Oxidative stress-alleviating strategies to improve recombinant protein production in CHO cells

Ala-Cys-Cys-Ala dipeptide dimer alleviates problematic cysteine and cystine levels in media formulations and enhances CHO cell growth and metabolism

Cysteine and cystine are essential amino acids present in mammalian cell cultures. While contributing to biomass synthesis, recombinant protein production, and antioxidant defense mechanisms, cysteine poses a major challenge in media formulations owing to its poor stability and oxidation to cystine, a cysteine dimer. Due to its poor solubility, cystine can cause precipitation of feed media, formation of undesired products, and consequently, reduce cysteine bioavailability. In this study, a highly soluble cysteine containing dipeptide dimer, Ala-Cys-Cys-Ala (ACCA), was evaluated as a suitable alternative to cysteine and cystine in CHO cell cultures. Replacing cysteine and cystine in basal medium with ACCA did not sustain cell growth. However, addition of ACCA at 4 mM and 8 mM to basal medium containing cysteine and cystine boosted cell growth up to 15% and 27% in CHO-GS and CHO-K1 batch cell cultures respectively and led to a proportionate increase in IgG titer. 13C-Metabolic flux analysis revealed that supplementation of ACCA reduced glycolytic fluxes by 20% leading to more efficient glucose metabolism in CHO-K1 cells. In fed-batch cultures, ACCA was able to replace cysteine and cystine in feed medium. Furthermore, supplementation of ACCA at high concentrations in basal medium eliminated the need for any cysteine equivalents in feed medium and increased cell densities and viabilities in fed-batch cultures without any significant impact on IgG charge variants. Taken together, this study demonstrates the potential of ACCA to improve CHO cell growth, productivity, and metabolism while also facilitating the formulation of cysteine- and cystine-free feed media. Such alternatives to cysteine and cystine will pave the way for enhanced biomanufacturing by increasing cell densities in culture and extending the storage of highly concentrated feed media as part of achieving intensified bioproduction processes.

Simulation and experimental study of a cold atmospheric pressure plasma and comparison of efficiency in boosting recombinant Endoglucanase II production in Pichia pastoris

Recombinant proteins are essential in various industries, and scientists employ genetic engineering and synthetic biology to enhance the host cell's protein production capacity. Stress response pathways have been found effective in augmenting protein secretion. Cold atmospheric pressure plasma (CAP) can induce oxidative stress and enhance protein production. Previous studies have confirmed the applicability of CAP jets on Phytase and green fluorescent protein (GFP) production in Pichia pastoris hosts. This study investigates the effect of CAP treatment on another valuable recombinant protein, Endoglucanase II (EgII), integrated into the Pichia pastoris genome. The results demonstrated that plasma induction via two different ignition modes: sinusoidal alternating current (AC) and pulsed direct current (DC) for 120, 180, and 240 s has boosted protein secretion without affecting cell growth and viability. The AC-driven jet exhibited a higher percentage increase in secretion, up to 45%. Simulation of plasma function using COMSOL software provided a pattern of electron temperature (Te) and density distribution, which determine the plasma cocktail's chemistry and reactive species production. Furthermore, electron density (ne) and temperature were estimated from the recorded optical spectrum. The difference in electron properties may explain the moderately different impressions on expression capability. However, cell engineering to improve secretion often remains a trial-and-error approach, and improvements are, at least partially, specific to the protein produced.

Catechins prevent monoclonal antibody fragmentation during production via fed-batch culture of Chinese hamster ovary cells

Chinese hamster ovary (CHO) cells are widely used for the industrial production of therapeutic monoclonal antibodies (mAbs). To meet the increasing market demands, high productivity, and quality are required in cell culture. One of the critical attributes of mAbs, from a safety perspective, is mAb fragmentation. However, methods for preventing mAbs fragmentation in CHO cell culture are limited. In this study, we observed that the antibody fragment content increased with increasing titers in fed-batch cultures for all three cell lines expressing recombinant antibodies. Adding copper sulfate to the culture medium further increased the fragment content, suggesting the involvement of reactive oxygen species (ROS) in the fragmentation process. Though antioxidants may be helpful to scavenge ROS, several antioxidants are reported to decrease the productivity of CHO cells. Among the antioxidants examined, we observed that the addition of catechin or (-)-epigallocatechin gallate to the culture medium prevented fragmentation content by about 20% and increased viable cell density and titer by 30% and 10%, respectively. Thus, the addition of catechins or compounds of equivalent function would be beneficial for manufacturing therapeutic mAbs with a balance between high titers and good quality.

Recombinant human fibroblast growth factor 7 obtained from stable Chinese hamster ovary cells enhances wound healing

Although fibroblast growth factor 7 (FGF7) is known to promote wound healing, its mass production poses several challenges and very few studies have assessed the feasibility of producing FGF7 in cell lines such as Chinese hamster ovary (CHO) cells. Therefore, this study sought to produce recombinant FGF7 in large quantities and evaluate its wound healing effect. To this end, the FGF7 gene was transfected into CHO cells and FGF7 production was optimized. The wound healing efficacy of N-glycosylated FGF7 was evaluated in animals on days 7 and 14 post-treatment using collagen patches (CPs), FGF7-only, and CP with FGF7 (CP+FGF7), whereas an untreated group was used as the control. Wound healing was most effective in the CP+FGF7 group. Particularly, on day 7 post-exposure, the CP+FGF7 and FGF7-only groups exhibited the highest expression of hydroxyproline, fibroblast growth factor, vascular endothelial growth factor, and transforming growth factor. Epidermalization in H&E staining showed the same order of healing as hydroxyproline content. Additionally, the CP+FGF7 and FGF7-only group exhibited more notable blood vessel formation on days 7 and 14. In conclusion, the prepared FGF7 was effective in promoting wound healing and CHO cells can be a reliable platform for the mass production of FGF7.

Harnessing metabolic plasticity in CHO cells for enhanced perfusion cultivation

Chinese Hamster Ovary (CHO) cells have rapidly become a cornerstone in biopharmaceutical production. Recently, a reinvigoration of perfusion culture mode in CHO cell cultivation has been observed. However, most cell lines currently in use have been engineered and adapted for fed-batch culture methods, and may not perform optimally under perfusion conditions. To improve the cell's resilience and viability during perfusion culture, we cultured a triple knockout CHO cell line, deficient in three apoptosis related genes BAX, BAK, and BOK in a perfusion system. After 20 days of culture, the cells exhibited a halt in cell proliferation. Interestingly, following this phase of growth arrest, the cells entered a second growth phase. During this phase, the cell numbers nearly doubled, but cell specific productivity decreased. We performed a proteomics investigation, elucidating a distinct correlation between growth arrest and cell cycle arrest and showing an upregulation of the central carbon metabolism and oxidative phosphorylation. The upregulation was partially reverted during the second growth phase, likely caused by intragenerational adaptations to stresses encountered. A phase-dependent response to oxidative stress was noted, indicating glutathione has only a secondary role during cell cycle arrest. Our data provides evidence of metabolic regulation under high cell density culturing conditions and demonstrates that cell growth arrest can be overcome. The acquired insights have the potential to not only enhance our understanding of cellular metabolism but also contribute to the development of superior cell lines for perfusion cultivation.

A strategy of novel molecular hydrogen-producing antioxidative auxiliary system improves virus production in cell bioreactor

In the increasing demand for virus vaccines, large-scale production of safe, efficient, and economical viral antigens has become a significant challenge. High-cell-density manufacturing processes are the most commonly used to produce vaccine antigens and protein drugs. However, the cellular stress response in large-scale cell culture may directly affect host cell growth and metabolism, reducing antigen production and increasing production costs. This study provided a novel strategy of the antioxidant auxiliary system (AAS) to supply molecular hydrogen (H2) into the cell culture media via proton exchange membrane (PEM) electrolysis. Integrated with a high-density cell bioreactor, the AAS aims to alleviate cellular stress response and increase viral vaccine production. In the results, the AAS stably maintained H2 concentration in media even in the high-air exposure tiding cell bioreactor. H2 treatment was shown safe to cell culture and effectively alleviated oxidative stress. In two established virus cultures models, bovine epidemic fever virus (BEFV) and porcine circovirus virus type 2 (PCV-2), were employed to verify the efficacy of AAS. The virus yield was increased by 3.7 and 2.5 folds in BEFV and PCV-2 respectively. In conclusion, the AAS-connected bioreactor effectively alleviated cellular oxidative stress and enhanced virus production in high-density cell culture.

Targeting myostatin using quercetin as a media supplement to improve myogenesis for cultured meat production: An in silico and in vitro study

Cultured meat (CM) is an alternative protein food and is produced by cultivating muscle satellite (stem) cells (MSCs) derived from livestock animals (bovine, chickens, and porcine) through myogenesis leading to generate muscle mass. Myostatin (MSTN) is well well-known negative regulator of myogenesis, and in the present study, in silico screening of natural compounds was performed to identify MSTN inhibitors. Interestingly, quercetin was found to inhibit MSTN (binding energy -7.40 kcal/mol), and this was further validated by a 100 ns molecular dynamics simulation. Quercetin was added to culture media to boost myogenesis, and its potent antioxidant property helped maintain media pH. Furthermore, quercetin increased the myotube thickness and length, increased MSC differentiation, and upregulated the gene and protein expressions of myoblast determination protein 1 (MYOD), Myogenin (MYOG), and Myosin heavy chains (MYH) in vitro. In addition, quercetin inhibited the activities of MSTN, activin receptor type-2B (ACVR2B), and SMAD2 and 3, and thus significantly enhanced MSC differentiation and myotube formation. Overall, this study shows that quercetin might be useful for enhancing large-scale CM production. It is hoped that this study provides a starting point for research in the CM area aimed to enhancing product quality, nutritional values, and the efficacy of large-scale production.

Rosmarinic acid enhances CHO cell productivity and proliferation through activation of the unfolded protein response and the mTOR pathway

Rosmarinic acid (RA) has gained attraction in bioprocessing as a media supplement to improve cellular proliferation and protein production. Here, we observe up to a two-fold increase in antibody production with RA-supplementation, and a concentration-dependent effect of RA on cell proliferation for fed-batch Chinese hamster ovary (CHO) cell cultures. Contrary to previously reported antioxidant activity, RA increased the reactive oxygen species (ROS) levels, stimulated endoplasmic reticulum (ER) stress, activated the unfolded protein response (UPR), and elicited DNA damage. Despite such stressful events, RA appeared to maintained cell health via mammalian target of rapamycin (mTOR) pathway activation; both mTOR complex 1 (mTORC1) and mTOR complex 2 (mTORC2) were stimulated in RA-supplemented cultures. By reversing such mTOR pathway activity through either chemical inhibitor addition or siRNA knockdown of genes regulating the mTORC1 and mTORC2 complexes, antibody production, UPR signaling, and stress-induced DNA damage were reduced. Further, the proliferative effect of RA appeared to be regulated selectively by mTORC2 activation and have reproduced this observation by using the mTORC2 stimulator SC-79. Analogously, knockdown of mTORC2 strongly reduced X-box binding protein 1 (XBP1) splicing, which would be expected to reduce antibody folding and secretion, sugging that reduced mTORC2 would correlate with reduced antibody levels. The crosstalk between mTOR activation and UPR upregulation may thus be related directly to the enhanced productivity. Our results show the importance of the mTOR and UPR pathways in increasing antibody productivity, and suggest that RA supplementation may obviate the need for labor-intensive genetic engineering by directly activating pathways favorable to cell culture performance.

New high-throughput screening method for Chinese hamster ovary cell lines expressing low reduced monoclonal antibody levels: application of a system controlling the gas phase over cell lysates in miniature bioreactors and facilitating multiple sample setup

Interchain disulfide bonds in monoclonal antibodies may be reduced during large-scale mAb production using Chinese hamster ovary (CHO) cells. This reaction lowers the mAb product yield and purity; however, it may be prevented by screening cell lines that are unsusceptible to reduction and using them in mAb production. Antibody reduction susceptibility may be cell line-dependent. To the best of our knowledge, however, an efficient method of screening reduction-unsusceptible CHO cell lines has not been previously reported. Here, we report a novel screening method that can simultaneously detect and identify mAb reduction susceptibility in lysates containing ≤ 48 CHO cell lines. This evaluation system was equally effective and generated similar results at all culture scales, including 250 mL, 3 L, and 1000 L. Furthermore, we discovered that reduction-susceptible cell lines contained higher total intracellular nicotinamide adenine dinucleotide phosphate (NADPH) and NADP+ concentrations than reduction-unsusceptible cell lines, regardless of whether they expressed immunoglobulin (Ig)G4 or IgG1. NADPH or NADP+ supplementation in the lysate of reduction-unsusceptible cells resulted in mAb reduction. Application of the innovative CHO cell line screening approach could mitigate or prevent reductions in large-scale mAb generation from CHO cells.

Discovery and Characterization of an Acid-Labile Serine-Lysine Cross-Link in Antibody High-Molecular-Weight Species Using a Multipronged Mass Spectrometry Approach

Characterizing the cross-links responsible for the covalent high-molecular-weight (HMW) species in therapeutic monoclonal antibodies (mAbs) is of great importance as it not only provides a framework for risk assessment but also offers insights for process improvement. However, owing to the complexity and low abundance, identification of novel and unknown cross-links in mAb products can be very challenging. Here, applying a multipronged MS-based approach, we report the discovery of a novel covalent cross-link formed via an imine bond between lysine and serine residues. In particular, this Ser-Lys cross-link was found to be acid-labile and can be easily overlooked by conventional LC-MS techniques operated at low pH. It is worth noting that although imine-based cross-link has been previously reported in collagen protein cross-linking, this is the first time that a Ser-Lys cross-link has been found in a mAb product that contributes to covalent HMW species formation.

The pathology of oxidative stress-induced autophagy in a chronic rotator cuff enthesis tear

Partial-thickness rotator cuff tears (PTRCTs) are often found in daily orthopedic practice, with most of the tears occurring in middle-aged patients. An anaerobic process and imbalanced oxygenation have been observed in PTRCTs, resulting in oxidative stress. Studies have shown the roles of oxidative stress in autophagy and the potential of unregulated mechanisms causing disturbance in soft tissue healing. This article aims to review literature works and summarize the potential pathology of oxidative stress and unregulated autophagy in the rotator cuff enthesis correlated with chronicity. We collected and reviewed the literature using appropriate keywords, in addition to the manually retrieved literature. Autophagy is a normal mechanism of tissue repair or conversion to energy needed for the repair of rotator cuff tears. However, excessive mechanisms will degenerate the tendon, resulting in an abnormal state. Chronic overloading of the enthesis in PTRCTs and the hypovascular nature of the proximal tendon insertion will lead to hypoxia. The hypoxia state results in oxidative stress. An autophagy mechanism is induced in hypoxia via hypoxia-inducible factors (HIFs) 1/Bcl-2 adenovirus E1B 19-kDa interacting protein (BNIP) 3, releasing beclin-1, which results in autophagy induction. Reactive oxygen species (ROS) accumulation would induce autophagy as the regulator of cell oxidation. Oxidative stress will also remove the mammalian target of rapamycin (mTOR) from the induction complex, causing phosphorylation and initiating autophagy. Hypoxia and endoplasmic reticulum (ER) stress would initiate unfolded protein response (UPR) through protein kinase RNA-like ER kinase (PERK) and activate transcription factor 4, which induces autophagy. Oxidative stress occurring in the hypovascularized chronic rotator cuff tear due to hypoxia and ROS accumulation would result in unregulated autophagy directly or autophagy mediated by HIF-1, mTOR, and UPR. These mechanisms would disrupt enthesis healing.

Rapid detection of varicella-zoster virus based on an immunochromatographic strip

Varicella-zoster virus (VZV) is a highly infectious DNA virus that can cause varicella (chickenpox) and herpes zoster (HZ). A simple, sensitive and specific detection method is desirable for the VZV infection. In this study, VZV gE protein, expressed in CHO cells, was used to immunize BALB/c mice for the generation of monoclonal antibodies (mAbs). For the first time, we developed a colloidal gold-based immunochromatographic strip for rapid detection of VZV using a pair of mAbs against gE protein. The limit of detection (LOD) of the strip was 30 ng mL-1 of purified VZV gE antigen, and it could specifically test VZV without cross-reactivity with Enterovirus 71 (EV-71), Herpes simplex virus 1 (HSV-1) and Herpes simplex virus 2 (HSV-2). The coincidence rate between the strip and commercial real-time PCR diagnostic kit was 100% using vesicle as the clinical sample. Our strip provided a technical support for rapid and specific detection of VZV.

Understanding the effect of temperature downshift on CHO cell growth, antibody titer and product quality by intracellular metabolite profiling and in vivo monitoring of redox state

The strategy of temperature downshift has been widely used in the biopharmaceutical industry to improve antibody production and cell-specific production rate (qp ) with Chinese hamster ovary cells (CHO). However, the mechanism of temperature-induced metabolic rearrangement, especially important intracellular metabolic events, remains poorly understood. In this work, in order to explore the mechanisms of temperature-induced cell metabolism, we systematically assessed the differences in cell growth, antibody expression, and antibody quality between high-producing (HP) and low-producing (LP) CHO cell lines under both constant temperature (37°C) and temperature downshift (37°C→33°C) settings during fed-batch culture. Although the results showed that low-temperature culture during the late phase of exponential cell growth significantly reduced the maximum viable cell density (p < 0.05) and induced cell cycle arrest in the G0/G1 phase, this temperature downshift led to a higher cellular viability and increased antibody titer by 48% and 28% in HP and LP CHO cell cultures, respectively (p < 0.001), and favored antibody quality reflected in reduced charge heterogeneity and molecular size heterogeneity. Combined extra- and intra-cellular metabolomics analyses revealed that temperature downshift significantly downregulated intracellular glycolytic and lipid metabolic pathways while upregulated tricarboxylic acid (TCA) cycle, and particularly featured upregulated glutathione metabolic pathways. Interestingly, all these metabolic pathways were closely associated with the maintenance of intracellular redox state and oxidative stress-alleviating strategies. To experimentally address this, we developed two high-performance fluorescent biosensors, denoted SoNar and iNap1, for real-time monitoring of intracellular nicotinamide adenine dinucleotide/nicotinamide adenine dinucleotide + hydrogen (NAD+ /NADH) ratio and nicotinamide adenine dinucleotide phosphate (NADPH) amount, respectively. Consistent with such metabolic rearrangements, the results showed that temperature downshift decreased the intracellular NAD+ /NADH ratio, which might be ascribed to the re-consumption of lactate, and increased the intracellular NADPH amount (p < 0.01) to scavenge intracellular reactive oxygen species (ROS) induced by the increased metabolic requirements for high-level expression of antibody. Collectively, this study provides a metabolic map of cellular metabolic rearrangement induced by temperature downshift and demonstrates the feasibility of real-time fluorescent biosensors for biological processes, thus potentially providing a new strategy for dynamic optimization of antibody production processes.

RNAs as Sensors of Oxidative Stress in Bacteria

Oxidative stress is an important and pervasive physical stress encountered by all kingdoms of life, including bacteria. In this review, we briefly describe the nature of oxidative stress, highlight well-characterized protein-based sensors (transcription factors) of reactive oxygen species that serve as standards for molecular sensors in oxidative stress, and describe molecular studies that have explored the potential of direct RNA sensitivity to oxidative stress. Finally, we describe the gaps in knowledge of RNA sensors-particularly regarding the chemical modification of RNA nucleobases. RNA sensors are poised to emerge as an essential layer of understanding and regulating dynamic biological pathways in oxidative stress responses in bacteria and, thus, also represent an important frontier of synthetic biology.

Overexpression of SIRT6 alleviates apoptosis and enhances cell viability and monoclonal antibody expression in CHO-K1 cells

BACKGROUND

Chinese hamster ovary (CHO) cells are the most predominantly utilized host for the production of monoclonal antibodies (mAbs) and other complex glycoproteins. A major challenge in the process of CHO cell culture is the occurrence of cell death following different stressful conditions, which hinders the production yield. Engineering genes involved in pathways related to cell death is a remarkable strategy to delay apoptosis, improve cell viability and enhance productivity. SIRT6 is a stress-responsive protein that regulates DNA repair, maintains genome integrity, and is critical for longevity and cell survival in organisms.

METHODS AND RESULTS

In this study, SIRT6 was stably overexpressed in CHO-K1 cells and the impact of its expression on apoptosis related gene expression profile, viability, apoptosis, and mAb productivity was investigated. While a significant increase was observed in Bcl-2 mRNA level, caspase-3 and Bax mRNA levels were decreased in the SIRT6 engineered cells compared to the parental CHO-K1 cells. Moreover, improved cell viability and decreased rate of apoptotic progression was observed in a SIRT6-derived clone in comparision to the CHO-K1 cells during 5 days of batch culture. anti-CD52 IgG1 mAb titers were improved up to 1.7- and 2.8-fold in SIRT6-derived clone during transient and stable expression, respectively.

CONCLUSIONS

This study indicates the positive effects of SIRT6 overexpression on cell viability and anti-CD52 IgG1 mAb expression in CHO-K1 cells. Further studies are needed to examine the potential of SIRT6-engineered host cells for the production of recombinant biotherapeutics in industrial settings.

Cold atmospheric plasma treatment enhances recombinant model protein production in yeast Pichia pastoris

Cold atmospheric pressure plasma (CAP) has been described as a novel technology with expanding applications in biomedicine and biotechnology. In the present study, we provide a mildly stressful condition using non-lethal doses of CAP (120, 180, and 240 s) and evaluate its potential benefits on the recombinant production of a model protein (enhanced green fluorescent protein (eGFP)) in yeast Pichia pastoris. The measured eGFP fluorescence augmented proportional to CAP exposure time. After 240 s treatment with CAP, the measured fluorescent intensity of culture supernatant (after 72 h) and results of real-time PCR (after 24 h) indicated an 84% and 76% increase in activity and related RNA concentration, respectively. Real-time analysis of a list of genes involved in oxidative stress response revealed a significant and durable improvement in their expression at five h and 24 h following CAP exposure. The improvement of the recombinant model protein production may be partly explained by the impact of the RONS on cellular constituents and altering the expression of specific stress genes. In conclusion, using CAP strategy may be considered a valuable strategy to improve recombinant protein production, and deciphering the molecular background mechanism could be inspiring in the reverse metabolic engineering of host cells.

Boost dynamic protocols for producing mammalian biopharmaceuticals with intensified DoE—a practical guide to analyses with OLS and hybrid modeling

Introduction: For the implementation of robust bioprocesses, understanding of temporal cell behavior with respect to relevant inputs is crucial. Intensified Design of Experiments (iDoE) is an efficient tool to assess the joint influence of input parameters by including intra-experimental changes.

Methods: We applied iDoE to the production phase of a monoclonal antibody in a mammalian bioprocess. The multidimensional design space spanned by temperature, dissolved oxygen (DO), timing of change, and growth category was investigated in 12 cultivations. We built ordinary least squares (OLS) and hybrid models (HM) on the iDoE-data, validated them with classical DoE (cDoE)-derived data, and used the models as in silico representation for process optimization.

Results: If the complexity of interactions between changing setpoints of inputs is sufficiently captured during planning and modeling, iDoE proved to be valid for characterizing the mammalian biopharmaceutical production phase. For local behavior and flexible composition of optimization goals, OLS regressions can easily be implemented. To predict global and interconnected dynamics while incorporating mass balances, HM holds potential.

Discussion: iDoE will boost protocols that optimize inputs for different bioprocess phases. The described key aspects of OLS- and HM-based analyses of iDoE-data shall guide future applications during manufacturing.

Comprehensive Analysis of Signal Peptides in Saccharomyces cerevisiae Reveals Features for Efficient Secretion

Signal peptides (SPs) are N-terminus sequences on the nascent polypeptide for protein export or localization delivery, which are essential for maintaining cell function. SPs are also employed as a key element for industrial production of secreted recombinant proteins. Yet, detailed information and rules about SPs and their cellular interactions are still not well understood. Here, systematic bioinformatics analysis and secretion capacity measurement of genome-wide SPs from the model organism Saccharomyces cerevisiae is performed. Several key features of SPs, including region properties, consensus motifs, evolutionary relationships, codon bias, e.g., are successfully revealed. Diverse cell metabolism can be trigged by using different SPs for heterologous protein secretion. Influences on SPs with different properties by chaperones can cause different secretory efficiencies. Protein secretion by the SP NCW2 in SEC72 deletion strain is 10 times than the control. These findings provide insights into the properties and functions of SPs and contribute to both fundamental research and industrial application.

Development of an Indirect ELISA Kit for Rapid Detection of Varicella-Zoster Virus Antibody by Glycoprotein E

Varicella-zoster virus (VZV), a highly infectious agent that causes varicella (chickenpox), can also cause zoster (shingles), a disorder that is frequently associated with severe neuralgia. A reliable serological VZV diagnostic assay would be useful for identifying unprotected individuals and for surveilling post-vaccination immunoprotection status. Toward this goal, VZV membrane glycoprotein E (gE), the immunodominant VZV protein, served as target antigen in an indirect ELISA kit developed here to detect anti-VZV antibodies in clinical samples. For target antigen preparation, Chinese hamster ovary (CHO) cells were modified to express and secrete the VZV gE ectodomain, which was subsequently purified and used as coating antigen in an indirect ELISA. Ultimately, the optimal purified gE coating antigen concentration was determined to be 2 μg.ml⁻¹ and the OD_450nm detection cutoff value was 0.286. The coefficient of variation (CV) of intra-assay and inter-assay were <10 and 15%, respectively. A comparative test of 66 clinical samples showed that the coincidence rate was 93.9% between the indirect ELISA and a commercial varicella-zoster virus IgG ELISA kit. Thus, the indirect ELISA kit developed here may be useful for achieving rapid, sensitive, and specific detection of anti-VZV antibodies.

Chromosomal instability drives convergent and divergent evolution toward advantageous inherited traits in mammalian CHO bioproduction lineages

Genetic instability of Chinese hamster ovary (CHO) cells is implicated in production inconsistency through poorly defined mechanisms. Using a multi-omics approach, we analyzed the variations of CHO lineages derived from CHO-K1 cells. We identify an equilibrium between random genetic variation of the CHO genome and heritable traits driven by culture conditions, selection criteria, and genetic linkage. These inherited changes are associated with the selection pressures related to serum removal, suspension culture transition, protein expression, and secretion. We observed that a haploid reduction of a Chromosome 2 region after serum-free, suspension adaptation, was consistently inherited, suggesting common adaptation mechanisms. Genetic variations also included ∼200 insertions/deletions, ∼1000 single-nucleotide polymorphisms, and ∼300-2000 copy number variations, which were exacerbated after gene editing. In addition, heterochromatic chromosomes were preferentially lost as cells continuously evolved. Together, these observations demonstrate a highly plastic signature for adapted CHO cells and paves the way towards future host cell engineering.

Metabolic Regulation of Hepatitis B Virus Infection in HBV-Transgenic Mice

Hepatitis B virus (HBV) infection is a worldwide health burden. Metabolomics analysis has revealed HBV-induced metabolism dysregulation in liver tissues and hepatocytes. However, as an infectious disease, the tissue-specific landscape of metabolic profiles of HBV infection remains unclear. To fill this gap, we applied untargeted nuclear magnetic resonance (NMR) metabolomic analysis of the heart, liver, spleen, lung, kidney, pancreas, and intestine (duodenum, jejunum, ileum) in HBV-transgenic mice and their wild-type littermates. Strikingly, we found systemic metabolic alterations induced by HBV in liver and extrahepatic organs. Significant changes in metabolites have been observed in most tissues of HBV-transgenic mice, except for ileum. The metabolic changes may provide novel therapeutic targets for the treatment of HBV infection. Moreover, tissue-specific metabolic profiles could speed up the study of HBV induced systemic metabolic reprogramming, which could help follow the progression of HBV infection and explain the underlying pathogenesis.

Hyperosmolality in CHO cell culture: effects on the proteome

Chinese hamster ovary (CHO) cells are the most commonly used host cell lines for therapeutic protein production. Exposure of these cells to highly concentrated feed solution during fed-batch cultivation can lead to a non-physiological increase in osmolality (> 300 mOsm/kg) that affects cell physiology, morphology, and proteome. As addressed in previous studies (and indeed, as recently addressed in our research), hyperosmolalities of up to 545 mOsm/kg force cells to abort proliferation and gradually increase their volume—almost tripling it. At the same time, CHO cells also show a significant hyperosmolality-dependent increase in mitochondrial activity. To gain deeper insight into the molecular mechanisms that are involved in these processes, as detailed in this paper, we performed a comparative quantitative label-free proteome study of hyperosmolality-exposed CHO cells compared with control cells. Our analysis revealed differentially expressed key proteins that mediate mitochondrial activation, oxidative stress amelioration, and cell cycle progression. Our studies also demonstrate a previously unknown effect: the strong regulation of proteins can alter both cell membrane stiffness and permeability. For example, we observed that three types of septins (filamentous proteins that form diffusion barriers in the cell) became strongly up-regulated in response to hyperosmolality in the experimental setup. Overall, these new observations correlate well with recent CHO-based fluxome and transcriptome studies, and reveal additional unknown proteins involved in the response to hyperosmotic pressure by over-concentrated feed in mammalian cells.

Key points

• First-time comparative proteome analysis of CHO cells exposed to over-concentrated feed.

• Discovery of membrane barrier-forming proteins up-regulation under hyperosmolality.

• Description of mitochondrial and protein chaperones activation in treated cells.

Engineering redox sensors into CHO cells enables near real-time quantification of intracellular redox in bioprocesses

The production of biologics that treat complex diseases, such as cancer, autoimmune, and infectious disease, requires careful monitoring and control of cell cultures. While bioprocess optimizations have dramatically improved production yields, a lack of analytical tools has made it challenging to identify accompanying intracellular improvements. Intracellular redox can diminish the growth and productivity of biologics-producing cells and adversely impact product quality profiles yet characterizing redox is challenging due to its complex and highly transient nature. In this study, we integrated a fluorescent thiol-based redox biosensor to monitor intracellular redox in one bisAb- and two mAb-producing clonal cell lines in a 14-day fed-batch bioreactor. We characterized biosensor functionality using three fluorescence measurement techniques and determined sensor oxidation correlates with the intracellular ratio of reduced and oxidized glutathione (GSH:GSSG), an important cellular antioxidant. Our fed-batch bioreactor studies showed that sensor expression minimally affected bioprocess outcomes, including growth, productivity, product quality attributes, or intracellular redox attributes, including mitochondrial reactive oxygen species and total cellular glutathione levels in all cell lines tested. Biosensor measurements taken throughout the culture revealed that the intracellular environment in these cell lines became more reduced throughout the culture, with the exception of a high pH condition which became more oxidized. Our results demonstrate the potential of using biosensors to monitor intracellular changes in near-real-time with minimal process effects, thus potentially improving future bioprocess optimizations. This article is protected by copyright. All rights reserved.

Interaction of Periplasmic Fab Production and Intracellular Redox Balance in Escherichia coli Affects Product Yield

Antibody fragments such as Fab's require the formation of disulfide bonds to achieve a proper folding state. During their recombinant, periplasmic expression in Escherichia coli, oxidative folding is mediated by the DsbA/DsbB system in concert with ubiquinone. Thereby, overexpression of Fab's is linked to the respiratory chain, which is not only immensely important for the cell's energy household but also known as a major source of reactive oxygen species. However, the effects of an increased oxidative folding demand and the consequently required electron flux via ubiquinone on the host cell have not been characterized so far. Here, we show that Fab expression in E. coli BL21(DE3) interfered with the intracellular redox balance, thereby negatively impacting host cell performance. Production of four different model Fab's in lab-scale fed-batch cultivations led to increased oxygen consumption rates and strong cell lysis. An RNA sequencing analysis revealed transcription activation of the oxidative stress-responsive soxS gene in the Fab-producing strains. We attributed this to the accumulation of intracellular superoxide, which was measured using flow cytometry. An exogenously supplemented ubiquinone analogue improved Fab yields up to 82%, indicating that partitioning of the quinone pool between aerobic respiration and oxidative folding limited ubiquinone availability and hence disulfide bond formation capacity. Combined, our results provide a more in-depth understanding of the profound effects that periplasmic Fab expression and in particular disulfide bond formation has on the host cell. Thereby, we show new possibilities to elaborate cell engineering and process strategies for improved host cell fitness and process outcome.

Generation and Characterization of Stable Redox-Reporter Mammalian Cell Lines of Biotechnological Relevance

Cellular functions such as DNA replication and protein translation are influenced by changes in the intracellular redox milieu. Exogenous (i.e., nutrients, deterioration of media components, xenobiotics) and endogenous factors (i.e., metabolism, growth) may alter the redox homeostasis of cells. Thus, monitoring redox changes in real time and in situ is deemed essential for optimizing the production of recombinant proteins. Recently, different redox-sensitive variants of green fluorescent proteins (e.g., rxYFP, roGFP2, and rxmRuby2) have been engineered and proved suitable to detect, in a non-invasive manner, perturbations in the pool of reduced and oxidized glutathione, the major low molecular mass thiol in mammals. In this study, we validate the use of cytosolic rxYFP on two cell lines widely used in biomanufacturing processes, namely, CHO-K1 cells expressing the human granulocyte macrophage colony-stimulating factor (hGM-CSF) and HEK-293. Flow cytometry was selected as the read-out technique for rxYFP signal given its high-throughput and statistical robustness. Growth kinetics and cellular metabolism (glucose consumption, lactate and ammonia production) of the redox reporter cells were comparable to those of the parental cell lines. The hGM-CSF production was not affected by the expression of the biosensor. The redox reporter cell lines showed a sensitive and reversible response to different redox stimuli (reducing and oxidant reagents). Under batch culture conditions, a significant and progressive oxidation of the biosensor occurred when CHO-K1-hGM-CSF cells entered the late-log phase. Medium replenishment restored, albeit partially, the intracellular redox homeostasis. Our study highlights the utility of genetically encoded redox biosensors to guide metabolic engineering or intervention strategies aimed at optimizing cell viability, growth, and productivity.

Small molecule epigenetic modulators for enhancing recombinant antibody production in CHO cell cultures

Small molecule epigenetic modulators that modify epigenetic states in cells are useful tools for regulating gene expression by inducing chromatin remodeling. To identify small molecule epigenetic modulators that enhance recombinant protein expression in CHO cells, we examined eight histone deacetylase inhibitors (iHDACs) and six DNA methyltransferase inhibitors as chemical additives in recombinant CHO (rCHO) cell cultures. Among these, a benzamide-based iHDAC, CI994, was the most effective in increasing monoclonal antibody (mAb) production. Despite suppressing cell growth, the addition of CI994 to mAb-expressing GSR cell cultures at 10 μM resulted in a 2.3-fold increase in maximum mAb concentration due to a 3.0-fold increase in specific mAb productivity (q _mAb ). CI994 increased mAb mRNA levels and histone H3 acetylation in GSR cells, and ChIP-qPCR analysis revealed that CI994 significantly increased the histone H3 acetylation level at the CMV promoter driving mAb gene expression, indicating that chromatin remodeling in the promoter region results in enhanced mAb gene transcription and q _mAb . Similar beneficial effects of CI994 on mAb production were observed in mAb-expressing CS13-1.00 cells. Collectively, our findings indicate that CI994 increases mAb production in rCHO cell cultures by chromatin remodeling resulting from acetylation of histones in the mAb gene promoter. This article is protected by copyright. All rights reserved.

Off-Gas-Based Soft Sensor for Real-Time Monitoring of Biomass and Metabolism in Chinese Hamster Ovary Cell Continuous Processes in Single-Use Bioreactors

In mammalian cell culture, especially in pharmaceutical manufacturing and research, biomass and metabolic monitoring are mandatory for various cell culture process steps to develop and, finally, control bioprocesses. As a common measure for biomass, the viable cell density (VCD) or the viable cell volume (VCV) is widely used. This study highlights, for the first time, the advantages of using VCV instead of VCD as a biomass depiction in combination with an oxygen-uptake- rate (OUR)-based soft sensor for real-time biomass estimation and process control in single-use bioreactor (SUBs) continuous processes with Chinese hamster ovary (CHO) cell lines. We investigated a series of 14 technically similar continuous SUB processes, where the same process conditions but different expressing CHO cell lines were used, with respect to biomass growth and oxygen demand to calibrate our model. In addition, we analyzed the key metabolism of the CHO cells in SUB perfusion processes by exometabolomic approaches, highlighting the importance of cell-specific substrate and metabolite consumption and production rate qS analysis to identify distinct metabolic phases. Cell-specific rates for classical mammalian cell culture key substrates and metabolites in CHO perfusion processes showed a good correlation to qOUR, yet, unexpectedly, not for qGluc. Here, we present the soft-sensoring methodology we developed for qPyr to allow for the real-time approximation of cellular metabolism and usage for subsequent, in-depth process monitoring, characterization and optimization.

Raman based chemometric model development for glycation and glycosylation real time monitoring in a manufacturing scale CHO cell bioreactor process

The Quality by Design (QbD) approach to the production of therapeutic monoclonal antibodies (mAbs) emphasizes an understanding of the production process ensuring product quality is maintained throughout. Current methods for measuring critical quality attributes (CQAs) such as glycation and glycosylation are time and resource intensive, often, only tested offline once per batch process. Process analytical technology (PAT) tools such as Raman spectroscopy combined with chemometric modeling can provide real time measurements process variables and are aligned with the QbD approach. This study utilizes these tools to build partial least squares (PLS) regression models to provide real time monitoring of glycation and glycosylation profiles. In total, seven cell line specific chemometric PLS models; % mono-glycated, % non-glycated, % G0F-GlcNac, % G0, % G0F, % G1F, and % G2F were considered. PLS models were initially developed using small scale data to verify the capability of Raman to measure these CQAs effectively. Accurate PLS model predictions were observed at small scale (5 L). At manufacturing scale (2000 L) some glycosylation models showed higher error, indicating that scale may be a key consideration in glycosylation profile PLS model development. Model robustness was then considered by supplementing models with a single batch of manufacturing scale data. This data addition had a significant impact on the predictive capability of each model, with an improvement of 77.5% in the case of the G2F. The finalized models show the capability of Raman as a PAT tool to deliver real time monitoring of glycation and glycosylation profiles at manufacturing scale.

Untargeted proteomics reveals upregulation of stress response pathways during CHO-based monoclonal antibody manufacturing process leading to disulfide bond reduction

Monoclonal antibody (mAb) interchain disulfide bond reduction can cause a loss of function and negatively impact the therapeutic’s efficacy and safety. Disulfide bond reduction has been observed at various stages during the manufacturing process, including processing of the harvested material. The factors and mechanisms driving this phenomenon are not fully understood. In this study, we examined the host cell proteome as a potential factor affecting the susceptibility of a mAb to disulfide bond reduction in the harvested cell culture fluid (HCCF). We used untargeted liquid-chromatography-mass spectrometry-based proteomics experiments in conjunction with a semi-automated protein identification workflow to systematically compare Chinese hamster ovary (CHO) cell protein abundances between bioreactor conditions that result in reduction-susceptible and reduction-free HCCF. Although the growth profiles and antibody titers of these two bioreactor conditions were indistinguishable, we observed broad differences in host cell protein (HCP) expression. We found significant differences in the abundance of glycolytic enzymes, key protein reductases, and antioxidant defense enzymes. Multivariate analysis of the proteomics data determined that upregulation of stress-inducible endoplasmic reticulum (ER) and other chaperone proteins is a discriminatory characteristic of reduction-susceptible HCP profiles. Overall, these results suggest that stress response pathways activated during bioreactor culture increase the reduction-susceptibility of HCCF. Consequently, these pathways could be valuable targets for optimizing culture conditions to improve protein quality.

Mapping the molecular basis for growth related phenotypes in industrial producer CHO cell lines using differential proteomic analysis

Background

The ability to achieve high peak viable cell density earlier in CHO cell culture and maintain an extended cell viability throughout the production process is highly desirable to increase recombinant protein yields, reduce host cell impurities for downstream processing and reduce the cost of goods. In this study we implemented label-free LC-MS/MS proteomic profiling of IgG4 producing CHO cell lines throughout the duration of the cell culture to identify differentially expressed (DE) proteins and intracellular pathways associated with the high peak viable cell density (VCD) and extended culture VCD phenotypes.

Results

We identified key pathways in DNA replication, mitotic cell cycle and evasion of p53 mediated apoptosis in high peak VCD clonally derived cell lines (CDCLs). ER to Golgi vesicle mediated transport was found to be highly expressed in extended culture VCD CDCLs while networks involving endocytosis and oxidative stress response were significantly downregulated.

Conclusion

This investigation highlights key pathways for targeted engineering to generate desirable CHO cell phenotypes for biotherapeutic production.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12896-021-00704-8.

Redox as a bioprocess parameter: analytical redox quantification in biological therapeutic production

Engineered Chinese hamster ovary (CHO) cells are the most widely utilized cell line for protein-based therapeutics production at industrial scales. Process development strategies which improve production capacity and quality are often implemented without an understanding of underlying intracellular changes. Intracellular redox conditions drive reactions in pathways critical to biologics production, including bioenergetic and biosynthetic pathways, necessitating methods to quantify redox-related changes. Advances in methods for analytical redox quantification presented here, including bioreactor probes, redox-targeted proteomics, genetically encoded redox-sensitive fluorescent proteins, and biochemical assays, are creating new opportunities to characterize the effects of redox in biologics production. Implementing these methods will lead to enhanced media formulations, improved bioprocess strategies, and new cell line engineering targets and ultimately develop redox into an optimizable bioprocess parameter to improve the yield and quality of these lifesaving medicines.

Effect of iron addition on mAb productivity and oxidative stress in Chinese hamster ovary culture

Trace metals play a critical role in the development of culture media used for the production of therapeutic proteins. Iron has been shown to enhance the productivity of monoclonal antibodies during Chinese hamster ovary (CHO) cell culture. However, the redox activity and pro-oxidant behavior of iron may also contribute toward the production of reactive oxygen species (ROS). In this work, we aim to clarify the influence of trace iron by examining the relationship between iron supplementation to culture media, mAb productivity and glycosylation, and oxidative stress interplay within the cell. Specifically, we assessed the impacts of iron supplementation on (a) mAb production and glycosylation; (b) mitochondria-generated free hydroxyl radicals (ROS); (c) the cells ability to store energy during oxidative phosphorylation; and (d) mitochondrial iron concentration. Upon the increase of iron at inoculation, CHO cells maintained a capacity to rebound from iron-induced viability lapses during exponential growth phase and improved mAb productivity and increased mAb galactosylation. Fluorescent labeling of the mitochondrial hydroxyl radical showed enhanced environments of oxidative stress upon iron supplementation. Additional labeling of active mitochondria indicated that, despite the enhanced production of ROS in the mitochondria, mitochondrial membrane potential was minimally impacted. By replicating iron treatments during seed train passaging, the CHO cells were observed to adapt to the shock of iron supplementation prior to inoculation. Results from these experiments demonstrate that CHO cells have the capacity to adapt to enhanced environments of oxidative stress and improve mAb productivity and mAb galactosylation with minimal perturbations to cell culture.

Effect of vitamins and metal ions on productivity and charge heterogeneity of IgG1 expressed in CHO cells

Recombinant monoclonal antibodies have emerged as the most successful modality of biotherapeutics. They are primarily expressed in Chinese Hamster Ovary (CHO) cells. It is well known that post-translational modifications (PTM) contribute significantly to heterogeneity with respect to charge, glycosylation, and size. These attributes in turn impact stability, pharmacokinetics, and pharmacodynamics of the biotherapeutic product. Cell culture media components are known to significantly contribute to both cellular productivity as well as post-translational modifications. Thus, it is highly desirable to understand how media components affect product quality. This study aims to explore the impact of vitamins and metal ions on protein expression and post-translational modifications specifically charge heterogeneity. Biotin, choline chloride, D-calcium pantothenate, folic acid, pyridoxine hydrochloride, thiamine hydrochloride vitamins and Fe, Cu, Mg, Co, Zn, Mn, Ni metal ions were examined in this study. The results indicate that pyridoxine enhances productivity while Zn, Cu, Fe, Mn, and biotin impact charge heterogeneity. While, Fe, Mn and Ni enhance production of the acidic variants, Cu and biotin inhibit it. Zn reduces formation of basic variants while biotin enhances it. The results from this investigation could be used for process control so as to get consistent charge variant profile, in particular for biosimilars.

Expression of Secreted Neutrophil Gelatinase-Associated Lipocalin in 293T Cell Using the Inducible Dual-Function System

Neutrophil gelatinase-associated lipocalin (NGAL) has emerged as a promising biomarker for the early prediction of acute kidney injury (AKI). The production of recombinant NGAL is considered to be necessary for the development of a detection method. This study intended to express the recombinant NGAL protein in 293T cell under the Tet-On inducible system and human serum albumin signal sequence (HSA-SS). The transfection efficiency and protein modulation were assessed by detecting the expression of the enhanced green fluorescent protein (EGFP) and secreted NGAL protein. Both proteins were detected only in the presence of a doxycycline (Dox) inducer. Cell toxicity was not found under any conditions. Moreover, a higher level of soluble NGAL protein in the supernatant secreted by HSA-SS compared with a native signal peptide (Nat-SS) was observed. In summary, this work successfully optimized the conditions for induction of NGAL expression. This system will provide as an efficient strategy to produce other recombinant proteins secreted from a mammalian cell.

Predictive macroscopic modeling of cell growth, metabolism and monoclonal antibody production: Case study of a CHO fed-batch production

We describe a systematic approach to establish predictive models of CHO cell growth, cell metabolism and monoclonal antibody (mAb) formation during biopharmaceutical production. The prediction is based on a combination of an empirical metabolic model connecting extracellular metabolic fluxes with cellular growth and product formation with mixed Monod-inhibition type kinetics that we generalized to every possible external metabolite. We describe the maximum specific growth rate as a function of the integral viable cell density (IVCD). Moreover, we also take into account the accumulation of metabolites in intracellular pools that can influence cell growth. This is possible even without identification and quantification of these metabolites as illustrated with fed-batch cultures of Chinese Hamster Ovary (CHO) cells producing a mAb. The impact of cysteine and tryptophan on cell growth and cell productivity was assessed, and the resulting macroscopic model was successfully used to predict the impact of new, untested feeding strategies on cell growth and mAb production. This model combining piecewise linear relationships between metabolic rates, growth rate and production rate together with Monod-inhibition type models for cell growth did well in predicting cell culture performance in fed-batch cultures even outside the range of experimental data used for establishing the model. It could therefore also successfully be applied for in silico prediction of optimal operating conditions.

A novel hydrogen peroxide evolved CHO host can improve the expression of difficult to express bispecific antibodies

The manufacture of bispecific antibodies by Chinese hamster ovary (CHO) cells is often hindered by lower product yields compared to monoclonal antibodies. Recently, reactive oxygen species have been shown to negatively impact antibody production. By contrast, strategies to boost cellular antioxidant capacity appear to be beneficial for recombinant protein expression. With this in mind, we generated a novel hydrogen peroxide evolved host using directed host cell evolution. Here we demonstrate that this host has heritable resistance to hydrogen peroxide over many generations, displays enhanced antioxidant capacity through the upregulation of several, diverse antioxidant defense genes such as those involved in glutathione synthesis and turnover, and has improved glutathione content. Additionally, we show that this host has significantly improved transfection recovery times, improved growth and viability properties in a fed‐batch production process, and elevated expression of two industrially relevant difficult to express bispecific antibodies compared to unevolved CHO control host cells. These findings demonstrate that host cell evolution represents a powerful methodology for improving specific host cell characteristics that can positively impact the expression of difficult to express biotherapeutics.

CHOK1SV GS-KO SSI expression system: A combination of the Fer1L4 locus and glutamine synthetase selection

There are an ever-increasing number of biopharmaceutical candidates in clinical trials fueling an urgent need to streamline the cell line development process. A critical part of the process is the methodology used to generate and screen candidate cell lines compatible with GMP manufacturing processes. The relatively large amount of clone phenotypic variation observed from conventional "random integration" (RI)-based cell line construction is thought to be the result of a combination of the position variegation effect, genome plasticity and clonal variation. Site-specific integration (SSI) has been used by several groups to temper the influence of the position variegation effect and thus reduce variability in expression of biopharmaceutical candidates. Following on from our previous reports on the application of the Fer1L4 locus for SSI in CHOK1SV (10E9), we have combined this locus and a CHOK1SV glutamine synthetase knockout (GS-KO) host to create an improved expression system. The host, CHOK1SV GS-KO SSI (HD7876), was created by homology directed integration of a targetable landing pad flanked with incompatible Frt sequences in the Fer1L4 gene. The targeting vector contains a promoterless GS expression cassette and monoclonal antibody (mAb) expression cassettes, flanked by Frt sites compatible with equivalent sites flanking the landing pad in the host cell line. SSI clones expressing four antibody candidates, selected in a streamlined cell line development process, have mAb titers which rival RI (1.0-4.5 g/L) and robust expression stability (100% of clones stable through the 50 generation "manufacturing window" which supports commercial manufacturing at 12,000 L bioreactor scale).

Application of metabolic modeling for targeted optimization of high seeding density processes

Process intensification by application of perfusion mode in pre‐stage bioreactors and subsequent inoculation of cell cultures at high seeding densities (HSD) has the potential to meet the increasing requirements of future manufacturing demands. However, process development is currently restrained by a limited understanding of the cell's requirements under these process conditions. The goal of this study was to use extended metabolite analysis and metabolic modeling for targeted optimization of HSD cultivations. The metabolite analysis of HSD N‐stage cultures revealed accumulation of inhibiting metabolites early in the process and flux balance analysis led to the assumption that reactive oxygen species (ROS) were contributing to the fast decrease in cell viability. Based on the metabolic analysis an optimized feeding strategy with lactate and cysteine supplementation was applied, resulting in an increase in antibody titer of up to 47%. Flux balance analysis was further used to elucidate the surprisingly strong synergistic effect of lactate and cysteine, indicating that increased lactate uptake led to reduced ROS formation under these conditions whilst additional cysteine actively reduced ROS via the glutathione pathway. The presented results finally demonstrate the benefit of modeling approaches for process intensification as well as the potential of HSD cultivations for biopharmaceutical manufacturing.

Use of novel cystine analogs to decrease oxidative stress and control product quality

Continuous improvements of cell culture media are required in order to ensure high yield and product quality. However, some components can be instable and lead to detrimental effects on bioprocess performances. l-cysteine is an essential amino acid commonly used in cell culture media. Despite its beneficial effect on recombinant protein production, in some cases, this component can be responsible for product microheterogeneity. In this context, alternative components have to be found in order to reduce product variants while maintaining high productivity. In this study, we have assessed the performance of different cysteine and cystine analogs : N-acetyl-cysteine, s-sulfocysteine, N,N'-diacetyl-l-cystine and the N,N'-diacetyl-l-cystine dimethylester (DACDM). Replacement of cysteine by cystine analogs, and especially DACDM, has shown positive impact on charge variants level and recombinant protein coloration level. Moreover, this molecule contributed to the increase of the intracellular glutathione pool, which suggests a close relationship with the oxidative stress regulation.

Exploration the Mechanism of Doxorubicin-Induced Heart Failure in Rats by Integration of Proteomics and Metabolomics Data

Heart failure is a common systemic disease with high morbidity and mortality worldwide. Doxorubicin (DOX) is a commonly used anthracycline broad-spectrum antitumor antibiotic with strong antitumor effect and definite curative effect. However, cardiotoxicity is the adverse reaction of drug dose cumulative toxicity, but the mechanism is still unclear. In this study, proteomics and metabonomics techniques were used to analyze the tissue and plasma of DOX-induced heart failure (HF) in rats and to clarify the molecular mechanism of the harmful effects of DOX on cardiac metabolism and function in rats from a new point of view. The results showed that a total of 278 proteins with significant changes were identified by quantitative proteomic analysis, of which 118 proteins were significantly upregulated and 160 proteins were significantly downregulated in myocardial tissue. In the metabonomic analysis, 21 biomarkers such as L-octanoylcarnitine, alpha-ketoglutarate, glutamine, creatine, and sphingosine were detected. Correlation analysis showed that DOX-induced HF mainly affected phenylalanine, tyrosine, and tryptophan biosynthesis, D-glutamine and D-glutamate metabolism, phenylalanine metabolism, biosynthesis of unsaturated fatty acids, and other metabolic pathways, suggesting abnormal amino acid metabolism, fatty acid metabolism, and glycerol phospholipid metabolism. It is worth noting that we have found the key upstream target of DOX-induced HF, PTP1B, which inhibits the expression of HIF-1α by inhibiting the phosphorylation of IRS, leading to disorders of fatty acid metabolism and glycolysis, which together with the decrease of Nrf2, SOD, Cytc, and AK4 proteins lead to oxidative stress. Therefore, we think that PTP1B may play an important role in the development of heart failure induced by doxorubicin and can be used as a potential target for the treatment of heart failure.

Effect of Sialic Acid on Mammalian Cell Culture and Protein Expression: A Potential Productivity Enhancer for Biopharmaceutical Cell Culture Processes

Improved productivity of the two most commonly used cell lines in the biopharmaceutical industry, such as human embryonic kidney 293 (HEK293) and Chinese hamster ovary (CHO), could reduce production costs and increase manufacturing capacity. One method for increasing protein productivity is the addition of antioxidants during the cell culture process. In this study, we examined the effect of sialic acid (SA) on one HEK293 cell line and two CHO cell lines. The addition of SA to HEK293 cell led to a higher viable cell density (VCD), viability (Via), and a lower lactate content in the later stage of cultures. Further results showed that SA reduced the reactive oxygen species (ROS), improved cell viability, reduced lactate production, and increased antibody expression by more than 20% in the later stage of the two CHO cell lines cultures. Besides, an optimized dose of SA had no significant effect on acidic variants level aggregation level, N-linked glycosylation pattern, and SA content on antibodies. These results suggest that the addition of SA can improve the productivity of biopharmaceutical cell culture processes.

Applications of small molecules in modulating productivity and product quality of recombinant proteins produced using cell cultures

Mammalian cell cultures have been used extensively for production of recombinant protein therapeutics such as monoclonal antibodies, fusion proteins and enzymes for decades. Small molecules have been investigated as media supplements to improve process productivity and reduce cost of goods. Those chemicals can lead to significant yield improvement through different mechanisms such as cell cycle modulation, cellular redox regulation, etc. In addition to productivity, small molecules have also been routinely used to regulate post-translational modifications of recombinant proteins. This review summarizes key applications of small molecules in protein productivity improvement and product quality control.

Chlorella vulgaris Extract as a Serum Replacement That Enhances Mammalian Cell Growth and Protein Expression

The global cell culture market is experiencing significant growth due to the rapid advancement in antibody-based and cell-based therapies. Both rely on the capacity of different living factories, namely prokaryotic and eukaryotic cells, plants or animals for reliable and mass production. The ability to improve production yield is of important concern. Among many strategies pursued, optimizing the complex nutritional requirements for cell growth and protein production has been frequently performed via culture media component titration and serum replacement. The addition of specific ingredients into culture media to modulate host cells’ metabolism has also recently been explored. In this study, we examined the use of extracted bioactive components of the microalgae Chlorella vulgaris, termed chlorella growth factor (CGF), as a cell culture additive for serum replacement and protein expression induction. We first established a chemical fingerprint of CGF using ultraviolet-visible spectroscopy and liquid chromatography-mass spectrometry and evaluated its ability to enhance cell proliferation in mammalian host cells. CGF successfully promoted the growth of Chinese hamster ovary (CHO) and mesenchymal stem cells (MSC), in both 2D and 3D cell cultures under reduced serum conditions for up to 21 days. In addition, CGF preserved cell functions as evident by an increase in protein expression in CHO cells and the maintenance of stem cell phenotype in MSC. Taken together, our results suggest that CGF is a viable culture media additive and growth matrix component, with wide ranging applications in biotechnology and tissue engineering.

The Gut Microbiota and Oxidative Stress in Autism Spectrum Disorders (ASD)

Autism spectrum disorders (ASDs) are a kind of neurodevelopmental disorder with rapidly increasing morbidity. In recent years, many studies have proposed a possible link between ASD and multiple environmental as well as genetic risk factors; nevertheless, recent studies have still failed to identify the specific pathogenesis. An analysis of the literature showed that oxidative stress and redox imbalance caused by high levels of reactive oxygen species (ROS) are thought to be integral parts of ASD pathophysiology. On the one hand, this review aims to elucidate the communications between oxidative stress, as a risk factor, and ASD. As such, there is also evidence to suggest that early assessment and treatment of antioxidant status are likely to result in improved long-term prognosis by disturbing oxidative stress in the brain to avoid additional irreversible brain damage. Accordingly, we will also discuss the possibility of novel therapies regarding oxidative stress as a target according to recent literature. On the other hand, this review suggests a definite relationship between ASD and an unbalanced gastrointestinal tract (GIT) microbiota (i.e., GIT dysbiosis). A variety of studies have concluded that the intestinal microbiota influences many aspects of human health, including metabolism, the immune and nervous systems, and the mucosal barrier. Additionally, the oxidative stress and GIT dysfunction in autistic children have both been reported to be related to mitochondrial dysfunction. What is the connection between them? Moreover, specific changes in the GIT microbiota are clearly observed in most autistic children, and the related mechanisms and the connection among ASD, the GIT microbiota, and oxidative stress are also discussed, providing a theory and molecular strategies for clinical practice as well as further studies.

Oxidative stress-alleviating strategies to improve recombinant protein production in CHO cells

Large scale biopharmaceutical production of biologics relies on the overexpression of foreign proteins by cells cultivated in stirred tank bioreactors. It is well recognized and documented fact that protein overexpression may impact host cell metabolism and that factors associated with large scale culture, such as the hydrodynamic forces and inhomogeneities within the bioreactors, may promote cellular stress. The metabolic adaptations required to support the high‐level expression of recombinant proteins include increased energy production and improved secretory capacity, which, in turn, can lead to a rise of reactive oxygen species (ROS) generated through the respiration metabolism and the interaction with media components. Oxidative stress is defined as the imbalance between the production of free radicals and the antioxidant response within the cells. Accumulation of intracellular ROS can interfere with the cellular activities and exert cytotoxic effects via the alternation of cellular components. In this context, strategies aiming to alleviate oxidative stress generated during the culture have been developed to improve cell growth, productivity, and reduce product microheterogeneity. In this review, we present a summary of the different approaches used to decrease the oxidative stress in Chinese hamster ovary cells and highlight media development and cell engineering as the main pathways through which ROS levels may be kept under control.