Hormesis enables cells to handle accumulating toxic metabolites during increased energy flux

Low salinity influences the dose-dependent transcriptomic responses of oysters to cadmium

Species in estuaries tend to undergo both cadmium (Cd) and low salinity stress. However, how low salinity affects the Cd toxicity has not been fully understood. Investigating the impacts of low salinity on the dose-response relationships between Cd and biological endpoints has potential to enhance our understanding of the combined effects of low salinity and Cd. In this work, changes in the transcriptomes of Pacific oysters were analyzed following exposure to Cd (5, 20, 80 μg/L Cd2+) under normal (31.4 psu) and low (15.7 psu) salinity conditions, and then the dose-response relationship between Cd and transcriptome was characterized in a high-throughput manner. The benchmark dose (BMD) of gene expression, as a point of departure (POD), was also calculated based on the fitted dose-response model. We found that low salinity treatment significantly influenced the dose-response relationships between Cd and transcripts in oysters indicated by altered dose-response curves. In details, a total of 219 DEGs were commonly fitted to best models under both normal and low salinity conditions. Nearly three quarters of dose-response curves varied with salinity condition. Some monotonic dose-response curves in normal salinity condition even were replaced by nonmonotonic curves in low salinity condition. Low salinity treatment decreased the PODs of differentially expressed genes induced by Cd, suggesting that gene differential expression was more prone to being triggered by Cd in low salinity condition. The changed sensitivity to Cd in low salinity condition should be taken into consideration when using oyster as an indicator to assess the ecological risk of Cd pollution in estuaries.

Dietary intake of dicarbonyl compounds and changes in body weight over time in a large cohort of European adults

Dicarbonyl compounds are highly reactive precursors of advanced glycation end products (AGE), produced endogenously, present in certain foods and formed during food processing. AGE contribute to the development of adverse metabolic outcomes, but health effects of dietary dicarbonyls are largely unexplored. We investigated associations between three dietary dicarbonyl compounds, methylglyoxal (MGO), glyoxal (GO) and 3-deoxyglucosone (3-DG), and body weight changes in European adults. Dicarbonyl intakes were estimated using food composition database from 263 095 European Prospective Investigation into Cancer and Nutrition-Physical Activity, Nutrition, Alcohol, Cessation of Smoking, Eating Out of Home in Relation to Anthropometry participants with two body weight assessments (median follow-up time = 5·4 years). Associations between dicarbonyls and 5-year body-weight changes were estimated using mixed linear regression models. Stratified analyses by sex, age and baseline BMI were performed. Risk of becoming overweight/obese was assessed using multivariable-adjusted logistic regression. MGO intake was associated with 5-year body-weight gain of 0·089 kg (per 1-sd increase, 95 % CI 0·072, 0·107). 3-DG was inversely associated with body-weight change (-0·076 kg, -0·094, -0·058). No significant association was observed for GO (0·018 kg, -0·002, 0·037). In stratified analyses, GO was associated with body-weight gain among women and older participants (above median of 52·4 years). MGO was associated with higher body-weight gain among older participants. 3-DG was inversely associated with body-weight gain among younger and normal-weight participants. MGO was associated with a higher risk of becoming overweight/obese, while inverse associations were observed for 3-DG. No associations were observed for GO with overweight/obesity. Dietary dicarbonyls are inconsistently associated with body weight change among European adults. Further research is needed to clarify the role of these food components in overweight and obesity, their underlying mechanisms and potential public health implications.

Methylglyoxal in Cardiometabolic Disorders: Routes Leading to Pathology Counterbalanced by Treatment Strategies

Methylglyoxal (MGO) is the major compound belonging to reactive carbonyl species (RCS) responsible for the generation of advanced glycation end products (AGEs). Its upregulation, followed by deleterious effects at the cellular and systemic levels, is associated with metabolic disturbances (hyperglycemia/hyperinsulinemia/insulin resistance/hyperlipidemia/inflammatory processes/carbonyl stress/oxidative stress/hypoxia). Therefore, it is implicated in a variety of disorders, including metabolic syndrome, diabetes mellitus, and cardiovascular diseases. In this review, an interplay between pathways leading to MGO generation and scavenging is addressed in regard to this system's impairment in pathology. The issues associated with mechanistic MGO involvement in pathological processes, as well as the discussion on its possible causative role in cardiometabolic diseases, are enclosed. Finally, the main strategies aimed at MGO and its AGEs downregulation with respect to cardiometabolic disorders treatment are addressed. Potential glycation inhibitors and MGO scavengers are discussed, as well as the mechanisms of their action.

The Effect of Calorie Restriction on Protein Quality Control in Yeast

Initially, protein aggregates were regarded as a sign of a pathological state of the cell. Later, it was found that these assemblies are formed in response to stress, and that some of them serve as signalling mechanisms. This review has a particular focus on how intracellular protein aggregates are related to altered metabolism caused by different glucose concentrations in the extracellular environment. We summarise the current knowledge of the role of energy homeostasis signalling pathways in the consequent effect on intracellular protein aggregate accumulation and removal. This covers regulation at different levels, including elevated protein degradation and proteasome activity mediated by the Hxk2 protein, the enhanced ubiquitination of aberrant proteins through Torc1/Sch9 and Msn2/Whi2, and the activation of autophagy mediated through ATG genes. Finally, certain proteins form reversible biomolecular aggregates in response to stress and reduced glucose levels, which are used as a signalling mechanism in the cell, controlling major primary energy pathways related to glucose sensing.

Habitual intake of dietary dicarbonyls is associated with greater insulin sensitivity and lower prevalence of type 2 diabetes: The Maastricht Study

BACKGROUND

Dicarbonyls are reactive precursors of advanced glycation endproducts (AGEs). Dicarbonyls are formed endogenously, but also during food processing. Circulating dicarbonyls are positively associated with insulin resistance and type 2 diabetes, but consequences of dietary dicarbonyls are unknown.

OBJECTIVE

To examine the associations of dietary intake of dicarbonyls with insulin sensitivity, β-cell function, and prevalence of prediabetes or type 2 diabetes.

METHODS

In 6282 participants (60±9 years, 50% men, 23% type 2 diabetes (oversampled)) of the population-based cohort The Maastricht Study, we estimated habitual intake of the dicarbonyls methylglyoxal (MGO), glyoxal (GO), and 3-deoxyglucosone (3-DG) using Food Frequency Questionnaires. Insulin sensitivity (n=2390), β-cell function (n=2336) and glucose metabolism status (n=6282) were measured by a seven-point oral glucose tolerance test. Insulin sensitivity was assessed as the Matsuda index. Additionally, insulin sensitivity was measured as HOMA2-IR (n=2611). β-cell function was assessed as C-peptidogenic index, overall insulin secretion, glucose sensitivity, potentiation factor, and rate sensitivity. Cross-sectional associations of dietary dicarbonyls with these outcomes were investigated using linear or logistic regression adjusting for age, sex, cardio-metabolic risk-factors, lifestyle, and dietary factors.

RESULTS

Higher dietary MGO and 3-DG intakes were associated with greater insulin sensitivity after full adjustment, indicated by both a higher Matsuda index (MGO: Std. β [95% CI]=0.08 [0.04, 0.12] and 3-DG: 0.09 [0.05, 0.13]) and a lower HOMA2-IR (MGO: Std. β=-0.05 [-0.09, -0.01] and 3-DG: -0.04 [-0.08, -0.01]). Moreover, higher MGO and 3-DG intakes were associated with lower prevalence of newly diagnosed type 2 diabetes (OR [95%CI]=0.78 [0.65, 0.93] and 0.81 [0.66, 0.99]). There were no consistent associations of MGO, GO, and 3-DG intakes with β-cell function.

CONCLUSIONS

Higher habitual consumption of the dicarbonyls MGO and 3-DG was associated with better insulin sensitivity and with lower prevalence of type 2 diabetes, after excluding individuals with known diabetes. These novel observations warrant further exploration in prospective cohorts and intervention studies.

Oxidative stress, inflammation and hormesis: The role of dietary and lifestyle modifications on aging

Oxidative stress (OS) is primarily caused by the formation of free radicals and reactive oxygen species; it is considered as one of the prominent factors in slowing down and degrading cellular machinery of an individual, and it eventually leads to aging and age-related diseases by its continuous higher state. The relation between molecular damage and OS should be particularized to understand the beginning of destruction at the cellular levels, extending outwards to affect tissues, organs, and ultimately to the organism. Several OS biomarkers, which are established at the biomolecular level, are useful in investigating the disease susceptibility during aging. Slowing down the aging process is a matter of reducing the rate of oxidative damage to the cellular machinery over time. The breakdown of homeostasis, the mild overcompensation, the reestablishment of homeostasis, and the adaptive nature of the process are the essential features of hormesis, which incorporates several factors, including calorie restriction, nutrition and lifestyle modifications that play an important role in reducing the OS. In the current review, along with the concept and theories of aging (with emphasis on free radical theory), various manifestations of OS with special attention on mitochondrial dysfunction and age-related diseases have been discussed. To alleviate the OS, hormetic approaches including caloric restriction, exercise, and nutrition have also been discussed.

Synonymous mutations in the phosphoglycerate kinase 1 gene induce an altered response to protein misfolding in Schizosaccharomyces pombe

Background

Proteostasis refers to the processes that regulate the biogenesis, folding, trafficking, and degradation of proteins. Any alteration in these processes can lead to cell malfunction. Protein synthesis, a key proteostatic process, is highly-regulated at multiple levels to ensure adequate adaptation to environmental and physiological challenges such as different stressors, proteotoxic conditions and aging, among other factors. Because alterations in protein translation can lead to protein misfolding, examining how protein translation is regulated may also help to elucidate in part how proteostasis is controlled. Codon usage bias has been implicated in the fine-tuning of translation rate, as more-frequent codons might be read faster than their less-frequent counterparts. Thus, alterations in codon usage due to synonymous mutations may alter translation kinetics and thereby affect the folding of the nascent polypeptide, without altering its primary structure. To date, it has been difficult to predict the effect of synonymous mutations on protein folding and cellular fitness due to a scarcity of relevant data. Thus, the purpose of this work was to assess the effect of synonymous mutations in discrete regions of the gene that encodes the highly-expressed enzyme 3-phosphoglycerate kinase 1 (pgk1) in the fission yeast Schizosaccharomyces pombe.

Results

By means of systematic replacement of synonymous codons along pgk1, we found slightly-altered protein folding and activity in a region-specific manner. However, alterations in protein aggregation, heat stress as well as changes in proteasome activity occurred independently of the mutated region. Concomitantly, reduced mRNA levels of the chaperones Hsp9 and Hsp16 were observed.

Conclusion

Taken together, these data suggest that codon usage bias of the gene encoding this highly-expressed protein is an important regulator of protein function and proteostasis.

Habitual intake of dietary methylglyoxal is associated with less low-grade inflammation: the Maastricht Study

BACKGROUND

Dicarbonyls are major reactive precursors of advanced glycation endproducts (AGEs). Dicarbonyls are formed endogenously and also during food processing. Circulating dicarbonyls and AGEs are associated with inflammation and microvascular complications of diabetes, but for dicarbonyls from the diet these associations are currently unknown.

OBJECTIVES

We sought to examine the associations of dietary dicarbonyl intake with low-grade inflammation and microvascular function.

METHODS

In 2792 participants (mean ± SD age: 60 ± 8 y; 50% men; 26% type 2 diabetes) of the population-based cohort the Maastricht Study, we estimated the habitual intake of the dicarbonyls methylglyoxal (MGO), glyoxal (GO), and 3-deoxyglucosone (3-DG) by linking FFQ outcome data to our food composition database of the MGO, GO, and 3-DG content of >200 foods. Low-grade inflammation was assessed as six plasma biomarkers, which were compiled in a z score. Microvascular function was assessed as four plasma biomarkers, compiled in a zscore; as diameters and flicker light-induced dilation in retinal microvessels; as heat-induced skin hyperemic response; and as urinary albumin excretion. Cross-sectional associations of dietary dicarbonyls with low-grade inflammation and microvascular function were investigated using linear regression with adjustments for age, sex, potential confounders related to cardiometabolic risk factors, and lifestyle and dietary factors.

RESULTS

Fully adjusted analyses revealed that higher intake of MGO was associated with a lower z score for inflammation [standardized β coefficient (STD β): -0.05; 95% CI: -0.09 to -0.01, with strongest inverse associations for hsCRP and TNF-α: both -0.05; -0.10 to -0.01]. In contrast, higher dietary MGO intake was associated with impaired retinal venular dilation after full adjustment (STD β: -0.07; 95% CI: -0.12 to -0.01), but not with the other features of microvascular function. GO and 3-DG intakes were not consistently associated with any of the outcomes.

CONCLUSION

Higher habitual intake of MGO was associated with less low-grade inflammation. This novel, presumably beneficial, association is the first observation of an association between MGO intake and health outcomes in humans and warrants further investigation.

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

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

The Influence of Intracellular Glutathione Levels on the Induction of Nrf2-Mediated Gene Expression by α-Dicarbonyl Precursors of Advanced Glycation End Products

α-Dicarbonyl compounds, particularly methylglyoxal (MGO), glyoxal (GO), and 3-deoxyglucosone (3-DG), are highly reactive precursors for the formation of advanced glycation end products (AGEs). They are formed in vivo and during food processing. This study aimed to investigate the role of intracellular glutathione (GSH) levels in the induction of Nrf2-mediated gene expression by α-dicarbonyl compounds. The reactions between α-dicarbonyl compounds (MGO, GO, and 3-DG) and GSH were studied by LC-MS in a cell-free system. It was shown that these three α-dicarbonyl compounds react instantaneously with GSH, with the GSH-mediated scavenging decreasing in the order MGO > GO > 3DG. Furthermore, in a cell-based reporter gene assay MGO, GO, and 3-DG were able to induce Nrf2-mediated gene expression in a dose-dependent manner. Modulation of intracellular GSH levels showed that the cytotoxicity and induction of the Nrf2-mediated pathway by MGO, GO and 3-DG was significantly enhanced by depletion of GSH, while a decrease in Nrf2-activation by MGO and GO but not 3-DG was observed upon an increase of the cellular GSH levels. Our results reveal subtle differences in the role of GSH in protection against the three typical α-dicarbonyl compounds and in their induction of Nrf2-mediated gene expression, and point at a dual biological effect of the α-dicarbonyl compounds, being reactive toxic electrophiles and -as a consequence- able to induce Nrf2-mediated protective gene expression, with MGO being most reactive.

Higher habitual intake of dietary dicarbonyls is associated with higher corresponding plasma dicarbonyl concentrations and skin autofluorescence: the Maastricht Study

BACKGROUND

Dicarbonyls are highly reactive compounds and major precursors of advanced glycation end products (AGEs). Both dicarbonyls and AGEs are associated with development of age-related diseases. Dicarbonyls are formed endogenously but also during food processing. To what extent dicarbonyls from the diet contribute to circulating dicarbonyls and AGEs in tissues is unknown.

OBJECTIVES

To examine cross-sectional associations of dietary dicarbonyl intake with plasma dicarbonyl concentrations and skin AGEs.

METHODS

In 2566 individuals of the population-based Maastricht Study (age: 60 ± 8 y, 50% males, 26% with type 2 diabetes), we estimated habitual intake of the dicarbonyls methylglyoxal (MGO), glyoxal (GO), and 3-deoxyglucosone (3-DG) by combining FFQs with our dietary dicarbonyl database of MGO, GO, and 3-DG concentrations in > 200 commonly consumed food products. Fasting plasma concentrations of MGO, GO, and 3-DG were measured by ultra-performance liquid chromatography-tandem mass spectrometry. Skin AGEs were measured as skin autofluorescence (SAF), using the AGE Reader. Associations of dietary dicarbonyl intake with their respective plasma concentrations and SAF (all standardized) were examined using linear regression models, adjusted for age, sex, potential confounders related to cardiometabolic risk factors, and lifestyle.

RESULTS

Median intake of MGO, GO, and 3-DG was 3.6, 3.5, and 17 mg/d, respectively. Coffee was the main dietary source of MGO, whereas this was bread for GO and 3-DG. In the fully adjusted models, dietary MGO was associated with plasma MGO (β: 0.08; 95% CI: 0.02, 0.13) and SAF (β: 0.12; 95% CI: 0.07, 0.17). Dietary GO was associated with plasma GO (β: 0.10; 95% CI: 0.04, 0.16) but not with SAF. 3-DG was not significantly associated with either plasma 3-DG or SAF.

CONCLUSIONS

Higher habitual intake of dietary MGO and GO, but not 3-DG, was associated with higher corresponding plasma concentrations. Higher intake of MGO was also associated with higher SAF. These results suggest dietary absorption of MGO and GO. Biological implications of dietary absorption of MGO and GO need to be determined. The study has been approved by the institutional medical ethical committee (NL31329.068.10) and the Minister of Health, Welfare and Sports of the Netherlands (Permit 131088-105234-PG).

Metformin prevents methylglyoxal-induced apoptosis by suppressing oxidative stress in vitro and in vivo

Methylglyoxal (MGO) is an active metabolite of glucose and plays a prominent role in the pathogenesis of diabetic vascular complications, including endothelial cell apoptosis induced by oxidative stress. Metformin (MET), a widely prescribed antidiabetic agent, appears to reduce excessive reactive oxygen species (ROS) generation and limit cell apoptosis. However, the molecular mechanisms underlying this process are still not fully elucidated. We reported here that MET prevents MGO-induced apoptosis by suppressing oxidative stress in vitro and in vivo. Protein expression and protein phosphorylation were investigated using western blotting, ELISA, and immunohistochemical staining, respectively. Cell viability and apoptosis were assessed by the MTT assay, TUNEL staining, and Annexin V-FITC and propidium iodide double staining. ROS generation and mitochondrial membrane potential (MMP) were measured with fluorescent probes. Our results revealed that MET prevented MGO-induced HUVEC apoptosis, inhibited apoptosis-associated biochemical changes such as loss of MMP, the elevation of the Bax/Bcl-2 ratio, and activation of cleaved caspase-3, and attenuated MGO-induced mitochondrial morphological alterations in a dose-dependent manner. MET pretreatment also significantly suppressed MGO-stimulated ROS production, increased signaling through the ROS-mediated PI3K/Akt and Nrf2/HO-1 pathways, and markedly elevated the levels of its downstream antioxidants. Finally, similar results were obtained in vivo, and we demonstrated that MET prevented MGO-induced oxidative damage, apoptosis, and inflammation. As expected, MET reversed MGO-induced downregulation of Nrf2 and p-Akt. In addition, a PI3K inhibitor (LY-294002) and a Nrf2 inhibitor (ML385) observably attenuated the protective effects of MET on MGO-induced apoptosis and ROS generation by inhibiting the Nrf2/HO-1 pathways, while a ROS scavenger (NAC) and a permeability transition pores inhibitor (CsA) completely reversed these effects. Collectively, these findings broaden our understanding of the mechanism by which MET regulates apoptosis induced by MGO under oxidative stress conditions, with important implications regarding the potential application of MET for the treatment of diabetic vascular complications.

Mapping protein carboxymethylation sites provides insights into their role in proteostasis and cell proliferation

Posttranslational mechanisms play a key role in modifying the abundance and function of cellular proteins. Among these, modification by advanced glycation end products has been shown to accumulate during aging and age-associated diseases but specific protein targets and functional consequences remain largely unexplored. Here, we devise a proteomic strategy to identify sites of carboxymethyllysine modification, one of the most abundant advanced glycation end products. We identify over 1000 sites of protein carboxymethylation in mouse and primary human cells treated with the glycating agent glyoxal. By using quantitative proteomics, we find that protein glycation triggers a proteotoxic response and indirectly affects the protein degradation machinery. In primary endothelial cells, we show that glyoxal induces cell cycle perturbation and that carboxymethyllysine modification reduces acetylation of tubulins and impairs microtubule dynamics. Our data demonstrate the relevance of carboxymethyllysine modification for cellular function and pinpoint specific protein networks that might become compromised during aging.

Less Can Be More: The Hormesis Theory of Stress Adaptation in the Global Biosphere and Its Implications

A dose-response relationship to stressors, according to the hormesis theory, is characterized by low-dose stimulation and high-dose inhibition. It is non-linear with a low-dose optimum. Stress responses by cells lead to adapted vitality and fitness. Physical stress can be exerted through heat, radiation, or physical exercise. Chemical stressors include reactive species from oxygen (ROS), nitrogen (RNS), and carbon (RCS), carcinogens, elements, such as lithium (Li) and silicon (Si), and metals, such as silver (Ag), cadmium (Cd), and lead (Pb). Anthropogenic chemicals are agrochemicals (phytotoxins, herbicides), industrial chemicals, and pharmaceuticals. Biochemical stress can be exerted through toxins, medical drugs (e.g., cytostatics, psychopharmaceuticals, non-steroidal inhibitors of inflammation), and through fasting (dietary restriction). Key-lock interactions between enzymes and substrates, antigens and antibodies, antigen-presenting cells, and cognate T cells are the basics of biology, biochemistry, and immunology. Their rules do not obey linear dose-response relationships. The review provides examples of biologic stressors: oncolytic viruses (e.g., immuno-virotherapy of cancer) and hormones (e.g., melatonin, stress hormones). Molecular mechanisms of cellular stress adaptation involve the protein quality control system (PQS) and homeostasis of proteasome, endoplasmic reticulum, and mitochondria. Important components are transcription factors (e.g., Nrf2), micro-RNAs, heat shock proteins, ionic calcium, and enzymes (e.g., glutathion redox enzymes, DNA methyltransferases, and DNA repair enzymes). Cellular growth control, intercellular communication, and resistance to stress from microbial infections involve growth factors, cytokines, chemokines, interferons, and their respective receptors. The effects of hormesis during evolution are multifarious: cell protection and survival, evolutionary flexibility, and epigenetic memory. According to the hormesis theory, this is true for the entire biosphere, e.g., archaia, bacteria, fungi, plants, and the animal kingdoms.

Dicarbonyl derived post-translational modifications: chemistry bridging biology and aging-related disease

In living systems, nucleophilic amino acid residues are prone to non-enzymatic post-translational modification by electrophiles. α-Dicarbonyl compounds are a special type of electrophiles that can react irreversibly with lysine, arginine, and cysteine residues via complex mechanisms to form post-translational modifications known as advanced glycation end-products (AGEs). Glyoxal, methylglyoxal, and 3-deoxyglucosone are the major endogenous dicarbonyls, with methylglyoxal being the most well-studied. There are several routes that lead to the formation of dicarbonyl compounds, most originating from glucose and glucose metabolism, such as the non-enzymatic decomposition of glycolytic intermediates and fructosyl amines. Although dicarbonyls are removed continuously mainly via the glyoxalase system, several conditions lead to an increase in dicarbonyl concentration and thereby AGE formation. AGEs have been implicated in diabetes and aging-related diseases, and for this reason the elucidation of their structure as well as protein targets is of great interest. Though the dicarbonyls and reactive protein side chains are of relatively simple nature, the structures of the adducts as well as their mechanism of formation are not that trivial. Furthermore, detection of sites of modification can be demanding and current best practices rely on either direct mass spectrometry or various methods of enrichment based on antibodies or click chemistry followed by mass spectrometry. Future research into the structure of these adducts and protein targets of dicarbonyl compounds may improve the understanding of how the mechanisms of diabetes and aging-related physiological damage occur.

Environmental toxicology and ecotoxicology: How clean is clean? Rethinking dose-response analysis

Global agendas for sustaining clean environments target remediation of multimedia contaminants, but how clean is clean? Environmental Toxicology and Ecotoxicology focus on issues concerning "clean". However, the models used to assess the effects of environmental multimedia on individual living organisms and communities or populations in Environmental Toxicology and Ecotoxicology may fail to provide reliable estimates for risk assessment and optimize health. Recent developments in low-dose effects research provide a novel means in Environmental Toxicology and Ecotoxicology to improve the quality of hazard and risk assessment.

The Glyoxalase System-New Insights into an Ancient Metabolism

The glyoxalase system was discovered over a hundred years ago and since then it has been claimed to provide the role of an indispensable enzyme system in order to protect cells from a toxic byproduct of glycolysis. This review gives a broad overview of what has been postulated in the last 30 years of glyoxalase research, but within this context it also challenges the concept that the glyoxalase system is an exclusive tool of detoxification and that its substrate, methylglyoxal, is solely a detrimental burden for every living cell due to its toxicity. An overview of consequences of a complete loss of the glyoxalase system in various model organisms is presented with an emphasis on the role of alternative detoxification pathways of methylglyoxal. Furthermore, this review focuses on the overlooked posttranslational modification of Glyoxalase 1 and its possible implications for cellular maintenance under various (patho-)physiological conditions. As a final note, an intriguing point of view for the substrate methylglyoxal is offered, the concept of methylglyoxal (MG)-mediated hormesis.

Exercise influences the impact of polychlorinated biphenyl exposure on immune function

Polychlorinated biphenyls (PCBs) are environmental pollutants and endocrine disruptors, harmfully affecting reproductive, endocrine, neurological and immunological systems. This broad influence has implications for processes such as wound healing, which is modulated by the immunological response of the body. Conversely, while PCBs can be linked to diminished wound healing, outside of PCB pollution systems, exercise has been shown to accelerate wound healing. However, the potential for moderate intensity exercise to modulate or offset the harmful effects of a toxin like PCB are yet unknown. A key aim of the present study was to examine how PCB exposure at different doses (0, 100, 500, 1000 ppm i.p.) altered wound healing in exercised versus non-exercised subgroups of mice. We examined PCB effects on immune function in more depth by analyzing the concentrations of cytokines, interleukin-1β (IL-1β), tumor necrosis factor-α (TNF-α), Interleukin-6 (IL-6) and granulocyte macrophage colony stimulating factor (GM-CSF) in these wounds inflicted by punch biopsy. Mice were euthanized at Day 3 or Day 5 after PCB injection (n = 3-6) and skin excised from the wound area was homogenized and analyzed for cytokine content. Results revealed that wound healing was not signficantly impacted by either PCB exposure or exercise, but there were patterns of delays in healing that depended on PCB dose. Changes in cytokines were also observed and depended on PCB dose and exercise experience. For example, IL-1β concentrations in Day 5 mice without PCB administration were 33% less in exercised mice than mice not exercised. However, IL-1β concentrations in Day 3 mice administered 100 ppm were 130% greater in exercised mice than not exercisedmice. Changes in the other measured cytokines varied with mainly depressions at lesser PCB doses and elevations at higher doses. Exercise had diverse effects on cytokine levels, but increased cytokine levels in the two greater doses. Explanations for these diverse effects include the use of young animals with more rapid wound healing rates less affected by toxin exposure, as well as PCB-mediated compensatory effects at specific doses which could actually enhance immune function. Future work should examine these interactions in more detail across a developmental time span. Understanding how manipulating the effects of exposure to environemntal contaminants using behavioral modification could be very useful in certain high risk populations or exposed individuals.

Methylglyoxal Metabolism and Aging-Related Disease: Moving from Correlation toward Causation

Methylglyoxal (MG) is a ubiquitous metabolite that spontaneously reacts with biopolymers forming advanced glycation end-products (AGEs). AGEs are strongly associated with aging-related diseases, including cancer, neurodegenerative diseases, and diabetes. As the formation of AGEs is nonenzymatic, the damage caused by MG and AGEs has been regarded as unspecific. This may have resulted in the field generally been regarded as unappealing by many researchers, as detailed mechanisms have been difficult to probe. However, accumulating evidence highlighting the importance of MG in human metabolism and disease, as well as data revealing how MG can elicit its signaling function via specific protein AGEs, could change the current mindset, accelerating the field to the forefront of future research.

Methylglyoxal, a Highly Reactive Dicarbonyl Compound, in Diabetes, Its Vascular Complications, and Other Age-Related Diseases

The formation and accumulation of methylglyoxal (MGO), a highly reactive dicarbonyl compound, has been implicated in the pathogenesis of type 2 diabetes, vascular complications of diabetes, and several other age-related chronic inflammatory diseases such as cardiovascular disease, cancer, and disorders of the central nervous system. MGO is mainly formed as a byproduct of glycolysis and, under physiological circumstances, detoxified by the glyoxalase system. MGO is the major precursor of nonenzymatic glycation of proteins and DNA, subsequently leading to the formation of advanced glycation end products (AGEs). MGO and MGO-derived AGEs can impact on organs and tissues affecting their functions and structure. In this review we summarize the formation of MGO, the detoxification of MGO by the glyoxalase system, and the biochemical pathways through which MGO is linked to the development of diabetes, vascular complications of diabetes, and other age-related diseases. Although interventions to treat MGO-associated complications are not yet available in the clinical setting, several strategies to lower MGO have been developed over the years. We will summarize several new directions to target MGO stress including glyoxalase inducers and MGO scavengers. Targeting MGO burden may provide new therapeutic applications to mitigate diseases in which MGO plays a crucial role.

Dicarbonyl Stress at the Crossroads of Healthy and Unhealthy Aging

Dicarbonyl stress occurs when dicarbonyl metabolites (i.e., methylglyoxal, glyoxal and 3-deoxyglucosone) accumulate as a consequence of their increased production and/or decreased detoxification. This toxic condition has been associated with metabolic and age-related diseases, both of which are characterized by a pro-inflammatory and pro-oxidant state. Methylglyoxal (MGO) is the most reactive dicarbonyl and the one with the highest endogenous flux. It is the precursor of the major quantitative advanced glycated products (AGEs) in physiological systems, arginine-derived hydroimidazolones, which accumulate in aging and dysfunctional tissues. The aging process is characterized by a decline in the functional properties of cells, tissues and whole organs, starting from the perturbation of crucial cellular processes, including mitochondrial function, proteostasis and stress-scavenging systems. Increasing studies are corroborating the causal relationship between MGO-derived AGEs and age-related tissue dysfunction, unveiling a previously underestimated role of dicarbonyl stress in determining healthy or unhealthy aging. This review summarizes the latest evidence supporting a causal role of dicarbonyl stress in age-related diseases, including diabetes mellitus, cardiovascular disease and neurodegeneration.

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

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

Impairing L-Threonine Catabolism Promotes Healthspan through Methylglyoxal-Mediated Proteohormesis

Whether and how regulation of genes and pathways contributes to physiological aging is topic of intense scientific debate. By performing an RNA expression-based screen for genes downregulated during aging of three different species, we identified glycine-C-acetyltransferase (GCAT, EC 2.3.1.29). Impairing gcat expression promotes the lifespan of C. elegans by interfering with threonine catabolism to promote methylglyoxal (MGO; CAS 78-98-8) formation in an amine oxidase-dependent manner. MGO is a reactive dicarbonyl inducing diabetic complications in mammals by causing oxidative stress and damaging cellular components, including proteins. While high concentrations of MGO consistently exert toxicity in nematodes, we unexpectedly find that low-dose MGO promotes lifespan, resembling key mediators of gcat impairment. These were executed by the ubiquitin-proteasome system, namely PBS-3 and RPN-6.1 subunits, regulated by the stress-responsive transcriptional regulators SKN-1/NRF2 and HSF-1. Taken together, GCAT acts as an evolutionary conserved aging-related gene by orchestrating an unexpected nonlinear impact of proteotoxic MGO on longevity.