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At least 487 records · Page 27Linked to original sources
PubMed2005

p16(INK4a) as a complementary marker of high-grade intraepithelial lesions of the uterine cervix. I: Experience with squamous lesions in 189 consecutive cervical biopsies.

AIM: To test the usefulness of p16(INK4a) immunostaining for improving the diagnostic accuracy of cervical punch biopsies referred to a routine laboratory setting during the investigation of women with abnormal Papanicolaou smears. METHODS: A total of 188 consecutive and unselected colposcopically directed cervical biopsies and a single contemporaneous cervical polyp were accessioned prospectively over a 3-month period, step-serially sectioned and examined by H&E and immunostained for p16(INK4a). The clinical context, results of concurrent Papanicolaou smears/ThinPrep slides and Digene hybrid capture tests for high-risk human papillomavirus (HPV) subtypes, as well as follow-up cervical smears/ThinPrep, biopsies and loop excisions of transformation zones or cone biopsies were all correlated with the morphological and immunohistochemical findings. RESULTS: Seventy-seven biopsies (40.7%) displayed a high-grade squamous intraepithelial lesion (HGSIL; cervical intraepithelial neoplasia [CIN] 2-3), 27 (14.3%) showed a low grade squamous intraepithelial lesion (HPV +/- CIN1) and 85 (45%) showed a range of non-dysplastic (inflammatory or reactive) changes. Diffuse strong parabasal immunostaining for p16(INK4a), suggestive of integrated high-risk HPV DNA into the host genome, was observed in 81 biopsies (42.9%, including the cervical polyp) and correlated (>90%) with HGSIL in the H&E sections. Only one case revealed irreconcilable discordance between the histological features and this strong parabasal immunostaining pattern. Focal and weaker midzonal or superficial p16(INK4a) immunostaining, suggestive of episomal HPV infection, was noted in 19 biopsies (10%) and these biopsies exhibited a range of histological changes but predominantly low grade squamous intraepithelial lesion (LGSIL). No staining of the squamous epithelium was seen in 89 biopsies (47.1%). Again, only one case revealed irreconcilable discordance between the histological features and this negative immunostaining pattern. On review of all cases where discordant results were noted between the H&E appearances and expected p16(INK4a) immunostaining, we found 26 cases (13.7%) in which this discordance prompted justifiable modification of the original diagnosis. CONCLUSIONS: Thus, within a routine diagnostic laboratory, p16(INK4a) immunostaining appears to be a very useful adjunctive test in the examination of colposcopically directed cervical biopsies, in the diagnostic cascade of women investigated for abnormal Papanicolaou smears. It is possible, as further data accumulate concerning the importance of integration of high-risk HPV DNA into the host cell genome and the reliability with which this can be identified by p16(INK4a) immunostaining, that this will become the diagnostic 'lesion of interest', replacing the subjective histological grading of cervical dysplasia, in the management of such patients; i.e., the discriminatory watershed between continued surveillance and active intervention.

Biomarkers, Tumor↗
PubMed2002

Micrometer-sized short-lived radioactive aerosol particles for convenient use in laboratory measurements.

For calibration and testing of radioactive aerosol measuring equipment such as continuous air monitors and cascade impactors, and other research applications, it is helpful to have a convenient and relatively safe means of producing radioactive aerosol particles of controlled size and activity. We describe a technique for producing such particles in the micrometer-diameter size range using electrostatic deposition of radon decay products onto otherwise nonradioactive powders of different sizes. An electric field focuses radon decay products (primarily 218Po) onto the surface of a powdered substrate that is then suspended by a technique such as pneumatic dry dispersion. Only a modest-activity commercial 222Rn source (e.g., containing as little as 10(5) Bq of 226Ra) is required, and issues of radioactive cleanup and contamination are minimized due to the short half-lives (26.8 min or less) of the decay products. We report representative results using powders of glass beads, iron oxide, and iron and gold metals in the size range of 0.3 to 30 microm. Yields for the deposited radioactivity per unit concentration of 222Rn gas were of the order of 5 x 10(-7) Bq (214Bi) per milligram substrate per Bq m(-3) of 222Rn for an electrostatic collection time of 30 min.

Aerosols↗
PubMed1999

Calpeptin and methylprednisolone inhibit apoptosis in rat spinal cord injury.

Intracellular free Ca2+ and free radicals are increased following spinal cord injury (SCI). These can activate calpain to degrade cytoskeletal proteins leading to apoptotic and necrotic cell death. Primary injury triggers a cascade of secondary injury, which spreads to rostral and caudal areas. We tested calpain involvement in apoptosis in five 1-cm segments of rat spinal cord with injury (40 g-cm) induced at T12 by weight-drop. Animals were immediately treated with calpeptin (250 micrograms/kg) and methylprednisolone (165 mg/kg) and sacrificed at 48 hr. Untreated SCI rats manifested 68-kD neurofilament protein (NFP) degradation (indicating calpain activity), and internucleosomal DNA fragmentation (indicating apoptosis). Both calpain activity and apoptosis were highest in the lesion, and decreased with increasing distance from the lesion. Treatment decreased 68-kD NFP degradation with reduction in apoptosis in all five areas. Thus, calpeptin and methylprednisolone are found to be neuroprotective in SCI.

Animals↗
PubMed2000

The value of transgenic models for the study of neurodegenerative diseases.

Transgenic animal models are useful in studying the features of APP- and PS1-linked FAD and SOD1-linked FALS. These models help to investigate the nature of the cellular/biochemical/molecular alterations in neural tissue; the character and evolution of neuronal and/or glial abnormalities; the ways mutant proteins cause damage to neurons; and the biochemical pathways associated with cell death. New technologies will help to define changes in a variety of genes/gene products and the events and conformational changes in mutant proteins that are implicated in pathogenic cascades. It is hoped such study will result in novel treatments for testing in transgenic models that can then be translated into new treatments for human neurodegenerative diseases.

Alzheimer Disease↗
PubMed1998

Evidence of nitric oxide, a flow-dependent factor, being a trigger of liver regeneration in rats.

The hypothesis tested was that the hemodynamic consequence of partial hepatectomy (PHX) triggers the cascade of events that leads to liver regeneration. After PHX, all the portal flow must go through the remaining vascular bed, thus producing increased shear stress and release of nitric oxide (NO), which then initiates the next stages of the regeneration process. As an index of triggering of the regeneration cascade, we used an in vitro bioassay detecting the appearance of proliferating factors (PFs; various growth factors, cytokines, and hormones) in plasma 4 h after two-thirds PHX in rats. PF levels, assessed using proliferation of cultured hepatocytes, were elevated in two-thirds PHX rats, fully blocked by the NO synthase inhibitor N(G)-nitro-L-arginine methyl ester (L-NAME), and restored by L-arginine. L-NAME inhibited liver weight restoration at 48 h but resulted in high mortality. L-NAME lacked toxic effects in non-PHX rats. NO was directly antiproliferative on cultured cells, suggesting that the proliferative effect of NO in vivo was secondary to the activation of other proliferative stimuli. The data support the hypothesis that vascular shear stress induced release of NO following PHX serves as a primary trigger to initiate the regeneration process.

Adenosine↗
PubMed1999

Hypertension-induced end-organ damage : A new transgenic approach to an old problem.

Angiotensin (Ang) II-induced organ damage has fascinated students of hypertension since the work of Wilson and Byrom. We are investigating a double transgenic rat (dTGR) model, in which rats transgenic for the human angiotensinogen and renin genes are crossed. These rats develop moderately severe hypertension but die of end-organ cardiac and renal damage by week 7. The heart shows necrosis and fibrosis, whereas the kidneys resemble the hemolytic-uremic syndrome vasculopathy. Surface adhesion molecules (ICAM-1 and VCAM-1) are expressed early on the endothelium, while the corresponding ligands are found on circulating leukocytes. Leukocyte infiltration in the vascular wall accompanies PAI-1, MCP-1, and VEGF expression. The expression of TGF-beta and deposition of extracellular matrix proteins follows, which is accompanied by fibrinoid vasculitis in small vessels of the heart and kidneys. Angiotensin-converting enzyme inhibitors and AT1 receptor blockers each lowered blood pressure and shifted pressure natriuresis partially leftward by different mechanisms. When combined, they normalized blood pressure, pressure natriuresis, and protected from vasculopathy completely. Renin inhibition lowered blood pressure partially, but protected from vasculopathy completely. Endothelin receptor blockade had no influence on blood pressure but protected from vasculopathy and improved survival. We show evidence that Ang II stimulates oxidative stress directly or indirectly via endothelin 1 and that NFkappaB is upregulated in this model. We speculate that the transcription factors NFkappaB and AP-1 are involved with initiating chemokine and cytokine expression, leading to the above cascade. The unique model and our pharmacological probes will enable us to test these hypotheses.

Angiotensin II↗
PubMed1999

Geophysical variables and behavior: LXXXV. Sudden infant death, bands of geomagnetic activity, and pc1 (0.2 to 5 HZ) geomagnetic micropulsations.

Pc1s (continuous pulsations) within the geomagnetic field, whose durations are about 30 minutes but which can reoccur several times nightly, are observed during periods when global geomagnetic activity is very low (less than 10 nT). The hypothesis that these 0.2 to 5 Hz synchronized micropulsations or hydromagnetic emissions might stimulate physical chemical cascades within the brain that precipitate the sudden death in infants was tested by correlational analysis for a two-year period (1960-1961) for Ontario. Results were consistent with the hypothesis that the monthly incidences of these unexpected deaths, pcl micropulsations and geomagnetic activity less than 10 nT displayed a shared source of variance. Implications are discussed.

California↗
PubMed2005

Inhibitory effects of chloride on the activation of caspase-1, IL-1beta secretion, and cytolysis by the P2X7 receptor.

The P2X7 receptor (P2X7R) is an ATP-gated cation channel that activates caspase-1 leading to the maturation and secretion of IL-1beta. Because previous studies indicated that extracellular Cl- exerts a negative allosteric effect on ATP-gating of P2X7R channels, we tested whether Cl- attenuates the P2X7R-->caspase-1-->IL-1beta signaling cascade in murine and human macrophages. In Bac1 murine macrophages, substitution of extracellular Cl- with gluconate produced a 10-fold increase in the rate and extent of ATP-induced IL-1beta processing and secretion, while reducing the EC50 for ATP by 5-fold. Replacement of Cl- with gluconate also increased the potency of ATP as an inducer of mature IL-1beta secretion in primary mouse bone marrow-derived macrophages and in THP-1 human monocytes/macrophages. Our observations were consistent with actions of Cl- at three levels: 1) a negative allosteric effect of Cl-, which limits the ability of ATP to gate the P2X7R-mediated cation fluxes that trigger caspase-1 activation; 2) an intracellular accumulation of Cl- via nonselective pores induced by P2X7R with consequential repression of caspase-1-mediated processing of IL-1beta; and 3) a facilitative effect of Cl- substitution on the cytolytic release of unprocessed pro-IL-1beta that occurs with sustained activation of P2X7R. This cytolysis was repressed by the cytoprotectant glycine, permitting dissociation of P2X7R-regulated secretion of mature IL-1beta from the lytic release of pro-IL-1beta. These results suggest that under physiological conditions P2X7R are maintained in a conformationally restrained state that limits channel gating and coupling of the receptor to signaling pathways that regulate caspase-1.

Animals↗
PubMed1996

Prevention. How much harm? How much benefit? 3. Physical, psychological and social harm.

Harm caused by preventive programs may be physical, psychological, social or, if informed consent has not been obtained, ethical. Adverse effects of preventive screening programs may occur at any of the three levels of the "screening cascade", the screening procedure itself, the investigation of abnormal results of screening tests or the treatment of detected abnormalities or diseases. The greatest harm occurs at the second and third levels. Examples of procedures that may cause physical harm are venipuncture, mammography, colonoscopy, breast biopsy, transrectal ultrasonography, prostate biopsy, weight-reducing and cholesterol-lowering diets and radical prostatectomy. The psychological and social harm of preventive programs involves anticipated discomfort or perception of adverse effects of preventive interventions; unpleasant interactions with health care workers, time required for preventive programs, excessive overall awareness of health, anxiety over the results of a screening test implications of a positive screening test, consequences of being labelled as "sick" or "at risk," psychopathologic effects induced directly by preventive programs and, in the case of a false-negative test result, false assurance of disease-free status. Since the positive predictive value of screening tests in the general population is always low, most abnormal test results are "false-positive," these engender a great deal of psychological discuss among patients.

Bias↗
PubMed1994

Protein-protein interactions in the yeast pheromone response pathway: Ste5p interacts with all members of the MAP kinase cascade.

We have used the two-hybrid system of Fields and Song to identify protein-protein interactions that occur in the pheromone response pathway of the yeast Saccharomyces cerevisiae. Pathway components Ste4p, Ste5p, Ste7p, Ste11p, Ste12p, Ste20p, Fus3p and Kss1p were tested in all pairwise combinations. All of the interactions we detected involved at least one member of the MAP kinase cascade that is a central element of the response pathway. Ste5p, a protein of unknown biochemical function, interacted with protein kinases that operate at each step of the MAP kinase cascade, specifically with Ste11p (an MEKK), Ste7p (an MEK), and Fus3p (a MAP kinase). This finding suggests that one role of Ste5p is to serve as a scaffold to facilitate interactions among members of the kinase cascade. In this role as facilitator, Ste5p may make both signal propagation and signal attenuation more efficient. Ste5p may also help minimize cross-talk with other MAP kinase cascades and thus ensure the integrity of the pheromone response pathway. We also found that both Ste11p and Ste7p interact with Fus3p and Kss1p. Finally, we detected an interaction between one of the MAP kinases, Kss1p, and a presumptive target, the transcription factor Ste12p. We failed to detect interactions of Ste4p or Ste20p with any other component of the response pathway.

Adaptor Proteins, Signal Transducing↗
PubMed2007

The Rho-associated kinase inhibitor fasudil hydrochloride enhances neural regeneration after axotomy in the peripheral nervous system.

BACKGROUND: The Rho family of small GTPases is responsible for various processes involving actin cytoskeleton in eukaryotic cells, including neurite outgrowth. Several substances found at the peripheral nerve injury site were shown to activate one member of this family, Rho. The activation of Rho leads to neurite outgrowth inhibition and the development of posttraumatic neuropathic pain. The authors used the clinically tested Rho-associated kinase inhibitor fasudil hydrochloride to enhance the functional recovery of the peripheral nerve in the rat. METHODS: In the peroneal nerve interpositional graft model, the authors administered fasudil (experimental groups) or saline (control groups) (1) intraperitoneally and (2) directly into the graft by microinjection (n = 6 animals per experimental condition). Neural recovery was assessed during postoperative follow-up lasting 80 days by peroneal functional index, electrophysiologic, and histomorphometric analyses. RESULTS: The peroneal functional index returned to values not significantly different from preoperative values on days 55 (fasudil injected into the graft) and 60 (fasudil injected intraperitoneally) in the experimental groups. In the control groups, this took 70 (saline injected intraperitoneally) and 75 days (saline injected into the graft). These results are supported by electrophysiologic and histomorphologic assessments. CONCLUSIONS: The authors determined that fasudil hydrochloride was capable of accelerating the functional regeneration after peripheral nerve axotomy, which is consistent with the results of reports about Rho cascade disruption in the central nervous system. Because fasudil hydrochloride is a clinically tested drug, it could be used to enhance neural regeneration in human patients as well.

1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine↗
PubMed1995

Special considerations for conducting genotoxicity tests with protein materials.

Standard genotoxicity tests are often inappropriate for testing new biological entities, in particular for recombinant proteins which are nature-identical. Arguments that these may contain mutagenic impurities are not substantiated; however, we have produced evidence that such impurities would be detected amidst a vast excess of protein. Concerns that human patients receiving therapy may be at risk from higher-than-physiological levels of proteins are also somewhat theoretical. However, it is apparent that genotoxicity testing will be required for these products for the time being, even if pragmatic approaches reduce the battery of in vitro tests to Ames and chromosomal aberrations only, and reduce the top dose in vivo to 1000x the human therapeutic dose. There is a number of physical and chemical properties of proteins that demand special approaches to methodology if the tests are to produce accurate results. The potential for adsorption to certain forms of glass and plastic means special care must be taken in dissolving and diluting test solutions; adherence to filters means special low protein binding, non-pyrogenic filters should be used for sterilisation of test solutions, where this is necessary; freeze-dried powders aliquotted in multiple vials should be dissolved in minimal solvent and cascaded from vial to vial rather than trying to empty the solid contents for bulk weighing. As proteins are often supplied in solution, in order to achieve sufficiently high test concentrations, it may be necessary to resuspend test bacteria/cells in the test solutions for short periods of time before centrifuging and resuspending in selective or growth media.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1995

Comparing two heat and moisture exchangers with one vaporizing humidifier in patients with minute ventilation greater than 10 L/min.

STUDY OBJECTIVE: To evaluate in patients submitted to minute ventilation > 10 L/min the ability to preserve patients' heat and humidity of two heat and moisture exchangers (HMEs) and one vaporizing humidifier (VH). DESIGN: Prospective, randomized, comparative, non-blinded study. SETTING: Intensive care unit of a university hospital. PATIENTS: Nine tracheally intubated, mechanically ventilated patients, sedated and submitted to mechanical ventilation with minute ventilation > 10 L/min. INTERVENTIONS: Using the psychrometric method, relative humidity (RH) and absolute humidity (AH) of inspired gas were obtained as well as temperature of inspired gas and tracheal temperatures (maximal and minimal). Following a randomized order, each patient was ventilated for two 24-h periods with a vaporizing humidifier (Bennett Cascade 2, Bennett; France) and one of two HMEs: Pall Ultipor filter BB50 (Pall Biomedical; France) or DAR Hygroster filter (Peters; France). Both were first tested for a 45-min period and then the HME that achieved the best performance in terms of temperature and water preservation was tested for 24 h. MEASUREMENTS AND RESULTS: During the 45-min test period, the Pall Ultipor HME achieved a lower performance than the other two systems for any of the studied parameters (p < 0.05 to p < 0.0001). The DAR Hygroster HME achieved lower temperature of inspired gas (29.9 vs 32.0 degrees C, p < 0.005) and lower absolute humidity (29.3 vs 33.2 mg H2O/L, p < 0.005) than the Bennett Cascade 2. After 24 h of use, lower values of temperature of inspired gas (28.5 vs 32.0 degrees C, p < 0.002) and of AH (28.0 vs 33.6 mg H2O/L, p < 0.001) were obtained with the DAR Hygroster HME than with the Bennett Cascade 2. No differences were found between the two systems for the other tested parameters. At that time, no patients had RH lower than 97% and absolute humidity lower than 23 mg H2O/L with the use of the DAR Hygroster HME. CONCLUSIONS: In patients with minute ventilation > 10 L/min, the DAR Hygroster HME showed a thermic and humidification capability similar to the reference system, the Bennett Cascade 2 VH. In these patients, the Pall Ultipor HME had a significantly lower capability.

Adolescent↗
PubMed2007

Inhibition of PI3-kinase signaling by glucocorticoids results in increased branched-chain amino acid degradation in renal epithelial cells.

Phosphatidylinositol 3-kinase(PI3K) is a pivotal enzyme involved in the control of a variety of diverse metabolic functions. Glucocorticoids have been shown to attenuate PI3K signaling in some nonrenal cell types, raising the possibility that some physiological effects of glucocorticoids in renal cells may be achieved by a similar mechanism. Therefore, we tested whether glucocorticoids affect signaling through the insulin receptor substrate (IRS)-1/PI3K/Akt signaling cascade in LLC-PK1-GR101 renal epithelial cells. Treatment of cells with dexamethasone for 24 h: 1) suppressed IRS-1-associated PI3K activity and Akt phosphorylation, 2) increased the level of the PI3K p85 regulatory subunit but not the p110 catalytic subunit, and 3) induced the phosphorylation of IRS-1 on inhibitory Ser(307). We have previously reported that glucocorticoids increase branched-chain ketoacid dehydrogenase (BCKD) activity in LLC-PK1-GR101 cells. This response was achieved, in part, by alterations in the transcription of BCKD subunits and BCKD kinase, which inactivates the enzyme complex by phosphorylation. Therefore, we tested whether inhibition of PI3K signaling would mimick glucocorticoids by increasing branched-chain amino acid degradation. Expression of a dominant negative PI3K p85 regulatory subunit (Adp85DeltaiSH2) increased BCKD activity, and dexamethasone did not further stimulate enzyme activity. Inhibition of PI3K using LY-294002 increased the transcription of the BCKD E2 subunit but not the E1alpha subunit or BCKD kinase. Thus, glucocorticoids inhibit signaling through the IRS-1/PI3K/Akt pathway with a consequence of increased branched-chain amino acid catabolism.

3-Methyl-2-Oxobutanoate Dehydrogenase (Lipoamide)↗
PubMed2006

Spatial memory formation and memory-enhancing effect of glucose involves activation of the tuberous sclerosis complex-Mammalian target of rapamycin pathway.

The tuberous sclerosis complex-mammalian target of rapamycin (TSC-mTOR) cascade integrates growth factor and nutritional signals to regulate the synthesis of specific proteins. Because both growth factor signaling and glucose have been implicated in memory formation, we questioned whether mTOR activity is required for long-term spatial memory formation and whether this cascade is involved in the memory-augmenting effect of centrally applied glucose. To test our hypothesis, we directly administered rapamycin (an inhibitor of mTOR), glucose, 5-aminoimidazole-4-carboxamide-1beta-4-ribonucleoside (AICAR; an activator of AMP kinase), or glucose plus rapamycin into the dorsal hippocampus after we trained rats in the Morris water maze task. The results from these studies indicate that glucose enhances, whereas AICAR and rapamycin both impair, long-term spatial memory. Furthermore, the memory-impairing effect of targeted rapamycin administration could not be overcome by coadministration of glucose. Consistent with these behavioral results, biochemical analysis revealed that glucose and AICAR had opposing influences on the activation of the TSC-mTOR cascade, as indicated by the phosphorylation of ribosomal S6 kinase (S6K) and 4E binding protein 1 (4EBP1), targets of mTOR. Together, these findings suggest that memory formation requires the mTOR cascade and that the memory-enhancing effect of glucose involves its ability to activate this pathway.

Aminoimidazole Carboxamide↗
PubMed2006

Short-cycle hypoxia in the intact heart: hypoxia-inducible factor 1alpha signaling and the relationship to injury threshold.

Hypoxia-inducible factor 1alpha (HIF-1alpha) transcriptionally activates multiple genes, which regulate metabolic cardioprotective and cross-adaptive mechanisms. Hypoxia and several other stimuli induce the HIF-1alpha signaling cascade, although little data exist regarding the stress threshold for activation in heart. We tested the hypothesis that relatively mild short-cycle hypoxia, which produces minimal cardiac dysfunction and no sustained or major disruption in energy state, can induce HIF-1alpha activation. We developed a short-cycle hypoxia protocol in isolated perfused rabbit heart to test this hypothesis. By altering cycling conditions, we identified a specific cycle with O(2) content and duration that operated near a threshold for causing functional injury in these rabbit hearts. Mild short-cycle hypoxia for 46 min elevated HIF-1alpha mRNA and protein within 45 min after reoxygenation. Expression also increased for multiple HIF-1alpha target genes, such as VEGF and heme oxygenase 1. After mild hypoxia, VEGF protein accumulation occurred, although HIF-1alpha and VEGF protein accumulation were suppressed after more severe hypoxia, which also caused depletion of ATP and nondiffusible nucleotides. In summary, these results indicate that mild near-threshold hypoxia induces HIF-1alpha cascade, but more severe hypoxia suppresses protein accumulation for this transcription factor and the target genes. Posttranscriptional suppression of these proteins occurs under conditions of altered energy state, exemplified by ATP depletion.

Animals↗
PubMedDate not supplied

Hemophilia in dogs, with special reference to hemophilia A among German shepherd dogs in Denmark. I: Pathophysiology, laboratory tests and genetics.

A review is given of the history and distribution of hemophilia in dogs. The current knowledge of Factor VIII relative to hemophilia A and von Willebrand's Disease is presented. The tests required for distinguishing between hemophilia A, hemophilia B, von Willebrand's Disease, and various disorders caused by other factor defects in the coagulation cascade are described. X-linked, recessive inheritance of hemophilia A is illustrated in genealogical diagrams. The precautions required in connection with blood sampling for diagnostic tests are emphasized.

Animals↗
PubMedDate not supplied

Optimal chemostat cascades for periplasmic protein production.

This theoretical work predicts the optimal system design for the steady-state production of secreted protein in a chemostat cascade, using bakers' yeast (Saccharomyces cerevisiae) as the host organism. The protein of interest, mutant invertase, is secreted to the periplasmic space instead of the culture medium on account of its large size. This work uses the secretion model developed and tested by Park and Ramirez (1988). It is shown that the highest productivity is achieved when the chemostat cascade contains two stages, although the improvement over the single-stage productivity is small. When no recycle is used, the advantage of two stages results from the tradeoff between maximizing the cell concentration and maximizing the rate of protein production per cell. When recycle is used, the cell concentration and protein productivity are increased, and the advantage of two stages results from the tradeoff between maximizing the specific protein production rate and maximizing the specific protein secretion rate. Cascades with three stages were also investigated, but these were found to have no improvement over the corresponding two-stage cascades.

Cloning, Molecular↗