Adenosine Triphosphate/adenosine Diphosphate Research Articles

MCNN_MC: Computational Prediction of Mitochondrial Carriers and Investigation of Bongkrekic Acid Toxicity Using Protein Language Models and Convolutional Neural Networks.

Mitochondrial carriers (MCs) are essential proteins that transport metabolites across mitochondrial membranes and play a critical role in cellular metabolism. ADP/ATP (adenosine diphosphate/adenosine triphosphate) is one of the most important carriers as it contributes to cellular energy production and is susceptible to the powerful toxin bongkrekic acid. This toxin has claimed several lives; for example, a recent foodborne outbreak in Taipei, Taiwan, has caused four deaths and sickened 30 people. The issue of bongkrekic acid poisoning has been a long-standing problem in Indonesia, with reports as early as 1895 detailing numerous deaths from contaminated coconut fermented cakes. In bioinformatics, significant advances have been made in understanding biological processes through computational methods; however, no established computational method has been developed for identifying mitochondrial carriers. We propose a computational bioinformatics approach for predicting MCs from a broader class of secondary active transporters with a focus on the ADP/ATP carrier and its interaction with bongkrekic acid. The proposed model combines protein language models (PLMs) with multiwindow scanning convolutional neural networks (mCNNs). While PLM embeddings capture contextual information within proteins, mCNN scans multiple windows to identify potential binding sites and extract local features. Our results show 96.66% sensitivity, 95.76% specificity, 96.12% accuracy, 91.83% Matthews correlation coefficient (MCC), 94.63% F1-Score, and 98.55% area under the curve (AUC). The results demonstrate the effectiveness of the proposed approach in predicting MCs and elucidating their functions, particularly in the context of bongkrekic acid toxicity. This study presents a valuable approach for identifying novel mitochondrial complexes, characterizing their functional roles, and understanding mitochondrial toxicology mechanisms. Our findings, that utilize computational methods to improve our understanding of cellular processes and drug-target interactions, contribute to the development of therapeutic strategies for mitochondrial disorders, reducing the devastating effects of bongkrekic acid poisoning.

Genetic improvement of photosynthetic nitrogen use efficiency of winter wheat in the Yangtze River Basin of China

ContextImproving the photosynthetic capacity of crops is key to achieving synergism between high crop yield and nitrogen (N) efficiency, and it is also an important target for future cultivar breeding and cultivation management. Although photosynthetic N use efficiency (PNUE) is commonly used to determine the N economy of leaves, it is unclear whether the PNUE of wheat has improved through genetic engineering of wheat cultivars. ObjectivesThe objectives of this study were to investigate the development of net photosynthetic rate (Pn) and PNUE, and to identify the key factors that limited Pn and PNUE in the tested cultivars. MethodsA 2-year field experiment with three different N fertilizer application rates using five wheat cultivars developed between 1950 s and 2010 s was conducted to examine the evolution and physiological processes of wheat Pn and PNUE. ResultsGrain yield, N recovery efficiency (NRE), leaf Pn, leaf area, the content of N in leaves (LNC), and the content of N per unit area in leaves (NA) increased through genetic engineering of wheat cultivars. However, the increase in Pn was lower than that in NA, resulting in a decrease in PNUE. Modern cultivars had a higher Pn, which was attributed to the improvement of NA, which likely enhanced the maximum ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) carboxylation rate (Vcmax), maximum electron transport rate (Jmax), electron transport rate from photosystem II (JF), and electron transport rate from the cytochrome b6f complex (Jc). The Rubisco content and activity of modern cultivars were higher than those of early cultivars, but the activation state decreased, which was related to the downregulation expression of TaRca1α and TaRca2β-A and the decrease of the adenosine diphosphate/adenosine triphosphate (ADP/ATP) ratio in modern cultivars, resulting in decreased Rubisco activase (Rca) content and activity. Increasing N application increased NA and Pn but decreased the PNUE. N fertilizer had a greater effect on Rubisco content and PNUE than genetic engineering, while it had a smaller effect on NA, leaf mass per area (LMA), Rubisco activity, and Rca content and activity than genetic engineering. ConclusionsOur results suggest that lower Rubisco activation is a major reason for the lower PNUE of modern wheat cultivars, and improving Rca content and activity in the future could enhance Pn and PNUE while improving the N utilization of leaves to enhance crop yield and N efficiency of wheat under current or lower leaf N conditions.

Berberine targets KIF20A and CCNE2 to inhibit the progression of nonsmall cell lung cancer via the PI3K/AKT pathway.

Nonsmall cell lung cancer (NSCLC) is the main type of lung cancer, accounting for approximately 85%. Berberine (BBR), a commonly used traditional Chinese medicine, has been reported to exhibit a potential antitumor effect in various cancers. In this research, we explored the function of BBR and its underlying mechanisms in the development of NSCLC. Cell Counting Kit-8 (CCK-8), 5-ethynyl-20-deoxyuridine (EdU), colony formation assays, flow cytometry, and transwell invasion assay were employed to determine cell growth, the apoptotic rate, cell invasion of NSCLC cells, respectively. Western blot was applied for detecting the protein expression of c-Myc, matrix metalloprotease 9 (MMP9), kinesin family member 20A (KIF20A), cyclin E2 (CCNE2), and phosphatidylinositol-3-kinase/protein kinase B (PI3K/AKT) pathway-related proteins. Glycolysis was evaluated by detecting glucose consumption, lactate production, and adenosine triphosphate/adenosine diphosphate (ATP/ADP) ratio with the matched kits. Real-time quantitative polymerasechain reaction(RT-qPCR) was conducted to analyze the level of KIF20A and CCNE2. Tumor model was established to evaluate the function of BBR on tumor growth in NSCLC in vivo. In addition, immunohistochemistry assay was employed to detect the level of KIF20A, CCNE2, c-Myc, and MMP9 in mice tissues. BBR exhibited suppressive effects on the progression of NSCLC, as evidenced by inhibiting cell growth, invasion, glycolysis, and facilitating cell apoptosis in H1299 and A549 cells. KIF20A and CCNE2 were upregulated in NSCLC tissues and cells. Moreover, BBR treatment significantly decreased the expression of KIF20A and CCNE2. KIF20A or CCNE2 downregulation could repress cell proliferation, invasion, glycolysis, and induce cell apoptosis in both H1299 and A549 cells. The inhibition effects of BBR treatment on cell proliferation, invasion, glycolysis, and promotion effect on cell apoptosis were rescued by KIF20A or CCNE2 overexpression in NSCLC cells. The inactivation of PI3K/AKT pathway caused by BBR treatment in H1299 and A549 cells was restored by KIF20A or CCNE2 upregulation. In vivo experiments also demonstrated that BBR treatment could repress tumor growth by regulating KIF20A and CCNE2 and inactivating the PI3K/AKT pathway. BBR treatment showed the suppressive impact on the progression of NSCLC by targeting KIF20A and CCNE2, thereby inhibiting the activation of the PI3K/AKT pathway.

Effects of preoperative intravenous glutamine administration on cardiac and renal functions in patients undergoing mitral valve replacement surgeries: A randomized double-blind controlled trial

ABSTRACT Background Preoperative poor nutrition greatly raises the risk of complications and increases length of stay (LOS). Glutamine deficiency may impair immune functions, reduce myocardial adenosine triphosphate–adenosine diphosphate (ATP-ADP) substrate and decrease myocardial glutathione level. We evaluated the effects of preoperative glutamine administration in patients undergoing mitral valve replacement surgery upon cardiac and renal outcomes or hospital/ICU LOS. Methods This prospective randomized double-blinded study included 60 patients above 18 up to 60 years undergoing mitral valve replacement. For 3 days preoperatively, Group N patients received glutamine intravenously 0.4 g/kg/day while Group C patients received intravenous normal saline as placebo. The primary outcome was to assess the effects of glutamine on cardiac function as reflected on proBNP (brain natriuretic peptide) during 4 postoperative days. Secondary outcomes included renal function, vasoactive inotropic score, duration of mechanical ventilation, and hospital/ICU stays. Results Postoperative proBNP was significantly lower in Group N during the entire period. It was significantly decreased on the first postoperative day in both groups in comparison to the preoperative values. No significant changes were recorded regarding renal functions, and duration of mechanical ventilation between groups. Also, there was signifiacant difference between the two studied groups regarding the vasoactive inotropic score at the 12th, 18th, 24th and 48th hours with lower scores in Group N. ICU and hospital stays were significantly lower in Group N than Group C. Conclusion Short term of preoperative intravenous glutamine 0.4 g/kg/day decreased the postoperative proBNP level and hospital/ICU stays in mitral valve replacement surgery. No significant implication was reported upon postoperative human NGAL level or kidney functions.

Characterization of Carnosine Effect on Human Microglial Cells under Basal Conditions

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

Numerical modelling of the effects of cold atmospheric plasma on mitochondrial redox homeostasis and energy metabolism

A biochemical reaction model clarifies for the first time how cold atmospheric plasmas (CAPs) affect mitochondrial redox homeostasis and energy metabolism. Fundamental mitochondrial functions in pyruvic acid oxidation, the tricarboxylic acid (TCA) cycle and oxidative phosphorylation involving the respiratory chain (RC), adenosine triphosphate/adenosine diphosphate (ATP/ADP) synthesis machinery and reactive oxygen species/reactive nitrogen species (ROS/RNS)-mediated mechanisms are numerically simulated. The effects of CAP irradiation are modelled as 1) the influx of hydrogen peroxide (H{}_{2}O{}_{2}) to an ROS regulation system and 2) the change in mitochondrial transmembrane potential induced by RNS on membrane permeability. The CAP-induced stress modifies the dynamics of intramitochondrial H{}_{2}O{}_{2} and superoxide anions, i.e., the rhythm and shape of ROS oscillation are disturbed by H{}_{2}O{}_{2} infusion. Furthermore, CAPs control the ROS oscillatory behaviour, nicotinamide adenine dinucleotide redox state and ATP/ADP conversion through the reaction mixture over the RC, the TCA cycle and ROS regulation system. CAPs even induce a homeostatic or irreversible state transition in cell metabolism. The present computational model demonstrates that CAPs crucially affect essential mitochondrial functions, which in turn affect redox signalling, metabolic cooporation and cell fate decision of survival or death.

Actions of p-synephrine on hepatic enzyme activities linked to carbohydrate metabolism and ATP levels in vivo and in the perfused rat liver.

p-Synephrine is one of the main active components of the fruit of Citrus aurantium (bitter orange). Extracts of the bitter orange and other preparations containing p-synephrine have been used worldwide to promote weight loss and for sports performance. The purpose of the study was to measure the action of p-synephrine on hepatic enzyme activities linked to carbohydrate and energy metabolism and the levels of adenine mononucleotides. Enzymes and adenine mononucleotides were measured in the isolated perfused rat liver and in vivo after oral administration of the drug (50 and 300mg/kg) by using standard techniques. p-Synephrine increased the activity of glycogen phosphorylase in vivo and in the perfused liver. It decreased, however, the activities of pyruvate kinase and pyruvate dehydrogenase also in vivo and in the perfused liver. p-Synephrine increased the hepatic pools of adenosine diphosphate and adenosine triphosphate. Stimulation of glycogen phosphorylase is consistent with the reported increased glycogenolysis in the perfused liver and increased glycemia in rats. The decrease in the pyruvate dehydrogenase activity indicates that p-synephrine is potentially capable of inhibiting the transformation of carbohydrates into lipids. The capability of increasing the adenosine triphosphate-adenosine diphosphate pool indicates a beneficial effect of p-synephrine on the cellular energetics.

The key role of microtubules in hypoxia preconditioning-induced nuclear translocation of HIF-1α in rat cardiomyocytes.

BackgroundHypoxia-inducible factor (HIF)-1 is involved in the regulation of hypoxic preconditioning in cardiomyocytes. Under hypoxic conditions, HIF-1α accumulates and is translocated to the nucleus, where it forms an active complex with HIF-1β and activates transcription of approximately 60 kinds of hypoxia-adaptive genes. Microtubules are hollow tubular structures in the cell that maintain cellular morphology and that transport substances. This study attempted to clarify the role of microtubule structure in the endonuclear aggregation of HIF-1α following hypoxic preconditioning of cardiomyocytes.MethodsPrimary rat cardiomyocytes were isolated and cultured. The cardiomyocyte culture system was used to establish a hypoxia model and a hypoxic preconditioning model. Interventions were performed on primary cardiomyocytes using a microtubule-depolymerizing agent and different concentrations of a microtubule stabilizer. The microtubule structure and the degree of HIF-1α nuclear aggregation were observed by confocal laser scanning microscopy. The expression of HIF-1α in the cytoplasm and nucleus was detected using Western blotting. Cardiomyocyte energy content, reflected by adenosine triphosphate/adenosine diphosphate (ATP/ADP), and key glycolytic enzymes were monitored by colorimetry and high-performance liquid chromatography (HPLC). Reactive oxygen species (ROS) production was also used to comprehensively assess whether microtubule stabilization can enhance the myocardial protective effect of hypoxic preconditioning.ResultsDuring prolonged hypoxia, it was found that the destruction of the microtubule network structure of cardiomyocytes was gradually aggravated. After this preconditioning, an abundance of HIF-1α was clustered in the nucleus. When the microtubules were depolymerized and hypoxia pretreatment was performed, HIF-1α clustering occurred around the nucleus, and HIF-1α nuclear expression was low. The levels of key glycolytic enzymes were significantly higher in the microtubule stabilizer group than in the hypoxia group. Additionally, the levels of lactate dehydrogenase and ROS were significantly lower in the microtubule stabilizer group than in the hypoxia group.ConclusionThe microtubules of cardiomyocytes may be involved in the process of HIF-1α endonuclear aggregation, helping to enhance the anti-hypoxic ability of cardiomyocytes.

Paclitaxel-induced painful neuropathy is associated with changes in mitochondrial bioenergetics, glycolysis, and an energy deficit in dorsal root ganglia neurons.

Painful neuropathy is the major dose-limiting side effect of paclitaxel chemotherapy. Mitochondrial dysfunction and adenosine triphosphate (ATP) deficit have previously been shown in peripheral nerves of paclitaxel-treated rats, but the effects of paclitaxel in the dorsal root ganglia (DRGs) have not been explored. The aim of this study was to determine the bioenergetic status of DRG neurons following paclitaxel exposure in vitro and in vivo. Utilising isolated DRG neurons, we measured respiratory function under basal conditions and at maximal capacity, glycolytic function, and Adenosine diphosphate (ADP)/ATP levels at 3 key behavioural timepoints; prior to pain onset (day 7), peak pain severity and pain resolution. At day 7, maximal respiration and spare reserve capacity were significantly decreased in DRG neurons from paclitaxel-treated rats. This was accompanied by decreased basal ATP levels and unaltered ADP levels. At peak pain severity, respiratory function was unaltered, yet glycolytic function was significantly increased. Reduced ATP and unaltered ADP levels were also observed at the peak pain timepoint. All these effects in DRG neurons had dissipated by the pain resolution timepoint. None of these paclitaxel-evoked changes could be replicated from in vitro paclitaxel exposure to naive DRG neurons, demonstrating the impact of in vivo exposure and the importance of in vivo models. These data demonstrate the nature of mitochondrial dysfunction evoked by in vivo paclitaxel in the DRG for the first time. Furthermore, we have identified paclitaxel-evoked changes in the bioenergetics of DRG neurons, which result in a persistent energy deficit that is causal to the development and maintenance of paclitaxel-induced pain.

Transcription factor NF-kappa B represses ANT1 transcription and leads to mitochondrial dysfunctions

Mitochondria are intracellular organelles involved in cell survival and death, and dysfunctions of mitochondria are related to neurodegenerative diseases. As the most abundant protein in the mitochondrial inner membrane, adenine nucleotide translocator 1 (ANT1) plays a critical role in mitochondrial function, including the exchange of adenosine triphosphate/adenosine diphosphate (ATP/ADP) in mitochondria, basal proton leak and mitochondrial permeability transition pore (mPTP). Here, we show that ANT1 transcription is regulated by transcription factor NF-kappa B (NF-κB). NF-κB is bound to two NF-κB responsive elements (NREs) located at +1 to +20 bp and +41 to +61 bp in the ANT1 promoter. An NF-κB signalling stimulator, tumour necrosis factor alpha (TNFα), suppresses ANT1 mRNA and protein expression. Activation of NF-κB by TNFα impairs ATP/ADP exchange and decreases ATP production in mitochondria. Activation of NF-κB by TNFα decreases calcium induced mPTP opening, elevates mitochondrial potential and increases reactive oxygen species (ROS) production in both T98G human glioblastoma cells and rat cortical neurons. These results demonstrate that NF-κB signalling may repress ANT1 gene transcription and impair mitochondrial functions.

CXCR4 attenuates cardiomyocytes mitochondrial dysfunction to resist ischaemia-reperfusion injury.

The chemokine (C-X-C motif) receptor 4 (CXCR4) is expressed on native cardiomyocytes and can modulate isolated cardiomyocyte contractility. This study examines the role of CXCR4 in cardiomyocyte response to ischaemia-reperfusion (I/R) injury. Isolated adult rat ventricular cardiomyocytes were subjected to hypoxia/reoxygenation (H/R) to simulate I/R injury. In response to H/R injury, the decrease in CXCR4 expression was associated with dysfunctional energy metabolism indicated by an increased adenosine diphosphate/adenosine triphosphate (ADP/ATP) ratio. CXCR4-overexpressing cardiomyocytes were used to determine whether such overexpression (OE) can prevent bio-energetic disruption-associated cell death. CXCR4 OE was performed with adenoviral infection with CXCR4 encoding-gene or non-translated nucleotide sequence (Control). The increased CXCR4 expression was observed in cardiomyocytes post CXCR4-adenovirus transduction and this OE significantly reduced the cardiomyocyte contractility under basal conditions. Although the same extent of H/R-provoked cytosolic calcium overload was measured, the hydrogen peroxide-induced decay of mitochondrial membrane potential was suppressed in CXCR4 OE group compared with control group, and the mitochondrial swelling was significantly attenuated in CXCR4 group, implicating that CXCR4 OE prevents permeability transition pore opening exposure to overload calcium. Interestingly, this CXCR4-induced mitochondrial protective effect is associated with the enhanced signal transducer and activator of transcription 3 (expression in mitochondria. Consequently, in the presence of H/R, mitochondrial dysfunction was mitigated and cardiomyocyte death was decreased to 65% in the CXCR4 OE group as compared with the control group. I/R injury leads to the reduction in CXCR4 in cardiomyocytes associated with the dysfunctional energy metabolism, and CXCR4 OE can alleviate mitochondrial dysfunction to improve cardiomyocyte survival.

Mitochondrial energy metabolism in the hepatopancreas of freshwater crabs (Sinopotamon henanense) after cadmium exposure.

Energetic homoeostasis is a fundamental requirement in the defense against cadmium (Cd) stress. Using the freshwater crab Sinopotamon henanense as an example, we explored the effects of Cd on submicroscopic structures in hepatopancreatic cells through transmission electron microscopy (TEM) and energy-related parameters such as adenosine triphosphate/adenosine diphosphate (ATP/ADP) ratios, reduced/oxidized nicotinamide adenine dinucleotide (NADH/NAD(+)) ratios, and the mitochondrial membrane potential (Δψm). The impact of Cd on carbohydrate and protein metabolism, and metallothionein (MT) was also investigated. Experimental 10 day exposure increased NADH and NAD(+) and provided a higher NADH/NAD(+) ratio and Δψm in hepatopancreatic cells. The corresponding significantly increased levels of ATP and the ATP/ADP ratio in the hepatopancreas supported high energy production. The up-regulation of the MT content in exposed crabs suggests that protein synthesis for detoxification could partially be a major ATP consumer. With increasing exposure time, however, energy production was in decline. Excessive energy consumption was explained by substrate mobilization and mitochondrial impairment. Less carbohydrate and enhanced protein catabolism was observed. Ultrastructurally, there were changes in mitochondria with swelling, membrane disruption, shortening of cristae or the rupture and disappearance of entire mitochondria. The rough endoplasmic reticulum (rER) displayed expansion and membrane rupture, suggesting the destruction of protein-synthesizing structures in hepatopancreatic cells. Our findings suggest that energy-related parameters could be used as biomarkers in the monitoring of metal pollution and quantitative risk assessments of pollutant exposure.

Optimal Device and Method for Transportation of Isolated Porcine Islet

IntroductionWe investigated the optimal method for transportation of isolated porcine islets from an isolation facility to a transplant hospital or research center in terms of temperature, oxygen supply, and shaking effect. MethodsCommercially available insulator boxes with thermoregulators exposed for 5 hours under two external temperatures (4°C and 37°C) were monitored using HOBO temperature loggers. To find the optimal transport device, we compared islet counts, viability, quality, and function in conical tubes, gas-permeable bags (GPB) and gas-permeable flasks (GPF) after 1, 3 and 5 hours. To evaluate the effects of shaking on islets, we also analyzed the difference between a control and a shaking group in each device with time. ResultsCommercially available Styrofoam insulators with thermoregulators maintained the internal temperature near the target. Islet recovery rate for GPF, which was higher than other devices, was maintained, while those decreased with time for conical tube and GPB containers adenosine diphosphate/adenosine triphosphate (ADP/ATP) ratio for GPF was lower than other devices, albeit not significantly fluoroscein acrimide/propidium iodide (AO/PI) ratio for GPF was higher than other devices after 5 hours. Glucose stimulated index was not different among the devices. In comparison with the control group, shaking yielded comparable islet survival, viability and function. ConclusionOur study demonstrated that the use of commercially available insulator boxes with thermoregulators maintained internal temperature close to the target value and that GPF was more favorable for islet oxygenation during transportation. This study also suggested negligible impact of shaking on isolated porcine islets during transportation.

Ecto-Nucleoside Triphosphate Diphosphohydrolase 2 Modulates Local ATP-Induced Calcium Signaling in Human HaCaT Keratinocytes

Keratinocytes are the major building blocks of the human epidermis. In many physiological and pathophysiological conditions, keratinocytes release adenosine triphosphate (ATP) as an autocrine/paracrine mediator that regulates cell proliferation, differentiation, and migration. ATP receptors have been identified in various epidermal cell types; therefore, extracellular ATP homeostasis likely determines its long-term, trophic effects on skin health. We investigated the possibility that human keratinocytes express surface-located enzymes that modulate ATP concentration, as well as the corresponding receptor activation, in the pericellular microenvironment. We observed that the human keratinocyte cell line HaCaT released ATP and hydrolyzed extracellular ATP. Interestingly, ATP hydrolysis resulted in adenosine diphosphate (ADP) accumulation in the extracellular space. Pharmacological inhibition by ARL 67156 or gene silencing of the endogenous ecto-nucleoside triphosphate diphosphohydrolase (NTPDase) isoform 2 resulted in a 25% reduction in both ATP hydrolysis and ADP formation. Using intracellular calcium as a reporter, we found that although NTPDase2 hydrolyzed ATP and generated sustainable ADP levels, only ATP contributed to increased intracellular calcium via P2Y2 receptor activation. Furthermore, knocking down NTPDase2 potentiated the nanomolar ATP-induced intracellular calcium increase, suggesting that NTPDase2 globally attenuates nucleotide concentration in the pericellular microenvironment as well as locally shields receptors in the vicinity from being activated by extracellular ATP. Our findings reveal an important role of human keratinocyte NTPDase2 in modulating nucleotide signaling in the extracellular milieu of human epidermis.

Mapping multiple potential ATP binding sites on the matrix side of the bovine ADP/ATP carrier by the combined use of MD simulation and docking

The mitochondrial adenosine diphosphate/adenosine triphosphate (ADP/ATP) carrier-AAC-was crystallized in complex with its specific inhibitor carboxyatractyloside (CATR). The protein consists of a six-transmembrane helix bundle that defines the nucleotide translocation pathway, which is closed towards the matrix side due to sharp kinks in the odd-numbered helices. In this paper, we describe the interaction between the matrix side of the AAC transporter and the ATP(4-) molecule using carrier structures obtained through classical molecular dynamics simulation (MD) and a protein-ligand docking procedure. Fifteen structures were extracted from a previously published MD trajectory through clustering analysis, and 50 docking runs were carried out for each carrier conformation, for a total of 750 runs ("MD docking"). The results were compared to those from 750 docking runs performed on the X-ray structure ("X docking"). The docking procedure indicated the presence of a single interaction site in the X-ray structure that was conserved in the structures extracted from the MD trajectory. MD docking showed the presence of a second binding site that was not found in the X docking. The interaction strategy between the AAC transporter and the ATP(4-) molecule was analyzed by investigating the composition and 3D arrangement of the interaction pockets, together with the orientations of the substrate inside them. A relationship between sequence repeats and the ATP(4-) binding sites in the AAC carrier structure is proposed.

Interaction between NH2-tau fragment and Aβ in Alzheimer's disease mitochondria contributes to the synaptic deterioration

Although amyloid beta (Aβ) peptide can promote tau pathology and its toxicity is concurrently tau-dependent, the underlying mechanisms of the in vivo interplay of these proteins remain unsolved. Structural and functional mitochondrial alterations play an early, precipitating role in synaptic failure of Alzheimer's disease (AD) pathogenesis and an aggravated mitochondrial impairment has been described in triple APP/PS/tau transgenic mice carrying both plaques and tangles, if compared with mice overexpressing tau or amyloid precursor protein (APP) alone. Here, we show that a neurotoxic aminoterminal (NH2)-derived tau fragment mapping between 26 and 230 amino acids of the human tau40 isoform (441 amino acids)—but not the physiological full-length protein—preferentially interacts with Aβ peptide(s) in human AD synapses in association with mitochondrial adenine nucleotide translocator-1 (ANT-1) and cyclophilin D. The two peptides—Aβ 1–42 and the smaller and more potent NH2-26-44 peptide of the longest 20–22 kDa NH2-tau fragment—inhibit the ANT–1-dependent adenosine diphosphate-adenosine triphosphate (ADP/ATP) exchange in a noncompetitive and competitive manner, respectively, and together further aggravate the mitochondrial dysfunction by exacerbating the ANT-1 impairment. Taken together, these data establish a common, direct and synergistic toxicity of pathological APP and tau products on synaptic mitochondria and suggest potential, new pathway(s) and target(s) for a combined, more efficient therapeutic intervention of early synaptic dysfunction in AD.

Improved Quantification of Islet Transplants by Magnetic Resonance Imaging With Resovist

We aimed to develop an accurate and reproducible method to quantify transplanted islets and monitor their functional status in vivo. To support this aim, we investigated the cytotoxic effect of Resovist on islet function and survival. The average pixel number for a single Resovist-labeled islet was measured. To determine Resovist cytotoxicity, DNA fragmentation, adenosine diphosphate-adenosine triphosphate ratio, ion channel activity, and in vivo islet function were evaluated. To quantitatively monitor the fate of islet transplant, we transplanted Resovist-labeled islets into syngeneic C57BL/6 mice for magnetic resonance imaging analysis. The average pixel volume for a medium-sized islet (100-150 μm in diameter) was determined from the contrast signal void of magnetic resonance image. Toxicological analysis showed that Resovist did not affect islet at concentrations up to 40 times the labeling dose. In the quantitative analysis, the number of contrast spots did not correlated with the number of transplanted islets, whereas our newly adopted measure showed a significant correlation. Islet transplant survival may be safely and accurately monitored using magnetic resonance imaging with the Resovist. We found in this study that pixel number may correlate more closely than the number of contrast spots with the number of islets transplanted.

Mitochondrial membrane potential is a suitable candidate for assessing pollution toxicity in fish

Fish inhabiting polluted estuaries are highly exposed to severe stress characterized by an oxidant–antioxidant imbalance. The aim of the study was to explore the use of stress parameters such as adenosine triphosphate/adenosine diphosphate (ATP/ADP) ratio, mitochondrial membrane potential (∆ψm) and total protein expression patterns as biomarkers against oxidant exposures in hepatocytes of Mugil cephalus living in either a contaminated (Test; Ennore) or uncontaminated (Control; Kovalam) estuary. Earlier, the pollutant stress impact was determined through light and electron microscopy studies. The ATP/ADP ratio was measured using high performance liquid chromatography; ∆ψm by fluorescent probe 5, 5′, 6, 6′-tetrachloro-1, 1′, 3, 3′-tetraethyl benzimidazolcarbocyanine iodide (JC-1) dye and total protein expression patterns by protein profiling. The preponderance of stress impact was confirmed through microscopy studies that featured cytological alterations, disturbances in the surface morphology and in the cell organelles at the ultrastructural levels. Hepatocytes of test fish demonstrated a decrease in ATP and an increase in ADP and thereby alteration in ATP/ADP ratio ( p < 0.05; 20.75%). A significant disturbance ( p < 0.05; 26.57%) in ∆ψm with a ratio of J-aggregates/JC-1 monomer of 1 was observed for test fish hepatocytes compared to control group with a J-aggregates/JC-1 monomer ratio of 1.5. Quantitative assessment of protein expression levels also revealed enhanced induction of both low and high molecular weight proteins in test fish hepatocytes. The findings highlight the use of these parameters as the highly sensitive biomarkers in response to contaminant exposure compared to the routinely used antioxidant and oxidant stress parameters in biomonitoring programs. Among the measured parameters, the determination of ∆ψm may be suggested as a novel candidate as a biomarker because of its greater specificity and rapid quantitative risk assessment of pollutant exposures.

Respiration in Adipocytes is Inhibited by Reactive Oxygen Species

It is a desirable goal to stimulate fuel oxidation in adipocytes and shift the balance toward less fuel storage and more burning. To understand this regulatory process, respiration was measured in primary rat adipocytes, mitochondria, and fat-fed mice. Maximum O(2) consumption, in vitro, was determined with a chemical uncoupler of oxidative phosphorylation (carbonylcyanide p-trifluoromethoxyphenylhydrazone (FCCP)). The adenosine triphosphate/adenosine diphosphate (ATP/ADP) ratio was measured by luminescence. Mitochondria were localized by confocal microscopy with MitoTracker Green and their membrane potential (Delta psi(M)) measured using tetramethylrhodamine ethyl ester perchlorate (TMRE). The effect of N-acetylcysteine (NAC) on respiration and body composition in vivo was assessed in mice. Addition of FCCP collapsed Delta psi(M) and decreased the ATP/ADP ratio. However, we demonstrated the same rate of adipocyte O(2) consumption in the absence or presence of fuels and FCCP. Respiration was only stimulated when reactive oxygen species (ROS) were scavenged by pyruvate or NAC: other fuels or fuel combinations had little effect. Importantly, the ROS scavenging role of pyruvate was not affected by rotenone, an inhibitor of mitochondrial complex I. In addition, mice that consumed NAC exhibited increased O(2) consumption and decreased body fat in vivo. These studies suggest for the first time that adipocyte O(2) consumption may be inhibited by ROS, because pyruvate and NAC stimulated respiration. ROS inhibition of O(2) consumption may explain the difficulty to identify effective strategies to increase fat burning in adipocytes. Stimulating fuel oxidation in adipocytes by decreasing ROS may provide a novel means to shift the balance from fuel storage to fuel burning.

Structural dynamics of the mitochondrial ADP/ATP carrier revealed by molecular dynamics simulation studies

The mitochondrial adenosine diphosphate/adenosine triphosphate (ADP/ATP) carrier has been recently crystallized in complex with its specific inhibitor carboxyatractyloside (CATR). In the crystal structure, the six-transmembrane helix bundle that defines the nucleotide translocation pathway is closed on the matrix side due to sharp kinks in the odd-numbered helices. The closed conformation is further sealed by the loops protruding into the matrix that interact through an intricate network of charge-pairs. To gain insight into its structural dynamics we performed molecular dynamics (MD) simulation studies of the ADP/ATP carrier with and without its cocrystallized inhibitor. The two trajectories sampled a conformational space around two different configurations characterized by distinct salt-bridge networks with a significant shift from inter- to intrarepeat bonding on the matrix side in the absence of CATR. Analysis of the geometrical parameters defining the transmembrane helices showed that even-numbered helices can undergo a face rotation, whereas odd-numbered helices can undergo a change in the wobble angle with a conserved proline acting as molecular hinge. Our results provide new information on the dynamical properties of the ADP/ATP carrier and for the first time yield a detailed picture of a stable carrier conformation in absence of the inhibitor.