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At least 343 records · Page 19Linked to original sources
PubMed1991

Cell aggregates of Escherichia coli with benzylpenicillin amidase activity.

Intact cells Escherichia coli CCM 2843, exhibiting substantial benzylpenicillin amidase activity, were bound mutually with supporting waste microbial cells, native or treated, to obtain an inexpensive biocatalyst for the production of 6-aminopenicillanic acid (6-APA). The bond was effected by glutaraldehyde (GA) and Sedipur CL-930 (PEI), without any carrier. The optimal concentration of GA was 2%, that of PEI 1%. The optimal biocatalyst was obtained by immobilization of productive cells with their fragments at a mass ratio of 4:1. The cell aggregates were used for hydrolysis of potassium benzyl-penicillin at a concentration of 5% to 6-APA. After 25 repeated batch conversions the degree of conversion did not decrease; its average value was 96.4%.

Bacterial Adhesion↗
PubMed1978

The effects of tumour cells on embryonic cell aggregation, adhesion and detachment.

The presence of small numbers of tumour cells inhibits the aggregation of embryonic chicken neural retina cells grown in gyratory shaker culture. The aggregation of neural retina cells was also inhibited by ascites cell medium. We investigated whether the inhibitory effect of the tumour cells on aggregate size is effected by inhibition of the initial adhesion or by enhancement of their separation. The number of neural retina cells adherent to microtest plate surfaces was significantly reduced after incubation with either Ehrlich ascites cells or cell-free, conditioned medium, while the percentage of cells removed from glass by shearing was unchanged under those conditions. These results suggest that the reduction in neural retina cell aggregate size produced by Ehrlich ascites cells and their products is due to partial inhibition of neural retina cell adhesion processes, as distinct from enhancement of separation.

Animals↗
PubMed1989

Regulatory activity and topological distribution of folliculo-stellate cells in rat anterior pituitary cell aggregates.

An enriched population of cells immunoreactive to antiserum against S-100 protein, a marker of folliculo-stellate (FS) cells in the rat pituitary, was obtained by separation of dispersed pituitary cells from adult female rats by gradient sedimentation at unit gravity. The effect of FS cells on the stimulation and inhibition of prolactin (PRL) and growth hormone (GH) release was studied by coaggregation experiments of the FS cell-enriched population with respectively a lactotroph-enriched and a somatotroph-enriched population from adult female rats. The FS cell population not only attenuated the stimulation of PRL and GH release, but also significantly attenuated the inhibition of PRL release by 10, 30 or 300 nM dopamine (DA), and the inhibition of GH release by 0.1 nM somatostatin (SRIF). The stimulatory action of angiotensin II (AII) on PRL secretion in the presence of DA was also attenuated by the FS cells. Light microscopic evaluation of immunostained semithin sections showed a meshwork of cytoplasmic extensions of FS cells as well as follicular structures in the aggregates. There was no preferential association of FS cells with certain cell types. The permeability of the aggregates to diffusing molecules was tested at the ultrastructural level by the lanthanum hydroxide tracing technique. Lanthanum traced the intercellular gaps over the entire aggregate irrespective of whether the proportional number of FS cells was high or low, indicating that FS cells do not seal off certain areas in the aggregate by the formation of tight junctions. It is suggested that FS cells attenuate the action not only of stimulatory but also inhibitory secretagogues on hormone-secreting pituitary cells. The possible physiological relevance of the present findings is supported by the topological distribution of the FS cells in the aggregates, which closely resembles that of the intact pituitary.

Animals↗
PubMedDate not supplied

Effect of 6-diazo-5-oxo-L-norleucine (DON) on human carcinoid tumor cell aggregates.

The induction of glutamine starvation has been suggested as a potential target for antitumoral treatment using inhibitors of amidotransferase, an enzyme which mediates the conversion of glutamate to glutamine. Using multicellular aggregates from tumor cell lines, the effect of treatment with a suggested glutamine antagonist, 6-diazo-5-axo-L-norleucine (DON), was investigated. As indicators of treatment response, three different parameters were measured: aggregate size, uptake of 14C-methionine and secretion of Chromogranin A. Of six cell types evaluated (carcinoid, glioma, neuroblastoma pancreas and bladder cancer), the largest inhibition of 14Cmethionine uptake, amounting to 60%, was found in the carcinoid cell line BON. In this cell line the maximum effect was reached already at 10 microM concentration. DON induced marked growth inhibition in the BON aggregates which lasted 3-4 weeks after which regrowth started. During this period the secretion of chromogranin and methionine uptake was also inhibited. These studies suggest that the neuroendocrine cell line BON is especially vulnerable to treatment by DON and show that strong inhibitory effects are found at concentrations lower than that achieved in patient blood in previous clinical trials.

2-Aminoadipic Acid↗
PubMed1987

Cholinesterases and cell proliferation in "nonstratified" and "stratified" cell aggregates from chicken retina and tectum.

Dissociated single cells from chicken retina or tectum kept in rotation-mediated cell culture aggregate, proliferate and establish a certain degree of histotypical cell-to-cell relationships ("sorting out"), but these systems never form highly laminated aggregates ("nonstratified" R- and T-aggregates). In contrast, a mixture of retinal plus pigment epithelial cells forms highly "stratified" aggregates ("RPE-aggregates", see Vollmer et al. 1984). The present comparative study of "stratified" and "nonstratified" aggregates enables us to investigate the process of cell proliferation uncoupled from that of tissue stratification. Here we try to relate these two basic neurogenetic processes with patterns of expression of cholinesterases (AChE, BChE) during formation of both types of aggregates. During early aggregate formation, in both "stratified" and "nonstratified" aggregates an increased butyrylcholinesterase activity is observed close to mitotically active cells. Quantitatively both phenomena show their maxima after 2-3 days in culture. In contrast, AChE-expression in all systems increases with incubation time. In nonproliferative areas, in the center of RPE-aggregates, the formation of plexiform layers is characterized initially by weak BChE- and then strong AChE-activity. These areas correspond with the inner (IPL) and outer (OPL) plexiform layers of the retina in vivo. Although by sucrose gradient centrifugation we find that the 6S- and the fiber-associated 11S-molecules of AChE are present in all types of aggregates, during the culture period the ratio of 11S/6S-forms increases only in RPE-aggregates, which again indicates the advanced degree of differentiation within these aggregates.(ABSTRACT TRUNCATED AT 250 WORDS)

Acetylcholinesterase↗
PubMed1983

Concanavalin A increases spontaneous beat rate of embryonic chick heart cell aggregates.

The plant lectin concanavalin A (Con A), at concentrations of 5-200 micrograms/ml, induced a twofold to fivefold increase in spontaneous beat rate of cultured aggregates of ventricular cells from seven-day chick embryos. This response was time, dose, and temperature dependent and was accompanied by a decrease in transmembrane potential. It could be blocked or reversed by alpha-methyl-D-mannoside but was not reversed by dilution alone. Binding of the lectin occurred in the cold, but a temperature-dependent process was also necessary to produce the response. Divalent (succinyl) Con A did not cause a beat rate increase. Whole heart aggregates responded similarly but less intensely than ventricular aggregates. Atrial aggregates, and whole heart aggregates treated with 5 microgram/ml of Con A, produced a biphasic chronotropic response, first decreasing then increasing their beat rates. These results suggest that saccharide-bearing macromolecules on the heart cell surface play a role in regulating spontaneous beat rate.

Action Potentials↗
PubMed1979

Pathological cell aggregates in bone marrow cultures from patients with various hematological diseases.

Non-clonal growth of macroscopic cell aggregates in methylcellulose cultures of abnormal marrow is described. They were seen in all patients with Graft-versus-Host Disease, graft rejection, and autoimmune disease presumably directed against hemopoietic cells, we found them in 35% of patients with primary hematological neoplasias and rarely in patients with solid tumors. They were never encountered in 80 healthy controls. The aggregates originated from small cell clumps which sedimented with the "buffy coat" in contrast to normal bone marrow particles. They contained tumor cells, grafted myeloid cells, or target cells of autoimmune disease in association with a widely varying amount of macrophages. Preliminary results suggest that the frequency of macrophages within the aggregates correlates inversely with the aggressiveness of the clinical condition. We propose that appearance of such aggregates in an indicator of immune activation; we expect that further quantitation of the phenomenon will reveal important clinical correlations and provide a model for the study of host defense to "foreign" cells.

Anemia, Hemolytic, Autoimmune↗
PubMed1999

ICAM-3 (CD50) is expressed by human mast cells: induction of homotypic mast cell aggregation via ICAM-3.

Intercellular adhesion molecule-3 (ICAM-3, CD50), an adhesion receptor of the immunoglobulin superfamily, is suggested to play a key role in adhesive cellular interactions during the initial phase of an immune response. We here provide evidence that ICAM-3 is abundantly expressed by cells of the human mast cell line HMC-1 and, to a lower degree, by purified skin mast cells, as demonstrated by flow-cytometry, ELISA and RT-PCR. ICAM-3 immunoprecipitated from surface biotinylated HMC-1 cells migrates as a broad band of Mr 124,000 by Western blot analysis. We also demonstrate that monoclonal antibodies directed against ICAM-3 are capable of inducing rapid HMC-1 cell aggregation, the extent of which strongly depends on the epitope recognized by the mAb applied. Interestingly, although inhibitable by two of six mAbs against LFA-1, HMC-1 aggregation induced via ICAM-3 appears to be mediated by an adhesive pathway independent of LFA-1. Dermal mast cells are also aggregated with anti-ICAM-3 mAbs, a phenomenon which has not been described before for isolated tissue mast cells. However, this process displays slower kinetics, as compared to HMC-1 cells. That anti-ICAM-3 mAbs are able to mediate biological effects is further illustrated by their capability to increase stimulation-dependent release of the pro-inflammatory cytokines interleukin-6 (IL-6) and IL-8 from HMC-1 cells. Taken together, these results indicate that ICAM-3 is not only expressed by immature and mature human mast cells, but also possesses functional relevance and may therefore play a significant role in mast cell associated processes.

Animals↗
PubMed1999

Expression of the alpha 6A integrin splice variant in developing mouse embryonic stem cell aggregates and correlation with cardiac muscle differentiation.

Mouse embryonic stem (ES) cells grown in aggregates give rise to several different cell types, including cardiac muscle. Given the lack of cardiac muscle cell lines, ES cells can be a useful tool in the study of cardiac muscle differentiation. The laminin-binding integrin alpha 6 beta 1 exists in two different splice variant forms of the alpha chain (alpha 6A and alpha 6B), the alpha 6A form having been implicated as possibly playing a role in cardiac muscle development, based on its distribution pattern [4, 53]. In this study we characterise the ES cell model system in terms of the expression of the two different alpha 6 splice variants. We correlate their expression with that of muscle markers and the transcription factor GATA-4, using the reverse transcription-polymerase chain reaction (RT-PCR). We confirm that alpha 6B is constitutively expressed by ES cells. In contrast, alpha 6A expression appears later and overlaps in time with a period when the muscle marker myosin light chain-2V (MLC-2V) is expressed, but no MyoD is present, which indicates the presence of cardiac muscle cells in the aggregates. We further show that GATA-4 is present at the same time. Culturing the aggregates under conditions that stimulate (transforming growth factor beta 1 supplement) or inhibit (TGF beta 1 plus 10(-9) M retinoic acid supplement) cardiac muscle differentiation does not lead to any qualitative differences in the timing of expression of these genes, but quantitative changes cannot be excluded. The TGF beta 1 supplement does, however, lead to a relatively greater expression of alpha 6A compared to alpha 6B than the TGF beta 1 plus 10(-9) M RA supplement after 6 days in culture, suggesting that alpha 6A expression is favoured under conditions that stimulate cardiac muscle differentiation. The switch towards alpha 6A expression in ES cell aggregates is paralleled by expression of the binding receptor for TGF beta (T beta RII). Stable expression of a mutated (dominant negative) T beta RII in ES cells, however, still resulted in (TGF beta-independent) upregulation of alpha 6A, demonstrating that these events were not causally related and that parallel or alternative regulatory pathways exist. The initial characterisation of differentiating ES cell aggregates in terms of alpha 6A integrin subunit expression suggests that this model system could be a valuable tool in the study of the role of the alpha 6A beta 1 integrin in cardiac muscle differentiation.

Animals↗
PubMed1990

Size determination of red blood cell aggregates induced by dextran using ultrasound backscattering phenomenon.

Different methods are commonly used to study the red blood cell aggregation phenomenon. The major interest of the ultrasonic method presently discussed is to assess the mean size of red blood cell (RBC) aggregates by measuring ultrasonic intensity backscattered by blood. Applying Rayleigh theory of sound to blood medium, one can show that the scattered ultrasonic intensity is proportional to the 6th power of the size of the RBC aggregates. The ultrasonic method is used to evaluate the mean size of RBC aggregates induced by dextrans. RBCs are suspended at various hematocrits H, in solution of dextrans of different molecular weights M and at different weight concentrations Cw. Results are presented by using the ultrasonic backscattering coefficient chi which is a relevant quantity in a scattering experiment. For suspensions of RBCs aggregated with dextran of molecular weight 70,000 dalton (dextran 70) at concentration Cw = 40 g/l, variations of chi as a function of H are similar to those obtained for normal blood. At a fixed hematocrit, variation of chi versus Cw for dextran 70 exhibits a maximum at 40 g/l. In the case of RBCs suspended at hematocrit 20% and aggregated with dextrans of molecular weight M, 70,000 less than or equal to M less than or equal to 2,000,000, the variations of chi versus molar concentration Cm are similar to those of the microscopic aggregation index defined by Chien (1). Finally, a statistical model of the blood structure previously described (2) is applied to evaluate the mean size of the aggregates. According to this model, the mean size of aggregates is independent of hematocrit for H less than or equal to 40% and independent of the molecular weight of dextran for M greater than or equal to 150,000 dalton.

Dextrans↗
PubMed1990

The effect of alteration of extracellular Na+ or Ca2+ and inhibition of Ca2+ entry, Na(+)-H+ exchange, and Na(+)-Ca2+ exchange by diltiazem, amiloride, and dichlorobenzamil on the response of cardiac cell aggregates to epidermal growth factor.

The purpose of this study was to examine the effect of epidermal growth factor (EGF) on cardiac function and to explore ionic mechanisms as potential explanations for EGF-induced changes in cardiac contractile frequency. Cardiac cell aggregates were prepared from 7-day-old chick embryo hearts and were maintained in culture. EGF over a concentration range of 5 to 20 ng/ml produced a dose-dependent increase in cardiac contractile frequency. Inhibition of Na(+)-H+ exchange by amiloride antagonized the action of EGF. Inhibition of Na(+)-Ca2+ exchange by dichlorobenzamil prevented the effects of EGF. Inhibition of voltage-dependent calcium influx by diltiazem also antagonized the effect of EGF. The positive chronotropic action of EGF was significantly enhanced when the concentration of Na+ or Ca2+ was increased in the medium. These data indicate that EGF has a definite dose-dependent effect on the cardiac contractile frequency that is operative through ionic transport mechanisms that include increased calcium entry through voltage-dependent calcium channels and stimulation of Na(+)-H+ and Na(+)-Ca2+ exchange. The similarity in the effects of inhibition of these three ionic mechanisms suggests they are interrelated so that interference at any step in the process inhibits the action of EGF on cardiac myocytes.

Amiloride↗
PubMed1993

Enhancement of phorbol ester induced cell aggregation after alterations in asparagine-linked oligosaccharides.

Human erythroleukemia (K-562) cells grown in the presence of phorbol 12,13-dibutyrate formed aggregates of cells not seen in untreated control cultures. Furthermore, the proportion of cells in aggregates and the size of the aggregates both increased dramatically in cultures treated with both phorbol ester and kifunensine, an inhibitor of asparagine-linked oligosaccharide processing. Relative to control cells, phorbol ester treated cells exhibited a greater proportion of N-linked oligosaccharides of the complex-type. Kifunensine prevented this change and caused an accumulation of Man9GlcNAc2. The enhanced aggregation of cells treated with phorbol ester plus kifunensine depended on phorbol ester concentration and was blocked by inhibitors of protein kinase C (H7, sphinganine and sangivamycin). In flow cytometry analysis, phorbol ester treated K-562 cells showed an increase in CD44, a glycoprotein involved in cell adhesion. Moreover, monoclonal antibody to CD44 augmented reaggregation of phorbol ester treated cells. The results implicate phorbol ester induction of CD44 in aggregation of K-562 cells and demonstrate that the presence of high mannose-type asparagine-linked oligosaccharides on cell glycoproteins correlates with increased aggregation of phorbol ester treated cells.

Alkaloids↗
PubMed2006

A novel real-time system to monitor cell aggregation and trajectories in rotating wall vessel bioreactors.

Rotating wall vessel bioreactors (RWVs) constitute dynamic suspension culture venues for tissue engineering. Quantitative real-time assessment of the kinetics of cell-cell aggregation in RWVs can yield mechanistic information about the initial steps leading to the assembly of individual cells into tissue-like constructs. In our imaging system, fluorescently labeled cells suspended in a HARV-type RWV were irradiated by a laser-beam. Emission was recorded by a camera mounted at 90 degrees to the excitation plane. Using macro lenses, the system identified approximately 5 microm particles from a 5 cm working distance, distinguished aggregated 20 microm microspheres from larger (45 and 90 microm) microspheres, and plotted local trajectories of microspheres and cells. Sizes of PC12 cells assessed by our system matched conventional measurements. We validated the system's ability to follow HepG2 and PC12 aggregation in real time over 24h of RWV culture. Taken together, our system provides the means to measure and analyze in real time the processes that lead to the 3D tissue-like assembly of diverse cell types into spheroids. Future studies include development of intelligent feedback algorithms, allowing automatic control over RWV rotational speed required to maintain aggregating cells and nascent tissue in continual free fall.

Animals↗
PubMed2004

[Non-proliferative diabetic retinopathy and red blood cell aggregation].

The pathogenesis of diabetic retinopathy is not clear, but it is generally agreed, that in addition to vascular components hemorheological disturbances can play a role in the impairment of microvascular flow. The aim of this study was to correlate the severity of retinopathy in diabetic patients with red blood aggregation and some parameters of aggregation. The study was carried out on 52 patients suffering from type 2 diabetes mellitus with non-proliferative retinopathy--25 men and 27 women (mean age 63.8 +/- 6.5 years) and 43 healthy--20 men and 23 women (mean age 55.5 +/- 9.6 years). The fundus appearance of patients showed non-proliferative diabetic retinopathy. Red blood cell aggregation was determined by LORCA aggregometer. Aggregation index (AI), disaggregation shear rate (gamma(p)), time to the half of the disaggregation (t1/2), time constant of fast component in syllectogram (T1), time constant of slow component (T2) and amplitude (total extent of aggregation Am) were measured. In diabetics with non-proliferative retinopathy we observed the increase of AI (66.5 +/- 7.2 vs 59.4 +/- 5.8; p < 0.001), decrease of Am (19.8 +/- 3.3 vs 21.2 +/- 2.7; p < 0.05), decrease of T1 (2.4 +/- 0.5 vs 2.75 +/- 0.42; p < 0.005), increase of T2 (27.6 +/- 4.7 vs 25.75 +/- 4.11; p < 0.05), decrease of t1/2 (1.98 +/- 0.72 vs 2.7 +/- 0.77; p < 0.001) and increase of gamma(p) (215.6 +/- 23.3 vs 98.1 +/- 8.7; p < 0.001). The parameters of erythrocytes aggregation were correlated with intensification of diabetic retinopathy symptoms. Our results show the importance of red blood cell aggregation parameters in the development of diabetic microangiopathy.

Aged↗
PubMed2006

Medicinal plant extracts as anti-Escherichia coli O157:H7 agents and their effects on bacterial cell aggregation.

Ethanolic extracts of eight Thai medicinal plants (representing five families) that are used as traditional remedies for treating diarrhea were examined with a salt aggregation test for their ability to modulate cell surface hydrophobicity of enterohemorrhagic Escherichia coli strains, including E. coli O157:H7. Four of these medicinal plants, Acacia catechu, Peltophorum pterocarpum, Punica granatum, and Quercus infectoria, have high bacteriostatic and bactericidal activities. The ethanolic extract of Q. infectoria was the most effective against all strains of E. coli, with MICs of 0.12 to 0.98 mg/ml and MBCs of 0.98 to 3.91 mg/ml. The ethanolic extract of P. granatum had MICs of 0.49 to 1.95 mg/ml and MBCs of 1.95 to 3.91 mg/ml. Ethanolic extracts of Q. infectoria, P. pterocarpum, and P. granatum were among the most effective extracts against the two strains of E. coli O157:H7. The other four plants, Andrographis paniculata, Pluchia indica, Tamarindus indica, and Walsura robusta, did not have high bacteriostatic and bactericidal activities but were able to affect hydrophobicity characteristics on their outermost surface. All plants except Q. infectoria had some ability to increase cell surface hydrophobicity. There appears to be no correlation between antibacterial activity and cell aggregative properties.

Acacia↗
PubMed1980

Red blood cell aggregation in men with coronary artery disease.

The red blood cell aggregation value (AW) in a group of 39 patients with coronary artery disease (CAD) was measured and compared with that of an age- and sex-equivalent group of normals and a group of 12 patients with suspected CAD, whose coronary arteries were found to be normal by coronary arteriography. The AW was significantly higher in CAD patients than in both normal groups (2P < 0.01 and 2P < 0.02 respectively). The AW in a group of 12 CAD-patients treated with the aggregation lowering drug clofibrate was significantly lower than in the untreated CAD-group. The predictive value of AW was calculated by means of mathematical methods. Measurement of AW could be a useful aid in the study of detection of CAD.

Adult↗