes/Obesity and Critical Illness Spectrum of Diseases - edited by P. Hemachandra Reddy.

Glycation in Parkinson's disease and Alzheimer's disease

Glycation is a spontaneous age-dependent posttranslational modification that can impact the structure and function of several proteins. Interestingly, glycation can be detected at the periphery of Lewy bodies in the brain in Parkinson's disease. Moreover, α-synuclein can be glycated, at least under experimental conditions. In Alzheimer's disease, glycation of amyloid β peptide exacerbates its toxicity and contributes to neurodegeneration. Recent studies establish diabetes mellitus as a risk factor for several neurodegenerative disorders, including Parkinson's and Alzheimer's diseases. However, the mechanisms underlying this connection remain unclear. We hypothesize that hyperglycemia might play an important role in the development of these disorders, possibly by also inducing protein glycation and thereby dysfunction, aggregation, and deposition. Here, we explore protein glycation as a common player in Parkinson's and Alzheimer's diseases and propose it may constitute a novel target for the development of strategies for neuroprotective therapeutic interventions. © 2016 International Parkinson and Movement Disorder Society.

The Possible Mechanism of Advanced Glycation End Products (AGEs) for Alzheimer's Disease

Amyloid precursor protein (APP) has been modified by β and γ-secretase that cause amyloid deposits (plaques) in neuronal cells. Glyceraldhyde-derived AGEs has been identified as a major source of neurotoxicity in Alzheimer’s disease (AD). In a previous study, we demonstrated that glyceraldehyde-derived AGEs increase APP and Aβ via ROS. Furthermore, the combination of AGEs and Aβ has been shown to enhance neurotoxicity. In mice, APP expression is increased by tail vein injection of AGEs. This evidence suggests a correlation between AGEs and the development of AD. However, the role played by AGEs in the pathogenesis of AD remains unclear. In this report, we demonstrate that AGEs up-regulate APP processing protein (BACE and PS1) and Sirt1 expression via ROS, but do not affect the expression of downstream antioxidant genes HO-1 and NQO-1. Moreover, we found that AGEs increase GRP78 expression and enhance the cell death-related pathway p53, bcl-2/bax ratio, caspase 3. These results indicate that AGEs impair the neuroprotective effects of Sirt1 and lead to neuronal cell death via ER stress. Our findings suggest that AGEs increase ROS production, which stimulates downstream pathways related to APP processing, Aβ production, Sirt1, and GRP78, resulting in the up-regulation of cell death related pathway. This in-turn enhances neuronal cell death, which leads to the development of AD.

Effect of Amaranthus on Advanced Glycation End-Products Induced Cytotoxicity and Proinflammatory Cytokine Gene Expression in SH-SY5Y Cells

Amaranthus plants, or spinach, are used extensively as a vegetable and are known to possess medicinal properties. Neuroinflammation and oxidative stress play a major role in the pathogenesis of many neurodegenerative diseases, such as Alzheimer’s disease and Parkinson’s disease. Advanced glycation end-products (AGEs) cause cell toxicity in the human neuronal cell line, SH-SY5Y, through an increase in oxidative stress, as shown by reducing cell viability and increasing cell toxicity in a dose-dependent manner. We found that preincubation of SH-SY5Y cells with either petroleum ether, dichloromethane or methanol extracts of A. lividus and A. tricolor dose-dependently attenuated the neuron toxicity caused by AGEs treatment. Moreover, the results showed that A. lividus and A. tricolor extracts significantly downregulated the gene expression of the pro-inflammatory cytokines, TNF-α, IL-1 and IL-6 genes in AGEs-induced cells. We concluded that A. lividus and A. tricolor extracts not only have a neuroprotective effect against AGEs toxicity, but also have anti-inflammatory activity by reducing pro-inflammatory cytokine gene expression. This suggests that Amaranthus may be useful for treating chronic inflammation associated with neurodegenerative disorders.

Caffeoylquinic acids in Centella asiatica protect against amyloid-β toxicity

The accumulation of amyloid-β (Aβ) is a hallmark of Alzheimer's disease and is known to result in neurotoxicity both in vivo and in vitro. We previously demonstrated that treatment with the water extract of Centella asiatica (CAW) improves learning and memory deficits in Tg2576 mice, an animal model of Aβ accumulation. However the active compounds in CAW remain unknown. Here we used two in vitro models of Aβ toxicity to confirm this neuroprotective effect and identify several active constituents of the CAW extract. CAW reduced Aβ-induced cell death and attenuated Aβ-induced changes in tau expression and phosphorylation in both the MC65 and SH-SY5Y neuroblastoma cell lines. We confirmed and quantified the presence of several mono- and dicaffeoylquinic acids (CQAs) in CAW using chromatographic separation coupled to mass spectrometry and ultraviolet spectroscopy. Multiple dicaffeoylquinic acids showed efficacy in protecting MC65 cells against Aβ-induced cytotoxicity. Isochlorogenic acid A and 1,5-dicaffeoylquinic acid were found to be the most abundant CQAs in CAW, and the most active in protecting MC65 cells from Aβ-induced cell death. Both compounds showed neuroprotective activity in MC65 and SH-SY5Y cells at concentrations comparable to their levels in CAW. Each compound not only mitigated Aβ-induced cell death, but was able to attenuate Aβ-induced alterations in tau expression and phosphorylation in both cell lines, as seen with CAW. These data suggest that CQAs are active neuroprotective components in CAW, and therefore are important markers for future studies on CAW standardization, bioavailability, and dosing.

Glycation accelerates fibrillization of the amyloidogenic W7FW14F apomyoglobin

Neurodegenerative diseases are associated with misfolding and deposition of specific proteins, either intra or extracellularly in the nervous system. Advanced glycation end products (AGEs) originate from different molecular species that become glycated after exposure to sugars. Several proteins implicated in neurodegenerative diseases have been found to be glycated in vivo and the extent of glycation is related to the pathologies of the patients. Although it is now accepted that there is a direct correlation between AGEs formation and the development of neurodegenerative diseases, several questions still remain unanswered: whether glycation is the triggering event or just an additional factor acting on the aggregation pathway. To this concern, in the present study we have investigated the effect of glycation on the aggregation pathway of the amyloidogenic W7FW14F apomyoglobin. Although this protein has not been related to any amyloid disease, it represents a good model to resemble proteins that intrinsically evolve toward the formation of amyloid aggregates in physiological conditions. We show that D-ribose, but not D-glucose, rapidly induces the W7FW14F apomyoglobin to generate AGEs in a time-dependent manner and protein ribosylation is likely to involve lysine residues on the polypeptide chain. Ribosylation of the W7FW14F apomyoglobin strongly affects its aggregation kinetics producing amyloid fibrils within few days. Cytotoxicity of the glycated aggregates has also been tested using a cell viability assay. We propose that ribosylation in the W7FW14F apomyoglobin induces the formation of a cross-link that strongly reduces the flexibility of the H helix and/or induce a conformational change that favor fibril formation. These results open new perspectives for AGEs biological role as they can be considered not only a triggering factor in amyloidosis but also a player in later stages of the aggregation process.

Possible link between the cognitive dysfunction associated with diabetes mellitus and the neurotoxicity of methylglyoxal

This study was designed to describe the relationship between methylglyoxal (MG) and the cognitive abilities of streptozotocin (STZ)-induced diabetic rats. Animal study revealed that the diabetic rats had significantly higher escape latency, a shorter average swimming time in the target quadrant and a longer average distance traveled to the platform in the Morris water maze compared with control group. The serum levels of MG in STZ rats were higher than in the control group and were positively correlated with the levels of serum glucose in the blood. In the STZ group, TUNEL-staining levels and the expression of cleaved Caspase-3 and Bax were significantly increased, whereas Bcl-2 expression was significantly decreased. Cell culture study showed that MG significantly increased the percentage of apoptotic hippocampal neurons. After the exposure to MG for 24h, cleaved Caspase-3 and Bax expression increased, whereas Bcl-2 expression decreased. These data suggest a possible link between the cognitive dysfunction associated with diabetes mellitus and the neurotoxicity of MG, which may alter the expression levels of cleaved Caspase-3, Bcl-2 and Bax in the hippocampus.

Antagonism of neuronal prostaglandin E(2) receptor subtype 1 mitigates amyloid β neurotoxicity in vitro

Multiple lines of evidence indicate that regional brain eicosanoid signaling is important in initiation and progression of neurodegenerative conditions that have neuroinflammatory pathologic component, such as AD. We hypothesized that PGE(2) receptor subtype 1 (EP1) signaling (linked to intracellular Ca(2+) release) regulates Aβ peptide neurotoxicity and tested this in two complementary in vitro models: a human neuroblastoma cell line (MC65) producing Aβ(1-40) through conditional expression of the APP C-terminal portion, and murine primary cortical neuron cultures exposed to Aβ(1-42). In MC65 cells, EP1 receptor antagonist SC-51089 reduced Aβ neurotoxicity ~50 % without altering high molecular weight Aβ immunoreactive species formation. Inositol-3-phosphate receptor antagonist 2-aminoethoxy-diphenyl borate offered similar protection. SC-51089 largely protected the neuron cultures from synthetic Aβ(1-42) neurotoxicity. Nimodipine, a Ca(2+) channel blocker, was completely neuroprotective in both models. Based on these data, we conclude that suppressing neuronal EP1 signaling may represent a promising therapeutic approach to ameliorate Aβ peptide neurotoxicity.

Centella asiatica Extract Improves Behavioral Deficits in a Mouse Model of Alzheimer's Disease: Investigation of a Possible Mechanism of Action

Centella asiatica (CA), commonly named gotu kola, is an Ayurvedic herb used to enhance memory and nerve function. To investigate the potential use of CA in Alzheimer's disease (AD), we examined the effects of a water extract of CA (GKW) in the Tg2576 mouse, a murine model of AD with high β-amyloid burden. Orally administered GKW attenuated β-amyloid-associated behavioral abnormalities in these mice. In vitro, GKW protected SH-SY5Y cells and MC65 human neuroblastoma cells from toxicity induced by exogenously added and endogenously generated β-amyloid, respectively. GKW prevented intracellular β-amyloid aggregate formation in MC65 cells. GKW did not show anticholinesterase activity or protect neurons from oxidative damage and glutamate toxicity, mechanisms of current AD therapies. GKW is rich in phenolic compounds and does not contain asiatic acid, a known CA neuroprotective triterpene. CA thus offers a unique therapeutic mechanism and novel active compounds of potential relevance to the treatment of AD.

Glycation-altered proteolysis as a pathobiologic mechanism that links dietary glycemic index, aging, and age-related disease (in nondiabetics)

Epidemiologic studies indicate that the risks for major age-related debilities including coronary heart disease, diabetes, and age-related macular degeneration (AMD) are diminished in people who consume lower glycemic index (GI) diets, but lack of a unifying physiobiochemical mechanism that explains the salutary effect is a barrier to implementing dietary practices that capture the benefits of consuming lower GI diets. We established a simple murine model of age-related retinal lesions that precede AMD (hereafter called AMD-like lesions). We found that consuming a higher GI diet promotes these AMD-like lesions. However, mice that consumed the lower vs. higher GI diet had significantly reduced frequency (P < 0.02) and severity (P < 0.05) of hallmark age-related retinal lesions such as basal deposits. Consuming higher GI diets was associated with > 3 fold higher accumulation of advanced glycation end products (AGEs) in retina, lens, liver, and brain in the age-matched mice, suggesting that higher GI diets induce systemic glycative stress that is etiologic for lesions. Data from live cell and cell-free systems show that the ubiquitin-proteasome system (UPS) and lysosome/autophagy pathway [lysosomal proteolytic system (LPS)] are involved in the degradation of AGEs. Glycatively modified substrates were degraded significantly slower than unmodified substrates by the UPS. Compounding the detriments of glycative stress, AGE modification of ubiquitin and ubiquitin-conjugating enzymes impaired UPS activities. Furthermore, ubiquitin conjugates and AGEs accumulate and are found in lysosomes when cells are glycatively stressed or the UPS or LPS/autophagy are inhibited, indicating that the UPS and LPS interact with one another to degrade AGEs. Together, these data explain why AGEs accumulate as glycative stress increases.

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

BACKGROUND

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

D-ribose induces cellular protein glycation and impairs mouse spatial cognition

BACKGROUND

D-ribose, an important reducing monosaccharide, is highly active in the glycation of proteins, and results in the rapid production of advanced glycation end products (AGEs) in vitro. However, whether D-ribose participates in glycation and leads to production of AGEs in vivo still requires investigation.

METHODOLOGY/PRINCIPAL FINDINGS

Here we treated cultured cells and mice with D-ribose and D-glucose to compare ribosylation and glucosylation for production of AGEs. Treatment with D-ribose decreased cell viability and induced more AGE accumulation in cells. C57BL/6J mice intraperitoneally injected with D-ribose for 30 days showed high blood levels of glycated proteins and AGEs. Administration of high doses D-ribose also accelerated AGE formation in the mouse brain and induced impairment of spatial learning and memory ability according to the performance in Morris water maze test.

CONCLUSIONS/SIGNIFICANCE

These data demonstrate that D-ribose but not D-glucose reacts rapidly with proteins and produces significant amounts of AGEs in both cultured cells and the mouse brain, leading to accumulation of AGEs which may impair mouse spatial cognition.

A translational continuum of model systems for evaluating treatment strategies in Alzheimer's disease: isradipine as a candidate drug

A growing body of evidence supports the 'calcium hypothesis' of Alzheimer's disease (AD), which postulates that a variety of insults might disrupt the homeostatic regulation of neuronal calcium (Ca(2+)) in the brain, resulting in the progressive symptoms that typify the disease. However, despite ongoing efforts to develop new methods for testing therapeutic compounds that might be beneficial in AD, no single bioassay permits both rapid screening and in vivo validation of candidate drugs that target specific components of the Ca(2+) regulatory machinery. To address this issue, we have integrated four distinct model systems that provide complementary information about a trial compound: the human neuroblastoma MC65 line, which provides an in vitro model of amyloid toxicity; a transgenic Drosophila model, which develops age-dependent pathologies associated with AD; the 3×TgAD transgenic mouse, which recapitulates many of the neuropathological features that typify AD; and the embryonic nervous system of Manduca, which provides a novel in vivo assay for the acute effects of amyloid peptides on neuronal motility. To demonstrate the value of this 'translational suite' of bioassays, we focused on a set of clinically approved dihydropyridines (DHPs), a class of well-defined inhibitors of L-type calcium channels that have been suggested to be neuroprotective in AD. Among the DHPs tested in this study, we found that isradipine reduced the neurotoxic consequences of β-amyloid accumulation in all four model systems without inducing deleterious side effects. Our results provide new evidence in support of the Ca(2+) hypothesis of AD, and indicate that isradipine represents a promising drug for translation into clinical trials. In addition, these studies also demonstrate that this continuum of bioassays (representing different levels of complexity) provides an effective means of evaluating other candidate compounds that target specific components of the Ca(2+) regulatory machinery and that therefore might be beneficial in the treatment of AD.

Rosiglitazone protects neuroblastoma cells against advanced glycation end products-induced injury

AIM

To investigate the protective effects of rosiglitazone (RGZ) against the neuronal toxicity induced by advanced glycation end products (AGEs) and the underlying mechanisms.

METHODS

Neuroblastoma cell line SH-SY5Y was used. Cell viability and apoptosis were assessed using MTT assay and flow cytometry, respectively. Superoxide dismutase (SOD) and catalase activities were measured using biochemical methods. Intracellular reactive oxygen species (ROS) were monitored using 2',7'-dichlorodihydro-fluorescein diacetate (DCFH-DA). Secreted β-amyloid(1-42) (Aβ(1-42)) level was assessed by ELISA. The expression of mRNA of Bcl2, Bax, Caspase3, Aβ precursor protein (APP), β-site APP-cleaving enzyme 1 (BACE1), and insulin degrading enzyme (IDE) were measured using quantitative real-time PCR (Q-PCR), and their protein levels were examined using Western blot.

RESULTS

RGZ (0.1-10 μmol/L) significantly increased the cell viability that was reduced by AGEs (1000 μg/mL). RGZ (10 μmol/L) significantly ameliorated AGEs-triggered downregulation of SOD and catalase, and production of ROS. It also reversed Bcl2 downregulation, Bax upregulation and Caspase3 expression caused by AGEs. Moreover, it significantly attenuated AGEs-induced Aβ secretion and APP protein upregulation. RGZ did not affect BACE1 expression, but induced IDE expression, which promoted degradation of Aβ. All the effects were blocked by the specific PPARγ antagonist GW9662 (10 μmol/L).

CONCLUSION

RGZ protects the euroblastoma cells against AGEs-induced injury via its anti-oxidative, anti-apoptotic and anti-inflammatory properties that seems to be mediated by PPARγ activation. The results suggest a beneficial role for RGZ in the treatment of Alzheimer's disease.

Evaluation of coenzyme Q as an antioxidant strategy for Alzheimer's disease

Increasing evidence suggests that Alzheimer's disease (AD) is associated with oxidative damage that is caused in part by mitochondrial dysfunction. Here we investigated the feasibility of modifying Alzheimer pathology with the mitochondrial antioxidant coenzyme Q (CoQ). Exogenous CoQ protected MC65 neuroblastoma cells from amyloid-beta protein precursor C-terminal fragment (APP CTF)-induced neurotoxicity in a concentration dependent manner, with concentrations of 6.25 microM and higher providing near complete protection. Dietary supplementation with CoQ at a dose of 10 g/kg diet to C65/Bl6 mice for one month significantly suppressed brain protein carbonyl levels, which are markers of oxidative damage. Treatment for one month with 2 g lovastatin/kg diet, which interferes with CoQ synthesis, resulted in a significant lowering of brain CoQ10 levels. Mitochondrial energetics (brain ATP levels and mitochondrial membrane potential) were unaffected by either CoQ or lovastatin treatment. Our results suggest that oral CoQ may be a viable antioxidant strategy for neurodegenerative disease. Our data supports a trial of CoQ in an animal model of AD in order to determine whether a clinical trial is warranted.

Receptor for advanced glycation end products (RAGE) in a dash to the rescue: inflammatory signals gone awry in the primal response to stress

The multiligand receptor for advanced glycation end products (RAGE) of the Ig superfamily transduces the biological impact of discrete families of ligands, including advanced glycation end products, certain members of the S100/calgranulin family, high mobility group box-1, Mac-1 (alpha(M)beta(2), CD11b/CD18), and amyloid-beta peptide and beta-sheet fibrils. Although structurally dissimilar, at least at the monomeric level, recent evidence suggests that oligomeric forms of these RAGE ligands may be especially apt to activate the receptor and up-regulate a program of inflammatory and tissue injury-provoking genes. The challenge in probing the biology of RAGE and its impact in acute responses to stress and the potential development of chronic disease is to draw the line between mechanisms that evoke repair versus those that sustain inflammation and tissue damage. In this review, we suggest the concept that the ligands of RAGE comprise a primal program in the acute response to stress. When up-regulated in environments laden with oxidative stress, inflammation, innate aging, or high glucose, as examples, the function of these ligand families may be transformed from ones linked to rapid repair to those that drive chronic disease. Identification of the threshold beyond which ligands of RAGE mediate repair versus injury is a central component in delineating optimal strategies to target RAGE in the clinic.

The biology of RAGE and its ligands: uncovering mechanisms at the heart of diabetes and its complications

The interaction of glucose-modified and inflammation-promoting ligands with the receptor for advanced glycation end products (RAGE) is emerging as a central mechanism contributing to the diverse complications of diabetes. These ligands, particularly in oligomeric form, bind to RAGE and transduce intracellular signals. The consequences of this interaction, as elucidated in cultured cells and animal models, include upregulation of inflammatory and tissue-degradative pathways. Pharmacologic antagonism of RAGE may hold promise for the treatment of diabetic complications.

Escherichia coli glyoxalase II is a binuclear zinc-dependent metalloenzyme

Cytotoxic methylglyoxal is detoxified by the two-enzyme glyoxalase system. Glyoxalase I (GlxI) catalyzes conversion of non-enzymatically produced methylglyoxal-glutathione hemithioacetal into its corresponding thioester. Glyoxalase II (Glx II) hydrolyzes the thioester into d-lactate and free glutathione. Glyoxalase I and II are metalloenzymes, which possess mononuclear and binuclear active sites, respectively. There are two distinct classes of GlxI; the first class is Zn2+-dependent and is composed of GlxI from mainly eukaryotic organisms and the second class is composed of non-Zn2+-dependent (but Ni2+ or Co2+-dependent) GlxI enzymes (mainly prokaryotic and leishmanial species). GlxII is typically Zn2+-activated, containing Zn2+ and either Fe3+/Fe2+ or Mn2+ at the active site depending upon the biological source. To address whether two classes of GlxII might exist, glyoxalase II from Escherichia coli was cloned and overexpressed and characterized. Unlike E. coli GlxI, which is non-Zn2+-dependent, Zn2+ activates the E. coli GlxII enzyme, with no evidence for Ni2+ metal utilization.

The ligand/RAGE axis: lighting the fuse and igniting vascular stress

Vascular inflammation contributes critically to the initiation and progression of atherosclerosis. These processes are accelerated in hyperglycemia and play key roles in the increased incidence and severity of myocardial infarction and stroke observed in diabetes. Evidence suggests that the ligands of the receptor for advanced glycation endproducts (RAGE), a multiligand member of the immunoglobulin superfamily, interact with this receptor to play important roles in both early development and progression of atherosclerosis and vascular inflammation. Studies in animal models of vascular injury underscored the potent impact of RAGE blockade; administration of ligand-binding decoys of RAGE or antibodies to the receptor reduced the consequences of diabetes, hyperlipidemia, and physical injury to the vessel wall. This review focuses on the ligand repertoire of RAGE, the impact of ligand-RAGE interaction, and the potent effect of RAGE blockade in rodent models of vascular injury.

Intervention strategies to inhibit protein carbonylation by lipoxidation-derived reactive carbonyls

Protein carbonylation induced by reactive carbonyl species (RCS) generated by peroxidation of polyunsaturated fatty acids plays a significant role in the etiology and/or progression of several human diseases, such as cardiovascular (e.g., atherosclerosis, long-term complications of diabetes) and neurodegenerative diseases (e.g., Alzheimer's disease, Parkinson's disease, and cerebral ischemia). Most of the biological effects of intermediate RCS, mainly alpha,beta-unsaturated aldehydes, di-aldehydes, and keto-aldehydes, are due to their capacity to react with the nucleophilic sites of proteins, forming advanced lipoxidation end-products (ALEs). Because of the emerging deleterious role of RCS/protein adducts in several human diseases, different potential therapeutic strategies have been developed in the last few years. This review sheds focus on fundamental studies on lipid-derived RCS generation, their biological effects, and their reactivity with proteins, with particular emphasis to 4-hydroxy-trans-2-nonenal (HNE)-, acrolein (ACR)-, malondialdehyde (MDA)-, and glyoxal (GO)-modified proteins. It also discusses the recently developed pharmacological approaches for the management of chronic diseases in which oxidative stress and RCS formation are massively involved. Inhibition of ALE formation, based on carbonyl-sequestering agents, seems to be the most promising pharmacological tool and is reviewed in detail.

Molecular connexions between dementia and diabetes

Recent evidence suggests that the molecular defects associated with the development of diabetes also contribute to an increased risk of all types of dementia, including Alzheimer's disease, vascular dementia and Pick's disease. Indeed, the presence of type II diabetes mellitus results in a two to three fold higher risk of developing dementia [Fontbonne et al., 2001. Changes in cognitive abilities over a 4-year period are unfavourably affected in elderly diabetic subjects: results of the Epidemiology of Vascular Aging Study. Diabetes Care 24, 366-370; Gregg et al., 2000. Is diabetes associated with cognitive impairment and cognitive decline among older women? Study of Osteoporotic Fractures Research Group. Archives of Internal Medicine 160, 174-180; Peila et al., 2002. Type 2 diabetes, APOE gene, and the risk for dementia and related pathologies: The Honolulu-Asia Aging Study. Diabetes 51, 1256-1262]. There are currently 250 million people worldwide (>2 million in the UK) diagnosed with diabetes, and this number is predicted to double within the next 20 years, therefore the associated risk translates into a potential explosion in the appearance of dementia in the population. This review primarily focuses on the proposed molecular links between insulin action, Diabetes and Alzheimer's disease, while discussing the potential for therapeutic intervention to alleviate these disorders. In particular, we will review the regulation of glycogen synthase kinase-3 (GSK-3) and its neuronal substrates.

Effects of chemical chaperones on oxidative stress and detergent-insoluble species formation following conditional expression of amyloid precursor protein carboxy-terminal fragment

Oxidative stress, protein misfolding, protein complex formation, and detergent insolubility are biochemical features of Alzheimer's disease (AD). We tested the cause-and-effect relationships among these using MC65 human neuroblastoma cells that exhibit toxicity upon conditional expression of carboxy-terminal fragments (CTFs) of the human amyloid precursor protein (APP). Treatments with three different antioxidants (alpha-tocopherol, N-acetyl cysteine, and alpha-lipoic acid) or three different compounds (glycerol, trimethylamine-N-oxide, and 4-phenylbutyric acid) that have been described to have a "chemical chaperone" function in promoting protein folding all had a protective effect on MC65 cells and decreased markers of oxidative damage and accumulation of high molecular weight amyloid (A) beta-immunoreactive (IR) species. However, chaperones partially reduced detergent insolubility of the remaining Abeta-IR species, while antioxidants did not. These results suggest that protein misfolding associated with overexpression of APP CTFs promotes oxidative stress and cytotoxicity and contributes to formation of detergent-insoluble species that appear unrelated to cytotoxicity.

Toxic advanced glycation end products (TAGE) theory in Alzheimer's disease

Several epidemiological studies have reported moderately increased risks of Alzheimer's disease (AD) in diabetic patients compared with general population. In diabetes mellitus, the formation and accumulation of advanced glycation end products (AGEs) progress more rapidly. Recent understanding of this process has confirmed that interactions between AGEs and their receptor (RAGE) may play a role in the pathogenesis of diabetic complications and AD. The authors have recently found that glyceraldehyde-derived AGEs (AGE-2), which is predominantly the structure of toxic AGEs (TAGE), show significant toxicity on cortical neuronal cells and that the neurotoxic effect of diabetic serum is completely blocked by neutralizing antibody against the AGE-2 epitope. Moreover, in human AD brains, AGE-2 is distributed in the cytosol of neurons in the hippocampus and parahippocampal gyrus. These results suggest that TAGE is involved in the pathogenesis of AD as well as other age-related diseases. In this review, the authors discuss the molecular mechanisms of AD, especially focusing on TAGE-RAGE system.

Diabetes--a man made disease

The recent increase in both forms of diabetes must be caused by a modern change in the environment. Candidate agents must satisfy at least three criteria. Firstly, the agent must have increased in the environment recently, secondly that it causes diabetes in appropriate animal models, and thirdly that there is a plausible diabetogenic mechanism. Modern food processing can produce glycation end products, oxidised ascorbic acid and lipoic acid, all of which may cause diabetes. Infant formula in particular has high levels of glycation products, and added ascorbic acid. A casomorphin released from A1 beta-casein (but not the A2 variant) can become glycated and have adverse immune effects. Food processing and additives can be posited as a man made cause of the increase in both forms of diabetes. This hypothesis does not exclude other environmental agents which meet the above three criteria.

PGH2-derived levuglandin adducts increase the neurotoxicity of amyloid beta1-42

The body of evidence indicating that oligomers of amyloid beta(1-42) (Abeta(1-42)) produce toxicity to neurons, together with our demonstration that prostaglandin H(2) (PGH(2)) oligomerizes amyloid beta(1-42), led to the examination of the neurotoxicity of amyloid beta(1-42) treated with PGH(2). The neurotoxic effects of Abeta(1-42) incubated with PGH(2) was examined in primary cultures of cerebral neurons of mice, monitoring the reduction of 3-(4,5-dimethylthiazole-2-yl)-2,5-diphenyltetrazolium bromide (MTT) as an indicator of cell toxicity. Whereas Abeta(1-42) itself, incubated for 24 h, has little or no effect on MTT reduction, Abeta(1-42) 24 h after exposure to PGH(2) produced a marked inhibition of MTT reduction, comparable with the inhibition resulting from Abeta(1-42) that has been oligomerized by incubation for 6 days. Similar results were obtained when Abeta(1-42) was incubated with levuglandin E(2) (LGE(2)), a reactive aldehyde formed by spontaneous rearrangement of PGH(2). The oligomers formed from reaction of Abeta(1-42) with LGE(2) exhibit immunochemical similarity with amyloid-derived diffusible ligands (ADDLs), as determined by analysis of the products of reaction of Abeta(1-42) with LGE(2) using western blotting with an antibody that is selective for ADDLs.

Role of glutathione in intracellular amyloid-alpha precursor protein/carboxy-terminal fragment aggregation and associated cytotoxicity

Abstract Alterations in glutathione (GSH) metabolism are associated with neurodegeneration in Alzheimer's disease (AD), and GSH depletion follows application of exogenous fibrillar amyloid beta (Abeta) peptides in experimental systems; these results are commonly cited as evidence of oxidative damage in AD. We used MC65 human neuroblastoma cells that conditionally express carboxy-terminal fragments of the Abeta precursor protein (Abeta/CTFs) to directly test the hypothesis that GSH is part of the cellular response to stressors associated with Abeta/CTF accumulation and not simply a marker of oxidative damage. Our data showed that Abeta/CTFs accumulated by post-translational processes and were associated with progressive increases in oxidative damage and cytotoxicity. Ethycrinic acid (EA) or diethyl maleate (DEM), reagents that deplete GSH through non-specific thiol adduction, gave rise to dose-dependent cytotoxicity that was independent of Abeta/CTF expression and minimally responsive to alpha-tocopherol (AT). In contrast, buthionine sulfoximine (BSO), a selective inhibitor of GSH synthase, not only augmented Abeta/CTF-associated cell death but unexpectedly potentiated Abeta/CTF accumulation; both outcomes were completely suppressed by AT. These data suggest that antioxidants may serve as 'Abeta targeting' therapies that suppress toxic protein aggregation rather than simply acting as downstream radical scavengers.

Central role of PKCdelta in glycoxidation-dependent apoptosis of human neurons

Accumulation of advanced glycation end products (AGEs) induces alterations in the intracellular redox balance, leading cells to functional injury. Current literature reports that intracellular signaling triggered by the interaction of AGEs with their specific receptors RAGEs depends on the cell type and the state of activation/stress. In this work, NT2 human neurons were exposed for 48 h to glycated fetal serum containing 750-3000 pmol/ml pentosidine; the treatment induced an increase in apoptosis rate linear with AGE concentration up to 1500 pmol/ml, but necrotic death was elicited with the highest AGE amount employed (3000 pmol/ml pentosidine). Pentosidine at 1500 pmol/ml, which was the concentration responsible for the highest apoptotic effect (40% of apoptotic neurons), was able to determine early generation of intracellular reactive oxygen species and increase in RAGE levels. Under these conditions, protein kinase C (PKC) delta activity was increased approximately 2-fold, and DNA binding activity of redox-sensitive transcription factor activator protein-1 (AP-1) was enhanced 2.5-fold. A relationship among oxidative stress, PKCdelta activity, AP-1 activation, and apoptosis was demonstrated by pretreating neurons with 500 muM vitamin E, with 20 mug/ml Ginkgo biloba extract, or with 3 muM Rottlerin, inhibitor of PKCdelta; these pretreatments were able to protect neurons from the glycoxidation-dependent effects.

Advanced glycation end products and RAGE: a common thread in aging, diabetes, neurodegeneration, and inflammation

The products of nonenzymatic glycation and oxidation of proteins and lipids, the advanced glycation end products (AGEs), accumulate in a wide variety of environments. AGEs may be generated rapidly or over long times stimulated by a range of distinct triggering mechanisms, thereby accounting for their roles in multiple settings and disease states. A critical property of AGEs is their ability to activate receptor for advanced glycation end products (RAGE), a signal transduction receptor of the immunoglobulin superfamily. It is our hypothesis that due to such interaction, AGEs impart a potent impact in tissues, stimulating processes linked to inflammation and its consequences. We hypothesize that AGEs cause perturbation in a diverse group of diseases, such as diabetes, inflammation, neurodegeneration, and aging. Thus, we propose that targeting this pathway may represent a logical step in the prevention/treatment of the sequelae of these disorders.

Apolipoprotein E isoforms and apolipoprotein AI protect from amyloid precursor protein carboxy terminal fragment-associated cytotoxicity

Inheritance of the apolipoprotein (APO) E gene epsilon4 or epsilon2 allele alters the risk of developing Alzheimer disease (AD), while increased alpha-tocopherol (AT) intake appears to lower the risk of AD. As APOE is a major apolipoprotein in the CNS and AT in vivo is transported in lipoproteins, we tested the hypothesis that CNS lipoproteins, as modeled by relevant concentrations of high density lipoprotein (HDL), and AT would interact to suppress neurotoxicity in a cell culture model of amyloid beta (Abeta)- related toxicity. These cells conditionally express C99-derived peptides, proposed to be a key step in AD pathogenesis; this expression is closely associated with subsequent cell death. We found that physiologic concentrations of lipoproteins present in the CNS protected from C99-associated toxicity and provided evidence for two mechanisms of protection. The first was AT-independent, APOE isoform-dependent, and most potent for the APOE2 isoform. The second was a synergistic protection afforded by a combination of APOAI, or less so APOE, and AT. These data provide a novel explanation for the apparent AD-protective effect of inheriting an epsilon2 APOE allele, and suggest that optimizing AT enrichment of CNS lipoproteins or devising APOAI mimetics may augment AT efficacy in treating AD.