Selective vulnerability of spinal motor neurons to reactive dicarbonyl compounds, intermediate products of glycation, in vitro: implication of inefficient glutathione system in spinal motor neurons

Dynamic changes in butyrate levels regulate satellite cell homeostasis by preventing spontaneous activation during aging

The gut microbiota plays a pivotal role in systemic metabolic processes and in particular functions, such as developing and preserving the skeletal muscle system. However, the interplay between gut microbiota/metabolites and the regulation of satellite cell (SC) homeostasis, particularly during aging, remains elusive. We propose that gut microbiota and its metabolites modulate SC physiology and homeostasis throughout skeletal muscle development, regeneration, and aging process. Our investigation reveals that microbial dysbiosis manipulated by either antibiotic treatment or fecal microbiota transplantation from aged to adult mice, leads to the activation of SCs or a significant reduction in the total number. Furthermore, employing multi-omics (e.g., RNA-seq, 16S rRNA gene sequencing, and metabolomics) and bioinformatic analysis, we demonstrate that the reduced butyrate levels, alongside the gut microbial dysbiosis, could be the primary factor contributing to the reduction in the number of SCs and subsequent impairments during skeletal muscle aging. Meanwhile, butyrate supplementation can mitigate the antibiotics-induced SC activation irrespective of gut microbiota, potentially by inhibiting the proliferation and differentiation of SCs/myoblasts. The butyrate effect is likely facilitated through the monocarboxylate transporter 1 (Mct1), a lactate transporter enriched on membranes of SCs and myoblasts. As a result, butyrate could serve as an alternative strategy to enhance SC homeostasis and function during skeletal muscle aging. Our findings shed light on the potential application of microbial metabolites in maintaining SC homeostasis and preventing skeletal muscle aging.

Restoring Mitochondrial Function and Muscle Satellite Cell Signaling: Remedies against Age-Related Sarcopenia

Sarcopenia has a complex pathophysiology that encompasses metabolic dysregulation and muscle ultrastructural changes. Among the drivers of intracellular and ultrastructural changes of muscle fibers in sarcopenia, mitochondria and their quality control pathways play relevant roles. Mononucleated muscle stem cells/satellite cells (MSCs) have been attributed a critical role in muscle repair after an injury. The involvement of mitochondria in supporting MSC-directed muscle repair is unclear. There is evidence that a reduction in mitochondrial biogenesis blunts muscle repair, thus indicating that the delivery of functional mitochondria to injured muscles can be harnessed to limit muscle fibrosis and enhance restoration of muscle function. Injection of autologous respiration-competent mitochondria from uninjured sites to damaged tissue has been shown to reduce infarct size and enhance cell survival in preclinical models of ischemia-reperfusion. Furthermore, the incorporation of donor mitochondria into MSCs enhances lung and cardiac tissue repair. This strategy has also been tested for regeneration purposes in traumatic muscle injuries. Indeed, the systemic delivery of mitochondria promotes muscle regeneration and restores muscle mass and function while reducing fibrosis during recovery after an injury. In this review, we discuss the contribution of altered MSC function to sarcopenia and illustrate the prospect of harnessing mitochondrial delivery and restoration of MSCs as a therapeutic strategy against age-related sarcopenia.

Multisystem physiological perspective of human frailty and its modulation by physical activity

"Frailty" is a term used to refer to a state characterized by enhanced vulnerability to, and impaired recovery from, stressors compared with a nonfrail state, which is increasingly viewed as a loss of resilience. With increasing life expectancy and the associated rise in years spent with physical frailty, there is a need to understand the clinical and physiological features of frailty and the factors driving it. We describe the clinical definitions of age-related frailty and their limitations in allowing us to understand the pathogenesis of this prevalent condition. Given that age-related frailty manifests in the form of functional declines such as poor balance, falls, and immobility, as an alternative we view frailty from a physiological viewpoint and describe what is known of the organ-based components of frailty, including adiposity, the brain, and neuromuscular, skeletal muscle, immune, and cardiovascular systems, as individual systems and as components in multisystem dysregulation. By doing so we aim to highlight current understanding of the physiological phenotype of frailty and reveal key knowledge gaps and potential mechanistic drivers of the trajectory to frailty. We also review the studies in humans that have intervened with exercise to reduce frailty. We conclude that more longitudinal and interventional clinical studies are required in older adults. Such observational studies should interrogate the progression from a nonfrail to a frail state, assessing individual elements of frailty to produce a deep physiological phenotype of the syndrome. The findings will identify mechanistic drivers of frailty and allow targeted interventions to diminish frailty progression.

Neuroprotective effects of exercise on the aging human neuromuscular system

Human biological aging from maturity to senescence is associated with a gradual loss of muscle mass and neuromuscular function. It is not until very old age (>80 years) however, that these changes often manifest into functional impairments. A driving factor underlying the age-related loss of muscle mass and function is the reduction in the number and quality of motor units (MUs). A MU consists of a single motoneuron, located either in the spinal cord or the brain stem, and all of the muscle fibres it innervates via its peripheral axon. Throughout the adult lifespan, MUs are slowly, but progressively lost. The compensatory process of collateral reinnervation attempts to recapture orphaned muscle fibres following the death of a motoneuron. Whereas this process helps mitigate loss of muscle mass during the latter decades of adult aging, the neuromuscular system has fewer and larger MUs, which have lower quality connections between the axon terminal and innervated muscle fibres. Whether this process of MU death and degradation can be attenuated with habitual physical activity has been a challenging question of great interest. This review focuses on age-related alterations of the human neuromuscular system, with an emphasis on the MU, and presents findings on the potential protective effects of lifelong physical activity. Although there is some discrepancy across studies of masters athletes, if one considers all experimental limitations as well as the available literature in animals, there is compelling evidence of a protective effect of chronic physical training on human MUs. Our tenet is that high-levels of physical activity can mitigate the natural trajectory of loss of quantity and quality of MUs in old age.

The untwining of immunosenescence and aging

From a holistic point of view, aging results from the cumulative erosion of the various systems. Among these, the immune system is interconnected to the rest as immune cells are present in all organs and recirculate through bloodstream. Immunosenescence is the term used to define the remodelling of immune changes during aging. Because immune cells-and particularly lymphocytes-can further differentiate after their maturation in response to pathogen recognition, it is therefore unclear when senescence is induced in these cells. Additionally, it is also unclear which signals triggers senescence in immune cells (i) aging per se, (ii) specific response to pathogens, (iii) underlying conditions, or (iv) inflammaging. In this review, we will cover the current knowledge and concepts linked to immunosenescence and we focus this review on lymphocytes and T cells, which represent the typical model for replicative senescence. With the evidence presented, we propose to disentangle the senescence of immune cells from chronological aging.

The Antioxidant, Anti-Inflammatory, and Neuroprotective Properties of the Synthetic Chalcone Derivative AN07

Chalcones belong to a class of biologically active polyphenolic natural products. As a result of their simple chemical nature, they are easily synthesized and show a variety of promising biological activities. 2-Hydroxy-4′-methoxychalcone (AN07) is a synthetic chalcone derivate with potential anti-atherosclerosis effects. In this study, we demonstrated the novel antioxidant, anti-inflammatory, and neuroprotective effects of AN07. In RAW 264.7 macrophages, AN07 attenuated lipopolysaccharide (LPS)-induced elevations in reactive oxygen species (ROS) level and oxidative stress via down-regulating gp91^phox expression and stimulating the antioxidant system of nuclear factor erythroid 2-related factor 2 (Nrf2) and heme oxygenase-1 (HO-1) pathways, which were accompanied by increased glutathione (GSH) levels. Additionally, AN07 attenuated LPS-induced inflammatory factors, including NO, inducible NO synthase (iNOS), cyclooxygenase-2 (COX-2), and phosphorylated inhibitor of nuclear factor kappa B-alpha (p-IκBα) in RAW 264.7 macrophages. However, the effects of AN07 on promoting nuclear Nrf2 levels and decreasing COX-2 expressions were significantly abrogated by the peroxisome proliferator-activated receptor-γ (PPARγ) antagonist GW9662. In human dopaminergic SH-SY5Y cells treated with or without methylglyoxal (MG), a toxic endogenous by-product of glycolysis, AN07 up-regulated neurotrophic signals including insulin-like growth factor 1 receptor (IGF-1R), p-Akt, p-GSK3β, glucagon-like peptide 1 receptor (GLP-1R), and brain-derived neurotrophic factor (BDNF). AN07 attenuated MG-induced apoptosis by up-regulating the B-cell lymphoma 2 (Bcl-2) protein and down-regulating the cytosolic expression of cytochrome c. AN07 also attenuated MG-induced neurite damage via down-regulating the Rho-associated protein kinase 2 (ROCK2)/phosphorylated LIM kinase 1 (p-LIMK1) pathway. Moreover, AN07 ameliorated the MG-induced down-regulation of neuroprotective Parkinsonism-associated proteins parkin, pink1, and DJ-1. These findings suggest that AN07 possesses the potentials to be an anti-inflammatory, antioxidant, and neuroprotective agent

Naringenin, a dietary flavanone, enhances insulin-like growth factor 1 receptor-mediated antioxidant defense and attenuates methylglyoxal-induced neurite damage and apoptotic death

Objectives: Recent studies revealed the neuroprotective effects of naringenin (NGEN), a common dietary bioflavonoid contained in citrus fruits. However, there are limited data on its protection against methylglyoxal (MG), the most potent precursor of advanced glycation end-products. The present study was to investigate the protection of NGEN on MG-induced neurotoxicity and the involvement of insulin-like growth factor 1 receptor (IGF-1R) signaling. Methods: NSC34 motor neuron-like cells was used. Cell viability was measured by MTT assay. Protein expressions were analyzed by western blots. Morphological changes of neurites were observed by an inverted microscope. Reactive oxygen species (ROS) production and apoptotic cell numbers were measured by flow cytometer. Glutathione (GSH) level and superoxide dismutase (SOD) activity were measured by ELISA. Results: >NGEN attenuated ROS production and increased GSH level, SOD activity and nuclear factor erythroid 2-related factor 2 (Nrf2) nuclear expression in MG-treated NSC34 cells. NGEN also increased neurite length and enhanced IGF-1R and p-Akt in MG-treated NSC34 cells. Furthermore, NGEN attenuated MG-induced apoptotic death accompanied with down-regulation of cleaved-poly (ADP-ribose) polymerase (PARP) and up-regulation of B-cell lymphoma-2 (Bcl-2). However, AG1024, an IGF-1R antagonist, attenuated the anti-oxidative and anti-apoptotic effects of NGEN in MG-treated cells. Discussion: The present results demonstrated that NGEN decreased neuronal apoptosis and improved antioxidant defense in MG-treated NSC34 cells. Moreover, IGF-1R-mediated antioxidant defense plays an important role in this protective mechanism. These findings suggest the potential benefits of NGEN on the prevention of MG-induced or diabetes/hyperglycemia-related neurotoxicity. In vivo studies are needed for further confirmation on NGEN-mediated neuroprotection.

Sarcopenia: Aging-Related Loss of Muscle Mass and Function

Sarcopenia is a loss of muscle mass and function in the elderly that reduces mobility, diminishes quality of life, and can lead to fall-related injuries, which require costly hospitalization and extended rehabilitation. This review focuses on the aging-related structural changes and mechanisms at cellular and subcellular levels underlying changes in the individual motor unit: specifically, the perikaryon of the α-motoneuron, its neuromuscular junction(s), and the muscle fibers that it innervates. Loss of muscle mass with aging, which is largely due to the progressive loss of motoneurons, is associated with reduced muscle fiber number and size. Muscle function progressively declines because motoneuron loss is not adequately compensated by reinnervation of muscle fibers by the remaining motoneurons. At the intracellular level, key factors are qualitative changes in posttranslational modifications of muscle proteins and the loss of coordinated control between contractile, mitochondrial, and sarcoplasmic reticulum protein expression. Quantitative and qualitative changes in skeletal muscle during the process of aging also have been implicated in the pathogenesis of acquired and hereditary neuromuscular disorders. In experimental models, specific intervention strategies have shown encouraging results on limiting deterioration of motor unit structure and function under conditions of impaired innervation. Translated to the clinic, if these or similar interventions, by saving muscle and improving mobility, could help alleviate sarcopenia in the elderly, there would be both great humanitarian benefits and large cost savings for health care systems.

GLO1 gene polymorphisms and their association with retinitis pigmentosa: a case-control study in a Sicilian population

Glyoxalase 1 (GLO1) is a ubiquitous cellular enzyme involved in detoxification of methylglyoxal (MGO), a cytotoxic byproduct of glycolysis, whose excess can cause oxidative stress. In retinitis pigmentosa (RP), the prevalent cause of blindness just during working life in the industrialized countries, oxidative stress represents one of the possible mechanisms leading to death of cones following that of rods in the retina. To date, the causes of secondary death of cones remain unclear and among proposed mechanisms are: the deprivation of trophic factors normally produced by healthy rods, a compromised uptake of nutrients to cones due to irreversible destruction of RPE-cone outer segment, microglial activation and following release of pro-inflammatory cytokines and rod-derived toxins. In present paper, role of oxidative stress due to an excess of MGO was evaluated. In particular, we wanted to determine whether single nucleotide polymorphisms (SNPs) in GLO1 influence enzyme activity, contributing to cone death in advanced RP. 120 healthy controls and 80 RP patients from Sicilian population were genotyped for three GLO1 common SNPs, rs1130534 (c.372A>T, p.G124G), rs2736654 (c.A332C, p.E111A) and rs1049346 (c.-7C>T, 5'-UTR). While c.A332C polymorphism was not associated with RP, c.372A>T showed an allelic association (T372 allele frequency = 70% vs 60% in controls, p = 0.0071). Conversely, c.-7C>T showed both genotypic (χ² = 68.0952; p = 1.634e-15) and allelic associations (χ² = 51.7094; p = 6.435e-13): mutated allele frequency was higher in controls than in patients, suggesting its possible protective role. RP susceptibility may be associated with two of the analyzed GLO1 polymorphisms (rs1130534 and rs1049346).

Neuroprotective effect of phosphocreatine on oxidative stress and mitochondrial dysfunction induced apoptosis in vitro and in vivo: Involvement of dual PI3K/Akt and Nrf2/HO-1 pathways

Methylglyoxal (MGO), an active metabolite of glucose, is observed in high levels in the tissues and blood of diabetic patients. Phosphocreatine (PCr), a high-energy phosphate compound, exhibits a range of pharmacological actions but little is well known of its neuroprotective action. The aim of the present study was to investigate the neuroprotective effects and the possible mechanisms of PCr. Diabetes is closely associated with neurodegenerative diseases, leading not only to the peripheral nervous system (PNS) and but also to central nervous system (CNS) damage. Therefore, we established two rat models of diabetes in vivo induced by MGO and streptozocin (STZ) respectively, while utilized differentiated PC-12 cells in vitro. Treatment of PC-12 cells with PCr markedly attenuated MGO-induced change of viability, apoptosis, accompanied by decreased levels of caspase-3, casapse-9 and Bcl-2/Bax protein ratio. Determination of cellular respiratory function was performed with intact PC-12 cells and homogenized hippocampal neuron tissue of rat. Reactive oxygen species (ROS) generation was assessed by membrane permeable fluorescent probe DCFH-DA. The expressions of Akt, Nrf2 and HO-1 were examined by Western blot. PCr pretreatment significantly reduced oxidative stress-induced high LDH, MDA level, and ROS production of PC-12 cells. PCr pretreatment also significantly decreased mitochondrial dysfunction in vitro and in vivo. In addition, PCr pretreatment increased the expression of p-Akt, Nrf2 and HO-1, and reduced the apoptosis. Moreover, the expression of Cleaved caspase3 was partially increased and the p-Akt, Nrf2 and HO-1 was partially reduced by a PI3K inhibitor (LY294002). While, compared with LY294002 groups, pre-treatment with PCr at the concentrations of 20 mM significantly reduced the expression of Cleaved caspase3 and increased the expression of p-Akt, Nrf2 and HO-1. Molecular docking assay showed that PCr possessed powerful affinity towards to Akt with lower binding energy. In conclusion, the neuroprotective effects of PCr in vitro and in vivo rely on normalizing mitochondrial function and reducing oxidative stress via Akt mediated Nrf2/HO-1 pathway, suggesting that PCr may be a novel therapeutic candidate for the treatment of diabetes-associated neurodegenerative diseases.

Gclc deficiency in mouse CNS causes mitochondrial damage and neurodegeneration

Gamma glutamyl cysteine ligase (GCL) is the rate-limiting enzyme for intracellular glutathione (GSH) synthesis. The GSH concentration and GCL activity are declining with age in the central nervous system (CNS), and is accompanied by elevated reactive oxygen species (ROS). To study the biological effects of low GSH levels, we disrupted its synthesis both at birth by breeding a Gclc loxP mouse with a thy1-cre mouse (NEGSKO mouse) and at a later age by breeding with a CaMKII-ERT2-Cre (FIGSKO mouse). NEGSKO mice with deficiency of the Gclc in their entire CNS neuronal cells develop at 4 weeks: progressive motor neuron loss, gait problems, muscle denervation and atrophy, paralysis, and have diminished life expectancy. The observed neurodegeneration in Gclc deficiency is of more chronic rather than acute nature as demonstrated by Gclc targeted single-neuron labeling from the inducible Cre-mediated knockout (SLICK) mice. FIGSKO mice with inducible Gclc deficiency in the forebrain at 23 weeks after tamoxifen induction demonstrate profound brain atrophy, elevated astrogliosis and neurodegeneration, particularly in the hippocampus region. FIGSKO mice also develop cognitive abnormalities, i.e. learning impairment and nesting behaviors based on passive avoidance, T-Maze, and nesting behavior tests. Mechanistic studies show that impaired mitochondrial glutathione homeostasis and subsequent mitochondrial dysfunction are responsible for neuronal cell loss. This was confirmed by mitochondrial electron transporter chain activity analysis and transmission electron microscopy that demonstrate remarkable impairment of state 3 respiratory activity, impaired complex IV function, and mitochondrial swollen morphology in the hippocampus and cerebral cortex. These mouse genetic tools of oxidative stress open new insights into potential pharmacological control of apoptotic signaling pathways triggered by mitochondrial dysfunction.

Arg354 in the catalytic centre of bovine liver catalase is protected from methylglyoxal-mediated glycation

BACKGROUND

In addition to controlled post-translational modifications proteins can be modified with highly reactive compounds. Usually this leads to a compromised functionality of the protein. Methylglyoxal is one of the most common agents that attack arginine residues. Methylglyoxal is also regarded as a pro-oxidant that affects cellular redox homeostasis by contributing to the formation of reactive oxygen species. Antioxidant enzymes like catalase are required to protect the cell from oxidative damage. These enzymes are also targets for methylglyoxal-mediated modification which could severely affect their catalytic activity in breaking down reactive oxygen species to less reactive or inert compounds.

RESULTS

Here, bovine liver catalase was incubated with high levels of methylglyoxal to induce its glycation. This treatment did not lead to a pronounced reduction of enzymatic activity. Subsequently methylglyoxal-mediated arginine modifications (hydroimidazolone and dihydroxyimidazolidine) were quantitatively analysed by sensitive nano high performance liquid chromatography/electron spray ionisation/tandem mass spectrometry. Whereas several arginine residues displayed low to moderate levels of glycation (e.g., Arg93, Arg365, Arg444) Arg354 in the active centre of catalase was never found to be modified.

CONCLUSIONS

Bovine liver catalase is able to tolerate very high levels of the modifying α-oxoaldehyde methylglyoxal so that its essential enzymatic function is not impaired.

Neuroprotective effect of sulforaphane against methylglyoxal cytotoxicity

Glycation, an endogenous process that leads to the production of advanced glycation end products (AGEs), plays a role in the etiopathogenesis of different neurodegenerative diseases, such as Alzheimer's disease (AD). Methylglyoxal is the most potent precursor of AGEs, and high levels of methylglyoxal have been found in the cerebrospinal fluid of AD patients. Methylglyoxal may contribute to AD both inducing extensive protein cross-linking and mediating oxidative stress. The aim of this study was to investigate the role of sulforaphane, an isothiocyanate found in cruciferous vegetables, in counteracting methylglyoxal-induced damage in SH-SY5Y neuroblastoma cells. The data demonstrated that sulforaphane protects cells against glycative damage by inhibiting activation of the caspase-3 enzyme, reducing the phosphorylation of MAPK signaling pathways (ERK1/2, JNK, and p38), reducing oxidative stress, and increasing intracellular glutathione levels. For the first time, we demonstrate that sulforaphane enhances the methylglyoxal detoxifying system, increasing the expression and activity of glyoxalase 1. Sulforaphane modulated brain-derived neurotrophic factor and its pathway, whose dysregulation is related to AD development. Moreover, sulforaphane was able to revert the reduction of glucose uptake caused by methylglyoxal. In conclusion, sulforaphane demonstrates pleiotropic behavior thanks to its ability to act on different cellular targets, suggesting a potential role in preventing/counteracting multifactorial neurodegenerative diseases such as Alzheimer's.

A newly discovered neurotoxin ADTIQ associated with hyperglycemia and Parkinson's disease

BACKGROUND

Diabetes is associated with an increased risk of Parkinson's disease (PD). Number of studies have suggested that methylglyoxal (MGO) induced by diabetes is related to PD. However, very little is known about its molecular mechanism. On other hand, 1-acetyl-6, 7- dihydroxyl-1, 2, 3, 4- Tetrahydroisoquinoline(ADTIQ) is a dopamine (DA)-derived tetrahydroisoquinoline (TIQ), a novel endogenous neurotoxins, which was first discovered in frozen Parkinson's disease human brain tissue. While ADTIQ precursor methylglyoxal was also found in diabetic patients related to the glucose metabolism and diabetic patients.

METHODS

LC-MS/MS, 1H NMR and infrared spectroscopy identified the structure of ADTIQ. The Annexin V-FITC/PI, MTT and western blot analysis were used to measure the neurotoxicity of ADTIQ. The levels of ADTIQ and methylglyoxal were detected by LC-MS/MS.

RESULTS

Here we report the chemical synthesis of ADTIQ, demonstrate its biosynthesis in SH-SY5Y neuroblastoma cell line and investigate its role in the pathogenesis of PD. In addition, a significant increase in the level of ADTIQ was detected in the brains of transgenic mice expressing mutant forms (A53T or A30P) of α-synuclein. ADTIQ also reduced the cell viability and induced mitochondrial apoptosis in dopaminergic cells, suggesting that ADTIQ acts as an endogenous neurotoxin and potentially involved in the pathogenesis of PD. Methylglyoxal, a major byproduct of glucose metabolism and abnormalities in glucose metabolism could influence the levels of ADTIQ. Consistent with the hypothesis, increased levels of ADTIQ and methylglyoxal were detected in the striatum of diabetic rats and SH-SY5Y cells cultured in the presence of high glucose concentrations.

CONCLUSIONS

Increased levels of ADTIQ could be related with Hyperglycemia and death of dopaminergic neurons.

GENERAL SIGNIFICANCE

The increased levels of ADTIQ could be a reason of dopamine neuron dysfunction in diabetes. Therefore, ADTIQ may play a key role in increasing the risk for PD in patients with diabetes.

Methylglyoxal increases dopamine level and leads to oxidative stress in SH-SY5Y cells

More and more studies have suggested that methylglyoxal (MGO) induced by type-2 diabetes is related to Parkinson's disease (PD). However, little is known about the molecular mechanism. In this study, we explored the MGO toxicity in neuroblastoma SH-SY5Y cells. Neurotoxicity of MGO was measured by mitochondrial membrane potential, malondialdehyde, and methylthiazoletetrazolium assays. The levels of dopamine, 3,4-dihydroxyphenylacetic acid (DOPAC), and 1-methyl-4-phenyl-1,2,3,4-tetrahydroisoquinoline (salsolinol) were detected by liquid chromatography-mass spectrometry/mass spectrometry. The expressions of tyrosine hydroxylase (TH) and dopamine transporter (DAT) were detected by reverse transcriptase polymerase chain reaction and western blot analysis. The results showed that MGO induced an increase in TH and DAT expressions in SH-SY5Y neuroblastoma cells, while the levels of dopamine, DOPAC, and endogenous neurotoxin salsolinol also increased. Aminoguanidine (AG) is an inhibitor of MGO. It was found that AG could decrease the reactive oxygen species (ROS) level induced by MGO, but could not inhibit an increase of TH, DAT and dopamine. The increase of dopamine, DOPAC and salsolinol levels could lead to high ROS and mitochondrial damage. This study suggests that ROS caused by dopamine could contribute to the damage of dopaminergic neurons when MGO is increased during the course of diabetes.

Role of methylglyoxal in Alzheimer's disease

Alzheimer's disease is the most common and lethal neurodegenerative disorder. The major hallmarks of Alzheimer's disease are extracellular aggregation of amyloid β peptides and, the presence of intracellular neurofibrillary tangles formed by precipitation/aggregation of hyperphosphorylated tau protein. The etiology of Alzheimer's disease is multifactorial and a full understanding of its pathogenesis remains elusive. Some years ago, it has been suggested that glycation may contribute to both extensive protein cross-linking and oxidative stress in Alzheimer's disease. Glycation is an endogenous process that leads to the production of a class of compounds known as advanced glycation end products (AGEs). Interestingly, increased levels of AGEs have been observed in brains of Alzheimer's disease patients. Methylglyoxal, a reactive intermediate of cellular metabolism, is the most potent precursor of AGEs and is strictly correlated with an increase of oxidative stress in Alzheimer's disease. Many studies are showing that methylglyoxal and methylglyoxal-derived AGEs play a key role in the etiopathogenesis of Alzheimer's disease.

High throughput assay for evaluation of reactive carbonyl scavenging capacity

Many carbonyl species from either lipid peroxidation or glycoxidation are extremely reactive and can disrupt the function of proteins and enzymes. 4-hydroxynonenal and methylglyoxal are the most abundant and toxic lipid-derived reactive carbonyl species. The presence of these toxics leads to carbonyl stress and cause a significant amount of macromolecular damages in several diseases. Much evidence indicates trapping of reactive carbonyl intermediates may be a useful strategy for inhibiting or decreasing carbonyl stress-associated pathologies. There is no rapid and convenient analytical method available for the assessment of direct carbonyl scavenging capacity, and a very limited number of carbonyl scavengers have been identified to date, their therapeutic potential being highlighted only recently. In this context, we have developed a new and rapid sensitive fluorimetric method for the assessment of reactive carbonyl scavengers without involvement glycoxidation systems. Efficacy of various thiol- and non-thiol-carbonyl scavenger pharmacophores was tested both using this screening assay adapted to 96-well microplates and in cultured cells. The scavenging effects on the formation of Advanced Glycation End-product of Bovine Serum Albumin formed with methylglyoxal, 4-hydroxynonenal and glucose-glycated as molecular models were also examined. Low molecular mass thiols with an α-amino-β-mercaptoethane structure showed the highest degree of inhibitory activity toward both α,β-unsaturated aldehydes and dicarbonyls. Cysteine and cysteamine have the best scavenging ability toward methylglyoxal. WR-1065 which is currently approved for clinical use as a protective agent against radiation and renal toxicity was identified as the best inhibitor of 4-hydroxynonenal.

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We describe a rapid method for assessment of reactive carbonyl scavengers.

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We evaluated the carbonyl scavenger activity of various pharmacophores.

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α-amino-β-mercaptoethane structure showed the highest degree of activity.

Methylglyoxal induces oxidative stress and mitochondrial dysfunction in osteoblastic MC3T3-E1 cells

Methylglyoxal is a reactive dicarbonyl compound produced by glycolytic processing and identified as a precursor of advanced glycation end products. The elevated methylglyoxal levels in patients with diabetes are believed to contribute to diabetic complications, including bone defects. The objective of this study was to evaluate the effect of methylglyoxal on the function of osteoblastic MC3T3-E1 cells. The data indicated that methylglyoxal decreased osteoblast differentiation and induced osteoblast cytotoxicity. Pretreatment of MC3T3-E1 cells with aminoguanidine (a carbonyl scavenger), Trolox (an antioxidant), and cyclosporin A (a blocker of the mitochondrial permeability transition pore) prevented methylglyoxal-induced cytotoxicity in MC3T3-E1 cells. However, BAPTA/AM (an intracellular Ca(2+) chelator) and dantrolene (an inhibitor of endoplasmic reticulum Ca(2+) release) did not reverse the cytotoxic effect of methylglyoxal. Methylglyoxal increased the formation of intracellular reactive oxygen species, mitochondrial superoxide, and cardiolipin peroxidation in osteoblastic MC3T3-E1 cells. Methylglyoxal also decreased the mitochondrial membrane potential and intracellular ATP and nitric oxide levels, suggesting that carbonyl stress-induced loss of mitochondrial integrity contributes to the cytotoxicity of methylglyoxal. Furthermore, the results demonstrated that methylglyoxal induced protein adduct formation, inactivation of glyoxalase I, and activation of glyoxalase II. Aminoguanidine reversed all aforementioned effects of methylglyoxal. Taken together, these data support the notion that high methylglyoxal concentrations have detrimental effects on osteoblasts through a mechanism involving oxidative stress and mitochondrial dysfunction.

Oxidative stress and aging: is methylglyoxal the hidden enemy?

Aging is a multifactorial process that involves changes at the cellular, tissue, organ and the whole body levels resulting in decreased functioning, development of diseases, and ultimately death. Oxidative stress is believed to be a very important factor in causing aging and age-related diseases. Oxidative stress is caused by an imbalance between oxidants such as reactive oxygen species (ROS) and antioxidants. ROS are produced from the mitochondrial electron transport chain and many oxidative reactions. Methylglyoxal (MG) is a highly reactive dicarbonyl metabolite formed during glucose, protein and fatty acid metabolism. MG levels are elevated in hyperglycemia and other conditions. An excess of MG formation can increase ROS production and cause oxidative stress. MG reacts with proteins, DNA and other biomolecules, and is a major precursor of advanced glycation end products (AGEs). AGEs are also associated with the aging process and age-related diseases such as cardiovascular complications of diabetes, neurodegenerative diseases and connective tissue disorders. AGEs also increase oxidative stress. In this review we discuss the potential role of MG in the aging process through increasing oxidative stress besides causing AGEs formation. Specific and effective scavengers and crosslink breakers of MG and AGEs are being developed and can become potential treatments to slow the aging process and prevent many diseases.

The modification of alpha-synuclein by dicarbonyl compounds inhibits its fibril-forming process

Oxidative modification of alpha-synuclein (alphaSyn) was reported to have significant effects on its amyloidogenic properties. Dicarbonyl compounds are metabolites accumulated by various oxidative processes in the intracellular environment. In this study, two dicarbonyl compounds, methylglyoxal (MGO) and glyoxal (GO), were investigated for their effects on the structural and fibril-forming properties of alphaSyn. Both compounds were found to induce the oligomerization of alphaSyn. By adding substoichiometric amounts of alphaSyn modified by MGO or GO, the fibrillization of alphaSyn was substantially inhibited. The heterogeneously-modified alphaSyns were separated into three fractions: monomers, oligomers, and high molecular mass oligomers. When each modified alphaSyn species was used to seed fibril formation, protein fibrillization was significantly suppressed. Temperature scanning and interactions with liposomes revealed that both MGO- and GO-modified monomers were not as susceptible as the unmodified alphaSyn to conformational changes into partially folded intermediates and alpha-helixes. Our observations suggest that dicarbonyl modification of alphaSyn reduces conformational flexibility of the protein, thereby contributing to a reduction in the ability of alphaSyn to form fibrils, and the modified protein inhibits the fibrillization of the unmodified alphaSyn.

Free radical generation by methylglyoxal in tissues

Methylglyoxal (MG) is a reactive dicarbonyl intermediate of the glycolytic pathway. Increased oxidative stress is associated with conditions of increased MG, such as diabetes mellitus. Increased oxidative stress is due to an increase in highly reactive by-products of metabolic pathways, the so-called reactive oxygen species, such as superoxide anion, hydroxyl radical, hydrogen peroxide, nitric oxide and peroxynitrite. These reactive species react with a variety of proteins, enzymes, lipids, DNA and other molecules and disrupt their normal function. Oxidative stress causes many pathological changes that lead to vascular complications of diabetes mellitus, hypertension, neurodegenerative diseases and aging. In this review we summarize the correlation of elevated MG and various reactive oxygen species, and the enzymes that produce them or take part in their disposal, such as antioxidant enzymes and cofactors. The findings reported in various studies reviewed have started filling in gaps in our knowledge that will ultimately provide us with a clear picture of how the whole process that causes cellular dysfunction is initiated.

Methylglyoxal causes strong weakening of detoxifying capacity and apoptotic cell death in rat hippocampal neurons

The hippocampus is known to play a crucial role in learning and memory. Recent data from literature show that cognitive problems, common to aged or diabetic patients, may be related to accumulation of toxic alpha-oxoaldehydes such as methylglyoxal. Thus, it is possible that methylglyoxal could be, at least in part, responsible for the impairment of cognitive functions, and the knowledge of the mechanisms through which this compound elicits neuronal toxicity could be useful for the development of possible therapeutic strategies. We previously reported a high susceptibility of hippocampal neurons to methylglyoxal, through an oxidation-dependent mechanism. In the present study, we extend our investigation on the molecular mechanisms which underlie methylglyoxal toxicity, focusing on possible effects on expression and activity of glyoxalases, its main detoxifying enzymes, and glutathione peroxidase, as well as on the levels of reduced glutathione. We also investigate methylglyoxal-induced modulation of brain derived neurotrophic factor and proinflammatory cytokines. Our results show that methylglyoxal causes a dramatic depletion of reduced glutathione and a significant inhibition of both glyoxalase and glutathione peroxidase activities. Furthermore, methylglyoxal treatment seems to affect the expression of inflammatory cytokines and survival factors. In conclusion, our findings suggest that methylglyoxal-induced neurotoxicity occurs through the impairment of detoxification pathway and depletion of reduced glutathione. This, in turn, triggers widespread apoptotic cell death, occurring through the convergence of both mitochondrial and Fas-receptor pathways.

Role of endogenous glutathione in the secondary damage in experimental spinal cord injury in mice

GSH plays multiple roles in the nervous system including free radical scavenger, redox modulator of ionotropic receptor activity, and possible neurotransmitter. A lot of evidence suggests that GSH is involved in the pathogenesis of neurodegenerative disorders, like spinal cord injury (SCI). This study was undertaken to determine if the inhibition of endogenous glutathione, by L-buthionine-(S,R)-sulfoximine (BSO), affords protection against peroxynitrite-mediated toxicity in response to the spinal cord injury in vivo. The spinal cord of damaged animals showed a significant elevation of biochemical, immunohistochemical and functional parameters, increasing, respectively, neutrophils infiltration, lipid peroxidation, nitrotyrosine formation, PAR expression, apoptosis (measured by TUNEL staining) and loss of hind legs movement in SCI-operated mice. In contrast, the administration of BSO led to worsening of this already compromised setting, increasing the degree of (1) neutrophil infiltration, (2) lipid peroxidation, (3) histological damage, (4) apoptosis, (5) nitrotyrosine formation, (6) PAR expression, (7) apoptosis (measured by TUNEL staining) and (7) loss of hind legs movement. Thus, endogenous glutathione plays an important protective role against secondary damage after SCI.

Protein-bound crotonaldehyde accumulates in the spinal cord of superoxide dismutase-1 mutation-associated familial amyotrophic lateral sclerosis and its transgenic mouse model

Growing evidence documents oxidative stress involvement in ALS. We previously demonstrated accumulation of a protein-bound form of the highly toxic lipid peroxidation product crotonaldehyde (CRA) in the spinal cord of sporadic ALS patients. In the present study, to the determine the role for CRA in the disease processes of superoxide dismutase-1 (SOD1) mutation-associated familial ALS (FALS), we performed immunohistochemical and semi-quantitative cell count analyses of protein-bound CRA (P-CRA) in the spinal cord of SOD1-mutated FALS and its transgenic mouse model. Immunohistochemical analysis revealed increased P-CRA immunoreactivity in the spinal cord of the FALS patients and the transgenic mice compared to their respective controls. In the FALS patients, P-CRA immunoreactivity was localized in almost all of the chromatolytic motor neurons, neurofilamentous conglomerates, spheroids, cordlike swollen axons, reactive astrocytes and microglia, and the surrounding neuropil in the affected areas represented by the anterior horns. In the transgenic mice, P-CRA immunoreactivity was localized in only a few ventral horn glia in the presymptomatic stage, in almost all of the vacuolated motor neurons and cordlike swollen axons and some of the ventral horn reactive astrocytes and microglia in the onset stage, and in many of the ventral horn reactive astrocytes and microglia in the advanced stage. Cell count analysis on mouse spinal cord sections disclosed a statistically significant increase in the density of P-CRA-immunoreactive glia in the ventral horns of the young to old G93A mice compared to the age-matched control mice. The present results indicate that enhanced CRA formation occurs in motor neurons and reactive glia in the spinal cord of SOD1-mutated FALS and its transgenic mouse model as well as sporadic ALS, sug- gesting implications for CRA in the pathomechanism common to these forms of ALS.

Methylglyoxal impairs glucose metabolism and leads to energy depletion in neuronal cells--protection by carbonyl scavengers

Advanced glycation end products (AGEs) are found in various intraneuronal protein deposits such as neurofibrillary tangles in Alzheimer's disease and Lewy bodies in Parkinson's disease. Among the many reactive carbonyl compounds and AGE precursors, methylglyoxal is most likely to contribute to intracellular AGE formation, since it is extremely reactive and constantly produced by degradation of triosephosphates. Furthermore, methylglyoxal levels increase under pathophysiological conditions, for example, when trisosephosphate levels are elevated, the expression or activity of glyoxalase I is decreased, as is the case when the concentration of reduced glutathione, the rate-determining co-factor of glyoxalase I, is low. However, the effects of methylglyoxal on mitochondrial function and energy levels have not been studied in detail. In this study, we show that methylglyoxal increases the formation of intracellular reactive oxygen species and lactate in SH-SY5Y neuroblastoma cells. Methylglyoxal also decreases mitochondrial membrane potential and intracellular ATP levels, suggesting that carbonyl stress-induced loss of mitochondrial integrity could contribute to the cytotoxicity of methylglyoxal. The methylglyoxal-induced effects such as ATP depletion and mitochondrial dysfunction can be prevented by pre-incubation of the cells with the carbonyl scavengers aminoguanidine and tenilsetam. In a clinical context, these compounds could not only offer a promising therapeutic strategy to reduce intracellular AGE-accumulation, but also to decrease the dicarbonyl-induced impairment of energy production in aging and neurodegeneration.

Carbonyl stress and NMDA receptor activation contribute to methylglyoxal neurotoxicity

Methylglyoxal (MG) is a reactive alpha-ketoaldehyde physiologically generated as a by-product of glycolysis. MG that is able to form protein adducts resulting in advanced glycation end products accumulates under conditions associated with neurodegeneration such as impaired glucose metabolism or oxidative stress. In the present study, short-term exposure of human neuroblastoma SH-SY5Y cells to MG was associated with an early depolarization of the plasma membrane, glutamate release, and formation of reactive oxygen species. In addition, long-term exposure (24 h) of SH-SY5Y cells to MG caused a decrease in cell viability, intracellular ATP, and rhodamine 123 (Rh-123) fluorescence. ATP depletion and the decrease in Rh-123 fluorescence were prevented by carbonyl scavengers, the nitric oxide synthase inhibitor L-NAME, and N-methyl-d-aspartate (NMDA) receptor antagonists. Furthermore, the MG-induced glutamate release and the loss in cell viability were prevented by NMDA receptor antagonists. Therefore, MG renders cells more vulnerable to excitotoxicity. In conclusion, carbonyl scavengers as well as NMDA receptor antagonists may represent effective therapeutic tools to reduce the risk of pathophysiological changes associated with carbonyl stress in neurodegenerative diseases.

Aldehyde sources, metabolism, molecular toxicity mechanisms, and possible effects on human health

Aldehydes are organic compounds that are widespread in nature. They can be formed endogenously by lipid peroxidation (LPO), carbohydrate or metabolism ascorbate autoxidation, amine oxidases, cytochrome P-450s, or myeloperoxidase-catalyzed metabolic activation. This review compares the reactivity of many aldehydes towards biomolecules particularly macromolecules. Furthermore, it includes not only aldehydes of environmental or occupational concerns but also dietary aldehydes and aldehydes formed endogenously by intermediary metabolism. Drugs that are aldehydes or form reactive aldehyde metabolites that cause side-effect toxicity are also included. The effects of these aldehydes on biological function, their contribution to human diseases, and the role of nucleic acid and protein carbonylation/oxidation in mutagenicity and cytotoxicity mechanisms, respectively, as well as carbonyl signal transduction and gene expression, are reviewed. Aldehyde metabolic activation and detoxication by metabolizing enzymes are also reviewed, as well as the toxicological and anticancer therapeutic effects of metabolizing enzyme inhibitors. The human health risks from clinical and animal research studies are reviewed, including aldehydes as haptens in allergenic hypersensitivity diseases, respiratory allergies, and idiosyncratic drug toxicity; the potential carcinogenic risks of the carbonyl body burden; and the toxic effects of aldehydes in liver disease, embryo toxicity/teratogenicity, diabetes/hypertension, sclerosing peritonitis, cerebral ischemia/neurodegenerative diseases, and other aging-associated diseases.

Age- and stage-dependent glyoxalase I expression and its activity in normal and Alzheimer's disease brains

The reaction of lysine and arginine residues of proteins with 1,2-dicarbonyl compounds result in the formation of advanced glycation end products (AGEs). Accumulation of AGEs is a characteristic feature of the aging brain and contributes to the development of neurodegenerative diseases such as Alzheimer's disease (AD). Therefore, it is of particular interest to study the cellular defense mechanisms against AGE formation and particularly the detoxification of their precursors. AGE precursor compounds such as methylglyoxal and glyoxal were cellulary detoxified by the glyoxalase system, consisting of glyoxalases I and II. Glyoxalase I levels are diminished in old aged brains but elevated in AD brains. However, it is still unknown how glyoxalase I level of AD brains changes in a disease and in an age-dependent manner. Therefore, we investigated the AD stage- and the age-dependent levels of glyoxalase I in the Brodmann area 22 of AD brains (n=25) and healthy controls (n=10). Our results obtained from RT-PCR reveal reducing glyoxalase I RNA levels with advancing stage of AD and with increasing age. Western Blot analysis indicates that in comparison to healthy controls, glyoxalase I protein amounts are 1.5-fold increased in early AD subjects and continuously decrease in middle and late stages of AD. The glyoxalase I protein amounts of AD patients also decrease with age. Results obtained from glyoxalase I activity measurement show 1.05-1.2-fold diminished levels in AD brains compared to healthy controls and no significant decrease neither with the stage of AD nor with age. The immunohistochemical investigations demonstrate an elevated number of glyoxalase I stained neurons in brains of early and middle but not in late AD subjects compared to age-matched healthy controls. In addition, the stage-dependent immunohistochemical investigation demonstrates that with reduced glyoxalase I staining AGE deposits prevail, specifically in late stage of AD. In conclusion, the decrease of glyoxalase I expression with increasing AD stage might be one reason for methylglyoxal-induced neuronal impairment, apoptosis, and AGE formation in plaques and tangles.

The carbonyl scavengers aminoguanidine and tenilsetam protect against the neurotoxic effects of methylglyoxal

Advanced glycation end products (AGEs) have been identified in age-related intracellular protein deposits of Alzheimer's disease (amyloid plaques and neurofibrillary tangles) and Parkinson disease (Lewy bodies), suggesting that these protein deposits have been exposed to AGE precursors such as the reactive dicarbonyl compound methylglyoxal. In ageing tissue and under diabetic pseudohypoxia, intracellular methylglyoxal levels rise through an impairment of triosephosphate utilization. Furthermore, methylglyoxal detoxification is impaired when reduced glutathione levels are low, conditions, which have all been described in Alzheimer's disease. However, there is less known about the toxicity of methylglyoxal, particularly about therapeutic strategies to scavenge such dicarbonyl compounds and attenuate their toxicity. In our study, extracellularly applied methylglyoxal was shown to be toxic to human neuroblastoma cells in a dose-dependent manner above concentrations of 150 microM with a LD50 of approximately 1.25 mM. Pre-incubation of methylglyoxal with a variety of carbonyl scavengers such as aminoguanidine or tenilsetam and the thiol antioxidant lipoic acid significantly reduced its toxicity. In summary, carbonyl scavengers might offer a promising therapeutic strategy to reduce the neurotoxicity of reactive carbonyl compounds, providing a potential benefit for patients with age-related neurodegenerative diseases.

The gene for paroxysmal non-kinesigenic dyskinesia encodes an enzyme in a stress response pathway

Paroxysmal non-kinesigenic dyskinesia (PNKD) is characterized by spontaneous hyperkinetic attacks that are precipitated by alcohol, coffee, stress and fatigue. We report mutations in the myofibrillogenesis regulator 1 (MR-1) gene causing PNKD in 50 individuals from eight families. The mutations cause changes (Ala to Val) in the N-terminal region of two MR-1 isoforms. The MR-1L isoform is specifically expressed in brain and is localized to the cell membrane while the MR-1S isoform is ubiquitously expressed and shows diffuse cytoplasmic and nuclear localization. Bioinformatic analysis reveals that the MR-1 gene is homologous to the hydroxyacylglutathione hydrolase (HAGH) gene. HAGH functions in a pathway to detoxify methylglyoxal, a compound present in coffee and alcoholic beverages and produced as a by-product of oxidative stress. Our results suggest a mechanism whereby alcohol, coffee and stress may act as precipitants of attacks in PNKD. Stress response pathways will be important areas for elucidation of episodic disease genetics where stress is a common precipitant of many common disorders like epilepsy, migraine and cardiac arrhythmias.

Accumulation of protein-bound 4-hydroxy-2-hexenal in spinal cords from patients with sporadic amyotrophic lateral sclerosis

4-Hydroxy-2-hexenal (HHE) is a toxic, reactive aldehydic intermediate formed by nonenzymatic peroxidation of n-3 polyunsaturated fatty acids. The aim of this study was to determine the implication for HHE in the pathomechanism of amyotrophic lateral sclerosis (ALS) by immunohistochemical and enzyme-linked immunosorbent assay (ELISA) techniques using a mouse monoclonal IgG(1) antibody mAbHHE53 specific for protein-bound HHE. Immunohistochemical analysis on formalin-fixed, paraffin-embedded sections and frozen sections of spinal cords obtained at autopsy from 10 sporadic ALS patients and 10 age-matched control subjects demonstrated that protein-bound HHE immunoreactivity was seen and was prominent in the entire gray matter in the ALS cases and localized in the neurons, reactive astrocytes, microglial cells, and the surrounding neuropil, while the immunoreactivity was obscure or undetectable in the control cases. No significant protein-bound HHE immunoreactivity was seen in sections processed with omission of mAbHHE53 or in sections incubated with the antibody with an excess of the respective antigen. Competitive ELISA analysis on trypsin-digested protein extracts of fresh-frozen spinal cord samples disclosed a significant increase in protein-bound HHE level in the ALS cases compared with the control cases. Our results indicate that enhanced HHE formation occurs in the entire gray matter of sporadic ALS spinal cords and suggest that the selective vulnerability of motor neurons to HHE mediates the pathomechanism of this disease.

Methylglyoxal induces oxidative stress-dependent cell injury and up-regulation of interleukin-1β and nerve growth factor in cultured hippocampal neuronal cells

Methylglyoxal (MG) is one of the most powerful glycating agents of proteins and other important cellular components and has been shown to be toxic to cultured cells. Under hyperglycaemic conditions, an increase in the concentration of MG has been observed in human body fluids and tissues that seems to be responsible for diabetic complications. Recent data suggest that diabetes may cause impairment of cognitive processes, according to a mechanism involving both oxidative stress and advanced glycation end product (AGE) formation. In this work, we explored the molecular mechanism underlying MG toxicity in neural cells, by investigating the effect of MG on both the interleukin-1beta (IL-1beta), as the major inducer of the acute phase response, and the nervous growth factor (NGF) expression. Experiments were performed on cultured neural cells from rat hippocampus, being this brain region mostly involved in cognitive processes and, therefore, possible target of diabetes-mediated impairment of cognitive abilities. Results show that MG treatment causes in hippocampal neural cells extensive, oxidative stress-mediated cell death, in consequence of a strong catalase enzymatic activity and protein inhibition. MG also causes a very significant increase in both transcript and protein expression of the NGF as well as of the pro-inflammatory cytokine IL-1beta. MG co-treatment with the antioxidant N-acetylcysteine (NAC) completely abrogates the observed effects. Taken together, these data demonstrate that hippocampal neurons are strongly susceptible to MG-mediated oxidative stress.

Glycation proceeds faster in mutated Cu, Zn-superoxide dismutases related to familial amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS) involves the progressive degeneration of motor neurons in the spinal cord and motor cortex. It has been shown that 15-20% of patients with familial ALS (FALS) have defects in the Sod1 gene that encodes Cu, Zn-superoxide dismutase (SOD). To elucidate the pathological role of mutated Cu, Zn-SODs in FALS, the susceptibility of mutants to glycation was examined. Mutated Cu, Zn-SODs (G37R, G93A, and I113T) related to FALS and wild type were produced in a baculovirus/insect cell expression system. Glycated and nonglycated proteins were separated on a boronate column, and the nonglycated fraction was then incubated with glucose. The mutated Cu, Zn-SODs were found to be highly susceptible to glycation compared with the wild-type enzyme as estimated by Western blot analysis using an anti-hexitol lysine antibody. The mutated Cu, Zn-SOD incubated with glucose generated higher levels of hydrogen peroxide than the wild-type enzyme. Mutated Cu, Zn-SODs were also shown to be highly susceptible to fructation, and the fructated mutant also produced higher levels of hydrogen peroxide than the wild type. These results suggest that high susceptibility of mutated Cu, Zn-SODs to glycation could be the origin of the oxidative stress associated with neuronal dysfunction in FALS.

Mitochondrial dysfunction and death in motor neurons exposed to the glutathione-depleting agent ethacrynic acid

This study investigated the mechanisms of toxicity of glutathione (GSH) depletion in one cell type, the motor neuron. Ethacrynic acid (EA) (100 microM) was added to immortalized mouse motor neurons (NSC-34) to deplete both cytosolic and mitochondrial glutathione rapidly. This caused a drop in GSH to 25% of the initial level in 1 h and complete loss in 4 h. This effect was accompanied by enhanced generation of reactive oxygen species (ROS) with a peak after 2 h of exposure, and by signs of mitochondrial dysfunction such as a decrease in 3-(4,5-dimethyl-2-thiazoyl)-2,5-diphenyltetrazolium bromide (MTT) (30% less after 4 h). The increase in ROS and the MTT reduction were both EA concentration-dependent. Expression of heme oxygenase-1 (HO-1), a marker of oxidative stress, also increased. The mitochondrial damage was monitored by measuring the mitochondrial membrane potential (MMP) from the uptake of rhodamine 123 into mitochondria. MMP dropped (20%) after only 1 h exposure to EA, and slowly continued to decline until 3 h, with a steep drop at 5 h (50% decrease), i.e. after the complete GSH loss. Quantification of DNA fragmentation by the TUNEL technique showed that the proportion of cells with fragmented nuclei rose from 10% after 5 h EA exposure to about 65% at 18 h. These results indicate that EA-induced GSH depletion rapidly impairs the mitochondrial function of motor neurons, and this precedes cell death. This experimental model of oxidative toxicity could be useful to study mechanisms of diseases like spinal cord injury (SCI) and amyotrophic lateral sclerosis (ALS), where motor neurons are the vulnerable population and oxidative stress has a pathogenic role.

Brefeldin A-induced neurotoxicity in cultured spinal cord neurons

Brefeldin A (BFA) is a fungus metabolite that is known to cause the disassembly of the Golgi complex and apoptosis in exposed cells, both of which have been suggested as playing roles in the pathogenesis of neurodegenerative diseases, particularly amyotrophic lateral sclerosis (ALS). This study showed that BFA caused neurotoxicity and apoptotic nuclear changes in cultured spinal neurons of rat spinal cord in a dose- and time-dependent manner. The spinal motor neurons were more vulnerable to this neurotoxicity. The cultured spinal neurons showed irreversible disassembly of the Golgi apparatus as early as 1 hr after exposure to BFA. BFA induced the expression and activation of caspase-12 beginning 8 hr after exposure. The level of the cleaved form of caspase-3 had increased 12 hr after the addition of BFA. Free radical generation and loss of mitochondrial membrane potential were observed in the later stages of neurotoxicity caused by BFA. Collectively, our data suggests that BFA is an excellent agent for reproducing the pathophysiological features of ALS. This in vitro model may be useful in attempts to study the mechanisms of this neurodegenerative disease and to examine therapeutic potentials.

DNA damage by carbonyl stress in human skin cells

Reactive carbonyl species (RCS) are potent mediators of cellular carbonyl stress originating from endogenous chemical processes such as lipid peroxidation and glycation. Skin deterioration as observed in photoaging and diabetes has been linked to accumulative protein damage from glycation, but the effects of carbonyl stress on skin cell genomic integrity are ill defined. In this study, the genotoxic effects of acute carbonyl stress on HaCaT keratinocytes and CF3 fibroblasts were assessed. Administration of the alpha-dicarbonyl compounds glyoxal and methylglyoxal as physiologically relevant RCS inhibited skin cell proliferation, led to intra-cellular protein glycation as evidenced by the accumulation of N(epsilon)-(carboxymethyl)-L-lysine (CML) in histones, and caused extensive DNA strand cleavage as assessed by the comet assay. These effects were prevented by treatment with the carbonyl scavenger D-penicillamine. Both glyoxal and methylglyoxal damaged DNA in intact cells. Glyoxal caused DNA strand breaks while methylglyoxal produced extensive DNA-protein cross-linking as evidenced by pronounced nuclear condensation and total suppression of comet formation. Glycation by glyoxal and methylglyoxal resulted in histone cross-linking in vitro and induced oxygen-dependent cleavage of plasmid DNA, which was partly suppressed by the hydroxyl scavenger mannitol. We suggest that a chemical mechanism of cellular DNA damage by carbonyl stress occurs in which histone glycoxidation is followed by reactive oxygen induced DNA stand breaks. The genotoxic potential of RCS in cultured skin cells and its suppression by a carbonyl scavenger as described in this study have implications for skin damage and carcinogenesis and its prevention by agents selective for carbonyl stress.

Glyceraldehyde-3-phosphate dehydrogenase activity as an independent modifier of methylglyoxal levels in diabetes

Methylglyoxal (MG) may be an important cause of diabetic complications. Its primary source is dihydroxyacetone phosphate (DHAP) whose levels are partially controlled by glyceraldehyde-3-phosphate dehydrogenase (GAPDH). Using a human red blood cell (RBC) culture, we examined the effect of modifying GAPDH activity on MG production. With the inhibitor koningic acid (KA), we showed a linear, concentration-dependent GAPDH inhibition, with 5 microM KA leading to a 79% reduction of GAPDH activity and a sixfold increase in MG. Changes in redox state produced by elevated pH also resulted in a 2.4-fold increase in MG production at pH 7.5 and a 13.4-fold increase at pH 7.8. We found substantial inter-individual variation in DHAP and MG levels and an inverse relationship between GAPDH activity and MG production (R=0.57, P=0.005) in type 2 diabetes. A similar relationship between GAPDH activity and MG was observed in vivo in type 1 diabetes (R=0.29, P=0.0018). Widely varying rates of progression of diabetic complications are seen among individuals. We postulate that modification of GAPDH by environmental factors or genetic dysregulation and the resultant differences in MG production could at least partially account for this observation.

Effect of geranylgeranylaceton on cellular damage induced by proteasome inhibition in cultured spinal neurons

We investigated the effect of two proteasome inhibitors, lactacystin and epoxomicin, on cultured spinal cord neurons. The incubation of spinal neurons with proteasome inhibitors for 24 hr induced neurotoxicity in a dose-dependent manner. We found motor neurons to be more vulnerable to proteasome-induced neurotoxicity than nonmotor neurons. The staining of cell bodies in treated motor neurons was markedly disrupted and showed characteristic granular patterns. Proteasome-induced neurotoxicity is accompanied by apoptotic nuclear changes, posttranslational modification of the cellular proteins, generation of intracellular free radicals, reduction in the amount of reduced glutathione, and mitochondrial dysfunction. Neurotoxicity was reduced by the administration of low concentrations (1-100 nM) of geranylgeranylacetone (GGA), which is widely used as an antiulcer drug, although higher concentrations of this drug produced neurotoxicity in spinal cord neurons. GGA was found to induce the expression of heat shock protein 70 as well as thioredoxin, which may partly contribute to the protective effect of GGA. These data suggest that the inhibition of proteasome may play a role in the mechanism of neurodegenerative diseases of the spinal cord, such as amyotrophic lateral sclerosis, and that the use of GGA may be effective in the treatment of these conditions.

Prostaglandin E1 protects cultured spinal neurons against the effects of nitric oxide toxicity

The effects of prostaglandin (PG) E(1) on NO neurotoxicity were examined using rat cultured spinal neurons. Rat cultured spinal neurons exposed to the NO donor, 2,2'-(hydroxynitrosohydrazono) bis-ethanamine (NOC18), showed neurotoxic effects that were accompanied by apoptotic nuclear change, free radical generation, a reduction in glutathione, and mitochondrial dysfunction. PGE(1), at concentrations of 1-100 nM, protected cultured spinal neurons from NO toxicity by reversing the oxidative and pro-apoptotic properties elicited by NOC18 exposure. The administration of PGE(1) increased the intracellular cyclic AMP (cAMP) levels in cultured spinal neurons. In addition, reverse transcriptase-polymerase chain reaction (RT-PCR) analysis confirmed the existence of EP4, a cAMP-elevating PGE receptor, in cultured spinal neurons. The protective effects of PGE(1) against NO neurotoxicity was partially blocked by an inhibitor of MEK [the mitogen-activated protein kinase (MAPK)/extracellular-signal-regulated kinase (ERK) kinase], suggesting that the MAPK/ERK pathway may play a significant role in the activity of PGE(1). PGE(1) up-regulated the expression of the anti-apoptotic protein, Bcl-2, as determined by Western blot analysis. PGE(1) also induced the expression of thioredoxin in cultured spinal neurons. Our data indicate that PGE(1) exerts a protective action against NO neurotoxicity in cultured spinal neurons, and suggests a therapeutic potential of PGE(1) against spinal cord disease, such as amyotrophic lateral sclerosis.

Identification of alpha-dicarbonyl scavengers for cellular protection against carbonyl stress

Tissue deterioration and aging have long been associated with the accumulation of chemically induced protein and DNA damage. Reactive oxygen species (ROS) and reactive carbonyl species (RCS), especially alpha-dicarbonyl compounds, are key mediators of damage caused by oxidative stress, glycation, and UV-irradiation. The toxic effects of ROS are counteracted in vivo by antioxidants and antioxidant enzymes, and the deleterious effects of one RCS, methylglyoxal, are counteracted by a ubiquitous glyoxalase system. Carbonyl stress as a result of toxic effects of various mono-dicarbonyls (e.g. 4-hydroxynonenal) and alpha-dicarbonyls (e.g. glyoxal and deoxyosones) cannot be directly antagonized by antioxidants, and only a small number of biological carbonyl scavengers like glutathione (GSH) have been identified to date. We have developed a new screening method for the identification of carbonyl scavengers using a rapid glycation system that proceeds independent of oxygen and therefore, excludes identification of inhibitory compounds acting as antioxidants. Using this screening assay adapted to 96-well microtiter plates, we have identified the cysteine derivative 3,3-dimethyl-D-cysteine as a potent inhibitor of non-oxidative advanced glycation. Comparative kinetic analyses demonstrated the superior alpha-oxoaldehyde-scavenging activity of D-penicillamine over that of aminoguanidine. D-Penicillamine traps alpha-oxoaldehydes by forming a 2-acylthiazolidine derivative as shown by structure elucidation of reaction products between D-penicillamine and methylglyoxal or phenylglyoxal. We demonstrated that upon co-incubation, D-penicillamine protects human skin keratinocytes and fibroblasts (CF3 cells) against glyoxal- and methylglyoxal-induced carbonyl toxicity. Our research qualifies alpha-amino-beta-mercapto-beta,beta-dimethyl-ethane as a promising pharmacophore for the development of related alpha-dicarbonyl scavengers as therapeutic agents to protect cells against carbonyl stress.

Morphological evidence for lipid peroxidation and protein glycoxidation in spinal cords from sporadic amyotrophic lateral sclerosis patients

For determining whether both the spinal cord motor neurons and glial cells are exposed to increased oxidative stress in amyotrophic lateral sclerosis (ALS), we performed an immunohistochemical investigation of end products of lipid peroxidation and protein glycoxidation in spinal cords from seven sporadic ALS patients and seven age-matched control individuals. In the ALS spinal cords, immunoreactivities for adducts of 4-hydroxy-2-nonenal-histidine and crotonaldehyde-lysine as markers of lipid peroxidation, N(epsilon)-(carboxymethyl)lysine as a marker of lipid peroxidation or protein glycoxidation, and pentosidine as a marker of protein glycoxidation were localized in the gray matter neuropil and almost all of the motor neurons, reactive astrocytes and microglia/macrophages, whereas none of the immunoreactivities for N(epsilon)-(carboxyethyl)lysine or argpyrimidine as markers of protein glycoxidation or enzymatic glycolysis, or pyrraline or imidazolone as markers of nonoxidative protein glycation were detectable. The control spinal cords displayed no significant immunoreactivities for any of these examined products. Our results indicate that in sporadic ALS, both lipid peroxidation and protein glycoxidation are enhanced in the spinal cord motor neurons and glial cells, and suggest that the formation of certain products in these abnormal reactions is implicated in motor neuron degeneration.

Effect of 1,25-dihydroxyvitamin D(3) on cultured mesencephalic dopaminergic neurons to the combined toxicity caused by L-buthionine sulfoximine and 1-methyl-4-phenylpyridine

A decrease in intracellular glutathione content may be related to the primary event in Parkinson's disease, so increasing the glutathione level may have a therapeutic benefit. The biologically active form of vitamin D, 1,25-dihydroxyvitamin D(3) [1, 25-(OH)(2)D(3)] has been recently reported to enhance the intracellular glutathione concentration in the central nervous system. Exposing rat cultured mesencephalic neurons for 24 hr to a mixture of L-buthionine sulfoximine (BSO) and 1-methyl-4-phenylpyridium ions (MPP(+)) resulted in a relatively selective damage to dopaminergic neurons. This damage has been accompanied by a reduction of intracellular glutathione levels. Low doses, i.e., 1-100 nM, of 1,25-(OH)(2)D(3) protect cultured dopaminergic neurons against this toxicity, although higher concentrations of this active form of vitamin D have been found to enhance the toxic effect. Generation of reactive oxygen species (ROS) by this toxicity has been attenuated in cultures being pretreated with low concentrations of 1,25-(OH)(2)D(3). Because the hormone increases the intracellular glutathione content in cultures, determining how this hormone suppresses ROS generation may involve the enhancement of the antioxidative system. These data suggest that low doses of 1,25-(OH)(2)D(3) are able to protect mesencephalic dopaminergic neurons against BSO/MPP(+)-induced toxicity that causes a depletion in glutathione content.