The rate of oxygen utilization by cells

Enhancing Viability in Static and Perfused 3D Tissue Constructs Using Sacrificial Gelatin Microparticles

Current limitations in engineered tissues arise from the inability to provide sufficient nutrients to cells deep within constructs, restricting their viability. This study focuses on enhancing diffusion by creating a microporous microenvironment using gelatin microparticles within collagen scaffolds. By leveraging the FRESH (Freeform Reversible Embedding of Suspended Hydrogels) 3D bioprinting technique, gelatin microparticles are utilized both as a support material and as a thermoresponsive porogen to establish interconnected pores. The results indicate that scaffolds with 75% porosity significantly increase diffusion rates and cell viability, extending beyond the conventional ∼200 μm limit. Additionally, integrating vascular-like channels with porous scaffolds and applying perfusion improved nutrient transport, leading to enhanced cell survival in larger constructs. This combination of microporosity and perfusion represents a promising approach to create thicker tissues without necrotic regions, potentially paving the way for scalable tissue engineering applications. The findings suggest that optimizing pore sizes and scaffold perfusion can bridge the gap between rapid tissue formation and slower vascularization processes, enabling the future development of functional tissue constructs at clinically relevant scales.

Cell Seeding Strategy Influences Metabolism and Differentiation Potency of Human Induced Pluripotent Stem Cells Into Pancreatic Progenitors

Human induced pluripotent stem cells (iPSCs) are an invaluable endless cell source for generating various therapeutic cells and tissues. However, their differentiation into specific cell lineages, such as definitive endoderm (DE) and pancreatic progenitor (PP), often suffers from poor reproducibility, due partially to their pluripotency. In this work, we investigated the impact of iPSC confluency during cell self-renewal and seeding density on cell metabolic activity, glycolysis to oxidative phosphorylation shift, and differentiation potential toward DE and PP lineages. Our findings demonstrated that cell seeding strategy influences cellular metabolic activity and the robustness of iPSC differentiation. iPSCs maintained at higher seeding density exhibited lower initial oxygen consumption rate (OCR) and metabolic activity. There is an optimal seeding density to ensure sufficient oxygen consumption during differentiation and to yield high expression of SOX17 in the DE lineage and high PDX1/NKX6.1 dual-positive cells in PPs. Interestingly, we found that cell confluency at the time of harvest has less impact on the efficacy of pancreatic lineage formation or metabolic activity. This study sheds light on the interplay between metabolic activity and iPSC lineage specification, offering new insights into the robustness of iPSC self-renewal and differentiation for creating human tissues.

Investigating the metabolic load of monoclonal antibody production conveyed to an inducible CHO cell line using a transfer-rate online monitoring system

Shake flasks are a foundational tool in early process development by allowing high throughput exploration of the design space. However, lack of online data at this scale can hamper rapid decision making. Oxygen transfer rate (OTR) monitoring has been readily applied as an online process characterization tool at the benchtop bioreactor scale. Recent advances in modern sensing technology have allowed OTR monitoring to be available at the shake flask level. It is now possible to multiplex time-of-action (e.g., Induction, temperature shift, pH shift, feeding initiation, point of harvest) characterization studies by relying on careful analysis of OTR profile kinetics. As a result, there is potential to save time and capital expenditures while exploring process intensification studies though accurate and physiologically relevant online data. In this article, we detail the application of OTR monitoring to characterize the impact that recombinant protein production has on an inducible CHO cell line expressing Palivizumab. We then test out time-of-action studies to intensify protein production outcomes. We observe that recombinant protein expression causes a metabolic load that diminishes potential biomass growth. As a result, when compared to a control standard process, delaying induction and temperature shift has the potential to improve viable cell densities (VCD) by 2-fold thus increasing recombinant protein yield by over 30 %. The study also demonstrates that OTR can serve as a useful tool to detect cessation of exponential growth. Consequently, time-of-action points that are characteristic of inducible systems can be formulated accurately and reliably to maximize production performance.

A ceramic microbridge microfluidic chip to study osteogenic differentiation of mesenchymal stem cells in bioactive ceramic immune microenvironment

Bioactive ceramics have been used in bone tissue repair and regeneration. However, because of the complex in vivo osteogenesis process, long cycle, and difficulty of accurately tracking, the mechanism of interaction between materials and cells has yet to be fully understood, hindering its development. The ceramic microbridge microfluidic chip system may solve the problem and provide an in vitro method to simulate the microenvironment in vivo. Nevertheless, the complex microenvironment parameters of the chip system need to be studied in detail. Computer simulation bionics can provide clues for the setting of microenvironment parameters. This study used a computational bionic model to simulate the bone growth process in the presence of immune-related factors. The osteoblast differentiation of mesenchymal stem cells of calcium phosphate ceramics in a macrophage-dominated immune microenvironment was studied using a microfluidic chip system. The computational biomimetic model and microfluidic chip findings were basically consistent with the reported results of the animal experiments. These findings suggest that studying the osteogenic behavior of calcium phosphate ceramics using a microfluidic chip model is feasible. The method model provided in this study can be extended to other biomaterials, providing a viable path for their research and evaluation.

Radiation-induced rescue effect on human breast carcinoma cells is regulated by macrophages

The susceptibility of cancer cells to DNA damages is influenced by their microenvironment. For example, unirradiated neighbors of irradiated cells can produce signals that reduce DNA damages. This phenomenon, known as Radiation-Induced Rescue Effect (RIRE), has profound implications on the efficacy of radiotherapy. Using bystander cells co-cultured with mock-irradiated cells as a control, we demonstrated, for the first time, two types of RIRE. Conditioned medium from naïve by stander cells, i.e., cells not exposed to irradiated cells, could mitigate UV-induced DNA damages in human breast carcinoma MCF7 cells, as judged by phospho-H2AX and 53BP1 immunostaining. This protective effect could be further enhanced by the prior treatment of bystander cells with factors from UV-irradiated cells. We named the former effect "basal RIRE" and the latter "active RIRE" which were cell type-dependent. As bystanders, MCF7 showed a significant active RIRE, whereas THP1-derived macrophages showed a strong basal RIRE but no active RIRE. Interestingly, RIRE of macrophages could further be modulated by polarisation. The basal RIRE of macrophages was abolished by M1 polarisation, while M2 and Tumour Associated Macrophages (TAM) demonstrated pronounced basal and active RIRE. When mixtures of MCF7 cells and polarised macrophages were used as bystanders, the overall RIRE was dictated by macrophage phenotypes: RIRE was suppressed by M1 macrophages but significantly enhanced by M2 and TAM. This study shows a previously unappreciated role of the innate immune system in RIRE. Depending on polarised phenotypes, macrophages in the tumour microenvironment can interfere with the effectiveness of radiotherapy by adjusting the RIRE magnitudes.

Pericellular oxygen dynamics in human cardiac fibroblasts and iPSC-cardiomyocytes in high-throughput plates: insights from experiments and modeling

Adequate oxygen supply is crucial for proper cellular function. The emergence of high-throughput (HT) expansion of human stem-cell-derived cells and HT in vitro cellular assays for drug testing necessitate monitoring and understanding of the oxygenation conditions, yet virtually no data exists for such settings. For metabolically active cells like cardiomyocytes, variations in oxygenation may significantly impact their maturation and function; conversely, electromechanical activity can drive oxygen demands. We used HT label-free optical measurements and computational modeling to gain insights about oxygen availability (peri-cellular oxygen dynamics) in syncytia of human induced pluripotent stem cell derived cardiomyocytes (hiPSC-CM) and human cardiac fibroblasts (cFB) grown in glass-bottom 96-well plates under static conditions. Our experimental results highlight the critical role of cell density and solution height (oxygen delivery path) in peri-cellular oxygen dynamics. The developed 3D reaction-diffusion model with Michaelis-Menten kinetics, trained on the obtained comprehensive data set, revealed that time-variant maximum oxygen consumption rate, Vmax, is needed to faithfully capture the complex peri-cellular oxygen dynamics in the excitable hiPSC-CMs, but not in the cFB. For the latter, accounting for cell proliferation was needed. Interestingly, we found both hypoxic (< 2%) and hyperoxic (> 7%) conditions can easily emerge in these standard HT plates in static culture and that peri-cellular oxygen dynamics evolves with days in culture. Our results and the developed computational model can directly be used to optimize cardiac cell growth in HT plates to achieve desired physiological conditions, important in cellular assays for cardiotoxicity, drug development, personalized medicine and heart regeneration applications.

Design, fabrication, and characterization of a user-friendly microfluidic device for studying liver zonation-on-chip (ZoC)

Liver zonation is a fundamental characteristic of hepatocyte spatial heterogeneity, which is challenging to recapitulate in traditional cell cultures. This study presents a novel microfluidic device designed to induce zonation in liver cell cultures by establishing an oxygen gradient using standard laboratory gases. The device consists of two layers; a bottom layer containing a gas channel network that delivers high (cell incubator air, 19% oxygen) and low oxygenated (nitrogen) gases to create three distinct zones within the cell culture chamber in the layer above. Computational simulations and ratiometric oxygen sensing were employed to validate the oxygen gradient, demonstrating that stable oxygen levels were achieved within two hours. Liver zonation was confirmed using immunofluorescence staining, which showed zonated albumin production in HepG2 cells directly correlating with oxygen levels and mimicking in-vivo zonation behavior. This user-friendly device supports studies on liver zonation and related metabolic disease mechanisms in vitro. It can also be utilized for experiments that necessitate precise gas concentration gradients, such as hypoxia-related research areas focused on angiogenesis and cancer development.

Impact of Oxygen Availability on the Organelle-Specific Redox Potentials and Stress in Recombinant Protein Producing Komagataella phaffii

The yeast Komagataella phaffii (syn. Pichia pastoris) is a highly effective and well-established host for the production of recombinant proteins. The redox balance of its secretory pathway, which is multi-organelle dependent, is of high importance for producing secretory proteins. Redox imbalance and oxidative stress can significantly influence protein folding and secretion. Glutathione serves as the main redox buffer of the cell and cellular redox conditions can be assessed through the status of the glutathione redox couple (GSH-GSSG). Previous research often focused on the redox potential of the endoplasmic reticulum (ER), where oxidative protein folding and disulphide bond formation occur. In this study, in vivo measurements of the glutathione redox potential were extended to different subcellular compartments by targeting genetically encoded redox sensitive fluorescent proteins (roGFPs) to the cytosol, ER, mitochondria and peroxisomes. Using these biosensors, the impact of oxygen availability on the redox potentials of the different organelles was investigated in non-producing and producing K. phaffii strains in glucose-limited chemostat cultures. It was found that the transition from normoxic to hypoxic conditions affected the redox potential of all investigated organelles, while the exposure to hyperoxic conditions did not impact them. Also, as reported previously, hypoxic conditions led to increased recombinant protein secretion. Finally, transcriptome and proteome analyses provided novel insights into the short-term response of the cells from normoxic to hypoxic conditions.

Capacity and limitations of microfluidic flow to increase solute transport in three-dimensional cell cultures

Culturing living cells in three-dimensional environments increases the biological relevance of laboratory experiments, but requires solutes to overcome a diffusion barrier to reach the centre of cellular constructs. We present a theoretical and numerical investigation that brings a mechanistic understanding of how microfluidic culture conditions, including chamber size, inlet fluid velocity and spatial confinement, affect solute distribution within three-dimensional cellular constructs. Contact with the chamber substrate reduces the maximally achievable construct radius by 15%. In practice, finite diffusion and convection kinetics in the microfluidic chamber further lower that limit. The benefits of external convection are greater if transport rates across diffusion-dominated areas are high. Those are omnipresent and include the diffusive boundary layer growing from the fluid-construct interface and regions near corners where fluid is recirculating. Such regions multiply the required convection to achieve a given solute penetration by up to 100, so chip designs ought to minimize them. Our results define conditions where complete solute transport into an avascular three-dimensional cell construct is achievable and applies to real chambers without needing to simulate their exact geometries.

CHO stable pool fed-batch process development of SARS-CoV-2 spike protein production: Impact of aeration conditions and feeding strategies

Technology scale-up and transfer are a fundamental and critical part of process development in biomanufacturing. Important bioreactor hydrodynamic characteristics such as working volume, overhead gas flow rate, volumetric power input (P/V), impeller type, agitation regimen, sparging aeration strategy, sparger type, and kLa must be selected based on key performance indicators (KPI) to ensure a smooth and seamless process scale-up and transfer. Finding suitable operational setpoints and developing an efficient feeding regimen to ensure process efficacy and consistency are instrumental. In this investigation, process development of a cumate inducible Chinese hamster ovary (CHO) stable pool expressing trimeric SARS-CoV-2 spike protein in 1.8 L benchtop stirred-tank bioreactors is detailed. Various dissolved oxygen levels and aeration air caps were studied to determine their impact on cell growth and metabolism, culture longevity, and endpoint product titers. Once hydrodynamic conditions were tuned to an optimal zone, various feeding strategies were explored to increase culture performance. Dynamic feedings such as feeding based on current culture volume, viable cell density (VCD), oxygen uptake rate (OUR), and bio-capacitance signals were tested and compared to standard bolus addition. Increases in integral of viable cell concentration (IVCC) (1.25-fold) and protein yield (2.52-fold), as well as greater culture longevity (extension of 5 days) were observed in dynamic feeding strategies when compared to periodic bolus feeding. Our study emphasizes the benefits of designing feeding strategies around metabolically relevant signals such as OUR and bio-capacitance signals.

Oxygen control in cell culture - Your cells may not be experiencing what you think!

Oxygen (O2)-controlled cell culture has been pivotal in studying mammalian mechanisms of O2 sensing, regulation, and utilization. We posit, however, that O2-controlled cell culture is paradoxically not controlling O2. There is overwhelming evidence that the pericellular O2 is lower than the surrounding gas phase due to cellular O2 consumption. Standard hypoxic cell culture is at high risk of inducing pericellular anoxia. We discuss the implications of poor O2 control for cellular O2 regulation mechanisms, bioenergetics, and redox signaling. We also highlight the evidence of frequent under-oxygenation in standard (i.e., normoxic) cell culture. This issue has been largely overlooked because strategies to control pericellular O2 have been lacking. Here, we propose a framework to control pericellular O2 based on our recent investigation into the nature of the gas/pericellular O2 gradient. Implementing this framework into standard practice will unlock quantitative O2 control in vitro, improving our ability to understand the role of O2 in biology.

Revolutionizing our understanding of Parkinson's disease: Dr. Heinz Reichmann's pioneering research and future research direction

Millions of individuals around the world are afflicted with Parkinson's disease (PD), a prevalent and incapacitating neurodegenerative disorder. Dr. Reichmann, a distinguished professor and neurologist, has made substantial advancements in the domain of PD research, encompassing both fundamental scientific investigations and practical applications. His research has illuminated the etiology and treatment of PD, as well as the function of energy metabolism and premotor symptoms. As a precursor to a number of neurotransmitters and neuromodulators that are implicated in the pathophysiology of PD, he has also investigated the application of tryptophan (Trp) derivatives in the disease. His principal findings and insights are summarized and synthesized in this narrative review article, which also emphasizes the challenges and implications for future PD research. This narrative review aims to identify and analyze the key contributions of Reichmann to the field of PD research, with the ultimate goal of informing future research directions in the domain. By examining Reichmann's work, the study seeks to provide a comprehensive understanding of his major contributions and how they can be applied to advance the diagnosis and treatment of PD. This paper also explores the potential intersection of Reichmann's findings with emerging avenues, such as the investigation of Trp and its metabolites, particularly kynurenines, which could lead to new insights and potential therapeutic strategies for managing neurodegenerative disorders like PD.

Soft sensor for viable cell counting by measuring dynamic oxygen uptake rate

Regulatory authorities in biopharmaceutical industry emphasize process design by process understanding but applicable tools that are easy to implement are still missing. Soft sensors are a promising tool for the implementation of the Quality by Design (QbD) approach and Process Analytical Technology (PAT). In particular, the correlation between viable cell counting and oxygen consumption was investigated, but problems remained: Either the process had to be modified for excluding CO2 in pH control, or complex kLa models had to be set up for specific processes. In this work, a non-invasive soft sensor for simplified on-line cell counting based on dynamic oxygen uptake rate was developed with no need of special equipment. The dynamic oxygen uptake rates were determined by automated and periodic interruptions of gas supply in DASGIP® bioreactor systems, realized by a programmed Visual Basic script in the DASware® control software. With off-line cell counting, the two parameters were correlated based on linear regression and led to a robust model with a correlation coefficient of 0.92. Avoidance of oxygen starvation was achieved by gas flow reactivation at a certain minimum dissolved oxygen concentration. The soft sensor model was established in the exponential growth phase of a Chinese Hamster Ovary fed-batch process. Control studies showed no impact on cell growth by the discontinuous gas supply. This soft sensor is the first to be presented that does not require any specialized additional equipment as the methodology relies solely on the direct measurement of oxygen consumed by the cells in the bioreactor.

A gravity-driven tissue chip to study the efficacy and toxicity of cancer therapeutics

Tissue chip and organs-on-chip technologies have emerged as promising tools in preclinical studies. In oncology, this is driven by the high failure rates of candidate drugs in clinical trials mainly due to inadequate efficacy or intolerable toxicity and the need for better predictive preclinical models than those traditionally used. However, the intricate design, fabrication, operation, and limited compatibility with automation limit the utility of tissue chips. To tackle these issues, we designed a novel 32-unit tissue chip in the format of standard 96-well plates to streamline automation, fabricated it using 3D printing, and leveraged gravity-driven flow to bypass the need for external flow devices. Each unit includes three interconnected tissue compartments that model liver, tumor, and bone marrow stroma. The focus on liver and bone marrow stroma was due to their respective roles in drug metabolism and disturbances to the bone marrow niche from off-target toxicity of chemotherapies. We analyzed flow patterns, mixing, and oxygen transport among and within the compartments through finite element simulations and demonstrated the utility of the tissue chip to study the efficacy of commonly-used cytotoxic cancer drugs against tumor cells and their toxicity toward liver and bone marrow cells. The ability to simultaneously study drug efficacy and toxicity in high throughput can help select promising therapeutics in early stages of drug discovery in preclinical studies.

Tumor growth and vascular redistribution contributes to the dosimetric preferential effect of microbeam radiotherapy: a Monte Carlo study

The radiobiological mechanisms behind the favorable response of tissues to microbeam radiation therapy (MRT) are not fully described yet. Among other factors, the differential action to tumor and normal tissue vasculature is considered to contribute to MRT efficacy. This computational study evaluates the relevance of tumor growth stage and associated vascular redistribution to this effect. A multiscale approach was employed with two simulation softwares: TOPAS and CompuCell3D. Segmentation images of the angioarchitecture of a non-bearing tumor mouse brain were used. The tumor vasculature at different tumor growth stages was obtained by simulating the tumor proliferation and spatial vascular redistribution. The radiation-induced damage to vascular cells and consequent change in oxygen perfusion were simulated for normal and tumor tissues. The multiscale model showed that oxygen perfusion to tissues and vessels decreased as a function of the tumor proliferation stage, and with the decrease in uniformity of the vasculature spatial distribution in the tumor tissue. This led to an increase in the fraction of hypoxic (up to 60%) and necrotic (10%) tumor cells at advanced tumor stages, whereas normal tissues remained normoxic. These results showed that tumor stage and spatial vascular distribution contribute to the preferential effect of MRT in tumors.

Label-Free Raman Spectroscopy for Assessing Purity and Maturation of hiPSC-Derived Cardiac Tissue

I.

BACKGROUND

Human induced pluripotent stem cell (hiPSC) derived cardiomyocytes (CMs) have been utilized in drug toxicity evaluation, drug discovery, and treating heart failure patients, showing substantial effects. Ensuring the quality, purity, and maturation of hiPSC-CMs during large-scale production is crucial. There is a growing demand for a novel method to characterize cell molecular profiles without labels and without causing damage. II.

METHODS

In this study, we employed label-free Raman microscopy to evaluate hiPSC-derived CMs. The study involved the characterization of cell molecular profiles without labels and without causing damage. The correlation between Raman spectroscopy of specific components, such as cytochrome c and myoglobin, and CM purity and maturation following hiPSC differentiation was investigated. Additionally, the validation of this correlation was performed by assessing mixtures of commercially available CMs (iCell cardiomyocytes2) and fibroblasts at various ratios as well as hiPSC-derived CMs with different efficiencies. Furthermore, CMs were matured using rapid pacing of traveling waves, and the Raman profiles of matured CMs were compared to those of immature ones. III.

RESULTS

Raman spectroscopy indicated that the cytochrome c and myoglobin showed correlation with the purity and maturation of CMs following differentiation of hiPSCs. This correlation was validated through experiments involving different CM-fibroblast mixtures and hiPSC-derived CMs with varying efficiencies. Moreover, matured CMs exhibited markedly different Raman profiles compared to immature ones, indicating the potential of Raman imaging as a tool for assessing CM maturation. IV.

CONCLUSIONS

We discovered that Raman spectroscopy of certain components, such as cytochrome c and myoglobin, correlates with the CM purity and maturation following hiPSC differentiation. The findings of this study highlight the potential of label-free Raman microscopy as a nondestructive, high-content, and time-efficient method for quality control of hiPSC-derived CMs. This approach could significantly contribute to ensuring the quality and maturity of hiPSC-CMs for various applications in drug discovery and regenerative medicine.

Extracellular matrix production and oxygen diffusion regulate chemotherapeutic response in osteosarcoma spheroids

BACKGROUND

Osteosarcoma (OS) survival rates and outcome have not improved in 50 years since the advent of modern chemotherapeutics. Thus, there is a critical need for an improved understanding of the tumor microenvironment to identify better therapies. Extracellular matrix (ECM) deposition and hypoxia are known to abrogate the efficacy of various chemical and cell-based therapeutics. Here, we aim to mechanistically investigate the combinatorial effects of hypoxia and matrix deposition with the use of OS spheroids.

METHODS

We use two murine OS cell lines with differential metastatic potential to form spheroids. We form spheroids of two sizes, use ascorbate-2-phosphate supplementation to enhance ECM deposition, and study cell response under standard (21% O2) and physiologic (5% O2) oxygen tensions. Finally, we examine chemotherapeutic responses to doxorubicin treatment.

RESULTS

ECM production and oxygen tension are key determinants of spheroid size through cell organization based on nutrient and oxygen distribution. Interestingly, highly metastatic OS is more susceptible to chemotherapeutics compared to less metastatic OS when matrix production increases. Together, these data suggest that dynamic interactions between ECM production and oxygen diffusion may result in distinct chemotherapeutic responses despite inherent tumor aggressiveness.

CONCLUSION

This work establishes OS spheroids as a valuable tool for early OS tumor formation investigation and holds potential for novel therapeutic target and prognostic indicator discovery.

Multivariate data analysis of process parameters affecting the growth and productivity of stable Chinese hamster ovary cell pools expressing SARS-CoV-2 spike protein as vaccine antigen in early process development

The recent COVID-19 pandemic revealed an urgent need to develop robust cell culture platforms which can react rapidly to respond to this kind of global health issue. Chinese hamster ovary (CHO) stable pools can be a vital alternative to quickly provide gram amounts of recombinant proteins required for early-phase clinical assays. In this study, we analyze early process development data of recombinant trimeric spike protein Cumate-inducible manufacturing platform utilizing CHO stable pool as a preferred production host across three different stirred-tank bioreactor scales (0.75, 1, and 10 L). The impact of cell passage number as an indicator of cell age, methionine sulfoximine (MSX) concentration as a selection pressure, and cell seeding density was investigated using stable pools expressing three variants of concern. Multivariate data analysis with principal component analysis and batch-wise unfolding technique was applied to evaluate the effect of critical process parameters on production variability and a random forest (RF) model was developed to forecast protein production. In order to further improve process understanding, the RF model was analyzed with Shapley value dependency plots so as to determine what ranges of variables were most associated with increased protein production. Increasing longevity, controlling lactate build-up, and altering pH deadband are considered promising approaches to improve overall culture outcomes. The results also demonstrated that these pools are in general stable expressing similar level of spike proteins up to cell passage 11 (~31 cell generations). This enables to expand enough cells required to seed large volume of 200-2000 L bioreactor.

Revisiting reactive oxygen species production in hypoxia

Cellular responses to hypoxia are crucial in various physiological and pathophysiological contexts and have thus been extensively studied. This has led to a comprehensive understanding of the transcriptional response to hypoxia, which is regulated by hypoxia-inducible factors (HIFs). However, the detailed molecular mechanisms of HIF regulation in hypoxia remain incompletely understood. In particular, there is controversy surrounding the production of mitochondrial reactive oxygen species (ROS) in hypoxia and how this affects the stabilization and activity of HIFs. This review examines this controversy and attempts to shed light on its origin. We discuss the role of physioxia versus normoxia as baseline conditions that can affect the subsequent cellular response to hypoxia and highlight the paucity of data on pericellular oxygen levels in most experiments, leading to variable levels of hypoxia that might progress to anoxia over time. We analyze the different outcomes reported in isolated mitochondria, versus intact cells or whole organisms, and evaluate the reliability of various ROS-detecting tools. Finally, we examine the cell-type and context specificity of oxygen's various effects. We conclude that while recent evidence suggests that the effect of hypoxia on ROS production is highly dependent on the cell type and the duration of exposure, efforts should be made to conduct experiments under carefully controlled, physiological microenvironmental conditions in order to rule out potential artifacts and improve reproducibility in research.

Size-related variability of oxygen consumption rates in individual human hepatic cells

Accurate descriptions of the variability in single-cell oxygen consumption and its size-dependency are key to establishing more robust tissue models. By combining microfabricated devices with multiparameter identification algorithms, we demonstrate that single human hepatocytes exhibit an oxygen level-dependent consumption rate and that their maximal oxygen consumption rate is significantly lower than that of typical hepatic cell cultures. Moreover, we found that clusters of two or more cells competing for a limited oxygen supply reduced their maximal consumption rate, highlighting their ability to adapt to local resource availability and the presence of nearby cells. We used our approach to characterize the covariance of size and oxygen consumption rate within a cell population, showing that size matters, since oxygen metabolism covaries lognormally with cell size. Our study paves the way for linking the metabolic activity of single human hepatocytes to their tissue- or organ-level metabolism and describing its size-related variability through scaling laws.

Controlling Pericellular Oxygen Tension in Cell Culture Reveals Distinct Breast Cancer Responses to Low Oxygen Tensions

In oxygen (O2)-controlled cell culture, an indispensable tool in biological research, it is presumed that the incubator setpoint equals the O2 tension experienced by cells (i.e., pericellular O2). However, it is discovered that physioxic (5% O2) and hypoxic (1% O2) setpoints regularly induce anoxic (0% O2) pericellular tensions in both adherent and suspension cell cultures. Electron transport chain inhibition ablates this effect, indicating that cellular O2 consumption is the driving factor. RNA-seq analysis revealed that primary human hepatocytes cultured in physioxia experience ischemia-reperfusion injury due to cellular O2 consumption. A reaction-diffusion model is developed to predict pericellular O2 tension a priori, demonstrating that the effect of cellular O2 consumption has the greatest impact in smaller volume culture vessels. By controlling pericellular O2 tension in cell culture, it is found that hypoxia vs. anoxia induce distinct breast cancer transcriptomic and translational responses, including modulation of the hypoxia-inducible factor (HIF) pathway and metabolic reprogramming. Collectively, these findings indicate that breast cancer cells respond non-monotonically to low O2, suggesting that anoxic cell culture is not suitable for modeling hypoxia. Furthermore, it is shown that controlling atmospheric O2 tension in cell culture incubators is insufficient to regulate O2 in cell culture, thus introducing the concept of pericellular O2-controlled cell culture.

Innovative fixed bed bioreactor platform: Enabling linearly scalable adherent cell biomanufacturing with real-time biomass prediction from nutrient consumption

Scalable single-use adherent cell-based biomanufacturing platforms are essential for unlocking the full potential of cell and gene therapies. The primary objective of this study is to design and develop a novel fixed bed bioreactor platform tailored specifically for scaling up adherent cell culture. The bioreactor comprises a packed bed of vertically stacked woven polyethylene terephthalate mesh discs, sandwiched between two-fluid guide plates. Leveraging computational fluid dynamics modeling, we optimized bioreactor design to achieve uniform flow with minimal shear stress. Residence time distribution measurements demonstrated excellent flow uniformity with plug flow characteristics. Periodic media sampling coupled with offline analysis revealed minimal gradients of crucial metabolites (glucose, glutamine, lactate, and ammonia) across the bioreactor during cell growth. Furthermore, the bioreactor platform demonstrated high performance in automated cell harvesting, with ≈96% efficiency and ≈98% viability. It also exhibited linear scalability in both operational parameters and performance for cell culture and adeno-associated virus vector production. We developed mathematical models based on oxygen uptake rates to accurately predict cell growth curves and estimate biomass in real-time. This study demonstrates the effectiveness of the developed fixed-bed bioreactor platform in enabling scalable adherent cell-based biomanufacturing with high productivity and process control.

Prototyping in Polymethylpentene to Enable Oxygen-Permeable On-a-Chip Cell Culture and Organ-on-a-Chip Devices Suitable for Microscopy

With the rapid development and commercial interest in the organ-on-a-chip (OoC) field, there is a need for materials addressing key experimental demands and enabling both prototyping and large-scale production. Here, we utilized the gas-permeable, thermoplastic material polymethylpentene (PMP). Three methods were tested to prototype transparent PMP films suitable for transmission light microscopy: hot-press molding, extrusion, and polishing of a commercial, hazy extruded film. The transparent films (thickness 20, 125, 133, 356, and 653 µm) were assembled as the cell-adhering layer in sealed culture chamber devices, to assess resulting oxygen concentration after 4 days of A549 cell culture (cancerous lung epithelial cells). Oxygen concentrations stabilized between 15.6% and 11.6%, where the thicker the film, the lower the oxygen concentration. Cell adherence, proliferation, and viability were comparable to glass for all PMP films (coated with poly-L-lysine), and transparency was adequate for transmission light microscopy of adherent cells. Hot-press molding was concluded as the preferred film prototyping method, due to excellent and reproducible film transparency, the possibility to easily vary film thickness, and the equipment being commonly available. The molecular orientation in the PMP films was characterized by IR dichroism. As expected, the extruded films showed clear orientation, but a novel result was that hot-press molding may also induce some orientation. It has been reported that orientation affects the permeability, but with the films in this study, we conclude that the orientation is not a critical factor. With the obtained results, we find it likely that OoC models with relevant in vivo oxygen concentrations may be facilitated by PMP. Combined with established large-scale production methods for thermoplastics, we foresee a useful role for PMP within the OoC field.

Mitochondrial Thermogenesis Can Trigger Heat Shock Response in the Nucleus

Mitochondrial thermogenesis is a process in which heat is generated by mitochondrial respiration. In living organisms, the thermogenic mechanisms that maintain body temperature have been studied extensively in fat cells with little knowledge on how mitochondrial heat may act beyond energy expenditure. Here, we highlight that the exothermic oxygen reduction reaction (ΔH f° = -286 kJ/mol) is the main source of the protonophore-induced mitochondrial thermogenesis, and this heat is conducted to other cellular organelles, including the nucleus. As a result, mitochondrial heat that reached the nucleus initiated the classical heat shock response, including the formation of nuclear stress granules and the localization of heat shock factor 1 (HSF1) to chromatin. Consequently, activated HSF1 increases the level of gene expression associated with the response to thermal stress in mammalian cells. Our results illustrate heat generated within the cells as a potential source of mitochondria-nucleus communication and expand our understanding of the biological functions of mitochondria in cell physiology.

Protocol for analyzing energy metabolic pathway dependency in human liver cancer cell lines

Cellular energy metabolism analysis is complex, expensive, and indirect. We present a protocol to analyze relative contribution of metabolic pathways to ATP production by directly measuring ATP levels. We describe steps for cell counting and seeding in 96-well plate, treating with metformin, and systematic inhibition with metabolic inhibitors. We then detail procedures for a viability and ATP assay and calculating energy metabolism dependency. This high-throughput and accessible protocol works with any cell line and allows for flexible perturbation studies.

An in-silico analysis of hydrodynamics and gas mass transfer characteristics in scale-down models for mammalian cell cultures

Bioprocess scale-up and technology transfer can be challenging due to multiple variables that need to be optimized during process development from laboratory scale to commercial manufacturing. Cell cultures are highly sensitive to key factors during process transfer across scales, including geometric variability in bioreactors, shear stress from impeller and sparging activity, and nutrient gradients that occur due to increasing blend times. To improve the scale-up and scale-down of these processes, it is important to fully characterize bioreactors to better understand the differences that will occur within the culture environment, especially the hydrodynamic profiles that will vary in vessel designs across scales. In this study, a comprehensive hydrodynamic characterization of the Ambr® 250 mammalian single-use bioreactor was performed using time-accurate computational fluid dynamics simulations conducted with M-Star computational fluid dynamics software, which employs lattice-Boltzmann techniques to solve the Navier-Stokes transport equations at a mesoscopic scale. The single-phase and two-phase fluid properties within this small-scale vessel were analyzed in the context of agitation hydrodynamics and mass transfer (both within the bulk fluid and the free surface) to effectively characterize and understand the differences that scale-down models possess when compared to their large-scale counterparts. The model results validate the use of computational fluid dynamics as an in-silico tool to characterize bioreactor hydrodynamics and additionally identify important free-surface transfer mechanics that need to be considered during the qualification of a scale-down model in the development of mammalian bioprocesses.

Organosilica Nanosensors for Monitoring Spatiotemporal Changes in Oxygen Levels in Bacterial Cultures

Oxygen plays a central role in aerobic metabolism, and while many approaches have been developed to measure oxygen concentration in biological environments over time, monitoring spatiotemporal changes in dissolved oxygen levels remains challenging. To address this, we developed a ratiometric core-shell organosilica nanosensor for continuous, real-time optical monitoring of oxygen levels in biological environments. The nanosensors demonstrate good steady state characteristics (KpSV = 0.40 L/mg, R2 = 0.95) and respond reversibly to changes in oxygen concentration in buffered solutions and report similar oxygen level changes in response to bacterial cell growth (Escherichia coli) in comparison to a commercial bulk optode-based sensing film. We further demonstrated that the oxygen nanosensors could be distributed within a growing culture of E. coli and used to record oxygen levels over time and in different locations within a static culture, opening the possibility of spatiotemporal monitoring in complex biological systems.

Exploring chronic and transient tumor hypoxia for predicting the efficacy of hypoxia-activated pro-drugs

Hypoxia, a low level of oxygen in the tissue, arises due to an imbalance between the vascular oxygen supply and oxygen demand by the surrounding cells. Typically, hypoxia is viewed as a negative marker of patients' survival, because of its implication in the development of aggressive tumors and tumor resistance. Several drugs that specifically target the hypoxic cells have been developed, providing an opportunity for exploiting hypoxia to improve cancer treatment. Here, we consider combinations of hypoxia-activated pro-drugs (HAPs) and two compounds that transiently increase intratumoral hypoxia: a vasodilator and a metabolic sensitizer. To effectively design treatment protocols with multiple compounds we used mathematical micro-pharmacology modeling and determined treatment schedules that take advantage of heterogeneous and dynamically changing oxygenation in tumor tissue. Our model was based on data from murine pancreatic cancers treated with evofosfamide (as a HAP) and either hydralazine (as a vasodilator), or pyruvate (as a metabolic sensitizer). Subsequently, this model was used to identify optimal schedules for different treatment combinations. Our simulations showed that schedules of HAPs with the vasodilator had a bimodal distribution, while HAPs with the sensitizer showed an elongated plateau. All schedules were more successful than HAP monotherapy. The three-compound combination had three local optima, depending on the HAPs clearance from the tissue interstitium, each two-fold more effective than baseline HAP treatment. Our study indicates that the three-compound therapy administered in the defined order will improve cancer response and that designing complex schedules could benefit from the use of mathematical modeling.

Microfluidic design for in-vitro liver zonation-a numerical analysis using COMSOL Multiphysics

The liver is one of the most important organs, with a complex physiology. Current in-vitro approaches are not accurate for disease modeling and drug toxicity research. One of those features is liver zonation, where cells display different physiological states due to different levels of oxygen and nutrient supplements. Organ-on-a-chip technology employs microfluidic platforms that enable a controlled environment for in-vitro cell culture. In this study, we propose a microfluidic design embedding a gas channel (of ambient air), creating an oxygen gradient. We numerically simulate different flow rates and cell densities with the COMSOL Multiphysics package considering cell-specific consumption rates of oxygen and glucose. We establish the cell density and flow rate for optimum oxygen and glucose distribution in the cell culture chamber. Furthermore, we show that a physiologically relevant concentration of oxygen and glucose in the chip is reached after 24 h and 30 min, respectively. The proposed microfluidic design and optimal parameters we identify in this paper provide a tool for in-vitro liver zonation studies. However, the microfluidic design is not exclusively for liver cell experiments but is foreseen to be applicable in cell studies where different gas concentration gradients are critical, e.g., studying hypoxia or toxic gas impact.

Strategic Replication of the Hepatic Zonation In Vitro Employing a Biomimetic Approach

The varied functions of the liver are dependent on the metabolic heterogeneity exhibited by the hepatocytes within the liver lobule spanning the porto-central axis. This complex phenomenon plays an important role in maintaining the physiological homeostasis of the liver. Standard in vitro culture models fail to mimic this spatial heterogeneity of hepatocytes, assuming a homogeneous population of cells, which leads to inaccurate translation of results. Here, we demonstrate the development of an in vitro model of hepatic zonation by mimicking the microarchitecture of the liver using a 3D printed mini bioreactor and decellularized liver matrix to provide the native microenvironmental cues. There was a differential expression of hypoxic and metabolic markers across the developed mini bioreactor, showing the establishment of gradients of oxygen, Wnt/β-catenin pathway, and other metabolic pathways. The model also showed the establishment of zone-dependent toxicity on treatment with acetaminophen. The developed model would thus be a promising avenue in the field of tissue engineering for understanding the liver physiology and pathophysiology and for drug screening to evaluate the potential of new pharmaceutical interventions.

Stability of aqueous solutions of ascorbate for basic research and for intravenous administration

Ascorbate (vitamin C) can rapidly oxidize in many near-neutral pH, aqueous solutions. We report on the stability of ascorbate solutions prepared for infusion into patients using standard pharmacy protocols, for example, 75 g of ascorbate/L in water for infusion. The concentration of ascorbate was monitored for changes over time using direct UV-Vis spectroscopy. The pH of the solution was about 5.7 with no significant change over 24 h. There was only an approximate loss of 1% per day over the first 3 days of storage. This information allows decisions on how far ahead of need such preparations can be made. We also provide laboratory approaches to minimize or control the rate of oxidation of ascorbate solutions for use in chemical and biochemical studies as well as preclinical animal studies. The goal is to have the amount of ascorbate intended to be used in experiments be the actual amount available.

Biomimetic Construction of Degradable DNAzyme-Loaded Nanocapsules for Self-Sufficient Gene Therapy of Pulmonary Metastatic Breast Cancer

Pulmonary metastasis of breast cancer is the major cause of deaths of breast cancer patients, but the effective treatment of pulmonary metastases is still lacking at present. Herein, a degradable biomimetic DNAzyme biocapsule is developed with the poly(ethylenimine) (PEI)-DNAzyme complex encapsulated in a Mn2+/Zn2+-coordinated inositol hexaphosphate (IP6) capsule modified with the cRGD targeting peptide for high-efficiency gene therapy of both primary and pulmonary metastatic breast tumors. This DNAzyme biocapsule is degradable inside acidic lysosomes, leading to the release of DNAzyme and abundant Mn2+/Zn2+ for catalytic cleavage of EGR-1 mRNA. We find that PEI promotes the lysosomal escape of the released DNAzyme. Both in vitro and in vivo experiments demonstrate the apparent downregulation of EGR-1 and Bcl-2 protein expression after treatment with the DNAzyme biocapsule, thereby inducing apoptotic death of tumor cells. We further verify that the DNAzyme biocapsule exhibits potent therapeutic efficacy against both primary and pulmonary metastatic breast tumors with significant inhibition of peri-pulmonary metastasis. This study provides a promising effective strategy for constructing degradable DNAzyme-based platforms with self-supply of abundant metal ion cofactors for high-efficiency gene therapy of metastatic breast cancer.

Can Single Cell Respiration be Measured by Scanning Electrochemical Microscopy (SECM)?

Ultramicroelectrode (UME), or, equivalently, microelectrode, probes are increasingly used for single-cell measurements of cellular properties and processes, including physiological activity, such as metabolic fluxes and respiration rates. Major challenges for the sensitivity of such measurements include: (i) the relative magnitude of cellular and UME fluxes (manifested in the current); and (ii) issues around the stability of the UME response over time. To explore the extent to which these factors impact the precision of electrochemical cellular measurements, we undertake a systematic analysis of measurement conditions and experimental parameters for determining single cell respiration rates via the oxygen consumption rate (OCR) in single HeLa cells. Using scanning electrochemical microscopy (SECM), with a platinum UME as the probe, we employ a self-referencing measurement protocol, rarely employed in SECM, whereby the UME is repeatedly approached from bulk solution to a cell, and a short pulse to oxygen reduction reaction (ORR) potential is performed near the cell and in bulk solution. This approach enables the periodic tracking of the bulk UME response to which the near-cell response is repeatedly compared (referenced) and also ensures that the ORR near the cell is performed only briefly, minimizing the effect of the electrochemical process on the cell. SECM experiments are combined with a finite element method (FEM) modeling framework to simulate oxygen diffusion and the UME response. Taking a realistic range of single cell OCR to be 1 × 10-18 to 1 × 10-16 mol s-1, results from the combination of FEM simulations and self-referencing SECM measurements show that these OCR values are at, or below, the present detection sensitivity of the technique. We provide a set of model-based suggestions for improving these measurements in the future but highlight that extraordinary improvements in the stability and precision of SECM measurements will be required if single cell OCR measurements are to be realized.

Controlling pericellular oxygen tension in cell culture reveals distinct breast cancer responses to low oxygen tensions

Oxygen (O2) tension plays a key role in tissue function and pathophysiology. O2-controlled cell culture, in which the O2 concentration in an incubator's gas phase is controlled, is an indispensable tool to study the role of O2 in vivo. For this technique, it is presumed that the incubator setpoint is equal to the O2 tension that cells experience (i.e., pericellular O2). We discovered that physioxic (5% O2) and hypoxic (1% O2) setpoints regularly induce anoxic (0.0% O2) pericellular tensions in both adherent and suspension cell cultures. Electron transport chain inhibition ablates this effect, indicating that cellular O2 consumption is the driving factor. RNA-seq revealed that primary human hepatocytes cultured in physioxia experience ischemia-reperfusion injury due to anoxic exposure followed by rapid reoxygenation. To better understand the relationship between incubator gas phase and pericellular O2 tensions, we developed a reaction-diffusion model that predicts pericellular O2 tension a priori. This model revealed that the effect of cellular O2 consumption is greatest in smaller volume culture vessels (e.g., 96-well plate). By controlling pericellular O2 tension in cell culture, we discovered that MCF7 cells have stronger glycolytic and glutamine metabolism responses in anoxia vs. hypoxia. MCF7 also expressed higher levels of HIF2A, CD73, NDUFA4L2, etc. and lower levels of HIF1A, CA9, VEGFA, etc. in response to hypoxia vs. anoxia. Proteomics revealed that 4T1 cells had an upregulated epithelial-to-mesenchymal transition (EMT) response and downregulated reactive oxygen species (ROS) management, glycolysis, and fatty acid metabolism pathways in hypoxia vs. anoxia. Collectively, these results reveal that breast cancer cells respond non-monotonically to low O2, suggesting that anoxic cell culture is not suitable to model hypoxia. We demonstrate that controlling atmospheric O2 tension in cell culture incubators is insufficient to control O2 in cell culture and introduce the concept of pericellular O2-controlled cell culture.

Efficient single-cell oxygen consumption rate characterization based on frequency domain fluorescence lifetime imaging microscopy measurement and microfluidic platform

Cell metabolism is critical in regulating normal cell functions to maintain energy homeostasis. In order to monitor cell metabolism, the oxygen consumption rate (OCR) of cells has been characterized as an important factor. In conventional cell analysis, the cells are characterized in bulk due to technical limitations. However, the heterogeneity between the cells cannot be identified. Therefore, single-cell analysis has been proposed to reveal cellular functions and their heterogeneity. In this research, an approach integrating a microfluidic device and widefield frequency domain fluorescence imaging lifetime microscopy (FD-FLIM) for single-cell OCR characterization in an efficient manner is developed. The microfluidic device provides an efficient platform to trap and isolate single cells in microwells with the buffer saline containing an oxygen-sensitive phosphorescent dye. The oxygen tension variation within the microwells can be efficiently estimated by measuring the fluorescence lifetime change using the FD-FLIM, and the OCR values of the single cells can then be calculated. In the experiments, breast cancer (MCF-7) cells are exploited for the OCR measurement. The results demonstrate the functionality of the developed approach and show the heterogeneity among the cells. The developed approach possesses great potential to advance cellular metabolism studies with single-cell resolution.

A sense of proximity: Cell packing modulates oxygen consumption

Accurately modeling oxygen transport and consumption is crucial to predict metabolic dynamics in cell cultures and optimize the design of tissue and organ models. We present a methodology to characterize the Michaelis-Menten oxygen consumption parameters in vitro, integrating novel experimental techniques and computational tools. The parameters were derived for hepatic cell cultures with different dimensionality (i.e., 2D and 3D) and with different surface and volumetric densities. To quantify cell packing regardless of the dimensionality of cultures, we devised an image-based metric, referred to as the proximity index. The Michaelis-Menten parameters were related to the proximity index through an uptake coefficient, analogous to a diffusion constant, enabling the quantitative analysis of oxygen dynamics across dimensions. Our results show that Michaelis-Menten parameters are not constant for a given cell type but change with dimensionality and cell density. The maximum consumption rate per cell decreases significantly with cell surface and volumetric density, while the Michaelis-Menten constant tends to increase. In addition, the dependency of the uptake coefficient on the proximity index suggests that the oxygen consumption rate of hepatic cells is superadaptive, as they modulate their oxygen utilization according to its local availability and to the proximity of other cells. We describe, for the first time, how cells consume oxygen as a function of cell proximity, through a quantitative index, which combines cell density and dimensionality. This study enhances our understanding of how cell-cell interaction affects oxygen dynamics and enables better prediction of aerobic metabolism in tissue models, improving their translational value.

Customized small-sized clinostat using 3D printing and gas-permeable polydimethylsiloxane culture dish

Over the past few decades, research on life in space has increased. Owing to the expensive nature of and the challenges associated with conducting experiments in real space, clinostats, which continuously randomize the gravity vector by using motors, have been used to generate simulated microgravity (SMG) on Earth. Herein, by using a 3D printing method, we develop a customized small-sized clinostat (CS clinostat) that is easy to manufacture, inexpensive, and robust. Moreover, we develop and fabricate a gas-permeable polydimethylsiloxane culture dish that fits inside the CS clinostat. To validate SMG generation, ovarian cancer cells (OV- 90, TOV-21G, and Caov-3) were applied to demonstrate a significant reduction in caveolin-1 expression, a biomarker of SMG, indicating SMG generation. The proposed CS clinostat system has good accessibility for SMG research, which makes it useful as a tool for biologists, who are unfamiliar with conventional clinostat equipment, to conduct preliminary studies in the space environment.

Diversity of cells and signals in the cardiovascular system

This white paper is the outcome of the seventh UC Davis Cardiovascular Research Symposium on Systems Approach to Understanding Cardiovascular Disease and Arrhythmia. This biannual meeting aims to bring together leading experts in subfields of cardiovascular biomedicine to focus on topics of importance to the field. The theme of the 2022 Symposium was 'Cell Diversity in the Cardiovascular System, cell-autonomous and cell-cell signalling'. Experts in the field contributed their experimental and mathematical modelling perspectives and discussed emerging questions, controversies, and challenges in examining cell and signal diversity, co-ordination and interrelationships involved in cardiovascular function. This paper originates from the topics of formal presentations and informal discussions from the Symposium, which aimed to develop a holistic view of how the multiple cell types in the cardiovascular system integrate to influence cardiovascular function, disease progression and therapeutic strategies. The first section describes the major cell types (e.g. cardiomyocytes, vascular smooth muscle and endothelial cells, fibroblasts, neurons, immune cells, etc.) and the signals involved in cardiovascular function. The second section emphasizes the complexity at the subcellular, cellular and system levels in the context of cardiovascular development, ageing and disease. Finally, the third section surveys the technological innovations that allow the interrogation of this diversity and advancing our understanding of the integrated cardiovascular function and dysfunction.

Singlet Oxygen In Vivo: It Is All about Intensity-Part 2

Recently, we reported induced anoxia as a limiting factor for photodynamic tumor therapy (PDT). This effect occurs in vivo if the amount of generated singlet oxygen that undergoes chemical reactions with cellular components exceeds the local oxygen supply. The amount of generated singlet oxygen depends mainly on photosensitizer (PS) accumulation, efficiency, and illumination intensity. With illumination intensities above a certain threshold, singlet oxygen is limited to the blood vessel and the nearest vicinity; lower intensities allow singlet oxygen generation also in tissue which is a few cell layers away from the vessels. While all experiments so far were limited to light intensities above this threshold, we report experimental results for intensities at both sides of the threshold for the first time, giving proof for the described model. Using time-resolved optical detection in NIR, we demonstrate characteristic, illumination intensity-dependent changes in signal kinetics of singlet oxygen and photosensitizer phosphorescence in vivo. The described analysis allows for better optimization and coordination of PDT drugs and treatment, as well as new diagnostic methods based on gated PS phosphorescence, for which we report a first in vivo feasibility test.

Formulation strategies to provide oxygen-release to contrast local hypoxia for transplanted islets

Islet transplantation refers to the transfusion of healthy islet cells into the diabetic recipients and reconstruction of their endogenous insulin secretion to achieve insulin independence. It is a minimally invasive surgery that holds renewed prospect as a therapeutic method for type 1 diabetes mellitus. However, poor oxygenation in the early post-transplantation period is considered as one of the major causes of islet loss and dysfunction. Due to the metabolism chacteristics, islets required a high supply of oxygen for cell survival while a hypoxia environment would lead to severe islet loss and graft failure. Emerging strategies have been proposed, including providing external oxygen and speeding up revascularization. From the perspective of formulation science, it is feasible and practical to protect transplanted islets by oxygen-release before revascularization as opposed to local hypoxia. In this study, we review the potential formulation strategies that could provide oxygen-release by either delivering external oxygen or triggering localized oxygen generation for transplanted islets.

Application of Polymethylpentene, an Oxygen Permeable Thermoplastic, for Long-Term on-a-Chip Cell Culture and Organ-on-a-Chip Devices

The applicability of a gas-permeable, thermoplastic material polymethylpentene (PMP) was investigated, experimentally and analytically, for organ-on-a-chip (OoC) and long-term on-a-chip cell cultivation applications. Using a sealed culture chamber device fitted with oxygen sensors, we tested and compared PMP to commonly used glass and polydimethylsiloxane (PDMS). We show that PMP and PDMS have comparable performance for oxygen supply during 4 days culture of epithelial (A549) cells with oxygen concentration stabilizing at 16%, compared with glass control where it decreases to 3%. For the first time, transmission light images of cells growing on PMP were obtained, demonstrating that the optical properties of PMP are suitable for non-fluorescent, live cell imaging. Following the combined transmission light imaging and calcein-AM staining, cell adherence, proliferation, morphology, and viability of A549 cells were shown to be similar on PMP and glass coated with poly-L-lysine. In contrast to PDMS, we demonstrate that a film of PMP as thin as 0.125 mm is compatible with high-resolution confocal microscopy due to its excellent optical properties and mechanical stiffness. PMP was also found to be fully compatible with device sterilization, cell fixation, cell permeabilization and fluorescent staining. We envision this material to extend the range of possible microfluidic applications beyond the current state-of-the-art, due to its beneficial physical properties and suitability for prototyping by different methods. The integrated device and measurement methodology demonstrated in this work are transferrable to other cell-based studies and life-sciences applications.

Rapid generation of homogenous tumor spheroid microtissues in a scaffold-free platform for high-throughput screening of a novel combination nanomedicine

Combination nanomedicine is a potent strategy for cancer treatment. Exploiting different mechanisms of action, a novel triple drug delivery system of 5-fluorouracil, curcumin, and piperine co-loaded human serum albumin nanoparticles (5FU-CUR-PIP-HSA-NPs) was developed via the self-assembly method for suppressing breast tumor. Both hydrophobic and hydrophilic drugs were successfully encapsulated in the HSA NPs with a high drug loading efficiency (DLE) of 10%. Successful clinical translation of nanomedicines, however, is a challenging process requiring considerable preclinical in vitro and in vivo animal tests. The aim of this study was to develop a homemade preclinical 3D culture model in the standard 96-well plates in a cost and time-effective novel approach for the rapid generation of homogenous compact tumor spheroids for disease modeling, and anticancer therapeutic/nanomedicine screening. The knowledge of drug screening can be enhanced by employing such a model in a high-throughput manner. Accordingly, to validate the formulated drug delivery system and investigate the cellular uptake and cytotoxicity effect of the nanoformulation, 3D tumor spheroids were employed. The practicality of the nanomedicine system was substantiated in different tests. The in vitro uptake of the NPs into the tight 3D tumor spheroids was facilitated by the semi-spherical shape of the NPs with a proper size and surface charge. 5FU-CUR-PIP-HSA-NPs demonstrated high potency of migration inhibition as a part of successful anti-metastatic therapy as well. The remarkable differences in 2D and 3D cytotoxicities emphasize the importance of employing 3D tumor models as an intermediate step prior to in vivo animal experiments for drug/nanomedicine screening.

Engineering of the microenvironment to accelerate vascular regeneration

Blood vessels are crucial for tissue development, functionality, and homeostasis and are typically a determinant in the progression of healing and regeneration. The tissue microenvironment provides physicochemical cues that affect cellular function, and the study of the microenvironment can be accelerated by the engineering of approaches capable of mimicking various aspects of the microenvironment. In this review, we introduce the major components of the vascular niche and focus on the roles of oxygen and the extracellular matrix (ECM). We demonstrate how vascular engineering approaches enhance our understanding of the microenvironment's impact on the vasculature towards vascular regeneration and describe the current limitations and future directions towards clinical utilization.

The role of mitochondria in pharmacological ascorbate-induced toxicity

At pharmacological levels, ascorbate (P-AscH^-) acts as a pro-oxidant by generating H₂O₂, depleting ATP in sensitive cells leading to cell death. The aim of this study was to determine the role of ATP production by oxidative phosphorylation or glycolysis in mechanisms of resistance to P-AscH^-induced cell death. Pancreatic cancer cells were used to generate ρ⁰ cells by mitochondrial overexpression of the Y147A mutant uracil-N-glycosylase or Herpes Simplex Virus protein. The ρ⁰ phenotype was confirmed by probing for mitochondrial DNA, mitochondrial DNA-encoded cytochrome c oxidase subunit 2, and monitoring the rate of oxygen consumption. In ρ⁰ cells, glycolysis accounted for 100% of ATP production as there was no mitochondrial oxygen consumption. Even though the activities of H₂O₂-removing antioxidant enzymes were similar in both the parental and ρ⁰ clones, P-AscH^- -induced clonogenic cell death in ρ⁰ cells showed more resistance than the parental cell line. In addition, P-AscH^- induced more DNA damage and more consumption of NAD⁺ and greater decreases in the production of ATP in the parental cell line compared to the ρ⁰ cells. Thus, cancer cells that largely use oxidative phosphorylation to generate ATP may be more sensitive to P-AscH^- compared with cells that are glycolysis-dependent.

Towards an In Vitro 3D Model for Photosynthetic Cancer Treatment: A Study of Microalgae and Tumor Cell Interactions

As hypoxic tumors show resistance to several clinical treatments, photosynthetic microorganisms have been recently suggested as a promising safe alternative for oxygenating the tumor microenvironment. The relationship between organisms and the effect microalgae have on tumors is still largely unknown, evidencing the need for a simple yet representative model for studying photosynthetic tumor oxygenation in a reproducible manner. Here, we present a 3D photosynthetic tumor model composed of human melanoma cells and the microalgae Chlamydomonas reinhardtii, both seeded into a collagen scaffold, which allows for the simultaneous study of both cell types. This work focuses on the biocompatibility and cellular interactions of the two cell types, as well as the study of photosynthetic oxygenation of the tumor cells. It is shown that both cell types are biocompatible with one another at cell culture conditions and that a 10:1 ratio of microalgae to cells meets the metabolic requirement of the tumor cells, producing over twice the required amount of oxygen. This 3D tumor model provides an easy-to-use in vitro resource for analyzing the effects of photosynthetically produced oxygen on a tumor microenvironment, thus opening various potential research avenues.

Expansion and differentiation of ex vivo cultured erythroblasts in scalable stirred bioreactors

Transfusion of donor-derived red blood cells (RBCs) is the most common form of cell therapy. Production of transfusion-ready cultured RBCs (cRBCs) is a promising replacement for the current, fully donor-dependent therapy. A single transfusion unit, however, contains 2 × 10¹² RBC, which requires large scale production. Here, we report on the scale-up of cRBC production from static cultures of erythroblasts to 3 L stirred tank bioreactors, and identify the effect of operating conditions on the efficiency of the process. Oxygen requirement of proliferating erythroblasts (0.55-2.01 pg/cell/h) required sparging of air to maintain the dissolved oxygen concentration at the tested setpoint (2.88 mg O₂ /L). Erythroblasts could be cultured at dissolved oxygen concentrations as low as 0.7 O₂ mg/ml without negative impact on proliferation, viability or differentiation dynamics. Stirring speeds of up to 600 rpm supported erythroblast proliferation, while 1800 rpm led to a transient halt in growth and accelerated differentiation followed by a recovery after 5 days of culture. Erythroblasts differentiated in bioreactors, with final enucleation levels and hemoglobin content similar to parallel cultures under static conditions.

Studies on oxygen availability and the creation of natural and artificial oxygen gradients in gelatin-methacryloyl hydrogel 3D cell culture

Three-dimensional (3D) cultivation platforms allow the creation of cell models, which more closely resemble in vivo-like cell behavior. Therefore, 3D cell culture platforms have started to replace conventional two-dimensional (2D) cultivation techniques in many fields. Besides the advantages of 3D culture, there are also some challenges: cultivation in 3D often results in an inhomogeneous microenvironment and therefore unique cultivation conditions for each cell inside the construct. As a result, the analysis and precise control over the singular cell state is limited in 3D. In this work, we address these challenges by exploring ways to monitor oxygen concentrations in gelatin methacryloyl (GelMA) 3D hydrogel culture at the cellular level using hypoxia reporter cells and deep within the construct using a non-invasive optical oxygen sensing spot. We could show that the appearance of oxygen limitations is more prominent in softer GelMA-hydrogels, which enable better cell spreading. Beyond demonstrating novel or space-resolved techniques of visualizing oxygen availability in hydrogel constructs, we also describe a method to create a stable and controlled oxygen gradient throughout the construct using a 3D printed flow-through chamber.

Computational Modeling and Imaging of the Intracellular Oxygen Gradient

Computational modeling can provide a mechanistic and quantitative framework for describing intracellular spatial heterogeneity of solutes such as oxygen partial pressure (pO₂). This study develops and evaluates a finite-element model of oxygen-consuming mitochondrial bioenergetics using the COMSOL Multiphysics program. The model derives steady-state oxygen (O₂) distributions from Fickian diffusion and Michaelis–Menten consumption kinetics in the mitochondria and cytoplasm. Intrinsic model parameters such as diffusivity and maximum consumption rate were estimated from previously published values for isolated and intact mitochondria. The model was compared with experimental data collected for the intracellular and mitochondrial pO₂ levels in human cervical cancer cells (HeLa) in different respiratory states and under different levels of imposed pO₂. Experimental pO₂ gradients were measured using lifetime imaging of a Förster resonance energy transfer (FRET)-based O₂ sensor, Myoglobin-mCherry, which offers in situ real-time and noninvasive measurements of subcellular pO₂ in living cells. On the basis of these results, the model qualitatively predicted (1) the integrated experimental data from mitochondria under diverse experimental conditions, and (2) the impact of changes in one or more mitochondrial processes on overall bioenergetics.