Calculation of ATP production rates using the Seahorse XF Analyzer

Oxidative phosphorylation and glycolysis are the dominant ATP-generating pathways in mammalian metabolism. The balance between these two pathways is often shifted to execute cell-specific functions in response to stimuli that promote activation, proliferation, or differentiation. However, measurement of these metabolic switches has remained mostly qualitative, making it difficult to discriminate between healthy, physiological changes in energy transduction or compensatory responses due to metabolic dysfunction. We therefore present a broadly applicable method to calculate ATP production rates from oxidative phosphorylation and glycolysis using Seahorse XF Analyzer data and empirical conversion factors. We quantify the bioenergetic changes observed during macrophage polarization as well as cancer cell adaptation to in vitro culture conditions. Additionally, we detect substantive changes in ATP utilization upon neuronal depolarization and T cell receptor activation that are not evident from steady-state ATP measurements. This method generates a single readout that allows the direct comparison of ATP produced from oxidative phosphorylation and glycolysis in live cells. Additionally, the manuscript provides a framework for tailoring the calculations to specific cell systems or experimental conditions.

Abstract 810: Differential use of lactate for mitochondria respiration by NSCLC cells

Metabolic liabilities in cancer cells provide the opportunity for novel therapeutic approaches. This is especially true as the dogma that all cancer cells are glycolytic is being challenged. Phenotypic screening of cancer cell lines can demonstrate what these liabilities are and suggest approaches for drugs that target these vulnerabilities. As an example, non-small cell lung cancer (NSCLC) is typically driven by oncogenic mutations in either KRAS or EGFR. However, the impact of these mutations on cellular metabolic phenotype is not well-studied. In this study, we observed that the two KRAS-mutated NSCLC cell lines (A549 and H460) primarily relied on glycolysis for ATP production while EGFR-mutated cell lines (H1975 and PC9) were more reliant on mitochondrial respiration to meet energy demands. There is emerging evidence to suggest that lactate is a major fuel for cancer cell energy metabolism especially in the glucose-limited tumor microenvironment. Thus, we next compared the use of lactate with other carbon sources for ATP production in NSCLC cells. We found there was differential usage of lactate for mitochondrial respiration between KRAS and EGFR-mutated NSCLC cells. EGFR-mutated NSCLC cells used lactate and increased mitochondrial respiration when lactate was acutely administrated regardless of glucose availability. In contrast, the use of lactate for the mitochondrial respiration by KRAS-mutated cells was limited. In A549 cells, no significant change in mitochondrial respiration rate was observed at all by acute injection of lactate. Together, these results imply that NSCLC variants have adopted different metabolic phenotypes depending on the oncogenic background and more oxidative phenotype may be correlated to higher lactate use for TCA cycle in production of ATP.

Citation Format: Pamela Swain, Natalia Romero, Yoonseok Kam, Brian P. Dranka. Differential use of lactate for mitochondria respiration by NSCLC cells [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 810.

Abstract 2092: Metabolic approach to EGFR-targeted therapy in non-small cell lung cancer

Mutation of the epidermal growth factor receptor (EGFR) is a major genetic driver of non-small cell lung cancer (NSCLC). While first-line tyrosine-kinase inhibitors (TKIs) have improved patient survival, many patients eventually develop resistance to these drugs. Combination therapies are now being researched to overcome this resistance. Pathways that may synergize with EGFR signaling are of interest since a liability created with one compound may then be exploited by a second. It is well known that glycolysis is controlled by EGFR signaling in cancer cells. However, the interplay of cell metabolism and EGFR inhibitors is not fully understood. Using PC9 cells which have known constitutive EGFR activation, we examined the relative poise of ATP production from mitochondria and glycolysis. In response to any of four different TKIs: afatinib, CO-1686, dacomitinib and erlotinib, a rapid decrease in glycolytic activity was induced. However, the total ATP production rates were not changed significantly as a result of increased mitochondrial ATP production. We next examined the mitochondrial fuel sources which support this increase by selectively blocking individual fuel pathways. In the presence of either a mitochondrial pyruvate carrier or glutaminase inhibitor, total ATP production rate decreased, and cell viability followed. Taken together, these data suggest that a combinational application of EGFR-targeted therapy and mitochondrial-targeted therapy may provide metabolic stress to cancer cells. Further study is required to understand the interplay of the tumor microenvironment and metabolic niches that may be found therein.

Citation Format: Yoonseok Kam, Pamela Swain, Natalia Romero, Brian P. Dranka. Metabolic approach to EGFR-targeted therapy in non-small cell lung cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 2092.

Differential modulation of T cell activation

Dysregulated T cell responses cause inflammation and autoimmune diseases. These conditions are managed with agents to limit and down-modulate the diverse cellular processes that control T cell activation. Cellular metabolism is a primary regulator of immune cell fate and function. T cell activation is correlated with metabolic shifts, especially in glycolysis, providing increased metabolic flux to support high rates of cellular proliferation. In this study we evaluated the impact of immunosuppressive compounds on the magnitude and kinetics of early anti-CD3/CD28 mediated T cell activation from a metabolic perspective. We employed compounds with divergent inhibitory mechanisms in order to understand the relationship of specific inhibitory pathways and metabolic function. Using an Agilent Seahorse XF Analyzer, T cells were activated in situ and activation was quantified in real time using proton efflux rate (PER) as a measure of glycolysis. Here, we report that anti-CD3/CD28-mediated T cell activation was suppressed when cells were pretreated with 20 μM prednisone. In contrast, activation was increased in the presence of 20 μM cyclosporin A. In non-activated cells, neither compound had a measurable effect on metabolism within 30 min of treatment. These data show a correlation in timing of suppression with the context of the drugs action. Future studies will utilize additional inhibitory pathway modulators to further examine the mechanisms of T cell activation in the context of immunosuppression.

Etomoxir Inhibits Macrophage Polarization by Disrupting CoA Homeostasis

Long-chain fatty acid (LCFA) oxidation has been shown to play an important role in interleukin-4 (IL-4)-mediated macrophage polarization (M(IL-4)). However, many of these conclusions are based on the inhibition of carnitine palmitoyltransferase-1 with high concentrations of etomoxir that far exceed what is required to inhibit enzyme activity (EC₉₀ < 3 μM). We employ genetic and pharmacologic models to demonstrate that LCFA oxidation is largely dispensable for IL-4-driven polarization. Unexpectedly, high concentrations of etomoxir retained the ability to disrupt M(IL-4) polarization in the absence of Cpt1a or Cpt2 expression. Although excess etomoxir inhibits the adenine nucleotide translocase, oxidative phosphorylation is surprisingly dispensable for M(IL-4). Instead, the block in polarization was traced to depletion of intracellular free coenzyme A (CoA), likely resulting from conversion of the pro-drug etomoxir into active etomoxiryl CoA. These studies help explain the effect(s) of excess etomoxir on immune cells and reveal an unappreciated role for CoA metabolism in macrophage polarization.

Abstract A67: Bi-phasic metabolic responses to in situ macrophage activation

The cellular metabolism of macrophages is an emerging element regulating inflammatory macrophages which are a critical component of tumor microenvironment. The inflammatory macrophage with highly glycolytic phenotype is also known to elevate the glycolytic activity upon pathogenic stimulation such as lipopolysaccharide (LPS). In this study, the dynamic changes in glycolysis were traced in a real-time manner by measuring proton efflux rates (PERs) and oxygen consumption rates (OCR) after an in-situ activation using Seahorse XFe96 analyzer. The PER of human peripheral blood monocyte (PBMC) derived M1 macrophages was increased within an hour after injection of LPS, which corresponding to cytokine release, tumor necrosis factor α (TNFα) and interleukin 1β (IL-1β). In contrast to PBMC-derived M1 macrophage activation, macrophage cell lines of RAW264.7 and J774.A1 required co-stimulation with interferon γ (IFNγ) for the full activation. Interestingly, the LPS and IFNγ co-stimulation modulates glycolytic rates in a bi-phasic manner which was identified only in long term (&gt; 6 hr) monitoring. A series of long term XF analysis using in situ activation revealed that the immediate early glycolytic response fully relies on LPS stimulation while the secondary elevation in PER depends on IFNγ stimulus, which turns on inducible nitric oxide synthase (iNOS) signaling and in turn suppresses mitochondrial respiration. The TNFα production is closely related to the immediate early glycolytic elevation, but independent from IFNγ-induced second elevation. The IFNγ-dependent second glycolysis increase was totally abolished by iNOS inhibitors whereas the immediate early glycolysis elevation was not affected at all. These data imply a temporal orchestration mechanism of LPS and IFNγ signaling in the metabolic regulation and activation of inflammatory macrophages.

Citation Format: Yoonseok Kam, Pamela M. Swain, Brian P. Dranka. Bi-phasic metabolic responses to in situ macrophage activation [abstract]. In: Proceedings of the AACR Special Conference on Tumor Immunology and Immunotherapy; 2017 Oct 1-4; Boston, MA. Philadelphia (PA): AACR; Cancer Immunol Res 2018;6(9 Suppl):Abstract nr A67.

Abstract 62: Effect of cancer cell-derived exosome on energy metabolism associated with macrophage activation

Macrophage is a critical microenvironmental component which can control tumor progression, and dynamic changes in cellular metabolism accompany the polarization. As well as other immune cells, the activation of macrophages can be modulated by cancer cells. Cancer-derived exosome is a newly emerging microenvironmental factor enables cancer cells to communicate with macrophages. In this study, examined were the activation-associated bioenergetic changes and the effect of cancer cell-derived exosome on the changes by a) monitoring the early metabolic kinetics and b) profiling bioenergetic phenotype resulted. In vitro activation of RAW264.7 macrophage cell line by injecting lipopolysaccharide (LPS) and interferon γ (IFNγ) in a Seahorse XF analyzer induced an immediate early increase in glycolytic rate. It also showed a delayed down-regulation of mitochondrial respiration, which resulted in a secondary elevation of glycolytic rate. This secondary glycolytic response was only obtained by LPS-IFNγ co-stimulation and mediated by induced nitric oxide synthase (iNOS) signaling. In contrast to the dynamic changes in metabolic phenotype, the total ATP production rate appeared to be stably maintained according to the XF data normalized by cell number. However, macrophage activation significantly increased glycolysis-dependent portion of ATP production. ATPs were generated almost solely by glycolysis after the delayed mitochondrial down-regulation by iNOS. Co-injection of cancer cell-derived exosomes with LPS slightly but significantly accelerated the immediate early glycolytic response as well as the delayed mitochondrial down-regulation. Furthermore, exosomes induced the immediate early glycolytic response even in the absence of LPS. These results imply that presence of cancer cell-derived exosomes may promote macrophage activation and accelerate pro-inflammatory immune response in a tumor microenvironment.

Citation Format: Yoonseok Kam, Brian P. Dranka. Effect of cancer cell-derived exosome on energy metabolism associated with macrophage activation [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 62.

Abstract 3487: Bioenergetic profiling of cancer cell lines: Quantifying the impact of glycolysis on cell proliferation

Fast proliferating cells require tight regulation to achieve a balance between the use of nutrients for ATP production (through glycolysis and oxidative phosphorylation) and the use of intermediate metabolites to sustain the increased biosynthetic activity. Cancer cells, but also high proliferative non-transformed cells exhibit high glycolytic activity during rapid proliferation even in the presence of normal oxygen concentrations in culture. However, despite the high glycolytic activity, the role of glycolysis is not necessary as a major contributor of ATP but to allow nutrient assimilation into biosynthetic precursors. Using Agilent Seahorse extracellular flux analysis, we have developed a cell-based assay which allows simultaneous measurement of the two-main cellular metabolic pathways to calculate the total rate of cellular ATP production as well as the fractional contribution from each pathway. The assay allows for real time changes in total ATP production rate to be quantified, and also the relative source of that ATP after exposure to drugs or changes in extracellular fuel supply. When we applied this new assay to a panel of 20 cancer and highly proliferative cell lines, we found that even in cell lines considered highly glycolytic, ATP production from glycolysis never represents more than 65% of total energy production and between 30-50% for most of the cell lines analyzed. The correlation between glycolytic ATP contribution to total ATP production and other cell phenotypes such as proliferation rate and motility was also analyzed. The use of this assay will allow for improved characterization of the bioenergetic profile of cancer cell variants, discrimination between normal and cancer cell types, and allow researchers to better understand the role of aerobic glycolysis in cell proliferation.

Citation Format: Natalia Romero, Pamela M. Swain, Yoonseok Kam, George Rogers, Brian P. Dranka. Bioenergetic profiling of cancer cell lines: Quantifying the impact of glycolysis on cell proliferation [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 3487.

Modulation of oxidative burst with exposure to cytokines in neutrophil cell activation

Neutrophils are essential for killing microorganisms and have a significant role in regulation of inflammatory response. Generation of reactive oxygen species (ROS) is one of the critical events that modulate the immune response in phagocytic cells. Stimulated neutrophils activate membrane-associated NADPH oxidase (NOX2) resulting in a powerful oxidative burst during which a large amount of oxygen is consumed generating ROS. The Agilent Seahorse XF analyzer is used to quantify oxygen consumption rate (OCR) as a direct non-invasive measure of neutrophil activation. In this study, neutrophil activation in the presence of cytokines known to be expressed within microenvironments in normal and disease states is evaluated. Treatment of neutrophils with the inflammatory cytokine TNFα induces oxidative burst within an hour of treatment, as observed in real time using the XF analyzer. Interestingly, pretreatment with TNFα reduces the oxidative burst observed when neutrophils were activated with phorbol myristate acetate (PMA). In contrast, treatment with GM-CSF and IL1 β had no acute effect in inducing oxidative burst. Rather, pretreatment of neutrophils with GM-CSF and IL1 β primed them for an enhanced response to PMA and a reduced elapsed time to reach maximal activation. Of note, the oxidative burst observed is associated with simultaneous increased of proton efflux rate (PER), indicative of the dependence on glycolysis and pentose phosphate pathway for production of NADPH during oxidative burst. These results, show the utility of the XF neutrophil activation assay to study the effect of modulators such drug treatments, microenvironment and disease progression during innate immune response.

Changes in metabolic phenotype and cellular ATP production during CD4+ T cell activation

Activation of CD4+ T cells is followed by rapid proliferation and differentiation into specific subsets (Treg or Teff). These transitions are accompanied by tight regulated changes in energetic demand and cellular metabolic reprogramming. Using Agilent Seahorse extracellular flux analysis, we have developed a cell-based assay for simultaneous measurement of the two-main cellular ATP-producing pathways, i.e. glycolysis and oxidative phosphorylation. The assay allows for quantification of real time changes in total ATP production rate, and the fractional contribution of the individual pathways to support bioenergetic demands. We found that naïve CD4+ T cells obtain most of its ATP from mitochondrial oxidative phosphorylation. After activation with anti CD3/CD28 conjugated beads, total ATP production rate significantly increases, and that rise is sustained by an increase in glycolytic ATP production, but also in mitochondrial ATP production. When glucose is replaced by galactose in the assay medium, T cell activation is inhibited despite partial compensation of total ATP production through mitochondrial respiration. Time-course of bioenergetic phenotype during T-cell expansion shows a deep increase in ATP production rate up to day 6–7 with glycolysis contributing up to 70% of total ATP production. When glucose is replaced by galactose 72 hr after activation, total ATP production rate was fully compensated by mitochondrial ATP production but still the inhibition of glycolytic activity by galactose reduces cell proliferation. The results obtained highlight the role of glycolytic activity beyond energetic supply and its importance for biosynthetic and redox requirements or cell activation and proliferation.

Abstract 5432: Characterization of metabolic fuel dependency in multidrug resistant breast cancer cells

Multidrug resistance (MDR) is a common resistant mechanism of cancer cells to cytotoxic drugs in systemic therapy. MDR is characterized by increased expression of ATP-dependent drug exporting pumps which remove cytotoxic compounds from the cytosol. However, the mechanism whereby cancer cells rapidly respond to this increased ATP demand is not fully understood although the glycolytic nature of MDR phenotype has been evidenced repeatedly by previous reports. We thus hypothesized that flexibility and dependency on mitochondrial fuels would be altered in concert with the switch to glycolysis. In order to more accurate analyze glycolytic pathway, we newly developed an assay to improve glycolytic rate measurements by accounting for TCA-dependent CO2 contribution to extracellular acidification and to correlate Seahorse extracellular flux data with lactate production. In a comparison of glycolytic rates between MCF7 breast cancer cell line and its MDR variant MCF7/Dox using this new assay, we confirmed that in MCF7/Dox cells glycolysis rate under basal conditions is significantly increased compared to wild type cells. Furthermore, MCF7Dox presents a significant increase in compensatory glycolysis when mitochondrial ATP production is blocked. This metabolic profile switch is accompanied by a decreased dependency on glutamine to fuel mitochondrial respiration an increased tolerance of the MCF7/Dox cells to glutamine deprivation as compared to the MCF7 wild type. In contrast, dependency on glucose and fatty acids mitochondrial-oxidation was largely unchanged in MDR cells. Additionally, an increase in long chain fatty acid oxidation is observed when glucose and glutamine oxidation is blocked indicating that MDR cells has higher mitochondrial flexibility to compensate for inhibition of alternative fuels utilization although it preferentially uses glucose. Together these data demonstrate that acquisition of multidrug resistance in MCF7 cells fundamentally changes their metabolism from a glutamine-driven, oxidative phosphorylation dependent phenotype to a highly glycolytic and glucose-dependent phenotype. These findings have potential therapeutic relevance in the context of inhibition of specific mitochondrial fuel pathways to prevent therapy resistance.

Citation Format: Yoonseok Kam, Natalia Romero, Pamela Swain, Brian P. Dranka. Characterization of metabolic fuel dependency in multidrug resistant breast cancer cells [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 5432. doi:10.1158/1538-7445.AM2017-5432

Reductive carboxylation supports redox homeostasis during anchorage-independent growth

Cells receive growth and survival stimuli through their attachment to an extracellular matrix (ECM). Overcoming the addiction to ECM-induced signals is required for anchorage-independent growth, a property of most malignant cells. Detachment from ECM is associated with enhanced production of reactive oxygen species (ROS) owing to altered glucose metabolism. Here we identify an unconventional pathway that supports redox homeostasis and growth during adaptation to anchorage independence. We observed that detachment from monolayer culture and growth as anchorage-independent tumour spheroids was accompanied by changes in both glucose and glutamine metabolism. Specifically, oxidation of both nutrients was suppressed in spheroids, whereas reductive formation of citrate from glutamine was enhanced. Reductive glutamine metabolism was highly dependent on cytosolic isocitrate dehydrogenase-1 (IDH1), because the activity was suppressed in cells homozygous null for IDH1 or treated with an IDH1 inhibitor. This activity occurred in absence of hypoxia, a well-known inducer of reductive metabolism. Rather, IDH1 mitigated mitochondrial ROS in spheroids, and suppressing IDH1 reduced spheroid growth through a mechanism requiring mitochondrial ROS. Isotope tracing revealed that in spheroids, isocitrate/citrate produced reductively in the cytosol could enter the mitochondria and participate in oxidative metabolism, including oxidation by IDH2. This generates NADPH in the mitochondria, enabling cells to mitigate mitochondrial ROS and maximize growth. Neither IDH1 nor IDH2 was necessary for monolayer growth, but deleting either one enhanced mitochondrial ROS and reduced spheroid size, as did deletion of the mitochondrial citrate transporter protein. Together, the data indicate that adaptation to anchorage independence requires a fundamental change in citrate metabolism, initiated by IDH1-dependent reductive carboxylation and culminating in suppression of mitochondrial ROS.

Abstract P2-12-08: Chemotherapy-induced fatigue and mitochondrial function in early stage breast cancer

Introduction

Patients with early stage breast cancer receiving chemotherapy (CT) may experience persistent fatigue. The mechanisms for fatigue are not well understood. We hypothesized that CT-induced fatigue may involve perturbations in mitochondrial function. We therefore examined the development of fatigue in patients during adjuvant or neoadjuvant CT and measured mitochondrial function in their peripheral blood mononuclear cells (PBMCs).

Methods

Females with Stage I-III breast cancer patients, ages 35-75 years, were enrolled in an IRB-approved study. Patients with coexisting illnesses associated with chronic fatigue were excluded. Patients self-reported fatigue severity using the 14-question Fatigue Symptom Inventory (FSI) that rates fatigue intensity on a 10-point scale. Data [FSI and PBMCs] were collected prior to CT, mid-point in the course of CT, 2 - 3 weeks after completion of CT, and 3 and 6 months later. Mitochondrial function in PBMCs from patients was measured using a Seahorse Bioscience XF24 analyzer at corresponding times.

Results

Results on CT-induced fatigue are available for 67 patients. The overall fatigue score for each patient was measured as the sum of the scores for all 14 questions in the FSI. The average fatigue score for the 67 patients prior to chemotherapy was 20. Baseline fatigue scores for patients who had adjuvant CT were much greater than for patients receiving neoadjuvant CT (R2=1). Patient fatigue scores doubled after starting chemotherapy (average score 40, p &lt; 0.001). Even though fatigue scores improved after treatment completion (average score 26 at 6 months), the scores did not return to baseline 6 months later (p=0.02).

In our population, CT-induced fatigue did not correlate with patient age regardless of the CT regimen [r=0.3 and r= -.2, for doxorubicin plus cyclophosphamide (AC) vs docetaxel plus cyclophosphamide (TC) groups, respectively)] or a decrease in hemoglobin (r= -.3 and r=0.03, for AC and TC, respectively). None of these correlations could explain more than 9% of the change in treatment-induced fatigue (p=0.2).

Preliminary analysis of mitochondrial function in 12 patients shows that 9 patients had a decrease in mitochondrial reserve capacity with an increase in CT-induced fatigue following completion of 4 cycles of CT. 3 patients had a decrease in mitochondrial reserve capacity but reported no significant change in their fatigue scores. Mitochondrial function data on all patients have been collected and are presently being analyzed.

Conclusion

Our study shows that early stage breast cancer patients treated with adjuvant or neoadjuvant CT may experience fatigue that can persist for months after completion of treatment and cannot be explained by the CT regimen, age, or anemia. Our initial results suggest a link between CT-induced fatigue and changes in mitochondrial function in some patients. Mitochondrial function analysis and its correlation with fatigue for all 67 patients will be completed and reported at SABCS. Mitochondrial function may prove to be a biomarker for CT-induced fatigue in certain patients and may help identify patients for whom interventions that stimulate mitochondria biogenesis, including pharmacologic agents and exercise, may be beneficial in ameliorating this side-effect.

Citation Format: Kanchana Herath, Brian P Dranka, George M Lessmann, Donna McAllister, Raymond G Hoffmann, Balaraman Kalyanaraman, Christopher R Chitambar, Namrata I Peswani. Chemotherapy-induced fatigue and mitochondrial function in early stage breast cancer [abstract]. In: Proceedings of the Thirty-Seventh Annual CTRC-AACR San Antonio Breast Cancer Symposium: 2014 Dec 9-13; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2015;75(9 Suppl):Abstract nr P2-12-08.

Abstract B07: Metabolic liabilities of human colon carcinoma spheroids are different compared to standard 2D cultures

The search for metabolic liabilities in tumor cells is typically performed in standard 2D cultures. This approach lacks the 3D context and heterogeneity of tumor tissue in vivo, which has significant impact on their metabolic behavior. One solution to modeling complex tumor cell interactions is to use cultured tumor spheroids. To assess bioenergetic function in individual spheroids, a modified, 96-well plate for the Seahorse Bioscience XFe96 Extracellular Flux Analyzer was created. Here, we demonstrate the capability of measuring mitochondrial oxygen consumption – a measure or mitochondrial respiration – and extracellular acidification – a measure of glycolytic flux – in individual HCT116 colon carcinoma spheroids. Spheroids were cultured using the hanging drop method for 4 days. Mitochondrial function was determined using the Cell Mito Stress Test which profiles 6 specific indices of mitochondrial activity. Cells grown in spheroids had a markedly increased spare respiratory capacity compared to cells in 2D culture. These data are consistent with a shift from the highly proliferative nature of 2D culture to a more physiological model where proliferation and differentiation is more balanced. We hypothesize that viewing metabolism holistically allows for a more complete view of cellular bioenergetic function and potential liabilities. To understand the metabolic potential of cells in the context of their basal metabolism, two new metrics for describing mitochondrial function were established. By stimulating maximal oxygen consumption by combined exposure to oligomycin and FCCP, and maximal extracellular acidification rate (ECAR) using rotenone, antimycin A, and oligomycin, the potential to switch metabolic pathways was determined. Metabolic Capacity Index was identified using the maximal responses in each direction, and Metabolic Flexibility Index was calculated as the angle of the line to identify cellular preference for OXPHOS or glycolysis. Interestingly, plastic-adherent HCT116 cells only exhibited potential to increase glycolysis, while HCT116 spheroids had a more balanced response. These data are consistent with the finding that spheroids have increased spare capacity. Implications of this work for future studies in cancer biology will be discussed.

Citation Format: Brian P. Dranka, Pamela Swain, George W. Rogers, Ajit S. Divakaruni, Andy Neilson, David A. Ferrick. Metabolic liabilities of human colon carcinoma spheroids are different compared to standard 2D cultures. [abstract]. In: Abstracts: AACR Special Conference on Cellular Heterogeneity in the Tumor Microenvironment; 2014 Feb 26-Mar 1; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2015;75(1 Suppl):Abstract nr B07. doi:10.1158/1538-7445.CHTME14-B07

A novel mitochondrially-targeted apocynin derivative prevents hyposmia and loss of motor function in the leucine-rich repeat kinase 2 (LRRK2(R1441G)) transgenic mouse model of Parkinson's disease

Recently, we demonstrated that dimeric apocynin prevented loss of motor function in the leucine-rich repeat kinase 2 (LRRK2(R1441G)) transgenic (tg) mouse (treated with 200mg/kg, three times per week) [B.P. Dranka et al., Neurosci. Lett. 549 (2013) 57-62]. Here we extend those studies by treating LRRK2(R1441G) mice with an orally-available, mitochondrially-targeted apocynin derivative. We hypothesized that the increased mitochondrial permeability of Mito-apocynin, due to the triphenylphosphonium moiety, would allow improvement of Parkinson's disease (PD) symptoms at lower doses than those required for diapocynin. Tests of motor coordination (pole test, Rotor-Rod) revealed a significant deficit in coordinated motor function in LRRK2(R1441G) mice by 15 months of age. Decreased performance on the pole test and Rotor-Rod in the LRRK2(R1441G) mice was prevented with Mito-apocynin treatment (3mg/kg, three times per week). Decreased olfactory function is an early indication of PD in human patients. LRRK2(R1441G) tg mice displayed deficits in sense of smell in both the hidden treat test, and a radial arm maze test. Interestingly, treatment with Mito-apocynin prevented this hyposmia, and animals retained normal ability to identify either a scented treat or a food pellet as well as wild type littermates. Together, these data demonstrate that the mitochondria-targeted apocynin analog is effective in preventing early PD-like symptoms in the LRRK2(R1441G) mouse model.

Docosahexaenoic acid attenuates breast cancer cell metabolism and the Warburg phenotype by targeting bioenergetic function

Docosahexaenoic acid (DHA; C22:6n-3) depresses mammary carcinoma proliferation and growth in cell culture and in animal models. The current study explored the role of interrupting bioenergetic pathways in BT-474 and MDA-MB-231 breast cancer cell lines representing respiratory and glycolytic phenotypes, respectively and comparing the impacts of DHA with a non-transformed cell line, MCF-10A. Metabolic investigation revealed that DHA supplementation significantly diminished the bioenergetic profile of the malignant cell lines in a dose-dependent manner. DHA enrichment also resulted in decreases in hypoxia-inducible factor (HIF-1α) total protein level and transcriptional activity in the malignant cell lines but not in the non-transformed cell line. Downstream targets of HIF-1α, including glucose transporter 1 (GLUT 1) and lactate dehydrogenase (LDH), were decreased by DHA treatment in the BT-474 cell line, as well as decreases in LDH protein level in the MDA-MB-231 cell line. Glucose uptake, total glucose oxidation, glycolytic metabolism, and lactate production were significantly decreased in response to DHA supplementation; thereby enhancing metabolic injury and decreasing oxidative metabolism. The DHA-induced metabolic changes led to a marked decrease of intracellular ATP levels by 50% in both cancer cell lines, which mediated phosphorylation of metabolic stress marker, AMPK, at Thr172. These findings show that DHA contributes to impaired cancer cell growth and survival by altering cancer cell metabolism, increasing metabolic stress and altering HIF-1α-associated metabolism, while not affecting non-transformed MCF-10A cells. This study provides rationale for enhancement of current cancer prevention models and current therapies by combining them with dietary sources, like DHA.

Diapocynin prevents early Parkinson's disease symptoms in the leucine-rich repeat kinase 2 (LRRK2R¹⁴⁴¹G) transgenic mouse

The most prominent mechanism proposed for death of dopaminergic neurons in Parkinson's disease (PD) is elevated generation of reactive oxygen/nitrogen species (ROS/RNS). Recent studies suggest that ROS produced during PD pathogenesis may contribute to cytotoxicity in cell culture models of PD. We hypothesized that inhibition of ROS production would prevent PD symptoms in the LRRK2(R1441G) transgenic (tg) mouse model of PD. These mice overexpress a mutant form of leucine-rich repeat kinase 2 (LRRK2) and are reported to develop PD-like symptoms at approximately 10 months of age. Despite similar expression of the transgene, our colony did not recapitulate the same type of motor dysfunction originally reported. However, tests of motor coordination (pole test, Rotor-Rod) revealed a significant defect in LRRK2(R1441G) mice by 16 months of age. LRRK2(R1441G) tg mice, or wild type littermates, were given diapocynin (200mg/kg, a proposed NADPH oxidase inhibitor) three times per week by oral gavage starting at 12 weeks of age. Decreased performance on the pole test and Rotor-Rod in the LRRK2(R1441G) mice was prevented with diapocynin treatment. No loss in open field movement or rearing was found. As expected, tyrosine hydroxylase staining was similar in both the substantia nigra and striatum in all treatment groups. Together these data demonstrate that diapocynin is a viable agent for protection of neurobehavioral function.

HPLC-based monitoring of products formed from hydroethidine-based fluorogenic probes--the ultimate approach for intra- and extracellular superoxide detection

BACKGROUND

Nearly ten years ago, we demonstrated that superoxide radical anion (O2⋅¯) reacts with the hydroethidine dye (HE, also known as dihydroethidium, DHE) to form a diagnostic marker product, 2-hydroxyethidium (2-OH-E(+)). This particular product is not derived from reacting HE with other biologically relevant oxidants (hydrogen peroxide, hydroxyl radical, or peroxynitrite). This discovery negated the longstanding view that O2⋅¯ reacts with HE to form the other oxidation product, ethidium (E(+)). It became clear that due to the overlapping fluorescence spectra of E(+) and 2-OH-E(+), fluorescence-based techniques using the "red fluorescence" are not suitable for detecting and measuring O2⋅¯ in cells using HE or other structurally analogous fluorogenic probes (MitoSOX(TM) Red or hydropropidine). However, using HPLC-based assays, 2-OH-E(+) and analogous hydroxylated products can be easily detected and quickly separated from other oxidation products.

SCOPE OF REVIEW

The principles discussed in this chapter are generally applicable in free radical biology and medicine, redox biology, and clinical and translational research. The assays developed here could be used to discover new and targeted inhibitors for various superoxide-producing enzymes, including NADPH oxidase (NOX) isoforms.

MAJOR CONCLUSIONS

HPLC-based approaches using site-specific HE-based fluorogenic probes are eminently suitable for monitoring O2⋅¯ in intra- and extracellular compartments and in mitochondria. The use of fluorescence-microscopic methods should be avoided because of spectral overlapping characteristics of O2⋅¯-derived marker product and other, non-specific oxidized fluorescent products formed from these probes.

GENERAL SIGNIFICANCE

Methodologies and site-specific fluorescent probes described in this review can be suitably employed to delineate oxy radical dependent mechanisms in cells under physiological and pathological conditions. This article is part of a Special Issue entitled Current methods to study reactive oxygen species - pros and cons and biophysics of membrane proteins. Guest Editor: Christine Winterbourn.

Anti-inflammatory and neuroprotective effects of an orally active apocynin derivative in pre-clinical models of Parkinson's disease

Background

Parkinson’s disease (PD) is a devastating neurodegenerative disorder characterized by progressive motor debilitation, which affects several million people worldwide. Recent evidence suggests that glial cell activation and its inflammatory response may contribute to the progressive degeneration of dopaminergic neurons in PD. Currently, there are no neuroprotective agents available that can effectively slow the disease progression. Herein, we evaluated the anti-inflammatory and antioxidant efficacy of diapocynin, an oxidative metabolite of the naturally occurring agent apocynin, in a pre-clinical 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) mouse model of PD.

Methods

Both pre-treatment and post-treatment of diapocynin were tested in the MPTP mouse model of PD. Diapocynin was administered via oral gavage to MPTP-treated mice. Following the treatment, behavioral, neurochemical and immunohistological studies were performed. Neuroinflammatory markers, such as ionized calcium binding adaptor molecule 1 (Iba-1), glial fibrillary acidic protein (GFAP), gp91phox and inducible nitric oxide synthase (iNOS), were measured in the nigrostriatal system. Nigral tyrosine hydroxylase (TH)-positive neurons as well as oxidative markers 3-nitrotyrosine (3-NT), 4-hydroxynonenal (4-HNE) and striatal dopamine levels were quantified for assessment of the neuroprotective efficacy of diapocynin.

Results

Oral administration of diapocynin significantly attenuated MPTP-induced microglial and astroglial cell activation in the substantia nigra (SN). MPTP-induced expression of gp91phox and iNOS activation in the glial cells of SN was also completely blocked by diapocynin. Notably, diapocynin markedly inhibited MPTP-induced oxidative markers including 3-NT and 4-HNE levels in the SN. Treatment with diapocynin also significantly improved locomotor activity, restored dopamine and its metabolites, and protected dopaminergic neurons and their nerve terminals in this pre-clinical model of PD. Importantly, diapocynin administered 3 days after initiation of the disease restored the neurochemical deficits. Diapocynin also halted the disease progression in a chronic mouse model of PD.

Conclusions

Collectively, these results demonstrate that diapocynin exhibits profound neuroprotective effects in a pre-clinical animal model of PD by attenuating oxidative damage and neuroinflammatory responses. These findings may have important translational implications for treating PD patients.

Alterations in bioenergetic function induced by Parkinson's disease mimetic compounds: lack of correlation with superoxide generation

In vitro and in vivo models of Parkinson's disease (PD) suggest that increased oxidant production leads to mitochondrial dysfunction in dopaminergic neurons and subsequent cell death. However, it remains unclear if cell death in these models is caused by inhibition of mitochondrial function or oxidant production. The objective of this study was to determine the relationship between mitochondrial dysfunction and oxidant production in response to multiple PD neurotoxicant mimetics. MPP(+) caused a dose-dependent decrease in the basal oxygen consumption rate in dopaminergic N27 cells, indicating a loss of mitochondrial function. In parallel, we found that MPP(+) only modestly increased oxidation of hydroethidine as a diagnostic marker of superoxide production in these cells. Similar results were found using rotenone as a mitochondrial inhibitor, or 6-hydroxydopamine (6-OHDA) as a mechanistically distinct PD neurotoxicant, but not with exposure to paraquat. In addition, the extracellular acidification rate, used as a marker of glycolysis, was stimulated to compensate for oxygen consumption rate inhibition after exposure to MPP(+), rotenone, or 6-OHDA, but not paraquat. Together these data indicate that MPP(+), rotenone, and 6-OHDA dramatically shift bioenergetic function away from the mitochondria and towards glycolysis in N27 cells.

Boronate probes as diagnostic tools for real time monitoring of peroxynitrite and hydroperoxides

Boronates, a group of organic compounds, are emerging as one of the most effective probes for detecting and quantifying peroxynitrite, hypochlorous acid, and hydrogen peroxide. Boronates react with peroxynitrite nearly a million times faster than with hydrogen peroxide. Boronate-containing fluorogenic compounds have been used to monitor real time generation of peroxynitrite in cells and for imaging hydrogen peroxide in living animals. This perspective highlights potential applications of boronates and other fluorescent probes to high-throughput analyses of peroxynitrite and hydroperoxides in toxicological studies.

Mitochondria-targeted drugs synergize with 2-deoxyglucose to trigger breast cancer cell death

Cancer cells are long known to exhibit increased aerobic glycolysis, but glycolytic inhibition has not offered a viable chemotherapeutic strategy in part because of the systemic toxicity of antiglycolytic agents. However, recent studies suggest that a combined inhibition of glycolysis and mitochondrial function may help overcome this issue. In this study, we investigated the chemotherapeutic efficacies of mitochondria-targeted drugs (MTD) in combination with 2-deoxy-d-glucose (2-DG), a compound that inhibits glycolysis. Using the MTDs, termed Mito-CP and Mito-Q, we evaluated relative cytotoxic effects and mitochondrial bioenergetic changes in vitro. Interestingly, both Mito-CP and Mito-Q synergized with 2-DG to decrease ATP levels in two cell lines. However, with time, the cellular bioenergetic function and clonogenic survival were largely restored in some cells. In a xenograft model of human breast cancer, combined treatment of Mito-CP and 2-DG led to significant tumor regression in the absence of significant morphologic changes in kidney, liver, or heart. Collectively, our findings suggest that dual targeting of mitochondrial bioenergetic metabolism with MTDs and glycolytic inhibitors such as 2-DG may offer a promising chemotherapeutic strategy.

Global profiling of reactive oxygen and nitrogen species in biological systems: high-throughput real-time analyses

Herein we describe a high-throughput fluorescence and HPLC-based methodology for global profiling of reactive oxygen and nitrogen species (ROS/RNS) in biological systems. The combined use of HPLC and fluorescence detection is key to successful implementation and validation of this methodology. Included here are methods to specifically detect and quantitate the products formed from interaction between the ROS/RNS species and the fluorogenic probes, as follows: superoxide using hydroethidine, peroxynitrite using boronate-based probes, nitric oxide-derived nitrosating species with 4,5-diaminofluorescein, and hydrogen peroxide and other oxidants using 10-acetyl-3,7-dihydroxyphenoxazine (Amplex® Red) with and without horseradish peroxidase, respectively. In this study, we demonstrate real-time monitoring of ROS/RNS in activated macrophages using high-throughput fluorescence and HPLC methods. This global profiling approach, simultaneous detection of multiple ROS/RNS products of fluorescent probes, developed in this study will be useful in unraveling the complex role of ROS/RNS in redox regulation, cell signaling, and cellular oxidative processes and in high-throughput screening of anti-inflammatory antioxidants.

Assessing bioenergetic function in response to oxidative stress by metabolic profiling

It is now clear that mitochondria are an important target for oxidative stress in a broad range of pathologies, including cardiovascular disease, diabetes, neurodegeneration, and cancer. Methods for assessing the impact of reactive species on isolated mitochondria are well established but constrained by the need for large amounts of material to prepare intact mitochondria for polarographic measurements. With the availability of high-resolution polarography and fluorescence techniques for the measurement of oxygen concentration in solution, measurements of mitochondrial function in intact cells can be made. Recently, the development of extracellular flux methods to monitor changes in oxygen concentration and pH in cultures of adherent cells in multiple-sample wells simultaneously has greatly enhanced the ability to measure bioenergetic function in response to oxidative stress. Here we describe these methods in detail using representative cell types from renal, cardiovascular, nervous, and tumorigenic model systems while illustrating the application of three protocols to analyze the bioenergetic response of cells to oxidative stress.

What part of NO don't you understand? Some answers to the cardinal questions in nitric oxide biology

Nitric oxide (NO) regulates biological processes through signaling mechanisms that exploit its unique biochemical properties as a free radical. For the last several decades, the key aspects of the chemical properties of NO relevant to biological systems have been defined, but it has been a challenge to assign these to specific cellular processes. Nevertheless, it is now clear that the high affinity of NO for transition metal centers, particularly iron, and the rapid reaction of NO with oxygen-derived free radicals can explain many of its biological and pathological properties. Emerging studies also highlight a growing importance of the secondary metabolites of NO-dependent reactions in the post-translational modification of key metabolic and signaling proteins. In this minireview, we emphasize the current understanding of the biochemistry of NO and place it in a biological context.

Mitochondrial reserve capacity in endothelial cells: The impact of nitric oxide and reactive oxygen species

The endothelium is not considered to be a major energy-requiring organ, but nevertheless endothelial cells have an extensive mitochondrial network. This suggests that mitochondrial function may be important in response to stress and signaling in these cells. In this study, we used extracellular flux analysis to measure mitochondrial function in adherent bovine aortic endothelial cells (BAEC). Under basal conditions, BAEC use only approximately 35% of their maximal respiratory capacity. We calculate that this represents an intermediate respiratory state between States 3 and 4, which we define as State(apparent) equal to 3.64. Interestingly, the apparent respiratory control ratio (maximal mitochondrial oxygen consumption/non-ADP-linked respiration) in these cells is on the order of 23, which is substantially higher than that which is frequently obtained with isolated mitochondria. These results suggest that mitochondria in endothelial cells are highly coupled and possess a considerable bioenergetic reserve. Because endothelial cells are exposed to both reactive oxygen (ROS) and reactive nitrogen species in the course of vascular disease, we hypothesized that this reserve capacity is important in responding to oxidative stress. To test this, we exposed BAEC to NO or ROS alone or in combination. We found that exposure to nontoxic concentrations of NO or low levels of hydrogen peroxide generated from 2,3-dimethoxy-1,4-napthoquinone (DMNQ) had little impact on basal mitochondrial function but both treatments reversibly decreased mitochondrial reserve capacity. However, combined NO and DMNQ treatment resulted in an irreversible loss of reserve capacity and was associated with cell death. These data are consistent with a critical role for the mitochondrial reserve capacity in endothelial cells in responding to oxidative stress.

Regulation of vascular smooth muscle cell bioenergetic function by protein glutathiolation

Protein thiolation by glutathione is a reversible and regulated post-translational modification that is increased in response to oxidants and nitric oxide. Because many mitochondrial enzymes contain critical thiol residues, it has been hypothesized that thiolation reactions regulate cell metabolism and survival. However, it has been difficult to differentiate the biological effects due to protein thiolation from other oxidative protein modifications. In this study, we used diamide to titrate protein glutathiolation and examined its impact on glycolysis, mitochondrial function, and cell death in rat aortic smooth muscle cells. Treatment of cells with diamide increased protein glutathiolation in a concentration-dependent manner and had comparably little effect on protein-protein disulfide formation. Diamide increased mitochondrial proton leak and decreased ATP-linked mitochondrial oxygen consumption and cellular bioenergetic reserve capacity. Concentrations of diamide above 200 microM promoted acute bioenergetic failure and caused cell death, whereas lower concentrations of diamide led to a prolonged increase in glycolytic flux and were not associated with loss of cell viability. Depletion of glutathione using buthionine sulfoximine had no effect on basal protein thiolation or cellular bioenergetics but decreased diamide-induced protein glutathiolation and sensitized the cells to bioenergetic dysfunction and death. The effects of diamide on cell metabolism and viability were fully reversible upon addition of dithiothreitol. These data suggest that protein thiolation modulates key metabolic processes in both the mitochondria and cytosol.

Methods for imaging and detecting modification of proteins by reactive lipid species

Products of lipid peroxidation are generated in a wide range of pathologies associated with oxidative stress and inflammation. Many oxidized lipids contain reactive functional groups that can modify proteins, change their structure and function, and affect cell signaling. However, intracellular localization and protein adducts of reactive lipids have been difficult to detect, and the methods of detection rely largely on antibodies raised against specific lipid-protein adducts. As an alternative approach to monitoring oxidized lipids in cultured cells, we have tagged the lipid peroxidation substrate arachidonic acid and an electrophilic lipid, 15-deoxy-Delta(12,14)-prostaglandin-J2 (15d-PGJ2), with either biotin or the fluorophore BODIPY. Tagged arachidonic acid can be used in combination with conditions of oxidant stress or inflammation to assess the subcellular localization and protein modification by oxidized lipids generated in situ. Furthermore, we show that reactive lipid oxidation products such as 15d-PGJ2 can also be labeled and used in fluorescence and Western blotting applications. This article describes the synthesis, purification, and selected application of these tagged lipids in vitro.