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PubMed2005

Oxidative stability measurement of high-stability oils by pressure differential scanning calorimeter (PDSC).

High-stability oils are used as coatings on food products that require long shelf life. The high stability oils produced from high-oleic oils require less processing and bring additional nutritional benefits such as lower trans and saturated fat contents. Accurate and reproducible oxidative stability measurement of these oils is necessary to assess the performance. The accelerated oxidative stability measurement method often used in the fats and oils industry, the oxidative stability index (OSI, AOCS Cd 12b-92) is unreliable for higher stability oils due to poor reproducibility. This study presents a pressure differential scanning calorimetry (PDSC) method, which is highly reproducible and versatile and applies to oils from low to very high oxidative stability. PDSC has been used in industrial applications such as lubricants (ASTM D 6186-98) and measures the oxidative induction time (OIT) of oils under high temperature and pressure in the presence of pure oxygen. The OITs of a number of hydrogenated oils with different unsaturation and oxidative stability are measured. Unlike OSI data, the PDSC OIT measurement is highly reproducible and precise and requires only a small sample and a couple of hours. The regression analysis of the PDSC data indicated the natural log OIT of all samples linearly correlated with the temperature. The equation derived from this relationship helps to compare the oxidative stabilities of the same or different oils determined at different temperatures. The development of this method into an approved method will benefit the fats/oils and food industry.

Calorimetry, Differential Scanning↗
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↗
PubMed2004

Effect of chain length on coiled-coil stability: decreasing stability with increasing chain length.

The de novo design and biophysical characterization of three series of two-stranded alpha-helical coiled coils with different chain lengths are described. Our goal was to examine how increasing chain length would affect protein folding and stability when one or more heptad repeat(s) of K-A-E-A-L-E-G (gabcdef) was inserted into the central region of different coiled-coil host proteins. This heptad was designed to maintain the continuous 3-4 hydrophobic repeat of the coiled-coil host and introduce an Ala and Leu residue in the hydrophobic core at the a and d position, respectively, and a pair of stabilizing interchain ionic i to i' + 5 (g to e') interactions per heptad inserted. The secondary structures of the three series of disulfide-bridged polypeptides were studied by CD spectroscopy and their stabilities determined by chemical and thermal denaturation. The results showed that successive insertions of this heptad systematically decreased the stability of all the coiled coils studied regardless of the overall initial stability of the host coiled coil. These observations are in contrast to the generally accepted implication that the folding and stability of coiled coils are enhanced with increasing chain length. Our results imply that, in these examples where an Ala and Leu hydrophobic residue were introduced into the coiled-coil core per inserted heptad, there was still insufficient stability to overcome unfavorable entropy associated with chain length extension, even though the inserted heptad contained the most stabilizing hydrophobic residue (Leu) at position d and stabilizing ionic attractions.

Peptides↗
PubMed1982

Dynamic stability of steady states and static stabilization in unbranched metabolic pathways.

The paper is concerned with the conditions of dynamic (asymptotic) stability of steady states in unbranched metabolic pathways. The stationary flux in such pathways is generally determined by the concentration of the end product due to the effector action of this product on the reactions proceeding in its synthetic pathway. The delay in feedback circuits causes violation of dynamic stability at large static stabilization factors. A methods permitting analytic estimation of the critical stabilization factor is suggested. Sufficient and necessary conditions for asymptotic stability of the steady state in the general case of the pathway with a single feedback loop have been established. Mechanisms for maintenance of the steady state asymptotic stability at large static stabilization factors are studied. It has been shown that the range of dynamic stability can be widened greatly, if the pathway contains one or two reactions (but not more) of relatively small effective rate constants. Short strong negative feedback is also found to extend considerably the range of dynamic stability of the pathway. The feedback is more effective if it acts on the reaction with small effective rate constant.

Feedback↗
PubMed2004

Influence of screw-cement enhancement on the stability of anterior thoracolumbar fracture stabilization with circumferential instability.

The influence of additional dorsal structure damage on anterior stabilization of a thoracolumbar fracture is still unknown. Screw-cement enhancement can be used to reinforce the stability of anterior instrumentation. We have developed a new anchorage system for fixation of anterior stabilization devices, adapted through geometric optimization and the additional option of cementation after screw insertion. This study examines the question of whether this enhancement is strong enough to enable a single anterior procedure and still compensate for dorsal instability. Various spinal reconstruction procedures were evaluated biomechanically in an increasing ventrodorsal instability model for thoracolumbar fracture stabilization. A biomechanical in vitro study, simulating stabilized defect situations (corporectomy/vertebrectomy) with strut grafting and overbridging instrumentation, was performed on six human T10-L2 cadaveric specimens. The primary stability parameters, range of motion and neutral zone, were evaluated with or without anterior screw-cement enhancement. This was compared with a single conventional anterior stabilization without a dorsal defect (corporectomy). It was also compared with a single anterior, posterior or combined procedure in the presence of additional dorsal structure damage (vertebrectomy). The use of an additional cementable screw dowel enhanced the primary stability of the anterior instrumentation, compensating for dorsal instability. These results are warranted for the clinical use of minimally open or endoscopic techniques, creating the highest possible primary stability while performing a single anterior enhanced instrumentation with a tissue-preserving approach.

Biomechanical Phenomena↗
PubMed1998

Stabilization and stability of twitch force during mechanomyography of the adductor pollicis muscle.

OBJECTIVE: In order to study the stabilization time, the increase in twitch force during stabilization and the maintenance of stability during mechanomyography of the adductor pollicis muscle, neuromuscular function was monitored in 20 patients anaesthetized without the use of a neuromuscular blocking agent. The effect of the type of stimulation (single twitch [ST; 0.1 Hz], or train-of-four [TOF; 4 stimuli at 2 Hz, repeated every 12 s]) on these variables was studied. When applying TOF stimulation, the variables were also investigated for the TOF percentage [quotient of fourth and first twitch of a TOF stimulus x 100%]. METHODS: Two groups of ten patients were monitored with either ST or TOF stimulation. Measurements continued for at least 45 minutes. Multiple linear regression analysis was applied to examine the effect of stimulation on the stabilization time and the increase in twitch force. RESULTS: According to our criteria for stability, we found that the stabilization time did not differ for ST (13.7 [10.2] min; mean [sd]) and TOF stimulation (18.1 [9.6] min) (p > 0.10). Stabilized twitch forces were larger during TOF than during ST stimulation (134% [19] and 113% [11]; p = 0.01). In both groups of stimulation, six patients showed an interruption of stability. The TOF percentage was stable throughout the measurement period in all patients. CONCLUSIONS: Stabilization of twitch force takes too long for many studies of neuromuscular function in the clinical research setting. Therefore, we do not recommend its routine use when performing mechanomyography of the adductor pollicis muscle.

Adult↗
PubMed2002

Surgical stabilization of internal pneumatic stabilization? A prospective randomized study of management of severe flail chest patients.

BACKGROUND: We compared the clinical efficacy of surgical stabilization and internal pneumatic stabilization in severe flail chest patients who required prolonged ventilatory support. METHODS: Thirty-seven consecutive severe flail chest patients who required mechanical ventilation were enrolled in this study. All the patients received identical respiratory management, including end-tracheal intubation, mechanical ventilation, continuous epidural anesthesia, analgesia, bronchoscopic aspiration, postural drainage, and pulmonary hygiene. At 5 days after injury, surgical stabilization with Judet struts (S group, n = 18) or internal pneumatic stabilization (I group, n = 19) was randomly assigned. Most respiratory management was identical between the two groups except the surgical procedure. Statistical analysis using two-way analysis of variance and Tukey's test was used to compare the groups. RESULTS: Age, sex, Injury Severity Score, chest Abbreviated Injury Score, number of rib fractures, severity of lung contusion, and Pao2/Fio2 ratio at admission were all equivalent in the two groups. The S group showed a shorter ventilatory period (10.8 +/- 3.4 days) than the I group (18.3 +/- 7.4 days) (p < 0.05), shorter intensive care unit stay (S group, 16.5 +/- 7.4 days; I group, 26.8 +/- 13.2 days; p < 0.05), and lower incidence of pneumonia (S group, 24%; I group, 77%; p < 0.05). Percent forced vital capacity was higher in the S group at 1 month and thereafter (p < 0.05). The percentage of patients who had returned to full-time employment at 6 months was significantly higher in the S group (11 of 18) than in the I group (1 of 19). CONCLUSION: This study proved that in severe flail chest patients, surgical stabilization using Judet struts has beneficial effects with respect to less ventilatory support, lower incidence of pneumonia, shorter trauma intensive care unit stay, and reduced medical cost than internal fixation. Moreover, surgical stabilization with Judet struts improved percent forced vital capacity from the early phase after surgical fixation. Also, patients with surgical stabilization could return to their previous employment quicker than those with internal pneumatic stabilization, even in those with the same severity of flail chest. We therefore concluded that surgical stabilization with Judet struts may be preferably applied to patients with severe flail chest who need ventilator support.

Flail Chest↗
PubMed2005

Anticoagulation in patients with non-valvular atrial fibrillation: an evaluation of stability and early factors that predict longer-term stability on warfarin in a large UK population.

OBJECTIVE: To determine the proportion of patients with non-valvular atrial fibrillation (NVAF) treated with warfarin that achieved a 6-month period within the target INR range (stability). To then evaluate any associations between stability and outcome and to determine whether stability can be predicted by clinical factors at an early stage in warfarin treatment. METHODS: This study was a record linkage study in 1513 patients with NVAF treated with warfarin for a minimum of 6-months, carried out in a large UK population. The main outcome measures were stability (defined as six months within the target INR range [2.0-3.0]), thromboembolic and bleeding event rates and mortality. Secondary outcome measures were the predictive value of baseline characteristics and other treatment variables. RESULTS: Stability was achieved in 52% of the study group. Standardised mean survival was significantly higher in the group who achieved stability (Delta = 16.91 months, p < 0.001) with a hazard ratio of 4.36 (p < 0.001). The stable group had a lower rate of both thromboembolic events (0.8% vs. 2.3% per patient year) and bleeds recorded on inpatient diagnoses (0.4% vs. 1.2% per patient year). Failure to achieve stable control was associated with age (Odds Ratio [OR] 1.011 (95% Confidence Interval [CI] 1.001-1.021)) and morbidity at baseline (OR 1.015; 95% CI 1.007-1.022). An increase in mean time between visits (OR 0.939; 95% CI 0.926-0.952) and the percentage time in range (OR 0.889; 95% CI 0.879-0.900) was associated with a decrease in the chance of instability. Greater variability in INR was also associated with a failure to achieve stability (OR 1.518; 95% CI 1.427-1.615). Receiver Operator Characteristic (ROC) analysis using data from the first three months of treatment demonstrated good discrimination of stability using age and morbidity at baseline and percentage time in range and frequency of visits during the first three months of treatment (area under curve [AUC] 0.780; standard error [SE] 0.012; 95% CI 0.757-0.803). CONCLUSIONS: Many patients never achieved a period of 6-months stability and were at increased risk of thromboembolic events and bleeds. Age, morbidity at baseline and variability of INR control in the first three months could be used to predict instability using warfarin. This study infers that patients should be treated more intensively in the early stages of warfarinisation in order to improve outcome.

Adult↗
PubMed1996

Interfacial properties as stability predictors of lecithin-stabilized perfluorocarbon emulsions.

The purpose of this study was to determine whether the addition of small quantities of minor lecithin components (phosphatidylinositol, phosphatidic acid, lysophosphatidylethanolamine, and cholesterol) and Pluronic F68 to lecithin could improve the stability of lecithin-stabilized perfluorocarbon emulsions. Attempts were made to correlate emulsion stability with interfacial properties (tension and charge). Dynamic interfacial tension was determined using a Teflon Wilhelmy plate method [reported previously (1)]. Emulsions were prepared by microfluidization. Microelectrophoresis was used to measure emulsion droplet charge, and photon correlation spectroscopy and Coulter analysis were used to determine emulsion stability as a function of droplet size. Thermal kinetic accelerated stability testing was conducted. Various droplet size parameters were used to compare emulsion stabilities, and an overall stability ranking, based on these parameters, was obtained for each emulsion. Small quantities of additives altered emulsion stability and these data were correlated with interfacial properties and initial droplet diameters. The addition of cholesterol to lecithin resulted in the most stable perfluorocarbon emulsion.

Chemical Phenomena↗
PubMed2001

Chemotaxis, viability, and labeling stability of leukocytes labeled with (99m)Tc-exametazime stabilized with methylene blue.

UNLABELLED: The in vitro viability, chemotaxis, and labeling stability of leukocytes labeled using (99m)Tc-exametazime stabilized with methylene blue were evaluated and compared with those obtained using nonstabilized (99m)Tc-exametazime. METHODS: Two identical leukocyte populations, from 30 healthy donors, were labeled simultaneously using freshly prepared and 2-h-old stabilized (99m)Tc-exametazime. The following quality control techniques were performed on each labeled leukocyte sample: eosin Y staining, chemotaxis radioassay, and labeling stability at 2 h after labeling. RESULTS: Eosin Y staining showed a cell viability of at least 98% in all samples, without a significant statistical difference between the populations. Chemotactic indices obtained with leukocytes labeled with freshly prepared, unstabilized (99m)Tc-exametazime were statistically greater than those obtained using (99m)Tc-exametazime stabilized with methylene blue (z = 2.41; P<0.02). Labeling stability at 2 h after labeling was the same for both populations. CONCLUSION: The use of (99m)Tc-exametazime stabilized with methylene blue for leukocyte radiolabeling does not affect either cell membrane integrity or labeling stability but can cause a decrease in the cell chemotactic capacity that discourages its clinical use.

Cell Survival↗
PubMed2002

Biochemical stabilization enhances red blood cell recovery and stability following cryopreservation.

Glycerolized red blood cells (RBC) are approved for long-term cryopreservation. However, the need to remove the glycerol cryoprotectant prior to transfusion has limited the usefulness of this cryopreservation method. This report describes using non-cryoprotectant biochemical stabilization techniques to substitute for the standard glycerol cryoprotectant. The glycerolized RBC method was compared to a newly developed LC-V method that combines transfusable cryoprotectants (hydroxyethyl starch and dextran) and specific non-cryoprotectant biochemical stabilizers (nicotinamide, nifedipine, and flurbiprofen). Results demonstrate that the biochemical stabilizers significantly reduce cryopreservation-induced hemolysis compared to cryopreservation in their absence and that thaw hemolysis levels approach those of standard 40% (w/v) glycerolized RBC (3.1+/-0.2% for 40% glycerol compared to 8.7+/-0.9% for the LC-V protocol). Furthermore, LC-V cryopreserved RBC exhibit a significantly enhanced post-thaw stability compared to glycerolized RBC as determined by osmotic fragility index (0.557+/-0.034 for 40% glycerol compared to 0.478+/-0.016 for the LC-V protocol). Analysis of biochemically stabilized RBC proteins revealed a transient translocation of carbonic anhydrase to the membrane fraction. However, the enhanced RBC recovery and stability could not be attributed to this event. Finally, DSC analysis demonstrated that the biochemical stabilizers of the LC-V process were not functioning as surrogate cryoprotectants in that they did not affect the quantity or quality of ice formed. Overall, this work demonstrates that cryopreservation-induced RBC damage may be corrected or prevented through specific biochemical stabilization and represents a significant step toward a directly transfusable cryopreserved RBC product.

Blood Preservation↗
PubMed2000

The asparagine-stabilized beta-turn of apamin: contribution to structural stability from dynamics simulation and amide hydrogen exchange analysis.

Molecular dynamics simulations of bee venom apamin, and an analogue having an Asn to Ala substitution at residue 2 (apamin-N2A), were analyzed to explore the contribution of hydrogen bonds involving Asn2 to local (beta-turn residues N2, C3, K4, A5) and global stability. The wild-type peptide retained a stable conformation during 2.4 ns of simulation at 67 degrees C, with high beta-turn stability characterized by backbone-side chain hydrogen bonds involving beta-turn residues K4 and A5, with the N2 side chain amide carbonyl. The loss of stabilizing interactions involving the N2 side chain resulted in the loss of the beta-turn conformation in the apamin N2A simulations (27 or 67 degrees C). This loss of beta-turn stability propagates throughout the peptide structure, with destabilization of the C-terminal helix connected to the N-terminal region by two disulfide bonds. Backbone stability in a synthetic peptide analogue (apamin-N2A) was characterized by NMR and amide hydrogen exchange measurements. Consistent with the simulations, loss of hydrogen bonds involving the N2 side chain resulted in destabilization of both the N-terminal beta-turn and the C-terminal helix. Amide exchange protection factors in the C-terminal helix were reduced by 9-11-fold in apamin N2A as compared with apamin, corresponding to free energy (deltaDeltaG(uf)) of around 1.5 kcal M(-1) at 20 degrees C. This is equivalent to the contribution of hydrogen bond interactions involving the N2 side chain to the stability of the beta-turn. Together with additional measures of exchange protection factors, the three main contributions to backbone stability in apamin that account for virtually the full thermodynamic stability of the peptide have been quantitated.

Amides↗
PubMed1999

The destabilization of IL-2 mRNA by a premature stop codon and its differential stabilization by trans-acting inhibitors of protein synthesis do not support a role for active translation in mRNA stability.

To investigate the role that translation plays in the stabilization of the IL-2 mRNA, we inhibited protein synthesis in both cis and trans. To block translation in trans, we utilized the inhibitors puromycin (PUR) and cycloheximide (CHX), which differentially effect polysome structure. We found that CHX enhances the stability of IL-2 mRNA in cells stimulated with anti-TCR Ab alone, but it inhibits CD28-induced message stabilization in costimulated cells. In contrast, PUR had a minimal effect on IL-2 mRNA stability in either the presence or absence of costimulation. The differential effects of these two inhibitors suggest that: 1) CHX is unlikely to stabilize the IL-2 mRNA by inhibiting the expression of a labile RNase; 2) CD28-mediated IL-2 mRNA stabilization does not require translation; and 3) IL-2 mRNA decay is not coupled to translation. To block translation in cis, we generated sequence-tagged IL-2 genomic reporters that contain a premature termination codon (PTC). In both the presence and absence of costimulation, these PTC-containing mRNAs exhibit drastically diminished stability. Interestingly, the addition of CHX but not PUR completely restored CD28-mediated stabilization, suggesting that CHX can block the enhanced decay induced by a PTC. Finally, CHX was able to superinduce IL-2 mRNA levels in anti-TCR Ab-stimulated cells but not in CD28-costimulated cells, suggesting that CHX may also act by other mechanisms.

Animals↗
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↗
PubMed2003

Why is trehalose an exceptional protein stabilizer? An analysis of the thermal stability of proteins in the presence of the compatible osmolyte trehalose.

Trehalose, a naturally occurring osmolyte, is known to be an exceptional stabilizer of proteins and helps retain the activity of enzymes in solution as well as in the freeze-dried state. To understand the mechanism of action of trehalose in detail, we have conducted a thorough investigation of its effect on the thermal stability in aqueous solutions of five well characterized proteins differing in their various physico-chemical properties. Among them, RNase A has been used as a model enzyme to investigate the effect of trehalose on the retention of enzymatic activity upon incubation at high temperatures. 2 m trehalose was observed to raise the transition temperature, Tm of RNase A by as much as 18 degrees C and Gibbs free energy by 4.8 kcal mol-1 at pH 2.5. There is a decrease in the heat capacity of protein denaturation (DeltaCp) in trehalose solutions for all the studied proteins. An increase in the DeltaG and a decrease in the DeltaCp values for all the proteins points toward a general mechanism of stabilization due to the elevation and broadening of the stability curve (DeltaG versus T). A direct correlation of the surface tension of trehalose solutions and the thermal stability of various proteins has been observed. Wyman linkage analysis indicates that at 1.5 m concentration 4-7 molecules of trehalose are excluded from the vicinity of protein molecules upon denaturation. We further show that an increase in the stability of proteins in the presence of trehalose depends upon the length of the polypeptide chain. The pH dependence data suggest that even though the charge status of a protein contributes significantly, trehalose can be expected to work as a universal stabilizer of protein conformation due to its exceptional effect on the structure and properties of solvent water compared with other sugars and polyols.

Animals↗
PubMed2001

A specific molar ratio of stabilizer to protein is required for storage stability of a lyophilized monoclonal antibody.

The selection of the appropriate excipient and the amount of excipient required to achieve a 2-year shelf-life is often done by using iso-osmotic concentrations of excipients such as sugars (e.g., 275 mM sucrose or trehalose) and salts. Excipients used for freeze-dried protein formulations are selected for their ability to prevent protein denaturation during the freeze-drying process as well as during storage. Using a model recombinant humanized monoclonal antibody (rhuMAb HER2), we assessed the impact of lyoprotectants, sucrose, and trehalose, alone or in combination with mannitol, on the storage stability at 40 degrees C. Molar ratios of sugar to protein were used, and the stability of the resulting lyophilized formulations was determined by measuring aggregation, deamidation, and oxidation of the reconstituted protein and by infrared (IR) spectroscopy (secondary structure) of the dried protein. A 360:1 molar ratio of lyoprotectant to protein was required for storage stability of the protein, and the sugar concentration was 3-4-fold below the iso-osmotic concentration typically used in formulations. Formulations with combinations of sucrose (20 mM) or trehalose (20 mM) and mannitol (40 mM) had comparable stability to those with sucrose or trehalose alone at 60 mM concentration. A formulation with 60 mM mannitol alone provided slightly less protection during storage than 60 mM sucrose or trehalose. The disaccharide/mannitol formulations also inhibited deamidation during storage to a greater extent than the lyoprotectant formulations alone. The reduction in aggregation and deamidation during storage correlated directly with inhibition of unfolding during lyophilization, as assessed by IR spectroscopy. Thus, it appears that the protein must be retained in its native-like state during freeze-drying to assure storage stability in the dried solid. Long-term studies (23-54 months) performed at 40 degrees C revealed that the appropriate molar ratio of sugar to protein stabilized against aggregation and deamidation for up to 33 months. Therefore, long-term storage at room temperature or above may be achieved by proper selection of the molar ratio and sugar mixture. Overall, a specific sugar/protein molar ratio was sufficient to provide storage stability of rhuMAb HER2.

Antibodies, Monoclonal↗