Alternative antiglycation mechanisms: are spermine and fructosamine-3-kinase part of a carbonyl damage control pathway?

Differential Role of Active Compounds in Mitophagy and Related Neurodegenerative Diseases

Neurodegenerative diseases, such as Alzheimer’s disease or Parkinson’s disease, significantly reduce the quality of life of patients and eventually result in complete maladjustment. Disruption of the synapses leads to a deterioration in the communication of nerve cells and decreased plasticity, which is associated with a loss of cognitive functions and neurodegeneration. Maintaining proper synaptic activity depends on the qualitative composition of mitochondria, because synaptic processes require sufficient energy supply and fine calcium regulation. The maintenance of the qualitative composition of mitochondria occurs due to mitophagy. The regulation of mitophagy is usually based on several internal mechanisms, as well as on signals and substances coming from outside the cell. These substances may directly or indirectly enhance or weaken mitophagy. In this review, we have considered the role of some compounds in process of mitophagy and neurodegeneration. Some of them have a beneficial effect on the functions of mitochondria and enhance mitophagy, showing promise as novel drugs for the treatment of neurodegenerative pathologies, while others contribute to a decrease in mitophagy.

The Taming of Nuclear Factor Erythroid-2-Related Factor-2 (Nrf2) Deglycation by Fructosamine-3-Kinase (FN3K)-Inhibitors-A Novel Strategy to Combat Cancers

Simple Summary

Aim of this review is to provide an overview on (a) Fructosamine-3-Kinase (FN3K) and its role in regulating Nuclear Factor Erythorid-2-Related Factor-2 (Nrf2); (b) the role of glycation and deglycation mechanisms in modulating the functional properties of proteins, in particular, the Nrf2; (c) the dual role of Nrf2 in the prevention and treatment of cancers. Since controlling the glycation of Nrf2 is one of the key mechanisms determining the fate of a cell; whether to get transformed into a cancerous one or to stay as a normal one, it is important to regulate Nrf2 and deglycating FN3K using pharmacological agents. Inhibitors of FN3K are being explored currently to modulate Nrf2 activity thereby control the cancers.

Abstract

Glycated stress is mediated by the advanced glycation end products (AGE) and the binding of AGEs to the receptors for advanced glycation end products (RAGEs) in cancer cells. RAGEs are involved in mediating tumorigenesis of multiple cancers through the modulation of several downstream signaling cascades. Glycated stress modulates various signaling pathways that include p38 mitogen-activated protein kinase (p38 MAPK), nuclear factor kappa–B (NF-κB), tumor necrosis factor (TNF)-α, etc., which further foster the uncontrolled proliferation, growth, metastasis, angiogenesis, drug resistance, and evasion of apoptosis in several cancers. In this review, a balanced overview on the role of glycation and deglycation in modulating several signaling cascades that are involved in the progression of cancers was discussed. Further, we have highlighted the functional role of deglycating enzyme fructosamine-3-kinase (FN3K) on Nrf2-driven cancers. The activity of FN3K is attributed to its ability to deglycate Nrf2, a master regulator of oxidative stress in cells. FN3K is a unique protein that mediates deglycation by phosphorylating basic amino acids lysine and arginine in various proteins such as Nrf2. Deglycated Nrf2 is stable and binds to small musculoaponeurotic fibrosarcoma (sMAF) proteins, thereby activating cellular antioxidant mechanisms to protect cells from oxidative stress. This cellular protection offered by Nrf2 activation, in one way, prevents the transformation of a normal cell into a cancer cell; however, in the other way, it helps a cancer cell not only to survive under hypoxic conditions but also, to stay protected from various chemo- and radio-therapeutic treatments. Therefore, the activation of Nrf2 is similar to a double-edged sword and, if not controlled properly, can lead to the development of many solid tumors. Hence, there is a need to develop novel small molecule modulators/phytochemicals that can regulate FN3K activity, thereby maintaining Nrf2 in a controlled activation state.

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

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

Methylglyoxal synthase regulates cell elongation via alterations of cellular methylglyoxal and spermidine content in Bacillus subtilis

Methylglyoxal regulates cell division and differentiation through its interaction with polyamines. Loss of their biosynthesizing enzyme causes physiological impairment and cell elongation in eukaryotes. However, the reciprocal effects of methylglyoxal and polyamine production and its regulatory metabolic switches on morphological changes in prokaryotes have not been addressed. Here, Bacillus subtilis methylglyoxal synthase (mgsA) and polyamine biosynthesizing genes encoding arginine decarboxylase (SpeA), agmatinase (SpeB), and spermidine synthase (SpeE), were disrupted or overexpressed. Treatment of 0.2mM methylglyoxal and 1mM spermidine led to the elongation and shortening of B. subtilis wild-type cells to 12.38±3.21μm (P<0.05) and 3.24±0.73μm (P<0.01), respectively, compared to untreated cells (5.72±0.68μm). mgsA-deficient (mgsA^-) and -overexpressing (mgsA^OE) mutants also demonstrated cell shortening and elongation, similar to speB- and speE-deficient (speB^- and speE^-) and -overexpressing (speB^OE and speE^OE) mutants. Importantly, both mgsA-depleted speB^OE and speE^OE mutants (speB^OE/mgsA^- and speE^OE/mgsA^-) were drastically shortened to 24.5% and 23.8% of parental speB^OE and speE^OE mutants, respectively. These phenotypes were associated with reciprocal alterations of mgsA and polyamine transcripts governed by the contents of methylglyoxal and spermidine, which are involved in enzymatic or genetic metabolite-control mechanisms. Additionally, biophysically detected methylglyoxal-spermidine Schiff bases did not affect morphogenesis. Taken together, the findings indicate that methylglyoxal triggers cell elongation. Furthermore, cells with methylglyoxal accumulation commonly exhibit an elongated rod-shaped morphology through upregulation of mgsA, polyamine genes, and the global regulator spx, as well as repression of the cell division and shape regulator, FtsZ.

Schiff bases of putrescine with methylglyoxal protect from cellular damage caused by accumulation of methylglyoxal and reactive oxygen species in Dictyostelium discoideum

Polyamines protect protein glycation in cells against the advanced glycation end product precursor methylglyoxal, which is inevitably produced during glycolysis, and the enzymes that detoxify this α-ketoaldehyde have been widely studied. Nonetheless, nonenzymatic methylglyoxal-scavenging molecules have not been sufficiently studied either in vitro or in vivo. Here, we hypothesized reciprocal regulation between polyamines and methylglyoxal modeled in Dictyostelium grown in a high-glucose medium. We based our hypothesis on the reaction between putrescine and methylglyoxal in putrescine-deficient (odc^-) or putrescine-overexpressing (odc^oe) cells. In these strains, growth and cell cycle were found to be dependent on cellular methylglyoxal and putrescine contents. The odc^- cells showed growth defects and underwent G1 phase cell cycle arrest, which was efficiently reversed by exogenous putrescine. Cellular methylglyoxal, reactive oxygen species (ROS), and glutathione levels were remarkably changed in odc^oe cells and odc̄ cells. These results revealed that putrescine may act as an intracellular scavenger of methylglyoxal and ROS. Herein, we observed interactions of putrescine and methylglyoxal via formation of a Schiff base complex, by UV-vis spectroscopy, and confirmed this adduct by liquid chromatography with mass spectrometry via electrospray ionization. Schiff bases were isolated, analyzed, and predicted to have molecular masses ranging from 124 to 130. We showed that cellular putrescine-methylglyoxal Schiff bases were downregulated in proportion to the levels of endogenous or exogenous putrescine and glutathione in the odc mutants. The putrescine-methylglyoxal Schiff base affected endogenous metabolite levels. This is the first report showing that cellular methylglyoxal functions as a signaling molecule through reciprocal interactions with polyamines by forming Schiff bases.

"Blinding" of AMP-dependent kinase by methylglyoxal: a mechanism that allows perpetuation of hepatic insulin resistance?

AMP-dependent kinase (AMPK) is a regulatory carrefour and a key target for therapeutics. The role of AMPK in regulating cellular energy status (by sensing low energy using [AMP] as its signal) and activating catabolic pathways while inhibiting anabolic routes, places this enzyme at a central control point in maintaining energy homeostasis. The exquisite allosteric sensing of AMP is done by a domain with three arginine residues, which make it very vulnerable to glycation, especially by the alpha-dicarbonyl methylglyoxal (MG). MG accumulates in hyperglycemia, insulin resistance, diabetes and when there is excess flux of reactive oxygen species coming from the mitochondria. We hypothesize that excess MG in the above-mentioned conditions blocks the sensing of AMP by AMPK, thereby favoring gluconeogenesis (thus hepatic glucose output and hyperglycemia) and lipogenesis (hepatic steatosis and high VLDL), hallmarks of insulin resistance and diabetes. Our hypothesis may explain, for instance, the perpetuation of hepatic insulin resistance, as well as part of the action of metformin, which is a potent anti-glycation agent. Future targets for type 2 diabetes treatments will likely be those that can effect beneficial changes in the activity of AMPK, and our theory predicts that anti-glycation agents may become part of that armamentarium.

Clinical impact of variability in HbA1c as assessed by simultaneously measuring fructosamine and use of error grid analysis

BACKGROUND

Haemoglobin A1c (HbA1c) is the only measure of glycaemic control used for many patients with diabetes, but it has limitations and might sometimes be misleading. HbA(1c) concentrations are influenced by conditions that alter red-cell life and there is evidence that biochemical variation in intracellular glycation rates also influence HbA1c concentrations. This paper is the first to propose a method of using simultaneously measured HbA1c and fructosamine, and error grid analysis, in the clinical setting, to gain a better understanding of glycaemic control.

METHODS

Cross-sectional analytical study using HbA1c and fructosamine measures on the same blood sample from 1744 patients having blood taken for hospital diabetes clinic appointments. No other selection or exclusion criteria were applied.

RESULTS

The fructosamine results were converted to a HbA1c equivalent which was then compared with the HbA1c. In an Altman-Bland plot, the paired result differences ranged between -6.9% and +5.5% HbA1c with 1139 (65%), 438 (25%), 130 (8%) and 37 (2%) being < or =1%, 1-2%, 2-3% or >3% of HbA1c difference, respectively. In clinical error grid analysis, 864 (50%) results had tight concordance for clinical interpretation, 761 (43%) had one block disunity of probably little clinical significance, but 105 (6%) were two blocks and 14 (1%) were three blocks discordant.

CONCLUSION

HbA1c may not accurately reflect glucose control. Our method, utilizing co-assessment with serum fructosamine, evaluates the possible clinical impact of this. We suggest the analysis used in this paper should be used routinely in diabetes practice.

Relationships among carbohydrate intermediate metabolites and DNA damage and repair in yeast from a systems biology perspective

Glucose and fructose are major dietary carbohydrates that are essential for general metabolism. The elevated consumption of these two monosaccharides by the human population is related to the development of pluri-metabolic syndromes (e.g., diabetes mellitus and obesity). Glucose and fructose are metabolized by specific biochemical pathways to generate energy and metabolites. Many of these metabolites are mono- and bi-phosphorylated compounds, which renders them likely to generate reactive carbonyl species (RCS). Under physiological conditions, RCS react non-enzymatically with macromolecules and small molecules by means of Maillard reactions, forming stable glycated/fructated compounds called advanced glycation end products (AGEs). DNA and dNTPs are prone to react with RCS, forming DNA- and dNTP-AGEs, and many of these compounds are genotoxic and/or mutagenic. Unfortunately, little is understood about the genotoxicity and/or mutagenicity of carbohydrate intermediate metabolites or their interactions with DNA repair and carbohydrate metabolic-associated proteins. To elucidate these associations between carbohydrate metabolic pathways, DNA repair mechanisms, and dNTP-/DNA-AGEs, a systems biology study was performed by employing algorithms to mine literature data and construct physical protein-protein interactions. The results obtained in this work allow us to construct a model suggesting that yeast carbohydrate metabolic-associated enzymes activate different mechanisms for DNA repair and dNTP synthesis and act during DNA replication to protect the genome against the effects of RCS.

Protection against glycation and similar post-translational modifications of proteins

Glycation and other non-enzymic post-translational modifications of proteins have been implicated in the complications of diabetes and other conditions. In recent years there has been extensive progress in the search for ways to prevent the modifications and prevent the consequences of the modifications. These areas are covered in this review together with newer ideas on possibilities of reversing the chemical modifications.

Does chronic glycolysis accelerate aging? Could this explain how dietary restriction works?

The mechanisms by which dietary restriction (DR) suppresses aging are not understood. Suppression of glycolysis by DR could contribute to controlling senescence. Many glycolytic intermediates can glycate proteins and other macromolecules. Methyglyoxal (MG), formed from dihydroxyacetone- and glyceraldehyde-3-phosphates, rapidly glycates proteins, damages mitochondria, and induces a prooxidant state to create a senescent-like condition. Ad libitum-fed and DR animals differ in mitochondrial activity and glycolytic flux rates. Persistent glycolysis in the unrestricted condition would increase the intracellular load of glycating agents (e.g., MG) and increase ROS generation by inactive mitochondria. Occasional glycolysis during DR would decrease MG and reactive oxygen species (ROS) production and could be hormetic, inducing synthesis of glyoxalase-1 and anti-glycating agents (carnosine and polyamines).

On the mechanisms of ageing suppression by dietary restriction-is persistent glycolysis the problem?

The mechanism(s) by which dietary restriction (DR) suppresses ageing and onset of age-related pathologies are discussed in relation to frequency of glycolysis, and the reactivity of glycolytic intermediates. Most glycolytic intermediates are potentially toxic and readily modify (i.e. glycate) proteins and other macromolecules non-enzymically. Attention is drawn to the reactivity of methyglyoxal (MG) which is formed predominantly from the glycolytic intermediates dihydroxyacetone- and glyceraldehyde-3-phosphates. MG rapidly glycates proteins, damages mitochondria and induces a pro-oxidant state, similar to that observed in aged cells. It is suggested that because DR animals' energy metabolism is less glycolytic than in those fed ad libitum, intracellular MG levels are lowered by DR The decreased glycolysis during DR may delay senescence by lowering intracellular MG concentration compared to ad libitum-fed animals. Because of the reactivity MG and glycolytic intermediates, occasional glycolysis could be hormetic where glyoxalase, carnosine synthetase and ornithine decarboxylase are upregulated to control cellular MG concentration. It is suggested that in ad libitum-fed animals persistent glycolysis permanently raises MG levels which progressively overwhelm protective processes, particularly in non-mitotic tissues, to create the senescent state earlier than in DR animals. The possible impact of diet and intracellular glycating agents on age-related mitochondrial dysfunction is also discussed.