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

Cancer stem cells, epithelial-mesenchymal transition, ATP and their roles in drug resistance in cancer

The cancer stem cell (CSC) state and epithelial-mesenchymal transition (EMT) activation are tightly interconnected. Cancer cells that acquire the EMT/CSC phenotype are equipped with adaptive metabolic changes to maintain low reactive oxygen species levels and stemness, enhanced drug transporters, anti-apoptotic machinery and DNA repair system. Factors present in the tumor microenvironment such as hypoxia and the communication with non-cancer stromal cells also promote cancer cells to enter the EMT/CSC state and display related resistance. ATP, particularly the high levels of intratumoral extracellular ATP functioning through both signaling pathways and ATP internalization, induces and regulates EMT and CSC. The three of them work together to enhance drug resistance. New findings in each of these factors will help us explore deeper into mechanisms of drug resistance and suggest new resistance-associated markers and therapeutic targets.

The heme synthesis-export system regulates the tricarboxylic acid cycle flux and oxidative phosphorylation

Heme is an iron-containing porphyrin of vital importance for cell energetic metabolism. High rates of heme synthesis are commonly observed in proliferating cells. Moreover, the cell-surface heme exporter feline leukemia virus subgroup C receptor 1a (FLVCR1a) is overexpressed in several tumor types. However, the reasons why heme synthesis and export are enhanced in highly proliferating cells remain unknown. Here, we illustrate a functional axis between heme synthesis and heme export: heme efflux through the plasma membrane sustains heme synthesis, and implementation of the two processes down-modulates the tricarboxylic acid (TCA) cycle flux and oxidative phosphorylation. Conversely, inhibition of heme export reduces heme synthesis and promotes the TCA cycle fueling and flux as well as oxidative phosphorylation. These data indicate that the heme synthesis-export system modulates the TCA cycle and oxidative metabolism and provide a mechanistic basis for the observation that both processes are enhanced in cells with high-energy demand.

Evaluation of anticancer effects in vitro of new iridium(III) complexes targeting the mitochondria

Iridium(III) complexes have the potential to serve as novel therapeutic drugs for treating tumor. In this work, three new complexes [Ir(ppy)₂(cdppz)](PF₆) (1) (ppy = 2-phenylpyridine, cdppz = 11-chlorodipyrido[3,2-a,2',3'-c]phenazine), [Ir(bzq)₂(cdppz)](PF₆) (2) (bzq = benzo[h]quinolone) and [Ir(piq)₂(cdppz)](PF₆) (3) (piq = 1-phenylisoquinoline) were prepared as well as characterized. MTT (3-(4,5-dimethylthiazole)-2,5-diphenyltetraazolium bromide) assay revealed that the complex 2 exerted potent cytotoxicity against to various cancer cells lines and particularly for SGC-7901 cells. Meanwhile, the complexes could suppress cell colonies formation and migration ability. Apoptosis assays of AO/EB staining as well as flow cytometry revealed that the synthesized complexes may cause apoptosis of SGC-7901 cells. Moreover, the decline of mitochondrial membrane potential (MMP), elevation of intracellular reactive oxygen species (ROS) levels and release of cytochrome c demonstrated the complexes could cause apoptosis mainly through the mitochondrial death pathway and arrest cell at G0/G1 phase. Additionally, the complexes have significant influence on the expression of proteins which is interrelated to cell apoptosis. In summary, our studies provided fundamental information regarding the further study of the possible anticancer mechanisms of iridium (III) complexes.

In Vitro Liver Toxicity Testing of Chemicals: A Pragmatic Approach

The liver is among the most frequently targeted organs by noxious chemicals of diverse nature. Liver toxicity testing using laboratory animals not only raises serious ethical questions, but is also rather poorly predictive of human safety towards chemicals. Increasing attention is, therefore, being paid to the development of non-animal and human-based testing schemes, which rely to a great extent on in vitro methodology. The present paper proposes a rationalized tiered in vitro testing strategy to detect liver toxicity triggered by chemicals, in which the first tier is focused on assessing general cytotoxicity, while the second tier is aimed at identifying liver-specific toxicity as such. A state-of-the-art overview is provided of the most commonly used in vitro assays that can be used in both tiers. Advantages and disadvantages of each assay as well as overall practical considerations are discussed.

Biological insights from the direct measurement of purine release

Although purinergic signalling has been a well-established and accepted mechanism of chemical communication for many years, it remains important to measure the extracellular concentration of ATP and adenosine in real time. In this review I summarize the reasons why such measurements are still needed, how they provide additional mechanistic insight and give an overview of the techniques currently available to make spatially localised measurements of ATP and adenosine in real time. To illustrate the impact of direct real-time measurements, I explore CO2 and nutrient sensing in the medulla oblongata and hypothalamus. In both of these examples, the sensing involves hemichannel mediated ATP release from glial cells. For CO2 the hemichannels involved, connexin26, are directly CO2-sensitive. This mechanism contributes to the chemosensory control of breathing. In the hypothamalus, specialised glial cells, tanycytes, directly contact the cerebrospinal fluid in the 3rd ventricle and sense nutrients via sweet and umami taste receptors. Nutrient sensing by tanycytes is likely to contribute to the control of body weight as their selective stimulation alters food intake. To illustrate the importance of direct adenosine measurements, I consider the complex and multiple mechanisms of activity-dependent adenosine release in different brain regions. This activity dependent release of adenosine is likely to mediate important feedback regulation and may also be involved in controlling the sleep-wake state. I finish by briefly considering the potential of whole blood purine measurements in clinical practice.

Mitochondrial Function as a Potential Tool for Assessing Function, Quality and Adulteration in Medicinal Herbal Teas

Quality control has been a significant issue in herbal medicine since herbs became widely used to heal. Modern technologies have improved the methods of evaluating the quality of medicinal herbs but the methods of adulterating them have also grown in sophistication. In this paper we undertook a comprehensive literature search to identify the key analytical techniques used in the quality control of herbal medicine, reviewing their uses and limitations. We also present a new tool, based on mitochondrial profiling, that can be used to measure medicinal herbal quality. Besides being fundamental to the energy metabolism required for most cellular activities, mitochondria play a direct role in cellular signalling, apoptosis, stress responses, inflammation, cancer, ageing, and neurological function, mirroring some of the most common reasons people take herbal medicines. A fingerprint of the specific mitochondrial effects of medicinal herbs can be documented in order to assess their potential efficacy, detect adulterations that modulate these effects and determine the relative potency of batches. Furthermore, through this method it will be possible to assess whole herbs or complex formulas thus avoiding the issues inherent in identifying active ingredients which may be complex or unknown. Thus, while current analytical methods focus on determining the chemical quality of herbal medicines, including adulteration and contamination, mitochondrial functional analysis offers a new way of determining the quality of plant derived products that is more closely linked to the biological activity of a product and its potential clinical effectiveness.

A naturally occurring mutation in ATP synthase subunit c is associated with increased damage following hypoxia/reoxygenation in STEMI patients

Preclinical models of ischemia/reperfusion injury (RI) demonstrate the deleterious effects of permeability transition pore complex (PTPC) opening in the first minutes upon revascularization of the occluded vessel. The ATP synthase c subunit (Csub) influences PTPC activity in cells, thus impacting tissue injury. A conserved glycine-rich domain in Csub is classified as critical because, when mutated, it modifies ATP synthase properties, protein interaction with the mitochondrial calcium (Ca²⁺) uniporter complex, and the conductance of the PTPC. Here, we document the role of a naturally occurring mutation in the Csub-encoding ATP5G1 gene at the G87 position found in two ST-segment elevation myocardial infarction (STEMI) patients and how PTPC opening is related to RI in patients affected by the same disease. We report a link between the expression of ATP5G1^G87E and the response to hypoxia/reoxygenation of human cardiomyocytes, which worsen when compared to those expressing the wild-type protein, and a positive correlation between PTPC and RI.

Early-Phase Luciferase Signals of Islet Grafts Predicts Successful Subcutaneous Site Transplantation in Rats

PURPOSE

The transplantation of pancreatic islets is a promising cell replacement therapy for type 1 diabetes. Subcutaneous islet transplantation is currently under investigation as a means to circumvent problems associated with standard intra-hepatic islet transplantation. As modifications are being developed to improve the efficacy of subcutaneous islet transplantation, it is important to have robust methods to assess engraftment. Experimentally, ATP-dependent bioluminescence imaging using luciferase reporter genes has been effective for non-invasively tracking engraftment. However, it was heretofore unknown if the bioluminescence of subcutaneously transplanted luciferase-expressing islet grafts correlates with diabetes reversal, a primary outcome of transplantation.

PROCEDURES

A retrospective analysis was conducted using data obtained from subcutaneous islet transplantations in Lewis rats. The analysis included transplantations from our laboratory in which islet donors were transgenic rats ubiquitously expressing luciferase and recipients were wild type, streptozotocin-induced diabetic rats. Data from 79 bioluminescence scans were obtained from 27 islet transplantations during the post-transplant observation period (up to 6 weeks). The bioluminescence intensity of the subcutaneously transplanted grafts, captured after the intravenous administration of luciferin, was correlated with diabetes reversal.

RESULTS

After subcutaneous transplantation, islet bioluminescence decreased over time, dropping > 50 % from 1 to 3 weeks post-transplant. Bioluminescence intensity in the early post-transplant phase (1-2 weeks) correlated with the subsequent reversal of diabetes; based on optimized bioluminescence cutoff values, the bioluminescence intensity of islets at 1 and 2 weeks predicted successful transplantations. However, intensity in the late post-transplant phase (≥ 4 weeks) did not reflect transplantation outcomes.

CONCLUSIONS

Early-phase bioluminescence imaging of luciferase-expressing islets could serve as a useful tool to predict the success of subcutaneous islet transplantations by preceding changes in glucose homeostasis.

Monocytes in the Tumor Microenvironment

Immunotherapy has revolutionized cancer treatment over the past decade. Nonetheless, prolonged survival is limited to relatively few patients. Cancers enforce a multifaceted immune-suppressive network whose nature is progressively shaped by systemic and local cues during tumor development. Monocytes bridge innate and adaptive immune responses and can affect the tumor microenvironment through various mechanisms that induce immune tolerance, angiogenesis, and increased dissemination of tumor cells. Yet monocytes can also give rise to antitumor effectors and activate antigen-presenting cells. This yin-yang activity relies on the plasticity of monocytes in response to environmental stimuli. In this review, we summarize current knowledge of the ontogeny, heterogeneity, and functions of monocytes and monocyte-derived cells in cancer, pinpointing the main pathways that are important for modeling the immunosuppressive tumor microenvironment.

P2X7 is a cytotoxic receptor….maybe not: implications for cancer

The tumor microenvironment is rich in extracellular ATP. This nucleotide affects both cancer and infiltrating immune cell responses by acting at P2 receptors, chiefly P2X7. ATP is then degraded to generate adenosine, a very powerful immunosuppressant. The purinergic hypothesis put forward by Geoff Burnstock prompted innovative investigation in this field and provided the intellectual framework to interpret a myriad of experimental findings. This is a short appraisal of how Geoff's inspiration influenced cancer studies and my own investigation highlighting the key role of the P2X7 receptor.

AIEgen-based nanoprobe for the ATP sensing and imaging in cancer cells and embryonic stem cells

A turn-on fluorescent nanoprobe (named AAP-1), based on an aggregation-induced emission luminogen (AIEgen), is disclosed for the detection of adenosine triphosphate (ATP), which is an essential element in the biological system. Organic fluorophore (named TPE-TA) consists of tetraphenylethylene (TPE, sensing and signaling moiety) and mono-triamine (TA, sensing moiety), and it forms an aggregated form in aqueous media as a nanoprobe AAP-1. The nanoprobe AAP-1 has multiple electrostatic interactions as well as hydrophobic interactions with ATP, and it displays superior selectivity toward ATP, reliable sensitivity, with a detection limit around 0.275 ppb, and fast responsive (signal within 10 s). Such a fluorescent probe to monitor ATP has been actively pursued throughout fundamental and translational research areas. In vitro assay and a successful cellular ATP imaging application was demonstrated in cancer cells and embryonic stem cells. We expect that our work warrants further ATP-related studies throughout a variety of fields.

Bioluminescence Imaging Applications in Cancer: A Comprehensive Review

Bioluminescence imaging (BLI), an optical preclinical imaging modality, is an invaluable imaging modality due to its low-cost, high throughput, fast acquisition times, and functional imaging capabilities. BLI is being extensively used in the field of cancer imaging, especially with the recent developments in genetic-engineering, stem cell, and gene therapy treatments. The purpose of this paper is to provide a comprehensive review of the principles, developments, and current status of BLI in cancer research. This paper covers the fundamental BLI concepts including BLI reporters and enzyme-substrate systems, data acquisition, and image characteristics. It reviews the studies discussing the use of BLI in cancer research such as imaging tumor-characteristic phenomena including tumorigenesis, metastasis, cancer metabolism, apoptosis, hypoxia, and angiogenesis, and response to cancer therapy treatments including chemotherapy, radiotherapy, immunotherapy, gene therapy, and stem cell therapy. The key advantages and disadvantages of BLI compared to other common imaging modalities are also discussed.

P2Y receptors for extracellular nucleotides: Contributions to cancer progression and therapeutic implications

Purinergic receptors for extracellular nucleotides and nucleosides contribute to a vast array of cellular and tissue functions, including cell proliferation, intracellular and transmembrane ion flux, immunomodulation and thrombosis. In mammals, the purinergic receptor system is composed of G protein-coupled P1 receptors A₁, A_2A, A_2B and A₃ for extracellular adenosine, P2X1-7 receptors that are ATP-gated ion channels and G protein-coupled P2Y_{1,2,4,6,11,12,13 and 14} receptors for extracellular ATP, ADP, UTP, UDP and/or UDP-glucose. Recent studies have implicated specific P2Y receptor subtypes in numerous oncogenic processes, including cancer tumorigenesis, metastasis and chemotherapeutic drug resistance, where G protein-mediated signaling cascades modulate intracellular ion concentrations and activate downstream protein kinases, Src family kinases as well as numerous mitogen-activated protein kinases. We are honored to contribute to this special issue dedicated to the founder of the field of purinergic signaling, Dr. Geoffrey Burnstock, by reviewing the diverse roles of P2Y receptors in the initiation, progression and metastasis of specific cancers with an emphasis on pharmacological and genetic strategies employed to delineate cell-specific and P2Y receptor subtype-specific responses that have been investigated using in vitro and in vivo cancer models. We further highlight bioinformatic and empirical evidence on P2Y receptor expression in human clinical specimens and cover clinical perspectives where P2Y receptor-targeting interventions may have therapeutic relevance to cancer treatment.

Applications of bioluminescence in biotechnology and beyond

Bioluminescent probes have hugely benefited from the input of synthetic chemistry and protein engineering. Here we review the latest applications of these probes in biotechnology and beyond, with an eye on current limitations and future directions.

5,5-Dialkylluciferins are thermal stable substrates for bioluminescence-based detection systems

Firefly luciferase-based ATP detection assays are frequently used as a sensitive, cost-efficient method for monitoring hygiene in many industrial settings. Solutions of detection reagent, containing a mixture of a substrate and luciferase enzyme that produces photons in the presence of ATP, are relatively unstable and maintain only a limited shelf life even under refrigerated conditions. It is therefore common for the individual performing a hygiene test to manually prepare fresh reagent at the time of monitoring. To simplify sample processing, a liquid detection reagent with improved thermal stability is needed. The engineered firefly luciferase, Ultra-Glo™, fulfills one aspect of this need and has been valuable for hygiene monitoring because of its high resistance to chemical and thermal inactivation. However, solutions containing both Ultra-Glo™ luciferase and its substrate luciferin gradually lose the ability to effectively detect ATP over time. We demonstrate here that dehydroluciferin, a prevalent oxidative breakdown product of luciferin, is a potent inhibitor of Ultra-Glo™ luciferase and that its formation in the detection reagent is responsible for the decreased ability to detect ATP. We subsequently found that dialkylation at the 5-position of luciferin (e.g., 5,5-dimethylluciferin) prevents degradation to dehydroluciferin and improves substrate thermostability in solution. However, since 5,5-dialkylluciferins are poorly utilized by Ultra-Glo™ luciferase as substrates, we used structural optimization of the luciferin dialkyl modification and protein engineering of Ultra-Glo™ to develop a luciferase/luciferin pair that shows improved total reagent stability in solution at ambient temperature. The results of our studies outline a novel luciferase/luciferin system that could serve as foundations for the next generation of bioluminescence ATP detection assays with desirable reagent stability.

A Cerium Vanadate Nanozyme with Specific Superoxide Dismutase Activity Regulates Mitochondrial Function and ATP Synthesis in Neuronal Cells

Nanoparticles that functionally mimic the activity of metal-containing enzymes (metallo-nanozymes) are of therapeutic importance for treating various diseases. However, it is still not clear whether such nanozymes can completely substitute the function of natural enzymes in living cells. In this work, we show for the first time that a cerium vanadate (CeVO₄ ) nanozyme can substitute the function of superoxide dismutase 1 and 2 (SOD1 and SOD2) in the neuronal cells even when the natural enzyme is down-regulated by specific gene silencing. The nanozyme prevents the mitochondrial damage in SOD1- and SOD2-depleted cells by regulating the superoxide levels and restores the physiological levels of the anti-apoptotic Bcl-2 family proteins. Furthermore, the nanozyme effectively prevents the mitochondrial depolarization, leading to a significant improvement in the cellular levels of ATP under oxidative stress.

P2X receptors in cancer growth and progression

It is increasingly appreciated that ion channels have a crucial role in tumors, either as promoters of cancer cell growth, or modulators of immune cell functions, or both. Among ion channels, P2X receptors have a special status because they are gated by ATP, a common and abundant component of the tumor microenvironment. Furthermore, one P2X receptor, i.e. P2X7, may also function as a conduit for ATP release, thus fuelling the increased extracellular ATP level in the tumor interstitium. These findings show that P2X receptors and extracellular ATP are indissoluble partners and key regulators of tumor growth, and suggest the exploitation of the extracellular ATP-P2X partnership to develop innovative therapeutic approaches to cancer.

Extracellular ATP: A Feasible Target for Cancer Therapy

Adenosine triphosphate (ATP) is one of the main biochemical components of the tumor microenvironment (TME), where it can promote tumor progression or tumor suppression depending on its concentration and on the specific ecto-nucleotidases and receptors expressed by immune and cancer cells. ATP can be released from cells via both specific and nonspecific pathways. A non-regulated release occurs from dying and damaged cells, whereas active release involves exocytotic granules, plasma membrane-derived microvesicles, specific ATP-binding cassette (ABC) transporters and membrane channels (connexin hemichannels, pannexin 1 (PANX1), calcium homeostasis modulator 1 (CALHM1), volume-regulated anion channels (VRACs) and maxi-anion channels (MACs)). Extracellular ATP acts at P2 purinergic receptors, among which P2X7R is a key mediator of the final ATP-dependent biological effects. Over the years, P2 receptor- or ecto-nucleotidase-targeting for cancer therapy has been proposed and actively investigated, while comparatively fewer studies have explored the suitability of TME ATP as a target. In this review, we briefly summarize the available evidence suggesting that TME ATP has a central role in determining tumor fate and is, therefore, a suitable target for cancer therapy.

An ATP responsive fluorescent supramolecular assembly based on a polyelectrolyte and an AIE active tetraphenylethylene derivative

Aggregation induced emission (AIE) active probes have attracted enormous attention due to their wide-spread and ever increasing number of applications in the sensing of chemically and biologically important molecules. AIE probes undergo drastic modulation in their photophysical features from a monomeric to aggregated state. In the current work, we report the aggregation of tetra-anionic Su-TPE (AIE active probe) in the presence of a cationic polyelectrolyte, poly(allylaminehydrochloride) (PAH). A supramolecular assembly is formed by the electrostatic interaction between cationic PAH and anionic Su-TPE molecules, which leads to drastic modulations in the spectral features of anionic Su-TPE upon addition of cationic PAH. The Su-TPE-PAH aggregate assembly has been investigated using various photophysical techniques, such as, ground-state absorption, steady-state and time-resolved emission spectroscopic techniques along with 1H NMR measurements. The Su-TPE-PAH aggregate assembly is found to be responsive towards the ionic strength of the medium and temperature which results in drastic modulations of the spectral features of the emissive supramolecular aggregate assembly. Finally, the specific recognition of an important bioanalyte, ATP, has been achieved using the formed Su-TPE-PAH supramolecular aggregate assembly as a sensing platform which displays good selectivity and high sensitivity towards ATP. Importantly, the developed sensor platform could also function in the human serum matrix, hence, demonstrating the potential of the established sensor platform for real-life applications in near future.

Near-Infrared Fluorescence MOF Nanoprobe for Adenosine Triphosphate-Guided Imaging in Colitis

Adenosine triphosphate (ATP) is mainly produced in mitochondria and plays an important role in lots of pathological processes such as colitis. Unfortunately, to date, few suitable fluorescence probes have been developed for monitoring the ATP level in colitis. Herein, a fluorescence nanoprobe named NIR@ZIF-90 is proposed and prepared by encapsulating a rhodamine-based near-infrared (NIR) dye into zeolitic imidazolate frameworks (ZIF-90). The nanoprobe is nonfluorescent because the emission of NIR is suppressed by the encapsulation, while in the presence of ATP, the framework of ZIF-90 is dissembled to release NIR and thus NIR fluorescence at 750 nm is observed. The nanoprobe shows high sensitivity to ATP with a 72-fold increase and excellent selectivity to ATP over other nucleotides. Moreover, with low cytotoxicity and good mitochondria-targeted ability, NIR@ZIF-90 is used to image ATP in colorectal cancer cells (HCT116). In addition, due to the NIR emission, the nanoprobe is further employed to successfully monitor the ATP level in a colitis mouse model. To the best of our knowledge, the nanoprobe is the first example to study colitis in vivo with the guidance of ATP, which will provide an efficient tool for understanding colitis.

H3 relaxin protects against calcium oxalate crystal-induced renal inflammatory pyroptosis

OBJECTIVES

Calcium oxalate (CaOx) crystals can activate inflammatory cytokines by triggering inflammasomes, which cause damage to the adhered epithelium, a dysfunctional microenvironment and even renal failure. However, a comprehensive and in-depth understanding of the mechanisms underlying the effects of these crystals on damage and cytokine function in renal tubular epithelial cells (TECs) remains limited and to be explored.

MATERIALS AND METHODS

We detected the pyroptosis of TECs induced after exposure to CaOx crystals and demonstrated the significance of cytokine activation in the subsequent inflammatory processes through a proteomic study. We then conducted animal and cell experiments to verify relevant mechanisms through morphological, protein, histological and biochemical approaches. Human serum samples were further tested to help explain the pathophysiological mechanism of H3 relaxin.

RESULTS

We verified that crystal-induced extracellular adenosine triphosphate (ATP) upregulation via the membrane purinergic 2X₇ receptor (P2X₇ R) promotes ROS generation and thereby activates NLRP3 inflammasome-mediated interleukin-1β/18 maturation and gasdermin D cleavage. Human recombinant relaxin-3 (H3 relaxin) can act on the transmembrane receptor RXFP1 to produce cAMP and subsequently improves crystal-derived damage via ATP consumption. Additionally, endogenous relaxin-3 was found to be elevated in patients with renal calculus and can thus serve as a biomarker.

CONCLUSIONS

Our results provide previously unidentified mechanistic insights into CaOx crystal-induced inflammatory pyroptotic damage and H3 relaxin-mediated anti-inflammatory protection and thus suggest a series of potential therapeutic targets and methods for but not limited to nephrocalcinosis.

Shining light on the electronic structure and relaxation dynamics of the isolated oxyluciferin anion

Firefly bioluminescence is exploited widely in imaging in the biochemical and biomedical sciences; however, our fundamental understanding of the electronic structure and relaxation processes of the oxyluciferin that emits the light is still rudimentary. Here, we employ photoelectron spectroscopy and quantum chemistry calculations to investigate the electronic structure and relaxation of a series of model oxyluciferin anions. We find that changing the deprotonation site has a dramatic influence on the relaxation pathway following photoexcitation of higher lying electronically excited states. The keto form of the oxyluciferin anion is found to undergo internal conversion to the fluorescent S₁ state, whereas we find evidence to suggest that the enol and enolate forms undergo internal conversion to a dipole bound state, possibly via the fluorescent S₁ state. Partially resolved vibrational structure points towards the involvement of out-of-plane torsional motions in internal conversion to the dipole bound state, emphasising the combined electronic and structural role that the microenvironment plays in controlling the electronic relaxation pathway in the enzyme.

The NTP generating activity of pyruvate kinase II is critical for apicoplast maintenance in Plasmodium falciparum

The apicoplast of Plasmodium falciparum parasites is believed to rely on the import of three-carbon phosphate compounds for use in organelle anabolic pathways, in addition to the generation of energy and reducing power within the organelle. We generated a series of genetic deletions in an apicoplast metabolic bypass line to determine which genes involved in apicoplast carbon metabolism are required for blood-stage parasite survival and organelle maintenance. We found that pyruvate kinase II (PyrKII) is essential for organelle maintenance, but that production of pyruvate by PyrKII is not responsible for this phenomenon. Enzymatic characterization of PyrKII revealed activity against all NDPs and dNDPs tested, suggesting that it may be capable of generating a broad range of nucleotide triphosphates. Conditional mislocalization of PyrKII resulted in decreased transcript levels within the apicoplast that preceded organelle disruption, suggesting that PyrKII is required for organelle maintenance due to its role in nucleotide triphosphate generation.

Real-time in vivo imaging of extracellular ATP in the brain with a hybrid-type fluorescent sensor

Adenosine 5' triphosphate (ATP) is a ubiquitous extracellular signaling messenger. Here, we describe a method for in-vivo imaging of extracellular ATP with high spatiotemporal resolution. We prepared a comprehensive set of cysteine-substitution mutants of ATP-binding protein, Bacillus FoF1-ATP synthase ε subunit, labeled with small-molecule fluorophores at the introduced cysteine residue. Screening revealed that the Cy3-labeled glutamine-105 mutant (Q105C-Cy3; designated ATPOS) shows a large fluorescence change in the presence of ATP, with submicromolar affinity, pH-independence, and high selectivity for ATP over ATP metabolites and other nucleotides. To enable in-vivo validation, we introduced BoNT/C-Hc for binding to neuronal plasma membrane and Alexa Fluor 488 for ratiometric measurement. The resulting ATPOS complex binds to neurons in cerebral cortex of living mice, and clearly visualized a concentrically propagating wave of extracellular ATP release in response to electrical stimulation. ATPOS should be useful to probe the extracellular ATP dynamics of diverse biological processes in vivo.

Aluminum-induced alterations of purinergic signalling in embryonic neural progenitor cells

The ubiquitous presence of aluminum in the environment leads to a high likelihood of human exposure. Neurotoxicity of the trivalent cationic form of this metal (Al3+) occurs in the central nervous system via accumulation of Al in cells of neural origin, including neural progenitor cells (NPCs). NPCs play a key role in the development and regeneration of the brain throughout life; therefore, this metal may contribute to neuropathological conditions. Here, we evaluated the effects of different Al³⁺ concentrations (0-50 μM) on the purinergic system of NPCs isolated from embryonic telencephalons, cultured as neurospheres. Al³⁺ adhered to the cell surface of neurospheres reducing extracellular ATP release, as well as ATP, ADP, and AMP hydrolysis by NTPDase and 5'-nucleotidase, respectively. In addition, impaired nucleotide release by Al³⁺ reduced P2Y1 and adenosine A2A receptors expression in differentiated neurospheres. These receptors are crucial for NPC proliferation during brain development and self-repair against external stimuli, such as metal exposure. Thus, Al³⁺ represents an environmental agent linked to neurodegeneration through alterations in the ATP-signalling pathway, proving to be a potential mechanism associated with NPC proliferation and brain degeneration.

P2X7 in Cancer: From Molecular Mechanisms to Therapeutics

P2X7 is a transmembrane receptor expressed in multiple cell types including neurons, dendritic cells, macrophages, monocytes, B and T cells where it can drive a wide range of physiological responses from pain transduction to immune response. Upon activation by its main ligand, extracellular ATP, P2X7 can form a nonselective channel for cations to enter the cell. Prolonged activation of P2X7, via high levels of extracellular ATP over an extended time period can lead to the formation of a macropore, leading to depolarization of the plasma membrane and ultimately to cell death. Thus, dependent on its activation state, P2X7 can either drive cell survival and proliferation, or induce cell death. In cancer, P2X7 has been shown to have a broad range of functions, including playing key roles in the development and spread of tumor cells. It is therefore unsurprising that P2X7 has been reported to be upregulated in several malignancies. Critically, ATP is present at high extracellular concentrations in the tumor microenvironment (TME) compared to levels observed in normal tissues. These high levels of ATP should present a survival challenge for cancer cells, potentially leading to constitutive receptor activation, prolonged macropore formation and ultimately to cell death. Therefore, to deliver the proven advantages for P2X7 in driving tumor survival and metastatic potential, the P2X7 macropore must be tightly controlled while retaining other functions. Studies have shown that commonly expressed P2X7 splice variants, distinct SNPs and post-translational receptor modifications can impair the capacity of P2X7 to open the macropore. These receptor modifications and potentially others may ultimately protect cancer cells from the negative consequences associated with constitutive activation of P2X7. Significantly, the effects of both P2X7 agonists and antagonists in preclinical tumor models of cancer demonstrate the potential for agents modifying P2X7 function, to provide innovative cancer therapies. This review summarizes recent advances in understanding of the structure and functions of P2X7 and how these impact P2X7 roles in cancer progression. We also review potential therapeutic approaches directed against P2X7.

Identification of an ATP metabolism-related signature associated with prognosis and immune microenvironment in gliomas

As the core element of material and energy metabolism pathways, the biological functions and prognostic significance of ATP metabolism in diffuse gliomas have so far remained unclear. Based on comprehensive analysis of ATP metabolism‐related gene expression profiles, we constructed an ATP metabolism‐related risk signature to determine the role of ATP metabolism. We found that this ATP metabolism‐related gene expression profile could divide patients into 2 robust groups with distinct clinical characteristics and prognosis. Patients in the high‐risk group tended to be predicted as malignant entities, indicating that the activation of ATP metabolism may promote the malignant progress of diffuse gliomas. Cox regression and Kaplan‐Meier analyses suggested that this risk signature was an independent predictor for prognosis. Furthermore, we constructed an individualized prognosis prediction model through nomogram and time‐dependent receiver operating characteristic (ROC) curve analyses. Functional analysis suggested that, in addition to material and energy metabolism, ATP metabolism also played an essential role in the regulation of the tumor immune microenvironment. In brief, the ATP metabolism‐related signature was tightly associated with regulation of the tumor immune microenvironment and could serve as an independent prognostic biomarker in diffuse gliomas.

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.

ATP Measurement in Cerebrospinal Fluid Using a Microplate Reader

Imbalance in extracellular ATP levels in brain tissue has been suggested as a triggering factor for several neurological disorders. Here, we describe the most sensitive and reliable technique for monitoring the ATP levels in mice cerebrospinal samples collected by cisterna magna puncture technique and quantified using a microplate reader.

An Enteric-Coated Polyelectrolyte Nanocomplex Delivers Insulin in Rat Intestinal Instillations when Combined with a Permeation Enhancer

The use of nanocarriers is being researched to achieve oral peptide delivery. Insulin-associated anionic polyelectrolyte nanoparticle complexes (PECs) were formed that comprised hyaluronic acid and chitosan in an optimum mass mixing ratio of 5:1 (MR 5), followed by coating with a pH-dependent polymer. Free insulin was separated from PECs by size exclusion chromatography and then measured by HPLC. The association efficiency of insulin in PECs was >95% and the loading was ~83 µg/mg particles. Dynamic light scattering and nanoparticle tracking analysis of PECs revealed low polydispersity, a negative zeta potential range of −40 to −50 mV, and a diameter range of 95–200 nm. Dissolution studies in simulated small intestinal fluid (FaSSIF-V2) revealed that the PECs were colloidally stable. PECs that were coated with Eudragit^® L-100 delayed insulin release in FaSSIF-V2 and protected insulin against pancreatin attack more than uncoated PECs. Uncoated anionic PECs interacted weakly with mucin in vitro and were non-cytotoxic to Caco-2 cells. The coated and uncoated PECs, both concentrated further by ultrafiltration, permitted dosing of 50 IU/kg in rat jejunal instillations, but they failed to reduce plasma glucose or deliver insulin to the blood. When ad-mixed with the permeation enhancer (PE), sucrose laurate (100 mM), the physicochemical parameters of coated PECs were relatively unchanged, however blood glucose was reduced by 70%. In conclusion, the use of a PE allowed for the PEC-released bioactive insulin to permeate the jejunum. This has implications for the design of orally delivered particles that can release the payload when formulated with enhancers.

Multifunctional Single-Layered Graphene Quantum Dots Used for Diagnosis of Mitochondrial Malfunction-Related Diseases

Mitochondria are critical organelles in eukaryotes that efficiently generate adenosine 5'-triphosphate (ATP) for various biological activities, and any defect in the process of ATP synthesis may lead to mitochondrial dysfunction and directly link to a variety of medical disorders. Monitoring the ATP variations in cells is key for innovative early diagnosis of mitochondrial diseases. Herein, multifunctional single-layered graphene quantum dots (s-GQDs) with bright green emission were constructed, which exhibit strong binding affinity for ATP and good mitochondria targeting ability. Using the proposed s-GQDs, we successfully discriminated the primary smooth muscle cells isolated from the transgenic mouse (heterozygote sarco/endoplasmic reticulum Ca²⁺ ATPase (SERCA) 2 C674S knock-in mouse) with mitochondrial disorders or their littermate controls, indicating s-GQDs as promising probes for the study of cell metabolism and mitochondrial malfunction-related diseases, and targeting endoplasmic reticulum stress is an effective way to modulate metabolic pathways relevant to SERCA 2 inactivity mitochondrial dysfunction.

Engineering a Reversible Fluorescent Probe for Real-Time Live-Cell Imaging and Quantification of Mitochondrial ATP

Real-time imaging and quantification of adenosine triphosphate (ATP) fluctuation in cells are significant for understanding the relationship between energy metabolism and cell functions. However, few synthetic fluorescent probes have been reported to tackle this challenge due to lack of accurate fluorescence readout and suitable response concentration. Herein we designed and synthesized a ratiometric fluorescent probe (Rh6G-ACFPN) for quantitatively detecting the fluctuation of mitochondrial ATP in living cells. Rh6G-ACFPN selectively and reversibly responds to ATP with an ideal dissociation constant (K_d) of 4.65 mM (3-10 mM: the range of mitochondrial ATP concentrations). Live-cell imaging allows us to directly monitor the dynamic changes of mitochondrial ATP in high temporal resolution. Moreover, for the first time, mitochondrial ATP in normal and cancer cells lines was successfully quantified and discriminated. These results demonstrate the versatility of Rh6G-ACFPN as a useful imaging tool to elucidate the function of mitochondrial ATP in living cells.

Single-Cell Adenosine Triphosphate Content Monitoring during Hyperthermia Cell Death by Using Plasmonic Fluorescent Nanoflare

Gold nanorods-based plasmonic photothermal therapy (AuNRs-PPTT) is a prospective anticancer approach in which AuNRs absorb near-infrared (NIR) light and convert it into heat, leading to cell death. Investigating the molecular energy metabolism of single cells, especially cancer cells, during the hyperthermia cell death process is therefore of great significance, as it can help us to better understand the photothermal lethal mechanism of cancer cells and design new photothermal probes more rationally. However, during the AuNRs-PPTT process, how the cells respond to heat stimulation and how their energy metabolism changes have rarely been studied. Herein, we selected adenosine triphosphate (ATP) as a target molecule, and by preparing a plasmonic and turn-on type fluorescent nanoprobe, we examined the ATP metabolism difference between cancerous cells and normal cells during the AuNRs-PPTT process. We found that the fluorescence intensity increased ∼60% after 5 min laser irradiation as compared to the initial intensity in single HeLa cells, but only ∼20% increase was observed for single H8 cells; obviously, the increase of ATP content in cancerous cells was notably higher than that in normal cells during the hyperthermia cell death.

A supramolecule based fluorescence turn-on and ratiometric sensor for ATP in aqueous solution

Considering the biological relevance of adenosine triphosphate (ATP) as an "energy currency" in all organisms and significance of its detection in various diseased conditions, enormous efforts have been made to develop selective and sensitive fluorescent sensors for the detection of ATP. However, these developed sensor probes frequently involve technically challenging and time-consuming synthetic protocols for the production of sensor molecules and often suffer from poor solubility in aqueous medium. Another major disadvantage of these developed sensor systems is their single wavelength based operation which makes their performance susceptible to minute changes in experimental conditions. Herein, we report a fluorescence turn-on ratiometric sensor for the detection of ATP which operates by the dissociation of Thioflavin-T-sulphated-β-cyclodextrin supramolecular assembly by Zn²⁺ followed by ATP induced reassociation of the same. This modulation of the monomer/aggregate equilibrium of the supramolecular assembly followed by subsequent interactions with Zn²⁺ and ATP acts as an optimal scheme for the ratiometric detection of ATP. Overall this supramolecular ensemble based sensing platform provides a simple, sensitive, selective and label free detection approach for ATP in aqueous solution. Importantly, our sensor platform responds to ATP in the biologically complex media of serum samples suggesting its potential for possible applications in real-life scenarios.

New frontiers in probing the dynamics of purinergic transmitters in vivo

Purinergic transmitters such as adenosine, ADP, ATP, UTP, and UDP-glucose play important roles in a wide range of physiological processes, including the sleep-wake cycle, learning and memory, cardiovascular function, and the immune response. Moreover, impaired purinergic signaling has been implicated in various pathological conditions such as pain, migraine, epilepsy, and drug addiction. Examining the function of purinergic transmission in both health and disease requires direct, sensitive, non-invasive tools for monitoring structurally similar purinergic transmitters; ideally, these tools should have high spatial and temporal resolution in in vivo applications. Here, we review the recent progress with respect to the development and application of new methods for detecting purinergic transmitters, focusing on optical tools; in addition, we provide discussion regarding future perspectives.

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.

Theoretical Study of the Wavelength Selection for the Photocleavage of Coumarin-caged D-luciferin

The equilibrium structures and optical properties of the photolabile caged luciferin, (7-diethylaminocoumarin-4-yl)methyl caged D-luciferin (DEACM-caged D-luciferin), in aqueous solution were investigated via quantum chemical calculations. The probable conformers of DEACM-caged D-luciferin were determined by potential energy curve scans and structural optimizations. We identified 40 possible conformers of DEACM-caged D-luciferin in water by comparing the Gibbs free energy of the optimized structures. Despite the difference in their structures, the conformers were similar in terms of assignments, oscillator strengths and energies of the three low-lying excited states. From the concentrations of the conformers and their oscillator strengths, we obtained a theoretical UV/Vis spectrum of DEACM-caged D-luciferin that has two main bands of shape nearly identical to the experimental UV/Vis spectrum. The absorption bands with maxima ~ 384 and 339 nm were attributed to the electronic excitations of the caged group and the luciferin moiety, respectively, by analysis of the theoretical UV/Vis spectrum. Furthermore, the analysis showed that DEACM-caged D-luciferin is excited in the caged group only by light of wavelength ranging within 400-430 nm, which is in the long-wavelength tail of the 384 nm band. This should be tested to lower damage upon photocleavage.

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.

PTEN-Induced Putative Kinase 1 (PINK1)/Parkin-Mediated Mitophagy Protects PC12 Cells Against Cisplatin-Induced Neurotoxicity

Background

The pathogenesis of chemotherapy-induced neuropathy, a dose-dependent adverse effect of cisplatin, involves mitochondrial dysfunction. PTEN-induced putative kinase 1 (PINK1)/Parkin-mediated mitophagy removes damaged mitochondria under various pathological conditions. The objective of this study was to determine mitophagy status and its effects on mitochondrial function and neuronal cell damage after cisplatin treatment using an in vitro model of cisplatin-induced neurotoxicity.

Material/Methods

PC12 cells were transfected with Parkin or Parkin siRNA using lentiviral particles and Lipofectamine 3000™, respectively, and then were exposed to 10 μM cisplatin. The expression of autophagic proteins was measured by Western blot analysis. Mitophagy in PC12 cells was detected by confocal microscopy analysis of mitochondria-lysosomes colocalization and autophagic flux. The effects of PINK1/Parkin-mediated mitophagy on cisplatin-induced neurotoxicity were assessed via mitochondrial function, neuritic length, nuclear diameter, and apoptosis.

Results

Cisplatin activated PINK1/Parkin-mediated mitophagy in PC12 cells. Autophagic flux analysis revealed that cisplatin inhibits the late stage of the autophagic process. The knockdown of Parkin suppressed cisplatin-induced mitophagy, aggravating cisplatin-induced depolarization of mitochondria, cellular ATP deficits, reactive oxygen species outburst, neuritic shortening, nuclear diameter reduction, and apoptosis, while Parkin overexpression enhanced mitophagy and reversed these effects.

Conclusions

PINK1/Parkin-regulated mitophagy can protect against cisplatin-related neurotoxicity, suggesting therapeutic enhancement of mitophagy as a potential intervention for cisplatin-induced peripheral neuropathies. The interference of cisplatin with autophagosome-lysosome fusion may be partly responsible for cisplatin-induced neurotoxicity.

Nano-lantern on paper for smartphone-based ATP detection

ATP-driven bioluminescence relying on the D-luciferin-luciferase reaction is widely employed for several biosensing applications where bacterial ATP detection allows to verify microbial contamination for hygiene monitoring in hospitals, food processing and in general for cell viability studies. Several ATP kit assays are already commercially available but an user-friendly ATP biosensor characterized by low-cost, portability, and adequate sensitivity would be highly valuable for rapid and facile on site screening. Thanks to an innovative freeze-drying procedure, we developed a user-friendly, ready-to-use and stable ATP sensing paper biosensor that can be combined with smartphone detection. The ATP sensing paper includes a lyophilized "nano-lantern" with reaction components being rapidly reconstituted by 10 μL sample addition, enabling detection of 10^-14 mol of ATP within 10 min. We analysed urinary microbial ATP as a biomarker of urinary tract infection (UTI), confirming the capability of the ATP sensing paper to detect the threshold for positivity corresponding to 10⁵ colony-forming units of bacteria per mL of urine.

Luciferase-assisted detection of extracellular ATP and ATP metabolites during immunogenic death of cancer cells

The efficacy of cancer chemotherapy is enhanced by induction of sustainable anti-tumor immune responses. Such responses involve accumulation of immunogenic mediators, such as extracellular ATP and ATP metabolites, within the tumor microenvironment. Recent studies have identified nucleotide-permeable plasma membrane channels or pores that are activated as early downstream consequences of different regulated cell death pathways: pannexin-1 channels in apoptosis, MLKL pores in necroptosis, and gasdermin-family pores in pyroptosis. This chapter describes the use of highly quantitative and semi-high-throughput methods based on the ATP sensor luciferase to measure dynamic changes in extracellular ATP, ADP, and AMP in tissue/cell culture models of cancer cells during various modes of regulated cell death in response to chemotherapeutic drugs, death receptors, or metabolic perturbation.

A Survey on Optical Technologies for IoT, Smart Industry, and Smart Infrastructures

In the Internet of Things (IoT), a huge number of sensors, actuators and other equipment for data acquisition and processing will be interconnected by means of an omnipresent communication network able to efficiently support heterogeneous transmission technologies and applications. On the one hand, advanced optical communication systems, which already play a significant role in modern networks, are currently evolving to meet very high requirements of modern applications. On the other hand, there are already many ways to utilize optical components and effects for building precise, efficient, and reliable sensors. Thus, optical technologies have the potential to greatly help in realizing future smart infrastructures and systems. This paper gives an overview of currently available and emerging optical technologies for sensing and communication applications and reviews their possible application in the context of the IoT for realizing smart systems and infrastructures.

Pleiotropic Roles of P2X7 in the Central Nervous System

The purinergic receptor P2X7 is expressed in neural and immune cells known to be involved in neurological diseases. Its ligand, ATP, is a signaling molecule that can act as a neurotransmitter in physiological conditions or as a danger signal when released in high amount by damaged/dying cells or activated glial cells. Thus, ATP is a danger-associated molecular pattern. Binding of ATP by P2X7 leads to the activation of different biochemical pathways, depending on the physiological or pathological environment. The aim of this review is to discuss various functions of P2X7 in the immune and central nervous systems. We present evidence that P2X7 may have a detrimental or beneficial role in the nervous system, in the context of neurological pathologies: epilepsy, Alzheimer’s disease, multiple sclerosis, amyotrophic lateral sclerosis, age-related macular degeneration and cerebral artery occlusion.

Structure, function and techniques of investigation of the P2X7 receptor (P2X7R) in mammalian cells

The P2X7 receptor [P2X7R or P2RX7 in National Center for Biotechnology Information (NCBI) gene nomenclature] is a member of the P2X receptor (P2XR) subfamily of P2 receptors (P2Rs). The P2X7R is an extracellular ATP-gated ion channel with peculiar permeability properties expressed by most cell types, mainly in the immune system, where it has a leading role in cytokine release, oxygen radical generation, T lymphocyte differentiation and proliferation. A role in cancer cell growth and tumor progression has also been demonstrated. These features make the P2X7R an appealing target for drug development in inflammation and cancer. The functional P2X7R, recently (partially) crystallized and 3-D solved, is formed by the assembly of three identical subunits (homotrimer). The P2X7R is preferentially permeable to small cations (Ca2+, Na+, K+), and in most (but not all) cell types also to large positively charged molecules of molecular mass up to 900Da. Permeability to negatively charged species of comparable molecular mass (e.g., Lucifer yellow) is debated. Several highly selective P2X7R pharmacological blockers have been developed over the years, thus providing powerful tools for P2X7R studies. Biophysical properties and coupling to several different physiological responses make the P2X7R amenable to investigation by electrophysiology and cell biology techniques, which allow its identification and characterization in many different cell types and tissues. A careful description of the physiological features of the P2X7R is a prerequisite for an effective therapeutic development. Here we describe the most common techniques to asses P2X7R functions, including patch-clamp, intracellular calcium measurements, and membrane permeabilization to large fluorescent dyes in a selection of different cell types. In addition, we also describe common toxicity assays used to verify the effects of P2X7R stimulation on cell viability.

Pharmacological blockade of the P2X7 receptor reverses retinal damage in a rat model of type 1 diabetes

AIMS

Retinopathy is a leading cause of vision impairment in diabetes. Its pathogenesis involves inflammation, pathological angiogenesis, neuronal and glial dysfunction. The purinergic P2X7 receptor (P2X7R) has a leading role in inflammation and angiogenesis. Potent and selective P2X7R blockers have been synthesized and tested in Phase I/II clinical studies. We hypothesize that P2X7R blockade will ameliorate diabetes-related pathological retinal changes.

METHODS

Streptozotocin (STZ)-treated rats were intraperitoneally inoculated with either of two small molecule P2X7R receptor inhibitors, A740003 and AZ10606120, and after blood glucose levels increased to above 400 mg/dL, retinae were analyzed for P2X7R expression, vascular permeability, VEGF, and IL-6 expression.

RESULTS

STZ administration caused a near fourfold increase in blood glucose, a large increase in retinal microvasculature permeability, as well as in retinal P2X7R, VEGF, and IL-6 expression. P2X7R blockade fully reversed retinal vascular permeability increase, VEGF accumulation, and IL-6 expression, with no effect on blood glucose.

CONCLUSION

P2X7R blockade might be promising strategy for the treatment of microvascular changes observed in the early phases of diabetic retinopathy.

ATP and adenosine: Role in the immunopathogenesis of rheumatoid arthritis

Rheumatoid arthritis (RA) is a classic inflammatory autoimmune disease. Local joint destruction and extra-articular manifestations of RA deeply compromise the life quality of the affected patients. RA immunopathogenesis depends on continuous immunogenic activation in which the purinergic system participates. The purinergic system comprises the signaling and metabolism of purines such as adenosine triphosphate (ATP) and adenosine. ATP signaling is involved in the activation and maintenance of the inflammatory state of RA through the activation of P2X7 and the production of cytokines, which orchestrate the pathogenesis of RA. The breakdown of ATP through the CD39/CD73 axis produces adenosine, which mostly inhibits the inflammatory process through activation of specific P1 receptors. Adenosine is hydrolyzed by adenosine deaminase (ADA) that interacts with other molecules playing additional roles in this disease. This review explores the release, metabolism, and the effects of binding of ATP and adenosine to their respective receptors in the context of RA, as well as their potential use as biomarkers and therapeutic targets.

Extracellular ATP promotes breast cancer invasion and epithelial-mesenchymal transition via hypoxia-inducible factor 2α signaling

Extracellular ATP has been shown to play an important role in invasion and the epithelial-mesenchymal transition (EMT) process in breast cancer; however, the mechanism is unclear. Here, by using a cDNA microarray, we demonstrated that extracellular ATP could stimulate hypoxia-inducible factor (HIF) signaling and upregulate hypoxia-inducible factor 1/2α (HIF-1/2α) expression. After knocking down HIF-1/2α using siRNA, we found that ATP-driven invasion and EMT were significantly attenuated via HIF2A-siRNA in breast cancer cells. By using ChIP assays, we revealed that the biological function of extracellular ATP in invasion and EMT process depended on HIF-2α direct targets, among which lysyl oxidase-like 2 (LOXL2) and matrix metalloproteinase-9 (MMP-9) mediated ATP-driven invasion, and E-cadherin and Snail mediated ATP-driven EMT, respectively. In addition, using silver staining and mass spectrometry, we found that phosphoglycerate kinase 1 (PGK1) could interact with HIF-2α and mediate ATP-driven HIF-2α upregulation. Furthermore, we demonstrated that expressions of HIF-2α and its target proteins could be regulated via ATP by AKT-PGK1 pathway. Using a Balb/c mice model, we illustrated the function of HIF-2α in promoting tumor growth and metastasis in vivo. Moreover, by exploring online databases, we found that molecules involved in ATP-HIF-2α signaling were highly expressed in human breast carcinoma tissues and were associated with poor prognosis. Altogether, these findings suggest that extracellular ATP could promote breast carcinoma invasion and EMT via HIF-2α signaling, which may be a potential target for future anti-metastasis therapy.