Methods to monitor and compare mitochondrial and glycolytic ATP production

Advancements in Adenine Nucleotides Extraction and Quantification from a Single Drop of Human Blood

Adenine nucleotides (ANs)-adenosine 5'-triphosphate (ATP), adenosine 5'-diphosphate (ADP), and adenosine 5'-monophosphate (AMP)-are essential for energy transfer and the supply of countless processes within cellular metabolism. Their concentrations can be expressed as adenylate energy charge (AEC), a measure of cellular metabolic energy that directly correlates with the homeostasis of the organism. AEC index has broad diagnostic potential, as reduced ATP levels are associated to various conditions, such as inflammatory diseases, metabolic disorders, and cancer. We introduce a novel methodology for rapid isolation, purification, and quantification of ANs from a single drop of capillary blood. Of all the stationary phases tested, activated carbon proved to be the most efficient for the purification of adenine nucleotides, using an automated micro-solid phase extraction (µ-SPE) platform. An optimized µ-SPE method, coupled with RP-HPLC and a run time of 30 min, provides a reliable analytical framework for adenine nucleotide analysis of diverse biological samples. AN concentrations measured in capillary blood samples were 1393.1 µM, 254.8 µM, and 76.9 µM for ATP, ADP, and AMP molecules aligning with values reported in the literature. Overall, this study presents a streamlined and precise approach for analyzing ANs from microliters of blood, offering promising applications in clinical diagnostics.

Recent advances in fluorescent probes for ATP imaging

Adenosine-5'-triphosphate (ATP) is a critical biological molecule that functions as the primary energy currency within cells. ATP synthesis occurs in the mitochondria, and variations in its concentration can significantly influence mitochondrial and cellular performance. Prior studies have established a link between ATP levels and a variety of diseases, such as cancer, neurodegenerative conditions, ischemia, and hypoglycemia. Consequently, researchers have developed many fluorescent probes for ATP detection, recognizing the importance of monitoring intracellular ATP levels to understand cellular processes. These probes have been effectively utilized for visualizing ATP in living cells and biological samples. In this comprehensive review, we categorize fluorescent sensors developed in the last five years for ATP detection. We base our classification on fluorophores, structure, multi-response channels, and application. We also evaluate the challenges and potential for advancing new generations of fluorescence imaging probes for monitoring ATP in living cells. We hope this summary motivates researchers to design innovative and effective probes tailored to ATP sensing. We foresee imminent progress in the development of highly sophisticated ATP probes.

Thonzonium bromide inhibits progression of malignant pleural mesothelioma through regulation of ERK1/2 and p38 pathways and mitochondrial uncoupling

BACKGROUND

Malignant Pleural Mesothelioma (MPM) is a rare malignancy with a poor prognosis. Current therapies are unsatisfactory and novel cures are urgently needed. In a previous drug screening, we identified thonzonium bromide (TB) as one of the most active compounds against MPM cells. Since the biological effects of TB are poorly known, in this work we departed from some hints of previous studies and investigated several hypotheses. Moreover, we evaluated the efficacy of TB in an in vivo xenograft rodent model.

METHODS

In vitro assessment was made on five MPM (Mero-14, Mero-25, Ren, NCI-H28, MSTO-211H) and one SV40-immortalized mesothelial cell line (MeT-5A). We evaluated TB ability to affect proliferation, apoptosis, mitochondrial functions and metabolism, and the mevalonate pathway. In vivo assay was carried out on MPM-xenograft NOD-SCID mice (4 mg/kg delivered intraperitoneally, twice a week for 4 weeks) and the overall survival was analysed with Kaplan-Meier curves.

RESULTS

After TB treatment, we observed the suppression of ERK 1/2 phosphorylation, the increase of BAX expression and p38 phosphorylation. TB affected Ca2+ homeostasis in both mitochondrial and cytosolic compartments, it regulated the mitochondrial functioning, respiration, and ATP production as well as the mevalonate pathway. The in vivo study showed an increased overall survival for TB treated group vs. vehicle control group (P = 0.0076).

CONCLUSIONS

Both in vitro and in vivo results confirmed the effect of TB on MPM and unravelled novel targets with translational potential.

Mitochondrial techniques for physiologists

Mitochondria serve several important roles in maintaining cellular homeostasis, including adenosine triphosphate (ATP) synthesis, apoptotic signalling, and regulation of both reactive oxygen species (ROS) and calcium. Therefore, mitochondrial studies may reveal insights into metabolism at higher levels of physiological organization. The apparent complexity of mitochondrial function may be daunting to researchers new to mitochondrial physiology. This review is aimed, therefore, at such researchers to provide a brief, yet approachable overview of common techniques used to assess mitochondrial function. Here we discuss the use of high-resolution respirometry in mitochondrial experiments and common analytical platforms used for this technique. Next, we compare the use of common mitochondrial preparation techniques, including adherent cells, tissue homogenate, permeabilized fibers and isolated mitochondria. Finally, we outline additional techniques that can be used in tandem with high-resolution respirometry to assess additional aspects of mitochondrial metabolism, including ATP synthesis, calcium uptake, membrane potential and reactive oxygen species emission. We also include limitations to each of these techniques and outline recommendations for experimental design and interpretation. With a general understanding of methodologies commonly used to study mitochondrial physiology, experimenters may begin contributing to our understanding of this organelle, and how it affects other physiological phenotypes.

SEPN1-related myopathy depends on the oxidoreductase ERO1A and is druggable with the chemical chaperone TUDCA

Selenoprotein N (SEPN1) is a protein of the endoplasmic reticulum (ER) whose inherited defects originate SEPN1-related myopathy (SEPN1-RM). Here, we identify an interaction between SEPN1 and the ER-stress-induced oxidoreductase ERO1A. SEPN1 and ERO1A, both enriched in mitochondria-associated membranes (MAMs), are involved in the redox regulation of proteins. ERO1A depletion in SEPN1 knockout cells restores ER redox, re-equilibrates short-range MAMs, and rescues mitochondrial bioenergetics. ERO1A knockout in a mouse background of SEPN1 loss blunts ER stress and improves multiple MAM functions, including Ca2+ levels and bioenergetics, thus reversing diaphragmatic weakness. The treatment of SEPN1 knockout mice with the ER stress inhibitor tauroursodeoxycholic acid (TUDCA) mirrors the results of ERO1A loss. Importantly, muscle biopsies from patients with SEPN1-RM exhibit ERO1A overexpression, and TUDCA-treated SEPN1-RM patient-derived primary myoblasts show improvement in bioenergetics. These findings point to ERO1A as a biomarker and a viable target for intervention and to TUDCA as a pharmacological treatment for SEPN1-RM.

CD8+ T cell metabolic changes in breast cancer

Immunometabolism has advanced our understanding of how the cellular environment and nutrient availability regulates immune cell fate. Not only are metabolic pathways closely tied to cell signaling and differentiation, but can induce different subsets of immune cells to adopt unique metabolic programs, influencing disease progression. Dysregulation of immune cell metabolism plays an essential role in the progression of several diseases including breast cancer (BC). Metabolic reprogramming plays a critical role in regulating T cell functions. CD8⁺ T cells are an essential cell type within the tumor microenvironment (TME). To induce antitumor responses, CD8⁺ T cells need to adapt their metabolism to fulfill their energy requirement for effective function. However, different markers and immunologic techniques have made identifying specific CD8⁺ T cells subtypes in BC a challenge to the field. This review discusses the immunometabolic processes of CD8⁺ T cell in the TME in the context of BC and highlights the role of CD8⁺ T cell metabolic changes in tumor progression.

Activation of the sigma-1 receptor chaperone alleviates symptoms of Wolfram syndrome in preclinical models

The Wolfram syndrome is a rare autosomal recessive disease affecting many organs with life-threatening consequences; currently, no treatment is available. The disease is caused by mutations in the WSF1 gene, coding for the protein wolframin, an endoplasmic reticulum (ER) transmembrane protein involved in contacts between ER and mitochondria termed as mitochondria-associated ER membranes (MAMs). Inherited mutations usually reduce the protein's stability, altering its homeostasis and ultimately reducing ER to mitochondria calcium ion transfer, leading to mitochondrial dysfunction and cell death. In this study, we found that activation of the sigma-1 receptor (S1R), an ER-resident protein involved in calcium ion transfer, could counteract the functional alterations of MAMs due to wolframin deficiency. The S1R agonist PRE-084 restored calcium ion transfer and mitochondrial respiration in vitro, corrected the associated increased autophagy and mitophagy, and was able to alleviate the behavioral symptoms observed in zebrafish and mouse models of the disease. Our findings provide a potential therapeutic strategy for treating Wolfram syndrome by efficiently boosting MAM function using the ligand-operated S1R chaperone. Moreover, such strategy might also be relevant for other degenerative and mitochondrial diseases involving MAM dysfunction.

Metabolic therapy and bioenergetic analysis: The missing piece of the puzzle

BACKGROUND

Aberrant metabolism is recognized as a hallmark of cancer, a pillar necessary for cellular proliferation. Regarding bioenergetics (ATP generation), most cancers display a preference not only toward aerobic glycolysis ("Warburg effect") and glutaminolysis (mitochondrial substrate level-phosphorylation) but also toward other metabolites such as lactate, pyruvate, and fat-derived sources. These secondary metabolites can assist in proliferation but cannot fully cover ATP demands.

SCOPE OF REVIEW

The concept of a static metabolic profile is challenged by instances of heterogeneity and flexibility to meet fuel/anaplerotic demands. Although metabolic therapies are a promising tool to improve therapeutic outcomes, either via pharmacological targets or press-pulse interventions, metabolic plasticity is rarely considered. Lack of bioenergetic analysis in vitro and patient-derived models is hindering translational potential. Here, we review the bioenergetics of cancer and propose a simple analysis of major metabolic pathways, encompassing both affordable and advanced techniques. A comprehensive compendium of Seahorse XF bioenergetic measurements is presented for the first time.

MAJOR CONCLUSIONS

Standardization of principal readouts might help researchers to collect a complete metabolic picture of cancer using the most appropriate methods depending on the sample of interest.

Physiological, metabolomic, and transcriptomic analyses reveal the dynamic redox homeostasis upon extended exposure of Dunaliella salina GY-H13 cells to Cd

The study was done to elucidate the molecular mechanisms underlying the steady maintenance of the green microalga Dunaliella salina GY-H13 in successive subcultures in F/2 medium supplemented with the high cadmium (Cd) concentration (5 mg L^-1) for 3 months or 84 days using physiological, metabolomic, and transcriptomic methodologies. Physiological analysis indicated that Cd suppressed growth rate, photosynthetic efficiency, and pigment contents and promoted Cd accumulation, reactive oxygen species (ROS) generation and lipid peroxidation. UPLC-MS/MS-based metabolic analysis identified the top most upregulated and downregulated metabolites, the 5'-dehydroxyadenosine and thiamine acetic acid that were associated with the formation and removal of H₂O₂. RNA-seq-based transcriptomic analysis showed the overrepresentation of low-CO₂-inducible genes in the most downregulated gene set. Metabolomic and transcriptomic analyses further showed that the decreased GSSG/GSH-based redox potential, increased oxidative-phosphorylation gene expression, and reduced activity of TCA cycle in cells after extended exposure to Cd. Taken together, our results imply that cellular defense to Cd in D. salina is achieved by upregulation of ROS-scavenging activities including depletion of thiamine acetic acid. Dynamic redox homeostasis is maintained in cells with extended exposure to Cd by production of both oxidants and antioxidants through multiple pathways.

Validation of a method evaluating T cell metabolic potential in compliance with ICH Q2 (R1)

BACKGROUND

Metabolic cell features are able to give reliable information on cell functional state. Thus, metabolic potential assessment of T cells in malignancy setting represents a promising area, especially in adoptive cell therapy procedures. Easy to set up and convenient Seahorse technology have recently been proposed by Agilent Technologies and it could be used to monitor T cells metabolic potential. However, this method demonstrates an inter-assay variability and lacks practices standardization.

RESULTS

We aimed to overcome these shortcomings thanks to a lymphoblastic derived JURKAT cell line seeding in each experiment to standardize the Seahorse process. We used an adapted XF Cell MitoStress Kit protocol, consisting in the evaluation of basal, stressed and maximal glycolysis and oxidative phosphorylation related parameters, through sequential addition of oligomycin and carbonyl cyanide 4-(trifluoromethoxy)phenylhydrazone (FCCP) to a glucose containing medium. Data were acquired and analyzed through Agilent Seahorse XFe96 analyzer. Indeed, we validated this method in the light of ICH Q2 (R1) guidelines. We were able to confirm the specificity and accuracy of the method. We also demonstrated the precision, linearity and range of the method in our experimental conditions.

CONCLUSION

The validation of the method consisting in a JURKAT cell line experimental incorporation as a control material contributes to improve the Seahorse technology's robustness. These results lay the groundwork for the implementation of this technology to optimize T cell based cellular therapy products production process and monitoring.

Antimicrobial Peptide against Mycobacterium Tuberculosis That Activates Autophagy Is an Effective Treatment for Tuberculosis

Mycobacterium tuberculosis (MTB) is the principal cause of human tuberculosis (TB), which is a serious health problem worldwide. The development of innovative therapeutic modalities to treat TB is mainly due to the emergence of multi drug resistant (MDR) TB. Autophagy is a cell-host defense process. Previous studies have reported that autophagy-activating agents eliminate intracellular MDR MTB. Thus, combining a direct antibiotic activity against circulating bacteria with autophagy activation to eliminate bacteria residing inside cells could treat MDR TB. We show that the synthetic peptide, IP-1 (KFLNRFWHWLQLKPGQPMY), induced autophagy in HEK293T cells and macrophages at a low dose (10 μM), while increasing the dose (50 μM) induced cell death; IP-1 induced the secretion of TNFα in macrophages and killed Mtb at a dose where macrophages are not killed by IP-1. Moreover, IP-1 showed significant therapeutic activity in a mice model of progressive pulmonary TB. In terms of the mechanism of action, IP-1 sequesters ATP in vitro and inside living cells. Thus, IP-1 is the first antimicrobial peptide that eliminates MDR MTB infection by combining four activities: reducing ATP levels, bactericidal activity, autophagy activation, and TNFα secretion.

Various Aspects of Calcium Signaling in the Regulation of Apoptosis, Autophagy, Cell Proliferation, and Cancer

Calcium (Ca²⁺) is a major second messenger in cells and is essential for the fate and survival of all higher organisms. Different Ca²⁺ channels, pumps, or exchangers regulate variations in the duration and levels of intracellular Ca²⁺, which may be transient or sustained. These changes are then decoded by an elaborate toolkit of Ca²⁺-sensors, which translate Ca²⁺ signal to intracellular operational cell machinery, thereby regulating numerous Ca²⁺-dependent physiological processes. Alterations to Ca²⁺ homoeostasis and signaling are often deleterious and are associated with certain pathological states, including cancer. Altered Ca²⁺ transmission has been implicated in a variety of processes fundamental for the uncontrolled proliferation and invasiveness of tumor cells and other processes important for cancer progression, such as the development of resistance to cancer therapies. Here, we review what is known about Ca²⁺ signaling and how this fundamental second messenger regulates life and death decisions in the context of cancer, with particular attention directed to cell proliferation, apoptosis, and autophagy. We also explore the intersections of Ca²⁺ and the therapeutic targeting of cancer cells, summarizing the therapeutic opportunities for Ca²⁺ signal modulators to improve the effectiveness of current anticancer therapies.

The induction of AMPK-dependent autophagy leads to P53 degradation and affects cell growth and migration in kidney cancer cells

The most common subtype of renal cell carcinoma (RCC) is the clear cell RCC (ccRCC) that accounts for 70-80% of cases. The fate of ccRCC is linked to alterations of genes that regulate TP53. The dysfunction of p53 affects several processes including autophagy, which is increased in different advanced carcinomas and could be associated with cancer progression. We report that different kidney cancer cell lines show higher levels of autophagy than control cells. The increased autophagy is associated with the upregulation of miR501-5p, which stimulates mTOR-independent autophagy by the activation of AMP kinase. AMPK activation occurs through the decrease of ATP generation caused by the downregulation of the mitochondrial calcium uniporter (MCU) that leads to the reduction of mitochondrial calcium uptake. Autophagy induction promotes the degradation of p53 through the autophagolysosomal machinery. Consistently, the inhibition of autophagy reduces both cell proliferation and migration enhancing the expression of p53, p21 and E-Cadherin as well as decreasing Vimentin synthesis. Taken together, these findings indicate that autophagy is involved in the progression of kidney cancer. Therefore, the pharmacological targeting of this process could be considered an interesting option for the treatment of advanced renal carcinoma.

Detection of Extracellular ATP in the Tumor Microenvironment, Using the pmeLUC Biosensor

ATP is one of the main components of the tumor microenvironment, where it affects cell growth, tumor progression and antitumor immune response. The development of the pmeLUC probe, a luciferase engineered to be expressed on the outer facet of the plasma membrane, allowed real-time measurement of extracellular ATP in vitro and in vivo systems, among which the tumor microenvironment. Here we describe the experimental procedures to measure extracellular ATP levels in the tumor microenvironment of three different cancer models generated by the implant of pmeLUC-expressing tumor cells into the appropriate mice strain: ACN human neuroblastoma (nude/nude mice host), WEHI-3B murine leukemia (BALB/c host), and B16F10 murine melanoma (C57Bl/6 host). The procedure to obtain stable expression of pmeLUC in different cell types and methods for the measurement of extracellular ATP with pmeLUC in vitro are also described.

3D bimetallic Au/Pt nanoflowers decorated needle-type microelectrode for direct in situ monitoring of ATP secreted from living cells

Adenosine triphosphate (ATP) plays a crucial role in energy metabolism and extracellular purinergic signaling. A 3D bimetallic Au/Pt nanoflowers decorated ATP microelectrode biosensor prepared by facile and effective template-free electrodeposition was firstly reported, realizing local detection of cellular ATP secretion. The ATP biosensor was developed by co-immobilization of glucose oxidase and hexokinase, exhibiting long-term stability (79.39 ± 9.15% of its initial value remained after 14 days at 4 °C) and high selectivity with a limit of detection down to 2.5 μM (S/N = 3). The resulting ATP biosensor was then used for direct in situ monitoring of ATP secreted from living cells (PC12) with the stimulation of high K⁺ solutions. The obtained current was about 21.6 ± 3.4 nA (N = 6), corresponding to 12.2 ± 2.8 μM ATP released from cells, right in the micromolar range and consistent with the suggested levels. The 3D bimetallic Au/Pt nanoflowers possess excellent catalytic activity and large electroactive surface area, contributing to enzymatic activity preservation and long-term stability. This work provides a promising platform for long-time monitoring of other neurotransmitters and secretions in cellular glycolysis and apoptosis processes in the future.

Measurement of ATP concentrations in mitochondria of living cells using luminescence and fluorescence approaches

Adenosine 5'-triphosphate (ATP) is the central metabolite in the energy metabolism of cells and is hydrolyzed to ADP and inorganic phosphate to provide free energy in various cellular processes. ATP also functions as an intracellular signaling molecule. Thus, it is important to know the ATP concentration within cells to understand cellular activities. Here, we describe two methods to detect ATP concentrations in the cytoplasm and mitochondrial matrix using genetically encoded luminescent or fluorescent biosensors. These methods enable quantitative investigation of ATP concentration dynamics in living cells, single cells and cell populations.

Understanding and leveraging cell metabolism to enhance mesenchymal stem cell transplantation survival in tissue engineering and regenerative medicine applications

In tissue engineering and regenerative medicine, stem cell-specifically, mesenchymal stromal/stem cells (MSCs)-therapies have fallen short of their initial promise and hype. The observed marginal, to no benefit, success in several applications has been attributed primarily to poor cell survival and engraftment at transplantation sites. MSCs have a metabolism that is flexible enough to enable them to fulfill their various cellular functions and remarkably sensitive to different cellular and environmental cues. At the transplantation sites, MSCs experience hostile environments devoid or, at the very least, severely depleted of oxygen and nutrients. The impact of this particular setting on MSC metabolism ultimately affects their survival and function. In order to develop the next generation of cell-delivery materials and methods, scientists must have a better understanding of the metabolic switches MSCs experience upon transplantation. By designing treatment strategies with cell metabolism in mind, scientists may improve survival and the overall therapeutic potential of MSCs. Here, we provide a comprehensive review of plausible metabolic switches in response to implantation and of the various strategies currently used to leverage MSC metabolism to improve stem cell-based therapeutics.

Vimentin disruption by lipoxidation and electrophiles: Role of the cysteine residue and filament dynamics

The intermediate filament protein vimentin constitutes a critical sensor for electrophilic and oxidative stress, which induce extensive reorganization of the vimentin cytoskeletal network. Here, we have investigated the mechanisms underlying these effects. In vitro, electrophilic lipids, including 15-deoxy-Δ12,14-prostaglandin J2 (15d-PGJ2) and 4-hydroxynonenal (HNE), directly bind to vimentin, whereas the oxidant diamide induces disulfide bond formation. Mutation of the single vimentin cysteine residue (Cys328) blunts disulfide formation and reduces lipoxidation by 15d-PGJ2, but not HNE. Preincubation with these agents differentially hinders NaCl-induced filament formation by wild-type vimentin, with effects ranging from delayed elongation and increased filament diameter to severe impairment of assembly or aggregation. Conversely, the morphology of vimentin Cys328Ser filaments is mildly or not affected. Interestingly, preformed vimentin filaments are more resistant to electrophile-induced disruption, although chemical modification is not diminished, showing that vimentin (lip)oxidation prior to assembly is more deleterious. In cells, electrophiles, particularly diamide, induce a fast and drastic disruption of existing filaments, which requires the presence of Cys328. As the cellular vimentin network is under continuous remodeling, we hypothesized that vimentin exchange on filaments would be necessary for diamide-induced disruption. We confirmed that strategies reducing vimentin dynamics, as monitored by FRAP, including cysteine crosslinking and ATP synthesis inhibition, prevent diamide effect. In turn, phosphorylation may promote vimentin disassembly. Indeed, treatment with the phosphatase inhibitor calyculin A to prevent dephosphorylation intensifies electrophile-induced wild-type vimentin filament disruption. However, whereas a phosphorylation-deficient vimentin mutant is only partially protected from disorganization, Cys328Ser vimentin is virtually resistant, even in the presence of calyculin A. Together, these results indicate that modification of Cys328 and vimentin exchange are critical for electrophile-induced network disruption.

A brief review of bioluminescent systems (2019)

Despite being widely used in reporter technologies, bioluminescent systems are largely understudied. Of at least forty different bioluminescent systems thought to exist in nature, molecular components of only seven light-emitting reactions are known, and the full biochemical pathway leading to light emission is only understood for two of them. Here, we provide a succinct overview of currently known bioluminescent systems highlighting available tools for research and discussing future applications.

The enigmatic ATP supply of the endoplasmic reticulum

The endoplasmic reticulum (ER) is a functionally and morphologically complex cellular organelle largely responsible for a variety of crucial functions, including protein folding, maturation and degradation. Furthermore, the ER plays an essential role in lipid biosynthesis, dynamic Ca²⁺ storage, and detoxification. Malfunctions in ER‐related processes are responsible for the genesis and progression of many diseases, such as heart failure, cancer, neurodegeneration and metabolic disorders. To fulfill many of its vital functions, the ER relies on a sufficient energy supply in the form of adenosine‐5′‐triphosphate (ATP), the main cellular energy source. Despite landmark discoveries and clarification of the functional principles of ER‐resident proteins and key ER‐related processes, the mechanism underlying ER ATP transport remains somewhat enigmatic. Here we summarize ER‐related ATP‐consuming processes and outline our knowledge about the nature and function of the ER energy supply.

Bioenergetics of life, disease and death phenomena

In this article, some new aspects of unified cell bioenergetics are presented. From the perspective of unified cell bioenergetics certain subsequent stages of cancer development, from initiation stage, through transformation to metastasis, are analyzed. Here we show that after transformation, cancer cells are permanently exposed to reactive oxygen species, that causes continual random DNA mutations and as a result genome and chromosomal destabilizations. The modern cancer attractor hypothesis has been extended in explaining cancer development. Discussion is conducted in light of current cancerogenesis research, including bioenergetic cancer initiation, the somatic mutation theory and the tissue organization field theory. In the article reasons complicating the discovery of patterns of cancer genome changes and cancer evolution are presented. In addition certain cancer therapeutic aspects are given attention to.

1001 lights: luciferins, luciferases, their mechanisms of action and applications in chemical analysis, biology and medicine

Bioluminescence (BL) is a spectacular phenomenon involving light emission by live organisms. It is caused by the oxidation of a small organic molecule, luciferin, with molecular oxygen, which is catalysed by the enzyme luciferase. In nature, there are approximately 30 different BL systems, of which only 9 have been studied to various degrees in terms of their reaction mechanisms. A vast range of in vitro and in vivo analytical techniques have been developed based on BL, including tests for different analytes, immunoassays, gene expression assays, drug screening, bioimaging of live organisms, cancer studies, the investigation of infectious diseases and environmental monitoring. This review aims to cover the major existing applications for bioluminescence in the context of the diversity of luciferases and their substrates, luciferins. Particularly, the properties and applications of d-luciferin, coelenterazine, bacterial, Cypridina and dinoflagellate luciferins and their analogues along with their corresponding luciferases are described. Finally, four other rarely studied bioluminescent systems (those of limpet Latia, earthworms Diplocardia and Fridericia and higher fungi), which are promising for future use, are also discussed.

Use of luciferase probes to measure ATP in living cells and animals

ATP, the energy exchange factor that connects anabolism and catabolism, is required for major reactions and processes that occur in living cells, such as muscle contraction, phosphorylation and active transport. ATP is also the key molecule in extracellular purinergic signaling mechanisms, with an established crucial role in inflammation and several additional disease conditions. Here, we describe detailed protocols to measure the ATP concentration in isolated living cells and animals using luminescence techniques based on targeted luciferase probes. In the presence of magnesium, oxygen and ATP, the protein luciferase catalyzes oxidation of the substrate luciferin, which is associated with light emission. Recombinantly expressed wild-type luciferase is exclusively cytosolic; however, adding specific targeting sequences can modify its cellular localization. Using this strategy, we have constructed luciferase chimeras targeted to the mitochondrial matrix and the outer surface of the plasma membrane. Here, we describe optimized protocols for monitoring ATP concentrations in the cytosol, mitochondrial matrix and pericellular space in living cells via an overall procedure that requires an average of 3 d. In addition, we present a detailed protocol for the in vivo detection of extracellular ATP in mice using luciferase-transfected reporter cells. This latter procedure may require up to 25 d to complete.

Mitoenergetic Dysfunction Triggers a Rapid Compensatory Increase in Steady-State Glucose Flux

ATP can be produced in the cytosol by glycolytic conversion of glucose (GLC) into pyruvate. The latter can be metabolized into lactate, which is released by the cell, or taken up by mitochondria to fuel ATP production by the tricarboxylic acid cycle and oxidative phosphorylation (OXPHOS) system. Altering the balance between glycolytic and mitochondrial ATP generation is crucial for cell survival during mitoenergetic dysfunction, which is observed in a large variety of human disorders including cancer. To gain insight into the kinetic properties of this adaptive mechanism we determined here how acute (30 min) inhibition of OXPHOS affected cytosolic GLC homeostasis. GLC dynamics were analyzed in single living C2C12 myoblasts expressing the fluorescent biosensor FLII(12)Pglu-700μδ6 (FLII). Following in situ FLII calibration, the kinetic properties of GLC uptake (V1) and GLC consumption (V2) were determined independently and used to construct a minimal mathematical model of cytosolic GLC dynamics. After validating the model, it was applied to quantitatively predict V1 and V2 at steady-state (i.e., when V1 = V2 = Vsteady-state) in the absence and presence of OXPHOS inhibitors. Integrating model predictions with experimental data on lactate production, cell volume, and O2 consumption revealed that glycolysis and mitochondria equally contribute to cellular ATP production in control myoblasts. Inhibition of OXPHOS induced a twofold increase in Vsteady-state and glycolytic ATP production flux. Both in the absence and presence of OXPHOS inhibitors, GLC was consumed at near maximal rates, meaning that GLC consumption is rate-limiting under steady-state conditions. Taken together, we demonstrate here that OXPHOS inhibition increases steady-state GLC uptake and consumption in C2C12 myoblasts. This activation fully compensates for the reduction in mitochondrial ATP production, thereby maintaining the balance between cellular ATP supply and demand.

A Fluorescent, Reagentless Biosensor for ATP, Based on Malonyl-Coenzyme A Synthetase

A fluorescent reagentless biosensor for ATP has been developed, based on malonyl-coenzyme A synthetase from Rhodopseudomonas palustris as the protein scaffold and recognition element. Two 5-iodoacetamidotetramethylrhodamines were covalently bound to this protein to provide the readout. This adduct couples ATP binding to a 3.7-fold increase in fluorescence intensity with excitation at 553 nm and emission at 575 nm. It measures ATP concentrations with micromolar sensitivity and is highly selective for ATP relative to ADP. Its ability to monitor enzymatic ATP production or depletion was demonstrated in steady-state kinetic assays in which ATP is a product or substrate, respectively.

Breast Cancer Metabolism and Mitochondrial Activity: The Possibility of Chemoprevention with Metformin

Metabolic reprogramming refers to the ability of cancer cells to alter their metabolism in order to support the increased energy request due to continuous growth, rapid proliferation, and other characteristics typical of neoplastic cells. It has long been believed that the increase of metabolic request was independent of the mitochondrial action but recently we know that mitochondrial activity together with metabolism plays a pivotal role in the regulation of the energy needed for tumor cell growth and proliferation. For these reasons the mitochondria pathways could be a new target for therapeutic and chemopreventive intervention. Metformin in particular is actually considered a promising agent against mitochondrial activity thanks to its ability to inhibit the mitochondrial complex I.