Dissolved oxygen concentration in the medium during cell culture: Defects and improvements

Cloning, Expression and Characterization of an Alginate Lyase in Bacillus subtilis WB600

The aim of this study was to further broaden the heterologous expression of alginate lyase from Vibrio alginolyticus in a Bacillus subtilis expression vector. A B. subtilis WB600/pP43NMK-alg62 strain was constructed. (NH4)2SO4 precipitation and Ni-affinity chromatography were performed to purify the enzyme. We then characterized the enzyme. Its molecular weight was 57.64 kDa, and it worked optimally at 30 °C with a pH of 8.0. Ca2+ markedly enhanced the enzymatic activity of Alg62 while Cu2+ and Ni2+ inhibited its activity. Alg62 had a wide range of substrate specificity, showing high activity toward sodium alginate and polyG. Following optimization of the fermentation process, the optimal conditions for the recombinant expression of Alg62 were as follows: temperature of 37 °C, pH of 7.0, medium consisting of glycerol 15 g/L, yeast powder 25 g/L and K+ 1.5 mmol/L. At these optimal conditions, enzyme activity reached 318.21 U/mL, which was 1.54 times higher than the initial enzyme activity.

O2-sensitive microcavity arrays: A new platform for oxygen measurements in 3D cell cultures

Oxygen concentration plays a crucial role in (3D) cell culture. However, the oxygen content in vitro is usually not comparable to the in vivo situation, which is partly due to the fact that most experiments are performed under ambient atmosphere supplemented with 5% CO₂, which can lead to hyperoxia. Cultivation under physiological conditions is necessary, but also fails to have suitable measurement methods, especially in 3D cell culture. Current oxygen measurement methods rely on global oxygen measurements (dish or well) and can only be performed in 2D cultures. In this paper, we describe a system that allows the determination of oxygen in 3D cell culture, especially in the microenvironment of single spheroids/organoids. For this purpose, microthermoforming was used to generate microcavity arrays from oxygen-sensitive polymer films. In these oxygen-sensitive microcavity arrays (sensor arrays), spheroids cannot only be generated but also cultivated further. In initial experiments we could show that the system is able to perform mitochondrial stress tests in spheroid cultures to characterize mitochondrial respiration in 3D. Thus, with the help of sensor arrays, it is possible to determine oxygen label-free and in real-time in the immediate microenvironment of spheroid cultures for the first time.

Practical Considerations of Dissolved Oxygen Levels for Platelet Function under Hypoxia

Investigating human platelet function in low-oxygen environments is important in multiple settings, including hypobaric hypoxia (e.g., high altitude), sea level hypoxia-related disease, and thrombus stability. These studies often involve drawing blood from which platelets are isolated and analysed at atmospheric conditions or re-exposed to low oxygen levels in hypoxia chambers before testing. However, it remains unknown how the in vitro handling of the samples itself changes their dissolved oxygen concentration, which might affect platelet function and experimental results. Here, we prepared healthy donor platelet-rich plasma and washed platelet (WP) suspensions and exposed them to 2% oxygen. We found that the use of hypoxia pre-equilibrated tubes, higher platelet concentrations (>2 × 10⁸/mL versus 2 × 10⁷/mL), smaller volumes (600 µL versus 3 mL), and presence of plasma reduced the time for samples to reach 2% oxygen. Notably, oxygen levels decreased below 2% in most suspensions, but also in WP maintained at atmospheric 21% oxygen. Additionally, platelet spreading on fibrinogen was decreased when using hypoxic fibrinogen-coated culture plates regardless of the oxygen percentage (2% or 21%) in which platelet incubation took place. Thus, sample handling and experimental conditions should be carefully monitored in platelet-hypoxia studies as they might compromise results interpretation and comparison across studies.

Rapid Evaluation of Novel Therapeutic Strategies Using a 3D Collagen-Based Tissue-Like Model

2D cell cultures are commonly used to rapidly evaluate the therapeutic potential of various treatments on living cells. However, the effects of the extracellular matrix (ECM) including the 3D arrangement of cells and the complex physiology of native environment are missing, which makes these models far from in vivo conditions. 3D cell models have emerged in preclinical studies to simulate the impact of the ECM and partially bridge the gap between monolayer cultures and in vivo tissues. To date, the difficulty to handle the existing 3D models, the cost of their production and their poor reproducibility have hindered their use. Here, we present a reproducible and commercially available "3D cell collagen-based model" (3D-CCM) that allows to study the influence of the matrix on nanoagent uptake and radiation effects. The cell density in these samples is homogeneous. The oxygen concentration in the 3D-CCM is tunable, which opens the opportunity to investigate hypoxic effects. In addition, thanks to the intrinsic properties of the collagen, the second harmonic imaging microscopy may be used to probe the whole volume and visualize living cells in real-time. Thus, the architecture and composition of 3D-CCMs as well as the impact of various therapeutic strategies on cells embedded in the ECM is observed directly. Moreover, the disaggregation of the collagen matrix allows recovering of cells without damaging them. It is a major advantage that makes possible single cell analysis and quantification of treatment effects using clonogenic assay. In this work, 3D-CCMs were used to evaluate the correlative efficacies of nanodrug exposure and medical radiation on cells contained in a tumor like sample. A comparison with monolayer cell cultures was performed showing the advantageous outcome and the higher potential of 3D-CCMs. This cheap and easy to handle approach is more ethical than in vivo experiments, thus, giving a fast evaluation of cellular responses to various treatments.

Modeling the effect of oxygen on the chemical stage of water radiolysis using GPU-based microscopic Monte Carlo simulations, with an application in FLASH radiotherapy

Oxygen plays a critical role in determining the initial DNA damages induced by ionizing radiation. It is important to mechanistically model the oxygen effect in the water radiolysis process. However, due to the computational costs from the many body interaction problem, oxygen is often ignored or treated as a constant continuum radiolysis-scavenger background in the simulations using common microscopic Monte Carlo tools. In this work, we reported our recent progress on the modeling of the chemical stage of the water radiolysis with an explicit consideration of the oxygen effect, based upon our initial development of an open-source graphical processing unit (GPU)-based MC simulation tool, gMicroMC. The inclusion of oxygen mainly reduces the yields of [Formula: see text] and [Formula: see text] chemical radicals, turning them into highly toxic [Formula: see text] and [Formula: see text] species. To demonstrate the practical value of gMicroMC in large scale simulation problems, we applied the oxygen-simulation-enabled gMicroMC to compute the yields of chemical radicals under a high instantaneous dose rate [Formula: see text] to study the oxygen depletion hypothesis in FLASH radiotherapy. A decreased oxygen consumption rate (OCR) was found associated with a reduced initial oxygen concentration level due to reduced probabilities of reactions. With respect to dose rate, for the oxygen concentration of 21% and electron energy of 4.5 [Formula: see text], OCR remained approximately constant (∼0.22 [Formula: see text]) for [Formula: see text]'s of [Formula: see text], [Formula: see text] and reduced to 0.19 [Formula: see text] at [Formula: see text], because the increased dose rate improved the mutual reaction frequencies among radicals, hence reducing their reactions with oxygen. We computed the time evolution of oxygen concentration under the FLASH irradiation setups. At the dose rate of [Formula: see text] and initial oxygen concentrations from 0.01% to 21%, the oxygen is unlikely to be fully depleted with an accumulative dose of 30 Gy, which is a typical dose used in FLASH experiments. The computational efficiency of gMicroMC when considering oxygen molecules in the chemical stage was evaluated through benchmark work to GEANT4-DNA with simulating an equivalent number of radicals. With an initial oxygen concentration of 3% (∼10⁵ molecules), a speedup factor of 1228 was achieved for gMicroMC on a single GPU card when comparing with GEANT4-DNA on a single CPU.

Proteomics analysis of human intestinal organoids during hypoxia and reoxygenation as a model to study ischemia-reperfusion injury

Intestinal ischemia-reperfusion (IR) injury is associated with high mortality rates, which have not improved in the past decades despite advanced insight in its pathophysiology using in vivo animal and human models. The inability to translate previous findings to effective therapies emphasizes the need for a physiologically relevant in vitro model to thoroughly investigate mechanisms of IR-induced epithelial injury and test potential therapies. In this study, we demonstrate the use of human small intestinal organoids to model IR injury by exposing organoids to hypoxia and reoxygenation (HR). A mass-spectrometry-based proteomics approach was applied to characterize organoid differentiation and decipher protein dynamics and molecular mechanisms of IR injury in crypt-like and villus-like human intestinal organoids. We showed successful separation of organoids exhibiting a crypt-like proliferative phenotype, and organoids exhibiting a villus-like phenotype, enriched for enterocytes and goblet cells. Functional enrichment analysis of significantly changing proteins during HR revealed that processes related to mitochondrial metabolism and organization, other metabolic processes, and the immune response were altered in both organoid phenotypes. Changes in protein metabolism, as well as mitophagy pathway and protection against oxidative stress were more pronounced in crypt-like organoids, whereas cellular stress and cell death associated protein changes were more pronounced in villus-like organoids. Profile analysis highlighted several interesting proteins showing a consistent temporal profile during HR in organoids from different origin, such as NDRG1, SDF4 or DMBT1. This study demonstrates that the HR response in human intestinal organoids recapitulates properties of the in vivo IR response. Our findings provide a framework for further investigations to elucidate underlying mechanisms of IR injury in crypt and/or villus separately, and a model to test therapeutics to prevent IR injury.

Effect of increased oxygen availability and astaxanthin supplementation on the growth, maturation and developmental competence of bovine oocytes derived from early antral follicles

In vitro growth (IVG) culture of bovine oocyte-cumulus-granulosa complexes (OCGCs) is generally carried out for 12 or 14 days using conventional gas impermeable culture devices. The culture duration may be longer compared to follicular development in vivo. During follicular development, follicles receive oxygen from micro vessels; however, oxygen supply is limited under the culture using conventional gas impermeable devices. The purpose of this study was to investigate the effect of increasing dissolved oxygen availability using a gas permeable (GP) culture device with or without antioxidant (astaxanthin, Ax) supplementation on 8-day IVG culture systems for bovine OCGCs derived from early antral follicles. We cultured OCGCs in GP, GP supplemented with Ax (GP + Ax), and a conventional gas impermeable device (control) for 8 or 12 days. OCGC viability were significantly higher when cultured for 8 days than 12 days (p < 0.001) in all culture condition, but significant difference was not observed between groups (p > 0.05). Antrum formation rates of OCGCs were higher after 12 days than 8 days of culture in all culture condition (p < 0.001) and were significantly higher in the control than GP groups regardless of Ax supplementation (p < 0.05). Oocyte diameters were similar among day-8 GP + Ax, day-8 control and day-12 control groups (p > 0.05). Nuclear maturation rates of oocytes grown in vitro for 8 days were significantly higher in the GP + Ax group than in the control and the GP groups (p < 0.05) and similar to oocytes grown for 12 days regardless of the culture conditions (p > 0.05). The generation of reactive oxygen species in OCGCs on day 8 of IVG culture was significantly lower in the GP + Ax group than those of the GP and control groups (p < 0.05). IVG oocytes after eight days of culture developed into blastocysts, and the cleavage and blastocyst rates were similar in all treatment groups. However, in vivo-grown oocytes had significantly higher (p < 0.05) cleavage and blastocyst rates than the IVG oocytes in all groups. The present study demonstrates that increased oxygen availability using a GP culture device with Ax supplementation promotes oocyte growth and maturation competence but inhibits proliferation of granulosa cells and antrum formation compared with a conventional gas impermeable culture device, and that OCGCs can attain developmental competence after 8 days of IVG culture.

In Vitro Anti-Prostate Cancer Activity of Two Ebselen Analogues

Scientific research has been underway for decades in order to develop an effective anticancer drug, and it has become crucial to find a novel and effective chemotherapeutics in the case of prostate cancer treatment. Ebselen derivatives have been shown to possess a variety of biological activities, including cytostatic and cytotoxic action against tumor cells. In this study, the cytotoxic effect and anticancer mechanism of action of two organoselenium compounds— (N-allyl-1,2-benzisoselenazol-3(2H)-one (N-allyl-BS) and N-(3-methylbutyl)-1,2-benzisoselenazol-3(2H)-one) (N-(3-mb)-BS)—were investigated on two phenotypically different prostate cancer cell lines DU 145 and PC-3. The influence of analyzed compounds on the viability parameter was also assessed on normal prostate cell line PNT1A. The results showed that both organoselenium compounds (OSCs) efficiently inhibited cancer cell proliferation, whereas normal PNT1A cells were less sensitive to the analazyed ebselen analouges. Both OSCs induced G2/M cell cycle arrest and prompted cell death through apoptosis. The detection of cleaved Poly (ADP-ribose) Polymerase (PARP) confirmed this. In addition, N-allyl-BS and N-(3-m)-b-BS increased the level of reactive oxygen species (ROS) formation, however only N-allyl-BS induced DNA damage. Based on our data, we assume that OSCs’ anticancer action can be associated with oxidative stress induction and inactivation of the Akt- dependent signalling pathway. In conclusion, our data demonstrate that ebselen derivatives showed strong cytotoxic efficiency towards prostate cancer cells and may be elucidated as a novel, potent anticancer agent.

Enhancement of pyruvic acid production in Candida glabrata by engineering hypoxia-inducible factor 1

Dissolved oxygen (DO) supply plays essential roles in microbial organic acid production. Candida glabrata, as a dominant strain for producing pyruvic acid, principally converts glucose to pyruvic acid through glycolysis. However, this process relies excessively on high extracellular DO content. In this study, in combination with specific motif analysis of gene promoters, hypoxia-inducible factor 1 (HIF1) was engineered to improve the transcription level of some enzymes related to pyruvic acid synthesis under low DO level and directly led to increased pyruvic acid production and glycolysis efficiency. Moreover, the intracellular stability of HIF1 was further optimized from different aspects to maximize pyruvic acid accumulation. Finally, the pyruvic acid titer in a 5-L batch bioreactor with 10% DO level reached 53.1 g/L. As pyruvic acid is involved in the biosynthesis of various products, these findings suggest that HIF1-enabled regulation method has significant potential for increasing the synthesis of other chemicals in microorganisms.

A microfluidic-based lid device for conventional cell culture dishes to automatically control oxygen level

Most conventional hypoxic cell culture systems undergo reoxygenation during experimental manipulations, resulting in undesirable effects including the reduction of cell viability. A lid device was developed herein for conventional cell culture dishes to resolve this limitation. The integration of multilayered microfluidic channels inside a thin membrane was designed to prevent the reoxygenation caused by reagent infusion and automatically control the oxygen level. The experimental data clearly show the reducibility of the dissolved oxygen in the infusing reagent and the controllability of the oxygen level inside the dish. The feasibility of the device for hypoxia studies was confirmed by HIF-1α experiments. Therefore, the device could be used as a compact and convenient hypoxic cell culture system to prevent reoxygenation-related issues.

Comparative proteomic analysis unravels a role for EsrB in the regulation of reactive oxygen species stress responses in Edwardsiella piscicida

As a leading pathogen, Edwardsiella piscicida can cause hemorrhagic septicemia in fish and gastro-intestinal infections in humans. The two-component regulatory system EsrA-EsrB plays essential roles in pathogenesis through the type III and type VI secretion systems, and hemolysin production in E. piscicida It is unclear whether other virulence- or stress response-associated genes are regulated by EsrA-EsrB. In this study, the proteomes of wild-type E. piscicida EIB202 and esrB mutant strains were compared to reveal EsrB regulon components after growth in Luria-Bertani broth (LB). Overall, the expression levels of nine genes exhibited significant changes, and five of them required the presence of EsrB, while others exhibited higher levels in the esrB mutant. The diverse functions of these proteins were identified, including amino acid metabolism, oxidative stress defense and energy production. Interestingly, superoxidase dismutase and thiol peroxidase were the most significantly down-regulated by EsrB. Furthermore, other reported reactive oxygen species (ROS) resistance-related genes were also down-regulated by EsrB as revealed by quantitative real-time. Compared with the wild-type and the complement strain esrB⁺, ΔesrB displayed a significantly enhanced ROS resistance. These results demonstrated that EsrB plays important roles in the ROS resistance pathway in E. piscicida grown in LB conditions.