Fragmented DNA and apoptotic bodies document the programmed way of cell death in hybridoma cultures

Pro-haloacetate Nanoparticles for Efficient Cancer Therapy via Pyruvate Dehydrogenase Kinase Modulation

Anticancer agents based on haloacetic acids are developed for inhibition of pyruvate dehydrogenase kinase (PDK), an enzyme responsible for reversing the suppression of mitochondria-dependent apoptosis. Through molecular docking studies mono- and dihaloacetates are identified as potent PDK2 binders and matched their efficiency with dichloroacetic acid. In silico screening directed their conversion to phospholipid prodrugs, which were subsequently self-assembled to pro-haloacetate nanoparticles. Following a thorough physico-chemical characterization, the functional activity of these novel agents was established in wide ranges of human cancer cell lines in vitro and in vivo in rodents. Results indicated that the newly explored PDK modulators can act as efficient agent for cancer regression. A Pyruvate dehydrogenase (PDH) assay mechanistically confirmed that these agents trigger their activity through the mitochondria-dependent apoptosis.

Catabolic control of hybridoma cells by glucose and glutamine limited fed batch cultures

Substrate limited fed batch cultures were used to study growth and overflow metabolism in hybridoma cells. A glucose limited fed batch, a glutamine limited fed batch, and a combined glucose and glutamine limited red batch culture were compared with batch cultures. In all cultures mu reaches its maximum early during growth and decreases thereafter so that no exponential growth and decreases thereafter so that no exponential growth rate limiting, although the glutamine concentration (>0.085mM) was lower than reported K(s) vales and glucose was below 0.9mM; but some other nutrients (s) was the cause as verified by simulations. Slightly more cells and antibodies were produced in the combined fed batch compared with the batch culture. The specific rates for consumption of glucose and glutamine were dramatically influenced in fed batch cultures resulting in major metabolic changes. Glucose limitation decreased lactate formation, but increased glutamine consumption and ammonium formation. Glutamine limitation decreased ammonium and alanine formation of lactate, alanine, and ammonium was negligible in the dual-substrate limited fed batch culture. The efficiency of the energy metabolism increased, as judged by the increase in the cellular yield coefficient for glucose by 100% and for glutamine by 150% and by the change in the metabolic ratios lac/glc, ala/ln, and NH(x)/ln, in the combined fed culture. The data indicate that a larger proportion of consumed glutamine enters the TCA cycle through the glutamate dehydrogenase pathway, which releases more energy from glutamine than the transamination pathway. We suggest that the main reasons for these changes are decreased uptake rates of glucose and glutamine, which in turn lead to a reduction of the pyruvate pool and a restriction of the flux through glutaminase and lactate dehydrogenase. There appears to be potential for further cell growth in the dual-substrate-limited fed batch culture as judged by a comparison of mu in the different cultures. (c) 1994 John Wiley & Sons, Inc.

Cell suicide in starving hybridoma culture: survival-signal effect of some amino acids

Two mouse hybridoma cell lines cultured in different basal media withthe iron-rich protein-free supplement were subjected to deliberatestarvation by inoculation into media diluted with saline to 50% or less.In the diluted media the growth was markedly suppressed and a largefraction of cells died by apoptosis. The cells could be rescued fromapoptotic death by individual additions of amino acids, such as glycine,L-alanine, L-serine, L-threonine, L-proline, L-asparagine, L-glutamine,L-histidine, D-serine, β-alanine or taurine. Amino acids withhydrophobic or charged side chains were without effect. The apoptosispreventing activity manifested itself even in extremely diluted media,down to 10% of the standard medium. The activity of L-alanine in theprotection of cells starving in 20% medium was shown also in semicontinuousculture. In the presence of 2 mM L-alanine the steady-state viable cell density more than doubled, with respect to control, andthe apoptotic index dropped from 37% in the control to 16%. It wasconcluded that the apoptosis-preventing amino acids acted as signalmolecules, rather than nutrients, and that the signal had a character ofa survival factor. The specificity of present results, obtained with twodifferent hybridomas, supports our view (Franěk and Chládková-Šrámková, 1995) that the membranetransport macromolecules themselves may play the role of therecognition elements in a signal transduction pathway controlling thesurvival of hybridoma cells.

Effects of dissolved oxygen levels and the role of extra- and intracellular amino acid concentrations upon the metabolism of mammalian cell lines during batch and continuous cultures

The effects of dissolved oxygen and the concentration of essential amino acids upon the metabolism of two mammalian cell lines (rCHO producing human active (t-PA) and a mouse-mouse hybridoma) were investigated in batch, chemostat, and perfusion cultures. Intracellular amino acid concentrations were measured for both cell lines during repeated batch cultures and the K(S)-values for the essential amino acids were calculated using Monod equations via computer simulation. The K(S)-values were in the range of 10 mmol L(-1) and the pool of most intracellular amino acids remained constant at about 10-100 fold higher in concentration than in the medium. No significant differences were observed between the hybridoma and CHO cell. The specific nutrient uptake rates corresponded with the cell specific growth rate and the effects of reduced dissolved oxygen concentrations only became evident when the DO dropped below 5% of air saturation (critical concentration below 1%). Nevertheless, a correlation between nutrient concentration and specific oxygen uptake was detected.

Effects of temperature shift on cell cycle, apoptosis and nucleotide pools in CHO cell batch cultues

Temperature reduction in CHO cell batch culture may be beneficial in the production of recombinant protein and in maintenance of viability. The effects on cell cycle, apoptosis and nucleotide pools were studied in cultures initiated at 37°C and temperature shifted to 30 °C after 48 hours. In control cultures maintained at 37 °C, viable cells continued to proliferate until the termination of the culture, however, temperature reduction caused a rapid decrease in the percent of cells in S phase and accumulation of cells in G-1. This was accompanied by a concurrent reduction in U ratio (UTO/UDP-GNAc), previously shown to be a sensitive indicator of growth rate. Culture viability was extended following temperature shift, as a result of delayed onset of apoptosis, however, once initiated, the rate and manner of cell death was similar to that observed at 37 °C. All nucleotide pools were similarly degraded at the time of apoptotic cell death. Temperature reduction to 30 °C did not decrease the energy charge of the cells, however, the overall rate of metabolism was reduced. The latter may be sufficient to extend culture viability via a reduction in toxic metabolites and/or limitation of nutrient deprivation. However, the possibility remains that the benefits of temperature reduction in terms of both viability and productivity are more directly associated with cultures spending extended time in G-1.

Cell suicide in starving hybridoma culture: survival-signal effect of some amino acids

Two mouse hybridoma cell lines cultured in different basal media with the iron-rich protein-free supplement were subjected to deliberate starvation by inoculation into media diluted with saline to 50% or less. In the diluted media the growth was markedly suppressed and a large fraction of cells died by apoptosis. The cells could be rescued from apoptotic death by individual additions of amino acids, such as glycine, L-alanine, L-serine, L-threonine, L-proline, L-asparagine, L-glutamine, L-histidine, D-serine, β-alanine or taurine. Amino acids with hydrophobic or charged side chains were without effect. The apoptosis preventing activity manifested itself even in extremely diluted media, down to 10% of the standard medium. The activity of L-alanine in the protection of cells starving in 20% medium was shown also in semicontinuous culture. In the presence of 2 mM L-alanine the steady-state viable cell density more than doubled, with respect to control, and the apoptotic index dropped from 37% in the control to 16%. It was concluded that the apoptosis-preventing amino acids acted as signal molecules, rather than nutrients, and that the signal had a character of a survival factor. The specificity of present results, obtained with two different hybridomas, supports our view (Franěk and Chládková-Šrámková, 1995) that the membrane transport macromolecules themselves may play the role of the recognition elements in a signal transduction pathway controlling the survival of hybridoma cells.

Effect of bcl-2 expression on hybridoma cell growth in serum-supplemented, protein-free and diluted media

Two transfected hybridoma cell lines TB/C3-bcl2 (overexpressing the Bcl-2 protein) and TB/C3-pEF (control cell line), were compared in batch suspension cultures using a medium supplemented either with horse serum or with a protein-free, iron-rich supplement. The membrane intact index (percentage of cells with intact membranes determined by trypan blue staining) of the TB/C3-bcl2 cell line decreased much slower than that of the control cell line during the dying phase of the cultures. No significant difference in antibody, lactate and ammonia production as well as glucose and glutamine consumption was noted in the exponential phase of the experiments. Both cell lines were also compared in batch experiments using media diluted with saline to further investigate the effect of Bcl-2 under sub-optimal conditions. The Bcl-2 overexpressing cell line again exhibited a higher membrane intact index at increasing dilution steps.

Prolongation of murine hybridoma cell survival in stationary batch culture by Bcl-xL expression

While the ectopic expression of the anti-apoptoticprotein Bcl-2 has been shown to significantly increaseboth cell viability and antibody production in batchculture, some cell lines are refractory to thesemanipulations. For example, the NS/O and theP3x63Ag8.653 murine myelomas, which express highendogenous levels of the Bcl-2 homologue Bcl-xL, areboth resistant to the anti-apoptotic effect of Bcl-2.This indicates that, in these cells, Bcl-2 and Bcl-xLmay be functionally redundant. In order to define therole which Bcl-xL plays in hybridoma cultures, we usedthe Sp2/0-Ag14 cell line. This murine hybridomaexpresses low levels of Bcl-xL and is highly sensitiveto apoptosis induction by cycloheximide (CHX) and byamino acid depletion. Bcl-xL-transfected Sp2/0-Ag14cells were more resistant than the wild type and theplasmid-containing cells to apoptosis induced by CHXand by glutamine depletion. Moreover, when compared tothe vector-transfected control, Bcl-xL-Sp2/0 cellsexhibited a substantial increase in viability instationary batch culture. Interestingly, Sp2/0-Ag14cells overexpressing Bcl-xL showed a growth behaviourthat was similar to the parent myeloma cell lineP3x63Ag8.653. Our results suggest that Bcl-xLexpression levels are sufficient to account for therelative robustness of some hybridoma cell lines instationary batch cultures.

Modulation of cell cycle progression and of antibody production in mouse hybridomas by a nucleotide analogue

The nucleotide analogue 9-[2-(phosphonomethoxy)ethyl]guanine (PMEG) has been identified as a powerful antiproliferative substance when acting on hybridoma cells. In the range of 10 nM to 100 nM concentrations this agent reduces cell growth rate, while its apoptosis-inducing activity is marginal. Marked induction of apoptosis can be observed at micromolar and higher order concentrations. In PMEG-supplemented media the cell cycle progression is perturbed, the flow-cytometric DNA profile shows a higher proportion of cells in the S and G2/M phases of the cell cycle. Concomitantly with the reduction of the growth rate, the specific monoclonal antibody production rate may rise by 20-27%. Addition of PMEG at the end of the exponential phase of a batch culture results in an enhancement of the final monoclonal antibody concentration.

Diverse effects of the cyclin-dependent kinase inhibitor bohemine: Concentration- and time-dependent suppression or stimulation of hybridoma culture

An analog of aromatic cytokinins, the 2,6,9-trisubstituted purine derivative bohemine, was applied to cultures of mouse hybridoma cells in order to analyze its capacity of suppressing cell growth and maintaining or enhancing the production of monoclonal antibody. Addition of bohemine at concentrations in the range of1-10 muM resulted in a short-term arrest of growth and of monoclonal antibody production. The short-term suppression of cell functions was followed by a significant temporary increase of specific growth rate and of specific production rate. The steady-state viable cell density values, found in semicontinuous cultures, showed a certain stimulation of cell growth in the range of micromolar concentrations of bohemine, and inhibition of growth at 10 and 30 muM concentrations. The profiles of cell cycle phases indicated that hybridoma cells are retarded both at the G(1)/S boundary and at the G(2)/M boundary, depending on bohemine concentration. The existence of the sequence of events,from suppression to stimulation, suggests that bohemine probably modulates more than one regulatory pathway in the cell.

The effect of Bcl-2, YAMA, and XIAP over-expression on apoptosis and adenovirus production in HEK293 cell line

Many viruses induce cell death and lysis as part of their replication and dissemination strategy, and in many cases features of apoptosis are observed. Attempts have been made to further increase productivity by prolonging cell survival via the over-expression of anti-apoptotic genes. Here, we extend the study to investigate the association between virus replication and apoptosis, pertinent to large-scale vector production for gene therapy. Infection of an HEK293 cell line with a replication defective type-5-adenovirus expressing a GFP reporter (Ad5GFP) resulted in rapid decline in viability associated with increased virus titer. The over-expression of bcl-2 resulted in improved cell resistance to apoptosis and prolonged culture duration, but reduced virus specific and total productivity. In contrast, the over-expression of pro-caspase-3 (Yama/CPP32/apopain) resulted in reduced cell survival but increased virus productivity. The treatment of infected cells with caspase inhibitors support the preposition that caspase-3 dependent apoptosis, and to a lesser degree caspase-9 dependent apoptosis, represent important steps in virus production, thus implicating the intrinsic apoptosis pathway in the production of adenovirus from HEK293 cells. The suppression of apoptosis by the over-expression of XIAP (inhibitors of caspase family cell death proteases) further shows that caspase-mediated activation plays an important role in virus infection and maturation.

Survival Factor-Like Activity of Small Peptides in Hybridoma and CHO Cells Cultures

Synthetic peptides containing three to six amino acid residues were previously shown to improve key parameters of monoclonal antibody-producing mouse hybridoma cultures. The aim of the current work was to investigate whether small peptides also exert analogous beneficial impact on a CHO-K1-derived cell line (XMK-111-10) engineered for production of the human model glycoprotein SEAP (secreted alkaline phosphatase). Similar to hybridoma cultures, growth and SEAP production profiles of CHO XMK-111-10 were modulated by peptides. Both viable cell density and SEAP production were increased by tetraalanine or by a fraction of wheat gluten hydrolysate. Whereas tetraglycine increased the peak viable cell density, the growth-suppressing tripeptide Gly-Lys-Gly significantly boosted SEAP production. All peptide-supplemented cultures showed slight improvement of culture viability during the decline phase of the batch cultures, suggesting a survival factor-like activity of the peptides.

Keratocyte loss in corneal infection through apoptosis: a histologic study of 59 cases

BACKGROUND

Keratocyte loss by apoptosis following epithelial debridement is a well-recognized entity. In a study of corneal buttons obtained from patients of corneal ulcer undergoing therapeutic keratoplasty, we observed loss of keratocytes in the normal appearing corneal stroma, surrounding the zone of inflammation. Based on these observations, we hypothesized that the cell loss in the inflammatory free zone of corneal stroma is by apoptosis that could possibly be a non-specific host response, independent of the nature of infectious agent.

METHODS

To test our hypothesis, in this study, we performed Terminal deoxyribonucleotidyl transferase-mediated d-Uridine 5" triphosphate Nick End Labelling (TUNEL) staining on 59 corneal buttons from patients diagnosed as bacterial, fungal, viral and Acanthamoeba keratitis. The corneal sections were reviewed for morphologic changes in the epithelium, stroma, type, degree and depth of inflammation, loss of keratocytes in the surrounding stroma (posterior or peripheral). TUNEL positivity was evaluated in the corneal sections, both in the zone of inflammation as well as the surrounding stroma. A correlation was attempted between the keratocyte loss, histologic, microbiologic and clinical features.

RESULTS

The corneal tissues were from 59 patients aged between 16 years and 85 years (mean 46 years) and included fungal (22), viral (15), bacterial (14) and Acanthamoeba (8) keratitis. The morphological changes in corneal tissues noted were: epithelial ulceration (52, 88.1%), destruction of Bowman's layer (58, 99%), mild to moderate (28; 47.5%) to severe inflammation (31; 52.5%). Morphologic evidence of disappearance or reduced number of keratocytic nuclei in the corneal stroma was noted in 49 (83%) cases; while the TUNEL positive brown cells were identified in all cases 53/54 (98%), including cases of fungal (19), bacterial (14), viral (13), and Acanthamoeba keratitis. TUNEL staining was located mostly in the deeper stroma and in few cases the peripheral stroma. TUNEL positivity was also noted with the polymorphonuclear infiltrates and in few epithelial cells (10 of 59, 17%) cases, more with viral infections (6/10; 60%).

CONCLUSIONS

We report apoptotic cell death of keratocytes in the corneal stroma in infectious keratitis, a phenomenon independent of type of infectious agent. The inflammatory cells in the zone of inflammation also show evidence of apoptotic cell death. It could be speculated that the infective process possibly triggers keratocyte loss of the surrounding stroma by apoptosis, which could possibly be a protective phenomenon. It also suggests that necrotic cell death and apoptotic cell deaths could occur simultaneously in infective conditions of the cornea.

Gluten of spelt wheat (Triticum aestivum subspecies spelta) as a source of peptides promoting viability and product yield of mouse hybridoma cell cultures

The enzymic hydrolysate of gluten from spelt wheat (Triticum aestivum subsp. spelta), an ancient protein-rich wheat subspecies, was subjected to repeated chromatography runs on the small pore size exclusion chromatography matrix, Biogel P-2. Two small peptide fractions were purified by rechromatography. The amino acid analyses carried out upon total hydrolysis of these fractions have shown a very high proportion of glutamic acid/glutamine, leucine, and methionine. The biological activity of the peptide fractions was tested on a model hybridoma at a concentration range from 0.02 to 0.2%. The most striking effect of peptide fractions, apparent even at the lowest concentrations tested, was a significantly higher persistence of viable cells on day 6, i.e., at the decline phase of the cultures. Culture viability values in the presence of peptide fractions were 64-74%, in comparison with 56% in the control culture. The results of this work are consistent with the concept that peptide molecules may act as antiapoptotic agents, survival factors, rather than serving as metabolic substrates.

Early changes in metabolism of leukemic cell lines upon induction of apoptosis by cytotoxic drugs

We evaluated real-time changes in extracellular acidification rates of human U937 and K562 leukemic cells treated with camptothecin or taxol. U937 cells treated with camptothecin or taxol for 30-60 min showed a continuous, irreversible decrease in extracellular acidification rate that was sensitive to amiloride. In contrast, U937 cells exposed to sodium azide showed an immediate, steep decrease in extracellular acidification rate that was reversible upon azide withdrawal. K562 cells required a >20-fold higher dose of camptothecin to promote similar changes in the extracellular acidification rate, with a corresponding resistance in their susceptibility to camptothecin- or taxol-induced apoptosis. The data show that irreversible commitment to apoptosis is associated with rapid metabolic changes that are reflected by decreased extracellular acidification rate and regulated by the Na(+)/H(+) antiporter. Moreover, detection of extracellular acidification rate changes was not restricted to a particular cell type or apoptosis pathway, making this a potentially useful tool to screen compounds for pro-apoptotic activity.

24-Epibrassinolide at Subnanomolar Concentrations Modulates Growth and Production Characteristics of a Mouse Hybridoma

Brassinosteroids are known to stimulate plant growth and to possess antistress activities in plants. This work was aimed at exploring possible beneficial effects of 24-epibrassinolide on cultured mammalian cells. A mouse hybridoma was cultured either in standard serum-free medium, or in medium diluted to 30%, in which the cells underwent nutritional stress. Steady-state parameters of semicontinuous cultures conducted at 24-epibrassinolide concentrations from 10-16 to 10-9 mol l-1 were evaluated. Typical effects of the agent found both in standard and in diluted media were (i) increase in the value of mitochondrial membrane potential, (ii), drop of intracellular antibody level, (iii) increase in the fraction of the cells in the G0/G1 phase, and (iv) decrease in the fraction of the cells in the S phase. Alleviation of nutritional stress manifested itself in cultures conducted in diluted media. Viable cell density was significantly higher (relative to control) at 24-epibrassinolide concentrations 10-13 and 10-12 mol l-1. The results of this exploratory study show that the plant hormone 24-epibrassinolide may induce perturbations in the cell division mechanism, in mitochondria performance, and in secreted protein synthesis in a mammalian cell line. At the lowest brassinosteroid concentrations, the number of steroid molecules in the culture was of the same order of magnitude as the number of viable cells in the culture. This implies involvement of a complex cascade mechanism, through which the steroid molecule induces alterations in gene expression leading finally to significant changes in cell culture parameters.

Impact of coexpression and coamplification of sICAM and antiapoptosis determinants bcl-2/bcl-x(L) on productivity, cell survival, and mitochondria number in CHO-DG44 grown in suspension and serum-free media

We have engineered dihydrofolate reductase-negative (dhfr-/-) Chinese hamster ovary (CHO) DG44 cells adapted for growth in serum-free suspension cultures for simultaneous expression of the common cold therapeutic, the soluble intercellular adhesion molecule 1 (sICAM), and the antiapoptosis determinants bcl-2 or bcl-x(L). Detailed analyses of titer and antiapoptosis characteristics of these production cell lines included an independent (sICAM; bcl-2/bcl-x(L)) as well as a cocistronic (sICAM-(bcl-2/bcl-x(L))) expression set-up in which translation-initiation of the survival cistron is driven by an internal ribosome entry site (IRES) of the encephalomyocarditis virus (EMCV). In transient transfections or stable mixed populations and in comparison to isogenic sICAM-only control vectors, both bcl-x(L)-encoding configurations achieved higher sICAM yields while bcl-2 over-expression resulted in decreased product levels. Overall, the death-protective impact of bcl-2 and bcl-x(L) in engineered CHO-DG44 was not significant under typical batch-mode operation, an observation that was confirmed by clonal analysis. bcl-2 and bcl-x(L) displayed their antiapoptosis potential only following dhfr-based amplification in sICAM-producing CHO-DG44 cell lines. In all cases, bcl-x(L) outperformed bcl-2 in its cell death-protective capacity. Amplification-dependent high-level expression of mitochondria-localized bcl-2 family members required for successful antiapoptosis engineering may be essential to compensate for increased mitochondria numbers found to be associated with production cell lines grown in serum-free medium.

Antiapoptotic and proapoptotic action of various amino acids and analogs in starving MOLT-4 cells

This study is based on our previous findings showing that certain amino acids may protect hybridoma cells against starvation-induced apoptosis. In the present work we have screened 44 amino acids and analogs for their capacity of modulating apoptosis in human T-lymphoblastic leukemia cell line MOLT-4 exposed to starvation in a nutrient-poor medium. The panel of tested substances was found to contain not only compounds with antiapoptotic activity (e.g., l-glutamine, l-histidine, glycine, l-proline, and l-2-aminopentanoic acid), but also compounds with proapoptotic activity (e.g., l-phenylalanine, l-tryptophan, l-arginine, and l-2-aminohexanoic acid). The apoptosis-modulating effects were dependent on fine details of the structure of the compounds. A switch from antiapoptotic activity to proapoptotic activity was found between 6-aminohexanoic acid and 7-aminoheptanoic acid, as well as between l-2-aminopentanoic acid and l-2-aminohexanoic acid. D-amino acids tested were without effect.

Effect of the Purine Derivative Myoseverin and of Its Analogues on Cultured Hybridoma Cells

Two 2,6,9-trisubstituted purine derivatives, 9-isopropyl-2,6-bis[(4-methoxybenzyl)amino]-9H-purine (myoseverin, PMYO, 1) and 9-isopropyl-2,6-bis[(2-methoxybenzyl)amino]-9H-purine (OMYO, 2), and two 6,9-disubstituted derivatives, 9-isopropyl-6-[(4-methoxybenzyl)amino]-9H-purine (3) and 9-isopropyl-6-[(2-methoxybenzyl)amino]-9H-purine (4), were synthesized with the aim to examine their cell proliferation inhibiting activity, and possible additional effects in cultures of hybridoma cells producing monoclonal antibody. The substances were tested over a concentration range from 0.003 to 30 μmol l-1. The most active compound 1 caused a total loss of cell viability at 1 μmol l-1, while its isomer 2 showed the same effect at 10 μmol l-1 concentration. In the presence of compound 1, but not of compound 2, the character of the cell cycle phases profile changed dramatically, most cells being arrested in the G2/M phase. At intermediate concentrations of compound 2 a substantially higher viable cell concentration was observed, relative to control. These differences demonstrated the principal significance of the position of the methoxy groups on the benzene rings for the biological effect. The 6,9-disubstituted derivatives 3 and 4 were without significant effect in the whole range of concentrations tested. The enhancement of monoclonal antibody production, observed in certain concentration intervals of added substances, was of marginal character.

A human anti-dsDNA monoclonal antibody caused hyaline thrombi formation in kidneys of 'leaky' SCID mice

There are few studies assessing the pathogenicity of human monoclonal anti-DNA antibodies. The use of SCID mice avoids the problem of rejection of the human hybridoma cells thus allowing in vivo assessment of human immunoglobulins. Using electron microscopy we have shown that the human IgG anti-dsDNA monoclonal antibody, RH14, is nephritogenic in SCID mice, causing morphological changes in the kidney due to immunoglobulin deposition. The problem with using SCID mice is that they have an abnormal immune system; normally they are used at about 2 months of age, at which time they have virtually no functional T or B cells. It is known that older SCID mice become increasingly 'leaky', that is they develop some mature lymphocyte clones. Our aim was to assess if implanting anti-DNA antibodies into older 'leaky' SCID mice would result in pathology which was observable by light microscopy. Eight-month-old SCID mice were implanted with human hybridoma cells secreting either RH14 an anti-dsDNA IgG, CL24, an antiphospholipid antibody or an irrelevant human IgG control. As previously, RH14 deposited in the kidney and caused proteinuria but unexpectedly we also observed hyaline thrombi in the kidney glomeruli and peritubular capillaries. These thrombi occurred only in the case of RH14 implanted mice and were found to stain positively for human IgG and fibrin. However, apart from the interesting thrombi, we did not observe any greater pathological damage resulting from the anti-dsDNA antibody deposition than we had seen in the younger mice; indeed, the electron microscopic findings were more limited.

CFTR modulates programmed cell death by decreasing intracellular pH in Chinese hamster lung fibroblasts

To study the potential influence of cystic fibrosis conductance regulator (CFTR) on intracellular pH regulation during apoptosis induction, we used PS120 Chinese hamster lung fibroblasts devoid of the Na(+)/H(+) exchanger (NHE1 isoform) transfected with constructs, allowing the expression of CFTR and/or NHE1. Kinetics of lovastatin-induced apoptosis were measured by orcein staining, double staining with Hoechst-33258, propidium iodide, DNA fragmentation, and annexin V labeling. In PS120 control cells, the percentage of apoptotic cells after 40 h of lovastatin treatment was 23 +/- 3%, whereas in PS120 CFTR-transfected cells, this percentage was 40 +/- 4%. In PS120 NHE1 cells, the transfection with CFTR did not modify the percentage of apoptotic cells after 40 h (control: 19 +/- 3%, n = 8; CFTR: 17 +/- 1%, n = 8), indicating that blocking intracellular acidification by overexpressing the Na(+)/H(+) exchanger inhibited the enhancement of apoptosis induced by CFTR. In all cell lines, the initial pH values were identical (pH = 7.46 +/- 0.04, n = 9), and treatment with lovastatin led to intracellular acidification. However, the pH value after 40 h was lower in PS120 CFTR-transfected cells (pH = 6.85 +/- 0.02, n = 10) than in PS120 cells (pH = 7.15 +/- 0.03, n = 10). To further investigate the origin of this increased intracellular acidification observed in CFTR-transfected cells, the activity of the DIDS-inhibitable Cl(-)/HCO exchanger was studied. 8-Bromoadenosine 3',5'-cyclic monophosphate incubation resulted in Cl(-)/HCO exchanger activation in PS120 CFTR-transfected cells but had no effect on PS120 cells. Together, our results suggest that CFTR can enhance apoptosis in Chinese hamster lung fibroblasts, probably due to the modulation of the Cl(-)/HCO exchanger, resulting in a more efficient intracellular acidification.

Characterization of bimodal cell death of insect cells in a rotating-wall vessel and shaker flask

In previous publications, we reported the benefits of a high-aspect rotating-wall vessel (HARV) over conventional bioreactors for insect-cell cultivation in terms of reduced medium requirements and enhanced longevity. To more fully understand the effects that HARV cultivation has on longevity, the present study characterizes the mode and kinetics of Spodoptera frugiperda cell death in this quiescent environment relative to a shaker-flask control. Data from flow cytometry and fluorescence microscopy show a greater accumulation of apoptotic cells in the HARV culture, by a factor of at least 2 at the end of the cultivation period. We present a kinetic model of growth and bimodal cell death. The model is unique for including both apoptosis and necrosis, and further, transition steps within the two pathways. Kinetic constants reveal that total cell death is reduced in the HARV and the accumulation of apoptotic cells in this vessel results from reduced depletion by lysis and secondary necrosis. The ratio of early apoptotic to necrotic cell formation is found independent of cultivation conditions. In the model, apoptosis is only well represented by an integral term, which may indicate its dependence on accumulation of some factor over time; in contrast, necrosis is adequately represented with a first-order term. Cell-cycle analysis shows the percent of tetraploid cells gradually decreases during cultivation in both vessels. For example, between 90% and 70% viability, tetraploid cells in the HARV drop from 43 +/- 1% to 24 +/- 4%. The data suggests the tetraploid phase as the likely origin for apoptosis in our cultures. Possible mechanisms for these changes in bimodal cell death are discussed, including hydrodynamic forces, cell-cell interactions, waste accumulation, and mass transport. These studies may benefit insect-cell cultivation by increasing our understanding of cell death in culture and providing a means for further enhancing culture longevity. Copyright 1999 John Wiley & Sons, Inc.

Separation of oligonucleosomal DNA fragments from apoptotic animal cells using a triad of Sephacryl columns

The degradation of DNA, resulting in information of oligonucleosomal fragments, is a characteristic feature of apoptosis, i.e., the process of programmed cell death. In this work we have developed a method for exact determination of the proportion of fragmented DNA in an apoptotic cell population. To this end we employed Sephacryl gel chromatography matrices and UV detection of DNA concentration. The disturbing effect of low-molecular-mass UV-absorbing contaminants was eliminated by insertion of a Sephacryl S-200 HR pre-column. Optimum resolution of DNA samples isolated from apoptotic cells was achieved using a triad of Sephacryl S-200 HR, Sephacryl S-500 HR and Sephacryl S-1000 SF columns.

Protection of B lymphocyte hybridoma against starvation-induced apoptosis: survival-signal role of some amino acids

The phenomenon of starvation-induced apoptosis was studied in cultures of a mouse B lymphocyte hybridoma. In a continuous culture the limitation of nutrients was modelled by dilution of a protein-free medium with saline to 15%. Surprisingly, the hybridoma clone did not die out under extreme starvation conditions. A steady state was established in which the cells continued to grow at very low viable cell concentration, concomitantly with an enhanced rate of apoptotic death. Suppression of the death rate, and increase of steady-state viable cell concentration, could be achieved by additions of L-alanine, L-asparagine or L-glutamine, but not by addition of L-phenylalanine. This specificity pattern is in agreement with previous screening experiments that have identified a set of apoptosis-preventing amino acids (glycine, L-alanine, L-serine, L-threonine, L-proline, L-asparagine, L-glutamine, L-histidine). The analysis of amino acid consumption and production showed a consistent production of alanine and serine both in standard medium and in diluted media. When alanine was added at a final concentration of 2 mM to media diluted either to 40 or 20%, apoptosis was partly suppressed. A limited production of alanine was observed also in alanine-enriched diluted media. It is concluded that the apoptosis-preventing amino acids act as signal molecules, besides their nutritive function, and that the signal has a character of a survival factor. The observed phenomena are interpreted in terms of a survival-control mechanism that regulates the viable cell number of a lymphocyte clone in an adequate proportion with the level of available nutrients.

Implications and applications of apoptosis in cell culture

Numerous stimuli, including viral infection and deprivation of cell growth factors, can induce apoptosis (programmed cell death) of cells grown in culture. The genetic machinery that controls the apoptotic response is currently being investigated. The expression of genes involved in this process using recombinant DNA technology has been utilized to control and limit programmed cell death in cultured cells. In the future, this technology may be used to increase the productive lifetime of cell culture systems.

Modeling of cell culture processes

Models of cell processes can be particularly useful in simulating, optimizing and controlling cell culture systems. Models reported in the literature are of various degrees of biological structure and mathematical complexity and describe cell growth, death, metabolism, and product formation, alone or in combination with each other. This paper reviews these modeling efforts, discusses their results, potential and limitations, and identifies areas where future modeling studies may be especially valuable.

Induction of apoptosis in oxygen-deprived cultures of hybridoma cells

It is now well documented that apoptosis represents the prevalent mode of cell death in hybridoma cultures. Apoptotic or programmed cell death occurs spontaneously in late exponential phase of batch cultures. Until lately, no specific triggering factors had been identified. Recently, we observed that glutamine, cystine or glucose deprivation induced apoptosis in both hybridoma and myeloma cell lines whereas accumulation of toxic metabolites induced necrotic cell death in these cells. Other triggering factors such as oxygen deprivation might also be responsible for induction of apoptosis. In the present study, induction of cell death by exposure to anoxia was examined in batch culture of the SP2/0-derived hybridoma D5 clone. The mode of cell death was studied by morphological examination of acridine orange-ethidium bromide stained cells in a 1.5 L bioreactor culture grown under anoxic conditions for 75 hours. Under such conditions, viable cell density levelled off rapidly and remained constant for 25 hours. After 45 hours of anoxia, cell viability had decreased to 30% and the dead cell population was found to be 90% apoptotic. In terms of cellular metabolism, anoxia resulted in an increase in the utilization rates of glucose and arginine, and in a decrease in the utilization rate of glutamine. The lactate production rate and the yield of lactate on glucose increased significantly while the MAb production rate decreased. These results demonstrate that glycolysis becomes the main source of energy under anoxic conditions. Cells incubated for 10 hours or less under anoxic conditions were able to recuperate almost immediately and displayed normal growth rates when reincubated in oxic conditions whereas cells incubated for 22 hours or more displayed reduced growth rates. Nonetheless, even after 22 h or 29 h of anoxia, cells reincubated in oxic conditions showed no further progression into apoptosis. Therefore, upon removal of the triggering signal, induction of apoptosis ceased.

Genetically engineering mammalian cell lines for increased viability and productivity

The generation of new host cell lines for the production of foreign proteins can be achieved by cell engineering. This approach can be used to enhance the cell's ability to produce proteins that are properly processed and secreted at elevated levels and consequently can increase the overall productivity of an expression system. One potential target for cell engineering is the modification of the cell's protein folding capacity. The appropriate folding, assembly, localization and secretion of newly synthesized proteins is dependent upon the action of a group of proteins known as molecular chaperones. Improving the host cell's chaperoning capacity might increase the yield of properly folded recombinant proteins by preventing the formation of insoluble aggregates. Another potentially beneficial cell engineering goal is the inhibition of physiological cell death. The productivity of genetically engineered cells is dependent upon the maintenance of high levels of cell viability throughout the bioprocess period. Fluctuations in a cell's environment can trigger a deliberate form of cell death known as apoptosis. The proteins that mediate this self-destruction are currently being characterized. Regulating the expression of these death genes by cellular engineering could limit the loss of productivity that results from the physiological death of the recombinant cell line.

Essential role of optimal protein synthesis in preventing the apoptotic death of cultured B cell hybridomas

The monoclonal antibody productivity of cell culture systems is strongly dependent on the maintenance of hybridoma cell viability. We report that partial (< 50%) and transient (3 h) inhibition of protein synthesis by cycloheximide or deprivation of an essential amino acid induces apoptosis (programmed cell death) in B cell hybridomas. This unusual mechanism of apoptosis induction is likely to play a significant role in limiting cell viability in batch and perfusion cultures of hybridomas and emphasizes the importance of constantly maintaining a near optimal rate of macromolecular synthesis by optimization of all culture parameters. Inhibition of apoptosis in hybridomas by cell engineering and other technologies should permit, in the near future, a significant increase in the antibody productivity of existing cell culture systems.