Methylglyoxal-induced AMPK activation leads to autophagic degradation of thioredoxin 1 and glyoxalase 2 in HT22 nerve cells

Thioredoxin1 Binding Metastasis-Associated Lung Adenocarcinoma Transcript 1 Attenuates Inflammation and Apoptosis after Intracerebral Hemorrhage

Post-transcriptional regulation and RNA-binding proteins (RBPs) play vital roles in the occurrence of secondary injury after intracerebral hemorrhage (ICH). Therefore, we identified RBPs distinctively expressed after ICH by screening and determined thioredoxin1 (Txn1) as one of the most distinctive RBPs. We employed an ICH model and in vitro experiments to investigate the role of Txn1 in ICH. Firstly, we found that Txn1 was mainly expressed in microglia and neurons in the central nervous system, and its expression was significantly reduced in perihematomal tissue. Additionally, adeno-associated virus (AAV) carrying Txn1 was injected into the ICH rat model. Our results showed that overexpression of Txn1 reduced secondary injury and improved outcome in the ICH rat model. Moreover, to understand the therapeutic mechanism of Txn1 after ICH, we performed RNA immunoprecipitation combined with high-throughput sequencing. The results showed that Txn1 binds to inflammation- and apoptosis-related mRNAs and affects gene expression through RNA splicing and translation. Finally, RNA pull-down assays and in vitro experiments confirmed that Txn1 binds to metastasis-associated lung adenocarcinoma transcript 1 (MALAT1), leading to reduced inflammation and apoptosis. Our study suggests that Txn1 is a potential therapeutic target for alleviating ICH-induced brain injury.

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

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

Metformin inhibits methylglyoxal-induced retinal pigment epithelial cell death and retinopathy via AMPK-dependent mechanisms: Reversing mitochondrial dysfunction and upregulating glyoxalase 1

Diabetic retinopathy (DR) is a major cause of blindness in adult, and the accumulation of advanced glycation end products (AGEs) is a major pathologic event in DR. Methylglyoxal (MGO), a highly reactive dicarbonyl compound, is a precursor of AGEs. Although the therapeutic potential of metformin for retinopathy disorders has recently been elucidated, possibly through AMPK activation, it remains unknown how metformin directly affects the MGO-induced stress response in retinal pigment epithelial cells. Therefore, in this study, we compared the effects of metformin and the AMPK activator A769662 on MGO-induced DR in mice, as well as evaluated cytotoxicity, mitochondrial dynamic changes and dysfunction in ARPE-19 cells. We found MGO can induce mitochondrial ROS production and mitochondrial membrane potential loss, but reduce cytosolic ROS level in ARPE-19 cells. Although these effects of MGO can be reversed by both metformin and A769662, we demonstrated that reduction of mitochondrial ROS production rather than restoration of cytosolic ROS level contributes to cell protective effects of metformin and A769662. Moreover, MGO inhibits AMPK activity, reduces LC3II accumulation, and suppresses protein and gene expressions of MFN1, PGC-1α and TFAM, leading to mitochondrial fission, inhibition of mitochondrial biogenesis and autophagy. In contrast, these events of MGO were reversed by metformin in an AMPK-dependent manner as evidenced by the effects of compound C and AMPK silencing. In addition, we observed an AMPK-dependent upregulation of glyoxalase 1, a ubiquitous cellular enzyme that participates in the detoxification of MGO. In intravitreal drug-treated mice, we found that AMPK activators can reverse the MGO-induced cotton wool spots, macular edema and retinal damage. Functional, histological and optical coherence tomography analysis support the protective actions of both agents against MGO-elicited retinal damage. Metformin and A769662 via AMPK activation exert a strong protection against MGO-induced retinal pigment epithelial cell death and retinopathy. Therefore, metformin and AMPK activator can be therapeutic agents for DR.

Sesquiterpenoid-rich Java Ginger rhizome extract prompts autophagic cell death in cervical cancer cell SiHa mainly by modulating cellular redox homeostasis

Java Ginger or Curcuma zanthorrhiza Roxb. has long gained focus among tribal people of Java, for its medicinal properties mainly against gynaecological challenges. The present study aims to identify the most potent phytocompound present in the extract and determine primary mode of action accountable for cytotoxic activity of Curcuma zanthorrhiza rhizome extract against HPV16-positive SiHa cervical cancer cells. The phytochemically-rich extract of rhizome (CZM) was capable to inhibit proliferation of target cells in a dose-dependent manner with an IC50 of 150 μg/ml. Dysregulation of intercellular antioxidant defence system resulted to surges in ROS and RNS level, increased calcium concentration and compromised mitochondrial membrane potential. Nucleus got affected, cell cycle dynamics got impaired while clonogenicity and migration ability diminished. Expression of viral oncogenes E7 and E6 decreased significantly. Accumulation of toxic cell metabolite and decrease in level of essential ones continued. Finally, alteration in PI3K/AKT/mTOR signalling route was followed by onset of autophagic cell death concomitant with the upregulated expression of Beclin1, Atg5-12 and LC3II. Curcumin and a novel crystal as well as few phyto-fractions were isolated by column chromatography. Of these, curcumin was found to be most potent in inducing cytotoxicity in SiHa while two other fractions also showed significant activity. Thus, CZM acted against SiHa cells by inducing autophagy that commences in compliance to the changes in PI3K/AKT/mTOR pathway mainly in response to oxidative stress. To the best of our knowledge this is the first report of Curcuma zanthorrhiza Roxb. inducing autophagy.

Supplementary Information

The online version contains supplementary material available at 10.1007/s13205-022-03415-9.

Glyoxalase 2: Towards a Broader View of the Second Player of the Glyoxalase System

Glyoxalase 2 is a mitochondrial and cytoplasmic protein belonging to the metallo-β-lactamase family encoded by the hydroxyacylglutathione hydrolase (HAGH) gene. This enzyme is the second enzyme of the glyoxalase system that is responsible for detoxification of the α-ketothaldehyde methylglyoxal in cells. The two enzymes glyoxalase 1 (Glo1) and glyoxalase 2 (Glo2) form the complete glyoxalase pathway, which utilizes glutathione as cofactor in eukaryotic cells. The importance of Glo2 is highlighted by its ubiquitous distribution in prokaryotic and eukaryotic organisms. Its function in the system has been well defined, but in recent years, additional roles are emerging, especially those related to oxidative stress. This review focuses on Glo2 by considering its genetics, molecular and structural properties, its involvement in post-translational modifications and its interaction with specific metabolic pathways. The purpose of this review is to focus attention on an enzyme that, from the most recent studies, appears to play a role in multiple regulatory pathways that may be important in certain diseases such as cancer or oxidative stress-related diseases.

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

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

Protection of pancreatic β-cell by phosphocreatine through mitochondrial improvement via the regulation of dual AKT/IRS-1/GSK-3β and STAT3/Cyp-D signaling pathways

Diabetes mellitus (DM) is a metabolic syndrome, caused by insufficient insulin secretion or insulin resistance (IR). DM enhances oxidative stress and induces mitochondrial function in different kinds of cell types, including pancreatic β-cells. Our previous study has showed phosphocreatine (PCr) can advance the mitochondrial function through enhancing the oxidative phosphorylation and electron transport ability in mitochondria damaged by methylglyoxal (MG). Our aim was to explore the potential role of PCr as a molecule to protect mitochondria from diabetes-induced pancreatic β-cell injury with insulin secretion deficiency or IR through dual AKT/IRS-1/GSK-3β and STAT3/Cyclophilin D (Cyp-D) signaling pathways. MG-induced INS-1 cell viability, apoptosis, mitochondrial division and fusion, the morphology, and function of mitochondria were suppressed. Flow cytometry was used to detect the production of intracellular reactive oxygen species (ROS) and the changes of intracellular calcium, and the respiratory function was measured by oxygraph-2k. The expressions of AKT, IRS-1, GSK-3β, STAT3, and Cyp-D were detected using Western blot. The result showed that the oxidative stress-related kinases were significantly restored to the normal level after the pretreatment with PCr. Moreover, PCr pretreatment significantly inhibited cell apoptosis, decreased intracellular calcium, and ROS production, and inhibited mitochondrial division and fusion, and increased ATP synthesis damaged by MG in INS-1 cells. In addition, pretreatment with PCr suppressed Cytochrome C, p-STAT3, and Cyp-D expressions, while increased p-AKT, p-IRS-1, p-GSK-3β, caspase-3, and caspase-9 expressions. In conclusion, PCr has protective effect on INS-1 cells in vitro and in vivo, relying on AKT mediated STAT3/ Cyp-D pathway to inhibit oxidative stress and restore mitochondrial function, signifying that PCr might become an emerging candidate for the cure of diabetic pancreatic cancer β-cell damage.

Defining a pharmacological inhibitor fingerprint for oxytosis/ferroptosis

Ferroptosis was first described in 2012 as an iron- and lipid peroxidation-dependent form of regulated cell death. Since its initial description, these two characteristics have informed numerous cell culture studies where inhibitors of lipid peroxidation and/or iron chelators have been shown to prevent cell death induced by a wide range of insults. However, it is not clear whether these two characteristics are sufficient to distinguish ferroptosis from other forms of regulated cell death. Thus, the primary goal of this study was to determine whether a unique combination of features could be identified that would provide an approach to more clearly separate ferroptosis from other forms of regulated cell death. To this end, multiple pharmacological inhibitors based on a variety of studies were tested. Many of these inhibitors were previously shown to protect cells from oxytosis, a regulated cell death pathway that mechanistically overlaps with ferroptosis and is induced by some of the same chemicals as ferroptosis. These inhibitors were not only tested against both known ferroptosis and oxytosis inducers but also a number of other insults that have been suggested to induce ferroptosis. The results show that a pharmacological fingerprint for ferroptosis can be established and used to categorize toxic insults into those that overlap with oxytosis/ferroptosis and those that do not.

Methylglyoxal induces p53 activation and inhibits mTORC1 in human umbilical vein endothelial cells

Methylglyoxal (MGO), a precursor of advanced glycation end products (AGEs), is regarded as a pivotal mediator of vascular damage in patients with diabetes. We have previously reported that MGO induces transcriptional changes compatible with p53 activation in cultured human endothelial cells. To further substantiate this finding and to explore the underlying mechanisms and possible consequences of p53 activation, we aimed (1) to provide direct evidence for p53 activation in MGO-treated human umbilical vein endothelial cells (HUVECs), (2) to assess putative mechanisms by which this occurs, (3) to analyze down-stream effects on mTOR and autophagy pathways, and (4) to assess the potential benefit of carnosine herein. Exposure of HUVECs to 800 µM of MGO for 5 h induced p53 phosphorylation. This was paralleled by an increase in TUNEL and γ-H2AX positive cells, indicative for DNA damage. Compatible with p53 activation, MGO treatment resulted in cell cycle arrest, inhibition of mTORC1 and induction of autophagy. Carnosine co-treatment did not counteract MGO-driven effects. In conclusion, our results demonstrate that MGO elicits DNA damage and p53 activation in HUVECs, resulting in modulation of downstream pathways, e.g. mTORC1.

Kuwanon G protects HT22 cells from advanced glycation end product-induced damage

The incidence of diabetic encephalopathy is increasing as the population ages. Evidence suggests that formation and accumulation of advanced glycation end products (AGEs) plays a pivotal role in disease progression, but limited research has been carried out in this area. A previous study demonstrated that Kuwanon G (KWG) had significant anti-oxidative stress and anti-inflammatory properties. As AGEs are oxidative products and inflammation is involved in their generation it is hypothesized that KWG may have effects against AGE-induced neuronal damage. In the present study, mouse hippocampal neuronal cell line HT22 was used. KWG was shown to significantly inhibit AGE-induced cell apoptosis in comparison with a control treatment, as determined by both MTT and flow cytometry. Compared with the AGEs group, expression of pro-apoptotic protein Bax was reduced and expression of anti-apoptotic protein Bcl-2 was increased in the AGEs + KWG group. Both intracellular and extracellular levels of acetylcholine and choline acetyltransferase were significantly elevated after KWG administration in comparison with controls whilethe level of acetylcholinesterase decreased. These changes in protein expression were accompanied by increased levels of superoxide dismutase and glutathione peroxidase synthesis and reduced production of malondialdehyde and reactive oxygen species. Intracellular signaling pathway protein levels were determined by western blot and immunocytochemistry. KWG administration was found to prevent AGE-induced changes to the phosphorylation levels of Akt, IκB-α, glycogen synthase kinase 3 (GSK3)-α and β, p38 MAPK and NF-κB p65 suggesting a potential neuroprotective effect of KWG against AGE-induced damage was via the PI3K/Akt/GSK3αβ signaling pathway. The findings of the present study suggest that KWG may be a potential treatment for diabetic encephalopathy.

Methylglyoxal-Mediated Dopamine Depletion, Working Memory Deficit, and Depression-Like Behavior Are Prevented by a Dopamine/Noradrenaline Reuptake Inhibitor

Methylglyoxal (MGO) is an endogenous toxin, mainly produced as a by-product of glycolysis that has been associated to aging, Alzheimer's disease, and inflammation. Cell culture studies reported that MGO could impair the glyoxalase, thioredoxin, and glutathione systems. Thus, we investigated the effect of in vivo MGO administration on these systems, but no major changes were observed in the glyoxalase, thioredoxin, and glutathione systems, as evaluated in the prefrontal cortex and the hippocampus of mice. A previous study from our group indicated that MGO administration produced learning/memory deficits and depression-like behavior. Confirming these findings, the tail suspension test indicated that MGO treatment for 7 days leads to depression-like behavior in three different mice strains. MGO treatment for 12 days induced working memory impairment, as evaluated in the Y maze spontaneous alternation test, which was paralleled by low dopamine and serotonin levels in the cerebral cortex. Increased DARPP32 Thr75/Thr34 phosphorylation ratio was observed, suggesting a suppression of phosphatase 1 inhibition, which may be involved in behavioral responses to MGO. Co-treatment with a dopamine/noradrenaline reuptake inhibitor (bupropion, 10 mg/kg, p.o.) reversed the depression-like behavior and working memory impairment and restored the serotonin and dopamine levels in the cerebral cortex. Overall, the cerebral cortex monoaminergic system appears to be a preferential target of MGO toxicity, a new potential therapeutic target that remains to be addressed.

Advanced glycation end products and their adverse effects: The role of autophagy

The critical roles played by advanced glycation endproducts (AGEs) accumulation in diabetes and diabetic complications have gained intense recognition. AGEs interfere with the normal functioning of almost every organ with multiple actions like apoptosis, inflammation, protein dysfunction, mitochondrial dysfunction, and oxidative stress. However, the development of a potential treatment strategy is yet to be established. Autophagy is an evolutionarily conserved cellular process that maintains cellular homeostasis with the degradation and recycling systems. AGEs can activate autophagy signaling, which could be targeted as a therapeutic strategy against AGEs induced problems. In this review, we have provided an overview of the adverse effects of AGEs, and we put forth the notion that autophagy could be a promising targetable strategy against AGEs.

Prospects of honey in fighting against COVID-19: pharmacological insights and therapeutic promises

Honey and its compounds are drawing attention as an effective natural therapy because of its ability to attenuate acute inflammation through enhancing immune response. Several studies have proved its potential healing capability against numerous chronic diseases/conditions, including pulmonary disorders, cardiac disorders, diabetes, hypertension, autophagy dysfunction, bacterial, and fungal infections. More importantly, honey has proved its virucidal effect on several enveloped viruses such as HIV, influenza virus, herpes simplex, and varicella-zoster virus. Honey may be beneficial for patients with COVID-19 which is caused by an enveloped virus SARS-CoV-2 by boosting the host immune system, improving comorbid conditions, and antiviral activities. Moreover, a clinical trial of honey on COVID-19 patients is currently undergoing. In this review, we have tried to summarize the potential benefits of honey and its ingredients in the context of antimicrobial activities, some chronic diseases, and the host immune system. Thus, we have attempted to establish a relationship with honey for the treatment of COVID-19. This review will be helpful to reconsider the insights into the possible potential therapeutic effects of honey in the context of the COVID-19 pandemic. However, the effects of honey on SARS-CoV-2 replication and/or host immune system need to be further investigated by in vitro and in vivo studies.

Downregulation of the Glo1 Gene Is Associated with Reduced Adiposity and Ectopic Fat Accumulation in Spontaneously Hypertensive Rats

Methylglyoxal (MG), a potent precursor of advanced glycation end-products (AGE), is increased in metabolic disorders such as diabetes and obesity. MG and other dicarbonyl metabolites are detoxified by the glyoxalase system in which glyoxalase 1, coded by the Glo1 gene, serves as the rate-limiting enzyme. In this study, we analyzed the effects of Glo1 downregulation on glucose and lipid metabolism parameters in spontaneously hypertensive rats (SHR) by targeting the Glo1 gene (SHR-Glo1^+/− heterozygotes). Compared to SHR wild-type animals, SHR-Glo1^+/− rats showed significantly reduced Glo1 expression and lower GLO1 activity in tissues associated with increased MG levels. In contrast to SHR controls, SHR-Glo1^+/− rats exhibited lower relative weight of epididymal fat, reduced ectopic fat accumulation in the liver and heart, and decreased serum triglycerides. In addition, compared to controls, SHR-Glo1^+/− rats showed reduced serum insulin and increased basal and insulin stimulated incorporation of glucose into white adipose tissue lipids (lipogenesis). Reduced ectopic fat accumulation in the heart was associated with significantly increased pAMPK/AMPK ratio and GLUT4 activity. These results provide evidence that Glo1 downregulation in SHR is associated with reduced adiposity and ectopic fat accumulation, most likely mediated by AMPK activation in the heart.

Methylglyoxal-Induced Dysfunction in Brain Endothelial Cells via the Suppression of Akt/HIF-1α Pathway and Activation of Mitophagy Associated with Increased Reactive Oxygen Species

Methylglyoxal (MG) is a dicarbonyl compound, the level of which is increased in the blood of diabetes patients. MG is reported to be involved in the development of cerebrovascular complications in diabetes, but the exact mechanisms need to be elucidated. Here, we investigated the possible roles of oxidative stress and mitophagy in MG-induced functional damage in brain endothelial cells (ECs). Treatment of MG significantly altered metabolic stress as observed by the oxygen-consumption rate and barrier-integrity as found in impaired trans-endothelial electrical resistance in brain ECs. The accumulation of MG adducts and the disturbance of the glyoxalase system, which are major detoxification enzymes of MG, occurred concurrently. Reactive oxygen species (ROS)-triggered oxidative damage was observed with increased mitochondrial ROS production and the suppressed Akt/hypoxia-inducible factor 1 alpha (HIF-1α) pathway. Along with the disturbance of mitochondrial bioenergetic function, parkin-1-mediated mitophagy was increased by MG. Treatment of N-acetyl cysteine significantly reversed mitochondrial damage and mitophagy. Notably, MG induced dysregulation of tight junction proteins including occludin, claudin-5, and zonula occluden-1 in brain ECs. Here, we propose that diabetic metabolite MG-associated oxidative stress may contribute to mitochondrial damage and autophagy in brain ECs, resulting in the dysregulation of tight junction proteins and the impairment of permeability.

Autophagy Functions to Prevent Methylglyoxal-Induced Apoptosis in HK-2 Cells

Methylglyoxal (MGO), a reactive carbonyl species, causes cellular damage and is closely related to kidney disease, particularly diabetic nephropathy. Although MGO has been reported to induce autophagy and apoptosis, the relationships between the two pathways are unclear. Here, we evaluated whether autophagy may be the underlying mechanism inhibiting MGO-induced apoptosis. MGO treatment induced concentration- and time-dependent apoptosis in HK-2 cells. Moreover, MGO upregulated the autophagy markers p62 and LC3-II. Apoptosis caused by MGO was increased in ATG5-knockdown cells compared to that in wild-type cells. In contrast, autophagy activation by 5-aminoimidazole-4-carboxamide ribonucleotide resulted in reduced apoptosis, suggesting that autophagy played a role in protecting against MGO-induced cell death. To examine the mechanisms through which autophagy occurred following MGO stimulation, we investigated changes in AKT/mammalian target of rapamycin (mTOR) signaling. Autophagy induction by MGO treatment was not related to AKT/mTOR signaling; however, it did involve autophagy-related gene expression promoted by AMP-activated protein kinase-mediated transcription factors, such as forkhead box 1. Overall, our findings indicate that MGO-induced cellular damage can be mitigated by autophagy, suggesting that autophagy may be a potential therapeutic target for diseases such as diabetic nephropathy.

Protection of diabetes-induced kidney injury by phosphocreatine via the regulation of ERK/Nrf2/HO-1 signaling pathway

Diabetic nephropathy is the most common long-term complication of diabetes mellitus. The Methylglyoxal (MGO) production is mainly by metabolic pathways, such as lipolysis and glycolysis, its increases in the DM enhances oxidative stress and plays a crucial role in the diabetic nephrotic pathogenesis. Phosphocreatine (PCr) can improve lipopolysaccharide, ox-LDL-induced atherosclerosis, and alleviate vascular endothelial cell injury in diabetes. The aim of our present study is to examine the potential role of phosphocreatine (PCr) as a molecule protects against diabetes-induced Kidney Injury in-vitro and in-vivo through ERK/Nrf2/HO-1 signaling pathway. NRK-52E cells treatment with PCr obviously suppressed MGO-induced change of viability, apoptosis, coupled with decreased Bax/Bcl-2ratio, casapse-9 and caspase-3expressions. We determined the generation of reactive oxygen species (ROS) using membrane permeable fluorescent probe DCFH-DA as well as intracellular calcium by flow cytometry. ERK, Nrf2 and HO-1 expressions were determined by Western blot. PCr pretreatment significantly returned the oxidative stress enzymes to normal condition in-vitro and in-vivo. PCr pretreatment significantly reduced apoptosis, calcium and ROS production, induced by MGO, in NRK-52E cells. Moreover, pretreatment with PCr significantly inhibited cleaved caspase-3, cleaved caspase-9 and p-ERK expressions, while increased Nrf-2 and HO-1 expressions. Furthermore, PCr pretreatment significantly decreased p-ERK expression of MGO-induced injury in NRK-52E cells transfected with p-ERK cDNA. In conclusion, the renal protective effect of PCr in-vitro and in-vivo depends on suppressing apoptosis and ROS generation through ERK mediated Nrf-2/HO-1 pathway, suggesting that PCr may be a novel therapeutic candidate for the diabetic nephropathy treatment.

Repeated Methylglyoxal Treatment Depletes Dopamine in the Prefrontal Cortex, and Causes Memory Impairment and Depressive-Like Behavior in Mice

Methylglyoxal (MGO) is a highly reactive dicarbonyl molecule that promotes the formation of advanced glycation end products (AGEs), which are believed to play a key role in a number of pathologies, such as diabetes, Alzheimer's disease, and inflammation. Here, Swiss mice were treated with MGO by intraperitoneal injection to investigate its effects on motor activity, mood, and cognition. Acute MGO treatment heavily decreased locomotor activity in the open field test at higher doses (80-200 mg/kg), an effect not observed at lower doses (10-50 mg/kg). Several alterations were observed 4 h after a single MGO injection (10-50 mg/kg): (a) plasma MGO levels were increased, (b) memory was impaired (object location task), (c) anxiolytic behavior was observed in the open field and marble burying test, and (d) depressive-like behavior was evidenced as evaluated by the tail suspension test. Biochemical alterations in the glutathione and glyoxalase systems were not observed 4 h after MGO treatment. Mice were also treated daily with MGO at 0, 10, 25 and 50 mg/kg for 11 days. From the 5th to the 11th day, several behavioral end points were evaluated, resulting in: (a) absence of motor impairment as evaluated in the open field, horizontal bars and pole test, (b) depressive-like behavior observed in the tail suspension test, and (c) cognitive impairments detected on working, short- and long-term memory when mice were tested in the Y-maze spontaneous alternation, object location and recognition tests, and step-down inhibitory avoidance task. An interesting finding was a marked decrease in dopamine levels in the prefrontal cortex of mice treated with 50 mg/kg MGO for 11 days, along with a ~ 25% decrease in the Glo1 content. The MGO-induced dopamine depletion in the prefrontal cortex may be related to the observed memory deficits and depressive-like behavior, an interesting topic to be further studied as a potentially novel route for MGO toxicity.

Rapid and persistent loss of TXNIP in HT22 neuronal cells under carbonyl and hyperosmotic stress

Thioredoxin interacting protein (TXNIP) binds to thioredoxin thereby limiting its activity, but it also promotes internalization of glucose transporters, participates in inflammasome activation, and controls autophagy. Published data and this work demonstrate that TXNIP responds to a number of apparently unrelated stresses, such as serum deprivation, pH change, and oxidative, osmotic and carbonyl stress. Interestingly, we noticed that hyperosmotic (NaCl) and carbonyl (methylglyoxal, MGO) stresses in HT22 neuronal cells produced a rapid loss of TXNIP (half-life ∼12 min), prompting us to search for possible mechanisms controlling this TXNIP loss, including pH change, serum deprivation, calcium metabolism and inhibition of the proteasome and other proteases, autophagy and MAPKs. None of these routes stopped the TXNIP loss induced by hyperosmotic and carbonyl stress. Besides transcriptional, translational and microRNA regulation, there is evidence indicating that mTOR and AMPK also control TXNIP expression. Indeed, AMPK-deficient mouse embryonic fibroblasts failed to respond to phenformin (AMPK activator) and compound C (AMPK inhibitor), while rapamycin induced a marked increase in TXNIP levels, confirming the known AMPK/mTOR control over TXNIP. However, the TXNIP loss induced by NaCl or MGO were observed even in AMPK deficient MEFs or after mTOR inhibition, indicating AMPK/mTOR does not participate in this rapid TXNIP loss. These results suggest that rapid TXNIP loss is a general and immediate response to stress that can improve energy availability and antioxidant protection, eventually culminating in better cell survival.

Ginsenoside Rb1 mitigates oxidative stress and apoptosis induced by methylglyoxal in SH-SY5Y cells via the PI3K/Akt pathway

Diabetic encephalopathy is a severe diabetic complication characterized by cognitive dysfunction and neuropsychiatric disability. Methylglyoxal (MGO), a highly reactive metabolite of hyperglycemia, serves as a major precursor of advanced glycation end products that play key roles in diabetic complications. Ginsenoside Rb1 (abbreviated as Rb1) has received extensive attention due to its potential therapeutic effects on diabetes and neurodegeneration. Therefore, this study aimed to investigate the effects of Rb1 on MGO-induced damage in SH-SY5Y cells and the related mechanism. SH-SY5Y cells were pretreated with Rb1 for 8 h and then exposed to MGO (0.5 mM) for 24 h. Cell survival was assessed by the MTT assay. Cell apoptosis was assessed using Hoechst 33342/propidium iodide (PI) staining and an Annexin-V/PI kit. The activities of oxidative stress markers were examined using commercial kits. Reactive oxygen species (ROS) staining and JC-1 staining were used to evaluate mitochondria injury. In addition, protein levels were measured by Western blot analysis. As a result, Rb1 alleviated the injury induced by MGO by increasing the activities of superoxide dismutase, catalase and total glutathione, decreasing the level of malondialdehyde, and alleviating mitochondrial damage and ROS production. Furthermore, Rb1 could enhance the Bcl-2/Bax ratio, inhibit the expression of cleaved caspase-3 and cleaved caspase-9, and enhance the levels of phosphorylated Akt. Moreover, the protective effects of Rb1 against MGO-induced apoptosis were partly abolished by LY294002, a specific inhibitor of phosphatidylinositol 3-kinase (PI3K) phosphorylation. Our results demonstrated that Rb1 ameliorated MGO-induced oxidative stress and apoptosis in SH-SY5Y cells via activating the PI3K/Akt signaling pathway.

Synthesis and metabolism of methylglyoxal, S-D-lactoylglutathione and D-lactate in cancer and Alzheimer's disease. Exploring the crossroad of eternal youth and premature aging

Both cancer and Alzheimer's disease (AD) are emerging as metabolic diseases in which aberrant/dysregulated glucose metabolism and bioenergetics occur, and play a key role in disease progression. Interestingly, an enhancement of glucose uptake, glycolysis and pentose phosphate pathway occurs in both cancer cells and amyloid-β-resistant neurons in the early phase of AD. However, this metabolic shift has its adverse effects. One of them is the increase in methylglyoxal production, a physiological cytotoxic by-product of glucose catabolism. Methylglyoxal is mainly detoxified via cytosolic glyoxalase route comprising glyoxalase 1 and glyoxalase 2 with the production of S-D-lactoylglutathione and D-lactate as intermediate and end-product, respectively. Due to the existence of mitochondrial carriers and intramitochondrial glyoxalase 2 and D-lactate dehydrogenase, the transport and metabolism of both S-D-lactoylglutathione and D-lactate in mitochondria can contribute to methylglyoxal elimination, cellular antioxidant power and energy production. In this review, it is supposed that the different ability of cancer cells and AD neurons to metabolize methylglyoxal, S-D-lactoylglutathione and D-lactate scores cell fate, therefore being at the very crossroad of the "eternal youth" of cancer and the "premature death" of AD neurons. Understanding of these processes would help to elaborate novel metabolism-based therapies for cancer and AD treatment.

Hyperosmotic Stress Initiates AMPK-Independent Autophagy and AMPK- and Autophagy-Independent Depletion of Thioredoxin 1 and Glyoxalase 2 in HT22 Nerve Cells

Background

Hyperosmotic stress is an important pathophysiologic condition in diabetes, severe trauma, dehydration, infection, and ischemia. Furthermore, brain neuronal cells face hyperosmotic stress in ageing and Alzheimer's disease. Despite the enormous importance of knowing the homeostatic mechanisms underlying the responses of nerve cells to hyperosmotic stress, this topic has been underrepresented in the literature. Recent evidence points to autophagy induction as a hallmark of hyperosmotic stress, which has been proposed to be controlled by mTOR inhibition as a consequence of AMPK activation. We previously showed that methylglyoxal induced a decrease in the antioxidant proteins thioredoxin 1 (Trx1) and glyoxalase 2 (Glo2), which was mediated by AMPK-dependent autophagy. Thus, we hypothesized that hyperosmotic stress would have the same effect.

Methods

HT22 hippocampal nerve cells were treated with NaCl (37, 75, or 150 mM), and the activation of the AMPK/mTOR pathway was investigated, as well as the levels of Trx1 and Glo2. To determine if autophagy was involved, the inhibitors bafilomycin (Baf) and chloroquine (CQ), as well as ATG5 siRNA, were used. To test for AMPK involvement, AMPK-deficient mouse embryonic fibroblasts (MEFs) were used.

Results

Hyperosmotic stress induced a clear increase in autophagy, which was demonstrated by a decrease in p62 and an increase in LC3 lipidation. AMPK phosphorylation, linked to a decrease in mTOR and S6 ribosomal protein phosphorylation, was also observed. Deletion of AMPK in MEFs did not prevent autophagy induction by hyperosmotic stress, as detected by decreased p62 and increased LC3 II, or mTOR inhibition, inferred by decreased phosphorylation of P70 S6 kinase and S6 ribosomal protein. These data indicating that AMPK was not involved in autophagy activation by hyperosmotic stress were supported by a decrease in p^S555-ULK1, an AMPK phosphorylation site. Trx1 and Glo2 levels were decreased at 6 and 18 h after treatment with 150 mM NaCl. However, this decrease in Trx1 and Glo2 in HT22 cells was not prevented by autophagy inhibition by Baf, CQ, or ATG5 siRNA. AMPK-deficient MEFs under hyperosmotic stress presented the same Trx1 and Glo2 decrease as wild-type cells.

Conclusion

Hyperosmotic stress induced AMPK activation, but this was not responsible for its effects on mTOR activity or autophagy induction. Moreover, the decrease in Trx1 and Glo2 induced by hyperosmotic stress was independent of both autophagy and AMPK activation.

Methylglyoxal down-regulates the expression of cell cycle associated genes and activates the p53 pathway in human umbilical vein endothelial cells

Although methylglyoxal (MGO) has emerged as key mediator of diabetic microvascular complications, the influence of MGO on the vascular transcriptome has not thoroughly been assessed. Since diabetes is associated with low grade inflammation causing sustained nuclear factor-kappa B (NF-κB) activation, the current study addressed 1) to what extent MGO changes the transcriptome of human umbilical vein endothelial cells (HUVECs) exposed to an inflammatory milieu, 2) what are the dominant pathways by which these changes occur and 3) to what extent is this affected by carnosine, a putative scavenger of MGO. Microarray analysis revealed that exposure of HUVECs to high MGO concentrations significantly changes gene expression, characterized by prominent down-regulation of cell cycle associated genes and up-regulation of heme oxygenase-1 (HO-1). KEGG-based pathway analysis identified six significantly enriched pathways of which the p53 pathway was the most affected. No significant enrichment of inflammatory pathways was found, yet, MGO did inhibit VCAM-1 expression in Western blot analysis. Carnosine significantly counteracted MGO-mediated changes in a subset of differentially expressed genes. Collectively, our results suggest that MGO initiates distinct transcriptional changes in cell cycle/apoptosis genes, which may explain MGO toxicity at high concentrations. MGO did not augment TNF-α induced inflammation.

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.