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At least 19 recordsLinked to original sources
PubMed1990

Preparation and evaluation of sterically stabilized liposomes: colloidal stability, serum stability, macrophage uptake, and toxicity.

Sterically stabilized liposomes were produced by incorporating a nonionic surfactant, polysorbate 80 (Tween 80), into the lipid bilayer. The sterically stabilized liposomes exhibited a superior entrapment stability compared with surfactant-free liposomes (i.e., liposomes prepared with lipids and cholesterol). The sterically stabilized liposomes were stable at high calcium ion concentrations, and liposome-entrapped carboxyfluorescein was retained within the stabilized liposomes in the presence of serum for at least 5 h. The macrophage uptake of the sterically stabilized liposomes was comparable to that of liposomes containing lipids and cholesterol. The sterically stabilized liposomes were non-toxic, in concentrations up to 3.0 mM, to macrophages. These results indicate that polysorbate 80 can be used to produce stable liposomes without changing the unique macrophage distribution of this drug delivery system.

Cells, Cultured↗
PubMed1976

Continuous Proteolysis with a stabilized stabilized protease. I. Chemical stabilization of an alkaline protease.

Due to the loss of enzymatic activity as a function of time, an alkaline protease, selected for the continuous preparation of protein hydrolysates (J. Boudrant and C. Cheftel, Biotechnol. Bioeng., 18,1735, 1976), was chemically stabilized by a simple treatment with glutaraldehyde. Two fractions, soluble and insoluble, were obtained. The activities of these two fractions were measured with casein and N-benzoyl-L-arginine ethyl ester (BAEE) as a function of glutaraldehyde concentration used. It was noted that the insoluble fraction was practically inactive with the first substrate and that the heat stability of the soluble form was likewise enhanced. Molecular weights of these two forms were unchanged, but the uv-spectrum of the soluble form was modified. From amino acid analysis, it appears that this treatment mainly provokes a decrease in lysine content.

Aldehydes↗
PubMed1992

Formulation and stability of freeze-dried proteins: effects of moisture and oxygen on the stability of freeze-dried formulations of human growth hormone.

This research presents the results of a series of stability studies on freeze-dried formulations of human growth hormone (hGH). Chemical decomposition via methionine oxidation and asparagine deamidation as well as irreversible aggregation are characterized by HPLC. Water sorption isotherms, DSC thermograms, and pulsed proton NMR data are also obtained. No glass transition temperatures are observed in the temperature range of the stability studies. The pulsed NMR data suggest onset of greater mobility in the solid at a water content slightly higher than BET "monolayer" level. Stability of freeze-dried solids at 25 degrees C and 40 degrees C is studied as a function of residual moisture and exposure to oxygen. Formulations with and without a glycine/mannitol excipient system are studied. Significant levels of chemical decomposition and irreversible aggregation occur under most conditions with the effects of residual water content and "headspace oxygen" strongly dependent on the formulation. At low water content with minimal oxygen in the vial headspace, the glycine/mannitol formulation yields optimum stability. However, for either high water content or high oxygen content in the vial, stability of hGH without excipients is superior. The qualitative effect of residual moisture on stability depends on the temperature of the stability study. Generally, the stability of a sample adjusted to a given water content by desorption (during freeze-drying) is identical to the stability of a sample prepared by sorption of water on to a previously highly dried sample.

Calorimetry, Differential Scanning↗
PubMed1989

Rotational stability of a posterior stabilized total knee arthroplasty.

The effect of the posterior stabilizing mechanism on rotational stability in total knee arthroplasty (TKA) was investigated in six cadaver knees using a special knee-testing device. The device evaluated varus-valgus, rotational, and anteroposterior (AP) stability in the normal knee compared to a posterior stabilized TKA with either a rotationally constrained or an unconstrained articular surface. None of the stability parameters was significantly different from normal in either configuration of the tibial surface, but the constrained surface did decrease rotational deflection compared to the rotationally unconstrained surfaces. These findings show that rotational constraint in a posterior stabilized TKA is not necessary to achieve rotational stability as long as varus-valgus stability is achieved by appropriately tensioning the collateral ligaments.

Humans↗
PubMed1978

The stability properties of golden beet and red beet pigments: influence of pH, temperature, and some stabilizers.

Golden beet (Beta vulgaris var. lutea) color was found to contain 8 components, of which the most important seemed to be vulgaxanthin-I and -II. Purified vulgazanthin -I solutions are easily degraded at high temperatures. The stability is, however, strongly dependent on pH: the stability is best at pH values between 5 and 6, the poorest at low pH values, but at pH 7 the stability is better than that of betanin. Vulgaxanthin-I is more stable in the raw extract than in a purified solution. EDTA, even in ppm amounts, was found to improve the stability of betanin. The effect was dependent on pH value, being most efficient at pH 2.0 and 5.0. Stability of vulgaxanthin-I was not improved by EDTA. Tannin did not show stabilizing influence. Ascorbic acid was found to have an unfavorable influence on stability, especially in the case of betanin.

Drug Stability↗
PubMed1979

[Comparative studies on the stability of aqueous drug solutions in the isothermal and the non-isothermal short-time test as well as in the long-time test. Part 2: The stability of aqueous tetracaine solutions in the non-isothermal short-time test (author's transl)].

A study of the hydrolytic degradation of tetracaine solutions at various pH values demonstrates that the results from non-isothermal stability testing with logarithmic rise in temperature are in good agreement with the activation energies determined, under analogous conditions, by means of the isothermal short-time test and long-time test. The range of the maximum of stability is more clearly evinced by the non-isothermal short-time test than by the isothermal stability test. The comparison of the two methods reveals that the deviation of the reaction rate constants is greater in the non-isothermal test, which is due to the calculation required for the logarithmic rise in temperature. The results obtained with tetracaine evidence that the non-isothermal stability test is an appropriate method for the rapid determination of stability parameters (e.g. stability maximum, hydrolysis velocities) in the frame-work of testing potential drugs for stability and in the optimization of prescriptions.

Chemistry, Pharmaceutical↗
PubMed1989

Static and dynamic forward stability of occupied wheelchairs: influence of elevated footrests and forward stabilizers.

With 20 able-bodied subjects, three hypotheses were tested: (1) that elevating the footrests reduces the forward stability of occupied wheelchairs, (2) that placing simulated plaster casts on the occupant's legs further reduces stability, and (3) that forward stabilizers limit the extent of dynamic forward instability. Static stability was studied on a tilting platform; dynamic stability was tested by having subjects descend a ramp. Elevating one or both footrests and adding one or two simulated casts each significantly reduced static forward stability. During dynamic testing with lowered footrests, only seven subjects tipped forward, and the extent of tip was limited by the footrests. With both footrests elevated, eight subjects tipped transiently, and 12 continued to tip until the footrests hit the floor. With the addition of simulated casts, all 20 subjects tipped fully. Elevating one footrest (with or without a cast) caused only transient tips. On a high-friction floor surface, 19 and 18 subjects (with and without casts) experienced full tips or yawing falls to the side of the elevated footrest. The addition of forward stabilizers prevented wheelchairs from full tips or falls, when the users had both legs elevated, or when one of the users' legs (p less than 0.005), was elevated while located on a high friction floor (p less than 0.005). These findings have implications for wheelchair design and prescription.

Adult↗
PubMed1992

Effect of terminal heat sterilization on the stability of phospholipid-stabilized submicron emulsions.

Parenteral emulsions similar in composition to the commercially available fat emulsions were prepared using a Microfluidizer. The relationship of pH and terminal heat sterilization by autoclaving on the stability of phospholipid-stabilized emulsions was evaluated. The stability of these formulations was determined by using droplet size and zeta potential measurements. It was found that the zeta potentials of emulsions stabilized by more purified phospholipid were lower in magnitude compared to those stabilized by less purified phospholipid. Furthermore, acidic emulsions (between pH 5.0 and 7.0) showed an increased droplet size upon autoclaving, whereas the emulsions adjusted to an alkaline pH (pH 8.0 to 10.0) did not show a significant change in their droplet sizes upon autoclaving. The zeta potentials of all the emulsions "increased" (in magnitude) upon autoclaving and achieved values between -40 and -50 mV. The results of our studies could be explained on the basis of hydrolysis of phosphatidylcholine at different pH values, leading to a breakdown of the film surrounding the oil droplet, which results in coalescence and/or cracking of the emulsions.

Drug Stability↗
PubMed1989

Comparison of alpha-helix stability in peptides having a negatively or positively charged residue block attached either to the N- or C-terminus of an alpha-helix: the electrostatic contribution and anisotropic stability of the alpha-helix.

An estimation of the thermodynamic effects of a charged random coil, which is attached either to the N- or C-terminus of polyalanine, upon alpha-helix stability is attempted. A temperature-induced helix-coil transition of Ala20Lys20Phe and Lys20Ala20Phe was studied under various conditions of salt concentration and pH. By combining the results with previous ones for Ala20Glu20Phe and Glu20Ala20Phe, which have opposite electric charges to the present system [S. Ihara et al. (1982) Biopolymers 21, 131-145], the free energy of the coil to helix transition of the polyalanine block could be separated into two terms--one term for the electrostatic interaction of electric charges in the random-coil block with the alpha-helix dipole, and a second term for the intrinsic stability of the helix. The first term indicates the significance of the helix dipole-charge interactions, which affects the helix stability depending on the attaching side of the charged block and on the sign of the charges. This clearly shows the anisotropic stability of the alpha-helix. Furthermore, analysis of the dependence of these thermodynamic quantities on salt concentrations showed, assuming that the effect of the attached electric charges was symmetric (in other words, the absolute values of the electrostatic interaction terms were independent of the sign of electric charges), that the intrinsic stability of the alpha-helix was dependent on which side of the helix was attached to the random coil: a random coil attached to the N-terminus of the alpha-helix had little effect while that attached to a C-terminal significantly destabilized the helix.

Circular Dichroism↗
PubMed1986

What is psychophysically perfect image stabilization? Do perfectly stabilized images always disappear?

High-contrast luminance gratings stabilized on the retina with a Purkinje image eyetracker do not disappear completely. This could be due to small errors of stabilization, or the visual system could include mechanisms capable of responding to temporally constant images. We examined the visual system's sensitivity to small movements of gratings. We (1) replicated previous measurements of contrast sensitivity for gratings with controlled retinal-drift velocities, (2) developed a method for calculating sensitivity to small oscillations of gratings using thresholds for flickering stabilized gratings, and (3) examined the calculations empirically. We calculated that movements of only 8 sec of arc peak to peak produce detectable temporal changes. Since existent stabilization systems cannot eliminate movements this small, residual stabilized-grating detectability does not require detectors sensitive to temporally constant images.

Humans↗
PubMed1991

Cervical spine stabilization. A three-dimensional, biomechanical evaluation of rotational stability, strength, and failure mechanisms.

The three-dimensional rotational biomechanical properties of several different types of posterior stabilizing procedures are reported. A severe ligamentous and bony injury was simulated with three vertebral body human cervical spine segments. Good stabilization was noted for all of the repairs in flexion loading. Without polymethylmethacrylate supplementation, none of the repairs was stable in extension. All of the repairs provided reasonable stabilization for lateral bending except for the posterior wiring without methacrylate, and all but the posterior wiring and facet fusion provided reasonable stabilization against axial rotation loading. The supplementation of all of these repairs with polymethylmethacrylate added considerably to the stability of all the constraints. These findings may be useful in clinical decision-making for determining the kind of repairs and postoperative brace protection to use.

Biomechanical Phenomena↗
PubMed1990

Erythrocyte nucleotide stability and plasma hypoxanthine concentrations: improved ATP stability with short-term storage at room temperature.

We have measured erythrocyte nucleotide concentrations at timed intervals over 24 h in heparinised blood stored at 4 degrees C, room temperature, or 37 degrees C. The objective was to determine whether the grossly altered NAD concentrations found in the erythrocytes of patients with two different inherited purine disorders could be related to altered stability or turnover rates. An unexpected finding was the improved stability of all erythrocyte nucleotides in blood stored at room temperature compared with 4 degrees C. Not only was the breakdown of ATP greater at 4 degrees C compared with room temperature, higher hypoxanthine concentrations were present in the plasma associated with a fictitious increment in inosine. NAD and NADP, by contrast, showed remarkable stability in both control and patient erythrocytes, irrespective of their original value. Although these studies failed to establish an explanation for the altered NAD levels in the patients, the superior ATP stability in blood stored at room temperature in the erythrocytes from both patients and controls suggests that current practices of storing blood on ice for short-term studies require re-evaluation.

Adenosine Triphosphate↗
PubMed1992

Stability and stabilization of fluorocarbon emulsions destined for injection.

The factors that have an impact on the stability, and the mechanisms of degradation of fluorocarbon emulsions suited for intravascular use, are briefly reviewed. Various ways of prolonging shelf stability are discussed. The effectiveness of perfluoroalkylated surfactants and/or co-surfactants as stabilizers is demonstrated. New means of stabilizing fluorocarbon-in-water emulsions using molecular dowels are presented.

Blood Substitutes↗
PubMed1992

End-stabilized microtubules observed in vitro: stability, subunit, interchange, and breakage.

We report a reliable method to prepare, in vitro, microtubules that are stabilized at both ends by axonemal structures, and report studies of their properties. Such "end-stabilized" microtubules neither grow nor shorten over times of several hours when tubulin subunits are present in the surrounding solution. When subunits are removed, the microtubules eventually break. Breakage occurs within a sinuous and flexible region, a few microns in length, that begins at a single point on the microtubule and grows. When breakage does occur, the resulting two free ends shorten very rapidly until the flexible part has depolymerized and the region of straight microtubule is reached. The remainder of the microtubule then shortens at rates comparable to those ordinarily observed in dynamic instability. Formation of the flexible region can be reversed if subunits are added to the buffer prior to breakage. End-stabilized microtubules are a useful tool for studying interactions of molecules with the microtubular wall. They may be a good model for interpreting stabilizing events that happen in the cell. A preliminary study of the effects of microtubule poisons on the wall is presented.

Alkaloids↗
PubMed1988

Effects of crosslinking on the thermal stability of hemoglobins. II. The stabilization of met-, cyanomet-, and carbonmonoxyhemoglobins A and S with bis(3,5-dibromosalicyl) fumarate.

Hemoglobins A and S were crosslinked between Lys 82 beta 1 and Lys 82 beta 2 using bis (3,5-dibromosalicyl) fumarate (J. A. Walder et al. (1979) Biochemistry 18, 4265). Thermal denaturation experiments were used to compare the stabilities of the met, cyanomet, and carbonmonoxy forms of these crosslinked hemoglobins to the corresponding uncrosslinked proteins. Uncrosslinked carbonmonoxy- and cyanomethemoglobins had transition temperatures about 11 degrees C higher than the corresponding met samples. The increase in denaturation temperature (Tm) due to crosslinking was 15 degrees C for the methemoglobins, 10 degrees C for the cyanomethemoglobins, and 4 degrees C for the carbonmonoxy ones. There was no significant difference in stability between the met and carbonmonoxy crosslinked proteins. In order of increasing stability the samples were: met Hb S less than met Hb A less than CO Hb S less than CO Hb A = CN-met Hb A less than met XL-Hb S = CO XL-Hb S less than met XL-Hb A = CO XL-Hb A less than CN-met XL-Hb A. The slight decrease in the stability of Hb S (beta 6 Glu----Val) compared to Hb A can be explained by the replacement of an external ionic group by a hydrophobic residue in Hb S. In mixtures of crosslinked and normal Hb A, the Tm of the uncrosslinked material was slightly increased by the presence of the more stable crosslinked hemoglobin. The effects of both crosslinking and cyanide or carbon monoxide binding can be explained by Le Chatelier's principle since both would favor the native form of the protein.

Aspirin↗
PubMed1976

Light-absorbing properties, stability, and spectral stabilization of indocyanine green.

The absorption spectrum of indocyanine green depends on the nature of the solvent medium and on the dye concentration. Binding to plasma proteins causes the principal peaks in the absorption spectrum to shift about 25 nm toward the higher wavelengths. The much greater influence on the spectrum of the dye concentration results from progressive aggregate formation with increasing concentration. Indocyanine green solutions therefore do not follow Lambert-Beer's law above 15 mg-I-1 (in plasma). Indocyanine green solutions in plasma and concentrated (1,000 mg-I-1) solutions in distilled water are stable for at least 4 h. In long-term experiments the optical density of indocyanine green solutions in plasma as well as in distilled water generally diminishes, even in the dark. On the 7th day a new absorption maximum starts to appear at gamma=900 nm, possibly caused by further aggregate formation leading to much larger particles. Spectral stabilization after injection of a concentrated solution into the blood is most rapid when the dye is dissolved in distilled water. Spectral stabilization slows down with decreasing temperature. As rapid spectral stabilization is essential in quantitative dye dilution studies, the practice of adding a albumin and/or isotonic saline solution to the injectate should be discontinued. When a 10 g-1(-1) aqueous solution of indocyanine green is used, spectral stabilization takes less than 1.5 a (at 37 degrees C), which is sufficiently fast for almost any application.

Blood↗