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PubMed2005

Stability assessment of pharmaceuticals and biopharmaceuticals by isothermal calorimetry.

The assessment of stability (of actives, excipients and/or formulated products) is an important, and often time-consuming, part of pharmaceutical product development. Conventionally, HPLC is used to quantify the concentrations of a parent compound and any degradation products as a function of storage time. HPLC, however, is relatively insensitive to small changes in concentration and it is often the case that stability assays are conducted under stress conditions, in order to accelerate any degradation processes. The Arrhenius relationship is then employed to give an initial prediction of stability under storage conditions while long-term studies, under storage conditions, are conducted to confirm these predictions. The properties of isothermal calorimetry, such as its intrinsic sensitivity to small changes in heat and invariance to the physical form of a sample, make it ideally suited for stability assessment because it obviates the need for an Arrhenius analysis. In addition, the ability to conduct titration or gas perfusion experiments vastly increases its range of applications. Recent advances in instrumental design and data analysis have made it easier to analyse data quantitatively for complex systems. It is the purpose of this review to highlight some of these developments, discuss them in the context of pharmaceutical and biopharmaceutical examples and explore some of the future challenges and applications of the technique.

Biological Products↗
PubMed1994

Adipocyte lipid-binding protein complexed with arachidonic acid. Titration calorimetry and X-ray crystallographic studies.

The association of the adipocyte lipid-binding protein (ALBP) with arachidonic acid (all cis, 20:4 delta 5,8,11,14) and oleic acid (cis, 18:1 delta 9) has been examined by titration calorimentry. In addition, the crystal structure of ALBP with bound arachidonic acid has also been obtained. Crystallographic analysis of the arachidonic acid.ALBP complex along with the previously reported oleic acid-ALBP structure (Xu, Z., Bernlohr, D. A., and Banaszak, L. J. (1993) J. Biol. Chem. 268, 7874-7884) provides a framework for the molecular examination of protein-lipid association. Isothermal titration calorimetry revealed high affinity association of both unsaturated fatty acids with the protein. The calorimetric data yielded the following thermodynamic parameters for arachidonic acid: Kd = 4.4 microM, n = 0.8, delta G = -7370 cal/mol, delta H = -6770 cal/mol, and T delta S = +600 cal/mol. For oleic acid, the thermodynamic parameters were Kd = 2.4 microM, n = 0.9, delta G = -7770 cal/mol, delta H = -6050 cal/mol, and T delta S = +1720 cal/mol. The identification of thermodynamically dominating enthalpic factors for both fatty acids are consistent with the crystallographic studies demonstrating the interaction of the fatty acid carboxylate with a combination of Arg106, Arg126, and Tyr128. The crystallographic refinement of the protein-arachidonate complex was carried out to 1.6 A with the resultant R factor of 0.19. Within the cavity of the crystalline binding protein, the arachidonate was found in a hairpin conformation. The conformation of the bound ligand is consistent with acceptable torsional angles and the four cis double bonds in arachidonate. These results demonstrate that arachidonate is a ligand for ALBP. They provide thermodynamic and structural data concerning the physical basis for protein-lipid interaction and suggest that intracellular lipid-binding proteins may mediate the biological effects of polyunsaturated fatty acids in vivo.

Adipocytes↗
PubMed1999

Analysis of polymerization behavior of dental dimethacrylate monomers by differential scanning calorimetry.

The polymerization and copolymerization activity of dental monomers was investigated using the dynamic differential scanning calorimetry (DSC) method. As aliphatic dimethacrylate monomers, ethyleneglycol dimethacrylates with different lengths of ethyleneglycol and urethane dimethacrylates were used. As aromatic dimethacrylates, Bis-GMA (2,2-bis[4-(3-methacryloxy-2-hydroxypropoxy)phenyl]propane), BMPEPP (2,2-bis(4-methacryloxy poly-ethoxyphenyl)propane), and DMB (1,2-dimethacryloyloxy benzene) were used. Ethyleneglycol dimethacrylates showed sharp exothermic peaks, and the maximum temperatures (Tp) at the exothermic peaks of the DSC curves decreased according to the lengths of ethyleneglycols. Among urethane dimethacrylates, UDMA (dimethacryloxyethyl 2,2,4-trimethylhexamethylene diurethane) and DMPHU (di-(2-methacryloxypropyl) hexamethylene diurethane) showed sharp exothermic peaks, but DMEHU (di-(2-methacryloxyethyl) hexamethylene diurethane) showed an endothermic peak as well as exothermic peaks. This suggests that reactions other than polymerization occurred in the case of DMEHU. The polymerization activity of aromatic dimethacrylates was lower than that of ethyleneglycol dimethacrylates and urethane dimethacrylates. The copolymerization activity of TEGDMA (triethyleneglycol dimethacrylate) and DMB was also investigated using the dynamic DSC method. The DSC curves of the copolymerization between DMB and UDMA or BMPEPP showed broad peaks, but the DSC curves of the copolymerization between TEGDMA and UDMA or BMPEPP showed sharp peaks. The copolymerization activity of TEGDMA was better than that of DMB.

Bisphenol A-Glycidyl Methacrylate↗
PubMed1980

Modifications of glucose storage and oxidation in nonobese diabetics, measured by continuous indirect calorimetry.

A new application of continuous indirect calorimetry is described for measuring the disposal of a glucose load. In a group of 10 normal subjects, 3 h after a 100 g oral glucose load, 20 g glucose was oxidized at basal rate, 19 g in response to the load and 63 g stored, while a decrease of 2 g was observed in the glucose space (GS). In a group of four type I, insulin-dependent diabetics, both glucose oxidation (9 g at the basal rate and 4 g in response to the load) and glucose storage (9 g) were markedly decreased, with the remainder either being lost in the urine (36 g) or remaining in the glucose space (42 g). In a group of eight nonobese type II, non-insulin-dependent diabetics, glucose oxidation both in the basal rate and in response to the load was slightly decreased (13 and 14 g, respectively) and glucose storage decreased to 40 g. These results suggest that, in type I diabetics, complete insulin deficiency seriously impairs two major mechanisms regulating glucose homeostasis, i.e., glucose storage and oxidation, while, in type II diabetics, the remaining insulin secretion attentuates these disturbances.

Adolescent↗
PubMed2003

Effect of aerosolized albuterol sulfate on resting energy expenditure determined by use of open-flow indirect calorimetry in horses with recurrent airway obstruction.

OBJECTIVE: To evaluate effects of sedation on stability of resistance of the respiratory system (RRS) and measures of resting energy expenditure (REE) by use of open-flow indirect calorimetry (IC) and treatment with aerosolized albuterol on REE in horses with recurrent airway obstruction (RAO). ANIMALS: 9 clinically normal horses and 8 horses with RAO. PROCEDURE: In phase 1, RRS was measured by using forced oscillometry (FOT) in 5 clinically normal horses before and after sedation with xylazine. In phase 2, REE was measured in 4 clinically normal horses between 20 and 25 minutes and again 35 to 40 minutes after sedation with xylazine. In phase 3, IC was performed between 20 and 25 minutes and FOT was performed between 30 and 35 minutes after xylazine administration in 8 horses with RAO; after administration of 450 microg of albuterol, IC and FOT were repeated. RESULTS: In phase 1, RRS values were significantly lower 5 and 10 minutes after sedation. In phase 2, diminishing sedation did not significantly affect REE. In phase 3, there was a significant decrease in mean RRS (1.15 +/- 0.25 vs 0.84 +/- 0.14 cm H20/L/s) and REE (30.68 +/- 17.89 vs 27.46 = 16.54 kcal/kg/d) after albuterol administration. CONCLUSIONS AND CLINICAL RELEVANCE: FOT and IC are useful in obtaining repeatable measurements of RRS and REE, respectively, in sedated horses. Concurrent bronchodilation and decreased REE after albuterol administration suggest that increased work of breathing as a result of airway obstruction may contribute to increased energy demands in horses with RAO.

Aerosols↗
PubMed2004

Comparison of the standard predictive equation for calculation of resting energy expenditure with indirect calorimetry in hospitalized and healthy dogs.

OBJECTIVE: To determine the level of clinical agreement between 2 methods for the measurement of resting energy expenditure (REE). DESIGN: Prospective case series. ANIMALS: 77 dogs. PROCEDURE: Oxygen consumption (Vo2) and CO2 production (Vco2) were measured with an open-flow indirect calorimeter in healthy (n = 10) and ill (67) dogs. Measurements were collected at 3 time periods on 2 days. The Vo2 and the Vco2 measurements were then used to calculate the REE values. RESULTS: Mean values of measured (MREE) and predicted (PREE) REEs in healthy dogs and a dog with medical illnesses or trauma were not significantly different. There was a significant difference on day 2 between the MREE and PREE in the group of dogs recovering from major surgery. More importantly, there was significant variation between the PREE and MREE on an individual-dog basis. The PREE only agreed to within +/- 20% of the MREE in 51% to 57% of the dogs. CONCLUSIONS AND CLINICAL RELEVANCE: The level of agreement between these two methods for determining the 24-hour REE was poor in individual dogs. The level of disagreement between the 2 methods indicates that these methods may not be used interchangeably in a clinical setting. Measurement of REE by use of indirect calorimetry may be the only reliable method of determining REE in an individual ill or healthy dog.

Animals↗
PubMed1988

Construction and operation of an open-circuit indirect calorimetry system for small ruminants.

An open-circuit indirect respiration calorimetry system for the collection of long-term metabolic heat production data for medium and small animals is described. The system is designed for use with small ruminants, but it has the capacity for measuring heat production in nonruminant species up to 150 kg. The system consists of an internal climatic control system, air flow control and volume measuring system, and gas analyzers for O2, CO2 and CH4. Carbon dioxide recovery checks of the four chambers produced recovery values ranging from 96.73 to 100.89%. The actual mean fasting heat production measured for 12 wether sheep was 63.13 kcal/kg.75 +/- .83. The total estimated cost of four chambers and the associated instrumentation was less than $17,000 in 1984.

Animal Husbandry↗
PubMed1991

Differential scanning calorimetry characterization of rabbit brain membrane fractions.

Various membrane fractions have been prepared from rabbit brain synaptosomes by centrifugation on discontinuous sucrose gradients after osmotic shock. These fractions were characterized by electron microscopy (E.M.), SDS-PAGE and GABA binding. The fractions were then studied by differential scanning calorimetry (DSC). The calorimetric results indicate that all the fractions studied show thermal transitions at around 60 degrees C which correspond to the "melting" of membrane structures. An additional transition at higher temperature (82 degrees C) seems to be associated with an enrichment in central myelin fragments.

Animals↗
PubMedDate not supplied

Hyperthermia (heat shock)-induced protein denaturation in liver, muscle and lens tissue as determined by differential scanning calorimetry.

Protein denaturation has been shown to occur in cells during heat shock and is closely correlated with the cellular responses to hyperthermia; however, little is known about protein denaturation in tissue. This study describes an analysis of endothermic transitions in the hyperthermic region using differential scanning calorimetry (DSC) in liver, white muscle, and lens tissue from Wistar rat, New Zealand white rabbit, and Rainbow trout. Complex DSC profiles consisting of several transitions were obtained for each tissue. Evidence is given that these transitions are due primarily to protein denaturation. Onset temperatures of denaturation (Tl) for rat liver, muscle, and lens are about 38, 39 and 48 degrees C, respectively. Thus, significant protein denaturation occurs in liver and muscle during mild hyperthermia (40-45 degrees C) with lens considerably more stable. The values of Tl for the same tissue from the different animals correlates well with body temperature (rabbit 39.4, rat 38.2, and trout grown at 11 degrees C); Tl increased in the same order as the body temperature for each tissue. Thus, there is correlation between the onset temperature for protein denaturation in these tissues and body temperature.

Animals↗
PubMed1998

Characterization of the sucrose/glycine/water system by differential scanning calorimetry and freeze-drying microscopy.

The objective of this study was to characterize the thermal properties of systems containing various ratios of amorphous and crystalline components using both differential scanning calorimetry (DSC) and freeze-drying microscopy. The glycine/sucrose system was used as a model system, since it is routinely used in protein formulations. DSC analysis revealed that the addition of glycine to sucrose solutions resulted in a decrease in the glass transition (T'g) of the system. The T'g of a pure sucrose solution (7% w/v) decreased from -32.3 to -51.5 degrees C for a mixture containing a sucrose/glycine ratio of 2:5. The glass transition of the sucrose/glycine mixture decreased linearly as more glycine was added to the system. This decrease in glass transition resulted in severe collapse during freeze-drying of these mixtures above T'g. However, collapse was not observed during freeze-drying if the DSC thermogram of the sucrose/glycine mixture exhibited a transition resulting from recrystallization of the amorphous glycine. Mixtures having a sucrose/glycine ratio of 3:4 and 2:5 had a glass transition of -48 degrees C and -51.5 degrees C, respectively. Despite their low glass transition temperatures, these samples freeze-dried readily at a product temperature > T'g using a fast freeze-drying cycle (primary drying at a shelf temperature of +20 degrees C and chamber pressure of 100 mTorr) without any sign of collapse. The crystallization of the amorphous glycine from the frozen mixture of sucrose and glycine provided support during freeze-drying which prevented the macroscopic collapse of the final product. Freeze-drying microscopy visually revealed the crystallization and allowed for prediction of cake quality upon lyophilization. Although the freeze-drying microscope is not as sensitive as the DSC in detecting all transitions (it cannot detect a glass transition), it clarifies the interpretation of DSC, and together they provide valuable information regarding the relevance of each of the transitions to the final freeze-dried product elegance.

Calorimetry, Differential Scanning↗
PubMed2000

The effects of alcoholic compounds on the stability of type I collagen studied by differential scanning calorimetry.

The interaction between bovine tendon collagen and a series of homologous alcohols were investigated using a differential scanning calorimetry. For all alcoholic substances, as well as 2-hydroxyethyl methacrylate (HEMA), the concentration dependence of the denaturation temperature of collagen was observed, which showed a minimum at 30%. Clearly there are two opposing actions on the stabilization of the collagen structure; destabilization dominates over stabilization at lower concentrations, and vice versa at higher concentrations. The concentration dependence became greater for longer chain alcohols, while it was suppressed by the increased number of OH groups. The chain length-dependent surface tension may be related, which controls the permeation of the additives through the collagen fibers. Overall hydrophobicity, indicated by the hydrophile-lipophile balance (HLB) numbers, suggests the importance of the hydrophobic effect in the interaction of collagen and alcoholic substances, including adhesive monomers such as HEMA.

Alcohols↗
PubMed1990

Heat curing behavior of light-cured composite resins investigated by dynamic differential scanning calorimetry.

The heat curing behavior of light-cured restorative composite resins, light-cured crown and bridge veneering resins, pure dimethacrylate monomers, Bis-GMA monomers containing various initiators, and monomer mixtures were investigated by slow heating at a constant rate with differential scanning calorimetry (DSC) without any light irradiation--the so-called dynamic DSC measurement. Some of the light-cured restorative composite resins and the light-cured crown and bridge veneering resins showed a sharp exothermic peak due to heat curing. Pure TEDMA also showed a sharp exothermic peak, whereas the Bis-GMA monomers containing catalysts for light curing showed no exothermic peak. It seems that heat curing behavior of light-cured composite resins depends not on the decomposition of camphorquinone, but on that of the monomer itself.

Acrylic Resins↗
PubMed2002

A product inhibition study on adenosine deaminase by spectroscopy and calorimetry.

Kinetic and thermodynamic studies have been made on the effect of the inosine product on the activity of adenosine deaminase in a 50 mM sodium phosphate buffer, pH 7.5, at 27 degrees C using UV spectrophotometry and isothermal titration calorimetry (ITC). A competitive inhibition was observed for inosine as a product of the enzymatic reaction. A graphical-fitting method was used for determination of the binding constant and enthalpy of inhibitor binding by using isothermal titration microcalorimetry data. The dissociation-binding constant is equal to 140 microM by the microcalorimetry method, which agrees well with the value of 143 microM for the inhibition constant that was obtained from the spectroscopy method

Adenosine↗
PubMed2002

Thermal stability of Phaseolus vulgaris leucoagglutinin: a differential scanning calorimetry study.

Phaseolus vulgaris phytohemagglutinin L is a homotetrameric-leucoagglutinating seed lectin. Its three-dimensional structure shows similarity with other members of the legume lectin family. The tetrameric form of this lectin is pH dependent. Gel filtration results showed that the protein exists in its dimeric state at pH 2.5 and as a tetramer at pH 7.2. Contrary to earlier reports on legume lectins that possess canonical dimers, thermal denaturation studies show that the refolding of phytohemagglutinin L at neutral pH is irreversible. Differential scanning calorimetry (DSC) was used to study the denaturation of this lectin as a function of pH that ranged from 2.0 to 3.0. The lectin was found to be extremely thermostable with a transition temperature around 82 degrees C and above 100 degrees C at pH 2.5 and 7.2, respectively. The ratio of calorimetric to vant Hoff enthalpy could not be calculated because of its irreversible-folding behavior. However, from the DSC data, it was discovered that the protein remains in its compact-folded state, even at pH 2.3, with the onset of denaturation occurring at 60 degrees C.

Calorimetry, Differential Scanning↗
PubMed2006

Transition state characterization of the low- to physiological-temperature nondenaturational conformational change in bovine adenosine deaminase by slow scan rate differential scanning calorimetry.

Bovine adenosine deaminase undergoes a nondenaturational conformational change at 29 degrees C upon heating which is characterized by a large increase in heat capacity. We have determined the transition state thermodynamics of the conformational change using a novel application of differential scanning calorimetry (DSC) which employs very slow scan rates. DSC scans at the conventional, and arbitrary, scan rate of 1 degree C/min show no evidence of the transition. Scan rates from 0.030 to 0.20 degrees C/min reveal the transition indicating it is under kinetic control. The transition temperature T(t) and the transition temperature interval deltaT increase with scan rate. A first order rate constant k1 is calculated at each T(t) from k1 = r(scan)/deltaT, where r(scan) is the scan rate, and an Arrhenius plot is constructed. Standard transition state analysis reveals an activation free energy deltaG(double dagger) of 88.1 kJ/mole and suggests that the conformational change has an unfolding quality that appears to be on the direct path to the physiological-temperature conformer.

Adenosine Deaminase↗
PubMed2000

Characterization of dimethyldiacyloxysilanes by differential scanning calorimetry, Raman scattering and X-ray diffraction.

The phase behaviour of diacyloxydimethylsilanes (DMS Cn; n = 10, 12, 14, 16, 18, 20, 22) was investigated by differential scanning calorimetry, X-ray diffraction and Raman spectroscopy. All DMS Cn melt from a crystalline phase to an isotropic liquid with a single sharp transition. On cooling, the homologous DMS C16 up to DMS C22 show a characteristic monotropic phase (L beta'H). In contrast to the calorimetrical investigations, it was not possible to analyse the monotropic phase of DMS C16 by X-ray diffraction. This behaviour is due to a two-phase region (gel phase--crystalline phase). The Raman spectra of all DMS are very similar. Only in the low frequency range we find different bands of the longitudinal acoustic modes. The Raman measurements demonstrate undoubtedly that in the solid state the alkyl chains are in all-trans conformation. The factor group splitting of the CH2 scissoring Raman mode show that the DMS Cn are arranged in a subcell packing with two molecules per unit cell. The highly ordered all-trans structure of the alkyl chains is present up to the melting transition. On melting there are changes in different regions of the Raman spectra: C-H stretching, CH2 scissoring mode, C-C skeletal stretching, CH3 rocking and longitudinal acoustic modes. On cooling DMS C18 and DMS C20 from the melt to the crystalline state, the gel phase is also proved by Raman scattering. Based on the results of the Raman and X-ray data the gel phase is characterized by a hexagonal subcell packing and by an ordered structure of the alkyl chain residues.

Calorimetry, Differential Scanning↗
PubMed1975

[Measurement of carbohydrate oxidation by means of indirect continuous calorimetry in normal and diabetic subjects].

The use of continuous indirect calorimetry in the course of a 100 g OGTT in 10 normal subjects has shown that carbohydrate oxidation rises with the secondary fall in blood glucose, suggesting that it could result from glucose stored under the influence of insulin. The experimental increase in FFA by a neutral fat infusion in 8 normal subjects decreased this oxidation in spite of the insulin rise. In a group of 5 non-obese, non-ketotic insulin-deficient diabetics, carbohydrate oxidation was found to be normal and directly correlated with plasma glucose levels. On the other hand, in 7 obese diabetics with high plasma insulin levels carbohydrate oxidation was found to be low, suggesting that carbohydrate intolerance could result from the non-oxidation of glucose. This study shows heterogeneity of diabetes, since glucose intolerance could result from non-oxidation of glucose as well as from insufficient pancreatic secretion.

Administration, Oral↗