Extracellular proteins produced by yeast have been observed to stratify in the extracellular fluid of a batch bioreactor, thus creating a vertical concentration gradient. We observed that, in the four different experiments conducted, each varied in their protein recovery characteristics. For example, sparging the system with gas accentuates the separation, though even in a nonsparged system, the in situ generation of minute carbon dioxide bubbles by yeast cells creates a protein gradient as the bubbles carry proteins upward. Based on these and other observations, we propose possible strategies for recovering the individual proteins from a system containing the four major proteins considered. A simple steady-state mathematical model, based on convective upward protein transport being balanced by downward protein diffusion, has been used to describe the behavior of each of these four extracellular proteins in the fermentation broth.

Fermentation↗

PubMedDate not supplied

The culture of human osteoblasts upon bone graft substitutes.

In order to assess the ability of six potential bone graft substitutes to support the growth of human osteoblasts, these cells were grown in culture and then plated onto fragments of the six materials and cultured for a further period of 15 days. Tests to confirm the osteoblastic phenotype of the cells included spectrophotometric alkaline phosphatase assay; Western blotting of secreted osteocalcin, osteonectin, bone sialoprotein, and collagen type I; and mineralization within the cultures provided with a supplemented medium. Cells were seeded onto the materials in 24-well plates (Nunc, Naperville, IL) at density levels 12,500 cells/cm2 and 25,000 cells/cm2. Specimens were examined after the 15-day culture period by scanning electron microscopy. At a seeding density of 12,500 cells/cm2 results showed that the human osteoblasts had greatest affinities for demineralized rat bone and demineralized Surgibone, whilst few osteoblasts were found attached to Pyrost, Surgibone, or coral. The collagen matrix of Callopat hydrated in the culture media exposing the hydroxyapatite crystals within it, and these became the foci for cell attachment and growth. At a seeding density of 25,000 cells/cm2 the osteoblasts had attached to and proliferated upon the surfaces of all the materials, forming multilayers, with the exception of Surgibone. These experiments demonstrated that all the materials, with the exception of nondemineralized Surgibone, were biocompatible for human osteoblasts.(ABSTRACT TRUNCATED AT 250 WORDS)

Aged↗

PubMedDate not supplied

Artificial airways: a survey of cuff management practices.

OBJECTIVE: To determine current endotracheal and tracheostomy tube cuff management practices in adult and pediatric populations, and to compare current adult cuff management practice with those reported in use in 1984 and 1987. DESIGN: Descriptive survey. SETTING: Sixty-four acute care hospitals in the northeastern United States. SAMPLE: Responders represented 93 critical care units: 59 adult and 34 pediatric units. MEASUREMENTS: Subjects completed a survey questionnaire. RESULTS: Forty-one percent reported cuffs were routinely deflated, with most (88%) reporting cuff deflation every 8 to 12 hours or daily. In the pediatric population, minimal occlusive volume was the most frequent technique (29%); whereas in the adult population, both minimal occlusive volume technique and minimal leak technique were used more frequently (36%). Most (93%) cuff pressures were measured every 8 to 12 hours or daily with a recommended maximum range of 20 to 30 mm Hg. Cuff deflation and cuff inflation were performed more often by the nursing staff (36%). Cuff pressures were performed more often by respiratory staff (71%). There were no statistically significant differences in the cuff management practices between the adult and pediatric populations. In comparing the results for adults to the data of 1984 and 1987, most cuff management practices changed from every 8 hours or less to every 8 to 12 hours or daily, and the nursing responsibility for these techniques increased (22%). CONCLUSION: Most responders do not routinely deflate cuffs. Cuff management practices are performed less frequently, and nursing responsibility for these techniques has increased.

Adult↗

PubMedDate not supplied

Chemical models for the lethality curves of toxic metal ions.

Several equilibrium models are presented for the calculation of the lethality curves due to toxic metal ions. In the first, a generalized Langmuir model is used to examine the occupancy of linear arrays of 1, 2, ..., 6 interacting adsorption sites on a macromolecular species. This model permits one to take into account cooperative or anticooperative interaction of occupied adjacent sites. In the second model, a variety of nonlinear distributions of interacting sites (in triangular, square, tetrahedral, and octahedral array) are analyzed, and the corresponding adsorption isotherms are calculated. The third model treated, the Ising model, represents a linear infinite array of sites with nearest-neighbor interactions. The fourth and fifth models examined are the Bragg-Williams model and the quasi-chemical model, both of which permit approximate treatment of infinite arrays of adsorption sites having arbitrary numbers of interacting nearest neighbors. These models are then combined with the assumption that the differential distribution of mortality is a known function of the fraction of sites occupied by the toxic metal ion to generate lethality curves. Results are computed for the special case in which the differential mortality distribution is Gaussian, and it is shown that all of the models are capable of generating lethality curves of the sort found experimentally when plots are made of percentage lethality versus log dosage. The models can also be used for situations in which toxic effects other than lethality arise from the interaction of a toxic molecule or ion with more than one site on a linear macromolecule or for reactions involving certain other arrays of specified configuration.

Binding Sites↗

PubMedDate not supplied

An in vitro model for the in vivo mobilization of cadmium by chelating agents using 113Cd-NMR spectroscopy.

An in vitro method, based on 113Cd-NMR spectroscopy, that provides an alternative to the use of animals for an initial screening of cadmium antagonists is presented. The relative values of the effective stability constants of potential chelating antagonists for cadmium are estimated by using 113Cd-NMR spectroscopy to determine the concentrations of the cadmium species involved in appropriate competitive equilibria. This is accomplished via an examination of the competition between the proposed antagonist and EDTA (ethylenediaminetetraacetic acid) for cadmium-113; previously, EDTA has been shown to be capable of removing cadmium from such in vivo binding sites as metallothionein. The reactions proceed via the stepwise addition of three dithiocarbamate groups to the cadmium accompanied by the concurrent stepwise release of donor groups from the EDTA. The resulting 113Cd-NMR data allow for the determination of the overall stability constant for the complex formed between cadmium and N-methyl-D-glucamine dithiocarbamate, iminodiacetic acid dithiocarbamate, proline dithiocarbamate, sarcosine dithiocarbamate. The use of 113Cd-NMR spectroscopy has the potential for providing direct evidence on the effectiveness of chelate antagonists to compete with endogenous ligands for other toxic metal ions. This technique could prove very useful for other compounds that are not stable enough toward acid and/or base to be examined by standard titrimetric methods.

Cadmium↗

PubMedDate not supplied

Comparison of cancellous bone-derived cell proliferation in autologous human and fetal bovine serum.

Conventionally, culture medium is supplemented with fetal bovine serum (FBS): such serum presents potential risks of foreign protein contamination and transmission of viral or prion-related disease if used in culture of cells intended for human reimplantation. As it has been suggested that a composite of cultured human cancellous bone-derived cells and a bone graft substitute may present a solution to the well-recognized complications and limited availability associated with harvest of fresh bone graft, this study aimed to compare the proliferative response of human cancellous bone-derived cells supplemented with FBS or autologous human serum (AHS) to determine whether AHS is a practical alternative. Explant cultures were established using greater trochanter trabecular bone from 10 consenting patients (aged 57-84) undergoing total hip arthroplasty. At the same time, serum was harvested. The cells were characterized by alkaline phosphatase expression and by in vitro mineralization in enhanced medium. At confluence, cells were aliquoted into multiwell plates and grown for 9 days in medium supplemented with 5%, 10%, 15%, or 20% AHS or 10% FBS. Proliferative response was determined by a crystal violet dye binding assay. There was no significant difference between proliferation in 5% AHS and 10% FBS. However, 10%, 15%, and 20% AHS all produced significantly greater proliferation than 10% FBS. The proliferative response was dose related. FBS is said to be rich in growth and attachment factors, which is why it is widely used in tissue culture. These results suggest that species specificity, even when using adult serum, outweighs these advantages. It should therefore be considered as a prerequisite for any program involving reimplantation of cultured human cells. Clinical trials of cultured human cancellous bone-derived cells have now begun.

Aged↗

PubMedDate not supplied

Large bony defects: can bone cell culture fill the gap?

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Animals↗

PubMedDate not supplied

Efficacy of strength training in prepubescent to early postpubescent males and females: effects of gender and maturity.

There has been considerable debate concerning the benefits of children participating in weight training programs. With the potential benefits of such training in specific rehabilitation regimens, the safety/efficacy of weight training is a topic in need of scientific study. Fifty-two experimental and 39 control subjects participated in this study. A 2 x 2 x 2 (gender by treatment by Tanner stage) ANOVA was used to examine pre- to post-test differences in six strength measures, eight anthropometric measures, five motor performance measures, and one flexibility measure associated with participation in a 12-week progressive resistance programme. In addition, safety of the weight training programme was examined. For strength differences, there were two significant main effects favouring strength gains in males and four favouring the experimental group. For anthropometric changes, 3-way interactions occurred that were not easily explained. However, the predominant main effect was treatment; the experimental group generally experienced gains in body segment girths with decreases in skinfold thickness. For motor performance, the experimental group had greater improvements in three of five parameters. The experimental group also had significantly greater gains in flexibility. The weight training programme was associated with only one injury. These findings support the general observation that physical benefits can be gained safely by children who participate in a weight training programme.

Adolescent↗

PubMedDate not supplied

Hepatic encephalopathy associated with cobalt deficiency and white liver disease in lambs.

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Animals↗