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PubMed1993

Repeatability of energy expenditure measurements in clinically normal dogs by use of indirect calorimetry.

Energy expenditure (EE) was determined, using an open-flow indirect calorimetry system in a group of 20 clinically normal, apparently resting, client-owned dogs. Five evaluations were performed over an 8-hour period to determine reliability of the method. The intraclass correlation coefficient was calculated as the ratio of within- and between-subject variances, using repeated-measures ANOVA. When only the middle 3 evaluations were included, the intraclass correlation coefficient was 0.87, indicating good reliability. The first evaluation was higher than the subsequent 4 evaluations for rate of O2 consumption (Vo2/kg and Vo2/kg0.75; (P < or = 0.01), and EE/kg and EE/kg0.75 (P < or = 0.005). The respiratory quotients at the first (P = 0.004) and second (P = 0.013) evaluations were different from the respiratory quotient at the fourth evaluation. Therefore, the first evaluation may not be representative of the actual EE. The mean value of at least 3 subsequent evaluations after an adequate adaptation period (5 to 10 minutes) to the equipment will be useful for predicting energy requirements of apparently resting, clinically normal dogs.

Animals↗
PubMed1993

[Basic indicators of energy metabolism in patients with rheumatoid arthritis evaluated by indirect calorimetry].

The objective of the investigation was to examine basic parameters of the energy metabolism (energy expenditure at rest (REE), the respiratory quotient (RQ) and evaluate their relationship with age, basic parameters of the activity of the disease, serum positivity, basal therapy and corticoid therapy in patients with rheumatoid arthritis. The investigation comprised 26 patients with rheumatoid arthritis selected at random, incl. 12 serum positive ones. The mean age af the patients was 62.2 +/- 11.0 years, BMI 26.65 +/- 4.35, the mean duration of the disease was 11.8 +/- 9.9 years (range 1-36 years). A total of 12 patients had basal therapy, 12 patients took glucocorticoids regularly. The examination comprised a record of the case-history, clinical examination (Thompson's articular index), REE was evaluated by indirect calorimetry. The assessed REE value was compared with the expected value calculated according to Harris-Benedict's empirical formula (BMR) and expressed in per cent of the calculated value (REE%). The respiratory quotient (RQ) was calculated from the assessed CO2 and O2 consumption. The authors found a close correlation between REE and REE% (r = 0.606, p < 0.01) but no correlation between BMR and REE% (r = 0.115). The above parameters did not differ in serum positive and serum negative patients with RA treated with corticoids and those without corticotherapy, only in patients with basal therapy there are statistically significantly higher REE values (6456.7 +/- 790.5 kJ/24 h vs. 5396.4 +/- 826.7 kJ/24 h, p < 0.01) and REE% (110.6% +/- 99.2%, p < 0.05), as compared with subjects without basal therapy.(ABSTRACT TRUNCATED AT 250 WORDS)

Arthritis, Rheumatoid↗
PubMed1993

The influence of effectors and subunit interactions on Escherichia coli carbamoyl-phosphate synthetase studied by differential scanning calorimetry.

Differential scanning calorimetry of Escherichia coli carbamoyl-phosphate synthetase and its isolated large and small subunits reveals in each case an irreversible, kinetically controlled transition, at a temperature 14 degrees C higher for the holoenzyme than for the subunits, indicating dramatic stabilization of the subunits in the heterodimer. The deletion of the COOH-terminal 171 (mutant CarB'2373) or 385 (mutant CarB2177) residues of the large subunit results in more asymmetric transitions at a temperature 7 degrees C lower than for the wild type. The allosteric effectors IMP, UMP, and ornithine induce small reversible transitions at low temperature in the endotherm for the wild-type enzyme, but not for CarB'2373, as expected if the effectors bind in the 171-residue, COOH-terminal region. In contrast, two ligands that bind outside the deleted region, Ap5A (a ligand of both ATP sites) and glycine (an analog of glutamine) decrease and increase, respectively, the stability of the two mutants and of the wild type. The stabilization by glycine requires that the subunits are associated. The results support the implication of the 20-kDa COOH-terminal domain of the large subunit in the allosteric modulation by all the effectors and are consistent with the folding of the large subunit as a pseudohomodimer of its two homologous halves.

Allosteric Regulation↗
PubMed1977

Calorimetry, a time-honored technique with a potential in analytical work and cellular biology.

Different types of calorimeters are briefly reviewed, stressing those instruments likely to be of interest in the clinical chemistry laboratory. The unspecific nature of the measuring procedure is emphasized and various pitfalls likely to cause analytical errors are pointed out. Recent work is reviewed where calorimeters have been used as analytical tools for the determination of glucose, protein, enzymes, and other substances. The results generally compared favorably with those obtained by conventional analytical procedures. In recent reports the time per analysis has been brought down to 2 min, with sample volumes in the micro range. Valuable information on the coagulation process has been obtained by use of calorimetry. I also review studies showing that intact cellular elements such as human blood cells, bacteria, and spermatozoa can successfully be investigated with calorimetric techniques. In particular, studies on human blood cells stimulated with various agents appear to be able to give valuable diagnostic information. I believe that new designs of microcalorimeters have placed an easily handled tool at the disposal of the worker in a clinical laboratory and that use of this tool can contribute to the development of our discipline.

Bacterial Physiological Phenomena↗
PubMed1995

Using differential scanning calorimetry to elucidate metal-protein binding sites in alpha- and gamma-chymotrypsin.

Crystalline alpha-chymotrypsin preparations are contaminated by the post translational variant, gamma-chymotrypsin. The contaminant can account for 5-50 weight percent of the preparation based on thermal analysis. Such contamination can be problematic because this serine protease has both commercial and deactivation model system utility, and the presence of the contaminant may not be detectable by activity assays. Prior work has shown that simple pH gradient elution can separate the two chymotrypsins when loaded to a Cu(2+)-IMAC column; gamma-chymotrypsin eluted first indicating that its interaction with immobilized Cu2+ is weaker. The molecular features that endow these serine proteases with metal affinity has been investigated further by performing differential scanning calorimetry (DSC) studies in the presence and absence of Cu2+, and at different pH values. The dependence of thermostability on pH for fixed metal concentration reveals an interplay between stabilizing and destabilizing metal binding events. The results are consistent with Cu(2+)-chymotrypsin interaction occurring, in part, through binding to a glutamate- or aspartate-containing chelation site. The strength of this site may differ in the two chymotrypsins.

Binding Sites↗
PubMed1977

Comparison of indirect calorimetry and direct heat flow discs results in measuring R+C heat loss in burned patients.

This study was carried out on 17 burned patients. Metabolic heat production, rectal and skin temperatures, and heat exchanges by R+C were measured. It was found that R+C heat loss takes into account 60 to 80% of the increased metabolic heat production. Two methods were used to measure R+C heat loss: calculation by indirect calorimetry and direct measurements by using heat flow discs. The direct relationship which exists between the results of these two methods showed the reliability of the use of heat flow discs for measuring R+C heat loss. This fast-responding techniques may allow the elaboration of a thermal setting system which could modulate ambient air temperature, thus limiting exagerated heat loss due to the skin lesions.

Body Temperature Regulation↗
PubMed1995

Mechanism of the formation of DNA triplex and effect of chemical modifications on its stability as studied by isothermal titration calorimetry.

The thermodynamic properties of DNA triplex formation with various single-stranded oligo-DNAs as well as mismatched sequences were investigated by isothermal titration calorimetry (ITC). For the triplex formation of perfectly matched sequences, enthalpy changes and dissociation constants were measured and their temperature-dependences suggest that conformational change of pyrimidine single-strand and the intermediate state(s) are involved in the triplex formation. Effects of mismatches and chemical modifications on stability and specificity of the triplex formation will also be discussed.

Base Sequence↗
PubMed1996

Effect of anesthesia and surgery on energy expenditure determined by indirect calorimetry in dogs with malignant and nonmalignant conditions.

OBJECTIVE: To determine energy expenditure (EE) of apparently resting, client-owned dogs with malignant or nonmalignant diseases that were recovering from anesthesia and surgery, and compare those values with values from clinically normal, apparently resting, client owned dogs. ANIMALS: 40 apparently resting, client-owned dogs that had been given general anesthesia for various elective and nonelective surgical procedures, and 30 apparently resting, clinically normal client-owned dogs used as controls. PROCEDURE: EE was determined, using an open-flow indirect calorimetry system. Each dog was evaluated before and after surgery (0, 1, 2, and 3 days after surgery, then at suture removal > 14 days later) and compared with apparently resting, clinically normal, client-owned dogs (n = 30). Parameters evaluated were rate of oxygen consumption (Vo2/kg of body weight: ml/min/kg; Vo2/kg0.75: ml/min/kg0.75), EE (EE/kg: kcal/kg/d; EE/kg0.75: kcal/kg0.75/d), and respiratory quotient. RESULTS: Surgery and anesthesia did not significantly alter any of these parameters at any time assessed in any group. The pretreatment Vo2 and EE were significantly lower in the dogs with cancer, compared with dogs of other groups. CONCLUSIONS: These data suggest that the EE of a restricted group of dogs that undergo anesthesia and surgery for malignant and nonmalignant conditions does not increase from baseline values or when compared with values in clinically normal, client-owned dogs. CLINICAL RELEVANCE: This information may be of value when planning nutritional treatment for dogs recovering from anesthesia and surgery.

Anesthesia, General↗
PubMedDate not supplied

[Melting of ordered structures in denatured collagen depending on biological age by differential scanning calorimetry].

Using the differential scanning calorimetry we were able for the first time to establish the correlation between the biological age of the collagen tissue (rat tail tendon, age from 20 days to 24 months) and the melting parameters of gels, which are formed after the collagen denaturation. We have found that the half-width of the gel melting curves delta T1/2, as well as the ratio of the gel melting heat to the denaturation heat Qm/Qd are sensitive to the biological age of the tissue. The gel melting temperature Tm, in distinction to the denaturation temperature, was found to be not sensitive to the age but entirely dependent on the gel formation temperature. As it was experimentally demonstrated the above mentioned correlations can be observed only at well characterized thermal prehistory of samples and strictly fixed regime of gel formation.

Animals↗
PubMed1996

Differential scanning calorimetry of the irreversible thermal denaturation of cellulase from Streptomyces halstedii JM8.

High-sensitivity differential scanning calorimetry has been applied to characterize the irreversible thermal denaturation of a cellulase, assuming that thermal denaturation takes place according to the kinetic scheme N-k-->D, where k is a first-order kinetic constant that changes with temperature, as given by the Arrhenius equation; N the native state, and D the denatured one. On the basis of this model, the values of the rate constant as a function of temperature and the activation energy were calculated. The analytical data obtained with the fluorescence method as well by measurement of the enzymatic activity temperature dependence support this two-state kinetic model.

Calorimetry, Differential Scanning↗
PubMedDate not supplied

Use of subambient differential scanning calorimetry to monitor the frozen-state behavior of blends of excipients for freeze-drying.

The purpose of this study was evaluation of mannitol and its blends with other excipients commonly used as freeze-drying cryoprotectants or bulking agents in simulated lyophilization conditions. Subambient differential scanning calorimetry (DSC) has been used as an analytical tool to evaluate the phenomena from both a qualitative and a quantitative point of view. The DSC scans were performed at rates comparable to those generally practicable in industrial lyophilizators. During a simulated freeze-drying process, three crystallization events have been observed on mannitol solutions: the first two on freezing, and the last one on heating. The phenomena are dependent on each other. The addition of other excipients can significantly influence this behavior by specifying the crystallization of mannitol in freezing or by inhibiting it fully. This means that the final physical state of the freeze-dried product (amorphous, crystalline, or partially amorphous/partially crystalline) can be tailored by accurately choosing not only the freeze-drying conditions but also the composition of the solution to be lyophilized. The results point out how the physical state of freeze-dried products can be controlled by an accurate choice of both excipients and their relative ratios, with the possibility of reducing the number of preformulation activities required to design the most appropriate formulation for each new drug candidate.

2-Hydroxypropyl-beta-cyclodextrin↗
PubMed1997

Synthesis and antimycobacterial activity of nitroxanthones. 1st communication: synthesis and differential scanning calorimetry analysis.

The syntheses of mono-; di-, tri- and tetranitroxanthones via intramolecular Friedel-Crafts acylation of nitrated 2-phenoxybenzoic acids as well as via selective stepwise nitration of xanthone and the nitroxanthones gained from the first route are described. The synthesized nitroxanthones investigated by DSC (differential scanning calorimetry) analysis show a surprisingly high thermodynamic stability which was confirmed by quantum chemical calculations.

Anti-Infective Agents↗
PubMed1997

Indirect calorimetry.

Indirect calorimetry can be a useful tool to define nutritional status, determine nutritional requirements, and assess response to nutritional interventions. Measurements of oxygen consumption and carbon dioxide production may be used to determine cardiac output and work of breathing, and estimate the components of minute ventilation. An understanding of the potential technical and physiological pitfalls is necessary to obtain meaningful and useful information.

Acid-Base Equilibrium↗
PubMed1997

[Interaction of lipid membranes and neutral polymers by differential scanning calorimetry (DSC)].

Polymer-free and polymer-bearing liposomes from dimyristoylphosphatidylcholine (DMPC), dimyristoylphosphatidylglycerol (DMPG) and cholesterol (Ch) 10:1:1 (w/w/w) were prepared. Polymer-bearing liposomes were formed by incorporating an uncharged polymer [poly(vinyl alcohol) (PVA), poly(vinyl alcohol-co-vinylacetal) (PVA-Al), poly(vinyl alcohol-co-vinyl propional) (PVA-Prol) poly(vinyl alcohol-co-vinyl butiral) (PVA-Bul) copolymer, polyvinyl pyrrolidone (PVP) or polyethylene glycol (PEG) respectively]. The effect of some polymers on the phase transition parameter of phospholipids (DMPC and DMPG) has been studied by differential scanning calorimetry (DSC). DSC has become a standard technique for studying the thermally induced transition of phospholipid molecules from an ordered crystalline-like state at low temperature (gel phase) to a liquid crystalline-like state at higher temperature. The interaction between phospholipids and polymers was characterized by the alteration of the phase transition parameters (Tp, Tm, delta T1/2, delta Hp, delta Hm) measured by DSC. It was observed that some phase transition parameters were affected by all polymers but in different extent. PVA-Prol copolymer exhibited a prominent effect in increasing the membrane cooperativity. The influence of PVA-Bul was unique; it decreased the cooperativity of phospholipid molecules. It was also shown that the lipid membranepolymer interaction considerably depends on both the chemical structure and the molecular mass of the polymers.

Calorimetry, Differential Scanning↗
PubMedDate not supplied

[Evaluation of energy metabolism in burn patients: indirect calorimetry predictive equations].

INTRODUCTION: Knowing the most reliable method for measuring the metabolic energy use (MEU), is of great importance in patients with severe burns. For the calculation of the energetic requirements of large burn patients, several predictive equations (PE's) are used, based on weight, size, age, body surface area (BSA), and burned body surface (BBS). Previous studies note the tendency for over-or underestimating the MEU, depending on whether one or another PE is used, which is why it is considered necessary to calculate the energy requirements in the most exact manner possible, which can be done by means of indirect calorimetry (IC). MATERIAL AND METHODS: 18 patients (14 men and 4 women) who were admitted to the Burn Unit between 1994 and 1995, were included in the study, with the following inclusion criteria; age > 18 years and < 65 years, and who presented deep burns on are than 15% of the body surface. The MEU of the patients was evaluated by means of IC, using a Deltatrac il unit. The MEU calculated by means of IC was compared with that calculated by means of the four most commonly used PE's in literature: Long Formula: MEU = Basal energy use (BEU) x activity factor x aggression factor which is variable according to the BBS; Curreri Formula: MEU = (Weight x 25) + (total BBS x 40); MEU = 2000 x BSA. As statistical methods, one looked for the existence of correlation, by means of the Pearson method, and the "r" were compared by means of the Fischer conversion. The regression coefficient was found among the values obtained through the PE's and those measured by IC, as well as among those of IC and the percentage of deep burn and the total burned body surface. RESULTS: All the formulate included overestimated the MEU measured between 30.6% and 43.8% with the 2 x MEU formula being the one which did so least (30.6%). In any of them, there is an important variation of the percentage of overestimation with respect to the average MEU in this group. All are correlated in an important way with the MEU. The reliability of these PE's is variable, as is shown by the slopes of the regression lines, with the most reliable PE being that of 2000 x BSA, and that of 2 x MEU, by Harris-Benedict. There is also correlation between the average MEU by IC and the deeply burned body surface. CONCLUSION: This study proves the usefulness of the IC for knowing the EME in burn patients, to prevent their hypernutrition, as well as the relative value of the formulae usually used clinically to estimate this parameter.

Adolescent↗
PubMed1998

Wavelength-dependent photoacoustic calorimetry study of melanin.

Photoacoustic calorimetry is used to examine the energy dissipation in melanin under physiological conditions (pH 7.2) following irradiation by UV and visible (VIS) light. Four different excitation wavelengths were examined: 264 nm, representative of UVC radiation, 351 nm and 400 nm (UVA-I radiation) and 527 nm, representative of VIS radiation. Following absorption at 527 nm, essentially all of the photon energy is released nonradiatively on a sub-nanosecond of excitation. Similar results are observed at 400 nm. At 351 nm, most of the energy was released as heat; a small amount of energy was retained (5 +/- 5%). When melanin is excited at 264 nm, 29 +/- 7% of the photon energy is retained by the molecule for a time period longer than a few hundred nanoseconds. These results show that a long-lived excited state or reactive intermediate is generated upon UV irradiation, whereas all of the excitation energy is dissipated nonradiatively in the visible portion of the spectrum. These results establish that the photochemistry of melanin is wavelength dependent.

Calorimetry↗
PubMedDate not supplied

[Human calorimetry in sealed hermetic enclosures].

The paper gives the results of an experimental assessment of personal biocalorimeter and calorimetric garment. The paper is addressed to biologists, physiologists and physicians investigating heat exchange and thermal regulation of the human body as well as to thephysicists developing calorimetric theories and methods. It presents theoretical concepts underlying direct calorimetry of a suited man and contains a block-diagram of the biocalorimeter that was used to examine energy parameters of the human body, including metabolic rate, heat production, heat release and heat balance. The data obtained were statistically treated and heat effects were characterized by empiric expressions. It was for the first time in medical practice that the personal calorimeter and calorimetric garment made it possible to accumulate information on the thermal state of the human body. This information helps to diagnose the health condition of man, to standardise environmental parameters in aviation, space and such like suits and to automatize their maintenance in experimental and real life situations.

Body Temperature Regulation↗
PubMed1995

Protein location in liposomes, a drug carrier: a prediction by differential scanning calorimetry.

Location of protein drugs in lipid carriers often determines the stability, loading efficiency, and release rate of these drugs from the carriers following administration. On the basis of conventional differential scanning calorimetry (DSC) measurements, Papahadjopoulos et al. (Biochim. Biphys. Acta 1975, 401, 317-335) proposed that proteins can be classified into three categories depending on their effects on the thermotropic behavior of the lipids, e.g., transition temperature and enthalpy. Interactions are usually electrostatic, hydrophobic, or their combination. The nature of these interactions are reflected by changes in various thermotropic parameters. Our study aims to test the validity of Papahadjopoulos' classification. Hydrophilic ribonuclease A, cytochrome c, and superoxide dismutase (SOD), as well as hydrophobic cyclosporin A, are used as model proteins. Neutral lipids, e.g., dipalmitoylphosphatidylcholine, and/or negatively charged lipids, e.g., dipalmitoylphosphatidylglycerol (DPPG), are used to prepare liposomes. Results from conventional and high-sensitivity DSC are compared. High-sensitivity DSC gives significant, more reproducible results. We find that the classification of Papahadjopoulos et al. needs to be modified. No hydrophilic proteins bind to liposomes exclusively on the surface by electrostatic interactions, and some degree of penetration is observed in most cases. An unexpected binding between SOD and DPPG liposomes is observed. The binding of SOD to negatively charged lipids may account, at least in part, for its ability to protect lipid membranes against oxygen-mediated injury.

Cyclosporine↗