Evaluation of insulin-mimetic trace metals as insulin replacements in mammalian cell cultures

Dietary sucrose determines the regulatory activity of lithium on gene expression and lifespan in Drosophila melanogaster

The amount of dietary sugars and the administration of lithium both impact the lifespan of the fruit fly Drosophila melanogaster. It is noteworthy that lithium is attributed with insulin-like activity as it stimulates protein kinase B/Akt and suppresses the activity of glycogen synthase kinase-3 (GSK-3). However, its interaction with dietary sugar has largely remained unexplored. Therefore, we investigated the effects of lithium supplementation on known lithium-sensitive parameters in fruit flies, such as lifespan, body composition, GSK-3 phosphorylation, and the transcriptome, while varying the dietary sugar concentration. For all these parameters, we observed that the efficacy of lithium was significantly influenced by the sucrose content in the diet. Overall, we found that lithium was most effective in enhancing longevity and altering body composition when added to a low-sucrose diet. Whole-body RNA sequencing revealed a remarkably similar transcriptional response when either increasing dietary sucrose from 1% to 10% or adding 1 mM LiCl to a 1% sucrose diet, characterized by a substantial overlap of nearly 500 differentially expressed genes. Hence, dietary sugar supply is suggested as a key factor in understanding lithium bioactivity, which could hold relevance for its therapeutic applications.

Dietary lithium stimulates female fecundity in Drosophila melanogaster

The trace element lithium exerts a versatile bioactivity in humans, to some extend overlapping with in vivo findings in the model organism Drosophila melanogaster. A potentially essential function of lithium in reproduction has been suggested since the 1980s and multiple studies have since been published postulating a regulatory role of lithium in female gametogenesis. However, the impact of lithium on fruit fly egg production has not been at the center of attention to date. In the present study, we report that dietary lithium (0.1-5.0 mM LiCl) substantially improved life time egg production in D. melanogaster w1118 females, with a maximum increase of plus 45% when supplementing 1.0 mM LiCl. This phenomenon was not observed in the insulin receptor mutant InRE19, indicating a potential involvement of insulin-like signaling in the lithium-mediated fecundity boost. Analysis of the whole-body and ovarian transcriptome revealed that dietary lithium affects the mRNA levels of genes encoding proteins related to processes of follicular maturation. To the best of our knowledge, this is the first report on dietary lithium acting as an in vivo fecundity stimulant in D. melanogaster, further supporting the suggested benefit of the trace element in female reproduction.

A new animal product free defined medium for 2D and 3D culturing of normal and cancer cells to study cell proliferation and migration as well as dose response to chemical treatment

Cell culturing methods are increasingly used to reduce and replace the use of live animals in biomedical research and chemical toxicity testing. Although live animals are avoided when using cell culturing methods, they often contain animal-derived components of which one of the most commonly used is foetal bovine serum (FBS). FBS is added to cell culture media among other supplements to support cell attachment/spreading and cell proliferation. The safety, batch-to-batch variation, and ethical problems with FBS are acknowledged and therefore world-wide efforts are ongoing to produce FBS free media. Here, we present the composition of a new defined medium with only human proteins either recombinant or derived from human tissues. This defined medium supports long-term culturing/routine culturing of normal cells and of cancer cells, and can be used for freezing and thawing of cells, i.e. for cell banking. Here, we show for our defined medium, growth curves and dose response curves of cells grown in two and three dimensions, and applications such as cell migration. Cell morphology was studied in real time by phase contrast and phase holographic microscopy time-lapse imaging. The cell lines used are human cancer-associated fibroblasts, keratinocytes, breast cancer JIMT-1 and MDA-MB-231 cells, colon cancer CaCo-2 cells, and pancreatic cancer MiaPaCa-2 cells as well as the mouse L929 cell line. In conclusion, we present the composition of a defined medium without animal-derived products which can be used for routine culturing and in experimental settings for normal cells and for cancer cells, i.e. our defined medium provides a leap towards a universal animal product free cell culture medium.

Increased recombinant adeno-associated virus production by HEK293 cells using small molecule chemical additives

Recombinant adeno-associated virus (rAAV) has established itself as a highly efficacious gene delivery vector with a well characterised safety profile allowing broad clinical application. Recent successes in rAAV-mediated gene therapy clinical trials will continue to drive demand for improved rAAV production processes to reduce costs. Here, we demonstrate that small molecule bioactive chemical additives can significantly increase recombinant AAV vector production by human embryonic kidney (HEK) cells up to three-fold. Nocodazole (an anti-mitotic agent) and M344 (a selective histone deacetylase inhibitor) were identified as positive regulators of rAAV8 genome titre in a microplate screening assay. Addition of nocodazole to triple-transfected HEK293 suspension cells producing rAAV arrested cells in G2/M phase, increased average cell volume and reduced viable cell density relative to untreated rAAV producing cells at harvest. Final crude genome vector titre from nocodazole treated cultures was >2-fold higher compared to non-treated cultures. Further investigation showed nocodazole addition to cultures to be time critical. Genome titre improvement was found to be scalable and serotype independent across two distinct rAAV serotypes, rAAV8 and rAAV9. Furthermore, a combination of M344 and nocodazole produced a positive additive effect on rAAV8 genome titre, resulting in a three-fold increase in genome titre compared to untreated cells.

Establishment of a Suspension MDBK Cell Line in Serum-Free Medium for Production of Bovine Alphaherpesvirus-1

The Madin–Darby bovine kidney (MDBK) cell line is currently used for the production of bovine alphaherpesvirus-1 (BoHV-1) vaccine. For the purpose of vaccine manufacturing, suspension cells are preferred over adherent ones due to simplified sub-cultivation and an easier scale-up process, both of which could significantly reduce production cost. This study aimed to establish a procedure for the culture of BoHV-1 in the suspended MDBK cell line in serum-free medium. We screened several commercially available serum-free media and chose ST503 for subsequent experiments. We successfully adapted the adherent MDBK cells to suspended growth in ST503 in the absence of serum. The maximum density of suspension-adapted MDBK cells could reach 2.5 × 10⁷ cells/mL in ST503 medium with optimal conditions. The average size of suspension-adapted cells increased to 18 ± 1 µm from 16 ± 1 µm. Moreover, we examined tumorigenicity of the suspended cells and found no sign of tumorigenicity post adaptation. Next, we developed a protocol for the culture of BoHV-1 in the cell line described above and found that ultrasonic treatment could facilitate virus release and enhance virus yield by 11-fold, with the virus titer reaching 8.0 ± 0.2 log₁₀TCID₅₀/mL. Most importantly, the prototype inactivated BoHV-1 vaccine we generated using the suspension cultures of MDBK cells induced neutralizing antibodies to a titer comparable to that of the commercial inactivated BoHV-1 vaccine. Overall, we established and optimized a protocol for the production of inactivated BoHV-1 vaccine in MDBK cells adapted for suspension culture, which provides insights for future large-scale manufacturing of BoHV-1 vaccine.

Quantifying the impact of cell culture media on CHO cell growth and protein production

In recombinant protein production, cell culture media development and optimization is typically seen as a useful strategy to increase titer and cell density, reduce by-products, as well as improve product quality (with cell density and titer often serving as the primary reported outcome of media studies). However, despite the large number of media optimization studies, there have been few attempts to comprehensively assess the overall effectiveness of media additives. The aim of this review is therefore both to document published media optimization studies over the last twenty years (in the context of Chinese hamster ovary cell recombinant production) and quantitatively estimate the impact of this media optimization on cell culture performance. In considering 78 studies, we have identified 238 unique media components that have been supplemented over the last 20 years. Among these additives, trace elements stood out as having a positive impact on cell density while nucleotides show potential for increasing titer, with commercial supplements benefiting both. However, we also identified that the impact of specific additives is far more variable than often perceived. With relatively few media studies considering multiple cell lines or multiple basal media, teasing out consistent and general trends becomes a considerable challenge. By extracting cell density and titer values from all of the reviewed studies, we were able to build a mixed-effect model capable of estimating the relative impact of additives, cell line, product type, basal medium, cultivation method (flask or reactor), and feeding strategy (batch or fed-batch). Overall, additives only accounted for 3% of the variation in cell density and 1% of the variation in titer. Similarly, the impact of basal media was also relatively modest, at 10% for cell density and 0% for titer. Cell line, product type, and feeding strategy were all found to have more impact. These results emphasize the need for media studies to consider more factors to ensure that reported observations can be generalized and further developed.

Continuous integrated antibody precipitation with two-stage tangential flow microfiltration enables constant mass flow

Continuous precipitation is a new unit operation for the continuous capture of antibodies. The capture step is based on continuous precipitation with PEG6000 and Zn⁺⁺ in a tubular reactor integrated with a two‐stage continuous tangential flow filtration unit. The precipitate cannot be separated with centrifugation, because a highly compressed sediment results in poor resolubilization. We developed a new two‐stage tangential flow microfiltration method, where part of the concentrated retentate of the first stage was directly fed to the second stage, together with the wash buffer. Thus, the precipitate was concentrated and washed in a continuous process. We obtained 97% antibody purity, a 95% process yield during continuous operation, and a fivefold reduction in pre‐existing high‐molecular‐weight impurities. For other unit operations, surge tanks are often required, due to interruptions in the product mass flow out of the unit operation (e.g., the bind/elute mode in periodic counter‐current chromatography). Our setup required no surge tanks; thus, it provided a truly continuous antibody capture operation with uninterrupted product mass flow. Continuous virus inactivation and other flow‐through unit operations can be readily integrated downstream of the capture step to create truly continuous, integrated, downstream antibody processing without the need for hold tanks.

V(v)-Schiff base species induce adipogenesis through structure-specific influence of genetic targets

Appropriately designed Schiff-base substrates enhance V(v)-bioavailability and insulin-mimetic biomolecular gene profiling, inducing adipogenesis in a structure-specific manner.

Zinc supplementation decreases galactosylation of recombinant IgG in CHO cells

Trace element composition of culture medium can be altered to modulate glycoform of recombinant glycoproteins. In this study, we show that Zn²⁺ supplementation at or above 100 μM decreases galactosylation of recombinant IgG expressed in Chinese Hamster Ovary cells. This decrease in galactosylation is not due to reduced galactosyltransferase expression. This effect persists upon supplementation of galactose and uridine to the culture, indicating that it may not be due to reduced UDP-Gal availability. Measurements of galactosyltransferase activity in the cell lysate show that activity decreases with increasing Zn²⁺/Mn²⁺ ratio. This suggests that one possible explanation of the effect of Zn²⁺ may be reduced intracellular galactosyltransferase activity due to increase in Zn²⁺/Mn²⁺ ratio. Consistent with this, the decrease in galactosylation of IgG could be reversed by supplementation of Mn²⁺ (a cofactor of galactosyltransferase) which increases intracellular Mn²⁺ content. Measurement of total intracellular Zn²⁺ content, however, indicates no significant upregulation of total intracellular Zn²⁺ content and no significant downregulation of intracellular Mn²⁺ content with Zn²⁺ supplementation. One possible explanation could be that cellular detoxification response to higher extracellular Zn²⁺ concentration might lead to changes in intracellular distribution of Mn²⁺. In this case, Zn²⁺ supplementation would be expected to interfere with other known effects of Mn²⁺. Indeed, the previously reported increase in high mannose glycans upon Mn²⁺ supplementation in the absence of glucose is reversed by Zn²⁺ supplementation. This study also suggests the use of Mn²⁺ supplementation as a strategy to overcome the effect of lot-to-lot variability in trace element concentrations on galactosylation.

Development of a low-serum medium for the production of monoclonal antibody against congenital adrenal hyperplasia by hybridoma culture

Statistically designed experiments were used in developing a low-serum medium for the production of a diagnostic monoclonal antibody against congenital adrenal hyperplasia using hybridoma 192. A two-level half-fractional factorial design was used for screening six components (Minimum Essential Medium Eagle amino acids, 2-mercaptoethanol, ethanolamine, ferric citrate, zinc sulfate, and sodium selenite). The experimental design was then augmented to central composite design. The basal Dulbecco's modified Eagle's medium (DMEM; containing 4 mM L-glutamine, 1% antibiotic-antimycotic agent) supplemented with 0.4% by volume fetal bovine serum (FBS), 311.8 mM ferric citrate, 17.3 nM sodium selenite, and 4.5 mM zinc sulfate (LSD) was found to support the growth of the hybridoma. Specific cell growth rate in the LSD (0.033 ± 0.001/h) was slightly lower than in the control medium (i.e., basal DMEM supplemented with 2% FBS; 0.0045 ± 0.003/h). Nevertheless, the specific MAb production rate for LSD was higher (0.057 ± 0.015 pg/cell · h versus 0.004 ± 0.002 pg/cell · h in LSD and control, respectively). The antibody produced in the LSD showed high specificity and no cross-reactivity with the other structural resemblance's steroid hormones, revealing no structural changes owing to the new medium formulation developed. The new medium formulation effectively reduced the medium cost by up to 64.6%.

Zinc stimulates glucose consumption by modulating the insulin signaling pathway in L6 myotubes: essential roles of Akt-GLUT4, GSK3β and mTOR-S6K1

The present study was performed to evaluate the insulin-like effects of zinc in normal L6 myotubes as well as its ability to alleviate insulin resistance. Glucose consumption was measured in both normal and insulin-resistant L6 myotubes. Western blotting and immunofluorescence revealed that zinc exhibited insulin-like glucose transporting effects by activating key markers that are involved in the insulin signaling cascade (including Akt, GLUT4 and GSK3β), and downregulating members of the insulin signaling feedback cascade such as mammalian target of rapamycin (mTOR) and ribosomal protein S6 kinase (S6K1). In normal L6 myotubes, zinc enhanced glucose consumption via a mechanism that might involve the activation of Akt phosphorylation, glucose transporter 4 (GLUT4) translocation and GSK3β phosphorylation. In contrast, zinc exerted insulin-mimetic effects in insulin-resistant L6 myotubes by upregulating Akt phosphorylation, GLUT4 translocation and GSK3β phosphorylation, and downregulating the expression of mTOR and S6K1. In conclusion, zinc might enhance glucose consumption by modulating insulin signaling pathways including Akt-GLUT4, GSK3β, mTOR and S6K1.

Serum-free medium optimization based on trial design and support vector regression

The Plackett-Burman design and support vector machine (SVM) were reported to be used on many fields such as some feature selections, protein structure prediction, or forecasting of other situations. Here, with suspension adapted Chinese hamster ovary (CHO) cells as the object of study, a serum-free medium for the culture of CHO cells in suspension was optimized by this method. Support vector machine based on genetic algorithm was used to predict the growth rate of CHO and prove the results from the trial designs. Experimental results indicated that ZnSO₄, transferrin, and bovine serum albumin (BSA) were important ones. The same conclusion was arrived at when the support vector regression model analyzed the experimental results. With the methods mentioned, the influence of 7 medium supplements on the growth of CHO cells in suspension was evaluated efficiently.

Albumin and mammalian cell culture: implications for biotechnology applications

Albumin has a long historical involvement in design of media for the successful culture of mammalian cells, in both the research and commercial fields. The potential application of albumins, bovine or human serum albumin, for cell culture is a by-product of the physico-chemical, biochemical and cell-specific properties of the molecule. In this review an analysis of these features of albumin leads to a consideration of the extracellular and intracellular actions of the molecule, and importantly the role of its interactions with numerous ligands or bioactive factors that influence the growth of cells in culture: these include hormones, growth factors, lipids, amino acids, metal ions, reactive oxygen and nitrogen species to name a few. The interaction of albumin with the cell in relation to these co-factors has a potential impact on metabolic and biosynthetic activity, cell proliferation and survival. Application of this knowledge to improve the performance in manufacturing biotechnology and in the emerging uses of cell culture for tissue engineering and stem cell derived therapies is an important prospect.

Influence of the rapeseed protein hydrolysis process on CHO cell growth

Different protein hydrolysates were prepared from enzymatic hydrolyses of a rapeseed isolate (>90% protein content) using different commercial enzymes of non-animal origin. The extent of hydrolysis was controlled to produce hydrolysates corresponding to various degrees of hydrolysis (DH) from 5 to 30. These hydrolysates were characterized according to their solubility and size peptide pattern. Different growth behaviours of Chinese Hamster Ovary cells were observed when these various hydrolysates were added in serum-free medium containing transferrin, albumin and insulin. Hydrolysates from low degree of hydrolysis generally did not exhibit significant positive effect on cell growth; conversely hydrolysates from extensive hydrolysis, corresponding to a major low molecular size peptides content, usually allowed an increase of the maximal cell density. However, depending on the enzyme used, the supplementation with hydrolysates corresponding to a high degree of hydrolysis and composed of at least 70% peptides with a molecular size under 1kDa, led to different maximal cell density values, indicating the importance of enzyme specificity and consequently the nature of the released peptides. This result showed that the positive influence of the rapeseed hydrolysates on cell growth was not only due to a nutritional support tied to the addition of small peptides but may be related to the presence of peptides exhibiting growth or survival factor effects. Furthermore, total substitution of proteins (transferrin, albumin and insulin) in the cell culture medium by some rapeseed hydrolysates appeared to be a promising alternative to improve the cell growth in protein-free media.

The role of recombinant proteins in the development of serum-free media

Early developments in serum-free media led to a variety of formulations in which components normally provided in serum and required for growth (insulin, transferrin, lipid supplements, trace elements) and poorly defined components (extracts, hydrolysates) were added to defined basal media. These additives were mostly animal-derived. Given recent concerns about TSEs (transmissible spongiform encephalopathies) and other adventitious agents, the drive in media formulations must be towards elimination of animal-origin materials while maintaining cell line productivity. The progress made towards removing animal-derived components and the use of recombinant proteins in serum-free media for mammalian cells is reviewed.

Evaluation of recombinant human transferrin (DeltaFerrin(TM)) as an iron chelator in serum-free media for mammalian cell culture

DeltaFerrin(TM), a yeast-derived recombinant human transferrin produced by Delta Biotechnology Ltd. (Nottingham UK), was found to be a suitable replacement for holo human transferrin in serum-free culture media of the MDCK cell line (chosen because of its transferrin dependence) in short-term screening assays. Long-term subculture was achieved with DeltaFerrin(TM) supporting growth equivalent to that of holo human transferrin. DeltaFerrin(TM) and a selection of chemical iron chelators were found in short-term assays to be equivalent to holo human transferrin in supporting growth of MDCK, BHK-21-PPI-C16 and Vero-PPI. In long-term subcultures, however, only DeltaFerrin(TM) was found to support cell growth in a manner essentially equivalent to holo human transferrin in all three cell lines. For both BHK and Vero variants tested, recombinant preproinsulin production was unaltered by replacing holo human transferrin with DeltaFerrin(TM). As such, this is the first report of a recombinant human transferrin produced under animal-free conditions that can act as a universal iron chelator for cells grown in serum-free media (SFM).

Zinc as an insulin replacement in hybridoma cultures

There are many advantages to the use of protein-free media for biologics production, including a reduced risk of viral contamination from animal-derived proteins and simplification of downstream purification. In the course of developing protein-free media for hybridoma and myeloma cells, zinc was found to be an effective replacement for insulin, with no negative impact on viable cell density and antibody production. Transcript profiling using DNA microarrays indicated no major change in the global expression profile between the insulin and zinc-supplemented cultures, which is consistent with their similar growth and metabolic characteristics. Both DNA microarray and quantitative RT-PCR analysis showed increase in insulin receptor substrate 1 (Irs1) expression in zinc-supplemented cultures, while several key genes downstream of Irs1 in the insulin-signaling pathway, such as protein kinase B (PKB/Akt) and 3-phosphoinositide dependent protein kinase 1 (Pdpk1) did not show significant differences at the transcript level. Comparison of transcript profiles from cultures with low versus optimal zinc supplementation implicated the involvement of the insulin-related genes Pax6 and Phas1. Subtle differences were also observed between insulin and zinc in the serine-473 phosphorylation of Akt. Zinc increased serine-473 phosphorylation of Akt, but to a lesser extent than insulin. The phosphoinositide 3-kinase (PI3K) inhibitor, wortmannin, totally blocked the effect of both zinc and insulin on Akt activation, indicating the involvement of PI3K in the activation of Akt by zinc, rather than zinc acting on Akt directly. Our results highlight the impact of trace metal supplementation as protein-free media formulations move towards greater chemical definition.

A novel function for selenium in biological system: Selenite as a highly effective iron carrier for Chinese hamster ovary cell growth and monoclonal antibody production

As the market for biopharmaceuticals especially monoclonal antibodies (MAbs) rapidly grows, their manufacturing methods are coming under increasing regulatory scrutiny, particularly due to concerns about the potential introduction of adventitious agents from animal-sourced components in the media used for their production in mammalian cell culture. Chinese hamster ovary (CHO) cells are by far the most commonly used production vehicles for these recombinant glycoproteins. In developing animal-component free media for CHO and other mammalian cell lines, the iron-transporter function of serum or human/bovine transferrin is usually replaced by certain organic or inorganic chelators capable of delivering iron for cell respiration and metabolism, but few of them are sufficiently effective. Selenium is a well-known essential trace element (TE) for cell growth and development, and its positive role in biological system includes detoxification of free radicals by activating glutathione peroxidase. In cell culture, selenium in the form of selenite can help cells to detoxify the medium thus protect them from oxidative damage. In this presentation, we describe the discovery and application of a novel function of selenite, that is, as a highly effective carrier to deliver iron for cell growth and function. In our in-house-developed animal protein-free (APF) medium for CHO cells, using an iron-selenite compound to replace the well-established tropolone delivery system for iron led to comparable or better cell growth and antibody production. A high cell density of >10 x 10(6) viable cells/mL and excellent antibody titer of approximately 3 g/L were achieved in 14-day fed-batch cultures in shake flasks, followed by successful scale-up to stirred bioreactors. The preparation of the commercially unavailable iron-selenite compound from respective ions, and its effectiveness in cell-culture performance, were dependent on reaction time, substrates, and other conditions.

Development of Animal-free, Protein-Free and Chemically-Defined Media for NS0 Cell Culture

There has been a recent boom of monoclonal antibodies on the market, and a significant portion of them were produced by NS0 cell lines. As regulations become more stringent in ensuring production processes are free of potential contamination by adventitious agents, it is highly desirable to further develop serum-free media into ones that do not contain any components of animal origin, or 'animal-free media'. Using a shake-flask batch culture system, recombinant proteins (human albumin and human insulin) and synthetic compounds (tropolone and ferric ammonium citrate) were identified to be capable of replacing the animal-sourced proteins commonly found in serum-free media for NS0 cell culture, namely bovine albumin, insulin and transferrin. The cholesterol requirement of NS0 cells was satisfied by the use of a commercially available non-proteinaceous, non-animal sourced cholesterol/fatty acid mix in place of bovine lipoproteins, which in effect also eliminated the need for recombinant albumin. In the animal-free medium thus formulated, NS0 cell lines, either the host or recombinant constructs, were all able to grow in batch culture to 1~ 3x10(6) viable cells/ml for multiple passages, with no requirement for gradual adaptation even when seeded from 10% serum-containing cultures. It was surprising to observe that the recombinant insulin was essentially ineffective as sodium salt compared to its zinc salt. Studies showed that the zinc deficiency in the former resulted in a rapid decline of cell viabilities. Supplementation of zinc ions greatly improved growth, and even led to the total replacement of recombinant insulin and hence the formulation of a protein-free medium. When the cell lines were adapted to cholesterol-independent growth which eliminated the need for any lipid source, a completely chemically-defined animal-free medium was formulated. In all cases, antibody production by various GS-NS0 constructs in animal-free media was stable for multiple passages and at least similar to the original serum-free medium containing the animal-sourced proteins. The medium also served well for cryopreservation of NS0 cells in the absence of serum.