Single-sample preparation for simultaneous cellular redox and energy state determination

Comparative evaluation of cigarette smoke and a heated tobacco product on microglial toxicity, oxidative stress and inflammatory response

BACKGROUND

Tobacco smoking is the leading cause of preventable death and disease worldwide, with over 8 million annual deaths attributed to cigarette smoking. This study investigates the impact of cigarette smoke and heated tobacco products (HTPs) on microglial function, focusing on toxicological profiles, inflammatory responses, and oxidative stress using ISO standard and clinically relevant conditions of exposure.

METHODS

We assessed cell viability, reactive oxygen species (ROS) production, lipid peroxidation, mitochondrial function, unfolded protein response, and inflammation in human microglial cells (HMC3) exposed to cigarette smoke, HTP aerosol or nicotine.

RESULTS

Our findings show that cigarette smoke significantly reduces microglial viability, increases ROS formation, induces lipid peroxidation, and reduces intracellular glutathione levels. Cigarette smoke also alters the expression of genes involved in mitochondrial dynamics and biogenesis, leading to mitochondrial dysfunction. Additionally, cigarette smoke impairs the unfolded protein response, activates the NF-κB pathway, and induces a pro-inflammatory state characterized by increased TNF and IL-18 expression. Furthermore, cigarette smoke causes DNA damage and decreases the expression of the aging marker Klotho β. In contrast, HTP, exhibited a lesser degree of microglial toxicity, with reduced ROS production, lipid peroxidation, and mitochondrial dysfunction compared to conventional cigarettes.

CONCLUSION

These results highlight the differential toxicological profile of cigarette smoke and HTP on microglial cells, suggesting a potential harm reduction strategy for neurodegenerative disease for smokers unwilling or unable to quit.

Glioblastoma mesenchymal subtype enhances antioxidant defence to reduce susceptibility to ferroptosis

Glioblastoma (GBM) represents an aggressive brain tumor, characterized by intra- and inter-tumoral heterogeneity and therapy resistance, leading to unfavourable prognosis. An increasing number of studies pays attention on the regulation of ferroptosis, an iron-dependent cell death, as a strategy to reverse drug resistance in cancer. However, the debate on whether this strategy may have important implications for the treatment of GBM is still ongoing. In the present study, we used ferric ammonium citrate and erastin to evaluate ferroptosis induction effects on two human GBM cell lines, U-251 MG, with proneural characteristics, and T98-G, with a mesenchymal profile. The response to ferroptosis induction was markedly different between cell lines, indeed T98-G cells showed an enhanced antioxidant defence, with increased glutathione levels, as compared to U-251 MG cells. Moreover, using bioinformatic approaches and analysing publicly available datasets from patients' biopsies, we found that GBM with a mesenchymal phenotype showed an up-regulation of several genes involved in antioxidant mechanisms as compared to proneural subtype. Thus, our results suggest that GBM subtypes differently respond to ferroptosis induction, emphasizing the significance of further molecular studies on GBM to better discriminate between various tumor subtypes and progressively move towards personalized therapy.

Over-expression of N-acetylaspartate synthase exacerbates pathological energetic deficit and accelerates cognitive decline in the 5xFAD mouse

N-acetylaspartate (NAA) is an abundant central nervous system amino acid derivative that is tightly coupled to mitochondria and energy metabolism in neurons. A reduced NAA signature is a prominent early pathological biomarker in multiple neurodegenerative diseases and becomes progressively more pronounced as disease advances. Because NAA synthesis requires aspartate drawn directly from mitochondria, we argued that this process is in direct competition with oxidative phosphorylation for substrate and that sustained high levels of NAA synthesis would be incompatible with pathological energy crisis. We show here that over-expression of the rate-limiting NAA synthetic enzyme in the hippocampus of the 5x familial Alzheimer's disease (5xFAD) mouse results in an exaggerated pathological ATP deficit and accelerated cognitive decline. Over-expression of NAA synthase did not increase amyloid burden or result in cell loss but did significantly deplete mitochondrial aspartate and impair the ability of mitochondria to oxidize glutamate for adenosine triphosphate (ATP) synthesis. These results define NAA as a sink for energetic substrate and suggest initial pathological reductions in NAA are part of a response to energetic crisis designed to preserve substrate bioavailability for mitochondrial ATP synthesis.

(+)-Lipoic acid reduces mitochondrial unfolded protein response and attenuates oxidative stress and aging in an in vitro model of non-alcoholic fatty liver disease

BACKGROUND

Non-alcoholic fatty liver disease (NAFLD) is a liver disorder characterized by the ac-cumulation of fat in hepatocytes without alcohol consumption. Mitochondrial dysfunction and endoplasmic reticulum (ER) stress play significant roles in NAFLD pathogenesis. The unfolded protein response in mitochondria (UPRmt) is an adaptive mechanism that aims to restore mitochondrial protein homeostasis and mitigate cellular stress. This study aimed to investigate the effects of ( +)-Lipoic acid (ALA) on UPRmt, inflammation, and oxidative stress in an in vitro model of NAFLD using HepG2 cells treated with palmitic acid and oleic acid to induce steatosis.

RESULTS

Treatment with palmitic and oleic acids increased UPRmt-related proteins HSP90 and HSP60 (heat shock protein), and decreased CLPP (caseinolytic protease P), indicating ER stress activation. ALA treatment at 1 μM and 5 μM restored UPRmt-related protein levels. PA:OA (palmitic acid:oleic acid)-induced ER stress markers IRE1α (Inositol requiring enzyme-1), CHOP (C/EBP Homologous Protein), BIP (Binding Immunoglobulin Protein), and BAX (Bcl-2-associated X protein) were significantly reduced by ALA treatment. ALA also enhanced ER-mediated protein glycosylation and reduced oxidative stress, as evidenced by decreased GPX1 (Glutathione peroxidase 1), GSTP1 (glutathione S-transferase pi 1), and GSR (glutathione-disulfide reductase) expression and increased GSH (Glutathione) levels, and improved cellular senescence as shown by the markers β-galactosidase, γH2Ax and Klotho-beta.

CONCLUSIONS

In conclusion, ALA ameliorated ER stress, oxidative stress, and inflammation in HepG2 cells treated with palmitic and oleic acids, potentially offering therapeutic benefits for NAFLD providing a possible biochemical mechanism underlying ALA beneficial effects.

SIRT5 rs12216101 T>G variant is associated with liver damage and mitochondrial dysfunction in patients with non-alcoholic fatty liver disease

BACKGROUND & AIMS

Sirtuin 5, encoded by the SIRT5 gene, is a NAD+-dependent deacylase that modulates mitochondrial metabolic processes through post-translational modifications. In this study, we aimed to examine the impact of the SIRT5 rs12216101 T>G non-coding single nucleotide polymorphism on disease severity in patients with non-alcoholic fatty liver disease (NAFLD).

METHODS

The rs12216101 variant was genotyped in 2,606 consecutive European patients with biopsy-proven NAFLD. Transcriptomic analysis, expression of mitochondrial complexes and oxidative stress levels were measured in liver samples from a subset of bariatric patients. Effects of SIRT5 pharmacological inhibition were evaluated in HepG2 cells exposed to excess free fatty acids. Mitochondrial energetics in vitro were investigated by high-performance liquid chromatography.

RESULTS

In the whole cohort, the frequency distribution of SIRT5 rs12216101 TT, TG and GG genotypes was 47.0%, 42.3% and 10.7%, respectively. At multivariate logistic regression analysis adjusted for sex, age >50 years, diabetes, and PNPLA3 rs738409 status, the SIRT5 rs12216101 T>G variant was associated with the presence of non-alcoholic steatohepatitis (odds ratio 1.20, 95% CI 1.03-1.40) and F2-F4 fibrosis (odds ratio 1.18; 95% CI 1.00-1.37). Transcriptomic analysis showed that the SIRT5 rs12216101 T>G variant was associated with upregulation of transcripts involved in mitochondrial metabolic pathways, including the oxidative phosphorylation system. In patients carrying the G allele, western blot analysis confirmed an upregulation of oxidative phosphorylation complexes III, IV, V and consistently higher levels of reactive oxygen species, reactive nitrogen species and malondialdehyde, and lower ATP levels. Administration of a pharmacological SIRT5 inhibitor preserved mitochondrial energetic homeostasis in HepG2 cells, as evidenced by restored ATP/ADP, NAD+/NADH, NADP+/NADPH ratios and glutathione levels.

CONCLUSIONS

The SIRT5 rs12216101 T>G variant, heightening SIRT5 activity, is associated with liver damage, mitochondrial dysfunction, and oxidative stress in patients with NAFLD.

IMPACT AND IMPLICATIONS

In this study we discovered that the SIRT5 rs12216101 T>G variant is associated with higher disease severity in patients with non-alcoholic fatty liver disease (NAFLD). This risk variant leads to a SIRT5 gain-of-function, enhancing mitochondrial oxidative phosphorylation and thus leading to oxidative stress. SIRT5 may represent a novel disease modulator in NAFLD.

(+)-Lipoic Acid Reduces Lipotoxicity and Regulates Mitochondrial Homeostasis and Energy Balance in an In Vitro Model of Liver Steatosis

Non-alcoholic fatty liver disease (NAFLD) is characterized by the accumulation of lipids within hepatocytes, which compromises liver functionality following mitochondrial dysfunction and increased production of reactive oxygen species (ROS). Lipoic acid is one of the prosthetic groups of the pyruvate dehydrogenase complex also known for its ability to confer protection from oxidative damage because of its antioxidant properties. In this study, we aimed to investigate the effects of lipoic acid on lipotoxicity and mitochondrial dynamics in an in vitro model of liver steatosis. HepG2 cells were treated with palmitic acid and oleic acid (1:2) to induce steatosis, without and with 1 and 5 µM lipoic acid. Following treatments, cell proliferation and lipid droplets accumulation were evaluated. Mitochondrial functions were assessed through the evaluation of membrane potential, MitoTracker Red staining, expression of genes of the mitochondrial quality control, and analysis of energy metabolism by HPLC and Seahorse. We showed that lipoic acid treatment restored membrane potential to values comparable to control cells, as well as protected cells from mitochondrial fragmentation following PA:OA treatment. Furthermore, our data showed that lipoic acid was able to determine an increase in the expression of mitochondrial fusion genes and a decrease in mitochondrial fission genes, as well as to restore the bioenergetics of cells after treatment with palmitic acid and oleic acid. In conclusion, our data suggest that lipoic acid reduces lipotoxicity and improves mitochondrial functions in an in vitro model of steatosis, thus providing a potentially valuable pharmacological tool for NAFLD treatment.

VDAC1 Knockout Affects Mitochondrial Oxygen Consumption Triggering a Rearrangement of ETC by Impacting on Complex I Activity

Voltage-Dependent Anion-selective Channel isoform 1 (VDAC1) is the most abundant isoform of the outer mitochondrial membrane (OMM) porins and the principal gate for ions and metabolites to and from the organelle. VDAC1 is also involved in a number of additional functions, such as the regulation of apoptosis. Although the protein is not directly involved in mitochondrial respiration, its deletion in yeast triggers a complete rewiring of the whole cell metabolism, with the inactivation of the main mitochondrial functions. In this work, we analyzed in detail the impact of VDAC1 knockout on mitochondrial respiration in the near-haploid human cell line HAP1. Results indicate that, despite the presence of other VDAC isoforms in the cell, the inactivation of VDAC1 correlates with a dramatic impairment in oxygen consumption and a re-organization of the relative contributions of the electron transport chain (ETC) enzymes. Precisely, in VDAC1 knockout HAP1 cells, the complex I-linked respiration (N-pathway) is increased by drawing resources from respiratory reserves. Overall, the data reported here strengthen the key role of VDAC1 as a general regulator of mitochondrial metabolism.

Characterization of Carnosine Effect on Human Microglial Cells under Basal Conditions

The activity of microglia is fundamental for the regulation of numerous physiological processes including brain development, synaptic plasticity, and neurogenesis, and its deviation from homeostasis can lead to pathological conditions, including numerous neurodegenerative disorders. Carnosine is a naturally occurring molecule with well-characterized antioxidant and anti-inflammatory activities, able to modulate the response and polarization of immune cells and ameliorate their cellular energy metabolism. The better understanding of microglia characteristics under basal physiological conditions, as well as the possible modulation of the mechanisms related to its response to environmental challenges and/or pro-inflammatory/pro-oxidant stimuli, are of utmost importance for the development of therapeutic strategies. In the present study, we assessed the activity of carnosine on human HMC3 microglial cells, first investigating the effects of increasing concentrations of carnosine on cell viability. When used at a concentration of 20 mM, carnosine led to a decrease of cell viability, paralleled by gene expression increase and decrease, respectively, of interleukin 6 and heme oxygenase 1. When using the maximal non-toxic concentration (10 mM), carnosine decreased nitric oxide bioavailability, with no changes in the intracellular levels of superoxide ion. The characterization of energy metabolism of HMC3 microglial cells under basal conditions, never reported before, demonstrated that it is mainly based on mitochondrial oxidative metabolism, paralleled by a high rate of biosynthetic reactions. The exposure of HMC3 cells to carnosine seems to ameliorate microglia energy state, as indicated by the increase in the adenosine triphosphate/adenosine diphosphate (ATP/ADP) ratio and energy charge potential. The improvement of cell energy metabolism mediated by 10 mM carnosine could represent a useful protective weapon in the case of human microglia undergoing stressing conditions.

Hindering NAT8L expression in hepatocellular carcinoma increases cytosolic aspartate delivery that fosters pentose phosphate pathway and purine biosynthesis promoting cell proliferation

N-acetylaspartate (NAA) is synthesized by the mitochondrial enzyme NAT8L, which uses acetyl-CoA and aspartate as substrates. These metabolites are fundamental for bioenergetics and anabolic requirements of highly proliferating cells, thus, NAT8L modulation may impinge on the metabolic reprogramming of cancer cells. Specifically, aspartate represents a limiting amino acid for nucleotide synthesis in cancer. Here, the expression of the NAT8L enzyme was modulated to verify how it impacts the metabolic adaptations and proliferative capacity of hepatocellular carcinoma. We demonstrated that NAT8L downregulation is associated with increased proliferation of hepatocellular carcinoma cells and immortalized hepatocytes. The overexpression of NAT8L instead decreased cell growth. The pro-tumoral effect of NAT8L silencing depended on glutamine oxidation and the rewiring of glucose metabolism. Mechanistically, NAT8L downregulation triggers aspartate outflow from mitochondria via the exporter SLC25A13 to promote glucose flux into the pentose phosphate pathway, boosting purine biosynthesis. These results were corroborated by the analyses of human and mouse hepatocellular carcinoma samples revealing a decrease in NAT8L expression compared to adjacent non-tumoral tissues. Overall, this work demonstrates that NAT8L expression in liver cells limits the cytosolic availability of aspartate necessary for enhancing the pentose phosphate pathway and purine biosynthesis, counteracting cell proliferation.

L-2-Hydroxyglutarate Protects Against Cardiac Injury via Metabolic Remodeling

BACKGROUND

L-2-hydroxyglutarate (L2HG) couples mitochondrial and cytoplasmic energy metabolism to support cellular redox homeostasis. Under oxygen-limiting conditions, mammalian cells generate L2HG to counteract the adverse effects of reductive stress induced by hypoxia. Very little is known, however, about whether and how L2HG provides tissue protection from redox stress during low-flow ischemia (LFI) and ischemia-reperfusion injury. We examined the cardioprotective effects of L2HG accumulation against LFI and ischemia-reperfusion injury and its underlying mechanism using genetic mouse models.

METHODS AND RESULTS

L2HG accumulation was induced by homozygous (L2HGDH [L-2-hydroxyglutarate dehydrogenase]-/-) or heterozygous (L2HGDH+/-) deletion of the L2HGDH gene in mice. Hearts isolated from these mice and their wild-type littermates (L2HGDH+/+) were subjected to baseline perfusion and 90-minute LFI or 30-minute no-flow ischemia followed by 60- or 120-minute reperfusion. Using [13C]- and [31P]-NMR (nuclear magnetic resonance) spectroscopy, high-performance liquid chromatography, reverse transcription quantitative reverse transcription polymerase chain reaction, ELISA, triphenyltetrazolium staining, colorimetric/fluorometric spectroscopy, and echocardiography, we found that L2HGDH deletion induces L2HG accumulation at baseline and under stress conditions with significant functional consequences. In response to LFI or ischemia-reperfusion, L2HG accumulation shifts glucose flux from glycolysis towards the pentose phosphate pathway. These key metabolic changes were accompanied by enhanced cellular reducing potential, increased elimination of reactive oxygen species, attenuated oxidative injury and myocardial infarction, preserved cellular energy state, and improved cardiac function in both L2HGDH-/- and L2HGDH+/- hearts compared with L2HGDH+/+ hearts under ischemic stress conditions.

CONCLUSION

L2HGDH deletion-induced L2HG accumulation protects against myocardial injury during LFI and ischemia-reperfusion through a metabolic shift of glucose flux from glycolysis towards the pentose phosphate pathway. L2HG offers a novel mechanism for eliminating reactive oxygen species from myocardial tissue, mitigating redox stress, reducing myocardial infarct size, and preserving high-energy phosphates and cardiac function. Targeting L2HG levels through L2HGDH activity may serve as a new therapeutic strategy for cardiovascular diseases related to oxidative injury.

Propofol and α2-Agonists Attenuate Microglia Activation and Restore Mitochondrial Function in an In Vitro Model of Microglia Hypoxia/Reoxygenation

Cerebrovascular ischemia is a common clinical disease encompassing a series of complex pathophysiological processes in which oxidative stress plays a major role. The present study aimed to evaluate the effects of Dexmedetomidine, Clonidine, and Propofol in a model of hypoxia/reoxygenation injury. Microglial cells were exposed to 1%hypoxia for 3 h and reoxygenated for 3 h, and oxidative stress was measured by ROS formation and the expression of inflammatory process genes. Mitochondrial dysfunction was assessed by membrane potential maintenance and the levels of various metabolites involved in energetic metabolism. The results showed that Propofol and α2-agonists attenuate the formation of ROS during hypoxia and after reoxygenation. Furthermore, the α2-agonists treatment restored membrane potential to values comparable to the normoxic control and were both more effective than Propofol. At the same time, Propofol, but not α2-agonists, reduces proliferation (Untreated Hypoxia = 1.16 ± 0.2, Untreated 3 h Reoxygenation = 1.28 ± 0.01 vs. Propofol hypoxia = 1.01 ± 0.01 vs. Propofol 3 h Reoxygenation = 1.12 ± 0.03) and microglial migration. Interestingly, all of the treatments reduced inflammatory gene and protein expressions and restored energy metabolism following hypoxia/reoxygenation (ATP content in hypoxia/reoxygenation 3 h: Untreated = 3.11 ± 0.8 vs. Propofol = 7.03 ± 0.4 vs. Dexmedetomidine = 5.44 ± 0.8 vs. Clonidine = 7.70 ± 0.1), showing that the drugs resulted in a different neuroprotective profile. In conclusion, our results may provide clinically relevant insights for neuroprotective strategies in intensive care units.

Biochemical Discrimination of the Down Syndrome-Related Metabolic and Oxidative/Nitrosative Stress Alterations from the Physiologic Age-Related Changes through the Targeted Metabolomic Analysis of Serum

Down Syndrome (DS) is a neurodevelopmental disorder that is characterized by an accelerated aging process, frequently associated with the development of Alzheimer’s disease (AD). Previous studies evidenced that DS patients have various metabolic anomalies, easily measurable in their serum samples, although values that were found in DS patients were compared with those of age-matched non-DS patients, thus hampering to discriminate the physiologic age-related changes of serum metabolites from those that are truly caused by the pathologic processes associated with DS. In the present study we performed a targeted metabolomic evaluation of serum samples from DS patients without dementia of two age classes (Younger DS Patients, YDSP, aging 20–40 years; Aged DS Patients, ADSP, aging 41–60 years), comparing the results with those that were obtained in two age classes of non-DS patients (Younger non-DS Patients, YnonDSP, aging 30–60 years; Aged-nonDS Patients, AnonDSP, aging 75–90 years). Of the 36 compounds assayed, 30 had significantly different concentrations in Pooled non-DS Patients (PnonDSP), compared to Pooled DS Patients (PDSP). Age categorization revealed that 11/30 compounds were significantly different in AnonDSP, compared to YnonDSP, indicating physiologic, age-related changes of their circulating concentrations. A comparison between YDSP and ADSP showed that 19/30 metabolites had significantly different values from those found in the corresponding classes of non-DS patients, strongly suggesting pathologic, DS-associated alterations of their serum levels. Twelve compounds selectively and specifically discriminated PnonDSP from PDSP, whilst only three discriminated YDSP from ADSP. The results allowed to determine, for the first time and to the best of our knowledge, the true, age-independent alterations of metabolism that are measurable in serum and attributable only to DS. These findings may be of high relevance for better strategies (pharmacological, nutritional) aiming to specifically target the dysmetabolism and decreased antioxidant defenses that are associated with DS.

CXCL12/CXCR4 axis supports mitochondrial trafficking in tumor myeloma microenvironment

Mesenchymal stromal cells (MSCs) within the protective microenvironment of multiple myeloma (MM) promote tumor growth, confer chemoresistance and support metabolic needs of plasma cells (PCs) even transferring mitochondria. In this scenario, heterocellular communication and dysregulation of critical signaling axes are among the major contributors to progression and treatment failure. Here, we report that myeloma MSCs have decreased reliance on mitochondrial metabolism as compared to healthy MSCs and increased tendency to deliver mitochondria to MM cells, suggesting that this intercellular exchange between PCs and stromal cells can be consider part of MSC pro-tumorigenic phenotype. Interestingly, we also showed that PCs promoted expression of connexin 43 (CX43) in MSCs leading to CXCL12 activation and stimulation of its receptor CXCR4 on MM cells favoring protumor mitochondrial transfer. Consistently, we observed that selective inhibition of CXCR4 by plerixafor resulted in a significant reduction of mitochondria trafficking. Moreover, intracellular expression of CXCR4 in myeloma PCs from BM biopsy specimens demonstrated higher CXCR4 colocalization with CD138+ cells of non-responder patients to bortezomib compared with responder patients, suggesting that CXCR4 mediated chemoresistance in MM. Taken together, our data demonstrated that CXCL12/CXCR4 axis mediates intercellular coupling thus suggesting that the myeloma niche may be exploited as a target to improve and develop therapeutic approaches.

Comparison of three methods for in vivo quantification of glutathione in tissues of hypertensive rats

Glutathione (γ-L-glutamyl-L-cysteinyl-glycine, GSH) is a tripeptide that is part of the antioxidant defense system and contributes to numerous redox-regulatory processes. In vivo, reduced GSH and oxidized glutathione disulfide (GSSG) are present in redox equilibrium and their ratio provides important information on the cellular redox state. Here, we compared three different methods for in vivo quantification of glutathione in tissues of hypertensive rats, an accepted animal model of oxidative stress. In the present study, we used hypertensive rats (infusion of 1 mg/kg/d angiotensin-II for 7 days) to determine the levels of reduced GSH and/or GSH/GSSG ratios in different tissue samples. We used an HPLC-based method with direct electrochemical detection (HPLC/ECD) and compared it with Ellman's reagent (DTNB) dependent derivatization of reduced GSH to the GS-NTB adduct and free NTB (UV/Vis HPLC) as well as with a commercial GSH/GSSG assay (Oxiselect). Whereas all three methods indicated overall a decreased redox state in hypertensive rats, the assays based on HPLC/ECD and DTNB derivatization provided the most significant differences. We applied a direct, fast and sensitive method for electrochemical GSH detection in tissues from hypertensive animals, and confirmed its reliability for in vivo measurements by head-to-head comparison with two other established assays. The HPLC/ECD but not DTNB and Oxiselect assays yielded quantitative GSH data but all three assays reflected nicely the qualitative redox changes and functional impairment in hypertensive rats. However, especially our GSH/GSSG values are lower than reported by others pointing to problems in the work-up protocol.

Interferon-γ Impairs Human Coronary Artery Endothelial Glucose Metabolism by Tryptophan Catabolism and Activates Fatty Acid Oxidation

BACKGROUND

Endothelial cells depend on glycolysis for much of their energy production. Impaired endothelial glycolysis has been associated with various vascular pathobiologies, including impaired angiogenesis and atherogenesis. IFN-γ (interferon-γ)-producing CD4⁺ and CD8⁺ T lymphocytes have been identified as the predominant pathological cell subsets in human atherosclerotic plaques. Although the immunologic consequences of these cells have been extensively evaluated, their IFN-γ-mediated metabolic effects on endothelial cells remain unknown. The purpose of this study was to determine the metabolic consequences of the T-lymphocyte cytokine, IFN-γ, on human coronary artery endothelial cells.

METHODS

The metabolic effects of IFN-γ on primary human coronary artery endothelial cells were assessed by unbiased transcriptomic and metabolomic analyses combined with real-time extracellular flux analyses and molecular mechanistic studies. Cellular phenotypic correlations were made by measuring altered endothelial intracellular cGMP content, wound-healing capacity, and adhesion molecule expression.

RESULTS

IFN-γ exposure inhibited basal glycolysis of quiescent primary human coronary artery endothelial cells by 20% through the global transcriptional suppression of glycolytic enzymes resulting from decreased basal HIF1α (hypoxia-inducible factor 1α) nuclear availability in normoxia. The decrease in HIF1α activity was a consequence of IFN-γ-induced tryptophan catabolism resulting in ARNT (aryl hydrocarbon receptor nuclear translocator)/HIF1β sequestration by the kynurenine-activated AHR (aryl hydrocarbon receptor). In addition, IFN-γ resulted in a 23% depletion of intracellular nicotinamide adenine dinucleotide in human coronary artery endothelial cells. This altered glucose metabolism was met with concomitant activation of fatty acid oxidation, which augmented its contribution to intracellular ATP balance by >20%. These metabolic derangements were associated with adverse endothelial phenotypic changes, including decreased basal intracellular cGMP, impaired endothelial migration, and a switch to a proinflammatory state.

CONCLUSIONS

IFN-γ impairs endothelial glucose metabolism by altered tryptophan catabolism destabilizing HIF1, depletes nicotinamide adenine dinucleotide, and results in a metabolic shift toward increased fatty acid oxidation. This work suggests a novel mechanistic basis for pathological T lymphocyte-endothelial interactions in atherosclerosis mediated by IFN-γ, linking endothelial glucose, tryptophan, and fatty acid metabolism with the nicotinamide adenine dinucleotide balance and ATP generation and their adverse endothelial functional consequences.

Altered Follicular Fluid Metabolic Pattern Correlates with Female Infertility and Outcome Measures of In Vitro Fertilization

Nearly 40-50% of infertility problems are estimated to be of female origin. Previous studies dedicated to the analysis of metabolites in follicular fluid (FF) produced contrasting results, although some valuable indexes capable to discriminate control groups (CTRL) from infertile females (IF) and correlate with outcome measures of assisted reproduction techniques were in some instances found. In this study, we analyzed in blind FF of 35 control subjects (CTRL = patients in which inability to obtain pregnancy was exclusively due to a male factor) and 145 IF (affected by: endometriosis, n = 19; polycystic ovary syndrome, n = 14; age-related reduced ovarian reserve, n = 58; reduced ovarian reserve, n = 29; unexplained infertility, n = 14; genetic infertility, n = 11) to determine concentrations of 55 water- and fat-soluble low molecular weight compounds (antioxidants, oxidative/nitrosative stress-related compounds, purines, pyrimidines, energy-related metabolites, and amino acids). Results evidenced that 27/55 of them had significantly different values in IF with respect to those measured in CTRL. The metabolic pattern of these potential biomarkers of infertility was cumulated (in both CTRL and IF) into a Biomarker Score index (incorporating the metabolic anomalies of FF), that fully discriminated CTRL (mean Biomarker Score value = 4.00 ± 2.30) from IF (mean Biomarker Score value = 14.88 ± 3.09, p < 0.001). The Biomarker Score values were significantly higher than those of CTRL in each of the six subgroups of IF. Posterior probability curves and ROC curve indicated that values of the Biomarker Score clustered CTRL and IF into two distinct groups, based on the individual FF metabolic profile. Furthermore, Biomarker Score values correlated with outcome measures of ovarian stimulation, in vitro fertilization, number and quality of blastocysts, clinical pregnancy, and healthy offspring. These results strongly suggest that the biochemical quality of FF deeply influences not only the effectiveness of IVF procedures but also the following embryonic development up to healthy newborns. The targeted metabolomic analysis of FF (using empowered Redox Energy Test) and the subsequent calculation of the Biomarker Score evidenced a set of 27 low molecular weight infertility biomarkers potentially useful in the laboratory managing of female infertility and to predict the success of assisted reproduction techniques.

ILB® Attenuates Clinical Symptoms and Serum Biomarkers of Oxidative/Nitrosative Stress and Mitochondrial Dysfunction in Patients with Amyotrophic Lateral Sclerosis

Oxidative/nitrosative stress and mitochondrial dysfunction is a hallmark of amyotrophic lateral sclerosis (ALS), an invariably fatal progressive neurodegenerative disease. Here, as an exploratory arm of a phase II clinical trial (EudraCT Number 2017-005065-47), we used high performance liquid chromatography(HPLC) to investigate changes in the metabolic profiles of serum from ALS patients treated weekly for 4 weeks with a repeated sub-cutaneous dose of 1 mg/kg of a proprietary low molecular weight dextran sulphate, called ILB®. A significant normalization of the serum levels of several key metabolites was observed over the treatment period, including N-acetylaspartate (NAA), oxypurines, biomarkers of oxidative/nitrosative stress and antioxidants. An improved serum metabolic profile was accompanied by significant amelioration of the patients' clinical conditions, indicating a response to ILB® treatment that appears to be mediated by improvement of tissue bioenergetics, decrease of oxidative/nitrosative stress and attenuation of (neuro)inflammatory processes.

Clobetasol promotes neuromuscular plasticity in mice after motoneuronal loss via sonic hedgehog signaling, immunomodulation and metabolic rebalancing

Motoneuronal loss is the main feature of amyotrophic lateral sclerosis, although pathogenesis is extremely complex involving both neural and muscle cells. In order to translationally engage the sonic hedgehog pathway, which is a promising target for neural regeneration, recent studies have reported on the neuroprotective effects of clobetasol, an FDA-approved glucocorticoid, able to activate this pathway via smoothened. Herein we sought to examine functional, cellular, and metabolic effects of clobetasol in a neurotoxic mouse model of spinal motoneuronal loss. We found that clobetasol reduces muscle denervation and motor impairments in part by restoring sonic hedgehog signaling and supporting spinal plasticity. These effects were coupled with reduced pro-inflammatory microglia and reactive astrogliosis, reduced muscle atrophy, and support of mitochondrial integrity and metabolism. Our results suggest that clobetasol stimulates a series of compensatory processes and therefore represents a translational approach for intractable denervating and neurodegenerative disorders.

Lung Surfactant Decreases Biochemical Alterations and Oxidative Stress Induced by a Sub-Toxic Concentration of Carbon Nanoparticles in Alveolar Epithelial and Microglial Cells

Carbon-based nanomaterials are nowadays attracting lots of attention, in particular in the biomedical field, where they find a wide spectrum of applications, including, just to name a few, the drug delivery to specific tumor cells and the improvement of non-invasive imaging methods. Nanoparticles inhaled during breathing accumulate in the lung alveoli, where they interact and are covered with lung surfactants. We recently demonstrated that an apparently non-toxic concentration of engineered carbon nanodiamonds (ECNs) is able to induce oxidative/nitrosative stress, imbalance of energy metabolism, and mitochondrial dysfunction in microglial and alveolar basal epithelial cells. Therefore, the complete understanding of their "real" biosafety, along with their possible combination with other molecules mimicking the in vivo milieu, possibly allowing the modulation of their side effects becomes of utmost importance. Based on the above, the focus of the present work was to investigate whether the cellular alterations induced by an apparently non-toxic concentration of ECNs could be counteracted by their incorporation into a synthetic lung surfactant (DPPC:POPG in 7:3 molar ratio). By using two different cell lines (alveolar (A549) and microglial (BV-2)), we were able to show that the presence of lung surfactant decreased the production of ECNs-induced nitric oxide, total reactive oxygen species, and malondialdehyde, as well as counteracted reduced glutathione depletion (A549 cells only), ameliorated cell energy status (ATP and total pool of nicotinic coenzymes), and improved mitochondrial phosphorylating capacity. Overall, our results on alveolar basal epithelial and microglial cell lines clearly depict the benefits coming from the incorporation of carbon nanoparticles into a lung surfactant (mimicking its in vivo lipid composition), creating the basis for the investigation of this combination in vivo.

Inhibition of TLR4 Signaling Affects Mitochondrial Fitness and Overcomes Bortezomib Resistance in Myeloma Plasma Cells

Multiple myeloma (MM) is a B-cell malignancy requiring inflammatory microenvironment signals for cell survival and proliferation. Despite improvements in pharmacological tools, MM remains incurable mainly because of drug resistance. The present study aimed to investigate the implication of Toll-like receptor 4 (TLR4) as the potential mechanism of bortezomib (BTZ) resistance. We found that TLR4 activation induced mitochondrial biogenesis and increased mitochondrial mass in human MM cell lines. Moreover, TLR4 signaling was activated after BTZ exposure and was increased in BTZ-resistant U266 (U266-R) cells. A combination of BTZ with TAK-242, a selective TLR4 inhibitor, overcame drug resistance through the generation of higher and extended oxidative stress, strong mitochondrial depolarization and severe impairment of mitochondrial fitness which in turn caused cell energy crisis and activated mitophagy and apoptosis. We further confirmed the efficacy of a TAK-242/BTZ combination in plasma cells from refractory myeloma patients. Consistently, inhibition of TLR4 increased BTZ-induced mitochondrial depolarization, restoring pharmacological response. Taken together, these findings indicate that TLR4 signaling acts as a stress-responsive mechanism protecting mitochondria during BTZ exposure, sustaining mitochondrial metabolism and promoting drug resistance. Inhibition of TLR4 could be therefore be a possible target in patients with refractory MM to overcome BTZ resistance.

Loss of macroH2A1 decreases mitochondrial metabolism and reduces the aggressiveness of uveal melanoma cells

Uveal melanoma (UM) is the most common primary intraocular tumour in adults. The most accurate prognostic factor of UM is classification by gene expression profiling. Currently, the role of epigenetics is much less defined compared to genetic mechanisms. We recently showed a strong prognostic role of the expression levels of histone variant macroH2A1 in UM patients. Here, we assessed the mechanistic effects of macroH2A1 on UM progression.

UM cell lines were stably knocked down (KD) for macroH2A1, and proliferation and colony formation capacity were evaluated. Mitochondrial function was assayed through qPCR and HPLC analyses. Correlation between mitochondrial gene expression and cancer aggressiveness was studied using a bioinformatics approach.

MacroH2A1 loss significantly attenuated UM cells proliferation and aggressiveness. Furthermore, genes involved in oxidative phosphorylation displayed a decreased expression in KD cells. Consistently, macroH2A1 loss resulted also in a significant decrease of mitochondrial transcription factor A (TFAM) expression, suggesting impaired mitochondrial replication. Bioinformatics analyses uncovered that the expression of genes involved in mitochondrial metabolism correlates with macroH2A1 and with cancer aggressiveness in UM patients. Altogether, our results suggest that macroH2A1 controls UM cells progression and it may represent a molecular target to develop new pharmacological strategies for UM treatment.

Mitochondrial Functions, Energy Metabolism and Protein Glycosylation are Interconnected Processes Mediating Resistance to Bortezomib in Multiple Myeloma Cells

The proteasome inhibitor bortezomib (BTZ) has emerged as an effective drug for the treatment of multiple myeloma even though many patients relapse from BTZ therapy. The present study investigated the metabolic pathways underlying the acquisition of bortezomib resistance in multiple myeloma. We used two different clones of multiple myeloma cell lines exhibiting different sensitivities to BTZ (U266 and U266-R) and compared them in terms of metabolic profile, mitochondrial fitness and redox balance homeostasis capacity. Our results showed that the BTZ-resistant clone (U266-R) presented increased glycosylated UDP-derivatives when compared to BTZ-sensitive cells (U266), thus also suggesting higher activities of the hexosamine biosynthetic pathway (HBP), regulating not only protein O- and N-glycosylation but also mitochondrial functions. Notably, U266-R displayed increased mitochondrial biogenesis and mitochondrial dynamics associated with stronger antioxidant defenses. Furthermore, U266-R maintained a significantly higher concentration of substrates for protein glycosylation when compared to U266, particularly for UDP-GlcNac, thus further suggesting the importance of glycosylation in the BTZ pharmacological response. Moreover, BTZ-treated U266-R showed significantly higher ATP/ADP ratios and levels of ECP and also exhibited increased mitochondrial fitness and antioxidant response. In conclusions, our findings suggest that the HBP may play a major role in mitochondrial fitness, driving BTZ resistance in multiple myeloma and thus representing a possible target for new drug development for BTZ-resistant patients.

Partial impairment of insulin receptor expression mimics fasting to prevent diet-induced fatty liver disease

Excessive insulin signaling through the insulin receptor (IR) may play a role in the pathogenesis of diet-induced metabolic disease, including obesity and type 2 diabetes. Here we investigate whether heterozygous impairment of insulin receptor (IR) expression limited to peripheral, i.e. non-CNS, tissues of adult mice impacts the development of high-fat diet-induced metabolic deterioration. While exhibiting some features of insulin resistance, PerIRKO^+/− mice display a hepatic energy deficit accompanied by induction of energy-sensing AMPK, mitochondrial biogenesis, PPARα, unexpectedly leading to protection from, and reversal of hepatic lipid accumulation (steatosis hepatis, NAFLD). Consistently, and unlike in control mice, the PPARα activator fenofibrate fails to further affect hepatic lipid accumulation in PerIRKO^+/− mice. Taken together, and opposing previously established diabetogenic features of insulin resistance, incomplete impairment of insulin signaling may mimic central aspects of calorie restriction to limit hepatic lipid accumulation during conditions of metabolic stress.

Hyper-insulinemia associated with excess calorie intake may cause metabolic dysfunction. Here the authors report that mice with partially reduced insulin receptor expression in peripheral tissues are protected from and experience reversal of fatty liver disease.

Modulation of Pro-Oxidant and Pro-Inflammatory Activities of M1 Macrophages by the Natural Dipeptide Carnosine

Carnosine is a natural endogenous dipeptide widely distributed in mammalian tissues, existing at particularly high concentrations in the muscles and brain and possesses well-characterized antioxidant and anti-inflammatory activities. In an in vitro model of macrophage activation, induced by lipopolysaccharide + interferon-gamma (LPS + IFN-γ), we here report the ability of carnosine to modulate pro-oxidant and pro-inflammatory activities of macrophages, representing the primary cell type that is activated as a part of the immune response. An ample set of parameters aimed to evaluate cytotoxicity (MTT assay), energy metabolism (HPLC), gene expressions (high-throughput real-time PCR (qRT-PCR)), protein expressions (western blot) and nitric oxide production (qRT-PCR and HPLC), was used to assess the effects of carnosine on activated macrophages challenged with a non cytotoxic LPS (100 ng/mL) + IFN-γ (600 U/mL) concentration. In our experimental model, main carnosine beneficial effects were: (1) the modulation of nitric oxide production and metabolism; (2) the amelioration of the macrophage energy state; (3) the decrease of the expressions of pro-oxidant enzymes (Nox-2, Cox-2) and of the lipid peroxidation product malondialdehyde; (4) the restoration and/or increase of the expressions of antioxidant enzymes (Gpx1, SOD-2 and Cat); (5) the increase of the transforming growth factor-β1 (TGF-β1) and the down-regulation of the expressions of interleukins 1β and 6 (IL-1β and IL-6) and 6) the increase of the expressions of Nuclear factor (erythroid-derived 2)-like 2 (Nrf2) and heme oxygenase-1 (HO-1). According to these results carnosine is worth being tested in the treatment of diseases characterized by elevated levels of oxidative stress and inflammation (atherosclerosis, cancer, depression, metabolic syndrome, and neurodegenerative diseases).

Aconitase 2 inhibits the proliferation of MCF-7 cells promoting mitochondrial oxidative metabolism and ROS/FoxO1-mediated autophagic response

Background

Deregulation of the tricarboxylic acid cycle (TCA) due to mutations in specific enzymes or defective aerobic metabolism is associated with tumour growth. Aconitase 2 (ACO2) participates in the TCA cycle by converting citrate to isocitrate, but no evident demonstrations of its involvement in cancer metabolism have been provided so far.

Methods

Biochemical assays coupled with molecular biology, in silico, and cellular tools were applied to circumstantiate the impact of ACO2 in the breast cancer cell line MCF-7 metabolism. Fluorescence lifetime imaging microscopy (FLIM) of NADH was used to corroborate the changes in bioenergetics.

Results

We showed that ACO2 levels are decreased in breast cancer cell lines and human tumour biopsies. We generated ACO2- overexpressing MCF-7 cells and employed comparative analyses to identify metabolic adaptations. We found that increased ACO2 expression impairs cell proliferation and commits cells to redirect pyruvate to mitochondria, which weakens Warburg-like bioenergetic features. We also demonstrated that the enhancement of oxidative metabolism was supported by mitochondrial biogenesis and FoxO1-mediated autophagy/mitophagy that sustains the increased ROS burst.

Conclusions

This work identifies ACO2 as a relevant gene in cancer metabolic rewiring of MCF-7 cells, promoting a different utilisation of pyruvate and revealing the potential metabolic vulnerability of ACO2-associated malignancies.

Pyruvate Dehydrogenase and Tricarboxylic Acid Cycle Enzymes Are Sensitive Targets of Traumatic Brain Injury Induced Metabolic Derangement

Using a closed-head impact acceleration model of mild or severe traumatic brain injury (mTBI or sTBI, respectively) in rats, we evaluated the effects of graded head impacts on the gene and protein expressions of pyruvate dehydrogenase (PDH), as well as major enzymes of mitochondrial tricarboxylic acid cycle (TCA). TBI was induced in anaesthetized rats by dropping 450 g from 1 (mTBI) or 2 m height (sTBI). After 6 h, 12 h, 24 h, 48 h, and 120 h gene expressions of enzymes and subunits of PDH. PDH kinases and phosphatases (PDK1-4 and PDP1-2, respectively), citrate synthase (CS), isocitrate dehydrogenase (IDH), oxoglutarate dehydrogenase (OGDH), succinate dehydrogenase (SDH), succinyl-CoA synthase (SUCLG), and malate dehydrogenase (MDH) were determined in whole brain extracts (n = 6 rats at each time for both TBI levels). In the same samples, the high performance liquid chromatographic (HPLC) determination of acetyl-coenzyme A (acetyl-CoA) and free coenzyme A (CoA-SH) was performed. Sham-operated animals (n = 6) were used as controls. After mTBI, the results indicated a general transient decrease, followed by significant increases, in PDH and TCA gene expressions. Conversely, permanent PDH and TCA downregulation occurred following sTBI. The inhibitory conditions of PDH (caused by PDP1-2 downregulations and PDK1-4 overexpression) and SDH appeared to operate only after sTBI. This produced almost no change in acetyl-CoA and free CoA-SH following mTBI and a remarkable depletion of both compounds after sTBI. These results again demonstrated temporary or steady mitochondrial malfunctioning, causing minimal or profound modifications to energy-related metabolites, following mTBI or sTBI, respectively. Additionally, PDH and SDH appeared to be highly sensitive to traumatic insults and are deeply involved in mitochondrial-related energy metabolism imbalance.

Carnosine Decreases PMA-Induced Oxidative Stress and Inflammation in Murine Macrophages

Carnosine is an endogenous dipeptide composed of β-alanine and L-histidine. This naturally occurring molecule is present at high concentrations in several mammalian excitable tissues such as muscles and brain, while it can be found at low concentrations in a few invertebrates. Carnosine has been shown to be involved in different cellular defense mechanisms including the inhibition of protein cross-linking, reactive oxygen and nitrogen species detoxification as well as the counteraction of inflammation. As a part of the immune response, macrophages are the primary cell type that is activated. These cells play a crucial role in many diseases associated with oxidative stress and inflammation, including atherosclerosis, diabetes, and neurodegenerative diseases. In the present study, carnosine was first tested for its ability to counteract oxidative stress. In our experimental model, represented by RAW 264.7 macrophages challenged with phorbol 12-myristate 13-acetate (PMA) and superoxide dismutase (SOD) inhibitors, carnosine was able to decrease the intracellular concentration of superoxide anions (O2-•) as well as the expression of Nox1 and Nox2 enzyme genes. This carnosine antioxidant activity was accompanied by the attenuation of the PMA-induced Akt phosphorylation, the down-regulation of TNF-α and IL-6 mRNAs, and the up-regulation of the expression of the anti-inflammatory mediators IL-4, IL-10, and TGF-β1. Additionally, when carnosine was used at the highest dose (20 mM), there was a generalized amelioration of the macrophage energy state, evaluated through the increase both in the total nucleoside triphosphate concentrations and the sum of the pool of intracellular nicotinic coenzymes. Finally, carnosine was able to decrease the oxidized (NADP+)/reduced (NADPH) ratio of nicotinamide adenine dinucleotide phosphate in a concentration dependent manner, indicating a strong inhibitory effect of this molecule towards the main source of reactive oxygen species in macrophages. Our data suggest a multimodal mechanism of action of carnosine underlying its beneficial effects on macrophage cells under oxidative stress and inflammation conditions.

DHA protects PC12 cells against oxidative stress and apoptotic signals through the activation of the NFE2L2/HO-1 axis

Docosahexaenoic acid (DHA) is an omega‑3 polyunsaturated fatty acid, derived mainly from fish oil. It is well known that DHA is present in high concentrations in nervous tissue and plays an important role in brain development and neuroprotection. However, the molecular mechanisms underlying its role remain to be fully elucidated. In this study, to enhance our understanding of the pathophysiological role of DHA, we investigated the possible neuroprotective mechanisms of action of DHA against hydrogen peroxide (H2O2)‑induced oxidative damage in a rat pheochromocytoma cell line (PC12). Specifically, we evaluated the viability, oxidation potential, and the expression and production of antioxidant/cytoprotective enzymes, and eventual apoptosis. We found that pre‑treatment with DHA (24 h) protected the cells from H2O2‑induced oxidative damage. In particular, pre‑treatment with DHA: i) Antagonized the consistent decrease in viability observed following exposure to H2O2 for 24 h; ii) reduced the high levels of intracellular reactive oxygen species (ROS) associated with H2O2‑induced oxidative stress; iii) increased the intracellular levels of enzymatic antioxidants [superoxide dismutase (SOD) and glutathione peroxidase (GSH‑Px)] both under basal conditions and following H2O2 exposure; iv) augmented the intracellular levels of reduced glutathione (GSH) and ascorbic acid, while it reduced the malondialdehyde (MDA) levels under conditions of oxidative stress; v) upregulated the expression of nuclear factor (erythroid‑derived 2)‑like 2 (NFE2L2) and its downstream target protein, heme‑oxygenase‑1 (HO‑1); and vi) induced an anti‑apoptotic effect by decreasing Bax and increasing Bcl2 expression. These findings provide evidence suggesting that DHA is able to prevent H2O2‑induced oxidative damage to PC12 cells, which is attributed to its antioxidant and anti‑apoptotic effects via the regulation NFE2L2/HO‑1 signaling. Therefore, DHA may play protective role in neurodegenerative diseases associated with oxidative stress.

Targeted Determination of Tissue Energy Status by LC-MS/MS

Intracellular nucleotides and acyl-CoAs are metabolites that are central to the regulation of energy metabolism. They set the cellular energy charge and redox state, act as allosteric regulators, modulate signaling and transcription factors, and thermodynamically activate substrates for oxidation or biosynthesis. Unfortunately, no method exists to simultaneously quantify these biomolecules in tissue extracts. A simple method was developed using ion-pairing reversed-phase high-performance liquid chromatography–electrospray-ionization tandem mass spectrometry (HPLC-ESI-MS/MS) to simultaneously quantify adenine nucleotides (AMP, ADP, and ATP), pyridine dinucleotides (NAD⁺ and NADH), and short-chain acyl-CoAs (acetyl, malonyl, succinyl, and propionyl). Quantitative analysis of these molecules in mouse liver was achieved using stable-isotope-labeled internal standards. The method was extensively validated by determining the linearity, accuracy, repeatability, and assay stability. Biological responsiveness was confirmed in assays of liver tissue with variable durations of ischemia, which had substantial effects on tissue energy charge and redox state. We conclude that the method provides a simple, fast, and reliable approach to the simultaneous analysis of nucleotides and short-chain acyl-CoAs.

Role of Mitochondria in Regulating Lutein and Chlorophyll Biosynthesis in Chlorella pyrenoidosa under Heterotrophic Conditions

The green alga Chlorella pyrenoidosa can accumulate lutein and chlorophyll under heterotrophic conditions. We propose that the mitochondrial respiratory electron transport chain (mRET) may be involved in this process. To verify this hypothesis, algal cells were treated with different mRET inhibitors. The biosynthesis of lutein and chlorophyll was found to be significantly stimulated by salicylhydroxamic acid (SHAM), whereas their contents substantially decreased after treatment with antimycin A and sodium azide (NaN₃). Proteomic studies revealed profound protein alterations related to the redox and energy states, and a network was proposed: The up-regulation of peroxiredoxin reduces oxidized glutathione (GSSG) to reduced glutathione (GSH); phosphoenolpyruvate carboxykinase (PEPCK) catalyzes the conversion of oxaloacetic acid to phosphoenolpyruvate, and after entering the methylerythritol phosphate (MEP) pathway, 4-hydroxy-3-methylbut-2-en-1yl diphosphate synthase reduces 2-C-methyl-d-erythritol-2,4-cyclodiphosphate (ME-Cpp) to 1-hydroxy-2-methyl-2-(E)-butenyl 4-diphosphate (HMBPP), which is closely related to the synthesis of lutein; and coproporphyrinogen III oxidase and ChlI play important roles in the chlorophyll biosynthetic pathway. These results supported that for the heterotrophic C. pyrenoidosa, the signaling, oriented from mRET, may regulate the nuclear genes encoding the enzymes involved in photosynthetic pigment biosynthesis.

Non-toxic engineered carbon nanodiamond concentrations induce oxidative/nitrosative stress, imbalance of energy metabolism, and mitochondrial dysfunction in microglial and alveolar basal epithelial cells

Engineered nanoparticles are finding a wide spectrum of biomedical applications, including drug delivery and capacity to trigger cytotoxic phenomena, potentially useful against tumor cells. The full understanding of their biosafety and interactions with cell processes is mandatory. Using microglial (BV-2) and alveolar basal epithelial (A549) cells, in this study we determined the effects of engineered carbon nanodiamonds (ECNs) on cell viability, nitric oxide (NO) and reactive oxygen species (ROS) production, as well as on energy metabolism. Particularly, we initially measured decrease in cell viability as a function of increasing ECNs doses, finding similar cytotoxic ECN effects in the two cell lines. Subsequently, using apparently non-cytotoxic ECN concentrations (2 µg/mL causing decrease in cell number < 5%) we determined NO and ROS production, and measured the concentrations of compounds related to energy metabolism, mitochondrial functions, oxido-reductive reactions, and antioxidant defences. We found that in both cell lines non-cytotoxic ECN concentrations increased NO and ROS production with sustained oxidative/nitrosative stress, and caused energy metabolism imbalance (decrease in high energy phosphates and nicotinic coenzymes) and mitochondrial malfunctioning (decrease in ATP/ADP ratio).These results underline the importance to deeply investigate the molecular and biochemical changes occurring upon the interaction of ECNs (and nanoparticles in general) with living cells, even at apparently non-toxic concentration. Since the use of ECNs in biomedical field is attracting increasing attention the complete evaluation of their biosafety, toxicity and/or possible side effects both in vitro and in vivo is mandatory before these highly promising tools might find the correct application.

Extraction and Quantitation of Nicotinamide Adenine Dinucleotide Redox Cofactors

AIMS

Accurate analysis of dinucleotide redox cofactors nicotinamide adenine dinucleotide phosphate reduced (NADPH), nicotinamide adenine dinucleotide phosphate (NADP⁺), nicotinamide adenine dinucleotide reduced (NADH), and nicotinamide adenine dinucleotide (NAD⁺) from biological samples is important to understanding cellular redox homeostasis. In this study, we aimed to develop a simple protocol for quenching metabolism and extracting NADPH that avoids interconversion among the reduced forms and the oxidized forms.

RESULTS

We compared seven different solvents for quenching and extraction of cultured mammalian cells and mouse tissues: a cold aqueous buffer commonly used in enzyme assays with and without detergent, hot aqueous buffer, and cold organic mixtures (80% methanol, buffered 75% acetonitrile, and acidic 40:40:20 acetonitrile:methanol:water with either 0.02 M or 0.1 M formic acid). Extracts were analyzed by liquid chromatography-mass spectrometry (LC-MS). To monitor the metabolite interconversion, cells were grown in ¹³C₆-glucose medium, and unlabeled standards were spiked into the extraction solvents. Interconversion between the oxidized and reduced forms was substantial except for the enzyme assay buffer with detergent, 80% methanol and 40:40:20 acetonitrile:methanol:water, with the 0.1 M formic acid mix giving the least interconversion and best recoveries. Absolute NAD⁺, NADH, NADP⁺, and NADPH concentrations in cells and mouse tissues were measured with this approach.

INNOVATION

We found that the interconversion between the reduced and oxidized forms during extraction is a major barrier to accurately measuring NADPH/NADP⁺ and NADH/NAD⁺ ratios. Such interconversion can be monitored by isotope labeling cells and spiking NAD(P)(H) standards.

CONCLUSION

Extraction with 40:40:20 acetonitrile:methanol:water with 0.1 M formic acid decreases interconversion and, therefore, is suitable for measurement of redox cofactor ratios using LC-MS. This solvent is also useful for general metabolomics. Samples should be neutralized immediately after extraction to avoid acid-catalyzed degradation. When LC-MS is not available and enzyme assays are accordingly used, inclusion of detergent in the aqueous extraction buffer reduces interconversion. Antioxid. Redox Signal. 28, 167-179.

Contribution of mitochondria to injury of hepatocytes and liver tissue by hyperthermia

OBJECTIVE

The aim of this study was to investigate functional changes of liver mitochondria within the experimentally modeled transition zone of radiofrequency ablation and to estimate possible contribution of these changes to the energy status of liver cells and the whole tissue.

MATERIALS AND METHODS

Experiments were carried out on mitochondria isolated from the perfused liver and isolated hepatocytes of male Wistar rats. Hyperthermia was induced by changing the temperature of perfusion medium in the range characteristic for the transition zone (38-52°C). After 15-min perfusion, mitochondria were isolated to investigate changes in the respiration rates and the membrane potential. Adenine nucleotides extracted from isolated hepatocytes and perfused liver subjected to hyperthermic treatment were analyzed by HPLC.

RESULTS

Hyperthermic liver perfusion at 42-52°C progressively impaired oxidative phosphorylation in isolated mitochondria. Significant inhibition of the respiratory chain components was observed after perfusion at 42°C, irreversible uncoupling became evident after liver perfusion at higher temperatures (46°C and above). After perfusion at 50-52°C energy supplying function of mitochondria was entirely compromised, and mitochondria turned to energy consumers. Hyperthermia-induced changes in mitochondrial function correlated well with changes in the energy status and viability of isolated hepatocytes, but not with the changes in the energy status of the whole liver tissue.

CONCLUSIONS

In this study the pattern of the adverse changes in mitochondrial functions that are progressing with increase in liver perfusion temperature was established. Results of experiments on isolated mitochondria and isolated hepatocytes indicate that hyperthermic treatment significantly and irreversibly inhibits energy-supplying function of mitochondria under conditions similar to those existing in the radiofrequency ablation transition zone and these changes can lead to death of hepatocytes. However, it was not possible to estimate contribution of mitochondrial injury to liver tissue energy status by estimating only hyperthermia-induced changes in adenine nucleotide amounts on the whole tissue level.

N-acetylaspartate supports the energetic demands of developmental myelination via oligodendroglial aspartoacylase

Breakdown of neuro-glial N-acetyl-aspartate (NAA) metabolism results in the failure of developmental myelination, manifest in the congenital pediatric leukodystrophy Canavan disease caused by mutations to the sole NAA catabolizing enzyme aspartoacylase. Canavan disease is a major point of focus for efforts to define NAA function, with available evidence suggesting NAA serves as an acetyl donor for fatty acid synthesis during myelination. Elevated NAA is a diagnostic hallmark of Canavan disease, which contrasts with a broad spectrum of alternative neurodegenerative contexts in which levels of NAA are inversely proportional to pathological progression. Recently generated data in the nur7 mouse model of Canavan disease suggests loss of aspartoacylase function results in compromised energetic integrity prior to oligodendrocyte death, abnormalities in myelin content, spongiform degeneration, and motor deficit. The present study utilized a next-generation "oligotropic" adeno-associated virus vector (AAV-Olig001) to quantitatively assess the impact of aspartoacylase reconstitution on developmental myelination. AAV-Olig001-aspartoacylase promoted normalization of NAA, increased bioavailable acetyl-CoA, and restored energetic balance within a window of postnatal development preceding gross histopathology and deteriorating motor function. Long-term effects included increased oligodendrocyte numbers, a global increase in myelination, reversal of vacuolation, and rescue of motor function. Effects on brain energy observed following AAV-Olig001-aspartoacylase gene therapy are shown to be consistent with a metabolic profile observed in mild cases of Canavan disease, implicating NAA in the maintenance of energetic integrity during myelination via oligodendroglial aspartoacylase.

Severity of experimental traumatic brain injury modulates changes in concentrations of cerebral free amino acids

In this study, concentrations of free amino acids (FAA) and amino group containing compounds (AGCC) following graded diffuse traumatic brain injury (mild TBI, mTBI; severe TBI, sTBI) were evaluated. After 6, 12, 24, 48 and 120 hr aspartate (Asp), glutamate (Glu), asparagine (Asn), serine (Ser), glutamine (Gln), histidine (His), glycine (Gly), threonine (Thr), citrulline (Cit), arginine (Arg), alanine (Ala), taurine (Tau), γ‐aminobutyrate (GABA), tyrosine (Tyr), S‐adenosylhomocysteine (SAH), l‐cystathionine (l‐Cystat), valine (Val), methionine (Met), tryptophane (Trp), phenylalanine (Phe), isoleucine (Ile), leucine (Leu), ornithine (Orn), lysine (Lys), plus N‐acetylaspartate (NAA) were determined in whole brain extracts (n = 6 rats at each time for both TBI levels). Sham‐operated animals (n = 6) were used as controls. Results demonstrated that mTBI caused modest, transient changes in NAA, Asp, GABA, Gly, Arg. Following sTBI, animals showed profound, long‐lasting modifications of Glu, Gln, NAA, Asp, GABA, Ser, Gly, Ala, Arg, Citr, Tau, Met, SAH, l‐Cystat, Tyr and Phe. Increase in Glu and Gln, depletion of NAA and Asp increase, suggested a link between NAA hydrolysis and excitotoxicity after sTBI. Additionally, sTBI rats showed net imbalances of the Glu‐Gln/GABA cycle between neurons and astrocytes, and of the methyl‐cycle (demonstrated by decrease in Met, and increase in SAH and l‐Cystat), throughout the post‐injury period. Besides evidencing new potential targets for novel pharmacological treatments, these results suggest that the force acting on the brain tissue at the time of the impact is the main determinant of the reactions ignited and involving amino acid metabolism.

Metabolic, enzymatic and gene involvement in cerebral glucose dysmetabolism after traumatic brain injury

In this study, the metabolic, enzymatic and gene changes causing cerebral glucose dysmetabolism following graded diffuse traumatic brain injury (TBI) were evaluated. TBI was induced in rats by dropping 450g from 1 (mild TBI; mTBI) or 2m height (severe TBI; sTBI). After 6, 12, 24, 48, and 120h gene expressions and enzymatic activities of glycolysis and pentose phosphate pathway (PPP) enzymes, and levels of lactate, ATP, ADP, ATP/ADP (indexing mitochondrial phosphorylating capacity), NADP(+), NADPH and GSH were determined in whole brain extracts (n=9 rats at each time for both TBI levels). Sham-operated animals (n=9) were used as controls. Results demonstrated that mTBI caused a late increase (48-120h post injury) of glycolytic gene expression and enzymatic activities, concomitantly with mitochondrial functional recovery (ATP and ATP/ADP normalization). No changes in lactate and PPP genes and enzymes, were accompanied by transient decrease in GSH, NADP(+), NADPH and NADPH/NADP(+). Animals following sTBI showed early increase (6-24h post injury) of glycolytic gene expression and enzymatic activities, occurring during mitochondrial malfunctioning (50% decrease in ATP and ATP/ADP). Higher lactate and lower GSH, NADP(+), NADPH, NADPH/NADP(+) than controls were recorded at anytime post injury (p<0.01). Both TBI levels caused metabolic and gene changes affecting glucose metabolism. Following mTBI, increased glucose flux through glycolysis is coupled to mitochondrial glucose oxidation. "True" hyperglycolysis occurs only after sTBI, where metabolic changes, caused by depressed mitochondrial phosphorylating capacity, act on genes causing net glycolytic flux increase uncoupled from mitochondrial glucose oxidation.

Stability of energy metabolites-An often overlooked issue in metabolomics studies: A review

Recent advances in analytical chemistry have set the stage for metabolite profiling to help understand complex molecular processes in physiology. Despite ongoing efforts, there are concerns regarding metabolomics workflows, since it has been shown that internal (enzyme activity, blood contamination, and the dynamic nature of metabolite concentrations) as well as external factors (storage, handling, and analysis method) may affect the metabolome profile. Many metabolites are intrinsically instable, particularly some of those associated with central carbon metabolism. While enzymatic conversions have been studied in great detail, nonenzymatic, chemical conversions received comparatively little attention. This review aims to give an in-depth overview of nonenzymatic energy metabolite degradation/interconversion chemistry focusing on a selected range of metabolites. Special attention will be given to qualitative (degradation pathways) as well as quantitative aspects, that may affect the acquisition of accurate data in the context of metabolomics studies. Problems related to the use of isotopically labeled internal standards hindering the quantitative analysis of common metabolites will be presented with an experimental example. Finally, general conclusions and perspectives are given.

Increased production of inosine and guanosine by means of metabolic engineering of the purine pathway in Ashbya gossypii

Background

Inosine and guanosine monophosphate nucleotides are convenient sources of the umami flavor, with attributed beneficial health effects that have renewed commercial interest in nucleotide fermentations. Accordingly, several bacterial strains that excrete high levels of inosine and guanosine nucleosides are currently used in the food industry for this purpose.

Results

In the present study, we show that the filamentous fungus Ashbya gossypii, a natural riboflavin overproducer, excretes high amounts of inosine and guanosine nucleosides to the culture medium. Following a rational metabolic engineering approach of the de novo purine nucleotide biosynthetic pathway, we increased the excreted levels of inosine up to 27-fold.

Conclusions

We generated Ashbya gossypii strains with improved production titers of inosine and guanosine. Our results point to Ashbya gossypii as the first eukaryotic microorganism representing a promising candidate, susceptible to further manipulation, for industrial nucleoside fermentation.

Electronic supplementary material

The online version of this article (doi:10.1186/s12934-015-0234-4) contains supplementary material, which is available to authorized users.

NAD(P)H:quinone oxidoreductase 1 activation reduces blood pressure through regulation of endothelial nitric oxide synthase acetylation in spontaneously hypertensive rats

BACKGROUND

Endothelial nitric oxide synthase (eNOS) is involved in blood pressure (BP) regulation through the production of nitric oxide. Sirtuin I (SIRT1), an NAD-dependent protein deacetylase, promotes vascular relaxation through deacetylation and activation of eNOS. β-Lapachone (βL) increases the cellular NAD(+)/NADH ratio by activating

NAD(P)H

quinone oxidoreductase 1 (NQO1). In this study, we verified whether activation of NQO1 by βL modulates BP through regulation of eNOS acetylation in a hypertensive animal model.

METHODS

Spontaneously hypertensive rats (SHRs) and an endothelial cell line (bEnd.3 cells) were used to investigate the hypotensive effect of βL and its mechanism of action.

RESULTS

βL treatment significantly lowered the BP in SHRs, but this hypotensive effect was completely blocked by eNOS inhibition with ω-nitro-l-arginine methyl ester. In vitro studies revealed that βL activated eNOS, which was accompanied by an increased NAD(+)/NADH ratio. Moreover, βL significantly decreased acetylation of eNOS; however, this reduced eNOS acetylation was completely precluded by inhibition of SIRT1 in the bEnd.3 cells and in the aorta of the SHRs. Consistent with these effects, βL-induced reduction in BP was also abolished by SIRT1 inhibition in the SHRs.

CONCLUSIONS

To the best of our knowledge, this is the first study to demonstrate that eNOS acetylation can be regulated by NQO1 activation in an SIRT1-dependent manner, which is correlated with the relief of hypertension. These findings provide strong evidence that NQO1 might be a new therapeutic target for hypertension.

β-Lapachone attenuates mitochondrial dysfunction in MELAS cybrid cells

Mitochondrial myopathy, encephalopathy, lactic acidosis, and stroke-like episodes (MELAS) is a mitochondrial disease caused by mutations in the mitochondrial genome. This study investigated the efficacy of β-lapachone (β-lap), a natural quinone compound, in rescuing mitochondrial dysfunction in MELAS cybrid cells. β-Lap significantly restored energy production and mitochondrial membrane potential as well as normalized the elevated ROS level in MELAS cybrid cells. Additionally, β-lap reduced lactic acidosis and restored glucose uptake in the MELAS cybrid cells. Finally, β-lap activated Sirt1 by increasing the intracellular NAD(+)/NADH ratio, which was accompanied by increased mtDNA content. Two other quinone compounds (idebenone and CoQ10) that have rescued mitochondrial dysfunction in previous studies of MELAS cybrid cells had a minimal effect in the current study. Taken together, these results demonstrated that β-lap may provide a novel therapeutic modality for the treatment of MELAS.

3-Nitropropionic acid-induced ischemia tolerance in the rat brain is mediated by reduced metabolic activity and cerebral blood flow

Tissue tolerance to ischemia can be achieved by noxious stimuli that are below a threshold to cause irreversible damage ('preconditioning'). Understanding the mechanisms underlying preconditioning may lead to the identification of novel therapeutic targets for diseases such as stroke. We here used the oxidative chain inhibitor 3-nitropropionic acid (NPA) to induce ischemia tolerance in a rat middle cerebral artery occlusion (MCAO) stroke model. Cerebral blood flow (CBF) and structural integrity were characterized by longitudinal magnetic resonance imaging (MRI) in combination with behavioral, histologic, and biochemical assessment of NPA-preconditioned animals and controls. Using this approach we show that the ischemia-tolerant state is characterized by a lower energy charge potential and lower CBF, indicating a reduced baseline metabolic demand, and therefore a cellular mechanism of neural protection. Blood vessel density and structural integrity were not altered by NPA treatment. When subjected to MCAO, preconditioned animals had a characteristic MRI signature consisting of enhanced CBF maintenance within the ischemic territory and intraischemic reversal of the initial cytotoxic edema, resulting in reduced infarct volumes. Thus, our data show that tissue protection through preconditioning occurs early during ischemia and indicate that a reduced cellular metabolism is associated with tissue tolerance to ischemia.

Dietary triheptanoin rescues oligodendrocyte loss, dysmyelination and motor function in the nur7 mouse model of Canavan disease

The inherited pediatric leukodystrophy Canavan disease is characterized by dysmyelination and severe spongiform degeneration, and is currently refractory to treatment. A definitive understanding of core disease mechanisms is lacking, but pathology is believed to result at least in part compromised fatty acid synthesis during myelination. Recent evidence generated in an animal model suggests that the breakdown of N-acetylaspartate metabolism in CD results in a heightened coupling of fatty acid synthesis to oligodendrocyte oxidative metabolism during the early stages of myelination, thereby causing acute oxidative stress. We present here the results of a dietary intervention designed to support oxidative integrity during developmental myelination in the nur7 mouse model of Canavan disease. Provision of the odd carbon triglyceride triheptanoin to neonatal nur7 mice reduced oxidative stress, promoted long-term oligodendrocyte survival, and increased myelin in the brain. Improvements in oligodendrocyte survival and myelination were associated with a highly significant reduction in spongiform degeneration and improved motor function in triheptanoin treated mice. Initiation of triheptanoin treatment in older animals resulted in markedly more modest effects on these same pathological indices, indicating a window of therapeutic intervention that corresponds with developmental myelination. These results support the targeting of oxidative integrity at early stages of Canavan disease, and provide a foundation for the clinical development of a non-invasive dietary triheptanoin treatment regimen.

Neuroglobin expression and oxidant/antioxidant balance after graded traumatic brain injury in the rat

Neuroglobin is a neuron-specific hexacoordinated globin capable of binding various ligands, including O2, NO, and CO, the biological function of which is still uncertain. Various studies seem to indicate that neuroglobin is a neuroprotective agent when overexpressed, acting as a potent inhibitor of oxidative and nitrosative stress. In this study, we evaluated the pathophysiological response of the neuroglobin gene and protein expression in the cerebral tissue of rats sustaining traumatic brain injury of differing severity, while simultaneously measuring the oxidant/antioxidant balance. Two levels of trauma (mild and severe) were induced in anesthetized animals using the weight-drop model of diffuse axonal injury. Rats were then sacrificed at 6, 12, 24, 48, and 120 h after traumatic brain injury, and the gene and protein expression of neuroglobin and the concentrations of malondialdehyde (as a parameter representative of reactive oxygen species-mediated damage), nitrite + nitrate (indicative of NO metabolism), ascorbate, and glutathione (GSH) were determined in the brain tissue. Results indicated that mild traumatic brain injury, although causing a reversible increase in oxidative/nitrosative stress (increase in malondialdehyde and nitrite + nitrate) and an imbalance in antioxidants (decrease in ascorbate and GSH), did not induce any change in neuroglobin. Conversely, severe traumatic brain injury caused an over nine- and a fivefold increase in neuroglobin gene and protein expression, respectively, as well as a remarkable increase in oxidative/nitrosative stress and depletion of antioxidants. The results of this study, showing a lack of effect in mild traumatic brain injury as well as asynchronous time course changes in neuroglobin expression, oxidative/nitrosative stress, and antioxidants in severe traumatic brain injury, do not seem to support the role of neuroglobin as an endogenous neuroprotective antioxidant agent, at least under pathophysiological conditions.

Rosiglitazone causes cardiotoxicity via peroxisome proliferator-activated receptor γ-independent mitochondrial oxidative stress in mouse hearts

This study aims to test the hypothesis that thiazolidinedione rosiglitazone (RSG), a selective peroxisome proliferator-activated receptor γ (PPARγ) agonist, causes cardiotoxicity independently of PPARγ. Energy metabolism and mitochondrial function were measured in perfused hearts isolated from C57BL/6, cardiomyocyte-specific PPARγ-deficient mice, and their littermates. Cardiac function and mitochondrial oxidative stress were measured in both in vitro and in vivo settings. Treatment of isolated hearts with RSG at the supratherapeutic concentrations of 10 and 30 μM caused myocardial energy deficiency as evidenced by the decreases in [PCr], [ATP], ATP/ADP ratio, energy charge with a concomitant cardiac dysfunction as indicated by the decreases in left ventricular systolic pressure, rates of tension development and relaxation, and by an increase in end-diastolic pressure. When incubated with tissue homogenate or isolated mitochondria at these same concentrations, RSG caused mitochondrial dysfunction as evidenced by the decreases in respiration rate, substrate oxidation rates, and activities of complexes I and IV. RSG also increased complexes I- and III-dependent O₂⁻ production, decreased glutathione content, inhibited superoxide dismutase, and increased the levels of malondialdehyde, protein carbonyl, and 8-hydroxy-2-deoxyguanosine in mitochondria, consistent with oxidative stress. N-acetyl-L-cysteine (NAC) 20 mM prevented RSG-induced above toxicity at those in vitro settings. Cardiomyocyte-specific PPARγ deletion and PPARγ antagonist GW9662 did not prevent the observed cardiotoxicity. Intravenous injection of 10 mg/kg RSG also caused cardiac dysfunction and oxidative stress, 600 mg/kg NAC antagonized these adverse effects. In conclusion, this study demonstrates that RSG at supratherapeutic concentrations causes cardiotoxicity via a PPARγ-independent mechanism involving oxidative stress-induced mitochondrial dysfunction in mouse hearts.

Effect of partially protected butyrate used as feed additive on growth and intestinal metabolism in sea bream (Sparus aurata)

Butyrate is a short-chain fatty acid extensively used in animal nutrition since it promotes increases in body weight and other multiple beneficial effects on the intestinal tract. Although such effects have been demonstrated in several species, very few studies have assessed them in fish. On the other hand, little is known about the metabolic processes underlying these effects. In the present work, growth parameters and changes in more than 80 intestinal metabolites (nucleotides, amino acids and derivatives, glycolytic intermediates, redox coenzymes and lipid metabolism coenzymes) have been quantified in juvenile sea bream fed a butyrate-supplemented diet. Results showed a significant increase in the weight of fish receiving butyrate, while metabolomics provided some clues on the suggested effects of this feed additive. It seems that butyrate increased the availability of several essential amino acids and nucleotide derivatives. Also, the energy provision for enteric cells might have been enhanced by a decrease in glucose and amino acid oxidation related to the use of butyrate as fuel. Additionally, butyrate might have increased transmethylation activity. This work represents an advance in the knowledge of the metabolic consequences of using butyrate as an additive in fish diets.

Chemical and technical challenges in the analysis of central carbon metabolites by liquid-chromatography mass spectrometry

This review deals with chemical and technical challenges in the analysis of small-molecule metabolites involved in central carbon and energy metabolism via liquid-chromatography mass-spectrometry (LC-MS). The covered analytes belong to the prominent pathways in biochemical carbon oxidation such as glycolysis or the tricarboxylic acid cycle and, for the most part, share unfavorable properties such as a high polarity, chemical instability or metal-affinity. The topic is introduced by selected examples on successful applications of metabolomics in the clinic. In the core part of the paper, the structural features of important analyte classes such as nucleotides, coenzyme A thioesters or carboxylic acids are linked to "problematic hotspots" along the analytical chain (sample preparation and-storage, separation and detection). We discuss these hotspots from a chemical point of view, covering issues such as analyte degradation or interactions with metals and other matrix components. Based on this understanding we propose solutions wherever available. A major notion derived from these considerations is that comprehensive carbon metabolomics inevitably requires multiple, complementary analytical approaches covering different chemical classes of metabolites.