Increased t-PA yields using ultrafiltration of an inhibitory product from CHO fed-batch culture

Fed-batch operation for the production of t-PA using Chinese Hamster Ovary (CHO) cells was optimized using serial and parallel experimentation. The feed, an isotonic concentrate, was improved to obtain 2- to 2.5-fold increases in integrated viable cell days versus batch. With a low glucose inoculum train, the viability index was further increased up to 4.5-fold. Hydrolysates were substituted for the amino acid portion of the concentrate with no significant change in fed-batch results. The concentrate addition rate was based on a constant 4 pmol/cell.day glucose uptake rate that maintained a relatively constant glucose concentration (approximately 3 mM). Increased viable cell indices did not lead to concomitant increases in t-PA concentrations compared to batch. The fed-batch concentrate and feeding strategy were shown to be effective in hybridoma culture, where a 4-fold increase in viable cell index yielded a 4-fold increase in antibody concentration. The half-life of t-PA decreased from 43 to 15 days with decreasing cell viability (from 92% to 71%), but this was not sufficient to explain the apparent t-PA threshold. Instead, the CHO results were explained by a reduction in t-PA production at higher extracellular t-PA concentrations that limited the fed-batch maximum at 35 mg/L for the cell line investigated. Analysis of both the total and t-PA mRNA levels revealed no response to increasing extracellular t-PA concentrations upon exogenous additions. Instead, intracellular t-PA levels were increased, revealing a possible secretory pathway limitation. A new reactor configuration was developed using an acoustic filter to retain the cells in the reactor while an ultrafiltration module stripped t-PA from the clarified medium before the permeate was returned to the reactor. By adding this harvesting step, the t-PA fed-batch production was increased over 2-fold, up to a yield of 80 mg/L.     

Liposome mediated delivery of retinoids and aromatic polyamidines: Effects on growth of tumor cell lines

Ceramic pieces composed of 99.5% Al₂O₃, 3 to 6 mm long, were found to be a good matrix for growth of the human embryonic lung diploid fibroblast, IMR-90 cells. The tissue plasminogen activator (t-PA) was secreted in DME medium containing proteose peptone as a t-PA inducer. In addition, production of t-PA was enhanced by increasing extracellular CaCl₂, from 3.6 to 5.4 mM. In order to eliminate negative feed-back control caused by t-PA produced and thus raise productivity, perfusion cultivation was performed using a ceramic-packed bed column, with a recirculating vessel. The recirculating vessel was used to mix fresh medium with spent medium, and to control dissolved oxygen concentrations in the extracellular environment by stirring. In continuous production using the packed bed column with 2 kg of ceramics (Ø=H=150 mm), increasing dilution rate to 0.5 day^-1 could reduce product inhibition at 3–4×10⁵cells/ml. Cellular productivity of 560 IU/10⁶cells/day was obtained over 40 days and corresponded to the volumetric productivity of 183 IU/ml/day.Abbreviations CBR Ceramic Bed Reactor - Lv Linear Velocity     

Microbial production of 2-chloro-alpha-methylbenzyl alcohol and its adsorptive recovery

An adsorptive process was combined with yeast-mediated production of chiral 2-chloro-alpha-methylbenzyl alcohol (o-Cl-1-PA) for effective product recovery and reuse of the reaction medium. Low temperature was suitable for long-term reactor operation, and continuous production using a shallow-bed reactor was achieved for at least 22 days while maintaining a high conversion. The appropriate size of the adsorption column for product recovery from the reactor effluent was estimated through measurement of breakthrough curves of o-Cl-1-PA in a packed bed of the resin at various adsorbate concentrations and feed flow rates. Using the adsorption column, 98% of the product and the residual substrate were recovered from the reactor effluent, and the effluent from the adsorption column was successfully reused as the reaction medium after microfiltration to save the medium consumption.     

Design and characterization of a rotating bed system bioreactor for tissue engineering applications

The main challenge in the development of bioreactors for tissue engineering is the delivery of a sufficient nutrient and oxygen supply for cell growth in a 3D environment. Thus, a new rotating bed system bioreactor for tissue engineering applications was developed. The system consists of a culture vessel as well as an integrated rotating bed of special porous ceramic discs and a process control unit connected with the reactor to ensure optimal culturing conditions. The aim of the project was the design and construction of a fully equipped rotating bed reactor, and in particular, the characterization and optimization of the system with regard to technical parameters such as mixing time and pH-control to guarantee optimal conditions for cell growth and differentiation. Furthermore, the applicability of the developed system was demonstrated by cultivation of osteoblast precursor cells. The porous structure of the ceramic discs and the external medium circulation loop provide an optimal environment for tissue generation in long-term cultivations. Mass transfer limitations were minimized by the slow rotation, which also provides the cells with sufficient nutrients and oxygen through alternate contact to air and medium. An osteoblast precursor cell line was successfully cultivated in this bioreactor for 28 days.     

Observations on the influence of glutamine,asparagine and peptone on growth and t-PA production of Chinese hamster ovary (CHO) cells

When a transfected CHO cell, that produces tissue-type Plasminogen Activator, t-PA, was transferred from a medium based on 5% Fetal Calf Serum, FCS, to a medium based on 0.8% casein peptone with variable glutamine and asparagine content, it was observed, that the growth of the cells changed from anchorage dependant to suspension culture giving more reproducible cultivations. In the FCS culture t-PA was unstable, observed as a decline in t-PA concentration after 250 h. This decline in t-PA concentration was not observed in the serum free culture, although there was a decline in productivity after 200 h. This change in production profile may be attributed to either no proteolytic attack from serum or by scavenging of proteolytic activities produced by the cells from the peptone peptides. Increasing amounts of glutamine/asparagine gave higher production of t-PA in synchrony with an increasing production of ammonia/ammonium ions. Ammonia inhibition does not seem to be a key factor for this cell line as seen with many others.     

Production of tissue plasminogen activator (t-PA) in Aspergillus niger

A protease-deficient strain of Aspergillus niger has been used as a host for the production of human tissue plasminogen activator (t-PA). In defined medium, up to 0.07 mg t-PA (g biomass)(-1) was produced in batch and fed-batch cultures and production was increased two- to threefold in two-phase batch cultures in which additional glucose was provided as a single pulse at the end of the first batch growth phase. Production was increased [up to 1.9 mg t-PA (g biomass)(-1)] by the addition of soy peptone to the defined medium. The rate of t-PA production in batch cultures supplemented with soy peptone (0.2 to 0.6 mg t-PA L(-1) h(-1)) was comparable to rates observed previously in high-producing mammalian or insect cell cultures. In glucose-limited chemostat culture supplemented with soy peptone, t-PA was produced at a rate of 0.7 mg t-PA L(-1) h(-1). Expression of t-PA in A. niger resulted in increased expression of genes (bipA, pdiA, and cypB) involved in the unfolded protein response (UPR). However, when cypB was overexpressed in a t-PA-producing strain, t-PA production was not increased. The t-PA produced in A. niger was cleaved into two chains of similar molecular weight to two-chain human melanoma t-PA. The two chains appeared to be stable for at least 16 h in culture supernatant of the host strain. However, in general, <1% of the t-PA produced in A. niger was active, and active t-PA disappeared from the culture supernatant during the stationary phase of batch cultures, suggesting that the two-chain t-PA may have been incorrectly processed or that initial proteolytic cleavage occurred within the proteolytic domain of the protein. Total t-PA (detected by enzyme-linked immunoassay) also eventually disappeared from culture supernatants, confirming significant extracellular proteolytic activity, even though the host strain was protease-deficient.     

里氏木霉306产t-PA固态发酵条件的研究

对基因工程菌株里氏木霉(Trichodermareesei)306生物合成组织型纤溶酶原激活剂(t-PA)的固态发酵培养基成分和发酵条件进行了研究;分析了发酵过程中t-PA的生成、总糖的消耗和菌体生长的规律。在优化的固体发酵条件下,t-PA的最大酶活是924.63IU/g干重培养基,较初始条件下提高了5倍。通过浅盘进行了放大实验,最大酶活为983.64IU/g干重培养基,t-PA合成速率为:13.66IU/g干重培养基.h,较三角瓶固态发酵最高产酶提高了6.38%,产酶速率提高了24.07%。     

Role of Ca2+ in t-PA production by human embryonic lung diploid fibroblast, IMR-90 cells, stimulated by proteose peptone

Proteose peptone (p.peptone) remarkably induced tissue plasminogen activator (t-PA) activity in the conditioned medium of confluently cultured human embryonic lung diploid fibroblast, IMR-90 cells, in a dose-dependent manner. t-PA activity correlated well with the amount of t-PA antigen found in the conditioned medium of IMR-90 cells stimulated by p.peptone. t-PA production by IMR-90 cells stimulated by p.peptone was dependent on extracellular Ca2+ concentration and maximum t-PA production required approximately 3.6 mM extracellular Ca2+. Conversely, elimination of Ca2+ from the culture medium by EGTA, Ca2+ chelate agent, strongly inhibited t-PA production induced by p.peptone. t-PA production induced by p.peptone was inhibited in a dose-dependent manner by Verapamil, which inhibits Ca2+ uptake through the slow channels and also by W-7, an inhibitor of calmodulin. These results suggested that influx of extracellular Ca2+ into IMR-90 cells was caused by p.peptone and induced t-PA production by the cells.     

培养条件对里氏木霉306菌体形态和t-PA生物合成的影响

里氏木霉（Trichoderrna reesei）306是能够生物合成组织型纤溶酶原激活剂（t-PA）的基因工程菌株。在对其液态深层培养时,发现随培养夸件和培养时间的变化,其菌体能以松散和菌丝球的两种形态存在。菌体形态和t-PA的产生密切相关。培养基中无机盐和表面活性剂的种类和添加量以及接种量和pH等培养条件是影响里氏木霉306菌体形态和t-PA合成的主要因素。在液态深层培养过程中,菌体以松散的菌丝体形态生长,形成纸浆状发酵液,利于t-PA的合成。     

A comparison of the effects of various stimulatory agents on t-PA secretion by normal and malignant cell lines

Succinyl con A and acetyl con A both stimulated epithelial cells to produce similar yields of tissue plasminogen activator (t-PA) to those previously obtained with native con A. However, unlike con A, the derivatized lectins did not adversely affect cell morphology and viability, and cells treated with succinyl con A could secrete t-PA for a prolonged period. Con A and the two derivatives produced similar morphological effects in Bowes melanoma cells, but t-PA production was not increased. Elevated cyclic nucleotide concentrations did not affect t-PA production from epithelial cells, but calcium ionophore treatment generated t-PA yields similar to those obtained with lectins. Azacytidine, which enhanced t-PA production from epithelial cells, did not increase yields from Bowes melanoma cells, and also sodium butyrate, reported to increase t-PA yields from human endothelial cells, had no effect on either cell line.     

Cultivation of virus antigen in fibroblast cells using a glass fiber bed reactor

The anchorage-dependent cell line, MRC-5, was cultivated successfully on glass fibers with diameters ranging from 24 to 120 mum, despite vast differences in substrate curvature. Multilayer cell growth was observed, particularly for fiber diameters 30 mum and below, which differed from the typical monolayer growth observed in T-flask cultivations. Cells were maintainable at a reduced incubation temperature and were demonstrated to support virus replication for the 21-day antigen production period. Direct microscopic observation, along with indirect calculations, indicated that only a small fraction (about 10%) of the total available fiber surface area was occupied by cells. Thus, productivity per unit surface area was replaced by productivity per unit medium volume when evaluating fiber bed performance. Antigen and protein yields, as well as nutrient uptakes, were 1.5- to 2.5-fold greater than parallel T-flask cultures when compared on this basis. Corresponding available surface area-based values were 10- to 15-fold lower for the fiber bed reactor. The multilayer cell morphology obtained in the fiber bed was attractive for antigen production when immobilized in a column reactor system. (c) 1993 John Wiley & Sons, Inc.     

Structure and function of human tissue-type plasminogen activator (t-PA)

Full-length tissue-type plasminogen activator (t-PA) cDNA served to construct deletion mutants within the N-terminal "heavy" (H)-chain of the t-PA molecule. The H-chain cDNA consists of an array of structural domains homologous to domains present on other plasma proteins ("finger," "epidermal growth factor," "kringles"). These structural domains have been located on an exon or a set of exons. The endpoints of the deletions nearly coincide with exon-intron junctions of the chromosomal t-PA gene. Recombinant t-PA deletion mutant proteins were obtained after transient expression in mouse Ltk- cells, transfected with SV40-pBR322-derived t-PA cDNA plasmids. It is demonstrated that the serine protease moiety of t-PA and its substrate specificity for plasminogen is entirely contained within the C-terminal "light" (L)-chain of the protein. The presence of cDNA, encoding the t-PA signal peptide preceding the remaining portion of t-PA, suffices to achieve secretion of (mutant) t-PA into the medium. The stimulatory effect of fibrin on the plasminogen activator activity of t-PA was shown to be mediated by the kringle K2 domain and, to a lesser extent, by the finger domain. The other domains on the H-chain, kringle K1, and the epidermal growth-factor-like domain, do not contribute to this property of t-PA. These findings correlate well with the fibrin-binding properties of the rt-PA deletion-mutant proteins, indicating that stimulation of the activity is based on aligning of the substrate plasminogen and its enzyme t-PA on the fibrin matrix. The primary target for endothelial plasminogen activator inhibitor (PAI) is located within the L-chain of t-PA. Deleting specific segments of t-PA H-chain cDNA and subsequent transient expression in mouse Ltk- cells of t-PA deletion-mutant proteins did not affect the formation of a stable complex between mutant t-PA and PAI.     

Effect of monensin on secretion of t-PA from melanoma (Bowes)

The secretion of tissue-type plasminogen activator (t-PA) from melanoma cells (Bowes) was investigated with or without monensin treatment. Monensin inhibited secretion of t-PA from the cells to the medium in a dose-and time-dependent manner. The inhibition was accompanied by an intracellular accumulation of t-PA. Electrophoretic enzymography of the cell homogenate showed the main lytic zone at 72 kDa, which reacted with the IgG of anti-t-PA. Analysis of the cell organelles using ultracentrifugation with a discontinuous sucrose density gradient revealed that the activity and the antigen of t-PA were observed near the discontinuous phase of the sucrose gradient. Analysis of 3H-mannose- and 35S-methionine-labeled t-PA in the cell organelles revealed that the radioactivity of each was increased by monensin treatment, and that such treatment increased the ratio of 3H-mannose-related glycoprotein to 35S-methionine-related protein. The sugar chain of intracellular t-PA was analyzed with endoglycosidase H and N-glycanase, which reduced the molecular weight of t-PA by 4.5-10 kDa, indicating the intracellular presence of a high-mannose type sugar chain and a complex-type sugar chain of t-PA. t-PA secreted from the monensin-treated cells possesses a high-mannose type sugar chain only. Therefore, monensin alters the secretion of t-PA by abnormal glycosylation.     

Hairy root culture in a liquid-dispersed bioreactor: characterization of spatial heterogeneity

A liquid-dispersed reactor equipped with a vertical mesh cylinder for inoculum support was developed for culture of Atropa belladonna hairy roots. The working volume of the culture vessel was 4.4 L with an aspect ratio of 1.7. Medium was dispersed as a spray onto the top of the root bed, and the roots grew radially outward from the central mesh cylinder to the vessel wall. Significant benefits in terms of liquid drainage and reduced interstitial liquid holdup were obtained using a vertical rather than horizontal support structure for the biomass and by operating the reactor with cocurrent air and liquid flow. With root growth, a pattern of spatial heterogeneity developed in the vessel. Higher local biomass densities, lower volumes of interstitial liquid, lower sugar concentrations, and higher root atropine contents were found in the upper sections of the root bed compared with the lower sections, suggesting a greater level of metabolic activity toward the top of the reactor. Although gas-liquid oxygen transfer to the spray droplets was very rapid, there was evidence of significant oxygen limitations in the reactor. Substantial volumes of non-free-draining interstitial liquid accumulated in the root bed. Roots near the bottom of the vessel trapped up to 3-4 times their own weight in liquid, thus eliminating the advantages of improved contact with the gas phase offered by liquid-dispersed culture systems. Local nutrient and product concentrations in the non-free-draining liquid were significantly different from those in the bulk medium, indicating poor liquid mixing within the root bed. Oxygen enrichment of the gas phase improved neither growth nor atropine production, highlighting the greater importance of liquid-solid compared with gas-liquid oxygen transfer resistance. The absence of mechanical or pneumatic agitation and the tendency of the root bed to accumulate liquid and impede drainage were identified as the major limitations to reactor performance. Improved reactor operating strategies and selection or development of root lines offering minimal resistance to liquid flow and low liquid retention characteristics are possible solutions to these problems.     

Enhancement of tissue plasminogen activator production from human normal fibroblast IMR-90 cells by limitation of cell growth

Summary Tissue plasminogen activator (t-PA) production induced by proteose peptone from IMR-90 cells was investigated. Cells monolayered on plastic surfaces had a higher ability to produce t-PA per unit cell compared to those grown tri-dimensionally on ceramic pieces. Furthermore, confluent monolayers of the cells, which suffered contact inhibition and resulted in limited growth, were available for t-PA production. Repeated batch production with microcarriers, on which the cells were almost confluent monolayers similar to those in T-flasks, was performed. Utilization of the cells, which had limited serum in the growth phase, resulted in an increase in production. Moreover, dilution of the basal components of the medium at initiation of the production phase markedly promoted t-PA production. The volumetric productivity was stable for 30 days at 100 IU/cm³ per day. The cells were then mostly retained on microcarriers. Thus, an effective and scalable method of t-PA production by normal fibroblast cells was developed. Offprint requests to: S. Mitsuda     

Continuous ethanol production in an immobilized whole cell fermenter using untreated sugar cane bagasse as carrier

Summary Saccharomyces cerevisiae was immobilised by adsorption to untreated sugar cane bagasse in a packed bed reactor. Complete conversion of glucose to ethanol was obtained at a dilution rate of 0.19 h⁻¹. Continuous ethanol production was maintained for up to 57 days. Reactor productivity increased with increasing packing density of the bagasse. Plugging of void spaces due to cell overgrowth led to channelling of the feed and decreased reactor productivity. Increasing the average column temperature alleviated plugging and restored column performance over a short period; however prolonged exposure to the high temperature resulted in decreased ethanol production rates. Bagasse has advantages as a support material for ethanol production from sugar cane or beet, including negligible cost, ready availability and the capacity to support a high yeast population.     

Continuous adsorption and recovery of Cr(VI) in different types of reactors

This study reports the results of experiments on continuous adsorption and desorption of Cr(VI) ions by a chemically modified and polysulfone-immobilized biomass of the fungus Rhizopus nigricans. A fixed quantity of polymer-entrapped biomass beads corresponding to 2 g of dry biomass powder was employed in packed bed, fluidized bed, and stirred tank reactor for monitoring the continuous removal and recovery of Cr(VI) ions from aqueous solution and synthetic chrome plating effluent. Parameters such as flow rate (5, 10 and 15 mL/min), inlet concentration of Cr(VI) ions (50, 100, 150 and 250 mg/L) and the depth of biosorbent packing (22.8, 11.2 and 4.9 cm) were evaluated for the packed bed reactor. The breakthrough time and the adsorption rates in the packed bed column were found to decrease with increasing flow rate and higher Cr inlet concentrations and to increase with higher depths of sorbent packing. To have a comparative analysis of Cr adsorption efficiency in different types of reactors, the fluidized bed reactor and stirred tank reactor were operated using the same quantities of biosorbent material. For the fluidized bed reactor, Cr(VI) solution of 100 mg/L was pumped at 5 mL/min and fluidized by compressed air at a flow rate of 0.5 kg/cm.(2) The stirred tank reactor had a working volume of 200 mL capacity and the inlet/outlet flow rate was 5 mL/min. The maximum removal efficiency (mg Cr/g biomass) was obtained for the stirred tank reactor (159.26), followed by the fluidized reactor (153.04) and packed bed reactor (123.33). In comparison to the adsorption rate from pure chromate solution, approximately 16% reduction was monitored for synthetic chrome plating effluent in the packed bed. Continuous desorption of bound Cr ions from the reactors was effective with 0.01 N Na(2)CO(3) and nearly 80-94% recoveries have been obtained for all the reactors.     

Identification and partial characterization by chemical cross-linking of a binding protein for tissue-type plasminogen activator (t-PA) on rat hepatoma cells. A plasminogen activator inhibitor type 1-independent t-PA receptor.

Plasma tissue-type plasminogen activator (t-PA) is cleared rapidly in vivo by the liver. Previous studies with the human hepatoma cell line HepG2 have identified a clearance system for t-PA modulated by plasminogen activator inhibitor type 1 (PAI-1). In the present study, a rat hepatoma cell line MH1C1 is shown to contain a PAI-1-independent t-PA clearance system. At 4 degrees C, binding of 125I-t-PA to MH1C1 cells was rapid, specific, and saturable. Scatchard analysis of the binding data yielded a mean estimate of 105,000 high affinity binding sites per cell (Kd = 4.1 nM). When the bound ligand was analyzed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, the majority (about 90%) of the specific binding was in the form of uncomplexed 125I-t-PA. This is in contrast to HepG2 cells in which specific binding was mainly in the form of a sodium dodecyl sulfate-stable 125I-t-PA.PAI-1 complex. When availability of matrix-associated PAI-1 was blocked by preincubation with anti-PAI-1 antibody or removed by elastase treatment, specific 125I-t-PA binding to MH1C1 cells was unaffected, whereas most of the specific 125I-t-PA binding to HepG2 cells was abolished. Furthermore, when the active site of t-PA was inactivated with diisopropyl fluorophosphate, the diisopropyl fluorophosphate-t-PA specifically competed for binding of 125I-t-PA to MH1C1 cells, but failed to block specific 125I-t-PA binding to HepG2 cells. At 37 degrees C, PAI-1-independent t-PA binding to MH1C1 cells was followed by ligand uptake and degradation with kinetics similar to that seen in HepG2 cells. Chemical cross-linking of t-PA to MH1C1 cells revealed a specific t-PA binding protein with a molecular mass of about 500,000 daltons. Ligand-receptor complexes generated by chemical cross-linking were immunoprecipitable by anti-t-PA antibody but not by anti-PAI-1 antibody, further supporting the finding that binding of t-PA to MH1C1 cells is PAI-1-independent.     

Scopolamine release into media by Duboisia leichhardtii hairy root clones

Summary The hairy root clones of Duboisia leichhardtii were found to release scopolamine into the medium. Among media examined, a modified Heller's medium that had 37 mm nitrate and no ammonium was suitable for scopolamine release. Scopolamine in the medium was efficiently recovered by the use of an Amberlite XAD-2 column. A reactor system consisting of a 2-1 airlift reactor and a 25-ml column packed with Amberlite XAD-2 was constructed for production of scopolamine by the culture of the hairy root clone. The culture medium was passed through the column and the eluent from the column was back into the reactor continuously by using a low-pressure pump. When the hairy root clone DL47-1 was cultured in the reactor, 245 mg/l of scopolamine was released into the medium during 6 weeks and 97% scopolamine in the medium was recovered by the column. The scopolamine production was about five times higher in the column-combined reactor than in the reactor without the column. Scopolamine was recovered as the hydrobromide salt with more than 90% purity. Correspondence to: T. Muranaka