The rate of oxygen utilization by cells

Testing Lab-on-a-Chip Technology for Culturing Human Melanoma Cells under Simulated Microgravity

The dynamic development of the space industry makes space flights more accessible and opens up new opportunities for biological research to better understand cell physiology under real microgravity. Whereas specialized studies in space remain out of our reach, preliminary experiments can be performed on Earth under simulated microgravity (sµg). Based on this concept, we used a 3D-clinostat (3D-C) to analyze the effect of short exposure to sµg on human keratinocytes HaCaT and melanoma cells A375 cultured on all-glass Lab-on-a-Chip (LOC). Our preliminary studies included viability evaluation, mitochondrial and caspase activity, and proliferation assay, enabling us to determine the effect of sµg on human cells. By comparing the results concerning cells cultured on LOCs and standard culture dishes, we were able to confirm the biocompatibility of all-glass LOCs and their potential application in microgravity research on selected human cell lines. Our studies revealed that HaCaT and A375 cells are susceptible to simulated microgravity; however, we observed an increased caspase activity and a decrease of proliferation in cancer cells cultured on LOCs in comparison to standard cell cultures. These results are an excellent basis to conduct further research on the possible application of LOCs systems in cancer research in space.

Measuring Both pH and O2 with a Single On-Chip Sensor in Cultures of Human Pluripotent Stem Cell-Derived Cardiomyocytes to Track Induced Changes in Cellular Metabolism

In vitro studies which focus on cellular metabolism can benefit from time-resolved readouts from the living cells. pH and O₂ concentration are fundamental parameters upon which cellular metabolism is often inferred. This work demonstrates a novel use of a ruthenium oxide (RuO_x) electrode for in vitro studies. The RuO_x electrode was characterized to measure both pH and O₂ using two different modes. When operated potentiometrically, continuous pH reading can be obtained, and O₂ concentration can be measured chronoamperometrically. In this work, we demonstrate the use of the RuO_x electrodes in inferring two different types of metabolism of human pluripotent stem cell-derived cardiomyocytes. We also show and discuss the interpretation of the measurements into meaningful extracellular acidification rates and oxygen consumption rates of the cells. Overall, we present the RuO_x electrode as a versatile and powerful tool in in vitro cell metabolism studies, especially in comparative settings.

Developing Analysis Protocols for Monitoring Intracellular Oxygenation Using Fluorescence Lifetime Imaging of Myoglobin-mCherry

Oxygen (O2) is a critical metabolite for cellular function as it fuels aerobic cellular metabolism; further, it is a known regulator of gene expression. Monitoring oxygenation within cells and organelles can provide valuable insights into how O2, or lack thereof, both influences and responds to cell processes. In recent years, fluorescence lifetime imaging microscopy (FLIM) has been used to track several probe concentration independent intracellular phenomena, such as pH, viscosity, and, in conjunction with Förster resonance energy transfer (FRET), protein-protein interactions. Here, we describe methods for synthesizing and expressing the novel FLIM-FRET intracellular O2 probe Myoglobin-mCherry (Myo-mCherry) in cultured cell lines, as well as acquiring FLIM images using a laser scanning confocal microscope configured for two-photon excitation and a time-correlated single photon counting (TCSPC) module. Finally, we provide step-by-step protocols for FLIM analysis of Myo-mCherry using the commercial software SPCImage and conversion of fluorescence lifetime values in each pixel to apparent intracellular oxygen partial pressures (pO2).

Triphenylphosphonium derivatives disrupt metabolism and inhibit melanoma growth in vivo when delivered via a thermosensitive hydrogel

Despite dramatic improvements in outcomes arising from the introduction of targeted therapies and immunotherapies, metastatic melanoma is a highly resistant form of cancer with 5 year survival rates of <35%. Drug resistance is frequently reported to be associated with changes in oxidative metabolism that lead to malignancy that is non-responsive to current treatments. The current report demonstrates that triphenylphosphonium(TPP)-based lipophilic cations can be utilized to induce cytotoxicity in pre-clinical models of malignant melanoma by disrupting mitochondrial metabolism. In vitro experiments demonstrated that TPP-derivatives modified with aliphatic side chains accumulated in melanoma cell mitochondria; disrupted mitochondrial metabolism; led to increases in steady-state levels of reactive oxygen species; decreased total glutathione; increased the fraction of glutathione disulfide; and caused cell killing by a thiol-dependent process that could be rescued by N-acetylcysteine. Furthermore, TPP-derivative-induced melanoma toxicity was enhanced by glutathione depletion (using buthionine sulfoximine) as well as inhibition of thioredoxin reductase (using auranofin). In addition, there was a structure-activity relationship between the aliphatic side-chain length of TPP-derivatives (5–16 carbons), where longer carbon chains increased melanoma cell metabolic disruption and cell killing. In vivo bio-distribution experiments showed that intratumoral administration of a C¹⁴-TPP-derivative (12-carbon aliphatic chain), using a slow-release thermosensitive hydrogel as a delivery vehicle, localized the drug at the melanoma tumor site. There, it was observed to persist and decrease the growth rate of melanoma tumors. These results demonstrate that TPP-derivatives selectively induce thiol-dependent metabolic oxidative stress and cell killing in malignant melanoma and support the hypothesis that a hydrogel-based TPP-derivative delivery system could represent a therapeutic drug-delivery strategy for melanoma.

An insight into the functional role of antioxidant and detoxification enzymes in adult Rhipicephalus microplus female ticks

Ticks have developed physiological adaptations to transport, store, metabolize and secrete toxic components from the diet and environment. Different classes of enzymes are involved in these processes, however, the role of several of them is not yet characterized in Rhipicephalus microplus. In this context, this work investigated the action of antioxidant and detoxification enzymes, as well as the levels of essential cellular reductants in R. microplus partially engorged females (PEF) and fully engorged females (FEF). Results demonstrated that enzymes transcriptional levels and enzymatic activity from ovary and fat body were higher in PEF than in FEF, except for ovary Glutathione peroxidase (GPx), which was the only enzyme showing highest activity in the FEF stage. These results indicated a higher demand for antioxidant potential in these organs at the initial feeding phase than during egg-laying. In midgut, however, there was more variability in the transcriptional levels and activity of the different enzymes between the PEF and FEF phases. Similar NADPH levels were found in PEF and FEF phases, suggesting a remarkable capacity to maintain a regular supply of reducing power, despite the developmental changes and large intake of heme and iron. However, reduced glutathione (GSH) levels were variable between PEF and FEF when distinct organs were compared. Taken together, our data suggest a higher demand for reducing potential in FEF ticks. The silencing of catalase (CAT) or thioredoxin reductase (TRx) genes in females did not impair feeding, egg-laying capacity, or larvae hatching. CAT-silenced ticks had increased ovary peroxidase activity, a possible compensatory antioxidant mechanism. Altogether, the results shed light on the complexity of the antioxidant and detoxification enzyme system in ticks and its involvement in different physiological mechanisms.

Current Perspective: 3D Spheroid Models Utilizing Human-Based Cells for Investigating Metabolism-Dependent Drug-Induced Liver Injury

Drug-induced liver injury (DILI) remains a leading cause for the withdrawal of approved drugs. This has significant financial implications for pharmaceutical companies, places increasing strain on global health services, and causes harm to patients. For these reasons, it is essential that in-vitro liver models are capable of detecting DILI-positive compounds and their underlying mechanisms, prior to their approval and administration to patients or volunteers in clinical trials. Metabolism-dependent DILI is an important mechanism of drug-induced toxicity, which often involves the CYP450 family of enzymes, and is associated with the production of a chemically reactive metabolite and/or inefficient removal and accumulation of potentially toxic compounds. Unfortunately, many of the traditional in-vitro liver models fall short of their in-vivo counterparts, failing to recapitulate the mature hepatocyte phenotype, becoming metabolically incompetent, and lacking the longevity to investigate and detect metabolism-dependent DILI and those associated with chronic and repeat dosing regimens. Nevertheless, evidence is gathering to indicate that growing cells in 3D formats can increase the complexity of these models, promoting a more mature-hepatocyte phenotype and increasing their longevity, in vitro. This review will discuss the use of 3D in vitro models, namely spheroids, organoids, and perfusion-based systems to establish suitable liver models to investigate metabolism-dependent DILI.

Temperature Sensing in Cells Using Polymeric Upconversion Nanocapsules

Monitoring local temperature inside cells is crucial when interpreting biological activities as enhanced cellular metabolism leads to higher heat production and is commonly correlated with the presence of diseases such as cancer. In this study, we report on polymeric upconversion nanocapsules for potential use as local nanothermometers in cells by exploiting the temperature dependence of the triplet-triplet annihilation upconversion phenomenon. Nanocapsules synthesized by the miniemulsion solvent evaporation technique are composed of a polymer shell and a liquid core of rice bran oil, hosting triplet-triplet annihilation upconversion active dyes as sensitizer and emitter molecules. The sensitivity of the triplet-triplet annihilation upconversion to the local oxygen concentration was overcome by the oxygen reduction ability of the rice bran oil core. The triplet-triplet annihilation upconversion process could thus successfully be applied at different levels of oxygen presence including at ambient conditions. Using this method, the local temperature within a range of 22 to 40 °C could be determined when the upconversion nanocapsules were taken up by HeLa cells with good cellular viability. Thus, the higher cell temperatures where the cells show enhanced metabolic activity led to a significant increase in the delayed fluorescence spectrum of the upconversion nanocapsules. These findings are promising for further development of novel treatment and diagnostic tools in medicine.

Production of superoxide and hydrogen peroxide in the mitochondrial matrix is dominated by site IQ of complex I in diverse cell lines

Understanding how mitochondria contribute to cellular oxidative stress and drive signaling and disease is critical, but quantitative assessment is difficult. Our previous studies of cultured C2C12 cells used inhibitors of specific sites of superoxide and hydrogen peroxide production to show that mitochondria generate about half of the hydrogen peroxide released by the cells, and site IQ of respiratory complex I produces up to two thirds of the superoxide and hydrogen peroxide generated in the mitochondrial matrix. Here, we used the same approach to measure the engagement of these sites in seven diverse cell lines to determine whether this pattern is specific to C2C12 cells, or more general. These diverse cell lines covered primary, immortalized, and cancerous cells, from seven tissues (liver, cervix, lung, skin, neuron, heart, bone) of three species (human, rat, mouse). The rate of appearance of hydrogen peroxide in the extracellular medium spanned a 30-fold range from HeLa cancer cells (3 pmol/min/mg protein) to AML12 liver cells (84 pmol/min/mg protein). The mean contribution of identified mitochondrial sites to this extracellular hydrogen peroxide signal was 30 ± 7% SD; the mean contribution of NADPH oxidases was 60 ± 14%. The relative contributions of different sites in the mitochondrial electron transport chain were broadly similar in all seven cell types (and similar to published results for C2C12 cells). 70 ± 4% of identified superoxide/hydrogen peroxide generation in the mitochondrial matrix was from site IQ; 30 ± 4% was from site IIIQo. We conclude that although absolute rates vary considerably, the relative contributions of different sources of hydrogen peroxide production are similar in nine diverse cell types under unstressed conditions in vitro. Identified mitochondrial sites account for one third of total cellular hydrogen peroxide production (half each from sites IQ and IIIQo); in the mitochondrial matrix the majority (two thirds) of superoxide/hydrogen peroxide is from site IQ.

Metabolic Constrains Rule Metastasis Progression

Metastasis formation accounts for the majority of tumor-associated deaths and consists of different steps, each of them being characterized by a distinctive adaptive phenotype of the cancer cells. Metabolic reprogramming represents one of the main adaptive phenotypes exploited by cancer cells during all the main steps of tumor and metastatic progression. In particular, the metabolism of cancer cells evolves profoundly through all the main phases of metastasis formation, namely the metastatic dissemination, the metastatic colonization of distant organs, the metastatic dormancy, and ultimately the outgrowth into macroscopic lesions. However, the metabolic reprogramming of metastasizing cancer cells has only recently become the subject of intense study. From a clinical point of view, the latter steps of the metastatic process are very important, because patients often undergo surgical removal of the primary tumor when cancer cells have already left the primary tumor site, even though distant metastases are not clinically detectable yet. In this scenario, to precisely elucidate if and how metabolic reprogramming drives acquisition of cancer-specific adaptive phenotypes might pave the way to new therapeutic strategies by combining chemotherapy with metabolic drugs for better cancer eradication. In this review we discuss the latest evidence that claim the importance of metabolic adaptation for cancer progression.

Oxidative pentose phosphate pathway and glucose anaplerosis support maintenance of mitochondrial NADPH pool under mitochondrial oxidative stress

Mitochondrial NADPH protects cells against mitochondrial oxidative stress by serving as an electron donor to antioxidant defense systems. However, due to technical challenges, it still remains unknown as to the pool size of mitochondrial NADPH, its dynamics, and NADPH/NADP+ ratio. Here, we have systemically modulated production rates of H2O2 in mitochondria and assessed mitochondrial NADPH metabolism using iNap sensors, 13C glucose isotopic tracers, and a mathematical model. Using sensors, we observed decreases in mitochondrial NADPH caused by excessive generation of mitochondrial H2O2, whereas the cytosolic NADPH was maintained upon perturbation. We further quantified the extent of mitochondrial NADPH/NADP+ based on the mathematical analysis. Utilizing 13C glucose isotopic tracers, we found increased activity in the pentose phosphate pathway (PPP) accompanied small decreases in the mitochondrial NADPH pool, whereas larger decreases induced both PPP activity and glucose anaplerosis. Thus, our integrative and quantitative approach provides insight into mitochondrial NADPH metabolism during mitochondrial oxidative stress.

ATP Production Relies on Fatty Acid Oxidation Rather than Glycolysis in Pancreatic Ductal Adenocarcinoma

Glycolysis is known as the main pathway for ATP production in cancer cells. However, in cancer cells, glucose deprivation for 24 h does not reduce ATP levels, whereas it does suppress lactate production. In this study, metabolic pathways were blocked to identify the main pathway of ATP production in pancreatic ductal adenocarcinoma (PDAC). Blocking fatty acid oxidation (FAO) decreased ATP production by 40% in cancer cells with no effect on normal cells. The effects of calorie balanced high- or low-fat diets were tested to determine whether cancer growth is modulated by fatty acids instead of calories. A low-fat diet caused a 70% decrease in pancreatic preneoplastic lesions compared with the control, whereas a high-fat diet caused a two-fold increase in preneoplastic lesions accompanied with increase of ATP production in the Kras (G12D)/Pdx1-cre PDAC model. The present results suggest that ATP production in cancer cells is dependent on FAO rather than on glycolysis, which can be a therapeutic approach by targeting cancer energy metabolism.

Kinetic modeling of H2O2 dynamics in the mitochondria of HeLa cells

Hydrogen peroxide (H2O2) promotes a range of phenotypes depending on its intracellular concentration and dosing kinetics, including cell death. While this qualitative relationship has been well established, the quantitative and mechanistic aspects of H2O2 signaling are still being elucidated. Mitochondria, a putative source of intracellular H2O2, have recently been demonstrated to be particularly vulnerable to localized H2O2 perturbations, eliciting a dramatic cell death response in comparison to similar cytosolic perturbations. We sought to improve our dynamic and mechanistic understanding of the mitochondrial H2O2 reaction network in HeLa cells by creating a kinetic model of this system and using it to explore basal and perturbed conditions. The model uses the most current quantitative proteomic and kinetic data available to predict reaction rates and steady-state concentrations of H2O2 and its reaction partners within individual mitochondria. Time scales ranging from milliseconds to one hour were simulated. We predict that basal, steady-state mitochondrial H2O2 will be in the low nM range (2-4 nM) and will be inversely dependent on the total pool of peroxiredoxin-3 (Prx3). Neglecting efflux of H2O2 to the cytosol, the mitochondrial reaction network is expected to control perturbations well up to H2O2 generation rates ~50 μM/s (0.25 nmol/mg-protein/s), above which point the Prx3 system would be expected to collapse. Comparison of these results with redox Western blots of Prx3 and Prx2 oxidation states demonstrated reasonable trend agreement at short times (≤ 15 min) for a range of experimentally perturbed H2O2 generation rates. At longer times, substantial efflux of H2O2 from the mitochondria to the cytosol was evidenced by peroxiredoxin-2 (Prx2) oxidation, and Prx3 collapse was not observed. A refined model using Monte Carlo parameter sampling was used to explore rates of H2O2 efflux that could reconcile model predictions of Prx3 oxidation states with the experimental observations.

Live reporting for hypoxia: Hypoxia sensor-modified mesenchymal stem cells as in vitro reporters

Natural oxygen gradients occur in tissues of biological organisms and also in the context of three-dimensional (3D) in vitro cultivation. Oxygen diffusion limitation and metabolic oxygen consumption by embedded cells produce areas of hypoxia in the tissue/matrix. However, reliable systems to detect oxygen gradients and cellular response to hypoxia in 3D cell culture systems are still missing. In this study, we developed a system for visualization of oxygen gradients in 3D using human adipose tissue-derived mesenchymal stem cells (hAD-MSCs) modified to stably express a fluorescent genetically engineered hypoxia sensor HRE-dUnaG. Modified cells retained their stem cell characteristics in terms of proliferation and differentiation capacity. The hypoxia-reporter cells were evaluated by fluorescence microscopy and flow cytometry under variable oxygen levels (2.5%, 5%, and 7.5% O₂ ). We demonstrated that reporter hAD-MSCs output is sensitive to different oxygen levels and displays fast decay kinetics after reoxygenation. Additionally, the reporter cells were encapsulated in bulk hydrogels with a variable cell number, to investigate the sensor response in model 3D cell culture applications. The use of hypoxia-reporting cells based on MSCs represents a valuable tool for approaching the genuine in vivo cellular microenvironment and will allow a better understanding of the regenerative potential of AD-MSCs.

Changes in volumetric and metabolic parameters relate to differences in exposure to sub-concussive head impacts

Structural and calibrated magnetic resonance imaging data were acquired on 44 collegiate football players prior to the season (PRE), following the first four weeks in-season (PTC) and one month after the last game (POST). Exposure data collected from g-Force accelerometers mounted to the helmet of each player were used to split participants into HIGH (N = 22) and LOW (N = 22) exposure groups, based on the frequency of impacts sustained by each athlete. Significant decreases in grey-matter volume specific to the HIGH group were documented at POST (P = 0.009), compared to baseline. Changes in resting cerebral blood flow (CBF0), corrected for partial volume effects, were observed within the HIGH group, throughout the season (P < 0.0001), suggesting that alterations in perfusion may follow exposure to sub-concussive collisions. Co-localized significant increases in cerebral metabolic rate of oxygen consumption (CMRO2|0) mid-season were also documented in the HIGH group, with respect to both PRE- and POST values. No physiological changes were observed in the LOW group. Therefore, cerebral metabolic demand may be elevated in players with greater exposure to head impacts. These results provide novel insight into the effects of sub-concussive collisions on brain structure and cerebrovascular physiology and emphasize the importance of multi-modal imaging for a complete characterization of cerebral health.

Delta-9-tetrahydrocannabinol disrupts mitochondrial function and attenuates syncytialization in human placental BeWo cells

The psychoactive component in cannabis, delta-9-tetrahydrocannabinol, can restrict fetal growth and development. Delta-9-tetrahydrocannabinol has been shown to negatively impact cellular proliferation and target organelles like the mitochondria resulting in reduced cellular respiration. In the placenta, mitochondrial dysfunction leading to oxidative stress prevents proper placental development and function. A key element of placental development is the proliferation and fusion of cytotrophoblasts to form the syncytium that comprises the materno-fetal interface. The impact of delta-9-tetrahydrocannabinol on this process is not well understood. To elucidate the nature of the mitochondrial dysfunction and its consequences on trophoblast fusion, we treated undifferentiated and differentiated BeWo human trophoblast cells, with 20 µM delta-9-tetrahydrocannabinol for 48 hr. At this concentration, delta-9-tetrahydrocannabinol on BeWo cells reduced the expression of markers involved in syncytialization and mitochondrial dynamics, but had no effect on cell viability. Delta-9-tetrahydrocannabinol significantly attenuated the process of syncytialization and induced oxidative stress responses in BeWo cells. Importantly, delta-9-tetrahydrocannabinol also caused a reduction in the secretion of human chorionic gonadotropin and the production of human placental lactogen and insulin growth factor 2, three hormones known to be important in facilitating fetal growth. Furthermore, we also demonstrate that delta-9-tetrahydrocannabinol attenuated mitochondrial respiration, depleted adenosine triphosphate, and reduced mitochondrial membrane potential. These changes were also associated with an increase in cellular reactive oxygen species, and the expression of stress responsive chaperones, HSP60 and HSP70. These findings have important implications for understanding the role of delta-9-tetrahydrocannabinol-induced mitochondrial injury and the role this might play in compromising human pregnancies.

Coronary vascular growth matches IGF-1-stimulated cardiac growth in fetal sheep

As loss of contractile function in heart disease could often be mitigated by increased cardiomyocyte number, expansion of cardiomyocyte endowment paired with increased vascular supply is a desirable therapeutic goal. Insulin-like growth factor 1 (IGF-1) administration increases fetal cardiomyocyte proliferation and heart mass, but how fetal IGF-1 treatment affects coronary growth and function is unknown. Near-term fetal sheep underwent surgical instrumentation and were studied from 127 to 134 d gestation (term = 147 d), receiving either IGF-1 LR3 or vehicle. Coronary growth and function were interrogated using pressure-flow relationships, an episode of acute hypoxia with progressive blockade of adenosine receptors and nitric oxide synthase, and by modeling the determinants of coronary flow. The main findings were that coronary conductance was preserved on a per-gram basis following IGF-1 treatment, adenosine and nitric oxide contributed to hypoxia-mediated coronary vasodilation similarly in IGF-1-treated and Control fetuses, and the relationships between coronary flow and blood oxygen contents were similar between groups. We conclude that IGF-1-stimulated fetal myocardial growth is accompanied by appropriate expansion and function of the coronary vasculature. These findings support IGF-1 as a potential strategy to increase cardiac myocyte and coronary vascular endowment at birth.

A New Non-invasive Technique for Measuring 3D-Oxygen Gradients in Wells During Mammalian Cell Culture

Oxygen tension plays an important role in overall cell function and fate, regulating gene expression, and cell differentiation. Although there is extensive literature available that supports the previous statement, little information is to be found about accurate O2 measurements during culture. In fact, O2 concentration at the cell layer during culture is commonly assumed to be equal to that of the incubator atmosphere. This assumption does not consider oxygen diffusion properties, cell type, cell density, media composition, time in culture nor height of the cell culture medium column. In this study, we developed a non-invasive, optical sensor foil-based technique suitable for measuring the 3D oxygen gradient that is formed during cell culture as a result of normal cell respiration. For this propose, we created a 3D printed ramp to which surface an oxygen optode sensor foil was attached. The ramps were positioned inside the culture wells of 24 well plate prior cell seeding. This set up in conjunction with the VisiSens TD camera system allows to investigate the oxygen gradient formation during culture. Cultivation was performed with three different initial cell densities of the cell line A549 that were seeded on the plate containing the ramps with the oxygen sensors. The O2 gradient obtained after 96 h of culture showed significantly lower O2 concentrations closer to the bottom of the well in high cell density cultures compared to that of lower cell density cultures. Furthermore, it was very interesting to observe that even with low cell density culture, oxygen concentration near the cell layer was lower than that of the incubator atmosphere. The obtained oxygen gradient after 96 h was used to calculate the oxygen consumption rate (OCR) of the A549 cells, and the obtained value of ~100 fmol/h/cell matches the OCR value already reported in the literature for this cell line. Moreover, we found our set up to be unique in its ability to measure oxygen gradient formation in several wells of a cell culture plate simultaneously and in a non-invasive manner.

A mechanistic study and review of volatile products from peroxidation of unsaturated fatty acids: an aid to understanding the origins of volatile organic compounds from the human body

The assessment of volatile compounds (VOCs) for disease diagnosis is a growing area of research. There is a need to provide hard evidence i.e. biochemical routes, to justify putative VOC biomarkers, as in many cases this remains uncertain, which weakens their authenticity. Recently reports of volatile hydrocarbons and or aldehydes in bodily fluids and breath have been attributed to oxidative stress, although as discussed here, fewer compounds have been reported than expected from a mechanistic examination. Oxidative stress can result from many disease states which produce inflammation, and a better understanding of the interconnection between oxidative stress and the release of VOCs from target diseased and healthy organs could greatly help diagnoses. It is generally considered that oxidation of unsaturated fatty acids are a major source of these VOCs. An investigation listing the many possible volatile oxidation products has not been undertaken. This is described here using a mechanistic analysis (based on the literature) of the compounds derived from molecular cleavage and the results compared with a recent review of all the VOCs emanating from the human body, which satisfactorily explains the presence of at least 100 VOCs. Six important unsaturated fatty acids, oleic, palmitoleic, linoleic, linolenic, arachidonic, and cervonic acids have been shown to be capable of producing up to 18 n+6 unique breakdown products (where n = the number of alkene double bonds in the fatty acid hydrocarbon chain), in total 299 compounds. In many cases these have not been reported. We suggest several reasons for this: these VOCs have not been expected, so researchers are not looking for them and importantly some are not present in the mass spectral libraries, or they are too low a concentration to have been detected, or are not present. Furthermore a theoretical explanation for the origins of branched aldehydes and other compounds arising from bacterial oxidative metabolism of unsaturated fatty acids are described.

A Multiscale Agent-Based Model of Ductal Carcinoma In Situ

OBJECTIVE

we present a multiscale agent-based model of Ductal Carcinoma in Situ (DCIS) in order to gain a detailed understanding of the cell-scale population dynamics, phenotypic distributions, and the associated interplay of important molecular signaling pathways that are involved in DCIS ductal invasion into the duct cavity (a process we refer to as duct advance rate here).

METHODS

DCIS is modeled mathematically through a hybridized discrete cell-scale model and a continuum molecular scale model, which are explicitly linked through a bidirectional feedback mechanism.

RESULTS

we find that duct advance rates occur in two distinct phases, characterized by an early exponential population expansion, followed by a long-term steady linear phase of population expansion, a result that is consistent with other modeling work. We further found that the rates were influenced most strongly by endocrine and paracrine signaling intensity, as well as by the effects of cell density induced quiescence within the DCIS population.

CONCLUSION

our model analysis identified a complex interplay between phenotypic diversity that may provide a tumor adaptation mechanism to overcome proliferation limiting conditions, allowing for dynamic shifts in phenotypic populations in response to variation in molecular signaling intensity. Further, sensitivity analysis determined DCIS axial advance rates and calcification rates were most sensitive to cell cycle time variation.

SIGNIFICANCE

this model may serve as a useful tool to study the cell-scale dynamics involved in DCIS initiation and intraductal invasion, and may provide insights into promising areas of future experimental research.

Polylactic is a Sustainable, Low Absorption, Low Autofluorescence Alternative to Other Plastics for Microfluidic and Organ-on-Chip Applications

Organ-on-chip (OOC) devices are miniaturized devices replacing animal models in drug discovery and toxicology studies. The majority of OOC devices are made from polydimethylsiloxane (PDMS), an elastomer widely used in microfluidic prototyping, but posing a number of challenges to experimentalists, including leaching of uncured oligomers and uncontrolled absorption of small compounds. Here we assess the suitability of polylactic acid (PLA) as a replacement material to PDMS for microfluidic cell culture and OOC applications. We changed the wettability of PLA substrates and demonstrated the functionalization method to be stable over a time period of at least 9 months. We successfully cultured human cells on PLA substrates and devices, without coating. We demonstrated that PLA does not absorb small molecules, is transparent (92% transparency), and has low autofluorescence. As a proof of concept of its manufacturability, biocompatibility, and transparency, we performed a cell tracking experiment of prostate cancer cells in a PLA device for advanced cell culture.

Dual Oxidase-Induced Sustained Generation of Hydrogen Peroxide Contributes to Pharmacologic Ascorbate-Induced Cytotoxicity

Pharmacologic ascorbate treatment (P-AscH-, high-dose, intravenous vitamin C) results in a transient short-term increase in the flux of hydrogen peroxide that is preferentially cytotoxic to cancer cells versus normal cells. This study examines whether an increase in hydrogen peroxide is sustained posttreatment and potential mechanisms involved in this process. Cellular bioenergetic profiling following treatment with P-AscH- was examined in tumorigenic and nontumorigenic cells. P-AscH- resulted in sustained increases in the rate of cellular oxygen consumption (OCR) and reactive oxygen species (ROS) in tumor cells, with no changes in nontumorigenic cells. Sources for this increase in ROS and OCR were DUOX 1 and 2, which are silenced in pancreatic ductal adenocarcinoma, but upregulated with P-AscH- treatment. An inducible catalase system, to test causality for the role of hydrogen peroxide, reversed the P-AscH--induced increases in DUOX, whereas DUOX inhibition partially rescued P-AscH--induced toxicity. In addition, DUOX was significantly downregulated in pancreatic cancer specimens compared with normal pancreas tissues. Together, these results suggest that P-AscH--induced toxicity may be enhanced by late metabolic shifts in tumor cells, resulting in a feed-forward mechanism for generation of hydrogen peroxide and induction of metabolic stress through enhanced DUOX expression and rate of oxygen consumption. SIGNIFICANCE: A high dose of vitamin C, in addition to delivering an acute exposure of H2O2 to tumor cells, activates DUOX in pancreatic cancer cells, which provide sustained production of H2O2.

Technical Feasibility and Physiological Relevance of Hypoxic Cell Culture Models

Hypoxia is characterized as insufficient oxygen delivery to tissues and cells in the body and is prevalent in many human physiology processes and diseases. Thus, it is an attractive state to experimentally study to understand its inner mechanisms as well as to develop and test therapies against pathological conditions related to hypoxia. Animal models in vivo fail to recapitulate some of the key hallmarks of human physiology, which leads to human cell cultures; however, they are prone to bias, namely when pericellular oxygen concentration (partial pressure) does not respect oxygen dynamics in vivo. A search of the current literature on the topic revealed this was the case for many original studies pertaining to experimental models of hypoxia in vitro. Therefore, in this review, we present evidence mandating for the close control of oxygen levels in cell culture models of hypoxia. First, we discuss the basic physical laws required for understanding the oxygen dynamics in vitro, most notably the limited diffusion through a liquid medium that hampers the oxygenation of cells in conventional cultures. We then summarize up-to-date knowledge of techniques that help standardize the culture environment in a replicable fashion by increasing oxygen delivery to the cells and measuring pericellular levels. We also discuss how these tools may be applied to model both constant and intermittent hypoxia in a physiologically relevant manner, considering known values of partial pressure of tissue normoxia and hypoxia in vivo, compared to conventional cultures incubated at rigid oxygen pressure. Attention is given to the potential influence of three-dimensional tissue cultures and hypercapnia management on these models. Finally, we discuss the implications of these concepts for cell cultures, which try to emulate tissue normoxia, and conclude that the maintenance of precise oxygen levels is important in any cell culture setting.

What is pH regulation, and why do cancer cells need it?

Metabolism is a continuous source of acids. To keep up with a desired metabolic rate, tumors must establish an adequate means of clearing their acidic end-products. This homeostatic priority is achieved by various buffers, enzymes, and transporters connected through the common denominator of H⁺ ions. Whilst this complexity is proportionate to the importance of adequate pH control, it is problematic for developing an intuition for tracking the route taken by acids, assessing the relative importance of various acid-handling proteins, and predicting the outcomes of pharmacological inhibition or genetic alteration. Here, with the help of a simplified mathematical framework, the genesis of cancer pH regulation is explained in terms of the obstacles to efficient acid venting and how these are overcome by specific molecules, often associated with cancer. Ultimately, the pH regulatory apparatus in tumors must (i) provide adequate lactic acid permeability through membranes, (ii) facilitate CO₂/HCO₃⁻/H⁺ diffusivity across the interstitium, (iii) invest in a form of active transport that strikes a favorable balance between intracellular pH and intracellular lactate retention under the energetic constraints of a cell, and (iv) enable the necessary feedback to complete the homeostatic loop. A more informed and quantitative approach to understanding acid-handling in cancer is mandatory for identifying vulnerabilities, which could be exploited as therapeutic targets.

Successful energy shift from glycolysis to mitochondrial oxidative phosphorylation in freshly isolated hepatocytes from humanized mice liver

Mitochondrial toxicity is a factor of drug-induced liver injury. Previously, we reported an in vitro rat hepatocyte assay where mitochondrial toxicity was more sensitively evaluated, using sugar resource substitution and increased oxygen supply. Although this method could be applicable to human cell-based assay, cryopreserved human hepatocyte (CHH) has some disadvantages/uncertainty, including unstable same donor supply and potential organelle damage due to cryopreservation. Herein, we compared the mitochondrial functions of freshly-isolated hepatocytes from humanized chimeric mice liver (PXB-cells) and three CHH lots to determine the better cell source for mitochondrial toxicity assay. Two CHH lots declined after replacing glucose with galactose. To confirm the shift in energy production from glycolysis to oxidative phosphorylation, lactate and oxygen consumption rate (indicators of glycolytic activity and mitochondrial oxidative phosphorylation, respectively) were measured. In PXB-cells, lactate amount decreased, while oxygen consumption in 100 min increased. These effects were less evident in CHH. The cytotoxicity of the select respiratory chain inhibitors was enhanced in PXB-cells upon sugar replacement, but no change occurred with negative control drugs (bicalutamide and metformin). Altogether, PXB-cells was less vulnerable to sugar resource substitution than CHH. The substitution activated mitochondrial function and enhanced cytotoxicity of respiratory chain inhibitors in PXB-cells.

New approach to measuring oxygen diffusion and consumption in encapsulated living cells, based on electron spin resonance microscopy

Cell microencapsulation within biocompatible polymers is an established technology for immobilizing living cells that secrete therapeutic products.  These can be transplanted into a desired site in the body for the controlled and continuous delivery of the therapeutic molecules.  One of the most important properties of the material that makes up the microcapsule is its oxygen penetrability, which is critical for the cells' survival.  Oxygen reaches the cells inside the microcapsules via a diffusion process.  The diffusion coefficient for the microcapsules' gel material is commonly measured using bulk techniques, where the gel in a chamber is first flushed with nitrogen and the subsequent rate of oxygen diffusion back into it is measured by an oxygen electrode placed in the chamber.  This technique does not address possible heterogeneities between microcapsules, and also cannot reveal O₂ heterogeneity inside the microcapsule resulting from the living cells' activity.  Here we develop and demonstrate a proof of principle for a new approach to measuring and imaging the partial pressure of oxygen (pO₂) inside a single microcapsule by means of high-resolution and high-sensitivity electron spin resonance (ESR).  The proposed methodology makes use of biocompatible paramagnetic microparticulates intercalated inside the microcapsule during its preparation.  The new ESR approach was used to measure the O₂ diffusion properties of two types of gel materials (alginate and extracellular matrix - ECM), as well as to map a 3D image of the oxygen inside single microcapsules with living cells. STATEMENT OF SIGNIFICANCE: The technology of cell microencapsulation offers major advantages in the sustained delivery of therapeutic agents used for the treatment of various diseases ranging from diabetes to cancer. Despite the great advances made in this field, it still faces substantial challenges, preventing it from reaching the clinical practice. One of the primary challenges in developing cell microencapsulation systems is providing the cells with adequate supply of oxygen in the long term. Nevertheless, there is still no methodology good enough for measuring O2 distribution inside the microcapsule with sufficient accuracy and spatial resolution without affecting the microcapsule and/or the cells' activity in it. In the present work, we introduce a novel magnetic resonance technique to address O2 availability within cell-entrapping microcapsules. For the first time O2 distribution can be accurately measured and imaged within a single microcapsule. This new technique may be an efficient tool in the development of more optimal microencapsulation systems in the future, thus bringing this promising field closer to clinical application.

Flow-Encoded Oxygen Control to Track the Time-Dependence of Molecular Changes Induced by Static or Cycling Hypoxia

Detecting the effects of low oxygen on cell function is often dependent on monitoring the expression of a number of hypoxia markers. The time dependence of the appearance and stability of these markers varies between cell lines. Assessing cellular marker dynamics is also critical to determining how quickly cells respond to transient changes in oxygen levels that occurs with cycling hypoxia. We fabricated a manifold designed to use flow-encoding to produce sequential changes in gas mixtures delivered to a permeable-bottom 96-well plate. We show how this manifold and plate design can be used to expose cells to either static or cycling hypoxic conditions for eight different time periods thereby facilitating the study of the time-response of cells to altered oxygen environments. Using this device, we monitored the time-dependence of molecular changes in human PANC-1 pancreatic carcinoma and Caco-2 colon adenocarcinoma cells exposed to increasing periods of static or cycling hypoxia. Using immunohistochemistry, both cell lines show detectable levels of the marker protein hypoxia-inducible factor-1α (HIF-1α) after 3 h of exposure to static hypoxia. Cycling hypoxia increased the expression level of HIF-1α compared to static hypoxia. Both static and cycling hypoxia also increased glucose uptake and aldehyde dehydrogenase activity. This new device offers a facile screening approach to determine the kinetics of cellular alterations under varying oxygen conditions.

A multiscale in silico model of endothelial to mesenchymal transformation in a tumor microenvironment

Endothelial to mesenchymal transformation (EndMT) is a process in which endothelial cells gain a mesenchymal-like phenotype in response to mechanobiological signals that results in the remodeling or repair of underlying tissue. While initially associated with embryonic development, this process has since been shown to occur in adult tissue remodeling including wound healing, fibrosis, and cancer. In an attempt to understand the role of EndMT in cancer progression and metastasis, we present a multiscale, three-dimensional, in silico model. The model couples tissue level phenomena such as extracellular matrix remodeling, cellular level phenomena such as migration and proliferation, and chemical transport in the tumor microenvironment to mimic in vitro tissue models of the cancer microenvironment. The model is used to study the presence of EndMT-derived activated fibroblasts (EDAFs) and varying substrate stiffness on tumor cell migration and proliferation. The simulations accurately model the behavior of tumor cells under given conditions. The presence of EDAFs and/or an increase in substrate stiffness resulted in an increase in tumor cell activity. This model lays the foundation of further studies of EDAFs in a tumor microenvironment on a cellular and subcellular physiological level.

An in vitro intestinal platform with a self-sustaining oxygen gradient to study the human gut/microbiome interface

An oxygen gradient formed along the length of colonic crypts supports stem-cell proliferation at the normoxic crypt base while supporting obligate anaerobe growth in the anoxic colonic lumen. Primary human colonic epithelial cells derived from human gastrointestinal stem cells were cultured within a device possessing materials of tailored oxygen permeability to produce an oxygen-depleted luminal (0.8% ± 0.1% O2) and oxygen-rich basal (11.1% ± 0.5% O2) compartment. This oxygen difference created a stable oxygen gradient across the colonic epithelial cells which remained viable and properly polarized. Facultative and obligate anaerobes Lactobacillus rhamnosus, Bifidobacterium adolescentis, and Clostridium difficile grew readily within the luminal compartment. When formed along the length of an in vitro crypt, the oxygen gradient facilitated cell compartmentalization within the crypt by enhancing confinement of the proliferative cells to the crypt base. This platform provides a simple system to create a physiological oxygen gradient across an intestinal mimic while simultaneously supporting anaerobe co-culture.

Oxygen Consumption Characteristics in 3D Constructs Depend on Cell Density

Oxygen is not only crucial for cell survival but also a determinant for cell fate and function. However, the supply of oxygen and other nutrients as well as the removal of toxic waste products often limit cell viability in 3-dimensional (3D) engineered tissues. The aim of this study was to determine the oxygen consumption characteristics of 3D constructs as a function of their cell density. The oxygen concentration was measured at the base of hepatocyte laden constructs and a tightly controlled experimental and analytical framework was used to reduce the system geometry to a single coordinate and enable the precise identification of initial and boundary conditions. Then dynamic process modeling was used to fit the measured oxygen vs. time profiles to a reaction and diffusion model. We show that oxygen consumption rates are well-described by Michaelis-Menten kinetics. However, the reaction parameters are not literature constants but depend on the cell density. Moreover, the average cellular oxygen consumption rate (or OCR) also varies with density. We discuss why the OCR of cells is often misinterpreted and erroneously reported, particularly in the case of 3D tissues and scaffolds.

Three-dimensional tumor growth in time-varying chemical fields: a modeling framework and theoretical study

Background

Contemporary biological observations have revealed a large variety of mechanisms acting during the expansion of a tumor. However, there are still many qualitative and quantitative aspects of the phenomenon that remain largely unknown. In this context, mathematical and computational modeling appears as an invaluable tool providing the means for conducting in silico experiments, which are cheaper and less tedious than real laboratory experiments.

Results

This paper aims at developing an extensible and computationally efficient framework for in silico modeling of tumor growth in a 3-dimensional, inhomogeneous and time-varying chemical environment. The resulting model consists of a set of mathematically derived and algorithmically defined operators, each one addressing the effects of a particular biological mechanism on the state of the system. These operators may be extended or re-adjusted, in case a different set of starting assumptions or a different simulation scenario needs to be considered.

Conclusion

In silico modeling provides an alternative means for testing hypotheses and simulating scenarios for which exact biological knowledge remains elusive. However, finer tuning of pertinent methods presupposes qualitative and quantitative enrichment of available biological evidence. Validation in a strict sense would further require comprehensive, case-specific simulations and detailed comparisons with biomedical observations.

Radical Stress Is More Cytotoxic in the Nucleus than in Other Organelles

Cells are exposed to reactive oxygen species (ROS) as a by-product of mitochondrial metabolism, especially under hypoxia. ROS are also enzymatically generated at the plasma membrane during inflammation. Radicals cause cellular damage leading to cell death, as they react indiscriminately with surrounding lipids, proteins, and nucleotides. However, ROS are also important for many physiological processes, including signaling, pathogen killing and chemotaxis. The sensitivity of cells to ROS therefore likely depends on the subcellular location of ROS production, but how this affects cell viability is poorly understood. As ROS generation consumes oxygen, and hypoxia-mediated signaling upregulates expression of antioxidant transcription factor Nrf2, it is difficult to discern hypoxic from radical stress. In this study, we developed an optogenetic toolbox for organelle-specific generation of ROS using the photosensitizer protein SuperNova which produces superoxide anion upon excitation with 590 nm light. We fused SuperNova to organelle specific localization signals to induce ROS with high precision. Selective ROS production did not affect cell viability in most organelles except for the nucleus. SuperNova is a promising tool to induce locally targeted ROS production, opening up new possibilities to investigate processes and organelles that are affected by localized ROS production.

Oxygen Uptake Rate Soft-Sensing via Dynamic k L a Computation: Cell Volume and Metabolic Transition Prediction in Mammalian Bioprocesses

In aerobic cell cultivation processes, dissolved oxygen is a key process parameter, and an optimal oxygen supply has to be ensured for proper process performance. To achieve optimal growth and/or product formation, the rate of oxygen transfer has to be in right balance with the consumption by cells. In this study, a 15 L mammalian cell culture bioreactor was characterized with respect to k_La under varying process conditions. The resulting dynamic k_La description combined with functions for the calculation of oxygen concentrations under prevailing process conditions led to an easy-to-apply model, that allows real-time calculation of the oxygen uptake rate (OUR) throughout the bioprocess without off-gas analyzers. Subsequently, the established OUR soft-sensor was applied in a series of 13 CHO fed-batch cultivations. The OUR was found to be directly associated with the amount of viable biomass in the system, and deploying of cell volumes instead of cell counts led to higher correlations. A two-segment linear model predicted the viable biomass in the system sufficiently. The segmented model was necessary due to a metabolic transition in which the specific consumption of oxygen changed. The aspartate to glutamate ratio was identified as an indicator of this metabolic shift. The detection of such transitions is enabled by a combination of the presented dynamic OUR method with another state-of-the-art viable biomass soft-sensor. In conclusion, this hyphenated technique is a robust and powerful tool for advanced bioprocess monitoring and control based exclusively on bioreactor characteristics.

Fluid shear stress stimulates breast cancer cells to display invasive and chemoresistant phenotypes while upregulating PLAU in a 3D bioreactor

Breast cancer cells experience a range of shear stresses in the tumor microenvironment (TME). However most current in vitro three-dimensional (3D) models fail to systematically probe the effects of this biophysical stimuli on cancer cell metastasis, proliferation, and chemoresistance. To investigate the roles of shear stress within the mammary and lung pleural effusion TME, a bioreactor capable of applying shear stress to cells within a 3D extracellular matrix was designed and characterized. Breast cancer cells were encapsulated within an interpenetrating network hydrogel and subjected to shear stress of 5.4 dynes cm^-2 for 72 hr. Finite element modeling assessed shear stress profiles within the bioreactor. Cells exposed to shear stress had significantly higher cellular area and significantly lower circularity, indicating a motile phenotype. Stimulated cells were more proliferative than static controls and showed higher rates of chemoresistance to the anti-neoplastic drug paclitaxel. Fluid shear stress-induced significant upregulation of the PLAU gene and elevated urokinase activity was confirmed through zymography and activity assay. Overall, these results indicate that pulsatile shear stress promotes breast cancer cell proliferation, invasive potential, chemoresistance, and PLAU signaling.

New developments in online OUR monitoring and its application to animal cell cultures

The increasing demand for biopharmaceuticals produced in mammalian cells has driven the industry to enhance the productivity of bioprocesses through intensification of culture process. Fed-batch and perfusion culturing strategies are considered the most attractive choices, but the application of these processes requires the availability of reliable online measuring systems for the estimation of cell density and metabolic activity. This manuscript reviews the methods (and the devices used) for monitoring of the oxygen consumption, also known as oxygen uptake rate (OUR), since it is a straightforward parameter to estimate viable cell density and the physiological state of cells. Furthermore, as oxygen plays an important role in the cell metabolism, OUR has also been very useful to estimate nutrient consumption, especially the carbon (glucose and glutamine) and nitrogen (glutamine) sources. Three different methods for the measurement of OUR have been developed up to date, being the dynamic method the golden standard, even though DO and pH perturbations generated in the culture during each measurement. For this, many efforts have been focused in developing non-invasive methods, such as global mass balance or stationary liquid mass balance. The low oxygen consumption rates by the cells and the high accuracy required for oxygen concentration measurement in the gas streams (inlet and outlet) have limited the applicability of the global mass balance methodology in mammalian cell cultures. In contrast, stationary liquid mass balance has successfully been implemented showing very similar OUR profiles compared with those obtained with the dynamic method. The huge amount of studies published in the last years evidence that OUR have become a reliable alternative for the monitoring and control of high cell density culturing strategies with very high productivities.

Bacterial hopping and trapping in porous media

Diverse processes-e.g. bioremediation, biofertilization, and microbial drug delivery-rely on bacterial migration in disordered, three-dimensional (3D) porous media. However, how pore-scale confinement alters bacterial motility is unknown due to the opacity of typical 3D media. As a result, models of migration are limited and often employ ad hoc assumptions. Here we reveal that the paradigm of run-and-tumble motility is dramatically altered in a porous medium. By directly visualizing individual Escherichia coli, we find that the cells are intermittently and transiently trapped as they navigate the pore space, exhibiting diffusive behavior at long time scales. The trapping durations and the lengths of "hops" between traps are broadly distributed, reminiscent of transport in diverse other disordered systems; nevertheless, we show that these quantities can together predict the long-time bacterial translational diffusivity. Our work thus provides a revised picture of bacterial motility in complex media and yields principles for predicting cellular migration.

High-throughput, label-free, single-cell photoacoustic microscopy of intratumoral metabolic heterogeneity

Intratumoral heterogeneity, which is manifested in almost all of the hallmarks of cancer, including the significantly altered metabolic profiles of cancer cells, represents a challenge to effective cancer therapy. High-throughput measurements of the metabolism of individual cancer cells would allow direct visualization and quantification of intratumoral metabolic heterogeneity, yet the throughputs of current measurement techniques are limited to about 120 cells per hour. Here, we show that single-cell photoacoustic microscopy can reach throughputs of approximately 12,000 cells per hour by trapping single cells with blood in an oxygen-diffusion-limited high-density microwell array and by using photoacoustic imaging to measure the haemoglobin oxygen change (that is, the oxygen consumption rate) in the microwells. We demonstrate the capability of this label-free technique by performing high-throughput single-cell oxygen-consumption-rate measurements of cultured cells and by imaging intratumoral metabolic heterogeneity in specimens from patients with breast cancer. High-throughput single-cell photoacoustic microscopy of oxygen consumption rates should enable the faster characterization of intratumoral metabolic heterogeneity.

An integrated physico-chemical approach for explaining the differential impact of FLASH versus conventional dose rate irradiation on cancer and normal tissue responses

For decades the field of radiation oncology has sought to improve the therapeutic ratio through innovations in physics, chemistry, and biology. To date, technological advancements in image guided beam delivery techniques have provided clinicians with their best options for improving this critical tool in cancer care. Medical physics has focused on the preferential targeting of tumors while minimizing the collateral dose to the surrounding normal tissues, yielding only incremental progress. However, recent developments involving ultra-high dose rate irradiation termed FLASH radiotherapy (FLASH-RT), that were initiated nearly 50 years ago, have stimulated a renaissance in the field of radiotherapy, long awaiting a breakthrough modality able to enhance therapeutic responses and limit normal tissue injury. Compared to conventional dose rates used clinically (0.1-0.2 Gy/s), FLASH can implement dose rates of electrons or X-rays in excess of 100 Gy/s. The implications of this ultra-fast delivery of dose are significant and need to be re-evaluated to appreciate the fundamental aspects underlying this seemingly unique radiobiology. The capability of FLASH to significantly spare normal tissue complications in multiple animal models, when compared to conventional rates of dose-delivery, while maintaining persistent growth inhibition of select tumor models has generated considerable excitement, as well as skepticism. Based on fundamental principles of radiation physics, radio-chemistry, and tumor vs. normal cell redox metabolism, this article presents a series of testable, biologically relevant hypotheses, which may help rationalize the differential effects of FLASH irradiation observed between normal tissue and tumors.

Entrainment of superoxide rhythm by menadione in HCT116 colon cancer cells

Reactive oxygen species (ROS) are primary effectors of cytotoxicity induced by many anti-cancer drugs. Rhythms in the pseudo-steady-state (PSS) levels of particular intracellular ROS in cancer cells and their relevance to drug effectiveness are unknown thus far. We report that the PSS levels of intracellular superoxide (SOX), an important ROS, exhibit an inherent rhythm in HCT116 colon cancer cells, which is entrained (reset) by the SOX inducer, menadione (MD). This reset was dependent on the expression of p53, and it doubled the sensitivity of the cells to MD. The period of oscillation was found to have a linear correlation with MD concentration, given by the equation, T, in h = 23.52 - 1.05 [MD concentration in µM]. Further, we developed a mathematical model to better understand the molecular mechanisms involved in rhythm reset. Biologically meaningful parameters were obtained through parameter estimation techniques; the model can predict experimental profiles of SOX, establish qualitative relations between interacting species in the system and serves as an important tool to understand the profiles of various species. The model was also able to successfully predict the rhythm reset in MD treated hepatoma cell line, HepG2.

Evaluating CAR-T Cell Therapy in a Hypoxic 3D Tumor Model

Despite its revolutionary success in hematological malignancies, chimeric antigen receptor T (CAR-T) cell therapy faces disappointing clinical results in solid tumors. The poor efficacy has been partially attributed to the lack of understanding in how CAR-T cells function in a solid tumor microenvironment. Hypoxia plays a critical role in cancer progression and immune editing, which potentially results in solid tumors escaping immunosurveillance and CAR-T cell-mediated cytotoxicity. Mechanistic studies of CAR-T cell biology in a physiological environment has been limited by the complexity of tumor-immune interactions in clinical and animal models, as well as by a lack of reliable in vitro models. A microdevice platform that recapitulates a 3D tumor section with a gradient of oxygen and integrates fluidic channels surrounding the tumor for CAR-T cell delivery is engineered. The design allows for the evaluation of CAR-T cell cytotoxicity and infiltration in the heterogeneous oxygen landscape of in vivo solid tumors at a previously unachievable scale in vitro.

Loss of SLC25A11 causes suppression of NSCLC and melanoma tumor formation

Background

Fast growing cancer cells require greater amounts of ATP than normal cells. Although glycolysis was suggested as a source of anabolic metabolism based on lactate production, the main source of ATP to support cancer cell metabolism remains unidentified.

Methods

We have proposed that the oxoglutarate carrier SLC25A11 is important for ATP production in cancer by NADH transportation from the cytosol to mitochondria as a malate. We have examined not only changes of ATP and NADH but also changes of metabolites after SLC25A11 knock down in cancer cells.

Findings

The mitochondrial electron transport chain was functionally active in cancer cells. The cytosolic to mitochondrial NADH ratio was higher in non-small cell lung cancer (NSCLC) and melanoma cells than in normal cells. This was consistent with higher levels of the oxoglutarate carrier SLC25A11. Blocking malate transport by knockdown of SLC25A11 significantly impaired ATP production and inhibited the growth of cancer cells, which was not observed in normal cells. In in vivo experiments, heterozygote of SLC25A11 knock out mice suppressed KRAS^LA2 lung tumor formation by cross breeding.

Interpretation

Cancer cells critically depended on the oxoglutarate carrier SLC25A11 for transporting NADH from cytosol to mitochondria as a malate form for the purpose of ATP production. Therefore blocking SLC25A11 may have an advantage in stopping cancer growth by reducing ATP production.

Fund

The Basic Science Research Program through the National Research Foundation of Korea funded by the Ministry of Science and ICT to SYK (NRF-2017R1A2B2003428).

TREM-1 regulates neutrophil chemotaxis by promoting NOX-dependent superoxide production

Neutrophil migration across tissue barriers to the site of injury involves integration of complex danger signals and is critical for host survival. Numerous studies demonstrate that these environmental signals fundamentally alter the responses of extravasated or "primed" neutrophils. Triggering receptor expressed on myeloid cells 1 (TREM-1) plays a central role in modulating inflammatory signaling and neutrophil migration into the alveolar airspace. Using a genetic approach, we examined the role of TREM-1 in extravasated neutrophil function. Neutrophil migration in response to chemoattractants is dependent upon multiple factors, including reactive oxygen species (ROS) generated either extracellularly by epithelial cells or intracellularly by NADPH oxidase (NOX). We, therefore, questioned whether ROS were responsible for TREM-1-mediated regulation of migration. Thioglycollate-elicited peritoneal neutrophils isolated from wild-type (WT) and TREM-1-deficient mice were stimulated with soluble and particulate agonists. Using electron paramagnetic resonance spectroscopy, we demonstrated that NOX2-dependent superoxide production is impaired in TREM-1-deficient neutrophils. Consistent with these findings, we confirmed with Clark electrode that TREM-1-deficient neutrophils consume less oxygen. Next, we demonstrated that TREM-1 deficient neutrophils have impaired directional migration to fMLP and zymosan-activated serum as compared to WT neutrophils and that deletion or inhibition of NOX2 in WT but not TREM-1-deficient neutrophils significantly impaired direction sensing. Finally, TREM-1 deficiency resulted in decreased protein kinase B (AKT) activation. Thus, TREM-1 regulates neutrophil migratory properties, in part, by promoting AKT activation and NOX2-dependent superoxide production. These findings provide the first mechanistic evidence as to how TREM-1 regulates neutrophil migration.

Targeting cancer energy metabolism: a potential systemic cure for cancer

Long-term investigation and extensive efforts using sequencing and -omics analysis identified thousands of mutations in a single tumor. However, we cannot succeed at curing cancer by targeting mutations as the cause of cancer. Therefore, as an alternate therapeutic approach from classical oncology study, stimulation of the inherent ability of the immune system to attack tumor cells was welcome as a new principle in cancer therapy. However, it cannot be a permanent solution for the question of "which is the common factor that can distinguish cancer from normal?" Targeting the cancer energy metabolism may be a cancer-specific therapy for all kinds of cancer because normal cells do not rely on cancer energy metabolism under normal conditions. Here, trends of cancer metabolism as well as a new theory of cancer energy metabolism in the therapeutic approach is summarized.

Cell-matrix tension contributes to hypoxia in astrocyte-seeded viscoelastic hydrogels composed of collagen and hyaluronan

Astrocyte activation is crucial for wound contraction and glial scar formation following central nervous system injury, but the mechanism by which activation leads to astrocyte contractility and matrix reorganization in the central nervous system (CNS) is unknown. Current means to measure cell traction forces within three-dimensional scaffolds are limited to analyzing individual or small groups of cells, within extracellular matrices, whereas gap junctions and other cell-cell adhesions connect astrocytes to form a functional syncytium within the glial scar. Here, we measure the viscoelastic properties of cell-seeded hydrogels to yield insight into the collective contractility of astrocytes as they exert tension on the surrounding matrix and change its bulk mechanical properties. Our results indicate that incorporation of the CNS matrix component hyaluronan into a collagen hydrogel increases expression of the intermediate filament protein GFAP and results in a higher shear storage modulus of the cell/matrix composite, establishing the correlation between astrocyte activation and increased cell contractility. The effects of thrombin and blebbistatin, known mediators of actomyosin-mediated contraction, verify that cell-matrix tension dictates the hydrogel mechanical properties. Viability assays indicate that increased cell traction exacerbates cell death at the center of the scaffold, and message level analysis reveals that cells in the hyaluronan-containing matrix have a ~ 3-fold increase in HIF-1α gene expression. Overall, these findings suggest that astrocyte activation not only increases cell traction, but may also contribute to hypoxia near sites of central nervous system injury.

Methylseleninic Acid Induces Lipid Peroxidation and Radiation Sensitivity in Head and Neck Cancer Cells

Combination radiation and chemotherapy are commonly used to treat locoregionally advanced head and neck squamous cell carcinoma (HNSCC). Aggressive dosing of these therapies is significantly hampered by side effects due to normal tissue toxicity. Selenium represents an adjuvant that selectively sensitizes cancer cells to these treatments modalities, potentially by inducing lipid peroxidation (LPO). This study investigated whether one such selenium compound, methylseleninic acid (MSA), induces LPO and radiation sensitivity in HNSCC cells. Results from 4,4-difluoro-4-bora-3a,4a-diaza-S-indacene (BODIPY) C11 oxidation and ferric thiocyanate assays revealed that MSA induced LPO in cells rapidly and persistently. Propidium iodide (PI) exclusion assay found that MSA was more toxic to cancer cells than other related selenium compounds; this toxicity was abrogated by treatment with α-tocopherol, an LPO inhibitor. MSA exhibited no toxicity to normal fibroblasts at similar doses. MSA also sensitized HNSCC cells to radiation as determined by clonogenic assay. Intracellular glutathione in cancer cells was depleted following MSA treatment, and supplementation of the intracellular glutathione pool with N-acetylcysteine sensitized cells to MSA. The addition of MSA to a cell-free solution of glutathione resulted in an increase in oxygen consumption, which was abrogated by catalase, suggesting the formation of H₂O₂. Results from this study identify MSA as an inducer of LPO, and reveal its capability to sensitize HNSCC to radiation. MSA may represent a potent adjuvant to radiation therapy in HNSCC.

Singlet oxygen phosphorescence detection in vivo identifies PDT-induced anoxia in solid tumors

Extracorporeal measurements through the skin achieve sufficient SNR to analyze ¹O₂ kinetics and evaluate PDT efficiency.